Elaboration, characterisation, and magnetic properties of cobalt fine particles

M. Respaud, J. M. Broto, L. Thomas, B. Barbara, H. Rakoto, M. Goiran, A. R. Fert, E. Snoeck, M. Verelst, P. Lecante, J. Osuna, T. Ould Ely, C. Amiens, B. Chaudret

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)

Abstract

Nanoparticles of cobalt have been prepared by an original method using the decomposition under hydrogen of an organometallic precursor in the presence of a stabilizing polymer. Two colloïds (C1, C2) have been obtained by changing the organometallic concentration in the polymer. Observation by HRTEM and WAXS showed that Co particles have diameter around 1.5 nm (C1) and 2 nm (C2). They are well isolated and regularly scattered in the polymer, with an original bcc structure. These particles show a superparamagnetic behavior above the blocking temperature (TB). Analysis of the magnetization curves above TB confirms the very weak volume dispersion of the particles centered around 150±10 atoms (C1) and 310±20 atoms (C2), and their homogeneous distribution in the polymer observed by HRTEM. Enhanced effective anisotropy energy with uniaxial symmetry has been deduced from magnetization and ferromagnetic resonance measurements in the FIR range (100-700 Ghz). Magnetization at 5 K seems to saturate in fields up to 5 T leading to an enhanced mean magnetic moment per atom, <μCo> = 1.94±0.05 μB for the smallest particles. These values still increase in field up to 35T reaching <μCo> = 2.1±0.1 μB (C1), exhibiting a canted spin structure due to high surface anisotropy. This set of data allows us to conclude that the enhanced magnetization, its increase with applied magnetic field, and the enhanced effective magnetic anisotropy, these effects being more significant with decreasing size, are associated to the large influence of the surface atoms.

Original languageEnglish
Pages (from-to)949-954
Number of pages6
JournalMaterials Science Forum
Volume269-272
Issue numberPART 2
Publication statusPublished - Dec 1 1998

Keywords

  • FMR
  • Fine Particle
  • High fields
  • Magnetic Anisotropy
  • Magnetization
  • Surface Effects

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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