Yoshinori Muraoka

Susceptibility analysis of two-dimensional antiferromagnet FeTa2O6

The paramagnetic susceptibility of FeTa 2 O 6 is analyzed by the method of high-temperature series expansion based on a two-dimensional Heisenberg model with single-ion anisotropy. Both the nearest and next-nearest neighbor exchange interactions aretaken into consideration and estimated in a compatible form with the spin structure.

Monte Carlo simulations of the Spin-2 Blume-Emery-Griffiths model

The magnetic properties of the spin S = 2 Ising system with the bilinear exchange interaction J1SizSjz, the biquadratic exchange interaction J2Siz2Sjz2 and the single-ion anisotropy DSiz2are discussed by making use of the Monte Carlo (MC) simulation for the magnetization , sub-lattice magnetizations and , the magnetic specific heat CM and spin structures. This Ising spin system of S = 2 with interactions J1 and J2 and with anisotropy D corresponds to the spin-2 Blume-Emery-Griffiths model. The phase diagram of this Ising spin system on a two-dimensional square lattice has been obtained for exchange parameter J2/J1 and anisotropy parameter D/J1. The shapes of the temperature dependence of sublattice magnetizations and are related with abnormal behavior of temperature dependence of at low temperatures and affected significantly by the single-ion anisotropy D. The staggered quadrupolar (SQ) ordering turns out to be different largely between Ising systems with the single-ion anisotropy (D ? 0) and without the one (D = 0).

Partially disordered states of the three-dimensional ANNNI model

Abstract We analyze the three-dimensional axial next-nearest-neighbor Ising model composed of two kinds of alternately stacked ferromagnetic layers with different intralayer interactions by using Monte Carlo (MC) simulation. The detailed analyses of the magnetization and the spin correlations perpendicular to the stacked direction, assure and clarify the existence and the nature of the paramagnetic layers in some modulated phases with wave numbers, 1 4 , 1 8 , 3 16 . This is the first MC confirmation of the partially disordered states which have been predicted by previous molecular field calculation and/or observed in materials such as CsCoCl3, CuFeO2 and CeSb.

Nonequilibrium dynamic phase transition in the ferromagnetic potts model

The nonequilibrium dynamic phase transition arises in various magnetic systems such as ferromagnetic Ising model when system is driven by both an external field and temperature simultaneously. In this paper, the nonequilibrium dynamic phase transition in the q-state Potts model in the presence of a time dependent oscillating magnetic field on a simple cubic lattice is investigated by mean field theory and time dependent Ginzburug-Landau equation. For the case of q = 2, with decrease of the temperature the system undergoes a dynamically ordered phase transition, which is characterized by the period averaged magnetization Q, from a dynamically disordered state Q = 0 to the dynamically ordered state Q ≠ 0. On the other hand, for the case of q = 3 the system has indicated more complicated behavior than that of q = 2. We investigated those characteristic features of the dynamical phase state from the behavior of the dynamic magnetization and the Liapunov exponent.

Monte Carlo simulation of the one-dimensional N-state clock model with long range inverse square interaction

Using Monte Carlo simulation, the one dimensional N-state clock model with long range inverse square interaction has been studied. In the case of N = 6, the temperature dependence of the specific heat shows two peaks at T1 and T2 (< T1). The critical exponent η calculated from the system size dependence of magnetization changes with temperature in the region between T1 and T2. The behaviors are very similar to those of the two-dimensional 6-state clock model with the nearest neighbor interaction which shows two steps of phase transition, Berezinskii-Kosterlitz-Thouless transition and ordinary long range order. We have also confirmed that the temperature T2 shift toward zero with the increase of N.

Monte Carlo Study of the Partially Disordered States of Mixed-spin Axial Next-nearest-neighbor Ising Model

The three-dimensional axial next-nearest-neighbor Ising model, which is composed of alternately stacked ferromagnetic spin-1/2 and spin-1 layers with competing interlayer interactions along the c-axis, is studied by using the Monte Carlo (MC) calculation. The partially disordered phases predicted in the previous molecular field calculation is numerically confirmed by the investigation of the temperature and lattice-size dependencies of magnetization together with those of intra- and inter-layer spin-correlations by the MC calculation.