CORRELATION BETWEEN MAGNETIC HYSTERESIS AND MAGNETIC-RELAXATION IN YBACUO SINGLE-CRYSTALS

The dependence of the magnetic moment m obtained from the hysteresis loops on the speed of the magnetic field sweep {Mathematical expression} =dHext/dt is explained on the basis of Anderson's interpretation of the magnetic flux creep. In addition, a phenomenological model is suggested which predicts a linear dependence of m on ln {norm of matrix} {Mathematical expression}{norm of matrix} with the slope ∂m/∂ ln {norm of matrix} {Mathematical expression}{norm of matrix}, numerically equal to the relaxation rate ∂m/∂ ln (t) from the usual magnetic relaxation. Such linear relations between m and ln {norm of matrix} {Mathematical expression}{norm of matrix} were observed experimentally in single crystals of YBaCuO. Preliminary experiments on the complementary time dependent relaxation of m after a simulated step change of Hext gave mostly relaxation rates close to the predicted values. The model here presented also enables one to compare the critical state in the superconductor at a field sweep rate {Mathematical expression} with the critical state at some time teff after a step change of Hext. The values of {Mathematical expression} analyzed in our experiments actually correspond to the critical state at times teff between 0.04 and 4 sec after an imaginary large step change of Hext. © 1990 Plenum Publishing Corporation.