Effect of Sintering Temperature on the Structural, Dielectric, and Magnetic Properties of Garnet-Spinel Ferrite Composites for Use in L-Band Devices

Herein we have reported the influence of sintering temperature on the structural, dielectric, and magnetic properties of garnet ferrite composite. The composite of gadolinium iron garnet and magnesium ferrite (Gd3Fe5O12[x]/MgFe2O4[1−x] at x = 0.75) was synthesized by the mechanical blending method and then sintered at 900°C and 1,300°C. X-ray diffraction study suggests that both of the phases of ferrites are present in the composites without any impurities. Field emission scanning electron microscopy images indicate the change in microstructure with sintering temperature. Dielectric study reveals that the sample sintered at 900°C has a higher value of dielectric constant (ε′r). The grain and grain boundary contributions in the composites have been elucidated by fitting the Nyquist plot with an electrical equivalent circuit. The extracted grain boundary resistance was found to increase from 64.7 MΩ to 2 × 1018 MΩ, and grain resistance has been decreased to 1.78 × 10−22 Ω from 293.5 Ω with an increase in temperature. From the magnetic hysteresis loop we have calculated the anisotropy constant (Keff) = 770, anisotropy field (Ha) = 168.5 Oe, squareness ratio (SQR) = 0.07, and microwave operating frequency (ωm) = 2 GHz for the sample sintered at 1,300 °C. These parameter values suggest the potential use of these composites for microwave devices operating in the L band.