demagnetization

Demagnetization is the process by which the magnetic moment of a material is reduced or eliminated. It typically targets ferromagnetic or ferrimagnetic substances in which many microscopic magnetic domains are aligned. Demagnetization seeks to reduce net magnetization and residual magnetic fields that may cause attraction of ferrous objects, interference with sensors, or data retention in storage media.

There are several mechanisms and methods. Thermal demagnetization occurs when a magnet is heated toward or above its Curie temperature, at which magnetic order breaks down and spontaneous magnetization vanishes. Magnetic demagnetization uses external magnetic fields: exposure to a strong reverse field followed by a gradual decrease to zero can reorient domains randomly and reduce net magnetization. A common practical method is alternating-field demagnetization (AC demagnetization) or degaussing, where an initially high-amplitude alternating field is slowly reduced while the material is kept in a demagnetizing environment. Mechanical shocks or plastic deformation can also disturb domain structure, though they are less controlled.

Measurements of demagnetization relate to the material's hysteresis behavior. The remanent flux density (Br) and coercivity (Hc) describe how much magnetization remains after removal of a field and how resistant the material is to demagnetization.

Applications include erasing data on magnetic storage media, removing unwanted magnetization from tools or shielding, and preparing components for precision sensors or imaging devices. See also Curie temperature, magnetic domains, and magnetic hysteresis.