First-principles calculations of the electronic structure and magnetism of nanostructured CoFe2O4 microgranules and nanoparticles

Abstract

A detailed study of the structural and magnetic properties of inverse spinel $\mathrm{Co}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ nanoparticles and nanostructured $\mathrm{Co}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ microgranules is made by the first-principles calculations. We have estimated the relative strengths of crystal fields, exchange fields, and magnetic exchange interactions using the electronic structure calculations and electron density maps. We find that the electron-electron correlation plays a significant role in obtaining the correct ground-state structure. A significant local structural distortion at the octahedral site and ``inverted'' sublattice occupancy in $\mathrm{Co}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ affects the magnetic exchange interactions substantially. The trends in magnetic exchange interactions are analyzed in terms of structural parameters and the features of their electronic structures and magnetic properties. We find that Fe states in $\mathrm{Co}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ are extremely localized, irrespective of the symmetry of the site. Also, Co and Fe ions prefer their high-spin configurations with higher spin moments at octahedral sites.