Magnetic properties of solids

The magnetic properties of a solid follow from the classical picture of the spinning electron: a spinning electron behaves like a tiny magnet, its spin generating an induced magnetic field. An orbital containing a single, unpaired electron therefore shows unbalanced spin and magnetism, whereas two paired electrons have opposed, cancelling spins and show no net magnetic moment. On this basis solids fall into three classes.

i. Diamagnetic solids : All the electrons are paired, so the magnetic moments cancel completely; the substance is weakly repelled by an external magnetic field. $N_2$, $F_2$, NaCl, $H_2O$ and benzene are examples of diamagnetic substances.

ii. Paramagnetic solids : The presence of unpaired electrons gives the particles a net magnetic moment, and the substance is weakly attracted by an external magnetic field. Paramagnetic substances are magnetic only while the external field is present -- the magnetism is lost as soon as the field is removed. Oxygen, $Cu^{2+}$, $Fe^{3+}$ and $Cr^{3+}$ are examples. …