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BioCARS, a NIH-supported national user facility for macromolecular time-resolved X-ray crystallography at the Advanced Photon Source (APS), has recently completed commissioning of an upgraded undulator-based beamline optimized for single-shot laser-pump X-ray-probe measurements with time resolution as short as 100 ps. The source consists of two in-line undulators with periods of 23 and 27 mm that together provide high-flux pink-beam capability at 12 keV as well as first-harmonic coverage from 6.8 to 19 keV. A high-heat-load chopper reduces the average power load on downstream components, thereby preserving the surface figure of a Kirkpatrick–Baez mirror system capable of focusing the X-ray beam to a spot size of 90 µm horizontal by 20 µm vertical. A high-speed chopper isolates single X-ray pulses at 1 kHz in both hybrid and 24-bunch modes of the APS storage ring. In hybrid mode each isolated X-ray pulse delivers up to ∼4 × 1010photons to the sample, thereby achieving a time-averaged flux approaching that of fourth-generation X-FEL sources. A new high-power picosecond laser system delivers pulses tunable over the wavelength range 450–2000 nm. These pulses are synchronized to the storage-ring RF clock with long-term stability better than 10 ps RMS. Monochromatic experimental capability with Biosafety Level 3 certification has been retained.

We report an experimental study of Langmuir monolayers of dodecanethiol-ligated gold nanoparticles with in situ optical microscopy and X-ray scattering. The particle spacing increases with thiol concentration but does not depend on surface pressure. Compression beyond the full coverage of the monolayers causes the monolayers to wrinkle. With the presence of excess thiol molecules, the wrinkles unfold back to monolayer upon the expansion of the surface area. A theoretical model based on van der Waals' attraction and tunable steric repulsion is adopted to explain this reversibility.

Coherent hard x‐ray beams with a flux exceeding 109 photons/sec with a bandwidth of 0.1% will be provided by undulators at the third‐generation synchrotron radiation sources such as APS, ESRF, and Spring‐8. The availability of such high flux coherent x‐ray beams offers excellent opportunities for extending the coherence‐based techniques developed in the visible and soft x‐ray part of the electromagnetic spectrum to the hard x‐ray region. These x‐ray techniques (e.g., diffraction‐limited microfocusing, holography, interferometry, phase contrast imaging, and signal enhancement) may offer substantial advantages over noncoherence‐based x‐ray techniques currently used. For example, the signal‐enhancement technique may be used to enhance an anomalous x‐ray or magnetic x‐ray scattering signal by several orders of magnitude. Coherent x rays can be focused to a very small (diffraction‐limited) spot size, thus allowing construction of high spatial resolution microprobes. This paper will discuss the feasibility of e...

A Fresnel phase zone plate with an unprecedented focusing efficiency of 33% was fabricated using an x‐ray lithographic technique and was tested using synchrotron x rays. Contributions by the zeroth‐order x ray to the focus were minimal. Spatial resolution in the micrometer range was achieved. The measured spot size was dominated by geometric demagnification of the source. It should be possible to obtain submicrometer resolution by aperturing the source. Experimental results of focusing efficiency measurements, intensity distribution at the focal plane, and spatial resolution tests are reported.

Third generation synchrotron light sources present new challenges to x-ray optics calculations. Due to the high brilliance (thus small dimensions) of the source and the long optical paths, the transverse coherence lengths are quite nonnegligible, often of order of hundreds of microns. In such situation beam propagation calculations based on purely geometrical optics may yield large errors and a more complete wave treatment is needed. This is especially true for beam defining apertures. The purpose of this paper is to present a calculational approach which, utilizing a 'variance matrix' representation of the beam allows to evaluate the wave propagation along an optical system and through arbitrary apertures, in a straightforward manner. In addition the notoriously thorny problem of partial coherence is adequately dealt with and the transition from wave optics to ray optics obtains in a smooth and seamless fashion.

A detailed thermal deformation and slope-error analysis is performed on an indirectly-cooled design of a high-heat-load vertical-focusing mirror.THe cooling of the mirror is through copper plates inserted into two grooves along the sides of the mirror. The contact between the mirror and the copper plate is through a gallium-indium eutectic bath in the groove. This configuration provides efficient thermal contact between the mirror substrate and the cooling block without applying stress to the mirror from the cooling block. This mirror will be used at the Advanced Photon Source Sector-15 ChemMatCARS undulator beamline for vertical focusing. It will be exposed to white beam with a heat load of about 1.1 kw.

Most calculational techniques used to evaluate beam propagation are geared towards either fully coherent or fully incoherent beams. The intermediate partial-coherence regime, while in principle known for a long time, has received comparably little attention so far. The resulting shortage of adequate calculational techniques is currently being felt in the realm of x-ray optics where, with the advent of third generation synchrotron light sources, partially coherent beams become increasingly common. The purpose of this paper is to present a calculational approach which, utilizing a ``variance matrix'' representation of paraxial beams, allows for a straightforward evaluation of wave propagation through an optical system. Being capable of dealing with an arbitrary degree of coherence, this approach covers the whole range from wave to ray optics, in a seamless fashion.

A series of experimental measurements was conducted for the characterization of a transmission circular zone plate. The zone plate (ZP), with a primary focal length of 40 cm for 8 keV photons, was illuminated by monochromatized synchrotron x rays. Focusing efficiency of the ZP was measured as a function of x-ray energy between 5 - 1 keV, from which the ZP thickness was determined. Focal spot sizes at the first, second, and third order focus were measured, and they agreed very well with the calculated values. Images of a 1000 mesh/inch gold grid were also obtained at the three focal planes. The grid scans indicated that the spatial resolution is about 2 (mu) in the image obtained at the third order focus.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A polarimeter for x-ray and vacuum ultraviolet (XUV) radiation was built to measure the spatial and spectral dependence of the polarization of the light produced by the new undulator at the U5 beamline at NSLS. The fourth-harmonic radiation was measured, and it does not agree with predictions based on ideal simulation codes in the far-field approximation.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A zone plate capable of focusing hard x-rays to less than 1 {mu}m spot size is designed and specified. This design is based on the state-of-art fabrication technology available today. This zone plate consists of Cu/Al layers sputtered alternatively on a round stainless steel core. Parameters of this zone plate are given. The focal length f is given for 8Kev x-rays and the thickness is optimized for focusing efficiency of the same x-ray energy.

The powerful beams of x-ray radiation generated by insertion devices at high power synchrotron facilities deposit substantial amounts of localized heat in the front end and optical components that they intercept. X-ray beams from undulator sources in particular are confined to very narrow solid angles and therefore impose very high absorbed heat fluxes. This paper is devoted to a detailed study of the design of windows for the Advanced Photon Source undulators and wigglers emphasizing alternative design concepts material considerations and cooling techniques necessary for handling the high heat load of the insertion devices. Various designs are thermally and structurally analyzed by numerically simulating full-power operating conditions. This analysis also has relevance to the design and development of other beam line components which are subjected to the high heat loads of insertion devices. Key indices: synchrotron radiation high heat load insertion devices undulators wigglers beryllium window. 2.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Insertion device (ID) synchrotron x-ray sources on present day and next-generation synchrotron facilities have very attractive spectral properties. In addition however they are capable of producing x-ray beams with large powers and in some cases unprecedented power densities. An overview of the spatial and frequency distributions of these sources including the effects of synchrotron particle beam emittance is presented. 1.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The Advanced Photon Source (APS) to be constructed at Argonne National Laboratory (ANL) utilizes magnetic devices which generate X-ray beams with very intense heat flux levels. The Fixed Mask Assembly (FMA) is the first component to interact with the X-ray beam. Two sets of a pair of FMA channels vertically and horizontally disposed contain the beam rather than define it. They are subject to very large heat fluxes during containment. In current practice the FMA channels are made of heavy seamless copper have rectangular cross-sections and are cooled internally with water. Channels are set at grazing angles ranging from 1 to 6 degrees with respect to the beam depending on the type of insertion device. APS insertion devices will impose higher heat fluxes on FMAs. Therefore a need exists to improve the FMA engineering keeping in mind the current design criteria and philosophy of FMAs. A comparative investigation of the conventionally achievable heat transfer coefficient h" with water and the wall conductance of a heavy wall copper tube reveals that major resistance is on the coolant side. Therefore there exists a significant opportunity to improve heat transfer in the tubes by enhancement of the coolant side. To this end an experimentally and analytically based research program has been adopted at the APS for investigating enhanced cooling methods and techniques. Currently a variety of copper wool filled tubes as well as a© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Spatial resolution and focusing efficiency are two important properties of a zone plate in x-ray focusing applications. A general expression of the zone plate equation describing its zone registration is derived from the interference of spherical waves emited from two mutually coherent point sources. An analytical expression of the focusing efficiency in terms of the zone plate thickness and x-ray refractive indices of the zones is also derived. Validity condition for using this expression is considered. Thickness required for obtaining adequate focusing efficiency is calculated as a function of x-ray energy for several representative materials. The spatial resolution of a finite thickness zone plate is worse than that of an infinetly thin zone plate which is approximately equal to the smallest zone width of the zone plate. The effect of the finite thickness on the spatial resolution is considered. This manuscript has been authored under contract number W-31-109-ENG-38 with the U. S. Department of Energy. Accordingly the U. S. Government retains a non-exclusive royalty-free license to publish or reproduce the published form of this contribution or allow others todo so for U. S. Government purposes. 146 / SPIE Vol 1345 Advanced X-Ray/EUV Radiation Sources andApplications(1990)© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

X‐ray beams of varying degrees of partial spatial coherence have been prepared and characterized, and the diffraction of these beams from patterned surfaces measured. The experiments were carried out at a bending magnet source at the NSLS (X‐19C). The resulting diffraction patterns for a pair of slits and an optical grating are analyzed in terms of an x‐ray mutual coherence function used to describe the propagation of the coherent wave front in the visible light regime. The diffraction and speckle pattern from the surface are the result of the mutual coherence function convoluted with the interference function of the grating. Forming diffraction patterns, or x‐ray speckles, with partially coherent x‐rays relaxes the requirement for the interference, thereby increasing the ‘‘effective’’ coherent flux. This detailed knowledge of the propagation of the x‐ray spatial coherence aids in defining the physical characteristics of beamline optical elements that must preserve the coherent x‐ray wave front.

Future synchrotron radiation facilities such as the Advanced Photon Source to be constructed at Argonne National Laboratory will produce dedicated and powerful beams ofx-ray radiation instrumental in advanced research in key areas of science, engineering, and medicine. The development of critical beamline optical components such as monochromators is pivotal in the successful utilization of the generated x-ray beam. The high heat load of the beam can severely distort, and thus adversely affect the performance of, such components. In this paper, a five-step numerical procedure to predict the performance of an x-ray monochromator subjected to high-power synchrotron radiation is described. The predicted performance of a model double-crystal monochromator system expressed in terms of its rocking curves satisfactorily presents the experimental results. This procedure can reliably be used in the design, evaluation, and optimization of monochromators and other optical components.

X-ray absorption near edge structure (XANES) spectra of gaseous Kr, solid Kr and solid KrF2 have been obtained and compared to differentiate between continuum resonances near the edge and bound state transitions. By comparing experimental and ab initio (MSW-Xα) calculated spectra the influence of environment as well as molecular bonding on XANES is demonstrated.

The Mossbauer effect has been used to study the magnetic properties of pseudobinary (Er,Gd)Fe3 compounds. The spectra show that the spin-reorientation temperature, Tr, decreases with increasing Gd concentration. This decrease is explained by the concentration dependence of the average crystal field anisotropy at the (Er, Gd) sites. A simple single-ion model for the free energy was used to describe the magnetocrystalline anisotropy. The model adequately describes the concentration dependence of the reorientation temperature.

Measurements are made of 57Fe Mossbauer effect, 181Hf time differential perturbed angular correlation, and magnetization measurements in the intermetallic compound HfFe2-Evidence is given for segregations of a hexagonal phase in the predominant cubic C15 matrix. The hyperfine fields at the Hf site are (130 ± 4) kOe for the cubic phase and (85 ± 5) kOe for the hexagonal phase at 20°C. At the two inequivalent iron sites in the cubic phase, the hyperfine fields are (176 ± 4) kOe, and (184 ± 4) kOe at 20°C. The easy magnetization direction is determined to be the 〈111〉 axis. Nous nous referons aux mesures effetues par l'effet Mossbauer, par la correlation angulaire perturbee diferentielle et par la magnetometrie dans le compose intermetalique HfFe2. On y remarque l'evidence pour l'existence de segregations d'une phase hexagonale dans la matrice predominant cubique C15. Les champs hyperfins dans la position du Hf sont de (130 ± 4) kOe pour la phase cubique et de (85 ± 5) kOe pour la phase hexagonale a 20°C. Dans les deux positions non equivalentes du fer dans la phase cubique, les champs hyperfins sont de (176 ± 4) kOe et (184 ± 4) kOe a 20°C. La direction de magnetization facile a ete determinee comme etant l'axe 〈111〉.

The pressure-composition isotherm at 22 °C for ErMn2Hx between 1 and 104 Torr shows the formation of two hydride phases with compositions x = 4.6 andx = 4.0 and with equilibrium hydrogen pressures of 15 Torr and less than 1 Torr respectively. Both hydrides are expanded versions of the C14 hexagonal Laves structure of ErMn2 with volume expansions of 23% and 37% for the lower and higher order phases respectively. A slight preferential expansion parallel to the c0 axis is observed. The 166 Er Mossbauer results show that the magnetic moment of erbium in both hydride phases is below the free-ion value measured for ErMn2. The ferromagnetic ordering present in ErMn2 and ErMn2H4 is absent in ErMn2H4.6 down to 1.5 K. Two erbium sites are detected in ErMn2H4 instead of the one expected for the C14 structure. The origin of these sites is discussed in terms of possible configurations of hydrogen site occupancy.

Results of magnetisation and 57Fe Mossbauer measurements show that the strong ferromagnetic coupling in Pd3Fe is markedly altered in the hydride Pd3FeH0.7. The magnetic moment of (4.59+or-0.03) mu B is reduced by the presence of hydrogen to (0.83+or-0.03) mu B. This reduction is accompanied by a decrease of approximately 46% in the magnetic transition temperature of the hydride compared with that of Pd3Fe (499K). In addition Mossbauer spectra at 4.2K in external magnetic fields indicate that anisotropic antiferromagnetic coupling dominates in the hydride. Results are compared with those for Pd2AuFe where similar effects are observed.

Many intermetallic compounds based on rare earths reversibly absorb hydrogen to form ternary hydrides at moderate temperatures and pressures. The absorption of hydrogen alters the physical properties of the intermetallic compound dramatically. We shall illustrate some of the important changes in the magnetic behavior of such systems. The chemical stability of the hydrides will also be discussed with special reference to the Laves phase GdFe 2 hydrides.

The purpose of this review is to acquaint the reader with the new field of ternary hydrides and to expose him to its relevance to modern energy technology. Studying their fundamental properties is one fascinating aspect in view of their novel and unusual nature. The methods of hyperfine interactions have an important role to play in their microscopic understanding, as we have illustrated through a few examples. The absorption mechanism of hydrogen has been shown to be closely related to the nature of surface overlayers and their catalytic activity. Similar measurements will be of importance also in many of the other catalytic reactions used in industry. The microscopic nature of hyperfine interaction tools also helps in determining the hydrogen site occupancy. In addition, such methods can in principle yield dynamic information which are useful in investigating relevant properties such as diffusion rates of hydrogen.

The use of multilayer reflectors under intense synchroton x‐ray beams requires to develop a new generation of multilayered materials that can withstand a high‐power load in excess of 100 W/mm2. Multilayers with the high‐Z layer consisting either of a pure element or of compounds such as carbides, nitrides, or silicides have been produced. Because the fabrication conditions are not yet optimized, thin films with satisfactory layer were not obtained leading to poor reflectivities. Such multilayers have been both thermally annealed in a furnace and exposed to a synchrotron beam with a power density of about 1 W/mm2. The resulting damage ranges from the total destruction of the layering to a reduction of the reflectivity by typically 40%–60%. In some cases an only 1%–15% loss in reflectivity has been observed.

The ternary hydride phases DyFe 3 H x (with x = 1.7, 2.5 and 4.2) all retain the PuNi 3 rhombohedral structure of DyFe 3 , with a maximum volume expansion of 18% for DyFe 3 H 4.2 . All the phases show a preferential expansion parallel to the c 0 axis. From bulk magnetization measurements the DyFe moment compensation temperature is found to decrease linearly, from 545 K for DyFe 3 to 150 K for DyFe 3 H 4.2 , with increasing volume of the hydride phases. The 161 Dy Mossbauer results for the two dysprosium sites in the structure indicate that a slight reduction occurs in the free-ion moment found for DyFe 3 in all the hydride phases. In addition, the 57 Fe Mossbauer data show that the average iron moment for the five inequivalent iron sites increases with hydrogen concentration up to x = 2.5. These trends in the local moments indicate that the variation in the compensation temperature, which is related to the Dy-Fe exchange, is associated with lattice expansion effects due to the presence of hydrogen.

The pressure-composition-temperature phase diagram for the absorption of hydrogen in the cubic Laves phase compound ErFe2 has been investigated. At least three stable hydrides ErFe2Hn are found with n ≈ 2, 3.4 and 4. At 20 °C, the equilibrium pressures for these phases are 0.04, 10 and 4000 Torr, respectively. The implications of these results on the preparation of samples for the measurement of physical properties is discussed.

The ternary hydride phases ErFe3Hx (with x=1.5 and 2.7) has been studied by57Fe Mossbauer effect. The spectra show that the spin reorientation temperature is increased by the presence of hydrogen in the ErFe3 lattice and is independent of hydrogen concentration for the two hydrides investigated. A preferential filling of the interstitial sites in the RFe3 structure is indicated by the data.

$^{57}\mathrm{Fe}^{3+}$ M\"ossbauer absorption spectra were collected for powder specimens of ${\mathrm{LiFe}}_{x}{\mathrm{Al}}_{5\ensuremath{-}x}{\mathrm{O}}_{8}$ with $x=0.005$. The effects on the spectra of applied magnetic fields with strength less than 1 kOe are interpreted in detail. A comparison of the calculated spectra using EPR parameters to the data is made. This comparison indicates (a) that the observed resonances which are sensitive to applied magnetic fields are associated with the \ifmmode\pm\else\textpm\fi{}1/2-spin Kramers's doublet of the ionic ground term; (b) that for zero applied field the field-sensitive resonances are affected drastically by dipolar fields originating from neighboring nuclei. The sign of the zero-field-splitting parameter $D$ is found to be negative. The value of the ground-state hyperfine-coupling constant is ${A}_{g}=(\ensuremath{-}2.45\ifmmode\pm\else\textpm\fi{}0.03)$ mm/sec, and that of the quadrupole-coupling constant is $2P=(+0.67\ifmmode\pm\else\textpm\fi{}0.03)$ mm/sec.

The fluorescence and excitation spectra of ${\mathrm{Fe}}^{3+}$ in the ordered and disordered phases of the spinel Li${\mathrm{Al}}_{5}$${\mathrm{O}}_{8}$ have been measured at 77 and 4.2 K. At these temperatures, a strong zero-phonon line is observed in the ordered-phase fluorescence accompanied by relatively well-defined vibronic sidebands. These sidebands are separated by a common frequency interval of 199 ${\mathrm{cm}}^{\ensuremath{-}1}$. Their origin is attributed to local modes of an [Fe${\mathrm{O}}_{4}$] center. Several large splittings are observed. A splitting of approximately 600 ${\mathrm{cm}}^{\ensuremath{-}1}$ is seen in the $^{4}T_{1}(^{4}G)$ and $^{4}T_{2}(^{4}G)$ levels at the tetrahedral sites. A splitting of 16 ${\mathrm{cm}}^{\ensuremath{-}1}$ seen in the zero-phonon line is believed due to spin-orbit effects. Good agreement is obtained between calculated and observed level positions. Our earlier suggestion that the fluorescence of the ordered phase is due to ${\mathrm{Fe}}^{3+}$ at tetrahedral ($A$) sites while the fluorescence of the disordered phase is due to ${\mathrm{Fe}}^{3+}$ at octahedral ($B$) sites is strengthened. Finally, we present a comparison of certain basic features of Li${\mathrm{Al}}_{5}$${\mathrm{O}}_{8}$: ${\mathrm{Fe}}^{3+}$ obtained from optical measurements with those obtained from M\"ossbauer-effect measurements. The latter will be published separately.

Mossbauer spectroscopy of 57 Fe conversion electrons was used to study FeTi subjected to 51 hydrogen absorption-desorption cycles. This technique probes both the surface and part of the bulk, and it can also distinguish between magnetic and non-magnetic iron in the lattice. Our measurements suggest the presence of a magnetic overlayer on FeTi made up of iron clusters and the absence of magnetic moments on the iron contained in the bulk. This results shows that the magnetic moment observed in bulk magnetization studies in fact originates from this segregated iron layer on the surface of FeTi.

Mossbauer effect measurements have been carried out using 166Er and 119Sn in the re-entrant ternary superconductor ErRh1.1Sn3.6. The Er moment at 0.26 K is found to be 7.6 ± 0.2 μB. At 4.2 K the ground state doublet is predominantly occupied with g| = 15.7 ± 0.1 and g∥=1.77 ± 0.15. The 119Sn resonance reveals two chemically inequivalent sites in this compound and the 1.5 K spectrum shows the presence of a spin density. f

Ordered alloys of Pd 3 Fe are shown to readily absorbe hydrogen through electrolytic loading. The resultant ternary hydride phase is observed to retain the fcc structure of Pd 3 Fe with approximately the same lattice constant. The 57 Fe hyperfine field determined by Mossbauer spectroscopy is found to be 30% smaller in the hydride compared to Pd 3 Fe. The reduction appears to be associated with a perturbation of the Pd moment by hydrogen. The results suggest the occupation of one type of interstitial site in the structure. The absence of the site in disordered Pd 3 Fe would explain the much smaller hydrogen capacity observed for this alloy.

57Fe Mossbauer spectroscopy under external magnetic fields of up to 72 kOe has been used to study the magnetic ordering in amorphous (FexMn1−x)75P16B6Al3 (0.25⩽x⩽1) at 4.2 K. From the behavior of the magnetic hyperfine fields one concludes that the Fe‐rich samples are soft ferromagnets and the Mn‐rich samples exhibit spin glass‐like properties. In the samples with intermediate Fe concentrations, a magnetic ordering where both ferromagnetic and spin glass‐like orderings coexist occurs.

The magnetic structure and spectral properties of a 7.5‐cm, 30‐period hybrid undulator are described. The device will be installed at the U5 port of the VUV storge ring at Brookhaven National Laboratory and will be a tunable source of very high brillance soft x‐ray radiation over the range of 13 to approximately 150 eV.

Mossbauer effect measurements on the ternary superconductor Sc 2 Fe 3 Si 5 in an applied magnetic field show that the magnetic moment on both the iron sites is less than 0.03 μ B .

The values of the magnetic moments and the electric field gradient in TmNi3 and TmCo3 are obtained from 169Tm Mossbauer spectroscopy. These values are compared to those from crystal field model based on point charge calculations for these intermetallics.

Members of the R2Fe3Si5 series become either superconducting or magnetically ordered depending on whether the metal atom R( = rare earth, Y or Sc) is diamagnetic or paramagnetic respectively. We have taken Mossbauer effect and magnetization measurements to determine the magnetic state of the iron and the nature of the superconducting electrons. 57Fe Mossbauer measurements on the Sc, Dy and Er compounds all showed two partially resolved, quadrupole split spectra at all temperatures from 300 K to 1.5 K, indicating that there is no resolvable magnetic interaction at the iron site. No major change in the spectrum of Dy2Fe3Si5 was observed in passing through its antiferromagnetic ordering temperature of ∼4 K. Measurements in an applied field of 5.6 T set an upper limit of 0.03 μB for the iron moment in Sc2Fe3Si5. However, measurements at 4.2 K in fields up to 7 T for the Dy compound gave an internal field ∼9% smaller than the applied field and linear with applied field. This corresponds to an induced moment at the iron site of ∼0.07 μB at 7 T applied field. The 161Dy Mossbauer resonance clearly showed the onset of magnetic order around 4 K and the magnetic moment Dy at 1.5 K was found to be 7.0±0.2 μB consistent with the magnetization measurements. The nature of the superconducting electrons in the R2Fe3Si5 series is discussed in the light of available measurements.

A Mossbauer source of 57Co in diamond has been produced by implanting 57Co with an isotope separator directly into a diamond single crystal. The Mossbauer spectra taken at 80 and 300°K and in the [100] and [110] orientations displays two peaks of equal intensity. These two peaks can be interpreted as quadrupole splitting caused by the displacement of the iron interstitial from its site of tetrahedral symmetry.

We have used neutron scattering to study the structure and magnetic ordering of a series of hydrides and deuterides of the rare earth-iron compounds RFe2. The parent RFe2’s have the cubic close packed Laves phase (C15) structure for R Heavier than Nd and order ferrimagnetically at ∿600 K with the full free ion moment on each R and ∿1.6μB/Fe at saturation. The stable hydride phases with ∿2 and ∿3.5 H(D) per formula unit are known from x-ray and neutron diffraction to retain the C15 cubic structure, with lattice parameters increased by ∿5% and ∿7%. The RFe2H4 phase is rhombohedrally distorted and is not ordered at 4.2 K (1).

There are only a few Fe-based compounds which are superconducting since the depairing of Cooper pairs is unavoidable in the presence of an Fe moment. In Sc2Fe3Si5 and Th7Fe3, Mössbauer measurements on 57Fe show that there is no magnetism at the Fe site in either compound. The isomer shift values indicate the reason behind this identical magnetic behavior to be quite different in its electronic origin.

The formation of ternary hydrides is often accompanied by significant changes in the structural, electronic and magnetic properties of the binary host intermetallic. Since Mossbauer spectroscopy is in essence a technique which probes the local structural, electronic and magnetic properties of the employed isotope, we used this technique to study the changes which occur in the ternary hydrides. Data from 57Fe, 161Dy, 166Er will be discussed and compared with results from other techniques.

The hydrogen rich ternary hydride phases of RFe2Hx (R=Y Dy, Er) with x>4 have been investigated using 57Fe, 161Dy and 166Er Mössbauer spectroscopy and bulk magnetization. In all cases, the presence of hydrogen results in a dramatic reduction in the moment on Fe as well as the magnetic transition temperature. The data also imply a simultaneous weakening of the R-Fe magnetic exchange.

The combined results of EXAFS and Moessbauer effect spectroscopies have been used to deduce the oxidation state and local structure of iron in iron containing Na, K- and H-chabazites. In the mineral Na,K(Fe) chabazite iron is found to be present as oxo- or hydroxo-bridged Fe(III) oligimers, while in the H-chabazite it is found to be present as Fe(III) ions bridged by oxo- or hydroxo-groups to the zeolite framework. 25 references, 7 figures, 1 table.

A single phase stable hydride with nominal composition DyFe2H2 is shown to have the cubic C15 Laves structure with a 5% larger lattice constant. 57Fe Mossbauer spectra show two sites with nearly equal population and with different isomer shifts and hyperfine fields. Based on the average hyperfine field at 4.2 K, an Fe moment of approximately 1.6 μB is estimated. From the 161Dy data at 4.2 K, which show a single site, a nearly free‐ion moment of 9.8 μB is determined. Relaxation effects in the 161Dy spectra above 77 K, combined with a sharp decrease in the moment with increasing temperature, imply a weakening of the Dy‐Fe magnetic coupling induced by the presence of the hydrogen.