Implication of La2O3 doping on phase transformation, grain morphology, optical, microwave dielectric with low loss, and magnetic behaviour of (Mg0.5Mn0.5)Fe2O4
摘要
The Mg0.5Mn0.5Fe2-xLaxO4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5) was fabricated by the solid-state reaction route. XRD analysis confirms the existence of a spinel cubic phase and the formation of a secondary phase of LaFeO3 orthorhombic structure for La-doped (Mg0.5Mn0.5)Fe2O4. For higher concentrations of lanthanum substitution, the doped La3+ions do not enter into the MgMn ferrite sublattice and form more of the secondary LaFeO3 phase due to the difference between the ionic radii of both La3+ (1.06 Ao) and Fe3+ (0.67 Ao). The Williamson–Hall graph shows that the average crystallite size varies between 45.63 nm and 40.20 nm with increasing La concentration. The FESEM images confirm the formation of well-defined grains with grain boundaries. UV spectra analysis shows an increasing trend of band gap after incorporating La3⁺ and exhibits high resistive properties. In this investigation, the parent material is MgMnFe₂O₄ with a band gap of 1.05 eV, which is semiconducting in nature. After substitution of the lanthanum ion, the band gap rises from 2.68 eV to 2.78 eV for MgMnFe2-xLaxO4 (x = 0.1–0.5), which are semiconductors and suitable for operation at higher voltages, frequencies, and temperatures with minimum loss. The dielectric constant shows a decreasing trend with increasing frequency for all the ferrites. Dielectric loss is found to increase with frequency and attains a maximum at 15 GHz, and decreases afterwards. The optimal behaviour is seen in Mg0.5Mn0.5La0.3Fe1.7O4, for which the maximum dielectric constant and minimal value of dielectric loss are observed at higher frequency. The nature of the M-H loop for all the specimens shows soft ferromagnetic behaviour. The synthesized samples have modified electrical and magnetic behaviours, hence suitable for microwave applications.