Interfacial Dzyaloshinskii-Moriya Interaction Research Articles

Designing Layered 2D Skyrmion Lattices in Moiré Magnetic Heterostructures

AbstractSkyrmions are promising for the next generation of spintronic and magnonic devices, but their zero‐field stability and controlled nucleation through chiral interactions remain challenging. In this theoretical study, the potential of moiré magnetic heterostructures to generate ordered skyrmion lattices from the stacking‐dependent magnetism in 2D magnets is explored. Heterostructures formed by twisting ultrathin CrBr3 films on top of CrI3 substrates are considered, assuming a moderate interfacial Dzyaloshinskii–Moriya interaction. At large moiré periodicity and appropriate substrate thickness, a moiré skyrmion lattice emerges in the interfacial CrBr3 layer due to the weaker exchange interactions in CrBr3 compared to CrI3. This lattice is then projected to the remaining layers of the CrBr3 film via chiral interlayer exchange fields. By varying the pristine stacking configurations within the ultrathin CrBr3 film, layered ferromagnetic and antiferromagnetic skyrmion lattices without the need for a permanent magnetic field are realized. These findings suggest the possibility of creating ordered skyrmion lattices in moiré magnetic heterostructures, enabling further exploration of their fundamental properties and technological relevance.

Chirality-dependent energy induced by spin-orbit torque-driven artificial spin texture

Recently, vast research has been under investigation on the role of chirality in magnetization dynamics, an area that currently lacks a comprehensive understanding. To gain further insight into the importance of chirality, we explore the effects of varying the degree of chirality. To investigate these effects, we have fabricated samples with perpendicular magnetic anisotropy symmetry breaking through local helium ion irradiation with various azimuthal angles and degrees of irradiation. In this system, the spin-orbit torque can induce artificial spin texture, and our azimuthal angle and degree of chirality dependent results reveal a clear cosine dependence and a nonlinear increase, respectively. It implies the system not only follows the energy contribution of interfacial Dzyaloshinskii-Moriya interaction but also has a nonlinear impact depending on anisotropy asymmetry induced chirality differences. These experimental observations are consistent with our theoretical model and micromagnetic simulations, supporting our experimental results. Overall, our findings provide further insights into the role of chirality in magnetization dynamics and may have important implications for the development of future magnetic devices.

Infinite critical boson non-Fermi liquid on heterostructure interfaces

We study the emergence of non-Fermi liquid on heterostructure interfaces where there exists an infinite number of critical boson modes accounting for the magnetic fluctuations in two spatial dimensions. The interfacial Dzyaloshinskii-Moriya interaction naturally arises in magnetic interactions due to the absence of inversion symmetry, resulting in a degenerate contour for the low-energy bosonic modes in the momentum space which simultaneously becomes critical near the magnetic phase transition. The itinerant electrons are scattered by the critical boson contour via the Yukawa coupling. When the boson contour is much smaller than the Fermi surface, it is shown that, there exists a regime with a dynamic critical exponent {z=3} while the boson contour still controls the low-energy magnetic fluctuations. Using a self-consistent renormalization calculation for this regime, we uncover a prominent non-Fermi liquid behavior in the resistivity with a characteristic temperature scaling power. These findings open up new avenues for understanding boson-fermion interactions and the novel fermionic quantum criticality.

Ferromagnetic monolayer with interfacial Dzyaloshinskii-Moriya interaction: Magnon spectrum and effect of quenched disorder

Ferromagnetic monolayer with interfacial Dzyaloshinskii-Moriya interaction: Magnon spectrum and effect of quenched disorder

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.

Magnetic properties of Pt/Co/Pt trilayers with W insert layer

The results of magnetic investigations of epitaxial trilayers Pt/Co/Pt asymmetrically modified by inserting W layer at the bottom or top Co interfaces in the wide ranges of Co and W layer thicknesses are reported. The samples were epitaxially grown on Pt buffer in double wedge geometry: the dCo thickness gradient of the continuous Co wedge was orthogonal to the dW thickness gradient of non-magnetic W underlayer (overlayer) deposited either as step-like or continuous wedge. Resulting samples have Pt/W/Co/Pt (Pt/Co/W/Pt) stacking sequences. The influence of (dCo, dW) on static magnetization reversal processes were studied using magnetooptical Kerr effect; Brillouin light scattering (BLS) method was applied for dynamical characterization. The magnetic dead layer thickness d0 abruptly increases until dW reaches ∼ 0.5 nm for both orderings. Then its value saturates for Pt/Co/W/Pt, while for Pt/W/Co/Pt samples a slow growth is observed. For dCo corresponding to out-of-plane magnetization the inserting of W layer leads to the strong reduction in coercivity (two orders of magnitude) and transition to in-plane magnetization in the case of Pt/W/Co/Pt ordering, while the Pt/Co/W/Pt samples demonstrates weak changes of coercivity with small change in magnetic anisotropy. The strength of interfacial Dzyaloshinskii-Moriya interaction (iDMI) and spin wave damping for selected dCo thicknesses as a function of dW were derived from BLS measurements. Inserting W with thickness dW ∼ 0.1 nm induces significant iDMI changes, iDMI saturates for dW > 0.4 nm. Our findings demonstrate the efficiency of thin W interlayer on modification of magnetic parameters in Pt/Co/Pt trilayer.

Magnetic field assisted stabilization of circular double wall domain lattice in oxidized Fe3GeTe2 flakes

The family of 2D ferromagnets is in the center of research for novel spintronics applications. Among the various 2D ferromagnets, Fe3GeTe2 has drawn significant attention since it combines a high Curie temperature with a van der Waals structure, which allows easy exfoliation, and a high spin polarization/large spin–orbit coupling. The presence of interfacial DMI in 2D ferromagnets have a significant impact on the behavior of magnetic domain walls, which are fundamental in magnetic memory and logic devices. By controlling the interfacial DMI, it is possible to manipulate the motion of domain walls and the magnetic domain configuration, which is essential for the development of efficient and reliable magnetic devices. In this study, we investigate the effect of an, inversion symmetry breaking, oxidized layer on the magnetic domain structure of Fe3GeTe2 flakes due to the emergence of interfacial DMI. By combining magneto-optical Kerr effect microscopy images and micromagnetic simulations, we study the formation of a circular double wall (CDW) domain lattice in oxidized flakes under specific field cooling and magnetic field sweeping protocols. Their formation is attributed to a competition between the exchange interaction both symmetric and antisymmetric (associated to interfacial DMI), magnetocrystalline anisotropy and the external magnetic field. The CDW domains have a diameter of several microns, a magnetic structure resembling that of a skyrmionium and are arranged in regular lattice that survives thermal fluctuations close to T c. Our results suggest that these CDW domains transition to Néel type skyrmions after a magnetic field threshold. These findings could have important implications for the design and optimization of 2D ferromagnetic materials for spintronic applications.

Phase transitions driven by magnetoelectric and interfacial Dzyaloshinskii-Moriya interaction

In this paper, we study phase transitions in a magnetoelectric bilayer with two order parameters using Monte Carlo simulation. We investigate the effects of temperature, magnetoelectric coupling, and anisotropy in the multiferroic bilayer formed by a frustrated antiferromagnetic layer with Heisenberg spins and a triangular lattice ferroelectric layer. We show that magnetic frustration induces creation of skyrmions and a skyrmion lattice at moderate values of Dzyaloshinskii-Moriya interaction and interface magnetoelectric coupling with adjacent ferroelectric layer. The skyrmion crystal is stable up to relatively high temperatures. The effect of anisotropy is to cause only a shift of the critical temperature without changing the type of the phase transition. The phase of the skyrmion lattice becomes more resistant and stable to temperature fluctuations in the case of a highly anisotropic frustrated film.

The Stack Optimization of Magnetic Heterojunction Structures for Next-Generation Spintronic Logic Applications.

Magnetic heterojunction structures with a suppressed interfacial Dzyaloshinskii-Moriya interaction and a sustainable long-range interlayer exchange coupling are achieved with an ultrathin platinum insertion layer. The systematic inelastic light scattering spectroscopy measurements indicate that the insertion layer restores the symmetry of the system and, then, the interfacial Dzyaloshinskii-Moriya interaction, which can prevent the identical magnetic domain wall motions, is obviously minimized. Nevertheless, the strong interlayer exchange coupling of the system is maintained. Consequently, synthetic ferromagnetic and antiferromagnetic exchange couplings as a function of the ruthenium layer thickness are observed as well. Therefore, these optimized magnetic multilayer stacks can avoid crucial issues, such as domain wall tilting and position problems, for next-generation spintronic logic applications. Moreover, the synthetic antiferromagnetic coupling can open a new path to develop a radically different NOT gate via current-induced magnetic domain wall motions and inversions.

Enhancement in Interfacial Dzyaloshinskii–Moriya Interaction in Pt/CoFe(B)/MgO Structures by Suppression of FePt Interface Phases with the Addition of Boron

Enhancement in Interfacial Dzyaloshinskii–Moriya Interaction in Pt/CoFe(B)/MgO Structures by Suppression of FePt Interface Phases with the Addition of Boron

Correlation between anisotropy and concentration profiles of Ir/Co/Pt system modified by Ga+ bombardment with different energies

In thin-film systems, effects induced by interfaces play a crucial role which makes them the source of many important magnetic properties (e.g., the perpendicular magnetic anisotropy, interfacial Dzyaloshinskii-Moriya interaction, etc.). Therefore, the ability to design interfaces in controlled ways is very important. Here, we will show that a proper choice of Ga+ ion energy permits control of modification efficiency at the bottom and at the top interfaces. We used this fact totune the perpendicular magnetic anisotropy of an Ir/Co/Pt layered system. Analyzing theexperimental data and Monte-Carlo simulations using TRIDYN code, we found that the mixing of elements is stronger for the top interface (Co/Pt) than for the bottom interface (Ir/Co) and this difference can be enhanced by reducing the ion energy. This technique opens a new way to control the magnetic properties of layered systems on which structural asymmetries (between thebottom and top interfaces of the magnetic layer) influence magnetic properties.

2D-Perovskite Multiferroics: Interface-Induced Magnetoelectric Effect in Perovskite-Based Multiferroic Superlattices

Multiferroics are materials crucial for energy-efficient scalable electronics. The implementation of an effective combination of ferroic orderings on the nanoscale requires the design of new multiferroic materials. Recently, there have been observations of magnetoelectricity in the antiferromagnetic Ruddlesden-Popper and perovskite oxides with the interfacial Dzyaloshinskii-Moriya interaction. We propose a model for studying magnetic states and magnetoelectric effects in magnetoelectrically coupled antiferromagnetic–ferroelectric bi-layers with the interfacial Dzyaloshinskii–Moriya interaction. The ground magnetic states are calculated for a system on a rectangular lattice, with Heisenberg spins interacting with each other via an antiferromagnetic exchange interaction and a Dzyaloshinskii–Moriya interaction in the absence of an external magnetic field. Our calculations show that the interfacial Dzyaloshinskii-Moriya interaction in the considered system leads to the stabilization of topological skyrmionic states in a zero magnetic field. We explore transformations of magnetic states considering the changes in the in-plane magnetic anisotropy constant and the magnetoelectric coupling parameter. Our findings have shown the possibility of the existence of several magnetic configurations: a skyrmion lattice, a skyrmion state, and a uniform antiferromagnetic ordering realized at a definite ratio of the system parameters. We determine the areas of the phases existence and the conditions required for spin-reorientation phase transitions.

Slonczewski-spin-current driven dynamics of 180∘ domain walls in spin valves with interfacial Dzyaloshinskii–Moriya interaction

Steady-flow dynamics of ferromagnetic 180∘ domain walls (180DWs) in long and narrow spin valves (LNSVs) with interfacial Dzyaloshinskii–Moriya interaction (IDMI) under spin currents with Slonczewski factor are examined. Depending on the magnetization orientation of polarizers (pinned layers of LNSVs), dynamics of 180DWs in free layers of LNSVs are subtly manipulated: (i) for parallel polarizers, stronger spin polarization leads to higher Walker limit thus ensures the longevity of faster steady flows. Meantime, IDMI induces both the stable-region flapping and its width enlargement. (ii) For perpendicular polarizers, a wandering of 180DWs between bi- and tri-stability persists with the criticality adjusted by the IDMI. (iii) For planar-transverse polarizers, IDMI makes the stable region of steady flows completely asymmetric and further imparts a high saturation wall velocity under large current density. Under the last two polarizers, the ultrahigh differential mobility of 180DWs survives. The combination of Slonczewski spin current and IDMI provides various possibilities of fine controlling on 180DW dynamics, hence opens avenues for magnetic nanodevices with rich functionality and high robustness.

Variable spin texture in Mn3Sn/Pt heterostructures revealed by magnetic circular dichroism

Non-collinear antiferromagnets with a D019 hexagonal structure have attracted tremendous attention for their potential applications in topological spintronics. Exploring the relationship between spin texture and electronic band structure is crucial for understanding the physical nature of these chiral antiferromagnets. Here, we systematically investigated the variation of topological spin texture of the non-collinear antiferromagnet Mn3Sn film using magnetic circular dichroism (MCD) spectroscopy. The evolution of Mn spin texture from coplanar inverted triangular structure to swirling spin texture was achieved in Mn3Sn/Pt heterostructures through introducing an interfacial Dzyaloshinskii–Moriya interaction (DMI) at room temperature. Correspondingly, unconventional zero-crossing points in energy-resolved MCD spectra as well as a gradual shift of a zero-crossing point to longer wavelength were observed. Our work provides a spin texture modulation approach via interfacial DMI and an effective non-contact magneto-optical detection method to reveal the spin texture in the non-collinear antiferromagnet/heavy metal system.

Manipulation of spin–orbit torque and Dzyaloshinskii-Moriya interaction by varying Mn concentration in Pt1-xMnx/Co bilayer

Reducing critical current density (JC) of current-driven magnetization switching via power-efficient spin–orbit torque (SOT) is a key challenge in spin-based memory and logic devices. The Pt1-xMnx alloy shows prospect for enhancing the damping-like SOT efficiency (ξDL) while maintaining relatively low resistivity and power consumption. In this work, we investigated the Mn concentration x dependence of ξDL in Pt1-xMnx/Co bilayer and observed a nonmonotonic variation with the maximum ξDL ≈ 0.25 appearing around x = 0.2. The increase of the Pt1-xMnx layer resistivity is the main contribution to the enhancement of ξDL. Mn atoms doped in Pt not only modulate ξDL originating from the spin Hall effect of the Pt1-xMnx layer, but also affect the interfacial phenomena at the Pt1-xMnx/Co interface. We find that the related interfacial Dzyaloshinskii-Moriya interaction (DMI) is also tunable by x with the maximum appearing around x = 0.15. The significantly reduced JC of Pt1-xMnx/Co bilayer is mainly due to the enhancement of ξDL and the attenuation of effective perpendicular magnetic anisotropy energy density. Meanwhile, Pt1-xMnx/Co bilayer maintains low power consumption and necessary thermal stability. Our work highlights the potential of alloying Pt with Mn as a valuable means to achieve high-performance SOT spintronic devices.

Suppression of spin-wave nonreciprocity due to interfacial Dzyaloshinskii-Moriya interaction by lateral confinement in magnetic nanostructures

Suppression of spin-wave nonreciprocity due to interfacial Dzyaloshinskii-Moriya interaction by lateral confinement in magnetic nanostructures

Analytic theory for Néel skyrmion size, accounting for finite film thickness

The energy of a Néel skyrmion in a magnetic film with interfacial DMI is developed analytically, with the finite thickness of the film taken into account. Many theories for the energy of magnetic skyrmions use models that are only accurate in the limit that the film thickness vanishes. One theory [Büttner et al. Sci. Rep. 8, 4464 (2018)] provides exceptionally accurate expressions for the skyrmion energy for finite thickness films, but does not yield an analytic solution for the skyrmion size, plus it contains contributions which are found using fitting methods. Here, we approximate the demagnetizing energy of a skyrmion by examining the form of magnetostatic Green’s function expressions for the demagnetizing fields. Then, analytic expressions for the skyrmion radius and the skyrmion domain wall width are derived in the limit of zero applied field. Our methods are rigorously compared to other calculation methods and compare well to numerical calculations and experimental results, both with and without an applied magnetic field. The approximations that allow for an analytic result lead to a loss of accuracy for the skyrmion radius of up to 20% but this loss in accuracy may be offset by the simplicity of the developed physical expressions. Finite thickness is important to consider for skyrmions existing in multilayer stacks with total thickness of a few nanometers.

Experimental Observation of Flat Bands in One-Dimensional Chiral Magnonic Crystals.

Spin waves represent the collective excitations of the magnetization field within a magnetic material, providing dispersion curves that can be manipulated by material design and external stimuli. Bulk and surface spin waves can be excited in a thin film with positive or negative group velocities and, by incorporating a symmetry-breaking mechanism, magnetochiral features arise. Here we study the band diagram of a chiral magnonic crystal consisting of a ferromagnetic film incorporating a periodic Dzyaloshinskii-Moriya coupling via interfacial contact with an array of heavy-metal nanowires. We provide experimental evidence for a strong asymmetry of the spin wave amplitude induced by the modulated interfacial Dzyaloshinskii-Moriya interaction, which generates a nonreciprocal propagation. Moreover, we observe the formation of flat spin-wave bands at low frequencies in the band diagram. Calculations reveal that depending on the perpendicular anisotropy, the spin-wave localization associated with the flat modes occurs in the zones with or without Dzyaloshinskii-Moriya interaction.

Magnetic bubbles with alternating chirality in domain walls

In magnetic multilayers with perpendicular anisotropy, the competition of short-range and long-range interactions gives rise to the stability of cylindrical magnetic domains, also known as magnetic bubbles. The presence of Dzyaloshinsky-Moriya interaction induced by asymmetric interfaces between magnetic and nonmagnetic layers may lead to the formation of cylindrical bubble domains with Neel-type domain walls across the whole thickness of the multilayer. Such domain walls produce no contrast in Lorentz TEM under the normal incidence of the electron beam to the film. The latter is often used as an argument for the presence of Dzyaloshinskii-Moriya interaction in the system. Here we show that in magnetic multilayers, the absence of the Lorentz TEM contrast might also have another origin. In particular, in the absence of interfacial Dzyaloshinskii-Moriya interaction and weak interlayer exchange coupling, the magnetic bubbles might have Bloch-type domain walls of alternate chirality in adjacent layers. Such domain walls also do not produce magnetic contrast in Lorentz TEM at normal incidence of the electron beam. We show that, in the absence of interlayer exchange coupling, the magnetic bubble domains with the domain walls of fixed and alternate chirality have nearly identical energies and can coexist in the same range of magnetic fields. Using the geodesic nudged elastic band method, we prove that these states are separated by finite energy barriers. Furthermore, we demonstrate that magnetic multilayers with only dipolar coupling, besides the magnetic bubbles with nontrivial topology in all layers, can accommodate solutions with trivial topology within the internal layers.

Measurement of the Dzyaloshinskii-Moriya Interaction in Mn4N Films That Host Skyrmions.

Mn4N thin film is one of the potential magnetic mediums for spintronic devices due to its ferrimagnetism with low magnetization, large perpendicular magnetic anisotropy (PMA), thermal stability, and large domain wall velocity. Recent experiments confirmed the existence of tunable magnetic skyrmions in MgO/Mn4N/CuxPt1-x(x = 0, 0.5, 0.9, 0.95), and density functional theory (DFT) calculation provided a large theoretical value of the interfacial Dzyaloshinskii-Moriya interaction (iDMI) of Mn4N/Pt, which is consistent with the predicted chemical trend of the DMI in transition metal/Pt films. So far, the measured DMI has not been reported in Mn4N, which is needed in order to support the predicted large DMI value. This paper reports the average DMI of MgO/Mn4N(17 nm)/CuxPt1-x(3 nm) extracted from the anomalous Hall effect with various tilted angles, which is based on magnetic droplet theory with DMI effects. The DMI decreases from 0.267 mJ/m2 to 0.011 mJ/m2 with non-linear tendencies as Cu concentration in the CuxPt1-x capping layer increases from 0 to 1, demonstrating the control of the DMI through the CuxPt1-x capping layer. Furthermore, a solid solution model is developed based on an X-ray photoelectron spectroscopy (XPS) compositional depth profile to analyze the possible effects on the DMI from the mixing layers at the surface of Mn4N. After taking into account the mixing layers, the large DMI in Mn4N film with Pt capping is consistent with the predicted DMI.