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

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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.