CANADIAN JOURNAL OF PHYSICS, vol.96, no.12, pp.1321-1332, 2018 (SCI-Expanded)
Magnetization relaxation and the steady state response of the S = 1 Ising model with random crystal field to a time varying magnetic field with a frequency omega is modelled and studied here by a method that combines the statistical equilibrium theory with the theory of irreversible thermodynamics. The method offers information on the relaxation time (tau) of the system as well as the temperature (theta) and omega dependencies of the complex (AC or dynamical) susceptibility (i. e., chi(omega) = chi'(omega)-i chi ''(omega)). The so-called low- and high-frequency regions are separated by tau because tau(-1) -> 0 as theta approaches the critical temperatures (theta(c)). One can choose to keep the frequency omega fixed and observe the low-frequency behaviors followed by the high-frequency behaviors when theta -> theta(c). It is shown that chi(omega) exhibits different behaviors in low- and high-frequency regimes that are separated by the quantity omega tau : chi'(omega) converges to static susceptibility and chi ''(omega) -> 0 for omega tau << 1. However, in the high-frequency region where omega tau >> 1, chi'(omega) vanishes and chi ''(omega) displays a peak at the critical temperature (theta(c)). Besides the above, the logarithm of the susceptibility components versus log(omega) is also plotted. From these plots, one plateau (a step-like) region and a shifted peak with rising temperature is observed for the real and imaginary parts, respectively.