Dynamic Response of 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 meanfield dynamical equation of motion for the Ising model. The ratio R_p of the response magnetisation half-width to the width of the external field pulse has been observed to diverge and pulse susceptibility χ_p (ratio of the response magnetisation 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 Ising system on square lattice show that R_p diverges at T_c, with the exponent $νz \cong 2.0$, while χ_p shows a peak at $T_c^e$, which is a function of the field pulse width $δt$. A finite size (in time) scaling analysis shows that $T_c^e = T_c + C (δt)^{-1/x}$, with $x = νz \cong 2.0$. The meanfield results show that both the divergence of R and the peak in χ_p occur at the meanfield transition temperature, while the peak height in $χ_p \sim (δt)^y$, $y \cong 1$ for small values of $δt$. These results also compare well with an approximate analytical solution of the meanfield equation of motion.