Structure and compositional evolution in epitaxial Co/Pt core-shell nanoparticles on annealing

Kazuhisa Sato, Keigo Yanajima, Toyohiko J. Konno

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)

Abstract

We report on the alloying of epitaxial Co/Pt core-shell nanoparticles using transmission electron microscopy (TEM) and electron diffraction. In as-deposited nanoparticles followed by in situ annealing at 823 K for 10.8 ks, high-angle annular dark-field (HAADF) imaging by scanning TEM (STEM) clearly revealed formation of Co-shell/Pt-core structures due to the large atomic number (Z) difference between Co (Z = 27) and Pt (Z = 78). We identified a formation of locally ordered areas of the L1 0 ordered phase at the core of the nanoparticles. After ex situ annealing at 873 K for 0.6 ks, some of the ordered areas showed complicated contrasts in the HAADF-STEM images. Based on image simulations, we found that these atypical contrasts arise from the stacking of two orthogonal variants of the L1 0 phase in the electron beam direction. Furthermore, the simulation showed that image contrast strongly reflects the structure of the variant located closer to the beam entrance rather than to the bottom side. Solid solution phase was formed by further annealing at 873 K for 3.6 ks, while high-density {111} stacking faults were observed inside the Co-Pt alloy nanoparticles. Magnetic coercivity remained at values as low as ∼ 15.9 kA/m at 300 K, irrespective of the formation of local L1 0 ordered areas and/or a high-density stacking faults.

Original languageEnglish
Pages (from-to)3544-3552
Number of pages9
JournalThin Solid Films
Volume520
Issue number9
DOIs
Publication statusPublished - 2012 Feb 29

Keywords

  • Alloying
  • Atomic ordering
  • Cobalt-Platinum
  • Core-shell particles
  • Stacking faults

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Metals and Alloys
  • Materials Chemistry

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