THE change in shape of a body, when magnetised, may be accounted for by two causes. First the stresses produced by the magnetic forces act on the magnetic poles of the magnetised body. This effect, which we shall call the classical magnetostriction, is in a given magnetic field completely determined by the magnetic susceptibility and the elastic constants of the body. In general it will result in a contraction for diamagnetic substances and an expansion for paramagnetic ones. The classical magnetostriction is very small even for a strongly diamagnetic substance like bismuth, where δl/l in a field of 300 kilogauss is only 1.3 × 10-6. It is evident that the discovery of an effect of this order would amount to a verification of the classical theory of magnetisation and would afford no new information on the property of the substance.
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KAPITZA, P. Magnetostriction of Diamagnetic Substances in Strong Magnetic Fields. Nature 124, 53 (1929). https://doi.org/10.1038/124053a0