Superconductivity and magnetic order in La-Ce alloys

Abstract

Superconductivity and magnetic order have been studied both above and below the Kondo temperature for the La-Ce system. Electrical resistivity measurements on La 0.2, 1.0, 2.0, 3.2, and 4.0 wt. % Ce have been made from 0.06 K to 20 K. All samples showed a Kondo-like minimum, T min, in the resistivity with a subsequent maximum, Tmax. Tmin was found to be proportional to n 1/7, where n is the concentration, and Tmax (H = 0) was proportional to n 2. The slope of the resistivity due to the magnetic impurities went as pαlnT on both sides of Tmax. Above Tmax the proportionality constant, pα, was almost independent of n, and below Tmax it was proportional to n2. Applied magnetic fields had little effect on pα even though Tmax increased linearly with H. The magnitude of the resistivity at the peak was essentially independent of n but decreased for increased H. The superconducting transition temperature was depressed as n increased, but more slowly than predicted by Abrikosove and Gor'kov, and the critical field curves were considerably depressed below the multiple pair breaking theory of Fulde and Maki.