Heat capacity data are presented for DyCoNi in the temperature range 4.2 to 300 K. The sample exhibits an anomaly peaking at 63 K. This is interpreted as arising from ferromagnetic ordering. Resistivity measurements also indicate an anomaly at 63 K. The magnetic entropy, evaluated by using the heat capacity data of LaNi2 as “a blank” ins nearly R in 4. These results are interpreted on the basis of an accidental four-fold degeneracy of the ground state of the Dy3+. The itinerant nature of the cobalt moment proposed by Taylor et al. appears to be valid in this compound.

Heat capacity data and calculated thermodynamic functions are presented for DyNi5, HoNi5 and ErNi5. λ-type thermal anomalies are noted at 12.0 K (DyNi5), 4.1 K (HoNi5) and 8.0 K (ErNi5). 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(2J + 1), is noted corresponding roughly to Rln2. This suggests that the ground state in the ordered materials is a doublet. ErNi5 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 ErNi5. Ordering temperatures are not proportional to the de Gennes function.

The heat capacity, Cp, of CeCo5, PrCo5, NdCo5, SmCo5, and GdCo5 were measured from 5–300 K. Cv/m, the “magnetic” contribution to Cp, was estimated “experimentally”, using the heat capacity of LaNi5 as a “blank”. Cvm was also estimated theoretically, assuming a model which considered the crystal field and molecular field interactions of the rare earth ion. Although most of the gross features of Cvm(expt) vs temperature, T, could be qualitatively reproduced using a point charge‐plus‐molecular field model, some significant features remain unexplained. The magnetic moment of the rare earth sublattice vs T was also estimated.

We have accurately determined the critical behavior of the magnetic contribution to the heat capacity in GdNi2, using both a phase sensitive A.C. technique in the critical region and a calorimetric technique from helium temperature up to room temperature. The deduced values of critical exponents are α = 0.36 and α′ = 0.026.