Structural and Magnetic Properties of Gold and Silica Doubly Coated -Fe2O3 Nanoparticles

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• 作者：Keeseong Park ; Gan Liang ; Xiaojun Ji ; Zhi-Ping Luo ; Chun Li ; Mark C. Croft ; John T. Markert
• 刊名：Journal of Physical Chemistry C
• 出版年：2007
• 出版时间：December 20, 2007
• 年：2007
• 卷：111
• 期：50
• 页码：18512 - 18519
• 全文大小：940K
• 年卷期：v.111,no.50(December 20, 2007)
• ISSN：1932-7455

文摘

Extensive structural and magnetic characterization measurements were carried out on gold and silica doublycoated -Fe₂O₃ nanoparticles, which were recently demonstrated to have an efficient photothermal effect andhigh transverse relaxivities for MRI applications. Powder X-ray diffraction and X-ray absorption spectroscopyshow the phase of the uncoated and coated nanoparticles to be that of the -Fe₂O₃ structure. The sizes, structure,and chemical compositions of the nanoparticles were determined by transmission electron microscopy. Themagnetization results indicate that coating of the iron oxide nanoparticles by gold/silica decreases the blockingtemperature from 160 to 80 K. Such a decrease can be well-explained by spin disorder, causing reduction ofthe effective volume of the -Fe₂O₃ core. Moreover, it was found that in the temperature (T) range between100 K and room temperature, the gold/silica coating can cause a slight magnetic change in the -Fe₂O₃ coresfrom superparamagnetic to almost superparamagnetic. Finally, it was found that the coercivity for both theuncoated and the coated nanoparticles decreases almost linearly with T^1/2 with the former decreasing fasterthan the latter, and this coercivity result confirms that the blocking temperature is decreased by gold/silicacoating. These results are valuable for evaluating the future applications of this class of multifunctional,hybrid magnetic nanoparticles in biomedicine.