We report on the surfactant/additives free synthesis of single domain superparamagnetic Fe₃O₄ nanoparticles (FNPs) by rapid microwave synthesis method. X-Ray diffraction (XRD) and Scanning Electron Microscopy (SEM) studies reveal that FNPs were crystallized in the magnetite (Fe₃O₄) lattice and have granular shape with average particles size of ∼14 nm. The band gap of FNPs calculated from UV–Visible absorption spectrum is ∼2.3 eV. FNPs exhibit single domain superparamagnetic behaviour as confirmed from magnetic hysteresis loops. The nanocomposites of FNPs and β-phase of PVDF were prepared via mixed solvent approach using THF/DMF with different concentrations of FNPs. The rheological behaviour of the nanocomposites was studied with and without ageing in an applied magnetic field of 3500 Gauss for 3 h. Samples depicts shear thinning to shear thickening transition, decrease in zero shear viscosity and long frequency range viscoelastic behaviour as function of increasing FNP concentration. Increase in CST region, fluidity and complex modulus are the main consequences of magnetic aging. FNP-PVDF nanocomposites with such properties could find applications in flexible magnetic and mechanical films for soft body armor and memory storage.