Tuning the Magnetic Properties of Metal Oxide Nanocrystal Heterostructures by Cation Exchange

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• 作者：Mykhailo Sytnyk ; Raimund Kirchschlager ; Maryna I. Bodnarchuk ; Daniel Primetzhofer ; Dominik Kriegner ; Herbert Enser ; Julian Stangl ; Peter Bauer ; Michael Voith ; Achim Walter Hassel ; Frank Krumeich ; Frank Ludwig ; Arno Meingast ; Gerald Kothleitner ; Maksym V. Kovalenko ; Wolfgang Heiss
• 刊名：Nano Letters
• 出版年：2013
• 出版时间：February 13, 2013
• 年：2013
• 卷：13
• 期：2
• 页码：586-593
• 全文大小：582K
• 年卷期：v.13,no.2(February 13, 2013)
• ISSN：1530-6992

文摘

For three types of colloidal magnetic nanocrystals, we demonstrate that postsynthetic cation exchange enables tuning of the nanocrystal鈥檚 magnetic properties and achieving characteristics not obtainable by conventional synthetic routes. While the cation exchange procedure, performed in solution phase approach, was restricted so far to chalcogenide based semiconductor nanocrystals, here ferrite-based nanocrystals were subjected to a Fe²⁺ to Co²⁺ cation exchange procedure. This allows tracing of the compositional modifications by systematic and detailed magnetic characterization. In homogeneous magnetite nanocrystals and in gold/magnetite core shell nanocrystals the cation exchange increases the coercivity field, the remanence magnetization, as well as the superparamagnetic blocking temperature. For core/shell nanoheterostructures a selective doping of either the shell or predominantly of the core with Co²⁺ is demonstrated. By applying the cation exchange to FeO/CoFe₂O₄ core/shell nanocrystals the Ne茅l temperature of the core material is increased and exchange-bias effects are enhanced so that vertical shifts of the hysteresis loops are obtained which are superior to those in any other system.

Keywords:

magnetic nanocrystals; cation exchange; exchange bias; nanoheterostructures; ferrites