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Title: Off-axis electron holography of ferromagnetic multilayer nanowires

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 CoFeBmore » 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.« less

Authors:
;  [1];  [2];  [3];  [3]; ;  [4];  [5];  [6];  [7];  [8]
  1. Department of Physics, Simon Fraser University, Burnaby, British Columbia V5A1S6 (Canada)
  2. Apollo Microwaves, 1650 Trans-Canada Highway, Dorval, Quebec H9P 1H7 (Canada)
  3. (Canada)
  4. Department of Engineering Physics, École Polytechnique de Montréal, Montréal, Quebec, H3C 3A7 Canada (Canada)
  5. Center for Electron Nanoscopy, Technical University of Denmark, DK-2800 Kongens Lyngby (Denmark)
  6. Department of Mechanical Engineering, University of Victoria, Victoria, British Columbia V8W 3P6 (Canada)
  7. Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Institute for Microstructure Research, D-52425 Jülich (Germany)
  8. Department of Physics, Arizona State University, Tempe, Arizona 85287-1504 (United States)
Publication Date:
OSTI Identifier:
22308968
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 116; Journal Issue: 2; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
77 NANOSCIENCE AND NANOTECHNOLOGY; ANISOTROPY; BORON COMPOUNDS; COBALT COMPOUNDS; COPPER; ELECTRODEPOSITION; FERROMAGNETIC MATERIALS; HOLOGRAPHY; IRON COMPOUNDS; LAYERS; MAGNETIC FIELDS; MAGNETIZATION; MEMBRANES; NANOWIRES; PERIODICITY; QUANTUM WIRES; SATURATION; SPECTROSCOPY; TERNARY ALLOY SYSTEMS; THICKNESS; TRANSMISSION ELECTRON MICROSCOPY

Citation Formats

Akhtari-Zavareh, Azadeh, Kavanagh, K. L., Carignan, L. P., Department of Engineering Physics, École Polytechnique de Montréal, Montréal, Quebec, H3C 3A7 Canada, Department of Electrical Engineering, École Polytechnique de Montréal, Montréal, Quebec, H3C 3A7 Canada, Yelon, A., Ménard, D., Kasama, T., Herring, R., Dunin-Borkowski, R. E., and McCartney, M. R. Off-axis electron holography of ferromagnetic multilayer nanowires. United States: N. p., 2014. Web. doi:10.1063/1.4887488.
Akhtari-Zavareh, Azadeh, Kavanagh, K. L., Carignan, L. P., Department of Engineering Physics, École Polytechnique de Montréal, Montréal, Quebec, H3C 3A7 Canada, Department of Electrical Engineering, École Polytechnique de Montréal, Montréal, Quebec, H3C 3A7 Canada, Yelon, A., Ménard, D., Kasama, T., Herring, R., Dunin-Borkowski, R. E., & McCartney, M. R. Off-axis electron holography of ferromagnetic multilayer nanowires. United States. doi:10.1063/1.4887488.
Akhtari-Zavareh, Azadeh, Kavanagh, K. L., Carignan, L. P., Department of Engineering Physics, École Polytechnique de Montréal, Montréal, Quebec, H3C 3A7 Canada, Department of Electrical Engineering, École Polytechnique de Montréal, Montréal, Quebec, H3C 3A7 Canada, Yelon, A., Ménard, D., Kasama, T., Herring, R., Dunin-Borkowski, R. E., and McCartney, M. R. Mon . "Off-axis electron holography of ferromagnetic multilayer nanowires". United States. doi:10.1063/1.4887488.
@article{osti_22308968,
title = {Off-axis electron holography of ferromagnetic multilayer nanowires},
author = {Akhtari-Zavareh, Azadeh and Kavanagh, K. L. and Carignan, L. P. and Department of Engineering Physics, École Polytechnique de Montréal, Montréal, Quebec, H3C 3A7 Canada and Department of Electrical Engineering, École Polytechnique de Montréal, Montréal, Quebec, H3C 3A7 Canada and Yelon, A. and Ménard, D. and Kasama, T. and Herring, R. and Dunin-Borkowski, R. E. and McCartney, M. R.},
abstractNote = {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.},
doi = {10.1063/1.4887488},
journal = {Journal of Applied Physics},
number = 2,
volume = 116,
place = {United States},
year = {Mon Jul 14 00:00:00 EDT 2014},
month = {Mon Jul 14 00:00:00 EDT 2014}
}
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