Scaling behavior of thermally assisted magnetization reversal in nanomagnets

Energy barriers and the corresponding magnetization configurations of a nanowire of arbitrary length are derived analytically. The results interpolate between the Néel-Brown theory and the soliton-antisoliton mechanism for long samples. It is shown that the reversal mechanism depends on the time scale being probed. For sufficient size, one and the same particle reverses uniformly for fields close to the anisotropy field at short time scales, but reverses nonuniformly at low fields and large time scales. Remarkably, the energy barrier for nonuniform reversal is considerably lower than that for uniform reversal at small time scales.