Enhancement of voltage-controlled magnetic anisotropy through precise control of Mg insertion thickness at CoFeB | MgO interface

We studied the impact of different insertion layers (Ta, Pt, and Mg) at the CoFeB vertical bar MgO interface on voltage-controlled magnetic anisotropy (VCMA) effect and other magnetic properties. Inserting a very thin Mg layer of 0.1-0.3 nm yielded a VCMA coefficient of 100 fJ/V-m, more than 3 times higher than the average values of around 30 fJ/V- m reported in TajCoFeB vertical bar MgO- based structures. Ta and Pt insertion layers also showed a small improvement, yielding VCMA coefficients around 40 fJ/V-m. Electrical, magnetic, and X-ray diffraction results reveal that a Mg insertion layer of around 1.2 nm gives rise to the highest perpendicular magnetic anisotropy, saturation magnetization, as well as the best CoFe and MgO crystallinity. Other Mg insertion thicknesses give rise to either under- or over- oxidation of the CoFe vertical bar MgO interface; a strong over- oxidation of the CoFe layer leads to the maximum VCMA effect. These results show that precise control over the Mg insertion thickness and CoFe oxidation level at the CoFeB vertical bar MgO interface is crucial for the development of electric-field-controlled perpendicular magnetic tunnel junctions with low write voltage. Published by AIP Publishing.