Ferromagnetic Particles Research Articles

The Microwave Absorption in Composites with Finemet Alloy Particles and Carbon Nanotubes.

The absorption of waves of the centimeter and millimeter wavebands in composites with Finemet alloy particles and carbon nanotubes has been studied. It has been established that ferromagnetic resonance and antiresonance are observed in such composites. A method is proposed for calculating the effective dynamic magnetic permeability of a composite containing both a random distribution of ferromagnetic particles and a part of the particles oriented in the same way. In the approximation of effective parameters, the dependences of the transmission and reflection coefficients of microwaves are calculated. It is shown that the theoretical calculation confirms the existence of resonant features of these dependences caused by ferromagnetic resonance and antiresonance. The theory based on the introduction of effective parameters satisfactorily describes the course of the field dependence of the coefficients and the presence of resonance features in these dependences. The frequency dependence of the complex permittivity of the composite is determined. The dependence of the complex magnetic permeability on the magnetic field for millimeter-wave frequencies is calculated.

Silver Nanoflakes-Enhanced Anisotropic Hybrid Composites for Integratable Pressure Sensors.

Flexible pressure sensors based on polymer elastomers filled with conductive fillers show great advantages in their applications in flexible electronic devices. However, integratable high-sensitivity pressure sensors remain understudied. This work improves the conductivity and sensitivity of PDMS-Fe/Ni piezoresistive composites by introducing silver flakes and magnetic-assisted alignment techniques. As secondary fillers, silver flakes with high aspect ratios enhance the conductive percolation network in composites. Meanwhile, a magnetic field aligns ferromagnetic particles to further improve the conductivity and sensitivity of composites. The resistivity of the composite decreases sharply by 1000 times within a tiny compression strain of 1%, indicating excellent sensing performance. On the basis of this, we demonstrate an integratable miniature pressure sensor with a small size (2 × 2 × 1 mm), high sensitivity (0.966 kPa-1), and wide sensing range (200 kPa). Finally, we develop a flexible E-skin system with 5 × 5 integratable sensor units to detect pressure distribution, which shows rapid real-time response, high resolution, and high sensitivity.

Spark Plasma Sintered Soft Magnetic Composite Based on Fe-Si-Al Surface Oxidized Powders.

Soft magnetic composites (SMCs) need a stable matrix to apply heat treatments for enhancing their magnetic characteristics. A stable matrix can be offered by alumina, but the densification of the ferromagnetic particles covered by this oxide (by sintering) can be very difficult. This paper proposes a feasible synthesis route for obtaining alumina matrix SMCs. An Fe-Si-Al alloy with nominal composition Fe85Si9Al6 was obtained by mechanical alloying of elemental Fe, Si, and Al powders, and further, the as-milled powders were superficially oxidized by immersion in HCl solution. The oxide layer was composed of iron, silicon, and aluminum oxides, as the Fourier-transform infrared spectroscopy technique revealed. The Fe-Si-Al@oxide powder was densified by the spark plasma sintering technique-SPS. Upon sintering, a continuous matrix of oxide (mainly alumina) was formed by the reaction of the Fe-Si-Al powder coreswith their oxide layer. The main part of the composite compacts after sintering consisted of an Fe3Si-ordered phase dispersed in an oxide matrix. The DC and AC tests of magnetic composite compacts showed that upon increasing the sintering temperature, the density, magnetic induction, and magnetic permeability increased. The initial magnetic permeability was constant in the entire range of testing frequencies and the magnetic losses increased linearly. The stability of the magnetic characteristics in frequency is promising for developing further such types of magnetic composite.

Magnetic Field Sensing Using Tapered Small-Core Optical Fibre Surrounded by Different Concentrations of Magnetic Fluid.

In this paper, a high-sensitivity magnetic field sensor based on a single-mode-tapered small-core-single-mode (STSCS) optical fibre structure is investigated. The tapered small-core section of STSCS is surrounded by magnetic fluid (MF) containing ferromagnetic particles (FMPs) of different concentrations. The FMPs align themselves along the magnetic field, depending on the strength of the magnetic field. This alignment of FMPs changes the refractive index around the tapered small-core section, which in turn changes the output spectral response of the STSCS optical fibre structure. The change in spectral response is then calibrated for sensing the magnetic field strength. This paper also investigates the effect of both the taper waist diameter of the STSCS optical fibre structure and the concentration of MF surrounding it on the magnetic field sensitivity. The maximum sensitivity demonstrated in this paper is 0.46 nm/mT for a taper waist diameter of 10 μm surrounded by 1.22% FMPs in the MF. The magnetic sensor demonstrates reversible results, and its effects on the orientation of the magnetic field along the X-Y, X-Z and Y-Z axes are also investigated, which suggest that the sensor is capable of vector magnetic field measurement.

A novel film eddy current probe having a detection coil interleaved to the excitation coil and the amplified effect by ferromagnetic amorphous alloys particles

This paper presents the development of a square-film eddy current (EC) probe with a detection coil interleaved to the excitation coil to detect cracks on the surface of aluminum. The probe with an interleaved design between the detection coil and the excitation coil can eliminates the distance between the test piece surface and both coils and improves the signal-to-noise ratio. Furthermore, iron-based ferromagnetic amorphous alloy particles (FAAP) without conductivity placed above the probe to increase the magnetic flux density and enhance the ECs induced on the surface of the test piece. Moreover, FAAP also increases the interlinkage magnetic flux to the detection coil. A finite element simulation was conducted for the film EC probe to confirm the advantages of FAAP. Furthermore, experiments with probes were conducted using an aluminum plate with artificial cracks. In addition, the measurement results were analyzed to confirm the enhancement of the crack-detection ability of the FAAP. • A film probe with a detection coil interleaved to the excitation coil to detect was proposed. • The amorphous magnetic alloy particles was installed above the film eddy current probe. • The amorphous magnetic alloy particles enhanced the eddy current induced on the test piece. • The signal amplitudes significantly increased by the amorphous magnetic alloy particles.

Research on the Influence of Coil LC Parallel Resonance on Detection Effect of Inductive Wear Debris Sensor.

The coil structure of the inductive wear debris sensor plays a significant role in the effect of wear debris detection. According to the characteristics of LC parallel resonance, the capacitor and coil are connected in parallel to make sensor coils in the LC parallel resonance state, which is beneficial to improve the ability to detect wear particles. In this paper, the mathematical model of output-induced electromotance of the detection coil is established to analyze the influence of the structure on the detection sensitivity and enhance the sensor’s current rate of change to the disturbance magnetic field, which is essential to resist noise interference. Based on the coherent demodulation principle, the AD630 lock-in amplifier is applied to the test platform to amplify and identify weak signals. In addition, experiments are designed to test the output signals of debris under the condition of different original output voltages of the sensor with a parallel structure. Meanwhile, the near-resonance state of the detection coil with LC parallel circuit is tested by output signal information. Results show that the sensor detection sensitivity will be effectively improved with the LC parallel coil structure. For the sensor structure parameters designed in this paper, the optimal raw output amplification voltage for abrasive particle detection is 4.49 V. The detection performance of ferromagnetic particles and non-ferromagnetic particles is tested under this condition, realizing the detection ability of 103.33 μm ferromagnetic abrasive particles and 320.74 μm non-ferromagnetic abrasive particles.

Magnetic‐Anisotropy‐Enhanced Electrical Transport Properties of Co/Bi0.5Sb1.5Te3/PVDF Flexible Thermoelectromagnetic Films

AbstractA built‐in magnetic field by magnetic embedding has been proven to be an effective approach to improve the electro‐thermal conversion performance of thermoelectric materials. However, the function of the built‐in magnetic field direction is still unknown. In this study, ferromagnetic Co particles with different morphologies are introduced into Bi0.5Sb1.5Te3/PVDF thermoelectric films to control the direction of the built‐in magnetic field. Co particles with shape anisotropy establish magnetic anisotropy fields inside the flexible thermoelectromagnetic films, which make the magnetic moments tend to be aligned parallel to the film surface, causing spiral motion of carriers. The atomic‐scale micro‐electric field established by the in situ reaction of Co and Te induces hopping migration of carriers. The coupling of the magnetic anisotropy field and micro‐electric field brings about a substantial increase in carrier mobility, thus greatly enhancing conductivity. The carrier energy filtering effect generated by Bi0.5Sb1.5Te3/CoTe2/Co hetero interface and additional magnetic scattering provided by the CoTe2/Co micro‐magnetic field maintain the Seebeck coefficient at a high level. The maximum power factor of Co/Bi0.5Sb1.5Te3/PVDF flexible thermoelectromagnetic film with sheet Co particles reaches 1.45 mW m−1 K−2 at 300 K, increased by 54% and 6% as compared with that of Bi0.5Sb1.5Te3/PVDF thermoelectric film and Co/Bi0.5Sb1.5Te3/PVDF flexible thermoelectromagnetic film with spherical Co particles, respectively.

To the theory of remagnetization kinetics of ferromagnetic nanoparticles. Non linear effects

The paper deals with theoretical study of remagnetization kinetics of a single-domain ferromagnetic particles in an alternating magnetic field, arbitrary directed with respect to the particle axis of easy magnetization. Period of the field is not supposed large as compared with the characteristic time of the particle Neel remagnetization. The nonlinear magnetization of the particle is considered. At the assumption of the particle strong magnetic anisotropy, a new equation for its average magnetic moment is derived.

Classification of demagnized magnetite in an upward laminar flow

The paper presents experimental results of completely demagnetized fine ferromagnetic particles classification in an upward laminar flow. The efficiency of classification was estimated and mathematical model of the process was defined using software for data analysis and visualization SigmaPlot. The attention is paid to the fact, that classification of demagnetized particles is about 5 times more effective. It can be explained with the fact of magnetic flocculation. That is, fine ferromagnetic particles form large floccules, and if these floccules are not broken, all of them fall into underflow product, regardless to the fineness of the sample. Conclusions are drawn about the fact that residual magnetization of magnetite particles effects on the efficiency of their classification. Moreover, classification of completely demagnetized magnetite allows to reduce its cost, as the number of grinding equipment can be significantly reduced.

Effect of sintering routes on CIP/EIP – Al2O3 composite magnetic abrasive for chemo-mechanical magneto-rheological finishing of aluminium 6061

In magnetorheological fluid-based finishing processes, the lower gripping of abrasives in between ferromagnetic particle’s chain structure limits its finishing speed, resulting in a lower material removal rate and desired surface standard. In addition, tool ageing has significantly impacted these finishing processes at a higher speed. To improve the efficiency of finishing processes, composite magnetic abrasives are fabricated by using powder metallurgy techniques via both microwave and conventional processing (sintering) routes. Comparison studies were performed on these samples based on ferromagnetic materials (CIPs and EIPs) used and sintering at 950°C under fixed element composition. A newly advanced chemo-mechanical magneto-rheological finishing (CMMRF) process for aluminium alloy surface polishing was also proposed, combining mechanical abrasion and chemical action for the performance evaluation of composite magnetic abrasives. Most notably, the microwave processed composite magnetic abrasive outperformed conventionally processed samples in terms of magnetic and rheological properties. The composite magnetic abrasives significantly increased the rate of material removal from the metal surface while reducing the tool ageing effect. The surface profile and observation show that a nearly defect-free surface was produced at higher speeds using these composite magnetic abrasives compared to simply mixed abrasives based results.

Factors affecting thickness and frequency of turbidites triggered by earthquakes in Kumburgaz Basin, Sea of Marmara

Submerged fault ruptures generate earthquake-triggered mass flow deposits, which are extensively used as a tool in subaqueous paleoseismology. In tectonically active deep sedimentary basins, such as the Sea of Marmara (SoM), these mass flow deposits are defined as turbidite-homogenite units (THUs), consisting essentially of a coarse basal part and an overlying homogeneous mud (homogenite). Detailed characterization of THUs is crucial in order to establish meaningful criteria to link these units with earthquakes events and to identify their transport routes and depositional mechanisms. Here, we combine μ-X-ray Fluorescence (μ-XRF), Anisotropy of Magnetic Susceptibility (AMS) and additional rock magnetism analyses of a 21-m long piston core from the Kumburgaz Basin of SoM to define the upper stratigraphic boundary of THUs with hemipelagic sediments and investigate the controls of hydrological changes on turbidite frequency and thickness over the last 15 kyrs BP. The sedimentary succession of this period includes a lower lacustrine and an upper marine unit with two Holocene sapropel intervals. The sequence is interrupted by a total of 70 THUs, characterized by a significant magnetic foliation related to the depositional setting rather than the magnetic signature. Magnetic mineralogy of the coarse basal parts of THUs have more ferromagnetic particles than the overlying homogenites and background sediments. While the homogenite parts have a more constant mineralogy than the basal parts, they do not differ the background sediments.Based on an event-free chronostratigraphic model derived from radiocarbon ages and the published age of lacustrine-marine (L-M) transition, the average THU occurrence intervals in the lacustrine (14.8–12.6 kyrs BP), lower sapropel (11.2–5.7 kyrs BP), upper sapropel (5.4–2.7 kyrs BP) and non-sapropelic part of the marine unit (2.7 kyrs BP-present) are 235 yrs., 287 yrs., 114 yrs. and 160 yrs. respectively. The average thickness of the THUs in the same units are 20.8 cm, 15.7 cm, 6.1 cm and 6.1 cm. The variability of average THU occurrence intervals and THU thicknesses are controlled by the sea level rise and salinity increase following the full marine connection of the SoM at 12.6 kyrs BP, which caused changes in slope stability, sediment composition and sediment deposition in different parts of the basin. Geomechanical properties of the lower sapropel appears to have been important in resulting long THU recurrence intervals and relatively high THU thicknesses.

Simulation of a passive position control for ferromagnetic particles with multiple Halbach rings

Abstract Various types of magnetic nanoparticles have been developed for a range of medical applications and some have the potential to treat diseases. In this paper, a new method for controlling the position of these magnetic particles by changing the magnetic field surrounding them using three Halbach ringsis investigated with the aid of a simulation. The inner ring controls the direction, and the position of the two outer rings can keep the group of particles together. In the simulation, the magnetic field is calculated analytically for each time step and the movement of the particles is simulated by applying the corresponding forces. These result from the manipulable external magnetic field, the magnetic field between the particles, the Lennard-Jones potential to model attractive interactions between the particles and the drag. In the simulation, we show how the particles are manipulated using a Levenberg-Marquard algorithm and develop a closedloop control for the position of the grouped particles by manipulating the magnetic field inside the Halbach rings by changing the angular position of these rings.

Liquid-Metal-Coated Magnetic Particles toward Writable, Nonwettable, Stretchable Circuit Boards, and Directly Assembled Liquid Metal-Elastomer Conductors.

Liquid metal is a promising conductor material for producing soft and stretchable circuit "boards" that can enable next-generation electronics by electrically connecting and mechanically supporting electronic components. While liquid metal in general can be used to fabricate soft and stretchable circuits, magnetic liquid metal is appealing because it can be used for self-healing electronics and actuators by external magnetic fields. Liquid metal can be rendered into particles that can then be used for sensors and catalysts through sonication. We used this feature to produce "novel" conductive and magnetic particles. Mixing ferromagnetic iron particles into the liquid metal (gallium) produces conductive ferrofluids that can be rendered into gallium-coated iron particles by sonication. The gallium shell of the particles is extremely soft, while the rigid iron core can induce high friction in response to mechanical pressure; thus, hand-sintering of the particles can be used to directly write the conductive traces when the particles are cast as a film on elastic substrates. The surface topography of the particles can be manipulated by forming GaOOH crystals through sonication in DI water, thus resulting in nonwettable circuit boards. These gallium-coated iron particles dispersed in uncured elastomer can be assembled to form conductive microwires with the application of magnetic fields.

Numerical Analysis of an Electromagnetic Stirring System for Composite Plastic Materials with Ferromagnetic Particles

AbstractThis paper deals with a Finite Element (FE) numerical analysis of an electromagnetic stirring system for composite plastic materials with ferromagnetic particles. The electromagnetic stirring process is ensured by the magnetic forces acting on the ferromagnetic particles spread in the plastic matrix. These forces are produced by the rotating magnetic field of the stator of a three‐phase induction motor supplied from an inverter. The analysis is carried out using the professional software package Flux for electromagnetic field computation based on the FE method. The 2D computations allowed to estimate the magnetic forces and their orientation acting on micrometric particles spread in a fluid plastic material. A preliminary experimental setup is also built for studying the proposed solution.

A Qubit Represented by the Oscillator’s Quantum States in Magnetic Resonance Force Microscopy

We consider magnetic resonance force microscopy (MRFM) in the situation when the frequency of the electron spin resonance matches the fundamental frequency of the cantilever with a ferromagnetic particle attached to its tip. We suggest that in this situation, the quantum states of the oscillating cantilever may represent a qubit. We develop a scheme for manipulation with the qubit state and derive the expression describing the Rabi oscillations of the qubit.

Investigation on rheological characteristics of magnetorheological shear thickening fluids mixed with micro CBN abrasive particles

The novel magnetorheological shear thickening polishing fluids (MRSTPFs) were developed by mixing micro cubic boron nitride (CBN) abrasive particles into traditional magnetorheological shear thickening fluids. MRSTPFs were constructed by uniformly fumed silica and polyethylene glycol as shear thickening fluids, carbonyl iron particles (CIPs) as ferromagnetic phase and CBN particles as abrasive phase. In this work, various MRSTPFs were prepared to explore their rheological characteristics. Sweeps of steady shear rate and dynamic shear frequency were conducted under different magnetic flux densities, respectively. A mathematical model was presented to explain shear rate variation with shear stress. The magnetorheological shear thickening mechanism was well described. The rheological experiment results have revealed that shear thickening effect was still existing in magnetic flux density. However, the increased magnetic flux density played a negative role on the shear thickening effect. Particle size optimization of CIPs was thus essential to maximize the shear thickening effect. On the other hand, with increased shear frequency, the viscoelastic feature of MRSTPFs was converted from linear to non-linear. It was found that the shear yield stress of the MRSTPFs was magnified with the stronger magnetic flux density and larger CIPs size. The investigation of rheological characteristics demonstrated that MRSTPFs could enhance polishing performance, which contributed to developing a high-efficiency and ultra-precision polishing process.

Effects of Different Fatty Acids as Surfactants on the Rheological Properties of Kerosene-Based Magnetic Fluids

Three types of surfactants (oleic acid, linoleic acid, and a mixture of oleic acid and linoleic acid) were coated on ferromagnetic particles, which were dispersed in kerosene to prepare magnetic fluids, to study the effect of different fatty acids as surfactants on the rheological properties of magnetic fluids. The particles were analyzed by XRD, TEM, FT-IR, and VSM. Furthermore, a rheometer was used to examine the rheological properties of kerosene-based magnetic fluids dispersed with various surfactants. The yield stress at different magnetic fields was calculated by fitting the Herschel–Bulkley model. The fitted curve and the observed values of mixed fatty acids are identical. The graphs of viscosity increase with the shear rate for each magnetic fluid were measured at constant magnetic field strengths. At constant shear rates, the curves of viscosity increase with magnetic field intensity were measured. In the absence of a magnetic field, the relative change in viscosity from 40°C to 0°C was observed. The rheological measurements of the mixed fatty acid-dispersed ferrofluid with a rising magnetic field at a constant shear rate are smoother than the single-fatty-acid-dispersed ferrofluid, indicating that it is more stable. As the temperature is dropped, the viscosity–temperature curve evidence that mixed fatty acids as surfactants can lower the proportion of magnetic fluid viscosity rise.

Monitoring Metal Wear Particles of Friction Pairs in the Oil Systems of Gas Turbine Power Plants

In the example of the aviation gas turbine engine the problem of monitoring metal wear particles of friction pairs in the oil systems of gas turbine power plants is considered. The solution based on using the multi-channel cluster single-coil eddy current sensor (CSCECS) with sensitive elements in the form of single circuits is proposed. The CSCECS provides the detection of ferromagnetic and non-ferromagnetic particles and their ranking by several size groups. The sensor is invariant to the size (inner diameter) of the monitored oil pipeline and has high throughput and identical sensitivity across all channels. Two variants of the hardware structure of the debris continuous monitoring system (DCMS) prototype implementing the proposed approach are suggested. The first variant is intended for engine bench tests and contains the CSCECS with integrated preamplifiers and forced air cooling of the electronic modules. The second variant of the DCMS prototype involves the use of the uncooled sensors without built-in electronics and it focuses on operation in autonomous mode not only in bench tests but also during the engine normal operation. A brief description of the DCMS operational algorithm is given. The algorithm is the same for both hardware versions but differs at the software implementation level. The correctness of the algorithm for the detection and size identification of the wear metal particles was verified during the laboratory experiments with a total duration of 5 h and 30 min. The DCMS prototype was also examined during the full-scale engine bench tests. The experiments indicated that the number, size, and magnetic properties of the particles detected by DCMS generally corresponded to the number, size, and magnetic properties of the particles fixed by the MetalSCAN oil debris monitoring system which was used for verification of the DCMS functional capability. The results were also confirmed through laboratory analysis of the wipe samples on the debris filters. However, unlike the existing approaches, the design of the CSCECS additionally made it possible to evaluate the oil flow features in the pipeline of the engine lubrication system.

Magnetoresistive behaviour of ternary Cu-based materials processed by high-pressure torsion

Severe plastic deformation using high-pressure torsion of ternary Cu-based materials (CuFeCo and CuFeNi) was used to fabricate bulk samples with a nanocrystalline microstructure. The goal was to produce materials featuring the granular giant magnetoresistance effect, requiring interfaces between ferro- and nonmagnetic materials. This magnetic effect was found for both ternary systems; adequate subsequent annealing had a positive influence. The as-deformed states, as well as microstructural changes upon thermal treatments, were studied using scanning electron microscopy and X-ray diffraction measurements. Deducing from electron microscopy, a single-phase structure was observed for all as-deformed samples, indicating the formation of a supersaturated solid solution. However, judging from the presence of the granular giant-magnetoresistive effect, small ferromagnetic particles have to be present. The highest drop in room temperature resistivity (2.45% at 1790 kA/m) was found in Cu62Fe19Ni19 after annealing for 1 h at 400 °C. Combining the results of classical microstructural studies and magnetic measurements, insights into the evolution of ferromagnetic particles are accessible.

Research on the influence of inductive wear particle sensor coils on debris detection

The debris detection characteristics of the inductive wear monitoring are researched by the method of combining theoretical research and simulation analysis in this paper. The mathematical model of the change in inductance is established based on the change in the coil magnetic field by the abrasive particles. By the COMSOL simulation software, the physical model of the three-coil wear monitoring is established, and the influence of the coil structure parameters on the output induced electromotance is compared and analyzed, resulting in the optimization of the coil parameters. For metal particles with different properties and sizes, the changes in the induced electromotance during the process of passing through the coil are analyzed, obtaining the mapping relationship between each particle size and the output induced electromotance. The simulation results show that the output voltage corresponding to the particles is related to the coil structure parameters, and the larger the particle size, the larger the output voltage. Finally, through experiments, the designed sensor coil structure has been proved to have a better detection effect on metal particles, realizing the detection of ferromagnetic abrasive particles above 100 µm and non-ferromagnetic abrasive particles above 200 µm.