Magnetic Ordering of AuCr: An Ultrasonic Investigation

Abstract

The magnetic properties of the noble metal-3d transition metal spin glass alloys show a number of unusual characteristics, as summarized in the experimental review paper by Mydosh.¹ In particular, the sharp peaks in the magnetic susceptibility which scale systematically with transition metal concentration are suggestive of the onset of some kind of magnetic ordering. Recently a careful search has been made for evidence of such ordering in the specific heat, both for AuFe² and CuMn³ spin glass alloys. No sharp changes were observed in the vicinity of the susceptibility peak temperature, T_o, although the previously reported^4,5 linear dependence of the low temperature magnetic contribution to the specific heat, C_m, was confirmed, and in the case of CuMn,³ rounded maxima were observed at temperatures above T_o. Results of measurements of the changes in magnetic entropy in the same experiments^2,3 indicate that fewer than one third of the transition metal ions participate in magnetic ordering between T_o and O K. Specific heat measurements of AuCr have also been carried out recently.⁶ Broad maxima were observed for a range of Cr concentration 0.02 at.% ⪝ C ⪝ 0.1 at.%, at temperatures which scale linearly with C. This region of concentration does not quite overlap that of the existing susceptibility data^1,7 (0.2 at.% ⪝ C ⪝ 10 at.%).