Coexistence of superconductivity and antiferromagnetism in Ca${}_{0.74(1)}$La${}_{0.26(1)}$(Fe${}_{1-x}$Co${}_x$)As${}_2$ single crystals

Abstract

We report the transport, thermodynamic, $\mu$SR and neutron study of the Ca${}_{0.74(1)}$La${}_{0.26(1)}$(Fe${}_{1-x}$Co${}_x$)As${}_2$ single crystals, mapping out the temperature-doping level phase diagram. Upon Co substitution on the Fe site, the structural/magnetic phase transitions in this 112 compound are suppressed and superconductivity up to 20 K occurs. Our measurements of the superconducting and magnetic volume fractions show that these two phases coexist microscopically in the underdoped region, in contrast to the related 10-3-8 Ca${}_{10}$(Pt${}_3$As${}_8$)((Fe${}_{1-x}$Pt${}_x$)${}_2$As${}_2$)${}_5$ compound, where coexistence is absent. Supported by model calculations, we discuss the differences in the phase diagrams of the 112 and 10-3-8 compounds in terms of the FeAs interlayer coupling, whose strength is affected by the character of the spacer layer, which is metallic in the 112 and insulating in the 10-3-8.

5 pages, 4 figures