Magnetic characterization of rare-earth barium cuprate superconductors.

Abstract

We report magnetic characterization of barium rare-earth cuprate superconductors to determine critical current densities as a function of rare-earth constituent. A vibrating sample magnetometer was used to measure $M\ensuremath{-}H$ loops for fields to 15 kOe of oriented single crystals. Critical current densities are insensitive to rare-earth constituent despite the magnetic moment on the rare-earth ion. Values of critical current densities in the $a\ensuremath{-}b$ plane vary from \ensuremath{\sim}3\ifmmode\times\else\texttimes\fi{}${10}^{5}$ A/${\mathrm{cm}}^{2}$ at 10 K to \ensuremath{\sim}2\ifmmode\times\else\texttimes\fi{}${10}^{4}$ A/${\mathrm{cm}}^{2}$ at 77 K. Anisotropy in the critical current density in the $a\ensuremath{-}b$ plane and perpendicular to this plane was a factor of 2 in a ${\mathrm{Ba}}_{2}$Yb${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ crystal at $T=38$ K. Aluminum impurities lower critical currents but also reduce the superconducting transition temperature.