What is a remanence?

Remanence or residual magnetism is the magnetization that remains in a ferromagnetic material (such as iron) after an external magnetic field is removed. Remanence occurs within ferromagnetic materials and is the flux density that a magnetic material retains. High values of remanence and coercivity are particularly required for permanent magnets, so the Magnets maintain a strong field and are not demagnetized by a reaction to external magnetic interactions.