Influence of nano-NiZn and Bi2O3 additives on grain size and magnetic properties of Ni-Zn ferrites for ultra-low loss and enhanced gyromagnetic performance

NiCuZn ferrites with high saturation magnetization and low magnetic loss in the microwave band have attracted significant attention for applications in microwave devices, especially in phased-array systems. However, achieving device miniaturization and integration while simultaneously maintaining low loss and excellent gyromagnetic performance remains a major challenge. In this study, the grain size effect on the gyromagnetic properties and magnetic loss suppression in NiCuZn ferrites was investigated by incorporating Bi 2 O 3 and nano-NiZn ferrite additives. The results show that the addition of Bi 2 O 3 effectively lowers reaction activation energy and reduces the sintering temperature, facilitating easy densification of the ferrite material. Benefiting from the synergistic effect of nano-NiZn ferrite addition and Bi 2 O 3 -assisted liquid-phase sintering, dense NiCuZn ferrites with a uniform grain size (G avg.  = 7.62) and a high density ( ρ m  = 5.32 g/cm 3 ) are obtained, leading to enhanced gyromagnetic properties and reduced magnetic loss. Consequently, the NiCuZn ferrite ceramic with optimized composition exhibits an ultra-low magnetic loss ( ΔH  = 126 Oe), low dielectric loss (tanδ ε  = 0.033) and an improved saturation magnetization (4π M s  = 4159 G). This study provides a simple and effective strategy for achieving dense and compact grain structures, offering guidance for the design of miniaturized and low-loss microwave devices.