In the nonlocal spin valve (NLSV) geometry, four-terminal electrical Hanle effect measurements have the potential to provide a particularly simple determination of the lifetime $({\ensuremath{\tau}}_{s})$ and diffusion length $({\ensuremath{\lambda}}_{\mathrm{N}})$ of spins injected into nonmagnetic (N) materials. Recent papers, however, have demonstrated that traditional models typically used to fit such data provide an inaccurate measurement of ${\ensuremath{\tau}}_{s}$ in ferromagnet (FM)/N metal devices with low interface resistance, particularly when the separation of the source and detector contacts is small. In the transparent limit, this shortcoming is due to the back diffusion and subsequent relaxation of spins within the FM contacts, which is not properly accounted for in standard models of the Hanle effect. Here we have used the separation dependence of the spin accumulation signal in NLSVs with multiple FM/N combinations, and interfaces in the diffusive limit, to determine ${\ensuremath{\lambda}}_{\mathrm{N}}$ in traditional spin valve measurements. We then compare these results to Hanle measurements as analyzed using models that either include or exclude spin sinking. We demonstrate that differences between the spin valve and Hanle measurements of ${\ensuremath{\lambda}}_{\mathrm{N}}$ can be quantitatively modelled provided that both the FM contact-induced isotropic spin sinking and the full three-dimensional geometry of the devices, which is particularly important at small contact separations, are accounted for. We find, however, that considerable difficulties persist, in particular due to the sensitivity of fitting to the contact interface resistance and the FM contact magnetization rotation, in precisely determining ${\ensuremath{\lambda}}_{\mathrm{N}}$ with the Hanle technique alone, particularly at small contact separations.

Measurements of the longitudinal elastic constants c(11), c(22) and c(33) and the ultrasonic attenuation alpha of the quasi-two-dimensional triangular-lattice spin-1/2 Heisenberg antiferromagnet Cs2CuCl4 reveal distinct anomalies near the B-induced quantum-critical point (QCP). These anomalies are particularly strongly pronounced in the ultrasonic attenuation. In isothermal field sweeps performed at low temperatures 0.027 K <= T <= 0.3 K around the saturation field B-s, the ultrasonic attenuation of all three modes shows a pronounced double-peak structure, indicating two anomalies of different origin. Upon cooling, however, both features merge suggesting a coincidence at the QCP. While one peak, which can be attributed to the ordering temperature T-N(B), becomes critically enhanced upon approaching the QCP, the other one reduces in size and narrows upon cooling. The latter effect has been tentatively assigned to the material's spin-liquid features which precede the long-range antiferromagnetic ordering.

We report measurements and theoretical calculations of the magnetocaloric properties of low-dimensional spin-1/2 antiferromagnets close to their magnetic field-induced quantum critical points. We demonstrate that the accumulation of entropy around the quantum critical point, giving rise to a critically enhanced magnetocaloric effect ΓB, can be used for realizing a very efficient low-temperature magnetic cooling.

We report on a systematic study of the magnetic properties on single crystals of the solid solution Cs2CuCl4-xBrx (0 <= x <= 4), which include the two known end-member compounds Cs2CuCl4 and Cs2CuBr4, classified as quasi-two-dimensional quantum antiferromagnets with different degrees of magnetic frustration. By comparative measurements of the magnetic susceptibility chi(T) on as many as 18 different Br concentrations, we found that the in-plane and out-of-plane magnetic correlations, probed by the position and height of a maximum in the magnetic susceptibility, respectively, do not show a smooth variation with x. Instead, three distinct concentration regimes can be identified, which are separated by critical concentrations x(c1) = 1 and x(c2) = 2. This unusual magnetic behavior can be explained by considering the structural peculiarities of the materials, especially the distorted Cu-halide tetrahedra, which support a site-selective replacement of Cl- by Br- ions. Consequently, the critical concentrations x(c1) (x(c2)) mark particularly interesting systems, where one (two) halide-sublattice positions are fully occupied.

Starting from Cs2CuCl4 and Cs2CuBr4, we focus on the growth of the Cs2CuCl4−xBrx mixed crystals from aqueous solution and the investigation of the occurring structural variations. The well-known orthorhombic structure (space group Pnma) of the end members of this system is interrupted within the intermediate composition range from Cs2CuCl3Br1 to Cs2CuCl2Br2, if the growth takes place at room temperature. Within this range, a new tetragonal phase is found (space group I4/mmm). However, in case the growth temperature is increased to 50 °C, the existence of the orthorhombic structure can be extended over the whole Cs2CuCl4−xBrx mixed system. A detailed analysis of the composition dependence of the lattice parameters is used to draw conclusions about the incorporation of Cl and Br ions at different sites, which is important for the magnetic interactions between the Cu ions.

The main goal of this project was to carry out a study of the environmental impacts of the new by-pass road L4 in Goetterswickerhamm, North Rhine Westfalia, in the Federal Republic of Germany, using two methods of environmental impact assessment. These methods are "analysis of ecological risks" and "analysis of utility values (2nd generation)". Another goal was to find and assess alternative routes to this road with the objective of taking a decision on which of the routes demonstrates the most environmental compatibility. The use of the two methods and the investigation of their realization was carried out with the use of the geographical information system ARC/INFO. It was not an objective of the project to achieve a model of assessment in which individual factors are produced and evaluated. The two methods were applied separately and this led to the production of two different space resistance maps. These maps make it possible to deduce variants of routes that demonstrate minimum conflicts. Different route alternatives were arrived at, but what is noteworthy is that a decision about which route alternative demonstrates that the most environmental compatibility alternative could only be taken, not without argument, through the analysis of ecological risks method. The difficulty in taking a concrete decision through the analysis of utility values method arose from a 0·3 difference in the total utility values of three route alternatives. The project orientated itself by a study that was carried out by the planning office of Froelich and Sporbeck.