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Magnetic fluid is a new type of functional materials. The seal of reciprocating shaft is a typical application of the magnetic fluid. However, there is little research on the magnetic fluid reciprocating seals, thus improving the sealing life and seal capacity is the key problem of studying the reciprocating seals. This paper presents a structure of the seal to test the sealing life and other characteristics. The magnetic field of the seal is estimated using the finite-element method. The thickness of the magnetic fluid on the surface of reciprocating shaft and the flow rate of magnetic fluid are obtained theoretically. The experimental result shows that the static seal capacity is related to the fluid volume. The static seal capacity obtained by experiment is approximately equal to the value through the simulation with sufficient magnetic fluid. The relationship between sealing life and the motion of the reciprocating shaft is obtained experimentally. The sealing life decreases rapidly with the increase of the stroke and velocity. [ABSTRACT FROM AUTHOR]

In recent studies, we introduced the concept of functionalized magnetic force as a method to prevent nanoparticles from sticking to vessel walls caused by extensive simulation and in vitro experiments involving a Y-shaped channel. In this paper, we further investigated the effectiveness of the functionalized magnetic force with a realistic 3-D vessel through simulations. For the simulations, we considered a more realistic continuous injection of particles with different magnetic forces and frequencies. Based on the results from our simulation studies, we performed in vivo mice experiments to evaluate the effectiveness of using a functionalized magnetic force to aid magnetic nanoparticles (MNPs) in crossing the blood–brain barrier (BBB). To implement the functionalized magnetic force, we developed an electromagnetic actuator regulated by a programmable direct current power supply. Our results indicate that a functionalized magnetic field (FMF) can effectively prevent MNPs from sticking, and also guide them across the BBB. We used 770 nm fluorescent carboxyl MNPs in this paper. Following intravenous administration of MNPs into mice, we applied an external magnetic field to mediate transport of the MNPs across the BBB and into the brain. Furthermore, we evaluated the differential effects of FMFs (0.25, 0.5, and 1 Hz) and constant magnetic fields (CMFs) on the transport of MNPs across the BBB. Our results showed that an FMF is more effective than a CMF in the transport and uptake of MNPs across the BBB in mice. In particular, applying an FMF with a 3 A current and 0.5 Hz frequency mediated the greatest transport and uptake of MNPs across the BBB in mice. [ABSTRACT FROM PUBLISHER]

This paper presents a method that has been developed to determine the quantity of accumulated magnetic particles in mice tissues using magnetization measurements. Dispersions of platelet Fe3O4 particles with the size of 30–50 nm and a saturation magnetization of $\sim 80$ Am2/kg were intravenously administered to mice. Primary tissues were dried to measure the magnetization. The amounts of Fe3O4 particles accumulated in the tissues were obtained by dividing the magnetization of tissues by the magnetization of Fe3O4 particles under a magnetic field of 39.8 kA/m. A remarkable accumulation of particles was observed in the liver and the spleen, being supported by the observation of tissues using Prussian blue staining. Total Fe3O4 particles accumulated in primary tissues were $\sim 38$ –40 and 40–44 wt% against the particles in administered dispersions with 3 and 0.4 wt% contents, respectively. The method developed in this paper is considered to be effective for verifying magnetic hyperthermia and thermoablation therapies, in which the quantity of accumulated particles directly reflects the heating power required for those therapies. [ABSTRACT FROM AUTHOR]

The soft magnetic composite (SMC), which consists of insulated iron particles, has been used for electric machines and devices. The magnetic permeability of SMC is underestimated when it is assumed that SMC is composed of homogeneous particles without magnetic contact. In this paper, SMC is modeled by the discrete element method, considering the inhomogeneity in particle size and contact among particles. It is shown that the measured permeability of SMC can be reproduced by considering these effects. Moreover, the frequency characteristics of SMC are evaluated by the proposed method, and the Ollendorff formula modified with an anomaly factor is introduced. [ABSTRACT FROM AUTHOR]

In this paper, we report a mixing frequency method (MFM) that has two driving fields, in which one is a high frequency of fH=300 kHz and the other is a low frequency field with fL=500 Hz. Two traditional magnetic particle imaging technologies are compared with an MFM, one with driving field frequency of fM=25 kHz and the other at 10 kHz. An assumed iron–cobalt magnetic nanoparticle (MNP) suspension of which the sizes follow normal distribution is modeled and their magnetic response is modeled by Langevin function. Odd harmonics induced from the nonlinear magnetic response of MNPs under driving fields are extracted from the magnetization response spectroscopy. The signal-to-noise ratio, harmonic strengths at field-free points (FFPs) over strengths at non-FFPs, is defined as an evaluation standard to assess which technology is better for imaging spatial distribution of MNPs. [ABSTRACT FROM PUBLISHER]

This paper presents a simple 2-D model to study the kinematics of capture of 1 \mu \textm diameter magnetic particles (MPs) by a periodic array of magnetic wires, which are aligned perpendicularly to Poiseuille flow in a rectangular 2-D channel in order to suggest improvements in the design of stent-assisted drug-targeting systems. The model examines the following: 1) the kinematics of particles near the wires; 2) the distribution of captured particles across the array of wires; and 3) the final position of particles that are not captured. An external homogenous magnetic field is applied perpendicularly to the axis of the wires and either perpendicular to or along the flow in order to magnetize the particles and the wires to saturation. The trajectories of MPs are determined using the first-order stiff ordinary differential equations that are solved numerically using MATLAB. These trajectories reveal that regardless of the orientation of external magnetizing field, it is always the first wire that captures the MPs. In addition, the particles that are not captured are found to be repelled to the center of the channel when compared with their starting position. This is an unexpected phenomenon indicating that the repulsive effect of the magnetic stent is stronger than the attractive effect, and the simplicity of our model allowed us to expose this previously undiscovered effect. [ABSTRACT FROM PUBLISHER]

We developed an advanced particulate magnetic tape using fine barium ferrite (BaFe) particles with a high broadband signal-to-noise ratio (BB-SNR) and thermal stability. The newly developed tape achieved a BB-SNR 4 dB higher than that of the commercially available BaFe tape used for linear tape-open generation 7 tape-storage systems, at a linear density of 350 kilo flux changes per inch. Furthermore, the thermal decay rate, which is an index of thermal stability, of this tape was sufficiently high, 0.029 dB/decade, although the tape is composed of fine particles. This value is acceptable for long-term archiving over approximately 30 years. This paper describes the characteristics of the new tape particles and medium, which are expected to be employed in the future high-capacity linear tape systems. [ABSTRACT FROM PUBLISHER]

In this paper, the birefringence properties of the magnetic fluid exposed to magnetic field at 300 K were studied by simulation and experimental measurement. In addition, the arrangement of magnetic particles in the magnetic fluid was simulated using Monte Carlo method, and was verified by the experiment. It was concluded that the change of birefringence is influenced by the anisotropy of the magnetic fluid microstructure in the magnetic field. In addition, the sensitivities of the birefringence in simulation and measurement were 1.2245\times 10^\mathrm \mathbf -5 /Gs and 4.4\times 10^\mathrm \mathbf -6 /Gs, respectively, when the magnetic field intensity was in the insensitive interval of 0–300 Gs. In summary, the birefringence of magnetic fluid would increase with the increasing magnetic field intensity, and vice versa. This research on the birefringence characteristics of magnetic fluid could be used in the optical sensing technology. [ABSTRACT FROM PUBLISHER]

The main purpose of this paper is to describe a new algorithmic method to imitate 3-D geometries of soft magnetic composite materials. This method allows constructing various kinds of geometries for experimenting how certain geometric features affect different electromagnetic properties of the materials. Using the geometry imitations, we demonstrate that in order to explain the nonlinear static magnetic behavior of a certain composite, it is not necessary to assume contacts between the neighboring particles in the material. The contacts may instead be replaced by thin gaps. [ABSTRACT FROM AUTHOR]

This paper investigates microwave (MW)-assisted magnetization reversal (MAMR) in dispersed nanosized barium ferrite (BaFe) particles. MAMR in dispersed nanosized BaFe particles was observed using vector network analyzer ferromagnetic resonance spectroscopy with coplanar waveguides, in this investigation. The average size of BaFe particles was 1750 nm3. A frequency-dependent reduction in the switching field was observed in response to an MW impulse of duration 50 ns and with a frequency of approximately 22 GHz. This result suggests that MAMR was observed in dispersed nanosized BaFe particles. [ABSTRACT FROM AUTHOR]

A high-gradient magnetic separator that utilizes two kinds of plate including flat and lattice plates to provide a high-gradient magnetic field and separate magnetic particles from suspension was investigated in this paper. The separation of magnetic particles by in-situ observation has been carried out, and the results indicated that the magnetic particles formed shapes like a spike at the entrance of the separation system where magnetic particles were influenced by the magnetic field. Although long spike shapes were also observed at lower flow rates and lower magnetic field, the spikes appeared to be denser under the conditions of high magnetic field and high flow rates. The results achieved from in-situ observations can provide valuable information for the simulation of such a system. The two most important experimental variables, flow rate and distance between magnets, have been optimized for the separation of magnetic particles from suspension. The most efficient backwash system was also offered to reuse magnetic particles. The suggested system can be used to separate magnetic particles larger than 50 μm where using filter matrix is limited due to fast clogging. [ABSTRACT FROM AUTHOR]

Transportation of microscale subject is important in the MEMS application. In this paper, movement of a non-magnetic particle driven by a chain consisted of several magnetic particles in a rotational field is experimentally manipulated and observed. The results reveal two distinct motion behaviors of the non-magnetic particle depending on its initial position. For an “outer” particle, whose initial position is at the edge of gyration region, the angular movement is most significant at the timing when contacting with the chain. The net rotating angle of an outer particle per contact remains nearly constant regardless of the length of the rotating chain. Nevertheless, interaction with an “inner” particle, whose initial position is well covered by the gyration, would cause the chain drifting, so that its radial distance to the rotational origin varies continuously. As a result, the overall movement of an inner particle follows a spiral-like trajectory with varying radius in each cycle. Based on the experimental measures, a kinematic model is developed, which enables to numerically predict the trajectory of a non-magnetic particle. [ABSTRACT FROM AUTHOR]

We propose a new measurement method for the simultaneous evaluation of permittivity and permeability of small amount of materials in powder, liquid, or gel form. A plastic toroidal case was used to encapsulate non-solid material under test (MUT), and the whole case was subjected to coaxial line analysis. The volume of MUT required for the case was established as approximately 70 $\mu \text{L}$ , and we removed the plastic parts using high-frequency circuit theory. As a result, constant and nearly ideal relative permittivity and permeability of air were confirmed. Measuring permeability at microwave band of magnetic powder above 45 vol% became possible using the proposed method. [ABSTRACT FROM AUTHOR]

The viscosity of a magnetorheological fluid (MRF) changes with the magnetic field; however, the behavior of magnetic particles in an MRF under the application of a magnetic field has not been fully clarified. In our previous work, we proposed a real-time observation system in which the torque is simultaneously measured. Textured poles concentrated on a magnetic field, increasing the transfer of torque. In this paper, the behavior of magnetic particles, such as the formation, fracture, and sliding of clusters, in the presence of textured poles as well as the transfer of torque was investigated by in situ observation using our torque measurement system. With increasing depth of the pole texture, the magnetic-field gradient increased, the magnetic field at the edges of the texture increased, the clusters became concentrated in a narrower region, and the maximum torque increased. These results are expected to lead to the design of more efficient torque transfer devices using MRFs. [ABSTRACT FROM AUTHOR]

The interstitial rare earth–iron compounds exhibiting a variety of magnetocrystalline anisotropies, large saturation magnetization, and high Curie temperature provide the basis for high-performance magnetic materials. In this paper, a manufacturing process for mass production of anisotropic magnetic powders has been successfully developed for Nd(Fe, M)12N (NdFeN) and Sm2Fe17N3 (SmFeN) compounds with uniaxial anisotropy. The magnetic powders of Nd(Fe, M)12N have maximum energy products [(BH)max] around 22 MGOe. The calendar magnets of NdFeN show the rolling anisotropy and have a (BH)max up to 5.9 MGOe with excellent mechanical properties and good anticorrosion ability. The (BH)max of SmFeN magnetic powders is up to 41 MGOe, which is favorable for fabricating high-performance injection magnets and extrusion magnets. On the other hand, it was found that cone or planar anisotropic R2Fe17Nx (R = Ce, Pr, Nd) and paraffin composites can improve the Snoek limit and exhibit a high microwave reflection loss of up to −35 dB at about 14 GHz, presenting an advantage for application as a high-performance thin-layer microwave absorber. These results open up broad prospects for technological applications using interstitial modified compounds. [ABSTRACT FROM AUTHOR]

In order to optimize the preformation of the field free line (FFL) for human-targeted clinical magnetic particle imaging, an advanced design for the generation of FFL with two pairs of concentric circular coils is proposed in this paper. Simulation study using FEM software was performed to study the relationship between the coil geometric parameters and the FFL quality. Particle-swarm optimization algorithm was performed to optimize the coil topology to gain a highly homogenous gradient field. The results demonstrated that high quality FFL can be generated by the concentric circular coil pairs and the topology of the concentric circle coils is also promising for the human target clinical usage, with the rotation of the FFL just perpendicular to the movement direction of patients inside. [ABSTRACT FROM AUTHOR]

Magnetic systems have the potential to control the motion of microparticles and microrobots during targeted drug delivery. During their manipulation, a nominal magnetic force-current map is usually derived and used as a basis of the control system design. However, the inevitable mismatch between the nominal and actual force-current maps along with external disturbances affects the positioning accuracy of the motion control system. In this paper, we devise a control system that allows for the realization of the nominal magnetic force-current map and the point-to-point positioning of paramagnetic microparticles. This control is accomplished by estimating and rejecting the 2-D disturbance forces using an inner loop based on a disturbance force observer. In addition, an outer loop is utilized to achieve stable dynamics of the overall magnetic system. The control system is implemented on a magnetic system for controlling microparticles of paramagnetic material, which experience magnetic forces that are related to the gradient of the field-squared. We evaluate the performance of our control system by analyzing the transient- and steady-state characteristics of the controlled microparticle for two cases. The first case is done without estimating and rejecting the mismatch and the disturbance forces, whereas the second case is done while compensating for these disturbance forces. We do not only obtain 17% faster response during the transient state, but we are also able to achieve 23% higher positioning accuracy in the steady state for the second case (compensating disturbance forces). Although the focus of this paper is on the wireless magnetic-based control of paramagnetic microparticle, the presented control system is general and can be adapted to control microrobots. [ABSTRACT FROM PUBLISHER]

Based on the micromagnetic method using Landau–Lifshitz (LL) or the equivalent LL–Gilbert equations, the motion of magnetic moments can be solved for typical ferromagnetic materials and devices; however, these calculations, in which the magnitude of magnetization moment \vec M in a micromagnetic cell is set to a constant, cannot account for thermal fluctuation effects at finite temperatures. In this paper, a new micromagnetic method is brought up for ferromagnets based on the hybrid Monte Carlo algorithm, such that the magnetic properties—including M – H loops and domain structures—can be obtained at arbitrary temperature below Curie point Tc . At low temperatures below Tc , we test the standard problem 3 of micromagnetics, the results of the new model basically agree with the conventional micromagnetic model using LL equations, but the singularity due to the \vec M\times \vec H term in the LL equations can be avoided, thus the simulated loops are more dependable especially for the soft magnetic materials; in the test for hard magnetic particles, the new model reduces back to the Stoner–Wohlfarth model. At higher temperatures, the new method is checked using a mean-field inspired free-energy model, the $M$ – $H$ loops can also be obtained and the decrease of coercivity versus $T$ can be illustrated. [ABSTRACT FROM PUBLISHER]

The ferrofluids synthesized from platelet magnets in liquid media are quite interesting due to their shape-induced magnetic response. In this paper, the magnetoviscosity of barium ferrite (BaM) ferrofluid is studied to understand the magnetic response of BaM platelet particles. The platelet particles were synthesized by the hydrothermal method and coated with oleic acid. The X-ray diffraction data confirm the platelets consisting of BaM phase. The field-emission scanning electron microscopy and transmission electron microscopy micrographs show hexagonal platelets of 3–5 nm thickness and 50–250 nm in size. The magnetization versus magnetic field plot shows hard ferromagnetic behavior of the nanoparticles. The ferrofluid was synthesized by dispersing coated platelets in paraffin. The flow curves of the ferrofluid exhibit shear thinning with power law behavior in the presence of magnetic field. The yield stress values are determined by extrapolating shear stress versus shear rate plots to zero shear rate at various applied magnetic field values using Herschel–Bulkley equation. The magnetoviscosity, $\eta $ , of the ferrofluid as a function of magnetic field is investigated at various shear rates. The $\eta $ value increases with the increase in magnetic field, reaches a maximum value and then saturates at higher fields. This trend is due to the alignment of platelet-shaped magnetic particles along the direction of magnetic field at different shear rates. With the increase in magnetic field, the interaction between the magnetic nanoparticles and their arrangement becomes stronger leading to stacked plate chain formation. This shows that the variation of magnetoviscosity as a function of shear rate can be controlled by competition between the flow field and the magnetic field. [ABSTRACT FROM PUBLISHER]

In this paper, an open gradient magnetic separator for turbulent flowing water purification has been designed, optimized, and experimentally tested. This device consists of an arrangement of identical electromagnets that operate as capture elements. In the first stage of the optimization, we have identified the optimal size of the elementary capture element and its excitation current that allow the separation of ferromagnetic particles (particle radius Rp< 3\times 10^{{ {-5}}} m) from a water flow of representative velocity ( uf = 0.5 m/s) in a channel of small diameter D= 2.5\times 10^\mathrm -2 m. For this, we have minimized an objective function, which is the distance between the capture site of a given separated particle and the central point of the capture element. For such minimization, the Tabu search method has been applied. Second, we have optimized the number and the arrangement of capture elements that permit the separation for a channel of important diameter D= 5\times 10^\mathrm -2 m and reduced flow velocity uf=0.2 m/s. In this case, the optimization is based on the comparison between the capture efficiencies of several proposed configurations of the separator. To validate the obtained results, experiments have been carried out on a turbulent water flow (Reynolds number Re= 10^{\mathrm { {4}}} ) containing fine ferromagnetic particles ( \mu r= 8 ) with a concentration Cp= 0.8 g/L. The verification is based on the control of the evolution of the separated particles buildup and the quantifying of the volume of separated particles. For such quantifying, the Hall effect sensing technology has been used. [ABSTRACT FROM AUTHOR]

In this paper, we have synthesized multifunctional magnetic particles (MNPs) using by two different ferrite submicrometer paticles (Fe3O4@HP and CoFe2O4@HP) with different surface properties. Two different multifunctional particles have the same particle sizes within the error tolerance of 4.5%. The concentration measurement of the hematoporphyrin (HP) molecule indicates that the weight of HP molecules bonded to the surface of the Fe3O4 particles is smaller than that of the CoFe2O4 particles. Moreover, we have evaluated their biocompatibilities and photodynamic anticancer activities on mammalian cells. The two MNPs have demonstrated that they both have good biocompatibilities without any cytotoxicity and anticancer activities in the concentration range of 0–50 \(\mu \) g/mL. Specifically, photodynamic-killing activities of both MNPs were measured to be 100% for CoFe2O4@HP, and were measured to be 37.9 ± 3.5% and 9.2 ± 2.5% for Fe3O4@HP in 25 and 50 \(\mu \) g/mL of both MNPs. These results suggest that both MNPs can be safely used to for clinical photodynamic cancer therapy, although the CoFe2O4@HP showed a slightly better photo-killing efficacy compared with the Fe3O4@HP in prostate cancer. [ABSTRACT FROM AUTHOR]

In this paper, we derive a quantitative model for the manipulation of superparamagnetic particles by superposition of a homogeneous magnetic field and magnetic field gradients. Our results show that by this combination, the magnitude as well as the sign of the force on a magnetic particle can be controlled. By quantitatively modeling the magnetic force on a representative superparamagnetic particle, we find that for a common lab-on-chip scenario large repulsive forces can be achieved by adding a homogeneous field perpendicular to the plane of the chip. This offers new perspectives for the on-chip manipulation of magnetic particles. As a first example, in-plane positioning of particles with an accuracy of \(\sim 1 \mu \) m is experimentally demonstrated. [ABSTRACT FROM AUTHOR]

This paper presents an integrated solution toward an on-chip microfluidic diagnostic system using the magnetically induced motion of functionalized magnetic microparticles (MPs) in combination with giant magnetoresistance (GMR) sensors. The innovative aspect of the proposed method is that the induced velocity on MPs in suspension, while imposed to a magnetic field gradient, is inversely proportional to their volume. Specifically, a velocity variation of suspended functionalized MPs inside a detection microchannel with respect to a reference velocity, specified in a parallel reference microchannel, indicates an increase in their nonmagnetic volume. This volumetric increase of the MPs is caused by the binding of pathogens (e.g., bacteria) to their functionalized surface. The new formed compounds, which have an increased nonmagnetic volume, are called loaded MPs (LMPs). Experiments with functionalized MPs and LMPs with Escherichia coli attached to their surface were conducted as a proof of concept. Their movement was demonstrated optically by means of a microscope with a mounted CCD camera as well as by measuring the resistance change of the integrated GMR sensors. [ABSTRACT FROM AUTHOR]

Technologies that control matter at the nano- and micro-scale are crucial to realizing engineered systems that can assemble, transport, and manipulate materials at submicron length scales. Two principles: 1) the domain wall structure of patterned magnetic structures and 2) the superparamagnetic properties of nanoparticles, have been previously used to remotely manipulate and transport magnetic entities to specific sites on a platform. In this paper, changes to the energy landscape during transport as well as the local energy profile of individual stationary traps, both of which are central to the functionality of the platform, are evaluated using directed forces and stochastic (Brownian) trajectories of trap-confined microparticles. Hybrid magnetic-fluorescent micelle nanoconstructs, which are compatible with physiological conditions and safeguard functionality of biomaterials, are shown to be viable markers to label and manipulate individual cells across the platform. [ABSTRACT FROM AUTHOR]

Magnetic fluid is a kind of colloidal suspension comprised of magnetic nanoparticles, surfactant, and carried liquid. The microstructure and optical properties of the magnetic fluid have become the research hotspots in recent years. In this paper, a new molecular dynamics method based on rod-like magnetic nanoparticles was used to simulate the microstructure change of the magnetic fluid over time by applying different magnetic field. The results indicated that the effect of the applied magnetic field played an important role on microstructure change. The concept of duty cycle was used to quantitatively analyze the degree of magnetic nanoparticles chaining along the direction of the applied magnetic field. It was found that when the applied magnetic field increased from 45 to 315 Oe, the duty cycle of the microstructure decreased from 0.192 to 0.068. In addition, Monte Carlo method was used to analyze the transmission spectrum of magnetic fluid film. The transmittance at the wavelength of 1500 nm increased from 0.71 to 0.84 when the applied magnetic field increased from 45 to 225 Oe. These results revealed that the magnetic fluid could be well applied in the optical sensing area in the future. [ABSTRACT FROM AUTHOR]

(DyPr)CoFeB microparticles are the building blocks of sintered magnets. The magnetic properties of powdered (DyPr)(CoFe)B microparticles and the effects of annealing, surface states, fixation of easy axis and magnetic dipole interaction on the magnetic hysteresis loop, and temperature dependencies of magnetization have been analyzed. Fixation of the annealed microparticles in polymer enhances the coercive field up to 11 times and the energy product up to six times. This fact indicates extraction of the true magnetic parameters from the magnetic measurements of powder. Thermal stability of the anisotropy field has been improved by the replacement of Fe atoms with Co atoms. [ABSTRACT FROM PUBLISHER]

The paper is dedicated to the micromagnetic study of the temperature dependence of interactions in nanoparticulate systems. This study confirms the hypothesis used In the variable variance Preisach-Neel model concerning the interaction distribution as well as recent experimental evidence. [ABSTRACT FROM AUTHOR]

We report the directed transport of superparamagnetic microbeads (SPBs) on antidot arrays patterned from multilayered Co/Pt films with perpendicular magnetic anisotropy (PMA). The dynamics of water-suspended SPBs driven across the substrate surface by elliptical rotating magnetic fields is studied experimentally and modeled analytically. Bead motion on PMA substrates is shown to be significantly faster than on similarly patterned films based on in-plane magnetized materials. Furthermore, we show different SPB trajectories on different lattice geometries, suggesting that the magnetic potential distribution plays a crucial role in determining the dynamics. Our findings provide new insights into the enhanced transport of SPBs using PMA thin films as stray field sources that enable dynamic magnetic potential landscapes. [ABSTRACT FROM AUTHOR]

Beating of ependymal cilia in the mammalian brain ventricle causes cerebrospinal fluid circulation. Beating of ependymal cilia is studied in vitro in many laboratories but has not been monitored non-invasively in live animals. We have developed a new method for remote sensing of the magnetic flux density changes associated with the reciprocal movement of a magnetic particle bound to cilia in the lateral ventricle of a newborn rat brain with superconducting quantum interference device (SQUID). We detected an oscillatory signal (10–20 Hz and ca. 10 pT amplitude) from a small neodymium magnetic particle attached to cilia with the SQUID above the specimen; the distance between the cilia to the SQUID sensor was 12 mm. This successful detection provides a new sensing platform that enables the non-invasive measurement of beating of ependymal cilia from a live animal. [ABSTRACT FROM AUTHOR]

Magnetic induction field (MIF) of the magnetite particles with five Johnson solid shapes was analyzed using the finite-element method. A new method is proposed to calculate the MIF of irregular magnetite particles by studying their magnetic flux density, and the results show that sphericity is a key factor affecting the MIF of a regular-shaped particle. Moreover, the calculation value of the MIF using particle volume radius ($r$) is more accurate with the higher sphericity. In addition, the relative position is another important factor affecting the accuracy of MIF calculation. The further the distance from the particle center, the more accurate is the MIF. More specifically, when the distance is $4r$ , the average value of the relative difference drops to less than 5.0% with the sphericity of 0.91, 0.92, and 0.93, respectively. Therefore, we suggest that it is feasible to use a sphere MIF instead of an irregular particle MIF to simulate the interaction and motion of massive magnetite particles. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles have drawn attention recently due to their interesting nanoscopic features and potential applications. Various kinds of ferrite nanoparticles with diameters between 3 and 34 nm encapsulated by amorphous SiO2 were functionalized and examined for biomedical applications. From dc and ac magnetic susceptibility measurements, it was found that these particles followed the Néel relaxation system. Co–Zn ferrite (Co0.8Zn0.2Fe2O4) nanoparticles were prepared and the increase in temperature in the ac field was estimated for hyperthermia treatment. In vitro experiments using cultured human breast cancer cells were carried out, and a dramatic hyperthermia effect was observed. As one of the diagnostic methods, magnetic resonance (MR) measurements were performed for CoFe2O4 nanoparticles, and the samples were also evaluated as potential contrast media for MR imaging. [ABSTRACT FROM AUTHOR]

We report on the magnetic properties of NdFeB powders produced by gas atomization, which is a powder manufacturing technology scarcely used in the past to produce such alloys. Using this technique, we have produced several ternary NdFeB alloys with Nd contents between 26.9 wt.% and 28.5 wt.%. The as-atomized powders were split into different size fractions by sieving. Subsequently, we measured the magnetic properties as a function of temperature, between 10 and 400 K, and particle size. The magnetic behavior depends strongly on the microstructure of the material, which in turn is determined by the particle size. It is reported a slope anomaly in the curve of magnetization as a function of temperature at around 150 K due to a spin-reorientation transition. Since gas-atomized powders are isotropic, this magnetic transition produces an increment of the magnetization below this temperature. [ABSTRACT FROM AUTHOR]

We recently developed a SQUID system for magnetic immunoassays which allows fast measurements of the remanent magnetization of samples containing magnetic particles used as markers in biomedical applications. In this paper, we propose to quantify the immunoassays by estimating the specific magnetization of the samples, after magnetic flux measurements and remanent magnetic moment calculations. Since the SQUID and the sample have about the same size, we need to take into account their geometries in order to calculate properly their magnetic moments. This is accomplished by means of mutual inductance calculations. The values for the mass of particles obtained from the specific magnetization are compared with those estimated by using sample dilution factors. [ABSTRACT FROM AUTHOR]

Chemically ordered L10 phase FePt nanoparticles has been considered one of the best candidates for future magnetic recording media with areal density beyond 1 Tbit/in². However, current preparation methods via phase transformation must overcome many obstacles, including particle agglomeration, twinning and difficulty of easy axis alignment. In this paper, the direct preparation of L10 phase FePt nanoparticles without phase transformation and particles' aqueous phase self-assembly are reported. The mechanism for L10 phase formation during nucleation and growth processes are discussed. The unique octahedron shape makes these highly ordered FePt nanoparticles even better choice for advanced magnetic recording media because they tend to form tilted and patterned media simultaneously due to the shape effect. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles (NPs) have attracted attention for their potential use in electronic devices and nano-bioengineering applications. Fe NPs made by thermal decomposition from an Fe(CO)x-Oleylamine (OlAm) reacted precursor show high saturation magnetization (Ms) (\sim 140 emu/gnet at 300 K). However, the Ms never reaches to the bulk value (218 emu/g at 300 K) of iron due to the unique crystalline structure of the Fe NPs. Fe NPs coated with OlAm (OlAm-Fe NP) have an expanded \alpha (b.c.c.) structure and ultra-fine grains. In this paper, we focus on the adsorption ability of the surfactant to improve Ms via control of phase and grain size. Fe NPs with high saturation magnetization were synthesized by thermal decomposition of Fe(CO)5 with some surfactants that had weak absorption ability, such as tribenzylamine, trioctylamine, and their mixture. Slow decomposition rate of Fe(CO)5 and large grain size were obtained by applying surfactants with weak adsorption ability. Especially, Fe NPs that were synthesized by mixed surfactants (mixed surfactant-Fe NPs) have polygonal shape with 6.7 nm in diameter. HRTEM and XRD results suggest that mixed surfactant-Fe NPs are single crystallines of \alpha-Fe. Ms of mixed surfactant-Fe NPs is 194 and 183 emu/gnet at 5 K and 300 K, respectively. These results strongly indicate that single crystallization of \alpha-Fe enhances the Ms of Fe NPs and also suggest that optimization of the surfactant adsorption ability is indispensable to promote the single crystallization of Fe NPs. [ABSTRACT FROM PUBLISHER]

The design of a ring trap for the confinement of magnetic microparticles based on thin-film technology is proposed. The study is conducted with a commercial electromagnetic software, using design specifications obtained from a preliminary analytical and technological study. A two-ring trap system is optimized to obtain the required magnetic flux density able to trap the magnetic microparticles while satisfying the heating constraints. In particular, the temperature in the area where the particles are collected is kept below 37 °C, in order to prevent thermal effects on the particles, allowing their manipulation without bud formation, fragmentation, and hemolysis. The resulting configuration represents a viable solution for the fabrication of microanalytical devices featuring on-chip ring traps without the need of external active cooling systems. [ABSTRACT FROM PUBLISHER]

Ultrashort magnetic field pulses of tens of picoseconds duration are able to reverse the magnetization of a particle if the applied field is perpendicular to the initial magnetization vector. Here, a dual write head structure combining ring and single pole type (SPT) heads is proposed to generate such fields in a recording medium in order to increase the rate at which data can be written. Using such a head, the magnetization reversal time can be reduced to 1/2–1/3 of that when using an SPT head. [ABSTRACT FROM PUBLISHER]

It is revealed that the contact of magnetic particles in soft magnetic composite (SMC) significantly increases the macroscopic permeability. It is shown that Ollendorff’s formula, which assumes homogenous magnetic particles and insulation layers, underestimates the macroscopic permeability of SMC. It is suggested that the excess in the permeability is due to the local contacts among the magnetic particles. The effect of the magnetic contact is evaluated using a magnetic circuit model. [ABSTRACT FROM AUTHOR]

We developed a narrowband magnetic particle imaging (MPI) system that uses third-harmonic signal detection and electrical scanning of the field free point (FFP). Comparing with mechanical scanning, we can decrease the measurement time significantly and increase the signal-to-noise ratio as well. For electrical scanning, we designed and constructed gradient and shift coils. The gradient coil consisting of four pieces of planar coils generated the gradient field with a field gradient of 0.4 T/m at a height of 25 mm from the coil surface. The FFP can be moved ±8 mm by supplying a current of ±6.6 A to the shift coil. Using the developed system, we detected two magnetic nanoparticle (MNP) samples located at a depth of 35 mm below the pickup coil with a spacing of 10 mm. By applying an excitation field of 1 mT at 22.75 kHz, we measured the third-harmonic signal from the MNP samples and obtained a contour map of the signal field in an area of 16 $\times$ 16 mm2. Then, we converted the field map into an MNP distribution using singular value decomposition method. It was shown that the spatial resolution of the reconstructed MNP distribution was improved compared with that of the measured contour map of the signal field. The spatial resolution for MNP detection in MNP distribution was 5 mm and two MNP samples were distinguished clearly. This result indicated that MPI using electrical scanning of the FFP was successfully performed. [ABSTRACT FROM AUTHOR]

Motile magnetotactic bacteria are normally separated from a solution by applying a low intensity (mT) orientating magnetic field. This constrains the bacteria to swim in the required direction. High gradient magnetic separation (HGMS) is a well established method for the extraction of magnetic particles from solutions. This paper reports on the separation properties of both motile and non-motile magnetotactic bacteria using both techniques. A comparison of HGMS separation with low field orientational magnetic separation is made and the conditions under which HGMS becomes beneficial are considered. [ABSTRACT FROM PUBLISHER]

A study of the effect of non-magnetic particles on the magnetic properties of nickel is reported. The presence of inclusions is known to affect the structure sensitive magnetic properties of materials. In this work, two kinds of inclusions, namely, alumina particles and voids were studied and their effects on the magnetic properties were investigated. Powder metallurgy techniques were used to produce nickel compacts with varying amounts of alumina present. While coercivity increased with the volume of inclusions present, initial permeability decreased. Other properties such as remanence and hysteresis loss did not show a significant variation due to their sensitivity to the demagnetizing effects of the inclusions. An attempt has been made in this paper to explain quantitatively the variation in the magnetic properties in terms of the amount of inclusions present. Magnetic property measurements could be a useful non-destructive technique for determining porosity in magnetic materials. [ABSTRACT FROM PUBLISHER]

Accommodation (reptation) is a magnetizing process which occurs when the field is cycled between two extrema. The resulting minor loops do not close upon themselves, but rather approach a closed limit cycle with each application of the applied field extrema. This paper shows that there is significant accommodation in an evaporated nanograin iron powder. The shape of the accommodating loops depends on the applied field extrema. [ABSTRACT FROM PUBLISHER]

Encapsulation of fine metal particles by graphite would not only provide an oxidation protective layer but also acts as a solid lubricant that enables high speed scanning of magnetic tapes against a writing/recording head. In this paper, we propose a novel method to produce the graphite layer on the surface of magnetic particles. First, the surfactant is adsorbed onto the particle and then reduced/decomposed by bombardment with ionized He atoms in the arc discharge chamber. As a result of this treatment, the magnetite particles are uniformly coated with a graphite layer of a few nanometers thick. [ABSTRACT FROM PUBLISHER]

Signal generation in magnetic particle imaging and magnetic particle spectroscopy is generally described via the Langevin function of superparamagnetism. To include the magnetization dynamics, the Langevin function is augmented with a frequency-dependent term derived from the linear Debye model. Here, we extend that expression to cover the dynamics of higher harmonics, where each harmonic is multiplied with a complex-valued weighting factor, obtaining a frequency-domain model for application in the context of viscosity-/binding-dependent magnetic particle spectroscopy measurements. [ABSTRACT FROM AUTHOR]

The Nd–Fe–B magnets were prepared using conventional and microware sintering processes. A finely tuned microwave cavity operating in the 2.45 GHz, which works in single mode of electric field (e-field), was used to investigate the microwave sintering of Nd–Fe–B powders. The highest sintering temperature used was 1173 K, and the sintering lasted up to 610 s. The density of microwave sintered Nd–Fe–B magnets could reach values as high as 7.43 g/cc. We have managed to sinter Nd–Fe–B powders and produce magnets at a fraction of the time and energy used in conventional resistive/radiant heating, which is in excess of 1273 K for many hours, and in many cases after homogenization at high temperatures. [ABSTRACT FROM AUTHOR]

We have developed a 2-D magnetic nanoparticle (MNP) imaging system using an orthogonal gradient field and third-harmonic signal detection. An ac excitation field was applied to generate third-harmonic signals from MNP on the basis of their nonlinear magnetization curves, and a dc gradient field was applied perpendicular to the excitation field. The dependence of the third-harmonic signal on the dc field was very different from that in the conventional parallel case. We obtained a contour map of the signal field from the MNP located at \({\boldsymbol {z}} \) = 35 mm below the pickup coil using an excitation field of 1 mT and gradient field of 0.4 T/m. We could obtain spatial resolution of 10 mm even in this small gradient field. Then, we analyzed the contour map using singular value decomposition (SVD) to improve the spatial resolution of the position estimation of MNP. Using SVD, we converted the field map to the MNP distribution. The spatial resolution was improved from 10 to 6.7 mm. We could clearly distinguish three MNP samples separated with 10 mm spacing located at \({\boldsymbol {z}}\) = 35 mm. [ABSTRACT FROM AUTHOR]

We report the effect of \(\alpha \) -particle irradiation on the magnetic properties of nickel (Ni) nanowires (NWs) arrays with diameter of each NW \(\sim 100\) nm prepared by electrodeposition using anodic alumina oxide (AAO) membranes. Different doses of \(\alpha \) -particles irradiation, up to \(2\times 10^{16}\alpha \vphantom {\sum ^{R^{R}}}\) /cm \(^{2}\) were used to observe the effect. Structural characterization indicates the reduction in crystallinity of Ni NWs after irradiation. Coercivity ( \(H_{c}\) ) was found to increase with \(\alpha \) -particle dose due to the formation of pinning centers. The magnetic easy axis changed direction from in-plane (with AAO template) to the out-of-plane due to the decrease in magnetocrystalline anisotropy by \(\alpha \) -particle irradiation. Furthermore, the effect of \(\alpha \) -particle irradiation on Ni NWs was studied by magnetic Barkhausen noise measurements. [ABSTRACT FROM AUTHOR]

Soft magnetic carbonyl iron (CI)-based magnetorheological (MR) fluids with different loadings of halloysite nanoclay were prepared, in which the MR fluid is a complex colloidal suspension consisting of magnetic particles dispersed in a liquid, showing its rapid, reversible, and tunable change between a liquid-like and solid-like state with an applied external magnetic field. The MR characteristics were measured via rotational tests, in which the flow curves exhibited a non-Newtonian behavior for all investigated samples under applied magnetic fields. Flow curves showed not only the dynamic yield stress change measured as a function of magnetic field strength using a power law fit, but also the existence of a solid-like character. Sedimentation of the MR fluid with and without an additive was also examined. [ABSTRACT FROM AUTHOR]

General principles are developed using a finite element model regarding how time-dependent power dissipation of magnetic nanoparticles can be used to optimize hyperthermia selectivity. To make the simulation more realistic, the finite size and spatial location of each individual nanoparticle is taken into consideration. When energy input into the system and duration of treatment is held constant, increasing the maximum power dissipation of nanoparticles increases concentrations of energy in the tumor. Furthermore, when the power dissipation of magnetic nanoparticles rises linearly, the temperature gradient on the edge of the tumor increases exponentially. With energy input held constant, the location and duration of maximum power dissipation in the treatment time scheme will affect the final energy concentration inside the tumor. Finally, connections are made between the simulation results and optimization of the design of nanoparticle power dissipation time-schemes for hyperthermia. [ABSTRACT FROM PUBLISHER]

Microstructure of magnetic fluid under the applied external magnetic field was simulated by the Monte Carlo method, which could be used to research the transmission characteristics of the magnetic fluid film. Transmittance of a 10 \mum magnetic fluid film at the 1550 nm wavelength was obtained by tracing the path of a single photon in the film, which could be explained by the phenomenon of microstructure change with various applied magnetic fields. Moreover, the transmittances were measured in the experiment when the light direction was, respectively, parallel and perpendicular to the direction of the applied magnetic field. Maximum errors between the experimental and simulation results are \pm8.3\% and \pm4.4\% , respectively, for the above two different cases. In summary, transmittance of magnetic fluid will increase with the increasing of magnetic field intensity when light is parallel to the magnetic field, while transmittance will reduce at first, and then increase with the increasing of the magnetic field intensity when the light is perpendicular to the magnetic field. [ABSTRACT FROM AUTHOR]