Tatuo Kawasaki

Size dependence of relaxation time in the fuzzy spin model

Abstract Distribution of relaxation time in the fuzzy spin model (FSM) is studied when the model is quenched from an infinite temperature to a temperature below the ordering point. It is found that the time becomes longer proportionally to an exponential of the linear size of the system L , namely τα exp( aL ).

Dynamics of solitons in an easy-plane ferromagnetic chain. A discrete lattice model

Numerical analysis is carried out for soliton modes in a one-dimensional easy-plane ferromagnetic lattice with an in-plane magnetic field. Lifetime of the sine-Gordon soliton is studied as a measure of difference between the lattice model and the continuum one. Three oscillatory modes are observed as collective motions of spin vectors, which are not in the continuum media. Lattice discreteness is found to be essential to the soliton dynamics in the solid material.

Theory of temperature dependence of spin-wave impurity modes in an antiferromagnetic perovskite

Abstract The method of two-time Green function is applied to the study of the behaviour of spin-wave impurity modes at low temperatures. Results are compared with two experiments on Ni 2+ and Eu 3+ impurities in KMnF 3 .

Relaxation phenomena of the fuzzy‐spin model

We study the slow relaxation phenomena of the Fuzzy spin model which is an Ising ferromagnetic model with random spin length. Distribution of the relaxation time to the equilibrium ferromagnetic state after rapid quenching from the infinite temperature is investigated by a Monte Carlo method. We study the mechanism of the slow relaxation using a cluster picture of strongly coupled spins. The dynamics of domain wall is also investigated using a one dimensional stochastic model.

Dynamical behavior of solitons in a magnetic chain

Abstract Effect of lattice discreteness on magnetic solitons has been numerically simulated in a one-dimensional easy-plane ferromagnet. The sine-Gordon soliton as an initial input shows three types of oscillations as well as damped motion and pinning or trapping at a lattice site.

Modulated phases in diluted ANNNI models

Abstract Persistency of the modulated phases in an anisotropic Ising model with nearest- and next-nearest-neighbor interactions is examined in the diluted system, by using the high-temperature series expansion. There appears to be no remarkable difference from the pure system in the wider range of concentration.

Interface structure in a magnetic binary alloy (Monte Carlo simulation)

Abstract The effect of magnetic interaction on the phase separation of a binary alloy is examined during the study of the behavior of interface structure using a computer. Near the roughening temperature TR, roughness ≈(TR − T)−0.51±0.05, diffuseness ≈(TR − T)−0.47±0.03 and interface thickness ≈ (TR − T)−0.71±0.10. The structure function S(k, t) is also studied.

Possibility of inverse Suhl instability processes by optical pumping in antiferromagnets

Abstract Strong excitation of the zone-boundary magnons in antiferromagnets by optical pumping may produce the possibility of the process which is the inverse of the so-called Suhl Instability. The threshold condition for this process is found to be a minimum density of the zone-boundary mode of (K/zJ) (ΔH0/ωres).