Absence of itinerant ferromagnetism in a cobalt-based oxypnictide

Abstract

We report a layered transition-metal-ordered oxypnictide ${\mathrm{Sr}}_2{\mathrm{CrCoAsO}}_3$. The new material was synthesized by solid-state reactions under vacuum. It has an intergrowth structure with a perovskite-like ${\mathrm{Sr}}_3{\mathrm{Cr}}_2{\mathrm{O}}_6$ unit and ${\mathrm{ThCr}}_2{\mathrm{Si}}_2$-type ${\mathrm{SrCo}}_2{\mathrm{As}}_2$ block stacking coherently along the crystallographic $c$ axis. The measurements of electrical resistivity, magnetic susceptibility, and specific heat indicate metallic conductivity from the CoAs layers and short-range antiferromagnetic ordering in the ${\mathrm{CrO}}_2$ planes. No itinerant-electron ferromagnetism expected in CoAs layers is observed. This result, combined with the first-principles calculations and the previous reports of other CoAs-layer-based materials, suggests that the $\mathrm{Co}-\mathrm{Co}$ bond length plays a crucial role in the emergence of itinerant ferromagnetism.