Spin-Torque Manipulation for Hydrogen Sensing

External manipulation of spin-orbit torques (SOTs) promises not only energy-efficient spin-orbitronic devices but also versatile applications of spin-based technologies in diverse fields. However, the external electric-field control, widely used in semiconductor spintronics, is known to be ineffective in conventional metallic spin-orbitronic devices due to the very short screening length. Here, an alternative approach to control the SOTs by using gases is shown. It is demonstrated that the spin-torque generation efficiency of a Pd/Ni₈₁Fe₁₉ bilayer can be reversibly manipulated by the absorption and desorption of H₂ gas, which appears concomitantly with the change of the electrical resistance. It is found that compared with the change of the Pd resistance induced by the H₂ absorption, the change of the spin-torque generation efficiency is almost an order of magnitude larger. This result provides a new method to externally manipulate the SOTs and paves a way for developing more sensitive hydrogen sensors based on the spin-orbitronic technology.