Volume 5, number 1 PHYSICS LETTERS 1 June 1963 10) E.A.Shapoval, J. Exptl. Theoret. Phys. (USSR) 41 (1961) 877; translation: Soviet PhyS. JETP 14 (1962) 628. 11) L. P. Gor'kov, J. Exptl. Theoret. Phys. (USSR) 37 (1959) 833; translation: Soviet Phys. JETP 10 (1960) 593. 12) B.S.Chandrasekhar, Appl. Phys. Letters 1 (1962) 7. 13) A.M. Clogston, Phys. Rev. Letters 9 (1962) 266. ***** SUPERCONDUCTIVE TRANSITION OF ALUMINIUM CONTAINING TRANSITION METAL IMPURITIES * G. BOATO, G. GALL/NARO and C. RIZZUTO Istituto di Fisica dell'UniversitY, Genova, Italy Received 6 May 1963 The effect of transition metal impurities on the critical temperature of superconducting non-transi- tion metals has been studied in thin films 1), but not in bulk metals. As a consequence, possible correlations of this effect with other metallic prop- erties of the alloys were not clarified. These pecu- liar superconducting alloys have received recently renewed interest, due to the finding by Reif and Woolf 2), of a vanishing energy gap as measured by the Giaever method. This can be related with the theoretical discussion by Abrikosov and Gor'kov 3). We have studied the critical temperature of three aluminium alloys, containing small concen- trations of Cr, Mn and Fe. The samples were pre- pared starting from pure aluminium (Raffinal 99.995%), by the Istituto Sperirnentale Metalli Leg- geri, Novara, Italy. In order to hornogenise the samples and dissolve all precipitations, the sam- ples, in form of wires, were annealed by us at about 610°C for a few days; afterwards, they were quenched in iced salt water in order to keep the transition metal in solution. The effect of quenching on the superconducting temperature was found to be negligible. The homogenisation process was con- trolled by measuring for all specimens the residual resistivity ratio, ~) = R4.2/(R273 - R4.2). When the metal was completely dissolved, a strict propor- tionality of this ratio with the concentration was observed (all concentrations smaller than 0.4 at.%). The proportionality factor is in agreement with the data in the literature. The measurements were performed with the aid of an all-metal helium-three cryostat of large ex- perimental space 5). The critical temperature of the solid solutions was determined magnetically, by linearly increasing the field and recording the * Work performed under the auspices of CNR - Comitato per la Fisica and INFN - Sezione di Genova. 20 ~:~ ~ 0.4 O:G -0.4 ~o -0.6 -0.1' ~ n ,o Fig. 1. The decrease in critical temperature of A1 alloys with respect to pure aluminium as a function of residual resistivity ratio, o Value found by Mar- tin for a single A1-Mn alloy. transition signal on a detecting coil by means of a Kipp recording microvoitmeter. The results are shown in fig. 1, where the critical temperatures are plotted as a function of the residual resistivity ratio p. The initial slope of the curves is given in table 1, together with the initial value of - d Tc/dc and the p/c ratio. A1 Fe Al Mn A1 C r Table 1 (c: atomic )ercent) - dTc/dp p/c 1.00 1.09 2.25 3.24 0.80 3.37 - dTc/dc 1.1 7.3 2.7