X-ray Absorption and X-ray Magnetic Circular Dichroism Studies of a Monatomic Fe(001) Layer Facing a Single-Crystalline MgO(001) Tunnel Barrier

We studied the electronic and magnetic states of a monatomic bcc Fe(001) layer facing a single crystalline MgO(001) tunnel barrier by using X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) at the Fe L2,3 core edges in order to clarify the origin of the huge tunnel magnetoresistance (TMR) effect observed in Fe/MgO/Fe magnetic tunnel junctions. Both the XAS and XMCD revealed that the 1 ML-Fe is not oxidized, which is crucial to the huge TMR effect. A sum-rule analysis of the XMCD shows that the 1 ML-Fe(001) has an enhanced total magnetic moment of about 2.6 µB per Fe atom compared with that of bulk Fe.