Enhancement of magnetic and dielectric properties of low temperature sintered NiCuZn ferrite by Bi₂O₃-CuO additives

With a series of 1.0 wt%Bi_2O_3-x wt% CuO (x =0.0, 0.2, 0.4, 0.6, and 0.8) serving as sintering additives, Ni_0.23Cu_0.32Zn_0.45Fe_2O_4 ferrites are successfully synthesized at a low temperature (900 ^\circC) by using the solid state reaction method. The effects of the additives on the phase formation, magnetic and dielectric properties as well as the structural and gyromagnetic properties are investigated. The x-ray diffraction (XRD) results indicate that the added Bi_2O_3-CuO can lower the synthesis temperature significantly without the appearing of the second phase. The scanning electron microscope (SEM) images confirm that Bi_2O_3 is an important factor that determines the sintering behaviors, while CuO affects the grain size and densification. With CuO content x=0.4 or 0.6, the sample shows high saturation magnetization, low coercivity, high real part of magnetic permeability, dielectric permittivity, and small ferromagnetic resonance linewidth (\Delta H). The NiCuZn ferrites are a promising new generation of high-performance microwave devices, such as phase shifters and isolators.