Reversible Hydrogenation Induced Spin-Reorientation Transition in Co50Pd50alloy Thin Films
Po-Chun Chang1*, Yu-Chan Chen1, Chuan-Che. Hsu1, V. R. Mudinepalli1, W. C. Lin1
1Department of Physics, National Taiwan Normal University, Taipei, Taiwan
* presenting author:Po-Chun Chang,
The hydrogenation effect on the magnetic properties of 10-60 nm Co50Pd50 alloy thin films grown on Al2O3 (0001) substrates was investigated using magneto-optical Kerr effect (MOKE) with various hydrogen gas pressure. For 10-30 nm Co50Pd50 alloy thin films, hydrogenation induced a reversible spin reorientation transition (SRT) as the hydrogen gas pressure increased. The magnetic easy axis switched from perpendicular to in-plane direction after hydrogen absorption and switched back to perpendicular direction after hydrogen desorption. Our data shows the perpendicular MOKE (P-MOKE) hysteresis loops of a 30 nm Co50Pd50 film, measured in various hydrogen gas pressures. In the initial condition of air environment and a vacuum, the P-MOKE revealed square shaped hysteresis loops, indicating the stable magnetization in perpendicular direction. Under the hydrogen gas pressure of 50-500 mbar, the hysteresis loop became tilted, indicating the switching of magnetization toward the in-plane direction. When the hydrogen gas was pumped out to reach a vacuum again, the square hysteresis recovered. Besides, the reversible changes of magnetic coercivity (Hc) and squareness (Mr/Ms) for a 10 nm Co50Pd50 film, was also measured as a function of cyclic changed hydrogen gas pressure. This hydrogenation induced SRT disappeared in a 60 nm Co50Pd50 film, because of its dominant in-plane magnetic anisotropy. Besides, the SRT was accompanied by demagnetization effect. The cyclic change of hydrogen pressure not only switched the magnetization but also led to randomization of magnetic domain, which was observed in the initial magnetization curve of MOKE measurement. These observations will be valuable in future technology development of spintronic devices in hydrogen sensing and related applications.

Keywords: spin-reorientation transition, demagnetization, hydrogenation effect