Growth and atomic ordering of hard magnetic L10-FePt, FePd and CoPt alloy nanoparticles studied by transmission electron microscopy: Alloy system and particle size dependence

Yoshihiko Hirotsu, Kazuhisa Sato

    Research output: Contribution to journalArticlepeer-review

    22 Citations (Scopus)

    Abstract

    Atomic ordering of 10-nm-sized L10-FePt, FePd and CoPt nanoparticles have been studied by transmission electron microscopy and electron diffraction. Proceeding of the atomic ordering was confirmed by the increase of coercivity as well as electron diffraction. Among these three kinds of L1 0 nanoparticles, the atomic ordering reaction proceeded at the lowest temperature as low as 773 K for FePd nanoparticles. Coercivities of FePt and FePd nanoparticles largely increased with particle diameter and reached 10 kOe for 20-nm-sized FePt particles at room temperature. The large coercivity is attributed to the rotation magnetization of single-domain particles. For CoPt nanoparticles the observed coercivity was very small even after annealing at 1023 K for 1h. The slow rate of the L10 ordering can be attributed to the lowest Tc/Tm value in CoPt nanoparticles. L1 0 ordering was also confirmed even in very small FePt particles as small as 2-3 nm in diameter. By contrast, FePd nanoparticles with sizes less than 5 nm showed disordered fcc even after annealing at 873 K. The coercivity of 4-nm-sized L10-FePt nanoparticles were quite low and the observed largest coercivity was 490 Oe at 10 K after annealing at 873 K for 12 h.

    Original languageEnglish
    Pages (from-to)236-244
    Number of pages9
    JournalJournal of Ceramic Processing Research
    Volume6
    Issue number3
    Publication statusPublished - 2005

    Keywords

    • Atomic ordering
    • CoPt
    • Electron diffraction
    • FePd
    • FePt
    • L1 structure
    • Large coercivity
    • Nanoparticle
    • TEM

    ASJC Scopus subject areas

    • Ceramics and Composites

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