With the development of society, magnets have been used more and more widely. From high-tech products to the simplest packaging magnets, NdFeB strong magnets and ferrite magnets are still the most widely used.
From the perspective of the development history of permanent magnetic materials, the magnetic energy product (BH) max (the physical quantity measuring the stored magnetic energy density of permanent magnets) of carbon steel used at the end of the 19th century is less than 1MGOe (Mega High Altitude), while the magnetic energy product of Nd-Fe-B permanent magnetic materials produced in batches abroad has reached more than 50MGOe. Since this century, the remanence Br of materials has been improved very little, and the improvement of energy product is attributed to the improvement of coercive force Hc. The improvement of coercivity is mainly due to the understanding of its nature, the discovery of highly magnetic crystalline anisotropic compounds, and the progress of preparation technology.
At the beginning of the 20th century, people mainly used carbon steel, tungsten steel, chromium steel and cobalt steel as permanent magnetic materials. At the end of the 1930s, the successful development of AlNiCo permanent magnetic materials made the large-scale application of permanent magnetic materials possible. In the 1950s, the appearance of barium ferrite not only reduced the cost of permanent magnets, but also broadened the application scope of permanent magnet materials to high-frequency fields. In the 1960s, the appearance of rare earth cobalt permanent magnet opened up a new era for the application of permanent magnets.
In 1967, Strut et al. of Dayton University in the United States successfully made SmCo5 permanent magnets by powder bonding, marking the arrival of the era of rare earth permanent magnets. So far, the rare earth permanent magnet has experienced the first generation SmCo5, the second generation of precipitation hardening Sm2Co17, and developed into the third generation Nd-Fe-B permanent magnet material.
In addition, Cu Ni Fe, Fe Co Mo, Fe Co V, MnBi, A1MnC alloys have been used as permanent magnetic materials in history. These alloys have been rarely used in most occasions due to their low performance and cost. AlNiCo, FeCrCo, PtCo and other alloys are also used in some special occasions. At present, Ba and Sr ferrites are still the most used permanent magnetic materials, but many of their applications are gradually being replaced by Nd-Fe-B materials. Moreover, the output value of rare earth permanent magnetic materials has greatly exceeded that of ferrite permanent magnetic materials, and the production of rare earth permanent magnetic materials has developed into a major industry [2].
In short, The development of permanent magnetic materials has gone through several stages of development. Before the 1950s, it was a metal permanent magnet. In the 1950s and 1980s, it was a golden age of permanent ferrite. Since the 1990s, the rise of nanostructured magnetic materials has become a strong competitor of ferrite. At present, the search for the next generation of permanent magnetic materials with better performance is still the focus of attention in the magnetic field. Nanocrystalline exchange coupling permanent magnetic materials are the most promising materials at present. Superconducting permanent magnets are at low temperatures Another possible choice of using super strong permanent magnet.
