Magnetics

Magnetics is the field that studies magnetic fields and the interactions of magnets, magnetic materials, and moving charges. It covers the forces that arise from magnetic moments of elementary particles and from electric currents, and it underpins a wide range of technologies as well as fundamental physical theory.

The behavior of magnetic fields is described by Maxwell's equations. In materials, the magnetic flux density B is related to the magnetic field H and the magnetization M by B = μ0(H + M), where μ0 is the vacuum permeability and μ = μ0μr characterizes a material's response. Magnetic circuits use the concept of reluctance in analogy to resistance, aiding design of devices that control magnetic flux.

Materials exhibit different magnetic responses. Diamagnetic materials are weakly repelled by a magnetic field; paramagnetic materials are weakly attracted; ferromagnetic and ferrimagnetic materials can show spontaneous magnetization and complex domain structures. Ferromagnets often exhibit hysteresis, remanence, and coercivity, and their behavior changes with temperature, notably near the Curie temperature where magnetization changes abruptly.

Applications of magnetics span energy, information, and sensing. Key technologies include electric motors, generators, and transformers; magnetic storage for data (such as hard disks and magnetic tapes); magnetic resonance imaging; sensors and actuators; and magnetic levitation and nondestructive testing. Fundamental research in magnetics explores quantum magnetism, spintronics, and materials science to develop new devices and improve performance.

Common units include the tesla for magnetic flux density and the ampere per meter for magnetic field strength. Magnetic concepts continue to play a central role in physics and engineering.