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Advances in Materials Science and Engineering
Volume 2014, Article ID 760584, 7 pages
Research Article

Magnetic Behavior of Sintered NdFeB Magnets on a Long-Term Timescale

1Prizztech Oy, Magnet Technology Centre, 28100 Pori, Finland
2Tampere University of Technology, 28100 Pori, Finland
3Neorem Magnets Oy, 28400 Ulvila, Finland

Received 14 May 2013; Accepted 30 October 2013; Published 16 January 2014

Academic Editor: You Song

Copyright © 2014 Minna Haavisto 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.


Stable polarization of permanent magnets over the lifetime of the application is an important aspect in electrical machine design. Specification of the long-term stability of magnet material is difficult, since knowledge of the phenomenon is incomplete. To be able to optimize magnet material selection, the long-term magnetic behavior of the material must also be understood. This study shows that material with a very square JH curve is stable until a certain critical operating temperature is reached. Major losses are detected as the critical temperature is exceeded. Material with a rounder JH curve does not show a well-defined critical temperature, but increasing losses over a large temperature range. The critical temperature of a material is also dependent on the field conditions. Results differ whether the tests are performed in an open or closed magnetic circuit. In open-circuit tests, the opposing field is not homogeneously distributed throughout the volume of the magnet and thus the long-term behavior is different than that in closed-circuit conditions. Open-circuit tests seem to give bigger losses than closed-circuit tests in cases where the permeance coefficient of the open-circuit sample is considered to be the average permeance coefficient, calculated according to the dimensions of the magnet.