Tunable ferromagnetic resonance linewidth of cobalt-substituted NiCuZn ferrites

Polycrystalline ferrites Ni0.5-xCu0.12Zn0.4CoxFe1.98O4-δ with different cobalt-substituted contents (x = 0, 0.003, 0.006, 0.009, 0.012, 0.015) are synthetized via the solid-state reaction method. The magnetocrystalline anisotropy constant is calculated based on the law of approach to saturation. As the amount of cobalt substitution increases, the absolute value of the magnetocrystalline anisotropy constant first decreases and then rises due to the positive compensation by the Co2+ ions. The value of the magnetocrystalline anisotropy constant tends to be zero for the samples with cobalt substitution contents in the range of 0.003-0.006. Meanwhile, when the cobalt substitution content is 0.003, the NiCuZn ferrite shows minimum ferromagnetic resonance linewidth (9.87 kA/m) and low dielectric loss tangent (tgδε, 1.1 × 10−4) at 9.4 GHz as well as a high magnetization (Ms, 406 kA/m) and high squareness ratio (Br/Bs, 0.83). Furthermore, the linewidth contribution is identified by the anisotropy and porosity linewidth broadening model based on the spin-wave approach, and the results show that porosity linewidth broadening is the predominant effect.