Number Of Fe Atoms Research Articles

A simple physical model for simulation and design magneto-plethysmograph in application non-invasive hemoglobin measurement

The magneto-plethysmograph method is a combination of magnetic field and sensors used to detect changes in blood flow pulsation. However, to detect the magnetic properties of blood related to hemoglobin concentration, physical modeling and simulation are required. This approach involves designing simulations using magnetic field equations and magnetic susceptibility, where a permanent magnet is placed on the surface of blood vessels, and sensors based on giant magnetoresistance are placed at a distance r. The design originates from a simple approach involving the magnetization and detection of Fe atoms in hemoglobin. Parameters involved include the magnetic susceptibility of oxyhemoglobin and deoxyhemoglobin, with an external magnetic field exceeding 1 Tesla. From the physical modeling and simulation, graphs are obtained depicting the influence of hemoglobin concentration on the number of Fe atoms and its magnetization. This enables the design of non-invasive hemoglobin measurement sensor devices. The uniqueness of this simple physical model and simulation lies in its ability to produce specially designed device models for measuring hemoglobin concentration. This differs from other research focusing on blood flow pulse measurements; the results of this study provide new insights into the benefits of simple physics equations that can be developed for medical diagnostic research and device development.

Theoretical analysis of AgFen (n = 1–5) clusters: A DFT study

Study based on transition metal based clusters are of large interest because of its potential uses in photovoltaic, semiconductor fabrication and life sciences. In this work, Ag - doped Fe clusters AgFen (n = 1–5) is examined by using Density Functional Theory (DFT) method. Conceptual DFT based descriptors such as HOMO-LUMO energy gap, molecular hardness, softness, electronegativity, electrophilicity index and dipole moment are computed and discussed. The computed data confirms that HOMO-LUMO energy gap of AgFen clusters is varying between 0.198 eV and 1.281 eV. System AgFe3 displays peak value of energy gap i.e., 1.281 eV. It states that AgFe3 may be suitable candidate for applications in molecular electronics, spin electronic and photovoltaic devices. The calculated energy gap exhibits an odd–even swinging behaviour with number of Fe atoms, n. It specifies that system with odd Fe atoms display large value of energy gap than their immediate cluster with even Fe atoms. Our computed data reveals a nice correlation between energy gap of Ag - doped Fe clusters and DFT based descriptors.

First principles study on the functionalization of graphene with Fe catalyst for the detection of CO2: Effect of catalyst clustering

The surface functionalization of graphene plays an important role in the development of graphene-based sensors for gas detection and removal. Here, we report the effect of decoration of graphene with Fe catalyst, as either scattered adatoms (Feadatoms@G) or clustered (Fecluster@G) on the detection of CO2 gas molecule and its influence on the structural, adsorption, electronic and magnetic properties of graphene using the spin-polarized density functional theory (DFT). The results show that the adsorption of scattered Fe-adatoms and Fe4-cluster on graphene would break the degeneracy of spin-up and spin-down states, resulting in ferromagnetic adsorption-bed for the detection of CO2 molecules. The magnetic moment of Feadatoms@G remains the same for all concentration of CO2, while the magnetic moment of Fecluster@G decreases from 10.03 µB to 4 µB by increasing the concentration of CO2 from one to four molecules. It is found that the scattered Fe-adatoms on graphene have the higher tendency to adsorb more CO2 molecules than that of the cluster with the same number of Fe atoms, whereas Fe4-cluster on graphene detects CO2 molecules using magnetism. Our results have indeed a direct application to fabricate solid-state and magnetic-based gas sensors using graphene to detect CO2 gas molecules.

Influence of local surrounding on magnetism in Fe-Ni alloy: A first principles study

Abstract Magnetism of Fe-Ni system is calculated from the first-principles. Results show that the atomic magnetic moments are determined by their local surrounding atoms. In both FM and AFM cases, the Fe atomic magnetic moment declines with increasing number of Fe atoms in its local surroundings. The relation between atomic volume and atomic magnetic moment indicates that Fe-rich local surroundings would cause relatively small volumes. Our work is of significance to understanding the relation between the local surroundings with anomalous thermal expansion coefficient in the Invar alloy.

Adsorption of Nitrate and Bicarbonate on Fe-(Hydr)oxide.

In this work, we used density functional theory calculations to study the resulting complexes of adsorption and of inner- and outer-sphere adsorption-like of bicarbonate and nitrate over Fe-(hydr)oxide surfaces using acidic, neutral, and basic simulated pH conditions. High-spin states that follow the 5N + 1 (N is the number of Fe atoms, each having five unpaired electrons) rule are preferred. Monodentate mononuclear (MM1) surface complexes are shown to lead to the most favorable thermodynamic adsorption for both bicarbonate and nitrate with -63.91 and -28.25 kJ/mol, respectively, under neutral conditions. Our results suggest that four types of regular and charged-assisted hydrogen bonds are involved in the adsorption process; all of them can be classified as closed-shell (long-range or ionic). The formal charges induce unusually short and strong hydrogen bonds. The ability of high multiplicity states of Fe clusters to adsorb oxyanions in solvated environments arises from orbital interactions: the 4s virtual orbitals in Fe have a large affinity for the 2p-type electron pairs of oxygens.

Calculations of stability of alloyed cementite from valance electron structure

Based on the empirical electronic theory of solids and molecules (EET), the actual model for unit cell of cementite (θ-Fe3C) was built and the valence electron structures (VES) of cementite with specified site and a number of Fe atoms substituted by alloying atoms of M ( M=Cr, V, W, Mo, Mn ) were computed by statistical method. By defining P as the stability factor, the stability of alloyed cementite with different numbers and sites of Fe atoms substituted by M was calculated. Calculation results show that the density of lattice electrons, the symmetry of distribution of covalent electron pairs and bond energy have huge influence on the stability of alloyed cementite. It is more stable as M substitutes for Fe2 than for Fe1. The alloyed cementite is the most stable when Cr, Mo, W and V substitute for 2 atoms of Fe2 at the sites of Nos. 2 and 3 (or No. 6 and No. 7). The stability of alloyed cementite decreases gradually as being substitutional doped by W, Cr, V, Mo and Mn.

Global minimum structures, stability and electronic properties of small NixSny (x + y ≤ 5) bimetallic clusters; a DFT study

We report DFT calculations about the global minimum structures, the stability and electronic properties of small free Fe x Cu y nanoalloys (x + y ≤ 5), by using DFT as implemented in SIESTA code. Our results show that the optimized structures of these binary nanoalloys prefer planar geometries in the majority of the cases, these geometries correspond to the same geometry that the corresponding pure Cu clusters. The nanoalloys present magnetic behavior where the ferromagnetic-like order is prefered by the ground state structures, our results show that the total magnetization increases with the number of Fe atoms in the cluster. The electronic behavior is analyzed through the ionization potential, electron affinity, and the hardness.

Study of high-temperature oxidation of ultrathin fe films on Pt(100) by using X-ray photoelectron spectroscopy

High-temperature oxidation of iron thin films deposited on Pt(100) surfaces was studied by using X-ray photoelectron spectroscopy (XPS). Upon an oxygen exposure of 300 Langmuir onto a 7.5- monolayer (ML) Fe film at 830 K, about 2 monolayers of the Fe film were oxidized as Fe3O4 while the remaining Fe atoms diffused into the substrate. For 1.25-, 2.5-, and 3.75-monolayer Fe films, only about a monolayer of the Fe film was oxidized as FeO, regardless of the number of Fe atoms. The oxide layers on the 7.5-monolayer Fe film were observed to be stable upon post-annealing at 1030 K.

Finite temperature magnetic properties of small Fe chains and clusters on Pt(111)

The magnetic properties of Fe chains and clusters on Pt(111) are investigated in the framework of a functional-integral theory of itinerant magnetism. The considered nanostructures show a ferromagnetic (FM) ground state with nearly saturated Fe local magnetic moments ${\ensuremath{\mu}}_{\text{Fe}}^{0}\ensuremath{\simeq}3.15{\ensuremath{\mu}}_{\text{B}}$. In addition, small moments ${\ensuremath{\mu}}_{\text{Pt}}^{0}\ensuremath{\simeq}0.1--0.3{\ensuremath{\mu}}_{\text{B}}$ are induced at the Pt substrate, which depend sensitively on the number of Fe atoms in their nearest-neighbor (NN) shell. The spin-fluctuation (SF) energies $\mathrm{\ensuremath{\Delta}}{F}_{l}(\ensuremath{\xi})$ at the different atoms $l$ are calculated as a function of the local exchange fields ${\ensuremath{\xi}}_{l}$, by using a real-space recursive expansion of the local Green's functions. Results for the temperature dependence of the average magnetization per atom ${\overline{\ensuremath{\mu}}}_{N}$, local magnetic moments ${\ensuremath{\mu}}_{l}$, and spin correlation functions ${\ensuremath{\gamma}}_{lk}$ are derived. At the Fe atoms the dominant magnetic excitations are fluctuations of the local-moment orientations. The spin-flip energies $\mathrm{\ensuremath{\Delta}}{F}_{l}(\ensuremath{\xi})$ in the deposited Fe clusters are found to be about $50%$ smaller than in free-standing clusters of comparable size. This results in flatter SF-energy landscapes and in a weaker stability of the FM order at $Tg0$. The effective exchange interactions between the Fe local moments, which are derived from the electronic calculations, reveal competing FM and antiferromagnetic couplings at different distances. In contrast to Fe, the main spin excitations at the Pt atoms are fluctuations of the size of the induced local magnetic moments. The interplay between the different types of spin excitations and their effect on the temperature-dependent magnetic properties is discussed.

Magnetic hardening of CeFe12−xMox and the effect of nitrogenation

Abstract We report the magnetic hardening of CeFe 12− x Mo x by melt spinning at surface wheel speeds between 10 m/s and 30 m/s. The synthesis range of CeFe 12− x Mo x has been extended to CeFe 11 Mo, which uses the least amount of Mo substitution to stabilize the ThMn 12 -type structure. X-ray diffraction indicates that as-spun samples are multi-phased, typically consisting of a primary ThMn 12 -type phase with impurity phases of Fe–Mo alloy, Ce 2 Fe 17 and CeFe 2 . However, nearly pure ThMn 12 -type phase can be obtained either by directly melt spinning at specific wheel speeds or by annealing the over-quenched ribbons at an optimum temperature. The magnetic moment of CeFe 12− x Mo x is found to be affected not only by the number of Fe atoms but also by weakening of the Fe moment from Mo substitution. Nitriding is effective in enhancing the Curie temperature T c and saturation magnetization 4π M s . T c was enhanced by at least 151 °C after nitrogenation for all compositions. The newly identified CeFe 11 Mo compound exhibits the best magnetic properties in the alloy series, having T c = 370 °C and 4π M s > 13.0 kG after nitriding and ( BH ) max = 0.3 MGOe after annealing.

Study of phase stability in the σ-FeCr system

Formation energy of the σ-phase in the Fe-Cr alloy system, ΔE, was computed versus the occupancy changes on each of the five possible lattice sites. Its dependence on a number of Fe-atoms per unit cell, NFe, was either monotonically increasing or decreasing function of NFe, depending on the site on which Fe-occupancy was changed. Based on the calculated ΔE values, the average formation energy, 〈ΔE〉, was determined as a weighted over probabilities of different atomic configurations. The latter has a minimum in the concentration range where the σ-phase exists. The minimum in that range of composition was also found for the free energy calculated for 2000 K and taking only the configurational entropy into account.

Theoretical study of magnetic properties and hyperfine interactions in σ-FeV alloys

Electronic structure Korringa-Kohn-Rostoker calculations for the σ-phase in Fe 100− x V x were performed in compositional range of its occurrence (∼34 ≤ x ≤ ∼65). Fe and V magnetic moments and hyperfine fields were determined for five inequivalent lattice sites in two models of magnetic structure, namely ferromagnetic FM and so-called anti-parallel one, APM, dominated by antiferromagnetic coupling. The average magnetic moments calculated for FM state overestimate the experimental data, whereas the corresponding quantities computed for APM state, underestimate them. Such a behavior remains in line with total energy values being similar for both models. The calculations showed that both average magnetic moments and hyperfine fields (on Fe and V atoms) vary with a number of Fe atoms in the nearest neighbor shell, NN Fe, starting from critical values of NN Fe, characteristic of each site. The calculated hyperfine fields for Fe and V showed an important role of valence contributions, being strongly dependent on local magnetic moments arrangements. In the case of Fe, the computed hyperfine fields are overestimated with respect to the Mossbauer data, while the corresponding values for V are underestimated with respect to the NMR results. However, the linear correlation between average magnetic moment and hyperfine fields, observed experimentally in FeV σ-phase, can be well reproduced when combining theoretical results for the two above-mentioned magnetic structure models.

Role of iron in the incorporation of uranium in ferric garnet matrices

The structural relaxations and electronic structure of U-containing Ca${}_{3}$(Ti,Zr,Hf,Sn)${}_{2}$(Fe${}_{2}$Si)O${}_{12}$ garnet systems have been investigated using ab initio methods within density functional theory (DFT) in the generalized gradient approximation with a Hubbard correction $U$ (GGA + $U$). The calculations provide a fundamental understanding of the role of Fe in the incorporation and stability of U in the garnet structure. The atomic relaxations around U are controlled by a delicate balance between the Coulomb interactions among the ions and the size effect of the large U atom. The relaxation pattern indicates that when U occupies the $A$ site, a charge transfer occurs from U to its nearest-neighbor (NN) Fe atom. This is further verified by the detailed analysis of the electronic band structures and charge density distribution. The double exchange coupling of the U $f$ and the NN Fe $d$ shells via the transfer of electrons lowers the energy of the system when the spins of the $f$ and $d$ shells are antiparallel. The incorporation energy of U at the $A$ site (substituting Ca) increases dramatically with the decrease in the number of Fe atoms in the neighboring tetrahedral sites. The presence of Fe is crucial, since it accommodates the extra valence electrons introduced by U and the electron transfer allows the lowering of the total energy of the structure. Comparing the incorporation energies at the $A$ and $B$ site (octahedral site), U clearly prefers the A site, provided that there are sufficient Fe atoms in its vicinity to facilitate the charge transfer.

Electronic, Magnetic, and Transport Properties of Fe-COT Clusters: A Theoretical Study

Using density functional theory calculations combined with nonequilibrium Green’s function method, we report the electronic, magnetic, and transport properties of iron-cyclooctatetraene (Fe-COT) sandwich clusters. Four Fen COTn+1 (n = 1−4) clusters with linear sandwich structure are highly stable because of the strong Fe-COT coupling. The ground state of Fe-COT clusters is ferromagnetic, Fe atoms couple ferromagnetically to the neighboring COT rings, and the large total magnetic moments increase with the number of Fe atoms. The spin-polarized transport calculations indicate that Fe-COT clusters coupled to gold electrodes act as nearly perfect spin-filters. The revealed properties indicate that the Fe-COT clusters would be ideal materials for promising molecular spintronics.

An XPS study of the interatomic charge distribution in stainless steels

AbstractThe secondary spectral feature of the Al Kα‐excited Ni 2p spectrum, positioned at a kinetic energy of approximately 6 eV lower than the main Ni 2p peak, is known as either the 2p satellite (in the case of inorganic materials) or a plasmon loss peak (in the case of metals). This feature was used to probe changes in the local electronic structure of Ni in stainless steels. The results were compared with a previous study on Auger parameter and core–core–valence (CCV) Auger lines acquired using Cu Kα radiation. The position of the secondary peak shifts to higher binding energy as the number of Fe atoms around Ni increases and this is consistent with the idea of charge transfer from Fe to Ni 3d irrespective of whether the peak is treated as a plasmon or satellite. Previous studies on Ni alloys showed that as the concentration of the more electropositive partners in the Ni alloy (such as Fe in a NiFe alloy) increased compared to Ni, the intensity of the Ni energy loss decreased. However, contrary to previous studies, in steels that we studied, the intensity of the secondary peak increases as the concentration of Fe (or even Cr) increases. Copyright © 2010 John Wiley & Sons, Ltd.

From Metal Binding to Nanoparticle Formation: Monitoring Biomimetic Iron Oxide Synthesis within Protein Cages using Mass Spectrometry

Mass measurements of metal-mineralized protein cages allowed quantitative examination of the effects of metal-ion concentration on the final nanoparticle size. Modeling using a kinetic master equation suggests that particle growth involves both a binding phase and a growth phase (see picture; I: relative abundance; LiDps: a DNA binding protein; (n)Fe: number of Fe atoms).

Effect of vanadium neighbors on the hyperfine properties of iron–vanadium alloys

The electronic and magnetic structures of Fe–V alloys are calculated using the discrete-variational and full-potential linearized-augmented-plane wave methods. The derived hyperfine properties at Fe sites are studied against the number of Fe atoms in the neighbouring shells. As expected the magnetic hyperfine field depends strongly on the number of Fe atoms in the first and second shells of neighbours while its dependence on the variation of atoms in the third shell is weak. The calculated distribution of the magnetic hyperfine fields at the Fe sites, are compared to the experimental data of Krause et al. (Phys Rev B 61:6196–6204, 2000). The contact charge densities and the magnetic moments are also calculated. It was found that the contact charge density increases with increasing V contents and this leads to negative isomer shift on addition of V.

Effects of random distribution of Mn,Fe in Co2Mn1−xFexSi Heusler compounds probed by Mn55 nuclear magnetic resonance

Recent spin echo nuclear magnetic resonance (NMR) revealed that the half-metallic Co2Mn1−xFexSi Heusler alloys exhibit the L21 structure with random distribution of Mn and Fe on the 4b Wyckoff position. This random distribution is most prominent in the third coordination shell of the Mn55 nuclei, as this shell is the first magnetically active shell, leading to a line splitting in the Mn55 NMR spectra. A comparison, as presented in this paper, of all Mn55 NMR satellite lines shows that the resonance frequencies corresponding to the same number of Fe atoms in the third shell of Mn55 shift to slightly different resonance frequencies with increasing overall Fe content x. This shift is related to the constructive contribution of higher shells to the hyperfine field. These higher shells affect also the satellite linewidth, leading to a parabolic behavior with increasing Fe concentration x. This parabolic behavior is modified by the frequency spacing related to the replacement of Mn by Fe.

Experimental study of Fe3+ solubility in cristobalite and its application to a metamorphosed quartz-magnetite rock from Mt. Riiser-Larsen area, Napier Complex, East Antarctica

This report concerns the Fe3+ solubility in cristobalite coexisting with hematite obtained from heating experiments in air at 990-1460 °C in the SiO2-Fe2O3 system. The ferric iron substitutes for the tetrahedral silicon in cristobalite and Si4+ also substitutes for the octahedral Fe3+ in hematite. Combining the chemical and P-T data of the quartz in the high-pressure eclogite from Sanbagawa belt, central Shikoku, Japan with the present experimental data, we found the content of ferric iron in quartz increases with increasing pressure and temperature: lnXFe = (−1092 − 5.254T + 7.75P)/T,where XFe, T and P are the number of Fe atoms in quartz per formula unit based on a 2-oxygen atom normalization (cationic mole fraction of Fe), temperature in Kelvin and pressure in kbar, respectively. This new geothermometer is applied to the ultrahigh-temperature metamorphosed quartz-magnetite rock from Mt. Riiser-Larsen area, Napier Complex, East Antarctica, resulting that the metamorphic temperatures are estimated as about 994-1095 °C for pressures 5-15 kbar.

Interpreting Mössbauer spectra reflecting an infinite number of sites: An application toFe1−xSisynthesized by pulsed laser annealing

We present a study on the interpretation of conversion electron M\"ossbauer spectra reflecting an infinite number of sites, in casu M\"ossbauer spectroscopy on ${\mathrm{Fe}}_{1\ensuremath{-}x}\mathrm{Si}$ layers on Si, synthesized by pulsed laser annealing. These spectra display a broad double-peaked resonance, reflecting the numerous different environments of the $^{57}\mathrm{Fe}$ probe due to a distribution of vacancies on the Fe sublattice. The spectra can be fitted in many different ways; hence finding a reliable physical interpretation is not straightforward. Therefore ab initio calculations have been performed in order to obtain a priori information about the hyperfine interaction parameter distributions. For this material, the electric-field gradient on the $^{57}\mathrm{Fe}$ atoms turns out to depend on details in the configuration of neighbors as far as the sixth neighbor shell. The isomer shift appears to be determined by the number of Fe atoms in the first and second Fe neighbor shells only. This leads to the construction of an ab initio based model predicting the mean isomer shift and its distribution for a given ${\mathrm{Fe}}_{1\ensuremath{-}x}\mathrm{Si}$ layer with a known Fe concentration profile. By applying this model new information from the experimental data can be extracted: we show that after applying one or two laser pulses, the Fe atoms are not completely randomized at an atomic scale. The relation of this model to other approaches of analyzing M\"ossbauer spectra with a distribution of sites is discussed, as well as the difference between the present results on $[\mathrm{Cs}\mathrm{Cl}]{\mathrm{Fe}}_{1\ensuremath{-}x}\mathrm{Si}$ and earlier interpretations in the literature. This work reveals how a combination of M\"ossbauer experiments and ab initio calculations leads to a more reliable interpretation of M\"ossbauer spectra reflecting an infinite number of sites.