A phenomenal behaviour of nanocrystalline NiFe2O4: influence of secondary and parasitic phases on structure and magnetic property

In this paper, we report the influence of secondary and parasitic magnetic phases on NiFe2O4 (NFO) nanoparticles synthesised during citrate gel method. Annealing at 773 K showed the presence of secondary and parasitic phases, whereas annealing at 1,073 K for 3 h showed the quenching of the secondary and parasitic phases. X-ray diffraction (XRD) analysis confirmed the nickel ferrite phase, with a trace amount of α-Fe2O3 peak found and other phases being not traceable. The observed α-Fe2O3 peak vanished at 1,073 K annealing, and a single phase of nickel ferrite was formed. The surface morphology of the samples was studied by SEM, which showed the fine grains of nickel ferrite. Raman spectra of the annealed samples were measured and analysed in the range of 1,000–100 cm−1. Further analysis of isothermal M–H curve, zero-field-cooled and field-cooled (ZFC–FC) measurement and thermo-magnetisation M (T) measurements were performed with the aid of vibrating sample magnetometer on the prepared samples. The measured ZFC–FC curve showed an existence of spin-glass behaviour due to the parasitic phase for 773 K annealed sample, which is quite difficult to be identified using XRD and Raman spectra. Further, we also observed the room temperature coercivity Hc = 430 Oe from the M–H curve for the sample annealed at 773 K. Remarkably, both low-temperature and high-temperature M–T curve measurements showed the influence of secondary and parasitic phases for 773 and 1,073K annealed samples.