Discontinuous Changes in Length Accompanying the Barkhausen Effect in Nickel

Abstract

A heterodyne beat method is described by means of which displacements as small as 9\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}9}$ cm may be measured. When a nickel wire, 1.96 cm long and 0.01 cm in diameter, is subjected to a steadily changing magnetic field there is evidence of a sudden length change at the instant of a Barkhausen discontinuity of magnetization. For a nickel wire 2 cm long and 0.002 cm in diameter these sudden length changes were larger and could easily be measured. They were associated with every Barkhausen jump observed in the specimen. The largest one measured was 4.7\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ cm. Calculations based on the measurements of these magnetostrictive jumps give 3.7\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ cc. for the minimum value of the volume of the element which suffers the jumps. Reasons are advanced for believing that the sudden change in intensity of magnetization of this volume element cannot be less than 40 units nor more than 330. A qualitative theory of the phenomenon is given.