Observation of a Weak Ferromagnetic Ground State Structure for the Lithium-Insertion Compound Li2Fe2(MoO4)3

The low-temperature magnetism and neutron structure of orthorhombic Li2Fe2(MoO4)3, synthesized via the topotactic redox-insertion reaction of LiI with Fe2(MoO4)3, is discussed. dc magnetic susceptibility measurements in an applied field of 30 G, and very low field (Ho=1 G) ac susceptibility measurements (real and imaginary (out-of-phase) components) show a weakly ferromagnetic state, below 12.5 K, that is most likely due to intrinsic canting of antiferromagnetically coupled lattices. An analysis of the magnetic scattering from powder neutron diffraction data at 4.2 K shows an antiferromagnetic spin arrangement. Although it was not possible to refine a small magnetic component that would give rise to a net ferromagnetic moment, the magnetic space group symmetry permits a ferromagnetic component parallel to thexaxis, which accounts for the weak ferromagnetism observed in the susceptibility studies.