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

Abstract

A series of Indium doped Calcium-Barium M−type hexaferrite with nominal compositions Ca0.5Ba0.5Fe12-xO19Inx (x = 0.00, 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 nm (0.5 μm). 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 = 0.25. The decrease in coercivity Hc was observed for x = 0.05 but it increased and remained nearly constant on further Indium addition. The effective dielectric constant showed resonance peaks at 4.3 and 8 GHz for all compositions and the effective loss decreases with frequency with maximum loss for x = 0.05, indicating the slight effect of In doping. The effective magnetic permeability showed small values and a resonance peak around 9 GHz, 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.