Elastic and Magnetoelastic Effects in Magnetite

Abstract

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\ifmmode^\circ\else\textdegree\fi{}K, where there is an easy-axis change from the [111] to the [100]. Both shear and longitudinal velocities show sharp increases of 7\textonehalf{}% and 0.2%, respectively, at 119\ifmmode^\circ\else\textdegree\fi{}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\ifmmode^\circ\else\textdegree\fi{}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\ifmmode^\circ\else\textdegree\fi{}K.