Low loss and tailored high‐frequency performances of BaO‐doped NiZnCo magneto‐dielectric ferrites

Abstract

Spinel ferrite ceramics of nominal composition Ni0.5Zn0.3Co0.2Fe2O4 (NiZnCo) with various BaO doping were successfully synthesized for applications as novel high‐frequency magneto‐dielectric materials. The influences of BaO doping on the crystal phase, density, microstructure, and magnetic and dielectric performances in the frequency range of 0.1 to 5 GHz were systematically studied. It is revealed that the doped Ba2+ ions aggregate to the grain‐boundary regions and lead to the formation of BaFe2O4 phase that significantly restrains the growth of NiZnCo ferrite grains. Correspondingly, permeability and permittivity are effectively tailored through the varied grain size and density, which is demonstrated by the magnetic circuit model and the modified effective medium theory proposed herein. As BaO content x = 1.2‐1.8 mol%, the NiZnCo ferrites reveal the excellent performance with almost equal values of μ′ and ε′, yielding a characteristic impedance to be nearly identical as that of free space over a wide frequency range of the VHF and UHF bands. Furthermore, the magnetic loss is effectively reduced at high frequencies, where the typical tan δμ at 0.5 GHz is decreased to ~0.043 with a reduction of up to 37% and the loss factor (tan δμ/μ′) is as low as ~0.006.

Cold‐sintered Na2WO4‐Ni0.2Cu0.2Zn0.6Fe2O4 ceramics with matched permittivity and permeability for miniaturized antenna

“…The permittivity of a composite can be estimated using Bruggeman's formula (Equation ) and the Lichtenecker’s logarithmic formula (Equation ) 24,25 where ε c is the effective permittivity of the composite; ε 1 and ε 2 is the effective permittivity of material 1 and material 2, respectively; v 1 and v 2 is the volume fraction of material 1 and material 2, respectively; and v 1 + v 2 = 1.…”

Impact of V substitution on the physical properties of Ni–Zn–Co ferrites: structural, magnetic, dielectric and electrical properties

“…Saini et al [27] have investigated In substituted Ni-Co-Zn ferrites. Y and La Substituted Ni-Co-Zn ferrites have been investigated by Stergiou et al [28], Gd and La-doped Ni-Zn-Co ferrites are studied by Zhou et al [29] BaO-doped Ni-Zn-Co magneto-dielectric ferrites have been studied by Zheng et al [30]. We have also studied the Gd substituted Ni-Zn-Co ferrites [31].…”

Crystal structure and magneto‐dielectric properties of Co‐Zr co‐substituted Co2Z hexaferrites

“…In particular, ferrites have a relative permeability and permittivity greater than one, which make them ideal materials for antenna substrates. [3][4][5] Nevertheless, spinel ferrites can hardly be used in the frequency range of several hundred MHz or GHz due to their low cut-off frequency. This poses a limitation to the high-frequency application of antennas.…”

“…The miniaturization of antennas can be achieved by increasing the permeability and permittivity of the substrate material. In particular, ferrites have a relative permeability and permittivity greater than one, which make them ideal materials for antenna substrates 3 – 5 . Nevertheless, spinel ferrites can hardly be used in the frequency range of several hundred MHz or GHz due to their low cut‐off frequency.…”