Exploring the annealing temperature impacting on the magnetic coupling of nanometer soft grain and microstructure hard grain nanocomposites

Nanocomposites of 70% MgFe₂O₄ and 30% BaFe₁₂O₁₉ have been prepared by the mechano-chemical coprecipitation method. The prepared samples were annealed at different temperatures (400, 600, 800, and 1000 °C). The thermal gravimetric analysis (TGA) measurements of the as prepared samples has detected three weight losses attributed to evaporation, the decomposition of citric acid and nitrate combustion and the crystal transformation. The crystal growth of the soft phase has been proved by X-ray diffraction (XRD) and high resolution transmission electron microscope (HRTEM) measurements. The bonds have been detected by FT-IR measurements and are assigned to the two ferrite phases constituting the nanocomposites, which means that there are no intruder phases that have been detected. The vibrating sample magnetometer measurements (VSM) have displayed a gradually increasing of the saturation magnetization (Ms) with the annealing temperature, while the coercivity (H_c) and remnance (M_r) have exhibited a maximum value at the annealing temperature 600 °C. The ferromagnetic resonance (FMR) and VSM measurements have clarified the magnetic ordering changing inside the nanocomposites at the system transformation from the as prepared amorphous/hexagonal phase to the spinel/hexagonal phase with increasing annealing temperature. The porosity (P), the anisotropy (K) and the line width (ΔH) calculated parameters have been used to study the agreement between the FMR and VSM magnetic measurements.