P. Lejay

Magnetic ordering in TbRh2Si2 and CeRh2Si2

Abstract Magnetic measurements and a neutron diffraction study have been carried out on the ternary compounds TbRH2Si2 and CeRh2Si2 with a tetragonal structure of ThCr2Si2-type. TbRh2Si2 is found to order antiferromagnetically below TN = 92K with moments along the c-axis. The structure of wave vector k=[001], consists of a stacking of ferromagnetic (001) planes with a +−+− sequence. CeRh2Si2 develops below TN = 36 K a structure described by a wave vector k=[ 1 2 1 2 0] in which the coupling within a (001) plane is antiferromagnetic. This change of coupling together with the large negative value of θp=−61K has been attributed to a change of the sign of the first nearest neighbour in-plane interaction which would correspond to an exchange mechanism different from the usual RKKY one in CeRh2Si2.

A new family of rare earth compounds, the ternary silicides RE2RhSi3 (RE = Y, La, Ce, Nd, Sm, Gd, Tb, Dy, Ho, Er) - crystal structure electrical and magnetic properties

Abstract New ternary silicides RE 2 RhSi 3 (RE = Y, La, Ce, Nd, Sm, Gd, Tb, Dy, Ho, Er) have been prepared. They crystallize with a hexagonal symmetry structure which is derived from the AlB 2 -type. Si and Rh atoms are inside RE 6 distorted trigonal prisms and are ordered in a two dimensional sublattice perpendicular to the c axis. The a and c parameters are approximately twice those of the corresponding disilicides RESi 2 . La 2 RhSi 3 and Y 2 RhSi 3 are not superconducting down to 1.6 K. Nd 2 RhSi 3 is ferromagnetic at 15 K, but the other silicides order antiferromagnetically with metamagnetic phase transitions for certain of them.

Superconducting and magnetic properties of ternary silicides in some rare earth-noble metal (Rh or Ir)-silicon systems

Abstract New families of ternary silicides have been prepared in the RE - Rh or Ir -Si systems and the crystal structures have been determined: RERh 3 Si 2 , RE 2 Rh 3 Si 5 , RE 2 RhSi 3 (RE = Y, La → Er), RERhSi (Y, La, Gd → Er), REIrSi (RE = La, Ce, Nd), RERhSi 2 and REIrSi 2 (RE = La → Gd). The RE 2 RhSi 3 compounds crystallize with a new structural type, the other ones are isostructural with already known silicides or borides. Some of the silicides studied whose rare earths are diamagnetic (Y, La) show superconducting transitions above 1.6 K. They have been compared with other superconducting ternary borides, silicides, germanides and phosphides containing rare earths and noble metals. Except the phases with Y and La which are diamagnetic or show Pauli paramagnetism, the other materials order magnetically at low temperature. The onset of magnetic transitions vs. field has been observed for some compounds below 20 kOe at 4.2 K.

Structure, superconductivity and magnetism of new rare earth-rhodium silicides RE2Rh3Si5 of U2Co3Si5-type

Abstract New ternary silicides RE 2 Rh 3 Si 5 (RE = Y, La, Nd, Sm, Gd, Tb, Dy, Ho, Er) have been prepared. They crystalize in the U 2 Co 3 Si 5 -type structure. Only the silicides containing the diamagnetic rare earths Y and La show a superconducting transition at T Cr = 4.4 ± 0.2K and T Cr = 2.7 ± 0.1K respectively, those with magnetic rare earths order antiferromagnetically at low temperature.

Crystal structure of new superconducting materials LaIrSi3 and LaRhSi3. Structural relation between LaRh2Si2, La2Rh3Si5 and LaRhSi3

Abstract New superconducting ternary silicides LaRhSi 3 and LaIrSi 3 have been prepared by arc melting from the elements and annealing for ten days at 900°C. A single crystal study shows these materials to be of tetragonal symmetry and isostructural with BaPtSn 3 . Their superconducting transition temperature which depends strongly on stoichiometry and thermal treatment occurs between 1.9 K and 2.7 K. The structures have been compared to those of the superconducting compounds LaRh 2 Si 2 and La 2 Rh 3 Si 5 . The occurence of superconductivity in these materials seems to be related to the presence of similar coordination polyhedra for Rh or Ir and Si atoms.

Crystal structure and magnetic properties of new rare earth ternary equiatomic silicides RERhSi

Abstract New ternary silicides RERhSi (RE=Y, Gd, Tb, Dy, Ho, Er) have been prepared by arc melting from the elements and annealed for for several days at 800°C. Single crystal studies show these materials to be of orthorhombic symmetry and isostructural with TiNiSi (anti-PbCl 2 structure). Gd, Tb and Dy compounds show a spontaneous magnetization and their ordering consists probably of a non-colinear arrangement of the moments. HoRhSi and ErRhSi order antiferromagnetically at 8K and 7.5K respectively. At 4.2K HoRhSi undergoes a metamagnetic transition above 6kOe. A field transition appears also at 4.2K for ErRhSi above 12kOe.

Influence of composition on the structural and superconducting properties of the two polymorphic forms of iridium- or silicon-substituted YIr2Si2

Abstract The structural and superconducting properties of the low and high temperature forms of YIr2−xSi2+x compounds, which have structures of the ThCr2Si2 and CaBe2Ge2 types respectively, were studied. Each modification exhibits a narrow homogeneity range spreading over the silicon-poor and silicon-rich sides. The materials were obtained as pure phases only for 0⩽ x

New ternary silicides in rare earth-rhodium-silicon systems. Crystal structure and magnetic properties

New ternary silicides have been prepared in rare earth-rhodium-silicon systems. They have the hexagonal CeCo3B2- type structure (space group P6/mmm-D16h) with the general formulae RERh3Si2 (RE = Y, La, Nd, Sm, Gd, Dy, Ho, Er). Except the Y and La compounds which are diamagnetic, they are ferromagnetically ordered at low temperature. No superconductivity has been found for YRh3Si2 and LaRh3Si2 at temperatures as low as 50 mK.

Crystal structure, superconducting and magnetic properties of new ternary silicides LaRhSi, LaIrSi and NdIrSi

Abstract New ternary silicides LaRhSi, LaIrSi and NdIrSi have been synthesized by arc melting. On the basis of the ZrOS structure, their powder patterns have been indexed using a primitive cubic unit cell with space group p213. LaRhSi and LaIrSi have a superconducting transition at 4.35K and 2.3K respectively. NdIrSi shows spontaneous magnetization below TC = 10K and its magnetic structure is probably non colinear.

Influence of some metal substitutions on the superconducting behaviour of molybdenum borocarbide

Abstract The superconducting properties of the Mo2−xMxBC borocarbides (M ue5fc Zr, Nb, Rh, Hf, Ta, W) are reported. They have an Mo2BC-type structure with orthorhombic symmetry and the space group Cmcm. Stoichiometric powder samples were prepared by arc melting. A large single crystal of Mo2BC was obtained by a Czochralski-type method. The upper limit of x depends mainly on the size of the M atoms. A study of the magnetization as a function of field at different temperatures shows that all borocarbides are type II superconductors. Resistivity measurements give generally a critical temperature Tcr above 4.2 K. Tcr and the critical fields Hc2 increase for rhodium substitution but decrease in the other cases. For comparison the superconducting properties are discussed in terms of the valence electron concentration and the molar volume.