Magnetic hysteresis

Magnetic hysteresis is the dependence of a material’s magnetization on its magnetic history. It appears as a lag between an applied magnetic field and the material’s response.

Magnetic domain: A region in a magnetic material whose atomic magnetic moments are aligned in a common direction. Hysteresis develops as domains grow, shrink, and reorient under changing fields.
Magnetization: The magnetic dipole moment per unit volume of a material. It is the material response whose dependence on field history defines hysteresis.
Permanent magnet: A material that maintains substantial magnetization without a continuously applied magnetic field. High remanence and coercivity let a permanent magnet retain its state.
Magnetic susceptibility: A measure of how strongly a material magnetizes in response to an applied magnetic field. A single-valued susceptibility describes reversible response, unlike a history-dependent loop.
Domain wall: A boundary between magnetic domains, across which the direction of magnetization changes. Pinning and motion of domain walls contribute to irreversible magnetization changes.
Magnetic field: A vector field that exerts forces on moving electric charges and magnetic dipoles. The applied field is the control variable traced against magnetization in a hysteresis loop.
Soft magnetic material: A magnetic material that is readily magnetized and demagnetized, usually with low coercivity. Its narrow hysteresis loop reduces losses in alternating-field devices.
Superparamagnetism: A nanoscale magnetic state in which thermal fluctuations rapidly reverse particle moments above a characteristic temperature. Rapid reversals can erase remanence and coercivity that ordinary hysteresis would preserve.
Magnetization curve: A graph showing a material’s magnetization as a function of an applied magnetic field. Its field-dependent path reveals the history dependence measured in hysteresis.
Magnetic flux density: A vector measure of magnetic field that includes contributions from magnetization within matter. Some hysteresis loops plot flux density against field rather than magnetization.

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