Ferrite with very little coercive force becomes a magnet that generates powerful magnetic force when wire is wound around a ferrite core that has been sintered in a cylindrical shape (this is called an inductor) and electrical current flows through the wires. The magnetic force, which is generated inside the core, is proportional to the resulting magnetic field. This is an electromagnet. When the current is cut off, the magnetic force disappears and everything returns to its prior state. If the direction of the electric current is alternated, the electromagnet has alternating north and south poles. This type of ferrite is referred to as soft ferrite.
In contrast to this, when a powerful external magnetic field is applied to ferrite with high coercive force, a permanent magnet is created. Even when the magnetic field is removed, the ferrite maintains a strong magnetic force. Ferrite that can be made into permanent magnets in this way is called hard ferrite.
