Non-collinear spin DFT study of the ground state magnetic structure, optical and electronic properties of the hexagonal LuFeO3 multiferroic

Abstract

Hexagonal LuFeO3 compound is a multiferroic material whose ground state magnetic structure, band gap, and optical absorption spectra are matters of debate in the literature. In the present paper, these properties have been investigated by the employment of the calculations based on non-collinear spin density functional theory, with the exchange and correlation effects treated by local spin density approximation (LSDA) including effective Hubbard (Ueff) correction (LSDA + Ueff). It was concluded that the results with Ueff = 4.0 eV correlate to the experimental facts in the best manner. The ground state magnetic configuration is found to be Γ1 + Γ2, characterized by weak ferromagnetism along the c-axis (0.07 μB/Fe-atom). The calculated band gap is found to be 1.03 eV, supporting those experimental works which conclude that the gap value should be ∼1.1 eV. The optical absorption spectrum is computed and found to be in reasonable agreement with experimental data. Its edge (up to 5 eV) is generated by electronic transitions between the occupied and unoccupied Fe 3d- and the O 2p-states, with energy transfer occurring within the basal planes of the hexagonal crystal structure. The controversial lowest energy peak (centered between 1 and 2 eV) is generated by absorption of the light polarized perpendicularly to the hexagonal c-axis.