Transmission electron microscopy study on the polycrystalline CoFeB∕MgO∕CoFeB based magnetic tunnel junction showing a high tunneling magnetoresistance, predicted in single crystal magnetic tunnel junction

Abstract

We carried out a detailed transmission electron microscopy study on the polycrystalline CoFeB∕MgO∕CoFeB based magnetic tunnel junction, which shows high magnetoresistance predicted theoretically only in single crystal magnetic tunnel junction. Previously it has been suggested that the crystallinity and degree of texture of MgO tunnel barrier play a crucial role in the polycrystalline system. Here we suggest, on top of the crystallinity issue of MgO, that a grain-to-grain epitaxy of CoFeB∕MgO∕CoFeB satisfies the prerequisite for the coherent tunneling for the giant tunneling magnetoresistance theoretically predicted.