What is diamagnetism?

The so-called diamagnetism, together with the para- and ferromagnetism, describes different magnetic properties of matter. A paramagnetic material, according to the definition of diamagnetism, is attracted only very weakly. The reason behind this is mainly due to the nature of the atoms and the position of the electrons within certain materials.

How to recognize diamagnetic substances?

Diamagnetic substances are easily detected by a short test. Once a material does not adhere to a magnet, it is considered non-magnetic. If it is also easily repelled by a magnet, it is considered diamagnetic. Diamagnetism simply means that the elementary magnets in the material are opposite to the external field, that is, the magnet. Without an external magnetic field these substances are not magnetic.

Properties of diamagnetic materials

Diamagnetism was shaped by Michael Faraday's discovery that every element in nature responds to specific magnetic fields. Diamagnetic elements weaken a magnetic field. This happens proportionally and is defined by the measuring principle of the relative permeability μ_r. It indicates the factor by which the magnetic flux density of the respective material is increased or decreased by its nature. For diamagnets this is always less than 1. Depending on the material properties, a different susceptibility of the substances results. This depends on:

  • temperature of the material
  • physical state
  • crystal system
  • Direction of the respective crystal lattice

In addition, diamagnetic materials that are associated with paramagnetic, for example, can cause the diamagnetism of the whole object. That depends on the composition and direction of the electrons in the material, the so-called electron spin. It should be noted at this point that each material initially reacts diamagnetically. As soon as it is introduced into an external magnetic field H_0, the so-called induction of the circulating currents I with magnetic moments m occurs. These are directly opposite the outer field. This property is also called Lenz's rule:

This means that the diamagnet has a slightly negative magnetic susceptibility X.

Superconductor: floating diamagnets

So-called superconductors are considered the absolute diamagnets. The repulsive power of these elements is particularly strong. So they completely displace the magnetic flux density inside. As a result, these materials can even hover over magnets. However, this requires a particularly strong magnetic field of more than 15 Tesla in the laboratory. Diamagnetism is often used in simulations of absolute weightlessness under the influence of the Earth's gravitational field.