Largely improved Jc at low temperatures observed in Y123 single crystals with chemically introduced point defects

Abstract

Most of studies on pinning properties and relating vortex nature of the RE123 system were performed at high temperatures around 77 K. However, the pinning characteristics of RE123 at low temperatures have not been well understood yet, while extensive applications using the cryocooling system are also strongly expected. In the present study, the Jc-H-T properties have been studied for Gd123 single crystal with a low level Gd substitution for Ba and Y123 single crystals substituted by small amount of impurity ions, such as Sr and Co, which improve Jc properties accompanying huge peak effect in their Jc-H curves. It was found that the increase in Fp with decreasing temperature of the impurity doped Y123 samples were much larger than that of the Gd123 sample, while the Gd123 sample exhibited higher Jc than these Y123 samples above 77 K. The Jc performance below 50 K of the Gd123 sample was even lower than that of the undoped Y123 sample. This result strongly indicates that the RE123 with RE/Ba substitution does not appropriate for low temperature applications, such as high field magnets despite their good Jc performance at high temperatures e.g. 77 K.