Non-coplanar Structure Research Articles

Novel phenolphthalein-based aromatic polyesters: The investigations of the relationships between refractive index and structure

Aromatic polyesters are an attractive class of engineering thermoplastics with excellent chemical properties, thermal stability and environmental stability, as well as good optical properties, but they have rarely been reported. Refractive index (RI) is one of the properties commonly used to compare the optical properties of materials. The higher the refractive index, the thinner the lens made of the corresponding material; however, the preparation of high-refractive-index polymers is currently a thorny issue, in which the structure of the polymer molecules has a great impact on their refractive index, to design high-refractive-index materials requires starting from the structure of the molecules. Phenolphthalein has a unique structure with a molecular skeleton consisting of three benzene rings and a cyclic lactone that exhibits a twisted non-coplanar structure. This cyclic side group can hinder the accumulation between the polymer molecular chains, not only improving the solubility of the polymer molecules, but also increasing the transparency of the polymer films. In this work, we used phenolphthalein (PHT) and its derivatives to polymerize with terephthaloyl chloride (TPC), respectively, through the structural differences between them, the influence of polymer structure on the refractive index and thermal properties was discussed. Among them, polyester PAR-NPHT had the highest refractive index ( nd>1.67), and is expected to be a new generation of optical materials.

Noncoplanar magnetic structures in Mn4N epitaxial films evaluated by alternating magnetic force microscopy

Abstract Noncoplanar magnetic structures in the Mn4N epitaxial thin films grown on the 001-oriented MgO and SrTiO3 (STO) substrates were studied, based on the measurements of topological Hall effect (THE) and the observation of magnetic domain nucleation. The typical nucleation diameter of domain was determined using an alternating magnetic force microscope, which proved advantageous for the visualization of the domain with an out-of-plane magnetic component. The nucleation diameter of the domains on the MgO substrate were ∼150 nm for the thickness of 30 nm and ∼110 nm for 10 nm, while ∼130 nm for 30 nm on the STO substrate. The value of THE was one or two orders of magnitude larger than that estimated based on the nucleation diameter, indicating that the existence of a noncoplanar magnetic structure is the primary factor contributing to the THE in the Mn4N films, comparing to the effect from domain nucleation. The noncoplanar magnetic structure was more pronounced with decreasing thickness and substrate-induced strain.

Topological Hall effect instigated in kagome Mn3–xSn due to Mn-deficit induced noncoplanar spin structure

Magnetic topological semimetals are manifestations of the interplay between electronic and magnetic phases of matter, leading to peculiar characteristics such as the anomalous Hall effect (AHE) and the topological Hall effect (THE). Mn3Sn is a time-reversal symmetry-broken magnetic Weyl semimetal showing topological characteristics within the Kagome lattice network. This study reveals a large THE in Mn2.8Sn (6% Mn deficit Mn3Sn) at room temperature in thexy-plane, despite being an antiferromagnet. We argue that the magnetocrystalline anisotropy induced noncoplanar spin structure is responsible for the observed THE in these systems. Further, the topological properties of these systems are highly anisotropic, as we observe a large AHE in thezx-plane. We find that Fe doping at the Mn site, Mn3-xFexSn (x= 0.2, 0.25, & 0.35), tunes the topological properties of these systems. These findings promise the realization of potential topotronic applications at room temperature.

Exchange bias and topological Hall effect of Fe and Co intercalated NbS2 single crystals

In recent years, the topological Hall effect generated by noncoplanar magnetic structures has been studied extensively. Some two-dimensional chalcogenides with 3d transition metal intercalations also exhibit similar properties. In this study, we investigated the crystalline structure and the magnetic and transport properties of Fe and Co codoped NbS2 single crystals. The structural results indicate disorder between the Fe and Co atoms within the interlayers of NbS2. Magnetic measurements showed that the vertical exchange bias effect appeared below the Néel temperature (TN), with a maximum value of approximately 2.5 mμB/f.u. at 2 K, which can be ascribed to the appearance of a spin-glass state. Additionally, accompanying the antiferromagnetic phase transition, nontrivial electrical transport properties were observed. Below TN, the magnetoresistance became positive and exhibited an initial increase, followed by a decrease with decreasing temperature. The Hall resistivity shows a hump-like curve near TN, indicating a topological Hall effect. This behavior is related to fluctuations in the spin chirality, which affects the scattering of charge carriers. Based on the correlation between the magnetoresistance and Hall resistivity responses, it is believed that the magnetic moments of the doped Fe and Co atoms in a single crystal compete with each other near the Néel temperature, resulting in complex magnetic structures such as noncoplanar and noncollinear arrangements. Such a two-dimensional antiferromagnetic material system provides an ideal platform for studying unconventional transport mechanisms.

From Molecular Design to Practical Applications: Strategies for Enhancing the Optical and Thermal Performance of Polyimide Films.

Polyimide (PI) films are well recognized for their outstanding chemical resistance, radiation resistance, thermal properties, and mechanical strength, rendering them highly valuable in advanced fields such as aerospace, sophisticated electronic components, and semiconductors. However, improving their optical transparency while maintaining excellent thermal properties remains a significant challenge. This review systematically checks over recent advancements in enhancing the optical and thermal performance of PI films, focusing on various strategies through molecular design. These strategies include optimizing the main chain, side chain, non-coplanar structures, and endcap groups. Rigid and flexible structural characteristics in the proper combination can contribute to the balance thermal stability and optical transparency. Introducing fluorinated substituents and bulky side groups significantly reduces the formation of charge transfer complexes, enhancing both transparency and thermal properties. Non-coplanar structures, such as spiro and cardo configurations, further improve the optical properties while maintaining thermal stability. Future research trends include nanoparticle doping, intrinsic microporous PI polymers, photosensitive polyimides, machine learning-assisted molecular design, and metal coating techniques, which are expected to further enhance the comprehensive optical and thermal performance of PI films and expand their applications in flexible displays, solar cells, and high-performance electronic devices. Overall, systematic molecular design and optimization have significantly improved the optical and thermal performance of PI films, showing broad application prospects. This review aims to provide researchers with valuable references, stimulate more innovative research and applications, and promote the deep integration of PI films into modern technology and industry.

Enhancement of the anomalous Hall effect by distorting the Kagome lattice in an antiferromagnetic material

In topological magnetic materials, the topology of the electronic wave function is strongly coupled to the structure of the magnetic order. In general, ferromagnetic Weyl semimetals generate a strong anomalous Hall conductivity (AHC) due to a large Berry curvature that scales with their magnetization. In contrast, a comparatively small AHC is observed in noncollinear antiferromagnets. We investigated HoAgGe, an antiferromagnetic (AFM) Kagome spin-ice compound, which crystallizes in a hexagonal ZrNiAl-type structure in which Ho atoms are arranged in a distorted Kagome lattice, forming an intermetallic Kagome spin-ice state in the ab-plane. It exhibits a large topological Hall resistivity of ~1.6 µΩ-cm at 2.0 K in a field of ~3 T owing to the noncoplanar structure. Interestingly, a total AHC of 2,800 Ω-1 cm-1 is observed at ~45 K, i.e., 4 TN, which is quite unusual and goes beyond the normal expectation considering HoAgGe as an AFM Kagome spin-ice compound with a TN of ~11 K. We demonstrate further that the AHC below TN results from the nonvanishing Berry curvature generated by the formation of Weyl points under the influence of the external magnetic field, while the skew scattering led by Kagome spins dominates above the TN. These results offer a unique opportunity to study frustration in AFM Kagome lattice compounds.

Giant Room-Temperature Topological Hall Effect in a Square-Net Ferromagnet LaMn2Ge2.

A topological magnetic material showcases a multitude of intriguing properties resulting from the compelling interplay between topology and magnetism. These include notable phenomena such as a large anomalous Nernst effect (ANE), an anomalous Hall effect (AHE), and a topological Hall effect (THE). In most cases, topological transport phenomena are prevalent at temperatures considerably lower than room temperature, presenting a challenge for practical applications. However, the noncollinear ferromagnetic (FM) LaMn2Ge2, characterized by a Mn square-net lattice and a notably high Curie temperature (TC) of approximately 325 K, defies this trend as a topological semimetal. This work observes a giant topological Hall resistivity, , of ≈4.5 µΩ cm at room temperature when the angle between the applied field and the c-axis is 75°, which is significantly higher than state-of-the-art materials with noncoplanar spin structures. The single crystal neutron diffraction measurements agree with an incommensurate conical magnetic structure as the ground state. This observation suggests the enhanced spin chirality resulting from the noncoplanar spin configuration when the applied field is away from the magnetic easy axis as the origin of a large contribution to the observed THE. The findings unequivocally demonstrate that the FM LaMn2Ge2 holds great promise as a potential topological semimetal for spintronic applications even at room temperature.

Cubic double perovskites host noncoplanar spin textures

Magnetic materials with noncoplanar magnetic structures can show unusual physical properties driven by nontrivial topology. Topologically-active states are often multi-q structures, which are challenging to stabilize in models and to identify in materials. Here, we use inelastic neutron-scattering experiments to show that the insulating double perovskites Ba2YRuO6 and Ba2LuRuO6 host a noncoplanar 3-q structure on the face-centered cubic lattice. Quantitative analysis of our neutron-scattering data reveals that these 3-q states are stabilized by biquadratic interactions. Our study identifies double perovskites as a highly promising class of materials to realize topological magnetism, elucidates the stabilization mechanism of the 3-q state in these materials, and establishes neutron spectroscopy on powder samples as a valuable technique to distinguish multi-q from single-q states, facilitating the discovery of topologically-nontrivial magnetic materials.

Adhesion and Transparency Enhancement between Flexible Polyimide-PDMS Copolymerized Film and Copper Foil for LED Transparent Screen.

With the increasing demand for innovative electronic products, LED transparent screens are gradually entering the public eye. Polyimide (PI) materials combine high temperature resistance and high transparency, which can be used to prepare flexible copper-clad laminate substrates. The physical and chemical properties of PI materials differ from copper, such as their thermal expansion coefficients (CTEs), surface energy, etc. These differences affect the formation and stability of the interface between copper and PI films, resulting in a short life for LED transparent screens. To enhance PI-copper interfacial adhesion, aminopropyl-terminated polydimethylsiloxane (PDMS) can be used to increase the adhesive ability. Two diamine monomers with a trifluoromethyl structure and a sulfone group structure were selected in this research. Bisphenol type A diether dianhydride is a dianhydride monomer. All three of the above monomers have non-coplanar structures and flexible structural units. The adhesion and optical properties can be improved between the interface of the synthesized PI films and copper foil. PI films containing PDMS 0, 1, 3, and 5 wt% were analyzed using UV spectroscopy. The transmittance of the PI-1/3%, PI-1/5%, PI-2/3%, and PI-2/5% films were all more than 80% at 450 nm. Meanwhile, the Td 5% and Td 10% heat loss and Tg temperatures decreased gradually with the increase in PDMS. The peel adhesion of PI-copper foil was measured using a 180° peel assay. The effect of PDMS addition on peel adhesion was analyzed. PIs-3% films had the greatest peeling intensities of 0.98 N/mm and 0.85 N/mm.

Investigation of flame-retardant characteristics of a polyaryl ether containing phthalazinone moiety

The aerospace, automotive and other industries require very safe specialty engineered plastics that can be used for long times at high temperatures and produce few harmful fumes during combustion in the event of a safety accident, which is essential for protecting personal life and property in a confined environment. The twisted noncoplanar structures give poly (phthalazinone ether) resins excellent temperature resistance and solubility, but clarifying the flame retardancies of the resins is the key to broader application. Herein, a comprehensive comparison has been made between poly (phthalazinone ether) resins and the specialty engineered plastic polysulfone (PSF) based on flame resistance. In vertical burning test, the poly (phthalazinone ether) resin showed a very short flame self-extinguishing time (within 1 s), furthermore, the light transmittance of poly (phthalazinone ether) resin was 100 % at 300 s in the smoke density test, whereas, this value was 10 % for PSF. And the thermal decomposition process and flame retardancy mechanism were investigated by microscale combustion calorimetry, scanning electron microscopy, X-ray photoelectron spectroscopy and thermogravimetric-infrared spectra mass spectrometry. The results indicated that the introduction of phthalazinone moiety not only enhanced the glass transition temperature of the polyaryl ether, but also delayed the smoke generation. This work deepens our understanding of the effects of the molecular structure on the flame retardancy of polyaryl ether resins and provides useful guidance for the design and preparation of polyaryl ether resins with excellent comprehensive properties.

Metamagnetic multiband Hall effect in Ising antiferromagnet ErGa2

Frustrated rare-earth-based intermetallics provide a promising platform for emergent magnetotransport properties through exchange coupling between conduction electrons and localized rare-earth magnetic moments. Metamagnetism, the abrupt change of magnetization under an external magnetic field, is a signature of first-order magnetic phase transitions; recently, metamagnetic transitions in frustrated rare earth intermetallics have attracted interest for their accompanying nontrivial spin structures (e.g., skyrmions) and associated nonlinear and topological Hall effects (THE). Here, we present metamagnetism-induced Hall anomalies in single-crystalline ErGa2, which recalls features arising from the THE but wherein the strong Ising-type anisotropy of Er moments prohibits noncoplanar spin structures. We show that the observed anomalies are neither due to anomalous Hall effect nor THE; instead, can be accounted for via 4f-5d interactions which produce a band-dependent mobility modulation. This leads to a pronounced multiband Hall response across the magnetization process-a metamagnetic multiband Hall effect that resembles a topological-Hall-like response but without nontrivial origins. The present findings may be of general relevance in itinerant metamagnetic systems regardless of coplanar/noncoplanar nature of spins and are important for the accurate identification of Hall signals due to emergent magnetic fields.

Non-coplanar spin structure in a metallic thin film of triangular lattice antiferromagnet CrSe

An antiferromagnetic metal with a two-dimensional triangular network offers a unique playground of intriguing magneto-transport properties and functionalities stemming from the interplay between conducting electrons and intricate magnetic phases. A NiAs-type CrSe is one of the candidates owing to alternate stackings of Cr and Se triangular atomic networks in its crystal structure. While the fabrication of CrSe thin films is indispensable to develop functional devices, studies on its thin-film properties have been limited to date due to the lack of metallic samples. Here, we report on the realization of metallic conductivities of CrSe thin films, which allows us to investigate their intrinsic magneto-transport properties. The metallic sample exhibits a co-occurrence of weak ferromagnetism with perpendicular magnetic anisotropy and antiferromagnetic behavior, indicating the presence of non-coplanar spin structures. In addition, control of the polarity and tilting angle of the non-coplanar spin structure is accomplished by a sign of cooling magnetic fields. The observed non-coplanar spin structure, which can be a source of emergent magnetic field acting on the conducting electrons, highlights the high potential of the triangular lattice antiferromagnet and provides a unique platform for functional thin-film devices composed of NiAs-type derivative Cr chalcogenides and pnictides.

The Photophysics of Diphenyl Polyenes Analyzed by Their Solvatochromism

The solvent-dependent intensity changes in the first UV/Vis absorption band of the three polyenes DPH, DPHb, and ttbP3 dissolved in a hydrocarbon solvent with temperature allow for the conclusion that, at temperatures above 233 K, the two phenyl groups of DPH are rotated out-of-plane to yield a non-coplanar molecular structure. This leads to the conclusion that DPH becomes increasingly less coplanar as the temperature rises above 233 K. When the phenyl groups rotate out-of-plane, the polarizability decreases, and the energy of the first electronic transition increases by an extra value. Therefore, below 233 K, the correlation lines between the absorption energy of the 0–0 component of the UV/Vis absorption band and the solvent polarizability, as measured by the SP values, show bilinear behavior. The unexpected behavior shown by DPH dissolved in tetrachloro- and dichloromethane is discussed. We dedicate this research as a tribute to the very important contribution to the solvent effect made by Prof. Christian Reichardt and also to his generous and altruistic scientific help that he has always shown.

Comprehensive characterization of polyproline tri-helix macrocyclic nanoscaffolds for predictive ligand positioning.

Multivalent ligands hold promise for enhancing avidity and selectivity to simultaneously target multimeric proteins, as well as potentially modulating receptor signaling in pharmaceutical applications. Essential for these manipulations are nanosized scaffolds that precisely control ligand display patterns, which can be achieved by using polyproline oligo-helix macrocyclic nanoscaffolds via selective binding to protein oligomers and cell surface receptors. This work focuses on synthesis and structural characterization of different-sized polyproline tri-helix macrocyclic (PP3M) scaffolds. Through combined analysis of circular dichroism (CD), small- and wide-angle X-ray scattering (SWAXS), electron spin resonance (ESR) spectroscopy, and molecular modeling, a non-coplanar tri-helix loop structure with partially crossover helix ends is elucidated. This structural model aligns well with scanning tunneling microscopy (STM) imaging. The present work enhances the precision of nanoscale organic synthesis, offering prospects for controlled ligand positioning on scaffolds. This advancement paves the way for further applications in nanomedicine through selective protein interaction, manipulation of cell surface receptor functions, and developments of more complex polyproline-based nanostructures.

Synthesis and properties of novel bismaleimide containing allyl group and twisted structure

In this work, a bismaleimide (ABFBMI) monomer with allyl group, cardo, and oxazine structures was synthesized for the first time. The monomer was characterized with the help of Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H NMR), and nuclear magnetic resonance carbon spectroscopy (13C NMR). The curing kinetics and polymerization process were studied using differential scanning calorimetry (DSC) and in-situ FTIR. Thermogravimetry (TGA), DSC and scanning electron microscope (SEM) were used to examine the thermal properties and fracture morphology. The ABFBMI was found to have polymerized through self-catalytic curing. Thermosetting materials (poly(ABFBMI)) underwent structural transformation at high temperatures to form polybenzoxazole resin (cPBO-ABFBMI). Poly(ABFBMI) and cPBO-ABFBMI both have excellent thermal stability. The flexible allyl group side chains enhance the toughness of poly(ABFBMI). The stable twisted non-coplanar and allyl group structure are responsible for the excellent solubility and melt processability of ABFBMI.

Nonreciprocal Antisymmetric Magnetoresistance and Unconventional Hall Effect in a Two-Dimensional Ferromagnet.

Two-dimensional (2D) ferromagnets with high Curie temperatures provide a rich platform for exploring the exotic phenomena of 2D magnetism and the potential of spintronic devices. As a prototypical 2D ferromagnet, Fe5-xGeTe2 has recently been reported to possess a high Curie temperature with Tc ∼ 310 K, making it a promising candidate for advancing 2D nanoelectromechanical systems. However, due to its intricate magnetic ground state and magnetic domains, a thorough study of the transport behavior related to its lattice and domain structures is still lacking. Here, we report a nonreciprocal antisymmetric magnetoresistance in Fe5-xGeTe2 nanoflakes observed under an external magnetic field between 85-120 K. Through a detailed examination of its temperature, field orientation, and sample thickness dependence, we trace its origin to an additional electric field induced by the domain structure. This differs from the previously reported antisymmetric magnetoresistance due to thickness inhomogeneity. Notably, at lower temperatures, we observed an unconventional Hall effect (UHE), which can be attributed to the Dzyaloshinskii-Moriya interaction (DMI) resulting from the non-coplanar magnetic moment structure. The pronounced influence of sample thickness on magneto-transport properties underscores the competition between magnetic anisotropy and DMI in Fe5-xGeTe2 flakes with varying thicknesses. Our findings provide a deeper understanding of the magneto-transport behavior of the exotic magnetic structure in 2D ferromagnetic materials, which may benefit future spintronic device applications.

Possible Topological Hall Effect in a Spin Gapless Semiconducting Mn2CoAl Heusler Compound

Topological Hall effect (THE), induced by the interaction of charge carriers with mesoscopic or microscopic noncoplanar spin structures, holds promising applications in the field of spintronics. In the present study, a giant THE of about 2 μΩ cm at room temperature is reported in a bulk spin gapless semiconducting Mn2CoAl cubic Heusler compound. Temperature‐dependent investigation of magneto‐transport data reveals that the Mn2CoAl has the large THE over a wide temperature range of 2–300 K. The alternating current (AC) susceptibility as a function of magnetic field exhibits a smooth and continuous response rather than any kink or anomaly, suggests that the observed THE in the Mn2CoAl compound results from the interaction of charge carriers with the microscopic noncoplanar spin texture. The observed THE as a function of temperature follows the same behavior as the magnetocrystalline anisotropy (MCA) of the cubic Mn2CoAl, indicating the competition of the MCA with ferromagnetic and antiferromagnetic exchange interactions as the origin of the noncoplanar spin texture and hence THE. Micromagnetic simulations further support the emergence of noncoplanar spin structure as a result of the competition between different energies.

Magnetic anisotropy and planar topological Hall effect in SrMn x Ir1− x O3 films

Strong Coulomb repulsion and spin–orbit coupling are known to give rise to exotic physical phenomena in transition metal oxides. Here, we report magnetic and transport characteristics of (001) oriented epitaxial SrMn x Ir1−x O3 thin films, having both 3d and 5d elements on the perovskite B sites. With the increase of Mn concentration, perpendicular magnetic anisotropy (PMA) decreases gradually in accompany with the magnetic easy axis tilting away from the out-of-plane [001] direction. X-ray absorption spectroscopy reveals that Mn e g electrons preferentially occupy the orbital, which produces the observed PMA in the framework of spin-orbital coupling. A planar topological Hall effect appears in SrMn x Ir1−x O3 films with x about 0.30 when the magnetic field is applied along the current, which is a result of the noncoplanar spin structure due to the competition among the PMA, the magnetic exchange interaction and the Zeeman energy. These results provide an example to show the subtle balance among complex competitions in materials with both strong correlation and spin-orbit coupling.

Topological Hall Effect in (Mn1−xFex)3.25Ge (x = 0.4) Hexagonal Magnet

Topologically protected nontrivial spin structures attract significant interest in condensed matter physics for their utilization in low‐power‐consumption spintronics devices, memory devices, etc. The topological Hall effect (THE) is an additional Hall resistivity in the system arising from real‐space Berry curvature picked up by conduction electron passing through the nontrivial spin texture. Compared to expensive neutron diffraction measurements, THE is often used as a cost‐effective tool to investigate nontrivial spin texture in the materials. In the present manuscript, THE in the (Mn1−xFex)3.25Ge (x = 0.4) alloy is studied using magneto‐transport measurements. Maximum THE is found in the system about 0.65 μΩ cm at 150 K, which is in contrast to the pristine Mn3Ge that has zero THE. The strong temperature variation of THE suggests that the noncoplanar spin structure due to competition among the magneto‐crystalline anisotropy, antiferromagnetic coupling, and ferromagnetic exchange interaction is the main source of THE in the present system. Herein, it is shown that chemical doping can be an effective way to induce THE in the material with vanishing THE in its parent phase.

Spoof surface plasmon polaritons of complementary periodic units with negative group velocity effect

AbstractPeriodically patterned conductor surfaces can transmit electromagnetic modes similar to surface plasmon polaritons, which are called spoof surface plasmon polaritons (SSPPs). In this paper, noncoplanar dentate complementary structure units are proposed. In this case, the fundamental SSPP is split into two modes, of which the mode in the high‐frequency side exhibits negative group velocity (NGV) near the cutoff frequency. The dispersion characteristics of NGV modes can be controlled by manipulating the symmetry of the complementary structure. It is confirmed that the actual transmission wave in the SSPP waveguide is the superposition result of the two split‐mode wave components.