Transport and pinning properties of Ag-doped FeSe0.94

TL;DR

This study explores how Ag doping improves the superconducting and pinning properties of FeSe0.94, leading to sharper transitions, higher Tc, and enhanced critical fields, with detailed analysis of vortex pinning mechanisms.

Contribution

It demonstrates that Ag addition suppresses hexagonal phase formation and enhances grain connectivity, significantly improving superconducting and pinning properties of FeSe0.94.

Findings

Ag doping suppresses hexagonal phase formation

Superconducting transition becomes sharper and Tc increases

A crossover from single-vortex to collective creep pinning is observed

Abstract

We investigated the superconducting transition and the pinning properties of undoped and Ag-doped FeSe0.94 at magnetic fields up to 14 T. It was established that due to Ag addition the hexagonal phase formation in melted FeSe0.94 samples is suppressed and the grain connectivity is strongly improved. The obtained superconducting zero-field transition becomes sharp (with a transition width below 1 K), Tc and the upper critical field were found to increase, whereas the normal state resistivity significantly reduces becoming comparable with those of FeSe single crystals. In addition, a considerable magnetoresistance was observed due to Ag doping. The resistive transition of undoped and Ag-doped FeSe0.94 is dominated by thermally activated flux flow. From the activation energy U vs H dependence, a crossover from single-vortex pinning to a collective creep pinning behavior was found with increasing the magnetic field.