All ferromagnetic1 substances remain magnetised tosome extent after the external field is removed, andthis feature characterises ferromagnetism. Somematerials retain a state of magnetisation almostindefinitely. These are called magnetically hardmaterials and are used to make permanent magnets.However, many ferromagnetic materials appear tolose most of their magnetisation rather easily. Theseare called magnetically soft materials.If the ordering forces between the atomic magnetic moments are strong enough to lead to ferromagnetism, it is reasonable to ask why softferromagnetic materials often show no obviousmagnetic properties. The answer lies in the microstructure of hard and soft magnetic solids. On thisscale, all such crystals are permanently magnetisedbut are composed of magnetic domains or Weissdomains, which are regions that have all of the elementary magnetic dipoles aligned to give an overall
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