Electron spin resonance and antiferromagnetic resonance of single crystals of yttrium doped with gadolinium

The nonlinear interaction of oscillation modes is investigated on the basis of Lagrangian formalism. Equations describing the changes of the bound mode amplitudes versus time, are obtained. It is shown that the energy transformation between different modes is of a periodic nature: if in the initial moment of time an appreciable part of the energy is contained, for example, in them-th mode, then after a period of timeTt (called a time of nonlinear interaction) the energy will be transformed to then-th mode. Expressions forT _t for cases with the interaction of two and three modes are obtained. As a particular case the process of nonlinear interaction of the electron “transverse” and “longitudinal” oscillations in the highfrequency hybrid resonance region of a “weakly” inhomogeneous plasma was investigated.     

Kolloide Phosphate

Ohne Zusammenfassung Dem an silikatische Achate erinnernden Mineral, das in Hohlr?umen der Lava gebildet ist, und sich mit den sogenannten Schneekopfskugeln in mancher Beziehung vergleichen l?\t, habe ich den Namen „Meyersit“ gegeben, nach Herrn H. H. Meyers, Spezialsachverst?ndiger für Phosphate und Düngemittel am Mellon Institut der Universit?t Pittsburgh.     

ESR of Gd-impurities in the heavy fermion compounds CeCu2Si2 and CeAl3

The heavy fermion systems CeCu₂Si₂ and CeAl₃ are characterized by a huge quasiparticle density of states responsible for the large electronic specific heat. The observation of a Gd³⁺ electron spin resonance (ESR) in single crystals CeCu₂Si₂ and in polycrystalline CeAl₃ clearly demonstrates the local character of these quasiparticles. Nevertheless, the Gd-spin relaxation shows remarkable anomalies with respect to the isostructural compounds LaCu₂Si₂ and LaAl₃: Probably via RKKY coupling, Ce 4f-spin fluctuations give rise to an enhanced Gd-spin relaxation resulting in an unusual non-linear thermal broadening around the Kondo temperature. From this we obtain information about the temperature dependence of the Ce 4f-spin correlation time.     

The double-layer potential operator over polyhedral domains II: Spline Galerkin methods

We examine the numerical approximation of the integral equation (λ ? K)u =f, where K is the double layer (harmonic) potential operator on a closed polyhedral surface in ?³ and λ, ∣λ∣≥1, is a complex constant. The solution is approximated by Galerkin's method, which is based on piecewise polynomials of arbitrary degree on graded triangulations. By utilizing spline spaces which are modified in that the trial functions vanish on some of the triangles closest to the vertices and edges, we investigate the stability of this method in L². Furthermore, the use of suitably graded meshes leads to the same quasioptimal error estimates as in the case of a smooth surface.     

New glassy liquid crystals for optical data-storage applications

Low-molar-mass liquid crystals consisting of a binary nematic mixture of two-naphthylester which exhibit an anisotropic glassy state at room temperature have recently proven to be a suitable material for erasable optical data-storage applications. Using the holographic-grating technique, it is shown that more than 1000 all-optical write, read and erase cycles can be realized without remarkable loss of reversibility. The recording intensities are of the order of 100 W/cm² and optical erasure can be achieved with about twice that intensity. The times for recording and erasure of the optical gratings range on the millisecond scale and the stored gratings persist several months with a diffraction efficiency of typically 1 %. The spatial resolution has been proven down to 2 µm so far. The obtained results are compared with other reversible recording materials.     

The oxidation behaviour of niobium containing γ-TiAl based intermetallics in air and argon/oxygen

The oxidation behaviour of -TiAl based alloys with different Nb contents (2–10 At.%) was investigated in air and in argon-20% oxygen at 900 °C using thermogravimetric analysis. The oxide scales were characterized by a combination of optical microscopy, SEM/EDX and X-ray diffraction analyses. Although in all studied cases the presence of niobium improves the oxidation resistance of -TiAl, the oxidation kinetics, scale morphology and composition in air differed strongly from that in argon-oxygen. In air the oxidation resistance increases with increasing niobium-content. In Ar/O₂ the niobium dependence is far more complex because internal oxidation occurs which is favoured by the presence of niobium. SNMS analysis revealed that the differences in behaviour in the two atmospheres are related to the formation of Ti-rich nitride at the scale/alloy interface during air oxidation. The positive effect of niobium on the oxidation resistance of -TiAl is mainly caused by a decrease of the transport processes in the heterogeneous TiO₂/Al₂O₃-surface scale. Nitride formation and/or niobium enrichment at the scale/alloy interface also affect the oxidation behaviour, however these factors are believed to be the result of the decreased transport processes rather than the main reason for the niobium effect.     

Gd3+-ESR in the intermediate valent cerium compounds Ce x La1-x Os2

In the intermediate valent compounds Ce _x La_1–x Os₂ the Gd³⁺-ESR shows a non-linear increase of the linewidth H(T) in the temperature range 4.2K<T<300K for 0.3x1.0. This non-linearity of the thermal broadening is strongly altered by changing the Ce-concentration. The experimental results H(T,x) can quantitatively be described via hybridization of conduction electrons with Ce4f electrons: Due to hybridization, the Ce4f states are broadened but remain localized. The conduction electron density of states is reduced in the vicinity of the 4f states. In addition we observe a maximum in the electrical resistivity (T) of CeOs₂ at 270 K.