Hysteresis loop areas in kinetic Ising models: Effects of the switching mechanism

Experiments on ferromagnetic thin films have measured the dependence of thehysteresis loop area on the amplitude and frequency of the external field,$A$=$A(H_{0},\omega)$, and approximate agreement with numerical simulations ofIsing models has been reported. Here we present numerical and theoreticalcalculations of $A$ in the low-frequency regime for two values of $H_{0}$,which bracket a temperature and system-size dependent crossover field. Ourprevious Monte Carlo studies have shown that the hysteretic response of thekinetic Ising model is qualitatively different for amplitudes above and belowthis crossover field. Using droplet theory, we derive analytic expressions forthe low-frequency asymptotic behavior of the hysteresis loop area. In bothfield regimes, the loop area exhibits an extremely slow approach to anasymptotic, logarithmic frequency dependence of the form $A \propto - [\ln(H_{0} \omega)]^{-1}$. Our results are relevant to the interpretation of datafrom experiments and simulations, on the basis of which power-law exponents forthe hysteresis-loop area have been reported.Comment: 9 pages including 3 figures. Submitted as a manuscript for the 7th Joint MMM-Intermag conference. To be published in the Journal of Applied Physics and the IEEE Transactions on Magnetics. Contains 1 updated figure and revised tex