Annealing effects on the properties of BFe2As2 (B = Ca, Sr, Ba) superconducting parents

Abstract

The effects of thermal-annealing on the antiferromagnetic (T_N) and structural (T_s) transition temperatures of ThCr₂Si₂-type BaFe₂As₂ and SrFe₂As₂ (‘122’) crystals are reported and compared to that of CaFe₂As₂. Although the shift in transition temperature for CaFe₂As₂ can be as high as 75 K, we find modest changes of ∼6 K for BaFe₂As₂ and SrFe₂As₂. Such findings are based on the measurements of temperature dependence of electrical resistivity, magnetization, and heat capacity. Residual resistivity ratios show an improvement of crystal quality upon annealing for both BaFe₂As₂ and SrFe₂As₂. We confirm the pressure-like influence of annealing on the 122 crystals.