Abstract:
A series of polycrystalline spinel type ferrites with the nominal composition
LixMg0.4Ni0.6-2xFe2+xO4, where x = 0.0 to 0.3 in steps of 0.05, has been investigated
thoroughly. The samples are fabricated using conventional solid state reaction technique.
Pellet and toroid shaped samples are prepared from each composition and sintered at
temperatures of 1050, 1100,1150 and 1200˚C in air for 6 hours. Structural and surface
morphology are studied by x-ray diffraction technique and high resolution optical
microscopy, respectively. The AC magnetic properties of these ferrites are characterized by
high frequency (300 kHz-110 MHz) complex permeability measurements. DC
magnetizations of all samples are measured by Vibrating Sample Magnetometer (VSM).
The influence of microstructure, various cation substitution and sintering temperatures on
the complex permeability of above mentioned ferrites are discussed. A possible correlation
among sintering temperature, average grain size and density is also discussed.
It is noticeable that X-ray diffraction patterns of all samples show the formation of
spinel crystal structure. Lattice parameters are calculated using the Nelson Riley function.
The lattice constants increase linearly with the increase of Li content, obeying Vegard s
law. This result is explained with the help of ionic radii of substituted cations. The
microstructural study shows that both sintering temperatures and cations substitutions have
great influence on the average grain size. In LixMg0.4Ni0.6-2xFe2+xO4 ferrites the real part of
initial permeability, /
i
and saturation magnetization, Ms, increase with the increase of Li
content up to x= 0.25 and beyond x= 0.25, both /
i
and Ms decrease. The decrease of /
i
and
Ms beyond x= 0.25 indicate the possibility of noncollinear spin canting effect. It is also
found that /
i
increases with increasing average grain size of the samples. It is also
observed that /
i
increases with sintering temperatures for all ferrites because high sintering
temperature performs uniform grain growth. Highest value of /
i
and Q-factor is observed
for various LixMg0.4Ni0.6-2xFe2+xO4 ferrites sintered at 1100˚C and among these, highest /
i
( /
i =
66 )
and maximum Q-factor (
Q
value=4653) is found for Li0.25Mg0.40Ni0.10Fe2.25O4,
ferrite. From DC magnetization data it is found that Li0.25Mg0.40Ni0.10Fe2.25O4 ferrite has
maximum saturation magnetization value among LixMg0.4Ni0.6-2xFe2+xO4 ferrites.
