Thermomagnetic properties of Co1−xZnxFe2O4 (x=0.1–0.5) nanoparticles

Ultra fine particles of Co1−xZnxFe2O4 with stoichiometric proportion (x) varying from 0.1 to 0.5 were prepared by the usual co-precipitation method. The preparation procedure favored the formation of complex Co–Zn-substituted ferrite nanoparticles. The particles were characterized by XRD. The particle size was calculated by using the Debye-Scherrer formula. The size of the particles precipitated was less than 12 nm. Thermal studies were carried out using simultaneous TG-DTA studies. TG-DTA studies confirmed the presence of associated water content in the precipitated nanoparticles and indicated that ferritization was complete. The temperature-dependent magnetization was recorded at two different fields (5 and 1 kOe). Curie temperature of the powder samples was calculated by extrapolating the linear part of the temperature-dependent magnetization data measured at 1 kOe. Thermomagnetic coefficient which is the first derivative of the temperature-dependent magnetization curve help us in understanding the redistribution of cations between the A and B sites, taking place during the process of heating in the case of nanoparticles. The temperature at which cation redistribution takes place depends on the zinc concentration. From the value of thermomagnetic coefficient and the temperature range, where kT is maximum, it is clear that Co0.5Zn0.5Fe2O4 particles can be used for the preparation of temperature-sensitive ferrofluid.