ferromaterial

Ferromaterial, or ferromagnetic material, is a material that exhibits ferromagnetism—spontaneous alignment of magnetic moments due to quantum mechanical exchange interactions that favors parallel alignment. Below a characteristic temperature called the Curie temperature, these moments align to produce a net magnetization even without external magnetic field. Above the Curie temperature, the material becomes paramagnetic and loses permanent magnetization.

In ferromagnets, magnetic moments tend to form domains, regions where moments are aligned. Within a domain the magnetization is nearly uniform; between domains, walls separate different orientations. When exposed to a magnetic field, domains grow or walls move, leading to magnetization that eventually saturates. The response exhibits hysteresis, with remanent magnetization and coercivity dependent on material structure and temperature. Permeability is high; anisotropy and microstructure control direction and magnitude of magnetization.

Common elemental ferromagnets are iron, cobalt, and nickel, with many alloys and compounds optimized for specific properties. Alloys such as steel and alnico, permalloy (Ni-Fe), and mu-metal are used for high permeability and magnetic shielding. Permanent magnets based on rare-earth materials such as NdFeB and SmCo provide very high magnetization and coercivity. Curie temperatures vary widely: Fe about 770°C, Ni about 358°C, Co about 1125°C.

Applications include transformer cores, electric motors and generators, magnetic recording devices, and magnetic shielding. Understanding ferromagnetism is essential in physics and materials science, and the term covers both soft ferromagnets used for efficient magnetic circuits and hard ferromagnets used as permanent magnets.