Role of induced exchange bias in zero field spin–orbit torque magnetization switching in Pt/[Ni/Co]/PtMn

Abstract

Current induced magnetization switching is of particular interest to develop non-volatile magnetic memories (MRAM). We studied spin–orbit torque (SOT) switching in a Pt/ferromagnet/antiferromagnet Pt/[Co/Ni]2/PtMn Hall cross. For the as-deposited sample, which showed no exchange bias effect, SOT switching is observed only under an in-plane applied field. In this case, when the in-plane applied field tends to zero, the current switching required diverges and the Hall voltage signal generated by the switching tends to zero. However, the same sample is annealed perpendicular to the plane and then in an in-plane applied field, which demonstrated not only square Hall voltage vs current hysteresis loops but also a moderate switching current in zero magnetic field. This procedure induces an out-of-plane exchange bias with strengthened perpendicular magnetic anisotropy and an in-plane exchange bias, which induces zero field SOT switching. The study of the SOT switching for both annealing procedures as a function of the injected current and the in-plane field is shown. These results could impact the design of future spintronics devices such as SOT-MRAM.