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 constituent despite the magnetic moment on the rare-earth ion. Values of critical current densities in the a-b plane vary from {~}3×{}10⁵ A/cm² at 10 K to {~}2×{}10⁴ A/cm² at 77 K. Anisotropy in the critical current density in the a-b plane and perpendicular to this plane was a factor of 2 in a Ba₂YbCu₃{O}₇$ crystal at $T=38$ K. Aluminum impurities lower critical currents but also reduce the superconducting transition temperature.