arXiv subjects

Ao Du

Publications and source records attributed to Ao Du.

8 recordsLinked to original sources

arXiv2026

High-mobility inertial domain walls driven by spin-transfer torque in a ferrimagnetic spinel oxide

Efficient electrical manipulation of domain walls is key to developing magnetic devices with fast switching capabilities and low energy consumption. Here we demonstrate Bloch-type domain wall velocities exceeding 1 km s$^{-1}$ in the single-layer ferrimagnetic spinel oxide NiCo$_2$O$_4$ induced by spin-transfer torque at a current density of $2 \times 10^{11}$ A m$^{-2}$. This exceptional domain wall mobility is attributed to the combination of giant nonadiabatic spin-transfer torque, low magnetization, and high spin polarization. Additionally, we report a pronounced domain wall inertia effect in this ferrimagnet due to the large nonadiabaticity of the torque. The characteristic time for domain wall acceleration and deceleration is $\sim 1$ ns, shorter than that reported for typical ferromagnets. Our findings highlight the potential of spinel oxides as a promising platform for engineering high-performance domain wall devices that take advantage of ultrafast ferrimagnetic dynamics.

cond-mat.mes-hall↗

arXiv2025

Itinerant Orbital Hall Effect Mechanism Leading to Large Negative Orbital Torques from Light Metal Vanadium

The orbital Hall effect (OHE) has attracted significant attention for developing energy-efficient electronic devices. However, utilizing it in fast, low-power devices requires an enhanced understanding of underlying extrinsic and intrinsic contributions to OHE at timescales ranging from quasi-static to picoseconds. Here, we investigate OHE in light metal vanadium (V) using a combination of selected measurement schemes, spanning the full frequency range. We observe a negative damping-like torque efficiency from V, opposite to conventional theoretical predictions, with a magnitude that depends on the adjacent ferromagnet, a dependence that indicates orbital effects. These results, with consistent torque efficiencies across all frequencies, corroborate a negative and intrinsic OHE in V with a large effective orbital Hall conductivity of $-(1.44 \pm 0.34)\,\frac{\hbar}{2e}\,\times 10^{5}\,\Omega^{-1}\,\mathrm{m}^{-1}$ and a long orbital diffusion length of $(15.0 \pm 2.5)\,\mathrm{nm}$. To explain the observed OHE, we develop a theoretical model incorporating both local and itinerant circulation contributions to OHE. The model agrees excellently with the experimental results, demonstrating that itinerant contributions are essential for a complete physical understanding of intrinsic OHE. Our consistent experimental and theoretical data highlight the importance of itinerant contributions governing the fundamental understanding of intrinsic OHE and the large effects found open pathways for energy-efficient orbitronic devices.

cond-mat.mes-hall↗

arXiv2025

Covalently Integrated CNT@rGO for Superior Conductivity and Cycling Stability in Lithium-Ion Batterie

The limitations of conventional conductive agents in lithium-ion batteries, such as carbon black and graphite flakes, have driven the search for high-performance alternatives. Carbon nanotubes (CNTs) and graphene offer exceptional conductivity and lower dosage requirements, but face challenges related to high costs and complex fabrication processes. Here, we report a simple and cost-effective one-step chemical vapor deposition (CVD) method for the ultra-high yield growth (7692.31%) of CNTs on a reduced graphene oxide (rGO) substrate, forming a three-dimensional CNT@rGO composite with covalent integration. When employed as a conductive agent for lithium iron phosphate (LiFePO4) cathodes, the CNT@rGO composites significantly enhance rate performance across 1-6C rates, and demonstrate exceptional cycling stability, achieving 96.32% capacity retention after 300 cycles at 1C. The synergistic structure facilitates multiple conductive pathways, minimizes catalyst residue (0.52%), and ensures uniform dispersion, providing an effective and cost-efficient solution for next-generation battery technology. This study lays the foundation for the large-scale application of high-performance carbon conductive agents in battery technology.

physics.chem-ph↗

arXiv2025

Nonlinearity Modulation of Auto-oscillations in Three-terminal Magnetic Tunnel Junctions

Spin torque nano-oscillators (STNOs) hold encouraging promise for nanoscale microwave generators, modulators, and new types of intelligent computing. The nonlinearity, describing the current-induced tunability of oscillating frequency, is a distinctive feature of STNOs, which plays important roles in efficient manipulation of microwave frequencies, rapid spec-trum analysis, and the design of neuromorphic devices. However, experimental research on its efficient modulation remains limited. Here, we comprehensively studied the impact of several factors on nonlinearity in nanoscale three-terminal MTJ-STNOs, including the external magnetic field, the thickness of CoFeB free layer, and the combination of spin-transfer torque (STT) and spin-orbit torque (SOT). Among these factors, nonlinearity can be significantly tuned by the direction of magnetic field as well as the thickness of CoFeB free layer. Notably, it reaches zero in 1.1 nm CoFeB, where the oscillation frequency is not affected by the drive current. Such property provides a more intrinsic and robust approach to achieve zero nonlinearity in STNOs, which is advantageous for high-quality microwave generators. More importantly, we found that nonlinearity can also be electrically modulated by both STT and SOT currents, and develop a refined model that accounts for the additional contribution of the SOT current to explain the mechanism. This electrical approach is more convenient, energy-efficient, and well-suited for miniaturization. Our findings offer a comprehensive understanding and open up a new dimension for the current tunability of nonlinearity in MTJ-STNOs, benefiting further optimization in nanoscale STNO-based microwave generators and neuromorphic computing devices.

physics.app-ph↗

arXiv2025

QUEST: A Quantized Energy-Aware SNN Training Framework for Multi-State Neuromorphic Devices

Neuromorphic devices, leveraging novel physical phenomena, offer a promising path toward energy-efficient hardware beyond CMOS technology by emulating brain-inspired computation. However, their progress is often limited to proof-of-concept studies due to the lack of flexible spiking neural network (SNN) algorithm frameworks tailored to device-specific characteristics, posing a significant challenge to scalability and practical deployment. To address this, we propose QUEST, a unified co-design framework that directly trains SNN for emerging devices featuring multilevel resistances. With Skyrmionic Magnetic Tunnel Junction (Sk-MTJ) as a case study, experimental results on the CIFAR-10 dataset demonstrate the framework's ability to enable scalable on-device SNN training with minimal energy consumption during both feedforward and backpropagation. By introducing device mapping pattern and activation operation sparsity, QUEST achieves effective trade-offs among high accuracy (89.6%), low bit precision (2-bit), and energy efficiency (93 times improvement over the ANNs). QUEST offers practical design guidelines for both the device and algorithm communities, providing insights to build energy-efficient and large-scale neuromorphic systems.

physics.app-ph↗

arXiv2024

Anatomy of Thermally Interplayed Spin-Orbit Torque Driven Antiferromagnetic Switching

Current-induced antiferromagnetic (AFM) switching remains critical in spintronics, yet the interplay between thermal effects and spin torques still lacks clear clarification. Here we experimentally investigate the thermally interplayed spin-orbit torque induced AFM switching in magnetic tunnel junctions via pulse-width dependent reversal and time-resolved measurements. By introducing the Langevin random field into the AFM precession equation, we establish a novel AFM switching model that anatomically explains the experimental observations. Our findings elucidate the currentinduced AFM switching mechanism and offer significant promise for advancements in spintronics.

cond-mat.mes-hall↗

arXiv2024

NAND-like SOT-MRAM-based Approximate Storage for Error-Tolerant Applications

We demonstrate approximate storage based on NAND-like spin-orbit torque (SOT) MRAM, through "device-modeling-architecture" explorations. We experimentally achieve down to 1E-5 level selectivity. Selectivity and low-power solutions are established by numerical calculation workflow. System-level power consumption is evaluated in the 512 KB last-level cache according to 5 quality levels. Error-tolerant applications, such as image processing, alleviate the demand for selectivity down to the 5E-2 level, leading to 54% ~ 61% energy-saving. Our proposal paves the novel and suitable path for high-density and low-power NAND-like SOT-MRAM.

physics.app-ph↗

arXiv2020

Observation of Magnetic Droplets in Magnetic Tunnel Junctions

Magnetic droplets, a class of highly non-linear magnetodynamical solitons, can be nucleated and stabilized in nanocontact spin-torque nano-oscillators where they greatly increase the microwave output power. Here, we experimentally demonstrate magnetic droplets in magnetic tunnel junctions (MTJs). The droplet nucleation is accompanied by a power increase of over 300 times compared to its ferromagnetic resonance modes. The nucleation and stabilization of droplets are ascribed to the double-CoFeB free layer structure in the all-perpendicular MTJ which provides a low Zhang-Li torque and a high pinning field. Our results enable better electrical sensitivity in the fundamental studies of droplets and show that the droplets can be utilized in MTJ-based applications.

physics.app-ph↗