High cut-off frequency and low magnetic loss of Bi3+-Cr3+ co-substitution NiCuZn ferrite for chip inductors applications

Abstract

With the rapid growth of high-frequency chip inductors, there is an urgent demand for NiCuZn ferrite that exhibits low magnetic loss and high cut-off frequency. To enhance its electromagnetic features, this study investigates the doping of Bi3+-Cr3 + ions into NiCuZn ferrite. The research examines the effects of different Cr3+ concentrations on the electric and magnetic properties, as well as the crystal structure of NiCuZn ferrites. The results showed that using a low sintering temperature of 925℃ can obtain NiCuZn ferrite with high population density and uniform microstructure. The inclusion of Cr3+ causes the lattice parameter to decrease, with a preference for octahedral B-sites. Furthermore, the saturation magnetization declines as the concentration of Cr3+ increases, according to the results of the magnetic hysteresis loops. The permittivity measurements demonstrate that the addition of Cr3+ ions can enhance permittivity and reduce dielectric loss. Lastly, NiCuZn ferrite co-doped with 0.30 wt% Bi2O3 and x = 0.15 of Cr3+ ions had appropriate saturation magnetization (∼57.05 emu/g) and coercivity (∼0.680 kA/m), meanwhile exhibited the highest dielectric constant (∼12.32 @ 1 MHz) and cut-off frequency (218 MHz), the lowest permeability loss tangent (0.0036@1 MHz) and imaginary part of the permittivity (0.54@1 MHz), making it a suitable for high-frequency chip inductors.