Effects of Ni-doping on microstructure, magnetic and microwave absorption properties of CoFe2O4

Highlights: • Nano-spinel powder samples of Co_1–xNi_xFe₂O₄(x = 0, 0.1, 0.3, 0.5) were successfully synthesized by sol–gel method. • Ni doping changes the ion concentration at the [A][B] position and affects the magnetic properties of CoFe₂O₄. • Different microwave absorption mechanisms of Co_1–xNi_xFe₂O₄ (x = 0, 0.1, 0.3, 0.5) samples. • The Co_1–xNi_xFe₂O₄(x = 0, 0.1, 0.3, 0.5) samples exhibit excellent microwave absorption performance. In this paper, the Co_1−xNi_xFe₂O₄ (x = 0, 0.1, 0.3, 0.5) ferrite material sample was successfully synthesized by the sol–gel combustion method. Using XRD to detect the phase, it was found that a pure sample was prepared, and the corresponding unit cell model was established using XRD data. At the same time, using Raman spectroscopy analysis, the change of the T2g(1) peak in the Raman spectrum indicates that the doping of Ni²⁺ ions replaces the Co²⁺ ions in the tetrahedral position, and the high-frequency shoulder-like characteristics also indicate that the octahedral position has been replaced. The substitution of Ni²⁺ ions for Co²⁺ ions causes lattice distortion, which leads to the destruction of the ferromagnetic sequence and thus changes in magnetic properties. Microscopic observation was performed with SEM to observe the structure. It was found that with the doping of Ni²⁺ iron, the grain size gradually decreased, and the decrease of the grain size would have an impact on the space charge polarization. At the same time, the phenomenon of electronic polarization was found in the analysis of the microwave absorption mechanism. To explain the occurrence of this phenomenon, Raman detection was performed on the sample. The Raman detection is combined with the bond length and bond angle changes in the unit cell to analyze the Ni element. The reason for doping electron polarization. When the Ni doping amount is 0.1, the reflection loss of Co_1−xNi_xFe₂O₄ at 16.24 GHz is 37.66 dB, the corresponding thickness is 2.1 mm, and the effective frequency band is 2.64 GHz, which meets the requirements of light, thin and wide microwave absorbing materials.