Ferromagnetism is the effect that creates permanently magnetized materials, such as ordinary horseshoe magnets. Although the effect is most common in pure iron, it can also be reproduced in iron-like substances, including compounds like barium ferrite, and heterogeneous compounds that unite iron with aluminum, nickel, cobalt, and tin.

Ferromagnetism occurs when magnetic moments of the atoms inside a material interact, leading to the overall magnetism of the object. Ferromagnetic substances will maintain their magnetism until the atoms are forced out of alignment. The easiest way to do this is to heat the substance. Above a certain temperature, the heat is enough to break the alignment and that subsequent cooling is not enough to allow realignment to take place. This temperature is known as the Curie temperature, T, named after Marie Curie's husband, Pierre Curie.

Magnetic moments of atoms are created by the contribution of individual magnetic moments of...