Mössbauer study of amorphous alloys irradiated with energetic heavy ions

The Mössbauer spectroscopy was applied to study radiation damage in metal-metalloid amorphous alloys irradiated with⁴⁰Ar/E=225 MeV/ or¹³²Xe/E=120 MeV/ ions at room temperature. The observed dose dependent changes in the intensity of the Mössbauer lines and of the hyperfine field distributions can be associated with structural changes in short-range order of the irradiated amorphous alloys.     

Ion beam induced reactions in Fe-PVC thin film structures

Films of⁵⁷Fe, 50–100 Å thick, were evaporated onto PVC substrates. Samples were irradiated with 48 McV Br⁸⁺ ions. Recoiling target atoms, ejected from the sample, were collected in a time of flight-energy detector telescope to monitor effects induced by the impinging Br ions. Conversion electron Mössbauer spectra were recorded before and after ion irradiation. Substantial radiation induced alterations were observed both in recoil and Mössbauer spectra.     

Magnetic properties of neutron irradiated RPV steel

The neutron irradiated reactor pressure vessel (RPV) steels at various dose of 0–10¹⁸ n/cm² have been studied with Mössbauer, x-ray diffraction, and VSM. The Mössbauer data shows that the value of magnetic hyperfine field of Fe atom that exist at martensite is 330 kOe at site 1 and 305 kOe at site 2. At room temperature, the total absorption area of Mössbauer spectra with respect to irradiation of neutron is constant for the dose of 0–10¹⁶ n/cm², while over the dose of 0–10¹⁷ n/cm² the absorption area decreases rapidly. But the doublet area for the dose of 0–10¹⁶ n/cm² is constant, while over the dose of 10¹⁷ n/cm² it increases with increasing the fluence level of neutron. The coercivity and remanence of the neutron irradiated samples do not change significantly. But the maximum induction decreases by 5% at 10¹⁸ n/cm², compared with that of the as-received sample.     

Location of 125I implanted in silicon and germanium

A Mössbauer study of ¹²⁵I implanted into silicon and germanium lattices with various dose values was performed. The spectra measured after thermal annealing suggested an off-substitutional site population for I in the silicon lattice. The Mössbauer spectra showed no difference in the hyperfine splitting of ¹²⁵Te after electron capture of ¹²⁵I in comparison with that obtained after the isomeric transition of implanted ^125mTe. The site populations of Te and I atoms after implantation and thermal annealings were concluded as being the same.     

Depth selective conversion electron spectrometer for magnetic characterisation of thin films

A high transmission spherical electrostatic electron spectrometer for Mössbauer conversion electron spectroscopy was built. Depth selective Mössbauer studies can be carried out from T=4 K to 350 K in a 10^?8 Torr vacuum changing the electron energies and/or the electron escape angles.     

Magnetic Study of Nanocrystalline Ferrites and the Effect of Swift Heavy Ion Irradiation

100 MeV Si⁺⁷ irradiation induced modifications in the structural and magnetic properties of Mg_0.95Mn_0.05Fe₂O₄ nanoparticles have been studied by using X-ray diffraction, Mössbauer spectroscopy and a SQUID magnetometer. The X-ray diffraction patterns indicate the presence of single-phase cubic spinel structure of the samples. The particle size was estimated from the broadened (311) X-ray diffraction peak using the well-known Scherrer equation. The milling process reduced the average particle size to the nanometer range. After irradiation a slight increase in the particle size was observed. With the room temperature Mössbauer spectroscopy, superparamagnetic relaxation effects were observed in the pristine as well as in the irradiated samples. No appreciable changes were observed in the room temperature Mössbauer spectra after ion irradiation. Mössbauer spectroscopy performed on a 12 h milled pristine sample (6 nm) confirmed the transition to a magnetically ordered state for temperatures less than 140 K. All the samples showed well-defined magnetic ordering at 5 K, whereas, at room temperature they were in a superparamagnetic state. From the magnetization studies performed on the irradiated samples, it was concluded that the saturation magnetization was enhanced. This was explained on the basis of SHI irradiation induced modifications in surface states of the nanoparticles.     

Comparative Mössbauer study of EuBa2 (Cu1-x 57Fe x )3O7-d and EuBa2Cu1-x 57Fe x )4O8 superconductors

Structural differences between the 1-2-3 type and 1-2-4 type high temperature superconductors were studied by comparing their¹⁵¹Eu and⁵⁷Fe Mössbauer spectra. The similarities between the corresponding Mössbauer parameters of Eu Mössbauer spectra of 1-2-3 and 1-2-4 compounds demonstrate that the Eu state can be considered to be identical in both perovskites. The changes in the Fe Mössbauer parameters of 1-2-4 type superconductor compared to those of 1-2-3 type compound can be associated with structural differences.     

Electron delocalization observed in the Mössbauer spectrum of ilvaite

Mössbauer spectroscopy is used to detect species associated with delocalized electrons undergoing Fe²⁺ → Fe³⁺ electron delocation in ilvaite. Mössbauer spectra of a suite of naturally occurring ilvaites were recorded from 80K to 575K and fit to five quadrupole doublets assigned to Fe²⁺ (A), Fe²⁺ (B), Fe³⁺ (A), and Fe²⁺ (A) → Fe³⁺ (A)6c and ⊥c. These assignments disagree with earlier interpretations of temperature dependent quadrupole splitting and isomer shift in ilvaite.     

Mössbauer study of Tl containing highT c superconductors

Mössbauer spectroscopy, X-ray diffractometry, ESR and electrical resistivity measurements, were used to study highT _c (above 100 K) superconducting materials in order to get information about the effect of the preparation circumstances as well as about the anomalous behaviour in⁵⁷Fe and¹¹⁹Sn doped TlBaCaCu(⁵⁷Fe)O_4.5+δ and TlBaCuCu(¹¹⁹Sn)O_4.5+δ superconductors. We have found that the Mössbauer parameters strongly depend on the preparation circumstances. In many cases the presence of Mössbauer lines of nonsuperconducting oxide phases indicated that the iron and tin could not entirely built in into the lattice of superconductor. Four valence state tin and four valence state iron sites were identified in the superconducting phases. We have found anomalous temperature dependent changes in the⁵⁷Fe Mössbauer spectra of TlBaCaCu(⁵⁷Fe)O_4.5+δ samples around theT _c between 105–135 K. In this temperature range the total area of the spectrum temporary increases.     

The magnetic hyperfine interaction of iron atoms isolated in a xenon matrix in the presence of an external magnetic field

The Mössbauer effect has been used to measure the magnetic hyperfine interaction of isolated ⁵⁷Fe atoms in solid xenon with an applied external magnetic field. A field dependent Mössbauer absorption spectrum is observed. The ground state of these iron atoms is a triplet, which is split in the external field. The Mössbauer spectrum was analyzed taking into consideration relaxation effects. For an applied external field of 28 kOe an internal magnetic field at the ⁵⁷Fe nucleus of 700± 15 kOe was observed (external field included).     

Experimental search for laser-induced effects in <Superscript>151</Superscript>Eu and <Superscript>57</Superscript>Fe doped crystals

We studied the Mössbauer effect in ¹⁵¹Eu and ⁵⁷Fe doped crystals in the search for laser-induced effects caused by changes in the hyperfine interaction due to electronic excitation. The Mössbauer spectra observed in the presence of laser radiation demonstrated a notable change of the shape of the ¹⁵¹Eu spectrum and the appearance of an additional hyperfine pattern in the case of the ⁵⁷Fe Mössbauer resonance.     

Mössbauer study on the deformed surface of high-manganese steel

Conversion electron, X-ray backscattering and conventional transmission⁵⁷Fe Mössbauer measurements have been performed to investigate the origin of the remarkable work hardening at the surface of a high-manganese steel which is called Hadfield steel. Mössbauer results show that α′ martensite has no relation to work hardening. From the comparison of conversion electron to X-ray backscattering spectra, the occurrence of decarbonization is suggested at the surface. The transmission Mössbauer spectrum at 20 K for deformed specimen shows the existence of ε martensite which could be related to the work hardening of Hadfield steel.     

The Investigation of the Magnetic Properties of Metallic Multilayers by Angle Dependent Mössbauer Spectroscopy

Hyperfine Interactions - Hyperfine fields (hff) in Fe/V and Fe/Co superlattices have been investigated using angle dependent Mössbauer spectroscopy. Conversion electron Mössbauer (CEM)...     

Electronic and magnetic properties of the iron borate Fe2BO4

Polycrystalline Fe₂BO₄ was prepared by solid state reactions and its electronic and magnetic properties were investigated by Mössbauer spectroscopy and magnetization measurements. The Mössbauer spectra of Fe₂BO₄ below 270 K indicate the presence of Fe²⁺ and Fe³⁺ sites in the structure, in a ratio 1 : 1. Above this temperature electron delocalization sets in between the divalent and trivalent iron ions and Fe^2.5+ states are observed. The temperature dependence of the Mössbauer spectra and magnetization measurements clearly show the onset of magnetic order below 155 K.     

A Mössbauer effect investigation of the magnetic behaviour of (Fe,Co)S1 + x solid solutions

The Mössbauer spectra of (Fe, Co)S_{1 + x} were recorded at room temperature and 4.2 K for samples of varying composition to study the magnetic behaviour of the solid solutions. The Mössbauer spectra are split magnetically at iron concentrations above 16% Fe. For samples with less than 16%Fe, the Mössbauer spectra show no evidence of magnetic splitting down to 4.2 K. The room temperature centre shift data appear to vary continuously with composition and the hyperfine magnetic field decreases with decreasing Fe²⁺ concentration. A Mössbauer spectrum of ⁵⁷Fe:CoS at 4.2 K in an external field of 25 kOe showed no evidence of magnetic splitting beyond that caused by the applied field, indicating a net zero internal field.A high spin to low spin transition in Fe²⁺ is ruled out as being responsible for the observed magnetic behaviour on the basis of the centre shift data. The Mössbauer data are interpreted to indicate a substantial increase in electron delocalization towards the ligands as the 〈M-S〉 distance decreases with decreasing Fe²⁺concentration. This causes a reduction in the magnitude of the internal magnetic field contributions as well as a decrease of shielding of the nucleus, giving rise to the observed Mössbauer parameters.The Mössbauer spectrum of ⁵⁷Fe:CoS at room temperature is compared with the spectrum of FeS above the 6.7 GPa phase transition at room temperature. The similarities of the centre shift and the 〈M-S〉 distance in the two phases indicate that covalency may also be responsible for the observed high pressure behaviour of FeS, and not the presence of Fe³⁺ as was originally suggested.     

First Principles Calculations of Mössbauer Spectra of Intermetallic Anodes for Lithium-Ion Batteries

Changes in ¹¹⁹Sn and ¹²¹Sb Mössbauer spectra due to lithium insertion in tin and antimony based anode materials for lithium-ion batteries are analysed. Due to the complexity of the spectra linear augmented plane wave calculations of the electronic density were used to evaluate the electron density and the electric field gradients at the nucleus. The ¹¹⁹Sn Mössbauer spectrum of SnO+3.5 Li was evaluated from the theoretical spectra of the Li–Sn alloys. The observed good agreement between experimental and ab initio spectra is consistent with the reversible lithium insertion mechanism based on the formation of Li–Sn alloys. The analysis of the ¹²¹Sb Mössbauer spectra for Li insertion into CoSb₃ is somewhat more complex but calculations of the Mössbauer parameters clearly indicate the existence of Li₃Sb at the end of the first discharge.

     

Phonon-induced charge transfer in ZnO

Using the high-resolution 93.3 keV Mössbauer transition in ⁶⁷Zn we studied the temperature dependence of the center shift in ZnO single crystals between 4.2 and 77.3 K. Already at low temperature dependent isomer shift is present. The latter originates from phonon-induced electron transfer from zinc to oxygen     

Application of 57Fe Mössbauer spectroscopy as a tool for mining exploration of bornite (Cu5FeS4) copper ore

Nuclear resonance methods, including Mössbauer spectroscopy,are considered as unique techniques suitable for remote on-line mineralogical analysis. The employment of these methods provides potentially significant commercial benefits for mining industry. As applied to copper sulfide ores, Mössbauer spectroscopy method is suitable for the analysis noted. Bornite (formally Cu₅FeS₄) is a significant part of copper ore and identification of its properties is important for economic exploitation of commercial copper ore deposits. A series of natural bornite samples was studied by ⁵⁷Fe Mössbauer spectroscopy. Two aspects were considered: reexamination of ⁵⁷Fe Mössbauer properties of natural bornite samples and their stability irrespective of origin and potential use of miniaturized Mössbauer spectrometers MIMOS II for in-situ bornite identification. The results obtained show a number of potential benefits of introducing the available portative Mössbauer equipment into the mining industry for express mineralogical analysis. In addition, results of some preliminary ^63,65Cu nuclear quadrupole resonance (NQR) studies of bornite are reported and their merits with Mössbauer techniques for bornite detection discussed.     

Quadrupole Splitting Distributions in Grandidierite and Kornerupine from Antarctica

The Mössbauer spectra of grandidierite and kornerupine at 298 and 90 K were measured. The quadrupole splitting distributions from the Mössbauer spectra were obtained by using the Voigt-based method, and the assignments for QSDs in the Mössbauer spectra of both minerals are presented. Site occupancies of iron in the crystal structures of two minerals were determined, and the chemical formulas of grandidierite and kornerupine were rewritten based on the relative absorption areas and Mössbauer fraction f for Fe³⁺ and Fe²⁺.     

Clays and clay minerals: The firing process

⁵⁷Fe Mössbauer spectroscopy reveals changes in iron valence and iron site geometry when clays and clay minerals are heated, and allows a distinction to be made between paramagnetic and magnetically ordered phases. Mössbauer spectra can thus reveal the extent of iron retention in silicate structures upon heating, the identity of iron oxides initially present or formed during the heating process and their transformations, and the character of the atmosphere under which heating was carried out. This makes Mössbauer spectroscopy the most effective tool for the characterization of changes induced by heating phyllosilicates and iron oxides.