D-Type Anti-Ferromagnetic Ground State in Ca_2Mn_2O_5

We study the electronic and magnetic properties of an oxygen-deficient perovskite Ca_2Mn_2O_5 based on the first principle calculations. The calculations show that the ground state of Ca_2Mn_2O_5 is a D-type anti-ferromagnetic structure with the anti-ferromagnetic spin coupling along the c-direction. The corresponding electronic structure of the D-type state is investigated, and the results display that Ca_2Mn_2O_5 is an insulator with an indirect energy gap of \sim2.08 eV. By the partial density-of-state analysis, the valence band maximum is mainly contributed to by the O-2p orbitals and the conduction band minimum is contributed to by the O-2p and Mn-3d orbitals. Due to the Coulomb repulsion interaction between electrons, the density of state of Mn-3d is pulled to -6–-4.5 eV.