Strength Of Magnetic Coupling Research Articles

Realizing Synthetic Dimensions and Artificial Magnetic Flux in a Trapped-Ion Quantum Simulator.

Synthetic dimension is a potent tool in quantum simulation of topological phases of matter. Here we propose and demonstrate a scheme to simulate an anisotropic Harper-Hofstadter model with controllable magnetic flux on a two-leg ladder using the spin and motional states of a single trapped ion. We verify the successful simulation of this model by comparing the measured dynamics with theoretical predictions under various coupling strength and magnetic flux, and we observe the chiral motion of wave packets on the ladder as evidence of the topological chiral edge modes. We develop a quench path to adiabatically prepare the ground states for varying magnetic flux and coupling strength, and we measure the chiral current on the ladder for the prepared ground states, which allows us to probe the quantum phase transition between the Meissner phase and the vortex phase. Our work demonstrates the trapped ion as a powerful quantum simulation platform for topological quantum matter.

Manipulable ferromagnetic properties and half-metallic behavior in hole-doped PbClI monolayer: A DFT study

The remarkable performance exhibited by two-dimensional (2D) materials holds tremendous promise for transformative applications in the domains of electronics and spintronics. This study through first-principles calculations presents a systematic investigation of the novel 2D material PbClI monolayer. It is found that the PbClI monolayer exhibits desirable semiconductor properties, characterized by a large gap of 3.75 eV. Furthermore, it has been observed that mechanical strain can effectively tune this bandgap. Importantly, due to its unique flat valence band edge, hole doping in PbClI gives rise to pronounced features of ferromagnetism and half-metallicity, and hole doping levels can effectively tune its magnetic properties, including magnetic coupling strength, easy magnetization axis, and Curie temperature. In addition, PbClI monolayer shows outstanding multidirectional piezoelectricity. The calculations serve as a pivotal theoretical framework for the realization of stable magnetism in 2D materials.The study uncovers the vast possibilities in PbClI monolayer to position it as a potential candidate in the domains of spintronics and optoelectronics.

RKKY exchange interactions in two-dimensional Mn-doped ZnO dilute magnetic semiconductor

In this paper, we have theoretically studied the RKKY indirect exchange interactions in a two-dimensional model of Zn1-xMnxO dilute magnetic semiconductor. Under the RKKY interaction framework, we have calculated the exchange coupling constants for four different doped samples of host ZnO, which are 5%, 10%, 15%, and 20%. The carrier density for the respective configurations is taken as 0.1, 0.5, 0.75, and 1 hole per dopant, considering long-range interactions controlled by the cutoff scale in the RKKY range function. The variation of magnetic coupling strength with the carrier density is also examined, and the overall magnetic behavior of the proposed 2-D system is estimated.

Modulational instability in vector exciton-polariton condensates with photonic spin-orbit coupling

The paper demonstrates the existence of modulational instability (MI) in nonlinear exciton-polariton condensates (EPCs). A set of coupled two-dimensional (2D) driven-dissipative Gross-Pitaevskii equations describing the spin-up and spin-down polaritons, containing the photonic spin-orbit (SO) coupling and the rate equations describing the density of incoherent excitonic reservoir density, is reduced to a system of two coupled 2D complex Ginzburg-Landau (2DCGL) equations, with saturable nonlinearities for complex polariton order parameters, thanks to the adiabatic approximation and small density fluctuations approximation. The analytical approach relies on the linear stability analysis of continuous waves (CWs) to derive an expression for the growth rate and conduct a parametric study of MI. The effect of different parameters on the growth rate spectrum is discussed with an emphasis on the photonic SO coupling and the pumping power. The predictions are verified against a direct simulation of the 2DCGL equations, and excellent agreement is found. The emergence of solitonic clusters manifests the evolution of MI. Phase diagrams on a MI spectrum for the CWs are presented against the magnetic field ($B$) and SO coupling strength ($\ensuremath{\sigma}$), based on which the dynamical behaviors of the emerging structures are debated, along with their response to changing $\ensuremath{\sigma}$ and $B$. The results suggest that the photonic SO coupling and the magnetic field constitute efficient tools for nonlinear mode selection and characterization via the MI process and are equally important in any eventual experimental realization of such a process in the studied EPC system.

Field coupling-induced synchronization of a functional neuron with magnetic field perception

It is difficult to explore the induced mechanism of neuronal firing activity and the cooperation between neurons experimentally, so some neuronal circuits are established to train mode transformation and selection. Furthermore, some functional device, for example, piezoelectric ceramic, thermistor, phototube are inset in neuronal circuits and the functional neurons are developed to perceive some specific physical signal. In this paper, a linear resistance and an ideal Josephson junction are parallelly connected to FitzHugh-Nagumo (FHN) neuronal circuit, and then a functional neuron is established to percept the induction currents induced by the external magnetic field. Some basic dynamics are analyzed in terms of two-parameter bifurcation, one-parameter bifurcation and interspike interval(ISI for short) bifurcation, it is indicated that the functional neuron is sensitive to the electromagnetic stimulation and has rich multimodal transformations. The period-adding bifurcations accompanied by multi-period and chaos between two period cascades occupy the entire bifurcation interval when the external magnetic field is given in steady state, while the irregular modal transformations between period and chaos can be observed when the functional neuron encounters a periodic external magnetic field. Furthermore, two functional neurons are bridged with a capacitor, so field coupling is induced, then the effects of coupling strengths on complete synchronization are investigated by calculating the synchronization error function and the bifurcation diagram. In addition, the local dynamics of the network node play an important role in collective behavior and synchronous transition, so two capacitor-coupled functional neurons is presented as the network nodes, and a chain neural network is constructed to explore the effects of external magnetic field and coupling strength on network synchronous behavior. Obviously, the orderliness of the neural network can enhance or destroy under different modulation of external magnetic stimulation and coupling strength. It can give insights to investigate synchronization on neural networks with field coupling and useful guidance for implementing artificial synapse for signal processing.

Ab-initio and Monte Carlo studies of the structural, electronic and magnetic properties of V-doped ZnO compound

Realizing room-temperature ferromagnetic interactions in diluted magnetic semiconductors is a precondition for the future application of next-generation spin-based information technologies. However, finding effective strategies to alter the inherent magnetic coupling remains difficult. This paper aims to propose an approach for manipulating the ferromagnetism of (0.12%, 0.18%, 0.25%) V-doped ZnO (V-ZnO). The influence of V doping on the structural, electronic, and magnetic properties of ZnO is studied using first principles pseudo-potential plane wave method within the density functional theory (DFT). According to the first-principles calculations, the ferromagnetic ground state is maintained by a half-metallic electronic structure resulting from substantial hybridization between V-3d and O-2p electrons, and the calculations suggest that the ferromagnetism could be governed by the interactions between cluster spines in the VO4 tetrahedra. With the magnetic coupling strengths obtained by the green’s function method with the Wannier functions as a localized basis, the Monte Carlo simulation based on the Classical Ising model predicts the ferromagnetism of Zn1−xVxO (x = 0.12%, 0.18%, 0.25%) with Tc = 55 K, 165 K and 345 K. The observed results show that, as a diluted magnetic semiconductor, V-doped ZnO is an excellent candidate.

A multi-stable ultra-low frequency energy harvester using a nonlinear pendulum and piezoelectric transduction for self-powered sensing

This paper presents the design, theoretical modelling and experimental validation of a quad-stable energy harvester for harnessing ultra-low frequency random motions using a nonlinear pendulum and piezoelectric transduction. The multi-stable pendulum is created by the magnetic forces between magnets on the pendulum and a tip magnet on a piezoelectric cantilever beam. Two attractive and one repulsive magnetic forces in combination with the gravitational force of the pendulum create multiple stable positions for the pendulum. The multi-stable dynamics allow the pendulum to effectively convert low-frequency random kinetic motions from the host, e.g. human motion or wind turbine tower oscillation into the pendulum oscillation, enabling effective plucking of the piezoelectric beam with enhanced output power. A theoretical model, including the magnetic interaction, piezoelectric conversion and pendulum dynamics, is established to describe the electromechanical dynamics of the whole harvester. A prototype is fabricated and tested on a linear shaker at ultra-low frequencies (1–3 Hz) to showcase the capability of the harvester and to validate the theoretical results. Around 8 μW Root-Mean-Square output power was obtained at 2.5 Hz and 0.8 g of excitation. Using the experimentally validated theoretical model, a parametric study was carried out to examine the influence of different structural and operating parameters, such as pendulum mass and length, magnetic coupling strength, excitation frequency and amplitude, on the output power and operating frequency range of the energy harvester. The operation frequency range and output power can be effectively adjusted by changing the above-mentioned parameters. The self-powered sensing capability is then illustrated by integrating the harvester with an off-the-shelf power management circuit and a 22 μF storage capacitor. The capacitor was charged from 2.8 V to 4 V in 90 s, showing its capability of implementing battery-free wireless sensing for different Internet of Things (IoT) applications.

Hybridized magnetic lattice resonances for narrowband perfect absorption

The realization of multiple sharp collective resonances and their implications for ultrathin and narrowband perfect absorber without using back reflector is promising for the design of high performance nanophotonic devices. This study proposes and demonstrates that for double metallic/dielectric core/shell nanoparticle arrays, sharp hybridized magnetic lattice resonances can be excited and used to generate narrowband perfect absorption. Both coupled dipole approximation and full-wave simulations reveal that the magnetic (electric) coupling strength and coupling phase between the two nanoparticles in a unit cell can be effectively tuned by adjusting their relative positions, which leads to the selective excitation of the magnetic (electric) lattice modes for individual nanoparticle arrays or the hybridized magnetic (electric) lattice modes for the whole structures. When the hybridized magnetic lattice resonances are spectrally overlapping with electric modes by manipulating the lattice spacing, both balanced Kerker and critical coupling conditions are satisfied, thereby resulting in the formation of narrowband perfect absorptions. The flexible tunability of multiple sharp magnetic (electric) lattice resonances and the realization of narrowband perfect absorptions make the double nanoparticle arrays a promising platform for implications of linear and nonlinear nanophotonic devices.

Spin-orbit coupling effects on transport properties of electronic Lieb lattice in the presence of magnetic field

In this paper, the transport properties of a two-dimensional Lieb lattice that is a line-centered square lattice are investigated in the presence of magnetic field and spin-orbit coupling. Specially, we address the temperature dependence of electrical and thermal conductivities as well as Seebeck coefficient due to spin-orbit interaction. We have exploited Green’s function approach in order to study thermoelectric and transport properties of Lieb lattice in the context of Kane–Mele model Hamiltonian. The results for Seebeck coefficient show the sign of thermopower is positive in the presence of spin-orbit coupling. Also the temperature dependence of transport properties indicates that the increase of spin-orbit coupling leads to decrease thermal conductivity however the decrease of gap parameter causes the reduction of thermal conductivity. There is a peak in temperature dependence of thermal conductivity for all values of magnetic fields and spin-orbit coupling strengths. Both electrical and thermal conductivities increase with increasing the temperature at low amounts of temperature due to the increasing of transition rate of charge carriers and excitation of them to the conduction bands. Also we have studied the temperature dependence of Seebeck coefficient of Lieb monolayer due to both spin orbit coupling and magnetic field factors in details.

Hole-mediated ferromagnetic coupling in two-dimensional CrI3/VSe2 van der Waals heterostructures

Two-dimensional (2D) ferromagnetic (FM) semiconductors play imperative roles in the development of spintronic devices. However, the Curie temperature (Tc) of most 2D FM semiconductors are fairly low for practical applications. Herein, using the first-principles calculations, it revealed that the magnetic coupling strength within CrI3 can be modulated via the construction of CrI3/VSe2 van der Waals heterostructure. The system remains semiconducting with the band gap of 0.22 eV (GGA level). Its Tc can be boosted to ∼210 K via p-type doping, well above the liquid nitrogen temperature, which makes it a step closer to practical application. The greatly promoted FM coupling is originated from the additional super-exchange paths as well as the enhanced in-plane Cr-I-Cr super-exchange interaction. It is found that the interlayer magnetic coupling is tunable upon the stacking alignment, which is feasible to manipulate the magnetic orders using external mechanical motion.

Tuning the electronic, magnetic and optical properties of monolayer Cr2Ge2Te6 through surface adsorption

Based on first-principles calculations, we investigated the enhancement of magnetic coupling strength of two-dimensional Cr2Ge2Te6 through interfacial engineering by adsorbing three typical atoms, such as H, Cl and OH. We found that charge transfer and adsorption concentration are two key factors affecting the electronic and magnetic properties. Furthermore, different atomic adsorption produces a diversity of electronic properties, in which adsorbing H is semiconducting, while adsorbing Cl/OH is metallic. In adsorbing Cl/OH, the magnetic anisotropy energy gradually increases with the increase of the adsorption concentration, revealing that interfacial engineering can effectively modulate the electrical and magnetic properties of two-dimensional materials.

Enhancing magnetic coupling through protonation of benzylideneaniline-bridged diradicals and comparison with stilbene- and azobenzene-based diradicals.

Taking nitroxide radicals as spin sources, we explore the intramolecular magnetic coupling interactions of the trans- and cis-forms of benzylideneaniline (BA)-bridged diradicals, in which the central -CH[double bond, length as m-dash]N- unit can undergo single protonation to convert to its protonated counterpart or vice versa. The calculated results for these two pairs of diradicals (protonated versus unprotonated trans and cis forms) verify that the signs of their magnetic coupling constants J do not change, but the magnitudes significantly increase after protonation. In the structure, the better conjugation of the protonated trans diradical and two reduced CCNC and CCCN torsion angles of the protonated cis one make for a more efficient spin transport, promoting the spin polarization, thus leading to larger spin couplings. In terms of mechanism, the proton-induced magnetic enhancement should be attributed to strong participation of the coupler BA through its lowest unoccupied molecular orbital (LUMO) with a lower energy level after protonation, and the small HOMO-LUMO (HOMO: highest occupied molecular orbital) gap of the coupler BA through protonation is crucial in explaining such remarkable spin-coupling enhancement. Furthermore, different linking modes of the radical groups to the couplers are also considered to confirm our conclusions. In addition, we also make a comparison of the magnetic coupling strengths among their isoelectronic analogues of BA-, AB- and stilbene-bridged nitroxide diradicals before or after protonation, and find a linear correlation among them. It should be noted that the magnetic behaviors of all these diradicals obey the spin alternation rule and singly occupied molecular orbital (SOMO) effect. This work provides helpful information for the rational design of promising magnetic molecular switches.

Magnetic coupling engineering-induced excellent spin transport in covalently linked nanographene dimers

A generally accepted viewpoint is that molecules with a spin S = 1/2 did not show any magnetic coupling when assembled into molecular dimers. However, a recent experiment successfully synthesizes covalently linked five-membered ring decorated nanographene dimers that are antiferromagnetically coupled with each other [Phys. Rev. Lett. 124 (2020) 147206]. Motivated by this work, we further study the effect of magnetic coupling engineering on spin transport properties in covalently linked nanographene dimers-based molecular devices. Our results show that excellent spin transport properties are strongly dependent on the magnetic coupling strength of the covalently linked five-membered ring decorated nanographenes. A variety of interesting spin transport properties are found, including “inverse Schottky” characteristic, high spin polarization, reverse of spin polarization, and large magnetoresistance. These results indicate that the covalently linked five-membered ring decorated nanographene dimers can be designed as over-current protection devices, and information storage and logic devices by engineering of magnetic coupling. Our works confirm an efficient way for building high-performance carbon-based molecular spintronic devices.

Measurement uncertainty and entanglement in the hybrid-spin Heisenberg model

In this work, we study the dynamics of entropy-based uncertainty under a hybrid-spin (1, 1/2) Heisenberg XXZ model with an inhomogeneous magnetic field. Specifically, we examine the effect of the magnetic field strength B and coupling strength J of the two spins on the measurement uncertainty and the entanglement of the considered system, and nontrivially reveal that the magnetic field and coupling strength are responsible for the uncertainty dynamics associated with incompatible measurements. Interestingly, the entropic uncertainty eventually reaches a stable value with growing B, and the entanglement quantified by negativity eventually reduces to zero. Contrarily, a larger coupling constant J effectively reduces uncertainty. In addition, the effects of temperature T also are evaluated in the current framework. Furthermore, the relationship between uncertainty and entanglement is discussed; we claim that negativity and entropic uncertainty are approximately inversely correlated. Therefore, our observations are expected to be helpful in illustrating the dynamical entropy-based uncertainty in a hybrid Heisenberg spin-chain model and thus would be useful for realistic quantum information processing.

Modeling and dynamics of double Hindmarsh–Rose neuron with memristor-based magnetic coupling and time delay* *Project supported by the National Natural Science Foundation of China (Grant No. 61873186).

The firing of a neuron model is mainly affected by the following factors: the magnetic field, external forcing current, time delay, etc. In this paper, a new time-delayed electromagnetic field coupled dual Hindmarsh – Rose neuron network model is constructed. A magnetically controlled threshold memristor is improved to represent the self-connected and the coupled magnetic fields triggered by the dynamic change of neuronal membrane potential for the adjacent neurons. Numerical simulation confirms that the coupled magnetic field can activate resting neurons to generate rich firing patterns, such as spiking firings, bursting firings, and chaotic firings, and enable neurons to generate larger firing amplitudes. The study also found that the strength of magnetic coupling in the neural network also affects the number of peaks in thedischarge of bursting firing. Based on the existing medical treatment background of mental illness, the effects of time lag in the coupling process against neuron firing are studied. The results confirm that the neurons can respond well to external stimuli and coupled magnetic field with appropriate time delay, and keep periodic firing under a wide range of external forcing current.

Effect of Van Hove singularities on Shiba states in two-dimensionals-wave superconductors

Magnetic impurities in a superconductor induce Yu-Shiba-Rusinov (YSR) states inside the superconducting gap, whose energy depends on the strength of the coupling to the impurity and on the density of states (DOS) at the Fermi level. We consider DOS exhibiting a logarithmic or a power-law divergence at the Fermi level due to Van Hove singularities (VHS) and high-order Van Hove singularities (HOVHS), respectively. We find that the energy of the YSR states has the same functional form as in the constant DOS scenario, with the effect of the singularity being an enhancement of the effective coupling constants. In particular, the critical magnetic coupling strength at which the Shiba transition occurs is always lowered by a factor $1/\rho(\Delta/E_{\mathrm{c}}$), where $\Delta$ is the superconducting gap, $E_{\mathrm{c}}$ is the bandwidth, and $\rho(E)$ is the factor in DOS which diverges at $E=0$ for a VHS or HOVHS. Further, since the critical magnetic coupling is significantly reduced, a new regime becomes accessible where the transition point is controlled by the non-magnetic coupling constant. Interestingly, the slope of the Shiba energy curve at the Shiba transition is independent of impurity parameters and purely reflects the band structure. Additionally, we find that our main conclusions remain valid even when the Fermi level is not precisely tuned to the Van Hove singularity, but instead lies on an energy range of order the superconducting gap. Our results show that tuning a superconducting material towards a VHS or HOVHS enhances the possibilities for engineering YSR states, and for characterizing the superconductor itself.

Phase diagram for strongly interacting matter in the presence of a magnetic field using the Polyakov–Nambu–Jona-Lasinio model with magnetic field dependent coupling strengths

We study the phase diagram for strongly interacting matter using the 't Hooft determinant extended Nambu--Jona-Lasinio model with a Polyakov loop in the light and strange quark sectors (\emph{up}, \emph{down} and \emph{strange}) focusing on the effect of a magnetic field dependence of the coupling strengths of these interactions. This dependence was obtained so as to reproduce recent lattice QCD results for the magnetic field dependence of the quarks dynamical masses. A finite magnetic field is known to induce several additional first-order phase transition lines with the respective Critical End Points (CEP) in the temperature-quark chemical potential phase diagram when compared to the zero magnetic field case. A study of the magnetic field dependence in the range $eB=0-0.6~\mathrm{GeV}^2$ of the location of these CEPs reveals that the initial one as well as several of the new ones only survive up to a critical magnetic field. Only two remain in the upper limit of the studied magnetic field strength. A comparison of the results obtained with versions of the model with and without Polyakov loop is also done. We also found that the inclusion of the magnetic field dependence on the coupling strengths, while not changing the qualitative features of the phase diagram, affects the location of these CEPs. The comparison of results with and without a regularization cutoff in the medium part of the integrals does not show a significant change.

Monte Carlo simulations of the thermodynamic behavior of exchange graded ferromagnets

In this work, we investigate the thermodynamic behavior of exchange graded ferromagnetic films using Monte Carlo simulations. The systems are modeled by using a classical Heisenberg Hamiltonian, considering only nearest neighbor exchange interactions and a linear depth-dependent effective magnetic exchange coupling strength profile. Our quantitative assessment of the local physical quantities shows that each layer exhibits rather isolated thermodynamic behavior, since both layerwise magnetization and susceptibility data indicate layer-specific ``local'' Curie temperatures as a consequence of the depth-dependent change in the exchange coupling strength. We also propose and evaluate a predictive formulation for such profiles of ``local'' Curie temperatures, whose only input is the pre-selected exchange coupling profile. Having this very precise predictive tool, we show how it can be used to obtain the temperature-dependent ferromagnetic state including its depth-dependent magnetization profile at any given temperature. Thus, it is possible to predict which exchange profile will produce a desired thermodynamic behavior and associated functionality, without the need to perform complex experiments or time-consuming computations. With this study, we furthermore demonstrate that nonlocal aspects of the thermodynamic state formation in graded magnetic materials are relevant only over very short length scales, which is in outstanding qualitative agreement with prior numerical and experimental work.

Monte Carlo simulation to study the effect of molecular spin state on the spatio-temporal evolution of equilibrium magnetic properties of magnetic tunnel junction based molecular spintronics devices

With a variable spin state, paramagnetic molecules can affect the impact of magnetic exchange coupling strength between two ferromagnetic electrodes. Our magnetic tunnel junction based molecular spintronics devices (MTJMSD) were successful in connecting paramagnetic single molecular magnet (SMM) between two ferromagnetic electrodes. Isolated SMM exhibited a wide range of spin states. However, it was extremely challenging to identify the SMM spin state when connected to the ferromagnetic electrodes. Our prior experimental and Monte Carlo Simulations (MCS) studies showed that paramagnetic molecules produced unprecedented strong antiferromagnetic coupling between two ferromagnets at room temperature. The overall antiferromagnetic coupling occurred when a paramagnetic SMM made antiferromagnetic coupling to the first electrode and ferromagnetic coupling to the second ferromagnetic electrode. This paper studies the impact of variable molecular spin states of the SMMs, producing strong antiferromagnetic coupling between the ferromagnetic electrodes of MTJMSD. The MTJMSD used in this study was represented by an 11 x 50 x 50 Ising model, with 11 being the thickness of the MTJMSD and 5 x 10 x 50 being each electrode’s size. We employed a continuous MCS algorithm to investigate SMM’s spin state’s impact as a function of molecular exchange coupling strength and thermal energy.

3D Rotation‐Trackable and Differentiable Micromachines with Dimer‐Type Structures for Dynamic Bioanalysis

Utilizing the magnetic interactions between microparticle building blocks allows creating long‐range ordered structures and constructing smart multifunctional systems at different scales. The elaborate control over the inter‐particle magnetic coupling interaction is entailed to unlock new magnetoactuation functionalities. Herein, dimer‐type microstructures consisting of a pair of magnetic emulsions with tailorable dimension and magnetic coupling strength are fabricated using a microfluidic emulsion‐templated assembly approach. The magnetite nanoparticles dispersed in vinylbenzene monomers are partitioned into a pair of emulsions with conserved volume, which are wrapped by an aqueous hydrogel shell and finally polymerized to form discrete structures. Tunable synchronous–asynchronous rotation over 60 dB is unlocked in magnetic dimers, which is shown to be dependent on the magnetic moments induced. This leads to a new class of magnetic actuators for the parallelized assay of distinctive virus DNAs and the dynamic optical evaluation of 3D cell cultures. The work suggests a new perspective to design smart multifunctional microstructures and devices by exploring their natural variance in magnetic coupling.