Magnetic structure of Fe₂WO₆, a neutron diffraction study

The structure of the compound Fe₂WO₆ is of the tri-α-PbO₂ type, and it belongs to the crystallographic space group Pbcn (D¹⁴_2h). The lattice constants are a = 4.576, b = 16.766 and c = 4.967 Å, with four formula units per lattice point. Neutron (λ ~ 2.4 Å) diffraction patterns were taken at 300, 170, 77 and 4.2 K. Some intensity-temperature curves were also taken. The results may be summarized as follows. (1) The room- temperature pattern agrees with the reported X-ray determination of the crystallographic structure and ion positions. (2) Reflexions with h + k odd not allowed by Pbcn, {010}, {030}, {100}, {031}, appear, on cooling, at T₁ ~ 240 K and increase in intensity down to liquid-helium temperature. (3) Reflexions with h + k even, allowed by Pbcn: {020}, {021}, {040}, {110}, {111}, {150}, show, on cooling, an increase in intensity starting at T₂ ~ 150 K. The first set of reflexions is consistent with Cz⁺, i.e. ferromagnetic (100) planes coupled antiferromagnetically with spin along [001]. This structure belongs to Pbc'n'. The space group Pbc'n', however, allows the modes Cz⁺ and Fx⁺ or Cz⁺ and Fx^- which is equivalent to a spin component along [100]. The second set of reflexions is consistent with Fx⁺ and/or changes in the ion positions.