What Is a Neodymium Magnet? Sintered NdFeB Grades, Shapes and Applications Explained

A neodymium magnet is a permanent magnet made from a neodymium-iron-boron (NdFeB) alloy. In its sintered form it offers the highest energy product among commercial permanent magnets, which is why it becomes the default choice when a design has to generate strong magnetic flux from a small volume: motor rotors and stators, position sensors, magnetic couplings and holding assemblies.

JLmagnet is the brand of Ningbo Jinlun Magnet Technology Co., Ltd., a sintered NdFeB magnet manufacturer based in Cixi, Ningbo, China. The company was founded in 1996 as Cixi Jiwei Magnetoelectric Material Factory, was formally incorporated in 2006, and has more than 30 years of experience in the R&D, production and sales of sintered NdFeB magnets.

This guide is written for engineers, product managers and sourcing teams working at the discovery and research stage. It explains what a sintered NdFeB magnet is, how to read a grade code such as N42SH or 48EH, why shape and magnetization matter as much as grade, what coatings actually do, how to structure a supplier qualification, and where the practical limits are.

The Problem: “Strong Magnet” Is Not a Purchasing Specification

When a magnet project underperforms, the root cause is usually the specification rather than the material. Three failures repeat across motor, sensor and coupling projects.

Failure 1: a grade number without a temperature class

A neodymium magnet grade code carries two independent pieces of information. The number describes the maximum energy product class; the letter describes the intrinsic coercivity class, which governs how strongly the magnet resists demagnetization as temperature rises. Choosing the highest available number while ignoring the letter is a frequent and expensive mistake. The useful question is not “which grade is strongest?” but “which grade still holds its flux at my operating temperature, in my magnetic circuit, at my worst-case demagnetizing field?” The practical check is the hot-demagnetization curve — Hcj at the operating temperature — not the room-temperature grade printed on the data sheet.

Failure 2: designing around glued segments when one-piece rings are available

Rotors are often built by bonding several arc segments onto a hub. A radially oriented ring or a multipole ring replaces that assembly with an integrated one-piece magnet: no glued segments, better concentricity and dynamic balance, a smoother sinusoidal field distribution, lower torque ripple and quieter operation, tight dimensional tolerance, and a simplified rotor assembly process that reduces assembly cost compared with spliced segment magnets. Segments still make sense for geometries that cannot be produced as a single ring, but that trade-off belongs at the design stage, not on the assembly line.

Failure 3: treating coating, tolerance and batch records as afterthoughts

Coating choice determines corrosion life; dimensional tolerance determines whether the rotor or sensor assembles at all; batch records determine whether the next shipment behaves like the sample. Projects that specify only “N42, nickel plated” tend to discover the difference between a data sheet and a delivered lot the hard way. Each of these three variables is a purchasing criterion, and each can be written into the specification and verified with a test report.

Industry Background: Where Sintered NdFeB Magnets Are Used

Sintered NdFeB magnets serve the automotive, consumer electronics, synchronous motor, wind power, medical device and aerospace industries. Typical functions include rotor and stator magnets in motors and generators, sensor elements, and magnetic components in chucks, separators and assemblies.

Three market pressures shape sourcing decisions at the moment. First, electrification and automation continue to push motor designs toward higher torque density, which favours the compact flux of sintered NdFeB. Second, rare-earth supply and export-control questions have made heavy rare-earth content a commercial issue as well as a technical one, and low/non-heavy-rare-earth formulations are increasingly requested. Third, documentation expectations have risen: automotive and industrial buyers now ask for per-batch magnetic test reports, process traceability and, where relevant, third-party inspection.

Ferrite magnets remain the cheaper option for cost-sensitive, low-performance applications, and the choice between magnet families depends on torque density and cost targets. Bonded neodymium magnets are a separate product family with different process economics; this guide focuses on sintered NdFeB, the material covered by the data cited here.

What a Sintered NdFeB Magnet Is, and How to Read Its Grade

From alloy to finished part

Ningbo Jinlun Magnet Technology Co., Ltd. owns full vertical production capacity covering melting, hydrogen-decrepitation, powder preparation, pressing, sintering, precision CNC machining, multi-type surface treatment and final performance testing. Production is organised around four in-house bases — sintering, machining, plating and testing — with an annual capacity of 8,000 tons of high-performance magnets. The manufacturing facility covers approximately 80,000 m² across two manufacturing sites and employs approximately 400 staff, including an R&D team of 45 engineers and technicians.

Reading a grade code: N42SH, 48EH, 28AH

The material grade range spans N25–N58, 33M–56M, 30H–56H, 30SH–56SH, 30UH–54UH, 28EH–48EH and 28AH–42AH. Across that range, remanence (Br) covers 0.96–1.47 T and maximum energy product ((BH)max) covers 23–53 MGOe. Minimum intrinsic coercivity values are ≥12 kOe for N and M classes, ≥16 kOe for H, ≥20 kOe for SH, ≥25 kOe for UH and ≥30 kOe for EH.

Two practical notes follow. SH, UH, EH and AH grades are the series produced for demanding high-temperature operating scenarios, and the letter class — not the number — is what keeps a magnet alive at temperature. For AH grades, and for any grade used near its limit, ask the supplier for the demagnetization curve at the actual operating temperature instead of extrapolating from the room-temperature data sheet.

Worked examples from the product range

• N52 ring, D20×10×5 mm: Br > 1.42 T, Hcb > 860 kA/m, Hcj > 955 kA/m, Hk/Hcj > 95%, (BH)max 398–422 kJ/m³, maximum working temperature 80 °C. Designed for consumer electronics, precision automation equipment, high-performance motors and sensors, medical device components and advanced audio-acoustic products.
• 38M block, L20×W10×T5 mm: maximum operating temperature up to 100 °C, magnetized through thickness, tight tolerance, Ni-Cu-Ni coating, non-heavy-rare-earth formula with Dy/Tb content below 0.1%. Used in brushless DC motors for household appliances, encoders and position sensors, office automation equipment, small vibration motors, magnetic coupling assemblies and automated door and window actuators.
• 45SH segment, OR32.5 × IR29 × H24.9 × 60°: Br > 1.33 T, Hcb > 995 kA/m, Hcj > 1592 kA/m, maximum working temperature 150 °C, diametral magnetization, dimensional tolerance ±0.1 mm. Suited to permanent-magnet BLDC motors for industrial pumps, servo motors for automation, high-efficiency electric generators, HVAC fan motors, EV auxiliary motors and refrigeration compressor motors.
• 42H multipole ring, OD25 × ID16 × H5 mm, 8/12 poles: one-piece multipole design with no glued segments, dimensional tolerance ±0.05 mm, standard Ni-Cu-Ni coating, maximum working temperature 120 °C for this model, with grade options in the family covering continuous operating temperature up to 180 °C. Used in high-precision magnetic encoders, precision magnetic speed sensors, small industrial BLDC servo motors, automotive auxiliary EPS motors, high-speed spindle motors and magnetic coupler assemblies.
• 40H radial ring, OD18 × ID10 × H4 mm, 4/6 poles: radially oriented one-piece ring, tolerance ±0.05 mm, grade options from 42H to 40UH with maximum working temperature up to 180 °C.
• N35 disc, 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 — a cost-effective grade for packaging, consumer electronics, home appliances, automation, automotive interiors and laboratory use.

Shape, Magnetization and Coating: Three Variables Buyers Underestimate

Shapes

Standard structural configurations include discs and cylinders, rings, blocks, arcs (tiles), trapezoids, multipole radial rings, Halbach components and custom shapes. JLmagnet's naming code keeps drawings readable: D for disc or cylinder, F for block, R for arc, followed by dimensions, with features such as steps, holes, counterbores and chamfers appended after a hyphen — for example D15×3.8 (disc), D50×D13.5×20-D20×8 (ring with counterbore), F18×9.5×2 (block) or R90×R85×40×50 (arc).

Magnetization patterns

Grade and shape describe the material; magnetization describes the field. Radially oriented rings and multipole rings are produced with multipolar and radial orientation technologies, giving high pole-to-pole consistency for small motors, sensors and actuators. Custom magnetization patterns — radial, multipole and Halbach — are available, and the pole count, magnetization direction and tolerance must be confirmed on the drawing before tooling is developed.

Coatings and corrosion protection

NdFeB material corrodes if it is left unprotected, so the coating system is part of the specification rather than a cosmetic detail. JLmagnet runs an in-house electroplating centre and offers bright Ni-Cu-Ni and matte Ni-Cu-Ni for general motors, single-layer nickel, black oxide, colour zinc, chemical nickel and epoxy resin, plus zinc, nickel, epoxy and parylene protection options for diverse working environments. Everlube and parylene are used for special conditions. For automotive and outdoor applications, Ni-Cu-Ni or epoxy with a salt-spray test report is the recommended combination, and the choice should be matched to the actual environment rather than to habit.

Step-by-Step: Selecting and Qualifying a Sintered NdFeB Magnet

1. Define the operating point. Record the required flux or torque, the air gap, the maximum continuous and peak operating temperatures, and the worst-case demagnetizing field from the winding. The magnet is sized against this envelope, not against a catalogue grade.
2. Choose the coercivity class first, then the energy product. Select the letter class (N, M, H, SH, UH, EH, AH) so that Hcj at the operating temperature exceeds the demagnetizing field with margin; then pick the highest number within that class that fits the space and the cost target.
3. Choose the shape and magnetization pattern. Compare a one-piece radially oriented or multipole ring against an assembly of segments. Monolithic rings remove glued joints and improve concentricity, dynamic balance and torque-ripple behaviour, while also simplifying rotor assembly.
4. Fix dimensional tolerance and coating together. Tolerances of ±0.05 mm are used for multipole and radial rings, and ±0.1 mm for segments and blocks. Specify the coating by environment — Ni-Cu-Ni for general motor duty, epoxy for high humidity, parylene or Everlube for special conditions — and require the corresponding test data.
5. Validate with samples before tooling and volume. JLmagnet supports rapid prototyping and pilot-run trial production before large-volume serial manufacturing, with a sample lead time of approximately 15 days. Ask for the magnetic property report for the sample lot.
6. Qualify the supplier and lock batch control. Verify certifications (IATF 16949, ISO 9001, ISO 14001 and IPMS), capacity, in-house machining and plating, batch consistency data and the documentation package. JLmagnet passed IATF 16949 automotive quality management certification in 2019 and holds magnetic performance batch fluctuation within ±2%, with a key dimensional pass rate of 99.5% and magnetic property test reports (Br, Hcj, (BH)max) issued per batch or lot.

Use Cases: Matching Magnets to Applications

• Automotive EPS and drive motors. EPS and drive motors typically use high-coercivity grades such as N38SH, N42SH, 45SH, N48H or UH grades, depending on operating temperature and demagnetization resistance. JLmagnet produces grades from 48M/48H/42SH/45SH up to 52UH and supplies magnets for automotive auxiliary EPS motors.
• Industrial servo, spindle and appliance motors. Small industrial BLDC servo motors, high-speed spindle motors for automation equipment, HVAC fan motors, industrial pump motors and refrigeration compressor motors.
• Encoders and speed sensors. High-precision magnetic encoders and precision magnetic speed sensors use radially oriented and multipole rings where pole-to-pole consistency matters.
• Wind power and generators. Wind power generation equipment, wind turbine generators and high-efficiency electric generators use sintered NdFeB magnets as key magnetic components.
• Magnetic couplings and assemblies. Magnetic coupler and magnetic transmission assemblies, magnetic separators and custom magnetic assemblies for motion and transmission designs.
• Synchronous machines and industrial drives. Synchronous motors, including the permanent-magnet synchronous designs used in industrial drives and elevator traction machines, are a core application area for sintered NdFeB magnets.
• Medical, aerospace, electronics and general industry. Medical imaging and device components, aerospace subsystem magnetic components, consumer electronics and acoustics, home appliances, office automation, packaging and gift applications, and education and laboratory use.

Comparison Table: Two Decisions That Change Assembly and Cost

Frequently Asked Questions

Conclusion: Start From the Operating Point, Not the Grade Number

Sintered NdFeB magnets are not selected by picking the largest number on a grade chart. They are selected by matching a coercivity class to an operating temperature, a shape and magnetization pattern to a rotor or sensor geometry, and a coating and tolerance to the working environment — then verifying all of it with batch test data from a supplier whose certifications, capacity and process control match the risk level of the project.

Those are also the questions that decide whether a magnet project is repeatable in production: which class survives the heat, whether a one-piece ring can replace a glued segment assembly, what the coating must withstand, what the sample proves, and how the next lot will be verified. Answering them before tooling starts is what turns a magnet request into a purchasing specification.