Magnetostriction and Crystal Anisotropy of Single Crystals of Hexagonal Cobalt

Abstract

Magnetostriction at saturation has been measured in various crystallographic directions in a single crystal of cobalt. Results are described by Mason's formula [see Eq. (1)] with 4 constants, which are now evaluated. Magnetization causes contractions as large as 100\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$, and expansions up to 150\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$, depending on crystallographic direction. A fractional decrease in volume, associated with domain orientation, is observed to be as large as 26\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$. Superposed on this contraction is a small isotropic increase in volume of 0.6\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}9}$ per oersted. Magnetic crystal anisotropy constants are determined and used in a calculation of the magnetostriction as dependent on the magnitude of the field applied to a disk with given demagnetizing factor. Calculation and observation agree, and show that the direction and magnitude of magnetization and of true field can be calculated in any applied field as long as it is considerably above the coercive force.