Spin-Orbit Torque Induced Magnetization Switching In Co/Pt Multilayer-based Synthetic Antiferromagnets.

摘要

Summary form only given. Spin-orbit torques (SOTs) switching have been observed in Co/Pt multilayers with strong perpendicular magnetic anisotropy (PMA). In bilayers system made of heavy-nonmagnetic metals (HMs) and ferromagnets (FMs), SOTs are derived from spin Hall effect (SHE) and interfacial Rashba spin orbit coupling. However, in multilayers, SOTs arise from the global imbalance of the spin currents from the top and bottom interfaces for each Co layer. Moreover, synthetic antiferromagnets (SyAFs) can be switched by SOTs, and the switching mechanism does not obey the usual SOTs switching rule of the macrospin model. Therefore, it is important to clarify the mechanism of SyAFs based SOTs switching. In this work, we report SOTs switching in Co/Pt multilayer-based SAFs with the stacking structure of Si/SiO₂/Ta(2)/Pt(5)/[Pt(1)/Co (0.4)]₃/Ru (0.8)/[Co (0.4)/Pt (1)]₅ (thickness in nanometer). The film was deposited by magnetron sputtering and patterned into a Hall bar using electron beam lithography (EBL) and an Ar ion milling technique. Figures 1(a) and (b) present the normalized magnetization curve (M/Ms) and the Hall resistance curve (R_AHE ) as a function of the out-of plane magnetic field with a DC current of 1 mA, respectively. It is obvious that both of the M-H and R-H loops indicate an antiferromagnetic (AFM) interlayer coupling as well as a strong PMA in the multilayer structure. The current-induced magnetization switching is presented in Fig. 2. As shown in Fig. 2(a), the saturated R_H increases with increasing the applied maximum channel current under an external field of +300 Oe, which indicates that more domains can be reversed under a large current. Fig 2.(b) presents that the magnetization can be switched and the orientation depends on the direction of the external field. The anomalous switching behavior is also shown in Fig 2.(b). The switching orientation changes with a larger in-plane external field, indicating the anomalous switching mechanism in SyAFs. According to our study, the total thickness of magnetic layer Co is up to 3.2 nm, which is much thicker than previous reports, which is meaningful for real application in spintronics devices.