paramagnetism and diamagnetism

출처 : http://skullsinthestars.com/2009/04/13/levitation-and-diamagnetism-or-leave-earnshaw-alone/

In a paramagnetic material, electrons still act like little bar magnets, but under normal conditions they are arranged randomly, so that there is no ‘net’ north and south pole to the material.  However, when an external magnetic field is applied, the dipoles twist to line themselves up with the magnetic field.  The result is that, when an external magnetic field is applied, the paramagnetic material becomes a bar magnet with total dipole parallel to the external field:

Materials which are not paramagnetic are usually diamagnetic, in which a dipole moment is induced in a material which points antiparallel to the applied field:

The explanation for diamagnetism lies not in the spin of an electron but in the orbit of an electron around the nucleus of an atom, and this orbital motion itself acts like a little current loop.  We may consider these loops to be randomly oriented, as in the case of paramagnetism.  When a magnetic field is applied to an electron traveling in its little current loop, Faraday induction causes the electron to speed up or slow down.  This in turn changes the effective current in the loop, which changes the strength of the dipole: