As a kind of permanent magnet with good temperature stability and excellent magnetic properties, SmFeN magnets have potential application value in the field of automobiles, Ad shows, and electronic appliances. Now, more and more magnet producers have invested in the research and development of SmFeN magnets.
Concept of SmFeN Magnets
SmFeN magnets refer to the ternary or polymetallic compounds such as Sm2Fe17Nx formed by Sm2Fe17 through nitriding treatment. Nitrogen atoms enter Sm2Fe17 to generate a new gap-filling compound, Sm2Fe17Nx, which not only increases the single-cell volume of Sm2Fe17 by about 3% but also increases the Curie temperature significantly. It has excellent saturation magnetization strength and an anisotropic field at room temperature.
Characterization of SmFeN Magnets
Promising permanent magnetic materials should have three characteristics: first, the magnetic energy product must be powerful so that smaller, lighter, and more energy-efficient devices can be produced. Second, good coercivity is required to ensure good thermal stability of the magnets in high-temperature applications. Lastly, it needs to be cost-effective.
Magnetic Properties | The theoretical maximum magnetic energy product of samarium iron nitride (Sm2Fe17Nx) magnets can reach 62 MGOe, which is slightly lower than that of neodymium iron boron (NdFeB) magnets at 64 MGOe. In addition to this, Sm2Fe17Nx not only has an excellent saturation magnetization strength (1.57 T) and magnetocrystalline anisotropy (20.7 MA/m). Other advantages include higher Curie temperature (743 K/470°C), better oxidation resistance and corrosion resistance. So the samarium iron nitrogen type permanent magnet material not only takes over the high-temperature stability of samarium cobalt magnets but also further enhances magnetic properties.
| Materials | Saturation Magnetization Js/T | BHmax/(kJ∙m−3) | Curie Temperature Tc/K | Rare Earth Atom Content R/TM | Base Metal |
| SmCo5 | 1.15 | 248 | 1013 | 0.33 | Co |
| Sm2Co17 | 1.56 | 480 | 1163 | 0.105 | Co |
| Nd2Fe14B | 1.61 | 528 | 583 | 0.117 | Fe |
| Sm2Fe17 | 0.94 | 176 | 392 | 0.105 | Fe |
| Sm2Fe17Nx | 1.54 | 472 | 743 | 0.0989 | Fe |
Cost Advantage | Nd2Fe14B magnet is a permanent magnetic material with Nd2Fe14B as the main phase, the specific composition is iron ~ 64-69%, neodymium ~ 24-27.5%, praseodymium ~ 5%, boron ~ 1.1-1.2%, dysprosium ~ 0.6-8%, terbium ~ 0.4-1.2%. The high price of heavy rare earths such as dysprosium and terbium makes NdFeB magnets expensive. Samarium is the 40th most abundant element, and in terms of raw material cost, the price of samarium oxide used in SmFeN magnets is only about one-fifth of the price of neodymium oxide.
The Market of SmFeN Magnets
As the third generation of rare earth permanent magnet material, NdFeB has been widely used for its excellent magnetic properties. However, due to the high price of NdFeB magnets, low Curie temperature, and environmental damage, magnet producers are also actively developing other new permanent magnets. As an important and novel magnet, the global samarium iron nitrogen magnet market size was $43 million in 2022 and is estimated to reach $53 million by 2029, growing at a CAGR of 3.6%.
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Production Process of SmFeN Magnets
Bonded SmFeN magnets can now be produced on a large scale. The process involves mixing Sm2Fe17Nx powder with a binder and then going through a series of processes to produce the desired samarium iron nitride magnets, which have controllable magnetic properties and can be made into a variety of shapes. There are four ways to manufacture bonded magnets, calendering, injection molding, extrusion, and molding. The binder can be an organic binder or a low melting point metal binder like Zn.
Application of SmFeN Magnets
Bonded Samarium Iron Nitride Magnet is the main development direction at present, it can meet the demand for high-performance adhesion. Because the raw material cost of Samarium Iron Nitride is low, the temperature resistance and corrosion resistance are better, it has a strong competitive advantage in bonding magnets.
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High-Temperature Environment | SmFeN magnets are more suitable for applications that need high stability in high-temperature environments, high corrosion resistance, and high mechanical properties, such as automobile motors, sensors, aerospace, and other fields.
Large Area Exhibition | The adsorption function material made of Samarium Iron Nitride can be used in outdoor advertisements that require high adsorption force.
Civil Life | NdFeB magnets are used in magnetic hooks and other adsorption products. Due to the strong magnetism and hardness of NdFeB magnets, during the process of adsorption, the strong suction force will cause damage to the surface of the object to be adsorbed. At present, the main way to reduce such damage is to add flannel on the surface of NdFeB material, but this way reduces the adsorption force of the product and increases the cost of the product. The use of SmFeN flexible magnets can effectively avoid the problems.
Problems of SmFeN Magnets
Nitrogen Decomposition | SmFeN magnets are interstitial compounds, and nitrogen decomposition occurs when they are heated up to a specific temperature. SmFeN decomposes into SmN and Fe at temperatures higher than 873K and loses its permanent magnetic properties, so sintered SmFeN magnets are not yet applied on a large scale. SmFeN magnets can only be used to make injection magnets, bonded magnets, and rubber magnets.
Binder | Initially, people used organic materials such as nylon, and epoxy resin as binder. These binders can only be used below 200 ℃, and could not fully show the advantages of Sm2Fe17Nx high-temperature performance. So how to make a breakthrough in the process is the key to the competition between Sm2Fe17Nx magnets and Nd-Fe-B magnets. In recent years, some low melting point metals have begun to receive widespread attention, and people use low melting point metals such as Zn and Sn as binders, but because low melting point metals such as Zn as a binder will reduce the saturation magnetization strength, which in turn leads to a lower (BH)max.
Nowadays, the enhancement of material density is still a difficult point in the application of SmFeN magnets. Once the problem is solved, the commercialization of Samarium Iron Nitride magnets will be accelerated.
