magnetizmus

Magnetizmus, or magnetism, is a class of physical phenomena associated with magnets and magnetic fields. It arises from electric currents and the intrinsic magnetic moments of elementary particles, especially electrons. Magnetic fields exert forces on moving charges and on magnetic dipoles, and they propagate through space as magnetic flux described by Maxwell's equations.

Key quantities include the magnetic field B (or flux density) and the auxiliary field H; the magnetization M describes how a material responds to external fields. Magnetic dipoles align in materials, yielding magnetization and, in some cases, permanent magnets. Materials are commonly described by their magnetic susceptibility and how they react to external fields.

Materials can be categorized by their response to external fields: ferromagnetic materials exhibit spontaneous alignment of magnetic moments and strong, nonlinear magnetization; paramagnetic materials show a weak, positive susceptibility; diamagnetic materials develop a weak, negative susceptibility. More complex ordering includes antiferromagnetism and ferrimagnetism. Magnetic behavior also depends on temperature, with characteristic Curie or Néel temperatures at which ordering changes.

The origin of magnetism lies in electron spin and orbital motion, coupled by exchange interactions. The collective alignment of spins in ferromagnets creates magnetic domains, which can exhibit hysteresis. Magnetic properties underpin many technologies and natural phenomena, including data storage, motors and transformers, sensors, and magnetic resonance imaging, as well as compasses and various electronic and spintronic devices.

Historically, magnetism developed from the study of lodestones to electromagnetism, with key contributions from Oersted, Ampère, Faraday, and Maxwell. Modern magnetism is described by quantum mechanics and classical field theory, linking microscopic moments to macroscopic magnetic behavior.