Dynamic response of an Ising system to a pulsed field

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 ${\mathrm{R}}_{\mathrm{p}}$ of the response magnetization half-width to the width of the external field pulse has been observed to diverge and pulse susceptibility ${\mathrm{\chi }}_{\mathrm{p}}$ (ratio of the response magnetization peak height and the pulse height) gives a peak near the order-disorder transition temperature ${\mathrm{T}}_{\mathrm{c}}$ (for the unperturbed system). The Monte Carlo results for the Ising system on a square lattice show that ${\mathrm{R}}_{\mathrm{p}}$ diverges at ${\mathrm{T}}_{\mathrm{c}}$, with the exponent νz≅2.0, while ${\mathrm{\chi }}_{\mathrm{p}}$ shows a peak at ${\mathrm{T}}_{\mathrm{c}}^{\mathrm{e}}$, which is a function of the field pulse width δt. A finite-size (in time) scaling analysis shows that ${\mathrm{T}}_{\mathrm{c}}^{\mathrm{e}}$=${\mathrm{T}}_{\mathrm{c}}$+C(δt${)}^{\mathrm{-}1\mathrm{/}\mathrm{x}}$, with x=νz≅2.0. The mean-field results show that both the divergence of R and the peak in ${\mathrm{\chi }}_{\mathrm{p}}$ occur at the mean-field transition temperature, while the peak height in ${\mathrm{\chi }}_{\mathrm{p}}$∼(δt${)}^{\mathrm{y}}$, y≅1 for small values of δt. These results also compare well with an approximate analytical solution of the mean-field equation of motion.