Crystal and magnetic structures of the brownmillerite Ca2Cr2O5

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.