Magnetic Effects Research Articles

Ground-state magnetic structures of topological kagome metals RV6Sn6 (R=Tb,Dy,Ho,Er)

Magnetic kagome metals have attracted tremendous research interests recently, because they represent an ideal playground for exploring the fascinating interplay between their intrinsically inherited topologically nontrivial electron band structures, magnetism and electronic correlation effects, and the resultant novel electronic/magnetic states and emergent excitations. In this work, we report a comprehensive single-crystal neutron diffraction investigation of the ground-state magnetic structures of the recently discovered V-based topological kagome metals RV6Sn6 ( = Tb, Dy, Ho, Er). Furthermore, the sample synthesis details and our systematic studies of crystal structure, low-temperature magnetic and thermodynamic properties of these compounds via various in-house characterization techniques are also reported. Our single-crystal neutron diffraction measurements confirm that the long-range magnetic order forms below 4.3 K for R=Tb, 3.0 K for R=Dy, 2.4 K for R=Ho, and 0.6 K for R=Er, respectively. The ground-state magnetic structures of the studied compounds are comprehensively determined via the magnetic crystallography approaches. It can be revealed that RV6Sn6 (R = Tb, Dy, Ho) have a collinear ferromagnetic order in the ground state, with the ordered magnetic moment aligned along the c axis for R = Tb, Ho, while approximately 20∘ tilted off from the c axis for R = Dy. In contrast, ErV6Sn6 shows an A-type antiferromagnetic structure with a magnetic propagation vector = (0, 0, 0.5), and with the ordered magnetic moment aligned in the ab plane. The ordered magnetic moments are determined as 9.4(2) µB, 6.6(2) µB, 6.4(2) µB, and 6.1(2) µB for R = Tb, Dy, Ho, and Er, respectively. A comparison of the low-temperature magnetic structures for both the extensively investigated topological kagome metal series of RV6Sn6 and RMn6Sn6 is given in detail. This allows to gain new insights into the complex magnetic interactions, diverse single-ion magnetic anisotropies and spin dynamics in these compounds. The reported ground-state magnetic structures in RV6Sn6 (R = Tb, Dy, Ho, Er) can pave the way for further explorations of the possible interplay between magnetism and topologically nontrivial electron band structures in the magnetically ordered phase regime. Published by the American Physical Society 2024

Intrinsic Localized Excitons in MoSe2/CrSBr Heterostructure.

Despite extensive studies on magnetic proximity effects, the fundamental excitonic properties of the 2D semiconductor-magnet heterostructures remain elusive. Here, the presence of localized excitons in MoSe2/CrSBr heterostructures is unveiled, represented by a new photoluminescence emission feature, X*. Our findings reveal that X* originates from excitons confined by intrinsic defects in the CrSBr layer. Additionally, the degrees of valley polarization of the X* and trion peaks exhibit opposite polarities under a magnetic field and closely correlate with the magnetic order of CrSBr. This is attributed to spin-dependent charge transfer across the heterointerface, supported by density functional theory calculations which reveal a type-II band alignment. Furthermore, the strong in-plane anisotropy of CrSBr induces unique polarization-dependent responses in MoSe2 emissions. This study highlights the crucial role of defects in shaping excitonic properties and offers valuable insights into spectrally resolved proximity effects in semiconductor-magnet van der Waalsheterostructures.

The Inhibitory Effect of Magnetism on the Thermal Transport in Nd-Ce-Fe-B Sintered Magnet

The Inhibitory Effect of Magnetism on the Thermal Transport in Nd-Ce-Fe-B Sintered Magnet

The effect of a magnetic field on the generation of free radicals in the interaction of quaternary ammonium compounds with hydroperoxides

The magnetic effects (ME) of a moderate magnetic field (MF, 600 mT) on the rate of radical generation (Wi) in mixed micellar systems of quaternary ammonium compounds with hydroperoxides (QAC-ROOH), measured by the inhibitor method, and the effect of magnetic field on the rate of radical polymerization initiated by radicals, generated from the surface by QAC chemisorbed on a solid carrier upon interaction with hydroperoxide dissolved in the monomer are compared. It has been established that in micellar solutions MF reduces Wi, ME ≈ –0.45. In the case of radical polymerization of styrene containing cumyl hydroperoxide on the surface of mica plates with a chemisorbed monolayer of QAC (CTAB or ACh), the polymerization rate increases in MF.

Efficient and Stable Red‐Orange Emission from Polaronic Magnetic Excitons in Mn (II)‐Doped 0D All‐Inorganic Rb4CdCl6

AbstractThe impact of magnetic coupling effects on the luminescence of 0D (zero‐dimensional) perovskite materials doped with TM (transition metal) ions remains underexplored. This study synthesizes Mn2+‐doped 0D Rb4CdCl6 halide structures using a solvent‐based method, with Rb+ ions systematically arranged around isolated [CdCl6]4− octahedra. The resulting Rb4Cd1‐xMnxCl6 powder exhibits stable orange‐red luminescence under UV (ultraviolet) excitation, achieving a PLQY (photoluminescence quantum yield) of 88.96%. The parent Rb4CdCl6 is non‐luminescent, but doping with Mn2+ induces strong luminescence due to combined emissions from d‐d transitions of Mn2+, weakly ferromagnetically coupled Mn2+ pairs, and STEs (self‐trapped excitons). Characterization via XRD (X‐ray diffraction) and DFT (density functional theory) reveals that Mn2+ doping occurs through both substitutional and interstitial processes, facilitating magnetic coupling. Raman spectroscopy identifies strong electron‐phonon coupling at a phonon mode of 112 cm−1, supporting STEs generation. Magnetic property analysis shows significant ferromagnetic coupling between Mn2+ pairs and paramagnetic single Mn2+ ions, enhancing luminescence. The material demonstrates remarkable structural and thermal stability, positioning Rb4Cd1‐xMnxCl6 as a promising candidate for optoelectronic applications.

Low-Temperature Glassy Behavior of Sr2Ni3(C2O4)3(OH)4·3H2O with Frustrated Spin Hexamers.

In this paper, we studied the synthesis, crystal structure, magnetism, and memory effect of a spin hexamer compound Sr2Ni3(C2O4)3(OH)4·3H2O. The basic magnetic unit of this compound is a ringed spin hexamer (Ni6 cluster). These Ni6 clusters are connected by an oxalate group, constituting a two-dimensional framework along the ab plane. With decreasing temperature, three anomalies are detected in susceptibility curves, corresponding to the formation of short-range spin correlation around 42.5 K, the onset of an antiferromagnetic ordering at 21.4 K, and a reentrant cluster spin-glass state below 12 K. A strong spin frustration is demonstrated with a frustrated factor f ∼ 11. The dominant exchange interactions are J1/kB = -17.1 K and J2/kB = -81.1 K, evaluated by exact diagonalization analysis with an isolated Ni6 cluster model. A nonequilibrium dynamics study of magnetic memory effect indicates the evolution of several intermediate metastable states.

Internal and Boundary Control of Piezoelectric Beams with Magnetic Effects and Voltage Controller: Exponential and Polynomial Decay Rates

Internal and Boundary Control of Piezoelectric Beams with Magnetic Effects and Voltage Controller: Exponential and Polynomial Decay Rates

The theoretical approach for description of magnetic properties and magnetocaloric effect in all-d-metal Heusler alloys Ni2−xCoxMn1.25Ti0.75

This paper investigates the influence of Co addition and atomic ordering on the magnetic and magnetocaloric properties of all-d-metal Heusler alloys Ni2−xCoxMn1.25Ti0.75, which exhibit a second-order magnetic phase transition. The modeling approach employed is based on the density functional theory and Monte Carlo method. The atomic ordering is considered with reference to the fully ordered structure, L21, and the partially ordered structure, B2. It is demonstrated that in both structures, the predominant magnetic state within the cubic austenitic phase is characterized by ferromagnetic ordering. An increase in the Co content results in the strengthening of the ferromagnetic exchange interactions between Mn, Ni, and Co, as well as an increase in the Curie temperature. For the ground state L21 structure, the largest Curie temperature values are observed, exceeding those of the B2 structure by almost 100 K. The temperature dependencies of the magnetization and magnetocaloric effect (ΔSmag) in magnetic fields up to 2 T are calculated using the Heisenberg Hamiltonian by the Monte Carlo method. The largest effect (ΔSmag≈1.4 J/kg K) is observed for the compound with x = 0.375 and B2 structure at temperature ≈150 K, whereas for L21-Ni1.5Co0.5Mn1.25Ti0.75 and B2-Ni1.25Co0.75Mn1.25Ti0.75, ΔSmag of 1.05 J/kgK appears in the vicinity of room temperature.

New method to clarify the contribution of the chiral magnetic effect in small collision systems p↑+A involving a transversely polarized proton

In this Letter, we propose a new experimental method to check the contribution of the chiral magnetic effect (CME). With experimental data of deep inelastic scattering (DIS) involving transversely polarized proton, we have calculated the three-dimensional charge density inside the polarized proton, which is found to have a significant violation to spherical symmetry. Then we have calculated the property of electromagnetic field (EM field) generated by a single transversely polarized proton (p↑). Based on them, the EM fields generated in small collision system p↑+A are studied. We find that the orientation of this EM field has a significant dependence on the polarization direction of the proton, and the correlator (Δγ) has also significant dependence on the angle between the reaction plane and polarization direction. As background contributions are canceled comparing two collision geometry schemes, only the contribution of CME remains. Published by the American Physical Society 2024

Melanin in the Retinal Epithelium and Magnetic Sensing: A Review of Current Studies.

Coming in a variety of forms, melanin is one of the most abundant, stable, diverse, and evolutionarily ancient pigments found in living things in nature. These pigments often serve protective functions, typically well-adapted to their specific roles. One such protective function is metal chelation and cation exchange, which help regulate and buffer metal concentrations within cells. By binding to certain metals, melanin can acquire magnetic properties. Because of this, it may play a role in magnetic effects and possibly in the response of organisms to external magnetic fields and magnetic sensing. While there is melanin in plants, microbes, fungi, and invertebrates, certain types of melanin are specifically associated with the retina in vertebrates, including migrating bird and fish species. In this review, we examine studies focusing on the properties of melanin in these parts of the body and their possible association with magnetic sensing, and generally, magnetic sensing in the retina.

Heuristic based physics informed neural network (H-PINN) approach to analyze nanotribology for viscous flow of ethylene glycol and water under magnetic effects among parallel sheets

In this article, we have conducted the study for the flow and thermal transfer of magneto-hydrodynamic squeezing nanofluid in the middle of two collateral plates extending to infinity using artificial neural network (ANN). The fluid employed in this research is a combination of Ethylene Glycol and water, and we delve into the utilization of a hybrid nanoparticle consisting of Fe3O4 and MoS2 particles. To solve the governing differential equations, we used unsupervised heuristic based physics informed neural network (H-PINN) based fitness function. In this research, the weights and biases of neural network were optimized using a hybridization of heuristic algorithms to achieve high accuracy. The fitness values obtained from proposed approach ranging from10−05 to10−08. The optimal results were then compared with numerical solutions obtained by using Runge-Kutta order-4 method through BVP4c tool as a reference solution, demonstrating the effectiveness of the unsupervised ANN method. The absolute error between the reference solution and proposed heuristic based physics informed neural networks approaches are ranging from2.36×10−04to3.46×10−06, 2.77×10−05to1.20×10−05 and1.10×10−06to6.53×10−07. Our findings demonstrate a strong agreement with the numerical approach, with the maximum discrepancy in the profiles of flow speed and energy profiles. Notably, we observed that an increase in the squeeze number and the Hartman number resulted in a reduction in the velocity profile.

Simulation of the charged particle deflection from the sweeping magnet array in the Lunar Environment heliospheric X-ray imager.

The Lunar Environment heliospheric X-ray Imager (LEXI) is an instrument built to image x-rays from solar wind charge exchange in Earth's magnetosheath. Monitoring the position of the magnetopause at the inner boundary of the magnetosheath allows us to understand how magnetic reconnection regulates how energy from the solar wind is deposited into Earth's magnetosphere. LEXI is part of an upcoming lunar lander mission set to land in Mare Crisium. To repel unwanted charged particles, the instrument carries a permanent magnet array composed of 48 neodymium magnets. The array was designed to maximize charged particle deflection while minimizing stray magnetic fields, which could impact other instruments or spacecraft operation. A Runge-Kutta-based fully kinetic particle tracing model was created to evaluate the effectiveness of LEXI's unique charged particle deflector array. Combined with the other particle suppression measures of the instrument, including physical structures and filters, the simulations show proton and electron transmission to the LEXI detector is expected to be sufficiently reduced to allow successful imaging. The flexible simulation model can be generalized to be used in examining the magnetic deflector array effectiveness of other instruments whose signals could be compromised by unwanted charged particle contamination.

Unveiling spin magnetic effect of TM doped SnS2 nanosheet with enhanced hydrogen evolution reaction

Photoelectrochemical hydrogen evolution reaction (HER) is taken into account as an alternative to effective hydrogen production, emphasizing the importance of catalysts. The magnetism of catalysts could modulate the adsorption of the H atom and further enhance the HER activity. Herein, doping the double transition metal atoms on SnS2 nanosheet (TM2@SnS2) to form the efficient magnetic catalyst is proposed to explore the spin magnetic effect on the HER performance. By performing first-principles calculations, nonmagnetic V2@SnS2 is proved to be the candidate of the HER catalyst; nevertheless, the HER activities of antiferromagnetic and ferromagnetic V2@SnS2 are relatively inferior due to the spin-induced charge redistribution. Meanwhile, machine learning analysis shows the absolute importance of the electronic structure of TM dopants and surrounding S ligands, and the HER activity could be predicted by the modified band centers of S-3pz and TM-d. Furthermore, the proof-of-concept experiment has substantiated the above theoretical predictions by significantly increasing photocurrent with applied magnetic field. This work provides a new avenue for uncovering the spin catalytic mechanism and the exploration and design of efficient HER catalysts.

The Magnet Effect of Price Limits: An Agent-Based Approach

ABSTRACT In this paper, we study the magnet effect within the context of circuit breaker events that transpired in global stock markets during March 2020. Our analysis encompasses nine such events across six countries. Employing a time-distanced quadratic function to model trading activities leading up to limit hits, we observe a substantial acceleration in return movement and the convergence of traders’ behavior preceding limit hits. Furthermore, most circuit breaker events manifest a distinct reduction in trading volume and amplified market stability during this crucial phase. To gain deeper insights into the magnet effect, we employ an agent-based model of the stock market that incorporates price limits. Our model replicates the stylized facts associated with limit hit events and the magnet effect. Importantly, our simulation results closely align with empirical observations. We also emphasize the importance of market environment changes and shifts in traders’ behavior in influencing limit hit events and the magnet effect.

Numerical analysis of Nano-encapsulated PCM magnetohydrodynamics double-diffusive convection and entropy generation in vertical enclosures with porous layer

This study investigates the effects of Nano-Encapsulated Phase Change Materials (NEPCMs) on double diffusive free convection in a partially porous cavity, considering Soret-Dufour effects and magnetohydrodynamics. The problem is modeled using non-dimensional governing equations, solved numerically through a Galerkin finite element method. The research examines the influence of key parameters including Rayleigh number (Ra: 103–105), Darcy number (Da: 10–4 -10–1), Hartmann number (Ha:0−80), NEPCM volume fraction (ϕ:0−0.04), Lewis number (Le:0.1−10), fusion temperature (θf:0.1−0.9), and Stefan number (Ste:0.1−0.9) on heat and mass transfer characteristics and entropy generation. Results show that increasing Ra significantly enhances heat and mass transfer, with Nusselt and Sherwood numbers rising by 424.8 % and 547.3 % respectively as Ra increases from 103 to 105. Higher Da and ϕ improve heat transfer, while stronger magnetic fields suppress both heat and mass transfer. An optimal fusion temperature (θf=0.5) is identified for maximum heat transfer enhancement. Total entropy generation, considering thermal diffusion, nanofluid friction, magnetic effects, porous medium, and mass diffusion contributions, increases by 15,957 % with Ra and decreases by 42.5 % with increasing Ha. The Bejan number analysis reveals that non-thermal irreversibilities become increasingly dominant at higher Ra and Ha values. The study concludes that NEPCMs can effectively enhance heat transfer in partially porous cavities, with their performance strongly influenced by Ra, Da, and Ha. The findings provide valuable insights for optimizing thermal management systems incorporating NEPCMs, particularly in applications involving porous media and magnetic fields.

Repercussions of thermally stratified magnetic dipole for mixed convectively heated Darcy-Forchheimer Carreau-Yasuda nanofluid flow via viscous dissipation analysis

Nowadays nanotechnology is progressing speedily with the passage of time, consequently the research on innovative fluid termed as nanofluid is at its peak. Invention of nanofluid has made a revolution in engineering and chemical processes due to its enhanced heat transmission characteristics along with environmental friendliness as well as financially affordability of nanofluid are causes of its attraction among the research community. In current study the basic aim is to scrutinize a rheological ferrofluid model with magnetic effects. The procedure for conversion of coupled P.D. Es into coupled set of O.D.Es which is performed by use of similarity variables. The numerical scheme used here is bvp4c scheme for obtaining the required numerical outcomes. A comprehensive review of graphical illustration for fluid's temperature, velocity as well as concentration is delivered here. We inspected that with upsurge of parameter for Brownian motion resultantly concentration of fluid declines while increase in thermal profile is noted.

Interaction of thermal, electrical, and magnetic effects on the nonlinear thermally induced vibrations functionally graded magneto-electro-thermo-elastic (FG-METE) beams

Interaction of thermal, electrical, and magnetic effects on the nonlinear thermally induced vibrations functionally graded magneto-electro-thermo-elastic (FG-METE) beams

Neural network analysis of bioconvection effects on heat and mass transfer in Non-Newtonian chemically reactive nanofluids

Using artificial neural networks, this study sought to investigate the magneto Williamson two-phase nanofluid, taking into account chemical reactions and the motion of gyrotactic motile microorganisms. Fluid flow behavior is influenced by chemical reactions, magnetic effects, Brownian motion, and thermophoresis, according to the study. Thermal transmission is enhanced in non-Newtonian fluids as a result of their propensity to thin under shear, increased turbulence, and superior convective heat transfer. As a result of the fluid's increased thermal conductivity, the incorporation of nanoparticles enhances heat conduction. Additionally, epidermis friction, Nusselt and Sherwood numbers, and the quantity of motile microorganisms were assessed in the study. The overall Absolute Errors lies in the range of 10−2to10−10.The mean squared error generated by Neural Networks lies in the range of 10−02−10−10, and 10−02−10−09 respectively. Suction or injection parameter and Prandtl number have an inverse relation with fluid temperature, while Thermophoretic parameter have a direct relation. Thermophoretic parameter, Schmidt number and suction or injection parameter have an inverse relation with the concentration of nanofluid and gyrotactic microorganisms' density, while micro-organisms density have a direct relation with the microorganisms. Engineering and medicine have utilized bioconvection, a process involving heat transfer and microorganism motion, in the development of nanomedicine, pharmacokinetics, drug delivery, and biosensors, among others. Solvers utilizing stochastic numerical computing include nonlinear networks, atomistic physics, thermodynamics, astrometry, fluid mechanics, nanobiology. As a result, variant scenarios are then tested, trained, and validated, in order to prove its accuracy.

Tuning of magnetic properties and giant magnetoimpedance effect in multilayered microwires

We studied the magnetic properties and Giant Magnetoimpedance (GMI) effect in amorphous Co-rich microwires with similar chemical compositions and different diameters with magnetic (Co, Permalloy) and non-magnetic (Cu) layers deposited by magnetic sputtering onto glass-coating. Studies of magnetic properties and GMI effect of as-prepared microwires and the same microwires with deposited magnetic and non-magnetic layers reveal substantial impact of such layers on GMI effect and hysteresis loops. Both as-prepared samples present soft magnetic properties and high GMI effect. The contribution of magnetic layers is observed in hysteresis loop at higher magnetic field, with hysteresis loops similar to those observed in microwires with mixed amorphous-crystalline structure. Meanwhile, both magnetic and non-magnetic layers affect low field hysteresis loops of both samples. Additionally, the GMI ratio, ΔZ/Z, and magnetic field dependences of GMI ratio are substantially affected by the presence of magnetic and non-magnetic layers deposited onto glass-coating. We discussed the observed experimental dependences considering both change of the internal stresses originated by the sputtered layer as well as the magnetostatic interaction between the amorphous ferromagnetic nucleus and deposited magnetic layers.

Linear instability in thermally stratified quasi-Keplerian flows

Quasi-Keplerian flow, a special regime of Taylor–Couette co-rotating flow, is of great astrophysical interest for studying angular momentum transport in accretion disks. The well-known magnetorotational instability (MRI) successfully explains the flow instability and generation of turbulence in certain accretion disks, but fails to account for these phenomena in protoplanetary disks where magnetic effects are negligible. Given the intrinsic decrease of the temperature in these disks, we examine the effect of radial thermal stratification on three-dimensional global disturbances in linearised quasi-Keplerian flows under radial gravitational acceleration mimicking stellar gravity. Our results show a thermo-hydrodynamic linear instability for both axisymmetric and non-axisymmetric modes across a broad parameter space of the thermally stratified quasi-Keplerian flow. Generally, a decreasing Richardson or Prandtl number stabilises the flow, while a reduced radius ratio destabilises it. This work also provides a quantitative characterisation of the instability. At low Prandtl numbers $Pr$ , we observe a scaling relation of the linear critical Taylor number $Ta_c\propto Pr^{-6/5}$ . Extrapolating the observed scaling to high $Ta$ and low $Pr$ may suggest the relevance of the instability to accretion disks. Moreover, even slight thermal stratification, characterised by a low Richardson number, can trigger the flow instability with a small axial wavelength. These findings are qualitatively consistent with the results from a traditional local stability analysis based on short wave approximations. Our study refines the thermally induced linearly unstable transition route in protoplanetary disks to explain angular momentum transport in dead zones where MRI is ineffective.