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ferromagnetism
A type of magnetism in which the magnetic moments of atoms in a solid are aligned within domains, which can in turn be aligned with each other by a weak magnetic field. The total magnetic moment of a sample of the substance is the vector sum of the magnetic moments of the component domains.
In an unmagnetized piece of ferromagnetic material the magnetic moments of the domains themselves are not aligned; when an external field is applied those domains that are aligned with the field increase in size at the expense of the others.
Ferromagnetic materials can retain their magnetization when the external field is removed, as long as the temperature is below a critical value, the Curie temperature. They are characterized by a large positive magnetic susceptibility. Examples of ferromagnetic substances include iron, nickel, cobalt and some of the rare earth elements, such as gadolinium and dysprosium.
Related category
• ELECTRICITY AND MAGNETISM
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