Dynamic response of an Ising system to a pulsed field

Abstract

The dynamical response to a pulsed magnetic field has been studied here both using Monte Carlo simulation and by solving numerically the mean-field dynamical equation of motion for the Ising model. The ratio R_p of the response magnetization half-width to the width of the external field pulse has been observed to diverge and pulse susceptibility X_p (ratio of the response magnetization peak height and the pulse height) gives a peak near the order-disorder transition temperature T_c (for the unperturbed system). The Monte Carlo results for the Ising system on a square lattice show that R_p diverges at T_c, with the exponent vz≅2.0, while X_p shows a peak at T_c^e, which is a function of the field pulse width dt. A finite-size (in time) scaling analysis shows that T_c^e=T_c+C(δt)^-1/x, with x=vz≅2.0. The mean-field results show that both the divergence of R and the peak in X_p occur at the mean-field transition temperature, while the peak height in X_p~(δt)^y, y≅1 for small values of δt. These results also compare well with an approximate analytical solution of the mean-field equation of motion.