Interlayer Exchange Interaction Research Articles

Antiferro skyrmion crystals consisting of skyrmions and anti-skyrmions on a bilayer square lattice

An antiferro-type skyrmion crystal consisting of skyrmions with a negative topological charge and antiskyrmions with a positive topological charge manifests itself in its peculiar topological magnetism. We theoretically investigate the emergence of such an antiferro-type skyrmion crystal, where the topological charge exists in each sublattice but vanishes in the whole system. By performing the simulated annealing for an effective spin model with competing exchange interactions and staggered Dzyaloshinskii-Moriya interaction in momentum space on a bilayer square lattice, we find that the synergy between the antiferromagnetic interlayer exchange interaction and high-harmonic wave-vector interaction in addition to the staggered Dzyaloshinskii-Moriya interaction results in the antiferro-type skyrmion crystal in an external magnetic field. We show that the antiferro-type skyrmion crystal turns into the ferro-type skyrmion crystal with the same topological charge for both layers when the magnitude of the external magnetic field is varied. We also demonstrate that the competing interactions between ordering wave-vector channels and their high-harmonic wave-vector channels are essential in stabilizing the antiferro-type skyrmion crystal. Our results provide important ingredients to realize the antiferro-type skyrmion crystal by the external magnetic field, which can be utilized for low-power and high-speed spintronic devices based on antiferromagnetic materials.

Temperature Effect on the Interlayer Exchange Interaction in a Co/Pd/Co Heterostructure

Using Kerr microscopy, the magnetization reversal of the Co(0.4 nm)/Pd(6 nm)/Co(0.4 nm) heterostructure was studied in the temperature range 15–300 K. The temperature dependence of the domain nucleation field in a sample magnetized to saturation was obtained. The nucleation field in both ferromagnetic layers was shown to decrease monotonically with increasing temperature. A region of unstable temperatures of 160–174 K was found, below which the through domains of the new phase nucleated simultaneously in both layers, while in this region domains also nucleated simultaneously in different layers, but in different sites of the sample. The temperature dependence of the effective field HJ of the interlayer exchange interaction was obtained, which increased or decreased the pressure on the domain wall depending on whether this field was added to or subtracted from the external field.

Enhanced Ferromagnetism and Tunable Magnetic Anisotropy in a van der Waals Ferromagnet.

2D van der Waals (vdW) magnets have recently emerged as a promising material system for spintronic device innovations due to their intriguing phenomena in the reduced dimension and simple integration of magnetic heterostructures without the restriction of lattice matching. However, it is still challenging to realize Curie temperature far above room temperature and controllable magnetic anisotropy for spintronics application in 2D vdW magnetic materials. In this work, the pressure-tuned dome-like ferromagnetic-paramagnetic phase diagram in an iron-based 2D layered ferromagnet Fe3GaTe2 is reported. Continuously tunable magnetic anisotropy from out-of-plane to in-plane direction is achieved via the application of pressure. Such behavior is attributed to the competition between intralayer and interlayer exchange interactions and enhanced DOS near the Fermi level. The study presents the prominent properties of pressure-engineered 2D ferromagnetic materials, which can be used in the next-generation spintronic devices.

Homochiral antiferromagnetic merons, antimerons and bimerons realized in synthetic antiferromagnets

The ever-growing demand for device miniaturization and energy efficiency in data storage and computing technology has prompted a shift towards antiferromagnetic topological spin textures as information carriers. This shift is primarily owing to their negligible stray fields, leading to higher possible device density and potentially ultrafast dynamics. We realize in this work such chiral in-plane topological antiferromagnetic spin textures namely merons, antimerons, and bimerons in synthetic antiferromagnets by concurrently engineering the effective perpendicular magnetic anisotropy, the interlayer exchange coupling, and the magnetic compensation ratio. We demonstrate multimodal vector imaging of the three-dimensional Néel order parameter, revealing the topology of those spin textures and a globally well-defined chirality, which is a crucial requirement for controlled current-induced dynamics. Our analysis reveals that the interplay between interlayer exchange and interlayer magnetic dipolar interactions plays a key role to significantly reduce the critical strength of the Dzyaloshinskii-Moriya interaction required to stabilize topological spin textures, such as antiferromagnetic merons, in synthetic antiferromagnets, making them a promising platform for next-generation spintronics applications.

Magneto-ionic modulation of the interlayer exchange interaction in synthetic antiferromagnets

The electric-field control of magnetism is a highly promising and potentially effective approach for realizing energy-efficient applications. Recent interest has focused on the magneto-ionic effect in synthetic antiferromagnets, driven by its potential to enable high-density data storage devices with ultra-low power consumption. However, the underlying mechanism responsible for the magneto-ionic effect on the interlayer exchange coupling remains elusive. In our work, we find that the modulation of the interlayer exchange coupling is highly sensitive to the thickness of the ferromagnetic layer. We have identified that the changes in the interlayer exchange coupling induced by the gate voltage can be associated with the magneto-ionic effects on the top ferromagnetic layer of the synthetic antiferromagnet. The direct contact between the high ion mobility oxide and the top ferromagnetic layer plays a crucial role in facilitating these effects, largely modifying the anisotropy of the layers. Our findings highlight the important role of magneto-ionic control over the properties of the top ferromagnetic layer in governing the observed modifications in the interlayer exchange coupling. This study provides crucial insight into the intricate interplay between stack structure and magneto-ionic effect on magnetic properties in synthetic antiferromagnetic thin film systems.

Magnetic ordering in strong anisotropic ferromagnetic bilayers with dipolar and antiferromagnetic interlayer exchange interactions: Monte Carlo approach.

In this work, multilayer films consisting of two strong-anisotropic ferromagnetic layers antiferromagnetically coupled by a nonmagnetic spacer are studied by Monte Carlo simulations. The system is modeled by an Ising-based Hamiltonian that depends on both the intralayer exchange and dipolar constants and on the interlayer exchange constant (IEC). The ground state of the monolayers (null IEC) corresponds to alternate stripe domains with width h defined by the ratio between the exchange and dipolar constants (δ). The results show that IEC alters the energy balance that controls the stripe domain formation, leading to a ground state characterized by in-plane stripes out-plane antiferromagnetically coupled. When temperature increases two regimes are identified: an IEC-dominated regime where the orientational and positional orders are simultaneously lost in both layers, driving the system to the tetragonal liquid (TL) phase, and a dipolar-dominated one where signs of layers decoupling and the onset of positional disorder are observed. The last could be related with an intermediate nematic phase (NM). From the study of the nonequilibrium dynamics, the phase transitions to TL phase are characterized as continuous and those to the NM one as Kosterlitz-Thouless type. Also, for both layers the critical temperatures are the same and increase with IEC magnitude. Furthermore, the obtained critical exponents depend on the IEC values, which is indicative of a weak universality. For the dipolar-dominated regime, the decoupling between layers is also evidenced by the difference between their critical exponents.

Моделирование методами Монте-Карло магнитных свойств спин-вентильных наноструктур

The Monte Carlo simulation of behavior and magnetic properties of three types of active used spin-valve structures is carried out. It is identified the effect of magnetic anisotropy and intra- and interlayer exchange interaction influence on hysteresis phenomena in a spin-valve structures upon varying the thickness of nanosized ferromagnetic films.

Manipulation of valley-pseudospin in 2D WTe2/CrI3 van der Waals heterostructure by magnetic proximity effect

Lifting the valley degeneracy is an essential condition for exploiting the valley degrees of freedom to process and store information in valleytronics. The magnetic proximity effect (MPE) has been proven to be an effective method for introducing a magnetic field via interlayer exchange interaction, which can be conveniently achieved by two-dimensional (2D) van der Waals (vdW) heterostructure engineering. We have investigated the electronic properties and valley physics of 2D WTe2/CrI3 heterostructure using first-principles calculations. The results show that a significant valley splitting of 34.01 meV can be obtained in the WTe2/CrI3 heterostructure due to the simultaneous breaking of inversion and time-reversal symmetry, which sensitively depends on the atomic overlap of the projected position in the specific stacking model. In addition, we also show that the valley splitting can be enhanced by applying a vertical external electric field (E-field) or reducing the interlayer distance. More than that, it can be boosted by an order of magnitude (∼115.25 meV) through Cr ion intercalation. This is attributed to that the self-intercalated Cr ion has ferromagnetic (FM) ordering and perpendicular magnetic anisotropy due to the exchange coupling of the CrI3 layer. This result provides fundamental insights and valuable guidance for the application of 2D WTe2/CrI3 heterostructure in novel spintronic and valleytronic devices.

Ferroelectric phase transitions of nanoislands based on transverse ising model

Based on the transverse field Ising model, the phase transition properties of nanoislands with a spin-1/2 are studied by using the usual decoupling approximation of Fermi-type Green’s function. The phase diagram indicates that the phase transition curve (J S /J = t c , Ω S /J ∼ t c ) is highly sensitive to the interlayer exchange interaction (J R /J) and the ratio of surface to center transverse fields (Ω S /Ω). The polarization diagram reveals that the polarization curve exhibits steps attributed to spin inversion, and the temperature of the step point corresponds to the temperature at which spin configuration changes.

Ruderman-Kittel-Kasuya-Yosida-Type Interlayer Dzyaloshinskii-Moriya Interaction in Synthetic Magnets.

Conduction electron spins interacting with magnetic impurity spins can mediate an interlayer exchange interaction, namely, the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. This discovery opened the way to significant technological developments in the field of magnetic storage and spintronics. So far, the RKKY-type interlayer interaction has been found to construct symmetric coupling of magnetism; however, the asymmetric counterpart remains unexplored. Here we report unprecedented RKKY-type interlayer Dzyaloshinskii-Moriya interaction (DMI) in synthetic magnets, exhibiting a damped oscillatory feature. This asymmetric interlayer interaction is found to be dramatically dependent on the intermediate coupling layer. By introducing the Fert-Lévy model to the trilayer system, we reveal that the in-plane inversion symmetry breaking plays a pivotal role for generating interlayer DMI and the RKKY oscillation is an intrinsic behavior in metallic multilayers. Our finding fills up the empty block for RKKY-type asymmetric interlayer exchange coupling in comparison to the well-known (symmetric) RKKY-type interlayer exchange coupling.

Spacer Thickness and Temperature Dependences of the Interlayer Exchange Coupling in a Co/Pt/Co Three-Layer Structure

Domain wall mobility as a function of nonmagnetic interlayer thickness and temperature was studied in ultrathin exchange-coupled ferromagnetic layers using magneto-optic Kerr microscopy. The system under study is a Pt/Co/Pt/Co/Pt heterostructure having perpendicular magnetic anisotropy and a middle Pt layer with spatially variable thickness. The ferromagnetic interaction between the Co layers is observed when the Pt interlayer thickness varies from 5 to 6 nm in a temperature range of 200–300 K. There is a certain interval of Pt layer thickness where domain walls in both ferromagnetic layers move independently. Nonlinear dependence of the domain wall displacement on the applied field was measured. It is shown that an equilibrium position of the relaxed domain wall depends on field, temperature, and the nonmagnetic interlayer thickness. This position is determined by the energy balance: (i) domain wall displacement provided by the applied field, (ii) interlayer exchange interaction in the area swept by the domain wall, and (iii) domain wall coercivity. The mechanism of domain wall stabilization in terms of independent wall motion near critical thickness was considered. It is found that both the coercivity of the Co layer and the critical thickness decrease at higher temperature, while the interlayer exchange constant J is changed weakly.

Nucleation and manipulation of skyrmions by spin currents mediated by an antiferromagnetic layer

Magnetic skyrmions can be used as information carriers in advanced memories, logic gates and computing devices in the future. How to generate skyrmions rapidly in zero field becomes an urgent problem. The application of spin currents will play a major role in promoting the applications of skyrmions in spintronic devices. In this paper, we propose a mechanism based on spin currents to generate skyrmions. A multilayer structure (Pt/Cr2O3/Co/Pt) is designed, where an antiferromagnetic layer (Cr2O3) is inserted into the traditional trilayer structure (Pt/Co/Pt). A spin current generated on the heavy metal layer makes the magnetizations of the antiferromagnetic layer oscillate, and then the magnetizations in the ferromagnetic layer are driven to oscillate through the interlayer exchange interaction, and magnetic skyrmions can finally be nucleated in the Co layer. Through this unique combination of spin currents and antiferromagnetic layers, we effectively reduce the current density and increase operability, and this application provides more possibilities for future information transmission.

Magnetic characteristics of the ferrimagnetic bilayer MXene-like nanostructure with interlayer exchange interactions: Monte Carlo study

Monte Carlo simulations are used to investigate the magnetic properties of the nanostructured spin-7/2 and spin-1 ferrimagnetic bilayers within interlayer exchange interactions. The effects of nonmagnetic layers thickness, magnetic coupling and the crystal field on the blocking temperature, magnetization and hysteresis loops are studied. It is found that the blocking temperature decreases when increasing the magnetic coupling between layers and/or increasing the thickness of the magnetic layer. Besides, the model exhibits multiple hysteresis loops for which the area decreases when increasing the thickness of the magnetic layer, the crystal field and/or the temperature. Moreover, the effect of temperature on the behavior of the partial and the total magnetization and the total susceptibility are also as investigated.

Tailing the Magnetoelectric Properties of Cr2Ge2Te6 by Engineering Covalently Bonded Cr Self-Intercalation: Ferromagnetic Half-Metal

Two-dimensional intrinsic ferromagnetic half-metals (HMs) are important for spintronics. Based on a systematic research of CrGeTe3 (CGT) bilayers and multilayers with the self-intercalated (SI) Cr (CrSI) atom, we find that self-intercalation can enhance interlayer magnetic coupling, which results in a super-exchange interaction between interlayers. The CGT bilayer keeps half-metallicity with the interlayer ferromagnetic (FM) order after Cr’s self-intercalation, independent of CrSI atoms’ concentration and stacking orders. Moreover, SI-CGT multilayers with interlayer FM order transform from HMs into normal spin-polarized metals, as the states at the Fermi level increase. Moreover, the magnetic anisotropy energies (MAEs) of SI-CGT-AA and SI-CGT-AB are −0.160 and −0.42 meV/f.u., respectively, which are modulated by the CrSI atoms. The MAEs of SI-CGT-AA and SI-CGT-AB are different, as the hybridization interactions between Cr’s d orbitals are different from each other. SI-CGT bilayers’ magnetic easy axis (EA) switches from the original [001] of CGT to the [100] direction, independent of the stacking orders. It is inferred that the MAE is mainly contributed by the hybridization between Te’s px and py, py and pz orbitals, and that this hybridization interaction is obviously weakened as CrSI atom is inserted. The SI-CGT bilayers and multilayers show good dynamic and thermal stability at 300 and 500 K. These findings offer a promising way to manipulate the interlayer exchange interaction and magnetoelectric properties of CGT multilayers and other vdW magnets.

Effect of Co doping on structural and magnetic properties of kagome like La based cuprate francisite Cu3La(SeO3)2O2Cl

The effects of Co doping on the structural and magnetic properties of a frustrated layered rare earth based synthetic analog of mineral francisite [Cu3La(SeO3)2O2Cl;(LaCufr)] have been investigated experimentally with a prior theoretical input. We have estimated intra-layer and inter-layer exchange interactions from density functional theory, which reveals the strong antiferromagnetic (AFM) nature of the studied compounds. 10 at. % Co-doped CuLafr confirms incorporation of Co2+ at the Cu2+ site with the local environment around dopant Co nearly similar around that of host Cu. An observed field-induced meta-magnetic transition and a spin reorientation transition have been interpreted considering magnetic exchange interactions. Co-doped LaCufr exhibits a decrease in the AFM ordering temperature and the critical field corresponding to a meta-magnetic spin-flip type transition. The competition and modulation among different intra-layer exchange interactions upon incorporation of Co into the Cu site may lead to such situations. The evidence of spin–phonon coupling from Raman analysis in both compounds is noteworthy and enriches their magnetic properties.

Tunable topological magnon phases in layered ferrimagnets

The introduction of effective spin-orbit couplings into magnon systems provides the opportunities to discover exotic and fascinating topological phases. In this work, we theoretically study the magnon spin-orbit coupling due to the natural dipole-dipole interaction in a layered collinear easy-axis ferrimagnet with two types of ferromagnetic sublayers coupled via antiferromagnetic interlayer exchange interaction, where we predict a nodal-loop semimetal phase and a Weyl semimetal phase in perpendicularly and laterally magnetized geometries, respectively. By driving the spin texture into a spin-canting phase with a magnetic field perpendicular to the easy axis, the nodal loop with a normal easy axis reduces to two Weyl points in the noncollinear spin configuration. Magnon arcs in the Weyl semimetal phases in both geometries are predicted in ferrimagnetic film with finite layers. Our results reveal the role of noncollinear spin texture on magnon topology, which may enrich the investigations in topological ferrimagnonics.

Impact of organic amine cations on photoluminescence and magnetic properties in Dion-Jacobson hybrid manganese halide perovskites

A strenuous effort has been made to design multifunctional lead-free organic–inorganic hybrid (OIH) halide compounds, which are envisioned as next generation solar cell materials. However, it is challenging to design OIH halides that can exhibit both long-range magnetic ordering and high photoluminescence quantum yield (PLQY) since the dimensionality of the compounds has a contrasting effect on them. In this article, we have shown an approach to enhance PLQY in two-dimensional (2D) Heisenberg antiferromagnets by increasing the alkylene chain length of [H3N–(CH2)m–NH3]MnCl4 (m = 2, 3, and 4) compounds. All these compounds exhibit 2D layers of corner-sharing MnCl6 octahedra where the organic cations are intercalated between them. These compounds exhibit long-range antiferromagnetic ordering confirmed by the DC magnetic susceptibility and heat capacity measurements. The Néel temperature (TN) decreases with increasing the length of spacer cations due to a decrease in interlayer exchange interactions; however, interestingly, the lifetime of photoexcited electrons and PLQY enhances from 24 to 56 µs and 8% to 23%, respectively. Furthermore, the temperature-dependent photoluminescence measurements provide insight into thermal quenching and exciton binding energy. We believe this study can help to design new OIH halides with long-range magnetic ordering and high PLQY.

Anisotropy and delayed relaxation of the anomalous Hall effect in GdFeCo/Ir/GdFeCo synthetic ferrimagnets

In synthetic ferrimagnets with perpendicular anisotropy GdFeCo/Ir/GdFeCo, the dependence of the hysteresis loops of the anomalous Hall resistance and the characteristics of the loops on the angle between the magnetic field and the plane of the sample are analyzed. The part of the anomalous Hall resistance corresponding to the spin-orbit torque has been identified. The field dependences of the resistance are sensitive to switching between the magnetic states of the two-layer ferrimagnet and they reproduce the shapes of the magnetization hysteresis loops, calculated with the interlayer exchange interaction, crystal anisotropy, and Zeeman energies at different angles between the field and sample. A slow (~30 min) magnetic relaxation of resistivity hysteresis after reorientation of the sample in magnetic field was found. Specific domain dynamics inherent in two-layer samples was revealed by Kerr microscopy. It was found that slow restoration of the resistivity hysteresis loop is due to domain propagation. Keywords: spin Hall effect, spin-orbit torque, magnetic relaxation, domain wall dynamics.

Анизотропия и медленная релаксация аномального эффекта Холла в синтетических ферримагнетиках GdFeCo/Ir/GdFeCo

In synthetic ferrimagnets with perpendicular anisotropy GdFeCo/Ir/GdFeCo, the dependence of the hysteresis loops of the anomalous Hall resistance and the characteristics of the loops on the angle between the magnetic field and the plane of the sample are analyzed. The part of the anomalous Hall resistance corresponding to the spin-orbit torque has been identified. The field dependences of the resistance are sensitive to switching between the magnetic states of the two-layer ferrimagnet and they reproduce the shapes of the magnetization hysteresis loops, calculated with the interlayer exchange interaction, crystal anisotropy, and Zeeman energies at different angles between the field and sample. A slow (~30 min) magnetic relaxation of resistivity hysteresis after reorientation of the sample in magnetic field was found. Specific domain dynamics inherent in two-layer samples was revealed by Kerr microscopy. It was found that slow restoration of the resistivity hysteresis loop is due to domain propagation.

Quantum phase transitions driven by sliding in bilayer MnBi2Te4

Layered material ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ has bridged the fields of topology, magnetism and two-dimensional (2D) van der Waals materials, and attracted tremendous interest recently. Based on the first-principles calculation, we find that the topological, magnetic and ferroelectric properties of ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ bilayer can be engineered by interlayer sliding. By sliding bilayer ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$, the interlayer exchange interaction can be tuned between ferromagnetic and antiferromagnetic, enabling the transition from ferromagnetic insulators to Chern insulators, and the charge transfer would lead to coexistence with antiferromagnetic and ferroelectric phases. Our work paves a different mechanical way to engineer quantum phases in 2D magnetic materials.