SmFeN Samarium Iron Nitrogen Rare Earth Permanent Magnetic Materials
In 1990, Professor Coey from Ireland synthesized RE2Fe17Nx interstitial intermetallic compounds using gas-solid phase reaction. Through research, it was found that Sm2Fe17Nx compounds have excellent intrinsic magnetic properties, announcing the birth of SmFeN rare earth permanent magnet materials. The theoretical maximum magnetic energy product of samarium iron nitrogen permanent magnet reaches 62 MGOe (slightly lower than Nd2Fe14B, 64 MGOe), and its coercivity and Curie temperature are much higher than neodymium iron boron, making it more widely used in high-temperature environments such as motors.
In addition to excellent comprehensive magnetic properties, samarium iron nitrogen has good corrosion resistance and oxidation resistance, and compared to samarium cobalt, it does not contain strategic metal elements; Compared to neodymium iron boron, it does not require the consumption of expensive rare earth elements such as praseodymium, neodymium, dysprosium, and terbium (with relatively high samarium content and low price), and fully meets the conditions to become a new type of permanent magnet material. The attractive prospects have made samarium iron nitrogen the hottest topic in the research and development of permanent magnet materials. Since Coey et al. discovered Sm2Fe17Nx rare earth permanent magnet materials, there has been a rapid wave of research on Sm2Fe17Nx permanent magnet materials around the world, with hundreds of laboratories investing in this area at that time. But a series of subsequent experiments proved that this permanent magnet material was not successful on the path of industrialization, and a situation of hot and cold research emerged.
In recent years, with the rapid development of the automotive industry and the miniaturization and lightweighting of electronic appliances, people have put forward higher environmental temperature and magnetic performance requirements for permanent magnets. Sm2Fe17Nx rare earth permanent magnet materials, as a permanent magnet material with good temperature stability and excellent magnetic properties, have once again attracted people's attention to their potential application value. Sm2Fe17Nx permanent magnet materials have also ushered in a new research and development trend. Due to the extensive development and use of rare earths, prices have risen. The price increase of Nd has led to an increase in the cost of producing Nd-Fe-B, while the rare earth Sm is in a relatively surplus state. Developing Sm-Fe-N is beneficial for reducing costs and strengthening the comprehensive utilization of rare earth resources. So, Sm-Fe-N is likely to replace Nd-Fe-B and become the expected fourth generation rare earth permanent magnet material, both in terms of magnetic properties and production costs.
After more than 20 years of research and exploration, the problem of industrial large-scale production of Sm-Fe-N has not been solved. Research has found that Sm-Fe-N decomposes into SmN and Fe at temperatures above 873K, losing its permanent magnetic properties, which greatly limits its application in sintered magnets. At present, Sm-Fe-N can only be used to prepare injection molded magnets, bonded magnets, and rubber magnets. Initially, organic compounds such as nylon and epoxy resin were used as binders. However, these binders could only be used below 200 ℃ and could not fully utilize the high temperature performance advantages of Sm2Fe17Nx. Therefore, how to make breakthroughs in the process and whether new binders can be developed is the key to the competition between Sm2Fe17Nx magnets and Nd-Fe-B magnets. In recent years, some low melting point metals have received widespread attention, and people use low melting point metals such as Zn and Sn as binders. However, due to the use of low melting point metals such as Zn as binders, the saturation magnetization strength is reduced, resulting in a lower (BH) max. It can be seen that in order to fully utilize the performance of Sm2Fe17Nx, it is crucial to find a good adhesive. Meanwhile, the preparation of Sm2Fe17Nx densified magnets is still the pursuit of researchers, as densified magnets can better exhibit theoretical magnetic properties.
According to the statistics of the Japan Adhesive Magnet Association, based on the high magnetic performance, high corrosion resistance, high temperature demagnetization resistance, and good forming freedom advantages of samarium iron nitrogen magnetic materials, their application directions are mainly in the fields of information communication, industrial production, household electronics, and automobiles, including speakers/speakers, camera shutter motors, spindle motors, disk adsorption, magnetic rollers, fan motors, linear engines, fully automatic machine equipment, high-speed motors, air conditioners, household motors, magnetic sensors, pumps, auxiliary machines, etc.
At present, Sm2Fe17Nx has made significant progress in the preparation and application of bonded magnets, but densification remains a goal pursued and pursued by many magnetic material workers. Once a suitable preparation process is developed, it may be possible to achieve its theoretical magnetic properties and accelerate the commercialization process of samarium iron nitride magnets.