The Electronic Structures And Magnetism In Y Doped ZnO

Recently, some experiments show that Sc doped ZnO and TiO2 thin films, In2O3, HfO2 and TiO2 thin films, CaB6, SrB6 and radiated graphite are ferromagnetic and all exhibit Tc above room temperature. They all don't contain transition metal or rare earth element in which electrons partially filled d or f shell, so the origins of ferromagnetism are different from conventional ferromagnetic materials.Some experiments and theoretical calculations showed that the origins of ferromagnetism were related to defects of crystal lattices. As for graphite, it has been proved experimentally that the nonmagnetic graphite is ferromagnetic after it is radiated with high energy particles. The radiation will introduce vacancies and interstitials in graphite. And the calculations proved that vacancies of graphite carried magnetic moment. It is well known that the defects in film are more than in bulk. The experiments for CaB6 and SrB6 show that the magnetic moments per formula unit in thin film are two and four orders of magnitude greater than that in the single crystal or polycrystalline materials. The TiO2 and In2O3 which are nonmagnetic in bulks are ferromagnetism in thin films. And the magnetism of TiO2,In2O3 and HfO2 films are varing as time. The calculations based on DFT indicate that the B6 vacancy in CaB6 carries a magnetic moment of 2.4μB and the Hf vacancy in HfO2 exhibits a magnetic moment of 3.5μB, and the magnetic moments are ferromagnetic coupled. For CaO, the magnetic moment of a neutral Ca vacancy is 1.9μB, but the negative vacancy with 1.0μB and two neutral vacancies within the distance are FM coupling. As for Zn0.95Sc0.05O, it will produce Zn vacancy in (Zn_0.95Sc_0.05)O when Zn⁺² is substituted with Sc⁺³. We calculated the electronic structures of Sc doped ZnO by using plane-wave pseudo-potential method based on the state-of-art DFT. The calculated results are as follows: Sc doped ZnO without vacancies is nonmagnetic, one with vacancies is magnetic; The introduction of Sc result that the formation energy of VZn reduced apparently, which means Sc doping favors the formation of VZn. The magnetism originates from the spin-polarized O atoms around the Zn vacancy.In this work, we studied the influence of the intrinsic defects such as VO and VZn on the magnetism of ZnO thin film and the effect of Y in Y doped ZnO on VZn. To research on Y doped ZnO and the intrinsic defects of ZnO, we built 2×2×2 and 2×2×4 supercells. We performed spin-polarized electronic calculation on ZnO, Zn₁₆O₁₅ with one O vacancy, Y doped ZnO (Zn₁₅Y₁O₁₆) with 2×2×2 supercells and the results show that they are nonmagnetic. We also calcaulated the Zn₁₅O₁₆ containing a Vzn , Y doped ZnO including one VZn for exmple Zn₁₄Y₁O₁₆, and Zn₂₉Y₁O₃₂ with a 2×2×4 supercell. We got 1.87μB in Zn₁₅O₁₆ ,1.0μB for Zn₁₄Y₁O₁₆ and 0.29μB for Zn₂₉Y₁O₃₂ . From above data ,we can draw a conclusion that VZn is the origin of magnetism in ZnO films and Y doped films. In order to study the effect of Y on the formation energy of VZn by comparing the total energy of Zn₁₄Y₁O₁₆ with Zn₁₅O₁₆'s, we found that with the introduction of Y, the formation energy of VZn reduced by 0.028eV. It shows that Y favors the formation of VZn. As for Zn₁₀Y₄O₁₆, .we also calculated and compared the total energy of Zn₁₀Y₄O₁₆ with the magnetism moment coupled ferromagnetically and antiferromagnetically. We found that the ferromagnetic configuration has smaller energy than AF, so the ferromagnetic coupling is stable. Finally we make a conclusion that: Y doped ZnO may be ferromagnetic and VZn is the origin of ZnO thin film with Y doping.