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Magnetic skyrmions are mobile topological spin textures that can be manipulated by different means. Their applications have been frequently discussed in the context of information carriers for racetrack memory devices, which on the other hand, exhibit a skyrmion Hall effect as a result of the nontrivial real-space topology. While the skyrmion Hall effect is believed to be detrimental for constructing racetrack devices, we show here that it can be implemented for realizing a three-terminal skyrmion circulator. In analogy to the microwave circulator, nonreciprocal transportation and circulation of skyrmions are studied both numerically and experimentally. In particular, successful control of the circulating direction of being either clockwise or counterclockwise is demonstrated, simply by changing the sign of the topological charge. Our studies suggest that the topological property of skyrmions can be incorporated for enabling novel spintronic functionalities; the skyrmion circulator is just one example.

Magnetic skyrmion, which is a kind of swirl-like topological protected spin structure, shows great potential in the racetrack memory. So far, this progress is in obstacle by the skyrmion Hall effect which means that the direction of skyrmion motion will deviate from the driving direction. In our work, based on the hybrid skyrmion, we propose a new way to solve the deviation problem. Instead of the acquirement of great nanotechnology to confine the skyrmion in the one-dimensional (1D) potential well, the hybrid skyrmion in a three-layer film can also be guided by only an edge formed through etching the surface layer. The edge will provide a local spatial asymmetry for the skyrmion. This asymmetry can both constrain the skyrmion to a heart shape and equilibrate the moving skyrmion to the etched line. Further simulations confirm that the heart-shaped skyrmion is also available in the multi-racetrack memory. It is thinked that our proposal might be another efficient method to help to solve the skyrmion Hall effect, and the study might be able to contribute to the skyrmion-based device.

We investigated femto- and picosecond-time magnetization dynamics in a ferromagnetic Ni80Fe20 film with varying thicknesses (wedge-shaped film). We observed that the thickness gradient strongly affects the magnetic moment distribution, causing a magnetization reorientation from in-plane to out-of-plane, and formatting a stripe domain (SD) at the thicker end of the wedge. The magnetization dynamics measurements reveal that the part of the film displaying SDs follows a substantially faster demagnetization and magnetization recovery and smaller magnetization quenching compared to the in-plane domain film. The experiments and micromagnetic simulations support that the decrease in relaxation time is caused by a magnetic anisotropy of the films introduced by SD formation. Our results point out that the micromagnetic structure plays an important role in the magnetization dynamics in ferromagnetic films after optically triggered demagnetization.

Chiral magnets endowed with topological spin textures are expected to have promising applications in next-generation magnetic memories. In contrast to the well-studied 2D or 3D magnetic skyrmions, the authors report the discovery of 1D nontrivial magnetic solitons in a transition metal dichalcogenide 2H-TaS2 via precise intercalation of Cr elements. In the synthetic Cr1/3 TaS2 (CTS) single crystal, the coupling of the strong spin-orbit interaction from TaS2 and the chiral arrangement of the magnetic Cr ions evoke a robust Dzyaloshinskii-Moriya interaction. A magnetic helix having a short spatial period of ≈25 nm is observed in CTS via Lorentz transmission electron microscopy. In a magnetic field perpendicular to the helical axis, the helical spin structure transforms into a chiral soliton lattice (CSL) with the spin structure evolution being consistent with the chiral sine-Gordon theory, which opens promising perspectives for the application of CSL to fast-speed nonvolatile magnetic memories. This work introduces a new paradigm to soliton physics and provides an effective strategy for seeking novel 2D magnets.

The gelation properties of three peptides containing different hydrophilic heads, I 3 R, I 3 K and I 3 H, in the presence of group 1B metal salts were investigated in detail. Nanofibers, nanotubes and helical ribbons were obtained in hydrogels of I 3 R/M n+ , I 3 K/M n+ and I 3 H/M n+ , respectively, which were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The nanostructures were not influenced by group 1B metal ions. We proposed a possible self-assembly mechanism based on circular dichroism (CD) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and X-ray diffraction (XRD) measurements. The results indicated that coordination interactions and hydrogen bonding are the main driving forces in the self-assembly process. Additionally, Cu, Ag and Au nanoparticles (NPs) were produced in situ on the surfaces of the nanostructures because peptides with electron-rich groups (amino, multiple hydroxyl) show weak reducing capacity. At the same concentrations, the hydrogels formed by I 3 R and I 3 H with metal ions show higher viscoelasticity than those formed by I 3 K. Furthermore, the hydrogels of I 3 X/M n+ (X = R, K and H) presented good conductivity and printable properties, and various structures, such as characters, triangles, and hearts, were obtained via simple injection.

Skyrmions are nanoscale and topologically protected objects, which are promising candidates for information carriers of magnetic storage devices. To this end, the rapid creation and manipulation of a single skyrmion is required. In this work, a spin-valve device with a single-skyrmion reference layer is considered. Using micromagnetic simulations, we find that a skyrmion is likely to nucleate in the free layer as a picosecond current pulse is applied. In addition, we also demonstrate that the skyrmion in the free layer can be reversed by injecting an alternating current. It is promising that such a study can benefit the development of skyrmion-based storage devices.

With the development of society, the number of all kinds of enterprises continues to increase, but it must also contain some bad businesses, and these bad businesses will cause unnecessary impact on our daily life to a certain extent. To address these problems, an enterprise entity recognition system based on AttentionOCR and the pointer network was proposed, combined with an improved ResNet101-FPN text network and an improved pointer network based on joint extraction of shared parameters. Both of the two optimized models improved their recognition accuracy by 1–2%, and the number of model parameters for entity recognition decreased by 12%. Under the practical application of image access via mobile devices and the improved text recognition and semantic analysis network access to the name of the enterprise, and then returned from the database, relevant information to the user of the enterprise system as a whole for the single image recognition arithmetic average speed in 1 s or so, to sum up, the system under natural scene has stronger robustness, decision making to provide reliable data for the user.

Magnetic skyrmions have been proposed as promising information carriers in the application of spintronics, while the material imperfections are inevitable, thus an understanding of pinning effects on skyrmions in confined geometry is crucial for both fundamental research and development of spintronic devices. Here, we present the interactions of a skyrmion with a point and an extended ring defect, in a Co nanodisk which can be applied in skyrmion oscillator, based on micromagnetic simulations. By comparing with the skyrmion preferred position which is in the nanodisk center without defects, we identify the pinning strength and skyrmion preferred positions with a point defect as a function of skyrmion-defect distance and different local parameters of defect region being considered. The pinning centers range from skyrmion center, domain wall and off-center regions. We find a confinement effect on the skyrmion size with a ring defect. Moreover, we also show the rotation of the skyrmion in the presence of a ring defect, that can lead to a variation of oscillation frequency in a large range. These findings provide a complete understanding of the interaction between skyrmion and defects in a nanodisk and may provide a guidance for the design of skyrmion oscillators.

University identification is one of the important ways to ensure the security management of today’s open campus. It can effectively detect and identify the suspicious person’s identity and ensure the security of the university campus. However, traditional university identity recognition systems have slow detection speeds, relatively low recognition rates, and inability to process low-resolution images. In view of the above problems, this paper proposes a university identity recognition system based on FaceNet and FSRNet. Combining virtual sample generation technology, face rectification algorithm, and improved MTCNN face detection. It effectively improves performance indicators such as detection speed and recognition rate, and provides solutions for low-resolution face images. The experimental results show that compared with the traditional university identity recognition system, the implementation method proposed in this paper improves the recognition rate of unconstrained natural environment by 1–2%, reduces the system face detection time, and effectively resolves low-resolution Facial face image for information restoration.

Controllable manipulation of skyrmion motion is important for next-generation spintronics. Here, a gradient of voltage-controlled magnetic anistropy (VCMA) induced skyrmion motion in a Co/Pt nanotrack was reported using micromagnetic simulations. The results show that a magnetic skyrmion, driven by the gradient of VCMA, can move straightly along the nanotrack without deflection due to boundary effects. The velocity and diameter of the magnetic skyrmion increases in proportion to the gradient of VCMA, which are in agreement with the analytical model. Effects of notch on the VCMA gradient-induced skyrmion motion are also investigated. This work provides an effective approach to drive skyrmion motion, which can give guidance for next-generation spintronic devices.

Recently, magnetic skyrmion bags have been numerically and experimentally discovered in a thick FeGe plate. Here, we systematically investigated the spin eigenmodes of skyrmion bags in a confined magnetic disk. A weak peak at lower frequency is found for the skyrmion bags with Q ≠ 0 rather than skyrmionium due to the reduced rotational symmetry. In addition, it is found that a lot of spin eigenmodes for skyrmion bags which are more complex than the breathing mode of ordinary skyrmion can also be excited due to the inner interaction between skyrmions. Afterward, the spin eigenmodes at different external fields as well as in different disk sizes are further investigated. The results reveal rich physical phenomena and help us understand the interactions between skyrmions well. In addition, it can also be used as a detection and characterization mechanism for skyrmion bags.

Magnetic skyrmions are chiral spin magnetization structures with topological properties and have attracted great interest due to their small size and extremely low manipulation current density in the next generation spintronic devices. In this work, we introduced skyrmion into the magnetic tunnel junction and designed a dumbbell-shaped microwave detector based on skyrmion. It has a very high sensitivity, reaching more than 280000 mV/mW without any external bias field. Moreover, we expand this dumbbell-shaped detector into an array combination, which is expected to increase its sensitivity. Our studies may present guidance for the design of skyrmion based microwave detectors.

An investigation of the angular dependence of the dynamic permeability spectra has been performed. Three Permalloy films with different thickness were used as the study samples that possess the stripe domains. In order to better understand the magnetization distribution in stripe domains, a theoretical approach was proposed to analyze the variation of the resonance intensity of permeability spectra. By fitting the angular dependence of the mu"(max) using a theoretical function, a coefficient K that can be used to evaluate the average value of the periodic function of the anting angle theta in a periodic stripe is obtained. As the film thickness increases, the decrease of the ratio between domain wall width and stripe domain width is happen. This enables that the coefficient K decreases with the increase of film thickness. By deducing this coefficient K, one can estimate the maximum canting angle theta(0) similar to 8 degrees for the Permalloy films in our experiments. (C)2017 Elsevier B. V. All rights reserved.

The 2π isolated chiral skyrmion is a magnetic configuration. Since the total topological charge is zero, the 2π isolated skyrmion driven by a spin-polarized current propagates strictly along the racetrack. The manipulation of 2π-skyrmion, e.g., pinning/depinning at a specific position of the racetrack, is significant. Here, we investigated the 2π-skyrmion pinning in a racetrack using exchange bias. A series of transversal AFM wires were set above the ferromagnetic (FM) racetrack. Spin waves were employed to induce 2π-skyrmion motion to study the dynamics of the 2π-skyrmion pinning. The AFM wires induce exchange bias at the AFM/FM crossing points, which can act as pinning sites. The working window for a 2π-skyrmion in a racetrack was investigated as a function of the exchange bias field, the frequency and amplitude of the oscillating magnetic field for exciting spin waves. The interaction mechanism between the 2π-skyrmion and the exchange bias was also studied. This work may provide guidance for the design of next-generation spintronics.

Additional file 1: Figure S1. Gene ontology analysis shows that haemorrhoids contain many physiological and biochemical abnormalities. (A–F) The target genes of upregulated miRNAs are mainly involved in biological regulation (BP), cell part (CC), and protein binding (MF). (G–L) The target genes of downregulated miRNAs are mainly involved in biological regulation (BP), cell part (CC), and protein binding (MF). Figure S2. Differentially expressed microRNAs (miRNAs) in haemorrhoids have many potential target genes. (A) Target gene prediction results showed that there are 184 potential target genes of significantly upregulated miRNAs (common to both TargetScan7.1 and MirdbV5 databases) and there are 372 potential target genes of significantly downregulated miRNAs (common to both TargetScan7.1 and MirdbV5 databases). (B) and (C) show corresponding potential target genes of significantly upregulated miRNAs. (D) and (E) show corresponding potential target genes of significantly downregulated miRNAs. Figure S3. Endocytosis signalling pathway. Figure S4. Synaptic vesicle cycle signalling pathway.

Twisted skyrmions, whose helicity angles are different from that of Bloch skyrmions and N\'eel skyrmions, have already been demonstrated in experiments recently. In this work, we first contrast the magnetic structure and origin of the twisted skyrmion with other three types of skyrmion including Bloch skyrmion, N\'eel skyrmion and antiskyrmion. Following, we investigate the dynamics of twisted skyrmions driven by the spin transfer toque (STT) and the spin Hall effect (SHE) by using micromagnetic simulations. It is found that the spin Hall angle of the twisted skyrmion is related to the dissipative force tensor and the Gilbert damping both for the motions induced by the STT and the SHE, especially for the SHE induced motion, the skyrmion Hall angle depends substantially on the skyrmion helicity. At last, we demonstrate that the trajectory of the twisted skyrmion can be controlled in a two dimensional plane with a Gilbert damping gradient. Our results provide the understanding of current-induced motion of twisted skyrmions, which may contribute to the applications of skyrmion-based racetrack memories.

FeNi films with the stripe domain (SD) pattern are prepared by electrodeposition and sputtering methods. The magnetic domain, static magnetic parameters, and quality factor, as well as dynamic properties of the two films, are respectively performed. The results show the magnetizations of the film were dependent on the direction of SD, and the rotation of the SD is lagging behind the magnetization reversal. The microwave properties of the SD emerge dynamic hysteresis before the saturation magnetic field. These microwave properties are selectively excited with acoustic mode, optical mode, and spin-wave mode. The frequency and intensity of different resonance modes of stripe domain are determined by the local magnetization. The magnetization variations and the rotation of SD of different modes are further illuminated by the micromagnetic simulation. The magnetic anisotropy and the resonance intensity of permeability of different modes were finally described by the modified resonance equations., 10 pages, 9 figures

We study the angle dependence of the spin wave resonance spectra in FeNi–MgO granular films fabricated by magnetron sputtering, using ferromagnetic resonance technology. Seven Portis-type spin resonances with the same magnetic field spacing are observed when the magnetic field is perpendicular to the film. By varying the field angle θH, we find that there are at least two resonance modes at θH = 14°, indicating that the critical angle θc of the ferromagnetic resonance mode is in the range of 14°–15°. Furthermore, we obtained the exchange stiffness constant and distortion parameter through the surface inhomogeneity model and the volume inhomogeneity model. Moreover, in order to figure out the types of spin wave, we also investigate the dependence of spin wave resonance spectra on temperature, which reveals an excitation of the perpendicular spin standing wave.

Fabricating flexible and large-scale graphene-based films through a simple process to achieve excellent electromagnetic interference (EMI) shielding performance is still a daunting challenge. Herein, the flexible and large-area EMI shielding films with ultrathin coating thickness (i.e., 10 μm) and low coating density (i.e., 2.4 mg/cm2) were fabricated through a simple drop-casting approach by using graphene-based conductive ink at room temperature. With the aid of electromagnetic simulation, the optimal square resistance of conductive film for desirable EMI shielding effectiveness is predicted, avoiding the unnecessary costs of error and trial. To solve the vital issue of poor conductivity of reduced graphene oxide (RGO) arising from defects and the serious agglomeration of each filler in ink, a three-dimensional network was constructed by connecting RGO with flexible one-dimensional (1D) conductive fibers (i.e., carbon nanotubes (CNT) and Ag nanowire (AgNW)). The square resistance of the RGO/CNT@Epoxy/AgNW composite film could reach as low as 1.94 ± 0.63 Ω/sq, which exhibited the shielding effectiveness value of 40 dB at a minimum in 8.2–12.5 GHz. These attributes could satisfy the EMI shielding and flexibly conformal demands of most communication equipment.

Here, we report a facile, one-pot strategy for the fabrication of copper nanoclusters (CuNCs) with orange-red fluorescent emission in the presence of an ultrashort peptide, I3R, and GSH. The effects of the reaction temperature, pH value, GSH and I3R concentrations on the fluorescence properties of I3R-GSH-CuNCs were investigated in detail. By forming compact and ordered self-assembled microstructures, such as nanofibers and helical nanofibers, the as-prepared I3R-GSH-CuNCs exhibit an aggregation-induced emission enhancement effect. Due to the coordination interaction between the Cu core and the capping ligands, which facilitates ligand-to-metal charge transfer (LMCT), the photoluminescence lifetime of I3R-GSH-CuNCs can be prolonged to 19.3 μs. The CD spectra of samples with helical nanofibers exhibit a negative band in the range of 300 ∼ 320 nm, indicating that the CuNCs obtained in this work are chiral, and their chirality was induced by the chiral ligands GSH and I3R. A possible mechanism of the self-assembly-induced emission enhancement is proposed. Furthermore, stable CuNCs were used to fabricate prototype down conversion LEDs with orange emission.

Skyrmion bags are found in liquid crystals and predicted to exist in ferromagnetic films. They are expected to become the information carriers of the new generation racetrack memory due to their high-degree of freedom of topological charge number. Here, we numerically and theoretically investigate the dynamics of skyrmion bags driven by the spin–orbit torque in an infinite ferromagnetic film and a nanostrip with a finite length. It is found that the constant velocity of the skyrmion bag in the ferromagnetic film depends on its topological charge number, while in the case of motion in nanostrips with the skyrmion bag moving along the boundary, the velocity in the first approximation is independent of the topological charge number. The simulation results are in good agreement with the calculation results. Finally, we show that the skyrmion bag can pass through defects and impurities in the nanostrip due to topological protection. Our results reveal the dynamics of skyrmion bags driven by the spin–orbit torque and may also be beneficial for the development of racetrack memory based on skyrmion bags.

The spin torque nano-oscillators (STNOs) have garnered significant interest as a potential nanosized microwave signal generator. However, the core of magnetic radial vortex may be annihilated at the edge with the large spin polarized current density, which leads to unstable STNOs. In this work, we propose new STNOs based on a magnetic radial vortex by overcoming the annihilation of core at the edge, which was realized by adding high magnetic crystal anisotropy materials on the boundary of the nanodisk. It is found that the oscillation frequency reaches up to 2.8 GHz through a circular motion of core of magnetic radial vortex, and the radial vortex-based STNOs have advantages of small size, lower driving current. Our result has important significance to design new STNOs and provide a possible candidate for designing of spintronic devices based on magnetic radial vortex. © 2020 IOP Publishing Ltd.

Chiral 1,2-diols with a high yield could be directly prepared from asymmetric di-hydroxylation of olefins via an eco-friendly and enduring catalyst, in which abundant “chiral pools” of polyoxometalate-ionic liquid were target-designed into the silicic framework (POM-ILS) and well stabilized in aqueous media.

Hemorrhoid is a common and recurrent proctological disease, which is often accompanied by angiogenesis and edema. MicroRNAs in the DLK1-DIO3 imprinted clusters are involved in the development and pathogenesis of mammalian hemorrhoids. Results of the present study indicated multiple, differential expression of DLK1-DIO3 imprinted cluster microRNA between hemorrhoid and normal tissues, where miR-412-5p expression in hemorrhoid tissue was significantly decreased. Fluorescein reporter assays showed that miR-412-5p silenced Xpo1 mRNA expression by targeting its 3'-UTR. Overexpression of miR-412-5p in human umbilical vein endothelial cells (HUVECs) indicated that proliferation, migration and formation of vascular structures in HUVECs were inhibited in vitro. In addition, overexpression of miR-412-5p significantly inhibited Xpo1 expression and promoted upregulation of the p53 protein and its retention in the nucleus. Simultaneously, expression of p66SHC and p16 proteins was activated. In summary, downregulation of endogenous miR-412-5p expression in hemorrhoid vascular endothelial cells leads to high expression of the target gene Xpo1 and translocation of the p53 protein out of the nucleus, rendering it unable to activate p66SHC and p16. This ultimately weakens regulation of the vascular endothelial cell cycle, thereby accelerating the division of hemorrhoid vascular endothelial cells, leading to angiogenesis.

Magnetic bubbles are topologically spin textures that offering the interesting physics and great promise for next-generation information storage technologies. The main obstacles so far are that magnetic bubbles are generated with no field stimuli in new material systems at room temperature. Here, we report the observation of individual magnetic bubbles and its high frequency measurement at room temperature in an exchange-coupled [Co/Pd]4/Py multilayers. We demonstrate that the emergence of magnetic bubbles at remanence can be tuned by the in-plane tilted magnetic field (roughly 3{\deg}) along the film plane at room temperature. High frequency results indicate that the presence of magnetic bubbles leads to broadening of the magnetic permeability spectrum lines (due to the non-uniformity of the magnetic moments). Our findings open the door to the bubble-based spintronics at room temperature in exchange-coupled magnetic multilayers., Comment: 15 pages, 7 figures

Spin-transfer nano-oscillators (STNOs) have a lot of potential as memory devices or microwave sources, but low output power limits their application. Reliable synchronization of a collection of many STNOs would improve a device's power. The authors propose a dumbbell-shaped STNO in which the repulsive force between a magnetic domain wall and a skyrmion provides mechanical synchronization, rather than the traditional phase-locking approach. In principle, there is no limit to the number of STNOs that can be synchronized via this mechanism.

We investigate the static and dynamic magnetic properties of a wedge Permalloy film. The spin distribution of the wedge film depends on the film thickness, ranging from the homogeneous in-plane to the out-of-plane component. The spin reorientation region of the wedge film is determined by using a magnetic force microscopy and magneto-optical Kerr effect measurements as well as the micromagnetic simulation. The dynamic properties of the spin distribution depending on the thickness are investigated by the microwave method. The acoustic and optical mode resonances of the wedge film are controlled by changing the direction of the microwave magnetic field and the stripe domains. The resonance frequency could be influenced by its domain structure and reveals the different anisotropies of the film. The results show that the spin distribution of the stripe domain depending on the thickness can be used to control the spin dispersion and precession frequency of the film for high-frequency applications.

Radial vortex is regarded as one of the information candidates in next generation spintronic devices. Owing to the advantage of topological protected stability, low driven current and small size. In this work, we obtained four types radial vortex in permalloy nanodisk by varying the value of interfacial Dzyaloshinskii-Moriya interaction, and then investigated the current-induced reversal of these magnetic structures using micromagnetic simulation. Four different reversal modes are observed, that is precession mode, breathing mode, mixed mode and disarray mode. Among these modes, the precession mode and breathing mode emerge under the spin-polarized current with different densities moreover the switching time of breathing mode is almost ten times faster than that of precession mode. Our results provide a possible application of designing of radial-vortex-based spintronic devices.

The basic magnetic properties of isolated skyrmions in thin films are fundamental to understanding the physics of magnetic skyrmions and their applications in potential spintronic devices. Here, we study the static and dynamic magnetic properties of isolated skyrmions under an in-plane magnetic field and a magnetic anisotropy gradient using micromagnetic simulations. The results demonstrate that the rotational symmetry of skyrmions is broken under the in-plane field. The radius and domain wall width of the isolated skyrmion exhibits the dependence of the external stimuli. Furthermore, the skyrmion velocity can be effectively modulated by the anisotropy gradient as well as the in-plane field. An analysis model is also derived. This work may provide guidance for the design of next-generation spintronic devices.The basic magnetic properties of isolated skyrmions in thin films are fundamental to understanding the physics of magnetic skyrmions and their applications in potential spintronic devices. Here, we study the static and dynamic magnetic properties of isolated skyrmions under an in-plane magnetic field and a magnetic anisotropy gradient using micromagnetic simulations. The results demonstrate that the rotational symmetry of skyrmions is broken under the in-plane field. The radius and domain wall width of the isolated skyrmion exhibits the dependence of the external stimuli. Furthermore, the skyrmion velocity can be effectively modulated by the anisotropy gradient as well as the in-plane field. An analysis model is also derived. This work may provide guidance for the design of next-generation spintronic devices.

Recently, the stabilization of antiskyrmions in the presence of anisotropic Dzyaloshinskii-Moriya interaction and its dynamics have been investigated. Here, we report the antiskyrmion motion with the combined action of the in-plane magnetic field and perpendicular microwave electric fields. The in-plane magnetic field breaks the rotation symmetry of the antiskyrmion, and the microwave electric field induces the parametric pumping of magnetic anisotropy, leading to antiskyrmion breathing mode. Antiskyrmion moving velocity depends on the frequency, amplitude of anisotropy pumping, and damping constant as well as strength of in-plane field, which reaches the maximum value when the frequency of microwave electric field is in consist with the resonance frequency of antiskyrmion. Moreover, we show that the antiskyrmion motion depends on the direction of magnetic field, where the antiskyrmion Hall angle can be suppressed or enhanced. At a critical direction of magnetic field, the Hall angle is zero. Our results introduce a promising manipulation method for antiskyrmion in both metallic and insulating magnetic materials, and also provide a guidance for the design and application of antiskyrmion-based spintronic devices with lower energy consumption.

Magnetic skyrmionium is a novel magnetization configuration with zero skyrmion number, which is composed by two skyrmions with opposite skyrmion number. Here, we study the dynamics of skyrmionium under an anisotropy gradient. We find that the skyrmionium can be efficiently driven by an anisotropy gradient with moving straightly along the direction of gradient. The skyrmion Hall angle for skyrmionium is close to zero which is much smaller than that of skyrmion. while the speed is much larger. We also demonstrate that the skyrmionium motion depends on the damping cofficient, and the skyrmionium stabilization in the motion can be modulated by narrowing the width of the nanowire. Our work shows a efficient driven method for skyrmionium, which may be promising in the application of skyrmionium based racetrack memory., Comment: 5 pages, 5 figures

Magnetic skyrmions are promising for the application of racetrack memories, logic gates, and other nano-devices, owing to their topologically protected stability, small size, and low driving current. In this work, we propose a skyrmion-based multi-channel racetrack memory where the skyrmion moves in the selected channel by applying voltage-controlled magnetic anisotropy gates. It is demonstrated numerically that a current-dependent skyrmion Hall effect can be restrained by the additional potential of the voltage-controlled region, and the skyrmion velocity and moving channel in the racetrack can be operated by tuning the voltage-controlled magnetic anisotropy, gate position, and current density. Our results offer a potential application of racetrack memory based on skyrmions.

Current-induced domain wall motion (CIDWM) in perpendicularly magnetized materials exhibits large potential in spintronic device applications. The Dzyaloshinskii domain walls (DWs) are nucleated in ultrathin ferromagnetic/heavy-metal bilayers with high perpendicular magnetocrystalline anisotropy (PMA) in the presence of interfacial Dzyaloshinskii–Moriya interaction (DMI). Here, we investigate the effect of magnetic fields on Dzyaloshinskii DWs driven by spin Hall effect (SHE) by means of micromagnetic simulations. We find that magnetic fields can modify the dynamics of Dzyaloshinskii DW. When applying out-of-plane magnetic fields, the velocity of Dzyaloshinskii DWs increases when the field-driven and current-driven DW motion are in same direction, while it decreases with opposite direction. In the case of in-plane longitudinal magnetic fields, Dzyaloshinskii DW velocity increases when the direction of the magnetic field and Dzyaloshinskii DW propagation direction are same, and it decreases when applying opposite in-plane magnetic fields. These manifestations may offer a new method for manipulating Dzyaloshinskii DWs and promise applications in DW-based nanodevices.

Magnetic skyrmion moved by the spin-Hall effect is promising for the application of the generation racetrack memories. However, the Magnus force causes a deflected motion of skyrmion, which limits its application. Here, we create an antiferromagnetic skyrmion by injecting a spin-polarized pulse in the nanostripe and investigate the spin Hall effect-induced motion of antiferromagnetic skyrmion by micromagnetic simulations. In contrast to ferromagnetic skyrmion, we find that the antiferromagnetic skyrmion has three evident advantages: (i) the minimum driving current density of antiferromagnetic skyrmion is about two orders smaller than the ferromagnetic skyrmion; (ii) the velocity of the antiferromagnetic skyrmion is about 57 times larger than the ferromagnetic skyrmion driven by the same value of current density; (iii) antiferromagnetic skyrmion can be driven by the spin Hall effect without the influence of Magnus force. In addition, antiferromagnetic skyrmion can move around the pinning sites due to its p...

An investigation of the annealing influence on the stripe domains structure in Permalloy films has been performed by comparing the static and dynamic magnetic properties. An increasing exchange stiffness constant A ex is found when the annealing temperature rises. The magnetic force microscopy images show that the width of stripe domain increases with the increase of annealing temperature, and the increasing exchange stiffness constant is considered to be the most prominent reason. A perpendicular standing spin-wave model is used to deduce the A ex from the evolution of resonance frequencies, and the A ex increases nearly twice from 7.2 × 10−7 ergs cm−1 for the as-deposited film to 12.9 × 10−7 ergs cm−1 for the film annealing at 400 °C. Micromagnetic calculation is also used to compute the magnetization configuration, and the results agree well with the experimental conclusions.

By using micromagnetic simulations, we studied the dynamic response for different bubble-like magnetic solitons in the [CoPt-CoNi]/Cu/CoNi magnetic multilayer with perpendicular magnetic anisotropy. It is found that a localized spin-polarized current can not only nucleate a dissipative magnetic droplet but also excite the in-plane domain wall (DW) oscillation at the edge of bubble-like magnetic solitons. The dependence of oscillation frequency on current for the dissipative magnetic droplet is hysteretic in the absence of the Dzyaloshinskii–Moriya interactions (DMI). In the presence of DMI, three different bubble-like magnetic solitons are excited: (1) singular magnetic droplet, (2) pseudonormal magnetic droplet, (3) dynamical skyrmion. Meanwhile, the oscillation frequencies of these magnetic solitons have different response as current density varies. These results open up new possibilities for the applications of magnetic soliton-based spin transfer nano-oscillators.

By micromagnetic simulation, we investigated the effect of the Dzyaloshinskii–Moriya interaction (DMI) on the static and dynamic characteristics of a 360° domain wall. Simulation results show that both the energy and the size of a 360° domain wall decrease with the increase of DMI intensity. In the presence of DMI, the stable motion of a 360° domain wall can be either along the +x direction or −x direction depending on the sign of the DMI. For stable motion, the maximum velocity of a 360° domain wall is 19.87% larger than that without the DMI. Increasing the current density beyond the Walker threshold, conversion between the 360° domain wall state and the vortex state was observed. Further increasing the current density, the proliferation of 360° domain walls becomes possible. Moreover, the 360° domain wall becomes more flexible and easier to pass a notch by considering the DMI. These findings may offer guidance for the development of 360° domain wall-based racetrack memories.