Physical properties and electronic structure ofSr2Cr3As2O2containingCrO2andCr2As2square-planar lattices

Abstract

We report the physical properties and electronic structure calculations of a layered chromium oxypnictide, ${\mathrm{Sr}}_{2}{\mathrm{Cr}}_{3}{\mathrm{As}}_{2}{\mathrm{O}}_{2}$, which crystallizes in a ${\mathrm{Sr}}_{2}{\mathrm{Mn}}_{3}{\mathrm{As}}_{2}{\mathrm{O}}_{2}$-type structure containing both ${\mathrm{CrO}}_{2}$ planes and ${\mathrm{Cr}}_{2}{\mathrm{As}}_{2}$ 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 ${\mathrm{Cr}}_{2}{\mathrm{As}}_{2}$ layers. Another transition is broad, occurring at around 38 K, and possibly due to a short-range spin order in the ${\mathrm{CrO}}_{2}$ planes. Our first-principles calculations indicate predominant two-dimensional antiferromagnetic exchange couplings, and suggest a KG-type [i.e., ${\mathrm{K}}_{2}{\mathrm{NiF}}_{4}$ (abbreviated as ``K'') type in the ${\mathrm{CrO}}_{2}$ sublattice and N\'eel (usually denoted by ``G'') type in the ${\mathrm{Cr}}_{2}{\mathrm{As}}_{2}$ sublattice] magnetic structure, with reduced moments for both Cr sublattices. The corresponding electronic states near the Fermi energy are mostly contributed from $\mathrm{Cr}\ensuremath{-}3d$ orbitals which weakly (modestly) hybridize with the $\mathrm{O}\ensuremath{-}2p$ ($\mathrm{As}\ensuremath{-}4p$) orbitals in the ${\mathrm{CrO}}_{2}$ (${\mathrm{Cr}}_{2}{\mathrm{As}}_{2}$) layers. The bare band structure density of states at the Fermi level is only $\ensuremath{\sim}1/4$ 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.