Electromagnetic properties of nickel-zinc ferrites based materials make them potential candidates for applications linked to telecommunications. In the present study, nanosized particles of spinel ferrite Ni 0.5 Zn 0.3 Co 0.2 Fe 2 O 4 were prepared by coprecipitation method. An optimized material is obtained after adequate heat treatment and partial filling of the porosity by epoxy resin. This material lies between ceramic and composite medium ͑with porosity close to 40%͒, and shows almost constant complex permeability and permittivity in the frequency range from 0.1-0.7 GHz, and equal to ϳ3.5-j0.15 ͑loss tangentϳ 0.04͒ and ϳ4-j0.2 ͑loss tangentϳ 0.02͒, respectively. The refractive index n is close to 3.75. These electromagnetic properties, in particular the low levels of losses, show that this material could be useful to the design of miniaturized antennas in the VHF-uhf ͑300-700 MHz͒ range of frequency.
Experimental studies on the complex susceptibility of soft magnetic composite materials (magnetostrictive Ni-Zn and Ni-Zn-Co spinels) in their region of ferrimagnetic resonance (FMR) show that the FMR is an increasing function of the applied pressure. It is shown that powders could advantageously replace their sintered materials counterpart to measure without any ambiguity the natural ferrimagnetic resonance (NFMR) frequencies of bulk materials. It is also shown that such soft ferrite composites can be realized in order to shift FMR to higher values, and to obtain low magnetic losses up to 900 MHz. High frequencies applications can be envisaged.
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