Magnetic circular dichroism in resonant x-ray emission from impurities: Results at the $L_{2,3}$ edges of Mn in Ni

We present a study of Mn magnetic impurities (about 2%) in Ni with resonant x-ray emission spectroscopy excited at the $L_{2,3}$ edges of Mn using circularly polarized x rays incident almost parallel/antiparallel to the magnetization. The results are discussed jointly with absorption magnetic circular dichroism and complemented with elastic reflectivity measurements. Moreover, we show that emission spectroscopy is particularly suitable to the impurity problem, since the self-absorption/saturation corrections to the measurements are rather limited. The problem is treated also theoretically with a full multiplet splitting calculation of a single ${\mathrm{Mn}}^{2+}$ ${(3d}^5)$ ion with cubic crystal field. The theory reproduces satisfactorily all experimental trends of the features dispersing with the incident photon energy in the whole $L_3$ region, whereas it is not adequate just below the $L_2$ excitation. The joint use of the theory and of the measurements allows us to extract the nondispersive component from the measured spectra. It is shown that this component does not correlate directly with the $3d$-Mn local density of states. The general implications of the results are discussed.