Simple and fast preparation of pure maghemite nanopowders through sol gel self-combustion

Pure maghemite nanopowders made up of nanocrystals with average size of 19 nm was prepared by a simple sol-gel self combustion process. The gel pH and the primer temperature turned out the key parameters for the obtaining of the maghemite phase, that often is accompanied by the most thermodynamically stable hematite. Pure maghemite was achieved only with a gel pH value of 7 and with a primer temperature between 290 and 325 °C. XRD and IR pointed out the formation of maghemite with tetragonal structure and HRTEM indicated the high degree of crystallinity of the powder. Mossbauer measurements allowed to confirm the presence of maghemite phase with Fe(octa):Fe(tetra) ratio of 1.62 which is very close to the theoretical value and the presence spin canting strongly dependent on applied magnetic field. This picture is confirmed by dc magnetic measurements.