Abstract
Magnetic tunnel junctions (MTJ) which consist of two ferromagnetic electrodes separated by a thin (∼10Å) tunnel barrier can exhibit a magnetoresistance of greater than 40% at 295 K. They hold substantial potential for application as computer memory and magnetic field sensors. Much about the spin-dependent tunneling process is still not understood. in order to identify features that may affect the spin-polarization of the tunnel current, we have used the UHV STEM at Cornell University to perform atomic-scale imaging and EELS on an MTJ system. The MTJ was sputter deposited on (100) Si with layer sequence Co 60Å/Al 12AÅO2 exposure/Co 100Å.The annular dark field (ADF) image (Fig. la) shows the A10x barrier layer has a fairly uniform thickness of about 15 Å. Its profile (Fig. 1c) appears diffuse partly due to layer roughness rather than atomic mixing. in bright field (BF) the appearance of strong Fresnel fringes (Figs. 1b,c), due to a large difference in average electrostatic potential between Co and AlOx, complicates interpretation.
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