Optimal Spin Polarization for Spin–Orbit-Torque Memory and Oscillator

Spin–orbit-torque arising from in-plane polarized spin current has attracted considerable attention for its potential in high-performance magnetic random access memories and spin torque oscillators (STOs). Recent studies have shown that an out-of-plane spin polarization can be even more efficient to drive the magnetization dynamics. In this work, we thoroughly examine the effect of the out-of-plane polarized spin current through macro-spin simulations. We propose separately the desirable conditions of spin polarization for spintronic memory and oscillator devices. It is found that for memory applications, a comparable strength of out-of-plane and in-plane spin polarization is necessary to simultaneously achieve a reduced switching current density and a faster switching speed. Besides, in STOs, the presence of a sizable out-of-plane polarization can provide an increase of oscillation amplitude and/or an improvement on frequency tunability. Our results address the importance of deliberate control on the spin polarization in designing efficient spintronic devices.