Anisotropic Interactions Research Articles

Anisotropy of exchange interactions in honeycomb ladder compound ReCl5

The Re5+(5d2) compounds possess large spin-orbital interaction which urges for large anisotropy, non – collinear structures and other phenomena. Here we present ReCl5 composed by separate [Re2Cl10] units formed by edge – shared chlorine octahedra. It demonstrates the formation of antiferromagnetically ordered state in two steps at TN1 = 35.5 K and TN2 = 13.2 K seen in dc-, ac - magnetic susceptibility and in specific heat. At 4K it can be transformed to the state with spontaneous magnetic moment by relatively weak magnetic field μ0H = 0.5 T via metamagnetic phase transition. Ab initio calculations give anisotropic ferromagnetic exchange interactions J1 and J2 within and between rhenium pairs forming the zig-zag chains along the a – axis. Pairs of zig-zag chains are coupled by ferromagnetic interaction J3 along the c – axis into magnetic honeycomb ladders. The ladders are coupled by significantly weaker interaction J4.

Multi-dimensional anisotropic feature interaction with machine learning to predict the thermal conductivity of A2B2O7-type high-entropy ceramics

Multi-dimensional anisotropic feature interaction with machine learning to predict the thermal conductivity of A2B2O7-type high-entropy ceramics

Competing and Anisotropic Exchange Interactions in the Kagome Lattice Ferromagnet Co3Sn2S2

The kagome lattice ferromagnet, Co3Sn2S2, serves as template for a host of materials that exhibit exotic topological states, as well as a giant anomalous Hall state—a momentous realization in condensed matter physics. The anisotropic exchange interactions are probed by applying external magnetic fields in various directions along major crystal axes and the magneto‐optical response is recorded. When magnetic fields are applied along the a–b plane, long‐range magnetism forms and grows with increasing temperature. This counterintuitive behavior does not take place when the magnetic field is applied at a slight angle off the a–b plane. In fact, the opposite effect is observed for this exact configuration, as well as for other fields arrangements. Ab initio theoretical calculations reveal that anisotropic exchange interactions are the underlying mechanism leading to this peculiar behavior. Furthermore, the long‐range ferromagnetic order along the c‐axis is thought to coexist with an antiferromagnetic, or spin glass, state in the a–b plane, before becoming paramagnetic above the Curie temperature (Tc). These two coexisting magnetic states are thought to compete as the temperature approaches Tc, with the antiferromagnetic state gaining strength compared to the ferromagnetic order.

The spin-wave energy spectrum and transition temperature of the two-dimensional VSe2-like: a retarded Green’s function method study

Based on the recent discovery of intrinsic magnetism in monolayer films VSe2, we have constructed a two-dimensional (2D) Heisenberg model incorporating the 1Tand 2Hstructures. These configurations consist of three layers: the upper and lower surface layers and a middle layer. Using the retarded Green's function method, we investigate the spin-wave energy spectrum, spin-wave density of states, and transition temperature of the system. It is found that in the 2Hstructure, the spin-wave energy spectrum of the system exhibits three direct energy gaps, with one branch being independent of the wave vector. Further analysis shows that at this constant energy, a particular surface state emerges in the 2Hstructure. In contrast, the spin-wave energy spectrum in the 1Tstructure features only two energy gaps-one direct energy gap1 and one indirect energy gap3-without forming a unique surface state. Single-ion anisotropy and interlayer interactions between the upper and lower surface layers influence the energy gaps in the spin-wave energy spectrum and the system's transition temperature. This theoretical work sheds light on forming particular surface states in monolayer 2Hstructure magnetic materials. It provides crucial theoretical support for designing and fabricating next-generation low-dimensional magnetic random-access memory.

Criticality behaviours in mixtures of liquid crystals and thermoreversible gels

ABSTRACT A mean-field theory is presented to describe the sol-gel (SGT) and nematic-isotropic phase transitions (NIT) in mixtures of thermoreversible reactive molecules and low-molecular-weight liquid crystalline molecules (LCs). By incorporating anisotropic interactions between the LC and gel, phase diagrams are calculated on the temperature-concentration plane. The theory predicts four distinct phases: isotropic sol, isotropic gel, nematic sol, and nematic gel. Furthermore, it identifies a critical point within the gel phase. The theoretical predictions are qualitatively consistent with experimental observations.

Nonclassicality of photons in mean-field anisotropic quantum light-matter interacting lattices: Two-photon correlation function and quadrature squeezing

Abstract The generation of nonclassical photons via quantum light-matter interactions is of fundamental importance in quantum optics. Here we investigate steady-state two-photon correlation function and photon squeezing in an open anisotropic Rabi lattice by applying quantum dressed master equation embedded with the mean-field approximation. The expanded antibunching effect of photons due to anisotropic qubit-photon interaction, is strongly suppressed by including inter-site photon tunneling, whereas the giant photon bunching keeps robust with weak inter-site photon tunneling strength. The microscopic processes for photon antibunching and bunching effects are presented based on incoherent transitions between eigenstates. The photon squeezing is also analyzed under the influences of qubit-photon coupling and anisotropic factor. The quadrature squeezing shows persistency by tuning on the inter-site photon tunneling, and becomes dramatically pronounced at the small anisotropic factor. Moreover, the increasing number of qubits significantly enhances quadrature squeezing with strong qubit-photon interaction. We hope such results may provide physical insights into efficient generation and manipulation of nonclassical features of photons in quantum light-matter interacting lattice systems.

Lattice-guided growth of dense arrays of aligned transition metal dichalcogenide nanoribbons with high catalytic reactivity.

Transition metal dichalcogenides (TMDs) exhibit unique properties and potential applications when reduced to one-dimensional (1D) nanoribbons (NRs), owing to quantum confinement and high edge densities. However, effective growth methods for self-aligned TMD NRs are still lacking. We demonstrate a versatile approach for lattice-guided growth of dense, aligned MoS2 NR arrays via chemical vapor deposition (CVD) on anisotropic sapphire substrates, without tailored surface steps. This method enables the synthesis of NRs with widths below 10 nanometers and longitudinal axis parallel to the zigzag direction, being also extensible to the growth of WS2 NRs and MoS2-WS2 heteronanoribbons. Growth is influenced by both substrate and CVD temperature, indicating the role of anisotropic precursor diffusion and substrate interaction. The 1D nature of the NRs was asserted by the observation of Coulomb blockade at low temperatures. Pronounced catalytic activity was observed at the edges of the NRs, indicating their promise for efficient catalysis.

Room-Temperature Magnetic Antiskyrmions in Canted Ferrimagnetic CoHo Alloy Films.

Magnetic antiskyrmions, the anti-quasiparticles of magnetic skyrmions, possess alternating Bloch- and Néel-type spin spirals, rendering them promising for advanced spintronics-based information storage. To date, antiskyrmions are demonstrated in a few bulk materials featuring anisotropic Dzyaloshinskii-Moriya interactions and a limited number of artificial multilayers. Identifying novel film materials capable of hosting isolated antiskyrmions is critical for memory applications in topological spintronics. Herein, the formation of room-temperature antiskyrmions in single ferrimagnetic CoHo rare-metal alloy films of varying thicknesses, observed using Lorentz transmission electron microscopy is reported. Furthermore, rotating magnetic fields (H) are proposed to facilitate antiskyrmion nucleation and enhance their areal density by an order of magnitude compared to that in the same area under individual vertical H. In addition, experimental and phenomenological analysis confirm that antiskyrmion nucleation can be attributed to spin reorientation involving spontaneous canted magnetism, as evidenced by polarized neutron reflectometry. Micromagnetic simulations further show that the antiskyrmion density significantly depends on the magnitude of the rotating field. These findings expand the family of known antiskyrmion-hosting materials and provide insights into their formation mechanisms, thus serving as a basis for their application in topological spintronics.

Magnetization nutation in magnetic semiconductors: Effective spin model with anisotropic RKKY exchange interaction

Magnetization nutation in magnetic semiconductors: Effective spin model with anisotropic RKKY exchange interaction

A machine learned potential for investigating single crystal to single crystal transformations in complex organic molecular systems.

The packing of organic molecular crystals is often dominated by weak non-covalent interactions, making their in situ rearrangement under external stimuli challenging to understand. We investigate a pressure-induced single-crystal-to-single-crystal (SCSC) transformation between two polymorphs of 2,4,5-triiodo-1H-imidazole using machine learning potentials. This process involves the rearrangement of halogen and hydrogen bonds combined with proton transfer within a complex solid-state system. We developed a strategy to progressively approach the transition state along the phase transition path from both ends by using both the α and β crystal phases as initial structures for active learning. This method allowed us to develop a DFT-based machine learning potential that faithfully describes both of the stable phases and the transition processes. Our results demonstrate that these anisotropic interactions are represented accurately during molecular dynamic simulations. Bond breaking and reforming during proton transfer is observed and analysed in detail. This approach holds promise for simulating SCSC transitions in organic molecular crystals involving anisotropic interactions and chemical bond changes.

Gd3+ doped CoCr2O4 nanoparticles: tuning the physical properties and optimizing the hyperthermia efficacy.

Tuning the physical properties of nanomaterials is essential to enhance their capabilities for modern technological applications. Incorporating appropriate dopant ions is expected to modify the physical properties of nanomaterials significantly. In this study, the microstructural, magnetic, electronic and optical properties of cobalt chromite nanoparticles have been tuned by incorporating Gd ions to obtain the optimized conditions for self-heating efficiency. Four chromite samples with varying Gd3+ dopant concentrations [CoGd x Cr2-x O4: x = 0, 0.04, 0.08 and 0.12] were prepared using the standard chemical co-precipitation method and their physical properties were explored thoroughly. The Gd3+ dopants in the host CoCr2O4 structure were shown to be capable of regulating the physical properties of the doped nanomaterials. Formation of a pure cubic spinel crystallographic phase together with size, shape and developed microstrain in the synthesized doped chromites were analyzed precisely and it was found that the mean size decreased gradually as the Gd content increased. Higher Gd content chromite nanoparticles showed a distinct blue shift in their absorption spectra and an increase in specific surface area, as evidenced by the BET study confirming the reduction in mean diameter. Substituted Gd ions also tuned the dielectric characteristics of the host chromite nanomaterial. A careful investigation of electrical conductivity in varying electric fields indicated that electron hopping occurs mostly during charge conduction. All the chromite samples exhibited lossy dielectric behavior as the dopant fraction increased. Introducing Gd ions in nanocrystalline cobalt chromite diluted the magnetic properties, which was evident from the reduction of the coercive field, and also provided the superparamagnetic ground state above 95 K. The spin-spiral transition became visible near 26 K as the Gd content in pure CoCr2O4 nanoparticles increased. The induction heating properties of nanosized chromite samples were modified using Gd doping, and the impacts of both the anisotropic energy barrier and magnetic dipole-dipole interactions on hyperthermia efficacy were extensively investigated. All of the prepared chromite samples at low concentration (1 mg mL-1) attained temperatures between 34.7 °C and 35.7 °C from ambient temperature in 900 seconds with an observed drop in the induction heating temperature with increasing Gd content in nanosized cobalt chromites. It was observed that the dispersion level of nanoparticles in solution also determined the heating efficiency. It was observed that Gd doped CoCr2O4 nanoparticles have the potential to be used in magnetic hyperthermia applications.

Rela2x: Analytic and automatic NMR relaxation theory.

Spin relaxation is modelled using the so-called relaxation superoperator Γˆˆ. Analytic forms of Γˆˆ have been derived in the literature in the simplest cases of one- or two-spin systems, with S=12 nuclei and no more than two different simultaneous relaxation mechanisms involved. Beyond that, for systems of more than two spins, with S>12 and/or multiple relaxation mechanisms at play, the derivations become notoriously complicated, which is why analytic relaxation theory has mostly been considered a dead end. Instead, numerical methods of constructing Γˆˆ have been popular. However, they lack some of the physical, chemical and pedagogical insight that can be provided by analytic expressions. To this end, we present a general, interactive and freely available Python programme, named Rela2x, to automatically compute the analytic matrix representation of Γˆˆ for high-field NMR. Tools to analyse, approximate and visualize Γˆˆ are built into Rela2x. As a demonstration of the functionality, Γˆˆ is presented both for the familiar dipole-dipole coupled 1H-1H spin system and for more complicated 1H-14N and 1H-13C-14N systems with dipole-dipole coupling, chemical shift anisotropy and quadrupole interaction. We envision that the code will provide much-needed clarity in the form of a helpful tool for the study of relaxation effects, and constitute a reference source for scientists in the field of NMR.

Anisotropic interactions for continuum modeling of protein-membrane systems.

In this work, a model for anisotropic interactions between proteins and cellular membranes is proposed for large-scale continuum simulations. The framework of the model is based on dynamic density functional theory, which provides a formalism to describe the lipid densities within the membrane as continuum fields while still maintaining the fidelity of the underlying molecular interactions. Within this framework, we extend recent results to include the anisotropic effects of protein-lipid interactions. As applications, we consider two membrane proteins of biological interest: a RAS-RAF complex tethered to the membrane and a membrane embedded G protein-coupled receptor. A strong qualitative and quantitative agreement is found between the numerical results and the corresponding molecular dynamics simulations. Combining the scope of continuum level simulations with the details from molecular level particle simulations enables research into protein-membrane behaviors at a more biologically relevant scale, which crucially can also be accessed via experiment.

Compensation temperature of a three-sublattice ferrimagnetic Heisenberg model

Using the double-time Green’s function method in combination with the random phase approximation and Anderson–Callen approximation, we investigate the magnetic properties of the ferrimagnetic Heisenberg model on a decorated square lattice. The effects of nearest-neighbor interactions and single-ion anisotropy on the compensation temperature are explored. Our results indicate that the next-nearest-neighbor interaction and/or single-ion anisotropy are not a necessary condition of the appearance of compensation temperature. When considering only the nearest-neighbor interaction, the system can also exhibit a compensation temperature. By comparing the impact of the nearest-neighbor interaction and single-ion anisotropy on the sublattice magnetizations of the system, a general condition of the appearance of compensation temperature is claimed.

Capillary-driven self-assembly of soft ellipsoidal microgels at the air–water interface

The adsorption of ellipsoidal colloidal particles on liquid interfaces induces interfacial deformation, resulting in anisotropic interface-mediated interactions and the formation of superstructures. Soft prolate-shaped microgels at the air-water interface offer an ideal model for studying spontaneous capillary-driven self-assembly due to their tunable aspect ratio, controlled functionality, and softness. These microgels consist of a polystyrene core surrounded by a cross-linked, fluorescently labeled poly([Formula: see text]-isopropylmethylacrylamide) shell. By uniaxially stretching the particles embedded in polyvinyl alcohol films, the aspect ratio [Formula: see text] can be finely adjusted. [Formula: see text] was found to vary from 1 to 8.8 as estimated in their swollen conformation at 20 °C from confocal laser scanning microscopy. The spontaneous interfacial self-assembly at the air-water interface is investigated through fluorescence microscopy, theoretical calculations, and computer simulations. A structural transition occurs from a seemingly random assembly for small aspect ratios to compact clusters, which transform into a side-to-side assembly forming long chains for high aspect ratios. The influence of the poly([Formula: see text]-isopropylmethacrylamide) shell on the assembly indicates a significant [Formula: see text]-dependent microgel deformation. This deformation, in turn, determines the average distance between the particles. Consequently, capillary-driven self-assembly of soft anisotropic colloids becomes a powerful mechanism for structuring interfaces and designing microstructured materials.

Double-Q Instability in Noncentrosymmetric Tetragonal Magnets with Bond-Dependent Magnetic Anisotropy Under an In-Plane Magnetic Field

We investigate the instability toward a double-Q state, which consists of a superposition of two spin density waves at different wave vectors, on a two-dimensional noncentrosymmetric square lattice in an in-plane external magnetic field. By performing the simulated annealing for the spin model with the Dzyaloshinskii–Moriya interaction and bond-dependent anisotropic interaction, we obtain four types of double-Q states depending on the sign of the bond-dependent anisotropic interaction. On the other hand, only the single-Q spiral state appears in the absence of the bond-dependent anisotropic interaction. The present results suggest that the interplay between the Dzyaloshinskii–Moriya interaction and bond-dependent anisotropic interaction can give rise to multiple-Q states for both zero and nonzero in-plane magnetic fields.

Extracting Orientation and Distance-Dependent Interaction Potentials between Proteins in Solutions Using Small-Angle X-ray/Neutron Scattering.

Nonspecific protein-protein interactions (PPIs) are key to understanding the behavior of proteins in solutions. However, experimentally measuring anisotropic PPIs as a function of orientation and distance has been challenging. Here, we propose to measure a new parameter, the generalized second virial coefficient, B22(Q), to address this challenge. B22(Q) can be measured by using small-angle X-ray/neutron scattering (SAXS/SANS) at finite Q values, where Q is the magnitude of the scattering wave vector. We develop the analytical theory here to calculate B22(Q) with any known interprotein potentials including anisotropic interaction potentials. This method overcomes the challenges and limitations of commonly used methods for extracting PPI information, namely, using integral approximations to solve the Ornstein-Zernike equation by fitting SAXS/SANS data. The accuracy of this analytical theory is further evaluated with computer simulations using a model system. Not only can our method greatly extend the capability of SAXS/SANS to investigate PPIs of many proteins, but it is also applicable to a wide variety of colloidal systems where anisotropic interaction potentials are important.

Anisotropy of the zigzag order in the Kitaev honeycomb magnet α−RuBr3

Kitaev materials often order magnetically at low temperatures due to the presence of non-Kitaev interactions. Torque magnetometry is a very sensitive technique for probing the magnetic anisotropy, which is critical in understanding the magnetic ground state. In this paper, we report detailed single-crystal torque measurements in the proposed Kitaev candidate honeycomb magnet α−RuBr3, which displays zigzag order below 34 K. Based on angular-dependent torque studies in magnetic fields up to 16 T rotated in the plane normal to the honeycomb layers, we find an easy-plane anisotropy with a temperature dependence of the torque amplitude following closely the behavior of the powder magnetic susceptibility. The torque for the field rotated in the honeycomb plane has a clear sixfold periodicity with a sawtooth shape, reflecting the threefold symmetry of the crystal structure and stabilization of different zigzag domains depending on the field orientation, with a torque amplitude that follows an order parameter form inside the zigzag phase. By comparing experimental data with theoretical calculations we highlight the importance of relevant anisotropic interactions and the role of the competition between different zigzag domains in this candidate Kitaev magnet. Published by the American Physical Society 2024

Anisotropic magnetic interactions in a candidate Kitaev spin liquid close to a metal-insulator transition

In the Kitaev honeycomb model, spins coupled by strongly-frustrated anisotropic interactions do not order at low temperature but instead form a quantum spin liquid with spin fractionalisation into Majorana fermions and static fluxes. The realization of such a model in crystalline materials could lead to major breakthroughs in understanding entangled quantum states, however achieving this in practice is a very challenging task. The recently synthesized honeycomb material RuI3 shows no long-range magnetic order down to the lowest probed temperatures and has been theoretically proposed as a quantum spin liquid candidate material on the verge of an insulator to metal transition. Here we report a comprehensive study of the magnetic anisotropy in un-twinned single crystals via torque magnetometry and detect clear signatures of strongly anisotropic and frustrated magnetic interactions. We attribute the development of sawtooth and six-fold torque signal to strongly anisotropic, bond-dependent magnetic interactions by comparing to theoretical calculations. As a function of magnetic field strength at low temperatures, torque shows an unusual non-parabolic dependence suggestive of a proximity to a field-induced transition. Thus, RuI3, without signatures of long-range magnetic order, displays key hallmarks of an exciting candidate for extended Kitaev magnetism with enhanced quantum fluctuations.

Influence of disordered and anisotropic interactions on relaxation dynamics and propagation of correlations in tweezer arrays of Rydberg dipoles

Influence of disordered and anisotropic interactions on relaxation dynamics and propagation of correlations in tweezer arrays of Rydberg dipoles