Long range interactions and magnetic frustration in multiferroic MnWO4 Feng Ye Oak Ridge National Laboratory The observation of spontaneous electric polarization and magnetic control of ferroelectricity in perovskite manganite TbMnO3 has inspired much theoretical and experimental effort searching for new magnetoelectric multiferroic materials due to their great technological and fundamental importance. The mineral hübnerite MnWO4 is one of few multiferroics that is ideal for studying the complex spin orders caused by magnetic frustrations and the interplay between magnetism and ferroelectricity. In this talk, I will present recent single crystal neutron diffraction investigation of the doped multiferroic Mn1-xTxWO4 (T: Fe, Zn, Co), and inelastic neutron scattering study of the spin dynamics in undoped MnWO4. While the substitution of magnetic Fe stabilizes the low temperature collinear up-up-down-down spin structure, the doping of non-magnetic Zn ions has been shown to suppress the commensurate collinear phase and stabilizes the spiral order. Furthermore, the Co-doped MnWO4 shows a complex evolution of the low temperature spin configurations that undergoes two spin flop transitions with increasing Co concentration. The rich phase diagram of MnWO4 upon chemical substitution indicates the system is highly frustrated and subjected to small perturbation. Using inelastic neutron scattering technique, we show that the collinear spin state in the pure MnWO4 result from the delicate balance of the competing long range interactions. The strong magnetic frustration within the zigzag chain along the c-axis and between chains along the a-axis gives rise to the incommensurate spiral order along those two directions.