Diamagnetism is a form of magnetism exhibited by materials that are not attracted to a magnetic field and, in fact, create an opposing magnetic field when exposed to one. This property arises from the paired electrons in the atoms of diamagnetic materials, which cause them to exhibit a weak repulsion when subjected to an external magnetic field. Understanding diamagnetism is essential in the context of crystal field theory, as it helps explain the behavior of certain transition metal complexes and their electronic configurations.