The magnetoelastic contributions to the pure shear wave elastic constants of single crystal dysprosium
Koo, Jen-Wei Carl
Donoho, Paul L.
Master of Arts
The pure shear wave elastic constants, C and Cgg, was measured with echo overlap method as functions of the applied magnetic field. The elastic constants were measured in applied fields of to 17.5 KOe and temperatures between 18°K and 3°K. Different directions of applied field and polarization of the ultrasonic wave in the basal plane were used in order to investigate the contributions to the elastic constants due to the rotational terms. The theroretical approachs of Southern and Goodings and of Freyne were discussed and the inadaquacy of Southern and Goodings's theorey was shown by compare to the experimental results of longitudinal elastic constants. Kale calculated the magnetoelastic constants numerically using a thermodynamic approach which was a modified version of freyne's theory and had a much better fit to the longitudinal elastic constants. This thermodynamic calculation which included only first-order elastic interactions and second-order magnetoelastic interactions can not explain some of the behaviors of the shear wave elastic constants found here. In order to explain these anomalous behaviors, higher order terms must be included. The contributions to the elastic constants due to third-order elastic energy was calculated and the estimated value was found to be able to account for part of the discrepancies.