Magnetic properties of (La,Gd)Al2 alloys

Theac anddc susceptibilities of (La_1–x Gd _x )Al₂ alloys were measured for moderate Gd concentrations (0.01x0.08) between 0.05 and 4.2 K. Sharp spin glass like maxima in ^AC are observed at temperaturesT _f which scale asT _f /x 26 K for all samples. However, scaling of ^AC is not observed indicating that the RKKY interaction at short distances which becomes more important with increasing Gd concentration, is ferromagnetic in this system. The amplitudeV ₀ of the RKKY interaction is obtained from both the approach to the saturation magnetization and ^AC forT0, yielding a mean value ₀=(1.5±0.3) 10^–26 eV cm³ which is in agreement with that observed in other systems with Gd impurities. Furthermore, the inferred value of the exchange integral is in accord with other measurements (T _c depression, reverse resistance anomaly) on (La, Gd)Al₂. A superposeddc magnetic field rounds the maximum of ^AC and shifts it to lower temperatures. ^AC is completely flat below 4.2 K in a field which saturates the isothermal remanent magnetization, showing once again the correlation between the peak in ^AC and the onset of irreversible properties.This work is part of the research program of the Sonderforschungsbereich 125 Aachen/Jülich/Köln     

Synthesis and Diels-Alder Reactions of a New Kind of Chiral Dienophiles: Cyclic Vinyl-p-tolylsulfilimines

A new kind of chiral dienophiles, cyclic vinyl-p-tolylsulfilimines (2a and 2b), were obtained from the corresponding (Z)-sulfinylacrylonitriles with HBF(4) and methanol. The asymmetric Diels-Alder reaction of optically pure 2a with cyclopentadiene under mild thermal or catalyzed conditions afforded only the endo-4a adduct with complete endo and pi-facial selectivities. The ability of the sulfilimine moiety to enhance the dienophilic reactivity of the double bond is similar to that of the sulfinyl group.     

Spin glass properties of vanadium diluted in Ti2O3

The initial magnetic susceptibility χ_r, the thermoremanent and isothermal remanent magnetizations have been measured below 10 K on single crystals of (Ti_1?xV_x)₂O₃ for x = 0.03, 0.05 and 0.07. The data clearly show a spin glass behaviour, with peaks in the curve χ_r(T). These results are related to the anomaly in the low temperature specific heat of these compounds, reported elsewhere. It is shown that this anomaly is mainly due to spin glass properties and only partly to electronic properties. This leads to a reinterpretation of the mechanism by which V in Ti₂O₃ induces the metallic phase and at the same time carries a magnetic moment.     

Spinglass properties of W(Fe) with Fe-concentrations 0.1, 0.23 and 0.35 at.%

The d.c. magnetic susceptibility of W(Fe) samples with 0.1, 0.23 and 0.35 at.% Fe was measured with zero field and field cooling below 4.2 K with the samples as received and after an additional annealing. The heat-treatment did not influence the results. Similarities and differences with respect to known spinglass properties are discussed briefly.     

Magnetic phase diagram of γ-FeNiMn alloys with a mixed exchange interaction

The magnetic phase diagram of (Fe_cNi_85?c)Mn₁₅, (Fe_cNi80?c)Mn₂₀ alloys with f.c.c. structure has been determined. The ground state in the transition region between ferromagnetism and antiferromagnetism is found to be either a ferro-spin-glass mixed phase or a spin glass phase. The general feature of the magnetic phase diagram is in good agreement with recent theoretical calculations [2–10].     

Zeros of the Whittaker function associated to Coulomb waves

The zeros in the complex z plane of the Whittaker function W_c/z,µ(z),closely related to spherical waves in the quantum-mechanicalCoulomb problem, are investigated for varying real values ofthe parameters c and µ