Field dependence of orbital magnetic moments in the Heusler compounds Co2FeAl and Co2Cr0.6Fe0.4Al

Orbital and spin magnetic moments of the Heusler compounds Co2FeAl and Co2Cr0.6Fe0.4Al were measured by magnetic circular dichroism in X-ray absorption (XMCD). The orbital magnetic moments per spin are quite large (0.1-0.2) compared to bulk values of Fe and Co metals, indicating a considerable spin-orbit coupling in these Heusler compounds. A strong localization of the 3d electron states might be responsible for this observation. The Co and Fe orbital to spin moment ratio shows a distinct decrease of Deltar(Fe) = 0.04 +/- 0.02 and Deltar(Co) = 0.06 +/- 0.02 with increasing external field for the ternary compound Co2FeAl, while the ratio is within error limits independent of the field for Co2Cr0.6Fe0.4Al. This is discussed in terms of a relation to magnetocrystalline anisotropies.