Electron Holography of Nanostructured Magnetic Materials
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M. R. SCHEINFEINef, DAVID J. SMITHa'e aCenter for Solid State Science, Arizona State University, Tempe, AZ 85287-1704 Now at: Department of Materials, University of Oxford, Parks Road, Oxford OXI 3PH, UK Center For Solid State Electronics Research, Arizona State University, Tempe, AZ 85287-6206 Now at: Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX I 3PU, UK e Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287-1504 at: FEI, SNow 7451 NW Evergreen Parkway, Hillsboro, OR 97124 ABSTRACT Off-axis electron holography and micromagnetic calculations that involve solutions to the Landau-Lifshitz-Gilbert equations are used to study magnetization reversal processes in lithographically patterned submicron-sized Co and Co/Au/Ni magnetic elements. INTRODUCTION A detailed understanding of magnetic nanostructures is essential for their utilization in information storage applications such as high density recording media and read heads. Such applications require reproducible magnetic domain structures and a good understanding of the interactions between neighboring elements. Here, we use off-axis electron holography in the transmission electron microscope (TEM) [1] to study the magnetic microstructure of submicronsized elements that have been patterned lithographically onto electron transparent Si3N4 windows. We then compare our results with solutions to the Landau-Lifshitz-Gilbert equations [2]. The microscope geometry for off-axis electron holography and the approach used to obtain the phase of the holographic interference fringes, which is sensitive to the in-plane component of the magnetic induction integrated in the incident beam direction, are shown in Figs. la and lb,
respectively. Further details about the application of the technique can be found elsewhere [3]. Off-axis electron holograms were recorded at 200 kV using a Philips CM200-FEG TEM equipped with a field-emission electron source, an electrostatic (rotatable) biprism located in the selected-area aperture plane and a 1024x1024 pixel Gatan 794 multi-scan CCD camera. An additional Lorentz minilens (Cs = 8m and 1.2 nm line resolution at 200 kV), located in the bore of the objective lens pole-piece, allowed images to be obtained with the main objective lens switched off and the sample located in almost field-free conditions. The objective lens could also be excited slightly and the sample tilted by up to ±300 in order to apply a known in-plane magnetic field, allowing magnetization processes to be followed in situ through hysteresis cycles. Reference holograms were acquired from the adjacent silicon nitride to remove artifacts caused by local irregularities of the image/recording system, and the mean inner potential contribution to the holographic phase was always subtracted to obtain the magnetic contribution of primary interest [3].
13 Mat. Res. Soc. Symp. Proc. Vol. 589 @2001 Materials Research Society
a)
Lorentz lens
b)
FEG
Sample Fourier transform
Biprism
Phase
Fig.1. a) Setup used to generate off-axis elect
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