Thermal Stability of the Magnetization in Perpendicularly Magnetized Thin Film Nanomagnets

摘要

Understanding the stability of thin film nanomagnets with perpendicularmagnetic anisotropy (PMA) against thermally induced magnetization reversal isimportant when designing perpendicularly magnetized patterned media andmagnetic random access memories. The leading-order dependence of magnetizationreversal rates are governed by the energy barrier the system needs to surmountin order for reversal to proceed. In this paper we study the reversal dynamicsof these systems and compute the relevant barriers using the string method ofE, Vanden-Eijnden, and Ren. We find the reversal to be often spatiallyincoherent; that is, rather than the magnetization flipping as a rigid unit,reversal proceeds instead through a soliton-like domain wall sweeping throughthe system. We show that for square nanomagnetic elements the energy barrierincreases with element size up to a critical length scale, beyond which theenergy barrier is constant. For circular elements the energy barrier continuesto increase indefinitely, albeit more slowly beyond a critical size. In bothcases the energy barriers are smaller than those expected for coherentmagnetization reversal.