| 1. |
- Almessiere, M. A., et al.
(author)
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Effects of Ce-Dy rare earths co-doping on various features of Ni-Co spinel ferrite microspheres prepared via hydrothermal approach
- 2021
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In: Journal of Materials Research and Technology. - : Elsevier BV. - 2238-7854 .- 2214-0697. ; 14, s. 2534-2553
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Journal article (peer-reviewed)abstract
- The effects of Ce-Dy co-doping on the crystal structure, optical, dielectric, magnetic properties, and hyperfine interactions of Ni-Co spinel ferrite microspheres synthesized hydrothermally have been studied. A series of ferrites with the general formula Ni0.5-Co0.5CexDyxFe2-2xO4 were synthesized with x values ranging from 0.00 to 0.10. The phase, crystallinity, and morphology of ferrite microspheres were analyzed by X-ray powder diffractometry (XRD), scanning and transmission electron microscopes (SEM and TEM), respectively. The structural analyses of the synthesized ferrite microspheres confirmed their high purity and cubic crystalline phase. The Diffuse reflectance spectroscopic (DRS) measurements were presented to calculate direct optical energy band gaps (E-g) and is found in the range 1.63 eV - 1.84 eV. Fe-57 Mossbauer spectroscopy showed that the hyperfine magnetic field of tetrahedral (A) and octahedral (B) sites decreased with the substitution of Dy3+-Ce3+ ions that preferrentially occupy the B site. The impact of the rare-earth content (x) on the magnetic features of the prepared NiCo ferrite microspheres was investigated by analyzing M-H loops, which showed soft ferrimagnetism. The magnetic features illustrate a great impact of the incorporation of Ce3+-Dy3+ ions within the NiCo ferrite structure. The saturation magnetization (M-s), remanence (M-r), and coercivity (H-c) increased gradually with increasing Ce-Dy content. At x = 0.04, M-s, M-r, and H-c attain maximum values of about 31.2 emu/g, 11.5 emu/g, and 512.4 Oe, respectively. The Bohr magneton (n(B)) and magneto-crystalline anisotropy constant (K-eff) were also determined and evaluated with correlation to other magnetic parameters. Further increase in Ce3+-Dy3+ content (i.e., x >= 0.06) was found to decrease M-s, M-r, and H-c values. The variations in magnetic parameters (M-s, M-r, and H-c) were largely caused by the surface spins effect, the variations in crystallite/particle size, the distribution of magnetic ions into the different sublattices, the evolutions of magneto-crystalline anisotropy, and the variations in the magnetic moment (n(B)). The squareness ratios were found to be lower than the predicted theoretical value of 0.5 for various samples, indicating that the prepared Ce-Dy substituted NiCo ferrite microspheres are composed of NPs with single-magnetic domain (SMD). Temperature and frequency-dependent electrical and dielectric measurements have been done to estimate the ac/dc conductivity, dielectric constant, and tangent loss values for all the samples. The ac conductivity measurements confirmed the power-law rules, largely dependent on Ce-Dy content. Impedance analysis stated that the conduction mechanisms in all samples are mainly due to the grains-grain boundaries. The dielectric constant of NiCo ferrite microspheres give rise to normal dielectric distribution, with the frequency depending strongly on the Ce-Dy content. The observed variation in tangential loss with frequency can be attributed to the conduction mechanism in ferrites, like Koop's phenomenological model.
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| 2. |
- Slimani, Y., et al.
(author)
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Ultrasound-assisted synthesis and magnetic investigations of Ni0.4Cu0.4Zn0.2GaxGdxFe2-2xO4 (0.00 <= x <= 0.04) nanosized spinel ferrites
- 2022
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In: Applied Physics A. - : Springer Nature. - 0947-8396 .- 1432-0630. ; 128:7
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Journal article (peer-reviewed)abstract
- This study focused on the impact of Ga-Gd co-substitution on the structural, magnetic features and hyperfine interactions of nanosized NiCuZn spinel ferrites [Ni0.4Cu0.4Zn0.2GaxGdxFe2-2xO4 (0.00 <= x <= 0.04) NSFs] synthesized via sonochemical approach using ultrasonic irradiation. X-ray powder pattern (XRD) analyses confirmed cubic spinel structures of products. Crystallites and particle sizes of all samples are found to be between 9-14 nm and 18-22 nm, respectively. The NSF morphology and chemical composition were investigated by transmission and scanning electron microscope (TEM and SEM) along with energy-dispersive X-ray (EDX). The cation distribution of all ions was evaluated by Mossbauer spectroscopy. The high spin Fe3+ ions determined the isomer shift (I.S.) values. For lower rare-earth dopant ratios, we found that Gd3+ ions occupy B sites, while Ga3+ ions reside in A sites, and thereafter, some Ga3+ ions start to enter B sites. Magnetometry measurements were used to evaluate the effect of magnetic field (H) and temperature (T) on the magnetization of products. For each sample, both coercivity (H-c) and saturation magnetization (M-s) increase when the T decreases below ambient temperature. All substituted samples display M-s values higher than those of non-substituted ones; however, H-c values diminish for x content up to 0.02 and thereafter enlarge. Different magnetization measurements revealed superparamagnetic-to-ferromagnetic transition below the blocking temperature (T-B).
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