Spin-wave modes and magnetic skyrmions excitation in ultranarrow spin Hall nano-oscillators

Abstract Nano-constriction spin Hall nano-oscillators (NC-SHNOs) are pivotal for next-generation low-power and high-frequency spintronics, including neuromorphic computing and spin-wave logic. Scaling the constriction width below 20 nm is critical for reducing power consumption, yet its impact on nonlinear spin-wave dynamics and potential topological states remains unexplored. Here, using micromagnetic simulations, we systematically investigate the effect of NC width (from 100 nm down to 10 nm) in perpendicularly magnetized SHNOs. Extreme geometric confinement drives amplified nonlinearity, where coupled current-driven fields and spin-waves trigger spontaneous chirality. Consequently, a single bidirectional mode evolves into three distinct regimes: bidirectionally coupled oscillation, leftward-propagating, and rightward-propagating modes, with propagation distances modulated by thermal noise. Crucially, narrower (10 nm) NCs enable auto-oscillation at higher frequencies with significantly lower threshold currents, directly addressing power reduction goals. Furthermore, upon enhancing the Dzyaloshinskii-Moriya interaction beyond a critical value, these SHNOs facilitate the large-scale localized excitation of magnetic skyrmions. Skyrmion dynamics analyzed via the Thiele equation show excellent agreement with simulations. This work elucidates the width-dependent spin-wave evolution in scaled SHNOs and demonstrates their capability for controlled skyrmion generation. The discovered multi-mode dynamics offer promising avenues for neuromorphic architectures, while the efficient excitation of localized skyrmions presents a significant advancement towards scalable skyrmion-based devices.