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Selecting the Right Magnet Grade During the Design Phase: Balancing Performance, Temperature, and Cost

Guide - 24 Sep , 2026

Selecting the right magnet grade is one of the critical stages in the project lifecycle. An error at this early stage can lead to two opposite but equally damaging scenarios: under-dimensioning, which can cause premature degradation or device failure due to demagnetization, or over-dimensioning, which unnecessarily increases production costs and makes the product less competitive on the market.

To explore the available solutions and design possibilities, you can consult our dedicated guide to custom magnets.

What Is Magnet Grade and How Is It Defined?

The grade of a permanent magnet defines the quality of the material, its fundamental magnetic properties, and its temperature tolerance. In the case of sintered neodymium magnets, the alphanumeric designation consists of two main elements:

• The N + Number designation (e.g. N35, N45, N52): The number represents the Maximum Energy Product, BHmax, expressed in Mega-Gauss-Oersted (MGOe). The higher this value, the greater the magnetic strength for the same magnet volume.
• The Temperature-Tolerance Letters (e.g. M, H, SH, UH, EH): These indicate the recommended maximum operating temperature and the material’s resistance to heat-induced demagnetization.

Understanding the interaction between magnetic strength and heat resistance is the first step toward correctly selecting the NdFeB grade.

Defining Performance: Remanence and Coercivity

To make the right choice during the design phase, engineers must analyze the material’s demagnetization curve (B-H curve). The key parameters to consider are:

• Remanence (Br): This represents the residual magnetic flux density within the magnet when the external magnetic field is zero. It determines the magnet’s “strength” in open magnetic circuits or direct-attraction applications.
• Coercivity (Hcb) and Intrinsic Coercivity (Hcj): These indicate the magnet’s ability to withstand external demagnetizing fields or heat without losing its magnetization. A high Hcj value is essential in electric motors, where opposing magnetic fields generated by the stator continuously attempt to demagnetize the rotor magnets.

When evaluating the magnet grade during the design process, the BHmax value provides a direct measure of how much magnetic energy the component can store within a given volume. Optimizing this parameter makes it possible to reduce the physical size of the device and achieve greater miniaturization.

Magnet Grade and Temperature: The Impact of Heat

Temperature is one of the main challenges for NdFeB magnets. As temperature increases, two types of magnetic losses can occur:

• Reversible Losses: A temporary decrease in remanence (Br) and coercivity (Hcj) caused by thermal agitation of the atoms. Once the magnet returns to room temperature, its original performance is restored. This variation is defined by the temperature coefficients of Br and Hcj.
• Irreversible Losses: Partial demagnetization caused by the operating point crossing a critical threshold at a given temperature. This loss is not recovered when the magnet cools down and requires the component to be re-magnetized.
• Curie Temperature: The temperature above which the material permanently loses its ability to retain permanent magnetism. For NdFeB, this is typically around 310–340 °C.

In high-performance applications, using a standard N52 grade can be highly problematic: at temperatures around 90 °C, an N52 magnet can experience significant performance degradation and may be at risk of irreversible demagnetization.

In these situations, part of the remanence may be sacrificed in favor of grades such as N38SH or N40UH, which are enhanced with heavy rare earth elements (HREEs) such as Dysprosium (Dy) or Terbium (Tb), capable of significantly increasing intrinsic coercivity Hcj.

Have You Already Defined the Temperature and Performance Requirements for Your Magnet?

Selecting the most suitable NdFeB grade requires balancing magnetic performance, operating temperature, geometry, and cost. A higher-grade magnet is not always the most efficient solution: in many cases, the same performance can be achieved by optimizing the material, dimensions, and magnet configuration.

Talk to our technical team: we will analyze your application requirements and help you identify the magnetic solution best suited to your project.

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Optimizing Magnet Cost

Cost plays a key role in the industrialization of any component. Optimizing magnet cost does not mean simply purchasing the cheapest grade available, but rather finding the ideal balance between material volume and unit cost.

Factors affecting the cost of a magnet grade include:

• Dysprosium (Dy) and Terbium (Tb) content: Grades with higher temperature tolerance (SH, UH, EH, AH) may require greater amounts of heavy rare earth elements, which are scarce materials subject to significant fluctuations in global market prices. An EH grade can cost significantly more than an N grade of the same dimensions.
• Dimensions and Geometry: Increasing the volume of a lower-grade magnet (e.g. N35) to achieve the same magnetic field as a smaller N52 magnet is only advantageous if the available space in the design allows for it and if the total raw material cost does not exceed that of the smaller, higher-grade magnet.
• Manufacturing Tolerances and Coatings: Dimensional accuracy and the choice of surface finish (Nickel-Copper-Nickel, Epoxy, Passivation) directly affect the final supply cost.

NdFeB Grade Selection Procedure

To guide the R&D team through the decision-making process, it is advisable to follow a structured methodology.

Step 1: Calculate the Actual Magnetic Field at the Operating Point

Determine the magnetic flux density B required in the air gap. Using FEM (Finite Element Method) analysis, it is possible to simulate the magnetic flux lines and understand how the geometry of the magnetic circuit affects magnet stability.

Step 2: Map the Actual Thermal Profile

Do not limit the analysis to the theoretical ambient temperature. Consider:

• Heat dissipated through the Joule effect in adjacent windings.
• Mechanical friction.
• Temporary temperature peaks during overload conditions.

Step 3: Check the Operating Point on the B-H Curve

Make sure that, at the maximum expected operating temperature and in the presence of the maximum external demagnetizing field, the magnet’s operating point remains above the “knee” of the demagnetization curve. If the operating point falls below the knee, irreversible demagnetization will occur.

Step 4: Compare Different Grade and Geometry Solutions

Evaluate different alternatives to achieve the same performance target. For example:

• Option A: Small N45UH magnet (high cost per kg, reduced volume).
• Option B: Slightly larger N40H magnet (lower Dy content, lower cost per kg, larger volume).

Option B can often provide a more cost-effective solution for large-scale production.

Best Practices and Common Mistakes to Avoid

• Avoid over-engineered grades: Specifying an N48UH grade for an application operating at 40 °C in an environment free from demagnetizing fields can result in a significant and unnecessary increase in costs.
• Consider NdFeB oxidation: Neodymium magnets are highly susceptible to corrosion. The appropriate coating (e.g. epoxy resin for humid environments, Ni-Cu-Ni for standard environments) should be selected as part of the overall magnet design.
• Involve manufacturers at an early stage: Working with the magnet supplier during the prototyping phase makes it possible to verify the actual market availability of specific grades and reduce lead times.

Selecting the magnet grade during the design phase is not simply a matter of choosing an item from a catalogue, but rather an engineering balancing process. Carefully evaluating the interaction between the required magnetic field, thermal stresses, and raw material costs helps ensure the development of reliable, high-performance, and commercially sustainable products.

Do you have a project underway and are unsure which magnet grade to choose?

Contact us and we will analyze your technical requirements together and guide you toward selecting the grade best suited to your application.