An investigation of structural and magnetic properties of Ba2Ni2-xZnxFe12O22 hexaferrites

Abstract

Ba Ni Zn Fe O −x x (0.0 ≤ x ≤ 0.7 with a step of 0.1) hexaferrites were prepared by conventional solid state reaction method. Stoichiometric amounts of BaCO3, Fe2O3, NiO and ZnO were ball milled for12 h. After milling, compositions were subjected to calcining wherein it was controlled at 900°C and calcined powder was crushed into fine powder. Pellet and toroid shaped samples were prepared from the fine powder and sintered at 1150, 1200 and 1250 °C for 5 h. The X-ray diffraction (XRD) patterns for different compositions were analyzed. This analysis and the comparison of obtained XRD patterns with previously reported XRD patterns of Y-type hexaferrites confirm the formation of the hexagonal phase. The lattice parameters ‘a’ and ‘c’, and c/a ratio for all samples are calculated. The values of lattice parameters are close to the reported values for Y-type hexaferrite. The lattice parameters are found to be increase with Zn substitution. The increase in lattice parameters with increasing Zn content can be explained on the basis of the ionic radii. The bulk density of the samples increases with increasing Zn content up to x = 0.2. This increase in density with increasing Zn content can be explained on the basis of the atomic weight of the substituted cations. The bulk density of the various polycrystalline 2 2 12 22 Ba Ni Zn Fe O −x x increases with increasing sintering temperature up to an optimum temperature (1200oC) above that this decreases. Structural and surface morphology were studied by high resolution optical microscope for different compositions. The micrographs show that grain size increases with Zn content. The ac magnetic properties of the hexaferrites are characterized within the frequency range 100 kHz – 120 MHz. The real part ( / i μ ) of the complex initial permeability * / // i i i μ = μ − iμ for different compositions indicates that / i μ decreases with increase in frequency. The decreasing trend in permeability / i μ with frequency is a general phenomenon and is ascribed to the limited speed of spin and domain wall movement (displacement/ rotation) in the samples. It is observed that permeability increases for almost all the samples as the sintering temperature increases from 1150 to 1200°C and above this sintering temperature permeability decreases. Magnetization was measured using the Superconducting Quantum Interference Device (SQUID) magnetometer. The saturation magnetization (Ms) increases with Zn content up to x = 0.1 and then decreases.