Magnet Testing: Magnetic Properties, Standards & Measurement Methods
What Is Magnet Testing?
Magnet testing encompasses a range of laboratory and field test methods used to characterize the magnetic properties of permanent magnets, soft magnetic materials, and magnetic components. These tests verify that magnetic materials meet performance specifications for their intended applications, from electric motors and generators to sensors, MRI systems, and consumer electronics.
Magnet testing is fundamental to quality control and engineering design across the electric vehicle, industrial motor, aerospace, defense, and renewable energy industries, where magnetic component performance directly determines energy efficiency, power density, and system reliability.
Key Magnetic Properties Measured in Testing
Remanence (Br)
The residual magnetic flux density that remains in a permanent magnet after the external magnetizing field is removed. Measured in Tesla (T) or Gauss (G). Higher Br delivers more magnetic flux for a given magnet volume—critical for motor torque density.
Coercivity (Hc and HcJ)
- Hc (coercive field): The reverse field required to reduce flux density to zero.
- HcJ (intrinsic coercivity): The reverse field required to reduce magnetization to zero. HcJ governs demagnetization resistance—critical for high-temperature or shock-exposed applications.
Maximum Energy Product ((BH)max)
The area of the largest rectangle that can be inscribed under the second-quadrant demagnetization curve (B-H curve). Expressed in kJ/m³ or MGOe. It is the single most important figure of merit for permanent magnets—representing the maximum magnetic energy stored per unit volume.
Permeability (µ)
For soft magnetic materials (transformer cores, inductor cores), permeability describes how easily the material is magnetized. High permeability is desirable for efficient magnetic flux conduction.
Curie Temperature (Tc)
The temperature above which a ferromagnetic material loses its permanent magnetism. Permanent magnets used in motors must have Tc well above the maximum operating temperature.
Magnet Testing Methods
B-H Curve Measurement (Hysteresis Loop Tracing)
A magnetometer or hysteresisgraph traces the complete magnetic hysteresis loop (B vs. H), from which Br, Hc, HcJ, and (BH)max are extracted. This is the fundamental characterization test for permanent magnets, performed per ASTM A977 and IEC 60404-5.
Helmholtz Coil Testing
A Helmholtz coil system provides a uniform magnetic field region for calibration and measurement of total magnetic moment of permanent magnet components. Used for production acceptance testing of assembled magnets and magnetic subassemblies.
Flux Meter / Search Coil Testing
A calibrated search coil connected to a flux meter measures the total magnetic flux linkage of a magnet or magnetic circuit. Used for comparative production testing and magnet assembly verification.
Demagnetization Curve at Temperature
For applications involving elevated temperature operation (EV motors, aerospace), the demagnetization curve is measured at operating temperature to verify that flux density and coercivity meet specifications under the worst-case thermal condition.
Common Permanent Magnet Types and Their Testing Significance
| Magnet Type | Key Properties | Primary Test Concern |
| NdFeB (sintered) | Highest (BH)max; low Tc | Demagnetization at temperature |
| SmCo | High Tc; good corrosion resistance | High-temperature Br retention |
| Alnico | High Tc; low coercivity | Easy demagnetization in service |
| Ferrite (ceramic) | Low cost; corrosion resistant | Lower (BH)max; temperature stability |
| Bonded NdFeB | Complex shapes; lower properties | Dimensional and flux uniformity |
Why Choose Infinita Lab for Magnet Testing?
Infinita Lab offers comprehensive magnet characterization testing, including B-H curve measurement, Helmholtz coil flux testing, and high-temperature demagnetization curves, through its nationwide accredited laboratory network. Our magnetic materials specialists provide expert analysis and reporting for permanent magnet qualification and production quality control.
Looking for a trusted partner to achieve your research goals? Schedule a meeting with us, send us a request, or call us at (888) 878-3090 to learn more about our services and how we can support you. Request a Quote
Frequently Asked Questions (FAQs)
What is the difference between Hc and HcJ in permanent magnet testing? Hc (coercive field) is where the flux density B = 0 on the demagnetization curve. HcJ (intrinsic coercivity) is where the magnetization M = 0. HcJ is always greater than or equal to Hc and is the more relevant parameter for evaluating demagnetization resistance, especially in high-temperature or high-reverse-field applications.
Why is (BH)max the most important figure of merit for permanent magnets? (BH)max quantifies the maximum energy product—the maximum magnetic energy density that can be extracted from the magnet. For a given magnetic circuit requirement, a higher (BH)max magnet allows the same magnetic performance to be achieved with smaller, lighter magnet volume, directly impacting motor power density and weight.
How does temperature affect NdFeB magnets? NdFeB magnets have a relatively low Curie temperature (~310–370°C) and significant reversible temperature coefficients of Br (−0.09 to −0.12%/°C) and HcJ (−0.5 to −0.6%/°C). Elevated operating temperatures in EV motors can reduce flux density and coercivity significantly. Grade selection must account for the maximum operating temperature to prevent irreversible demagnetization.
What is meant by "N52" in NdFeB magnet specifications? The number in NdFeB grade designations (N35, N42, N52) represents the nominal maximum energy product in MGOe. N52 indicates a (BH)max of approximately 52 MGOe—among the highest commercially available grades. Higher N-grade magnets offer greater flux density but typically have lower coercivity and less temperature resistance.
Can magnet testing be performed without removing magnets from an assembled motor? Some magnetic properties can be assessed on assembled motors using back-EMF measurements and flux linkage calculations, but direct magnet property measurement requires extracting the magnet from the assembly. Non-destructive field mapping of assembled motor magnets using 3D Hall probe arrays can verify flux distribution uniformity without disassembly.
