Inverse tunnel magnetoresistance in over-oxidized FeCo/AlOx/Co junctions

Inverse tunnel magnetoresistance (TMR) has been observed in over-oxidized FeCo/AlOx/Co magnetic tunnel junctions (MTJs) with FeCo to be the bottom electrode. Electron-holography (EH), which is a special technique capable of exploring the microstructure of ferromagnet-insulator (FM-I) interface, has been performed to profile the inner potential V-0 within the MTJs. EH results show unambiguously that the phase jump across the AlOx/FeCo interface differs remarkably from that across the Co/AlOx interface, which implies that the bottom FeCo electrode has been partially oxidized and more likely one FeCo-oxide layer forms near the interface. We think that this oxide layer provides a negative spin polarization in contrast with a positive one for Co/AlOx interface, therefore results in an inverse TMR. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.