Editing Paramagnetism (section)

===Systems with minimal interactions===
The narrowest definition would be: a system with unpaired spins that ''do not interact'' with each other. In this narrowest sense, the only pure paramagnet is a dilute gas of [[monatomic hydrogen]] atoms. Each atom has one non-interacting unpaired electron.

A gas of lithium atoms already possess two paired core electrons that produce a diamagnetic response of opposite sign. Strictly speaking Li is a mixed system therefore, although admittedly the diamagnetic component is weak and often neglected. In the case of heavier elements the diamagnetic contribution becomes more important and in the case of metallic gold it dominates the properties. The element hydrogen is virtually never called 'paramagnetic' because the monatomic gas is stable only at extremely high temperature; H atoms combine to form molecular H<sub>2</sub> and in so doing, the magnetic moments are lost (''quenched''), because of the spins pair. Hydrogen is therefore ''diamagnetic'' and the same holds true for many other elements. Although the electronic configuration of the individual atoms (and ions) of most elements contain unpaired spins, they are not necessarily paramagnetic, because at ambient temperature quenching is very much the rule rather than the exception. The quenching tendency is weakest for f-electrons because ''f'' (especially 4''f'') orbitals are radially contracted and they overlap only weakly with orbitals on adjacent atoms.  Consequently, the lanthanide elements with incompletely filled 4f-orbitals are paramagnetic or magnetically ordered.<ref>{{Cite book|url=http://www2.nbi.ku.dk/page40667.htm|title=Rare Earth Magnetism|author1=Jensen, J.|author2=MacKintosh, A. R.|name-list-style=amp|publisher=Clarendon Press|place=Oxford|year=1991|access-date=2009-07-12|archive-url=https://web.archive.org/web/20101212232011/http://www2.nbi.ku.dk/page40667.htm|archive-date=2010-12-12|url-status=dead}}</ref>

{|class="wikitable sortable" style="float:right; margin:20px" width="200px"
|+μ<sub>eff</sub> values for typical d<sup>3</sup> and d<sup>5</sup> transition metal complexes.<ref>Orchard, A. F. (2003) ''Magnetochemistry''. Oxford University Press.</ref>
!Material!!μ<sub>eff</sub>/μ<sub>B</sub>
|-
|[Cr(NH<sub>3</sub>)<sub>6</sub>]Br<sub>3</sub>||3.77
|-
|K<sub>3</sub>[Cr(CN)<sub>6</sub>]||3.87
|-
|K<sub>3</sub>[MoCl<sub>6</sub>]||3.79
|-
|K<sub>4</sub>[V(CN)<sub>6</sub>]||3.78
|-
|[Mn(NH<sub>3</sub>)<sub>6</sub>]Cl<sub>2</sub>||5.92
|-
|(NH<sub>4</sub>)<sub>2</sub>[Mn(SO<sub>4</sub>)<sub>2</sub>]·6H<sub>2</sub>O||5.92
|-
|NH<sub>4</sub>[Fe(SO<sub>4</sub>)<sub>2</sub>]·12H<sub>2</sub>O||5.89
|-
|}
Thus, condensed phase paramagnets are only possible if the interactions of the spins that lead either to quenching or to ordering are kept at bay by structural isolation of the magnetic centers. There are two classes of materials for which this holds:
*Molecular materials with a (isolated) paramagnetic center.
** Good examples are [[coordination complex]]es of d- or f-metals or proteins with such centers, e.g. [[myoglobin]]. In such materials the organic part of the molecule acts as an envelope shielding the spins from their neighbors.
** Small molecules can be stable in radical form, [[oxygen]] O<sub>2</sub> is a good example. Such systems are quite rare because they tend to be rather reactive.
* Dilute systems.
** Dissolving a  paramagnetic species in a diamagnetic lattice at small concentrations, e.g. Nd<sup>3+</sup> in CaCl<sub>2</sub> will separate the neodymium ions at large enough distances that they do not interact. Such systems are of prime importance for what can be considered the most sensitive method to study paramagnetic systems: [[Electron paramagnetic resonance|EPR]].