Formation Of Magnetic Domains Research Articles

Procedure to reveal the mechanism of pattern formation process by topological data analysis

Topological data analysis (TDA) is a versatile tool that can be used to extract scientific knowledge from complex pattern formation processes. However, the physics correspondence between the features obtained from TDA and pattern dynamics does not agree one-to-one, and the physical interpretation of the TDA features needs to be set appropriately according to the phenomenon to be analyzed. In this study, we propose an analytical procedure to physically interpret pattern dynamics through TDA and machine learning techniques. The proposed procedure was applied to the process of magnetic domain pattern formation to quantify non-trivial domain pattern classifications and reveal the nature of the underlying dynamics. On the basis of these findings, we also propose a candidate reduction model to understand the nature of magnetic domain formation.

Nanoengineered pure Fe in a citrate matrix (Fe–CIT) with significant and tunable magnetic properties

This work demonstrates the synthesis and characterization of Fe nanoparticles surrounded by a citrate (CIT) matrix prepared at various temperatures and concentrations of metal, capping agent and reducing agent at standard conditions. We study the effect of reactant ratio and reaction temperature on the magnetization of the produced nanoparticles and their crystal structure. We found that for optimal metal concentrations, magnetic saturation increases with increase in the concentration of capping and reducing agents but decreases as the temperature of the reaction increases. Synthesis conditions were tailored to reveal nucleation of particles with average sizes ranging from 24 to 105 nm and a spherical shape. The ultra-high saturation magnetization of 228 emu g-1obtained for samples prepared at a metal precursor concentration of 27.8 mol l-1was attributed to the formation of small magnetic domains. Energy band gap measurements revealed a band gap energy for the Fe nanoparticles in the CIT matrix which is associated with CIT concentration and/or possible formation of a few thin layers of iron oxide shell and does not have a significant effect on the magnetic properties of the samples. Herein, we demonstrate that the synthesis parameters are crucial for the nucleation of Fe-CIT nanoparticles tailoring their magnetizatic properties as well as their potential for different applications.

Nanostructural Modification of Fe2O3 Nanoparticles: Carbon Coating for Enhanced Magnetic Behavior

In this study, the enhancement of magnetic properties in Fe2O3 nanoparticles through nanostructural modification via carbon coating is investigated. Fe2O3 and carbon‐coated Fe2O3 nanoparticles are synthesized using the solvothermal method. Structural, morphological, optical, and magnetic properties are comprehensively analyzed. The results demonstrate a significant reduction in particle size upon carbon coating, effectively mitigating agglomeration. Furthermore, carbon‐coated nanoparticles exhibit substantial enhancement in coercivity, remanence, and saturation magnetization suggesting improved magnetic behavior in comparison to their uncoated counterparts. This enhancement is attributed to the prevention of spin misalignment at the nanoparticle surface by the carbon coating, as well as the formation of distinct magnetic domains due to the reduced particle size. The observed improvements underscore the effectiveness of carbon coating in tailoring the magnetic properties of Fe2O3 nanoparticles for applications in magnetic devices and biomedical systems, such as magnetic hyperthermia and drug delivery systems, where precise control over magnetic behavior is crucial.

Influence of Magnetic Sublattice Ordering on Skyrmion Bubble Stability in 2D Magnet Fe5GeTe2.

The realization of above room-temperature ferromagnetism in the two-dimensional (2D) magnet Fe5GeTe2 represents a major advance for the use of van der Waals (vdW) materials in practical spintronic applications. In particular, observations of magnetic skyrmions and related states within exfoliated flakes of this material provide a pathway to the fine-tuning of topological spin textures via 2D material heterostructure engineering. However, there are conflicting reports as to the nature of the magnetic structures in Fe5GeTe2. The matter is further complicated by the study of two types of Fe5GeTe2 crystals with markedly different structural and magnetic properties, distinguished by their specific fabrication procedure: whether they are slowly cooled or rapidly quenched from the growth temperature. In this work, we combine X-ray and electron microscopy to observe the formation of magnetic stripe domains, skyrmion-like type-I, and topologically trivial type-II bubbles, within exfoliated flakes of Fe5GeTe2. The results reveal the influence of the magnetic ordering of the Fe1 sublattice below 150 K, which dramatically alters the magnetocrystalline anisotropy and leads to a complex magnetic phase diagram and a sudden change of the stability of the magnetic textures. In addition, we highlight the significant differences in the magnetic structures intrinsic to slow-cooled and quenched Fe5GeTe2 flakes.

Multilayer Metamaterials with Ferromagnetic Domains Separated by Antiferromagnetic Domain Walls

AbstractMagnetic nano‐objects possess great potential for more efficient data processing, storage, and neuromorphic‐type applications. Using high perpendicular magnetic anisotropy synthetic antiferromagnets in the form of multilayer‐based metamaterials, the antiferromagnetic interlayer exchange energy is purposefully reduced below the out‐of‐plane demagnetization energy, which controls magnetic domain formation. In this unusual magnetic energy regime, as demonstrated via macroscopic magnetometry and microscopic Lorentz transmission electron microscopy, it becomes possible to stabilize nanometer‐scale stripe and bubble textures consisting of ferromagnetic out‐of‐plane domain cores separated by antiferromagnetic in‐plane Bloch‐type domain walls. This unique coexistence of mixed ferromagnetic/antiferromagnetic order on the nanometer scale opens so far unexplored perspectives in the architecture of magnetic domain landscapes as well as the design and functionality of individual magnetic textures, such as bubble domains with depth‐wise alternating chirality.

Obtaining extremely low coercivity of high Bs FeCoBSiCPCu nanocrystalline alloys through modulation of magnetic anisotropy

Longitudinal magnetic field annealing is utilized for modifying the magnetic anisotropy and enhancing the magnetic softness of Fe75Co8(B10Si3C3P1)1-x/17Cux (x = 0.5, 0.75, 1, 1.25) nanocrystalline alloys. All of the magnetic field-annealed nanocrystalline alloys with Cu content more than 0.5 at.% exhibit significantly improved soft-magnetic properties, including high saturation magnetic flux density up to 1.87 T, effective permeability of 13,000–16,000 under the condition of 1 A/m and 1 kHz, coercivity as low as 1.6 A/m, and core loss of 0.11–0.45 W/kg under the condition of 1.0 T and 50 Hz. The application of a magnetic field promotes the nucleation and inhibits the growth of grains, leading to an increase in the number density of nanocrystals and the crystalline volume fraction, and a reduction in the grain size. The magnetic field annealing reduces the effective magneto-crystalline anisotropy energy to 2–4 J/m3, and induces longitudinal magnetic anisotropy with anisotropy energy density of 400–900 J/m3 which shows dependence on the crystalline volume fraction. The field-induced magnetic anisotropy dominates over the random local magnetic anisotropies, and results in the formation of regular magnetic domains aligned longitudinally, pinning-free domain wall displacement, and thus enhanced soft-magnetic properties.

Single-step generation of 1D FeCo nanostructures

Magnetic one-dimensional structures are attractive nanomaterials due to the variety of potential applications they can provide. The fabrication of bimetallic 1D structures further expands the capabilities of such structures by tailoring the magnetic properties. Here, a single-step template-free method is presented for the fabrication of 1D FeCo alloy nanochains. In this approach, charged single-crystalline FeCo nanoparticles are first generated by the co-ablation of pure Fe and Co electrodes under a carrier gas at ambient pressures and attracted to a substrate using an electric field. When reaching the surface, the particles are self-assembled into parallel nanochains along the direction of an applied magnetic field. The approach allows for monitoring the self-assembly particle by particle as they are arranged into linear 1D chains with an average length controlled by the deposited particle concentration. Magnetometry measurements revealed that arranging nanoparticles into nanochains results in a 100% increase in the remanent magnetization, indicating significant shape anisotropy. Furthermore, by combining x-ray microscopy and micromagnetic simulations, we have studied the local magnetization configuration along the nanochains. Our findings show that variations in magnetocrystalline anisotropy along the structure play a crucial role in the formation of magnetic domains.

Coupling between magnetic and thermodynamic properties in RRh2Si2(R = Dy, Ho)

Single crystals of DyRh2Si2 and HoRh2Si2 were investigated by thermal expansion and magnetostriction. The different types of magnetic order can clearly be seen in these measurements, particularly the canting of the moments away from the crystallographic c direction below about 12 K and the spin flip for magnetic field applied along the c direction. For HoRh2Si2, an additional transition just below TN is analyzed by means of the Grüneisen ratio and is likely caused by a change in the magnetic structure. Our results nicely corroborate findings from other magnetic and thermodynamic measurements on these materials and provide further evidence suggesting the formation of magnetic domains. Published by the American Physical Society 2024

Efficient surrogate models for materials science simulations: Machine learning-based prediction of microstructure properties

Determining, understanding, and predicting the so-called structure–property relation is an important task in many scientific disciplines, such as chemistry, biology, meteorology, physics, engineering, and materials science. Structure refers to the spatial distribution of, e.g., substances, material, or matter in general, while property is a resulting characteristic that usually depends in a non-trivial way on spatial details of the structure. Traditionally, forward simulations models have been used for such tasks. Recently, several machine learning algorithms have been applied in these scientific fields to enhance and accelerate simulation models or as surrogate models. In this work, we develop and investigate the applications of six machine learning techniques based on two different datasets from the domain of materials science: data from a two-dimensional Ising model for predicting the formation of magnetic domains and data representing the evolution of dual-phase microstructures from the Cahn–Hilliard model. We analyze the accuracy and robustness of all models and elucidate the reasons for the differences in their performances. The impact of including domain knowledge through tailored features is studied, and general recommendations based on the availability and quality of training data are derived from this.

Incremental Analysis of Magnetic Domains in Multiple Types of Ferromagnetic CoFe Nanolayer Patterns

In this article, the results of incremental analysis on the thickness, aspect ratio, and crystallographic substrate orientation dependence of magnetic domain formation in CoFe nanolayer patterns (NPs) on GaAs (001) substrates by magnetic force microscopy are reported. All the 35 nm thick CoFe NPs show multiple magnetic domains under as‐deposition condition whereas the 13 nm thick CoFe NPs have a single magnetic domain in the case of the patterns with a relatively small size and high aspect ratio. Subsequently, the magnetic fields are applied in the direction parallel to the <110> and <1–10> directions of the substrates to analyze a magnetization switching behavior in the patterns. The results reveal that the magnetic fields required for magnetization switching markedly tend to increase, with decreasing the thickness of the patterns and increasing their aspect ratio. A general tendency is obtained, which a higher magnetic field is needed for a higher aspect ratio and a thinner thickness of the NPs. Even in the case of the patterns with an aspect ratio of unity and a thickness of 35 nm (but, a smaller size), a single magnetic domain is formed at a relatively high applied magnetic field of 1500 Gauss.

Influence of geometric structure on information entropy in spin-1 ferromagnetic dipolar Bose–Einstein condensates

In this study, we investigate the dynamics properties of spin-1 ferromagnetic Bose–Einstein condensates (BECs) with dipole–dipole interaction (DDI). Numerical results are obtained by solving the mean-field nonlocal Gross–Pitaevskii equation. We find that the population of the information entropy in momentum space [Formula: see text] is greatly affected by geometric structure and dipole strength. The prolate condensate is favorable to obtain bigger [Formula: see text] than oblate condensate. The density distribution verifies that the formation of magnetic domain is associated with the variation of [Formula: see text]. In addition, the kinetic energy displays that dramatical oscillation appears for strong dipolar interaction and it is larger in prolate condensate. Also, we use the order parameter to describe the order–disorder crossover. It is shown that BECs develop toward the disordered state with prolate condensate under strong DDI.

Effect of Underlayer Quality on Microstructure, Stoichiometry, and Magnetic Properties of Hexaferrite BaFe12O19 Grown on YSZ(111) by Pulsed Laser Deposition.

We have studied the effect of platinum underlayer for two deposited thicknesses on the microstructure, crystalline quality, morphology, chemical composition, and magnetic properties as well as magnetic domain formation of BaFe12O19 (BaM) grown on YSZ(111) by pulsed laser deposition (PLD). We found that PLD platinum deposited with a thickness of 25 nm cannot withstand the dewetting phenomenon occurring during the subsequent BaM layer growth. A smooth and continuous Pt underlayer that possesses a sharp interface and omits the intermixing between the BaM and substrate was successfully achieved for a deposited Pt film thickness of 75 nm. Independent of the thickness of the deposited Pt layer, the c-axis orientation as well as coercivity Hc and the anisotropy HA fields were significantly improved due to a remarkable improvement of lattice mismatch in comparison with the BaM layer grown without a Pt underlayer on YSZ(111). By applying high-resolution X-ray diffraction, scanning and transmission electron microscopy (SEM/TEM), and atomically resolved scanning TEM imaging combined with energy-dispersive X-ray spectroscopy, as well as atomic and magnetic force microscopy, a comprehensive investigation of both structure and chemical composition of the deposited BaM films and their interfacial regions was performed. This study aimed to correlate the enhancement of the overall magnetic properties and of the local spin magnetic domain orientation with the modification of BaM microstructure and chemical composition at the nanometer scale due to the Pt underlayer. Finally, we attempted to understand the mechanisms that control the magnetic properties of these BaM films in order to be able to tailor them.

Tunable magnetic properties and magnetic domain structure of nanocomposite permanent materials via Ti addition into Nd-Fe-Co-B alloys

In this work, the effect of tunable Ti content on the microstructure, magnetic domain structure, and magnetic properties of as-spun and annealed Nd9.5Fe79-xCo5TixB6.5(x = 0,1,2,3,4) alloys at the quench speed of 18 m/s were investigated. For the as-spun alloy, augmenting the Ti content enhanced the initial crystallization temperature and the stability of the amorphous phase. Simultaneously, the incorporation of Ti led to augmentation in the quantity of nanocrystals within the amorphous matrix, thereby facilitating the formation of vortex-like magnetic domains with large size but reduced the saturation magnetization Ms. For the annealed alloy, the incorporation of Ti inhibited the precipitation of α-Fe phase, refined the grain, enhanced the exchange coupling between the soft and hard magnetic phase and facilitated the formation of smaller, more uniform vortex-like magnetic domains, These alterations were beneficial to improve the comprehensive magnetic properties. Furthermore, the addition of tunable Ti resulted in a remarkable impact on coercivity enhancement. The coercivity value exhibited a significant increase of 54.30%, surging from 374.24 kA/m to 577.51 kA/m. Upon a thorough analysis of the magnetic domains and coercive force mechanisms, it was ascertained that the introduction of Ti substantially augmented the creation of vortex-like domains. These domains effectively impede domain motion, consequently elevating the material's coercivity.

Spontaneous Chiral Symmetry Breaking and Lane Formation in Ferromagnetic Ferrofluids.

Ferromagnetic ferrofluids are synthetic materials consisting of magnetic nanoplatelets dispersed in an isotropic fluid. Their main characteristics are the formation of stable magnetic domains and the presence of macroscopic magnetization even in the absence of a magnetic field. Here, the authors report on the experimental observation of spontaneous stripe formation in a ferromagnetic ferrofluid in the presence of an oscillating external magnetic field. The striped structure is identified as elongated magnetic domains, which exhibit reorientation upon reversal of the magnetic field. The stripes are oriented perpendicular to the magnetic field and are separated by alternating flow lanes. The velocity profile is measured using a space-time correlation technique that follows the motion of the thermally excited fluctuations in the sample. The highest velocities are found in the depleted regions between individual domains and reach values up to several µms-1 . The fluid in adjacent lanes moves in the opposite directions despite the applied magnetic field being uniform. The formation of bidirectional flow lanes can be explained by alternating rotation of magnetic nanoparticles in neighboring stripes, which indicates spontaneous breaking of the chiral symmetry in the sample.

Exchange biased surface acoustic wave magnetic field sensors

Magnetoelastic composites which use surface acoustic waves show great potential as sensors of low frequency and very low amplitude magnetic fields. While these sensors already provide adequate frequency bandwidth for most applications, their detectability has found its limitation in the low frequency noise generated by the magnetoelastic film. Amongst other contributions, this noise is closely connected to domain wall activity evoked by the strain from the acoustic waves propagating through the film. A successful method to reduce the presence of domain walls is to couple the ferromagnetic material with an antiferromagnetic material across their interface and therefore induce an exchange bias. In this work we demonstrate the application of a top pinning exchange bias stack consisting of ferromagnetic layers of (Fe90Co10)78Si12B10 and Ni81Fe19 coupled to an antiferromagnetic Mn80Ir20 layer. Stray field closure and hence prevention of magnetic edge domain formation is achieved by an antiparallel biasing of two consecutive exchange bias stacks. The set antiparallel alignment of magnetization provides single domain states over the complete films. This results in a reduction of magnetic phase noise and therefore provides limits of detection as low as 28 pT/Hz1/2 at 10 Hz and 10 pT/Hz1/2 at 100 Hz.

Microscale Metasurfaces for On‐Chip Magnetic Flux Concentration

AbstractMagnetic metamaterials have demonstrated promising perspectives to improve the efficiency of magnetic flux concentrators. In this work, the effects of downscaling these devices for on‐chip integration is investigated. The influence of the non‐linear magnetic response of the ferromagnetic components, their magnetic irreversibility, the formation of magnetic domains, as well as the effects of geometry and size of the devices are scrutinized. The results demonstrate that the implementation of metasurfaces at the microscale opens up new technological possibilities for enhancing the performance of magnetic field detectors and remotely charging small electric devices, thus paving the way toward new approaches in information and communication technologies.

Magnetic domain control and its dependence on aspect ratio and thickness in Ni nanolayer patterns for nanowire spintronic devices

We investigate the aspect ratio and thickness dependence of magnetic domain formation in multiple types of ferromagnetic Ni nanolayer electrode patterns. Controlling magnetic domains is critical for spintronic devices using a group IV semiconductor, e.g. Si and Ge, nanowire as the electrodes with magnetic tunnel junction require parallel and anti-parallel magnetization configurations. Single magnetic domains are obtained in the Ni nanolayer electrode patterns on SiO2/Si substrate with an aspect ratio of 20 and a thickness of 40 nm even under the as-deposition condition, while other electrode patterns are mostly showing multiple magnetic domains. The results obtained by magnetic force microscopy also show that the magnetization switching is observed in the electrode pattern with a single magnetic domain. The results in this study show that the suitable design of the dimensions of nanolayer patterns is key to constructing a single magnetic domain in a ferromagnetic electrode for nanowire spintronic devices.

Effect of proton irradiation on the performance of fluxgate sensors

The fluxgate magnetometers have been used in many space missions due to their stability, low cost, low mass, and good measuring sensitivity and range. Space weather conditions around the Earth and solar system may be dangerous for the sensors of these crucially important devices. Proton irradiation was used to simulate space weather conditions near the Earth’s magnetosphere in Van Allen belts. The effect of proton irradiation on the structural, magnetic, and sensor performance of our fluxgate sensors was studied with irradiation doses up to 60 kRad. Sensor’s materials were prepared using a planar flow casting technique having two different compositions, namely Fe38Co38Mo8CuB15 (Fe38) and Fe42Co42CuB15 (Fe42). Structural investigation of the alloys was performed by X-ray diffraction patterns and SEM micrographs. A magnetic force microscope and vibrating sample magnetometer were used to investigate surface and bulk magnetic properties, respectively. The characterization of the sensors was done by determination of the working field range, transfer function, and noise at 1 Hz. The amorphous structure of the Fe38Co38Mo8CuB15 alloy did not change with irradiation, while some degree of crystallization was depicted in the Fe42Co42CuB15 alloy, probably due to the local heating of the ribbon. The formation of magnetic domains was clearly observed in Fe38Co38Mo8CuB15 alloy in MFM images after the irradiation. On the contrary, it was not observed in Fe42Co42CuB15 alloy due to excessive domain growth. The magnetic parameters, namely coercivity (Hc) and saturation magnetization (Ms) were affected by the proton irradiation in a different way. The former increases with irradiation dose, while the latter first decreases and then rises to its initial value or a little smaller. On the other hand, with increasing doses, for both alloys, the transfer functions of the sensors show a decrease while the noise increases substantially. The noise parameters of the sensors were raised 4–5 times after the maximum irradiation dose; similarly, sensitivities decreased more than 100 times.

Magnetohydrodynamic stability of magnetars in the ultrastrong field regime – II. The crust

ABSTRACT We study the stability of Hall magnetohydrodynamic with strong magnetic fields in which Landau quantization of electrons is important. We find that the strong-field Hall modes can be destabilized by the dependence of the differential magnetic susceptibility on magnetic field strength. This hydrodynamic instability, thermodynamic in origin and stabilized by magnetic domain formation, is studied using linear perturbation theory. It is found to have typical growth time of order ≲103 yr, with the growth time decreasing as a function of wavelength of the perturbation. The instability is self-limiting, turning off following a period of local field growth by a few per cent of the initial value. Finite temperature is also shown to limit the instability, with sufficiently high temperatures eliminating it altogether. Alfvén waves can show similar unstable behaviour on shorter time-scales. We find that Ohmic heating due to the large fields developed via the instability and magnetic domain formation is not large enough to account for observed magnetar surface temperatures. However, Ohmic heating is enhanced by the oscillatory differential magnetic susceptibility of Landau-quantized electrons, which could be important to magnetothermal simulations of neutron star crusts.

Influence of the magnetic sublattices in the double perovskite LaCaNiReO6

The magnetism of double perovskites is a complex phenomenon, determined from intra- or interatomic magnetic moment interactions, and strongly influenced by geometry. We take advantage of the complementary length and timescales of the muon spin rotation, relaxation, and resonance (${\ensuremath{\mu}}^{+}\mathrm{SR}$) microscopic technique and bulk ac/dc magnetic susceptibility measurements to study the magnetic phases of the ${\mathrm{LaCaNiReO}}_{6}$ double perovskite. As a result, we are able to discern and report ferrimagnetic ordering below ${T}_{\mathrm{C}}=102\phantom{\rule{4pt}{0ex}}\mathrm{K}$ and the formation of different magnetic domains above ${T}_{\mathrm{C}}$. Between ${T}_{\mathrm{C}}<T<270\phantom{\rule{4pt}{0ex}}\mathrm{K}$, the following two magnetic environments appear, a dense spin region and a static-dilute spin region. The paramagnetic state is obtained only above $T>270\phantom{\rule{4pt}{0ex}}\mathrm{K}$. An evolution of the interaction between Ni and Re magnetic sublattices, in this geometrically frustrated fcc perovskite structure, is revealed as a function of temperature through the critical behavior and thermal evolution of microscopic and macroscopic physical quantities.