Multiferroicity in the spin-1/2 quantum matter of LiCu2O2
  Multiferroicity in LiCu2O2 single crystals is studied using resonant soft x-ray magnetic scattering, hard x-ray diffraction, heat capacity, magnetic susceptibility, and electrical polarization. Two magnetic transitions are found at 24.6 K (T1) and 23.2 K (T2). Our data are consistent with a sinusoidal spin structure at T2<T<T1 and with a helicoidal spin structure at T<T2 giving rise to ferroelectricity. Surprisingly, above T2 the correlation lengths of the spin structures increase as the temperature increases with dramatic changes of ~42% along the c-axis. Our results demonstrate the interplay of the geometrical frustration and the electronic and magnetic polarizations. 
A. Rusydi, I. Mahns, S. Mueller, and M. Ruebhausen, S. Park, Y.J.   Choi, C. L. Zhang, S-W. Cheong, S. Smadici, P. Abbamonte...