Iron-57 Mossbauer spectroscopic investigation of manganese-doped γ-Fe2O3

Manganese-doped gamma-Fe2O3 has been prepared by precipitation techniques and shown by Mn K-edge XANES and EXAFS to contain Mn3+ in the octahedral sites of the spinel-related structure. The Fe-57 Mossbauer spectra recorded in situ between 295 and 750 K show that conversion of the spinel-related gamma-Fe2O3 -to the corundum-related alpha-Fe2O3-structure occurs at ca. 700 and 730 K in the samples containing ca. 1.5 and 4.1% manganese, respectively. The presence of manganese therefore stabilises the gamma-Fe2O3-related structure relative to conversion to the alpha-Fe2O3 phase. The temperature dependence of the spectra recorded from the manganese-doped alpha-Fe2O3 is similar to that of pure alpha-Fe2O3 but with a smaller hyperfine magnetic field reflecting the presence of the manganese dopant.