Scaling-dependent tunability of spin-driven photocurrents in magnetic metamaterials

Spin currents - flows of spin angular momentum without net charge - are central to next-generation spintronic technologies but remain difficult to generate and control efficiently. Magnetic metamaterials provide a powerful platform, as engineered structures allow symmetry design and tailored light-matter interactions. Here, we demonstrate that lateral scaling of triangular-hole Co/Pt magnetic metamaterials exerts a strong, nonlinear influence on spin-current generation via the photogalvanic and magneto-photogalvanic effects. By systematically varying the pattern size, we observe unexpected behaviors: sign reversals, and even complete suppression of photocurrents at specific wavelengths. These phenomena reveal an intimate link between optical resonance conditions and spin current generation. Our findings establish metamaterial geometry as a new degree of freedom for engineering spin currents, offering dynamic tunability of magnitude, and sign - an essential step toward tunable, optically controlled spintronic devices.