Stabilization of the elliptical spiral phase and the spin-flop transition in multiferroic Mn1-xCoxWO4

We have studied the effect of Co doping on the magnetic properties of multiferroic Mn1-xCoxWO4 using vibrating sample magnetometry and neutron powder diffraction. We find that Co doping at x greater than or similar to 0.05 suppresses the commensurate AF1 phase and stabilizes the incommensurate spiral AF2 phase down to the lowest temperature. As the Co doping concentration increases further, a spin-flop transition occurs with the spiral-basal plane tilting off the b axis. Such magnetic structure expects a ferroelectric polarization component along the a axis. The resulting phase diagram is richer than the case of Fe doping.