Room Temperature Ferromagnetism in Vacuum-Annealed CoO Nanospheres

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• 作者：Guijin Yang ; Daqiang Gao ; Zhenhua Shi ; Zhaohui Zhang ; Jing Zhang ; Jinlin Zhang ; Desheng Xue
• 刊名：Journal of Physical Chemistry C
• 出版年：2010
• 出版时间：December 23, 2010
• 年：2010
• 卷：114
• 期：50
• 页码：21989-21993
• 全文大小：272K
• 年卷期：v.114,no.50(December 23, 2010)
• ISSN：1932-7455

文摘

Single-crystalline CoO nanospheres with the size distribution between 40 and 250 nm were prepared by a solvothermal method. Magnetic measurements indicate that the vacuum-annealed samples show room temperature ferromagnetism except for the CoO nanospheres of 250 nm, which still exhibit paramagnetism after being postannealed in vacuum atmosphere (10⁻³ Pa) at 250 °C as others. The saturation magnetization of all postannealed samples monotonically increases with the decrease of nanosphere diameter. No other impurity phases are observed for the postannealed samples, indicating that the revealed ferromagnetism is an intrinsic property. The fitted XPS results of O 1s spectra indicate that the variations of oxygen vacancies concentration are consistent with the variations of saturation magnetization for the vacuum-annealed samples, suggesting that the formed oxygen vacancies at the surface of the CoO nanospheres during the vacuum-annealing process account for the observed ferromagnetism.