A heat-capacity study of the intermetallic compounds R2Fe17Xy(R=Er, Tm, Gd; X=N, D)

Adiabatic heat-capacity measurements of some of the intermetallic compounds R₂Fe₁₇X_y(R=Er, Tm, Gd; X=N, D) have been performed from 5 K to 350 K. Magnetic ordering phase transitions have been observed at 291.9 K for Er₂Fe₁₇ and at 260 K for Tm₂Fe₁₇. The anomalous enthalpy and entropy of these transitions are much smaller than expected in a pure localized model for the magnetic moments. In Tm₂Fe ₁₇ a spin reorientation phase transition of second order character has been observed at 94 K. Theoretical calculations of the free energy and thermodynamic functions have been developed. In the interstitial compounds Er₂Fe₁₇D_3.4, Tm ₂Fe₁₇D_2.13, Gd₂Fe₁₇ N_2.18 and Er₂Fe₁₇N_2.4 no anomalies have been observed