[Paper Review] Giant Damping-like Spin-Torque Conductivity in a GeTe/Py van der Waals Heterostructure

Himanshu Bangar, Pratik Sahu+8 more|arXiv (Cornell University)|Jan 18, 2026

2D Materials and Applications0 citations

TL;DR

The paper reports a giant damping-like spin-torque conductivity at a GeTe/Py van der Waals interface, driven by cooperative spin and orbital Hall/ Rashba effects with interfacial charge transfer, achieving record-like values comparable to heavy metals.

ABSTRACT

Recent observations of large unconventional spin-orbit torques in van der Waals (vdW) materials are driving intense interest for energy-efficient spintronic applications. A key limitation of ferromagnet (FM)/vdW heterostructures is their lower value of damping-like torque conductivity ($σ{ m_{DL}^{y}}$) compared to the conventional heavy metal-based systems, limiting their prospects for commercial spintronic devices. Here, we report both a giant $σ{ m_{DL}^{y}}$ of $-(1.25 \pm 0.11) imes 10^{5}~\hbar/ 2e~Ω^{-1}$m$^{-1}$ and an unconventional spin-orbit torque in a heterostructure comprising an FM (Ni$_{80}$Fe$_{20}$) and the vdW material GeTe. The value of $σ{ m_{DL}^{y}}$ represents the highest reported torque conductivity for any FM/vdW interface and is comparable to benchmark heavy metal heterostructures. First-principles calculations reveal that this substantial torque originates from the cooperative interplay of the spin Hall effect, orbital Hall effect, and orbital Rashba effect, assisted by interfacial charge transfer. These findings demonstrate the potential of carefully engineered vdW heterostructures to achieve highly efficient electrical manipulation of magnetization at room temperature, paving the way for next-generation low-power spintronic devices.

Motivation & Objective

• Motivate energy-efficient spintronic devices by enhancing damping-like torque in FM/vdW interfaces.
• Demonstrate a record-high damping-like torque conductivity at GeTe/Py interfaces.
• Understand the microscopic mechanisms enabling large SOT via spin, orbital, and interfacial effects.

Proposed method

• Grow polycrystalline α-GeTe thin films on Si(111) by pulsed laser deposition and cap with Al to prevent oxidation.
• Fabricate GeTe(15 nm)/Py(8 nm) bilayer devices and measure spin-torque ferromagnetic resonance (STFMR).
• Decompose STFMR signals into symmetric and antisymmetric components to extract in-plane and out-of-plane torques.
• Quantify torque conductivities using established relations between torque, RF current, and device geometry.
• Perform first-principles calculations (DFT-based tight-binding with Wannierization) to compute spin and orbital Hall conductivities and assess charge transfer effects.

Figure 1: Crystal structure and characterization of GeTe thin films. (a) Crystal structure of $\alpha$ -GeTe (rhombohedral structure, $R3m$ ). The lower panel illustrates the GeTe structure viewed along the $c-$ axis, where the Ge and Te atoms are bonded by three shorter (2.83 Å ) and three longer (

Experimental results

Research questions

• RQ1 What is the damping-like spin-torque conductivity at GeTe/Py interfaces and how does it compare to benchmark HM systems and other vdW heterostructures?
• RQ2 What are the microscopic mechanisms (SHE, OHE, ORE, interfacial Rashba) contributing to SOT in GeTe/Py?
• RQ3 How does interfacial charge transfer modify the electronic structure and spin/orbital transport properties?
• RQ4 Can GeTe/Py achieve large out-of-plane or unconventional torques suitable for perpendicular magnetization switching?

Key findings

• Giant damping-like torque conductivity σ_DL^y = -(1.25 ± 0.11) × 10^5 ħ/2e Ω^-1 m^-1, the highest reported for any FM/vdW interface.
• σ_DL^y in GeTe/Py is comparable to benchmark heavy-metal heterostructures and significantly higher than other vdW materials studied.
• First-principles calculations show the large damping-like torque arises from cooperative interplay of spin Hall, orbital Hall, and orbital Rashba effects, aided by interfacial charge transfer.
• Observed unconventional damping-like torque σ_DL^z supports the presence of orbital-related contributions.
• Comparison with Py alone confirms GeTe as the source of the large torque.
• Table 1 quantifies independent OHC/SHC components and their contributions to the total torque at the deffined Fermi level, illustrating dominant orbital contributions.

Figure 2: Spin-torque ferromagnetic resonance measurements in GeTe/Py heterostructures. (a) The schematic of the device consisting of a GeTe/Py bilayer, the setup for STFMR measurements, and a scanning electron microscopy image of the microstrip device with a co-planar waveguide. The top panel shows