  We experimentally study the dynamical modes excited by spin current in Spin
Hall nano-oscillators based on the 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 was observed at currents close to the transition
between different modes and in the mode coexistence regimes. The mode hopping
was suppressed at cryogenic temperatures, confirming that the coupling between
modes is mediated by thermal magnons. We also demonstrate that coherent
single-mode oscillations with linewidth of 5 MHz can be achieved without
applying 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.
