Crystal and Magnetic Structures of Monoclinic FeOHSO4

The crystal and magnetic structures and properties of the monoclinic form of the iron hydroxysulfate FeOHSO₄ were investigated by magnetometry and neutron powder diffraction. The space group C2/c was confirmed, and the proton position was located close to that predicted by ab initio calculations. The collinear antiferromagnetic k(0,0,0) structure forming below the Néel temperature T_N ∼ 125 K is described by the C2'/c' (No. 15.89) magnetic space group, with the moments along the b axis. Overall, FeOHSO₄ is isostructural to FeSO₄F in terms of both the crystal and magnetic structures.