Origin of antiferromagnetism in CoO: A density functional theory study

We have investigated the origin of antiferromagnetism of CoO in the rocksalt structure using spin-polarized density functional theory calculations. We find that in the rocksalt structure, the superexchange interaction between the occupied and unoccupied $eg$ states plays the dominant role, which leads to an antiferromagnetic ground state, but the system also has a strong direct exchange interaction between the partially occupied minority spin $t2g$ states that leads to the unusual situation that the ferromagnetic phase is more stable than most antiferromagnetic configurations.