L. Romaka

Physical properties and superconductivity of skutterudite-related Yb3Co4.3Sn12.7 and Yb3Co4Ge13

Rietveld analysis was performed for the intermetallics Yb3Co4.3Sn12.7 and Yb3Co4Ge13 crystallizing with the closely related structure types, Yb3Rh4Sn13 and Yb3Co4Ge13. Below Tc = 3.4 K Yb3Co4.3Sn12.7 crosses over into a type-II superconducting ground state with Hc2(0)~2.5 T. Yb3Co4Ge13 stays in the normal state down to 300 mK. The γ value of 2.3(2) mJ gat-1 K-2 and the Debye temperature ΘD = 207(5) K deduced from the specific heat as well as Tc correspond to that of elementary Sn, thus indicating conventional BCS superconductivity. Hydrostatic pressure applied to Yb3Co4.3Sn12.7 reveals both an overall decrease of the absolute resistivity values, as well as a decrease of Tc, which vanishes for a critical pressure below 10 kbar. The magnetoresistance of both Yb-based compounds is positive at low temperature but does not exceed 8% in fields of 12 T. The Seebeck coefficient has a maximum value of about 18 µV K-1 at T~250 K. LIII and magnetic susceptibility measurements reveal intermediate valence: 2.66(3) and 2.18(3) for Yb3Co4Ge13 and Yb3Co4.3Sn12.7, respectively.

Crystal structure and physical properties of (Ti,Sc)NiSn and (Zr,Sc)NiSn solid solutions

Crystal structure, electrotransport and magnetic properties for Ti1−xScxNiSn and Zr1−yScyNiSn solid solutions were studied. Stability ranges of the limited solubility for these phases were established. All alloys of these solid solutions crystallize with the MgAgAs structure type. A gradual semiconductor–semimetal transition was observed in the resistivity when increasing the Sc content for these substitutional series of alloys. The samples with small Sc content have quite a high positive thermopower value at elevated temperatures. The room temperature magnetic susceptibility of the (Ti,Sc)NiSn solid solution samples shows enhanced paramagnetism, while the (Zr,Sc)NiSn ones are characterized by weak Pauli paramagnetism.

Magnetic and electrical properties of R2CuGe6 compounds (R=Y, Ce, Nd, Gd, Tb, Dy, Ho, Er, Yb)

Abstract The temperature dependence of the magnetic susceptibility of the R2CuGe6 (R=Y, Gd, Tb, Dy, Ho, Er, Yb) compounds was measured in the range 84–300 K. It is shown that these rare earth compounds are Langevin type paramagnets except the Y2CuGe6 compound which is a Pauli paramagnet with low and temperature independent magnetic susceptibility. The resistivity of the compounds with R=Y, Ce, Nd, Gd, Tb, Ho, Yb was measured in the range 78–380 K. The differential thermopower of the Ce2CuGe6 and Tb2CuGe6 compounds was investigated in the range 78–380 K. Specific resistivity of the above-mentioned germanides increases linearly with increasing temperature and adopts values normally found in intermetallics.

Electrical resistivity and magnetism in some ternary intermetallics

Abstract We report on structure and transport properties of novel materials Er 3 Co 6 Sn 5 , Y 3 Co 6 Sn 5 , HfCu 6 Sb 3 , Ti 5 Cu 0.45 Sb 2.55 , Tm 2 Ni 3 Sn 2 and Er 6 Ni 2 Sn studied in polycrystalline form in connection to their magnetic behavior. For the latter compound also the specific-heat data are presented. The first two compounds crystallize in the Dy 3 Co 6 Sn 5 -type structure. HfCu 6 Sb 3 forms in a new structure type characterized by space group P 6 3 mc and lattice parameters a =4.259 A and c =11.5112 A. The W 5 Si 3 structure type has been determined for Ti 5 Cu 0.45 Sb 2.55 . Er 6 Ni 2 Sn possesses the orthorhombic Ho 6 Ni 2 Ga-type structure with lattice constants a =9.245 A, b =9.417 A and c =9.819 A. Specific features of the temperature dependence of resistivity will be discussed in the context of results of magnetic measurements, e.g. the ρ vs. T curve for Er 6 Ni 2 Sn exhibits two pronounced cusp-like anomalies at T 1 ≈18 K and T N ≈35 K. These anomalies are connected with magnetic phase transitions confirmed by magnetization data.

Phase equilibria in the Hf–Ni–Sn ternary system and crystal structure of the Hf2Ni2Sn compound

Abstract The isothermal sections of the phase diagram of the Hf–Ni–Sn system have been constructed at 1070 and 870 K. The new ternary Hf 2 Ni 2 Sn compound with Mo 2 FeB 2 crystal structure (space group P 4/ mbm , a =0.70423(2), c =0.33695(1) nm) was found. The presence of Hf 5 NiSn 3 compound is unproven.

{Sm, Er}-Cu-Sn ternary systems

Abstract The isothermal section of the phase diagrams has been constructed for the Er–Cu–Sn and Sm–Cu–Sn ternary systems at 670 and 770 K, the existence of six ternary intermetallic compounds has been confirmed and four new ternary compounds have been found. The crystal structure for two of them has been established. Magnetic and electrical properties of some compounds in the {Er,Sm}–Cu–Sn ternary systems have been measured in the 78–300 and 80–400 K temperature ranges, respectively.

Synthesis, crystal structure and physical properties of ZrNiSn semiconductor doped with Mn

The resistivity, thermopower, dc magnetic susceptibility and electron paramagnetic resonance (EPR) spectra of ZrNi, x Mn x Sn solid solution with low (0.001≤x≤0.05) Mn concentration were investigated in the 78-400 K temperature range. Polycrystalline samples of the ZrNi x Mn x Sn compounds were prepared by arc-melting of the pure metals. Quantitative atomic emission spectroscopy confirmed the appropriate Mn contents in all alloys. The lattice parameters of the ZrNi 1-x Mn x Sn compounds with different Mn concentration are almost unchanged. Magnetic susceptibility shows the linear dependence versus inverse magnetic field for all samples, what is evidence for the magnetic interactions in the ZrNi 1-x Mn x Sn compounds The temperature dependence of magnetic susceptibility for the compounds with 0.005≤x≤0.05 can be described approximately by a Curie-Weiss law. The results of static magnetic measurements were confirmed by EPR technique. The broad line of I type belongs to Mn 2+ ions in the Ni-sites in crystal lattice coupled by magnetic dipolar interaction. The narrow line of II type is interpreted as an EPR spectrum of exchange-coupled pairs or clusters of more than two Mn 2+ ions. The unusual magnetic properties and the features of dipolar and exchange interaction of the Mn 2 ions in the lattice of ZrNi 1-x Mn x Sn solid solution are discussed.

Solid solutions ZrNi1 − xMxSn (M Cr, Mn, Cu) and their electrical and magnetic properties

Abstract Solid solutions of ZrNi 1 − x M x Sn (M  Cr, Mn, Cu) were obtained on the basis of the ZrNiSn semiconducting compound with MgAgAs structure type, X-ray analysis was used to define the stability range of solid solutions: x = 0.4, 0.5, and 0.1 for Cr, Mn, and Cu, respectively. The temperature dependence of resistivity changes from semiconducting to metallic type with increasing x; the thermopower remains negative for all investigated samples. The temperature dependence of the magnetic susceptibility for ZrNl 1 − x Mn x Sn and ZrNi 1 − 3 Cr x Sn can be described approximately by Curie-Weiss law, and the onset of a spontaneous magnetization occurs for small quantities of Mn or Cr. Solid solutions with Cu are paramagnetic.

Zr–Cu–Sb ternary system and the crystal structure of new ternary compounds

Abstract The isothermal section of the Zr–Cu–Sb ternary system at 770 K has been investigated by X-ray phase analysis. The already known Zr2CuSb3 antimonide with the new structure type (space group P 4 m2 ) and two new ternary compounds were obtained and their crystal structures were determined. The Zr5Cu0.45Sb2.55 structure belongs to the W5Si3 structure type (I4/mcm space group, a=1.0937(1) nm, c=0.55437(1) nm). The Zr2Cu3.03Sb2.97 compound crystallizes with HfCuSi2 structure type (P4/nmm space group, a=0.39589(2) nm, c=0.98182(5) nm).

Magnetic and transport properties of Er6Ni2Sn

Abstract Results of structure analysis, and magnetization, susceptibility and electrical resistivity measurements on Er 6 Ni 2 Sn as functions of temperature and magnetic field are presented and analyzed. Antiferromagnetic ordering is indicated below T N =35 K and the occurrence of two other order–order transitions at 7 and 17 K are concluded from the available data.