A semi-microscopic calculation for the (2p-1f) nuclei59Ni,56Fe and57Fe

The level scheme, spectroscopic factors and electromagnetic properties of⁵⁹Ni,⁵⁶Fe and⁵⁷Fe are described in a semi-microscopic model where either two- or three-particle clusters are coupled to a quadrupole vibrational field. The present results are compared with the available experimental data and with the results of previous theoretical investigations.     

Experimental evidences of clusters with different short range order in amorphous alloys

⁵⁶Fe,⁵⁷Fe,¹⁰B and¹¹B isotopes were used for binary alloys. The signals of B (40,5 MHz) and Fe (43 MHz) from α-Fe in binary Fe−B crystalline and amorphous alloys were found besides the signals of these nuclei in t-and o-phase or clusters like these phases. The NMR on (51)V impurity nuclei in Fe−B alloys was used as well. Only amorphous Fe-(^<15 at.%B) alloys had the clusters with o-, t-Fe₃B and α-Fe short range order.     

Local states of iron in iron implanted hematite Fe2O3

Powder samples of⁵⁷Fe₂O₃ and⁵⁶Fe₂O₃ were implanted with⁵⁶Fe and⁵⁷Fe ions, respectively. By the use of Conversion Electron Mössbauer Spectroscopy it was possible to observe the local states of implanted ions (⁵⁷Fe in⁵⁶Fe₂O₃) or the states of iron atoms from the target which were displaced during implantation due to the ballistic processes (⁵⁶Fe in⁵⁷Fe₂O₃). The implanted and displaced iron atoms appear in three different states: (i) in regular substitutional positions of Fe₂O₃, (ii) as magnetite Fe₃O₄-type structures and (iii) paramagnetic FeO_1?x state. The observed fractions of each state agree rather well with the calculated values obtained from the local iron atom enrichment at the surface as well as from the analysis of the equilibrium phase diagram for the binary Fe?O system. However, in⁵⁷Fe implanted samples some enhancement of the FeO_1?x fraction was found in comparison with the⁵⁶Fe implanted hematite.     

31P NMR in the ferromagnetic state of amorphous Fe75P15C10

The first observation of a metalloid site hyperfine field (hf) distribution in a ferromagnetic amorphous alloy is reported using a spin-echo NMR technique. The ³¹P nuclei in amorphous Fe₇₅P₁₅C₁₀ show a hf distribution with a maximum at about 27 kOe. The sample was prepared with Fe enriched to 99.93% in ⁵⁶Fe. A comparison of the NMR spectra on samples containing natural Fe and ⁵⁶Fe also provides the ⁵⁷Fe hf distribution whose peak value agrees with Mössbauer results.     

Variation of superparamagnetic properties with iron loading in mammalian ferritin

The average blocking temperatures of ferritin molecules containing differing amounts of iron were determined by Mossbauer spectroscopy. The results imply that the magnetic anisotropy of the ferritin core particles is a function of particle volume. By addition of⁵⁷Fe to ferritin core particles it was determined that, at a given temperature within the superpara-magnetic temperature region, the “last-in” ferric ions have average relaxation times that are shorter than those of the bulk ferric ions.     

Mössbauer study of cobalt and iron in the cyanobacterium (blue green alga)

Mössbauer emission and absorption studies have been performed on cobalt and iron in the cyanobacterium (blue-green alga). The Mössbauer spectrum of the cyanobacterium cultivated with⁵⁷Co is decomposed into two doublets. The parameters of the major doublet are in good agreement with those of cyanocobalamin (vitamin B₁₂) labeled with⁵⁷Co. The other minor doublet has parameters close to those of Fe(II) coordinated with six nitrogen atoms. These suggest that cobalt is used for the biosynthesis of vitamin B₁₂ or its analogs in the cyanobacterium. The spectra of the cyanobacterium grown with⁵⁷Fe show that iron is in the high-spin trivalent state and possibly in the form of ferritin, iron storage protein.     

Mössbauer and vibrational DOS studies of diluted magnetic tin oxides and nano iron oxides

The magnetic properties and Mössbauer results for SnO₂ doped with ⁵⁷Fe are reviewed, and the values of isomer shift and quadrupole splitting are compared with the results obtained by ab initio calculations. It is concluded that the exchange interactions between oxygen defects and magnetic atoms are responsible for long range magnetic interactions of dilute Fe ions dispersed in SnO₂. Fe atom precipitated clusters may be formed in highly Fe doped SnO₂ samples by annealing at relatively high temperatures for several hours. The reduction of the particle size to nano-scale dimensions induces magnetization, which can be associated with oxygen defects. We have measured the nuclear inelastic scattering (NIS) spectra of Fe oxides, and ⁵⁷Fe and (Co or Mn) doped SnO₂ synthesized mainly by sol–gel methods and we have derived the vibration density of states (VDOS). The local phonons are sensitive to the presence of precipitated clusters.     

Magnetic and quadrupolar studies of the iron storage overload in livers

Absorption⁵⁷Fe Mössbauer spectra, performed directly on tissues of liver with iron overload due to an excessive intestinal iron absorption or induced by hypertransfusional therapeutics, have pointed out a new high spin ferric storage iron besides the ferritin and hemosiderin. Mössbauer studies, carried out on ferritin and hemosiderin fractions isolated from normal and overloaded livers, show that this compound, only present in the secondary iron overload (transfusional pathway), seems characteristic of the physiological process which induces the iron overload.     

Morin transition suppression in Polycrystalline 57Hematite (α-Fe2O3) exposed to 56Fe(II)

We used the isotope selectivity of ⁵⁷Fe Mössbauer spectroscopy to investigate changes in the magnetic properties of polycrystalline hematite exposed to ferrous iron (Fe(II)). We found that sorption of ⁵⁶Fe(II), followed by interfacial electron exchange, alters the bulk magnetic properties of ⁵⁷hematite. After reaction with ⁵⁶Fe(II), we observed partial suppression of the Morin transition of ⁵⁷hematite to below 13 K. This is significantly lower than the Morin temperature (T _M) of ～230 K measured for isotopically enriched polycrystalline ⁵⁷hematite, as well as the T _M of 264?±?2 K reported for normal polycrystalline hematite.     

Surface sensitivity of low energy electron Mössbauer spectroscopy (LEEMS) using57Fe

Very low energy electrons (LEE) (E _e ≤15 eV) are produced with high intensity directly by Mössbauerabsorption and conversion in the case of⁵⁷Fe [1, 4, 5]. These electrons should be very surface sensitive due to their very low attenuation length compared to the 7.3 keV K-Conversion electrons of⁵⁷Fe [5, 11]. We have examined the surface sensitivity of these resonant LEE, using nonresonant⁵⁶Fe metal and⁵⁶Fe stainless steel foils coated with about 20 Å and 50 Å⁵⁷Fe, respectively. They were exposed to air after evaporation: The 20 Å samples are found to be fully oxidized [5]. Depth Selective Conversion Electron Mössbauer Spectroscopy (DCEMS), performed with a high transmission orange type magnetic spectrometer [5, 6, 13] reveals a two layer structure of the 50 Å samples. Low Energy Electron Mössbauer Spectroscopy (LEEMS) [5] is found to be significantly more surface sensitive than conventional DCEMS, but not as surface sensitive as Auger Electron Mössbauer Spectroscopy (AEMS) using LMM-Auger electrons of 500–600 eV, as expected due to the different mean free path. But because of the very low intensity of these Auger electrons this mode appears to be not very useful for practical application.     

Non-Langevin behaviour of the uncompensated magnetization in nanoparticles of artificial ferritin

The magnetic behaviour of nanoparticles of antiferromagnetic artificial ferritin has been investigated by ⁵⁷Fe M?ssbauer absorption spectroscopy and magnetization measurements, in the temperature range 2.5-250 K and with magnetic fields up to 7 T. Samples containing nanoparticles with an average number of ⁵⁷Fe atoms ranging from 400 to 2 500 were studied. By analysing the magnetic susceptibility and zero field M?ssbauer data, the anisotropy energy per unit volume is found, in agreement with some of the earlier studies, to have a value typical for ferric oxides, i.e. a few 10⁵ ergs/cm³. By comparing the results of the two experimental methods at higher fields, we show that, contrary to what is currently assumed, the uncompensated magnetization of the ferritin cores in the superparamagnetic regime does not follow a Langevin law. For magnetic fields below the spin-flop field, we propose an approximate law for the field and temperature variation of the uncompensated magnetization, which was early evoked by Néel but has so far never been applied to real antiferromagnetic systems. More generally, this approach should apply to randomly oriented antiferromagnetic nanoparticles systems with weak uncompensated moments. Received 20 January 2000     

Comparison of the dynamics of the magnetic order above Tf in (Au,Fe) and Y(Fe,Al)2

⁵⁷Fe Mössbauer spectra in external fields up to 13.5 T are recorded for two typical cluster glasses (Au, Fe) and Y(Fe, Al)₂ to investigate the spin dynamics above the freezing temperature. The spectra are analyzed with a model in which magnetic clusters are assumed to form and decay stochastically.     

57Fe Mössbauer Spectroscopic Investigation of Low-Iron Coals and Their Flyash

Trends in the speciation of iron and sulfur in high iron/sulfur coals are well-established. Less is known concerning iron and sulfur speciation in low sulfur coals such as those investigated in this study. Low sulfur coals and their flyash from Thunder Bay, Ontario, Canada and Atikokan, West Virginia, U.S.A. have been investigated by means of ⁵⁷Fe Mössbauer spectroscopy, X-ray diffraction and X-ray fluorescence. Virgin coals, containing approximately 0.1% Fe, exhibited Mössbauer spectra too low in intensity to characterize the phases present. The flyash exhibited well-resolved, simple doublets with ΔE_Q=1.16 mm s^?1 (Canada) and 1.26 mm s^?1 (U.S.A.) and isomer shift values (w.r.t. Fe) of 0.22 mm s^?1 and 0.23 mm s^?1, respectively, characteristic of Fe³⁺. The linewidths of ～0.80 mm s^?1 are unusually large. Treatment of the flyash with cold, hydrofluoric acid resulted in a sample that exhibited very little absorption in its ⁵⁷Fe Mössbauer spectrum. This result, in conjunction with the linewidths, indicates that the Fe is present in the flyash mainly as a silicate glass.     

CEMS study of defect annealing in Fe implanted AlN

An AlN thin film grown on sapphire substrate was implanted with 45 keV ⁵⁷Fe and ⁵⁶Fe ions at several energies to achieve a homogeneous concentration profile of approximately 2.6 at.%. in the AlN film. Conversion electron Mössbauer Spectroscopy data were collected after annealing the sample up to 900 °C. The spectra were fitted with three components, a single line attributed to small Fe clusters, and two quadrupole split doublets attributed to Fe substituting Al in the wurtzite AlN lattice and to Fe located in implantation induced lattice damage. The damage component shows significant decrease on annealing up to 900 °C, accompanied by corresponding increases in the singlet component and the substitutional Fe.     

The relationship between ferritin and haemosiderin

Under conditions of iron overload haemosiderin may replace ferritin as a major iron store. Much of this haemosiderin is contained within secondary lysosomes, known as sidersomes, where it is thought to have arisen by breakdown of ferritin. We report on⁵⁷Fe Mössbauer studies of ferritin and haemosiderin prepared from iron loaded rat livers and measured over a wide temperature range. Our results indicate significantly different superparamagnetic blocking temperatures consistent with the model whereby haemosiderin is derived from ferritin by lysosomal degradation.     

Neutron in-beam Mössbauer spectroscopic study of iron disulfide at room temperature

An in-beam emission Mössbauer spectrum of ⁵⁷Fe arising from the ⁵⁶Fe(n, γ) ⁵⁷Fe reaction in iron disulfide at room temperature was measured with a parallel plate avalanche counter. It was clearly observed that the nuclear reaction and the following process lead to the production of a new chemical species of iron different from the parent compound.     

Ion-beam induced changes in magnetic and microstructural properties of thin iron films

Changes in magnetic and structural properties of 60–82 nm iron films induced by heavy-ion implantation were studied using the magneto-optical Kerr effect, M?ssbauer spectroscopy, Rutherford backscattering spectroscopy, X-ray diffraction, and X-ray absorption fine structure. The influence of ion-beam parameters (ion mass, fluence) and of sample parameters (external magnetic field and stress during implantation) were investigated. The Fe films, some of them containing a thin ⁵⁷Fe marker layer for M?ssbauer spectroscopy, were deposited on Si(100) substrates, by electron-beam and effusion-cell evaporation. The films were irradiated with ²⁰Ne, ⁵⁶Fe, ⁸⁶Kr and ¹³²Xe ions at energies chosen so that the implantation profiles peaked near the middle of the Fe films. The as-deposited films were magnetically isotropic and had a high coercivity. After ion implantation, the coercivity decreased and magnetic anisotropy developed. Both changes correlated with a decrease in the internal film stress. External mechanical stress applied during the irradiation had hardly any influence on the magnetic texture, opposite to an external magnetic field applied during or before ion implantation. The results are compared with those obtained for ion-irradiated polycrystalline Ni films and epitaxial Fe films and discussed with respect to the role of radiation-induced extended defects as pinning centers.     

Bulk properties of iron isotopes

Nuclear level densities and radiative strength functions (RSFs) in ⁵⁶Fe and ⁵⁷Fe were measured using the ⁵⁷Fe(³He, αγ) and ⁵⁷Fe(³He, ³He′γ) reactions, respectively, at the Oslo Cyclotron Laboratory. A low-energy enhancement in the RSF below 4-MeV energy was observed. This finding cannot be explained by common theoretical models. In a second experiment, two-step cascade intensities with soft primary transitions from the ⁵⁶Fe(n, 2γ) reaction were measured. The agreement between the two experiments confirms the low-energy enhancement in the RSFs. In a third experiment, the neutron evaporation spectrum from the ⁵⁵Mn(d, n)⁵⁶Fe reaction was measured at 7-MeV deuteron energy at the John Edwards Accelerator Laboratory at Ohio University. Comparison of the level density of ⁵⁶Fe obtained from the first and third experiments gives an overall good agreement. Furthermore, observed enhancement for soft γ rays is strengthened by the last experiment. The text was submitted by the authors in English.     

Isolated atoms,molecules and clusters

The basic constituents of matter, namely, atoms molecules and small clusters can be isolated in a solid rare-gas-matrix (RGM) and be characterized by Mössbauer Spectroscopy (MS). Experiments can be conducted both by the absorption method using a co-evaporation method of Mössbauer isotopes or by emission spectroscopy where source nuclei are isolated in the RGM. Experimental aspects of both techniques are outlined. Examples of applications of RGMI-MS are described, namely,⁵⁷Fe clustering with noble-metals (Cu, Ag, Au); unusual electronic states of Fe following⁵⁷Co e.c. decay; species formed by the bonding of Fe⁰, in its ground state, to small molecules are compared with those formed by Fe in its various excited states; and finally, the characterization of atomic I⁰ and Te⁰ and Te^?1 embedded in a solid argon matrix.     

NMR study of rapidly quenched crystalline and amorphous Fe-B alloys

Amorphous and microcrystalline Fe-B alloys (4–25 at % B) obtained by rapid quenching of the melt were studied using the pulsed nuclear magnetic resonance (NMR) of ¹¹B nuclei at 4.2 K. Alloy samples were prepared from both a natural isotope mixture and a mixture of the ⁵⁶Fe and ¹¹B isotopes. The NMR spectra were measured as a function of the boron content. The maximum hyperfine fields at the ¹¹B nuclei sites are 25–29 kOe and overlap the values of the hyperfine fields at the ¹¹B nuclei sites in the tetragonal and orthorhombic Fe₃B phases and also in the α-Fe phase containing boron as a substitutional impurity. The short-range order and local atomic structure of the amorphous Fe-B alloys were determined. The amorphous alloys are found to consist of microregions (clusters) with a short-range order similar to that in the tetragonal or orthorhombic Fe₃B phase or the α-Fe phase.