Magnetic Materials Research Papers - Academia.edu (original) (raw)

Introduction • Theory • The waveguide with reactance boundaries • The Inhomogeneous Resonator • Conclusion Abstract • The nonstandard (general) eigenvalue problem is defined in operator by L(λ) = 0 and B(λ) = 0. • For a standard problem L... more

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- Functional Analysis, Magnetic Materials, Writing, Integral Equations

Magnetorheological fluids (MRFs) are typically thought of as Bingham-plastic (BP) fluids characterized by a yield stress. Partial substitution of micrometer-scale Fe particles with nanometer-scale Fe particles leads to bidisperse MRFs. This partial substitution mitigates particle sedimentation, but can reduce yield stress for high nanoparticle concentrations. We examine tradeoffs between increasing suspension stability versus decreasing in yield stress as nanoparticles are substituted for microparticles. Four groups of fluids with total Fe concentration of 50, 60, 70, and 80 wt% were considered. A sedimentation measuring device quantified sedimentation velocity of MRFs in a gravitational field. This sensor relates the rate of change of inductance relative to settling rate as Fe wt% decreases because of sedimentation. MRF flow curves were measured using a parallel disk rheometer and yield stress was identified using the BP flow model.

- by Norman Wereley
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- Engineering, Materials Science, Magnetic Materials, Stress
- by Caroline Ross
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- Engineering, Magnetic Materials, Applied Physics, Mathematical Sciences

Motivated by exploring spin-orbit coupled magnetism in 5d-based transition metal oxides (TMOs) beyond the iridates, we present a powder inelastic neutron scattering study of magnetic excitations in Ba2FeReO6-a member of the double perovskite family of materials which exhibit half-metallic behavior and high Curie temperatures Tc. We find clear evidence of two well-defined dispersing magnetic modes in its low temperature ferrimagnetic state. We develop a local moment model, which incorporates the interaction of Fe spins with spin-orbital locked magnetic moments on Re, and show that it captures our experimental observations. This allows us to extract moment sizes and exchange couplings, explain the magnitude of Tc, and to infer that magneto-structural locking terms are weak. Our study further opens up Re-based compounds as model systems to explore the interplay of strong correlations and spin-orbit coupling in 5d TMOs.

- by Jeffrey Lynn
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- Materials Science, Magnetic Materials, Applied Physics, Band Structure

This paper examines quasi-static magnetic processes such as those found in magnetic recording. We shall discuss the hysteresis in medium-hard magnetic materials of the type used in recording media, and the magnetizability of soft magnetic materials such as those used in recording heads. There are two general modeling techniques used to described these processes: physical modeling and phenomenological modeling. In physical modeling, the basic processes involved are simulated in order to be able to describe the basic magnetizing modes. On the other hand, in phenomenological models, the gross behavior of the material is described mathematically by Preisach-type models in order to couple the material properties to Maxwell's equations so as to obtain solutions of field problems. The latter models are computationally more efficient than the former, but they do not give any insight into the physical principles involved. Edward Della Torre (Fellow, IEEE) was born i n Milano, Italy, and received the B.E.E. degree from the Polytechnic Institute of Brooklyn, the M.Sc. (E.E.) degree from Princeton University, the M.Sc. (physics) from Rutgers University, and the D.Sc. degree from Columbia University.

- by Edward Della Torre
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- Biomedical Engineering, Computational Modeling, Modeling, Magnetic Materials

Polycrystalline ferrites with general formula Ni 1−x Zn x Fe 2 O 4 (x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) were prepared by oxalate precipitation method. The samples were characterized by X-ray diffraction (XRD), IR and scanning electron microscope (SEM) techniques. All compositions show cubic Spinel structure. Lattice constant increases with increase in zinc content, obeying Vegard's law. The physical densities are about 98.14% of their X-ray density. Average crystallite size lies in the range 27.59-31.49 nm. Infrared studies show two absorption bands near about 400 cm −1 and 600 cm −1 for octahedral and tetrahedral sites, respectively. The resistivity of all the samples was studied. It is observed that the resistivity of nickel-zinc ferrites prepared by oxalate precipitation method is higher than that prepared by ceramic and citrate precursor method. It is attributed to greater homogeneity and smaller grain size. Activation energy in paramagnetic region is higher than that of ferrimagnetic region.

- by Edgar Osorio
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- Engineering, Magnetic Materials, Nanoparticles, Polymers

We have investigated the relationship between the magnetism and the magnetoresistance effect in the Co/Au, Ag multilayer films with layers produced in the atomic level by pulse electrodeposition method. The magnetoresistance effect is dependent on both the thickness of Co ferromagnetic layer and Ag,Au non-magnetic layers. The magnetization of these films shows the minimum value against the Ag and Au layer thickness. The Ag and Au layer thickness showing the maximum of MR ratio is not of necessary in
agreement with the Ag and Au layer thickness showing the minimum of magnetization. Antiparallel alignment of magnetic spin is a necessary but not sufficient condition in order to generate the GMR of multilayer films. For the Co/Au multilayer films, the Au layer thickness showing the minimum of the magnetization shifts to higher side of the Au layer thickness.

- by Conrad Rizal, PhD
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- Magnetic Materials, Magnetic multilayers, Saturation Magnetization

Air stable cobalt nanoparticles have been prepared continuously at a production rate of 30 g h 21 by a modified flame synthesis method under highly reducing conditions. Nanoparticles of 20-60 nm in diameter consisted of metallic face-centered-cubic cobalt. The metal particles were protected against oxidation by a surface layer of less than 1 nm of cobalt oxide. The material was highly magnetic exhibiting a high saturation magnetisation (>124 emu g 21 ) together with a low (,100 Oe) coercivity. Experiments under varying fuel to oxygen ratio were combined with thermodynamic calculations to illustrate the necessity for highly reducing conditions and enhanced gas mixing to enable the formation of metallic cobalt nanoparticles in flames. 63310 83; Tel: +41 44 632 09 80 { Electronic supplementary information (ESI) available: schematic showing both the original flame spray set up used for run 4 and the modified reducing flame spray set-up used for runs 1-3. See

- by Robert N Grass
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- Engineering, Materials Chemistry, Magnetic Materials, Nanoparticles
- by Christopher Rahn
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- Engineering, Magnetic Materials, Finite Element Analysis, Permanent Magnets

We report the synthesis of superparamagnetic nanoparticles of iron oxide in magnetite phase with diameters of approximately 15 nm. Nanoparticles of magnetite were synthesized by forced hydrolysis method, controlling the oxidation with a nitrogen atmosphere during the synthesis. Nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Mössbauer spectroscopy and vibrating sample magnetometry. Quantitative analysis of crystalline phases was done by performing Rietveld refinement of the XRD profiles. In order to obtain nanometers sizes of magnetite phase solely, the parameters of formation such a pH and molar concentration were analyzed and determined by an equilibrium thermodynamics model with the chemical computer code MINTEQA [Allison Geoscience Consultants, Inc., HydroGeoLogic, Inc., MINTEQA2 for Windows, Equilibrium Speciation Model. Ver 1.5 ].

- by Jairo Martinez
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- Engineering, Physics, Magnetic Materials, Nanoparticles

In this contribution it is proven mathematically that it is in principle impossible to determine the magnetic charge distribution inside a magnetic material by a method which measures the stray field outside the sample, such as magnetic force microscopy (MFM). A general source of stray field, E N , is defined and it is shown that different solutions can be found for E N that result in the same stray field. It is also shown how both a perpendicular and a longitudinal medium can be described with the same E N . Using the equations for stray field, resulting from E N , it is also proven that performing the same MFM measurement at different scanning heights does not provide any new information on the stray field for sample; from a measurement at one (constant) height, the stray field at all other heights can be calculated. Moreover, the component of the field parallel to the same plane can be obtained from a measurement of the field component perpendicular to the sample plane.

- by Bas Vellekoop and +1
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- Mechanical Engineering, Condensed Matter Physics, Magnetic Materials, Magnetic Force Microscopy

The need to reduce electricity consumption by electrical devices, including electric motors, is the reason for the development of new designs. Designers strive to improve operational parameters, including efficiency, using, for example, new types of magnetic materials, new types of stator windings, etc. Currently, in mass production, motor cores are made of punched laminations-punching causes damage of core parts. For motors of relatively large geometrical sizes, this effect is ignored during design. For motors having small dimensions, this negative effect results in a reduction in efficiency, which is mostly small for this type of motor. In this paper, the authors propose a new rapid algorithm based on simple measurements to determine the material characteristics of the damaged material part. Then, using them in the FEM models, they determine the efficiency of motors with various powers and frame sizes. On this basis, the conclusions are formulated, they may be helpful for motor designers.

- by Zbigniew Gmyrek and +1
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- Electrical Engineering, Magnetic Materials, Electrical Motors, Efficiency

The magnetic properties of tilted easy axis L10 CoPt(111)/Pt(111)/MgO(100) film, deposited by pulsed laser deposition, were investigated by magnetization angular dependence measurements and magnetic force microscopy (MFM). The room temperature anisotropy constant, evaluated measuring the in-plane variation of transverse magnetization under a rotating magnetic field, is K = 5x10^6 erg/cm^3. The domain structure, observed by MFM, consists of decoupled single domain grains, unlike the maze-like structure usually observed for similar systems. This was confirmed by the analysis of dc demagnetization and isothermal remanence magnetization curves, which provided evidence of predominant magnetostatic interactions.

- by Gaspare Varvaro
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- Engineering, Magnetic Materials, Magnetic thin film, Physical sciences
- by Anderson Dias
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- Materials Engineering, Kinetics, Magnetic Materials, Scanning Electron Microscopy

Single-crystals of MnFe2O4 nanorods with an average diameter of 20 nm and length of 250 nm were synthesized by a hydrothermal process at 180 °C after 12 h. High-resolution transmission electron microscopy (HRTEM) and electron diffraction (ED) analysis revealed that the nanorods grow along the [110] axis, which is one of the easy magnetization axes of the material MnFe2O4. It was found that the nanorods exhibited a saturation magnetization (Ms) of 68.02 emu/g, which is much higher than that of quasi-spherical particles of MnFe2O4, prepared by other approaches such as solid-state reaction methods (Ms = 36.7 emu/g), and coprecipitation processes followed by annealing in vacuo at 400 °C (Ms = 24.4 emu/g). The oriented growth along the easy magnetization axis of MnFe2O4 was suggested to be responsible for the improvement of magnetic properties of MnFe2O4 nanorods. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

- by Binyang Hou
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- Engineering, Materials Engineering, Condensed Matter Physics, Quantum Physics

Well-dispersed nickel nanoparticles in polystyrene were obtained by a sonochemical method. The properties of the as-prepared nanocomposite materials were characterized by XRD, TEM, EDAX, TGA, DSC, and a vibrating sample magnetometer (VSM). The nickel particles were 5 nm in diameter and were very well dispersed in the polystyrene. The magnetization measurements established that the as-prepared nanocomposite materials are superparamagnetic due to their small size. The saturation magne-tization (30.1 emu/g) and coercivity (5 Oe) of the materials were significantly smaller than were those of the bulk nickel, reflecting the nanoparticle nature.

- by O. Palchik
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- Engineering, Magnetic Materials, Nanocomposites, Ultrasound
- by C. Batista and +1
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- Materials Engineering, Condensed Matter Physics, Thermodynamics, Water Purification

Designing pores of nanoscale dimension into a magnetic material can engineer the surface nanostructure, resulting in a mesoporous material with unique physicochemical properties. Here we report a simple soft-templating approach for the synthesis of new mesoporous iron oxide materials having semi-crystalline pore wall by using an anionic surfactant sodiumdodecylsulfate as the structure-directing agent (SDA) or template at low temperature. On removal of the SDA molecules through solvent extraction the mesostructure is preserved and the material shows considerably high BET surface area and type IV isotherms corresponding to the mesopores. This mesoporous Fe2O3 material showed superparamagnetic behavior and hence this template-assisted synthesis of mesoporous Fe2O3 can find its potential utility in designing magnetic nanostructured materials.

- by Atanu Mitra
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- Engineering, Magnetic Materials, Solvent Extraction, Iron Oxide

The properties of magnetic material are normally described by the permeability tensor, while the magnetically nonlinear properties of electromagnetic devices (EMDs) can be described by the current-dependent characteristics of flux linkages. This paper presents and evaluates different experimental methods appropriate for determining the magnetically nonlinear characteristics of EMDs. The tested device is supplied by a controlled voltage source. Sinusoidal voltages, sinusoidal voltages with offset, and stepwise changing voltages are applied. Current-dependent characteristics of flux linkages are determined from the measured voltages and currents, either by numerical integration or by Fourier analysis and calculation of impedances.

- by B. Polajzer
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- Engineering, Magnetic Materials, Magnetic field, Fourier Analysis

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- by Jiming Bao and +1
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- Science, Magnetic Materials, Metamaterials, Self Assembly

This paper analyzes the performances of an embedded closed-loop control system with a compensated magnetostrictive actuator (e.g., a Terfenol-D based device) for micropositioning tasks. The control system and the compensation algorithm are implemented, as a standalone application, on a microcontroller. The embedded application and its performance in terms of tracking error reduction is evaluated with respect to both open and closed loop configurations. The uncompensated case is used as a reference.

- by Alessandro Giustiniani
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- Engineering, Embedded Systems, Magnetic Materials, Control Systems

As for standard positron emission tomography (PET) scanners, MR-compatible PET scanners will require gamma shielding to suppress the influence of activity outside the PET field of view (FOV). Suitable materials must have very specific properties, including magnetic properties close to those of water, high density, high atomic number, and ideally a low conductivity. In order to identify potential suitable materials, we have selected several heavy-metal-based candidates based on the available data for magnetic and shielding properties. These materials include several nonferromagnetic metals and metal oxides, two scintillating crystals (bismuth germanate and lead tungstate) and two metal/epoxy compounds. The magnetic resonance imaging (MRI) compatibility of these materials was assessed under various conditions, both on a human and a small-animal MRI scanner. In parallel, we assessed the shielding efficiency at 661 keV of the most promising candidates. These experiments showed that there is a range of possibilities for the design of MR-compatible gamma shields. Lead has acceptable magnetic compatibility but can induce significant conductivity-related artefacts. Heavy-metal-based minerals are fully insulating and hot-pressed lead monoxide showed good MR compatibility combined with good shielding properties. Other possibilities include the use of lead based powders and heavy-metal oxide composites.

- by Daniel Strul
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- Biomedical Engineering, Water, Magnetic Resonance Imaging, Magnetic Materials

In the present paper we discuss antenna miniaturization using magneto-dielectric substrates. Recent results found in the literature reveal that advantages over conventional dielectric substrates can only be achieved if natural magnetic inclusions are embedded into the substrate. This observation is revised and the physical background is clarified. We present a detailed discussion concerning magnetic materials available in the microwave regime and containing natural magnetic constituents. The effects of magnetic dispersion and loss are studied: constraints on the microwave permeability are used to estimate the effect of magnetic substrates on the achievable impedance bandwidth. Microwave composites filled with thin ferromagnetic films are considered as a prospective antenna substrate. We calculate the impedance bandwidth for a λ/2-patch antenna loaded with the proposed substrate, and challenge the results against those obtained with conventional dielectric substrates. It is shown that the radiation quality factor is strongly minimized with the proposed substrate even in the presence of realistic losses. Estimates for the radiation efficiency are given as a function of the magnetic loss factor.

- by Sergei Tretyakov
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- Antennas, Microstrip Antennas, Magnetic Materials, Composite Materials

Yttrium iron garnet (YIG) is a synthetic Ferrimagnetic material. YIG is cubic in structure; having space group Ia3d. In YIG, out of 5 Fe 3+ ions, 3 Fe ions occupy tetrahedral site and 2 Fe ions occupy octahedral site. Difference in the spin orientation of the Fe 3+ ions present in tetrahedral and octahedral sites results in the origin of the magnetic properties of YIG. Yttrium iron garnet with the empirical formula Y 3 Fe 5 O 12 has been synthesized by regular ceramic route and sintering at 1200˚C for 30 minutes using microwave furnace. The structural and morphological characterization of the synthesized YIG are performed by X-ray diffractometer (XRD), and scanning electron microscopy (SEM). X-ray diffraction pattern revealed pure YIG phase as reported by Musa et al [1]. The crystallite size from the Scherrer equation is found to be 2.82Å. A saturation magnetization of 16.88emu/g is achieved by VSM.

- by Abhijeet Nayak
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- Materials Science, Magnetic Materials, FTIR spectroscopy, Structural Analysis

A Lorentz force flowmeter is a device for the contactless measurement of flow rates in electrically conducting fluids. It is based on the measurement of a force on a magnet system that acts upon the flow. We formulate the theory of the Lorentz force flowmeter which connects the measured force to the unknown flow rate. We first apply the theory to three specific cases, namely (i) pipe flow exposed to a longitudinal magnetic field, (ii) pipe flow under the influence of a transverse magnetic field and (iii) interaction of a localized distribution of magnetic material with a uniformly moving sheet of metal. These examples provide the key scaling laws of the method and illustrate how the force depends on the shape of the velocity profile and the presence of turbulent fluctuations in the flow. Moreover, we formulate the general kinematic theory which holds for arbitrary distributions of magnetic material or electric currents and for any velocity distribution and which provides a rational framework for the prediction of the sensitivity of Lorentz force flowmeters in laboratory experiments and in industrial practice.

- by Evgeny Votyakov
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- Magnetic Materials, Magnetic field, Physical sciences, Laboratory experiment

Using a finite-element method, we have calculated fluxmetric and magnetometric demagnetizing factors and for square cross-section bars as functions of susceptibility and length-to-width ratio over the range = 1 to and = 0 01 to 100. We present the results in figures and tables and compare them with those for cylinders. We give an approximate conjugate relation for ( ) of a cube.

- by alvaro sanchez
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- Engineering, Distributed Computing, Finite Element Methods, Magnetic Materials

In this paper, using suitable three-dimensional finite element method (FEM) approaches, either in frequency or in time domain, we will analyze the real magnetic behavior of a commercial Epstein machine, prescribed as standard magnetic measurement system. The analysis of magnetic field and eddy currents explains some facts that can affect the accuracy of Epstein frames as measuring systems for the magnetic characterization of laminated Si-Fe steels. The same FEM approaches shall be applied here to outline and define quantitatively some advantages in accuracy can be obtained using Single Sheet testers instead of Epstein frames.

- by E. Cardelli and +1
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- Engineering, Finite Element Methods, Magnetic Materials, Finite element method

Shielding of magnetic fields at power frequencies has been investigated by computation and experiment. Different types of low-cost soff magnetic laminations (low-carbon steel, nonoriented FeSi, grain-oriented Fe-Si) and different shield geometries (plane, U-shaped and box-like) have been considered. The shielding factors of model screens have been measured, together with the magnetic flux density in the sheets employed, under field levels typical of industrial environment (-lOOpT).

The functionalized silica coating mercapto on iron sand magnetic material (MM/SiO2/MBI)has been done through sol-gel process. The successfully synthesized material is used as adsorbent (MM/SiO2/MBI) in the Adsorpi Au (III) process. Material characterization is carried out with an adsorbent stability test against acids. Adsorption is performed in a batch system and the unadsorped Au (III) ion is analyzed with the Atomic Absorption Spectrophotometer (AAS). Characterization results indicate the synthesis of PB/SiO2-MBI adsorbent has been successfully performed. The coating of iron sand magnetic material enhances stability to acid. ADsorbent (MM/SiO2/MBI) is capable of adjudisorate ion Au (III) with the highest adsorption occurring at pH 1. Kinetics review indicates that the adsorption of the ion (III) is following the second-order pseudo kinetics with a value of k 3.57 × 10-3 g/mg. Minute and adsorption isotherm follows the isotherm pattern of Langmuir with an adsorption capacity of 125 mg/g.

- by Martasiana Karbeka
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- Magnetic Materials, Magnetism and Magnetic Materials

Magnetic and NMR relaxivity properties of γ-Fe2O3 nanoparticles embedded into the walls of polyelectrolyte multilayer capsules and freely dispersed in a sodium borate buffer solution have been investigated. The different geometric distribution of both configurations provides the opportunity to study the relationship of water accessibility and magnetic properties of particles on the NMR relaxivity. Changes in their blocking temperature and average dipolar field were modeled as a function of packing fraction in the ensemble of free and entrapped nanoparticles. For free nanoparticles with relatively low concentration, relaxivity values increase with packing fraction according to an increase in the dipolar field and larger water accessibility. However, for embedded nanoparticles in the capsule wall, packing fractions should be limited to optimize the efficiency of this system as magnetic resonance imaging (MRI) contrast agent.

Precise contactless DC and AC magnetic sensors are required by car industry, chemical industry, for measurement of power and many other applications. The emphasis is given on current sensors based on magnetic materials, but other methods... more

- by Pavel Ripka
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- Magnetic Materials, Optical physics, Chemical Industry, Magnetic Sensor

Ferromagnetic materials, such as steel, are used for shielding of power and telecommunication cables. These shields often provide path for currents during faults or lightning and are important for the integrity and safety of electrical systems and devices. Since such currents might be with low-or high-frequency content, and of low or high intensity, ferromagnetic shield behavior might be quite different due to hysteresis. This paper describes a method for analyzing the dynamic behavior of ferromagnetic cable shields based on the Jiles model of hysteresis. The solution is implemented in ATP-EMTP, which allows one to analyze the complex behavior of ferromagnetic cable shields in conjunction with that of the other elements of the power system. Due to limitations of the model of hysteresis, application of the proposed model is limited to frequencies up to about 10 kHz. The model is illustrated for a practical 100-m-long cable.

- by Leonid Grcev
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- Power System, Magnetic Materials, Low Frequency, Magnetic field

A tetrazole based metal organic framework [Cu(Metet)]n (MOF-1) (MetetH = 5-methyl-1H-tetrazole) has been prepared under solvothermal condition using sodium azide and nitrile in presence of CuCl2·2H2O. The crystalline product thus obtained was characterized by spectral (FTIR, UV–visible and fluorescence) and single crystal X-ray diffraction analysis. Tetrazole ligand is formed in situ by the reaction of azide and nitrile used. X-ray data confirm the tetrahedral geometry around the Cu(II) ion where all the four coordination sites are provided by four N of the four different ligand (Metet). MOF-1 has trigonal crystal system with R-3 m space group. Topological analysis of MOF-1 shows 4,4-c binodal net with uncommon ptr topology and stoichiometry, (4-c)(4-c). The detailed structural analysis reveals the porous nature of the MOF with channel of dimensions, Rf = 0.6 Å and Rfi = 2 Å. Further, the present MOF shows excellent adsorption properties towards organic dye, Methylene blue (MB) and thus can be employed as a good adsorbent for organic pollutants to remove MB from waste water. The possible rationale behind the dye adsorption is the porous nature of the MOF-1.

- by M. Shahnawaz Khan
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- Chemistry, Inorganic Chemistry, Water quality, Magnetic Materials

Semiconductor devices generally take advantage of the charge of electrons, whereas magnetic materials are used for recording information involving electron spin. To make use of both charge and spin of electrons in semiconductors, a high concentration of magnetic elements can be introduced in nonmagnetic III-V semiconductors currently in use for devices. Low solubility of magnetic elements was overcome by low-temperature nonequilibrium molecular beam epitaxial growth, and ferromagnetic (Ga,Mn)As was realized. Magnetotransport measurements revealed that the magnetic transition temperature can be as high as 110 kelvin. The origin of the ferromagnetic interaction is discussed. Multilayer heterostructures including resonant tunneling diodes (RTDs) have also successfully been fabricated. The magnetic coupling between two ferromagnetic (Ga,Mn)As films separated by a nonmagnetic layer indicated the critical role of the holes in the magnetic coupling. The magnetic coupling in all semiconductor ferromagnetic/nonmagnetic layered structures, together with the possibility of spin filtering in RTDs, shows the potential of the present material system for exploring new physics and for developing new functionality toward future electronics.

- by sachin kumar
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- Science, III-V Semiconductors, Magnetic Materials, Semiconductor Devices

The preparation of superparamagnetic magnetite (Fe 3 O 4 ) nanoparticles by electro-precipitation in ethanol is proposed. Particle average size can be set from 4.4 to 9 nm with a standard deviation around 20%. Combination of wide-angle X-ray scattering (WAXS), Electron energy loss spectroscopy (EELS) and Mö ssbauer spectroscopy characterizations clearly identifies the particles as magnetite single-crystals (Fe 3 O 4 ).

This study presents a comprehensively and systematically structural, chemical and magnetic characterization of *9.5 nm virtually monodispersed nickel ferrite (NiFe 2 O 4 ) nanoparticles prepared using a modified liquid-solid-solution (LSS) assisted hydrothermal method. Lattice-resolution scanning transmission electron microscope (STEM) and converged beam electron diffraction pattern (CBED) techniques are adapted to characterize the detailed spatial morphology and crystal structure of individual NiFe 2 O 4 particles at nano scale for the first time. It is found that each NiFe 2 O 4 nanoparticle is single crystal with an fcc structure. The morphology investigation reveals that the prepared NiFe 2 O 4 nanoparticles of which the surfaces are decorated by oleic acid are dispersed individually in hexane. The chemical composition of nickel ferrite nanoparticles is measured to be 1:2 atomic ratio of Ni:Fe, indicating a pure NiFe 2 O 4 composition. Magnetic measurements reveal that the as-synthesized nanocrystals displayed superparamagnetic behavior at room temperature and were ferromagnetic at 10 K. The nanoscale characterization and magnetic investigation of monodispersed NiFe 2 O 4 nanoparticles should be significant for its potential applications in the field of biomedicine and magnetic fluid using them as magnetic materials.

- by Nigel Mellors
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- Magnetic Materials, Nanowires

Eddy-current couplings are becoming popular devices for speed and torque control. Efficiency of these couplings depends on the excitation level; therefore, the routes and density of induced currents affect it significantly. This paper focuses on the design of a squirrel cage-type coupling disk, which forces eddy currents to flow perpendicular to both magnetic field lines and the axis of rotation. Lorentz force and transmitted torque are consequently optimized. The investigation is performed both numerically and experimentally, with results being presented for variable air gaps and speeds. A comparison between plain and slotted disk conductors, tested under identical setups , demonstrates the effect of the proposed design on torque throughput and efficiency. In addition to this, the influence of number and size of slots and the effect of filling slots with iron are studied by parametric finite-element modeling verified by experiments.

- by Michael Lampérth
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- Engineering, Design, Magnetic Materials, Finite element method

The existing rocket propulsion mechanism derives energy from rocket fuels. The rocket fuel is burnt inside a chamber and gas produced due to combustion is expelled out through a nozzle, which produces the upward thrust for rockets or spacecrafts.
The currently available rocket fuels are in solid liquid and as from Hydrogen peroxide is one of the commonly used rocket fuels. Cold gas is another gaseous propellant. The disadvantage of these rocket fuels is that it produces low thrust.Kerosene is a liquid propellant. The liquid fuel requires cryogenic systems for their implementation. The combustion of these fuels produces toxic gases, which are expelled to the space to obtain the required thrust. Thus it creates pollution in the outer space. The system that use solid fuels are unregulated. They produce lower thrust also.
Nuclear energy can be used as a propellant. But it produces radiations, which are very harmful. These radiations can penetrate the atmosphere and affect the human kind and other living things. The effect of nuclear radiations lasts for years that can jeopardize life on earth. So the use of nuclear propulsion technique is very risky. An Electrodynamic tether with its unique features put forward a better option for propulsion of rockets and spacecrafts.

- by Sai Charan Bharadwaj
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- Electrical Engineering, Electromagnetism, Space Sciences, Magnetic Materials

The dynamic mechanical properties in terms of the storage modulus E′, loss modulus E″, and the loss tangent δ has been studied for highly filled magnetic polymer composites. The effect of surface treatment on the relaxation spectra has been clearly elucidated and quantitative values indicating the extent of polymer–filler interactions have been given. Various models have been tested for describing the viscoelastic behavior of such highly filled systems. The Wiechert model using a single-arm with a Cole–Cole parameter has been shown to effectively fit the Argand diagram in the case of the present highly filled systems

- by Dr Aroon Shenoy
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- Polymer Engineering, Rheology, Magnetic Materials, Polymer Engineering & Rheology

Here we study the effect of La doping in EuO thin films using SQUID magnetometry, muon spin rotation ($\mu$SR), polarized neutron reflectivity (PNR), and density functional theory (DFT). The mu\mumuSR data shows that the La$_{0.15}$Eu$_{0.85}$O is homogeneously magnetically ordered up to its elevated TrmCT_{\rm C}TrmC. It is concluded that bound magnetic polaron behavior does not explain the increase in TrmCT_{\rm C}TrmC and an RKKY-like interaction is consistent with the mu\mumuSR data. The estimation of the magnetic moment by DFT simulations concurs with the results obtained by PNR, showing a reduction of the magnetic moment per La$_{x}$Eu$_{1-x}$O for increasing lanthanum doping. This reduction of the magnetic moment is explained by the reduction of the number of Eu-4$f$ electrons present in all the magnetic interactions in EuO films. Finally, we show that an upwards shift of the Fermi energy with La or Gd doping gives rise to half-metallicity for doping levels as high as 3.2 %.

- by Nicholas Hine and +1
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- Physics, Condensed Matter Physics, Semiconductor Physics, Magnetic Materials

The selection of proper material for each application is a critical part in every manufacturing industry. In the field of aerospace and automobile the major requirement is light weight yet strong material which can possess every aspect of design parameters. Magnesium alloy one of the major raw material used in these industries due to its light weight, good thermal conductivity etc. Also Friction stir welding is the joining process that is being used in these industries as it is a solid state joining process. This paper gives a detailed review about Friction Stir welding of Mg alloys. The review period is considered from 2009 to 2015.A detailed review about Friction stir welding of Mg alloys has not been done before in this manner. This review work may be a ready reference for subsequent researchers.

- by Edwin Raja Dhas
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- Mechanical Engineering, Materials Science, Energy, Magnetic Materials

Growth, characterization, and properties of ultra-thin magnetic films and inultilayers I editors, Berend T. Jonker, Joseph P. Heremans, Ernesto E. Marinero. p. cm.-(Materials Research Society symposium proceedings : ISSN 0272-9172; v.... more

- by Joseph Heremans
- •
- Microstructure, Crystal Growth, Control, Magnetic Materials

We investigate the binding surface along the Bain path and phonon dispersion relations for the cubic phase of the ferromagnetic binary alloys Fe3X (X = Ni, Pd, Pt) for L12 and DO22 ordered phases from first principles by means of density functional theory. The phonon dispersion relations exhibit a softening of the transverse acoustic mode at the M-point in the L12-phase in accordance with experiments for ordered Fe3Pt. This instability can be associated with a rotational movement of the Fe-atoms around the Ni-group element in the neighboring layers and is accompanied by an extensive reconstruction of the Fermi surface. In addition, we find an incomplete softening in [111] direction which is strongest for Fe3 Ni. We conclude that besides the valence electron density also the specific Fe-content and the masses of the alloying partners should be considered as parameters for the design of Fe-based functional magnetic materials.

- by Waheed Adeagbo
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- Magnetic Materials, Structural Stability, Physical sciences, Dispersion Relation

The formation and magnetic behaviour of nanoparticles of various manganese oxides have been studied. For synthesis, manganese oxalate dihydrate is first produced via sol-gel process and then decomposed in oxygen, air, nitrogen, or argon ambient at different temperatures. The decomposition process leads to emergence of Mn 3 O 4 which undergoes oxidation, oxidation-reduction, or reduction process subsequently depending upon the availability of oxygen to yield Mn 2 O 3 in air/O 2 and MnO in argon/nitrogen ambient. A partial reaction causes retention of some Mn 3 O 4 alone or Mn 3 O 4 and Mn 5 O 8 together as secondary phase(s). The magnetic susceptibility ( ) data reveal (i) antiferro-magnetic nature for Mn 2 O 3 , Mn 5 O 8 and MnO with Néel temperature 75 K, 131 K and 115 K, respectively, (ii) orthorhombic to cubic crystallographic transition in Mn 2 O 3 at 310 K for the first time, and (iii) ferri-magnetic character for Mn 3 O 4 with Curie temperature 46 K. Further, it is demonstrated that a small quantity of Mn 3 O 4 always remains in the products and can be detected by susceptibility data below 50 K only with bifurcation in ZFC and FC curves and blocking temperature in the range 30-40 K. Also, the decomposition of manganese oxalate at 1100 • C for 4 h in air leads to formation of pure Mn 3 O 4 with saturation magnetization of 1.85 B per molecule and coercivity of 4750 Oe at 10 K.

- by Bhagwati Joshi
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- Engineering, Magnetic Materials, Sol Gel Process, Physical sciences

Magnetic separations have for decades been essential processes in diverse industries ranging from steel production to coal desulfurization. In such settings magnetic fields are used in continuous flow processes as filters to remove magnetic impurities. High gradient magnetic separation (HGMS) has found even broader use in wastewater treatment and food processing. Batch scale magnetic separations are also relevant in industry, particularly biotechnology where fixed magnetic separators are used to purify complex mixtures for protein isolation, cell separation, drug delivery, and biocatalysis. In this review, we introduce the basic concepts behind magnetic separations and summarize a few examples of its large scale application. HGMS systems and batch systems for magnetic separations have been developed largely in parallel by different communities. However, in this work we compare and contrast each approach so that investigators can approach both key areas. Finally, we discuss how new advances in magnetic materials, particularly on the nanoscale, as well as magnetic filter design offer new opportunities for industries that have challenging separation problems.

In this paper, an experimental investigation, an analytical analysis and a numerical model of a typical four-point bending test on a honeycomb sandwich panel are proposed. The honeycomb core is modelled as a single solid layer of equivalent material properties. Analytical and numerical (finite element) homogenization approaches are used to compute the effective properties of the honeycomb core. A general kinematic model (unified formulation) has been adopted and used for the modelling of honeycomb sandwich panel submitted to the bending test. A comparative study of major classes of representative theories has been considered. Qualitative and quantitative assessments of displacement, stress have been presented and discussed.

- by Salim Belouettar
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- Engineering, Materials Engineering, Mechanical Engineering, Chemical Engineering

A mathematical homogenization technique is applied to the computation of eddy currents in strip-wound amorphous cores. The results are compared with a standard finite-element (FE) solution of a test problem. The method is applied to the... more

- by Oriano Bottauscio and +1
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- Engineering, Magnetic Materials, Finite Element, Physical sciences