Ramir Ristić

Superconductivity in zirconium-nickel glasses

Abstract The superconducting transition temperatures (Tc) and magnetic susceptibilities of amorphous Zr100−xNix alloys have been measured. Tc decreases linearly with increasing x. The results are compared to those for amorphous ZrPd and ZrCu alloys and discussed in terms of changes in the electron to atom ratio on alloying.

Correlation between mechanical, thermal and electronic properties in Zr–Ni, Cu amorphous alloys

We show that mechanical properties (stiffness and hardness) of Zr–Ni, Cu amorphous alloys increase linearly with Ni, Cu content over a wide composition range (22 ≤ x Ni,Cu ≤ 65 at%). This correlates with the observed increase in the Debye temperatures and densities with x and shows that the strength of interatomic bonding increases with x in these alloys. Accordingly, the thermal stability (e.g. the crystallization and glass transition temperatures) of these alloys also increases with x. Since the electronic density of states at the Fermi level decreases linearly with x within the same x-range, a very simple relationship exists between the electronic structure and mechanical and thermal properties. We also deduce the mechanical properties of hypothetic amorphous Zr and briefly discuss the possibility of its preparation.

Quantum corrections to conductivity of glassy Zr100−xCux alloys

Abstract The variation of the conductivity of glassy Zr100−xCux alloys (x=50, 58, 67 and 71) in the temperature range 2–300 K is discussed in some detail. It is shown that the conductivity varies as √T for T θ D 3 and T for the lower temperatures which is consistent with the predictions of a weak localization theory. Another strong temperature variation of the conductivity sets at the lowest temperatures which could be either due to interaction effects or due to electron scattering on the unstable ionic configurations. Some support to the latter effects is presented.

Enhanced superconductivity in Hf-base metallic glasses

A systematic study of electrical resistivity of Hf100?xFex?(x = 20,25), Hf100?xCux(x = 30,40,50) and Ti65Cu35 metallic glasses has been done in the temperature range 0.3?290?K, and in magnetic fields B?5?T. All Hf-base alloys are superconducting with Tc?0.44?K, which is well above the Tc of pure crystalline Hf (0.13?K). From the initial slopes of the upper critical fields, (dHc2/dT)Tc, and resistivities we determined the dressed electronic densities of states, N?(EF), for all alloys. Both Tc and N?(EF) decrease with increasing x (Fe?and Cu content). The results are compared with those for corresponding Zr-base metallic glasses and ion-implanted Hf films.

Looking for footprint of bulk metallic glass in electronic and phonon heat capacities of Cu55Hf45−xTix alloys

We report on the heat capacity investigation of Cu55Hf45−xTix metallic glasses. The most appropriate procedure to estimate low temperature electronic and phonon contributions has been determined. Both contributions exhibit monotonous Ti concentration dependence, demonstrating that there is no relation of either the electron density of states at the Fermi level or the Debye temperature to the increased glass forming ability in the Ti concentration range x = 15–30. The thermodynamic parameters (e.g., reduced glass temperature) remain better indicators in assessing the best composition for bulk metallic glass formation.

On the origin of bulk glass forming ability in Cu-Hf, Zr alloys

Understanding the formation of bulk metallic glasses (BMG) in metallic systems and finding a reliable criterion for selection of BMG compositions are among the most important issues in condensed matter physics and material science. Using the results of magnetic susceptibility measurements performed on both amorphous and crystallized Cu-Hf alloys (30-70 at% Cu) we find a correlation between the difference in magnetic susceptibilities of corresponding glassy and crystalline alloys and the variation in the glass forming ability (GFA) in these alloys. Since the same correlation can be inferred from data for the properties associated with the electronic structure of Cu-Zr alloys, it seems quite general and may apply to other glassy alloys based on early and late transition metals. This correlation is plausible from the free energy considerations and provides a simple way to select the compositions with high GFA.

Electrical transport in ternary glassy Zr2(Ni1 − xMx)1 alloys

Abstract The addition of a third transition element M (Ti, V, Cr, Mn, Fe, Co or Cu) to the amorphous Zr 2 Ni alloy causes, for fixed M content, a systematic decrease in superconducting transition temperature T c , magnetic susceptibility χ and coefficient A of linear conductivity variation Δσ ∝ T below 100 K (which measures the electron-phonon interaction) in going from M = Ti towards M = Cu. A minimum of A and ΔT c /Δx (gradient of the change in the superconducting transition temperature with concentration of M) and maximum of δ χ for M = Cr and Mn can be associated with the appearance of the magnetic correlation in these alloys. The measurements of the magnetoresistivity in the field B up to 1.2 T and for different temperatures show that the magnetoresistivity also increases when going from M = Cu towards M = Ti; we can explain magnetoresistivity as a combination of the contributions of the electron localization and superconducting fluctuations. Our results agree with measurements of UPS spectra and specific heat capacity for similar alloys.

Electronic band structure and magnetic effects in ternary Zr2(Ni1-xMx)1 glassy alloys

Abstract The electronic and magnetic properties of the amorphous Zr 2 (Ni 1−x M x ) 1 alloys (M = Ti, V, Cr, Mn, Fe, Co, Ni and Cu) have investigated in the temperature range from 1.5K to 300K. As for the other Zr-3d glassy alloys (3d = Fe, Co, Cu or Ni) the temperature dependence of the electrical resistivity(T ≥ 20K) could be described in terms of the incipient electron localization. The new features are the pronounced variations of the magnetic and electron-transport properties with M. The origin of these variations are the systematic changes in the electronic band structure of the alloys on going from M = Cu towards M = Ti and the tendency to the formation of localized magnetic moments for M around the middle of 3d-series (M = V, Cr, Mn and Fe). The magnetic interactions strongly suppress the effects of the incipient localization.

Electronic structure and glass forming ability in early and late transition metal alloys

Abstract A correlation between the change in magnetic susceptibility (Δχexp) upon crystallisation of Cu–Zr and Hf metallic glasses (MG) with their glass forming ability (GFA) observed recently, is found to apply to Cu–Ti and Zr–Ni alloys, too. In particular, small Δχexp, which reflects similar electronic structures, ES, of glassy and corresponding crystalline alloys, corresponds to high GFA. Here, we studied Δχexp for five Cu–Ti and four Cu–Zr and Ni–Zr MGs. The fully crystalline final state of all alloys was verified from X-ray diffraction patterns. The variation of GFA with composition in Cu–Ti, Cu–Zr and Cu–Hf MGs was established from the variation of the corresponding critical casting thickness, dc. Due to the absence of data for dc in Ni–Zr MGs their GFA was described using empirical criteria, such as the reduced glass transition temperature. A very good correlation between Δχexp and dc (and/or other criteria for GFA) was observed for all alloys studied. The correlation between the ES and GFA showed up best for Cu–Zr and NiZr2 alloys where direct data for the change in ES (ΔES) upon crystallisation are available. The applicability of the Δχexp (ΔES) criterion for high GFA (which provides a simple way to select the compositions with high GFA) to other metal-metal MGs (including ternary and multicomponent bulk MGs) is briefly discussed.

Structure property relationship in (TiZrNbCu)1−xNix metallic glasses

The atomic structure, electronic structure and physical properties of