Spin-fluctuations in Ti0.6V0.4 alloy and its influence on the superconductivity

Abstract

We report experimental studies of the temperature and magnetic field dependence of resistivity and dc magnetic susceptibility and the temperature dependence of zero field heat capacity in a Ti 0.6 V 0.4 alloy. The temperature dependence of the normal state dc magnetic susceptibility in this Ti 0.6 V 0.4 alloy shows T 2 lnT behavior. The temperature dependence of resistivity follows a T 2 behaviour in the range 20-50 K. On the other hand, a term T 3 lnT is needed in the expression containing the electronic and lattice heat capacities to explain the temperature dependence of heat capacity at temperatures where T 2 dependence of resistivity is observed. Such temperature dependence of dc magnetic susceptibility, resistivity and heat capacity are indications of the presence of spin-fluctuations in the system. Further experimental evidence for the spin fluctuations is obtained in the form of a negative value of T 5 term in the temperature dependence of resistivity. The influence of spin-fluctuations on the superconducting properties of Ti 0.6 V 0.4 is discussed in detail. We show from our analysis of resistivity and the susceptibility in normal and superconducting states that the spin fluctuations present in Ti 0.6 V 0.4 alloy are itinerant in nature. There is some evidence of the existence of preformed Cooper-pairs in the temperature range well above the superconducting transition temperature. Our study indicates that the interesting correlations between spin-fluctuations and superconductivity may actually be quite widespread amongst the superconducting materials, and not necessarily be confined only to certain classes of exotic compounds.Spin-fluctuations in Ti 0.6 V 0.4

Grain Refinement and Enhancement of Critical Current Density in the V0.60Ti0.40 Alloy Superconductor With Gd Addition

“…Beyond x = 0.01, the flux line pinning mechanisms are probably affected by the larger size Gd clusters and stronger FM correlations. We recall here that our previous studies show that the V-Ti alloys have itinerant spin fluctuations that suppress the Tc to about half its theoretically estimated value [12]. The FM clusters of Gd mentioned above might affect the coherence of the spin fluctuations, and this might be the reason for the slight enhancement of the Tc with Gd addition.…”

Strong electron–phonon coupling and multiband effects in the superconductingβ-phase Mo1−xRexalloys

“…This observation is further substantiated by the results of temperature dependent resistivity (presented latter in this paper) showing a very small contribution from the T 2 term, which rule out a predominant role of spin-fluctuations in this composition range. Furthermore, the results of our preliminary investigation of normal state dc magnetization do not reveal the typical signature of spin fluctuations as was observed in Ti-V alloys [35,37]. Tulina and Zaitsev pointed out from the point contact spectroscopy studies that the λ ep estimated from the phonon spectral function α F 2 (ω) alone cannot explain completely the enhancement of T C in the − Mo x…”

“…For Mo and the − Mo x 1 Re x alloys with x up to 0.05, the estimated T C is much higher than the experimentally obtained one. We had observed such differences in Ti-V alloys as well and we have attributed this to the presence of spin fluctuations in those alloys [35,37]. In the composition range 0.075-0.25, the experimental T C is higher than the estimated T C (shaded region in figure8), and the λ ep estimated from γ is smaller than that estimated from ΔC/γT C and T C .…”

“…It is to be noted here that any possible influence of spinfluctuations was not taken into account while estimating λ γ ep in the present − Mo x 1 Re x alloys. In the presence of spin-fluctuations, λ γ ep is renormalized by a factor (1 + λ sf ) −1 , where λ sf is electron spin-fluctuations coupling constant [35,37]. On the other hand while estimating λ sc ep using Δ γ C T C , the effect of spin-fluctuations is already taken in to account in the experimentally determined value of T C .…”

“…Therefore, it becomes important to investigate the possible influence of the electron-phonon coupling constant λep on the TC of the system. The electron-phonon coupling constant can be estimated from the γ as [34,35] [2]…”