UC Irvine

Spin Hall effect in a heavy metal (HM) generates a pure spin current flowing perpendicular to an applied electric charge current. When injected into a ferromagnet (FM), this pure spin current can act as negative magnetic damping thereby exciting self-oscillations of magnetization. In a simple HM/FM bilayer geometry, the current-driven self-oscillations of magnetization result in a microwave voltage generation due to anisotropic magneto-resistance (AMR) of the FM. Since AMR in thin films of typical FM materials such as Permalloy (Py) is relatively small, the output microwave signal generated by the HM/FM bilayer spin Hall oscillators (SHOs) is typically limited to ~ 0.1 nW. Here we report a new type of SHO by replacing FM layer with spin valve multilayers. In this type of devices, the microwave power generation relies on current-in-plane (CIP) giant magneto-resistance (GMR) instead of AMR. Since the magnitude GMR typically exceeds that of AMR, this new type of SHO can generate significantly higher power than the AMR-based SHOs. The maximum microwave power generated by the device exceeds 1 nW, which is over an order of magnitude higher than that in HM/FM bilayer SHO nanowire devices.