Microstructural and superconducting properties in single-domain Gd–Ba–Cu–O bulk superconductors with<i>in situ</i>formed Fe₃O₄ferrimagnetic particles

Abstract

Introducing secondary-phase inclusions into the superconducting matrix is regarded as an effective way to enhance the flux pinning performance of high temperature superconductors. The effect of Fe–B alloy additives on the microstructure and superconducting properties of top-seeded melt growth processed GdBa2Cu3O7 − δ/Ag bulk superconductors has been investigated systematically. GdBa2Cu3O7 − δ/Ag bulks 17 mm in diameter were melt-textured for various amounts of Fe–B additives in the range of 0–1.4 mol%. By means of scanning and transmission electron microscopy observations, the Fe–B alloy additives were found to decompose into ferrimagnetic Fe3O4, embedded inside or in the vicinity of silver particles. These ferrimagnetic particles may assist in reducing the Lorentz force exerted on the vortices and enhance the flux trapping capability and critical current density of Gd–Ba–Cu–O bulks. It was also found that the refinement of Gd2BaCuO5 and its homogeneous distribution was improved together with increase of the number of Gd2BaCuO5 particles when we increase the addition of Fe–B alloy particles. The amount added introduces a systematic change in the particle distribution dependent on both size and the numbers. The observed enhancement of the trapped flux may inherently include the magnetic interactions between the ferrimagnetic Fe3O4 with the surrounding compounds, which has a critical effect on the nucleation process of Gd2BaCuO5 inclusions.