Evolution of Morphology and Magnetic Properties in Silica/Maghemite Nanocomposites

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• 作者：Dan Li ; Wey Yang Teoh ; Robert C. Woodward ; John D. Cashion ; Cordelia Selomulya ; Rose Amal
• 刊名：Journal of Physical Chemistry C
• 出版年：2009
• 出版时间：July 16, 2009
• 年：2009
• 卷：113
• 期：28
• 页码：12040-12047
• 全文大小：324K
• 年卷期：v.113,no.28(July 16, 2009)
• ISSN：1932-7455

文摘

The morphological evolution of SiO₂/γ-Fe₂O₃ nanocomposites was systematically synthesized in a one-step flame spray pyrolysis. Under these conditions, a gradual transformation from discrete γ-Fe₂O₃ nanoparticles to thin SiO₂ coatings, segregated single γ-Fe₂O₃ core, and multiple γ-Fe₂O₃ cores within a SiO₂ matrix was obtained as a function of SiO₂ loading. The presence of SiO₂ up to 13% has a pronounced effect on the γ-Fe₂O₃ crystallite structure (transforming from P4₁32 to Fdm space group) and its cationic vacancy ordering. Decrease in the latter was further reflected through the intrinsic magnetic properties of the γ-Fe₂O₃ cores (i.e., decreasing specific saturation magnetization and increasing coercivity and exchange bias). Deviation from the magnon-type thermal dependence, T^3/2 Bloch law, was observed for nanocomposites with SiO₂ content above 13%. The M_s vs T curves could be fitted with the sum of an exponential component and a Bloch law component, where the magnitude of the exponential component increased with increasing SiO₂ content above 13% SiO₂. The thermal dependence of the saturation magnetization for these samples could not be adequately explained by a finite size effect or via freezing of canted spins.