Magnet Assembly Research Articles

Control of spin liquid-like dynamics by geometry of 2D nanocluster networks

Network structures of magnetic molecular assemblies on a two-dimensional (2D) material are attractive platforms for molecular spintronics and for the study of 2D magnetic materials. However, it is still a challenging task to connect such assemblies with appropriate magnetic interactions. Recently, uniform nanoclusters consisting of about 100 magnetic amino-ferrocene molecules were self-organized on a graphene oxide nanosheet by on-surface synthesis. Here, the dynamics of weakly interacting molecular spins in the nanocluster networks is investigated by exploiting the tunability of the intercluster distance through the chemical reaction. The stochastic simulation shows that the entanglement of the spin orientations at the sites in the nanocluster by magnetic dipole interactions leads to a liquid-like behavior of the spins (S = 5/2) at T ≲ 15 K, generating spin correlations and slow dynamics observed in Mössbauer spectroscopy and magnetic susceptibility. The energy barrier for generating magnetic relaxation and the deviation temperature from thermally activated relaxation depend on the intercluster distance, i.e., the interactions between the nanoclusters, indicating that the relaxation can be tuned by the geometry of the nanocluster networks. The present results pave the way for the chemical design of 2D nanocluster networks and chemically functionalized 2D materials.

Magnetic assembly of microwires on a flexible substrate for minimally invasive electrophysiological recording

Understanding the neural system in the brain requires the detection of signals from the tissue. Microscale electrodes enable high spatiotemporal neural recording, whereas traditional microelectrodes cause material and geometry mismatches between the electrode and the tissue, leading to injury and signal loss during recording. In this study, we propose a fabrication technique that uses magnetic force to facilitate assembly of vertical microscale wire-electrodes on a flexible substrate. Two-channel 15-μm-diameter and 400-μm-length nickel-microwire electrodes on a 5-μm-thick flexible parylene film are designed and fabricated. Impedance characteristics of these electrodes are <500 kΩ at 1 kHz, with output/input signal amplitude ratios of over 90%. In vivo acute neural recording in mice demonstrates that both local field potentials and action potentials are detected through each wire electrode, confirming the minimal invasiveness during the electrode penetration and through immunohistochemical tissue analysis.

Development of a high current density, high temperature superconducting cable for pulsed magnets

Abstract A low AC loss Rare Earth Barium Copper Oxide (REBCO) cable, based on the VIPER cable technology has been developed by Commonwealth Fusion Systems for use in high field, REBCO based tokamaks. The new cable is composed of partitioned and transposed copper ‘petals’ shaped to fit together in a circular pattern with each petal containing a REBCO tape stack and insulated from each other to reduce AC losses. A stainless steel jacket adds mechanical robustness—also serving as a vessel for solder impregnation—while a tube runs through the middle for cooling purposes. Additionally, fiber optic sensors are placed under the tape stacks for quench detection. To qualify this design, a series of experiments were conducted as part of the SPARC tokamak Central Solenoid Model Coil program—to retire the risks associated with full scale, fast ramping, high flux HTS Central Solenoid (CS) and Poloidal Field (PF) coils for tokamak fusion power plants and net energy demonstrators. These risk study and risk reduction experiments include (1) AC loss measurement and model validation in the range of ~5 T/s, (2) an IxB electromagnetic loading of over 850 kN/m at the cable level and up to 300 kN/m at the stack level, (3) a transverse compression resilience of over 350 MPa, (4) manufacturability at tokamak relevant speeds and scales, (5) cable to cable joint performance, (6) fiber optic based quench detection speed, accuracy, and feasibility, and (7) overall winding pack integration and magnet assembly. The result is a cable technology, now referred to as PIT VIPER, with AC losses that measure fifteen times lower (at ~5 T/s) than its predecessor technology; a 2% or lower degradation of critical current (Ic) at high IxB electromagnetic loads; no detectable Ic degradation up to 570 MPa of transverse compression on the cable unit cell; end to end magnet manufacturing, consistently producing Ic values within 7% of the model prediction; cable to cable joint resistances at 20 K on the order of ~15 nΩ; and fast, functional quench detection capabilities that do not involve voltage taps. This cable technology will be tested comprehensively in a Central Solenoid Model Coil to prove its readiness for compact, high field tokamak operation.

Magnetic-field-controllable elasticity of helical spring magnets composed of magnetic-particle-polymer composites

Abstract We experimentally demonstrated the ability to control the spring constant of helical mechanical springs using a magnetic field. These springs were composed of magnetic nanoparticles embedded within an elastic polymer matrix. The composite material, in its gel form, was injected into a 3D-printed mold featuring a helical-spring-shaped cavity. An external magnetic field applied perpendicular to the coil axis of the spring allows the aligmment of the magnetic nanoparticle assemblies (chain axis) in the field direction. This alignment process determines the preferred magnetization orientation of the particle assembly chain, thereby balancing the magnetic force between the magnetic anisotropy field and the Zeeman field under a given external field. When the spring is subjected to compression or stretching loads under an externally applied magnetic field, these two magnetic fields modify the effective spring constant of the magnetic helical spring by ~ 31 %, incresing it from 8.7 N/m (under no field) to 11.5 N/m at 300 mT. Analytical modeling using a simplified rod geometry aptly explains the experimental results, demonstrating that the spring constant linearly increases with the field strength up to 300 mT. Such composite magnetic helical springs could be utilized as active vibration absorbers or isolators due to their field-controllable elasticity.&amp;#xD;

Tunable and temperature compensated permanent magnet assemblies for green particle accelerators

Particle accelerators are developed worldwide for several societal, industrial, and scientific applications. With the advent of high-strength permanent magnets, the focus is shifting to building particle accelerators using permanent magnets for beam handling. This shift offers the distinct advantage of power efficiency and compactness, over electromagnets. However, such systems face inherent limitations related to temperature sensitivity and lack of tuneability. This paper explores and demonstrates methods for reducing temperature sensitivity and incorporating tuneability in permanent magnet-based systems. Accelerators employing a large number of permanent magnets are more energy efficient as they do not incur running expenditures and are therefore classified as green in this paper. Moreover, we believe that future particle accelerators will be able to leverage these advantages even more. A temperature-compensated magnet using a Nickel–Iron special alloy is designed using the measured temperature-dependent B–H curve of the material. The optimum thickness of the temperature-compensated shunt was determined and cross-verified by constructing a magnet and measuring it in a temperature-controlled environment. Additionally, this paper discusses the design of hybrid magnets integrating permanent magnets and electromagnetic coils highlighting their utility in temperature compensation and tunability. Furthermore, other methods for incorporating tunability and making a permanent magnet system more resilient to temperature changes are also briefly outlined.

Investigating the effect of rolling deformation on the electro-mechanical limits of Nb3Sn wires produced by RRP® and PIT technologies

Future high-field magnets for particle accelerators hinge on the crucial development of advanced Nb3Sn wires engineered to withstand the large stresses generated during magnet assembly and operation. The superconducting properties of Nb3Sn enable the design of compact accelerator-quality magnets above 10 T, but at the same time the brittleness and strain sensitivity of the material impose careful consideration of the mechanical limits. In addition, accelerator magnets are wound using Rutherford cables and the cabling process generates deformations in the wire that can affect its electro-mechanical performance. This paper reports on the impact of the rolling deformation on the transverse stress tolerance of high-performance restacked-rod-process (RRP®) and powder-in-tube (PIT) Nb3Sn wires. Rolling deformation was used to mimic the effect of cabling on the wire shape. Deformed samples were compared to reference round wires in term of stress dependence and irreversible limit (σ irr) of the critical current (I c) under transverse compressive loads up to 240 MPa. Experiments were performed at 4.2 K, 19 T, on resin-impregnated single wires that imitate the operating conditions in a Rutherford cable of an accelerator magnet. The results show that rolling deformation has a detrimental effect on the initial I c of PIT wires, but it does not influence the behavior of the wire under stresses above 70 MPa. On the other hand, the deformation of RRP® wires leads to an improved σ irr without affecting the initial I c. Additionally, a 2D-mechanical finite element method model of the RRP® wire was developed to investigate the impact of the wire geometry on the plastic deformation of the copper matrix, which induces residual stresses on Nb3Sn and is the main cause for the permanent reduction of I c. Based on the model results, an alternative layout of the wire was proposed that improves its stress tolerance without affecting its electrical transport properties.

Design and development of a scanning magnet for high-resolution mass spectrometry

The magnets play a crucial role in sector mass spectrometers, directly influencing the resolution, sensitivity, and stability of these instruments. This study is based on the design requisites for high-resolution scanning magnet, alongside the optical layout schematics for mass spectrometer instrumentation. The analysis is conducted on the design parameters encompassing magnetic structure, field quality, and response dynamics. Utilizing Opera-3D simulation software, optimization designs are executed for the magnetic structure and performance, resulting in a magnet design exhibiting commendable attributes such as response time, magnetic field distortion characteristics, field range, linearity, and homogeneity. Following the completion of magnet fabrication and assembly, comprehensive evaluations of magnetic field performance and instrument testing are conducted. Results demonstrate good magnetic field linearity and minimal eddy current distortion, with a magnetic field homogeneity reaching up to ±0.05 % within the desired field region. The magnet exhibits versatility across a scan range spanning 7 to 238 u, with a scanning speed of 140 ms. Sensitivity and resolution tests, conducted using In-115, validated the magnet's compliance with the stringent design requirements of high-resolution mass spectrometry scanning magnets.

Development of a new technological scheme of the carousel milking platform based on the principles of magnetic levitation

The Carousel, the most capital–intensive and loaded milking unit, is a rotating platform that carries a large mechanical load. Its own weight, combined with the weight of the animals being moved, can reach 1200 kg per milking place or more. To reduce friction in the wheeled systems of high-loaded vehicles, large-sized assemblies and mechanisms of machinery and equipment, including agricultural machinery and aggregates, the use of magnetic suspension technology is promising. The research was carried out in order to develop a new technological scheme of a levitating rotating milking platform Carousel based on the principles of magnetic levitation. The creation of a fundamentally new resource-saving design of the Carousel milking platform based on the principles of magnetic levitation in order to increase its reliability and reduce operating costs due to the exclusion of wear on the propellers of the rail-wheel system is possible. A new scheme of a rotating milking platform Carousel using permanent magnet magnetic suspension technology without the use of wheel thrusters is proposed. Its force calculation was performed in the main mode of steady motion with the platform fully filled with animals and partially filled at the beginning and end of the milking cycle of animals, obtaining basic equations for determining the necessary repulsive forces in horizontal and vertical magnetic assemblies providing magnetic levitation (suspension) and lateral stabilization (centering) of the rotating platform.

Spatially Confined Assembly and Immobilization of Hierarchical Nanoparticle Architectures inside Microdroplets in Magnetic Fields.

Magnetic field-directed colloidal interactions offer facile tools for assembly of structures that range from linear chains to multidimensional hierarchical architectures. While the field-driven assembly of colloidal particles has commonly been investigated in unbounded media, a knowledge gap remains concerning such assembly in confined microenvironments. Here, we investigate how confinement of ferromagnetic nanoparticles in microspheres directs their magnetic assembly into hierarchical architectures. Microdroplets from polydimethylsiloxane (PDMS) liquid precursor containing dispersed iron oxide magnetic nanoparticles (MNPs) were placed in a static magnetic field leading to the formation of organized assemblies inside the host droplets. By changing the MNP concentrations, we revealed a sequence of microstructures inside the droplets, ranging from linear chains at a low MNP loading, transitioning to a combination of chains and networked bundles, to solely 3D bundles at high MNP loading. These experimental results were analyzed with the aid of COMSOL simulations where we calculated the potential energy to identify the preferred assembly conformations. The chains at high MNP loading minimized their energy by aggregating laterally to form bundles with their MNP dipoles being out-of-registry. We cured these PDMS droplets to immobilize the assemblies by forming soft microbeads. These microbeads constitute an "interaction toolbox" with different magnetic macroscale responses, which are governed by the structuring of the MNPs and their magnetic polarizability. We show that thanks to their ability to rotate by field-induced torque under a rotating field, these microbeads can be employed in applications such as optical modulators and microrollers.

Chiral Effect on the Electrochemistry of Magnetic Ferrite Colloidal Nanocrystal Assembly Modified by Amino Acids.

Chirality on the molecular or nanometer scale is particularly significant in chemistry, materials science, and biomedicine. Chiral electrochemical reactions on solid surfaces are currently a hot research topic. Herein, a chiral solid surface is constructed in aqueous solutions by mixing chiral molecules, d- and l-glutamic, with γ-Fe2O3 and Fe3O4 nanoparticles (NPs) and MnFe2O4 colloidal nanocrystal assembly (CNA). Cyclic voltammetry and differential pulse voltammetry measurements are conducted in a phosphate buffer solution (PBS) containing ascorbic acid (AA) or isoascorbic acid (IAA), and a chiral effect appears on the electroreduction of ferric ions of amino acid-modified magnetic samples. A negative or positive potential shift is observed, respectively, for magnetic structures modified by l- and d-glutamic acid in aqueous AA electrolyte, while the opposite is observed for these samples in IAA electrolyte. The reduction peak current increases by 0.8-1.2 times for the electrodes modified with l- and d-glutamate molecules, improving the electron transport efficiency. The chiral effect is absent when the electrolytes contain achiral uric acid or dopamine, or even chiral l-/d-/ld-tartaric acid. The chiral recognition between d-/l-glutamic acid and AA/IAA at the electrochemical interface is suggested to be related to their spinal configurations. These observations will be helpful for the rational design of inorganic functional chiral micro/nanostructures.

Site-selective core/shell deposition of tin on multi-segment nanowires for magnetic assembly and soldered interconnection

The field of nanotechnology continues to grow with the ongoing discovery and characterization of novel nanomaterials with unconventional size-dependent properties; however, the ability to apply modern manufacturing strategies for practical device design of these nanoscale structures is significantly limited by their small size. Although interconnection has been previously demonstrated between nanoscale components, such approaches often require the use of expensive oxidation-resistant noble metal materials and time-consuming or untargeted strategies for welded interconnection such as laser ablation or plasmonic resonance across randomly oriented component networks. In this work, a three-segment gold–nickel–gold nanowire structure is synthesized using templated electrodeposition and modified via monolayer-directed aqueous chemical reduction of tin solder selectively on the gold segments. This core/shell nanowire structure is capable of directed magnetic assembly tip-to-tip and along substrate pads in network orientation. Upon infrared heating in a flux vapor atmosphere, the solder payload melts and establishes robust and highly conductive wire–wire joints. The targeted solder deposition strategy has been applied to various other multi-segment gold/nickel nanowire configurations and other metallic systems to demonstrate the capability of the approach. This core/shell technique of pre-loading magnetically active nanowires with solder material simplifies the associated challenges of size-dependent component orientation in the manufacture of nanoscale electronic devices.

Magnetic Assembly of Magnetite/Perovskite Hybrid Nanorods for Circularly Polarized Luminescence

AbstractMagnetic fields are uniquely valuable for creating colloidal nanostructured materials, not only providing a means for controlled synthesis but also guiding their self‐assembly into distinct superstructures. In this study, a magnetothermal process for synthesizing hybrid nanostructures comprising ferrimagnetic magnetite nanorods coated with fluorescent perovskite nanocrystals is reported and their magnetic assembly into superstructures capable of emitting linear and circularly polarized light are demonstrated. Under UV excitation, the superstructures assembled in a liner magnetic field produce linear polarized luminescence, and those assembled in a chiral magnetic field exhibit strong circularly polarized luminescence (CPL) with a glum value up to 0.44 (±0.004). The CPL is believed to originate from the dipolar interaction between neighboring perovskite nanocrystals attached to the chiral assemblies and the chiral‐selective absorption of the perovskite emission by the magnetite phase. The magnetic synthesis and assembly approaches and the resulting distinctive chiral superstructures are anticipated to open up new avenues for designing diverse functional chiroptical devices.

Frequency tunable magnetostatic wave filters with zero static power magnetic biasing circuitry

A single tunable filter simplifies complexity, reduces insertion loss, and minimizes size compared to frequency switchable filter banks commonly used for radio frequency (RF) band selection. Magnetostatic wave (MSW) filters stand out for their wide, continuous frequency tuning and high-quality factor. However, MSW filters employing electromagnets for tuning consume excessive power and space, unsuitable for consumer wireless applications. Here, we demonstrate miniature and high selectivity MSW tunable filters with zero static power consumption, occupying less than 2 cc. The center frequency is continuously tunable from 3.4 GHz to 11.1 GHz via current pulses of sub-millisecond duration applied to a small and nonvolatile magnetic bias assembly. This assembly is limited in the area over which it can achieve a large and uniform magnetic field, necessitating filters realized from small resonant cavities micromachined in thin films of Yttrium Iron Garnet. Filter insertion loss of 3.2 dB to 5.1 dB and out-of-band third order input intercept point greater than 41 dBm are achieved. The filter’s broad frequency range, compact size, low insertion loss, high out-of-band linearity, and zero static power consumption are essential for protecting RF transceivers from interference, thus facilitating their use in mobile applications like IoT and 6 G networks.

Magnetically modified bacteriophage-triggered ATP release activated EXPAR-CRISPR/Cas14a system for visual detection of Burkholderia pseudomallei

Burkholderia pseudomallei, widely distributed in tropical and subtropical ecosystems, is capable of causing the fatal zoonotic disease melioidosis and exhibiting a global trend of dissemination. Rapid and sensitive detection of B. pseudomallei is essential for environmental monitoring as well as infection control. Here, we developed an innovative biosensor for quantitatively detecting B. pseudomallei relies on ATP released triggered by bacteriophage-induced bacteria lysis. The lytic bacteriophage vB_BpP_HN01, with high specificity, is employed alongside magnetic nanoparticles assembly to create a biological receptor, facilitating the capture and enrichment of viable target bacteria. Following a brief extraction and incubation process, the captured target undergoes rapid lysis to release contents including ATP. The EXPAR-CRISPR cascade reaction provides an efficient signal transduction and dual amplification module that allowing the generated ATP to guide the signal output as an activator, ultimately converting the target bacterial amount into a detectable fluorescence signal. The proposed bacteriophage affinity strategy exhibited superior performance for B. pseudomallei detection with a dynamic range from 10^2 to 10^7 CFU mL−1, and a LOD of 45 CFU mL−1 within 80 min. Moreover, with the output signal compatible across various monitoring methods, this work offers a robust assurance for rapid diagnosis and on-site environmental monitoring of B. pseudomallei.

Hollow Fe3O4/Fe@C nanocubes for broadband microwave absorption spanning low- and high-frequency bands

Rationally constructing hollow structures with heterogeneous interface is usually an effective strategy to regulate the electromagnetic response behavior for lightweight and strong absorption, but achieving low-frequency and broadband absorption is a major challenge. This work adopts a novel Fe(II)/Fe(III) ions regulation strategy to design and synthesize hollow Fe(OH)X (x = 2, 3) nanocubes, which addresses the disadvantages of time-consuming or using etchant. Subsequently, a unique hollow Fe3O4/Fe@C nanoboxes with adjustable magnetic composition and uniformly coated shell have been successfully synthesized by in-situ carbonization with the assistance of phenolic resin and hydrogen thermal reduction. Notably, the different magnetic components induce the magnetic coupling assembly and play a crucial role in determining its electromagnetic parameters, whereas Fe3O4 contributes to more dipole polarization and stronger low-frequency response characteristics. For Fe3O4@C hollow nanoboxes, the minimum reflection loss (RLmin) is as low as –119.9 dB at 2.3 mm, and extremely wide effective absorption bandwidth (EAB) of 11.4 GHz is achieved spanning low-frequency band of 2.8 ∼ 7.2 GHz and high-frequency band of 11.0 ∼ 18 GHz at 5.0 mm. Surprisingly, the Fe3O4@C also has satisfactory EAB20 (RL＜ –20 dB) reaching 7.1 GHz (14.9 ∼ 18 GHz) at a thin thickness of 1.8 mm. The RLmin of other hollow nanoboxes is also below –30 dB, and the EAB is greater than 9 GHz. This study provides a competitive candidate for efficient microwave absorption in complex frequency bands, especially low-frequency bands.

Atomic-scale magnetic doping of monolayer stanene by revealing Kondo effect from self-assembled Fe spin entities

Atomic-scale spin entity in a two-dimensional topological insulator lays the foundation to manufacture magnetic topological materials with single atomic thickness. Here, we have successfully fabricated Fe monomer, dimer and trimer doped in the monolayer stanene/Cu(111) through a low-temperature growth and systematically investigated Kondo effect by combining scanning tunneling microscopy/spectroscopy (STM/STS) with density functional theory (DFT) and numerical renormalization group (NRG) method. Given high spatial and energy resolution, tunneling conductance (dI/dU) spectra have resolved zero-bias Kondo resonance and resultant magnetic-field-dependent Zeeman splitting, yielding an effective spin Seff = 3/2 with an easy-plane magnetic anisotropy on the self-assembled Fe atomic dopants. Reduced Kondo temperature along with attenuated Kondo intensity from Fe monomer to trimer have been further identified as a manifestation of Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between Sn-separated Fe atoms. Such magnetic Fe atom assembly in turn constitutes important cornerstones for tailoring topological band structures and developing magnetic phase transition in the single-atom-layer stanene.

Long-term cold storage of platelets for transfusion based on zwitterionic magnetic microgels

Hypothermic preservation of platelets at 22 °C with an agitation process realizes their rapid transfusion to treat hemorrhage and thrombocytopenia in the clinic. However, platelets suffer from activation, aggregation, and bacterial contamination during storage, resulting in a limited shelf life of 5 days. Cold storage in a refrigerator can effectively prevent bacterial growth, but this condition is challenging to preserve platelets, owing to cold-induced reactive oxygen species (ROS) overproduction or platelet desialylation. Here, we design a zwitterionic magnetic microgel assembly to preserve platelets for a long time without agitation at 4 °C. The microgel assembly can scavenge cold-induced ROS and provide a super-hydrophilic 3D environment to isolate platelets, preventing platelet activation, aggregation, and desialylation. Moreover, the antifouling property of microgel assembly at 4 °C can ensure the anti-bacterial environment for platelets. As a result, the cold storage time of platelets significantly extended to 7 days. This work serves as a springboard for the development of platelet-based clinical applications.

Study on the Speed Control and Heat Dissipation Performance of Cone-tube Permanent Magnet Governor

The speed regulation range, output torque, and heat dissipation performance are important performance indicators of permanent magnet speed regulators. Enhancing the speed regulation range and output torque, and reducing the heat generation power are of significant importance for expanding the application range of permanent magnet speed regulators. To address the issues of a single adjustment process, insufficient heat dissipation space, and inadequate torque transmission capability of the traditional straight-barrel permanent magnet speed regulator, a cone-barrel permanent magnet speed regulator with a magnetic rotor assembly structure was designed through the analysis of the structure and transmission characteristics of the traditional straight-barrel permanent magnet speed regulator. Using the ANSYS Maxwell finite element analysis software, the output torque characteristics of the cone-barrel structure were studied. Considering the effect of eddy current heating, a conjugate heat transfer model for the permanent magnet speed regulator was developed, and the heat dissipation performance of the cone-barrel structure was explored through ANSYS Fluent simulation analysis. The results indicate that compared to the traditional straight-barrel permanent magnet speed regulator, the cone-barrel regulator can provide greater output torque when fully coupled; at maximum power consumption, the air velocity over the surface of the cone-barrel permanent magnet speed regulator conductor is higher, resulting in better heat dissipation and thus a lower operating temperature.

Magnetic field directed assembly of magnetic non-spherical microparticles

This study reports on the fabrication and assembly of anisotropic microparticles as versatile building blocks for directed magnetic assemblies. Although spherical microparticles have received extensive attention, the assembly of non-spherical magnetic microparticles remains underexplored. Herein, we present a fabrication approach that utilizes photolithography and soft lithography to create prism-shaped magnetic microparticles. In order to investigate their assembly, a switching rotating magnetic field was employed. To support our experimental findings, a numerical model which takes into account the magnetic dipole moments induced by the field of other particles was developed. This model helps in understanding the forces and torques governing particle behavior during assembly. Simulations were conducted using the numerical model to complement our experimental findings. In the two particle experiments, attractive magnetic interactions led to various configurations depending on initial positions. For three particles, a tip-to-tip configuration suggested closed or stable ring-like structures. Our work highlights the feasibility of producing highly responsive, non-spherical magnetic microparticles and their potential for assemblies. The versatile fabrication method, coupled with the added degree of freedom conferred by prismatic shapes, opens promising avenues for applications in biology and material science.

Magnetic beads-assisted split DNAzyme cleavage-driven assembly of functionalized covalent organic frameworks for highly sensitive electrochemical detection of microRNA

Specific and sensitive detection of microRNA is significant for early diagnosis of cancer. In this work, a novel electrochemical biosensor was proposed for microRNA-155 detection based on target-triggered magnetic beads (MBs)-assisted split DNAzyme cleavage-driven assembly of functionalized covalent organic frameworks (COFs). COFs were served as efficient nanocarriers of DNA and signal molecules, which acted as electroactive probe with good hybridization ability and cargo loading ability. The MBs-assisted split DNAzyme held the features of easy manipulation, excellent anti-interference ability and increased of the load capacity of DNAzyme for signal amplification. With the presence of target, the cleavage activity of Mg2+-dependent split DNAzyme on MBs was triggered, resulting in the generation of DNA fragments (A1) and the recycling of target. The released A1 participated in the catalytic hairpin assembly process on the electrode, leading to large amount of COFs probe assembled on the electrode to achieve amplified signal output. Using miRNA-155 as a model target, the proposed electrochemical biosensor realized highly sensitive detection of miRNA-155 with a wide liner range from 10 fM to 5 nM and a low detection limit of 1.2 fM. The proposed multiple-amplified biosensing platform demonstrated a novel method for miRNA analysis, holding potential application in early diagnosis of disease.