Effect of Transition-Metal Impurities on the Critical Temperature of Superconducting Al, Zn, In, and Sn

Abstract

The depression in critical temperature T c of several dilute solid solutions of transition elements in Al, Zn, In, and Sn was measured as a function of residual resistivity and concentration. In Zn-Mn and Zn-Cr, localized moments are present and T c decreases linearly with concentration with a slope -dT c /dc of 315 and 170°K/at.%, respectively. By comparing these numbers with theory, a value of about 1.4 eV was found for the s-d exchange integral. In all other alloys, the critical temperature is still depressed but much less than in Zn-Mn and Zn-Cr, and the depression becomes less rapid with increasing concentration of impurities. However, no saturation is found up to the maximum concentrations reached. The effect here found is different from that taking place in dilute alloys containing nontransition metals in that the depression of T c is larger, giving rise to suppression of superconductivity at sufficiently high impurity concentration. An analysis of the data for Al-Mn, Al-Cr, Al-Fe, Zn-Fe, Zn-Co, and Zn-Ni shows that in these systems the observed decrease of T c is satisfactorily accounted for by the smoothing out of the gap anisotropy and by the formation of localized virtual states, whose effect on the superconducting properties has been studied theoretically by Zuckermann. In-Mn and Sn-Mn do not fit the foregoing picture; however, the results obtained rule out the presence of magnetic moments in these two systems in bulk form. The apparent contrast with the results obtained in thin films is discussed. Some results on ternary alloys are also reported. It is shown that no effect on the critical temperature of In-Mn dilute solutions is produced by the addition of Pb.

Superconducting Spin Switch with Infinite Magnetoresistance Induced by an Internal Exchange Field

“…Al 2 O 3 barriers as thin as 0.3 nm at the interface was enough to destroy the proximity effect. Also, it is observed that the T C is much higher in EuS/Al 2 O 3 /Al/Al 2 O 3 /EuS sample compared with T AP C of the EuS/Al/EuS structure, indicating less interplay between the superconductivity and ferromagnetism in the former due to the blocking of the exchange field by the barrier, whereas in EuS/Al/EuS trilayers possible unaligned Eu 2+ magnetic moments at the EuS/Al interfaces may act as magnetic impurities lowering the T C [35,36]. Given the extreme sensitivity of superconductivity to magnetic impurities, which in this case carry 7 µ B per Eu 2+ magnetic moment, T C change is not surprising.…”

Transition temperature depression in quench condensed Zn-Mn dilute alloy films

“…T~-depression values (dTddc)inltial as high as 300 K/at~o Mn have been measured by a number of groups [16][17][18]. This is, however, more an average value.…”

Selection of materials for concentrators designed for optical pumping of ultraviolet and vacuum ultraviolet lasers

“…yo copper, less than 0.1. In pure zinc the evidence from measurements of the superconducting transition temperature (Boato, Gallinaro and Rizzuto 1966) is that iron carries no moment. In figure 6(a) we use these estimates to sketch the position of the virtual bound state as a function of solvent composition; for the sake of definiteness we have chosen m, = 5 and the width of the state as 0.5 ev.…”