Multiferroic phases of the frustrated quantum spin-chain compound linarite

The dielectric properties of the prototypical frustrated ferromagnetic spin-chain compound PbCuSO4(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.