Direct Observation of Magnetic Domain and Magnetization Reversal on Prussian Blue-Based Magnetic Films.

Knowledge of the magnetic domain is indispensable for understanding the magnetostatic properties of magnets. However, to date, the magnetic domain has not yet been reported in the field of molecule-based magnets. Herein, we study the magnetic domains of molecule-based magnets.

Atomistic theory of thermally activated magnetization processes in NdFeB permanent magnet.

To study the temperature dependence of magnetic properties of permanent magnets, methods of treating the thermal fluctuation causing the thermal activation phenomena must be established. To study finite-temperature properties quantitatively, we need atomistic energy information to calculate the canonical distribution. In the present review, we report our recent studies on the thermal properties of the NdFeB magnet and the methods of studying them.

Macroscopic nucleation phenomena in continuum media with long-range interactions.

Nucleation, commonly associated with discontinuous transformations between metastable and stable phases, is crucial in fields as diverse as atmospheric science and nanoscale electronics. Traditionally, it is considered a microscopic process (at most nano-meter), implying the formation of a microscopic nucleus of the stable phase. Here we show for the first time, that considering long-range interactions mediated by elastic distortions, nucleation can be a macroscopic process, with the size of the critical nucleus proportional to the total system size.

Molecular dynamics and transfer integral investigations of an elastic anharmonic model for phonon-induced spin crossover.

Based on a vibronic description of the spin-crossover (SC) molecule, the electronic and elastic properties of a chain of anharmonically coupled SC molecules are studied by means of transfer integral (TI) and molecular dynamics (MD) simulations. The thermodynamical properties (high spin fraction and lattice deformation) are derived and show the existence of a first-order transition driven by the phonon field. The MD investigations of the velocity autocorrelation function evidenced that the density of phonon states shows a redshift and a broadening at high temperature, attributed to the enhancement of the phonon entropy.

Monte Carlo simulation of pressure-induced phase transitions in spin-crossover materials.

Pressure-induced phase transitions of spin-crossover materials are studied in a microscopic model taking into account the elastic interaction among distortions of lattice due to the difference of the molecular sizes between the high-spin state and the low-spin state. We perform Monte Carlo simulations in the constant pressure ensemble and reproduce several important properties of the pressure effect in a unified way with a microscopic mechanism for the first time. The simulation newly reveals how the temperature dependence of the ordering process changes with the pressure.

Simple two-dimensional model for the elastic origin of cooperativity among spin states of spin-crossover complexes.

We study the origin of the cooperative nature of spin crossover (SC) between low-spin and high-spin (HS) states from the viewpoint of elastic interactions among molecules. As the size of each molecule changes depending on its spin state, the elastic interaction among the lattice distortions provides the cooperative interaction of the spin states. We develop a simple model of SC with intra and intermolecular potentials which accounts for the elastic interaction including the effect of the inhomogeneity of the spin states and apply constant temperature molecular dynamics based on the Nosé-Hoover formalism.

Nontrivial quantum effect of defect-induced magnetic moments in spin chains.

Low dimensional strongly correlated systems have great potential for new quantum devices. Among them, quantum wires are actively investigated with development of new methods based on self-organized formation. For magnetic wires (chains), impurity doping, which causes inhomogeneity of magnetic interaction, can bring new magnetic properties to the systems.

Structures of a peptide fragment of beta2-microglobulin studied by replica-exchange molecular dynamics simulations - towards the understanding of the mechanism of amyloid formation.

We investigate in detail the structural properties of the monomeric peptide fragment that corresponds to residues 21-31 of beta(2)-microglobulin. As a first step towards the understanding of the mechanism of the amyloid formation, we have performed a replica-exchange molecular dynamics simulation of this peptide with explicit water molecules. We analyze various structural properties as functions of temperature.