Repository Collection: null

The anatomy of magnetic field pulse induced transverse domain wall dynamics

2026-07-07T01:10:13Z

Title: The anatomy of magnetic field pulse induced transverse domain wall dynamics Author(s): Cho, Jaehun; Yun, Won Seok; Kim, June-Seo Abstract: The microscopic anatomy of the precessional torque-induced magnetic domain wall racetrack memory is numerically investigated. A systematic analysis is performed to explain the efficiency and limitations of this domain wall motion architecture. A transverse domain wall in an in-plane magnetic nanowire is chosen, and the direction of the applied magnetic field is applied to be perpendicular to the film plane. The domain wall displacement upon the application of an out-of-plane magnetic field pulses is shown to be driven by the precessional torque and subsequently decelerated by the damping torque, causing the domain wall to settle at a specific position. Crucially, a characteristic frequency is exhibited by this domain wall dynamics. After removing the magnetic field, a reverse domain wall dynamics is observed with the same frequency, causing the domain wall to revert to its original position. To realize continuous domain wall motion, a notch structure is introduced, and the depinning field is calculated as a function of the out-of-plane field strength. The analysis reveals that the depinning field decreases linearly as the out-of-plane field strength increases. Finally, the principle of domain wall hopping in a multiple-notched nanowire is verified by the application of sequential out-of-plane field pulses. © The Author(s) 2026.

Polarity-Programmable Bismuth Oxide Overlayers on Bi(111)/MoS2 Heterostructures via Oxidation and Annealing

2026-07-06T07:40:13Z

Title: Polarity-Programmable Bismuth Oxide Overlayers on Bi(111)/MoS2 Heterostructures via Oxidation and Annealing Author(s): Han, Sang Wook; Yun, Won Seok; Seong, Seungho; Kang, Jeongsoo; Ko, Minji; Ryu, Sunmin; Kim, Yong Soo Abstract: Band-structure engineering in bismuth (Bi) oxides is frequently hampered by their amorphous or poorly ordered nature, which obscures the relationship among stoichiometry, band dispersion, and transport polarity. We find that native BiOx overlayers on epitaxial Bi(111)/MoS2 undergo a reversible n → p → n polarity control of the heterostructure system under controlled air exposure and annealing. As-grown BiOx-rich surfaces are n-type and exhibit a photoluminescence peak at ∼2.1–2.2 eV. Mild air annealing (100 °C, 1 h) of native BiOx overlayers on epitaxial Bi(111)/MoS2 yields a p-type surface with a phase-mixed Bi2O3 (α+β) overlayer, characterized by a highly dispersive Bi–O valence band, and in-situ annealing at 300 °C reduces the thickness of the oxide layer and restores the n-type band alignment governed by the Bi(111)/MoS2 stack. First-principles calculations for hexagonal Bi2O3 monolayers and Bi2O3/Bi(111) heterostructures reveal a transition from a wide-gap, O-2p-dominated oxide to a narrow, Bi-dominated direct gap at Γ, which supports the observed p → n band structure evolution. These findings provide a fundamental mechanism for tuning the polarity and band alignment of Bi-oxide-based interfaces on 2D semiconductors. © 2026 American Chemical Society

Quantized Conductance through Surface States in High Quality Three-Dimensional Dirac Semimetal Cd3As2 Nanowire/Nanoribbon p-n Junctions

2026-06-19T00:10:14Z

Title: Quantized Conductance through Surface States in High Quality Three-Dimensional Dirac Semimetal Cd3As2 Nanowire/Nanoribbon p-n Junctions Author(s): An, Sungjin; Siu, Zhuo Bin; Kaladzhyan, Vardan; Bardarson, Jens H.; Lee, Sunghun; Lee, Myoung-Jae; Park, Kidong; Park, Jeunghee; Jalil, Mansoor B. A.; Seo, Jungpil; Jung, Minkyung Abstract: We report the observation of quantized conductance in high-mobility three-dimensional Dirac semimetal Cd3As2 nanowire and nanoribbon p-n junctions. By employing suspended device geometries with dual local gates, we form tunable p-n junctions and realize ballistic transport across sub-micron channel lengths. In a wide nanoribbon device with a channel width of similar to 330 nm, conductance plateaus appear at integer multiples of 2e(2)/h in the n-n regime under high magnetic fields. Numerical simulations suggest that these features represent unresolved spin split subbands due to the smaller subband spacing in wider channels and support the interpretation that the observed quantization may originate from surface-state-dominated conduction. In contrast, narrower nanoribbons and nanowires exhibit conductance steps of 1e(2)/h, demonstrating spin-resolved subbands likely due to enhanced confinement effects. From spin-resolved subband spectroscopy, we extract an effective Land & eacute; g-factor of similar to 43 for the first subband in the bulk gap, establishing these nanostructures as a prospective platform for fault-tolerant quantum electronics.

Relationship between Nd-rich phase and oxygen content for additive-free sintering with regenerated powder from magnet sludge waste

2026-04-15T08:10:41Z

Title: Relationship between Nd-rich phase and oxygen content for additive-free sintering with regenerated powder from magnet sludge waste Author(s): Galkin, Vitalii; Kim, Jeongmin; Roh, Jong Wook; Kim, Dongsoo Abstract: Recycling of Nd-Fe-B magnet sludge into high-performance powders is critical for sustainable rare-earth resource utilization. In this study, Nd-Fe-B powders were regenerated via a reduction-diffusion process and subjected to different washing treatments to investigate their effects on microstructure, phase composition, and magnetic properties. Conventional water washing at larger scales resulted in increased oxidation, depletion of Nd-rich phase, while requiring prolonged washing cycles and excessive water consumption. In contrast, scale up washing with an NH4NO3 solution in methanol effectively minimized oxidation, preserved Nd-rich, and maintained a uniform 1–2μm particle size distribution. The resulting powders exhibited superior magnetic properties, including high coercivity, enhanced squareness, and an improved maximum energy product. The NH4NO3 in MeOH washing method also demonstrated higher yield, improved processing efficiency, and scalability, highlighting its potential as a practical approach for sustainable production of regenerated Nd-Fe-B powders. These findings provide a promising pathway for recycling magnet sludge into high-quality powders suitable for sintered magnet fabrication, contributing to resource conservation and the advancement of rare-earth recycling technologies.