Sonochemical preparation of nanosized amorphous NiFe2O4 particles

Nanosized amorphous NiFe2O4 powder was prepared by sonochemical decomposition of solutions of volatile organic precursors, Fe(CO)(5) and Ni(CO)(4), in decalin at 273 K, under an oxygen pressure of 100-150 kPa. The amorphous nature of these particles was confirmed by various techniques, such as SEM, TEM, electron microdiffraction, and X-ray diffractograms. Magnetic measurements, Mossbauer, and EPR spectral studies indicated that the as-prepared NiFe2O4 ferrite particles were superparamagnetic. The Mossbauer spectrum of the crystallized sample showed a clear sextet pattern, with hyperfine field values of 500 and 508 kOe for A (tetrahedral) and B (octahedral) sublattices, respectively, of the inverse spinel NiFe2O4. Saturation magnetization of the annealed sample (25 emu/g) was significantly lower than that for the reported multidomain bulk prticles (55 emu/g), reflecting the ultrafine nature of the sample. Thermogravimetric measurements with a permanent magnet gave Curie temperatures of 440 degrees C for amorphous and 560 degrees C for the crystallized forms.