Magnetoelastic interactions in NdVO4: Finite strain and rotational effects

Propagation of transverse- and longitudinal-acoustic waves in single-crystal neodymium vanadate NdV${\mathrm{O}}_4$, in the presence of an external magnetic field, was investigated experimentally as a function of magnetic field angle and strength at 9.9, 77, and 292 K. The dependence of the relative change in velocity $\frac{\Delta v}{v}$ on magnetic field angle, not heretofore reported, is explicitly demonstrated for both transverse and longitudinal distortions. The results are in agreement with theory of spin-lattice coupling in paramagnetic systems proposed by Melcher and collaborators. In this theory, both finite-strain and rotational effects are taken into account in correctly predicting a difference in the shift, for example, of the elastic constant $C_{44}$, due to spin-lattice coupling for transverse $\mathrm{xz}$ and $\mathrm{zx}$ acoustic modes. The present results, in their dependence on magnetic field strength, are in qualitative agreement with those of Bonsall and Melcher. The elastic constants $C_{11}$, $C_{44}$, and $C_{33}$ of NdV${\mathrm{O}}_4$, in addition, were measured as a function of temperature between 9.9 and 292 K.