Journal articles: 'Skyrmion dynamics'

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Yu, X. Z., D. Morikawa, K. Nakajima, K. Shibata, N. Kanazawa, T. Arima, N. Nagaosa, and Y. Tokura. "Motion tracking of 80-nm-size skyrmions upon directional current injections." Science Advances 6, no. 25 (June 2020): eaaz9744. http://dx.doi.org/10.1126/sciadv.aaz9744.

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Nanometer-scale skyrmions are prospective candidates for information bits in low–power consumption devices owing to their topological nature and controllability with low current density. Studies on skyrmion dynamics in different classes of materials have exploited the topological Hall effect and current-driven fast motion of skyrmionic bubbles. However, the small current track motion of a single skyrmion and few-skyrmion aggregates remains elusive. Here, we report the tracking of creation and extinction and motion of 80-nm-size skyrmions upon directional one–current pulse excitations at low current density of the order of 109 A m−2 in designed devices with the notched hole. The Hall motion of a single skyrmion and the torque motions of few-skyrmion aggregates have been directly revealed. The results exemplify low–current density controls of skyrmions, which will pave the way for the application of skyrmions.

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Shimojima, Takahiro, Asuka Nakamura, Xiuzhen Yu, Kosuke Karube, Yasujiro Taguchi, Yoshinori Tokura, and Kyoko Ishizaka. "Nano-to-micro spatiotemporal imaging of magnetic skyrmion’s life cycle." Science Advances 7, no. 25 (June 2021): eabg1322. http://dx.doi.org/10.1126/sciadv.abg1322.

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Magnetic skyrmions are self-organized topological spin textures that behave like particles. Because of their fast creation and typically long lifetime, experimental verification of skyrmion’s creation/annihilation processes has been challenging. Here, we successfully track skyrmion dynamics in defect-introduced Co9Zn9Mn2 by using pump-probe Lorentz transmission electron microscope. Following the nanosecond photothermal excitation, we resolve 160-nm skyrmion’s proliferation at <1 ns, contraction at 5 ns, drift from 10 ns to 4 μs, and coalescence at ~5 μs. These motions relay the multiscale arrangement and relaxation of skyrmion clusters in a repeatable cycle of 20 kHz. Such repeatable dynamics of skyrmions, arising from the weakened but still persistent topological protection around defects, enables us to visualize the whole life of the skyrmions and demonstrates the possible high-frequency manipulations of topological charges brought by skyrmions.

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Shu, Yun, Qianrui Li, Jing Xia, Ping Lai, Zhipeng Hou, Yonghong Zhao, Degang Zhang, Yan Zhou, Xiaoxi Liu, and Guoping Zhao. "Realization of the skyrmionic logic gates and diodes in the same racetrack with enhanced and modified edges." Applied Physics Letters 121, no. 4 (July 25, 2022): 042402. http://dx.doi.org/10.1063/5.0097152.

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Magnetic skyrmions are topological quasiparticles with nanoscale size and high mobility, which have potential applications in information storage and spintronic devices. Here, we computationally investigate the dynamics of isolated skyrmions in a ferromagnetic racetrack, where magnetic properties of the edges are enhanced and modified, forming a channel with lower magnetic anisotropy for skyrmion motion. It is found that the rectangular notch at the edge can have a pinning effect on the skyrmion and enrich the dynamics of the skyrmion. Based on the racetrack with modified edges and the notch, we design a racetrack that realizes the skyrmionic logic AND, OR, and NOT gates as well as the diode in the same magnetic racetrack. It is found that the driving current density could be much smaller than those used in previous designs of skyrmion-based logic gates. By slightly altering the shape of the racetrack, we also design the NAND and NOR gates. Finally, we study the feasibility of our design at finite temperatures. Our results may contribute to the design of nonvolatile spintronic devices with integrated multiple functions and ultra-low energy consumption.

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Zhao, Xuebing, Chiming Jin, Chao Wang, Haifeng Du, Jiadong Zang, Mingliang Tian, Renchao Che, and Yuheng Zhang. "Direct imaging of magnetic field-driven transitions of skyrmion cluster states in FeGe nanodisks." Proceedings of the National Academy of Sciences 113, no. 18 (April 5, 2016): 4918–23. http://dx.doi.org/10.1073/pnas.1600197113.

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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 field-driven 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.

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Lin, Jia-Qiang, Ji-Pei Chen, Zhen-Yu Tan, Yuan Chen, Zhi-Feng Chen, Wen-An Li, Xing-Sen Gao, and Jun-Ming Liu. "Manipulation of Skyrmion Motion Dynamics for Logical Device Application Mediated by Inhomogeneous Magnetic Anisotropy." Nanomaterials 12, no. 2 (January 16, 2022): 278. http://dx.doi.org/10.3390/nano12020278.

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Magnetic skyrmions are promising potential information carriers for future spintronic devices owing to their nanoscale size, non-volatility and high mobility. In this work, we demonstrate the controlled manipulation of skyrmion motion and its implementation in a new concept of racetrack logical device by introducing an inhomogeneous perpendicular magnetic anisotropy (PMA) via micromagnetic simulation. Here, the inhomogeneous PMA can be introduced by a capping nano-island that serves as a tunable potential barriers/well which can effectively modulate the size and shape of isolated skyrmion. Using the inhomogeneous PMA in skyrmion-based racetrack enables the manipulation of skyrmion motion behaviors, for instance, blocking, trapping or allowing passing the injected skyrmion. In addition, the skyrmion trapping operation can be further exploited in developing special designed racetrack devices with logic AND and NOT, wherein a set of logic AND operations can be realized via skyrmion–skyrmion repulsion between two skyrmions. These results indicate an effective method for tailoring the skyrmion structures and motion behaviors by using inhomogeneous PMA, which further provide a new pathway to all-electric skyrmion-based memory and logic devices.

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Bao, Bei, Mingming Yang, and Ming Yan. "Asymmetric Motion of Magnetic Skyrmions in Ferromagnetic Nanotubes Induced by a Magnetic Field." Symmetry 14, no. 6 (June 9, 2022): 1195. http://dx.doi.org/10.3390/sym14061195.

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Magnetic skyrmions, featuring topological stability and low driving current density, are believed to be a promising candidate of information carriers. One of the obstacles to application is the skyrmion Hall effect, which can lead to the annihilation of moving skyrmions at the lateral boundary of thin-film tracks. In order to resolve this issue, it was recently proposed to exploit ferromagnetic nanotubes as alternative skyrmion guides. In this work, we investigate the field-effect of current-driven skyrmion motion in nanotubes using micromagnetic simulations. It is found that, in the presence of an axial field, the skyrmion motion becomes asymmetric in tubes. This is fundamentally different from the flat strip, in which a field has little influence on the skyrmion dynamics. Based on the dissipation tensor determined by the spin texture of the skyrmions, the solution of the Thiele equation is obtained, yielding a perfect match with simulations. We argue that the asymmetry of the skyrmion dynamics originates from the curvature of the nanotube.

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Coelho, Rodrigo C. V., Mykola Tasinkevych, and Margarida M. Telo da Gama. "Dynamics of flowing 2D skyrmions." Journal of Physics: Condensed Matter 34, no. 3 (October 29, 2021): 034001. http://dx.doi.org/10.1088/1361-648x/ac2ca9.

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Abstract We investigate, numerically, the effects of externally imposed material flows on the structure and temporal evolution of liquid crystal (LC) skyrmions. The dynamics of a 2D system of skyrmions is modeled using the Ericksen–Leslie theory, which is based on two coupled equations, one for material flow and the other for the director field. As the time scales of the velocity and director fields differ by several orders of magnitude for realistic values of the system parameters, we have simplified the calculations by assuming that the velocity relaxes instantaneously when compared to the relaxation of the director field. Thus, we have used a finite-differences method known as artificial compressibility with adaptive time step to solve the velocity field and a fourth-order Runge-Kutta method for the director field. We characterized the skyrmion shape or configuration as a function of the time and the average velocity of the flow field. We found that for velocities above a certain threshold, the skyrmions stretch in the direction perpendicular to the flow, by contrast to the regime of weak flows where the skyrmions stretch along the streamlines of the flow field. These two regimes are separated by an abrupt (first-order) dynamical transition, which is robust with respect to e.g., the LC elastic anisotropy. Additionally, we have found how the presence of a second skyrmion affects the evolution of the shape of the skyrmions, by comparing the evolution of pairs of skyrmions to the evolution of a single-skyrmion.

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Coelho, Rodrigo C. V., Mykola Tasinkevych, and Margarida M. Telo da Gama. "Dynamics of flowing 2D skyrmions." Journal of Physics: Condensed Matter 34, no. 3 (October 29, 2021): 034001. http://dx.doi.org/10.1088/1361-648x/ac2ca9.

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Abstract We investigate, numerically, the effects of externally imposed material flows on the structure and temporal evolution of liquid crystal (LC) skyrmions. The dynamics of a 2D system of skyrmions is modeled using the Ericksen–Leslie theory, which is based on two coupled equations, one for material flow and the other for the director field. As the time scales of the velocity and director fields differ by several orders of magnitude for realistic values of the system parameters, we have simplified the calculations by assuming that the velocity relaxes instantaneously when compared to the relaxation of the director field. Thus, we have used a finite-differences method known as artificial compressibility with adaptive time step to solve the velocity field and a fourth-order Runge-Kutta method for the director field. We characterized the skyrmion shape or configuration as a function of the time and the average velocity of the flow field. We found that for velocities above a certain threshold, the skyrmions stretch in the direction perpendicular to the flow, by contrast to the regime of weak flows where the skyrmions stretch along the streamlines of the flow field. These two regimes are separated by an abrupt (first-order) dynamical transition, which is robust with respect to e.g., the LC elastic anisotropy. Additionally, we have found how the presence of a second skyrmion affects the evolution of the shape of the skyrmions, by comparing the evolution of pairs of skyrmions to the evolution of a single-skyrmion.

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Brearton, Richard, Maciej W. Olszewski, Shilei Zhang, Morten R. Eskildsen, Charles Reichhardt, Cynthia J. O. Reichhardt, Gerrit van der Laan, and Thorsten Hesjedal. "Skyrmions in anisotropic magnetic fields: strain and defect driven dynamics." MRS Advances 4, no. 11-12 (2019): 643–50. http://dx.doi.org/10.1557/adv.2019.43.

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ABSTRACTMagnetic skyrmions are particle-like, topologically protected magnetization entities that are promising candidates for information carriers in racetrack-memory schemes. The transport of skyrmions in a shift-register-like fashion is crucial for their embodiment in practical devices. Recently, we demonstrated experimentally that chiral skyrmions in Cu2OSeO3 can be effectively manipulated by a magnetic field gradient, leading to a collective rotation of the skyrmion lattice with well-defined dynamics in a radial field gradient. Here, we employ a skyrmion particle model to numerically study the effects of resultant shear forces on the structure of the skyrmion lattice. We demonstrate that anisotropic peak broadening in experimentally observed diffraction patterns can be attributed to extended linear regions in the magnetic field profile. We show that topological (5-7) defects emerge to protect the six-fold symmetry of the lattice under the application of local shear forces, further enhancing the stability of proposed magnetic field driven devices.

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Li, Yang, and Hua Pang. "The skyrmion annihilations induced by local reversal of background field in a skyrmion lattice." Journal of Physics D: Applied Physics 55, no. 20 (February 22, 2022): 205303. http://dx.doi.org/10.1088/1361-6463/ac4a39.

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Abstract The understanding of the creation and annihilation dynamics of a magnetic skyrmion is significant due to its potential applications in information storage and spintronics. Although there have been extensive investigations on the annihilation of isolated skyrmions, topological annihilation in a periodic skyrmion lattice is a more complex process. We report a micromagnetic simulation study about the annihilation process of a two-dimensional (2D) skyrmion triangular lattice triggered by a uniform field H REV of comparable size to the skyrmion, which is opposite to the direction of the background field, revealing two annihilation modes. When the H REV center is within the range of a skyrmion, the neighboring skyrmions annihilate in-situ, while the center is between adjacent skyrmions, an anti-skyrmion is induced in the interstitial region. Both mechanisms tend to experience the intermediate topological vortex or antivortex structure, and the spin system undergoes a long period of relaxation to reach a stable state after the topological charge is stabilized. Our results present a local annihilation scheme that is easy to achieve in a 2D skyrmion lattice and highlight the role of interaction between skyrmions in the transformation between different kinds of topological defects.

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Liu, Jiahao, Zidong Wang, Teng Xu, Hengan Zhou, Le Zhao, Soong-Guen Je, Mi-Young Im, Liang Fang, and Wanjun Jiang. "The 20-nm Skyrmion Generated at Room Temperature by Spin-Orbit Torques." Chinese Physics Letters 39, no. 1 (January 1, 2022): 017501. http://dx.doi.org/10.1088/0256-307x/39/1/017501.

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The discovery of magnetic skyrmions provides a promising pathway for developing functional spintronic memory and logic devices. Towards the future high-density memory application, nanoscale skyrmions with miniaturized diameters, ideally down to 20 nm are required. Using x-ray magnetic circular dichroism transmission microscopy, nanoscale skyrmions are observed in the [Pt/Co/Ir]15 multilayer at room temperature. In particular, small skyrmions with minimum diameters approaching 20 nm could be generated by the current-induced spin-orbit torques. Through implementing material specific parameters, the dynamic process of skyrmion generation is further investigated by performing micromagnetic simulations. According to the simulation results, we find that both the tube-like Néel-type skyrmions and the bobber-like Néel-type skyrmions can be electrically generated. In particular, the size of the bobber-like Néel-type skyrmions can be effectively reduced by the spin-orbit torques, which leads to the formation of 20 nm Néel-type skyrmions. Our findings could be important for understanding the formation dynamics of nanoscale Néel-type spin textures, skyrmions and bobber in particular, which could also be useful for promoting nanoscale skyrmionic memories and logic devices.

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Zhong, Anruo, Xiaoming Lan, Yangfan Hu, and Biao Wang. "Dynamics and stability of skyrmions in a bent nano-beam." New Journal of Physics 24, no. 3 (March 1, 2022): 033019. http://dx.doi.org/10.1088/1367-2630/ac3a82.

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Abstract Magnetic skyrmions are attracting much attention due to their nontrivial topology and high mobility to electric current. Nevertheless, suppression of the skyrmion Hall effect and maintaining high velocity of skyrmions with low energy cost are two major challenges concerning skyrmion-based spintronic devices. Here we show theoretically that in a nano-beam suffering appropriate bending moment, both Bloch-type and Néel-type skyrmions move with a vanishing Hall angle under a current density smaller than that required when the bending is absent. Moreover, bending alone can be used to move skyrmions, whose velocity is solved analytically from the Thiele equation. Generally speaking, inhomogeneous elastic fields affect the stability and dynamics of skyrmions, where the local stability is dominantly determined by the local bulk stress. These findings throw new light on how to drive skyrmions in a straight line with lower energy cost, which is vital for utilizing skyrmions as information carriers.

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Wu, Kai, Sheng Yang, Yuelei Zhao, Xue Liang, Xiangjun Xing, and Yan Zhou. "Tunable skyrmion–edge interaction in magnetic multilayers by interlayer exchange coupling." AIP Advances 12, no. 5 (May 1, 2022): 055210. http://dx.doi.org/10.1063/5.0084546.

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Magnetic skyrmions are appealing for applications in emerging topological spintronic devices. However, when magnetic skyrmions in a nanowire are driven by an in-plane current, a transverse Magnus force deflects their trajectories from the current direction, which tends to push the skyrmion toward the edge. If the current density is exceedingly large, the skyrmion will be annihilated around the edge, leading to a greatly reduced propagation distance and a maximum speed of the skyrmion, which is detrimental to skyrmion-based spintronic applications. Here, we prepare a magnetic multilayer Ta/[Pt/Co]3/Ru/[Co/Pt]3 and tailor the interlayer exchange coupling strength by varying the thickness of the Ru layer. Based on the magneto-optic Kerr effect microscope, we find that the skyrmion–edge interaction is tunable by the interlayer exchange coupling strength, namely, the strength of the repulsive potential from the film edge is tailored by the interlayer exchange coupling strength. Our results unveil the significant role of the interlayer exchange coupling in skyrmion dynamics.

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Ahrens, Valentin, Luca Gnoli, Domenico Giuliano, Simon Mendisch, Martina Kiechle, Fabrizio Riente, and Markus Becherer. "Skyrmion velocities in FIB irradiated W/CoFeB/MgO thin films." AIP Advances 12, no. 3 (March 1, 2022): 035325. http://dx.doi.org/10.1063/9.0000287.

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In recent years magnetic skyrmions attracted great attention for the possibility to move them with low current density, their intrinsic stability and their robustness against defects and edge roughness compared to other magnetic textures. For applications, it is very important to be able to influence the behaviour of skyrmions locally. In this article, we present an evaluation on the effects of FIB Ga+ irradiation on skyrmion motion in W/CoFeB/MgO thin films. The influence of FIB irradiation is evaluated both, in terms of modification of the skyrmion Hall angle and the skyrmion velocity. An overview of the effects of the pulsing parameters on the skyrmion motion, shows low influence of the pulses rise-time and an external magnetic field. In addition the analysis after the irradiation shows that it influences notably the dynamics of skyrmions. In the irradiated zone the speed and angle of motion of these magnetic textures are strongly reduced.

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Trukhanova, Mariya Iv. "Quantum hydrodynamics approach for the research of magnetic skyrmions." Modern Physics Letters B 34, no. 18 (June 2, 2020): 2050204. http://dx.doi.org/10.1142/s0217984920502048.

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We propose a new approach of many-particle quantum hydrodynamics to describe a system of interacting magnetic skyrmions in the external fields. The model is based on the description of skyrmions as a fluid of point-like particles. The equations of many-particle quantum hydrodynamics are obtained for a system of skyrmions with induced dipole moments and charges. The dipole–dipole interaction between dipoles and the Coulomb interaction between charges are taken into account. The influence of quantum effects in the form of the Bohm quantum potential is obtained. The contribution of Magnus effect to the dynamics of dipoles current density is predicted. The electron–skyrmion interactions are considered, based on a two-fluid model of quantum hydrodynamics with separate description of spin-up and spin-down electrons on the background of skyrmion lattice. The proposed model can be further used to study the dynamical effects in a system of skyrmions in the external fields.

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Dai, Y. Y., H. Wang, T. Yang, and Z. D. Zhang. "Resonant excitation of coupled skyrmions by spin-transfer torque." International Journal of Modern Physics B 30, no. 02 (January 20, 2016): 1550254. http://dx.doi.org/10.1142/s0217979215502549.

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Resonant excitations of coupled skyrmions in Co/Ru/Co nanodisks activated by spin-transfer torque (STT) have been studied by micromagnetic simulations. It is found that STT is an effective method to manipulate skyrmion dynamics. Unlike the dynamics driven by a microwave field, two skyrmions with opposite chiralities move synchronously in the same direction when they are driven by STT, which makes it easier to observe the dynamics of coupled skyrmions in experiments. Resonant excitations of coupled skyrmions can be controlled by changing the frequency or amplitude ratio of a dual-frequency alternating current (AC). In addition, the magnetostatic interaction between the two skyrmions plays an important role in the dynamics of coupled skyrmions.

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Davis, Timothy J., David Janoschka, Pascal Dreher, Bettina Frank, Frank-J. Meyer zu Heringdorf, and Harald Giessen. "Ultrafast vector imaging of plasmonic skyrmion dynamics with deep subwavelength resolution." Science 368, no. 6489 (April 23, 2020): eaba6415. http://dx.doi.org/10.1126/science.aba6415.

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Plasmonic skyrmions are an optical manifestation of topological defects in a continuous vector field. Identifying them requires characterization of the vector structure of the electromagnetic near field on thin metal films. Here we introduce time-resolved vector microscopy that creates movies of the electric field vectors of surface plasmons with subfemtosecond time steps and a 10-nanometer spatial scale. We image complete time sequences of propagating surface plasmons as well as plasmonic skyrmions, resolving all vector components of the electric field and their time dynamics, thus demonstrating dynamic spin-momentum coupling as well as the time-varying skyrmion number. The ability to image linear optical effects in the spin and phase structures of light in the single-nanometer range will allow for entirely novel microscopy and metrology applications.

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Andrade Santece, Isaac, Josiel Carlos Souza Gomes, Danilo Toscano, Maxwel Gama Monteiro Jr., João Paulo Almeida de Mendonça, Clodoaldo Irineu Levartoski de Araujo, Fernando Sato, Sidiney De Andrade Leonel, and Pablo Zimmermann Coura. "Quantitative behavior study of velocity, radius and topological charge on skyrmion/edge interaction dynamics on Co/Pt nanotrack." Quarks: Brazilian Electronic Journal of Physics, Chemistry and Materials Science 3, no. 1 (November 28, 2020): 50–65. http://dx.doi.org/10.34019/2674-9688.2020.v3.31402.

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Skyrmions are considered promising candidates to be the information carriers in the next generation of data storage and logic devices, due to its stability and easy control under the application of an electric current. For future technological applications in spintronic devices, it is important to study the properties behavior of these topological excitations during its movement on magnetic nanotracks, specially because in ferromagnetic materials they suffer a kind of magnus effect which tends to spell the skyrmion through the borders, preventing its transport throughout the nanotrack. We used micromagnetic simulations to study the dynamics of a skyrmion on a magnetic nanotrack induced by a spin polarized electric current. We considered thin magnetic nanotrack made of cobalt and platinum multilayers, whose magnetic state is perpendicular to the track plane and contain a single Néel-type Skyrmion. To describe this magnetic system, we used a Hamiltonian containing exchange, Dzyaloshinskii-Moriya, perpendicular magnetic anisotropy and dipole-dipole interactions. In our study we observed the well-known Skyrmion Hall effect and changes in the structure of the skyrmion when it approaches of the border. This alteration can be measured by determining the radius and the topological charge of the Skyrmion. Our simulation results show that both the radius and the topological charge decrease when it approaches of the border. Our study also demonstrates that the skyrmion-border interaction is repulsive, but there is a minimum distance from the border at which the interaction becomes attractive. If the skyrmion exceeds this critical position yc, it will be attracted and annihilated at the border of the nanotrack. We also performed simulations to obtain the limit value jc of the applied current density that the skyrmion can be transported along of the nanotrack without escaping from the side edge. From a technological point of view for possible applications in spintronic devices, the estimate of jc is of crucial importance.

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Choi, Byoung, Mukesh Aryal, Minyeong Choi, and Yang-Ki Hong. "Spin–orbit torque driven nano-oscillators based on synthetic Néel-like skyrmion in magnetic tunnel junction." AIP Advances 12, no. 5 (May 1, 2022): 055013. http://dx.doi.org/10.1063/5.0088199.

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A synthetic skyrmion-based magnetic tunnel junction spintronic nano-oscillator is proposed. The oscillator consists of a Pt/Co/AlOx/Co heterostructure. It exploits the high-frequency eigenoscillations of a synthetic chiral nanomagnet, which is imprinted in the Pt/Co layer by the local manipulation of the magnetic anisotropy and interfacial Dzyaloshinskii–Moriya interaction. This synthetic nanomagnet has the spin texture equivalent to the Néel skyrmion, and its topological stabilization remains resilient with respect to the thermal fluctuations at finite temperatures. The oscillator is activated by spin Hall effect-induced spin–orbit torques, and an eigenoscillation with a frequency of ∼2.5 GHz is achieved. When the drive current exceeds a threshold value, the eigenfrequency shifts toward lower frequencies. This redshift is associated with the transition of skyrmion dynamics, in which its eigenmode evolves from the counter-clockwise rotation mode to a complex hybrid mode. Our result verifies the working performance of the proposed synthetic skyrmion-based oscillator and suggests promising prospects for using such artificial nanomagnets in future spintronic applications. It is also found that the synthetic skyrmions are topologically protected from annihilation under high drive currents and finite temperatures, and this resilience, thus, offers new opportunities to better design next generation skyrmion-based spintronic devices.

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Zhao, Xuefeng, Di Wang, Hao Zhang, Long Liu, Huai Lin, Ziwei Wang, Xueying Zhang, et al. "Tailoring skyrmion motion dynamics via magnetoelectric coupling: Toward highly energy-efficient and reliable non-volatile memory applications." Journal of Applied Physics 132, no. 8 (August 28, 2022): 084902. http://dx.doi.org/10.1063/5.0103237.

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Owing to the intriguing physical properties and significant spintronic applications, magnetic skyrmions have recently drawn intensive attention. Particularly, the skyrmion-based non-volatile memory (Sky-NVM) devices promise to be spintronic building blocks with high efficiency. However, tailoring Sky-NVM to achieve an energy-efficient and reliable operation in a synthetic, CMOS compatible, and magnetic-field-free integration is a challenging issue. Here, we report a new type of compact Sky-NVM with tailored skyrmion motion dynamics via in-plane strain gradient engineering. The skyrmion motion is merely driven by an in-plane electric field utilizing the magnetoelectric coupling effect, and the programmable switching is realized by gate biasing the potential barrier height via a voltage-controlled magnetic anisotropy. The proposed device is CMOS process compatible, and the comprehensive micromagnetic simulation results demonstrate that by applying a 0.3 V in-plane voltage combined with −0.17 V gate voltage, its write latency and the energy consumption reach 5.85 ns and 4.77 aJ/bit, respectively, superior to the state-of-the-art counterparts. Our work paves a new path toward ultra-low-power spintronic memory devices.

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MAITY, ARUN. "SKYRME MODEL OF BARYONS AND WEAK RADIATIVE DECAYS." International Journal of Modern Physics A 09, no. 19 (July 30, 1994): 3353–65. http://dx.doi.org/10.1142/s0217751x94001321.

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We study the weak radiative decays of baryons when these are considered to be composed of baby Skyrmions. Weak interaction gauge bosons take a prominent role when a baby Skyrmion interacting with such a boson governs the main dynamics. This mechanism effectively gives rise to the pole model where the parity-conserving and parity-violating poles are not arbitrary but are dictated by the mechanism itself.

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Castillo-Sepúlveda, Sebastián, Javier A. Vélez, Rosa M. Corona, Vagson L. Carvalho-Santos, David Laroze, and Dora Altbir. "Skyrmion Dynamics in a Double-Disk Geometry under an Electric Current." Nanomaterials 12, no. 18 (September 6, 2022): 3086. http://dx.doi.org/10.3390/nano12183086.

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In this work, we present an analysis of skyrmion dynamics considering Dzyaloshinskii–Moriya interactions in an STNO device with a double-disk geometry. Three regimes were observed as a function of geometric parameters and the electric current density: (i) the skyrmion is annihilating at the system’s border; (ii) the skyrmion moves in a non-circular trajectory alternating its position between the two disks, and (iii) the skyrmion only rotates inside a one-disk subsystem. For the annihilation state, we found that the transient time decays within a stretched exponential law as a function of the electric current. Our results show a 2D state diagram that can guide new experimental work in order to obtain these specific behaviors for new applications based on skyrmion dynamics.

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Chen, Xing, Wang Kang, Daoqian Zhu, Xichao Zhang, Na Lei, Youguang Zhang, Yan Zhou, and Weisheng Zhao. "Skyrmion dynamics in width-varying nanotracks and implications for skyrmionic applications." Applied Physics Letters 111, no. 20 (November 13, 2017): 202406. http://dx.doi.org/10.1063/1.5005953.

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ZUK, JOSEF A. "ASYMPTOTIC BEHAVIOUR OF THE VACUUM ENERGY FOR SMALL SKYRMIONS." International Journal of Modern Physics A 05, no. 18 (September 20, 1990): 3549–97. http://dx.doi.org/10.1142/s0217751x90001549.

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Various schemes for deriving effective Lagrangians, involving both quark and meson degrees of freedom, which are intermediate between QCD and low-energy pion dynamics have been proposed. While integration over the fermion fields within the framework of renormalized field theory leads to a vacuum instability, physically reasonable results are obtained for the theory taken with finite cut-off. In principle, properties of the nucleon, such as its mass, can be obtained from a self-consistent calculation in the Skyrmion sector. This procedure can be simplified by implementing an analytical approximation for the fermion vacuum energy which plays a central role. We discuss such an approximation, and use it to calculate exactly the asymptotic behaviour of the vacuum energy for small Skyrmions. It is found that, unlike in the renormalized theory, its functional dependence on the Skymion radius in this limit depends on the characteristics of the Skyrmion profile and choice of regularization scheme; however, the cut-off field theory exhibits no vacuum instability.

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Zhao, Rongzhi, Wenchao Chen, Chenglong Hu, Luyang Chen, Jian Zhang, Xianguo Liu, Xuefeng Zhang, and Mi Yan. "Tuning Resonance Frequency of Spin Wave Localized in an Isolated Skyrmion by Magnetoelectric Couplings." SPIN 09, no. 03 (May 20, 2019): 1950009. http://dx.doi.org/10.1142/s2010324719500097.

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Understanding the dynamic behavior of an isolated skyrmion with external perturbations has been obstructed due to the difficulty in experimentally observing such an instantaneous phenomenon within picoseconds. Herein, we theoretically investigated the spin-transfer-torque-induced dynamics of an isolated skyrmion excited by external nanosecond-pulse perturbations. It is found that a redshift of the resonant frequency appears under a pulse polarized current with [Formula: see text][Formula: see text]A/m2 and [Formula: see text][Formula: see text]GHz, while a blueshift is presented under a combined perturbation of the pulse polarized current and an out-of-plane ac magnetic field. The physic origins of the redshift and the blueshift are ascribed to the increased average energy of system from [Formula: see text][Formula: see text]J to [Formula: see text][Formula: see text]J and integer multiple (twofold and fourfold) oscillation frequencies of total energy, respectively. The present study could thus provide an insight to the micromagnetic dynamics of skyrmion under the magnetoelectric couplings.

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26

Lee, Oscar, Jan Sahliger, Aisha Aqeel, Safe Khan, Shinichiro Seki, Hidekazu Kurebayashi, and Christian H. Back. "Tunable gigahertz dynamics of low-temperature skyrmion lattice in a chiral magnet." Journal of Physics: Condensed Matter 34, no. 9 (December 13, 2021): 095801. http://dx.doi.org/10.1088/1361-648x/ac3e1c.

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Abstract Recently, it has been shown that the chiral magnetic insulator Cu2OSeO3 hosts skyrmions in two separated pockets in temperature and magnetic field phase space. It has also been shown that the predominant stabilization mechanism for the low-temperature skyrmion (LTS) phase is via the crystalline anisotropy, opposed to temperature fluctuations that stabilize the well-established high-temperature skyrmion (HTS) phase. Here, we report on a detailed study of LTS generation by field cycling, probed by GHz spin dynamics in Cu2OSeO3. LTSs are populated via a field cycling protocol with the static magnetic field applied parallel to the ⟨100⟩ crystalline direction of plate and cuboid-shaped bulk crystals. By analyzing temperature-dependent broadband spectroscopy data, clear evidence of LTS excitations with clockwise (CW), counterclockwise (CCW), and breathing mode (BR) character at temperatures below T = 40 K are shown. We find that the mode intensities can be tuned with the number of field-cycles below the saturation field. By tracking the resonance frequencies, we are able to map out the field-cycle-generated LTS phase diagram, from which we conclude that the LTS phase is distinctly separated from the high-temperature counterpart. We also study the mode hybridization between the dark CW and the BR modes as a function of temperature. By using two Cu2OSeO3 crystals with different shapes and therefore different demagnetization factors, together with numerical calculations, we unambiguously show that the magnetocrystalline anisotropy plays a central role for the mode hybridization.

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27

Lim, Zhi Shiuh, Hariom Jani, T. Venkatesan, and A. Ariando. "Skyrmionics in correlated oxides." MRS Bulletin 46, no. 11 (November 2021): 1053–62. http://dx.doi.org/10.1557/s43577-021-00227-9.

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AbstractWhile chiral magnets, metal-based magnetic multilayers, or Heusler compounds have been considered as the material workhorses in the field of skyrmionics, oxides are now emerging as promising alternatives, as they host special correlations between the spin–orbital–charge–lattice degrees of freedom and/or coupled ferroic order parameters. These interactions open new possibilities for practically exploiting skyrmionics. In this article, we review the recent advances in the observation and control of topological spin textures in various oxide systems. We start with the discovery of skyrmions and related quasiparticles in bulk and heterostructure ferromagnetic oxides. Next, we emphasize the shortcomings of implementing ferromagnetic textures, which have led to the recent explorations of ferrimagnetic and antiferromagnetic oxide counterparts, with higher Curie temperatures, stray-field immunity, low Gilbert damping, ultrafast magnetic dynamics, and/or absence of skyrmion deflection. Then, we highlight the development of novel pathways to control the stability, motion, and detection of topological textures using electric fields and currents. Finally, we present the outstanding challenges that need to be overcome to achieve all-electrical, nonvolatile, low-power oxide skyrmionic devices. Graphical abstract

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28

Yokouchi, Tomoyuki, Shintaro Hoshino, Naoya Kanazawa, Akiko Kikkawa, Daisuke Morikawa, Kiyou Shibata, Taka-hisa Arima, et al. "Current-induced dynamics of skyrmion strings." Science Advances 4, no. 8 (August 2018): eaat1115. http://dx.doi.org/10.1126/sciadv.aat1115.

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29

Diep, H. T., Sahbi El Hog, and Aurélien Bailly-Reyre. "Skyrmion crystals: Dynamics and phase transition." AIP Advances 8, no. 5 (May 2018): 055707. http://dx.doi.org/10.1063/1.5006269.

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30

Ferrer, A. Villares, and A. O. Caldeira. "Skyrmion dynamics in quantum Hall ferromagnets." Physical Review B 61, no. 4 (January 15, 2000): 2755–64. http://dx.doi.org/10.1103/physrevb.61.2755.

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31

Din, A. M., and W. J. Zakrzewski. "Skyrmion dynamics in 2 + 1 dimensions." Nuclear Physics B 259, no. 4 (September 1985): 667–76. http://dx.doi.org/10.1016/0550-3213(85)90006-9.

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32

Piette, Bernard, and Wojtek J. Zakrzewski. "Skyrmion dynamics in (2 + 1) dimensions." Chaos, Solitons & Fractals 5, no. 12 (December 1995): 2495–508. http://dx.doi.org/10.1016/0960-0779(94)e0111-2.

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33

Zhang, Zhiyu, Min Xu, Guiqian Jiang, Jinyu Zhang, Dexiang Meng, Wenlong Chen, Yuliang Chen, and Changjing Hu. "High-density racetrack memory based on magnetic skyrmion bags controlled by voltage gates." Journal of Applied Physics 132, no. 11 (September 21, 2022): 113901. http://dx.doi.org/10.1063/5.0098999.

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Skyrmion bags are spin structures with arbitrary topological degrees. They are expected to be promising next-generation information carriers due to their inherent high topological degrees. Here, we report the dynamics of the topological transition process when a skyrmion bag passes through a voltage gate driven by spin current in a synthetic antiferromagnetic racetrack with voltage-controlled magnetic anisotropy. The topological degrees of skyrmion bags controlled by voltage gate and driving current density are investigated. It is found that the different topological degrees of skyrmion bags transformed in this process are related to the interaction between antiskyrmions inside skyrmion bags, and the energy of each inner antiskyrmion after topological transformation is on the order of [Formula: see text]. Furthermore, we have realized the successive transition of a skyrmion bag from a high topological degree to a low topological degree on a racetrack with three voltage gates. This work is helpful for designing high-density racetrack memory and logical devices based on skyrmion bags.

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34

Charilaou, Michalis. "Bloch point dynamics in exchange-spring heterostructures." APL Materials 10, no. 7 (July 1, 2022): 071103. http://dx.doi.org/10.1063/5.0097610.

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Magnetization textures that are stabilized by topological constraints, such as skyrmions and chiral bobbers, as well as the emergent electrodynamics associated with their motion, provide a promising avenue toward novel energy-efficient nanomagnetic devices. Here, it is shown that exchange-spring-type heterostructures, where soft ferromagnets with azimuthal symmetry are exchange-coupled to a ferromagnetic layer with perpendicular magnetic anisotropy, can be used for the creation and control of skyrmion tubes and Bloch points during magnetization reversal of the soft ferromagnet, where the rapid motion of the Bloch points induces an emergent electric field with a magnitude of the order of megavolts per meter. The exchange coupling to the hard ferromagnet restores the system to its original configuration, making the process fully reversible and repeatable, and the duration of the magnetization processes and the motion of the Bloch points can be tuned by adjusting the size of the ferromagnet. Based on these numerical predictions, it is proposed that exchange-spring heterostructures could be used to generate picosecond electromagnetic pulses.

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35

Kim, Joo-Von, and Myoung-Woo Yoo. "Current-driven skyrmion dynamics in disordered films." Applied Physics Letters 110, no. 13 (March 27, 2017): 132404. http://dx.doi.org/10.1063/1.4979316.

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36

Kim, Tae-Hoon, Licong Peng, Ying Zhang, Liqin Ke, Brandt Jensen, X. G. Zhang, Matthew J. Kramer, and Lin Zhou. "Formation and Relaxation Dynamics of Magnetic Skyrmion." Microscopy and Microanalysis 25, S2 (August 2019): 36–37. http://dx.doi.org/10.1017/s1431927619000916.

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37

Martinez, J. C., and M. B. A. Jalil. "Current-Induced Dynamics in a Skyrmion Lattice." IEEE Transactions on Magnetics 51, no. 11 (November 2015): 1–4. http://dx.doi.org/10.1109/tmag.2015.2436401.

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38

Gareeva, Zukhra V., and Konstantin Y. Guslienko. "Magnetic skyrmion dynamics in thin cylindrical dots." physica status solidi (RRL) - Rapid Research Letters 10, no. 3 (January 5, 2016): 227–32. http://dx.doi.org/10.1002/pssr.201510419.

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39

Reinhardt, H., and D. Ebert. "Extended skyrmion model from quark flavour dynamics." Physics Letters B 173, no. 4 (June 1986): 459–64. http://dx.doi.org/10.1016/0370-2693(86)90415-6.

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40

Iwasaki, Junichi, Masahito Mochizuki, and Naoto Nagaosa. "Current-induced skyrmion dynamics in constricted geometries." Nature Nanotechnology 8, no. 10 (September 8, 2013): 742–47. http://dx.doi.org/10.1038/nnano.2013.176.

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41

Luis, Ricardo Francisco, Victor Raposo, Oscar Alejos, and Eduardo Martinez. "Current-Driven Skyrmion Dynamics Along Curved Tracks." IEEE Transactions on Magnetics 55, no. 7 (July 2019): 1–8. http://dx.doi.org/10.1109/tmag.2019.2898011.

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42

Green, A. G. "Quantum-critical dynamics of the Skyrmion lattice." Physical Review B 61, no. 24 (June 15, 2000): R16299—R16302. http://dx.doi.org/10.1103/physrevb.61.r16299.

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43

Yasin, Fehmi, Kosuke Karube, Akiko Kikkawa, Yasujiro Taguchi, Yoshinori Tokura, and Xiuzhen Yu. "Current-driven Dynamics of Magnetic Skyrmion Bunches." Microscopy and Microanalysis 27, S1 (July 30, 2021): 382–83. http://dx.doi.org/10.1017/s1431927621001896.

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44

Goto, Minori, Hikaru Nomura, and Yoshishige Suzuki. "Stochastic skyrmion dynamics under alternating magnetic fields." Journal of Magnetism and Magnetic Materials 536 (October 2021): 167974. http://dx.doi.org/10.1016/j.jmmm.2021.167974.

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45

Cui, Shuting, Mingmin Zhu, Yang Qiu, Rongdi Guo, Guohua Wu, Guoliang Yu, and Haomiao Zhou. "Micromagnetic prediction strain and current co-mediated spindynamics in skyrmion-based spin-torque nano-oscillator." Journal of Physics D: Applied Physics 55, no. 17 (February 2, 2022): 175003. http://dx.doi.org/10.1088/1361-6463/ac4dcb.

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Abstract In this article, we theoretically investigate the influence of strain on the oscillation frequency characteristics of a skyrmion-based spin-torque nano-oscillator (STNO) using micromagnetic simulations. The system consists of an ultrathin nanopillar magnetic film with interfacial Dzyaloshinskii–Moriya interactions and a ring-shaped region to offer a tunable spatial strain source. The applied strain gives rise to an extra effective field in the magnetic film through magnetoelastic coupling and forms a strong confined potential for skyrmion dynamics. Our simulation results show that the operation frequency of the STNO can be effectively modulated by the strain. Furthermore, we introduce a simplified analytical expression of the skyrmion gyration dynamics to explain the micromagnetic simulation results. Our results will be useful in the development of wide-range frequency-tunable microwave emitters and frequency-shift keying for wireless communication.

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BATTYE, RICHARD A., and PAUL M. SUTCLIFFE. "SKYRMIONS, FULLERENES AND RATIONAL MAPS." Reviews in Mathematical Physics 14, no. 01 (January 2002): 29–85. http://dx.doi.org/10.1142/s0129055x02001065.

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We apply two very different approaches to calculate Skyrmions with baryon number B ≤ 22. The first employs the rational map ansatz, where approximate charge B Skyrmions are constructed from a degree B rational map between Riemann spheres. We use a simulated annealing algorithm to search for the minimal energy rational map of a given degree B. The second involves the numerical solution of the full non-linear time dependent equations of motion, with initial conditions consisting of a number of well separated Skyrmion clusters. In general, we find a good agreement between the two approaches. For B ≥ 7 almost all the solutions are of fullerene type, that is, the baryon density isosurface consists of twelve pentagons and 2B - 14 hexagons arranged in a trivalent polyhedron. There are exceptional cases where this structure is modified, which we discuss in detail. We find that for a given value of B there are often many Skyrmions, with different symmetries, whose energies are very close to the minimal value, some of which we discuss. We present rational maps which are good approximations to these Skyrmions and accurately compute their energy by relaxation using the full non-linear dynamics.

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Savchenko, Andrii S., Vladyslav M. Kuchkin, Filipp N. Rybakov, Stefan Blügel, and Nikolai S. Kiselev. "Chiral standing spin waves in skyrmion lattice." APL Materials 10, no. 7 (July 1, 2022): 071111. http://dx.doi.org/10.1063/5.0097651.

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This work studies the resonance excitations of the three-dimensional skyrmions lattice in the finite thickness plate of an isotropic chiral magnet using spin dynamics simulations. We found that the absorption spectra and resonance modes differ from those predicted by the two-dimensional model and the model of the unconfined bulk crystal. The features observed on the spectra can be explained by the formation of chiral standing spin waves, which, contrary to conventional standing spin waves, are characterized by the helical profile of dynamic magnetization of fixed chirality that is defined by the Dzyaloshinskii–Moriya interaction. In this case, the dynamic susceptibility becomes a function of the plate thickness, which gives rise to an interesting effect that manifests itself in periodical fading of the intensity of corresponding modes and makes excitation of these modes impossible at specific thicknesses.

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Chen, Xing, Wang Kang, Daoqian Zhu, Xichao Zhang, Na Lei, Youguang Zhang, Yan Zhou, and Weisheng Zhao. "A compact skyrmionic leaky–integrate–fire spiking neuron device." Nanoscale 10, no. 13 (2018): 6139–46. http://dx.doi.org/10.1039/c7nr09722k.

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49

Allder, A. E., S. E. Koonin, R. Seki, and H. M. Sommermann. "Dynamics of Skyrmion Collisions in 3 + 1 Dimensions." Physical Review Letters 59, no. 25 (December 21, 1987): 2836–39. http://dx.doi.org/10.1103/physrevlett.59.2836.

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50

Ang, Calvin Ching Ian, Weiliang Gan, and Wen Siang Lew. "Bilayer skyrmion dynamics on a magnetic anisotropy gradient." New Journal of Physics 21, no. 4 (April 8, 2019): 043006. http://dx.doi.org/10.1088/1367-2630/ab1171.

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Journal articles on the topic 'Skyrmion dynamics'

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