Single Crystal Growth and the Upper Critical Field of the Superconductor U6Fe

Single crystals of superconducting U 6 Fe were grown by both the zone-melting method and the Czochralski pulling method. The upper critical field H c 2 was determined from the electrical resistivity in applied magnetic fields, and H c 2 is found to be anisotropic; 13.1 T for the field along the [001] direction and 10.4 T for [110]. Anisotropy of H c 2 is well explained by the effective mass model.