Magnetic phases in Mn1-xFexWO4 studied by neutron powder diffraction

The magnetic structures of Mn 1-x Fe x WO 4 with x = 0.0, 0.16. 0.21, 0.225. 0.232, 0.24, 0.27, 0.29, and 1.0 were refined from neutron powder diffraction data. The magnetic phase diagram could be completed in the coexistence range of different magnetic structures up to x = 0.29. For the magnetic state at 1.5 K a commensurate antiferromagnetic structure with a propagation vector k = (±1/4, 1/2, 1/2) was found for x ≤ 0.22 while the magnetic spins order with k = (1/2, 0, 0) for x ≥ 0.22. In the latter phase, additionally, weak magnetic reflections indexed to an incommensurate ordering with k = (-0.214, 1/2, 0.457) occur in the diffraction pattern up to x = 0.29 indicating the occurence of a reentrant phase. For 0.12 ≤ x < 0.29 the low temperature phases are separated from a magnetic high temperature phase showing only magnetic reflections indexed to a spin arrangement with k = (1/2, 0.0). The magnetic phase diagram is discussed qualitatively considering random superexchange between the statistically distributed Mn 2+ - and Fe 2+ -ions in the coexistence range 0.12 < x ≤ 0.29 of different magnetic structures related to those of pure MnWO 4 and FeWO 4 .