Individual Magnetic Particles Research Articles

Nanoscale physical and chemical properties of individual airborne magnetic particles from vehicle emissions

Diesel and petrol powered vehicles are contributors to the magnetic fraction of atmospheric particles in the urban atmosphere. For an assessment of the health effects of vehicle-emitted magnetic particles, the mineralogical characters of particles present in engine exhaust vs. those produced by braking need to be understood. We collected magnetically separated individual particles directly from both brake wear and engine exhaust, from the air inside a car cabin while driving on a motorway, and from the ambient urban atmosphere. The morphologies, sizes, chemical compositions and spatial associations of magnetic particles with other constituents of vehicle emissions were characterized using scanning and transmission electron microscopy techniques. Magnetic separates typically contained particles that were aggregates of a large number of nanocrystals. Particles from engine exhaust, car cabin and urban air were similar, with diameters ∼1–4 μm, consisting predominantly of ∼10 nm-sized, randomly oriented crystals of magnetite and minor hematite. In contrast, brake debris particles were larger (∼1–10 μm in diameter) and contained mostly ∼7 nm-sized hematite, in addition to metallic iron and minor goethite. Particles in all samples comprised carbonaceous constituents besides iron oxides. In the exhaust and ambient particles carbon was present in both amorphous and semi-ordered forms, encompassing the nanocrystals, suggesting a high-temperature formation. In contrast, only amorphous carbon was found in brake wear. Besides the main components (Fe, O, C) several additional elements, including Mg, Al, Si, P, S, Cl, Sn, Ca, Mn, Zn, Cu, Pb and Zr occurred in the particles, with some minor differences between the distinct types of samples. Whereas the overall characteristics of magnetic particles in exhaust emissions were similar to those of ambient particles, the brake emissions produced slightly different particle types, particularly in terms of size and mineralogy. Thus, based on the qualitative assessment of particle properties in direct emissions and ambient air, a significant portion of magnetic particles in urban air appears to originate from vehicle emissions. Although the aggregate particles have sizes in the μm range, they still may represent a potential health risk on inhalation. Synopsis: This article discusses the nanoscale properties of magnetic particles from vehicle emissions, for a better understanding of their sources and health effects. • The magnetic fraction of vehicle-derived airborne particulate matter can be collected using a simple device. • Exhaust emissions may constitute a substantial source of magnetic particles in urban environments. • Magnetic fraction of brake wear predominantly originates from the corrosion of the brake disc. • The primary magnetic agglomerates are small enough to reach the lungs upon inhalation.

Theoretical Modeling of Magnetoactive Elastomers on Different Scales: A State-of-the-Art Review.

A review of the latest theoretical advances in the description of magnetomechanical effects and phenomena observed in magnetoactive elastomers (MAEs), i.e., polymer networks filled with magnetic micro- and/or nanoparticles, under the action of external magnetic fields is presented. Theoretical modeling of magnetomechanical coupling is considered on various spatial scales: from the behavior of individual magnetic particles constrained in an elastic medium to the mechanical properties of an MAE sample as a whole. It is demonstrated how theoretical models enable qualitative and quantitative interpretation of experimental results. The limitations and challenges of current approaches are discussed and some information about the most promising lines of research in this area is provided. The review is aimed at specialists involved in the study of not only the magnetomechanical properties of MAEs, but also a wide range of other physical phenomena occurring in magnetic polymer composites in external magnetic fields.

Magneto-optical studies of kerosene based ferrofluid

Magnetic fluids are technologically important due to their tunable magnetic, electrical and optical properties. The magneto optical properties of ferrofluid have a major role for the development of optoelectronic devices. This paper represents the detailed analysis of kerosene based ferrofluid, their structure and magneto optical properties will be investigated. Iron oxide nanofluids are synthesised by a Co-precipitation method. The X-ray diffraction technique is used for structural characterization. The magneto optical property of the iron oxide nanofluid have been investigated by linear dichroism measurements. Individual magnetic particle’s intrinsic optical anisotropy or shape anisotropy create linear dichroism. The magnetic susceptibility of ferrofluid with different volume fractions is measured using Quincke’s method.

Magnetic hysteresis of individual Janus particles with hemispherical exchange biased caps

We use sensitive dynamic cantilever magnetometry to measure the magnetic hysteresis of individual magnetic Janus particles. These particles consist of hemispherical caps of magnetic material deposited on micrometer-scale silica spheres. The measurements, combined with corresponding micromagnetic simulations, reveal the magnetic configurations present in these individual curved magnets. In remanence, ferromagnetic Janus particles are found to host a global vortex state with vanishing magnetic moment. In contrast, a remanent onion state with significant moment is recovered by imposing an exchange bias to the system via an additional antiferromagnetic layer in the cap. A robust remanent magnetic moment is crucial for most applications of magnetic Janus particles, in which an external magnetic field actuates their motion.

THE ROTATIONAL EFFECT OF MAGNETIC PARTICLES ON CELLULAR APOPTOSIS BASED ON FOUR ELECTROMAGNET FEEDBACK CONTROL SYSTEM

Objectives: Magnetic drug targeting offers the latest popular alternative option to deliver magnetic drug carriers into targeting region body parts through manipulation of an external magnetic field. However, the effectiveness of using an electromagnetic field to manipulate and directing magnetic particles is yet to be established. Methods: In this paper, a homemade cost-effective electromagnet system was built for the purpose of studying the control and directing the magnetic drug carriers. The electromagnet system was built with four electromagnetic sources and tested the capability in directing the particles’ movement in different geometry patterns. Besides that, the creation of the self-rotation of individual magnetic particle clusters was achieved by using fast switching between magnetic fields. This self-rotation allows the possibility of cell apoptosis study to carry out. The system was constructed with four electromagnets integrated with a feedback control system and built to manipulate a droplet of commercially available iron (II, III) oxide nanoparticles to steer the magnetic droplet along different arbitrary trajectories (square, circle, triangle, slanted line) in 2-dimensional. Results: A dynamic magnetic field of 25 Hz was induced for magnetic nanoparticles rotational effect to observe the cell apoptosis. A profound outcome shows that the declining cell viability of the cell lines by 40% and the morphology of shrinking cells after the exposure of the dynamic magnetic field. Conclusion: The outcome from the pilot study gives an idea on the laboratory setup serves as a fundamental model for studying the electromagnetic field strength in applying mechanical force to target and to rotate for apoptosis on cancer cell line study.

Single Particle Multipole Expansions From Micromagnetic Tomography.

Micromagnetic tomography aims at reconstructing large numbers of individual magnetizations of magnetic particles from combining high‐resolution magnetic scanning techniques with micro X‐ray computed tomography (microCT). Previous work demonstrated that dipole moments can be robustly inferred, and mathematical analysis showed that the potential field of each particle is uniquely determined. Here, we describe a mathematical procedure to recover higher orders of the magnetic potential of the individual magnetic particles in terms of their spherical harmonic expansions (SHE). We test this approach on data from scanning superconducting quantum interference device microscopy and microCT of a reference sample. For particles with high signal‐to‐noise ratio of the magnetic scan we demonstrate that SHE up to order n = 3 can be robustly recovered. This additional level of detail restricts the possible internal magnetization structures of the particles and provides valuable rock magnetic information with respect to their stability and reliability as paleomagnetic remanence carriers. Micromagnetic tomography therefore enables a new approach for detailed rock magnetic studies on large ensembles of individual particles.

Automatic Noncontact Extraction and Independent Manipulation of Magnetic Particles Using Electromagnetic Needle

Selective and independent manipulation of microparticles is important for a wide range of applications. Compared to other physical principles, magnetic field is promising due to its ability to penetrate most materials and affect only magnetic objects. However, in most noncontact magnetic manipulation systems, all particles in the workspace are moved simultaneously. This article reports an automatic single-source noncontact magnetic manipulation technique that can selectively extract individual magnetic particles from a population of similar particles and then independently manipulate the extracted particles. We use an electromagnetic needle to create a highly localized magnetic field to achieve the local addressability. The motion of single particles is controlled by adjusting the position of the electromagnetic needle using visual servoing, where two control laws, velocity and position control, have been developed. Experimental results show that a predefined velocity vector can be followed accurately with a directional error of 8.5 $^{\circ }$ and a norm error of 5 $\mu \text{m/s}$ . Similarly, a predefined path can be followed with a position error of 0.5 $\mu \text{m}$ . The capabilities of the proposed method has been demonstrated in four cases: selective extraction of a single particle from a population, separation of two magnetic particles with 10.6 $\mu \text{m}$ initial gap, independent manipulation of four particles, and targeted delivery of two particles onto two separate cells.

Spin-Valve based magnetoresistive nanoparticle detector for applications in biosensing

A magnetoresistive sensor platform for the detection of individual magnetic reporter particles is presented. The sensing scheme is based on the detection of the shift in the sensor’s magnetoresistance-switching field in the presence of magnetic particle(s). A bottom-pinned spin-valve multilayer (Co/Ru/Co)/Cu/(Co/Ru/Co) device structure (with Ta/Ru seed and Ta capping layers) used for the sensor was deposited using ultra-high vacuum magnetron sputtering and patterned using conventional microfabrication techniques. Inexpensive electronics to measure device magnetoresistance (using DC currents) was used for testing. The detection of individual 500nm Fe3O4 nanoparticles as well as the detection of up to ten (10) nanoparticles was demonstrated and verified using scanning electron microscopy (SEM). The developed sensors are readily integratable into a biosensing platform for the detection of biomolecules at ultra-low concentration using magnetic nanoparticles as reporters.

A magnetometer for estimating the magnetic moment of magnetic micro-particles

Magnetic micro-particles find a variety of applications as actuators at the micrometer and nanometer length scales. While the actuation gain is directly proportional to their magnetic moment, there are relatively few technologies available to estimate the magnetic moment of individual magnetic particles. This paper proposes a magnetometer for direct measurement of the magnetic moment of ferromagnetic micro-particles. The magnetometer comprises a novel micro-scale force sensor capable of interacting with magnetic particles and deflecting in response to the force of interaction. It also comprises a high-resolution measurement system, a source of magnetizing field, and a nanopositioner. The principle of operation of the magnetometer is discussed and is shown to enable the determination of the magnetic moment even of the buried magnetic particles, and those of irregular geometry. Subsequently, the force sensor, the measurement system, and the magnetic field sources are designed, fabricated, and calibrated. Finally, the magnetometer is employed to measure the magnetic moments of both fixed and untethered permanent magnetic particles and also of a fixed soft ferromagnetic particle. In all cases, the estimated magnetic moment is shown to agree with the theoretical estimate with an average error of about 16%.

Layer-by-Layer Self-Assembly: Toward Magnetic Films with Tunable Anisotropy

Highly anisotropic magnetic films are possible to fabricate by control of the coupling between individual magnetic particles. Selective control over coupling in the horizontal and vertical directions are of both fundamental and practical interest. Here we show such control in the multiple layer-by-layer (LBL) self-assembly of layered double hydroxide (LDH) nanosheets (x = 1, 2, 3 and 4) with thicknesses of 5–15 nm, co-assembled with 3-aminopropyl-trimethoxysilane (APTS) modified spherical Fe3O4 nanoparticles (APTS-Fe3O4 NPs) on quartz substrates. The electrostatic charge density on the LDH sheets, controlled by the Mg/Al composition ratio, affects the NP packing in a single horizontal layer, while the thickness of the LDH sheets controls magnetic coupling between layers. The tunable magnetic properties (coercivity Hc, saturation magnetization Ms, anisotropy, and blocking temperatures) are measured as a function of these parameters. The maximum saturation magnetizations Ms, 36.3 and 25.1 emu·g–1 in the per...

A statistical simulation of magnetic particle alignment in sediments

S U M M A R Y Sedimentary magnetizations are fundamental to palaeomagnetism, but the mechanisms that control remanence acquisition remain poorly constrained. Observed sedimentary natural remanent magnetizations are often orders of magnitude smaller than the saturation remanent magnetization of the same sediment, which indicates inefficient remanence acquisition. We present a statistical model, based on the vonMises–Fisher distribution, in which magnetic particle reorientations towards an ambient field are considered, without representing the physics of the magnetization acquisition process. The results provide insights into the nature of sedimentary magnetizations. Specifically, an assemblage of randomly oriented magnetic particles can acquire a high-fidelity palaeomagnetic signal with only small rotations (in some cases <1◦) of particles towards the ambient field direction. This demonstrates that the action of a geomagnetic torque on individual magnetic mineral particle orientation may be minor, and that a weak directional bias on an assemblage of particles could be responsible for the typically observed inefficiency of sedimentary remanence acquisition. Additionally, we demonstrate that weak fields produce sedimentary magnetizations with larger directional uncertainties. For natural sediments, however, these uncertainties appear to be small enough to allow reliable recording of directional geomagnetic field behaviour during periods with weak fields, such as palaeomagnetic reversals and excursions.

Novel methods for in situ characterization of individual micro- and nanoscale magnetic particles

Abstract

Single particle demultiplexer based on domain wall conduits

The remote manipulation of micro and nano-sized magnetic particles carrying molecules or biological entities over a chip surface is of paramount importance for future on-chip applications in biology and medicine. In this paper, we present a method for the on-chip demultiplexing of individual magnetic particles using bifurcated magnetic nano-conduits for the propagation of constrained domain walls (DWs). We demonstrate that the controlled injection and propagation of a domain wall in a bifurcation allow capturing, transporting, and sorting a single magnetic particle between two predefined paths. The cascade of n levels of such building blocks allows for the implementation of a variety of complex sorting devices as, e.g., a demultiplexer for the controlled sorting among 2n paths.

Brownian Relaxation of Interacting Magnetic Nanoparticles in a Colloid Subjected to a Pulsatile Magnetic Field

We have investigated and modeled the effect of interaction among magnetic particles and the magnitude and duration of external applied magnetic field on Brownian relaxation in a colloidal suspension. In the case of interacting magnetic particles, Brownian relaxation depends on the interparticle dipole-dipole interaction, which slows down the overall Brownian relaxation process of magnetic particles in the colloidal suspension. The individual magnetic particle experiences torque when a pulsatile magnetic field is applied. The torque due to the external field randomizes the particle rotation similar to that of the thermal energy. A faster Brownian relaxation is observed when individual magnetic particles are magnetized for a short duration. Magnetizing the magnetic particle for a longer duration suppress the rotational motion hence the effect of torque on Brownian relaxation.

The rotating particles probe: A new technique to measure interactions between particles and a substrate

We demonstrate a new probing technique to measure physicochemical interactions between particles and a substrate in a fluid. The technique is based on the measurement of field-induced rotation of individual magnetic particles in contact with the substrate. The parallel measurement of many particles with single-particle resolution gives reliable statistics in a short time. Using this technique, the interaction between streptavidin-coated magnetic particles and a glass substrate is measured for various buffer conditions. Increased binding is quantified for increasing ionic strength and decreasing pH. The results are found to be in agreement with calculations of electrostatic interactions. We also apply the technique to study how binding is reduced by blocking the substrate with albumin.

A Caveat for Single‐Molecule Magnetism: Non‐linear Arrhenius Plots

Single-molecule magnets (SMMs) are molecules that, below a certain temperature (TB), function as individual nanoscale magnetic particles, exhibiting magnetization hysteresis loops. As such, they represent an alternative and molecular (bottom-up) route to nanomagnetism, complementing the top-down approach to traditional magnetic nanomaterials. SMMs also exhibit fascinating quantum behavior such as quantum tunneling of the magnetization (QTM) and quantum phase interference (QPI), showing that they are truly mesoscale entities straddling the classical/quantum divide. The barrier causing slow magnetization relaxation arises from a combination of a large ground-state spin (S) and easy-axis anisotropy (negative zerofield splitting parameter, D). The most studied SMMs are the [Mn12O12 ACHTUNGTRENNUNG(O2CR)16 ACHTUNGTRENNUNG(H2O)4] family with S=10 ground states, and their derivatives, while in recent years others have been discovered. Alternating current (ac) magnetic susceptibility studies are a convenient method of assessing whether a compound might be an SMM; frequency-dependent out-of-phase (c’’M) signals are indicative of the superparamagnet-like properties of an SMM. The variation in signal position with ac frequency can then be used as a source of rate vs T kinetic data, because the c’’M peak maximum is the temperature at which the angular frequency of the oscillating field equals the rate (1/t, where t is the relaxation lifetime) of spin vector reversal. This allows construction of a ln ACHTUNGTRENNUNG(1/t) vs 1/T plot based on the Arrhenius relationship given in Equation (1), the behavior expected of a thermally-activated process over a single barrier :

Analysis of individual magnetic particle motion near a chip surface

We describe an analysis of the dynamics of individual superparamagnetic micro- and nanoparticles in order to quantify their magnetic properties and mobility near a chip surface. The particles are attracted to the chip surface by integrated microscopic current wires. We show that it is possible to accurately analyze particles with a diameter of about 1 μm by the magnetophoretic movement between current wires because of the very high field gradients. This reveals distinct differences in volume susceptibilities of particles with the same outer diameter. Smaller particles are characterized using the technique of confined Brownian motion analysis. By capturing 300 nm particles on a current wire with surface barriers or a focused shape, the magnetization of the particles can be measured with an accuracy better than 10%.

From micro- to nano-SQUIDs: applications to nanomagnetism

Due to a growing interest in quantum information processing based on spin systems, themicro-SQUID technique has been finding new interest and fabrication improvements haveled to nano-SQUIDs. There are two types of nano-SQUIDs: either the cross section of theJosephson junctions is reduced to about 1 nm by using carbon nanotube junctions, orthe loop size is reduced to a few 100 nm. This paper reviews the basic ideas ofthe micro-SQUID technique applied to magnetic nanostructures and shows thatboth types of nano-SQUIDs lead to a significant improvement concerning thedetection of magnetization switching of individual magnetic particles or molecules.

Simplification of the anisotropy-based inclination correction technique for magnetite- and haematite-bearing rocks: a case study for the Carboniferous Glenshaw and Mauch Chunk Formations, North America

SUMMARY An anisotropy-based inclination correction was applied to the Carboniferous Glenshaw Formation from southwestern Pennsylvania. A combination of low-temperature thermal demagnetization followed by alternating field demagnetization isolated a palaeomagnetic remanence direction similar to that previously reported for these rocks. The inclination correction was conducted by fitting the samples’ anisotropy of anhysteretic remanence (AAR) to the theoretical correction curves for a magnetite remanence that yielded a remanence individual magnetic particle anisotropy, the aγ factor, equal to 1.86. Direct measurement of individual particle anisotropy in magnetic grain extracts, yielded an aγ value of 2 in good agreement with the curve fitting technique. The inclination-corrected formation mean directions for these two a factors were statistically indistinguishable. This result shows that curve fitting is an easier, but accurate, method of applying an anisotropy-based inclination correction than direct measurement of the individual grain anisotropy in magnetic grain extracts. The corrected Glendale Formation magnetite-based palaeopole is very similar to haematite-based palaeopoles from the Carboniferous Canadian Maritimes. A new technique is described that extracts the detrital haematite grains from red sedimentary rocks. The measured haematite aγ factors from the Carboniferous Mauch Chunk and Cretaceous Kapusaliang Formations yield values consistent with susceptibility individual particle anisotropies, aχ , determined previously by curve fitting techniques, extending the use of curve fitting for individual particle anisotropy determination to haematite-bearing rocks. However, the corrected Mauch Chunk Formation palaeopole is significantly different from the corrected Glendale Formation palaeopole, calling the accuracy of the Mauch Chunk palaeopole into question. Tectonic strain during folding may have added to the compaction strain in the rocks, leading to an overcorrection of the inclination. A new, inclination-corrected palaeopole for the North American Carboniferous is reported for the Glenshaw Formation at 28.6uN, 119.9uE.

Carbon nanotube based magnetic flux detector for molecular spintronics

AbstractThis work describes the study of a superconducting quantum interference device (SQUID) with single‐walled carbon nanotube (CNT) Josephson junctions. Quantum confinement in each junction induces a discrete quantum dot (QD) energy level structure, which can be controlled with two lateral electrostatic gates. The gates are also used to directly tune the quantum phase interference of the Cooper pairs circulating in the SQUID ring. Optimal modulation of the switching current with magnetic flux is achieved when both QD junctions are in the ‘on’ or ‘off’ state. In particular, the SQUID design establishes that these CNT Josephson junctions can be used as gate‐controlled π junctions. Besides, the CNT‐SQUIDs are sensitive local magnetometers, which are very promising for the study of magnetization reversal of an individual magnetic particle or molecule placed on one of the two CNT Josephson junctions. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)