Abstract:
Polycrystalline Ni0.48Cu0.12Zn0.40GdxFe2-xO4 (x varies from 0 to 0.10 insteps of
0.02) ferrites were prepared by standard solid state reaction technique. The samples
prepared from each composition were sintered at various temperatures in air for 1 hour.
Structural and surface morphology were studied by X-ray diffraction and optical
microscopy, respectively. The magnetic properties of these ferrites were characterized
with high frequency (100Hz-120MHz) complex permeability and temperature
dependent permeability measurements. The DC magnetizations as a function of applied
magnetic field were measured at room temperature by vibrating sample magnetometer.
The effects of microstructure, composition and sintering temperatures on the complex
permeability of various Ni0.48Cu0.12Zn0.40GdxFe2-xO4 are discussed. A possible
correlation among sintering temperature, grain size and density is also discussed.
It was observed that the compositions are single phase and formed spinel
structure for small amount of Gd substitution. For x=0.04 sample formed spinel
structure with some less intense additional peaks. A gradual increase in the intensity of
the additional peaks is noticed with increasing Gd concentration and the peaks are
identified to be corresponding to GdFeO3 (orthoferrite phase). The lattice constant of all
these samples follow Vegard’s law. The X-ray densities of the samples increase with
increasing Gd3+ content. On the other hand, the bulk densities of the samples increases
and the corresponding porosity of the samples decreases with increasing of Gd3+ content
up to x=0.08. Beyond this value of x, density decreases as well as porosity increases.
The sintering densities of the polycrystalline Ni0.48Cu0.12Zn0.40GdxFe2-xO4 increases in
increasing sintering temperature up to optimum temperature above that the densities
decreases. The microstructural study shows that grain size increases with increasing Gd3+ content up to an optimum concentration after that it decrease. The compositional
variation of complex permeability spectra, loss factor and relative quality factor (Q)
were studied with frequency for the samples sintered at various temperatures. The
general characteristic of the permeability spectra is that the real part of initial
permeability ( /
μ i ) remain fairly constant in the frequency range up to some critical
frequency characterized by the onset of resonance, while at higher frequencies it drops
rapidly to a very small value and imaginary part ( //
i μ
) increase to have a peak. The Q is
found to be increase with increasing Gd3+ content up to an optimum level beyond that it
decreases. It is also observed that the Q value decreases with increasing of sintering
temperature and loss factors are minimum for frequency up to 1 MHz.The Néel
temperature, TN,, of these samples are determined from the temperature dependent initial
permeability which shows a decreasing trend as a function of composition due to the
weakening of the A-B interaction. Compositional variation saturation magnetization,
saturating field, Bohr magneton were calculated from M-H loops measurement. The
variation saturation magnetizations were described on the basis of cation distribution.