Magnetoelectric coupling in a triangular lattice antiferromagnet CuCrO$_{2}$

A triangular lattice antiferromagnet CuCrO$_{2}$ shows an out- of-plane 120\r{ } spin structure. Recently, ferroelectricity in the 120\r{ } phase has been reported for polycrystalline samples. However, no anisotropic information (e.g. direction of polarization) has been provided for lack of single-crystal measurement [1]. Therefore, we grew single crystals of CuCrO$_{2}$ and investigated their magnetic and ferroelectric properties [2]. We found that CuCrO$_{2}$ undergoes two successive magnetic phase transitions ($T_{N2} \quad \approx $ 24.2 K and $T_{N1} \quad \approx $ 23.6 K), probably into a collinear antiferromagnetic phase and then the out-of-plane 120$^{\circ}$ phase. Ferroelectric polarization within the triangular lattice plane appears only in the 120$^{\circ}$ phase. In the talk, we also discuss the magnetoelectric properties. [1] S. Seki et al., \textit{Phys. Rev. Lett.} \textbf{101}, 067204 (2008). [2] K. Kimura et al., \textit{Phys. Rev. B }\textbf{78}, 140401(R) (2008).