Dense and half-dense NiZnCo ferrite ceramics: Their respective relevance for antenna downsizing, according to their dielectric and magnetic properties at microwave frequencies

作者：Mattei J L^*; Le Guen E; Chevalier A

来源：Journal of Applied Physics, 2015, 117(8): 084904.

DOI：10.1063/1.4913700

Spinel ferrite Ni0.5Zn0.3Co0.2Fe1.98O4-x nanoparticles were synthesized by co-precipitation method, and samples were realized by moulding and annealing at key temperatures (T-M = 800 degrees C, 900 degrees C, 1050 degrees C, determined beforehand through shrinkage measurements) going with calcining and sintering processes. Annealing at 800 degrees C and 900 degrees C led to half-dense ceramics (porosity similar to 50 vol. %), whereas bulky ferrite was obtained after annealing at 1050 degrees C. Elemental analysis, X-ray diffraction and ion chromatography analysis were performed. Complex dielectric permittivity (epsilon*) and magnetic permeability (mu*) were investigated up to 6 GHz. With increasing T-M, a decreasing amount of Fe2+ was observed, going with increasing sample density. Coupled effects of the Fe2+ concentration and of the porosity, both on dielectric and magnetic properties, were chiefly investigated and discussed. The materials show almost constant permittivities (epsilon' = 5.0, 6.0, and 14.8 for T-M = 800 degrees C, 900 degrees C and 1050 degrees C, respectively). The bulk value at f = 1 GHz (epsilon' = 14.8) can be interpreted well according to Shannon's theory. The permittivities of the half-dense ceramics are discussed on the basis of Bruggeman's Effective Medium Theory. The materials annealed at 800 degrees C and 900 degrees C show almost constant magnetic permeabilities in the frequency range from 0.2 to 1GHz (mu' = 3.4 and 6.0 for T-M = 800 degrees C and 900 degrees C). The observed permeability behavior is typical of monodomain particles, except for the sample annealed at 1050 degrees C, for which domain wall contribution to mu* is suspected because of non-negligible losses at low frequency (mu '' = 1.3-1.8 at f<0.3 GHz). This finding is supported by estimations of the upper and lower values for the critical grain size, on the basis of Brown-Van der Zaag's theory. Facing bulk ceramics, and in view of using Ni0.5Zn0.3Co0.2Fe1.98O4-x ferrite as substrate for antenna miniaturization, the electromagnetic properties of half-dense ceramics materials seem to be very competitive at frequencies beyond 0.2 GHz, and up to 0.7-0.8 GHz.

• 出版日期2015-2-28