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

• Published in: Applied physics letters Vol. 110; no. 5
• Main Authors: Li, Xiang, Fitzell, Kevin, Wu, Di, Karaba, C. Ty, Buditama, Abraham, Yu, Guoqiang, Wong, Kin L., Altieri, Nicholas, Grezes, Cecile, Kioussis, Nicholas, Tolbert, Sarah, Zhang, Zongzhi, Chang, Jane P., Khalili Amiri, Pedram, Wang, Kang L.
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 30-01-2017; American Institute of Physics (AIP)
• Subjects: Anisotropy; Applied physics; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Electric potential; Electrical junctions; ENGINEERING; Insertion; Magnesium oxide; Magnetic anisotropy; Magnetic properties; Magnetic saturation; MATERIALS SCIENCE; Oxidation; phonons; Physics; spin dynamics; spintronics; Tantalum; thermal conductivity; thermoelectric; Thickness; Tunnel junctions; X-ray diffraction
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.4975160

We studied the impact of different insertion layers (Ta, Pt, and Mg) at the CoFeB|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 Ta|CoFeB|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|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|MgO interface is crucial for the development of electric-field-controlled perpendicular magnetic tunnel junctions with low write voltage.