Cycloidal magnetism driven ferroelectricity in double tungstate LiFe(WO₄)₂

M. Liu, L.-F. Lin, Y. Zhang, S. Li, Q. Huang, V. O. Garlea, T. Zou, Y. Xie, Y. Wang, C. Lu, L. Yang, Z. Yan, X. Wang, S. Dong, J.-M. Liu