Average Magnetic Moment Research Articles

A High-Entropy B2 Heusler Alloy

The properties of high-entropy alloys containing five or more elements show systematic evolutions with varying valence-electron concentration. This can allow them to be tailored to carry a particular feature or a property. We have prepared a six-component alloy (MnFeCoNiCu)75\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{75}$$\\end{document}Al25\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{25}$$\\end{document}, where MnFeCoNiCu makes up the high-entropy part with e/a=9.0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$e/a=9.0$$\\end{document} and the added 25 at.% Al causes the whole of the material to take up a B2-ordered structure with e/a=7.5\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$e/a=7.5$$\\end{document}. Because the structure becomes ordered, the material partially loses its high-entropy character but acquires a ferromagnetic Heusler-like property with a Curie temperature of 525 K and an average magnetic moment of 0.8 μB\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\upmu _{\ ext {B}}$$\\end{document}. The whole of the system mimics Co3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_3$$\\end{document}Al, which cannot be stabilized under normal conditions.

Anomalous behavior of magnetic linear dichroism in HoFe3(BO3)4 crystal with spiral magnetic ordering

Spectra of magnetic linear dichroism of the optical transition 5I8 → 5F3 were studied in the HoFe3(BO3)4 single crystal as a function of magnetic field directed along the trigonal c axis at the temperature 2 K. It has been found that dichroism in the basal plane appears even in low magnetic field in the easy-axis state of the crystal. This indicates a violation of the axial symmetry of spiral structure of Ho magnetic moments. Moreover, the sign of dichroism is changed with the change of the magnetic field sign both below and above the field of spin-reorientation transition. This could mean that the average magnetic moment of three Ho3+ ions forming the spiral rotates in magnetic field both relative to the c axis and in the ab plane.

The Effect of the Interface Width on the Exchange Interaction Constant between Ferro- and Antiferromagnets

In the approximation of the average spin method, a system of equations for determining the average magnetic moments of atoms at the interface between a ferromagnet and an antiferromagnet is formulated. It is possible to simulate the dependences of interfacial exchange interaction constant Ain on the temperature, antiferromagnetic layer thickness, and interface width by solving the system of equations for an ultrathin Ni/NiO film. It is found that the interfacial exchange interaction constant in a film with a fixed interface width at low temperatures increases with an increase in the thickness of the antiferromagnetic layer. With anincrease in the interface width, the Ain value decreases by a factor of 1.3 and reaches its minimum level.

Boron migration during amorphous to crystalline transformation in CoFeB/MgO multilayers: A reflectivity study

Migration of boron in CoFeB/MgO multilayer during amorphous to crystalline transformation in CoFeB has been studied using Polarized Neutron Reflectivity (PNR) and anomalous Soft X-ray Reflectivity (SXR). PNR gives information about the possible redistribution of B in the multilayer during thermal annealing, as well as about the variation in the average magnetic moment. Sensitivity of the soft X-ray reflectivity to the movement of boron is enhanced by doing a series of measurements with X-ray energy spanning across the K absorption edge of B. Both the PNR and anomalous SXR results clearly suggest that upon thermal annealing, boron prefers to move away from the MgO/CoFeB interfaces, and forms a layer of boride in the middle of the magnetic layer. These results are important in view of the existing ambiguity regarding the role of boron in CoFeB/MgO based magnetic tunnel junctions.

Experimental and computational study on the influence of cobalt substitution on the structural, impedance, electronic, magnetic, and optical properties of pseudobrookite-structured Fe2TiO5.

We report on how Co substitution of the Fe sites of pseudobrookite (Fe2TiO5) influences the crystal structure, high-temperature electric permittivity, impedance, electronic structure, magnetic, and optical properties via experimental and theoretical investigations. The pseudobrookite phase contains two types of octahedral sites, Fe atoms reside on type of the sites while Ti on the others and replacing Fe with Co can have a huge influence on one or more physical properties that can render the material more useful for solar energy applications. X-ray diffraction and high-temperature electric permittivity/impedance were the experimental tools used. A temperature range of 20-300 °C and a frequency range of 100 Hz to 1 MHz were used for studying various types of relaxation mechanism via impedance analysis, including grains, grain boundaries, and interfacial effects. To explore the electronic structure, magnetic, and optical properties from first principles, dispersion-corrected density functional theory (PBE-D2/U) was employed. The structure as well as the electric impedance properties are impacted slightly by the Co substitution of Fe in Fe2TiO5 whereas the electronic structure and magnetic properties are influenced significantly. The bandgap is reduced slightly and the average magnetic moment per Fe ion is reduced upon Co substitution of Fe in Fe2TiO5.

Влияние атомов углерода на магнитный момент в системе Fe-C: расчет из первых принципов

From the first principles, the influence of carbon content on the magnetic moment of the BCC and BCC Fe-C systems was evaluated. The systems Fe-0.40 C, Fe-0.79 C and Fe-1.19 with mass% were considered. It is shown that the tetragonality of the Fe-C system increases linearly with increasing carbon content and is in good agreement with experimental results. The average magnetic moment on Fe atoms also increases linearly with increasing carbon content. At the same time, the magnetic moment of Fe atoms located in the immediate vicinity of carbon atoms is less than in pure iron, and the atoms of the second coordination sphere, on the contrary, have more. It is shown that this is primarily due to the magneto-volume effect, whereas the effect of tetragonal distortion of the lattice is secondary

The influence of carbon atoms on the magnetic moment in the Fe-C system: calculation from the first principles

From the first principles, the influence of carbon content on the magnetic moment of theBCC- and BCC Fe-C systems was evaluated. The systems Fe-0.40C, Fe-0.79C and Fe-1.19C mass% with mass% were considered. It is shown that the tetragonality of the Fe-C system increases linearly with increasing carbon content and is in good agreement with experimental results. The average magnetic moment on Fe atoms also increases linearly with increasing carbon content. At the same time, the magnetic moment of Fe atoms located in the immediate vicinity of carbon atoms is less than in pure iron, and the atoms of the second coordination sphere, on the contrary, have more. It is shown that this is primarily due to the magneto-volume effect, whereas the effect of tetragonal distortion of the lattice is secondary. Keywords: computer simulation, Fe-C, magnetic moment, tetragonality, magneto-volume effect.

СРАВНЕНИЕ РЕЗУЛЬТАТОВ ТЕРМОДИНАМИЧЕСКОГО И ПЕРВОПРИНЦИПНОГО МОДЕЛИРОВАНИЯ НЕУПОРЯДОЧЕННЫХ РАСТВОРОВ СИСТЕМЫ Fe–V

This paper considers the concentration dependences of the average magnetic moment of the Fe–V system and solution enthalpy as a function of the vanadium concentration from 1 to 10 at% for a disordered Fe–V solid solution in an orderly magnetic state using first-principle calculations of the electronic structure in the WIEN2k software package. The results are compared with data obtained using CALPHAD-models in previous studies. A conclusion about the prospects of finding a possible inversion of the short-range order in Fe–V alloys similar to the inversion in Fe–Cr systems has been made on this basis.

Effect of an external magnetic field on the phase states and dynamic properties of the strongly anisotropic antiferromagnet

The effect of an external magnetic field on both the static and spectral properties of a highly anisotropic Ising antiferromagnet with magnetic ion spin S = 1 is studied. It is shown that at sufficiently low fields and large values of the single-ion anisotropy constant, a state with a zero value of the average magnetic moment (at the site), which is characterized by tensor order parameters (QU phase), is realized in the system. A further increase in the magnetic field turns the magnet (via a first-order transition) into the “quasi-ferrmagnetic” state. In this state is characterized by the fact that one of the sublattices is magnetized to saturation, whereas in the second the average magnetic moment (per site) is equal to zero. We called this phase the LS (low spin) phase. A further increase in the field leads to the realization of a ferromagnetic phase. All phase transitions are first-order transitions, as evidenced by the behavior of their spectra of elementary excitations.

Effect of W Addition on Fe-P-C-B Soft-Magnetic Amorphous Alloy

In this work, the thermal behavior, soft magnetic properties, and structure of Fe86-xP11C2B1Wx (x = 0, 0.1, 0.2, 0.4, 0.6, 0.8, 1, 2, and 4) amorphous alloys were researched by several experimental methods and ab initio molecular dynamics. The addition of W improved the thermal stability of the alloy system when the first onset crystallization temperature (Tx1) increased from 655 K to 711 K, significantly reduced the coercivity Hc, and decreased the saturation magnetization Bs. The Fe85.6P11C2B1W0.4 alloy showed optimal soft magnetic performance, with low Hc of 1.4 A/m and relatively good Bs of 1.52 T. The simulation results suggested that W atoms increased the distance of the neighboring Fe-Fe pair, reduced the coordination number, narrowed the gap between the spin-up and spin-down electrons of each atom, and decreased the average magnetic moment of the Fe atoms. This work demonstrates a micro-alloying strategy to greatly reduce Hc while maintaining high Bs.

Non-collinear magnetic structure of the MAX phase Mn2GaC epitaxial films inferred from zero-field NMR study (CE-5:L05)

Zero-field NMR investigations on the 69Ga, 71Ga, and 55Mn nuclei have been performed at 4.2 K on a 100 nm thick epitaxial Mn2GaC(0001) MAX phase film grown on a MgO(111) substrate. This nano-laminated structure consists of ferromagnetic Mn–C–Mn stacks interleaved with monolayers of gallium. A resolved quadrupolar structure of the observed gallium resonances is a fingerprint of a well-defined crystal field confirming high crystal quality. The nuclei of non-magnetic gallium atoms are shown to experience the transferred hyperfine magnetic field of 15.75 T (±0.05 T), which is due to polarization of their 4s electron shell by the magnetic moments of manganese neighbors, evidencing the presence of an uncompensated ferromagnetic moment within the manganese sublattice. The average magnetic moment of manganese was found to be around 2 μB, strongly contrasting with the reported remnant magnetization of only 0.3 μB. Moreover, the 55Mn NMR spectrum indicates the presence of magnetically non-equivalent manganese sites within this structure. The observed features of the 69,71Ga and 55Mn NMR spectra cannot be reconciled with any of the hitherto proposed collinear arrangements of manganese moments and suggest their non-collinear arrangement across a gallium layer. Nevertheless a more advanced study is required to elucidate the detailed nature of magnetic structure in this material.

To the theory of remagnetization kinetics of ferromagnetic nanoparticles. Non linear effects

The paper deals with theoretical study of remagnetization kinetics of a single-domain ferromagnetic particles in an alternating magnetic field, arbitrary directed with respect to the particle axis of easy magnetization. Period of the field is not supposed large as compared with the characteristic time of the particle Neel remagnetization. The nonlinear magnetization of the particle is considered. At the assumption of the particle strong magnetic anisotropy, a new equation for its average magnetic moment is derived.

A study of the crystal structure of a Tb-Dy-Fe alloy during annealing via rietveld analysis

The crystal structure and magnetic structure of Tb-Dy-Fe compounds before and after annealing heat treatment were researched, in order to further study the influence factors on the magnetic performance besides the orientation and phases. The Rietveld method was used to refine the structural data and obtain small changes in the structure. The results confirm the existence of tetragonal and rhombohedral phases at room temperature, which is consistent with previous findings. Both samples had tetragonal structures and rhombohedral distortion structures at room temperature. The lattice constants of the rhombohedral structure were a = 5.18160 Å and c = 12.72178 Å, while the volume diagonal of the tetragonal cell was 12.69513 Å, indicating the amount of change between the two structures. The volume proportion of the hexagonal phase increased from 25% to 51% after heat treatment. The refinements made on the basis of the neutron patterns indicated that the refined Tb/Dy and Fe moments are antiparallel, while the average atomic magnetic moment of Tb/Dy increased in the annealed state compared with that in the as-cast state. By combining all the analytical results, we discussed the effect of structural distortion on the magnetostriction of Tb-Dy-Fe.

Models of Ni- and Co-ion occupation in LiNi0.5Co0.5PO4 orthophosphate and its magnetic structure

The neutron diffraction, magnetic and heat capacity measurements have been carried out to study the polycrystalline sample LiNi0.5Co0.5PO4 prepared by the glycerol-nitrate synthesis method. Models of Ni- and Co-ion occupation the 4c octahedral position in a crystal structure LiNi0.5Co0.5PO4 are calculated for a paramagnetic state. The best model is the Ni- and Co-ions occupy the 4c site in Pnma patent space-group in sequence Ni–Co–Ni–Co or Co–Ni–Co–Ni. It is shown that nickel ions form ab planes alternating with the planes of cobalt ions in the direction of the c crystallographic axis. At 7 K, an average magnetic moment of 3d-ions is equal to 1.90 (9) μ B. The moments are ordering antiferromagnetically and parallel to the bc plane decreasing to zero at 15 K. In the high-spin state a temperature dependence of the Ni2+/Co2+ ion-magnetic moment is well described within the 2D Ising model with order parameter β = 0.198 and Néel temperature T N = 14.1 (1) K, obtained from heat capacity data. This temperature agrees well with T cr = 14.3 (2) K, determined with magnetic measurement. Maybe the short-range magnetic order exists in LiNi0.5Co0.5PO4 over temperature region (14–16) K, that is confirmed by the maximum on a temperature dependence of the magnetization at 16.1 (5) K.

Electromagnetic Properties of Polypyrrole Metallic Magnetic Nanocomposites: First‐Principles Study

AbstractConductive polypyrrole (PPy) is an excellent polymer material for microwave absorption, which is vital for reducing electromagnetic interference (EMI) for electronic devices. To improve the microwave absorption capability and enhance the thermal stability and mechanical ductility of conductive PPy, metallic magnetic nanoparticles can be added to form PPy nanocomposites. In this paper, we present the first study to compute the electromagnetic properties of PPy nanocomposites based on the first principles method. It is discovered that (1) while doping can improve the microwave absorbing properties of PPy material, the absorption performance does not necessarily increase with the number of doping position; (2) conductivity and absorption coefficient increase significantly for the PPy nanocomposite compared with PPy. The dielectric loss is more than 2 at about 2 eV; (3) reflectivity and absorption coefficient decrease with the increase of PPy content in PPy/Co nanocomposite; (4) the average magnetic moment of the PPy nanocomposite is the same as that of pure nanoparticles, and this indicates that only nanoparticles generate magnetic loss for the nanocomposite.

Fabrication and characterization of superparamagnetic nickel ferrite ferrofluid

Because of their unique magnetic characteristics, magnetic nanoparticles are being used in various applications. We used a two-step method to create nickel ferrite ferrofluid in this study. The first step included hydrothermal preparation of oleic acid-capped nickel ferrite nanoparticles, followed by surface functionalization of the particles with citric acid, which made the nanoparticles hydrophilic. The materials' phase purity, functional groups, and magnetic behaviour were investigated. The production of mono-dispersed spherical nanoparticles with an average diameter of 9 ± 3.6 nm was shown by TEM images. With a blocking temperature of 53 K, ZFC-FC measurements verified the sample's superparamagnetic properties. The average magnetic moment per particle and the average size of the magnetic particle were calculated using the Langevin function.

Unconventional ferrimagnetism and enhanced magnetic ordering temperature in monolayer CrCl3 by introducing O impurities and Cl vacancies

Among chromium trihalides, a specific group of layered van der Waals magnetic materials, chromium trichloride (CrCl3) is the only system relatively stable under ambient conditions. This is also observed in reduced dimensionality where the emergence of extrinsic long-range ordered oxidized and Cl-vacancy-defective CrCl3 phases is experimentally reported. In this work, the magnetic properties of such two-dimensional (2D) systems are studied using density functional theory (DFT) calculations, including the electron-electron (U) repulsion interactions, and Monte Carlo (MC) simulations. Once the Cl vacancies are introduced, the results indicate that the monolayer CrCl3 has a magnetic moment that is enhanced linearly (up to 3.14 µ B /Cr) in the (1%–10%) vacancy concentration range. This determines a strengthening of the ferromagnetic state and a two-fold increase of the Curie temperature (up to 146 K) as valuated from MC simulations. More interestingly, once oxygen extrinsic impurities are considered, the monolayer CrCl3 structure is hybridized forming a stable ordered phase (O–CrCl3) with oxygen atoms allocated on the Cr atomic layer in the center of the honeycomb ring formed by Cr atoms. The magnetic moments of the O–CrCl3 system are localized on both Cr and O atoms, with oxygen antiferromagnetically coupled to chromium, resulting in a 2D ferrimagnetic hexagonal lattice system with an average magnetic moment of 2.14 µ B /Cr and a high magnetic ordering temperature (110 K) predicted with DFT in the mean field approach.

High frequency magnetic behavior of FeCoNiMnxAl1−x high-entropy alloys regulated by ferromagnetic transformation

Fe-Co-Ni-Al high entropy alloys (HEAs) with lower coercivity (Hc) and high permeability are considered as a new generation of candidates for microwave absorbing materials. Expecting to obtain higher saturation magnetization (Ms) and high frequency permeability, we designed a series of FeCoNiMnxAl1−x (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, and 1) HEAs, and first principles calculations were used to explore the spin state and magnetic changes of Mn with different Al content under the ferromagnetic transition of Mn. Firstly, the face-centered-cubic (FCC) and body-centered-cubic (BCC) phases with almost equal content were determined by experiments. The atomic models of HEAs were successfully established using the obtained crystal structure information and the spin states and magnetic moments of elements in HEAs with different Mn content were calculated. Due to the magnetic moments of ferromagnetic elements and the anti-ferromagnetic to ferromagnetic transformation of Mn elements, when Mn content is 0.2, the average magnetic moment reached 0.85/atom. The experimental results authenticate that FeCoNiMn0.2Al0.8 has the highest Ms of 95.0 emu/g. Higher Ms is favorable for HEAs to exhibit favorable high frequency magnetic properties, the maximum value of μ′ is 2.341, and that of μ″ is 0.823 in GHz frequency. This work illustrates the importance of the ferromagnetic transformation of Mn in HEAs for regulating high frequency magnetic properties and shows the guiding significance for predicting the magnetic properties of absorbing materials via using first principles calculations.

Defect Engineering: Electron-Exchange Integral Manipulation to Generate a Large Magnetocaloric Effect in Ni41Mn43Co6Sn10 Alloys.

A promising magnetocaloric effect has been obtained in Ni-(Co)-Mn-X (X = Sn, In, Sb)-based Heusler alloys, but the low isothermal magnetic entropy change ΔSM restricts the further promotion of such materials. Defect engineering is a useful method to modulate magnetic performance and shows great potential in improving the magnetocaloric effect. In this work, dense Ni vacancies are introduced in Ni41Mn43Co6Sn10 alloys by employing high-energy electron irradiation to adjust the magnetic properties. These vacancies bring about intense lattice distortion to change the distance between adjacent magnetic atoms, leading to a significant enhancement of the average magnetic moment. As a result, the saturation magnetization of ferromagnetic austenite is accordingly improved to generate a high isothermal magnetic entropy change ΔSM of 20.0 J/(kg K) at a very low magnetic field of ∼2 T.

Influence of oxygen vacancies on the ferromagnetism in Co-doped ZnO: An ab-initio study

Electronic and magnetic properties of cobalt doped ZnO, with and without O vacancies, were investigated using ab-initio calculations. Calculation shows that Co-doped ZnO can achieve different magnetic stable configurations as dependent on oxygen vacancy (VO) concentrations. The electronic structure illustrates that when there are VO in the structure, the ferromagnetic phase is the most stable configuration with the highest Curie temperature. Also, DOS and pDOS show that the total magnetic moment mainly consists of interaction between Co, VO, and O atoms, where the largest contributions come from the d-Co and p-O orbitals. The magnetization per Co atom shows a strong correlation with the formation energy decrease, which increases with the impurity-vacancy distance. Finally, the presence of VO results in a lower average magnetic moment per unit cell, which was also observed in the spatial spin-density distribution. These results indicate that VO in Co-doped ZnO could be the crucial key to achieve stable ferromagnetism in this diluted magnetic semiconductor with potential applications in spintronic devices.