Spin, charge, and orbital orderings in oxides with dual-valent transition metal ions

Using generalized-gradient-corrected full-potential density-functional calculations, we have studied the electronic structure and magnetic properties of YBaMn2O5, Sr4Fe4O11, and Ca3Co2O6. In these phases, the 3d transition metal ions have dual valence. We have studied the electronic structure using site-, angular momentum-, and orbital-projected density of states. The charge and orbital ordering are analyzed in terms of the calculated electron-density distribution, charge density, and electron localization function. The oxygen vacancy, cation radii, and crystal-field effects are found to play an important role for the various ordering phenomena in these compounds.