Abstract
Spin-Hall nano-oscillators are a promising class of microwave spintronic devices with potential applications in RF/microwave communication and neuromorphic computing. The nano-constriction spin-Hall nano-oscillators (NC-SHNO) have relatively high power, narrow linewidth, and low drive current. Several synchronization schemes e.g. arrays of spin-wave coupled oscillators have been proposed for more stable operation and higher output power. For such arrays, it is crucial to have good oscillator stability and small device-to-device variability. Here, a micromagnetic simulation technique is proposed that includes realistic material properties and hence enables variability and modal stability to be investigated. It is demonstrated, using both measurements and simulation, that the presence of physical grains in the free magnetic layer can induce multiple oscillation modes or frequency sidebands. Our investigation could help in the development of more stable NC-SHNOs that would enable oscillator arrays with stronger synchronization.
Highlights
Spin-based microwave generators [1] are promising in a variety of applications from RF/microwave communication [2] to neuromorphic computing [3], [4]
In order to achieve narrow linewidth and higher output power, synchronization via a propagating spin wave has been demonstrated in various configurations, including multi-constriction nano-constriction spin-Hall nanooscillators (NC-SHNO) [8]–[10] and NC-SHNO arrays [11], [12]
Similar instabilities were observed in so-called nano-gap SHNOs [14]–[16] while this study addresses them for nano-constrictions for the first time
Summary
Spin-based microwave generators [1] are promising in a variety of applications from RF/microwave communication [2] to neuromorphic computing [3], [4]. In order to achieve narrow linewidth and higher output power, synchronization via a propagating spin wave has been demonstrated in various configurations, including multi-constriction NC-SHNO [8]–[10] and NC-SHNO arrays [11], [12]. For these multiple oscillator configurations, the frequency output stability and variability of each individual oscillator are crucial, to guarantee the phase synchronization within the array. Other recent experimental and micromagnetic simulation work on spin-torque oscillators [17], [18] indicated that the presence of a grain structure in the magnetic thin films contributes to device-to-device variability and the presence of multiple oscillation modes. Our realistic simulation results show good qualitative agreement with dual mode features in experimental data
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