Magnetic Structure Research Articles

Novel Designs of Magnetic Coupled Structure With 360° Rotation Misalignment Tolerance for AUVs’ Wireless Charging System

Novel Designs of Magnetic Coupled Structure With 360° Rotation Misalignment Tolerance for AUVs’ Wireless Charging System

Effects of Lu-doping on the magnetic behaviour and ordering of (Ho[formula omitted]Lu[formula omitted])2Fe2Si2C

We have investigated the effects of Lu substitution on the magnetic behaviour and ordering of (Ho1−xLux)2Fe2Si2C (x = 0.32 and 0.46) by high-resolution neutron powder diffraction, magnetisation and specific heat over the temperature range 2 to 300 K. Our study has establised that the antiferromagnetic (AFM) state is weakened upon Lu substitution and that the Néel temperature TN shifts towards lower temperature with increasing Lu content. The replacement of the magnetic Ho3+ ion by the non-magnetic Lu3+ ion of smaller atomic radius, leads to a modification of the crystal field levels, as indicated by the specific heat measurements. Neutron diffraction data analysis reveals that the magnetic structure of undoped Ho2Fe2Si2C, which exhibits a commensurate, antiferromagnetic ordering of the Ho sublattice along the b-axis with a propagation vector k = [0, 0, 12], is maintained in the Lu-doped (Ho1−xLux)2Fe2Si2C compounds.

Multiwavelength Campaign Observations of a Young Solar-type Star, EK Draconis. II. Understanding Prominence Eruption through Data-driven Modeling and Observed Magnetic Environment

EK Draconis, a nearby young solar-type star (G1.5V, 50–120 Myr), is known as one of the best proxies for inferring the environmental conditions of the young Sun. The star frequently produces superflares, and Paper I presented the first evidence of an associated gigantic prominence eruption observed as a blueshifted Hα Balmer line emission. In this paper, we present the results of the dynamical modeling of the stellar eruption and examine its relationship to the surface starspots and large-scale magnetic fields observed concurrently with the event. By performing a 1D freefall dynamical model and a 1D hydrodynamic simulation of the flow along the expanding magnetic loop, we found that the prominence eruption likely occurred near the stellar limb (12 −5+5 -16 −7+7 degrees from the limb) and was ejected at an angle of 15−5+6 -24 −6+6 degrees relative to the line of sight, and the magnetic structures can expand into a coronal mass ejection. The observed prominence displayed a terminal velocity of ∼0 km s−1 prior to disappearance, complicating the interpretation of its dynamics in Paper I. The models in this paper suggest that prominence’s Hα intensity diminishes at around or before its expected maximum height, explaining the puzzling time evolution in observations. The Transiting Exoplanet Survey Satellite light curve modeling and (Zeeman) Doppler Imaging revealed large midlatitude spots with polarity inversion lines and one polar spot with dominant single polarity, all near the stellar limb during the eruption. This suggests that midlatitude spots could be the source of the gigantic prominence we reported in Paper I. These results provide valuable insights into the dynamic processes that likely influenced the environments of early Earth, Mars, Venus, and young exoplanets.

Multimodal reconstruction of TbCo thin-film structure with Bayesian analysis of polarized neutron reflectivity

Bayesian analysis has been applied to polarized neutron reflectivity data. Reflectivity data from a magnetic TbCo thin-film structure were studied using a combination of a Monte Carlo Markov-chain algorithm, likelihood estimation and error modeling. By utilizing Bayesian analysis, it was possible to investigate the uniqueness of the solution beyond reconstructing the magnetic and structure parameters. The expedience of this approach has been demonstrated, as several probable reconstructions were found (the multimodality case) concerning the isotopic composition of the surface cover layer. Such multimodal reconstruction emphasizes the importance of rigorous data analysis instead of the direct data fitting approach, especially in the case of poor statistically conditioned data typical for neutron reflectivity experiments. This article presents details of the analysis and a discussion of multimodality.

Thermodynamics and entropic inference of nanoscale magnetic structures in Gd

A bulk gadolinium (Gd) single crystal exhibits virtually zero remnant magnetization, a common trait among soft uniaxial ferromagnets. This characteristic is reflected in our magnetometry data showing virtually hysteresis free isothermal magnetization loops with large saturation magnetization. The absence of hysteresis allows to model the measured easy axis magnetization as a function of temperature and applied magnetic field, rather than a relation, which permits the application of Maxwell relations from equilibrium thermodynamics. Demagnetization effects broaden the isothermal first-order transition from negative to positive magnetization. By analyzing magnetization data within the coexistence regime, we deduce the isothermal entropy change and the field-induced heat capacity change. Comparing the numerically inferred heat capacity with relaxation calorimetric data confirms the applicability of the Maxwell relation. Analysis of the entropy in the mixed phase region suggests the presence of hitherto unresolved nanoscale magnetic structures in the demagnetized state of Gd. To support this prediction, Monte Carlo simulations of a 3D Ising model with dipolar interactions are performed. Analyzing the cluster size statistics and magnetization from the model provides strong qualitative support of our analytic approach.

Noncoplanar magnetic structures in Mn4N epitaxial films evaluated by alternating magnetic force microscopy

Abstract Noncoplanar magnetic structures in the Mn4N epitaxial thin films grown on the 001-oriented MgO and SrTiO3 (STO) substrates were studied, based on the measurements of topological Hall effect (THE) and the observation of magnetic domain nucleation. The typical nucleation diameter of domain was determined using an alternating magnetic force microscope, which proved advantageous for the visualization of the domain with an out-of-plane magnetic component. The nucleation diameter of the domains on the MgO substrate were ∼150 nm for the thickness of 30 nm and ∼110 nm for 10 nm, while ∼130 nm for 30 nm on the STO substrate. The value of THE was one or two orders of magnitude larger than that estimated based on the nucleation diameter, indicating that the existence of a noncoplanar magnetic structure is the primary factor contributing to the THE in the Mn4N films, comparing to the effect from domain nucleation. The noncoplanar magnetic structure was more pronounced with decreasing thickness and substrate-induced strain.

Kernel polynomial method for linear spin wave theory

Calculating dynamical spin correlations is essential for matching model magnetic exchange Hamiltonians to momentum-resolved spectroscopic measurements. A major numerical bottleneck is the diagonalization of the dynamical matrix, especially in systems with large magnetic unit cells, such as those with incommensurate magnetic structures or quenched disorder. In this paper, we demonstrate an efficient scheme based on the kernel polynomial method for calculating dynamical correlations of relevance to inelastic neutron scattering experiments. This method reduces the scaling of numerical cost from cubic to linear in the magnetic unit cell size.

3D Topological Toron‐Like Domains in Magnetic Nanoparticles: A Micromagnetic Simulation

Abstract3D topological textures have attracted significant attention from researchers due to their distinctive spatial arrangements and intriguing physical properties. However, investigating their topological domain structures at the submicron scale (<1000 nm) proves exceedingly elusive and under‐explored. Here, the size‐dependent behaviors of non‐uniform magnetic domain structures within submicron‐sized FeNi magnetic nanoparticles by micromagnetic simulations are systematically explored. Notably, the existence of magnetic toron‐like structures at the submicron scale and discuss their spatial arrangement and topological properties are identified. Furthermore, critical transition sizes are calculated under various aspect ratios, and the domain structure phase diagram based on nanoparticle size and aspect ratio is constructed. Through visualizations of domain flipping processes and dynamic energy changes, the stable existence of toron‐like magnetic configuration resulting from the competition among demagnetization energy, magnetic anisotropy energy, and magnetic exchange energy are unveiled. Finally, the utilization of core‐shell structures to achieve the stable existence of 3D topological textures are proposed. This work provides important theoretical insights for understanding and designing multi‐domain structures of FeNi nanoparticles at the submicron scale, as well as for constructing topological textures.

Interplanetary Rotation of 2021 December 4 Coronal Mass Ejection on Its Journey to Mars

The magnetic orientation of coronal mass ejections (CMEs) is of great importance to understand their space weather effects. Although plenty of evidence suggests that CMEs can undergo significant rotation during the early phases of evolution in the solar corona, there are few reports that CMEs rotate in the interplanetary space. In this work, we use multispacecraft observations and a numerical simulation starting from the lower corona close to the solar surface to understand the CME event on 2021 December 4, with an emphatic investigation of its rotation. This event is observed as a partial halo CME from the back side of the Sun by coronagraphs and reaches the BepiColombo spacecraft and the Mars Atmosphere and Volatile EvolutioN/Tianwen-1 as a magnetic flux-rope-like structure. The simulation discloses that in the solar corona the CME is approximately a translational motion, while the interplanetary propagation process evidences a gradual change of axis orientation of the CME’s flux-rope-like structure. It is also found that the downside and the right flank of the CME moves with the fast solar wind, and the upside does in the slow-speed stream. The different parts of the CME with different speeds generate the nonidentical displacements of its magnetic structure, resulting in the rotation of the CME in the interplanetary space. Furthermore, at the right flank of the CME exists a corotating interaction region, which makes the orientation of the CME alter and also deviates from its route due to the CME. These results provide new insight into interpreting CMEs’ dynamics and structures during their traveling through the heliosphere.

Zero Thermal Expansion via the Unconventional Sublattice‐Magnetovolume Effect in Rare‐Earth Ferrimagnets

AbstractZero thermal expansion (ZTE) alloys are critically needed in sophisticated modern industries, including telescope manufacturing, satellite technology, and semiconductor production, owing to their exceptional dimensional stability. In this study, high‐performance ZTE with a negligible coefficient of thermal expansion αv = 2.7 ppm K−1 over a broad temperature range of 10–220 K is discovered in ErCo2.8Fe0.2 magnet. Owing to an unconventional sublattice‐magnetovolume effect in the Er atoms, the negative thermal expansion in Fe‐substituted ErCo3−xFex magnets can be easily tuned to high‐performance ZTE. Moreover, the direct visualization of the magnetic transition in the predominant magnetization from the Er to the Co/Fe sublattices, as observed by the Lorentz transmission electron microscopy, further elucidates the manipulation mechanism behind the high‐performance ZTE. This study reports a convenient and effective strategy to optimize the thermal expansion characteristics of Er‐Co‐Fe magnets, which can guide future research that broadens the application scope of magnetic materials by leveraging the significant correlation between the magnetic properties and crystal structure of such systems.

Pseudo-easy-axis anisotropy in antiferromagnetic S=1 diamond-lattice systems

We investigate the magnetic properties of S=1 antiferromagnetic diamond-lattice, NiX2(pyrimidine)2 (X=Cl, Br), hosting a single-ion anisotropy (SIA) orientation which alternates between neighboring sites. Through neutron diffraction measurements of the X=Cl compound, the ordered state spins are found to align collinearly along a pseduo-easy axis, a unique direction created by the intersection of two easy planes. Similarities in the magnetization, exhibiting spin-flop transitions, and the magnetic susceptibility in the two compounds imply that the same magnetic structure and a pseduo-easy axis is also present for X=Br. We estimate the Hamiltonian parameters by combining analytical calculations and Monte Carlo (MC) simulations of the spin-flop and saturation field. The MC simulations also reveal that the spin-flop transition occurs when the applied field is parallel to the pseduo-easy axis. Contrary to conventional easy-axis systems, there exist field directions perpendicular to the pseduo-easy axis for which the magnetic saturation is approached asymptotically and no symmetry-breaking phase transition is observed at finite fields. Published by the American Physical Society 2024

The Relationship Between Spin Crossover (SCO) Behaviors, Cation and Ligand Motions, and Intermolecular Interactions in a Series of Anionic SCO Fe(III) Complexes with Halogen-Substituted Azobisphenolate Ligands.

To investigate the halogen substitution effect on the anionic spin crossover (SCO) complexes, azobisphenolate ligands with 5,5'-dihalogen substituents from fluorine to iodine were synthesized, and their anionic FeIII complexes 1F, 1Cl, 1Br, and 1I were isolated. The temperature dependence of magnetic susceptibility and crystal structure revealed that 1F, 1Cl, and 1Br are all isostructural and exhibit SCO with the rotational motion of the cation and ligands, whereas 1I shows incomplete SCO. Note that 1Cl and 1Br showed irreversible and reversible cooperative SCO transitions, respectively. Short intermolecular contacts between the FeIII complex anions were found despite Coulomb repulsions for all the complexes. The topological analysis of the electron density distributions revealed the existence of X···X halogen bonds, C-H···X, C-H···N, and C-H···O hydrogen bonds, and C-H···π interactions are evident. The dimensionality of intermolecular interactions is suggested to be responsible for the cooperative SCO transitions in 1Cl and 1Br, whereas the disorder due to the freezing of ligand rotations in 1Cl is revealed to inhibit the SCO cooperativity.

Controlled Separation of Skyrmions and Antiskyrmions by Kitaev Interaction.

As topological quasi-particles in magnetic materials, skyrmions and antiskyrmions show potential in spintronics for information storage and computing. However, effectively controlling and separating these entities remain significantly challenging. Here, we demonstrate that anisotropic Kitaev exchange can distinctly influence the static and dynamic behaviors for skyrmions and antiskyrmions, thus aiding their manipulation and separation. Employing the monolayer frustrated magnet NiBr2 as a model system, we construct a magnetic field-strain phase diagram to explore the strain-controlled stability of these topological structures. The introduction of the Kitaev term breaks the energy degeneracy among magnetic structures with various helicities, leading to a translation-rotation mode transition with an increase in current. Importantly, due to their different rotational symmetries, the skyrmion and antiskyrmion show distinct critical behaviors and rotational dynamics, which are governed by the Kitaev parameters. These phenomena enable the design of two proof-of-concept spintronics devices, i.e., a skyrmion separator and a non-gate logic unit.

Design of magneto-inductive waveguide in 2-d magnetic metamaterial structure for wireless power transfer and near-field communications

<p>Recently, significant research has been conducted on magnetic metamaterials that exhibit negative permeability and operate within the GHz and MHz frequency ranges. These metamaterial structures can be utilized to improve the efficiency of near-field wireless power transfer systems, subterranean communication, and position sensors. However, in most cases, they are only designed to work for a single application. This study focuses on examining the transmission of magneto-inductive waves in magnetic metamaterial structures with ordered arrangements. This structure can be used simultaneously for wireless power transfer and near-field communications. The unit cell is formed by a spiral with five turns that is implanted on a FR-4 substrate. An external capacitor was used to regulate the resonant frequency of the magnetic metamaterial unit cell. The properties of magneto-inductive waves, including reflection, transmission response, and field distribution on the waveguide, have been extensively computed and simulated. The obtained results indicate that both 1-dimensional and 2-dimensional magnetic metamaterial configurations possess the ability to conduct electromagnetic waves and propagate magnetic field energy at a frequency of 13.56 MHz. The straight and cross path configurations were also investigated to identify the optimal configuration on the 2-dimensional metamaterial slab.</p>

First-principles study and mesoscopic modeling of two-dimensional spin and orbital fluctuations in FeSe

We calculated the structural, electronic, and magnetic properties of FeSe within density-functional theory at the generalized gradient approximation level. First, we studied how the bandwidth of the d-bands at the Fermi energy is renormalized by adding simple corrections: Hubbard U, Hund's J, and by introducing long-range magnetic orders. We found that introducing either a striped or a staggered dimer antiferromagnetic order brings the bandwidths—which are starkly overestimated at the generalized gradient approximation level—closer to those experimentally observed. Second, for the ferromagnetic, the striped, checkerboard, and staggered dimer antiferromagnetic order, we investigate the change in magnetic formation energy with local magnetic moment of Fe at a pressure up to 6 GPa. The bilinear and biquadratic exchange energies are derived from the Heisenberg model and noncollinear first-principles calculations, respectively. We found a nontrivial behavior of the spin-exchange parameters on the magnetization, and we put forward a field-theory model that rationalizes these results in terms of two-dimensional spin and orbital fluctuations. The character of these fluctuations can be either that of a standard density wave or a topological vortex. Topological vortices can result in mesoscopic magnetization structures. Published by the American Physical Society 2024

Distinct topological Hall responses in CeCu2-type EuZn2 and EuCd2 films

Rare-earth intermetallic compounds crystallized in AlB2-type and its low-symmetry derivative CeCu2-type structures potentially host diverse frustrated magnetic structures and rich magnetotransport phenomena. We report the film growth of CeCu2-type EuZn2 by molecular beam epitaxy and the observation of topological Hall responses highly contrastive to isostructural EuCd2. While their magnetization curves are rather similar, the topological Hall effect observed in EuZn2 is simpler, with the only one component enhanced at the magnetic transition field. EuZn2 may be a unique system for studying the magnetic domain boundary effect on topological Hall responses among the CeCu2-type rare-earth intermetallic compounds.

Engineering Two-Dimensional Magnetic Heterostructures: A Theoretical Perspective.

Two-dimensional (2D) magnetic materials have attracted great attention due to their promise for applications in future high-speed, low-energy quantum computing and memory devices. By integrating 2D magnetic materials with other magnetic or nonmagnetic materials to form heterostructures, the synergistic effects of interlayer orbital hybridization, spin-orbit coupling, and symmetry breaking can surpass the performance of single-layer materials and lead to novel physical phenomena. This review provides a comprehensive theoretical analysis of engineering 2D magnetic heterostructures, emphasizing the fundamental physics of interlayer interactions and the resulting enhancements and novel properties. It reviews the mechanisms and progress in tuning the magnetic ordering, enhancing the Curie temperature (Tc) and modulating properties such as topological magnetic structures, spin polarization, electronic band topology, valley polarization, and magnetoelectric coupling through the construction of 2D magnetic heterostructures. Additionally, this review discusses the current challenges faced by 2D magnetic heterostructures, aiming to guide the future design of higher-performance magnetic heterostructures.

Geophysical Methods Applied to the Mineralization Discovery of Rare-Earth Elements at the Fazenda Buriti Alkaline Complex, Goiás Alkaline Province, Brazil

In this case study, exploratory techniques were applied for the selection of potential targets for rare-earth elements (REEs) in the Fazenda Buriti Mafic–Ultramafic Complex, part of the Goiás Alkaline Province. The results of the processing and interpretation of aeromagnetic and radiometric data associated with the direct measurements of magnetic susceptibility and radiometry in rock samples collected in the study area allowed for the characterization and delimitation of the geological units. The application of Boolean logic in the radiometric data of uranium (U), thorium (Th), and the U/Th ratio allowed for the generation of a prospective map with the delimitation of two exploration targets. A 100 m deep exploratory drill hole was drilled at the main target, intercepting REE mineralization and validating the developed prospective technique. The results contributed to the detailing of a 1:25,000 scale geological map and the interpretation of shallow and deep magnetic structures. Petrophysical data allowed for the estimation of the magnetite content in the main units of the study area. The delimitation of targets with the applied method proved to be efficient after positive geochemical results for REE from the drilled rocks. The total sum of ∑REEs reached 19,629 ppm in the superficial part of the hole and 3,560 ppm in the fresh rock. Mineralogical results in two follow-up drill core samples indicated that monazite was the main REE mineral. Total REE ranged from 34,746 ppm in HG1 to 30,017 ppm in HG2, with LREEs in its majority. The bulk and clay XRD analyses indicated that monazite consisted of 5.7% (HG1) and 5.1% (HG2). The mineral abundance from the TIMA-X analysis indicated 4.2% (HG1) and 4.4% (HG2) in monazite content.

Discovery of Intrinsic Ferromagnetism Induced by Memory Effects in Low-Dimensional System

The impact of dynamic processes on equilibrium properties is a fundamental issue in condensed matter physics. This study investigates the intrinsic ferromagnetism generated by memory effects in the low-dimensional continuous symmetry Landau–Ginzburg model, demonstrating how memory effects can suppress fluctuations and stabilize long-range magnetic order. Our results provide compelling evidence that tuning dynamical processes can significantly alter the behavior of systems in equilibrium. We quantitatively evaluate how the emergence of the ferromagnetic phase depends on memory effects and confirm the presence of ferromagnetism through simulations of hysteresis loops, spontaneous magnetization, and magnetic domain structures in the 1D continuous symmetry Landau–Ginzburg model. This research offers both theoretical and numerical insights for identifying new phases of matter by dynamically modifying equilibrium properties.

A Special Kind of Interplanetary Coronal Mass Ejections

Abstract It is generally believed that Coronal mass ejections (CMEs) have magnetic flux rope structures because of their helical shapes. However, only about 30-40% of interplanetary CMEs (ICMEs) have a local magnetic flux rope structure. The usually explanations are that the spacecraft only crossed the flank of the ropes and failed to detect the complete magnetic flux rope structure, or some processes destruct these magnetic flux rope structure. Several studies suggest that some ICMEs inherently possess disordered magnetic fields and consequently exhibit no magnetic flux-rope structures. We introduce a special kind of ICMEs. They have low magnetic field magnitude and stable magnetic field direction, relatively fast expansion speed, lower proton temperature and density. Their all three measured magnetic field components are relatively stable. We want to know whether these ICMEs also have magnetic flux rope structures or not. We identified 20 special ICMEs and analyzed their evolution based on their observed characteristics. We took a special ICME as example, which had apparent rope configuration at 1 AU but evolved to a special ICME at 5.4 AU, to illustrated that this kind of ICMEs may come from magnetic clouds (MCs) whose rope structure had been being stretched due to expansion. We inferred that the missing of obvious flux rope structure may be due to the expansion of MCs, not the flank crossing effect. However, more than 50% of the events were associated with dominant x-component of the magnetic filed, which indicates a leg crossing. Therefore, the detection of part of these special ICMEs may also be results of leg crossing effect.