What is SmFeN Magnet

What is SmFeN Magnet

SmFeN magnetic material uses abundant rare-earth Sm element instead of expensive elements of Nd, Dy, Co, etc, and is the most cost-effective rare earth permanent magnetic material. Compared with the bonded neodymium magnet, the bonded SmFeN magnet has higher magnetic properties and lower prices. Moreover, curie temperature, corrosion resistance, and thermal stability of bonded SmFeN magnet perform much better than bonded neodymium magnet. Bonded SmFeN magnet as an alternative of bonded neodymium magnet has broad application prospects.

SmFeN magnet, also known as Sm2Fe17N3, has always been expected as a potential option for next generation of permanent magnetic material, thus attracted many attentions since its discovered by Michael Coey in 1990. SmFeN has many advantages, include:

The curie temperature can reach 476 degrees Celsius which much higher than conventional sintered Neodymium magnet.
Magnetocrystalline anisotropy field is three times as big as Nd2Fe14B and has huge potential to fabricate high coercivity magnets.
SmFeN magnet did not have to add Cobalt or other heavy rare earth elements (HREEs) to adjust magnetic properties.
Superior corrosion and oxidation resistance.

Sm2Fe17N3 phase will decompose into SmN phase and α-Fe phase once the ambient temperature exceeds 650 degrees Celsius. Thereby, sintered SmFeN magnets cannot be manufactured via conventional sintering technology. Commercialization of SmFeN magnet is firstly realized in bonded magnet area by Japanese companies. Either isotropic magnet or anisotropic magnet needs stable raw SmFeN powder. Daido applied rapidly quenched technology to prepare isotropic powder and magnet’s performance even higher than compression molded NdFeB magnet. Both Nichia and Sumitomo utilized reduction-diffusion technology to obtain anisotropic powder which well suited to injection molded magnet.

Magnetic Properties of Injection Molded SmFeN Magnet

Material	Grade	Remanence Br		Coercivity Hcb		Intrinsic Coercivity Hcj		Max. Energy Product (BH)max		Temperature Coefficient %/℃		Density ρ	Flexural Strength
Material	Grade	T	kGs	kA/m	kOe	kA/m	kOe	kJ/m³	MGOe	α (Br)	β (Hcj)	g/cm³	MPa
SmFeN/Ferrite Hybrid Magnet	30A	0.37	3.70	213	2.67	336	4.22	25.5	3.20	-0.13	-0.35	3.61	98
	40A	0.45	4.50	220	2.76	398	5.00	32.4	4.07	-0.09	-0.48	3.70	91
	50A	0.48	4.80	270	3.39	423	5.32	40.6	5.10	-0.08	-0.48	3.79	89
SmFeN Magnet	60A	0.52	5.20	349	4.39	576	7.23	50.3	6.32	-0.07	-0.48	3.62	92
	70A	0.57	5.70	363	4.57	554	6.96	57.9	7.27	-0.08	-0.48	3.88	91
	80A	0.60	6.00	371	4.66	525	6.60	64.7	8.13	-0.08	-0.48	4.11	91
	90A	0.64	6.40	400	5.02	550	6.91	75.2	9.45	-0.08	-0.48	4.33	88
SmFeN/NdFeB Hybrid Magnet	100A	0.69	6.90	408	5.12	701	8.81	82.0	10.30	-0.10	-0.57	4.45	99
SmFeN/NdFeB Hybrid Magnet	120A	0.78	7.80	454	5.70	812	10.20	99.3	12.47	-0.10	-0.57	4.95	91
The above-mentioned data of magnetic properties and physical properties are given at room temperature. The max working temperature of magnet is changeable due to length-diameter ratio and other environment factors.

What is SmFeN Magnet

Sm2Fe17N3, which was discovered about seven years after Nd2Fe14B, has excellent intrinsic magnetic properties. Its uniaxial anisotropy, K1, Curie temperature, Tc and spontaneous magnetization, Ms are superior or comparable to those of earlier rare-earth permanent magnet materials. The ternary nitride is prepared from Sm2Fe17 by gas-phase interstitial modification with ammonia or nitrogen gas; nitrogen atoms occupy interstitial sites, so that the Th2Zn17-type structure crystal structure of Sm2Fe17 is retained. Other types of nitride magnet materials such as NdFe11TiNx (ThMn12-type structure) and SmFe7Nx (TbCu7-type structure) were discovered soon after. A drawback of these materials is that the nitrogenated phase is metastable, and has decomposed at about 600 °C, which rules out high-temperature sintering; fully dense, oriented permanent magnets cannot be produced. On the other hand, Sm-Fe-N enjoys some advantages when fabricated as a polymer- or zinc-bonded magnet; a large coercivity can be obtained in the powder state, the powder has excellent corrosion/oxidation resistance compared with Nd-Fe-B powders and the Curie temperature is higher. Thus, high performance anisotropic polymer-bonded magnets with Sm2Fe17N3 powder and isotropic polymer-bonded magnets with SmFe9Nx powder have been commercialized by magnet manufacturers in Japan and China. This chapter reviews basic research on the structural and magnetic properties of Sm-Fe-N materials. It then discusses magnet processing and presents characteristics of the bonded magnets, with some examples of their applications.

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