Structural and magnetic properties of Sn-, Ti-, and Mg-substituted α-Fe2O3:: A study by neutron diffraction and Mossbauer spectroscopy

Hydrothermal techniques have been used to synthesize samples of alpha-Fe2O3 in which ca. 10% of the Fe cations have been replaced by Sn4+, Ti4+, and Mg2+. Neutron powder diffraction data show the dopant ions to occupy both interstitial and substitutional sites in the corundum-related alpha-Fe2O3 structure. The details of the defect cluster depend on the charge on the dopant ion. The magnetic structures are related to that of alpha-Fe2O3 with ambient temperature Fe3+ moments of 4.01(5), 3.89(3), and 3.92(4) BM for Sn-, Ti-, and Mg-doped samples, respectively. The Fe-57 Mossbauer spectra recorded in situ at elevated temperatures show the Neel temperatures of Sn- and Mg-doped alpha-Fe2O3 to be between 890 and 910 K and 910 and 930 K, respectively, as compared to 950-960 K for pure alpha-Fe2O3. (C) 2000 Academic Press.