Effect Of Magnetic Interactions Research Articles

Predictions of spin-valley properties in ferromagnetic Janus 2H-CeXY (X, Y = Cl, Br, I, X ≠ Y) monolayers: Merger of valleytronics with spintronics

In this work, the Janus 2H-CeXY monolayers are predicted as 2D intrinsic ferrovalley materials with bipolar ferromagnetic (FM) semiconductor characters, high Tc of 511–540 K, robust in-plane/perpendicular magnetic anisotropy (IMA/PMA) and spontaneous valley polarization through first-principles calculations. The d-p-d indirect exchange interaction between the Ce atom and X(Y) atoms is responsible for the observed FM ordering. Applying the biaxial strain ε from −6 % to 6 %, the Janus 2H-CeXY monolayers keep energy bandgap and large magnetic anisotropy. While a transition from PMA to IMA character is observed for the 2H-CeBrCl monolayer, which is due to the competition between Ce-p/d and Br/Cl-p orbitals. The intrinsic magnetic interaction and strong SOC effect induce a large spontaneous valley polarization of 29.1–78.7 meV for the Janus 2H-CeXY monolayers, which is also robust under various ε. Besides, the anomalous valley Hall effect (AVHE) can be observed due to the nonzero Ωz(k) induced by the broken space/time-reversal symmetry. Overall, the Janus 2H-CeXY monolayers provides a new candidate for the spintronic and valleytronic devices.

Mirror symmetry breaking of superradiance in a dipolar Bose-Einstein condensate

Dicke superradiance occurs when two or more emitters cooperatively interact via the electromagnetic field. This collective light-scattering process has been extensively studied across various platforms, from atoms to quantum dots and organic molecules. Despite extensive research, the precise role of direct interactions between emitters in superradiance remains elusive, particularly in many-body systems where the complexity of interactions poses significant challenges. In this study, we investigate the effect of dipole-dipole interaction between 18 000 atoms in dipolar Bose-Einstein condensates (BECs) on the superradiance process. In dipolar BECs, we simplify the complex effect of anisotropic magnetic dipole-dipole interaction with Bogoliubov transformation. We observe that anisotropic Bogoliubov excitation breaks the mirror symmetry in decay modes of superradiance. Published by the American Physical Society 2024

QPOs from charged particles around magnetized black holes in braneworlds

Quasiperiodic oscillations (QPOs) are a powerful tool for testing gravity theories, probing gravitational and electromagnetic field properties, and obtaining constraints on the black hole and field parameters. This work considers charged particle dynamics near uniformly magnetized black holes in braneworlds. First, we obtain the solution of the Maxwell equation for magnetic fields and calculate the radial and angular magnetic field components. We derive and analyze the effective potential of charged particles for circular orbits and investigate the energy and angular momentum for the circular orbits. We also analyze the combined effects of magnetic interaction and braneworlds on the charged particles’ innermost stable circular orbits (ISCOs). We calculate the angular momentum of charged particles in Keplerian orbits in the presence of an external magnetic field and braneworlds. Also, we investigate frequencies of the particle oscillations along vertical and angular directions. We applied our studies on particle oscillations to the QPO studies in the relativistic precession model. Finally, we obtain constraints on magnetic interaction and braneworld parameters together with the black hole mass and QPO orbits using Monte Carlo Markov Chain (MCMC) simulation in the four-dimensional parameter space for the QPOs observed in the microquasars XTE J1550-564, GRO J1655-40 & GRS 1915-105, and at the center of galaxies M82 and Milky Way.

Effect of magnetic anisotropy and interaction on spatial focused hyperthermia for rotating and oscillating fields

The behavior of magnetic nanoparticles in a time-varying magnetic field has several practical applications. One of these is hyperthermia used in the treatment of cancer. The nanoparticles injected in the tumor cells release the energy absorbed from the time dependent external magnetic field in the form of heat to its environment in a well-localized way. The aim of the research in this area is to maximize the amount of the dissipated energy. Using a combination of an oscillating and static magnetic field, this dissipated energy can be more focused in space. In this article, we investigated whether this spatial focusing is also present using a rotating and static field together. Furthermore, we investigated the effects of anisotropy and interaction between nanoparticles on this spatial focusing effect using the jump-diffusion model for Néel relaxation in both cases. This kinetic Monte Carlo (MC) method was validated and compared with the stochastic Landau-Lifshitz-Gilbert (SLLG) equation based model. We have shown that the spatial focusing effect is also present for these non-idealized experimentally realizable cases. Also, the effect of rotating magnetic field on magnetic nanoparticles was not investigated in kinetic Monte Carlo simulations before.

Single-domain structure of Fe3O4 nanoparticles encapsulation by magnetic surfactant M(AOT)2 (M=Co, Ni)

Investigating the magnetic nanoparticle size and the effective magnetic interactions that form the magnetic domain can lead us to nanoparticles with targeted applications, such as targeted drug delivery and higher resolution MRI imaging. In this study magnetic susceptibility and coercive field properties, and the structure size range of single-domain magnetic capsules with high magnetization were obtained by structural analysis of volumetric DLS properties. In this regard, the role of exchange, anisotropy, and magnetostatic interaction was investigated in the structure of a magnetic capsule containing Fe3O4 nanoparticles (MCap-NPs). The stable capsules were synthesized in an emulsion solution with magnetic surfactants M(AOT)2 (M = Co, Ni). Vibrating Sample Magnetometer (VSM) and capsule relative volume (CRV) of Dynamic Light Scattering (DLS) were used to determine the magnetic properties of the single-domain (SD) structure. The produced emulsion samples were found to have superparamagnetic properties property with saturation magnetization in the range of 2–6 × 10−3emu/g for NiCap-NPs, and 5-13 × 10−3emu/g for CoCap-NPs. The results show that nanoparticles have the most significant effect on magnetization. The coercive field, the anisotropy energy values, and the SD of M(AOT)2 were determined using magnetic susceptibility distribution. The outcome results show that the surface of the magnetic capsule plays an essential role in forming a single-domain structure. It was also found that the saturation magnetization of the samples in the emulsion solution is proportional to the nanoparticle density and not to the mass of nanoparticles. All produced samples have distinct peaks in CRV versus capsule size, and each peak follows a log-normal distribution. For both samples, except for the samples with molar ratios ω of 23 (Co3 and Ni4 samples), the positions of the second and third relative volume peaks were constant at 269 ± 3 nm and 424±6 nm, respectively. The behavior of the CRV function normalized to the peak size showed a proportionality between the coercive field and the CRV.

Circular motion and collisions of particles with magnetic dipole moment and electric charge in dipolar magnetosphere around Schwarzschild black holes

No-hair theorem indicates that black holes cannot have their own magnetic dipole moment. They can be weakly magnetized in binary systems with a neutron star companion and an accretion disc of charged particles. A simple model suggested by Petterson states that a current loop accreting a Schwarzschild black hole generates dipole-like magnetic fields in the outer region of the loop that are uniform in the inner region. This study considers circular motion and collisions of charged test particles with magnetic dipole moments in the inner and outer regions. First, we derive the effective potential taking into account the magnetic interactions between external magnetic fields with electric charge and the magnetic dipole moment of the particle. We investigate the possible innermost stable circular orbits (ISCOs) of the charged and magnetized particles orbiting the magnetized Schwarzschild black hole inside and outside the current loop. Finally, we explore the collisional processes of these particles near the black hole horizons, examining the effects of magnetic interactions on the critical angular momentum of particles that may collide and the center of mass energy of the colliding particles. We discuss astrophysical relevant objects with magnetic dipole moment and electric charge: magnetized neutron stars, white dwarfs, rotating stellar-mass black holes, electrons, and protons, and also estimate the interaction parameters for them.

Hydrogen-annealing modulated magnetocaloric effect and critical behavior of Weyl semimetallic Co3Sn2S2

Modulating the electron interaction and magnetic domains is an essential strategy to evoke novel physical properties, both for fundamental research and for related magnetic applications. The emerging annealing process attracted attention due to its capability of tuning the magnetic performance, but it has been rarely studied. Herein, we conducted hydrogen annealing on the Weyl semimetallic Co3Sn2S2 and investigated the magnetic interaction, critical behavior, and magnetocaloric effect (MCE). Hydrogen-annealed Co3Sn2S2 (HA-Co3Sn2S2) exhibits a distinct anisotropy-dependent magnetic behavior, where a typical second-order transition with an easy magnetization process is observed under H//c. However, a frustrated magnetic state composed of ferromagnetic (FM), antiferromagnetic (AFM), and/or spin glass phases is observed when H//ab. Critical analyses illustrate that the ground state of HA-Co3Sn2S2 lies between the 3D-Ising model and the Mean-filed model, indicating the presence of both long-range and short-range magnetic interactions in the system. Additionally, we found that HA-Co3Sn2S2 exhibits an enhanced saturation magnetization (Ms) and magnetic refrigeration capacity, both showing anisotropic dependence, compared to the pristine Co3Sn2S2. Our work develops hydrogen annealing to modulate electron coupling and magnetic domains, paving the way for further studies of anisotropic magnetic behavior and applications in magnetic refrigeration.

Cooperative effects in dense cold atomic gases including magnetic dipole interactions

We theoretically investigate cooperative effects in cold atomic gases exhibiting both electric and magnetic dipole-dipole interactions, such as occurs, for example, in clouds of dysprosium atoms. After introducing a general framework capturing both the quantum degenerate and nondenegerate cases, we focus on the emergence of tailorable spin models in the quantum nondegenerate regime. In the low-excitation limit, we provide analytical and numerical results detailing the effect of magnetic interactions on the directionality of scattered light and characterize sub and superradiant effects. Published by the American Physical Society 2024

Spin-orbit coupled Hubbard skyrmions

When the material phases exhibit topological quantum numbers, they host defects protected by the nontrivial topology. Magnetic skyrmions are such “quantized” objects, and although many of them are metals, they had been most likely treated in theories as purely classical spin states. Here, we show that the electrons described by the Hubbard model with strong spin-orbit couplings can exhibit various nano- or flake-size skyrmions in their ground state. Importantly, the conducting electrons forming Fermi pockets themselves carry textured magnetic moments in both real and momentum space and on top of that possess Chern numbers in their energy bands. This quantum and conducting skyrmion is related to small skyrmions observed in atomic-layered compounds. We clarify how the effective magnetic interactions and magnetic anisotropies are tied to the spin-orbit coupling, and how they influence the stability of skyrmions beyond the phenomenology. Published by the American Physical Society 2024

Magnetic field impact on ferronanofluid laminar flow

A comprehensive understanding of the magnetic field interaction with the flow of ferronanofluids is essential to determine the heat transfer effect and the potential for use in industrial applications. The purpose of this work is to determine the effects of magnetic field orientation and intensity, as well as inertia forces, on heat transfer in the laminar flow of a ferronanofluid. The experiment involved the use of five permanent magnets positioned both below and above the flowing magnetite-based ferronanofluid. The analysis of the effect on heat transfer is carried out using the similarity numbers, Reynolds number (ratio of inertia and viscous forces), magnetic number (ratio of magnetic and inertia forces) and product of the two (ratio of magnetic and viscous forces).The findings indicate that the orientation of the magnetic field relative to temperature gradient-induced secondary motions plays a crucial role in either enhancing or inhibiting heat transfer. The magnet positioned below the flow leads to improved heat transfer, while placement above hinders it. To determine the magnetic field effect on heat transfer, the ratio of magnetic to viscous force introduced as MnRe is used. Taking the 5 % Nusselt number change as the threshold, the critical value for the orientation of magnet above the tube is MnRe = 24,000, while for the configuration with the magnet below, MnRe = 32,000 for Re = 109 and MnRe = 88,000 for Re = 150 and 163. The magnetic field effect is local and diminishes as the fluid flows, ultimately causing the heat transfer parameters to revert to their reference state. However, an increase in the ratio of inertia and viscosity forces enables the magnetic field interaction effect to propagate over a longer distance.

Pressure-Tuned Intrinsic Anomalous Hall Conductivity in Kagome Magnets RV6Sn6 (R = Gd, Tb)

Exploration of exotic phenomena in magnetic topological systems is at the frontier of condensed matter physics, holding a significant promise for applications in topological spintronics. However, complex magnetic structures carrying nontrivial topological properties hinder its progresses. Here, we investigate the pressure effect on the novel topological kagome magnets GdV6Sn6 and TbV6Sn6 to dig out the interplay between magnetic Gd/Tb layers and nonmagnetic V-based kagome sublattice. The pressure-tuned magnetic transition temperature T m in both the compounds exhibit a turning point at the critical pressure P c, accompanied with a sign reversal in anomalous Hall effect (AHE). The separation of intrinsic and extrinsic contributions using the Tian–Ye–Jin scaling model suggests that the intrinsic mechanism originating from the electronic Berry curvature holds the priority in the competition with extrinsic mechanism in AHE. The above-mentioned findings can be attributed to the combined effect of pressure-tuned band topology and magnetic interaction in segregated layers. Our results provide a practical route to design and manipulate the intrinsic AHE in magnetic topological materials.

Collisions and dynamics of particles with magnetic dipole moment and electric charge near magnetized rotating Kerr black holes

Analysis of test magnetized and charged particles around black holes immersed in external magnetic fields may help to explain the observed astrophysical phenomena related to black holes, such as the acceleration of particles up to high energies. In this sense, we studied the circular motion of test-charged particles with magnetic dipole orbiting around magnetized rotating Kerr black holes. First, we derive the effective potential for the circular motion of such particles, including interactions between the external magnetic field and the electric charge, and the magnetic interaction between the magnetic dipole. In addition, we analyze the angular momentum and energy of particles corresponding to circular orbits. The effects of magnetic interaction and coupling parameters on the position of innermost stable circular orbits (ISCOs), the energy and angular momentum of the particles at ISCO, and the energy efficiency from the Novikov-Thorne accretion disc have been investigated. We also find cases of degeneracy between magnetic dipole interaction and magnetic coupling parameters, giving the same ISCO radius. Finally, we studied various cases of collisions of neutral, magnetized, and electrically charged particles near rotating Kerr black holes in the presence of external magnetic fields. The critical angular momentum of spinning charged particles is found in which the particles can collide. We also analyze the effects of both magnetic interactions on the center-of-mass energy of the colliding particles.

Coexisting magnetic interaction, critical behavior and magnetocaloric effect at high temperature in Fe50Ni50 soft ferromagnetic alloy

Herein, we report the structural, magnetic and magnetocaloric properties of Fe50Ni50 alloy prepared through the planetary ball-mill. Rietveld analysis of the X-ray profiles confirmed the cubic crystallographic phase with the Fm-3 m space group. The magnetic characterization demonstrates that Fe50Ni50 alloy exhibits the coexistence of magnetic interaction within the ferromagnetic phase with Curie temperature 762 K. The Arrott plot results confirmed the second-order nature of the alloy. Critical exponents were also determined using the modified Arrott plot, Kouvel-Fisher plot and critical isotherm analysis. Obtained results indicated coexisting magnetic behavior, i.e., long-range ferromagnetism and inhomogeneous magnetic state. This alloy also noted a significant magnetocaloric parameters, i.e., magnetic entropy change (−ΔSM ∼ 2.3 J/kg-K) and relative cooling power (RCP ∼ 230 J/kg) at 30 kOe applied field. Both parameters followed power law dependence of magnetic field, and the exponent value supports the ferromagnetic nature along with the coexisting magnetic state. By normalizing the ΔSM curve with rescaled temperature, a universal master curve is also constructed for this alloy, reiterating the second-order nature of the magnetic transition.

Magnetic interaction effects in Fe3O4@CoFe2O4 core/shell nanoparticles

The magnetic properties of core/shell nanoparticles (NPs) depend on the various parameters, including the magnetic interactions, but these effects have not been well studied. Here, we systematically investigated the structure and magnetic properties of Fe3O4@CoFe2O4 core/shell NPs. X-ray diffraction (XRD), scanning electron microscopy (SEM), and scanning transmission electron microscopy (STEM) confirmed the formation of Fe3O4@CoFe2O4 core/shell NPs. Magnetic measurements of the core/shell NPs were performed on both dried-pressed and well-dispersed in wax states. For the dried-pressed NPs, we found that the temperature-dependent magnetization curves of core/shell NPs vary significantly compared to that of core NPs due to spin interactions at the core/shell interface. Besides, the hysteresis loops of the core/shell NPs at 10 K are constricted, probably due to the interparticle interaction. For the core/shell NPs dispersed in wax, the hysteresis loops were smooth at all temperatures between 10 and 300 K due to the attenuated interparticle interaction. The high HC of 9.14 kOe (at 10 K) of the dispersed NPs is twice larger than that of the dried-pressed powders (4.23 kOe). Our study provides new insights into the effects of shell thickness and interparticle interaction on the magnetic properties of Fe3O4@CoFe2O4 core/shell NPs.

Dorsal Striatal Functional Connectivity and Repetitive Behavior Dimensions in Children and Youths With Neurodevelopmental Disorders

BackgroundImpairing repetitive behaviors are one of the core diagnostic symptoms in autism spectrum disorder and obsessive-compulsive disorder, but they also manifest in attention-deficit/hyperactivity disorder. Although the dorsal striatal circuit has been implicated in repetitive behaviors, extensive heterogeneity in and cross-diagnostic manifestations of these behaviors have suggested phenotypic and likely neurobiological heterogeneity across neurodevelopmental disorders (NDDs). MethodsIntrinsic dorsal striatal functional connectivity was examined in 3 NDDs (autism spectrum disorder, obsessive-compulsive disorder, and attention-deficit/hyperactivity disorder) and typically developing control participants in a large single-cohort sample (N = 412). To learn how diagnostic labels and overlapping behaviors manifest in dorsal striatal functional connectivity measured with functional magnetic resonance imaging, the main and interaction effects of diagnosis and behavior were examined in 8 models (2 seed functional connectivity [caudate and putamen] × 4 sub-behavioral domains [sameness/ritualistic, self-injury, stereotypy, and compulsions]). ResultsThe obsessive-compulsive disorder group demonstrated distinctive patterns in visual and visuomotor coordination regions compared with the other diagnostic groups. Lower-order repetitive behaviors (self-injury and stereotypy) manifesting across all participants were implicated in regions involved in motor and cognitive control, although the findings did not survive effects of multiple comparisons, suggesting heterogeneity in these behavioral domains. An interaction between self-injurious behavior and an attention-deficit/hyperactivity disorder diagnosis were observed on caudate-cerebellum functional connectivity. ConclusionsThese findings confirmed high heterogeneity and overlapping behavioral manifestations in NDDs and their complex underlying neural mechanisms. A call for diagnosis-free symptom measures that can capture not only observable symptoms and severity across NDDs but also the underlying functions and motivations of such behaviors across diagnoses is needed.

Charged particles motion and quasiperiodic oscillation in Simpson–Visser spacetime in the presence of external magnetic fields

The present work is devoted to the study of the dynamics of charged particles around Simpson–Visser black holes (with the length parameter lle 2) and wormholes (l>2) immersed in an external asymptotically uniform magnetic field. To do this, first, we solve the Maxwell equation for 4-potentials of the electromagnetic field and show that the difference between the numerical solution and Wald’s solution is small enough to neglect it, which may allow us to use the solution obtained by Wald. We also study fundamental frequencies of in the vertical and radial oscillations of charged particles around circular stable orbits around the magnetized black hole. The effects of the magnetic interaction and length parameters on the fundamental frequencies. We investigate the quasiperiodic oscillations (QPOs) around the black hole in relativistic precession and epicyclic resonance models. It is also shown that the combined effects of magnetic interaction for negatively charged particles and length parameters can mimic the spacetime effects of the Schwarzschild black hole compensating for their effects, as well as the spin of rotating Kerr black holes. The distance between an orbit where a QPO is generated with the ratio of upper and lower frequencies 3: 2 and innermost stable circular orbits is also studied. It is found that the QPO orbits are very close to ISCO in the RP model at l<2. This implies that the obtained result helps to determine the ISCO around black holes. We also study the applications of observed QPOs around stellar-mass black holes in microquasars and supermassive black holes.

Dynamic susceptibility of ferrogels. Effect of interparticle interaction

We present results of theoretical study of effect of magnetic interparticle interaction on kinetics of remagnetization of magnetic gels with immobilized single-domain particle. Magnetic anisotropy of the particle is supposed very strong. The particles axes of easy magnetization are randomly oriented. Our results demonstrate that effect of interparticle interaction on kinetics of the particles remagnetization is determined by the strength of the applied field: this interaction slows down the composite remagnetization when applied magnetic field is weak and speeds up it when the field is high.

How particle interactions and clustering affect the dynamic magnetic susceptibility of ferrofluids

The effects of magnetic interparticle interactions on the frequency-dependent, dynamic magnetic susceptibility of ferrofluids are summarised with reference to recent theoretical and simulation studies. With weak to moderate interactions, the dynamic magnetic susceptibility qualitatively resembles the classic Debye prediction, but with features shifted to lower frequencies as the particle concentration and/or interaction strength are increased. This shows that the mutual spatial and orientational correlations arising from the interactions lead to slower collective motions. With strong interactions, and at low concentrations, the particles form chain-like and ring-like clusters, and this leads to distinct collective and intracluster motions being apparent in the dynamic magnetic susceptibility. The initial formation of chains increases the static susceptibility, while the subsequent formation of rings decreases it.

Nanocomposite Didymium-Fe-B/Alnico magnetic alloys with core shell structure and improved magnetic properties

NdFeB-based permanent magnets have the highest maximum energy products, but their low Curie temperatures limit their applications. Alnico permanent magnets have relatively modest magnetic energy products, but have very high Curie and working temperatures. In this manuscript, we report new NdPrFeB/Alnico nanocomposite magnetic materials with enhanced Curie temperatures and maximum magnetic energy products. A special microstructure with the Alnico phase dispersed within the NdPrFeB phase results in excellent magnetic properties. The Curie temperature of the composite alloys is enhanced from 570 K to 643 K by adding 25% low-grade Alnico. The enhanced Curie temperature which results from the cobalt and nickel replacement for iron in the 2:14:1 phase, and the molecular field penetration improves the temperature stability of the magnets. The beneficial heterogeneous distribution of the constituent phases and elements was confirmed by transmission electron microscopy and electron diffraction spectroscopy analyses. The maximum energy product is enhanced from 110 kJ/m3 to 133 kJ/m3. Magnetostatic interaction and exchange interaction in the alloys were studied by means of Henkel plots and minor hysteresis loop measurements. Despite the high content of the Alnico phase with relatively large special dimensions, there were no kinks in the demagnetization curves either at 300 K or 400 K. Furthermore, no kink was noted at low and high applied fields in the demagnetization-magnetization process which shows the effective magnetic interactions. This work would elucidate the development of nanocomposite magnetic material with high energy product without the use of heavy rare earths and with the economical use of Nd and Pr.

The Effect of Resveratrol and Static Magnetic Field Interactions on the Oxidation–Reduction Parameters of Melanoma Malignant Cells

Background: Scientific research has confirmed the biological activity of resveratrol, which includes its antioxidant, anti-inflammatory, cardioprotective and anticancer properties. There is no known interaction between a static magnetic field and resveratrol that can modulate resveratrol’s effect on cells. Thus, the main aim of our research was to assess the effect of the co-exposure to resveratrol and a static magnetic field on the oxidation–reduction homeostasis of C32 and Colo829 melanoma cells. Methods: The studies consisted of determining the activity of the antioxidant enzymes that constitute the body’s first line of defense—SOD, GPx and CAT—and determining the lipid peroxidation product—MDA—and the value of the total antioxidant status of melanoma cells. Results and conclusions: Resveratrol was shown to exhibit anticancer properties, possibly through the ferroptosis of melanoma cells. A static magnetic field was also found to abolish the anticancer properties of resveratrol and to have a protective effect against melanoma cells by restoring the redox balance in the cells.