Electronic structures of normal and inverse spinel ferrites from first principles

Abstract

We apply the self-interaction corrected local spin density approximation to study the electronic structure and magnetic properties of the spinel ferrites MnFe2O4, Fe3O4, CoFe2O4, and NiFe2O4. We concentrate on establishing the nominal valence of the transition metal elements and the ground state structure, based on the study of various valence scenarios for both the inverse and normal spinel structures for all the systems. For both structures we find all the studied compounds to be insulating, but with smaller gaps in the normal spinel scenario. On the contrary, the calculated spin magnetic moments and the exchange splitting of the conduction bands are seen to increase dramatically when moving from the inverse spinel structure to the normal spinel kind. We find substantial orbital moments for NiFe2O4 and CoFe2O4.

Controlling the electronic structure of Co1−xFe2+xOMoyer1, Vaz2, Negusse3 et al. 2011Phys. Rev. B8917740View full textAdd to dashboardCite

“…Cobalt ferrite, like magnetite, is ferrimagnetic with a magnetic moment predicted by different theoretical models to be between 2.73 -3 µ B /f.u. for a perfect inverse spinel crystal structure; 11,12,15 the magnetic moment will increase with increased mixing of the Co 2+ cations between the octahedral and tetrahedral sites. Cobalt ferrite has a large magnetic anisotropy due to a spin-orbit stabilized doublet (with unquenched orbital momentum l z = ±1) ground state caused by a trigonal crystal field on the Co 2+ octahedral cations, 27, 39-45 with a cubic magnetocrystalline anisotropy constant, K 1 , which is positive and larger by over an order of magnitude than the other 3d-transition-metal spinel ferrites.…”

“…[33][34][35] The tetrahedral and octahedral sites are antiferromagnetically coupled; resulting in a magnetic moment varying between 3.65 -4.43 μ B , depending on the theoretical model. 11,12,14,15,36 Hence, magnetite is a ferrimagnet, with a large critical temperature of T c = 858 K.…”

First-principles study of ferroelectricity induced by p–d hybridization in ferrimagnetic NiFe 2 O 4

“…This is comparable with the conventional ferroelectrics and therefore implies the presence of spontaneous polarization in the bulk NFO. However, the ferroelectricity of bulk NFO has neither been calculated nor measured yet, though the intensive studies of electronic [32][33][34], magnetic [35], and epitaxial strain and magnetoelastic properties [36][37][38] Fe 3+ and Ni 2+ over B-sites in the F d3m unit cell with the periodic boundary condition rather than in infinite bulk crystal, it might be possible to generate different space groups whose symmetries are lowered from F d3m. It is only recent year that, through the Raman spectra measurements, both NFO single crystals [39] and thin films [40] exhibit short range B-site ordering with tetragonal P 4 1 22 (No.…”

“…This is comparable with the conventional ferroelectrics and therefore implies the presence of spontaneous polarization in the bulk NFO. However, the ferroelectricity of bulk NFO has neither been calculated nor measured yet, though the intensive studies of electronic [32][33][34], magnetic [35], and epitaxial strain and magnetoelastic properties [36][37][38] have been conducted.Which is the most stable structure?-It is well accepted that NFO crystallizes in the completely inverse spinel structure with a face-centered cubic space group F d3m (No. 227), where half of the Fe 3+ cations occupy the tetrahedral A-sites (8a), the rest of Fe 3+ and Ni 2+ cations are equally distributed over the octahedral B-sites (16d), and the sites of oxygen anions are distinguished into O 1 and O 2 .…”

“…This is comparable with the conventional ferroelectrics and therefore implies the presence of spontaneous polarization in the bulk NFO. However, the ferroelectricity of bulk NFO has neither been calculated nor measured yet, though the intensive studies of electronic [32][33][34], magnetic [35], and epitaxial strain and magnetoelastic properties [36][37][38] have been conducted.…”