Showing papers on "Magneto published in 2005"

Ultrafast Magneto-Optics in Ferromagnetic III-V Semiconductors

Abstract: We investigate various ultrafast optical processes in ferromagnetic (III,Mn)V semiconductors induced by femtosecond laser pulses. Two-colour timeresolved magneto-optical spectroscopy has been developed, which allows us to observe a rich array of dynamical phenomena. We isolate several distinct temporal regimes in spin dynamics, interpreting the fast (< 1p s) dynamics as spin heating through sp–d exchange interaction between photo-carriers and Mn ions while the ∼100 ps component is interpreted as a manifestation of spin– lattice relaxation. Charge carrier and phonon dynamics were also carefully studied, showing an ultrashort charge lifetime of photo-injected electrons (∼ 2p s) and propagating coherent acoustic phonon wavepackets with a strongly probe energy dependent oscillation period, amplitude and damping. (Some figures in this article are in colour only in the electronic version)

Relativistic Fluids and Magneto-fluids

Abstract: RELATIVISTIC FLUIDS AND MAGNETO FLUIDS WITH APPLICATIONS IN ASTROPHYSICS AND PLASMA PHYSICS PDF Are you looking for relativistic fluids and magneto fluids with applications in astrophysics and plasma physics Books? Now, you will be happy that at this time relativistic fluids and magneto fluids with applications in astrophysics and plasma physics PDF is available at our online library. With our complete resources, you could find relativistic fluids and magneto fluids with applications in astrophysics and plasma physics PDF or just found any kind of Books for your readings everyday.

Josephson vortex state across the phase diagram ofLa2−xSrxCuO4: A magneto-optics study

Abstract: We present a detailed doping dependent study of the Josephson vortex state in La2−xSrxCuO4 using infrared spectroscopy. A magnetic field as high as 17 tesla, applied along the CuO2 planes, is found to suppress the Josephson plasmon in all measured samples. We find the strongest suppression in samples with dopings close to x=1/8 and attribute this effect to the spontaneous formation of in-plane charge inhomogenities at this doping level. Several theoretical models of the Josephson vortex state are applied to explain the observed effects.

Magneto-spectroscopy and development of terahertz quantum cascade lasers

Abstract: In this work we concentrate our efforts on the generation of laser emission at low THz frequencies (3-1 THz range) employing the quantum cascade technology. Quantum cascade (QC) lasers are unipolar semiconductor lasers based on intersubband transitions in quantum wells that cover a large portion of the Mid and Far Infrared electromagnetic spectrum. Two main research lines have been followed: (i) the development of quantum cascade lasers based on population inversion between parabolic subbands and (ii) the development of low frequency QC lasers based on a three-dimensional electron confinement induced by an external magnetic field. (i) Gain and laser action have been demonstrated in different systems at frequencies of 3.4-3.6 THz exploiting bound-to-bound and bound-to-continuum optical transition. A QC laser emitting at 3.6 THz and based on a vertical transition and resonant tunneling in a single quantum well has been demonstrated. To overcome the limitations in performance of such a system, an heterostructure laser based on a bound-to-continuum transition has been developed. The structure was the first one to operate above the technologically important temperature of liquid nitrogen. With a further development of the bound-to-continuum design that includes lower state lifetime reduction by optical phonon emission, laser action was successfully achieved at 115 K. A study of different waveguide mechanisms suitable for different THz frequencies has also been carried out. (ii) THz quantum cascade lasers based on the in-plane confinement introduced by a strong magnetic field applied perpendiculary to the plane of the layers have been developed. A model system based on large single quantum wells (50-60 nm wide) has been exploited i

Gigantic Enhancement of Magneto-Chiral Effect in Photonic Crystals

Abstract: We theoretically propose a method to enhance dramatically a magneto-chiral(MC) effect by using the photonic crystals composed of a multiferroic material. The MC effect, the directional birefringence even for unpolarized light, is so small that it has been difficult to observe experimentally. Two kinds of periodic structures are investigated; (a) a multilayer and (b) a stripe composed of a magneto-chiral material and air. In both cases, the difference in reflectivity between different magnetization directions is enhanced by a factor of hundreds compared with a bulk material.

Magneto rotor magnetizing and detecting apparatus

Abstract: A magneto rotor magnetizing and detecting apparatus, which contains magnetizing coil located at the position of magneto stator The coil has the same size with magneto stator periphery and connects with diverter switch In another pole of diverter switch, one receiving terminal connects with magnetizing device and the other receiving terminal connects with generation capacity detecting device Magneto rotor is installed on central axis of equilibrator that concerts with computer and is driven by servomotor Magnetizing coil is squeezed into magneto rotor to be located by compressing apparatus driven by pulling cylinder On the same rack, on which equilibrator and pulling cylinder are installed, a gravity-alleviated drilling machine is installed The apparatus also has a device to push out rotor One computer controls every device

Piezo-Magneto-Electric Effects in p-Doped Semiconductors

Abstract: We predict the appearance of a uniform magnetization in strained three-dimensional $p$-doped semiconductors with inversion symmetry breaking subject to an external electric field. We compute the magnetization response to the electric field as a function of the direction and magnitude of the applied strain. This effect could be used to manipulate the collective magnetic moment of hole mediated ferromagnetism of magnetically doped semiconductors.

Machining Spindle Speed Probes

Abstract: Spindle speed probes and spindles including such speed probes. The speed probe is arranged to sense the speed of rotation of a shaft making use of a magneto resistive sensor. The magneto resistive sensor is arranged in a stack with a circuit board substrate, an electronics module and a permanent magnet. An additional magnet may be provided to provide additional drag to help prevent undesirable windmilling.

Giant magneto resistive sensing of critical power system parameters

Abstract: Several experimental and computational attempts to sense and measure the most critical electromechanical operating parameters of power system are conducted in the laboratory. In this paper, power system parameters such as load current (I), partial discharge (PD), corona discharge (CD), capacitive charging current (CCC), and applied high voltage (HV) are under investigation. The objective is to optimize the utilization of some newly developed, low cost, and commercially available hardware sensors and equipment. The hardware includes some novel elements such as, giant magneto resistive (GMR) current/magnetic field sensors. All components are contained around power conductors in a specially designed, none-magneto equipotential cylindrical structure (NECS) prototype. Objectives are being met to manipulate GMR to sense I and HV. From the experimental results and feasibility calculations, GMR sensors are found to maintain their known wide linearity range and accuracy. The manipulations to measure I include: distance, current, bias, and orientation alterations. The manipulations of sensing PD, CD, CCC, and HV include the utilization of a sensitive GMR earth field sensor to measure the short circuited CCC through the NECS prototype.

Horizontal type tunnelling magnetometer

Abstract: The invention relates to a horizontal tunneling magneto meter, which belongs to sensor technology field In order to solve the problem of current tunneling magneto meter that the processing difficulty is large, the invention discloses a small horizontal tunneling magneto meter for magnetic field measurement, the meter includes a head chip and feedback control circuit The head chip is made up of silicon plate and glass The silicon plate includes quality spring system and coil, in the quality spring system, there only has one surface is processed with coil, the Lorentz force direction generated by the current in the coil is parallel to the surface processed with coil in spring system The merits of the invention lie in: only one surface of the sensitive element need to be processed, thus the difficulty can be decreased greatly

Method for manufacturing rare earth sintered magnet

Abstract: PROBLEM TO BE SOLVED: To enable increase of yield by restraining fusion welding of a component which is used at the time of sintering to a magneto compact. SOLUTION: In a method for manufacturing a rare earth sintered magnet wherein the magneto compact containing rare earth elements is sintered, the magneto compact is sintered in the state that the magneto compacts are laminated through the board of a mesh type. Alternatively, the magneto compact is sintered in the state that the magneto compact is wrapped with a metal foil and the board of a mesh type is interposed between the metal foil and the magneto compact. Since the board of a mesh type has a small contact area with the magneto compact and is hardly adhered, fusion welding to the magneto compact is restrained even in a case that the magneto compacts are laminated and sintered. COPYRIGHT: (C)2005,JPO&NCIPI

Simulation of Solar Magneto-Convection

Abstract: We describe the methods for realistic three-dimensional, time-dependent simulations of the interaction between convective flows, magnetic field and radiation near the visible solar surface and show some results recent of our computations: 1) the formation of magnetic patterns and small-scale intense magnetic fields for different amount of magnetic flux in the computational domain and, 2) the structure and dynamics of a larger flux concentration, a so-called pore. Experiences with running our code on the Hitachi SR80000 of HLRB are briefly described.

Start mageto stator

Abstract: The utility model discloses a start magneto stator, which belongs to a permanent magneto. The start magneto stator is especially suitable to the start magneto with two functions of direct current motor and alternating current dynamo. The winding of the utility model has a construction of three phase six winding, and the windings are not over lapped. Because of the utility model, smooth torque can be output, operating current can be reduced, copper wires can be saved and manufacturing technology can be simplified.

On artificial magneto-dielectric substrates with microstrip antennas: the role of frequency dispersion

Abstract: In the present paper we discuss the effect of artificial magneto-dielectric substrates on the impedance bandwidth properties of microstrip antennas. A realistic dispersive behavior of a practically realizable substrate is embedded into the model, and we show that frequency dispersion of the substrate plays a very important role in the impedance bandwidth characteristics of the loaded antenna. The impedance bandwidths of miniaturized size patch antennas loaded with dispersive magneto-dielectric substrates and high-permittivity substrates are compared. It is shown that practically realizable substrates with dispersive magnetic permeability are not advantageous in antenna miniaturization. This observation is experimentally validated. INTRODUCTION During the first heyday of metamaterials, artificial high-permeability materials working at microwave regime have gained increasing attention [1, 2]. The possibility to create artificial magnetism at microwave frequencies has heated the discussion on the possibility to enhance the impedance bandwidth properties of microstrip antennas using magneto-dielectric substrates [3, 4, 5]. According to the work of Hansen and Burke [6], inductive (magnetic) loading leads to an efficient size miniaturization of a microstrip antenna. A transmission-line (TL) model for a normal half-wavelength patch antenna predicts that increase in the permeability of the antenna substrate does not reduce the impedance bandwidth of the miniaturized radiator (when the material parameters are dispersion-free, and μeff ≫ ǫeff , μeff ≫ 1) [6]. However, at microwave frequencies only moderate permeabilitites can be achieved with a complex mixture of electrically small inhomogeneities (resonating unit cells). Moreover, to achieve a paramagnetic response, one has to operate rather close to the resonance of the artificial magneto-dielectric substrate. Thus, it is clear that the substrate obeys strong frequency dispersion. To reveal the benefits achieved in practise with artificial magneto-dielectric substrates it is necessary to consider realistic values for the substrate material parameters, and take into account frequency dispersion. IMPEDANCE BANDWIDTH BEHAVIOR WITH A DISPERSIVE SUBSTRATE In this section we use a TL-model and calculate the impedance bandwidth properties of a half-wavelength patch antenna loaded with a dispersive artificial magneto-dielectric substrate, and with a dispersion-free reference dielectric substrate. The empty antenna is designed to resonate at 3.0 GHz. A schematic illustration of the analyzed antenna structure and the equivalent TL-model are presented in Fig. 1 (detailed derivation for the model and the antenna dimensions are presented in [7]). The practically realizable magneto-dielectric substrate is implemented as an array of metasolenoids [2]. The estimated dispersive behavior of μeff of the substrate is shown in Fig. 2(a). The effective permittivity of the substrate is estimated Figure 1: Schematic illustration of the antenna geometry and the equivalent circuit of a strip fed antenna. to be ǫeff = 8.5(1 − j0.001). The value for the relative permittivity of the reference dielectric substrate (offering the same size reduction) is ǫ r = 10.1(1 − j.001). To better see the possible effect of frequency dispersion, we will also consider a loading scenario in which the dispersive magneto-dielectric substrate is replaced with a substrate having dispersion-free material parameters μeff = 1.21(1 − j0.0024) (picked up from the dispersion curve at the operational frequency of the loaded antenna) and ǫeff = 8.5(1 − j0.001). Fig. 2(b) shows the calculated reflection coefficient with different material fillings. The main calculated parameters are gathered in Table 1 (V is the volume of the radiators, BW is the bandwidth, and Q0 is the unloaded quality factor). The obtained result indicates that practically realizable magneto-dielectric substrate offers no advantages over high-permittivity dielectrics (when it comes to impedance bandwidth). If the realistic dispersive behavior of the magneto-dielectric substrate is replaced with a scalar constant permeability, the TL-model predicts wider impedance bandwidth with magneto-dielectrics than with pure high-permittivity dielectrics. RELATIVE RADIATION QUALITY FACTOR Next an expression explicitly explaining the negative effect of frequency dispersion will be derived. We consider a λ/2 long section of a transmission line filled with a certain material having material parameters μ, ǫ. Moreover, we assume the line to be terminated by ideal open ends, and that the losses are only due to radiation losses. Taking into account the frequency dispersion in the material parameters one obtains the radiation quality factor of the line in the following form: Qr = πY 8Gr ( 1 μ ∂(ωμ) ∂ω + 1 ǫ ∂(ωǫ) ∂ω ) . (1) Above Y is the characteristic admittance of the line, and Gr is the radiation conductance. For an antenna (line) having the same dimensions and loaded with a reference dispersion-free magneto-dielectric material we have Qr = πY ref 4Gr , (2) 2.8 3 3.2 3.4 3.6 3.8 −15 −10 −5 0 5 10 F [GHz] Re{μ eff } Im{ μ eff } (a) Dispersive behavior of μeff of a practically realizable substrate. 2.7 2.8 2.9 3 3.1 3.2 3.3 −12 −10 −8 −6 −4 −2 0

Micro acoustic device based on magneto resistance effect

Abstract: The utility model discloses a micro acoustic device based on magneto resistance effect, which belongs to the field of semiconductor device. The device is composed of a structure of movable diaphragm with hard magnetic thin film as the sediment and a fixed structure of multilayer film of magneto resistor as the sediment. The structure of movable diaphragm is successively combined by silicon bulk, silicon dioxide, layer of silicon nitride and layer of silicon dioxide from the substratum to the upper position. The structure of the fixed part is the same as the structure of the movable diaphragm, except that the layer of permanent magnet material is changed into the GMR multilayer film of magneto resistor. The utility model makes use of the movable diaphragm and multilayer film of magneto resistor to realize the transmission between the signals of electricity and sound, which makes the kind of acoustical device with high sensibility, low noise, and broad range of response available. The subsequent processing circuit is very simple. Because of the simple processing steps, the performance of the product is reliable, the rate of finished products is high and the device can meet the requirements of the volume-production.

Surface waves excitation in cylindrical antennas

Abstract: In present report the conditions of surface wave excitation in radiating structure are analyzed. This structure includes system of electric longitudinal dipoles on perfectly conducting circular cylinder in magneto dielectric layer. Analysis of the conditions is carried out on the base of rigorous solution of problem of excitation of magneto dielectric layer on perfectly conducting circular cylinder by longitudinal electric dipole. In conclusion of report the results of modeling are given.

Current measurement device for e.g. truck, has calculating unit with correctors to correct errors of measurements of Hall Effect and magneto-resistive sensors respectively using measurements from magneto-resistive and Hall Effect sensors

Abstract: The device (1) has Hall Effect sensors (101, 102) and magneto-resistive sensors (201, 202) that are placed close to each other and on both sides of a conductor (40) carrying current to be measured. A calculating unit (30) has correctors to correct errors of measurements of the sensors (101, 102, 201, 202) respectively using the measurements from the sensors (201, 202, 101, 102) based on amplitude of the current.