From superconductivity to ferromagnetism in amorphous Gd--La--Au alloys. [(La/sub 100-x/Gd/sub x/)/sub 80/Au/sub 20/, x = 0 to 100, 1. 7 to 300/sup 0/K

Abstract

Splat-cooled alloys of composition (La/sub 100-x/Gd/sub x/)/sub 80/Au/sub 20/ have been obtained by complete substitution of gadolinium for lanthanum in amorphous La/sub 80/Au/sub 20/ matrix. Results of high-field magnetization (up to 70 kOe), ac and dc low-field susceptibility, and resistivity measurements over temperature range of 1.7 to 300/sup 0/K for these alloys are reported. The La/sub 90/Au/sub 20/ alloys are superconducting at 3.5/sup 0/K. For x approximately less than 1, a suppression of T/sub c/ described by the relation dT/sub c//dx approximately equal to -4.0/sup 0/K per atomic per cent gadolinium is observed. For alloys within the concentration range 1 approximately less than x approximately less than 70, maxima in low field susceptibility measurements are observed. The ''ordering'' temperature, T/sub M/, are proportional to x for 1 less than or equal to x less than or equal to 16, similar to those observed in crystalline spin-glass alloys. For 16 approximately less than x approximately less than 70, T/sub M/ is increasing at a faster rate than in the low concentration region, and this intermediate type of ordering corresponds to a mictomagnetic regime. At x approximately greater than 70, a ferromagnetic regime emerges. The maximum Curie temperature is observed for Gd/sub 80/Au/sub 20/ at approximately 150/sup 0/K. The moment per gadolinium atom is found to be constant and close to that of the crystalline value throughout the concentration range investigated. Results of resistivity measurements are correlated with the magnetic properties of different regimes in the magnetic phase diagram. 4 figures, 1 table.