lowcoercivity

Low coercivity refers to the property of magnetic materials that have a very small coercive field, the field strength required to reduce the magnetization to zero after the material has been saturated. It is typically determined from a magnetic hysteresis loop as the value of the external field when magnetization crosses zero. In SI units, low coercivity materials generally have Hc well below 100 A/m, and often well below 10 A/m for the softest alloys.

Materials with low coercivity are usually called soft magnetic materials because they respond readily to external magnetic fields and demagnetize easily when the field is removed. This behavior yields high magnetic permeability and low hysteresis losses, which is advantageous in applications involving alternating or rapidly changing fields.

The low coercivity arises from a combination of low magnetocrystalline anisotropy and microstructural features that permit easy movement of magnetic domain walls. Processing techniques such as annealing, controlled cooling, and alloying to reduce internal stresses and pinning centers further lower Hc. Common soft magnetic materials include iron-silicon alloys (silicon steel), nickel-iron alloys (Permalloy), amorphous metals (Metglas), and nanocrystalline alloys (Finemet).

Applications are concentrated in power electronics and electromagnetic devices where efficient magnetic circuits are essential. Typical uses include transformer cores, inductors, chokes, and stator/rotor cores in motors, as well as magnetic shielding. Limitations of low-coercivity materials include sensitivity to temperature and mechanical stress, which can raise Hc or increase losses, and their relatively lower resistance to permanent demagnetization compared with hard magnets.

See also: Soft magnetic material, Hysteresis, Permeability.