The quality or magnetic quality is an indicator of the energy content of a magnet. To give you an idea of ​​this, let me give you an example: a bar magnet with a diameter of 2 cm and a flat south or north pole surface and a grade of about 50 can lift a 20 kg heavy iron block. From this example, it also shows that the goodness has no unity, it is sometimes given only with a prefixed letter. It would have been just as possible to give it a unity, since the quality is basically the magnetic energy per unit volume. The preceding letter in turn stands for the maximum operating temperature of the magnet.

The maximum usage temperature as a letter abbreviation

Above the maximum operating temperature, damage to the magnet or magnetic field occurs because either the material is damaged or the orientation of the single electron spin is changed. The reason for this is that a permanent magnet is created by the magnetization or the resulting remanence. This remanence decreases with increasing temperature. Even at low temperatures, it may therefore come to a partial demagnetization, so the maximum operating temperature should not be exceeded. The following list shows the letters or the respective maximum operating temperature:

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

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

Energy product

From the so-called energy product basically follows the quality of a magnet. The energy product, in turn, is the product of the magnetic field strength H and the magnetic flux density B. It measures the stored magnetic energy per unit volume. There is a proportionality between the force effect and the energy product when comparing two magnets of the same size. Thus, if two magnets have a completely identical shape but one that is twice as strong, it will have twice the force on the ferromagnetic material.

Magnetic energy and examples to understand

The magnetic energy stored in a good permanent magnet is several hundred kJ / cubic meter. This equates to several tens of millions of GaussOsted. GaussOersted is the measure of the energy product. The goodness, in turn, is basically the same value as that of the energy product, but in the unit million (mega) GaussOersted (MGOe). Usually the unit is omitted in the indication of the quality. A magnet with the quality designation UH50 has a magnetic energy of 50 MGOe and can be easily used up to a temperature of about 180 °. In turn, an M55 magnet has about 10% more magnetic energy and would therefore hold about 10% more weight. However, especially in comparisons with examples in which magnets hold any heavy bodies, the shape of the particular magnet as well as the attracted body and the quality of the surface are very important. The values ​​given for the carrying capacity of a magnet are usually idealized - that is, the iron block as well as the poles of the magnet are perfectly smooth, besides, the attracted body is pure iron. Even a thin coating of the attracted iron block or a few scratches in the pole surface can reduce the holding force quite drastically.