Magnet Quality: everything about magnetic quality and strength

The quality of a magnet is a crucial indicator of its energy content and performance. Learn what magnet quality indicates and how it affects holding force and strength.

What is the magnetic quality?

The quality, or magnetic quality, is an indicator of the energy content of a magnet. Quality has no unit; it is sometimes simply indicated by a letter prefix, which in turn represents the magnet's maximum operating temperature. But it could just as easily have been given a unit, since magnet quality is essentially the magnetic energy per unit volume.

EXAMPLE
A rod magnet with a diameter of 2 cm and a flat south or north pole surface and a quality of about 50 can already lift a 20 kg iron block.

Maximum operating temperature and magnetic quality

The maximum operating temperature is crucial for their performance and longevity. Exceeding this temperature can result in the following adverse effects:

• Damage to the magnet
• Changes in the magnetic field
• Disturbance of the alignment of electron spins

Permanent magnets derive their magnetic properties from magnetization, which results in what is known as remanence. However, remanence decreases with increasing temperature. Even at low temperatures, partial demagnetization can occur, which is why the maximum operating temperature should not be exceeded. The following list shows the letters and the respective maximum operating temperature:

• N: 80 °C
• M: 100 °C
• H: 120 °C
• SH: 150 °C
• UH: 180 °C
• EH: 200 °C

NOTICE
When the so-called Curie temperature is exceeded (depending on the material), the remanence is completely eliminated.

Energy product and magnetic quality

The energy product, the product of the magnetic field strength H and the magnetic flux density B, determines the quality of a magnet. It measures the stored magnetic energy per unit volume. When comparing two magnets of the same size, there is a proportional relationship between the force and the energy product. For magnets of the same shape, a magnet with twice the energy product also exerts twice the force on ferromagnetic material, thus twice the magnetic quality.

Magnetic energy in practice

The magnetic energy of a high-quality permanent magnet is several hundred kJ/cubic meters. This corresponds to several tens of millions of GaussOersteds, the unit of measurement for the energy product, with the magnet's quality being expressed in millions (mega) GaussOersteds (MGOe). This unit is usually omitted when specifying the quality.

Examples of magnet quality and performance

- UH50 magnet: with the quality designation it has a magnetic energy of 50 MGOe and can be used without problems up to a temperature of about 180°
- M55 magnet: has about 10% more magnetic energy and would therefore also hold about 10% more weight.

Note on the quality of magnets: theory vs. practice

When considering examples where magnets hold heavy objects, several factors play a crucial role:

- Geometry of the magnet
- Condition of the attracted body
- Surface quality of both elements

These factors significantly influence the actual adhesive force.

Idealized theory

Manufacturers' specifications on load-bearing capacity are generally based on idealized conditions :

• Perfectly smooth surfaces of both the magnet and the attracted object
• Use of pure iron as reference material

Reality for end consumers

Even minor deviations from these ideal conditions can significantly impair the magnet's performance. A thin coating on the attracted object or fine scratches on the magnet's surface can significantly reduce the holding force. These real-world influences underscore the importance of always considering practical application conditions when selecting and using magnets.