The study of magnetic properties and structures of Zn and Cd substituted
mixed ferrites has been carried out using Mossbauer spectroscopy and X-ray
diffraction on powdered samples at about 300 K. Two series of mixed ferrites,
(Cd, Zn)xCol-xFe2-xAlxO4 and (Cd, Zn)xCo0.9Fe1.7-xTi0.4O 4 (where 0≤ x≤1.0)
were synthesized. In the former series the effect of simultaneous site dilution
by Zn or Cd and Ai atoms on tetrahedral (A) and octahedral (B) sites is investigated
and in the latter the effect of single site dilution by Zn or Cd is also
studied. The Mossbauer spectra show that the compounds transform with increase
in x from ordered to disordered magnetic states. Systematic decrease
in the hyperfine fields indicating weakening of the magnetic coupling with an
increase in x is observed. We report the presence of a cross over effect with
respect to the hyperfine fields on A and B sites at low concentration of diamagnetic
ions in the simultaneously diluted series. Both series of compounds show
no significant changes in isomer shifts with x. Differences in the evolution of
Fe atoms on A and B sites between Zn and Cd based compounds are observed.
The results of our analysis show that Zn and Cd ions occupy both tetrahedral
and octahedral sites. The spinel structure of the compounds studied in this
work is confirmed by X-ray diffraction (XRD). The lattice parameters derived
from XRD show systematic change with x consistent with Vergard's law. In
Cd based samples an increase of the lattice parameter with x is explained on
the basis of the size difference of the cations involved. However, an anomalous
behavior of the lattice parameter is observed in Zn based samples. The
average grain sizes of the samples were determined from the line width of the
(311) XRD intensity lines using the Scherrer formula. These vary between 50
nm and 70 nm for all the samples except for Zn and Al substituted samples
which show a systematic anomalous reduction for x ≥ 0.4 in grain size. The
porosity, x-ray and bulk densities of the samples are also presented. / Thesis (M.Sc.)-University of Natal, Durban, 2002.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/4412 |
| Date | January 2002 |
| Creators | Msomi, Justice Zakhele. |
| Contributors | Moyo, T. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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