Interplay between magnetic coupling and spin–orbit torque in current induced exchange bias manipulation in Pt/Co/IrMn heterostructure

In recent years, several experimental results consistently show switching of perpendicular exchange bias by spin–orbit torque (SOT), which is induced by electric current via spin–orbit coupling, in heavy metal (HM)–ferromagnet (FM)–antiferromagnet (AFM) heterostructure. However, no consensus has been reached on the detailed mechanism behind the SOT induced uniaxial exchange bias switching owing to the complex interplay between SOT, exchange coupling of FM-AFM, and thermal fluctuation.

Here, we systemically study current induced exchange bias switching in HM–FM–AFM heterostructure. We aim to experimentally clarify and separate the roles of magnetic coupling, SOT, and its interplay. We demonstrate both out-of-plane and in-plane manipulations of the exchange bias induced by electric current via SOT over uniaxial ferromagnetic anisotropy in HM–FM–AFM heterostructure. By measuring the switching magnitude of the exchange bias field under applied in-plane and out-of-plane magnetic fields, we elucidate the role of magnetic coupling between FM-AFM. We show that the exchange bias direction by current induced exchange bias manipulation is determined by the orientation of the magnetization of the FM rather than the external magnetic field direction. Furthermore, electric current dependence of exchange bias switching and a model calculation using the macro-spin approach substantiate that current-induced exchange bias manipulation stems from SOT induced oscillation of AFM spins.