The present paper covers the unprecedented preparation of stable aqueous Dy-ferrite ferrofluids, whereby colloidal Dy δ Fe 3- δ O4 ultrafine particles were dispersed by using polymeric surfactant PMAA. The stabilities of the series of the ferrofluids were studied according to the stability indexes. The susceptibility measurements were made with a Farady-type magnetic balance at various temperatures and magnetic field intensities. In terms of Langevin function, the σ versus H/T curves showed that Dy-ferrite ferrofluids exhibited superparamagnetism behavior and the blocking temperatures were in the range from 160 to 200 K. Moreover, the ferrofluids were characterized by means of Infra-red spectroscopy, transmission electron microscopy, X-ray diffraction, and Mssbauer spectroscopy.
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