MAGNETIZATION OF SUPERCONDUCTING HG3NBF6 AND HG3TAF6

The magnetization of the bulk superconducting transitions of Hg3NbF6 a nd Hg3TaF6 Was Measured in the temPerature range from 0.1 to 1 K and i n magnetic fields from 0 to 50 G. Measurements were performed on both samples in the zero-field-cooled (ZFC) and field-cooled (FC) modes. Th e magnetization was also measured as the sample warmed through its sup erconducting transition in the same field in which it had been cooled; this was referred to as the return-warming (RW) mode. A large differe nce in magnitude between the ZFC and FC modes for both samples indicat ed the presence of multiply connected regions (or type-II superconduct ivity). Evidence for both samples of the trapping of flux due to inhom ogeneities and defects was provided by the hysteresis measured between the FC and RW modes. The observation of excess magnetization above th e critical temperature in magnetic fields below 30 G was attributed to a proximity effect between the observed free mercury and the Hg3NbF6 and Hg3TaF6 metals. For the average of the data from the three modes, the Hg3NbF6 sample exhibited a critical field at absolute zero, H(c)(0 ), of 150 G and a critical temperature, T(c), of 0.38 K. The Hg3TaF6 h ad a lower H(c)(0) of 60 G, with a T(c) of 0.44 K.