Effect of nominal Indium substitution on structural, magnetic and microwave properties of Calcium-Barium M−type hexaferrites

Abstract

Abstract A series of Indium doped Calcium-Barium M−type hexaferrite with nominal compositions Ca0.5Ba0.5Fe12-xO19Inx (x\xa0=\xa00.00, 0.05, 0.10, 0.15, 0.20, 0.25) was prepared by sol–gel method. The x-ray diffraction (XRD) analysis of the synthesized compositions revealed two phases; M−type hexaferrite phase as a main phase and α-Fe2O3 hematite phase. The gradual increasing trend in lattice parameters was observed on increasing Indium concentration showing incorporation of Indium in M−type hexagonal crystal structure. The grain size of M−type hexagonal phase was calculated using Debye–Scherer formula from non-overlapping peaks and it varied from 20 to 500\xa0nm (0.5\xa0μm). The scanning electron microscopy (SEM) micrographs showed hexagonal platelet-shaped, randomly distributed and agglomerated grains. The high resolution transmission electron microscopy (HRTEM) patterns further confirmed the observations of phases from x-ray diffraction (XRD). The remnant magnetization Mr and saturation magnetization Ms showed humped behaviour with maximum value for x\xa0=\xa00.25. The decrease in coercivity Hc was observed for x\xa0=\xa00.05 but it increased and remained nearly constant on further Indium addition. The effective dielectric constant showed resonance peaks at 4.3 and 8\xa0GHz for all compositions and the effective loss decreases with frequency with maximum loss for x\xa0=\xa00.05, indicating the slight effect of In doping. The effective magnetic permeability showed small values and a resonance peak around 9\xa0GHz, similarly magnetic losses also showed low values and a decreasing trend with frequency, not much noticeable influence of Indium doping was observed. These materials can be used in microwave frequency devices such as phase shifters and permanent magnets.