Diamagnetism - definition

Diamagnetism is one of the fundamental magnetic phenomena, involving the production by a substance of a weak magnetic field opposite to the external magnetic field in which the substance is located. It is an effect resulting from the orbital and spin interactions of electrons in the atoms of a material, independent of the presence of permanent magnetic moments.

In contrast to ferromagnets or paramagnets, the atoms of diamagnetic substances do not have uncompensated magnetic moments in the ground state. Under the influence of an external magnetic field, however, the trajectory of the orbital motion of the electrons is altered, which, according to Lenz's rule, results in a counteracting magnetic field. This results in the repulsion of the material from the source of the magnetic field.

A characteristic feature of diamagnetics is a negative magnetic susceptibility, usually of very small value, which does not depend on temperature. This phenomenon occurs in all substances, but in most cases is masked by stronger paramagnetic or ferromagnetic effects. Exceptions are materials in which diamagnetism is the dominant feature, such as e.g. bismuth, copper, water or lead.

The phenomenon of diamagnetism is of practical importance in, among other things, magnetic levitation techniques, precise magnetic field measurements and in describing the properties of materials used in superconductivity. In the case of type I superconductors, diamagnetism takes the form of complete displacement of the magnetic field from within the material, which is known as the Meissner effect.

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