X-ray magnetic circular dichroic spectrum at theKedge of the transition metal inR−Tintermetallics and its relationship with the magnetism of the rare earth

Abstract

We present here a study of the x-ray magnetic circular dichroism (XMCD) at the $K$ edge of the transition metal on rare-earth $(R)$ transition-metal $(T)$ intermetallics. The analysis of the $T\text{ }K$-edge XMCD in the $R{T}_{2}$ compounds $(T=\text{Fe},\text{Co})$ reveals that, when $R$ is magnetic, there is a rare-earth contribution to these spectra which is as intense as to dominate the overall shape and sign of the XMCD signal. As a result, for a given $R$, the XMCD signal recorded in $R{\text{Fe}}_{2}$ is very similar to that of $R{\text{Co}}_{2}$ despite the magnitude of the $\text{Co}\text{ }3d$ magnetic moment is quite different from that of Fe in these compounds. The study of ${\text{XMCD}}_{R}$ as a function of the rare earth itself suggests that the rare-earth contribution to the $T\text{ }K$-edge XMCD has an orbital origin and that its magnitude is related to the orbital component of the magnetic moment, ${L}_{4f}$, instead of the total magnetic moment. Moreover, despite no significant variation in the signals is found when Fe is changed by Co, the amplitude of the signals decreases remarkably as Fe or Co are diluted by nonmagnetic Al. Since aluminum substitution affects only slightly the magnitude of the individual ${\ensuremath{\mu}}_{T}$ and ${\ensuremath{\mu}}_{R}$ magnetic moments but strongly reduces the exchange interaction, this points out that ${\text{XMCD}}_{R}$ shows also a dependence on the strength of the $R\text{\ensuremath{-}}T$ interaction. Therefore, our results suggest that the behavior of ${\text{XMCD}}_{R}$ can be accounted for in terms of a ``molecular fieldlike'' (with ${B}_{RT}\ensuremath{\propto}{n}_{RT}{L}_{R}$) model.