| Compared with traditional semiconductor, half-metalllic materials can control the spins of electrons and transmission of charges simultaneously due to its100%spin polarization. Nowadays, they are the key for high performance microelectronic devices and the development of electronics industry. Among them, the II B-type half-metal Fe3O4has attracted much more attention due to their special advantages, such as higher courier temperature, stable performance, easy preparation. However, its magnetoresistance is not large enough to satisfy the increasing technology needs. In this paper, the electronic structures and magnetic properties of many transition metals doped Fe3O4have been investigated by using first principle methods to design and predict new spinel half-metals with larger magnetoresistance.First of all, the electromagnetic properties of Fe3O4and the3d transition metals Mn, Cr, V, Ti, Sc doped Fe3O4are studied and the results agree quite well with the experimental and theoretical reports, which confirm the accuracy of the methods and parameters used in this paper. Then the doping effects of5d transition metals La, Hf, Ta, W and Re on the half-metallicity of Fe3O4are also investigated. Combined with the3d and4d transition metals doping effects, we summary the following principles:a) when the A-site Fe atoms of Fe3O4are doped by transition metals with less than5d-orbital electrons, the structures maintain the half-metallic character, and molecular magnetic moments increase from5uB to9.0uB linearly as the number of d electrons decreases form5to1. b) As for metals with only one d electron, for example Sc, Y and La. When they doped into the B-site Fe atoms to form FeM2O4, the materials also display half-metallic electronic structure, and their molecular magnetic moments are all4uB.The electronic structures and Mulliken population of6d transition metals Ac and Th doped Fe3O4are calculated and analyzed. Two better candidates for spintronic devices AcFe2O4and ThFe2O4are predicted. They are new spinel rare-earth half-metals with molecular magnetic moments9.0uB and8.1uB,both much larger than that of Fe3O4. And their conductivities are also improved. For Ce doped Fe3O4structures, only CeFe2O4and FeCe2O4are predicted to be half-metallic materials with the molecular moments10.0uB and6.0uB, respectively, which are both quite large. Although with only one4f electron, the electron spin polarization of Ce is very high. Its atom magnetic moment is1.16uB.So CeFe2O4and FeCe2O4are both strong ferromagnetic half-metals. The O atoms in MFe2O4(M=Mn, Cr,V) are further replaced by F atoms, and the electronic structures and magnetic properties of MFe2F4(M=Mn,Cr,V) are studied. Not only does MnFe2F4maintain half-metallic properties but its molecular magnetic moment is increased to be11.8uB. which is amazingly large. And its conductivity is also improved. So F doping brings great effects to MFe2F4but this doesn’t happen to CrFe2F4which lose the half-metallic character. MFe2F4(M=V, Ti, Sc) is calculated to be half-metal and its conductivity is larger than that of MFe2O4(M=V, Ti, Sc). But they still keeps the ferromagnetic character, the atomic moments of V, Ti, Sc are calculated to be-3.76uB,-1.84uB and-0.08uB, respectively, and their molecular moment decreases to3.4uB,,5.0uB and6.7uB, respectively, which results in weaker magnetoresistance effects.A small change of the lattice parameter may shift EF with respect to the half-metallic gap, which clearly affects the half-metallicity as well as the transport properties. Therefore, it is necessary to consider the influence of lattice distortion on half-metallicity. Except for MFe2F4(M=V, Ti, Sc) of which the half-metallicity is very sensitive to lattice compression, the new half-metals with much larger molecular moments all can maintain half-metallic character up to a large lattice distortion. |
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