Multiferroic hysteresis in MnWO4

Multiferroic materials or compounds with a strong magnetoelectric effect posses a large application potential in data storage techniques: one would like to replace the common magnetic writing by an electric process, as the generation of the magnetic fields is energy expensive. Quite recently, systems with a peculiar spiral magnetic order were shown to directly induce a spontaneous electric polarization and to exhibit giant magnetoelectric and magnetocapacitance effects, among them MnWO4, which crystallizes in a monoclinic structure and undergoes several magnetic phase transitions as a function of temperature. From these phases only the incommensurate non-collinear ordering in the AF2-phase induces an electric polarization and large magnetoelectric effects, fully consistent with recent theories. We have succeeded for the first time to observe a chirality hysteresis curve driven by the electric field. These data can give important information about the pinning of the multiferroic order, which is relevant in view of future applications. We present our temperature dependent studies on the multiferroic hysteresis as well as a characterization of the second harmonics of the spiral.