A new method for estimating the critical current density of a superconductor from its hysteresis loop

Abstract

The critical current density J c of some of the superconducting samples, calculated on the basis of the Bean’s model, shows negative curvature for low magnetic field with a downward bending near H = 0. To avoid this problem Kim’s expression of the critical current density, J c = k/( H 0 + H), where J c has positive curvature for all H, has been employed by connecting the positive constants k and H 0 with the features of the hysteresis loop of a superconductor. A relation between the full penetration field H p and the magnetic field H min , at which the magnetization is minimum, is obtained from the Kim’s theory. Taking the value of J c at H = H p according to the actual loop width, as in the Bean’s theory, and at H = 0 according to an enhanced loop width due to the local internal field, values of k and H 0 are obtained in terms of the magnetization values M +(− H min ), M −( H min ), M +( H p ) and M −( H p ). The resulting method of estimating J c from the hysteresis loop turns out to be as simple as the Bean’s method.