O. Laborde

Flux pinning, specific heat and magnetic properties of the laves phase superconductor CeRu2

A sharp transition from reversible behaviour to irreversible behaviour in the superconducting mixed state of single-crystal samples of CeRu2 is described. Magnetization, AC susceptibility, resistivity and specific heat measurements under an applied field are reported. The results are discussed in relation to conventional models and those of more novel superconductivity, such as the Fulde-Ferrel state.

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.

Some transport properties of single crystals of group Va transition metal disilicides

Abstract Although transition metal disilicides are used in the form of thin films, single crystals are needed to study their intrinsic properties. Single crystals of Group Va transition metal disilicides, namely VSi 2 , NbSi 2 and TaSi 2 , have been successfully grown by Czochralski pulling from a levitated melt. The good quality of our crystals is shown by the high residual resistance ratios (VSi 2 : RRR 20; NbSi 2 : RRR 220; TaSi 2 : RRR 400). The three compounds crystallize in the same hexagonal structure (C40, space group P6 2 22). Crystallographic and temperature dependences of the resistivity and of the magnetoresistance ( H ⊥ ⩽ 7.4 T) have been measured from 4.2 K up to room temperature. All the three materials show a metallic behaviour and some anisotropy, which is of the order of 2 for the three compounds. The magnetoresistance measurements show that VSi 2 and TaSi 2 are compensated metals with relatively small charge carrier concentrations (VSi 2 : n ≈ 0.15 electrons/formula unit; TaSi 2 : n ≈ 0.20–0.25 electrons/formula unit).

Anisotropy of the magnetic and electrical properties of CeSix

The authors report magnetic and resistivity measurements between 2 and 300 K on well characterised CeSix single crystals (x=1.71 and 1.86). Both the magnetic and the transport properties of this ferromagnetic dense Kondo system are strongly anisotropic. They compare the resistivity results with those of NdSi1.7 which crystallises with the same structure and exhibits a simpler magnetic behaviour. An anomaly is observed at high temperatures (230 K and 260 K respectively for x=1.71 and x=1.86) in the resistivity of CeSix which could result from some structural mechanism.

Magnetoresistance of RuO2-Based Thick Film Resistors

In a series of samples whose composition was systematically changed, we have studied the magnetoresistance (ΔR/R = [R(B)-R]/R) of RuO2-based thick film resistors (TFRs) in magnetic fields (B) up to 20 Tesla and in a temperature range (1.2 K < T < 40 K) in which their resistance exhibits insulating behavior at the boundary between the strong and the weak localization. At the higher temperatures, ΔR/R exhibits a positive bump that does not depend on the RuO2concentration but it changes with the concentration of magnetic Mn impurities diluted in the glassy matrix. For T ≤ 20 K magnetoresistance is entirely negative and it has a quadratic magnetic field dependence at low field. We use the weak localization theory to relate these features of the high temperature magnetoresistance to the composition of TFRs. At low temperature (T < 4.2 K) the negative magnetoresistance shows some peculiarities. The quadratic term shrinks within a vanishing magnetic field range and the magnetoresistance linearly increases in a wide range of B. At the strongest fields and the lowest temperature ΔR/R shows a tendency to saturation. Although these results do not enable to discriminate among different mechanisms, we note that the low temperature (T < 4.2 K) behavior is essentially consistent with recent theory of Nguen et al.

Anisotropy of superconducting properties of Bi-Sr-Ca-Cu-O thin films

Angular dependence of the magneto resistance and of the critical current up to 20 tesla in the bismuth 2212 phase shows remarkable anisotropic behavior. Samples are highly c-axis oriented thin films. The field dependence of the critical current is shown to be essentially dominated by the component of the magnetic field perpendicular to the CuO 2 layers.

Thermal and superconducting properties of Zr-based amorphous alloys; effect of structural relaxation

Abstract The low-temperature thermal and superconducting properties of sputtered amorphous Zr-based alloys are presented. Comparison is made to corresponding alloys prepared by fast quenching from the melt. The different behaviour of these two kinds of alloys is ascribed to a more highly disordered structure for the sputtered samples.

The Normal-State Magnetoresistance of BSCCO 2:2:1:2 Single-Crystal Whiskers

The temperature dependence of the magnetoresistance (MR) of BSCCO 2:2:1:2 single-crystal whiskers in the normal state is shown to violate the Kohler rule above Tc up to room temperatures. The appropriate magnetoconductance data prove that the origin of the MR is due to the suppression of two-dimensional superconducting fluctuations rather than resulting from two different scattering times in the normal state.

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.

Oscillatory behaviour of magnetoresistance and Hall effect of NbSe3 up to 28 Tesla

We report resistivity and Hall-coefficient measurements at very low temperatures (down to 70 mK) and very high fields (up to 28 tesla) of the one-dimensional metallic compound NbSe3. Hall effect displays quantum oscillating behaviour equivalent to the Shubnikov-de Haas oscillations of the resistivity. Weak hysteresis is observed in the whole range of magnetic field, between increasing and decreasing B, in the resistance oscillations. A larger hysteretic effect occurs near 20 tesla and appears in both resistivity and Hall coefficient.