Structure, Ferromagnetism, Optical And Electrical Properties Of Li?Al-doped SnO₂ Diluted Magnetic Materials

SnO₂ is a kind of multifunctional transparent oxide semiconductor, with the cheapness, non-toxic and harmlessness, low preparation temperature, high thermal stability and stable physical and chemical properties, etc. It has been applied to the transparent conductive electrode, solar cells, gas sensor and architectural glass, etc.In addition, SnO₂ material has the wide band gap and large exciton binding energy?130 meV?, therefore it is a kind of promising ultraviolet light-emitting materials. In2003, Ogale et al. discovered the gaint magnetic moment and high Curie temperature in Co doped SnO₂ thin film, which attracted the attention of many researchers. Many research works has been made, but there is no definite conclusion about the magnetic origins of SnO₂ based materials. According to the theory of d⁰ ferromagnetism, the production of local magnetic moment and the establishment of the long-range ferromagnetic ordering are attributed to the presence of point defects in the semiconductor. However, there is less paper about d⁰ magnetism of SnO₂ base material. In this paper, therefore, two works were carried out.?1? The epitaxial Li doped SnO₂ thin films grown on Al₂O₃ substrate were prepared by the magnetron sputtering method. Li doping widened the optical band gap of the film sample. XRD results show that we successfully prepared the epitaxial SnO₂ thin film. The existence of Li is detected by using XPS and Li doping can lead to the emergence of hole in the system. There is no oxygen vacancy related defects in the samples by using XPS and PL. Hall tests show that the conductive type of films turns to p type from n type with the increase of doping concentration. In the thin films of p type, its magnetism is closely relative to the carrier concentration,which showed the holes are important role in regulating the magnetism of the doped SnO₂ thin film samples.?2? We had fabricated Al doped SnO₂ nanoparticles by sol gel method. Al doping can induce the distortion of crystal lattice and create a large number of point defects in the crystal for the different ionic radii of Al3+ and Sn4+. This was verified by the XRD and HRTEM and absorption spectrum. We not only detected the presence of Al, but also found the existence of the oxygen vacancy defects in the sample by using XPS. The PL studies indicated the presence of yellow-green emission in the all NPs, which is closely related to VO+defects. The saturation magnetization intensity and the oxygen vacancy of Al doped SnO₂ nanoparticles hadthe same change trend with doping concentration. According to the above results, the ferromagnetic mechanism in SnO₂-based diluted magnetic materials is reasonably explained using oxygen vacancies.