Temperature dependence of the vortex pinning enhancement by gamma irradiation of Bi1.6Pb0.4Sr2Ca2Cu3O10 polycrystals

The saturation remanent magnetization M-RS, taken to represent the vortex p inning strength, was measured at various temperatures from 4.2 K up to near T-c on two similarly prepared polycrystalline samples of B1.6Pb0.4Sr2Ca2Cu 3O10 (BPSCCO), one of which had been subsequently gamma-irradiated. For bot h samples, the decrease of MRS With rising temperature (T) is found to cons ist of two distinct components, one of which varies linearly with t (= 1 - T/T-c) up to T-c, and the other decays very rapidly, essentially as t(beta) with beta just under 10. The gamma irradiation is seen to produce a threef old enhancement of the linear-t component, but its major effect is a 10-fol d enhancement of the exponential-t(beta) component. The direct connection b etween M, and the vortex pinning strength is tested and confirmed by sample -rotational magnetization measurements. Hence, the MRS component whose temp erature decay is exponentially rapid can be attributed to a thermal decoupl ing of vortices from localized pinning sites. The pronounced irradiation-en hancement of this component thus implies that the defects produced by the g amma-rays are acting primarily as vortex pinning sites that are effectively very restricted in size. (C) 2000 Elsevier Science B.V. All rights reserve d.