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technical paper
Efficient field free spin
Spin-orbit torque (SOT) arising from spin-orbit coupling promises efficient magnetization switching in spintronic devices. It is important for device applications that the SOT switches perpendicular magnetizations without an external magnetic field. In addition to field-free switching, reducing SOT switching current is another essential requirement for low energy consumption. In this talk, we first demonstrate spin currents and associated SOT in ferromagnet/non-magnet/ferromagnet trilayers, in which the torque on the top magnetic layer can be controlled by changing the magnetization of the bottom ferromagnetic layer. In this structure, by aligning the magnetization of the bottom magnetization parallel to the current direction, spin current can carry out-of-plane spin polarization, enabling field-free SOT switching of the top perpendicular magnetization 1. The out-of-plane SOT is generated by spin current precession at the interface due to the interfacial spin-orbit field. Second, we show that the spin current caused by the spin anomalous Hall effect can be additionally exploited in epitaxial Co-based magnetic trilayers (2). The large in-plane magnetic anisotropy of the epitaxial Co makes it possible to control the magnetic easy axis of the bottom magnetic layer away from the current direction. It is found that the critical current for field-free switching is reduced when the magnetization is at an angle between 30 and 45 degrees from the current direction where the spin anomalous Hall effect is non-negligible. References (1) S-h. C. Baek, et al, Nat. Mater. 17, 509 (2018) (2) J. Ryu, et al, Nat. Electron. 5, 217 (2022)