Material layer stack structures to provide a magnetic tunnel junction (MTJ) having improved perpendicular magnetic anisotropy (PMA) characteristics. In an embodiment, a free magnetic layer of the material layer stack is disposed between a tunnel barrier layer and a cap layer of magnesium oxide (Mg). The free magnetic layer includes a Cobalt-Iron-Boron (CoFeB) body substantially comprised of a combination of Cobalt atoms, Iron atoms and Boron atoms. A first Boron mass fraction of the CoFeB body is equal to or more than 25% (e.g., equal to or more than 27%) in a first region which adjoins an interface of the free magnetic layer with the tunnel barrier layer. In another embodiment, the first Boron mass fraction is more than a second Boron mass fraction in a second region of the CoFeB body which adjoins an interface of the free magnetic layer with the cap layer.