Spin wave excitations in the pyrovanadate α−Cu2V2O7

The pyrovanadate $\ensuremath{\alpha}\ensuremath{-}{\mathrm{Cu}}₂{\mathrm{V}}₂{\mathrm{O}}₇$ belongs to the orthorhombic ($Fdd2$) class of crystals with noncentrosymmetric crystal structure. Recently, the compound has been identified to be a magnetic multiferroic with a substantial electric polarization below the magnetic transition temperature ${T}_C$ = 35 K. Here we report the results of our inelastic neutron-scattering (INS) studies on a polycrystalline sample of $\ensuremath{\alpha}\ensuremath{-}{\mathrm{Cu}}₂{\mathrm{V}}₂{\mathrm{O}}₇$. Our INS data clearly show the existence of dispersive spin wave excitations below ${T}_C$ with a zone-boundary energy of 11 meV at 5 K. We have analyzed the data using linear spin wave theory, which shows good agreement between the experiment and calculation. The analysis is consistent with the third-nearest-neighbor exchange interaction playing a dominant role in the magnetism of the material.