Magnetic Structure and Properties of the Li-Ion Battery Materials FeSO₄F and LiFeSO₄F

Using magnetic susceptibility and low-temperature neutron diffraction experiments we present a thorough characterization of the magnetic properties of LiFeSO 4 F and FeSO 4 F. Temperature dependent magnetic susceptibility measurements show a transition to long-range antiferromagnetic order at 100 K in FeSO 4 F whereas the ordering temperature in LiFeSO 4 F is 25 K. We attribute the decreased ordering temperature to a structural change which decreases the strength of the magnetic interactions along the length of the chains and to the difference of supersuper-exchange interactions between Fe 2+ and Fe 3+ ions. Powder neutron diffraction experiments were used to determine the magnetic structures of both compounds, which are discussed in terms of exchange interactions and the anisotropy of Fe 2+ . The iron magnetic moments are antiparallel within the chains, whereas the coupling between the chains is different in the lithiated compound compared to the delithiated one, resulting in different spin arrangements.