Sintered NdFeB magnets, i.e. sintered neodymium iron boron magnets, are those permanent magnetic materials that based on a Nd-Fe-B tetragonal crystal structure, and they are manufactured through a powder metallurgy (PM) process. They contain three basic elements neodymium, iron and boron. The neodymium element can be substituted by a portion of other rare earth elements (REEs) including praseodymium (Pr), dysprosium (Dy), terbium (Tb), cerium (Ce), etc. The iron element can be substituted by a portion of cobalt (Co) element to increase the magnets’ Curie temperature (Tc), thermal stability and corrosion resistance. In order to control the microstructure and the microchemistry so as to meet required performance, it also adds a small portion of other metal elements including aluminium (Al), copper (Cu), niobium (Nb), gallium (Ga), etc.
Almost at the same time in the early 1980s, NdFeB magnets were invented by M. Sagawa’s and J. J. Croat’s teams through a powder metallurgical process and a melt-spinning technique, respectively. Due to their outstanding magnetic properties (high remanence Br: 1.1-1.5 T, middle high coercivity Hcj: 800-3000 kA/m3 and high maximum energy product (BH)max: 220-430 kJ/m3) together with competitive cost, sintered NdFeB magnets are widely applied in direct current (DC) motors, servo motors, stepper/stepping motors, synchronous motors, linear motors, voice coil motors (VCMs), wind turbines and generators, magnetic resonance imaging (MRI), electric power steering (EPS), magnetic separation, etc.