Hyperfine interactions in the anisotropic layer compound FeOCl from57Fe Mössbauer studies

The anisotropic layer compound FeOCl has been synthesized by two different techniques to give, respectively, a large single crystal blade-like product (SC) and a polycrystalline powder product (PC), each of which was examined by temperature dependent⁵⁷Fe Mössbauer spectroscopy over the range 4.2≤T≤300 K. In particular, the onset of magnetic ordering on sample cooling (near 90 K) has been studied in detail, in the light of the 2-dimensional ordering of the paramagnetic ion spins in the crystallographica, c plane. The high temperature (～300 K) and low temperature (～4.2 K) Mössbauer parameters for the SC and PC material are identical within experimental error. The persistence in the spectra of the paramagnetic doublet due to h.s. Fe(III) below the magnetic ordering temperature in the PC material is shown to be consistent with the superparamagnetism of small particles in those samples.