Heavy rare earth metals (HRE) such as Dy and Tb have for many years been used as a standard substitute for Nd, in order to increase the intrinsic coercive field strength HcJ and thereby the temperature stability of sintered NdFeB magnets. Due to the high costs of these HRE metals, there is a strong demand for reducing the HRE content by increasing the coercive field strength of NdFeB magnets in other ways. One way of increasing the coercive field strength of HRE free magnets is to substitute Al in combination with optimized quantities of Co, Cu, and Ga for HRE. By choosing an optimized quantity of these elements, HRE free magnet types with an increased coercive field strength HcJ can be manufactured under industrial conditions.
These magnets are suitable for many applications up to about 150 °C and almost independent of the supply of heavy rare earths.