Superparamagnetic transition and local disorder in CuFe2O4 nanoparticles

We present X-ray diffraction (XRD), Mossbauer spectroscopy (MS) and d.c. magnetization measurements performed on ball-milled CuF2O4 samples. The average particle size < d > was found to decrease to the nanometer range after t=15 min of milling. Room temperature Mossbauer data showed that the fraction of particles above the blocking temperature Tg increases with milling time, and almost complete superparamagnetic samples are obtained for < d > = 7(2) nm. Magnetization measurements below Tg suggest spin canting in milled samples. The values of saturation moment Cts reveal that site populations are slightly affected by milling. Mossbauer resonant intensities are accounted for on the basis of local disorder of Fe3+ environments, and the development of sample inhomogeneities of CuxFe3-xO4 composition. (C) 1998 Acta Metallurgica Inc.