Explanation of Diamagnetism

Diamagnetism occurs in those substances whose atoms consist of an even number of electrons. The electrons of such atoms are paired. The electrons in such pair have orbital motions as well as spin emotions in opposite sense. The resultant magnetic dipole moment of the atom is thus zero. Hence when such a substance is placed in a magnetic field, the field does not tent to align the atoms (dipoles) of the substance. The field, however, modifies the motion of the electrons in orbits which are equivalent to tiny current-loops. The electron moving in a direction so as to produce a magnetic field in the same direction as the external field is slowed down, while the other is accelerated (Lenz’s law). The electron pair, and hence the atom, thus acquire an effective magnetic dipole moment which is opposite to the applied field. Hence for diamagnetic materials M is opposite to H. So the susceptibility χm of a diamagnetic substance is negative and is very small.