Effects of particles’ size and composition on magnetic properties of substituted ferrite nanoparticles
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Date
2024
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University of Zululand
Abstract
This project presents the effects of particle size and composition on the magnetic
properties of ferrites investigated by magnetization and electron spin resonance
(ESR) spectroscopy. CuxMn1−xFe2O4, (Zn, Cd)Fe1.2Al0.8O4, NixCo1−xFe2O4 and
Cu0.5Ni0.5Fe2O4 nanoferrites were produced by glycol-thermal reaction under a low
reaction temperature of 200 ◦C. Structural properties were analysed by transmission electron microscopy (TEM) and X-ray diffraction (XRD).
For CuxMn1−xFe2O4, the majority of the XRD peaks were indexed to the cubic
spinel phase. However, a small impurity peak at 2θ ≈ 52◦ attributed to α-Fe2O3
and Mn2O3 phases for samples 0.4≤ x ≤ 0.8 was observed. The particle sizes varied
between 8 nm and 16 nm. The particle size for the sample x = 0.3 (Cu0.3Mn0.7O4),
which did not show any impurity phases was about 8 nm. The reduction of lattice
parameters as a function of increasing Cu content is attributed to the smaller Cu
replacing Mn ions. Magnetization data revealed superparamagnetic Cu0.3Mn0.7Fe2O4 fine particles and spin-glass behaviour. Enhanced magnetization and coercive fields at 10 K were explained by the core-shell model and spin freezing.
An attempt to produce (Zn, Cd)Fe1.2Al0.8O4 was made. The XRD spectrum of the
Cd-based sample showed impurity phases. XRD analysis showed clean ZnFe1.2Al0.8O4 with a particle size of about 6 nm. TEM images revealed nearly spherical particles with a reasonably narrow distribution of particle size which compared well with the value estimated from XRD data. ESR measurements showed a single-line signal indicative of dominant superexchange interactions. A small peak at very low magnetic field (about -500 ≤ H ≤ 500 G) was observed for the Zn- based oxide annealed at 1000 ◦C. This anomalous peak may be due to the low field microwave absorption(LFMA) phenomenon that is not fully understood in magnetic materials.
NixCo1−xFe2O4 were successfully indexed to the cubic spinel. An additional peak
associated with α-Fe2O3 was observed for samples with 0.7 ≤ x ≤ 0.9. XRD spectra
revealed crystallite sizes ranging from 8 nm to 13 nm. There was no significant change in lattice parameters with increasing Ni concentration due to the small difference in their atomic radii. The ESR results showed single-line signals. Additional resonances were observed at low fields which need further measurements. We suspect these additional resonance peaks to be due to LFMA. The Land´e g-values varied between 1.98 and 3.6.
Nanosized Cu0.5Ni0.5Fe2O4 fine particles with particle sizes of about 12 nm were
produced. XRD did not show any impurity phases. The as-prepared oxide was
annealed from 500 ◦C to 1100 ◦C to investigate particle size effects. Grain growth to about 46 nm was observed after annealing at 900 ◦C. ESR data revealed enhanced magnetization on the sample annealed at 900 ◦C due to the large ferromagnetic domains.
Description
A Thesis submitted to the Faculty of Science, Agriculture and Engineering in fulfilment of the requirements for the Degree of Master of Science in the Department of Physics and Engineering at the University of Zululand, South Africa [2023].