Dzyaloshinskii-Moriya Interaction Research Articles

Structural, magnetic, optical and electronic properties of Gd2NiIrO6

Polycrystalline Gd2NiIrO6 double perovskite compound was synthesized by the solid-state route. Rietveld refinement of the X-ray diffraction pattern revealed that the compound was crystallized in a monoclinic structure with P21/n space group (IUCr. No. 14). The scanning electron micrograph showed that the grains were spherical and well distributed with an average grain size of around 1 μm. The temperature-dependent magnetic measurements showed magnetic transitions at 165 K and 149 K in the low-temperature region. Below the transition temperatures, weak ferromagnetism was evidenced by field-dependent magnetization measurements. Exchange bias effects were observed which were driven by Dzyaloshinsky–Moriya interactions in the compound. The UV–visible measurement evidenced that the compound had an optical band gap of 1.8 eV. The electronic structure calculations using the DFT + U method revealed that Gd2NiIrO6 compound exhibited a bandgap only when on-site correlations for the d-states were included, and the calculation showed that the AF1 configuration was energetically favourable.

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.

Reduced energies for thin ferromagnetic films with perpendicular anisotropy

We derive four reduced two-dimensional models that describe, at different spatial scales, the micromagnetics of ultrathin ferromagnetic materials of finite spatial extent featuring perpendicular magnetic anisotropy and interfacial Dzyaloshinskii–Moriya interaction. Starting with a microscopic model that regularizes the stray field near the material’s lateral edges, we carry out an asymptotic analysis of the energy by means of [Formula: see text]-convergence. Depending on the scaling assumptions on the size of the material domain versus the strength of dipolar interaction, we obtain a hierarchy of the limit energies that exhibit progressively stronger stray field effects of the material edges. These limit energies feature, respectively, a renormalization of the out-of-plane anisotropy, an additional local boundary penalty term forcing out-of-plane alignment of the magnetization at the edge, a pinned magnetization at the edge, and, finally, a pinned magnetization and an additional field-like term that blows up at the edge, as the sample’s lateral size is increased. The pinning of the magnetization at the edge restores the topological protection and enables the existence of magnetic skyrmions in bounded samples.

Multiferroic quantum material Ba2Cu1−xMnxGe2O7 (0 ≤ x ≤ 1) as a potential candidate for frustrated Heisenberg antiferromagnet

Multiferroic Ba2CuGe2O7 was anticipated as a potential member of the exciting group of materials hosting a skyrmion or vortex lattice because of its profound Dzyaloshinskii–Moriya interaction (DMI) and the absence of single ion anisotropy (SIA). This phase, however, could not be evidenced and instead, it exhibits a complex incommensurate antiferromagnetic (AFM) cycloidal structure. Its sister compound Ba2MnGe2O7, in contrast, is characterized by a relatively strong in-plane exchange interaction that competes with a non-vanishing SIA and the weak DMI, resulting in a quasi-two-dimensional commensurate AFM structure. Considering this versatility in the magnetic interactions, a mixed solid solution of Cu and Mn in Ba2Cu1−xMnxGe2O7 can hold an interesting playground for its interactive DMI and SIA depending on the mixed spin states of the transition metal ions towards the skyrmion physics. Here, we present a detailed study of the micro- and macroscopic spin structure of the Ba2Cu1−xMnxGe2O7 solid solution series using high-resolution neutron powder diffraction techniques. We have developed a remarkably rich magnetic phase diagram as a function of the applied magnetic field and x, which consists of two end-line phases separated by a potentially quantum-critical phase at x = 0.57. An AFM conical structure at zero magnetic field is demonstrated to persist up to x = 0.50. Our results provide crucial information on the spin structure and magnetic properties, which are necessary for the general understanding and theoretical developments on multiferroicity in the frame of skyrmion type or frustrated AFM lattice where DMI and SIA play an important role.

Anisotropic magnon frequency comb based on antiferromagnetic bimerons

The interaction between propagating magnons and topological spin textures is attracting a lot of recent attention from the magnonic community. It has been shown that the three-wave mixing between magnons and breathing skyrmion can induce the magnon frequency comb (MFC) with equidistant coherent peaks. However, a magnetic bimeron is a nontrivial spin texture and is regarded as the counterpart of the skyrmion in easy-plane magnets with Dzyaloshinskii–Moriya interaction, which allows anisotropic magnon propagations. This raises the question of whether the nonlinear interaction between magnons and bimerons can generate an MFC. If so, how does the direction of magnon propagation affect the characteristics of the MFC? In this Letter, we demonstrate that the three-wave mixing between propagating magnons and locally breathing bimerons can induce a terahertz MFC in easy-plane antiferromagnets. Micromagnetic simulations reveal that the three-wave coupling strength weakly depends on the driving frequency, but it strongly relies on the propagation direction of incident magnons. Our findings uncover the anisotropic nature of MFC in bimeron structures, which may have potential applications for ultrafast magnonic devices with spectroscopy, metrology, and sensing functionalities.

Theoretical description of the thermodynamic properties and the magnetocaloric effect in R2Cu2Cd (R = Dy,Ho)

In this paper, we present a theoretical discussion of the magnetocaloric effect in the compounds Dy2Cu2Cd and Ho2Cu2Cd whose curves of the heat capacity and isothermal entropy change exhibit two peaks. For this purpose, we use a model Hamiltonian of local magnetic moments with two anisotropic magnetic sublattices. In the model, it is considered that exchange interactions between magnetic moments depend on their xyz components. Besides, it is also included in the model a single ion uniaxial anisotropy and the Dzyaloshinskii-Moriya interaction to account for the canted magnetic moments. Our theoretical calculations show that the existence of these two peaks is associated with a spin reorientation transition at a lower temperature and a ferromagnetic-paramagnetic one at a higher temperature. The results of our theoretical calculations are in reasonable agreement with the existing experimental data of heat capacity and the isothermal entropy change.

Skyrmions Subtractor Based on Dzyaloshinskii-Moriya Interaction Gate.

Skyrmions are increasingly favored in developing various spintronic devices as efficient information carriers. The proposed voltage-controlled Dzyaloshinskii-Moriya interaction (VCDM) offers an additional means to manipulate the movement of skyrmions. In this study, we investigated how the skyrmions behave when passing through the VCDM gate in ferromagnetic nanotracks driven by current. Our findings suggest that reducing the strength of the Dzyaloshinskii-Moriya interaction (DMI) can more effectively block skyrmions, while increasing the DMI strength can more effectively attract them. This indicates that the motion behavior of skyrmions can be controlled by changing the shape of the VCDM gate, thereby demonstrating the effectiveness of VCDM gates in controlling skyrmion motion. Due to the ability of VCDM gates to block skyrmions, we have designed a robust subtractor based on skyrmions. These results provide valuable insights for the development of future skyrmion-based devices using the DMI method.

Entropic uncertainty relations and quantum coherence in the two-dimensional XXZ spin model with Dzyaloshinskii–Moriya interaction

Quantum renormalization group (QRG) is a tractable method for studying the criticalities of one-dimensional (1D) and two-dimensional (2D) many-body systems. By employing the QRG method, we first derive the effective Hamiltonian and QRG equations of a 2D XXZ model with Dzyaloshinskii–Moriya (DM) interaction analytically. The linear-entropy-based uncertainty, the quantum discord (QD), and the multipartite quantum coherence based on the square root of the quantum Jensen–Shannon divergence of the 2D XXZ model are then studied as the indicators of quantum phase transitions (QPTs). The nonanalytic and scaling behaviors of the uncertainty, QD and quantum coherence are also analyzed through numerical calculations. Moreover, we investigate the effect of the easy-axis anisotropy parameter and DM interaction on the QPT. We find that the uncertainty, QD, and quantum coherence can all be utilized to detect QPTs. Our findings could shed new light on the observable of the QPT of the many-body system with the uncertainty and quantum coherence, and enrich the application of QRG method to Heisenberg spin models.

Spin waves in antiferromagnetically coupled bilayers of transition-metal dichalcogenides with Dzyaloshinskii–Moriya interaction

In this paper we analyse quantized spin waves (also referred to as magnons) in bilayers of two-dimensional van der Waals materials, like Vanadium-based dichalcogenides, VX2 (X = S, Se, Te) and other materials of similar symmetry. We assume that the materials exhibit Dzyaloshinskii–Moriya interaction and in-plane easy-axis magnetic anisotropy due to symmetry breaking induced externally (e.g. by strain, gate voltage, proximity effects to an appropriate substrate/oberlayer, etc.). The considerations are limited to a collinear spin ground state, stabilized by a sufficiently strong in-plane magnetic anisotropy. The theoretical analysis is performed within the general spin wave theory based on the Holstein–Primakoff–Bogoliubov transformation. Accordingly, the description takes into account quantum antiferromagnetic fluctuations. However, it is limited to linear spinwave modes. The Dzyaloshinskii–Moriya interaction is shown to modify the spin wave spectrum of the bilayers, making its low energy part qualitatively similar to the electronic spectrum of the Rashba spin–orbit model.

Spin and lattice dynamics of the two-dimensional van der Waals ferromagnet CrI3

Chromium tri-iodide (CrI3) is a prototypical ferromagnetic van der Waals insulator with its genuinely two-dimensional (2D) long-range magnetic order below 45 K demonstrated recently. The underlying magnetic anisotropy has not been completely understood while both the Dzyaloshinskii-Moriya (DM) interaction and the Kitaev−Γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-\\Gamma$$\\end{document} type interaction have been considered as the relevant magnetic Hamiltonian. In addition, the relation between the crystal structure and the magnetic order needs to be further elucidated concerning their possible coupling in few-layer samples and in the topmost surface layers of bulk samples. Here, we investigate these issues via temperature- and magnetic field-dependent terahertz spectroscopy on bulk CrI3 single crystals, focusing on the dynamics of ferromagnetic resonances (FMRs) and optical phonons in the terahertz (THz) region from 4 to 120 cm−1 (from 0.5 to 15 meV). We narrow down the possible ranges of the interaction parameters such as the off-diagonal symmetric terms and the single-ion anisotropy. The accurate values of these parameters significantly constrain the magnitude of possible Kitaev−Γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-\\Gamma$$\\end{document} exchange interaction and the topological magnon gap. Moreover, the structure-magnetism relationship was critically analyzed based on the temperature- and field-dependences of two Eu\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\\rm{E}}}_{{\\rm{u}}}$$\\end{document} in-plane optical phonon modes, which shows that the commonly believed structural phase diagram of CrI3, derived from surface-preferential data, has to be seriously modified.

Real-space calculation of thermal Hall effects in strained and disordered kagome ferromagnets

Ferromagnetic insulators may exhibit magnon Hall effects when subjected to a temperature gradient due to the Dzyaloshinsky–Moriya interaction. In this study, we investigate the magnon thermal Hall conductivity κxy of kagome ferromagnets in real space using the kernel polynomial method. We first establish the formalism in real space within the framework of linear response theory, which enables efficient numerical calculations of thermal transport properties under various imperfections. The validity and accuracy of the real-space approach are confirmed by comparing the calculations with those obtained in momentum space. This approach is particularly advantageous for computing the thermal transport coefficients of disordered lattices. We consider two types of disorder in kagome ferromagnets and observe that both types significantly influence κxy across the entire temperature range. This is in contrast to the effects of strains, where strains primarily impact the maximum values of κxy .

Decoupling the influences of chiral damping and Dzyaloshinskii-Moriya interaction in chiral magnetic domain walls

We revisit the nature and impact of both the chiral damping (CD) and Dzyaloshinskii-Moriya interaction (DMI) in uniaxial chiral ferromagnetic nanowires with broken inversion symmetry. We propose that CD, akin to its chiral energy counterpart (DMI), can be described in terms of the Lifshitz invariants permissible by the underlying symmetry of the system. This representation offers a clearer foundation for integrating CD into the dynamics of various chiral magnetic textures. We theoretically investigate the current-induced motion of chiral domain walls (DWs), driven by both spin-transfer torque and the spin Hall effect in the presence of CD. We demonstrate that it is possible to unambiguously separate the influence of CD from that of DMI by analyzing the current-induced dynamics. In particular, below the Walker breakdown (WB), the DMI does not affect the DW velocity, whereas increases in the strength of CD result in a decrease in the DW velocity. Moreover, for the spin-orbit torque driven motion, while the DMI enhances both the WB current density and the maximum attainable velocity below the WB, the CD only enhances the WB without affecting the maximum attainable velocity below the WB. Our findings open up intriguing opportunities for exploitation in exotic magnetic textures. Published by the American Physical Society 2024

Energy Barriers for the Spontaneous Magnetization Reversal of the Atomic Co Chains on Pt(664) Surface in the Model with Dzyaloshinskii–Moriya Interaction

The analytical approach has been developed in the framework of the continuous XY-model. This approach allows calculating the spontaneous magnetization reversal time of finite-length atomic chains on the metallic surface. The interaction of the magnetic moments of atoms is described by the classical Hamiltonian, which includes the Heisenberg exchange interaction, the Dzyaloshinskii–Moriya interaction, and the magnetic anisotropy energy. Using the Co/Pt(664) system as an example, it has been shown that the proposed method is in a good agreement with the results of the numerical simulation in the limit of short and long atomic chains. And for atomic chains of intermediate length, it can be used to estimate an upper bound on the spontaneous magnetization reversal time. We obtained the dependences of the spontaneous magnetization reversal time of finite-length Co chains the value of the exchange integral, parameters of the magnetic anisotropy, and also on the value of the projection of the Dzyaloshinskii vector onto the axis perpendicular to the plane containing the magnetic moments of the atoms. It is shown that the proposed method has a wide range of applicability both in terms of temperature and the values of the physical parameters characterizing the magnetic properties of the atomic chains.

Quantum correlation, entanglement in the kagome lattice non-Hermitian quantum systems

Quantum correlation in the antiferromagnetic XXZ model on kagome lattice and non-Hermitian tight binding model on kagome lattice are investigated. For the Hermitian XXZ model on kagome lattice, the calculations are performed for different extensions of the model with single-ion anisotropy and out-of-plane Dzyaloshinskii–Moriya interaction (DMI). We get the von Neumann entropy as a function of the DMI interaction, anisotropy and single-ion anisotropy with aim to verify the effect of these corrections that occurs in real magnetic systems on quantum correlation. Moreover, the effect of DMI interaction, anisotropy and single-ion anisotropy is investigated on concurrence and entanglement negativity as well. For the non-Hermitian tight binding model on kagome lattice, we analyzed quantum correlation using the entanglement negativity as entanglement measure which is more adequate in this case.

Tailoring Dzyaloshinskii-Moriya Interaction and Spin-Hall Topological Hall Effect in Insulating Magnetic Oxides by Interface Engineering.

Chiral spin textures, as exotic phases in magnetic materials, hold immense promise for revolutionizing logic, and memory applications. Recently, chiral spin textures have been observed in centrosymmetric magnetic insulators (FMI), due to an interfacial Dzyaloshinskii-Moriya interaction (iDMI). However, the source and origin of this iDMI remain enigmatic in magnetic insulator systems. Here, the source and origin of the iDMI in Pt/Y3Fe5O12 (YIG)/substrate structures are deeply delved by examining the spin-Hall topological Hall effect (SH-THE), an indication of chiral spin textures formed due to an iDMI. Through carefully modifying the interfacial chemical composition of Pt/YIG/substrate with a nonmagnetic Al3+ doping, the obvious dependence of SH-THE on the interfacial chemical composition for both the heavy metal (HM)/FMI and FMI/substrate interfaces is observed. The results reveal that both interfaces contribute to the strength of the iDMI, and the iDMI arises due to strong spin-orbit coupling and inversion symmetry breaking at both interfaces in HM/FMI/substrate. Importantly, it is shown that nonmagnetic substitution and interface engineering can significantly tune the SH-THE and iDMI in ferrimagnetic iron garnets. The approach offers a viable route to tailor the iDMI and associated chiral spin textures in low-damping insulating magnetic oxides, thus advancing the field of spintronics.

Quantum Battery in the Heisenberg Spin Chain Models with Dzyaloshinskii‐Moriya Interaction

AbstractQuantum battery (QB) is an energy storage and extraction device conforming to the principles of quantum mechanics. In this study, the characteristics of QBs are considered for the Heisenberg spin chain models in the absence and presence of Dzyaloshinskii‐Moriya (DM) interaction. The results show that the DM interaction can enhance the ergotropy and power of QBs, which shows the collective charging can outperform parallel charging regarding QB's performance. Besides, it turns out that first‐order coherence is a crucial quantum resource during charging, while quantum steering between the cells is not conducive to the energy storage of QBs. The investigations offer insight into the properties of QBs with Heisenberg spin chain models with DM interaction and facilitate us to acquire the performance in the framework of realistic quantum batteries.

Emergent chiral spin textures in centrosymmetric iron garnet with spin alignment constraints

Chiral spin textures have emerged as a captivating class of topological matter. These intriguing structures harbor localized and topologically protected magnetic textures, rendering them promising candidates for novel spintronic applications. Here, the emergent chiral spin textures in an iron garnet with nanodisk configuration have been micromagnatically simulated based on the Landau-Lifshitz-Gilbert equation (LLG) of COMSOL Multiphysics. The modification of magnetic spin texture in the considered iron garnet has been controlled by introducing the interfacial Dzyaloshinskii-Moriya interaction (I-DMI) and spin alignment constraints as locally pinned spins and curvilinear defects at edges. These boundary conditions induced interesting chiral textures not commonly observed in such iron garnet due to its centrosymmetric crystal structure. The simulation results showed the presence of two distinct regions of spin texture: inside and outside the pinning boundary. By systematically varying the DMI strength (D) with the size of the pinning boundary (Rpin) and the number of defects (Ndef), the emerging chiral spin textures have been explored and reported, including the existence of ramified helical stripes, skyrmions, and skyrmions-like textures such as elongated skyrmions, chiral horseshoe domains, biskyrmions and target skyrmions (TSk) (2π-TSk and 3π-TSk). Also, it has been reported that various collapses occur in the final spin texture states, leading to the transition from one state to another when varying the values of Rpin and Ndef with D.

Dzyaloshinskii-Moriya interaction in Ni/Cu(001)

Dzyaloshinskii-Moriya interaction (DMI) is found in the epitaxial Ni/Cu(001) system by imaging magnetic domain wall profiles with high resolution and by Brillouin light scattering. The domain walls have right-handed chirality and deviate from both the Néel and Bloch configurations for Ni thicknesses up to 9 nm. From a detailed structural analysis it is found that strain in the Ni film is inhomogeneous with film thickness. We suggest that this strain field is responsible for the symmetry breaking that is required for a sizable DMI to appear, even in absence of a heavy metal. Published by the American Physical Society 2024

Temperature and medium structurization effect on spontaneous evolution of domains and bubbles in magnetic nanostructures

Spontaneous evolutions of domains in magnetic nanowires and of magnetic bubbles in open ferromagnetic nanolayers are investigated using micromagnetic simulations. We compare temperature dependent dynamics of domain wall (DW) systems in Permalloy (Py) nanowires and systems of chiral DWs in ultra-thin nanowires with perpendicular magnetic anisotropy (PMA) and Dzyaloshinskii-Moriya interaction (DMI). In Py nanowires DWs collide and, in majority of cases, the collision leads to the DW annihilation in disagreement with the expectation of topological protection of sums of all the magnetic charges attached to the nanowire edges which are carried by DWs. For our purpose of discussing the DW collision in the presence of thermal excitations, we revisit the problem of field-driven collisions of DWs in Py nanowires at zero temperature. We claim that thermal fluctuations can counteract the collision-induced annihilation of DWs, thought further improvement of stabilization of domain structures is achievable via structurization of the magnetic nanowires (dividing them into grains). In PMA-DMI nanowires, thermally-excited chiral DWs can be randomly approaching or moving away while not being annihilated. A problem related to the motion of chiral DWs is the spontaneous motion of magnetic bubbles in open PMA-DMI planes. The magnetic bubbles expand or shrink to vanishing dependent on strength of the DMI interaction. Such a motion appears to be be strongly influenced by temperature and by structural discontinuities of the magnetic layer.

Magnon bands and transverse transport in a proposed two-dimensional [formula omitted] ferrimagnet

The copper fluoride Cu2F5 is a proposed stable compound that can be seen as a layered lattice of S=1 and S=1/2 sites, corresponding to copper ions. Intending to cast light on the transport properties of ferrimagnetic magnons, we use the linear spin wave approach to study the magnon band structure of the 2D lattice in a ferrimagnetic off-plane order, as well as the transverse transport of magnons in the crystal bulk. A magnetic field or temperature gradient can induce transverse (Hall-like) transport within the linear response theory generated by the Berry curvature of the eigenstates. As in most cases involving magnons, the Berry curvature is related to Dzyaloshinskii–Moriya interactions between next-near-neighbors The band structure of the system is non-degenerate and the transport coefficients are non-null. The novel and interesting feature of the system is that, within certain conditions, the transport coefficients versus temperature curves are non-monotonic and present a sign change, opening the exciting possibility of controlling the transverse magnon flow direction and magnitude with the temperature change.