Microstructure and magnetic properties of iron-based rare-earth magnets

The magnetic properties of various commercial Fe-Nd-B magnets have been measured and compared with their microstructure and magnetic domain structure. The coercivity is found to be strongly dependent on both the applied field and temperature. Remanent magnetization curves indicate two possible domain wall pinning mechanisms. The microstructure of all magnets studied is very similar showing the predominant Fe
14
Nd
2
B grain in coexistence with some Nd-rich phases and the tetragonal Fe
4
NdB
4
phase. The higher coercivities observed in Neo30H are attributed to the presence of a small amount of Dy in this magnet leading to higher anisotropy fields.