An ab initio DFT study of the optical and magnetic properties of Mn doped GaFeO3

Abstract

In this study, the effect of Mn substitution on the structural, magnetic, electronic and optical properties of GaFeO3 (GFO) were investigated with density functional theory (DFT). A detailed discussion on the magnetic exchange interaction was performed and new aspects like antiferromagnetic coupling strength and exchange coupling parameter were studied. GFO has an antiferromagnetic structure and spontaneous electric polarization in the ground state. The antiferromagnetic structure arises from the magnetic exchange interaction between Fe1 and Fe2 atoms via O atoms. Replacing the Fe1 atom with the Mn atom changes the magnetic exchange interaction in GFO and as a result alters the ground state properties of GFO. Structural investigations indicate that the lattice parameters and unit cell volume are increased with Mn substitution. Also, increasing the Mn concentration leads to an increment in the total spin magnetic moment because of the different magnetic moments of Fe and Mn atoms. This increase is accompanied by an antiferromagnetic to ferrimagnetic (AFM-FIM) transition. Furthermore, the antiferromagnetic coupling strength is decreased with the Mn substitution. Also, electronic investigations reveal the formation of new states around the Fermi surface in spin up channel after the substitution of Mn in the GFO host structure. These new states make possible optical transitions at energies less than the GFO band gap. The number of these new states is increased with increasing the Mn concentration. The imaginary component of the dielectric function, absorption coefficient, and real component of optical conductivity are increased with an increase in the Mn concentration in the energy range up to about 3 eV.