Effect Of Transition Metal Impurities Research Articles

Recent developments in the use of the thermoelectric power of metals and alloys as a research tool

Abstract The thermoelectric power of metals and alloys is a relatively easily measured physical property that has become increasingly valuable in recent years for the information it can yield on electron and phonon transport processes. It is a particularly sensitive property for investigating dilute alloys, the effect of transition metal impurities in metals, and magnetic ordering. Links with other transport properties are provided by the use of the Wiedemann-Franz law and the Matthiesson rule in the basic theory. This review covers recent developments in the use of thermoelectric power as a research tool.

The effect of transition-metal impurities on the residual resistivity of Al, Zn, In and Sn

Dilute solid solutions of several transition metals in Al, Zn, In and Sn were prepared; in a few cases the solubility limit at the melting temperature was found to be less than 102 p.p.m. The residual resistivity per unit concentration due to these impurities was measured and found to be larger than that caused by nontransition metal impurities. Interesting features are found by plotting the residual resistivity as a function of the atomic number of the impurities. The data are discussed in the light of the Friedel-Anderson model for a localized virtual state in metals and its magnetization. This model is found to account very satisfactorily for the resistivity data, if the assumption is made that the transition-atom impurity gives only one electron to the conduction band of the host metal. The only anomalous system is In-Mn, which shows also an anomalous behavior of the superconducting critical temperature as a function of concentration.

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

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 $\ensuremath{-}\frac{d{T}_{c}}{\mathrm{dc}}$ of 315 and 170\ifmmode^\circ\else\textdegree\fi{}K/at.%, respectively. By comparing these numbers with theory, a value of about 1.4 eV was found for the $s\ensuremath{-}d$ 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.

Effect of Transition Metal Impurities on the Critical Temperature of Nontransition Metals

Effect of Transition Metal Impurities on the Critical Temperature of Nontransition Metals

Superconductive transition of aluminium containing transition metal impurities

The effect of transition metal impurities on the critical temperature of superconducting non-transition metals was examined by criticai temperature measurements on samples of pure Al containing traces of Cr, Fe, and Mn. A noticeable depression of the critical temperature was observed, and a nonlinear dependence of the critical temperature on the residual resistivity ratio was noted. Mean-free-path effects and scattering are believed to contribute to the depression. (D.C.W.)