Preparation of Dy-ferrite Ferrofluids and Magnetochemical Studies on the Superparamagnetism

This paper reports unprecedented preparation of Dy-ferrite water-based ferrofluids stabilized by polymeric surfactant PMAA. The stability of ferrofluids was characterized in terms of the equation of criterion for the stability of ferrofluids. Magnetic susceptibility was measured with a Faraday-type magnetic balance at different temperature and with different magnetic field intensity. According to the Langevin function, superparamagnetism of Dy-ferrite ferrofluids has been confirmed by the curves of saturation magnetization σ versus H/ T, and the blocking temperature is between 160 and 200 K. In terms of the simplified Langevin function in the low magnetic field, the average particle size is 20 nm that coincides with the result evaluated by FHMW. In addition, chemical analysis, infrared spectra and Mossbauer spectroscopy were utilized to analyze the main components of the ferrofluids.