The magnetism of a substance is related to its internal electronic structure.In the atoms of diamagnetic metal, the electrons have been paired, the number of positive and anti-spin electrons is equal, the magnetic moment generated by the electron spin cancels each other, so the atomic magnetic moment is zero, so it is not attracted by the external magnetic field.In paramagnetic metal atoms, the number of positive and negative spin electrons is different, and the magnetic moment of the atom is not zero.Due to irregular thermal motion, atomic magnetic moments vary in direction.When the magnetic field is put in, the atomic magnetic moment is slightly deflected along the direction of the magnetic field, showing a weak magnetization.

The origin of ferromagnetism is similar to paramagnetism and comes from unpaired electrons in atoms.However, in ferromagnetic materials, there are also many local small regions called "magnetic domains". In these small regions, the adjacent atoms have the same magnetic moment orientation and tend to arrange with each other equally.The direction of spontaneous magnetization among the magnetic domains is disordered, so the macroscopic magnetic moment of the whole material is zero, and no magnetism is displayed externally.When in a magnetic field, the magnetic moments of the domains align to a certain extent in the direction of the field, so that one domain aligned once along the field corresponds to the aligned magnetic moments of many atoms.Therefore, the interaction between ferromagnetic materials and magnetic fields is much greater than that between paramagnetic materials.

In addition to the magnetic field, the domains try to retain as much orientation as possible as they did when the original field was present, and the partial alignment of the domains thus results in the material remaining magnetic and being "permanently" magnetized.The ferromagnetic material can be magnetized permanently by rubbing it with a piece of permanent iron.The magnetism of permanent magnetic materials can also be destroyed by heating or violent impact, which causes the domain direction to become disordered.