Impact of Tm3+ and Tb3+ Rare Earth Cations Substitution on the Structure and Magnetic Parameters of Co-Ni Nanospinel Ferrite

Effect of High-Anisotropic Co2+ Substitution for Ni2+ on the Structural, Magnetic, and Magnetostrictive Properties of NiFe2O4: Implications for Sensor Applications

This work reports on the effect of substituting a low-anisotropic and low-magnetic cation (Ni²⁺, 2μ_B) by a high-anisotropic and high-magnetic cation (Co²⁺, 3μ_B) on the crystal structure, phase, microstructure, magnetic properties, and magnetostrictive properties of NiFe₂O₄ (NFO). Co-substituted NFO (Ni_1-xCo_xFe₂O₄, NCFO, 0 ≤ x ≤ 1) nanomaterials were synthesized using glycine-nitrate autocombustion followed by postsynthesis annealing at 1200 °C. The X-ray diffraction measurements coupled with Rietveld refinement analyses indicate the significant effect of Co-substitution for Ni, where the lattice constant (a) exhibits a functional dependence on composition (x). The a-value increases from 8.3268 to 8.3751 Å (±0.0002 Å) with increasing the "x" value from 0 to 1 in NCFO. The a-x functional dependence is derived from the ionic-size difference between Co²⁺ and Ni²⁺, which also induces grain agglomeration, as evidenced in electron microscopy imaging. The chemical bonding of NCFO, as probed by Raman spectroscopy, reveals that Co(x)-substitution induced a red shift of the T_2g(2) and A_1g(1) modes, and it is attributed to the changes in the metal-oxygen bond length in the octahedral and tetrahedral sites in NCFO. X-ray photoelectron spectroscopy confirms the presence of Co²⁺, Ni²⁺, and Fe³⁺ chemical states in addition to the cation distribution upon Co-substitution in NFO. Chemical homogeneity and uniform distribution of Co, Ni, Fe, and O are confirmed by EDS. The magnetic parameters, saturation magnetization (M_S), remnant magnetization (M_r), coercivity (H_C), and anisotropy constant (K₁) increased with increasing Co-content "x" in NCFO. The magnetostriction (λ) also follows a similar behavior and almost linearly varies from -33 ppm (x = 0) to -227 ppm (x = 1), which is primarily due to the high magnetocrystalline anisotropy contribution from Co²⁺ ions at the octahedral sites. The magnetic and magnetostriction measurements and analyses indicate the potential of NCFO for torque sensor applications. Efforts to optimize materials for sensor applications indicate that, among all of the NCFO materials, Co-substitution with x = 0.5 demonstrates high strain sensitivity (-2.3 × 10^-9 m/A), which is nearly 2.5 times higher than that obtained for their intrinsic counterparts, namely, NiFe₂O₄ (x = 0) and CoFe₂O₄ (x = 1).

Role of vanadium ions substitution on spinel MnCo2O4 towards enhanced electrocatalytic activity for hydrogen generation

Improving efficient electrocatalysts (ECs) for hydrogen generation through water splitting is of significant interest in tackling the upcoming energy crisis. Sustainable hydrogen generation is the primary prerequisite to realizing the future hydrogen economy. This work examines the electrocatalytic activity of hydrothermally prepared vanadium doped MnCo spinel oxide microspheres (MC), MnV_xCo_2-xO₄ (V_x-MnCo MC, where x ≤ 0.4) in the HER (hydrogen evolution reaction) process. Magnetization measurements demonstrated a paramagnetic (at high temperatures) to a ferrimagnetic (at low temperatures) transition below the Curie temperature (Tc) in all the samples. The magnetization is found to intensify with the rising vanadium content of MCs. The optimized catalyst V_x-MnCo MCs (x = 0.3) outperformed other prepared ECs with a Tafel slope of 84 mV/dec, a low onset potential of 78.9 mV, and a low overpotential of 85.9 mV at a current density of 10 mA/cm², respectively. The significantly improved HER performance of hydrothermally synthesized V_x-MnCo MCs (x = 0.3) is principally attributable to many exposed active sites, accelerated electron transport at the EC/electrolyte interface, and remarkable electron spectroscopy for chemical analysis (ECSA) value was found ~ 11.4 cm². Moreover, the V_x-MnCo MCs (x = 0.3) electrode exhibited outstanding electrocatalytic stability after exposure to 1000 cyclic voltametric cycles and 36 h of chronoamperometric testing. Our results suggest a feasible route for developing earth-abundant transition metal oxide-based EC as a superior electrode for future water electrolysis applications.

Synthesis and Characterization of Cobalt-Doped Ferrites for Biomedical Applications

Novel materials for biomedical applications are in critical need of time. In the present work, the antibacterial properties of Co_1-x Ni _x Mg _x Fe₂O₄ nanoparticles (NPs) are assessed by the disc diffusion method for the common pathogen, that is, Gram-negative (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus) bacteria. Overnight grown bacterial cultures were individually lawn-cultured on nutrient agar plates. All samples of NP concentrations (2 mg/mL) were prepared in sterile water and dispensed by sonication. Sterile filter paper discs (1.0 mm) were saturated by the (doped CoFe₂O₄) NP solution and incubated at 37 ± 0.1 °C for 24 h. The NPs with a fine size of 30-70 nm of Co_1-x Ni _x Mg _x Fe₂O₄ were achieved using the sol-gel method by doping CoFe₂O₄ initially with Ni and codoping with Mg, and their properties were studied by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier transform infrared techniques. According to the results, Co_0.5Ni_0.25Mg_0.25Fe₂O₄ NPs exhibited potent antibacterial activities against s. aureus having an inhibition zone of 6.5 mm and P. aeruginosa having an inhibition zone of 6 mm as that were examined. The result shows that the bacteriostatic properties of NPs are used for numerous applications such as hyperthermia, antibacterial treatments, and targeted drug delivery.

Influence of Y3+ and La3+ ions on the structural, magnetic, electrical, and optical properties of cobalt ferrite nanoparticles

In the current study, nanocrystalline CoY_0.5xLa_0.5xFe_2-xO₄ (where x = 0.00, 0.02, 0.04, 0.06, 0.08, and 0.10) ferrites have been synthesized via a sol-gel auto combustion process. The synthesized powders were pressed into pellet forms and sintered at 900 °C for 4 h in the air. X-ray diffractometry (XRD) confirmed the single-phase cubic spinel structure of the synthesized samples having the mean crystallite domain sizes ranging from 122 and 54 nm. FTIR spectroscopic analyses revealed two strong bands within the range of 600 to 350 cm^-1, further confirming the cubic inverse spinel structure of the prepared materials. The surface morphologies and composition were investigated by Field Emission Scanning Electron Microscopy (FE-SEM) and Energy Dispersive X-ray (EDX) Spectroscopy. The magnetic hysteresis curves recorded at room temperature exhibit ferrimagnetic behavior. The highest coercivity (Hc∼1276 Oe) was found at a high doping (x = 0.10) concentration of Y³⁺ and La³⁺ in cobalt ferrite. Dielectric constant increase with increased doping concentration whereas real-impedance and dielectric loss decrease with increased in doping concentration and applied frequency. The band gap energy increased from 1.48 to 1.53 eV with increasing Y³⁺ and La³⁺concentrations in the UV-Vis region. The elevated levels of magnetic and dielectric substances in the ferrite nanoparticles suggest that the material could be used for magnetic recording media and high-frequency devices.

Combined Effect of Microstructure, Surface Energy, and Adhesion Force on the Friction of PVA/Ferrite Spinel Nanocomposites

Nanocomposite films based on spinel ferrite (Mg_0.8Zn_0.2Fe_1.5Al_0.5O₄) in a PVA matrix were obtained. An increase in the spinel concentration to 10 wt.% caused an avalanche-like rise in roughness due to the formation of nanoparticle agglomerates. The lateral mode of atomic force microscopy (AFM) allowed us to trace the agglomeration dynamics. An unexpected result was that the composite with 6 wt.% of filler had a low friction coefficient in comparison with similar composites due to the successfully combined effects of low roughness and surface energy. The friction coefficient decreased to 0.07 when the friction coefficient of pure PVA was 0.72. A specially developed method for measuring nano-objects' surface energy using AFM made it possible to explain the anomalous nature of the change in tribological characteristics.

Effect of praseodymium in cation distribution, and temperature-dependent magnetic response of cobalt spinel ferrite nanoparticles

This work reports cation distribution, magnetic, structural, and morphological studies of rare-earth Pr doped cobalt ferrite nanoparticles CoFe_2-xPr_xO₄(x= 0, 0.02, 0.04, 0.06 at%) fabricated by sol-gel auto-combustion method. X-ray diffraction analysis, field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and Fourier-transform infrared (FTIR) microscopy were utilized to study the structural and morphological characteristics of the prepared samples. Rietveld refinement by the Material Analyses Using Diffraction (MAUD) software showed the formation of mono-phase cubic spinel structure with Fd-3m space group; however, there was a trace of impure PrFeO₃phase for the sample CoFe_1.96Pr_0.04O₄(x= 0.06). Cation distribution was inferred from the XRD patterns using MAUD program. FESEM analysis revealed the spherical-shaped particles with dimensions close to the data extracted from XRD analysis and HRTEM images confirmed it. FTIR measurements revealed the presence of two prominent stretching vibrational modes confirming the successful formation of ferrite spinel structure. Magnetic properties of the nanoparticles were measured at two different temperatures 300 K and 10 K. For the low temperature of 10 K a high sensitive measurement method as Superconducting Quantum Interference Device (SQUID) magnetometry was used and Vibrating Sample Magnetometer (VSM) recorded the magnetic data at 300 K. Comparison of the magnetic results exhibited a significant enhancement with temperature drop due to the reduction in thermal fluctuations. Paramagnetic nature of rare-earth ions may be the main reason forM_Sdecrement from 76 emu g^-1(x= 0.0) to 60 emu g^-1(x= 0.02) at 300 K. At 10 K, the estimated cation distribution played a vital role in justification of obtained magnetic results. All the obtained data showed that the synthesized magnetic nanoparticles can be implemented in permanent magnet industry and information storage fields, especially when it comes to lower temperatures.