What is "diamagnetism"

Diamagnetism \Di`a*mag"net*ism\, n.

1. The science which treats of diamagnetic phenomena, and of the properties of diamagnetic bodies.

2. The magnetic action which characterizes diamagnetic substances, the magnetic moments of which tend to oppose an externally applied magnetic field. Contrasted with paramagnetism and ferromagnetism.

n. (context physics English) a weak form of magnetism that is only observed in the presence of an external magnetic field; due to an induced magnetic field in an opposite direction

n. phenomenon exhibited by materials like copper or bismuth that become magnetized in a magnetic field with a polarity opposite to the magnetic force; unlike iron they are slightly repelled by a magnet

Diamagnetic materials create an induced magnetic field in a direction opposite to an externally applied magnetic field, and are repelled by the applied magnetic field. In contrast, the opposite behavior is exhibited by paramagnetic materials. Diamagnetism is a quantum mechanical effect that occurs in all materials; when it is the only contribution to the magnetism the material is called a diamagnet. Unlike a ferromagnet, a diamagnet is not a permanent magnet. Its magnetic permeability is less than μ, the permeability of vacuum. In most materials diamagnetism is a weak effect, but a superconductor repels the magnetic field entirely, apart from a thin layer at the surface.

Diamagnets were first discovered when Sebald Justinus Brugmans observed in 1778 that bismuth and antimony were repelled by magnetic fields. In 1845, Michael Faraday demonstrated that it was a property of matter and concluded that every material responded (in either a diamagnetic or paramagnetic way) to an applied magnetic field. He adopted the term diamagnetism after it was suggested to him by William Whewell.