In the case of no external magnetic field, ferromagnetic materials, can achieve a certain degree of magnetization, but the whereabouts of the magnetization is messy, the magnetic moment cancel each other out, the whole magnetic material does not show. When the applied magnetic field, the magnetic domain of the magnetic moment are turned to the direction of the external magnetic field, indicating a strong magnetic.

Ferromagnetic material in general can be divided into three categories: soft magnetic materials, magnetic materials, and other materials, this feature. Soft magnetic materials are characterized by high permeability, low coercivity, a large number for the manufacture of motors, transformers and other electromagnetic devices of the core, commonly used are silicon steel, pure iron, and soft ferrite, etc.; other magnetic functional materials, including Magneto-optical materials, magnetoresistive materials, magnetic sensitive materials, magnetostrictive materials. With scientific and technological development, a new type of magnetic functional materials continue to emerge. Permanent-magnet materials with high remanence, high coercivity magnetic material, upon magnetization can provide a stable magnetic circuit for the external magnetic field, in the electromagnetic device instead of field winding section, the application is widely used.