Angle dependence of levitation force in a YBa2Cu3Ox sphere

Crystal angle dependence of the levitation force has been measured for a YB a2Cu3Ox sphere at 77 K and low magnetic field (similar to 2000 Gauss). The spherically-shaped sample is obtained from a single-domain material process ed by the seeded melt growth (SMG) method. The levitation force has been fo und to vary in a cosine law fashion with the crystal orientation from 0 deg rees-360 degrees regardless of the height between the sample and the testin g magnet. However, the exponential height dependence of the levitation forc e that has been commonly observed in previous studies no longer holds for t he spherical sample at various orientations. A physical model is proposed t o explain the observed angle dependence. (C) 1998 Published by Elsevier Sci ence B.V. All rights reserved.