Hydrogen-mediated long-range magnetic ordering in Pd-rich alloy film

The effect of hydrogenation on a 14 nm Co₁₄Pd₈₆/Al₂O₃(0001) thin film was investigated on the basis of the magnetooptical Kerr effect. After exposure to H₂ gas, the squareness of the hysteresis loop showed a large transition from approximately 10% to 100% and the saturation Kerr signal was reduced to nearly 30% of the pristine value. The reversibility of the transition was verified and the response time was within 2-3 s. These observations indicate that the hydride formation transformed the short-range coupled and disordered magnetic state of the Co₁₄Pd₈₆ film to a long-range-ordered ferromagnetic state and induced appreciable decrease in the magnetic moment. The enhanced long-range-ordering and the reduction of the magnetic moment were attributed to the change of electronic structure in Co₁₄Pd₈₆ with hydrogen uptake.