Most studies of magnetization reversal have looked at the classical regime in which a magnetic field larger than the critical switching field is applied at low temperature (zero temperature limit); magnetization reversal starts immediately and finishes within several nanoseconds. However, as most devices will operate at finite temperature, a better understanding of the microscopic dynamics of magnetization reversal is required, especially as magnetic memory devices get even smaller.
Koch et al., using spin-polarized electron tunneling to investigate magnetic thin films, found that when a magnetic field lower than the critical field was applied, the extra energy required for reversal could be made up thermally. Their results, which show the probability of reversal initially increasing before exponentially decreasing, are consistent with a model in which a ladder of energy states separate the two metastable states of magnetic orientation. Thermal energy can provide the boost needed to step up to the higher rungs.—ISO
Phys. Rev. Lett.84, 5419 (2000).