Dynamical Mode Coupling and Coherence in a Spin Hall Nano-Oscillator with Perpendicular Magnetic Anisotropy

We experimentally study the dynamical modes excited by spin current in spin Hall nano-oscillators based on Pt/[Co/Ni] multilayers with perpendicular magnetic anisotropy. Both propagating spin-wave and localized solitonic modes of the oscillation are achieved and controlled by varying the applied magnetic field and current. At room temperature, the generation linewidth broadening associated with mode hopping is observed at currents close to the transition between different modes and in the mode-coexistence regimes. The mode hopping is suppressed at cryogenic temperatures, confirming that the coupling between modes is mediated by thermal-magnon-mediated scattering. We also demonstrate that coherent single-mode oscillations with a linewidth of 5 MHz can be achieved without applying an external magnetic field. Our results provide insight into the mechanisms controlling the dynamical coherence in nanomagnetic oscillators and guidance for optimizing their applications in spin-wave-based electronics.