Dependence of giant tunneling magnetoresistance in MgO based magnetic tunnel junctions on the structure of Co electrodes

The giant tunneling magnetoresistance recently reported at room temperature in magnetic tunnel junctions (MTJs) with crystalline MgO(100) barriers is related to the bcc structure and (100) orientation of the Co-Fe ferromagnetic electrodes[1]. We have investigated the relationship between the tunneling magnetoresistance of MTJs with ultra-thin Co layer thicknesses inserted between the CoFe and MgO barrier layers and the structure of the Co layer. The electronic structure of the Co layers was studied with x-ray emission spectroscopy (XES) and near edge x-ray absorption fine structure (NEXAFS). The structure of these layers was studied using x-ray scattering. The magnitude of the TMR effect is found to be correlated with the structure of the Co layers. [1] S. S. P. Parkin, C. Kaiser, A. Panchula, P. M. Rice, B. Hughes, M. Samant, S.-H. Yang, Nature Materials, in press (2004).