Grain refinement and enhancement of critical current density in the V_0.60Ti_0.40 alloy superconductors with Gd addition

TL;DR

Adding Gd to V-Ti superconductors refines grains and significantly boosts critical current density, making them more competitive for high magnetic field applications despite ferromagnetic effects.

Contribution

This study demonstrates that Gd addition refines grain structure and enhances critical current density in V-Ti alloys, a novel approach for improving superconductor performance.

Findings

J_c and F_P increase with Gd content, peaking at 1 at.% Gd

Gd addition causes grain refinement and cluster formation at grain boundaries

Superconducting transition temperature slightly increases with Gd

Abstract

The V-Ti alloys are promising materials as alternate to the commercial Nb-based superconductors for high current-high magnetic field applications. However, the critical current density (J_c) of these alloys are somewhat low due to their low grain-boundary density. We show here that grain refinement of the V-Ti alloys and enhancement of the J_c can be achieved by the addition of Gd into the system, which precipitates as clusters along the grain boundaries. Both the J_c and the pinning force density (F_P) increase with the increasing Gd content up to 1 at. % Gd, where they are more than 20 times higher than those of the parent V_0.60Ti_0.40 alloy. Introduction of Gd into the system also leads to ferromagnetic (FM) correlations, and the alloys containing more than 0.5 at. % Gd exhibit spontaneous magnetization. In spite of the FM correlations, the superconducting transition temperature increases slightly with Gd-addition.