Magnetic Properties Of Materials Induced By Impurities And Vacancies From First Principles

The recent discoveries of ferromagnetism in nanostructure materials of nonmetallic light-element have attracted much attention. However, the origin magnetism of such dO materials is complex, and is different from the normal magnetization. The related research indicates that magnetism induced by impurities and vacancies is basic fashion. So we use the ab initio method based on the density functional theory to investigate the magnetic properties induced by the vacancies in graphitic boron nitride sheet (g-BN) and single walled boron nitride naotubes (SWNTS), silicon atom doped in the SWNTs, and the carbon nanotube Terminally Connecting Metal Molecular Complexes. The following innovative conclusions are obtained:1. Single nitrogen or boron vacancy in the g-BN can induce spontaneous magnetization, and the magnetic moment is 1.0 and 3.0μB, respectively. More interestingly, the boron vacancy in g-BN appears to have desired half-metallic behavior.2. The boron vacancies pair in g-BN with arbitrary configurations can induce spontaneous magnetization. The induced magnetic moment is twice over the case of single vacancy. With the three kinds of neighboring nitrogen vacancies, only the third neighboring nitrogen vacancies can induce spontaneous magnetization. The magnetic moment is 2.0μB The neighbor boron and nitrogen vacancy pair can't change the properties of semiconductor.3. The configurations of the single vacancy in SWNTs depend on chiralities and diameters of the tubes, and the vacancy is magnetic. The symmetry broken is induced by the Jahn-Teller distortion. Finally we also investigated three different vacancy pairs in (5,5) SWNT and found that only the next neighbor boron and nitrogen vacancy pair is magnetic.4. The silicon substitution in SWNTs can induce spontaneous magnetization, and the local symmetry of the system is broken by the silicon atom extending outward of the tube. By applying a full spin-polarized description to the system, appears dispersionlessπband near the Fermi energy. The magnetization can be attributed to the 3p unpaired electron of silicon.5. From the investigations of dinuclear iron metal molecular complexes connected by carbon nanotubes, we found the coupling is ferro-magnetic and is not depend on connecting bridge type (carbon or BN nanotube) or the number of intervening atoms. In the case of carbon naotube, the polarized is not continuous; however, the magnetic moment can't transfer through the tube with BN nanotube bridge.