Temperature-composition phase diagrams for Ba1−xSrxFe2As2 (0 ≤x≤ 1) and superconducting Ba0.5Sr0.5(Fe1−yCoy)2As2 (0 ≤y≤ 0.141)

Abstract

Single crystals of mixed alkaline earth metal iron arsenide materials, Ba1−xSrxFe2As2 with 0.185 ≤ x ≤ 0.762 and Ba0.5Sr0.5(Fe1−yCoy)2As2 with 0.028 ≤ y ≤ 0.141, are synthesized via the self-flux method. Ba1−xSrxFe2As2 display spin-density wave features (TN) at temperatures intermediate to the parent materials, x = 0 and 1, with TN(x) following an approximately linear trend. Cobalt doping of the 1:1 Ba:Sr mixture, Ba0.5Sr0.5(Fe1−yCoy)2As2, results in a superconducting dome with maximum transition temperature of TC = 19 K at y = 0.092, close to the maximum transition temperatures observed in unmixed A(Fe1−yCoy)2As2; however, an annealed crystal with y = 0.141 showed a TC increase from 11 to 16 K with a decrease in Sommerfeld coefficient γ from 2.58(2) to 0.63(2) mJ/(K2 mol atom). For the underdoped y = 0.053, neutron diffraction results give evidence that TN and structural transition (TO) are linked at 78 K, with anomalies observed in magnetization, resistivity, and heat capacity data, while a superconducting transition at TC ≈ 6 K is seen in resistivity and heat capacity data. Scanning tunneling microscopy measurements for y = 0.073 give Dynes broadening factor Γ = 1.15 and a superconducting gap Δ = 2.37 meV with evidence of surface inhomogeneity.

Source-reported materials — not catalogue approval

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