Preparation and magnetization of hematite nanocrystals with amorphous iron oxide layers by hydrothermal conditions

Hematite nanocrystals modified with surface layers of amorphous hydrous iron oxides were prepared by hydrothermal conditions in the absence of alkali. The formation temperature was found to be ca. 130°C. When the temperature was lower than 130°C, no product was formed, while above this temperature, the amount of amorphous hydrous iron oxides at the surface of hematite nanocrystals was drastically decreased. The amorphous layers on the hematite nanocrystals obtained at 130°C were determined to be Fe₂O₃·1.64H₂O. The coercivity for the hematite nanocrystals with modified layers was 0.534 kOe, which is slightly larger than the values for hematite nanocrystals with few agglomerations.