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High Performance Magnets - Microstructure and Coercivity

Published online by Cambridge University Press:  21 February 2011

J. Fidler ,
S. Sasaki  and
E. Estevez-Rams
J. Fidler
Affiliation:
Vienna University of Technology, Institute of Applied and Technical Physics, Wiedner Hauptstr. 8-10, A-1040 Wien, Austria, http://atp6000.tuwien.ac.at/MAGNET/
S. Sasaki
Affiliation:
Vienna University of Technology, Institute of Applied and Technical Physics, Wiedner Hauptstr. 8-10, A-1040 Wien, Austria, http://atp6000.tuwien.ac.at/MAGNET/
E. Estevez-Rams
Affiliation:
Vienna University of Technology, Institute of Applied and Technical Physics, Wiedner Hauptstr. 8-10, A-1040 Wien, Austria, http://atp6000.tuwien.ac.at/MAGNET/
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Abstract

The importance of newly developed permanent magnetic materials in many electro-, magnetomechanical and electronic applications can be attributed to the drastic improvement of the magnetic energy density product and coercive field. A systematic study has been undertaken in order to determine the influence of oxygen content on microstructure and coercivity of high remanence Nd2Fe14B based sintered magnets. The energy density product >400 kJ/m3 (50 MGOe) and the coercive field of 800 kA/m were obtained after a combination of rubber isostatic and transverse die pressing methods. Magnets of the composition Nd151−xFe78+xB6Cu0.03A10.7 [x= 0-2.5] were prepared using strip cast materials. The high oxygen content of the magnets was gradually decreased from values of 4000-6000 ppm to a value < 1000 ppm. Abnormal grain growth (AGG) of the 2:14:1 grains occurred preferentially in magnets with low oxygen content, thus the squareness of the demagnetisation curve drastically decreased. The oxygen content strongly affects the AGG and the magnets with higher oxygen content have the higher critical temperatures at which the AGG occurs. On the other hand, isotropic magnets tend to have the lower critical temperatures than anisotropic magnets by 10-20°C. In the second part of the paper examples of the influence of intergranular phases, grain size and grain shape observed by TEM on coercivity of sintered and melt-spun Nd-Fe-B magnets are compared.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 577: Symposium H – Advanced Hard and Soft Magnetic Materials , 1999 , 291
Copyright
Copyright © Materials Research Society 1999

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