Electronic and optical properties of spinel zinc ferrite: $Ab$ $initio$ hybrid functional calculations

TL;DR

This study uses advanced ab initio hybrid functional calculations to explore how different magnetic interactions and cation arrangements affect the structural, electronic, and optical properties of zinc ferrite, providing insights into its magnetic ground state.

Contribution

It demonstrates that hybrid functional calculations better predict zinc ferrite's properties and clarifies the influence of cation inversion and magnetic coupling on its behavior.

Findings

Hybrid functional calculations align better with experimental properties.

Normal spinel structure is energetically favored with ferromagnetic coupling in hybrid calculations.

Cation inversion significantly affects magnetic and electronic properties.

Abstract

Spinel ferrites in general show a rich interplay of structural, electronic, and magnetic properties. Here, we particularly focus on zinc ferrite (ZFO), which has been observed experimentally to crystallise in the cubic $normal$ spinel structure. However, its magnetic ground state is still under dispute. In addition, some unusual magnetic properties in ZFO thin films or nanostructures have been explained by a possible partial cation inversion and a different magnetic interaction between the two cation sublattices of the spinel structure compared to the crystalline bulk material. Here, density functional theory has been applied to investigate the influence of different inversion degrees and magnetic couplings among the cation sublattices on the structural, electronic, magnetic, and optical properties. Effects of exchange and correlation have been modelled using the generalised gradient approximation (GGA) together with the Hubbard `+$U$' parameter, and the more elaborate hybrid functional PBE0. While the GGA+$U$ calculations yield an antiferromagnetically coupled $normal$ spinel structure as the ground state, in the PBE0 calculations the ferromagnetically coupled $normal$ spinel is energetically slightly favoured, and the hybrid functional calculations perform much better with respect to structural, electronic and optical properties.