Spontaneous magnetization

Spontaneous magnetization is a nonzero net magnetization that a material develops without an applied magnetic field, typically below a critical temperature because its magnetic moments order.

Ferromagnetism: A form of magnetic order in which interactions align moments and produce a net magnetization. It is the principal ordering phenomenon that produces spontaneous magnetization.
Magnetic moment: A vector quantity that measures the strength and orientation of a source’s magnetic behavior. Spontaneous magnetization is the collective alignment of many microscopic moments.
Paramagnetism: A form of magnetism in which applied fields weakly align otherwise disordered magnetic moments. A paramagnet lacks persistent spontaneous magnetization in zero field.
Permanent magnet: A material or device that maintains a magnetic field without continuous electrical power. Its useful field relies on robust magnetic order and resistance to demagnetization.
Exchange interaction: A quantum-mechanical interaction between spins that favors particular relative orientations. In ferromagnets, it can favor parallel alignment of neighboring magnetic moments.
Spin (physics): An intrinsic form of angular momentum carried by quantum particles. Electron spin supplies much of the magnetic moment in common ferromagnets.
Antiferromagnetism: Magnetic order in which neighboring moments align oppositely, usually giving zero net magnetization. It has ordered moments but generally no spontaneous net magnetization.
Hysteresis: Dependence of a system’s response on its prior states, often shown by a loop in a field-response curve. Magnetic hysteresis governs how spontaneous order persists as fields change.
Curie temperature: The temperature above which a ferromagnet loses its spontaneous magnetization and becomes paramagnetic. It marks the thermal transition that destroys ferromagnetic order.
Magnetization: Magnetic dipole moment per unit volume in a material. Spontaneous magnetization is magnetization that persists without an applied field.

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Symmetry breakingBroader topic: It gives a concrete order parameter for a state that chooses a direction.