Investigating the different magnetic phases of a new type-II multiferroic MnBi2S4

Multiferroics are the rare class of materials known, where two or more ferroic order parameters coexist simultaneously. Recently, spin driven ferroelectricity was reported in the centrosymmetric monoclinic sulphide MnSb2S4, in which incommensurate spin structure induces electric polarization. Along this line, we have discovered multiferroicity in MnBi2S4, which crystallizes in the monoclinic (C2/m) structure. It exhibits magnetic phase transitions at TN1=26.5, TN2=22.7, and TN3=21.3 K, where TN2 and TN3 are associated with ferroelectricity. The distortion associated with the lone pair of Bi3+- ion in BiS5 polyhedra expected to play crucial role in the observed multiferroicity and makes this compound different from MnSb2S4. It is necessary to know the magnetic spin structure to understand the origin of multiferroicity.