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

摘要

The upper critical field was measured upto 12 T for three BaFe2-xCoxAs2single crystals with estimated Co concentrations of x = 0.082, x = 0.117 and x= 0.143. HC2 versus temperature was measured from temperature dependentresistivity, for various applied magnetic fields, H || ab and H || c. The[dHC2/dT]T=Tc, normalized with the corresponding TC, decreases with increasingCo content, for both directions. The anisotropy {\gamma} defined as HC2 || ab /HC2 || c shows a distinct increase with Co content, and its temperaturedependence shows a peak close to the TC. Magneto transport measurements, in thespin density wave regions, showed significant negative MR for H || ab andpositive MR of H || c in the x = 0.082 sample. The implications of theseresults are discussed.