Ferromagnetic materials

Ferromagnetic materials are those which when placed in a magnetic field, gets strongly magnetized in the direction of the applied magnetic field. They exhibit permanent magnetic dipole moment. On increasing the temperature, ferromagnetic property decreases. At Curie temperature, a ferromagnetic material changes to paramagnetic state. Curie temperature of Iron, Copper and Nickel are 1093 K, 1428 K and 650 K respectively. Domains are small regions in a ferromagnetic substance when it is in an unmagnetized state. Within a domain, magnetic dipole moments are aligned in the same direction. But this direction and adjacent domain dipole moment direction are oriented differently. Two adjacent domains which are aligned in different directions are separated by a thin film. Thin thin film is termed as domain wall. All domains are in the state of magnetic saturation even in the absence of magnetic field. But resultant magnetic moment is zero since different domains are randomly distributed. When magnetic field is applied, these domains tend to align or orient themselves parallel or nearly parallel to the applied field. On the withdrawal of applied external magnetic field, the substance retains a little magnetism. This magnetism is known as residual magnetism or remnant magnetism.