magnetizmust

Magnetizmus (magnetism) is a branch of physics describing magnetic phenomena arising from electric charges in motion and the magnetic moments of elementary particles, notably electrons. It also refers to magnetization, the process by which materials acquire a magnetic moment in response to an external magnetic field.

In materials, magnetization M describes the density of magnetic moments per unit volume, and is related to the magnetic field B and the auxiliary field H by B = μ0 (H + M). The degree of response is captured by magnetic susceptibility χ and permeability μ = μ0(1+χ). The magnetic field B exerts torques on dipoles and can induce alignment of moments.

Materials show different magnetism: diamagnetism (weak, negative susceptibility; induced moments oppose the field), paramagnetism (weak, positive susceptibility; moments align with applied field), ferromagnetism (large, spontaneous magnetization due to exchange interactions; domains form; can retain magnetization—hysteresis). Ferrimagnetism and antiferromagnetism involve opposite alignment with partial cancellation. Temperature can disrupt order; the Curie temperature marks transition to paramagnetism in ferromagnets.

Magnetism is governed by Maxwell's equations: ∇·B = 0, ∇×H = Jf + ∂D/∂t, and B = μ0(H+M). In static cases, Jf is the free current density; bound currents arise from M.

Applications span electric machines (motors, generators), transformers, magnetic data storage, magnetic resonance imaging, compasses, and magnetic levitation.

Key historical milestones include William Gilbert's early magnetism studies, Oersted's discovery that current creates a magnetic field, Faraday's law of induction, and the unification by Maxwell's equations.