ULTRAFINE ALLOYS MAKE THEIR MARK

The surprising properties of magnetic alloys with nanometer-sized grains are being used to design better permanent magnets. The alloys based on neodymium-iron-boron have a complex tetragonal crystal structure. They have been developed progressively so that commercial magnets made from these alloys now have (BH) max values of up to 360 kJ m-3. The discovery of the phenomenon of exchange coupling and remanence enhancement in these alloys and the accompanying improvements in properties are described.