Effect on Structural, Morphological, and Magnetic Hysteresis of Ni2+–Zr4+ Co-Substituted Barium Hexaferrites by Hydrothermal Synthesis

BaFe_12–2xNi_xZr_xO₁₉ (x = 0–1) ferrites were successfully synthesized by hydrothermal method based on metal chloride. The synergistic effects of Ni²⁺–Zr⁴⁺ ions doping and heat treatment on microstructure and ions distribution to tailoring the magnetic properties were studied. Without calcination the traces of BaCO₃ appears in all samples where the Fe₂O₃ phase appears at x > 0.6. It exhibits very good hexagonal crystals with doping content x < 0.8, but deviate from hexagonal flakes for x = 1. With low temperature 950°C calcination, the pure phase and the uniform distribution of particle size were obtained. XPS characterization show that the concentrations of non-lattice oxygen decrease, where Fe²⁺ contents slightly increase and then decrease with increasing Ni²⁺–Zr⁴⁺ ions. The comprehensive magnetic properties, especially the saturation magnetization, of doped ferrites prepared by hydrothermal method decrease sharply when x > 0.6. The anisotropy field also decreases to the lowest at x = 0.6. By comparing the magnetic properties under heat treatment conditions, the optimum annealing temperature is 1000°C, where the saturation magnetization (Ms) increases up to 59.54 emu/g at x = 0.8. Thus, the as-synthesized Ni²⁺–Zr⁴⁺ doping strontium barium hexaferrite will be useful for the applications in security switching, microwave absorption and recording media.