MgO (001)∕ CoFeB magnetic tunnel junctions (MTJs) at room temperature. A
magnetoresistance (MR) ratio as high as 138%, seven times that of state-of-the-art MTJs for
magnetic sensor application, was obtained at room temperature in MTJs with a resistance-
area product (RA) as low as 2.4 Ω μ m 2. Such a high MR ratio at such a low resistance
was made possible by introducing an ultrathin Mg metal layer with a thickness of 4 Å …