Exploring van der Waals heterostructure magnetic devices for high-efficiency and high-density memory

这项拟议的研究将探索基于范德华异质结构的磁性器件，能够提供高效的抗阻尼自旋轨道扭矩来切换垂直磁化强度。随着存储密度的增大，降低开关磁存储器件的能量消耗越来越具有挑战性，这就需要创新的方法来大幅提高能量效率。具有强各向异性的垂直磁化是高密度存储器件稳定的必要条件。这项研究涉及一种特殊类型的van der Waals异质结构，它由具有强垂直磁各向异性的原子层状磁体(如Fe3GeTe2)和具有强自旋动量锁定和低晶体对称性的原子层状Weyl半金属(如1T‘-WTe2)组成。与普通三维、高对称材料产生的自旋轨道扭矩不同，1T‘-WTe2产生的独特反阻尼力矩有望导致在这种van der Waals异质结构中切换Fe3GeTe2磁化强度的临界电流密度要低得多。除了原子上平坦、化学上和磁性上锋利的界面，这两种材料的结合提供了无与伦比的内在和外在特性，适合未来几代高密度磁随机存取存储器设备。这项拟议的研究将提供极好的机会来教育PI学院跨学科的研究生，特别是代表不足的少数族裔学生，通过让他们参加由PI新开发的关于van der Waals异质结构的选修课，并通过培训招募的学生来进行该项目的前沿研究。该研究的目标包括：(A)通过剥离制造拟议的van der Waals异质结构纳米器件；(B)表征相关的物理性质，包括垂直磁各向异性常数和饱和磁化强度，以及它们的温度和厚度依赖关系，以及磁性质的调节，如磁各向异性和居里温度；(C)在几个原子层厚度和横向尺寸小于100 nm的限制下，通过实验确定临界开关电流密度和自旋轨道扭矩效率；(D)优化范德华异质结构材料、界面和器件几何形状，以最大限度地提高能效。原子薄磁性材料的成功剥离和纳米器件的制作是最新的科学成果，最近还完成了低对称性、原子层状Weyl半金属WTe2中特殊的离面自旋轨道扭矩的演示。整合这些新发现的范德华材料以形成独特的基于异质结构的器件是一项大胆的努力，将导致新现象的发现，并促进当前对用于高效率和高密度存储器的磁性器件的材料科学和物理学的理解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This proposed research will explore van der Waals heterostructure-based magnetic devices capable of delivering highly efficient antidamping spin-orbit torque for switching perpendicular magnetization. Reducing energy dissipation for switching magnetic memory devices is increasingly challenging as the memory density scales up, which calls for innovative ways to greatly enhance the energy efficiency. Perpendicular magnetization with strong anisotropy is a requisite for the stability of high-density memory devices. The proposed research deals with a particular type of the van der Waals heterostructures which are composed of an atomically layered magnet with strong perpendicular magnetic anisotropy such as Fe3GeTe2 and another atomically layered Weyl semimetal with strong spin-momentum locking and low crystalline symmetry such as 1T’-WTe2. Unlike spin-orbit torques created by ordinary three-dimensional, high-symmetry materials, the unique antidamping torque generated by 1T’-WTe2 is expected to result in a much lower critical current density for switching the Fe3GeTe2 magnetization in this van der Waals heterostructure. Along with the atomically flat, chemically and magnetically sharp interface, the combination of these two materials provides unparalleled intrinsic and extrinsic properties suitable for future generations of high-density magnetic random access memory devices. The proposed research will provide excellent opportunities to educate graduate students across disciplines at PI’s institution, especially the underrepresented minority students by enrolling them in a newly developed elective course by the PI on van der Waals heterostructures and by training the student recruited for doing the cutting-edge research in this project.The objectives of this proposed research include (a) fabrication of the proposed van der Waals heterostructure nanoscale devices by exfoliation; (b) characterization of relevant physical properties including the perpendicular magnetic anisotropy constant, and saturation magnetization, and their temperature and thickness dependences, and tuning of magnetic properties such as magnetic anisotropy and Curie temperature; (c) experimental determination of critical switching current density and spin-orbit torque efficiency in the limits of few atomic layers in thickness and sub-100 nm in lateral dimensions; (d) optimization of van der Waals heterostructure materials, interfaces, and device geometry to maximize the energy efficiency. Successful exfoliation and nanoscale device fabrication of atomically thin magnetic materials are very recent scientific achievements and demonstration of the special out-of-plane spin-orbit torque in low-symmetry, atomically layered Weyl semimetal WTe2 was also accomplished recently. Integration of these newly discovered van der Waals materials to form unique heterostructures-based devices represents a bold endeavor that will lead to discoveries of new phenomena and advance the current understanding of materials science and physics of magnetic devices for high-efficiency and high-density memory.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.