Magnetic substances

Magnetic fields influence all materials. But not all materials act on magnets with the same intensity or are influenced by them in the same way. A distinction is made between:

  • ferromagnetic substances
  • diamagnetic substances
  • paramagnetic substances
Each of the three substance classes has certain properties that set them apart from the others.

Which substances are attracted by magnets?

Diamagnetic substances, which include zinc, copper, and water, do not adhere to magnets, and are even easily repelled by them. This is since their permeability - i.e., their ability to absorb and transmit magnetic fields - is particularly low.

Paramagnetic substances such as aluminum, platinum and oxygen are easily attracted by permanent magnets or electromagnets but cannot themselves be magnetized and therefore cannot be used as magnets. Their permeability number is slightly above 1 - the magnetic field acting on them is only minimally strengthened.

Ferromagnetic objects, on the other hand, adhere to magnets themselves and are also referred to as magnetizable substances, since they become one themselves when they meet a magnet. They have a permeability that is well above 1, in some cases even more than 1,000. Therefore, they can significantly increase the flux density of a magnetic field. They are classic magnetic substances.

A distinction is also made between magnetically soft and magnetically hard materials. The former are easily magnetized, but quickly lose their own magnetic properties when the external magnetic field is removed. Hard magnetics experience minimal demagnetization once magnetized. Such substances that have a high remanence - i.e. a long-lasting, strong residual magnetization - are themselves referred to as permanent magnets.

Which substances are magnetic depends in particular on their permeability. The following metals, for example, have a particularly high permeability for magnetic fields at a temperature of around 20 degrees Celsius:

  • Iron
  • Nickel
  • Cobalt
At lower temperatures, the following substances are also strongly influenced by magnets:
  • Erbium
  • Gadolinium
  • Holmium
  • Terbium
  • Dysprosium
There are also some special alloys that are sometimes used for magnetic shielding in high-quality technology, as they have an extremely high permeability. These include, for example, nickel-iron alloys such as mu-metal and neodymium-iron-boron compounds, which are used in the strongest permanent magnets.

How do magnets act on magnetic substances?

Ferromagnetic materials contain tiny elementary magnets, which are magnetically aligned in the same area within a body - the so-called Weiss areas. However, these domains are not in harmony with one another in non-magnetized materials. The different orientations of the elementary magnets in the Weiss districts ensure that the existing magnetic fields cancel each other out.

If an external magnet comes close to a magnetic body, the individual domains and the elementary magnets contained therein turn towards it. The walls between the shrinking Weiss areas fold over and the ferromagnetic body becomes a magnet itself due to its reorganized elementary magnetic structure.

This process can also be recognized if one takes a closer look at the field lines running in and around the magnetic body. These become visible when iron filings are placed on a sheet or cardboard on said body.

Initially disordered, the magnetization creates two magnetic poles - a north and a south pole - each of which shows a particularly high field strength due to a high density of iron filings. From the north pole, the closed field lines run in curves to the south pole of the newly created magnet. If you bring the two magnets together and align their force flow in the same way, their forces are bundled and strengthened to form a common magnetic field.


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