part 1 - Why are things magnetic ?   diamagnetic materials 1
Fig. 1.5 Fig. 1.5 shows an atom with filled s-orbital. It contains two electrons and they have opposite spin, which in mechanical terms means they orbit the nucleus in opposite directions. (Here is where our classical explanation falls apart as we are strictly speaking about the electron spin rather than the orbital spin) Both electrons cause a magnetic moment μ, but they are of equal magnitude yet opposite direction. Therefore, the net magnetic moment of the atom equals zero.

Such substances are called diamagnetic substances. In the absence of a magnetic field they are non-magnetic, or have no net-magnetic moment. They can, however, be magnetized when placed into a magnetic field but have negative magnetic susceptibility. (add link once page is created) In chemical compounds one has to consider the electron configuration of the charged ion. For example O2-, Ca2+ and C4+ all have completely filled shells, therefore CaCO3 is a diamagnetic mineral. Other common diamagnetic geological materials are quartz or organic matter.

Next we will investigate the magnetic properties of most materials where the net-magnetic moment per atom does not cancel out to zero.

next - paramagnetic materials 1
part 1 - index 1.1 currents 1.2 solenoids 1.3 electromagnets 1.4 mag. moment 1.5 diamagnets 1.6 paramagnets 1.7 mag. ordering