Sintered Neodymium Magnets | SDM Magnetics Co., Ltd.

Neodymium magnets are a type of permanent magnet made from an alloy of Neodymium (Nd), Iron (Fe), and Boron (B) to form the Nd₂Fe₁₄B phase. They are commonly referred to as “Neo magnets” or “NdFeB magnets,” as “Neo” and “NdFeB” are abbreviations for “Neodymium” and “Neodymium Iron Boron,” respectively. Additionally, Neodymium magnets are sometimes classified as rare earth magnets due to the rare earth elements in their composition.

Neodymium magnets can be categorized into sintered, bonded, and hot pressed types based on the manufacturing process. However, the term “Neodymium magnets” typically refers specifically to sintered magnets, owing to their unparalleled magnetic performance and market share. Invented independently in 1983 by Masato Sagawa and John Croat, Neodymium magnets still provide the strongest magnetic power available today and have found widespread applications across numerous industries, including electronics, automotive, renewable energy, and medical devices, driving innovation in modern technology.

Neodymium Arc Magnets

Neodymium Bar Magnets

Neodymium Block Magnets

Neodymium Countersunk Magnets

Neodymium Disc Magnets

Neodymium Ring Magnets

Neodymium Rod Magnets

Neodymium Sphere Magnets

Manufacturing Process of Sintered Neodymium Magnets

The manufacturing process of Neodymium magnets begins with the production of an alloy using vacuum melting and the strip-casting (SC) method. The resulting alloy flakes are converted into coarse powder through hydrogen decrepitation, followed by jet milling to produce a fine powder with particle sizes ranging from 3 to 7 microns. This fine powder is then filled into molds and pressed under an applied magnetic field to orient the individual particles. The compacted green body is subsequently sintered in a vacuum furnace at approximately 1100 degrees Celsius. After sintering, the blanks are machined to the desired shapes, subjected to surface treatment, and magnetized.

Magnetic Properties of Sintered Neodymium Magnets

Neodymium magnet grades are typically specified in the format of the letter N followed by a number and one or two letters. The letter N stands for the abbreviation of the Neodymium element. The subsequent number represents the maximum energy product (BH)max of the magnet in the CGS unit of Mega-Gauss Oersteds (MGOe). The one or two letters appended at the end indicate the intrinsic coercivity and maximum operating temperature of the Neodymium magnets. The intrinsic coercivity for M (medium), H (high), SH (super high), UH (ultra high), EH (extreme high), and AH (abnormal high) grades should be greater than 14, 17, 20, 25, 30, and 35 kOe, respectively, with corresponding maximum operating temperatures reaching 100, 120, 150, 180, 200, and 220 degrees Celsius.

It should be noted that some grades lack a trailing letter, particularly the well-known N35 and N52. For these grades, the intrinsic coercivity is no less than 12 kOe, and the maximum operating temperature should be below 80 degrees Celsius. Furthermore, grades for grain boundary diffused Neodymium magnets incorporate a prefix G to highlight their manufacturing characteristics.

Magnetic Properties Chart of Sintered Neodymium Magnets

Grade	Remanence Br		Coercivity Hcb		Intrinsic Coercivity Hcj		Max. Energy Product (BH)max		Max. Working Temperature
Grade	T	kGs	kA/m	kOe	kA/m	kOe	kJ/m³	MGOe	℃
N30	1.08-1.13	10.8-11.3	≥798	≥10.0	≥955	≥12	223-247	28-31	80
N33	1.13-1.17	11.3-11.7	≥836	≥10.5	≥955	≥12	247-271	31-34	80
N35	1.17-1.22	11.7-12.2	≥868	≥10.9	≥955	≥12	263-287	33-36	80
N38	1.22-1.25	12.2-12.5	≥899	≥11.3	≥955	≥12	287-310	36-39	80
N40	1.25-1.28	12.5-12.8	≥907	≥11.4	≥955	≥12	302-326	38-41	80
N42	1.28-1.32	12.8-13.2	≥915	≥11.5	≥955	≥12	318-342	40-43	80
N45	1.32-1.38	13.2-13.8	≥923	≥11.6	≥955	≥12	342-366	43-46	80
N48	1.38-1.42	13.8-14.2	≥923	≥11.6	≥955	≥12	366-390	46-49	80
N50	1.40-1.45	14.0-14.5	≥796	≥10.0	≥876	≥11	382-406	48-51	80
N52	1.43-1.48	14.3-14.8	≥796	≥10.0	≥876	≥11	398-422	50-53	80
N55	1.46-1.52	14.6-15.2	≥796	≥10.0	≥876	≥11	414-430	52-54	80
N35M	1.17-1.22	11.7-12.2	≥868	≥10.9	≥1114	≥14	263-287	33-36	100
N38M	1.22-1.25	12.2-12.5	≥899	≥11.3	≥1114	≥14	287-310	36-39	100
N40M	1.25-1.28	12.5-12.8	≥923	≥11.6	≥1114	≥14	302-326	38-41	100
N42M	1.28-1.32	12.8-13.2	≥955	≥12.0	≥1114	≥14	318-342	40-43	100
N45M	1.32-1.38	13.2-13.8	≥995	≥12.5	≥1114	≥14	342-366	43-46	100
N48M	1.37-1.43	13.7-14.3	≥1027	≥12.9	≥1114	≥14	366-390	46-49	100
N50M	1.40-1.45	14.0-14.5	≥1033	≥13.0	≥1114	≥14	382-406	48-51	100
N52M	1.43-1.48	14.3-14.8	≥1050	≥13.2	≥1114	≥14	398-422	50-53	100
N54M	1.45-1.50	14.5-15.0	≥1051	≥13.2	≥1114	≥14	414-438	52-55	100
N35H	1.17-1.22	11.7-12.2	≥868	≥10.9	≥1353	≥17	263-287	33-36	120
N38H	1.22-1.25	12.2-12.5	≥899	≥11.3	≥1353	≥17	287-310	36-39	120
N40H	1.25-1.28	12.5-12.8	≥923	≥11.6	≥1353	≥17	302-326	38-41	120
N42H	1.28-1.32	12.8-13.2	≥955	≥12.0	≥1353	≥17	318-342	40-43	120
N45H	1.32-1.36	13.2-13.6	≥963	≥12.1	≥1353	≥17	342-366	43-46	120
N48H	1.37-1.43	13.7-14.3	≥995	≥12.5	≥1353	≥17	366-390	46-49	120
N50H	1.40-1.45	14.0-14.5	≥1011	≥12.7	≥1353	≥17	382-406	48-51	120
N52H	1.43-1.48	14.3-14.8	≥1027	≥12.9	≥1353	≥17	398-422	50-53	120
N35SH	1.17-1.22	11.7-12.2	≥876	≥11.0	≥1592	≥20	263-287	33-36	150
N38SH	1.22-1.25	12.2-12.5	≥907	≥11.4	≥1592	≥20	287-310	36-39	150
N40SH	1.25-1.28	12.5-12.8	≥939	≥11.8	≥1592	≥20	302-326	38-41	150
N42SH	1.28-1.32	12.8-13.2	≥987	≥12.4	≥1592	≥20	318-342	40-43	150
N45SH	1.32-1.38	13.2-13.8	≥1003	≥12.6	≥1592	≥20	342-366	43-46	150
N48SH	1.37-1.43	13.7-14.3	≥1027	≥12.9	≥1592	≥20	366-390	46-49	150
N50SH	1.40-1.45	14.0-14.5	≥1003	≥12.6	≥1592	≥20	382-406	48-51	150
N28UH	1.04-1.08	10.4-10.8	≥764	≥9.6	≥1990	≥25	207-231	26-29	180
N30UH	1.08-1.13	10.8-11.3	≥812	≥10.2	≥1990	≥25	223-247	28-31	180
N33UH	1.13-1.17	11.3-11.7	≥852	≥10.7	≥1990	≥25	247-271	31-34	180
N35UH	1.17-1.22	11.7-12.2	≥860	≥10.8	≥1990	≥25	263-287	33-36	180
N38UH	1.22-1.25	12.2-12.5	≥876	≥11.0	≥1990	≥25	287-310	36-39	180
N40UH	1.25-1.28	12.5-12.8	≥899	≥11.3	≥1990	≥25	302-326	38-41	180
N42UH	1.28-1.32	12.8-13.2	≥899	≥11.3	≥1990	≥25	318-342	40-43	180
N45UH	1.32-1.36	13.2-13.6	≥908	≥11.4	≥1990	≥25	342-366	43-46	180
N48UH	1.37-1.43	13.7-14.3	≥908	≥11.4	≥1990	≥25	366-390	46-49	180
N28EH	1.04-1.08	10.4-10.8	≥780	≥9.8	≥2388	≥30	207-231	26-29	200
N30EH	1.08-1.13	10.8-11.3	≥812	≥10.2	≥2388	≥30	223-247	28-31	200
N33EH	1.13-1.17	11.3-11.7	≥836	≥10.5	≥2388	≥30	247-271	31-34	200
N35EH	1.17-1.22	11.7-12.2	≥876	≥11.0	≥2388	≥30	263-287	33-36	200
N38EH	1.22-1.25	12.2-12.5	≥899	≥11.3	≥2388	≥30	287-310	36-39	200
N40EH	1.25-1.28	12.5-12.8	≥899	≥11.3	≥2388	≥30	302-326	38-41	200
N42EH	1.28-1.32	12.8-13.2	≥899	≥11.3	≥2388	≥30	318-342	40-43	200
N45EH	1.32-1.36	13.2-13.6	≥899	≥11.3	≥2388	≥30	342-366	43-46	200
N28AH	1.04-1.08	10.4-10.8	≥787	≥9.9	≥2786	≥35	207-231	26-29	230
N30AH	1.08-1.13	10.8-11.3	≥819	≥10.3	≥2786	≥35	223-247	28-31	230
N33AH	1.13-1.17	11.3-11.7	≥843	≥10.6	≥2786	≥35	247-271	31-34	230
N35AH	1.17-1.22	11.7-12.2	≥876	≥11.0	≥2786	≥35	263-287	33-36	230
N38AH	1.22-1.25	12.2-12.5	≥899	≥11.3	≥2786	≥35	287-310	36-39	230
The above-mentioned data of magnetic properties are given at room temperature. The max working temperature of magnet is changeable due to length-diameter ratio, coating thickness and other environment factors.

Magnetic Properties Chart for Grain Boundary Diffused Neodymium Magnets

Grade	Remanence Br				Coercivity Hcb				Intrinsic Coercivity Hcj		Max. Energy Product (BH)max				Max. Operating Temperature
	Typ.		Min.		Typ.		Min.		Min.		Typ.		Min.		Max. Operating Temperature
	T	kGs	T	kGs	kA/m	kOe	kA/m	kOe	kA/m	kOe	kJ/m³	MGOe	kJ/m³	MGOe	℃
G54H	1.47	14.7	1.45	14.5	1136	14.3	1109	13.9	1353	17	430	54	414	52	120
G52H	1.44	14.4	1.43	14.3	1113	14	1090	13.7	1353	17	414	52	398	50	120
G54SH	1.47	14.7	1.45	14.5	1136	14.3	1109	13.9	1592	20	430	54	414	52	150
G52SH	1.44	14.4	1.43	14.3	1113	14	1090	13.7	1592	20	414	52	398	50	150
G50SH	1.42	14.2	1.4	14	1097	13.8	1071	13.5	1592	20	398	50	382	48	150
G48SH	1.39	13.9	1.37	13.7	1074	13.5	1048	13.2	1592	20	382	48	366	46	150
G45SH	1.35	13.5	1.33	13.3	1043	13.1	1018	12.8	1592	20	358	45	342	43	150
G52UH	1.44	14.4	1.43	14.3	1113	14	1090	13.7	1990	25	414	52	398	50	180
G50UH	1.42	14.2	1.4	14	1097	13.8	1071	13.5	1990	25	398	50	382	48	180
G48UH	1.39	13.9	1.37	13.7	1074	13.5	1048	13.2	1990	25	382	48	366	46	180
G45UH	1.35	13.5	1.33	13.3	1043	13.1	1018	12.8	1990	25	358	45	342	43	180
G42UH	1.31	13.1	1.29	12.9	1012	12.7	987	12.4	1990	25	334	42	318	40	180
G40UH	1.28	12.8	1.26	12.6	989	12.4	964	12.1	1990	25	318	40	303	38	180
G48EH	1.39	13.9	1.37	13.7	1074	13.5	1048	13.2	2389	30	382	48	366	46	200
G45EH	1.35	13.5	1.33	13.3	1043	13.1	1018	12.8	2389	30	358	45	342	43	200
G42EH	1.31	13.1	1.29	12.9	1012	12.7	987	12.2	2389	30	334	42	318	40	200
G40EH	1.28	12.8	1.26	12.6	989	12.4	964	12.1	2389	30	318	40	303	38	200
G38EH	1.25	12.5	1.23	12.3	966	12.1	941	11.8	2389	30	302	38	287	36	200
G35EH	1.2	12	1.18	11.8	927	11.7	903	11.3	2389	30	279	35	263	33	200
G45AH	1.35	13.5	1.33	13.3	1043	13.1	1018	12.8	2787	35	358	45	342	43	220
G42AH	1.31	13.1	1.29	12.9	1012	12.7	987	12.4	2787	35	334	42	318	40	220
G40AH	1.28	12.8	1.26	12.6	989	12.4	964	12.1	2787	35	318	40	303	38	220
G38AH	1.25	12.5	1.23	12.3	966	12.1	941	11.8	2787	35	302	38	287	36	220
G35AH	1.2	12	1.18	11.8	927	11.7	903	11.3	2787	35	279	35	263	33	220
G33AH	1.16	11.6	1.14	11.4	986	11.3	872	11	2787	35	263	33	247	31	220
G30AH	1.1	11	1.08	10.8	850	10.7	826	10.4	2787	35	239	30	223	28	220

The above-mentioned data of magnetic properties are given at room temperature.
The max working temperature of magnet is changeable due to length-diameter ratio, coating thickness and other environment factors.

Additional Magnetic Properties of Sintered Neodymium Magnets

Parameters	Unit	Reference Range
Temperature Coefficient of Br / α(Br)	%/℃	-0.08 ~ -0.13
Temperature Coefficient of Hcj / β(Hcj)	%/℃	-0.35 ~ -0.80
Curie Temperature / T_c	℃	310-380
Recoil Permeability / μ_rec	–	1.05

Physical Properties of Sintered Neodymium Magnets

In addition to their permanent magnetic and chemical properties, the long-term operational stability of Neodymium magnets is closely tied to their physical properties, including mechanical, electrical, and thermal characteristics. Mechanical properties are primarily assessed by compressive strength, tensile strength, and bending strength. These metrics significantly influence the machinability and long-term service performance of Neodymium magnets. Electrical properties of metallic materials are measured by electrical resistivity. Neodymium magnets exhibit relatively low electrical resistivity and are susceptible to eddy current losses when used in rotary machinery. Thermal properties of Neodymium magnets are typically characterized by the coefficient of thermal expansion. Thermal expansion inevitably leads to dimensional changes, which can generate stress in the magnets within a device due to differences in expansion rates between the magnets and assembly materials, potentially causing mechanical damage and deterioration in magnetic performance.

Physical Properties Chart of Sintered Neodymium Magnets

Items	Parameters	Unit	Reference Range
Regular Physical Properties	Density / ρ	g/cm³	7.40-7.80
Regular Physical Properties	Vickness Hardness / HV	–	550-650
Electrical Properties	Electrical Resistivity	μΩ·m	1.4
Mechanical Properties	Compressive Strength	MPa	1050
	Tensile Strength	MPa	80
	Bending Strength	MPa	290
Thermal Properties	Thermal Conductivity	W/(m·K)	6-8
Thermal Properties	Coefficient of Thermal Expansion	10^-6/K	C⊥: -1.5, C∥: 6.5.

Surface Treatments of Sintered Neodymium Magnets

Surface treatment is a necessary procedure for Neodymium magnets. Neodymium magnets possess a multi-phase microstructure, primarily consisting of the Nd₂Fe₁₄B main phase, Nd-rich phase, and B-rich phase. The Nd-rich phase exhibits a very strong oxidation tendency and forms a galvanic couple with Nd₂Fe₁₄B grains in humid environments. A small amount of substitutional elements can enhance the stability of the magnets but at the expense of magnetic performance. Therefore, corrosion protection for Neodymium magnets is achieved by applying a barrier layer of material.

Surface treatments for Neodymium magnets can be classified into wet and dry processes. The wet process involves treating the magnets in pure water, inorganic solutions, or organic solutions. Commonly used wet processes include phosphating, electroplating, electroless plating, spray coating, and dip coating. The dry process involves treating the magnets through physical or chemical methods without contact with solutions. Dry processes typically include physical vapor deposition (PVD) and chemical vapor deposition (CVD).

Surface Treatment Types for Sintered Neodymium Magnets

Coating	Thickness (μm)	Color	SST (hrs)	PCT (hrs)	Characteristics
BW-Zn	4-15	Bright blue	≥24	–	Secondly commonly used single layer coating. Poor anti-corrosion ability.
Color-Zn	4-15	Shining color	≥48	–	Anti-corrosion ability is better than BW-Zn.
Ni-Cu-Ni	5-20	Bright silver	≥48	≥48	Most regular used multi-layer coating. Excellent humidity and salt spray resistance.
Chemical-Ni	5-20	Dark silver	≥72	≥48	Excellent humidity and salt spray resistance with uniform appearance.
Ni-Cu-Ni-Au	5-20	Golden	≥72	≥96	Excellent electrical conductivity and decorative.
Ni-Cu-Ni-Ag	5-20	Silver	≥72	≥96	Excellent electrical conductivity and decorative.
Ni-Cu-Ni-Sn	5-20	Silver	≥72	≥96	Excellent humidity resistance.
Phosphate	1-3	Dark grey	–	–	Temporary protection.
Aluminum	2-15	Bright silver	≥24	≥24	Noticeable coating.
Epoxy resin	10-30	Black/Grey	≥72	≥72	Excellent humidity and salt spray resistance. Superir binding force.
Parylene	5-20	Colorless	≥96	–	Excellent humidity, salt spray, corrosive vapors, and solvents resistance. Free of pore.
Everlube	10-15	Golden yellow	≥120	≥72	Excellent humidity resistance.
Teflon	8-15	Black	≥24	≥24	High temperature and rub resistance. Self-lubricant and 100% water-proof.
Note: anti-corrosion capability of coating is also influenced by the shape and size of magnet.

Magnetization Directions of Sintered Neodymium Magnets

Most permanent magnets need to be magnetized prior to serving in their specific applications. The magnetization process involves applying an external magnetic field along a specified direction to the permanent magnet to achieve saturation. Neodymium magnets possess relatively high coercivity and therefore require a stronger external magnetic field for saturation. Fast impulse magnetization is the preferred method for Neodymium magnets. The impulse magnetization system consists of two main components: the magnetizer and the magnetizing fixture. The magnetizer is a device that stores electrical energy in a capacitor and discharges it into the magnetizing fixture. The magnetizing fixture, also known as a magnetizing coil or magnetizing yoke, is designed to provide the necessary magnetic field strength in the appropriate magnetization patterns or directions. As anisotropic magnets, Neodymium magnets have a preferred direction of magnetization, allowing for various pole configurations as long as they do not conflict with the orientation direction.