Structural, electronic and magnetic properties of partially inverse spinel CoFe₂O₄: a first-principles study

Abstract

Partially inverse spinel CoFe2O4, which may be prepared through various heat treatments, differs remarkably from the ideal inverse spinel in many properties. The structure of partially inverse spinel CoFe2O4 as well as its electronic and magnetic properties through a systemic theoretical calculation of (Co1−x Fe x )Tet(Co x Fe2−x )OctO4 (x = 0, 0.25, 0.5, 0.75 and 1.0) have been investigated by the generalized gradient approximation (GGA) + U approach. It is found that the Co and Fe ions prefer their high spin configurations with higher spin moments at octahedral sites in all the studied cases, in line with experimental observations. The Co ions at the octahedral sites favour being far away from each other in the partial inverse spinels, which also show half metallicity at certain inversion degrees.

Effect of epitaxial strain on the cation distribution in spinel ferrites CoFe2O4 and NiFe2O4: A density functional theory study

“…19,20 However, it can be seen from our first principles results that there are also significant energy differences between different cation arrangements corresponding to the same value of k. This indicates the importance of other factors such as higher order ligand-field effects and local structural relaxations. We note that configurations in which the Co (Ni) cations are clustered together, i.e., configuration Pm* for k ¼ 0.75 and P 4m2 for k ¼ 1, are energetically less favorable than configurations where Co (Ni) cations are distributed more uniformly, in agreement with similar findings of Hou et al 17 Next, we turn to the question of whether the cation distribution and degree of inversion can be influenced by epitaxial strain. Figs.…”

“…It can be seen that for both CFO and NFO, the total energy decreases with increasing inversion, so that the fully inverse spinel structure (k ¼ 1) is energetically most favorable. The calculated energy difference between the normal spinel structure and the most favorable inverse configuration is 0.37 eV with the value of 0.339 eV reported for CFO by Hou et al 17 The much larger preference for the inverse spinel structure of NFO compared to CFO is consistent with the experimental observation that NFO samples usually exhibit complete inversion, whereas the exact degree of inversion in CFO depends on the heat treatment during sample preparation and can vary between 0.76-0.93. 1, 18 The same energetic preference also follows from a simple ligand-field analysis of the Ni 2þ and Co 2þ cations within octahedral and tetrahedral coordination.…”

On stoichiometry and intermixing at the spinel/perovskite interface in CoFe2O4/BaTiO3 thin films

“…However, already from Figure 4, the ratio Fe T d at position 7(nm) is seen to be equal to 2:1, corresponding to a fully inverse spinel structure. It is noted that the degree of inversion of the spinel CoFe 2 O 4 has been related to the magnetic moment previously both experimentally [28] and theoretically [29]. All previous studies suggest that the total magnetic moment decreases with decreasing inversion, inducing an exchange mechanism of Co ions on octahedral sites with tetrahedrally coordi-nated Fe ions.…”

First-Principles Study of the Adsorption/Dissociation Reactions of Water on a Fe- and Co−Al₂O₄Cluster

“…The electronic states ware calculated by projector augmented-wave method [7] within a framework of spin-polarized density functional theory, in which the generalized gradient approximation [8] was used for the exchange-correlation energy. To consider the on-site Coulomb repulsion among the localized electrons, the DFT+U method was employed with U eff = 3.29 eV for Co 3d and 3.42 eV for Fe 3d electrons [9]. The planewave cutoff energies were 30 and 300 Ry for the electronic pseudo-wave functions and pseudo-charge density, respectively.…”