Role of anisotropic Coulomb interactions in the superexchange coupling of mixed-valent Mn3O4

Abstract

We report the importance of anisotropic Coulomb interactions in DFT+ U calculations of the electronic and magnetic properties of Mn3O4. The effects of anisotropic interactions in Mn2+ and Mn3+ are examined separately by defining two different sets of Hubbard parameters: U2+ and J(2+) for Mn2+ and U3+ and J(3+) for Mn3+. The anisotropic interaction in Mn3+ has significant effects on the physical properties of Mn3O4 including local magnetic moments, canted angle, spontaneous magnetic moment, and superexchange coupling, but that in Mn2+ has no noticeable effect. Weak ferromagnetic interchain superexchange observed experimentally is predicted only if a sizable anisotropic interaction is considered in Mn3+. By analyzing the eigenoccupations of the on-site Mn density matrix, we find that the spin channel involving Mn3+ d(x)(2)-y(2) orbitals, which governs the 90 degrees correlation superexchange, is directly controlled by the anisotropic interactions. These findings indicate that the exchange correction J for the intraorbital Coulomb potential is critical for the first-principles description of Mn oxides containing Mn3+ or Mn4+.