Two New Superconducting Elements

Abstract

THE low temperatures produced by adiabatic demagnetization of potassium chrome alum have been used to cool various pure metals to about 0.1° K.; a copper rod was used for providing thermal contact between the metal and the salt¹. The occurrence of any superconducting transition in the metal was indicated by a change in the magnetic susceptibility of the metal in an alternating field. Superconductivity was observed in osmium and ruthenium with transition temperatures of 0.71° K. and 0.47° K. respectively. A superconducting transition in ruthenium at 2.04° K. was previously reported by McLennan, Allen and Wilhelm², but their specimen had a high residual resistance; and since no transition was observed by Meissner and Voigt³ down to 1.2° K. in a specimen with much lower residual resistance, it is probable that the high transition temperature was associated with impurity. The critical magnetic fields were found to satisfy the relation H_c = H_o (1 – (T/T_c)²); the values of H_o and T_c are compared in the accompanying table with recent measurements by Goodman and Mendoza⁴ on a number of other elements with low transition termperatures. The values for aluminium and zinc differ only slightly from those found by Daunt and Heer⁵.