Superconductivity and magnetism of complex rhodium borides

A number of complex rhodium borides with an LuRu₄B₄-type structure is synthesized; these are DyRh₄B₄ (samples HP) with T _c ≈ 4.5 K, DyRh_3.8Ru_0.2B₄ (samples AM) with T _c ≈ 4.5 K, Dy_0.8Er_0.2Rh_3.8Ru_0.2B₄ (samples AM) with T _c ≈ 6.3 K, and HoRh_3.8Ru_0.2B₄ (samples AM) with T _c ≈ 6.0 K. The temperature dependence of upper critical field B _c2(T) for all the samples under study exhibits an anomalous behavior. In all cases, the curve B _c2(T) demonstrates a point of inflection, after which the curve deviates from the classical parabolic law abruptly upward for DyRh₄B₄ and DyRh_3.8Ru_0.2B₄ (the 1st group of compounds) and downward for the Dy_0.8Er_0.2Rh_3.8Ru_0.2B₄ and HoRh_3.8Ru_0.2B₄ compounds (the 2nd group). These compounds are found to be characterized by of the following phase transitions: paramagnet → ferrimagnet → superconductor (retained ferrimagnetism) → antiferromagnet (retained superconductivity). The latter transition to the antiferromagnetic state occurs only in the compounds of the 1st group. It is found that, for the DyRh_3.8Ru_0.2B₄ compound, no traditional Meissner effect is observed but the so-called Volleben effect (paramagnetic Meissner effect) takes place.     

Standard enthalpy of formation of Sc5Si3

The standard enthalpy of formation of Sc₅Si₃ has been determined by solute-solvent drop calorimetry at (1473±2) K. The following value is reported: ΔH _f ^o (mean)=−(719.1±34.0) kJ mol⁻¹. This result is compared with corresponding published values for the enthalpies of formation of Me₅Si₃, with Me=Mn, Cr, V, Ti. This comparison shows regularly increasing negative enthalpies of formation from Mn₅Si₃ to Sc₅Si₃. LETTTIA TOPOR, formerly Senior Research Associate, The James Franck Institute, The University of Chicago,     

Thermodynamic properties of the gadolinium silicides Gd5Si4 and Gd5Si3

The thermodynamic properties of the gadolinium silicides Gd₅Si₄ (600–725 K) and Gd₅Si₃ (780–910 K) were investigated by measuring the electromotive force of concentration galvanic cells.