The Magnetostriction of Pure and Alloyed Bi Single Crystals

The existence of a magnetostrictive effect (Joule effect) in nonferromagnetic substances, first demonstrated by Kapitza for large transient fields, is here shown for steady fields of moderate (20 to 25 kg) values. Pure (99.97 percent) Bi single crystals and crystals with dissolved foreign atoms are used. A recording dilatometer permitted measurements of a change in length of 2.5×${10}^{-7\mathrm{}}$ cm. The sum of errors amounted to approximately 10 percent. The modulus of magnetostriction ($m$) is defined by $\frac{\Delta l}{l}=\frac{1}{2}m{H}^2$. For pure Bi crystals $m=+5.7\mathrm{}\times {10}^{-16\mathrm{}}$ (elongation) parallel to trigonal axis and $m=-7.0\mathrm{}\times {10}^{-16\mathrm{}}$ (contraction) normal to trigonal axis. Bi crystals with Pb, Sn and Te in concentration within the solubility range were studied. Sn and Pb (electropositive) first cause the contraction normal to the trigonal axis to diminish and finally with increasing concentrations, cause an elongation, Sn being four times as effective as Pb. Parallel to the axis small concentrations of Sn decrease the elongation, larger concentrations increase the elongation. The effect of Pb in this direction is small. Te (electronegative) produced a much larger specific effect but no change in sign. The effect was of the same order of magnitude for the two principal crystal orientations. The data are discussed with special reference to the influence of foreign atoms on the magnetic susceptibility, studied previously by Goetz and Focke. It was found that the change of the stress coefficient of the susceptibility with the concentration of foreign atoms normal to the principal axis is inversely proportional to the concentration and furthermore: the variation of the stress coefficient with the concentration is nearly equal to the variation of the susceptibility at higher concentrations, in other words the stress coefficient of the susceptibility is proportional to the susceptibility itself. It is furthermore concluded that the results presented justify the previous assumption of the existence of two types of insertion of foreign atoms in the crystal lattice, i.e., selective adsorption for small concentrations and volume absorption for larger concentrations.