The low temperature specific heat of Gd-Cu-Y metallic glasses

Abstract

The specific heat of a series of amorphous aloys of composition Gd x Cu 0.37Y 0.63− x with 0 ⩽ x ⩽ 0.63 has been measured in the temperature range 2 to 50 K. A magnetic contribution to the specific heat is apparent in all the samples and has been determined with fair accuracy by subtracting the specific heat of corresponding nonmagnetic amorphous samples prepared with Lu rather than Gd. A qualitative study of the low field ac susceptibility of the magnetic samples has also been made. Samples with less than 35 at% Gd appear to be spin glasses, the results being qualitatively in accord with the predictions of the cluster mean field theory of concentrated spin glasses. As the Gd concentration is increased above 35 at% the samples behave increasingly like ferromagnets. However additional evidence from magnetisation measurements shows that even the sample with the highest concentration of Gd is not a simple ferromagnet.