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Advances in Materials Science and Engineering
Volume 2017, Article ID 6412042, 12 pages
Research Article

A Combined TEM/STEM and Micromagnetic Study of the Anisotropic Nature of Grain Boundaries and Coercivity in Nd-Fe-B Magnets

1Institute of Solid State Physics, TU Wien, Wiedner Hauptstrasse 8-10, 1040 Vienna, Austria
2University Service Center for Transmission Electron Microscopy, TU Wien, Wiedner Hauptstrasse 8-10, 1040 Vienna, Austria
3Center for Integrated Sensor Systems, Danube University Krems, Viktor Kaplan Str. 2 E, 2700 Wiener Neustadt, Austria

Correspondence should be addressed to Josef Fidler;

Received 11 October 2016; Accepted 29 November 2016; Published 15 January 2017

Academic Editor: Jamal Berakdar

Copyright © 2017 Gregor A. Zickler et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The nanoanalytical high resolution TEM/STEM investigation of the intergranular grain boundary phase of anisotropic sintered and rapidly quenched heavy rare earth-free Nd-Fe-B magnet materials revealed a difference in composition for grain boundaries parallel (large Fe-content) and perpendicular (low Fe content) to the alignment direction. This behaviour vanishes in magnets with a high degree of misorientation. The numerical finite element micromagnetic simulations are based on the anisotropic compositional behaviour of GBs and show a decrease of the coercive field with an increasing thickness of the grain boundary layer. The magnetization reversal and expansion of reversed magnetic domains primarily start as Bloch domain wall at grain boundaries parallel to the -axis and secondly as Néel domain wall perpendicular to the -axis into the adjacent hard magnetic grains. The increasing misalignment of grains leads to the loss of the anisotropic compositional behaviour and therefore to an averaged value of the grain boundary composition. In this case the simulations show an increase of the coercive field compared to the anisotropic magnet. The calculated coercive field values of the investigated magnet samples are in the order of for a mean grain boundary thickness of 4 nm, which agrees perfectly with the experimental data.