Rotational magnetic processes in a dirty superconductor.

Magnetization-vector ({rvec M}) measurements were made on a thin disk of impure Nb rotated relative to a fixed field {rvec H} at 4.2 K. For all H, {rvec M} is found to be separable into a non-rotating diamagnetic component {rvec M}{sub d} plus a penetrating-flux component {rvec M}{sub p} that turns rigidly with the sample for small rotation angles. For H below H{sub c1} on a hysteresis loop, {rvec M}{sub p} diminishes in size but continues to rotate rigidly up to 360{degree}. For H between H{sub c1} and H{sub c2}, {rvec M}{sub p} rotates up to and then remains at some critical angle, indicating a constant frictional torque between {rvec M}{sub p} and the sample, which presumably arises from vortex-flux jumps between pinning centers. Moreover, {rvec M}{sub d} closely equals {minus}{rvec H}/4{pi} for H above as well as below H{sub c1}. 6 refs., 3 figs.