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High-performance permanent magnets (pms) are based on compounds with outstanding intrinsic magnetic properties as well as on optimized microstructures and alloy compositions. The most powerful pm materials at present are RE-TM intermetallic alloys which derive their exceptional magnetic properties from the favourable combination of rare earth metals (RE = Nd, Pr, Sm) with transition metals (TM = Fe, Co), in particular magnets based on (Nd.Pr)2Fe14B and Sm2(Co,Cu,Fe,Zr)17. Their development during the last 20 years has involved a dramatic improvement in their performance by a factor of > 15 compared with conventional ferrite pms therefore contributing positively to the ever-increasing demand for pms in many (including new) application fields, to the extent that RE-TM pms now account for nearly half of the worldwide market. This review article first gives a brief introduction to the basics of ferromagnetism to confer an insight into the variety of (permanent) magnets, their manufacture and application fields. We then examine the rather complex relationship between the microstructure and the magnetic properties for the two highest-performance and most promising pm materials mentioned. By using numerical micromagnetic simulations on the basis of the Finite Element technique the correlation can be quantitatively predicted, thus providing a powerful tool for the further development of optimized high-performance pms.

Rapidly quenched Sm(CobalCu0.08Fe0.22Zr0.02)8.5 (Cu-/Fe-rich) and Sm(CobalCu0.05Fe0.10Zr0.03)8.5 (Cu-/Fe-poor) ribbons have been prepared by means of the melt-spinning technique. By applying an appropriate annealing procedure a microstructure similar to that of sintered magnets can be obtained. The energy dispersive x-ray microanalysis of the compositional dependence near the cell boundaries suggests a model for the profile of the crystal anisotropy constants responsible for the magnetic hardening. The Cu-/Fe-rich alloy shows a normal temperature dependence of coercivity with a negative temperature coefficient, but the Cu-/Fe-poor ribbons show a positive temperature coefficient in the temperature range from 400–700 K. The different temperature coefficients are discussed in terms of a pinning model.