Browsing by Author "Majozi, Prince Phathizwe"

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    Effects of particles’ size and composition on magnetic properties of substituted ferrite nanoparticles
    (University of Zululand, 2024) Majozi, Prince Phathizwe; Msomi, J. Z. and Jili, T. P.
    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.