  The interfacial Dzyaloshinskii-Moriya interaction (iDMI) is attracting great
interests for spintronics. An iDMI constant larger than 3 mJ/m^2 is expected to
minimize the size of skyrmions and to optimize the DW dynamics. In this study,
we experimentally demonstrate an enhanced iDMI in Pt/Co/X/MgO ultra-thin film
structures with perpendicular magnetization. The iDMI constants were measured
using a field-driven creep regime domain expansion method. The enhancement of
iDMI with an atomically thin insertion of Ta and Mg is comprehensively
understood with the help of ab-initio calculations. Thermal annealing has been
used to crystallize the MgO thin layer for improving tunneling
magneto-resistance (TMR), but interestingly it also provides a further increase
of the iDMI constant. An increase of the iDMI constant up to 3.3 mJ/m^2 is
shown, which could be promising for the scaling down of skyrmion electronics.

Mesoscale and Nanoscale Physics