Fe L2 Research Articles

EEL-spectroscopy analysis for a metallic film covering on an as-grown diamond single crystal from Fe–Ni–C system

The variation of sp3 fractions from carbon K-edge and the 3d-state occupancy on Fe–L2–3 edges in different layers of Fe-based metallic film covering on an as-grown diamond single crystal in diamond synthesis have been investigated by electron energy loss spectroscopy (EELS). It shows that from the diamond/film interface to the inner, the sp3 fractions decrease from 87.33% to 78.15%, the 3d-state occupancy for Fe increase from 4.54 to 5.64 electrons/atom. Moreover, by X-ray diffraction (XRD), only γ-Fe, Fe3C and (Fe,Ni)23C6 are found on the interface, which suggests that these carbon atoms with changed electronic configuration come from Fe3C. Based on the valence bonding theory, formation of Fe3C should make 3d occupancy increase, inconsistent with experimental observations. It can be concluded that, the 3d unpaired electrons of γ-Fe affect carbon atoms in Fe3C lattice and make them transform into sp3-like state. These sp3-like carbon atoms are separated from Fe3C and stack on the growing diamond crystal, eventually resulting in the reduction of 3d-state occupancy of Fe on the interface.

Examining the chemistry and magnetism of magnetotactic bacterium Candidatus Magnetovibrio blakemorei strain MV-1 using scanning transmission X-ray microscopy

Scanning transmission X-ray microscopy (STXM) measurements at the CK, O K and Fe L3 edges were used to study the magnetotactic bacterium Candidatus Magnetovibrio blakemorei strain MV-1 on an individual cell basis. Improved data acquisition methodologies resulting in higher quality results are presented. Visualization of magnetosomes from their O K-edge signal is demonstrated. The Fe L3 X-ray magnetic circular dichroism (XMCD) signal was used to characterize the magnetic properties of several MV-1 cells on an individual magnetosome basis. The absolute magnetic moment from two cells was evaluated and found to be 0.93(6) of that of saturated abiotic magnetite, or 3.6(2) μB. Previously observed excess Fe (II) was not found in this study, suggesting the prior observation (Lam et al., Chem. Geol 270 (2010) 110) may have been a radiation damage artifact.

Inverse TMR in a nominally symmetric CoFe/AlOx/CoFe junction induced by interfacial Fe3O4 investigated by STEM-EELS

We have found inverse tunneling magnetoresistance (TMR) with a non-symmetric bias voltage dependence in a nominally symmetric Si (001)/Ag/CoFe/AlOx/CoFe/IrMn/Ag magnetic tunnel junction after field cooling. The O K edge fine structure extracted from electron energy loss spectroscopy spectrum images taken at the interfaces of junctions with inverse TMR shows a thin, discontinuous Fe3O4 layer at the CoFe/AlOx interfaces. The Fe L2,3 edge core level shifts are also consistent with those of Fe3O4. We find no Fe3O4 layer in junctions with normal TMR. We believe this Fe3O4 layer is responsible for the inverse TMR.

XANES Analysis of Phthalocyanine Molecular Conductor

The dicyano(phthalocyaninato)iron molecular conductor shows the Giant Magnetoresistance (GMR) effect. In order to investigate the effect of the molecular structure and charge on the X-ray absorption in the Fe(Pc)(CN)2 molecule, we measured the Fe K-edge X-ray Absorption Near Edge Structure (XANES) spectra in the TPP[Fe(Pc)L2]2 (L=CN, Br, and Cl), DMDP[Fe(Pc)(CN)2], and [(n-C7H15)4N][Fe(Pc)(CN)2]. In 7134-7152 eV, we found the clear difference in the XANES spectra between these Fe(Pc)(CN)2 compounds. Our multiple scattering calculations indicate that the local structure of the iron and CN ligand, which tends to be changed by the nominal charge in the Pc ring, causes the spectral change. [DOI: 10.1380/ejssnt.2012.92]

Magnetic Ground-State and Systematic X-ray Photoreduction Studies of an Iron-Based Star-Shaped Complex

We revisit the star-shaped iron-based single-molecule magnet [FeIII{FeIII(L)2}3] (2) (exact chemical formula C30H66Fe4N6O12, H2L = N-methyldiethanolamine) in order to clarify some open questions concerning the exact electronic and magnetic properties arising from earlier studies on this specific compound. Namely, we address the internal magnetic structure by applying X-ray magnetic circular dichroism to the Fe L2,3 edges and carefully investigate radiation photochemistry. We observe an Fe3+ to Fe2+ photoreduction process, taking place under soft X-ray radiation.

Large hidden orbital moments in magnetite

AbstractThe orbital magnetic moments in magnetite have recently been discussed with strong controversy. Here, the presence of orbital moments has been revealed by the independent analysis of the Fe L2,3 edge X‐ray absorption spectroscopy (XAS) spectra, a moment analysis fit of the Fe L2,3 edge X‐ray magnetic circular dichroism (XMCD), and by the comparison with O K edge XMCD. These orbital moments are located at the A and B sites of magnetite and aligned antiparallel with each other, similar to the spin moments. They also cancel each other and are not observable by methods averaging over the whole unit cell. These findings have strong implications for the understanding of the A and B site valence states, because the existence of orbital moments is also an indicator for the half‐metallic character of magnetite.

Co2+xFe1−xSi/MgO(001) Heusler alloys: Influence of off-stoichiometry and lattice distortion on the magnetic properties in bulk and on MgO(001)

We investigate the influence of lattice distortion and off-stoichiometry on the electronic and magnetic properties of Co2+xFe1−xSi Heusler alloys in their L21 bulk phase and on MgO(001) using the density functional theory. Our investigations show that Co excess does not significantly change the magnetic properties, whereas an increase of the Fe content can reduce the spin polarization. In addition, the influence of off-stoichiometry on x-ray absorption spectra is studied. For comparison, x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements have been carried out for Co2FeSi/MgO(001) at the Co and Fe L2,3 edges.

Characterization of magnetic domain walls using electron magnetic chiral dichroism

Domain walls and spin states of permalloy were investigated by electron magnetic chiral dichroism (EMCD) technique in Lorentz imaging mode using a JEM-2100F transmission electron microscope. EMCD signals from both Fe and Ni L3,2 edges were detected from the Bloch lines but not from the adjacent main wall. The magnetic polarity orientation of the circular Bloch line is opposite to that of the cross Bloch line. The orientations of Fe and Ni spins are parallel rather than antiparallel, both at the cross Bloch line and circular Bloch line.

NEXAFS studies of La0.8Bi0.2Fe1−xMnxO3(0.0 ⩽ x ⩽ 0.4) multiferroic system using x-ray absorption spectroscopy

We report the electronic structure studies of well-characterized La0.8Bi0.2Fe1−xMnxO3 (LBFM, 0.0 ⩽ x ⩽ 0.4) multiferroic samples investigated by soft x-ray absorption spectroscopy at O K-, Mn L3,2-, Mn K-, Fe L3,2- and La M4,5-edges along with the spectra of reference compounds. The investigations are performed to find out the chemical states and crystal field symmetry of ions present in the LBFM multiferroic samples after the substitution of Mn ions at Fe sites. Studies reveal a slight shift in the peak positions of O K-edge spectra along with growth in intensities of low-energy features. An analysis of the Mn L3,2- and K-edge, in addition to the comparison with the spectra of reference compounds, indicates that the Mn ions are present in mixed valence states. It is found that the Mn ions are mainly in +3 states along with a small contribution of +2 and +4 ones. The study of Fe L3,2-edge confirms the trivalent state of Fe ion. M4,5-edges of La corroborate the +3 state of La in the system. Atomic multiplet calculations are also performed on Fe L3,2-, Mn L3,2- and La M4,5-edges to further verify the valency, symmetry and the crystal field splitting.

Localized and Dispersive Electronic States at Ordered FePc and CoPc Chains on Au(110)

Iron and cobalt phthalocyanines assemble on the Au(110) surface lying parallel to the surface, as deduced by near-edge X-ray absorption fine structure (NEXAFS) taken with linearly polarized radiation at the C and N K edges. The molecular chains, firmly anchored to the underlying metal surface, arrange into long-range ordered rows with a (5 × 3) symmetry along the [001] azimuthal direction at completion of the first single layer. The interaction process is mainly determined by the d orbitals associated with the central Fe and Co atoms, as observed by valence band photoemission and NEXAFS at the Fe and Co L2,3 edges. The spin and orbital configuration of the FePc and CoPc molecules is strongly influenced by the interface with a charge transfer from the underlying metal to the out-of-plane empty states located at the Fe and Co centers of the molecules. This interaction process induces electronic states located at the interface, localized on the central metal atoms and close to the Fermi level (0.2 eV binding...

Structural, electronic structure and magnetic studies of SmFe1−xNixO3 (x≤0.5)

Abstract We present the structural, electronic structure and magnetic studies of Ni doped SmFeO3. The X-ray diffraction (XRD) studies confirm the single phase nature of the samples having orthorhombic Pbnm structure and the unit-cell volume is decreasing with the increase of Ni concentration. X-ray absorption spectroscopy (XAS) studies on O K, Fe L3,2, Ni L3,2 and Sm M5,4 edges of SmFe1−xNixO3 (x ≤ 0.5) samples along with the reference compounds revealed the homo-valence state of Fe and Ni in these materials. From magnetization studies it has been observed the materials exhibit ferromagnetic and antiferromagnetic sub-lattices, which are strongly dependent on the thermo-magnetic state of the system.

Magnetism of 3d transition metal nanoparticles on surfaces probed with synchrotron radiation – from ensembles towards individual objects

AbstractMass‐filtered Fe, Co and FeCo nanoparticles in the size regime from 7 to 25 nm have been deposited under soft‐landing conditions onto ferromagnetic films, non‐magnetic surfaces as well as embedded into Al matrices. In situ X‐ray magnetic circular dichroism (XMCD) measurements reveal a ferromagnetic behaviour of FeCo nanoparticles (size: 10 nm) on Si‐substrates at room temperature whereas the respective Co nanoparticles are superparamagnetic. Besides measurements on ensembles of nanoparticles, we have also carried out in situ measurements on individual Fe nanoparticles using X‐ray photoemission electron microscopy at the Fe L3,2 edges. Fe nanoparticles on Co films show a magnetic contrast depending on the direction of the underlying poly‐crystalline Co domains. This technique also allows to record XMCD spectra on individual nanoparticles.Spectroscopy and spectro‐microscopy on magnetic particles.magnified image

Electronic states of magnetic refrigerator materials Mn0.9Fe1.1P0.55As0.45 using soft x-ray magnetic circular dichroism

The system of MnFeP1−xAsx is a candidate of a magnetic refrigerator material. We have investigated the temperature (T)- and magnetic field (H)-dependence of the magnetic properties of the Mn and Fe ions for Mn0.9Fe1.1P0.55As0.45 using a soft x-ray magnetic circular dichroism (XMCD) in the regions of the Mn and Fe L2,3 absorption edges. In the ferromagnetic states, the magnetic moments of the Mn and Fe ions turn to the same direction. It is considered that the Mn ions are close to divalent (Mn2+) states and that the Fe ions are a mixture of trivalent (Fe3+) and divalent (Fe2+) states. However, we deduce that the ferromagnetic properties of the Fe ions are mainly derived from the Fe2+ states. Using the XMCD sum rules, we have found that the magnitude of the magnetic moment of the Mn ions is larger than that of the Fe ions. The paramagnetic to ferromagnetic transitions are clearly observed by the T- and H- dependent XMCD measurements. Scince the shapes of the spectra don't change in all experiment conditions, the electronic configurations of the Mn and Fe ions are not changed by the PM-FM transition.

ENHANCEMENT OF SEPARATION PERFORMANCES OF A NEW AZOIC DERIVATIVE FROM INDUSTRIAL WATER AND THE POSIBILITY TO RECOVER ITS COMPLEX AS NANOMATERIAL

In order to obtain new complexes of Fe(III) with multiple uses, their characteristics, important applications and also the obtaining conditions are studied. The obtaining conditions consist in mixing solutions of the same concentrations of ligand 2 amino-6methoxy-benzothiazole sulphonic acid.1-naphtol-4-sulphonic acid with FeCl3. The solutions are mixed in molar ratios of 1:1, 2:1 and 3:1 (ligand to central metallic atom). For determining the molar ratio ligand:central metallic atom, the methods applied were: pH-metry, conductometry, UV-VIS spectrophotometry. Also, the stability constants for new obtained compounds were determined using Molar Ratio method (J.H.Yoe and A.L.Jones), Continuous Variation method (Job) and Harvay-Manning method. The stability of the new obtained compounds is studied by varying the pH of its solution. The values are K1 = 2.56 106 L/mol for FeL1; K2 = 19.76 1013 L/mol for Fe L2 and K3 = 30.03 1032 L/mol for Fe L3. The higher value for stability is assigned to the compound with molar ratio 3:1 (ligand: metal) in the 1.5 6.5 pH range. The maxim value for the absorbance was measured at .max= 601 nm for FeL1, .max= 601 nm for FeL2 and respective .max= 600 nm for FeL3. The studied complexes are very stable in the above-mentioned pH range and could be used for spectrophotometric determination of Fe(III) in visible domain. Another practical importance is represented by wastewater treatments by membranar separation. Thus, the separation process is improved by increasing the volume of these complexes in comparison with both ligand and Fe(III) and further the iron recovery by calcinations was accomplished.

X-ray magnetic circular dichroism studies of Fe doped fullerene and highly oriented pyrolytic graphite

We report the x-ray magnetic circular dichroism (XMCD) studies on Fe doped fullerene thin film and bulk highly oriented pyrolytic graphite. The element-specific hysteresis curves were recorded by measuring the XMCD at the Fe L3 edge as a function of the applied field strength at different temperatures. These investigations suggest that Fe doped fullerene is ferromagnetic at room temperature, while Fe atoms are driven to a nonmagnetic/paramagnetic state with the interaction of graphite matrix.

Local and electronic structure of tribological materials: XANES analysis

Tribological materials from the wheel and the wheel chock of a railway train were studied. The samples were taken from new and used wheels and wheel chock. Experimental x-ray absorption near edge spectra (XANES) spectra above the Fe L2,3 edges show the variations in the shape of the Fe L 2,3 edge fine structure, that correspond to the formation of Fe oxidized layer during the process of dry friction. Elemental analysis shows the large variations of element's distribution along the surface within 10 nm depth of damaged sample.

Soft resonant x-ray scattering in highly stoichiometric magnetite

We report here soft resonant x-ray scattering (SRXS) measurements on a single crystal of highly stoichiometric Fe3O4 (Verwey transition at Tv = 123.5 K). Resonant intensity was observed at the Fe L2,3 and the O K edges for the (0,0,1/2) reflection and at the Fe L1-edge for the (001) reflection in the low temperature phase. The energy, azimuthal angle and temperature dependence was explored using either σ- or π-incidence. The (001) reflection is active in the σ-σ' polarization channel whereas the (0,0,1/2) reflection is in the σ-π' polarization one. The (0,0,1) reflection is also observed at energies below the Fe L1-edge, confirming that this reflection is permitted by the crystal symmetry of the low temperature phase. On the other hand, the (0,0,1/2) reflection is strictly forbidden and scattered intensity is only observed on resonance. The resonant and non-resonant signals simultaneously disappear at TV for the two studied reflections at both the Fe L-edges and the O K-edge. This result indicates that the resonant reflections and the associated electronic anisotropy of the Fe d, Fe p and O p-states are explained by the lattice distortions.

Synthesis, Characterization, and Electrochemistry of a Series of Iron(II) Complexes Containing Self-Assembled 1,5-Diaza-3,7-diphosphabicyclo[3.3.1]nonane Ligands

The reaction between PPh(CH(2)OH)(2), iron(II) sulfate, ammonium sulfate, and formaldehyde in aqueous solution gives the iron(II) complex [Fe(kappa(2)-O(2)SO(2))L(2)] (1), where L is the bidentate phosphine ligand 3,7-diphenyl-1,5-diaza-3,7-diphosphabicyclo[3.3.1]nonane. During the course of the reaction, the ligand L self-assembles on the metal center. The reaction between PPh(CH(2)OH)(2), iron(II) chloride, ammonium chloride, and formaldehyde under similar conditions gives cis-[FeCl(2)L(2)] (cis-2). The complex cis-2 is converted into trans-2 in Et(2)O, whereas in water it is converted into cis-[Fe(OH(2))(2)L(2)](2+), though both of these interconversions are reversible. The chloro ligands in cis-2 are readily displaced by reaction with thiocyanate, azide, and carbonate to give cis- and trans-[Fe(NCS)(2)L(2)] (cis- and trans-3), cis- and trans-[Fe(N(3))(2)L(2)] (cis- and trans-4), and [Fe(kappa(2)-O(2)CO)L(2)] (5), respectively. The complex cis-2 reacts with CO in water to give trans-[FeCl(CO)L(2)]Cl (trans-6), whereas trans-2 reacts with CO in diethyl ether to give cis-[FeCl(CO)L(2)]Cl (cis-6), though cis-6 isomerizes in water to form trans-6. The reaction of cis-2 with sodium borohydride gives the hydride chloride complex trans-[FeCl(H)L(2)] (7). Electrochemical studies have been undertaken on complexes 1, cis-2, and 7. These reveal reversible oxidations for cis-2 and 7, with the latter giving rise to an unusual 17-electron iron(III) hydride chloride complex. Crystal structures have been obtained for 1, trans-2, trans-3, 5, and 7.

Effects of proton irradiation on electronic structure of NdFeB permanent magnets

Effects of proton irradiation on electronic structure and atomic local structure of N35EH-type NdFeB permanent magnet were investigated by soft X-ray absorption spectrometry and Mössbauer spectrometry. The local coordination environment of Fe atoms changes after proton irradiation, and the average hyperfine field Hin of the magnets decreases from 288.4 to 286.9kOe. The effects of irradiation on Fe atoms local environment at different lattice sites are different. The near edge structure of Fe L3 edge is changed, indicating the density of unoccupied state of Fe 3d electrons increases after proton irradiation.

Structural and magnetic properties of chemically synthesized Fe doped ZnO

We report on the synthesis of Fe-doped ZnO with nominal composition of Zn0.99Fe0.01O by using a coprecipitation method. X-ray diffraction and selective area electron diffraction studies reveal a single phase wurtzite crystal structure without any secondary phase. Field emission transmission electron microscopy measurements infer that Zn0.99Fe0.01O have nanorod-type microstructures. Magnetic hysteresis measurement performed at different temperatures show that Zn0.99Fe0.01O exhibits a weak ferromagnetic behavior at room temperature. A detailed investigation of the electronic and local structure using O K-, Fe L3,2 near edge x-ray absorption fine structure suggests that Fe is substituting Zn in ZnO matrix and is in Fe3+ state.