Lower critical field and magnetization critical current density in the oxide superconductor TmBa2Cu3O7−y

Abstract

We have carried out detailed magnetic measurements on the oxide superconductor TmBa2Cu3O7−y at various temperatures and applied fields. From the hysteresis loop obtained at 5 K and the temperature dependence of the remanent magnetization, values of the lower critical field (Hc1), magnetization critical current density and its temperature dependence are determined. Field penetration in the superconducting state occurs for fields higher than Hc1 which results in a paramagnetic contribution from the Tm3+ ions. Above the superconducting transition temperature (Tc), the susceptibility follows Curie-Weiss behavior with an effective moment close to the value of the free Tm3+ ion. The strong magnetism of the rare earth ion does not very much influence the Tc.