Irreversible field determined by pulsed magnetization and compositional fluctuation of melt-processed (Sm, Eu, Gd)Ba2Cu3O7-δ superconductors

Irreversible fields B-irr of melt-processed (Sm, Eu, Gd)Ba2Cu3O7-delta bulk superconductors with varying (Sm, Eu, Gd)(2)BaCuO5 concentrations have been measured with pulsed magnetic fields up to 28 T in a temperature range from 55 to 85 K. The temperature dependence of B-irr was studied by taking account of the effect of heat generation. In comparison with that including 5 mol% (Sm, Eu, Gd)(2)BaCuO5 phase the samples with 40 mol% (Sm, Eu, Gd)(2)BaCuO5 inclusion displayed a lower B-irr value for temperatures above 75 K, while B-irr was enhanced below 75 K. TEM observation unveiled a sharp contrast between a uniform nano-scaled compositional modulation in compositions with 40% (Sm, Eu, Gd)(2)BaCuO5 inclusion and an inhomogeneous distribution with very low (Sm, Eu, Gd)(2)BaCuO5 concentration. The present result could thus be understood in the context of different defect states induced by locally compositional fluctuation.