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Dynamic control of magnetic nanowires by light-induced domain-wall kickoffs Controlling the speed at which systems evolve is a challenge shared by all disciplines, and otherwise unrelated areas use common theoretical frameworks towards this goal. A particularly widespread model is Glauber dynamics, which describes the time evolution of the Ising model and can be applied to any binary system. In the article it is shown, using molecular nanowires under irradiation, that Glauber dynamics can be controlled by a novel domain-wall kickoff mechanism. In contrast to known processes, the kickoff has unambiguous fingerprints, slowing down the spin-flip attempt rate by several orders of magnitude, and following a scaling law. The required irradiance is very low, a substantial improvement over present methods of magneto-optical switching. These results provide a new way to control and study stochastic dynamic processes. Being general for Glauber dynamics, they can be extended to different kinds of magnetic nanowires and to numerous fields, ranging from social evolution to neural networks and chemical reactivity. Eric Heintze, Fadi El Hallak, Conrad Clauß, Angelo Rettori, Maria Gloria Pini, Federico Totti, Martin Dressel, Lapo Bogani, Dynamic control of magnetic nanowires by light-induced domain-wall kickoffs, Nature Materials 12 (2013) 202

Magnetic cluster excitations Magnetic clusters, i.e., assemblies of a finite number (between two or three and several hundred) of interacting spin centers which are magnetically decoupled from their environment, can be found in many materials ranging from inorganic compounds and magnetic molecules to artificial metal structures formed on surfaces and metalloproteins. Their magnetic excitation spectra are determined by the nature of the spin centers and of the magnetic interactions, and the particular arrangement of the mutual interaction paths between the spin centers. Small clusters of up to four magnetic ions are ideal model systems in which to examine the fundamental magnetic interactions, which are usually dominated by Heisenberg exchange, but often complemented by anisotropic and/or higher-order interactions. In large magnetic clusters, which may potentially deal with a dozen or more spin centers, there is the possibility of novel many-body quantum states and quantum phenomena. In this review the necessary theoretical concepts and experimental techniques to study the magnetic cluster excitations and the resulting characteristic magnetic properties are introduced, followed by examples of small clusters, demonstrating the enormous amount of detailed physical information that can be retrieved. The current understanding of the excitations and their physical interpretation in the molecular nanomagnets which represent large magnetic clusters is then presented, with a section devoted to the subclass of single-molecule magnets, distinguished by displaying quantum tunneling of the magnetization. Finally, there is a summary of some quantum many-body states which evolve in magnetic insulators characterized by built-in or field-induced magnetic clusters. The review concludes by addressing future perspectives in the field of magnetic cluster excitations. Albert Furrer, Oliver Waldmann, Magnetic cluster excitations, Rev. Mod. Phys. 85 (2013) 367

Switchable materials: A new spin on bistability Many different kinds of switchable molecules and materials are based on transition metal ions, but similar properties are also possible in organic materials. Now, two separate studies reveal new insights into the ability of organic radicals to associate reversibly and cooperatively in the solid state, and in so doing create bistable, hysteretic materials. The solid-state electronic structure and properties of a phenalenyl-based butyl-substituted neutral radical, that shows a hysteretic phase transition just above room temperature have been investigated. The electron density distribution of this radical throughout both branches of the hysteretic phase transition was analyzid using solid-state X-ray structures and two distinct electronic states were found in the hysteresis loop that accompanies the phase transition. The bistability of the two electronic states was observed through a number of measurements, including IR transmittance spectra of single crystals in the vicinity of the phase transition. Sushanta K. Pal, Pradip Bag, Arindam Sarkar, Xiaoliu Chi, Mikhail E. Itkis, Fook S. Tham, Bruno Donnadieu, and Robert C. Haddon, Hysteretic Spin and Charge Delocalization in a Phenalenyl-Based Molecular Conductor, JACS 132 (2010) 17258 Robin G. Hicks, Switchable materials: A new spin on bistability, Nature Chemistry 3 (2011) 189

Inelastic Neutron Scattering at its height INS is as powerful as it has never been before. Read the three following highlights to understand its success and importance for nowadays research in quantum magnetism. Spin dynamics of molecular nanomagnets unravelled at atomic scale by four-dimensional inelastic neutron scattering Molecular nanomagnets are among the first examples of finite-size spin systems and have been test beds for addressing several phenomena in quantum dynamics. In fact, for short-enough timescales the spin wavefunctions evolve coherently according to an appropriate spin Hamiltonian, which can be engineered to meet specific requirements. Unfortunately, so far it has been impossible to determine these spin dynamics directly. Here we show that recently developed instrumentation yields the four-dimensional inelastic-neutron scattering function in vast portions of reciprocal space and enables the spin dynamics to be determined directly. We use the Cr8 antiferromagnetic ring as a benchmark to demonstrate the potential of this approach which allows us, for example, to examine how quantum fluctuations propagate along the ring or to test the degree of validity of the Neel-vector-tunnelling framework. Michael L. Baker, Tatiana Guidi, Stefano Carretta, Jacques Ollivier, Hannu Mutka, Hans U. Güdel, Grigore A. Timco, Eric J. L. McInnes, Giuseppe Amoretti, Richard E. P. Winpenny, Paolo Santini, Spin dynamics of molecular nanomagnets unravelled at atomic scale by four-dimensional inelastic neutron scattering, Nature Physics 8 (2012) 906 See also this nice work: Michael L. Baker, Grigore A. Timco, Stergios Piligkos, Jennifer S. Mathieson, Hannu Mutka, Floriana Tuna, Piotr Kozlowski, Michal Antkowiak, Tatiana Guidi, Tulika Gupta, Harapriya Rath, Robert J. Woolfson, Grzegorz Kamieniarz, Robin G. Pritchard, Høgni Weihe, Leroy Cronin, Gopalan Rajaraman, David Collison, Eric J. L. McInnes, and Richard E. P. Winpenny, A classification of spin frustration in molecular magnets from a physical study of large odd-numbered-metal, odd electron rings, , PNAS (2012) Discrete antiferromagnetic spin-wave excitations in the giant ferric wheel Fe18 The low-temperature elementary spin excitations in the AFM molecular wheel Fe18 were studied experimentally by inelastic neutron scattering and theoretically by modern numerical methods, such as dynamical density matrix renormalization group or quantum Monte Carlo techniques, and analytical spin-wave theory calculations. Fe18 involves eighteen spin-5/2 FeIII ions with a Hilbert space dimension of 1014, constituting a physical system that is situated in a region between microscopic and macroscopic. The combined experimental and theoretical approach allowed us to characterize and discuss the magnetic properties of Fe18 in great detail. It is demonstrated that physical concepts such as the rotational-band or L and E-band concepts developed for smaller rings are still applicable. In particular, the higher-lying low-temperature elementary spin excitations in Fe18 or AFM wheels, in general, are of discrete antiferromagnetic spin-wave character. J. Ummethum, J. Nehrkorn, S. Mukherjee, N. B. Ivanov, S. Stuiber, Th. Strässle, P. L. W. Tregenna-Piggott, H. Mutka, G. Christou, O. Waldmann, J. Schnack, Discrete antiferromagnetic spin-wave excitations in the giant ferric wheel Fe18, Phys. Rev. B 86 (2012) 104403 Ferromagnetic Cluster Spin Waves in Molecular Disks Studied by Inelastic Neutron Scattering Structurally, the two mixed-valence manganese disks Mn7-11 and Mn7-16 differ only in the peripheral ligand but, as a result of a subtle interplay of intramolecular exchange interactions, differ strongly in their magnetic properties, e.g., Mn7-11 possesses a ground-state spin of S=11 and Mn7-16 of S=16. The exchange interactions in the disks were studied by inelastic neutron scattering. The analysis of the Q dependence of the observed magnetic transition intensities reveals that ferromagnetic cluster spin-wave excitations were observed. In this framework, it was possible to successfully model the experimental data and provide a physical understanding of the magnetism in the two disks. J. Nehrkorn, S. Mukherjee, S. Stuiber, H. Mutka, Th. Strässle, G. Christou, O. Waldmann, Ferromagnetic Cluster Spin Waves in Molecular Disks Studied by Inelastic Neutron Scattering, Phys. Rev. B 86 (2012) 134417

Hysteresis in the ground and excited spin state up to 10 T of a [MnIII6MnIII]3+ triplesalen single-molecule magnet We have synthesized the triplesalen-based single-molecule magnet (SMM) [MnIII6MnIII]3+ as a variation of our SMM [MnIII6CrIII](BPh4)3. The use of the rod-shaped anion lactate (lac) was intended to enforce a rod packing and resulted in the crystallization of [MnIII6MnIII](lac)3 in the highly symmetric space group R-3-bar. This entails a crystallographic S6 symmetry of the [MnIII6MnIII]3+ molecules, which in addition are all aligned with the crystallographic c axis. Moreover, the molecular environment of each [MnIII6MnIII]3+ molecule is highly symmetric. Single-crystals of [MnIII6MnIII](lac)3 exhibit a double hysteresis at 0.3 K with a hysteretic opening not only for the spin ground state up to 1.8 T, but also for an excited state becoming the ground state at about 3.4 T with a hysteretic opening up to 10 T. Ab initio calculations including spin-orbit coupling establish a non-magnetic behavior of the central MnIII low-spin (l.s.) ion at low temperatures, demonstrating that predictions from ligand-field theory are corroborated in the case of MnIII l.s. by ab intio calculations. Simulations of the field- and temperature-dependent magnetization data indicate that [MnIII6MnIII]3+ is in the limit of weak exchange with antiferromagnetic interactions in the trinuclear MnIII3 triplesalen subunits resulting in intermediate S* = 2 spins. Slight ferromagnetic interactions between the two trinuclear MnIII3 subunits lead to a ground state in zero-field that is approximately described by a total spin quantum number S = 4. This ground state exhibits only a very small anisotropy barrier due to the misalignment of the local zero-field splitting tensors. At higher magnetic fields of about 3.4 T, the spin configuration changes to an all-up orientation of the local MnIII spins, with the main part of the Zeeman energy needed for the spin-flip being required to overcome the local MnIII anisotropy barriers, while only minor contributions of the Zeeman energy are needed to overcome the antiferromagnetic interactions. These combined theoretical analyses provide a clear picture of the double-hysteretic behavior of the [MnIII6MnIII]3+ single-molecule magnet with hysteretic openings up to 10 T. Veronika Hoeke, Klaus Gieb, Paul Müller, Liviu Ungur, Liviu F. Chibotaru, Maik Heidemeier, Erich Krickemeyer, Anja Stammler, Hartmut Bögge, Christian Schröder, Jürgen Schnack, Thorsten Glaser, Hysteresis in the ground and excited spin state up to 10 T of a [MnIII6MnIII]3+ triplesalen single-molecule magnet, Chem. Sci. 3 (2012) 2868

Electronic read-out of a single nuclear spin using a molecular spin transistor Quantum control of individual spins in condensed-matter devices is an emerging field with a wide range of applications, from nanospintronics to quantum computing. The electron, possessing spin and orbital degrees of freedom, is conventionally used as the carrier of quantum information in proposed devices. However, electrons couple strongly to the environment, and so have very short relaxation and coherence times. It is therefore extremely difficult to achieve quantum coherence and stable entanglement of electron spins. Alternative concepts propose nuclear spins as the building blocks for quantum computing, because such spins are extremely well isolated from the environment and less prone to decoherence. However, weak coupling comes at a price: it remains challenging to address and manipulate individual nuclear spins. In this publication it is shown that the nuclear spin of an individual metal atom embedded in a single-molecule magnet can be read out electronically. The observed long lifetimes (tens of seconds) and relaxation characteristics of nuclear spin at the single-atom scale open the way to a completely new world of devices in which quantum logic may be implemented. Romain Vincent, Svetlana Klyatskaya, Mario Ruben, Wolfgang Wernsdorfer, Franck Balestro, Electronic read-out of a single nuclear spin using a molecular spin transistor, Nature 488 (2012) 357

How good can spin densities be calculated? An approach for the calculation of spin density distributions for molecules is presented, that require very large active spaces for a qualitatively correct description of their electronic structure. It is based on the density-matrix renormalization group (DMRG) algorithm to calculate the spin density matrix elements as a basic quantity for the spatially resolved spin density distribution. The spin density matrix elements are directly determined from the second-quantized elementary operators optimized by the DMRG algorithm. As an analytic convergence criterion for the spin density distribution, we employ our recently developed sampling-reconstruction scheme to build an accurate complete-active-space configuration-interaction (CASCI) wave function from the optimized matrix product states. The spin density matrix elements can then also be determined as an expectation value employing the reconstructed wave function expansion. Furthermore, the explicit reconstruction of a CASCI-type wave function provides insight into chemically interesting features of the molecule under study such as the distribution of alpha and beta electrons in terms of Slater determinants, CI coefficients, and natural orbitals. The methodology is applied to an iron nitrosyl complex which we have identified as a challenging system for standard approaches. Katharina Boguslawski, Konrad H. Marti, Örs Legeza, and Markus Reiher, Accurate ab Initio Spin Densities, J. Chem. Theory Comput., 2012, 8 (6), pp 1970-1982

Fragmenting Gadolinium: Mononuclear Polyoxometalate-Based Magnetic Coolers for Ultra-Low Temperatures The polyoxometalate clusters with formula [Gd(W5O18)2] and [Gd(P5W30O110)] each carry a single magnetic ion of gadolinium, which is the most widespread element among magnetic refrigerant materials. In an adiabatic demagnetization, the lowest attainable temperature is limited by the presence of magnetic interactions that bring about magnetic order below a critical temperature. The authors demonstrate that this limitation can be overcome by chemically engineering the molecules in such a way to effectively screen all magnetic interactions, suggesting their use as ultra-low-temperature coolers. Martínez-Pérez, María-José and Montero, Oscar and Evangelisti, Marco and Luis, Fernando and Sesé, Javier and Cardona-Serra, Salvador and Coronado, Eugenio, Fragmenting Gadolinium: Mononuclear Polyoxometalate-Based Magnetic Coolers for Ultra-Low Temperatures, Adv. Mater. 24 (2012) 4301-4305

Inelastic neutron scattering studies on the odd-membered antiferromagnetic wheel Cr8Ni Roughly 50 % of Europe's molecular magnetism community contributed to the following article: A detailed characterization of the magnetic properties of the odd-membered antiferromagnetic "wheel" Cr8Ni has been conducted. Inelastic neutron scattering (INS) is used to investigate the energy and momentum transfer dependence of the low-lying spin excitations, including excited states inaccessible by other experimental techniques. The richness of the INS data, in conjunction with microscopic spin Hamiltonian simulations, enables an accurate characterization of the magnetic properties of Cr8Ni. Nearest-neighbor exchange constants of JCrCr = 1.31 meV and JCrNi = 3.22 meV are determined, and clear evidence of axial single-ion anisotropy is found. The parameters determined by INS are shown to fit magnetic susceptibility. The spectroscopic identification of several successive S=1 excited total spin states and lowest spin band excitations show that the rotational band picture, valid for bipartite AFM wheels, breaks down for this odd-numbered wheel. The exchange constants determined here differ from previous efforts based on bulk measurements, and possible reasons are discussed. The large JCrNi/JCrCr ratio in Cr8Ni puts this wheel into a regime with strong quantum fluctuations in which the ground state can be described with a valence bond solid state picture. Michael L. Baker, Oliver Waldmann, Stergios Piligkos, Roland Bircher, Olivier Cador, Stefano Carretta, David Collison, Felix Fernandez-Alonso, Eric J. L. McInnes, Hannu Mutka, Andrew Podlesnyak, Floriana Tuna, Stefan Ochsenbein, Roberta Sessoli, Andreas Sieber, Grigore A. Timco, Høgni Weihe, Hans U. Güdel, and Richard E. P. Winpenny, Inelastic neutron scattering studies on the odd-membered antiferromagnetic wheel Cr8Ni, Phys. Rev. B 86, 064405 (2012)

Self-Assembled Monolayer of Cr7Ni Molecular Nanomagnets by Sublimation We show, by complementary spectroscopic and STM analysis, that Cr7Ni derivatives are suitable to be sublimed in UHV conditions. Cr7Ni-bu weakly bonds to gold surface and can diffuse relatively freely on it, forming monolayers with hexagonal 2D packing. Conversely, by adding a functional thiol group to the central dibutylamine, a covalent bond between the molecule and surface gold adatoms is promoted, leading to a strong molecular grafting and the formation of a disordered monolayer. These two examples demonstrate the possibility to control the assembly of a large molecular complex, as rationalized by DFT calculations that establish different energy scales in the deposition processes. Moreover, low-temperature XMCD sprectra show that the magnetic features of Cr7Ni rings deposited in UHV on gold remain unchanged with respect to those of the corresponding bulk sample. Alberto Ghirri, Valdis Corradini, Valerio Bellini, Roberto Biagi, Umberto del Pennino, Valentina De Renzi, Julio C. Cezar, Christopher A. Muryn , Grigore A. Timco , Richard E. P. Winpenny , and Marco Affronte, Self-Assembled Monolayer of Cr7Ni Molecular Nanomagnets by Sublimation, ACS Nano, 2011, 5 (9), pp 7090-7099

Ultrafast Spin Avalanches in Crystals of Nanomagnets in Terms of Magnetic Detonation Recent experiments [W. Decelle et al., Phys. Rev. Lett. 102, 027203 (2009)] have discovered ultrafast propagation of spin avalanches in crystals of nanomagnets, which is 3 orders of magnitude faster than the traditionally studied magnetic deflagration. The new regime has been hypothetically identified as magnetic detonation. Here we demonstrate unequivocally the possibility of magnetic detonation in the crystals, as a front consisting of a leading shock and a zone of Zeeman energy release. We study the key features of the process and find that the magnetic detonation speed only slightly exceeds the sound speed in agreement with the experimental observations. For combustion science, our results provide a unique physical example of extremely weak detonation. M. Modestov, V. Bychkov, and M. Marklund, Ultrafast Spin Avalanches in Crystals of Nanomagnets in Terms of Magnetic Detonation, Phys. Rev. Lett. 107, 207208 (2011)

Theoretical Study of Exchange Coupling in 3d-Gd Complexes: Large Magnetocaloric Effect Systems Polynuclear 3d transition metal-Gd complexes are good candidates to present large magnetocaloric effect. This effect is favored by the presence of weak ferromagnetic exchange interactions that have been investigated using methods based on Density Functional Theory.The results show the crucial role of the Gd 5d orbitals in the exchange interaction while the 6s orbital seems to have a negligible participation. The analysis of the atomic and orbital spin populations reveals that the presence of spin density in the Gd 5d orbital is mainly due to a spin polarization effect, while a delocalization mechanism from the 3d orbitals of the transition metal can be ruled out. We propose a numerical DFT approach using pseudopotentials to calculate the exchange coupling constants in four polynuclear first-row transition metal-Gd complexes. Despite the complexity of the studied systems, the numerical approach gives coupling constants in excellent agreement with the available experimental data and, in conjunction with exact diagonalization methods (or Monte Carlo simulations), it makes it possible to obtain theoretical estimates of the entropy change due to the magnetization/demagnetization process of the molecule. Eduard Cremades , Silvia Gómez-Coca , Daniel Aravena , Santiago Alvarez , and Eliseo Ruiz, Theoretical Study of Exchange Coupling in 3d-Gd Complexes: Large Magnetocaloric Effect Systems, J. Am. Chem. Soc., 2012, 134 (25), pp 10532-10542

Molecular Cluster Magnets This work covers new developments in the field of molecular nanomagnetism, complementing previous books in this area. The book is written by experts in the field and is intended as a compilation of critical reviews of new areas rather than a comprehensive text. Contents: Supramolecular Polymetallic 2D [n x n] Transition Metal Grids – Approaches to Ordered Molecular Assemblies and Functional Molecular Devices (Laurence K Thompson, Louise N Dawe and Konstantin V Shuvaev) Recent Synthetic Results Involving Single Molecule Magnets (Guillem Aromí, Eric J L McInnes and Richard E P Winpenny) The Nanoscopic V15 Cluster: A Unique Magnetic Polyoxometalate (Boris Tsukerblat and Alex Tarantul) Neutron Spectroscopy of Molecular Nanomagnets (Tatiana Guidi) Recent Developments in EPR Spectroscopy of Molecular Nanomagnets (Eric J L McInnes) Simulating Computationally Complex Magnetic Molecules (Larry Engelhardt and Christian Schröder) World Scientific Series in Nanoscience and Nanotechnology- Vol. 3, MOLECULAR CLUSTER MAGNETS, edited by Richard Winpenny (The University of Manchester, UK), 312pp, 978-981-4322-94-2 & 978-981-4322-95-9(ebook)

Single-molecule magnets in carbon nanotubes Next-generation electronic, photonic or spintronic devices will be based on nanoscale functional units, such as quantum dots, isolated spin centres or single-molecule magnets. The key challenge is the coupling of the nanoscale units to the macroscopic world, which is essential for read and write purposes. Carbon nanotubes with one macroscopic and two nanoscopic dimensions provide an excellent means to achieve this coupling. Although the dimensions of nanotube internal cavities are suitable for hosting a wide range of different molecules, to our knowledge, no examples of molecular magnets inserted in nanotubes have been reported up to date. Here, we report on the successful encapsulation of single-molecule magnets in carbon nanotubes yielding a new type of hybrid nanostructure that combines all the key single-molecule magnet properties of the guest-molecules with the functional properties of the host-nanotube. This breakthrough paves the way for the construction of spintronic or ultrahigh-density magnetic data storage devices. Maria del Carmen Gimenez-Lopez, Fabrizio Moro, Alessandro La Torre, Carlos J. Gomez-Garcia, Paul D. Brown, Joris van Slageren, Andrei N. Khlobystov, Encapsulation of single-molecule magnets in carbon nanotubes, Nature Communications 2, 407 (2011)

A delocalized arene-bridged diuranium single-molecule magnet Single-molecule magnets (SMMs) are multinuclear clusters whose behaviour typically relies on intramolecular spin-coupling interactions between neighbouring metal ions. A diuranium-arene complex has now been prepared that shows behaviour characteristic of an SMM without relying on this type of superexchange mechanism. This may enable the construction of SMMs that maintain their magnetism at higher temperatures. David P. Mills, Fabrizio Moro, Jonathan McMaster, Joris van Slageren, William Lewis, Alexander J. Blake, Stephen T. Liddle, A delocalized arene-bridged diuranium single-molecule magnet, Nature Chemistry, 3, 454 - 460 (2011)

Magnetic Ground-State and Systematic X-ray Photoreduction Studies of an Iron-Based Star-Shaped Complex XPS methods are valuable tools in order to characterize magnetic substances, but radiation damages might spoil the investigation. In a recent paper a the star-shaped iron-based single-molecule magnet is investigated in order to clarify some open questions concerning the exact electronic and magnetic properties. To this end the internal magnetic structure is studied by applying X-ray magnetic circular dichroism to the Fe L2,3 edges and the occuring radiation photochemistry is investigated. A Fe3+ to Fe2+ photoreduction process, taking place under soft X-ray radiation, is reported. Karsten Kuepper, Christian Taubitz, Daniel Taubitz, Ulf Wiedwald, Andreas Scheurer, Stefan Sperner, Rolf W. Saalfrank, Jean-Paul Kappler, Loc Joly, Paul Ziemann, and Manfred Neumann, Magnetic Ground-State and Systematic X-ray Photoreduction Studies of an Iron-Based Star-Shaped Complex, J. Phys. Chem. Lett., 2011, 2 (13), pp 1491-1496

Supramolecular spin valves Magnetic molecules are potential building blocks for the design of spintronic devices. Moreover, molecular materials enable the combination of bottom-up processing techniques, for example with conventional top-down nanofabrication. In a new publication the authors present an original spin-valve device in which a non-magnetic molecular quantum dot, made of a single-walled carbon nanotube contacted with non-magnetic electrodes, is laterally coupled through supramolecular interactions to TbPc2 single-molecule magnets (Pc=phthalocyanine). Their localized magnetic moments lead to a magnetic field dependence of the electrical transport through the single-walled carbon nanotube, resulting in magnetoresistance ratios up to 300% at temperatures less than 1 K. M. Urdampilleta, S. Klyatskaya, J-P. Cleuziou, M. Ruben, W. Wernsdorfer, Supramolecular spin valves, Nature Materials 10, 502-506 (2011)

World Record: The Highest Magnetic Fields Are Created in Dresden On June 22, 2011, the Helmholtz-Zentrum Dresden-Rossendorf set a new world record for magnetic fields with 91.4 Tesla. To reach this record, Sergei Zherlitsyn and his colleagues at the High Magnetic Field Laboratory Dresden (HLD) developed a coil weighing about 200 kilograms in which electric current create the giant magnetic field for a period of a few milliseconds. The coil survived the experiment unscathed. Press release of the Helmholtz-Zentrum Dresden-Rossendorf

Strong exchange and magnetic blocking in N23--radical-bridged lanthanide complexes Single-molecule magnets approach the ultimate size limit for spin-based devices. These complexes can retain spin information over long periods of time at low temperature, suggesting possible applications in high-density information storage, quantum computing and spintronics. Notably, the success of most such applications hinges upon raising the inherent molecular spin-inversion barrier. Although recent advances have shown the viability of lanthanide-containing complexes in generating large barriers, weak or non-existent magnetic exchange coupling allows fast relaxation pathways that mitigate the full potential of these species. In a recent article the authors show that the diffuse spin of an N23--radical bridge can lead to exceptionally strong magnetic exchange in dinuclear Ln(III) (Ln = Gd, Dy) complexes. The Gd(III) congener exhibits the strongest magnetic coupling yet observed for that ion, while incorporation of the high-anisotropy Dy(III) ion gives rise to a molecule with a record magnetic blocking temperature of 8.3 K at a sweep rate of 0.08 T/s. Jeffrey D. Rinehart, Ming Fang, William J. Evans, Jeffrey R. Long, Strong exchange and magnetic blocking in N23--radical-bridged lanthanide complexes, Nature Chemistry (2011) Published online 22 May 2011

Chemical Society Reviews, Themed issue: Molecule-based magnets Guest editors Joel Miller and Dante Gatteschi introduce the molecule-based magnets themed issue of Chemical Society Reviews. With contributions of Gatteschi, Cornia, Sessoli, Winpenny, Meisel, Dunbar, Tsukerblat, Coronado, Verdaguer, Oshio, ... Chemical Society Reviews, Themed issue Molecule-based magnets, Chem. Soc. Rev., 2011, 40, Issue 6

The first magnetization experiment after March 11 from IMR, Tohoku On 26th of April the first low temperature magnetization experiment after the earthquake was performed at the Institute for Materials Research, Tohoku University in collaboration with Leroy Cronin at Glasgow University. The material is newly synthesized clusters with multi-magentic centers. A clear temperature dependence of the hysteresis as well as the clean magnetization curve at 0.5 K exhibit the full recovery of the research. Luckily, no serious damage of the instrument was caused by the earthquake, however, the laboratory has worked carefully to built up the solid safety in the last 45 days. Moreover, some time is needed to exchange the transfer tube of Helium liquefier. Now IMR group declares the restart from the spring break with sincere thanks for all supports given to us in the last several weeks. Recovery reports from the Institute for Materials Research, Tohoku University

Room-Temperature Electrical Addressing of a Bistable Spin-Crossover Molecular System A switchable molecular device is constructed by contacting an individual nanoparticle based on spin-crossover molecules between nanometer-spaced electrodes. The switching and memory effects near room temperature are a consequence of the intrinsic bistability of the nanoparticle. Interestingly, for molecular spintronics, the spin crossover can also be induced by applying a voltage, showing that its magnetic state is electrically controllable. Ferry Prins, María Monrabal-Capilla, Edgar A. Osorio, Eugenio Coronado, Herre S. J. van der Zant, Room-Temperature Electrical Addressing of a Bistable Spin-Crossover Molecular System, Advanced Materials, Volume 23, Issue 13, pages 1545-1549 (2011)

A Density-Functional Study of Heterometallic Cr-Based Molecular Rings Density-functional theoretical investigation of the electronic and magnetic properties of octametallic Cr-based molecular antiferromagnetic rings are presented. The presence of the divalent magnetic ion M unbalances the charge and the spin of the parent Cr8 ring, leading to a finite total spin in the molecules. Exchange interaction parameters have been extracted from broken-symmetry calculations and compared with the available experiments; in agreement with them, we find that exchange parameters are rather similar in the two derivatives. The analysis of the electronic properties shows some differences depending on M, in particular in the size of the highest occupied molecular orbital to lowest unoccupied molecular orbital (HOMO-LUMO) gaps. V. Bellini and M. Affronte, A Density-Functional Study of Heterometallic Cr-Based Molecular Rings, J. Phys. Chem. B, 2010, 114 (46), 14797-14806

A Double-Switching Multistable Fe4 Grid Complex with Stepwise Spin-Crossover and Redox Transitions A [2×2] Fe4 grid complex featuring two orthogonal switching modes, namely stepwise spin-crossover and sequential redox processes, is presented as the cover article of issue 48/2010 of Angewandte Chemie. Of particular interest are the resulting twofold-degenerate configurations [HS-LS-HS-LS] and [FeII2FeIII2], where two identical metal centers occupy opposite corners of the Fe4 square. Such an arrangement qualifies this new grid complex as a potential building block for quantum cellular automata. B. Schneider, S. Demeshko, S. Dechert, F. Meyer, A Double-Switching Multistable Fe4 Grid Complex with Stepwise Spin-Crossover and Redox Transitions, Angew. Chem. 2010, 122, 9461-9464; Angew. Chem. Int. Ed. 2010, 49, 9274-9277.

A New Family of 1D Exchange Biased Heterometal Single-Molecule Magnets: Observation of Pronounced Quantum Tunneling Steps in the Hysteresis Loops of Quasi-Linear {Mn2Ni3} Clusters First members of a new family of heterometallic Mn/Ni complexes [Mn2Ni3X2L4(LH)2(H2O)2] (X = Cl: 1; X = Br: 2) with the new ligand 2-{3-(2-hydroxyphenyl)-1H-pyrazol-1-yl}ethanol (H2L) have been synthesized. The molecular structures feature a quasi-linear Mn-Ni-Ni-Ni-Mn core with six-coordinate metal ions, where elongated axes of all the distorted octahedral coordination polyhedra are aligned parallel and are fixed with respect to each other by intramolecular hydrogen bonds. The compounds exhibit a quite strong ferromagnetic exchange. Slow relaxation of the magnetization at low temperatures and single-molecule magnet (SMM) behavior are evident from frequency-dependent peaks in the out-of-phase ac susceptibilities and magnetization versus dc field measurements, with significant energy barriers to spin reversal Ueff = 27 K (1) and 22 K (2). Pronounced quantum tunnelling steps are observed in the hysteresis loops. Animesh Das, Klaus Gieb, Yulia Krupskaya, Serhiy Demeshko, Sebastian Dechert, Rüdiger Klingeler, Vladislav Kataev, Bernd Büchner, Paul Müller, Franc Meyer, A New Family of 1D Exchange Biased Heterometal Single-Molecule Magnets: Observation of Pronounced Quantum Tunneling Steps in the Hysteresis Loops of Quasi-Linear {Mn2Ni3} Clusters, J. Am. Chem. Soc. (2011)

Tim And The Pan-Galactic Civil Servants "One night Timothy Becket woke to an adventure that would take him beyond his wildest dreams. With the Pan-Galactic Civil Servants - Clarence Smith, Marvelious Fermionus, Coola Baloola, Garvin McGuffin and Colonel Glumm - at his side, Tim must find the all-powerful Cerulean Circlet before the forces of darkness can claim it for their own. Before the Big Bang, the Architects used the Cerulean Circlet to create the Universe. ..." Damian J.J. Farnell, usually known for his scientific contributions to the physics of spin systems (coupled cluster method), invites us to enjoy his first work of fiction. Damian J.J. Farnell, Tim And The Pan-Galactic Civil Servants, CreateSpace, ISBN-10: 1453776303, ISBN-13: 978-1453776308

Rational design of single-molecule magnets: a supramolecular approach Rational design of single-molecule magnets with C3-symmetry is reported in a new Feature Article in the Emerging Investigators issue of Chemical Communications. C3-symmetry minimizes the quantum tunneling of the magnetization through the anisotropy barrier and thus stabilizes the magnetization. Based on a purposely designed triplesalen ligand heptanuclear complexes of the form [Mt6Mc]n+ could be synthesized, among them the isostructural series [MnIII6CrIII]3+, [MnIII6FeIII]3+, and [MnIII6CoIII]3+ with [MnIII6CrIII]3+ being a SMM. A detailed analysis and comparison of the magnetic properties provides significant insight for further optimization of the SMM properties. Thorsten Glaser, Rational design of single-molecule magnets: a supramolecular approach, Chem. Commun., 2011, 47, 116-130

Spin- and Energy-Dependent Tunneling through a Single Molecule with Intramolecular Spatial Resolution The spin- and energy-dependent tunneling through a single organic molecule (CoPc) adsorbed on a ferromagnetic Fe thin film is investigated: spatially resolved by low-temperature spin-polarized scanning tunneling microscopy. Interestingly, the metal ion as well as the organic ligand show a significant spin dependence of tunneling current flow. State-of-the-art DFT calculations including also van der Waals interactions reveal a strong hybridization of molecular orbitals and substrate 3d states. The molecule is anionic due to a transfer of one electron, resulting in a nonmagnetic (S=0) state. Nevertheless, tunneling through the molecule exhibits a pronounced spin dependence due to spin-split molecule-surface hybrid states. Jens Brede, Nicolae Atodiresei, Stefan Kuck, Predrag Lazi, Vasile Caciuc, Yoshitada Morikawa, Germar Hoffmann,Stefan Blügel, and Roland Wiesendanger, Spin- and Energy-Dependent Tunneling through a Single Molecule with Intramolecular Spatial Resolution, Phys. Rev. Lett. 105, 047204 (2010)

X-ray absorption and magnetic circular dichroism investigation of bis(phthalocyaninato)terbium single-molecule magnets deposited on graphite Magnetization as a function of the external field at T=7 K. Bisphthalocyaninato terbium complexes show a long magnetization relaxation time at relatively high temperatures, which makes them very interesting as magnets at single-molecule level. Their technological exploitation, however, requires the addressing of the individual molecules, therefore the deposition of single-molecule magnets on surfaces is a topic of great interest as the interaction with the substrate can play a crucial role in the definition of the molecule properties. In the present work the electronic and magnetic properties of anionic and neutral forms of a bis(phthalocyaninato)terbium derivative deposited on graphite are investigated by means of x-ray absorption spectroscopy and x-ray magnetic circular dichroism. The comparison of the magnetization values and their dependence on the external magnetic field and temperature suggest that the magnetic properties of molecules are preserved when adsorbed onto the graphite surface. R. Biagi, J. Fernandez-Rodriguez, M. Gonidec, A. Mirone, V. Corradini, F. Moro, V. De Renzi, U. del Pennino, J. C. Cezar, D. B. Amabilino, and J. Veciana, X-ray absorption and magnetic circular dichroism investigation of bis(phthalocyaninato)terbium single-molecule magnets deposited on graphite, Phys. Rev. B 82, 224406 (2010)

Probing Superexchange Interaction in Molecular Magnets by Spin-Flip Spectroscopy and Microscopy The superexchange mechanism in cobalt phthalocyanine (CoPc) thin films was studied by a low temperature scanning tunneling microscope. The CoPc molecules were found to form one-dimensional antiferromagnetic chains in the film. Collective spin excitations in individual molecular chains were measured with spin-flip associated inelastic electron tunneling spectroscopy. By spatially mapping the spin-flipping channels with submolecular precision, the authors are able to explicitly identify the specific molecular orbitals that mediate the superexchange interaction between molecules. Xi Chen, Ying-Shuang Fu, Shuai-Hua Ji, Tong Zhang, Peng Cheng, Xu-Cun Ma, Xiao-Long Zou, Wen-Hui Duan, Jin-Feng Jia, and Qi-Kun Xue, Probing Superexchange Interaction in Molecular Magnets by Spin-Flip Spectroscopy and Microscopy, Phys. Rev. Lett. 101, 197208 (2008)

Co-Gd phosphonate complexes as magnetic refrigerants Three 3d-4f phosphonate complexes, [CoII8GdIII8(Ì3-OH)4(NO3)4(O3PtBu)8(O2CtBu)16], [CoII8GdIII4(O3PtBu)6(O2CtBu)16] and [CoII4GdIII6(O3PCH2Ph)6(O2CtBu)14(MeCN)2], have been synthesized and have structures that can be related to molecular grids. Magnetic studies show they have promise as low temperature magnetic refrigerants. See also RCS Publishing, Chemical Science Blog. Yan-Zhen Zheng, Marco Evangelisti and Richard E. P. Winpenny, Co-Gd phosphonate complexes as magnetic refrigerants, Chem. Sci., 2011, 2, 99-102

FIT-MART fits smart The FIT-MART package is a "Fully Integrated Tool for Magnetic Analysis in Research & Teaching" (hence the acronym) which provides a very simple interface for defining complex quantum spin models, carrying out complex calculations, and visualizing the results using several graphical representations. These representations include plots of the energy spectrum as well as plots of the magnetization and magnetic susceptibility as a function of temperature and magnetic field. The FIT-MART package is an Open Source Physics package written to help students as well as researchers who are studying magnetism. It is distributed as a ready-to-run (compiled) Java archive. Larry Engelhardt and Cameron Rainey, FIT-MART package

High-spin ground states via electron delocalization in mixed-valence imidazolate-bridged divanadium complexes Structure of [(PY5Me2)VII(µ-Lbr) VIII(PY5Me2)]4+ Many magnetic molecules rely on the superexchange mechanism. The possibility of instead using a double-exchange mechanism (based on electron delocalization rather than Heisenberg exchange through a non-magnetic bridge) presents a tantalizing prospect for synthesizing molecules with high-spin ground states that are well isolated in energy. In the article it is demonstrated that magnetic double exchange can be sustained by simple imidazolate bridging ligands, known to be well suited for the construction of coordination clusters and solids. A series of mixed-valence vanadium dimers were synthesized and their electron delocalization probed through cyclic voltammetry and spectroelectrochemistry. Magnetic susceptibility data reveal a well-isolated S = 5/2 ground state arising from double exchange. Bettina Bechlars, Deanna M. D'Alessandro, David M. Jenkins, Anthony T. Iavarone, Starla D. Glover, Clifford P. Kubiak, Jeffrey R. Long, High-spin ground states via electron delocalization in mixed-valence imidazolate-bridged divanadium complexes, Nature Chemistry 2, 362 - 368 (2010)

Molecular Magnets themed issue of Dalton Transactions Dalton Trans. 39 (2010) "The study of magnetic cluster complexes, from the fundamental chemistry and physics that governs their properties to their potential applicability in a range of technologies, is a topic that transcends traditional scientific boundaries, with current research producing ground-breaking science. With the Molecular Magnets themed issue, Dalton Transactions continues its efforts in covering all areas represented by the subject including synthesis, structural characterisation, functional properties, physics and materials science, theory and application." Euan K. Brechin Molecular Magnets themed issue, Dalton Trans. 39 (2010)

Review on cobalt(II) single-molecule magnets Structure of [Co4(cit)4]8− This short tutorial review covers recent progress in the field of polynuclear cobalt(II)-based complexes, which display slow magnetic relaxation at low temperature. Cobalt(II) single-molecule magnets (SMMs) can display much larger magnetic anisotropies and hence, potentially higher blocking temperatures than SMMs based on ions where the zero-field splitting originates from a second order spin-orbit coupling, such as manganese(III). Mark Murrie, Cobalt(II) single-molecule magnets, Chem. Soc. Rev., 2010, 39, 1986-1995

Experimental and theoretical investigations of magnetic molecules with non-collinear local d-tensors Mn3Cr: scetch of exchange interactions and directions of local easy axes In spite of its topologically simple magnetic structure, the [CrIIIMnII3 (PyA)6Cl3] (CrMn3) molecule exhibits nontrivial magnetic properties, which emerge from the combined action of single-ion anisotropy and frustration. The present work elucidates the underlying electronic and magnetic properties of the heteronuclear, spin-frustrated CrMn3 molecule by applying X-ray magnetic circular dichroism (XMCD), as well as magnetization measurements in high magnetic fields, density functional theory, ligand-field multiplet calculations as well as quantum and classical spin model calculations. Manuel Prinz, Karsten Kuepper, Christian Taubitz, Michael Raekers, Sumit Khanra, Biplab Biswas, Thomas Weyhermüller, Marc Uhlarz, Joachim Wosnitza, Jürgen Schnack, Andrei V. Postnikov, Christian Schröder, Simon J. George, Manfred Neumann, and Phalguni Chaudhuri, A Star-shaped Heteronuclear CrIIIMnII3 Species and Its Precise Electronic and Magnetic Structure: Spin Frustration Studied by X-ray Spectroscopic, Magnetic and Theoretical Methods, Inorg. Chem. 49 (2010) 2093-2102 V4: anisotropy easy axis and easy planes Magnetic studies of clusters [V4Cl6(thme)2(bipy)3] and related compounds reveal very weak intramolecular antiferromagnetic exchange and very strong local zero-field splitting effects that dominate the magnetization behavior. Ian S. Tidmarsh, Luke J. Batchelor, Emma Scales, Rebecca H. Laye, Lorenzo Sorace, Andrea Caneschi, Jürgen Schnack and Eric J. L. McInnes, Tri-, tetra- and octa-metallic vanadium(III) clusters from new, simple starting materials: interplay of exchange and anisotropy effects, Dalton Trans. (2009) 9402-9409

Co Dimers on Hexagonal Carbon Rings Proposed as Subnanometer Magnetic Storage Bits Magnetic anisotropy energy of Co atoms in different chemical and structural environments. Black squares denote experimental data, blue circles and red diamonds denote lower and upper estimate theoretical data, In the article it is demonstrated by means of density functional and ab initio quantum chemical calculations, that transition-metal-carbon systems have the potential to enhance the presently available area density of magnetic recording by 3 orders of magnitude. As a model system, Co2 benzene with a diameter of 0.5 nm is investigated. It shows a magnetic anisotropy of the order of 0.1 eV per molecule, large enough to store permanently 1 bit of information at temperatures considerably larger than 4 K. A similar performance can be expected, if cobalt dimers are deposited on graphene or on graphite. Xiao, Ruijuan and Fritsch, Daniel and Kuzmin, Michael D. and Koepernik, Klaus and Eschrig, Helmut and Richter, Manuel and Vietze, Knut and Seifert, Gotthard, Co Dimers on Hexagonal Carbon Rings Proposed as Subnanometer Magnetic Storage Bits, Phys. Rev. Lett. 103 (2009) 187201

Electronic Control of Spin Coupling in Keplerate-Type Polyoxomolybdates In the article it could be shown that the partial reduction of polyoxomolybdate building blocks in Keplerate cluster structures allows the magnetic superexchange mediated by these diamagnetic blocks to be altered. The isolation of a 16-fold reduced {Mo72Fe30} species illustrates how Raman-monitored synthesis can result in such clusters comprising a well-defined assembly of spin centers. Bogdan Botar, Arkady Ellern, Raphael Hermann, Paul Kögerler Electronic Control of Spin Coupling in Keplerate-Type Polyoxomolybdates, Angew. Chem. Int. Ed. 2009, 48, 9080-9083

Ab initio investigation of the non-collinear magnetic structure and the lowest magnetic excitations in dysprosium triangles The unusual magnetism exhibited by dysprosium triangles is explained using the recently developed ab initio methodology for the simulation of magnetic properties of complexes. The local anisotropy axes on the dysprosium sites are found to lie in the plane of the Dy3 triangle and to make angles of ca. 120° with each other. The small antiferromagnetic exchange interaction between sites leads to a non-magnetic Kramers doublet in the ground state of the complex. The arrangement of the local magnetization vectors in this state is close to toroidal. By contrast, the lowest excited states are characterized by a huge magnetic moments of ca. 20 Bohr magnetons and show very different behavior of magnetization for fields applied along and perpendicular to the plane of the Dy3 triangle. Liviu Ungur, Willem Van den Heuvel and Liviu F. Chibotaru Ab initio investigation of the non-collinear magnetic structure and the lowest magnetic excitations in dysprosium triangles, New J. Chem., 2009, 33, 1224-1230

Towards odd-membered spin rings Structure of the oxovanadium heptagons sandwiched by beta-cyclodextrins (l.h.s.) and magnetization curves exhibiting characteristic steps (r.h.s.). For a long time it seemed to be practically impossible to synthesize odd-membered spin rings due to steric hindrance of the (bulky) ligands. A recent article reports the successful synthesis and magnetic characterization of a seven-membered vanadium spin ring. Antiferromagnetically coupled odd-membered rings are expected to show a qualitatively different behavior due to spin frustration. For example, the ground state is fourfold degenerate for half-integer spins, but non-degenerate for integer ones, see Ref. Bärwinkel et al.. In the recent investigation the characteristic behavior for the half-integer case was investigated by means of magnetization measurements. Norihisa Hoshino, Motohiro Nakano, Hiroyuki Nojiri, Wolfgang Wernsdorfer, and Hiroki Oshio, Templating Odd Numbered Magnetic Rings: Oxovanadium Heptagons Sandwiched by beta-Cyclodextrins, J. Am. Chem. Soc. 131 (2009) 15100 K. Bärwinkel, P. Hage, H.-J. Schmidt, J. Schnack, Quantum numbers for relative ground states of antiferromagnetic Heisenberg spin rings, Phys. Rev. B 68, 054422 (2003) see also: Hong-Chang Yao, Jun-Jie Wang, Yun-Sheng Ma, Oliver Waldmann, Wen-Xin Du, You Song, Yi-Zhi Li, Li-Min Zheng, Silvio Decurtins and Xin-Quan Xin, An iron(III) phosphonate cluster containing a nonanuclear ring, Chem. Commun. (2006) 1745

Tuning Molecule-Mediated Spin Coupling in Bottom-Up-Fabricated Vanadium-Tetracyanoethylene Nanostructures Highly resolved STM images and structural models of (a) TCNE, (b) V-TCNE, (c) V(TCNE)2, (d) V2TCNE@27°, and (e) V2TCNE@11° on Ag(100). In this article the fabrication of a hybrid magnetic complexes from V atoms and tetracyanoethylene ligands via atomic manipulation with a cryogenic scanning tunneling microscope is reported. Using tunneling spectroscopy one observes spin-polarized molecular orbitals as well as Kondo behavior. For complexes having two V atoms, the Kondo behavior can be quenched for different molecular arrangements, even as the spin-polarized orbitals remain unchanged. This is explained by variable spin-spin (i.e., V-V) ferromagnetic coupling through a single tetracyanoethylene (TCNE) molecule, as supported by density functional calculations. Daniel Wegner and Ryan Yamachika and Xiaowei Zhang and Yayu Wang and Tunna Baruah and Mark R. Pederson and Bart M. Bartlett and Jeffrey R. Long and Michael F. Crommie, Tuning Molecule-Mediated Spin Coupling in Bottom-Up-Fabricated Vanadium-Tetracyanoethylene Nanostructures, Phys. Rev. Lett. 103, 087205 (2009)

Condensed Matter Physics special issue on spin systems Condensed Matter Physics special issue on spin systems, CONDENSED MATTER PHYSICS, 2009, vol. 12, No. 3 Nowadays spin model theory is a very broad field in condensed physics and statistical physics. The Condensed Matter Physics special issue on spin systems touches only upon a small part of the existing studies and by no means exhausts numerous investigations on spin systems. Editor of the issue: O.V. Derzhko

Deutsche Forschungsgemeinschaft Molecular Magnetism Research Report Deutsche Forschungsgemeinschaft Molecular Magnetism Research Report, Coordination Chemistry Reviews, Volume 253, Issues 19-20, Pages 2241-2460 (October 2009) This volume of the Coordination Chemistry Reviews highlights the research results of the German priority program SPP 1137 on Molecular Magnetism (2002-2008) which was a joined effort of chemists and physicists to explore the new and very vivid field of molecular magnetism. The priority program was financed by the Deutsche Forschungsgemeinschaft.

Tailoring the Nature of Magnetic Coupling of Fe-Porphyrin Molecules to Ferromagnetic Substrates We demonstrate that an antiferromagnetic coupling between paramagnetic Fe-porphyrin molecules and ultrathin Co and Ni magnetic films on Cu(100) substrates can be established by an intermediate layer of atomic oxygen. The coupling energies have been determined from the temperature dependence of x-ray magnetic circular dichroism measurements. By density functional theory+U calculations the coupling mechanism is shown to be superexchange between the Fe center of the molecules and Co surface-atoms, mediated by oxygen. M. Bernien, J. Miguel, C. Weis, Md. E. Ali, J. Kurde, B. Krumme, P. M. Panchmatia, B. Sanyal, M. Piantek, P. Srivastava, K. Baberschke, P. M. Oppeneer, O. Eriksson, W. Kuch, and H. Wende, Tailoring the Nature of Magnetic Coupling of Fe-Porphyrin Molecules to Ferromagnetic Substrates, Phys. Rev. Lett. 102, 047202 (2009)

Microscopic Understanding of Negative Magnetization in Cu, Mn, and Fe Based Prussian Blue Analogues Rietveld refined neutron diffraction pattern for Cu0.73Mn0.77[Fe(CN)6]·zH2O at room temperature. A crossover of the field-cooled magnetization from positive to negative has been observed below the magnetic ordering temperature (17.9 K) in a multimetal Prussian Blue analogue (PBA), Cu0.73Mn0.77[Fe(CN)6]·zH2O. The reverse Monte Carlo (RMC) modeling (using the program RMCPOW) has been used to derive the various scattering contributions (e.g., nuclear diffuse, nuclear Bragg, magnetic diffuse, and magnetic Bragg) from the observed neutron diffraction patterns. The RMC analysis combined with the Rietveld refinement technique show an antiferromagnetic ordering of Mn moments with respect to the Cu as well as the Fe moments. Our study gives the first neutron magnetic structure evidence towards the microscopic understanding of the negative magnetization in the PBAs. Amit Kumar, S. M. Yusuf, L. Keller, and J. V. Yakhmi, Microscopic Understanding of Negative Magnetization in Cu, Mn, and Fe Based Prussian Blue Analogues, Phys. Rev. Lett. 101, 207206 (2008)

Maximum use of symmetry For small enough quantum systems numerical exact and complete diagonalization of the Hamiltonian enables one to evaluate and discuss all static, dynamic, and thermodynamic properties. In a recent article the range of applicability of the exact diagonalization method for Heisenberg spin systems is extend by showing how the irreducible tensor operator technique can be combined with an unrestricted use of general point-group symmetries. Results for numerical exact diagonalizations of Heisenberg spin systems of unprecedented size are presented as e.g. for the antiferromagnetic cuboctahedron with total Hilbert space dimension is 16,777,216. Low-lying energy spectrum of the antiferromagnetic cuboctahedron with s=3/2 in subspaces of S=0,1,2,3. Symbols denote the irreducible representations of the Oh group. R. Schnalle, J. Schnack, Numerically exact and approximate determination of energy eigenvalues for antiferromagnetic molecules using irreducible tensor operators and general point-group symmetries, Phys. Rev. B 79 (2009) 104419 Also in this work, the spin system consisting of four Ni ions (s=1) was analyzed by making massive use of symmetries. Especially it is shown that in the molecular Ni4 clusters with S4 symmetry, not only the local anisotropy but also the antisymmetric exchange interaction contributes to the observed fourth-order anisotropy terms in the single-spin Hamiltonian. N. Kirchner, J. van Slageren, B. Tsukerblat, O. Waldmann, M. Dressel, Antisymmetric exchange interactions in Ni4 clusters, Phys. Rev. B 78, 094426 (2008)

Engineering the coupling between molecular spin qubits by coordination chemistry The ability to assemble weakly interacting subsystems is a prerequisite for implementing quantum information processing and generating controlled entanglement. In a new article it is shown that Cr7Ni rings can be chemically linked to each other and that the coupling between their spins can be tuned by choosing the linker. Calculations that demonstrate how realistic microwave pulse sequences could be used to generate maximally entangled states in such molecules are presented. Grigore A. Timco, Stefano Carretta, Filippo Troiani, Floriana Tuna, Robin J. Pritchard, Christopher A. Muryn, Eric J. L. McInnes, Alberto Ghirri, Andrea Candini, Paolo Santini, Giuseppe Amoretti, Marco Affronte, Richard E. P. Winpenny, Engineering the coupling between molecular spin qubits by coordination chemistry, Nature Nanotechnology, Published online: 01 February 2009;

Magnetic memory of a single-molecule quantum magnet wired to a gold surface In the field of molecular spintronics the use of magnetic molecules for information technology is a main target and the observation of magnetic hysteresis on individual molecules organized on surfaces is a necessary step to develop molecular memory arrays. So far no magnetic hysteresis has been reported for monolayers of SMMs on various non-magnetic substrates, most probably owing to the chemical instability of clusters on surfaces. Using X-ray absorption spectroscopy and X-ray magnetic circular dichroism synchrotron-based techniques, pushed to the limits in sensitivity and operated at sub-kelvin temperatures, it has been found that robust, tailor-made Fe4 complexes retain magnetic hysteresis at gold surfaces. Matteo Mannini, Francesco Pineider, Philippe Sainctavit, Chiara Danieli, Edwige Otero, Corrado Sciancalepore, Anna Maria Talarico, Marie-Anne Arrio, Andrea Cornia, Dante Gatteschi, Roberta Sessoli, Magnetic memory of a single-molecule quantum magnet wired to a gold surface, Nature Materials 8, 194 - 197 (2009) See also News and Views: Heiko Wende, Molecular magnets: How a nightmare turns into a vision, Nature Materials 8, 165 - 166 (2009)

Landing a manganese cluster on a POM The functionalization of a pre-formed, high oxidation state {CeIVMnIV6} cluster with a lacunary phosphotungstate, [Alpha-P2W15O56]12-, exemplifies a straightforward route for grafting redox-active building blocks to existing Mn-carboxylate clusters and modeling their deposition onto metal oxide surfaces. Xikui Fang and Paul Kögerler, A polyoxometalate-based manganese carboxylate cluster, Chem. Commun., 2008, 3396 - 3398

New polyoxometalates Several new polyoxomatelate cluster could be synthesized. Among them are octa- and nonanuclear nickel(II) polyoxometalate clusters and a 16-Metal-Centre Iron Oxide Nanocluster that is the result of anucleation process in the Cavity of a 48-Tungstophosphate Wheel. Another cluster that contains a Cu3 spin triangle was investigated in detail using pulsed-field magnetization, electron spin resonance, and nuclear spin-lattice relaxation. The latter compound shows an unusual hysteresis loop. Pichon, Celine; Mialane, Pierre; Dolbecq, Anne; Marrot, Jerome; Riviere, Eric; Bassil, Bassem; Kortz, Ulrich; Keita, Bineta; Nadjo, Louis; Secheresse, Francis, Octa- and Nonanuclear Nickel(II) Polyoxometalate Clusters: Synthesis and Electrochemical and Magnetic Characterizations Inorg. Chem., 2008, 47 (23), pp 11120-11128 Mal, Sib Sankar; Dickman, Michael H.; Kortz, Ulrich; Todea, Ana Maria; Merca, Alice; Boegge, Hartmut; Glaser, Thorsten; Mueller, Achim; Nellutla, Saritha; Kaur, Narpinder; van Tol, Johan; Dalal, Naresh S.; Keita, Bineta; Nadjo, Louis, Nucleation Process in the Cavity of a 48-Tungstophosphate Wheel Resulting in a 16-Metal-Centre Iron Oxide Nanocluster Chem. Eur. J. 2008, 14, 1186-1195 Kwang-Yong Choi and Naresh S. Dalal and Arneil P. Reyes and Philip L. Kuhns and Yasuhiro H. Matsuda and Hiroyuki Nojiri and Sib Sankar Mal and Ulrich Kortz, Pulsed-field magnetization, electron spin resonance, and nuclear spin-lattice relaxation in the {Cu3} spin triangle Phys. Rev. B 77, 024406 (2008)

Visualizing the Spin of Individual Cobalt-Phthalocyanine Molecules CoPc molecules adsorbed on cobalt nanoislands grown on Cu(111). Low-temperature spin-polarized scanning tunneling microscopy is employed to study spin transport across single cobalt-phthalocyanine molecules adsorbed on well-characterized magnetic nanoleads. A spin-polarized electronic resonance is identified over the center of the molecule and exploited to spatially resolve stationary spin states. These states reflect two molecular spin orientations and, as established by density functional calculations, originate from a ferromagnetic molecule-lead exchange interaction. C. Iacovita, M. V. Rastei, B. W. Heinrich, T. Brumme, J. Kortus, L. Limot, and J. P. Bucher Visualizing the Spin of Individual Cobalt-Phthalocyanine Molecules, Phys. Rev. Lett. 101, 116602 (2008)

Direct Observation of Quantum Coherence in Single-Molecule Magnets Rabi oscillations obtained by recording the echo intensity as a function of nutation pulse length. For two positions in the Rabi cycle the corresponding path on the Bloch sphere is shown on the right. Direct evidence of quantum coherence in a single-molecule magnet in a frozen solution is reported with coherence times as long as T2=630±30 ns. We can strongly increase the coherence time by modifying the matrix in which the single-molecule magnets are embedded. The electron spins are coupled to the proton nuclear spins of both the molecule itself and, interestingly, also to those of the solvent. The clear observation of Rabi oscillations indicates that we can manipulate the spin coherently, an essential prerequisite for performing quantum computations. C. Schlegel, J. van Slageren, M. Manoli, E. K. Brechin, and M. Dressel, Direct Observation of Quantum Coherence in Single-Molecule Magnets, Phys. Rev. Lett. 101, 147203 (2008)

Spin Chirality in a Molecular Dysprosium Triangle: the Archetype of the Non-Collinear Ising Model Molecular nanomagnetism has provided benchmark systems to investigate new and fascinating phenomena in magnetism like magnetic memory at the molecular level, quantum tunneling of the magnetization or destructive interferences in the tunneling pathways. In this field rare earth ions like dysprosium(III) are currently investigated because of their large magnetic anisotropy. In the course of our synthetic efforts to obtain new molecular nanomagnets we recently obtained trinuclear DyIII clusters with almost ideal trigonal symmetry but with the unusual property of possessing a non magnetic ground state. Cancellation of the magnetic moments, resulting in a non-magnetic ground doublet, originates from the non-collinearity of the single ion easy axes of magnetization, as demonstrated by single crystal magnetic studies. The peculiar chiral nature of the ground non-magnetic doublet and the resonant quantum tunneling of the magnetization at the crossings of the discrete energy levels open new perspectives in quantum computation and data storage in molecular nanomagnets. Structure of the Dy3 cluster and its low energy levels as a function of the applied magnetic field. Below 8 kOe two degenerate non magnetic states with opposite spin chirality have the lowest energy. J. Luzon, K. Bernot, I. J. Hewitt, C. E. Anson, A. K. Powell, and R. Sessoli, Spin Chirality in a Molecular Dysprosium Triangle: the Archetype of the Non-Collinear Ising Model, Phys. Rev. Lett. 100, 247205 (2008)

Strong magneto-chiral dichroism in enantiopure chiral ferromagnets Temperature dependence of the MChD effect (diamonds) measured at 615 nm and field-cooled (squares) magnetization. As materials science is moving towards the synthesis, the study and the processing of new materials exhibiting well-defined and complex functions, the synthesis of new multifunctional materials is one of the important challenges. One of these complex physical properties is magneto-chiral dichroism which arises, at second order, from the coexistence of spatial asymmetry and magnetization in a material. Recently the first measurement of strong magneto-chiral dichroism in an enantiopure chiral ferromagnet was reported. The ab initio synthesis of the enantiopure chiral ferromagnet is based on an enantioselective self-assembly, where a resolved chiral quaternary ammonium cation imposes the absolute configurations of the metal centres within chromium–manganese two-dimensional oxalate layers. The ferromagnetic interaction between Cr(III) and Mn(II) ions leads to a Curie temperature of 7 K. The magneto-chiral dichroic effect is enhanced by a factor of 17 when entering into the ferromagnetic phase. Cyrille Train, Ruxandra Gheorghe, Vojislav Krstic, Lise-Marie Chamoreau, Nikolai S. Ovanesyan, Geert L. J. A. Rikken, Michel Gruselle, Michel Verdaguer, Strong magneto-chiral dichroism in enantiopure chiral ferromagnets, Nature Materials 7, 729 - 734 (2008)

Observation of a quantum phase transition in a molecular scale transistor Atomic Force Microscope image of the molecular transistor. The inset represents a x100 zoom view of the inserted C60 molecule. As physical objects become smaller, quantum effects become dominant and easier to measure. Thus, nanometer size quantum objects (in this work a C60 molecule) are propitious for observation of the new quantum phenomena associated with spin electronics. Such objects act as artificial atoms and can be controlled by external parameters such as magnetic field, electric potential or light. We have shown that a molecular transistor based on fullerene (C60) can be switched electrostatically between two different spin states, corresponding to distinct resistance properties of the nanocircuit. In this case, the magnetized state is associated with an entanglement of the spin of the molecule with the conduction electron spins. An electrostatic coupling induces the transition from a spin zero state to a spin 1/2 state. The quantum critical point is then characterized by a spin1/2 that is not entangled with the conduction electrons. This kind of physics is of great current interest and, in addition, our experimental results offer new possibilities for controlling and manipulating the states in molecular spintronics. N. Roch, S. Florens, V. Bouchiat, W. Wernsdorfer and F. Balestro, Quantum phase transition in a single-molecule quantum dot, Nature, 453, 633 (2008)

Calculation of the Zero-Field Splitting Tensor Prof. Dr. Frank Neese receives this year's Klung-Wilhelmy-Weberbank prize for chemistry. He receives the prize for his pioneering work on electronic structure calculations for (magnetic) molecules. We would like to highlight some of his recent results especially on the evaluation of zero-field splitting tensors. The zero-field splitting (ZFS) (expressed in terms of the D tensor) is the leading spin-Hamiltonian parameter for systems with a ground state spin S>1/2. To first order in perturbation theory, the ZFS arises from the direct spin-spin dipole-dipole interaction. To second order, contributions arise from spin-orbit coupling (SOC). The latter contributions are difficult to treat since the SOC mixes states of different multiplicities. This is an aspect of dominant importance for the correct prediction of the D tensor. In Frank Neese's work, the theory of the D tensor is discussed from the point of view of analytic derivative theory. F. Neese, Calculation of the Zero-Field Splitting Tensor Using Hybrid Density Functional and Hartree-Fock Theory, J. Chem. Phys. 127 (2007) 164112 Dmitry Ganyushin and F. Neese, First-principles calculations of zero-field splitting parameters, J. Chem. Phys. 125 (2006) 024103 F. Neese, Importance of Direct Spin-Spin Coupling and Spin-Flip Excitations for the Zero-Field Splittings of Transition Metal Complexes: A Case Study, J. Am. Chem. Soc. 128 (2006) 10213-10222

Polyoxometalate-Mediated Self-Assembly of Single-Molecule Magnets The first two examples of MnII/III-based Single Molecule Magnets (SMMs) encapsulated within a polyoxometalate ligand system are reported. These clusters both contain a central, mixed-valence {Mn6} cluster core that is anchored between two rigid lacunary polyoxometalate clusters. Chris Ritchie, Alan Ferguson, Hiroyuki Nojiri, Haralampos N. Miras, Yu-Fei Song, De-Liang Long, Eric Burkholder, Mark Murrie, Paul Kögerler, Euan K. Brechin, Leroy Cronin, Polyoxometalate-Mediated Self-Assembly of Single-Molecule Magnets: {[XW9O34]2[MnIII4MnII2O4(H2O)4]}12-, Angewandte Chemie International Edition 47 (2008) 5609

Quantum oscillations in a molecular magnet The observation and analysis of Rabi oscillations (quantum oscillations resulting from the coherent absorption and emission of photons driven by an electromagnetic wave) of the molecular magnet "V15" in a hybrid system, in which discrete and well-separated magnetic clusters are embedded in a self-organized non-magnetic environment. Each cluster contains 15 antiferromagnetically coupled S = 1/2 spins, leading to an S = 1/2 collective ground state. When this system is placed into a resonant cavity, the microwave field induces oscillatory transitions between the ground and excited collective spin states, indicative of long-lived quantum coherence. The present observation of quantum oscillations suggests that low-dimension self-organized qubit networks having coherence times of the order of 100 micro seconds (at liquid helium temperatures) are a realistic prospect. S. Bertaina, S. Gambarelli, T. Mitra, B. Tsukerblat, A. Müller, B. Barbara, Quantum oscillations in a molecular magnet, Nature 453, 203-206 (8 May 2008)

A star-shaped manganese-based molecule an S = 10 high-spin state A comprehensive study of the electronic and magnetic properties of a star-shaped molecule comprising a MnII4O6 core is reported. One feature of this compound is weak magnetic coupling constants compared to other similar polyoxo compounds. This leads to complicated low-lying magnetic states in which the ground state is not well separated from the upper-lying states, yielding a high-spin molecule with a giant magnetic moment of up to 20 μB/formula unit. Sumit Khanra, Karsten Kuepper, Thomas Weyhermüller, Manuel Prinz, Michael Raekers, Sebastian Voget, Andrei V. Postnikov, Frank M. F. de Groot, Simon J. George, Marin Coldea, Manfred Neumann, and Phalguni Chaudhuri, Star-Shaped Molecule of MnII4O6 Core with an St = 10 High-Spin State. A Theoretical and Experimental Study with XPS, XMCD, and Other Magnetic Methods, Inorg. Chem. 7 (11), 4605-4617 (2008)

Ground state tuning by high magnetic fields in Ni-compounds An important property of a molecular magnet is the possibility to tune its spin state by an external parameter such as the magnetic field. To address this issue we have measured electron spin resonance (ESR) and magnetization in fields up to 55 T of the novel multicenter complex [L2Ni4(N3)O2CAda)4(ClO4)] (a) and the S = 1 two leg spin ladder [Na2Ni2(C2O4)3(H2O)2] (b). Both complexes show a non-magnetic ground state. However, by applicaton of a strong external magnetic field, H > Hc we can turn the ground state to a strongly magnetic one. At Hc the S = 0 singlet is crossed by the excited |S = 1, Sz = -1> spin state. From ESR and magnetization we find that the critical field Hc at which the spin-level crossings occur are at Hc=25 T in (a), Hc=30 T in (b). Furthermore, appreciable zero-field splittings have been observed which are due to the large single-ion anisotropy (11.5 K (a) and -4.8 K (b)) of nickel. C. Golze , A. Alfonsov, R. Klingeler, B. Büchner, V. Kataev , C. Mennerich, H.-H. Klauss, M. Goiran, J.-M. Broto, H. Rakoto, S. Demeshko, G. Leibeling and F. Meyer, Tuning the Magnetic Ground State of a Tetranuclear Nickel(II) Molecular Complex by High Magnetic Fields, Phys. Rev. B 73 (2006) 224403 C. Mennerich, H.-H. Klauss, M. Broekelmann, F. J. Litterst, C. Golze, R. Klingeler, V. Kataev, B. Büchner, S.-N. Grossjohann W. Brenig, M. Goiran, H. Rakoto, J.-M. Broto, O. Kataeva and D.-J. Price, AFM Dimers of Ni(II) in the S = 1 Spin-Ladder Na2Ni2(C2O4)3(H2O)2, Phys. Rev. B 73 (2006) 104415 S. Demeshko, G. Leibeling, W. Maringgele, F. Meyer, C. Mennerich, H.-H. Klauss, and H. Pritzkow. Structural Variety and Magnetic Properties of Tetranuclear Nickel(II) Complexes with a Central μ4-azide. Inorg. Chem. 44, 519 (2005). D. J. Price, A.K. Powell, and P. T. Wood, A new series of layered transition metal oxalates: Hydrothermal synthesis, structural and magnetic properties. J. Chem. Soc., Dalton Trans., 2478-2482 (2003).

Magnetocaloric properties of frustrated antiferromagnetic molecules and low-dimensional spin systems Antiferromagnetically coupled low-dimensional spin systems showing geometric frustration like the sawtooth chain and the kagome lattice as well as frustrated antiferromagnetic molecules have been investigated with respect to their magnetocaloric properties recently. A key feature is the remarkably large adiabatic cooling rate close to the saturation field as shown in the figure for the example of an antiferromagnetic icosahedron. J. Schnack, R. Schmidt, J. Richter, Enhanced magnetocaloric effect in frustrated magnetic molecules with icosahedral symmetry, Phys. Rev. B 76 (2007) 054413 O. Derzhko and J. Richter, Finite low-temperature entropy of some strongly frustrated quantum spin lattices in the vicinity of the saturation field, Phys. Rev. B 70 (2004) 104415 A. Honecker and J. Richter, Entropy of fermionic models on highly frustrated lattices, Condens. Matter Phys. 8, 813 (2005) M.E. Zhitomirsky, A. Honecker, Magnetocaloric Effect in One-Dimensional Antiferromagnets, J. Stat. Mech.: Theor. Exp. (2004) P07012

Density functional studies of molecular magnets After a general introduction into the field of molecular magnets the discussion focuses on a more specific description of their most important representative species, single-molecule magnets incorporating transition metal ions. We overview traditional model approaches for the phenomenological description of such systems and outline some ways used to parameterize the corresponding models from experiment and from first-principle calculations. The latter can be either multi-determinantal quantum chemical schemes or those based on the density functional theory. In particular we discuss Heisenberg exchange parameters and magnetic anisotropy constants. As a practical example, an introduction into problems and properties of some single-molecule magnets which gained much attention within last years, namely Mn12-acetate, Fe8 and V15 systems, is given. This introduction into systems is followed by a critical comparison of calculation schemes based on the density functional theory that are particularly well suited for the study of molecular magnets. For the above systems we select some benchmark results, obtained by different methods. Finally, we outline our recent progress in the study of other single-molecule magnets, including six-membered "ferric wheels", "ferric stars" and "Ni4" molecules, which we studied with the use of firstprinciples methods SIESTA and NRLMOL. Andrei V. Postnikov, Jens Kortus, Mark R. Pederson, Density functional studies of molecular magnets, physica status solidi (b) 243, 2533-2572 (2006)

A Ferromagnetically Coupled Mn19 Aggregate with a Record S=83/2 Ground Spin State We report on the realization of the maximum-spin ground state of 83/2 for a Mn ixed-valence compound. The combination of using an organic ligand which can bridge to multiple metal centers and using azido ligands has resulted in a Mn19 aggregate that exhibits dominant ferromagnetic interactions with the maximum-spin ground state possible. Achieving such a high ground spin state is clearly one of the elusive goals in the search for obtaining superior SMMs. However, although the MnIII centers in the compound show a high degree of Jahn-Teller distortion, their geometrical arrangement and the strong ferromagnetic interactions between spin carriers lead to a system with a very low anisotropy. The challenge now is to find a means of introducing not only maximum spin but also greater anisotropy. Ayuk M. Ako, Ian J. Hewitt, Valeriu Mereacre, Rodolphe Clerac, Wolfgang Wernsdorfer, Christopher E. Anson, Annie K. Powell, Magnetic relaxation studies on a single-molecule magnet by time-resolved inelastic neutron scattering, Angew. Chem. Int. Ed. 45 (2006) 4926-4929

Magnetic relaxation studies on a single-molecule magnet by time-resolved inelastic neutron scattering Time-resolved inelastic neutron scattering measurements on an array of single-crystals of the single-molecule magnet Mn12ac are presented. The data facilitate a spectroscopic investigation of the slow relaxation of the magnetization in this compound in the time domain. O. Waldmann, G. Carver, C. Dobe, D. Biner, A. Sieber, H. U. Güdel, H. Mutka, J. Ollivier, and N. E. Chakov, Magnetic relaxation studies on a single-molecule magnet by time-resolved inelastic neutron scattering, Appl. Phys. Lett. 88 (2006) 042507

Field-Induced Magnetoelastic Instabilities in Antiferromagnetic Molecular Wheels The magnetic torque of the antiferromagnetic molecular wheel CsFe8 was studied down to 50 mK and up to 28 T. Below about 0.5 K phase transitions were observed at the field-induced level crossings (LCs). Intermolecular magnetic interactions are very weak excluding field-induced magnetic ordering. A magnetoelastic coupling was considered. A generic model shows that the wheel structure is unconditionally unstable at the LCs, and the predicted torque curves explain the essential features of the data well. Figure: (a) dtau/dB at the first LC for a single crystal of compound 1 for several temperatures from 55 mK to 1 K. (b) B-T phase diagram as derived from the data shown in panel (a) (lines are guides to the eyes). The solid symbols indicate the critical fields, the open symbols the half-maximum fields for T >T_c. The dashed line indicates the field of the S=0 to S=1 LC. The dash-dotted lines indicate the halfmaximum fields as expected for thermal broadening. O. Waldmann, C. Dobe, T. Ochsenbein, H. U. Güdel,and I. Sheikin, Field-Induced Magnetoelastic Instabilities in Antiferromagnetic Molecular Wheels, Phys. Rev. Lett. 96 (2006) 027206

Addressing the Metal Centers of [2x2] CoII4 Grid-Type Complexes by STM/STS In their Communication the authors describe the spectroscopic dissecting of a single molecular square into regions of different electronic properties by STM/STS techniques. Figure: a) DFT calculation of occupied orbitals within an energy window between EF and -0.7 eV and the electron density map in superposition with the crystal structure data. b) 3D representation of DFT-calculated electron density maps within an energy window between EF and -0.55 eV and between EF and -1 eV (upper row). Lower row: Central section of the measured CITS maps of Figure. Mohammad Sahabul Alam, Stefan Strömsdörfer, Viacheslav Dremov, Paul Müller, Jens Kortus, Mario Ruben, Jean-Marie Lehn, Addressing the Metal Centers of [2x2] CoII4 Grid-Type Complexes by STM/STS, Angewandte Chemie International Edition, Volume 44, Issue 48 , Pages 7896 - 7900 (2005)

[{(Mo)Mo5O21(H2O)3(SO4)}12(VO)30(H2O)20]36?: A molecular quantum spin icosidodecahedron Self-assembly of aqueous solutions of molybdate and vanadate under reducing, mildly acidic conditions results in a polyoxomolybdate-based {Mo72V30} cluster compound Na8K16(VO)(H2O)5[K10{(Mo)Mo5O21(H2O)3(SO4)}12 (VO)30(H2O)20] *150H2O, a quantum spin-based Keplerate structure. Bogdan Botar, Paul Kögerler, and Craig L. Hill, [{(Mo)Mo5O21(H2O)3(SO4)}12(VO)30(H2O)20]36-: A molecular quantum spin icosidodecahedron, Chem. Commun. 2005, 3138-3140 (2002)

The inverse Landau-Zener-Problem When applying a magnetic field sweep that is linear in time to a two-level system the probability to tunnel can be evaluated according to the works of Landau, Zener, Stueckelberg, and Majorana. But what if one woulkd like to reverse the problem, i.e. how should the functional form of a field sweep W(t) look like in order to obtain a desired tunneling probability function p(t)? This problem was solved theoretically by D.A. Garanin and R. Schilling and awaits its experimental verification. D.A. Garanin and R. Schilling, Inverse problem for the Landau-Zener effect, Europhys. Lett. 59, 7 (2002) D.A. Garanin and R. Schilling, Effects of nonlinear sweep in the Landau-Zener-Stueckelberg effect, Phys. Rev. B 66, 174438 (2002)

Hysteretic Magnetic Bistability Based on a Molecular Azide Switch Like a molecular toggle switch, the bridging azide ion in a highly preorganized dinickel(II) complex turns strong antiferromagnetic coupling on or off. Single crystals of the compound stay intact over the entire temperature range studied and feature hysteretic magnetic bistability not far from ambient temperature. Guido Leibeling, Serhiy Demeshko, Sebastian Dechert, Franc Meyer, Hysteretic Magnetic Bistability Based on a Molecular Azide Switch, Angew. Chem. 2005, 117, 7273-7276; Angew. Chem. Int. Ed. 2005, 44, 7111-7114.

Anions get wheely big A Cu20-containing polyoxotungstate of large size and high symmetry was synthesized by making use of the template effect. The wheel-shaped [Cu20Cl(OH)24(H2O)12(P8W48O184)]25- ion (see picture; black W, turquoise Cu, yellow P, violet Cl, red O) is the first transition-metal-substituted derivative of [H7P8W48O184]33- and incorporates more paramagnetic 3d metal ions than any other polyoxotungstate to date. Sib Sankar Mal and Ulrich Kortz, The Wheel-Shaped Cu20 Tungstophosphate [Cu20Cl(OH)24(H2O)12(P8W48O184)]25- Ion, Angew. Chem. Int. Ed., 44 (2005) 3777-3780

Terahertz Faraday Effect in Single Molecule Magnets For the first time, Faraday rotation in the terahertz frequency range was observed in molecular magnetic systems. The effect is strongest near the magnetic resonance of the single molecule magnet Mn12Ac at ν = 300 GHz, where the Faraday rotation exceeds 150°/mm. Below the magnetization blocking temperature, the effect was observed in the magnetized state of the sample in zero field. Surprisingly, it could even be detected in nonmagnetized states, applying small magnetic fields (H ≤ 1 T), that do not create net magnetization of the sample. All observations were quantitatively explained without fit procedures using known Mn12Ac spin-Hamiltonian parameters. Figure: (top) Transmission spectrum recorded on a single crystal mosaic of Mn12Ac at T = 1.77 K. (middle) radiation ellipticities calculated from angle dependent measurements (c) Faraday rotation angle calculated from angle dependent measurements J. van Slageren, S. Vongtragool, A. Mukhin, B. Gorshunov, M. Dressel, Terahertz Faraday Effect in Single Molecule Magnets, Phys. Rev. B. 72 (2005) 020401R

Néel-Vector Tunneling in Antiferromagnetic Molecular Clusters From inelastic neutron scattering experiments quantum tunneling of the Néel vector in the antiferromagnetic molecular ferric wheel CsFe8 is demonstrated. Analysis of the linewidth of the tunneling transition evidences coherent tunneling. Figure: (a) Crystal structure of CsFe8, (b) Classical ground state spin configuration for the two orientations of the Néel vector. (c) Low-lying energy spectrum. At small anisotropies the levels can be classified by quantum numbers S and M (blue shading). For large anisotropy S looses its significance, but M remains a good quantum number (green shading). This is the region of Néel-vector tunneling. O. Waldmann, C. Dobe, H. Mutka, A. Furrer, and H. U. Güdel, Néel-Vector Tunneling in Antiferromagnetic Molecular Clusters, Phys. Rev. Lett. 95 (2005) 057202

[V30Mo72]: Quantum Keplerate Adding vanadyl sulfate to an acidified molybdate solution, in presence of K+ cations, results in formation of the compound abbreviated as [V30Mo72]. The vanadyl ions form a slightly distorted icosadodecahedron. This fascinating, highly symmetric structure is a spherical arrangement of pentagons and triangles. The S = 1/2 vanadyl ions are strongly exchange coupled. Quantum Monte Carlo simulations show that the average interaction is around J = 245 K. Strong exchange interactions between vanadyl ions despite long exchange pathways is a phenomenon that has been found in other vanadyl polyoxomolybdates. It is much stronger than the exchange interaction in [Fe30Mo72]. The higher spin of the iron ions (S = 5/2) compared to vanadium allowed the application of various classical calculation methods in that case. In that sense [V30Mo72] can be compared as the quantum analogue of [Fe30Mo72] Figure: (top) Combined polyhedral and ball-and-stick representation of the structure of [V30Mo72], showing the triangles and pentagons of the icosidodecahedron, and additionally the basic {VO5} and {VO6} units as green polyhedra; (Mo atoms blue, O atoms red, K atoms purple, and SO42- groups yellow tetrahedra, disordered S atoms yellow). A. Müller, A.M. Todea, M. Dressel, J. van Slageren, H. Bögge, M. Schmidtmann, M. Luban, L. Engelhardt, M. Rusu, On Triangular Geometrical and Magnetic Motifs Uniquely Linked on a Spherical Capsule-Surface, Angew. Chem. Int. Ed. 44 (2005) 3857 - 3861

Fast switching of bistable magnets The use of magnetic nanowires as memory units is made possible by the exponential divergence of the characteristic time for magnetization reversal at low temperature, but the slow relaxation makes the manipulation of the frozen magnetic states difficult. We suggest that finite-size segments can show a fast switching if collective reversal of the spins is taken into account. This mechanism gives rise at low temperatures to a scaling law for the dynamic susceptibility that has been experimentally observed for the dilute molecular chain Co(hfac)2NitPhOMe. These results suggest a possible way of engineering nanowires for fast switching of the magnetization. Alessandro Vindigni, Angelo Rettori, Lapo Bogani, Andrea Caneschi, Dante Gatteschi, Roberta Sessoli, and Miguel A. Novak, Fast switching of bistable magnetic nanowires through collective spin reversal, Appl. Phys. Lett. 87 (2005) 073102

Hysteresis without anisotropy Normally hysteretic behaviour of magnetic systems is the outcome of anisotropic terms in the Hamiltonian. In a recent work we could show that the classical Heisenberg icosahedral antiferromagnet exhibits a hysteresis loop when the external field is swept (see figure). In this hypothetical magnetic molecule the spins are mounted at the vertices of an icosahedron and interact solely via antiferromagnetic nearest neighbor coupling. In the corresponding quantum system the (T=0) magnetization curve exhibits anusual jumps. The whole behavior can be charcterized as a first order metamagnetic phase transition. C. Schröder, H.-J. Schmidt, J. Schnack, and M. Luban, Metamagnetic phase transition of the antiferromagnetic Heisenberg icosahedron, Phys. Rev. Lett. 94 (2005) 207203

Competing Spin Phases in Fe30 Frustrated spin systems such as the kagome lattice antiferromagnet show a pronounced (T=0) magnetization plateau at one third saturation magnetization. Since the magnetic molecule Fe30 is built of spins mounted at the vertices of a perfect icosidodecahedron it is structurally a "little brother" of the kagome antiferromagnet and shares several properties. In a recent experiment we could show that the differential suscptibility dM/dB features a pronounced minimum around one third of the saturation field which gives clear evidence that in this zero-dimensional system the related plateau is produced by competing spin phases just in the same way as on the two-dimensional kagome lattice. C. Schröder, H. Nojiri, J. Schnack, P. Hage, M. Luban, P. Kögerler, Competing Spin Phases in Geometrically Frustrated Magnetic Molecules, Phys. Rev. Lett. 94 (2005) 017205

Giant magnetization jumps For a class of frustrated spin lattices including the Kagome lattice we construct exact eigenstates consisting of several independent, localized one-magnon states and argue that they are ground states for high magnetic fields. If the maximal number of local magnons scales with the number of spins in the system, which is the case for the Kagome lattice, the effect persists in the thermodynamic limit and gives rise to a macroscopic jump in the zero-temperature magnetization curve just below the saturation field. The effect decreases with increasing spin quantum number and vanishes in the classical limit. Thus it is a true macroscopic quantum effect. J. Schulenburg, A. Honecker, J. Schnack, J. Richter, H.-J. Schmidt, Macroscopic magnetization jumps due to independent magnons in frustrated quantum spin lattices, Phys. Rev. Lett. 88 (2002) 167207