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 chi(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 nu z congruent to 2.0, while chi(p) shows a peak at T-c(e), which is a function of the field pulse width delta t. A finite-size (in time) scaling analysis shows that T-c(e) = T-c + C(delta t)(-1/x), with x=nu z congruent to 2.0. The mean-field results show that both the divergence of R and the peak in chi(p) occur at the mean-field transition temperature, while the peak height in chi(p) similar to(delta t)(y), y congruent to 1 for small values of delta t. These results also compare well with an approximate analytical solution of the mean-field equation of motion.
展开▼
