Specific heat investigations of Pd Mn, Pd Gd and Pd Dy: magnetic ordering and crystal - field splitting

Measurements of the heat capacity for a series Pd Mn (2.7 to 9.5 at.% Mn) alloys indicate that other interactions (presumably direct Mn-Mn interactions) start to dominate the ferromagnetic indirect interactions characteristic for dilute Pd-alloys. A model, in which different interactions are allowed, dependent on the distances between the magnetic atoms, qualitatively describes the observed change of the temperature dependence of the magnetic contribution to the specific heat. A collection of various data: specific heat, electrical resistivity and low field magnetic susceptibility are presented in the context of the, sometimes puzzling, data published on the Pd Gd alloy system up till now. A comparison between Pd Mn (c < 2.5 at.%) and Pd Gd alloys can, at least to some extent, be made. A sharp transition to ferromagnetism is found for Pd Gd. The possibility of a polarization of the Pd 4d-band is discussed. It is emphasized that extreme attention should be paid to the quality and preparation of the specimens. Specific heat results for some Pd Dy alloys are presented. The data in zero magnetic field at temperatures between 0.1 and 20 K contain sufficient information to derive the crystal-field contribution to the specific heat. An estimation of the electronic and lattice parts of the specific heat is made on the basis of results for Pd Lu alloys. In addition the nuclear or hyperfine contribution is roughly estimated. The analysis of the crystal-field contribution to the specific heat results in a GAMMA8 ground state, which is split. The other levels are at 10 K or higher above the ground state. (Auth.)