Tunable intrinsic phase shift between a spin torque nano-oscillator and an AC current

Abstract

We present magnetodynamic simulations, based on the Landau-Lifshitz- Gilbert-Slonczewski equations, of the interaction between a spin torque oscillator (STO) and an ac current (Iać). To avolde any extrinsic phase shift we inject the ac current at the intrinsic frequency (f STO) of the STO. We nevertheless And an unexpected intrinsic preferred phase shift Δφ 0 between the STO and I ac In the in-plane precession mode (IP) the STO adjusts to a state where its resistance (or voltage) lags lac about a quarter of a wave length (Δφ 0=87- 94°). In this regime Δφ 0 increases somewhat with the dc current. However, as the precession changes into the Out-Of-Plane (OOP) mode, Δφ 0 exhibits a dramatic jump by about 180°, i.e. the STO resistance now precedes Iac about a quarter of a wave length (|Δφ 0|=86°). Δφ 0 can furthermore be tuned by changing one or more of the anisotropy field, the demagnetizing field or the applied field. At the IP/OOP boundary, the ac current mixes the two oscillation modes and both chaotic and periodic mixing is observed. We argue that the intrinsic Δφ 0 will impact any circuit design based on STO technology and will e.g. have direct consequences for phase locking in networks of serially connected STOs. © 2007 IEEE.