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Coercivity of hard magnetic materials

Permanent magnets based on the iron(14)neodymium(2)boron intermetallic compound have been produced by the 4 different techniques sintering, melt spinning, extrusion and mechanical alloying. Due to the deteriorating effects of the microstructure these different techniques have so far led to only 10-20% of the theoretically achievable coercive field. Investigations of magnetisation processes, hysteresis loops, magnetic after effects and domain patterns have been performed on these different materials as a function of temperature and different types of pretreatment. These magnetic measurements have been combined with studies of the microstructure by transmission electron microscopy. In particular, the role of nonmagnetic precipitation, misaligned grains, incompletely magnetically decoupled grains, structure of the intergranular phase have been studied in detail. From a comparison of the different types of permanent magnets a deeper insight into the role of the microstructure with respect to their hard magnetic properties has been obtained. Combining the results of the microstructural and the micromagnetic analysis of the different types of permanent magnets the procedures for optimising the coercive field have been determined.
The above mentioned types of magnets have been prepared with different compositions and additive elements. Melt spun materials have been prepared and analysed in a wide range of preparation parameters. By a well defined optimisation of the microstructure the coercive field of a melt spun iron(72)neodymium(17)boron(7.5)gallium(1.5)niobium magnet could be increased up to 940 kAm{-1} at a temperature of 150 C.

Reported by

Max-Planck-Institut fuer Metallforschung
Heisenbergstrasse 1
70569 Stuttgart
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