Heat capacity and magnetic properties in the (PdCO y )H x -system at low temperatures

Results of heat capacity measurements on (PdCo _y )H _x (y 2.5 at %; 0 x 0.8) in the temperature range from 2 to 12 K are reported. The dependence of the coefficient of the electronic heat capacity on the Co content and on the x value is considered. For the binary alloy PdCo _y a decreasing spin wave contribution to the heat capacity (T ^3/2) is found, which agrees well with the known ferromagnetic properties of the alloy. In contrast, for the phase of (PdCo _y )H _x a contribution to the heat capacity can be separated, probably caused by the thermal excitation of magnetic clusters. The temperature dependence of this cluster contribution can be well explained by means of an Einstein function. Conclusions are drawn with regard to the intercluster interaction and to the number of atoms per cluster.