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Dimensional crossover in spin Hall oscillators

Smith, A.; Sobotkiewich, K.; Khan, A.; Montoya, E. A.; Yang, L.; Duan, Z.; Schneider, T.; Lenz, K.; Lindner, J.; An, K.; Li, X.; Krivorotov, I. N.

Auto-oscillations of magnetization driven by direct spin current have been previously observed in multiple quasi-zero-dimensional (0D) ferromagnetic systems such as nanomagnets and nanocontacts. Recently, it was shown that pure spin Hall current can excite coherent auto-oscillatory dynamics in quasi-one-dimensional (1D) ferromagnetic nanowires but not in quasi-two-dimensional (2D) ferromagnetic films. Here we study the 1D to 2D dimensional crossover of current-driven magnetization dynamics in wire-based Pt/Ni80Fe20 bilayer spin Hall oscillators via varying the wire width.We find that increasing the wire width results in an increase of the number of excited auto-oscillatory modes accompanied by a decrease of the amplitude and coherence of each mode. We also observe a crossover from a hard to a soft onset of the auto-oscillations with increasing wire width. The amplitude of auto-oscillations rapidly decreases with increasing temperature suggesting that interactions of the phase-coherent auto-oscillatory modes with incoherent thermal magnons play an important role in suppression of the auto-oscillatory dynamics. Our measurements set the upper limit on the dimensions of an individual spin Hall oscillator and elucidate the mechanisms leading to suppression of coherent auto-oscillations with increasing oscillator size.

Keywords: Spin hall oscillators, ferromagnetism, spin currents, magnetization dynamics, spin waves

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Permalink: https://www.hzdr.de/publications/Publ-31443
Publ.-Id: 31443