magnetism

磁性
  • 文章类型: Journal Article
    二维(2D)范德华(vdW)磁性材料的发展为探索新的物理现象和有价值的应用提供了诱人的机会。在这些材料中,Fe3GeTe2(FGT)表现出多种显著的性质,并且已经获得显著的关注。在这里,我们首次在薄FGT薄片上创建了纳米网状结构-蜂窝状的六角形纳米孔阵列-具有之字形孔边缘原子结构,并且没有孔边缘的氧化。结果表明,与没有纳米网的块状薄片相比,两种样品的铁磁性(FM)幅度均显着增加。临界温度退火导致形成锯齿形孔边缘和孔间锯齿形边缘纳米带。我们揭示了这些锯齿形边缘上的Fe悬挂键的非氧化物(O)终止增强了FM行为,而O终止通过边缘O-Fe耦合引入反铁磁行为(AFM)来抑制这种FM。FGT纳米网有望创建强大的FM及其在磁性和自旋电子系统中的有效应用。 .
    The growth of two-dimensional van der Waals magnetic materials presents attractive opportunities for exploring new physical phenomena and valuable applications. Among these materials, Fe3GeTe2(FGT) exhibits a variety of remarkable properties and has garnered significant attention. Herein, we have for the first time created a nanomesh structure-a honeycomb-like array of hexagonal nanopores-with the zigzag pore-edge atomic structure on thin FGT flakes with and without oxidation of the pore edges. It is revealed that the magnitude of ferromagnetism (FM) significantly increases in both samples compared with bulk flakes without nanomeshes. Critical temperature annealing results in the formation of zigzag pore edges and interpore zigzag-edge nanoribbons. We unveil that the non-oxide (O) termination of the Fe dangling bonds on these zigzag edges enhances FM behavior, while O-termination suppresses this FM by introducing antiferromagnetic behavior through edge O-Fe coupling. FGT nanomeshes hold promise for the creation of strong FM and their effective application in magnetic and spintronic systems.
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  • 文章类型: Journal Article
    我们研究了磁化对具有向列超导性的$\\text{Bi}_2\\text{Se}_3$族掺杂拓扑绝缘体性质的影响。我们发现,平面内磁化的方向固定了系统中线虫的方向。对于较大的平面外磁化值,手性态比向列态更有利。总的来说,向列型超导的临界温度对磁化具有鲁棒性。我们详细探讨了向列序参数$\\Delta_{y}$的固定方向的系统频谱。没有磁化,由于有限的六边形翘曲,光谱中有一个完整的间隙。在足够强的平面外$m_z$或正交平面内$m_x$磁化时,频谱在被磁化分裂的节点处是封闭的。平坦的Majorana表面状态连接了这种分裂的散装节点。平行磁化$m_y$抬起节点并在频谱中打开一个完整的间隙。我们讨论了相关的实验,并提出了我们理论的实验验证。
    We study the effects of magnetisation on the properties of the doped topological insulator of theBi2Se3family with nematic superconductivity. We found that the direction of the in-plane magnetisation fixes the direction of the nematicity in the system. The chiral state is more favourable than the nematic state for large values of out-of-plane magnetisation. Overall, the critical temperature of the nematic superconductivity is robust against magnetisation. We explore in detail the spectrum of the system with the pinned direction of the nematic order parameterΔy. Without magnetisation, there is a full gap in the spectrum because of finite hexagonal warping. At an out-of-planemzor orthogonal in-planemxmagnetisation that is strong enough, the spectrum is closed at the nodal points that are split by the magnetisation. Flat Majorana surface states connect such split bulk nodal points. Parallel magnetisationmylifts the nodal points and opens a full gap in the spectrum. We discuss relevant experiments and propose experimental verifications of our theory.
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  • 文章类型: Journal Article
    了解磁共振成像中调节T1信号的复杂现象对于临床实践中更有效地表征病理过程至关重要。作者回顾了T1弛豫时间的物理基础以及可能影响此参数的物理和化学的基本方面。主要物质(水,脂肪,大分子,高铁血红蛋白,黑色素,钆,然后评估影响T1的钙)和可以应用于增强其在诊断图像中的存在的不同MRI采集技术。广泛的案例说明CNS领域的不同现象和技术,腹部-骨盆,还提出了骨关节病理学。关键相关声明:T1弛豫时间受与组织特征相关的许多因素以及某些特定物质在病变中的存在强烈影响。据报道,通过广泛的MRI例证对这些现象进行了检查。关键点:本文的目的是说明T1弛豫时间的化学物理基础。列出了根据各种临床适应症的MRI方法。报道了在腹骨盆和CNS病理学中的几个临床应用实例。
    A knowledge of the complex phenomena that regulate T1 signal on Magnetic Resonance Imaging is essential in clinical practice for a more effective characterization of pathological processes. The authors review the physical basis of T1 Relaxation Time and the fundamental aspects of physics and chemistry that can influence this parameter. The main substances (water, fat, macromolecules, methemoglobin, melanin, Gadolinium, calcium) that influence T1 and the different MRI acquisition techniques that can be applied to enhance their presence in diagnostic images are then evaluated. An extensive case illustration of the different phenomena and techniques in the areas of CNS, abdomino-pelvic, and osteoarticular pathology is also proposed. CRITICAL RELEVANCE STATEMENT: T1 relaxation time is strongly influenced by numerous factors related to tissue characteristics and the presence in the context of the lesions of some specific substances. An examination of these phenomena with extensive MRI exemplification is reported. KEY POINTS: The purpose of the paper is to illustrate the chemical-physical basis of T1 Relaxation Time. MRI methods in accordance with the various clinical indications are listed. Several examples of clinical application in abdominopelvic and CNS pathology are reported.
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  • 文章类型: Journal Article
    纳米材料的多样化应用,以及他们迅速增长的需求,促进了新型多功能材料的发展。因此,本研究旨在合成和表征一种磁发光纳米复合材料,由磁铁矿和荧光量子点(NaGdF4:Nd3+@Fe3O4)组成。通过溶剂热和共沉淀方法完成纳米材料的合成。zeta电位为-19.57±0.42mV的稳定纳米粒子(NPs),获得4.55±1.44nm的尺寸。NPs的晶体结构,通过X射线衍射验证,肯定了NaGdF4:Nd3+NPs的六方格局和Fe3O4NPs的反尖晶石格局。在NaGdF4:Nd3+@Fe3O4NPs的衍射图中,只确定了与Fe3O4NP有关的相,表明它们对纳米复合材料的影响。磁测量揭示了材料的超顺磁行为。NaGdF4:Nd3和NaGdF4:Nd3@Fe3O4NPs的光致发光光谱验证了约1060nm的发光发射;Nd3离子的辐射跃迁特征。根据评估的特征,纳米复合材料的多功能性得到证实,定位材料在各个领域的潜在用途,比如生物医学。 .
    The diverse applications of nanomaterials, and their rapidly increasing demand, have spurred the development of novel multifunctional materials. As such, this study aimed to synthesize and characterize a magneto-luminescent nanocomposite, composed of magnetite and fluorescent quantum dots (NaGdF4:Nd3+@Fe3O4). Nanomaterial synthesis was accomplished through solvothermal and co-precipitation methods. Stable nanoparticles (NPs) with a zeta potential of -19.57 ± 0.42 mV, and a size of 4.55 ± 1.44 nm were obtained. The crystalline structure of the NPs, verified via x-ray diffraction, affirmed the hexagonal pattern of the NaGdF4:Nd3+NPs and the inverse spinel pattern of Fe3O4NPs. In the diffraction pattern of the NaGdF4:Nd3+@Fe3O4NPs, only the phase pertaining to the Fe3O4NPs was identified, indicating their influence on the nanocomposite. Magnetic measurements revealed the superparamagnetic behavior of the material. Photoluminescence spectra of NaGdF4:Nd3+and NaGdF4:Nd3+@Fe3O4NPs verified the luminescent emission around 1060 nm; a feature of the radiative transitions of Nd3+ions. Based on the assessed characteristics, the nanocomposite\'s multifunctionality was confirmed, positioning the material for potential use in various fields, such as biomedicine.
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  • 文章类型: Journal Article
    1T和1H范德华层组合产生的相关现象的出现是激烈研究的重点。这里,我们在NbSeTe中合成了一个自堆叠的6R相,显示了沿c方向连贯生长的完美交替的1T和1H层,通过扫描透射电子显微镜显示。角度分辨光发射光谱显示出三角和八面体Nb带对费米能级的混合贡献。扩散散射揭示了与温度无关的短程电荷波动,传播矢量qCO=(0.250),从1T层中纵向模式的冷凝中得出,而长程电荷密度波因配体无序而猝灭。磁化测量表明存在不均匀的,短程磁序,进一步支持在比热中没有明显的相变。这些实验分析与从头计算相结合表明,6R-NbSeTe的基态由配体无序驱动的短程电荷调制和自旋相关区域的统计分布来描述。我们的结果表明,如何使用自然的1T-1H自堆叠体异质结构来设计物质的新兴相。
    The emergence of correlated phenomena arising from the combination of 1T and 1H van der Waals layers is the focus of intense research. Here, we synthesize a self-stacked 6R phase in NbSeTe, showing perfect alternating 1T and 1H layers that grow coherently along the c-direction, as revealed by scanning transmission electron microscopy. Angle-resolved photoemission spectroscopy shows a mixed contribution of the trigonal and octahedral Nb bands to the Fermi level. Diffuse scattering reveals temperature-independent short-range charge fluctuations with propagation vector qCO = (0.25 0), derived from the condensation of a longitudinal mode in the 1T layer, while the long-range charge density wave is quenched by ligand disorder. Magnetization measurements suggest the presence of an inhomogeneous, short-range magnetic order, further supported by the absence of a clear phase transition in the specific heat. These experimental analyses in combination with ab initio calculations indicate that the ground state of 6R-NbSeTe is described by a statistical distribution of short-range charge-modulated and spin-correlated regions driven by ligand disorder. Our results demonstrate how natural 1T-1H self-stacked bulk heterostructures can be used to engineer emergent phases of matter.
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  • 文章类型: Journal Article
    基于密度泛函理论中的第一性原理计算,我们系统地研究了可能的界面结构,磁性,全Heusler合金Co2MnGe/CoTiMnGe(100)异质结的电子性能。计算表明,Co2MnGeHeusler合金是半金属,磁矩为4.97μB。CoTiMnGe是窄带隙半导体并且可以充当超敏感光催化剂。在CoCo终止和MnGe终止中,我们找不到100%的“理想”自旋极化。由于界面交互,直接磁性杂交或间接RKKY交换将被削弱,导致界面层的原子磁矩增加。对于八种可能的异质结结构,Co2MnGe块体中的半金属间隙已被不可避免的界面态破坏。CoCo-TiGe-B异质结中94.31%的自旋极化值表明它是最稳定的结构。通过人工构造合适的全赫斯勒合金异质结来寻找高性能的磁隧道结是可行的。
    Based on first-principles calculations in the density functional theory, we systematically investigated the possible interface structure, magnetism, and electronic properties of the all-Heusler alloy Co2MnGe/CoTiMnGe(100) heterojunction. The calculation indicated that the Co2MnGe Heusler alloy is a half-metal with a magnetic moment of 4.97 μB. CoTiMnGe is a narrow-band gap semiconductor and may act as an ultra-sensitive photocatalyst. We cannot find an \"ideal\" spin-polarization of 100% in CoCo termination and MnGe termination. Due to the interface interaction, the direct magnetic hybridization or indirect RKKY exchange will be weakened, leading to an increase in the atomic magnetic moment of the interfacial layer. For eight possible heterojunction structures, the half-metallic gaps in the Co2MnGe bulk have been destroyed by the inevitable interface states. The spin-polarization value of 94.31% in the CoCo-TiGe-B heterojunction revealed that it is the most stable structure. It is feasible to search for high-performance magnetic tunnel junction by artificially constructing suitable all-Heusler alloy heterojunctions.
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  • 文章类型: Journal Article
    癌症,一种致命的疾病,拥有多种治疗替代方案来对抗它的存在,金属配合物已经成为重要的药用化合物,表现出相当大的生物学功效,尤其是作为抗癌剂。顺铂在各种癌症类型治疗中的应用,包括乳腺癌,为设计用于乳腺癌治疗的新型纳米结构金属配合物提供了灵感。值得注意的是,创新的多官能醚配体(包含Mn(II),Ni(II),Cu(II),Zn(II),Hg(II),和Ag(I)离子)已合成。为了确定它们的结构特征,元素和光谱分析,包括IR,UV-Vis,1H-NMR,质量和电子自旋共振(ESR)光谱,磁矩,摩尔电导,热分析,和电子显微镜,被雇用。这些络合物在DMF中的摩尔电导证明了非电解性质。通过电子显微镜数据鉴定了复合物的纳米结构形式。在环境温度下,固体配合物的ESR光谱表现出各向异性和各向同性的变化,表明共价键合。对配体及其几种金属配合物进行了针对乳腺癌蛋白3S7S和肝癌蛋白4OO6的细胞毒性测试,其中Ag(I)配合物(7)显示出最有效的作用,其次是Cu(II)与配体(配合物(2)),顺铂,配体本身,和Cu(II)/Zn(II)配合物(8)。分子对接数据揭示了几种复合物的抑制顺序。
    Cancer, a lethal ailment, possesses a multitude of therapeutic alternatives to combat its presence, metal complexes have emerged as significant classes of medicinal compounds, exhibiting considerable biological efficacy, especially as anticancer agents. The utilization of cis-platin in the treatment of various cancer types, including breast cancer, has served as inspiration to devise novel nanostructured metal complexes for breast cancer therapy. Notably, homo- and hetero-octahedral bimetallic complexes of an innovative multifunctional ether ligand (comprising Mn(II), Ni(II), Cu(II), Zn(II), Hg(II), and Ag(I) ions) have been synthesized. To ascertain their structural characteristics, elemental and spectral analyses, encompassing IR, UV-Vis, 1H-NMR, mass and electron spin resonance (ESR) spectra, magnetic moments, molar conductance, thermal analysis, and electron microscopy, were employed. The molar conductance of these complexes in DMF demonstrated a non-electrolytic nature. Nanostructured forms of the complexes were identified through electron microscopic data. At ambient temperature, the ESR spectra of the solid complexes exhibited anisotropic and isotropic variants, indicative of covalent bonding. The ligand and several of its metal complexes were subjected to cytotoxicity testing against breast cancer protein 3S7S and liver cancer protein 4OO6, with the Ag(I) complex (7) evincing the most potent effect, followed by the Cu(II) with ligand (complex (2)), Cis-platin, the ligand itself, and the Cu(II)/Zn(II) complex (8). Molecular docking data unveiled the inhibitory order of several complexes.
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  • 文章类型: Journal Article
    多晶型物工程涉及通过受控的结构修饰来操纵材料特性,并且是用于创建独特的二维过渡金属二硫属化物(TMDC)纳米器件的候选技术。尽管承诺,磁性TMDC单层的多晶型物工程尚未得到证实。在这里,我们通过分子束外延生长FeSe2单层,并发现它们对磁性多晶型物工程有很大的希望。使用扫描隧道显微镜(STM)和光谱学(STS),我们发现FeSe2单层在5K时主要表现出1T的结构多晶型。从STM尖端施加电压脉冲会导致局部,从1T阶段到1T阶段的可逆过渡。密度泛函理论计算表明,这种单层结构相变伴随着从反铁磁结构到铁磁结构的磁转变。这些结果为通过多晶型物工程创建具有TMDC单层的功能性磁性设备开辟了新的可能性。
    Polymorph engineering involves the manipulation of material properties through controlled structural modification and is a candidate technique for creating unique two-dimensional transition metal dichalcogenide (TMDC) nanodevices. Despite its promise, polymorph engineering of magnetic TMDC monolayers has not yet been demonstrated. Here we grow FeSe2 monolayers via molecular beam epitaxy and find that they have great promise for magnetic polymorph engineering. Using scanning tunneling microscopy (STM) and spectroscopy (STS), we find that FeSe2 monolayers predominantly display a 1T\' structural polymorph at 5 K. Application of voltage pulses from an STM tip causes a local, reversible transition from the 1T\' phase to the 1T phase. Density functional theory calculations suggest that this single-layer structural phase transition is accompanied by a magnetic transition from an antiferromagnetic to a ferromagnetic configuration. These results open new possibilities for creating functional magnetic devices with TMDC monolayers via polymorph engineering.
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  • 文章类型: Journal Article
    我们对烧绿石状NaCu3F7化合物的磁性进行了理论研究,令人惊讶的是经历很少或没有挫折。磁有效交换相互作用是使用明确处理电子相关的从头方法计算的。根据这些相互作用建立了哈密顿量模型,用于确定零温度磁阶与磁场的关系。使用量子海森堡哈密顿量或,为了比较,自旋1/2伊辛哈密顿量。在零磁场处的磁阶是非受挫的,并且与传播矢量q=(0,0,0)相关联。磁化强度与磁场的关系揭示了在高脉冲磁场实验中可以观察到的1/3平台的存在。分析磁相互作用,我们强调了磁离子性质和晶格畸变的重要性,在NaCu3F7磁性结构的非受挫性质中,尽管它的三角/Kagome子网。我们认为,这种不受挫的行为也可能发生在其他三角形铜基系统中。 .
    We present a theoretical study of the magnetic properties for the pyrochlore-like NaCu3F7compound, which surprisingly experience little or no frustration. The magnetic effective exchange interactions were calculated usingab-initiomethods explicitly treating the electronic correlation. A model Hamiltonian (quantum Heisenberg Hamiltonian, and for comparison a spin 1/2 Ising Hamiltonian) was built from these interactions and used to determine the zero temperature magnetic order versus magnetic field. The magnetic order at zero magnetic field is non frustrated and associated with the propagation vectorq→=(0,0,0). The magnetization versus magnetic field reveals the existence of a 1/3 plateau that could be observed in high-pulsed magnetic field experiments. Analyzing the magnetic interactions, we highlight the importance of the magnetic ion nature, and the lattice distortion, in the non-frustrated nature of the NaCu3F7magnetic structure, despite its triangular/Kagome subnetworks. We believe that this non-frustrated behavior could also take place in other triangular copper-based systems.
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  • 文章类型: Journal Article
    共振共价键(RVB)态是理解二维(2D)系统中量子自旋液体的基础。RVB状态是自旋解耦的集体现象。二维晶格,如三角形,蜂窝,使用Hubbard模型和精确对角化方法研究了骰子晶格。我们分析了总旋转,自旋-自旋相关函数,局部磁矩,自旋和电荷间隙是现场库仑斥力的函数,电子浓度,和电子跳变参数。相图表明,RVB态可以存在于半填充和空穴掺杂的各向异性三角形晶格中。我们发现了两种类型的RVB状态:一种在蜂窝子晶格中,另一种在三角形晶格中的中心六边形中。由于在扭曲的双层石墨烯和过渡金属二硫属体系中的三角摩尔{e}图案中发现了奇异的磁性有序,我们的结果为这些层状材料中磁性和可能的自旋液体状态的发生提供了物理见解。
    Resonating valence bond (RVB) states are fundamental for understanding quantum spin liquids in two-dimensional (2D) systems. The RVB state is a collective phenomenon in which spins are uncoupled. 2D lattices such as triangular, honeycomb, and dice lattices were investigated using the Hubbard model and exact diagonalization method. We analyzed the total spin, spin-spin correlation functions, local magnetic moments, and spin and charge gaps as a function of on-site Coulomb repulsion, electron concentration, and electronic hopping parameters. Phase diagrams showed that RVB states can live in half-filled and hole-doped anisotropic triangular lattices. We found two types of RVB states: one in the honeycomb sublattice and the other in the centered hexagons in the triangular lattices. Owing to the novel discovery of exotic magnetic ordering in triangular moiré patterns in twisted bilayer graphene and transition metal dichalcogenide systems, our results provide physical insights into the onset of magnetism and possible spin liquid states in these layered materials.
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