permanentmagnet

A permanent magnet is a material that produces a magnetic field without external power. Its field arises from the spontaneous alignment of microscopic magnetic domains within the material and can persist after an external magnetizing field is removed. The strength and stability of a permanent magnet depend on material composition, temperature, and magnetic history.

The magnetic behavior is described by parameters such as remanent flux density, coercivity, and the maximum energy product (BH max). The Curie temperature marks the point above which thermal agitation destroys long-range magnetic order, causing loss of magnetization. In practice, performance degrades with heat, shock, or exposure to opposing magnetic fields.

Common permanent magnet families are ferrites (ceramic magnets), alnico, neodymium-iron-boron (NdFeB), and samarium-cobalt (SmCo). Ferrites are inexpensive and corrosion-resistant but relatively weak. Alnico offers good temperature stability and ductility but lower coercivity. NdFeB magnets provide the highest energy products and are widely used, though they are more sensitive to heat and moisture without coatings. SmCo magnets combine strong magnetism with excellent temperature stability and corrosion resistance, but at higher cost.

Applications include electric motors and generators, loudspeakers, magnetic separation, and various sensing and actuation devices in consumer electronics and industry. Design considerations include protection from demagnetization, thermal management, and, in some cases, corrosion protection through coatings.