Spin structures with frustrated moments in RNiAl intermetallic compounds

Magnetic order in the ternary equiatomic intermetallic compounds PrNiAl, DyNiAl and HoNiAl is investigated by means of neutron powder diffraction and dc- and ac-susceptibility measurements. DyNiAl shows two magnetic phases: It is ferromagnetic between T₁ =15 K and T_c = 31 K and a tilted antiferromagnet below T₁. HoNiAl is a ferromagnet in a narrow temperature region just below T_c = 14.5 K, but furthermore exhibits two tilted antiferromagnetic phases (T₁ =5.5 K, T₂ = 12.5 K). The corresponding magnetic structures differ in the ordering of some of the magnetic moments which are coupled by frustrated bonds. The existence of those frustrated moments, which is induced by the topology is a common phenomenon in the hexagonal RNiAl series. They are manifested with reduced mean values of their moments in the elastic neutron spectra. Another interesting observation is the scaling of the second temperature T₁ at which the frustrated spins change their order: For all heavy rare earths investigated so far (R = Tb, Dy, Ho) we find T₁: T_N,C ≈ 1: 2. PrNiAl displays an incommensurate sinusoidal (TSW) structure with XY spin behaviour below T_N = 6.9 K, and only one ordered phase is found. The observed ordering temperatures roughly follow the de Gennes scaling factor.     

Cyclodextrins as chiral stationary phases in capillary gas chromatography. Part IV: Heptakis(2,3,6-tri-O-pentyl)-β-cyclodextrin

O-Perpentylated β-cyclodextrin has been evaluated as chiral stationary phase in capillary gas chromatography. Enantioselectivity is observed towards many chiral hydroxy compounds, including cyanohydrins and carbohydrates. Most importantly, the enantiomers of many olefins and alkyl halides can be resolved on this chiral phase. The thermal stability of the cyclodextrin derivative exceeds 200°C.     

Investigations of the Vicarious C‐Aminations of 5,7‐Dinitrobenzotriazole and 4,6‐Dinitrobenzotriazol‐3‐ium‐1‐oxide and Their Energetic Properties

This combined experimental and theoretical study details the vicarious nucleophilic substitution by amination of 5,7‐dinitrobenzotriazol ( 1 ) and 4,6‐dinitrobenzotriazole‐3‐ium‐1‐oxide ( 4 ) with trimethylhydrazinium iodide to afford the new corresponding one‐ and two‐time aminated compounds and investigations of its mechanism by EPR spectroscopy. The preferred position for the first amination is computed by spin density population and verified by X‐ray crystallography. The zwitterionic structure of 4 is investigated in solution by ¹H NMR spectroscopy and in solid state by X‐ray diffraction. Furthermore, the crystal structure of 1 is presented. The energetic behavior of the aminated products as well as the starting materials 1 and 4 was investigated, regarding sensitivities and performance.     

A single-surface yield function for geomaterials

Summary The article outlines a seven-parametric yield function for geomaterials such as soils and rocks. Proceeding from a geometric representation in the principal stress space, the yield surface exhibits a closed shape, thus reflecting the sensitivity of the plastic response of this type of media to hydrostatic stresses. The yield function is able to describe the effects of primary yielding, as well as of isotropic and kinematic hardening. In addition the failure envelope contains an open cone when the number of material parameters is reduced from seven to five.Dedicated to F. G. Kollmann on the occasion of his 60th birthday     

Zur Hönl-Dehnenschen Formulierung des Machschen Prinzips

It is shown that the classification of curved space-times into Machian and antiMachian world models proposed byHönl andDehnen is inadequate. We prove that even the static Einstein model would be anti-Machian according to the definition of these authors, in contrast to their assertion. The proof is based on the theorem, established in this paper, that any Robertson-Walker space-time admits regular source-free Maxwell fields.