Electronic structure of charge-ordered Fe3O4 from calculated optical, megneto-optical Kerr effect, and O K-edge x-ray absorption spectra

TL;DR

This paper investigates the electronic structure of low-temperature Fe3O4 using LSDA and LSDA+U methods, revealing charge order, magnetic properties, and optical spectra that align well with experimental data.

Contribution

It provides a detailed theoretical analysis of charge ordering, magnetic moments, and spectra in Fe3O4, incorporating relativistic effects and comparing with experiments.

Findings

Charge order characterized by a [001] charge density wave.

Weak Fe orbital moments (~0.07 μB) consistent with experiments.

Calculated spectra agree well with experimental optical and x-ray data.

Abstract

The electronic structure of the low-temperature (LT) monoclinic magnetite, Fe3O4, is investigated using the local spin density approximation (LSDA) and the LSDA+U method. The self-consistent charge ordered LSDA+U solution has a pronounced [001] charge density wave character. In addition, a minor [00{1/2}] modulation in the phase of the charge order (CO) also occurs. While the existence of CO is evidenced by the large difference between the occupancies of the minority spin t_{2g} states of ``2+'' and ``3+'' Fe_B cations, the total 3d charge disproportion is small, in accord with the valence-bond-sum analysis of structural data. Weak Fe orbital moments of ~0.07 mB are obtained from relativistic calculations for the CO phase which is in good agreement with recent x-ray magnetic circular dichroism measurements. Optical, magneto-optical Kerr effect, and O K-edge x-ray absorption spectra calculated for the charge ordered LSDA+U solution are compared to corresponding LSDA spectra and to available experimental data. Reasonably good agreement between the theoretical and experimental spectra supports the relevance of the CO solution obtained for the monoclinic LT phase. The results of calculations of effective exchange coupling constants between Fe spin magnetic moments are also presented.