X-ray investigation of the magnetoelastic instability ofα′−NaV2O5

Abstract

We present an x-ray diffuse scattering study of the pretransitional structural fluctuations of the magnetoelastic transition in ${\ensuremath{\alpha}}^{\ensuremath{'}}\ensuremath{-}{\mathrm{NaV}}_{2}{\mathrm{O}}_{5}.$ This transition is characterized by the appearance below ${T}_{\mathrm{sp}}\ensuremath{\sim}35\mathrm{K}$ of satellite reflections at the reduced wave vector $(\frac{1}{2},\frac{1}{2},\frac{1}{4}).$ A large regime of structural fluctuations is measured up to 90 K. These fluctuations are three-dimensional between ${T}_{\mathrm{sp}}$ and $\ensuremath{\sim}50\mathrm{K}$ and quasi-one-dimensional above $\ensuremath{\sim}60\mathrm{K}.$ At 40 K the anisotropy ratio $({\ensuremath{\xi}}_{b}:{\ensuremath{\xi}}_{a}:{\ensuremath{\xi}}_{c})$ is found to be (3.8:1.8:1), which reveals the importance of transverse interactions in the stabilization of the low-temperature phase. We discuss our results within the framework of recent theories dealing with the simultaneous occurrence of a charge ordering, a spin gap, and a lattice distortion in this intriguing compound.