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arXiv · 1210.6638

Temperature-composition Phase Diagrams for Ba1-xSrxFe2As2 and Ba0.5Sr0.5(Fe1-yCoy)2As2

Jonathan E. Mitchell·Bayrammurad Saparov·Wenzhi Lin·Stuart Calder·Qing Li·Sergei V. Kalinin·Minghu Pan·Andrew D. Christianson·Athena S. Sefat
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Abstract

Single crystals of mixed alkaline earth metal iron arsenide materials of Ba1-xSrxFe2As2 and Ba0.5Sr0.5(Fe1-yCoy)2As2 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 to 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 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 of 1.15 and a superconducting gap of 2.37 meV with evidence of surface inhomogeneity.

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Jonathan E. Mitchell, Bayrammurad Saparov, Wenzhi Lin, Stuart Calder, Qing Li, Sergei V. Kalinin, Minghu Pan, Andrew D. Christianson, Athena S. Sefat. 2012-10-24. Temperature-composition Phase Diagrams for Ba1-xSrxFe2As2 and Ba0.5Sr0.5(Fe1-yCoy)2As2. https://doi.org/10.1103/physrevb.86.174511

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