Visualization of vortex core polarity in NiFe nanodots by tilted Fresnel images

Duc-The Ngo, Stephen McVitie

Research output: Contribution to journalJournal articleResearchpeer-review


We illustrate an approach which allows determining the out-of-plane component of the vortex core (polarity) in NiFe nanodots using Fresnel imaging in Lorentz electron microscopy. Using tilted Fresnel images, contribution of the polarity is introduced into the Fresnel image. However, this contribution is relatively small and a difference image from two symmetrically tilted Fresnel images must be used to eliminate the strong contribution from the in-plane curling magnetization and non-magnetic contrast. The sense of the polarity appears as a bipolar white–black contrast in the difference image on the tilt axis. A vortex core with a diameter of 16.5±2.5nm is experimentally measured. Image tilting, displacement and geometrical distortion may disturb the difference image, and hence subtraction of the difference image must be aligned by cross-correlation. The method is also justified by a study of the observed contrast characteristic due to misalignment. The method is confirmed to be superior to similar approach with direct interpretation of information and more information subtracted.
Original languageEnglish
Issue number8
Pages (from-to)1276-1285
Publication statusPublished - 2011
Externally publishedYes


  • Magnetic thin film
  • Domain walls and domain structure
  • Magnetic vortex
  • Lorentz microscopy
  • Fresnel image


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