Controlling spin waves by inhomogeneous spin-transfer torques

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We investigate the interplay between spin currents and spin waves in nanofabricated Permalloy waveguides with geometrical constrictions. Using propagating spin-wave spectroscopy, micromagnetic simulations, and analytical modeling, we provide experimental evidence that spin-wave phase can be modulated by inhomogeneous spin-transfer torques generated by current-density gradients shaped by the constriction geometry. Narrower constrictions enhance these gradients and modify the internal field for Damon–Eshbach spin waves, resulting in pronounced changes in spin-wave group velocity and phase. We show a quantitative experimental demonstration of deterministic spin-wave phase modulation enabled by geometry-engineered nonuniform spin-transfer torques. Beyond enabling a scalable route to magnonic interferometry—a building block for spin-wave-based computing—our findings establish a platform to control spin-wave dynamics in spatially varying current landscapes, relevant for analog-gravity experiments in condensed matter systems.