Spiral magnetic structure of Fe in Van der Waals gapped FeOCl and polyaniline-intercalated FeOCl

High-resolution and magnetic neutron-diffraction measurements were performed to investigate the crystal and magnetic structures of bilayered FeOCl and polyaniline-intercalated FeOCl. A quasi-two-dimensional crystallographic structure, where charge neutral $({\mathrm{Fe}}_{2}{\mathrm{O}}_{2}{\mathrm{Cl}}_{2}{)}_{n}$ lamellas are weakly linked via Van der Waals interactions, has made FeOCl a good host for accommodating guest molecules. A three-dimensional long-range ordering of the Fe spins in FeOCl develops below 80 K, with a magnetic unit cell 28 times the size of the nuclear one. A spiral magnetic structure was obtained, reflecting the competition between antiferromagnetic superexchange coupling and ferromagnetic direct exchange coupling. Polyaniline intercalation interrupts the magnetic correlations between the neighboring bilayers, rendering a coupled-bilayer quasi-two-dimensional magnetic order for the Fe spins in $({\mathrm{C}}_{6}{\mathrm{D}}_{4}\mathrm{ND}{)}_{0.16}\mathrm{FeOCl}.$ No significant change on the ordering temperature of the Fe spins by the intercalation reaction was observed.