Voltage controlled spintronic devices

本计画的目标是在三维过渡铁磁体为基础的自旋电子元件中，达成电压控制磁异向性的基本了解。虽然由于自由电子对电场的强屏蔽，电压对金属磁性的影响通常很弱，但在磁各向异性由表面或界面主导的系统中，电压可能具有深远的影响。本计画将从实验与理论两方面探讨金属铁磁体中电控磁性的关键问题。以具有大磁电阻和界面垂直磁各向异性的磁性隧道结为研究平台，系统研究了电压效应对结构、电子、磁性和输运性质的影响。智力优势：该研究解决了自旋电子器件在磁化反转过程中大能耗的关键挑战。电压控制的磁各向异性提供了一种很有前途的方式来实现在纳米磁体中大大降低的开关能量。通过一种新的磁性隧道结纳米柱的制备方法，通过调节界面氧化态，研究了界面磁各向异性、隧穿磁电阻和电压效应之间的相互作用。 元素分辨的轨道磁矩将被确定并与磁性和输运性质相关，为理解电压效应提供重要信息。具有高k氧化物和新颖结构的器件也将被制造以增强电压对磁各向异性的改变。更广泛的影响：对压控磁各向异性基本机理的认识为实现电压感应超低能开关开辟了新的途径，这将直接使包括磁随机存储器、自旋逻辑单元和微波纳米振荡器在内的许多器件受益。这项研究所取得的成果预计将在无线通信、空间探索、传感器技术和运输安全等许多领域产生广泛的技术影响。作为该项目的一个组成部分，还将努力对研究生/本科生和高中教师进行教育和培训，并在地方、区域和国家各级开展外联活动，重点是代表性不足的少数群体的参与。

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.