Current-driven Domain Wall Motion Research Articles

MODVORTEx: computer vision-driven automation for magnetic domain wall velocity analysis

Abstract This paper presents Magneto Optic Domain Velocity Observation and Real-Time Extraction (MODVORTEx), a comprehensive software solution for automating domain wall (DW) velocity measurements in magnetic materials using magneto-optic Kerr effect microscopy. Building upon our previous work on bubble domain structures, we introduce a versatile graphical user interface (GUI) that accommodates arbitrary domain shapes and employs advanced computer vision techniques. The software provides different methods for DW detection and velocity calculation, catering to various domain structures of arbitrary shape. Our approach significantly reduces the time and effort required for data extraction, transforming a process that previously took days of manual work into a task completable within minutes. We provide the details of the algorithmic implementation which is organized into pre-processing, DW detection, displacement measurement, and velocity extraction. This tool is applicable to a wide range of scenarios, including bubble domain dynamics, Dzyaloshinskii–Moriya interaction studies in perpendicular magnetic anisotropy systems, current-driven DW motion in patterned strips etc. By providing both GUI and Application Programing Interface, our software offers flexibility for integration into existing measurement systems and adaptability for specific research needs. This automation promises to accelerate research in spintronics and magnetic materials, enabling more comprehensive and accurate studies of DW dynamics.

Current-driven domain wall motion in ferrimagnetic nanowires

Current-driven domain wall motion in ferrimagnetic nanowires

Predicted multiple Walker breakdowns for current-driven domain wall motion in antiferromagnets

Predicted multiple Walker breakdowns for current-driven domain wall motion in antiferromagnets

Current-driven fast magnetic octupole domain-wall motion in noncollinear antiferromagnets

Antiferromagnets (AFMs) have the natural advantages of terahertz spin dynamics and negligible stray fields, thus appealing for use in domain-wall applications. However, their insensitive magneto-electric responses make controlling them in domain-wall devices challenging. Recent research on noncollinear chiral AFMs Mn3X (X = Sn, Ge) enabled us to detect and manipulate their magnetic octupole domain states. Here, we demonstrate a current-driven fast magnetic octupole domain-wall (MODW) motion in Mn3X. The magneto-optical Kerr observation reveals the Néel-like MODW of Mn3Ge can be accelerated up to 750 m s-1 with a current density of only 7.56 × 1010 A m-2 without external magnetic fields. The MODWs show extremely high mobility with a small critical current density. We theoretically extend the spin-torque phenomenology for domain-wall dynamics from collinear to noncollinear magnetic systems. Our study opens a new route for antiferromagnetic domain-wall-based applications.

The Combined Effect of Spin-Transfer Torque and Voltage-Controlled Strain Gradient on Magnetic Domain-Wall Dynamics: Toward Tunable Spintronic Neuron

Magnetic domain wall (DW), as one of the promising information carriers in spintronic devices, have been widely investigated owing to its nonlinear dynamics and tunable properties. Here, we theoretically and numerically demonstrate the DW dynamics driven by the synergistic interaction between current-induced spin-transfer torque (STT) and voltage-controlled strain gradient (VCSG) in multiferroic heterostructures. Through electromechanical and micromagnetic simulations, we show that a desirable strain gradient can be created and it further modulates the equilibrium position and velocity of the current-driven DW motion. Meanwhile, an analytical Thiele’s model is developed to describe the steady motion of DW and the analytical results are quite consistent with the simulation data. Finally, we find that this combination effect can be leveraged to design DW-based biological neurons where the synergistic interaction between STT and VCSG-driven DW motion as integrating and leaking motivates mimicking leaky-integrate-and-fire (LIF) and self-reset function. Importantly, the firing response of the LIF neuron can be efficiently modulated, facilitating the exploration of tunable activation function generators, which can further help improve the computational capability of the neuromorphic system.

Spin wave-assisted enhanced current-driven domain wall movement

The track memory based on current driven magnetic domain wall motion is a potential device for the next generation of magnetic information storage. To improve the speed of current driven domain wall motion and reduce the Joule heat, the relevant laws and physical mechanisms of the spin wave assisting current driven domain wall motion in long linear magnetic nanoribbons has been investigated to achieve spin wave assisted enhancement of current driven domain wall motion. The results show that the spin wave assisting can both enhances and weakens current driven domain wall motion depends on the driving current. Further research has shown that, for giving frequency spin waves, in the low current, spin wave assistance can enhance the current driven magnetic domain wall movement, and the enhancement of its movement speed increases non-monotonically with the increase of spin wave amplitude, but in the high current, spin wave assistance weakens the current driven magnetic domain wall movement, and the weakening of its movement speed nearly linear increases with the increase of spin wave amplitude. The critical current for distinguishing between the high and the low current depends on the amplitude and frequency of the assisting spin wave. On the other hand, for giving the amplitude spin wave, the increase or decrease of the spin wave assisting current driven domain wall motion exhibits a multimodal non-monotonic behavior as the frequency of the spin wave increases. Therefore, the appropriate spin wave assisting track storage technology can reduce the threshold current of track memory operation, making it more widely used. Also it can reduce Joule heat and improve the working efficiency of track memory.

Field-free spin-orbit torque switching in interlayer exchange coupled Co/Ta/CoTb

This study investigates a T-type field-free spin-orbit torque device with an in-plane magnetic layer coupled to a perpendicular magnetic layer via a non-magnetic spacer. The device utilizes a Co/Ta/CoTb structure, in which the in-plane Co layer and the perpendicular CoTb layer are ferromagnetically (FM) coupled through the Ta spacer. ‘T-type’ refers to the magnetization arrangement in the FM/spacer/FIM structure, where the magnetization in FM is in-plane, while in FIM, it is out-of-plane. This configuration forms a T-shaped arrangement for the magnetization of the two magnetic layers. Additionally, ‘interlayer exchange coupling (IEC)’ denotes the interaction between the two magnetic layers, which is achieved by adjusting the material and thickness of the spacer. Our results show that an in-plane effective field from the IEC enables deterministic current-induced magnetization switching of the CoTb layer. The field-driven and the current-driven asymmetric domain wall motion are observed and characterized by magneto-optic Kerr effect measurements. The functionality of multistate synaptic plasticity is demonstrated by understanding the relationship between the anomalous Hall resistance and the applied current pulses, indicating the potential for the device in spintronic memory and neuromorphic computing.

Position-reconfigurable pinning for magnetic domain wall motion

Precise control of magnetic domain wall (DW) motion is crucial for DW-based spintronic devices. To date, artificially designed DW pinning sites, such as notch structures, have been used to precisely control the DW position. However, the existing DW pinning methods are not reconfigurable because they cannot change the position of pinning site after being fabricated. Herein, a novel method for attaining reconfigurable DW pinning is proposed, which relies on the dipolar interactions between two DWs located in different magnetic layers. Repulsion between DWs in both layers was observed, indicating that one of the DWs acts as a pinning barrier for the other. Because the DW is mobile in the wire, the position of pinning can be modulated, thereby resulting in reconfigurable pinning that was experimentally demonstrated for current-driven DW motion. These findings provide additional controllability of DW motion, which may expand the functionality of DW-based devices to broader spintronic applications.

Control of field- and current-driven magnetic domain wall motion by exchange bias in Cr2O3/Co/Pt trilayers

We investigate the motion of magnetic domain walls driven by magnetic fields and current-driven spin-orbit torques in an exchange-biased system with perpendicular magnetization. We consider Cr2O3/Co/Pt trilayers as model system, in which the magnetization of the Co layer can be exchanged-biased out-of-plane or in-plane depending on the field cooling direction. In field-driven experiments, the in-plane exchange bias favors the propagation of the domain walls with internal magnetization parallel to the exchange bias field. In current-driven experiments, the domain walls propagate along the current direction, but the domain wall velocity increases and decreases symmetrically (anti-symmetrically) for both current polarities when the exchange bias is parallel (perpendicular) to the current line. At zero external field, the exchange bias modifies the velocity of current-driven domain wall motion by a factor of ten. We also find that the exchange bias remains stable under external fields up to 15 kOe and ns-long current pulses with current density up to 3.5x10^12 A/m^2. Our results demonstrate versatile control of the domain wall motion by exchange bias, which is relevant to achieve field-free switching of the magnetization in perpendicular systems and current-driven manipulation of domain walls velocity in spintronic devices.

Experimental verification of domain-wall tilting induced by Dzyaloshinskii Moriya interaction in current-driven domain-wall motion

Current-driven domain-wall motion is inevitably accompanied by tilting of the domain wall. There are two possible tilting mechanisms proposed either by the Oersted field or by the Dzyaloshinskii Moriya interaction (DMI). Here, we present the experimental observation that the DMI-induced mechanism plays decisive role in the domain-wall tilting for various films. Despite of opposite signs of the DMI and spin–orbit torque, all films showed that the domain-wall tilting direction follows the domain-wall propagation direction as predicted by DMI-induced mechanism. The present observation therefore indicates that the DMI-induced mechanism—rather than the Oersted-field-induced mechanism—is dominant in the domain-wall tilting for practical films of efficient current-driven domain-wall motion.

Engineering the Spin-Orbit-Torque Efficiency and Magnetic Properties of Tb / Co Ferrimagnetic Multilayers by Stacking Order

We measure the spin-orbit torques (SOTs), current-induced switching, and domain wall (DW) motion in synthetic ferrimagnets consisting of $\mathrm{Co}$/$\mathrm{Tb}$ layers with differing stacking order grown on a $\mathrm{Pt}$ underlayer. We find that the SOTs, magnetic anisotropy, compensation temperature, and SOT-induced switching are highly sensitive to the stacking order of $\mathrm{Co}$ and $\mathrm{Tb}$ and to the element in contact with $\mathrm{Pt}$. Our study further shows that $\mathrm{Tb}$ is an efficient SOT generator when in contact with $\mathrm{Co}$, such that its position in the stack can be adjusted to generate torques additive to those generated by $\mathrm{Pt}$. With optimal stacking and layer thickness, the dampinglike SOT efficiency reaches 0.3, which is more than twice that expected from the $\mathrm{Pt}$/$\mathrm{Co}$ bilayer. Moreover, the magnetization can be easily switched by the injection of pulses with current density of about (0.5--$2)\ifmmode\times\else\texttimes\fi{}{10}^{7}\phantom{\rule{0.2em}{0ex}}\mathrm{A}/{\mathrm{cm}}^{2}$ despite the extremely high perpendicular magnetic anisotropy barrier (up to 7.8 T). Efficient switching is due to a combination of large SOTs and low saturation magnetization owing to the ferrimagnetic character of the multilayers. We observe current-driven DW motion in the absence of any external field, which is indicative of homochiral N\'eel-type DWs stabilized by the interfacial Dzyaloshinkii-Moriya interaction. These results show that the stacking order in transition metal/rare-earth synthetic ferrimagnets plays a major role in determining the magnetotransport properties relevant for spintronic applications.

Experimental Verification of Domain-Wall Tilting Induced by Dzyaloshinskii Moriya Interaction in Current-Driven Domain-Wall Motion

Experimental Verification of Domain-Wall Tilting Induced by Dzyaloshinskii Moriya Interaction in Current-Driven Domain-Wall Motion

Current-Driven Domain Wall Motion in Curved Ferrimagnetic Strips Above and Below the Angular Momentum Compensation

Current driven domain wall motion in curved Heavy Metal/Ferrimagnetic/Oxide multilayer strips is investigated using systematic micromagnetic simulations which account for spin-orbit coupling phenomena. Domain wall velocity and characteristic relaxation times are studied as functions of the geometry, curvature and width of the strip, at and out of the angular momentum compensation. Results show that domain walls can propagate faster and without a significant distortion in such strips in contrast to their ferromagnetic counterparts. Using an artificial system based on a straight strip with an equivalent current density distribution, we can discern its influence on the wall terminal velocity, as part of a more general geometrical influence due to the curved shape. Curved and narrow ferrimagnetic strips are promising candidates for designing high speed and fast response spintronic circuitry based on current-driven domain wall motion.

Domain wall dynamics in two-dimensional van der Waals ferromagnets

Domain wall motion is in the core of many information technologies ranging from storage [Beach et al., J. Magn. Magn. Mater. 320, 1272–1281 (2008)], processing [Tatara et al., Phys. Rep. 468, 213–301 (2008)], and sensing [Ralph and Stiles, J. Magn. Magn. Mater. 320, 1190–1216 (2008)] up to novel racetrack memory architectures [Parkin et al., Science 320, 190–194 (2008)]. The finding of magnetism in two-dimensional (2D) van der Waals (vdW) materials [Huang et al., Nature 546, 270 (2017); Gong et al., Nature 546, 265–269 (2017); Guguchia et al., Sci. Adv. 4, eaat3672 (2018); Klein et al., Science 360, 1218–1222 (2018)] has offered a new frontier for the exploration and understanding of domain walls at the limit of few atom-thick layers. However, to use 2D vdW magnets for building spintronics nanodevices such as domain-wall based logic [Allwood et al., Science 309, 1688–1692 (2005); Luo et al., Nature 579, 214–218 (2020); Xu et al., Nat. Nanotechnol. 3, 97–100 (2008)], it is required to gain control of their domain wall dynamics by external driving forces such as spin-polarized currents or magnetic fields, which have so far been elusive. Here, we show that electric currents as well as magnetic fields can efficiently move domain walls in the recently discovered 2D vdW magnets CrI3 and CrBr3 at low temperatures and robust down to monolayer. We realize field- and current-driven domain wall motion with velocities up to 1020 m s−1, which are comparable to the state-of-the-art materials for domain-wall based applications [Yang et al., Nat. Nanotechnol. 10, 221–226 (2015); Woo et al., Nat. Mater. 15, 501–506 (2016); Vélez et al., Nat. Commun. 10, 4750 (2019); Siddiqui et al., Phys. Rev. Lett. 121, 057701 (2018); Ryu et al., Nat. Nanotechnol. 8, 527–533 (2013)]. Domain walls keep their coherence driven by the spin-transfer torque induced by the current and magnetic fields up to large values of about 12×109 A cm−2 and 5 T, respectively. For larger magnitudes of current or field, a transition to a hydrodynamic spin-liquid regime is observed with the emission of a periodic train of spin-wave solitons with modulational instability [Rabinovich and Trubetskov, Oscillations and Waves: In Linear and Nonlinear Systems, Mathematics and its Applications (Springer Netherlands, 2011)]. The emitted waveform achieves terahertz (THz) frequency in a wide range of fields and current densities, which opens up perspectives for reconfigurable magnonic devices. Moreover, we found that these spin-waves can transport spin angular momentum through the layers over distances as long as 10 μm without losses for the transport of spin information. Our results push the boundary of what is currently known about the dynamics of domain walls in 2D vdW ferromagnets and unveil strategies to design ultrathin, high-speed, and high-frequency spintronic devices.

Suppression of Walker breakdown in nanowires with periodic holes

The application based on current-driven domain wall (DW) motion mainly depends on the effective control of the moving velocity of the DW and its structural stability. In this paper, we show that a single square hole has a certain suppression effect on Walker breakdown (WB), and by introducing periodic square holes and improving the relevant design, a suppression effect on WB can be achieved in a limited time. As a result, the domain wall remains structurally stable while moving at a very high velocity. The size and position of the holes have an important influence on energy dissipation (ΔE) which plays a crucial role in the suppression of WB. We find that the ΔE strongly relies on the hole size (a), and theΔE has a polynomial relationship with the critical distance. When the current density is the critical value of JWB, the square hole size a = 16 nm and the distance between adjacent holes l = 1500 nm, WB can be suppressed perfectly, and the magnetic domain wall can keep moving at high speed for a long time.

Effect of a local temperature region on the suppression of walker breakdown in a permalloy nanowire

Magnetic domain walls are potential data carriers in future spintronic devices and the application based on current-driven domain wall (DW) motion primarily relies on the effective control of the moving velocity of the DW and its structural stability. In this work, the propagation of the magnetic domain walls along a ferromagnetic nanowire with a localized temperature region is studied by micromagnetic simulation. The research indicates that the local temperature field can suppress the generation of Walker breakdown (WB) and make the transverse domain wall (TDW) move to a longer distance with a stable structure. The degree of suppression is the result of the joint influence of temperature difference (ΔT) and temperature region width (d). When both of the ΔT and the d are relatively large, the suppression effect is comparatively strong, while either of the ΔT and the d are small, the suppression effect is weak. The results reveal the local temperature field makes the exchange energy in the region reach a very high value rapidly, and the out-of-plane magnetic moment Mz of the DW keeps at a high level, which promotes the high-speed motion of the DW and suppresses the WB by destroying the periodic transition of the DW structure.

Spin-Polarized Current-Driven Ferromagnetic Domain Wall Motion with a Skyrmion-Like Building Block

The purpose of the research is the construction of an analytic model for the description of a spin-polarized current-driven ferromagnetic domain wall motion with a skyrmion-like building block. The motion velocity of the ferromagnetic domain wall with a skyrmion-like building block is found as a function of the driving torques and an external magnetic field strength.

Novel interpretation of recent experiments on the dynamics of domain walls along ferrimagnetic strips

Domain wall motion along ferrimagnets is evaluated using micromagnetic simulations and a collective-coordinates model, both considering two sublattices with independent parameters. Analytical expressions are derived for strips on top of either a heavy metal or a substrate with negligible interfacial Dzyaloshinskii–Moriya interaction. The work focuses its findings in this latter case, with a field-driven domain wall motion depicting precessional dynamics which become rigid at the angular momentum compensation temperature, and a current-driven dynamics presenting more complex behavior, depending on the polarization factors for each sublattice. Importantly, our analyses provide also novel interpretation of recent evidence on current-driven domain wall motion, where walls move either along or against the current depending on temperature. Besides, our approach is able to substantiate the large non-adiabatic effective parameters found for these systems.

Electrical Generation and Detection of Terahertz Signal Based on Spin-Wave Emission From Ferrimagnets

Terahertz (THz) signals, mainly generated by photonic or electronic approaches, are being sought for various applications, whereas the development of magnetic source might be a necessary step to harness the magnetic nature of electromagnetic radiation. We show that the relativistic effect on the current-driven domain-wall motion induces THz spin-wave emission in ferrimagnets. The required current density increases dramatically in materials with strong exchange interaction and rapidly exceeds ${10}^{12}\phantom{\rule{0.1em}{0ex}}\mathrm{A}\phantom{\rule{0.1em}{0ex}}{\mathrm{m}}^{\ensuremath{-}2}$, leading to the device breakdown and thus the lack of experimental evidence. By translating the collective magnetization oscillations into voltage signals, we propose a three-terminal device for the electrical detection of THz spin wave. Through material engineering, a wide frequency range from 264 GHz to 1.1 THz and uniform continuous signals with improved output power can be obtained. As a reverse effect, the spin wave generated in this system is able to move the ferrimagnetic domain wall. Our work provides guidelines for the experimental verification of THz spin wave, and could stimulate the design of THz spintronic oscillators for wideband applications as well as the all-magnon spintronic devices.

Giant localised spin-Peltier effect due to ultrafast domain wall motion in antiferromagnetic metals

Spin thermo-electric phenomena have attracted wide attention recently, e.g., the spin Peltier effect—heat generation by magnonic spin currents. Here, we find that the spin Peltier effect also manifests as a heat wave accompanying fast moving magnetic textures. High speed and extreme magnetic excitation localisation are paramount for efficient transfer of energy from the spin-degrees of freedom to electrons and lattice. While satisfying both conditions is subject to severe restrictions in ferromagnets, we find that domain walls in antiferromagnets can overcome these limitations due to their ultrahigh mobility and ultra-small widths originating from the relativistic contraction. To illustrate our findings, we show that electric current driven domain wall motion in the antiferromagnetic metal Mn2Au can carry a localised heat wave with temperature up to 1 K. Since domain walls are localised magnetic objects, this effect has the potential for nanoscale heating sensing and functionalities.