Superparamagnetic transition and local disorder in CuFe2O4 nanoparticles

We present X-ray diffraction (XRD), Mossbauer spectroscopy (MS) and d.c. ma gnetization measurements performed on ball-milled CuF2O4 samples. The avera ge particle size < d > was found to decrease to the nanometer range after t =15 min of milling. Room temperature Mossbauer data showed that the fractio n of particles above the blocking temperature Tg increases with milling tim e, 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 a re slightly affected by milling. Mossbauer resonant intensities are account ed for on the basis of local disorder of Fe3+ environments, and the develop ment of sample inhomogeneities of CuxFe3-xO4 composition. (C) 1998 Acta Met allurgica Inc.