Dissertation Title: Field-free Room Temperature van der Waals Spintronics
Abstract:
The sustained growth of computation is colliding with energy limits, motivating device primitives that reduce data movement and enable low-energy, non-volatile operation. Spintronics pursues this goal by storing information in magnetic order and switching it electrically through current-induced torques. Spin–orbit torque (SOT) is a leading mechanism for fast control of perpendicular magnets; however, conventional SOT stacks built from sputtered heavy-metal/ferromagnet multilayers face materials and symmetry constraints: interfacial roughness and interdiffusion can reduce interfacial spin transparency, and limited crystalline-symmetry control often necessitates an external in-plane bias field for deterministic switching. Metallic van der Waals (vdW) ferromagnets and vdW spin-source layers expand this design space by enabling atomically sharp interfaces and symmetry-selectable heterostructures assembled by stacking.
This thesis addresses a central bottleneck in adapting vdW spintronics for practical technologies: reproducible, efficient electrical switching of metallic vdW ferromagnets at and above room temperature without applied magnetic fields. First, a glovebox-centered “materials-to-measurement” workflow is developed for air-sensitive vdW magnets, spanning deterministic transfer and encapsulation, microfabrication of Hall-bar devices, and quantitative magneto-transport and polar magneto-optical Kerr probes. Second, Fe₃GaTe₂/Pt bilayers are established as benchmark vdW SOT devices: second-harmonic Hall metrology yields effective damping-like torque efficiencies 𝜉DL = 0.093–0.098, and current-pulsed experiments demonstrate non-volatile, deterministic switching up to 320 K under a modest in-plane assist field, with a lowest threshold current density Jsw = 1.69×10⁷ A/cm² at 300 K. Third, deterministic field-free switching is realized in an all-vdW Fe₃GaTe₂/WTe₂ heterostructure by leveraging low crystal symmetry and crystallographic-axis engineering. Polarized Raman spectroscopy registers the WTe₂ axes, and directional current injection along the low-symmetry axis enables an out-of-plane anti-damping torque that drives fully deterministic switching at zero applied field up to 325 K, with Jsw ≈ 2.23×10⁷ A/cm² at 300 K.
Together, these results establish a quantitative experimental foundation and a symmetry-based design principle for room-temperature, field-free vdW SOT devices, and they define the materials, scaling, and integration challenges for translating vdW spintronics toward practical memory and logic technologies.
Committee members:
Deblina Sarkar (Advisor)
Assistant Professor
Media Arts and Science
Massachusetts Institute of Technology
Caroline A. Ross
Ford Professor of Materials Science & Engineering
Department of Materials Science and Engineering
Massachusetts Institute of Technology
Mingda Li
Associate Professor
Department of Nuclear Science and Engineering
Massachusetts Institute of Technology