Magnetic and dielectric properties in the UHF frequency band of half-dense Ni-Zn-Co ferrites ceramics with Fe-excess and Fe-deficiency

Publication date: 1 February 2018
Source:Journal of Magnetism and Magnetic Materials, Volume 447
Author(s): Jean-Luc Mattei, David Souriou, Alexis Chevalier
This work investigates electromagnetic properties of half-dense ceramics with compositions Ni0.5Zn0.3Co0.2FeyO4-δ where y=1.98 (Iron deficient, noted ID) or y=2.3 (Iron in excess, noted IE). IE and ID materials are obtained by chemical coprecipitation route. The obtained nano-sized powders are pressed and annealed at two temperatures (800°C, 900°C), so has to obtain half-massive ceramics. Ferrous and ferric ions coexist in the crystalline structures, but the former in a less extend for ID ferrite. The concomitant influences of Fe²⁺ and Fe³⁺ on the dielectric and magnetic losses (ε″/ε′ and µ″/µ′, respectively) are considered at frequency up to 6GHz. The permeability dispersion changes from relaxation-like to resonance-like with the decrease in ferrous ions. In reason of the relaxing-like behavior of Fe²⁺, and because of a relatively high amount in Fe²⁺, IE sample shows lower total losses (magnetic and dielectric) than ID sample. These conclusions applied for TA=900°C. At frequencies above 700MHz, the total loss values (IE and ID samples) are prohibitive for antenna downsizing whatever is the firing temperature value (800°C and 900°C). Whereas at frequencies below 700MHz Ni0.5Zn0.3Co0.2Fe2.3O4+δ may leads to better antenna performances than Ni0.5Zn0.3Co0.2Fe1.98O4-δ.



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