A. Ravex

Effect of structural relaxation on the low temperature thermal properties of the superconducting amorphous alloy Zr .76Ni 0.24

Abstract We have measured the low temperature (from 50 mK up to 5 K) specific heat and thermal conductivity of an amorphous ZrNi superconducting alloy as sputtered and after annealing in the amorphous state. We observe after annealing a decrease of the specific heat anomaly below 0.5 K together with an increase of the thermal conductivity. These variations are in agreement with a decrease of the density of two-level systems (T.L.S.) due to the structural relaxation.

Heat treatment effect on thermal, superconducting and structural properties of amorphous sputtered Zr76Cu24 alloy

The authors report and discuss measurements of low-temperature specific heat and thermal conductivity, upper critical field near Tc, electrical resistivity, mass density and X-ray diffraction, performed on an amorphous superconducting Zr76Cu24 alloy obtained by high-rate sputtering deposition at 77K. A thermal annealing of the samples in the amorphous state before crystallisation induces a large decrease of the very low-temperature specific heat related to the two-level system excitations, whereas the thermal conductivity increases in a correlative way. Both electron and phonon contributions to the specific heat in the normal state decrease and tend towards the values of liquid-quenched (LQ) alloys of corresponding composition. At the same time, the other properties studied are less affected, likewise in LQ alloys. The occurrence upon annealing of a chemical phase separation in the amorphous state is proposed to explain the results.

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.

Superconducting properties of amorphous sputtered Zr70Mo30

Abstract Specific heat, resistivity and critical superconducting fields (Hc and Hc2) measurements show that amorphous Zr70Mo30 is an intermediate superconductor (Tc = 4.3 K; λ = 0.77). The coupling strength is mainly governed by the electronic properties. Like in the Zr−3d alloys previously investigated, a discrepancy between the measured and calculated upper critical field slope is reported. The effect of two-level systems (TLS) needs to be clarified.

Low-Energy Excitations in Zr-Based Amorphous Alloys Studied by Thermal Conductivity and Specific Heat

For temperatures well below their superconducting transition Tc, the thermal properties of amorphous superconducting alloys become very similar to amorphous insulators, that means governed by the low-energy excitations (Two-Level Systems) successfully proposed by the tunneling model [1]: T1.9–T2 regime for thermal conductivity below about 1 K and a residual specific heat anomaly roughly linear with T and almost universal in magnitude, of the order of a few erg/g.K at 100 mK.

Effect of structural relaxation on critical fields Hc and Hc2 in sputtered amorphous alloys Zr76Cu74 and Zr76Ni24

On rapporte des resultats de champ critique pour des alliages amorphes Zr 76 Cu 24 et Zr 76 Ni 24 prepares par pulverisation. Le champ critique H c (T) obtenu par calorimetrie est bien decrit en supposant que les deux systemes sont des supraconducteurs a couplage faible. On ne trouve pas un accord semblable pour H c2 (T) obtenu par une methode resistive

STRUCTURAL RELAXATION IN SPUTTERED Zr-Cu ALLOYS STUDIED BY LOW-TEMPERATURE THERMAL CONDUCTIVITY AND X-RAY SCATTERING

Publisher Summary The structural relaxation of metallic glasses obtained by annealing induces a decrease of their free-energy and consequently significant changes for some of their properties. This chapter presents the effect of structural relaxation on the low-temperature thermal conductivity, which is determined by intrinsic excitations of the disordered state together with very sensitive X-ray scattering experiments, which give direct information about the structural evolution. In the experiments, samples of Zr76Cu24 and Zr80Cu20 were prepared in the form of large foils by a high-rate DC magnetron sputtering technique. X-ray measurements were carried out with a specific small-angle scattering camera. It allows measurements over a large angular scale from the small-angle region to the first diffraction halo. Furthermore, heating of the sample can be carried out in situ inside the vacuum chamber; consequently, tiny variations of the scattered intensities upon annealing can be revealed by this highly sensitive device.

Effect of structural relaxation on critical fieldsHc andHc2 and on resistivity in sputtered amorphous alloys Zr76Cu24 and Zr76Ni24

We report critical field results on sputtered amorphous Zr76Cu24 and Zr76Ni24 alloys. TheHc(T) obtained from calorimetric measurements is well described by assuming that both systems are weak coupling superconductors. A similar good agreement is not found forHc2(T) obtained by a resistive method; tentative explanations of this discrepancy are suggested. We also report resistivity measurements in the normal state on Zr76Ni24 alloys. Results are well interpreted in the framework of the Faber-Ziman diffraction model. An alternative explanation, the Kondo-like model for two-level systems, is also discussed.

Two-level systems in zirconium-based amorphous alloys: Evidence of a coupling with Zr nuclei

Abstract We report very low-temperature specific heat measurements on a series of amorphous superconducting zirconium-based alloys. From the analysis of the data in a large temperature interval, we determine the specific heat excess due to the low-energy excitations (T.L.S.) characteristic of the amorphous state. At the lowest temperature (T ≲ 0.1 K) the onset of a nuclear contribution is observed, numerically corelated to that of the TLS, which suggests a coupling between the 91 Zr nuclear spins and these excitations.