Structural and magnetic properties of Sn-, Ti-, and Mg-substituted alpha-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Hydrothermal techniques have been used to synthesize samples of alpha-Fe2O3 in which ca. 10% of the Fe cations have been replaced by Sn4+, Ti4+, and M g2+. Neutron powder diffraction data show the dopant ions to occupy both in terstitial and substitutional sites in the corundum-related alpha-Fe2O3 str ucture. The details of the defect cluster depend on the charge on the dopan t ion. The magnetic structures are related to that of alpha-Fe2O3 with ambi ent temperature Fe3+ moments of 4.01(5), 3.89(3), and 3.92(4) BM for Sn-, T i-, and Mg-doped samples, respectively. The Fe-57 Mossbauer spectra recorde d 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, respectiv ely, as compared to 950-960 K for pure alpha-Fe2O3. (C) 2000 Academic Press .