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

The structural and physical properties of the β polymorph of iron tungstate FeWO have been investigated by synchrotron and neutron diffraction vs temperature, combined with magnetization and dielectric properties measurements. The monoclinic 2/ crystal structure of β-FeWO has been determined and consists of an original network of zigzag chains of FeO and WO octahedra sharing trans and skew edges, connected through corners into a 3D structure. Magnetization measurements indicate an antiferromagnetic transition at = 264 K, which corresponds to a ↑↑↓↓ nearly collinear ordering of iron moments inside sequences of four edge-sharing FeO octahedra, as determined by neutron diffraction. A canting of the moments out of the plane is observed below 150 K, leading to a noncollinear antiferromagnetic structure, the 2/' magnetic space group remaining unchanged. These results are discussed in comparison with the crystal and magnetic structures of γ-FeWO and with the magnetic couplings in other iron tungstates and trirutile FeTeO.