2.3.1 Perfect diamagnetism
Diamagnetism is due to currents induced in atomic orbitals by an applied magnetic field. The induced currents produce a magnetisation within the diamagnetic material that opposes the applied field, and the magnetisation disappears when the applied field is removed. However, this effect is very small: the magnetisation generally reduces the applied field by less than one part in 105 within the material. In diamagnetic material, B = μμ0H, with the relative permeability μ slightly less than unity.
Superconductors take the diamagnetic effect to the extreme, since in a superconductor the field B is zero – the field is completely screened from the interior of the material. Thus the relative permeability of a superconductor is zero.