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Photocontrol of magnetic structure in an itinerant magnet
摘要： We study the photoinduced magnetic transition in an itinerant magnet described by the double-exchange model, in which conduction electrons couple with localized spins through the ferromagnetic (FM) Hund coupling. It is shown that intense light applied to the FM ground state induces an antiferromagnetic (AFM) order, in contrast to the AFM-to-FM transition due to the photocarrier injection. In particular, we focus on the mechanism for instability of the FM structure by the light irradiation. The magnon spectrum in the Floquet state is formulated on the basis of the perturbative expansion of the Floquet Green’s function. The magnon dispersion shows softening at momentum (π, π ) in the square lattice with increasing the light amplitude, implying photoinduced AFM instability. This result is mainly attributed to a nonequilibrium electron distribution, which promotes low-energy Stoner excitations. The transient optical conductivity spectra characterized by interband excitations and Floquet sidepeaks are available to identify the photoinduced AFM state.
关键词： photoinduced magnetic transition,magnon spectrum,double-exchange model,itinerant magnet,optical conductivity,Floquet state
更新于2025-09-04 15:30:14
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摘要： The spin-orbit coupling (SOC) interactions, electron-correlation effects, and Hund coupling cooperate and compete with each other, leading to novel properties, quantum phase, and nontrivial topological electronic behavior in iridium oxides. Because of the well-separated IrO6 octahedra approaching cubic crystal-field limit, the hexagonal iridates Sr3MIrO6 (M = Sr, Na, and Li) serve as canonical model systems to investigate the underlying physical properties that arise from the novel jeff state. Based on density-functional theory calculations complemented by Green’s function methods, we systematically explore the critical role of SOC on the electronic structure and magnetic properties of Sr3MIrO6. The crystal-field splitting combined with correlation effects are insufficient to account for the insulating nature, but the SOC interaction is the intrinsic source to trigger the insulating ground states in these hexagonal iridates. The decreasing geometry connectivity of IrO6 octahedra gives rise to the increase of effective electronic correlations and SOC interactions, tuning the hexagonal iridates from low-spin jeff = 1/2 states with large local magnetic moments for the Ir4+ (5d 5) ions in Sr4IrO6 to nonmagnetic singlet Jeff = 0 states without magnetic moments for the Ir5+ (5d 4) ions in Sr3NaIrO6 and Sr3LiIrO6. The theoretical calculated results are in good agreement with available experimental data, and explain the magnetic properties of Sr3MIrO6 well.
关键词： electronic structure,insulating state,magnetic properties,iridates,spin-orbit coupling
更新于2025-09-04 15:30:14
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[IEEE 2018 14th International Conference on Power Electronics (CIEP) - Cholula, Puebla, Mexico (2018.10.24-2018.10.26)] 2018 14th International Conference on Power Electronics (CIEP) - DC-AC-AC Converter for PV Plant in Medium Voltage Grid-Connected Systems
摘要： Large-scale PV plants (hundreds of MW) are a reality and are being used to generate high-power levels in medium-voltage (MV) utilities. To achieve this goal, some new power electronics systems based on medium-frequency AC-links (MFAC) and multilevel output configurations have been proposed to interfacing with the MV utility. Most of these systems rectify the MFAC voltage, generating a DC bus and then invert the DC voltage to generate a line frequency AC voltage. This paper presents a three-phase cascaded multilevel converter topology with reduced-energy conversion stage and multiples AC medium-frequency (MF) links. The proposed converter is composed by modules connected in cascaded. Each module has three conversion stages: input converter (DC-AC), isolation stage (medium-frequency transformer) and output converter (AC-AC). In order to validate the proposed topology simulations of a 100 kW system are performed, taking into account balanced and unbalanced DC source cases. The proposed system is validated through a 1.5 kW single-phase five-level laboratory prototype.
关键词： AC-links,medium-frequency magnetic link,photovoltaic power systems
更新于2025-09-04 15:30:14
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[IEEE 2018 19th International Conference of Young Specialists on Micro/Nanotechnologies and Electron Devices (EDM) - Erlagol (Altai Republic), Russia (2018.6.29-2018.7.3)] 2018 19th International Conference of Young Specialists on Micro/Nanotechnologies and Electron Devices (EDM) - Multifunctional Magnetophotonic Structure Creation Based on Magnetic Properties of Micro and Nanoscale Clusters
摘要： The optical and magnetic properties, phenomena and effects of nano- and microparticles of clusters and other formations can potentially influence the propagation and processing of optical signals in magnetophotonic structures. The analysis of existing devices and the ones proposed for interpretation of their implementation allows the correct operation algorithm in correlation to structural characteristics and to multi-functional magnetophotonic structures of micro- and nanoscale. The magnetophotonic structure models are considered and analyzed, which makes it possible to find the correct approaches for their implementation. The choice of the specific magnetophotonic medium for a functional simulator is determined by the requirements of functional orientation, simplicity and efficiency, manufacturability and other factors.
关键词： nanoclusters,magnetic phase transitions,superparamagnetism,Photonics,resonance
更新于2025-09-04 15:30:14
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Perfluorocarbon‐Based <sup>19</sup> F?MRI Nanoprobes for In?Vivo Multicolor Imaging
摘要： In vivo multicolor imaging is important for monitoring multiple biomolecular or cellular processes in biology. 19F magnetic resonance imaging (MRI) is an emerging in vivo imaging technique because it can non-invasively visualize 19F nuclei without endogenous background signals. Therefore, 19F MRI probes capable of multicolor imaging are in high demand. Herein, we report five types of perfluorocarbon-encapsulated silica nanoparticles that show 19F NMR peaks with different chemical shifts. Three of the nanoprobes, which show spectrally distinct 19F NMR peaks with sufficient sensitivity, were selected for in vivo multicolor 19F MRI. The nanoprobes exhibited 19F MRI signals with three colors in a living mouse. Our in vivo multicolor system could be utilized for evaluating the effect of surface functional groups on the hepatic uptake in a mouse. This novel multicolor imaging technology will be a practical tool for elucidating in vivo biomolecular networks by 19F MRI.
关键词： multicolor imaging,fluorine,magnetic resonance imaging,nanoparticles,imaging agents
更新于2025-09-04 15:30:14
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Diffusion-weighted imaging and diffusion tensor imaging as adjuncts to?conventional MRI for the diagnosis and management of peripheral nerve sheath tumors: current perspectives and future directions
摘要： Peripheral nerve sheath tumors (PNSTs) account for ~ 5% of soft tissue neoplasms and are responsible for a wide spectrum of morbidities ranging from localized neuropathy to fulminant metastatic spread and death. MR imaging represents the gold standard for identification of these neoplasms, however, current anatomic MR imaging markers do not reliably detect or differentiate benign and malignant lesions, and therefore, biopsy or excision is required for definitive diagnosis. Diffusion-weighted MR imaging (DWI) serves as a useful tool in the evaluation and management of PNSTs by providing functional information regarding the degree of diffusion, while diffusion tensor imaging (DTI) aids in determining the directional information of predominant diffusion and has been shown to be particularly useful for pre-operative planning of these tumors by delineating healthy and pathologic fascicles. The article focuses on these important neurogenic lesions, highlighting the current utility of diffusion MR imaging and future directions including computerized radiomic analysis.
关键词： Diffusion tensor imaging,Nerve sheath neoplasms,Diagnostic techniques, neurological,Diffusion magnetic resonance imaging,Peripheral nerves
更新于2025-09-04 15:30:14
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Electric field-induced creation and directional motion of domain walls and skyrmion bubbles
摘要： Magnetization dynamics driven by an electric field could provide long-term benefits to information technologies because of its ultralow power consumption. Meanwhile, the Dzyaloshinskii-Moriya interaction in interfacially asymmetric multilayers consisting of ferromagnetic and heavy-metal layers can stabilize topological spin textures, such as chiral domain walls, skyrmions, and skyrmion bubbles. These topological spin textures can be controlled by an electric field, and hold promise for building advanced spintronic devices. Here, we present an experimental and numerical study on the electric field-induced creation and directional motion of topological spin textures in magnetic multilayer films and racetracks with thickness gradient and interfacial Dzyaloshinskii-Moriya interaction at room temperature. We find that the electric field-induced directional motion of chiral domain wall is accompanied with the creation of skyrmion bubbles at certain conditions. We also demonstrate that the electric field variation can induce motion of skyrmion bubbles. Our findings may provide opportunities for developing skyrmion-based devices with ultralow power consumption.
关键词： perpendicular magnetic anisotropy,micromagnetics,skyrmion bubbles,spintronics,electric field effects,Skyrmions
更新于2025-09-04 15:30:14
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Hilbert Curve-Based Metasurface to Enhance Sensitivity of Radio Frequency Coils for 7-T MRI
摘要： In this paper, we propose a compact, lightweight, and easy-to-fabricate Hilbert curve-based metasurface resonator that can effectively increase the sensitivity (radio frequency (RF) field intensity) and penetration depth of an RF coil for 7-T magnetic resonance imaging scanner. A circuit model is proposed to accurately calculate the resonance frequency of Hilbert curve resonators of different orders. A single element of a transverse electromagnetic (EM) coil was used for this paper. The increase in the field sensitivity introduced by the proposed metasurface to an RF coil was successfully demonstrated through simulations and experiments. The EM field produced by the RF coil is redistributed due to the presence of the proposed metasurface. The key feature of the proposed structure is its significant increase in the penetration depth of magnetic fields into the imaging volume. An enhancement of the magnetic field by more than four times was observed at 13.5 cm away from the coil experimentally. Flexibility for matching the coil integrated with the proposed surface is shown.
关键词： metasurface,magnetic resonance imaging (MRI),radio frequency (RF) coil,Hilbert curve
更新于2025-09-04 15:30:14
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Electrolyte-based ionic control of functional oxides
摘要： The use of electrolyte gating to electrically control electronic, magnetic and optical properties of materials has seen strong recent growth, driven by the potential of the many devices and applications that such control may enable. Contrary to initial expectations of a purely electrostatic response based on electron or hole doping, electrochemical mechanisms based on the motion of ions are now understood to be common, suggesting promising new electrical control concepts.
关键词： optical properties,electrochemical mechanisms,electrostatic response,electronic properties,electrolyte gating,magnetic properties
更新于2025-09-04 15:30:14
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Magnetic Properties of Pure and Doped Gallium Nitride Nanocrystals
摘要： In the present paper, Ga1?xCoxN, Ga1?xNixN and Ga1?xTbxN (0 ≤ x ≤ 0.1) nanocrystals have been synthesized by a facile solvothermal method. Crystallographic characterization of synthesized materials has been done using powder X-ray diffraction technique. Recorded diffraction patterns reveal the formation of wurtzite (hexagonal) structured GaN nanocrystals. Electron microscopic studies have been carried for the detailed topographical and morphological analyses of synthesized nanomaterials. Recorded electron micrographs indicate the formation of nearly mono-disperse nanoparticles, having average size ～4 nm. Magnetic measurements of doped nanocrystals revealed ferromagnetic behavior at room temperature however pure GaN is diamagnetic at room temperature.
关键词： Crystallography,Doping,Gallium Nitride Nanocrystals,Magnetic Properties
更新于2025-09-04 15:30:14