Hydrogenation effect on magnetic properties of Pd–Co alloys

The magnetic properties of Pd–Co alloys and their hydrides were investigated. From the temperature dependences of magnetization of Pd–Co alloys, simple ferromagnetic behaviors were observed, and the Curie temperatures are estimated to be 220, 315, and 350 K for Pd_0.96Co_0.04, Pd_0.92Co_0.08, and Pd_0.90Co_0.10, respectively. The Pd–Co alloys were hydrogenated under 100 kPa hydrogen gas pressure. After hydrogenation, the temperature variations of magnetization revealed two magnetic transitions implying that there are two phases in the hydrogenated Pd–Co: the hydrogen dissolution and hydride phases. The hydrogen contents ([H]/[Pd–Co]) and the Curie temperature (T_C) of the hydride phase are deduced that [H]/[Pd–Co] = 0.53, 0.43 and 0.36 with T_C = ≤50, 100 and 120 K for Pd_0.96Co_0.04, Pd_0.92Co_0.08, and Pd_0.90Co_0.10 hydrides, respectively. The magnetization against externally applied field measured at 50 and 300 K indicated that the magnetic moments per a single ion (Pd, Co) of the hydrides are always smaller than those of the original Pd–Co alloys. First principle calculations for the magnetic moments provided quite consistent results with the experimental ones.