Large Dzyaloshinskii-Moriya Interaction Research Articles

Dzyaloshinskii–Moriya interaction and field-free sub-10 nm topological magnetism in Fe/bismuth oxychalcogenides heterostructures

Abstract Topological magnetism with strong robustness, nanoscale dimensions and ultralow driving current density (∼ 106 A/m2) is promising for applications in information sensing, storage, and processing, and thus sparking widespread research interest. Exploring candidate material systems with nanoscale size and easily tunable properties is a key for realizing practical topological magnetism-based spintronic devices. Here, we propose a class of ultrathin heterostructures, Fe/Bi2O2 X (X = S, Se, Te) by deposing metal Fe on quasi-two-dimensional (2D) bismuth oxychalcogenides Bi2O2 X (X = S, Se, Te) with excellent ferroelectric/ferroelastic properties. Large Dzyaloshinskii–Moriya interaction (DMI) and topological magnetism can be realized. Our atomistic spin dynamics simulations demonstrate that field-free vortex–antivortex loops and sub-10 nm skyrmions exist in Fe/Bi2O2S and Fe/Bi2O2Se interfaces, respectively. These results provide a possible strategy to tailor topological magnetism in ultrathin magnets/2D materials interfaces, which is extremely vital for spintronics applications.

Investigation of stabilization and survival of skyrmion vortices in the presence of magnetic field disorder in two-dimensional lattices: a case study for Janus dichalcogenides

Due to the lack of inversion symmetry, very large Dzyaloshinskii–Moriya interaction (DMI) has been reported for a series of Janus monolayers of manganese dichalcogenides within the framework of first-principles calculations (Liang et al 2020 Phys. Rev. B 101 184401). However, from the viewpoint of potential applications, the current ongoing research mainly focuses on the magnetism in pristine two-dimensional (2D) materials exhibiting non-zero DMI, and the effects of disorder in such systems remain an open problem since the influence of randomness may create some drastic effects on the magnetism of low dimensional systems. Here, we present Monte Carlo simulation results regarding the magnetic properties of a 2D manganese based Janus dichalcogenide material MnSTe in the presence of quenched random magnetic fields where the local field variables have been sampled from a Gaussian distribution. For the selected benchmark material, it has been found that the magnetic skyrmion vortexes emerging at (10 K, 3 T) may survive in the presence of weak and moderate quenched randomness, which is important from the viewpoint of technological applications. In both the pristine and random field cases, the stabilization of magnetic skyrmions are achieved by the major contribution of the ferromagnetic exchange energy to the total energy of the system, and the materials exhibiting large DMI/exchange ratios may exhibit resilient magnetic skyrmion vortexes in the presence of weak and moderate amount of randomness.

Layer-dependent Dzyaloshinskii–Moriya interaction and field-free topological magnetism in two-dimensional Janus MnSTe

Magnetic skyrmions, as topologically protected whirl-like solitons, have been the subject of growing interest in non-volatile spintronic memories and logic devices. Recently, much effort has been devoted to searching for skyrmion host materials in two-dimensional (2D) systems, where intrinsic inversion symmetry breaking and a large Dzyaloshinskii–Moriya interaction (DMI) are desirable to realize a field-free skyrmion state. Among these systems, 2D magnetic Janus materials have become important candidates for inducing a sizable DMI and chiral spin textures. Herein, we demonstrate that layer-dependent DMI and field-free magnetic skyrmions can exist in multilayer MnSTe. Moreover, strong interlayer exchange coupling and Bethe–Slater curve-like behaviors arising from the Mn–Mn double exchange mechanism are found in bilayer MnSTe. We also uncover that the distribution of DMIs in multilayer MnSTe can be understood as making a significant contribution to the intermediate DMI using the three-site Fert–Lévy model. Our results unveil great potential for designing skyrmion-based spintronic devices in multilayer 2D materials.

Skyrmion formation in Ni-based Janus dihalide monolayers: Interplay between magnetic frustration and Dzyaloshinskii-Moriya interaction

We present a comprehensive theory of the magnetic phases in monolayer nickel-based Janus dihalides (NiIBr, NiICl, NiBrCl) through a combination of first-principles calculations and atomistic simulations. Phonon band structure calculations and finite-temperature molecular dynamics simulations show that Ni-dihalide Janus monolayers are stable. The parameters of the interacting spin Hamiltonian extracted from ab initio calculations show that nickel-dihalide Janus monolayers exhibit varying degrees of magnetic frustration together with a large Dzyaloshinskii-Moriya interaction due to their inherent inversion symmetry breaking. The atomistic simulations reveal a delicate interplay between these two competing magnetic interactions in giving rise to skyrmion formation.

D0 Magnetic Skyrmions in Two‐Dimensional Lattice

AbstractMagnetic skyrmions are topologically protected chiral spin textures that hold great promise for information storage and processing. The current research efforts on magnetic skyrmions are exclusively based on d‐orbital magnetism, which restricts their existence in a narrow window of temperature‐external magnetic field (T‐B) phase diagram. Herein, employing first‐principles and Monte‐Carlo simulations, the work reports the identification of d0 magnetic skyrmions in 2D lattice of Tl2NO2. Arising from inversion asymmetry and strong spin‐orbit coupling compensated by ligand of heavy element, large Dzyaloshinskii–Moriya interaction is obtained in monolayer Tl2NO2. This, competed with p‐orbital exchange interaction, leads to the d0 skyrmion physics under external magnetic field. Importantly, different from d‐orbital topological magnetism, the d0 magnetic skyrmions can be stabilized in a wide window of T‐B phase diagram. The underlying physics is related to the small magnetic moment and delocalization character of d0 magnetism. Furthermore, the work also demonstrates that the d0 magnetic skyrmions are strongly coupled with ferroelectricity. These findings open a new direction for magnetic skyrmion research.

Tuning the magnetic interactions in van der Waals Fe3GeTe2 heterostructures: A comparative study of ab initio methods

We investigate the impact of mechanical strain, stacking order, and external electric fields on the magnetic interactions of a two-dimensional (2D) van der Waals (vdW) heterostructure in which a 2D ferromagnetic metallic Fe$_3$GeTe$_2$ monolayer is deposited on germanene. Three distinct computational approaches based on \textit{ab initio} methods are used, and a careful comparison is given: (i) The Green's function method, (ii) the generalized Bloch theorem, and (iii) the supercell approach. First, the shell-resolved exchange constants are calculated for the three Fe atoms within the unit cell of the freestanding Fe$_3$GeTe$_2$ monolayer. We find that the results between methods (i) and (ii) are in good qualitative agreement and also with previously reported values. An electric field of ${\cal E}= \pm 0.5$~V/{\AA} applied perpendicular to the Fe$_3$GeTe$_2$/germanene heterostructure leads to significant changes of the exchange constants. We show that the Dzyaloshinskii-Moriya interaction (DMI) in Fe$_3$GeTe$_2$/germanene is mainly dominated by the nearest neighbors, resulting in a good quantitative agreement between methods (i) and (ii). Furthermore, we demonstrate that the DMI is highly tunable by strain, stacking, and electric field, leading to a large DMI comparable to that of ferromagnetic/heavy metal (FM/HM) interfaces. The geometrical change and hybridization effect explain the origin of the high tunability of the DMI at the interface. The electric-field driven DMI obtained by method (iii) is in qualitative agreement with the more accurate \textit{ab initio} method used in approach (ii). However, the field-effect on the DMI is overestimated by method (iii) by about 50\%. The magnetocrystalline anisotropy energy can also be drastically changed by the application of compressive or tensile strain in the Fe$_3$GeTe$_2$/germanene heterostructure.

Dzyaloshinskii-Moriya interaction and skyrmions in antiferromagnetic-based heterostructures

The Dzyaloshinskii-Moriya interaction (DMI), an antisymmetric exchange format, plays a key role in the formation of chiral magnetic states. Here, a systematic study on the magnetic properties, including DMI, Heisenberg exchange coupling, and magnetocrystalline anisotropy of IrMn (PtMn) and MgO/IrMn (MgO/PtMn) stacks were carried out by first-principles calculation. Furthermore, the effect of DMI on topological magnetism in the above structures was investigated by micromagnetic simulations based on magnetic parameters from first-principles calculation. A large DMI and microscopic mechanisms of DMI at MgO/IrMn interface were unveiled. This interfacial DMI originates from the dominant contribution from the Ir layer and the orbital hybridization with Ir 3d orbit. The micromagnetic simulation indicates that the labyrinth domains with chiral domain walls and antiferromagnetic skyrmions appear for MgO/IrMn heterostructure, and isolated antiferromagnetic skyrmions are induced for MgO/PtMn heterostructure without any external magnetic fields. Our results may open up a new route to generate the magnetic antiferromagnetic skyrmions at oxide/antiferromagnetic interfaces, which can be an ideal information carrier.

Influence of Dzyaloshinskii–Moriya interaction and perpendicular anisotropy on spin waves propagation in stripe domain patterns and spin spirals

Texture-based magnonics focuses on the utilization of spin waves in magnetization textures to process information. Using micromagnetic simulations, we study how (1) the dynamic magnetic susceptibility, (2) dispersion relations, and (3) the equilibrium magnetic configurations in periodic magnetization textures in a ultrathin ferromagnetic film in remanence depend on the values of the Dzyaloshinskii–Moriya interaction and the perpendicular magnetocrystalline anisotropy. We observe that for large Dzyaloshinskii–Moriya interaction values, spin spirals with periods of tens of nanometers are the preferred state; for small Dzyaloshinskii–Moriya interaction values and large anisotropies, stripe domain patterns with over a thousand times larger period are preferable. We observe and explain the selectivity of the excitation of resonant modes by a linearly polarized microwave field. We study the propagation of spin waves along and perpendicular to the direction of the periodicity. For propagation along the direction of the periodicity, we observe a bandgap that closes and reopens, which is accompanied by a swap in the order of the bands. For waves propagating in the perpendicular direction, some modes can be used for unidirectional channeling of spin waves. Overall, our findings are promising in sensing and signal processing applications and explain the fundamental properties of periodic magnetization textures.

Generation of magnetic skyrmions in two-dimensional magnets via interfacial proximity

Two-dimensional (2D) magnetic van der Waals materials provide a fertile platform for the design and control of topological spin textures such as skyrmions. However, despite studies reporting skyrmions in many 2D magnetic systems, the hosting van der Waals materials are still limited. Here, via first-principles calculations and Monte Carlo simulations, we propose a series of 2D magnetic heterostructures as a different materials' family hosting skyrmions. Unlike previously studied van der Waals heterostructures, a strong interface coupling generates here a significant inversion symmetry breaking, which then results in an inherently large Dzyaloshinskii-Moriya interaction (DMI). Furthermore, upon applying a moderate magnetic field, isolated skyrmions and skyrmions lattices emerge in various types of these heterostructures, and are robust within a relatively wide temperature range. Our work thus suggests a general method to induce DMI and paves the way toward topological magnetism in 2D materials through interfacial engineering.

Bloch-type magnetic skyrmions in two-dimensional lattices.

Magnetic skyrmions in two-dimensional lattices are a prominent topic of condensed matter physics and materials science. Current research efforts in this field are exclusively constrained to Néel-type and antiskyrmions, while Bloch-type magnetic skyrmions are rarely explored. Here, we report the discovery of Bloch-type magnetic skyrmions in a two-dimensional lattice of MnInP2Te6, using first-principles calculations and Monte-Carlo simulations. Arising from the joint effect of broken inversion symmetry and strong spin-orbit coupling, monolayer MnInP2Te6 presents large Dzyaloshinskii-Moriya interaction. This, along with ferromagnetic exchange interaction and out-of-plane magnetic anisotropy, gives rise to skyrmion physics in monolayer MnInP2Te6, in the absence of a magnetic field. Remarkably, different from all previous works on two-dimensional lattices, the resultant magnetic skyrmions feature Bloch-type magnetism, which is protected by D3 symmetry. Furthermore, Bloch-type magnetic bimerons are also identified in monolayer MnTlP2Te6. The phase diagrams of these Bloch-type topological magnetisms under a magnetic field, temperature and strain are mapped out. Our results greatly enrich the research on magnetic skyrmions in two-dimensional lattices.

Ferroelectrically tunable magnetic skyrmions in two-dimensional multiferroics.

Magnetic skyrmions are topologically protected entities that are promising for information storage and processing. Currently, an essential challenge for future advances of skyrmionic devices lies in achieving effective control of skyrmion properties. Here, through first-principles and Monte-Carlo simulations, we report the identification of nontrivial topological magnetism in two-dimensional multiferroics of Co2NF2. Because of ferroelectricity, monolayer Co2NF2 exhibits a large Dzyaloshinskii-Moriya interaction. This together with exchange interaction can stabilize magnetic skyrmions with the size of sub-10 nm under a moderate magnetic field. Importantly, arising from the magnetoelectric coupling effect, the chirality of magnetic skyrmions is ferroelectrically tunable, producing the four-fold degenerate skyrmions. When interfacing with monolayer MoSe2, the creation and annihilation of magnetic skyrmions, as well as phase transition between skyrmion and skyrmion lattice, can be realized in a ferroelectrically controllable fashion. A dimensionless parameter κ' is further proposed as the criterion for stabilizing magnetic skyrmions in such multiferroic lattices. Our work greatly enriches the two-dimensional skyrmionics and multiferroics research.

Multiple Topological Magnetism in van der Waals Heterostructure of MnTe2/ZrS2

Topological magnetism in low-dimensional systems is of fundamental and practical importance in condensed-matter physics and material science. Here, using first-principles and Monte Carlo simulations, we present that multiple topological magnetism (i.e., skyrmion and bimeron) can survive in van der Waals heterostructure MnTe2/ZrS2. Arising from interlayer coupling, MnTe2/ZrS2 can harbor a large Dzyaloshinskii-Moriya interaction. This, combined with exchange interaction, yields an intriguing skyrmion phase under a tiny magnetic field of 75 mT. Meanwhile, upon harnessing a small electric field, magnetic bimeron can be observed in MnTe2/ZrS2, suggesting the existence of multiple topological magnetism. Through interlayer sliding, both topological magnetisms can be switched on-off. In addition, the impacts of d∥ and Keff on these spin textures are revealed, and a dimensionless parameter κ is utilized to describe their joint effect. These explored phenomena and insights not only are useful for fundamental research in topological magnetism but also enable novel applications in nanodevices.

Theoretical Prediction of Antiferromagnetic Skyrmion Crystal in Janus Monolayer CrSi2N2As2.

An antiferromagnetic skyrmion crystal (AF-SkX), a regular array of antiferromagnetic skyrmions, is a fundamental phenomenon in the field of condensed-matter physics. So far, very few proposals have been made to realize the AF-SkX, and most have been based on three-dimensional (3D) materials. Herein, using first-principles calculations and Monte Carlo simulations, we report the identification of AF-SkX in a two-dimensional lattice of the Janus monolayer CrSi2N2As2. Arising from the broken inversion symmetry and strong spin-orbit coupling, a large Dzyaloshinskii-Moriya interaction is obtained in the Janus monolayer CrSi2N2As2. This, combined with the geometric frustration of its triangular lattice, gives rise to the skyrmion physics and long-sought AF-SkX in the presence of an external magnetic field. More intriguingly, this system presents two different antiferromagnetic skyrmion phases, and such a phenomenon is distinct from those reported in 3D systems. Furthermore, by contacting with Sc2CO2, the creation and annihilation of AF-SkX in Janus monolayer CrSi2N2As2 can be achieved through ferroelectricity. These findings greatly enrich the research on antiferromagnetic skyrmions.

Enhanced Curie temperature and skyrmion stability by strain in room temperature ferromagnetic semiconductor CrISe monolayer

We report a CrISe monolayer as a room temperature ferromagnetic (FM) semiconductor with the Curie temperature (TC), magnetic anisotropy energy (MAE), and bandgap being 322 K, 113 μeV, and 1.76 eV, respectively. The TC and MAE can be further enhanced up to 385 K and 313 μeV by a tensile strain. Interestingly, the magnetic easy axis can be switched between off-plane and in-plane by compressive strain. Particularly, due to the broken inversion symmetry and strong spin–orbital coupling of Se atoms, a large Dzyaloshinskii–Moriya interaction (DMI) of 2.40 meV is obtained. More importantly, by micromagnetic simulations, stable skyrmions with sub-10 nm radius are stabilized by the large DMI above room temperature in a wide range of strain from −2% to 6%. Our work demonstrates CrISe as a promising candidate for next-generation skyrmion-based information storage devices and provides guidance for the research of DMI and skyrmions in room temperature FM semiconductors.

Strong Dzyaloshinskii-Moriya interaction in monolayer CrI3 on metal substrates

Dzyaloshinskii-Moriya interaction (DMI) is the primary mechanism for realizing real-space chiral spin textures, which are regarded as key components for the next-generation spintronics. However, DMI arises from a perturbation term of the spin-orbit interaction and is usually weak in pristine magnetic semiconductors. To date, large DMI and the resulting skyrmions are only realized in a few materials under stringent conditions. Using first-principles calculations, we demonstrate that significant DMI occurs between nearest-neighbor Cr atoms in two-dimensional (2D) magnetic semiconductor CrI$_3$ on Au or Cu substrates. This exceptionally strong DMI is generated by the interfacial charge transfer and weak chemical interactions between chromium halides and metal substrates, which break the spatial inversion symmetry. These findings highlight the significance of substrate effects in 2D magnets and expand the inventory of feasible materials with strong DMI.

Large Dzyaloshinskii-Moriya interaction and field-free topological chiral spin states in two-dimensional alkali-based chromium chalcogenides

Noncentrosymmetric ferromagnetic systems with large Dzylochinskii-Moriya interaction (DMI) have gained intensive attention for hosting topologically protected solitons such as skyrmions and bimerons. Recently, a series of two-dimensional (2D) Li- and Na-based chromium chalcogenides has been theoretically predicted to be a new family of intrinsic inversion asymmetric ferromagnets. Here, by combining first-principles calculations and atomistic spin model simulations, we unveil that there is very large DMI in these series of 2D alkali-based chromium chalcogenides, which enables a variety of filed-free topological spin textures in these structures. Furthermore, we find robust hole-doping tunable DMI in the ${\mathrm{LiCrSe}}_{2}$ and ${\mathrm{NaCrSe}}_{2}$ monolayers. Our finding opens up further possibilities toward 2D materials in spintronic devices.

Domain wall velocity asymmetries driven by saturation magnetization gradients without a Dzyaloshinskii-Moriya interaction

The discovery of asymmetric domain wall velocities in magnetic alloys and multilayers without a heavy metal underlayer has given rise to claims of a large Dzyaloshinskii-Moriya interaction (DMI) driven by compositional non-uniformities. However, these non-uniformities also give rise to vertically non-uniform magnetic properties which can influence the dynamic properties of domain walls. In this work, we use micromagnetic simulations to show that vertical modulation of the saturation magnetization can give rise to asymmetric domain wall velocities for field and current driven motion, closely resembling the presence of a DMI. For field driven motion, by comparing the velocity asymmetries for varying saturation magnetization gradients, film thicknesses, and average saturation magnetization, we show that the magnitude of effective symmetry breaking field resulting from the non-uniformity can be comparable to those resulting from DMI. These effects scale with thickness and degree of modulation, mirroring recent results in single layer materials. However, the scaling of domain velocity asymmetries is largely suppressed for SOT driven domain dynamics. Therefore, great care needs to be taken when evaluating DMI in non-uniform systems.

Spontaneous Magnetic Skyrmions in Single-Layer CrInX3 (X = Te, Se).

The realization of magnetic skyrmions in nanostructures holds great promise for both fundamental research and device applications. Despite recent progress, intrinsic magnetic skyrmions in two-dimensional lattice are still rarely explored. Here, using first-principles calculations and Monte Carlo simulations, we report the identification of spontaneous magnetic skyrmions in single-layer CrInX3 (X = Te, Se). Because of the joint effect of broken inversion symmetry and strong spin-orbit coupling, inherent large Dzyaloshinskii-Moriya interaction occurs in both systems, endowing the intriguing Néel-type skyrmions. By further imposing moderate magnetic field, the skyrmion phase can be obtained and is stable within a wide temperature range. Particularly for single-layer CrInTe3, the size of skyrmions is sub-10 nm and the skyrmion phase can be maintained at an elevated temperature of ∼180 K. In addition, the phase diagrams of their topological spin textures under the variation of magnetic parameters of D, J, and K are mapped out.

Large Dzyaloshinskii-Moriya interaction and atomic layer thickness dependence in a ferromagnet- WS2 heterostructure

Two-dimensional transition metal dichalcogenides (TMDs) have immense potential for spintronics applications. Here, we report atomic layer thickness dependence in ${\mathrm{WS}}_{2}/{\mathrm{Co}}_{3}\mathrm{FeB}$ heterostructures. The layer dependence is predicted by density functional theory and demonstrated experimentally by the layer dependence of the Dzyaloshinskii-Moriya interaction (DMI). Notably, we have observed the DMI in ${\mathrm{WS}}_{2}$ to be larger than that for heavy metals such as W and Ta, which is important to stabilize chiral structures. Inversion symmetry is not preserved with an odd number of layers, while it exists with an even number of layers. This symmetry rule is reflected in the temperature dependence of the effective damping parameter of the heterostructure. That the damping parameter decreases (increases) in odd (even) layers can be resolved at low temperature. This suggests that the layer dependence has its origin at the ${\mathrm{WS}}_{2}$ interface, where the spin-valley coupling and spin-orbit coupling activate these features. Large DMI, pure spin current, and unique layer dependence in TMDs provide valuable information and fundamental understanding for designing TMD-based quantum information storage devices.

Comment on “Proper and improper chiral magnetic interactions”

In a recent paper by dos Santos Dias et al. [Phys. Rev. B 103, L140408 (2021)], a critique of earlier works analyzing low-energy spin Hamiltonians is put forth. To be precise, it is the large noncollinear contributions to the Dzyaloshinskii-Moriya interaction (DMI) that is the main concern of dos Santos Dias et al. In this Comment, we clarify the microscopic mechanisms for the large DMI that can be found in noncollinear magnets. Furthermore, we outline the complementary nature of the different parametrizations of a spin Hamiltonian, with strengths and weaknesses of both approaches. Specifically, we stress the physical insight in the interpretation of the DMI, when decomposed in microscopic electron and spin densities and currents.