First-principles Study On Electronic Structure And Magnetic Properties Of Spinel Ferrite

The crystal structure, electronic structure, magnetic properties and dielectric properties of ZnFe₂O₄ ferrite, Zn_0.5Mn_0.5Fe₂O₄ ferrite, MnFe₂O₄ ferrite and NiFe₂O₄ ferrite have been systematically studied by the first-principle ultra-soft pseudopotential plane-wave method based on the density function theory. The effect of increasing Mn doped content on magnetic properties of ZnFe₂O₄ ferrite, Zn_0.5Mn_0.5Fe₂O₄ ferrite, and MnFe₂O₄ ferrite has been invesigated. In addition, the mechanism of electrical conductivity and magnetic properties of the above systems is revealed.The study shows that the pure zinc ferrite is a non-magnetic direct bandgap semiconductor materials. The conduction band is mainly due to the Fe-3d electron orbit and the O-2p electron orbit. The valence band is contributed to the Fe-3d electron orbit. It is found that Fe-3d electron orbit and O-2p electron orbit overlap strongly, indicating that there is a strong interaction between Fe and O, which play an important role on structural stability.Calculations show that the Zn_0.5Mn_0.5Fe₂O₄ ferrite, and MnFe₂O₄ ferrite by Mn-doped remain a single spinel structure, but the cell volume increases, weakening the stability of spinel structure. Zn_0.5Mn_0.5Fe₂O₄ ferrite, and MnFe₂O₄ ferrite are half-metal and have magnetic properties. As the Mn doping concentration increases, the total magnetic moments of ZnFe₂O₄ ferrite, Zn_0.5Mn_0.5Fe₂O₄ ferrite, and MnFe₂O₄ ferrite increase first and then decrease. Our calculations indicate that the Zn_0.5Mn_0.5Fe₂O₄ ferrite's magnetic moment is larger than those of MnFe₂O₄ ferrite and the NiFe₂O₄ ferrite. Electronic density of states analysis shows that in Zn_0.5Mn_0.5Fe₂O₄ ferrite, the Zn atom enhance the hybrid between Mn and Fe atoms, leading to spin magnetic moment of increases. Therefore total magnetic moment increases. The calculation of dielectric constant of Zn_0.5Mn_0.5Fe₂O₄ ferrite show that its dielectric properties exhibit relaxation-type dispersion characteristics.The calculation results of inverse spinel structure NiFe₂O₄ ferrite demonstrate that NiFe₂O₄ ferrite is a kind of half-metal, and has stable structure. Moreover, it can be seen that the spin magnetic moment of B-site is larger than that of A-site due to the enhanced hybrid between Ni atom of B-site and Fe atom in the B-site, resulting in the increase of Fe atom's spin magnetic moment.