Structure and electromagnetic properties of NiZn spinel ferrite with nano-sized ZnAl2O4 additions

In this study, nanocrystalline ZnAl2O4 (ZA) (x = 0-20 wt%) were introduced into Ni0.4Zn0.6Fe2O4 ferrite (NZ) by a solid-state reaction method combining a sol-gel auto-combustion method. The effects of ZA addition on the crystalline phase formation, microstructures, magnetic and dielectric properties were systematically investigated. X-ray diffraction and scanning electron microscope results reveal that the added ZA can fully solve into the NZ to form a ceramic with single-phase cubic spinel structure, and the grain size decreases obviously as x > 5 wt%. Meanwhile, the magnetic and dielectric properties exhibit significantly dependent on the ZA addition content. With the increasing addition level of ZA from 0 to 20 wt%, the initial permeability μi is found increased initially and then decreased with the maximum 679 at x = 0.5 wt%. For the samples with x ≤ 5 wt%, permittivity ε′ is relatively higher at low frequencies (ε′ = 91-138 at 1 MHz) and dielectric loss tan δε shows distinct peak behavior. When x reaches 10 wt%, however, the ε′ and tan δε show very stable spectra from 1 MHz to 1 GHz.