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A material that exhibits significant magnetic permeability is attracted to magnets, and in many cases can be permanently magnetised. Typical ferromagnets are iron, nickel, cobalt, and some of their alloys and compounds. Ferromagnetism allows temporary magnetization in an external magnetic field. The atoms of such materials have a magnetic moment, determined by the arrangement of electrons and their motion in the electron shell, and act as miniature magnets. In an external magnetic field, they align along magnetic lines and the ferromagnetic material then acquires the properties of a magnet. When a sufficiently intense magnetic field is applied, these properties become permanent and the material becomes a permanent magnet.