Conversion Electron Mossbauer Spectra Research Articles

Simultaneous Measurement of γ-ray and Conversion Electron Mössbauer Spectra of Fe Films under Total Reflection Conditions Using Synchrotron Mössbauer Source

Simultaneous measurements of γ-ray and conversion electron Mossbauer spectra of Fe thin films under total reflection (TR) conditions were performed using an 57Fe synchrotron Mossbauer source. The c...

57Fe conversion electron Mössbauer study on tin oxide films doped with dilute two metal ions

Tin dioxide (SnO2) films codoped with 1% mole ratio of (Co, Fe) ions, (Cu, Fe) ions, and (Ti, Fe) ions were prepared on SnO2 (1% Sb) thin film on glass by a spray pyrolysis. Fe species included in these films were characterized by 57Fe conversion electron Mossbauer (CEM) spectra measured at room temperature (RT) and low temperatures (50 K and 16 K). Three paramagnetic Fe3+ species were observed in RT CEM spectra of two metal ions codoped SnO2 films. The broad magnetic sextet was observed in 16 K CEM spectra of (Co, Fe) codoped SnO2 and (Cu, Fe) codoped SnO2 films, but not even at low temperature for (Ti, Fe) codoped SnO2 film. The relationship between isomer shift and quadrupole splitting were shown and compared with the results of ab initio calculations based on the configuration models of metal ions and oxygen defects.

Nanocrystalline α-Fe Layer Examined by Mössbauer Spectrometry

by Mossbauer Spectrometry B. Davida,∗, O. Schneeweiss, N. Pizurova, A. Rek, V. Kudrle, O. Ja2ek CEITEC IPM, Institute of Physics of Materials, ASCR, v.v.i., šiokova 22, CZ 61662 Brno, Czech Republic Institute of Scienti c Instruments, ASCR, v.v.i., Kralovopolska 147, CZ 61264 Brno, Czech Republic DPE, Faculty of Science, Masaryk University, Kotla°ska 2, CZ 61137 Brno, Czech Republic CEITEC MU, Masaryk University, Kamenice 753/5, CZ 62500 Brno, Czech Republic A few micrometers thick nanocrystalline α-Fe layer with the mean crystallite size dXRD = 14 nm was deposited in low-pressure microwave plasma, using Fe(CO)5 vapour. Its nanocrystalline character was proved on its surface under SEM (surface was formed of deposited nanoparticles) and in its volume using TEM (deposited nanoparticles were stacked up, creating columns). No signi cant iron oxide phases were observed in the transmission Fe Mossbauer spectrum measured at 5 K nor in the surface-sensitive Fe conversion electron Mossbauer spectrum measured at 293 K.

CEMS study of corrosion products formed by NaCl aqueous solution

Conversion electron Mossbauer spectroscopy was used to study corrosion products by NaCl aqueous solution. A drop of the solution is put on an iron foil and the foil is left at RT. During the evaporation of the solution, corrosion products are formed. Conversion electron Mossbauer spectra were taken at temperatures between 15 K and room temperature (RT). In the Mossbauer spectra a ferric doublet is observed at RT, but sextets are found at 15 K. These results show that the corrosion product mainly consists of γ - FeOOH and a small amount of β - FeOOH is noticed. As NaCl concentration increases, the corrosion layer becomes thick and β- FeOOH / γ - FeOOH ratio increases slightly. Consequently, it has been concluded that the produced amount of β- FeOOH increases more rapidly than that of γ - FeOOH with increasing NaCl concentration.

Magnetic Moments' Arrangement in Fe Layers Deposited from Acetone Based Electrolyte

The acetone based electrolyte was used for electrodeposition of iron layers on the copper substrate. Two types of surfaces of the deposited layer can be obtained: shiny or black. Magnetic properties of the near-surface regions were studied by the conversion electron Mossbauer spectroscopy. The conversion electron Mossbauer spectra revealed apparent dependence of magnetic moments’ arrangement on the deposition time. Those results were compared with the magnetization measurements. Composition of black coating was examined by the X-ray photoelectron spectroscopy measurements.

Hematite thin films: growth and characterization

We have grown hematite (α–Fe 2 O 3) thin films on stainless steel and (001)-silicon single-crystal substrates by RF magnetron sputtering process in argon atmosphere at substrate temperatures from 400 to 800°C. Conversion Electron Mossbauer (CEM) spectra of the sample grown on stainless steel at 400°C exhibit values for hyperfine parameter characteristic of bulk hematite phase in the weak ferromagnetic state. Also, the relative line intensity ratio suggests that the magnetization vector of the polycrystalline film is aligned preferentially parallel to the surface. The X-ray diffraction (XRD) pattern of the polycrystalline thin film grown on steel substrates also corresponds to α–Fe 2 O 3. The samples were also analyzed by Atomic Force Microscopy (AFM), those grown on stainless steel reveal a morphology consisting of columnar grains with random orientation, given the inhomogeneity of the substrate surface.

Site location of Co in β-FeSi2

In order to reveal cationic site preference in β-FeSi2, Co-substituted samples synthesized by various techniques such as molecular beam epitaxy, ion implantation, and chemical vapor transport were investigated by Fe57 conversion electron Mössbauer (CEM) as well as Co57 Mössbauer emission (ME) spectroscopy. Literature on the structure of β-FeSi2 is somewhat contradictory, especially on the point of the population of the two iron sites in the orthorhombic structure. Co57 ME and Fe57 CEM spectra both showed two quadrupole split spectral components in the crystalline phase. Hyperfine parameters indicate that Co atoms substitute Fe in both Fe positions in the orthorhombic lattice. The aim of the present study was to get reliable results on the relative population of the two iron sites and determine the substitution of the iron sites by Co atoms in the β-FeSi2 lattice. The relative intensities of the two components in the absorption and emission Mössbauer spectra were found to be very similar for the samples prepared by different techniques, indicating a homogeneous distribution of Co on both Fe sites.

Phase composition at surface of Fe-3%Si alloy

The structure, phase and chemical compositions of surface layers in different depths of Fe-3%Si alloy were investigated. According to the X-ray Photoelectron Spectroscopy (XPS) spectrum (penetration depth of up to ∼ 1nm) of the as-prepared sample, a layer of SiO2 was present on the top. After the subsequent Ar+ sputtering (removing the SiO2 layer), a segregation of Si atoms and two other phases were observed. The phases were described as the cubic c-FeSi and Fe3Si. The emission57Fe Mossbauer spectra confirmed a presence of these phases. The α-Fe and solid solution of α-Fe + 1wt.%Si were recognized in the Conversion Electron Mossbauer spectra (penetration depth ∼ 300nm) while the Mossbauer spectra taken in scattering geometry with detection of 14.4 keV gamma radiation (scanning depth of ∼ 30 µm) indicate Fe-3wt.%Si solid solution as a main phase.

Magnetic moment distributions in α- Fe nanowire array

α-Fe nanowire array has been electrodeposited into anodic aluminum oxide template. The magnetic moment distributions, in the interior and near the extremities of α-Fe nanowire with 60 nm in diameter, have been studied by means of transmission Mossbauer spectroscopy (MS), conversion electron Mossbauer spectroscopy (CEMS) and micromagnetic simulation. Transmission Mossbauer spectrum (MS) shows that the magnetic moments, inside the α-Fe nanowire array, are well parallel to nanowire, while conversion electron Mossbauer spectrum (CEMS) reveals that the magnetic moments, near the extremities of nanowire, diverge from the long axis of wire, and the average diverging angle calculated by the intensity ratio of the 2,5 peaks is about 24.0°. Moreover, the magnetic moment distributions of different depths to the top of wire are counted using micromagnetic simulation, which indicates that, the interior magnetic moments are strictly parallel to nanowire, and the closer the magnetic moment to the top of wire, the larger the diverging angle. Magnetic measurement shows that this α-Fe nanowire array represents a strong magnetic anisotropy.

Structural and Magnetic Properties of Helicon-Sputtered Fe/Si Multilayers

In Fe/Si multilayers (MLs) prepared by helicon plasma sputtering, we have investigated the structural and magnetic properties as a function of Fe and Si layer thickness systematically. In [Fe 2 nm/ Si 1 nm] 30 and [Fe 3 nm/Si 1 nm] 20 MLs, large lateral Fe grains grow suggesting small atomic intermixing of Fe and Si, and antiferromagnetic coupling between Fe layers occurs, causing a magnetoresistance of about 0.1%. With decreasing the Fe layer thickness and increasing the Si layer thickness, X-ray diffraction patterns indicate peak broadening due to atomic intermixing between Fe and Si layers, and the magnetization curves indicate the change from antiferromagnetic to ferromagnetic coupling between Fe. Furthermore, in this case, the conversion electron Mossbauer spectra show that the hyperfine field decreases due to the solution of Si atoms in the bulk Fe phase. Doublet peaks appear because of the formation of iron silicides which cause the degradation of antiferromagnetic coupling.

A magnetic and conversion electron Mossbauer spectral study of amorphous Dy/sub 20/Fe/sub 80-y/-Co/sub y/ thin films

Amorphous thin films of Dy/sub 20/Fe/sub 80-y/Co/sub y/, with 0<y<20 and of ca. 40 nm thickness, have been prepared by sputtering on polyimide substrates. The 295 K conversion electron Mossbauer spectra (CEMS) of these films consist of broadened sextets which have been analyzed with a distribution of hyperfine fields in which the iron moments are oriented perpendicular to the plane of the film, an orientation which is in agreement with the perpendicular magnetic anisotropy observed herein at 295 K by vibrating sample magnetometry. The average hyperfine field and isomer shift increase linearly with increasing Co content. Both increases arise from an increase in the electron occupation of the 3d states as the cobalt content increases.

A conversion electron Mossbauer spectral study of Dy/sub 3/Fe/sub 5/O/sub 12/ thin films

Thin films of the garnet, Dy/sub 3/Fe/sub 5/O/sub 12/, have been sputtered on quartz plates using both a ceramic target of powdered Dy/sub 3/Fe/sub 5/O/sub 12/ and a metallic target of Dy and Fe. In the latter case, the metallic DyFe thin film has subsequently been oxidized at temperatures between 1173 and 1373 K. The x-ray diffraction patterns and conversion electron Mossbauer spectra, CEMS, of the thin films prepared from the ceramic target show only the garnet phase, whereas those of the thin films prepared from the metallic target show the garnet phase and two impurity phases, Fe/sub 2/O/sub 3/ and DyFeO/sub 3/. The CEMS of the ceramic target thin films indicate that the iron magnetic moments are not oriented along the [111] axis, as is usually observed in bulk materials, but are compatible with moments oriented along the [211] axis. Further, the relative areas of the six lines of the five component sextets used to model the spectra reveal that the hyperfine fields are rotated by 34/spl deg/ from the normal to the thin films. In contrast, the relative areas of the Dy/sub 3/Fe/sub 5/O/sub 12/ spectrum in the metallic target films reveal that the hyperfine fields are rotated by 60/spl deg/ from the normal to the thin films. Hence, the orientation of the iron moments is influenced by the film preparation route.

Mössbauer studies of α″-Fe16N2 and α′-Fe8N films

Conversion-electron Mossbauer spectra of epitaxial α″-Fe16N2 and α′-Fe8N films have been studied and their differences are discussed in detail. The Mossbauer spectrum of α″-Fe16N2 can be decomposed into three subspectra, which correspond to the 4d, 8h and 4c sites. The Mossbauer spectrum of α′-Fe8N can be fitted using four spectra based on a nitrogen-atom-random-distribution model. The average hyperfine field is larger (3%) for α″-Fe16N2 than for α′-Fe8N, which is approximately consistent with a 4.1% enhancement of the magnetic moments for α″-Fe16N2. The iron moments tend to locate in the film plane for α″-Fe16N2 and to arrange perpendicularly to the film plane for α′-Fe8N.

Certain features of high-dose and intensive implantation of aluminium ions in iron

Abstract Using a proton microbeam proton-induced X-ray emission (PIXE) and RBS, a formation of local surface segregations of Al in an Fe layer, has been found for the first time at an initial stage of high-dose intensive implantation (from 8×10 16 to 2×10 17 cm −2 dose irradiation). Using a slow positron beam, a profile of vacancy defects, whose depth is comparable with a depth profile of Al ions implanted into Fe with 5×10 17 cm −2 dose implantation, has been measured. The revealed regions with a local surface segregation of Al turned out to be partially amorphized after 2×10 17 cm −2 dose irradiation, according to conversion electron Mossbauer spectra (CEMS) measurements.

Some Mechanical Properties of Austempered Ductile Iron

In the present investigation the influence of the microstructure, obtained after an austempering treatment in a "process window", on the mechanical properties of austempered ductile iron has been investigated. These properties include tensile strength, elongation and hardness. Conversion electron Mossbauer spectra (CEMS) were measured, after heat treatment.

Micromagnetic and Mössbauer spectroscopic investigation of strain-induced martensite in austenitic stainless steel

Strain-induced martensite in 18/8 austenitic stainless steel was studied. Magnetic measurements and Mossbauer spectroscopic investigations were performed to characterize the amount of α’-martensite due to room-temperature plastic tensile loading. The effects of cold work and annealing heat treatment were explored using magnetic Barkhausen noise, saturation polarization, coercive force, hardness, and conversion electron Mossbauer spectra measurements. The results of the magnetic measurements were compared to results obtained by Mossbauer spectroscopy. The suggested Barkhausen noise measurement technique proved to be a useful quantitative and nondestructive method for determining the ferromagnetic phase ratio of the studied alloy.

M�ssbauer study of the spatial distribution of the active species in Cs doped Fe2O3-V2O5 catalysts

From a Cs doped Fe2O3-V2O5 (Fe:V=1.4) catalyst exhibiting an inhomogeneous composition after calcination, three different fractions have been separated by visual inspection. One fraction has been found to consist of mainly α-Fe2O3, another one of mainly FeVO4. The third fraction (S1 in the text) is the catalytically most active fraction containing besides both of the former components an amorphous phase of FexVyOz and also the dopant. By combining the results from transmission and conversion electron Mossbauer spectra it has been concluded that the amorphous component is enriched in the surface region of the crystallites of the catalyst. In addition, the formation of a thin surface layer of iron sulfide (Fe1−xS) on the third fraction has been identified. This sulfide is assumed to be formed during calcination from Cs2SO4 used for the preparation of the catalyst.

CEMS investigation of surface hyperfine interactions in Fe81B13.5Si3.5C2 glass

Ferromagnetic amorphous samples of Fe81B13.5Si3.5C2 were exposed isochronally to pulsed radio frequency (rf) annealing (vrf=54.8 MHz, τpulse=0.1 s) by employing field strengthsHrfwhich ranged from 3–12 Oe. Conversion electron Mossbauer spectra (CEMS) were analyzed in terms of the rf energy dependence of magnetic hyperfine field (HF) distribution. For field strengthsHrf>6 Oe, CEMS spectra of the rf annealed samples showed an additional quadrupole splitting (QS) distribution, which was assigned to FeSi clusters. The relative areal intensity of the QS distribution, linearly dependent on the rf field energy, is proposed as an appropriate order parameter for the onset of compositional short-range order (CSRO). An activation energy of 1.7 eV is estimated for the onset of surface CSRO in the rf annealed FeBSiC system.

Mössbauer study of boron-implanted materials: Armco-iron, carbide-rich steel X90CrMoV18 and austenitic steel X10CrNiTi189

Boron implantation was used to modify the phase composition at the surface of three different steels. Conversion electron Mossbauer spectra reveal the modification of the existing phases by the implanted boron. Furthermore, a thin amorphous layer is formed in the topmost region of all three materials.

A study of a fullyc-axis oriented dc-sputtered thin film of YBa2(Cu0.98 57Fe0.02)3O6.8 by means of CEMS, XRD and SEM

A fullyc-axis oriented thin film of YBa2(Cu0.9857Fe0.02)3O6.8 prepared by planar dcsputtering has been investigated by means of Mossbauer spectroscopy. Room temperature57Fe conversion electron Mossbauer spectra taken at different angles between the γ-ray direction and the normal (=c-axis) of the film show four subspectra: A (quadrupole splitting ΔEQ≈1.9 mm/s), B (ΔEQ≈1 mm/s), C (ΔEQ≈0.5 m/s) and D (ΔEQ≈1.6 mm/s). For subspectra A, B and C, we found the same hyperfine parameters as already published on other samples. The hyperfine parameters for subspectrum D are determined for the first time using a fully oriented sample. For D, we found the asymmetry parameterη ≥0.6 andVzz (the main component of the electric field gradient) lying in the a-b-plane.