Crystal and magnetic structures of the brownmillerite Ca2Cr2O5

Abstract

Powder neutron diffraction and magnetic susceptibility measurements at 10–300 K have been used to determine the crystal and magnetic structures of brownmillerite type Ca₂Cr₂O₅, which was obtained by reduction of the high pressure phase CaCrO₃ through hard–soft chemistry. The ambient temperature crystal structure of Ca₂Cr₂O₅ is refined in space group I2mb and the unusual tetrahedral coordination of Cr³⁺ results in local structural distortions. Cr³⁺ spins order antiferromagnetically below 220 K and a substantial observed canting of moments shows that Heisenberg exchange is weak or frustrated and competes with antisymmetric Dzialoshinskii–Moriya interactions.