coercivitet

Coercivity, or coercivitet in Danish, is a property of magnetic materials that describes their resistance to demagnetization. It is defined as the magnitude of the external magnetic field required to bring the magnetization of a saturated sample to zero.

In practical terms, coercivity is read from a magnetization versus magnetic field (M–H) loop. The coercive field, Hc, is the field value at which the magnetization crosses zero when the external field is reduced from saturation. Coercivity is typically expressed in units of amperes per meter (A/m) in SI, or oersteds (Oe) in older cgs units.

Materials are commonly categorized by their coercivity. Hard magnetic materials have high coercivity, allowing them to retain magnetization and function as permanent magnets. Soft magnetic materials have low coercivity, enabling easy magnetization and demagnetization, which is advantageous for transformer cores and high-frequency devices. The coercivity of a material is influenced by its composition, crystallographic anisotropy, grain size, and microstructure, as well as processing history and texture.

Coercivity varies with temperature and applied mechanical or magnetic fields. It generally decreases as temperature rises and approaches the Curie temperature, where magnetic ordering vanishes. Processing methods such as alloying, heat treatment, and controlled grain growth can tailor coercivity to suit specific applications.

Understanding coercivity helps in selecting materials for permanent magnets, magnetic recording, electrical machinery, and other technologies that rely on stable or easily switchable magnetic states.