Spin glass behaviour in doped and pure UPt₃—A possible key

While studying doped UPt₃, we employed the standard technique of measuring χ_dc in both zero-field–cooled and field-cooled states to check for possible spin glass behaviour. The results of these studies lead to the discovery that nominally pure UPt₃ itself has a tendency towards spin glass behaviour. This instability makes for very sample-dependent properties (as is typical in spin glasses), especially for superconductivity, and is likely the long-sought "hidden parameter" linking a large number of the unusual behaviours in UPt₃. Thus, the measured spin glass behaviour in UPt₃ reported here can explain the extreme sample dependence of T_c, the observed aging effect on T_c, and the destruction of superconductivity in UPt₃ by grinding. In addition, the discovery of spin glass behaviour in UPt₃ may have implications for understanding the small-moment magnetism below 5 K and the double superconducting transition in some samples, as well as helping to explain the known important role of defects in UPt₃.