Papers by Keyword: Magnetic Properties

Abstract: Although magnetic nanoparticles have been widely studied, limited research has compared different ferrite types and synthesis routes for use in hyperthermia-based bioactive glass applications. This study aims to synthesize magnetic materials from two types of ferrites: magnesium ferrite (MgFe₂O₄) and zinc ferrite (ZnFe₂O₄). These ferrite nanoparticles were synthesized using two distinct methods; the conventional solid-state reaction and the co-precipitation method in order to identify the optimal synthesis route and the most suitable type of magnetic material for hyperthermia treatment. The data demonstrated that MgFe₂O₄ powder with synthesis by using the solid-state method consistently presented higher value of magnetic properties compared to those synthesized by co-precipitation method under higher calcination temperature. Moreover, ZnFe₂O₄ powder was found to be unsuitable for use as a precursor in hyperthermia treatment because of its structure typically leads to antiferromagnetic or superparamagnetic behavior. The effect of MgFe₂O₄ containing in bioactive glass was investigated. The oxide precursors of bioactive glass were mixed with varying amounts of MgFe₂O₄ and subsequently melted to form glass at 1400 °C. The phase formation presented SiO₂ was the dominant phase and coexisted with Na₂CO₃, MgSiO₃, Fe₃O₄, Na₂Ca (PO₄)₂SiO₄, Ca₂SiO₄, and Na₄Ca₄Si₆O₁₈. However, the MgFe₂O₄ phase was not observed in all of glass-ceramic samples. This may be due to MgFe₂O₄ decomposed during the high-temperature melting process at 1400 °C. Nevertheless, these magnetic bioactive glass ceramic samples exhibited magnetic properties, which were attributed primarily to the presence of Fe₃O₄.

Abstract: Hybrid magnets integrate permanent and soft magnetic materials, resulting in enhanced magnetic performance suitable for a variety of applications. Neodymium-iron-boron (NdFeB) magnets, known for their high energy output, exhibit limitations at elevated frequencies due to eddy current effects. To address this problem, it is beneficial to combine NdFeB with high-resistivity nickel zinc ferrites (NZF) to optimize their magnetic properties. This study focuses on the synthesis of NZF and the fabrication of NdFeB/NZF hybrid composites with varying ratios of NdFeB-to-NZF (40:60, 50:50, and 60:40) and different configurations. Their structural, microstructural, and magnetic characteristics were analyzed to identify the optimum fraction for the hybrid composite formulations. In this work, a commercially available NdFeB and NZF were synthesized via high-energy ball milling while NdFeB was used for the composite’s fabrication. Among the synthesized samples, the mixture-composites of a 60:40 ratio exhibited the highest saturation magnetization of 43.01 emu/g with a notable Curie temperature of 390 °C. The results indicate that increasing the hard phase of NdFeB enhances both saturation magnetization and Curie temperature in all composite samples. Conversely, the stacked-composites with a 40:60 ratio displayed the highest resistivity at 7.96x10⁶ Ωm, suggesting that a higher proportion of NZF significantly contributes to increased resistivity. The observed enhancements in magnetic properties can be attributed to the exchange spring mechanism between the soft and hard magnetic phases, as well as the larger grain size in the samples, which promotes a greater number of magnetic domains and reduction of the grain boundaries. Thus, it facilitates more efficient domain wall movement in response to the external magnetic field.

Abstract: Graphene is an interesting 2D material to research and develop. The applications of graphene are certainly many and promising, one of which is as a semiconductor device. However, in its development as a semiconductor device, this material still has limitations such as having a zero energy band gap. Many methods and research continue to be carried out to overcome these limitations. One method of researching graphene material for its development is to modify the structure of the material. Modifications that can be made are by providing void defects and substitutions in the structure. Through material computational studies with Density Functional Theory (DFT) based calculations, this research analyzes the impact of the presence of Nitrogen with a pyridinic configuration model on modified graphene sheets. Calculations were carried out on a graphene sheet with a supercell size of 4 x 4 x 1, with the Perdew-Burke-Ernzerhof (PBE) function used as Generalized Gradient Approximation (GGA) to complete the correlation and exchange functions. The results obtained successfully provide information that there is an open energy gap and there is information regarding changes in the properties of graphene material to become a magnetic material. The research carried out has an impact on the further development of graphene.

Abstract: Graphene, with its hexagonal arrangement of carbon atoms, exhibits high electrical conductivity and charge carrier mobility due to its zero bandgap. However, its semi-metallic nature limits its application in semiconductor devices. This study explores the modification of graphene’s electronic and magnetic properties by introducing defects and nitrogen substitutions in its crystal structure using spin-polarized density functional theory (DFT). Structural relaxation showed variations in supercell expansion with increasing nitrogen doping. The DFT results revealed that nitrogen substitution in a 4 × 4 × 1 graphene supercell opened an energy gap, and converting graphene into a p-type semiconductor. Additionally, nitrogen doping induced a magnetic transition, with pyridinic and combined pyrolic-pyridinic configurations showing notable spin polarization. These findings highlight the potential of nitrogen-doped graphene for magnetic and electronic applications.

Abstract: This paper delves into the magnetic properties of transition metal FeNi doping with heavy rare earth (RE) elements (including Gd and Nd) magnetic nanomultilayer films. Through experimental methods such as Vibrating Sample Magnetometer magnetic measurements and Ferromagnetic Resonance, the influence of rare earth element doping on the magnetic properties of FeNi alloy films is systematically analyzed. The experimental results reveal that the addition of rare earth elements significantly alters the saturation magnetization, coercivity, and magnetic anisotropy of FeNi alloys, with notable impacts on their ferromagnetic resonance behavior. This study not only provides crucial insights into the unique structures and magnetic mechanisms of rare earth-transition metal alloys but also offers theoretical support for the development of high-performance magnetic materials.

Abstract: Mössbauer spectroscopy (MS), was used to characterize the synthesized materials prepared from the elemental powders by hydrothermal method which are binary iron-based nanoparticles (NPs) Fe₁₅Co₈₅ and Fe₁₀Co₉₀ alloys. The transmission ⁵⁷Fe Mössbauer spectra were measured at room temperature RT (T~300K), using ⁵⁷Co γ-ray source with an Activity ~ 1.85 GBq (50 mCi). The analysis of Mössbauer spectra curves was by using WinNormos with two subspectra with the “Site” option and then with the “Dist” option in order to learn more about hyperfine interactions and parameters such as isomer shifts IS, quadruple splitting QS and hyperfine magnetic field B_hf. MS results observe only one Zeeman sextet with a relative area of ~77.125% with parameter B_hf = 32.727 T and line width Γ=0.693 mm/s for Fe₁₀Co₉₀, and a relative area of ~84.719% with parameter B_hf = 34.354 T and line width Γ=1.043 mm/s for Fe₁₅Co₈₅ and one broad singlet which confirms the body-centered cubic structure BCC. The main contribution to the spectra comes from the magnetic sextet which is assigned to ferromagnetic FeCo phase which is the dominant one while the singlet is assigned to paramagnetic phase. As a result of the analysis of the distributions hyperfine magnetic field the average values of the hyperfine parameters of the Mössbauer spectra were obtained <B_hf>Fe₁₀Co₉₀ = 28.3363 T and <B_hf>Fe₁₅Co₈₅ = 31.4657 T. Therefore, it is observed that the increasing of the cobalt concentration decreases the hyperfine field. The results observe indicates Co concentration dependence, where for Co-rich alloys (Fe₁₀Co₉₀) the FCC (face-centered cubic structure) contributing to the decrease in B_hf due to the absence of BCC. the obtained NPs most likely to be in disordered structure A2.

Abstract: Utilising an uncomplicated, environmentally friendly strategy to synthesise nanoparticles presents a prospective substitute for dangerous chemical and expensive physical techniques. Therefore, this study was initiated with the objectives of synthesising Co₃O₄ nanoparticles using a facile green route and evaluating their magnetic properties and photocatalytic activities. Spherical Co₃O₄ nanoparticles with dimensions ranging from 8 to 32 nm were successfully produced using garlic extract. Magnetic analysis revealed weak ferromagnetism at low temperatures, with a coercive field of 14×10^-4 T. This low-temperature weak ferromagnetism may be attributed to uncompensated surface spins that form a short-range ordered cluster of spins. However, inside the sample, an antiferromagnetic exchange interaction occurs between non-magnetic tetrahedral Co²⁺ ions and magnetic octahedral Co³⁺ ions. Consequently, an exchange bias field of approximately 8.76 ×10^-4 T was observed. Above the Néel temperature, the thermal energy overcomes the antiferromagnetic ordering, resulting in paramagnetic behaviour at room temperature. Furthermore, the photocatalytic activity of the green synthesised Co₃O₄ nanoparticles demonstrated 55% degradation of methyl orange (MO) dye within 90 minutes. However, more efficient degradation (63% degradation within 90 minutes) of MO was achieved in the presence of a small amount of NaBH₄, which typically functions as a source of electrons to enhance the degradation rate. The photocatalytic (dye degradation) activity of these green synthesised room temperature paramagnetic Co₃O₄ nanoparticles could be applicable for water purification processes.

Abstract: The paper presents research findings on the structure of armchair silicene nanoribbons doped with arsenic (As) by using density functional theory and the quantum simulation program VASP. The identified electrical and magnetic properties include the electronic band structure, electronic density of states, charge density distribution, spin density distribution, and wave function characteristics. The results indicate that the ASiAsNR structure exhibits metallic properties. Near the Fermi level, contributions from both Si and As are predominant, with Si contributing more near the Fermi level and As contributing more below it. There is a notable electronic density of states around the Fermi level. The findings also show that the σ bonds formed by Si-3s, Si-3p_x, Si-3p_y, As-4s, As-4p_x, and As-4p_y orbitals are relatively stronger than the π bonds formed by Si-3p_z and As-4p_z orbitals. Additionally, a distinct correlation is observed between spin-up and spin-down states around the As atoms.

Abstract: In this study beads like nanoparticles of manganese oxide with different doping of iron concentrations from 2% to 10% were deposited on ultrasonically cleaned glass substrate by chemical bath deposition technique. Different analytical techniques including XRD, SEM, DRS and VSM were utilized to analyze the structure, morphology, optical and magnetic properties. XRD analysis confirms the crystallite size of Fe-MnO₂ were between 13.70 nm to 46.46 nm, morphological examination indicated that Fe-MnO₂ have cubic and beads-like structures. SEM have revealed the average grain size of 613.3 nm and non-uniform deposition of thin film, DRS analysis confirms that pure MnO has band gap energy 2.90 eV and is decreased with increasing concentration of iron i.e shifted towards lower band gap energy semiconductor materials, VSM reveals that magnetization increases with increase in iron concentration. The best properties were obtained at 6% iron doping because, with further increase in doping concentration, the structure started to distort.

Abstract: The combined of superparamagnetic properties (magnetite) and surface characteristics (silica), can produce structures with multiple capacities. The preparation of such magnetite-silica core-shell nanoparticles involves high costs in their execution and longer time. In this work, Fe₃O₄@SiO₂ CSNPs were synthesized in two stages to control their size and the possibility of adjusting their characteristics. First, Fe₃O₄ NPs were synthesized by a green method using carob leaf extract, then coating the magnetite nanoparticles with a silica layer was done by using Tetraethylorthosilicate (TEOS) as a silica precursor. X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscope (AFM), Fourier transform infrared, and vibrating sample magnetometer techniques were used to characterize the magnetite-silica CSNPs. TEM images confirms that Fe₃O₄NPS and Fe₃O₄@SiO₂ CSNPs synthesized had a spherical shape and were within 9 and 17 nm. The average crystallite sizes of the synthesized Fe₃O₄ NPs and Fe₃O₄@SiO₂CSNPs were found to be 17.8 nm and 20 nm. The VSM indicated that the magnetization decreased due to being coated with silica.