<p>This study investigates the effect of Co doping on the magnetic properties of Ni_0.5Zn_0.5-<i>x</i>Co_<i>x</i>Fe₂O₄ and explores its potential applications at high frequencies. Co-doped NiZn spinel ferrite powders, Ni_0.5Zn_0.5-<i>x</i>Co_<i>x</i>Fe₂O₄ (0.00 ≤ <i>x</i> ≤ 0.10), were synthesized using the solid-state reaction method. The effects of Co-doped NiZn ferrite powders on the material structure and properties were investigated using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), vibrating sample magnetometry (VSM), and precision impedance analysis (LCR). The results indicate that with the increase in Co substitution, the phase structure of the NiZn ferrite samples remains unchanged, with all samples exhibiting a single NiZn ferrite phase. The lattice constant of the samples first decreases and then increases. The saturation magnetization (Ms) first increases and then decreases with the increase in Co doping level (<i>x</i>), while the coercive force (Hc) initially decreases and then increases as the Co doping level (<i>x</i>) rises. Simultaneously, with the increase in Co doping, the initial permeability (μ') of the samples exhibits a trend of first decreasing, then increasing, and finally decreasing again. Meanwhile, the quality factor (<i>Q</i>) and the cutoff frequency (<i>f</i>r) of the samples gradually increase. When the Co doping level (<i>x</i>) is 0.08, the sample achieves the highest saturation magnetization. This study provides theoretical guidance on the effects of Co substitution in NiZn ferrites on their material structure, magnetic properties, and high-frequency applications.</p>