Messung der Spinabhängigkeit der Rayleighstreuung mit Hilfe der Interferenz von Mößbauer- und Rayleighstreuung

The interference of Mößbauer scattering and Rayleigh scattering was examined and it was found that this interference can be easily observed on certain conditions. The experiment was initially carried out with a single-line transition of the 14 keV energy level of Fe⁵⁷. From the experimental data the contribution of Rayleigh scattering could be determined relative to Mößbauer scattering and it could be shown that by measuring the interference of Mößbauer scattering and Rayleigh scattering one will have a sensitive detector for Rayleigh scattering. This was used to test the spin dependence of Rayleigh scattering. For this purpose, a similar experiment was carried out with circularly polarizedγ-quanta and polarized electrons, making use of the splitting of the Fe⁵⁷ hyperfine structure. By comparison of the measured values for left-handed and right-handed circularly polarized components a strong spin dependence of the Rayleigh scattering was found.     

On the movement of iron microcrystals in high magnetic fields

The temperature dependence of the Mößbauer line intensities for iron particles coated with iron oxide is found to be the same for both the iron and the iron oxide subspectra. For the first time, this result gives direct experimental evidence that the dramatic decrease of the line intensities with raising temperaures /1,2/ is not due to changes in the phonon spectrum, but to motions of the particles instead. These motions are not influenced by external magnetic fields up to 10 T. The result is discussed in terms of different possibilities for the movement of the particles. Further more it is shown, that the geometric arrangement is different for the particles contributing to the Mößbauer effect at high, from those contributing at low temperatures.     

In beam Mößbauer spectroscopy: 57Fe in semiconductors

Abstract

An overview of results on microscopic properties, implantation features and dynamics of Fe ions implanted into Si, Ge and ZnS as investigated with in beam Mößbauer spectroscopy(IBMS) is given. Potential and limitations of the method are discussed.     

Mößbauereffekt anFe 57 nach Neutroneneinfang in Fe56

Mößbauer effect measurements with the 14.4 keV gamma rays of Fe⁵⁷ following thermal neutron capture in Fe⁵⁶ are reported. During the transition from the capture level at 7.6 MeV to the first excited state at 14.4 keV recoil energies up to 549 eV are imparted to the Fe⁵⁷ nuclei. Thus the Mößbauer gamma rays are emitted by nuclei displaced from their normal lattice positions. The measurements have been performed in order to get informations about the final position of the recoiled nuclei in metallic iron and in ordered Fe-Al alloys. Mößbauer spectra of recoil atoms in metallic iron did not show any significant deviation from the spectra of atoms on normal lattice positions. In ordered FeAl alloys of CsCl structure changes in the isomer shift due to recoil effects have been found. In a Fe₃Al alloy of DO₃ type order additional changes in the internal magnetic field have been observed. All results are discussed in terms of possible final positions for the primary recoiled iron atoms in the lattice.     

A comparison of the measurement of internal fields in magnetic materials by Mössbauer and μSR spectroscopy

A comparison is made between the application of Mößbauer spectroscopy and Muon Spin Rotation for the study of magnetic materials. Some of the problems and the strengths of the two methods are discussed in connection with the determination internal fields.     

Degradation of the Giant Magnetoresistance in Fe/Cr Multilayers Due to Ar-Ion Beam Mixing

The influence of 200 keV Ar-ion irradiation on the interlayer coupling in the Fe/Cr multilayer system exhibiting the giant magnetoresistance effect (GMR) is studied by conversion electron Mössbauer spectroscopy (CEMS), VSM hysteresis loops, magnetoresistivity and electric resistivity measurements and supplemented by the small-angle X-ray diffraction (SAXRD). The increase of Ar ion dose causes an increase of interface roughness, as evidenced by the increase of the Fe step-sites detected by CEMS as a result of which the GMR gradually decreases and vanishes at doses exceeding 1×10¹⁴ Ar/cm². A degradation of GMR with increasing Ar-ion dose is related to the formation of pinholes between Fe layers and the decrease of the antiferromagnetically coupled fraction.

     

Quadrupolaufspaltung und Isomerieverschiebung der 14,4 keV γ-Linie von Fe57 in metall-organischen Eisenverbindungen

The Mößbauer absorption of the 14.4 keVγ-ray of Fe⁵⁷ was investigated in Ferrocene, Fe(C₅H₅)₂, and in a Ferriciniumcation [Fe(C H₅)₂]BF₄. The resonance absorption spectra reveal a quadrupole splitting and an isomeric shift of the 14.4 keV level in both compounds. The data give some evidence of the occupation of the molecular orbits formed in these complexes.     

Structural-Phase Transformations and Short-Range Order Evolution in the Fe–Cr System during Mechanical Alloying

Physics of the Solid State - Using Mössbauer spectroscopy on 57Fe nuclei and X-ray diffraction, the mechanism of mechanical alloying in a planetary ball mill of the Fe–Cr nanocrystalline...     

CEMS characterisation of Fe/high-κ oxide interfaces

The interfaces between Fe and different high-κ oxides are investigated by means of conversion electron Mössbauer spectroscopy (CEMS). Information on the magnetic ordering at the interface is obtained from the magnetic hyperfine splitting of the Mössbauer spectra. The reactivity of the Fe atoms at the interface (intermixing) is also estimated by CEMS. X-ray diffraction (XRD) and X-ray reflectivity (XRR) provide additional information on the intermixing and different phases present at the interface. CEM-spectra show the presence of both ferromagnetic and paramagnetic phases. CEMS and XRD results show that the Fe/HfO₂ and Fe/Al₂O₃ interfaces are the least reactive. The degree of intermixing between Fe and the high-κ oxide is determined by the oxide surface roughness.     

Mössbauer studies of a martensitic transformation and of cryogenic treatments of a D2 tool steel

A D2 tool steel X153CrVMo12 with composition C1.53 Cr12 V0.95 Mo0.80 Mn0.40(wt% Fe balanced) was studied by use of Mössbauer spectroscopy and X-ray diffraction. It was observed that the study of carbides by X-ray diffraction was difficult while Mössbauer spectroscopy gives some light on the process occurring during cryogenic treatment. With the increase of the martensitic phase the carbides decrease and are dissolved in solid solution of martensite as well as the chromium element.     

151Eu and57Fe Mössbauer effect studies of magnetic interactions in europium transition element oxides solution

The solid state solutions of europium transition element oxides Eu (Fe0.8M0.2)O₃ (M=Sc,Cr,Mn,Co) are synthesized. The X-ray diffraction of the compound shows that all the compounds possess the perovskite structures. Both the¹⁵¹Eu Mössbauer spectra and the⁵⁷Fe Mössbauer spectra are measured. The hyperfine magnetic field and non-axisymmetric electric field gradient are observed in the¹⁵¹Eu Mössbauer spectrum. The⁵⁷Fe Mössbauer spectrum shows that there are four components of hyperfine fields corresponding to four kinds of different neighbours of the Fe ion.     

Hyperfine-interaction studies of surfaces

Applications of hyperfine-interaction techniques, like NMR, PAC and Mößbauer spectroscopy, to well-characterized surfaces are discussed and the present knowledge of surface hyperfine fields is reviewed. Measurements of nuclear spin relaxation permit to extract the local density of electron states at the Fermi level of adsorbed alkali atoms. From the observed electric-field-gradient properties surface probe sites and diffusion processes can be inferred; the experimentally determined magnetic hyperfine fields give access to the electron-spin behaviour at magnetic surfaces.     

Über einige Probleme bei instabilen quantenmechanischen Systemen

If an exponential decay law is measured (which clearly need not be found in every case) it cannot be concluded that the line shape must be lorentzian. To show that the possible energy spectra may differ from a Lorentz shape by a well measurable amount an example of such a spectrum is constructed, leading to an exponential decay law in an even better approximation than a lorentzian spectrum. Hereafter various facts about decaying systems are discussed in connection with scattering theory. Finally it is shown that ordinary Mößbauer experiments are not suited for line shape measurements and modified experiments are proposed.     

Observation of localized modes in TbO x using the Mößbauer effect

The resonant absorption of the 58 keV Mößbauer line under excitation of one phonon states in TbO _x was investigated. Using an ultra centrifuge, theγ energy was shifted by ±25meV. Narrow absorption lines at 14.1 meV, 16.0 meV and presumably at 12.3 meV are interpreted as being caused by localized modes of the terbium ion.     

Interface study of Ag/57Fe/Ag trilayer using Mössbauer and X-ray standing wave analysis

Interface of Ag/⁵⁷Fe/Ag trilayer has been studied with a depth resolution of a fraction of a nanometer using x-ray standing waves generated by a W/Si multilayer mirror used as a substrate. Two interfaces of 38 Å thick Fe layer in Ag/⁵⁷Fe/Ag trilayer are clearly resolved. It is found that the rms roughness of the two interfaces Fe-on-Ag and Ag-on-Fe are 10 ± 1.0 and 6 ± 1.0 Å, respectively. Conversion electron Mössbauer spectroscopy (CEMS) has been used to get information about the volume fraction of the intermixed region and the estimated roughness from the relative area of the two sextets of CEMS spectra is found to be 7.0 Å which is consistent with the average roughness obtained by X-ray fluorescence measurements. However, the asymmetry of the interfaces can not be inferred from CEMS measurements.     

Mössbauer study of the mechanical alloying of highly concentrated Fe–Cr alloys

Mössbauer spectroscopy and X-ray diffraction are used to investigate the kinetics of the mechanical alloying (MA) of Fe and Cr powdered mixtures with Cr contents of 20 to 48 at % in the initial mixtures. Variations during mechanical alloying in specimens with Cr contents of ≤30% and >30% in the initial mixtures are observed for the first time. After MA, specimens are characterized by heterogeneous concentration distributions of Cr and Fe atoms in particles, especially at Cr concentrations of >30% in the initial mixture.     

Optimization of a conversion electron Mössbauer spectroscopy gas flow He/CH4 proportional counter

A new detector for CEMS has been built and optimized with respect to the statistical quality of spectra obtained. The optimization has been performed by measuring Mößbauer and pulse height spectra at in- and off-resonance. Single channel analyzer settings were calculated by a new optimization routine. A comparison of different detector designs has been performed using the statistical utility rate of spectra obtained from a stainless steel foil. A procedure for determining optimal operating parameters for ICEMS gas flow proportional counters is proposed.     

Mechanical alloying of Fe and Cr: Structural and magnetic studies

Mechanical milling of a mixture of pure iron and chromium powders with a nominal composition of 28 at. % of Fe and 72 at. % of Cr was performed using two kinds of tools. The alloying process was followed by X ray diffraction and⁵⁷Fe Mössbauer spectroscopy. The room temperature Mössbauer spectra revealed the formation of a broad single line at the expense of the area of α-Fe sextet. At 4.2 °K most of the singlet still remains unsplit. This behavior may be due to some metastable structure induced by the preparation method.     

Study of the magnetic properties of GdZn compound using PAC spectroscopy with 140Ce and 111Cd as probe nuclei

Nanocrystalline Al₆₄Cu₂₃Fe₁₃ icosahedral quasicrystal has been obtained by milling of solid quasicrystal precursors prepared by arc-melt. The local structure around Fe atoms was studied by Mössbauer spectroscopy using a quadrupole splitting distribution method. Mössbauer results of annealed and milled samples show the existence of a broadened distribution of Fe sites which is associated to intrinsic disorder. The structural characterization was determined using x-ray diffraction. The average grain-size of the nanostructured quasicrystal, obtained from the line broadening of the X-ray diffraction peaks, was estimated to be of the order of 10 nm for a sample milled by 5 h.     

Mössbauer and magnetic studies of nanocomposites containing iron oxides and humic acids

A sample of volcanic ashes emanated from the Osorno volcano, southern Chile, was characterized with X-ray fluorescence, X-ray diffraction and ⁵⁷Fe Mössbauer spectroscopy, in an attempt to identify the iron-bearing minerals of that geologically recent magmatic deposit. X-ray patterns indicated that the sample is mainly constituted of anorthite, Fe-diopside-type and Ca-magnetite. The crystallographic structures of these dominant iron minerals are proposed on basis of their chemical composition and corresponding Mössbauer data to support models refined by fitting powder X-ray diffraction data with the Rietveld algorithm.