Tuning the magnetic properties of ultrathin magnetic films with MgO as the buffer layer

Abstract

To minimize the screening effect of a metallic ferromagnetic film and improve the effectiveness of electric field modulation, high-quality ultrathin magnetic film is one of the critical prerequisites. Here ultrathin magnetic films and synthetic antiferromagnetics (SAFs) are deposited on SiO2 substrates at room temperature using the magnetron sputtering. Atomic force microscopy is used to characterize the roughness of MgO, Nb, Ru, W, and CoFeB films, revealing their atomic-level flatness, with root mean square roughness values below 0.3 nm, which are crucial in the subsequent preparation of ultrathin SAF to achieve high-quality interfaces. The results from the magneto-optical Kerr microscopy suggest that when MgO is 1.48 nm, ultrathin 0.6 nm CoFeB exhibits stable room-temperature perpendicular magnetic anisotropy (PMA) and there is a correlation between room-temperature ferromagnetism and MgO thickness. For SAFs, ultrathin 0.6 nm CoFeB-based SAF exhibits room-temperature antiferromagnetism via the Ruderman-Kittel-Kasuya-Yosida interaction mechanism. The exchange coupling field demonstrates that the transition between ferromagnetic coupling and antiferromagnetic coupling can be regulated by adjusting both the thickness of the non-magnetic spacer layer and the CoFeB layer. This work lays the ground for the potential applications of high-density storage and efficient electric field modulation of ferromagnetic multilayers for improving energy efficiency.