Magnetic Chains Research Articles

High On/Off Ratio Spintronic Multi‐Level Memory Unit for Deep Neural Network (Adv. Sci. 13/2022)

Spintronic Multi-Level Memory Unit In article number 2103357 by Kun Zhang, Yue Zhang, and co-workers, a spintronic multi-level memory unit (MLMU) with high on/off ratio is constructed by integrating a magnetic tunnel junction chain and a diode in parallel. This MLMU can enable high-accuracy artificial intelligence applications, such as a deep neural network accelerator for image classification. Just as described in the cover design, the MLMUs are regarded as building blocks to assemble the artificial-intelligence brain.

Chain Assembly Kinetics from Magnetic Colloidal Spheres.

Magnetic colloidal chains are a microrobotic system with promising applications due to their versatility, biocompatibility, and ease of manipulation under magnetic fields. Their synthesis involves kinetic pathways that control chain quality, length, and flexibility, a process performed by first aligning superparamagnetic particles under a one-dimensional magnetic field and then chemically linking them using a four-armed maleimide-functionalized poly(ethylene glycol). Here, we systematically vary the concentration of the poly(ethylene glycol) linkers, the reaction temperature, and the magnetic field strength to study their impact on the physical properties of synthesized chains, including the chain length distribution, reaction temperature, and bending modulus. We find that this chain fabrication process resembles step-growth polymerization and can be accurately described by the Flory-Schulz model. Under optimized experimental conditions, we have successfully synthesized long flexible colloidal chains with a bending modulus, which is 4 orders of magnitude smaller than previous studies. Such flexible and long chains can be folded entirely into concentric rings and helices with multiple turns, demonstrating the potential for investigating the actuation, assembly, and folding behaviors of these colloidal polymer analogues.

Bio-Inspired Bianisotropic Magneto-Sensitive Elastomers with Excellent Multimodal Transformation.

Magneto-sensitive soft materials that can accomplish fast, remote, and reversible shape morphing are highly desirable for practical applications including biomedical devices, soft robotics, and flexible electronics. In conventional magneto-sensitive elastomers (MSEs), there is a tradeoff between employing hard magnetic particles with costly magnetic programming and utilizing soft magnetic particle chains causing tedious and small deformation. Here, inspired by the shape and movement of mimosa, a novel soft magnetic particle doped shape material bianisotropic magneto-sensitive elastomer (SM bianisotropic MSE) with multimodal transformation and superior deformability is developed. The high-aspect-ratio shape anisotropy and the material anisotropy in which the magnetic particles are arranged in a chainlike structure together impart magnetic anisotropy to the SM bianisotropic MSE. A magneto-elastic analysis model is proposed, and it is elucidated that magnetic anisotropy leads to peculiar field-direction-dependent multimodal transformation. More importantly, a quadrilateral assembly and a regular hexagon assembly based on this SM bianisotropic MSE are designed, and they exhibit 2.4 and 1.7 times the deformation capacity of shape anisotropic samples, respectively. By exploiting the multidegree of freedom and excellent deformability of the SM bianisotropic MSE, flexible logic switches and ultrasoft magnetic manipulators are further demonstrated, which prove its potential applications in future intelligent flexible electronics and autonomous soft robotics.

Quantum spins and hybridization in artificially-constructed chains of magnetic adatoms on a superconductor

Magnetic adatom chains on surfaces constitute fascinating quantum spin systems. Superconducting substrates suppress interactions with bulk electronic excitations but couple the adatom spins to a chain of subgap Yu-Shiba-Rusinov (YSR) quasiparticles. Using a scanning tunneling microscope, we investigate such correlated spin-fermion systems by constructing Fe chains adatom by adatom on superconducting NbSe2. The adatoms couple entirely via the substrate, retaining their quantum spin nature. In dimers, we observe that the deepest YSR state undergoes a quantum phase transition due to Ruderman-Kittel-Kasuya-Yosida interactions, a distinct signature of quantum spins. Chains exhibit coherent hybridization and band formation of the YSR excitations, indicating ferromagnetic coupling. Longer chains develop separate domains due to coexisting charge-density-wave order of NbSe2. Despite the spin-orbit-coupled substrate, we find no signatures of Majoranas, possibly because quantum spins reduce the parameter range for topological superconductivity. We suggest that adatom chains are versatile systems for investigating correlated-electron physics and its interplay with topological superconductivity.

Motion synchronicity of a micro-magnetic-particle chain in a rotating field

A magnetic chain consisted of micro-sized beads in a rotating magnetic field is experimented to observe its motion synchronicity with the external field. If the field frequency is sufficiently high, reverse motion occurs to slow down the average angular speed, so that the chain rotates much slower than the external field. A square field configuration, in which the instantaneous strength and angular speed vary with time within every rotating period, is proposed to improve the chaining stability and the motion synchronicity while a same overall frequency with the conventionally used circular field configuration is preserved.

Enhanced Magnetorheological Behavior of a Carbonyl‐Iron‐Based Fluid via Addition of Fe3O4/Halloysite‐Nanotube Composite Particles

Composite additives for enhancing the yield stress, sedimentation stability, and long‐term reversibility of bidisperse magnetorheological fluids (MRFs) are reported herein. The design and introduction of magnetic Fe3O4/halloysite‐nanotube (HNT) composite additives to carbonyl‐iron (CI)‐based MRFs are described, and the effects of Fe3O4/HNT addition on the MRF behavior are elucidated. The rheological, viscoelastic, and cyclic reversibility analyses of the bidisperse Fe3O4/HNT‐CI MRFs indicate that the MR performance increases and subsequently decreases with the increasing content of the Fe3O4/HNTs. The MRF containing 1.0 wt% Fe3O4/HNTs shows optimal MR properties and long‐term reversibility. Under a magnetic field, the 1.0 wt% Fe3O4/HNTs are embedded in the interstices of the magnetic chains, enhancing the magnetic dipole–dipole interactions between the particles, strengthening the rigidity of the magnetic chains, and increasing the yield stress of the MRF. The Fe3O4/HNTs are adsorbed on the surfaces of the CI particles in the absence of a magnetic field, occupying the free space between the CI particles and forming support structures, which prevents aggregation and improves sedimentation stability. Moreover, the designed MRFs respond quickly to magnetic field switching and exhibit enhanced long‐term reversibility.

Chain-Like Structures of Biogenic and Nonbiogenic Magnetic Nanoparticles in Vascular Tissues.

In this paper, slices of organs from various organisms (animals, plants, fungi) were investigated by using atomic force microscopy and magnetic force microscopy to identify common features of localization of both biogenic and nonbiogenic magnetic nanoparticles. It was revealed that both biogenic and nonbiogenic magnetic nanoparticles are localized in the form of chains of separate nanoparticles or chains of conglomerates of nanoparticles in the walls of the capillaries of animals and the walls of the conducting tissue of plants and fungi. Both biogenic and nonbiogenic magnetic nanoparticles are embedded as a part of the transport system in multicellular organisms. In connection with this, a new idea of the function of biogenic magnetic nanoparticles is discussed, that the chains of biogenic magnetic nanoparticles and chains of conglomerates of biogenic magnetic nanoparticles represent ferrimagnetic organelles of a specific purpose. Besides, magnetic dipole-dipole interaction of biogenic magnetic nanoparticles with magnetically labeled drugs or contrast agents for magnetic resonance imaging should be considered when designing the drug delivery and other medical systems because biogenic magnetic nanoparticles in capillary walls will serve as the trapping centers for the artificial magnetic nanoparticles. The aggregates of both artificial and biogenic magnetic nanoparticles can be formed, contributing to the risk of vascular occlusion. Bioelectromagnetics. 43:119-143, 2022. © 2021 Bioelectromagnetics Society.

Indeno[2,1-a]fluorene-11,12-dione Radical Anions: Synthesis, Characterization, and Properties.

The one-electron reduction of indeno[2,1-a]fluorene-11,12-dione (IF) with various alkali metals prepare the radical anion salts. The data about different structures, properties, and characterization was obtained by single-crystal X-ray diffraction, electron paramagnetic resonance (EPR) spectroscopy, superconducting quantum interference device (SQUID) measurements, and physical property measurement system (PPMS). Compound IF.- K+ (18-c-6) is regarded as a one-dimensional magnetic chain through C-H⋅⋅⋅C interaction. Theoretical calculations and magnetic results showed that [IF.- K+ (15-c-5)]2 is a dimer with an open-shell ground state. Compounds IF.- Na+ (15-c-5) and IF.- K+ (cryptand) are monoradical anion salts: IF2 .- Li+ possesses unique π-stack structure with an interplanar separation less than 3.46 Å, making it a semiconductor (δRT =1.9×10-4 S ⋅ cm-1 ). This work gives insights into multifunctional radical anions, and describes the design and development of different functional radicals.

Analyzing magnetic nanofluid structure

Aqueous magnetic nanofluid consists of superparamagnetic nanoparticles, with a typical size of 10–12 nm. On the application of a magnetic field, these nanoparticles align heterogeneously and form a chain or chain-like structure. This structure is observed using a microscope. Although many articles report such chain or microstructure formation well, the method to identify and determine chain parameters, e.g., chain length, width, and associated counts, is scarce. Similarly, interchain or successive distance is one of the critical parameters for developing magnetic nanofluid-based devices. The work describes magnetic field-induced chain parameters (MFCP) and magnetic field-induced interchain distance (MFID), a set of developed protocols in the ImageJ software to identify and determine the (i) chain length, width, and associated counts, along with (ii) successive distance of the magnetic chains in the magnetic nanofluid. This utilizes a macro file such as MFCPji.txt and MFIDji.txt for ImageJ, which can be used on microscopic images of magnetic nanofluids without applying a magnetic field. The protocol does not require specialized scientific equipment and can be carried out using open-source software ImageJ/Fiji. The examples of microstructure formations in two different magnetic fluids (A and B) are discussed. In addition, the results of the associated weighted average chain length, chain width, number of chains, and the successive chain distance are reported. The chain parameters are helpful to determine diffraction grating angles. The MFCPji and MFIDji macros have been integrated into a macro toolset that can be configured to be run on ImageJ startup. The MFCPji and MFIDji are available from the following Uniform Resource Locator (URLs): https://github.com/urveshsoni/ImageJ-Macros and https://ruchadesailab.wordpress.com/publication/

Preparation, characterization and DFT+U study of the polar Fe3+-based phase Ba5Fe2ZnIn4S15 containing S = 5/2 zigzag chains

The polar chalcogenide phase Ba5Fe2ZnIn4S15 possesses weakly interacting magnetic zig-zag chains made of corner-sharing Fe3+S4 thus forming an AFM S = 5/2 spin chain system. The intrinsic polarization is mostly due to the anionic framework.

Ti3C2 MXene-anchored photoelectrochemical detection of exosomes by in situ fabrication of CdS nanoparticles with enzyme-assisted hybridization chain reaction.

Exosomes that carry large amounts of tumor-specific molecular information have been identified as a potential non-invasive biomarker for early warning of cancer. In this work, we reported an enzyme-assisted photoelectrochemical (PEC) biosensor for quantification of exosomes based on the in situ synthesis of Ti3C2 MXene/CdS composites with magnetic separation technology and hybridization chain reaction (HCR). First, exosomes were specifically bound between aptamer-labeled magnetic beads (CD63-MBs) and a cholesterol-labeled DNA anchor. The properly designed anchor ends acted as a trigger to enrich the alkaline phosphatase (ALP) through HCR. It catalyzed more sodium thiophosphate to generate the sulfideion (S2−), which combined with Cd2+ for in situ fabrication of CdS on Ti3C2 MXene resulting in elevated photocurrent. The Ti3C2 MXene-anchored PEC method was realized for the quantitative detection of exosomes, which exhibited the dynamic working range from 7.3 × 105 particles per mL to 3.285 × 108 particles per mL with a limit of detection of 7.875 × 104 particles per mL. The strategy showed acceptable stability, high sensitivity, rapid response and excellent selectivity. Furthermore, we believe that the PEC biosensor has huge potential as a routine bioassay method for the precise quantification of exosomes from breast cancer in the future.

Two Possible Ways of Forming Ordered Magnetic Chains on a Metal Surface: Monte Carlo Simulations

Two Possible Ways of Forming Ordered Magnetic Chains on a Metal Surface: Monte Carlo Simulations

The catenation of a singlet diradical dication and modulation of diradical character by metal coordination.

A singlet bis(triarylamine) diradical dication and its zigzag 1D magnetic chain catenated by silver cations were isolated and characterized by single-crystal X-ray crystallography, EPR spectroscopy, SQUID measurements, cyclic voltammetry, and UV-Vis-NIR absorption spectroscopy in conjunction with DFT calculations. The ΔEOS-T has significantly changed due to the coordination of carbonyls (Lewis base) with Ag+ (Lewis acid), revealing that the diradical character can be modulated by Lewis acid-base coordination and interchain intermolecular coupling interactions.

Preparation and processing properties of magnetically controlled abrasive solidification orientation—solid-phase Fenton reaction lapping-polishing plate for single-crystal 4H-SiC

To improve the ultraprecision processing efficiency and surface quality of single-crystal 4H-SiC substrates, a lapping-polishing plate combining magnetically controlled abrasive solidification orientation and a solid-phase Fenton reaction was prepared. Furthermore, the effects of the concentration ratio of abrasive to Fe3O4 and abrasive types on the physical properties of the lapping-polishing plate and the processing properties for single-crystal 4H-SiC substrates were studied to reveal the lapping-polishing mechanism of magnetically controlled abrasive solidification orientation—solid-phase Fenton reaction. The results show that the concentration ratio of abrasive to Fe3O4 and abrasive types affects the distribution of the magnetic chain string structure and the distribution of abrasive materials, affecting the plate's processing properties. The higher the abrasive concentration is, the higher the material removal rate (MRR), but it affects the abrasive orientation and the solid-phase Fenton reaction. In contrast, the high Fe3O4 concentration strengthens the solid-phase Fenton reaction and weakens the mechanical removal of the abrasive, resulting in low MRR and poor processing quality. When the abrasive and the concentration ratio of abrasive to Fe3O4 are diamond and 1:5, the MRR is the largest (46.5 nm/min), and a smooth surface with a surface roughness Ra of 0.89 nm can be obtained. The magnetically controlled abrasive solidification orientation—solid-phase Fenton reaction lapping-polishing process—is a chemical reaction and mechanical removal process. The chemical reaction can promote MRR and improve the lapping-polishing quality while affecting the lapping-polishing plate's surface microstructure and processing properties. The dynamic equilibrium between the material removal process of SiC substrates and the wear of lapping-polishing plates enable high-efficiency, high-quality and low-damage processing of SiC substrates. This method and plates can be potentially used to achieve the fine lapping and polishing of SiC substrates and other optoelectronic substrates.

Instability of Majorana states in Shiba chains due to leakage into a topological substrate

We revisit the problem of Majorana states in chains of scalar impurities deposited on a superconductor with a mixed s-wave and p-wave pairing. We also study the formation of Majorana states for magnetic impurity chains. We find that the magnetic impurity chains exhibit well-localized Majorana states when the substrate is trivial, but these states hybridize and get dissolved in the bulk when the substrate is topological. Most surprisingly, and contrary to previous predictions, the scalar impurity chain does not support fully localized Majorana states except for very small and finely tuned parameter regimes, mostly for a non-topological substrate close to the topological transition. Our results indicate that a purely p-wave or a dominant p-wave substrate are not good candidates to support either magnetic or scalar impurity topological Shiba chains.

Subgap states at ferromagnetic and spiral-ordered magnetic chains in two-dimensional superconductors. I. Continuum description

We consider subgap bands induced in a two-dimensional superconductor by a densely packed chain of magnetic moments with ferromagnetic or spiral alignments. We show that by contrast with sparsely packed chains a consistent description requires that all wavelengths are taken into account for the scattering at the magnetic moments. The resulting subgap states are a composition of Yu-Shiba-Rusinov-type states and magnetic scattering states, whose mixture becomes especially important to understand the nature and dimensional renormalization of gap closures for spiral magnetic alignments under increasing scattering strength, particularly as the spiral becomes commensurate with the Fermi wavelength. The results are fully analytic in the form of Green's functions and provide the tools for further analysis of the properties of the subgap states.

Subgap states at ferromagnetic and spiral-ordered magnetic chains in two-dimensional superconductors. II. Topological classification

We investigate the topological classification of the subgap bands induced in a two-dimensional superconductor by a densely packed chain of magnetic moments with ferromagnetic or spiral alignments. The wave functions for these bands are composites of Yu-Shiba-Rusinov-type states and magnetic scattering states and have a significant spatial extension away from the magnetic moments. We show that this spatial structure prohibits a straightforward extraction of a Hamiltonian useful for the topological classification. To address the latter correctly we construct a family of spatially varying topological Hamiltonians for the subgap bands adapted for the broken translational symmetry caused by the chain. The spatial dependence in particular captures the transition to the topologically trivial bulk phase when moving away from the chain by showing how this, necessarily discontinuous, transition can be understood from an alignment of zeros with poles of Green's functions. Through the latter the topological Hamiltonians reflect a characteristic found otherwise primarily in strongly interacting systems.

A magnetic separation-assisted cascade hybridization chain reaction amplification strategy for sensitive detection of flap endonuclease 1

Sensitive and accurate detection of flap endonuclease 1 (FEN1) is essential to understand its roles in DNA replication and repair and explore its functions in tumor diagnosis and prognosis. Here, we designed a magnetic separation-assisted cascade hybridization chain reaction (HCR) amplification strategy for enzyme-free and sensitive detection of FEN1. Firstly, the forked dsDNAs contained the recognition site (5′ overhanging DNA flap) of FEN1 were modified on magbeads surface to form magnetic recognition probes. By the recognition and catalytic cleavage of FEN1, the 5′ flaps were removed into solution and then purified by magnetic separation. Then, the obtained flaps served as triggers to activate the linear-assembly of hairpin probes H1 and H2 (primary HCR), forming nicked double helices with split fragments. Finally, the fragments acted as new triggers to activate the branched-assembly of hairpin probes H3 and H4 (secondary HCR), causing fluorophore/quencher labeled on H3 far away and fluorescence recovery. Benefiting from the purification of triggers by magnetic separation and the signal amplification effect of cascade HCR, this strategy achieved a low detection limit of 3.6 × 10−5 U μL−1 for FEN1, and enabled the assay of it in actual samples. The results demonstrate that our strategy will provide a potent approach for sensitive detection of FEN1 in early tumor diagnosis and prognosis.

Fabrication of chitosan-coated mixed spinel ferrite integrated with graphene oxide (GO) for magnetic extraction of viral RNA for potential detection of SARS-CoV-2.

Genetic variants of the COVID-19 causative virus have been arising and circulating globally. In many countries, especially in developing ones with a huge population, vaccination has become one of the major challenges. SARS-CoV-2 variants’ fast transmission rate has an upsurge in the COVID cases, leading to more stress on health systems. In the current COVID-19 scenario, there is the requirement of more adequate diagnostic approaches to check the COVID-19 spread. Out of many diagnostic approaches, a magnetic nanoparticle-based reverse transcription polymerase chain reaction could be nontrivial. The use of magnetic nanoparticles is to separate nucleic acid of SARS-CoV-2 from the patient samples and apply for SARS-CoV-2 detection in an easy and more effective way. Herein, the magnetic nanoparticles are synthesized using the solgel autocombustion methods and then successfully coated with biopolymer (chitosan) using ultrasonication. Chitosan-coated nanoparticles are successfully integrated into the graphene oxide sheets to introduce carboxyl groups. Crystallite size calculation, morphological and magnetic studies of synthesized magnetic nanoparticles, and multifunctional magnetic nanoparticles are done using XRD, SEM, TEM, and VSM, respectively. Besides, the potentiality of the fabricated nanocomposites in RNA extraction protocol is also discussed with schematic representation.

Metastability and dynamic modes in magnetic island chains

The uniform states of a model for one-dimensional chains of thin magnetic islands on a nonmagnetic substrate coupled via dipolar interactions are described here. Magnetic islands oriented with their long axes perpendicular to the chain direction are assumed, whose shape anisotropy imposes a preference for the dipoles to point perpendicular to the chain. The competition between anisotropy and dipolar interactions leads to three types of uniform states of distinctly different symmetries, including metastable transverse or remanent states, transverse antiferromagnetic states, and longitudinal states where all dipoles align with the chain direction. The stability limits and normal modes of oscillation are found for all three types of states, even including infinite range dipole interactions. The normal mode frequencies are shown to be determined from the eigenvalues of the stability problem.