Ferromagnetic Microparticles Research Articles

Influence of plasticity on the magnetic-field-induced bending deformation in a magneto-active elastomer with superparamagnetic nanoparticles

The influence of residual plastic deformation on the bending deformation of a magnetoactive elastomer (MAE) beam with non-coercive superparamagnetic manganite (La0.6Ag0.2Mn1.2O3) nanoparticles induced by a transverse uniform magnetic field has been studied. It was found that the MAE bending induced by the magnetic field switching-on/switching-off is mainly cyclic elastic. Plastic deformation leads to the emergence of residual bending and hysteresis in the field dependence of the bending. It was shown that the residual bending that appears after the first magnetic field switch-on eliminates the uncertainty of the bending direction at the next magnetization. Due to the residual plastic deformation, the bending direction of the superparamagnetic MAE with nanoparticles does not change when the direction of the applied magnetic field is inverted, in contrast to the MAE with microparticles where the uncertainty of the bending direction is eliminated due to the residual magnetization of weakly coercive ferromagnetic microparticles; therefore, the bending direction changes its sign with magnetic field reversion. In the low fields, the bending value for the MAEs with superparamagnetic particles is proportional to the square of the magnetic field strength. Model estimates on the residual deformation influence on the beam bending at beam magnetization reversal were obtained.

Variation of color of magnetic noise in Er3+ molecular magnets contacting metal surface in ferromagnetic composite

Interaction between single molecule magnets (SMMs) and metal surface is a hot topic promising controllable deposition of SMMs, programmable frequency of magnetic relaxation and addressed reading of information. In this paper, we develop strategy of the Er3+ based SMM functionalization by its penetration inside the arrays of Ferromagnetic Micro Particles (FMPs). We show that predictable residual magnetic field of the FMPs arrays is an effective tool for regulation of the frequency maximum of imaginary magnetic susceptibility. We analyzed color of magnetic noise in respect to physical origin of magnetic relaxation. An additional channel for control over spin noise is formation of chemical bonds between SMM and the FMPs surface. Oxidation of an Er complex transforms 20 ± 5 % of the initial 10-coordinated SMM complex to the 9-coordinated complex with reduced relaxation time. Memorized residual magnetization of the composite material allows one to set desirable relaxation frequency in the individual micronized cells to create a sound frequency register. The proposed compaction of SMMs of different types in ferromagnetic composites provides engineering of the chemically designed spin interface on ferromagnetic surface for spintronics and quantum computing.

3D-Printed ferromagnetic Liquid Crystal Elastomer with Programmed Dual-Anisotropy And Multi-Responsiveness.

Liquid crystal elastomers (LCE) and magnetic soft materials are promising active materials in many emerging fields, such as soft robotics. Despite the high demand for developing active materials that combine the advantages of LCE and magnetic actuation, the lack of independent programming of the LCE nematic order and magnetization in a single material still hinders the desired multi-responsiveness. In this study, we developed a ferromagnetic LCE (magLCE) ink with nematic order and magnetization that can be independently programmed to be anisotropic, referred to as dual anisotropy, via a customized 3D printing platform. The magLCE ink was fabricated by dispersing ferromagnetic micro-particles in the LCE matrix, and a 3D printing platform was created by integrating a magnet with 3-DoF motion into an extrusion-based 3D printer. In addition to magnetic fields, magLCEs can also be actuated by heating sources (either environmental heating or photo-heating of the embedded ferromagnetic microparticles) with a high energy density and tunable actuation temperature. We demonstrated a programmed magLCE strip robot with enhanced adaptability to complex environments (different terrains, magnetic fields, and temperatures) using a multi-actuation strategy. The magLCE also has potential applications in mechanical memory, as demonstrated by the multi-stable mechanical metastructure array with remote writability and stable memory. This article is protected by copyright. All rights reserved.

Lab‐in‐a‐Bead: Magnetic Janus Bead Probe for the Detection of Biomarkers in Blood

AbstractRemotely handled miniaturized colorimetric sensor platforms with multiple functionalities are able to mimic conventional laboratory operations with reduced assets. The integration of a magnetic phase in a miniaturized hydrogel sensor system allows the manipulation of the sensor, under a magnetic field, in a programmable manner. However, dark color interferences from conventional magnetic phases (Fe3O4, Fe2O3, and Fe micro/nanoparticles) affect the signal readout, hindering the colorimetric response. Therefore, a novel Janus bead configuration is introduced and tested by the localized incorporation of ferromagnetic iron microparticles into a TiO2 nanotubes/alginate hydrogel bead biosystem, under an applied magnetic field. The so‐called hydrogel Janus bead shows both, magnetic translocation and biosensing properties in the same bead. These beads are used for the direct colorimetric analysis of biomarkers in blood. The surface of the Janus bead prevents the biofouling of red blood cells, keeping the sensor surface clean for accurate optical colorimetric analysis. Moreover, the external magnetic manipulation of the bead permits precise control of the time and position of the bead in the sample. Therefore, multiple functionalities are presented by a single magnetic TiO2 nanotubes/alginate Janus bead such as actuation, low biofouling, and sensing, positioning this technology as a truly Lab‐in‐a‐Bead System.

Soft Multi-Material Magnetic Fibers and Textiles.

Magnetically responsive soft materials are promising building blocks for the next generation of soft robotics, prosthesis, surgical tools, and smart textiles. To date, however, the fabrication of highly integrated magnetic fibers with extreme aspect ratios, that can be used as steerable catheters, endoscopes, or within functional textiles remains challenging. Here, we propose multi-material thermal drawing as a material and processing platform to realize 10s of meters long soft, ultra-stretchable, yet highly resilient magnetic fibers. We demonstrate fibers with a diameter as low as 300μm and an aspect ratio of 105 , integrating nano-composite domains with ferromagnetic micro-particles embedded in a soft elastomeric matrix. With the proper choice of filler content that must strike the proper balance between magnetization density and mechanical stiffness, we show fibers withstanding strains of more than 1000%, that can be magnetically actuated and lift up to 370 times their own weight. The magnetic fibers can also integrate other functionalities like micro-fluidic channels, and be weaved into conventional textiles. We show that the novel magnetic textiles can be washed and sustain extreme mechanical constraints, as well as be folded into arbitrary shapes when magnetically actuated, paving the way towards novel intriguing opportunities in medical textiles and soft magnetic systems. This article is protected by copyright. All rights reserved.

Rapid magnetically directed assembly of pre-patterned capillary-scale microvessels.

Capillary scale vascularization is critical to the survival of engineered 3D tissues and remains an outstanding challenge for the field of tissue engineering. Current methods to generate micro-scale vasculature such as 3D printing, two photon hydrogel ablation, angiogenesis, and vasculogenic assembly face challenges in rapidly creating organized, highly vascularized tissues at capillary length-scales. Within metabolically demanding tissues, native capillary beds are highly organized and densely packed to achieve adequate delivery of nutrients and oxygen and efficient waste removal. Here, we adopt two existing techniques to fabricate lattices composed of sacrificial microfibers that can be efficiently and uniformly seeded with endothelial cells (ECs) by magnetizing both lattices and ECs. Ferromagnetic microparticles (FMPs) were incorporated into microfibers produced by solution electrowriting (SEW) and fiber electropulling (FEP). By loading ECs with superparamagnetic iron oxide nanoparticles (SPIONs), the cells could be seeded onto magnetized microfiber lattices. Following encapsulation in a hydrogel, the capillary templating lattice was selectively degraded by a bacterial lipase that does not impact mammalian cell viability or function. This work introduces a novel approach to rapidly producing organized capillary networks within metabolically demanding engineered tissue constructs which should have broad utility for the fields of tissue engineering and regenerative medicine.

A Terahertz Radiation Linear Polarizer Based on Using a Magnetic Fluid in an External Magnetic Field

A model of a magnetically controlled linear polarizer of terahertz (THz) waves based on a cell filled with a magnetic fluid and controlled by an external magnetic field was proposed. The magnetic fluid consisted of a synthetic oil with high transparency in the THz range and ferromagnetic alloy microparticles. Selection of the ferromagnetic particles size and concentration, and also parameters of the external magnetic field was conducted. It was shown that when using ferromagnetic particles of 10–35 μm size, a concentration of 10 wt.%, and a magnetic field with induction of 6.7–57.2 mT, the created construction works as a linear polarizer of the THz wave in the ranged from 0.3 to 1.5 THz, with the degree of polarization of the initially non-polarized THz wave transmitted through the cell being at least of 80%.

Reprogrammable magnetization pattern and shape morphing of phase-change magnetic soft composites

Magnetic soft composites with programmable magnetization patterns are highly desirable for diverse applications due to their multimodal magnetic response and locomotion. Despite substantial progress achieved in magnetic programming approaches, reprogrammable magnetization using low magnetic fields is still in development and challenging. Here, we report a one-step multi-direction magnetic reorientation strategy capable of reprogramming magnetization patterns in soft composites consisting of an elastomer matrix and magnetized ferromagnetic microparticles encapsulated by a phase-change polymer. Our approach is first based on the overall heating of these soft composites to achieve polymer phase transition, and then use magnet arrays to locally regulate the magnetic field distribution to achieve magnetic reorientation and programmable magnetization. Importantly, this approach allows us to reconstruct the desired magnetization patterns by reheating and redesigning the applied magnetic field. Using this approach, we numerically and experimentally demonstrate that multimodal magnetization and deformation patterns of millimeter-level strip-shaped and multi-arm phase-change soft composites can be achieved without changing the composite structure and the externally applied magnetic field. Furthermore, we demonstrate its functional applications in developing a multistate circuit switching, as well as a flexible magnetic recording that can present a variety of information such as numbers, letters, and face-based patterns.

3D printing of high-precision and ferromagnetic functional devices

The development of projection-based stereolithography additive manufacturing techniques and magnetic photosensitive resins has provided a powerful approach to fabricate miniaturized magnetic functional devices with complex three-dimensional spatial structures. However, the present magnetic photosensitive resins face great challenges in the trade-off between high ferromagnetism and excellent printing quality. To address these challenges, we develop a novel NdFeB-Fe3O4 magnetic photosensitive resin comprising 20 wt.% solid loading of magnetic particles, which can be used to fabricate high-precision and ferromagnetic functional devices via micro-continuous liquid interface production process. This resin combining ferromagnetic NdFeB microparticles and strongly absorbing Fe3O4 nanoparticles is able to provide ferromagnetic capabilities and excellent printing quality simultaneously compared to both existing soft and hard magnetic photosensitive resins. The established penetration depth model reveals the effect of particle size, solid loading, and absorbance on the curing characteristics of magnetic photosensitive resin. A high-precision forming and ferromagnetic capability of the NdFeB-Fe3O4 magnetic photosensitive resin are comprehensively demonstrated. It is found that the photosensitive resin (NdFeB:Fe3O4 = 1:1) can print samples with sub-40 μm fine features, reduced by 87% compared to existing hard magnetic photosensitive resin, and exhibits significantly enhanced coercivity and remanence in comparison with existing soft magnetic photosensitive resins, showing by an increase of 24 times and 6 times, respectively. The reported NdFeB-Fe3O4 magnetic photosensitive resin is anticipated to provide a new functional material for the design and manufacture of next-generation micro-robotics, electromagnetic sensor, and magneto-thermal devices.

Spin noise in Er3+ single-ion magnets surrounded by ferromagnetic microparticles

Ferromagnetic microparticles significantly affect spin relaxation in the Er3+ single-ion magnet sandwiched in a composite material. The balance of thermal spin noise corresponding to Orbach, Raman, quantum tunneling, and direct relaxation channels is shifted in Er3+ complexes under the influence of surrounding ferromagnetic matrix. There are two competing sources of the electron spin noise controlled by ferromagnetic media. First, internal residual magnetic field delays spin relaxation in the Er3+ complexes due to the Zeeman interaction of the Er3+ spin even in the absence of external magnetic field. Second, chemical bonding between the Er 4d shell and the O 1s shell accelerates magnetic relaxation in the Er3+ ions on the surface of microparticles. Significance of these results is that composite media can be sliced into small elements with a variable frequency of spin noise depending on individual magnetization programmed within each element.

Interaction of [Er(HL)(L)]·4CHCl3·H2O Single-Ion Magnet Complexes with Ferromagnetic Microparticles

A new method is developed to control the spin relaxation in single-molecular magnets (SMMs) in order to eliminate spin decoherence to the level acceptable for quantum computing at a relaxation frequency of about 102 Hz and a temperature of 2 K. A significant part of the SMMs has rapid magnetic relaxation proceeding through several parallel channels sensitive to the presence of an external magnetic field. Some of the relaxation channels in such materials (also called single-ion magnets (SIMs)) are suppressed using an electromagnet in macroscopic volumes of complexes. This is unacceptable when individual SIM complexes are used as qubits and forces us to look for ways to use a local magnetic field and other types of complex interactions in a specially selected environment, which provides the Zeeman interaction in the absence of an external field. We demonstrate that a composite material made of SIM complexes with Er3+ ions and ferromagnetic microparticles exhibits a remanent magnetization, which is sufficient to decrease the spin relaxation frequency in the volume. In magnitude, this effect competes with the well-known effect of hybridization of the orbitals of a complex during its interaction with a metallic surface. Therefore, the microstructuring of an array of complexes in a ferromagnetic matrix can be used to create local regions with a controlled magnetic relaxation frequency

Simultaneous Optical Trapping and Electromagnetic Micromanipulation of Ferromagnetically Doped NaYF4 Microparticles

Optical trapping allows the trapping and manipulation of dielectric microparticles. However, full control over all six degrees of freedom of the trapped object is challenging. Here, we use ferromagnetic iron-doped upconversion microparticles for simultaneous optical trapping and magnetic micromanipulation that allows full control over all translational and rotational degrees of freedom. These microparticles have a low absorption that allows optical trapping and a high coercivity and saturation magnetization that allow magnetic manipulation. The particles will enable micromanipulation experiments, for example, in single-molecule biophysics.

Comparison of the domain structure reaction of various ferromagnetic microparticles under uniaxial mechanical stress

The results of studying the changes in the domain structure of a planar square microparticle with size 7.5 x 7.5 x 0.04 μm under uniaxial mechanical stress is presented. Microparticles were made from the following materials: permalloy (18% Fe, 82% Ni), permendur (50% Co, 50% Fe), halfenol (16% Ga, 84% Fe), Ni, terfenol (Tb0.3Dy0.7Fe1.92). The conclusions about the promising of using these materials for fabrication microsensors for stress detection and for fabrication straintronic devices for processing and storing information were made. Keywords: magnetoelastic effect, magnetic force microscopy, planar ferromagnetic particles, domain structure.

Gas generation due to photocatalysis as a method to reduce the resistance force in the process of motors motion at the air–liquid interface

HypothesisThe problem of the development of miniature motors able to move on the air–liquid interface at low Reynolds numbers is a crucial challenge due to dominating role of viscous force. To solve this problem the chemical generation of gas can be used. Generated gas pushes liquid out from the surfer surface, so the resistance force is reduced. ExperimentsSurfer composed of TiO2 nanoparticles and ferromagnetic cobalt microparticles moves at the interface of an aqueous solution of hydrogen peroxide under the action of magnetic force. After irradiation with UV or visible light, the gas cavern is formed at the surfer surface due to photo-catalytic decomposition of hydrogen peroxide. As a result, the area of surfer contact with liquid is reduced. FindingsThe resistance force acting on the surfer is reduced due to the liquid pushing out from the surfer surface. This effect is strengthened with the increase in the intensity of gas generation. The resistance force is increased when increasing the liquid viscosity or using a surfactant. The proposed method allows control of the velocity of the motors in a rather wide range by changing the gradient of the magnetic field and parameters of light.

Magnetoactive elastomers based on ferromagnetic and ferroelectric particles: A FORC approach

Composites based on ferromagnetic (FM) microparticles or a mixture of FM and ferroelectric (FE) microparticles embedded into a soft polymer matrix were studied. This class of materials belongs to magnetoactive elastomers (MAE) which received renewed interest stimulated by breakthroughs in their applications, for example, in soft robots and biomedical technologies. Moreover, the MAE with a mixture of FM and FE particles exhibit multiferroic properties which open new ways for their application. Here, the magnetic properties of this type of material were studied using the First Order Reversal Curve (FORC) method in terms of local distributions of the switching fields and interaction fields. In particular, the influence of FE particles on the magnetization reversal processes was determined. The latter is related to the influence of FE particles on the structural properties of the polymer and the possibility of displacement of FM particles in the matrix.

FORC analysis of magnetically soft microparticles embedded in a polymeric elastic environment

First-order reversal curve (FORC) analysis allows one to investigate composite magnetic materials by decomposing the magnetic response of a whole sample into individual responses of the elementary objects comprising the sample. In this work, we apply this technique to analysing silicone elastomer composites reinforced with ferromagnetic microparticles possessing low intrinsic coercivity. Even though the material of such particles does not demonstrate significant magnetic hysteresis, the soft matrix of the elastomers allows for the translational mobility of the particles and enables their magnetomechanical hysteresis which renders into a wasp-waisted major magnetization loop of the whole sample. It is demonstrated that the FORC diagrams of the composites contain characteristic wing features arising from the collective hysteretic magnetization of the magnetically soft (MS) particles. The influence of the matrix elasticity and particle concentration on the shape of the wing feature is investigated, and an approach to interpreting experimental FORC diagrams of the MS magnetoactive elastomers is proposed. The experimental data are in qualitative agreement with the results of the simulation of the particle magnetization process obtained using a model comprised of two MS particles embedded in an elastic environment.

A feedback-based manoeuvre planner for nonprehensile magnetic micromanipulation of large microscopic biological objects

This paper reports a feedback-based manoeuvre planning approach for automated nonprehensile selective micromanipulation of large, microscopic biological objects (∼100μm). We employ ferromagnetic micro-particles as microrobots actuated via a global magnetic field produced by electromagnetic coils placed in quadrupole configuration. The microrobot motion is programmed to push the target object to the goal location. We employ a three-step approach comprising: (a) generate a collision-free optimal path between the initial and the commanded goal location, (b) generate a manoeuvre planning algorithm that invokes one of the three motion manoeuvres, namely, ‘approach’, ‘push’, and ‘align’ depending upon the instantaneous locations of the microrobot, target object, and the desired waypoint, and (c) deploy a simple proportional controller that determines the currents required in the electromagnetic coils that can produce a suitable magnetic field for executing the manoeuvre invoked by the manoeuvre planner. This paper reports a number of validation experiments conducted on both zebrafish, i.e., Danio rerio embryos and silica beads as target objects. We envisage that the developed inexpensive approach can be useful in robotic manipulation of biological objects with sizes in hundreds of microns including large biological cells, polyploid giant cancer cells (PGCC), multicellular spheroids, Dictyostelium slug, human oocytes, and autophagy candidates. We also believe that functionalizing the microrobots with living cells or suitable chemicals will make it possible to perform on-chip biological experiments in future.

Spin Relaxation in Single-Ion Magnets under the Slowing Down Effect Produced by the Stray Field of Ferromagnetic Microparticles

Spin Relaxation in Single-Ion Magnets under the Slowing Down Effect Produced by the Stray Field of Ferromagnetic Microparticles

Reprogrammable Ferromagnetic Domains for Reconfigurable Soft Magnetic Actuators.

Soft magnetic materials have shown promise in diverse applications due to their fast response, remote actuation, and large penetration range for various conditions. Herein, a new soft magnetic composite material capable of reprogramming its magnetization profile without changing intrinsic magnetic properties of embedded magnetic particles or the molecular property of base material is reported. This composite contains magnetic microspheres in an elastomeric matrix, and the magnetic microspheres are composed of ferromagnetic microparticles encapsulated with oligomeric-PEG. By controlling the encapsulating polymer phase transition, the magnetization profiles of the magnetic composite can be rewritten by physically realigning the ferromagnetic particles. Diverse magnetic actuators with reprogrammable magnetization profiles are developed to demonstrate the complete reprogramming of complex magnetization profile.

Ferromagnetic Liquid Metal Putty-Like Material with Transformed Shape and Reconfigurable Polarity.

It is remarkably desirable and challenging to design reconfigurable ferromagnetic materials with high electrical conductivity. This has attracted great attention due to promising applications in many fields such as emerging flexible electronics and soft robotics. However, the shape and magnetic polarity of existing ferromagnetic materials with low conductivity are both hard to be reconfigured, and the magnetization of insulative ferrofluids is easily lost once the external magnetic field is removed. A novel reconfigurable ferromagnetic liquid metal (LM) putty-like material (FM-LMP) with high electrical conductivity and transformed shape, which is prepared through homogenously mixing neodymium-iron-boron microparticles into the gallium-based LM matrix, and turning this liquid-like suspension into the solid-like putty-like material by magnetization, is reported to achieve this. The induction magnetic field of FM-LMP is mainly attributed to the magnetic alignment of the dispersed ferromagnetic microparticles, which can be conveniently demagnetized by mechanical disordering and reversibly reconfigured through microparticle realignment by applying a weak magnetic field. FM-LMP with a low fraction of microparticles can be used as printable conductive ink for paper electronics, which are further exploited for applications including magnetic switching, flexible erasable magnetic recording paper, and self-sensing paper-based soft robotics using magnetic actuation.