Nanometer-Thick Palladium–Cobalt Alloy Films for Hydrogen Sensors and Hydrogen-Mediated Devices

Palladium–cobalt (PdCo) alloy nanofilms are expected to play important roles in future hydrogen (H) energy-based society and H-mediated spintronic devices due to their H absorption and large spin–orbit interaction (SOI). Large SOI causes magnetic anisotropy in PdCo films to be sensitive to film stress via the magnetoelastic coupling or inverse magnetostriction effect. Considering this situation, by employing several PdCo alloy nanofilms, we investigated the impact of initial magnetic anisotropy on H2 sensitivity. Our systematic investigation revealed that instability in magnetic anisotropy is important, as it enables absorbed H atoms to induce a large change in magnetic properties, resulting in higher H2 sensitivity. In addition to magnetic anisotropy, nanosized effects have also been revealed to be important for enhancing H2 sensitivity. Based on the measured results and discussion, design guidelines for H2 sensors and H-mediated devices are summarized. The results from this study facilitate the use of both present PdCo and other related alloy films and will help accelerate research and development on H2 sensors and H-mediated devices.