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.
