The Electronic Structures And Magnetism Of Nonmagnetic Oxides ZnO

Recently, some experiments show that Nonmagnetic oxides such as TiO₂,ZnO,In₂O₃,SnO₂,CeO₂,Al₂O₃ and HfO₂ thin films and nanoparticles, CaB6 SrB6 and BaB6 with the Structure of CsCl 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, Generally, In DMS materials are mostly metal and compound contain transition metal or rare earth element in which electrons partially filled d or f shell ,with the magnetism come from the atom's spin coupling.since they all don't contain transition metal or rare earth element ,the origins of ferromagnetism which are different from conventional ferromagnetic materials have aroused public interest.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. The experiment and theoretically calculation all show that the vacancy Play an important role in the ferromagnetism of DMS with few magnetic ion..So we can expect that the vacancy in the Material without magnetic ion can also play an important role in the Magnetic properties.The theory basiced on the density function theory is the most effective method of all the theories on the research of vancancy of oxides and the relationship between source of the ferromagnetism and the vancancy.In this work, we studied the influence of the intrinsic defects such as V_Zn on the magnetism of ZnO thin film and the effect of all kinds ofon V_Zn. To research on the intrinsic defects of ZnO, we built 2x2x2 supercells. We performed spin-polarized electronic calculation on ZnO, Zn₁₆O₁₅ with one O vacancy ,ZnO including one V_Zn for exmple Zn₁₅O₁₆ ,Zn₁₄O₁₆ with 2 Zn vacancy with 2x2x2 supercells and the results show that the ZnO and Zn₁₆O₁₅ are nonmagnetic. We also got1.87μB in Zn₁₅O₁₆ and 1.98μB in Zn₁₄O₁₆ .From above data ,we can draw a conclusion that V_Zn is the origin of magnetism in ZnO films。In order to study the effect of distance of V_Zn on the The electronic structures and magnetism in ZnO by comparing the total energy of 4 kinds of Zn₁₄O₁₆ , we found that as the distance of two Zn vacancies becomes longer,the total energy becomes samller,which means the system with longer distance of two Zn vacancies can keep stable. As for Zn₁₄O₁₆, .we also calculated and compared the total energy of Zn₁₄O₁₆ with the magnetism moment coupled ferromagnetically and antiferromagnetically. We found that the ferromagnetic configuration has smaller energy than AF, so the Ferromagnetism of ZnO possibly come form the ferromagnetic coupling of V_Zn.