Effect of interlayer coupling on the coexistence of antiferromagnetism and superconductivity in Fe pnictide superconductors: A study of Ca0.74(1)La0.26(1)(Fe1−xCox)As2 single crystals

We report the transport, thermodynamic, muon spin relaxation, and neutron study of the Ca0.74(1)La0.26(1)(Fe1−xCox)As2 single crystals, mapping out the temperature-doping level phase diagram. Upon Co substitution on the Fe site, the structural and 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 Ca10(Pt3As8)((Fe1−xPtx)2As2)5 (10-3-8) 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 compound and insulating in the 10-3-8 compound.