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External Magnetic Field (external + magnetic_field)
Selected AbstractsSingle-cell detection by gradient echo 9.4 T MRI: a parametric studyCONTRAST MEDIA & MOLECULAR IMAGING, Issue 4 2006P. Smirnov Abstract Recent studies have shown that cell migration can be monitored in vivo by magnetic resonance imaging after intracellular contrast agent incorporation. This is due to the dephasing effect on proton magnetization of the local magnetic field created by a labelled cell. Anionic iron oxide nanoparticles (AMNP) are among the most efficient and non-toxic contrast agents to be spontaneously taken up by a wide variety of cells. Here we measured the iron load and magnetization of HeLa tumour cells labelled with AMNP, as a function of the external magnetic field. High-resolution gradient echo 9.4,T MRI detected individual labelled cells, whereas spin echo sequences were poorly sensitive. We then conducted a systematic study in order to determine the gradient echo sequence parameters (echo time, cell magnetization and resolution) most suitable for in vivo identification of single cells. Copyright © 2006 John Wiley & Sons, Ltd. [source] Trivelpiece-Gould mode produced gas-discharges in a diffusion-controlled regimeCONTRIBUTIONS TO PLASMA PHYSICS, Issue 3-4 2003H. Schlüter Abstract The study presents a numerical fluid-plasma model of waveguide discharges sustained by travelling azimuthallysymmetric Trivelpiece-Gould modes. The results describe weakly-magnetized (, , ,e) plasma production in a diffusion-controlled regime (, being the wave frequency, ,e the electron gyro-frequency). However, with respect to the influence of the external magnetic field on the transverse ambipolar-diffusion coefficient, cases of both weak and strong impact of the magnetic field are covered. In its electrodynamical part, the model involves detailed description of the behaviour of the Trivelpiece-Gould waves in radially-inhomogeneous collisional plasmas. The gas-discharge part of the model specifies plasma production in an argon gas. The results are for the self-consistent structure of the discharge composed out of the interrelated variations of wavenumber, space damping rate, plasma density, electron temperature and power absorbed on average by an electron. The analysis is in terms of influence of gas-pressure and magnetic-field changes. [source] A micropillar-integrated smart microfluidic device for specific capture and sorting of cellsELECTROPHORESIS, Issue 24 2007Yan-Jun Liu Abstract An integrated smart microfluidic device consisting of nickel micropillars, microvalves, and microchannels was developed for specific capture and sorting of cells. A regular hexagonal array of nickel micropillars was integrated on the bottom of a microchannel by standard photolithography, which can generate strong induced magnetic field gradients under an external magnetic field to efficiently trap superparamagnetic beads (SPMBs) in a flowing stream, forming a bed with sufficient magnetic beads as a capture zone. Fluids could be manipulated by programmed controlling the integrated air-pressure-actuated microvalves, based on which in situ bio-functionalization of SPMBs trapped in the capture zone was realized by covalent attachment of specific proteins directly to their surface on the integrated microfluidic device. In this case, only small volumes of protein solutions (62.5,nL in the capture zone; 375,nL in total volume needed to fill the device from inlet A to the intersection of outlet channels F and G) can meet the need for protein! The newly designed microfluidic device reduced greatly chemical and biological reagent consumption and simplified drastically tedious manual handling. Based on the specific interaction between wheat germ agglutinin (WGA) and N -acetylglucosamine on the cell membrane, A549 cancer cells were effectively captured and sorted on the microfluidic device. Capture efficiency ranged from 62 to 74%. The integrated microfluidic device provides a reliable technique for cell sorting. [source] Magnetic Control of Tubular Catalytic Microbots for the Transport, Assembly, and Delivery of Micro-objectsADVANCED FUNCTIONAL MATERIALS, Issue 15 2010Alexander A. Solovev Abstract Recently a significant amount of attention has been paid towards the development of man-made synthetic catalytic micro- and nanomotors that can mimic biological counterparts in terms of propulsion power, motion control, and speed. However, only a few applications of such self-propelled vehicles have been described. Here the magnetic control of self-propelled catalytic Ti/Fe/Pt rolled-up microtubes (microbots) that can be used to perform various tasks such as the selective loading, transportation, and delivery of microscale objects in a fluid is shown; for instance, it is demonstrated for polystyrene particles and thin metallic films ("nanoplates"). Microbots self-propel by ejecting microbubbles via a platinum catalytic decomposition of hydrogen peroxide into oxygen and water. The fuel and surfactant concentrations are optimized obtaining a maximum speed of 275,µm,s,1 (5.5 body lengths per second) at 15% of peroxide fuel. The microbots exert a force of around 3.77,pN when transporting a single 5,µm diameter particle; evidencing a high propulsion power that allows for the transport of up to 60 microparticles. By the introduction of an Fe thin film into the rolled-up microtubes, their motion can be fully controlled by an external magnetic field. [source] An ellipticity criterion in magnetotelluric tensor analysisGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2004M. Becken SUMMARY We examine the magnetotelluric (MT) impedance tensor from the viewpoint of polarization states of the electric and magnetic field. In the presence of a regional 2-D conductivity anomaly, a linearly polarized homogeneous external magnetic field will generally produce secondary electromagnetic fields, which are elliptically polarized. If and only if the primary magnetic field vector oscillates parallel or perpendicular to the 2-D structure, will the horizontal components of the secondary fields at any point of the surface also be linearly polarized. When small-scale inhomogeneities galvanically distort the electric field at the surface, only field rotations and amplifications are observed, while the ellipticity remains unchanged. Thus, the regional strike direction can be identified from vanishing ellipticities of electric and magnetic fields even in presence of distortion. In practice, the MT impedance tensor is analysed rather than the fields themselves. It turns out, that a pair of linearly polarized magnetic and electric fields produces linearly polarized columns of the impedance tensor. As the linearly polarized electric field components generally do not constitute an orthogonal basis, the telluric vectors, i.e. the columns of the impedance tensor, will be non-orthogonal. Their linear polarization, however, is manifested in a common phase for the elements of each column of the tensor and is a well-known indication of galvanic distortion. In order to solve the distortion problem, the telluric vectors are fully parametrized in terms of ellipses and subsequently rotated to the coordinate system in which their ellipticities are minimized. If the minimal ellipticities are close to zero, the existence of a (locally distorted) regional 2-D conductivity anomaly may be assumed. Otherwise, the tensor suggests the presence of a strong 3-D conductivity distribution. In the latter case, a coordinate system is often found, in which three elements have a strong amplitude, while the amplitude of the forth, which is one of the main-diagonal elements, is small. In terms of our ellipse parametrization, this means, that one of the ellipticities of the two telluric vectors approximately vanishes, while the other one may not be neglected as a result of the 3-D response. The reason for this particular characteristic is found in an approximate relation between the polarization state of the telluric vector with vanishing ellipticity and the corresponding horizontal electric field vector in the presence of a shallow conductive structure, across which the perpendicular and tangential components of the electric field obey different boundary conditions. [source] Templated Synthesis of Mesoporous Superparamagnetic Polymers,ADVANCED FUNCTIONAL MATERIALS, Issue 14 2007B. Fuertes Abstract We present a novel synthetic strategy for fabricating superparamagnetic nanoparticles randomly dispersed in a mesoporous polymeric matrix. This method is based on the use of mesoporous silica materials as templates. The procedure used to obtain these mesoporous magnetic polymers consisted in: a),generating iron oxide ferrite magnetic nanoparticles (FMNP) of size ,,7,8,nm within the pores of the silica, b),loading the porosity of the silica/FMNP composite with a polymer (Polydivinylbenzene), c),selectively removing the silica framework from the resulting silica/FMNP/polymer composite. Such magnetic porous polymeric materials exhibit large surface areas (up to 630,m2,g,1), high pore volumes (up to 0.73,cm3,g,1) and a porosity made up of mesopores. In this way, it is possible to obtain superparamagnetic mesoporous hybrid nanocomposites that are easily manipulated by an external magnetic field and display different magnetic behaviours depending on the textural properties of the template employed. [source] Stray-Field-Induced Actuation of Free-Standing Magnetic Shape-Memory FilmsADVANCED MATERIALS, Issue 36 2009Michael Thomas Free-standing epitaxial NiMnGa films are used to demonstrate a novel thermal actuation mode. To avoid the high magnetostatic stray-field energy, the easy axis of the martensitic variants is aligned preferentially in-plane. This results in a maximum strain of up to 1.1% without the need for training or an external magnetic field. [source] High-frequency Impedance and Sensitivity of Micro-fluxgate Sensors Fabricated with Cobalt Base Amorphous FilmsIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 4 2008Kwang-Ho Shin Non-member Abstract Micro-fluxgate sensors 2 mm long, 1.5 mm wide were fabricated with CoZrNb amorphous films. Their high-frequency input/output impedance was measured and evaluated to investigate whether the sensor output and/or sensitivity could be estimated by the complex impedance, especially the reactance. The output reactance changed from 11.1 to 6.1 ohm at 8 MHz by applying the external magnetic field of 10.5 Oe, whereas the input impedance changed from 12.3 to 10.1 ohm. The parasitic capacitance was driven from the measured reactance and resonance frequency. The inductance and inductive reactance could be evaluated with the parasitic capacitance and measured reactance. The tendency of output voltage dependent on frequency is similar to that of inductive reactance. The sensitivity of the fabricated sensor was 17.6 mV/VOe at 8 MHz. Copyright © 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] Fluorescent Polystyrene,Fe3O4 Composite Nanospheres for In Vivo Imaging and HyperthermiaADVANCED MATERIALS, Issue 21 2009Donglu Shi Quantum dots (QDs) are immobilized on the surfaces of magnetic Fe3O4 -composite nanospheres (MNSs, see figure). The QDs exhibit intense visible-light emission in fluorescence spectroscopy and successfully facilitate, for the first time, in vivo soft-tissue imaging in live mice. The Fe3O4 nanoparticles respond to an external magnetic field by increasing the temperature of the surrounding environment (i.e., hyperthermia), which can be used therapeutically. [source] Inverse design of directional solidification processes in the presence of a strong external magnetic fieldINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2001Rajiv Sampath Abstract A computational method for the design of directional alloy solidification processes is addressed such that a desired growth velocity ,f under stable growth conditions is achieved. An externally imposed magnetic field is introduced to facilitate the design process and to reduce macrosegregation by the damping of melt flow. The design problem is posed as a functional optimization problem. The unknowns of the design problem are the thermal boundary conditions. The cost functional is taken as the square of the L2 norm of an expression representing the deviation of the freezing interface thermal conditions from the conditions corresponding to local thermodynamic equilibrium. The adjoint method for the inverse design of continuum processes is adopted in this work. A continuum adjoint system is derived to calculate the adjoint temperature, concentration, velocity and electric potential fields such that the gradient of the L2 cost functional can be expressed analytically. The cost functional minimization process is realized by the conjugate gradient method via the FE solutions of the continuum direct, sensitivity and adjoint problems. The developed formulation is demonstrated with an example of designing the boundary thermal fluxes for the directional growth of a germanium melt with dopant impurities in the presence of an externally applied magnetic field. The design is shown to achieve a stable interface growth at a prescribed desired growth rate. Copyright © 2001 John Wiley & Sons, Ltd. [source] Quasi-Epitaxial Growth of Ni Nanoshells on Au Nanorods,ADVANCED MATERIALS, Issue 17 2007M. Grzelczak Magnetic nickel shells can be grown on gold nanorods with platinum tips by reduction of Ni2+ with hydrazine in aqueous cetyl-trimethylammonium bromide (CTAB) solution, using Pt tips as catalysts. The plasmon absorption of the starting gold nanorods can be totally quenched by the metallic layer of nickel, while the magnetic character of these anisotropic, hybrid nanocrystals is demonstrated through alignment under an external magnetic field. Quasi-epitaxial growth is demonstrated by HRTEM and electron diffraction (see figure). [source] Palladium(II)-Phosphine Complexes Supported on Magnetic Nanoparticles: Filtration-Free, Recyclable Catalysts for Suzuki,Miyaura Cross-Coupling ReactionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2-3 2010Sankaranarayanapillai Shylesh Abstract An organic-inorganic hybrid heterogeneous nanocatalyst system was synthesized by covalent grafting a palladium dichloride complex of the type (L)2PdCl2 (L=trimethoxysilyl-functionalized triphenylphosphine) on silica-coated magnetic nanoparticles. It is a highly active and recyclable catalyst for the Suzuki,Miyaura cross-coupling reaction. The new catalyst can easily be separated from the reaction mixture by applying an external magnetic field and can be recycled many times without any loss of activity. [source] Platinum Nanoparticles Supported on Ionic Liquid-Modified Magnetic Nanoparticles: Selective Hydrogenation CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2007Raed Abu-Reziq Abstract A method for supporting platinum nanoparticles on magnetite nanoparticles is described. The method requires modification of the surface of the magnetic nanoparticles with ionic liquid groups. Before modification, the magnetic nanoparticles are not stable and easily aggregate and, after modification, the magnetite nanoparticles become highly stable and soluble in polar or non-polar organic solvents depending on the alkyl group of the linked ionic liquids. The supporting of platinum nanoparticles on the modified magnetic nanoparticles was achieved by adsorbing platinum salts (K2PtCl4) on the surface of the magnetite nanoparticles via ion exchange with the linked ionic liquid groups and then reducing them by hydrazine. The supported platinum nanoparticles were applied in the catalytic hydrogenation of alkynes in which cis -alkenes were selectively produced, and in the hydrogenation of ,,,-unsaturated aldehydes where the allyl alcohols were obtained as the exclusive products. The new catalyst can be easily separated from the reaction mixtures by applying an external magnetic field and recycled. [source] The dynamic behavior of magnetic colloids in suspensionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007Tina Autenrieth The dynamic behavior of magnetic colloidal particles in suspension is investigated. The particles of the core,shell colloid consist of a cobalt ferrite core embedded in a silica shell and are stabilized by surface charges. As the suspension is strongly opaque to visible light, it can not be probed by dynamic light scattering techniques as a result of strong multiple scattering as well as absorption effects. Therefore, the static and dynamic behavior is probed with small-angle X-ray scattering and X-ray photon correlation spectroscopy (XPCS), respectively. Using XPCS, we are able to study the diffusion coefficient of an opaque colloidal system as a function of the scattering vector. In this paper, we report on the behavior of the colloidal system in the absence of an external magnetic field, meaning that the magnetic moments of the particles are oriented randomly. We find no evidence for magnetic interactions in the static data, while the dynamic XPCS data deviate very significantly from the predictions of model calculations. [source] Benefits of polarized small-angle neutron scattering on magnetic nanometer scale structure modelingJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2003André Heinemann Recent use of polarized neutron technique in small-angle scattering (SANS) have led to impressive results in the case of magnetic nanometer-scale structure analysis. In some particular cases this method offers the possibility to survey structure models with the necessary accuracy for the first time. The different cross sections for spin-up and spin-down neutron scattering on magnetic precipitates can be combined with the method of chemical contrast variation. All data fitting using structure models will benefit of that kind of constraints. The analysis of the interference term of nuclear and magnetic scattering respectively enables the extraction of additional information about the composition and magnetization profiles of the samples. Here we place emphasis on the difference of spin-up and spin-down neutron scattering intensities to obtain this information. This technique profits by the clear distinction between magnetic and nonmagnetic scattering contributions and the strong auxiliary conditions for model fitting procedures. Depending on the relative orientations of the external magnetic field, the local magnetization of the precipitates and the scattering vector, significant scattering patterns can be scrutinized. Beside general formulas for some special cases of present experimental interest we exercise the approach to a nontrivial case of data obtained from polarised SANS experiments at the Berlin Neutron Scattering Center (BENSC). [source] Calculations of frequency-dependent molecular magnetizabilities with quasi-relativistic time-dependent generalized unrestricted Hartree,Fock methodJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 4 2007Terutaka Yoshizawa Abstract The time-dependent generalized unrestricted Hartree,Fock (TDGUHF) method combined with a two-component quasi-relativistic Hamiltonian generated from the Douglas,Kroll,Hess (DKH) transformation was developed to calculate frequency-dependent molecular magnetizabilities, which are the linear response quantity of a molecule to an external magnetic field. By calculating the magnetizabilities of H2X (X = O, S, Se, and Te), the noble gases (He, Ne, Ar, Kr, and Xe) and small open shell molecules (CH2, CH3, and O2), we found that scalar relativistic terms affect mainly the diamagnetic magnetizability and spin-orbit (SO) interaction affects the paramagnetic magnetizability. © 2007 Wiley Periodicals, Inc. J Comput Chem 28: 740,747, 2007 [source] A new approach to measuring high-resolution magnetic Compton profilesJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2006H. Kawata It is demonstrated that long-term stability in the polarization of incident photons delivered from an insertion device makes it possible to measure magnetic Compton profiles with a momentum resolution of 0.15 atomic units or better, without employing a solid-state detector and the traditional method of reversing the external magnetic field or the handedness of the polarization of incident photons in an asynchronous cycle with a short period of tens to hundreds of seconds. [source] Physicochemical parameters and magnetic speciation of Iron in Nakivubo Channel and Lake Victoria watersLAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 2 2009Naziriwo Betty Bbosa Abstract Magnetic speciation technique was used for the determination of iron species in Nakivubo Channel and Lake Victoria waters. The method consisted of a column of supported Dowex 1-X18, 20,50 US mesh (Cl) surrounded by movable permanent magnets. Dowex was supported by a porous material to permit adequate passage of the eluent through the column. In the presence of an external magnetic field, enhanced capacity for adsorption of iron III was observed. The enhanced capacity is primarily due to the magnetic field produced and ion exchange sorption mechanism. The results show that, most of the Iron in Nakivubo Channel waters is in reduced ferrous form while, in the Lake Victoria waters, it exists in the oxidized ferric form. Physicochemical parameters for the field samples are discussed in this study. Turbidity levels in catchments with substantial vegetation were significantly lower than those without. pH values up to 13 was observed for some of the point source. The physicochemical parameters along Nakivubo Channel waters were relatively higher than the Lake Victoria waters indicating slow increasing pollution load along the Nakivubo Channel. [source] Phase Biaxility in Smectic-A Side-Chain Liquid Crystalline ElastomersMACROMOLECULAR RAPID COMMUNICATIONS, Issue 8 2009Rebekka Storz Abstract 2H NMR investigations on the biaxial phase behavior of smectic-A liquid crystalline side-chain elastomers are presented. Biaxiality parameters were determined by measuring the quadrupolar splitting of two spin probes, namely benzene-d6 and hexamethylbenzene-d18, at various angles between the principal director and the external magnetic field: while for a uniaxial sample the angular dependence can be described by the second Legendre polynomial, an additional asymmetric term needs to be included to fit the data of the two investigated biaxial systems. Two elastomers synthesized from mesogens that differ in the molecular geometry in order to study the molecular origin of biaxiality were compared. Biaxiality is observed for both elastomers when approaching the glass transition, suggesting that the network dynamics dominate the formation of the biaxial phase. [source] Binding and Sulfonation of Poly(acrylic acid) on Iron Oxide Nanoparticles: a Novel, Magnetic, Strong Acid Cation Nano-AdsorbentMACROMOLECULAR RAPID COMMUNICATIONS, Issue 19 2005Sou-Yee Mak Abstract Summary: A novel, magnetic, strong acid cation nano-adsorbent has been developed by the covalent binding of poly(acrylic acid) on the surface of Fe3O4 nanoparticles followed by sulfonation using sulfanilic acid via carbodiimide activation. The nano-absorbent can be easily recovered or manipulated with an external magnetic field and shows a good capacity for the rapid and efficient adsorption of multivalent metal cations from aqueous solutions. An illustration for the binding and sulfonation of PAA on Fe3O4 nanoparticles to produce a magnetic, strong acid cation nano-adsorbent. [source] Environmentally friendly flame retardants.MAGNETIC RESONANCE IN CHEMISTRY, Issue S1 2007A detailed solid-state NMR study of melamine orthophosphate Abstract We used solid-state NMR spectroscopy to gain detailed information about the proton positions, proximities and the hydrogen-bonding network in the environmentally friendly flame retardant melamine orthophosphate (MP). High-resolution proton one- and two-dimensional solid-state NMR spectra were obtained at high external magnetic field in combination with fast magic angle spinning of the sample. Furthermore, we recorded homo- and heteronuclear correlation spectra of types 15N15N, 1H13C, 1H15N and 1H31P. In addition, we determined the geometry of the NH and NH2 groups in MP by 15N1H heteronuclear recoupling experiments. We were able to completely assign the different isotropic chemical shifts in MP. Furthermore, we could identify the protonation of the melamine and orthophosphate moieties. The experimental results are discussed in connection with the structural model obtained by powder X-ray diffraction together with a combined molecular modeling-Rietveld refinement approach (De Ridder et al. Helv. Chim. Acta 2004; 87: 1894). We show that the geometry of the NH2 groups can only be successfully estimated by solid-state NMR. Copyright © 2007 John Wiley & Sons, Ltd. [source] Parahydrogen-induced polarization in imaging: Subsecond 13C angiographyMAGNETIC RESONANCE IN MEDICINE, Issue 1 2001K. Golman Abstract High nuclear spin polarization of 13C was reached in organic molecules. Enhancements of up to 104, compared to thermal polarization at 1.5 T, were achieved using the parahydrogen-induced polarization technique in combination with a field cycling method. While parahydrogen has no net polarization, it has a high spin order, which is retained when hydrogen is incorporated into another molecule by a chemical reaction. By subjecting this molecule to a sudden change of the external magnetic field, the spin order is transferred into net polarization. A 13C angiogram of an animal was generated in less than a second. Magn Reson Med 46:1,5, 2001. © 2001 Wiley-Liss, Inc. [source] A relaxed model and its homogenization for nematic liquid crystals in composite materialsMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 10 2004Quan Shen Abstract We analyse a model for equilibrium configurations of composite systems of nematic liquid crystal with polymer inclusions, in the presence of an external magnetic field. We assume that the system has a periodic structure, and consider the relaxed problem on the unit length constraint of the nematic director field. The relaxation of the Oseen,Frank energy functional is carried out by including bulk as well as surface energy penalty terms, rendering the problem fully non-linear. We employ two-scale convergence methods to obtain effective configurations of the system, as the size of the polymeric inclusions tends to zero. We discuss the minimizers of the effective energies for, both, the constrained as well as the unconstrained models. Copyright © 2004 John Wiley & Sons, Ltd. [source] Dispersion characteristics of LiTi-Ferrite radomeMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 1 2010Naveen Kumar Saxena Abstract The dispersion characteristics of a magnetically switchable LiTi-Ferrite radome is presented. A thin layer of LiTi-ferrite is used as superstrate or radome layer, which control the radiation, reception, and scattering from a printed antenna or array by applying a DC magnetic bias field in the plane of the ferrite, orthogonal to the RF magnetic field. In this analysis, absorbing and transmission power coefficients are calculated to obtain the power loss in radome layer and transmitted power, respectively. The absorbing power coefficient verifies the switching behavior of radome for certain range of applied external magnetic field (Ho), which depends on the resonance width parameter (,H) of ferrite material. By properly choosing the bias field, quasi TEM wave propagation in the ferrite layer can be made to be zero or negative over a certain frequency range, results in a switching behavior in the ferrite layer. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 52,54, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24828 [source] Magneto-dielectric properties of the Y3Fe5O12 and Gd3Fe5O12 dielectric ferrite resonator antennasMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 11 2008P. B. A. Fechine Abstract The main objective of this work was to study the magnetic and dielectric properties of Y3Fe5O12 and Gd3Fe5O12 garnets resonator antennas obtained from a new procedure in the solid state ceramic technique. These ferrite resonator antennas (FRAs) had the ability to change their characteristics as a function of the applied magnetic field. The Y3Fe5O12 resonator was able to increase the antenna frequency range with application of external magnetic field. Some of the properties of dielectric resonator antennas (DRAs) can be actively controlled by using low-loss ferrite materials. When unbiased, these ferrite resonator antennas (FRAs) exhibit similar behavior to DRAs. However, when a DC magnetic bias is applied, the tensor nature of the ferrite permeability is invoked, and various parameters can be controlled electronically. We also studied the magnetic behavior of the antennas and did a numerical study of the gain and directivity of the ferrite resonator antennas. These results can be important to develop wideband third-generation (3G) cellular phones and other wireless products. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2852,2857, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23824 [source] Magnetoimpedance (MI) in amorphous wires: new materials and applicationsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2009Larissa V. Panina Abstract The discovery of the magnetoimpedance (MI) effect in 1994 had a strong impact on the development of magnetic sensors. Along with traditional areas of sensing applications (data storage, bio-medical electronics, robotics and security), the MI elements have a high potential for applications in smart sensory systems (self-sensing composites) operating at microwave frequencies owing to still very large MI ratios of 50,100% in Co-rich amorphous wires at GHz frequencies. Here we introduce two types of MI wire composites: 2D-arrays and mixtures of wire pieces. In such materials the effective permittivity has strong dispersion in a frequency band determined by a plasma frequency or a dipole resonance, respectively. If MI wires are used as constituent elements, this dispersion may be very sensitive to the magnetic properties of wires since the wire impedance determines the relaxation parameter of the effective permittivity. For example, increasing the wire impedance by establishing the magnetisation along the axis with an external magnetic field broadens the resonance band, decreases the reflection amplitude and may open a bandpass. Depending on the magnetic anisotropy in wires, tuning can be realized with both magnetic field and stress. It is foreseen that MI-wire composite materials could be suitable for large scale applications, in particular, for free space filters in secure wireless systems and for microwave nondestructive testing and control in civil engineering. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effects of uniaxial stress on the magnetic properties of thin films and GMR sensors prepared on polyimide substratesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2008Berkem Özkaya Abstract The effects of externally applied uniaxial stress on the magnetic properties of Co thin films and pseudo-spin-valve (PSV) structures on flexible polyimide substrates were investigated. The advantage of the polyimide substrate is its flexibility and high elasticity (,1%), which cannot be achieved using conventional crystalline substrates. The Co layers exhibit a macroscopic easy axis induced by the preparation process. When the stress is applied perpendicular to the induced in-plane easy axis, the magnetic domains in the film rotate towards the applied stress direction, which was confirmed using Kerr microscopy and magneto-optical Kerr effect (MOKE) magnetometer measurements. A Co/Cu/Ni PSV system was prepared on polyimide substrate with dc magnetron sputtering. Applying uniaxial stress leads to opposite rotation of the magnetisation directions in both layers to each other due to different signs of the magnetostriction coefficients of Co and Ni. The magnetisation and giant magnetoresistance (GMR) curves under applied stress were recorded using in situ MOKE and current in-plane four-point probe techniques, respectively. When the stress is applied perpendicular to the external magnetic field (Hext), the operating range of the GMR sensor increases, whereas the sensitivity decreases. Anisotropy energies and saturation magnetostriction values of the Co and Ni layer were determined by fitting the GMR and magnetisation curves using a micromagnetic model. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Self-sustained current oscillations in a multi-quantum-well spin polarized structure with normal contactsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2008R. Escobedo Abstract Self-sustained current oscillations (SSCO) are found in a nonlinear electron spin dynamics model of a n-doped dc voltage biased semiconductor II,VI multi-quantum well structure (MQWS) having one or more of its wells doped with Mn. Provided one well is doped with magnetic impurities, spin polarized current can be obtained even if normal contacts have been attached to this nanostructure. Under certain conditions, the system exhibits static electric field domains and stationary current or moving domains and time-dependent oscillatory current. We have found SSCO for nanostructures with four or more QWs. The presence of SSCO depends on the spin-splitting induced by both, the exchange interaction and the external magnetic field. We also calculate the minimal doping density needed to have SSCO, and a bound above which SSCO disappear. This range is crucial to design a device behaving as a spin polarized current oscillator. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spin-filtering effect in a two-dimensional electron gas under a local fringe fieldPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 12 2007Seon-Gu Huh Abstract We fabricated a spin-filtering device which consists of InAs based two-dimensional electron gas and two ferromagnetic pads. A fringe field at the edge of a ferromagnetic pad was used to induce spin polarization of the moving electrons in a two-dimensional electron gas. The direction of the fringe field was determined by the magnetization of the ferromagnetic pad, which was switched by using the external magnetic field. A current of which spins were aligned by one fringe field (polarizer) was filtered by the other fringe field (analyzer). The resistance of the device was in either a high state or a low state depending on the alignment of the fringe fields. The spin-filtering effect diminishes rapidly as the thermal energy exceeds the Zeeman splitting. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Fabrication and properties of InSb films with ion-beam sputtering for use in the amplification of magneto-surface-acoustic wavesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2004N. Obata Abstract The magnetic surface acoustic wave (MSAW) device can be manipulated by an external magnetic field. However the MSAW is attenuated largely at high frequencies above MHz. Therefore, we proposed a MSAW device having a hybrid structure consisting of FeB amorphous thin film/InSb semiconductor thin film/LiNbO3 substrate. This device is utilized for amplification of surface acoustic waves by the interaction between surface acoustic waves and the carriers in the InSb semiconductor. We prepared (111) InSb thin films by ion beam sputtering. We obtained InSb thin films having Hall mobilities of about 2000 cm2/Vs by subsequent annealing. This showed the possibility of MSAW amplification by low voltages. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||||||||||||||||||||||||||