Magnetic Moments Of Fe Atoms Research Articles

Effect of Y element on atomic structure, glass forming ability, and magnetic properties of FeBC alloy

Abstract The atomic structure of amorphous alloys plays a crucial role in determining both their glass-forming ability and magnetic properties. In this study, we investigate the influence of adding the Y element on the glass-forming ability and magnetic properties of Fe86−x Y x B7C7 (x = 0, 5, 10 at.%) amorphous alloys via both experiments and ab initio molecular dynamics simulations. Furthermore, we explore the correlation between local atomic structures and properties. Our results demonstrate that an increased Y content in the alloys leads to a higher proportion of icosahedral clusters, which can potentially enhance both glass-forming ability and thermal stability. These findings have been experimentally validated. The analysis of the electron energy density and magnetic moment of the alloy reveals that the addition of Y leads to hybridization between Y-4d and Fe-3d orbitals, resulting in a reduction in ferromagnetic coupling between Fe atoms. This subsequently reduces the magnetic moment of Fe atoms as well as the total magnetic moment of the system, which is consistent with experimental results. The results could help understand the relationship between atomic structure and magnetic property, and providing valuable insights for enhancing the performance of metallic glasses in industrial applications.

How La substitute doping affects the magnetic properties of the 2-14-1 magnets (Ce1-xLax)2Fe14B: Standard DFT and DFT + U studies

We investigated different amounts of La doping on the magnetic characterizations of the (Ce1-xLax)2Fe14B (x = 0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, 1) structures using standard density functional theory (DFT) and DFT plus U (DFT + U) methods. Substitutions of Ce atoms by La atoms increased the magnetic moment of Fe atoms. The absolute values of the magnetocrystalline anisotropy energy (MAE) calculated by standard DFT method gradually decreased with increasing amounts of La doping, while the MAE using DFT + U method exhibited non-monotonic dependence on La concentration. The optimal magnetic performance occurred within the range of x = 0.25 to 0.375. The DOS showed that the rare earth atomic magnetic moments were in the opposite direction to the magnetic moments of the Fe atoms, and the f-orbital electronic states of Ce atoms predicted by DFT + U method were generally larger than that predicted by standard DFT method.

Effect of lime (CaOH+) on chalcopyrite-arsenopyrite separation in high gradient magnetic separation: Experiment and molecular simulation

During the flotation of chalcopyrite from arsenopyrite, the addition of lime (with CaOH+ as the active component) can affect the subsequent high-gradient magnetic separation (HGMS) performance. However, this issue has been overlooked in previous researches. The present study confirms this effect and elucidates its underlying mechanism. Findings demonstrate that CaOH+ could decrease the magnetic moment of Fe atoms in chalcopyrite, deteriorating its separation from arsenopyrite via HGMS method. For a high-arsenic copper ore assaying 0.63 % Cu and 0.78 % As with chalcopyrite and arsenopyrite as the dominant copper-bearing and arsenic-bearing minerals, the HGMS results has confirmed that increasing the lime dosage from 0 kg/t to 14 kg/t reduced the copper grade in the copper concentrate from 0.92 % to 0.61 % and decreased the copper recovery from 67.03 % to 53.95 %. However, the arsenic grade and recovery in the concentrate were improved from 0.35 % to 0.64 % and from 28.27 % to 42.19 %, respectively. The calculations using Density Functional Theory and Crystal-Field Theory revealed that the interaction between Fe ions in chalcopyrite and CaOH+ in lime leads to a considerable change in the single electron occupancy of the d orbitals, that is, it transitions from a high-spin state to a low-spin state; thus, the magnetic susceptibility of the chalcopyrite decreases, reducing the HGMS efficiency for separation of chalcopyrite from arsenopyrite. The findings of this study provide considerable theoretical insights and improved understanding for the effect of lime on the chalcopyrite-arsenopyrite separation efficiency in HGMS process.

A critical comparative review of generalized gradient approximation: the ground state of Fe3Al as a test case

Quantum-mechanical calculations have become an indispensable tool for computational materials science due to their unprecedented versatility and reliability. Focusing specifically on the Density Functional Theory (DFT), the reliability of its numerous implementations was tested and verified mostly for pure elements. An extensive testing of binaries, ternaries and more-component phases is still rather rare due to a vast configurational space that is nearly infinite already for binaries. Importantly, there are well known cases of theoretical predictions contradicting experiments. In this paper, we analyze the failure of theory to reproduce correctly the ground state of the Fe3Al intermetallic compound. Namely, most exchange-correlation (xc) energies within the generalized gradient approximation (GGA) predict this material in the L12 structure instead of the experimentally found D03 structure. We test the performance of 36 combinations of 6 different GGA parametrizations and 6 different Fe and Al potentials. These combinations are evaluated employing a multi-dimensional multi-criteria descriptor {, a, {}, {C ij }} consisting of fundamental thermodynamic properties (energy difference between the D03 and L12 structures), a structural aspect (lattice parameter a), electronic-structure related magnetic properties (local magnetic moments of Fe atoms {}) and elastic properties (a complete set of second-order elastic constants {C ij }). Considering the thermodynamic stability as the most critical aspect, we identify the Perdew–Wang (1991) GGA xc-functional parametrization as the optimum for describing the electronic structure of the Fe3Al compound.

Insights into the growth law, electronic properties and spectra of Fenλ (n = 3–18; λ = 0, ±1) clusters

AbstractThe growth law, electronic properties and spectra of (n = 2–18; λ = 0, ±1) clusters have been examined by density functional theory (DFT) and an unbiased structure prediction method. Extensive geometry optimizations have been executed and show that the global minimum structures of clusters have a distinct growth law when n is 8–18. For n = 8–13 and 14–18, the iron atoms grow around a decahedral and icosahedral iron cluster core, respectively. Based on the present ground states, the calculated electronic parameters are in line with the experimental values. The thermal stability of charged iron cluster is higher than that of neutral iron cluster. The octahedral and icosahedral clusters are more stable than their neighbors. The former has low chemical activity and may be a superatom. The magnetic moment of Fe atom weakens in the cluster. The UV spectra, photoelectron spectra (PES) and infrared and Raman spectra of the clusters have been predicted and the global minimum structures of the clusters are determined by comparing the theoretical PES with the experimental results.

Oscillations of the Hall Resistivity in Natural Single Crystals of Pyrrhotite Associated with the Orientation of the Elementary Magnetic Moments of Fe Atoms

The Hall resistivity of natural single crystals of pyrrhotite Fe7S8 exhibits oscillations with the inverse external magnetic field 1/B at temperature 77 K and B up to 0.73 Tesla. This resembles phenomena due to Landau quantization of the carriers demanding very pure samples, temperatures near 4 K and magnetic fields of several Tesla. However, none of these requirements is met in the experiments. The oscillations appear only when there is orientation of the elementary magnetic moments of Fe atoms, which happens when B is parallel to the c‐plane at 77 K. At room temperature with the orientation destroyed by the thermal agitation and for B parallel to the c‐axis along which the alignment of the Fe magnetic moments is negligible, the oscillations disappear. According to the s–d model proposed for heavily doped magnetic semiconductors, defects and impurities produce large local fluctuations of carrier concentrations. These through the strong s–d exchange interaction between the carriers and the lattice magnetic moments of Fe establish variations of local magnetization. These constitute scattering centers which are enforced for certain values of B, though for others weaken giving the oscillatory behavior of the Hall resistivity.

Multiferroic and half-metallic character of hexagonal BaTi0.5Fe0.5O3: DFT based calculation

ABSTRACT In this paper, we report a density functional theory (DFT) calculation study based on the full potential linear augmented plane wave (FP-LAPW) to investigate the effect of Fe incorporation in hexagonal BaTiO3 with a high Fe content : BaTi0.5Fe0.5O3.We discuss the structural, mechanical, electronic and magnetic properties as well as the spontaneous electrical polarisation P. The partial Fe substitution in BaTiO3 conserves and doubles its initial polarisation value from 0.12 to 0.25 C/m2. In contrast to nonmagnetic BaTiO3, we observe a net magnetic moment of 6.0 μB/formula unit. But, when the strong correlations among d electrons of Fe atoms are taken into account, the total magnetic is increasing and is equal to 10 μB/formula unit, due to a net increasing of magnetic moment of Fe atoms. Therefore, the coexistence of spontaneous electrical polarisation P along with a magnetic moment leads to a new and interesting multiferroic behaviour. We also observe a half-metallic behaviour in which spin down bands structure shows metallic character whereas spin up bands structure shows semi-conductor character with an energy gap of 1.48 eV. This reveals that the multiferroic BaTi0.5Fe0.5O3 could be potential candidate for spintronics devices.

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.

Controlling Electronic Properties of FeCl2 Monolayer under LDA+U Approach

The electronic properties of FeCl2 monolayer were inspected by using the LDA+U approach and including the spin-orbit interaction. By observing the band dispersion, it was shown that the metallic state changes to the insulating state by increasing the Coulomb repulsion. Moreover, the band gap and magnetic moment of Fe atom also increase as the Coulomb repulsion increases. For the magnetic state, it was also found that the ferromagnetic ground state was shifted to the antiferromagnetic ground state as tuning the Coulomb repulsion. It can be deduced that combining the spin-orbit interaction and Coulomb repulsion controls the electronic properties of FeCl2 monolayer.

Structure and Magnetic Properties of a Nanosized Iron-Doped Bismuth Titanate Pyrochlore.

The nanosized (50-70 nm) pyrochlore Bi1.5Fe0.5Ti2O7-δ was prepared by a coprecipitation technique. Characterization of Bi1.5Fe0.5Ti2O7-δ was carried out by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Raman spectroscopy, Mössbauer spectroscopy, and magnetic susceptibility measurements. The study of Fe doping in Bi2Ti2O7 was performed by means of density functional theory (DFT) calculations. The nanosized Bi1.5Fe0.5Ti2O7-δ sample crystallizes in the structural type of pyrochlore (Fd3̅m). The distribution of Fe atoms over the sites of Bi and Ti was studied from DFT simulations and then confirmed by the XRD analysis and Mössbauer method. The local distribution, electronic structure, and magnetic behavior of nanosized Bi1.5Fe0.5Ti2O7-δ are determined by the local microstructure of the metastable nanosized sample. Based on the examination of the Mössbauer spectrum of the Bi1.5Fe0.5Ti2O7-δ nanopowder, the following states of oxidation were revealed for iron atoms: Fe4+ in the titanium sites with a fraction of ∼5.7% and two states of Fe3+ (in the Bi and Ti sites) with different geometries of the oxygen surrounding. The ratio of Fe3+ distributed over the sites correlates well with the distribution in the ceramic sample. The presence of Fe4+ was found only in the nanosized Bi1.5Fe0.5Ti2O7-δ. The experimental effective magnetic moment of Fe atoms in the nanosized Bi1.5Fe0.5Ti2O7-δ appeared noticeably lower than that in the ceramic sample. The temperature dependence of μeff within the temperature range of 50-300 K is adequately described by the model of coexistence of Fe3+ and Fe4+ and the existence of clusters.

Effects of B substitution for P on structure and magnetic properties of FePB amorphous alloys by first-principle investigation

Effects of the substitution of B for P on structure and magnetic properties of FePB amorphous alloys are investigated by first-principle molecular dynamics. Our analysis shows that Fe-centered polyhedra are mainly distorted icosahedral structures, and P- or B-centered polyhedra are mainly icosahedrons and triangular prisms. It is found that Fe80P5B15 amorphous alloy has the most 15xx bond pairs and higher local five-fold symmetry. With the increase of B atoms, magnetic moment of the amorphous alloy gradually increases, which is in good agreement with the experiments. Due to higher local symmetry, Fe80P5B15 amorphous alloy produces a larger splitting exchange energy and hence a higher magnetic moment. Fe atoms are easy to lose electrons to be positively charged, but B or P atoms are easily to gain electrons and are negatively charged. In addition, on account of the small radius of B atoms, more Fe atoms are aggregated locally in Fe80P5B15 amorphous alloy. The more the number of neighboring Fe atoms, the largrer the magnetic moment of Fe atoms is, which makes magnetic moment in amorphous alloys gradually increases. These findings provide intentional guidance for the development of new soft magnetic materials.

Enhancing glass forming ability and magnetic properties of Co–Fe–Si–B metallic glasses by similar element substitution: Experimental and theoretical investigations

The poor glass forming ability (GFA) and magnetic properties of Co-based metallic glasses limit their applications. Herein the effects of similar element substitution of Co by Fe on the GFA and magnetic properties of Co72.5-xFexSi12.5B15 (x = 0, 4.5, 20, and 36) amorphous alloys were studied by experiments and density functional theory (DFT) calculations. The experimental results indicate that Fe substitution for Co improves the GFA of the studied metallic glasses, but in a concentration dependent manner, where Co52.5Fe20Si12.5B15 shows the best GFA. Meanwhile, the saturated mass magnetization (Ms) enhances with increasing Fe content. The atomic structures were analyzed by pair distribution function, coordination number, chemical short-range order, Voronoi polyhedron, and locally five-fold symmetry, and it was found that the highest average degree of the locally five-fold symmetry in Co52.5Fe20Si12.5B15 is a critical factor for enhancing GFA, which improves the stability of the local atomic structures by increasing the packing density and reducing the potential energy. Density of states and magnetic moments calculated for the four metallic glasses manifest that the larger magnetic moment of Fe atoms and gradual increase in the contribution of the Fe 3d state are responsible for the increase in the Ms with Fe content. This work links the GFA and magnetic properties of Co–Fe–Si–B metallic glasses with their atomic/electronic structures, providing reference for designing Co-based metallic glasses with good GFA and enhanced magnetism.

Effect of Fe substitution with Co on the magnetic properties of Fe80P13C7 amorphous alloys: An abinitio molecular dynamics study

In this study, we analyze the effect of Fe substitution with Co on the magnetic properties of Fe80P13C7 amorphous alloy using experimental measurements and first-principle molecular dynamic calculations of the distribution functions, Voronoi polyhedra, and density of states of Fe80-xCoxP13C7 (x = 0, 5, 10, 15 at.%) alloys. The experimental results demonstrate that the saturation magnetization (Ms) of Fe80-xCoxP13C7 (x = 0, 5, 10, 15 at.%) increases and then decreases with increasing Co content, and that maximum Ms is achieved when the composition of Co is 5 at.%. This trend is consistent with the one determined using simulations. Compared to the other amorphous alloys investigated herein, Fe75Co5P13C7 exhibits the highest local symmetry, which explains why it has the largest exchange splitting energy and largest Ms. In addition, increasing substitution of Fe atoms with Co does not appreciably affect the magnetic moment of Co atoms, but it increases the magnetic moment of Fe atoms, particularly those adjacent to Co. This indicates that Co atoms can induce an increase in the magnetic moment of the Fe atoms surrounding them.

Chemical order-disorder nanodomains in Fe3Pt bulk alloy.

Chemical ordering is a common phenomenon and highly correlated with the properties of solid materials. By means of the redistribution of atoms and chemical bonds, it invokes an effective lattice adjustment and tailors corresponding physical properties. To date, however, directly probing the 3D interfacial interactions of chemical ordering remains a big challenge. In this work, we deciphered the interlaced distribution of nanosized domains with chemical order/disorder in Fe3Pt bulk alloy. HAADF-STEM images evidence the existence of such nanodomains. The reverse Monte Carlo method with the X-ray pair distribution function data reveal the 3D distribution of local structures and the tensile effect in the disordered domains at the single-atomic level. The chemical bonding around the domain boundary changes the bonding feature in the disordered side and reduces the local magnetic moment of Fe atoms. This results in a suppressed negative thermal expansion and extended temperature range in Fe3Pt bulk alloy with nanodomains. Our study demonstrates a local revelation for the chemical order/disorder nanodomains in bulk alloy. The understanding gained from atomic short-range interactions within the domain boundaries provides useful insights with regard to designing new functional compounds.

In-plane magnetization and electronic structures in BiFeO3/graphene superlattice

We predict the presence of gapped electronic structures in an artificial superlattice of graphene embedded in (111)-oriented BiFeO3 layers based on first-principles calculations. Due to the electron transfer and the proximity effect at the BiFeO3/graphene interface, we find that magnetic moments of Fe atoms near a graphene layer were slightly less than that of bulk Fe atoms. Regarding the ferromagnetic moment orientation of Fe atoms in perovskite BiFeO3, we reveal that the in-plane magnetization gives the ground state. The bandgap depends on the magnetization direction and the separation between the graphene layer and the perovskite BiFeO3 slab, which might be adjusted by applying external uniaxial stress in an experiment. Our results provide a route for designing hybrid 2D materials with emerging properties that are not available in single materials alone.

Tuning Ferromagnetism in a Single Layer of Fe above Room Temperature.

The crystallographic and magnetic properties of an Fe monolayer (ML) grown on 2 ML Au/W(110) substrate are studied with spin-polarized low-energy electron microscopy, density functional theory, and relativistic screened Korringa–Kohn–Rostoker calculations. The single layer of iron atoms possesses hexagonal symmetry and reveals a ferromagnetic order at room temperature. We experimentally demonstrate the possibility of tuning the Curie temperature and the magnitude of magnetization of the Fe monolayer by capping with Au. Taking into account several structural models, the calculation results mostly show ferromagnetic states with enhanced magnetic moments of Fe atoms compared to their bulk value and a further increase in their value after covering with Au. The theoretically calculated Curie temperatures are in fair agreement with those obtained in the experiments. The calculations, furthermore, found evidence for the presence of frustrated isotropic Fe–Fe exchange interactions, and a discussion of the structural effects on the magnetic properties is provided herein.

Integrating ferromagnetism and ferroelectricity in an iron chalcogenide monolayer: a first-principles study.

Two-dimensional (2D) ferro-type materials have received great attention owing to the remarkable polarization effect in optoelectronics and spintronics. Using the first-principles method, the coupling between ferromagnetism and ferroelectricity is investigated in a multiferroic Janus 1T-FeSSe monolayer, which has a strong Stoner ferromagnetic ground state. The magnetic anisotropy energy (MAE) is apparently impacted by the out-of-plane asymmetry donated ferroelectricity, which is reflected by the asymmetry of the Z-MAE image. The easy magnetization axis of Janus FeSSe is the +y axis with a large MAE of 0.59 meV, rooting in unpaired d electrons of Fe atoms. The transformation of band splitting and Fermi surface can be effectively engineered by different magnetic polarization directions. The ferromagnetic (FM) coupling of the FeSSe monolayer is very robust under external strain within the range of -6% to 6%, while the strength of magnetic moment of Fe atoms and polarization are easily strain-engineered, the intrinsic mechanism of which can be elaborated by the GKA rules that depend on angles and distances. This multiferroic FeSSe monolayer provides a new platform for exploring the coupling of 2D ferromagnetism and ferroelectricity and designing low-dimensional multiferroic electronics.

Mechanism of strain-induced magnetic properties changes for metal magnetic memory technology on atomic scale

Magnetic non-destructive testing technology is widely used to detect stresses and defects in ferromagnetic materials based on the magneto-mechanical coupling effect. In the existing studies, calculated are the magnetic moment variations of the <i>α</i>-Fe system under axial tension and compression by using first-principles study, and the magneto-mechanical coupling mechanism is preliminarily discussed at an atomic level for the magnetic testing technology. In this work, taking the more complex doping systems Fe-C and Fe-Mn for examples, under different loading conditions of tension, compression and shearing, the coupling mechanisms such as the magnetic moment changes in different types of atomic doping systems are discussed in detail. The results show that the <i>α</i>-Fe and doping systems follow different changing laws of magnetic moments and energy under different types of strains. The detailed analyses of the density of states, the band structure, and the atomic magnetic moment show that doping elements change the morphology of band structure and the peak value of density of states by affecting the magnetic moment of Fe atoms, which leads the changing laws of magnetic moment and energy to be different from each other. In this work, discussed are the magneto-mechanical effects on the atomic level for ferromagnetic materials with different loading types, different doping elements and different element content. The results can be used as an important part of the multi-field coupling mechanism for magnetic testing technology.

First-principles study of Fe atom adsorbed biphenylene monolayer

Biphenylene monolayer is composed of four-, six- and eight-membered carbon rings and has a monatomic layer structure similar to graphene. It was synthesized in experiment recently and reported in <i>Science</i> in May 2021, which has attracted considerable attention in the research field of two-dimensional materials. By the density functional method of the first principle, we study the adsorption configuration of Fe atoms on biphenylene monolayer and analyze its electronic structure. The calculation of structural optimization, adsorption energy and molecular dynamics show that the biphenylene monolayer is a good matrix of Fe atoms. For Fe atoms, the hollow site in the four-membered ring of the biphenylene monolayer is the most stable adsorption site, and the adsorption energy can reach 1.56 eV. The calculation of charge transfer and density of states show that a stable bond can be formed between biphenylene monolayer and Fe atoms, and 0.73 electron is transferred from Fe atom to the neighbored carbon atom. After Fe atom being absorbed, biphenylene monolayer is magnetic, and the magnetic moment of Fe atom is about 1.81 <inline-formula><tex-math id="M2">\begin{document}${\mu}_{\mathrm{B}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20211631_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20211631_M2.png"/></alternatives></inline-formula> and points out of the plane. Compared with graphene, biphenylene monolayer adsorbs Fe atoms more stably, which provides a new platform for studying the electromagnetic, transport and catalytic properties of two-dimensional materials with adatoms.