Ab initio investigation of the magnetic states of Ca2MnO4 and Ca2MnO3.5

An analysis of the electronic and magnetic properties of Ca₂MnO₄ and Ca₂MnO_3.5 is carried out within local spin density functional theory using the augmented spherical wave method. From energy differences between the hypothetic magnetic configurations both systems are found to be insulating antiferromagnets in the ground state with a 1 eV gap. However we identify an intermediate half metallic ferromagnetic state with the Hund’s rule expected moments for Mn^IV (3 μ_B) and Mn^III (4 μ_B, high spin HS configuration), respectively. The latter result of moment magnitude finds support in recent experimental evidence of Mn^III bismuth oxide as a ferromagnet in its ground state. This is characterized by a small density of states (DOS) magnitude of itinerant states in spin (↑) channel pointing to a metallic-like behavior as it is experimentally evidenced. For both Ca₂MnO₄ and Ca₂MnO_3.5 the chemical bonding characteristics are resolved for the two spin channels. Relationship to colossal magnetoresistive compounds is proposed.