Which materials are described as being repelled by an external magnetic field?

Diamagnetic materials are characterized by their tendency to be repelled by an external magnetic field. This phenomenon arises because diamagnetic materials have paired electrons, which produce no net magnetic moment. When an external magnetic field is applied to such materials, the motion of the electrons is altered in a way that generates a magnetic field opposite to that of the external field. This results in a weak repelling force exerted on the diamagnetic material, causing it to be pushed away from the magnetic field.

In contrast, ferromagnetic materials exhibit strong attraction to magnetic fields due to the alignment of unpaired electron spins, leading to a significant net magnetic moment. Paramagnetic materials, on the other hand, are only weakly attracted to magnetic fields, as their unpaired electrons may align in the direction of the external field but do not retain this alignment in the absence of the field. Superconducting materials also exhibit unique magnetic behavior, including the expulsion of magnetic fields when subjected to certain conditions, but this behavior is distinct from simple repulsion and is a result of the Meissner effect. Thus, while all these materials interact with magnetic fields, it is the diamagnetic materials that specifically demonstrate the property of being repelled.