Magnetic Interactions in ZnMnO₃: Active Role of Zn 3d¹⁰ Orbitals, in Comparison with MgMnO₃

The ilmenite-type MgMnO₃ and ZnMnO₃ with honeycomb Mn layers exhibit distinctive magnetic ground states. In experiments, MgMnO₃ exhibits a Néel antiferromagnetic alignment, in which both nearest-neighbor (NN) J₁ and next-nearest-neighbor (NNN) J₂ exchange interactions are antiferromagnetic, while ZnMnO₃ has zigzag antiferromagnetic ordering with NN ferromagnetic and NNN antiferromagnetic coupling. On the basis of ab initio band structure calculations, we explain the deviation of NN J₁ exchange coupling from antiferromagnetic (MgMnO₃) to ferromagnetic (ZnMnO₃) as originating from the intensive hybridization between the occupied Zn 3d¹⁰ orbitals with those of the bridging O 2p states, strongly depending on the position of the orbitals. In addition, our results indicate that, in combination with the NN J₁ coupling, the considerably large third-nearest-neighbor (TNN) J₃ exchange interaction plays an important role in erecting the magnetic ground states, rather than the experimentally proposed NNN J₂. Furthermore, our findings highlight the important role of not only the electronic configurations but also the positions of the nonmagnetic cations in determining the essence of the magnetic exchange interactions. Therefore, the hybridization effect of nonmagnetic cations should not be dismissed in an analysis of the magnetic properties of transition-metal oxides.