Magnetic transitions and structural characteristics of Mn-doped α-Fe2O3/silica nanocomposites

Hematite (alpha-Fe2O3) has become popular these days for their photocatalytic activities of water splitting. Metal-doped hematite materials are interesting as well for the bandgap engineering and for resolving fast charge-hole recombination. In this study, magnetism and ionic behaviors of rare manganese-doped alpha-Fe2O3/silica nanocomposites are investigated. These nanocomposites are prepared by the impregnation method with a mixture of metal halides, followed by rapid heating (30 degrees C/min) under air condition. When the molar ratio between FeCl3 center dot 6H(2)O and MnCl2 center dot 4H(2)O is 2.97, wasp-waisted hysteresis and ferromagnetism with the Curie temperatures of 56.1 and 58.0 K are observed for the nanocomposites annealed at 600 degrees C for the duration of 3 and 7 h, respectively, while dominant spin glass states are observed for the nanocomposites annealed at 500 degrees C. In x-ray diffraction patterns, mixed phases of alpha-Fe2O3 are identified, whereas crystalline metallic Mn or Mn oxides are hardly found. Electron energy-loss spectroscopy study indicates that Mn2+ is severely oxidized, and with this oxidation of Mn2+, Si becomes more metallic. When the molar ratio between Fe and Mn halides is 7.32, magnetism is affected by a small amount of gamma-Fe2O3, and spin glass states and the competition between ferromagnetism and antiferromagnetism are observed in the long temperature range.

Automated summary

In this study, the magnetism and ionic behaviors of rare manganese-doped alpha-Fe2O3/silica nanocomposites were investigated. The research found that specific molar ratios of Fe and Mn halides can lead to different magnetic properties and crystal structures in the nanocomposites.