Step Effect Of The Mixed Magnetic System Monte Carlo Simulation

With the rapid development of computer and computational science, great progress has been made in the materials physics. Recently, the magnetic materials, which are of great applicable values in the fields of magnetic recording and the magnetic sensor, have received considerable attention. The studies of spin glasses began in the 1970's, and now there are great interests in the study of properties of ferromagnetic (FM) and anti ferromagnetic (AFM) mixed magnetic system. We employ the Monte Carlo simulation to investigate the properties of the FM/AFM mixed magnetic system.In the present paper, the magnetic hysteresis of ± J Ising lattices and ± J Heisenberg square lattices is studied systematically on the base of Monte Carlo simulations. The origin of step effect is discussed in greater details. The simulation results are as follows. To begin with, we investigate the hysteresis in the Ising square lattices. The results indicate that the ± J Ising square lattices exhibit hystersis and that the hysteresis loops exist obvious steps. Secondly, we give a further investigation to the origin of the step effect and a reasonable explanation is made from the view of statistics. The numerical results of ± J Ising lattices are the followings: 1) the step width of each hysteresis curve is 2J;2) the number of steps is 2z (z is the coordination number);3) the nonuniform magnitudes of site spins make the steplike hysteresis loop smooth;4) by raising temperature the step effect tends to disappear. Furthermore, FM/AFM Heisenberg model with long-range dipolar interactions is employed and the exchange interactions are exposed to the Gaussian distribution. The properties of the step effect are studied and the numerical results give a further confirm to the phenomena of the step effect. The results indicate: 1) the hysteresis of the system of large size, which is N = 200 × 200 in our simulations, exists the step effect too. And the shape of the steplike hystersis is the same as that ofthe small size system;2) the steplike hysteresis loops are smoothed by decreasing uniaxial anisotropies;3) the increasing magnetic dipolar interaction makes the steplike loop smooth until a thin S shape is obtained;4) as the temperature increases, the steps are vanished too. Then we can say safely that it is high anisotropy, weak magnetic dipolar interaction, uniform magnitudes of site spins and low temperature that altogether induce the distinct step effect of FM/AFM system.