Synthesis and exchange-coupling interaction in nanocomposite SrFe₁₂O₁₉/γ-Fe₂O₃ permanent ferrites

Strontium hexaferrite powders have been prepared using the sol-gel method. The samples have been analyzed by X-ray diffraction(XRD), transmission electron microscope(TEM), and vibrating sample magnetometer(VSM). When the thermal treatment temperature is below 800°C, there are two coexisting phases of γ-Fe₂O₃ and SrFe₁₂O₁₉. Under the same conditions, the samples which are pressed into a flake show the exchange-coupling interaction on magnetic properties between the two nanostructured phases of γ-Fe₂O₃ and SrFe₁₂O₁₉. In this case the thermal treatment at 800°C produces a nanocompisite with an intrinsic coercivity of 478.9kA/m, a maximum magnetization at 1.8T of 75.6 A·m²/kg and a maximum energy product of 1.87 kJ/m³ as compared with the powder sample of 509.6 kA/m, 75.9 A·m²/kg and 12.1 kJ/m³ respectively. Only a compound SrFe₁₂O₁₉ is detected at temperatures over 850°C.