Ferromagnetic kinetic exchange interaction in magnetic insulators

TL;DR

This paper reveals that considering magnetic and bridging orbitals explicitly uncovers a significant ferromagnetic kinetic exchange interaction in magnetic insulators, challenging the traditional superexchange theory.

Contribution

It introduces a new perspective by explicitly including magnetic and bridging orbitals, showing the ferromagnetic kinetic exchange can be as strong as antiferromagnetic superexchange.

Findings

Ferromagnetic kinetic exchange can be comparable to superexchange.

Explicit orbital consideration reveals ferromagnetic interactions.

Large ferromagnetic coupling observed in Fe-Co-Fe complexes.

Abstract

The superexchange theory predicts dominant antiferromagnetic kinetic interaction when the orbitals accommodating magnetic electrons are covalently bonded through diamagnetic bridging atoms/groups. Here we show that explicit consideration of magnetic and (leading) bridging orbitals, together with the electron transfer between the former, reveals a strong ferromagnetic kinetic exchange contribution. First principle calculations show that it is comparable in strength with antiferromagnetic superexchange in a number of magnetic materials with diamagnetic metal bridges. In particular, it is responsible for a very large ferromagnetic coupling ($-10$ meV) between the iron ions in a Fe$^{3+}$-Co$^{3+}$-Fe$^{3+}$ complex.