Intralayer Exchange Interaction Research Articles

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.

Revealing intrinsic domains and fluctuations of moiré magnetism by a wide-field quantum microscope

Moiré magnetism featured by stacking engineered atomic registry and lattice interactions has recently emerged as an appealing quantum state of matter at the forefront of condensed matter physics research. Nanoscale imaging of moiré magnets is highly desirable and serves as a prerequisite to investigate a broad range of intriguing physics underlying the interplay between topology, electronic correlations, and unconventional nanomagnetism. Here we report spin defect-based wide-field imaging of magnetic domains and spin fluctuations in twisted double trilayer (tDT) chromium triiodide CrI3. We explicitly show that intrinsic moiré domains of opposite magnetizations appear over arrays of moiré supercells in low-twist-angle tDT CrI3. In contrast, spin fluctuations measured in tDT CrI3 manifest little spatial variations on the same mesoscopic length scale due to the dominant driving force of intralayer exchange interaction. Our results enrich the current understanding of exotic magnetic phases sustained by moiré magnetism and highlight the opportunities provided by quantum spin sensors in probing microscopic spin related phenomena on two-dimensional flatland.

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.

Calculated magnetic exchange interactions in the van der Waals layered magnet CrSBr

Intrinsic van der Waals materials layered magnets have attracted much attention, especially the air-stable semiconductor CrSBr. Herein, we carry out a comprehensive investigation of both bulk and monolayer CrSBr using the first-principles linear-response method. Through the calculation of the magnetic exchange interactions, it is confirmed that the ground state of bulk CrSBr is A-type antiferromagnetic, while there are five sizable large intralayer exchange interactions with small magnetic frustration, which results in a relatively high magnetic transition temperature of both bulk and monolayer CrSBr. Moreover, the significant electron doping effect and strain effect are demonstrated, with further increased Curie temperature for monolayer CrSBr, as well as an antiferromagnetic to ferromagnetic phase transition for bulk CrSBr. We also calculate the magnon spectra using linear spin-wave theory. These features of CrSBr can be helpful to clarify the microscopic magnetic mechanism and promote the application in spintronics.

Magnetic Skyrmion Lattices in a Novel 2D‐Twisted Bilayer Magnet

AbstractMagnetic skyrmions are topologically protected spin swirling vertices, which are promising in device applications due to their particle‐like nature and excellent controlability. Magnetic skyrmions are extensively studied in a variety of materials and proposed to exist in the extreme 2D limit, i.e., in twisted bilayer CrI3 (TBCI). Unfortunately, the magnetic states of TBCIs with small twist angles are disorderly distributed ferromagnetic and antiferromagnetic (AFM) domains in recent experiments, and thus the method to get rid of disorders in TBCIs is highly desirable. Here, intralayer exchange interactions up to the third nearest neighbors without empirical parameters and very accurate interlayer exchange interactions are used to study the magnetic states of TBCIs. The functions of interlayer exchange interactions obtained using first‐principles calculations and stored in symmetry‐adapted artificial neural networks are proposed. Based on these, the subsequent Landau–Lifshitz–Gillbert equation calculations explain the disorderly distributed FM‐AFM domains in TBCIs with small twist angles and predict the orderly distributed skyrmions in TBCIs with large twist angles. This novel twisted 2D bilayer magnet can be used to design memory devices, monochromatic spin wave generators and many kinds of skyrmion lattices.

First-Principles Calculations of the Exchange Interaction of the CrGeTe3/NiO Interface

Two-dimensional (2D) magnetic materials have recently attracted a great attention due to their potential applications in information processing and storage. It was observed in an experiment that the CrGeTe3/NiO heterostructure shows a higher Curie temperature and a stronger perpendicular anisotropy. This suggests that antiferromagnet NiO can be coupled with ferromagnetic CrGeTe3 by the proximity effect, which enhances ferromagnetism. However, the mechanism behind the coupling is unknown. In this work, we built a CrGeTe3/NiO heterostructure model and investigated the electronic structure and magnetic properties of the CrGeTe3/NiO interface by first-principles calculations. It is shown that the intralayer exchange interaction between the Cr atoms is ferromagnetic, and the interlayer exchange interaction between the Ni atoms and Cr atoms at the interface is antiferromagnetic. The interlayer interaction is equivalent to a magnetic field as strong as B=100.3 T applied by the NiO substrate to the CrGeTe3 layer, which results in the higher Curie temperature of CrGeTe3 observed in the experiment.

Near-room temperature ferromagnetic behavior of single-atom-thick 2D iron in nanolaminated ternary MAX phases

Mn+1AXn (MAX) phases' nanolaminated ternary carbides or nitrides possess a unique crystal structure in which single-atom-thick “A” sublayers are interleaved by alternative stacking of a “Mn+1Xn” sublayer; these materials have been investigated as promising high-safety structural materials for industrial applications because of their laminated structure and metal and ceramic properties. However, limited of A-site elements in the definition of Mn+1AXn phases, it is a huge challenge for designing nanolaminated ferromagnetic materials with single-atom-thick two-dimensional iron layers occupying the A layers in the Mn+1AXn phases. Here, we report three new ternary magnetic Mn+1AXn phases (Ta2FeC, Ti2FeN, and Nb2FeC) with A sublayers of single-atom-thick two-dimensional iron through an isomorphous replacement reaction of Mn+1AXn precursors (Ta2AlC, Ti2AlN, and Nb2AlC) with a Lewis acid salts (FeCl2). All these Mn+1AXn phases exhibit ferromagnetic behavior. The Curie temperatures of the Ta2FeC and Nb2FeC Mn+1AXn phases are 281 and 291 K, respectively, i.e., close to room temperature. The saturation magnetization of these ternary magnetic MAX phases is almost two orders of magnitude higher than V2(Sn,Fe)C, whose A-site is partially substituted by Fe. Theoretical calculations on magnetic orderings of spin moments of Fe atoms in these nanolaminated magnetic Mn+1AXn phases reveal that the magnetism can be mainly ascribed to an intralayer exchange interaction of the two-dimensional Fe atomic layers. Owing to the richness in composition of Mn+1AXn phases, our work provides a large imaginary space for constructing functional single-atom-thick two-dimensional layers in materials using these nanolaminated templates.

Systematic Study of Monolayer to Trilayer CrI3: Stacking Sequence Dependence of Electronic Structure and Magnetism

In recent years, two-dimensional magnetic materials have attracted a lot of attention due to their unique magnetic properties, which can be manipulated by various degrees of freedom in a van der Waals stacked heterostructure, where different interlayer stackings affect the properties in different ways by exploiting weak interlayer interactions. An interesting example is CrI3, where the interlayer magnetic coupling can be determined by the stacking sequence. Here we present a systematic study of the magnetic properties of monolayer, bilayer, and trilayer CrI3 by using density functional theory and Monte Carlo simulations. The effects of different stacking sequences and the number of layers on the magnetic interaction in multilayer CrI3 have been critically analyzed. We have found that the antiferromagnetic interlayer coupling occurs with specific interlayer shifting, while intralayer exchange interactions increase with the number of layers. It is noteworthy that interlayer interactions are independent of the number of layers, whereas the magnetic ordering temperature rises with the increasing number of layers. Moreover, we present the Curie temperatures obtained from Monte Carlo simulations and adiabatic magnon spectra for all the stacking sequences considered here.

Magnetic and electronic ordering phenomena in the Ru2O6 -layer honeycomb lattice compound AgRuO3

The silver ruthenium oxide AgRuO$_3$ consists of honeycomb [Ru$_2^{5+}$O$_6^{2-}$] layers, and can be considered an analogue of SrRu$_2$O$_6$ with a different intercalation stage. We present measurements of magnetic susceptibility and specific heat on AgRuO$_3$ single crystals which reveal a sharp antiferromagnetic transition at 342(3)K. The electrical transport in single crystals of AgRuO$_3$ is determined by a combination of activated conduction over an intrinsic semiconducting gap of $\approx$ 100 meV and carriers trapped and thermally released from defects. From powder neutron diffraction data a N\'eel-type antiferromagnetic structure with the Ru moments along the $c$ axis is derived. Raman and muon spin rotation spectroscopy measurements on AgRuO$_3$ powder samples indicate a further weak phase transition or a crossover in the temperature range 125-200 K. The transition does not show up in magnetic susceptibility and its origin is argued to be related to defects but cannot be fully clarified. The experimental findings are complemented by DFT-based electronic structure calculations. It is found that the magnetism in AgRuO$_3$ is similar to that of SrRu$_2$O$_6$, however with stronger intralayer and weaker interlayer magnetic exchange interactions.

Effect of biaxial strain and hydrostatic pressure on the magnetic properties of bilayer CrI3

Two-dimensional van der Waals magnetic materials are intriguing for applications in the future spintronics devices, so it is crucial to explore strategy to control the magnetic properties. Here, we carried out first-principles calculations and Monte Carlo simulations to investigate the effect of biaxial strain and hydrostatic pressure on the magnetic properties of the bilayer CrI3. We found that the magnetic anisotropy, intralayer and interlayer exchange interactions, and Curie temperature can be tuned by biaxial strain and hydrostatic pressure. Large compressive biaxial strain may induce a ferromagnetic-to-antiferromagnetic transition of both CrI3 layers. The hydrostatic pressure could enhance the intralayer exchange interaction significantly and hence largely boost the Curie temperature. The effect of the biaxial strain and hydrostatic pressure revealed in the bilayer CrI3 may be generalized to other two-dimensional magnetic materials.

Simulation of magnetic properties of spin valve nanostructures

The Monte Carlo study of spin-valve magnetic structures with giant magnetoresistance effects has been performed with the application of the Heisenberg anisotropic model to the description of the magnetic properties of ultrathin ferromagnetic films. The dependences of the magnetic characteristics on the temperature and external magnetic field have been obtained. Dependence of hysteresis phenomena on thickness of ferromagnetic films and various values of intralayer and interlayer exchange interaction is studied.

Effect of a Soft Magnetic Phase on the Processes of Magnetization Reversal of a Hard/Soft Magnetic Bilayer

Magnetization reversal of a hard/soft magnetic bilayer in an external magnetic field has been studied by the Monte Carlo method. The magnetization reversal curves of a magnetic bilayer have been built at various thicknesses of the soft magnetic layer. The effects of the intralayer exchange interaction and the anisotropy constant of the soft magnetic layer on the magnetization reversal have been studied, too. The phase diagrams of the magnetic bilayer are presented.

Critical behavior in the layered organic-inorganic hybrid (CH3NH3)2CuCl4**Project supported by the National Natural Science Foundation of China (Grant No. 51725104) and the Beijing Natural Science Foundation, China (Grant No. Z180009).

The critical properties and the nature of the ferromagnetic–paramagnetic phase transition in the 2D organic-inorganic hybrid (CH3NH3)2CuCl4 single crystal have been investigated by dc magnetization in the vicinity of the magnetic transition. Different techniques were used to estimate the critical exponents near the ferromagnetic–paramagnetic phase transition such as modified Arrott plots, the Kouvel–Fisher method, and the scaling hypothesis. Values of β = 0.22, γ = 0.82, and δ = 4.4 were obtained. These critical exponents are in line with their corresponding values confirmed through the scaling hypothesis as well as the Widom scaling relation, supporting their reliability. It is concluded that this 2D hybrid compound possesses strong ferromagnetic intra-layer exchange interaction as well as weak interlayer ferromagnetic coupling that causes a crossover from 2D to 3D long-range interaction.

Влияние магнитомягкой фазы на процессы перемагничивания магнитотвердого/магнитомягкого бислоя

Investigation of the magnetization reversal of a hard/soft magnetic bilayer in an external magnetic field was performed by the Monte Carlo method. The magnetization reversal curves of the magnetic bilayer are plotted for various values of the thickness of the soft magnetic layer. Also the effect of the intralayer exchange interaction and the anisotropy constant on the magnetization reversal processes was studied. The phase diagrams of the magnetic bilayer are plotted.

Phase transitions in the Ising model on a triangular lattice with different values of interlayer exchange interaction

The Monte Carlo method was used to study the phase transitions and thermodynamic properties of the three-dimensional antiferromagnetic Ising model on a layered triangular lattice at various values of interlayer exchange interaction. A number of investigations have been carried out for the ratios of the intralayer (J1) and interlayer (J2) exchange interactions within the range of r = J2/J1 = 0.01–1.0. The nature of the phase transitions was studied using the fourth-order Binder cumulant method and histogram data analysis. It has been shown that in the considered range r, the transition from a disordered phase to an ordered phase is a second-order phase transition.

Critical Properties in the Ising Model on a Triangular Lattice with the Variable Interlayer Exchange Interaction

Phase transitions and critical and thermodynamic properties of the three-dimensional antiferromagnetic Ising model on a layered triangular lattice with variable interlayer exchange interaction are studied by the replica algorithm of the Monte Carlo method. The studies are carried out for the ratios of the intralayer J1 and interlayer J2 exchange interactions in the range of r = J2/J1 = 0.01–1.0. It is established that a second-order phase transition is observed in the considered r interval. Using the finite size scaling theory, the static critical exponents of the heat capacity α, susceptibility γ, order parameter β, correlation radius ν, and Fisher index η are calculated. It is shown that the universality class of the critical behavior of this model is preserved in the interval of 0.05 < r ≤ 1.0. It was found that with a further decrease in the r value, a crossover from the three-dimensional critical behavior to the quasi-two-dimensional one is observed.

Magnetic properties of a tri-layer superlattice: Mean field study and Monte Carlo simulation

Magnetic properties of a superlattice that consists of three square layers with Ising spins σ=1/2, s=1 and q=5/2, are investigated by means of standard Monte Carlo simulations and Mean Field Theory. The Hamiltonian model comprises contributions of intralayer and interlayer exchange interactions and the applied external magnetic field. Effects of the external magnetic field on magnetic behaviors have been thoroughly studied in the presence of thermal excitation. Ground state and thermal phase diagrams are numerically computated by both methods. Ground state phase diagrams of the system exhibit one ferromagnetic phase (1/2, 1, 5/2) and three ferrimagnetic ones: (−1/2, 1, 5/2), (−1/2, −1, 5/2) and (−1/2, 1, −5/2). A number of interesting phase diagrams and phenomena have been found, including hysteresis behaviors.

Frustrated bilayer spin one XY model on the honeycomb lattice

The spin-one honeycomb bilayer XY antiferromagnet has been studied taking into account the effect of the next-near neighbor J2 exchange interactions and single-ion easy plane anisotropy, using a flavor wave theory. We found that, at a critical point αC=13.8, where α=J⊥/J1 is the ratio between the interlayer J⊥ to the intralayer near neighbor J1 exchange interaction, the system shows a quantum phase transition from an Néel ordered phase to a paramagnetic phase. The phase diagram at zero temperature is presented.

Phase transitions of the frustrated bilayer spin one XY model

In this paper we use the SU(3) Schwinger boson representation, followed by a mean field decoupling, to study the disordered phases of the bilayer spin one quantum XY antiferromagnet on a square lattice with next near neighbor and a single ion anisotropy. The phase diagram at zero temperature is obtained. The ratio η=J⊥/J1 between the interlayer J⊥ to the intralayer near neighbor J1 exchange interactions exhibits a quantum phase transition at a critical ratio ηc=21.725 that separates the small- η Nèel phase from the large η quantum disordered paramagnet. The effect of next near neighbor interactions is discussed. The Neel phase is studied using a self consistent harmonic approximation that takes into account topological effects.

Magnetic properties of undoped and Al doped layered [formula omitted]-Co(OH)2

Undoped, 10% and 20% Al doped samples of layered hexagonal α-Co(OH)2 are synthesized. X-ray diffraction patterns show that the samples are nanocrystalline with average crystallite size 15nm. Fourier transform infrared spectroscopy and thermogravimetric analysis are performed to establish molecular formula of samples. Analysis of susceptibility χ as a function of temperature T (5–300K) data indicates for ferromagnetic transitions in the system at lower temperatures. Curie transition temperature TC for undoped, 10% and 20% Al doped α-Co(OH)2 are found to be 9, 7.5 and 6.0K respectively. Fitting of χ vs. T data for T>TC to the high temperature series yields strength of intralayer and interlayer exchange interactions among Co2+ ions. For undoped sample values of these interactions are estimated to be 1.070 and 0.240K respectively. Strength of these interactions decrease with increasing concentration of Al3+ ions in the lattice. Magnetization as a function of applied magnetic field (up to ± 50kG) data confirm ferromagnetic nature of the samples at 5K.