Journal articles on the topic 'Skyrmions'
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1
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.
2
Portengen, T., J. R. Chapman, V. Nikos Nicopoulos, and N. F. Johnson. "Optics with Quantum Hall Skyrmions." International Journal of Modern Physics B 12, no. 01 (January 10, 1998): 1–35. http://dx.doi.org/10.1142/s0217979298000028.
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A novel type of charged excitation, known as a Skyrmion, has recently been discovered in quantum Hall systems with filling factor near ν=1. A Skyrmion — which can be thought of as a topological twist in the spin density of the electron gas — has the same charge as an electron, but a much larger spin. In this review we present a detailed theoretical investigation of the optical properties of Skyrmions. Our results provide means for the optical detection of Skyrmions using photoluminescence (PL) spectroscopy. We first consider the optical properties of Skyrmions in disordered systems. A calculation of the luminescence energy reveals a special optical signature which allows us to distinguish between Skyrmions and ordinary electrons. Two experiments to measure the optical signature are proposed. We then turn to the optical properties of Skyrmions in pure systems. We show that, just like an ordinary electron, a Skyrmion may bind with a hole to form a Skyrmionic exciton. The Skyrmionic exciton can have a lower energy than the ordinary magnetoexciton. The optical signature of Skyrmions is found to be a robust feature of the PL spectrum in both disordered and pure systems.
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Wolf, Daniel, Sebastian Schneider, Ulrich K. Rößler, András Kovács, Marcus Schmidt, Rafal E. Dunin-Borkowski, Bernd Büchner, Bernd Rellinghaus, and Axel Lubk. "Unveiling the three-dimensional magnetic texture of skyrmion tubes." Nature Nanotechnology 17, no. 3 (December 20, 2021): 250–55. http://dx.doi.org/10.1038/s41565-021-01031-x.
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AbstractMagnetic skyrmions are stable topological solitons with complex non-coplanar spin structures. Their nanoscopic size and the low electric currents required to control their motion has opened a new field of research, skyrmionics, that aims for the usage of skyrmions as information carriers. Further advances in skyrmionics call for a thorough understanding of their three-dimensional (3D) spin texture, skyrmion–skyrmion interactions and the coupling to surfaces and interfaces, which crucially affect skyrmion stability and mobility. Here, we quantitatively reconstruct the 3D magnetic texture of Bloch skyrmions with sub-10-nanometre resolution using holographic vector-field electron tomography. The reconstructed textures reveal local deviations from a homogeneous Bloch character within the skyrmion tubes, details of the collapse of the skyrmion texture at surfaces and a correlated modulation of the skyrmion tubes in FeGe along their tube axes. Additionally, we confirm the fundamental principles of skyrmion formation through an evaluation of the 3D magnetic energy density across these magnetic solitons.
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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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Yuan, Yingyue, Zhaozhuo Zeng, Jianing Wang, Yunxu Ma, Senfu Zhang, Jinwu Wei, Jianbo Wang, and Qingfang Liu. "A skyrmion helicity-based multistate memory in synthetic antiferromagnets." Journal of Applied Physics 132, no. 23 (December 21, 2022): 233903. http://dx.doi.org/10.1063/5.0130720.
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Skyrmions in synthetic antiferromagnets (SAFs) are famous for being immune to the skyrmion Hall effect and hold the advantages of significantly higher speed for motion and smaller size than ferromagnetic systems. Therefore, skyrmions in SAFs are promising in spintronic devices. Here, we investigated the formation and in-plane-current-driven motion of bilayer skyrmions in the absence of Dzyaloshinskii–Moriya interaction by using micromagnetic simulations. Then, we studied the spacing variation between consecutive skyrmionic bits on the antiferromagnetic coupled nanotrack; it is found that there is an equilibrium distance between two Bloch skyrmions with opposite helicities. We also propose a reasonable method to distinguish skyrmions with opposite helicities. Finally, we displayed that the SAF skyrmion could pass through impurities due to topological protection. Based on these results, we designed the skyrmion helicity-based multistate memory devices in the SAF system, which have the advantages of high density and energy efficiency.
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Hu, Ping, Hong-Wei Wu, Wen-Jun Sun, Nong Zhou, Xue Chen, Yong-Qiang Yang, and Zong-Qiang Sheng. "Observation of localized acoustic skyrmions." Applied Physics Letters 122, no. 2 (January 9, 2023): 022201. http://dx.doi.org/10.1063/5.0131777.
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Recently, acoustic skyrmions have been explored by tailoring velocity vectorial near-field distributions based on the interference of multiple spoof surface acoustic waves, providing new dimensions for advanced sound information processing, transport, and data storage. Here, we theoretically investigate and experimentally demonstrate that a deep-subwavelength spiral metastructure can also generate the acoustic skyrmion configuration. Analyzing the resonant response of the metastructure and observing the spatial profile of the velocity field, we find that the localized skyrmionic modes correspond to eigenmodes of the spiral structure. Thus, the skyrmionic modes do not require carefully tailored external excitation condition and they have multiple resonating frequencies unlike the single skyrmionic mode realized by the interference of multiple waves. We also demonstrate that the topological protected skyrmions supported by the subwavelength metastructure is robust against structure deformations and existence of structure defects. The real-space acoustic skyrmion topology may open new avenues for designing ultra-compact and robust acoustic devices, such as acoustic sensors, acoustic tweezers, and acoustic antennas.
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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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Chen, Chao, Tao Lin, Jianteng Niu, Yiming Sun, Liu Yang, Wang Kang, and Na Lei. "Surface acoustic wave controlled skyrmion-based synapse devices." Nanotechnology 33, no. 11 (December 23, 2021): 115205. http://dx.doi.org/10.1088/1361-6528/ac3f14.
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Abstract Magnetic skyrmions, which are particle-like spin structures, are promising information carriers for neuromorphic computing devices due to their topological stability and nanoscale size. In this work, we propose controlling magnetic skyrmions by electric-field-excited surface acoustic waves in neuromorphic computing device structures. Our micromagnetic simulations show that the number of created skyrmions, which emulates the synaptic weight parameter, increases monotonically with increases in the amplitude of the surface acoustic waves. Additionally, the efficiency of skyrmion creation is investigated systemically with a wide range of magnetic parameters, and the optimal values are presented accordingly. Finally, the functionalities of short-term plasticity and long-term potentiation are demonstrated via skyrmion excitation by a sequence of surface acoustic waves with different intervals. The application of surface acoustic waves in skyrmionic neuromorphic computing devices paves a novel approach to low-power computing systems.
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Deng, Panluo, Fengjun Zhuo, Hang Li, and Zhenxiang Cheng. "Mirroring Skyrmions in Synthetic Antiferromagnets via Modular Design." Nanomaterials 13, no. 5 (February 25, 2023): 859. http://dx.doi.org/10.3390/nano13050859.
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Skyrmions are promising for the next generation of spintronic devices, which involves the production and transfer of skyrmions. The creation of skyrmions can be realized by a magnetic field, electric field, or electric current while the controllable transfer of skyrmions is hindered by the skyrmion Hall effect. Here, we propose utilizing the interlayer exchange coupling induced by the Ruderman–Kittel–Kasuya–Yoshida interactions to create skyrmions through hybrid ferromagnet/synthetic antiferromagnet structures. An initial skyrmion in ferromagnetic regions could create a mirroring skyrmion with an opposite topological charge in antiferromagnetic regions driven by the current. Furthermore, the created skyrmions could be transferred in synthetic antiferromagnets without deviations away from the main trajectories due to the suppression of the skyrmion Hall effect in comparison to the transfer of the skyrmion in ferromagnets. The interlayer exchange coupling can be tuned, and the mirrored skyrmions can be separated when they reach the desired locations. Using this approach, the antiferromagnetic coupled skyrmions can be repeatedly created in hybrid ferromagnet/synthetic antiferromagnet structures. Our work not only supplies a highly efficient approach to create isolated skyrmions and correct the errors in the process of skyrmion transport, but also paves the way to a vital information writing technique based on the motion of skyrmions for skyrmion-based data storage and logic devices.
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Dohi, Takaaki, Robert M. Reeve, and Mathias Kläui. "Thin Film Skyrmionics." Annual Review of Condensed Matter Physics 13, no. 1 (March 10, 2022): 73–95. http://dx.doi.org/10.1146/annurev-conmatphys-031620-110344.
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In condensed matter physics, magnetic skyrmions, topologically stabilized magnetic solitons, have been discovered in various materials systems, which has intrigued the community in terms of not only fundamental physics but also with respect to engineering applications. In particular, skyrmions in thin films are easily manipulable by electrical means even at room temperature. Concomitantly, a variety of possible applications have been proposed and proof-of-concept devices have been demonstrated. Recently, the field of skyrmion-based electronics has been referred to as skyrmionics and this field has been rapidly growing and extended in multiple directions. This review provides recent progress for skyrmion research in thin film systems and we discuss promising new directions, which will further invigorate the field.
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Zhao, Li, Lei Qiu, Guoping Zhao, Ping Lai, Nian Ran, Xue Liang, Laichuan Shen, and Fang Wang. "Design and Optimization of Skyrmion-Based Racetrack Memory by Overcoming Clogging and Annihilation of Skyrmion Signals." SPIN 09, no. 03 (September 2019): 1950019. http://dx.doi.org/10.1142/s201032471950019x.
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Magnetic skyrmions are promising building blocks for next generation data storage due to their stability, small size and extremely low currents to drive them. Skyrmion-based metallic racetrack memory has potential to replace traditional domain walls to store information as data bits, in which, however, skyrmions can drift from the direction of electron flow due to the Magnus force. In addition, skyrmion-edge effect at the end of the racetrack can cause the clogging of the skyrmions at the end of the racetrack. Here, we show that the clogging of skyrmion signals can be avoided by adding various kinds of notch at the end of the racetracks. On the other hand, by adding high-[Formula: see text] materials (materials with high magnetic crystalline anisotropy) at the edges, the skyrmions can be confined in the center region of the metallic racetrack successfully. This design can overcome the problems of both clogging and annihilation according to our micromagnetic simulation. As a result, skyrmions can pass the right end of the racetrack efficiently at a very high speed (100–300[Formula: see text]m/s), whereas the driving current is much smaller in comparison with other racetrack design. Besides, we study the influence of the uneven part at the joint of the high-[Formula: see text] material and the CoPt racetrack on the skyrmionic motion. It is found that at the joint between the high-[Formula: see text] material and the CoPt racetrack, the concave part basically does not affect the passage of skyrmion, but the convex part does when the length and width of the convex part reach a certain value. The results show that the design has high feasibility.
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Bouhassoune, Mohammed, and Samir Lounis. "Friedel Oscillations Induced by Magnetic Skyrmions: From Scattering Properties to All-Electrical Detection." Nanomaterials 11, no. 1 (January 14, 2021): 194. http://dx.doi.org/10.3390/nano11010194.
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Magnetic skyrmions are spin swirling solitonic defects that can play a major role in information technology. Their future in applications and devices hinges on their efficient manipulation and detection. Here, we explore from ab-initio their nature as magnetic inhomongeities in an otherwise unperturbed magnetic material, Fe layer covered by a thin Pd film and deposited on top of Ir(111) surface. The presence of skyrmions triggers scattering processes, from which Friedel oscillations emerge. The latter mediate interactions among skyrmions or between skyrmions and other potential surrounding defects. In contrast to their wavelengths, the amplitude of the oscillations depends strongly on the size of the skyrmion. The analogy with the scattering-off atomic defects enables the assignment of an effective scattering potential and a phase shift to the skyrmionic particles, which can be useful to predict their behavior on the basis of simple scattering frameworks. The induced charge ripples can be utilized for a noninvasive all-electrical detection of skyrmions located on a surface or even if buried a few nanometers away from the detecting electrode.
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Zivieri, Roberto. "Statistical Properties and Configurational Entropy of a Two-Dimensional Néel Magnetic Skyrmions Population." Applied Sciences 10, no. 1 (January 3, 2020): 352. http://dx.doi.org/10.3390/app10010352.
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The study of the thermodynamic properties of topological defects is important not only for understanding their magnetic properties but also for suggesting novel applications. In this paper, the statistical and statistical thermodynamic properties of a population of Néel magnetic skyrmion diameters hosted in an ultrathin cylindrical dot is determined within a two-dimensional analytical approach. The statistical properties such as the skyrmion size are calculated in the region of skyrmion metastability and are compared with the ones obtained using a recent three-dimensional analytical approach based on the analogy with the Maxwell–Boltzmann distribution of dilute gas molecules. The investigation of the statistical thermodynamic properties focus on the calculation of the configurational entropy at thermodynamic equilibrium determined in the continuous limit from the Boltzmann order function. While the statistical properties are quantitatively similar passing from the two-dimensional to the three-dimensional approach, the configurational entropy calculated from the two-dimensional skyrmions distribution is considerably lower than the one obtained from the three-dimensional skyrmions distribution. Because of the strong resemblance between the statistical configurational entropy and Jaynes’s information entropy, it is suggested to use magnetic skyrmions as temperature and external field dependent information entropy carriers for a future potential technological application in the field of low-dimensional magnetic systems and skyrmionics.
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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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Bhatti, Sabpreet, H. K. Tan, M. I. Sim, V. L. Zhang, M. Sall, Z. X. Xing, R. Juge, et al. "Enhancement of skyrmion density via interface engineering." APL Materials 11, no. 1 (January 1, 2023): 011103. http://dx.doi.org/10.1063/5.0118147.
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Magnetic skyrmions are promising candidates for computing and memory applications. The static and dynamic behaviors of skyrmions are tunable by altering the interfacial magnetic properties. These interfacial magnetic properties are alterable by modifying the interface structure of thin films. However, the relationship between the structural properties of the interface and the skyrmions properties is not straightforward, and a comprehensive insight is required to facilitate better controllability of the skyrmions’ behaviors. Here, we comprehensively understand the relationship between atomic displacements at the interface and skyrmions’ static behavior. In this study, we used ion irradiation to achieve inter-atomic displacements. We observed that the inter-atomic displacements could tailor the physical properties of skyrmions. We noticed a peculiar increase in the magnetization, Dzyaloshinskii–Moriya interaction, and exchange stiffness. The modifications in magnetic properties reduced the domain wall energy, which enhanced the skyrmion density (by six-folds) and reduced the average skyrmion diameter (by 50%). Furthermore, we compared the observed results of ion irradiation with those from the annealing process (a well-studied method for modifying magnetic properties) to better understand the effect of atomic displacements. Our study provides a route to achieve a highly-dense skyrmion state, and it can be explored further to suppress the skyrmion Hall effect for skyrmion-based applications.
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Aranda, Arantxa, and Konstantin Guslienko. "Single Chiral Skyrmions in Ultrathin Magnetic Films." Materials 11, no. 11 (November 11, 2018): 2238. http://dx.doi.org/10.3390/ma11112238.
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The stability and sizes of chiral skyrmions in ultrathin magnetic films are calculated accounting for the isotropic exchange, Dzyaloshinskii–Moriya exchange interaction (DMI), and out-of-plane magnetic anisotropy within micromagnetic approach. Bloch skyrmions in ultrathin magnetic films with B20 cubic crystal structure (MnSi, FeGe) and Neel skyrmions in ultrathin films and multilayers Co/X (X = Ir, Pd, Pt) are considered. The generalized DeBonte ansatz is used to describe the inhomogeneous skyrmion magnetization. The single skyrmion metastability/instability area, skyrmion radius, and skyrmion width are found analytically as a function of DMI strength d . It is shown that the single chiral skyrmions are metastable in infinite magnetic films below a critical value of DMI d c , and do not exist at d > d c . The calculated skyrmion radius increases as d increases and diverges at d → d c − 0 , whereas the skyrmion width increases monotonically as d increases up to d c without any singularities. The calculated skyrmion width is essentially smaller than the one calculated within the generalized domain wall model.
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Lai, P., G. P. Zhao, F. J. Morvan, S. Q. Wu, and N. Ran. "Motion of Skyrmions in Well-Separated Two-Lane Racetracks." SPIN 07, no. 01 (March 2017): 1740006. http://dx.doi.org/10.1142/s2010324717400069.
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Magnetic skyrmions are topological structures which can be used to store information as data bits in metallic racetrack memories. Their good properties, such as their stability, small size and low currents needed to drive them make them better candidates than traditional magnetic domain walls for the building of the next generation data storage. A skyrmion racetrack memory has been suggested, with the binary data encoded in the distance between skyrmions when the racetrack is a single lane. Here, we propose a new skyrmion-based two-lane racetrack structure separated by a high-[Formula: see text] (high magnetocrystalline anisotropy) middle lane, which confines the skyrmions in their respective lanes. This design gives a new data presentation for the skyrmions on the racetrack. Phase diagrams for the skyrmion motion on the proposed racetrack as functions of the current density, middle lane anisotropy, middle lane width and DMI constant have been calculated and given, demonstrating that skyrmions can be driven in different lanes of the racetrack. This design offers the possibility of building an ultrafast and energy-efficient skyrmion transport device.
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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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He, Min, Tiankuo Xu, Yang Gao, Chaoqun Hu, Jianwang Cai, and Ying Zhang. "Mixed-Type Skyrmions in Symmetric Pt/Co/Pt Multilayers at Room Temperature." Materials 15, no. 22 (November 21, 2022): 8272. http://dx.doi.org/10.3390/ma15228272.
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We demonstrate the generation of mixed-type skyrmions (all are about 200 nm) that are primarily Bloch-type, hybrid-type, and a negligible amount of Néel-type in symmetric Pt/Co(1.55)/Pt multilayers at room temperature. The magnetic field dependence of skyrmion evolution is reversible. Brillouin light-scattering is used to quantitatively quantify the Dzyaloshinskii-Moriya interaction constant D in order to comprehend the mechanism. Interestingly, the D value is high enough to generate skyrmions in a symmetric sandwich structure. Micromagnetic simulations show that Néel-type skyrmions transform into Bloch-type skyrmions as the D value decreases. The interface-induced non-uniform D may be the cause to generate mixed-type skyrmions. This work broadens the flexibility to generate skyrmions by engineering skyrmion-based devices with nominally symmetric multilayers without the requirement of very large DMI.
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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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Ishikawa, Ryo, Minori Goto, Hikaru Nomura, and Yoshishige Suzuki. "Controlling the creation/annihilation and distribution of magnetic skyrmions by manipulating an externally applied voltage." Applied Physics Letters 121, no. 25 (December 19, 2022): 252402. http://dx.doi.org/10.1063/5.0128385.
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Magnetic skyrmions are currently gaining attention owing to their potential to act as information carriers in spintronic devices. However, conventional techniques which rely on modulating the electric current to write or manipulate information using skyrmions are not energy efficient. Therefore, in this study, a Ta/Co–Fe–B/Ta/MgO junction that hosts a skyrmion was utilized to fabricate a device to investigate the effect of applying a voltage in the direction perpendicular to the film plane. Magneto-optical Kerr effect microscopy was performed in a polar configuration to observe the difference in the perpendicular magnetic anisotropy by observing the behavior of the magnetic domain structure and the skyrmions. Our findings suggest that voltage-induced magnetic domain structure modulation and the creation/annihilation of skyrmions are both possible. Furthermore, manipulation of skyrmions was realized by utilizing repulsive magnetic dipole interaction between the voltage-created skyrmion and skyrmion, exhibiting Brownian motion, outside the top electrode. Thus, our proposed method can enable controlling the creation and annihilation of skyrmions and their positions by manipulating the externally applied voltage. These findings can advance unconventional computing fields, such as stochastic and ultra-low-power computing.
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Гареева, З. В., and К. Ю. Гуслиенко. "Динамика магнитных скирмионов в наноточках." Физика твердого тела 60, no. 6 (2018): 1135. http://dx.doi.org/10.21883/ftt.2018.06.45988.23m.
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AbstractBloch and Neel magnetic skyrmions have been studied in systems of confined geometry (nanodots, a linear array of nanodots). The spectra of low- and high-frequency excitation modes of a skyrmion state have been calculated. It has been shown that skyrmion spectrum asymmetry, namely, the characteristic difference between the frequencies of the azimuthal modes of the azimuthal skyrmion modes rotating clockwise and counterclockwise, is associated with asymmetry in the magnetization profiles of high-frequency spin waves propagating on the background of a skyrmion state in a nanodot. The low-frequency spectrum contains the only gyrotropic mode localized near the center of a nanodot. The gyrotropic frequency depends on the material parameters of a nanodot and the size of a skyrmion. The eigenfrequency of the gyrotropic mode of an isolated skyrmion in a nanodot in ultrathin films ( L ~ 1 nm) does not depend on the internal structure of a skyrmion and is the same for Bloch and Neel skyrmions. The interaction of skyrmions, in particular, in a linear chain of nanodots with the ground skyrmion state, leads to distinctions in low-frequency spectra. The structure of a skyrmion (of Bloch or Neel type) is exhibited as a shift of dispersion curves and a difference between the frequencies of ferromagnetic resonance in a system of interacting skyrmions.
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Chen, Zhenzhen, Xinyan He, Xinyi Cai, Yang Qiu, Mingmin Zhu, Guoliang Yu, and Haomiao Zhou. "Magnetic skyrmion nucleation via current injection in confined nanotrack with modified perpendicular anisotropy region." Applied Physics Letters 122, no. 14 (April 3, 2023): 142401. http://dx.doi.org/10.1063/5.0138688.
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Magnetic skyrmions, as spintronic information carriers, are promising for next-generation spin logic and memory devices. For such skyrmion-based devices, effective control of skyrmion nucleation and controllable motion in the nanotrack are of great importance. The ion irradiation process can modify magnetic properties, such as perpendicular magnetic anisotropy (PMA) and Dzyaloshinskii–Moriya interaction (DMI), at the nanoscale, which can be used to reduce the design complexity of devices. In this study, a nanoregion without PMA in the nanotrack is adopted as a skyrmion nucleation seed and a current-driven highly efficient, in-line, and on-demand skyrmion nucleation schematic is presented. A key factor for realizing this concept is that the disappearance of PMA and the existence of DMI induce magnetization tilts and create a chiral perpendicular stripe domain within the nucleation region. This stripe domain allows the effective control of the spin transfer torque, and it is ejected from the PMA-modified region and propelled into the nanotrack, forming a stable skyrmion. Our proposed device allows the controlled nucleation and propagation of a series of skyrmions, which allows binary information to be written in a controlled manner, consequently, yielding simple devices with two terminals. This study provides an efficient route for designing tunable skyrmionics-mechanic memory devices.
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Seki, Shinichiro. "Skyrmions in Multiferroic Insulator." Acta Crystallographica Section A Foundations and Advances 70, a1 (August 5, 2014): C1547. http://dx.doi.org/10.1107/s2053273314084526.
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Magnetic skyrmion is a topologically stable particle-like object, which appears as nanometer-scale vortex-like spin texture in a chiral-lattice magnet [1]. In metallic materials (MnSi, FeGe, Fe1-xCoxSi etc), electrons moving through skyrmion spin texture gain a nontrivial quantum Berry phase, which provides topological force to the underlying spin texture and enables the current-induced manipulation of magnetic skyrmion [2]. Such electric controllability, in addition to the particle-like nature, is a promising advantage for potential spintronic device applications. Recently, we newly discovered that skyrmions appear also in an insulating chiral-lattice magnet Cu2OSeO3 [3]. We find that the skyrmions in insulator can magnetically induce electric polarization through the relativistic spin-orbit interaction, which implies possible manipulation of the skyrmion by external electric field without loss of joule heating. The present finding of multiferroic skyrmion may pave a new route toward the engineering of novel magnetoelectric devices with high energy efficiency. In this talk, our recent attempts to drive skyrmions by external field are also introduced.
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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.
Full textAbstract:
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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One, Roxana-Alina, Sever Mican, Angela-Georgiana Cimpoeșu, Marius Joldos, Romulus Tetean, and Coriolan Viorel Tiușan. "Micromagnetic Design of Skyrmionic Materials and Chiral Magnetic Configurations in Patterned Nanostructures for Neuromorphic and Qubit Applications." Nanomaterials 12, no. 24 (December 10, 2022): 4411. http://dx.doi.org/10.3390/nano12244411.
Full textAbstract:
Our study addresses the problematics of magnetic skyrmions, nanometer-size vortex-like swirling topological defects, broadly studied today for applications in classic, neuromorphic and quantum information technologies. We tackle some challenging issues of material properties versus skyrmion stability and manipulation within a multiple-scale modeling framework, involving complementary ab-initio and micromagnetic frameworks. Ab-initio calculations provide insight into the anatomy of the magnetic anisotropy, the Dzyaloshinskii–Moriya asymmetric exchange interaction (DMI) and their response to a gating electric field. Various multi-layered heterostructures were specially designed to provide electric field tunable perpendicular magnetization and sizeable DMI, which are required for skyrmion occurrence. Landau–Lifshitz–Gilbert micromagnetic calculations in nanometric disks allowed the extraction of material parameter phase diagrams in which magnetic textures were classified according to their topological charge. We identified suitable ranges of magnetic anisotropy, DMI and saturation magnetization for stabilizing skyrmionic ground states or writing/manipulating them using either a spin-transfer torque of a perpendicular current or the electric field. From analyzing the different contributions to the total magnetic free energy, we point out some critical properties influencing the skyrmions’ stability. Finally, we discuss some experimental issues related to the choice of materials or the design of novel magnetic materials compatible with skyrmionic applications.
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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.
Full textAbstract:
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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Matsumoto, Takao, Yeong-Gi So, Yuji Kohno, Hidetaka Sawada, Yuichi Ikuhara, and Naoya Shibata. "Direct observation of Σ7 domain boundary core structure in magnetic skyrmion lattice." Science Advances 2, no. 2 (February 2016): e1501280. http://dx.doi.org/10.1126/sciadv.1501280.
Full textAbstract:
Skyrmions are topologically protected nanoscale magnetic spin entities in helical magnets. They behave like particles and tend to form hexagonal close-packed lattices, like atoms, as their stable structure. Domain boundaries in skyrmion lattices are considered to be important as they affect the dynamic properties of magnetic skyrmions. However, little is known about the fine structure of such skyrmion domain boundaries. We use differential phase contrast scanning transmission electron microscopy to directly visualize skyrmion domain boundaries in FeGe1−xSix induced by the influence of an “edge” of a crystal grain. Similar to hexagonal close-packed atomic lattices, we find the formation of skyrmion “Σ7” domain boundary, whose orientation relationship is predicted by the coincidence site lattice theory to be geometrically stable. On the contrary, the skyrmion domain boundary core structure shows a very different structure relaxation mode. Individual skyrmions can flexibly change their size and shape to accommodate local coordination changes and free volumes formed at the domain boundary cores. Although atomic rearrangement is a common structural relaxation mode in crystalline grain boundaries, skyrmions show very unique and thus different responses to such local lattice disorders.
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Pathak, Swapneel Amit, and Riccardo Hertel. "Geometrically Constrained Skyrmions." Magnetochemistry 7, no. 2 (February 12, 2021): 26. http://dx.doi.org/10.3390/magnetochemistry7020026.
Full textAbstract:
Skyrmions are chiral swirling magnetization structures with nanoscale size. These structures have attracted considerable attention due to their topological stability and promising applicability in nanodevices, since they can be displaced with spin-polarized currents. However, for the comprehensive implementation of skyrmions in devices, it is imperative to also attain control over their geometrical position. Here we show that, through thickness modulations introduced in the host material, it is possible to constrain three-dimensional skyrmions to desired regions. We investigate skyrmion structures in rectangular FeGe platelets with micromagnetic finite element simulations. First, we establish a phase diagram of the minimum-energy magnetic state as a function of the external magnetic field strength and the film thickness. Using this understanding, we generate preferential sites for skyrmions in the material by introducing dot-like “pockets” of reduced film thickness. We show that these pockets can serve as pinning centers for the skyrmions, thus making it possible to obtain a geometric control of the skyrmion position. This control allows for stabilization of skyrmions at positions and in configurations that they would otherwise not attain. Our findings may have implications for technological applications in which skyrmions are used as units of information that are displaced along racetrack-type shift register 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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Fragkos, Sotirios, Panagiotis Pappas, Evgenia Symeonidou, Yerassimos Panayiotatos, and Athanasios Dimoulas. "Magnetic skyrmion manipulation in CrTe2/WTe2 2D van der Waals heterostructure." Applied Physics Letters 120, no. 18 (May 2, 2022): 182402. http://dx.doi.org/10.1063/5.0089999.
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Magnetic skyrmions in two-dimensional van der Waals materials provide an ideal platform to push skyrmion technology to the ultimate atomically thin limit. In this work, we theoretically demonstrate the Dzyaloshinskii–Moriya interaction and the formation of a Néel-type skyrmion lattice at the CrTe2/WTe2 bilayer van der Waals heterostructure. Our calculations suggest a field-controlled Néel-type skyrmion lattice—a ferromagnet transition cycle. In addition, a spin-torque induced by spin-polarized current injection was simulated in order to study the motion of a skyrmion on a racetrack, where an increase in the skyrmion Hall angle is observed at high temperatures. Consequently, this study suggests that generation and annihilation of skyrmions can be achieved with temperature or field control and also manipulate the velocity and the direction of the Néel-type skyrmions through ultra-low current densities and temperature, thus shedding light on the general picture of magnetic skyrmion control and design of two-dimensional van der Waals heterostructures.
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Cubukcu, M., S. Pöllath, S. Tacchi, A. Stacey, E. Darwin, C. W. F. Freeman, C. Barton, et al. "Manipulation of Magnetic Skyrmion Density in Continuous Ir/Co/Pt Multilayers." Micromachines 13, no. 11 (November 4, 2022): 1911. http://dx.doi.org/10.3390/mi13111911.
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We show that magnetic skyrmions can be stabilised at room temperature in continuous [Ir/Co/Pt]5 multilayers on SiO2/Si substrates without the prior application of electric current or magnetic field. While decreasing the Co thickness, a transition of the magnetic domain patterns from worm-like state to separated stripes is observed. The skyrmions are clearly imaged in both states using magnetic force microscopy. The density of skyrmions can be significantly enhanced after applying the “in-plane field procedure”. Our results provide means to manipulate magnetic skyrmion density, further allowing for the optimised engineering of skyrmion-based devices.
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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.
Full textAbstract:
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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Ma, Mangyuan, Ke Huang, Yong Li, Sihua Li, Qiyuan Feng, Calvin Ching Ian Ang, Tianli Jin, et al. "Nano-engineering the evolution of skyrmion crystal in synthetic antiferromagnets." Applied Physics Reviews 9, no. 2 (June 2022): 021404. http://dx.doi.org/10.1063/5.0081455.
Full textAbstract:
The evolution of skyrmion crystals encapsulates skyrmion's critical behaviors, such as nucleation, deformation, and annihilation. Here, we achieve a tunable evolution of artificial skyrmion crystals in nanostructured synthetic antiferromagnet multilayers, which are composed of perpendicular magnetic multilayers and nanopatterned arrays of magnetic nanodots. The out-of-plane magnetization hysteresis loops and first-order reversal curves show that the nucleation and annihilation of the artificial skyrmion can be controlled by tuning the diameter of and spacing between the nanodots. Moreover, when the bottom layer thickness increases, the annihilation of skyrmion shifts from evolving into a ferromagnetic spin texture to evolving into an antiferromagnetic spin texture. Most significantly, nonvolatile multiple states are realized at zero magnetic field via controlling the proportion of the annihilated skyrmions in the skyrmion crystal. Our results demonstrate the tunability and flexibility of the artificial skyrmion platform, providing a promising route to achieve skyrmion-based multistate devices, such as neuromorphic spintronic devices.
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Sutcliffe, Paul. "Holographic Skyrmions." Modern Physics Letters B 29, no. 16 (June 20, 2015): 1540051. http://dx.doi.org/10.1142/s0217984915400515.
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Skyrmions are topological solitons that describe baryons within a nonlinear theory of pions. In holographic QCD, baryons correspond to topological solitons in a bulk theory with an extra spatial dimension. Thus, the three-dimensional Skyrmion lifts to a four-dimensional holographic Skyrmion in the bulk. We begin this review with a description of the simplest example of this correspondence, where the holographic Skyrmion is exactly the self-dual Yang–Mills instanton in flat space. This places an old result of Atiyah and Manton within a holographic framework and reveals that the associated Skyrme model extends the nonlinear pion theory to include an infinite tower of vector mesons, with specific couplings for a BPS theory. We then describe the more complicated curved space version that arises from the string theory construction of Sakai and Sugimoto. The basic concepts remain the same but the technical difficulty increases as the holographic Skyrmion is a curved space version of the Yang–Mills instanton, so self-duality and integrability are lost. Finally, we turn to a low-dimensional analog of holographic Skyrmions, where aspects such as multi-baryons and finite baryon density are amenable to both numerical computation and an approximate analytic treatment.
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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.
Full textAbstract:
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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He, Min, Jinzhi Li, Chaoqun Hu, Jine Zhang, Yang Gao, Zhuolin Li, Xinran Wang, et al. "Room temperature skyrmions in symmetric multilayers." Applied Physics Letters 121, no. 19 (November 7, 2022): 192403. http://dx.doi.org/10.1063/5.0117290.
Full textAbstract:
We experimentally demonstrate the generation of skyrmions (166 ± 42 nm) by controlling and modulating the skyrmion stability parameter κ through changing the Co layer thickness in the multilayer with repetitions of the symmetric Pt/Co/Pt trilayer. The magnetic field dependence of skyrmion evolution is reversible. Dzyaloshinskii–Moriya interaction constant D is quantitatively measured by Brillouin spectroscopy to understand the mechanism. Surprisingly, the D value is high enough to generate skyrmions in a symmetric sandwich structure although the value is smaller than that in an antisymmetric Pt/Co/Ta trilayer. The decreased D value with the increase in the Co layer thickness indicates that the Dzyaloshinskii–Moriya interaction is still contributed from the interfaces. This work broadens the flexibility to generate skyrmions by engineering skyrmion-based devices with nominally symmetric multilayer without the requirement of very large DMI.
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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.
Full textAbstract:
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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Wang, Kang, Yiou Zhang, Vineetha Bheemarasetty, Shiyu Zhou, See-Chen Ying, and Gang Xiao. "Single skyrmion true random number generator using local dynamics and interaction between skyrmions." Nature Communications 13, no. 1 (February 7, 2022). http://dx.doi.org/10.1038/s41467-022-28334-4.
Full textAbstract:
AbstractMagnetic skyrmions are of great interest to both fundamental research and applications in post-von-Neumann computing devices. The successful implementation of skyrmionic devices requires functionalities of skyrmions with effective controls. Here we show that the local dynamics of skyrmions, in contrast to the global dynamics of a skyrmion as a whole, can be introduced to provide effective functionalities for versatile computing. A single skyrmion interacting with local pinning centres under thermal effects can fluctuate in time and switch between a small-skyrmion and a large-skyrmion state, thereby serving as a robust true random number generator for probabilistic computing. Moreover, neighbouring skyrmions exhibit an anti-correlated coupling in their fluctuation dynamics. Both the switching probability and the dynamic coupling strength can be tuned by modifying the applied magnetic field and spin current. Our results could lead to progress in developing magnetic skyrmionic devices with high tunability and efficient controls.
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Bo, Lan, Chenglong Hu, Rongzhi Zhao, and Xuefeng Zhang. "Micromagnetic manipulation and spin excitation of skyrmionic structures." Journal of Physics D: Applied Physics, May 4, 2022. http://dx.doi.org/10.1088/1361-6463/ac6cb2.
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Abstract Magnetic skyrmions have attracted enormous research interest across a wide range of fields, from condensed matter physics to material science, since the first observation in 2009. Abundant theoretical, computational, and experimental studies have contributed to this emerging interdiscipline: skyrmionics. Especially, great expectations have been placed on exploiting the physics and dynamics of magnetic skyrmions as potential information carriers. In this topical review, we particularly focus on the computational studies of skyrmions during the last decade. After briefly introducing the mechanism of micromagnetic simulations, we review and discuss the manipulation of skyrmions, i. e., their creation, transformation, motion, and spin excitation, by both traditional and advanced methods, including electric currents, magnetic fields, spin waves, microwaves, etc. We take magnetic skyrmion as a typical example, while other skyrmion-related magnetic structures such as skyrmioniums and skyrmion tubes are also slightly involved. Through this review, we hope to give some insights into the further development of magnetic skyrmions in spintronics.
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Tyrpenou, Christos, Vasileios D. Stavrou, and Leonidas N. Gergidis. "Magnetic Skyrmions in FePt Square-Based Nanoparticles Around Room-Temperature." Journal of Physics D: Applied Physics, January 31, 2023. http://dx.doi.org/10.1088/1361-6463/acb782.
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Abstract Magnetic skyrmions formed at temperatures around room temperature in square-based parallelepiped magnetic FePt nanoparticles with perpendicular magnetocrystalline anisotropy (MCA) were studied during the magnetization reversal process using micromagnetic simulations. Finite Differences (FD) method were used for the solution of the Landau-Lifshitz-Gilbert equation. Magnetic configurations exhibiting Néel skyrmionic formations were detected. The magnetic skyrmions can be created in different systems by the variation of external field, side length and width of the squared-based parallelepiped magnetic nanoparticles. Micromagnetic configurations revealed a variety of states which include skyrmionic textures with one distinct skyrmion formed and stabilized for a range of external fields around room- temperature. The size of the nucleated Néel skyrmion is calculated as a function of the external field, temperature, MCA and nanoparticle’s geometrical characteristic lengths which can be adjusted to produce skyrmions on demand having diameters down to 12 nm. The micromagnetic simulations revealed that stable skyrmions in the temperature range of 270 - 330 K can be created for FePt magnetic nanoparticle systems lacking of chiral interactions such as Dzyaloshinskii-Moriya.
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Yasin, Fehmi Sami, Jan Masell, Kosuke Karube, Akiko Kikkawa, Yasujiro Taguchi, Yoshinori Tokura, and Xiuzhen Yu. "Real-space determination of the isolated magnetic skyrmion deformation under electric current flow." Proceedings of the National Academy of Sciences 119, no. 41 (October 3, 2022). http://dx.doi.org/10.1073/pnas.2200958119.
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The manipulation and control of electron spins, the fundamental building blocks of magnetic domains and spin textures, are at the core of spintronics. Of particular interest is the effect of the electric current on topological magnetic skyrmions, such as the current-induced deformation of isolated skyrmions. The deformation has consequences ranging from perturbed dynamics to modified packing configurations. In this study, we measured the current-driven real-space deformation of isolated, pinned skyrmions within Co 10 Zn 10 at room temperature. We observed that the skyrmions are surprisingly soft, readily deforming during electric current application into an elliptical shape with a well-defined deformation axis (semimajor axis). We found that this axis rotates unidirectionally toward the current direction irrespective of electric current polarity and that the elliptical deformation reverses back upon current termination. We quantified the average distortion δ, which increased by ∼90% during the largest applied current density | j | = 8.46 ×10 9 A/m 2 when compared with the skyrmion’s intrinsic shape ( j = 0 ). Additionally, we demonstrated an approximately 120% average skyrmion core size expansion during current application, highlighting the skyrmions’ inherent topological protection. This evaluation of in situ electric current–induced skyrmion deformation paints a clearer picture of spin-polarized electron–skyrmion interactions and may prove essential in designing spintronic devices.
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Chen, Gong, Colin Ophus, Alberto Quintana, Heeyoung Kwon, Changyeon Won, Haifeng Ding, Yizheng Wu, Andreas K. Schmid, and Kai Liu. "Reversible writing/deleting of magnetic skyrmions through hydrogen adsorption/desorption." Nature Communications 13, no. 1 (March 15, 2022). http://dx.doi.org/10.1038/s41467-022-28968-4.
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AbstractMagnetic skyrmions are topologically nontrivial spin textures with envisioned applications in energy-efficient magnetic information storage. Toggling the presence of magnetic skyrmions via writing/deleting processes is essential for spintronics applications, which usually require the application of a magnetic field, a gate voltage or an electric current. Here we demonstrate the reversible field-free writing/deleting of skyrmions at room temperature, via hydrogen chemisorption/desorption on the surface of Ni and Co films. Supported by Monte-Carlo simulations, the skyrmion creation/annihilation is attributed to the hydrogen-induced magnetic anisotropy change on ferromagnetic surfaces. We also demonstrate the role of hydrogen and oxygen on magnetic anisotropy and skyrmion deletion on other magnetic surfaces. Our results open up new possibilities for designing skyrmionic and magneto-ionic devices.
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Deng, Zi-Lan, Tan Shi, Alex Krasnok, Xiangping Li, and Andrea Alù. "Observation of localized magnetic plasmon skyrmions." Nature Communications 13, no. 1 (January 10, 2022). http://dx.doi.org/10.1038/s41467-021-27710-w.
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AbstractOptical skyrmions have recently been constructed by tailoring vectorial near-field distributions through the interference of multiple surface plasmon polaritons, offering promising features for advanced information processing, transport and storage. Here, we provide experimental demonstration of electromagnetic skyrmions based on magnetic localized spoof plasmons (LSP) showing large topological robustness against continuous deformations, without stringent external interference conditions. By directly measuring the spatial profile of all three vectorial magnetic fields, we reveal multiple π-twist target skyrmion configurations mapped to multi-resonant near-equidistant LSP eigenmodes. The real-space skyrmion topology is robust against deformations of the meta-structure, demonstrating flexible skyrmionic textures for arbitrary shapes. The observed magnetic LSP skyrmions pave the way to ultra-compact and robust plasmonic devices, such as flexible sensors, wearable electronics and ultra-compact antennas.
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Luo, Jia, Jia Hao Guo, Yun He Hou, Jun Lin Wang, Yong Bing Xu, Yan Zhou, Philip Wing Tat Pong, and Guo Ping Zhao. "Manipulating Skyrmion Motion on a Nanotrack with Varied Material Parameters and Tilted Spin Currents." Chinese Physics Letters, August 28, 2023. http://dx.doi.org/10.1088/0256-307x/40/9/097501.
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Abstract Magnetic skyrmions are topological quasiparticles with nanoscale size and high mobility, which have potential applications in information storage and spintronic devices. The manipulation of skyrmion’s dynamics in the track is an important topic due to the skyrmion Hall effect, which can deviate the skyrmions from the preferred direction. In this paper, a new model based on the ferromagnetic FM skyrmion is proposed, where the skyrmion velocity can be well controlled by adjusting the direction of the current. Using this design, we can avoid the annihilation of the skyrmion induced by the skyrmion Hall effect, which is confirmed by our micromagnetic simulation based on Mumax3. In the meantime, we increase the average velocity of the skyrmion by varying the intrinsic material parameters in the track, where the simulations agree well with our analytical results based on the Thiele equation. Finally, we give a phase diagram of the output of the skyrmion in the T-type track, which provides some practical ways for the design of logic gates by manipulating crystalline anisotropy through the electrical control.
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Wang, X. R., X. C. Hu, and H. T. Wu. "Stripe skyrmions and skyrmion crystals." Communications Physics 4, no. 1 (June 17, 2021). http://dx.doi.org/10.1038/s42005-021-00646-9.
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AbstractSkyrmions are important in quantum field theory and information technology for being topological solitons and for their attractive applications. Magnetic skyrmions are believed to be circular and stripy spin textures accompanied skyrmion crystals (SkXs) termed spiral/helical/cycloid orders have zero skyrmion number. Here we show that those stripy spin textures are skyrmions, siblings of circular skyrmions in SkXs and cousins of isolated circular skyrmions. Various irregular morphologies are the nature structures of skyrmions in the ground states. At the extreme of one skyrmion in the whole sample, the skyrmion is a ramified stripe. As the skyrmion number density increases, skyrmion shapes gradually change from ramified stripes to rectangular stripes, and eventually to circular objects. At a high skyrmion number density, SkXs are the preferred states. Our findings reveal the nature and properties of stripy spin texture, and open an avenue for manipulating skyrmions.
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Kwon, Hee Young, Kyung Mee Song, Juyoung Jeong, Ah-Yeon Lee, Seung-Young Park, Jeehoon Kim, Changyeon Won, Byoung-Chul Min, Hye Jung Chang, and Jun Woo Choi. "High-density Néel-type magnetic skyrmion phase stabilized at high temperature." NPG Asia Materials 12, no. 1 (December 2020). http://dx.doi.org/10.1038/s41427-020-00270-z.
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AbstractThe discovery of a thermally stable, high-density magnetic skyrmion phase is a key prerequisite for realizing practical skyrmionic memory devices. In contrast to the typical low-density Néel-type skyrmions observed in technologically viable multilayer systems, with Lorentz transmission electron microscopy, we report the discovery of a high-density homochiral Néel-type skyrmion phase in magnetic multilayer structures that is stable at high temperatures up to 733 K (≈460 °C). Micromagnetic simulations reveal that a high-density skyrmion phase can be stabilized at high temperature by deliberately tuning the magnetic anisotropy, magnetic field, and temperature. The existence of the high-density skyrmion phase in a magnetic multilayer system raises the possibility of incorporating chiral Néel-type skyrmions in ultrahigh-density spin memory devices. Moreover, the existence of this phase at high temperature shows its thermal stability, demonstrating the potential for skyrmion devices operating in thermally challenging modern electronic chips.
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Matsumoto, Takao, and Naoya Shibata. "Confinement of Magnetic Skyrmions to Corrals of Artificial Surface Pits with Complex Geometries." Frontiers in Physics 9 (January 28, 2022). http://dx.doi.org/10.3389/fphy.2021.774951.
Full textAbstract:
Magnetic skyrmion is a particle-like swirling spin texture promising for future memory devices. The geometric confinement and artificial control of skyrmions are crucial for such practical applications. In a previous research, we developed a technique to confine skyrmions to simple geometric corrals, such as a rectangle and a triangle, composed of artificial surface pits with nanometer-scale dimensions fabricated by using a focused electron beam. The technique has a potential advantage of facilitating more complex geometries, which has not been fully explored yet. Here we directly visualize skyrmions confined to surface-pit corrals with several complex geometries by using differential phase contrast scanning transmission electron microscopy. We find that individual skyrmions are deformed not only in shape but also in size under a moderate-bias field. We also find that deformed skyrmionic spin textures with opposite polarities coexist in the zero-field condition. The present study provides a guide to confine skyrmions, which should be useful for future applications.
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da Silva, Ricardo Lopes, Rodrigo Costa Silva, and Afranio Rodrigues Pereira. "Affecting the structure of skyrmions by using ferromagnetic nanodisks with inhomogeneous properties: switching the skyrmion helicity and polarity." Journal of Physics D: Applied Physics, October 19, 2022. http://dx.doi.org/10.1088/1361-6463/ac9b6d.
Full textAbstract:
Abstract Topological stability of skyrmions is an important element for using these objects in new technologies such as skyrmionics, spintronics and so on. Indeed, this kind of stability keeps the skyrmion structure unbending, shielding the information that, by chance, it could carry. On the other hand, a controlled manipulation of the skyrmion configuration could be an extra ingredient for technological applications. It is not an easy task and particularly, the control of skyrmion polarity and chirality (for Block-type), and helicity (for Néel-type) may be important in this direction. Here, we have investigated the skyrmion oscillatory motion in a hybrid nanodisk by using atomistic spin dynamics simulations. If a skyrmion is put to oscillate in a disk formed by two different materials, having opposite Dzyaloshinskii-Moriya interactions ($D_{1}=-D_{2}$), then, its helicity experiences an inversion. Nonetheless, if the skyrmion oscillations occur in a homogeneous disk submitted to opposites magnetic fields in distinct regions (for instance, semi-disks $1$ and $2$), the skyrmion polarity and helicity suffer an inversion. Such skyrmionic-oscillators could provide a dynamical degree of freedom, yielding new functionalities to skyrmion-based logic devices.