<P> Other types of liquid crystals are described in the main article on these states . Several types have technological importance, for example, in liquid crystal displays . </P> <P> Transition metal atoms often have magnetic moments due to the net spin of electrons that remain unpaired and do not form chemical bonds . In some solids the magnetic moments on different atoms are ordered and can form a ferromagnet, an antiferromagnet or a ferrimagnet . </P> <P> In a ferromagnet--for instance, solid iron--the magnetic moment on each atom is aligned in the same direction (within a magnetic domain). If the domains are also aligned, the solid is a permanent magnet, which is magnetic even in the absence of an external magnetic field . The magnetization disappears when the magnet is heated to the Curie point, which for iron is 768 ° C . </P> <P> An antiferromagnet has two networks of equal and opposite magnetic moments, which cancel each other out so that the net magnetization is zero . For example, in nickel (II) oxide (NiO), half the nickel atoms have moments aligned in one direction and half in the opposite direction . </P>

When were the three states of matter discovered