Magnetic circular x-ray dichroism in Ce intermetallic compounds

Abstract

Magnetic circular x-ray dichroism (MCXD) studies at ${\mathit{L}}_{2,3}$ absorption edges in intermediate-valence (IV) compounds ${\mathrm{CeFe}}_{2}$, Ce(${\mathrm{Fe}}_{0.8}$${\mathrm{Co}}_{0.2}$${)}_{2}$, ${\mathrm{CeCo}}_{5}$, ${\mathrm{Ce}}_{2}$${\mathrm{Co}}_{17}$, and trivalent 4${\mathit{f}}^{1}$ systems (${\mathrm{CeRu}}_{2}$${\mathrm{Ge}}_{2}$, ${\mathrm{Ce}}_{3}$${\mathrm{Al}}_{11}$, CePd, ${\mathrm{CeFe}}_{2}$${\mathrm{H}}_{3.8}$) at the Ce ${\mathit{L}}_{2,3}$ edges are presented. The comparison with reference compounds (La, Lu, Hf, Gd) confirms the existence, in such IV systems, of an ordered 5d magnetic moment on the Ce site antiferromagnetically coupled with the 3d Fe (Co) moment. Moreover, this study suggests, provided the 4f orbital moment is almost quenched, the existence of a simple proportionality between the MCXD intensity and the magnetic moment of the probed atom. For instance the MCXD method leads to a Ce 5d magnetic moment in ${\mathrm{CeFe}}_{2}$ of about 0.35${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ antiferromagnetically coupled with the 3d Fe moment, in good agreement with band-structure calculations. The MCXD applications in Ce(Fe,Co${)}_{2}$ and ${\mathrm{CeFe}}_{2}$${\mathrm{H}}_{\mathit{x}}$ permit us to define precisely the electronic structure of Ce in such compounds. Particularly we will show that MCXD experiments at the ${\mathit{L}}_{2,3}$ absorption edges of Ce are able to yield valuable information on the degree of hybridization of the 4f electrons in the ground state. Indeed, systematic comparison between the MCXD signals of IV and normal trivalent Ce compounds reveals the extreme sensitivity of the ${\mathit{L}}_{2,3}$ MCXD experiments to the degree of localization of the 4f electrons.