Moments Of Fe Atoms Research Articles

Ground State Magnetic Properties of Fe Nanoislands on Cu(111)

We investigate magnetic properties of Fe nanoislands on Cu(111) in the relaxed structure within the density functional theory. We observe that the nanoislands exhibit the ferromagnetic properties with large magnetic moment. We find that the change in the magnetic moment of each Fe atom is induced by deposition on Cu(111) and structure relaxation of Fe nanoislands. Moreover, we examine the stability of ferromagnetic states of Fe nanoislands by performing the total energy calculations.

Depth selective investigations of magnetic multilayers by X-ray resonant magnetic reflectivity

We have measured and analyzed the X-ray resonant Bragg reflectivity spectra from BCC [Fe/Co] n superstructure near the L 2,3 absorption edges of iron. The developed general computer code for the reflectivity calculations from arbitrary anisotropic multilayers allows us to test the different approaches to the treatment of the Bragg reflectivity spectra. We have proved that the observed asymmetry of the spectrum shape at the first-order Bragg peak for the right and left circular polarizations is predominantly caused by the magnetization of the central part of iron layers. The influence of interfaces is almost negligible. The fit of the energy dependence of the integral intensity of the Bragg reflection for the [Fe 6/Co 6] 50 sample gives the value of the magnetic moment of Fe atoms in the central parts of Fe layers ∼2.6 μ B, that is larger than the volume value.

Grain boundary characteristics and texture formation in a medium carbon steel during its austenitic decomposition in a high magnetic field

A 12-T magnetic field has been applied to a medium plain carbon steel during the diffusional decomposition of austenite and the effect of a high magnetic field on the distribution of misorientation angles, grain boundary characteristics and texture formation in the ferrite produced has been investigated. The results show that a high magnetic field can cause a considerable decrease in the frequency of low-angle misorientations and an increase in the occurrence of low Σ coincidence boundaries, in particular the Σ3 of ferrite. This may be attributed to the elevation in the transformation temperature caused by the magnetic field and, therefore, the reduction of the transformation stress. The wider temperature range for grain growth offers longer time to the less mobile Σ boundaries to enlarge their areas. Moreover, the magnetic field can enhance the transverse field-direction fiber (〈0 0 1〉∥TFD). It can be assumed that the effects of the field were caused by the dipolar interaction between the magnetic moments of Fe atoms.

Arrangements of magnetic moments in nanocrystallineFe48Al52

Combined techniques, EXAFS, magnetization, and M\ossbauer polarimetry are used to investigate the orientation of Fe magnetic moments in a ${\mathrm{Fe}}_{48}{\mathrm{Al}}_{52}$ disordered alloy prepared by mechanical grinding. Local Fe magnetic moments and their contributions to the net magnetization at selected external fields and temperatures were estimated. It was found that components of the Fe magnetic moments parallel to the net magnetizations reduce their values much faster with an increasing number of neighboring Al atoms than the total iron moments. Data analysis indicates that magnetic moments of Fe atoms surrounded by $(7\mathrm{Al}+1\mathrm{Fe})$ in the first coordination shell and by $(1\mathrm{Al}+5\mathrm{Fe})$ in the second coordination shell possess nonzero magnetic moments that form a noncolinear structure.

Ag(001) 표면 위에 놓인 Fe 선의 자성과 전자구조

The electronic structure and magnetism of Fe chain along the [110] direction on Ag(001) were investigated by using the all-electron full-potential linearized augmented plane wave (FLAPW) method within generalized gradient approximation (GGA). The magnetic moment of Fe atom in Fe chain is calculated to be , which is slightly larger than that () of the Fe[110] chain on Cu(001). The reduced coordination number for the Fe chain induced the Fe-d band narrowing and exchange-splitting enhancement, which are responsible for the large magnetic moment of the Fe chain. The calculated band width of the Fe-d band and the exchange-splitting are 1.7 eV and 3.2 eV, respectively.

Effect of Tm substitution on the magnetic properties and local magnetic anisotropy of amorphous Fe 80− xTm xB 20 ribbons

We have carried out magnetic and Mössbauer studies of amorphous Fe 80− x Tm x B 20 alloys (0 ≤ x ≤ 16). With an increasing Tm content, both the Curie temperature T C and the magnetic moment of Fe atom μ Fe decrease. We have extracted the value of exchange constant A from T C and that of the local magnetic anisotropy constant K L from the coercivity. Mössbauer studies were performed in a transmission geometry and also using the conversion electron spectroscopy. Both Mössbauer spectrometry techniques show that the average hyperfine field decreases linearly with the addition of rare-earth.

Magnetic interactions and phase transformations in FeM, M = (Pt, Rh) ordered alloys

We present results of the first-principles calculations for selected non-collinear magnetic configurations in L10 FePt and B2 FeRh. These results have been interpreted within the unified model of magnetic interactions which treats the Fe atomic moments as sufficiently localized degrees of freedom. The exchange fields of Fe atomic moment determine both the orientation and the value of the induced Rh/Pt atomic moments. The Pt moment fluctuations in FePt follow a relatively simple form while for the FeRh significant contributions of the non-linear susceptibility have to be taken into account. The latter, along with the remarkably strong Rh mediated exchange lead to a dominating contribution from the bi-quadratic non-Heisenberg terms. The effect of magnetic interactions mediated by the induced Rh/Pt moment on the order-order (FeRh) and order disorder (FePt) magnetic phase transition is discussed.

In-plane anisotropy of iron single-crystal thin film using x-ray magnetic circular dichroism

X-ray magnetic circular dichroism (XMCD) in the absorption of the single-crystal iron thin film deposited epitaxially on MgO substrate is studied to get the spin and orbital moment. The experiments show that along with different crystal axes, the change of orbital moment of Fe atoms is about 600%, the change of the spin moment is only about 50%, but the change of total moment is not so large. Researching the anisotropy by means of routine methods, the relation between the magnetic moment and the anisotropy of the thin film is studied.

Nanogranular Phase Formation During Devitrification of Fe(NiCo)ZrB Amorphous Alloys

A comprehensive review of our recent experimental and theoretical developments in the processing of nanocrystalline soft magnetic materials made by crystallization of amorphous precursors and containing new nanocrystalline phases is given. The relationship between the structures of the metastable and equilibrium phases and their transformations are discussed. Nickel-rich amorphous precursors with stoichiometry Ni64Fe16Zr7B12Au1 were produced by melt-spinning technique and then heat-treated at temperatures ranged from 420 °C to 600 °C for one hour to form nanostructured alloy. The transformation from the amorphous state into the nanocrystalline state was investigated by the differential scanning calorimetry (DSC), the x-ray diffraction (XRD), the vibrating sample magnetometry (VSM) and Mossbauer techniques. The annealing favours the emergence of cubic FexNi23-xB6 crystalline grains (10-25 nm in diameter). Magnetic measurements made at 4.2-1100 K reveal rather high value of saturation magnetization (nearly 60 and 40 Am2/kg at 4.2 K and room temperature, respectively) in amorphous as well as in nanocrystalline states. These facts are consistent with 300 K 57Fe Mossbauer results which are well supported by the calculations of Ni and Fe magnetic moments in Ni23B6 and Fe23B6 phases, using the spin polarized tight binding linear muffin-tin orbital (TB-LMTO) method. However, anomalous high magnetic moments of Fe and Co atoms were found in some inequivalent positions in the crystal structure.

Nanogranular FexNi23−xB6 phase formation during devitrificationof nickel-rich Ni64Fe16Zr7B12Au1 amorphous alloy

Nickel-rich amorphous precursors with chemical composition of Ni64Fe16Zr7B12Au1 were produced by melt-spinning technique and then heat treated at temperatures ranging from 435to600°C for 1h to form a nanostructure. Properties of the amorphous and the nanocrystalline samples were investigated by the differential scanning calorimetry, the x-ray diffraction (XRD), the vibrating sample magnetometry, and Mössbauer techniques. The annealing favors the emergence of cubic FexNi23−xB6 crystalline grains (10–25nm in diameter). Magnetic measurements made at 4.2–1100K reveal rather high value of saturation magnetization (nearly 60 and 40Am2∕kg at 4.2K and room temperature, respectively) in amorphous as well as in nanocrystalline states. These facts are consistent with 300K Fe57 Mössbauer effect results which are well supported by the calculations of Ni and Fe magnetic moments in Ni23B6 and Fe23B6 phases, using the spin polarized tight binding linear muffin-tin orbital method. However, anomalous high magnetic moments of Fe atoms were found in some inequivalent positions in the crystal structure.

Magnetic moments of ferromagnetic, superparamagnetic, and submonolayer Fe on a GaAs (100) surface

We have used x-ray magnetic circular dichroism (XMCD) to determine the spin and orbital magnetic moments of Fe atoms at the ferromagnetic/superparamagnetic boundary, superparamagnetic thickness, and submonolayer thickness at the interface. The samples, grown by molecular beam epitaxy at room temperature, were 5, 4, and 0.5 ML (monolayer) Fe on GaAs (100)-4×6 capped with 7 ML Cr, preceded in the case of the 0.5 ML Fe by 9 ML Co. The XMCD results show orbital moments enhanced by almost 300% with respect to the bulk and bulklike spin moments for all three thicknesses demonstrating unambiguously that the Fe/GaAs interface is magnetic.

Oscillations of magnetic parameters and giant magnetization of Fe/Be superlattices

AbstractThis research consists of the comprehensive study of structure and thickness dependences of basic magnetic parameters and of hyperfine fields on 57Fe nuclei from room‐temperature Mössbauer absorption spectroscopy of magnetic superlattices (MSL) of Fe with Be spacers synthesized using cathode sputtering in HV‐discharge with oscillating electrons. We report two series of MSL: [Fe(10 Å)/Be(tBe)] and [Fe(tFe)/Be(8 Å)]; in the former, deep oscillations of spontaneous magnetization (Js0) value vs. spacer thickness have been observed with period of 6–8 Å, while in the [Fe(tFe)/Be(8 Å)] series the oscillations do not show up. The observed giant values of Js0 normalized to Fe content (up to 5200 Gs) and the low values of hyperfine fields suggest the necessity of taking into account the orbital contributions to local magnetic moments of Fe atoms in Fe/Be superlattices. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electronic structure and ferromagnetism in the martensitic-transformation materialNi2FeGa

We calculated the electronic structures of the Heusler alloy Ni2FeGa for both the cubic and the orthorhombic structures by self-consistent full-potential linearized-augmented plane-wave method. The localized moment of Fe atom is interpreted based on the electronic structure and the popular explanation of the localized moment of Mn in Heusler alloy X2MnY. Comparing the density of states of cubic and orthorhombic structures, we observed that a Ni peak near the density of states of d band for the cubic structure splits for the orthorhombic structure, indicating a band Jahn-Teller mechanism should be responsible for the structural transition. Accompanied by this transformation, an increase of Ni moment and magnetization redistribution occurred. Temperature-dependence anisotropy field shows an evidence of martensitic transformation between 125 and 190 K. The magnetic behavior seems to contain a transition from Heisenberg-like at temperature below 70 K to itinerant magnetism at temperature higher than 160 K upon martensitic transformation. Temperature dependence of saturation magnetization reveals the spontaneous magnetization at martensite and parent phase are 3.170mu(B) and 3.035mu(B), respectively. The calculated magnetic moment at martensite is 3.171mu(B), which is quite consistent with the experimental value. The magnetic moment of Fe and Ni atom in Heusler alloy Ni2FeGa is analyzed based on the computational results and the experimental magnetization curves. It is found that the magnetic moment of Fe atoms is about 10-43% larger than that of alpha-Fe.

Fe-substitution effect on magnetic properties of Ce2Co7B3 compound

Magnetic and crystallographic properties have been observed for the compounds Ce 2 (Co 1− x Fe x ) 7 B 3 with x from 0 to 0.28. Metamagnetic properties of Ce 2 Co 7 B 3 transform to ferromagnetic characteristics by Fe substitution for the Co. It is revealed that the Fe atoms in the compounds substitute preferentially the Co atoms at the 2c-site. Magnetic moments of Fe atoms at the 2c- and 6i 1 -sites are estimated to be 2.8 μ B (Bohr magneton) and 0.35 μ B , respectively. Novel magnetic structure is proposed for the compounds Ce 2 (Co 1− x Fe x ) 7 B 3 .

Surface alloying and mixing at the Mn/Fe(001) interface: Real-time photoelectron spectroscopy and modified embedded atom simulations

Structural and magnetic properties of thin Mn films on the Fe(001) surface have been investigated by a combination of photoelectron spectroscopy and computer simulation in the temperature range $300\mathrm{K}l~Tl~750\mathrm{K}.$ Room-temperature as deposited Mn overlayers are found to be ferromagnetic up to 2.5-monolayer (ML) coverage, with a magnetic moment parallel to that of the iron substrate. The Mn atomic moment decreases with increasing coverage, and thicker samples (4-ML and 4.5-ML coverage) are antiferromagnetic. Photoemission measurements performed while the system temperature is rising at constant rate $(dT/dt\ensuremath{\sim}0.5\mathrm{K}/\mathrm{s})$ detect the first signs of Mn-Fe interdiffusion at $T=450\mathrm{K},$ and reveal a broad temperature range $(610\mathrm{K}l~Tl~680\mathrm{K})$ in which the interface appears to be stable. Interdiffusion resumes at $Tg~680\mathrm{K}.$ Molecular dynamics and Monte Carlo simulations allow us to attribute the stability plateau at $610\mathrm{K}l~Tl~680\mathrm{K}$ to the formation of a single-layer MnFe surface alloy with a $2\ifmmode\times\else\texttimes\fi{}2$ unit cell and a checkerboard distribution of Mn and Fe atoms. X-ray-absorption spectroscopy and analysis of the dichroic signal show that the alloy has a ferromagnetic spin structure, collinear with that of the substrate. The magnetic moments of Mn and Fe atoms in the alloy are estimated to be $0.8{\ensuremath{\mu}}_{B}$ and $1.1{\ensuremath{\mu}}_{B},$ respectively.

Sulfur adsorption on Fe(1 1 0): a DFT study

The adsorption of atomic S on the Fe(1 1 0) surface is examined using density functional theory (DFT). Three different adsorption sites are considered, including the atop, hollow and bridge sites and the S is adsorbed at a quarter monolayer coverage in a p(2 × 2) arrangement. The hollow site is found to be the most stable, followed by the bridge and atop sites. At all three sites, S adsorption results in relatively minor surface reconstruction, with the most significant being that for the hollow site, with lateral displacements of 0.09 Å. Comparisons between S-adsorbed and pure Fe surfaces revealed reductions in the magnetic moments of surface-layer Fe atoms in the vicinity of the S. At the hollow site, the presence of S causes an increase in the surface Fe d-orbital density of states between 4 and 5 eV. However, S adsorption has no significant effect on the structure and magnetic properties of the lower substrate layers.

The Crystal Structure and Magnetic Properties of Fe<SUB>3</SUB>Pt Martensite Determined by First Principle Calculations

The crystal structure and some magnetic properties of Fe 3 Pt martensite are investigated by first principle calculations. The crystal structure is optimized in such a way that the atom positions are changed according to the force acting on the nuclei. The positions are repeatedly changed until the forces are all less than 0.257 eV/nm. The final structure obtained is the same as expected from simple Bain distortion of austenite with L1 2 ordered structure. The magnetic moments of two kinds of Fe atoms in this structure are 2.6 and 2.8 Bohr magneton, and that of a Pt atom is 0.45. The magnetic moments of Fe atoms in Fe 3 Pt martensite are considerably larger than those in bcc Fe.

Electron spin resonance in an icosahedralAl63Cu25Fe12quasicrystal

An electron spin resonance (ESR) study of an icosahedral ${\mathrm{Al}}_{63}{\mathrm{Cu}}_{25}{\mathrm{Fe}}_{12}$ quasicrystal is presented. The ESR signal originates from two kinds of electronic spins\char22{}the itinerant conduction electrons and the localized d moments of magnetic Fe atoms. The ESR spectra are very broad, extending over up to 5 T in the magnetic-field-sweep experiment. The ESR signal could be detected by a high-field transmission ESR spectrometer operating at a frequency 109.270 GHz, whereas the too-small field sweep of 0\char21{}1 T prevented the ESR signal of the ${\mathrm{Al}}_{63}{\mathrm{Cu}}_{25}{\mathrm{Fe}}_{12}$ quasicrystal to be fully observed by the conventional X-band reflection spectrometer. The ESR spectra are compared to the NMR spectra of the same sample. Both spectra are extremely broad and the origin of this large broadening is found to be similar in both cases. It results from the distribution of local electric fields that are present in quasicrystals due to the lack of translation periodicity of the quasiperiodic lattice and from the s-d exchange interaction between the conduction electrons and the localized Fe d moments. An anomalous temperature dependence of the ESR linewidth that broadens on cooling above 20 K, but narrows from 20 to 5 K by a factor 3.7, was detected. General aspects of the ESR spectroscopy in quasicrystals are also discussed.

Magnetic properties of Fe–Rh alloys

We performed first-principles calculations on molecular clusters with the discrete variational method, in the spin-polarized case, to study the magnetic properties of Fe–Rh alloys. In ordered FeRh, our results showed a nearly constant local moment for both iron and rhodium atoms, in the ferromagnetic phase, for a wide range of lattice spacings. By shrinking the lattice, one observes the collapse of the magnetic moment for Fe and Rh atoms, in both ferromagnetic and antiferromagnetic phases. Our results showed a strong dependence of the hyperfine magnetic field at the iron sites on the atomic configurations in their neighborhood. A loss of magnetic coupling is expected by adding Rh atoms in the immediate vicinity of the iron sites.

Local Spin Configurations and Magnetic Ordering in Competing-Exchange System (Rh, Pd)90Fe10

Mössbauer spectroscopy technique has been used to investigate the evolution of the hyperfine field distributions and the local spin configurations of Fe atoms in the magnetically ordered (Rh1—xPdx)0.9Fe0.1 alloys over the concentration range 0 ≤ x ≤ 1. In the whole composition range, the magnetic behavior of the alloys is governed by the competition between two exchange interactions opposite in sign: the direct antiferromagnetic coupling between the nearest-neighbor Fe atoms and the ferromagnetic interaction due to the matrix polarization. For Rh-rich alloys, this leads to a spin-glass-like magnetic structure, where the ferro- and antiferromagnetic local spin configurations are realized with nearly equal probabilities. For the concentration range x ≤ 0.3, the magnetic ordering temperature is equal to about 32 K independent of the Pd concentration. In the same concentration range, a sharp increase of the magnetic moment of Fe atoms was observed. The severe influence of rhodium on the Curie temperature of the ferromagnetic PdFe alloy is explained by the spin reorientation effect, leading to a destruction of the ferromagnetic spin structure. The strong diffuseness of the magnetic transition in the intermediate concentration range 0.4 < x < 0.8 is due to the presence of Fe sites with both Rh-rich and Pd-rich local environments.