TEMPERATURE-DEPENDENCE OF THE MATERIAL PARAMETERS IN THE KIM-ANDERSONCRITICAL-STATE MODEL FOR A MELT-PROCESSED YBA2CU3O7

The magnetic response of a melt-processed YBa2Cu3O7 was measured to ma ke clear the physical meanings of the parameters k and B-0 in the Kim- Anderson critical-state model where the critical current density J(c) is assumed to be a function of the local internal magnetic-flux densit y B-i, J(c)(B-i) = k/(B-0 + \B-i\). The isothermal magnetization curve s of the sample were measured in the wide temperature region below the critical temperature, and the parameters were selected so as to fit t he calculated curve to the observed one at each temperature. We found that k and B-0 are proportional to (1 -T/T-c)(gamma), where gamma = 2. 5 - 3.0 and to (1 -T/T-c)(1.5), respectively. We propose that B-0 appr oximately corresponds to the irreversibility magnetic-flux density B-i rr.