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Synthesis and properties of Co–Pt alloy silica core-shell particles

  • Y. Kobayashi
  • H. Kakinuma
  • D. Nagao
  • Y. Ando
  • T. Miyazaki
  • M. Konno
Original Paper

Abstract

This paper describes a method for fabrication of silica-coated Co–Pt alloy nanoparticles in a liquid phase process. The Co–Pt nanoparticles were prepared from CoCl2 (4.2 × 10−5 M), H2PtCl6 (1.8 × 10−5 M), citric acid (4 × 10−4 M) and NaBH4 (1.2 × 10−2 M) with a Co:Pt mole ratio of 7:3. The silica coating was performed in water/ethanol solution with a silane coupling agent, 3-aminopropyltrimethoxysilane (8 × 10−5 M), and a silica source, tetraethoxyorthosilicate (7.2 × 10−4 M) in the presence of the Co–Pt nanoparticles. Observations with a transmittance electron microscope and a scanning transmission electron microscope revealed that the Co-rich and Pt-rich nanoparticles were coated with silica. According to X-ray diffraction measurements, core particles were crystallized to metallic Co crystallites and fcc Co–Pt alloy crystallites with annealing in air at 300–500 °C. Magnetic properties of the silica-coated particles were strongly dependent on annealing temperature. Maximum values of 11.4 emu/g-sample for saturation magnetization and 365 Oe for coercive field were obtained for the particles annealed at 300 and 500 °C, respectively. Annealing at a temperature as high as 700 °C destroyed the coating structures because of crystallization of silica shell, resulting in reduction in saturation magnetization and coercive field.

Keywords

Particle Alloy Co–Pt Silica Core-shell Sol–gel Coating Magnetic properties 

Notes

Acknowledgments

This research was partially supported by a Grant-in-Aid for Science Research (No. 15656163) and by the COE project, Giant Molecules and Complex Systems from the Ministry of Education, Culture, Sports, Science and Technology of Japan.

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Copyright information

© Springer Science+Business Media, LLC 2008

Authors and Affiliations

  • Y. Kobayashi
    • 1
    • 2
  • H. Kakinuma
    • 1
  • D. Nagao
    • 1
  • Y. Ando
    • 3
  • T. Miyazaki
    • 3
  • M. Konno
    • 1
  1. 1.Department of Chemical Engineering, Graduate School of EngineeringTohoku UniversitySendaiJapan
  2. 2.Department of Biomolecular Functional Engineering, College of EngineeringIbaraki UniversityHitachiJapan
  3. 3.Department of Applied Physics, Graduate School of EngineeringTohoku UniversitySendaiJapan

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