Unusual low temperature specific heat in ternary Gd intermetallic compounds

Specific heat measurements are reported for the alloy series Pd2GdxLa1-x In for 0 less than or equal to x less than or equal to 1.0, and also for Pd2LuIn and Cu2GdIn. A well defined anomaly associated with the onset of the magnetically ordered state is observed in the specific heat for Pd2GdIn at T = 9 K. As x decreases the anomaly becomes broader and the maximum reduces to a lower temperature. Measurements on the non-magnetic compounds Pd2LaIn and PdlLuIn were made to isolate the magnetic contribution to the heat capacity of the Gd compounds. Such an analysis reveals a significant magnetic contribution remaining at temperatures far above T-N ( > 2T(N)) for the compounds where x = 1.0, 0.75 and 0.50. The total magnetic entropy at 20 K is well in excess of the theoretical value of xR ln(8) for these compounds. Above 20 K magnetisation measurements on Pd2GdIn show a Curie-Weiss behaviour and the absence of short range magnetic order, whilst the specific heat of Pd2GdIn is still enhanced at 30 K. Above 20 K the enhanced specific heat varies linearly with temperature, suggesting a gamma-value of 202 mJ/K-2 mol. Subtraction of such a linear term over the entire temperature range yields a magnetic entropy more consistent with that expected for Gd. For the S-state element Gd, the existing theories put forward to explain such an enhanced gamma-value on the basis of heavy fermion behaviour are not applicable. The possibility of an additional conduction electron contribution to the magnetic specific heat is supported by measurements on Cu2GdIn, although the magnitude of the enhancement in Pd2GdIn is difficult to reconcile with this approach. (C) 1998 Elsevier Science B.V. All rights reserved.