Measurement of Magnetic Moment at the Atomic Scale in a High TC Molecular Based Magnet

The molecular-based magnet Cs^(I) [Ni^(II) Cr^(III) (CN)6]-2H2O is a ferromagnetic with a Curie temperature TC ) 90 K. Its structure consists of face-centered cubic lattice of Ni^(II) ions connected by Cr(CN)6 entities. We have recorded X-ray magnetic circular dichroism (XMCD) at nickel L2,3 edges. It clearly evidences that nickel(II) is in a high-spin configuration and ferromagnetically coupled to the surrounding Cr^(III) . Through ligand field multiplet calculations, we have determined the total magnetic moment carried by Ni^(II) . Special attention has been paid to the magnetic anisotropy that complicates the calculation of the cross section for a powder. By using sum rules derived for XMCD, it has been possible to extract the orbital and spin contributions to the total magnetic moment. A somewhat too small magnetic moment is found on nickel. A complete calculation taking into account the multiplet coupling effect and the covalent hybridization allowed to determine the precise ground state of nickel and showed that hybridization cannot be responsible for the experimental low nickel magnetic moment. The origin of this effect is discussed

Determination of the cation site distribution of the spinel in multiferroic CoFe2O4 / BaTiO3 layers by X-ray photoelectron spectroscopy

International audienceThe properties of CoFe2O4/BaTiO3 artificial multiferroic multilayers strongly depend on the crystalline structure, the stoichiometry and the cation distribution between octahedral (Oh) and tetrahedral (Td) sites (inversion factor). In the present study, we have investigated epitaxial CoFe2O4 layers grown on BaTiO3, with different Co/Fe ratios. We determined the cation distribution in our samples by X-ray magnetic circular dichroism (XMCD), a well accepted method to do so, and by X-ray photoelectron spectroscopy (XPS), using a fitting method based on physical considerations. We observed that our XPS approach converged on results consistent with XMCD measurements made on the same samples. Thus, within a careful decomposition based on individual chemical environments it is shown that XPS is fully able to determine the actual inversion factor

Bulk and surface switching in Mn-Fe-based Prussian Blue Analogues

Many Prussian Blue Analogues are known to show a thermally induced phase transition close to room temperature and a reversible, photo-induced phase transition at low temperatures. This work reports on magnetic measurements, X-ray photoemission and Raman spectroscopy on a particular class of these molecular heterobimetallic systems, specifically on Rb0.81Mn[Fe(CN)6]0.95_1.24H2O, Rb0.97Mn[Fe(CN)6]0.98_1.03H2O and Rb0.70Cu0.22Mn0.78[Fe(CN)6]0.86_2.05H2O, to investigate these transition phenomena both in the bulk of the material and at the sample surface. Results indicate a high degree of charge transfer in the bulk, while a substantially reduced conversion is found at the sample surface, even in case of a near perfect (Rb:Mn:Fe=1:1:1) stoichiometry. Thus, the intrinsic incompleteness of the charge transfer transition in these materials is found to be primarily due to surface reconstruction. Substitution of a large fraction of charge transfer active Mn ions by charge transfer inactive Cu ions leads to a proportional conversion reduction with respect to the maximum conversion that is still stoichiometrically possible and shows the charge transfer capability of metal centers to be quite robust upon inclusion of a neighboring impurity. Additionally, a 532 nm photo-induced metastable state, reminiscent of the high temperature Fe(III)Mn(II) ground state, is found at temperatures 50-100 K. The efficiency of photo-excitation to the metastable state is found to be maximized around 90 K. The photo-induced state is observed to relax to the low temperature Fe(II)Mn(III) ground state at a temperature of approximately 123 K.Comment: 12 pages, 8 figure

X-Ray Detected Magnetic Hysteresis of Thermally Evaporated Terbium Double-Decker Oriented Films

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Ultralow-temperature device dedicated to soft X-ray magnetic circular dichroism experiments

A new ultralow-temperature setup dedicated to soft X-ray absorption spectroscopy and X-ray magnetic circular dichroism (XMCD) experiments is described. Two experiments, performed on the DEIMOS beamline (SOLEIL synchrotron), demonstrate the outstanding performance of this new platform in terms of the lowest achievable temperature under X-ray irradiation (T = 220 mK), the precision in controlling the temperature during measurements as well as the speed of the cooling-down and warming-up procedures. Moreover, owing to the new design of the setup, the eddy-current power is strongly reduced, allowing fast scanning of the magnetic field in XMCD experiments; these performances lead to a powerful device for X-ray spectroscopies on synchrotron-radiation beamlines facilities

Probing Planckian physics: resonant production of particles during inflation and features in the primordial power spectrum

The phenomenon of resonant production of particles {\it after} inflation has received much attention in the past few years. In a new application of resonant production of particles, we consider the effect of a resonance {\em during} inflation. We show that if the inflaton is coupled to a massive particle, resonant production of the particle during inflation modifies the evolution of the inflaton, and may leave an imprint in the form of sharp features in the primordial power spectrum. Precision measurements of microwave background anisotropies and large-scale structure surveys could be sensitive to the features, and probe the spectrum of particles as massive as the Planck scale.Comment: 19 pages, 11 eps figure

Particle simulation approach for subcellular dynamics and interactions of biological molecules

BACKGROUND: Spatio-temporal dynamics within cells can now be visualized at appropriate resolution, due to the advances in molecular imaging technologies. Even single-particle tracking (SPT) and single fluorophore video imaging (SFVI) are now being applied to observation of molecular-level dynamics. However, little is known concerning how molecular-level dynamics affect properties at the cellular level. RESULTS: We propose an algorithm designed for three-dimensional simulation of the reaction-diffusion dynamics of molecules, based on a particle model. Chemical reactions proceed through the interactions of particles in space, with activation energies determining the rates of these chemical reactions at each interaction. This energy-based model can include the cellular membrane, membranes of other organelles, and cytoskeleton. The simulation algorithm was tested for a reversible enzyme reaction model and its validity was confirmed. Snapshot images taken from simulated molecular interactions on the cell-surface revealed clustering domains (size ~0.2 μm) associated with rafts. Sample trajectories of raft constructs exhibited "hop diffusion". These domains corralled the diffusive motion of membrane proteins. CONCLUSION: These findings demonstrate that our approach is promising for modelling the localization properties of biological phenomena