Electronic configuration of cerium in amorphous alloys (invited; abstract)

Abstract

We have investigated the effect of structural disorder on the valence of cerium in different families of amorphous alloys prepared by coevaporation on to cryogenic substrates. The Ce electronic configuration was characterized by LIII x-ray absorption spectroscopy and bulk magnetization measurements. Special attention was paid to the amorphous analogs of prototypic Kondo and strongly mixed valent compounds in the crystalline state, such as Ce Si2 (TK≂200 K), CemNin, CemCon. The cerium was found to be purely trivalent in amorphous CexSi1−x (0≤x≤0.75) alloys over both the metallic and nonmetallic concentration ranges, so that the weakly mixed valent state in crystalline CeSi2 is believed to rely on details of the crystalline symmetry and band structure. In contrast, the cerium was found to remain mixed valent in amorphous CexCo1−x (0.15≤x≤0.75) and CexNi1−x (0.30≤x≤0.60) alloys, without any significant effect of the structural disorder. The concentration dependence of the Ce valence anomaly was found to be different in the Ce Ni and Ce Co alloys. This different behavior is discussed in terms of electronic band structure.