Origin of ferromagnetic interactions in NaMnCl3: How the response theory reconciles with Goodenough-Kanamori-Anderson rules

Abstract

The on-site Coulomb repulsion U is the key ingredient for describing the magnetic properties of Mott insulators, leading to a popular belief that many limitations of the density-functional theory based methods can be cured by artificially incorporating such on-site interactions for localized electrons in the model form. The layered antiferromagnet NaMnCl3 reveals quite a different story: while the Coulomb U on the Mn sites controls the strength of antiferromagnetic superexchange interactions, an equally important parameter is the Stoner coupling ICl on the ligand sites. The latter is responsible for large ferromagnetic contributions to the interatomic exchange interactions, which in NaMnCl3 nearly cancel the effect of the superexchange interactions. Although such behavior is anticipated from the phenomenological Goodenough-Kamanori-Anderson rules, the quantitative description of the ligand-related contributions remains disputable. Considering NaMnCl3 as an example, we discuss how they can be generally taken into account in the linear response theory to regain the dependence of the exchange interactions on ICl. The problem is complicated by the fact that, for the nearly filled Cl 3p shell, the parameters ICl are sensitive to the model assumptions. © 2022 American Physical Society.