Engineering of interfacial structures has become important more than ever before to find new scientific observations and to create novel applications. Here, we show that the interface reconstructed by atomic layer-thick Mg insertion substantially improved the magneto-electrical properties of perpendicular magnetic tunnel junctions essential for modern spintronic applications. The 0.2-0.4 nm-thick Mg inserted between the MgO tunnel barrier and CoFeB ferromagnet restructured the interface in such ways as to protect the CoFeB from overoxidation, to strengthen the texture, to make the interfacial roughness smooth, and to relax the mechanical stress. Observed were great increases in the perpendicular magnetic moment and perpendicular magnetic anisotropy of the CoFeB by 2.1 and 1.8 times, respectively, which can be ascribed to the optimum interfacial condition because of the least possible chemical damage. The strong enhancement of (010) in-plane and (001) out-of-plane texture and of interfacial roughness led to a significant increase in the tunnel magnetoresistance by 4.4 times from 13.2 to 57.6% by the insertion. Most importantly, such optimum chemical and physical structures at the interface could modulate the perpendicular magnetic properties by an electric field. The electric field-controlled magnetic anisotropy coefficients became symmetrically bipolar to the electric field and were increased over 100 fJ/V·m, which is 6 times larger than one found before the Mg insertion. As a result, we could successfully demonstrate the voltage-induced magnetization switching of the perpendicular magnetic tunnel junctions with the help of an external magnetic field. Our findings will ignite further study on the new way of electrical control over magnetic switching and provide an essential ingredient to realize electric field-driven energy-effective magneto-electronic devices.
Keywords: interface modification; interfacial magnetic anisotropy; magnetic tunnel junctions; magnetization reversal; perpendicular magnetic anisotropy; voltage-controlled magnetic anisotropy.