Room-temperature Skyrmions Research Articles

Room temperature skyrmions in Pt/Co/Gd multilayers and their non-volatile electric-field creation in multiferroic heterostructure

This study delves into the formation and control of magnetic skyrmions within a Pt/Co/Gd multilayer system. By systematically varying the thickness of the Co layer, we observe the emergence of Néel-type skyrmions, characterized by confined magnetization curls with Lorentz transmission electron microscopy. The interplay between magnetic anisotropy, Dzyaloshinskii–Moriya interaction, and antiferromagnetic coupling at material interfaces is investigated to understand the stability and manipulation of these fascinating spin configurations. Additionally, we explore the impact of an external electric field on skyrmion generation, demonstrating a pathway for their controlled creation. The observed electric-field control of skyrmions offers a promising approach to achieving non-volatile magnetic states with low power consumption and negligible Joule heating. These findings hold great potential for advancing spintronics and magneto-electric devices, enabling modulation of skyrmions for information storage and processing applications.

Thickness- and Field-Dependent Magnetic Domain Evolution in van der Waals Fe3GaTe2.

The discovery of room-temperature ferromagnetism in van der Waals (vdW) materials opens new avenues for exploring low-dimensional magnetism and its applications in spintronics. Recently, the observation of the room-temperature topological Hall effect in the vdW ferromagnet Fe3GaTe2 suggests the possible existence of room-temperature skyrmions, yet skyrmions have not been directly observed. In this study, real-space imaging was employed to investigate the domain evolution of the labyrinth and skyrmion structure. First, Néel-type skyrmions can be created at room temperature. In addition, the influence of flake thickness and external magnetic field (during field cooling) on both labyrinth domains and the skyrmion lattice is unveiled. Due to the competition between magnetic anisotropy and dipole interactions, the specimen thickness significantly influences the density of skyrmions. These findings demonstrate that Fe3GaTe2 can host room-temperature skyrmions of various sizes, opening up avenues for further study of magnetic topological textures at room temperature.

Fast current-induced skyrmion motion in synthetic antiferromagnets.

Magnetic skyrmions are topological magnetic textures that hold great promise as nanoscale bits of information in memory and logic devices. Although room-temperature ferromagnetic skyrmions and their current-induced manipulation have been demonstrated, their velocity has been limited to about 100 meters per second. In addition, their dynamics are perturbed by the skyrmion Hall effect, a motion transverse to the current direction caused by the skyrmion topological charge. Here, we show that skyrmions in compensated synthetic antiferromagnets can be moved by current along the current direction at velocities of up to 900 meters per second. This can be explained by the cancellation of the net topological charge leading to a vanishing skyrmion Hall effect. Our results open an important path toward the realization of logic and memory devices based on the fast manipulation of skyrmions in tracks.

Electrical Detection and Nucleation of a Magnetic Skyrmion in a Magnetic Tunnel Junction Observed via Operando Magnetic Microscopy.

Magnetic skyrmions are topological spin textures which are envisioned as nanometer scale information carriers in magnetic memory and logic devices. The recent demonstrations of room temperature skyrmions and their current induced manipulation in ultrathin films were first steps toward the realization of such devices. However, important challenges remain regarding the electrical detection and the low-power nucleation of skyrmions, which are required for the read and write operations. Here, we demonstrate, using operando magnetic microscopy experiments, the electrical detection of a single magnetic skyrmion in a magnetic tunnel junction (MTJ) and its nucleation and annihilation by gate voltage via voltage control of magnetic anisotropy. The nucleated skyrmion can be manipulated by both gate voltages and external magnetic fields, leading to tunable intermediate resistance states. Our results unambiguously demonstrate the readout and voltage controlled write operations in a single MTJ device, which is a major milestone for low power skyrmion based technologies.

Room-temperature sub-100 nm Néel-type skyrmions in non-stoichiometric van der Waals ferromagnet Fe3-xGaTe2 with ultrafast laser writability

Realizing room-temperature magnetic skyrmions in two-dimensional van der Waals ferromagnets offers unparalleled prospects for future spintronic applications. However, due to the intrinsic spin fluctuations that suppress atomic long-range magnetic order and the inherent inversion crystal symmetry that excludes the presence of the Dzyaloshinskii-Moriya interaction, achieving room-temperature skyrmions in 2D magnets remains a formidable challenge. In this study, we target room-temperature 2D magnet Fe3GaTe2 and unveil that the introduction of iron-deficient into this compound enables spatial inversion symmetry breaking, thus inducing a significant Dzyaloshinskii-Moriya interaction that brings about room-temperature Néel-type skyrmions with unprecedentedly small size. To further enhance the practical applications of this finding, we employ a homemade in-situ optical Lorentz transmission electron microscopy to demonstrate ultrafast writing of skyrmions in Fe3-xGaTe2 using a single femtosecond laser pulse. Our results manifest the Fe3-xGaTe2 as a promising building block for realizing skyrmion-based magneto-optical functionalities.

Giant 2D Skyrmion Topological Hall Effect with Ultrawide Temperature Window and Low-Current Manipulation in 2D Room-Temperature Ferromagnetic Crystals

The discovery and manipulation of topological Hall effect (THE), an abnormal magnetoelectric response mostly related to the Dzyaloshinskii–Moriya interaction (DMI), are promising for next-generation spintronic devices based on topological spin textures such as magnetic skyrmions. However, most skyrmions and THE are stabilized in a narrow temperature window either below or over room temperature with high critical current manipulation. It is still elusive and challenging to achieve large THE with both wide temperature window till room temperature and low critical current manipulation. Here, using controllable, naturally oxidized sub-20 and sub-10 nm 2D van der Waals room-temperature ferromagnetic Fe3GaTe2−x crystals, we report robust 2D skyrmion THE with ultrawide temperature window ranging in three orders of magnitude from 2 to 300 K, in combination with giant THE of ∼ 5.4 μΩ⋅cm at 10 K and ∼ 0.15 μΩ⋅cm at 300 K, which is 1–3 orders of magnitude larger than that of all known room-temperature 2D skyrmion systems. Moreover, room-temperature current-controlled THE is also realized with a low critical current density of ∼ 6.2 × 105 A⋅cm−2. First-principles calculations unveil natural oxidation-induced highly enhanced 2D interfacial DMI reasonable for robust giant THE. This work paves the way to room-temperature electrically controlled 2D THE-based practical spintronic devices.

Spiral spin cluster in the hyperkagome antiferromagnet Mn3RhSi

Local spin correlation orders emerge in a paramagnetic state, with notable examples such as the partial order, cooperative paramagnetism, and soliton spin liquid. The noncentrosymmetric intermetallic antiferromagnet Mn3RhSi also exhibits the local spin correlation order in the paramagnetic state as magnetic short-range order in a wide temperature range. Here, we show that the local spin correlation order has a spiral structure by neutron scattering measurement of a Mn3RhSi single crystal. The possible origins of the magnetic cluster formation are discussed in terms of the Lifshitz invariant and the Griffiths phase, and compared with the room-temperature skyrmion phase of Co7Zn7Mn6 and non-Fermi liquid behavior of β-Mn.

Room-temperature creation and manipulation of skyrmions in MgO/FeNiB/Mo multilayers

Magnetic skyrmions in multilayer structures are considered as a new direction for the next generation of storage due to their small size, strong anti-interference ability, high current-driven mobility, and compatibility with existing spintronic technology. In this work, we present a tunable room temperature skyrmion platform based on multilayer stacks of MgO/FeNiB/Mo. We systematically studied the creation of magnetic skyrmions in MgO/FeNiB/Mo multilayer structures with perpendicular magnetic anisotropy (PMA). In these structures, the magnetic anisotropy changes from PMA to in-plane magnetic anisotropy (IMA) as the thickness of FeNiB layer increases. By adjusting the applied magnetic field and electric current, stable and high-density skyrmions can be obtained in the material system. The discovery of this material broadens the exploration of new materials for skyrmion and promotes the development of spintronic devices based on skyrmions.

Topological Spin Textures in a Non-Collinear Antiferromagnet System.

Topologically protected magnetic "whirls" such as skyrmions in antiferromagnetic materials have recently attracted extensive interests due to their nontrivial band topology and potential application in antiferromagnetic spintronics. However, the room-temperature skyrmions in natural metallic antiferromagnetic materials with merit of probably conveniently electrical manipulation have not been reported. Here, we realize room-temperature skyrmions in a non-collinear antiferromagnet Mn3 Sn capped with a Pt overlayer. The evolution of spin textures from coplanar inverted triangular structures to Bloch-type skyrmions is achieved via tuning the magnitude of interfacial Dzyaloshinskii - Moriya interaction. Beyond that, the temperature can induce an unconventional transition from skyrmions to antiferromagnetic meron-like spin textures at approximately 220 K in our Mn3 Sn/Pt samples. Combining with the theoretical calculations, we find the transition is originated from the temperature dependence of antiferromagnetic exchange interaction between kagome sublayers within the Mn3 Sn crystalline unitcell. Our findings open the avenue for the development of topological spin-swirling-based antiferromagnetic spintronics. This article is protected by copyright. All rights reserved.

Research Progress on Dynamics of Skyrmions Under the Effect of Pinning

Magnetic skyrmions offer the potential as an information carrier for the next-generation storage and computing devices such as racetrack memory devices, logic gates, and even neurocomputing owing to the topology-protected structure, nano-scale size and relatively low driving current compared to traditional devices. The discovery of magnetic skyrmions at room temperature also lays the foundation for realizing room-temperature magnetic skyrmion spintronic devices. Defects and impurities are unavoidable in real materials. These pinning centers significantly affect the dynamics of the skyrmion, including the critical driving current, and the Hall angle, etc. The study on room-temperature magnetic skyrmions in thin films has shown that the effect of pinning can be dominant at room temperature. Hence, the study of pinning effects and the skyrmion-pinning interaction is significant to the motion of magnetic skyrmions at room temperature and the realization of room-temperature magnetic skyrmion spin devices Magnetic skyrmion motion can be strongly modified under the effect of pinning (defects and purities). Moreover, these effects can inspire us to utilize artificial pinning centers to manipulate the dynamics of skyrmions. In this article, we introduce the models for skyrmion motion and pinning effect at room temperature and gives an overview of the methods for creating different types of pinning and their impact on the skyrmions. When pinning is induced by replacing or adding atoms, setting vacancies, changing the material thickness or curvature, or changing magnetic parameters, the skyrmions hall angle will vary. Moreover, the magnetic skyrmions can be fixed in a particular region, move along a specific orbit and overcome thermal perturbations at room temperature under the effect of pinning, which helps to realize magnetic skyrmion spin devices at room temperature.

Room-Temperature Magnetic Skyrmions and Large Topological Hall Effect in Chromium Telluride Engineered by Self-Intercalation.

Room-temperature magnetic skyrmion materials exhibiting robust topological Hall effect (THE) are crucial for novel nano-spintronic devices. However, such skyrmion-hosting materials are rare in nature. In this study, a self-intercalated transition metal dichalcogenide Cr1+ x Te2 with a layered crystal structure that hosts room-temperature skyrmions and exhibits large THE is reported. By tuning the self-intercalate concentration, a monotonic control of Curie temperature from 169 to 333K and a magnetic anisotropy transition from out-of-plane to the in-plane configuration are achieved. Based on the intercalation engineering, room-temperature skyrmions are successfully created in Cr1.53 Te2 with a Curie temperature of 295K and a relatively weak perpendicular magnetic anisotropy. Remarkably, a skyrmion-induced topological Hall resistivity as large as ≈106nΩ cm is observed at 290K. Moreover, a sign reversal of THE is also found at low temperatures, which can be ascribed to other topological spin textures having an opposite topological charge to that of the skyrmions. Therefore, chromium telluride can be a new paradigm of the skyrmion material family with promising prospects for future device applications.

Dynamics of Polar Skyrmion Bubbles under Electric Fields.

Room-temperature polar skyrmions, which have been recently discovered in oxide superlattice, have received considerable attention for their potential applications in nanoelectronics owing to their nanometer size, emergent chirality, and negative capacitance. For practical applications, their manipulation using external stimuli is a prerequisite. Herein, we study the dynamics of individual polar skyrmions at the nanoscale via insitu scanning transmission electron microscopy. By monitoring the electric-field-driven creation, annihilation, shrinkage, and expansion of topological structures in real space, we demonstrate the reversible transformation among skyrmion bubbles, elongated skyrmions, and monodomains. The underlying mechanism and interactions are discussed in conjunction with phase-field simulations. The electrical manipulation of nanoscale polar skyrmions allows the tuning of their dielectric permittivity at the atomic scale, and the detailed knowledge of their phase transition behaviors provides fundamentals for their applications in nanoelectronics.

Skyrmions in synthetic antiferromagnets and their nucleation via electrical current and ultra-fast laser illumination

Magnetic skyrmions are topological spin textures that hold great promise as nanoscale information carriers in non-volatile memory and logic devices. While room-temperature magnetic skyrmions and their current-induced motion were recently demonstrated, the stray field resulting from their finite magnetisation and their topological charge limit their minimum size and reliable motion. Antiferromagnetic skyrmions allow to lift these limitations owing to their vanishing magnetisation and net zero topological charge, promising ultra-small and ultra-fast skyrmions. Here, we report on the observation of isolated skyrmions in compensated synthetic antiferromagnets at zero field and room temperature using X-ray magnetic microscopy. Micromagnetic simulations and an analytical model confirm the chiral antiferromagnetic nature of these skyrmions and allow the identification of the physical mechanisms controlling their size and stability. Finally, we demonstrate the nucleation of synthetic antiferromagnetic skyrmions via local current injection and ultra-fast laser excitation.

High-temperature non-centrosymmetric magnets for skyrmionics

Such topological spin textures as magnetic skyrmions and antiskyrmions have attracted significant interest in recent years owing to their rich variety of underlying physics and potential applications in next-generation magnetic devices. In the domain of applications, it is essential to stabilize the topological spin textures over a wide range of temperatures, including room temperature, and manipulate them with various external stimuli. Significant developments have been made in room-temperature skyrmions and antiskyrmions arising from the Dzyaloshinskii–Moriya interaction (DMI) in several magnetic materials with broken inversion symmetry. In this Perspective, we review recent progress in non-centrosymmetric magnets with bulk DMI, which host skyrmions and antiskyrmions above room temperature. We first provide an overview of room-temperature Bloch-type skyrmions and the robustness of their metastability, the variety of their forms, and their dynamics in Co–Zn–Mn alloys with a β-Mn-type chiral structure. We then focus on room-temperature antiskyrmions as well as their topological transformations in Heusler alloys with D2d symmetry and Pd-doped (Fe,Ni)3P with S4 symmetry. The robust skyrmions and antiskyrmions, with versatile tunability in these non-centrosymmetric materials at room temperature, represent a step toward the long-sought milestone of “skyrmionics.”

Quantifying spin Hall topological Hall effect in ultrathin Tm3Fe5O12/Pt bilayers

Recent reports have shown that thulium iron garnet (TmIG) based bilayers are promising material platforms for realizing small, room-temperature skyrmions. For potential applications, it is imperative to accurately evaluate electrical readout signals of skyrmions. In this context, the topological Hall effect has been considered as a characteristic signature of skyrmion formation. Unlike previous studies that have modeled the anomalous Hall effect in ultrathin TmIG/Pt bilayers, we isolate its contribution to the electrical readout signal by directly measuring the magnetic hysteresis loops using a sensitive Sagnac magneto-optical Kerr effect technique. Our combined optical and electrical measurements reveal that the spin Hall topological Hall resistivity is considerably larger than previously estimated values. Our finding further indicates that skyrmions can exist at room-temperature and near-zero applied magnetic fields.

Non-volatile multi-state magnetic domain transformation in a Hall balance

High performance of the generation, stabilization and manipulation of magnetic skyrmions prompts the application of topological multilayers in spintronic devices. Skyrmions in synthetic antiferromagnets (SAF) have been considered as a promising alternative to overcome the limitations of ferromagnetic skyrmions, such as the skyrmion Hall effect and stray magnetic field. Here, by using the Lorentz transmission electron microscopy, the interconversion between the single domain, labyrinth domain and skyrmion state can be observed by the combined manipulation of electric current and magnetic field in a Hall balance (a SAF with the core structure of [Co/Pt]4/NiO/[Co/Pt]4 showing perpendicular magnetic anisotropy). Furthermore, high-density room temperature skyrmions can be stabilized at zero field while the external stimulus is removed and the skyrmion density is tunable. The generation and manipulation method of skyrmions in Hall balance in this study opens up a promising way to engineer SAF-skyrmion-based memory devices.

Large Dzyaloshinskii-Moriya interaction and room-temperature nanoscale skyrmions in CoFeB/MgO heterostructures

Magnetic skyrmions in heavy metal (HM)/CoFeB/MgO structures are of particular interest for skyrmion-based magnetic tunnel junction (MTJ) devices because of their reliable generation, stability, and readout through purely electrical methods. To optimize the properties, such as stability, a strong Dzyaloshinskii-Moriya interaction (DMI) is required at room temperature. Here, using first-principles calculations, we demonstrate that huge DMI can be obtained in Ir/CoFe structures with an Fe-terminated configuration. Moreover, Brillouin light-scattering measurements show that indeed Ta/Ir/Co 20 Fe 60 B 20 /MgO thin films with perpendicular magnetic anisotropy exhibit a large DMI value (1.13 mJ/m 2 ) when the thickness of the CoFeB layer is 1.1 nm, which can be attributed to the smooth and Fe-rich interface between Ir and CoFeB layers. Furthermore, we observe stable sub-100 nm magnetic skyrmions at room temperature in the Ir/CoFeB/MgO systems by magnetic force microscope. This work paves the way for promoting the application of skyrmions in CoFeB/MgO-based perpendicular anisotropy MTJ structures. Large DMI in Ir/CoFeB/MgO thin films with perpendicular magnetic anisotropy First-principles calculations combined with Brillouin light-scattering methods Significant role of interfacial configuration on the regulation of DMI Sub-100 nm room-temperature magnetic skyrmions in Ir/CoFeB/MgO multilayers Chen et al. observe a large Dzyaloshinskii-Moriya interaction, combined with the evidence of sub-100-nm room-temperature skyrmions in Ir/CoFeB/MgO structures. This material stack may provide a platform to realize skyrmionics, especially the nucleation and electrical detection of skyrmions in perpendicular anisotropy-based magnetic tunnel junctions.

Dependency of Anisotropy Field of Cofeb Layer on the Thickness of W Insert Layer for Manipulating Size of Skyrmions

Magnetic skyrmions are expected to offer novel functionalities for high density and low power spintronics devices in memory, logic and neuromorphic computing. [1] Since the recent observation at room temperature in which the skyrmion is stabilized by interfacial Dzyaloshinskii-Moriya interaction (DMI), many researches have focused on the creation and manipulating the motion of skyrmion in sub-100 nm size. [2-3] Observation of skyrmion sizes of sub-100 nm were reported at room temperature [4-5], however, there is little work on controlling the size of the skyrmions. In this work, we designed a novel structure, as shown in Figure 1, to manipulate the size of the skyrmion in engineering perspective. First, we investigated the roughness of the W seed layer depending on the sputtering power using atomic force microscopy (AFM). Then, we investigated the dependency of thickness of the W insert layer on the H k of CoFeB layer using vibrating sample magnetometer (VSM). The size of the skyrmions were determined by magneto-optical-kerr-effect (MOKE). Acknowledgement This research was supported by National R&D Program through the National Research Foundation of Korea(NRF) funded by Ministry of Science and ICT (2021M3F3A2A01037733) Reference [1] Nagaosa N. and Tokura Y., Nat. Nanotechnol. 8, 899-911 (2013)[2] Seonghoon W. et al. Observation of room-temperature magnetic skyrmions and their current-driven dynamics in ultrathin metallic ferromagnets, Nat. mat. 15, 501-506 (2016)[3] Wanjun J. et al. Science, 349(2645), 283-286 (2015)[4] Aranda A.R. et al. Journal of Magnetism and Magnetic Materials, 465, 471-479 (2018)[5] Mouad F. et al. Physics Letters A, 384(13), 126260 (2020)Figure 1. Dependency of skyrmion size on thickness of W insert. (a) skymion PMA structure with W insert, (b) Hk depending on W thickness, and (c) skymion formation under external field of 3.5 Oe Figure 1

Robust formation of nanoscale magnetic skyrmions in easy-plane anisotropy thin film multilayers with low damping

We experimentally demonstrate the formation of room-temperature skyrmions with radii of about 25 nm in easy-plane anisotropy multilayers with an interfacial Dzyaloshinskii-Moriya interaction (DMI). We detect the formation of individual magnetic skyrmions by magnetic force microscopy and find that the skyrmions are stable in out-of-plane fields up to about 200 mT. We determine the interlayer exchange coupling as well as the strength of the interfacial DMI. Additionally, we investigate the dynamic microwave spin excitations by broadband magnetic resonance spectroscopy. From the uniform Kittel mode we determine the magnetic anisotropy and low damping ${\ensuremath{\alpha}}_{\mathrm{G}}<0.04$. We also find clear magnetic resonance signatures in the nonuniform (skyrmion) state. Our findings demonstrate that skyrmions in easy-plane multilayers are promising for spin-dynamical applications.

Strain-Driven Dzyaloshinskii-Moriya Interaction for Room-Temperature Magnetic Skyrmions.

Dzyaloshinskii-Moriya interaction in magnets, which is usually derived from inversion symmetry breaking at interfaces or in noncentrosymmetric crystals, plays a vital role in chiral spintronics. Here we report that an emergent Dzyaloshinskii-Moriya interaction can be achieved in a centrosymmetric material, La_{0.67}Sr_{0.33}MnO_{3}, by a graded strain. This strain-driven Dzyaloshinskii-Moriya interaction not only exhibits distinctive two coexisting nonreciprocities of spin-wave propagation in one system, but also brings about a robust room-temperature magnetic skyrmion lattice as well as a spiral lattice at zero magnetic field. Our results demonstrate the feasibility of investigating chiral spintronics in a large category of centrosymmetric magnetic materials.