Evidence for a magnetic moment on Ir in IrMnAl from x-ray magnetic circular dichroism

We have observed x-ray magnetic circular dichroism (XMCD) in the helicity modulation mode at Ir $L_{2,3}$ edges in the ferromagnet IrMnAl (Curie temperature 379 K) at room temperature, 100 K and 30 K. This observation proves that Ir has a $5d$ magnetic moment in IrMnAl. Using the magneto-optic sum rules, which relate the integrated intensity of the XMCD and x-ray absorption spectra to the expectation values of spin and orbital angular momenta of Ir, the orbital moment to spin moment ratio, the spin moment and the orbital moment of Ir at 30 K have been deduced to be $-0.17\left(2\right),$ $0.018\left(1\right)\mathrm{}{\mu }_B,$ and $-0.0031\left(8\right)\mathrm{}{\mu }_B,$ respectively. dc magnetization measurements yielded a total moment of $0.123{\mu }_B/\mathrm{a}\mathrm{t}\mathrm{o}\mathrm{m}$ showing that the magnetic moment of Mn is also strongly reduced. We suggest that the extremely small moments of Mn and Ir in IrMnAl are associated with the suppression of local moments and delocalization of $3d$ and $5d$ electrons due to their strong hybridization with the $\mathrm{sp}$ electrons of Al atoms.