Magnetodielectric response of composites based on a natural garnet and spinel ferrites for sub-GHz wireless applications

A natural garnet with excellent dielectric properties was mixed with different weight percentages of two spinel ferrites, Ni_0.5Zn_0.5Fe₂O₄ (NZO) and LiFe₅O₈ (LFO) to tailor its magnetodilectric properties. 3 wt% B₂O₃ was added to enhance the density of the composites. X-ray diffraction study revealed the decomposition of the mineral into hematite and cordierite and vibrational spectroscopic analysis confirmed the non-reactivity of decomposed mineral with spinel ferrites. Microstructural analysis shows well densified and almost tightly packed grains for garnet-Ni_0.5Zn_0.5Fe₂O₄ (G-N) and garnet-LiFe₅O₈ (G-L) composites. The optimised dielectric and magnetic properties of 0.5 G-0.5 NZO are ε_r = 4.1, μ_r = 1.8, tan δ_ε = 0.02, tan δ_μ = 0.49, whereas that of 0.5 G–0.5 LFO are ε_r = 4.4, μ_r = 1.4, tan δ_ε = 0.001, tan δ_μ = 0.05 at 1 GHz. Due to the moderate permittivity of garnet, a better impedance matching compared to magnetodielectric composites based on high-permittivity dielectric counterparts is observed. Hence, the present study indicates that G-N and G-L composites are potential candidates for sub-gigahertz wireless applications.