From Superconductivity to Ferromagnetism in Amorphous Gd-La-Au Alloys

Abstract

Splat cooled alloys of composition (La100−xGdx)80Au20 have been obtained by complete substitution of gadolinium for lanthanum in amorphous La80Au20 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°K for these alloys are reported. The La80Au20 alloys are superconducting at 3.5°K. For x ≲ 1, a suppression of Tc described by the relation dTc/dx ≈ — 4.0°K per atomic per cent gadolinium is observed. For alloys within the concentration range 1 ≲x ≲ 70, maxima in low field susceptibility measurements are observed. The “ordering” temperatures TM are proportional to x for 1 ≤ x ≤ 16, similar to those observed in crystalline spin-glass alloys. For 1.6 ≲ x ≲ 70, TM is increasing at a faster rate than in the low concentration region, and this intermediate type of ordering corresponds to a mictomagnetic regime. As x ≳ 70, a ferromagnetic regime emerges. The maximum Curie temperature is observed for Gd80Au20 at ~ 150°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.