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1

A Coaxial Magnetic Gear With Halbach Permanent-Magnet Arrays  

Microsoft Academic Search

This paper proposes a coaxial magnetic gear that offers higher torque density, lower cogging torque, and lower iron losses than its counterparts. The key is to newly employ a Halbach permanent-magnet (PM) array to constitute the PM poles in the inner rotor and a partial Halbach array (two segments per pole) for the outer rotor. The corresponding magnetic field distributions,

Linni Jian; K. T. Chau

2010-01-01

2

Design of a Halbach Magnet Array Based on Optimization Techniques  

Microsoft Academic Search

We have designed a Halbach magnet array by using a numerical optimization method based on finite-element analysis. The magnetization direction of each element is defined as the design variable. The optimal magnet arrays composed of two and three linear magnet layers can then be investigated to increase the attractive, repulsive, and tangential magnetic forces between magnet layers. We have applied

Jae-Seok Choi; Jeonghoon Yoo

2008-01-01

3

Analysis and comparison of two two-dimensional Halbach permanent magnet arrays for magnetically levitated planar motor  

NASA Astrophysics Data System (ADS)

A novel 2-D Halbach permanent magnet array which can be used in magnetically levitated planar motor is proposed in this paper. The air-gap flux density distribution of the novel 2-D Halbach permanent magnet array is solved by the scalar magnetic potential equation. In order to compare with the well-known Halbach magnet array that was used by Jansen et al. [IEEE Trans. Ind. Appl. 44(4), 1108 (2008)], harmonic analysis of the x- and z- component of the air-gap flux density are carried out by Fourier decomposition. Comparison of Bx and Bz between the two 2-D Halbach magnet arrays are made. And it is verified that the performance of the new Halbach magnet array is superior to the existing Halbach magnet arrays, its higher magnetic flux density and lower high-order harmonics will help to improve the performance of the magnetically levitated planar motor.

Zhang, Lu; Kou, Baoquan; Xing, Feng; Zhang, He

2014-05-01

4

Radial Halbach Magnetic Bearings  

NASA Technical Reports Server (NTRS)

Radial Halbach magnetic bearings have been investigated as part of an effort to develop increasingly reliable noncontact bearings for future high-speed rotary machines that may be used in such applications as aircraft, industrial, and land-vehicle power systems and in some medical and scientific instrumentation systems. Radial Halbach magnetic bearings are based on the same principle as that of axial Halbach magnetic bearings, differing in geometry as the names of these two types of bearings suggest. Both radial and axial Halbach magnetic bearings are passive in the sense that unlike most other magnetic bearings that have been developed in recent years, they effect stable magnetic levitation without need for complex active control. Axial Halbach magnetic bearings were described in Axial Halbach Magnetic Bearings (LEW-18066-1), NASA Tech Briefs, Vol. 32, No. 7 (July 2008), page 85. In the remainder of this article, the description of the principle of operation from the cited prior article is recapitulated and updated to incorporate the present radial geometry. In simplest terms, the basic principle of levitation in an axial or radial Halbach magnetic bearing is that of the repulsive electromagnetic force between (1) a moving permanent magnet and (2) an electric current induced in a stationary electrical conductor by the motion of the magnetic field. An axial or radial Halbach bearing includes multiple permanent magnets arranged in a Halbach array ("Halbach array" is defined below) in a rotor and multiple conductors in the form of wire coils in a stator, all arranged so the rotary motion produces an axial or radial repulsion that is sufficient to levitate the rotor. A basic Halbach array (see Figure 1) consists of a row of permanent magnets, each oriented so that its magnetic field is at a right angle to that of the adjacent magnet, and the right-angle turns are sequenced so as to maximize the magnitude of the magnetic flux density on one side of the row while minimizing it on the opposite side. The advantage of this configuration is that it makes it possible to approach the theoretical maximum force per unit area that could be exerted by a given amount of permanent-magnet material. The configuration is named after physicist Klaus Halbach, who conceived it for use in particle accelerators. Halbach arrays have also been studied for use in magnetic-levitation ("maglev") railroad trains. In a radial Halbach magnetic bearing, the basic Halbach arrangement is modified into a symmetrical arrangement of sector-shaped permanent magnets mounted on the outer cylindrical surface of a drum rotor (see Figure 2). The magnets are oriented to concentrate the magnetic field on their radially outermost surface. The stator coils are mounted in a stator shell surrounding the rotor.

Eichenberg, Dennis J.; Gallo, Christopher A.; Thompson, William K.

2009-01-01

5

Modeling maglev passenger compartment static magnetic fields from linear Halbach permanent-magnet arrays  

Microsoft Academic Search

Passenger compartment magnetic field levels in a low-speed magnetic levitation (maglev) vehicle that uses linear Halbach permanent-magnet arrays for both levitation and propulsion are computed through superposition of fields due to patches of magnetization charge at surfaces where the magnetization is discontinuous. End effects due to the finite lengths of the arrays lead to fields that decay much less rapidly

James F. Hoburg

2004-01-01

6

Experiments on Inductive Magnetic Levitation with a Circular Halbach Array  

NASA Astrophysics Data System (ADS)

Using a ring Halbach array, we are investigating a repulsive levitating force and a drag force acting on the magnet from a ring of inductors rotating below the magnet. After measuring induced currents, voltages and magnetic fields in the individual inductors (in the form of short solenoids), we investigated the dependence of lift/drag forces on the speed of relative rotation. The ratio of lift to drag increases with the angular velocity, as expected from a related theory of the induction effects in a linear motion. We are experimenting with the shape and density of inductors, and their material, in an attempt to maximize the lift at a minimal velocity of rotation. Eventually this design could have applications as frictionless bearings or as frictionless gear in a wide range of systems, especially in machinery that cannot be easily accessed.

Bean, Ian; Goncz, Doug; Raymer, Austin; Specht, Jason; Zalles, Ricardo; Majewski, Walerian

2013-03-01

7

A new magnetic bearing using Halbach magnet arrays for a magnetic levitation stage.  

PubMed

Next-generation lithography requires a high precision stage, which is compatible with a high vacuum condition. A magnetic levitation stage with six degrees-of-freedom is considered state-of-the-art technology for a high vacuum condition. The noncontact characteristic of magnetic levitation enables high precision positioning as well as no particle generation. To position the stage against gravity, z-directional electromagnetic levitation mechanisms are widely used. However, if electromagnetic actuators for levitation are used, heat is inevitably generated, which deforms the structures and degrades accuracy of the stage. Thus, a gravity compensator is required. In this paper, we propose a new magnetic bearing using Halbach magnet arrays for a magnetic levitation stage. The novel Halbach magnetic bearing exerts a force four times larger than a conventional magnetic bearing with the same volume. We also discuss the complementary characteristics of the two magnetic bearings. By modifying the height of the center magnet in a Halbach magnetic bearing, a performance compromise between levitating force density and force uniformity is obtained. The Halbach linear active magnetic bearing can be a good solution for magnetic levitation stages because of its large and uniform levitation force. PMID:19405690

Choi, Young-Man; Lee, Moon G; Gweon, Dae-Gab; Jeong, Jaehwa

2009-04-01

8

Halbach Magnetic Rotor Development  

NASA Technical Reports Server (NTRS)

The NASA John H. Glenn Research Center has a wealth of experience in Halbach array technology through the Fundamental Aeronautics Program. The goals of the program include improving aircraft efficiency, reliability, and safety. The concept of a Halbach magnetically levitated electric aircraft motor will help reduce harmful emissions, reduce the Nation s dependence on fossil fuels, increase efficiency and reliability, reduce maintenance and decrease operating noise levels. Experimental hardware systems were developed in the GRC Engineering Development Division to validate the basic principles described herein and the theoretical work that was performed. A number of Halbach Magnetic rotors have been developed and tested under this program. A separate test hardware setup was developed to characterize each of the rotors. A second hardware setup was developed to test the levitation characteristics of the rotors. Each system focused around a unique Halbach array rotor. Each rotor required original design and fabrication techniques. A 4 in. diameter rotor was developed to test the radial levitation effects for use as a magnetic bearing. To show scalability from the 4 in. rotor, a 1 in. rotor was developed to also test radial levitation effects. The next rotor to be developed was 20 in. in diameter again to show scalability from the 4 in. rotor. An axial rotor was developed to determine the force that could be generated to position the rotor axially while it is rotating. With both radial and axial magnetic bearings, the rotor would be completely suspended magnetically. The purpose of this report is to document the development of a series of Halbach magnetic rotors to be used in testing. The design, fabrication and assembly of the rotors will be discussed as well as the hardware developed to test the rotors.

Gallo, Christopher A.

2008-01-01

9

Analysis of Halbach magnet array and its application to linear motor  

Microsoft Academic Search

Using Halbach magnet array, magnetic flux can be enhanced on one side (strong side) of the array while the flux cancelled on the other side (weak side). Inherently, rotor of rotary motor has infinite rotational length with respect to its rotation while mover of the linear motor has finite length with respect to mover’s translation. In this paper, we propose

Moon G. Lee; Sung Q. Lee; Dae-Gab Gweon

2004-01-01

10

Analysis of the tubular motor with Halbach and radial magnet array  

Microsoft Academic Search

In the machine tool industry, direct drive linear motor technology is of increasing interest as a means to achieve high acceleration, and to increase reliability. This paper analyzes and compares the characteristics of tubular motor with Halbach and radial magnet array respectively. The governing equations established analytically in terms of vector potential, two dimensional cylindrical coordinate system and Maxwell's equations.

Seok Myeong Jang; Jang Young Choi; Sung Ho Lee; Sung Kook Cho; Won Bum Jang

2003-01-01

11

Axial Halbach Magnetic Bearings  

NASA Technical Reports Server (NTRS)

Axial Halbach magnetic bearings have been investigated as part of an effort to develop increasingly reliable noncontact bearings for future high-speed rotary machines that may be used in such applications as aircraft, industrial, and land-vehicle power systems and in some medical and scientific instrumentation systems. Axial Halbach magnetic bearings are passive in the sense that unlike most other magnetic bearings that have been developed in recent years, they effect stable magnetic levitation without need for complex active control.

Eichenberg, Dennis J.; Gallo, Christopher A.; Thompson, William K.

2008-01-01

12

A low-field, low-cost Halbach magnet array for open-access NMR  

Microsoft Academic Search

A working prototype of a novel low-cost Halbach-array-based NMR system is described. The new design provides open access to the sample relative to conventional NMR magnet designs and this facilitates the simultaneous use of multi-sensor techniques on the same sample, in which NMR\\/MRI can potentially be combined with other spectroscopies such as impedance spectroscopy, laser scattering and rheological experiments.

B. P. Hills; K. M. Wright; D. G. Gillies

2005-01-01

13

The use of a linear Halbach array combined with a step-SPLITT channel for continuous sorting of magnetic species  

Microsoft Academic Search

The Quadrupole Magnetic Sorter (QMS), employing an annular flow channel concentric with the aperture of a quadrupole magnet, is well established for cell and particle separations. Here we propose a magnetic particle separator comprising a linear array of cylindrical magnets, analogous to the array proposed by Klaus Halbach, mated to a substantially improved form of a parallel plate SPLITT channel,

Mauricio Hoyos; Lee Moore; P. Stephen Williams; Maciej Zborowski

2011-01-01

14

Torque analysis and measurements of a permanent magnet type Eddy current brake with a Halbach magnet array based on analytical magnetic field calculations  

NASA Astrophysics Data System (ADS)

This paper presents the torque analysis and measurements of a permanent magnet (PM) type eddy current brake (ECB) with a Halbach magnet array based on analytical magnetic field calculations. On the basis of a magnetic vector potential and using a two-dimensional (2D) polar coordinate system, the analytical solution for magnetic flux density, including the eddy current reaction is evaluated. Based on these solutions, the magnetic torque is also determined analytically. A 2D finite element analysis is employed to validate the method used. Practical issues in the analytical study of the PM type ECBs, such as the maximum braking torque, the required rotor speed, and the segment-dependent, are fully discussed. Finally, the braking torque as a function of the rotor speed is measured to verify the results of the analytical study.

Park, Min-Gyu; Choi, Jang-Young; Shin, Hyeon-Jae; Jang, Seok-Myeong

2014-05-01

15

A two-pole Halbach permanent magnet guideway for high temperature superconducting Maglev vehicle  

Microsoft Academic Search

In order to improve the levitation performance of the high temperature superconducting (HTS) magnetic levitation (Maglev) vehicle, a two-pole Halbach array’s permanent magnet guideway (PMG) is proposed, which is called as Halbach PMG. The finite element method (FEM) calculations indicate that Halbach PMG has a wider high-field region than the present PMG of equal PM’s transverse section. The levitation force

H. Jing; J. Wang; S. Wang; L. Wang; L. Liu; J. Zheng; Z. Deng; G. Ma; Y. Zhang; J. Li

2007-01-01

16

Numerical simulation of a simple low-speed model for an electrodynamic levitation system based on a Halbach magnet array  

NASA Astrophysics Data System (ADS)

The design and analysis of a small prototype of a magnetic levitation system at low-speed using a Halbach-type magnet array is presented here. For that purpose, we have arranged a copper rim over a carbon fiber wheel, which is driven by an electric motor in presence of the magnet array, in such a manner that allows performing the experiment readily. The analysis of the system is undertaken under a two-dimensional (2D)-approach which permits computing and extending the study of our model to higher speeds. Our work is completed with a series of experimental measurements of lift and drag forces for different circumstances. Initially, the drag force is significant but after the compensation speed (when both forces balance) it slowly decreases. Conversely, the lift force becomes progressively bigger in such a manner that it attains quickly noteworthy values. We observe that the theoretical compensation speed is always minor than the experimental one and that the measured values for both forces are slightly smaller than the expected, although the main features of the experiment are well matched by our numerical simulation.

Íñiguez, J.; Raposo, V.

2010-05-01

17

Analysis and implementation of a tubular motor with Halbach magnet array  

Microsoft Academic Search

In the machine tool industry, direct-drive linear motor technology is of increasing interest as a means to achieve high acceleration, and to increase reliability. This paper discusses the analysis, design and operating characteristics of a novel ironless tubular linear motor that incorporates a magnet array with a magnetization pattern inspired by the Halbash array used in synchrotron light sources. The

W.-J. Kim; M. T. Berhan; D. L. Trumper; J. H. Lang

1996-01-01

18

Energy harvesting from electric power lines employing the Halbach arrays.  

PubMed

This paper proposes non-invasive energy harvesters to scavenge alternating magnetic field energy from electric power lines. The core body of a non-invasive energy harvester is a linear Halbach array, which is mounted on the free end of a piezoelectric cantilever beam. The Halbach array augments the magnetic flux density on the side of the array where the power line is placed and significantly lowers the magnetic field on the other side. Consequently, the magnetic coupling strength is enhanced and more alternating magnetic field energy from the current-carrying power line is converted into electrical energy. An analytical model is developed and the theoretical results verify the experimental results. A power of 566 ?W across a 196 k? resistor is generated from a single wire, and a power of 897 ?W across a 212 k? resistor is produced from a two-wire power cord carrying opposite currents at 10 A. The harvesters employing Halbach arrays for a single wire and a two-wire power cord, respectively, exhibit 3.9 and 3.2 times higher power densities than those of the harvesters employing conventional layouts of magnets. The proposed devices with strong response to the alternating currents are promising to be applied to electricity end-use environment in electric power systems. PMID:24182155

He, Wei; Li, Ping; Wen, Yumei; Zhang, Jitao; Lu, Caijiang; Yang, Aichao

2013-10-01

19

Halbach array DC motor/generator  

DOEpatents

A new configuration of DC motor/generator is based on a Halbach array of permanent magnets. This motor does not use ferrous materials so that the only losses are winding losses and losses due to bearings and windage. An ``inside-out`` design is used as compared to a conventional motor/generator design. The rotating portion, i.e., the rotor, is on the outside of the machine. The stationary portion, i.e., the stator, is formed by the inside of the machine. The rotor contains an array of permanent magnets that provide a uniform field. The windings of the motor are placed in or on the stator. The stator windings are then ``switched`` or ``commutated`` to provide a DC motor/generator much the same as in a conventional DC motor. The commutation can be performed by mechanical means using brushes or by electronic means using switching circuits. The invention is useful in electric vehicles and adjustable speed DC drives. 17 figs.

Merritt, B.T.; Dreifuerst, G.R.; Post, R.F.

1998-01-06

20

Halbach array DC motor/generator  

DOEpatents

A new configuration of DC motor/generator is based on a Halbach array of permanent magnets. This motor does not use ferrous materials so that the only losses are winding losses and losses due to bearings and windage. An "inside-out" design is used as compared to a conventional motor/generator design. The rotating portion, i.e., the rotor, is on the outside of the machine. The stationary portion, i.e., the stator, is formed by the inside of the machine. The rotor contains an array of permanent magnets that provide a uniform field. The windings of the motor are placed in or on the stator. The stator windings are then "switched" or "commutated" to provide a DC motor/generator much the same as in a conventional DC motor. The commutation can be performed by mechanical means using brushes or by electronic means using switching circuits. The invention is useful in electric vehicles and adjustable speed DC drives.

Merritt, Bernard T. (Livermore, CA); Dreifuerst, Gary R. (Livermore, CA); Post, Richard F. (Walnut Creek, CA)

1998-01-01

21

Development and Testing of a Radial Halbach Magnetic Bearing  

NASA Technical Reports Server (NTRS)

The NASA John H. Glenn Research Center has developed and tested a revolutionary Radial Halbach Magnetic Bearing. The objective of this work is to develop a viable non-contact magnetic bearing utilizing Halbach arrays for all-electric flight, and many other applications. This concept will help reduce harmful emissions, reduce the Nation s dependence on fossil fuels and mitigate many of the concerns and limitations encountered in conventional axial bearings such as bearing wear, leaks, seals and friction loss. The Radial Halbach Magnetic Bearing is inherently stable and requires no active feedback control system or superconductivity as required in many magnetic bearing designs. The Radial Halbach Magnetic Bearing is useful for very high speed applications including turbines, instrumentation, medical applications, manufacturing equipment, and space power systems such as flywheels. Magnetic fields suspend and support a rotor assembly within a stator. Advanced technologies developed for particle accelerators, and currently under development for maglev trains and rocket launchers, served as the basis for this application. Experimental hardware was successfully designed and developed to validate the basic principles and analyses. The report concludes that the implementation of Radial Halbach Magnetic Bearings can provide significant improvements in rotational system performance and reliability.

Eichenberg, Dennis J.; Gallo, Christopher A.; Thompson, William K.

2006-01-01

22

Development and Testing of an Axial Halbach Magnetic Bearing  

NASA Technical Reports Server (NTRS)

The NASA Glenn Research Center has developed and tested a revolutionary Axial Halbach Magnetic Bearing. The objective of this work is to develop a viable non-contact magnetic thrust bearing utilizing Halbach arrays for all-electric flight, and many other applications. This concept will help to reduce harmful emissions, reduce the Nation s dependence on fossil fuels and mitigate many of the concerns and limitations encountered in conventional axial bearings such as bearing wear, leaks, seals and friction loss. The Axial Halbach Magnetic Bearing is inherently stable and requires no active feedback control system or superconductivity as required in many magnetic bearing designs. The Axial Halbach Magnetic Bearing is useful for very high speed applications including turbines, instrumentation, medical systems, computer memory systems, and space power systems such as flywheels. Magnetic fields suspend and support a rotor assembly within a stator. Advanced technologies developed for particle accelerators, and currently under development for maglev trains and rocket launchers, served as the basis for this application. Experimental hardware was successfully designed and developed to validate the basic principles and analyses. The report concludes that the implementation of Axial Halbach Magnetic Bearings can provide significant improvements in rotational system performance and reliability.

Eichenberg, Dennis J.; Gallo, Christopher A.; Thompson, William K.

2006-01-01

23

Optimization shows Halbach arrays to be non-ideal for induction devices  

Microsoft Academic Search

Among the advantages of Halbach magnet arrays is the fact that the magnetic field behind the array is very small, and the magnets act as a natural flux guide. This paper discusses an optimization index that proves useful for objectively examining any magnet array used in induction applications. Multivariate spline tensor analysis and variable metric methods with a boundary element

Kent Davey

2000-01-01

24

Using the Halbach magnet array to develop an ultrahigh-speed spindle motor for machine tools  

Microsoft Academic Search

This report describes the results of the authors' research on the optimum rotor configuration for an ultra high-speed machine tool spindle motor with a rated speed of 50,000 RPM and rated power of 11 kW. In this research, using an IPM (interior permanent magnet) motor with permanent magnets embedded in the rotor, they performed experiments based on calculations and a

Yukio Honda; Shizuka Yokote; Toshiro Higaki; Yoji Takeda

1997-01-01

25

Optimal Halbach Permanent Magnet Designs for Maximally Pulling and Pushing Nanoparticles  

PubMed Central

Optimization methods are presented to design Halbach arrays to maximize the forces applied on magnetic nanoparticles at deep tissue locations. In magnetic drug targeting, where magnets are used to focus therapeutic nanoparticles to disease locations, the sharp fall off of magnetic fields and forces with distances from magnets has limited the depth of targeting. Creating stronger forces at depth by optimally designed Halbach arrays would allow treatment of a wider class of patients, e.g. patients with deeper tumors. The presented optimization methods are based on semi-definite quadratic programming, yield provably globally optimal Halbach designs in 2 and 3-dimensions, for maximal pull or push magnetic forces (stronger pull forces can collect nano-particles against blood forces in deeper vessels; push forces can be used to inject particles into precise locations, e.g. into the inner ear). These Halbach designs, here tested in simulations of Maxwell’s equations, significantly outperform benchmark magnets of the same size and strength. For example, a 3-dimensional 36 element 2000 cm3 volume optimal Halbach design yields a ×5 greater force at a 10 cm depth compared to a uniformly magnetized magnet of the same size and strength. The designed arrays should be feasible to construct, as they have a similar strength (? 1 Tesla), size (? 2000 cm3), and number of elements (? 36) as previously demonstrated arrays, and retain good performance for reasonable manufacturing errors (element magnetization direction errors ? 5°), thus yielding practical designs to improve magnetic drug targeting treatment depths.

Sarwar, A.; Nemirovski, A.; Shapiro, B.

2011-01-01

26

Magnet Guideways for Superconducting Maglevs: Comparison Between Halbach-Type and Conventional Arrangements of Permanent Magnets  

NASA Astrophysics Data System (ADS)

The characteristics of the permanent magnets composing the guideway in superconducting magnetic levitation devices are very important for their performance in terms of levitation force and stability. From a model based on minimizing the magnetic energy in the superconductor and considering realistic parameters of actual maglev devices, we calculate the levitation and guidance forces and stability arising from both conventional arrangements and recently proposed Halbach-like arrangements. When a comparison is carefully made under similar conditions, we conclude that not always complicated arrangements based on Halbach arrays bring significant improvements with respect to some simpler arrangements that also provide large force. These results may help improving the design of actual maglev devices.

Del-Valle, Nuria; Sanchez, Alvaro; Navau, Carles; Chen, Du-Xing

2011-01-01

27

Inductional Effects in a Halbach Magnet Motion Above Distributed Inductance  

NASA Astrophysics Data System (ADS)

We experimented with attempts to levitate a linear (bar) Halbach array of five 1" Nd magnets above a linear inductive track. Next, in order to achieve a control over the relative velocity, we designed a different experiment. In it a large wheel with circumferentially positioned along its rim inducting coils rotates, while the magnet is suspended directly above the rim of the wheel on a force sensor. Faraday’s Law with the Lenz's Rule is responsible for the lifting and drag forces on the magnet; the horizontal drag force is measured by another force sensor. Approximating the magnet's linear relative motion over inductors with a motion along a large circle, we may use formulas derived earlier in the literature for linear inductive levitation. We measured lift and drag forces as functions of relative velocity of the Halbach magnet and the inductive ``track,'' in an approximate agreement with the existing theory. We then vary the inductance and shape of the inductive elements to find the most beneficial choice for the lift/drag ratio at the lowest relative speed.

Tchatchoua, Yves; Conrow, Ary; Kim, Dong; Morgan, Daniel; Majewski, Walerian; Zafar, Zaeema

2013-03-01

28

Magnet arrays for synchronous machines  

Microsoft Academic Search

The authors demonstrate that the Halbach array is highly applicable for magnetic excitation in synchronous machines. To this end, they present the geometry of Halbach arrays in Cartesian, polar, and cylindrical coordinates. They also present the design of a Cartesian linear motor which has been optimized for use in conjunction with a class of high-precision magnetic suspension stages for photolithography.

David L. Trumper; Mark E. Williams; Tiep H. Nguyen

1993-01-01

29

Laboratory Scale Prototype of a Low-Speed Electrodynamic Levitation System Based on a Halbach Magnet Array  

ERIC Educational Resources Information Center

In this paper we analyse the behaviour of a small-scale model of a magnetic levitation system based on the Inductrack concept. Drag and lift forces acting on our prototype, moving above a continuous copper track, are studied analytically following a simple low-speed approach. The experimental results are in good agreement with the theoretical…

Iniguez, J.; Raposo, V.

2009-01-01

30

Optimal design of a double-sided linear motor with a multi-segmented trapezoidal magnet array for a high precision positioning system  

Microsoft Academic Search

A comparative analysis is performed for linear motors adopting conventional and multi-segmented trapezoidal (MST) magnet arrays, respectively, for a high-precision positioning system. The proposed MST magnet array is a modified version of a Halbach magnet array. The MST array has trapezoidal magnets with variable shape and dimensions while the Halbach magnet array generally has a rectangular magnet with identical dimensions.

Moon G. Lee; Dae-Gab Gweon

2004-01-01

31

Three-Dimensional Field Solutions for Multi-Pole Cylindrical Halbach Arrays in an Axial Orientation  

NASA Technical Reports Server (NTRS)

This article presents three-dimensional B field solutions for the cylindrical Halbach array in an axial orientation. This arrangement has applications in the design of axial motors and passive axial magnetic bearings and couplers. The analytical model described here assumes ideal magnets with fixed and uniform magnetization. The field component functions are expressed as sums of 2-D definite integrals that are easily computed by a number of mathematical analysis software packages. The analysis is verified with sample calculations and the results are compared to equivalent results from traditional finite-element analysis (FEA). The field solutions are then approximated for use in flux linkage and induced EMF calculations in nearby stator windings by expressing the field variance with angular displacement as pure sinusoidal function whose amplitude depends on radial and axial position. The primary advantage of numerical implementation of the analytical approach presented in the article is that it lends itself more readily to parametric analysis and design tradeoffs than traditional FEA models.

Thompson, William K.

2006-01-01

32

Investigation of a 7-pole/6-slot Halbach-magnetized permanent-magnet linear alternator used for free-piston stirling engines  

NASA Astrophysics Data System (ADS)

This paper investigates a 7-pole/6-slot Halbach-magnetized permanent-magnet linear alternator used for free piston Stirling engines (FPSEs). Taking the advantages of Halbach array, a 1 kW prototype alternator is designed. Considering the rms value of electromotive force (EMF) and harmonic distortion, the optimal length ratio of the axial- and radial-magnetized permanent magnets and thicknesses of the permanent magnets are optimized by 2D finite element method. The alternator detent force, which is an important factor for smooth operation of FPSEs, is studied by optimizing slot tip and end tooth. The load and thermal performances of the final design are simulated. A prototype alternator was designed, built and tested. Experimental data indicated satisfactory design.

Zheng, Ping; Tong, Chengde; Zhao, Jing; Yu, Bin; Li, Lin; Bai, Jingang; Zhang, Lu

2012-04-01

33

Comparison of Halbach magnetized brushless motors equipped with air-cored and iron-cored rotors  

NASA Astrophysics Data System (ADS)

The performance of Halbach magnetized brushless motors equipped with air-cored and iron-cored rotors is investigated theoretically and experimentally. It is shown that an optimal combination of magnet thickness and pole number exists for maximum air-gap flux density. By employing a rotor back iron, the air-gap field and hence the output torque can be enhanced significantly if the ratio of the radial thickness of the magnet to the pole pitch is small.

Xia, Z. P.; Zhu, Z. Q.; Jewell, G. W.; Howe, D.

2003-05-01

34

A portable Halbach magnet that can be opened and closed without force: the NMR-CUFF.  

PubMed

Portable equipment for nuclear magnetic resonance (NMR) is becoming increasingly attractive for use in a variety of applications. One of the main scientific challenges in making NMR portable is the design of light-weight magnets that possess a strong and homogeneous field. Existing NMR magnets can provide such magnetic fields, but only for small samples or in small regions, or are rather heavy. Here we show a simple yet elegant concept for a Halbach-type permanent magnet ring, which can be opened and closed with minimal mechanical force. An analytical solution for an ideal Halbach magnet shows that the magnetic forces cancel if the structure is opened at an angle of 35.3° relative to its poles. A first prototype weighed only 3.1 kg, and provided a flux density of 0.57 T with a homogeneity better than 200 ppm over a spherical volume of 5mm in diameter without shimming. The force needed to close it was found to be about 20 N. As a demonstration, intact plants were imaged and water (xylem) flow measured. Magnets of this type (NMR-CUFF = Cut-open, Uniform, Force Free) are ideal for portable use and are eminently suited to investigate small or slender objects that are part of a larger or immobile whole, such as branches on a tree, growing fruit on a plant, or non-metallic tubing in industrial installations. This new concept in permanent-magnet design enables the construction of openable, yet strong and homogeneous magnets, which aside from use in NMR or MRI could also be of interest for applications in accelerators, motors, or magnetic bearings. PMID:21036637

Windt, Carel W; Soltner, Helmut; van Dusschoten, Dagmar; Blümler, Peter

2011-01-01

35

Tubular modular permanent-magnet machines equipped with quasi-Halbach magnetized magnets-part I: magnetic field distribution, EMF, and thrust force  

Microsoft Academic Search

This paper describes the analysis, design, and experimental characterization of three-phase tubular modular permanent-magnet machines equipped with quasi-Halbach magnetized magnets. It identifies feasible slot\\/pole number combinations and discusses their relative merits. It establishes an analytical expression for the open-circuit magnetic field distribution, formulated in the cylindrical coordinate system. The expression has been verified by finite-element analysis. The analytical solution allows

Jiabin Wang; David Howe

2005-01-01

36

Magnetic arrays  

DOEpatents

Electromagnet arrays which can provide selected field patterns in either two or three dimensions, and in particular, which can provide single-sided field patterns in two or three dimensions. These features are achieved by providing arrays which have current densities that vary in the windings both parallel to the array and in the direction of array thickness.

Trumper, David L. (Plaistow, NH); Kim, Won-jong (Cambridge, MA); Williams, Mark E. (Pelham, NH)

1997-05-20

37

Magnetic arrays  

DOEpatents

Electromagnet arrays are disclosed which can provide selected field patterns in either two or three dimensions, and in particular, which can provide single-sided field patterns in two or three dimensions. These features are achieved by providing arrays which have current densities that vary in the windings both parallel to the array and in the direction of array thickness. 12 figs.

Trumper, D.L.; Kim, W.; Williams, M.E.

1997-05-20

38

The application of Halbach cylinders to brushless ac servo motors  

SciTech Connect

Halbach cylinders are applied to brushless ac servo motors. It is shown that a sinusoidal back-emf waveform and a low cogging torque can be achieved without recourse to conventional design features such as distributed windings and/or stator/rotor skew. A technique for imparting a multipole Halbach magnetization distribution on an isotropic permanent magnet cylinder is described, and it is shown that the torque capability of a Halbach ac servo motor can be up to 33% higher than conventional brushless permanent magnet ac motors.

Atallah, K.; Howe, D. [Univ. of Sheffield (United Kingdom). Dept. of Electronic and Electrical Engineering] [Univ. of Sheffield (United Kingdom). Dept. of Electronic and Electrical Engineering

1998-07-01

39

The Inductrack: a simpler approach to magnetic levitation  

Microsoft Academic Search

Arising out of research at the Lawrence Livermore National Laboratory on passive magnetic bearings, a new magnetic levitation system, the Inductrack, has been developed and tested at model scale. The system employs special arrays of permanent magnets (Halbach arrays) on the moving car. The magnetic field from the arrays induces repelling currents in a close-packed array of shorted circuits in

Richard F. Post; D. D. Ryutov

2000-01-01

40

Optimal design of a double-sided linear motor with a multi-segmented trapezoidal magnet array for a high precision positioning system  

NASA Astrophysics Data System (ADS)

A comparative analysis is performed for linear motors adopting conventional and multi-segmented trapezoidal (MST) magnet arrays, respectively, for a high-precision positioning system. The proposed MST magnet array is a modified version of a Halbach magnet array. The MST array has trapezoidal magnets with variable shape and dimensions while the Halbach magnet array generally has a rectangular magnet with identical dimensions. We propose a new model that can describe the magnetic field resulting from the complex-shaped magnets. The model can be applied to both MST and conventional magnet arrays. Using the model, a design optimization of the two types of linear motors is performed and compared. The magnet array with trapezoidal magnets can produce more force than one with rectangular magnets when they are arrayed in a linear motor where there is a yoke with high permeability. After the optimization and comparison, we conclude that the linear motor with the MST magnet array can generate more actuating force per volume than the motor with the conventional array. In order to satisfy the requirements of next generation systems such as high resolution, high speed, and long stroke, the use of a linear motor with a MST array as an actuator in a high precision positioning system is recommended from the results obtained here.

Lee, Moon G.; Gweon, Dae-Gab

2004-10-01

41

A permanent magnet tubular linear generator for wave energy conversion  

NASA Astrophysics Data System (ADS)

A novel three-phase permanent magnet tubular linear generator (PMTLG) with Halbach array is proposed for the sea wave energy conversion. Non-linear axi-symmetrical finite element method (FEM) is implemented to calculate the magnetic fields along air-gap for different Halbach arrays of PMTLGs. The PMTLG characteristics are analyzed and the simulation results are validated by the experiment. An assistant tooth is implemented to greatly minimize the end and cogging effects which cause the oscillatory detent force.

Yu, Haitao; Liu, Chunyuan; Yuan, Bang; Hu, Minqiang; Huang, Lei; Zhou, Shigui

2012-04-01

42

Structural parameter optimization design for Halbach permanent maglev rail  

NASA Astrophysics Data System (ADS)

Maglev rail is an important part of the magnetic levitation launch system. Reducing the manufacturing cost of magnetic levitation rail is the key problem for the development of magnetic levitation launch system. The Halbach permanent array has an advantage that the fundamental spatial field is cancelled on one side of the array while the field on the other side is enhanced. So this array used in the design of high temperature superconducting permanent maglev rail could improve the surface magnetic field and the levitation force. In order to make the best use of Nd-Fe-B (NdFeB) material and reduce the cost of maglev rail, the effect of the rail’s structural parameters on levitation force and the utilization rate of NdFeB material are analyzed. The optimal ranges of these structural parameters are obtained. The mutual impact of these parameters is also discussed. The optimization method of these structure parameters is proposed at the end of this paper.

Guo, F.; Tang, Y.; Ren, L.; Li, J.

2010-11-01

43

CMOS magnetic sensor arrays  

Microsoft Academic Search

The design of a monolithic 64×64-element array of magnetic sensors, which is implemented in a standard 3-?m CMOS process, is described. The individual magnetic field sensors are split-drain MAGFETS. A split-drain MAGFET is a field-effect transistor that has one source, one gate, and two drains. When current is flowing in the FET in the absence of a magnetic field, both

James J. Clark

1988-01-01

44

Edward A. Halbach 1909-2011  

NASA Astrophysics Data System (ADS)

Edward A. Halbach (1909-2011) was a dedicated, lifelong member of the AAVSO and the Milwaukee Astronomical Society. His service to these organizations, and his valuable contributions to variable star astronomy, are described.

Samolyk, G.

2011-06-01

45

Coherent magnetic semiconductor nanodot arrays  

PubMed Central

In searching appropriate candidates of magnetic semiconductors compatible with mainstream Si technology for future spintronic devices, extensive attention has been focused on Mn-doped Ge magnetic semiconductors. Up to now, lack of reliable methods to obtain high-quality MnGe nanostructures with a desired shape and a good controllability has been a barrier to make these materials practically applicable for spintronic devices. Here, we report, for the first time, an innovative growth approach to produce self-assembled and coherent magnetic MnGe nanodot arrays with an excellent reproducibility. Magnetotransport experiments reveal that the nanodot arrays possess giant magneto-resistance associated with geometrical effects. The discovery of the MnGe nanodot arrays paves the way towards next-generation high-density magnetic memories and spintronic devices with low-power dissipation.

2011-01-01

46

Magnetic properties of magnetic nanowire arrays  

Microsoft Academic Search

The arrays of NiFe and CoNiFe nanowires were grown in anodic alumina (alumite) and track etched polycarbonate (PCTE) membranes with various pore sizes by pulsed electrodeposition. Magnetic properties of the array were studied as functions of wire material, length, and diameter as well as field orientation. In PCTE membranes, as high as 0.92 of remanent squareness (S) was obtained for

G. C. Han; B. Y. Zong; Y. H. Wu

2002-01-01

47

Magnetic nanocap arrays with tilted magnetization  

NASA Astrophysics Data System (ADS)

In modern magnetic recording materials the ``superparamagnetic effect'' has become increasingly important as new magnetic hard disk drive products are designed for higher storage densities. In this regard, patterned media [1], where two-dimensional arrays of nanostructures are used, is one of the concepts that might provide the required areal density in future magnetic recording devices. However, also nanostructure arrays will ultimately need high anisotropy material such as L10-FePt to provid enough thermal stability and thus much higher writing fields than currently obtainable from perpendicular magnetic recording heads. One proposed solution to this problem is the use of tilted magnetic recording media [2]. The basic idea is to tilt the easy axis of the magnetic medium from the perpendicular direction to 45 degree. In this case, the switching field will be reduced by a foctor of two in the Stoner-Wohlfarth limit. Recently, this approach was realized by oblique film deposition onto arrays of self-assembled spherical particles [3-5]. In this presentation, recent results on different film systems including Co/Pt multilayers, FePt and CoPtCr-SiO2 alloys which have been deposited onto SiO2 particle monolayers will be presented. It turned out that by tuning the growth conditions single domain nanocaps with enhanced magnetic coercivity and tilted anisostropy axis can be achieved even for particle sizes below 50 nm. [4pt] [1] B. D. Terris and T. Thomson, J. Phys. D: Appl. Phys. 38 (2005) R199 [0pt] [2] J.-P. Wang, Nat. Mater. 4, 191 (2005). [0pt] [3] M. Albrecht et al., Nat. Mater. 4, 203 (2005). [0pt] [4] T. Ulbrich et al., Phys. Rev. Lett. 96 (2006) 077202. [0pt] [5] D. Makarov et al., Appl. Phys. Lett. 93, 153112 (2008).

Albrecht, Manfred

2009-03-01

48

Design and optimization of voice coil actuator for six degree of freedom active vibration isolation system using Halbach magnet array.  

PubMed

This paper describes the design, modeling, optimization, and validation of an active vibration isolation system using a voice coil motor. The active vibration isolating method was constructed with a passive isolator and an active isolator. A spring was used for passive isolating; an actuator was used for active isolating. The proposed active vibration isolation system (AVIS) can isolate disturbances for many kinds of instruments. Until now, developed AVIS were able to isolate a six degree-of-freedom disturbance effectively. This paper proposes the realization of such a six degree-of-freedom active vibration isolation system that can work as a bench top device for precision measuring machines such as atomic force microscope, scanning probe microscope, etc. PMID:23126814

Kim, MyeongHyeon; Kim, Hyunchang; Gweon, Dae-Gab

2012-10-01

49

Design and optimization of voice coil actuator for six degree of freedom active vibration isolation system using Halbach magnet array  

NASA Astrophysics Data System (ADS)

This paper describes the design, modeling, optimization, and validation of an active vibration isolation system using a voice coil motor. The active vibration isolating method was constructed with a passive isolator and an active isolator. A spring was used for passive isolating; an actuator was used for active isolating. The proposed active vibration isolation system (AVIS) can isolate disturbances for many kinds of instruments. Until now, developed AVIS were able to isolate a six degree-of-freedom disturbance effectively. This paper proposes the realization of such a six degree-of-freedom active vibration isolation system that can work as a bench top device for precision measuring machines such as atomic force microscope, scanning probe microscope, etc.

Kim, MyeongHyeon; Kim, Hyunchang; Gweon, Dae-Gab

2012-10-01

50

Note: Manipulation of supersonic atomic beams with static magnetic fields.  

PubMed

The inhomogeneous magnetic field of a permanent-magnet planar Halbach array is used to either deflect or to specularly reflect a supersonic beam of neutral atoms. Metastable neon and helium beams are tested to experimentally evaluate the performance of this array in a range of configurations. Results are compared with numerical simulations and the device is presented as a high precision tool for the manipulation of neutral atom beams. PMID:24028135

Gardner, Jamie; Castillo-Garza, Rodrigo; Raizen, Mark G

2013-09-01

51

Magnet arrays for use in a 3-D MEMS mirror array for optical switching  

Microsoft Academic Search

Magnet arrays for creating regions of high magnetic flux gradient are presented. These high-flux gradient regions are useful for actuation of two-axis micromirrors with quadrupole coils, which are an essential component of some optical switches. Three magnet arrays are presented: a checkerboard array made of individual magnets and two monolithic magnet arrays, an array with filled holes, and an array

William P. Taylor; Jonathan J. Bernstein; John D. Brazzle; Christopher J. Corcoran

2003-01-01

52

A bidirectional magnetic microactuator using electroplated permanent magnet arrays  

Microsoft Academic Search

A novel bidirectional magnetic microactuator using electroplated permanent magnet arrays has been designed, fabricated and characterized. To realize a bidirectional microactuator, CoNiMnP-based permanent magnet arrays have been fabricated first on a silicon cantilever beam using a new electroplating technique. In the fabricated permanent magnets, the vertical coercivity and retentivity have been achieved up to 87.6 kA\\/m (1100 Oe) and 190

Hyoung J. Cho; Chong H. Ahn

2002-01-01

53

Magnetically Actuated Nanorod Arrays as Biomimetic Cilia  

Microsoft Academic Search

We present a procedure for producing high-aspect-ratio cantilevered micro- and nanorod arrays of a PDMS-ferrofluid composite material. The rods have been produced with diameters ranging from 200 nm to 1 Ìm and aspect ratios as high as 125. We demonstrate actuation of these superparamagnetic rod arrays with an externally applied magnetic field from a permanent magnet and compare this actuation

B. A. Evans; A. R. Shields; R. Lloyd Carroll; S. Washburn; M. R. Falvo; R. Superfine

2007-01-01

54

Magnetic properties of arrays of electrodeposited nanowires  

Microsoft Academic Search

The fabrication and magnetic properties of arrays of short nanowires are reviewed. The arrays consist of electrodeposited ferromagnetic cylinders with aspect ratios of up to 3 and diameters of 57–180nm. Their hysteresis loops are characterized and their remanent states are related to the predictions of a three-dimensional micromagnetic model, which shows a transition from a single-domain ‘flower’ state to a

C. A. Ross; M. Hwang; M. Shima; Henry I. Smith; M. Farhoud; T. A Savas; W. Schwarzacher; J. Parrochon; W. Escoffier; H. Neal Bertram; F. B Humphrey; M. Redjdal

2002-01-01

55

The Inductrack Approach to Magnetic Levitation  

SciTech Connect

Concepts developed during research on passive magnetic bearing systems at the Lawrence Livermore National Laboratory gave rise to a new approach to magnetic levitation, the Inductrack. A passive induced-current system employing permanent magnets on the moving vehicle, the Inductrack maximizes levitation forces by a combination of two elements. First, the permanent magnets on the vehicle are arranged in a ''Halbach array,'' a magnet configuration that optimally produces a periodic magnetic field below the array, while canceling the field above the array. Second, the track is made up of close-packed shorted electrical circuits. These circuits couple optimally to the magnetic field of the Halbach array. As a result, levitating forces of order 40 metric tonnes per square meter of Halbach array can be generated, using NdFeB magnets whose weight is a few percent of the levitated weight. Being an induced-current system, the levitation requires motion of the vehicle above a low transition speed. For maglev applications this speed is a few kilometers per hour, walking speed. At rest or in the station auxiliary wheels are needed. The Inductrack is thus fail-safe, that is, drive system failure would only result in the vehicle slowing down and finally settling on its auxiliary wheels. On the basis of theoretical analyses a small model vehicle and a 20-meter-long track was built and tested at speeds of order 12 meters per second. A second model, designed to achieve 10-g acceleration levels and much higher speeds, is under construction under NASA sponsorship, en route to the design of maglev-based launchers for rockets. Some of the presently perceived practical problems of implementing full-scale maglev systems based on the Inductrack concept will be discussed.

Post, R.F.; Ryutov, D.D.

2000-04-19

56

A novel CMOS magnetic field sensor array  

Microsoft Academic Search

A CMOS magnetic field sensor array that can be implemented along with analog and digital signal processing circuitry in the form of a single integrated circuit for instrumentation or measurement is discussed. The design realizes a single sensor device through interconnection of a few n-channel magnetic-field-sensitive MOSFETs (MAGFETs) in one circuit. The experimental measurements suggest that the interconnection, which forms

Durgamadhab Misra

1990-01-01

57

Fabrication of magnetic nanodot arrays for patterned magnetic recording media.  

PubMed

Fabrication processes of arrayed magnetic nanodots for the use of patterned magnetic recording media were reviewed. One candidate for the patterned media is ordered assemble of magnetic nanoparticles, and the other is patterned magnetic thin films fabricated using various micro/nano scale machining processes. For the formation of patterned masks and molds, lithography processes as well as self-organized pattern formation are utilized. For the deposition processes of magnetic dots, electrochemical deposition processes were widely used. These fabrication processes are reviewed mainly from recent reports. The recording systems for the patterned media including probe-type-recording are also overviewed. PMID:17455486

Sato, Hirotaka; Homma, Takayuki

2007-01-01

58

A CMOS rotary encoder using magnetic sensor arrays  

Microsoft Academic Search

A new type of small magnetic rotary encoder is presented. The device detects the magnetic field of a permanent magnet attached to the end of the rotating shaft using complementary metal-oxide semiconductor (CMOS) magnetic sensors [magnetic field effect transistor (MAGFET) arrays] set in a square arrangement. The sensor array is integrated onto a CMOS chip along with angle-detection circuits, leading

Kazuhiro Nakano; Toru Takahashi; Shoji Kawahito

2005-01-01

59

EDDY-CURRENT TESTING WITH GMR MAGNETIC SENSOR ARRAYS  

Microsoft Academic Search

The advent of GMR magnetic sensors and GMR sensor arrays with frequency- independent sensitivity offers improvements in speed, depth, and resolution in eddy-current testing. Arrays of GMR magnetic sensors allow rapid scanning of an area for defects in a single pass. The small size and low power consumption of these solid-state magnetic sensors enable the fabrication of compact arrays of

C. H. Smith; R. W. Schneider; T. Dogaru

60

Magnetic field analysis of 2-D permanent magnet array for planar motor  

Microsoft Academic Search

A new permanent magnet array for planar motor is proposed. The flux density distribution for the array is solved analytically by using the scalar magnetic potential equation. It is verified that the performance of the new magnet array is superior to the existing magnet arrays presented in patents

Han-Sam Cho; Chang-Hwan Im; Hyun-Kyo Jung

2001-01-01

61

Thermal magnetization reversal in arrays of nanoparticles  

NASA Astrophysics Data System (ADS)

The results of large-scale simulations investigating the dynamics of magnetization reversal in arrays of single-domain nanomagnets after a rapid reversal of the applied field at nonzero temperature are presented. The numerical micromagnetic approach uses the Landau-Lifshitz-Gilbert equation including contributions from thermal fluctuations and long-range dipole-dipole demagnetizing effects implemented using a fast-multipole expansion. The individual model nanomagnets are 9 nm×9 nm×150 nm iron pillars similar to those fabricated on a surface with scanning tunneling microscope assisted chemical vapor deposition [S. Wirth et al., J. Appl. Phys. 85, 5249 (1999)]. Nanomagnets oriented perpendicular to the surface and spaced 300 nm apart in linear arrays are considered. The applied field is always oriented perpendicular to the surface. When the magnitude of the applied field is less than the coercive value, about 2000 Oe for an individual nanomagnet, magnetization reversal in the nanomagnets can only occur by thermally activated processes. Even though the interaction from the dipole moment of neighboring magnets in this geometry is only about 1 Oe, less than 1% of the coercive field, it can have a large impact on the switching dynamics. What determines the height of the free-energy barrier is the difference between the coercive and applied fields, and 1 Oe can be a significant fraction of that. The magnetic orientations of the neighbors are seen to change the behavior of the nanomagnets in the array significantly.

Brown, Gregory; Novotny, M. A.; Rikvold, Per Arne

2001-06-01

62

Magnetization reversal in arrays of Co rings  

Microsoft Academic Search

The magnetization behavior of arrays of individual and coupled Co rings has been studied using superconducting quantum interference device magnetometry, magneto-optical imaging, and Lorentz transmission and scanning transmission electron microscopy. The transition from the polarized into the vortex state of isolated rings is shown to occur through the motion and annihilation of head-to-head domain boundaries. The chirality of the vortex

U. Welp; V. K. Vlasko-Vlasov; J. M. Hiller; N. J. Zaluzec; V. Metlushko; B. Ilic

2003-01-01

63

Templated Assembly of Magnetic Cobalt Nanowire Arrays  

Microsoft Academic Search

A template-assisted assembly technique combined with a chemical synthesis approach has been used to produce high density magnetic\\u000a cobalt nanowire arrays. Cobalt nanowires were formed using chemical synthesis techniques, by borohydride reduction of cobalt\\u000a salt in the pores of anodic aluminum oxide (AAO) templates; the samples were annealed in order to achieve nanowires with hcp\\u000a crystal structure. The morphology and

A. K. Srivastava; R. S. Singh; K. E. Sampson; V. P. Singh; R. V. Ramanujan

2007-01-01

64

Thermal magnetization reversal in arrays of nanoparticles  

Microsoft Academic Search

The results of large-scale simulations investigating the dynamics of magnetization reversal in arrays of single-domain nanomagnets after a rapid reversal of the applied field at nonzero temperature are presented. The numerical micromagnetic approach uses the Landau–Lifshitz–Gilbert equation including contributions from thermal fluctuations and long-range dipole–dipole demagnetizing effects implemented using a fast-multipole expansion. The individual model nanomagnets are 9 nm×9 nm×150

Gregory Brown; M. A. Novotny; Per Arne Rikvold

2001-01-01

65

Magnetic flux array for spontaneous magnetic reconnection experiments  

SciTech Connect

Experimental investigation of reconnection in magnetized plasmas relies on accurate characterization of the evolving magnetic fields. In experimental configurations where the plasma dynamics are reproducible, magnetic data can be collected in multiple discharges and combined to provide spatially resolved profiles of the plasma dynamics. However, in experiments on spontaneous magnetic reconnection recently undertaken at the Versatile Toroidal Facility at MIT, the reconnection process is not reproducible and all information on the plasma must be collected in a single discharge. This paper describes a newly developed magnetic flux array which directly measures the toroidal component of the magnetic vector potential, A{sub {phi}}. From the measured A{sub {phi}}, the magnetic field geometry, current density, and reconnection rate are readily obtained, facilitating studies of the three-dimensional dynamics of spontaneous magnetic reconnection. The novel design of the probe array allows for accurate characterization of profiles of A{sub {phi}} at multiple toroidal angles using a relatively small number of signal channels and with minimal disturbance of the plasma.

Kesich, A.; Bonde, J.; Egedal, J.; Fox, W.; Goodwin, R.; Katz, N.; Le, A. [Massachusetts Institute of Technology, Plasma Science and Fusion Center, Cambridge, Massachusetts 02139 (United States)

2008-06-15

66

Micromachined thick permanent magnet arrays on silicon wafers  

Microsoft Academic Search

Using micromachining and electroplating techniques, micromachined thick CoNiMnP-based permanent magnet arrays have been designed, fabricated, and characterized for magnetic microelectromechanical systems (MEMS) device applications. The electroplated magnet arrays contain 1,500 magnets of 40 ?m×40 ?m×50 ?m in a cubic shape on the silicon substrate of 2.5 mm×2.5 mm, where the magnets have shown a fairly high magnetic vertical coercivity of

Trifon M. Liakopoulos; Wenjin Zhang; Chong H. Ahn

1996-01-01

67

Method of Making a Miniature Scale Periodic Permanent Magnet Array and Miniature Scaled Periodic Permanent Magnet Array So Formed.  

National Technical Information Service (NTIS)

A miniature scale periodic permanent magnet array is made from a magnetic material having a high intrinsic coercive force and a magnetic material having a low intrinsic coercive force by depositing alternating layers of the high and low intrinsic coercive...

F. J. Cadieu, T. D. Cheung

1986-01-01

68

Colocated Magnetic Loop, Electric Dipole Array Antenna (Preliminary Results).  

National Technical Information Service (NTIS)

We present a detailed electromagnetic analysis of an electrically small colocated electric dipole and magnetic loop antenna array. This antenna is the simplest example of the Grimes multipole class of antenna arrays. We have determined that since the inte...

P. L. Overfelt D. R. Bowling D. J. White

1994-01-01

69

Circular arrays of magnetic sensors for current measurement  

Microsoft Academic Search

A single solid-state magnetic sensor can measure a current flowing in a conductor in a noncontact way. In order to improve the accuracy of the measuring system and to reduce the crosstalk effects of other magnetic fields, circular arrays of magnetic sensors can be fabricated, still preserving low costs. In those kind of arrays, the sensing elements are assembled on

Luca Di Rienzo; Renzo Bazzocchi; Angelo Manara

2001-01-01

70

Assembly of ordered magnetic microsphere arrays  

NASA Astrophysics Data System (ADS)

We have developed a straightforward technique to assemble ordered arrays of magnetic microspheres on patterned thin Permalloy (Py) films deposited on the surface of a silicon wafer. Droplets containing micrometer-sized carboxyl paramagnetic microspheres are placed on a horizontally oriented wafer. The field produced by a permanent magnet placed under the wafer is rendered inhomogeneous by the patterned Py features and the resulting field gradients attract and hold the paramagnetic microspheres to these features. While the magnetic microspheres are being attracted to and secured on the pattered Permalloy features, a horizontal flow is created by a pipette, which also removes loose (unsecured) microspheres. By applying this technique to a cocktail of individually functionalized microspheres, a sensor could be realized, which will screen, in parallel, for a large number of targets per unit area. The ability to resolve individual microspheres is close to 100%. A desirable feature is that the substrate is reusable; removing the magnet allows an existing batch of microspheres, which may have lost sensitivity due to environmental exposure, to be flushed from the substrate and replaced with a new batch. The technique complements existing approaches in the field of microarrays widely used in immunoassay, DNA fragment detection, pathogen detection, and other applications in functional genomics and diagnostics.

Xu, Wanling; Ketterson, John

2008-08-01

71

Patterned magnetic bar array for high-throughput DNA detection  

Microsoft Academic Search

We have developed a simple elegant system based on an array of thin-film magnetic bars for creating a two-dimensional array of paramagnetic polymer beads that can be functionalized to bind fluorescently labeled DNA fragments. The resulting array can be scanned using conventional optical fluorescence instruments, to quantify the relative abundance of specific DNA sequence fragments in a biological sample. Parallel

Lester A. Roberts; Ankur M. Crawford; Stefan Zappe; Maneesh Jain; Robert L. White

2004-01-01

72

Vector Potential and Stored Energy of a Quadrupole Magnet Array  

SciTech Connect

The vector potential, magnetic field and stored energy of a quadrupole magnet array are derived. Each magnet within the array is a current sheet with a current density proportional to the azimuthal angle 2{theta} and the longitudinal periodicity (2m-1){pi}/L. Individual quadrupoles within the array are oriented in a way that maximizes the field gradient The array does not have to be of equal spacing and can be of a finite size, however when the array is equally spaced and is of infinite size the solution can be simplified. We note that whereas, in a single quadrupole magnet with a current density proportional to cos2{theta} the gradient is pure, such purity is not preserved in a quadrupole array.

Caspi, S.

1999-03-15

73

Design of a large area magnetic field sensor array  

Microsoft Academic Search

The circuit design of a Large Area Magnetic Field Sensor Array (LAMFSA) using CMOS 3 ?m process is described. This prototype is developed mainly for application in magnetic field mapping and tactile array sensors. In order to enable the production of such a device, redundancy schemes are implemented and a laser interconnection post fabrication technique is used. The basic sensing

Yves Audet; Glenn H. Chapman

1994-01-01

74

A CMOS smart rotary encoder using magnetic sensor arrays  

Microsoft Academic Search

This paper presents a new concept of small magnetic rotary encoders. The magnetic field induced by a rotatable magnet is detected by integrated CMOS magnetic sensors (MAGFETs) arranged in a square form. This magnetic sensor array is integrated on a CMOS chip with angle detection circuits, leading to the realization of a small-size and cost-effective rotary encoder. Commonly-used magnetic encoders

Kazuhiro Nakano; Toru Takahashi; Shoji Kawahito

2003-01-01

75

Levitation Force Investigation of Bulk HTSC Above Halbach PMG with Different Cross-Section Physical Dimensions by 3D-Modeling Numerical Method  

NASA Astrophysics Data System (ADS)

The levitation force of a bulk high temperature superconductor (HTSC) over Halbach permanent magnet guideways (PMG) with different cross-section configuration is studied by numerical method. The Halbach PMG is composed of three host permanent magnets (HPMs) and two slave permanent magnets (SPMs). One cylindrical bulk HTSC with a diameter of 30 mm and height of 15 mm is used. The 3D-modeling is formulated by the H-method. The numerical resolving codes are practiced using finite element method (FEM). The E-J power law is used to describe the electric current nonlinear characteristics of bulk HTSC. By the method, the influence of the cross-section physical dimensions of Halbach PMG on the levitation forces of bulk HTSC levitated above the PMG is studied. The simulation results show that increasing the width of SPM (W_SPM) can enhance the bulk HTSC levitation performance immediately under the condition of keeping the ratio of W_HPM (W_HPM : the width of HPM) to W_SPM between 1.6 and 1.8, the ratio of td (the height of the PMG) to W_HPM between 1.2 and 1.4. By the method, the bulk HTSC better levitation performance can be expected.

Lu, Yiyun; Liu, Guoliang; Qin, Yujie

2014-05-01

76

VERY DENSE MAGNETIC SENSOR ARRAYS FOR PRECISION MEASUREMENT AND DETECTION  

Microsoft Academic Search

Very dense arrays of micron-sized magnetic sensors combined with micron sensor spacing on a single chip can detect very small magnetic fields with high spatial resolution. These changes in magnetic fields are in the milligauss range, approximately 500 times less than Earth's field, and are required for magnetic biosensors, non- destructive test\\/inspection\\/evaluation, precision position measurement, document validation and magnetic imaging

Carl H. Smith; Robert W. Schneider

2003-01-01

77

Wettability and friction coefficient of micro-magnet arrayed surface  

NASA Astrophysics Data System (ADS)

Surface coating is an important part of surface engineering and it has been successfully used in many applications to improve the performance of surfaces. In this paper, magnetic arrayed films with different thicknesses were fabricated on the surface of 316 stainless steel disks. Controllable colloid - ferrofluids (FF) was chosen as lubricant, which can be adsorbed on the magnetic surface. The wettability of the micro-magnet arrayed surface was evaluated by measuring the contract angle of FF drops on surface. Tribological experiments were carried out to investigate the effects of magnetic film thickness on frictional properties when lubricated by FF under plane contact condition. It was found that the magnetic arrayed surface with thicker magnetic films presented larger contract angle. The frictional test results showed that samples with thicker magnetic films could reduce friction and wear more efficiently at higher sliding velocity under the lubrication of FF.

Huang, Wei; Liao, Sijie; Wang, Xiaolei

2012-01-01

78

Magnetic Focusing of Composite Fermions through Arrays of Cavities  

Microsoft Academic Search

The magnetoresistance Rxx was investigated in arrays of abutted square cavities with lengths L ranging from 500 nm to 1.2 mum near filling factor nu = 1\\/2. Maxima in Rxx occur for effective magnetic field values satisfying the magnetic focusing condition between the cavity spacing and the cyclotron radius of composite fermions, also for the effective magnetic field direction when

J. H. Smet; D. Weiss; R. H. Blick; G. Lütjering; K. von Klitzing; R. Fleischmann; R. Ketzmerick; T. Geisel; G. Weimann

1996-01-01

79

Structural and magnetic properties of electrodeposited Cobalt nanowire arrays  

Microsoft Academic Search

Ordered magnetic nanowires have tremendous potential in future magnetic storage and high frequency magnetic logic devices. Here, we present the fabrication of ordered arrays of Cobalt nanowires by electrodeposition through porous polycarbonate membranes. Vertically and horizontally aligned nanowires were produced in presence of an external bias field during post deposition etching of the polycarbonate membrane. Structural and compositional analyses have

S. Sharma; A. Barman; M. Sharma; L. R. Shelford; V. V. Kruglyak; R. J. Hicken

2009-01-01

80

A novel bi-directional magnetic microactuator using electroplated permanent magnet arrays with vertical anisotropy  

Microsoft Academic Search

A novel bi-directional magnetic microactuator using electroplated permanent magnet arrays has been fabricated and tested in this work. To realize the microactuator, a new electroplating technique has been developed to improve vertical magnetic anisotropy in CoNiMnP-based permanent magnet arrays. By applying magnetic field during electroplating, vertical coercivity and remanence have been increased up to 1100 Oe and 1900 G. After

Hyoung J. Cho; Chong H. Ahn

2000-01-01

81

Electroplated thick CoNiMnP permanent magnet arrays for micromachined magnetic device applications  

Microsoft Academic Search

Electroplated thick CoNiMnP permanent magnet arrays for micromachined magnetic device applications have been designed, fabricated, and tested. The electroplated arrays contain 5000 magnets of 40 ?m×40 ?m×50 ?m in a cubic shape on the silicon membrane of 4.6 mm×4.6 mm ×20 ?m, where the magnets have shown a fairly high magnetic vertical coercivity of 600 Oe, a retentivity of 0.2-0.3

T. M. Linkopoulos; Wenjin Zhang; G. H. Ahn

1996-01-01

82

Vectorial calibration of 3D magnetic field sensor arrays  

Microsoft Academic Search

The vectorial calibration of magnetic field sensor arrays along three axes is presented. In this context, a distinction must be made between the calibration of alignment errors between the 3D sensors and the calibration of orthogonality errors between the three axes of a 3D sensor. Alignment errors within the sensor array are determined by using a homogeneous vector field generated

M. P. Lassahn; G. Trenkler

1995-01-01

83

Magnetic behaviour of arrays of nickel nanowires with small diameter  

Microsoft Academic Search

Arrays of nickel nanowires have been fabricated within a template of porous alumina by electrochemical deposition. Measurements of magnetic hysteresis loops were performed at room temperature with a vibrating sample magnetometer. Coercivity and squareness of the arrays are closely related to l\\/D and diameter of the nanowires, and the angle ? between the normal line of the alumina surface and

Kuan-Hong Xue; Gu-Ping Pan; Ming-Hu Pan; Mu Lu; Guang-Hou Wang

2003-01-01

84

Eddy-current testing by flexible microloop magnetic sensor array  

Microsoft Academic Search

A flexible microloop magnetic sensor array has been developed for nondestructive evaluation in nuclear power plants and its fundamental characteristics have been investigated. A flexible micro-eddy current testing (micro-ECT) probe consists of a pancake-type exciting coil of the diameter of 3.2 ?m and a flexible microloop magnetic sensor array with an area of 14×14 mm2 and a thickness of 125

Mitsuru Uesaka; Kazumi Hakuta; Kenzo Miya; Kazuhiko Aoki; Ayumu Takahashi

1998-01-01

85

Magnetic properties of arrays of interacting Co nanocrystals  

Microsoft Academic Search

Monodisperse Co FCC nanocrystals with 12nm diameter were self-assembled into regular quasi-two-dimensional triangular periodic arrays on carbon substrates from a toluene-based colloidal suspension. At 300K the regular arrays show a collective magnetic behaviour due to dipolar coupling. A remanent magnetization with an easy axis in the film-plane and an uniaxial in-plane anisotropy field of 0.037T were determined by SQUID magnetometry

M. Spasova; U. Wiedwald; R. Ramchal; M. Farle; M. Hilgendorff; M. Giersig

2002-01-01

86

Low-cost magnetic interdigitated array on a plastic wafer  

Microsoft Academic Search

In this paper, a new magnetic interdigitated array (mIDA) has been designed, fabricated, and characterized for a magnetic bead separator on a plastic substrate, which can provide sampling capability in a low-cost disposable platform for magnetic bead-based biochemical detection systems. A mIDA was patterned and electroplated on a cyclic olefin copolymer (COC) substrate. To construct a magnetic bead sampler, an

Jin-Woo Choi; C. H. Ahn

2004-01-01

87

Vibrational Properties of High- Superconductors Levitated Above a Bipolar Permanent Magnetic Guideway  

NASA Astrophysics Data System (ADS)

A bipolar permanent magnetic guideway (PMG) has a unique magnetic field distribution profile which may introduce a better levitation performance and stability to the high- superconducting (HTS) maglev system. The dynamic vibration properties of multiple YBCO bulks arranged into different arrays positioned above a bipolar PMG and free to levitate were investigated. The acceleration and resonance frequencies were experimentally measured, and the stiffness and damping coefficients were evaluated for dynamic stability. Results indicate that the levitation stiffness is closely related to the field-cooling-height and sample positioning. The damping ratio was found to be low and nonlinear for the Halbach bipolar HTS-PMG system.

Liu, Lu; Wang, Jiasu

2014-05-01

88

Micro eddy current testing by micro magnetic sensor array  

Microsoft Academic Search

A micro Eddy Current Testing (ECT) system for planar thin specimens made of INCONEL 600 with flaws was proposed and developed. A micro ECT probe used here consists of a conventional pancake-type coil as an exciting coil and a micro magnetic sensor array as a set of pickup coils. Magnetic field perturbation due to a flaw was measured with high

Mitsuru Uesaka; Takahiro Nakanishi; Kenzo Miya; Hidenobu Komatsu; Kazuhiko Aoki; Kazuo Kasai

1995-01-01

89

Strategies for producing cluster-based magnetic arrays  

Microsoft Academic Search

Chelating ligands based on the iminodiacetic acid moiety can be used to control the solvolysis reactions of paramagnetic transition metal ions and allow various cluster-based magnetic materials to be isolated and characterised. This paper discusses the strategies that can be used to favour certain types of supramolecular interaction with the ultimate goal of engineering arrays of ‘single molecule magnets’. Ten

Wolfgang Schmitt; Muralee Murugesu; Jeremy C. Goodwin; Jonathan P. Hill; Alexander Mandel; Rajiv Bhalla; Christopher E. Anson; Sarah L. Heath; Annie K. Powell

2001-01-01

90

Magnetic behaviour of arrays of nickel nanowires with small diameter  

NASA Astrophysics Data System (ADS)

Arrays of nickel nanowires have been fabricated within a template of porous alumina by electrochemical deposition. Measurements of magnetic hysteresis loops were performed at room temperature with a vibrating sample magnetometer. Coercivity and squareness of the arrays are closely related to l/ D and diameter of the nanowires, and the angle ? between the normal line of the alumina surface and the applied magnetic field. For the same diameter of 10 nm, the coercivity and squareness increase remarkably with l/ D when the l/ D is less than 100. The diameter and angle ? dependences of coercivity do not follow the relationships of curling, fanning or coherent rotation mode of magnetization while thermal activation for magnetization reversal becomes remarkable for the arrays of Ni nanowires with the diameter less than 18 nm but the same l/ D of 50. The coercivity of the arrays with the magnetic field perpendicular to the film surface is linear with D-3/2 of Ni nanowires. From the fitting line, the critical diameter for superparamagnetism at room temperature and pure coercivity for such Ni nanowire arrays are found to be 6 nm and 1200 Oe respectively.

Xue, Kuan-Hong; Pan, Gu-Ping; Pan, Ming-Hu; Lu, Mu; Wang, Guang-Hou

91

A compact permanent magnet array with a remote homogeneous field  

Microsoft Academic Search

We present the design and construction of a single sided magnet array generating a homogeneous field in a remote volume. The compact array measures 11.5cm by 10cm by 6cm and weights ?5kg. It produces a B0 field with a ‘sweet spot’ at a point 1cm above its surface, where its first and second spatial derivatives are approximately zero. Unlike other

Andrew E. Marble; Igor V. Mastikhin; Bruce G. Colpitts; Bruce J. Balcom

2007-01-01

92

Selective actuation of arrays of carbon nanotubes using magnetic resonance.  

PubMed

We introduce the use of ferromagnetic resonance (FMR) to actuate mechanical resonances in as grown arrays of carbon nanotubes (CNTs) loaded with Ni particles (Ni-CNTs). This contactless method is closely related to the magnetic resonance force microscopy technique and provides spatial selectivity of actuation along the array. The Ni-CNT arrays are grown by chemical vapor deposition and are composed of homogeneous CNTs with uniform length (~600 nm) and almost equal diameter (~20 nm), which are loaded with Ni catalyst particles at their tips due to the tip growth mode. The vibrations of the Ni-CNTs are actuated by relying on the driving force that appears due to the FMR excited at about 2 GHz in the Ni particles (diameter ~100 nm). The Ni-CNT oscillations (frequency ~40 MHz) are detected mechanically by atomic force microscopy. The acquired oscillation images of the Ni-CNT uniform array reveal clear maxima in the spatial distribution of the oscillation amplitudes. We attribute these maxima to the "sensitive slices", i.e., the spatial regions of the Ni-CNT array where the FMR condition is met. Similar to magnetic resonance imaging, the sensitive slice is determined by the magnetic field gradient and moves along the Ni-CNT array as the applied magnetic field is ramped. Our excitation method does not require the presence of any additional microfabricated electrodes or coils near the CNTs and is particularly advantageous in cases where the traditional electrical actuation methods are not effective or cannot be implemented. The remote actuation can be effectively implemented also for arrays of other magnetic nanomechanical resonators. PMID:23742039

Volodin, Alexander; Santini, Claudia A; De Gendt, Stefan; Vereecken, Philippe M; Van Haesendonck, Chris

2013-07-23

93

Magnetic current loop array in a reflector antenna  

NASA Astrophysics Data System (ADS)

A magnetic current loop antenna array is designed, implemented, and measured. Radiation pattern, input impedance, and efficiency of the array are presented. The array is intended as a feed in a reflector antenna. Using a 360 mm solid dish, the overall gain of the reflector antenna is 24.6 dB at 9 GHz. The tolerance in placing the feed at the focal point of the dish is high. The present feed is low cost, self-supportive, robust, and easy to manufacture. It is an ideal substitute for the horn in a TVRO (television receive only) or VSAT (very small aperature terminal) antenna.

Yung, Edward K. N.; Lee, Wilson W. S.

1994-04-01

94

A colocated magnetic loop, electric dipole array antenna (preliminary results)  

NASA Astrophysics Data System (ADS)

We present a detailed electromagnetic analysis of an electrically small colocated electric dipole and magnetic loop antenna array. This antenna is the simplest example of the Grimes multipole class of antenna arrays. We have determined that since the interaction term between the two elements disappears from the radial complex power, we were able to set the radial reactance to zero by choosing appropriate current magnitudes and phases on the array elements. By driving the two elements in quadrature, we obtained a much increased radiation intensity and directivity as well as increased radiated power.

Overfelt, P. L.; Bowling, D. R.; White, D. J.

1994-09-01

95

Magnetic domain structure in small diameter magnetic nanowire arrays [rapid communication  

NASA Astrophysics Data System (ADS)

Fe 0.3Co 0.7 alloy nanowire arrays were prepared by ac electrodepositing Fe 2+ and Co 2+ into a porous anodic aluminum oxide (PAO) template with diameter about 50 nm. The surface of the samples were polished by 100 nm diamond particle then chemical polishing to give a very smooth surface (below ±10 nm/?m 2). The morphology properties were characterized by SEM and AFM. The bulk magnetic properties and domain structure of nanowire arrays were investigated by VSM and MFM respectively. We found that such alloy arrays showed strong perpendicular magnetic anisotropy with easy axis parallel to nanowire arrays. Each nanowire was in single domain structure with several opposite single domains surrounding it. Additionally, we investigated the domain structure with a variable external magnetic field applied parallel to the nanowire arrays. The MFM results showed a good agreement with our magnetic hysteresis loop.

Qin, Dong-Huan; Zhang, Hao-Li; Xu, Cai-Ling; Xu, Tao; Li, Hu-Lin

2005-01-01

96

Magnetic composite electrodeposition of micro-array magnets for MEMS actuators  

Microsoft Academic Search

This paper reports a new magnetic composite material deposition technique called magnetic composite electrodeposition (MCE). Thin films and micro-arrays of a composite matrix consisting of magnetic particles and a ferromagnetic alloy have been fabricated based on composite electroplating techniques. The magnetic particle selected is a barium ferrite magnet (BaFe12O19) and the ferromagnetic matrix is a pulse-reverse electrodeposited CoNiP alloy. The

S. Guan; B. J. Nelson

2004-01-01

97

Clock field in arrayed magnetic logic gates with a magnetic force microscope tip  

NASA Astrophysics Data System (ADS)

A magnetic logic gate (MLG), which is based on magnetic quantum dot cellular automata (MQCA), is capable of NAND/NOR logic operations. By arranging MLGs in a two-dimensional periodic array, a highly functional circuit can be created. However, NAND/NOR gates are difficult to form into a two-dimensional periodic arrangement. Here, we propose NOT/AND/ORs gate based on MLGs, which can be arranged in a two-dimensional periodic array. To demonstrate logic operations, we performed numerical simulations based on the macro-spin model. To execute logic operation in the arrayed structure, we used the stray field from a magnetic force microscope tip.

Nomura, H.; Imanaga, Y.; Hiratsuka, Y.; Nakatani, R.

2012-08-01

98

Preparation and magnetic behavior of arrays of electrodeposited Co nanowires  

Microsoft Academic Search

Cobalt nanowires have been synthesized by electrodeposition into porous track-etched polycarbonate membranes with a quoted pore diameter of Dp?200–400nm and a thickness of L?7?m. Magnetization curves and torque experiments of arrays of Co wires confirm that when the lengths of the wires are increased a crossover takes place from a parallel easy direction of magnetization towards an easy direction perpendicular

J Rivas; A Kazadi Mukenga Bantu; G Zaragoza; M. C Blanco; M. A López-Quintela

2002-01-01

99

Vortex Imaging in Superconducting Films with Periodic Magnetic Dot Arrays  

NASA Astrophysics Data System (ADS)

A regular lattice of magnetic dots underlying a superconducting thin film acts as an array of pinning sites for flux vortices. Scanning Hall probe microscopy studies of Nb-film/Ni-dot structures are reported. The arrays consisted of 1 ?m-diameter Ni dots on rectangular grids, with lattice constants ranging from 2 to 5 ?m. Magnetic field images were taken of the vortex configurations at fields up to 1.2:H_0, where H0 is the ``matching field'' that produces one flux quantum per unit cell of the dot lattice. These images show that well-defined ordering commensurate with the dot lattice occurs even for fields below H_0. They also show that in this field range, a significant number of vortices occupy high-symmetry interstitial sites at the center of the plaquettes between the dots. This is in contrast to superconducting films with arrays of holes, where no interstitial vortices are seen for H < H_0. This shows that pinning is significantly weaker in the magnetic dot arrays than in the hole arrays. It also suggests that there may be repulsive dot-vortex interactions at long range due to the field of the dots that can stabilize vortices at high-symmetry interstitial sites without the neighboring dots being occupied by vortices.

Silevitch, D. M.; Reich, D. H.; Field, S. B.; Shtrikman, H.

2001-03-01

100

High-density very efficient magnetic film memory arrays  

Microsoft Academic Search

Partially populated arrays using very small efficient DRO magnetic film memory cells have been constructed and tested to demonstrate the packaging and performance compatibility of such cells with integrated circuits. The experimental cells were made by vapor deposition of Permalloy, copper, and other materials through a mask in a flat wire configuration with an easy direction along the wire and

ARTHUR V. POHM; Jish-Min Wang; F. Lee; WILLIAM SCHNASSE; T. Smay

1969-01-01

101

Magnetic anisotropy of nickel nanowire array in porous silicon  

NASA Astrophysics Data System (ADS)

Ordered nickel nanowire arrays formed by electrochemical deposition in a mesoporous silicon matrix have been studied by the ferromagnetic resonance technique. It is established that the samples exhibit uniaxial magnetic anisotropy of the easy-axis or easy-plane type depending on the matrix porosity. Values of the anisotropy field and g-factor in the samples are determined.

Rusetskii, M. S.; Kazyuchits, N. M.; Baev, V. G.; Dolgii, A. L.; Bondarenko, V. P.

2011-05-01

102

Electrochemically synthesized magnetic nanowire heterostructures and arrays for acoustic sensing  

NASA Astrophysics Data System (ADS)

Biological cilia in humans and animals serve many functions, including sensing of acoustic and sensory signals and actuation for mobility in small species or for motion of bodily fluids in larger species. This work sought to fabricate nanowire arrays as artificial cilia. Arrays of tiny sensors at nanoscale dimensions have theoretical advantages to macroscale sensors including higher spatial resolution, miniscule size, and higher ultimate strength for each sensing element. Theoretical investigations showed that a magnetic/non-magnetic heterostructure would enable nanowires with improved sensitivity over single element nanowires. Here, nanowire structures included a soft magnetostrictive sensing segment (such as Ni or Fe1-xGax [also called galfenol]), a permanent magnetic segment to provide an integrated magnetic bias, and a long and hard non-magnetic end segment to increase the viscous drag force of the fluid on the nanowire. Galfenol is a new large magnetostrictive material that has moderate magnetostriction but excellent mechanical properties. This work included the first successful electroplating process for this unique alloy. This enabled the fabrication of these alloys into nanoscopic form. These nanowire structures were grown into nanoporous anodic aluminum oxide (AAO) templates using a robust two-step anodization process. When grown at the proper conditions (temperature, electrolyte, and voltage), the templates contained highly-ordered nanopores with small diameters (10-100 nm), short center-to-center distances (25-250 nm), and long lengths (0.1-100 mum). Metal contacts were deposited onto one side of the templates, and magnetostrictive, magnetic, and non-magnetic materials were sequentially electrodeposited into the nanopores. Controlling the non-magnetic segment lengths enabled control of the nanowire resonant frequency. By using graded nanowire lengths across the array, frequency filtering as a pre-filter for subsequent signal processing could be performed. The metallic electroplating of Fe-Ga alloys has been thoroughly described, and the process for producing the complete structure for magnetic heterostructures for biomimetic cilia has been achieved.

McGary, Patrick David

103

Emerging magnetic stability in atomically assembled spin arrays  

NASA Astrophysics Data System (ADS)

Magnetic stability is usually created by the interaction of a large ensemble of atomically small magnetic moments that are themselves unstable. We make use of the Scanning Tunneling Microscope's ability to move individual atoms and construct arrays of interacting spins. Owed to their smallness, the magnetic states of these spin arrays are quantized and we probe their energies by inelastic electron tunneling spectroscopy [1]. To gain access to the equally important dynamical properties we employ an all-electronic pump-probe measurement scheme with which we follow the evolution between the spin states at nanosecond speed [2]. The combination of energetic and dynamical information allows identification of the relevant spin interaction and spin relaxation mechanisms at the atomic level. We design arrangements of atoms that suppress quantum tunneling of magnetization and drastically stabilize different spin configurations. Tracing the emergence of magnetic stability in the progression from individual atoms to arrays of spins points to new avenues for spintronic applications at atomic dimensions. [4pt] [1] A. J. Heinrich, J. A. Gupta, C. P. Lutz, D. M. Eigler, Science 306 466 (2004).[0pt] [2] S. Loth, M. Etzkorn, C. P. Lutz, D. M. Eigler, A. J. Heinrich, Science 329 1628 (2010).

Loth, Sebastian; Baumann, Susanne; Lutz, Christopher P.; Eigler, D. M.; Heinrich, Andreas J.

2012-02-01

104

Investigation of Microscale Magnetic Forces for Magnet Array Self-Assembly  

Microsoft Academic Search

This paper focuses on quantification and optimization of micromagnetic bonding forces to enable a technique of magnet array self-assembly (MASA). MASA is envisioned to uniquely assemble different microscale components using arrays of hard micromagnets, which are pre-patterned onto the component surfaces via batch-fabrication. Finite-element (FEM) and analytical methods are used to analyze the dependence of magnetic bonding forces on the

Sheetal B. Shetye; Janhavi S. Agashe; David P. Arnold

2007-01-01

105

Analysis and comparison of two-dimensional permanent-magnet arrays for planar motor  

Microsoft Academic Search

This paper investigates three kinds of permanent-magnet arrays used in planar motors with polarity centers distributed in the lattices of a matrix. The magnetic field of every kind of magnet array is analyzed by analytical methods. First, we give a Laplace equation of magnetic scalar potential and a series of boundary conditions. Then, we derive the analytical expressions of magnet

Jiayong Cao; Y. Zhu; Jinsong Wang; Wensheng Yin; Guanghong Duan

2004-01-01

106

Optimisation of a brushless motor excited by multi-polar permanent magnet array  

Microsoft Academic Search

The paper investigates the optimal multi-polar magnetization of an interior magnet brushless machine rotor comprising a permanent magnet (PM) array made up from discrete anisotropic arc segments. The particular case where the magnet array is constructed from two arc segments per pole is considered where the magnets are alternatively magnetised normal and tangential to the rotor surface. The influence of

P. H. Mellor; R. Wrobel

2005-01-01

107

Angular resonant absorption curves in magnetic nanowire arrays  

NASA Astrophysics Data System (ADS)

We systematically probed the dynamics of two-dimensional Ni80Fe20 nanowire arrays with different strengths of interwire interactions using angular dependent microwave absorption spectroscopy. The experimental results are analyzed in terms of a graphical representation of the resonant absorption data through a critical-curve-like approach. This representation has the advantage of offering a direct and complete visual representation of anisotropy, interactions, and magnetization dynamics effects in nanomagnet arrays. In the paper, the connection between the proposed image of polar resonant absorption curves and the static switching field critical curves is substantiated using both macrospin and fully micromagnetic simulation approaches.

Cimpoesu, Dorin; Ding, Junjia; Stoleriu, Laurentiu; Adeyeye, Adekunle; Stancu, Alexandru; Spinu, Leonard

2013-06-01

108

Life on magnets: stem cell networking on micro-magnet arrays.  

PubMed

Interactions between a micro-magnet array and living cells may guide the establishment of cell networks due to the cellular response to a magnetic field. To manipulate mesenchymal stem cells free of magnetic nanoparticles by a high magnetic field gradient, we used high quality micro-patterned NdFeB films around which the stray field's value and direction drastically change across the cell body. Such micro-magnet arrays coated with parylene produce high magnetic field gradients that affect the cells in two main ways: i) causing cell migration and adherence to a covered magnetic surface and ii) elongating the cells in the directions parallel to the edges of the micro-magnet. To explain these effects, three putative mechanisms that incorporate both physical and biological factors influencing the cells are suggested. It is shown that the static high magnetic field gradient generated by the micro-magnet arrays are capable of assisting cell migration to those areas with the strongest magnetic field gradient, thereby allowing the build up of tunable interconnected stem cell networks, which is an elegant route for tissue engineering and regenerative medicine. PMID:23936425

Zablotskii, Vitalii; Dejneka, Alexandr; Kubinová, Šárka; Le-Roy, Damien; Dumas-Bouchiat, Frédéric; Givord, Dominique; Dempsey, Nora M; Syková, Eva

2013-01-01

109

Magnetization Reversal in Arrays of Perpendicularly Magnetized Ultrathin Dots Coupled by Dipolar Interaction  

Microsoft Academic Search

Arrays of micron size perpendicularly magnetized ultrathin Co dots with 20 nm separation were obtained using ion irradiation by a focused ion beam and studied by polar magneto-optical microscopy. Because irradiation induces easy nucleation regions along dot borders, magnetization reversal inside the dots under a perpendicular field is due only to domain wall propagation, driven by applied field and dipolar

T. Aign; P. Meyer; S. Lemerle; J. P. Jamet; J. Ferré; V. Mathet; C. Chappert; J. Gierak; C. Vieu; F. Rousseaux; H. Launois; H. Bernas

1998-01-01

110

Fabrication of magnetic nanodot arrays using ultrathin alumina membrane (UTAM)  

NASA Astrophysics Data System (ADS)

Fabrication of ultrathin alumina membranes were carried out using two step anodization from high purity aluminum foil. This membrane provides highly ordered nano pores with diameter of 80 nm and intra-pore distance of the order 110 nm. The membrane with thickness < 100 nm was used as a evaporation mask for the growth of magnetic nanodot arrays of Co, SmCo5 and CoPt on Si substrates. The structural investigations were carried out using Field Emission Scanning Electron Microscopy (FESEM). The elemental composition of nanodot arrays was confirmed using Energy Dispersive X-Ray (EDX) analysis. Magnetic characterizations were carried out to study the in-plane and out of-plane hysteresis behaviors and the coercive fields. The present novel two-step anodization approach is simple, efficient, and provides an inexpensive non-lithographic method to produce high density nano-structured materials for wide range of applications in nanotechnology and spintronics.

Chowdhury, P.; Sellarajan, S. Boominatha; Krishnan, M.; Barshilia, H. C.

2012-06-01

111

The Calibration of 3Axis Magnetic Sensor Array System for Tracking Wireless Capsule Endoscope  

Microsoft Academic Search

A magnetic localization and orientation system is proposed for tracking wireless capsule endoscope. This system uses a small magnet enclosed in the capsule to serve as excitation source. When the capsule moves, the magnet establishes a static magnetic field around. With the magnetic sensor array composed of Honeywell 3-axis magnetic sensors, HMC1053, the magnetic intensities in some pre-determined spatial points

Chao Hu; Max Q.-H. Meng; Mrinal Mandal

2006-01-01

112

Domain configuration and magnetization switching in arrays of permalloy nanostripes  

NASA Astrophysics Data System (ADS)

The proximity effect in the collective behavior of arrays of magnetic nanostripes is currently a subject of intensive research. The imperative of reducing the size and distances between elements in order to achieve higher storage capacity, faster access to the information as well as low energy consumption, brings consequences about the isolated behavior of the elements and devices. Parallel to each other permalloy nanostripes with high aspect ratio have been prepared by the nanolithography technique. The evolution of the closure domains and the magnetization direction in individual nanostructures has been imaged under applied magnetic fields using Variable Field Magnetic Force Microscopy. Moreover, the magnetostatic interactions between neighboring elements and the proximity effects in arrays of such nanostructures have been quantitatively analyzed by Magnetic Force Microscopy and micromagnetic simulations. The agreement between simulations and the experimental results allows us to conclude the relevance of those interactions depending on the geometry characteristics. In particular, results suggest that the magnetostatic coupling between adjacent nanostripes vanishes for separation distances higher than 500 nm.

Iglesias-Freire, Ó.; Jaafar, M.; Pérez, L.; de Abril, O.; Vázquez, M.; Asenjo, A.

2014-04-01

113

High sensitive magnetic GMI-based sensing elements array for biosensor protoptype  

Microsoft Academic Search

Magneto-impedance (MI) response in single glass-coated amorphous microwire and, respectively glass-coated amorphous microwires array in the presence of Fe-based magnetic liquid was studied. Major differences of the magneto-impedance response are obtained when microwires array is used. Magneto-impedance was strongly influenced by magnetic liquid covering only about 8% of array.

H. Chiriac; D. D. Herea; S. Corodeanu

2006-01-01

114

Magnetization reversal induced by irregular shape nanodots in square arrays  

NASA Astrophysics Data System (ADS)

Ni 80Fe 20 nanodots in square arrays of irregular shape (C 1h(m) and x-, y-translations symmetry) and circular shape (D 4h (4/mmm)) nanodots of the same area were fabricated under controlled exposure conditions by e-beam lithography, ion beam sputtering coating and further lift-off. The center-to-center nearest dot distances was 700 nm in all the measured arrays. An unpatterned film was fabricated in the same IBS batch for comparison purposes. Structures and magnetic properties were characterized using AFM, SEM and high-sensitivity focused magneto-optical Kerr effect (MOKE). The mechanism of the magnetization reversal of arrays is discussed in two different scenarios: vortex and single-domain. It has been shown that circular dots reverse only through vortex configuration whereas the irregular does either via single-domain and vortex configuration, depending of the dot size. Variable domain phases are confirmed by OOMMF (Object Oriented Micromagnetic Framework) micromagnetic simulations.

Redondo, C.; Sierra, B.; Moralejo, S.; Castano, F.

2010-07-01

115

MAGNET: MicroArray Gene expression and Network Evaluation Toolkit.  

PubMed

MicroArray Gene expression and Network Evaluation Toolkit (MAGNET) is a web-based application that provides tools to generate and score both protein-protein interaction networks and coexpression networks. MAGNET integrates user-provided experimental measurements with high-throughput proteomic datasets, generating weighted gene-gene and protein-protein interaction networks. MAGNET allows users to weight edges of protein-protein interaction networks using a logistic regression model integrating tissue-specific gene expression data, sub-cellular localization data, co-clustering of interacting proteins and the number of observations of the interaction. This provides a way to quantitatively measure the plausibility of interactions in protein-protein interaction networks given protein/gene expression measurements. Secondly, MAGNET generates filtered coexpression networks, where genes are represented as nodes, and their correlations are represented with edges. Overall, MAGNET provides researchers with a new framework with which to analyze and generate gene-gene and protein-protein interaction networks, based on both the user's own data and publicly available -omics datasets. The freely available service and documentation can be accessed at http://gurkan.case.edu/software or http://magnet.case.edu. PMID:22669910

Linderman, George C; Chance, Mark R; Bebek, Gurkan

2012-07-01

116

Magnetocaloric effect: permanent magnet array for generation of high magnetic fields  

NASA Astrophysics Data System (ADS)

The magnetocaloric effect (MCE), the heating or cooling of magnetic materials in a magnetic field, is unusually large in the Gd_5(Si_xGe_1-x)4 alloy system. Normally the maximum in the MCE occurs at the Curie temperature (Tc) because the spin entropy change is a maximum. By suitable selection of the composition of this alloy system the Curie temperature can be changed over the range 25 K for x = 0 to 340 K for x =1, and the composition range around x = 0.5 exhibits the largest magnetocaloric effect. In order to increase the amount of heat exchanged the change in applied magnetic field should be as large as possible, and in this research values above 1.5 Tesla are suggested. We have studied a permanent magnet array based on NdFeB, which with a remanent magnetization of only 1.2 Tesla can still generate a magnetic flux density, or magnetic induction B of 2-3 Tesla. In order to generate the high magnetic induction in the absence of a power supply, a modified hollow cylindrical permanent magnet array (HCPMA) has been designed to produce the required strength of magnetic field. Soft magnetic materials including permalloy (NiFe) were used for focusing the magnetic field in the central region. The magnitude of the magnetic flux density at the center was about 2 Tesla. The magnitude and homogeneity of the magnetic field for this design are comparable with the conventional C-shaped yoke and HCPMA. This can be easily adapted for a low power rotary system in which the magnetocaloric material can be exposed alternately to high and low magnetic fields so that it can accept and reject heat from its surroundings.

Lee, Seong-Jae; Kenkel, John; Jiles, David

2002-03-01

117

Magnetization reversal in arrays of Co-rings.  

SciTech Connect

The magnetization behavior of arrays of individual and coupled Co rings has been studied using superconducting quantum interference device magnetometry, magneto-optical imaging, and Lorentz transmission and scanning transmission electron microscopy. The transition from the polarized into the vortex state of isolated rings is shown to occur through the motion and annihilation of head-to-head domain boundaries. The chirality of the vortex state is fixed on subsequent magnetization cycles, indicating that it is predetermined by structural imperfections of the rings. The effect of interactions between the rings has been investigated in arrays of chains of touching rings. For fields applied parallel to the chains rings in extended sections of the chains are found to switch simultaneously. Neighboring rings in these sections can display alternating chirality as well as the same chirality accompanied by a 180{sup o} boundary on the nodes. For fields perpendicular to the chain direction the switching occurs pairwise. This coupling introduces a broad distribution of switching fields and correspondingly a magnetization curve that is significantly broader than that for the parallel orientation.

Welp, U.; Vlasko-Vlasov, V. K.; Hiller, J. M.; Zaluzec, N. J.; Metlushko, V.; Ilic, B.; Materials Science Division; Univ. of Illinois at Chicago; Cornell Univ.

2003-08-01

118

Development of a magnetic nanoparticle susceptibility magnitude imaging array.  

PubMed

There are several emerging diagnostic and therapeutic applications of magnetic nanoparticles (mNPs) in medicine. This study examines the potential for developing an mNP imager that meets these emerging clinical needs with a low cost imaging solution that uses arrays of digitally controlled drive coils in a multiple-frequency, continuous-wave operating mode and compensated fluxgate magnetometers. The design approach is described and a mathematical model is developed to support measurement and imaging. A prototype is used to demonstrate active compensation of up to 185 times the primary applied magnetic field, depth sensitivity up to 2.5 cm (p < 0.01), and linearity over five dilutions (R(2) > 0.98, p < 0.001). System frequency responses show distinguishable readouts for iron oxide mNPs with single magnetic domain core diameters of 10 and 40 nm, and multi-domain mNPs with a hydrodynamic diameter of 100 nm. Tomographic images show a contrast-to-noise ratio of 23 for 0.5 ml of 12.5 mg Fe ml(-1) mNPs at 1 cm depth. A demonstration involving the injection of mNPs into pork sausage shows the potential for use in biological systems. These results indicate that the proposed mNP imaging approach can potentially be extended to a larger array system with higher-resolution. PMID:24504184

Ficko, Bradley W; Nadar, Priyanka M; Hoopes, P Jack; Diamond, Solomon G

2014-02-21

119

Probing arrays of circular magnetic microdots by ferromagnetic resonance.  

SciTech Connect

X-band ferromagnetic resonance (FMR) was used to characterize in-plane magnetic anisotropies in rectangular and square arrays of circular nickel and Permalloy microdots. In the case of a rectangular lattice, as interdot distances in one direction decrease, the in-plane uniaxial anisotropy field increases, in good agreement with a simple theory of magnetostatically interacting uniformly magnetized dots. In the case of a square lattice a four-fold anisotropy of the in-plane FMR field H(r) was found when the interdot distance a gets comparable to the dot diameter D. This anisotropy, not expected in the case of uniformly magnetized dots, was explained by a non-uniform magnetization m(r) in a dot in response to dipolar forces in the patterned magnetic structure. It is well described by an iterative solution of a continuous variation procedure. In the case of perpendicular magnetization multiple sharp resonance peaks were observed below the main FMR peak in all the samples, and the relative positions of these peaks were independent of the interdot separations. Quantitative description of the observed multiresonance FMR spectra was given using the dipole-exchange spin wave dispersion equation for a perpendicularly magnetized film where in-plane wave vector is quantized due to the finite dot radius, and the inhomogenetiy of the intradot static demagnetization field in the nonellipsoidal dot is taken into account. It was demonstrated that ferromagnetic resonance force microscopy (FMRFM) can be used to determine both local and global properties of patterned submicron ferromagnetic samples. Local spectroscopy together with the possibility to vary the tip-sample spacing enables the separation of those two contributions to a FMRFM spectrum. The global FMR properties of circular submicron dots determined using magnetic resonance force microscopy are in a good agreement with results obtained using conventional FMR and with theoretical descriptions.

Kakazei, G. N.; Mewes, T.; Wigen, P. E.; Hammel, P. C.; Slavin, A. N.; Pogorelov, Y. G.; Costa, M. D.; Golub, V. O.; Guslienko, K. Y.; Novosad, V. (Materials Science Division); (Univ. of Porto); (National Academy of Sciences Ukraine); (Univ. of Alabama); (Ohio State Univ.); (Oakland Univ.)

2008-06-01

120

A superconducting quadrupole magnet array for a heavy ion fusion driver  

SciTech Connect

A multi-channel quadrupole array has been proposed to increase beam intensity and reduce space charge effects in a Heavy Ion Fusion Driver. A single array unit composed of several quadrupole magnets, each with its own beam line, will be placed within a ferromagnetic accelerating core whose cost is directly affected by the array size. A large number of focusing arrays will be needed along the accelerating path. The use of a superconducting quadrupole magnet array will increase the field and reduce overall cost. We report here on the design of a compact 3 x 3 superconducting quadrupole magnet array. The overall array diameter and length including the cryostat is 900 x 700 mm. Each of the 9 quadrupole magnets has a 78 mm warm bore and an operating gradient of 50 T/m over an effective magnetic length of 320 mm.

Caspi, S.; Bangerter, r.; Chow, K.; Faltens, A.; Gourley, S.; Hinkins, R.; Gupta, R.; Lee, E.; McInturff, A.; Scanlan, R.; Taylor, C.; Wolgast, D.

2000-06-27

121

Magnetic properties in epitaxial L10 FePt dot arrays  

Microsoft Academic Search

The dot arrays of epitaxially grown FePt ordered alloy were prepared by using a microfabrication process. The magnetic properties for the arrays of dots with different sizes and directions of the easy magnetization axis have been investigated. Furthermore, the effect of annealing on the magnetic properties has been also investigated.

T. Seki; T. Shima; K. Yakushiji; K. Takanashi; G. Q. Li; S. Ishio

2005-01-01

122

Preparation and magnetic properties of hard-magnetic (CoPt)/soft-magnetic (FeCo) composite nanocable array  

NASA Astrophysics Data System (ADS)

An array of hard-magnetic (CoPt)/soft-magnetic (FeCo) composite nanocable has been fabricated in the pores of porous anodic aluminum oxide templates: CoPt nanotubes were first prepared by high temperature chemical reduction method; FeCo alloy was then electrodeposited into the CoPt nanotubes. The morphology and structure of the nanocable array were characterized by scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. The magnetic measurements showed that two apparent kinks appear in the hysteresis loop after the FeCo alloy was deposited into the CoPt nanotubes, which may be attributed to the hard-magnetic phase being partly or even completely decoupled from the soft-magnetic phase.

Zhou, D.; Zhu, M. G.; Zhou, M. G.; Guo, Z. H.; Li, W.

2011-04-01

123

Position Sensing System for Magnet Based Autonomous Vehicle and Robot Using 1Dimensional Magnetic Field Sensor Array  

Microsoft Academic Search

In this paper, a position sensing system for magnet based autonomous vehicle and robot using 1-diemnsional magnetic field sensor array was described. In advanced vehicle and robot control, position sensing is an important task for the identification of their locations, such as the lateral position within a trajectory. The magnet based autonomous vehicle and robot was identified position using magnetic

Young-Yoon Jung; Dae-Young Lim; Young-Jae Ryoo; Young-Hak Chang; Jin Lee

2006-01-01

124

Conditions for the Spin Wave Nonreciprocity in an Array of Dipolarly Coupled Magnetic Nanopillars.  

National Technical Information Service (NTIS)

It is demonstrated that collective spin waves (SWs) propagating in complex periodic arrays of dipolarly coupled magnetic nanopillars existing in a saturated (single-domain) ground state in a zero bias magnetic field could be nonreciprocal. To guarantee th...

E. Bankowski, G. Melkov, R. Verba, T. Meitzler, V. Tiberkevich

2013-01-01

125

Magnetic wire trap arrays for biomarker-based molecular detection  

NASA Astrophysics Data System (ADS)

Submicrometer-scale magnetic devices built on chip-based platforms have recently been shown to present opportunities for new particle trapping and manipulation technologies. Meanwhile, advances in nanoparticle fabrication allow for the building of custom-made particles with precise control of their size, composition, and other properties such as magnetism, fluorescence, and surface biomarker characteristics. In particular, carefully tailored surface biomarkers facilitate precise binding to targeted molecules, self-actuated construction of hybrid structures, and fluorescence-based detection schemes. Based on these progresses, we present an on-chip detection mechanism for molecules with known surface markers. Hybrid nanostructures consisting of micelle nanoparticles, fluorescent quantum dots, and superparamagnetic iron oxide nanoparticles are used to detect proteins or DNA molecules. The target is detected by the magnetic and fluorescent functionalities of the composite nanostructure, whereas in the absence of the target these signals are not present. Underlying this approach is the simultaneous manipulation via ferromagnetic zigzag nanowire arrays and imaging via quantum dot excitation. This chip-based detection technique could provide a powerful, low cost tool for ultrasensitive molecule detection with ramifications in healthcare diagnostics and small-scale chemical synthesis.

Vieira, Gregory; Mahajan, Kalpesh; Ruan, Gang; Winter, Jessica; Sooryakumar, R.

2012-02-01

126

A Mobile Ferromagnetic Shape Detection Sensor Using a Hall Sensor Array and Magnetic Imaging  

PubMed Central

This paper presents a Mobile Hall Sensor Array system for the shape detection of ferromagnetic materials that are embedded in walls or floors. The operation of the Mobile Hall Sensor Array system is based on the principle of magnetic flux leakage to describe the shape of the ferromagnetic material. Two permanent magnets are used to generate the magnetic flux flow. The distribution of magnetic flux is perturbed as the ferromagnetic material is brought near the permanent magnets and the changes in magnetic flux distribution are detected by the 1-D array of the Hall sensor array setup. The process for magnetic imaging of the magnetic flux distribution is done by a signal processing unit before it displays the real time images using a netbook. A signal processing application software is developed for the 1-D Hall sensor array signal acquisition and processing to construct a 2-D array matrix. The processed 1-D Hall sensor array signals are later used to construct the magnetic image of ferromagnetic material based on the voltage signal and the magnetic flux distribution. The experimental results illustrate how the shape of specimens such as square, round and triangle shapes is determined through magnetic images based on the voltage signal and magnetic flux distribution of the specimen. In addition, the magnetic images of actual ferromagnetic objects are also illustrated to prove the functionality of Mobile Hall Sensor Array system for actual shape detection. The results prove that the Mobile Hall Sensor Array system is able to perform magnetic imaging in identifying various ferromagnetic materials.

Misron, Norhisam; Shin, Ng Wei; Shafie, Suhaidi; Marhaban, Mohd Hamiruce; Mailah, Nashiren Farzilah

2011-01-01

127

A mobile ferromagnetic shape detection sensor using a Hall sensor array and magnetic imaging.  

PubMed

This paper presents a mobile Hall sensor array system for the shape detection of ferromagnetic materials that are embedded in walls or floors. The operation of the mobile Hall sensor array system is based on the principle of magnetic flux leakage to describe the shape of the ferromagnetic material. Two permanent magnets are used to generate the magnetic flux flow. The distribution of magnetic flux is perturbed as the ferromagnetic material is brought near the permanent magnets and the changes in magnetic flux distribution are detected by the 1-D array of the Hall sensor array setup. The process for magnetic imaging of the magnetic flux distribution is done by a signal processing unit before it displays the real time images using a netbook. A signal processing application software is developed for the 1-D Hall sensor array signal acquisition and processing to construct a 2-D array matrix. The processed 1-D Hall sensor array signals are later used to construct the magnetic image of ferromagnetic material based on the voltage signal and the magnetic flux distribution. The experimental results illustrate how the shape of specimens such as square, round and triangle shapes is determined through magnetic images based on the voltage signal and magnetic flux distribution of the specimen. In addition, the magnetic images of actual ferromagnetic objects are also illustrated to prove the functionality of mobile Hall sensor array system for actual shape detection. The results prove that the mobile Hall sensor array system is able to perform magnetic imaging in identifying various ferromagnetic materials. PMID:22346653

Misron, Norhisam; Shin, Ng Wei; Shafie, Suhaidi; Marhaban, Mohd Hamiruce; Mailah, Nashiren Farzilah

2011-01-01

128

Microwave studies of magnetic anisotropy of Co nanowire arrays  

NASA Astrophysics Data System (ADS)

The effect of magnetocrystalline anisotropy and dipolar interactions in Co nanowire arrays is studied by ferromagnetic resonance (FMR). Microwave measurements performed by the microstripline method are reported for two series of crystalline hcp Co (with the c axis nominally perpendicular [Co(c?)] and parallel to the wires [Co(c?)]) and an amorphous alloy with Co as the main component-Co94Fe5B1. Extrapolation of the high field linear part of the resonance curve (frequency versus dc field) permitted an evaluation of the effective anisotropy fields for saturated samples, as well as of the intrinsic fields HK, showing that the great differences between the three series are due to the magnetocrystalline anisotropy. The HK values for the two series of Co are discussed in terms of a model which accounts for the effect of the distributions of the c axis orientation in systems of uniaxial ferromagnets. The observed dependence of the effective anisotropy fields on the array geometry (wire length and diameter) is interpreted in terms of the interwire dipolar interactions and found to be in agreement with theoretical predictions based on a micromagnetic model. The fact that the resonance frequencies at Hdc=0 are geometry dependent shows that magnetostatic interactions are still significant at remanence. A second series of FMR experiments was performed at constant frequency (38 GHz), with the purpose of obtaining the angle dependence of the resonance field. These experiments provided an alternative method for the evaluation of the effective anisotropy field. The angle dependence of the resonance field for Co(c?) fitted the simplest equation for magnets with uniaxial anisotropy, obtained considering only the first order term in the expression of the magnetocrystalline energy as a function of the magnetization orientation. The same is not true for Co(c?), which required inclusion of a second order term.

Sklyuyev, A.; Ciureanu, M.; Akyel, C.; Ciureanu, P.; Yelon, A.

2009-01-01

129

Magnetic dipolar interaction in NiFe nanodot arrays formed on vertical carbon nanotubes  

Microsoft Academic Search

A new and simple method for the fabrication of densely packed magnetic nanodot arrays was developed using conventional sputtering deposition at room temperature. An anodized alumina template was employed for the formation of nanodot assemblies, consisting of carbon nanotubes (CNTs) and magnetic nanodot arrays. Each nanodot was formed exactly on top of a CNT and was arranged with a well-ordered

Chunghee Nam; Youn-Su Kim; W. B. Kim; B. K. Cho

2008-01-01

130

Yield improvement of a large area magnetic field sensor array using redundancy schemes  

Microsoft Academic Search

The circuit design of a large area magnetic field sensor array (LAMSA) is described. This prototype is developed for applications in magnetic field mapping and tactile sensor arrays. To enable the production of such a large sensor system, redundancy schemes are implemented and a laser interconnection post fabrication technique is used for fault repairs. The design restructurable capabilities rely on

Yves Audet; Glenn H. Chapman

1997-01-01

131

Correlation of experimental data and three-dimensional finite element modeling of a spinning magnet array  

Microsoft Academic Search

A magnet array was spun above an aluminum disk, and the drag torque was measured for various speeds and gap sizes. Drag torques calculated using a three-dimensional finite element program were consistent with measured values. The finite element model was also used to determine the effects of the polarity and position of magnets in the source array. The peak torque

W. L. Lorimer; D. K. Lieu; J. R. Hull; T. M. Mulcahy; T. D. Rossing

1994-01-01

132

Dipolar interactions in two- and three-dimensional magnetic nanoparticle arrays  

Microsoft Academic Search

Uniform, organically functionalized, 8.5-nm-diameter nanocrystals of Fe3O4 were synthesized and assembled into close-packed monolayer as well as multilayer arrays using the Langmuir-Blodgett technique. The ac and dc magnetic susceptibility measurements on arrays in comparison with isolated particles indicate strong dipolar interactions and a spin-glass-like slowing down of relaxation times. Differences in magnetic characteristics between monolayer to multilayer arrays were observed,

Pankaj Poddar; Tamar Telem-Shafir; Tcipi Fried; Gil Markovich

2002-01-01

133

Self-organized magnetic nanowire arrays based on alumina and titania templates.  

PubMed

Densely packed arrays of magnetic nanowires have been synthesized by electrodeposition filling of nanopores in alumina and titania membranes formed by self-assembling during anodization process. Emphasis is made on the control of the production parameters leading to ordering degree and lattice parameter of the array as well as nanowires diameter and length. Structural, morphological and magnetic properties exhibited by nanowire arrays have been studied for several nanowire compositions, different ordering degree and for different nanowire aspect ratios. The magnetic behaviour of nanowires array is governed by the balance between different energy contributions: shape anisotropy of individual nanowires, the magnetostatic interaction of dipolar origin among nanowires, and magnetocrystalline and magnetoelastic anisotropies induced by the pattern templates. These novel nanocomposites, based on ferromagnetic nanowires embedded in anodic nanoporous templates, are becoming promising candidates for technological applications such as functionalised arrays for magnetic sensing, ultrahigh density magnetic storage media or spin-based electronic devices. PMID:17455492

Prida, V M; Pirota, K R; Navas, D; Asenjo, A; Hernández-Vélez, M; Vázquez, M

2007-01-01

134

Enhanced magnetism in highly ordered magnetite nanoparticle-filled nanohole arrays.  

PubMed

A new approach to develop highly ordered magnetite (Fe3 O4 ) nanoparticle-patterned nanohole arrays with desirable magnetic properties for a variety of technological applications is presented. In this work, the sub-100 nm nanohole arrays are successfully fabricated from a pre-ceramic polymer mold using spin-on nanoprinting (SNAP). These nanoholes a then filled with monodispersed, spherical Fe3 O4 nanoparticles of about 10 nm diameter using a novel magnetic drag and drop procedure. The nanohole arrays filled with magnetic nanoparticles a imaged using magnetic force microscopy (MFM). Magnetometry and MFM measurements reveal room temperature ferromagnetism in the Fe3 O4 -filled nanohole arrays, while the as-synthesized Fe3 O4 nanoparticles exhibit superparamagnetic behavior. As revealed by MFM measurements, the enhanced magnetism in the Fe3 O4 -filled nanohole arrays originates mainly from the enhanced magnetic dipole interactions of Fe3 O4 nanoparticles within the nanoholes and between adjacent nanoholes. Nanoparticle filled nanohole arrays can be highly beneficial in magnetic data storage and other applications such as microwave devices and biosensor arrays that require tunable and anisotropic magnetic properties. PMID:24706405

Duong, Binh; Khurshid, Hafsa; Gangopadhyay, Palash; Devkota, Jagannath; Stojak, Kristen; Srikanth, Hariharan; Tetard, Laurene; Norwood, Robert A; Peyghambarian, N; Phan, Manh-Huong; Thomas, Jayan

2014-07-01

135

Two-dimensional arrays of superconducting strips as dc magnetic metamaterials  

NASA Astrophysics Data System (ADS)

We theoretically investigate the magnetic response of two-dimensional arrays of superconducting strips, which are regarded as essential structures of dc magnetic metamaterials. We analytically obtain local distributions of the magnetic field for the ideal complete shielding state (i.e., ?/w?0, where 2w is the strip width, ?=?2/d is the Pearl length, ? is the London penetration depth, and d is the strip thickness), and derive effective permeability by averaging the local-field distributions. We also perform numerical calculations for a realistic case, taking finite ?/w>0 into account. We investigate two types of strip arrays: a rectangular array and a hexagonal array. The resulting effective permeability has large anisotropy that depends on the dimensions and arrangement of the superconducting strips, and the hexagonal array is found to be more advantageous for obtaining large anisotropy than the rectangular array.

Mawatari, Yasunori; Navau, Carles; Sanchez, Alvaro

2012-04-01

136

CoCrPt antidot arrays with perpendicular magnetic anisotropy made on anodic alumina templates  

SciTech Connect

Ti(5 nm)/CoCrPt(5-20 nm) bilayers with perpendicular magnetic anisotropy were deposited by rf sputtering onto porous alumina films to form antidot arrays with period 105 nm and pore diameters ranging from 18 to 56 nm. The coercivities of the antidot arrays are greater than those of unpatterned films and show only a weak dependence on antidot diameter. Magnetic force microscopy of ac-demagnetized samples shows that the antidot arrays have domain sizes larger than the 105 nm period. The magnetic behavior is discussed in terms of domain wall pinning by the antidots.

Navas, D.; Ilievski, F.; Ross, C. A. [Department of Materials Science and Engineering, MIT, Cambridge, Massachusetts 02139 (United States)

2009-06-01

137

Magnetic Sensor Array Having an Analog Frequency-Division Multiplexed Output.  

National Technical Information Service (NTIS)

A magnetic sensor array including magnetoresistive sensor elements having outputs combined by frequency division multiplexing (FDM) is provided. Each sensor element provides an input to a mixer which provides a distinct frequency shift. Preferably, time d...

S. J. Han S. X. Wang

2005-01-01

138

Ordered arrays of magnetic metal nanotubes and nanowires encapsulated with carbon tubes.  

PubMed

The ordered arrays of magnetic metal (including Fe, Co and Ni) nanotubes and nanowires encapsulated with carbon tubes are controllably synthesized by employing the array of C tubes as second-order template and combining with electrodeposition technique. The wall thickness and diameter of carbon nanotubes are uniform along the whole tubes; also the wall thickness of inner metal nanotubes is adjustable from 25 nm to solid nanowires. These composite structures are characterized by X-ray diffractometer (XRD), energy-dispersive spectrometry (EDS), Raman scattering spectrum, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The magnetic properties show that coaxial nanotubes and nanocables composite arrays all exhibit magnetic anisotropy with the easy direction perpendicular to axis of the metal nanotubes or nanowires except the Ni at C coaxial nanotubes array that has no preferable magnetization axis. PMID:19049046

Gao, Culling; Tao, Feifei; Lin, Weiwei; Xu, Zheng; Xue, Ziling

2008-09-01

139

Optimization of sensor arrays for magnetic marker monitoring in the human intestine  

Microsoft Academic Search

The purpose of this study was the development of an optimized sensor array for Magnetic Marker Monitoring (MMM) with anisotropic magnetoresistive sensors (AMR). For different types of sensor spaces an optimized sensor configuration was calculated using a Particle Swarm Optimizer algorithm. It could be shown that a sensor array around the body with optimized number and positions of sensors will

S. Biller; S. Lau; D. Baumgarten; L. Di Rienzo; J. Haueisen

140

Spatial Harmonic Expansion for Use With Magnetic Sensor Arrays  

Microsoft Academic Search

In order to reduce the effects of external magnetic fields on the accuracy of magnetic sensor measurements used for the reconstruction of ac electric currents flowing in massive parallel conductors, we use a spatial circular harmonic expansion of the magnetic scalar potential. Thanks to the linearity of the magnetic field problem with respect to the sources, we can then apply

L. Di Rienzo; Z. Zhang

2010-01-01

141

Measurements of the Azimuthal Magnetic Field within Imploding Multiwire Arrays in the Angara-5-1 Facility  

SciTech Connect

Results are presented from measurements of the azimuthal magnetic fields within imploding multiwire tungsten arrays in the Angara-5-1 facility at currents of 2.5-4 MA. It is shown that the penetration of the magnetic field into the axial region of the wire array lags behind the discharge current pulse. The current of a precursor produced at the array axis prior to the implosion of the bulk array mass is measured. It is found that the magnetic field in the initial stage of implosion is azimuthally nonuniform. The mass distribution inside the array is calculated from the measured magnetic field.

Zukakishvili, G.G.; Mitrofanov, K.N.; Aleksandrov, V.V.; Grabovskii, E.V.; Oleinik, G.M.; Porofeev, I.Yu.; Frolov, I.N. [Troitsk Institute for Innovation and Fusion Research, Troitsk, Moscow oblast, 142190 (Russian Federation); Sasorov, P.V. [Institute of Theoretical and Experimental Physics, Bol'shaya Cheremushkinskaya ul. 25, Moscow, 117218 (Russian Federation)

2005-11-15

142

Oscillating magnet array-based nanomagnetic gene transfection of human mesenchymal stem cells.  

PubMed

Aim: In this work, the potential of nanomagnetic transfection of primary human mesenchymal stem cells (hMSCs) and the effects of a novel nonviral oscillating magnet array system in enhancing transfection efficiency were investigated. Materials & methods: Green fluorescent protein plasmids coupled to magnetic nanoparticles (MNPs) were introduced onto hMSCs in culture. Magnetic fields generated by arrays of neodymium iron boron magnets positioned below the culture plates direct the MNP/DNA complexes into contact with the cells. The magnet arrays were oscillated, promoting more efficient endocytosis via mechanical stimulation. Green fluorescent protein expression, cell viability and stem cell surface markers were assayed. Results: MNP/DNA complexes were delivered into hMSCs, and the oscillating magnet array system appears to improve transfection efficiency as well as cell viability. The expression of hMSC-specific cell surface markers was unaffected. Conclusion: Nonviral transfection using MNPs and oscillating magnet arrays offers a more efficient and 'cell-friendly' method of transfecting hMSCs than other nonviral techniques, while preserving their stem cell characteristics. Original submitted 8 March 2012; Revised submitted 12 February 2013. PMID:23901783

Fouriki, Angeliki; Dobson, Jon

2014-05-01

143

Magnetic irreversibility of the Fe antidot arrays film by depositing on the porous alumina templates  

NASA Astrophysics Data System (ADS)

An Fe layer was sputter-deposited onto porous alumina templates and Kapton respectively. Fe layer on the porous alumina templates formed an antidot arrays nanostructure, while Fe layer on the Kapton substrate formed a continuous film. Scanning electron microscopy and grazing incidence X-ray diffraction were employed to characterize the morphology and crystal structure of the Fe antidot arrays and continuous film, respectively. The temperature dependence of magnetic properties was shown in the temperature range 2-300 K. The irreversibility of the magnetization of Fe antidot arrays film, as measured in zero-field cooling (ZFC) and field cooling (FC) states, was attributed to the pinning effect of the holes.

Jiang, Changjun; Wei, Wenwen; Liu, Qingfang; Guo, Dangwei; Xue, Desheng

2012-02-01

144

From collective behavior to computing in magnetic nanostructure arrays: Theory, modeling, and technology assessment  

NASA Astrophysics Data System (ADS)

Silicon microelectronics is arguably the most successful technological revolution ever seen. The number of transistors on a chip has increased by nine orders of magnitude over the past 45 years. However, growing technical and economic challenges have led to diminishing returns, and continued miniaturization may not be feasible beyond the next ten years. Thus, we need alternatives for the next generation of information technologies. In this work, we model the collective dynamics of nanoscale magnetic wire and disk arrays, to evaluate their potential circuit applications. We developed models based on structures grown in our laboratories using new non-lithographic methods. We describe the behavior of a new type of magnetic nanowire array, using a Monte-Carlo method to study the time evolution of these systems. We use a new mean field model to study the collective array properties and their hysteresis loops. We estimate nanowire inversion times using the Landau-Lifschitz-Gilbert (LLG) micromagnetic equations. We model the behavior of magnetic nanodisk arrays using a Monte-Carlo method based on the LLG equations, and expand this method to three dimensions to study the behavior of nanoscale magnetic logic devices. The results demonstrate that nanomagnet arrays can perform general purpose digital computation using prepared initial states and adiabatic clocking. These devices operate slowly, with extremely low power dissipation. Finally, we discuss the analogies between interacting nanostructure arrays and collective computation models in order to assess the potential applications of these arrays in information technology.

Bennett, Andrew John

145

Calibration of a fluxgate magnetometer array and its application in magnetic object localization  

NASA Astrophysics Data System (ADS)

The magnetometer array is effective for magnetic object detection and localization. Calibration is important to improve the accuracy of the magnetometer array. A magnetic sensor array built with four three-axis DM-050 fluxgate magnetometers is designed, which is connected by a cross aluminum frame. In order to improve the accuracy of the magnetometer array, a calibration process is presented. The calibration process includes magnetometer calibration, coordinate transformation and misalignment calibration. The calibration system consists of a magnetic sensor array, a GSM-19T proton magnetometer, a two-dimensional nonmagnetic rotation platform, a 12 V-dc portable power device and two portable computers. After magnetometer calibration, the RMS error has been decreased from an original value of 125.559 nT to a final value of 1.711 nT (a factor of 74). After alignment, the RMS error of misalignment has been decreased from 1322.3 to 6.0 nT (a factor of 220). Then, the calibrated array deployed on the nonmagnetic rotation platform is used for ferromagnetic object localization. Experimental results show that the estimated errors of X, Y and Z axes are -0.049 m, 0.008 m and 0.025 m, respectively. Thus, the magnetometer array is effective for magnetic object detection and localization in three dimensions.

Pang, Hongfeng; Luo, Shitu; Zhang, Qi; Li, Ji; Chen, Dixiang; Pan, Mengchun; Luo, Feilu

2013-07-01

146

Magnetic properties of arrays of superconducting strips in a perpendicular field  

Microsoft Academic Search

Current profiles and field lines and magnetization and ac losses are calculated for arrays of infinitely long superconducting strips in the critical state in a perpendicularly applied magnetic field. The strips are arranged vertically, horizontally, and in a matrix configuration, which are the geometries found in many actual high-Tc superconducting tapes. The finite thickness of the strips and the effects

Enric Pardo; Alvaro Sanchez; Carles Navau

2003-01-01

147

Yield improvement of a large area magnetic field sensor array design using redundancy schemes  

Microsoft Academic Search

Design of a Large Area Magnetic Field Sensor Array (LAMSA) using redundancy schemes concurrently with the laser link technology for fault repairs is presented. Experimental results obtained on a laser restructurable subarray of three magnetic field sensor cells are shown. An experimental yield measurement method to determine parameters of two yield detractors is described. These parameters obtained from regular sized

Y. Audet; Glenn H. Chapman

1995-01-01

148

Processing magnetic sensor array data for AC current measurement in multiconductor systems  

Microsoft Academic Search

The continuous progress in magnetic sensor research provides increasing accuracy in measurement systems based on magnetic sensor arrays. Many industrial applications in the field of protection for low-voltage electrical systems require novel technologies of AC current sensors characterized by lower costs and wider measuring range in amplitude and frequency. For this purpose, a promising solution is the utilization of sensor

G. D'Antona; L. Di Rienzo; R. Ottoboni; A. Manara

2001-01-01

149

Ordered arrays of magnetic nanowires investigated by polarized small-angle neutron scattering  

NASA Astrophysics Data System (ADS)

Polarized small-angle neutron scattering (PSANS) experimental results obtained on arrays of ferromagnetic Co nanowires (? ?13 nm) embedded in self-organized alumina (Al2O3) porous matrices are reported. The triangular array of aligned nanowires is investigated as a function of the external magnetic field with a view to determine experimentally the real space magnetization M?(r?) distribution inside the material during the magnetic hysteresis cycle. The observation of field-dependent SANS intensities allows us to characterize the influence of magnetostatic fields. The PSANS experimental data are compared to magnetostatic simulations. These results evidence that PSANS is a technique able to address real-space magnetization distributions in nanostructured magnetic systems. We show that beyond structural information (shape of the objects, two-dimensional organization) already accessible with nonpolarized SANS, using polarized neutrons as the incident beam provides information on the magnetic form factor and stray fields ?0Hd distribution in between nanowires.

Maurer, Thomas; Gautrot, Sébastien; Ott, Frédéric; Chaboussant, Grégory; Zighem, Fatih; Cagnon, Laurent; Fruchart, Olivier

2014-05-01

150

A decoupled control approach for magnetic suspension systems using electromagnets mounted in a planar array  

NASA Technical Reports Server (NTRS)

A decoupled control approach for a Large Gap Magnetic Suspension System (LGMSS) is presented. The control approach is developed for an LGMSS which provides five degree-of-freedom control of a cylindrical suspended element that contains a core composed of permanent magnet material. The suspended element is levitated above five electromagnets mounted in a planar array. Numerical results are obtained by using the parameters of the Large Angle Magnetic Suspension Test Fixture (LAMSTF) which is a small scale laboratory model LGMSS.

Groom, Nelson J.

1993-01-01

151

Nonlithographic fabrication of 25 nm magnetic nanodot arrays with perpendicular anisotropy over a large area  

NASA Astrophysics Data System (ADS)

A simple method is demonstrated to fabricate 25 nm magnetic nanodot arrays with perpendicular anisotropy over 10 cm2 coverage area. The nanodot arrays are fabricated by depositing Co/Pt multilayers (MLs) onto the SiO2 dot arrays formed on a Si wafer. At first, arrays of the SiO2 dots are fabricated on a Si wafer by anodizing a thin Al film deposited on it. The SiO2 dots are formed at the base of the anodized alumina (AAO) pores due to the selective oxidation of the Si through the AAO pores during over anodization of the Al film. The average diameter, periodicity, and height of the SiO2 dots are about 24, 43, and 17 nm, respectively. Then {Co(0.4 nm)/Pt(0.08 nm)}8 MLs with a 3 nm Pt buffer layer is deposited onto the SiO2 dot arrays by sputtering. The average diameter and periodicity of the Co/Pt nanodot arrays are 25.4 and 43 nm, respectively, with narrow distribution. The nanodot arrays exhibit strong perpendicular anisotropy with a squareness ratio of unity and negative nucleation fields. The coercivity of the nanodot arrays is about one order higher than that of the continuous film, i.e., the same structure deposited on the SiO2 substrate. The magnetization reversal of the continuous film is governed by domain-wall motion, while the magnetization reversal of the nanodot arrays is dominated by the Stoner-Wohlfarth-like rotation. These results indicate that the fabricated structure can be considered as an isolated nanodot array.

Rahman, M. Tofizur; Shams, Nazmun N.; Lai, Chih-Huang

2009-04-01

152

Nonlithographic fabrication of 25 nm magnetic nanodot arrays with perpendicular anisotropy over a large area  

SciTech Connect

A simple method is demonstrated to fabricate 25 nm magnetic nanodot arrays with perpendicular anisotropy over 10 cm{sup 2} coverage area. The nanodot arrays are fabricated by depositing Co/Pt multilayers (MLs) onto the SiO{sub 2} dot arrays formed on a Si wafer. At first, arrays of the SiO{sub 2} dots are fabricated on a Si wafer by anodizing a thin Al film deposited on it. The SiO{sub 2} dots are formed at the base of the anodized alumina (AAO) pores due to the selective oxidation of the Si through the AAO pores during over anodization of the Al film. The average diameter, periodicity, and height of the SiO{sub 2} dots are about 24, 43, and 17 nm, respectively. Then (Co(0.4 nm)/Pt(0.08 nm)){sub 8} MLs with a 3 nm Pt buffer layer is deposited onto the SiO{sub 2} dot arrays by sputtering. The average diameter and periodicity of the Co/Pt nanodot arrays are 25.4 and 43 nm, respectively, with narrow distribution. The nanodot arrays exhibit strong perpendicular anisotropy with a squareness ratio of unity and negative nucleation fields. The coercivity of the nanodot arrays is about one order higher than that of the continuous film, i.e., the same structure deposited on the SiO{sub 2} substrate. The magnetization reversal of the continuous film is governed by domain-wall motion, while the magnetization reversal of the nanodot arrays is dominated by the Stoner-Wohlfarth-like rotation. These results indicate that the fabricated structure can be considered as an isolated nanodot array.

Rahman, M. Tofizur; Shams, Nazmun N.; Lai, C.-H. [Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan (China)

2009-04-01

153

Periodic array of Bose-Einstein condensates in a magnetic lattice  

NASA Astrophysics Data System (ADS)

We report the realization of a periodic array of Bose-Einstein condensates (BECs) of Rb87 F =1 atoms trapped in a one-dimensional magnetic lattice close to the surface of an atom chip. A clear signature for the onset of BEC in the magnetic lattice is provided by in situ site-resolved radio-frequency spectra, which exhibit a pronounced bimodal distribution consisting of a narrow component characteristic of a BEC together with a broad thermal cloud component. Similar bimodal distributions are found for various sites across the magnetic lattice. The realization of a periodic array of BECs in a magnetic lattice represents a major step towards the implementation of magnetic lattices for quantum simulation of many-body condensed matter phenomena in lattices of complex geometry and arbitrary period.

Jose, S.; Surendran, P.; Wang, Y.; Herrera, I.; Krzemien, L.; Whitlock, S.; McLean, R.; Sidorov, A.; Hannaford, P.

2014-05-01

154

The role of magnetic field in the transition to streaming ablation in wire arrays  

SciTech Connect

In wire array Z-pinches, the magnetic field configuration and the global field penetration of individual wires play a key role in the ablation plasma dynamics. Knowledge of the magnetic field configuration is necessary to understand the ablation plasma acceleration process near the wires. Two-dimensional resistive magnetohydrodynamics simulations show that a change in the global magnetic field configuration is critical to initiating inward flow of the ablation plasma. Analysis of these simulations show that the initially compressive JxB force around a wire in its vacuum field configuration undergoes a transition to a configuration in which the Lorentz force can accelerate plasma toward the array axis. This transition is achieved through a low magnetic Reynolds number diffusive flow in which the plasma and the magnetic field are decoupled. The plasma current follows the expanding plasma toward the array axis and, after traveling a critical distance scaling with the array radius divided by the wire number, the global magnetic field threads the wire core, thereby allowing JxB coronal acceleration into ablation streams.

Martin, M. R.; Seyler, C. E.; Greenly, J. B. [Laboratory of Plasma Studies, Cornell University, 316 Rhodes Hall, Ithaca, New York 14850 (United States)

2010-05-15

155

Magnetization Reversal in Arrays of Ni Nanowires With Different Diameters  

Microsoft Academic Search

Arrays of Ni ferromagnetic nanowires of three different diameters (20, 40, and 170 nm) are obtained by electrodeposition into nanoporous alumina templates. Hysteresis curves parallel and perpendicular to the applied field are studied by angle dependent vector vibrating sample magnetometry. Hysteresis curves, from high remanence and coercivity for the smallest diameter, to nearly anhysteretic curves for the largest diameter, can

Louis-Philippe Carignan; Mathieu Massicotte; Christophe Caloz; Arthur Yelon; David Menard

2009-01-01

156

Interference rejection algorithm for current measurement using magnetic sensor arrays  

Microsoft Academic Search

Solid state magnetic sensors can measure a current by sensing the field near the conductor. Means are required to distinguish between useful and interference fields and that are those of conductors near the current under measurement and environmental fields.Starting from analytical expressions of the magnetic field, spatial harmonic analysis is performed. It is then possible to separate the effects of

R. Bazzocchi; L. Di Rienzo

2000-01-01

157

A Micromachined Permalloy Magnetic Actuator Array for Micro Robotics Assembly Systems  

Microsoft Academic Search

Arrays of permalloy magnetic actuators have been studied for the use as precision micro robotics assembly systems. The actuator arrays have been tested for lifting and moving silicon and glass chips. The actuator unit consists of a permalloy plate 1 mmx I mmx5 pm in size together with polysilicon bending supports. Experimentally, it can lift a 87 pN (or 8.88

Chang Liu; Thomas Tsao; Yu-Chong Tai; Wenheng Liu; Peter Will; Chih-Ming Ho

1995-01-01

158

Anisotropic transport and magnetic properties of arrays of sub-micron wires  

Microsoft Academic Search

We report a comparative study of anisotropic magnetoresistance and magnetic properties in arrays of sub-micron Ni and Co wires electro-deposited in the cylindrical pores of track-etched polymer membranes. The variation of coercivity and squareness as a function of wire diameter for arrays of almost isolated sub-micron wires is reported in the range 30–500 nm. The Ni and Co-based systems demonstrate

L. Piraux; S. Dubois; E. Ferain; R. Legras; K. Ounadjela; J. M. George; J. L. Maurice; A. Fert

1997-01-01

159

Synthesis and magnetic properties of ordered barium ferrite nanowire arrays in AAO template  

Microsoft Academic Search

BaFe12O19 nanowire arrays having single magnetic domain size (?460nm) in anodic aluminum oxide (AAO) templates were prepared by sol–gel and self-propagating high-temperature synthesis techniques. The diameter of the nanowire arrays is approximately 70nm and the length is about 2–4?m. The specimens were characterized using X-ray diffraction, vibrating sample magnetometer, field emission scan electron microscope, atomic force microscopy and microwave vector

Yuqing Li; Ying Huang; Li Yan; Shuhua Qi; Lu Miao; Yan Wang; Qiufen Wang

2011-01-01

160

Tiltable magnetic anisotropy in oblique-deposited Fe arrays using nanoporous anodic aluminum oxides  

Microsoft Academic Search

Tiltable magnetic anisotropy of self-assembled Fe arrays on nanoporous anodic aluminum oxide has been obtained via oblique evaporation. The rims of the pores, which induce a stacking variation to the stacked atoms, obstructed on the top and shadowed on the inner-wall, aid the formation of isolated arrays with extended ``sterns.'' The sterns, formed perpendicularly on the unshadowed inner-wall inducing out-of-plane

Kai-Tze Huang; Po-Cheng Kuo; Ger-Pin Lin; Chih-Lung Shen; Yeong-Der Yao

2010-01-01

161

Magnetic wall decoupling method for monopole coil array in ultrahigh field MRI: a feasibility test  

PubMed Central

Ultrahigh field (UHF) MR imaging of deeply located target in high dielectric biological samples faces challenges due to the reduced penetration depth at the corresponding high frequencies. Radiative coils, e.g., dipole and monopole coils, have recently been applied for UHF MRI applications to obtain better signal-noise-ratio (SNR) in the area deep inside the human head and body. However, due to the unique structure of radiative coil elements, electromagnetic (EM) coupling between elements in radiative coil arrays cannot be readily addressed by using traditional decoupling methods such as element overlapping and L/C decoupling network. A new decoupling method based on induced current elimination (ICE) or magnetic wall technique has recently been proposed and has demonstrated feasibility in designing microstrip transmission line (MTL) arrays and L/C loop arrays. In this study, an array of two monopole elements decoupled using magnetic wall decoupling technique was designed, constructed and analyzed numerically and experimentally to investigate the feasibility of the decoupling technique in radiative coil array designs for MR imaging at 7 T. An L-shaped capacitive network was employed as the matching circuit and the reflection coefficients (S11) of the monopole element achieved –30 dB or better. Isolation between the two monopole elements was improved from about –10 dB (without decoupling treatment) to better than –30 dB with the ICE/magnetic wall decoupling method. B1 maps and MR images of the phantom were acquired and SNR maps were measured and calculated to evaluate the performance of the ICE/magnetic wall decoupling method. Compared with the monopole elements without decoupling methods, the ICE-decoupled array demonstrated more independent image profiles from each element and had a higher SNR in the peripheral area of the imaging subject. The experimental and simulation results indicate that the ICE/magnetic wall decoupling technique might be a promising solution to reducing the EM coupling of monopole arrays for UHF MRI.

Yan, Xinqiang; Zhang, Xiaoliang; Wei, Long

2014-01-01

162

Magnetic wall decoupling method for monopole coil array in ultrahigh field MRI: a feasibility test.  

PubMed

Ultrahigh field (UHF) MR imaging of deeply located target in high dielectric biological samples faces challenges due to the reduced penetration depth at the corresponding high frequencies. Radiative coils, e.g., dipole and monopole coils, have recently been applied for UHF MRI applications to obtain better signal-noise-ratio (SNR) in the area deep inside the human head and body. However, due to the unique structure of radiative coil elements, electromagnetic (EM) coupling between elements in radiative coil arrays cannot be readily addressed by using traditional decoupling methods such as element overlapping and L/C decoupling network. A new decoupling method based on induced current elimination (ICE) or magnetic wall technique has recently been proposed and has demonstrated feasibility in designing microstrip transmission line (MTL) arrays and L/C loop arrays. In this study, an array of two monopole elements decoupled using magnetic wall decoupling technique was designed, constructed and analyzed numerically and experimentally to investigate the feasibility of the decoupling technique in radiative coil array designs for MR imaging at 7 T. An L-shaped capacitive network was employed as the matching circuit and the reflection coefficients (S11) of the monopole element achieved -30 dB or better. Isolation between the two monopole elements was improved from about -10 dB (without decoupling treatment) to better than -30 dB with the ICE/magnetic wall decoupling method. B1 maps and MR images of the phantom were acquired and SNR maps were measured and calculated to evaluate the performance of the ICE/magnetic wall decoupling method. Compared with the monopole elements without decoupling methods, the ICE-decoupled array demonstrated more independent image profiles from each element and had a higher SNR in the peripheral area of the imaging subject. The experimental and simulation results indicate that the ICE/magnetic wall decoupling technique might be a promising solution to reducing the EM coupling of monopole arrays for UHF MRI. PMID:24834419

Yan, Xinqiang; Zhang, Xiaoliang; Wei, Long; Xue, Rong

2014-04-01

163

Template-assisted CoPd nanowire arrays: magnetic properties and FORC analysis.  

PubMed

Highly hexagonally ordered CoPd alloy nanowire arrays were synthesized through electrochemical deposition techniques into the nanopores of anodic alumina membranes used as templates. Two different electrolytes were used for this purpose, one with pH = 4.1 and the other with pH = 7. Under applying different electrodeposition parameters and by adjusting both, the current density and the electrolyte composition, it could be possible make to vary the composition of CoPd alloy nanowires in a wide range. Their composition and morphology were investigated by SEM and EDX. The magnetic properties of the nanowires array have been measured with a VSM as a function of the temperature, ranging from RT down to 50 K, for different CoPd alloy nanowires composition. Also, the temperature influence on the reversible-irreversible magnetization processes related with the magnetization reversal of the CoPd nanowires array has been analyzed by first order reversal curve (FORC) method. PMID:22905524

Vega, V; Rosa, W O; García, J; Sánchez, T; Santos, J D; Béron, F; Pirota, K R; Prida, V M; Hernando, B

2012-06-01

164

Dilute plasma coupling currents to a high voltage solar array in weak magnetic fields  

NASA Technical Reports Server (NTRS)

The plasma coupling current to an approximately 2000 sq cm array was measured for externally biased positive and negative voltages on the array to 1000 V in applied magnetic field strengths from 0 to 0.93 G. The plasma density varied from 2,000 to 1.3 million electrons/cu cm. It was found that the magnetic field primarily increased the plasma coupling current for negative biases. For positive bias, the current could increase or decrease depending on the voltage, field strength, and plasma density. It was also found that the plasma coupling current was not very sensitive to how the plane of the array was oriented relative to the magnetic field.

Grier, N. T.

1984-01-01

165

Synthesis, Magnetic Anisotropy and Optical Properties of Preferred Oriented Zinc Ferrite Nanowire Arrays  

PubMed Central

Preferred oriented ZnFe2O4 nanowire arrays with an average diameter of 16 nm were fabricated by post-annealing of ZnFe2 nanowires within anodic aluminum oxide templates in atmosphere. Selected area electron diffraction and X-ray diffraction exhibit that the nanowires are in cubic spinel-type structure with a [110] preferred crystallite orientation. Magnetic measurement indicates that the as-prepared ZnFe2O4 nanowire arrays reveal uniaxial magnetic anisotropy, and the easy magnetization direction is parallel to the axis of nanowire. The optical properties show the ZnFe2O4 nanowire arrays give out 370–520 nm blue-violet light, and their UV absorption edge is around 700 nm. The estimated values of direct and indirect band gaps for the nanowires are 2.23 and 1.73 eV, respectively.

2010-01-01

166

Arrays  

NSDL National Science Digital Library

This interactive Flash applet helps students develop the concept of equal groups as a foundation for multiplication and division. The applet displays an array of dots, some of which are covered by a card. Student use the visible number of rows and columns to determine the total number of dots. Clicking on the card reveals the full array, and a voice announces the total.

2011-01-01

167

Magnetic dipolar interaction in NiFe nanodot arrays formed on vertical carbon nanotubes.  

PubMed

A new and simple method for the fabrication of densely packed magnetic nanodot arrays was developed using conventional sputtering deposition at room temperature. An anodized alumina template was employed for the formation of nanodot assemblies, consisting of carbon nanotubes (CNTs) and magnetic nanodot arrays. Each nanodot was formed exactly on top of a CNT and was arranged with a well-ordered structure in a wide range of area. It was also found that the size of dots and the distance between dots can be tailored by changing the length of CNTs, inducing a change of strength of dipolar interaction between nanodots. PMID:21836284

Nam, Chunghee; Kim, Youn-Su; Kim, W B; Cho, B K

2008-11-26

168

Magnetic dipolar interaction in NiFe nanodot arrays formed on vertical carbon nanotubes  

NASA Astrophysics Data System (ADS)

A new and simple method for the fabrication of densely packed magnetic nanodot arrays was developed using conventional sputtering deposition at room temperature. An anodized alumina template was employed for the formation of nanodot assemblies, consisting of carbon nanotubes (CNTs) and magnetic nanodot arrays. Each nanodot was formed exactly on top of a CNT and was arranged with a well-ordered structure in a wide range of area. It was also found that the size of dots and the distance between dots can be tailored by changing the length of CNTs, inducing a change of strength of dipolar interaction between nanodots.

Nam, Chunghee; Kim, Youn-Su; Kim, W. B.; Cho, B. K.

2008-11-01

169

Ambient-temperature passive magnetic bearings: Theory and design equations  

SciTech Connect

Research has been underway at the Lawrence Livermore National Laboratory to build a theoretical and experimental base for the design of ambient-temperature passive magnetic bearings for a variety of possible applications. in the approach taken the limitations imposed by Earnshaw`s theorem with respect to the stability of passive magnetic bearing systems employing axially symmetric permanent-magnet elements are overcome by employing special combinations of elements, as follows: Levitating and restoring forces are provided by combinations of permanent-magnet-excited elements chosen to provide positive stiffnesses (negative force derivatives) for selected displacements (i.e., those involving translations or angular displacement of the axis of rotation). As dictated by Eamshaw`s theorem, any bearing system thus constructed will be statically unstable for at least one of the remaining possible displacements. Stabilization against this displacement is accomplished by using periodic arrays (`Halbach arrays`) of permanent magnets to induce currents in close-packed inductively loaded circuits, thereby producing negative force derivatives stabilizing the system while in rotation. Disengaging mechanical elements stabilize the system when at rest and when below a low critical speed. The paper discusses theory and equations needed for the design of such systems.

Post, R.F.; Ryutov, D.D.

1997-12-30

170

Magnetic flux pinning in superconductors with hyperbolic-tessellation arrays of pinning sites  

NASA Astrophysics Data System (ADS)

We study magnetic flux interacting with arrays of pinning sites (APSs) placed on vertices of hyperbolic tessellations (HTs). We show that, due to the gradient in the density of pinning sites, HT APSs are capable of trapping vortices for a broad range of applied magnetic fluxes. Thus, the penetration of magnetic field in HT APSs is essentially different from the usual scenario predicted by the Bean model. We demonstrate that, due to the enhanced asymmetry of the surface barrier for vortex entry and exit, this HT APS could be used as a “capacitor” to store magnetic flux.

Misko, V. R.; Nori, Franco

2012-05-01

171

Ordered Magnetic Nanoparticle Arrays on Tunable Substrates for RF Applications.  

National Technical Information Service (NTIS)

This research project led to fabrication of tunable multilayer oxide structures based on Barium Strontium Titanate (BST) and Barium Hexaferrite (BaM) materials, demonstrate tunability of impedance when subject to external electrical and magnetic fields an...

H. Ikanth

2010-01-01

172

Magnetostatic interactions between magnetic arrays and superconducting thin films  

Microsoft Academic Search

Two-dimensional arrays of amorphous Gd-Co square particles with thickness around 200 nm were fabricated on 20 nm thick Nb films by means of high-resolution e-beam lithography and sputter deposition. Interesting oscillations due to the fluxoid quantization were observed in the magnetoresistance measured around the superconducting transition temperature of Nb films. The superconducting state of the Nb films seems to be

Y. Otani; B. Pannetier; J. P. Nozières; D. Givord

1993-01-01

173

Melting, pinning, and forced flow of two-dimensional magnetic bubble arrays  

SciTech Connect

Magnetic bubble arrays in thin garnet films form an experimental system in which structural and dynamical properties of two-dimensional solids can be studied. Bubbles are observed directly using the Faraday effect, bubble motion recorded using computer-video techniques, and dynamics of topological defects studied using Voronoi constructions of time-resolved images. Bubbles are subject to microscopic pinning due to substrate roughness in the sample, and an ac magnetic field simulates temperature. Observations are reported of a continuous hexatic-to-liquid melting transition as a function of density in magnetic bubble arrays. In the hexatic phase, the dislocations increase in concentration and form large transient clusters as the bubble density is reduced. At the hexatic-to-liquid transition, the defect clusters span the system, dislocations unbind into disclinations, and orientational order is lost. The liquid is characterized by exponentially decaying orientational and translational correlation functions, and ring shaped diffraction patterns. The hexatic displays long correlation lengths for orientational order, six-fold symmetry in diffraction patterns, and exponentially decaying translational correlation functions. At higher densities substrate roughness makes a hexatic glass the most ordered state. This hexatic glass has extended orientational order and few, immobile dislocations. Observations are presented of the influence of disorder on the forced flow of magnetic bubble arrays. Collective transport is produced by forcing the bubble array to move past a flat interface. The array is strongly pinned on the other side of the interface by permalloy disks. Far from the interface the array flows uniformly while close to the interface it shears. Substrate roughness exerts a frictional drag on the array. The gliding motion of interacting dislocations leads to slip events which add to produce the macroscopic shear flow. The shear viscosity increases with density.

Seshadri, R.

1992-01-01

174

Configuration-induced vortex motion in type-II superconducting films with periodic magnetic dot arrays  

NASA Astrophysics Data System (ADS)

Using the molecular dynamic method we investigate numerically the current driven vortex motion in a superconducting film with periodic arrays of both ferromagnetic (FM) and anti-parallel ferromagnetic (AFM) dots. The simulation results show that in the absence of thermal fluctuation the vortex motion is dominated by the configurations of the magnetic dot array. This guided vortex motion is only observed at the onset of the depinning of the interstitial vortices. Two guided vortex motion mechanisms are discussed in this work. For the AFM configuration the vortex motion is mainly originated by the existence of magnetic dots with opposite magnetized moments, while for the FM case it is mainly dependent on the degree of the condensed packing of the magnetic dot lattice constant.

Chen, Q. H.; Shi, D. Q.; Li, W. X.; Zhu, B. Y.; Moshchalkov, V. V.; Dou, S. X.

2014-06-01

175

Sino-Magnetic Array at Low Latitudes (SMALL) including initial results from the sister sites in the United States  

Microsoft Academic Search

The Sino-Magnetic Array at Low Latitudes (SMALL) is an ongoing project for the development of a two-dimensional (2-D) ground-based magnetometer array in China. The ultimate array will consist of 24 stations spanning over 3 hours in local time in the low-latitude (L

Y. F. Gao; P. J Chi; G. Le; C. T Russell; D. M Yang; X. Zhou; S. F Yang; V. Angelopoulos; F. K Chun

2000-01-01

176

High frequency umbilical magnetic probe array for SSX wind tunnel  

NASA Astrophysics Data System (ADS)

The Swarthmore Spheromak Experiment (SSX) wind tunnel consists of a high velocity plume of magnetized plasma injected into a copper flux conserver with dimensions L = 1 m and R = 0.08 m (aspect ratio 10:1). The plasma spheromaks in this wind tunnel typically have densities on the order of 1 - 5 x10^15 cm-3 and flow speeds of 50 km/s. In the past, fluctuations and turbulence in the SSX plasma wind tunnel during magnetic reconnection have been examined by means of two high resolution (16 position at 0.46 cm spacing) radial magnetic probes. Results from the radial probes show high frequency magnetic fluctuations at the site of reconnection. Four more probes have been design to help detect magnetic fluctuations and reconnection activity along the axial direction of the wind tunnel. The four new probes have 8 positions at 0.95 cm spacing and have a flexible bellow in vacuum and a quartz jacket. The bellows act as an umbilical giving the probe excellent flexibility and versatility. The flexibility allows the probe to be bent so it lies along the axis of the flux conserver.

Werth, A. M.; Gray, T.; Brown, M. R.

2012-10-01

177

Formation of a Cobalt Magnetic Dot Array via Block Copolymer Lithography  

Microsoft Academic Search

Single-domain cobalt dot arrayswith high magnetic particle density, patterned over large areas (e.g., 10 cm diameter wafers) are fabricated by self-assembled block copolymer lithography, using a polystyrene-poly(ferrocenyldimethylsilane) copolymer as a template. By varying the copolymer type and etching conditions the magnetic properties can be tuned. The Figure shows a typical array of Co dots with tungsten caps obtained via this

J. Y. Cheng; C. A. Ross; V. Z.-H. Chan; E. L. Thomas; R. G. H. Lammertink; G. Julius Vancso

2001-01-01

178

Structure and magnetic properties of CoNiP nanowire arrays embedded in AAO template  

Microsoft Academic Search

Ternary CoNiP nanowire (NW) arrays have been synthesized by electrochemical deposition inside the nanochannels of anodic aluminum oxide (AAO) template. The CoNiP NWs deposited at room temperature present soft magnetic properties, with both parallel and perpendicular coercivities less than 500Oe. In contrast, as the electrolyte temperature (Telc) increases from 323 to 343K, the NWs exhibit hard magnetic properties with coercivities

Xiaoli He; Guangbing Yue; Yufeng Hao; Qiaoling Xu; Qing Wei; Xiaoguang Zhu; Mingguang Kong; Lide Zhang; Xing Li

2008-01-01

179

Spin laser based on magnetic nano-contact array  

NASA Astrophysics Data System (ADS)

Arrays of 10 nm diameter point contacts of exchange-coupled spin-majority/spin-minority ferromagnetic metals, integrated into infrared-terahertz range photon resonators, are fabricated and measured electrically and optically. Giant, threshold-type electronic excitations under high-current pumping of the devices are observed as abrupt but reversible steps in device resistance, in many cases in excess of 100%, which correlate with optical emission from the devices. The results are interpreted as due to stimulated spin-flip electron-photon relaxation in the system.

Korenivski, V.; Iovan, A.; Kadigrobov, A.; Shekhter, R. I.

2013-10-01

180

Role of boundaries in micromagnetic calculations of magnonic spectra of arrays of magnetic nanoelements  

NASA Astrophysics Data System (ADS)

We have used micromagnetic simulations performed with open and periodic boundary conditions to study the influence of the presence of array boundaries on the spectra and spatial profiles of collective spin-wave excitations in arrays of magnetic nanoelements. The spectra and spatial profiles of collective spin waves excited in isolated arrays of nanoelements and those forming a part of quasi-infinite arrays are qualitatively different even if the same excitation field is used in the simulations. In particular, the use of periodic boundary conditions suppresses the excitation of nonuniform collective modes by uniform excitation fields. However, the use of nonuniform excitation fields in combination with periodic boundary conditions is shown to enable investigation of the structure of magnonic dispersion curves for quasi-infinite arrays (magnonic crystals) in different directions in the reciprocal space and for different magnonic bands. The results obtained in the latter case show a perfect agreement with those obtained with the dynamical matrix method for infinite arrays of nanoelements of the same geometry and magnetic properties.

Dmytriiev, O.; Kruglyak, V. V.; Franchin, M.; Fangohr, H.; Giovannini, L.; Montoncello, F.

2013-05-01

181

Miniature Antennas and Arrays Embedded Within Magnetic Photonic Crystals  

Microsoft Academic Search

This letter presents the performance of small antennas embedded within a new class of magnetic photonic crystals (MPCs) constructed from periodic arrangements of homogenous and anisotropic material layers. Earlier studies of these crystals demonstrated that they exhibit slow modes within their propagation bands associated with minimal reflection at the air-crystal interface, drastic slow down of the group velocity and concurrent

Gokhan Mumcu; Kubilay Sertel; John L. Volakis

2006-01-01

182

A DNA array sensor utilizing magnetic microbeads and magnetoelectronic detection  

Microsoft Academic Search

We describe a multi-analyte biosensor that uses magnetic microbeads as labels to detect DNA hybridization on a micro-fabricated chip. The beads are detected by giant magnetoresistance (GMR) magnetoelectronic sensors embedded in the chip. The prototype device is a tabletop unit containing electronics, a chip carrier with a microfluidic flow cell, and a compact electromagnet and is capable of simultaneous detection

M. M. Miller; P. E. Sheehan; R. L. Edelstein; C. R. Tamanaha; L. Zhong; S. Bounnak; L. J. Whitman; R. J. Colton

2001-01-01

183

Reactive near field magnetic coupling utilizing a staggered phased array  

Microsoft Academic Search

A rise in the need for dynamic energy allocation has been associated with the saturation of available portable wireless electronic devices. Currently, the availability for transmitting this energy efficiently has been limited to a number of methods, including near field resonant magnetic coupling. Previous research with mid range (d?4r) wireless power transfer has resulted in coupling efficiencies of close to

Devin Williams; Majid Manteghi

2011-01-01

184

Robotic apparatuses, systems and methods  

NASA Technical Reports Server (NTRS)

A mobile device for traversing a ferromagnetic surface. The device includes a frame and at least one surface contacting device attached to the frame. The device also includes a Halbach magnet array attached to the frame, wherein the Halbach magnet array provides a magnetic force to maintain the surface contacting device substantially into contact with the ferromagnetic surface.

Ross, William P. (Inventor); Hoburg, James F. (Inventor); Fromme, Christopher (Inventor); Bares, John (Inventor); DeLouis, Mark (Inventor)

2006-01-01

185

Fast-Sampling, Fixed Coil Array for Measuring the AC Field of Fermilab Booster Corrector Magnets.  

National Technical Information Service (NTIS)

A system employing an array of inductive pick-up coils around the perimeter of a cylinder has been developed for measurements of the rapidly changing field in the new corrector magnets for the Fermilab Booster. The coils are fabricated on printed circuit ...

C. Sylvester D. Orris D. J. Harding J. DiMarco M. Lamm W. Schappert

2007-01-01

186

Magnetic Field Measurements in Wire-Array Z-Pinches using Magneto-Optically Active Waveguides  

SciTech Connect

Understanding the magnetic field topology in wire-array Z-pinches as a function of time is of great significance to understanding these high-energy density plasmas especially for their ultimate application to stockpile stewardship and inertial confinement fusion. We are developing techniques to measure magnetic fields as a function of space and time using Faraday rotation of a single longitudinal mode (SLM) laser through a magneto-optically active bulk waveguide (multicomponent terbium borate glass) placed adjacent to, or within, the wire array in 1 MA experiments. We have measured fields >10 T with 100 ns rise times outside of a wire-array for the entire duration of the current pulse and as much as {approx}2 T inside a wire-array for {approx}40 ns from the start of current. This is the first time that such rapidly varying and large fields have been measured using these materials. In a dense Z-pinch, these sensing devices may not survive for long but may provide the magnetic field at the position of the sensor that can be used to corroborate magnetic probes, with which we compare our results.

Syed, Wasif [School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853 (United States); Laboratory of Plasma Studies, Cornell University, Ithaca, NY 14853 (United States); Blesener, Isaac; Hammer, David A. [School of Electrical and Computer Engineering, Cornell University, Ithaca, NY 14853 (United States); Laboratory of Plasma Studies, Cornell University, Ithaca, NY 14853 (United States); Lipson, Michal [School of Electrical and Computer Engineering, Cornell University, Ithaca, NY 14853 (United States)

2009-01-21

187

Directed Fluid Flow Produced by Arrays of Magnetically Actuated Core-Shell Biomimetic Cilia  

Microsoft Academic Search

We have developed a novel core-shell microstructure that we use to fabricate arrays of flexible, magnetically actuated biomimetic cilia. Our biomimetic cilia mimic the size and beat shape of biological cilia in order to replicate the transport of fluid driven by cilia in many biological systems including the determination of left-right asymmetry in the vertebrate embryonic nodal plate and mucociliary

B. L. Fiser; A. R. Shields; B. A. Evans; R. Superfine

2010-01-01

188

Fabrication of Magnetically Actuated Polymeric Nanorod Arrays to Mimic Biological Cilia  

NASA Astrophysics Data System (ADS)

We report on successful fabrication of free-standing polymer nanorod arrays capable of actuation via externally applied magnetic fields. Our primary motivation is to mimic the ability of epithelial lung cilia to promote microscale fluid transport. Additionally, nanoscale actuator arrays of this nature have a wide variety of possible applications including microfluidics, sensing, and photonics. To fabricate these structures we utilize porous polycarbonate track-etched membranes as templates for a dispersion of a magnetic nanoparticle ferrofluid in polydimethylsiloxane (PDMS). Crosslinking of the polymer followed by subsequent dissolution of the membrane releases the rod array. With this method we have successfully fabricated rods with diameters down to 200 nanometers and lengths of 10-25 microns. Rods of various sizes have been successfully actuated with permanent magnets as well as an integrated magnetic force microscope that was developed in-house. We have demonstrated that actuation induces local fluid flow and are currently developing increased control over the array's actuation pattern to more closely resemble that of biological cilia.

Shields, A. R.; Evans, B. A.; Carroll, R. L.; Superfine, R.

2006-11-01

189

Ordered arrays of magnetic polymer-based nanorods by template synthesis.  

PubMed

An ordered array of polymer-based magnetic nanorods has been prepared from poly(vinyl alcohol) solution with dispersed CoFe2O4 nanoparticles by template synthesis using nanoporous anodic alumina. The ordering of the alumina template is transferred to the magnetic nanocomposite in such a way that the magnetic nanorods are located in an orderly fashion. The organic-inorganic nature of the nanorods is proven and their first magnetic characterization reveals a little magnetic anisotropy. The proposed method of synthesis shows a good versatility to obtain ordered magnetopolymeric nanostructures with tailored geometric dimensions which together with their excellent mechanical behaviour open new opportunities of technological applications in the field of magnetic encoding and storage of information. PMID:19908472

Martín, Jaime; Vázquez, Manuel; Hernández-Vélez, Manuel; Mijangos, Carmen

2009-10-01

190

Determination of the plasma velocity in an imploding wire array from magnetic field measurements by a gradient probe  

NASA Astrophysics Data System (ADS)

A method for measuring the gradient of the magnetic field in the plasma of an imploding wire array is described. Results from measurements of the magnitude and gradient of the magnetic field in a tungsten wire array on the Angara-5-1 facility at currents of ˜3 MA are presented. A novel method for calculating the velocity of the current-carrying plasma in the framework of MHD equations from data on the magnitude and gradient of the magnetic field at a certain point inside the array is proposed. It is demonstrated that a gradient magnetic probe can be used to investigate the plasma current sheath in plasma focus facilities.

Grabovski, E. V.; Mitrofanov, K. N.; Koshelev, A. Yu.; Samokhin, A. A.; Aleksandrov, V. V.; Gritsuk, A. N.; Laukhin, Ya. N.; Oleinik, G. M.; Frolov, I. N.

2011-07-01

191

A high-density coupled-magnetic-film memory array  

Microsoft Academic Search

A high-density coupled-hard-axis (CHA) destructive readout (DRO) magnetic-film device which yields storage density ? 6400 cells per square inch and drive currents compatible with ICs is described. A thin word line design is unique in that its own resistance is used as its termination. This thin word line design permits word line grouping on the substrate level resulting in larger

F. Lee

1971-01-01

192

Ordered arrays of metal-organic magnets at surfaces  

NASA Astrophysics Data System (ADS)

We report here on the molecular self-assembly of 7, 7?, 8, 8? tetracyanoquinodimethane (TCNQ) (schematic representation of the molecule on figure 1(b)) on a single-crystal Cu(111) surface, followed by deposition of Fe and Mn, and on the formation of an ordered metal-organic coordination network of Fe (or Mn)-TCNQ units, which contains magnetic ions separated by 0.9 nm.

Barja, Sara; Stradi, Daniel; Borca, Bogdana; Garnica, Manuela; Díaz, Cristina; Rodriguez-García, Josefa M.; Alcamí, Manuel; Vázquez de Parga, Amadeo L.; Martín, Fernando; Miranda, Rodolfo

2013-12-01

193

Synthesis and magnetic properties of large-area ferromagnetic cylindrical nanoshell and nanocup arrays  

NASA Astrophysics Data System (ADS)

Large-area arrays of magnetic Ni80Fe20 cylindrical nanoshells, nanocups, and perforated nanocups were synthesized using oblique deposition into topographical templates patterned using laser interference lithography. The geometry of the template and the tilt angle of the sample during deposition provide versatile control over the final geometry and dimension of nanostructures with thickness below 10 nm. Decreasing shell thickness led to a magnetization switching path between onion (bidomain) and reverse onion states, bypassing the vortex (flux-closed) state. The variation of magnetization reversal processes with geometry was characterized using vibrating sample magnetometry, and the results were in good agreement with micromagnetic simulations.

Wang, Z.; Shimon, G.; Liu, X.; Thompson, C. V.; Ross, C. A.; Choi, W. K.; Adeyeye, A. O.

2013-06-01

194

Open-loop characteristics of magnetic suspension systems using electromagnets mounted in a planar array  

NASA Technical Reports Server (NTRS)

The open-loop characteristics of a Large-Gap Magnetic Suspension System (LGMSS) were studied and numerical results are presented. The LGMSS considered provides five-degree-of-freedom control. The suspended element is a cylinder that contains a core composed of permanent magnet material. The magnetic actuators are air core electromagnets mounted in a planar array. Configurations utilizing five, six, seven, and eight electromagnets were investigated and all configurations were found to be controllable from coil currents and observable from suspended element positions. Results indicate that increasing the number of coils has an insignificant effect on mode shapes and frequencies.

Groom, Nelson J.; Britcher, Colin P.

1992-01-01

195

Ordered sub-micron magnetic dot arrays using self-assembly template method  

NASA Astrophysics Data System (ADS)

Using a self-assembly double template method, we have prepared highly ordered magnetic dot arrays of Ni on sub-micron scales. For the template preparation we have used colloidal suspensions of polystyrene latex spheres with different diameters ranging from 200 to 700 nm combined with secondary templates of the conducting polymer polypyrrole. By variation of the template parameters and the deposition charge the material shape can be modified significantly from isolated dots to connected 3D networks. Samples have been characterized by magnetometry. Magnetic properties were found to depend strongly on dot size and connectivity leading to a rich variety of magnetic behaviors.

Goncharov, A.; Zhukov, A. A.; Bartlett, P. N.; Ghanem, M. A.; Boardman, R.; Fangohr, H.; de Groot, P. A. J.

2005-02-01

196

Pulse electrodeposition and electrochemical quartz crystal microbalance techniques for high perpendicular magnetic anisotropy cobalt nanowire arrays  

SciTech Connect

This research is focused on the development of pulse electrodeposition techniques to fabricate a high-density array of vertically oriented, high-magnetic anisotropy cobalt nanowires using a porous polymer film template. This type of array is a competitive candidate for future perpendicular magnetic media capable of storage densities exceeding 1 Terabit/in.{sup 2} The polymer template, derived from a self-assembling P(S-b-MMA) diblock copolymer film, provides precise control over the nanowire diameter (15 nm) and interwire spacing (24 nm), whereas nanowire length (typically 50 to 1000 nm) is controlled accurately with the aid of real-time electrochemical quartz crystal monitoring. Pulse and pulse-reversed electrodeposition techniques, as compared to dc, are shown to significantly enhance the perpendicular magnetic anisotropy of the magnetic nanowire array and ultimately result in coercivity as large as 2.7 kOe at 300 K. Magnetic and structural characterizations suggest that these properties arise from an improved degree of magnetocrystalline anisotropy (due to c-axis oriented crystal growth and improvements in crystal quality) that strongly supplements the basic shape anisotropy of the nanowires. Low temperature magnetometry is used to investigate exchange bias effects due to the incorporation of CoO antiferromagnetic impurities during the electrodeposition process and subsequent Co oxidation in air.

Ursache, Andrei; Goldbach, James T.; Russell, Thomas P.; Tuominen, Mark T. [Department of Physics, University of Massachusetts, 666 N Pleasant St., Hasbrouck Lab, Room 411, Amherst, Massachusetts 01003 (United States); Department of Polymer Science and Engineering, University of Massachusetts, 120 Governors Drive Amherst, Massachusetts 01003 (United States); Department of Physics, University of Massachusetts, 666 N Pleasant St., Hasbrouck Lab, Room 411, Amherst, Massachusetts 01003 (United States)

2005-05-15

197

Tunable ratchet effects for vortices pinned by periodic magnetic dipole arrays  

NASA Astrophysics Data System (ADS)

The ratchet effect is demonstrated theoretically for the simple model of a vortex in a thin superconducting film interacting with a periodic array of magnetic dipoles placed in the vicinity of the film . The pinning potential for the vortex is calculated in the London limit and found to break spatial inversion symmetry and to depend on the orientation of the magnetic dipole moments. The motion of the vortex at zero temperature driven by a force oscillating periodically in time is investigated numerically. Drift vortex motion consisting of displacements by a translation vector of the dipole array during each period of oscillation is obtained and studied in detail. The direction of drift differs in general from that of the driving force, except if the driving force oscillates in a direction of high symmetry of the dipole array. The vortex drift velocity depends on the orientation of the magnetic moments, and can be tuned by rotating the dipoles. It is pointed out that if the magnetic moments are free to rotate, the ratchet effect can be produced and tuned by a magnetic field applied parallel to the film surfaces.

Carneiro, Gilson

2005-11-01

198

Evolution of microwave ferromagnetic resonance with magnetic domain structure in FeCoBSi antidot arrays  

NASA Astrophysics Data System (ADS)

Magnetic domain structure of FeCoBSi antidot array thin films of varying thickness were characterized using surface magneto-optic Kerr effect. Vibrating sample magnetometry and microstrip transmission line measurements helped to associate the microwave magnetic analysis of the antidot arrays with hysteresis studies. The domain structure evolution from quasi-continuous domains to strip domains induced by the competing exchange and dipolar interaction resulted in the change of ferromagnetic resonance from multi-band to single-band. Hence, the mechanisms of multi-resonance are proposed to be related to domain wall motion, natural resonance and spin wave modes. This phenomenon can be used to control the magnetization dynamics in spin wave devices.

Zhou, Peiheng; Zhang, Nan; Liu, Tao; Xie, Jianliang; Deng, Longjiang

2014-08-01

199

A study of magnetic properties: Fe xCo 1- x alloy nanowire arrays  

NASA Astrophysics Data System (ADS)

Highly ordered arrays of Fe xCo 1- x ( x=0-1.0, nominally) alloy nanowire were prepared by electrodepositing Fe 2+ and Co 2+ into the porous anodic aluminum oxide (PAO) templates. XRD experiments proved that the crystal structure of alloy nanowire was bcc. The magnetic properties of Fe xCo 1- x nanowire arrays showed strong magnetic anisotropy, whose easy axis was parallel to the nanowires. Suitable annealing temperature caused coercivity and squareness of sample to increase rapidly, which was higher than those of as-prepared samples. The change in coercivity and squareness of all samples was discussed in detail. The magnetic reversal mechanism may be attributed to localized nucleation based on Zeng's theory [J. Appl. Phys. 87 (2000) 4718].

Qin, Dong-Huan; Peng, Yong; Cao, Lin; Li, Hu-Lin

2003-06-01

200

Experiments with 2D quasistatic and shaken arrays of permanent magnet N-mers (N >=1)  

NASA Astrophysics Data System (ADS)

We extend methods used to study macroscopic grains (contact forces) to 2D (x,y) arrays of N-mers of cylindrical (L=D=3.18 mm) Nd-Fe-B magnets in a rectangular cell with glass plates ?z ˜3.3 mm apart and parallel to magnet faces. Aligned monomers repel with a measured d-4 (dipole-dipole) force dependence, with d the separation between cylinder axes. With fixed, aligned monomers separated by 6.35 mm along the cell walls, hundreds of aligned monomers can move in the cell subject to magnet-glass friction and gravity (either or to z) but without contacting each other or the walls. Quasistatically moving one wall to decrease volume V increases pressure P on the magnetic particles and leads to ordering observed with annealing. Driving the array, e.g., by shaking one wall, can produce disorder; we study how this varies with driving strength at fixed V or P. Replacing all non-wall monomers with similarly aligned tetramers (3 magnets magnetically bound to an inverted magnet) allows for more ordered states in quasistatic experiments; macroscopic, internal degrees of freedom into which energy can flow in driven experiments; and rearrangements (``chemical reactions") for strong driving.

Koch, Peter; Shattuck, Mark

2010-03-01

201

The Magnetic Spectrometer PRISMA Combined With Large Gamma Arrays  

NASA Astrophysics Data System (ADS)

The large solid angle magnetic spectrometer for heavy ions PRISMA was operated at LNL in conjunction with the highly efficient CLARA set-up up to the end of March 2008. The AGATA Demonstrator is being mounted around the target area of PRISMA replacing the CLARA set-up. It will allow to carry out nuclear structure and reaction mechanism studies with better resolution and higher statistics. New detectors for light ions and slow moving heavy ions have been designed for the focal plane of the spectrometer.

Fioretto, E.; Beghini, S.; Corradi, L.; Montagnoli, G.; Scarlassara, F.; Stefanini, A. M.; Bazzacco, D.; de Angelis, G.; Farnea, E.; Gadea, A.; Guiot, B.; Lenzi, S. M.; Lunardi, S.; Marginean, N.; Mason, P.; Menegazzo, R.; Mengoni, D.; Napoli, D. R.; Pollarolo, G.; Recchia, F.; Sahin, E.; Silvestri, R.; Szilner, S.; Ur, C. A.; Valiente-Dobón, J. J.

2009-03-01

202

Power-law relaxation decay in two-dimensional arrays of magnetic dots interacting by long-range dipole-dipole interactions  

Microsoft Academic Search

The magnetic relaxation of two-dimensional arrays of dipolar coupled magnetic dots has been measured and simulated. Arrays (50×50) with perpendicular magnetized Co dots (2 mum×2 mum) were patterned using a high resolution Ga+ focused ion beam irradiation. Magnetic domain pattern and time relaxation of the dot arrays were investigated using Faraday magneto-optical microscopy. For arrays designed with high irradiation doses

L. C. Sampaio; R. Hyndman; F. S. de Menezes; J. P. Jamet; P. Meyer; J. Gierak; C. Chappert; V. Mathet; J. Ferré

2001-01-01

203

Magnetic force microscopy investigation of arrays of nickel nanowires and nanotubes.  

PubMed

The magnetic properties of arrays of nanowires (NWs) and nanotubes (NTs), 150 nm in diameter, electrodeposited inside nanoporous polycarbonate membranes are investigated. The comparison of the nanoscopic magnetic force microscopy (MFM) imaging and the macroscopic behavior as measured by alternating gradient force magnetometry (AGFM) is made. It is shown that MFM is a complementary technique that provides an understanding of the magnetization reversal characteristics at the microscopic scale of individual nanostructures. The local hysteresis loops have been extracted by MFM measurements. The influence of the shape of such elongated nanostructures on the dipolar coupling and consequently on the squareness of the hysteresis curves is demonstrated. It is shown that the nanowires exhibit stronger magnetic interactions than nanotubes. The non-uniformity of the magnetization states is also revealed by combining the MFM and AGFM measurements. PMID:24870297

Tabasum, M R; Zighem, F; De La Torre Medina, J; Encinas, A; Piraux, L; Nysten, B

2014-06-20

204

Magnetic force microscopy investigation of arrays of nickel nanowires and nanotubes  

NASA Astrophysics Data System (ADS)

The magnetic properties of arrays of nanowires (NWs) and nanotubes (NTs), 150 nm in diameter, electrodeposited inside nanoporous polycarbonate membranes are investigated. The comparison of the nanoscopic magnetic force microscopy (MFM) imaging and the macroscopic behavior as measured by alternating gradient force magnetometry (AGFM) is made. It is shown that MFM is a complementary technique that provides an understanding of the magnetization reversal characteristics at the microscopic scale of individual nanostructures. The local hysteresis loops have been extracted by MFM measurements. The influence of the shape of such elongated nanostructures on the dipolar coupling and consequently on the squareness of the hysteresis curves is demonstrated. It is shown that the nanowires exhibit stronger magnetic interactions than nanotubes. The non-uniformity of the magnetization states is also revealed by combining the MFM and AGFM measurements.

Tabasum, M. R.; Zighem, F.; De La Torre Medina, J.; Encinas, A.; Piraux, L.; Nysten, B.

2014-06-01

205

Investigation of energy harvesting for magnetic sensor arrays on Mars by wireless power transmission  

NASA Astrophysics Data System (ADS)

This paper proposes the energy harvesting for magnetic sensor arrays on Mars, which can receive the power from Mars Rover by wireless power transmission (WPT). The schematic idea is presented with the energy receiver as the magnetic sensor and the energy transmitter as the transducer on Mars Rover. The key is to adopt the resonant inductive power transmission (IPT) topology between the magnetic sensor and Mars Rover. The basic topology and its operating principle are discussed. By using the magnetic frequency analysis with the finite element method, the output power and efficiency of the WPT system are calculated. The results show that Mars Rover could flexibly transmit its power to different types of small-size magnetic sensors based on their energy on demand using different resonant frequencies and distances.

Liu, Chunhua; Chau, K. T.; Qiu, Chun; Lin, Fei

2014-05-01

206

A magnetic and magneto-optical investigation of Co-Pt alloy nanowire arrays.  

PubMed

We have investigated the magneto-optical properties of highly ordered Co-Pt alloy nanowire arrays embedded in anodic aluminum oxide templates. The magnetic field-dependent Stokes parameters, Faraday rotation angle and ellipticity were investigated by an in-house magneto-optical measurement system. The extracted hysteresis loops are broadly consistent with magnetic hysteresis loops obtained from the vibrating sample magnetometer. The maximum Faraday rotation angle and ellipticity of these samples were examined as a function of nanowire composition. With an increase of platinum content from 9 at.% to 86 at.% in the as-deposited nanowire arrays, the maximum Faraday rotation angle per length decreases linearly from 1.39 x 10(3) degrees/cm to 1.58 x 10(2) degrees/cm. The maximum ellipticity shows a similar behavior with the composition. These linear relationships suggest a dilution model for the magnetic moment in the alloy nanowires. Our results indicate that magneto-optical measurements comprise an effective and sensitive method for monitoring the behavior of AAO-based magnetic nanowire arrays. PMID:22629903

Zhang, Jun; Shen, Tiehan H; Jones, Grenville A; Jin, Yanxin; Wang, Hanbin; Wang, Hao

2012-02-01

207

A fully automated in vitro diagnostic system based on magnetic tunnel junction arrays and superparamagnetic particles  

NASA Astrophysics Data System (ADS)

A fully automated in vitro diagnostic (IVD) system for diagnosing acute myocardial infarction was developed using high sensitivity MTJ array as sensors and nano-magnetic particles as tags. On the chip is an array of 12 × 106 MTJ devices integrated onto a 3 metal layer CMOS circuit. The array is divided into 48 detection areas, therefore 48 different types of bio targets can be analyzed simultaneously if needed. The chip is assembled with a micro-fluidic cartridge which contains all the reagents necessary for completing the assaying process. Integrated with electrical, mechanical and micro-fluidic pumping devices and with the reaction protocol programed in a microprocessor, the system only requires a simple one-step analyte application procedure to operate and yields results of the three major AMI bio-markers (cTnI, MYO, CK-MB) in 15 mins.

Lian, Jie; Chen, Si; Qiu, Yuqin; Zhang, Suohui; Shi, Stone; Gao, Yunhua

2012-04-01

208

Magnetic Nanoparticles, Magnetic Detector Arrays, and Methods for Their Use in Detecting Biological Molecules.  

National Technical Information Service (NTIS)

Magnetic nanoparticles and methods for their use in detecting biological molecules are disclosed. The magnetic nanoparticles can be attached to nucleic acid molecules, which are then captured by a complementary sequence attached to a detector, such as a s...

C. D. Webb G. Li R. L. White S. X. Wang

2004-01-01

209

Magnetic design of trim excitations for the Advanced Light Source storage ring sextupole  

Microsoft Academic Search

The Advanced Light Source (ALS) storage ring sextupole is a unique multi-purpose magnet. It is designed to operate as a sextupole with three auxiliary trim modes: horizontal steering, vertical steering, and skew quadrupole. A perturbation theory for iron-dominated magnets developed by Klaus Halbach (1969) provides the basis for this design. The three trim excitations are produced by violating sextupole symmetry

S. Marks

1996-01-01

210

Magnetic design of trim excitations for the Advanced Light Source storage ring sextupole  

Microsoft Academic Search

The Advanced Light Source (ALS) storage ring sextupole is a unique multi-purpose magnet. It is designed to operate as a sextupole with three auxiliary trim modes: horizontal steering, vertical steering, and skew quadrupole. A perturbation theory for iron-dominated magnets developed by Klaus Halbach provides the basis for this design. The three trim excitations are produced by violating sextupole symmetry and

S Marks

1995-01-01

211

Magnetic properties of Fe20 Ni80 antidots: Pore size and array disorder  

NASA Astrophysics Data System (ADS)

Magnetic properties of nanoscale Fe20Ni80 antidot arrays with different hole sizes prepared on top of nanoporous alumina membranes have been studied by means of magnetometry and micromagnetic simulations. The results show a significant increase of the coercivity as well as a reduction of the remanence of the antidot arrays, as compared with their parent continuous film, which depends on the hole size introduced in the Fe20Ni80 thin film. When the external field is applied parallel to the antidots, the reversal of magnetization is achieved by free-core vortex propagation, whereas when the external field is applied perpendicular to the antidots, the reversal occurs through a process other than the coherent rotation (a maze-like pattern). Besides, in-plane hysteresis loops varying the angle show that the degree of disorder in the sample breaks the expected hexagonal symmetry.

Palma, J. L.; Gallardo, C.; Spinu, L.; Vargas, J. M.; Dorneles, L. S.; Denardin, J. C.; Escrig, J.

2013-10-01

212

Magnetic properties of Co/Pt nanoring arrays deposited on carbon nanotubes  

NASA Astrophysics Data System (ADS)

Multiple Co/Pt bilayers were deposited on vertically aligned carbon nanotubes on an anodic aluminum oxide template. The structural and the magnetic properties of the nanoring arrays were investigated by varying the number of Co/Pt bilayers in the ranges 3-10 in multilayers with a Ta(3.0 nm)/[Co(1.0 nm)/Pt(1.5 nm)]n/Ta(1.0 nm) structure. The thickness and diameter of the nanorings increased with increasing repeat number. Compared with Co/Pt films, the Co/Pt nanoring arrays showed a larger coercivity. However, the magnetostatic interactions between the nanorings became dominant in the reversal behavior and caused a nonsquare hysteresis loop. Giant magnetoresistance structures consisting of multiple Co/Pt bilayers and a thick Cu spacer exhibited magnetization curve that were in good agreement the summation of the moments of layers with varied bilayer repetition.

Yoon, Seungha; Ho Lee, Sang; Kwak, Wonyoung; Nam, Chunghee; Bae Kim, Won; Cho, B. K.

2014-05-01

213

A Fast-sampling, Planar Array for Measuring the AC Field of Fermilab Pulsed Extraction Magnets  

SciTech Connect

A system employing a planar array of inductive pick-up coils has been developed for measurements of the rapidly changing dipole field in pulsed extraction magnets for the Fermilab MuCool project. The magnets are of C-type and deigned to support a peak field of 0.65 T during 8.33 millisecond half-sine pulse at a 15 Hz repetition rate. The coils of the measurement system are fabricated on a single, 97.5 mm wide, 2-layer circuit board. The array of coils is simultaneously sampled at data rates of up to 100 kHz with 10 kHz bandwidth using 24-bit ADC's. A detailed overview of the system and data analysis is presented, along with a characterization of results and system performance.

DiMarco, E.Joseph; Johnstone, C.; Kiemschies, O.; Kotelnikov, S.K.; Lamm, M.J.; Makulski, A.; Nehring, R.; Orris, D.F.; Russell, A.D.; Tartaglia, Michael Albert; Velev, G.; /Fermilab

2008-06-25

214

Modeling of localized reflow in solder/magnetic nanocomposites for area-array packaging  

NASA Astrophysics Data System (ADS)

We have modeled the reflow process of FeCo magnetic nanoparticle (MNP)-based solder composites with eddy current power loss of substrate and magnetic power losses of solder bumps. For an area array package without MNPs when subjected to 300 kHz ac magnetic field, the eddy current power loss can result in excessive temperatures that can cause substrate damage. Temperature profiles with different MNP concentration were simulated and the results showed localized reflow of solders to enable low-temperature assembly. The temperatures at different times and positions in solder composites were analyzed. We also modeled thermal profiles for solder composites with 0.2 wt. % MNP in 1 MHz and 3 MHz magnetic field. Such high field frequency generated larger power losses in MNPs and is shown to increase the heating efficiency.

Xu, Siyang; Pickel, Andrea D.; Prasitthipayong, Anya; Habib, Ashfaque H.; McHenry, Michael E.

2013-05-01

215

Magnetic field alignment of randomly oriented, high aspect ratio silicon microwires into vertically oriented arrays.  

PubMed

External magnetic fields have been used to vertically align ensembles of silicon microwires coated with ferromagnetic nickel films. X-ray diffraction and image analysis techniques were used to quantify the degree of vertical orientation of the microwires. The degree of vertical alignment and the minimum field strength required for alignment were evaluated as a function of the wire length, coating thickness, magnetic history, and substrate surface properties. Nearly 100% of 100 ?m long, 2 ?m diameter, Si microwires that had been coated with 300 nm of Ni could be vertically aligned by a 300 G magnetic field. For wires ranging from 40 to 60 ?m in length, as the length of the wire increased, a higher degree of alignment was observed at lower field strengths, consistent with an increase in the available magnetic torque. Microwires that had been exposed to a magnetic sweep up to 300 G remained magnetized and, therefore, aligned more readily during subsequent magnetic field alignment sweeps. Alignment of the Ni-coated Si microwires occurred at lower field strengths on hydrophilic Si substrates than on hydrophobic Si substrates. The magnetic field alignment approach provides a pathway for the directed assembly of solution-grown semiconductor wires into vertical arrays, with potential applications in solar cells as well as in other electronic devices that utilize nano- and microscale components as active elements. PMID:23083440

Beardslee, Joseph A; Sadtler, Bryce; Lewis, Nathan S

2012-11-27

216

Self-organisation, orientation and magnetic properties of FePt nanoparticle arrays  

NASA Astrophysics Data System (ADS)

Self-organised magnetic arrays (SOMA) of high anisotropy particles are a promising candidate for ultra-high-density recording media. In principle SOMA media have the capability of storing 1 bit per particle, leading to possible reecording densities in excess of 10 Tbit/sq in. In this paper we consider two major aspects of SOMA media, namely the self-organisation process itself and the physics of the particle orientation process.

Verdes, C.; Chantrell, R. W.; Satoh, A.; Harrell, J. W.; Nikles, D.

2006-09-01

217

Magnetic nanodot arrays patterned by selective ion etching using block copolymer templates  

Microsoft Academic Search

In this paper, we report a novel method of fabricating patterned magnetic metal alloy CoCrPt nanodots via selective ion etching using a self-organized array of spherical domains of an ordered block copolymer (PS-b-PMMA) film as a template. Reactive ion etching and Ar+ ion milling were controlled accurately to avoid excess etching and pattern loss in the etching processes. The nanodot

Dae-Geun Choi; Jong-Ryul Jeong; Ki-Young Kwon; Hee-Tae Jung; Sung-Chul Shin; Seung-Man Yang

2004-01-01

218

Focusing of high-perveance planar electron beams in a miniature wiggler magnet array  

Microsoft Academic Search

The transport of planar electron beams is a topic of increasing interest for applications to high-power, high-frequency microwave devices. This paper describes two- and three-dimensional simulations of electron-beam transport in a notched wiggler magnet array. The calculations include self-consistent effects of beam-generated fields. The simple notched wiggler configuration can provide vertical and horizontal confinement of high-perveance sheet electron beams with

Stanley Humphries; Steven Russell; Bruce Carlsten; Lawrence Earley

2005-01-01

219

Development of 3-D magnetic nano-arrays by electrodeposition into mesoporous silica  

Microsoft Academic Search

The development of periodic nanostructures fabricated by self-assembly of surfactants and block co-polymers has opened up the possibility of generating periodic magnetic nanostructures of types not accessible by self-assembly of nano-particles. The fabrication of mesoporous silica thin films around self-assembled block co-polymers is well established. Common structures for such films are SBA-15 which consists of hexagonal arrays of cylindrical pores

R. Campbell; J. Manning; M. G. Bakker; X. Li; D. R. Lee; J. Wang

2006-01-01

220

Fabrication and magnetic properties of Ni nanowire arrays with ultrahigh axial squareness.  

PubMed

Poly- and single-crystalline Ni nanowire arrays showing ultrahigh axial squareness are fabricated by direct-current electrodeposition in pores of anodic aluminum oxide templates. High voltage is shown to be the key in order for Ni nanowires to have a (220) preferred orientation. 2-Dimensional nucleation theory is used to understand the growth of the nanowires. Based on the structure and growth analyses, the magnetic properties of different kinds of nanowires are explained. PMID:22618120

Tian, F; Huang, Z P; Whitmore, L

2012-05-22

221

Low-frequency noise in serial arrays of MgO-based magnetic tunnel junctions  

Microsoft Academic Search

We have studied the low-frequency noise in MgO-based magnetic tunnel junctions (MTJs) in serial configurations. Two types of junctions were compared: MTJ Wheatstone bridges and MTJ discrete resistors closely packed on a wafer die. We have characterized each individual junction to ensure that they have uniform parameters such as linear field sensitivity and noise level. In the array of bridges,

Wenzhe Zhang; Qiang Hao; Gang Xiao

2011-01-01

222

High spatial resolution Hall sensor array for edge plasma magnetic field measurements  

SciTech Connect

A one-dimensional, high-spatial resolution, 20-element Hall sensor array has been developed to directly measure the edge plasma perpendicular magnetic field and its fluctuations as a function of radius with 4-mm resolution. The array employs new small-area, high-sensitivity indium antimonide (InSb) Hall probes in combination with a high-density seven-layer printed circuit board to provide for connections to supply Hall current, record the measured Hall voltage output signals, and mitigate inductive pickup. A combination of bench and in situ measurements is described that provides absolute calibration of the diagnostic array in the presence of a strong transverse magnetic field component that is approximately 1000 times greater than the perpendicular fluctuating field needed to be resolved by the diagnostic. The Hall probes calibrated using this method are capable of magnetic field measurements with a sensitivity of 7 V/T over the frequency band from 0 to 20 kHz.

Liu Yuhong; Maurer, David A.; Navratil, Gerald A.; Rivera, Nicholas [Department of Applied Physics and Applied Mathematics, Columbia University in the City of New York, New York, New York 10027 (United States)

2005-09-15

223

MAGNETIC INDUCTION MAPPING IN TEM OF MICRO AND NANO PATTERNED CO/NI ARRAYS.  

SciTech Connect

Understanding magnetic structures and properties of patterned magnetic films at nanometer length-scale is the area of immense technological and fundamental scientific importance. The patterned magnetic films can be used for magnetic sensing . applications, magnetic recording, magnetoelectronics, microactuators and hybrid magneto-superconducting devices. The optimization of film properties is crucially dependent on the understanding of their magnetic properties, which in turn, become sensitive to the specific geometry and, hence, magnetic configurations of a given system when the elements diminish in size. Recent progress in the field of noninterferometric phase retrieval brings the ordinary Fresnel microscopy to a new quantitative level, capable of recovering both the amplitude and phase of the object from the experimental images [1,2], and thus induction mapping of small magnetic elements with known geometry ranging from micro- to few nanometers in size. The key concept behind this approach is the improvement of phase recovery algorithm derived from the transport-of-intensity (TIE) equation with a fast-solution via Fourier transform. A number of quantitative in-situ TEM magnetization experiments can be realized now with the help of magnetic-field calibrated microscope (see, for example [3]). To demonstrate the practical use of the new approach in TEM magnetic imaging with nanoscale resolution we have prepared several films directly on 3mm TEM-grids: (a) square-patterned magnetic films of Co islands with size of 6 pm (Fig. 1), and (b) nano-patterned arrays of Ni-nanodots (Fig.2) with lateral size about 40nm. The Co-films were prepared in UHV system by electron-beam evaporation of Co through an appropriate mask onto 30-nm-thick Si{sub 3}N{sub 4} membrane. The thickness of magnetic elements was approximately 40 nm as determined by EELS. The array of Ni-nanodots on a carbon membrane was prepared by electron-beam TEM-nanolithography followed by oblique angle deposition. Both types of the patterned arrays for Co and Ni films have been characterized by the TEM/ED methods. They were found to have a polycrystalline microstructure with the average crystallite size {approx}10 and 7 nm respectively. The Co films consisted of mixture of cubic and hcp phases. To experimentally check the sensitivity of TIE-recovered phase information to local magnetic configurations a set of in-focus and out-of-focus images was recorded on CCD (llarlk) during the in-situ magnetizing experiments in JEOL3000F microscope at different magnifications using the Gatan Imaging Filter (GIF) as function of applied field (H) and/or specimen tilt angle ({var_phi}) under constant external field. The results of the image processing (Figs.1-2), strongly suggest that TIE-phase retrieval method is a powerful tool suitable for local induction mapping B(x,y) of in-plane magnetization of magnetic elements down to few nanometers scale. The method is fast, robust, insensitive to noise, does not require the holographic equipment, and can be applied to a wide class of objects. The quantitative results can be obtained for films of known or uniform thickness.

VOLKOV,V.V.; ZHU,Y.; MALAC,M.; LAU,J.W.; SCHOFIELD,M.A.

2002-08-04

224

2D to 3D crossover of the magnetic properties in ordered arrays of iron oxide nanocrystals.  

PubMed

The magnetic 2D to 3D crossover behavior of well-ordered arrays of monodomain ?-Fe(2)O(3) spherical nanoparticles with different thicknesses has been investigated by magnetometry and Monte Carlo (MC) simulations. Using the structural information of the arrays obtained from grazing incidence small-angle X-ray scattering and scanning electron microscopy together with the experimentally determined values for the saturation magnetization and magnetic anisotropy of the nanoparticles, we show that MC simulations can reproduce the thickness-dependent magnetic behavior. The magnetic dipolar particle interactions induce a ferromagnetic coupling that increases in strength with decreasing thickness of the array. The 2D to 3D transition in the magnetic properties is mainly driven by a change in the orientation of the magnetic vortex states with increasing thickness, becoming more isotropic as the thickness of the array increases. Magnetic anisotropy prevents long-range ferromagnetic order from being established at low temperature and the nanoparticle magnetic moments instead freeze along directions defined by the distribution of easy magnetization directions. PMID:23238262

Faure, Bertrand; Wetterskog, Erik; Gunnarsson, Klas; Josten, Elisabeth; Hermann, Raphaël P; Brückel, Thomas; Andreasen, Jens Wenzel; Meneau, Florian; Meyer, Mathias; Lyubartsev, Alexander; Bergström, Lennart; Salazar-Alvarez, German; Svedlindh, Peter

2013-02-01

225

Magnetic nanoparticles as gene delivery agents: enhanced transfection in the presence of oscillating magnet arrays  

Microsoft Academic Search

Magnetic nanoparticle-based gene transfection has been shown to be effective in combination with both viral vectors and with non-viral agents. In these systems, therapeutic or reporter genes are attached to magnetic nanoparticles which are then focused to the target site\\/cells via high-field\\/high-gradient magnets. The technique has been shown to be efficient and rapid for in vitro transfection and compares well

S. C. McBain; U. Griesenbach; S. Xenariou; A. Keramane; C. D. Batich; E. W. F. W. Alton; J. Dobson

2008-01-01

226

Measurement of magnetic field fluctuations within last closed flux surface with movable magnetic probe array in the JIPP T-IIU tokamak  

Microsoft Academic Search

Poloidal and radial magnetic field fluctuations less than 100 kHz are measured with a newly developed movable magnetic probe array in the JIPP T-IIU tokamak. The probe array protected by a carbon-carbon composite with 20% boron is inserted beyond the last closed flux surface (LFCS) up to r\\/a 0.77 without deleterious effect on ohmically and neutra beam heated plasmas. From

K Kitachi; T Oike; S Ohdachi; K Toi; R Akiyama; A Ejiri; Y Hamada; H Kuramoto; K Narihara; T Seki

1997-01-01

227

Coupled microstructural and magnetic transition in Co-doped Ni nano-arrays  

NASA Astrophysics Data System (ADS)

A superparamagnetic (SM) to ferromagnetic (FM) phase transition was investigated in Co-doped (~6%) electroless plated Ni arrays. The introduction of Co altered the microstructure of the Ni arrays from nanocrystalline to polycrystalline, resulting in a SM-->FM transition. This Co-induced magnetic phase transition is similar to that observed after heat treatment of undoped samples [C. M. Liu, Y. C. Tseng, C. Chen, M. C. Hsu, T. Y. Chao, and Y. T. Cheng, Nanotechnology 20, 415703 (2009); C. C. Huang, C. C. Lo, Y. C. Tseng, C. M. Liu, and C. Chen, J. Appl. Phys. 109, 113905 (2011)]. The role of Co dopant was identified electronically using x-ray magnetic spectroscopy, revealing that the transition modified the Ni host's electronic structure and enhanced its moment by effectively spin-polarizing the Ni 3d conduction band. This was distinctly different than in the heat treatment case, which underwent an electronically independent phase transition. The element-specific magnetic hysteresis of Co and Ni was also probed, which showed that the two elements were magnetically coupled.

Yang, Chao-Yao; Huang, Chun-Chao; Tseng, Yuan-Chieh; Liu, Chien-Min; Chen, Chih; Lin, Hong-Ji

2011-10-01

228

3Axis Magnetic Sensor Array System for Tracking Magnet's Position and Orientation  

Microsoft Academic Search

In medical diagnoses and treatments, e.g., the endoscopy, the dosage transition monitoring, it is often desirable to wirelessly track an object that moves through the human GI tract. In this paper, we present a magnetic localization and orientation system for such applications. This system uses a small magnet enclosed in the object to serve as excitation source. It does not

Chao Hu; Max Q.-H. Meng; Mrinal Mandal; Xiaona Wang

2006-01-01

229

Tuning the magnetization reversal process of FeCoCu nanowire arrays by thermal annealing  

NASA Astrophysics Data System (ADS)

Arrays of hexagonally ordered Fe28Co67Cu5 nanowires with tailored diameter from 18 to 27 nm were prepared by electroplating into anodic alumina templates and annealed in the temperature range of 300-600 °C, preserving but refining their bcc crystal structure. Despite the partial reduction of saturation magnetization and corresponding shape anisotropy after annealing at 500 °C, larger coercivity, 0.36 T, and squareness ratio, Mr/Ms = 0.98, were obtained. This unexpected behavior is interpreted through micromagnetic simulations where the magnetic hardening is associated with the transition from vortex to transverse domain-wall reversal modes connected with the reduction of saturation magnetization. Simulations also predict a significant coercivity increase with decreasing nanowires diameter which agrees with experimental data in the overlapping diameter range.

Bran, C.; Ivanov, Yu. P.; García, J.; del Real, R. P.; Prida, V. M.; Chubykalo-Fesenko, O.; Vazquez, M.

2013-07-01

230

dc properties of series-parallel arrays of Josephson junctions in an external magnetic field  

SciTech Connect

A detailed dc theory of superconducting multijunction interferometers has previously been developed by several authors for the case of parallel junction arrays. The theory is now extended to cover the case of a loop containing several junctions connected in series. The problem is closely associated with high-{ital T}{sub {ital c}} superconductors and their clusters of intrinsic Josephson junctions. These materials exhibit spontaneous interferometric effects, and there is no reason to assume that the intrinsic junctions form only parallel arrays. A simple formalism of phase states is developed in order to express the superconducting phase differences across the junctions forming a series array as functions of the phase difference across the weakest junction of the system, and to relate the differences in critical currents of the junctions to gaps in the allowed ranges of their phase functions. This formalism is used to investigate the energy states of the array, which in the case of different junctions are split and separated by energy barriers of height depending on the phase gaps. Modifications of the washboard model of a single junction are shown. Next a superconducting inductive loop containing a series array of two junctions is considered, and this model is used to demonstrate the transitions between phase states and the associated instabilities. Finally, the critical current of a parallel connection of two series arrays is analyzed and shown to be a multivalued function of the externally applied magnetic flux. The instabilities caused by the presence of intrinsic serial junctions in granular high-{ital T}{sub {ital c}} materials are pointed out as a potential source of additional noise.

Lewandowski, S.J. (Instytut Fizyki, Polska Akademia Nauk, Al. Lotnikow 32, PL 02-668 Warszawa, Poland (PL))

1991-04-01

231

Design and Experimental Verification of a Linear Permanent Magnet Generator for a Free-Piston Energy Converter  

Microsoft Academic Search

This paper discusses issues that are pertinent to the design of a linear permanent magnet generator for application in a free-piston energy converter. To achieve the required high power density, high efficiency, and low moving mass, a tubular machine equipped with a modular stator winding and a quasi-Halbach magnetized armature is employed. It is shown that the machine design can

Jiabin Wang; David Howe; Hector Zelaya-De La Parra; Waqas M. Arshad

2007-01-01

232

Skew angle effects in shingled magnetic recording system with double/triple reader head array  

NASA Astrophysics Data System (ADS)

Shingled Magnetic Recording (SMR) is a scheme used to extend the life of the current perpendicular magnetic recording technology. SMR enables writing narrow tracks with a wide writer. Currently, SMR employs a single reader and will suffer inter-track interference (ITI) as the tracks become comparable in width to the reader. ITI can be mitigated by using narrower readers; however, narrower readers suffer from increased reader noise. Another approach to combat ITI is to process 2D readback and use ITI cancellation schemes to retrieve the data track. Multiple readbacks can be obtained either with a single reader and multiple revolutions or with a reader array. The former suffers from increased readback latency. In this work, we focus on the latter. When using a reader array, the skew angle poses major challenges. During writing, there is increased adjacent track erasure, and during readback the effective reader pitch varies and there is an increase in the 2D intersymbol interference caused by the rotated reader profile. In this work, we run micromagnetic simulations at different skew angles to train the grain flipping probability model, and then evaluate raw bit channel error rate performance at skew. In particular, we investigate the performance degradation caused by skewing of the 2 or 3 read head array for various read-head geometries.

Elidrissi, Moulay Rachid; Sann Chan, Kheong; Greaves, Simon; Kanai, Yasushi; Muraoka, Hiroaki

2014-05-01

233

Electrodeposition of Bi(x)Fe(1-x) intermetallic compound nanowire arrays and their magnetic properties.  

PubMed

There have been few reports on Bi-Fe intermetallic compounds because Bi and Fe are immiscible in the equilibrium states and neither alloy nor intermetallic compound exists in the binary system. In this paper, we show that, by using the nanometer-scale templates based synthesis in conjunction with the electrochemical deposition, it is possible to mix in solid solution elements that are immiscible in traditional fabrication methods. The preparation of Bi-Fe intermetallic compound nanowire arrays was investigated via an electrodeposition route by using a polycarbonate (PC) membrane template. Cyclic voltammetry, potentiostatic transient, and potentiostatic stripping were used to study the formation of Bi(x)Fe(1-x) intermetallic compounds. The compositions of Bi(1-x)Fe(x) intermetallic compound nanowire arrays were sensitive to the bath compositions and the electrodeposition potentials, and the length could be easily adjusted by varying the electrodeposition time. The electrodeposited Bi(1-x)Fe(x) intermetallic compound nanowire arrays had a parallel-to-the-wire easy magnetization. Furthermore, the spin-glass such as behavior and an unusually large characteristic time, which was about 5.26 h, were found in Bi(1-x)Fe(x) intermetallic compound nanowire arrays at room temperature. PMID:16671702

Li, Gao-Ren; Tong, Ye-Xiang; Kay, Lin-Gang; Liu, Guan-Kun

2006-05-11

234

Ferromagnetic resonance investigation in permalloy magnetic antidot arrays on alumina nanoporous membranes  

NASA Astrophysics Data System (ADS)

The magnetic properties of Ni80Fe20 antidot arrays with hole diameters of 18 and 70 nm fabricated by a template-assisted method were investigated using the ferromagnetic resonance technique. Tuning the antidot arrays by changing the hole diameter enables control on the angular dependence of the ferromagnetic resonance field. The scanning electron microscope images reveal a quite regular hexagonal arrangement of the pores, however the angular dependence of the resonance field do not exhibit the six-fold symmetry expected for this symmetry. Micromagnetic simulations performed on a perfect hexagonal lattice, when compared with those made on our real system taken from the scanning microscope images, reveal that the presence of defects in the antidot lattice affects the ferromagnetic resonance field symmetry.

Rodríguez-Suárez, R. L.; Palma, J. L.; Burgos, E. O.; Michea, S.; Escrig, J.; Denardin, J. C.; Aliaga, C.

2014-01-01

235

Spectral gap of shear Alfven waves in a periodic array of magnetic mirrors  

SciTech Connect

A multiple magnetic mirror array is formed at the Large Plasma Device (LAPD) [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991)] to study axial periodicity-influenced Alfven spectra. Shear Alfven waves (SAW) are launched by antennas inserted in the LAPD plasma and diagnosed by B-dot probes at many axial locations. Alfven wave spectral gaps and continua are formed similar to wave propagation in other periodic media due to the Bragg effect. The measured width of the propagation gap increases with the modulation amplitude as predicted by the solutions to Mathieu's equation. A two-dimensional finite-difference code modeling SAW in a mirror array configuration shows similar spectral features. Machine end-reflection conditions and damping mechanisms including electron-ion Coulomb collision and electron Landau damping are important for simulation.

Zhang Yang; Heidbrink, W. W.; Boehmer, H.; McWilliams, R.; Chen, Guangye; Breizman, B. N.; Vincena, S.; Carter, T.; Leneman, D.; Gekelman, W.; Pribyl, P.; Brugman, B. [Department of Physics and Astronomy, University of California, Irvine, California 92697 (United States); Department of Aerospace Engineering and Engineering Mechanics, University of Texas, Austin, Texas 78712 (United States); Institute for Fusion Studies, University of Texas, Austin, Texas 78712 (United States); Department of Physics and Astronomy, University of California, Los Angeles, California 90095 (United States)

2008-01-15

236

Conditions for free magnetic monopoles in nanoscale square arrays of dipolar spin ice  

NASA Astrophysics Data System (ADS)

We study a modified frustrated dipolar array recently proposed by Möller and Moessner [Phys. Rev. Lett. 96, 237202 (2006)]10.1103/PhysRevLett.96.237202, which is based on an array manufactured lithographically by Wang [Nature (London) 439, 303 (2006)]10.1038/nature04447 and consists of introducing a height offset h between islands (dipoles) pointing along the two different lattice directions. The ground states and excitations are studied as a function of h . We have found, in qualitative agreement with the results of Möller and Moessner, that the ground state changes for h>h1 , where h1=0.444a ( a is the lattice parameter or distance between islands). In addition, the excitations above the ground-state behave like magnetic poles but confined by a string, whose tension decreases as h increases, in such a way that for h?h1 its value is around 20 times smaller than that for h=0 . The system exhibits an anisotropy in the sense that the string tension and magnetic charge depends significantly on the directions in which the monopoles are separated. In turn, the intensity of the magnetic charge abruptly changes when the monopoles are separated along the direction of the longest axis of the islands. Such a gap is attributed to the transition from the antiferromagnetic to the ferromagnetic ground state when h=h1 .

Mól, L. A. S.; Moura-Melo, W. A.; Pereira, A. R.

2010-08-01

237

Remediation of hydrophobic, persistent pollutants using a magnetic permanently confined micelle array (Mag-PCMA)  

NASA Astrophysics Data System (ADS)

Natural and anthropogenic factors have resulted in the deposition of hydrophobic organic contaminants (HOCs) like PAHs and PCBs in elevated levels in soils and sediments. Currently there are 150 Superfund sites in the United States with contaminated sediments. Dredging is the most common practice for restoring Superfund sites to their preexisting conditions; this requires the transport of large volumes of material off-site for additional storage or processing. Our lab has designed a nano-hybrid material that can be used on-site; it combines a magnetic nanoscale iron oxide core coated with a cationic surfactant and is encased in a mesoporous silica matrix, called magnetic permanently confined micelle arrays, (Mag-PCMAs). This sorbent has been designed to remove HOCs from such scenarios. Surfactants are important in the enhancement of transport from binding sites in nature, such as organic matter, onto sorbents and other recoverable materials. The sorbent’s magnetic core allows for rapid separation by applying a magnetic field. It has also been shown to be reusable and maintain a removal efficiency of 95% over five cycles of reuse. Preliminary sorption studies show that the sorbent is capable of removing up to 98% of hydrophobic compounds from aqueous media. Current sorption studies are being done to test the efficiency of removing PAHs and PCBs from sediments, soils, and suspended sediments. Physicochemical properties that will influence the desorption/sorption hysteresis are being characterized to determine which properties enhance desorption from the contaminated media onto the Mag-PCMAs. Relevant applications are diverse as this material has the potential to recover a variety of HOCs in both ex situ and in situ remediation scenarios. Magnetic Permanently Confined Micelle Arrays

Clark, K. K.; Keller, A. A.

2009-12-01

238

Switching modes in easy and hard axis magnetic reversal in a self-assembled antidot array  

NASA Astrophysics Data System (ADS)

We study the reversal mechanisms in a self-assembled, hexagonally ordered Fe antidot array with a period of 200 nm and an antidot diameter of 100 nm which was prepared by polystyrene nanosphere lithography. Direction-dependent information in such a self-assembled sample is obtained by measuring the anisotropic magnetoresistance (AMR) through constrictions processed by focused ion beam milling in nearest neighbor and next nearest neighbor directions. We show that such an originally integral method can be used to investigate the strong in-plane anisotropy introduced by the antidot lattice. The easy and hard axis reversal mechanisms and corresponding AMR signals are modeled by micromagnetic simulations. Additional in-field magnetic force microscopy studies allow the correlation of microscopic switching to features in the integral AMR. We find that the easy axis of magnetization is connected to a distinct periodic magnetic domain pattern, which can be observed during the whole magnetization reversal. While this process is driven by nucleation and propagation of reversed domains, the hard axis reversal is characterized by a (stepwise) rotation of the magnetization via the antidot lattice’ easy axes.

Haering, Felix; Wiedwald, Ulf; Nothelfer, Steffen; Koslowski, Berndt; Ziemann, Paul; Lechner, Lorenz; Wallucks, Andreas; Lebecki, Kristof; Nowak, Ulrich; Gräfe, Joachim; Goering, Eberhard; Schütz, Gisela

2013-11-01

239

Direct patterning of magnetic media via focusing light by microsphere arrays  

NASA Astrophysics Data System (ADS)

An approach to nanoscale patterning using focused laser beams by two-dimensional lattices of microspheres is presented. The arrays were positioned in a controllable way near the sample surface with submicron accuracy to find the focal plane. This technique has been applied for direct patterning of Fe-Cr layers which exhibit laser-induced modifications in magnetic properties. The obtained data indicate the occurrence of some irregularities in the patterned features. To understand: (1) The reasons for the observed irregularities and (2) how small patterned features can be obtainable, the Mie solution for the intensity of scattered light has been used.

Polushkin, Nikolay I.

2005-03-01

240

Standing-wave excited soft x-ray photoemission microscopy: application to Co microdot magnetic arrays  

SciTech Connect

We demonstrate the addition of depth resolution to the usual two-dimensional images in photoelectron emission microscopy (PEEM), with application to a square array of circular magnetic Co microdots. The method is based on excitation with soft x-ray standing-waves generated by Bragg reflection from a multilayer mirror substrate. Standing wave is moved vertically through sample simply by varying the photon energy around the Bragg condition. Depth-resolved PEEM images were obtained for all of the observed elements. Photoemission intensities as functions of photon energy were compared to x-ray optical calculations in order to quantitatively derive the depth-resolved film structure of the sample.

Gray, Alexander; Kronast, Florian; Papp, Christian; Yang, See-Hun; Cramm, Stefan; Krug, Ingo P.; Salmassi, Farhad; Gullikson, Eric M.; Hilken, Dawn L.; Anderson, Erik H.; Fischer, Peter; Durr, Hermann A.; Schneider, Claus M.; Fadley, Charles S.

2010-10-29

241

Magnetically-Channeled SIEC Array (MCSA) Fusion Device for Interplanetary Missions  

NASA Astrophysics Data System (ADS)

A radical new Inertial Electrostatic Confinement (IEC) concept, the Magnetically-Channeled Spherical-IEC Array (MCSA) fusion propulsion system, was proposed earlier for use in the high performance Space Ship II fusion propulsion ship (Burton, 2003). This ship was designed for a fast manned round trip mission to Jupiter. The MCSA fusion power plant represents a key enabling technology needed for this mission. The details of the proposed MCSA design are presented here, along with a discussion of some possible experiments that could be performed to confirm key physics aspects.

Miley, G. H.; Stubbers, R.; Webber, J.; Momota, H.

2004-02-01

242

Implementation of a decoupled controller for a magnetic suspension system using electromagnets mounted in a planar array  

NASA Technical Reports Server (NTRS)

An implementation of a decoupled, single-input/single-output control approach for a large angle magnetic suspension test fixture is described. Numerical and experimental results are presented. The experimental system is a laboratory model large gap magnetic suspension system which provides five degree-of-freedom control of a cylindrical suspended element. The suspended element contains a core composed of permanent magnet material and is levitated above five electromagnets mounted in a planar array.

Cox, D. E.; Groom, N. J.

1994-01-01

243

Low-frequency noise in serial arrays of MgO-based magnetic tunnel junctions  

NASA Astrophysics Data System (ADS)

We have studied the low-frequency noise in MgO-based magnetic tunnel junctions (MTJs) in serial configurations. Two types of junctions were compared: MTJ Wheatstone bridges and MTJ discrete resistors closely packed on a wafer die. We have characterized each individual junction to ensure that they have uniform parameters such as linear field sensitivity and noise level. In the array of bridges, the low-frequency noise decreases with an increasing number (N) of bridges, but does not scale with 1/N, as expected from noise theory. The deviation is likely due to the statistical dispersions in MTJ bridge resistance and normalized voltage noise. The total noise of the discrete resistor series does not scale with 1/N either, but rather exhibits a sinusoidal-like variation with N. We attribute it to the possible enhancement of noise from magnetic coupling among the tightly spaced MTJ elements.

Zhang, Wenzhe; Hao, Qiang; Xiao, Gang

2011-09-01

244

Template-based synthesis and magnetic properties of Mn-Zn ferrite nanotube and nanowire arrays  

NASA Astrophysics Data System (ADS)

Template-based electrophoretic deposition of Mn-Zn ferrite nanotubes (NTs) and nanowires (NWs) were achieved using anodic alumina oxide (AAO) membranes. The effect of electrophoretic current and deposition time on the morphology of the tubes was investigated. The samples show cubic spinel structure with no preferred orientation. Room-temperature magnetic properties of the Mn-Zn ferrite NT/NW arrays were studied. The magnetic easy axis parallels the NT/NW's channel axis attributing to the large shape anisotropy in this direction, especially for the NTs with a small wall thickness. Magnetocrystalline anisotropy and magnetostatic interactions were found dominant in the samples when applied field was perpendicular to the channel axis.

Guo, Limin; Wang, Xiaohui; Zhong, Caifu; Li, Longtu

2012-01-01

245

Cryogenic characterization and testing of magnetically-actuated microshutter arrays for the James Webb Space Telescope  

NASA Astrophysics Data System (ADS)

Two-dimensional MEMS microshutter arrays (MSA) have been fabricated at the NASA Goddard Space Flight Center (GSFC) for the James Webb Space Telescope (JWST) to enable cryogenic (~35 K) spectrographic astronomy measurements at near-infrared wavelengths. Functioning as a focal plane object selection device, the MSA is a 2D programmable aperture mask with fine resolution, high efficiency and high contrast. The MSA are close-packed silicon nitride shutters (cell size of 100 µm × 200 µm) patterned with a torsion flexure to allow their opening to 90°. A layer of magnetic material is deposited onto each shutter to permit magnetic actuation. Two electrodes are deposited, one onto each shutter and another onto the support structure side-wall, permitting electrostatic latching and 2D addressing. New techniques were developed to test MSA under mission-similar conditions (8 K <= T < 300 K). The 'magnetic rotisserie' has proven to be an excellent tool for rapid characterization of MSA. Tests conducted with the magnetic rotisserie method include accelerated cryogenic lifetesting of unpackaged 128 × 64 MSA and parallel measurement of the magneto-mechanical stiffness of shutters in 'pathfinder' test samples containing multiple MSA designs. Lifetest results indicate a logarithmic failure rate out to ~106 shutter actuations. These results have increased our understanding of failure mechanisms and provide a means to predict the overall reliability of MSA devices.

King, T. T.; Kletetschka, G.; Jah, M. A.; Beamesderfer, M. A.; Li, M. J.; Wang, L. L.; Moseley, S. H.; Sparr, L. M.; Jhabvala, M. D.; Kutyrev, A. S.; Silverberg, R. F.; Rapchun, D.; Zheng, Y.; Schwinger, D. S.; Voellmer, G. M.

2005-08-01

246

Cryogenic Characterization and Testing of Magnetically-Actuated Microshutter Arrays for the James Webb Space Telescope  

NASA Technical Reports Server (NTRS)

Two-dimensional MEMS microshutter arrays (MSA) have been fabricated at the NASA Goddard Space Flight Center (GSFC) for the James Webb Space Telescope (JWST) to enable cryogenic (approximately 35 K) spectrographic astronomy measurements in the near-infrared region. Functioning as a focal plane object selection device, the MSA is a 2-D programmable aperture mask with fine resolution, high efficiency and high contrast. The MSA are close- packed silicon nitride shutters (cell size of 100 x 200 microns) patterned with a torsion flexure to allow opening to 90 degrees. A layer of magnetic material is deposited onto each shutter to permit magnetic actuation. Two electrodes are deposited, one onto each shutter and another onto the support structure side-wall, permitting electrostatic latching and 2-D addressing. New techniques were developed to test MSA under mission-similar conditions (8 K less than or equal to T less than 300K). The magnetic rotisserie has proven to be an excellent tool for rapid characterization of MSA. Tests conducted with the magnetic rotisserie method include accelerated cryogenic lifetesting of unpackaged 128 x 64 MSA and parallel measurement of the magneto-mechanical stiffness of shutters in pathfinder test samples containing multiple MSA designs. Lifetest results indicate a logarithmic failure rate out to approximately 10(exp 6) shutter actuations. These results have increased our understanding of failure mechanisms and provide a means to predict the overall reliability of MSA devices.

King, T. T.; Kletetschka, G.; Jah, M. A.; Li, M. J.; Jhabvala, M. D.; Wang, L. L.; Beamesderfer, M. A.; Kutyrev, A. S.; Silverberg, R. F.; Rapchun, D.; Schwinger, D. S.

2004-01-01

247

Graphoepitaxy of cylinder-forming block copolymers for use as templates to pattern magnetic metal dot arrays  

Microsoft Academic Search

We report a method to fabricate high-quality patterned magnetic dot arrays using block copolymer lithography, metal deposition, and a dry lift-off technique. Long-range order of cylindrical domains oriented perpendicular to the substrate and in hexagonal arrays was induced in the block copolymer films by prepatterning the substrate with topographic features and chemically modifying the surface to exhibit neutral wetting behaviour

Shuaigang Xiao; XiaoMin Yang; Erik W Edwards; Young-Hye La; Paul F Nealey

2005-01-01

248

Solid-State MultiSensor Array System for Real Time Imaging of Magnetic Fields and Ferrous Objects  

Microsoft Academic Search

In this paper the development of a solid-state sensors based system for real-time imaging of magnetic fields and ferrous objects is described. The system comprises 1089 magneto inductive solid state sensors arranged in a 2D array matrix of 33×33 files and columns, equally spaced in order to cover an approximate area of 300 by 300 mm. The sensor array is

D. Benitez; P. Gaydecki; S. Quek; V. Torres

2008-01-01

249

Measurements of the Axial Magnetic Field during the Implosion of Wire Arrays in the Angara-5-1 Facility  

SciTech Connect

Results are presented from measurements of the axial magnetic field during the implosion of tungsten wire arrays in the Angara-5-1 facility at currents of 2.5-4.5 MA. The azimuthal structure of the plasma produced from the wires is examined using the effect of the compression of the axial magnetic flux by this plasma. It is shown that the plasma starts to penetrate into the axial region of the wire array at the very beginning of implosion. A mechanism other than the formation of a closed current-carrying shell is proposed for describing the transfer of the external axial magnetic field to the central region of the array.

Zukakishvili, G.G.; Mitrofanov, K.N.; Grabovskii, E.V.; Oleinik, G.M. [Troitsk Institute for Innovation and Fusion Research, Troitsk, Moscow oblast, 142190 (Russian Federation)

2005-08-15

250

Study of the magnetic fields and soft X-ray emission generated in the implosion of double wire arrays  

SciTech Connect

Results are presented from measurements of the azimuthal magnetic field generated during the implosion of double (nested) tungsten wire arrays in the Angara-5-1 facility at currents of {approx}3 MA. It is found that the inner array affects the current distribution in the interarray space and that there is an optimal mass (an optimal number of wires) of the inner array at which the full width at half-maximum of the soft X-ray pulse (in the photon energy range of >100 eV) is minimal. On the average, double wire arrays provide a better reproductibility, higher power, and shorter duration of the soft X-ray pulse in comparison to single arrays.

Grabovskii, E. V.; Zukakishvili, G. G.; Mitrofanov, K. N.; Oleinik, G. M.; Frolov, I. N. [Troitsk Institute for Innovation and Fusion Research (Russian Federation); Sasorov, P. V. [Institute of Theoretical and Experimental Physics (Russian Federation)

2006-01-15

251

Development of novel techniques to study the magnetic field evolution in wire array Z-pinches and X pinches  

NASA Astrophysics Data System (ADS)

Understanding the magnetic field topology in wire-array Z-pinches is of great significance for their ultimate application to stockpile stewardship and inertial confinement fusion. We have developed and tested several novel techniques involving material-based sensors to measure magnetic fields as a function of space and time in high energy density plasmas on pulsed power machines. We first briefly introduce a technique that was used to measure a lower limit of the maximum magnetic field of a sub-microsecond duration pulse using magnetic reversal in CoPt thin films. The time-varying magnetic field was generated by an exploding wire array plasma called an X pinch produced on the 0.5 MA, 100 ns pulse duration, XP pulsed power generator. We then introduce a technique based on Faraday rotation that was used to measure magnetic fields in wire-array Z-pinches produced on the 1 MA, 100 ns rise time, COBRA pulsed power generator as well as on the XP generator. This technique measures magnetic fields as a function of space and time using Faraday rotation of a single longitudinal mode (SLM) laser through a magneto-optically active bulk waveguide, multicomponent terbium borate glass, placed adjacent to, or within, the wire array. We have measured fields > 10 T with 100 ns rise times outside of a wire-array Z-pinch for the entire duration (˜250 ns) of the current pulse and as much as ˜2 T inside a wire-array for ˜40 ns from the start of current. This is the first time that such rapidly varying and large fields have been measured using the terbium borate glass. The third method, also based on Faraday rotation of SLM laser light utilized an integrated optical fiber sensor (a fiber-sensor-fiber assembly) on the XP pulsed power generator that also yielded a measurement of the magnetic field of a wire-array Z-pinch for part of the current pulse. Finally, we repeated the third method by fabricating a "thin film waveguide" of terbium borate glass to increase the spatial resolution of the measurement. The thin film waveguide was then coupled to an optical fiber system. Although we successfully fabricated thin film nanowaveguides of terbium borate glass, the first time such waveguides have been made, due to poor coupling efficiency of light between components, preliminary Faraday rotation measurements were unsuccessful. The technique developed in this dissertation is potentially viable for magnetic field measurements in high current pulsed power systems if the device is protected from intimate interaction with the high energy density plasma during the time that a magnetic field measurement is to be made.

Syed, Wasif

252

Resolving sub-cellular force dynamics using arrays of magnetic microposts  

NASA Astrophysics Data System (ADS)

The biological response of cells to mechanical forces is integral to both normal cell function and the progression of many diseases, such as hypertensive vascular wall thickening. This likely results from the fact that mechanical stresses can directly affect many cellular processes, including signal transduction, gene expression, growth, differentiation, and survival. The need to understand the relationship between applied forces and the mechanical response of cells as a critical step towards understanding mechanotransduction calls for tools that can apply forces to cells while measuring their contractile response. This talk will describe an approach that simultaneously allows local mechanical stimulation of the adherent surface of a cell and spatially resolved measurement of the local force fields generated throughout the cell in response to this stimulation. Cells are cultured on the top surfaces of arrays of micrometer-scale posts made from a flexible elastomer (PDMS), and the contractile forces generated by an adherent cell bend the posts. Measurements of the displacement of each post allow the contractile force field of the cell to be mapped out with sub-cellular precision. To apply forces to cells, rod- shaped magnetic nanoparticles are embedded in some of the posts so that externally applied magnetic fields selectively deform these ``magnetic posts,'' thereby exerting tunable local, mechanical stresses to the adherent surface of attached cells. Alternatively, magnetic particles bound to or internalized by the cell may be employed to apply forces and torques to the cell. With either approach, measuring the deflection of the surrounding non-magnetic posts probes the full mechanical response of the cell to these stresses. Results that illustrate the temporal dynamics and spatial distribution of the non-local response of fibroblasts and smooth muscle cells to local stresses will be discussed.

Reich, Daniel

2010-03-01

253

Magnetization reversal and dynamics in non-interacting NiFe mesoscopic ring arrays  

NASA Astrophysics Data System (ADS)

The dynamics of magnetization (M) reversal and relaxation as a function of temperature (T) are reported in three non-interacting NiFe ring arrays having fixed ring outer diameter and varying widths. Additionally, the dependence of M(H) loop on the angle (?) between magnetic field (H) and the plane of the rings is addressed. The M(H) loops show a double step transition from onion state (OS) to vortex state (VS) at all temperatures (T = 3 to 300 K) and angles (? = 0 to 90°). The critical reversal fields HC1 (OS to VS) and HC2 (VS to OS) show a pronounced dependence on T, ring width, and ?. Estimation of the transverse and vortex domain wall energies reveals that the latter is favored in the OS. The OS is also the remanent state in the smallest rings and decays with the effective energy scale (U0/T) of 50 and 32 meV/K at 10 and 300 K, respectively. The robust in-plane anisotropy of magnetization of ring assemblies is established by scaling the M(H) with ?.

Kaur, M.; Husale, S.; Varandani, D.; Gupta, A.; Senguttuvan, T. D.; Mehta, B. R.; Budhani, R. C.

2014-04-01

254

Exotic magnetism of s-electron cluster arrays: Ferromagnetism, ferrimagnetism and antiferromagnetism  

NASA Astrophysics Data System (ADS)

Alkali metal nanoclusters can be stabilized in the regular cages of zeolite crystals by the loading of guest alkali metals. Cages are connected by the sharing of windows of the framework, and arrayed in simple cubic, diamond and body centered cubic structures in zeolites A, X and sodalite, respectively. The s-electrons have the localized nature of nanoclusters with magnetic moments, and have mutual interactions through the windows of cages. They show exotic magnetism depending on the structure type of zeolites, the kind of alkali metals and the average loading density of alkali atoms per cage. In zeolite A, potassium clusters are formed in ?-cages that have an inside diameter of 11 Å. They exhibit ferromagnetic properties explained by the canted antiferromagnetism of the Mott insulator, where the 1 p-like degenerate orbitals of clusters play an essential role in the magnetic properties. Na-K alloy clusters generated at supercages and ?-cages of low-silica X (LSX) zeolite exhibit Néel's N-type ferrimagnetism at specific loading densities of alkali metals. Alkali metal clusters in sodalite show the ideal Heisenberg antiferromagnetism of the Mott insulator.

Nakano, Takehito; Hanh, Duong Thi; Nozue, Yasuo; Nam, Nguyen Hoang; Duan, Truong Cong; Araki, Shingo

2013-08-01

255

Correlations among magnetic, electrical and magneto-transport properties of NiFe nanohole arrays  

NASA Astrophysics Data System (ADS)

In this work, we use anodic aluminum oxide (AAO) templates to build NiFe magnetic nanohole arrays. We perform a thorough study of their magnetic, electrical and magneto-transport properties (including the resistance R(T), and magnetoresistance MR(T)), enabling us to infer the nanohole film morphology, and the evolution from granular to continuous film with increasing thickness. In fact, different physical behaviors were observed to occur in the thickness range of the study (2 nm < t < 100 nm). For t < 10 nm, an insulator-to-metallic crossover was visible in R(T), pointing to a granular film morphology, and thus being consistent with the presence of electron tunneling mechanisms in the magnetoresistance. Then, for 10 nm < t < 50 nm a metallic R(T) allied with a larger anisotropic magnetoresistance suggests the onset of morphological percolation of the granular film. Finally, for t > 50 nm, a metallic R(T) and only anisotropic magnetoresistance behavior were obtained, characteristic of a continuous thin film. Therefore, by combining simple low-cost bottom-up (templates) and top-down (sputtering deposition) techniques, we are able to obtain customized magnetic nanostructures with well-controlled physical properties, showing nanohole diameters smaller than 35 nm.

Leitao, D. C.; Ventura, J.; Teixeira, J. M.; Sousa, C. T.; Pinto, S.; Sousa, J. B.; Michalik, J. M.; De Teresa, J. M.; Vazquez, M.; Araujo, J. P.

2013-02-01

256

Research on ambient temperature passive magnetic bearings at the Lawrence Livermore National Laboratory  

SciTech Connect

Research performed at the Lawrence Livermore National Laboratory on the equilibrium and stability of a new class of ambient-temperature passive bearing systems is described. The basic concepts involved are: (1) Stability of the rotating system is only achieved in the rotating state. That is, disengaging mechanical systems are used to insure stable levitation at rest (when Earnshaw`s theorem applies). (2) Stable levitation by passive magnetic elements can be achieved if the vector sum of the force derivatives of the several elements of the system is net negative (i.e. restoring) for axial, transverse, and tilt-type perturbations from equilibrium. To satisfy the requirements of (2) using only permanent magnet elements we have employed periodic ``Halbach arrays.`` These interact with passive inductive loaded circuits and act as stabilizers, with the primary forces arising from axially symmetric permanent-magnet elements. Stabilizers and other elements needed to create compact passive magnetic bearing systems have been constructed. Novel passive means for stabilizing classes of rotor-dynamic instabilities in such systems have also been investigated.

Post, R.F.; Ryitov, D.D.` Smith, J.R.; Tung, L.S.

1997-04-01

257

Degradation of Phosphate Ester Hydraulic Fluid in Power Station Turbines Investigated by a Three-Magnet Unilateral Magnet Array  

PubMed Central

A three-magnet array unilateral NMR sensor with a homogeneous sensitive spot was employed for assessing aging of the turbine oils used in two different power stations. The Carr-Purcell-Meiboom-Gill (CPMG) sequence and Inversion Recovery-prepared CPMG were employed for measuring the 1H-NMR transverse and longitudinal relaxation times of turbine oils with different service status. Two signal components with different lifetimes were obtained by processing the transverse relaxation curves with a numeric program based on the Inverse Laplace Transformation. The long lifetime components of the transverse relaxation time T2eff and longitudinal relaxation time T1 were chosen to monitor the hydraulic fluid aging. The results demonstrate that an increase of the service time of the turbine oils clearly results in a decrease of T2eff,long and T1,long. This indicates that the T2eff,long and T1,long relaxation times, obtained from the unilateral magnetic resonance measurements, can be applied as indices for degradation of the hydraulic fluid in power station turbines.

Guo, Pan; He, Wei; Garcia-Naranjo, Juan C.

2014-01-01

258

Degradation of phosphate ester hydraulic fluid in power station turbines investigated by a three-magnet unilateral magnet array.  

PubMed

A three-magnet array unilateral NMR sensor with a homogeneous sensitive spot was employed for assessing aging of the turbine oils used in two different power stations. The Carr-Purcell-Meiboom-Gill (CPMG) sequence and Inversion Recovery-prepared CPMG were employed for measuring the 1H-NMR transverse and longitudinal relaxation times of turbine oils with different service status. Two signal components with different lifetimes were obtained by processing the transverse relaxation curves with a numeric program based on the Inverse Laplace Transformation. The long lifetime components of the transverse relaxation time T2eff and longitudinal relaxation time T1 were chosen to monitor the hydraulic fluid aging. The results demonstrate that an increase of the service time of the turbine oils clearly results in a decrease of T2eff,long and T1,long. This indicates that the T2eff,long and T1,long relaxation times, obtained from the unilateral magnetic resonance measurements, can be applied as indices for degradation of the hydraulic fluid in power station turbines. PMID:24736132

Guo, Pan; He, Wei; García-Naranjo, Juan C

2014-01-01

259

Development of a solid-state multi-sensor array camera for real time imaging of magnetic fields  

Microsoft Academic Search

The development of a real-time magnetic field imaging camera based on solid-state sensors is described. The final laboratory comprises a 2D array of 33 x 33 solid state, tri-axial magneto-inductive sensors, and is located within a large current-carrying coil. This may be excited to produce either a steady or time-varying magnetic field. Outputs from several rows of sensors are routed

D. Benitez; P. Gaydecki; S. Quek; V. Torres

2007-01-01

260

Magnetic rotation in 139Pm nucleus and introduction on a new Ge detector array  

NASA Astrophysics Data System (ADS)

This paper comprises two separate parts. First, we present the high-spin states in 139Pm nucleus. Two negative-parity dipole bands have been observed and assigned as ?h11/2??(h11/2)-2 and ?h11/2??(h11/2)-4 configurations. From the systematic comparison with neighboring nuclei and SPAC (Shears mechanism with Principal Axis Cranking) model calculations, the two bands can be suggested as magnetic rotational bands. In the other part of this paper, the construction of one new array of eight Clover and sixteen HPGe detectors has been introduced. The characteristics of the Clover detector have been presented and compared with Geant4 simulations.

Zhang, N. T.; Zhou, X. H.; Zhang, Y. H.; Guo, Y. X.; Lei, X. G.; Liu, M. L.; Zheng, Y.; Fang, Y. D.; Wang, J. G.; Guo, S.; Qiang, Y. H.; Wu, X. G.; Zheng, Y.

2013-05-01

261

Size and space controlled hexagonal arrays of superparamagnetic iron oxide nanodots: magnetic studies and application.  

PubMed

Highly dense hexagonally arranged iron oxide nanodots array were fabricated using PS-b-PEO self-assembled patterns. The copolymer molecular weight, composition and choice of annealing solvent/s allows dimensional and structural control of the nanopatterns at large scale. A mechanism is proposed to create scaffolds through degradation and/or modification of cylindrical domains. A methodology based on selective metal ion inclusion and subsequent processing was used to create iron oxide nanodots array. The nanodots have uniform size and shape and their placement mimics the original self-assembled nanopatterns. For the first time these precisely defined and size selective systems of ordered nanodots allow careful investigation of magnetic properties in dimensions from 50?nm to 10?nm, which delineate the nanodots are superparamagnetic, well-isolated and size monodispersed. This diameter/spacing controlled iron oxide nanodots systems were demonstrated as a resistant mask over silicon to fabricate densely packed, identical ordered, high aspect ratio silicon nanopillars and nanowire features. PMID:24072037

Ghoshal, Tandra; Maity, Tuhin; Senthamaraikannan, Ramsankar; Shaw, Matthew T; Carolan, Patrick; Holmes, Justin D; Roy, Saibal; Morris, Michael A

2013-01-01

262

Magnetic Resonance Elastography with a Phased-Array Acoustic Driver System  

PubMed Central

Dynamic Magnetic Resonance Elastography (MRE) quantitatively maps the stiffness of tissues by imaging propagating shear waves in the tissue. These waves can be produced from intrinsic motion sources (e.g., due to cardiac motion), from external motion sources that produce motion directly at depth in tissue (e.g., amplitude-modulated focused ultrasound), and from external actuators that produce motion at the tissue surface that propagates into the tissue. With external actuator setups, typically only a single transducer is used to create the shear waves, which in some applications might have limitations due to shadowing and attenuation of the waves. To address these limitations, a phased-array acoustic driver system capable of applying independently controlled waveforms to each channel was developed and tested. It was found that the system produced much more uniform illumination of the object, improving the quality of the elastogram. It was also found that the accuracy of the stiffness value of any arbitrary region of interest could be improved by obtaining maximal shear wave illumination with the phased array capability of the system.

Mariappan, Yogesh K; Rossman, Phillip J; Glaser, Kevin J; Manduca, Armando; Ehman, Richard L

2010-01-01

263

Structure and magnetic properties of Fe96- x Zr x B4 nanowire arrays  

NASA Astrophysics Data System (ADS)

Fe96- x Zr x B4 (1< x<12) nanowires were prepared by electrodepositing into anodic aluminum oxide templates. The diameter of nanowires used is 100 nm and the aspect ratio is 75. The structure of the nanowire arrays was studied by selected area electron diffraction, X-ray diffraction and Mössbauer spectrometer. The phase structure of Fe96- x Zr x B4 nanowires is changed from a crystalline phase to a homogenous amorphous phase with the increasing of Zr content. The Fe96- x Zr x B4 nanowires are composed of ?-Fe-like and Zr-rich FeZrB phases. With the increasing of Zr composition, the atoms of Fe site in both phases are more disorderly, and the ?-Fe-like phase decreasing with the FeZrB phase increasing. The anisotropy of Fe96- x Zr x B4 nanowires becomes more obvious with the increasing of Zr content, and the easy magnetizing axis is parallel to the nanowire arrays.

Fu, JunLi; Zhu, Min; Wang, WenZhong; Xue, DeSheng

2013-10-01

264

Geometrical Design of a Scalable Overlapping Planar Spiral Coil Array to Generate a Homogeneous Magnetic Field  

PubMed Central

We present a design methodology for an overlapping hexagonal planar spiral coil (hex-PSC) array, optimized for creation of a homogenous magnetic field for wireless power transmission to randomly moving objects. The modular hex-PSC array has been implemented in the form of three parallel conductive layers, for which an iterative optimization procedure defines the PSC geometries. Since the overlapping hex-PSCs in different layers have different characteristics, the worst case coil-coupling condition should be designed to provide the maximum power transfer efficiency (PTE) in order to minimize the spatial received power fluctuations. In the worst case, the transmitter (Tx) hex-PSC is overlapped by six PSCs and surrounded by six other adjacent PSCs. Using a receiver (Rx) coil, 20 mm in radius, at the coupling distance of 78 mm and maximum lateral misalignment of 49.1 mm (1/?3 of the PSC radius) we can receive power at a PTE of 19.6% from the worst case PSC. Furthermore, we have studied the effects of Rx coil tilting and concluded that the PTE degrades significantly when ? > 60°. Solutions are: 1) activating two adjacent overlapping hex-PSCs simultaneously with out-of-phase excitations to create horizontal magnetic flux and 2) inclusion of a small energy storage element in the Rx module to maintain power in the worst case scenarios. In order to verify the proposed design methodology, we have developed the EnerCage system, which aims to power up biological instruments attached to or implanted in freely behaving small animal subjects’ bodies in long-term electrophysiology experiments within large experimental arenas.

Jow, Uei-Ming; Ghovanloo, Maysam

2014-01-01

265

Electromagnetic vibration energy harvesting with high power density using a magnet array  

NASA Astrophysics Data System (ADS)

Electromagnetic vibration energy harvesters have been widely used to convert the vibration energy into electricity. However, one of the main challenges of using electromagnetic vibration energy harvesters is that they are usually in very large size with low power density. In this paper, a new type of electromagnetic vibration energy harvester with remarkably high power density is developed. By putting the strong rare-earth magnets in alternating directions and using high-magnetic-conductive casing, magnetic flux density up to 0.9T are obtained. This configuration also has a small current loop with less electrical reluctance, which further increases the high power density when the coil is designed to follow the current loop. The prototype, the size of which is 142x140x86 mm3, can provided up to 727Ns/m damping coefficient, which means 428 kNs/m4 damping density when it is shunt with 70? external resistive load which is set to the same as the internal resistor of the harvester to achieve maximum power. The corresponding power density is 725 ?W/cm3 at 15HZ harmonic force excitation of 2.54mm peak-to-peak amplitude. When shot-circuited, 1091Ns/m damping coefficient and 638 kNs/m4 damping density is achieved. The effectiveness of this novel vibration energy harvester is shown both by FEA and experiments. The eddy current damper is also discussed in this paper for comparison. The proposed configuration of the magnet array can also be extended for both micro-scale and large-scale energy harvesting applications, such as vibration energy harvesting from tall buildings, long bridges and railways.

Tang, Xiudong; Lin, Teng; Zuo, Lei

2012-03-01

266

An integrated and sensitive detection platform for biosensing application based on Fe@Au magnetic nanoparticles as bead array carries.  

PubMed

A sensitive and selective biosensor platform suited for SNP type using Fe@Au magnetic nanoparticles (GMNPs) to fabricate bead array is described. This new platform integrates the rapid binding kinetics of magnetic nanoparticles carriers, the multiplexing and encoding capabilities of chips, and tagged array. As a DNA sensor, the biotinylated single-stranded DNA was obtained by asymmetry PCR amplification, and then captured by GMNPs modified with streptavidin to form GMNP-ssDNA complexes without further purification. The complexes were immobilized on the slide to fabricate bead array through magnetic field. The bead array was hybridized with the corresponding allele-specific tag probes for each locus, and a pair of given universal detectors were applied to these markers analysis. Using bead array, all samples can be analyzed in one hybridization chamber which lowers the cost of the assay. Using universal tags, only a pair of universal dual-color probes labeled fluorophores was used for multiplex genotyping. Without the need of laborious and time-consuming elution, the experiment process was simple, reproducible and easy to handle. Two SNPs loci from 12 individual samples were discriminated using this platform and the results demonstrated that the expected scores and good discrimination were obtained between the two alleles from the two SNP loci. In summary, the integrated sensitive platform is adaptable and versatile, while offering a high-throughput capability needed for genome research and clinical applications. PMID:20728338

Liu, Hongna; Li, Song; Liu, Lishang; Tian, Lan; He, Nongyue

2010-12-15

267

3 Tesla magnetic resonance imaging of the prostate with combined pelvic phased-array and endorectal coils  

Microsoft Academic Search

Rationale and objectivesHigh-resolution magnetic resonance imaging of the prostate at 1.5T has gained acceptance for pretherapeutic staging of prostate cancer. The aim of this study was to evaluate the potential clinical utility of combined pelvic phased-array and endorectal coils at 3T.

B. Nicolas Bloch; Neil M Rofsky; Ronaldo H Baroni; Robert P Marquis; Ivan Pedrosa; Robert E Lenkinski

2004-01-01

268

Endorectal ultrasonography versus phased-array magnetic resonance imaging for preoperative staging of rectal cancer  

PubMed Central

AIM: To compare the diagnostic accuracy of pelvic phased-array magnetic resonance imaging (MRI) and endorectal ultrasonography (ERUS) in the preoperative staging of rectal carcinoma. METHODS: Thirty-four patients (15 males, 19 females) with ages ranging between 29 and 75 who have biopsy proven rectal tumor underwent both MRI and ERUS examinations before surgery. All patients were evaluated to determine the diagnostic accuracy of depth of transmural tumor invasion and lymph node metastases. Imaging results were correlated with histopathological findings regarded as the gold standard and both modalities were compared in terms of predicting preoperative local staging of rectal carcinoma. RESULTS: The pathological T stage of the tumors was: pT1 in 1 patient, pT2 in 9 patients, pT3 in 21 patients and pT4 in 3 patients. The pathological N stage of the tumors was: pN0 in 19 patients, pN1 in 9 patients and pN2 in 6 patients. The accuracy of T staging for MRI was 89.70% (27 out of 34). The sensitivity was 79.41% and the specificity was 93.14%. The accuracy of T staging for ERUS was 85.29% (24 out of 34). The sensitivity was 70.59% and the specificity was 90.20%. Detection of lymph node metastases using phased-array MRI gave an accuracy of 74.50% (21 out of 34). The sensitivity and specificity was found to be 61.76% and 80.88%, respectively. By using ERUS in the detection of lymph node metastases, an accuracy of 76.47% (18 out of 34) was obtained. The sensitivity and specificity were found to be 52.94% and 84.31%, respectively. CONCLUSION: ERUS and phased-array MRI are complementary methods in the accurate preoperative staging of rectal cancer. In conclusion, we can state that phased-array MRI was observed to be slightly superior in determining the depth of transmural invasion (T stage) and has same value in detecting lymph node metastases (N stage) as compared to ERUS.

Halefoglu, Ahmet Mesrur; Yildirim, Sadik; Avlanmis, Omer; Sakiz, Damlanur; Baykan, Adil

2008-01-01

269

Geophysical Institute Magnetometer Array: Magnetic Field Data in Real-Time for Researchers  

NASA Astrophysics Data System (ADS)

Magnetometer data from eight remote stations across Alaska have been collected continuously since the early 1980's by the Geophysical Institute Magnetometer Array (GIMA). These three-axis, 1Hz data, with ~ 1 nT precision, are used to determine the currents associated with auroral activity in the Alaska polar regions. A primary function of the GIMA is to supply magnetic field deflection data in real time to researchers so they can determine when to launch a sub-orbital sounding rocket from the Poker Flat Research Range into the proper auroral conditions. The aurora is a key coupling mechanism between the Earth's magnetosphere and ionosphere, and the magnetometers are used to remotely sense the ionospheric currents associated with aurora. The real-time magnetometer data are displayed through a web-based interface that functions on desktop and mobile devices. The displays are highly configurable to allow researchers the flexibility to interpret the magnetic signature they need to make a successful launch decision. The data are also available for download within 24 hours of collection. The existence of real-time data has been and will continue to be critical for successful rocket launches, however the real-time system needs to improve to meet the ever growing needs of the user community. Planned upgrades will improve the reliability and resolution of the displays as well as the ease of data download, and integration into NASA virtual observatories.

Wolf, V. G.; Hampton, D. L.

2012-12-01

270

A digital magnetic resonance imaging spectrometer using digital signal processor and field programmable gate array.  

PubMed

A digital spectrometer for low-field magnetic resonance imaging is described. A digital signal processor (DSP) is utilized as the pulse programmer on which a pulse sequence is executed as a subroutine. Field programmable gate array (FPGA) devices that are logically mapped into the external addressing space of the DSP work as auxiliary controllers of gradient control, radio frequency (rf) generation, and rf receiving separately. The pulse programmer triggers an event by setting the 32-bit control register of the corresponding FPGA, and then the FPGA automatically carries out the event function according to preset configurations in cooperation with other devices; accordingly, event control of the spectrometer is flexible and efficient. Digital techniques are in widespread use: gradient control is implemented in real-time by a FPGA; rf source is constructed using direct digital synthesis technique, and rf receiver is constructed using digital quadrature detection technique. Well-designed performance is achieved, including 1 ?s time resolution of the gradient waveform, 1 ?s time resolution of the soft pulse, and 2 MHz signal receiving bandwidth. Both rf synthesis and rf digitalization operate at the same 60 MHz clock, therefore, the frequency range of transmitting and receiving is from DC to ~27 MHz. A majority of pulse sequences have been developed, and the imaging performance of the spectrometer has been validated through a large number of experiments. Furthermore, the spectrometer is also suitable for relaxation measurement in nuclear magnetic resonance field. PMID:23742570

Liang, Xiao; Binghe, Sun; Yueping, Ma; Ruyan, Zhao

2013-05-01

271

Directed Fluid Flow Produced by Arrays of Magnetically Actuated Core-Shell Biomimetic Cilia  

NASA Astrophysics Data System (ADS)

We have developed a novel core-shell microstructure that we use to fabricate arrays of flexible, magnetically actuated biomimetic cilia. Our biomimetic cilia mimic the size and beat shape of biological cilia in order to replicate the transport of fluid driven by cilia in many biological systems including the determination of left-right asymmetry in the vertebrate embryonic nodal plate and mucociliary clearance in the lung. Our core-shell structures consist of a flexible poly(dimethylsiloxane) (PDMS) core surrounded by a shell of nickel approximately forty nanometers thick; by using a core-shell structure, we can tune the mechanical and magnetic properties independently. We present the fabrication process and the long-range transport that occurs above the beating biomimetic cilia tips and will report on progress toward biomimetic cilia induced flow in viscoelastic fluids similar to mucus in the human airway. These flows may have applications in photonics and microfluidics, and our structures may be further useful as sensors or actuators in microelectromechanical systems.

Fiser, B. L.; Shields, A. R.; Evans, B. A.; Superfine, R.

2010-03-01

272

A digital magnetic resonance imaging spectrometer using digital signal processor and field programmable gate array  

NASA Astrophysics Data System (ADS)

A digital spectrometer for low-field magnetic resonance imaging is described. A digital signal processor (DSP) is utilized as the pulse programmer on which a pulse sequence is executed as a subroutine. Field programmable gate array (FPGA) devices that are logically mapped into the external addressing space of the DSP work as auxiliary controllers of gradient control, radio frequency (rf) generation, and rf receiving separately. The pulse programmer triggers an event by setting the 32-bit control register of the corresponding FPGA, and then the FPGA automatically carries out the event function according to preset configurations in cooperation with other devices; accordingly, event control of the spectrometer is flexible and efficient. Digital techniques are in widespread use: gradient control is implemented in real-time by a FPGA; rf source is constructed using direct digital synthesis technique, and rf receiver is constructed using digital quadrature detection technique. Well-designed performance is achieved, including 1 ?s time resolution of the gradient waveform, 1 ?s time resolution of the soft pulse, and 2 MHz signal receiving bandwidth. Both rf synthesis and rf digitalization operate at the same 60 MHz clock, therefore, the frequency range of transmitting and receiving is from DC to ~27 MHz. A majority of pulse sequences have been developed, and the imaging performance of the spectrometer has been validated through a large number of experiments. Furthermore, the spectrometer is also suitable for relaxation measurement in nuclear magnetic resonance field.

Liang, Xiao; Binghe, Sun; Yueping, Ma; Ruyan, Zhao

2013-05-01

273

Synthesis and Magnetism of High Curie Temperature Prussian Blue Analogue Molecular Nanomagnet-Chromium Cyanide Molecule Nanowire Arrays  

NASA Astrophysics Data System (ADS)

The goal to synthesize molecular nanomagnets that exhibit spontaneous magnetic ordering close to room temperature might enable one to apply them in the fields of magnetic memory devices and microelectronics. Chromium cyanide molecule nanowire arrays with diameters of about 50 nm and lengths up to 4?m have been synthesized by an electrodepositing technology based on anodizing anodic aluminum oxide films. Characterization measurements show that the oxidation state of the chromium ions in the chromium cyanide nanowires can be expressed as Cr^3+--CN--Cr^3+. Magnetic properties measurements indicate that the Curie temperature of chromium cyanide nanowire is 200 K, which is closer room temperature compared with current molecular nanomagnet systems.

Zhou, Pingheng; Xue, Desheng; Yao, Jinli

2009-03-01

274

Nonlinear effects in magnetic garnet films and nonreciprocal optical Bloch oscillations in waveguide arrays  

NASA Astrophysics Data System (ADS)

This dissertation presents detailed experimental and theoretical investigations of nonlinear and nonreciprocal effects in magnetic garnet films. The dissertation thus comprises two major sections. The first section concentrates on the study of a new class of nonlinear magneto-optic thin film materials possessing strong higher order magnetic susceptibility for nonlinear optical applications. The focus was on enlarging the nonlinear performance of ferrite garnet films by strain generation and compositional gradients in the sputter-deposition growth of these films. Under this project several bismuth-substituted yttrium iron garnet (Bi,Y)3(Fe,Ga)5O12 (acronym as Bi:YIG) films have been sputter-deposited over gadolinium gallium garnet (Gd 3Ga5O12) substrates and characterized for their nonlinear optical response. One of the important findings of this work is that lattice mismatch strain drives the second harmonic (SH) signal in the Bi:YIG films, in agreement with theoretical predictions; whereas micro-strain was found not to correlate significantly with SH signal at the micro-strain levels present in these films. This study also elaborates on the role of the film's constitutive elements and their concentration gradients in nonlinear response of the films. Ultrahigh sensitivity delivered by second harmonic generation provides a new exciting tool for studying magnetized surfaces and buried interfaces, making this work important from both a fundamental and application point of view. The second part of the dissertation addresses an important technological need; namely the development of an on-chip optical isolator for use in photonic integrated circuits. It is based on two related novel effects, nonreciprocal and unidirectional optical Bloch oscillations (BOs), recently proposed and developed by Professor Miguel Levy and myself. This dissertation work has established a comprehensive theoretical background for the implementation of these effects in magneto-optic waveguide arrays. The model systems we developed consist of photonic lattices in the form of one-dimensional waveguide arrays where an optical force is introduced into the array through geometrical design turning the beam sideways. Laterally displaced photons are periodically returned to a central guide by photonic crystal action. The effect leads to a novel oscillatory optical phenomenon that can be magnetically controlled and rendered unidirectional. An on-chip optical isolator was designed based on the unidirectionality of the magneto-opticBloch oscillatory motion. The proposed device delivers an isolation ratio as high as 36 dB that remains above 30 dB in a 0.7 nm wavelength bandwidth, at the telecommunication wavelength 1.55 mum. Slight modifications in isolator design allow one to achieve an even more impressive isolation ratio ~ 55 dB, but at the expense of smaller bandwidth. Moreover, the device allows multifunctionality, such as optical switching with a simultaneous isolation function, well suited for photonic integrated circuits.

Kumar, Pradeep

275

Autonomous low-power magnetic data collection platform to enable remote high latitude array deployment.  

PubMed

A major driver in the advancement of geophysical sciences is improvement in the quality and resolution of data for use in scientific analysis, discovery, and for assimilation into or validation of empirical and physical models. The need for more and better measurements together with improvements in technical capabilities is driving the ambition to deploy arrays of autonomous geophysical instrument platforms in remote regions. This is particularly true in the southern polar regions where measurements are presently sparse due to the remoteness, lack of infrastructure, and harshness of the environment. The need for the acquisition of continuous long-term data from remote polar locations exists across geophysical disciplines and is a generic infrastructure problem. The infrastructure, however, to support autonomous instrument platforms in polar environments is still in the early stages of development. We report here the development of an autonomous low-power magnetic variation data collection system. Following 2 years of field testing at the south pole station, the system is being reproduced to establish a dense chain of stations on the Antarctic plateau along the 40 degrees magnetic meridian. The system is designed to operate for at least 5 years unattended and to provide data access via satellite communication. The system will store 1 s measurements of the magnetic field variation (<0.2 nT resolution) in three vector components plus a variety of engineering status and environment parameters. We believe that the data collection platform can be utilized by a variety of low-power instruments designed for low-temperature operation. The design, technical characteristics, and operation results are presented here. PMID:19405679

Musko, Stephen B; Clauer, C Robert; Ridley, Aaron J; Arnett, Kennneth L

2009-04-01

276

The effects of annealing on the structure and magnetic properties of CoNi patterned nanowire arrays  

NASA Astrophysics Data System (ADS)

NiCo alloy nanowire arrays were fabricated by using an electrochemical method in a porous anodic aluminum oxide (PAO) template. X-ray-diffraction results showed that there was a preferred orientation in the CoNi nanowire arrays with Ni content ranging from 0.2 to 0.8 in the as-electro-deposited state, while a random orientation was observed after the sample was heat treated in an argon atmosphere. When the shape anisotropy is very high in the sample, it is found that the squareness (Mr/Ms) of the hysteresis loops for the samples is only about 0.6 before annealing, but increases to about 0.9 after annealing. All the results are discussed qualitatively and an explanation for the magnetic reversal mechanism in terms of a localized magnetization model is given. As the CoNi alloy nanowire arrays have high bit densities, they can be used as perpendicular magnetic recording media of high-density quantum magnetic disks.

Qin, D. H.; Wang, C. W.; Sun, Q. Y.; Li, H. L.

277

Magnetic property of a staggered-array undulator using a bulk high-temperature superconductor  

NASA Astrophysics Data System (ADS)

The magnetic field of a staggered-array undulator using a bulk high-temperature superconductor is calculated by analytical and numerical methods. Analytical formulas for the undulator field and the solenoid field required to generate the undulator field are derived from a simple two-dimensional model. The analytical calculation shows the degree of dependence of these fields on the undulator parameters, the generation of a high undulator field proportional to the critical current density of the bulk superconductor, and the good tunability of the undulator field over a wide range of values. The numerical calculation is performed in a three-dimensional geometry by two methods: the center field and energy minimization methods. The latter treats the current distribution inside the bulk, whereas the former neglects it as a natural extension of the analytical model. The calculation also reveals the dependence of the fields on the undulator parameters arising from the current distribution. From the comparison with experimental results, we find that the latter method reproduces the experimental results well, which indicates the importance of the current distribution inside the bulk. Therefore, we derive a semiempirical formula for the required solenoid field by modifying the analytical formula using the numerical results so as to include the effect of the current distribution. The semiempirical formula reproduces the numerical result with an error of 3%. Finally, we estimate the magnetic performance of the undulator as an example of using the formulas and values presented in this paper. The estimation shows that an undulator field twice as large as that of the present in-vacuum undulator but with an equal period and gap can be obtained at a temperature of approximately 20-40 K, and that deflection parameters (K values) of 1 and 2 can be achieved with periods of 5 and 10 mm at approximately 4-20 K.

Kinjo, Ryota; Mishima, Kenta; Choi, Yong-Woon; Omer, Mohamed; Yoshida, Kyohei; Negm, Hani; Torgasin, Konstantin; Shibata, Marie; Shimahashi, Kyohei; Imon, Hidekazu; Okumura, Kensuke; Inukai, Motoharu; Zen, Heishun; Kii, Toshiteru; Masuda, Kai; Nagasaki, Kazunobu; Ohgaki, Hideaki

2014-02-01

278

MAGNETIC INDUCTION MAPPING IN TEM OF MICRO AND NANO PATTERNED CO\\/NI ARRAYS  

Microsoft Academic Search

Understanding magnetic structures and properties of patterned magnetic films at nanometer length-scale is the area of immense technological and fundamental scientific importance. The patterned magnetic films can be used for magnetic sensing . applications, magnetic recording, magnetoelectronics, microactuators and hybrid magneto-superconducting devices. The optimization of film properties is crucially dependent on the understanding of their magnetic properties, which in turn,

V. V. VOLKOV; Y. ZHU; M. MALAC; J. W. LAU; M. A. SCHOFIELD

2002-01-01

279

Application of ferromagnetic nano-wires in porous alumina arrays for magnetic force generator  

Microsoft Academic Search

Magnetic chromatograph is a techniques that use magnetic force to separate small particles. It is interesting because the magnetic column can be used repeatedly and does not produce secondary wastes. In order to increase the efficiency of the separation, the magnetic force is desired to be as large as possible. The magnetic force increases in proportion to the magnetic field

S. Kato; H. Shinagawa; H. Okada; G. Kido; K. Mitsuhashi

2005-01-01

280

Controlled introduction of diameter modulations in arrayed magnetic iron oxide nanotubes.  

PubMed

To date, no large-scale preparative method for arrays of nanotube enables the experimentalist to arbitrarily define changes in the tubes' diameter along their length. To this goal, we start with anodic alumina substrates displaying controlled modulations in pore diameter obtained by alternating "mild" and "hard" electrochemical etching conditions. We then utilize atomic layer deposition (ALD) to coat the internal pore walls with conformal layers of an oxide. Ferromagnetic Fe(3)O(4) tubes of 10 nm wall thickness and 10-30 microm in length are thus prepared, which replicate the modulated silhouette of the template. Their magnetic properties strongly depend on the presence of diameter modulations. Introducing one or several very short segments of large diameter (150 nm) into an otherwise thin tube (70 nm diameter) brings its initially large coercive field down to a value close to the case of a homogeneously thick tube. Theoretical modeling emphasizes the major influence of the magnetostatic interactions between neighboring tubes. They are enhanced locally at the sites of diameter modulations, which directly translates into a reduction in coercive field. PMID:19803498

Pitzschel, Kristina; Moreno, Josep M Montero; Escrig, Juan; Albrecht, Ole; Nielsch, Kornelius; Bachmann, Julien

2009-11-24

281

Microfluidic sorting and multimodal typing of cancer cells in self-assembled magnetic arrays  

PubMed Central

We propose a unique method for cell sorting, “Ephesia,” using columns of biofunctionalized superparamagnetic beads self-assembled in a microfluidic channel onto an array of magnetic traps prepared by microcontact printing. It combines the advantages of microfluidic cell sorting, notably the application of a well controlled, flow-activated interaction between cells and beads, and those of immunomagnetic sorting, notably the use of batch-prepared, well characterized antibody-bearing beads. On cell lines mixtures, we demonstrated a capture yield better than 94%, and the possibility to cultivate in situ the captured cells. A second series of experiments involved clinical samples—blood, pleural effusion, and fine needle aspirates— issued from healthy donors and patients with B-cell hematological malignant tumors (leukemia and lymphoma). The immunophenotype and morphology of B-lymphocytes were analyzed directly in the microfluidic chamber, and compared with conventional flow cytometry and visual cytology data, in a blind test. Immunophenotyping results using Ephesia were fully consistent with those obtained by flow cytometry. We obtained in situ high resolution confocal three-dimensional images of the cell nuclei, showing intranuclear details consistent with conventional cytological staining. Ephesia thus provides a powerful approach to cell capture and typing allowing fully automated high resolution and quantitative immunophenotyping and morphological analysis. It requires at least 10 times smaller sample volume and cell numbers than cytometry, potentially increasing the range of indications and the success rate of microbiopsy-based diagnosis, and reducing analysis time and cost.

Saliba, Antoine-Emmanuel; Saias, Laure; Psychari, Eleni; Minc, Nicolas; Simon, Damien; Bidard, Francois-Clement; Mathiot, Claire; Pierga, Jean-Yves; Fraisier, Vincent; Salamero, Jean; Saada, Veronique; Farace, Francoise; Vielh, Philippe; Malaquin, Laurent; Viovy, Jean-Louis

2010-01-01

282

Design, fabrication, and calibration of a cryogenic search-coil array for harmonic analysis of quadrupole magnets  

SciTech Connect

A cryogenic search-coil array has been fabricated at LBL for harmonic error analysis of SSC model quadrupoles. It consists of three triplets of coils; the center-coil triplet is 10 cm long, and the end coil triplets are 70 cm long. Design objectives are a high bucking ratio for the dipole and quadrupole signals and utility at cryogenic operating currents (approx.6 kA) with sufficient sensitivity for use at room-temperature currents (approx.10 A). the design and fabrication are described. Individual coils are mechanically measured to +-5 ..mu..m, and their magnetic areas measured to 0.05%. A computer program has been developed to predict the quadrupole and dipole bucking ratios from the mechanical and magnetic measurements. The calibration procedure and accuracy of the array are specified. Results of measurements of SSC model quadrupoles are presented. 1 ref., 4 figs.

Green, M.I.; Barale, P.J.; Hassenzahl, W.V.; Nelson, D.H.; O'Neill, J.W.; Schafer, R.V.; Taylor, C.E.

1987-09-01

283

Enhanced magnetic performance of metal-organic nanowire arrays by FeCo/polypyrrole co-electrodeposition  

NASA Astrophysics Data System (ADS)

FeCo/polypyrrole (PPy) composite nanowire array, which shows enhanced magnetic remanence and coercivity along the nanowires, was fabricated by AC electrodeposition using anodic aluminum oxide templates. High resolution transmission electron microscopy shows that PPy grows on the surface of FeCo nanowires forming a coaxial nanowire structure, with a coating layer of about 4 nm. It suggests that the decreased dipolar interaction due to the reduced nanowire diameters is responsible for the enhancement of magnetic performance. The possible mechanism of this coating may be that PPy is inclined to nucleate along the pore wall of the templates.

Luo, X. J.; Xia, W. B.; Gao, J. L.; Zhang, S. Y.; Li, Y. L.; Tang, S. L.; Du, Y. W.

2013-05-01

284

Analysis of lightning induced magnetic field penetration through protective metal screens using an equivalent magnetic dipole moment representation of an array of elliptic apertures  

NASA Astrophysics Data System (ADS)

This investigation analyzed lightning induced magnetic field penetration through protective metal screens using an equivalent magnetic dipole moment representation of an array of elliptic apertures. Two metal screens with differing aperture sizes were modeled. Experiments, using lightning level currents, measured the magnetic field penetration through each screen. A comparison of model versus experimental results was performed. The effect of decreasing mesh sizes on field penetration is also presented. The analysis used linear superposition to sum the contributions from the magnetic dipole moment equivalent of each screen aperture. A computer program was developed to the number of screen model. Results indicate that the model is accurate in predicting the interior magnetic field decay rate with distance from the screen and in accounting for the increased protection provided by decreasing mesh sizes. The only model inaccuracies are the overestimates for interior magnetic field strengths. The overall results indicate that an equivalent magnetic dipole moment representation can be used to model lightning induced magnetic field penetration through protective metal screens.

Oneal, James L.

1986-12-01

285

Influence of asynchronous actuation of the Angara-5-1 facility modules on the penetration of the magnetic field inside a wire array  

NASA Astrophysics Data System (ADS)

The influence of asynchronous actuation of the Angara-5-1 facility modules on the implosion symmetry of the wire array plasma in the Z-pinch mode is studied. It is shown that an increase in the r.m.s. jitter in the start times of the modules leads to an appreciable azimuthal asymmetry of magnetic field penetration inside the wire array and, as a consequence, to an increase in the duration of the soft X-ray pulse, a decrease in its power, and a shift of the Z-pinch with respect to the array axis. Necessary conditions for axisymmetric pinch implosion are determined. Experimental data on the magnitude and azimuthal distribution of the current (magnetic field) inside the wire array were obtained from magnetic probe measurements. The position of the Z-pinch with respect to the wire array axis was determined from two-dimensional X-ray images and radial optical streak images.

Mitrofanov, K. N.; Aleksandrov, V. V.; Grabovski, E. V.; Gritsuk, A. N.; Oleinik, G. M.; Frolov, I. N.; Laukhin, Ya. N.; Samokhin, A. A.

2014-05-01

286

Power-law relaxation decay in two-dimensional arrays of magnetic dots interacting by long-range dipole-dipole interactions  

NASA Astrophysics Data System (ADS)

The magnetic relaxation of two-dimensional arrays of dipolar coupled magnetic dots has been measured and simulated. Arrays (50×50) with perpendicular magnetized Co dots (2 ?m×2 ?m) were patterned using a high resolution Ga+ focused ion beam irradiation. Magnetic domain pattern and time relaxation of the dot arrays were investigated using Faraday magneto-optical microscopy. For arrays designed with high irradiation doses (>=0.5 nC/cm), the magnetic relaxation of the array proceeds by the magnetization reversal of individual dots and follows a power-law time decay. The long-range character of the dipolar interaction is found to be responsible for magnetic relaxation with a power-law decay. Monte Carlo simulations, based on a modified Ising Hamiltonian, reproduce this time dependence, and show that the power law is not a consequence of either the finite size or the boundary of the arrays, and it is independent of the shape of dots as well.

Sampaio, L. C.; Hyndman, R.; de Menezes, F. S.; Jamet, J. P.; Meyer, P.; Gierak, J.; Chappert, C.; Mathet, V.; Ferré, J.

2001-11-01

287

A Linear Permanent Magnet Generator for a Free-Piston Energy Converter  

Microsoft Academic Search

This paper discusses the issues that are pertinent to the design of a linear permanent magnet generator for application in a free-piston energy converter. To achieve the required high power density, high efficiency and low moving mass, a tubular machine equipped with modular windings and quasi-Halbach magnetization is considered to be the most appropriate. Analytical expressions for predicting the open-circuit

Jiabin Wang; David Howe

2005-01-01

288

Tuning of structural, optical, and magnetic properties of ultrathin and thin ZnO nanowire arrays for nano device applications  

PubMed Central

One-dimensional (1-D) ultrathin (15 nm) and thin (100 nm) aligned 1-D (0001) and (0001¯) oriented zinc oxide (ZnO) nanowire (NW) arrays were fabricated on copper substrates by one-step electrochemical deposition inside the pores of polycarbonate membranes. The aspect ratio dependence of the compressive stress because of the lattice mismatch between NW array/substrate interface and crystallite size variations is investigated. X-ray diffraction results show that the polycrystalline ZnO NWs have a wurtzite structure with a?=?3.24 Å, c?=?5.20 Å, and [002] elongation. HRTEM and SAED pattern confirmed the polycrystalline nature of ultrathin ZnO NWs and lattice spacing of 0.58 nm. The crystallite size and compressive stress in as-grown 15- and 100-nm wires are 12.8 nm and 0.2248 GPa and 22.8 nm and 0.1359 GPa, which changed to 16.1 nm and 1.0307 GPa and 47.5 nm and 1.1677 GPa after annealing at 873 K in ultrahigh vacuum (UHV), respectively. Micro-Raman spectroscopy showed that the increase in E2 (high) phonon frequency corresponds to much higher compressive stresses in ultrathin NW arrays. The minimum-maximum magnetization magnitude for the as-grown ultrathin and thin NW arrays are approximately 8.45?×?10?3 to 8.10?×?10?3 emu/g and approximately 2.22?×?10?7 to 2.190?×?10?7 emu/g, respectively. The magnetization in 15-nm NW arrays is about 4 orders of magnitude higher than that in the 100 nm arrays but can be reduced greatly by the UHV annealing. The origin of ultrathin and thin NW array ferromagnetism may be the exchange interactions between localized electron spin moments resulting from oxygen vacancies at the surfaces of ZnO NWs. The n-type conductivity of 15-nm NW array is higher by about a factor of 2 compared to that of the 100-nm ZnO NWs, and both can be greatly enhanced by UHV annealing. The ability to tune the stresses and the structural and relative occupancies of ZnO NWs in a wide range by annealing has important implications for the design of advanced photonic, electronic, and magneto-optic nano devices.

2014-01-01

289

Tuning of structural, optical, and magnetic properties of ultrathin and thin ZnO nanowire arrays for nano device applications.  

PubMed

One-dimensional (1-D) ultrathin (15 nm) and thin (100 nm) aligned 1-D (0001) and (0001¯) oriented zinc oxide (ZnO) nanowire (NW) arrays were fabricated on copper substrates by one-step electrochemical deposition inside the pores of polycarbonate membranes. The aspect ratio dependence of the compressive stress because of the lattice mismatch between NW array/substrate interface and crystallite size variations is investigated. X-ray diffraction results show that the polycrystalline ZnO NWs have a wurtzite structure with a?=?3.24 Å, c?=?5.20 Å, and [002] elongation. HRTEM and SAED pattern confirmed the polycrystalline nature of ultrathin ZnO NWs and lattice spacing of 0.58 nm. The crystallite size and compressive stress in as-grown 15- and 100-nm wires are 12.8 nm and 0.2248 GPa and 22.8 nm and 0.1359 GPa, which changed to 16.1 nm and 1.0307 GPa and 47.5 nm and 1.1677 GPa after annealing at 873 K in ultrahigh vacuum (UHV), respectively. Micro-Raman spectroscopy showed that the increase in E2 (high) phonon frequency corresponds to much higher compressive stresses in ultrathin NW arrays. The minimum-maximum magnetization magnitude for the as-grown ultrathin and thin NW arrays are approximately 8.45?×?10-3 to 8.10?×?10-3 emu/g and approximately 2.22?×?10-7 to 2.190?×?10-7 emu/g, respectively. The magnetization in 15-nm NW arrays is about 4 orders of magnitude higher than that in the 100 nm arrays but can be reduced greatly by the UHV annealing. The origin of ultrathin and thin NW array ferromagnetism may be the exchange interactions between localized electron spin moments resulting from oxygen vacancies at the surfaces of ZnO NWs. The n-type conductivity of 15-nm NW array is higher by about a factor of 2 compared to that of the 100-nm ZnO NWs, and both can be greatly enhanced by UHV annealing. The ability to tune the stresses and the structural and relative occupancies of ZnO NWs in a wide range by annealing has important implications for the design of advanced photonic, electronic, and magneto-optic nano devices. PMID:24636275

Shrama, Satinder K; Saurakhiya, Neelam; Barthwal, Sumit; Kumar, Rudra; Sharma, Ashutosh

2014-01-01

290

Solid-State Multi-Sensor Array System for Real Time Imaging of Magnetic Fields and Ferrous Objects  

NASA Astrophysics Data System (ADS)

In this paper the development of a solid-state sensors based system for real-time imaging of magnetic fields and ferrous objects is described. The system comprises 1089 magneto inductive solid state sensors arranged in a 2D array matrix of 33×33 files and columns, equally spaced in order to cover an approximate area of 300 by 300 mm. The sensor array is located within a large current-carrying coil. Data is sampled from the sensors by several DSP controlling units and finally streamed to a host computer via a USB 2.0 interface and the image generated and displayed at a rate of 20 frames per minute. The development of the instrumentation has been complemented by extensive numerical modeling of field distribution patterns using boundary element methods. The system was originally intended for deployment in the non-destructive evaluation (NDE) of reinforced concrete. Nevertheless, the system is not only capable of producing real-time, live video images of the metal target embedded within any opaque medium, it also allows the real-time visualization and determination of the magnetic field distribution emitted by either permanent magnets or geometries carrying current. Although this system was initially developed for the NDE arena, it could also have many potential applications in many other fields, including medicine, security, manufacturing, quality assurance and design involving magnetic fields.

Benitez, D.; Gaydecki, P.; Quek, S.; Torres, V.

2008-02-01

291

Magnetic interaction and conical self-reorganization of aligned tin oxide nanowire array under field emission conditions  

NASA Astrophysics Data System (ADS)

Magnetic interactions are induced between non-magnetic, vertically aligned tin dioxide nanowires under field-emission conditions. Vertically aligned nanowires of tin dioxide are synthesized along the [100] direction by pulsed laser deposition of an epitaxial (200) seed layer on c-cut sapphire substrates followed by vapor-liquid-solid growth using catalyst-assisted pulsed laser deposition method. Due to the dense arrangement of the vertically aligned ultra-long nanowires deposited in this study, magnetic interactions between the nanowires carrying parallel currents become significant within 1 ?m radius and lead to their self-reorganization into conical tipi structures under field emission conditions. Optimization of the aerial density of the emission tips and reduction in the field screening effects upon self-reorganization of the nanowire array can account for the large field enhancement factor of 2.6 × 104 at low turn-on field of 3 V/?m.

Bazargan, Samad; Thomas, Joseph P.; Leung, K. T.

2013-06-01

292

Magnetic states and ferromagnetic resonance in geometrically frustrated arrays of multilayer ferromagnetic nanoparticles ordered on triangular lattices  

NASA Astrophysics Data System (ADS)

We present a theoretical investigation of magnetostatic interaction effects in geometrically frustrated arrays of anisotropic one-layer and multilayer ferromagnetic nanoparticles arranged in different spatially configured systems with triangular symmetry. The peculiarities of the magnetization reversal and microwave excitation of such systems are discussed. We show that the use of multilayer stacks significantly expands the opportunities to create magnetically frustrated systems due to additional interlayer interaction. In particular, the interlayer coupling leads to the considerable splitting of the ferromagnetic resonance (FMR) spectrum. In addition, the magnetizing and remagnetizing of the two- and three-layer systems induce transitions between different states with ferromagnetic, antiferromagnetic, or mixed ferromagnetic-antiferromagnetic interlayer ordering that are accompanied by dramatic changes of FMR spectra. These effects can be potentially used in developing field controlled tunable microwave devices.

Mironov, V. L.; Skorohodov, E. V.; Blackman, J. A.

2014-05-01

293

Observation of the switching fields of individual Permalloy particles in nanolithographic arrays via magnetic force microscopy  

Microsoft Academic Search

A technique has been developed for measuring the switching fields of individual submicron magnetic particles using a magnetic force microscope (MFM) in which an in situ magnetic field can be applied. This allows the study of the evolution of the particles' magnetic states as a function of applied field and the direct observation of cooperative switching. Observations of the switching

G. A. Gibson; J. F. Smyth; S. Schultz; D. P. Kern

1991-01-01

294

Magnetic field dependent small-angle neutron scattering on a Co nanorod array: evidence for intraparticle spin misalignment  

PubMed Central

The structural and magnetic properties of a cobalt nanorod array have been studied by means of magnetic field dependent small-angle neutron scattering (SANS). Measurement of the unpolarized SANS cross section d?/d? of the saturated sample in the two scattering geometries where the applied magnetic field H is either perpendicular or parallel to the wavevector k i of the incoming neutron beam allows one to separate nuclear from magnetic SANS, without employing the usual sector-averaging procedure. The analysis of the SANS data in the saturated state provides structural parameters (rod radius and centre-to-centre distance) that are in good agreement with results from electron microscopy. Between saturation and the coercive field, a strong field dependence of d?/d? is observed (in both geometries), which cannot be explained using the conventional expression of the magnetic SANS cross section of magnetic nanoparticles in a homogeneous nonmagnetic matrix. The origin of the strong field dependence of d?/d? is believed to be related to intradomain spin misalignment, due to magnetocrystalline and magnetoelastic anisotropies and magnetostatic stray fields.

Gunther, A.; Bick, J.-P.; Szary, P.; Honecker, D.; Dewhurst, C. D.; Keiderling, U.; Feoktystov, A. V.; Tschope, A.; Birringer, R.; Michels, A.

2014-01-01

295

First order reversal curve investigation of the hard and soft magnetic phases of annealed CoFeCu nanowire arrays  

NASA Astrophysics Data System (ADS)

(CoFe)1-xCux (x=0.12-0.84) nanowire arrays were ac-pulse electrodeposited into anodic aluminum oxide templates. The electrodeposition was performed in a constant electrolyte while Cu content was controlled by off-time between pulses. Nanowires with 30 nm diameter and the certain lengths with the both bcc-CoFe and fcc-Cu phases were obtained. Magnetization and coercivity of the nanowires decreased with increasing the Cu content. Annealing improved the coercivity and a remarkable increase in magnetization of nanowires with high Cu contents was observed. A two-phase treatment was seen for annealed samples with high Cu contents. First order reversal curves showed a hard magnetic phase with almost constant magnetic properties and coercivity of ~2500 Oe. The results showed that main source of the various magnetic behaviors of the samples may be attributed to increase in soft magnetic phase. A single domain treatment with a narrow interacting field and coercive field distributions was also observed for the annealed samples with high Cu content.

Almasi-Kashi, M.; Ramazani, A.; Golafshan, E.; Arefpour, M.; Jafari-Khamse, E.

2013-11-01

296

Cryogenic Characterization and Testing of Magnetically-Actuated Microshutter Arrays for the James Webb Space Telescope.  

National Technical Information Service (NTIS)

Two-dimensional MEMS microshutter arrays (MSA) have been fabricated at the NASA Goddard Space Flight Center (GSFC) for the James Webb Space Telescope (JWST) to enable cryogenic (approx 35 K) spectrographic astronomy measurements in the near-infrared regio...

T. T. King G. Kletetschka M. A. Jah M. J. Li

2004-01-01

297

Photoexcitation-induced magnetism in arrays of semiconductor nanoparticles with a strong excitonic oscillator strength  

Microsoft Academic Search

A type of magnetic metamaterial which exhibits strong magnetic activity within and below the optical region is presented. The metamaterial consists of semiconductor nanoparticles such as CuCl or Cu2O particles. The magnetic activity is attributed to the strong oscillator strength stemming from the exciton absorption line. The magnetic permeability of the proposed metamaterial is calculated from the extended Maxwell-Garnett theory,

V. Yannopapas; N. V. Vitanov

2006-01-01

298

Development of a solid-state multi-sensor array camera for real time imaging of magnetic fields  

NASA Astrophysics Data System (ADS)

The development of a real-time magnetic field imaging camera based on solid-state sensors is described. The final laboratory comprises a 2D array of 33 x 33 solid state, tri-axial magneto-inductive sensors, and is located within a large current-carrying coil. This may be excited to produce either a steady or time-varying magnetic field. Outputs from several rows of sensors are routed to a sub-master controller and all sub-masters route to a master-controller responsible for data coordination and signal pre-processing. The data are finally streamed to a host computer via a USB interface and the image generated and displayed at a rate of several frames per second. Accurate image generation is predicated on a knowledge of the sensor response, magnetic field perturbations and the nature of the target respecting permeability and conductivity. To this end, the development of the instrumentation has been complemented by extensive numerical modelling of field distribution patterns using boundary element methods. Although it was originally intended for deployment in the nondestructive evaluation (NDE) of reinforced concrete, it was soon realised during the course of the work that the magnetic field imaging system had many potential applications, for example, in medicine, security screening, quality assurance (such as the food industry), other areas of nondestructive evaluation (NDE), designs associated with magnetic fields, teaching and research.

Benitez, D.; Gaydecki, P.; Quek, S.; Torres, V.

2007-07-01

299

Bi-directional-bi-dimensionality alignment of self-supporting Mn3O4 nanorod and nanotube arrays with different bacteriostasis and magnetism.  

PubMed

Self-supported Mn3O4 patterns of aligned nanorods and nanotubes were synthesized through a bi-directional-bi-dimensionality growth model by using sodium gluconate and urea as additives under mild hydrothermal conditions without the use of any substrates. In one direction, Mn3O4 grows to form one-dimensional nanorods or nanotubes, while in the other direction Mn3O4 grows into two-dimensional nanoplates to support the nanorods or nanotubes to align into arrays. These two kinds of new nanostructures, a nanotube pattern and a nanorod pattern, show similar and good bacteriostasis for Gram positive bacteria, but for Gram negative bacteria the nanotube pattern shows much better bacterial restraint than the nanorod pattern. Magnetic studies show that the nanorod arrays display similar magnetic properties to the commercial Mn3O4, while the nanotube arrays show different ferromagnetic behaviors with enhanced remnant magnetization and saturation magnetization (Ms) at low temperature. PMID:24136592

Chen, Qun; Wei, Chengzhen; Gao, Feng; Pang, Huan; Lu, Qingyi

2013-12-21

300

Removing Strong Solar Array Disturbances and Telemetry Errors from DC Magnetic Field Measurements with a Dual Fluxgate Technique  

NASA Astrophysics Data System (ADS)

Due to a wrong wiring of the solar panels on a Double Star spacecraft, very large magnetic interferences (20- 30 nT) occurred in the magnetic field vector measure- ments. Furthermore, the shunting system of the space- craft solar power system caused sudden changes in the level of interferences. Finally the observations suffered from frequent telemetry errors causing random spikes in the data. With help of dual fluxgate measurements and signal processing technique, the data have been cleaned first from the spikes and then from the solar array dis- turbances to an accuracy of better than 0.5 nT for most of the time. This paper presents the basic steps of the cleaning procedures.

Laakso, H.; Klos, T.

2012-05-01

301

A radio-frequency source using direct digital synthesis and field programmable gate array for nuclear magnetic resonance.  

PubMed

A radio-frequency (rf) source for nuclear magnetic resonance (NMR) is described. With the application of direct digital synthesis (DDS), the rf source has the ability to yield rf pulses with short switching time and high resolution in frequency and phase. To facilitate the generation of a soft pulse, a field programmable gate array (FPGA) cooperating with a pulse programmer is used as the auxiliary controller of the DDS chip. Triggered by the pulse programmer, the FPGA automatically controls the DDS to generate soft pulse according to predefined parameters, and the operation mode of the pulse programmer is optimized. The rf source is suitable for being used as transmitter in low-field (<1 T) NMR applications, for example, magnetic resonance imaging and relaxation measurement. As a compact and low-cost module, the rf source is of general use for constructing low-field NMR spectrometer. PMID:20059160

Liang, Xiao; Weimin, Wang

2009-12-01

302

An 11-Channel Radio Frequency Phased Array Coil for Magnetic Resonance Guided High Intensity Focused Ultrasound of the Breast  

PubMed Central

In this study, a radio-frequency (RF) phased array coil was built to image the breast in conjunction with a Magnetic Resonance guided High Intensity Focused Ultrasound (MRgHIFU) device designed specifically to treat the breast in a treatment cylinder with reduced water volume. The MRgHIFU breast coil was comprised of a 10-channel phased array coil placed around an MRgHIFU treatment cylinder where nearest-neighbor decoupling was achieved with capacitive decoupling in a shared leg. In addition a single loop coil was placed at the chest wall making a total of 11-channels. The RF coil array design presented in this work was chosen based on ease of implementation, increased visualization into the treatment cylinder, image reconstruction speed, temporal resolution, and resulting signal-to-noise-ratio (SNR) profiles. This work presents a dedicated 11-channel coil for imaging of the breast tissue in the MRgHIFU setup without obstruction of the ultrasound beam and, specifically, compares its performance in SNR, overall imaging time, and temperature measurement accuracy to that of the standard single chest-loop coil typically used in breast MRgHIFU.

Minalga, E.; Payne, A.; Merrill, R.; Todd, N.; Vijayakumar, S.; Kholmovski, E.; Parker, D. L.; Hadley, J. R.

2012-01-01

303

An investigation of the applicability of permanent magnet quadrupole arrays for high-power microwave tubes  

Microsoft Academic Search

Summary form only given, as follows. Magnetic quadrupoles have long been used in accelerator research for focusing high-energy particle beams. The advent of high-field, rare-earth permanent magnet materials has also spurred interest in permanent magnet quadrupoles (PMQ's) since they are more lightweight and compact than their electromagnet counterparts and do not require power supplies or extraneous cooling. We study the

J. H. Booske; M. A. Basten; L. J. Louis; J. Joe; J. E. Scharer

1996-01-01

304

Tuning the Scattering Parameters of Magnetic Nanowire Arrays Near the Antiresonance at Photonic Frequencies  

Microsoft Academic Search

The diffraction of electromagnetic waves on arrays of ferromagnetic metallic (iron) nanowires at photonic frequencies is modeled at electromagnetic accuracy by solving the 3-D diffraction problem for Maxwell's equations with electrodynamic boundary conditions, complemented by the Landau-Lifshitz equation including the exchange term. Using the computational algorithm based on the decomposition approach by autonomous blocks with Floquet channels (FABs), the scattering

Galina S. Makeeva; Martha Pardavi-Horvath; Oleg A. Golovanov

2009-01-01

305

Experimental Investigation of a Staggered Array Magnetic Filter, July 17-September 16, 1981.  

National Technical Information Service (NTIS)

This report describes an experimental investigation of the performance of a staggered array of parallel ferromagnetic fibers in capturing small paramagnetic particles. These test results are intended to be compared with (W.H. Simons and R.P. Treat, J. App...

W. E. Vehse

1982-01-01

306

Efficiency improvement of wireless power transfer via magnetic resonance using transmission coil array  

Microsoft Academic Search

The transfer efficiency between a transmission coil and a reception coil for wireless power transfer via magnetic resonance is a function of the orientation between the coils. When two coils share a single axis, the transfer efficiency is maximal, but otherwise the efficiency becomes lower. In this paper, a wireless power transfer system via magnetic resonance using a transmission coil

Noriaki Oodachi; Kenichiro Ogawa; Hiroki Kudo; Hiroki Shoki; Shuichi Obayashi; Tasuku Morooka

2011-01-01

307

Development of a miniature permanent magnetic circuit for nuclear magnetic resonance chip  

NASA Astrophysics Data System (ADS)

The existing researches of miniature magnetic circuits focus on the single-sided permanent magnetic circuits and the Halbach permanent magnetic circuits. In the single-sided permanent magnetic circuits, the magnetic flux density is always very low in the work region. In the Halbach permanent magnetic circuits, there are always great difficulties in the manufacturing and assembly process. The static magnetic flux density required for nuclear magnetic resonance(NMR) chip is analyzed based on the signal noise ratio(SNR) calculation model, and then a miniature C-shaped permanent magnetic circuit is designed as the required magnetic flux density. Based on Kirchhoff's law and magnetic flux refraction principle, the concept of a single shimming ring is proposed to improve the performance of the designed magnetic circuit. Using the finite element method, a comparative calculation is conducted. The calculation results demonstrate that the magnetic circuit improved with a single shimming has higher magnetic flux density and better magnetic field homogeneity than the one improved with no shimming ring or double shimming rings. The proposed magnetic circuit is manufactured and its experimental test platform is also built. The magnetic flux density measured in the work region is 0.7 T, which is well coincided with the theoretical design. The spatial variation of the magnetic field is within the range of the instrument error. At last, the temperature dependence of the magnetic flux density produced by the proposed magnetic circuit is investigated through both theoretical analysis and experimental study, and a linear functional model is obtained. The proposed research is crucial for solving the problem in the application of NMR-chip under different environmental temperatures.

Lu, Rongsheng; Yi, Hong; Wu, Weiping; Ni, Zhonghua

2013-07-01

308

Magnetic field penetration through protective metal screens using an equivalent magnetic dipole representation of an array of elliptical apertures  

NASA Astrophysics Data System (ADS)

A model was developed to predict the coupling of external magnetic fields into a cylindrical object through an aperture shielded with a metal screen. Results from an experiment designed to test the model are presented. The coupling of these exterior fields through a single elliptical aperture is approximated by the radiation from an equivalent dipole into the object. The magnetic moments for this dipole are determined by the physical size of the aperture. The screen is then modeled as a linear superposition of many individual apertures. The total field at an interior point is calculated by summing the components of the fields from each of these apertures.

Richmond, Richard; O'Neal, James

309

Study of the radial distribution of the magnetic field in the wire array plasma at the Angara-5-1 facility  

NASA Astrophysics Data System (ADS)

Results are presented from experimental studies of the implosion of wire (tungsten, aluminum, and molybdenum) and fiber (kapron) arrays at the Angara 5-1 facility at currents of up to 4 MA. The radial distributions of the azimuthal magnetic field in the stage of plasma production in such arrays are measured in detail for the first time, and the radial profiles of the current density are evaluated. The data obtained using an optical streak camera are compared with the results of measurements of the current and voltage. Using the obtained experimental results, the rate of plasma production in the arrays made of different materials is estimated.

Mitrofanov, K. N.; Grabovski, E. V.; Oleinik, G. M.; Aleksandrov, V. V.; Gritsuk, A. N.; Frolov, I. N.; Laukhin, Ya. N.; Sasorov, P. V.; Samokhin, A. A.

2012-10-01

310

In-field magnetic force microscope study of dipolar interaction in an ideally ordered Co nanorod array fabricated using nanoimprint lithography  

NASA Astrophysics Data System (ADS)

We have performed experimental studies and numerical calculations on the dipolar interaction in an ideally ordered hexagonal nanorod array. The dipolar field in an ordered Co nanorod array was measured using an in-field magnetic force microscope (MFM) with a controlled applied field. The average dipolar fields of neighboring nanorods acting on a center nanorod were calculated by approximating the monopole with a magnetic charge m=MSS on the end of each nanorod. The largest dipolar field obtained from numerical calculation is agreement with that from in-field MFM measurements.

Wang, T.; Wang, Y.; Fu, Y.; Hasegawa, T.; Washiya, T.; Saito, H.; Ishio, S.; Li, F. S.; Oshima, H.; Itoh, K.; Nishio, K.; Masuda, H.

2008-05-01

311

Cryogenic phased-array for high resolution magnetic resonance imaging (MRI); assessment of clinical and research applications  

NASA Astrophysics Data System (ADS)

Magnetic Resonance (MR) imaging is one of the most powerful tools in diagnostic medicine for soft tissue imaging. Image acquisition techniques and hardware receivers are very important in achieving high contrast and high resolution MR images. An aim of this dissertation is to design single and multi-element room and cryogenic temperature arrays and make assessments of their signal-to-noise ratio (SNR) and SNR gain. In this dissertation, four sets of MR receiver coils are built. They are the receiver-only cryo-coils that are not commercially available. A tuning and matching circuit is attached to each coil. The tuning and matching circuits are simple; however, each device component has to operate at a high magnetic field and cryogenic temperature environment. Remote DC bias of the varactor controls the tuning and matching outside the scanner room. Active detuning of the resonator is done by two p-i-n junction (PIN) diodes. Cooling of the receiver is done by a customized liquid nitrogen cryostat. The first application is to build a 3-Tesla 2x1 horseshoe counter-rotating current (CRC) cryogenic array to image the tibia in a human body. With significant increase in SNR, the surface coil should deliver high contrast and resolution images that can show the trabecular bone and bone marrow structure. This structural image will be used to model the mechanical strength of the bone as well as bone density and chance of fracture. The planar CRC is a unique design of this surface array. The second application is to modify the coil design to 7-Tesla to study the growth of infant rhesus monkey eyes. Fast scan MR images of the infant monkey heads are taken for monitoring shapes of their eyeballs. The monkeys are induced with shortsightedness by eye lenses, and they are scanned periodically to get images of their eyeballs. The field-of-view (FOV) of these images is about five centimeters and the area of interest is two centimeters deep from the surface. Because of these reasons, the MR counter-rotating current coil is sufficient and demonstrated its simplicity over a phased array in this application.

Ip, Flora S.

312

Commensurate states on incommensurate lattices. [for superconducting arrays in magnetic fields  

NASA Technical Reports Server (NTRS)

A simple one-dimensional model related to flux quantization on superconducting networks or charged particles on a substrate is proposed to investigate whether commensurate states can exist on incommensurate lattices. For both periodic and quasi-crystalline patterns, a set of low-energy states is found which is related to decimation symmetry and periodicity. It is suggested that the present quasi-periodic arrays which possess a decimation operation can be generalized to more-dimensional quasi-crystalline systems.

Grest, Gary S.; Chaikin, Paul M.; Levine, Dov

1988-01-01

313

Fabrication of CoPt magnetic nanodot arrays by electrodeposition process  

Microsoft Academic Search

We attempted to fabricate patterned media using the electrochemical deposition process along with nanopatterned substrates prepared by the electron beam lithography (EBL), UV nanoimprint lithography (UV-NIL), and spin-on-glass nanoimprint lithography (SOG-NIL) approaches. CoPt was electrodeposited into the nanopatterned substrates and chemical mechanical polishing was carried out to planarize the surface. It was clarified that CoPt nanodot arrays were successfully deposited

Takanari Ouchi; Yuki Arikawa; Takayuki Homma

2008-01-01

314

Cryogenic characterization and testing of magnetically-actuated microshutter arrays for the James Webb Space Telescope  

Microsoft Academic Search

Two-dimensional MEMS microshutter arrays (MSA) have been fabricated at the NASA Goddard Space Flight Center (GSFC) for the James Webb Space Telescope (JWST) to enable cryogenic (?35 K) spectrographic astronomy measurements at near-infrared wavelengths. Functioning as a focal plane object selection device, the MSA is a 2D programmable aperture mask with fine resolution, high efficiency and high contrast. The MSA

T T King; G Kletetschka; M A Jah; M A Beamesderfer; M J Li; L L Wang; S H Moseley; L M Sparr; M D Jhabvala; A S Kutyrev; R F Silverberg; D Rapchun; Y Zheng; D S Schwinger; G M Voellmer

2005-01-01

315

Theory of superconducting wire networks and Josephson-junction arrays in magnetic fields  

Microsoft Academic Search

In this paper we study the superconducting-normal phase boundaries of a variety of wire networks and Josephson-junction arrays. We have obtained the mean-field phase diagrams for a number of geometries and compared them to the corresponding experimental data. We have introduced an analytical approach to the analysis of the structures present in the phase diagrams. We have shown in great

Qian Niu; Franco Nori

1989-01-01

316

Magnetic multipole analysis of kagome and artificial spin-ice dipolar arrays  

Microsoft Academic Search

We analyze an array of linearly extended monodomain dipoles forming square and kagome lattices. We find that its phase diagram contains two (distinct) finite-entropy kagome ice regimes---one disordered, one algebraic---as well as a low-temperature ordered phase. In the limit of the islands almost touching, we find a staircase of corresponding entropy plateaux, which is analytically captured by a theory based

G. Möller; R. Moessner

2009-01-01

317

An Efficient Gait Phase Detection Device Based on Magnetic Sensor Array  

Microsoft Academic Search

In this paper, we present a prototype of a gait phase detection device which can be used as a part of a gait training and\\u000a posture correction machine for monoplegia patients. The proposed detection device consists of a magnet shoes and magnetic\\u000a sensor plate, and it could replace the conventional expensive foot pressure sensors used to detect gait phase. The

J. H. Choi; Jongman Cho; J. H. Park; J. M. Eun; M. S. Kim

318

Magnetic resonance imaging-compatible tactile sensing device based on a piezoelectric array.  

PubMed

Minimally invasive surgery is a widely used medical technique, one of the drawbacks of which is the loss of direct sense of touch during the operation. Palpation is the use of fingertips to explore and make fast assessments of tissue morphology. Although technologies are developed to equip minimally invasive surgery tools with haptic feedback capabilities, the majority focus on tissue stiffness profiling and tool-tissue interaction force measurement. For greatly increased diagnostic capability, a magnetic resonance imaging-compatible tactile sensor design is proposed, which allows minimally invasive surgery to be performed under image guidance, combining the strong capability of magnetic resonance imaging soft tissue and intuitive palpation. The sensing unit is based on a piezoelectric sensor methodology, which conforms to the stringent mechanical and electrical design requirements imposed by the magnetic resonance environment The sensor mechanical design and the device integration to a 0.2 Tesla open magnetic resonance imaging scanner are described, together with the device's magnetic resonance compatibility testing. Its design limitations and potential future improvements are also discussed. A tactile sensing unit based on a piezoelectric sensor principle is proposed, which is designed for magnetic resonance imaging guided interventions. PMID:22913103

Hamed, Abbi; Masamune, Ken; Tse, Zion Tsz Ho; Lamperth, Michael; Dohi, Takeyoshi

2012-07-01

319

Magnetic and magnetotransport properties of arrays of nanostructured antidots obtained by self-assembling polystyrene nanosphere lithography  

SciTech Connect

A well-ordered nanopatterned structure has been obtained in sputtered magnetic thin films by self-assembling of polystyrene nanospheres. Arrays of holes in Co, Ni, and Ni{sub 80}Fe{sub 20} films having a mean size ranging in the interval of 200-400 nm depending on the experimental condition have been prepared. Sample microstructure has been studied by scanning electron microscopy and atomic force microscopy. Room-temperature hysteresis loops have been measured in the parallel and perpendicular configuration (H{sub max}=20 kOe). Magnetoresistance (MR) measurements have been performed by means of a standard four-contact technique at several angles between the current and the magnetic field (H{sub max}=70 kOe) in the temperature interval of 4-200 K. An anisotropic MR effect has been observed in all compositions independent on the hole mean dimension. The role on magnetic and magnetotransport properties of either sample microstructure or composition has been studied in such patterned structures.

Tiberto, Paola; Boarino, Luca; Celegato, Federica; Coiesson, Marco; De Leo, Natascia; Vinai, Franco [INRIM, Strada delle Cacce 91, Torino I-10135 (Italy); Allia, Paolo [DISMIC, Politecnico di Torino, Corso Duca degli Abruzzi 24, Torino, 1-10129 (Italy)

2010-05-15

320

A frequency-shift CMOS magnetic biosensor array with single-bead sensitivity and no external magnet  

Microsoft Academic Search

Future point-of-care (PoC) molecular-level diagnosis requires advanced biosensing systems that can achieve high sensitivity and portability at low power consumption levels, all within a low price-tag for a variety of applications such as in-field medical diagnostics, epidemic disease control, biohazard detection, and forensic analysis. Magnetically labeled biosensors are proposed as a promising candidate to potentially eliminate or augment the optical

Hua Wang; Yan Chen; Arjang Hassibi; Axel Scherer; Ali Hajimiri

2009-01-01

321

Spatially resolved magnetic hysteresis in a YBa2Cu3O7-y crystal measured by a Hall-probe array  

Microsoft Academic Search

We report local-magnetic-field measurements near a YBa2Cu3O7-y crystal by a linear array of Hall probes. Two distinct features are observed in the local-field hysteresis Hl vs H, which are not present in the integrated magnetization measured by a SQUID: (1) a peak in Hl right after the field reversal that we attribute to the field generated by the current flow

T. Tamegai; L. Krusin-Elbaum; P. Santhanam; M. J. Brady; W. T. Masselink; C. Feild; F. Holtzberg

1992-01-01

322

Electrodeposited magnetic nanowires: arrays, field-induced assembly, and surface functionalization  

NASA Astrophysics Data System (ADS)

Electrodeposition into nanoporous templates provides a means of fabricating large quantities of magnetic nanowires with diameters in the range 5 nm-10 ?m, and lengths up to 60 ?m. Several recent developments in nanoporous templates and Ni nanowires are described. Templates formed by ?-particle irradiation of single-crystal mica are shown to contain diamond-shaped nanopores with uniform size and orientation. Ni prisms deposited in these templates show anisotropic magnetic properties along all three axes of the prisms. The manipulation of isolated Ni nanowires in a variety of suspensions, and a quantitative analysis of the dynamics of the self-assembly of these nanowires under the control of external magnetic fields is described. Surface functionalization with porphyrin molecules yields fluorescent Ni nanowires that have potential for use in biotechnology and other applications.

Chien, C. L.; Sun, L.; Tanase, M.; Bauer, L. A.; Hultgren, A.; Silevitch, D. M.; Meyer, G. J.; Searson, P. C.; Reich, D. H.

2002-08-01

323

Structure and magnetic properties of the Co x Pt100- x nanowire arrays  

NASA Astrophysics Data System (ADS)

Co-Pt alloy nanowires with different components have been successfully fabricated by alternating current (AC) electro-deposition into the nanopores of the anodic aluminum oxide (AAO) template. SEM and TEM images reveal that the nanowires are uniform and parallel to each other. The aspect ratio of nanowires is over 100. XRD and EDS patterns indicate that Co-Pt nanowires are nanocrystalline at room temperature. For the as-prepared samples, the magnetocrystal anisotropy is very small, therefore, Co content and shape anisotropy play a dominant role in contributing to the improvement of coercivity and squareness. Meanwhile, the Co-Pt alloy nanowires transforms from a hard magnetic phase of fcc CoPt to a relatively soft magnetic phase of fcc CoPt3 when the annealing temperature is above 400 °C. The structure and magnetic properties of nanowires after annealing are studied and discussed in this paper.

Wen, X.; Zhang, X. X.; Zhang, Y.; Yue, G. H.; Wang, J. B.; Wang, Z. W.; Peng, D. L.

2013-09-01

324

Vortex Pinning in Superconducting MoGe Films Containing Conformal Arrays of Nanoscale Holes and Magnetic Dots  

NASA Astrophysics Data System (ADS)

Recent numerical simulations by Ray et al. predict that a conformal pinning array can produce stronger vortex pinning effect than other pinning structures with an equivalent density of pinning sites [1]. Here we present experimental investigations on conformal pinning structures. Direct and conformal pinning arrays of triangular and square lattices were introduced into MoGe superconducting films using focused-ion-beam milling or electron-beam lithography. Transport measurements on critical currents and magnetoresistances were carried out on these samples to reveal the advantages of conformal pinnings. Effects of random pinnings with the same average density were also studied for comparison. Details on sample fabrications and effects of pinning types (holes versus magnetic dots) will be presented. Reference: [1] D. Ray, C.J. Olson Reichhardt, B. Janko, C. Reichhardt, arXiv:1210.1229 (2012) Work supported by the US DoE-BES funded Energy Frontier Research Center (YLW), and by Department of Energy, Office of Science, Office of Basic Energy Sciences (MLL, ZLX, LEO, RD, UW, WKK), under Contract No. DE-AC02-06CH11357

Wang, Y. L.; Latimer, M. L.; Xiao, Z. L.; Ocola, L. E.; Divan, R.; Welp, U.; Crabtree, G. W.; Kwok, W. K.

2013-03-01

325

Ordered arrays of II/VI diluted magnetic semiconductor quantum wires: formation within mesoporous MCM-41 silica.  

PubMed

We present a novel way of synthesising highly ordered arrays of hollow Cd(1-x)Mn(x)S quantum wires with lateral dimensions of 3-4 nm separated by 1-2 nm SiO2 barriers by forming Cd(1-x)Mn(x)S (0 < or = x < or = 1) semiconductors inside the pore system of mesoporous MCM-41 SiO2 host structures. X-ray diffraction and transmission electron microscopy (TEM) studies reveal the hexagonal symmetry of these arrays (space group p6m) and confirm the high degree of order. Physisorption measurements show the filling of the pores of the MCM-41 SiO2. The X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS), electron paramagentic resonance (EPR), and Raman studies confirm the good crystalline quality of the incorporated (Cd,Mn)S guest. The effects of reducing the lateral dimensions on the magnetic and electronic properties of the diluted magnetic semiconductor were studied by photoluminescence (PL) and PL excitation spectroscopy and by SQUID and EPR measurements in the temperature range 2-400 K. Due to the quantum confinement of the excitons in the wires, an increase of about 200 meV in the direct band gap was observed. In addition, the p-d hybridisation-related bowing of the band gap as a function of Mn concentration in the wires is much stronger than in the bulk. This effect is related to the increase in the band gap due to quantum confinement, which shifts the p-like valence band edge closer to the 3d-related states of Mn in the valence band. Thus, the p-d hybridisation and the strength of the band gap bowing are increased. Compared to bulk (II,Mn)VI compounds, antiferromagnetic coupling between the magnetic moments of the Mn2+ ions is weaker. For the samples with high Mn concentrations (x > 0.8) this leads to a suppression of the phase transition of the Mn system from paramagnetic to antiferromagnetic. This effect can be explained by the fact that the lateral dimensions of the wires are smaller than the magnetic length scale of the antiferromagnetic ordering. PMID:11822450

Brieler, Felix J; Fröba, Michael; Chen, Limei; Klar, Peter J; Heimbrodt, Wolfram; Von, NiddaHans-AlbrechtKrug; Loidl, Alois

2002-01-01

326

Simulation of Field Coupled Computing Architectures Based on Magnetic Dot Arrays  

Microsoft Academic Search

In this paper, we demonstrate that field-coupled nanomagnets can be used for digital information processing. The operation of logic devices is based on a QCA-like architecture, where information propagates by magnetostatic interaction between individual magnetic dots. Micromagnetic simulations indicate that simple logic gates function properly. Efficient design tools, based on the single-domain approximation are developed.

ORGY CSABA; WOLFGANG POROD

2002-01-01

327

Preliminary design of a superconducting coil array for NASA prototype magnetic balance. M.S. Thesis  

NASA Technical Reports Server (NTRS)

Using a computer program a partly optimized configuration for a supeconducting version of side and lift coil system of NASA-MIT prototype is presented. Cable size for the mentioned coils and also for superconducting drag and magnetizing coils regarding the overall computed field was determined.

Alishahi, M. M.

1980-01-01

328

Multisegmented Magnet Array on Voice Coil Motor in Rotating Data Storage Devices  

Microsoft Academic Search

The swing-arm-type voice coil motor (VCM) is widely used as an actuator in rotating data storage devices. Recently, it has been found that to achieve a faster data transfer rate and a higher data storage areal density, a high performance actuator is required. Moreover, a small form factor has become desirable for portable devices. In this paper, a novel magnetic

Jaehwa Jeong; Moon G. Lee; Jun-Hee Lee; Hyoung-Kil Yoon; Dae-Gab Gweon

2004-01-01

329

Stability considerations for magnetic suspension systems using electromagnets mounted in a planar array  

NASA Technical Reports Server (NTRS)

Mathematical models of a 5, 6, 7, and 8 coil large gap magnetic suspension system (MSDS) are presented. Some of the topics covered include: force and torque equations, reduction of state-space form, natural modes, origins of modes, effect of rotation in azimuth (yaw), future work, and n-coil ring conclusions.

Groom, Nelson J.; Britcher, Colin P.

1991-01-01

330

Fabrication and characterization of ultra-uniform magnetic nanoparticle arrays in ordered aluminum oxide templates  

Microsoft Academic Search

Anodization of aluminum in acid solutions can generate unique morphologies of the resulting amorphous alumina films, consisting of long and columnar nanopores with approximately hexagonal ordering (alumite). Alumite has attracted broad attention, both on a fundamental and applied level, for more than half a century. In particular, the possibility of synthesizing nano-structures for magnetic recording technology makes this classic self-assembly

Ming Sun

2001-01-01

331

Magnetic coupling in epitaxial Fe/MgO/Fe microtunnel junction arrays  

NASA Astrophysics Data System (ADS)

The magnetic properties of planar 10 nm Fe/x nm MgO/10 nm Fe (x = 1, 2, 5 and 7 nm) epitaxial square-shaped elements have been measured for different edge sizes in the micrometre range. When the top and bottom electrodes magnetizations are exchange uncoupled, they orient in an antiparallel fashion in the zero-field state due to the magnetostatic energy reduction. On the other hand, the two electrodes magnetizations orient in a parallel way when they are are effectively exchange coupled through the barrier; most probably due to pinholes. This happens for a 1 nm thick MgO barrier (which is just about two MgO unit cells) for junctions that are ~4? m in lateral size. The field ranges where magnetic switching occurs agree reasonably well with predictions from a simple analytical model, in which we solve the energetic balance between magnetostatic energy reduction and potential energy gain for our Fe/MgO/Fe sandwich geometry. In addition, we obtain evidence that when the top and bottom electrodes are exchange uncoupled, the junctions can be placed closer before they interact laterally. This is due to a preferred magnetic flux closure along the growth direction instead of in the plane, reducing the field distribution at the neighbour's positions. The same argument implies that the junction electrodes retain their single domain character for smaller sizes than single layer Fe tiles (Costa-Krämer J L, Martín J I, Menéndez J L, Cebollada A, Anguita J V and Briones F and Vicent J L 2000 Appl. Phys. Lett. 76 3091).

Costa-Krämer, J. L.; Anguita, J.; Martín, J. I.; Martínez-Boubeta, C.; Cebollada, A.; Briones, F.

2002-10-01

332

Structure and magnetic properties of three-dimensional (La,Sr)MnO{sub 3} nanofilms on ZnO nanorod arrays  

SciTech Connect

Three-dimensional (3D) cubic perovskite (La,Sr)MnO{sub 3} (LSMO) nanofilms have been deposited on ZnO nanorod arrays with controlled dimensionality and crystallinity by radio frequency (rf) magnetron sputtering and post thermal annealing. Compared to the two-dimensional (2D) LSMO nanofilm on flat Si, the structure and magnetic properties of 3D LSMO nanofilms on ZnO nanorod arrays have a strong anisotropic morphology and thickness dependence. Ferromagnetic property has been observed in both 2D and 3D LSMO nanofilms while a ferromagnetic-superparamagnetic transition was revaled in 3D LSMO nanofilms on ZnO nanorod array with decreasing nanofilm thickness, due to a large surface dispersion effect. The LSMO/ZnO nanofilm/nanorod structures could open up new avenues for intriguing magnetic properties studies and applications of nanoscale perovskites.

Gao Haiyong; Gao Puxian; Shimpi, Paresh; Guo Yanbing; Cai Wenjie; Lin Huijan [Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269-3136 (United States); Department of Chemical, Materials, and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut 06269-3136 (United States); Staruch, M. [Department of Physics, University of Connecticut, Storrs, Connecticut 06269-3046 (United States); Jain, Menka [Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269-3136 (United States); Department of Physics, University of Connecticut, Storrs, Connecticut 06269-3046 (United States)

2011-03-21

333

Controlled changes in the microstructure and magnetic anisotropy in arrays of electrodeposited Co nanowires induced by the solution pH  

Microsoft Academic Search

The effects of the electrolytic bath acidity, or pH, on the magnetic properties in arrays of electrodeposited Co nanowires and their correlation with the crystalline properties have been studied using ferromagnetic resonance. The results show that, depending on the value of the pH of the electrolyte, appreciable changes in the effective anisotropy can be induced. These changes are attributed to

Michaël Darques; Armando Encinas; Laurent Vila; Luc Piraux

2004-01-01

334

Coherent all-optical control of ultracold atoms arrays in permanent magnetic traps.  

PubMed

We propose a hybrid architecture for quantum information processing based on magnetically trapped ultracold atoms coupled via optical fields. The ultracold atoms, which can be either Bose-Einstein condensates or ensembles, are trapped in permanent magnetic traps and are placed in microcavities, connected by silica based waveguides on an atom chip structure. At each trapping center, the ultracold atoms form spin coherent states, serving as a quantum memory. An all-optical scheme is used to initialize, measure and perform a universal set of quantum gates on the single and two spin-coherent states where entanglement can be generated addressably between spatially separated trapped ultracold atoms. This allows for universal quantum operations on the spin coherent state quantum memories. We give detailed derivations of the composite cavity system mediated by a silica waveguide as well as the control scheme. Estimates for the necessary experimental conditions for a working hybrid device are given. PMID:24663640

Abdelrahman, Ahmed; Mukai, Tetsuya; Häffner, Hartmut; Byrnes, Tim

2014-02-10

335

Electrodeposited magnetic nanowires: arrays, field-induced assembly, and surface functionalization  

Microsoft Academic Search

Electrodeposition into nanoporous templates provides a means of fabricating large quantities of magnetic nanowires with diameters in the range 5nm–10?m, and lengths up to 60?m. Several recent developments in nanoporous templates and Ni nanowires are described. Templates formed by ?-particle irradiation of single-crystal mica are shown to contain diamond-shaped nanopores with uniform size and orientation. Ni prisms deposited in these

C. L. Chien; L. Sun; M. Tanase; L. A. Bauer; A. Hultgren; D. M. Silevitch; G. J. Meyer; P. C. Searson; D. H. Reich

2002-01-01

336

Vortex pinning vs superconducting wire network: origin of periodic oscillations induced by applied magnetic fields in superconducting films with arrays of nanomagnets  

NASA Astrophysics Data System (ADS)

Hybrid magnetic arrays embedded in superconducting films are ideal systems to study the competition between different physical (such as the coherence length) and structural length scales such as are available in artificially produced structures. This interplay leads to oscillation in many magnetically dependent superconducting properties such as the critical currents, resistivity and magnetization. These effects are generally analyzed using two distinct models based on vortex pinning or wire network. In this work, we show that for magnetic dot arrays, as opposed to antidot (i.e. holes) arrays, vortex pinning is the main mechanism for field induced oscillations in resistance R(H), critical current Ic(H), magnetization M(H) and ac-susceptibility ? ac(H) in a broad temperature range. Due to the coherence length divergence at Tc, a crossover to wire network behaviour is experimentally found. While pinning occurs in a wide temperature range up to Tc, wire network behaviour is only present in a very narrow temperature window close to Tc. In this temperature interval, contributions from both mechanisms are operational but can be experimentally distinguished.

Gomez, A.; del Valle, J.; Gonzalez, E. M.; Chiliotte, C. E.; Carreira, S. J.; Bekeris, V.; Prieto, J. L.; Schuller, Ivan K.; Vicent, J. L.

2014-06-01

337

dc and high frequency magnetic properties of nanopatterned CoFe2O4 arrays fabricated using sol-gel precursors  

NASA Astrophysics Data System (ADS)

Nanostructures of ferromagnetic oxides having Curie temperatures above room temperature have potential for applications in memory devices and future spin-based electronic applications. In this article, we report on the dc and high frequency magnetic properties of arrays of elliptical CoFe2O4 nanopillars, covering a large area, fabricated by combined electron beam lithography, and a sol-gel based chemical route. The nanopillars were successfully fabricated on insulating oxidized silicon substrates and on epitaxial thin films of ferroelectric BiFeO3. We performed magnetic force microscopy and ferromagnetic resonance spectroscopy on the arrays to probe their magnetic properties. Due to the possible existence of dominant pinning sites, the CoFe2O4 nanopillars are not single-domain even at nanometer size scales.

Sheet, Goutam; Cunliffe, Alexandra R.; Offerman, Erik J.; Folkman, Chad M.; Eom, Chang-Beom; Chandrasekhar, Venkat

2010-05-01

338

MgO-based magnetic tunnel junction sensors array for non-destructive testing applications  

NASA Astrophysics Data System (ADS)

A MgO-based magnetic tunnel junction (MTJ) sensor including 72 MTJs in series with 50 × 50 ?m2 was successfully microfabricated. Due to a two-step annealing strategy, a linear transfer curve was obtained. The tunneling magnetoresistance (TMR) value is as high as 159% and the sensitivity reaches 2.9%/Oe. The field detectivity exhibits the lowest value at 1 V bias current, attaining 1.76 nT/Hz0.5 and 170 pT/Hz0.5 for 10 Hz and 1 kHz, respectively. The results show that the sensor could be applied in non-destructive testing systems which are used for detecting small defects inside conductive materials.

Guo, D. W.; Cardoso, F. A.; Ferreira, R.; Paz, E.; Cardoso, S.; Freitas, P. P.

2014-05-01

339

An improved permanent magnet quadrupole design with larger good field region for high intensity proton linacs  

NASA Astrophysics Data System (ADS)

The Low Energy High Intensity Proton Accelerator (LEHIPA), being developed at the Bhabha Atomic Research Centre (BARC) will produce a 20 MeV, 30 mA, continuous wave (CW) proton beam. At these low velocities, space-charge forces dominate, and could lead to larger beam sizes and beam halos. Hence in the design of the focusing lattice of the LEHIPA drift tube linac (DTL) using permanent magnet quadrupoles (PMQs), a larger good field region is preferred. Here we study, using the two dimensional (2D) and three dimensional (3D) simulation codes PANDIRA and RADIA, four different types of cylindrical PMQ designs: 16-segment trapezoidal Halbach configuration, bullet-nosed geometry and 8- and 16-segment rectangular geometries. The trapezoidal Halbach geometry is used in a variety of accelerators since it provides very high field gradients in small bores, while the bullet-nosed geometry, which is a combination of the trapezoidal and rectangular designs, is used in some DTLs. This study shows that a larger good field region is possible in the 16-segment rectangular design as compared to the Halbach and bullet-nosed designs, making it more attractive for high-intensity proton linacs. An improvement in good-field region by ˜16% over the Halbach design is obtained in the optimized 16-segment rectangular design, although the field gradient is lower by ˜20%. Tolerance studies show that the rectangular segment PMQ design is substantially less sensitive to the easy axis orientation errors and hence will be a better choice for DTLs.

Mathew, Jose V.; Rao, S. V. L. S.; Krishnagopal, S.; Singh, P.

2013-11-01

340

Magneto-optical diffraction by periodic lateral arrays composed of GMR structures of Pt/Co free layers having perpendicular magnetization  

NASA Astrophysics Data System (ADS)

A first-order beam diffracted by periodic arrays of GMR structures consisting of Pt/Co free layers having perpendicular magnetization without a top electrode is investigated. Linear and two-dimensional arrays of various shapes having sizes of 10-50 ?m and periods of 20-100 ?m embedded in SiO2 are fabricated. The angles of the plane of polarization for first or (1,0) diffraction spots at a wavelength of 633 nm are measured to be approximately 0.5° for all samples. The polarization angles for one- and two-dimensional arrays of magnetic patterns are studied theoretically by assuming that the structures have sinusoidal magnetic distributions. They are found to depend on the Kerr rotation angle of the Pt/Co multilayer and on the difference in reflectance between the Pt/Co and SiO2, but they are independent of the periodicities, sizes, and shapes of the patterns. On the other hand, the diffraction efficiencies due to the magneto-optical effect depend on the reflectance and Kerr rotation angles of the magnetic materials. The diffraction efficiency of the component arising from the magneto-optical effect is discussed.

Wada, Kakeru; Kobayashi, Tsukasa; Emoto, Akira; Aoshima, Ken-ichi; Machida, Kenji; Kuga, Kiyoshi; Shioda, Tatsutoshi; Ono, Hiroshi; Kikuchi, Hiroshi; Shimidzu, Naoki; Ishibashi, Takayuki

2014-07-01

341

Coronal temperature, density, and magnetic field maps of a solar acitve region using the Owens Valley Solar Array  

NASA Technical Reports Server (NTRS)

We present the first results of solar active region observations with the recently completed five-element Owens Valley Solar Array. On 1991 October 24, maps of Active Region AR 6891 were obtained at 22 frequencies from 1.2-7.0 GHz to provide brightness temperature spectra at each point. This is the first time that both high spatial and frequency-resolution brightness temperature spectra have been available over such a broad radio-frequency range. We find that over most of the region the spectra fall into one of the two well-defined categories: thermal free-free or thermal gyroresonance. In these cases, we use the spectra to deduce the spatial variation of physical parameters-electron temperature, column emission measure (intergral n(sup 2)(sub e) dl), and the coronal magnetic field strength-in and around the active region. Over a limited area of the region, the spectra resemble neither of the simple types, and alternative interpretations are required. The possibilties include the presence of fine structure that is unresolved at low frequencies; the presence of a small number of nonthermal electrons; or the presence of overlying, cooler 10(exp 6) K material which at low frequencies absorbs the hot (3 x 10(exp 6) K) thermal emission generated below.

Gary, Dale E.; Hurford, G. J.

1994-01-01

342

Fabrication and magnetic properties of cobalt nanorod arrays containing a number of ultrafine nanowires electrodeposited within an AAO/SBA-15 template  

NASA Astrophysics Data System (ADS)

Arrays of cobalt nanorods consisting of a number of nanowires have been fabricated by the electrochemical method using an anodic-aluminum oxide (AAO)/mesoporous-silica (SBA-15) composite. Microscopic studies clearly display that each nanorod (with a diameter of ˜200 nm) of the array was consisting of a number of cobalt nanowires which exhibit an average diameter of 3 nm. The observed hysteresis loops measured at room temperature indicate that the magnetic shape anisotropy of cobalt mesostructures, i.e. the parallel and perpendicular squarenesses of 0.5 and 0.1, respectively have been estimated. The maximum value of the coercivity measured perpendicular to the sample axis shows a value of 330 Oe and it was found that the coercivity decreases by increasing the temperature which is possibly caused by thermal disturbance inside the arrays.

Ji, Guangbin; Gong, Zhihong; Liu, Yousong; Chang, Xiaofeng; Du, Youwei; Qamar, M.

2011-09-01

343

Leaves and stems, rotons and solitons, magnets and arrays, one ground state lost, many found, and two fields  

NASA Astrophysics Data System (ADS)

A complete physical system typically requires three elements: particle, interaction, and manifold. Condensed matter physics provides a rich framework for generating new effective particles and new interactions such as quasiparticles, Cooper pairs or composite fermions. Rather than generate new effective particles or interactions within familiar flat space, one can also ask how novel geometrical constraints on the underlying manifold can generate new physics, even for old familiar interactions [1, 2]. Perhaps the simplest effective interaction is a featureless long-ranged repulsion, which leads to simple structures in flat space: in two dimensions, a triangular lattice. In contrast, interacting repulsive particles on a cylinder generate a rich degenerate family of helical structures that follow Fibonacci rules first seen in phyllotaxis, the study of plant morphology [3, 4, 5, 6, 7, 8]. After demonstrating phyllotactic patterns in an experimental "magnetic cactus" we show that linear dynamics of phyllotaxis generates rotons and the nonlinear regime supports a large family of dynamically stable topological solitons that can fragment, merge, or interconvert upon collision, with propagation speeds governed by energy conservation and phase matching. These new phenomena should be observable in a wide range of systems, from quantum to classical and from nanometer-scale to macroscopic. In an attempt to mimic the zero point entropy of water and spin ice [9, 10, 11], we have engineered arrays of nanoislands, called "artificial spin ice" such that their simple magnetic interaction can be frustrated by their mutual disposition. While the magnetic cactus was degenerate---although not extensively so---yet could be annealed into its ground state, the artificial spin ice is theoretically non degenerate, yet attempts to anneal it yield a disordered state, described by an athermal manifold of extensive degeneracy. We show how to predict its non trivial thermodynamics with good agreement with experimental data and no fitted parameters, using a principle of maximum likelihood reminiscent of entropy. When a flat graphene sheet is rolled in the cylindrical geometry of a carbon nanotube, a mesoscopic system is born, with macroscopic length, yet atomic scale radius [12, 13, 14]. We will show here how to adapt to it the standard elastic formalism for macroscopic objects so that its atomic complexities can be taken into account, and yet still solved analytically. Disparate experimental and numerical results find explanation in this unifying framework.

Nisoli, Cristiano

344

Magnetic and electrical properties of PbTiO3/Mn-Zn ferrite multiphase nanotube arrays by electro-deposition  

NASA Astrophysics Data System (ADS)

Composite nanotube (NT) array layers incorporating PbTiO3 and Mn-Zn ferrite were prepared by electrophoretic deposition and hydrothermal method using TiO2 NT arrays as templates. Crystal structure and micrograph of the hybrid NTs were characterized by x-ray diffraction and field-emission scanning electron microscopy. The samples showed multiphase of tetragonal PbTiO3 and spinel Mn-Zn ferrite structure. Temperature depended magnetic properties of the layers were studied when the applied field paralleled the NT's channel axis. Temperature increasing caused an increase in magnetization by the enhanced shape anisotropy at higher temperatures. Good ferroelectricity and piezoelectricity were well remained in the hybrid NT layers. A maximum displacement of 0.3 nm and d33* of 55 pm V-1 was observed in the layers.

Guo, Limin; Wang, Xiaohui; Nan, Cewen; Li, Longtu

2012-11-01

345

Lanthanide-Organic Coordination Frameworks Showing New 5-Connected Network Topology and 3D Ordered Array of Single-Molecular Magnet Behavior in the Dy Case.  

PubMed

Five isostructural lanthanide-organic coordination frameworks with a unique 3-D 5-connected (4(7).6(3))(4(3).6(5).8(2)) network, namely, [Ln(phen)(L)]n (Ln = Dy for 1, Gd for 2, Ho for 3, Er for 4, and Tb for 5), have been prepared based on bridging 5-hydroxyisophthalic acid (H3L) and chelating 1,10-phenanthroline (phen) coligand. Significantly, the Dy(III) complex 1 is an organized array of single-molecular magnets (SMMs), with frequency-dependent out-of-phase ac susceptibility signals and magnetization hysteresis at 4 K. Further analysis of the magnetic results can reveal that the SMM behavior of 1 should arise from the smaller ferromagnetic interaction between the Dy(III) ions. Complex 1 was also characterized by X-ray absorption spectra, which give the clear X-ray magnetic circular dichroism signal. PMID:24937442

Chen, Min; Sañudo, E Carolina; Jiménez, Erika; Fang, Shao-Ming; Liu, Chun-Sen; Du, Miao

2014-07-01

346

Spin-Polarized Scanning Tunneling Microscopy Study of Single-Crystallized Fe Nano-Magnet Arrays Fabricated with an Alumina Shadow Mask  

NASA Astrophysics Data System (ADS)

We have developed a method to grow patterned Fe-dot arrays by in situ deposition. Self-sustained porous alumina layer is fabricated from aluminum-coated Si substrate. Using the alumina layer with perfectly ordered pores, we fabricated the alumina shadow mask.(J. H. Choi, T.-H. Kim, J. Seo, and Y. Kuk (to be published).) Fe nano-dot arrays with 0.2--10 nm thicknesses, 50--100 nm diameters, and 100--200 nm periods were successfully grown on W(110) in an UHV system. Single-crystallized, Fe nano-dot arrays were obtained by mild heating. Spin-polarized scanning tunneling microscopy (SP-STM), the most powerful technique to study magnetic nanostructures, can detect the local spin density of the magnetic sample with atomic resolution.(S. Heinze, M. Bode, A. Kubetzka, O. Pietzsch, X. Nie, S. Blugel, and R. Wiesendanger, Science 288), 1805 (2000). The difference between randomly distributed Fe islands and regularly patterned Fe nano-dot arrays has been studied with SP-STM.

Kim, T.-H.; Choi, J. H.; Seo, J.; Kuk, Y.

2004-03-01

347

Dot size dependence of magnetic properties in microfabricated L10-FePt (001) and L10-FePt (110) dot arrays  

Microsoft Academic Search

L10-FePt (001) and L10-FePt (110) dot arrays with well-defined geometry were fabricated through the use of electron beam lithography and Ar ion etching. The lateral size of dots was varied in the range from 0.2×0.2 to 5×5 mum2. Coercivity (Hc) for the perpendicularly magnetized FePt (001) dots increases with decreasing the dot size. In the case of the FePt (110)

T. Seki; T. Shima; K. Yakushiji; K. Takanashi; G. Q. Li; S. Ishio

2006-01-01

348

A review of new wire arrays with open and closed magnetic configurations at the 1.6 MA Zebra generator for radiative properties and opacity effects  

NASA Astrophysics Data System (ADS)

The studies emphasize investigation of plasma formation, implosion, and radiation features as a function of two load configurations: compact multi-planar and cylindrical wire arrays. Experiments with different Z-pinch loads were performed on 1.6 MA, 100 ns, Zebra generator at University of Nevada, Reno. The multi-planar wire arrays (PWAs) were studied in open and closed configurations with Al, Cu, brass, Mo and W wires. In the open magnetic configurations (single, double, triple PWAs) magnetic fields are present inside the arrays from the beginning of discharge, while in closed configurations (prism-like PWA) the global magnetic field is excluded inside before plasma flow occurs. The new prism-like PWA allows high flexibility in control of implosion dynamics and precursor formation. The spectral modeling, magneto-hydrodynamic (MHD) and wire ablation dynamic model (WADM) codes were used to describe the plasma evolution and plasma parameters. Experimentally observed electron temperature and density in multiple bright spots reached 1.4 keV and 5 × 10 21 cm -3, respectively. Two types of bright spots were observed. With peak currents up to 1.3 MA opacity effects became more pronounced and led to a limiting of the X-ray yields from compact cylindrical arrays. Despite different magnetic energy to plasma coupling mechanisms early in the implosion a comparison of compact double PWA and cylindrical WA results indicates that during the stagnation stage the same plasma heating mechanism may occur. The double PWA was found to be the best radiator tested at University scale 1 MA generator. It is characterized by a combination of larger yield and power, mm-scale size, and provides the possibility of radiation pulse shaping. Further, the newer configuration, the double PWA with skewed wires, was tested and showed the possibility of a more effective X-ray generation.

Kantsyrev, V. L.; Safronova, A. S.; Esaulov, A. A.; Williamson, K. M.; Shrestha, I.; Yilmaz, F.; Osborne, G. C.; Weller, M. E.; Ouart, N. D.; Shlyaptseva, V. V.; Rudakov, L. I.; Chuvatin, A. S.; Velikovich, A. L.

2009-09-01

349

A 1-D Solid-State-Sensor-Based Array System for Magnetic Field Imaging of Steel Reinforcing Bars Embedded Within Reinforced Concrete  

Microsoft Academic Search

This paper describes a linear 1-D solid-state-based magneto-inductive sensor array for detecting and imaging steel-reinforcing bars embedded within prestressed and reinforced concrete. Using a square coil of 300 mm times 300 mm times 2.5 mm and by only measures of the vertical component of the magnetic flux density, pictorial representation of embedded rebars of different diameters and configurations can be

Diego S. Benitez; Sung Quek; Patrick Gaydecki; Vladimir Torres

2009-01-01

350

Magnetic Forces Simulation of Bulk HTS over Permanent Magnetic Railway with Numerical Method  

NASA Astrophysics Data System (ADS)

Magnetic levitation forces of bulk high temperature superconductor (HTS) above two types permanent magnet railway (PMR) is simulated using finite element method (FEM). The models are formulated by H-formulation and resolving codes is developed using Finite Element Program Generator (FEPG). The E- J power law is used to describe the electrical field vs. current density nonlinear characteristic of HTS. The applied magnetic fields induced by the PMR are calculated by the standard analysis method with the equivalent surface current model. By the method, the calculation formulation of magnetic fields generated by Halbach PMR and symmetrical PMR is derived respectively. The simulation results show that the finite element dynamic mesh rebuilding problem of HTS magnetic levitation transportation system comprised of bulk HTS and PMR can be easily avoided by the methods.

Lu, Yiyun; Zhuang, Shujun

2012-10-01

351

Striped Tape Arrays  

Microsoft Academic Search

How data striping ideas apply to arrays of magnetic tape drives is being investigated. Data striping increases throughput and reduces response time for large accesses to a storage system. Striped magnetic tape systems are particularly appealing because many inexpensive magnetic tape drives have low bandwidth. Striping may offer dramatic performance improvements for these systems. Several important issues in designing striped

Ann L. Drapeau; Randy H. Katz

1993-01-01

352

Array of Hall Effect Sensors for Linear Positioning of a Magnet Independently of Its Strength Variation. A Case Study: Monitoring Milk Yield during Milking in Goats  

PubMed Central

In this study we propose an electronic system for linear positioning of a magnet independent of its modulus, which could vary because of aging, different fabrication process, etc. The system comprises a linear array of 24 Hall Effect sensors of proportional response. The data from all sensors are subject to a pretreatment (normalization) by row (position) making them independent on the temporary variation of its magnetic field strength. We analyze the particular case of the individual flow in milking of goats. The multiple regression analysis allowed us to calibrate the electronic system with a percentage of explanation R2 = 99.96%. In our case, the uncertainty in the linear position of the magnet is 0.51 mm that represents 0.019 L of goat milk. The test in farm compared the results obtained by direct reading of the volume with those obtained by the proposed electronic calibrated system, achieving a percentage of explanation of 99.05%.

Garcia-Diego, Fernando-Juan; Sanchez-Quinche, Angel; Merello, Paloma; Beltran, Pedro; Peris, Cristofol

2013-01-01

353

The reliability of the seismo-magnetic method derived from ULF/ELF observations by the South European Geomagnetic Array (SEGMA)  

NASA Astrophysics Data System (ADS)

In the frame of the South European GeoMagnetic Array (SEGMA) project magnetic field variations are studied in the frequency range from several milli-Hz to several Hz. The fluxgate and induction coil magnetometers are located in Italy, Bulgaria and Hungary. The scientific objectives comprises field-line resonances, space weather phenomena and seismo-magnetic (SM) studies. In our present study on the reliability of the seismo-magnetic method we emphasize on the influence of external non-seismic sources on the quality of seismo-magnetic studies. External magnetic sources include lightning, power lines, railway and traffic as well as geomagnetic variations of magnetospheric origin. We observe anomalies of the ratio of the vertical to horizontal magnetic field component in the ultra/extreme-low-frequency (ULF/ELF) frequency range up to several Hz [2]. These signals can be produced in the lithosphere near a seismic active region and are interpreted as earthquake precursors. In order to differentiate geomagnetic from seismo-magnetic fluctuations, we use mainly observations around midnight because the night time geomagnetic fluctuations are much smaller than during day time. The SEGMA network provides the unique opportunity to use multipoint observations, which are also useful to distinguish local from global phenomena. In order to get undisturbed magnetic field observations, the stations are located outside populated areas [2]. The electrical conductivity of the soil in the vicinity of magnetometers on the terrestrial surface is a further source for interferences. This type of disturbances caused by induced electrical currents can be minimized either by a careful selection of the magnetometer site ans/or by the measurement of the conductivity profile in the vicinity of the instrument site. In the frame of the investigation of the April 6, 2009 L'Aquila earthquake magneto-telluric methods have been used to measure the conductivity profile near the epicenter of the earthquake and thus correct the observed magnetic field fluctuations [1]. A further interference source which can reduce the sensitivity of the seismo-magnetic methods (SM) is the mechanical vibration of the magnetometer sensors. We present a SM reliability number taking into account all above mentioned interference sources. The SM number can be used to improve the sensitivity of the seismo-magnetic method. References [1] G. Prattes, et al.: Ultra Low Frequency (ULF) European multi station magnetic field analysis before and during the 2009 earthquake at L'Aquila regarding regional geotechnical information, Nat. Hazards Earth Syst. Sci., 11, 1959-1968, 2011 [2] K. Schwingenschuh, et al.: 'Clean' observations of magnetic field fluctuations on planetary surfaces, Aerospace EMC, 2012 Proceedings ESA Workshop on 21-23 May 2012, 4 p., 2012.

Schwingenschuh, Konrad; Prattes, Gustav; Eichelberger, Hans Ulrich; Magnes, Werner; Berghofer, Gerhard; Aydogar, Özer; Besser, Bruno P.; Boudjada, Mohammed; Stangl, Günter; Zhang, Tie Long; Wolbang, Daniel; Vellante, Massimo; Villante, Umberto; Rozhnoi, Alexander; Solovieva, Maria; Nenovski, Petko; Veztergom, Victor; Szendr?i, Judith

2013-04-01

354

Novel magnetite-silica nanocomposite (Fe3O4-SBA-15) particles for DNA binding and gene delivery aided by a magnet array.  

PubMed

Novel magnetite-silica nanocomposite particles were prepared using SBA-15 nanoporous silica as template. Magnetite nanoparticles were impregnated into the nanopore array of the silica template through thermal decomposition of iron(III) acetylacetonate, Fe(AcAc)3 at 200 degrees C. These composite particles were characterized using TEM, XRD and SQUID magnetometry. The TEM images showed that the size of composite particles was around 500 nm and the particles retained the nanoporous array of SBA-15. The formation of magnetite nanoparticles was confirmed by the powder XRD study. These composite particles also exhibited ferrimagnetic properties. By coating with short chain polyethyleneimine (PEI), these particles are capable of binding DNA molecules for gene delivery and transfection. With an external magnetic field, the transfection efficiency was shown to have an increase of around 15%. The results indicated that these composite nanoparticles may be further developed as a new tool for nanomagnetic gene transfection. PMID:21776740

Yiu, Humphrey H P; McBain, Stuart C; Lethbridge, Zoe A D; Lees, Martin R; Palona, Iryna; Olariu, Cristina I; Dobson, Jon

2011-04-01

355

Tuning the magnetic anisotropy of Co-Ni nanowires: comparison between single nanowires and nanowire arrays in hard-anodic aluminum oxide membranes.  

PubMed

Co(x)Ni(1-x) alloy nanowires with varying Co content (0 ? x ? 0.95), having a diameter of 130 nm and length of around 20 ?m, are synthesized by template-assisted electrodeposition into the nanopores of SiO(2) conformal coated hard-anodic aluminum oxide membranes. The magneto-structural properties of both single isolated nanowires and hexagonally ordered nanowire arrays of Co-Ni alloys are systematically studied by means of magneto-optical Kerr effect magnetometry and vibrating sample magnetometry, respectively, allowing us to compare different alloy compositions and to distinguish between the magnetostatic and magnetocrystalline contributions to the effective magnetic anisotropy for each system. The excellent tunable soft magnetic properties and magnetic bistability exhibited by low Co content Co-Ni nanowires indicate that they might become the material of choice for the development of nanostructured magnetic systems and devices as an alternative to Fe-Ni alloy based systems, being chemically more robust. Furthermore, Co contents higher than 51 at.% allow us to modify the magnetic behavior of Co-rich nanowires by developing well controlled magnetocrystalline anisotropy, which is desirable for data storage applications. PMID:23095457

Vega, V; Böhnert, T; Martens, S; Waleczek, M; Montero-Moreno, J M; Görlitz, D; Prida, V M; Nielsch, K

2012-11-23

356

Rapid magnetic cell delivery for large tubular bioengineered constructs.  

PubMed

Delivery of cells into tubular tissue constructs with large diameters poses significant spatial and temporal challenges. This study describes preliminary findings for a novel process for rapid and uniform seeding of cells onto the luminal surface of large tubular constructs. Fibroblasts, tagged with superparamagnetic iron oxide nanoparticles (SPION), were directed onto the luminal surface of tubular constructs by a magnetic field generated by a k4-type Halbach cylinder device. The spatial distribution of attached cells, as measured by the mean number of cells, was compared with a conventional, dynamic, rotational cell-delivery technique. Cell loading onto the constructs was measured by microscopy and magnetic resonance imaging. The different seeding techniques employed had a significant effect on the spatial distribution of the cells (p < 0.0001). The number of attached cells at defined positions within the same construct was significantly different for the dynamic rotation technique (p < 0.05). In contrast, no significant differences in the number of cells attached to the luminal surface were found between the defined positions on the construct loaded with the Halbach cylinder. The technique described overcomes limitations associated with existing cell-delivery techniques and is amenable to a variety of tubular organs where rapid loading and uniform distribution of cells for therapeutic applications are required. PMID:22696487

Gonzalez-Molina, J; Riegler, J; Southern, P; Ortega, D; Frangos, C C; Angelopoulos, Y; Husain, S; Lythgoe, M F; Pankhurst, Q A; Day, R M

2012-11-01

357

Rapid magnetic cell delivery for large tubular bioengineered constructs  

PubMed Central

Delivery of cells into tubular tissue constructs with large diameters poses significant spatial and temporal challenges. This study describes preliminary findings for a novel process for rapid and uniform seeding of cells onto the luminal surface of large tubular constructs. Fibroblasts, tagged with superparamagnetic iron oxide nanoparticles (SPION), were directed onto the luminal surface of tubular constructs by a magnetic field generated by a k4-type Halbach cylinder device. The spatial distribution of attached cells, as measured by the mean number of cells, was compared with a conventional, dynamic, rotational cell-delivery technique. Cell loading onto the constructs was measured by microscopy and magnetic resonance imaging. The different seeding techniques employed had a significant effect on the spatial distribution of the cells (p < 0.0001). The number of attached cells at defined positions within the same construct was significantly different for the dynamic rotation technique (p < 0.05). In contrast, no significant differences in the number of cells attached to the luminal surface were found between the defined positions on the construct loaded with the Halbach cylinder. The technique described overcomes limitations associated with existing cell-delivery techniques and is amenable to a variety of tubular organs where rapid loading and uniform distribution of cells for therapeutic applications are required.

Gonzalez-Molina, J.; Riegler, J.; Southern, P.; Ortega, D.; Frangos, C. C.; Angelopoulos, Y.; Husain, S.; Lythgoe, M. F.; Pankhurst, Q. A.; Day, R. M.

2012-01-01

358

Anisotropic structural and magnetic properties of arrays of Fe 26Ni 74 nanowires electrodeposited in the pores of anodic alumina  

Microsoft Academic Search

The room temperature magnetization, magnetoresistance and structural properties of soft magnetic Fe26Ni74 nanowires of 18nm diameter and various lengths electrodeposited in the pores of anodic alumina are investigated. Nanowires show perpendicular magnetic anisotropy, anisotropic crystallographic and magnetoresistance behaviour with a coercivity of 967Oe and a remanence value of 85%. It should be noted that an electrodeposited Fe26Ni74 layer (6?m) on

H. R Khan; K Petrikowski

2000-01-01

359

Fabrication and magnetic properties of arrays of amorphous and polycrystalline ferromagnetic nanowires obtained by electron beam lithography  

Microsoft Academic Search

Long magnetic nanowires of amorphous and crystalline materials have been fabricated by electron beam lithography to compare their magnetic properties. The length of the wires is varied in the 200–500?m range, and their width and the interwire distance have been reduced down to 200nm. Magnetooptical and transport measurements show that, although the overall behavior is dominated by the shape anisotropy

J. I. Martín; M. Vélez; R. Morales; J. M. Alameda; J. V. Anguita; F. Briones; J. L. Vicent

2002-01-01

360

Room temperature direct detection of low frequency magnetic fields in the 100 pT/Hz0.5 range using large arrays of magnetic tunnel junctions  

NASA Astrophysics Data System (ADS)

We developed a highly sensitive magnetic tunnel junction (MTJ) based magnetic field sensor device with a magnetic field sensitivity of 1.29 ?/?T. For this, more than 1000 microstructured linear MgO based MTJ pillars were fabricated and connected in series. By current biasing the MTJ sensor device under small AC external magnetic fields (?0HAC), a large AC output voltage proportional to ?0HAC is induced. Carrying out noise spectral density measurements at such conditions, we demonstrate that our MTJ sensor device is able to detect magnetic fields down to 115 pT/Hz0.5 at frequencies fAC < 200 Hz in an unshielded environment without amplification of the MTJ AC output voltage.

Paz, E.; Serrano-Guisan, S.; Ferreira, R.; Freitas, P. P.

2014-05-01

361

OH Maser Sources in W49N: Probing Magnetic Field and Differential Anisotropic Scattering with Zeeman Pairs Using the Very Long Baseline Array  

NASA Astrophysics Data System (ADS)

Our analysis of a Very Long Baseline Array 12 hr synthesis observation of the OH masers in the well-known star-forming region W49N has yielded valuable data that enable us to probe distributions of magnetic fields in both the maser columns and the intervening interstellar medium (ISM). The data, consisting of detailed high angular resolution images (with beam width ~20 mas) of several dozen OH maser sources, or spots, at 1612, 1665, and 1667 MHz, reveal anisotropic scatter broadening with typical sizes of a few tens of milliarcseconds and axial ratios between 1.5 and 3. Such anisotropies have been reported previously by Desai et al. and have been interpreted as being induced by the local magnetic field parallel to the Galactic plane. However, we find (1) apparent angular sizes of, on average, a factor of about 2.5 less than those reported by Desai et al., indicating significantly less scattering than inferred previously, and (2) a significant deviation in the average orientation of the scatter-broadened images (by ~10°) from that implied by the magnetic field in the Galactic plane. More intriguingly, for a few Zeeman pairs in our set, significant differences (up to 6?) are apparent in the scatter-broadened images for the two hands of circular polarization, even when the apparent velocity separation is less than 0.1 km s-1. This may possibly be the first example of a Faraday rotation contribution to the diffractive effects in the ISM. Using the Zeeman pairs, we also study the distribution of the magnetic field in the W49N complex, finding no significant trend in the spatial structure function. In this paper, we present the details of our observations and analysis leading to these findings, discuss implications of our results for the intervening anisotropic magneto-ionic medium, and suggest possible implications for the structure of magnetic fields within this star-forming region.

Deshpande, Avinash A.; Goss, W. M.; Mendoza-Torres, J. E.

2013-09-01

362

Using magnetic fields and band gap engineering to achieve robust spin filtering in finite quantum dot arrays  

NASA Astrophysics Data System (ADS)

In periodic quantum dot arrays, conductance can be modulated by exploiting band gap effects. Since the backscattering effects that produce some of the band gaps are comparatively strong, an open array with as little as three dots can be utilized to achieve zero transmission. Utilizing Zeeman-splitting, one can create a situation where, by the shifting the gaps for the individual spins, one can achieve nearly 100% spin polarization. The energy scales over which this polarization is achieved depends on the size of the band gaps. Thus, the effect can be enhanced further by band gap engineering, picking the structure that maximizes the size of the gaps for a given Fermi energy and field.

Akis, R.; Ferry, D. K.

2008-03-01

363

Fabrication and structural characterization of highly ordered sub-100-nm planar magnetic nanodot arrays over 1 cm2 coverage area  

NASA Astrophysics Data System (ADS)

Porous alumina masks are fabricated by anodization of aluminum films grown on both semiconducting and insulating substrates. For these self-assembled alumina masks, pore diameters and periodicities within the ranges of 10-130 and 20-200 nm, respectively, can be controlled by varying anodization conditions. 20 nm periodicities correspond to pore densities in excess of 1012 per square inch, close to the holy grail of media with 1 Tbit/in.2 density. With these alumina masks, ordered sub-100-nm planar ferromagnetic nanodot arrays covering over 1 cm2 were fabricated by electron beam evaporation and subsequent mask lift-off. Moreover, exchange-biased bilayer nanodots were fabricated using argon-ion milling. The average dot diameter and periodicity are tuned between 25 and 130 nm and between 45 and 200 nm, respectively. Quantitative analyses of scanning electron microscopy (SEM) images of pore and dot arrays show a high degree of hexagonal ordering and narrow size distributions. The dot periodicity obtained from grazing incidence small angle neutron scattering on nanodot arrays covering ~2.5 cm2 is in good agreement with SEM image characterization.

Li, Chang-Peng; Roshchin, Igor V.; Batlle, Xavier; Viret, Michel; Ott, Frédéric; Schuller, Ivan K.

2006-10-01

364

Dot size dependence of magnetic properties in microfabricated L10-FePt (001) and L10-FePt (110) dot arrays  

NASA Astrophysics Data System (ADS)

L10-FePt (001) and L10-FePt (110) dot arrays with well-defined geometry were fabricated through the use of electron beam lithography and Ar ion etching. The lateral size of dots was varied in the range from 0.2×0.2 to 5×5 ?m2. Coercivity (Hc) for the perpendicularly magnetized FePt (001) dots increases with decreasing the dot size. In the case of the FePt (110) dots with in-plane magnetization, on the other hand, the dot size dependence of Hc is completely different from that for FePt (001) dots: Hc shows a slight decrease as the dot size decreases. After annealing at 600 °C, the values of Hc for both FePt (001) and FePt (110) dots are remarkably enhanced although the dot size dependence shows similar behavior to that before annealing. The magnetization reversal for all the dots occurs through the nucleation of reversed domains and subsequent domain wall propagation.

Seki, T.; Shima, T.; Yakushiji, K.; Takanashi, K.; Li, G. Q.; Ishio, S.

2006-08-01

365

Improvement in the microstructure and magnetic properties in arrays of dc pulse electrodeposited Co nanowires induced by Cu pre-plating  

NASA Astrophysics Data System (ADS)

Co nanowire arrays were pulse electrodeposited into nanoporous alumina templates via the dendrite pores of a thinned barrier layer formed by exponentially non-equilibrium anodization, either without or with Cu pre-plating. Electrolyte acidity (pH) dependence of the microstructure and magnetic properties of the prepared Co nanowires was investigated and compared. The process of Cu pre-plating prior to electrodeposition of Co nanowires along with an adjustment of the pH value was shown to significantly improve the magnetic properties of the Co nanowires and ultimately result in a high coercivity (about 3000 Oe) and squareness up to 98% at pH ? 5.7. The improvement of magnetic properties may be caused by the rotation of the hexagonal close packed c-axis of more crystal grains along with the wire axis, which supplements the shape anisotropy of the nanowires. The angular dependence of the coercivity (Hc(?)) of both types of prepared Co nanowires was also studied.

Ghaffari, M.; Ramazani, A.; Almasi Kashi, M.

2013-07-01

366

Structural and magnetic characterization of as-prepared and annealed FeCoCu nanowire arrays in ordered anodic aluminum oxide templates  

NASA Astrophysics Data System (ADS)

Herein, we report on the preparation, structure, and magnetic characterization of FeCoCu nanowire arrays grown by DC electrodeposition inside self-assembled ordered nanopores of anodic aluminum oxide templates. A systematic study of their structure has been performed both in as-prepared samples and after annealing in the temperature range up to 800 °C, although particular attention has been paid to annealing at 700 °C after which maximum magnetic hardening is achieved. The obtained nanowires have a diameter of 40 nm and their Fe0.28Co0.67Cu0.05 composition was confirmed by energy dispersive X-ray spectroscopy (EDS). Focused ion-beam lamellas of two samples (as-prepared and annealed at 700 °C) were prepared for their imaging in the high-resolution transmission electron microscopy (HRTEM) perpendicularly to the electron beam, where the obtained EDS compositional mappings show a homogeneous distribution of the elements. X-ray diffraction analysis, and selected area electron diffraction (SAED) patterns confirm that nanowires exhibit a bcc cubic structure (space group Im-3m). In addition, bright-dark field images show that the nanowires have a polycrystalline structure that remains essentially the same after annealing, but some modifications were observed: (i) an overall increase and sharpening of recrystallized grains, and (ii) an apparent shrinkage of the nanowires diameter. Obtained SAED patterns also show strong textured components with determined ?111? and ?112? crystalline directions parallel to the wires growth direction. The presence of both directions was also confirmed in the HRTEM images doing Fourier transform analyses. Magnetic measurements show strong magnetic anisotropy with magnetization easy axis parallel to the nanowires in as-prepared and annealed samples. The magnetic properties are tuned by suitable thermal treatments so that, maximum enhanced coercivity (˜2.7 kOe) and normalized remanence (˜0.91 Ms) values are achieved after annealing at temperature of 700 °C. The contribution of the changes in the crystalline structure, induced by the heat treatment, to the magnetic hardening of the FeCoCu nanowires is discussed.

Rodríguez-González, B.; Bran, C.; Warnatz, T.; Rivas, J.; Vazquez, M.

2014-04-01

367

Use of a SQUID array to detect T-cells with magnetic nanoparticles in determining transplant rejection  

NASA Astrophysics Data System (ADS)

Acute rejection in organ transplant is signaled by the proliferation of T-cells that target and kill the donor cells requiring painful biopsies to detect rejection onset. An alternative non-invasive technique is proposed using a multi-channel superconducting quantum interference device (SQUID) magnetometer to detect T-cell lymphocytes in the transplanted organ labeled with magnetic nanoparticles conjugated to antibodies specifically attached to lymphocytic ligand receptors. After a magnetic field pulse, the T-cells produce a decaying magnetic signal with a characteristic time of the order of a second. The extreme sensitivity of this technique, 10 5 cells, can provide early warning of impending transplant rejection and monitor immune-suppressive chemotherapy.

Flynn, Edward R.; Bryant, H. C.; Bergemann, Christian; Larson, Richard S.; Lovato, Debbie; Sergatskov, Dmitri A.

2007-04-01

368

Slow magnetic relaxation in a hydrogen-bonded 2D array of mononuclear dysprosium(III) oxamates.  

PubMed

The reaction of N-(2,6-dimethylphenyl)oxamic acid with dysprosium(III) ions in a controlled basic media afforded the first example of a mononuclear lanthanide oxamate complex exhibiting a field-induced slow magnetic relaxation behavior typical of single-ion magnets (SIMs). The hydrogen-bond-mediated self-assembly of this new bifunctional dysprosium(III) SIM in the solid state provides a unique example of 2D hydrogen-bonded polymer with a herringbone net topology. PMID:23597255

Fortea-Pérez, Francisco R; Vallejo, Julia; Julve, Miguel; Lloret, Francesc; De Munno, Giovanni; Armentano, Donatella; Pardo, Emilio

2013-05-01

369

Surface potential and magnetic properties of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} periodic arrays fabricated by direct electron beam writing  

SciTech Connect

It is demonstrated that magnetic periodic arrays can be easily fabricated from direct writing water developable La{sub 0.7}Sr{sub 0.3}MnO{sub 3} electron beam resist. Two unique features of our approach are (1) the patterned La{sub 0.7}Sr{sub 0.3}MnO{sub 3} resist film can be developed using nontoxic and environmentally friendly pure water and (2) either positive or negative patterns can be fabricated depending on the dosage of electron beam. The mechanism of the dual function characteristic of the resist was studied using Kelvin probe microscope. The surface potential of patterned La{sub 0.7}Sr{sub 0.3}MnO{sub 3} resist increases with increasing electron beam dosage due to the changes of resist composition. The formations of periodic magnetic arrays were confirmed by the studies of scanning electron microscope and magnetic force microscope. The magnetization of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} can be enhanced by postsintering the sample at 900 deg. C after electron beam irradiation. We have therefore provided a one-step, simple, and convenient alternative technique for the fabrication of nanoscale magnetic patterns, which form the building blocks for the study of physical properties in periodic magnetic arrays.

Wu, M.-C.; Wu, Y.-J.; Huang, Y.-C.; Chuang, C.-M. [Department of Materials Science and Engineering, National Taiwan University, Taipei 106-17, Taiwan (China); Cheng, K.-C. [Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, Taipei 106-08, Taiwan (China); Lin, C.-F. [Graduate Institute of Electro-optical Engineering and Department of Electrical Engineering, National Taiwan University, Taipei 106-17, Taiwan (China); Chen, Y.-F. [Department of Physics, National Taiwan University, Taipei 106-17, Taiwan (China); Center for Condensed Matter Sciences, National Taiwan University, Taipei 106-17, Taiwan (China); Su, W.-F. [Department of Materials Science and Engineering, National Taiwan University, Taipei 106-17, Taiwan (China); Center for Condensed Matter Sciences, National Taiwan University, Taipei 106-17, Taiwan (China)

2008-07-15

370

Magnetic and structural properties of fcc\\/hcp bi-crystalline multilayer Co nanowire arrays prepared by controlled electroplating  

Microsoft Academic Search

We report on the structural and magnetic properties of crystalline bi-phase Co nanowires, electrodeposited into the pores of anodized alumina membranes, as a function of their length. Co nanowires present two different coexistent crystalline structures (fcc and hcp) that can be controlled by the time of pulsed electrodeposition. The fcc crystalline phase grows at the early stage and is present

K. R. Pirota; F. Béron; D. Zanchet; T. C. R. Rocha; D. Navas; J. Torrejón; M. Vazquez; M. Knobel

2011-01-01

371

Influence of Y-doped induced defects on the optical and magnetic properties of ZnO nanorod arrays prepared by low-temperature hydrothermal process  

PubMed Central

One-dimensional pure zinc oxide (ZnO) and Y-doped ZnO nanorod arrays have been successfully fabricated on the silicon substrate for comparison by a simple hydrothermal process at the low temperature of 90°C. The Y-doped nanorods exhibit the same c-axis-oriented wurtzite hexagonal structure as pure ZnO nanorods. Based on the results of photoluminescence, an enhancement of defect-induced green-yellow visible emission is observed for the Y-doped ZnO nanorods. The decrease of E2(H) mode intensity and increase of E1(LO) mode intensity examined by the Raman spectrum also indicate the increase of defects for the Y-doped ZnO nanorods. As compared to pure ZnO nanorods, Y-doped ZnO nanorods show a remarked increase of saturation magnetization. The combination of visible photoluminescence and ferromagnetism measurement results indicates the increase of oxygen defects due to the Y doping which plays a crucial role in the optical and magnetic performances of the ZnO nanorods.

2012-01-01

372

Extended-aperture spatial diversity and polarizational diversity using a sparse array of electric dipoles or magnetic loops  

Microsoft Academic Search

A novel eigenstructure scheme of extended-aperture spatial diversity and polarizational diversity is proposed for 2D arrival angle estimation. This innovational method involves uniformly spaced triads (or pairs) of electric dipoles or magnetic loops, spaced much farther apart than a half-wavelength. An ESPRIT-based step produces arrival angle estimates that suffer cyclic ambiguity due to the extended spacing. Then, a closed-form integer

M. D. Zoltowski; K. T. Wong

1997-01-01

373

Method and apparatus for control of a magnetic structure  

SciTech Connect

A method and apparatus for independently adjusting the spacing between opposing magnet arrays in charged particle based light sources. Adjustment mechanisms between each of the magnet arrays and the supporting structure allow the gap between the two magnet arrays to be independently adjusted. In addition, spherical bearings in the linkages to the magnet arrays permit the transverse angular orientation of the magnet arrays to also be adjusted. The opposing magnet arrays can be supported above the ground by the structural support. 4 figs.

Challenger, M.P.; Valla, A.S.

1996-06-18

374

Method and apparatus for control of a magnetic structure  

DOEpatents

A method and apparatus for independently adjusting the spacing between opposing magnet arrays in charged particle based light sources. Adjustment mechanisms between each of the magnet arrays and the supporting structure allow the gap between the two magnet arrays to be independently adjusted. In addition, spherical bearings in the linkages to the magnet arrays permit the transverse angular orientation of the magnet arrays to also be adjusted. The opposing magnet arrays can be supported above the ground by the structural support.

Challenger, Michael P. (Bothell, WA); Valla, Arthur S. (Bothell, WA)

1996-06-18

375

Nanocylinder arrays  

DOEpatents

Pathways to rapid and reliable fabrication of nanocylinder arrays are provided. Simple methods are described for the production of well-ordered arrays of nanopores, nanowires, and other materials. This is accomplished by orienting copolymer films and removing a component from the film to produce nanopores, that in turn, can be filled with materials to produce the arrays. The resulting arrays can be used to produce nanoscale media, devices, and systems.

Tuominen, Mark (Shutesbury, MA); Schotter, Joerg (Bielefeld, DE); Thurn-Albrecht, Thomas (Freiburg, DE); Russell, Thomas P. (Amherst, MA)

2009-08-11

376

Crustal thickness and Vp/Vs estimates near the Brunswick magnetic anomaly using receiver functions from the SESAME array  

NASA Astrophysics Data System (ADS)

The Southeastern Suture of the Appalachian Margin Experiment (SESAME) is designed to investigate lithospheric dynamics associated with the Paleozoic collision between the Suwanee terrane and Laurentia as well as subsequent Mesozoic rifting and passive margin formation. So far, we have deployed 63 broadband instruments along two N-S trending profiles across Georgia and northern Florida. A third NW-trending profile consisting of 19 stations extends across accreted terranes of the southern Appalachians from Augusta, GA to eastern TN. The N-S profiles are intended to provide constraints on variations in crustal structure across the Brunswick magnetic anomaly (BMA), a prominent magnetic low coinciding with south-dipping crustal-scale seismic reflectors evident on COCORP profiles in south Georgia. The seismic reflectivity is likely a consequence of suturing, but the BMA has been interpreted as an edge effect related to collision as well as an effect of mafic magmatism south of the suture zone. H-k stacking using 10 teleseismic receiver functions from station W27, located ~50-km north of the suture on the western N-S profile, suggests a crustal thickness (H) of 42-44 km and average crustal Vp/Vs (k) of 1.73-1.80. These estimates are in agreement with previous well-constrained stacking results from USNSN station GOGA, located ~70-km to the northeast, that suggest a crustal thickness of 41-43 km and average Vp/Vs 1.72-1.76. The proposed suture zone itself lies beneath sediments of the Atlantic Coastal Plain, and receiver functions from stations in this region appear to be strongly affected by high-amplitude reverberations within the sedimentary column. Therefore, preliminary H-k stacking results from stations directly over the BMA may be unreliable. However, receiver functions from station W23 near the Inner Piedmont-Coastal Plain boundary (near the north, up-dip end of the suture zone) display variations in Ps delay time and amplitude with event back-azimuth. Receiver functions from the S-azimuth (South American trench) display a relatively weak Ps conversion at ~4 seconds, while receiver functions from the NW-azimuth (Aleutian trench) show a more complex signal with an arrival at ~4 s followed by a higher-amplitude arrival at ~6 seconds. This may be indicative of compositional heterogeneity across the suture, anisotropy within the crust or mantle, or complexity at the crust-mantle interface related to collision of the Suwanee terrane. Forthcoming data from additional stations will provide improved constraints on crustal structure across the BMA.

Parker, E. H.; Hawman, R. B.; Fischer, K. M.; Wagner, L. S.

2012-12-01

377

Chemical identification strategies using liquid chromatography-photodiode array-solid-phase extraction-nuclear magnetic resonance/mass spectrometry.  

PubMed

The identification of metabolites in biochemical studies is a major bottleneck in the proliferating field of metabolomics. In particular in plant metabolomics, given the diversity and abundance of endogenous secondary metabolites in plants, the identification of these is not only challenging but also essential to understanding their biological role in the plant, and their value to quality and nutritional attributes as food crops. With the new generation of analytical technologies, in which liquid chromatography (LC)-mass spectrometry (MS) and nuclear magnetic resonance (NMR) play a pioneering role, profiling metabolites in complex extracts is feasible at high throughput. However, the identification of key metabolites remains a limitation given the analytical effort necessary for traditional structural elucidation strategies. The hyphenation of LC-solid phase extraction (SPE)-NMR is a powerful analytical platform for isolating and concentrating metabolites for unequivocal identification by NMR measurements. The combination with LC-MS is a relatively straightforward approach to obtaining all necessary information for structural elucidation. Using this set-up, we could, as an example, readily identify five related glycosylated phenolic acids present in broccoli (Brassica oleracea, group Italica, cv Monaco): 1,2-di-O-E-sinapoyl-?-gentiobiose, 1-O-E-sinapoyl-2-O-E-feruloyl-?-gentiobiose, 1,2-di-O-E-feruloyl-?-gentiobiose, 1,2,2'-tri-O-E-sinapoyl-?-gentiobiose, and 1,2'-di-O-E-sinapoyl-2-O-E-feruloyl-?-gentiobiose. PMID:22351183

Moco, Sofia; Vervoort, Jacques

2012-01-01

378

Hybrid photomultiplier tube and photodiode parallel detection array for wideband optical spectroscopy of the breast guided by magnetic resonance imaging.  

PubMed

A new optical parallel detection system of hybrid frequency and continuous-wave domains was developed to improve the data quality and accuracy in recovery of all breast optical properties. This new system was deployed in a previously existing system for magnetic resonance imaging (MRI)-guided spectroscopy, and allows incorporation of additional near-infrared wavelengths beyond 850 nm, with interlaced channels of photomultiplier tubes (PMTs) and silicon photodiodes (PDs). The acquisition time for obtaining frequency-domain data at six wavelengths (660, 735, 785, 808, 826, and 849 nm) and continuous-wave data at three wavelengths (903, 912, and 948 nm) is 12 min. The dynamic ranges of the detected signal are 105 and 106 for PMT and PD detectors, respectively. Compared to the previous detection system, the SNR ratio of frequency-domain detection was improved by nearly 103 through the addition of an RF amplifier and the utilization of programmable gain. The current system is being utilized in a clinical trial imaging suspected breast cancer tumors as detected by contrast MRI scans. PMID:23979460

El-Ghussein, Fadi; Mastanduno, Michael A; Jiang, Shudong; Pogue, Brian W; Paulsen, Keith D

2014-01-01

379

Hybrid photomultiplier tube and photodiode parallel detection array for wideband optical spectroscopy of the breast guided by magnetic resonance imaging  

NASA Astrophysics Data System (ADS)

A new optical parallel detection system of hybrid frequency and continuous-wave domains was developed to improve the data quality and accuracy in recovery of all breast optical properties. This new system was deployed in a previously existing system for magnetic resonance imaging (MRI)-guided spectroscopy, and allows incorporation of additional near-infrared wavelengths beyond 850 nm, with interlaced channels of photomultiplier tubes (PMTs) and silicon photodiodes (PDs). The acquisition time for obtaining frequency-domain data at six wavelengths (660, 735, 785, 808, 826, and 849 nm) and continuous-wave data at three wavelengths (903, 912, and 948 nm) is 12 min. The dynamic ranges of the detected signal are 105 and 106 for PMT and PD detectors, respectively. Compared to the previous detection system, the SNR ratio of frequency-domain detection was improved by nearly 103 through the addition of an RF amplifier and the utilization of programmable gain. The current system is being utilized in a clinical trial imaging suspected breast cancer tumors as detected by contrast MRI scans.

El-Ghussein, Fadi; Mastanduno, Michael A.; Jiang, Shudong; Pogue, Brian W.; Paulsen, Keith D.

2014-01-01

380

Magnetic and dielectric properties of one-dimensional array of S = 1/2 linear trimer system Na2Cu3Ge4O12  

NASA Astrophysics Data System (ADS)

Magnetic susceptibility ?, specific heat C, capacitance Cp, and 23Na-NMR measurements have been carried out on polycrystalline samples of quantum spin linear trimer system Na2Cu3Ge4O12, which has the one-dimensional array of Cu3O8 trimers formed of edge-sharing three CuO4 square planes. The exchange interactions between the Cu2+ (S = 1/2) spins have been determined by analyzing ?-T and C-T curves. By employing the isolated S = 1/2 Heisenberg trimer model above 70 K, the nearest-neighbor exchange couplings J1 and the second-neighbor one J2 in trimer have been evaluated to J1/kB = 30 ± 20 K (antiferromagnetic) and J2/kB = 340 ± 20 K. At low temperature region, two spins of the edge in the Cu3O8 trimers form a nonmagnetic singlet by strong antiferromagnetic interaction J2, and the spin left in the center of the Cu3O8 trimer forms one-dimensional chains by the exchange interaction J3 between the trimers. By employing the S = 1/2 uniform Heisenberg chain model below 70 K, we have evaluated to J3/kB = 18 ± 1 K. The mechanism of multiferroic behavior at Tc = 2 K is discussed.

Yasui, Yukio; Kawamura, Yuji; Kobayashi, Yoshiaki; Sato, Masatoshi

2014-05-01

381

Striped tape arrays  

NASA Technical Reports Server (NTRS)

A growing number of applications require high capacity, high throughput tertiary storage systems. How data striping ideas apply to arrays of magnetic tape drives is investigated. Data striping increases throughput and reduces response time for large accesses to a storage system. Striped magnetic tape systems are particularly appealing because many inexpensive magnetic tape drives have low bandwidth; striping may offer dramatic performance improvements for these systems. There are several important issues in designing striped tape systems: the choice of tape drives and robots, whether to stripe within or between robots, and the choice of the best scheme for distributing data on cartridges. One of the most troublesome problems in striped tape arrays is the synchronization of transfers across tape drives. Another issue is how improved devices will affect the desirability of striping in the future. The results of simulations comparing the performance of striped tape systems to non-striped systems are presented.

Drapeau, Ann L.; Katz, Randy H.

1992-01-01

382

Magnetism  

NSDL National Science Digital Library

This radio broadcast discusses the history of magnetism from the time of its discovery by an apocryphal Greek sheperd until the late 16th century and the work of William Gilbert. There is also discussion of who pioneered the study of magnetism, what theories they constructed from its curious abilities, and how the power of the magnet was brought out of the realm of magic and into the service of science. The broadcast concludes with a discussion of why magnetism is still mysterious and how the modern search for the single magnetic pole, or magnetic monopole, could provide a fundamental unit of magnetism, essential for ultimate explanation. The broadcast is 41 minutes and 45 seconds in length.

2010-10-27

383

Design of a permanent magnet with a mechanical sweep suitable for variable-temperature continuous-wave and pulsed EPR spectroscopy  

NASA Astrophysics Data System (ADS)

A magnetic system is introduced which consists of three nested rings of permanent magnets of a Halbach dipolar layout and is capable for EPR spectroscopy. Two of the rings can be rotated independently to adjust the magnetic flux in the center and even allow for mechanical field sweeps. The presented prototype achieves a magnetic flux range of 0.0282-0.3013 T with a minimal sweep of 0.15 mT and homogeneity of about 10 -3. First applications with CW and pulsed Mims ENDOR as well as ESEEM experiments on a sample of a glycine single crystal doped with 1% copper nitrate demonstrate that flux range, sweep accuracy and homogeneity of this prototype is sufficient for EPR experiments on most solid samples. Together with a recently improved design magnets can be build which could serve as compact and easily transportable replacement of standard electromagnets with negligible consumption of power or coolants.

Bauer, C.; Raich, H.; Jeschke, G.; Blümler, P.

2009-06-01

384

An experimental investigation of the improvement in the reception of TM (Transverse Magnetic)-polarized LF (Low-Frequency) waves with a two-element spaced array  

NASA Astrophysics Data System (ADS)

For this study, a 2-element spaced array antenna system was developed and tested. This array consisted of two well-spaced vertical loops combined with a microwave link. The array was tested to show improvements in signal-to-noise ratio over omnidirectional antennas, using received transmissions from an aircraft towing a long wire antenna. Gains in signal-to-noise ratio of up to 12.8 dB were demonstrated.

Tingley, F. M.; Kahler, R. C.

1984-05-01

385

DNA Arrays  

NSDL National Science Digital Library

This animation from Cold Spring Harbor Laboratory's Dolan DNA Learning Center presents DNA arrays. The animation contains information on Pat Brown's discovery and the purpose of DNA arrays to study gene expression as well as its role in the development of pharmacogenomic treatment for diseases such as cancer.

2012-04-10

386

Magnetism  

NSDL National Science Digital Library

This overview of magnetism provides a brief history prior to 1600 and continues with the work of William Gilbert, Hans Christian Oersted, and Andre-Marie Ampere in describing and exploring the magnetosphere and learning the role that electric current plays in producing magnetism. Magnetic field lines are then discussed, citing the work of Michael Faraday. The work of James Clerk Maxwell and Heinrich Hertz is mentioned in a discussion of the relationship of light waves and radio waves as part of the electromagnetic spectrum.

Stern, David

387

Adaptive arrays  

Microsoft Academic Search

A method for adaptively optimizing the signal-to-noise ratio of an array antenna is presented. Optimum element weights are derived for a prescribed environment and a given signal direction. The derivation is extended to the optimization of a \\

S. Applebaum

1976-01-01

388

Enthalpy arrays  

NASA Astrophysics Data System (ADS)

We report the fabrication of enthalpy arrays and their use to detect molecular interactions, including protein-ligand binding, enzymatic turnover, and mitochondrial respiration. Enthalpy arrays provide a universal assay methodology with no need for specific assay development such as fluorescent labeling or immobilization of reagents, which can adversely affect the interaction. Microscale technology enables the fabrication of 96-detector enthalpy arrays on large substrates. The reduction in scale results in large decreases in both the sample quantity and the measurement time compared with conventional microcalorimetry. We demonstrate the utility of the enthalpy arrays by showing measurements for two protein-ligand binding interactions (RNase A + cytidine 2'-monophosphate and streptavidin + biotin), phosphorylation of glucose by hexokinase, and respiration of mitochondria in the presence of 2,4-dinitrophenol uncoupler.

Torres, Francisco E.; Kuhn, Peter; de Bruyker, Dirk; Bell, Alan G.; Wolkin, Michal V.; Peeters, Eric; Williamson, James R.; Anderson, Gregory B.; Schmitz, Gregory P.; Recht, Michael I.; Schweizer, Sandra; Scott, Lincoln G.; Ho, Jackson H.; Elrod, Scott A.; Schultz, Peter G.; Lerner, Richard A.; Bruce, Richard H.

2004-06-01

389

Cyclotron-resonance-maser arrays  

Microsoft Academic Search

The cyclotron-resonance-maser (CRM) array is a radiation source which consists of CRM elements coupled together under a common magnetic field. Each CRM-element employs a low-energy electron-beam which performs a cyclotron interaction with the local electromagnetic wave. These waves can be coupled together among the CRM elements, hence the interaction is coherently synchronized in the entire array. The implementation of the

Eli Jerby; Amit Kesar; Michael Korol; L. Lei; Vladimir Dikhtyar

1999-01-01

390

Magnetic Heading Sensor Alignment.  

National Technical Information Service (NTIS)

A magnetic heading sensor alignment device for an acoustic towed line array is described. It includes a generally cylindrical non-magnetic piece having a longitudinal opening along its central axis to accommodate the heading sensor. A plurality of longitu...

D. Strong

1990-01-01

391

Measured field performance of CEBAF beam transport magnets  

NASA Astrophysics Data System (ADS)

The 2200 magnets used in the CEBAF beam transport system have each undergone testing of their magnetic fields. Results of these measurements will be reported. INT Bdl profiles measurements (with a precision of approximately equal to 10(exp -5)) for the 270 major solid-core dipoles used a multi-turn stretched wire with a reference magnet; the range of INT Bdl for a given (1, 2, or 3 m) dipole family was +/-5 x 10(exp -4). The approximately 700 quadrupole magnets' INT B(n)dl (1 less than or equal to n less than or equal to 16, R = R(pole)) values were measured with an accuracy of 0.01% of the quadrupole field component using a multi-turn 'Halbach' bucked coil for 20% of the magnets and a reference magnet for all. They had (INT B(6)dl)/(INT B(2)dl) less than 0.03% R (pole) and (INT B(10)dl)/(INT B(2)dl) less than 0.2% R(pole).

Harwood, Leigh; Karn, Jefferey

1994-07-01

392

Sonar Arrays and Array Processing  

NASA Astrophysics Data System (ADS)

Arrays of hydrophones have been part of Navy sonar systems for over fifty years now. They are used both passively and actively and now are quite sophisticated. These arrays were used in fixed configuration such as the SOSUS system and towed arrays deployed from surface ships and submarines. One can assert that these arrays were a key factor in winning the cold war. Similarly, medical ultrasonics have used many of the techniques initially developed for sonar systems save four orders of magnitude in frequency. The major area where modern sonars differ involves the use of adaptive array processing whereby one usually needs to localize a weak signal in the presence of strong interference in a nonstationary environment. Most of the recent literature concerns advancing these techniques especially making them more robust to environmental uncertainties including calibration and properties of the ocean. This presentation will give an overview of the state of the art in sonar and hopefully establish a few points of relevance with nondestructive testing.

Baggeroer, A. B.

2005-04-01

393

Geophysical Institute Magnetometer Array  

NASA Astrophysics Data System (ADS)

The Geophysical Institute Magnetometer Array (GIMA) consists of twelve magnetometer stations distributed across Alaska cutting the auroral oval. Each station is equipped with a ring-core, fluxgate magnetometer, GPS clock and data logger. Data are returned from each station to the Geophysical Institute, University of Alaska where it is verified, archived, and made available to the space science community. The GIMA web page, at http://magnet.gi.alaska.edu/, provides the data from eight stations online in real-time. The GIMA web page also provides limited data access from five Russian magnetometer stations. The GIMA data set available online spans the time period 1995 to the present. This presentation describes the current operation of the array, its capabilities (data collection parameters), the web site, and methods for acessing the data set. Current efforts to improve data access and integrate the data set with online virtual observatories is described.

Wilkinson, D.; Heavner, M. J.

2006-12-01

394

Peripheral array processors  

SciTech Connect

This book contains papers presented at a conference on peripheral array processors. Topics include the following: Interactive Array Processing; Historical Aspects of Array Processors; Computer Architecture; Vibration, Noise and Array Processors; Array Processors for Microcomputers; Missile Simulation with Array Processors; and, Real Time Signal Processing with Array Processors.

Karplus, W.J.

1984-01-01

395

Advanced superconducting gradiometer\\/Magnetometer arrays and a novel signal processing technique  

Microsoft Academic Search

Recent developments in superconducting magnetic gradiometer technology have led to the construction of advanced ultrasensitive gradiometer\\/magnetometer arrays. Details of construction techniques and data showing operational capabilities are presented. The most recent of the gradiometer\\/magnetometer arrays simultaneously measures five independent spatial gradients of the magnetic field and three vector components of the magnetic field. The measured signals from this array are

W. Wynn; C. Frahm; P. Carroll; R. Clark; J. Wellhoner; M. Wynn

1975-01-01

396

The Allen Telescope Array  

NASA Astrophysics Data System (ADS)

The Allen Telescope Array, originally called the One Hectare Telescope (1hT) [1] will be a large array radio telescope whose novel characteristics will be a wide field of view (3.5 deg-GHz HPBW), continuous frequency coverage of 0.5 - 11 GHz, four dual-linear polarization output bands of 100 MHz each, four beams in each band, two 100 MHz spectral correlators for two of the bands, and hardware for RFI mitigation built in. Its scientific motivation is for deep SETI searches and, at the same time, a variety of other radio astronomy projects, including transient (e.g. pulsar) studies, HI mapping of the Milky Way and nearby galaxies, Zeeman studies of the galactic magnetic field in a number of transitions, mapping of long chain molecules in molecular clouds, mapping of the decrement in the cosmic background radiation toward galaxy clusters, and observation of HI absorption toward quasars at redshifts up to z=2. The array is planned for 350 6.1-meter dishes giving a physical collecting area of about 10,000 square meters. The large number of components reduces the price with economies of scale. The front end receiver is a single cryogenically cooled MIMIC Low Noise Amplifier covering the whole band. The feed is a wide-band log periodic feed of novel design, and the reflector system is an offset Gregorian for minimum sidelobes and spillover. All preliminary and critical design reviews have been completed. Three complete antennas with feeds and receivers are under test, and an array of 33 antennas is under construction at the Hat Creek Radio Observatory for the end of 2004. The present plan is to have a total of about 200 antennas completed by the summer of 2006 and the balance of the array finished before the end of the decade.

DeBoer, David R.; Welch, William J.; Dreher, John; Tarter, Jill; Blitz, Leo; Davis, Michael; Fleming, Matt; Bock, Douglas; Bower, Geoffrey; Lugten, John; Girmay-Keleta, G.; D'Addario, Larry R.; Harp, Gerry R.; Ackermann, Rob; Weinreb, Sander; Engargiola, Greg; Thornton, Doug; Wadefalk, Niklas

2004-10-01

397

Electromagnetically Clean Solar Arrays  

NASA Technical Reports Server (NTRS)

The term 'electromagnetically clean solar array' ('EMCSA') refers to a panel that contains a planar array of solar photovoltaic cells and that, in comparison with a functionally equivalent solar-array panel of a type heretofore used on spacecraft, (1) exhibits less electromagnetic interferences to and from other nearby electrical and electronic equipment and (2) can be manufactured at lower cost. The reduction of electromagnetic interferences is effected through a combination of (1) electrically conductive, electrically grounded shielding and (2) reduction of areas of current loops (in order to reduce magnetic moments). The reduction of cost is effected by designing the array to be fabricated as a more nearly unitary structure, using fewer components and fewer process steps. Although EMCSAs were conceived primarily for use on spacecraft they are also potentially advantageous for terrestrial applications in which there are requirements to limit electromagnetic interference. In a conventional solar panel of the type meant to be supplanted by an EMCSA panel, the wiring is normally located on the back side, separated from the cells, thereby giving rise to current loops having significant areas and, consequently, significant magnetic moments. Current-loop geometries are chosen in an effort to balance opposing magnetic moments to limit far-0field magnetic interactions, but the relatively large distances separating current loops makes full cancellation of magnetic fields problematic. The panel is assembled from bare photovoltaic cells by means of multiple sensitive process steps that contribute significantly to cost, especially if electomagnetic cleanliness is desired. The steps include applying a cover glass and electrical-interconnect-cell (CIC) sub-assemble, connecting the CIC subassemblies into strings of series-connected cells, laying down and adhesively bonding the strings onto a panel structure that has been made in a separate multi-step process, and mounting the wiring on the back of the panel. Each step increases the potential for occurrence of latent defects, loss of process control, and attrition of components. An EMCSA panel includes an integral cover made from a transparent material. The silicone cover supplants the individual cover glasses on the cells and serves as an additional unitary structural support that offers the advantage, relative to glass, of the robust, forgiving nature of the silcone material. The cover contains pockets that hold the solar cells in place during the lamination process. The cover is coated with indium tin oxide to make its surface electrically conductive, so that it serves as a contiguous, electrically grounded shield over the entire panel surface. The cells are mounted in proximity to metallic printed wiring. The painted-wiring layer comprises metal-film traces on a sheet of Kapton (or equivalent) polyimide. The traces include contact pads on one side of the sheet for interconnecting the cells. Return leads are on the opposite side of the sheet, positioned to form the return currents substantially as mirror images of, and in proximity to, the cell sheet currents, thereby minimizing magnetic moments. The printed-wiring arrangement mimics the back-wiring arrangement of conventional solar arrays, but the current-loop areas and the resulting magnetic moments are much smaller because the return-current paths are much closer to the solar-cell sheet currents. The contact pads are prepared with solder fo electrical and mechanical bonding to the cells. The pocketed cover/shield, the solar cells, the printed-wiring layer, an electrical bonding agent, a mechanical-bonding agent, a composite structural front-side face sheet, an aluminum honeycomb core, and a composite back-side face sheet are all assembled, then contact pads are soldered to the cells and the agents are cured in a single lamination process.

Stem, Theodore G.; Kenniston, Anthony E.

2008-01-01

398

Magnetometer array for cusp and cleft studies observations of the spatial extent of broadband ULF magnetic pulsations at cusp\\/cleft latitudes  

Microsoft Academic Search

The authors have used magnetometer data from 10 locations in Arctic Canada and Greenland, covering over 5 hours in magnetic local time at magnetic latitudes from 75° to 79°, to characterize the dayside patterns of enhanced long-period ULF (10- to 600-s period) wave power at cusp\\/cleft latitudes. They conclude the following: (1) In agreement with earlier single-station studies, the authors

M. J. Engebretson; J. L. Alford; W. J. Hughes; E. Zesta; L. J. Cahill; R. L. Arnoldy; G. D. Reeves

1995-01-01

399

Verification of Loss Reduction based on New Loss Analysis for Slotless PM Motor  

NASA Astrophysics Data System (ADS)

This paper presents the loss analysis and reduction of Slotless Permanent Magnet Motors (SLPMM). The resistance and current at the inverter carrier frequency are introduced, by which loss generated by the high frequency current (carrier loss) can be separated from the total loss. The experimental studies using 200W, 3000min-1 SLPMM with halbach magnet array show the effective reduction of carrier loss. Finally, the experimental studies using the SLPMM with a series reactor proved the proposed loss analysis.

Shikayama, Toru; Takaki, Mamoru; Ohto, Motomichi; Tsuji, Teruo; Kosaka, Takashi; Matsui, Nobuyuki

400

DTU Space magnetometer array  

NASA Astrophysics Data System (ADS)

DTU Space is monitoring the Earth's magnetic field with a network of ground stations in Greenland, Denmark, and the South Atlantic. An array with 17 stations at coastal locations is operated in Greenland. All stations provide full vector geomagnetic field variations with 1 Hz resolution, and 5 stations are geomagnetic observatories and calibrated to INTERMAGNET standards. The magnetometer array is listed as an asset for the ESA's Space Situational Awareness (SSA) program and it is an integral part in the EU FP7 project ESPAS. The outstanding location of the magnetometer array reaching from the geomagnetic pole over the auroral and subauroral region, and one observatory in the South Atlantic Anomaly region makes it useful for Space Weather applications and Space Physics investigations. The observatory in Narsarsuaq (NAQ) is one of 12 stations contributing to the auroral electrojet index distributed by the WDC Kyoto. However, even for low indices AE < 100 we found considerable geomagnetic disturbances northward of NAQ station that can be attributed to auroral electrojet activity. The distribution in local time and latitude of such disturbances will be presented and discussed in this paper.

Stolle, C.; Matzka, J.; Sarauw, E.; Pedersen, L. W.

2012-04-01

401

Monte Carlo Simulations for the AGATA Array  

SciTech Connect

The goal of the AGATA project is to develop an array of highly segmented high-purity germanium detectors based on the novel concepts of pulse shape analysis and {gamma}-ray tracking. In the initial phase, a smaller Demonstrator Array will be assembled to prove the practical feasibility of these concepts. The Demonstrator Array will be first placed at the Laboratori Nazionali di Legnaro, where it will be coupled with the PRISMA magnetic spectrometer. Some results of the extensive simulation work concerning the Demonstrator Array are presented here.

Farnea, E. [INFN, Sezione di Padova, 35131 Padova (Italy); Dipartimento di Fisica dell'Universita, 35131 Padova (Italy)

2006-08-14

402

Infinite Arrays of Sub-Array Antennas.  

National Technical Information Service (NTIS)

A unified network approach to the analysis of infinite regular arrays of antennas is presented. The periodically repeated constituent of the array is itself regarded as a sub-array, the sub-array taking a variety of particular forms. With the appropriate ...

W. Wasylkiwskyj W. K. Kahn

1970-01-01

403

Coupling Between Waveguide-Fed Slot Arrays  

NASA Technical Reports Server (NTRS)

Coupling between two waveguide-fed planar slot arrays has been investigated using full-wave analysis. The analysis employs the method-of-moments solution to the pertinent coupled integral equations for the aperture electric field of all slots. In order to compute coupling between two arrays, the input port of the first array is excited with a TE(sub 10) mode wave while the second one is match-terminated. After solving the moment method matrix equations, the aperture fields of all slots are obtained and thereby the TE(sub 10) mode wave received at the input port of the second array is determined. Coupling between two arrays is the ratio of the wave amplitude arriving in the second array port to the incident wave amplitude at the first array port. The coupling mechanism has been studied as a function of spacing between arrays in different directions, e.g. the electric field plane, the magnetic field plane, and the diagonal plane. Computed coupling values are presented for different array geometries. This work is novel since it provides a good understanding of coupling between waveguide-fed slot arrays as a function of spacing and orientation for different aperture distributions and array architectures. This serves as a useful tool for antenna design engineers and system engineers.

Rengarajan, Sembiam

2011-01-01

404

Arrays of magnetoresistive sensors for nondestructive testing  

Microsoft Academic Search

Magnetic field distributions were measured for test stripline structures with anisotropic magnetoresistive (AMR), thin film Permalloy sensors. Linear arrays of eight barber-pole-type AMR sensors were used to increase the speed of the imaging and stability of scanning. The magnetic field distributions were converted to the distribution of electric current density in a stripline by inverting Maxwell's equations.

Alexey V. Nazarov; Fabio C. S. da Silva; David P. Pappas

2004-01-01

405

Unexpectedly long-range influence on thin-film magnetization reversal of a ferromagnet by a rectangular array of FeMn pinning films  

NASA Astrophysics Data System (ADS)

Exchange bias in bilayer magnetic systems is usually ascribed to the existence of transient magnetic structures at the interfaces between adjacent layers on top of each other. Here, we report the observation of a similar phenomenon in the lateral direction, indicated by an asymmetry in the magnetization reversal of a ferromagnetic film covered with a square grid of an antiferromagnetic layer. We show the antiferromagnet not only changes the properties of the ferromagnet regions immediately underneath it, but despite the large pattern period, also drastically affects the remagnetization behavior in the adjacent uncovered parts of the ferromagnet. Specifically, we demonstrate pattern-controlled nucleation of domain walls and an overall asymmetry in the reversal behavior of the uncovered ferromagnet when the polarity of the in-plane field is reversed. A canted orientation of the intrinsic anisotropy of the ferromagnet with respect to an induced exchange anisotropy and the presence of artificial topologically stable domain walls are discussed as likely origins of the effects.

Kabanov, Yu. P.; Nikitenko, V. I.; Tikhomirov, O. A.; Egelhoff, W. F.; Shapiro, A. J.; Shull, R. D.

2009-04-01

406

Final Progress Report for the NASA Inductrack Model Rocket Launcher at the Lawrence Livermore National Laboratory  

SciTech Connect

The Inductrack magnetic levitation system, developed at the Lawrence Livermore National Laboratory, was studied for its possible use for launching rockets. Under NASA sponsorship, a small model system was constructed at the Laboratory to pursue key technical aspects of this proposed application. The Inductrack is a passive magnetic levitation system employing special arrays of high-field permanent magnets (Halbach arrays) on the levitating cradle, moving above a ''track'' consisting of a close-packed array of shorted coils with which are interleaved with special drive coils. Halbach arrays produce a strong spatially periodic magnetic field on the front surface of the arrays, while canceling the field on their back surface. Relative motion between the Halbach arrays and the track coils induces currents in those coils. These currents levitate the cradle by interacting with the horizontal component of the magnetic field. Pulsed currents in the drive coils, synchronized with the motion of the carrier, interact with the vertical component of the magnetic field to provide acceleration forces. Motional stability, including resistance to both vertical and lateral aerodynamic forces, is provided by having Halbach arrays that interact with both the upper and the lower sides of the track coils. At present, a 7.8 meter track composed of drive and levitation coils has been built and the electronic drive circuitry performs as designed. A 9 kg cradle that carries the Halbach array of permanent magnets has been built. A mechanical launcher is nearly complete which will provide an initial cradle velocity of 9 m/s into the electronic drive section. We have found that the drag forces from the levitation coils were higher than in our original design. However, measurements of drag force at velocities less than 1 m/s are exactly as predicted by theory. Provided here are recommended design changes to improve the track's performance so that a final velocity of 40 m/s can be achieved with the existing track. This project was designed and built as part of a Phase II contract that started in Feb. 1999 and ended in Sep. 2000 at a cost of $600K. A detailed budget on how this funding was spent is also included here.

Tung, L S; Post, R F; Martinez-Frias, J

2001-06-27

407

caArray - Array Data Management System  

Cancer.gov

Skip to Page Content Build 2.5.2_RC4 | Node: NCICB Welcome to caArray Browse Login Register About caArray What is caArray? Release Notes User Guide Global Quick Links National Cancer Institute (NCI) NCI Center for Biomedical Informatics and Information

408

Diode Laser Arrays  

NASA Astrophysics Data System (ADS)

Contributors; 1. Monolithic phase-locked semiconductor laser arrays D. Botez; 2. High power coherent, semiconductor laser master oscillator power amplifiers and amplifier arrays D. F. Welch and D. G. Mehuys; 3. Microoptical components applied to incoherent and coherent laser arrays J. R. Leger; 4. Modeling of diode laser arrays G. R. Hadley; 5. Dynamics of coherent semiconductor laser arrays H. G. Winfuland and R. K. Defreez; 6. High average power semiconductor laser arrays and laser array packaging with an emphasis for pumping solid state lasers R. Solarz; 7. High power diode laser arrays and their reliability D. R. Scifres and H. H. Kung; 8. Strained layer quantum well heterostructure laser arrays J. J. Coleman; 9. Vertical cavity surface emitting laser arrays C. J. Chang-Hasnain; 10. Individually addressed arrays of diode lasers D. Carlin.

Botez, Dan; Scifres, Don R.

2005-11-01

409

Magnetization reversal of ferromagnetic nanowires studied by magnetic force microscopy  

Microsoft Academic Search

The magnetization reversal of two-dimensional arrays of parallel ferromagnetic Fe nanowires embedded in nanoporous alumina templates has been studied. By combining bulk magnetization measurements (superconducting quantum interference device magnetometry) with field-dependent magnetic force microscopy (MFM), we have been able to decompose the macroscopic hysteresis loop in terms of the irreversible magnetic responses of individual nanowires. The latter are found to

T. G. Sorop; C. Untiedt; F. Luis; M. Kröll; M. Rasa; L. J. de Jongh

2003-01-01

410

Microshutter Arrays for the NGST NIRSpec  

NASA Technical Reports Server (NTRS)

We are developing a programmable multiobject field selector for the NGST NIRSpec. This device is a microshutter array, a close-packed 2000 x 2000 array of 100 micrometer x 100 micrometer shutters fabricated with Micro-ElectroMechanical Systems (MEMS) technologies. The shutters are opened using a magnet scanned over the array. The shutters are held open by electrostatic potentials on adjacent vertical electrodes. Modeling of the magnetic actuation of the microshutters allowed optimization of the magnetic field configuration, the distance between magnet and shutters, and the force and torque produced by the magnet. The results of laboratory tests are consistent with our modeling. We have demonstrated actuation, latching and addressing. We are able to rotate shutters out of the plane up to 90 degree and more, to latch them electrostatically to the walls and release them selectively. During the last six month all critical elements of the array have been demonstrated. Fabrication processes were developed to deposit vertical electrodes on support grid side walls and insulated light-shields that block the gaps between shutters and the support grid. Physical optics analysis was performed to assess the expected optical performance of the microshutters. A preliminary Fourier optics analysis on the microshutter array performance has been carried out. More detailed analysis of wave propagation through 3D structures is a next step. An optical test station for verifying optical parameters of the shutter array at room temperature has been developed. It allows to measure parameters, such as transmission, scattering, contrast ratio, and diffraction of the array structure. Initial data have been acquired and are being analyzed and compared to theoretical predictions.

Moseley, Harvey; Fisher, Richard R. (Technical Monitor)

2001-01-01

411

Development of a monolithic ferrite memory array  

NASA Technical Reports Server (NTRS)

The results of the development and testing of ferrite monolithic memory arrays are presented. This development required the synthesis of ferrite materials having special magnetic and physical characteristics and the development of special processes; (1) for making flexible sheets (laminae) of the ferrite composition, (2) for embedding conductors in ferrite, and (3) bonding ferrite laminae together to form a monolithic structure. Major problems encountered in each of these areas and their solutions are discussed. Twenty-two full-size arrays were fabricated and fired during the development of these processes. The majority of these arrays were tested for their memory characteristics as well as for their physical characteristics and the results are presented. The arrays produced during this program meet the essential goals and demonstrate the feasibility of fabricating monolithic ferrite memory arrays by the processes developed.

Heckler, C. H., Jr.; Bhiwandker, N. C.

1972-01-01

412

Status of the ''PATH'' magnetic optics design code  

SciTech Connect

The PATH codes are used to design magnetic optics subsystems for neutral particle beam systems. This paper describes several checks and modifications that have been made to PATH. The third order hard-edge quadrupole model in PATH has been checked against direct numerical integration (raytracing) and found to be accurate to better than 0.5 microradian. The original third order linear ramp quadrupole fringe field model in PATH has been checked against raytracing and against an alternative linear ramp fringe field model and found to be accurate to better than 0.1 microradian. An alternative third order nonlinear ramp quadrupole fringe field model has been added to PATH. This model is a close approximation to the fringe field of a Halbach ring magnet and has been checked by raytracing and has been found to be accurate to better than 0.1 microradian. PATH has been modified to model combined quadrupole/octupole elements through third order. The paper describes this model and presents results obtained by optimizing quadrupole and octupole elements to produce lowest beam divergence performance for a neutral particle beam expander.

Kashuba, R.J.; Schmitt, R.J.; Meads P.F. Jr.

1988-12-01

413

Laser array geometries  

NASA Astrophysics Data System (ADS)

Attention is given to the lateral locking mechanism in stripe array lasers. It is noted that strong coupling is required to insure the phase locking of the array elements, as well as in order to produce single-lobed far-field patterns. Single lobed far field operation is demonstrated for evanescently coupled arrays whose elements are placed in closed proximity, and for diffraction-coupled arrays with a single diffraction region. Results are presented for 5-, 7-, and 11-element arrays with 3-micron wide stripes and different spacings between the stripes. Close proximity of array elements yields consistent single-lobe array operation.

Jansen, Michael; Yang, Jane J.; Wilcox, Jaroslava

414

Designing MR shim arrays with irregular coil geometry: theoretical considerations.  

PubMed

In magnetic resonance imaging and spectroscopy, a highly uniform magnetic field is desired for minimizing image distortions and line broadening, respectively. Typically, shim coils are employed to provide correcting fields for inhomogeneities brought about by magnetic interactions with the sample under study. Flexible field modeling is possible using an array of regularly shaped conducting loops that are independently electrically driven. In this paper, a design method is presented for generating coil winding patterns for shim arrays with irregular geometry elements. These designs are compared theoretically to the use of circular loop arrays and are shown to provide considerable improvements in field accuracy and efficiency for generating low-order correcting fields. PMID:24845270

While, Peter T; Korvink, Jan G

2014-06-01

415

Solar array drive system  

NASA Technical Reports Server (NTRS)

A solar array drive system consisting of a solar array drive mechanism and the corresponding solar array drive electronics is being developed. The principal feature of the solar array drive mechanism is its bidirectional capability which enables its use in mechanical redundancy. The solar array drive system is of a widely applicable design. This configuration will be tested to determine its acceptability for generic mission sets. Foremost of the testing to be performed is the testing for extended duration.

Berkopec, F. D.; Sturman, J. C.; Stanhouse, R. W.

1976-01-01

416

In-plane anisotropy of coercive field in permalloy square ring arrays.  

SciTech Connect

Magnetic ring arrays are promising candidates for application in magnetic random access memory devices. The magnetic reversal processes and anisotropy of the coercivity in arrays of square-shaped nanorings with different spacings were investigated by vector magneto-optical Kerr effect magnetometry, magnetic force microscopy, and micromagnetic simulations. Two-step magnetization reversal demonstrates fourfold symmetry in the film plane resulting from the shape anisotropy in rings. Our numerical simulations show good agreement with the experiment.

Goncharov, A. V.; Zhukov, A. A.; Metlushko, V. V.; Bordignon, G.; Fangohr, H.; Karapetrov, G.; de Groot, P. A. J.; Ilic, B.; Materials Science Division; Univ. Southampton; Univ. Illinois at Chicago; Cornell Univ.

2006-04-15

417

Magnetic multipole redirector of moving plasmas  

DOEpatents

A method and apparatus for redirecting moving plasma streams using a multiple array of magnetic field generators (e.g., permanent magnets or current bearing wires). Alternate rows of the array have opposite magnetic field directions. A fine wire mesh may be employed to focus as well as redirect the plasma.

Crow, James T. (Albuquerque, NM); Mowrer, Gary R. (Cedar Crest, NM)

1999-01-01

418

Coil Array Design Inspired on the Kepler's Lenten Pretzel  

SciTech Connect

The RF coil arrays are an important part in Magnetic Resonance Imaging, since they are the main device for transmission and reception of the magnetic resonance signal. An RF coil array with a new configuration based on the Kepler's Lenten pretzel for the geocentric path of Mars is proposed in this work. The evenly distributed trajectories may serve as the basic configuration to form a coil array to adequately cover a region of interest for magnetic resonance experiments. The main goal is to investigate the electromagnetic properties of this coil array geometry to obtain an optimal design for its further construction. Hence, the electromagnetic properties of the coil array were numerical simulated using the finite element method and the quasi-static approach. Resulting simulations showed that there is an important concentration of magnetic field lines at the centre of the coil array. This is an advantage over other coil arrays where the magnetic field usually decreased at their geometrical centre. Both the electric and magnetic fields had also a very good uniformity. These characteristics made this coil design a good candidate for applications where the use of multi-coil technology is mandatory.

Vazquez, F.; Solis, S. E.; Rodriguez, A. O. [Centro de Investigacion e Instrumentacion e Imagenologia Medica, Universidad Autonoma Metropolitana Iztapalapa, Mexico, DF 09340 (Mexico)

2008-08-11

419

SUPERCONDUCTING QUADRUPOLE ARRAYS FOR MULTIPLE BEAM TRANSPORT  

SciTech Connect

The goal of this research was to develop concepts for affordable, fully functional arrays of superconducting quadrupoles for multi-beam transport and focusing in heavy ion fusion (HIF)accelerators. Previous studies by the Virtual National Laboratory (VNL) collaboration have shown that the multi-beam transport system (consisting of alternating gradient quadrupole magnets, a beam vacuum system, and the beam monitor and control system) will likely be one of the most expensive and critical parts of such an accelerator. This statement is true for near-term fusion research accelerators as well as accelerators for the ultimate goal of power production via inertial fusion. For this reason, research on superconducting quadrupole arrays is both timely and important for the inertial fusion energy (IFE) research program. This research will also benefit near-term heavy ion fusion facilities such as the Integrated Research Experiment (IRE)and/or the Integrated Beam Experiment (IBX). We considered a 2-prong approach that addresses the needs of both the nearer and longer term requirements of the inertial fusion program. First, we studied the flat coil quadrupole design that was developed by LLNL; this magnet is 150 mm long with a 50 mm aperture and thus is suitable for near term experiments that require magnets of a small length to aperture ratio. Secondly, we studied the novel double-helix quadrupole (DHQ) design in a small (3 x 3) array configuration; this design can provide an important step to the longer term solution of low-cost, easy to manufacture array constructions. Our Phase I studies were performed using the AMPERES magnetostatic analysis software. Consideration of these results led to plans for future magnet R&D construction projects. The first objective of Phase I was to develop the concept of a superconducting focusing array that meets the specific requirements of a heavy ion fusion accelerator. Detailed parameter studies for such quadrupole arrays were performed. Based on these studies, the primary magnet parameters and the general features required for a complete array system (including vacuum and cryostat) were identified. Basic system concepts were formulated to serve as guides for future development work. A related issue was to compare the applicability and benefits of two different magnet technologies for use in such a quadrupole array. Analytical studies were performed for each of the two coil designs, a flat coil based on an HCX quadrupole designed by LLNL and a doublehelix quadrupole designed by AML. These studies have confirmed the feasibility of using either of the two coil designs in a small array.

Rainer Meinke Carl Goodzeit Penny Ball Roger Bangerter

2003-10-01

420

High-density nickel nanowire arrays for data storage applications  

NASA Astrophysics Data System (ADS)

This paper is dedicated to a study of magnetic properties (magnetic anisotropy, coercive force and remanent magnetization) of spatially ordered high-density Ni nanowire arrays. The magnetic nanowires were prepared by electrodeposition of nickel from simple sulfate solutions into anodic aluminum oxide (AAO) nanoporous templates (with diameter of d = 20 and 40 nm) fabricated by potentiostatic anodization. We show that Ni nanowires have strong out-of-plane axial magnetic anisotropy (normal to the substrate plane) along with an in-plane anisotropy caused by hexagonal spatial distribution of nanowires in an array. An existence of the six-fold in-plane anisotropy proofs the long-range hexagonal order of nanowires. High quality of nanowire arrays makes possible of its usage as high-density (up to 2Tb/in2) magnetic recording media.

Samardak, A. S.; Sukovatitsina, E. V.; Ognev, A. V.; Chebotkevich, L. A.; Mahmoodi, R.; Peighambari, S. M.; Hosseini, M. G.; Nasirpouri, F.

2012-02-01

421

Parallel arrays of Josephson junctions for submillimeter local oscillators  

NASA Technical Reports Server (NTRS)

In this paper we discuss the influence of the DC biasing circuit on operation of parallel biased quasioptical Josephson junction oscillator arrays. Because of nonuniform distribution of the DC biasing current along the length of the bias lines, there is a nonuniform distribution of magnetic flux in superconducting loops connecting every two junctions of the array. These DC self-field effects determine the state of the array. We present analysis and time-domain numerical simulations of these states for four biasing configurations. We find conditions for the in-phase states with maximum power output. We compare arrays with small and large inductances and determine the low inductance limit for nearly-in-phase array operation. We show how arrays can be steered in H-plane using the externally applied DC magnetic field.

Pance, Aleksandar; Wengler, Michael J.

1992-01-01

422

Underwing reflector solar array  

SciTech Connect

A lightweight solar cell array for space vehicles powered by solar electric propulsion is disclosed. The array incorporates a plurality of hinged solar cell units which can be folded for stowage and thereafter extended into a planar configuration. Light is directed onto the solar cell array by a flexible reflector assembly which is carried below the array. The reflector assembly preferably comprises sheets of flexible material stowed on rolls whereby the sheets can be pulled from the rolls into extended positions. The solar cell array and the reflector are carried between two frames, one of which can be moved away from the other to deploy the array and the reflector assembly.

Lackey, J.A.; Nordwall, H.L.; Whitney, C.B.

1981-08-04

423

Future trends in magnetic storage technology  

Microsoft Academic Search

This paper gives a general overview of magnetic storage technology future trends. Areas covered include: perpendicular recording; magnetic head design; heat assisted magnetic recording (HAMR); media anisotropy; magnetic material isolated island patterned media; magnetic nanoparticle self-ordered arrays; and head-disk interface spacing.

Mark H. Kryder

2003-01-01

424

Magnetic composite electroplating for depositing micromagnets  

Microsoft Academic Search

This paper reports a novel magnetic composite materials deposition technique called magnetic composite electroplating (MCE). Thin films and micromagnets arrays of a composite matrix consisting of magnetic particles and a ferromagnetic alloy have been fabricated based on this technique. In a typical MCE process, magnetic particles are electrochemically and mechanically embedded into electroplated ferromagnetic thin films to form a magnetic

Shan Guan; Bradley J. Nelson

2006-01-01

425

Implosion Dynamics in Conical Wire Array Z-pinches  

NASA Astrophysics Data System (ADS)

We present initial results from imploding conical wire array experiments performed on both the MAGPIE generator (1MA, 240ns) at Imperial College London and the Nevada Terawatt Facility's Zebra generator (1MA, 100ns) at University of Nevada, Reno. This paper will discuss the implosion dynamics of conical wire arrays, including initial implosion of the cathode end of the array and the formation of a magnetic bubble.

Ampleford, D. J.; Lebedev, S. V.; Chittenden, J. P.; Bland, S. N.; Bott, S. C.; Hall, G. N.; Palmer, J. B. A.; Rapley, J.; Kantsyrev, V. L.; Safronova, A. S.; Ivanov, V. V.; Fedin, D. A.; Laca, P. J.; Sotnikov, V. I.; Yilmaz, F.; Ouart, N.; Nalajala, V.; Shrestha, I.; Pokala, S.; Jones, B.; Deeney, C.; Coverdale, C. A.; Lepell, P. D.

2006-01-01

426

A Mirnov loop array for field-reversed configurations  

NASA Astrophysics Data System (ADS)

An array of 64 magnetic pick-up loops has been used for stability studies of large field-reversed configurations in the FRX-C/LSM device. This array proved reliable, could resolve signals of a few Gauss, and allowed the detection of several plasma instabilities.

Tuszewski, Michel

427

Adaptive Arrays and Tracking.  

National Technical Information Service (NTIS)

Adaptive arrays and tracking share many concepts mathematical tools, practical issues, and algorithms. For example, ill-conditioning of the sample covariance matrix for adaptive arrays and ill-conditioning of the covariance matrix in a Kalman filter are b...

F. E. Daum

2004-01-01

428

Array to Multiply  

NSDL National Science Digital Library

In this lesson, students will understand the concept of arrays and will be able to create/draw an array for multiplication sentences. Engaging center game is used to help student with concrete visual representation of multiplication sentences.

2013-01-28

429

Vortices in Inductive Periodic Josephson Arrays  

Microsoft Academic Search

We derive a Hamiltonian for inductive Josephson junctions forming periodic two and three dimensional arrays. The variables to describe the system are the gauge invariant phase differences across the junctions. Therefore in this approach the phase of the superconducting order parameter and the magnetic vector potential are treated on equal footing, which makes it a useful tool to study phenomena

R. SáSik; L. N. Bulaevskii; A. R. Bishop; M. P. Maley

1997-01-01

430

Vortices in Inductive Periodic Josephson Arrays.  

NASA Astrophysics Data System (ADS)

We derive a Hamiltonian for inductive Josephson junctions forming periodic two and three dimensional arrays. The variables to describe the system are the gauge invariant phase differences across the junctions. Therefore in this approach the phase of the superconducting order parameter and the magnetic vector potential are treated on equal footing, which makes it a useful tool to study phenomena in which fluctuations of both magnetic field and the superconducting order parameter are relevant. Among such applications is the study of thermodynamics of the mixed state in highly anisotropic high-Tc superconductors at flux densities B<< H_c2 and in granular superconductors. We take into account screening by the superconducting currents in the electrodes forming the network. This screening is characterized by a length ?e determined by superconducting properties and the geometry of the electrodes. We show that in two dimensional arrays the magnetic interaction of currents is long ranged and the screening effect of electrodes is only important at distances smaller than ?_e. In three dimensional arrays the magnetic interaction of currents is short ranged with the characteristic length (?_ea/2)^1/2, where a is the periodicity of the array. We obtain time-dependent equations for the phase differences and a dispersion relation for the plasma mode at zero temperature in the absence of vortices.

ŠáŠik, R.; Bulaevskii, L. N.; Bishop, A. R.; Maley, M. P.

1997-03-01

431

Vortex chirality in an array of ferromagnetic dots.  

SciTech Connect

Magnetization of an array of submicron permalloy dots was investigated using the diffracted magneto-optical Kerr effect. The shapes of the higher-order hysteresis loops are explained by the magnetic form factors associated with a vortex spin structure in each disk. The imaginary part of the form factor also explains the unexpected measured differences between hysteresis loops obtained on positive and negative diffraction orders. Shape effects account for the coherent chirality of the vortices over the array.

Grimsditch, M.; Vavassori, P.; Novosad, V.; Metlushko, V.; Shima, H.; Otani, Y.; Fukamichi, K.; Materials Science Division; Univ. di Ferrara; Univ. of Illinois at Chicago; Tohoku Univ.; Japan Science and Technology Corp.

2002-05-01

432

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Cancer.gov

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433

Micromachined pipette arrays  

Microsoft Academic Search

The design and characterization of batch fabricated metallic micromachined pipette arrays is described. The process used to fabricate the micromachined pipette arrays (MPA) includes p + etch-stop membrane technology anisotropic etching of silicon in potassium hydroxide, sacrificial thick photoresist micromolding technology, and electrodeposition. Arrays of one to ten pipettes have been fabricated using nickel as the structural material and palladium

Ian Papautsky; John Brazzle; Harold Swerdlow; Robert Weiss; A. Bruno Frazier

2000-01-01