Elastic and Magnetoelastic Effects in Magnetite

The temperature dependence of the longitudinal and the shear sound-wave velocity along the [100] axis in ${\mathrm{Fe}}_3$ ${\mathrm{O}}_4$ is presented. The longitudinal velocity exhibits an anomaly at 130°K, where there is an easy-axis change from the [111] to the [100]. Both shear and longitudinal velocities show sharp increases of 7½% and 0.2%, respectively, at 119°K, where the structure changes from cubic to orthorhombic. In addition, the linear magnetoelastic birefringence effect and the shear-velocity changes as a function of magnetic field were used to determine the magnetoelastic coupling constant $b_{44}$ as a function of temperature from room temperature to 125°K. These results are compared with values of $b_{44}$ obtained from magnetostriction data. Transverse ferroacoustic resonance effects could be observed in the temperature interval 150-300°K.