Original Network of Zigzag Chains in the β Polymorph of Fe₂WO₆: Crystal Structure and Magnetic Ordering

The structural and physical properties of the β polymorph of iron tungstate Fe₂WO₆ have been investigated by synchrotron and neutron diffraction vs temperature, combined with magnetization and dielectric properties measurements. The monoclinic P2₁/a crystal structure of β-Fe₂WO₆ has been determined and consists of an original network of zigzag chains of FeO₆ and WO₆ octahedra sharing trans and skew edges, connected through corners into a 3D structure. Magnetization measurements indicate an antiferromagnetic transition at T_N = 264 K, which corresponds to a ↑↑↓↓ nearly collinear ordering of iron moments inside sequences of four edge-sharing FeO₆ octahedra, as determined by neutron diffraction. A canting of the moments out of the ac plane is observed below 150 K, leading to a noncollinear antiferromagnetic structure, the P2₁/a' magnetic space group remaining unchanged. These results are discussed in comparison with the crystal and magnetic structures of γ-Fe₂WO₆ and with the magnetic couplings in other iron tungstates and trirutile Fe₂TeO₆.