Editing Antiferromagnetism (section)

== Antiferromagnetic materials ==
Antiferromagnetic structures were first shown through [[neutron diffraction]] of transition metal oxides such as nickel, iron, and manganese oxides. The experiments, performed by [[Clifford Shull]], gave the first results showing that magnetic dipoles could be oriented in an antiferromagnetic structure.<ref>{{cite journal | last1=Shull | first1=C. G. | last2=Strauser | first2=W. A. | last3=Wollan | first3=E. O. | title=Neutron Diffraction by Paramagnetic and Antiferromagnetic Substances | journal=Physical Review | publisher=American Physical Society (APS) | volume=83 | issue=2 | date=1951-07-15 | issn=0031-899X | doi=10.1103/physrev.83.333 | pages=333–345| bibcode=1951PhRv...83..333S }}</ref>

Antiferromagnetic materials occur commonly among [[transition metal]] compounds, especially oxides. Examples include [[hematite]], metals such as [[chromium]], alloys such as iron manganese (FeMn), and oxides such as nickel oxide (NiO). There are also numerous examples among high nuclearity metal clusters. Organic molecules can also exhibit antiferromagnetic coupling under rare circumstances, as seen in radicals such as [[5-dehydro-m-xylylene]].

Antiferromagnets can couple to ferromagnets, for instance, through a mechanism known as [[exchange bias]], in which the ferromagnetic film is either grown upon the antiferromagnet or annealed in an aligning magnetic field, causing the surface atoms of the ferromagnet to align with the surface atoms of the antiferromagnet. This provides the ability to "pin" the orientation of a ferromagnetic film, which provides one of the main uses in so-called [[spin valves]], which are the basis of magnetic sensors including modern [[hard disk drive]] read heads. The temperature at or above which an antiferromagnetic layer loses its ability to "pin" the magnetization direction of an adjacent ferromagnetic layer is called the blocking temperature of that layer and is usually lower than the Néel temperature.