Hard magnetic SrFe12O19 (SrFe) nanostructures were synthesized via a facile sol–gel procedure. The effects of temperature concentration and different capping agents on the particle size and morphology of the magnetic nanoparticles were investigated. The synthesized ferrites were characterized by X-ray diffraction pattern (XRD), scanning electron microscope (SEM), and Fourier transform infrared (FT-IR) spectroscopy. The ferromagnetic property of the hexa-ferrite nanostructures was determined by alternating gradient force magnetometer (AGFM). SrFe12O19 was added to the poly carbonate (PC) matrix in order to prepare the magnetic and flexible polymer matrix nanocomposite. In the nanocomposite (20%) preparation, results show that coercivity was decreased because of a 20% decrease in saturation magnetization and agglomeration in the polymer matrix