Sintered Neodymium Magnet - SDM Magnetics Co., Ltd.

Ι What is Neodymium Magnet?

A Neodymium magnet is a type of permanent magnet made from an alloy of Neodymium (Nd), Iron (Fe), and Boron (B), forming the Nd₂Fe₁₄B phase. Commonly known as a “Neo magnet” or “NdFeB magnet,” these terms abbreviate “Neodymium” and “Neodymium Iron Boron,” respectively. A Neodymium magnet is also labeled as a rare earth magnet by many due to the rare earth elements in its composition.

A Neodymium magnet can be divided into sintered Neodymium magnet, bonded Neodymium magnet, and hot-pressed Neodymium magnet based on its manufacturing process. Typically, the term “Neodymium magnet” refers specifically to the sintered variety, prized for its unmatched magnetic strength and dominant market share.

Today, the Neodymium magnet remains the most powerful magnet available, powering industries like consumer electronics, industrial automation, automotive, green energy, home appliances, medical, aerospace, and telecommunications.

Neodymium Arc Magnet

Neodymium Bar Magnet

Neodymium Block Magnet

Neodymium Countersunk Magnet

Neodymium Disc Magnet

Neodymium Ring Magnet

Neodymium Cylinder Magnet

Neodymium Sphere Magnet

Manufacturing Process of Sintered Neodymium Magnet

The manufacturing process of a sintered Neodymium magnet begins with producing an alloy using the vacuum melting and strip-casting (SC) method. The alloy strip is transformed into a coarse powder through hydrogen decrepitation, then jet-milled into a fine powder with particle sizes of 3 to 7 microns. This fine powder is packed into molds and pressed under a magnetic field to align the particles. The resulting compacted green body is sintered in a vacuum furnace at around 1100°C. After sintering, the blanks are machined into specific shapes, surface-treated, and magnetized to create the final sintered Neodymium magnet.

Magnetic Properties of Sintered Neodymium Magnet

The grade of a sintered Neodymium magnet is typically denoted by a letter N followed by a number and, often, an additional letter. The “N” stands for Neodymium, the core element.

The number indicates the maximum energy product, (BH)max, measured in Mega-Gauss Oersted (MGOe) using the CGS unit. One or two trailing letters specify the intrinsic coercivity and maximum operating temperature of the sintered Neodymium magnet.

Grades with M (middle), H (high), SH (super high), UH (ultra high), EH (extreme high), and AH (abnormal high) have intrinsic coercivity exceeding 14, 17, 20, 25, 30, and 35 kOe, respectively, allowing maximum operating temperatures of 100, 120, 150, 180, 200, and 220°C.

Some grades, like the well-known N35 and N52, lack a trailing letter; these sintered Neodymium magnets have an intrinsic coercivity of at least 12 kOe and a maximum operating temperature below 80°C.

Additionally, the grade of grain boundary diffused Neodymium magnets adds a prefix “G” to highlight its unique manufacturing process.

Magnetic Properties of Sintered Neodymium Magnet

Magnetic Properties Chart for Sintered Neodymium Magnet

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 Magnet

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 Magnet

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 Magnet

Beyond permanent magnetic and chemical properties, the long-term stability of a sintered Neodymium magnet depends heavily on its physical properties, including mechanical, electrical, and thermal characteristics.

Mechanical properties—measured by compressive strength, tensile strength, and bending strength—greatly affect the machinability and durability of a sintered Neodymium magnet during extended use.

Electrical properties, assessed through electrical resistivity, reveal that sintered Neodymium magnets have relatively low resistivity, making them susceptible to eddy current losses in rotary machinery.

Thermal properties are typically defined by the coefficient of thermal expansion. Thermal expansion in Neodymium magnets causes dimensional changes, generating stress due to differences in expansion between the magnet and surrounding assembly materials. This stress can lead to mechanical damage and reduced magnetic performance over time.

Physical Properties Chart of Sintered Neodymium Magnet

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 Treatment of Sintered Neodymium Magnet

Surface treatment is essential for a sintered Neodymium magnet. These magnets feature a multi-phase microstructure, primarily composed of the Nd2Fe14B main phase, Nd-rich phase, and B-rich phase.

The Nd-rich phase has a strong tendency to oxidize and forms a galvanic couple with Nd2Fe14B grains in humid conditions, accelerating corrosion. Adding small amounts of substitutional elements can improve stability, but this often reduces magnetic performance.

Thus, protecting a sintered Neodymium magnet from corrosion requires applying a barrier layer through surface treatment. Surface treatment for a sintered Neodymium magnet is divided into wet and dry processes.

The wet process involves treating the magnet in pure water, inorganic solutions, or organic solutions, with common methods including phosphating, electroplating, electroless plating, spray coating, and dip coating. The dry process, in contrast, uses physical or chemical methods without liquid solutions.

Typical dry processes include physical vapor deposition (PVD) and chemical vapor deposition (CVD).

Surface Treatment Types for Sintered Neodymium Magnet

Coating	Thickness (μm)	Color	SST (hrs)	PCT (hrs)	Characteristics
BW-Zn	4-15	Bright blue	≥24	–	Secondly commonly used single layer coating. Poor corrosion resistance.
Color-Zn	4-15	Shining color	≥48	–	Corrosion resistance 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.
Electroless 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 performance.
Ni-Cu-Ni-Ag	5-20	Silver	≥72	≥96	Excellent electrical conductivity and decorative performance.
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 Magnet

Most permanent magnets require magnetization before they can serve their intended applications. This magnetization process involves applying an external magnetic field along a specific direction to fully saturate the magnet.

A sintered Neodymium magnet, with its relatively high coercivity, demands a stronger external magnetic field to achieve saturation compared to other magnets. For sintered Neodymium magnets, a fast impulse is the preferred magnetization method.

The impulse magnetization system consists of two key components: the magnetizer and the magnetizing fixture. The magnetizer, a device that stores electrical energy in a capacitor Lp releases this energy into the magnetizing fixture.

The magnetizing fixture—also called a magnetizing coil or yoke—generates the required magnetic field strength and directs it in the appropriate pattern or orientation. As an anisotropic magnet, a sintered Neodymium magnet has a fixed magnetization direction, allowing various pole configurations as long as they align with its orientation.