  In this study, to obtain perpendicular magnetic tunnel junctions (p-MTJs)
using half-metallic ferromagnets (HMFs), several methods were developed to
induce perpendicular magnetic anisotropy (PMA) in full-Heusler Co2FeSi (CFS)
alloy thin layers in an MTJ multilayer composed of a layered CFS/MgO/CFS
structure. Oxygen exposure at 2.0 Pa for 10 min after deposition of the bottom
CFS layer was effective for obtaining PMA in the CFS layer. One of the reasons
for the PMA is the formation of nearly ideal CFS/MgO interfaces due to oxygen
exposure before the deposition of the MgO layer. The annealing process was
effective for obtaining PMA in the top CFS layer capped with a Pd layer. PMA
was clearly observed in the top CFS layer of a Cr(40 nm)/Pd(50 nm)/bottom
CFS(0.6 nm)/MgO(2.0 nm)/top CFS(0.6 nm)/Pd(10 nm) multilayer, where the top CFS
and Pd thin films were deposited at RT and subsequently annealed at 300{\deg}C.
In addition to the continuous layer growth of the films, the crystalline
orientation alignment at the top CFS/Pd interface probably attributes to the
origin of PMA at the top CFS layer.
