Sintered Neodymium Magnets | Comprehensive Introduction for Industrial Buyers

Neodymium magnets, also known as NdFeB magnets or neo magnets, are the third generation of rare earth magnet, which were developed in early 1980s independently by General Motors and Sumitomo Special Metals. According to manufacturing process, they are divided into sintered neodymium magnets, plastic bonded neodymium magnets, and hot-pressed neodymium magnets. Sintered neodymium magnets have the highest energy product among all types of permanent magnets. Tengye Magnetic is a leading neodymium magnet manufacturer in China that produces high quality sintered neodymium magnets.

Geometry of Sintered Neodymium Magnets

Grade of Sintered Neodymium Magnets

According to remanence (Br) and coercivity (Hc), the grade of sintered neodymium magnets can vary in two ways. Take N42UH grade as an example, N represents Neodymium, 42 remanence, and UH coercivity (resistance to demagnetization). Generally, magnet grade can range from N30 to N55 in the perspective of remanence, N to TH in the perspective of coercivity or resistance to demagnetization. There are a variety of neodymium magnet grades that are suitable for different application requirements.

Grade

Remanence
(Br)

Intrinsic Coercivity
(Hcj)

Coercivity
(Hcb)

Maximum Energy Product
(BH)max

Temperature Coeffcient
(α)

Max.Working Temp.

kGs

kA/m

kOe

kA/m

kOe

kJ/m³

MGOe

^αBr

^αHcj

°C

℉

Max

Min

Max

Min

Max

Min

Max

Min

%/℃

(L/D=0.7)

N54	1.50	1.45	15.0	14.5	876	11	836	10.5	437	414	55	52	-0.12	-0.76	60	140
N52	1.47	1.42	14.7	14.2	876	11	836	10.5	422	390	53	49	-0.12	-0.76	80	176
N50	1.44	1.39	14.4	13.9	955	12	860	10.8	406	374	51	47	-0.12	-0.76	80	176
N48	1.42	1.37	14.2	13.7	955	12	860	10.8	390	358	49	45	-0.12	-0.76	80	176
N45	1.37	1.32	13.7	13.2	955	12	899	11.3	366	342	46	43	-0.12	-0.76	80	176
N42	1.32	1.28	13.2	12.8	955	12	899	11.3	342	318	43	40	-0.12	-0.76	80	176
N40	1.28	1.25	12.8	12.5	955	12	899	11.3	326	302	41	38	-0.12	-0.76	80	176
N38	1.25	1.22	12.5	12.3	955	12	899	11.3	310	287	39	36	-0.12	-0.76	80	176
N35	1.22	1.17	12.2	11.7	955	12	860	10.8	287	263	36	33	-0.12	-0.76	80	176
N33	1.17	1.13	11.7	11.3	955	12	836	10.5	271	247	34	31	-0.12	-0.76	80	176
N30	1.13	1.08	11.3	10.8	955	12	796	10.0	247	223	31	28	-0.12	-0.76	80	176
N52M	1.47	1.42	14.7	14.2	1114	14	1035	13.0	422	390	53	49	-0.12	-0.68	100	212
N50M	1.44	1.39	14.4	13.9	1114	14	1035	13.0	406	374	51	47	-0.12	-0.68	100	212
N48M	1.42	1.36	14.2	13.6	1114	14	1027	12.9	390	358	49	45	-0.12	-0.68	100	212
N45M	1.37	1.32	13.7	13.2	1114	14	995	12.5	366	342	46	43	-0.12	-0.68	100	212
N42M	1.32	1.28	13.2	12.8	1114	14	955	12.0	342	318	43	40	-0.12	-0.68	100	212
N40M	1.28	1.25	12.8	12.5	1114	14	923	11.6	326	302	41	38	-0.12	-0.68	100	212
N38M	1.25	1.22	12.5	12.3	1114	14	899	11.3	310	287	39	36	-0.12	-0.68	100	212
N35M	1.22	1.17	12.2	11.7	1114	14	868	10.9	287	263	36	33	-0.12	-0.68	100	212
N33M	1.17	1.13	11.7	11.3	1114	14	836	10.5	271	247	34	31	-0.12	-0.68	100	212
N30M	1.13	1.08	11.3	10.8	1114	14	796	10.0	247	223	31	28	-0.12	-0.68	100	212
N52H	1.47	1.42	14.7	14.2	1274	16	1043	13.1	422	390	53	49	-0.12	-0.66	120	248
N50H	1.44	1.39	14.4	13.9	1353	17	1035	13.0	406	374	51	47	-0.12	-0.66	120	248
N48H	1.42	1.36	14.2	13.6	1353	17	1027	12.9	390	358	49	45	-0.12	-0.66	120	248
N45H	1.37	1.32	13.7	13.2	1353	17	995	12.5	366	342	46	43	-0.12	-0.66	120	248
N42H	1.32	1.28	13.2	12.8	1353	17	955	12.0	342	318	43	40	-0.12	-0.66	120	248
N40H	1.28	1.25	12.8	12.5	1353	17	923	11.6	326	302	41	38	-0.12	-0.66	120	248
N38H	1.25	1.22	12.5	12.3	1353	17	899	11.3	310	287	39	36	-0.12	-0.66	120	248
N35H	1.22	1.17	12.2	11.7	1353	17	868	10.9	287	263	36	33	-0.12	-0.66	120	248
N33H	1.17	1.13	11.7	11.3	1353	17	836	10.5	271	247	34	31	-0.12	-0.66	120	248
N30H	1.13	1.08	11.3	10.8	1353	17	796	10	247	223	31	28	-0.12	-0.66	120	248
N52SH	1.44	1.42	14.4	14.2	1592	20	1076	13.5	422	390	53	49	-0.12	-0.66	140	284
N50SH	1.42	1.39	14.2	13.9	1592	20	1053	13.2	406	374	51	47	-0.12	-0.66	140	284
N48SH	1.40	1.36	14.0	13.6	1592	20	1035	13.0	390	358	49	45	-0.11	-0.56	150	302
N45SH	1.37	1.32	13.7	13.2	1592	20	995	12.5	366	342	46	43	-0.11	-0.56	150	302
N42SH	1.32	1.28	13.2	12.8	1592	20	955	12.0	342	318	43	40	-0.11	-0.56	150	302
N40SH	1.28	1.25	12.8	12.5	1592	20	939	11.8	326	302	41	38	-0.11	-0.56	150	302
N38SH	1.25	1.22	12.5	12.2	1592	20	907	11.4	310	287	39	36	-0.11	-0.56	150	302
N35SH	1.22	1.17	12.2	11.7	1592	20	876	11.0	287	263	36	33	-0.11	-0.56	150	302
N33SH	1.17	1.13	11.7	11.3	1592	20	844	10.6	271	247	34	31	-0.11	-0.56	150	302
N30SH	1.13	1.08	11.3	10.8	1592	20	804	10.1	247	223	31	28	-0.11	-0.56	150	302
N28SH	1.09	1.04	10.9	10.4	1592	20	788	9.9	223	199	29	25	-0.11	-0.56	150	302
N50SHT	1.42	1.39	14.2	13.9	1751	22	1053	13.2	406	374	51	47	-0.11	-0.56	150	302
N48SHT	1.40	1.36	14	13.6	1751	22	1031	12.9	390	358	49	45	-0.11	-0.56	160	320
N45SHT	1.37	1.32	13.7	13.2	1751	22	1003	12.6	366	342	46	43	-0.11	-0.56	160	320
N42SHT	1.32	1.28	13.2	12.8	1751	22	971	12.2	342	318	43	40	-0.11	-0.53	160	320
N40SHT	1.28	1.25	12.8	12.5	1751	22	947	11.9	326	302	41	38	-0.11	-0.53	160	320
N38SHT	1.25	1.22	12.5	12.2	1751	22	923	11.6	310	287	39	36	-0.11	-0.53	160	320
N35SHT	1.22	1.17	12.2	11.7	1751	22	884	11.1	287	263	36	33	-0.11	-0.53	160	320
N33SHT	1.17	1.13	11.7	11.3	1751	22	860	10.8	271	247	34	31	-0.11	-0.53	160	320
N30SHT	1.13	1.08	11.3	10.8	1751	22	812	10.2	247	223	31	28	-0.11	-0.53	160	320
N50UH	1.42	1.39	14.2	13.9	1990	25	1053	13.2	406	374	51	47	-0.11	-0.53	170	338
N48UH	1.40	1.36	14.0	13.6	1990	25	1031	12.9	390	358	49	45	-0.11	-0.53	180	356
N45UH	1.36	1.32	13.6	13.2	1990	25	1003	12.6	366	342	46	43	-0.11	-0.50	180	356
N42UH	1.32	1.28	13.2	12.8	1990	25	971	12.2	342	318	43	40	-0.10	-0.50	180	356
N40UH	1.28	1.25	12.8	12.5	1990	25	923	11.6	326	302	41	38	-0.10	-0.50	180	356
N38UH	1.25	1.22	12.5	12.2	1990	25	907	11.4	310	287	39	36	-0.10	-0.50	180	356
N35UH	1.22	1.17	12.2	11.7	1990	25	860	10.8	287	263	36	33	-0.10	-0.50	180	356
N33UH	1.17	1.13	11.7	11.3	1990	25	852	10.7	271	247	34	31	-0.10	-0.50	180	356
N30UH	1.13	1.08	11.3	10.8	1990	25	812	10.2	247	223	31	28	-0.10	-0.50	180	356
N48VH	1.40	1.36	14.0	13.6	2149	27	1031	12.9	390	358	49	45	-0.10	-0.50	180	356
N45VH	1.36	1.32	13.6	13.2	2149	27	1003	12.6	366	342	46	43	-0.10	-0.50	190	374
N42VH	1.32	1.28	13.2	12.8	2149	27	971	12.2	342	318	43	40	-0.10	-0.50	190	374
N40VH	1.28	1.25	12.8	12.5	2149	27	947	11.9	326	302	41	38	-0.10	-0.50	190	374
N38VH	1.25	1.22	12.5	12.2	2149	27	923	11.6	310	287	39	36	-0.10	-0.50	190	374
N35VH	1.22	1.17	12.2	11.7	2149	27	884	11.1	287	263	36	33	-0.10	-0.50	190	374
N33VH	1.17	1.13	11.7	11.3	2149	27	860	10.8	271	247	34	31	-0.10	-0.50	190	374
N30VH	1.13	1.08	11.3	10.8	2149	27	852	10.7	247	223	31	28	-0.10	-0.50	190	374
N48EH	1.35	1.40	13.5	14	2388	30	1051	13.2	390	358	49	45	-0.10	-0.45	200	392
N45EH	1.36	1.32	13.6	13.2	2388	30	1031	12.9	366	342	46	43	-0.10	-0.45	200	392
N42EH	1.32	1.28	13.2	12.8	2388	30	970	12.2	342	318	43	40	-0.10	-0.45	200	392
N40EH	1.28	1.25	12.8	12.5	2388	30	947	11.9	326	302	41	38	-0.10	-0.45	200	392
N38EH	1.25	1.22	12.5	12.2	2388	30	915	11.5	310	287	39	36	-0.10	-0.45	200	392
N35EH	1.22	1.17	12.2	11.7	2388	30	884	11.1	287	263	36	33	-0.10	-0.45	200	392
N33EH	1.17	1.13	11.7	11.3	2388	30	860	10.8	271	247	34	31	-0.10	-0.45	200	392
N30EH	1.13	1.08	11.3	10.8	2388	30	820	10.3	247	223	31	28	-0.10	-0.45	200	392
N45FH	1.36	1.32	13.6	13.2	2547	32	1031	12.9	366	342	46	43	-0.10	-0.45	210	410
N42FH	1.32	1.28	13.2	12.8	2547	32	970	12.2	342	318	43	40	-0.10	-0.45	210	410
N40FH	1.28	1.25	12.8	12.5	2547	32	947	11.9	326	302	41	38	-0.10	-0.45	210	410
N38FH	1.25	1.22	12.5	12.2	2547	32	915	11.5	310	287	39	36	-0.10	-0.45	210	410
N35FH	1.22	1.17	12.2	11.7	2547	32	884	11.1	287	263	36	33	-0.10	-0.45	210	410
N33FH	1.17	1.13	11.7	11.3	2547	32	860	10.8	271	247	34	31	-0.10	-0.45	210	410
N30FH	1.13	1.08	11.3	10.8	2547	32	820	10.3	247	223	31	28	-0.10	-0.45	210	410
N42AH	1.32	1.28	13.2	12.8	2786	35	970	12.2	342	318	43	40	-0.10	-0.45	230	446
N40AH	1.28	1.25	12.8	12.5	2786	35	947	11.9	326	302	41	38	-0.10	-0.45	230	446
N38AH	1.25	1.22	12.5	12.2	2786	35	915	11.5	310	287	39	36	-0.10	-0.45	230	446
N35AH	1.20	1.17	12.0	11.7	2786	35	883	11.1	287	263	36	33	-0.10	-0.45	230	446
N33AH	1.17	1.11	11.7	11.1	2786	35	844	10.6	271	239	34	31	-0.10	-0.45	230	446
N30AH	1.13	1.07	11.3	10.7	2786	35	812	10.2	247	215	31	27	-0.10	-0.45	230	446
N28AH	1.09	1.02	10.9	10.2	2786	35	772	9.7	231	199	29	25	-0.10	-0.45	230	446
N38TH	1.25	1.22	12.5	12.2	3182	40	915	11.5	310	287	39	36	-0.10	-0.42	260	500
N35TH	1.22	1.17	12.2	11.7	3182	40	867	10.9	287	263	36	33	-0.10	-0.42	260	500
N33TH	1.17	1.11	11.7	11.1	3182	40	851	10.7	271	239	34	31	-0.10	-0.42	260	500
N30TH	1.13	1.08	11.3	10.8	3182	40	820	10.3	247	223	31	28	-0.10	-0.42	260	500

Coating (surface treatment)

Coating (sintered NdFeB magnets)	Abbreviation	color	thickness (µm)	corrosion resistance (rating 1 to 10)			Recommended working Temp. (℃）	Surface Tension (γ)
				SST	HHT	PCT

Nickel (barrel)	NiCuNi	Bright silver	10-20	5	5	5	≤260	36
Nickel (rack)	NiCuNi	Bright silver	10-20	4	5	5	≤260	36
3+Cr Zinc (barrel)	Zn	Blue&white	5-10	4	3	3	≤160	38
3+Cr Zinc (rack)	Zn	Blue&white	5-10	3	3	3	≤160	38
3+Cr Color Zinc (barrel)	Colored Zn	Bright color	5-10	3	3	3	≤160	38
3+Cr Color Zinc (rack)	Colored Zn	Bright color	5-10	3	3	3	≤160	38
Electroless nickel plating (barrel)	Electroless Ni	Dark silver	12-20	5	5	4	≤260	36
Electroless nickel plating (rack)	Electroless Ni	Dark silver	12-20	4	5	4	≤260	36
Nickel+Chromium	Cr	Dark black	12-20	4	5	5	≤260	36
Teflon	PTFE	Dark grey		3	3	3	≤260	36
Nickel+Black Nickel	Black Ni	Black	12-20	5	5	5	≤260	36
Nickel+Tin	Sn	Bright silver	12-20	4	5	5	–	36
Nickel+Silver	Ag	Silver	12-20	4	5	5	–	36
Nickel+Gold	Au	Golden	10-20	4	5	5	–	36
Epoxy	Epoxy	Black	10-20	5	5	4	≤160	36
Nickel+Epoxy	NiCu+Epoxy	Black	15-25	5	5	3	≤160	36
Passivation/Phosphorization	Phosphate	Dark grey	1-3	–	–	–	≤240	37
Nano Coating	Nano	Gray/Black	15-30	6	6	7	≤300	33

Manufacturing Process of sintered NdFeB magnets

Sintered neodymium magnet (Neodymium-Iron-Born or Nd-Fe-B) is an alloy consisting of neodymium, iron, boron, cobalt, varying levels of praseodymium, dysprosium or terbium and other transition metals. The manufacturing process for sintered neodymium magnets are divided into two main stages: powder metallurgy and mechanical processing. There are are six critical manufacturing steps involved in the powder metallurgy stage.

1) Strip casting

Raw material including PrNd alloy, iron, copper, DyFe, etc. are mixed and melted together according to a certain proportion. These are heated in a vacuum furnace and a stream of molten metal is forced under pressure onto a cooled drum where it is rapidly cooled at approximately 100,000 degrees-per-second. As a result, strip cast NdFeB ingot is produced for further processing

2) Hydrogen decrepitation

After melting and casting, the NdFeB alloy ingot is subject to hydrogen atmosphere. Hydrogen slowly absorbs into the solid alloy and makes it brittle, which upon milling becomes fine powder.

3) Jet milling

The NdFeB powder produced from hydrogen decrepitation is protected in an inert gas atmosphere and handled in glove boxes before going to the automated press. The powder are then fed into a grinding chamber, where the high-velocity gas streams are introduced to cause particles clash violently against each other. As a result, extremely fine powder having a size ranging from 3 to 5 μm is produced.

4) Pressing and orientation

The powder from jet milling is pressed. During the pressing, a strong magnetic field is applied in order to rotate the powder particles so that their main crystal axes are aligned. That’s required to achieve anisotropy, which means that every piece of powder in the finished magnet will contribute to the magnetic field. Without the alignment, the c-axis (crystal axis) would be more or less randomly distributed, and only those particles which are roughly in the direction of the magnetization field would be magnetized, resulting in a significantly weaker magnet.

5) Isostatic pressing

The pressed NdFeB block is bagged and immersed into a cold isostatic press (CIP) under huge pressure. This process intends to remove the remaining air gaps within the block. NdFeB blocks coming out of CIP become a bit smaller than it was before it goes in.

6) Sintering and annealing

The pressed blocks are placed in a sintering furnace at an extremely high temperature just below the melting point of the NdFeB alloy. At this temperature of over 1000 degree, the individual atoms have a lot of motion, which enables the NdFeb alloy to develop their full magnetic and mechanical properties. The magnetic domains maintain the same orientation they had before sintering. At this temperature, shrinkage of NdFeB blocks takes place and full density is achieved.

After sintering, there are pent-up stresses in the metal from all the movement during sintering, so the blocks are heat-treated again in a step fashion at lower temperatures to reduce the stresses. The blocks are ramped up to a high holding temperature for a set time and then they are ramped down to a lower holding temperature. Once the holding time is achieved, the now stress-free blocks are slowly cooled to room temperature.

Direction of Magnetization

Sintered neodymium magnets are anisotropic and can only be magnetized in the predetermined direction. Generally, the magnets are axially magnetized (magnet in round shape) or magnetized through thickness (magnet in square or rectangular shape). However, it’s not uncommon to find a neodymium disc magnet diametrically magnetized because it’s used as rotary position sensor. Besides simple two-pole magnetization, sintered neodymium magnets can also be magnetized in sectors. Examples of different magnetization patterns are given below. (Sinter neodymium magnets in ring shape can have axial, diametrical, or radial magnetization. Arc magnets are usually diametrically magnetized in pair since they are used in electric motors. Thus the name, arc motor magnets.

Maximum Working Temperature of Neodymium Magnets

Sintered neodymium magnets are characterized by their excellent magnetic performance at room temperature. However, they have the least temperature resistance compared to other permanent magnets. N grade magnet only has a theoretical temperature limit of 80°C. (The practical maximum operating temperature is related to the L/D ratio of the magnet.) For higher temperature resistance, high-cost heavy rare earth elements (HREEs) are needed to increase the magnet coercivity. Even with the help of grain boundary diffusion (GBD) technology, less heavy rare earth is needed to increase the coercivity, the cost to produce sintered neodymium magnets that can withstand temperature over 200°C is still very high. That’s why the market for Sm2Co17 magnets still widely exists in e.g. aerospace, military industry, etc.

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Hitachi Licensed NdFeB Magnets

To avoid future potential litigation, companies who sell their products containing NdFeB magnets in North America or Japan usually require Hitachi licensed neodymium magnets. In China, there are eight Hitachi authorized NdFeB manufacturers in total. Our strategic partnership with some of these authorized NdFeB manufacturers allows us to specially outsource licensed magnets at a reasonable price even in low volume.

Raw Material "NdPr Price" | Neodymium Magnet Price

Neodymium magnets are known for its high price, but more importantly for its price volatility. Rare earth alloy – NdPr alloy is the determinant of the magnet price change. PrNd alloy is of vital importance to the production and cost of all types of neodymium magnets. It’s also an indictor of price trend of neodymium magnets.

About Tengye: Tengye Magnetic supplies finest neodymium magnet materials and custom magnetic assemblies to world industry. We work closely with our customer from designing stage to mass production.