magnetic

Magnetic refers to the phenomena and properties associated with magnets and magnetism, including magnetic fields, forces, and the magnetic properties of materials. Magnetism originates from moving electric charges and, at the quantum level, from electron spin and orbital motion. Magnetic fields are vector fields that interact with electric charges and magnetic dipoles, producing forces and torques described by the Lorentz force and related principles.

A magnetic field, denoted B, can exert a force on moving charges and align or rotate magnetic moments. In materials, the response to an external field is described by magnetization M, while the relationship between B, the applied field H, and M is B = μ0(H + M) in simple terms. The strength and behavior of magnetic materials depend on temperature and composition.

Materials are categorized by their magnetic properties. Ferromagnetic materials, such as iron, nickel, and cobalt, show strong, long-range order and can retain magnetization after an external field is removed. Ferrimagnetic materials (ferrites) have spontaneous magnetization arising from opposing sublattices. Paramagnetic materials are weakly attracted to magnetic fields, while diamagnetic materials are weakly repelled. The transition temperatures that destroy spontaneous magnetization, such as the Curie temperature for ferromagnets, are key characteristics.

Applications of magnetism include permanent magnets for motors and speakers, electromagnets for devices like transformers and relays, data storage technologies (hard drives and magnetic tapes), and medical imaging (MRI). Measurement units include the tesla and gauss for magnetic flux density and amperes per meter for magnetization. The study of magnetism contributed to foundational theories in physics, culminating in Maxwell’s equations that describe electricity and magnetism as a unified field.