This paper reports that the high-quality Co-doped ZnO single crystalline films have been grown on a-plane sapphire substrates by using molecular-beam epitaxy. The as-grown films show high resistivity and non-ferromagn...This paper reports that the high-quality Co-doped ZnO single crystalline films have been grown on a-plane sapphire substrates by using molecular-beam epitaxy. The as-grown films show high resistivity and non-ferromagnetism at room temperature, while they become more conductive and ferromagnetic after annealing in the reducing atmosphere either in the presence or absence of Zn vapour. The x-ray absorption studies indicate that all Co ions in these samples actually substituted into the ZnO lattice without formatting any detectable secondary phase. Compared with weak ferromagnetism (0.16 μB/Co2+) in the Zno.95 Co0.05 O single crystalline film with reducing annealing in the absence of Zn vapour, the films annealed in the reducing atmosphere with Zn vapour are found to have much stronger ferromagnetism (0.65 μB/Co2+) at room temperature. This experimental studies clearly indicate that Zn interstitials are more effective than oxygen vacancies to activate the high-temperature ferromagnetism in Co-doped ZnO films, and the corresponding ferromagnetic mechanism is discussed.展开更多
This paper reports that the Zn0.95Co0.05O polycrystalline powder and thin film were prepared by sol-gel technique under the similar preparation conditions. The former does not show typical ferromagnetic behaviour, whi...This paper reports that the Zn0.95Co0.05O polycrystalline powder and thin film were prepared by sol-gel technique under the similar preparation conditions. The former does not show typical ferromagnetic behaviour, while the latter exhibits obvious ferromagnetic properties at 5 K and room temperature. The UV-vis spectra and x-ray absorption spectra show that Co2+ ions are homogeneously incorporated into ZnO lattice without forming secondary phases.The distinct difference between film and powder sample is the c-axis (002) preferential orientation indicated by the x-ray diffraction pattern and field emission scanning electron microscopy measurement, which may be the reason why Zn0.95Co0.05O film shows ferromagnetic behaviour.展开更多
基金Project partially supported by National Science Foundation of China (Grant No. 10804017)National Science Foundation of Jiangsu Province of China (Grant No. BK2007118)+3 种基金Research Fund for the Doctoral Program of Higher Education of China(Grant No. 20070286037)Cyanine-Project Foundation of Jiangsu Province of China (Grant No. 1107020060)Foundation for Climax Talents Plan in Six-Big Fields of Jiangsu Province of China (Grant No. 1107020070)New Century Excellent Talents in University (NCET-05-0452)
文摘This paper reports that the high-quality Co-doped ZnO single crystalline films have been grown on a-plane sapphire substrates by using molecular-beam epitaxy. The as-grown films show high resistivity and non-ferromagnetism at room temperature, while they become more conductive and ferromagnetic after annealing in the reducing atmosphere either in the presence or absence of Zn vapour. The x-ray absorption studies indicate that all Co ions in these samples actually substituted into the ZnO lattice without formatting any detectable secondary phase. Compared with weak ferromagnetism (0.16 μB/Co2+) in the Zno.95 Co0.05 O single crystalline film with reducing annealing in the absence of Zn vapour, the films annealed in the reducing atmosphere with Zn vapour are found to have much stronger ferromagnetism (0.65 μB/Co2+) at room temperature. This experimental studies clearly indicate that Zn interstitials are more effective than oxygen vacancies to activate the high-temperature ferromagnetism in Co-doped ZnO films, and the corresponding ferromagnetic mechanism is discussed.
文摘This paper reports that the Zn0.95Co0.05O polycrystalline powder and thin film were prepared by sol-gel technique under the similar preparation conditions. The former does not show typical ferromagnetic behaviour, while the latter exhibits obvious ferromagnetic properties at 5 K and room temperature. The UV-vis spectra and x-ray absorption spectra show that Co2+ ions are homogeneously incorporated into ZnO lattice without forming secondary phases.The distinct difference between film and powder sample is the c-axis (002) preferential orientation indicated by the x-ray diffraction pattern and field emission scanning electron microscopy measurement, which may be the reason why Zn0.95Co0.05O film shows ferromagnetic behaviour.