Synthesis and Characterization of FeCoNiAl Nanocapsules by Plasma arc Discharge Process
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Woo-Young Park, Jin-Chun Kim, Ji-Hun Yu, and Chul-Jin Choi Korea Institute of Machinery and Materials, Changwon, Kyungnam 641-010, South Korea
Zhi-Dong Zhang Shenyang National Laboratory for Materials Science, Institute of Metal Research, and International Centre for Materials Physics, Chinese Academy of Sciences, Shenyang 110016, People’s Republic of China (Received 1 October 2004; accepted 7 June 2005)
A series of magnetic FeCoNiAl nanocapsules was synthesized by the plasma arc discharge method; the targets of Fe, Co, Ni, and Al powders were changed with varying compositions. The compositions of the nanocapsules were found to be quite different from those of the corresponding targets; the relative amount of Al (or Ni, Co) to Fe was increased (or decreased). Structures, particles sizes, composition, surface composition, magnetic properties, and thermal stability of the nanocapsules were investigated. The saturation magnetization Ms ⳱ 106.8 emu/g and coercive force iHc ⳱ 367 Oe were achieved for the nanocapsules with the Fe62.5Co21Ni13Al2.5 target. In the FeCoNiAl nanocapsules, the binding energies of Fe, Co, and Ni were different from those of the metals Fe, Co, and Ni. The binding energies of Fe2p3/2 and Fe2p1/2 of the nanocapsules were 708.2 and 721.3 eV, respectively. The four-layer structure was proposed to give a clear statement of how the composition and phase varied radially in the nanocapsules. The major contents of the four layers—i.e., the outer shell, the inner shell, the outer core and the inner core—were amorphous alumina, crystalline alumina, transition metal oxides, and transition metal alloy, respectively. The compositions, structures, particle size, and grain size of the nanocapsules all affect their magnetic properties. In the FeCoNiAl nanocapsules, the greater th amount of the body-centered-cubic phase, the stronger the ferromagnetic magnetic properties.
I. INTRODUCTION
Nanocapsules are composed of a core and a shell that are made of different materials.1 In the last two decades, nanocapsules have attracted great attention for their novel properties, which can be greatly different from those of bulk materials. The magnetic, optical, catalytic, and electronic properties of the nanocapsules show strong dependence on the composition, size, shape, structure, and surface composition. Nanoparticles, such as Fe(C), 2,3 Fe–Co(C), 4,5 Fe–Ni (C), 6 FeCoNi, 7 and
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0304 2534
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 9, Sep 2005 Downloaded: 14 Mar 2015
FeCoNiAl,8,9 etc., which possess unique properties, were prepared by the plasma arc discharge (PAD) method. Fe, Co, and Ni are the most important elements among transition metals as magnetic materials. Alnico alloys, having high Curie temperature (Tc) and excellent oxidation resistance, have been widely applied as well-known permanent magnetic materials. The Al2O3-coated ␣–Fe solid-solution nanocapsules prepared in our previous work by arc discha
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