Magnetic irreversibility and pinning force density in the Mo$_{100-x}$Re$_x$ alloy superconductors

TL;DR

This study investigates the magnetic irreversibility and pinning mechanisms in Mo-Re alloy superconductors, revealing the roles of structural defects and multiple energy gaps in flux pinning and critical current behavior.

Contribution

It provides new insights into flux pinning centers and the effects of multiple superconducting gaps in Mo-Re alloys, supported by comprehensive magnetization and structural analyses.

Findings

Dislocation networks and point defects are main flux pinning centers.

Critical current density remains robust in intermediate fields.

Flux creep affects critical current at higher fields.

Abstract

We have measured the isothermal field dependence of magnetization of the Mo$_{100-x}$Re$_x$ (15 $\leq$ x $\leq$ 48) alloys, and have estimated the critical current and pinning force density from these measurements. We have performed structural characterization of the above alloys using standard techniques, and analyzed the field dependence of critical current and pinning force density using existing theories. Our results indicate that dislocation networks and point defects like voids and interstitial imperfections are the main flux line pinning centres in the Mo$_{100-x}$Re$_x$ alloys in the intermediate fields, i.e., in the small bundle flux line pinning regime. In this regime, the critical current density is also quite robust against increasing magnetic field. In still higher fields, the critical current density is affected by flux creep. In the low field regime, on the other hand, the pinning of the flux lines seems to be influenced by the presence of two superconducting energy gaps in the Mo$_{100-x}$Re$_x$ alloys. This modifies the field dependence of critical current density, and also seems to contribute to the asymmetry in the magnetic irreversibility exhibited by the isothermal field dependence of magnetization