Spiral structure of a frustrated spinel CdCr$_{2}$O$_{4}$ studied by polarized neutron techniques

CdCr$_2$O$_4$ has the spinel structure, in which geometrical frustration exists between the Cr$^{3+}$ moments located at the corners of the tetrahedron. This compound shows a transition to a spiral magnetic structure with a characteristic wave vector of $Q=(0,\delta,1)$ ($\delta\sim0.09$) at 7.8 K, which is accompanied by a tetragonal structural distortion with the $c$ axis elongated. [1] We first performed a 1D polarized neutron analysis and determined that the Cr$^{3+}$ moments has a planer anisotropy in the $ac$ plane. Finally, spherical neutron polarimetry experiments were performed using a CRYOPAD on TAS-1 at JRR-3. It is found that the spiral structure is elliptical with the spin component $\sim$24\% elongated along the $c$ axis. [1] J.-H. Chung $et$ $al$., Phys. Rev. Lett. 95, 247204 (2005).