Stabilization of the elliptical spiral phase and the spin-flop transition in multiferroic Mn1-x Cox WO4

We have studied the effect of Co doping on the magnetic properties of multiferroic ${\text{Mn}}_{1\ensuremath{-}x}{\text{Co}}_{x}{\text{WO}}_{4}$ using vibrating sample magnetometry and neutron powder diffraction. We find that Co doping at $x\ensuremath{\gtrsim}0.05$ 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.