Magnetic tunnel junctions with single-crystal electrodes: A crystal anisotropy of tunnel magneto-resistance

A strong dependence of tunnel magnetoresistance (TMR) on the crystal orientation of ferromagnetic electrodes was confirmed experimentally. We studied the TMR of Fe/Al2O3/Fe50Co50 tunnel junctions with single-crystal Fe electrodes of different crystal orientations and found that the TMR ratio increased from 13% to 42% at 2K (8% to 26% at room temperature) when the crystal orientation was changed from (100) to (211). Such a TMR anisotropy could be explained in terms of the anisotropic spin polarization of Fe bulk and/or interface electronic states. The importance of the "momentum-filtering" effect of the tunnel barrier was also discussed.