Upper critical field anisotropy in BaFe2-xCoxAs2 single crystals synthesized without flux

TL;DR

This study investigates the anisotropy of the upper critical magnetic field in BaFe2-xCoxAs2 single crystals with varying cobalt content, revealing how doping influences superconducting properties and magnetic responses.

Contribution

It provides new measurements of upper critical field anisotropy in flux-free synthesized BaFe2-xCoxAs2 crystals across different Co concentrations, highlighting doping effects on superconductivity.

Findings

Anisotropy increases with Co doping.

Normalized slope of HC2 decreases with Co content.

Magnetoresistance varies with magnetic field orientation.

Abstract

The upper critical field was measured upto 12 T for three BaFe2-xCoxAs2 single crystals with estimated Co concentrations of x = 0.082, x = 0.117 and x = 0.143. HC2 versus temperature was measured from temperature dependent resistivity, for various applied magnetic fields, H || ab and H || c. The [dHC2/dT]T=Tc, normalized with the corresponding TC, decreases with increasing Co content, for both directions. The anisotropy {\gamma} defined as HC2 || ab / HC2 || c shows a distinct increase with Co content, and its temperature dependence shows a peak close to the TC. Magneto transport measurements, in the spin density wave regions, showed significant negative MR for H || ab and positive MR of H || c in the x = 0.082 sample. The implications of these results are discussed.