Magnetic and quadrupole interactions of rare earth in bone crystals

From emission Mössbauer spectra performed on¹⁶¹Tb-bone samples, the Mössbauer and hyperfine parameters are obtained. The lattice components of the EFG acting at Dy in bone crystals are evaluated. These values show that the rare earth ions are fixed on hydroxyapatite crystallites in a hydroxyde environment.     

Hyperfine interaction of rare earth impurities in ferromagnetic metals

The present knowledge concerning rare earth impurities implanted in iron and nickel is reviewed. New Mössbauer spectra on the isotopes¹⁶¹Dy,¹⁶⁶Er and¹⁶⁹Tm are presented. In the case of¹⁶¹DyFe and¹⁶¹DyNi both the annealing behaviour and the temperature dependence have been studied. It is shown that in almost all cases about half of the rare earth impurities end up in substitutional sites, whereas the other part probably is associated with vacancies. The temperature dependence for these systems is in accordance with the generally accepted local moment picture, with fast relaxation behaviour on the electronic moment at the substitutional sites. For the iron host the exchange interaction dominates the cubic crystalline electric field, but for nickel both interactions are of comparable magnitude, leading to a considerable decrease of the hyperfine interaction.     

Defect annealing in Sb/Sn implanted diamond investigated with Sn Mössbauer spectroscopy

The annealing of defects in Sb/Sn implanted diamond has been studied in ¹¹⁹Sn Mössbauer spectroscopy following the implantation of radioactive parent isotopes ¹¹⁹Xe and ^119mSn. Our results show that after annealing above 1300 K, 40% of the implanted ions are located at or near regular sites in the lattice. Significant implantation induced defects however remain.     

Mössbauer study of localized diffusion in an interstitial cage

Mössbauer investigations at various temperatures and in different directions with respect to an electron irradiatedAl ⁵⁷Co/⁵⁷Fe single crystal are reported. It is shown that the drastic decrease of the measured Mössbauer intensity in a narrow temperature range above 15 K is due to localized diffusion of Fe in an interstitial cage. The existence of the diffusive motion is demonstrated by the observation of a broadened component in the Mössbauer spectra above 15K. From the temperature dependence of the broadening the activation energy of the cage jumps is determined as 18±1 meV. Mössbauer spectra measured at sufficiently high temperature show only an unbroadened component, its intensity depending on the crystal orientation relative to the spectrometer. Comparison of this anisotropy with model calculations of the preceding part I of this paper shows that the Fe atom jumps between the corners of a cube, these corners being 0.52±0.02 Å distant in 111 directions from the octahedral lattice position.     

Mössbauer effect studies of the recovery of iron after heavy-ion implantation at 7 K

Mössbauer effect measurements were performed with sources of¹³³Xe implanted at 7 K in polycrystalline iron foils by means of an isotope separator. Information about the direct environment of an implanted radioactive probe atom is obtained through the hyperfine interaction of the daughter nucleus (¹³³Cs) with its surroundings. The Mössbauer spectra were analyzed on the basis of an earlier model, assuming three visible spectral components with high, intermediate and low hyperfine fields and recoilless fractions, respectively, and a fourth, invisible component with a recoilless fraction very close to zero. Annealing experiments showed no evidence for post-implantation recovery stage I in the iron foils, while recovery stage II only gave rise to small changes in the site occupations. These results can be explained in terms of the high energy density locally deposited in the lattice by each implanted atom, leading to stage I recovery during the very short time that is necessary for the thermal dissipation of this energy. Quantitatively, these results are confirmed by calculations of Sigmund on heavy-ion induced elastic-collision spikes in solids. After annealing at room temperature the site occupations agree with those obtained directly with room temperature implanted sources. In previous experiments we have shown that different results are obtained for annealing and for implantation at 200°C. From these results we estinate the migration energy of vacancies in iron at 1.27±0.09 eV.     

Electronic and vibrational properties of a novel mixed-valent europium compound: Eu14Cl33

The occurrence of discrete Eu(II) and Eu(III) valence states in Eu₁₄Cl₃₃, is consistently demonstrated from X-ray diffraction data, Mössbauer effect and magnetic susceptibility measurements. The ratio of the mean square amplitudes of lattice vibrations of the Eu(II) and Eu(III) ions deduced from Mössbauer data is in good agreement with the one obtained from X-ray Debye-Waller factors.     

Electronic structure and Mössbauer isomer shifts of119Sn defects in semiconductors

Although the Mössbauer isomer shift reflects the electronic configuration of the Mössbauer atom, in general, theoretical calculations are needed to express the IS unambiguously in terms of the occupation numbers of the valence shells. It turns out that this can be done using a Green-function procedure based on the parametrized tight-binding approximation including relativistic wave functions. In this way recent Mössbauer measurements on¹¹⁹Sn impurities implanted in group IV semiconductors and A^IIIb^V semiconducting compounds have been interpreted.     

Mössbauer study of119Sn defects in silicon from ion implantations of radioactive119In

Radioactive¹¹⁹In⁺ ions (T _1/2=2.1 min) obtained from the ISOLDE facility at CERN have been implanted into silicon single crystals at room temperature. Mössbauer emission spectra from the 24 keV -radiation of the daughter¹¹⁹Sn have been measured by fast resonance-counting technique. Five independent lines, characterized by their hyperfine parameters and Debye temperatures, have been found in the spectra. From the bonding configurations, deduced for the Sn impurity atoms, these are concluded to be located in four different defects in the silicon lattice. Simple models are proposed for the defects.     

119Sn Mössbauer study of the implantation behaviour of119In,119Sn,119mSn,119Sb and119mTe ions in SiC

The implantation behaviour of stable¹¹⁹Sn⁺ ions and radioactive¹¹⁹In⁺,^119mSn⁺,¹¹⁹Sb⁺ and^119mTe⁺ ions in SiC has been investigated by, respectively, conversion-electron Mössbauer spectroscopy on the 24 keV transition of¹¹⁹Sn, and by Mössbauer emission spectroscopy on the 24 keV radiation emitted by the¹¹⁹Sn daughter after the decays of the radioactive isotopes. The Mössbauer spectra could be decomposed in most cases into two groups of lines, one originating from¹¹⁹Sn atoms on substitutional Si sites, the other from various Sn-vacancy complexes distinguished by their Mössbauer parameters. Annealing experiments reveal a strong dependence of the structure of the defects and the formation and annealing kinetics on the chemical nature of the impurities. Defects formed in 297 K implantations with^119mSn and¹¹⁹Sb anneal above 500 C, resulting in a preferential location of the impurities on substitutional Si sites, whereas^119mTe atoms are efficient defect-trapping centres and no stable, substitutional fraction is observed on either lattice site. Possible structures for the Sn-vacancy complexes are discussed and comparison is made to similar defect complexes in group IV and in III–V semiconductors.     

Mössbauer studies of Dy2Fe17−yAly hydrides

The x-ray and Mössbauer measurements of both⁵⁷Fe and¹⁶¹Dy in Dy₂Fe_17–y Al (y=0, 1,5 and 3) compounds and their hydrides are reported.Hydrogenation slightly increases the lattice parameters. An appreciable increase of the isomer shift and the hyperfine field at⁵⁷Fe nuclei is observed after hydrogenation. The hyperfine field for both the parent compound and its hydride decreases with increasing Al content across the series. Only a small variation of the hyperfine field at¹⁶¹Dy nuclei is noticeable after hydrogenation.     

57Fe and119Sn Mössbauer investigations on some substituted barium hexaferrites

⁵⁷Fe and¹¹⁹Sn Mössbauer measurements have been carried out on powder samples of three differently substituted M-type barium hexaferrites. By⁵⁷Fe Mössbauer measurements in an external magnetic field applied parallel to the -ray direction, we found a canted spin structure for all samples. Furthermore, we detected a strong preference of the Sn⁴⁺ ions for the 4f₂ sites. From⁵⁷Fe Mössbauer measurements aboveT _N, we conclude that the substitution does not influence the 2b sites. The analysis of the magnetically split¹¹⁹Sn Mössbauer spectra at room temperature in the case of the Co-Sn and Zn-Sn substituted samples shows a strong difference between the two. The spectra were interpreted due to the different surroundings of the Sn⁴⁺ ions.     

Depth-selective57Fe mössbauer spectroscopy: An alternative

A method to obtain depth-selective⁵⁷Fe Mössbauer spectra is described. The depth selectivity is implemented by removing thin layers from a sample and measuring the conversion-electron Mössbauer spectrum. The layer spectra, i.e. the Mössbauer spectra associated with the removed layers, are then determined by calculating the number of electrons which originate from each layer and reach the surface of the sample. The computations are based on Liljequist's theory for⁵⁷Fe conversion-electron Mössbauer spectroscopy. In this way no energy-discriminating electron spectrometers are involved, and a simple proportional counter will suffice. The depth resolution is about 20–30 nm. The method is illustrated for an ion-implanted substituted YIG film, in which case the magnetization as a function of depth is obtained.     

57Fe Mössbauer study of Eu1−x Sr x FeO3−y

The samples of Eu_1–x Sr _x FeO_3–y (x=0.0–1.0) were prepared by the solid state reaction method. Their X-ray diffraction patterns and⁵⁷Fe Mössbauer spectra at room temperature were measured. It is found that Sr ions incorporate in the lattice of EuFeO₃, the change of crystal structure is related to the dopant.⁵⁷Fe Mössbauer spectra consist of one magnetic, one doublet and one single paramagnetic components. The Fe ions in the cubic phase are in intermediate valence state between Fe(III) and Fe(IV) and may participate in electron hopping.     

Mössbauer spectroscopy in the characterisation of new materials

The use of Mössbauer spectroscopy for the characterisation of new materials is illustrated here by examples of its application in the study of different types of solids. Firstly, the incorporation of large metal ions within the channels of the compound NbTiP₃O₁₂ which has a three-dimensional channel-type structure similar to that of the fast ion conductor called nasicon and the examination of the products by⁵⁷Fe and¹¹⁹Sn Mössbauer spectroscopy and X-ray powder diffraction is discussed. Secondly, the investigation by¹¹⁹Sn Mössbauer spectroscopy and X-ray photoelectron spectroscopy of new conducting tin dioxide pillared clays synthesised by microwave heating is described. Finally, the examination by¹²⁵Te Mössbauer spectroscopy and X-ray powder diffraction of conducting selenium-tellurium alloys prepared by precipitation techniques is discussed.     

Nuclear magnetic moment of161Tb

Nuclear orientation measurements on dilute TbGd are analysed to yield the magnetic dipole and electric quadrupole moments of¹⁶¹Tb g.s. and multipole mixing ratios of transitions in¹⁶¹Dy.     

Thermal annealing effects in LiF crystals implanted with57Fe ions

Thermal annealing effects in lithium fluoride single crystals implanted with⁵⁷Fe ions were studied by conversion electron Mössbauer spectroscopy. It was found that annealing in vacuum leads mostly to the precipitation of metallic aggregates in contrast to the annealing in He and H₂ when the formation of ferric compounds, having high magnetic transition temperatures, takes place.     

Structure and magnetic ordering in SrNpO3

In the course of studies of alkaline earth oxo-neptunates Mössbauer spectra of²³⁷Np in SrNpO₃ were taken. From the point of view of lattice symmetries two characteristically different sites for the Np ions were found. The transition temperature T_C=(30.5±0.5) K was confirmed. The phase transition turned out to be of second order. Below T_C the lattice orders antiferromagnetically.     

The quadrupole interaction of57Fe in Ti

The quadrupole interaction of⁵⁷Fe in titanium was studied by Mössbauer spectroscopy and by the time-differential perturted angular correlation technique, using an implanted and diffused source of⁵⁷Co in titanium. From the latter measurements a quadrupole interaction frequencyv _Q = 2.22 ± 0.42 MHz was derived. The modulation amplitude of the delayed coincidence spectrum combined with the Mössbauer spectra indicate a high degree of substitutionality of the cobalt in the titanium.     

Mössaauer studies of83Kr implanted in semiconductors and metals

Mössbauer spectroscopy of the 9.4 keV transition in⁸³Kr has been performed using sources of⁸³Rb implanted in the group IV semiconductors diamond, silicon, germanium and tin and in the metals Cu, Ag, Au, Mo and W. From the line widths and isomer shifts information has been obtained on possible lattice sites of the impurities. In most cases a site with large isomer shift, thought to correspond to a compression of the krypton atom was observed. This site is interpreted to represent purely substitutional impurities. In Mo and W a well-defined vacancy release stage was observed, leading to a reduction of the isomer shift and a line broadening.     

Mössbauer effect studies of the Dy12Fe82B6 system

The Mössbauer measurements of both⁵⁷Fe and¹⁶¹Dy in Dy₁₂Fe₈₂B₆ system are reported. The presence of B exceeds the magnetic hyperfine fields at both⁵⁷Fe and¹⁶¹Dy nuclei as compared to corresponding pure metals Fe and Dy respectively. The only small excess of the hyperfine field at⁵⁷Fe nucleus is observed. The excess at¹⁶¹Dy nucleus is about 12% of the free ion Dy³⁺ value.