Superconducting properties of eutectic high-entropy alloy superconductor NbScTiZr

TL;DR

This study investigates how annealing affects the superconducting properties and lattice strain in eutectic high-entropy alloy NbScTiZr, revealing that lattice strain influences flux pinning and the Maki parameter.

Contribution

It provides new insights into the relationship between lattice strain and superconducting parameters in eutectic high-entropy alloys, highlighting the role of annealing temperature.

Findings

Lattice strain peaks at 400°C annealing.

Flux pinning is enhanced in certain annealed samples.

The Maki parameter correlates with lattice strain.

Abstract

The influence of annealing on the superconducting properties of eutectic high-entropy alloy NbScTiZr was examined by measuring magnetization, electrical resistivity, and zero-field specific heat. Additionally, the extent of lattice strain was assessed via the analysis of lattice parameters and Vickers microhardness. The greatest lattice strain was inferred in the sample annealed at 400 $^{\circ}$C. Field-dependent magnetization datasets indicate enhanced flux pinning in the as-cast, 400 $^{\circ}$C annealed, and 600 $^{\circ}$C annealed samples. The superconducting parameters such as upper critical field, Ginzburg-Landau coherence length, and magnetic penetration depth do not strongly depend on the annealing temperature. However, the Maki parameter shows a peak at 400 $^{\circ}$C annealing temperature and correlates with the magnitude of lattice strain. This suggests that greater lattice strain may enhance the Maki parameter by altering the orbital-limited field through the modification of flux pinning strength. Although the influence of lattice strain is less discernible in zero-field specific heat measurements, the superconducting parameters deduced from specific heat data suggest a potential for strong-coupled superconductivity in samples heat-treated above 600 $^{\circ}$C. Our investigation underscores the substantial impact of lattice strain on the Maki parameter of eutectic HEA superconductors, primarily through the modulation of flux pinning strength.