Increase In Magnetic Moment Research Articles

Effects of Ga on the microstructure and magnetostriction of Fe-Ga alloys for actuators

The microstructure and magnetostrictive properties of Arc melted Fe100-x-Gax alloys (x = 20, 25) were studied. The results of the X-Ray Diffraction study confirm the presence of the A2 and DO3 phases in the body-centered cubic structure, which is consistent with previous findings. The increased lattice parameter of the alloy containing 25% Ga results in an increase in the alloy's total magnetic moment. According to the results of an optical microscopy study, the substitution of more Ga atoms results in an increase in grain size and a decrease in the number of dark pits. Due to interactions between domain walls, the coercivity (HC) of the Fe80-Ga20 alloy is lower than that of its counterpart alloy. Fe atoms' magnetic moments are directly proportional to the distance between them and their nearest neighbours in the local environment, and Ga does interrupt the Fe's nearest neighbours, resulting in an increase in saturation magnetization. The formation of the Ga-rich phase is also responsible for the increase in saturation and remanent magnetization. The alloy exhibited enhanced magnetostriction because of the structure and local symmetry placed at different lattices. Its improved magnetostriction makes the Fe75-Ga25 alloy particularly well suited for use in sensor and actuator applications.

Constructing spin pathways in LaCoO3 by Mn substitution to promote oxygen evolution reaction

Designing efficient oxygen evolution reaction (OER) electrocatalysts is essential for numerous sustainable energy conversion technologies. An obstacle that impedes the development of OER electrocatalysts is the insufficient emphasis on the spin attribution of electrons. Recently, the different spin configuration of reactants and products in the OER has been recognized as the factor that slows down the reaction kinetics. In this work, Mn substitution was introduced to LaCoO3, which brought about lattice expansion and reduced crystalline field splitting energy. This led to the increase in the effective magnetic moment, which triggers the transfer of Co3+ from low to higher spin states. Thus, the hybridization of Co eg and O 2p states across the Fermi level was strengthened. Specifically, with 25 at. % Mn substitution, LaCoO3 transits from a semiconductor to a half-metal, which benefits the spin-oriented electronic transport and resultantly promotes the OER. This method paves the way for the construction of spin pathways in catalysts.

Impact of Disorder on Properties of Vacancies: A Case Study of B2 and A2 Polymorphs of Non-Stoichiometric Fe2CoAl

We have performed an ab initio study of vacancy-induced changes in thermodynamic, structural and magnetic properties of single-phase ferromagnetic Fe2CoAl with a chemically disordered (i) two-sublattice B2 phase or (ii) single-sublattice A2 phase. The two polymorphs of slightly non-stoichiometric Fe2CoAl (Fe27Co14Al13) were modeled by two different 54-atom supercells with atoms distributed according to the special quasi-random structure (SQS) concept. Both the lower-energy B2 phase and a higher-energy A2 phase possess elastic constants that correspond to an auxetic material that is mechanically stable. The properties of vacancies were computed by systematically removing different atoms (one at a time) from the supercells and quite wide ranges of values of vacancy-related characteristics were obtained. The increase in the level of disorder (when changing from the B2 to the A2 phase) results in an increase in the scatter of calculated values. The Fe and Co vacancies have lower vacancy formation energies than the Al ones. The total magnetic moment of the supercell decreases when introducing Fe and Co vacancies but it increases due to Al ones. The latter findings can be partly explained by an increase of the local magnetic moment of Fe atoms when the number of Al atoms in the first neighbor shell of Fe atoms is reduced, such as due to Al vacancies.

Gyromagnetic ratio of oriented hcp Co1−x Ir x soft magnetic films

The gyromagnetic ratio γ is a key quantity that determines spin and magnetic properties. In this study, γ is investigated via the electric detection of ferromagnetic resonance and first-principles calculations for c-axis oriented hcp-Co1−x Ir x () soft magnetic films with easy-plane magnetocrystalline anisotropy. γ increases linearly from 19.13 GHz kOe−1 for pure Co film to 19.32 GHz kOe−1 at x= 0.23, which is in agreement with the calculated result. The calculations reveal that the primary reason for the variation of γ is the different trends in the spin and orbital magnetic moments of the neighboring Co atoms of Ir, especially the linear increase of the latter. An investigation into the electronic structure indicates that the increase in these orbital magnetic moments is due to the appearance of 3d unoccupied minority states moving towards the Fermi level, which is induced by the local lattice distortion centered at Ir. Our findings provide the important γ data for the applications of CoIr soft magnetic films in high-frequency electromagnetic and spintronic devices, and will provide guidance in the understanding of the dynamic magnetic properties in disordered binary magnetic alloys.

Thermal stability of interfacial mixed layers in c-Ni/a-Zr multilayer during annealing: Structural and magnetic properties

Annealing of crystalline multilayers composed of two miscible elements usually causes interfacial mixing of the constituent atoms, possibly leading to the formation of binary alloys at the interfaces. Magnetron sputtered c-Ni/a-Zr multilayers deposited at room temperature were vacuum annealed isochronally at 200 °C and 400 °C to observe thermal stability of the interfaces constituting the crystalline/amorphous multilayers. Control over the interfacial behaviour can aid the formation of materials with novel properties. The resultant changes in structural and magnetic properties of the multilayers were investigated in detail through X-ray Reflectivity, Polarized Neutron Reflectivity, SIMS and SQUID-based magnetization measurement techniques. The compositional variations in the amorphous mixed layers formed at the Ni-on-Zr and Zr-on-Ni interfaces due to atomic transport, were carefully observed as a function of annealing. Interface widths proceeded to increase with annealing at the expense of the Ni and Zr layers. The Ni-on-Zr interface was seen to be unstable at both temperatures; but the overall response of the interfaces to atomic diffusion was more pronounced when the multilayers were annealed at 400 °C. Under conditions of supersaturation of atoms within restricted spaces of the interfacial layers and the limited availability of components within the multilayer, unexpected demixing effects were observed at both the interfaces. A large increase in magnetic moment obtained after annealing at 400 °C, was attributed to the high densification of the Ni layers as well as to the incorporation of Ni crystallites into the Zr-on-Ni interface layers.

Interactions and electronic properties of adatom/Gra/adatom sandwich complexes

Optimization of graphene-metal contact materials with excellent performance has motivated extensively studies of metal-graphene interactions. Metal/Graphene/Metal (M/Gra/M) complexes can be fabricated by intercalating foreign elements into interface between graphene and its substrate. As a result, intercalation has been proved to be the most efficient method to modify electronic property of graphene. By using density functional theory (DFT) calculations combined with quasi-atomic minimal basis orbitals (QUAMBOs) method, we systematically study interaction and electronic property of M/Gra/M sandwich complexes. Charge transfer and bond order analyses based on QUAMBOs approaches show that interaction between transition metal adatoms and graphene is much stronger than interaction between simple metal adatoms and graphene. Our calculated results suggest that magnetic moment is noticeable enhanced while electronic dipole moment is significantly reduced for M/Gra/M complexes. The increase of magnetic moment is mainly attributed to metal adatoms. Besides, the depletion of dipole moment is ascribed to anti-parallel electronic dipole moment in metal adatoms for high symmetry M/Gra/M sandwich complexes. We believe M/Gra/M sandwich structures can be of great interest for applications as spin transport and magnetic storage devices.

Adsorption of habitat and industry-relevant molecules on the MoSi2N4 monolayer

The adsorption of various environmental gas molecules, including H2, N2, CO, CO2, O2, NO, NO2, SO2 H2O, H2S, NH3 and CH4, on the surface of the recently synthesized two dimensional MoSi2N4 (MSN) monolayer has been investigated by means of spin-polarized first-principles calculations. The most stable adsorption configuration, adsorption energy, and charge transfer have been computed. Due to the weak interaction between molecules studied with the MSN monolayer surface, the adsorption energy is small and does not yield any significant distortion of the MSN lattice, i.e., the interaction between the molecules and MSN monolayer surface is physisorption. We find that all molecules are physisorbed on the MSM surface with small charge transfer, acting as either charge acceptors or donors. The MSN monolayer is a semiconductor with an indirect band gap of 1.79 eV. Our theoretical estimations reveal that upon adsorption of H2, N2, CO, CO2, NO, H2O, H2S, NH3 and CH4 molecules, the semiconducting character of MSN monolayer is preserved and the band gap value is decreased to ~1.5 eV. However, the electronic properties of the MSN monolayer can be significantly altered by adsorption of O2, NO and SO2, and a spin polarization with magnetic moments of 2, 1, 2 μB, respectively, can be introduced. Furthermore, we demonstrate that the band gap and the magnetic moment of adsorbed MSN monolayer can be significantly modulated by the concentration of NO and SO2 molecules. As the concentration of NO2 molecule increases, the magnetic moment increase from 1 μB to 2 and 3 μB. In the case of the SO2 molecule with increasing of concentration, the band gap decreases from 1.2 eV to 1.1 and 0.9 eV. Obviously, our theoretical studies indicate that MSN monolayer-based sensor has a high application potential for O2, NO, NO2 and SO2 detection.

Electronic structure of a thermoelectric material: BiCuSO

We investigate transport properties and the electronic structure of BiCuSO, a thermoelectric material which was predicted as a possible parent compound for unconventional superconductivity. For the $p$-type BiCuSO samples studied in this paper, our transport measurements show metallic behavior down to 2 K, and we observe an increase of saturated magnetic moment around 4 K, which could be due to the reorientation of the magnetic easy axis. Using angle-resolved photoemission spectroscopy measurements, we acquired the comprehensive electronic structure of BiCuSO including the predicted flat band, and by carrying out photon polarization dependent measurements we further investigated the orbital characters of bands near the Fermi level. Compared with its sister compound, BiCuSeO, we find the flat band could be the origin of high figure of merit $(ZT)$ value in the $\mathrm{BiCu}Ch\mathrm{O}$ $(Ch=\mathrm{S}, \mathrm{Se})$ family.

Magnetic properties regulation by electric-field for α-Fe2O3/LiTaO3 thin film at room temperature

Ion migration driven by electric-field may cause multiple changes in stoichiometry, defect, and structure, thus provide approach for modulating properties. α-Fe2O3 have attracted tremendous attention as anode materials for lithium ion batteries. The magnetic properties of weakly-ferromagnetic α-Fe2O3/LiTaO3 films can be manipulated non-volatilely at room temperature by the applied room temperature electric-field. The regulation of magnetic properties induced by the room temperature electric-field may relate to the migration effects of lithium ions. A theoretical investigation on the microstructure and magnetic properties before and after the insertion of lithium ion into α-Fe2O3 shows that the insertion of lithium ion induces local structural distortion, charge redistribution and the magnetic moment increase. This study makes a step forward for electric control of magnetism in solid-state ferrite film and provides opportunities for the development of multifunctional structures

Magnetic and electronic properties of Zn-Ni ferrites: First principle calculations, mean-field theory, high-temperature series expansions and Monte Carlo study

The structural, electronic, and magnetic properties of the ZnxNi1-xFe2O4 compounds are studied using several theoretical methods such as first-principle calculations based on density functional theory (DFT+U), Monte Carlo simulations, High temperature series expansions(HTSE) combined with the Padé approximants(PA) and mean-field theory. The total magnetic moment increases and the Curie temperature decreases with Zn substitution. The gap energy results of 1.3 eV obtained using GGA+U are reasonable compared to the available experimental data. The ZnFe2O4 possesses the insulating ground state and antiferromagnetic ordering. The critical exponent γ associated with the magnetic susceptibility is obtained. The dependence of the magnetization and the magnetic susceptibility on temperature is established for ZnxNi1−xFe2O4 using Monte Carlo study.

Non-Fermi liquid behavior and signature of Griffiths phase in Ni–Cr binary alloy

Detailed magnetic, electrical, and thermal property measurements have been carried out on Ni100−xCrx binary alloys, mainly to study the effect of Cr. The following points emerge from this study: with the increase in Cr concentration, magnetic moment and Curie temperature linearly decreased and the ferromagnetic order is completely suppressed at the critical concentration (xcr ≈ 12.16 ± 0.03). The Rhodes–Wohlfarth ratio increases as the concentration approaches xcr, suggesting a weak itinerant ferromagnetic character of NiCr compositions (x < xcr). Analysis of low-temperature electrical resistivity and specific heat data suggests that the spin fluctuation’s contribution increases and the Fermi-liquid behavior breaks down as the concentration approaches xcr. For x ∼ xcr, the dc susceptibility χ(T) deviates from the Curie–Weiss law reminiscent to that of the Griffiths phase. The low-temperature magnetic isotherms of Ni–Cr follow power law, M(H)=M0+dλHλ, and the non-universal exponent (λ) shows a minimum at xcr ∼ 12. Further, temperature dependence of magnetization studies also support the presence of the quantum Griffiths phase, similar to that reported in the Ni–V alloy system. The temperature dependencies of the electrical resistivity, magnetization, and specific heat follow the theoretical predictions of a quantum critical point within experimental uncertainties.

Influence of tungsten substitution on structure, optical, vibrational and magnetic properties of hydrothermally prepared NiFe2O4

A series of single-phase NiFe2O4 powder with different W-doping (0.0 ≤ x ≤ 0.2) has been synthesized using hydrothermal processing route. The change in lattice parameter and magnetic properties with W-doping was correlated with the change in the occupancies of tetrahedral and octahedral sites with Fe(III) ions resulting from competence between Fe(III) and W(VI) ions. The total magnetic moment increases and the lattice parameter decreases with W-doping up to x = 0.1 (Ms = 49.0 emu/g). However, the lattice parameter increases and the total magnetic moment dramatically decreases to 27.0 emu/g with x = 0.2 doping. The microstrain (e) increases with increasing the level of W(VI) ion substitution. The e of pure NiFe2O4 sample is 3.5 × 10–3 and it increases to 9.7 × 10–3 for NiW0.2Fe1.6O4 (x = 0.2). The increase in e is due to the difference in ionic sizes of W(VI) an Fe(III) and the formation of cation vacancies. The latter is formed because W(VI) ion substituted for two Fe(III) ions, so that the produced ferrite will have the general formula; NiWxFe2-2xO4. The band gap slightly increases with increasing the increasing the level of W-doping.

Surface structures of magnetostrictive D03-Fe3Ga(0 0 1)

First-principles total energy calculations and scanning tunneling microscopy experiments were performed to study the surface reconstruction of the magnetostrictive Fe3Ga alloy. The inverse magnetostrictive behavior was evaluated in the bulk by compressing and stretching its lattice parameter, showing an increase in magnetic moments as strain increases. Surface analysis demonstrates two thermodynamically stable surfaces, the (1 × 1) and (3 × 1). The (1 × 1) is an ideal FeGa terminated surface, whereas the (3 × 1) is also FeGa terminated but it has a first-layer Fe atom substituted by a Ga atom every three unit-cells, forming a row-like surface structure. Tersoff–Hamann scanning tunneling microscopy simulations were obtained and compared with experimental results. We found good agreement between theory and experiment, in which the distance between rows is ~12.3 Å. Theoretical findings suggest that the substrate-induced strain may increase the stability of the (3 × 1) reconstruction. Analysis of the magnetic moments in the reconstructions showed that their behavior is affected by a surface effect, as well as by the inverse magnetostriction of the structure. A good understanding of the FeGa surface reconstructions is an important step towards further improvements in magnetic storage devices and sensors.

First-principles investigations of electronic and magnetic properties of Fe2V1-xCrxSi Heusler alloys

Full-Heusler alloys with chemical formula X2YZ (X and Y being 3d and 4d transition metal elements and Z is p-block element) are interesting intermetallics because of their half metallic and spintronics applications. In this paper, the effect of doping of Cr atom at V-site of full-Heusler Fe2V1-xCrxSi (x=0, 0.5, 1.0) on their electronic and magnetic response is studied using full potential linearized augmented plane wave method. It is observed that Fe2VSi and Fe2V0.5Cr0.5Si does not show half-metallic character while Fe2CrSi alloy shows half-metallicity. We observe increase in total magnetic moment with increasing Cr concentration in Fe2V1-xCrxSi. Further, density of states and energy bands are discussed to interpret the half-metallic character in Fe2V1-xCrxSi.

Correlation between Microstructure and Magnetism in Ball-Milled SmCo5/α-Fe (5%wt. α-Fe) Nanocomposite Magnets.

Magnetic nanocomposites SmCo5/α-Fe were synthesized mechanically by high-energy ball milling (HEBM) from SmCo5 and 5%wt. of α-Fe powders. The X-ray diffraction analysis reveals the hexagonal 1:5 phase as the main one accompanied by the cubic α-Fe phase and 2:17 rhombohedral as the secondary phase. The content of each detected phase is modified throughout the synthesis duration. A significant decrease in crystallite size with a simultaneous increase in lattice straining is observed. A simultaneous gradual reduction in particle size is noted from the microstructural analysis. Magnetic properties reveal non-linear modification of magnetic parameters associated with the strength of the exchange coupling induced by various duration times of mechanical synthesis. The highest value of the maximum energy product (BH)max at room temperature is estimated for samples milled for 1 and 6 h. The intermediate mixed-valence state of Sm ions is confirmed by electronic structure analysis. An increase in the Co magnetic moment versus the milling time is evidenced based on the performed fitting of the Co3s core level lines.

Tемпературная зависимость магнитных свойств и магнитополевого поведения тонкопленочных трехслойных Co/Gd/Co систем

The results of studies of the temperature dependences of the magnetic properties and magnetic field behavior of thin-film three-layer Co/Gd/Co system, obtained by ion-plasma magnetron sputtering, are present. The thickness of the cobalt layers is 5.0 nm, and the thickness of the Gd layers, tGd, varies from 3.0 to 10.0 nm. The bulk magnetic characteristics of the samples are measured on a vibrating magnetometer at the external magnetic field oriented parallel to the plane of the samples. The influence of the temperature and Gd thickness on the shape of the hysteresis loops, the values of the magnetic moment m and coercive force are discovered. In particular, with the temperature changes from 100 to 300 K, the decrease of the coercive force is observed. At a temperature above 150 K, magnetic moment increases. With increasing thickness of gadolinium, the value of m decreases.

First principles study of electrical and magnetic properties of two-dimensional ferromagnetic semiconductors CrI<sub>3</sub> adsorbed by atoms

Recent experimental discovery of intrinsic ferromagnetism (FM) in chromium triiodide (CrI<sub>3</sub>) monolayer opens a new way to low-dimensional spintronics. Two-dimensional (2D) CrI<sub>3</sub> monolayer is of great significance for its magnetic and electronic properties. Generally, surface atomic adsorption is an effective way to modify the physical properties of layered magnetic materials. Here in this work, we use the first-principles method based on density functional theory (DFT) to systematically study the electronic structure and magnetic properties of 2D CrI<sub>3</sub> monolayers that have adsorbed other metal atoms (specifically, alkali (alkaline earth) metal (Li, K and Mg), transition metal (Ti, V, Mn, Fe, Co and Ni) and non-metal (N, P, O and S) atoms). Our results show that the metal atoms tend to be adsorbed in the center of the ring formed by the six I atoms and stay at the same height as Cr atoms, while the positions of the optimized non-metal atoms are in the ring formed by the six I atoms and depend on the type of the atoms. The adsorption of atoms (except for Ti and Mn atoms) does not change the intrinsic ferromagnetic semiconducting properties of CrI<sub>3</sub> monolayer. The CrI<sub>3</sub> monolayers with Ti or Mn adsorption are antiferromagnetic semiconductors. Moreover, we find that the adsorption of different atoms regulates the local magnetic moments of Cr atoms. The adsorption of metal atoms increases the local magnetic moments of Cr atoms, but not exceeding 4<i>μ</i><sub>B</sub>. However, the adsorption of non-metallic atoms makes the local magnetic moments of Cr atoms diversified. The adsorption of O and N atoms retain the local magnetic moment of Cr atoms, while the adsorption of P and S atoms increase the local magnetic moment. By combining the projected density of states, we analyze in detail the local magnetic moments of Cr atoms. The increase of the local magnetic moments of Cr atoms is directly related to the charges transferring. Our results provide new ideas for regulating the performance of the magnetism of 2D intrinsic ferromagnetic semiconductor CrI<sub>3</sub>, which will have potential applications in the spintronics in the future.

Dependence of structural/morphological and magnetic properties of LaCoO3 nanoparticles prepared by citrate nitrate auto combustion

Perovskite LaCoO3 nanopowders were synthesized via solution auto-combustion chemical route, using lanthanum and cobalt nitrates as oxidants and citric acid as fuel. Qualitative and Quantitative phase analysis performed by Rietveld refinements indicated the presence of pure single LaCoO3 phase. From fit parameters, goodness of fit “S” parameter (close to 1) and the difference between the experimental and theoretical XRD patterns. FTIR spectra showed two characteristics bands at 408 and 589 cm−1 characteristics of metal oxygen bands vibration, thus confirming the formation of LaCoO3 phase, whereas the strong absorption band at 589 cm−1 was assigned to Co–O stretching vibration and O–Co–O deformation modes of LaCoO3 compound. SEM micrographs clearly revealed quite spherical particles with a mean size in the range 139–178 nm and high tendency to clustering, meanwhile EDAX analysis confirmed the corresponding chemical composition with homogeneous distribution of the constituent elements. A weak paramagnetic order is observed irrespective of F/O ratio, with slight increase of the effective magnetic moment with F/O ratio; 2.72–2.93 μB, due to the presence of more high spin states.

X-Ray Photoelectron Study of the Formation of the Chemical Bond and the Atomic Magnetic Moment in Nickel-Carbon Nanocomposites Modified by d-Metal Oxides

X-ray photoelectron spectroscopy is used to study the modification of Ni/C nickel-carbon nanocomposites with oxides (NiO, CuO, and Fe2O3) in the ratio of 0.5–1.0. Depending on the type of modifier used and its content, the magnetic moment of Ni atoms changes in the nanocomposite, i.e., during the redox process, the nanocomposite structure changes and the interaction between the carbon skeleton and the modifier metal is enhanced. In the presence of electron acceptors, the paired d electrons of the nanocomposite metal become unpaired and move to higher orbitals. This is indicative of self-organization processes in nanostructures, which leads to an increase in the atomic magnetic moment of the metal.

First-Principles Study on the Magnetoelectric and Optical Properties of Novel Magnetic Semiconductor Li(Mg, Cr)P With Decoupled Spin and Charge Doping.

The electronic structures, magnetic and optical properties of Li1±y(Mg1−xCrx) P (x, y = 0.125) are calculated by using the first principles method based on density functional theory. We find that the incorporation of Cr causes the strong hybridization between Li-2s, P-2p, and Cr-3d orbitals, resulting in a spin-polarized impurity band and forming stronger Cr-P polar covalent bonds. Li(Mg0.875Cr0.125)P becomes half-metallic ferromagnetism. The properties of the doped systems can be regulated by Li off-stoichiometry. When Li is deficient, the narrower impurity band and stronger p-d orbital hybridization enhance the half-metallicity. While the half-metallicity disappears, the band gap becomes wider, and the conductivity decreases for Li excess system, but its magnetic moments increase. Comparing optical properties show that the imaginary part of dielectric and complex refractive index function and optical absorption spectrum all have a new peak in the low energy region after Cr doping, and the new peaks are significantly enhanced when Li is deficient. The absorption range of low frequency electromagnetic wave is enlarged, and the energy loss functions show obvious red-shift effect for the doped systems. The results indicate that the properties of Li(Mg,Cr)P can be controlled by Cr doping and Li off-stoichiometry independently, which will benefit potential spintronics applications.