Development of a depth-resolved x-ray magnetic circular dichroism: application to Fe/Cu(100) ultrathin films

A depth-resolved technique is applied in the x-ray magnetic circular dichroism (XMCD) method by controlling the probing depth of the electron yield XMCD spectra. The usefulness of this technique is demonstrated for the study of magnetic structures of 4 and 8 ML Fe films grown on Cu(100), which are known to exhibit peculiar magnetic depth profiles. It was directly shown that the 4 ML film is uniformly magnetized, while the magnetic moment is localized at the surface in the case of the 8 ML film. The XMCD spectrum for each layer of the 4 ML film was separately extracted. All the extracted spectra were almost identical to each other, confirming the ferromagnetic coupling over the whole film. As for the 8 ML film, it was suggested that the surface two layers are ferromagnetically coupled, while the inner layers are in a spin density wave state with a wavenumber q = 2pi/2.4d.