Microstructure,magnetism, and high-frequency performance of polycrystalline Ni0.5Zn0.5Sm0.025HoxFe1.975?xO4 ferrites

Novel polycrystalline Ni_0.5Zn_0.5Sm_0.025Ho_xFe_1.975?xO₄ (x = 0-0.06) ferrites were fabricated by a traditional solid-state reaction sintering method. The codoping effects of Sm and Ho on the microstructure, magnetism, and high-frequency performance of Ni–Zn ferrites were investigated. The substitution of Sm³⁺ and Ho³⁺ ions led to an apparent increase in the lattice constants. However, further increasing the addition of both dopants introduced SmFeO₃ or HoFeO₃ foreign phases at the boundaries of the polycrystalline grains. As the content of Ho³⁺ ions increased, the relative density and average grain size of the specimens decreased accordingly. Moreover, the substitution of Sm³⁺ clearly decreased the saturation magnetization and complex permeability, which further decreased with the doping of Ho³⁺. The evolution of the Curie temperature showed an opposite trend, reaching the highest temperature of 278°C when x = 0.03. Similarly, the coercivity and resonance frequencies also displayed opposite trends compared to those of the saturation magnetization and complex permeability. The codoping of Sm³⁺ and Ho³⁺ more effectively lowered the magnetic and dielectric loss tangent of the specimens compared with the undoped or single dopant modified ferrites.