Reversible and Non‐Volatile Manipulation on the Spin‐Orbit Torque in 3d‐5d System of L10‐FePt via Hydrogen Migration

Current‐induced spin‐orbit torque (SOT)‐driven magnetization switching is a cornerstone for future low‐energy‐consumption spintronics. However, achieving effective and controllable SOT remains a significant challenge. Here, a highly modulable SOT‐device is demonstrated based on the 3d‐5d alloy system L10‐FePt, where the critical current density is modulated by ≈43% through the application of a gate voltage from a solid‐state hydrogen electrolyte. The harmonic measurements reveal that the SOT efficiency of L10‐FePt film is enhanced by over 65% under a positive gate voltage and fully recovered under a negative voltage. The underneath hydrogen ion (H+) migration induced by the gate voltage is confirmed by X‐ray photoelectron spectroscopy (XPS) and depth‐resolved secondary ion mass spectroscopy (SIMS). Furthermore, first‐principles calculations uncover a novel spin‐current generation mechanism in the special 3d‐5d alloy L10‐FePt, where both 3d and 5d electrons contribute large but competing spin currents, with the net effect dominated by the 3d electrons. The insertion of H+ enhances the spin Hall conductance by 130%, primarily due to the significant enhancement of the reactive 3d electrons. These findings pave the way for modulable, non‐volatile, and low‐power spintronic and iontronic devices.