Significant role of thermal effects in current-induced exchange bias field switching at antiferromagnet/ferromagnet interface

Abstract

The current-induced switching of in-plane exchange bias field (<i>H</i><sub>eb</sub>) has many advantages, such as, switching without assistance of external magnetic field, excellent immunity to magnetic field, and robust magnetic anisotropy. However, the blocking temperature of the nanoscale antiferromagnet/ferromagnet (AFM/FM) heterostructure is relatively low and susceptible to thermal effects. Therefore, the Joule heating theoretically plays a substantial role in the switching of <i>H</i><sub>eb</sub> driven by current, but its underlying mechanism requires further investigation and verification. We prepared a series of Pt/IrMn/Py heterostructures with varying antiferromagnet IrMn thicknesses and systematically investigated the role of thermal effects in current-driven <i>H</i><sub>eb</sub> switching. These results demonstrate that, under millisecond-level current pulses, Joule heating heats up the device above the blocking temperature, leading to the decoupling of exchange coupling at AFM/FM interface. Simultaneously, the Oersted field and spin-orbit torque field generated by the current switches the ferromagnetic moments, and then a new <i>H</i><sub>eb</sub> will be induced along the direction of the ferromagnetic moments during the cooling process. Furthermore, during the switching process of <i>H</i><sub>eb</sub>, the anisotropic magnetoresistance curve of the AFM/FM heterostructure exhibits a temperature-dependent two-step magnetization reversal phenomenon. Theoretical analysis indicates that this phenomenon arises from the competitive relationship between exchange bias coupling at AFM/FM interface and direct exchange coupling between the ferromagnetic moments. The findings of this study elucidate the crucial role of thermal effects in the current-driven switching of <i>H</i><sub>eb</sub>, thereby contributing to the advancement of spintronic devices based on electrically controlled <i>H</i><sub>eb</sub>.