  Magnetic tunnel junctions with perpendicular anisotropy form the basis of the
spin-transfer torque magnetic random-access memory (STT-MRAM), which is
non-volatile, fast, dense, and has quasi-infinite write endurance and low power
consumption. Based on density functional theory (DFT) calculations, we propose
an alternative design of magnetic tunnel junctions comprising
Fe(n)Co(m)Fe(n)/MgO storage layers with greatly enhanced perpendicular magnetic
anisotropy (PMA) up to several mJ/m2, leveraging the interfacial perpendicular
anisotropy of Fe/MgO along with a stress-induced bulk PMA discovered within bcc
Co. This giant enhancement dominates the demagnetizing energy when increasing
the film thickness. The tunneling magnetoresistance (TMR) estimated from the
Julliere model is comparable with that of the pure Fe/MgO case. We discuss the
advantages and pitfalls of a real-life fabrication of the structure and propose
the Fe(3ML)Co(4ML)Fe(3ML) as a storage layer for MgO-based STT-MRAM cells. The
large PMA in strained bcc Co is explained in the framework of Bruno's model by
the MgO-imposed strain and consequent changes in the energies of dyz and dz2
minority-spin bands.
