Thermally modulated hydrogenation in Fe_xPd_1-x alloy films: Temperature-driven peculiar variation of magnetism

The sensitive hydrogen effect on spintronic materials has been recently demonstrated to have high application potential. However, the correlation between hydrogen pressure (P H 2), temperature, and magnetic properties still remains unclear. In this study, the magnetic moment of Fe in an Fe-Pd alloy thin film was increased through hydrogen absorption, as evidenced by the enhanced X-ray magnetic circular dichroism signal of Fe. Hydrogen absorption and desorption hysteresis loops in the magnetic coercivity H_c-P H 2 diagram revealed that most hydrogen was absorbed when P H 2 was above 10 mbar and desorbed when P H 2 was approximately 10^-6 mbar. The hydrogenation effect on the magnetism of an Fe-Pd alloy film was eliminated at an annealing temperature of 360 K without considerable hydrogen desorption. The annealing-driven cyclic enhancement of H_c was demonstrated because of the competition between thermal activation and H bonding. These results clearly reveal the critical temperature dependence and provide applicable knowledge of the hydrogenation effect on magnetic Pd-alloys.