Magnetic Structure and Properties of the Rechargeable Battery Insertion Compound Na₂FePO₄F

The magnetic structure and properties of sodium iron fluorophosphate Na₂FePO₄F (space group <i>Pbcn</i>), a cathode material for rechargeable batteries, were studied using magnetometry and neutron powder diffraction. The material, which can be described as a quasi-layered structure with zigzag Fe-octahedral chains, develops a long-range antiferromagnetic order below ∼3.4 K. The magnetic structure is rationalized as a super-exchange-driven ferromagnetic ordering of chains running along the <i>a</i>-axis, coupled antiferromagnetically by super-super-exchange via phosphate groups along the <i>c</i>-axis, with ordering along the <i>b</i>-axis likely due to the contribution of dipole–dipole interactions