Superconducting properties of a single-crystal sphere of ErRh4B4.

We report on the superconducting and magnetic properties of a single-crystal sphere of the primitive tetragonal phase of ErRh{sub 4}B{sub 4}. Our data consist of magnetization and susceptibility measurements in fields up to 50 kOe and at temperatures down to 0.4 K. The crystal exhibits extreme anisotropy in its response to a magnetic field. It is a weak paramagnet when the external field is along the tetragonal {ital {bar c}} axis but reverts to a strong paramagnet when the field is in the basal plane. The magnetization curves reveal a first-order phase transition at {ital H}{sub {ital c}2} when the field is in the basal plane. Evidence for a temperature domain in which superconductivity and long-range ferromagnetic order appear to coexist is also presented. The magnetization curves are further analyzed to obtain the critical fields, the Ginzburg-Landau parameters, Curie plot, and the ferromagnetic moment of the system.