Structural, magnetic and hyperfine properties of single-phase SrFe 12 O 19 nanoparticles prepared by a sol–gel route

Single-phase nanocrystalline strontium hexaferrite (SrFe 12 O 19 ) powders have been synthesized by a sol–gel method and their structural, magnetic and hyperfine properties are discussed. The optimum annealing temperature of the as-prepared gel for formation of the single-phase SrFe 12 O 19 structure has been found to be 800 °C. X-ray diffraction and Fourier transform infrared studies confirmed formation of the hexaferrite phase. The cation distribution at crystallographic inequivalent sites of the hexaferrite structure has been examined by 57 Fe Mössbauer spectroscopy and found to be identical to that reported earlier. Single-phase SrFe 12 O 19 nanoparticles (NPs) showed a magnetic hysteresis loop with high coercivity and saturation magnetization denoting an irreversible magnetization character. The temperature dependent magnetization measurements reveal a difference between the zero-field-cooled and field-cooled curves throughout the measurement range 5–300 K that is attributed to superparamagnetic relaxation of finer hexaferrite particles and disordered spins at the surface of the NPs. Both hyperfine and magnetic studies confirm that magnetic anisotropy plays a crucial role in hexaferrite NPs.