Eco-friendly synthesis of magnetite (Fe₃O₄) nanoparticles with tunable size: Dielectric, magnetic, thermal and optical studies

In this paper, a detailed study on dielectric, magnetic, thermal, and optical properties of citric acid modified ultrafine superparamagnetic magnetite (Fe₃O₄) nanoparticles (Cit-USPMNs) was conducted. Water dispersible Cit-USPMNs were synthesized by modified co-precipitation technique. Hydrazine (N₂H₄) and sodium hydroxide were used as precipitating agents. The size of Cit-USPMNs was tuned by changing the volume of added N₂H_4. Lemon juice; a source of citric acid was used as a stabilizing agent for this ferrofluid. Phase purity was obtained by annealing at 150 and 250 °C for 4 h. The X-ray diffraction (XRD) pattern was used to confirm the formation of pure magnetite nanoparticles (NPs). The size of Cit-USPMNs lies in the range of 11–15 nm, as calculated by Scherrer's formula which was confirmed by TEM images. The prepared Cit-USPMNs were studied for magnetic and dielectric properties by vibrating sample magnetometer (VSM) and four probe LCR meter respectively. The MH-loop shows that the magnetic NPs are superparamagnetic in nature. The dielectric behavior and tangent losses as a function of required frequency range were also studied. Optical properties were studied with the help of UV–Vis spectrophotometer. Direct and indirect energy band gaps for Cit-USPMNs were calculated from the UV–Vis spectrum. Size, shape, and surface morphology were tested by TEM image. Surface functionality of Cit-USPMNs and formation of the Fe[sbnd]O bond was verified by FTIR spectroscopy. Thermal properties were studied by thermogravimetric analysis (TGA).