Feromagnetismu

Feromagnetismu refers to ferromagnetism, a form of magnetism in which a material exhibits spontaneous magnetization due to exchange interactions between atomic magnetic moments. This alignment produces a net magnetic moment even without an external magnetic field. In many ferromagnets the material is divided into magnetic domains, each with uniform magnetization; domain walls separate regions of different orientation. At high temperatures thermal agitation disrupts alignment, and the material becomes paramagnetic above the Curie temperature. Below this temperature, spontaneous magnetization emerges and grows as temperature decreases, eventually saturating in strong fields.

Materials that show ferromagnetism include iron, cobalt, nickel, and certain rare-earth elements such as gadolinium. The magnitude and direction of magnetization depend on magnetocrystalline anisotropy and geometric shape. Magnetic hysteresis is a key feature: after magnetization and subsequent removal or reversal of the external field, the material retains a remanent magnetization and requires a coercive field to demagnetize.

Theoretical descriptions employ models such as the Heisenberg exchange interaction and the Weiss molecular field, complemented by Landau theory of phase transitions. Spin waves (magnons) account for low-temperature excitations, and itinerant-electron ferromagnetism describes some metals where magnetism arises from conduction electrons rather than localized moments.

Applications rely on the stable remanent magnetization of ferromagnets: permanent magnets, transformers and other electrical machines, magnetic storage media, and read heads in data storage devices. Feromagnetismu thus underpins a wide range of technologies by providing robust, temperature-dependent magnetic order.