Magnetic properties of Y-Ba-Cu-O superconductors

The magnetic properties of polycrystalline and single-crystal samples of YBa2Cu3O7 are compared. Transition temperatures are in the range of 85 to 89 K. The Meissner effect is below 30% of the diamagnetic shielding in all cases. Based on the high-temperature susceptibility it is suggested that an itinerant antiferromagnetic 3d band of the Cu2+ is possible. Anisotropy occurs in the single crystal for applied fields above 200 Oe. There is a difference in the lower critical field of a factor of 20 where Hc1 is about 4000 Oe for H parallel to the orthorhombic c axis and 200 Oe for H perpendicular to the c axis of the crystal. © 1987 The American Physical Society.