The electronic and magnetic states of a monatomic bcc Fe(001) layer directly facing a single-crystalline MgO (001) tunnel barrier were studied by means of X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) at the Fe L2,3 edges to elucidate the underlying physics of huge tunnel magnetoresistance (TMR) effects observed in Fe/MgO/Fe magnetic tunnel junctions. Both XAS and XMCD results reveal that the 1-ML Fe is not oxidized, which should be crucial for the huge TMR effect. A sum-rule analysis of the XMCD spectra shows that the 1-ML Fe(001) has a total magnetic moment of about 2.6 μB per Fe atom, which is strongly enhanced as compared to that of bulk Fe.
