Tunneling interlayer exchange coupling between oxide ferrimagnets: Analysis for _Fe3 O₄ /vac/ Fe₃ O₄ case

We have investigated tunneling interlayer exchange coupling (TIEC) between ferrimagnetic Fe₃ O₄ films via a tunneling barrier. In this investigation we employ ab initio density functional theory to study a generic tunneling junction incorporating ferrimagnets Fe₃ O ₄ /vac/ Fe₃ O₄. In contrast with previously established TIEC theory, calculated thickness dependence is nonmonotonic and accompanied by TIEC sign change. Our calculations clearly demonstrate that TIEC is controlled mainly by an interfacial oxygen induced spin polarization. These results emphasize the importance of localized and strongly directional electronic interactions at the interface, thus showing limitations of free electron model treatment of the problem.