Anisotropy and pressure dependence of the upper critical field of the ferromagnetic superconductor UGe2 -: art. no. 220503

The temperature and pressure dependence of the upper critical field, H-c2, of the ferromagnetic superconductor UGe2 is reported for fields applied along all three crystallographic axes. For fields parallel to the easy magnetic a axis, the relationship between an unusual reentrant behavior of H-c2 and a field-induced transition associated with a change in the electronic density of states is reviewed. For transverse field directions a significant evolution in the behavior of H-c2 with pressure is found. As the pressure is decreased the dependence of H-c2 on temperature for fields along the crystal's c axis acquires a positive curvature that extends from the critical temperature, T-c, down to almost the lowest temperature measured (T-c/10) where H-c2 exceeds the usual weak coupling paramagnetic and orbital limits.