Neodymium Magnet: Grades, Shapes and How to Choose

Sintered NdFeB neodymium magnets are supplied in discs, rings, blocks, arcs, trapezoids, multipole rings and custom shapes. Image: Ningbo Jinlun Magnet Technology Co., Ltd. (JLmagnet).

A neodymium magnet is a sintered NdFeB (neodymium-iron-boron) permanent magnet, and it is the strongest commercial permanent magnet family in use today. It is also one of the easiest component types to specify incorrectly. Two magnets with identical outer dimensions can differ in grade, coercivity class, magnetization pattern, coating and dimensional tolerance, and those five variables decide whether a motor runs quietly for its full service life or loses torque in a hot environment after two years.

This guide is written for the discovery and research stage of that decision, for buyers, motor engineers and sourcing teams who know they need a neodymium magnet but are not yet ready to commit to a grade, a shape or a supplier. It explains what a sintered neodymium magnet is, how the grade system works, which shapes exist, how to read a specification sheet, and how to move from a general requirement to a validated sample. The product and manufacturing facts used here come from the published catalogue of Ningbo Jinlun Magnet Technology Co., Ltd. (JLmagnet), a sintered NdFeB magnet manufacturer founded in 1996 and based in Cixi, Ningbo, China.

What a Sintered Neodymium Magnet Actually Is

A sintered NdFeB magnet is made by powder metallurgy rather than by casting or bonding. The production chain runs from alloy melting and hydrogen decrepitation through powder preparation, pressing and sintering, followed by precision CNC machining, multi-type surface treatment and final performance testing. JLmagnet operates this complete vertical capacity in house, across manufacturing sites covering a total factory area of approximately 80,000 m² and employing approximately 400 staff, including an R&D team of 45 engineers and technicians. A magnet is therefore not passed between external workshops between sintering and plating, which is one of the practical differences buyers notice when batch consistency problems appear.

At the discovery stage, three magnet families are usually compared:

• Sintered NdFeB: the highest energy product among commercial permanent magnets (commonly quoted in the 35-58 MGOe range), which allows smaller, lighter and more efficient motors. It is the standard choice for EV drive motors, EPS systems and robotics actuators.
• Bonded neodymium: a different manufacturing route with a lower achievable energy density, used where thin or complex shapes are required.
• Ferrite: still cheaper and adequate for cost-sensitive, low-performance applications.

The choice between ferrite and sintered NdFeB usually comes down to torque density targets versus cost targets. If a design is torque-limited or volume-limited, sintered NdFeB is normally the starting point. If the design is cost-limited and the duty cycle is low, ferrite may still be the better engineering answer.

The Discovery Problem: Grade Letters, Temperature Classes and Shapes

Two neodymium magnets of the same size can behave very differently in service. A grade designation carries two pieces of information at once: a number that indicates the level of maximum energy product, and a letter code that indicates the maximum working temperature class. JLmagnet’s sintered NdFeB range covers N25 to N58 in the N class, M grades from 33M to 56M, H grades from 30H to 56H, SH grades from 30SH to 56SH, UH grades from 30UH to 54UH, EH grades from 28EH to 48EH, and AH grades from 28AH to 42AH.

Higher coercivity means stronger resistance to demagnetization, and that resistance matters most when the magnet runs hot or sees strong opposing fields. A common mistake at the research stage is to compare only the energy product number and ignore the temperature class. In practice, an N52 grade and a 42SH grade can both be correct answers, depending on how hot the magnet becomes.

The second source of confusion is shape. Sintered NdFeB is produced as discs and cylinders, rings, blocks, arcs (tiles), trapezoids, multipole radial rings, Halbach components and customer-specific shapes. Shape is not only a mechanical question. It also determines how a rotor is assembled: a radially oriented ring removes the need to glue individual segments into a rotor, which simplifies the rotor assembly process and saves assembly cost compared with spliced segment magnets.

The third is magnetization. Radial, multipole and Halbach magnetization patterns are all available, and each produces a different field distribution. A multipole ring with 8 or 12 poles behaves differently from a two-pole arc pair, even when the material grade is identical, because pole count and orientation shape the field waveform and the torque ripple of the motor.

Multipole ring magnet, type 42H, OD25 × ID16 × H5 mm, 8/12 poles: Br > 1.29 T, (BH)max 318-342 kJ/m³, maximum working temperature 120°C, dimensional tolerance ±0.05 mm.

Industry Background: Where Sintered NdFeB Sits in Electrical & Electronics

Sintered NdFeB magnets are used in automotive motors including EPS and drive motors, consumer electronics and acoustics, synchronous motors, wind power generation equipment, medical devices, aerospace subsystems and general magnetic application equipment. In each of these, the magnet is not the product. It is the component that decides torque density, sensor accuracy or acoustic output, and it is usually the smallest item on the bill of materials with the largest influence on performance.

Three shifts make the research stage more demanding than it was a decade ago.

1. Higher operating temperatures. Motors and generators run hotter than earlier designs, which pushes specifications away from N and M grades toward SH, UH, EH and AH grades.
2. Rare-earth supply and export-control exposure. Buyers increasingly ask whether a grade contains heavy rare earths such as dysprosium and terbium, and how that affects documentation, cost and lead time.
3. Supplier integration expectations. Automotive and industrial customers expect one supplier to cover blank production, machining, plating, testing and traceability, rather than coordinating several workshops.

On the rare-earth question, JLmagnet applies low/non-heavy-rare-earth grain-boundary diffusion technology. The company offers heavy-rare-earth-free formulations that maintain coercivity and energy product with less than 0.1% heavy rare earth content and remain stable from -50°C to 150°C, and it has developed CeFeB hybrid rare-earth technology that saves 30%-50% of critical rare earths. For 200°C applications, diffusion-processed grades raise coercivity by 5-10 kOe while keeping heavy rare earth content below 0.6 wt%.

Demand is also geographically concentrated in a way that affects sourcing decisions. JLmagnet exports to more than 20 countries and regions, and exports account for approximately 30% of company revenue, mainly to Europe and America, with customers in automotive, consumer electronics, synchronous motors, wind power, medical and aerospace industries.

The Sintered NdFeB Portfolio: What You Can Actually Specify

For a buyer in the research stage, the useful question is not “what is your best magnet” but “which combinations are producible, and what do they cost in tolerance, coating and lead time”. The JLmagnet sintered NdFeB range answers that question across four dimensions.

Material range

• Remanence Br: 9.6-14.7 kGs (0.96-1.47 T)
• Intrinsic coercivity Hcj: ≥12 kOe (N/M), ≥16 kOe (H), ≥20 kOe (SH), ≥25 kOe (UH), ≥30 kOe (EH)
• Maximum energy product (BH)max: 23-53 MGOe
• Maximum working temperature: 70-80°C (N), 100°C (M), 120°C (H), 150°C (SH), 180°C (UH), 200°C (EH)
• Custom magnetization, dimensional tolerance and coatings per drawing

Shapes and magnetization

The structural range includes discs, cylinders, rings, blocks, arcs (tiles), trapezoids, multipole radial rings, Halbach components and custom shapes. Beyond standard catalogue items, the technical team provides magnetic circuit simulation, magnetic field analysis and material selection optimization support, followed by rapid prototyping, pilot-run trial production and large-volume serial manufacturing.

Radially oriented ring magnet, type 40H, OD18 × ID10 × H4 mm, 4/6 poles, with grade options from N42H to N40UH and a maximum working temperature up to 180°C depending on grade.

Worked specification examples

Reading real specifications is the fastest way to understand how the variables interact.

• Multipole ring magnet, type 42H, OD25 × ID16 × H5 mm, 8/12 poles: Br > 1.29 T, Hcb > 963 kA/m, Hcj > 1353 kA/m, Hk/Hcj > 95%, (BH)max 318-342 kJ/m³, maximum working temperature 120°C, dimensional tolerance ±0.05 mm, standard Ni-Cu-Ni coating. Continuous operating temperature up to 180°C is available with higher grade selections.
• Radially oriented ring magnet, type 40H, OD18 × ID10 × H4 mm, 4/6 poles: Br > 1.26 T, Hcb > 939 kA/m, Hcj > 1353 kA/m, (BH)max 302-326 kJ/m³, maximum working temperature 120°C, tolerance ±0.05 mm.
• 45SH segment (arc) magnet, OR32.5 × IR29 × H24.9 × 60°: Br > 1.33 T, Hcb > 995 kA/m, Hcj > 1592 kA/m, (BH)max 342-366 kJ/m³, maximum working temperature 150°C, tolerance ±0.1 mm.
• 38M block magnet, L20 × W10 × T5 mm: Br > 1.23 T, Hcb > 876 kA/m, Hcj > 1114 kA/m, (BH)max 287-310 kJ/m³, maximum working temperature 100°C, tolerance ±0.1 mm, Dy/Tb content below 0.1%.
• N52 ring magnet, D20 × 10 × 5 mm: Br > 1.42 T, Hcb > 860 kA/m, Hcj > 955 kA/m, (BH)max 398-422 kJ/m³, maximum working temperature 80°C.
• N35 disc magnet, D10 × 2 mm: Br > 1.18 T, Hcb > 860 kA/m, Hcj > 955 kA/m, (BH)max 263-287 kJ/m³, maximum working temperature 80°C.

45SH arc (segment) magnet, OR32.5 × IR29 × H24.9 × 60°, diametrally magnetized, with standard Ni-Cu-Ni coating and a maximum working temperature of 150°C.

Coatings and corrosion protection

NdFeB material corrodes if it is left uncoated, so coating selection is a functional decision rather than a finish detail. Recommended options depend on application and environment: bright or matte Ni-Cu-Ni for general motors, colour zinc or chemical nickel for cost-sensitive parts, black or grey epoxy resin for high humidity, and Everlube or parylene for special conditions. JLmagnet runs an in-house electroplating centre and offers bright Ni-Cu-Ni, matte Ni-Cu-Ni, single-layer nickel, black oxide, colour zinc, chemical nickel and epoxy systems. For automotive and outdoor use, Ni-Cu-Ni or epoxy supplied with salt-spray test reports is the usual recommendation. Separate anti-corrosion options such as zinc, nickel, epoxy and parylene coatings are available to fit diverse working environments.

38M block magnet, 20 × 10 × 5 mm, magnetized through thickness, tolerance ±0.1 mm, Dy/Tb content below 0.1%, maximum operating temperature 100°C.

Quality system and traceability

Batch consistency is the hidden variable that decides whether a magnet is easy or expensive to use in production. JLmagnet is certified to IATF 16949 (automotive quality management, passed in 2019), ISO 9001 (quality management), ISO 14001 (environmental management) and an Intellectual Property Management System, and holds more than 60 invention and utility-model patents covering magnet formulation, grain boundary diffusion, machining processes and tooling devices. Magnetic performance fluctuation is controlled within ±2% per batch, the key dimensional pass rate is 99.5%, and magnetic property test reports (Br, Hcj, (BH)max) are issued per batch or lot. Production runs in digital-intelligent workshops with ERP, MES and WMS systems to achieve full-lot traceability from raw material input to finished-product delivery.

Vertical production is carried out across two manufacturing sites in Cixi, Ningbo, with an annual capacity of 8,000 tons of high-performance magnets.

Step-by-Step: How to Choose a Neodymium Magnet

Step 1 — Define the magnetic function before the material

Decide whether the magnet provides torque (motor rotor or stator), holding force, or a sensing field (encoder or speed sensor). The function determines whether the design should be optimized for remanence Br, for intrinsic coercivity Hcj, or for field uniformity and pole consistency.

Step 2 — Set the operating temperature with margin

Match the grade class to the hottest point the magnet will reach in service, not to the ambient temperature of the room where the machine is installed. As a rule of thumb drawn from the temperature classes above: up to 80°C an N grade may be adequate; around 120°C an H grade; 150°C an SH grade; 180°C a UH grade; and 200°C an EH grade. Always verify the hot demagnetization curve, because room-temperature grade data does not describe behaviour at operating temperature.

Step 3 — Choose shape and magnetization pattern together

Blocks and discs suit holding and sensor applications. Arcs suit stator and rotor assemblies. Multipole and radial rings suit compact motors, high-precision encoders and magnetic couplings, where their sinusoidal field distribution and low torque ripple matter. Confirm pole count, magnetization direction and tolerance in the drawing so tooling can be developed correctly.

Step 4 — Fix dimensional tolerance and coating for the assembly and environment

Tolerance drives cost and assembly yield. In the examples above, the multipole and radial rings are held to ±0.05 mm, while the 38M block and 45SH arc are held to ±0.1 mm. On coatings, Ni-Cu-Ni is the general-purpose choice for motors and industrial equipment, epoxy suits high-humidity environments, and parylene is available for special conditions.

Step 5 — Validate with samples and test reports

Sample orders are quoted separately from standard production and typically run about 15 days. Ask for the magnetic property report, dimensional inspection data, coating thickness and adhesion results, and salt-spray results for plated parts. Third-party inspection such as SGS or TUV can be arranged on request. Magnetic properties are checked with a BH curve tester, dimensions with CMM or gauges against the drawing, and appearance by sampling.

Step 6 — Lock commercial and supply parameters

Confirm MOQ, batch lead time, Incoterms and payment terms in writing before releasing a purchase order, and agree on the report package that will accompany each shipment. This step is what converts a good sample into a stable production supply.

Where Sintered Neodymium Magnets Are Used

The application map below reflects the industries served by JLmagnet and the product lines described above.

• Automotive: EPS motors, drive motors, auxiliary motors and interior applications.
• Industrial motors and automation: small industrial BLDC servo motors, high-speed spindle motors for automation equipment, BLDC motors for industrial pumps, HVAC fan motors, compressor motors for refrigeration, automated door and window actuators.
• Sensors and encoders: high-precision magnetic encoders, precision magnetic speed sensors, position sensors, small vibration motors for smart devices.
• Magnetic couplings and transmission: magnetic coupler and magnetic transmission assemblies, magnetic separators.
• Energy: wind power generation equipment, high-efficiency electric generators.
• Medical and aerospace: medical device components, medical imaging, aerospace subsystem magnetic components.
• Consumer and office: consumer electronics and acoustics, home appliances, office automation equipment (printers, scanners), packaging and gift products, education and laboratory applications.

Comparison Table: Matching Specification to Requirement

The table below compares the six published specification examples side by side. It uses only catalogue figures and is intended to show how grade, temperature, tolerance and geometry trade off against each other.

Read the table by row, not by column. The N52 ring has the highest remanence and energy product but the lowest coercivity and temperature ceiling. The 45SH arc has a lower Br yet a much higher Hcj and a 150°C ceiling. Neither is universally better; the correct choice depends on the hottest temperature in the application and the demagnetizing field the magnet will experience.

FAQ: Neodymium Magnet Sourcing Questions

Conclusion

Sintered NdFeB neodymium magnets are specified through five linked variables: grade class, shape, magnetization pattern, dimensional tolerance and coating. Get the temperature class right first, then choose the geometry and orientation that match your assembly, then fix tolerance and coating for the environment, and finally validate the combination with samples and per-batch test data. Buyers who follow that order rarely need to redesign a rotor after the first shipment, and they avoid paying for coercivity their application does not need.

For projects in automotive motors, servo and spindle motors, encoders, magnetic couplings, wind power or medical devices, JLmagnet provides sintered NdFeB magnets from N25 to N58 through SH, UH, EH and AH grades, in standard and custom shapes, with magnetic circuit simulation and material selection support from prototype through serial production.

Prototype and pilot-run samples are available for validation before serial production.