Magnetoresistance Hysteresis Evolution in the Granular Y-Ba-Cu-O High-Temperature Superconductor in a Wide Temperature Range

摘要

The temperature evolution of the magnetoresistance hysteresis in the granular YBa2Cu3O7-delta high-temperature (T-C approximate to 92K) superconductor has been investigated. The measurements have been performed in the high-temperature region (78-90K) and at the liquid helium temperature (4.2K). The results obtained have been analyzed using the developed model of the behavior of transport properties of a granular high-temperature superconductor in an external magnetic field. Within the discussed model, the dissipation of the grain boundary subsystem is determined by the intergrain spacing-averaged effective field B-eff, which is a superposition of external field H and the field induced by the magnetic moments of superconducting grains. Such a consideration yields the expression B-eff(H)=H-4 pi M(H) alpha for the effective field in the intergrain medium, where M(H) is the experimental hysteretic dependence of magnetization and alpha is the parameter of magnetic flux crowding in the intergrain medium. Here, the magnetoresistance is assumed to be proportional to the absolute value of the effective field: R(H) similar to |B-eff(H)|. Analysis of the experimental R(H) and M(H) dependences obtained under the same conditions for the investigated high-temperature superconductor sample showed that in the high-temperature region this parameter is alpha approximate to 25. At the low temperature (4.2K), we may state that the degree of flux crowding increases and the estimated alpha value is similar to 50. The estimates made are indicative of the strong effect of flux compression in the intergrain medium on the magnetotransport properties of the investigated granular high-temperature superconductor system. Possible reasons for a discrepancy between the developed model concepts and experimentally observed low-temperature R(H) hysteresis are analyzed.