The emergence of a topologically nontrivial vortex-like magnetic structure, the magnetic skyrmion, has launched new concepts for memory devices. Extensive studies have theoretically demonstrated the ability to encode information bits by using a chain of skyrmions in one-dimensional nanostripes. Here, we report experimental observation of the skyrmion chain in FeGe nanostripes by using high-resolution Lorentz transmission electron microscopy. Under an applied magnetic field, we observe that the helical ground states with distorted edge spins evolve into individual skyrmions, which assemble in the form of a chain at low field and move collectively into the interior of the nanostripes at elevated fields. Such a skyrmion chain survives even when the width of the nanostripe is much larger than the size of single skyrmion. This discovery demonstrates a way of skyrmion formation through the edge effect, and might, in the long term, shed light on potential applications.

Herein, the advances in low-dimensional core-shell EM wave absorption materials are outlined and a selection of the most remarkable examples is discussed. The derived key information regarding dimensional design, structural engineering, performance, and structure-function relationship are comprehensively summarized. Moreover, the investigation of the cuttingedge mechanisms is given particular attention. Additional applications, such as oxidation resistance and self-cleaning functions, are also introduced. Finally, insight into what may be expected from this rapidly expanding field and future challenges are presented.

Two-dimensional materials, especially the newly emerging MXene, have attracted numerous interests in the fields of energy conversion/storage and electromagnetic shielding/absorption. However, the inherently inevitable aggregation and absence of magnetic loss of MXene considerably limit its electromagnetic absorption application. The introduction of magnetic component and favorable structural engineering are the alternatives to improve the microwave absorption (MA) performance. Herein, we report a spheroidization strategy to assemble double-shell MXene@Ni microspheres, where the commonly lamellar MXene are reshaped into three-dimensional microspheres that provide the substrate for oriented growth of Ni nanospikes. Whereas this structural feature offers massive accessible active surfaces that effectively promote the dielectric loss ability, the introduction of magnetic Ni nanospikes enables the additional magnetic loss capacity. Benefiting from these merits, the synthesized 3D MXene@Ni microspheres exhibit superior MA performance with the minimum reflection loss value of −59.6 dB at an ultrathin thickness (∼1.5 mm) and effective absorption bandwidth of 4.48 GHz. Moreover, the electron holography results reveal that the high-density anisotropy magnetism plays an important role in the improvement of MA performance, which provides an insight for the design of MXene-based materials as high-efficient microwave absorbers.

Magnetic skyrmion is a nanosized magnetic whirl with nontrivial topology, which is highly relevant for applications on future memory devices. To enable the applications, theoretical efforts have been made to understand the dynamics of individual skyrmions in magnetic nanostructures. However, directly imaging the evolution of highly geometrically confined individual skyrmions is challenging. Here, we report the magnetic field-driven dynamics of individual skyrmions in FeGe nanodisks with diameters on the order of several skyrmion sizes by using Lorentz transmission electron microscopy. In contrast to the conventional skyrmion lattice in bulk, a series of skyrmion cluster states with different geometrical configurations and the fielddriven cascading phase transitions are identified at temperatures far below the magnetic transition temperature. Furthermore, a dynamics, namely the intermittent jumps between the neighboring skyrmion cluster states, is found at elevated temperatures, at which the thermal energy competes with the energy barrier between the skyrmion cluster states.T he complex spin configurations in helimagnets have attracted considerable attention recently, with the topologically stable particle-like spin texture with a size down to the nanoscale, namely magnetic skyrmion, as the focus of interest (1). Magnetic skyrmion is characterized as a nanoscale topological particle producing unconventional spin electronic phenomena (2, 3) that holds great promise for future spintronic devices, including racetrack memory (4), magnetic random access memory, and magnetic sensors (1). Essentially, such schemes rely on the controllable formation and manipulation of individual skyrmions at nanostructured elements with various shapes such as disks, stripes, or wires (5-7). Investigation of skyrmions in confined geometries has therefore become one of the major topics in the field of skyrmion physics (5-10).Unlike ordinary magnetic vortices in microsized soft magnetic disks due to the minimization of the dipolar energy (11), the key ingredient of stabilizing skyrmions in helimagnets is the antisymmetry Dzyaloshinskii−Moriya (DM) interactions originating from the broken inversion symmetry (12). The competition of the DM coupling with ferromagnetic exchange interaction results in periodic helical ground state in helimagnets. Under the action of a magnetic field and temperature, these magnetic helices transfer into skyrmion crystal with triangular lattice configuration, and finally to the field-polarized ferromagnetic state. Notably, both ferromagnetic and DM couplings occur among the neighboring spins and belong to short-range interaction. Thus, it was demonstrated theoretically that skyrmions cluster states, characterized by certain arrangements of limited skyrmions, still persist even in submicrometer objects (8, 13). There, the longrange lattice form of skyrmions in 2D or bulk helimagnets is broken, but a short-ranged ordering with specific geometrical symmetries still remains, and the number of skyrmions in the cluster...

With rapid development of 5G communication technologies, electromagnetic interference (EMI) shielding for electronic devices has become an urgent demand in recent years, where the development of corresponding EMI shielding materials against detrimental electromagnetic radiation plays an essential role. Meanwhile, the EMI shielding materials with high flexibility and functional integrity are highly demanded for emerging shielding applications. Hitherto, a variety of flexible EMI shielding materials with lightweight and multifunctionalities have been developed. In this review, we not only introduce the recent development of flexible EMI shielding materials, but also elaborate the EMI shielding mechanisms and the index for "green EMI shielding" performance. In addition, the construction strategies for sophisticated multifunctionalities of flexible shielding materials are summarized. Finally, we propose several possible research directions for flexible EMI shielding materials in near future, which could be inspirational to the fast-growing next-generation flexible electronic devices with reliable and multipurpose protections as offered by EMI shielding materials.

Magnetic skyrmions are topologically stable whirlpool-like spin textures that offer great promise as information carriers for future spintronic devices. To enable such applications, particular attention has been focused on the properties of skyrmions in highly confined geometries such as one-dimensional nanowires. Hitherto, it is still experimentally unclear what happens when the width of the nanowire is comparable to that of a single skyrmion. Here, we achieve this by measuring the magnetoresistance in ultra-narrow MnSi nanowires. We observe quantized jumps in magnetoresistance versus magnetic field curves. By tracking the size dependence of the jump number, we infer that skyrmions are assembled into cluster states with a tunable number of skyrmions, in agreement with the Monte Carlo simulations. Our results enable an electric reading of the number of skyrmions in the cluster states, thus laying a solid foundation to realize skyrmion-based memory devices.

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Electrostatic doping in materials can lead to various exciting electronic properties, such as metal-insulator transition and superconductivity, by altering the Fermi level position or introducing exotic phases. Cd 3 As 2 , a three-dimensional (3D) analog of graphene with extraordinary carrier mobility, was predicted to be a 3D Dirac semimetal, a feature confirmed by recent experiments. However, most research so far has been focused on metallic bulk materials that are known to possess ultra-high mobility and giant magneto-resistance but limited carrier transport tunability. Here we report on the first observation of a gate-induced transition from band conduction to hopping conduction in single-crystalline Cd 3 As 2 thin films via electrostatic doping by solid electrolyte gating. The extreme charge doping enables the unexpected observation of p-type conductivity in a ∼50-nm-thick Cd 3 As 2 thin film grown by molecular beam epitaxy. More importantly, the gate-tunable Shubnikov-de Haas oscillations and the temperature-dependent resistance reveal a unique band structure and bandgap opening when the dimensionality of Cd 3 As 2 is reduced. This is also confirmed by our first-principle calculations. The present results offer new insights toward nanoelectronic and optoelectronic applications of Dirac semimetals in general and provide new routes in the search for the intriguing quantum spin Hall effect in low-dimension Dirac semimetals, an effect that is theoretically predicted but not yet experimentally realized.