Manipulating exchange bias by spin–orbit torque

Abstract

Inspired by the success in switching FM magnetization by various electrical means, AFM spintronics has received a great deal of attention in recent years. While most efforts have focused on electrical manipulations of a bulk AFM, interfacial effects between FM and AFM layers are also vitally important for spintronic devices. Here we demonstrate that applying current pulses to Pt/Co/IrMn trilayers causes concurrent switching of FM magnetization and perpendicular exchange bias (EB)1. This implies that the FM magnetization and EB can be manipulated independently. When comparing with the conventional field-annealing approach to generate EB, SOT determines the FM magnetization direction and further provides effective disturbance to align the interfacial spins between the FM/AFM layers to the FM magnetization. We further develop a time-resolved resistance measurement technique to eliminate the possibility of EB reversal due to joule heating effects. Not only the direction of the exchange bias can be reversed, but its strength can also be controlled by electric current pulses. For manipulating in-plane exchange bias, we applied an anisotropic magneto-resistance (AMR) effect for studying the spin-orbit torque (SOT)-driven magnetization switching in PtMn/Co bilayer, under y-type SOT geometry2. The tailorable magneto-structural ordering of PtMn provides an additional dimension for the SOT switching. The results reveal the effective field generated by current in PtMn can be enhanced via forming L10 (antiferromagnetic) phase after annealing. On the other hand, the critical current for the y-type SOT switching is strongly associated with the PtMn/Co interfacial spin configuration. The lowest (highest) critical current is yielded when Co is antiferromagnetically (ferromagnetically) coupled to PtMn through the exchange bias. With further investigation and optimization along this direction, the current-pulse-induced EB shall have significant impacts on the SOT-MRAM and other spintronic devices. 1P.H. Lin, B. Y. Yang, M. H. Tsai, H. H. Lin, C.H. Lai, Nat. Mater. 18, 335, (2019) 2 C. Y Yang, L. C. He, Y. S. Yen, P. C. Chen, J. C. Chiu, S. D. Huang, C. H Tseng, and C. H. Lai, Appl. Phys. Lett. 118, 102403 (2021)