Magnetic structure and properties of NaFeSO4F and NaCoSO4F

NaFeSO₄F and NaCoSO₄F crystallize in the maxwellite crystal structure and consist of one-dimensional chains of corner-sharing MO₄F₂ octahedra linked together through F atoms sitting in a trans configuration with respect to each other. Magnetic susceptibility measurements and low-temperature powder neutron diffraction indicate that both the Fe- and Co-based phases establish G-type antiferromagnetic ground states below 36 and 29 K, respectively. We discuss the obtained magnetic structure in the context of the local anisotropy of the two magnetic ions.