Magnetism and superconductivity in La1.875Ba0.125-ySryCuO4+\delta and La1.6-yNd0.4SryCuO4

μ+SR and neutron diffraction measurements show that at low temperatures in La_1.875 Ba_0.125 CuO₄, there is phase separation into a long range ordered magnetic component of SDW‐like nature, identified with the LTT phase and a superconducting component, identified with the LTO phase. Partial substitution of Ba by Sr at a fixed doping level of 1/8 leads to gradual decrease of the magnetic freezing temperature, accompanied by a decrease in the fraction of the magnetic component. The La_1.875 Ba_0.025 Sr_0.100 CuO_4 composition exhibits freezing of the Cu electronic moments into a disordered arrangement. Excess interstitial oxygen leads to a rapid recovery of superconductivity and a marked depression of the magnetic volume fraction. Study of the LTT phase – after stabilisation with partial substitution of La by Nd – away from the 1/8 doping level, reveals no evidence of long range magnetic ordering with magnetic fluctuations surviving down to 3 K. This revised version was published online in August 2006 with corrections to the Cover Date.     

A μSR-study of UP and UTe

The materials crystallize in the NaCl structure. UP undergoes at 122 K a first order transition into a type I single-k antiferromagnetic state, followed by a second first order transition into a type I double-k-structure at 22 K. UTe is a ferromagnet withT _c =104 K. The two first order transitions of UP reveal themselves by abrupt changes of the transverse field damping rate. No spin rotation is observed in zero field for both antiferromagnetic spin structures which is in keeping with point dipolar lattice sums. In UTe we observe the characteristic critical behavior: a rapid increase of damping rate and paramagnetic frequency shift when approachingT _c from above. In the ferromagnetic regime the spin rotation in zero field damps out too rapidly to be observed. This work has been funded in part by the German Federal Minister for Research and Technology (BMFT) under contract Nr. 03-KA1-TUM-4.     

Die kritischen Felder von supraleitenden Indium-Blei-Legierungen

Resistance and magnetization measurements have been made onα-phase Indium Lead alloys in a longitudinal magnetic field. The results have been analyzed in terms of the Ginzburg-Landau-Abrikosov-Gorkov theory and the parameter? of the alloys has been determined. Alloys with concentrations greater than 4.2 at % Pb are superconductors of the second kind. The temperature variation of? depends on the mean free path and is somewhat less pronounced for the more dilute alloys. This behaviour is not adequately described by the recent theories. The phenomena of surface superconductivity and its critical fieldH _c3 are in good agreement with the theory ofSaint-James andde Gennes except for the constantC ₀=H _c3/H _c2 which for all the alloys studied is about 10% higher than the theoretical value 1.694. Electrolytic deposition of Cu on the surface reducesH _c3 and givesC _cu=1.15 and excludes the alternative explanation of surface filaments. The concentration dependences ofT _c andγ show irregularities at 7 at % Pb. They can be explained by the touching of the Fermi surface with the Brillouin zone boundary.     

Electric field gradients probed by μ+SR in Sc and \alpha\mbox-ScH_x solid solutions

In Sc and \alpha\mbox-ScH_x below 40 K two μ⁺ states are formed: a tunnelling state extending over two adjacent tetrahedral (T) interstices sharing one face in the ab‐plane of the hcp host lattice and a static μ⁺–Sc–H configuration analog to the T‐pair state formed by two H atoms across a Sc site along the crystalline c‐axis. This explains perfectly the high transverse‐field (TF) μSR measurements at low temperature and allows a qualitative understanding of the temperature dependence. The modelling of the low TF measurements requires in addition the consideration of the electric field gradient (EFG) components acting on the Sc nuclei near the μ⁺, i.e., of the radial EFG due to the μ⁺ and of the axially symmetric crystal field. The magnetic field dependence of the anisotropic μ⁺SR relaxation rate is strongly influenced by the H‐concentration in the solid solution system. This revised version was published online in August 2006 with corrections to the Cover Date.     

α-Chlor-nitrone I: Darstellung und Ag+-induzierte Reaktion mit Olefinen. Über synthetische Methoden, 5. (vorläufige) Mitteilung

Organic synthesis may be said to be in need of enophiles, i.e. reagents that would undergo cycloaddition reactions with any isolated olefinic double bond, in contrast to most of the classical Diels-Alder or 1,3-dipolar addition reagents which, as a rule, require activated olefins in order to participate smoothly in cycloaddition processes. This paper introduces α-chloronitrones as precursors of a new class of such reagents; they undergo an Ag⁺-induced reaction with unactivated olefins with great ease to give products considered to result from 1,4-cycloadditions of N-alkyl-N-vinyl-nitrosonium ions to the carbon-carbon double bond (see scheme 2). This process is believed to have a number of synthetic applications, two of them being illustrated in two subsequent communications.     

Development,validation, and application of a novel LC-MS/MS trace analysis method for the simultaneous quantification of seven iodinated X-ray contrast media and three artificial sweeteners in surface,ground, and drinking water

A new method for the simultaneous determination of iodated X-ray contrast media (ICM) and artificial sweeteners (AS) by liquid chromatography-tandem mass spectrometry (LC-MS/MS) operated in positive and negative ionization switching mode was developed. The method was validated for surface, ground, and drinking water samples. In order to gain higher sensitivities, a 10-fold sample enrichment step using a Genevac EZ-2 plus centrifugal vacuum evaporator that provided excellent recoveries (90?±?6 %) was selected for sample preparation. Limits of quantification below 10 ng/L were obtained for all compounds. Furthermore, sample preparation recoveries and matrix effects were investigated thoroughly for all matrix types. Considerable matrix effects were observed in surface water and could be compensated by the use of four stable isotope-labeled internal standards. Due to their persistence, fractions of diatrizoic acid, iopamidol, and acesulfame could pass the whole drinking water production process and were observed also in drinking water. To monitor the fate and occurrence of these compounds, the validated method was applied to samples from different stages of the drinking water production process of the Industrial Works of Basel (IWB). Diatrizoic acid was found as the most persistent compound which was eliminated by just 40 % during the whole drinking water treatment process, followed by iopamidol (80 % elimination) and acesulfame (85 % elimination). All other compounds were completely restrained and/or degraded by the soil and thus were not detected in groundwater. Additionally, a direct injection method without sample preparation achieving 3–20 ng/L limits of quantification was compared to the developed method.