Magnetic and microwave absorption properties of Co2+ and Zn2+ co-doped barium hexaferrite nanoparticles

Hexagonal ferrites are very well known materials used for electromagnetic radiation absorption for last many years. However, nano-hexagonal ferrites have recently caught the interest of many researchers worldwide. During this investigation, BaFe12O19 (BF) and BaCo0.5Zn0.25Fe11.25O19 nanoparticles (NPs) were synthesized by using sol-gel auto-combustion method. Characterization of NPs was done by using x-ray diffractometer (XRD) and scanning electron microscope (SEM). XRD pattern of these particles confirms the growth of M-type ferrites without any other impurity phase. Their crystal size was calculated from the diffraction peaks by using Debye Scherrer's formula and found in the range of 22.1 and 30.3 nm. The SEM also confirmed the spherical morphology of these particles. Transmission electron microscope (TEM) further confirmed the presence of nano-crystallites, which were agglomerated, may be, due to magnetic exchange interaction among themselves. The magnetic behavior of the synthesized NPs was studied by using vibrating sample magnetometer under an applied magnetic field of +/- 5 Tesla. The M/H curve revealed an increase in saturation magnetization (M-s), remanent (M-r), and coercivity (H-c) by co-doping of (Co2+ and Zn2+) cations in barium ferrite (BF). The complex permittivity and permeability were measured by using vector network analyzer in the frequency range of 2-18 GHz. An increase in the value of permittivity and permeability was observed by co-doping of (Co2+ and Zn2+) in BF. Finally it was also observed that absorption in effective bandwidth (>= 10 dB) increased from 2.76 to 3.60 GHz at the coating thickness of 1.8 mm.