View source for Curie laws

<Font color="blue"> Lois de Curie </Font>(''Fr''). <Font color="red"> Curie Gesetz </Font> (''Ge''). <Font color="green">Leyes de Curie </Font>(''Sp'').<Font color="black"> Leggi di Curie </Font>(''It'')


== Definition ==

Curie extended the notion of symmetry to include that of physical phenomena and stated that:

* the symmetry characteristic of a phenomenon is the highest compatible with the existence of the phenomenon;

* the phenomenon may exist in a medium which possesses that symmetry or that of a subgroup of that symmetry.

and concludes that some symmetry elements may coexist with the phenomenon but that their presence is not necessary. On the contrary, what is necessary is the absence of certain symmetry elements: ‘asymmetry creates the phenomenon’. Noting that physical phenomena usually express relations between a cause and an effect (an influence and a response), P. Curie restated the two above propositions in the following way, now known as Curie laws, although they are not, stricly speaking, laws (Curie himself spoke about 'the principle of symmetry'):

*the asymmetry of the effects must pre-exist in the causes;

* the effects may be more symmetric than the causes.

== Applications ==

Curie applied the above statements to determine the symmetry characteristic of physical quantities such as a polar vector, a force or an electrical field, ''A''<sub>&infin;</sub> &infin;''M'',  an axial vector or a magnetic field, (''A''<sub>&infin;</sub> /''M'') ''C''.

If one now considers a phenomenon resulting from the superposition of several causes in the same medium, one mau note that the symmetry of the global cause is the intersection of the groups of symmetry of the various causes: the asymmetries add up. This remark can be applied to the determination of the point groups where physical properties such as [[pyroelectricity]] or [[piezoelectricity]] are possible.

== History ==

Pierre Curie (1859-1906)'s principle of symmetry is stated in Curie P., 1894, ''J. Physique'', '''3''', 393-415, ''Sur la symétrie dans les phénomènes physiques, symétrie d'un champ électrique et d'un champ magnétique''. 

== See also ==

[[Neumann's principle]]<br>
Section 1.1.4 of ''International Tables of Crystallography, Volume D''

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[[Category:Physical properties of crystals]]<br>