Combined frequency and time domain measurements on injection-locked, constriction-based spin Hall nano-oscillators

We demonstrate a combined frequency and time domain investigation of injection-locked, constriction-based spin Hall nano-oscillators by Brillouin light scattering (BLS) and the time-resolved magneto-optical Kerr effect (TR-MOKE). This was achieved by applying an ac current in the GHz regime in addition to the dc current which drives auto-oscillations in the constriction. In the frequency domain, we analyze the width of the locking range, the increase in intensity, and the reduction in the linewidth as a function of the applied direct current. Then, we show that the injection locking of the auto-oscillation allows for its investigation by TR-MOKE measurements, a stroboscopic technique that relies on a phase stable excitation, in this case given by the synchronisation to the microwave current. Field sweeps at different dc currents clearly demonstrate the impact of the spin current on the Kerr amplitude. Two-dimensional TR-MOKE and BLS maps show a strong localization of the auto-oscillation within the constriction, independent of the external locking. Published under license by AIP Publishing.