M. El-Hagary

Magnetic phase transitions in SmNi2B2C

Abstract The magnetic properties of SmNi2B2C were studied by specific heat and magnetization measurements. Below the Neel temperature TN=10.2 (1) K a second anomaly in the heat capacity is observed. This may be associated with a spin reorientation transition at T ∗ =8.4 – 9.4 K being sensitive to tiny changes of the composition. The strong curvature of the inverse susceptibility is well described by a Curie–Weiss law with μeff≃0.59μB/f.u. and a temperature-independent Van Vleck susceptibility χ 0 ≃37×10 −7 cm 3 / g .

Kondo-lattice behaviour of CeNi9Si4

Abstract We have studied the crystal chemistry, thermodynamic and transport properties of ternary compounds RNi9Si4 with R=La and Ce. The Rietveld refinement of the X-ray diffraction pattern revealed a tetragonal crystal structure (space group I4/mcm) that is derived from the cubic NaZn13 structure type. In the case of CeNi9Si4 resistivity, magnetic susceptibility and specific heat measurements reveal Kondo-lattice behaviour with a T2 temperature dependence of the electrical resistivity, an enhanced Pauli susceptibility χ 0 =5×10 −3 emu / mol and a Sommerfeld value γ=155 (5) mJ / mol K 2 . The magnetic susceptibility and specific heat contribution is well described by the Coqblin–Schrieffer model with a fully degenerate J=5/2 ground state and a characteristic temperature T 0 ≃180 K . LaNi9Si4 exhibits simple Pauli paramagnetic, metallic behaviour with a Sommerfeld value γ=33 mJ / mol K 2 .

Disorder and/or density of states effect in YxLu1−xNi2B2C

Abstract The role of disorder and/or lattice strain due to the size mismatch between Y and Lu in the solid solution Y x Lu 1− x Ni 2 B 2 C was studied by specific heat measurements in magnetic fields up to 9 T. Thereby, the analysis of the superconducting and normal state heat capacity as well as the temperature dependence of the upper critical field H c2 shows that the reported reduction of T c within the solid solution correlates with a reduction of the electronic density of states N ( E f ). Thus, the major effect of Y/Lu substitution upon superconductivity is due to a band broadening arising from the R -ion size mismatch rather than from disorder scattering of Cooper electrons.