Magnetoelectricity in Spinel FeCr$_{2}$S$_{4}$*

We report on ferroelectricity, magnetic susceptibility, dielectric property, and specific heat capacity of the polycrystalline spinel FeCr$_{2}$S$_{4}$. We provide clear evidence of a ferroelectric transition at $\sim$ 8.5K, which accompanies an orbital-ordering transition and a dielectric anomaly. The polarization increases with decreasing temperature, and reaches 3.6$\mu $C/m$^{\mathrm{2}}$ at 2 K. We also carry out detailed multiferroic measurements, and a remarkable magnetoelectric coupling is observed. A very small magnetic filed $H$ $\sim$ 500Oe enhances the polarization to 8.13.6$\mu $C/m$^{\mathrm{2}}$ at 2 K, with a magnetoelectric coupling coefficient $\alpha \sim$ 120{\%}. However, the polarization rapidly decreases for fields beyond $H \sim$ 1T. The multiferroic behavior of FeCr$_{2}$S$_{\mathrm{4}}$ is proposed to arise from competition between the spin-orbital coupling and the Jahn-Teller effect for the Fe ion.\\[4pt] [1] V. Fritsch, et al, Phys. Rev. Lett. \textbf{92}, 116401 (2004).\\[0pt] [2] R. Fichtl, et al, Phys. Rev. Lett. \textbf{94}, 027601 (2004).\\[0pt] [3] V. Tsurkan et al, Phys. Rev. B \textbf{81}, 184426 (2010).