Low-loss Cd-substituted Mg ferrites with matching impedance for high-frequency-range antennas

Abstract

The effects of Cd2+ ions on the microstructure, magnetic properties, and dielectric properties of Bi2O3-added MgFe2O4 ferrites (CdxMg1-xFe2O4, x = 0.00, 0.15, 0.30 and 0.45) are obtained by adopting the solid-state reaction method at a low temperature (910 °C). The objective is to achieve matching impedances, low magnetic and dielectric losses (tan δμ and tan δε, respectively), and a relatively large miniaturization factor to reduce antenna size. Experimental results indicate that the cations occupying the tetrahedral (A) and octahedral (B) ion sites are redistributed, resulting in an enhanced super-exchange interaction between the two sublattices. As a result, improved magnetization, including the increase in saturation magnetization (41.74 emu/g) and decrease in coercivity (63.75 Oe), is realized. The real part of permeability (µ′) also increases with increasing concentration of Cd2+ ions. When x is 0.15, matching impedances with equivalent μ′ and ε′ values are obtained over a long frequency range (1–150 MHz). Moreover, the formation of a dense microstructure guarantees that losses occur at low orders of magnitude (tan δμ ≈ 10−2 and tan δε ≈ 10−3). Accordingly, these properties afford wide application perspectives for the proposed compounds in the high-frequency region, i.e., from high-frequency to very-high-frequency bands.