Formation of non-centrosymmetric covalent bonds due to the substitution of cobalt contents in M-type barium hexa-ferrites BaFe(12-x)O19

The evolution of various properties of cobalt-doped M-type barium hexa-ferrites has been investigated in this project. A series of cobalt-doped M-type barium hexa-ferrites having general composition BaCoxFe(12-x)O19 with x = 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 was prepared using powder metallurgy route. For the thermal decomposition, prepared powders were heat-treated at 1373 K-o for 2 h in a muffle furnace. The structural analysis, 3-D structural visualization, functional group analysis, surface morphology, elemental analysis, optical, dielectric, ferromagnetic, and ferroelectric properties of samples were characterized using different characterization techniques. X-ray diffractometer and Fourier transform infrared spectroscopy confirmed the formation of single-phase hexagonal structure of cobalt-doped M-type barium hexa-ferrite. The optical bandgap energy and saturation magnetization of the prepared samples increased with increasing cobalt concentration which made them suitable for light-emitting diodes and laser formation. Their dielectric properties show the insulting nature of the ferrites. Ferro-electric loop exhibits formation of non-centrosymmetric covalent bonds with an increase in the electric coercive field and remanent polarization. The electric polarization in the unit cell of barium hexa-ferrites is based on FeO6 octahedron. The oxygen O6 is located at three crystallographic sites (4f, 2a and 12 k). The iron ion is normally located at the center of the oxygen octahedron. The formation of non-centrosymmetric covalent bonds is due to the shifts off-center of iron ions under the application of external field. The ferroelectric loops are also not properly closed which indicates the magnetoelectric (ME) coupling and improves multiferroicity of the material.