Magnetism is a property of matter and it occurs in different forms and degrees in various Earth materials that act as conductors and insulators. For example, at low temperatures, metallic systems exhibit either superconducting or magnetic order. The degree of magnetism of a substance is due to the intrinsic magnetic dipole moment of its electrons. The degree of magnetism is also called magnetization and it is defined as the net magnetic dipole moment of the substance per unit volume.

In the nineteenth century, Michael Faraday was the first to start classifying substances according to their magnetic properties. Faraday classified them as either diamagnetic or paramagnetic and he based his classification on the force exerted on the materials when placed in an inhomogeneous magnetic field.

Diamagnetic substances have a negative magnetic susceptibility, (i.e., they are materials in which the magnetization and magnetic...