Tunable current–field minima induced by demagnetizing fields in nano-constriction spin Hall nano-oscillators

Abstract

This study micromagnetically investigates the intricate interplay among threshold current, constriction geometry-induced demagnetizing fields, and applied out-of-plane (OOP) magnetic fields in nano-constriction spin Hall nano-oscillators (SHNOs). While the threshold current scales linearly with magnetic damping at a fixed OOP field, a distinct non-monotonic behavior emerges with varying OOP field strength, giving rise to a tunable current–field minimum. This phenomenon is consistently observed across constriction widths ranging from 20 to 150 nm and is particularly pronounced in narrower constrictions. As the OOP angle decreases, the current–field minimum shifts toward lower field values, reflecting changes in spin-wave localization and spin-transfer torque efficiency. Analysis with an extended macrospin model reveals that the observed behavior results from transitions between distinct spin-wave localization regimes, each associated with varying degrees of radiation losses, driven by geometry-induced demagnetizing fields under different OOP field strengths. These findings provide key insight into the complex auto-oscillation dynamics of nano-constriction SHNOs and establish a strategic pathway to optimize current–field conditions, paving the way for energy-efficient and scalable SHNO networks in neuromorphic and unconventional computing applications.