Editing Diamagnetism (section)

== Materials ==
[[File:Diamagnetic material interaction in magnetic field.png|thumb|left|upright=1.4|Diamagnetic material interaction in [[magnetic field]]. On keeping diamagnetic materials in a magnetic field, the electron orbital motion changes in such a way that magnetic dipole moments are induced on the atoms / molecules in the direction opposite to the external magnetic field]]

Diamagnetism is a property of all materials, and always makes a weak contribution to the material's response to a magnetic field. However, other forms of magnetism (such as [[ferromagnetism]] or [[paramagnetism]]) are so much stronger such that, when different forms of magnetism are present in a material, the diamagnetic contribution is usually negligible. Substances where the diamagnetic behaviour is the strongest effect are termed diamagnetic materials, or diamagnets. Diamagnetic materials are those that some people generally think of as ''non-magnetic'', and include [[Water (properties)|water]], [[wood]], most organic compounds such as petroleum and some plastics, and many metals including [[copper]], particularly the heavy ones with many [[core electrons]], such as [[mercury (element)|mercury]], [[gold]] and [[bismuth]]. The magnetic susceptibility values of various molecular fragments are called [[Pascal's constants]] (named after {{ill|Paul Pascal (physicist)|fr|Paul Pascal|lt=Paul Pascal}}).

Diamagnetic materials, like water, or water-based materials, have a relative magnetic permeability that is less than or equal to 1, and therefore a [[magnetic susceptibility]] less than or equal to 0, since susceptibility is defined as {{nowrap|''χ''<sub>v</sub> {{=}} ''μ''<sub>v</sub> − 1}}. This means that diamagnetic materials are repelled by magnetic fields. However, since diamagnetism is such a weak property, its effects are not observable in everyday life. For example, the magnetic susceptibility of diamagnets such as water is {{nowrap|''χ''<sub>v</sub> {{=}} {{val|-9.05|e=-6}}}}. The most strongly diamagnetic material is [[bismuth]], {{nowrap|''χ''<sub>v</sub> {{=}} {{val|-1.66|e=-4}}}}, although [[pyrolytic carbon]] may have a susceptibility of {{nowrap|''χ''<sub>v</sub> {{=}} {{val|-4.00|e=-4}}}} in one plane. Nevertheless, these values are orders of magnitude smaller than the magnetism exhibited by paramagnets and ferromagnets. Because ''χ''<sub>v</sub> is derived from the ratio of the internal magnetic field to the applied field, it is a dimensionless value.

In rare cases, the diamagnetic contribution can be stronger than paramagnetic contribution. This is the case for [[gold]], which has a magnetic susceptibility less than 0 (and is thus by definition a diamagnetic material), but when measured carefully with [[X-ray magnetic circular dichroism]], has an extremely weak paramagnetic contribution that is overcome by a stronger diamagnetic contribution.<ref>{{cite journal |author=Suzuki |first=Motohiro |last2=Kawamura |first2=Naomi |last3=Miyagawa |first3=hayato |last4=Garitaonandia |first4=Jose S. |last5=Yamamoto |first5=Yoshiyuki |last6=Hori |first6=Hidenobu |date=24 Jan 2012 |title=Measurement of a Pauli and Orbital Paramagnetic State in Bulk Gold Using X-Ray Magnetic Circular Dichroism Spectroscopy |journal=Physical Review Letters |volume=108 |issue=4 |pages=047201 |bibcode=2012PhRvL.108d7201S |doi=10.1103/PhysRevLett.108.047201 |pmid=22400883}}</ref>


{|class="wikitable sortable"
|+Notable diamagnetic materials<ref name=hyper>{{cite web |last=Nave |first=Carl L. |title=Magnetic Properties of Solids |website=Hyper Physics |url=http://hyperphysics.phy-astr.gsu.edu/Hbase/tables/magprop.html |access-date=2008-11-09 |archive-date=22 August 2014 |archive-url=https://web.archive.org/web/20140822163112/http://hyperphysics.phy-astr.gsu.edu/Hbase/tables/magprop.html |url-status=live }}</ref>
!Material!! ''χ''<sub>v</sub> [× 10<sup>−5</sup> (SI units)]
|-
|Superconductor
| −10<sup>5</sup>
|-
|[[Pyrolytic carbon]]
| −40.9
|-
|[[Bismuth]]
| −16.6
|-
|[[Neon]]
| −6.74
|-
|[[Mercury (element)|Mercury]]
| −2.9
|-
|[[Silver]]
| −2.6
|-
|[[Diamond|Carbon (diamond)]]
| −2.1
|-
|[[Lead]]
| −1.8
|-
|[[Graphite|Carbon (graphite)]]
| −1.6
|-
|[[Copper]]
| −1.0
|-
|[[Properties of water|Water]]
| −0.91
|}

=== Superconductors ===
[[File:EXPULSION.png|thumb|Transition from ordinary [[electrical conductivity|conductivity]] (left) to [[superconductivity]] (right). At the transition, the [[superconductor]] expels the magnetic field and then acts as a perfect diamagnet.]]
[[superconductivity|Superconductors]] may be considered [[Superdiamagnetism|perfect diamagnets]] ({{nowrap|''χ''<sub>v</sub> {{=}} −1}}), because they expel all magnetic fields (except in a thin surface layer) due to the [[Meissner effect]].<ref>{{cite book | last=Poole | first=Charles P. Jr. |author1-link=Charles P. Poole |year=2007 |title=Superconductivity |edition=2nd |publisher=Academic Press |location=Amsterdam |isbn=9780080550480 |page=23}}</ref>