Zero-field critical current density from magnetization hysteresis loop

Bean formula is widely used to estimate the critical current density Jc from magnetization hysteresis loops. However, when the local critical current density decreases with magnetic field, the Bean estimate at zero field, Jc,Bean(0), is systematically lower than the true value jc0 of the critical current density. To overcome this underestimate, a correction term is suggested for refining the zero-field critical current density Jc(0). The accuracy of several simple combinations of characteristic magnetization values is evaluated by the root-mean-square deviation of the computed values of Jc(0) from jc0 for 100 loops computed with varied parameters. The most accurate formula Jc(0) = Jc,Bean(0) M–(Hmin)/M0(Hmin0) requires only two additional readings, taken at the minima on the initial magnetization branch and the envelop branch of the magnetization hysteresis loop. This formula also performs well for asymmetric magnetization hysteresis loops containing an equilibrium-magnetization contribution. Application of the proposed formula to experimental data for a (Y,Gd)BCO polycrystalline sample and a SmBCO single crystal gives the critical current density 1.23 and 1.45 times larger, respectively, than the Bean estimates.