The magnetostriction of bismuth single crystals

Abstract

The problem of magnetostriction has been recently discussed by Kapitza, who by his well-known method of large magnetic fields was able to show its existence in a number of diamagnetic substances. The effect was most marked in bismuth single crystals, but only longitudinal measurements could be conveniently made with the method used, and formal analysis showed that these were not sufficient to provide a complete description ( i.e. ,the scheme of magnetostriction moduli) of the phenomenon. The present paper describes an experimental investigation of transverse magnetostriction in bismuth crystals, showing how this completes the scheme of magnetostriction moduli, and what contribution this scheme makes to an understanding of the anomalous behaviour of bismuth. The work had also the object of confirming the general features of the magnetostriction that were found by Kapitza in large fields, for the region of much lower fields available in an ordinary electromagnet. A rough estimate showed that the magnetostriction change of length in these fields (~ 15,000 gauss) would be extremely small (~ 5 × 10 -7 cm for a crystal 10 cm long), and the first part of the paper describes a new magnification method which had to be developed for the measurement of such small changes of length. This is followed by an account of the results obtained and a discussion of their significance.