Fabrication of Core-shell Type FeCo-Au (Ag) High Moment Magnetic Nanoparticles
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Fabrication of Core-shell Type FeCo-Au (Ag) High Moment Magnetic Nanoparticles Jianmin Bai, Yunhao Xu, Jian-Ping Wang１ MINT Center, Department of Electrical & Computer Engineering, University of Minnesota, 200 Union St. SE, Minneapolis, MN 55455, USA Abstract We developed a physical vacuum deposition technique combining an on-line sputtering/evaporation process with an integrated nanocluster deposition process to prepare core-shell type nanoparticles. High magnetic moment (Fe60Co40)coreAushell and (Fe60Co40)coreAgshell superparamagnetic nanoparticles with controllable particle size of 10 – 20 nm and Au/Ag shell thickness of 1 – 3 nm were prepared successfully by using this method. Au shell is not only functional for the potential biocompatibility but also the key to prevent the oxidation of FeCo nanoparticles. Saturation magnetization of (Fe60Co40)coreAushell nanoparticles was found three times higher than that of iron oxide nanoparticles. This novel technique enables us to control independently the dimensions of core and shell and select individually materials for core and shell for any other core-shell type nanoparticles. Introduction The core-shell type magnetic nanoparticles are receiving a lot of attention because this heterostructure offers opportunities to develop devices and materials with new functions for magnetic recording, bio and medical applications.1-9 Especially, superparamagnetic nanoparticles with suitable biocompatible coatings are becoming important in the fields of biology, biotechnology and other biomedical disciplines. Applications include gene cloning, tissue engineering, drug delivery/targeting, magnetic resonance imaging, biological magnetic separation, and so on.2-9 The techniques for coating magnetic nanoparticles by biocompatible layers have been widely studied.3,6,10-12,13-22 The magnetic nanoparticles are required to possess uniform particle shape, narrow size distribution, good corrosion resistance, and high magnetic moment.4,5 So far superparamagnetic iron-based oxide nanoparticles are being widely used in these areas.2,9,24-28 Oxide type magnetic nanoparticles can be synthesized by various techniques, but their saturation magnetization is very low (σs ≈ 80 emu/g). High saturation magnetization materials are generally compounds or alloys, such as FeCo (σs ≈ 235 emu/g) which is one of materials with highest saturation magnetization.29 These materials cannot be directly used in bio or other applications because the concerns of oxidation and corrosion. A design of core-shell type nanoparticles consisting of high-moment (high saturation magnetization) superparamagnetic nanoparticles and protective thin shells which are biocompatible is a good solution for these problems. Usually, the chemistry methods are being widely employed to synthesize core-shell nanoparticles in solution environment.30-33. To the best of our knowledge, there is no report on fabrication of core-shell nanoparticles with controllable shell materials using a physical deposition method. A good environment for fa
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