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By combination of two independent approaches, nuclear resonant inelastic x-ray scattering and first-principles calculations in the framework of density functional theory, we demonstrate significant changes in the element-resolved vibrational density of states across the first-order transition from the ferromagnetic low temperature to the paramagnetic high temperature phase of LaFe(13-x)Si(x). These changes originate from the itinerant electron metamagnetism associated with Fe and lead to a pronounced magneto-elastic softening despite the large volume decrease at the transition. The increase in lattice entropy associated with the Fe subsystem is significant and contributes cooperatively with the magnetic and electronic entropy changes to the excellent magneto- and barocaloric properties.

A high-precision reflection high-energy electron diffraction (RHEED) analysis of the in-plane lattice spacing of the surface during epitaxial growth of fcc Fe films on a Cu(100) single crystal substrate is presented. As a function of Fe coverage, initially the in-plane fcc Fe lattice spacing is found to decrease drastically until a minimum is reached, while at higher coverages the smaller equilibrium value for bulk fcc Fe (3.59 A), rather than the value of the Cu substrate (3.615 A), is approached. This proves that fcc Fe films on Cu(100) grow strain free and are non-pseudomorphous, contrary to earlier assumptions.

Mossbauer effect studies were carried out on CoxGa(1−x) alloys, on pure Ga and on CoGa3 and FeGa3 intermetallics by using 57Co and 57Fe probe atoms. 57Co source spectra showed broad absorption lines in CoxGa(1−x) indicating distribution in the quadrupole split values. The concentration dependence of the distribution reflected the formation of the high vacancy concentration in the Co sublattice at low x values. The results obtained for 57Fe absorbers suggested that the location of iron in the lattice is vacancy concentration dependent. At high vacancy concentration a large fraction of iron atoms change position and are populated in the Co sublattice.

Mossbauer effect studies of implanted and synthesized alloys are presented. The spectra showed broad lines indicating at least two components corresponding to Co sites in the two sublattices. Ion implantation resulted in an increase of the Co population in antistructure positions. The broad spectral component of in the Co sublattice was attributed to electric quadrupole splitting induced by vacancies and antistructure atoms lowering the local symmetry. A new attribution of the Mossbauer parameters to the various atomic configurations is suggested.

We built a Debye-Scherrer type powder diffractometer with a57Co radiation source and a large-angle position-sensitive detector. We tuned the incident γ-ray beam on and off the Mossbauer effect resonance, and measured diffraction patterns from our textured samples of polycrystalline57Fe. Mossbauer effect diffraction dominated over X-ray diffraction for the higher order Bragg peaks.

We report on the preparation of polycrystalline austenitic 310 ({sup 57}Fe{sub 0.55}Cr{sub 0.25}Ni{sub 0.20}) stainless steel (SS) thin films on Si substrates and the characterization of their residual magnetism via {sup 57}Fe conversion-electron Moessbauer spectroscopy (CEMS). The films were structurally characterized at room temperature by X-ray diffraction (XRD). The virgin films were found to be structurally disordered. Subsequent annealing at moderate temperatures in ultrahigh vacuum produces the ordered martensitic and austenitic SS phases. Further annealing at higher temperatures (up to temperatures where long-range diffusion into the substrate is still weak) transforms the films into the austenitic phase with no trace of a magnetic hyperfine interaction. However, when a 2 nm thick SS thin film is embedded between two carbon layers, the as prepared disordered SS film does not transform to the martensitic or austenitic SS phase irrespective of the annealing temperature, probably because the interdiffusion with C prohibits the formation of these phases.

Recent investigations claimed the complete amorphization of elemental FeZr multilayer films by solid state reaction during vacuum annealing. In the present study it is established by57Fe conversion electron Mossbauer spectroscopy (CEMS) that annealing under ultrahigh vacuum conditions does not lead to complete amorphization: only a maximum thickness of ≈14 A interfacial α-Fe is transfered into the amorphous phase between 620–660 K. This thin amorphous layer apparently acts as a diffusion barrier and prohibits further growth of the amorphous phase. The average composition of the amorphous interfacial layer was determined from the Mossbauer spectral parameters.

Trivalent iron substituted hexagonal mesoporous aluminophosphate molecular sieve has been synthesized and characterized for the first time, which showed excellent catalytic activity and reusability for the cyclohexane oxidation reaction under mild conditions.

The photorefractive properties of LiNbO3∶Fe and LiNbO3∶Cu have been studied in combination with optical absorption-, Mossbauer- and EPR-measurements. The charge states of Fe in successively reduced LiNbO3∶Fe have been investigated with respect to the influence on the photorefractive sensitivity and saturation value of the refractive index change. The results of this experiment demonstrate clearly the close correlation between the concentration of Fe2+ impurities and the optical absorption band around 2.6 eV in LiNbO3∶Fe, which is known to give rise to an anisotropic charge transport upon optical excitation. The resulting photocurrents determine the photorefractive sensitivity mainly in the initial state of halographic exposure. With increasing conversion from Fe3+ to Fe2+ the photorefractive sensitivity saturates and the saturation value of the refractive index change decreases remarkably.

Etude par diffraction d'electrons lents, microscopie electronique en transmission et effet Mossbauer a electrons de conversion de couches minces epitaxiques Fe/Cu et Cu/Fe/Cu deposees sur supports de NaCl

Mossbauer effect studies of Pt 3− x Fe 1+ x fcc ordered alloys in the range 4.2 K T x = 0.16 to 0.28, are reported. The low-temperature spectra show several satellite lines which are related to different excess-Fe nearest-neighbor configurations. Experiments in external fields give information on the different local spin structure at different concentrations.

FCC (γ-) Fe(100)-films prepared by epitaxial growth in UHV on Cu(100)-films were investigated by Conversion Electron Mossbauer Spectroscopy (CEMS) at 295 K using a He-CH 4 flow-gas counter. The fcc structure of the Fe films was confirmed by LEED. The Mossbauer spectra clearly demonstrate that γ-Fe(100)-films are paramagnetic at 295 K. Depending on the Fe film thickness part of the Fe atoms exists in the α-Fe phase.

A simple electron-beam heated furnace is described which allows the controlled evaporation of small quantities of isotopes, particularly of 57Fe, for thin film deposition.