Direct spectroscopic observation of Berry-phase interference in the
Ni4 single-molecule magnet
|
Berry-phase effects in spin systems lead to the suppression of
tunneling effects when different tunneling paths interfere
destructively. Such effects have been seen in several
single-molecule magnets (SMMs) through measurements of
magnetization dynamics, where the experimental signal may arise
from the contributions of numerous energy levels. Here the
authors
present experimental measurements of Berry-phase interference
effects that are determined through electron-spin resonance on a
fourfold symmetric SMM. Specifically, the authors measure transitions
between tunnel-split excited states in the Ni4 SMM in
the presence of a transverse field in the hard plane of
the crystalline sample. By using a home-built rotation
apparatus, the direction of the sample can be changed in situ so
that the field direction can be swept through the entire hard
plane of the sample. When the field is in certain directions in
the plane, the authors observe a splitting of the transition, a hallmark
of Berry-phase interference. The experimental results are well
reproduced by numerical simulations, and fitting of the data
provides information about the effects of dipolar interactions
and sample misalignment.
|
Brendan C. Sheehan, Robert Kwark, Charles A. Collett, Thomaz
A. Costa, Rafael A. Allão Cassaro, and Jonathan R. Friedman,
Direct spectroscopic observation of Berry-phase interference in the
Ni4 single-molecule magnet,
Phys. Rev. B 102, 224428 (2020)
|
Understanding magnetic relaxation in single-ion magnets with high blocking temperature
|
The recent discovery of single-ion magnets with magnetic
hysteresis above liquid-nitrogen temperatures placed these
compounds among the best candidates to realize high-density
storage devices. Starting from a prototypical dysprosocenium
molecule, showing hysteresis up to 60 K, the authors derive here a
general recipe to design high-blocking-temperature rare-earth
single-ion magnets. The complex magnetic relaxation is unraveled
by combining magnetization and nuclear magnetic resonance
measurements with inelastic neutron scattering experiments and
ab initio calculations, thus disentangling the different
mechanisms and identifying the key ingredients behind slow
relaxation.
|
A. Chiesa, F. Cugini, R. Hussain, E. Macaluso, G. Allodi,
E. Garlatti, M. Giansiracusa, C. A. P. Goodwin, F. Ortu,
D. Reta, J. M. Skelton, T. Guidi, P. Santini, M. Solzi, R. De
Renzi, D. P. Mills, N. F. Chilton, and S. Carretta,
Understanding magnetic relaxation in single-ion magnets with high blocking temperature,
Phys. Rev. B 101, 174402 (2020)
|
Blocking like it's hot: a synthetic chemists’ path to high-temperature lanthanide single molecule magnets
|
Progress in the synthesis, design, and characterisation of
single-molecule magnets (SMMs) has expanded dramatically from
curiosity driven beginnings to molecules that retain
magnetization above the boiling point of liquid nitrogen. This
is in no small part due to the increasingly collaborative nature
of this research where synthetic targets are guided by
theoretical design criteria. This article aims to summarize
these efforts and progress from the perspective of a synthetic
chemist with a focus on how chemistry can modulate physical
properties. A simple overview is presented of lanthanide
electronic structure in order to contextualize the synthetic
advances that have led to drastic improvements in the
performance of lanthanide-based SMMs from the early 2000s to the
late 2010s.
|
Conrad A. P. Goodwin,
Blocking like it's hot: a synthetic chemists’ path to high-temperature lanthanide single molecule magnets,
Dalton Trans., 2020,49, 14320-14337
|
Secondary metal coordination using a tetranuclear complex as ligand leading to hexanuclear complexes with enhanced thermal barriers for electron transfer
|
Post-synthesis of the paramagnetic square-shaped complex
{[(Tp*Me)Fe(μ-CN)2(CN)][Co(dmbpy)2]}2(BPh4)2·6MeCN·H2O [ 1,
Tp*Me = tris(3,4,5-trimethylpyrazole)-borate; dmbpy =
4,4′-dimethyl-2,2′-bipyridine)] by grafting transition metal(II)
thiocyanates via its terminal cyano groups afforded three
hexanuclear [Fe2Co2M2] clusters (M = Zn, 2; Co, 3; Cd, 4). The
peripheral metal complex units serving as excellent electron
acceptors were found to help stabilize the low-temperature state
of FeII,LS-CoIII,LS within the complex core. As a result, the
desolvated complexes 2 to 4 underwent reversible and sharp
thermally induced electron-transfer behavior with the transition
temperatures (T1/2) up to 312, 296 and 365 K, respectively,
demonstrating an effective means of manipulating thermal
barriers of the celebrated cyano-bridged square core.
|
Shihao Liu, Yi-Fei Deng, Zi-Yi Chen, Lingyi Meng, Xiaoyong
Chang, Zhiping Zheng, and Yuan-Zhu Zhang,
Secondary metal coordination using a tetranuclear complex as ligand leading to hexanuclear complexes with enhanced thermal barriers for electron transfer,
CCS Chemistry
|
Recent progress on cyano-bridged transition-metal-based single-molecule magnets and single-chain magnets
|
Novel functional molecular-based magnetic materials, especially
some members of the Prussian blue family, have gained
significant attention over the past few decades as they can be
used beneficially in a variety of scientific fields. Herein, the authors
survey the latest developments in cyano-bridged
transition-metal-based single-molecule magnets (SMMs) and
single-chain magnets (SCMs) research. The cyanide ligand, which
has a strong affinity for transition metals, is a popular
bridging ligand to construct a variety of molecular-magnetic
materials, depending on the type of co-ligand. This review
mainly focuses on research into structural topologies and the
corresponding SMMs or SCMs. The first section provides a brief
introduction into SMM and SCM behavior and important principles
and strategies for constructing diverse magnetic materials. The
remaining sections provide overviews of significant achievements
reported in recent years. In the final section the authors conclude by
presenting perspectives on cyanometallate-based SMMs and SCMs
and by providing some new insight into this promising area.
|
Jin-Hua Wang, Zhao-Yang Li, Masahiro Yamashita, Xian-He Bu,
Recent progress on cyano-bridged transition-metal-based single-molecule magnets and single-chain magnets,
Coord. Chem. Rev. 428, 213617 (2021)
|
Observation of the asphericity of 4f-electron density and its relation to the magnetic anisotropy axis in single-molecule magnets
|
The distribution of electrons in the 4f orbitals of lanthanide
ions is often assigned a crucial role in the design of
single-molecule magnets, which maintain magnetization in zero
external field. Optimal spatial complementarity between the
4f-electron density and the ligand field is key to maximizing
magnetic anisotropy, which is an important factor in the ability
of lanthanide complexes to display single-molecule magnet
behaviour. Here the authors have experimentally determined the electron
density distribution in two dysprosium molecular complexes by
interpreting high-resolution synchrotron X-ray diffraction with
a multipole model. The ground-state 4f-electron density is found
to be an oblate ellipsoid, as is often deduced from a simplified
Sievers model that assumes a pure |+/-15/2> ground-state doublet
for the lanthanide ion. The large equatorial
asymmetry—determined by a model wavefunction was found to
contain considerable MJ mixing of |+/-11/2> and only 81% of
|+/-15/2>. The experimental molecular magnetic easy axes were
recovered, and found to deviate by 13.1° and 8.7° from those
obtained by ab initio calculations.
|
Chen Gao, Alessandro Genoni, Song Gao, Shangda Jiang, Alessandro
Soncini, Jacob Overgaard,
Observation of the asphericity of 4f-electron density and its relation to the magnetic anisotropy axis in single-molecule magnets,
Nature Chemistry 12, 213–219(2020)
compare also
Emil Damgaardâ€Møller, Lennard Krause, Kasper Tolborg,
Giovanni Macetti, Dr. Alessandro Genoni, Jacob
Overgaard,
Quantification of the Magnetic Anisotropy of a
Singleâ€Molecule Magnet from the Experimental Electron
Density,
Angew. Chem. Int. Ed. 59, 21203-21209 (2020)
|
Molecular Nanomagnets as Qubits with Embedded Quantum-Error Correction
|
The authors show that molecular nanomagnets have a potential advantage in
the crucial rush toward quantum computers. Indeed, the sizable
number of accessible low-energy states of these systems can be
exploited to define qubits with embedded quantum error
correction. The authors derive the scheme to achieve this crucial
objective and the corresponding sequence of
microwave/radiofrequency pulses needed for the error correction
procedure. The effectiveness of our approach is shown already
with a minimal S = 3/2 unit corresponding to an existing
molecule, and the scaling to larger spin systems is
quantitatively analyzed.
|
A. Chiesa, E. Macaluso, F. Petiziol, S. Wimberger, P. Santini,
and S. Carretta,
Molecular Nanomagnets as Qubits with Embedded Quantum-Error Correction,
Phys. Chem. Lett. 2020, 11, 20, 8610–8615
|
Modulating magnetic anisotropy in Ln(III) single-ion magnets using an external electric field
|
Single-molecule magnets have potential uses in several
nanotechnology applications, including high-density information
storage devices, the realisation of which lies in enhancing the
barrier height for magnetisation reversal (Ueff). However,
Ln(III) single-ion magnets (SIMs) that have been reported
recently reveal that the maximum value of Ueff values that can
be obtained by modulating the ligand fields has already been
achieved. Here, the authors have explored, using a combination of DFT and
ab initio CASSCF calculations, a unique way to enhance the
magnetisation reversal barrier using an oriented external
electric field in three well-known Ln(III) single-ion magnets:
[Dy(Py)5(OtBu)2]+ (1), [Er{N(SiMe3)2}3Cl]− (2) and [Dy(CpMe3)Cl]
(3). The study reveals that, for apt molecules, if the
appropriate direction and values of the electric fields are
chosen, the barrier height can be enhanced by twice that of the
limit set by the ligand field. The application of an electric
field along the equatorial direction was found to be suitable
for oblate shaped Dy(III) complexes and an electric field along
the axial direction was found to enhance the barrier height for
a prolate Er(III) complex. For complexes 2 and 3, the external
electric field was able to magnify the barrier height to 2–3
times that of the original complexes. However, a moderate
enhancement was noticed after application of the external
electric field in the case of complex 1. This novel non-chemical
fine-tuning approach to modulate magnetic anisotropy is expected
to yield a new generation of SIMs.
|
Arup Sarkar, Gopalan Rajaraman,
Modulating magnetic anisotropy in Ln(III) single-ion magnets using an external electric field,
Chem. Sci., 2020,11, 10324-10330
|
Metal-organic magnets with large coercivity and ordering temperatures up to 242°C
|
Magnets derived from inorganic materials (e.g., oxides,
rare-earth–based, and intermetallic compounds) are key
components of modern technological applications. Despite
considerable success in a broad range of applications, these
inorganic magnets suffer several drawbacks, including
energetically expensive fabrication, limited availability of
certain constituent elements, high density, and poor scope for
chemical tunability. A promising design strategy for
next-generation magnets relies on the versatile coordination
chemistry of abundant metal ions and inexpensive organic
ligands. Following this approach, we report the general, simple,
and efficient synthesis of lightweight, molecule-based magnets
by postsynthetic reduction of preassembled coordination networks
that incorporate chromium metal ions and pyrazine building
blocks. The resulting metal-organic ferrimagnets feature
critical temperatures up to 242°C and a 7500-oersted
room-temperature coercivity.
|
Panagiota Perlepe, Itziar Oyarzabal, Aaron Mailman, Morgane Yquel,
Mikhail Platunov, Iurii Dovgaliuk,Mathieu Rouzières, Philippe
Négrier, Denise Mondieig, Elizaveta A. Suturina, Marie-Anne
Dourges, Sébastien Bonhommeau, Rebecca A. Musgrave, Kasper
S. Pedersen, Dmitry Chernyshov, Fabrice Wilhelm, Andrei Rogalev,
Corine Mathonière, Rodolphe Clérac,
Metal-organic magnets with large coercivity and ordering temperatures up to 242°C,
Science 370, 587-592 (2020)
|
Enhancing Magnetic Hysteresis in Single-Molecule Magnets by Ligand Functionalization
|
Design criteria for dysprosium(III) single-molecule magnets
(SMMs) with large thermal energy barriers to magnetic reversal
have been established and proven, and the challenge to enhance
performance is in understanding and controlling
electron-vibration coupling that is the origin of magnetic
reversal. The authors have prepared an SMM, [Dy(L)2(py)5][BPh4] (HL =
(S)-(-)-1-phenylethanol), based on the archetype
[Dy(OtBu)2(py)5][BPh4]. Both compounds have similarly large
energy barriers of Ueff = 1,130(20) cm−1 and Ueff = 1,250(10)
cm−1, and yet the new SMM shows magnetic hysteresis at a far higher
temperature of 22 K cf. TH = 4 K for the archetype. Ab initio
calculation of
the electron-vibration coupling and spin dynamics shows that
substitution of the alkoxide ligand in fact enhances relaxation
over the energy barrier for the new SMM compared with to the
precursor, in agreement with
experiment, and that the higher temperature of magnetic
hysteresis likely owes to reduced quantum tunneling at low
temperatures.
|
Ke-Xin Yu, Jon G.C. Kragskow, You-Song Ding, Yuan-QiZhai, Daniel
Reta, Nicholas F. Chilton, Yan-Zhen Zheng,
Enhancing Magnetic Hysteresis in Single-Molecule Magnets by Ligand Functionalization,
Chem, Volume 6, Issue 7, 9 July 2020, Pages 1777-1793
|
Molecule-based magnetic materials constructed from paramagnetic organic ligands and two different metal ions
|
This paper reviews the most representative examples of
polynuclear complexes containing three spin carriers: a
paramagnetic organic ligand (nitronyl-nitroxide,
imino-nitroxide, TEMPO, verdazyl and TCNQradical dot-radicals)
and two different metal ions (3d-3d’, 3d-4f), focusing on their
magnetic properties. The synthetic approaches leading to such
compounds are presented. These compounds show a rich structural
variety, ranging from discrete species to coordination polymers
with various dimensionalities and spin topologies. The general
synthetic strategies leading to such compounds are discussed and
illustrated. Some 2p-3d-4f complexes have relevance in the field
of molecular nanomagnets (Single Molecule Magnets and Single
Chain Magnets).
|
Maria G.F. Vaz, Marius Andruh,
Molecule-based magnetic materials constructed from paramagnetic organic ligands and two different metal ions,
Coordination Chemistry Reviews 427, 2021, 213611
|
Engineering macrocyclic high performance pentagonal bipyramidal Dy(iii) single-ion magnets
|
The authors generate a new air-stable pseudo-D5h Dy(III) Single-Molecule
Magnet (Ueff = 1108 K, TB = 14 K) by combining a weak equatorial
ligand field from a macrocyclic LN5 ligand with a strong axial
ligand field. Based on their synthetic blueprint, they use ab initio
calculations to show the vast scope for macrocyclic engineering
of magnetic anisotropy.
|
Angelos B. Canaj, Sourav Dey, Claire Wilson, Oscar Céspedes, Gopalan
Rajaraman and Mark Murrie,
Engineering macrocyclic high performance pentagonal bipyramidal Dy(iii) single-ion magnets,
Chem. Commun., 2020, Advance Article
|
Constructing clock-transition-based two-qubit gates from dimers of molecular nanomagnets
|
A good qubit must have a coherence time long enough for gate
operations to be performed. Avoided level crossings allow for
clock transitions in which coherence is enhanced by the
insensitivity of the transition to fluctuations in external
fields. Because of this insensitivity, it is not obvious how to
effectively couple qubits together while retaining
clock-transition behavior. Here the authors present a scheme for
using a heterodimer of two coupled molecular nanomagnets, each
with a clock transition at zero magnetic field, in which all of the
gate operations needed to implement one- and two-qubit gates can
be implemented with pulsed radio-frequency radiation. The authors show
that given realistic coupling strengths between the nanomagnets
in the dimer, good gate fidelities can be achieved. The authors
identify the primary sources of error in
implementing gates and discuss how these may be mitigated, and
investigate the range of coherence times necessary for such a
system to be a viable platform for implementing quantum
computing protocols.
|
Charles A. Collett, Paolo Santini, Stefano Carretta, and
Jonathan R. Friedman,
Constructing clock-transition-based two-qubit gates from dimers of molecular nanomagnets,
Phys. Rev. Research 2, 032037(R) (2020)
|
Magnetocaloric and barocaloric effects of metal complexes for solid state cooling: Review, trends and perspectives
|
Solid state refrigeration is a viable alternative for the
conventional gas-compression technology due to the environmental
friendliness of its materials, energy efficiency, and low
noise. Research in this field is focused on the development of
advanced prototypes and smart materials. This Review focuses on
a special family of quantum materials: metal complexes. The author
introduces the fundamentals of caloric effects and magnetism of
these complexes, discussing their applications at different
ranges of temperature, based on different physical
mechanisms. At cryogenic temperatures (close to temperature of
liquid He), some metal complexes present a huge value of
magnetic entropy change, ranging from c.a. 10 J/kgK to c.a. 70
J/kgK (for 7 T of magnetic field change). These values make some
metal complexes appealing as cryogenic coolant materials. The
author
also presents a comprehensive collection of results from the
literature, organized on a chart as a function of time, for
different classes of metal complexes; those with 3d-3d magnetic
interactions, 3d-4f coupling, and 4f-4f interactions. The author
observed that those materials that achieved the maximum value of
entropy change, i.e., the spin-only value, follow an exponential
scaling law with time. This result helps to predict a new class
of metal complexes and further outcomes for the field. On the
other hand, for a small amount of applied pressure, these
materials produce large barocaloric effect around the spin
crossover transition (this transition occurs in a wide range of
temperature, even close to room temperature). Thus, the author introduces
the SCO mechanism and comprehensively review this topic, along
with the recent theoretical models and experimental results. The
recent results of barocaloric effect are considered enormously
significant (56 J/kgK for 0.9 kbar of pressure change, close to
room temperature), even in comparison with traditional metallic
barocaloric materials. Perspectives for this
subject, with discussions about new mechanisms for the models
(as the Jahn-Teller distortion and orbital contribution), are
also presented.
|
Mario S.Reis,
Magnetocaloric and barocaloric effects of metal complexes for solid state cooling: Review, trends and perspectives,
Coordination Chemistry Reviews,
Volume 417, 15 August 2020, 213357
|
Exploring the Magnetic Properties of the Largest Single-Molecule Magnets
|
The giant {Mn70} and {Mn84} wheels are the largest nuclearity
single-molecule magnets synthesized to date, and understanding
their magnetic properties poses a challenge to theory. Starting
from first-principles calculations, the authors explore the magnetic
properties and excitations in these wheels using effective spin
Hamiltonians. They find that the unusual geometry of the
superexchange pathways leads to weakly coupled {Mn7} subunits
carrying an effective S = 2 spin. The spectrum exhibits a
hierarchy of energy scales and massive degeneracies, with the
lowest-energy excitations arising from Heisenberg-ring-like
excitations of the {Mn7} subunits around the
wheel. The authors further
describe how weak longer-range couplings can select the precise
spin ground-state of the Mn wheels out of the nearly degenerate
ground-state band.
|
Henry F. Schurkus, Dianteng Chen, Matthew J. O'Rourke, Hai-Ping
Cheng, Garnet Kin-Lic Chan,
Exploring the Magnetic Properties of the Largest Single-Molecule Magnets,
J. Phys. Chem. Lett. 2020, 11, 10, 3789-3795
|
Modelling the properties of magnetic clusters with complex structures: how symmetry can help us
|
The purpose of this article is to answer the question of how
symmetry helps us to investigate and understand the properties
of nanoscopic magnetic clusters with complex structures. The
systems of choice will be the three types of polyoxometalates
(POMs): (1) POMs containing localised spins; (2) reduced
mixed-valence (MV) POMs; (3) partially delocalised POMs in which
localised and delocalised subunits coexist and interact. The
theoretical tools based on various kinds of symme- try are the
following: (1) irreducible tensor operator (ITO) approach based
on the so-called "spin-symmetry" and MAGPACK program; (2)
group-theoretical assignment of the exchange multiplets based on
spin- and point symmetries; (3) group-theoretical classification
of the delocalised electronic and electron-vibrational states of
MV POMs; (4) general approach (based on spin symmetry) to
evaluate the energy levels of large MV clusters and the
corresponding MVPACK program; (5) computational approach
(employing point symmetry) to solve multidimensional
non-adiabatic vibronic problems in the nanoscopic systems
realized as VIBPACK software. We made it our goal to avoid a
conventional deductive style of presentation. On the contrary,
we first consider specially selected complex POMs and then show
by what methods and in what way the theoretical problems arising
in the description of the properties of these molecules can be
properly solved.
|
Boris Tsukerblat, Andrew Paliib, Juan Modesto Clemente-Juan, Eugenio Coronado,
Modelling the properties of magnetic clusters with complex structures: how symmetry can help us,
INTERNATIONAL REVIEWS IN PHYSICAL CHEMISTRY 2020, VOL. 39, NO. 2, 217-265
|
Unbiased evaluation of zero-field splitting D parameter in
high-spin molecules from DC magnetic data with incomplete powder
averaging
|
A simple scheme is presented to account for preferential
orientation effects in the DC magnetic response of
polycrystalline samples of anisotropic high-spin molecules, like
single-molecule magnets. A single additional least-squares
parameter is introduced in the fitting of isothermal
magnetization vs. field data to describe the leading part of a
non-spherical distribution of anisotropy axes. The procedure is
shown to afford an accurate D parameter and is potentially
applicable whenever complete powder averaging cannot be
achieved.
|
Andrea Cornia, Anne-Laure Barra, Giordano Poneti, Erik Tancini, RobertaSessoli,
Unbiased evaluation of zero-field splitting D parameter in
high-spin molecules from DC magnetic data with incomplete powder
averaging,
JMMM 510 (2020) 166713
|
Single-Molecule Toroic Design through Magnetic Exchange Coupling
|
The big data era calls for larger capacity of our hard drive,
which in turn depends on the number of magnetic units that
store bits of 1 or 0. However, as the density of these units
increases, flipping one unit without affecting another becomes
more difficult because of undesired magnetic perturbations
from the reading/writing heads. Single-molecule toroics (SMTs)
that exploit vortex-like magnetic structures are insensitive
to homogeneous magnetic fields and hence are promising for
next-generation ultra-dense information storage. However, the
synthesis of such molecular materials is challenging. Here, we
show by using ferromagnetic interactions that this target can
be realized in a 16-membered heterometallic cluster {Fe8Dy8},
which shows a stable 4-fold degenerated magnetic toroidal
ground state at low temperatures. This is significantly
distinguished from the most studied dipole-dipole
interaction-based SMTs and demonstrates a promising strategy
for the next generation of SMT design.
|
Hao-Lan Zhang, Yuan-Qi Zhai, Lei Qin, Liviu Ungur, Hiroyuki Nojiri, Yan-Zhen Zheng,
Single-Molecule Toroic Design through Magnetic Exchange Coupling,
Matter, Volume 2, Issue 6, 3 June 2020, Pages 1481-1493
|
Vibrational coherences in manganese single-molecule magnets after ultrafast photoexcitation
|
Magnetic recording using femtosecond laser pulses has recently
been achieved in some dielectric media, showing potential for
ultrafast data storage applications. Single-molecule magnets
(SMMs) are metal complexes with two degenerate magnetic ground
states and are promising for increasing storage density, but
remain unexplored using ultrafast techniques. Here the authors have
explored the dynamics occurring after photoexcitation of a
trinuclear μ3-oxo-bridged Mn(III)-based SMM, whose magnetic
anisotropy is closely related to the Jahn-Teller
distortion. Ultrafast transient absorption spectroscopy in
solution reveals oscillations superimposed on the decay traces
due to a vibrational wavepacket. Based on complementary
measurements and calculations on the monomer Mn(acac)3, we
conclude that the wavepacket motion in the trinuclear SMM is
constrained along the Jahn-Teller axis due to the μ3-oxo and
µ-oxime bridges. The results provide new possibilities for
optical control of the magnetization in SMMs on femtosecond
timescales and open up new molecular-design challenges to
control the wavepacket motion in the excited state of
polynuclear transition-metal complexes.
|
Florian Liedy, Julien Eng, Robbie McNab, Ross Inglis, Thomas
J. Penfold, Euan K. Brechin, J. Olof Johansson,
Vibrational coherences in manganese single-molecule magnets after ultrafast photoexcitation,
Nature Chemistry volume 12, pages452-458(2020)
|
Dysprosiacarboranes: A New Type of Organometallic
Single-Molecule Magnet
|
The dicarbollide ion, nido-C2B9H112- is isoelectronic
with cyclopentadienyl. Here the authors make dysprosiacarboranes, namely
[(C2B9H11)2Ln(THF)2][Na(THF)5] (Ln = Dy, 1Dy ) and
[(THF)3(μ-H)3Li]2[{η5-C6H4(CH2)2C2B9H9
}Dy{η2:η5-C6H4 (CH2)2C2B9H9}2Li] 3Dy and
show that dicarbollide ligands impose strong magnetic axiality
on the central Dy(III) ion. The effective energy barrier ( U eff
) for loss of magnetisation can be varied by the substitution
pattern on the dicarbollide. This is demonstrated by comparing
complexes of
nido-C2B9H112- and
nido-[o-xylylene-C2B9H92-
which show U eff of 430(5) K and 804(7) K,
respectively. The blocking temperature defined by the open
hysteresis temperature of 3Dy reaches 6.8 K. Moreover, the
linear complex
[Dy(nido-C2B9H11)2]-
is predicted to have
comparable properties with linear [Dy(CpMe3)2]+ complex. As
such, carboranyl ligands and its derivatives may open a new type
of organometallic ligands for high-performance single-molecule magnets.
|
Peng-Bo Jin, Yuan-Qi Zhai, Ke-Xin Yu, Richard
E. P. Winpenny, Yan-Zhen Zheng,
Dysprosiacarboranes: A New Type of Organometallic
Single-Molecule Magnet,
Angew. Chem. Int. Ed., Volume59, Issue 24
June 8, 2020, Pages 9350-9354
|
Decoherence in Molecular Electron Spin Qubits:
Insights from Quantum Many-Body Simulations
|
Quantum states are described by wave functions whose phases
cannot be directly measured but which play a vital role in
quantum effects such as interference and entanglement. The loss
of the relative phase information, termed decoherence, arises
from the interactions between a quantum system and its
environment. Decoherence is perhaps the biggest obstacle on the
path to reliable quantum computing. Here we show that
decoherence occurs even in an isolated molecule, although not
all phase information is lost, via a theoretical study of a
central electron spin qubit interacting with nearby nuclear
spins in prototypical magnetic molecules. The residual
coherence, which is molecule-dependent, provides a microscopic
rationalization for the nuclear spin diffusion barrier proposed
to explain experiments. The contribution of nearby molecules to
the decoherence has a nontrivial dependence on separation,
peaking at intermediate distances. Molecules that are far away
affect only the long-time behavior. Because the residual
coherence is simple to calculate and correlates well with the
coherence time, it can be used as a descriptor for coherence in
magnetic molecules. This work will help establish design
principles for enhancing coherence in molecular spin qubits and
serve to motivate further theoretical work.
|
Jia Chen, Cong Hu, John F. Stanton, Stephen Hill, Hai-Ping
Cheng, Xiao-Guang Zhang,
Decoherence in Molecular Electron Spin Qubits: Insights from Quantum Many-Body Simulations,
J. Phys. Chem. Lett. 2020, 11, XXX, 2074-2078
see also:
P. Vorndamme, J. Schnack,
Decoherence of a singlet-triplet superposition state
under dipolar interactions of an uncorrelated environment,
Phys. Rev. B 101, 075101 (2020)
|
Adjustable coupling and in situ variable frequency
electron paramagnetic resonance probe with loop-gap
resonators for spectroscopy up to X-band
|
In standard electron paramagnetic resonance (EPR) spectroscopy,
the frequency of an experiment is set and the spectrum is
acquired using the magnetic field as the independent
variable. There are cases in which it is desirable instead to
fix the field and tune the frequency such as when studying
avoided level crossings. The have designed and tested an
adjustable frequency and variable coupling EPR probe with
loop-gap resonators (LGRs) that works at a temperature as low as
1.8 K. The frequency is tuned by adjusting the height of a
dielectric piece of sapphire inserted into the gap of an LGR;
coupling of the microwave antenna is varied with the height of
the antenna above the LGR. Both coupling antenna and dielectric
are located within the cryogenic sample chamber, but their
motion is controlled with external micrometers located outside
the cryostat. The frequency of the LGR (approx. 4 GHz) can be adjusted
by more than 1 GHz (>25%). To cover a wide range of frequencies,
different LGRs can be designed to cover frequencies up to
X-band. The authors demonstrate the operation of their probe by mapping out
avoided crossings for the Ni4 molecular nanomagnet to determine
the tunnel splittings with high precision.
|
G. Joshi, J. Kubasek, I. Nikolov, B. Sheehan,
T. A. Costa, R. A. Allao Cassaro, Jonathan R. Friedman,
Adjustable coupling and in situ variable frequency
electron paramagnetic resonance probe with loop-gap
resonators for spectroscopy up to X-band,
Review of Scientific Instruments 91,
023104 (2020)
|
There is nothing wrong with being soft: using sulfur ligands to increase axiality in a Dy(III) single-ion magnet
|
A new air-stable sulfur-ligated Dy(III) single-ion magnet has
been successfully isolated with Ueff = 638 K and hysteresis
loops open up to 7 K. In silico studies show that the S
co-ligands significantly boost the axiality and that Te- and
Se-donors have the potential to further enhance the magnetic
properties.
|
Angelos B. Canaj, Sourav Dey, Oscar Cespedes, Claire Wilson,
Gopalan Rajaraman, Mark Murrie,
There is nothing wrong with being soft: using sulfur ligands to increase axiality in a Dy(III) single-ion magnet,
Chem. Commun., 2020, Advance Article
|
Quantum units from the topological engineering of molecular graphenoids
|
Robustly coherent spin centers that can be integrated into
devices are a key ingredient of quantum technologies. Vacancies
in semiconductors are excellent candidates, and theory predicts
that defects in conjugated carbon materials should also display
long coherence times. However, the quantum performance of carbon
nanostructures has remained stunted by an inability to alter the
sp2-carbon lattice with atomic precision. Here, the authors demonstrate
that topological tailoring leads to superior quantum performance
in molecular graphene nanostructures. They unravel the decoherence
mechanisms, quantify nuclear and environmental effects, and
observe spin-coherence times that outclass most
nanomaterials. These results validate long-standing assumptions
on the coherent behavior of topological defects in graphene and
open up the possibility of introducing controlled
quantum-coherent centers in the upcoming generation of
carbon-based optoelectronic, electronic, and bioactive systems.
|
Federico Lombardi, Alessandro Lodi, Ji Ma, Junzhi Liu,
Michael Slota, Akimitsu Narita, William K. Myers, Klaus
Müllen, Xinliang Feng, Lapo Bogani,
Quantum units from the topological engineering of molecular graphenoids,
Science, Vol. 366, Issue 6469, pp. 1107-1110 (2019)
|
Machine learning guided design of single-molecule magnets for magnetocaloric applications
|
The authors present a data-driven approach to predict entropy changes
in small magnetic fields in single-molecule magnets (SMMs)
relevant to their application as magnetocaloric refrigerants. They
construct a database of SMMs with a representation scheme
incorporating aspects related to dimensionality, structure,
local coordination environment, ideal total spin of magnetic
ions, ligand type, and linking chemistry. They train machine
learning models for predicting the entropy change as a function
of structure and chemistry and use the models to arrive at the entropy change
for hypothetical molecules. They also identify key descriptors
that affect the entropy change, thus providing insights into
designing tailored SMMs with improved magnetocaloric properties.
|
Ludwig Holleis, B. S. Shivaram, and Prasanna
V. Balachandran,
Machine learning guided design of single-molecule magnets for magnetocaloric applications,
Appl. Phys. Lett. 114, 222404 (2019)
|
Molecular magnetism: from chemical design to spin control in molecules, materials and devices
|
The field of molecular magnetism is rapidly evolving towards the
use of magnetic molecules and molecule-based magnetic materials
in physics-driven and nanotechnology-driven fields, in
particular molecular spintronics, quantum technologies,
metal-organic frameworks (MOFs) and 2D materials. In molecular
spintronics, the goal is the development of a new generation of
spintronic devices based on molecular materials or, in the
longer term, on one or a few molecules. In the area of quantum
technologies, the milestones reached in the design of molecular
spin qubits with long quantum coherence times and in the
implementation of quantum operations have raised expectations
for the use of molecular spin qubits in quantum
computation. MOFs and 2D materials are two classes of materials
for which magnetism has been, until very recently, an elusive
property; molecular materials with attractive properties and
functionalities are now starting to be developed in both
areas. In MOFs, single-molecule magnets and spin crossover
complexes can be integrated into the nodes of the framework,
within the pores or both, sometimes giving rise to smart
magnetic materials or to hybrid materials exhibiting synergistic
combinations of properties. 2D molecular-based magnets can
provide a platform to study magnetism in the 2D limit and
exhibit superior properties compared with their inorganic
analogues in terms of chemical stability and tunability.
|
Eugenio Coronado,
Molecular magnetism: from chemical design to spin control in molecules, materials and devices,
Nature Reviews Materials (2019)
|
Uncertainty estimates for magnetic relaxation times and magnetic relaxation parameters
|
The use of alternating current (AC) magnetometry to measure
magnetic relaxation times is one of the most fundamental
measurements for characterising single-molecule magnets
(SMMs). These measurements, performed as a function of
frequency, temperature and magnetic field, give vital
information on the underlying magnetic relaxation process(es)
occurring in the material. The magnetic relaxation times are
usually fitted to model functions derived from spin-phonon
coupling theories that allow characterisation of the mechanisms
of magnetic relaxation. The parameters of these relaxation
models are then often compared between different molecules in
order to find trends with molecular structure that may guide the
field to the next breakthrough. However, such meta-analyses of
the model parameters are doomed to over-interpretation unless
uncertainties in the model parameters can be quantified. Here we
determine a method for obtaining uncertainty estimates in
magnetic relaxation times from AC experiments, and provide a
program called CC-FIT2 for fitting experimental AC data as well
as the resulting relaxation times, to obtain relaxation
parameters with accurate uncertainties. Applying our approach to
three archetypal families of high-performance dysprosium(III)
SMMs shows that accounting for uncertainties has a significant
impact on the uncertainties of relaxation parameters, and that
larger uncertainties appear to correlate with crystallographic
disorder in the compounds studied. We suggest that this type of
analysis should become routine in the community.
|
Daniel Reta and Nicholas F. Chilton,
Uncertainty estimates for magnetic relaxation times and magnetic relaxation parameters,
Phys. Chem. Chem. Phys., 2019, Advance Article
|
No time to read a book? Read this!
|
Two reviews cover the fascination of magnetic molecules from the
perspective of physicists. The articles treat single molecules
magnets, low-dimensional magnets, spin crossovers, magnetic
wheels as well as other compounds. Phenomena such as slow relaxation of magnetization,
magnetization tunneling, physical properties depending on
frustration, magnetocalorics and quantum phase transitions are
discussed. A rich bibliography is provided.
|
Stephen J. Blundell,
Molecular Magnets,
Contemporary Physics 48 (2008) 275-290
Jürgen Schnack,
Large magnetic molecules and what we learn from them,
Contemporary Physics 60 (2019) 127-144
|
Origin of Spin-Dependent Tunneling Through Chiral Molecules
|
The functionality of many biological systems depends on reliable
electron transfer with minimal heating. Interestingly, nature
realizes electron transport via insulating molecules, in
contrast to man-made electronic devices which are based on
metals and semiconductors. The high efficiency of electron
transfer through these organic molecules is unexpected for
tunneling-based transport, and it is one of the most compelling
questions in the field. Furthermore, it has been shown that the
electron tunneling probability is strongly spin-dependent. Here,
the authors demonstrate that the chiral structure of these molecules
gives rise to robust coherent electron transfer. The authors introduce
spin into the analysis of tunneling through organic helical
molecules and show that they support strong spin filtering
accompanied by enhanced transmission. Thus, the study resolves
two key questions posed by transport measurements through
organic molecules.
|
Karen Michaeli, Ron Naaman,
Origin of Spin-Dependent Tunneling Through Chiral Molecules,
J. Phys. Chem. C 2019, 123, 27, 17043-17048
|
Air-stable redox-active nanomagnets with lanthanide spins radical-bridged by a metal-metal bond
|
Engineering intramolecular exchange interactions between
magnetic metal atoms is a ubiquitous strategy for designing
molecular magnets. For lanthanides, the localized nature of 4f
electrons usually results in weak exchange coupling. Mediating
magnetic interactions between lanthanide ions via radical
bridges is a fruitful strategy towards stronger coupling. In
this work we explore the limiting case when the role of a
radical bridge is played by a single unpaired electron. We
synthesize an array of air-stable Ln2@C80(CH2Ph)
dimetallofullerenes (Ln2=Y2, Gd2, Tb2, Dy2, Ho2, Er2, TbY,
TbGd) featuring a covalent lanthanide-lanthanide bond. The
lanthanide spins are glued together by very strong exchange
interactions between 4f moments and a single electron residing
on the metal-metal bonding orbital. Tb2@C80(CH2Ph) shows a
gigantic coercivity of 8.2 Tesla at 5 K and a high 100-s
blocking temperature of magnetization of 25.2 K. The Ln-Ln
bonding orbital in Ln2@C80(CH2Ph) is redox active, enabling
electrochemical tuning of the magnetism.
|
Fupin Liu, Georgios Velkos, Denis S. Krylov, Lukas Spree, Michal
Zalibera, Rajyavardhan Ray, Nataliya A. Samoylova, Chia-Hsiang
Chen, Marco Rosenkranz, Sandra Schiemenz, Frank Ziegs,
Konstantin Nenkov, Aram Kostanyan, Thomas Greber, Anja
U. B. Wolter, Manuel Richter, Bernd Büchner, Stanislav
M. Avdoshenko & Alexey A. Popov,
Air-stable redox-active nanomagnets with lanthanide spins radical-bridged by a metal-metal bond,
Nature Communicationsvolume 10, Article number: 571 (2019)
|
Rare "Janus"-faced {FeII7} single-molecule magnet exhibiting intramolecular ferromagnetic interactions
|
A rare disk-like single-molecule magnet (SMM) exclusively
bridged by end-on azides with a spin ground state of S=14 was
prepared by the reaction of a divalent Fe(II) precursor with
Me3SiN3 under basic conditions. AC magnetic susceptibility
studies revealed unusual, "Janus"-faced SMM behavior for the
dried and pristine forms of the compound attributed to
solvation/de-solvation effects of the
coordinated MeCN ligands which leads to alterations in the
crystal field and symmetry of the metal ions. DFT calculations
confirmed the ferromagnetic nature of the interactions between
the FeII spin carriers with the zero-field splitting parameters
D=-0.2323 cm-1 and E/D=0.027. The results have important
implications for the future study of single-molecule magnets
incorporating volatile solvent molecules in the first
coordination sphere of the metal ions and their effect on the
relaxation dynamics.
|
Dimitris I. Alexandropoulos, Kuduva R. Vignesh, Theocharis
C. Stamatatos, Kim R. Dunbar, Rare "Janus"-faced {FeII7} single-molecule magnet exhibiting intramolecular ferromagnetic interactions,
Chem. Sci., 2019,10, 1626-1633
|
Chemistry and Quantum Mechanics in 2019: Give Us Insight and Numbers
|
This Perspective revisits Charles Coulson's famous statement
from 1959 "give us insight not numbers" in which he pointed out
that accurate computations and chemical understanding often do
not go hand in hand. The authors argue that today, accurate wave function
based first-principle calculations can be performed on large
molecular systems, while tools are available to interpret the
results of these calculations in chemical language. This leads
us to modify Coulson's statement to "give us insight and
numbers". Examples from organic, inorganic, organometallic and
surface chemistry as well as molecular magnetism illustrate the
points made.
|
Frank Neese, Mihail Atanasov, Giovanni Bistoni, Dimitrios
Maganas, Shengfa Ye,
Chemistry and Quantum Mechanics in 2019: Give Us Insight and Numbers,
J. Am. Chem. Soc.201914172814-2824
|
A linear cobalt(II) complex with maximal orbital angular momentum from a non-Aufbau ground state
|
Orbital angular momentum is a prerequisite for magnetic
anisotropy, although in transition metal complexes it is
typically quenched by the ligand field. By reducing the basicity
of the carbon donor atoms in a pair of alkyl ligands, the authors
synthesized a cobalt(II) dialkyl complex, Co(C(SiMe2ONaph)3)2
(where Me is methyl and Naph is a naphthyl group), wherein the
ligand field is sufficiently weak that interelectron repulsion
and spin-orbit coupling play a dominant role in determining the
electronic ground state. Assignment of a non-Aufbau (dx2-y2,
dxy)3(dxz, dyz)3(dz2)1 electron configuration is supported by dc
magnetic susceptibility data, experimental charge density maps,
and ab initio calculations. Variable-field far-infrared
spectroscopy and ac magnetic susceptibility measurements further
reveal slow magnetic relaxation via a 450-wave number magnetic
excited state.
|
Philip C. Bunting, Mihail Atanasov, Emil Damgaard-Moller,
Mauro Perfetti, Iris Crassee, Milan Orlita, Jacob
Overgaard, Joris van Slageren, Frank Neese, Jeffrey R. Long,
A linear cobalt(II) complex with maximal orbital angular momentum from a non-Aufbau ground state,
Science 21 Dec 2018, Vol. 362, Issue 6421, eaat7319
|
First-principles many-body models for electron transport through molecular nanomagnets
|
Impressive advances in the field of molecular spintronics allow
one to study electron transport through individual magnetic
molecules embedded between metallic leads in the purely quantum
regime of single electron tunneling. Besides fundamental
interest, this experimental setup, in which a single molecule is
manipulated by electronic means, provides the elementary units
of possible forthcoming technological applications, ranging from
spin valves to transistors and qubits for quantum information
processing. Theoretically, while for weakly correlated molecular
junctions established first-principles techniques do enable the
system-specific description of transport phenomena, methods of
similar power and flexibility are still lacking for junctions
involving strongly correlated molecular nanomagnets. Here the
authors
propose an efficient scheme based on the ab initio construction
of material-specific Hubbard models and on the master-equation
formalism. The authors apply this approach to a representative case, the
{Ni2} molecular spin dimer, in the regime of weak
molecule-electrode coupling, the one relevant for
quantum-information applications. The approach allows to
study in a realistic setting many-body effects such as current
suppression and negative differential conductance. The authors
think that
this method has the potential for becoming a very useful tool
for describing transport phenomena in strongly correlated
molecules. |
A. Chiesa, E. Macaluso, P. Santini, S. Carretta, and
E. Pavarini,
First-principles many-body models for electron transport through molecular nanomagnets,
Phys. Rev. B 99, 235145 (2019)
|
161Dy Time-Domain Synchrotron Mössbauer Spectroscopy for Investigating Single-Molecule Magnets Incorporating Dy Ions
|
Time-domain synchrotron Mössbauer spectroscopy (SMS) based on
the Mössbauer effect of 161Dy has been used to investigate the
magnetic properties of a DyIII-based single-molecule magnet
(SMM). The magnetic hyperfine field of
[Dy(Cy3PO)2(H2O)5]Br3 2(Cy3PO) 2H2O 2EtOH is with
B=582.3T significantly larger than that of the free-ion
DyIII with a 6H15/2 ground state. This
difference is attributed
to the influence of the coordinating ligands on the Fermi
contact interaction between the s and 4f electrons of the DyIII
ion. This study demonstrates that 161Dy SMS is an effective
local probe of the influence of the coordinating ligands on the
magnetic structure of Dy-containing compounds.
|
Dipl.-Phys. Lena Scherthan, Dr. Sebastian F. M. Schmidt,
Dipl.-Biophys. Hendrik Auerbach, Dipl.-Phys. Tim
Hochdörffer, Dr. Juliusz A. Wolny, Dr. Wenli Bi, Dr. Jiyong
Zhao, Dr. Michael Y. Hu, Dr. Tom Toellner, Dr. E. Ercan Alp,
Dr. Dennis E. Brown, Dr. Christopher E. Anson, Prof. Annie
K. Powell, Prof. Volker Schünemann,
161Dy Time-Domain Synchrotron Mössbauer Spectroscopy for Investigating Single-Molecule Magnets Incorporating Dy Ions,
Angew. Chem. Int. Ed. 58, 2019, 3444-3449
See also this press release.
|
Insight into D6h Symmetry: Targeting Strong Axiality in Stable Dysprosium(III) Hexagonal Bipyramidal Singleâ€Ion Magnets
|
Following a novel synthetic strategy where the strong uniaxial
ligand field generated by the Ph3SiO- (Ph3SiO- = anion of
triphenylsilanol) and the 2,4-di-tBu-PhO- (2,4-di-tBu-PhO- =
anion of 2,4-di-tert-butylphenol) ligands combined with the weak
equatorial field of the ligand LN6, leads to
[DyIII(LN6)(2,4-di-tBu-PhO)2](PF6) (1),
[DyIII(LN6)(Ph3SiO)2](PF6) (2) and [DyIII(LN6)(Ph3SiO)2](BPh4)
(3) hexagonal bipyramidal dysprosium(III) single-molecule
magnets (SMMs) with high anisotropy barriers of Ueff = 973 K for
1, Ueff = 1080 K for 2 and Ueff = 1124 K for 3 under zero
applied dc field. Ab initio calculations predict that the
dominant magnetization reversal barrier of these complexes
expands up to the 3rd Kramers doublet, thus revealing for the
first time the exceptional uniaxial magnetic anisotropy that
even the six equatorial donor atoms fail to negate, opening up
the possibility to other higher-order symmetry SMMs.
|
Mark Murrie, Angelos Canaj, Sourav Dey, Emma Regincos Marti,
Claire Wilson, Gopalan Rajaraman,
Insight into D6h Symmetry: Targeting Strong Axiality in Stable Dysprosium(III) Hexagonal Bipyramidal Single-Ion Magnets,
Angew. Chem. Int. Ed. (2019) accepted article
|
Quantum hardware simulating four-dimensional inelastic neutron scattering
|
Magnetic molecules, modelled as finite-size spin systems, are
test-beds for quantum phenomena1 and could constitute key
elements in future spintronics devices, long-lasting
nanoscale memories or noise-resilient quantum computing
platforms. Inelastic neutron scattering is the technique
of choice to probe them, characterizing molecular eigenstates on
atomic scales. However, although large magnetic
molecules can be controllably synthesized, simulating
their dynamics and interpreting spectroscopic measurements is
challenging because of the exponential scaling of the required
resources on a classical computer. Here, the authors show that quantum
computers have the potential to efficiently extract
dynamical correlations and the associated magnetic neutron
cross-section by simulating prototypical spin systems on a
quantum hardware.
|
A. Chiesa, F. Tacchino, M. Grossi, P. Santini, I. Tavernelli,
D. Gerace, S. Carretta,
Quantum hardware simulating four-dimensional inelastic neutron scattering,
Nature Physics 15, 455-459 (2019)
|
Giant Barocaloric Effect at the Spin Crossover Transition of a Molecular Crystal
|
The first experimental evidence for a giant, conventional
barocaloric effect (BCE) associated with a pressure-driven spin
crossover transition near room temperature is
provided. Magnetometry, neutron scattering, and calorimetry are
used to explore the pressure dependence of the SCO phase
transition in polycrystalline samples of protonated and
partially deuterated [FeL2][BF4]2
[L=2,6-di(pyrazol-1-yl)pyridine] at applied pressures of up to
120 MPa (1200 bar). The data indicate that, for a pressure change of
only 0-300 bar (0-30 MPa), an adiabatic temperature change of 3
K is observed at 262 K or 257 K in the protonated and deuterated
materials, respectively. This BCE is equivalent to the
magnetocaloric effect (MCE) observed in gadolinium in a magnetic
field change of 0-1 Tesla. The work confirms recent predictions
that giant, conventional BCEs will be found in a wide range of
SCO compounds.
|
Steven P. Vallone, Anthony N. Tantillo, Antonio M. dos Santos,
Jamie J. Molaison, Rafal Kulmaczewski, Antonin Chapoy, Pezhman
Ahmadi, Malcolm A. Halcrow, Karl G. Sandeman,
Giant Barocaloric Effect at the Spin Crossover Transition of a Molecular Crystal,
Adv. Mater. 2019, 1807334
|
After MAGPACK there comes VIBPACK
|
A FORTRAN code based on a new powerful and efficient
computational approach to solve multidimensional dynamic
Jahn-Teller and pseudo Jahn-Teller problems is presented. This
symmetry-assisted approach constituting a theoretical core of
the program is based on the full exploration of the point
symmetry of the electronic and vibrational states. The authors also
report some selected examples of increasing complexity aimed to
display the theoretical background as well as the advantages and
capabilities of the program to evaluate of the energy pattern,
magnetic and optical properties of large multimode vibronic
systems. |
Juan M. Clemente-Juan, Andrew Palii, Boris Tsukerblat, Eugenio
Coronado,
VIBPACK: A package to treat multidimensional electron-vibrational molecular problems with application to magnetic and optical properties,
Journal of Computational Chemistry 2018, 39, 1815-1827
|
Neutron Scattering in Coordination Chemistry
|
The application of four dimensional inelastic neutron scattering
to coordination chemistry is demonstrated in a special issue of
the European Journal of Inorganic Chemistry
by the guest editors John A. Stride, Wendy L. Queen, and
Antonio Romerosa.
See e.g. the following articles.
Elena Garlatti, Alessandro Chiesa, Tatiana Guidi, Giuseppe
Amoretti, Paolo Santini, Stefano Carretta,
Unravelling the Spin Dynamics of Molecular Nanomagnets with Four-Dimensional Inelastic Neutron Scattering,
Eur. J. Inorg. Chem. 2019 (2019) 1106-1118
Krunoslav Prša, Oliver Waldmann,
Inelastic Neutron Scattering Intensities of Ferromagnetic Cluster Spin Waves,
Eur. J. Inorg. Chem. 2019 (2019) 1128-1141
|
|
Electric field modulation of magnetic exchange in molecular helices
|
The possibility to operate on magnetic materials through the
application of electric rather than magnetic fields - promising
faster, more compact and energy efficient circuits - continues to
spur the investigation of magnetoelectric effects. Symmetry
considerations, in particular the lack of an inversion centre,
characterize the magnetoelectric effect. In addition, spin-orbit
coupling is generally considered necessary to make a spin system
sensitive to a charge distribution. However, a magnetoelectric
effect not relying on spin-orbit coupling is appealing for
spin-based quantum technologies. Here, we report the detection
of a magnetoelectric effect that we attribute to an electric
field modulation of the magnetic exchange interaction without
atomic displacement. The effect is visible in electron
paramagnetic resonance absorption of molecular helices under
electric field modulation and confirmed by specific symmetry
properties and spectral simulation.
|
Maria Fittipaldi, Alberto Cini, Giuseppe Annino, Alessandro
Vindigni, Andrea Caneschi, Roberta Sessoli,
Electric field modulation of magnetic exchange in molecular helices,
Nature Materials, volume 18, pages329-334 (2019)
|
Cages on a plane: a structural matrix for molecular 'sheets'
|
A family of heterometallic Anderson-type 'wheels' of general
formula
[MIII2MII5(hmp)12]4+
(MIII = Cr or Al and
MII = Ni or Zn, Hhmp =
2-pyridinemethanol) has been extended by the authors to include
MIII = Cr or Al and
MII = Co, Fe, Mn or Cu, affording five
new species of formulae
[Cr2Co5(hmp)12](ClO4)4
(1),
[Cr2Fe5(hmp)12](ClO4)4
(2),
[Cr2Mn5(hmp)12](ClO4)4
(3),
[Cr2Cu5(hmp)12](ClO4)2(NO3)2
(4) and
[Al2Co5(hmp)12](ClO4)4
(5). As per previous family members, the
metallic skeleton common to the cations of 1-5
describes a centred hexagon with the two
MIII sites disordered around the outer
wheel, with the exception of compound 4 where
the CuII sites are localised. A
structurally related, but enlarged planar disc possessing a
[MIII6MII]
hexagon capped on each edge by a CuII
ion can be formed, but only when MIII
= Al and MII = Cu. In
[AlIII6CuII7(OH)12(hmp)12](ClO4)6(NO3)2
(6) the Anderson moiety contains a central,
symmetry-imposed octahedral CuII ion
surrounded by a wheel of AlIII
ions. Solid-state dc susceptibility and magnetisation
measurements reveal the presence of competing exchange
interactions in 1-5, and very weak
antiferromagnetic exchange between the
CuII ions in 6 which
may be intra- and/or intermolecular in nature.
|
Hector W. L. Fraser, Gary S. Nichol, Amgalanbaatar
Baldansuren, Eric J. L. McInnes, Euan K. Brechin,
Cages on a plane: a structural matrix for molecular 'sheets',
Dalton Trans., 2018, 47, 15530-15537
|
Switchable cobalt coordination polymers: Spin crossover and valence tautomerism
|
Electronically labile, or switchable, cobalt coordination
polymers exhibit reversible spin crossover (SCO) or valence
tautomeric (VT) transitions upon the application of an external
stimulus, such as temperature variation. Spin crossover
transitions at pseudo-octahedral cobalt(II) centers with an
appropriate ligand field involve a heating-induced transition
from the low-spin to high-spin electronic
configurations. Valence tautomeric transitions are most commonly
observed for cobalt-dioxolene systems, which undergo an
intramolecular electron transfer and concomitant spin transition
at the cobalt center, from low-spin-cobalt(III)-catecholate at
low temperature to high-spin-cobalt(II)-semiquinonate upon
heating. The VT transition can also be induced by light, while
the cobalt(II) SCO transition cannot. Incorporation of these
switchable moieties into coordination polymers (CPs) is
generally achieved using polytopic nitrogen-donor linking
ligands. All but one of the switchable cobalt CPs that have been
structurally characterized are 1D chains, most of which exhibit
VT transitions rather than SCO. There is a single example of a
switchable 2D cobalt CP where VT cobalt-dioxolene moieties are
linked by a tetratopic nitrogen-donor bridging ligand. Efforts
to confer the VT properties to compounds suitable for
applications as materials or in devices have mainly focused on
the incorporation of the 1D chain VT CPs into nano- and
microparticles, in which the VT transition is generally
maintained. Valence tautomeric nanoparticles synthesized from 1D
chain CPs have been grafted on to gold surfaces as
self-assembled monolayers.
|
Olga Drath, Colette Boskovic,
Switchable cobalt coordination polymers: Spin crossover and valence tautomerism,
Coordination Chemistry Reviews, Volume 375, 2018, Pages 256-266
|
Electric Field Control of Spins in Molecular Magnets
|
Coherent control of individual molecular spins in nanodevices is
a pivotal prerequisite for fulfilling the potential promised by
molecular spintronics. By applying electric field pulses during
time-resolved electron spin resonance measurements, the authors measure
the sensitivity of the spin in several antiferromagnetic
molecular nanomagnets to external electric fields. They find a
linear electric field dependence of the spin states in
{Cr7Mn}, an antiferromagnetic ring with a
ground-state spin of S=1, and in a frustrated
{Cu3} triangle.Conversely, the antiferromagnetic ring
{Cr7Ni}, isomorphic with {Cr7Mn} but with
S=1/2, does not exhibit a detectable effect. The authors propose that the
spin-electric field coupling may be used for selectively
controlling individual molecules embedded in nanodevices.
|
Junjie Liu, Jakub Mrozek, William K. Myers, Grigore A. Timco,
Richard E.P. Winpenny, Benjamin Kintzel, Winfried Plass, and
Arzhang Ardavan,
Electric Field Control of Spins in Molecular Magnets,
Phys. Ref. Lett. 122, 037202 (2019)
|
Insights into Magnetic Interactions in a Monodisperse Gd12Fe14 Metal Cluster
|
The largest Ln-Fe metal cluster {Gd12Fe14}
and the core-shell monodisperse metal cluster of {Gd12Fe14}@SiO2
were prepared. Experimental and theoretical studies on the magnetic
properties reveal
that encapsulation of one cluster into one silica nanosphere not
only effectively decreases intermolecular magnetic interactions
but also significantly increases the zero-field splitting effect
of the outer layer Fe3+ ions.
|
Xiu-Ying Zheng, Hui Zhang, Zhenxing Wang, Pengxin Liu,
Ming-Hao Du, Ying-Zi Han, Rong-Jia Wei, Zhong-Wen Ouyang,
Xiang-Jian Kong, Gui-Lin Zhuang,
La-Sheng Long, Lan-Sun Zheng,
Insights into Magnetic Interactions in a Monodisperse Gd12Fe14 Metal Cluster,
Angew. Chem. Int. Ed. 56, 11475-11479 (2017)
|
Molecular electronic spin qubits from a spin-frustrated trinuclear copper complex
|
A new trinuclear copper(II) complex was
synthesized and characterized by experimental as well as
theoretical methods. This complex exhibits a strong
antiferromagnetic coupling (J = -298 cm-1) between the
copper(II) ions, mediated by the N-N diazine bridges of the
tritopic ligand, leading to a spin-frustrated system. This
compound shows a T2 coherence time of 340 ns in frozen pyridine
solution, which extends to 591 ns by changing the solvent to
pyridine-d5. Hence, the presented compound is a promising
candidate as a building block for molecular spintronics.
|
Benjamin Kintzel, Michael Böhme, Junjie Liu, Anja
Burkhardt, Jakub Mrozek, Axel Buchholz, Arzhang Ardavan, Winfried Plass,
Molecular electronic spin qubits from a spin-frustrated trinuclear copper complex,
Chem. Commun., 2018,54, 12934-12937
|
Element specific determination of the magnetic properties of two macrocyclic tetranuclear 3d-4f complexes with a Cu3Tb core by means of X-ray magnetic circular dichroism (XMCD)
|
We apply X-ray magnetic circular dichroism to study the internal
magnetic structure of two very promising star shaped macrocyclic
complexes with a CuII3TbIII core. These complexes are rare
examples prepared with a macrocyclic ligand that show
indications of SMM (Single Molecule Magnet) behavior, and they
differ only in ring size: one has a propylene linked macrocycle,
[CuII3TbIII(LPr)(NO3)2(MeOH)(H2O)2](NO3) 3H2O (nickname:
Cu3Tb(LPr)), and the other has the butylene linked analogue,
[CuII3TbIII(LBu)(NO3)2(MeOH)(H2O)](NO3) 3H2O (nickname:
Cu3Tb(LBu)). We analyze the orbital and spin contributions to
the Cu and Tb ions quantitatively by applying the spin and
orbital sum rules concerning the L2 (M4)/L3 (M5) edges. In
combination with appropriate ligand field simulations, we
demonstrate that the Tb(III) ions contribute with high orbital
magnetic moments to the magnetic anisotropy, whereas the ligand
field determines the easy axis of magnetization. Furthermore, we
confirm that the Cu(II) ions in both molecules are in a divalent
valence state, the magnetic moments of the three Cu ions appear
to be canted due to 3d-3d intramolecular magnetic
interactions. For Cu3Tb(LPr), the corresponding element specific
magnetization loops reflect that the Cu(II) contribution to the
overall magnetic picture becomes more important as the
temperature is lowered. This implies a low value for the 3d-4f
coupling.
|
K. Balinski, L. Schneider, J. Wöllermann, A. Buling,
L. Joly, C. Piamonteze, H. L. C. Feltham, S. Brooker,
A. K. Powell, B. Delley and K. Kuepper,
Element specific determination of the magnetic properties of two macrocyclic tetranuclear 3d-4f complexes with a Cu3Tb core by means of X-ray magnetic circular dichroism (XMCD),
Phys. Chem. Chem. Phys., 2018, g20, 21286-21293
Along similar lines compare
A. Alhassanat, C. Gamer, A. Rauguth, A. A. Athanasopoulou,
J. Sutter, C. Luo, H. Ryll, F. Radu, A. A. Sapozhnik,
T. Mashoff, E. Rentschler, and H. J. Elmers,
Element-specific magnetic properties of mixed 3d-4f metallacrowns,
Phys. Rev. B 98, 064428 (2018)
|
Novel Magnetic Nanostructures
|
A sharp increase in research activity in the field of magnetic
nanostructures prompted us to present new scientific results
obtained in the last decade. Magnetic nanoscale materials are
the key to the future of the storage industry.
The demand for higher density of information storage and the
emergence of completely new technologies call for entirely new
types of magnetic nanostructures. This book provides the latest
research on novel magnetic nanostructures, including molecular
nanomagnets, magnetic dendrimers, self-assembling magnetic
nanoparticles, nanoparticles with spin-crossover properties,
multifunctional nanostructures, and much more.
Nanomagnets based on d- and f-block coordination compounds as
single-molecule magnets demonstrate properties that are suitable
for quantum information processing. The book reviews the
synthesis, design, characterization, and detection of unusual
properties in new magnetic nanostructures. It discusses the
physical properties and potential industry-oriented applications
such as magnetic data storage, magnetic sensors, magnetic tunnel
junctions, spintronics, and biomedical applications.
This book is primarily intended for graduate students, but will
be of great interest also to all scientists and engineers
working in field of magnetic nanoscale materials.
|
Editor(s): Natalia Domracheva, Maria Caporali, Eva Rentschler,
Novel Magnetic Nanostructures,
Elsevier, 2018, ISBN 9780128135945,
|
The race goes on: record for ground state spin now at S=91
|
After the successful synthesis and characterization of a toric
cluster with S=60 (see npj Quantum Materials 3 (2018) 10 and below on
this page) a new cluster was produced featuring an S=91 ground
state.
The detailed analysis of magnetic interactions in such giant
molecules is difficult both because the synthesis of such
compounds is challenging and the number of energy levels
increases exponentially with the magnitude and number of
spins. The authors isolated a {Ni21Gd20} nanocage with a large
number of energy levels (approx 5 x 1030) and used
quantum Monte Carlo (QMC) simulations to perform a detailed
analysis of magnetic interactions. Based on magnetization
measurements above 2 K, the QMC simulations predicted very weak
ferromagnetic interactions that would give a record S=91 spin
ground state. Low-temperature measurements confirm the spin
ground state but suggest a more complex picture due to the single ion
anisotropy; this has also been modeled using the QMC
approach. The high spin and large number of low-lying states
lead to a large low-field magnetic entropy for this material.
|
Wei-Peng Chen, Jared Singleton, Lei Qin, Agustin Camon, Larry
Engelhardt, Fernando Luis, Richard E. P. Winpenny & Yan-Zhen
Zheng,
Quantum Monte Carlo simulations of a giant {Ni21Gd20} cage with a S=91 spin ground state,
Nature Communications 9, Article number: 2107 (2018)
|
Hyperfine-Interaction-Driven Suppression of Quantum Tunneling at Zero Field in a Holmium(III) Single-Ion Magnet
|
An extremely rare non-Kramers holmium(III) single-ion magnet
(SIM) is reported to be stabilized in the pentagonal-bipyramidal
geometry by a phosphine oxide with a high energy barrier of
237(4)/cm. The suppression of the quantum tunneling of
magnetization (QTM) at zero field and the hyperfine structures
originating from field-induced QTMs can be observed even from
the field-dependent alternating-current magnetic susceptibility
in addition to single-crystal hysteresis loops. These dramatic
dynamics were attributed to the combination of the favorable
crystal-field environment and the hyperfine interactions arising
from 165Ho (I=7/2) with a natural abundance of 100 %.
|
Yan-Cong Chen, Jun-Liang Liu, Wolfgang Wernsdorfer, Dan Liu, Liviu F. Chibotaru, Xiao-Ming Chen, Ming-Liang Tong,
Hyperfine-Interaction-Driven Suppression of Quantum Tunneling at Zero Field in a Holmium(III) Single-Ion Magnet,
Angew. Chem. Int. Ed. 56, 2017, 4996-5000
See also:
Jun-Liang Liu, Yan-Cong Chen, Ming-Liang Tong,
Symmetry strategies for high performance lanthanide-based single-molecule magnets,
Chem. Soc. Rev., 2018, 47, 2431-2453
|
Modeling Spin Interactions in a Triangular Cobalt(II) Complex with Triaminoguanidine Ligand Framework: Synthesis, Structure, and Magnetic Properties
|
The new tritopic triaminoguanidine-based ligand
1,2,3-tris[(pyridine-2-ylmethylidene)amino]guanidine (H2pytag)
was synthesized. The reaction of a mixture of cobalt(II)
chloride and cobalt(II) perchlorate with the ligand H2pytag in
pyridine solution leads to the formation of the trinuclear
cobalt(II) complex [Co3(pytag)(py)6Cl3]ClO4. Three octahedrally
coordinated high-spin cobalt(II) ions are linked through the
bridging triaminoguanidine backbone of the ligand leading to an
almost equilateral triangular arrangement. The magnetic
properties of the complex were investigated by magnetic
measurements, variable-temperature, variable-field magnetic
circular dichroism (MCD) spectroscopy, and density functional
theory as well as ab initio calculations. A rather strong
antiferromagnetic exchange interaction between the cobalt(II)
centers of ca. -12/cm is determined together with a strong
local anisotropy. The single-ion anisotropy of all three
cobalt(II) centers is found to be easy-plane, which coincides
with the tritopic ligand plane. MCD measurements and theoretical
investigations demonstrate the presence of rhombic distortion of
the local Co surrounding.
|
Daniel Plaul, Michael Böhme, Serghei Ostrovsky, Zbigniew
Tomkowicz, Helmar Görls, Wolfgang Haase, Winfried Plass,
Modeling Spin Interactions in a Triangular Cobalt(II) Complex with Triaminoguanidine Ligand Framework: Synthesis, Structure, and Magnetic Properties,
Inorg. Chem., 2018, 57 (1), pp 106-119
See also:
Eike T. Spielberg, Aksana Gilb, Daniel Plaul, Daniel Geibig,
David Hornig, Dirk Schuch, Axel Buchholz, Arzhang Ardavan,
Winfried Plass,
A Spin-Frustrated Trinuclear Copper Complex Based on Triaminoguanidine with an Energetically Well-Separated Degenerate Ground State,
Inorg. Chem., 2015, 54 (7), pp 3432-3438
|
Robust and Selective Switching of an FeIII Spin-Crossover Compound on Cu2N/Cu(100) with Memristance Behavior
|
The switching between two spin states makes spin-crossover
molecules on surfaces very attractive for potential applications
in molecular spintronics. Using scanning tunneling microscopy,
the successful deposition of [Fe(pap)2]+ (pap =
N-2-pyridylmethylidene-2-hydroxyphenylaminato) molecules on
Cu2N/Cu(100) surface is evidenced. The deposited FeIII
spin-crossover compound is controllably switched between three
different states, each of them exhibiting a characteristic
tunneling conductance. The conductance is therefore employed to
readily read the state of the molecules. A comparison of the
experimental data with the results of density functional theory
calculations reveals that all Fe(pap)2 molecules are initially
in their high-spin state. The two other states are compatible
with the low-spin state of the molecule but differ with respect
to their coupling to the substrate. As a proof of concept, the
reversible and selective nature of the switching is used to
build a two-molecule memory.
|
Torben Jasper-Toennies, Manuel Gruber, Sujoy Karan, Hanne
Jacob, Felix Tuczek , Richard Berndt,
Robust and Selective Switching of an FeIII Spin-Crossover Compound on Cu2N/Cu(100) with Memristance Behavior,
Nano Lett. 2017, 11, 6613-6619
|
Highly Ordered Surface Self-Assembly of Fe4 Single Molecule Magnets
|
Single molecule magnets (SMMs) have attracted considerable
attention due to low-temperature magnetic hysteresis and
fascinating quantum effects. The investigation of these
properties requires the possibility to deposit well-defined
monolayers or spatially isolated molecules within a
well-controlled adsorption geometry. Here the authors present a
successful fabrication of self-organized arrays of Fe4 SMMs on
hexagonal boron nitride (h-BN) on Rh(111) as template. Using a
rational design of the ligand shell optimized for surface
assembly and electrospray as a gentle deposition method, we
demonstrate how to obtain ordered arrays of molecules forming
perfect hexagonal superlattices of tunable size, from small
islands to an almost perfect monolayer. High-resolution low
temperature scanning tunneling microscopy (STM) reveals that the
Fe4 molecule adsorbs on the substrate in a flat geometry,
meaning that its magnetic easy axis is perpendicular to the
surface. By scanning tunneling spectroscopy (STS) and density
functional theory (DFT) calculations, we infer that the
majority- and minority-spin components of the spin-split lowest
unoccupied molecular orbital (LUMO) can be addressed separately
on a submolecular level.
|
Philipp Erler, Peter Schmitt, Nicole Barth, Andreas Irmler,
Samuel Bouvron, Thomas Huhn, Ulrich Groth, Fabian Pauly,
Luca Gragnaniello, Mikhail Fonin,
Highly Ordered Surface Self-Assembly of Fe4 Single Molecule Magnets,
Nano Lett., 2015, 15, 4546-4552
|
Mössbauer spectroscopy of a monolayer of single molecule magnets
|
The use of single molecule magnets (SMMs) as cornerstone
elements in spintronics and quantum computing applications
demands that magnetic bistability is retained when molecules are
interfaced with solid conducting surfaces. Here, the authors employ
synchrotron Mössbauer spectroscopy to investigate a monolayer of
a tetrairon(III) (Fe4) SMM chemically grafted on a gold
substrate. At low temperature and zero magnetic field, the authors
observe the magnetic pattern of the Fe4 molecule, indicating
slow spin fluctuations compared to the Mössbauer
timescale. Significant structural deformations of the magnetic
core, induced by the interaction with the substrate, as
predicted by ab initio molecular dynamics, are also
observed. However, the effects of the modifications occurring at
the individual iron sites partially compensate each other, so
that slow magnetic relaxation is retained on the
surface. Interestingly, these deformations escaped detection by
conventional synchrotron-based techniques, like X-ray magnetic
circular dichroism, thus highlighting the power of synchrotron
Mössbauer spectroscopy for the investigation of hybrid
interfaces.
|
Alberto Cini, Matteo Mannini, Federico Totti, Maria Fittipaldi,
Gabriele Spina, Aleksandr Chumakov, Rudolf Rüffer, Andrea
Cornia, Roberta Sessoli,
Mössbauer spectroscopy of a monolayer of single molecule magnets,
Nature Communications 9, 480 (2018)
|
Myriam Sarachik looks back in Annual Review of Condensed Matter Physics
|
This autobiographical narrative offers a brief account of Prof. Sarachik's
journey and adventures in condensed matter physics (a.k.a. solid
state physics) and some of the personal events that shaped her
life and career: early years in Europe, family's escape
from the Nazis, growing up in Cuba, the difficult road into a
field that was essentially closed to women, a personal disaster
that knocked the wind out of her sails for more than a decade,
and her return to a successful career in physics. In closing, she
argues that, although we have made remarkable progress, we know
but a thimble-full in our inexhaustible search for an
understanding of the laws of nature.
|
Myriam P. Sarachik,
Pushing Boundaries: My Personal and Scientific Journey,
Annual Review of Condensed Matter Physics 9, 1-15 (2018)
|
Effects of uniaxial pressure on the quantum tunneling of magnetization in a high-symmetry
Mn12 single-molecule magnet
|
The symmetry of single-molecule magnets dictates their spin
quantum dynamics, influencing how such systems relax via quantum
tunneling of magnetization (QTM). By reducing a system's
symmetry, through the application of a magnetic field or
uniaxial pressure, these dynamics can be modified. The authors report
measurements of the magnetization dynamics of a crystalline
sample of a high-symmetry Mn12 single-molecule magnet
as a function of uniaxial pressure applied either parallel or
perpendicular to the sample's "easy" magnetization axis. At
temperatures between 1.8 and 3.3 K, magnetic hysteresis loops
exhibit the characteristic steplike features that signal the
occurrence of QTM. After applying uniaxial pressure to the
sample in situ, both the magnitude and field position of the QTM
steps changed. The step magnitudes were observed to grow as a
function of pressure in both arrangements of pressure, while
pressure applied along (perpendicular to) the sample's easy axis
caused the resonant-tunneling fields to increase
(decrease). These observations were compared with simulations in
which the system's Hamiltonian parameters were changed. From
these comparisons, we determined that parallel pressure induces
changes to the second-order axial anisotropy parameter as well
as either the fourth-order axial or fourth-order transverse
parameter, or to both. In addition, we find that pressure
applied perpendicular to the easy axis induces a rhombic
anisotropy that can be understood as deriving from a
symmetry-breaking distortion of the molecule. |
James H. Atkinson, Adeline D. Fournet, Lakshmi Bhaskaran, Yuri
Myasoedov, Eli Zeldov, Enrique del Barco, Stephen Hill, George
Christou, and Jonathan R. Friedman,
Effects of uniaxial pressure on the quantum tunneling of magnetization in a high-symmetry
Mn12 single-molecule magnet,
Phys. Rev. B 95, 184403 (2017)
|
High spin cycles: topping the spin record for a single molecule verging on quantum criticality
|
The cyclisation of a short chain into a ring provides
fascinating scenarios in terms of transforming a finite array of
spins into a quasi-infinite structure. If frustration is
present, theory predicts interesting quantum critical points,
where the ground state and thus low-temperature properties of a
material change drastically upon even a small variation of
appropriate external parameters. This can be visualised as
achieving a very high and pointed summit where the way down has
an infinity of possibilities, which by any parameter change will
be rapidly chosen, in order to reach the final ground
state. The authors of the article in the new Nature journal npj
Quantum Materials report a mixed 3d/4f cyclic coordination cluster
that turns out to be very near or even at such a quantum
critical point. It has a ground state spin of S=60, the
largest ever observed for a molecule (120 times that of a single
electron). The molecule forms a nano-torus with alternating
gadolinium and iron ions with a
nearest neighbour Fe-Gd coupling and a frustrating next-nearest
neighbour Fe-Fe coupling. Such a spin arrangement corresponds to
a cyclic delta or saw-tooth chain, which can exhibit unusual
frustration effects. In the present case, the quantum critical
point bears a 'flatland' of tens of thousands of energetically
degenerate states between which transitions are possible at no
energy costs with profound caloric consequences. Entropy-wise
the energy flatland translates into the pointed summit
overlooking the entropy landscape. Going downhill several target
states can be reached depending on the applied physical
procedure which offers new prospects for addressability.
|
Amer Baniodeh, Nicola Magnani, Yanhua Lan, Gernot Buth,
Christopher E. Anson, Johannes Richter, Marco Affronte, Jürgen
Schnack, Annie K. Powell,
High spin cycles: topping the spin record for a single molecule verging on quantum criticality,
npj Quantum Materials 3 (2018) 10
For a structurally related compound see also:
Lei Qin, Jared Singleton, Wei-Peng Chen, Hiroyuki Nojiri, Larry
Engelhardt, Richard E. P. Winpenny, Yan-Zhen Zheng,
Quantum Monte Carlo Simulations and High-Field Magnetization Studies of Antiferromagnetic Interactions in a Giant Hetero-Spin Ring,
Angew. Chem. Int. Ed. 56, 2017, 16571-16574
|
Dynamical spin accumulation in large-spin magnetic molecules
|
The frequency-dependent transport through a nanodevice
containing a large-spin magnetic molecule is studied
theoretically in the Kondo regime. Specifically, the effect of
magnetic anisotropy on dynamical spin accumulation is of primary
interest. Such accumulation arises due to finite components of
frequency-dependent conductance that are off diagonal in
spin. Here, employing the Kubo formalism and the numerical
renormalization group method, the authors demonstrate that the dynamical
transport properties strongly depend on the relative orientation
of spin moments in electrodes of the device, as well as on
intrinsic parameters of the molecule. In particular, the effect
of dynamical spin accumulation is found to be greatly affected
by the type of magnetic anisotropy exhibited by the molecule,
and it develops for frequencies corresponding to the Kondo
temperature. For the parallel magnetic configuration of the
device, the presence of dynamical spin accumulation is
conditioned by the interplay of ferromagnetic-lead-induced
exchange field and the Kondo correlations.
|
Anna Plominska, Ireneusz Weymann, Maciej Misiorny,
Dynamical spin accumulation in large-spin magnetic molecules,
Phys. Rev. B 97, 035415 (2018)
|
Correlating electronic and magnetic coupling in large magnetic molecules via scanning tunneling microscopy
|
In an effort to improve the spin coupling in single-molecule
magnets, the authors rationally designed a new building-block molecule
with significantly enhanced spin coupling compared to a
previously established molecule. The authors relate this to a
stabilization of aromaticity in the central connecting carbon
ring, promoting the spin-polarization mechanism. This
correlation between magnetic and electronic properties is
supported by bulk measurements as well as submolecularly
resolved scanning tunneling microscopy and spectroscopy
experiments, where the authors found distinct differences in the local
density of states distribution of the two molecules, especially
at the central carbon ring. While the established molecule
exhibits localized, spatially decoupled and even switchable
states, the improved building block exhibits symmetric local
density of states delocalized over the entire molecule, also
revealing that this main characteristic electronic property is
preserved upon adsorption on a metal surface. Due to their
planar geometry, these molecules can serve as model systems for
scanning-probe based studies of molecular magnetism.
|
Judith Donner, Jan-Philipp Broschinski, Bastian Feldscher, Anja
Stammler, Hartmut Bögge, Thorsten Glaser, Daniel Wegner,
Correlating electronic and magnetic coupling in large magnetic molecules via scanning tunneling microscopy,
Phys. Rev. B 95, 165441 (2017)
|
The Mn12-story goes on
|
The discovery of magnetic bistability in Mn12 more
than 20 years ago marked the birth of molecular magnetism, an
extremely fertile interdisciplinary field and a powerful route
to create tailored magnetic nanostructures. However, the
difficulty to determine interactions in complex polycentric
molecules often prevents their understanding. Mn12 is
an outstanding example of this difficulty: although it is the
forefather and most studied of all molecular nanomagnets, an
unambiguous determination of even the leading magnetic exchange
interactions is still lacking. Here the authors exploit four-dimensional
inelastic neutron scattering to portray how individual spins
fluctuate around the magnetic ground state, thus fixing the
exchange couplings of Mn12 for the first time. The
results demonstrate the power of four-dimensional inelastic
neutron scattering as an unrivaled tool to characterize magnetic
clusters.
|
A. Chiesa, T. Guidi, S. Carretta, S. Ansbro, G.A. Timco,
I. Vitorica-Yrezabal, E. Garlatti, G. Amoretti,
R.E.P. Winpenny, and P. Santini,
Magnetic Exchange Interactions in the Molecular Nanomagnet Mn12,
Phys. Rev. Lett. 119, 217202 (2017)
|
Operating Quantum States in Single Magnetic Molecules: Implementation of Grover's Quantum Algorithm
|
Quantum algorithms use the principles of quantum mechanics, such
as, for example, quantum superposition, in order to solve
particular problems outperforming standard computation. They are
developed for cryptography, searching, optimization, simulation,
and solving large systems of linear equations. In this
publication the authors
implement Grover's quantum algorithm, proposed to find an
element in an unsorted list, using a single nuclear spin 3/2
carried by a Tb ion sitting in a single molecular magnet
transistor. The coherent manipulation of this multilevel quantum
system (qudit) is achieved by means of electric fields
only. Grover's search algorithm is implemented by constructing a
quantum database via a multilevel Hadamard gate. The Grover
sequence then allows us to select each state. The presented
method is of universal character and can be implemented in any
multilevel quantum system with nonequal spaced energy levels,
opening the way to novel quantum search algorithms.
|
C. Godfrin, A. Ferhat, R. Ballou, S. Klyatskaya, M. Ruben,
W. Wernsdorfer, and F. Balestro,
Operating Quantum States in Single Magnetic Molecules: Implementation of Grover's Quantum Algorithm,
Phys. Rev. Lett. 119, 187702
|
Topological Self-Assembly of Highly-Symmetric Lanthanide Clusters: A Magnetic Study of Exchange-Coupling "Fingerprints" in Giant Gadolinium(III) Cages
|
The creation of a perfect hollow nanoscopic sphere of metal
centres is clearly an unrealisable synthetic challenge. It is
however an inspirational challenge, from the viewpoint of
chemical architecture and also as finite molecular species may
provide unique microscopic insight into the origin and onset of
phenomena such as topological spin-frustration effects found in
infinite 2D and 3D systems. Herein, we report a series of high
symmetry gadolinium(III) (S = 7/2) polyhedra, Gd20, Gd32, Gd50
and Gd60, to test an approach based on assembling polymetallic
fragments that contain different polygons. Structural analysis
reveals the Gd20 cage resembles a dodecahedron; the vertices of
the Gd32 polyhedron exactly reveal symmetry Oh; Gd50 displays an
unprecedented polyhedron in which an icosidodecahedron Gd30 core
is encapsulated by an outer Gd20 dodecahedral shell with
approximate Ih symmetry; and the Gd60 shows a truncated
octahedron geometry. Experimental and theoretical magnetic
studies show that this series produces the expected
antiferromagnetic interaction that can be modelled based on
classical spins at the Gd sites. From the magnetization analyses
we can roughly correlate the derivative bands to the Gd-O-Gd
angles. Such a magneto-structural correlation may be used as
"fingerprints" to identify these cages.
|
Lei Qin, Guo-Jun Zhou, You-Zhu Yu, Hiroyuki Nojiri, Christian
Schröder, Richard E. P. Winpenny, and Yan-Zhen Zheng,
Topological Self-Assembly of Highly-Symmetric Lanthanide Clusters: A Magnetic Study of Exchange-Coupling "Fingerprints" in Giant Gadolinium(III) Cages,
J. Am. Chem. Soc. 139, 16405 (2017)
|
Molecular magnetic hysteresis at 60 Kelvin in dysprosocenium
|
Lanthanides have been investigated extensively for potential
applications in quantum information processing and high-density
data storage at the molecular and atomic scale. Experimental
achievements include reading and manipulating single nuclear
spins, exploiting atomic clock transitions for robust
qubits and, most recently, magnetic data storage in single
atoms. Single-molecule magnets exhibit magnetic hysteresis
of molecular origin - a magnetic memory effect and a prerequisite
of data storage - and so far lanthanide examples have exhibited
this phenomenon at the highest temperatures. However, in the
nearly 25 years since the discovery of single-molecule magnets,
hysteresis temperatures have increased from 4 Kelvin to only
about 14 Kelvin using a consistent magnetic field sweep
rate of about 20 oersted per second, although higher
temperatures have been achieved by using very fast sweep
rates (for example, 30 Kelvin with 200 oersted per
second).
Here the authors report a hexa-tert-butyldysprosocenium
complex which exhibits magnetic hysteresis at
temperatures of up to 60 Kelvin at a sweep rate of 22 oersted
per second. We observe a clear change in the relaxation dynamics
at this temperature, which persists in magnetically diluted
samples, suggesting that the origin of the hysteresis is the
localized metal-ligand vibrational modes that are unique to
dysprosocenium. Ab initio calculations of spin dynamics
demonstrate that magnetic relaxation at high temperatures is due
to local molecular vibrations. These results indicate that, with
judicious molecular design, magnetic data storage in single
molecules at temperatures above liquid nitrogen should be
possible.
|
Conrad A. P. Goodwin, Fabrizio Ortu, Daniel Reta, Nicholas
F. Chilton, David P. Mills,
Molecular magnetic hysteresis at 60 Kelvin in dysprosocenium,
Nature 548, 439-442 (2017)
Roberta Sessoli,
Materials science: Magnetic molecules back in the race,
Nature 548, 400-401 (2017)
|
Narrowing the Zero-Field Tunneling Resonance by Decreasing the Crystal Symmetry of Mn12 Acetate
|
The authors report the discovery of a less symmetric crystalline phase of
Mn12 acetate, a triclinic phase, resulting from recrystallizing
the original tetragonal phase reported by Lis in acetonitrile
and toluene. This new phase exhibits the same structure of Mn12
acetate clusters and the same positions of tunneling resonances
on the magnetic field as the conventional tetragonal
phase. However, the width of the zero-field resonance is at
least 1 order of magnitude smaller, can be as low as 50
Oe, indicating very small inhomogeneous broadening due to dipolar
and nuclear fields.
|
Jordi Espin, Ricardo Zarzuela, Nahuel Statuto, Jordi
Juanhuix, Daniel Maspoch, Inhar Imaz, Eugene Chudnovsky, Javier Tejada,
Narrowing the Zero-Field Tunneling Resonance by Decreasing the Crystal Symmetry of Mn12 Acetate,
J. Am. Chem. Soc., 2016, 138, 9065-9068
|
Put the spin in a cage
|
To increase the
temperature at which molecules behave as single-molecule
magnets (SMM) is a serious challenge in molecular magnetism. One
of the ways to address this problem is to create molecules with
strongly coupled lanthanide ions. In the presented work, endohedral metallofullerenes
Y2@C80 and
Dy2@C80 are obtained in the form of
air-stable benzyl monoadducts. Both feature an unpaired
electron trapped between metal ions, thus forming a
single-electron metal-metal bond. Giant exchange
interactions between lanthanide ions and the unpaired
electron result in single-molecule magnetism of
Dy2@C80(CH2Ph) with a
record-high 100 seconds blocking temperature of 18 K. All magnetic
moments in Dy2@C80(CH2Ph)
are parallel and couple ferromagnetically to form a single
spin unit of 21 Bohr magnetons with a
dysprosium-electron exchange constant of
32 cm-1. The barrier of the magnetization
reversal of 613 K is assigned to the state in which the spin
of one Dy centre is flipped.
|
Fupin Liu, Denis S. Krylov, Lukas Spree, Stanislav
M. Avdoshenko, Nataliya A. Samoylova, Marco Rosenkranz, Aram
Kostanyan, Thomas Greber, Anja U. B. Wolter, Bernd Büchner, Alexey A. Popov,
Single molecule magnet with an unpaired electron trapped between two lanthanide ions inside a fullerene,
Nature Communications 8, 16098 (2017)
D. S. Krylov, F. Liu, S. M. Avdoshenko, L. Spree,
B. Weise, A. Waske, A. U. B. Wolter, B. Büchner, A. A. Popov,
Record-high thermal barrier of the relaxation of magnetization in the nitride clusterfullerene Dy2ScN@C80-Ih,
Chem. Commun., 2017, 53, 7901-7904
|
A microscopic refrigeration process triggered through spin-crossover mechanism
|
The author reports the giant barocaloric effect determined in a
spin-crossover system using a microscopic model. Compared with
the widely used gas compression-expansion refrigeration
technology, field induced refrigeration in solid materials
reduces environmental damages and improves the energy
efficiency.
The origin of the giant effect was ascribed to the entropic
phonon contribution arising from low spin to high spin
phase transition, induced by a pressure change. Here, the author
shows
that for the applied pressure variation from 1 bar to 4.1 kbar,
the isothermal entropy change in a one-dimensional spin
crossover system
[Fe(hyptrz)3](4-chlorophenylsulfonate)2H2O
achieves a maximum value of 55.8 J/(mol K) at 191 K, leading to a huge
refrigerant capacity of 2160 J/mol. The results
were compared with the results of other giant solid refrigerant
materials such as (NH4)2SO4,
Gd5Si2Ge2, and
Gd5[Si0.43Ge0.57]4.
The potential of a solid refrigerant material is characterized
by the isothermal entropy change upon controlled external field
variations. If this quantity is
obtained upon magnetic field variations, a magnetocaloric effect
occurs; upon an electrical field change or a pressure change,
electrocaloric or barocaloric effects occur, respectively.
|
P. J. von Ranke,
A microscopic refrigeration process triggered through spin-crossover mechanism,
Appl. Phys. Lett. 110, 181909 (2017)
|
Recent progress in synchrotron-based frequency-domain Fourier-transform THz-EPR
|
We describe frequency-domain Fourier-transform THz-EPR as a
method to assign spin-coupling parameters of high-spin (S > 1/2)
systems with very large zero-field splittings. The instrumental
foundations of synchrotron-based FD-FT THz-EPR are presented,
alongside with a discussion of frequency-domain EPR simulation
routines. The capabilities of this approach is demonstrated for
selected mono- and multinuclear HS systems. Finally, we discuss
remaining challenges and give an outlook on the future prospects
of the technique.
|
Joscha Nehrkorn, Karsten Holldack, Robert Bittl, Alexander
Schnegg,
Recent progress in synchrotron-based frequency-domain Fourier-transform THz-EPR,
Journal of Magnetic Resonance 280, 10-19 2017
|
Long-range ferrimagnetic order in a two-dimensional supramolecular Kondo lattice
|
Realization of long-range magnetic order in surface-supported
two-dimensional systems has been challenging, mainly due to the
competition between fundamental magnetic interactions as the
short-range Kondo effect and spin-stabilizing magnetic exchange
interactions. Spin-bearing molecules on conducting substrates
represent a rich platform to investigate the interplay of these
fundamental magnetic interactions. Here we demonstrate the
direct observation of long-range ferrimagnetic order emerging in
a two-dimensional supramolecular Kondo lattice.
The lattice
consists of paramagnetic hexadeca-fluorinated iron
phthalocyanine (FeFPc) and manganese phthalocyanine (MnPc)
molecules co-assembled into a checkerboard pattern on
single-crystalline Au(111) substrates. Remarkably, the remanent
magnetic moments are oriented in the out-of-plane direction with
significant contribution from orbital moments.
|
First-principles
calculations reveal that the FeFPc-MnPc antiferromagnetic
nearest-neighbour coupling is mediated by the
Ruderman-Kittel-Kasuya-Yosida exchange interaction via the Au
substrate electronic states. Our findings suggest the use of
molecular frameworks to engineer novel low-dimensional
magnetically ordered materials and their application in
molecular quantum devices.
Jan Girovsky, Jan Nowakowski, Md. Ehesan Ali, Milos Baljozovic,
Harald R. Rossmann, Thomas Nijs, Elise A. Aeby, Sylwia
Nowakowska, Dorota Siewert, Gitika Srivastava, Christian
Wäckerlin, Jan Dreiser, Silvio Decurtins, Shi-Xia Liu, Peter
M. Oppeneer, Thomas A. Jung, Nirmalya Ballav,
Long-range ferrimagnetic order in a two-dimensional supramolecular Kondo lattice,
Nature Communications 8, 15388 (2017)
|
A chimeric design of heterospin 2p-3d, 2p-4f, and 2p-3d-4f complexes using a novel family of paramagnetic dissymmetric compartmental ligands
|
End-off bicompartmental ligands bearing a nitronyl-nitroxide arm
have been designed for synthesizing various heterospin molecular
systems. These ligands can selectively interact with 3d and 4f
metal ions, leading to 2p-4f, 2p-3d, and 2p-3d-4f complexes. The
magnetic properties of the 2p-4f and 2p-3d-4f complexes have
been investigated and rationalized by theoretical calculations.
|
Andrei A. Patrascu, Sergiu Calancea, Matteo Briganti,
Stephane Soriano, Augustin M. Madalan, Rafael A. Allao
Cassaro, Andrea Caneschi, Federico Totti, Maria
G. F. Vaz and Marius Andruh,
A chimeric design of heterospin 2p-3d, 2p-4f, and 2p-3d-4f complexes using a novel family of paramagnetic dissymmetric compartmental ligands,
Chem. Commun., 2017, 53, 6504
|
Portraying entanglement between molecular qubits with four-dimensional inelastic neutron scattering
|
Entanglement is a crucial resource for quantum information
processing and its detection and quantification is of paramount
importance in many areas of current research. Weakly coupled
molecular nanomagnets provide an ideal test bed for
investigating entanglement between complex spin
systems. However, entanglement in these systems has only been
experimentally demonstrated rather indirectly by macroscopic
techniques or by fitting trial model Hamiltonians to
experimental data. Here the authors show that four-dimensional inelastic
neutron scattering enables one to portray entanglement in weakly
coupled molecular qubits and to quantify it. To this end a
prototype (Cr7Ni)2 supramolecular dimer is
exploited as a benchmark to
demonstrate the potential of this approach, which allows one to
extract the concurrence in eigenstates of a dimer of molecular
qubits without diagonalizing its full Hamiltonian.
|
E. Garlatti, T. Guidi, S. Ansbro, P. Santini,
G. Amoretti, J. Ollivier, H. Mutka, G. Timco,
I.J. Vitorica-Yrezabal, G.F.S. Whitehead, R.E.P. Winpenny, S. Carretta,
Portraying entanglement between molecular qubits with four-dimensional inelastic neutron scattering,
Nature Communications 8, 14543 (2017)
|
Molecular magnetism, quo vadis? A historical perspective from a coordination chemist viewpoint
|
Molecular magnetism has travelled a long way from the pioneering
studies on electron exchange and double exchange or spin
crossover and valence tautomerism in small oligonuclear
complexes, from mono- to di- and tetranuclear species, to the
current investigations about magnetic anisotropy and spin
dynamics or quantum coherence of simple mono- or large
polynuclear complexes, behaving as switchable bistable molecular
nanomagnets for potential applications in information data
storage and processing. In this review, the authors focus on the origin
and development of the research in the field of molecular
magnetism from a coordination chemistry viewpoint, which dates
back to the establishment of magnetochemistry as a novel
discipline among the molecular sciences. This overview is
conceived as an attempt to orientate coordination chemists
regarding their role in the future direction that molecular
magnetism will undergo in its further evolution toward molecular
spintronics and quantum computation. A particular emphasis will
be given to some selected recent advances in single-molecule
spintronic circuitry and quantum computing devices based on the
large class of multiresponsive and multifunctional magnetic
metal complexes to stimulate the progress in the field of
molecular magnetism.
|
Jesús Ferrando-Soria,
Julia Vallejo,
María Castellano,
José Martínez-Lillo,
Emilio Pardo,
Joan Cano,
Isabel Castro,
Francesc Lloret,
Rafael Ruiz-García,
Miguel Julve,
Molecular magnetism, quo vadis? A historical perspective from a coordination chemist viewpoint,
Coordination Chemistry Reviews 339 (2017) 17-103
|
Room Temperature Magnetoresistance in Single-Molecule Devices
|
Two recent publications show that the appropriate choice of the transition metal
complex and metal surface electronic structure opens the
possibility to control the spin of the charge carriers through
the resulting hybrid molecule/metal spinterface in a
single-molecule electrical contact at room temperature.
|
Albert C. Aragones, Daniel Aravena, Francisco
J. Valverde-Munoz, Jose Antonio Real, Fausto Sanz, Ismael
Diez-Perez, Eliseo Ruiz,
Metal-Controlled Magnetoresistance at Room Temperature in Single-Molecule Devices,
J. Am. Chem. Soc., 2017, 139 (16), pp 5768-5778
Albert C. Aragones, Daniel Aravena, Jorge I. Cerda, Zulema
Acis-Castillo, Haipeng Li, Jose Antonio Real, Fausto Sanz,
Josh Hihath, Eliseo Ruiz, Ismael Diez-Perez,
Large Conductance Switching in a Single-Molecule Device through Room Temperature Spin-Dependent Transport,
Nano Lett., 2016, 16 (1), pp 218-226
|
Recent Development in Clusters of Rare Earths and Actinides: Chemistry and Materials
|
With contributions by
Zhonghao Zhang, Yanan Zhang, Zhiping Zheng,
Xiu-Ying Zheng, Xiang-Jian Kong, La-Sheng Long,
Jian-Wen Cheng, Guo-Yu Yang,
Sarah Hickam, Peter C. Burns,
Xiaoping Yang, Shiqing Wang, Chengri Wang, Shaoming Huang, Richard A. Jones,
Yan-Cong Chen, Jun-Liang Liu, Ming-Liang Tong,
Tian Han, You-Song Ding, Yan-Zhen Zheng,
Takanori Shima, Zhaomin Hou
|
Recent Development in Clusters of Rare Earths and Actinides: Chemistry and Materials,
Editors: Zhiping Zheng, Structure and Bonding, Volume 173 2017Springer,
ISBN: 978-3-662-53301-7 (Print) 978-3-662-53303-1 (Online),
online
|
Spin Dynamics and Low Energy Vibrations: Insights from Vanadyl-Based Potential Molecular Qubits
|
In this communication the authors report the investigation of
the magnetization dynamics of a vanadyl complex with
diethyldithiocarbamate (Et2dtc-) ligands in both solid-state and
frozen solution. The investigation showed an
anomalous and unprecedentedly observed field dependence of the
relaxation time, which was modeled with three contributions to
the relaxation mechanism. The temperature dependence of the
weight of the two processes dominating at low fields was found
to well correlate with the low energy vibrations as determined
by THz spectroscopy. This detailed experimental comparative
study represents a fundamental step to understand the spin
dynamics of potential molecular quantum bits and enriches the
guidelines to design molecule-based systems with enhanced
quantum coherence.
|
Matteo Atzori, Lorenzo Tesi, Stefano Benci, Alessandro Lunghi,
Roberto Righini, Andrea Taschin, Renato Torre, Lorenzo Sorace,
Roberta Sessoli,
Spin Dynamics and Low Energy Vibrations: Insights from Vanadyl-Based Potential Molecular Qubits,
J. Am. Chem. Soc., 2017, 139 (12), pp 4338-4341
|
The role of anharmonic phonons in under-barrier spin relaxation of single molecule magnets
|
The use of single molecule magnets in mainstream electronics
requires their magnetic moment to be stable over long times. One
can achieve such a goal by designing compounds with
spin-reversal barriers exceeding room temperature, namely with
large uniaxial anisotropies. Such strategy, however, has been
defeated by several recent experiments demonstrating
under-barrier relaxation at high temperature, a behaviour today
unexplained. Here the authors propose spin-phonon coupling to be
responsible for such anomaly. With a combination of electronic
structure theory and master equations the authors show that, in the
presence of phonon dissipation, the relevant energy scale for
the spin relaxation is given by the lower-lying phonon modes
interacting with the local spins. These open a channel for spin
reversal at energies lower than that set by the magnetic
anisotropy, producing fast under-barrier spin relaxation. The
findings rationalize a significant body of experimental work and
suggest a possible strategy for engineering room temperature
single molecule magnets.
|
Alessandro Lunghi, Federico Totti, Roberta Sessoli, Stefano
Sanvito,
The role of anharmonic phonons in under-barrier spin relaxation of single molecule magnets,
Nature Communications 8, 14620 (2017)
|
Pressure induced enhancement of the magnetic ordering temperature in rhenium(IV) monomers
|
Materials that demonstrate long-range magnetic order are
synonymous with information storage and the electronics
industry, with the phenomenon commonly associated with metals,
metal alloys or metal oxides and sulfides. A lesser known family
of magnetically ordered complexes are the monometallic compounds
of highly anisotropic d-block transition metals; the
'transformation' from isolated zero-dimensional molecule to
ordered, spin-canted, three-dimensional lattice being the result
of through-space interactions arising from the combination of
large magnetic anisotropy and spin-delocalization from metal to
ligand which induces important intermolecular contacts. Here the
authors report the effect of pressure on two such mononuclear
rhenium(IV) compounds that exhibit long-range magnetic order
under ambient conditions via a spin canting mechanism, with Tc
controlled by the strength of the intermolecular
interactions. As these are determined by intermolecular
distance, 'squeezing' the molecules closer together generates
remarkable enhancements in ordering temperatures, with a linear
dependence of Tc with pressure.
|
Christopher H. Woodall, Gavin A. Craig, Alessandro Prescimone,
Martin Misek, Joan Cano, Juan Faus, Michael R. Probert, Simon
Parsons, Stephen Moggach, Jose Martinez-Lillo, Mark Murrie,
Konstantin V. Kamenev, Euan K. Brechin,
Pressure induced enhancement of the magnetic ordering temperature in rhenium(IV) monomers,
Nature Communications 7, 13870 (2016)
|
Precision ESR measurements of transverse anisotropy in the single-molecule magnet Ni4
|
The authors present a method for precisely measuring the tunnel splitting
in single-molecule magnets (SMMs) using electron-spin resonance,
and use these measurements to precisely and independently
determine the underlying transverse anisotropy parameter, given
a certain class of transitions. By diluting samples of the SMM
Ni4 via cocrystallization in a diamagnetic isostructural analog
we obtain markedly narrower resonance peaks than are observed in
undiluted samples. Using custom loop-gap resonators we measure
the transitions at several frequencies, allowing a precise
determination of the tunnel splitting. Because the transition
under investigation occurs at zero field, and arises due to a
first-order perturbation from the transverse anisotropy, we can
determine the magnitude of this anisotropy independent of any
other Hamiltonian parameters. This method can be applied to
other SMMs with tunnel splittings arising from first-order
transverse anisotropy perturbations.
|
Charles A. Collett, Rafael A. Allao Cassaro, and Jonathan
R. Friedman,
Precision ESR measurements of transverse anisotropy in the single-molecule magnet Ni4,
Phys. Rev. B 94, 220402(R) (2016)
|
First cage-like pentanuclear Co(II)-silsesquioxane
|
A new pentanuclear cylinder-like cobalt(II)
phenylsilsesquioxane exhibits a slow
relaxation of the magnetization and a high catalytic activity
and stereoselectivity in the oxidation of alkanes and alcohols.
|
A. N. Bilyachenko, A. I. Yalymov, M. M. Levitsky,
A. A. Korlyukov, M. A. Es'kova, J. Long,
J. Larionova, Y. Guari, L. S. Shul'pina,
N. S. Ikonnikov, A. L. Trigub, Y. V. Zubavichus,
I. E. Golub, E. S. Shubina and G. B. Shul'pin,
First cage-like pentanuclear Co(II)-silsesquioxane,
Dalton Trans., 2016,45, 13663-13666
|
Molecular Magnetic Materials: Concepts and Applications
|
A comprehensive overview of this rapidly expanding interdisciplinary field of research.
After a short introduction to the basics of magnetism and
molecular magnetism, the text goes on to cover specific
properties of molecular magnetic materials as well as their
current and future applications. Design strategies for acquiring
molecular magnetic materials with desired physical properties
are discussed, as are such multifunctional materials as high Tc
magnets, chiral and luminescent magnets, magnetic sponges as
well as photo- and piezo-switching magnets.
The result is an excellent resource for materials scientists,
chemists, physicists and crystal engineers either entering or
already working in the field.
With contributions of:
Maria Balanda, Robert Pelka, Michael Shatruk, Silvia Gomez-Coca,
Kim R. Dunbar, Zhao-Ping Ni, Ming-Liang Tong, Masahiro
Yamashita, Keiichi Katoh, Paolo Santini, Stefano Carretta,
Giuseppe Amoretti, Kasper S. Pedersen, Alessandro Vindigni,
Roberta Sessoli, Claude Coulon, Rodolphe Clerac, Joel S. Miller,
Shin-ichi Ohkoshi, Andrea Cornia, Daniel R. Talham, Marco Affronte,
Ana B. Gaspar, Birgit Weber,
Wei-Xiong Zhang, Ming-Hua Zeng, Xiao-Ming Chen, Dawid Pinkowicz,
Robet Podgajny, Barbara Sieklucka,
Cyrille Train, Geert Rikken, Michel Verdaguer,
Corine Mathoniere, Hiroko Tokoro, Shin-ichi Ohkoshi ,
Mauro Perfetti, Fabrice Pointillart, Olivier Cador, Lorenzo Sorace, Lahcene Ouahab,
Yoshihiro Sekine, Wataru Kosaka, Kouji Taniguchi, Hitoshi Miyasaka,
Thomas T. M. Palstra, Alexey O. Polyakov, Jordi Cirera, Eliseo
Ruiz, Jürgen Schnack and Coen de Graaf.
|
Barbara Sieklucka (Editor), Dawid Pinkowicz (Editor),
Molecular Magnetic Materials: Concepts and Applications,
WILEY, 2016, ISBN: 978-3-527-33953-2
|
On Approaching the Limit of Molecular Magnetic Anisotropy: A Near-Perfect Pentagonal Bipyramidal Dysprosium(III) Single-Molecule Magnet
|
The authos report a monometallic dysprosium complex, that shows
the largest effective
energy barrier to magnetic relaxation of Ueff=1815 K. The
massive magnetic anisotropy is due to bis-trans-disposed
tert-butoxide ligands with weak equatorial pyridine donors,
approaching proposed schemes for high-temperature
single-molecule magnets (SMMs). The blocking temperature
is 14 K, defined by zero-field-cooled magnetization experiments,
and is the largest for any monometallic complex.
|
You-Song Ding,
Nicholas F. Chilton,
Richard E. P. Winpenny,
Yan-Zhen Zheng,
On Approaching the Limit of Molecular Magnetic Anisotropy: A Near-Perfect Pentagonal Bipyramidal Dysprosium(III) Single-Molecule Magnet,
Angew. Chem. Int. Ed. 55, 16071 (2016)
|
Research Update: The mechanocaloric potential of spin crossover compounds
|
The author presents a first evaluation of the potential for spin
crossover (SCO) compounds to be considered as a new class of
giant mechanocaloric effect materials. From literature data on
the variation of the spin crossover temperature with pressure,
we estimate the maximum available adiabatic temperature change
for several compounds and the relatively low pressures that may
be required to observe these effects.
|
Karl G. Sandeman,
Research Update: The mechanocaloric potential of spin crossover compounds,
APL Mater. 4, 111102 (2016)
|
Observation of Tunneling-Assisted Highly Forbidden Single-Photon Transitions in a Ni4 Single-Molecule Magnet
|
Forbidden transitions between energy levels typically involve
violation of selection rules imposed by symmetry and/or
conservation laws. A nanomagnet tunneling between up and down
states violates angular momentum conservation because of broken
rotational symmetry. Here the authors report observations of highly
forbidden transitions between spin states in a Ni4
single-molecule magnet in which a single photon can induce the
spin to change by several times hbar, nearly reversing the
direction of the spin. These observations are understood as
tunneling-assisted transitions that lift the standard Delta m=+/-1
selection rule for single-photon transitions. These transitions
are observed at low applied fields, where tunneling is dominated
by the molecule's intrinsic anisotropy and the field acts as a
perturbation. Such transitions can be exploited to create
macroscopic superposition states that are not typically
accessible through single-photon Delta m=+/-1 transitions.
|
Yiming Chen, Mohammad D. Ashkezari, Charles A. Collett, Rafael A. Allao Cassaro, Filippo Troiani, Paul M. Lahti, and Jonathan R. Friedman,
Observation of Tunneling-Assisted Highly Forbidden Single-Photon Transitions in a Ni4 Single-Molecule Magnet,
Phys. Rev. Lett. 117, 187202 (2016)
|
Experimental and theoretical investigation of the magnetization dynamics of an artificial square spin ice cluster
|
The authors study the magnetization dynamics of a spin ice
cluster which is a building block of an artificial square spin
ice fabricated by focused electron-beam-induced deposition both
experimentally and theoretically. The spin ice cluster is
composed of twelve interacting Co nanoislands grown directly on
top of a high-resolution micro-Hall sensor. By employing
micromagnetic simulations and a macrospin model, we calculate
the magnetization and the experimentally investigated stray
field emanating from a single nanoisland. The parameters
determined from a comparison with the experimental hysteresis
loop are used to derive an effective single-dipole macrospin
model that allows us to investigate the dynamics of the spin ice
cluster. Our model reproduces the experimentally observed
non-deterministic sequences in the magnetization curves as well
as the distinct temperature dependence of the hysteresis
loop.
|
Merlin Pohlit, Irina Stockem, Fabrizio Porrati, Michael Huth, Christian Schröder and Jens Müller,
Experimental and theoretical investigation of the magnetization dynamics of an artificial square spin ice cluster,
J. Appl. Phys. 120, 142103 (2016)
|
Understanding Thermodynamic and Spectroscopic Properties of Tetragonal Mn12 Single-Molecule Magnets from Combined Density Functional Theory/Spin-Hamiltonian Calculations
|
The authors apply broken-symmetry density functional theory to determine
isotropic exchange-coupling constants and local zero-field
splitting (ZFS) tensors for the tetragonal Mn12tBuAc
single-molecule magnet. The obtained parametrization of the
many-spin Hamiltonian (MSH), taking into account all 12 spin
centers, is assessed by comparing theoretical predictions for
thermodynamic and spectroscopic properties with available
experimental data. The magnetic susceptibility (calculated by
the finite-temperature Lanczos method) is well approximated, and
the intermultiplet excitation spectrum from inelastic neutron
scattering (INS) experiments is correctly reproduced. In these
respects, the present parametrization of the 12-spin model
represents a significant improvement over previous theoretical
estimates of exchange-coupling constants in Mn12, and
additionally offers a refined interpretation of INS
spectra. Treating anisotropic interactions at the third order of
perturbation theory, the MSH is mapped onto the giant-spin
Hamiltonian describing the S = 10 ground multiplet. Although the
agreement with high-field EPR experiments is not perfect, the
results clearly point in the right direction and for the first
time rationalize the angular dependence of the transverse-field
spectra from a fully microscopic viewpoint. Importantly,
transverse anisotropy of the effective S = 10 manifold is
explicitly shown to arise largely from the ZFS-induced mixing of
exchange multiplets. This effect is given a thorough analysis in
the approximate D2d spin-permutational symmetry group of the
exchange Hamiltonian.
|
Shadan Ghassemi Tabrizi, Alexei V. Arbuznikov, and Martin Kaupp,
Understanding Thermodynamic and Spectroscopic Properties of Tetragonal Mn12 Single-Molecule Magnets from Combined Density Functional Theory/Spin-Hamiltonian Calculations,
J. Phys. Chem. A, 2016, 120 (34), pp 6864-6879
|
Electron paramagnetic resonance of individual atoms on a surface
|
Electron paramagnetic resonance (EPR) usually detects atoms with
unpaired electrons as ensemble averages. The authors employed a
spin-polarized scanning tunneling microscope tip to measure EPR
spectra of single iron atoms adsorbed on a magnesium oxide
surface at cryogenic temperatures.
The high-energy resolution of conventional spin
resonance was combined with scanning tunneling
microscopy to measure electron paramagnetic resonance of
individual iron (Fe) atoms placed on a magnesium oxide film. The
spin resonance was driven with an oscillating electric field
between tip and sample. The readout of the Fe
atom's quantum state was performed by spin-polarized detection
of the atomic-scale tunneling magnetoresistance.
T1 and T2 times were determined.
The spin resonance
signals of different Fe atoms differ by much more than their
resonance linewidth; in a traditional ensemble measurement, this
difference would appear as inhomogeneous broadening.
|
Susanne Baumann, William Paul, Taeyoung Choi,
Christopher P. Lutz, Arzhang Ardavan, Andreas J. Heinrich,
Electron paramagnetic resonance of individual atoms on a surface,
Science 23 Oct 2015, Vol. 350, Issue 6259, pp. 417-420
|
Quantum Einstein-de Haas effect
|
The classical Einstein-de Haas experiment demonstrates that a
change of magnetization in a macroscopic magnetic object results
in a mechanical rotation of this magnet. This experiment can
therefore be considered as a macroscopic manifestation of the
conservation of total angular momentum and energy of electronic
spins. Since the conservation of angular momentum is a
consequence of a system's rotational invariance, it is valid for
an ensemble of spins in a macroscopic ferromaget as well as for
single spins. Here we propose an experimental realization of an
Einstein-de Haas experiment at the single-spin level based on a
single-molecule magnet coupled to a nanomechanical resonator. We
demonstrate that the spin associated with the single-molecule
magnet is then subject to conservation of total angular momentum
and energy, which results in a total suppression of the
molecule's quantum tunnelling of magnetization.
|
Marc Ganzhorn, Svetlana Klyatskaya, Mario Ruben, Wolfgang
Wernsdorfer,
Quantum Einstein-de Haas effect,
Nature Communications 7, 11443 (2016)
|
The classical and quantum dynamics of molecular spins on graphene
|
Controlling the dynamics of spins on surfaces is pivotal to the
design of spintronic and quantum computing devices. Proposed
schemes involve the interaction of spins with graphene to enable
surface-state spintronics and electrical spin manipulation.
However, the influence of the graphene
environment on the spin systems has yet to be unravelled. Here
we explore the spin-graphene interaction by studying the
classical and quantum dynamics of molecular magnets on
graphene. Whereas the static spin response remains unaltered,
the quantum spin dynamics and associated selection rules are
profoundly modulated. The couplings to graphene phonons, to
other spins, and to Dirac fermions are quantified using a newly
developed model. Coupling to Dirac electrons introduces a
dominant quantum relaxation channel that, by driving the spins
over Villain's threshold, gives rise to fully coherent, resonant
spin tunnelling. Our findings provide fundamental insight into
the interaction between spins and graphene, establishing the
basis for electrical spin manipulation in graphene nanodevices.
|
Christian Cervetti, Angelo Rettori, Maria Gloria Pini,
Andrea Cornia, Ana Repolles, Fernando Luis, Martin Dressel,
Stephan Rauschenbach, Klaus Kern, Marko Burghard, Lapo
Bogani,
The classical and quantum dynamics of molecular spins on graphene,
Nature Materials 15, 164-168 (2016)
|
Making hybrid [n]-rotaxanes as supramolecular
arrays of molecular electron spin qubits
|
Quantum information processing (QIP) would require that the
individual units
involved-qubits-communicate to other qubits while retaining their identity. In many ways this
resembles the way supramolecular chemistry brings together individual molecules into
interlocked structures, where the assembly has one identity but where the individual
components are still recognizable. Here a fully modular supramolecular strategy has been to
link hybrid organic-inorganic [2]- and [3]-rotaxanes into still larger [4]-, [5]- and
[7]-rotaxanes. The ring components are heterometallic octanuclear Cr7Ni
coordination cages and the thread components template the formation of the ring about
the organic axle, and are further functionalized to act as a ligand, which leads to large
supramolecular arrays of these heterometallic rings. As the rings have been proposed as
qubits for QIP, the strategy provides a possible route towards scalable molecular electron spin
devices for QIP. Double electron-electron resonance experiments demonstrate inter-qubit
interactions suitable for mediating two-qubit quantum logic
gates.
|
Antonio Fernandez, Jesus Ferrando-Soria, Eufemio Moreno Pineda, Floriana Tuna, Inigo J. Vitorica-Yrezabal,
Christiane Knappke, Jakub Ujma, Christopher A. Muryn, Grigore A. Timco, Perdita E. Barran,
Arzhang Ardavan, Richard E.P. Winpenny,
Making hybrid [n]-rotaxanes as supramolecular
arrays of molecular electron spin qubits,
NATURE COMMUNICATIONS 7, 10240 (2016)
|
Studies on the Magnetic Ground State of a Spin Möbius Strip
|
The authors report the synthesis, structure and detailed
characterisation of three n-membered oxovanadium rings. Their
alternating heterometallic vanadium/sodium cyclic core structures were
sandwiched between two CD moieties such that O-Na-O groups
separated the neighbouring vanadyl ions. Antiferromagnetic
interactions between the S=1/2 vanadyl ions led to S=0 ground
states for the even-membered rings, but to two quasi-degenerate
S=1/2 states for the spin-frustrated heptanuclear cluster.
This is one of the rather rare examples of odd membered
antiferromagnetic spin rings.
|
Graham N. Newton, Norihisa Hoshino, Takuto Matsumoto, Takuya Shiga,
Motohiro Nakano, Hiroyuki Nojiri, Wolfgang Wernsdorfer, Yuji Furukawa, and
Hiroki Oshio,
Studies on the Magnetic Ground State of a Spin Möbius Strip,
Chemistry - A European Journal 22 (2016) 14205
|
Dynamical effects on the magnetic properties of dithiazolyl bistable materials
|
The magnetic properties of molecule-based magnets are commonly
rationalized by considering only a single nuclear configuration
of the system under study (usually an X-ray crystal
structure). Here, by means of a computational study, we compare
the results obtained using such a static approach with those
obtained by explicitly accounting for thermal fluctuations, and
uncover the serious limitations of the static perspective when
dealing with magnetic crystals whose radicals undergo
wide-amplitude motions. As a proof of concept, these limitations
are illustrated for the magnetically bistable
1,3,5-trithia-2,4,6-triazapentalenyl (TTTA) material. For its
high-temperature phase at 300 K, we show that nuclear dynamics
induce large fluctuations in the magnetic exchange interactions
(J) between spins (up to 1000% of the average value). These
deviations result in a about 20% difference between the 300 K
magnetic susceptibility computed by explicitly considering the
nuclear dynamics and that computed using the X-ray structure,
the former being in better agreement with the experimental
data. The unveiled strong coupling between J interactions and
intermolecular vibrations reveals that considering J as a
constant value at a given temperature (as always done in
molecular magnetism) leads to a flawed description of the
magnetism of TTTA. Instead, the physically relevant concept in
this case is the statistical distribution of J values.
|
Sergi Vela, Merce Deumal, Motoyuki Shiga, Juan J. Novoa, Jordi Ribas-Arino,
Dynamical effects on the magnetic properties of dithiazolyl bistable materials,
Chem. Sci., 2015, 6, 2371-2381
|
Enhancing coherence in molecular spin qubits via atomic clock transitions
|
Quantum computing is an emerging area within the information
sciences revolving around the concept of quantum bits
(qubits). A major obstacle is the extreme fragility of these
qubits due to interactions with their environment that destroy
their quantumness. This phenomenon, known as decoherence, is of
fundamental interest. When dealing with spin qubits, the
strongest source of decoherence is the magnetic dipolar
interaction.
In This publication the authors present a way of enhancing coherence in
solid-state molecular spin qubits without resorting to extreme
dilution. It is based on the design of molecular structures with
crystal field ground states possessing large tunnelling gaps
that give rise to optimal operating points, or atomic clock
transitions, at which the quantum spin dynamics become protected
against dipolar decoherence. This approach is illustrated with a
holmium molecular nanomagnet in which long coherence times (up
to 8.4 microseconds at 5 kelvin) are obtained at unusually high
concentrations.
|
Muhandis Shiddiq, Dorsa Komijani, Yan Duan, Alejandro
Gaita-Arino, Eugenio Coronado, Stephen Hill,
Enhancing coherence in molecular spin qubits via atomic clock transitions,
Nature 531, 348-351 (2016)
|
A Mixed-Ligand Approach for a Gigantic and Hollow Heterometallic Cage {Ni64RE96} for Gas Separation and Magnetic Cooling Applications
|
Nanosized aggregations of metal ions shielded by organic ligands
possessing both exquisite structural aesthetics and intriguing
properties are fundamentally interesting. Three isostructural
gigantic transition-metal-rare-earth heterometallic coordination
cages are reported, abbreviated as {Ni64RE96} (RE=Gd, Dy, and Y)
and obtained by a mixed-ligand approach, each possessing a
cuboidal framework made of 160 metal ions and a nanosized
spherical cavity in the center. Along with the structural
novelty, these hollow cages show highly selective adsorptions
for CO2 over CH4 or N2 at ambient temperatures. Moreover, the
gadolinium analogue exhibits large magnetocaloric effect at
ultralow temperatures.
|
Wei-Peng Chen,
Pei-Qin Liao,
Youzhu Yu,
Zhiping Zheng,
Xiao-Ming Chen,
Yan-Zhen Zheng
A Mixed-Ligand Approach for a Gigantic and Hollow Heterometallic Cage {Ni64RE96} for Gas Separation and Magnetic Cooling Applications,
Angew. Chem. Int. Ed. 2016, 55, 9375-9379
|
Modelling spin Hamiltonian parameters of molecular nanomagnets
|
Molecular nanomagnets encompass a wide range of coordination
complexes possessing several potential applications. A
formidable challenge in realizing these potential applications
lies in controlling the magnetic properties of these
clusters. Microscopic spin Hamiltonian (SH) parameters describe
the magnetic properties of these clusters, and viable ways to
control these SH parameters are highly desirable. Computational
tools play a proactive role in this area, where SH parameters
such as isotropic exchange interaction (J), anisotropic exchange
interaction (Jx, Jy, Jz), double exchange interaction (B),
zero-field splitting parameters (D, E) and g-tensors can be
computed reliably using X-ray structures. In this feature
article the authors have attempted to provide a holistic view of the
modelling of these SH parameters of molecular magnets. The
determination of J includes various class of molecules, from di-
and polynuclear Mn complexes to the {3d-Gd}, {Gd-Gd} and {Gd-2p}
class of complexes. The estimation of anisotropic exchange
coupling includes the exchange between an isotropic metal ion
and an orbitally degenerate 3d/4d/5d metal ion. The
double-exchange section contains some illustrative examples of
mixed valance systems, and the section on the estimation of zfs
parameters covers some mononuclear transition metal complexes
possessing very large axial zfs parameters. The section on the
computation of g-anisotropy exclusively covers studies on
mononuclear DyIII and ErIII single-ion magnets. The examples
depicted in this article clearly illustrate that computational
tools not only aid in interpreting and rationalizing the
observed magnetic properties but possess the potential to
predict new generation MNMs.
|
Tulika Gupta, Gopalan Rajaraman,
Modelling spin Hamiltonian parameters of molecular nanomagnets,
Chem. Commun., 2016, 52, 8972-9008
|
A modular design of molecular qubits to implement
universal quantum gates
|
The physical implementation of quantum information processing
relies on individual modules - qubits - and operations that modify
such modules either individually or in groups, i.e. quantum
gates. Two examples of gates that entangle pairs of qubits are
the controlled NOT-gate (CNOT) gate, which flips the state of
one qubit depending on the state
of another, and the SQRT(iSWAP) gate that brings a two-qubit product state into a superposition
involving partially swapping the qubit states. Here we show that through supramolecular
chemistry a single simple module, molecular {Cr7Ni} rings, which act as the qubits, can be
assembled into structures suitable for either the CNOT or SQRT(iSWAP) gate by choice of linker,
and we characterize these structures by electron spin resonance
spectroscopy. We introduce two schemes for implementing such
gates with these supramolecular assemblies and perform detailed
simulations, based on the measured parameters including
decoherence, to demonstrate how the gates would operate.
|
Jesus Ferrando-Soria, Eufemio Moreno Pineda, Alessandro Chiesa, Antonio Fernandez, Samantha A. Magee, Stefano Carretta, Paolo Santini, Inigo J. Vitorica-Yrezabal, Floriana Tuna, Grigore A. Timco, Eric J.L. McInnes & Richard E.P. Winpenny,
A modular design of molecular qubits to implement
universal quantum gates,
NATURE COMMUNICATIONS | 7:11377 (2016)
see also:
Alessandro Chiesa, George F. S. Whitehead, Stefano
Carretta, Laura Carthy, Grigore A. Timco, Simon J. Teat,
Giuseppe Amoretti, Eva Pavarini, Richard E. P. Winpenny, Paolo Santini,
Molecular nanomagnets with switchable coupling for quantum simulation,
SCIENTIFIC REPORTS | 4:7423 (2014)
|
D5h makes the difference
|
Two more SIMs with record energy barrier and
record magnetic hysteresis temperature have been reported
recently.
Air-stable Dy(III) and Er(III) single-ion
magnets (SIMs) with pseudo-D5h symmetry, where the
Dy(III)-SIM exhibits a magnetization blocking (TB) up to 12 K,
defined from the maxima of the zero-field cooled magnetization
curve, with an anisotropy barrier (Ueff) as high as 735.4 K have
been reported. The Dy(III)-SIM exhibits a magnetic hysteresis up
to 12 K (30 K) with a large coercivity of ~0.9 T (~1.5 T) at a
sweep rate of ~0.0018 T/s (0.02 T/s). These high values
combined with
persistent stability under ambient conditions, render this
system as one of the best-characterized SIMs. Ab initio
calculations have been used to establish the connection between
the higher-order symmetry of the molecule and the quenching of
quantum tunnelling of magnetization (QTM) effects. The
relaxation of magnetization is observed via the second excited
Kramers doublet owing to pseudo-high-order symmetry, which
quenches the QTM. This study highlights fine-tuning of symmetry
around the lanthanide ion to obtain new-generation SIMs and
offers further scope for pushing the limits of Ueff and TB using
this approach.
|
Sandeep K. Gupta, Thayalan Rajeshkumar, Gopalan Rajaraman, Ramaswamy Murugavel,
An air-stable Dy(III) single-ion magnet with high anisotropy barrier and blocking temperature,
Chem. Sci., 2016, Advance Article
Sandeep K. Gupta, Thayalan Rajeshkumar, Gopalan Rajaraman, Ramaswamy Murugavel,
An unprecedented zero field neodymium(III) single-ion magnet based on a phosphonic diamide,
Chem. Commun., 2016,52, 7168-7171
|
Symmetry-Supported Magnetic Blocking at 20 K in Pentagonal
Bipyramidal Dy(III) Single-Ion Magnets
|
Two SIMs with record energy barrier and
record magnetic hysteresis temperature up to 20 K, respectively,
in two pentagonal bipyramidal Dy(III) SIMs have been reported
recently.
Single-molecule magnets (SMMs) that can be trapped in one of the
bistable magnetic states separated by an energy barrier are
among the most promising candidates for high-density information
storage, quantum processing, and spintronics. To date, a
considerable series of achievements have been made. However, the
presence of fast quantum tunnelling of magnetization (QTM) in
most SMMs, especially in single-ion magnets (SIMs), provides a
rapid relaxation route and often sets up a limit for the
relaxation time. Here, we pursue the pentagonal bipyramidal
symmetry to suppress the QTM. Magnetic characterizations
reveal fascinating SMM properties with high energy
barriers along with a record magnetic hysteresis temperature up
to 20 K. These results, combined with the ab initio
calculations, offer an illuminating insight into the vast
possibility and potential of what the symmetry rules can achieve
in molecular magnetism.
|
Yan-Cong Chen, Jun-Liang Liu, Liviu Ungur, Jiang Liu,
Quan-Wen Li, Long-Fei Wang, Zhao-Ping Ni, Liviu
F. Chibotaru, Xiao-Ming Chen, and Ming-Liang Tong,
Symmetry-Supported Magnetic Blocking at 20 K in Pentagonal Bipyramidal Dy(III) Single-Ion Magnets,
J. Am. Chem. Soc., 2016, 138 (8), pp 2829-2837
Jiang Liu, Yan-Cong Chen, Jun-Liang Liu, Veacheslav Vieru, Liviu
Ungur, Jian-Hua Jia, Liviu F. Chibotaru, Yanhua Lan, Wolfgang
Wernsdorfer, Song Gao, Xiao-Ming Chen, and Ming-Liang Tong,
A Stable Pentagonal Bipyramidal Dy(III) Single-Ion Magnet with a Record Magnetization Reversal Barrier over 1000 K,
J. Am. Chem. Soc., 2016, 138 (16), pp 5441-5450
|
Giant Hysteresis of Single-Molecule Magnets Adsorbed on a Nonmagnetic Insulator
|
It is demonstrated that TbPc2 single-molecule magnets adsorbed
on a magnesium oxide tunnel barrier exhibit record magnetic
remanence, record hysteresis opening, perfect out-of-plane
alignment of the magnetic easy axes, and self-assembly into a
well-ordered layer.
|
Christian Wäckerlin,
Fabio Donati,
Aparajita Singha,
Romana Baltic,
Stefano Rusponi,
Katharina Diller,
Francois Patthey,
Marina Pivetta,
Yanhua Lan,
Svetlana Klyatskaya,
Mario Ruben,
Harald Brune,
Jan Dreiser,
Giant Hysteresis of Single-Molecule Magnets Adsorbed on a Nonmagnetic Insulator,
Adv. Mater. 28 (2016) 5195-5199
|
Deciphering the origin of giant magnetic anisotropy and fast quantum tunnelling in Rhenium(IV) single-molecule magnets
|
Single-molecule magnets represent a promising route to achieve
potential applications such as high-density information storage
and spintronics devices. Among others, 4d/5d elements such as
Re(IV) ion are found to exhibit very large magnetic anisotropy,
and inclusion of this ion-aggregated clusters yields several
attractive molecular magnets. Here, using ab intio calculations,
the authors unravel the source of giant magnetic anisotropy associated
with the Re(IV) ions by studying a series of mononuclear Re(IV)
six coordinate complexes. The low-lying doublet states are found
to be responsible for large magnetic anisotropy and the sign of
the axial zero-field splitting parameter (D) can be
categorically predicted based on the position of the ligand
coordination. Large transverse anisotropy along with large
hyperfine interactions opens up multiple relaxation channels
leading to a fast quantum tunnelling of the magneti- zation
(QTM) process. Enhancing the Re-ligand covalency is found to
significantly quench the QTM process.
|
Saurabh Kumar Singh, Gopalan Rajaraman,
Deciphering the origin of giant magnetic anisotropy and fast quantum tunnelling in Rhenium(IV) single-molecule magnets,
NATURE COMMUNICATIONS 7, 10669 (2016)
|
Rotating Magnetocaloric Effect in an Anisotropic Molecular Dimer
|
In contrast to the mainstream research on molecular refrigerants
that seeks magnetically isotropic molecules, we show that the
magnetic anisotropy of dysprosium acetate tetrahydrate, can be
efficiently used for
cooling below liquid-helium temperature. This is attained by
rotating aligned single-crystal samples in a constant applied
magnetic field. The envisioned advantages are fast cooling
cycles and potentially compact refrigerators. |
Dr. Giulia Lorusso,
Dr. Olivier Roubeau,
Dr. Marco Evangelisti
Rotating Magnetocaloric Effect in an Anisotropic Molecular Dimer,
Angew. Chem. Int. Ed. 55 (2016) 3360-3363
|
Theoretical Modeling of the Magnetic Behavior of
Thiacalix[4]arene Tetranuclear
MnII2GdIII2 and
CoII2EuIII2
Complexes
|
In view of a wide perspective of 3d-4f complexes in
single-molecule magnetism, here we propose an explanation of the
magnetic behavior of the two thiacalix[4]arene tetranuclear
heterometallic complexes
MnII2GdIII2 and
CoII2EuIII2. The
energy
pattern of the MnII2GdIII2 complex evaluated in the framework of
the isotropic exchange model exhibits a rotational band of the
low-lying spin excitations within which the Lande intervals are
affected by the biquadratic spin-spin interactions. The
nonmonotonic temperature dependence of the Chi*T product observed
for the MnII2GdIII2
complex is attributed to the competitive
influence of the ferromagnetic Mn-Gd and antiferromagnetic Mn-Mn
exchange interactions, the latter being stronger.
The model for the
CoII2EuIII2 complex
includes uniaxial anisotropy of the
seven-coordinate Co ions and an isotropic exchange interaction
in the Co pair, while the Eu ions are diamagnetic in their
ground states. Best-fit analysis of Chi*T versus T showed that the
anisotropic contribution (arising from a large zero-field
splitting in Co ions) dominates (weak-exchange limit) in the
CoII2EuIII2. This
complex is concluded to exhibit an easy plane of
magnetization (arising from the Co pair). It is shown that the
low-lying part of the spectrum can be described by a highly
anisotropic effective spin-1/2 Hamiltonian that is deduced for
the CoII2 pair in the weak-exchange limit.
|
Sergey M. Aldoshin, Nataliya A. Sanina, Andrew V. Palii, Boris S. Tsukerblat,
Theoretical Modeling of the Magnetic Behavior of Thiacalix[4]arene Tetranuclear MnII2GdIII2 and CoII2EuIII2 Complexes,
Inorg. Chem. (2016) Article ASAP
|
Molecular Nanomagnets and Related Phenomena
|
With contributions by
M. Affronte, M.L. Baker, S.J. Blundell, L. Bogani,
L.F. Chibotaru, R. Clerac, A. Cornia, C. Coulon, N. Domingo,
M. Evangelisti, S. Gao, A. Ghirri, S. Hill, S.-D. Jiang,
F. Luis, M. Mannini, C.J. Milios, V. Pianet, F. Troiani,
M. Urdampilleta, R.E.P. Winpenny, B.-W. Wang,
|
Song Gao (Ed.),
Molecular Nanomagnets and Related Phenomena,
Structure and Bonding 164 (2015)
|
New single-ion magnets
|
Single-molecule magnets display magnetic bistability of
molecular origin, which may one day be exploited in magnetic
data storage devices. Recently it was realised that increasing
the magnetic moment of polynuclear molecules does not
automatically lead to a substantial increase in magnetic
bistability. Attention has thus increasingly focussed on ions
with large magnetic anisotropies. In
spite of large effective energy barriers towards relaxation of
the magnetic moment, this has so far not led to a big increase
in magnetic bistability. Here we present a comprehensive study
of a mononuclear, tetrahedrally coordinated cobalt(II)
single-molecule magnet, which has a very high effective energy
barrier and displays pronounced magnetic bistability. The
combined experimental-theoretical approach enables an in-depth
understanding of the origin of these favourable properties,
which are shown to arise from a strong ligand field in
combination with axial distortion. Our findings allow
formulation of clear design principles for improved materials.
|
Yvonne Rechkemmer, Frauke D. Breitgoff, Margarethe van
der Meer, Mihail Atanasov, Michael Hakl, Milan Orlita,
Petr Neugebauer, Frank Neese, Biprajit Sarkar, Joris van Slageren
A four-coordinate cobalt(II) single-ion magnet with coercivity and a very high energy barrier,
Nature Communications 7, 10467 (2016)
More on single-ion magnets:
Yvonne Rechkemmer, Julia E. Fischer, Raphael Marx, MariÌa Dörfel,
Petr Neugebauer, Sebastian Horvath, Maren Gysler, Theis
Brock-Nannestad, Wolfgang Frey, Michael F. Reid, Joris van Slageren,
Comprehensive Spectroscopic Determination of the Crystal Field Splitting in an Erbium Single-Ion Magnet,
JACS 137, 13114 (2015)
|
Supramolecular aggregates of single-molecule magnets:
exchange-biased quantum tunneling of magnetization in a
rectangular [Mn3]4 tetramer
|
The syntheses and properties of four magnetically-supramolecular
oligomers of triangular Mn3 units are reported.
Magnetization vs. dc field sweeps on a single crystal of the
tetrameric [Mn12O4(O2CR)12(pdpd)6](ClO4)4 (R = Me)
gave hysteresis loops below 1 K that exhibit exchange-biased
quantum tunneling of magnetization (QTM) steps with a bias field
of 0.19 T. Simulation of the loops determined that each Mn3 unit
is exchange-coupled to the two neighbors.
The work demonstrates a rational approach to synthesizing
magnetically-supramolecular aggregates of SMMs as potential
multi-qubit systems for quantum computing.
|
Tu N. Nguyen, Wolfgang Wernsdorfer, Muhandis Shiddiq, Khalil
A. Abboud, Stephen Hill, George Christou,
Supramolecular aggregates of single-molecule magnets:
exchange-biased quantum tunneling of magnetization in a
rectangular [Mn3]4 tetramer,
Chem. Sci. 7, 1156 (2016)
|
Thematic Issue: Phase Transition and Dynamical Properties of Spin Transition Materials
|
Great attention in the area of spin transition materials has been paid to the investigation of their
various phase transitions and dynamical properties which can be modulated by external parameters,
including temperature, pressure, photo-irradiation, or presence
of guest molecules.
The topics collected in the issue are focused on the four types
of spin transition materials: (1) Fe(II)-based spin crossover
compounds, (2) Dithiooxalato-bridged Fe-based charge transfer
systems, (3) Charge transfer active Prussian Blue Analogues, and
(4) Copper(II)-octacyanidomolybdate(IV) photomagnetic
materials.
The download of this thematic issue is free of charge.
|
Norimichi Kojima, Shin-ichi Ohkoshi and Seiji Miyashita (Eds.),
Thematic Issue: Phase Transition and Dynamical Properties of Spin Transition Materials,
Current Inorganic Chemistry, vol. 6, issue 1 (2016)
|
Millisecond Coherence Time in a Tunable Molecular Electronic Spin Qubit
|
Millisecond coherence time for a coordination complex qubit was
observed, surpassing the previous record for such a system by an
order of magnitude.
The results illuminate a path forward in synthetic design
principles, which should unite CS2 solubility with nuclear spin
free ligand fields to develop a new generation of molecular
qubits.
|
Joseph M. Zadrozny, Jens Niklas, Oleg G. Poluektov, and Danna
E. Freedman,
Millisecond Coherence Time in a Tunable Molecular Electronic Spin Qubit,
ACS Cent. Sci. 1, 488-492 (2015)
|
Ring, Ring
|
Long before molecular magnetism started, the advent of magnetic
molecular rings was announce in a prophetic publication (Björn
Benny & Agnetha Frida, Ring, Ring, Polar Music, 1973).
In the early days only even-membered rings could be synthesized,
odd rings were covered by strange theoretical prophecies (JMMM
220 (2000) 227; Phys. Rev. B 68 (2003) 054422).
Ring, ring, why don't you give me a call?
Ring, ring, the happiest sound of them all
Ring, ring, I stare at the phone on the wall
And I sit all alone impatiently
Won't you please understand the need in me
So, ring, ring, why don't you make an odd ring?
2016: here we go - an odd homometallic chromium ring is
reported, which is the first regular Cr9
antiferromagnetic ring. Its electronic relaxation dynamics was
probed by 1H-NMR, which allows to determine the spin-phonon
coupling strength. At very low temperatures, the relaxation is
characterized by a single dominating Arrhenius-type relaxation
process, whereas several relevant processes emerge at higher
temperatures.
|
E. Garlatti, S. Bordignon, S. Carretta, G. Allodi, G. Amoretti,
R. De Renzi, A. Lascialfari, Y. Furukawa, G. A. Timco,
R. Woolfson, R. E. P. Winpenny, and P. Santini,
Relaxation dynamics in the frustrated Cr9 antiferromagnetic ring probed by NMR,
Phys. Rev. B 93, 024424 (2016)
More stories on rings (Tell me, are we really through?):
McInnes, E. J. L., Timco, G. A., Whitehead, G. F. S. and
Winpenny, R. E. P.
Heterometallic Rings: Their Physics and use as Supramolecular Building Blocks,
Angew. Chem. Int. Ed., 54, 14244-14269 (2015)
Alternative interpretation (R.W.: The ring was made by Alberich?!):
|