Easy-Plane Spin Hall Nano-Oscillator

In spin Hall nano-oscillators (SHNO) based on ferromagnet (FM) and heavy non-magnetic metal (NM) bilayers, a dc current in NM induces a spin current from the spin Hall effect (SHE) that drives auto-oscillations of FM. Large power, low phase noise SHNOs require large precession cone angle. FMs with easy-plane anisotropy are predicted to have cone angle near 90^o when spin current is injected with polarization perpendicular to the easy-plane. Although thin FMs exhibit natural easy-plane anisotropy, the spin Hall current polarization lies in this easy-plane. Here we present a SHNO with FM easy-plane normal to the sample plane, allowing injection of spin Hall current with desired polarization. This SHNO device is a 50 nm wide Pt|Co|Ni|Ta nanowire with two electric leads separated by a 150 nm gap. Interfacial perpendicular magnetic anisotropy is used to tune out-of-plane anisotropy while the nanowire width is used to tune in-plane anisotropy. Careful control of anisotropies allows us to manufacture an easy-plane for the Co|Ni magnetization that is defined by the wire axis and the sample normal. We have found that such easy-plane Pt|Co|Ni|Ta nanowire SHNOs support large-amplitude auto-oscillations in low external field.