Ferromagnetic kinetic exchange interaction

Anderson's superexchange mechanism is indispensable for the description and prediction of the magnetic interactions in localized spin systems. Within the framework, weak ferromagnetism originates from Goodenough's mechanism and potential exchange when strong antiferromagnetic kinetic exchange interaction is suppressed. However, Anderson's model and also its modified version, Zaanen-Sawatzky's model, fail to catch an important ferromagnetic contribution. Here, we report ferromagnetic kinetic exchange mechanism arising from overlapping of magnetic orbitals and their strong covalency with the bridging orbitals. Contrary to the conventional weak ferromagnetic exchange mechanisms, the present one can be larger than the antiferromagnetic kinetic exchange interaction, resulting in strong stabilization of ferromagnetic state. Based on first principles calculations, we demonstrate that the present mechanism is responsible for strong ferromagnetism in several existing materials with diamagnetic metal bridges: Fe³⁺-Co³⁺-Fe³⁺ and Cu²⁺-Cr⁶⁺-Cu²⁺ complexes, quasi-one-dimensional Cu chain, La₄Ba₂Cu₂O₁₀, and Co chain, Ca₃Co₂O₆.