Dielectric and magnetic response of SrFe₁₂O₁₉–CoFe₂O₄ composites obtained by solid state reaction

Graphical abstract: - Highlights: • SrFe₁₂O₁₉–CoFe₂O₄ nanocomposites with exchange spring behavior are synthesized. • The exchange coupling is optimized for hard:soft magnetic wt. ratio of 4:1. • Dielectric response of the composites is similar to those of other ferrites. • Dielectric and electric properties are described within the Koops model. - Abstract: Nanocomposites of hard magnetic SrFe₁₂O₁₉ hexaferrite and soft magnetic CoFe₂O₄ spinel with exchange spring interaction were obtained by simple solid state reaction during 8 h and 14 h at 1050 °C. The structure and morphology of the composites was characterized by X-ray diffraction, infrared spectroscopy and scanning electron microscopy. Dielectric and electric response of the composites were found to be similar to the behavior of other ferrites and can be well described within the Koops model of the ceramic consisting of highly conducting grains separated by poorly conducting grain boundaries. Single-phase magnetic hysteresis loops obtained for SrFe₁₂O₁₉/CoFe₂O₄ composites with weight ratio 4:1 containing ∼1 wt.% hematite. The difference in magnetization below the temperature of irreversibility, measured in field cooling and zero field cooling experiments in fields exceeding doubled coercivity, was found to be greater for composites synthesized during 4–14 h than that obtained for 22 h.