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

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