Diamagnetism

Diamagnetism is the property of an object or material which causes it to create a magnetic field in opposition to an externally applied magnetic field. Unlike a ferromagnet, a diamagnet is not a permanent magnet. Diamagnetism is believed to be due to quantum mechanics (and is understood in terms of Landau levels) and occurs because the external field alters the orbital velocity of electrons around their nuclei, thus changing the magnetic dipole moment. According to Lenz's law, the field of these electrons will oppose the magnetic field changes provided by the applied field. The magnetic permeability of diamagnets is less than (a relative permeability less than 1)(Less permeable than free space). In most materials diamagnetism is a weak effect, but in a superconductor a strong quantum effect repels the magnetic field entirely, apart from a thin layer at the surface.