Zigzag Wire Research Articles

Chiral magnetoresistance in Pt/Co/Pt zigzag wires

The Rashba effect leads to a chiral precession of the spins of moving electrons, while the Dzyaloshinskii-Moriya interaction (DMI) generates preference towards a chiral profile of local spins. We predict that the exchange interaction between these two spin systems results in a “chiral” magnetoresistance depending on the chirality of the local spin texture. We observe this magnetoresistance by measuring the domain wall (DW) resistance in a uniquely designed Pt/Co/Pt zigzag wire and by changing the chirality of the DW with applying an in-plane magnetic field. A chirality-dependent DW resistance is found, and a quantitative analysis shows a good agreement with a theory based on the Rashba model. Moreover, the DW resistance measurement allows us to independently determine the strength of the Rashba effect and the DMI simultaneously, and the result implies a possible correlation between the Rashba effect, the DMI, and the symmetric Heisenberg exchange.

A liquid metal-based structurally embedded vascular antenna: I. Concept and multiphysical modeling

This work proposes a new concept for a reconfigurable structurally embedded vascular antenna (SEVA). The work builds on ongoing research of structurally embedded microvascular systems in laminated structures for thermal transport and self-healing and on studies of non-toxic liquid metals for reconfigurable electronics. In the example design, liquid metal-filled channels in a laminated composite act as radiating elements for a high-power planar zig-zag wire log periodic dipole antenna. Flow of liquid metal through the channels is used to limit the temperature of the composite in which the antenna is embedded. A multiphysics engineering model of the transmitting antenna is formulated that couples the electromagnetic, fluid, thermal, and mechanical responses. In part 1 of this two-part work, it is shown that the liquid metal antenna is highly reconfigurable in terms of its electromagnetic response and that dissipated thermal energy generated during high power operation can be offset by the action of circulating or cyclically replacing the liquid metal such that heat is continuously removed from the system. In fact, the SEVA can potentially outperform traditional copper-based antennas in high-power operational configurations. The coupled engineering model is implemented in an automated framework and a design of experiment study is performed to quantify first-order design trade-offs in this multifunctional structure. More rigorous design optimization is addressed in part 2.

The effect of semi-infinite crystalline electrodes on transmission of gold atomic wires using DFT

First principle calculations of the conductance of gold atomic wires containing chain of 3–8 atoms each with 2.39Å bond lengths are presented using density functional theory. Three different configurations of wire/electrodes were used. For zigzag wire with semi-infinite crystalline electrodes, even–odd oscillation is observed which is consistent with the previously reported results. A lower conductance is observed for the chain in semi-infinite crystalline electrodes compared to the chains suspended in wire-like electrode. The calculated transmission spectrum for the straight and zig-zag wires suspended between semi-infinite crystalline electrodes showed suppression of transmission channels due to electron scattering occurring at the electrode-wire interface.

Bound states in the continuum in zigzag quantum wire enforced by a finger gate

We consider electron transport in a zigzag quantum wire by the effect of finger gate potential. Using a non-Hermitian effective Hamiltonian, we calculate resonance positions and widths to show that the resonance widths are easily governed by the gate potential. In particular, the resonance width can be enforced to be equal to zero, which leads to an electron localization with the Fermi energy embedded in the propagation band of the wire, i.e., the bound state in the continuum (BSC). We show that, for positive values of the potential, a zigzag wire becomes a Fabry-Perot resonator to give rise to BSC too.

Small-size metamaterial perfect absorber operating at low frequency

A small-size metamaterial perfect absorber operating at low frequency is proposed. Due to the special design, the unit-cell dimension with respect to wavelength is very small, a/λ ∼ 1/17, at the absorption frequency of 377 MHz. The absorption frequency is strongly dependent on the length of zigzag wire. In addition, the absorption is more than 94% in a wide range of incident angle of electromagnetic wave up to 50°. The results show that the proposed absorber is promising to be applied into devices in radio region.

Linear and non-linear optical properties of GaAs nanowires

The linear and non-linear optical properties of different geometrical structures of gallium arsenide (GaAs) nanowires have been studied by employing ab initio method. We have calculated the optical response of four different GaAs nanowires, viz., two-atom linear wire, two-atom zigzag wire, four-atom square wire and six-atom hexagonal wire. We have investigated imaginary part of the zz component of the linear dielectric tensor and second-order susceptibility for different structures along with bulk material. We revealed that the strongest absorption occurs for four-atom square nanowire configuration.

Programmable Self-Assembly, Disassembly, Transport, and Reconstruction of Ordered Planar Magnetic Micro-Constructs

We present a method to seamlessly self-assemble, disassemble, transport, and reconstruct ordered 2-D structures of fluid-borne microspheres on a surface using an array of magnetic zigzag wire traps. Competition between and control over: 1) the trapping forces of underlying magnetic patterns; 2) magnetic dipole repulsion; and 3) Brownian motion gives rise to reproducible cluster structures. Weak external magnetic fields $({ tune the spacing between particles and enable the assembled structures to be remotely manipulated and reassembled on the platform. This method could be used in biological and photonic applications by utilizing the microspheres, for example, as carriers of host biomolecules or as linkers to fluorescent emitters.

VHF Collar Integrated Antenna for Ground Link of GPS Based Location System

This paper presents the design of a low-profile collar-integrated antenna operating at 154.5 MHz for use as a ground link in a GPS-based location system for wildlife tracking. The antenna is a conformal zigzag wire antenna that can be easily integrated into the collar. The power reduction caused by lower gain is overcome by improving the return loss. Input impedance matching at 154.5 MHz, which is the most important factor for return loss improvement, is done by changing the size of the antenna and by using a T-matching method that uses a shorting pin. The antenna efficiency is measured by Wheeler cap method. The design details and comparison of simulation and measurement results are presented.

Magnetic Microstructures for Control of Brownian Motion and Microparticle Transport

A platform of microscopic magnetic wires and discrete bits of disks patterned on a surface offers dynamic control over the motion of fluid borne magnetic particles. The energy landscape associated with the local domain wall field originating from zigzag wire vertices is tuned by weak external fields to vary Brownian trajectories between strong confinements and delocalized spatial excursions. The corresponding spatial coverage of single particle trajectories allows the energy profile of such a magnetic trap to be mapped. Remote manipulation and guided transport of these objects across various opaque and transparent rigid surfaces as well as flexible films supporting discrete magnetic disks is presented.

Optical properties of gallium phosphide (GaP) nanowires

The linear and non-linear optical properties of different geometrical structures of gallium phosphide (GaP) nanowires have been studied by employing ab initio method. We have calculated the optical response of four different GaP nanowires, viz., two atom linear wire, two atom zigzag wire, four atom square wire and six atom hexagonal wire. We have investigated imaginary part of the zz component of the linear dielectric tensor and second order susceptibility for different structures along with bulk material. We revealed that strongest absorption occurs for four atom square nanowire configuration.

Electronic Properties of GaP Nanowires of Different Shapes

The electronic properties of very thin gallium phosphide nanowires of different shapes were studied by ab-initio method using the generalized gradient approximation. We consider four different shapes of nanowires viz. linear wire, zigzag wire, square wire and hexagonal wire. The geometry optimization and the stability of all nanowires were investigated. We explore the minimum energy configuration for all the structures. The present study reveals that all of the wires are stable but four atom square wires have greater stability in comparison to other structures. The analysis of density of states and band structure of optimized nanowires predicts that nanowires made from bulk GaP can be either metallic, semi-metallic, semiconducting or insulating depending upon the geometrical shape of the wire.

Current-induced energy barrier suppression for electromigration from first principles

We present an efficient method for evaluating current-induced forces in nanoscale junctions, which naturally integrates into the nonequilibrium Green's function formalism implemented within density functional theory. This allows us to perform dynamic atomic relaxation in the presence of an electric current while evaluating the current--voltage characteristics. The central idea consists of expressing the system energy density matrix in terms of Green's functions. To validate our implementation, we perform a series of benchmark calculations, both at zero and at finite bias. First we evaluate the current-induced forces acting over an Al nanowire and compare them with previously published results for fixed geometries. Then we perform structural relaxation of the same wires under bias and determine the critical voltage at which they break. We find that although a perfectly straight wire does not break at any of the voltages considered, a zigzag wire is more fragile and snaps at 1.4 V, with the Al atoms moving against the electron flow. The critical current density for the rupture is estimated to be 9.6 \ifmmode\times\else\texttimes\fi{} 10${}^{10}$ A/cm${}^{2}$, in good agreement with the experimentally measured value of 5 \ifmmode\times\else\texttimes\fi{} 10${}^{10}$ A/cm${}^{2}$. Finally, we demonstrate the capability of our scheme to tackle the electromigration problem by studying the current-induced motion of a single Si atom covalently attached to the sidewall of a (4,4) armchair single-walled carbon nanotube. Our calculations indicate that if Si is attached along the current path, then current-induced forces can induce migration. In contrast, if the bonding site is away from the current path, then the adatom remains stable regardless of the voltage. An analysis based on decomposing the total force into a wind and an electrostatic component, as well as on a detailed evaluation of the bond currents, shows that this remarkable electromigration phenomenon is due solely to the position-dependent wind force.

Single layer atom chip for magnetically trapping one-dimensional array of ultracold atoms

We propose a wire configuration to create a one-dimensional (1D) array of magnetic microtraps for trapping ultracold atoms. The configuration is formed by replacing the central part of the Z-wire pattern with a zigzag wire. We simulate the performance of this pattern by the finite element method which can take both the width and depth of the wire into consideration. The result of simulation shows that this configuration can create magnetic microtraps which can be separated and combined by changing the bias magnetic field. We manage to split the Z-wire trap and prove that a similar result can occur for the new wire configuration. The fabrication processes of the atom chip are also introduced. Finally we discuss the loading method.

Noncollinear magnetism in manganese nanostructures

We present ab initio spin-density-functional calculations of the magnetic properties of Mn nanostructures with a geometry varying between a straight linear wire and a three-dimensional nanorod, including collinear and noncollinear, commensurate and incommensurate magnetic configurations. With decreasing tension along the axis of the nanostructure we find a series of transitions first from a straight to a zigzag wire, then to planar triangular or hexagonal stripes and further to a nanorod consisting of a periodic stacking of distorted octahedra. At local equilibrium all nanostructures are in a high-moment state, with absolute values of the local magnetic moments per atom varying between $3.79{\ensuremath{\mu}}_{B}$ for a straight noncollinear antiferromagnetic Mn monowire, $3.54{\ensuremath{\mu}}_{B}$ for a triangular collinear antiferromagnetic stripe, $3.40{\ensuremath{\mu}}_{B}$ for a hexagonal collinear ferrimagnetic stripe, and $2.96{\ensuremath{\mu}}_{B}$ for an octahedral noncollinear ferrimagnetic nanorod. For all low-dimensional nanostructures except the monowire we find collinear and noncollinear magnetic structures to be energetically nearly degenerate, if the geometric and magnetic degrees of freedom are relaxed simultaneously. The energetic consequences of a modest change in the interatomic distances are comparable to those of a large canting of the magnetic moments. Compression of the nanostructures leads to a decrease in the magnetic moments.

Wire fence as applique armour

In this paper, the behaviour of wire fence was investigated for potential as applique armour. The wire fence used was made from commercial high-strength patented wire and the supporting frames were made of mild steel L-profiles. Both patented wire and L-profiles are of-the-shelf materials. The fence was tested by firing 12.7 mm M8 API ammunition at four applique armour models: two of these models use a parallel wire arrangement, with one mounted at a 90° angle from the incoming projectile and the other at 70°; and two of these models use a zig-zag wire arrangement, one mounted at a firm 90° angle and the other is left in a hanging arrangement. Fence damage was correlated with RHA basic plate damage, on both the face and back. Wire fence has considerable potential as an improvised applique armour, except if the projectile impacts near the center of the wire or near the center between two wires. The latter case was successfully overcome by placing the armour model at an angle and by using a zig-zag wire arrangement. The lowest basic RHA plate damage level was found using the hanging armour model. However, from the point of view of ease of attachment, the most convenient was found to be the armour model with the zig-zag wire arrangement fixed at 90° angle from the incoming projectile. SEM fracto graphy revealed that the fracture surface was predominantly ductile, with dimples filled with debris from the incendiary effect of the projectile.

Structural stability and electronic properties of GaSb nanowires

The structural stability and electronic properties of four different shapes of GaSb nanowire have been studied by ab-initio method using the generalized gradient approximations. The different structures were two atom linear wire, two atom zigzag wire, four atom square wire and six atom hexagonal wire. The geometry optimization and the stability of all nanowires were investigated. We explore the minimum energy atomic configuration for all the considered shapes. We find that four atom square wire configuration has greater stability in comparison to other shapes. The analysis of density of states and band structures of optimized nanowires predicts that semiconducting nanowires may be metallic or semiconducting. The behavior entirely depends upon the geometrical structure.

Linear and second-order optical response of different GaN nanowires

By employing ab-initio method, we have investigated and analyze the calculation of linear and second-order optical response of four different GaN nanowires namely two atom linear wire, two atom zigzag wire, four atom square wire and six atom hexagonal wire. First we have analyzed the two atom linear wire for the convergence study with respect to k-point sampling. Then we have investigated the linear and second-order optical response of all considered configurations and predicted that the strongest absorption occurs for four atom square nanowire cross-section, which is also the stable structure for GaN nanowire as reported somewhere.

Electronic structure and magnetism of Fe wire in carbon nanotubes

We investigated electronic structures of the carbon nanotube (CNT) which includes Fe atoms using the first-principles molecular dynamics. We obtained the two stable geometries in which the Fe atoms form the zigzag and straight wires, respectively. The zigzag wire, showing the ferromagnetic configuration, is more stable than the straight one in the CNT. The latter has a novel antiferromagnetic configuration, which forms an antiparallel alignment of ferromagnetic dimers.

Magnetism of Zr atomic wires

By using the full-potential linearized augmented plane wave method to perform ab initio total energy calculations, we have explored magnetic ordering in one-dimensional Zr wires. The result shows that Zr can form linear, or dimerized, or zigzag wires and the magnetic properties strongly depend on their geometric structures. The linear and zigzag wires exhibit ferromagnetic ground states at the equilibrium bonding distance, while the dimerized wire, despite its higher stability than that of the linear one, exhibits nonmagnetic ground states. The most stable geometry is shown to be the zigzag wire with a magnetic moment of 0.26 μB per atom.

Domain structure and magnetoresistance in Ni 81Fe19 zigzag wires

Domain wall (DW) contribution to the magnetoresistance (MR) is illustrated by direct observation of field-dependent magnetic force microscope images that are correlated with MR curves for micron sized zigzag wires. The Permalloy zigzag wires were formed using focused ion beam milling, a simple one-step microfabrication technique. Our results show domain walls cause a decrease in the resistance that is more closely associated with the creation of a large amount of DWs in each segment of the zigzag wire than with the DWs pinned at the corners.