Dzyaloshinskii-Moriya Interaction Strength Research Articles

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.

Tailoring Interlayer Chiral Exchange by Azimuthal Symmetry Engineering.

Recent theoretical and experimental studies of the interlayer Dzyaloshinskii-Moriya interaction (DMI) have sparked great interest in its implementation into practical magnetic random-access memory (MRAM) devices, due to its capability to mediate long-range chiral spin textures. So far, experimental reports focused on the observation of interlayer DMI, leaving the development of strategies to control interlayer DMI's magnitude unaddressed. Here, we introduce an azimuthal symmetry engineering protocol capable of additive/subtractive tuning of interlayer DMI through the control of wedge deposition of separate layers and demonstrate its capability to mediate field-free spin-orbit torque (SOT) magnetization switching in both orthogonally magnetized and synthetic antiferromagnetically coupled systems. Furthermore, we showcase that the spatial inhomogeneity brought about by wedge deposition can be suppressed by specific azimuthal engineering design, ideal for practical implementation. Our findings provide guidelines for effective manipulations of interlayer DMI strength, beneficial for the future design of SOT-MRAM or other spintronic devices utilizing interlayer DMI.

Voltage-controlled magnetic anisotropy gradient-driven skyrmion-based half-adder and full-adder.

Spintronic devices have revolutionized the way we process or store information compared to dissipative charge-based electronics. Among various spin-based technologies, skyrmions - topologically protected nano-size spin textures - have emerged as the most promising alternative for future data processing. Here, we have proposed binary adder circuits - central to most digital logic circuits - based on skyrmions. Using micromagnetic simulations, we have demonstrated half-adder and full-adder logic functionalities by precisely driving the skyrmions through voltage-controlled magnetic anisotropy gradient, besides taking advantage of the physical effects such as the skyrmion Hall effect, skyrmion-skyrmion topological repulsion and skyrmion-edge repulsions. The proposed voltage-control-based method of driving the skyrmions is energy efficient compared to the electrical current-driven approach, and it also overcomes the issue of Joule heating. A reliable operation in a wide range of Dzyaloshinskii-Moriya interaction strengths, magnetic anisotropy gradient, and dimensional parameters has been shown, which offers robustness to the device design. The results pave the way for the skyrmion-based computational architecture, which is significant for next-generation non-volatile data processing.

Experimental evidence of the oscillation behavior of the interlayer DMI effect

Chiral spin interactions play an important role in magnetism. Recent reports have revealed a new type of antisymmetric and indirect spin interaction, namely, the interlayer Dzyaloshinskii–Moriya interaction (DMI), which is predicted to arise from the three-site spin–orbit scattering of delocalized electrons as an additional Ruderman–Kittel–Kasuya–Yosida (RKKY) effect. Here, we investigated the interlayer DMI and RKKY interaction in the similar Pt/Co/Pt/Ru/Pt/Co/Pt structures as a function of spacer thickness. Both interactions present a synchronous damping oscillation and support the predicted relevance between them. The coupling strength of the interlayer DMI was finely engineered by tunning thickness of the nonmagnetic spacer. This work can deepen the understanding of the interlayer DMI and guide the control and use of the interlayer DMI in the field-free spin–orbit torque switching or the design of three-dimensional chiral spin textures.

Magnetic Bimerons in Cylindrical Nanotubes

This work presents the analysis of the stability of magnetic bimerons in a cylindrical nanotube. Through micromagnetic simulations, we study the influence of magnetic and geometrical parameters on the bimeron existence and size. The obtained results allow us to present diagram states showing the stability region of a bimeron as a function of the nanotube’s height and radius for different anisotropy and Dzyaloshinskii–Moriya interaction strengths. We also obtain two other magnetic states in the range of parameters where the bimeron is not stable: helicoidal and saturated states.

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.

A Spin‐Orbit Torque Switch at Ferromagnet/Antiferromagnet Interface Toward Stochastic or Memristive Applications via Tailoring Antiferromagnetic Ordering

AbstractAntiferromagnet (AFM) has currently participated in the spin‐orbit torque (SOT) technology due to its great potential to be applied to the field‐free SOT switching and to promote the thermal stability of MRAM. However, the effect of varying AFM ordering on the SOT switching and the associated properties is still not comprehensively understood. This work reports how an AFM ordering modifies the strength of Dzyaloshinskii–Moriya‐interaction (DMI) in a heavy metal (Pt)/FM (Co)/AFM (IrMn) trilayer and its effects on SOT switching. Increasing the AFM ordering reflects the enhanced exchange bias through increasing IrMn thickness appears to significantly reduce the DMI strength of the trilayer. Controlling the IrMn thickness appears to serve as a unique switch to activate memristivity/stochasticity in the devices via tailoring AFM ordering on exchange bias: The strong AFM ordering via increasing IrMn thickness enables to increase the stability of multi‐levels for SOT switching, which promotes the memristivity for neuromorphic application. On the contrary, the weak AFM ordering via reducing IrMn thickness will lead to significant stochasticity for the physically unclonable functionality. This work demonstrates an intrinsic tuning over the AFM ordering will serve as a switch to turn the SOT device into a stochastic/memristive cell to bridge probabilistic and neuromorphic computing.

Low-temperature transport in the XY chain with staggered Dzyaloshinskii–Moriya interaction

The influence of staggered Dzyaloshinskii–Moriya (DM) interaction as well as external magnetic fields on transport properties of the spin-1/2 one-dimensional XY model with spatially modulated DM interaction which has been a complex topic in recent years is investigated. The longitudinal spin conductivity is calculated employing the fermionization approach, where we analyze the effect of the strength of DM interaction on continuum spin conductivity σreg(ω). In addition, the behavior of the Drude’s weight as a function of temperature T is presented, indicating a spin super-current behavior for all T.

Correlation of Interface Interdiffusion and Skyrmionic Phases.

Magnetic skyrmions are prime candidates for the next generation of spintronic devices. Skyrmions and other topological magnetic structures are known to be stabilized by the Dzyaloshinskii-Moriya interaction (DMI) that occurs when the inversion symmetry is broken in thin films. Here, we show by first-principles calculations and atomistic spin dynamics simulations that metastable skyrmionic states can also be found in nominally symmetric multilayered systems. We demonstrate that this is correlated with the large enhancement of the DMI strength due to the presence of local defects. In particular, we find that metastable skyrmions can occur in Pd/Co/Pd multilayers without external magnetic fields and can be stable even near room temperature conditions. Our theoretical findings corroborate with magnetic force microscopy images and X-ray magnetic circular dichroism measurements and highlight the possibility of tuning the intensity of DMI by using interdiffusion at thin film interfaces.

Effect of the Dzyaloshinskii-Moriya interaction on quantum speed limit and orthogonality catastrophe

We study the effect of the Dzyaloshinskii-Moriya (DM) interaction on the quantum speed limit (QSL) and orthogonality catastrophe (OC) in XY spin chains. With an initial sudden quench, the general expressions of fidelity and QSL time are derived in terms of the antisymmetric quasiparticle excitation spectra. The numerical and analytical studies show that depending on the system parameters, the DM interaction has various influences on QSL and fidelity. In general, the OC is witnessed and QSL time vanishes in the thermodynamic limit as the variance of the quenched Hamiltonian in ground states scales with the system size, and the conclusion is independent of the DM interaction strength. However, it is interesting to note that the QSL can uniquely detect the critical points and lines induced by the DM interaction. We further analyze the actual evolution speed, a measure of the criticality, and find its direct correspondence with the OC. We also study an interesting phenomenon arising from the magnetic field and DM interaction in the presence of classical noise. Notably, we find that the system dynamic is fault tolerant when the system is subject to a uniform classical noise in the DM interaction strength.

Separation of Rare-Earth and Transition-Metal Contributions to the Interfacial Dzyaloshinskii-Moriya Interaction in Ferrimagnetic Co - Gd Alloys

Ferrimagnetic materials composed of rare earth (RE) and transition metals (TM) are of great interest for spintronic devices due to their tunable net moments and magnetic transport behaviors. Here we experimentally study the Dzyaloshinskii-Moriya interaction (DMI) in $\mathrm{Co}\text{\ensuremath{-}}\mathrm{Gd}$ ferrimagnets and find that the DMI strength increases substantially as the temperature approaches its moment compensation point. By subtracting the contribution of Heisenberg exchange coupled $\mathrm{Co}$-$\mathrm{Co}$ moments mediated by $\mathrm{Pt}$ from the total DMI strength, we observe a relationship ${D}_{\text{Co - Gd}}\ensuremath{\sim}{M}_{s}^{0.2\ifmmode\pm\else\textpm\fi{}0.06}$. The lower order indicates the weaker Heisenberg exchange compared with $\mathrm{Co}$-$\mathrm{Co}$ moments in $\mathrm{Co}\text{\ensuremath{-}}\mathrm{Gd}$ alloys. Our results reveal the intrinsic physics of DMI in RE-TM alloys by separating the different contributions of TM-TM and RE-TM sublattice moments from the total DMI and show the promising prospect for the fabrication of skyrmions in RE-TM ferrimagnets near the compensation point.

Influence of magnetic structure on the performance of twisted skyrmion-based nano-oscillator

The spin torque nano-oscillator (STNO), a nanosize microwave signal generator, have caught the attention of a number of researchers due to its obvious advantages. Recently a chiral bulk material with twisted skyrmion has been discovered in studies with different helicity degrees. In this work, we design a new STNO based on twisted skyrmion existing in free layers of magnetic tunnel junction structure. We first investigate the effect of the magnetic moment of fixed layer on the twisted skyrmion and frequency of STNO. Although the magnetic moment of fixed layer does not affect the state of the twisted skyrmion but affects the precession frequency of STNO. Later, the current, external magnetic field and Dzyaloshinskii–Moriya interaction strength are changed to regulate the oscillation frequency of STNO. Our result may be favorable for the design of new twisted skyrmion-based STNO.

Nonreciprocal spin waves in ferrimagnetic domain-wall channels

We theoretically investigate the propagation of spin waves confined in a N\'eel-type ferrimagnetic domain-wall channel in the presence of the interfacial Dzyaloshinskii-Moriya interaction (DMI). We observe a nonreciprocal spin-wave propagation induced by the antisymmetric chiral DMI, which can be manipulated by changing the net angular momentum or the polarity of domain walls. Considering that the band gap of spin waves excited in domain walls is significantly reduced, the three-magnon processes are applied to nonlinearly detect this bounded mode in the narrow channel, which enables us to quantify the frequency and the wave vector by analyzing the spectrum of the transmitted spin wave outside the domain wall and to determine the DMI strength. These findings are useful for fabricating energy-efficient magnetic devices and measuring the interfacial DMI in ultra narrow ferrimagnetic stripes.

Simulating anti-skyrmions on a lattice

Magnetic skyrmions are meta-stable spin structures that naturally emerge in magnetic materials. While a vast amount of effort has gone into the study of their properties, their counterpart of opposite topological charge, the anti-skyrmion, has not received as much attention. We aim to close this gap by deploying Monte Carlo simulations of spin-lattice systems in order to investigate which interactions support anti-skyrmions, as well as skyrmions of Bloch and Néel type. We find that the combination of ferromagnetic exchange and Dzyaloshinskii–Moriya (DM) interactions is able to stabilize each of the three types, depending on the specific structure of the DM interactions. Considering a three-dimensional spin lattice model, we provide a finite-temperature phase diagram featuring a stable anti-skyrmion lattice phase for a large range of temperatures. In addition, we also shed light on the creation and annihilation processes of these anti-skyrmion tubes and study the effects of the DM interaction strength on their typical size.

Breathing skyrmions in chiral antiferromagnets

Breathing oscillations of skyrmions in chiral antiferromagnets can be excited by a brief modification of the Dzyaloshinskii-Moriya interaction or magnetocrystalline anisotropy strength. We employ an adiabatic approximation and derive a formula for the potential energy that directly implies breathing oscillations. We study the nonlinear regime and the features of larger-amplitude oscillations, and we verify the validity of the adiabatic approximation. We show that there is a maximum amplitude supported by the potential. As a consequence, we predict theoretically and observe numerically skyrmion collapse and subsequent annihilation events due to excitation of large-amplitude breathing oscillations. The process is efficient when the skyrmion is mildly excited so that its radius initially grows, while the annihilation event is eventually induced by the internal breathing dynamics. We reveal the counterintuitive property that the skyrmion possesses a nonzero kinetic energy at the instance of its annihilation. Finally, the frequency of small-amplitude breathing oscillations is determined.

Study of magnetization and specific heat of Heisenberg model on Lieb nanolattice: Anisotropic effects

We study the effects of longitudinal magnetic field and temperature on the thermodynamic properties of two dimensional Heisenberg antiferromagnet on the line-centered square lattice in the presence of anisotropic Dzyaloshinskii–Moriya interaction. We have studied the temperature dependence of specific heat and longitudinal magnetization of Lieb lattice for various physical parameters in the model Hamiltonian. Using a hard core bosonic representation, the behavior of thermodynamic properties has been studied by means of excitation spectrum of mapped bosonic gas. The effect of Dzyaloshinskii–Moriya interaction term on thermodynamic properties has also been studied via the bosonic model by exploiting Green’s function approach. Furthermore we have studied the magnetic field dependence of specific heat and magnetization for various Dzyaloshinskii–Moriya coupling strength. At low temperatures, the specific heat is found to be monotonically increasing with temperature for magnetic fields in the gapped field induced phase region. We have found the magnetic field dependence of specific heat shows a monotonic decreasing behavior for various magnetic fields due to increase of energy gap in the excitation spectrum. Also we have studied the dependence of magnetization on Dzyaloshinskii–Moriya interaction strength for different magnetic field values. • The study of thermodynamic properties of Lieb lattice in the context of Heisenberg model. • The study the temperature dependence of specific heat of Lieb lattice. • The study of magnetization with spin orbit coupling. • The study of specific heat of Lieb lattice.

Theoretical routes for current-free magnetization switching induced by joint effects of strain and Dzyaloshinskii–Moriya interaction

Voltage-induced strain is regarded as an energy-efficient choice of tuning spin-dynamics. However, studies on the strain-mediated switching of magnetization in a perpendicular-magnetic-anisotropy layer are few because of the uncertainties that arise from the magnetization oscillation at high strain. In this work, we demonstrate theoretically how to deterministically switch the perpendicular magnetization in an ultrathin magnetic nanodisk by combining biaxial in-plane strain with the Dzyaloshinskii–Moriya interaction (DMI). The magnetization-switching process is carefully investigated under different strains and DMI strengths. The underlying switching mechanism is attributed to the remnant magnetization component, which deviates away from the film plane during the strain-pulse-impulsion period and which is also highly dependent on the DMI. Based on simulation results, a theoretical route for obtaining deterministic switching regarding strain and DMI is established. In this route, the minimum duration of the strain pulse can be shortened to a critical time of 2.5 ns as the strain increases to 7000 ppm at a DMI value of 0.6 mJ/m2. Moreover, nonvolatile and reversible switching between the spin-up and spin-down states of perpendicular magnetization is realized using pulses of biaxial in-plane isotropic strain. This switching occurs via an intermediate skyrmion and shows potential in overcoming the edge-roughness-related pinning that occurs in spin–orbit-torque current-induced switching. This study provides a robust insight into strain-induced current-free magnetization switching, providing a guide for experimental research into the strain-mediated voltage control of memory applications.

Dynamical dephasing of bipartite and tripartite quantum coherence of spin-1/2 XXZ Heisenberg model in a renormalization group approach

The dynamical dephasing of a bipartite and tripartite quantum coherence in spin-1/2 Heisenberg model, driven by an applied magnetic field, in the presence of Dzyaloshinskii-Moriya interaction is investigated. The system is renormalized through the Kadanoof’s blocks approach. It is observed for both bipartite and tripartite schemes that by increasing the size of the system, the quantum coherence measure show an abrupt change at a quantum critical point (QCP). A further increase of the Dzyaloshinskii-Moriya coupling parameter affect the QCP, causing the dynamical dephasing which is the signature of second order quantum phase transition. The displacement of the QCP reduces the Quantum coherence of the system and can be controlled by the external magnetic field strength. Moreover, in a given range of Dzyaloshinskii-Moriya interaction strength and magnetic field, the monogamous and polygamous nature of quantum coherence is related to the size of the system.

Quantifying the Dzyaloshinskii-Moriya Interaction Induced by the Bulk Magnetic Asymmetry.

A broken interfacial inversion symmetry in ultrathin ferromagnet/heavy metal (FM/HM) bilayers is generally believed to be a prerequisite for accommodating the Dzyaloshinskii-Moriya interaction (DMI) and for stabilizing chiral spin textures. In these bilayers, the strength of the DMI decays as the thickness of the FM layer increases and vanishes around a few nanometers. In the present study, through synthesizing relatively thick films of compositions CoPt or FePt, CoCu or FeCu, FeGd and FeNi, contributions to DMI from the composition gradient-induced bulk magnetic asymmetry (BMA) and spin-orbit coupling (SOC) are systematically examined. Using Brillouin light scattering spectroscopy, both the sign and amplitude of DMI in films with controllable direction and strength of BMA, in the presence and absence of SOC, are experimentally studied. In particular, we show that a sizable amplitude of DMI (±0.15 mJ/m^{2}) can be realized in CoPt or FePt films with BMA and strong SOC, whereas negligible DMI strengths are observed in other thick films with BMA but without significant SOC. The pivotal roles of BMA and SOC are further examined based on the three-site Fert-Lévy model and first-principles calculations. It is expected that our findings may help to further understand the origin of chiral magnetism and to design novel noncollinear spin textures.

Spin-wave modes of elliptical skyrmions in magnetic nanodots

Magnetic skyrmions, whose shapes are ellipse due to the presence of anisotropic Dzyaloshinskii–Moriya interaction (DMI), have already been discovered in experiments recently. By using micromagnetic simulations, we discuss the ground state and the spin-wave modes of a single elliptical skyrmion in a confined nanodot. It is found that the shapes of skyrmion are stretched into a horizontal ellipse, vertical ellipse, or stripe shape under different strengths of anisotropic DMI. When elliptical skyrmions are excited by in-plane ac magnetic fields, the spin-wave mode contains a counterclockwise rotation mode at high frequencies and a clockwise (CW) rotation mode at low frequencies, and the CW mode depends on the strength of anisotropic DMI. When elliptical skyrmions are excited by out-of-plane ac magnetic fields, the spin-wave mode is split from a simple breathing mode into two complex breathing modes, including a mixed mode of CW rotation and breathing, and another anisotropic breathing mode. Our results provide an understanding of the rich spin-wave modes for skyrmions, which may contribute to the applications in magnonics.