Orbital magnetization of insulating perovskite transition-metal oxides with a net ferromagnetic moment in the ground state

Abstract

Modern theory of the orbital magnetization is applied to the series of insulating perovskite transition metal oxides (orthorhombic YTiO$_3$, LaMnO$_3$, and YVO$_3$, as well as monoclinic YVO$_3$), carrying a net ferromagnetic (FM) moment in the ground state. For these purposes, we use an effective Hubbard-type model, derived from the first-principles electronic-structure calculations and describing the behavior of magnetically active states near the Fermi level. The solution of this model in the mean-field Hartree-Fock approximation with the relativistic spin-orbit coupling typically gives us a distribution of the local orbital magnetic moments, which are related to the site-diagonal part of the density matrix $\hat{\cal D}$ by the "standard" expression $\boldsymbol{\mu}^0 = - \mu_{\rm B} \mathrm{Tr} \{ \hat{\textbf{L}} \hat{\cal D} \}$ and which are usually well quenched by the crystal field. In this work, we evaluate "itinerant" corrections $\Delta \boldsymbol{\cal M}$ to the net FM moment, suggested by the modern theory. We show that these corrections are small and in most cases can be neglected. Nevertheless, the most interesting aspect of our analysis is that, even for these compounds, which are typically regarded as normal Mott insulators, the "itinerant" corrections reveal a strong $\textbf{k}$-dependence in the reciprocal space, following the behavior of Chern invariants. Therefore, the small value of $\Delta \boldsymbol{\cal M}$ is the result of strong cancelation of relatively large contributions, coming from different parts of the Brillouin zone. We discuss details as well as possible implications of this cancelation, which depends on the crystal structure as well as the type of the magnetic ground state.