U. Gottlieb

Magnetic properties of single crystalline Mn4Si7

Abstract A single crystal of MnSi2−x was obtained by a modified Czochralski pulling technique in a cold copper crucible. The quality and the nature of the sample were checked by an accurate crystal structure determination, which revealed the sample to be Mn4Si7. Resistivity and magnetic measurements were performed on this sample in the temperature range between 2 K and room temperature and in magnetic fields up to 7.5 T. Mn4Si7 shows a metallic behaviour and the good crystal quality was revealed by the high residual resistance ratio of 360. For the magnetic susceptibility we observed a Curie–Weiss law above about 40 K with a low effective moment of peff=0.365 μB/Mn. Below this temperature, moments order in an anisotropic helical state, and in fields above 1 T, they align with a saturation moment of psat=0.012 μB/Mn. Mn4Si7 is a weak itinerant magnetic system that could be a good candidate for the observation of the critical quantum fluctuations expected for marginal Fermi liquids.

Structural and electronic transport properties of ReSi2−δ single crystals

We investigated some structural and transport properties of semiconducting ReSi2−δ . In the literature this silicides is reported to crystallize in an orthorhombic structure and to be stoichiometric ReSi2. Our investigations clearly show that the stable composition is ReSi1.75 crystallizing in the space group P1. Transport measurements show thermally activated behavior at high temperatures with one (or two) energy gap Eg=0.16 (0.30 eV). We also report Hall‐effect measurements on this material: we found that RH is positive between 30 and 660 K and at room temperature the Hall number nH=1/eRH is equal to 3.7×1018 cm−3. The Hall mobility at room temperature is relatively high (μH=370 cm2/V s) for a single crystal.

Magnetic susceptibilities of VSi2, NbSi2 and TaSi2 single crystals

We report magnetic susceptibility measurements on single crystals of very-high-purity VSi2, NbSi2 and TaSi2 from 4 K to room temperature. VSi2 is paramagnetic while NbSi2 and TaSi2 are diamagnetic. A systematic anisotropy of chi is observed for the three compounds. The results are in good agreement with previous investigations of the electronic properties of these materials. The different contributions of chi which account for these data are discussed.

Electron-phonon interaction spectra of TaSi2, NbSi2 and VSi2

Abstract Using point-contact spectroscopy, the spectral function for the electron-phonon interaction has been measured for the three silicides TaSi2, NbSi2, and VSi2. The difference in the energy-dependence of the phonon spectra between these isoelectronic compounds can be explained in terms of the standard mass dependence of the phonon frequencies.

Some physical properties of ReSi1.75 single crystals

We investigated the electronic transport properties and the magnetic susceptibility of the semiconducting silicide ReSi1.75. This compound crystallises in a monoclinic structure (space group P1). The resistivity of this silicide is anisotropic depending on the direction of the current flow. At high temperatures we observe thermally activated behaviour for the resistivity with one (or two) energy gap(s) Eg = 0.16 eV (0.30 eV). Hall effect measurements yield a positive Hall coefficient in the temperature range between 30 and 660 K. At room temperature we found a Hall carrier concentration of 3.7 × 1018 cm−3 and a quite high Hall mobility of 370 cm2/V · s. As the resistivity, the magnetic susceptibility of ReSi1.75 is anisotropic depending on the orientation of the magnetic field relative to the crystallographic axes. At room temperature χ is strongly diamagnetic. Below about 50 K, χ increases with decreasing temperature.

Magnetoresistance and Hall effect of NbSi2 single crystals

We measured the transverse angular magnetoresistance and the Hall effect on high-quality NbSi2 single crystals at low temperatures (4.2 K ≤ T ≤ 160 K) and high magnetic fields (B ≤ 20 T). The material behaves like a compensated metal, i.e. the magnetoresistance grows generally proportionally to B2. For some current–field configurations, however, saturation of the magnetoresistance occurs, giving evidence for the presence of an open orbit on the Fermi surface of NbSi2 parallel to the c axis. The Hall coefficient shows, as does the magnetoresistance, a low-field–high-field transition. It varies between −3.5 and −4.5 × 1010 m3 C−1 in low magnetic field to −10.5 × 10−10 m3 C−1 in the high-field region. We compare our results with those obtained for NbSi2 thin films and discuss the validity of parameters deduced from transport data.

High-Frequency Point-Contact Spectroscopy of TiSi2, TaSi2, and VSi2

High-frequency point-contact spectroscopy as well as conventional low-frequency PC spectroscopy has been used for determining the spectral functions of the electron-phonon interaction (EPI) for three disilicides TiSi2, TaSi2, and VSi2. The temperature dependences of resistivity have been calculated from obtained EPI functions. Comparison of calculated dependences with known experimental data allowed correction of the electron-phonon interaction constants for the studied disilicides.

Magnetic susceptibility of semiconducting ReSi1.75

Abstract We measured the magnetic susceptibility of a single crystal of semiconducting ReSi 1.75 with the magnetic field aligned along the three main crystallographic directions. The susceptibility of ReSi 1.75 is strongly diamagnetic and anisotropic. Below 40 K, χ increases with decreasing temperature. We discuss the different contributions to the susceptibility of ReSi 1.75 and we explain the low temperature behaviour of χ in analogy to the behaviour of a doped semiconductor near the metal-insulator transition

Angular dependence of the magnetoresistance of TiSi2 single crystals

Abstract We measured the transverse magnetoresistance Δϱ ϱ of good quality TiSi2 single crystals at low temperatures (4.2≤T≤112 K) in magnetic fields up to 7.8 Tesla. Single crystals were produced by a modified Czochralski pulling technique and they have low residual resistivity (typically ϱ(4.2 K ) = 0.15 μΩ· cm ) and high residual resistance ratio (typically RRR > 50). The angular dependence of magnetoresistance shows either minima or maxima when the magnetic field is parallel to the principal crystallographic axes. At high fields (B > 1 T). we found that the magnetoresistance has a magnetic field dependence weaker than the B2 law expected for compensated metals. At 7.8 T, the values of ωcτ obtained are of the order of unity. The Kohler scaling rule is observed within three orders of magnitude of the reduced parameter B ϱ (where ϱ is the zero field resistivity measured between 4.2 and 112 K).