Off-axis electron holography of ferromagnetic multilayer nanowires

Azadeh Akhtari-Zavareh, L. P. Carignan, A. Yelon, D. Menard, Takeshi Kasama, R. Herring, Rafal E. Dunin-Borkowski, M. R. McCartney, K. L. Kavanagh

    Research output: Contribution to journalJournal articleResearchpeer-review

    Abstract

    We have used electron holography to investigate the local magnetic behavior of isolated ferromagnetic nanowires (NWs) in their remanent states. The NWs consisted of periodic magnetic layers of soft, high-saturation magnetization CoFeB alloys, and non-magnetic layers of Cu. All NWs were fabricated by pulsed-potential electrodeposition in nanoporous alumina membranes. The NW composition and layer thicknesses were measured using scanning transmission electron microscopy and energy dispersive spectroscopy. The magnetization of individual NWs depended upon the thicknesses of the layers and the direction of an external magnetic field, which had been applied in situ. When the CoFeB was thicker than the diameter (50 nm), magnetization was axial for all external field directions, while thinner layers could be randomized via a perpendicular field. In some cases, magnetization inside the wire was detected at an angle with respect to the axis of the wires. In thinner Cu/CoFeB ((<10 nm each) multilayer, magnetic field vortices were detected, associated with opposing magnetization in neighbouring layers. The measured crystallinity, compositions, and layer thicknesses of individual NWs were found to be significantly different from those predicted from calibration growths based on uniform composition NWs. In particular, a significant fraction of Cu (up to 50 at. %) was present in the CoFeB layers such that the measured magnetic induction was lower than expected. These results will be used to better understand previously measured effective anisotropy fields of similar NW arrays. © 2014 AIP Publishing LLC.
    Original languageEnglish
    Article number023902
    JournalJournal of Applied Physics
    Volume116
    Issue number2
    Number of pages11
    ISSN0021-8979
    DOIs
    Publication statusPublished - 2014

    Keywords

    • PHYSICS,
    • MAGNETIC NANOWIRES
    • NI NANOWIRES
    • THIN-FILMS
    • ARRAYS
    • REVERSAL
    • MEDIA
    • ELECTRON holography

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