[en] Local symmetry (as evaluated from the electric field gradient tensor) and radial distribution functions (obtained by EXAFS measurement) are determined in a series of amorphous rare-earth base alloys. Local order is found to increase with the extent of heteroatomic interactions. Various magnetic phases (including ferromagnetic, spin-glass, reentrant spin-glass) occur for europium alloys with simple metals (Mg, Zn, Cd, Al, Au, ...). This variety reflects the sensitivity of exchange interactions to the presence of non-s conduction electrons. Asperomagnetic structures are established for the Dy alloys. The crystalline electric field interactions at the Dy³⁺ ions are interpreted with the help of local symmetry data. Quadratic axial and non-axial crystal field terms are sufficient and necessary in order to account for the hyperfine and bulk experimental results

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[en] Full text. The discovery of localized phonon modes in intermetallic compounds opens a new perspective for the study of electron-phonon and phonon-phonon interactions in solids. The families of the semiconducting clathrates and filled skutterudites are complex materials where this scenario is believed to take place. These are cage systems inside which a guest, or filler, atom may perform relatively large excursions. These excursions are described in terms of localized and isolated phonon modes (Einstein modes), usually called rattling modes. In this sense, the guest is referred as the rattler atom and its dynamics are fully characterized by a single parameter, the Einstein temperature. In this work we report evidence for a close relation between the thermal activation of the rattling motion of the filler guest atoms, in EuT₄Sb₁₂ (T = Ru, Os) skutterudite compounds, and an inhomogeneous spin dynamics of the Eu²⁺ spins. This interaction is probed directly by means of Eu²⁺ electron spin resonance (ESR) studies on single crystals grown in Sb flux. The measurements were performed in both X-band (∼ 9.4 GHz) and Q-band (∼ 34 GHz) frequencies in the temperature interval 4:2 < or ∼ T < or ∼ 300 K. A comparative study with ESR measurements on Ga flux grown single crystals of the Eu₈Ga₁₆Ge₃₀ clathrate compound is presented. Our results point to a correlation between the rattling motion and the spin dynamics which may be important for the general understanding of cage systems. (author)

[en] Rare earth (RE) doped materials have been widely exploited as the intriguing electronic configuration of RE ions offers diverse functionalities from optics to magnetism. However, the coupling of magnetism with photoluminescence (PL) in such materials has been rarely reported in spite of its fundamental significance. In the present paper, the effect of high pulsed magnetic field on the photoluminescence intensity of Eu³⁺-doped nano-glass-ceramics has been investigated. In our experiment, Eu-doped oxyfluoride glass and glass ceramic were prepared by the conventional melt-quenching process and controlled heat treatment. The results demonstrate that the integrated PL intensity of Eu³⁺ decreases with the enhancement of magnetic field, which can be interpreted in terms of cooperation effect of Zeeman splitting and magnetic field induced change in site symmetry. Furthermore, as a result of Zeeman splitting, both blue and red shift in the emission peaks of Eu³⁺ can be observed, and this effect becomes more prominent with the increase of magnetic field. Possible mechanisms associated with the observed magneto-optical behaviors are suggested. The results of the present paper may open a new gate for modulation of luminescence by magnetic field and remote optical detection of magnetic field.

[en] The pressure of saturated steam above the Eu-Mg alloys of eight compositions containing 0.196-0.945 atomic fractions of Mg in the temperature interval 953-1003 K is investigated by the method of flux. The values of thermodynamic activity of Mg and Eu, their partial-molar and integral Gibbs energies, enthalpy and entropy of liquid alloys and of EuMg₂ compound formation are calculated. It is supposed that the atomic 5d¹-electrons of lanthanoids do not participate in the coupling with magnesium, or their energy contribution to this coupling is negligible

[en] The values of the magnetic fields at which magnetization steps (MSs) occur due to exchange-coupled open and closed triplets of Eu²⁺ ions (S=7/2) are calculated for a Pb_1-xEu_xSe single crystal, taking into account the crystal-field (CF)-interaction, which causes the isotropic separation between two consecutive MSs, ΔB=B_l+1 - B_l(l=1,2,...,6), where B_l is the value of the l th MS, that exists in the absence of the crystal field to become anisotropic with respect to the orientation of the external magnetic field (B). The contribution of the single-ion anisotropic CF by an exchange-coupled open triplet (OT) leads to an average separation, ΔB_aυ^OT-CF, 10% higher than ΔB when B parallel [100], and 5 and 8% lower than ΔB for B parallel [110] and B parallel [111], respectively. As for the exchange-coupled closed triplet (CT), it was estimated that ΔB_av^CT-CF is 7.0% higher than ΔB when B parallel [100], and 3.4 and 4.1% lower than ΔB when B parallel [110] and B parallel [111], respectively. Furthermore, the values of ΔB_l^OT-CF and ΔB_l^CT-CF were found to depend on l (l 1,...,6 for OT, and l = 1,...,9 for CT), varying by up to about 40%. (author)

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[en] Strontium modified aluminum-silicon cast alloys are well known for their outstanding mechanical properties as they combine excellent strength with good ductility that is due to a modification of brittle Si in the eutectic with traces of Sr (0.3-0.5 wt%). Although the level of Sr addition is very low, formation of ternary AlSiSr phases with deleterious effects on the ductility can take place. Consequently, there is a certain need of alternative modifying elements. Following the theory of Lu and Hellawell which predicts an optimal atomic size for good modification, Eu, which has an atomic radius close to that optimal size, was additionally used as a modifying element. This study presents SIMS (secondary ion mass spectrometer) investigations of the 3D-distributions of the main alloying and trace elements in Al-Si feedstock alloys for thixocasting modified with Sr and Eu, respectively. (author)

[en] Al–5 wt.% Si-based alloys with 0.05 wt.% Eu addition were produced by controlled sand-casting and melt-spinning, respectively. The modification of eutectic Si caused by 0.05 wt.% Eu addition was investigated by thermal analysis, differential scanning calorimetry and multi-scale microstructure characterization techniques. In the case of controlled sand-casting, 0.05 wt.% Eu addition was found to modify the eutectic Si into a fibrous morphology. Multiply twinned Si particles were observed within eutectic Si. Furthermore, the Al₂Si₂Eu phase was also observed both in the vicinity of eutectic Si and within eutectic Si, which was believed to hinder Si growth. In the case of melt-spun samples, nanometer-sized Al₂Si₂Eu phases were observed. However, after controlled cooling in a differential scanning calorimeter, multiply twinned Si particles were observed. The formation of multiply twinned Si particles was attributed to the adsorption of Eu atoms along the 〈1 1 2〉_Si growth direction of Si and at the intersection of two {1 1 1}_Si facets. Twinning was observed in both fundamentally different casting processes: controlled sand-casting and melt-spinning. This is fully consistent with the well-known poisoning of the twin plane re-entrant edge and the impurity-induced twinning modification mechanisms