Heat capacities and related thermal properties of DyNi 5, HoNi 5 and ErNi 5 between 5 and 300 K

Abstract

Heat capacity data and calculated thermodynamic functions are presented for DyNi 5, HoNi 5 and ErNi 5. λ-type thermal anomalies are noted at 12.0 K (DyNi 5), 4.1 K (HoNi 5) and 8.0 K (ErNi 5). Schottky-type anomalies are observed at higher temperatures. The λ and Schottky anomalies are ascribed to the destruction of ferromagnetic order and to crystal field excitation, respectively. A deficiency of magnetic entropy, compared to Rln(2 J + 1), is noted corresponding roughly to Rln2. This suggests that the ground state in the ordered materials is a doublet. ErNi 5 is analyzed using a Hamiltonian containing terms representing the crystal field and magnetic interactions. The analysis shows that a doublet ground state can result with reasonable values of the crystal field parameters. The parameters are shown to be consistent with the heat capacity behavior of ErNi 5. Ordering temperatures are not proportional to the de Gennes function.