Upper critical fields well above 100 T for the superconductor SmFeAsO$_{0.85}$F$_{0.15}$ with T$_c$ = 46 K

TL;DR

This study measures the upper critical magnetic field of SmFeAsO$_{0.85}$F$_{0.15}$, revealing values well above 100 T, and explores its vortex dynamics and granularity through specific heat and magnetization experiments.

Contribution

It provides the first estimation of the upper critical field exceeding 100 T for this superconductor and investigates vortex behavior and granularity effects.

Findings

Upper critical field estimated at 150 T from specific heat data.

Evidence of granularity and a peak effect in vortex dynamics.

Magnetization measurements suggest a field dependence of critical current.

Abstract

We report specific heat measurements at magnetic fields up to 20 T on the recently discovered superconductor SmFeAsO$_{0.85}$F$_{0.15}$. The B-T diagram of a polycrystalline SmFeAsO$_{0.85}$F$_{0.15}$ sample with T$_c$ = 46 K was investigated. The temperature dependence of B$_{c2}$ was extracted from the specific heat curves, the corresponding B$_{c2}$(T = 0) value derived from the Werthamer-Helfand-Hohenberg formula being 150 T. Based on magnetization measurements up to 9 T, a first estimation of the field dependence of the inductive critical current J$_c$ is given. Evidence for granularity is found. The presence of a peak effect is reported, suggesting a crossover in the vortex dynamics, in analogy to the behaviour observed in high T$_c$ cuprates.