Influence of reducing anneal on the ferromagnetism in single crystalline Co-doped ZnO thin films |
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| Authors: | Lu Zhong-Lin Zou Wen-Qin Xu Ming-Xiang and ZhangFeng-Ming |
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| Affiliation: | Department of Physics, Southeast University, Nanjing 210096, China; Physics Department and Institute of Innovations and Advanced Studies (IIAS), National Cheng Kung University, Tainan 701, China; Jiangsu Provincial Laboratory for Nanotechnology, National Laboratory of Solid State Microstructure, and Department of Physics, Nanjing University, Nanjing 210093, China |
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| Abstract: | 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 good 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~$\mu _{\rm B}$/Co$^{2 + })$ in the Zn$_{0.95}$Co$_{0.05}$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~$\mu _{\rm
B}$/Co$^{2 + })$ 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. |
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| Keywords: | Co-doped ZnO diluted magnetic semiconductors x-ray
absorption fine structure single crystalline thin films |
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