Atomic-scale spectroscopic imaging of CoFeB/Mg–B–O/CoFeB magnetic tunnel junctions

Atomic-scale electron spectroscopic imaging on sputtered magnetic tunnel junctions (MTJs) with a thin, $<2nm$⁠, MgO layer and B-alloyed electrodes reveals B diffusion into the MgO, resulting in a Mg–B–O tunnel barrier. This $∼2nm$ thick interfacial layer forms due to oxidation of CoFeB during radio frequency sputtering of MgO and subsequent B diffusion into MgO during annealing. We measure a room-temperature tunneling magnetoresistance (TMR) of $∼200%$ in IrMn/CoFeB/Mg–B–O/CoFeB MTJs after annealing, demonstrating that thin Mg–B–O barriers can produce relatively high TMR.