Magnetic properties of Nd-Fe-B magnets with both Co and Al addition

Magnetic properties of Nd-Fe-B based magnets with both cobalt and aluminum addition have been investigated with respect to cobalt and aluminum concentration. Structural analyses were carried out for the sintered bodies. In cobalt containing alloys, Nd(Fe,Co)2phase was clearly observed by X-ray diffractometer, SEM and TEM, especially for the magnet with more than 30 at % cobalt. The coercive force behavior versus aluminum content for cobalt containing magnets can be divided into two stages. The first stage in which coercive force increases abruptly with the small amount addition of aluminum may result from Nd(Fe,Co)2phase being nonmagnetic by the addition of aluminum. The quantity of this Nd(Fe,Co)2phase increases with increasing cobalt content. It was shown that the greater the quantity of cobalt in the sintered body, the greater the addition of aluminum becomes necessary for obtaining high coercive force.