Magnetic Manipulation Research Articles

Optimized Dynamic Motion Performance for a 5-DoF Electromagnetic Manipulation

High precision manipulation and optimization of actuation current are major concerns in the design of magnetic manipulation systems. In this paper, a flexible magnetic field mapping model has been employed to determine the field distribution of a compact electromagnetic manipulation system in 3D space, and validated by a high-resolution magnetic calibration system and Finite Element Analysis, which enables an improved accuracy and performance of magnetic manipulation. In addition, an iterative current optimization scheme is used to optimize the actuation current through Iterated Tikhonov Regularization. Finally, a feedback control algorithm including a Proportional-Integral-Derivative controller and Extended State Observer is conducted to solve general external disturbance during the autonomous manipulation of magnetic objects. By incorporating magnetic field mapping, feedback control, and current optimization model, the accuracy of the system has been demonstrated by navigating a small-size permanent magnet through predefined trajectories (Z-shaped, spiral curve) with the average position error of 0.27 mm (body length of 1 mm) and maximum average velocity of 3.59 mm/s. Meanwhile, the results showed that the required maximum actuation current was reduced from 4.00 A to 1.81 A. Our work provides a reliable and systematic approach for high-precision magnetic manipulation and optimization of actuation currents.

Magnetic manipulation of discontinuous ferromagnetic fibers in viscous fluids: Dynamics of single fiber alignment

AbstractThe method of fiber morphology manipulation using magnetic field interaction is proposed for single discontinuous steel fibers dispersed in viscous fluids and subjected to low magnetic fields. The goal of this study was to investigate the fiber behavior under different test conditions. The effects of the fluid viscosity, the fiber aspect ratio and the strength of the magnetic field on the dynamics of fiber alignment were analyzed. In‐plane magnetic alignment tests with a single fiber were carried out to avoid fiber‐fiber interactions and fiber clustering. Based on the experimental results, a model to predict ferromagnetic fiber alignment caused by a static unidirectional magnetic field was provided. Existing models focus on the different torques occurring in the realignment process. The presented model is based on single‐term exponential equations and considers all previously mentioned variables. It is shown that a good agreement between experimental data and fiber realignment predictions for single fibers is achieved.

Characterization of a Droplet Containing the Clustered Magnetic Beads Manipulation by Magnetically Actuated Chips

A magnetically actuated chip was successfully developed in this study to perform the purpose of transportation for a droplet containing clustered magnetic beads. The magnetic field gradient is generated by the chip of the two-layer 4 × 4 array micro-coils, which was commercially fabricated by printing circuit board (PCB) technology. A numerical model was first established to investigate the magnetic field and thermal field for such a micro-coil. Consequently, the numerical simulations were in reasonable agreement with the experimental results. Moreover, a theoretical analysis was derived to predict the dynamic behaviors of the droplets. This analysis will offer the optimal operation for such a magnetically actuated chip. This study aims to successfully implement the concept of “digital microfluidics” in “point-of-care testing” (POCT). In the future, the micro-coil chip will be of substantial benefit to genetic analysis and infectious disease detection.

Tuning the Dynamics of Chiral Domain Walls of Ferrimagnetic Films by Magnetoionic Effects

The manipulation of magnetism with a gate voltage is expected to lead the way towards the realization of energy-efficient spintronics devices and high-performance magnetic memories. Exploiting magneto-ionic effects under micro-patterned electrodes in solid-state devices adds the possibility to modify magnetic properties locally, in a non-volatile and reversible way. Tuning magnetic anisotropy, magnetization and Dzyaloshinskii-Moriya interaction allows modifying at will the dynamics of non trivial magnetic textures such as skyrmions and chiral domain walls in magnetic race tracks. In this work, we illustrate efficient magneto-ionic effects in a ferrimagnetic Pt/Co/Tb stack using a ZrO2 thin layer as a solid state ionic conductor. When a thin layer of terbium is deposited on top of cobalt, it acquires a magnetic moment that aligns antiparallel to that of cobalt, reducing the effective magnetization. Below the micro-patterned electrodes, the voltage-driven migration of oxygen ions in a ZrO2 towards the ferrimagnetic stack partially oxidizes the Tb layer, leading to the local variation not only of the spontaneous magnetization, but also of the effective magnetic anisotropy and of the Dzyaloshinskii-Moriya interaction. This leads to a huge increase of the domain wall velocity, which varies from 10 m/s in the pristine state to 250 m/s after gating. This non-volatile and reversible tuning of the domain wall dynamics may lead to applications to reprogrammable magnetic memories or other spintronic devices.

Ferroelectricity controlled chiral spin textures and anomalous valley Hall effect in the Janus magnet-based multiferroic heterostructure

Realizing effective manipulation and explicit identification of topological spin textures are two crucial ingredients to make them as information carrier in spintronic devices with high storage density, high data handling speed and low energy consumption. Electric-field manipulation of magnetism has been achieved as a dissipationless method compared with traditional regulations. However, the magnetization is normally insensitive to the electric field since it does not break time-reversal symmetry directly, and distribution of topological magnetic quasiparticles is difficult to maintain due to the drift arising from external fluctuation, which could result in ambiguous recognition between quasiparticles and uniform magnetic background. Here, we demonstrate that electric polarization-driven skyrmionic and uniform ferromagnetic states can be easily and explicitly distinguished by transverse voltage arising from anomalous valley Hall effect in the Janus magnet-based multiferroic heterostructure LaClBr/In2Se3. Our work provides an alternative approach for data encoding, in which data are encoded by combing topological spin textures with detectable electronic transport.

Magnetic moiré effects and two types of topological transition in a twisted-bilayer hyperbolic metasurface with double-split ring arrays.

Moiré configurations have recently attracted much attention due to their ability to enhance photonic responses and manipulate surface waves in the subwavelength ranges. However, previous studies have usually been focused on natural hyperbolic materials with limitations on patterning procedures, controlling rotation angles, and merely manipulating electric surface plasmons. Here, we theoretically and numerically investigate a novel magnetic moiré hyperbolic metasurface in the terahertz region, which enables two types of topological transition and a plethora of unusual magnetic moiré effects (magnetic surface wave manipulation, dispersion engineering, magic angles, spacer-dependent topological transition, and local field enhancement). This work extends twistronics and moiré physics to the terahertz region and magnetic polaritons, with potential applications in quantum physics, energy transfer, and planarized magnetic plasmonic devices.

Observation of Spin-Splitter Torque in Collinear Antiferromagnetic RuO_{2}.

The spin-splitter effect is theoretically predicted to generate an unconventional spin current with x- and z- spin polarization via the spin-split band in antiferromagnets. The generated torque, namely, spin-splitter torque, is effective for the manipulation of magnetization in an adjacent magnetic layer without an external magnetic field for spintronic devices such as MRAM. Here, we study the generation of torque in collinear antiferromagnetic RuO_{2} with (100), (101), and (001) crystal planes. Next we find all x-, y-, and z-polarized spin currents depending on the Néel vector direction in RuO_{2}(101). For RuO_{2}(100) and (001), only y-polarized spin current was present, which is independent of the Néel vector. Using the z-polarized spin currents, we demonstrate field-free switching of the perpendicular magnetized ferromagnet at room temperature. The spin-splitter torque generated from RuO_{2} is verified to be useful for the switching phenomenon and paves the way for a further understanding of the detailed mechanism of the spin-splitter effect and for developing antiferromagnetic spin-orbitronics.

Magnetic Field Manipulation of Tetrahedral Units in Spinel Oxides for Boosting Water Oxidation

Magnetic field enhanced electrocatalysis has recently emerged as a promising strategy for the development of a viable and sustainable hydrogen economy via water oxidation. Generally, the effects of magnetic field enhanced electrocatalysis are complex including magnetothermal, magnetohydrodynamic and spin selectivity effects. However, the exploration of magnetic field effect on the structure regulation of electrocatalyst is still unclear whereas is also essential for underpinning the mechanism of magnetic enhancement on the electrocatalytic oxygen evolution reaction (OER) process. Here, it is identified that in a mixed NiFe2 O4 (NFO), a large magnetic field can force the Ni2+ cations to migrate from the octahedral (Oh ) sites to tetrahedral (Td ) sites. As a result, the magnetized NFO electrocatalyst (NFO-M) shows a two-fold higher current density than that of the pristine NFO in alkaline electrolytes. The OER enhancement of NFO is also observed at 1 T (NFO@1T) under an operando magnetic field. Our first-principles calculations further confirm the mechanism of magnetic field driven structure regulation and resultant OER enhancement. These findings provide a strategy of manipulating tetrahedral units of spinel oxides by a magnetic field on boosting OER performance.

Bioengineering 3D Neural Networks Using Magnetic Manipulations

AbstractControlling nerve cells to form pre‐designed 3D neural networks that recapitulate the intricate neural interconnectivity in the brain is essential for developing neuronal interfaces and new regeneration approaches. Here, nerve cells within 3D biomaterials are dynamically localized using nano‐based magnetic manipulations. Nerve cells are transformed into magnetic units and their organizational layout is manipulated using external magnetic field gradients. Iron oxide nanoparticles are incorporated into both Pheochromocytoma cell‐line 12 (PC12) cells and primary mice cortical neurons and the magnetized cells are subjected to multiple magnetic fields using pre‐designed magnetic arrays. Their movement is controlled inside multi‐layered 3D collagen scaffolds, which simulate the innate properties of in‐vivo tissue structures. Via these magnetic manipulations, functional 3D microarchitectures of neural networks are created. In light of the clustered and layered structure of the mammalian central nervous system, this strategy paves the way to creating customized 3D tissue architectures for bioengineering applications, enabling a broad range of advanced implementations and providing efficient models for investigating cellular and tissue behavior.

Enhancement of torque efficiency and spin Hall angle driven collaboratively by orbital torque and spin–orbit torque

Spin–orbit torque (SOT) has been extensively applied to magnetization manipulation in low power consumption logic and memory devices. However, it is believed that materials with strong spin–orbit coupling (SOC) are indispensable for magnetic torque generation. Recently, theoretical studies have indicated that the oxides of light materials with weak SOC can provide a sizable orbital torque (OT), inducing magnetization switching. Here, we experimentally report the extreme enhancement of torque efficiency and spin Hall angle through the natural oxidation of Cu with weak SOC in the perpendicularly magnetized Pt/Co/Cu–CuOx multilayers. The values of torque efficiency and spin Hall angle increase by approximately five times by tuning the surface oxidation at room temperature. The comparative analysis of the effective field reveals that the significant enhancement mainly originates from the collaborative drive of the OT at the Cu/CuOx interface and the SOT from the Pt layer. This finding provides a powerful way to engineer the high-efficient spintronic devices through combining OT and SOT to improve the torque efficiency.

Manipulation of swarm ferrofluid droplets on liquid surface

• The high-resolution manipulation based on the fixed module on the liquid surface . Limited the high remanence and the size of the permanent magnet, the high resolution manipulation ferrofluid droplets is difficult to achieve. In this paper, we utilized the simple method to obtain the micro magnetic field to obtain the delicacy control for the microscale ferrofluid. Furthermore, we utilize the fixed module to build the high resolution magnetic field to achieve the letter writing in a small region on the liquid surface. • The low resolution flexible magnetic control based on the digital magnetic control platform. Based on your comments, we design a digital magnetic field-controlled platform to achieve the ability of the digital encode. In this platform, we design two kinds of experiment. The first kind of experiments is the static number/geometry shapes display. Through on and off of the electromagnet in different positions, we obtain the different number or geometry shapes on the liquid surface. The second kind of experiment are the dynamic motion trajectory experiments. We use the digital controlled platform to dynamical letter writing different trajectory/characters. • Sum up, the highlights of the paper are the high-resolution manipulation ferrofluid based on the fixed module and flexible magnetic control based on the digital magnetic control platform. Manipulation of small liquid droplets is critical for many types of research and applications in the field of chemistry, biology, etc. Many methods based on different working principles were proposed to manipulate liquid droplets. Among them, magnetic manipulation is widely used because of its safety and contactless feature. However, current control strategies mainly focus on hydrophobic or superhydrophobic solid surfaces requiring costly special treatments and being vulnerable to external pollution, which is an obstacle for surface reusing. Besides, the existing technologies are difficult to balance size and quantity of liquid droplets. Here, we propose high precision, resolution and the manipulation control methods for achieving manipulation of both single and swarm ferrofluid droplets. Utilizing the proposed methods, we can achieve the letter writing on the liquid surface. The proposed method offers an efficient strategy for manipulation of ferrofluid droplets.

Stable Levitation of Pyrolytic Graphite Above Circular Magnet Arrays

The rotation of circular and annular pyrolytic graphite (PG) disks levitating above circular magnet arrays can be used for a novel method of magnetic manipulation, whereas the condition of stable levitation has not been figured out yet. In this article, a method to analyze the diamagnetic forces sustained by levitated PG is proposed to investigate the mechanism of stable levitation. When using this method, the whole PG disk is divided into multiple regions according to the distribution of magnetic field in order to determine the resultant diamagnetic force. With the help of the method, the exclusive levitation height of PG disk was determined, and the relationship between the relative size of circular and annular disks to magnet and its ability of stable levitation was clarified. The proposed method is the first one able to investigate the position stability of levitated PG and provides insights into local forces without heavy workload of finete element method (FEM) calculation. The analysis results are verified by the simulation of distribution of potential energy and can be a new way of magnetic manipulation.

Electrical manipulation of magnetization in magnetic heterostructures with perpendicular anisotropy

Magnetic materials with perpendicular magnetic anisotropy are significant for spintronics due to their potential to develop high-density magnetic memory with high thermal stability. Many methods have developed to manipulate perpendicular magnetization by electric current or electric field rather than magnetic field for realizing energy-efficient spintronics. In this review, we primarily focus on recent progress on electrical manipulation of perpendicular magnetization through spin-orbit torque and strain-mediated magnetoelectric coupling. We aim to summarize field-free switching of perpendicular magnetization and exchange bias induced by spin-orbit torque in the metallic magnetic heterostructures, spin-orbit torque switching of magnetization in the perovskite oxides, and magnetoelectric control of perpendicular magnetization mediated by piezostrain in multiferroic heterostructures. Finally, our perspectives on electrical manipulation of perpendicular magnetization by spin-orbit torque and magnetoelectric coupling are given to realize practical energy-efficient spintronic devices.

Nonlocal Manipulation of Magnetism in an Itinerant Two-Dimensional Ferromagnet.

Two-dimensional (2D) magnets are crucial in the construction of 2D magnetic and spintronic devices. Many devices, including spin valves and multiple tunneling junctions, have been developed by vertically stacking 2D magnets with other functional blocks. However, owing to limited local interactions at the interfaces, the device structures are typically extremely complex. To solve this problem, the nonlocal manipulation of magnetism may be a good solution. In this study, we use the magneto-optical Kerr effect technique to demonstrate the nonlocal manipulation of magnetism in an itinerant 2D ferromagnet, Fe3GeTe2 (FGT), whose magnetism can be manipulated via an antiferromagnet/ferromagnet interface or a current-induced spin-orbital torque placed distant from the local site. It is discovered that the coupling of a small piece of MnPS3 (∼40 μm2) with FGT can significantly enhance the coercive field and emergence of exchange bias in the entire FGT flake (∼2000 μm2). Moreover, FGT flakes with different thicknesses have the same coercive field at low temperatures if they are coupled together. Our study provides an understanding of the basic magnetism of 2D itinerant ferromagnets as well as opportunities for engineering magnetism with an additional degree of freedom.

Development of a photothermal bead-based nucleic acid amplification test (pbbNAAT) technique for a high-performance loop-mediated isothermal amplification (LAMP)–based point-of-care test (POCT)

We have developed a novel molecular diagnostic platform (photothermal bead-based nucleic acid amplification test; pbbNAAT) that greatly improves the low sensitivity of direct loop-mediated isothermal amplification (LAMP) and allows for specific detection of LAMP amplicons in complex samples. The pbbNAAT integrates specific ligand-functionalized polypyrrole-coated iron oxide particles (PPy@IOs) capable of photothermal conversion and single-molecule magnetic capture of target analytes, the released nucleic acid, and LAMP-amplified products under external light energy control and magnetic manipulations. This allows for sample pretreatment, pbbLAMP amplification, and subsequent amplicon detection with bead-based ELISA in a one-stop microreactor without loss. In addition, photonic heating with PPy@IOs and external light control provide instant and uniform heating for thermolysis and pbbLAMP implementations. Moreover, it generates higher primer annealing stringency for LAMP primers in pbbLAMP; thus, it can detect pathogen-specific DNA accurately and promptly in pathogen-spiked complex materials. The sample pretreatment procedure of pbbNAAT can greatly reduce inhibitors originating from complex samples, which enables the maintenance of maximal enzyme activities for highly sensitive detection. More importantly, the pbbLAMP assay coupled with magnetic capture permits subsequent bead-based ELISA detection to determine true positive LAMP amplicons on PPy@IOs. The pbbNAAT platform has a high tolerance to inhibitors originating from complex samples, high analytical specificity, and limitation of detection (LoD) as low as 8 CFU/reaction to detect E. coli spiked in human whole blood, bovine milk, and can be completed in less than 1 h. Therefore, we believe that pbbNAAT can serve as a suitable direct LAMP platform for on-site POCTs.

Field-Free Magnetization Switching in a Ferromagnetic Single Layer through Multiple Inversion Asymmetry Engineering.

A simple, reliable, and self-switchable spin-orbit torque (SOT)-induced magnetization switching in a ferromagnetic single layer is needed for the development of next generation fully electrical controllable spintronic devices. In this work, field-free SOT-induced magnetization switching in a CoPt single layer is realized by broken multiple inversion symmetry through simultaneously introducing both oblique sputtering and a vertical composition gradient. A quantitative analysis indicates that multiple inversion asymmetries can produce dynamical bias fields along both z- and x-axes, leading to the observed field-free deterministic magnetization switching. Our study provides a method to accomplish fully electrical manipulation of magnetization in a ferromagnetic single layer without the external magnetic field and auxiliary heavy metal layer, enabling flexible design for future spin-orbit torque-based memory and logic devices.

High-Efficiency Magnon-Mediated Magnetization Switching in All-Oxide Heterostructures with Perpendicular Magnetic Anisotropy.

The search for efficient approaches to realize local switching of magnetic moments in spintronic devices has attracted extensive attention. One of the most promising approaches is the electrical manipulation of magnetization through electron-mediated spin torque. However, the Joule heat generated via electron motion unavoidably causes substantial energy dissipation and potential damage to spintronic devices. Here, all-oxide heterostructures of SrRuO3 /NiO/SrIrO3 are epitaxially grown on SrTiO3 single-crystal substrates following the order of the ferromagnetic transition metal oxide SrRuO3 with perpendicular magnetic anisotropy, insulating and antiferromagnetic NiO, and metallic transition metal oxide SrIrO3 with strong spin-orbit coupling. It is demonstrated that instead of the electron spin torques, the magnon torques present in the antiferromagnetic NiO layer can directly manipulate the perpendicular magnetization of the ferromagnetic layer. This magnon mechanism may significantly reduce the electron motion-related energy dissipation from electron-mediated spin currents. Interestingly, the threshold current density to generate a sufficient magnon current to manipulate the magnetization is one order of magnitude smaller than that in conventional metallic systems. These findings suggest a route for developing highly efficient all-oxide spintronic devices operated by magnon current.

Magnetic control over the fundamental structure of atomic wires

When reducing the size of materials towards the nanoscale, magnetic properties can emerge due to structural variations. Here, we show the reverse effect, where the structure of nanomaterials is controlled by magnetic manipulations. Using the break-junction technique, we find that the interatomic distance in platinum atomic wires is shorter or longer by up to ∼20%, when a magnetic field is applied parallel or perpendicular to the wires during their formation, respectively. The magnetic field direction also affects the wire length, where longer (shorter) wires are formed under a parallel (perpendicular) field. Our experimental analysis, supported by calculations, indicates that the direction of the applied magnetic field promotes the formation of suspended atomic wires with a specific magnetization orientation associated with typical orbital characteristics, interatomic distance, and stability. A similar effect is found for various metal and metal-oxide atomic wires, demonstrating that magnetic fields can control the atomistic structure of different nanomaterials when applied during their formation stage.

Bioinspired Microplate Arrays for Magnetically Tuned Dynamic Color

AbstractFast responding and remote controllable dynamic color is critical in many fields such as image display, senors, and camouflage. In this work, inspired by the structural color of hummingbirds, magnetic‐field driven polymer microplate arrays with dynamic iridescence are demonstrated. The microplates are coated with a layer of photonic crystal (PC) assembled by monodispersed polystyrene nanospheres. The structural color of PC is angle‐dependent, which can be dynamically switched by tuning the tilting angle of the microplates. Magnetic field manipulation is achieved by incorporating ferromagnetic NbFeB powder into the polymer film. Pattern display is also demonstrated by pre‐programing the tilting angle of microplates. This strategy enables fast remote control of high‐resolution structural color. It merits potential applications in many fields such as iridescent mark and invisible patterns for anti‐counterfeiting.

Photoelectron-induced quantitative regulation of ferromagnetism in Permalloy at room temperature for photovoltaic flexible spintronics

Flexible spintronics has recently sparked an upsurge due to the growing demand for miniaturization, high-speed, integration and energy-saving in portable and wearable devices. However, the stress/strain during the substrate deformation process is inevitable for flexible spintronic devices and may be available to assist the switching of the magnetization, accordingly. Therefore, combined with the previously discovered high energy efficient sunlight controlled magnetization switching, we propose a bending-insensitive photovoltaic flexible spintronic device constructed by PET/Ta/Permalloy/(PC71BM: PTB7-Th)/Pt heterostructure. The bent device achieved a 281 Oe of maximal ferromagnetic resonance (FMR) field shift by photoelectrons in a reversible manner under the sunlight soaking at room temperature. And the magnetic change as a function of the external light radiation was precisely determined. These findings provide a feasible way to combine the flexible substrate and photoelectrons for energy-saving and precise manipulation of magnetism in bendable spintronic devices.