The development of rare earth magnets has experienced three generations,they are SmCo5 magnets,Sm2Co17 magnets and neodymium-iron-boron magnets(the following shorted as Nd-Fe-B magnet)
In 1968, Buschow et al. fabricated SmCo5 magnets with a maximum magnetic energy product of 18.5MGOe and a coercivity of 15.8kOe, which set a record of the magnetic energy product of permanent magnets at that time. This also marked the birth of the first generation of rare earth permanent magnets.Subsequently, with the continuous improvement of the preparation process and the progress of the technology, by the 1970s, the SmCo5 permanent magnet had been commercialized.At present, the maximum magnetic energy product of Sm Co5 magnets is 119~191 kJ/m3 (15~24MGOe),) coercivity up to 1200 ~ 3200kA/m (15~40kOe).The Curie temperature of SmCo5 is 740 ℃, which can work in the temperature range of -50~150 ℃. It is an ideal permanent magnet and has been widely used in science and technology industry.Its disadvantage is that it contains more strategic cobalt and less storage of rare earth metals Sm. Raw materials are expensive and their development prospects are limited by resources and prices.
Second generation, rare earth permanent magnet Sm2Co17
In 1977, Ojima et al developed Sm2Co17 permanent magnet
by powder metallurgy method. Its maximum magnetic energy product (BH) max=238.8 kJ/m3) (30MGOe),which marked the birth of the second generation rare earth permanent magnet material.At present, the maximum magnetic energy product of Sm2Co17 permanent magnet has reached 264 kJ/m3 (33MGOe).Based on its unique high temperature magnetic properties and excellent magnetic stability (excellent oxidation resistance and corrosion resistance),Sm2Co17-based sintered permanent magnet is still an irreplaceable permanent magnet material, which is widely used in defense, aerospace, microwave devices, sensors, magnetic pumps, high-end motors and other industries
The third generation, rare earth permanent magnet Nd-Fe-B
The industrial mass production of Nd-Fe-B magnet was realized in 1983, which is a typical representative of rare earth iron series permanent magnetic materials.The main components are rare earth elements (such as neodymium Nd), iron element (Fe) and boron element (B), of which rare earth elements are about 25-35%, iron about 65-75%, boron about 1%.Its molecular formula is Nd2Fe14B, which can improve its properties by changing the ratio and adding other elements according to the actual requirements.Nd-Fe-B magnet is the world's highest magnetic energy product permanent magnet materials, known as the "king of modern permanent magnets."This also means that for the same magnetic flux,the volume of NdFeB magnet is the smallest.At present, the magnetic energy product of commercial Nd-Fe-B magnet is about 223~414 kJ/m3 (28~52 MGOe).Nd-Fe-B series rare earth permanent magnet is a revolutionary change in the field of permanent magnetic materials.The continuous improvement of the performance of the products has promoted the development of permanent magnetic devices to high performance and miniaturization, and promoted the production of some devices, which is of epoch-making significance.