Abstract
We systematically study spectral characteristics of emission microwave signal by a spin current nano-oscillator (SCNO) based on $\mathrm{Ta}{\mathrm{O}}_{x}/\mathrm{Py}(3)/\mathrm{Pt}(2)$ trilayers as a function of current, in-plane magnetic field angle, electrostatic gating, and temperature. The current dependence of spectral characteristics shows that such SCNO exhibits a single coherent oscillation mode at low currents, and then transfers into a multimode coexistence regime with several oscillation peaks, related to spatially separated oscillation regions, at high currents. The linewidth of these modes shows an exponential temperature dependence, indicating thermally activated mode transitions or mode hopping behavior among these spatially separated oscillation regions due to the mode coupling caused by strong thermal-magnon-mediated scattering rate at high temperatures. Additionally, electrostatic gating on oscillation frequency shows a temperature-independent behavior, but gets enhanced in the strongly nonlinear oscillation regime. The enhanced phenomenon is caused by a combination of nonlinear frequency redshift and driving current shift due to electric-field modulation of current-induced spin-orbit torques. The demonstrated electric-field and current control of three-terminal SCNO provides an efficient approach to developing electrically tunable microwave generators in radio frequency integrated circuits and spin-wave-based logic gates in magnonic devices.
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