Ferromágnesesség

Ferromágnesesség is a phenomenon exhibited by certain materials that become strongly magnetized when exposed to an external magnetic field, and retain a significant amount of this magnetism even after the external field is removed. This property arises from the alignment of magnetic moments of atoms within the material. In ferromagnetic substances, these atomic magnetic moments are strongly coupled by a quantum mechanical interaction called the exchange interaction, which causes them to align parallel to each other within small regions called magnetic domains.

When an external magnetic field is applied, these domains tend to align themselves with the field, leading to a large net magnetization. The strength of this magnetization depends on the material's composition, temperature, and the strength of the applied field. Ferromagnetic materials typically exhibit hysteresis, meaning their magnetization does not follow the applied field linearly and depends on their magnetic history.

The most common ferromagnetic materials are iron, nickel, and cobalt, along with some of their alloys and certain rare-earth elements. These materials are crucial in many technological applications, including electric motors, generators, transformers, magnetic storage devices (like hard drives), and permanent magnets. The Curie temperature is a critical point for ferromagnetic materials; above this temperature, thermal agitation overcomes the exchange interaction, and the material loses its ferromagnetic properties, becoming paramagnetic instead.