First-Principles Study of the Structure, Electronic and Magnetic Properties of Fe-Doped ZnO

This study investigates the structural, electronic and magnetic properties of pure ZnO and Zn 1-x Fe x O (x = 0.125, 0.25, 0.375, 0.5) using first-principles calculations. Pure ZnO exhibits insulating and nonmagnetic behaviour with a band gap of 3.25 eV due to the occupation of all five Zn-3d states in both spin channels. The introduction of Fe creates parallelogram-shaped structures (PSSs) from the Zn and Fe atoms, with symmetry properties differing among the various Fe concentrations; Zn 0.875 Fe 0.125 O (12.5% Fe doping) and Zn 0.75 Fe 0.25 O (25% Fe doping) exhibit loss of crystal symmetry, while Zn 0.625 Fe 0.375 O (37.5% Fe doping) and Zn 0.5 Fe 0.5 O (50% Fe doping) preserve crystal symmetry. Notably, all four Zn 1-x Fe x O compounds display half-metallic behaviour with all five Zn-3d/Fe-3d states occupied in the majority spin channel. Compared to Zn 0.875 Fe 0.125 O, the electrical conductivity reduces drastically in Zn 0.75 Fe 0.25 O, Zn 0.625 Fe 0.375 O and Zn 0.5 Fe 0.5 O due to rapid reduction in Fe-3d carriers at the Fermi level. The half-metallic nature of Zn 0.875 Fe 0.125 O and Zn 0.75 Fe 0.25 O is attributed to the partial filling of the Fe-d xy , d yz , d xz and d x 2 -y 2 states in the minority spin channel. The presence of two types of Fe ions, namely Fe1 and Fe2, is observed in Zn 0.625 Fe 0.375 O and Zn 0.5 Fe 0.5 O, with distinct electronic behaviour leading to their half-metallic properties. The partial filling of Fe1-d xy , d yz , d xz , d x 2 -y 2 states results in the half-metallic character of Zn 0.625 Fe 0.375 O and Zn 0.5 Fe 0.5 O. Partial orbital ordering (OO) among the Fe-d xy , d yz , d xz and d x 2 -y 2 states is observed in Zn 0.875 Fe 0.125 O and Zn 0.75 Fe 0.25 O. On the other hand, partial (complete) OO is observed among the Fe1-d xy/yz and Fe1-d xz/x 2 -y 2 (Fe2-d xy/yz and Fe2-d xz ) states in Zn 0.625 Fe 0.375 O and Zn 0.5 Fe 0.5 O. The unequal distribution of electrons in the two spin channels facilitates ferrimagnetism in all four Zn 1-x Fe x O materials. The study observes p-d hybridization between Fe-3d and O-2p states, which becomes more pronounced with increased Fe concentration. The ferromagnetic coupling between Fe and O increases gradually as the Fe content in Zn 1-x Fe x O rises.