Magnetic characterization of rare earth barium cuprate superconductors.

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-H loops for fields to 15 kOe of oriented single crystals. Critical current densities are insensitive to rare earth despite the magnetic moment on the rare earth ion. Values of critical current densities in the a-b plane vary from ~3x10 sup 5 A/cm sup 2 at 10K to ~2x10 sup 4 A/cm sup 2 at 77K. Anisotropy in the critical current density in the a-b plane and perpendicular to this plane was a factor of two in a Ba sub 2 YbCu sub 3 O sub 7 crystal at T=38K. Aluminum impurities lower critical currents but also reduce the superconducting transition temperature.