Ab initio study of magnetite (Fe3O4). The Verwey transition, the Mössbauer spectrum, the half metallic character Vs the semiconducting nature and the role of the symmetry

H. H: MEDINA; K. L SALCEDO RODRÍGUEZ; A. V. GIL REBAZA; A. M. MUDARRA; J. J. MELO QUINTERO; L. A ERRICO; C. E. RODRÍGUES TORRES

Brasov

Conferencia; International Conference on the Applications of the Mössbauer Effect, ICAME 2021 and 3rd International Conference on Hyperfine Interactions and their applications; 2021

National Institute of Materials Physics (NIMP

Ferrites (XFe2O4) are a family of magnetic oxides that, due to their numerous technological applications and intriguing magnetic properties, becomes one of the most extensively studied magnetic materials. Ferrites crystallize in the spinel face-centered cubic structure and are characterized by an atomic arrangement of two cationic sites: sites A (tetrahedral oxygen coordination) and sites B (octahedral oxygen coordination). Two types of ferrites can be distinguished; Normal structure: X 2+ ions occupy the A sites and the Fe 3+ ions occupy the B sitesInverted structure: sites are populated by Fe 3+ ions and Fe 3+ and X 2+ ions occupy the B sites in the same proportion. (there are also cases of partial inversion). Iron-ferrite (Fe3O4, magnetite) is a magnetic material with many technological applications that has been extensively studied for the past half-century, but the charge order below the so-called Verwey transition temperature (TV, 120 K) has not been completely understood. Above TV magnetite presents a half metallicbehavior. Below TV the conductivity of the system decreases abruptly, and a semiconducting character is reported. This first-order metal-insulator transition is associated with a reduction of the symmetry from the cubic Fd-3m structure to a monoclinic Cc structure. The transition has been viewed as an orderdisorder transition related to the arrangement of cations on the B sites of the inverse spinel structure. We have performed ab initio calculations in order to determine the electronic, magnetic and hyperfine properties of Fe3O4 . We will show here that even considering the cubic structure, the reduction of the symmetry of the system generates the half-metallicsemiconducting transition. We also predict that the reduction of the symmetry split the B sublattice in mainly two groups of crystallographically equivalent sites characterised by 2+ and 3+ oxidation states, with slightly different magnetic moments and hyperfine parameters. Our results are in agreement with mossbauer experimental results and confirms calculations reported previously but now in the framework of extremely well converged calculations and considering state-of-the art exchange and correlation potentials