Characterization of the asymmetrical barrier potentials in CoFe/AlOx/Co magnetic tunneling junction by electron holography

Electron holography (EH) in a field emission gun transmission electron microscope has been used to profile the inner potential V0 across CoFe/AlOx/Co magnetic tunneling junctions (MTJs). The spatial dimension of the AlOx barrier layer can be accurately determined from the phase profile at the tunneling junctions. The EH results show unambiguously that the potential jump across the CoFe/AlOx interface is smaller than that across the Co/AlOx interface, which results in asymmetrical barriers in the MTJs. The inner potential difference and the asymmetrical barrier were discussed based on the different oxidation statuses between Co/AlOx and CoFe/AlOx interfaces.