Substances that significantly enhance the magnetic field are called ferromagnets.
In ferromagnets (iron, cobalt, nickel), entire macroregions, called domains, are magnetized. Domain sizes are 0.01-0.1 millimeters. Ferromagnetism is believed to be due to the spin magnetic field of the electrons in the atom. In ferromagnets, the spin magnetic moments of electrons have the same orientation and the total magnetic field of electrons determines the field of the domain. Each domain is a small magnet. In an unmagnetized ferromagnet, the magnetic moments of the domains are oriented randomly and the total magnetic field created by them is zero. When a ferromagnet is introduced into a magnetic field, the domain magnets are oriented along the field line, and the magnetic induction in the ferromagnet becomes substantially greater than the induction of the field into which it is introduced. In ferromagnets, magnetization remains when the external magnetic field is turned off.
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