The objective of this project is to achieve fundamental understanding on voltage controlled magnetic anisotropy in 3d transitional ferromagnet based spintronic devices. Although the influence of voltage on magnetic properties of metals is generally weak due to strong screening of electric field by free electrons, voltage may have profound effects in systems where the magnetic anisotropy is dominated by the surface or interface. This project will address the critical issues of electrically controlled magnetism in metallic ferromagnets both experimentally and theoretically. Using magnetic tunnel junctions with large magnetoresistance and interfacial perpendicular magnetic anisotropy as the research platform, systematic study will be carried out to investigate the dependence of the voltage effect on the structural, electronic, magnetic and transport properties.
Intellectual Merit: The proposed research addresses the critical challenge of large energy consumption of spintronic devices during magnetization reversal. Voltage controlled magnetic anisotropy offers a promising way to achieve a greatly reduced switching energy in nanomagnets. With a new fabrication method for magnetic tunnel junction nanopillars, the interplay among the interfacial magnetic anisotropy, tunneling magnetoresistance and voltage effect will be studied by tuning the interfacial oxidation states. Element-resolved orbital magnetic moments will be determined and correlated with magnetic and transport properties, providing vital information to understand the voltage effect. Devices with high-k oxides and novel structures will also be fabricated to enhance the change of magnetic anisotropy by voltage.
Broader Impact: The knowledge on the fundamental mechanism of voltage controlled magnetic anisotropy opens a new avenue to achieve voltage induced ultra-low energy switching that will directly benefit many devices including magnetic random access memory, spin logic unit and microwave nano-oscillators. The results obtained in this research are expected to have broad technological impact in many areas such as wireless communication, space exploration, sensor technology and transportation safety. As an integrated part of this project, effort will also be directed to the education and training of graduate/undergraduate students and high school teachers, as well as the outreach activities at local, regional and national level with emphasis on the participation of underrepresented minorities.
