HIGH-SENSITIVITY VIBRATING REED STUDIES OF SUPERCONDUCTORS

Recent improvements in the vibrating reed (VR) technique permit precis ion studies of the mixed state of complex superconducting materials fa r below the upper critical magnetic field H-c2 VR data for thin film, crystalline and ceramic (Ba0.6K0.4)BiO3 samples demonstrate the sensit ivity of the VR to microstructure and inhomogeneities, and a study of HoNi2B2C reveals previously inaccessible vortex dynamical anomalies an d minute details of a complex phase competition between magnetism and reentrant superconductivity. CeRu2 VR data are reversible near H-c2 wh ere giant hysteresis is observed in DC magnetization data, but are hys teretic over an extended region at lower temperatures and fields, indi cating vortex dynamics must be considered in testing the existence of unconventional pairing states proposed for this system.