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 comp ounds R2Fe17Xy (R = Er, Tm, Gd; X = N, D) have been performed from 5 K to 350 K. Magnetic ordering phase transitions have been observed at 2 91.9 K for Er2Fe17 and at 260 K for Tm2Fe17. The anomalous enthalpy an d entropy of these transitions are much smaller than expected in a pur e localized model for the magnetic moments. In Tm2Fe17 a spin reorient ation phase transition of second order character has been observed at 94 K. Theoretical calculations of the free energy and thermodynamic fu nctions have been developed. In the interstitial compounds Er2Fe17D3.4 , Tm2Fe17D2.13, Gd2Fe17N2.18 and Fr2Fe17N2.4 no anomalies have been ob served.