arXiv subjects

Sheng Qiu

Publications and source records attributed to Sheng Qiu.

9 recordsLinked to original sources

arXiv2026

Ferrimagnetic Skyrmions in a Tetragonal Mn1.9Co0.1Sb Single Crystal at Room Temperature

The development of room temperature small-sized ferrimagnetic skyrmion materials is significant for topological spintronic device applications. As a room temperature ferrimagnetic material, the tetragonal Mn1.9Co0.1Sb crystal exhibits multiple phase transitions, including spin reorientation transitions. However, the magnetic spin textures and their evolution mechanisms during magnetic phase transitions in Mn1.9Co0.1Sb crystals remain unexplored. Using Lorentz transmission electron microscopy, we discovered and verified dipolar skyrmion behavior and its magnetic evolution at room temperature. We established a stable phase diagram of magnetic textures as functions of temperature and magnetic field, while also investigating the evolution mechanisms of spin textures across multiple temperature-induced magnetic phase transitions. Through micromagnetic simulations, a ferrimagnetic configuration with in-plane ferromagnetic coupling and interlayer antiferromagnetic arrangement was established, which stands in contrast to synthetic ferrimagnetic/antiferromagnetic systems that exhibit interlayer antiferromagnetic coupling via the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. We determined that the intrinsic frequency of ferrimagnetic skyrmions can reach the THz regime due to strong interlayer antiparallel exchange interactions. These findings highlight the diversity of room temperature ferrimagnetic skyrmion regulation behaviors in Mn1.9Co0.1Sb and their dynamic evolution characteristics, opening new avenues for developing novel spintronic devices with enhanced functionalities capable of operating under ambient conditions.

cond-mat.mtrl-sci↗

arXiv2026

Enhanced Curie temperature and room-temperature 50-nm skyrmions achieved in hexagonal ferromagnet Mn5Ge3+x synthesized via a high-pressure method

The development of new high-temperature ultrasmall-size skyrmion materials holds immense significance for the promising applications of topological spintronic devices. In this study, we demonstrate that a high-pressure synthesis technique can significantly elevate the Curie temperature of Mn5Ge3+x crystals, from 294 K to 350 K. This enhancement is attributed to the combined effects of lattice contraction and increased Ge content, the conclusion supported by Density Functional Theory calculations. Additionally, our real-space magnetic imaging reveals the stability of dipolar skyrmions with diameters of approximately 50 nm at room temperature. Our micromagnetic simulations closely replicate the diverse experimental topological magnetic textures observed. Furthermore, magnetotransport measurements indicate the potential for the electrical distinction between various topological magnetic textures in skyrmion-based devices. We also report deterministic manipulations on single dipolar skyrmions in confined nanostructures by using in-plane currents. The observation, electrical manipulation, and electrical detection of room-temperature ultrasmall topological magnetic textures underscore the potential of Mn5Ge3+x as a promising platform for spintronic device applications.

cond-mat.mtrl-sci↗

arXiv2025

Deterministic Electrical Control of Single Magnetic Bubbles in Nanostructured Cells

Localized particle-like spin textures have been found to exhibit emergent electromagnetic properties, which hold promise for the development of intriguing spintronic devices. Among these textures, magnetic bubbles represent localized spin configurations that could serve as data bits. However, the precise methods for their electrical manipulation remain uncertain. Here, we demonstrate the deterministic electrical manipulations and detections of single magnetic bubbles in kagome-latticed Fe3Sn2 magnetic nanostructured cells. The current-induced dynamics of magnetic bubbles were explored using nanosecond pulsed currents. We show single pulsed currents with low and high densities can be applied for the creation and deletion of a single bubble, respectively. The mutual writing-deleting operations on single bubbles are attributed to the thermal heating and non-thermal spin-transfer torque effects in combination with micromagnetic simulations. We also realized the in-situ detection of a single bubble using the anisotropic magnetoresistance effect through a standard four-probe method. Our results could propel the development of bubble-based spintronic devices.

cond-mat.mes-hall↗

arXiv2025

Fresnel Magnetic Imaging of Ultrasmall Skyrmion Lattices

Magnetic skyrmions with ultrasmall nanometric dimensions hold significant promise for next-generation high-density spintronic devices. Direct real-space imaging of these topological spin textures is critical for elucidating their emergent properties at the nanoscale. Here, we present Lorentz transmission electron microscopy studies of nanometric skyrmion lattices in B20-structured Mn0.5Fe0.5Ge crystals using Fresnel mode. According to conventional chiral discrimination methods relying on static bright-dark contrast, we demonstrate an abnormal periodic chiral-reversal phenomenon retrieved through the transport of intensity equation analysis of defocus-dependent Fresnel images. Through systematic off-axis electron holography experiments and numerical simulations, we attribute these chiral misinterpretations to the sinusoidal modulation mechanism of the contrast transfer functionthat correlates with both defocus values and skyrmion dimensions. Our findings establish quantitative limitations of conventional Fresnel contrast analysis for ultrasmall skyrmions while revealing fundamental insights into defocus-mediated phase-to-intensity conversion processes in nanoscale magnetic imaging.

cond-mat.mtrl-sci↗

arXiv2025

Scavenger: Better Space-Time Trade-Offs for Key-Value Separated LSM-trees

Key-Value Stores (KVS) implemented with log-structured merge-tree (LSM-tree) have gained widespread acceptance in storage systems. Nonetheless, a significant challenge arises in the form of high write amplification due to the compaction process. While KV-separated LSM-trees successfully tackle this issue, they also bring about substantial space amplification problems, a concern that cannot be overlooked in cost-sensitive scenarios. Garbage collection (GC) holds significant promise for space amplification reduction, yet existing GC strategies often fall short in optimization performance, lacking thorough consideration of workload characteristics. Additionally, current KV-separated LSM-trees also ignore the adverse effect of the space amplification in the index LSM-tree. In this paper, we systematically analyze the sources of space amplification of KV-separated LSM-trees and introduce Scavenger, which achieves a better trade-off between performance and space amplification. Scavenger initially proposes an I/O-efficient garbage collection scheme to reduce I/O overhead and incorporates a space-aware compaction strategy based on compensated size to minimize the space amplification of index LSM-trees. Extensive experiments show that Scavenger significantly improves write performance and achieves lower space amplification than other KV-separated LSM-trees (including BlobDB, Titan, and TerarkDB).

cs.DB↗

arXiv2025

Scavenger+: Revisiting Space-Time Tradeoffs in Key-Value Separated LSM-trees

Key-Value Stores (KVS) based on log-structured merge-trees (LSM-trees) are widely used in storage systems but face significant challenges, such as high write amplification caused by compaction. KV-separated LSM-trees address write amplification but introduce significant space amplification, a critical concern in cost-sensitive scenarios. Garbage collection (GC) can reduce space amplification, but existing strategies are often inefficient and fail to account for workload characteristics. Moreover, current key-value (KV) separated LSM-trees overlook the space amplification caused by the index LSM-tree. In this paper, we systematically analyze the sources of space amplification in KV-separated LSM-trees and propose Scavenger+, which achieves a better performance-space trade-off. Scavenger+ introduces (1) an I/O-efficient garbage collection scheme to reduce I/O overhead, (2) a space-aware compaction strategy based on compensated size to mitigate index-induced space amplification, and (3) a dynamic GC scheduler that adapts to system load to make better use of CPU and storage resources. Extensive experiments demonstrate that Scavenger+ significantly improves write performance and reduces space amplification compared to state-of-the-art KV-separated LSM-trees, including BlobDB, Titan, and TerarkDB.

cs.DB↗

arXiv2025

Observation of Anomalous Hall Effect in Bulk Single Crystals of n-type Cr-doped Sb$_{2}$Te$_{3}$ Magnetic Topological Insulator

The exploration of topological Dirac surface states is significant in the realms of condensed matter physics and future technological innovations. Among the materials garnering attention is Sb$_{2}$Te$_{3}$, a compound that theoretically exhibits topological insulating properties. However, its inherent p-type nature prevents the direct experimental verification of its Dirac surface state due to the Fermi level alignment with the valence band. In this study, by doping Cr atoms into Sb$_{2}$Te$_{3}$, n-type behavior is observed in the Hall resistance measurements. Remarkably, the Cr-doped Sb$_{2}$Te$_{3}$ not only shows ferromagnetism with a high transition temperature of approximately 170 K but also exhibits an anomalous Hall effect (AHE). The Cr doping also allows for a controlled method for Fermi level tuning into the band gap. These properties spotlight its potential as an n-type magnetic topological insulator (MTI) as well as a material candidate for the quantum anomalous Hall effect (QAHE), opening new avenues for applications in spintronics and quantum devices.

cond-mat.mtrl-sci↗

arXiv2025

SmokeSVD: Smoke Reconstruction from A Single View via Progressive Novel View Synthesis and Refinement with Diffusion Models

Reconstructing dynamic fluids from sparse views is a long-standing and challenging problem, due to the severe lack of 3D information from insufficient view coverage. While several pioneering approaches have attempted to address this issue using differentiable rendering or novel view synthesis, they are often limited by time-consuming optimization under ill-posed conditions. We propose SmokeSVD, an efficient and effective framework to progressively reconstruct dynamic smoke from a single video by integrating the generative capabilities of diffusion models with physically guided consistency optimization. Specifically, we first propose a physically guided side-view synthesizer based on diffusion models, which explicitly incorporates velocity field constraints to generate spatio-temporally consistent side-view images frame by frame, significantly alleviating the ill-posedness of single-view reconstruction. Subsequently, we iteratively refine novel-view images and reconstruct 3D density fields through a progressive multi-stage process that renders and enhances images from increasing viewing angles, generating high-quality multi-view sequences. Finally, we estimate fine-grained density and velocity fields via differentiable advection by leveraging the Navier-Stokes equations. Our approach supports re-simulation and downstream applications while achieving superior reconstruction quality and computational efficiency compared to state-of-the-art methods.

cs.GR↗

arXiv2025

Stable Neel-Twisted Skyrmion Bags in a van der Waals Magnet Fe3-xGaTe2 at Room Temperature

Magnetic skyrmion bags with diverse topological charges Q, offer prospects for future spintronic devices based on freedom of Q. While their emergence in van der Waals magnets holds the potential in developing Q-based 2D topological spintronics. However, previous room-temperature skyrmion bags necessitate special anisotropy engineering through disorder Fe intercalation, and the stable phase diagram for skyrmion bags across room temperature regions is lacking. Here, we demonstrate the observation and electrical manipulation of room temperature skyrmion bags in Fe3-xGaTe2 without specially designed Fe intercalation. Combining the pulsed currents with the assistance of magnetic fields, skyrmion bags with various topological charges are generated and annihilated. Especially double nested skyrmion bags are also discovered at room temperature. The stable temperature-field diagram of skyrmion bags has been established. We also demonstrate the electrical-controlled topological phase transformations of skyrmion bags. Our results will provide novel insights for the design of 2D skyrmion-based high-performance devices.

cond-mat.mtrl-sci↗