Ferromagnetism is a property of certain materials, like iron, cobalt, and nickel, that allows them to become magnetized. In these materials, the magnetic moments of atoms align in the same direction, creating a strong overall magnetic field. This alignment occurs even without an external magnetic field. When a ferromagnetic material is exposed to a magnetic field, it can become permanently magnetized. The aligned magnetic moments can remain in place even after the external field is removed. This characteristic is what makes ferromagnetic materials useful in applications like permanent magnets and electromagnets.