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Off-Axis Electron Holography of Self-Assembled Co Nanoparticle Rings

Published online by Cambridge University Press:  01 February 2011

Takeshi Kasama ,
Rafal E. Dunin-Borkowski ,
Michael R. Scheinfein ,
Steven L. Tripp ,
Jie Liu  and
Alexander Wei
Takeshi Kasama
Affiliation:
tk305@cam.ac.uk, University of Cambridge, Materials Science and Metallurgy, Pembroke Street, Cambridge, CB2 3QZ, United Kingdom
Rafal E. Dunin-Borkowski
Affiliation:
rdb@cen.dtu.dk, Technical University of Denmark, Center for Electron Nanoscopy, Kongens Lyngby, DK-2800, Denmark
Michael R. Scheinfein
Affiliation:
llgmicro@mindspring.com, Simon Fraser University, Department of Physics, Burnaby, BC, V5A 1S6, Canada
Steven L. Tripp
Affiliation:
Steven.Tripp@indwes.edu, Purdue University, Department of Chemistry, West Lafayette, IN, 47907, United States
Jie Liu
Affiliation:
jieliu@purdue.edu, Purdue University, Department of Chemistry, West Lafayette, IN, 47907, United States
Alexander Wei
Affiliation:
alexwei@purdue.edu, Purdue University, Department of Chemistry, West Lafayette, IN, 47907, United States
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Abstract

We use off-axis electron holography in the transmission electron microscope (TEM) to study magnetic flux closure (FC) states in self-assembled nanoparticle rings that each contain between five and eleven 25-nm-diameter Co crystals. Electron holograms are acquired at room temperature in zero-field conditions after applying chosen magnetic fields to the samples in situ in the TEM by partially exciting the conventional microscope objective lens. Mean inner potential contributions to the phase shift are determined by turning the samples over, and subsequently subtracted from each recorded phase image to obtain magnetic induction maps. Our results show that most nanoparticle rings form FC remanent magnetic states, and occasionally onion-like states. Although the chiralities (the directions of magnetization) of the FC states are determined by the shapes, sizes and positions of the constituent nanoparticles, reproducible magnetization reversal of each ring can be achieved by using an out-of-plane magnetic field of between 1600 and 2500 Oe.

Keywords

Comagnetic propertiestransmission electron microscopy (TEM)
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1026: Symposium C – Quantitative Electron Microscopy for Materials Science , 2007 , 1026-C18-03
Copyright
Copyright © Materials Research Society 2008

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