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

Y. Kobayashi, H. Kakinuma, D. Nagao, Y. Ando, T. Miyazaki, Mikio Konno

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)


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 × 10-5M), H2PtCl 6 (1.8 × 10-5M), citric acid (4 × 10 -4M) and NaBH4 (1.2 × 10-2M) 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 -5M), and a silica source, tetraethoxyorthosilicate (7.2 × 10-4M) 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.

Original languageEnglish
Pages (from-to)16-22
Number of pages7
JournalJournal of Sol-Gel Science and Technology
Issue number1
Publication statusPublished - 2008 Jul


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

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Chemistry(all)
  • Biomaterials
  • Condensed Matter Physics
  • Materials Chemistry


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