Controlled growth of large-area arrays of Al-substituted CoNiZn ferrite rods with high saturation magnetization by solvothermal method

Co_0.5Ni_0.3Zn_0.2AlxFe_2−x O₄ (0.0 ≤ x ≤ 0.21) rods are synthesized by a solvothermal method using glycol as template and surfactant. X-ray diffraction, scanning electron microscope, and vibrating sample magnetometer are employed to evaluate structural, morphology, and magnetic properties of the as-prepared ferrites. The X-ray diffraction analysis indicates that single phase spinel ferrites are obtained when the precursor is calcined above 750 °C in air for 3 h. After being calcined at 950 °C, the lattice parameters of the ferrites initially decrease with increase in Al³⁺ content, but then increase (x = 0.21). The addition of Al³⁺ ion decreases the average crystallite size. This is because the electron orbital tends to be completed. The scanning electron microscope micrographs of the synthesized samples show the presence of large-area arrays of ferrite rods. The possible formation mechanism for the synthesis of ferrites rods has been preliminarily explained. Magnetic property tests indicates that when the Al³⁺ doping amount is increased from 0 to 0.21, the specific saturation magnetization (Ms) values initially increase from 74.37 to 80.01 emu/g and then decrease to 76.77 emu/g, while the coercivity (Hc) values increase from 245.61 to 345.96 Oe at first, then decrease to 317.04 Oe. The results can be explained by Neel’s two sublattice and Yafet-Kittle configuration models.