Structure and magnetic properties of nanostructured Ni-ferrite

The structural and magnetic properties of NiFe2 O-4 ultrafine powders synthesized by coprecipitation, a nonconventional method of preparation, were investigated. The samples were obtained by annealing at relatively low temperatures (300-600 degreesC) and characterized by X-ray diffraction, Mossbauer spectroscopy, and vibrating sample magnetometry. The average particle diameter ranges from 4 to 15 nm, as determined by X-ray diffraction. All nanometric powder samples presented strong superparamagnetic relaxation at room temperature and reduced magnetic hyperfine fields at - 193 degreesC. Magnetometry measurements indicated different magnetic behavior related with crystallinity of samples, coercivity as high as 168 Oe at 27 degreesC, value that is nearly two times higher than coercivity of bulk Ni-ferrite. (C) 2001 Elsevier Science B.V. All rights reserved.