Low-temperature synthesis of hexagonal barium ferrite (BaFe 12 O 19 ) nanoparticles by annealing at 450 °C followed by quenching

Citrate precursor method has been used to obtain nanosized particles of barium hexaferrite at low temperatures. Samples were annealed at 450 °C for 3 and 5 h. Quenching of the third sample was done by taking the crucible out from the muffle furnace after annealing it for 5 h and putting it abruptly into an ice bath. The saturation magnetization has been found to be 4.36 and 0.04 emu g −1 for the samples obtained upon annealing at 450 °C for 3 and 5 h, respectively, while that of the quenched sample has been found to be 4.61 emu g −1 . In case of the sample obtained after 5-h annealing, the squareness value was found to be maximum indicating significance in memory and switching applications. For the quenched and the 3-h annealing products, the magnetic data values are similar. Creation of spin disorders on the surface upon prolonged annealing, due to disappearance of oxygen ions and subsequent breakage of superexchange interactions between cations, has been undone upon quenching. The XRD and TEM data indicate that the particle size (9–17 nm) gets lower in case of the quenched samples. Photoluminescence study of the quenched sample furnished prominent peaks in UV, visible and near-IR regions under 200-nm excitation. The TG–DSC data were analysed for the kinetic parameters, activation energy ( E ), pre-exponential factor ( A ) using the Kissinger isoconversion and the Ozawa–Flynn–Wall methods for the first-step decomposition of the quenched sample.