Physical properties and electronic structure of Sr₂Cr₃As₂O₂ containing CrO₂ and Cr₂As₂ square-planar lattices

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We report the physical properties and electronic structure calculations of a layered chromium oxypnictide, Sr₂Cr₃As₂O₂, which crystallizes in a Sr₂Mn₃As₂O₂-type structure containing both CrO₂ planes and Cr₂As₂ layers. The newly synthesized material exhibits a metallic conduction with a dominant electron-magnon scattering. Magnetic and specific-heat measurements indicate at least two intrinsic magnetic transitions below room temperature. One is an antiferromagnetic transition at 291 K, probably associated with a spin ordering in the Cr₂As₂ layers. Another transition is broad, occurring at around 38 K, and possibly due to a short-range spin order in the CrO₂ planes. Our first-principles calculations indicate predominant two-dimensional antiferromagnetic exchange couplings, and suggest a KG-type (i.e. K₂NiF₄ type for CrO₂ planes and G type for Cr₂As₂ layers) magnetic structure, with reduced moments for both Cr sublattices. The corresponding electronic states near the Fermi energy are mostly contributed from Cr-3d orbitals which weakly (modestly) hybridize with the O-2p (As-4p) orbitals in the CrO₂ (Cr₂As₂) layers. The bare bandstructure density of states at the Fermi level is only 1/4 of the experimental value derived from the low-temperature specific-heat data, consistent with the remarkable electron-magnon coupling. The title compound is argued to be a possible candidate to host superconductivity.