Editing State of matter (section)

== Magnetically ordered states ==
[[Transition metal]] atoms often have [[magnetic moment]]s due to the net [[Spin (physics)|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.

In a [[ferromagnetism|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 {{convert|768|C|F}}.

An [[antiferromagnetism|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.

In a [[ferrimagnetism|ferrimagnet]], the two networks of magnetic moments are opposite but unequal, so that cancellation is incomplete and there is a non-zero net magnetization. An example is [[magnetite]] (Fe{{sub|3}}O{{sub|4}}), which contains Fe{{sup|2+}} and Fe{{sup|3+}} ions with different magnetic moments.

A [[quantum spin liquid]] (QSL) is a disordered state in a system of interacting quantum spins which preserves its disorder to very low temperatures, unlike other disordered states. It is not a liquid in physical sense, but a solid whose magnetic order is inherently disordered. The name "liquid" is due to an analogy with the molecular disorder in a conventional liquid. A QSL is neither a [[Ferromagnetism|ferromagnet]], where magnetic domains are parallel, nor an [[Antiferromagnetism|antiferromagnet]], where the magnetic domains are antiparallel; instead, the magnetic domains are randomly oriented. This can be realized e.g. by [[Geometrical frustration|geometrically frustrated]] magnetic moments that cannot point uniformly parallel or antiparallel. When cooling down and settling to a state, the domain must "choose" an orientation, but if the possible states are similar in energy, one will be chosen randomly. Consequently, despite strong short-range order, there is no long-range magnetic order.