214 research outputs found

    Quantum states and intertwining phases in kagome materials

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    In solid materials, nontrivial topological states, electron correlations, and magnetism are central ingredients for realizing quantum properties, including unconventional superconductivity, charge and spin density waves, and quantum spin liquids. The Kagome lattice, made up of connected triangles and hexagons, can host these three ingredients simultaneously and has proven to be a fertile platform for studying diverse quantum phenomena including those stemming from the interplay of these ingredients. In this review, we introduce the fundamental properties of the Kagome lattice as well as discuss the complex observed phenomena seen in several emergent material systems such as the intertwining of charge order and superconductivity in some Kagome metals, modulation of magnetism and topology in some Kagome magnets, and symmetry breaking with Mott physics in the breathing Kagome insulators. We also highlight many open questions in the field as well as future research directions of Kagome systems

    Magnetic Domains and Domain Wall Oscillations in Planar and 3D Curved Membranes

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    This dissertation presents a substantial contribution to a new field of material science, the investigation of the magnetic properties of 3D curved surfaces, achieved by using a self-assembled geometrical transformation of an initially planar membrane. Essential magnetic properties of thin films can be modified by the process of transforming them from a 2D planar film to a 3D curved surface. By investigating and controlling the reasons that influence the properties, it is possible to improve the functionality of existing devices in addition to laying the foundation for the future development of microelectronic devices based on curved magnetic structures. To accomplish this, it is necessary both to fabricate high-quality 3D curved objects and to establish reliable characterization methods based on commonly available technology. The primary objective of this dissertation is to develop techniques for characterizing the static and dynamic magnetic properties of self-assembled rolled 3D geometries. The second objective is to examine the origin of shape-, size- and strain/curvature-induced effects. The developed approach based on anisotropic magnetoresistance (AMR) measurement can quantitatively define the rolling-induced static magnetic changes, namely the induced magnetoelastic anisotropy, thus eliminating the need for microscopic imaging to characterize the structures. The interpretation of the AMR signal obtained on curved stripes is enabled by simultaneous visualization of the domain patterns and micromagnetic simulations. The developed approach is used to examine the effect of sign and magnitude of curvature on the induced anisotropies by altering the rolling direction and diameter of the 'Swiss-roll'. Furthermore, a time-averaged imaging technique based on conventional microscopies (magnetic force microscopy and Kerr microscopy) offers a novel strategy for investigating nanoscale periodic domain wall oscillations and hence dynamic magnetic characteristics of flat and curved structures. This method exploits the benefit of a position-dependent dwell time of periodically oscillating DWs and can determine the trajectory and amplitude of DW oscillation with sub-100 nm resolution. The uniqueness of this technique resides in the ease of the imaging procedure, unlike other DW dynamics imaging methods. The combined understanding of rolling-induced anisotropy and imaging DW oscillation is utilized to examine the dependence of DW dynamics on external stimuli and the structure's physical properties, such as lateral size, film thickness, and curvature-induced anisotropy. The presented methods and fundamental studies help to comprehend the rapidly expanding field of 3-dimensional nanomagnetism and advance high-performance magneto-electronic devices based on self-assembly rolling

    Fast non-volatile electric control of antiferromagnetic states

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    Electrical manipulation of antiferromagnetic states, a cornerstone of antiferromagnetic spintronics, is a great challenge, requiring novel material platforms. Here we report the full control over antiferromagnetic states by voltage pulses in the insulating Co3_3O4_4 spinel. We show that the strong linear magnetoelectric effect emerging in its antiferromagnetic state is fully governed by the orientation of the N\'eel vector. As a unique feature of Co3_3O4_4, the magnetoelectric energy can easily overcome the weak magnetocrystalline anisotropy, thus, the N\'eel vector can be manipulated on demand, either rotated smoothly or reversed suddenly, by combined electric and magnetic fields. We succeed with switching between antiferromagnetic states of opposite N\'eel vectors by voltage pulses within a few microsecond in macroscopic volumes. These observations render quasi-cubic antiferromagnets, like Co3_3O4_4, an ideal platform for the ultrafast (pico- to nanosecond) manipulation of microscopic antiferromagnetic domains and may pave the way for the realization of antiferromagnetic spintronic devices.Comment: 7 pages, 3 figure

    Synthèse et étude d'analogues du bleu de Prusse chiraux et de possibles liquides de spin quantiques

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    The design of multifunctional materials, combining magnetism with another physical property, is a fascinating subject. It becomes one of the most discussed topics in materials chemistry and physics. These compounds have attracted the attention of researchers because of the various potential applications they can offer, in particular in spintronics, a field of electronics that exploits both the charge and the spin of electrons, in low-energy data storage devices.The main goal of this study is to develop multifunctional molecular materials. Indeed, the non-centrosymmetry which is a crucial feature to promote ferroelectricity or even multiferroicity and magnetochiral dichroism is much easier to achieve in these materials. A strategy based on the introduction of chirality in Prussian blue analogs, compounds known to have some of the highest Curie temperatures of molecular materials, was used by adding a chiral co-ligand during synthesis. For this purpose, various divalent metal ions, cyanometallates, and three chiral co-ligands were tested to synthesize chiral cyanide-bridged materials, classified into three families according to the co-ligand used. These materials show a variety of crystallographic structures with different geometries around the metal centers. The magnetic, dichroic magneto-chiral, and electrical properties of these compounds have been studied. Most of these chiral magnetic materials have shown different signals related to magneto-chiral dichroism depending on the metal center used. A magneto-chiral dichroism factor gMChD comparable to those already reported was determined for some materials. A magneto-electric coupling has been observed in two materials among those studied so far.The second part of this work is mainly based on compounds consisting of cobalt(II) ions bridged by oxalate ligands, generating a two-dimensional honeycomb network. This type of system is attractive because it could present a Kitaev quantum spin liquid state. Magnetic measurements on the compound (A2)2[Co2(ox)3], obtained by solvothermal synthesis, have shown that this material presents an antiferromagnetic order with tilted spin, below Tc = 22 K and a possible reorientation of the spins at T = 13 K. Thus, preliminary neutron powder diffraction measurements were very encouraging to continue in this direction and showed an appearance of a magnetic peak at 2θ ~ 20 possibly related to a strong magnetic compound. In addition, a new two-step route, to overcome the problems of reproducibility of synthesis under solvothermal conditions, was initiated. For this purpose, an organic molecule that is supposed to play the role of the cation and help in forming the desired two-dimensional cobalt-based honeycomb network was synthesized.La conception des matériaux multifonctionnels, combinant le magnétisme à une autre propriété physique, est un sujet fascinant. Il compte parmi les thèmes les plus discutés de la chimie et physique des matériaux. Ces composés ont attiré l’attention des chercheurs en raison des diverses applications potentielles qu’ils peuvent offrir, en particulier en spintronique, un domaine de l'électronique qui exploite et la charge et le spin des électrons, dans les dispositifs de stockage de données à faible consommation énergétique.Le but principal de cette étude est de développer des matériaux moléculaires multifonctionnels. En effet, la non-centrosymétrie qui est une caractéristique cruciale pour favoriser la ferroélectricité voire la multiferroïcité et le dichroïsme magnéto-chiral est beaucoup plus facile à réaliser dans ces matériaux. Une stratégie basée sur l’introduction de la chiralité dans des analogues de bleu de Prusse, composés connus pour avoir les températures de Curie parmi les plus élevées des matériaux moléculaires, a été utilisée en ajoutant un co-ligand chiral pendant la synthèse. Pour cela, divers ions métalliques divalents, cyanométallates et trois co-ligands chiraux ont été testés pour synthétiser des matériaux chiraux à ponts cyanure, classés en trois familles selon le co-ligand utilisé. Ces matériaux montrent une variété de structures cristallographiques avec différentes géométries autour des centres métalliques. Les propriétés magnétiques, dichroïques magnéto-chiral et électriques de ces composés ont été étudiées. La plupart de ces matériaux magnétiques chiraux ont montré des signaux différents liés au dichroïsme magnéto-chiral selon le centre métallique utilisé. Un facteur de dichroïsme magnéto-chiral gMChD comparable à ceux déjà reportés a été déterminé pour certains matériaux. Un couplage magnéto-électrique a été observé dans deux matériaux parmi ceux étudiés à jusqu'à présent.La deuxième partie de ce travail est fondée sur des composés constitués d’ions cobalt(II) pontés par des ligands oxalate, générant un réseau bidimensionnel en nid d’abeille. Ce type de systèmes est très intéressant car il pourrait présenter un état liquide de spin quantique de Kitaev. Les mesures magnétiques sur le composé (A2)2[Co2(ox)3], obtenu par synthèse solvothermale, ont montré que ce matériau présent un ordre antiferromagnétique à spin incliné, en dessous de Tc = 22 K et une possible réorientation des spins à T = 13 K.Ainsi, les mesures préliminaires de diffraction des neutrons sur poudre étaient très encourageantes pour poursuivre dans cette direction et ont montré une apparition d’un pic magnétique à 2θ ~ 20 possiblement liée à une forte composent magnétique. En plus, une nouvelle voie en deux étapes a été initié, pour surmonter les problèmes de reproductibilité de synthèse sous conditions solvothermales. Pour cela, une molécule organique susceptible de jouer le rôle du cation et aider à former le réseau bidimensionnel en nid d’abeille à base de cobalt souhaité, a été synthétisé

    Monopole-like orbital-momentum locking and the induced orbital transport in topological chiral semimetals

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    The interplay between chirality and topology nurtures many exotic electronic properties. For instance, topological chiral semimetals display multifold chiral fermions that manifest nontrivial topological charge and spin texture. They are an ideal playground for exploring chirality-driven exotic physical phenomena. In this work, we reveal a monopole-like orbital-momentum locking texture on the three-dimensional Fermi surfaces of topological chiral semimetals with B20 structures (e.g., RhSi and PdGa). This orbital texture enables a large orbital Hall effect (OHE) and a giant orbital magnetoelectric (OME) effect in the presence of current flow. Different enantiomers exhibit the same OHE which can be converted to the spin Hall effect by spin-orbit coupling in materials. In contrast, the OME effect is chirality-dependent and much larger than its spin counterpart. Our work reveals the crucial role of orbital texture for understanding OHE and OME effects in topological chiral semimetals and paves the path for applications in orbitronics, spintronics, and enantiomer recognition.Comment: 23 pages, 5 figure

    Synthesis and study of chiral Prussian blue analogs and possible quantum spin liquids

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    La conception des matériaux multifonctionnels, combinant le magnétisme à une autre propriété physique, est un sujet fascinant. Il compte parmi les thèmes les plus discutés de la chimie et physique des matériaux. Ces composés ont attiré l’attention des chercheurs en raison des diverses applications potentielles qu’ils peuvent offrir, en particulier en spintronique, un domaine de l'électronique qui exploite et la charge et le spin des électrons, dans les dispositifs de stockage de données à faible consommation énergétique.Le but principal de cette étude est de développer des matériaux moléculaires multifonctionnels. En effet, la non-centrosymétrie qui est une caractéristique cruciale pour favoriser la ferroélectricité voire la multiferroïcité et le dichroïsme magnéto-chiral est beaucoup plus facile à réaliser dans ces matériaux. Une stratégie basée sur l’introduction de la chiralité dans des analogues de bleu de Prusse, composés connus pour avoir les températures de Curie parmi les plus élevées des matériaux moléculaires, a été utilisée en ajoutant un co-ligand chiral pendant la synthèse. Pour cela, divers ions métalliques divalents, cyanométallates et trois co-ligands chiraux ont été testés pour synthétiser des matériaux chiraux à ponts cyanure, classés en trois familles selon le co-ligand utilisé. Ces matériaux montrent une variété de structures cristallographiques avec différentes géométries autour des centres métalliques. Les propriétés magnétiques, dichroïques magnéto-chiral et électriques de ces composés ont été étudiées. La plupart de ces matériaux magnétiques chiraux ont montré des signaux différents liés au dichroïsme magnéto-chiral selon le centre métallique utilisé. Un facteur de dichroïsme magnéto-chiral gMChD comparable à ceux déjà reportés a été déterminé pour certains matériaux. Un couplage magnéto-électrique a été observé dans deux matériaux parmi ceux étudiés à jusqu'à présent.La deuxième partie de ce travail est fondée sur des composés constitués d’ions cobalt(II) pontés par des ligands oxalate, générant un réseau bidimensionnel en nid d’abeille. Ce type de systèmes est très intéressant car il pourrait présenter un état liquide de spin quantique de Kitaev. Les mesures magnétiques sur le composé (A2)2[Co2(ox)3], obtenu par synthèse solvothermale, ont montré que ce matériau présent un ordre antiferromagnétique à spin incliné, en dessous de Tc = 22 K et une possible réorientation des spins à T = 13 K.Ainsi, les mesures préliminaires de diffraction des neutrons sur poudre étaient très encourageantes pour poursuivre dans cette direction et ont montré une apparition d’un pic magnétique à 2θ ~ 20 possiblement liée à une forte composent magnétique. En plus, une nouvelle voie en deux étapes a été initié, pour surmonter les problèmes de reproductibilité de synthèse sous conditions solvothermales. Pour cela, une molécule organique susceptible de jouer le rôle du cation et aider à former le réseau bidimensionnel en nid d’abeille à base de cobalt souhaité, a été synthétisé.The design of multifunctional materials, combining magnetism with another physical property, is a fascinating subject. It becomes one of the most discussed topics in materials chemistry and physics. These compounds have attracted the attention of researchers because of the various potential applications they can offer, in particular in spintronics, a field of electronics that exploits both the charge and the spin of electrons, in low-energy data storage devices.The main goal of this study is to develop multifunctional molecular materials. Indeed, the non-centrosymmetry which is a crucial feature to promote ferroelectricity or even multiferroicity and magnetochiral dichroism is much easier to achieve in these materials. A strategy based on the introduction of chirality in Prussian blue analogs, compounds known to have some of the highest Curie temperatures of molecular materials, was used by adding a chiral co-ligand during synthesis. For this purpose, various divalent metal ions, cyanometallates, and three chiral co-ligands were tested to synthesize chiral cyanide-bridged materials, classified into three families according to the co-ligand used. These materials show a variety of crystallographic structures with different geometries around the metal centers. The magnetic, dichroic magneto-chiral, and electrical properties of these compounds have been studied. Most of these chiral magnetic materials have shown different signals related to magneto-chiral dichroism depending on the metal center used. A magneto-chiral dichroism factor gMChD comparable to those already reported was determined for some materials. A magneto-electric coupling has been observed in two materials among those studied so far.The second part of this work is mainly based on compounds consisting of cobalt(II) ions bridged by oxalate ligands, generating a two-dimensional honeycomb network. This type of system is attractive because it could present a Kitaev quantum spin liquid state. Magnetic measurements on the compound (A2)2[Co2(ox)3], obtained by solvothermal synthesis, have shown that this material presents an antiferromagnetic order with tilted spin, below Tc = 22 K and a possible reorientation of the spins at T = 13 K. Thus, preliminary neutron powder diffraction measurements were very encouraging to continue in this direction and showed an appearance of a magnetic peak at 2θ ~ 20 possibly related to a strong magnetic compound. In addition, a new two-step route, to overcome the problems of reproducibility of synthesis under solvothermal conditions, was initiated. For this purpose, an organic molecule that is supposed to play the role of the cation and help in forming the desired two-dimensional cobalt-based honeycomb network was synthesized

    Anomalous superconducting diode effect in a polar superconductor

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    A superconductor with broken time reversal and inversion symmetry may exhibit nonreciprocal charge transport, including a nonreciprocal critical current, also known as superconducting diode effect. We report an intrinsic superconducting diode effect in a polar strontium titanate film. Differential resistance measurements reveal a superconducting state whose depairing current is polarity dependent. There is, however, no measurable deviation from Ohmic behavior, implying that this state does not arise from a bulk magnetochiral anisotropy. In the entire measurement range, the only deviation from linearity in the differential resistance is on the edge of the superconducting transition at high magnetic fields, likely due to the motion of flux vortices. Furthermore, the magnitude of the effect is preserved even when the in-plane magnetic field is oriented parallel to the current, indicating that this effect truly does not originate from a bulk magnetochiral anisotropy

    Coherent two-dimensional THz magnetic resonance spectroscopies for molecular magnets: Analysis of Dzyaloshinskii-Moriya interaction

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    To investigate the novel quantum dynamic behaviors of magnetic materials that arise from complex spin-spin interactions, it is necessary to probe the magnetic response at a speed greater than the spin-relaxation and dephasing processes. Recently developed two-dimensional (2D) terahertz magnetic resonance (THz-MR) spectroscopy techniques use the magnetic components of laser pulses, and this allows investigation of the details of the ultrafast dynamics of spin systems. For such investigations, quantum treatment -- not only of the spin system itself but also of the environment surrounding the spin system -- is important. In our method, based on the theory of multidimensional optical spectroscopy, we formulate nonlinear THz-MR spectra using an approach based on the numerically rigorous hierarchical equations of motion. We conduct numerical calculations of both linear (1D) and 2D THz-MR spectra for a linear chiral spin chain. The pitch and direction of chirality (clockwise or anticlockwise) are determined by the strength and sign of the Dzyaloshinskii-Moriya interaction (DMI). We show that not only the strength but also the sign of the DMI can be evaluated through the use of 2D THz-MR spectroscopic measurements, while 1D measurements allow us to determine only the strength.Comment: 10 pages, 5 figure

    Chirality-induced spin splitting in 1D InSeI

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    Spin-orbit coupling (SOC) in chiral materials can induce chirality-dependent spin splitting, enabling electrical manipulation of spin polarization. Here, we use first-principles calculations to investigate the electronic states of chiral one-dimensional (1D) InSeI, which has two enantiomorphic configurations with left- and right-handedness. We find that opposite spin states exist in the left- and right-handed 1D InSeI with significant spin splitting. Although the spin states at the conduction band minimum (CBM) and valence band maximum (VBM) are both degenerate, a direct-to-indirect bandgap transition occurs when a moderate tensile strain (∼\sim4%) is applied along the 1D chain direction, leading to chirality-dependent and collinear spin-momentum locking at the CBM. These findings indicate that 1D InSeI is a promising material for chiral spintronics.Comment: 7 pages, 3 figure
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