Dependence of magnetic properties of pellets of nominal composition YBa2Cu3O7-x on processing conditions

We have studied the dependence of the magnetic properties of pellets of nominal composition YBa2Cu3O7-x on variations in preparation conditions. We find that rapid quenching of the pellets from annealing temperatures greater than 500-600°C causes the formation of significant amounts of secondary phases. Two of these phases, Y2BaCuO5 and BaCuO2, have magnetic moments of approximately 1.8 B per Cu atom. We find that Y2BaCuO5 orders antiferromagnetically below 30 K whereas BaCuO2 is paramagnetic down to at least 6 K. Eliminating these secondary phases by optimizing the processing conditions gives single-phase material (> 99.8% by mass) for which the magnetic susceptibility above the superconducting transition temperature is nearly independent of temperature. The magnitude of this susceptibility, after correction for ioncore diamagnetism, is enhanced by a factor of approximately 2 over the Pauli susceptibility estimated from the band-structure density of states, indicating the importance of electron-electron correlation effects. © 1988 The American Physical Society.