Multiferroic phases of the frustrated quantum spin-chain compound   linarite
  The dielectric properties of the prototypical frustrated ferromagnetic spin-chain compound PbCuSO$_4$(OH)$_2$ known as linarite, are studied across its strongly anisotropic magnetic phase diagram in single crystal samples. The ferroelectric character of the principal low-field spin spiral phase is confirmed. The measured polarization is fully consistent with the previously proposed magnetic structure. Spontaneous polarization is also detected in two other field-induced phases but in some cases is incompatible with previously suggested models for the spin arrangement. 
K. Yu. Povarov, Y. Feng, A. Zheludev
cond-mat.str-el