Effects of a thin Mg layer on the structural and magnetoresistance properties of CoFeB∕MgO∕CoFeB magnetic tunnel junctions

Abstract

We have combined in situ reflection high energy electron diffraction, high-resolution transmission electron microscopy, and magnetotransport experiments to investigate the role of a thin inserted Mg layer on the crystalline texture of MgO barriers in magnetic tunnel junctions grown in a standard sputtering system. It was found that an ultrathin Mg layer of 2–6Å can efficiently promote a MgO (001) texture prior to any annealing. For thicker Mg layers, the MgO (001) texture was found to degrade due to the hexagonal structure of Mg. For tunneling magnetoresistance (TMR), the efficient role of the MgO crystallization induced by the Mg layer appears after a 400°C annealing. The optimum was found for a 4Å inserted Mg layer with a TMR of 120% at room temperature (210% at 3K) which could be considerably improved for fully (001) oriented magnetic tunnel junctions.