Variations in magnetic behaviour of ferrimagnetic nanoparticles with temperature

This study successfully synthesised ferrimagnetic nanoparticles (FMNPs) at a temperature of 28°C using the chemical co-precipitation method. Comprehensive characterisation of the FMNPs was performed through XRD, FTIR, FESEM, zeta potential analysis, hydrodynamic particle size measurement at 28°C, and VSM over a temperature range of 100–500°C. Our findings unequivocally confirm the composition of the synthesised nanoparticles as pure magnetite, featuring a spinel structure devoid of impurities. Morphologically, the FMNPs exhibit a nearly spherical shape, characterised by a uniform size distribution with an average particle diameter of 19 nm. Studying the magnetic properties across the temperature range of 100–500 °C reveals a striking trend: as temperature increases, both coercivity and remanence in the hysteresis loop experience a gradual reduction, thereby demonstrating a superparamagnetic behaviour. To elucidate this intriguing superparamagnetic behaviour, we employ a developed model rooted in the core–shell theory, which yields calculated data closely aligning with the experimental magnetisation results. These observations underscore the potential of these synthesised FMNPs for diverse applications, ranging from heat transfer and enhanced oil recovery to phase change materials and magnetic separation, positioning them as promising candidates in these fields.