Abstract:
Polycrystalline NiOJobiOJO-xTirFe,OJ (O.OO~.50) and Nio5o-)7.J1n.J,Cr)Fe20J
(O.OO$'S.l.20) ferrites were prepared by a conventional solid stale reaction technique.
Tbe samples were sintered at different temperatures (1250"C, 1350'( and 1400"C) in air
for 5 hours. Structural and surface morphology were studied by x-ray diffraction and
optical microscopy respectively. The magnetic properties of these ferrites were studied
by bigb frequency (1 kHz-13 MHz) complex permeability and temperature dependent
permeability measurements. The effects of microstructure, composition and sintering
temperatures on the complex permeability of Nin.J"z,,05f1--JixFe,OJ and
Nio,o_,Z"o,,,cryFeJOJ ferrites arc discussed. A possible correlation among sintering
temperature, grain size and density is also discussed.
Lauice parameter decreases with the increase of Ti or Cr content for all
compositions. The decrease in laniee parameter with increasing Ti or Cr content can be
explained on the basis ofthe ionic radii. The microstructural study shows that grain size
decreases with increasing Ti or Cr conten!. The experimental density of the samples
decreases and the corresponding porosity oflhe samples increases with increasing Ti or
Cr content. The density of the polycrystallinc NioJ,;zn,'.JIJ_xnFe]OJ compositions
increases and the porosity decreases with increasing sinterlng temperature, T,. The
density of the polycrystalline Nio,'O-..znO,J.cr~e204 compositions increases as the
sintering temperature increases from 1250°C to J350"C and above 1350"( the density
decreases. On the other hand, porosity of the sample decreases with increasing sintering
temperature up to 1350"(, and above 1350"C the porosity increases.
The initial pel1T1eabilityvalue decreases with increasing Ti Or Cr wntent,
because the avemge gmin si7~ decreases with increasing Ti or Cr content. For the
polycrystalline Nio,s".,znoSOCr~e20., compositions, the real part of the initial
pel1T1eabilityis found to increase at firSI and then decreases with increasing sintering
temperature, T,. The real part of the initial permeability remains fairly constant in the
frequency range up to some critical frequency characterized by the onset of resonance.
At these frequencies, after a small rise, the curves drop rapidly. The relative quality
factor (Q) is found to decrease with increasing Ti or Crcontent.1t is also observed that
the Q factor decreases wilh increasing sintering temperature. The magnetization as a
function of applied magnctic field, M(H), for various Pol}crystalHne
Ni~5"znO_51J->TiJ'C204 and Nio_5r!_,zno,oCr,Fct04 samples at room temperature (300K)
were measured. The Curie temperatures of these ferrites were found to increase with
increasing Ti but it decreases with increasing Crcontent. The increase or decrease of To
with increasing Ti or Cr content may be explained by a modification of the A-B
exchange interaction as a result of substitution.
