Increase In Magnetic Moment Research Articles

Doping effects in strontium hexaferrite: Theoretical and experimental analysis

Hexagonal ferrites based on SrFe12O19 (SFO) are vital materials in the field of permanent magnets, valued for their cost-effectiveness and reliable magnetic properties, making them a more affordable alternative to rare-earth permanent magnets. This study focuses on understanding the doping effects of commonly used elements in SFO system. DFT calculation results show that doping La or La-Co can enhance the phase stability of SFO, in which Co has a preference for the 4f1 sites of Fe. The total magnetic moment was observed to slightly decrease with La doping, whereas it exhibited an increasing trend with La-Co and La-Ca-Co co-doping and the largest increase of 6.5 % can be obtained in Sr2LaCaFe44Co4O76 (SLCFCO). The increase in the total magnetic moment is mainly attributed to the smaller antiferromagnetic moment of Co than that of Fe on 4f1 sites, as well as the reduction in the antiferromagnetic Fe moments at 4f1 and 4f2 sites. The total density of states indicates a transition from semiconductor behavior to a metallic character both in the La-Co and La-Ca-Co doped versions. The experimental results validate the theoretical predictions, confirming enhancements in magnetic performance. The saturation magnetization increased from 63.86 Am2/kg in SrFe11.7O19 (SFO) to 67.53 Am2/kg in Sr0.4La0.4Ca0.2Fe10.5Co0.5O19 composition. These findings provide a vital understanding of tuning the magnetic and electronic properties in doped SFO, which will enable the development of advanced applications in magnetic materials.

Impact of Gd doping on structural and magnetic characteristics of SrFeO3 perovskite nanomaterial

The SrFeO3nanoparticles doped with 5% and 10% Gd were synthesized using the solution combustion method. The phase formation of the synthesized nanoparticles was confirmed by powder x-ray diffraction analysis. Field emission scanning electron microscope and HRTEM were employed to examine the morphology of the samples, revealing well-ordered, agglomerated nanoparticles. Energy dispersive x-ray spectroscopy analysis was conducted on all samples, confirming the presence of the desired elements. X-ray photoelectron spectroscopy confirmed the presence of mixed oxidation states of Fe3+and Fe4+. Magnetization studies, performed using a SQUID magnetometer, showed ferromagnetic behaviour in all samples, with a significant increase in magnetic moment observed with higher Gd doping. The enhanced magnetic moments and reduced coercivity in Gd-doped SrFeO3suggest that these materials could be suitable for spintronic applications.

Ortho to para hydrogen conversion over bimetallic iron and cobalt catalysts

The catalytic conversion of ortho-hydrogen (o-H2) to para-hydrogen (p-H2) serves as a crucial step in the storage of liquid hydrogen. A variety of iron-cobalt bimetallic catalysts (FCO) were synthesized using a precipitation method, incorporating diverse levels of Co doping into Fe-based catalysts. The effects of Co doping on the crystal structure, porosity, and magnetism of FCO catalysts were studied by XRD, N2 physical adsorption, FTIR, XPS, and VSM analyses. The efficiency of ortho-para hydrogen conversion over FCO at 77 K was evaluated. It was found that the catalyst’s lag coefficient was significantly improved by Co doping, leading to an increase of magnetic moment. The catalyst of FCO-5 with a Fe/(Fe + Co) molar ratio of 0.5 exhibited the highest activity in ortho-para hydrogen conversion. The corresponding conversion rate, outlet p-H2 content, and the reaction rate constant were 99.2%, 49.7% and 291.7 mol·L−1·s−1, respectively, under a gas hourly space velocity of 5400 h−1.

Tuning Magnetic and Semiconducting Properties of Cr-Doped CaTiO3 Perovskites for Advanced Spintronic Applications

The physical properties of perovskite-type materials are sensitive to their chemical composition and crystallographic structure, which makes them highly versatile for various advanced technological applications. In this theoretical study, density functional theory (DFT) is employed to investigate the electronic properties of the perovskite-like material CaTiO3, focusing on the substitution of Ti4+ with the magnetic transition metal Cr4+. The results reveal a systematic increase in the effective magnetic moment and a gradual decrease in the bandgap with increasing Cr4+ content in the CaTi1−xCrxO3 system (x = 0.0, 0.25, 0.5, 0.75, 1.0). The interactions between electronic orbitals associated with Ti-O-Cr inter-octahedral bonds modify the magnetic response of the material, leading to hybridizations between valence and conduction states that alter its semiconductor character. This tunability in electronic and magnetic properties underscores the potential of these materials for applications in spintronics. This study offers novel insights into the design of new magnetic semiconductor materials with tailored functionalities, contributing to the development of next-generation spintronic devices.

The role of Cu element in Fe9.4Co6.7Ni6.6Mn0.9V0.9Cu2.4 magnetic high-entropy alloys

Spark plasma sintering (SPS) technology has obvious advantages in the preparation of high entropy alloys (HEAs) with high mechanical properties, but the mechanism of their magnetic enhancement is not clear. In this work, HEAs with high saturation magnetization (Ms) and excellent mechanical properties were designed and prepared. The properties of Fe9.4Co6.7Ni6.6Mn0.9V0.9 HEA were optimized by adding Cu element, and the main phase of the HEAs was (face-centered cubic) FCC phase. The addition of Cu element mitigates the distortion of the FCC phase, resulting in an increase in the intensity of Ms value for the alloy from 118 emu/g to 143.7 emu/g. However, this also leads to a slight reduction in yield strength while still maintaining a high level at 1132 MPa. Theoretical calculations based on first principles indicate that the magnetic enhancement of these alloys is facilitated by an increase in the atomic magnetic moments of their ferromagnetic constituents.

Asymmetric dual-metal-hybridization in dual-atom dimers trigger a spin transition for electrochemical degradation from nitrate to ammonia

The dual-atom dimer with half-filled 3d orbital demonstrates a great advantage in electrochemical degradation from nitrate to ammonia, because their binding interaction and electron transfer between reactants and active sites are spin-dependent. Herein, we suggest a local structure distortion caused by a bimetallic hybridization to regulate the spin configuration from low to high by implanting one Fe atom into the Mn/Mn dimer on holey nitrogen-doped graphene, which makes the Mn magnetic moment increase to 3.31 μB from 0.48 μB. Meanwhile, the activation energy of the formed *NOH at rate-limiting step can be decreased to 0.79 eV, which is obviously lower than the pristine Fe/Fe (1.38 eV) and Mn/Mn (1.12 eV) dimers. These findings enlighten an intriguing strategy to enhance the reactive activity of dual-atom catalysts by regulating their spin configuration.

First-principles study of the structure, magnetism, and electronic properties of the all-Heusler alloy Co2MnGe/CoTiMnGe(100) heterojunction.

Based on first-principles calculations in the density functional theory, we systematically investigated the possible interface structure, magnetism, and electronic properties of the all-Heusler alloy Co2MnGe/CoTiMnGe(100) heterojunction. The calculation indicated that the Co2MnGe Heusler alloy is a half-metal with a magnetic moment of 4.97μB. CoTiMnGe is a narrow-band gap semiconductor and may act as an ultra-sensitive photocatalyst. We cannot find an "ideal" spin-polarization of 100% in CoCo termination and MnGe termination. Due to the interface interaction, the direct magnetic hybridization or indirect RKKY exchange will be weakened, leading to an increase in the atomic magnetic moment of the interfacial layer. For eight possible heterojunction structures, the half-metallic gaps in the Co2MnGe bulk have been destroyed by the inevitable interface states. The spin-polarization value of 94.31% in the CoCo-TiGe-B heterojunction revealed that it is the most stable structure. It is feasible to search for high-performance magnetic tunnel junction by artificially constructing suitable all-Heusler alloy heterojunctions.

The effect of different transition metal dopants on the magnetic properties of armchair antimonene, phosphorene, and their binary nanoribbons

Binary antimonene-phosphorene, a novel two-dimensional material with a medium band gap, high carrier mobility, and environmental stability, has attracted growing attention due to its wide applications in spintronics. Using density functional theory, we comprehensively investigate and compare the structural and magnetic properties of armchair Sb, P, and binary SbP nanoribbons doped with 3d transition metal atoms (Ti, Cr, Mn, Fe, Co, and Ni) with various concentrations of dopant atoms. We investigated magnetic properties, including magnetic moment, spin polarization, and spin density. It was found that the magnetic properties for single P and Sb nanoribbons do not depend on the substitution position of TM atoms. In contrast, for binary SbP nanoribbons, the substitution of TM atoms in P or Sb positions leads to different behaviors. For example, the magnetization for substitution of Fe and Co atoms in the P position of the binary SbP nanoribbon will be greater than those of the Sb position, but for other impurity atoms, the magnetization of the binary SbP nanoribbon does not strongly depend on the substitution position. The results show that with increasing the number of impurity atoms in the nanoribbon, the magnetic moment increases, except for the nickel atom in the Sb position of the SbP nanoribbon, in which the nanoribbon prefers the ferrimagnetic state. Also, the spin density results show that the magnetism of the doped systems is mainly attributed to the dopant atoms, and the neighboring atoms have a negligible contribution. The findings of antimonene-phosphorene nanoribbons doped with TM atoms may have potential applications in spintronic nanodevices.

Features of magnetic structure and properties of ceramics (1 − x)Pb(Fe1/2Nb1/2)o3—xPb(Fe2/3W1/3)o3

We studied solid solutions of the system (1−x)PbFe1/2Nb1/2O3 - xPbFe2/3W1/3O3 using X-ray and Neuron diffraction, and Mössbauer spectroscopy. To obtain ceramics, we used the method of two-stage solid-phase synthesis and sintering according to the conventional ceramic technology. Pure solid solutions of the (1−x)PbFe1/2Nb1/2O3-xPbFe2/3W1/3O3 system were obtained. A deviation of the unit cell parameters from the Vegard rule was revealed, which indicates stratification of the structure into microregions differing in composition. The introduction of PbFe2/3W1/3O3 into the system led to partial ordering (clustering) of cations in the B position. An increase in magnetic moment with growing amount of PbFe2/3W1/3O3 was shown.

Verification of ultrafast spin transfer effects in iron-nickel alloys

The optical intersite spin transfer (OISTR) effect was recently verified in Fe50Ni50 using extreme ultraviolet magneto-optical Kerr measurements. However, one of the main experimental signatures analyzed in this work, namely a magnetic moment increase at a specific energy in Ni, was subsequently found also in pure Ni, where no transfer from one element to another is possible. Hence, it is a much-discussed issue whether OISTR in FeNi alloys is real and whether it can be verified experimentally or not. Here, we present a comparative study of spin transfer in Fe50Ni50, Fe19Ni81 and pure Ni. We conclusively show that an increase in the magneto-optical signal is indeed insufficient to verify OISTR. However, we also show how an extended data analysis overcomes this problem and allows to unambiguously identify spin transfer effects. Concomitantly, our work solves the long-standing riddle about the origin of delayed demagnetization behavior of Ni in FeNi alloys.

Intrinsic origin of room temperature ferromagnetic ordering in (In0.97-xCoxMg0.03)2O3 thin films

The (In0.97-xCoxMg0.03)2O3 films with different Co concentration are prepared using RF magnetron sputtering. The XRD and XPS measurements show that the films are highly oriented and both Co and Mg elements present valence state of +2. The EXAFS spectra show that only substitutional Co ions exist in the film with x = 0.02. However, the films with higher Co concentration (x > 0.02) form separate phases of substitutional Co and metallic Co clusters. All the films exhibit n-type conductivity and the carrier concentration firstly decreases and then increases with Co doping. The transport mechanisms are dominated using Mott variable range hopping at low temperature and Hard bandgap hopping at high temperature. The Co dopant can effectively alter the MR characters, which undergoes a clear transition from negative MR to positive MR. All the films exhibit room temperature ferromagnetic hysteresis loop. Clear increase of ferromagnetic hysteresis loop and saturation magnetic moment are observed due to the incorporation of Co ions. The ferromagnetism is ascribed to oxygen vacancies-induced bound magnetic polarizations. The relative percentage of substitutional Co ions decrease with Co doping, which leads to the decreasing of number of bound magnetic polarons induced by oxygen vacancies, and then weaken the Ms.

Enhanced orbital magnetic moment of Co film grown on Fe3O4(001)

We investigate the magnetic and electronic properties of Co films on Fe3O4(001) achieved through epitaxial growth using magnetron sputtering. X-ray magnetic circularly dichroism measurements characterize the atomic magnetism. Compared to Co films on the MgO substrate, Co on Fe3O4 exhibits a 96% enhancement in orbital magnetic moment (from 0.25 to 0.49 µB/atom) and an increase in spin magnetic moment (from 1.37 to 1.53 µB/atom), resulting in an increased mratio(ml/ms) from 0.18 to 0.32. This enhancement of the orbital moment emerges as a consequence of the interface interaction between Co and Fe3O4. Density functional theory calculations attribute this heightened orbital magnetic moment to the robust electronic exchange interactions. Our findings not only offer insights into the modulation of magnetic and electronic characteristics in Co-based magnetic heterostructures but also provide valuable implications for the potential application of magnetic oxide/ferromagnetic heterostructures in future spintronic devices.

Interfacial negative magnetization in Ni encapsulated layer-tunable nested MoS2 nanostructure with robust memory applications.

Combining interfacial interactions and layer-number tunability, the evolution of magnetism in low-dimensional diamagnetic systems like MoS2 is indeed an interesting area of research. To explore this, Ni nanophases with an average size of 12 nm were encapsulated in MoS2 and the magnetization dynamics were studied over the temperature range of 2-300 K. Surprisingly, the newly formed hybrid nanostructure was found to have a negative magnetization state with giant exchange bias that showed a reversible temperature-induced increase in both spin magnetic moment and coercivity. Density functional theory calculations proved an interfacial charge transfer interaction with a spin-polarized density of states. The magnetization state, along with giant exchange correlation among the magnetic clusters, suggested the possibility of robust thermomagnetic memory. The dc magnetization and relaxation, investigated with different measurement protocols, unveiled robust thermoremanent magnetization as a memory effect. The time-dependent magnetization study indicated that contributions from the negative magnetization state along with charge transfer induced spin states are responsible for the memory effect, which can be controlled by both temperature and external field.

The comprehensive review of practical approaches of woe separation based on magnetic impact

The article presents an analytical review of magnetic oil treatment, which is an innovative method for preventing complications such as wax deposits and high viscosity of oil. It is concluded that the magnetic treatment of oil is associated with a change in the electrospin state and the evolution of radical pairs of asphaltenes, which are complex with ferromagnetic particles. This leads to an increase in intrinsic magnetic moments, structural rearrangement of supramolecular asphaltene structures and a change in the rheological parameters of oil. The destruction of the «armor shell» occurs due to the influence of the magnetic field on these complexes, which leads to the prevention of the formation of wax and salt deposits and the acceleration of water coagulation processes. The factors of effective magnetic treatment are oils with a high content of iron compounds, salt ions. The effective parameters of magnetic processing are generalized: high values of magnetic induction (up to 1 T), pulse repetition frequency from 5 to 30 Hz. The main advantages and disadvantages of permanent and alternating magnetic field devices are analyzed. A review of the results of industrial and laboratory studies on magnetic oil treatment is carried out. The maximum efficiency in reducing viscosity is 375%, reducing the deposition rate of paraffin is 87.5%, reducing the mass of wax deposits is 50%, reducing the corrosion rate is 45%. Keywords: magnetic treatment of crude oil; influence magnetic field on the oil; wax deposits; high-viscosity oil; heavy oil.

Structural characterization, electrical and magnetic properties of (In0.97-xFexMg0.03)2O3 films

Structural, electrical, and magnetic properties of (In0.97-xFexMg0.03)2O3 films with different Fe concentration are investigated. The doped Fe ions replace the In1 sites of In2O3 lattice with the mixed-valence of +2 and +3 states and form FeIn1+2VO complex based on the real-space multiple-scattering simulation. The room temperature ferromagnetic hysteresis loop of Fe/Mg co-doped In2O3 films shows ferromagnetic ordering with coercivity Hc of about 150-300 Oe. Obvious increase of ferromagnetic hysteresis loop and saturation magnetic moment with a maximum value of 8.45 emu/cm3 (x = 0.08) are observed due to the more incorporation of Fe ions. All the films exhibit n-type conductive behavior, which are mainly dominated by Mott variable range hopping with strong localization of carriers. Interestingly, the contribution of positive and negative magnetoresistance (MR) strongly correlates with Fe dopant and temperature. It can conclude that the FeIn1+2VO complex based on bound magnetic polaron model plays a key role for achieving the intrinsic ferromagnetism.

Influence of shock waves on bifunctional nickel particles: Enhancing magnetic properties and supercapacitor applications

In the present study, shock-wave impact experiments were conducted to investigate the structural properties of nickel metal powder when exposed to shock waves. Both X-ray diffractometry and scanning electron microscopy were used to evaluate the structural and surface morphological changes in the shock-loaded samples. Notably, the experimental results revealed variations in lattice parameters and cell structures as a function of the number of shock pulses and the increasing volume. The transition occurred from P2 (100 shocks) to P3 (200 shocks). Remarkably, P5 (400 shocks) exhibited attempts to return to its initial state, and intriguingly, P4 displayed characteristics reminiscent of the pre-shock condition. Additionally, significant morphological changes were observed with an increase in shock pulses. Magnetic measurements revealed an increase in magnetic moment for P2, P3, and P4, but a return to the original state was observed for P5. Moreover, the capacitance exhibited an upward trend with increasing shock pulses, except for P5, where it experienced a decline. These findings underscore the significant impact of even mild shock waves on the physical and chemical characteristics of bifunctional nickel particles. This research sheds light on the potential applications of shock wave-induced structural changes in enhancing the magnetic properties and supercapacitor performance of nickel particles.

Structural, electronic, and magnetic study on hematite nanorods: Effect of carbon coating and annealing temperature

In this work, spindle shape α-Fe2O3 nanorods and carbon-coated α-Fe2O3@C nanorods were synthesized using a simple hydrothermal method followed by calcination at a temperature of 600 °C. Morphology, structural, surface, and magnetic properties of the synthesized samples were studied before and after calcination. XRD results prove the formation of a single corundum phase α-Fe2O3 after hydrothermal preparation at 180 °C. The crystallite size of α-Fe2O3 decreases by calcination in contrast with α-Fe2O3@C. Through calcination, meso-size pores were formed as investigated by TEM. These pores are more in α-Fe2O3 nanorods. Using XPS surface analysis, more O-H bonds were found in α-Fe2O3 nanorods. TEM, XPS, and FTIR techniques were used to prove the formation of the Carbon layer on α-Fe2O3@C nanorods. Intensive characterization and the magnetic properties of α-Fe2O3 and α-Fe2O3@C nanorods were also carried out and reported. VSM measurements show an increase in magnetic moment with smaller coercivity and remanence via C-coating and calcination. The Morin transition as investigated using VSM and Mossbauer measurements, appears for pure hematite nanorods after calcination under atmospheric pressure. This transition is suppressed as shown for nanosize particles with c/a of ≥ 2.74 which was also applicable for samples made by other workers.

Structure, morphology, and magnetic properties of Fe microparticles as impact on shock waves

To analyze the stability of the physical and chemical properties of Fe, samples were investigated by subjecting them to shockwaves. The magnetic response of Fe to the external magnetic field mainly depends on the degree of magnetic ordering and the temperature of the sample. Powder X-ray diffraction (PXRD) characterization techniques were employed to analyze the crystallinity and cell volume of the structure obtained from Rietveld refinement. The sample was exposed to a shockwave ∼ 2.2 Mach with a different set of repetitions (such as 50, 100, 150, and 200). Refined data from PXRD shows no structural change in the crystallinity of the system. Williamson-Hall analysis demonstrates that the stress and strain between Fe change during the application of shocks. Thus, a noticeable change in the volume of the unit cell is observed. By subjecting the particles to repetitive shockwaves, their size was reduced. This was confirmed through imaging with a scanning electron microscope (SEM), which compared the particle images before and after the application of shockwaves from different sets. The magnetic field and temperature dependencies were applied to measure the ambient and shocked conditions. The magnetization results indicate an increase in magnetic moment due to the influence of the shockwave conditions. Also, 100 shocks show a transition behavior from ferromagnetic to paramagnetic. Based on its convincing reversible magnetic phase transition behavior, Fe is a potential material for applications in magnetic sensors and spintronics.

Effect of Electron Correlations on the Electronic Structure and Magnetic Properties of the Full Heusler Alloy Mn2NiAl

In this theoretical study, we investigate the effect of electron correlations on the electronic structure and magnetic properties of the full Heusler alloy Mn2NiAl in the framework of first-principles calculations. We investigate the electron correlation effect as employed within hybrid functional (HSE) and also within the DFT+U method with varied values of parameters between 0.9 and 6 eV. The XA-crystal structure was investigated with antiferromagnetic orderings of the magnetic moments of the manganese. It was found that with a growth of the Coulomb interaction parameter, the manganese ions magnetic moment increases, and it reaches the value of 4.15–4.46 μB per Mn. In addition, the total magnetic moment decreases because of the AFM ordering of the Mn ions and a small magnetic moment of Ni. The calculated total magnetic value agrees well with recent experiments demonstrating a low value of magnetization. This experimental value is most closely reproduced for the moderate values of the Coulomb parameter, also calculated in constrained LDA, while previous DFT studies substantially overestimated this value. It is also worth noticing that for all values of the Coulomb interaction parameter, this compound remains metallic in its electronic structure in agreement with transport measurements.

Assessing the stability of Kagome D019-Mn3Ga (0001) surfaces: A first-principles study

Using non-collinear spin-polarized first-principles calculations, we have investigated the properties of the hexagonal D019 (0001) Mn3Ga surface. Two different surface terminations were considered: type-1 and type-2, with opposite chiralities. In the case of pristine surfaces, the Kagome triangular AFM character remains on the surface and in inner layers, with a slight increase in the surface magnetic moments due to the low coordination of the surface atoms. An increase in the remnant out-of-plane FM character compared to the bulk is also noticed. The effect of Ga or Mn vacancies on both surfaces was also investigated. Ga vacancies in the 2nd monolayer are more stable than in other layers. Such vacancies distort the triangular AFM configuration of the neighboring layers. Despite this, the AFM layer-by-layer nature remains. Conversely, Mn vacancies stabilize in the most exposed layer. In this case, the neighboring layers completely lose the triangular alignment. However, Mn atoms rearrange to preserve the AFM layer-by-layer character. Upon evaluating the thermodynamic stability of these surfaces, we observe that the pristine Kagome AFM magnetic surfaces are the most stable. Ga vacancies are the least stable configurations because they break down the super-exchange interaction that holds the Kagome magnetic arrangement. Finally, our calculations show that the Kagome magnetic arrangement at the surface is stabilized by both the magnetic (Mn) and non-magnetic (Ga) atoms. Therefore, it is expected that D019-Mn3Ga will not present low-index reconstructions induced by vacancies.