  The concept of Perpendicular Shape-Anisotropy Spin-Transfer-Torque Magnetic
Random-Access Memory tackles the downsize scalability limit of conventional
ultrathin magnetic tunnel junctions (MTJ) below sub-20 nm technological nodes.
This concept uses a thicker storage layer with a vertical aspect ratio,
enhancing the thermal stability factor thanks to the favorable contribution of
the shape anisotropy. However, the increased aspect ratio comes with an
increase in switching time under applied voltage and the cross-over to
non-uniform reversal mechanism at higher aspect ratio, limiting the gain in
scalability. Additionally, the larger volume of the magnetic cell significantly
increases the stray field acting on the neighboring devices compared to thin
MTJs. In this work, we propose the use of a dipolar-coupled core-shell system
as a storage layer. This improves both bottlenecks, as predicted by
micromagnetic simulations for magnetisation reversal, and a macrospin model to
estimate the stray field in a dense array.
