Effect of Hydrostatic Pressure on the Elastic and Inelastic Behavior of Gadolinium in the Spin-Reorientation Region

Abstract

The effect of hydrostatic pressures, up to 6 kbar, on the anomalies occurring in the ultrasonic wave propagation in gadolinium single crystals below the Curie point, is investigated. The elastic softening of the $c_{33}$ elastic constants, and its pressure dependence, is discussed in terms of the molecular-field model of the magnetic-interaction Hamiltonian. It was shown that the elastic softening in gadolinium is of a magnetoelastic origin. Within the framework of the model presented in this study, it is shown why the shear elastic modes $c_{44}$ and $c_{66}$ do not exhibit anomalous behavior in the spin-reorientation region of gadolinium. The reason for the negligible elastic anomaly in ${\mathrm{c}}_{11}$, in this temperature region, is also discussed. The pressure dependence of the spin-reorientation temperature $T_f$ can be explained in terms of the pressure contribution to the first anisotropy-energy constant $K_1$ This calculated value of the shift in $T_f$ with pressure is in satisfactory agreement with the experimentally determined one.