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

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.