The upper critical field of the Chevrel phase superconductor lead-molybdenum-sulphide doped with gadolinium

Chevrel phase superconductors with upper critical field values of up to 50 T, are candidate materials for the next generation of high field magnets. We have investigated the effect of doping lead-molybdenum-sulphide with the magnetic ion gadolinium to improve the critical parameters and the flux pinning in this material. Samples were prepared at 1500/spl deg/C to ensure the gadolinium was uniformly distributed throughout the material and then sintered using a hot isostatic press operating at a pressure of 2000 atmospheres. Calorimetric measurements have been completed In magnetic fields up to 15 T as a function of temperature. The temperature dependence of the upper critical field of these isotropic Chevrel phase materials are presented. Upper critical field values of more than 60 T have been determined for both doped and undoped samples. The calorimetric data reported here show that material with low levels of gadolinium doping offers the possibility of strong flux pinning and high critical current densities in high magnetic fields. In highly doped materials, the low critical current density and irreversibility fields found are probably due to a reduction in the fundamental properties and not poor grain boundaries.