Ferromagnetism causes materials such as iron to be strongly attracted to magnets.
In a ferromagnetic material, many atomic magnetic moments can align in the same direction. Regions called magnetic domains may point in different directions in an unmagnetized sample, but an external field can make domains grow or rotate toward alignment. The material can then retain magnetization after the external field is removed.
Iron, nickel, and cobalt are familiar elemental ferromagnets, although their magnetic behavior depends on temperature and structure. Above its Curie temperature, a ferromagnet loses its long-range spontaneous alignment and becomes paramagnetic. Pure iron's Curie temperature is about 770 °C.
Ferromagnetism is not the same as simple attraction to a magnetic field. Paramagnetic substances are weakly attracted, while diamagnetic substances are weakly repelled. Permanent magnets commonly use ferromagnetic or ferrimagnetic materials engineered to retain strong magnetization.