Single Phase Spinel Structure Research Articles

Effect of Ga substitution on grain orientation and magnetostrictive properties of polycrystalline CoFe2O4 ceramics prepared by the solid-state method

As a kind of magnetostrictive ceramics, cobalt ferrites are widely concerned because of its large magnetostriction and high resistivity, which are ideal for high-frequency applications. But, the high driving magnetic field due to the high magnetocrystalline anisotropy limits the practical applications of cobalt ferrites, thus, it is a still a challenge to find a balance between high magnetostriction properties and low driving magnetic fields. In this work, we investigated the effects of partially substitution of Ga3+ for Fe3+ on grain orientation and magnetic properties, attempting to maintain high magnetostriction while reducing the driving magnetic field. The CoFe2-xGaxO4 (x=0, 0.05, 0.1, 0.15) with single-phase spinel structure were prepared by the conventional solid-state method. The saturation magnetization MS increased with the increase of Ga concentration, meanwhile the coercivity Hc and magnetocrystalline anisotropy constant K1 significantly decreased, which indicates the better soft magnetic characteristics of the Ga-doped cobalt ferrites. The oriented CoFe2-xGaxO4 samples were obtained using magnetic field orientation technique during the powder forming process. The <001> preferred orientation was achieved in CoFe2O4 samples. However, the <001> orientation degree decreased with the substitution of Ga, and the preferred orientation has changed into <111> at x=0.15. The Ga substitution affected the magnetocrystalline anisotropy and grain orientation, thereby affecting the magnetostrictive properties. As for the non-oriented samples, although the maximum magnetostrictive strain slightly decreased with Ga substitution, while there was a significant drop in the magnetostrictive saturation field. However, the magnetostriction of the oriented samples decreased significantly with the substitution of Ga due to the change of grain orientation from <001> to <111>.

Effect of rare earth (Ho and Er) co-substitution on the magnetic and dielectric properties of nanocrystalline cobalt ferrites

Nanocrystalline cobalt ferrites co-substituted with rare earth Ho and Er (CoFe2-2xHoxErxO4, 0 ≤x≤0.10) have been synthesized via the sol-gel method. X-ray Diffraction (XRD) confirmed the single-phase spinel structure with reduced crystallite sizes (65 nm–12 nm), micro-strain (ε) and increased lattice constant (a) with Ho–Er co-substitution. Rietveld refinement and theoretical computation revealed Ho and Er occupancy at octahedral sites and Fe and Co ions redistribution between the tetrahedral and octahedral sites. Infrared spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray spectroscopy (EDX) and X-ray Photoelectron Spectroscopy (XPS) supported the formation of the desired spinel structure, aggregated spherical morphology, chemical stoichiometry and elemental states. Magnetic measurements showed a systematic decrease in saturation magnetization (Ms), magnetocrystalline anisotropy (K1), coercivity (Hc) and Curie temperature (Tc) with Ho–Er co-substitution. Electron Spin Resonance (ESR) exhibited asymmetric resonance peaks, reduced resonance field (Hr), linewidth (ΔHpp) and deviation in Lande g values. Impedance spectroscopy revealed two conduction mechanisms (holes and electrons) with distinct activation energies (EaI and EaII). Modulus spectrum analysis confirmed the thermally activated sample-electrode effects and the Nyquist plots indicated the dominant contribution of the grain boundary resistance to the conduction process. A notable enhancement in the dielectric constant (ε′) was observed with Ho–Er co-substitution. The ac conductivity (σac) followed the Jonscher Power Law (JPL). The temperature-dependent frequency exponent s(T), suggests the existence of two conduction mechanisms: non-overlapping small polaron tunneling (NSPT) and correlated barrier hopping (CBH).

Enhancement of Cobalt Bismuth Nano-Ferrite via Heat Treatment to be Applied in High-Frequency and Antimicrobial Applications

AbstractCobalt bismuth nano-ferrite (Co/Bi) with the chemical formula CoBi0.02Fe1.98O4 was produced using a simple flash auto-combustion method at three different temperatures: as-prepared, 600°C, and 800°C. A single-phase spinel structure was confirmed using X-ray diffraction, and the nano-scale morphology was examined using AFM (atomic force microscopy). Magnetic measurements demonstrated that increasing the annealing temperature increased the saturation magnetization Ms by 1.3 times. However, the coercivity Hc changed from semi-hard ferrite (as-prepared sample) to soft ferrite (Co/Bi nano-ferrite at 800°C) and reduced 10.7 times that of as-prepared nanoparticles. Therefore, the 800°C Co/Bi nano-ferrite with a low coercive field is recommended for transformers, recording heads, inductor cores, magnetic shielding, and microwave devices. The as-prepared sample and that at 600°C displayed super-high microwave frequency (SHF) in the X band in high-frequency applications calculated from magnetic measurement. The 800°C sample also has an extremely high microwave frequency in the Ku band, which is utilized in radar and satellite communications. Antimicrobial characterization showed that raising the annealing temperature increased the effectiveness of the samples against tested microorganisms. Thus, the samples under investigation are highly suggested for ultra-high microwave frequency applications and biological antibacterial nanomaterials.

Effortless Fabrication of Bi2O3‐Co3O4 Nanocomposite Catalyst: Harnessing Photocatalytic Power for Efficient Cationic Dye Degradation

AbstractA cost‐effective and simple co‐precipitation approach was used to create an efficient photocatalyst Co3O4‐Bi2O3 with identical stoichiometry (1 : 1 of both Co3O4 and Bi2O3). XRD, FTIR, TEM, SEM‐EDS, XPS, UV‐DRS, PL, BET, and TGA were used to characterize the produced material‘s structural and optical properties. The presence of a single phase spinel structure with a distinctive plane (311) was verified by the XRD peak of 2 at 36.9° for Co3O4‐Bi2O3. The SEM pictures revealed clustered consolidated spheres, suggesting particle homogeneity and high interconnectedness. The HR‐TEM and SAED pictures revealed an average crystallite size of 28 nm for the Co3O4‐Bi2O3 heterojunction. The UV‐DRS spectral data demonstrated a 2.1 eV reduction in band gap energy for Co3O4‐Bi2O3 (whereas Co3O4 is 2.4 eV and Bi2O3 is 2.7 eV). Under solar light irradiation, pristine Co3O4, Bi2O3, and Co3O4‐Bi2O3 composites were investigated for photocatalytic degradation of Methylene Blue (MB) and Malachite green (MG) dyes. By adjusting factors such as pH, starting dye concentration, catalyst dosage, and agitation duration, the optimal efficiency was determined. The acquired results showed Co3O4‐Bi2O3 ′s superior activity over both precursors. The composite obtained maximal degradation of 98 % (at pH=11) and 97 % (at pH=9) for MB and MG, respectively. The enhanced photo degradation activity of Co3O4‐Bi2O3 can be due to larger visible light absorption, increased surface area, and decreased h+/e− recombination. The reactive species trapping study was performed to determine the importance of superoxide and hydroxyl radicals during photo degradation. Dye degradation was governed by a pseudo‐first‐order kinetic model. The reusability and stability of Co3O4‐Bi2O3 were confirmed by utilizing the same material for five consecutive runs with both MB and MG dyes. Mass spectra analysis provided insights into the successful degradation of dyes, elucidating intermediate products. The synthesized Co3O4‐Bi2O3 nanocomposite offers unrivalled advantages in terms of structural and optical properties, superior photocatalytic activity, and remarkable stability, making it a promising candidate for efficient dye degradation applications without the formation of toxic by‐products.

Rietveld analysis and dielectric spectroscopy of high conductivity and low dielectric loss Co Zn La ferrite

ABSTRACT This study investigates structural and dielectric characteristics of Co0.65Zn0.35LaxFe2-xO4 (CZL), with (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1), synthesized using the flash auto-combustion approach. The Fourier transform infrared spectroscopy supports the X-ray results for forming single-phase spinel structure. The Debye Scherer’s formula was used to evaluate the average crystallite size that found within the range of 31.5–46 nm. With increasing La3+ concentration, the lattice parameter, cell volume and density decreased. The formation of nanoparticles was supported by transmission electron microscopy TEM examination, which was coinciding with nanoparticle size from (XRD) data. The sample x = 0.06 has the highest value of resistivity and the lowest dielectric loss. The high value of electrical resistivity in ferrite is suitable for the high frequency application where eddy current losses are appreciable. The dielectric constant decreases with increasing La content, implying that the material’s dielectric properties are very useful for electron magnetic wave absorption applications.

Probing temperature-dependent magnetism in cobalt and zinc ferrites: A study through bulk and atomic-level magnetic measurements for spintronics

Spinel ferrites (MFe2O4) are integral to various industries, particularly spintronics, which utilizes the intrinsic spin of electrons as well as the electronic charge to develop devices that dictate spin-based transport, advancing new memory, logic applications, and improving magnetic storage technologies. These materials are valued for their exceptional optical, magnetic and electrical properties, and their easily tunable shape and size. This flexibility of spinel ferrites and their connection to the material’s magnetic behavior can be investigated by studying a range of spinel ferrite structures. In this study, the magnetic behaviors of cobalt ferrite (CFO) and zinc ferrite (ZFO) nanoparticles were examined using a vibrating sample magnetometer (VSM, bulk magnetometry) and X-ray Magnetic Circular Dichroism (XMCD, atomic magnetometry). The Rietveld refinement of XRD data supported single phase spinel structure, while X-ray Absorption Spectroscopy (XAS), particularly through the Co L-edge XANES analysis, detected both Co2+ and Co3+ ions in CFO, suggesting significant ferromagnetic behavior due to octahedral site occupation. In contrast, ZFO exhibited antiferromagnetic character, with Zn2+ ions in tetrahedral sites, and canted antiferromagnetism manifesting as a hysteresis loop below 300 K, potentially related to lattice distortions or strain. At the atomic scale, XMCD analysis, along with sum rules, estimated the average magnetic moments for cobalt and zinc ferrites to be 3.045 ± 0.1 (1.448 ± 0.1) and 0.657 ± 0.1 (2.12 ± 0.1) μB at temperatures of 300 K (90 K), respectively. However, VSM-based bulk measurements indicated magnetic moments of 2.566 (2.288) and 0.281 × 10−3 (0.6503 × 10−3) μB for CFO and ZFO, respectively, at the same temperatures. The observed variation between bulk and atomic-scale magnetic moments points to complex interstitial interactions within the spinel ferrite’s sublattices. This discrepancy between the atomic-scale and bulk magnetic moments suggests intricate interstitial interactions within the spinel ferrite’s sublattices. These insights into the structural and magnetic intricacies of spinel ferrite nanoparticles enhance our understanding, facilitating the design of cutting-edge spintronic devices.

Sustainable Industrial Wastewater Treatment and Antibacterial Activity using Environmental Friendly Ferrite Nanoparticles

A comparison studies of two unique bimetallic spinel ferrite nanoparticles synthesized by the sol-gel process, namely Co-NiFe2O4 andCu-ZnFe2O4 were investigated. Various characterization approaches were utilized to examine the structural, morphological, magnetic and electrical characteristics of the nanoparticles. Both Co-NiFe2O4 and Cu-ZnFe2O4 nanoparticles formed single-phase spinel structures, according to X-ray diffraction (XRD) research whereas FTIR spectra provided information about the vibrational modes and chemical bonding within the nanoparticles confirmed the presence of desired metal-oxygen bonds chemical bonding within the nanoparticles. The UV-Vis spectroscopy revealed the optical absorption properties of the nanoparticles indicating the presence of energy bandgaps in the visible range. Scanning electron microscopy (SEM) images suggested the uniform and well-dispersed nanoparticles with average sizes in the nanoscale range. Vibrating sample magnetometry (VSM) measurements demonstrated that both Co-NiFe2O4 and Cu-ZnFe2O4 nanoparticles exhibited ferromagnetic behaviour at room temperature. The saturation magnetization values were found to be higher for Co-NiFe2O4 nanoparticles compared to Cu-ZnFe2O4 nanoparticles, suggesting the superior magnetic properties of the former. As a result, ferrites demonstrate promise in industrial wastewater treatment, facilitating efficient heavy metal removal and advanced organic pollutant degradation, contributing to a sustainable and effective solution. The antibacterial efficacy of synthesized bimetallic ferrite nanoparticles against Salmonell typhi, Escherichia coli, Staphyloccus aureus, Bacillus cereus proves that the synthesized ferrite nanoparticles possess a good antibacterial activity against the selected pathogens.

Hydrothermal as a synthesis method for characterization of structural, morphological and magnetic properties of Co–Al ferrite nanoparticles

This work provides a set of structural, morphological, and magnetic results for the CoFe2-xAlxO4 (x = 0.00, 0.25, 0.50, 0.75, 1.00 at %) ferrite nanoparticles synthesized by the hydrothermal route. X-ray diffraction analysis (XRD), Field Emission Scanning Electron Microscopy (FESEM), Energy-Dispersive X-ray Spectroscopy (EDAX), High Resolution Transmission Electron Microscopy (HRTEM), Selected Area Electron Diffraction (SAED) microscopy and Fourier-Transform Infrared Microscopy (FTIR) were used to characterize the structural and morphological features of the prepared magnetic nanoparticles. Rietveld refinement carried out by the Material Analyses Using Diffraction (MAUD) software confirmed the formation of a single-phase spinel structure with no trace of impurity phase. FESEM micrographs showed the appearance of the ferrite nanoparticles with a size distribution in agreement with the data reported by XRD. HRTEM analysis showed the formation of cubic-shaped nanoparticles with dimensions near to the data extracted from XRD. The formation of spinel structure was approved by the FTIR spectra. The magnetic measurements through VSM analysis showed that the incorporation of Al3+ cations into the cobalt ferrite lattices decreases the values of saturation magnetization from about 69 emu/g to near 26 emu/g, which was attributed to the none-magnetic nature of Al3+ cations. The values of the coercive field, on the other hand, indicate a fluctuating trend as a function of Al3+ doping. The coercivity behavior was mainly affected by cation distribution, the variation of anisotropy constant, and the size of crystallites. All the obtained data showed that the magnetic ferrite nanoparticles could be synthesized successfully through the hydrothermal method as a technique that has not been used previously to prepare Co–Al ferrite nanoparticles.

Controlling magnetic and surface properties of cobalt ferrite nanoparticles: A comparison of co-precipitation and solvothermal synthesis methods

Cobalt ferrite (CoFe2O4) nanoparticles have been synthesized using two different wet-chemical methods: co-precipitation and solvothermal. Mesoporous cobalt ferrite nanoparticles were prepared using the co-precipitation method with 4, 6, and 8 wt% of Pluronic P123 and with the solvothermal method with 10, 15, and 20 wt% of PEG-4000. X-ray diffractometry confirmed the formation of a single-phase spinel structure. The saturation magnetization of the nanoparticles increased from 48 to 64 emu/g as the P123 concentration increased from 4 to 8 % wt, and decreased from 72 to 62 emu/g as the PEG-4000 concentration increased from 10 to 20 % wt. Generally, the samples synthesized by the solvothermal method had a higher specific surface area than those prepared by the co-precipitation method. In comparison to other samples, the 10 % PEG-4000 sample had the highest specific surface area and showed the highest level of dye degradation (93 %). The findings demonstrated that the concentration of Pluronic P123 and PEG-4000 had an impact on the saturation magnetization and specific surface area of the nanoparticles.

Enhanced Structural and Morphological Properties of Doped Cobalt Zinc Ferrite

In this study, Mn2+ substituted Co0.8−x Mnx Zn0.2 (where x = 0.0, 0.1, 0.2, and 0.3) ferrites are prepared by a coprecipitation method to study the effect of Mn2+ions on the structural and morphological properties. These ferrites are characterized by X-ray powder diffraction (XRD), and Fourier transform infrared. X-ray diffraction patterns of the prepared samples confirm partial substitution of Mn2+ ions that does not change the basic structure of Co0.8 Zn0.2 Fe2O4. It also provides information about the formation of a single-phase spinel structure without any secondary phase. It is concluded that Co0.6 Mn0.2 Zn0.2 Fe2O4 has a spherical shape with an average particle size of 22.51 nm based on TEM, as confirmed by the XRD analysis. FT-IR analysis confirms the formation of vibrational frequency bands associated with the entire spinel structure. The IR spectra of ferrites show two clear and sharp absorption bands in the range of 442.09 and 620.21 cm-1 in the range of 200–1000 cm-1, which confirms the formation of the ferrite composite.

Temperature dependent magnetic and electrical transport properties of lanthanum and samarium substituted nanocrystalline nickel ferrite and their hyperthermia applications

Structural, optical, temperature dependent magnetic and electrical properties have been investigated for the nanocrystalline NiFe1.97RE0.03O4 (RE = La3+ and Sm3+) compound. Without any signs of a secondary REFeO3 phase, the Rietveld refinement reveals a single-phase spinel structure possessing cubic symmetry for current samples. The decrease in lattice constant has been observed as a result of RE ions substitution. The TEM micrographs reveal nanosized particles with an average size of 35 ± 3 nm and 32 ± 3 nm for La3+ and Sm3+ substituted samples. EDX spectra of both samples show good compositional homogeneity. HRTEM micrographs of both samples show well resolved lattice fringes and their inter-planar spacing matches with that obtained from the Rietveld analysis of the XRD patterns. The concentration of Fe2+ and Fe3+ ions has been estimated from the XPS spectra analysis and it is found to be ∼ 22% and 78% for NiFe1.97La0.03O4 and, 20% and 80% for NiFe1.97Sm0.03O4 compound. The optical energy band gap for rare earth substituted samples is found to be more than that of pure nickel ferrite. The value of saturation magnetization (Ms) and magneto-crystalline anisotropy constant (K1) estimated from the “Law of Approach to Saturation” equation for rare earth substituted samples are found to be less than that of pure nickel ferrite. However, an enhanced value of coercivity has been observed with RE substitution. ZFC (zero field cooling) and FC (field cooling) DC magnetization curves measured at 100 Oe in the temperature range of 60–400 K reveal a combination of weak and intermediate forms of magnetic interaction between the particles for both samples. Temperature dependent analysis of saturation magnetization and coercivity employing modified Bloch’s law and Kneller’s relation supports the nanomagnetic behavior of both samples. Under an AC magnetic field of 14.92 kA/m and frequency 337 kHz, the SAR and ILP values have been found to be ∼ 331 W/g and 4.22 nHm2/kg for NiFe1.97La0.03O4 and, ∼ 241 W/g and 3.21 nHm2/kg for NiFe1.97Sm0.03O4. The dielectric relaxation data have been analyzed at various temperatures ranging from 40 to 300 0C over the frequency range 100 Hz-1 MHz using electrical impedance spectroscopy. The dielectric constant for rare earth substituted samples is found to be more and their AC conductivity is observed to be less than that of pure nickel ferrite. The analysis of temperature dependent AC conductivity employing Jonscher’s power law suggests that the charge carrier’s conduction mechanism of both samples follows the small polaron hopping mechanism below 200 0C, thereafter; it follows the correlated barrier hopping mechanism. The activation energy estimated by imaginary impedance spectra is found to be 0.411 eV and 0.398 eV for NiFe1.97La0.03O4 and NiFe1.97Sm0.03O4 which is more than that of pure nickel ferrite. The Cole-Cole plots at different temperatures suggest the presence of non-Debye-type relaxation. The modeling of Cole-Cole plots with equivalent circuits for both samples confirms the contribution of both grain and grain boundary in electrical conduction. The estimated stretching exponential factor by fitting the modified KWW (Kohlrausch-Williams-Watts) equation to the imaginary modulus curve reveals relatively more dipole-dipole interaction in NiFe1.97Sm0.03O4 than that of the La3+ substituted sample.

Formation of quaternary [formula omitted] epilayers driven by thermally induced interdiffusion between spinel [formula omitted] epilayer and [formula omitted] substrate

Zinc aluminogallate, Zn(AlxGa1−x)2O4 (ZAGO), a single-phase spinel structure, offers considerable potential for high-performance electronic devices due to its expansive compositional miscibility range between aluminum (Al) and gallium (Ga). Direct growth of high-quality ZAGO epilayers however remains problematic due to the high volatility of zinc (Zn). This work highlights a novel synthesis process for high-quality epitaxial quaternary ZAGO thin films on sapphire substrates, achieved through thermal annealing of a ZnGa2O4 (ZGO) epilayer on sapphire in an ambient air setting. In-situ annealing x-ray diffraction measurements show that the incorporation of Al in the ZGO epilayer commenced at 850 °C. The Al content (x) in ZAGO epilayer gradually increased up to around 0.45 as the annealing temperature was raised to 1100 °C, which was confirmed by transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy. X-ray rocking curve measurement revealed a small full width at half maximum value of 0.72 °, indicating the crystal quality preservation of the ZAGO epilayer with a high Al content. However, an epitaxial intermediate β–(AlxGa1−x)2O3 layer (β - AGO) was formed between the ZAGO and sapphire substrate. This is believed to be a consequence of the interdiffusion of Al and Ga between the ZGO thin film and sapphire substrate. Using density functional theory, the substitution cost of Ga in sapphire was determined to be about 0.5 eV lower than substitution cost of Al in ZGO. Motivated by this energetically favorable substitution, a formation mechanism of the ZAGO and AGO layers was proposed. Spectroscopic ellipsometry studies revealed an increase in total thickness of the film from 105.07 nm (ZGO) to 147.97 nm (ZAGO/AGO) after annealing to 1100 °C, which were corroborated using TEM. Furthermore, an observed increase in the direct (indirect) optical bandgap from 5.06 eV (4.7 eV) to 5.72 eV (5.45 eV) with an increasing Al content in the ZAGO layer further underpins the formation of a quaternary ZAGO alloy with a tunable composition.

Structural, magnetic, dielectric and spectroscopic impedance analysis of magnesium iron oxide thin films synthesized by electrodeposition: Effect of preferred orientation

Magnesium iron oxide is the most valuable and versatile spinel system with reduced eddy current and dielectric losses. Spinel ferrites are electrically non-conductive. The electrodeposition is used to synthesize thin films on Cu substrate. A set of five thin films is prepared by varying the in-situ oxidation time (10 min, 15 min, 20 min, 25 min and 30 min) and a fixed deposition time of 25 min. The x-ray diffractometer XRD (phase confirmation), Scanning Electron Microscope SEM (morphological analysis), Fourier transforms infra-red spectroscope FT-IR (bond-formation), impedance analyzer (dielectric-measurements) and vibratory sample magnetometer VSM (magnetic properties) has been utilized to examine the prepared samples. All the studied samples have been found, single-phase spinel structures. XRD shows the pure phase formation of spinel MgFe2O4 at 20 min, 25 min, and 30 min. The exchange of the preferred orientation (PO) from (731) mixed phase to (533) spinel is observed. This change in preferred orientation has been caused the changes in the properties of prepared thin films. The average lattice constant, cell volume, x-ray density and crystallite size of magnesium-iron oxide were found at 8.3814 Å, 588.58 (Å)3, 3.2098 g/cm3 and 24.0392 nm respectively. In FTIR analysis of magnesium-iron oxide, two characteristic spinel bands are observed below 700 cm−1. The SEM result showed a smooth granular structure at 30 min. The normal behavior of the dielectric constant and single semicircle is observed in cole-cole plot. All the prepared thin films are ferromagnetic in nature. At 30 min, a higher dielectric constant, 20.2 (log f = 5) and 162.3 emu/cm3 saturation magnetization. The remarkable dielectric and magnetic findings are promising for using electrodeposited thin films in electronic and spintronic devices.

Exploring Study of Magnetic and Electrical Properties of Tl3+ Doped Co0.5Ni0.5Fe2O4 Spinel Ferrites

Co0.5Ni0.5Fe2-xTlxO4 (x=0, 0.05, 0.1, 0.15, and 0.2) spinel ferrites were prepared via the sol-gel technique. The XRD analysis revealed a single-phase spinel structure. The lattice constant ‘a’ increased from 8.223-8.269Å with doping of Tl+3 due to larger ionic radii of Tl+3 than Fe+3 ions. The mass susceptibility at 300K decreased from 7.46 x 10-3-4.15 x 10-3 cm3/g due tothe weakening of AB interactions followed by a decrease in Curie temperature from 453K to 408K. The electrical permittivity follows the Maxwell-Wagner model and Koop’s theory. The dc resistivity of ferrites at 300K increased from 1.82x109-9.23x109 ?-cm with increasing Tl+3 contents due to increased hopping lengths. The activation energy obtained from Arrhenius plots increased from 0.126 to 0.131eV, increasing Tl+3contents

Hydrothermal synthesis of nickel substituted magnesium ferrites (NixMg1-xFe2O4) and insight into the detailed structural, magnetic and electrochemical properties

A series of single-phase nickel (Ni+2) substituted magnesium Mg-spinel ferrites (NixMg1-xFe2O4) were synthesized by hydrothermal technique and investigated for morphological, structural, magnetic, and electrochemical properties. Experimental characterization techniques revealed that single-phase spinel structure was confirmed by X-ray diffraction, lattice parameter dropped with increasing Ni concentrations, nanoparticles clustered together, the nanoparticles in the SEM micrographs of different sizes are clustered together. Raman spectra showed lower wave numbers, FTIR spectrum showed that peaks move towards lower wave numbers because of nickel's substitution, and this shortens the Fe-O bond hence reduces the lattice parameter, saturation magnetization increased, coercivity decreased, specific capacitance decreased, and loop size increased. These ferrites are suitable for energy storage applications.

Phase-Pure High-Entropy Spinel Oxide (Ni,Fe,Mn,Cu,Zn)3O4 via Thermal Plasma: A Promising Electrocatalyst for Oxygen Evolution Reaction

High-entropy oxide (HEO) has recently emerged as a potential candidate material for electrochemical water splitting, with excellent activity and catalytic stability, as an alternative to the state-of-the-art oxygen evolution reaction (OER) catalyst. The main characteristics of HEO are its unique structure and the ability to tune physical, chemical, and mechanical properties. On tuning these properties, it exhibits high thermal stability, electrical conductivity, and catalytic activity. In this work, by utilizing a carbonaceous thermal plasma with Ar and CO2 as the major plasma-forming gases, a single-phase (NiFeMnCuZn)3O4 high-entropy oxide material has been produced at a discharge power of 12 kW for the first time. The as-synthesized powder was annealed at various temperatures (300, 350, and 400 °C) and characterized using various microscopic and spectroscopic tools. The dynamic light scattering study showed that the as-synthesized powder had a single-phase spinel structure with an average particle size of ∼140 nm. The synthesized materials were subjected to electrocatalytic water oxidation reaction studies. The results show that HEO annealed at 350 °C has an excellent OER catalytic activity in 1 M KOH electrolyte, with an overpotential of 308 mV at a current density of 50 mA cm–2 and a Tafel slope of 54 mV dec–1. Further, Operando-EIS analysis at different potentials evidences that HEO annealed at 350 °C shows less resistance toward the charge-transfer kinetics at the interface. This work provides insight into the rapid synthesis of phase-pure HEO electrocatalysts with excellent performance in energy-related applications.

A Comparative Study on the Effect of Different Sintering Temperatures on Structural and Magnetic Properties of Mg–Zn Ferrite Nanoparticles

The current study involved the synthesis of magnesium zinc ferrite (Mg0.8Zn0.2Fe1.4Al0.6O4) using the sol–gel method. Various techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier Transform Infrared (FTIR), vibrating sample magnetometer (VSM), and radiofrequency (RF) induction were utilized to analyze the properties of the synthesized ferrite nanoparticles. The objective was to examine how different sintering temperatures affected the structural and magnetic characteristics of Mg0.8Zn0.2Fe1.4Al0.6O4. The XRD analysis confirmed the presence of a well-defined single phase crystalline structure with a spinel arrangement. Increasing the annealing temperature resulted in larger nanoparticles, ranging from 28.38 nm to 30.14 nm. SEM provided information about the morphology, agglomeration, and grain size of the ferrite, revealing a grain size ranging from 326 nm to 485 nm. The FTIR spectroscopy indicated a single-phase spinel structure for the prepared sample. The magnetic properties of the sample were evaluated using VSM, showing a maximum magnetization of 45.6 emu/gm and the least coercivity of 90 Oe at an annealing temperature of 900 °C. RF induction at a frequency of 108 kHz exhibited superior results for the sample annealed at 900 °C compared to those annealed at 700 °C and 800 °C. At this frequency, the specific absorption rate (SAR) value was high, making it suitable for magnetic hyperthermia applications. The prepared magnesium zinc ferrite demonstrated suitability for both low and high frequency devices, and it could be employed in various technological applications, including microwave devices, inductor cores, transformers, and other electronic devices.

Structural, optical, and electrical properties of Mn0.9La0.1Fe2O4 nanocrystalline ferrites and its synthesis through sol-gel method

This work reports the formation of La-doped nano-crystalline manganese ferrite Mn0.9La0.1Fe2O4 through sol–gel route and examined using XRD and dielectric spectroscopy techniques. The single-phased cubic spinel structure of the ferrite is supported by X-ray diffraction (XRD). The mean crystallite dimension appraised from XRD data has been found to be 21 nm and 11 nm for un-doped and La3+ doped MnFe2O4, respectively, along with a significant rebate in the optical band gap. At room temperature, the frequency-dependent dielectric properties were studied in the frequency range (42 Hz − 5 MHz). The dielectric constant of both the samples narrowly lowers with enhancing frequency and, consequently, shows exemplary dielectric dispersion. The AC-conductivity of the un-doped samples enhances with increasing frequency while it decreases with doping. The dispersion in ac-conductivity (σac) and dielectric properties imply the ordinary dispersion of Maxwell-Wagner type due to the process of hopping of electrons between the Fe2+ and Fe3+ ions and interfacial polarization. The band gap of energy is evaluated with the help of the UV–visible spectra and found to be decreased when La3+ doped with MnFe2O4 ferrite.

Hydrothermal synthesis of cobalt substitute zinc-ferrite (Co1-xZnxFe2O4) nanodot, functionalised by polyaniline with enhanced photocatalytic activity under visible light irradiation

Fabrication and development of effective visible-light-responsive photocatalysts are required to tackle critical environmental issues. The aim of this study was to develop a nanocomposite material with improved photocatalytic activity for the degradation of industrial dyes such as Reactive Orange-16 (RO-16), Reactive Blue (RB-222), Reactive Yellow-145 (RY-145), and Disperse Red-1 (DR-1) without the need for a post-separation process after use. Here we report the hydrothermal synthesis of nanodots of Co1-xZnxFe2O4 (x = 0.3, 0.5 and 0.7), coated with polyaniline, by in situ polymerization. The Co1-xZnxFe2O4 nanodots, coated with polyaniline (PANI) nanograins, facilitated optical properties by easily capturing visible light. X-ray Diffraction (XRD) patterns and Scanning Electron Microscopy (SEM) images have confirmed the single-phase spinel structure of Co1-xZnxFe2O4 nanodot and nano-pore size of the Co1-xZnxFe2O4/PANI nanophotocatalyst. The specific surface area of the Brunauer–Emmett–Teller (BET) of the Co1-xZnxFe2O4/PANI photocatalyst was determined to be 24.50 m2/g by multipoint analysis. The final Co1-xZnxFe2O4/PANI (x = 0.5) nanophotocatalyst showed high efficiency in the catalytic degradation of toxic dyes (∼98% within 5 min), with good mechanical stability and recyclability under visible light irradiation. The nanophotocatalyst was re-used and its efficiency was largely maintained, even after seven cycles (∼82%) of degradation. The effects of various parameters, such as initial dye concentration, nanophotocatalyst concentration, initial pH of dye solution, and reaction kinetics were studied. According to the Pseudo-first-order kinetic model, photodegradation data followed the first-order reaction rate (R2 > 0.95) of degradation of dyes. In conclusion, a simple and low-cost synthesis process, speedy degradation and excellent stability of polyaniline-coated Co1-xZnxFe2O4 nanophotocatalyst could be used as a promising photocatalyst for dye-wastewater treatment.

Impact of shape and size of particles on the magnetic properties of chromium doped cobalt ferrite

The hydrothermal method was used to synthesize CoCrxFe2−xO4 (x = 0, 0.2, 0.4, 0.6, 0.8 at %) nanoparticles. X-Ray Diffraction (XRD) analysis indicates that nanoparticles have a single-phase spinel structure. The lattice constant (a) was calculated by the Rietveld method through MAUD program. The crystallite size (D), mean ionic radii of A and B sites, bond lengths, interionic bond angels and distances of samples were also calculated. Variation of structural parameters agrees with the cation distribution determined in the magnetic study section. The FESEM images confirmed the data extracted from XRD analysis. The change of particles' shape from spherical to octahedral by Cr doping was also observed. The particles’ size of all the samples was studied by drawing the size distribution plots. It was indicated that the size of ferrite particles was varying in the range of 21–110 nm. Increment of Cr3+ content caused the saturation magnetization to be declined, while the coercive field illustrated an opposite behaviour. The effect of size and shape of particles as well as the cation distribution were key factors employed to justify the magnetic properties of Co–Cr ferrite structures. The novel outcome of this work is that the coercive field of the ferrite samples can be tailored as a parameter for high coercivity-needed applications by the effect of shape and size of particles.