Novel one-pot preparation of CoFe2O4–Ag nanocrystalline powders

• One-pot CoFe2O4–Ag nanocrystalline powders have been prepared.
• CoFe2O4 particle sizes close to the superparamagnetic limit have been obtained.
• Magnetic dipolar interaction between the ferrite nanoparticles was adjusted.
• Complex behavior has been observed in the hysteresis curves at low temperature.

We report the synthesis of the nanocomposite Ag100−x(CoFe2O4)x with x=20 and 93 wt%. The nanocomposite was synthesized in the pores of the biopolymer chitosan. The samples were analyzed by x-ray diffraction, transmission electron microscopy, scanning electron microscopy and magnetometry. The average sizes of the Ag nanoparticles ranged from 8.6 to 13.6 nm and the CoFe2O4 nanoparticles from 8.5 to 9.5 nm. The sizes of the CoFe2O4 particles were very close to the critical diameter for superparamagnetic behavior at room temperature. The zero field cooled magnetization measurements for both samples showed peak temperatures above 290 K, the coercive fields measured at 300 K were smaller than 100 Oe and increased with the size and the percentage of cobalt ferrite phase. Magnetization versus field measurement at 5 K for x=20 wt% showed coercive fields of 9.62 kOe, typical of hard cobalt ferrite, and for x=93 wt% complex magnetic behavior was observed. The results were discussed taking into account the magnetic dipolar coupling between the CoFe2O4 nanoparticles.