Effect of cobalt doping on the structural, magnetic, optical, and electronic properties of LiFeCr4O8

Abstract

Cobalt doping's influence on the structural, magnetic, and electronic properties of the double spinel LiFeCr4O8 was systematically investigated. Rietveld refinement revealed a consistent increase in lattice parameter a and unit cell volume with cobalt incorporation. Magnetic susceptibility measurements indicated three distinct transitions: an increase in the ferrimagnetic transition temperature (TN), a decrease in the magnetostructural transition temperature (TMS), and an increase in the spin gap transition by cobalt doping. Through diffuse reflectance spectroscopy the direct optical band gap (Eog) was obtained with values of 1.169 eV, 1.303 eV, 1.396 eV, and 1.230 eV for x = 0.0, 0.1, 0.2, and 0.5, respectively. The observed increase in Eog with cobalt doping suggests a widening of the band gap, which could be beneficial for optoelectronic applications. By means of X-ray photoelectron spectroscopy (XPS) the core levels of Li 1s, Co 3p, Fe 3p, Cr 3p, Fe 2p, Cr 2p, and O 1s were identified. XPS valence band (VB) analysis revealed a decreasing intensity at binding energy BE = 0 eV with respect to x = 0.0. Density functional theory calculations with Hubbard U correction (DFT + U) confirmed a ferrimagnetic semiconductor behavior with a direct electronic band gap (Eeg) of 1.085 eV.