Variation of structural, dielectric and magnetic properties of PVP coated γ-Fe₂O₃ nanoparticles

Structural, dielectric and magnetic properties of γ-Fe₂O₃ nanoparticles coated with Polyvinylpyrrolidone were synthesized via co-precipitation method. It was found that the PVP coating resulted in disordered maghemite with reduction in size of nanoparticles from 17 to 9 nm estimated by TEM. The attachment of polymer on the surface of nanoparticles was confirmed by FTIR and TGA and thickness of polymer layer was calculated to be 2.71 nm. The dielectric study shows a strong dependence on coating. The dielectric parameters (ε _r , tanδ and σ _ac ) reduced with PVP coating of γ-Fe₂O₃ nanoparticles. The dielectric permittivity (ε _r ) exhibits dispersion behavior and the dielectric loss factor (tanδ) exhibits the Debye’s relaxation peaks whose intensity reduced with PVP coating. The variation of dielectric properties and ac conductivity reveals that the dispersion is due to Maxwell–Wagner interfacial polarization and hopping of charge carriers between Fe²⁺/Fe³⁺. The high dielectric constant makes it a promising candidate for device application. The FC/ZFC magnetization measurements showed typical super paramagnetic behavior at room temperature and ferrimagnetic behavior below blocking temperature. It was observed that PVP coating has changed the magnetic properties of the maghemite nanoparticles; i.e. magnetization reduced and coercivity was enhanced. The blocking temperature was shifted towards lower value consistent with particles size reduction.