Interface control of domain wall depinning field

We study the impact of Mg insertion layer at the CoFeB|MgO interface on the domain wall depinning field and motion as well as other magnetic properties in a perpendicular magnetized Ta/CoFeB/Mg(wedged)/MgO structure. With the increase of the Mg layer from 0.4 nm to 0.8 nm, the field-induced domain wall moving velocity increases while the depinning field decreases. The minimum depinning field of around 10 Oe for as-grown sample and 7 Oe for annealed sample is found with a 0.8 nm Mg insertion layer, which is 2 times lower than the ones reported before. Further increase of the Mg layer leads to a lower velocity and higher depinning field. Similar phenomena happens to the magnetic properties such as the saturation magnetization and perpendicular magnetic anisotropy. Both for as-grown and annealed samples, the tendency is similar. This may be explained by the oxidation and crystallinity manipulation of the CoFeB|MgO interface. These results show an ultra-low depinning field in the Ta/CoFeB/MgO system as well as a possible way for controlling the depinning field.