Impact of Mn–O–O–Mn superexchange pathways in a honeycomb lattice Mn oxide with small charge-transfer energy

We investigated the electronic structure of layered Mn oxide Bi3Mn4O12(NO3) with a Mn honeycomb lattice by x-ray absorption spectroscopy and model calculations. The valence of Mn was determined to be 4 + with a small charge-transfer energy of ∼ 1 eV. The values of (J1, J2, J3, Jc, Jc1, and Jc2) obtained by unrestricted Hartree–Fock calculations on Mn 3d–O 2p lattice models show that intra-layer second and third neighbor superexchange interactions J2 and J3 as well as inter-layer superexchange interactions Jc, Jc1, and Jc2 are enhanced due to Mn–O–O–Mn pathways, which are activated by the smallness of charge-transfer energy. The present analysis indicates that the ferromagnetic Jc1 and antiferromagnetic Jc2 are responsible to the antiferromagnetic inter-layer coupling and that the intra-layer exchange interactions with the ferromagnetic J2 and antiferromagnetic J3 have no frustration effect.