Abstract:
PolycrystalHne Nio IMg,:usCuowlno5oFe2_xLax04 (with x = 0.00, 0,025, 0.050
and 0.075) were prepared by conventional solid state reaction technique. Pellet and
toroid shaped samples were preJlllred from each composition and were sintered at
various temperatures (T,) in air for 5 hours. The influences of microstructure, La
substitution in place of Fe and T, on the complex permeability of above mentioned
samples are discllssed. A possible correlation among T" C()mplex permeability and
density is also discussed. The Neel temperature (TN) of the samples is measllred from
the temperature dependent real part of initial permeability (11:). X-ray diffraction
patterns of the samples show the formation of cubic spinel structure. Lattice parameter
increases with increasing La substitution. This result is explained with the help of ionic
radii of snbstituted cations. The average grain size slightly decreases with increasing La
substitution whereas increases with increasing T,. Theoretical density (P'h) and bulk
density (Ps) both increase with increasing La C()nten!. This can be explained on the
basis of atomic weight. The PB increases with increasing T, np to 1200°C then decreases
for a further increase of T. up to 1250°C. On the other hand porosity has the opposite
trend. The p; decreases with increasing La substitution probably due to the decrease of
average grain size. It is also ObselVedthat P,' increases with increa5ing T, for all ferrites
up to 1200°C then decrea5es for sample sintered at 1250°C. It is expected that there
might have a correlation between PH and permeability. The J.I: remains fairly constant
in the frequency range up to 10 kHz or greater for parent composition and I MHz or
greater for La doped compositions. The imaginary pari of initial permeability starts
raising beyond this freqllency which is an indication of dispersion or resonance. At high
frequency, the loss factor of all La doped compositions is lower than parent composition
and decreases with increasing La substitution. The relative quality factor is found to be
maximwn in Nio,12Mgo,l!CUo,2(lZnQ.5oFeL915U1<JsGin7te5r0e4d at 1250°c. The TN was
found to decreases with La substitution up to x=0.050 beyond which TN increases. The
decrease of the TN is dlle to the weakening of the A-B exchange interaction and vice
versa The magnetization of all samples increases linearly with increasing applied
magnetic field up to 0.1 T. Beyond this fieid, magnetization increases slowly and then
saturation occurs. Saturation magnetization decreases with increasing La substillltion.
