Rotational magnetic processes in YB sub 2 Cu sub 3 O sub 7

A polycrystalline superconducting thin-disk sample was rotated in a fixed field ({rvec H}) at 4.2 K, and the vector magnitude and orientation of the total magnetization ({rvec M}) were measured as the sample-rotation angle ({Theta}) was slowly cycled between 0 and 360{degree}. The measured {rvec M} was decomposed into a penetrating (vortex) flux component {rvec M}{sub p} that rotates rigidly with the sample at very small {Theta} and a diamagnetic (shielding) component {rvec M}{sub d} that stays antiparallel to {rvec H}. As {Theta} is raised, {rvec M}{sub p} deviates from rigid rotation, and the deviations are very different for the zero-field-cooled (ZFC) and field-cooled (FC) states at the same H, indicating different distributions in the strengths of the initial pinning forces. However, M{sub d} is exactly the same for both states and closely equals {Chi}{sub o}H, where {Chi}{sub o} is the low-H (ZFC) diamagnetic susceptibility. At still higher {Theta}, {rvec M}{sub p} rotates up to some critical angle relative to {rvec H}, where it remains as the sample continues to turn. This frictional behavior presumably derives from the dissipative motion of the vortices between pinning centers. 6 refs., 3 figs