Ferromagnetic Wires Research Articles

On the Question of the Magnetic Susceptibility of Fractal Ferromagnetic Wires

With the help of a well-grounded measure, we have constructed an algorithm for calculating the longitudinal component of the magnetic susceptibility tensor of a fractal ferromagnetic wire. The calculations are based on the semiclassical kinetic equation for the magnon distribution function. The temperature and frequency dependences of the longitudinal magnetic susceptibility of a fractal wire is found.

Observing jumping domain walls

Nanomagnetism Domain walls, which separate regions of opposite magnetization in a ferromagnet, have rich dynamics that are difficult to characterize in small samples. Tetienne et al. imaged the magnetization of a thin ferromagnetic wire and observed the jumping of a domain wall between different

Micromagnetic Simulation of the Depinning Field Domain Wall on Symmetric Double Notch Ferromagnetic Wires

In this paper, we investigate the depinning field domain wall on symmetric double notch ferromagnetic wires by means of micromagnetic simulation for Permalloy (Py), Cobalt (Co), and Nickel (Ni) materials. T he depinning field domain wall increases as the size of the notch decreases. At a lower depinning field, the domain wall inner structure exhibited a transverse wall (TW), while at a higher depinning field, there was a transformation of the domain wall inner structure from transverse wall to antivortex wall (AVW). We also observed that the magnetization energy increased as the size of the notch decreased. This means that more energy was needed to release the domain wall from a smaller notch. Micromagnetic simulation showed that the depinning field domain wall depends on the size of the notch and on the ferromagnetic anisotropy.

Charge transfer statistics of transport through Majorana bound states

We analyze the full counting statistics of charge transfer through a Majorana bound state coupled to an STM tip and show how they can be used for an unambiguous identification of the bound state at the end of the wire. Additionally, we show how to generate Majorana bound states in a simple setup involving a ferromagnetic wire on a superconducting substrate.

Broadband spectroscopy of magnetic response in a nano-scale magnetic wire

We measure the broadband spectra of magnetic response in a single layered ferromagnetic nano-scale wire in order to investigate the size effect on the ferromagnetic resonance. We found that the resonance frequency difference between 300-nm- and 5-μm-wide wires was varied by about 5GHz due to the shape anisotropy. Furthermore, we experimentally detected the magnetization precession induced by the thermal fluctuation via the rectification of a radio-frequency (rf) current by incorporating an additional direct current (dc) by using Wheatstone bridge circuit. Our investigation renders that the shape anisotropy is of great importance to control the resonance frequency and to provide thermal stability of the microwave devices.

The left‐hand behaviour of polymer composites with Fe‐based microwires

AbstractIn the present paper, we deal with the electromagnetic properties of Fe‐rich microwire polymer meta‐composites prepared by embedding glass‐coated Fe‐based microwires into the E‐glass prepreg matrices in a parallel fashion. The free‐space measurement shows that a transmission window was created by adjusting the wire spacing below 7mm, which indicates that double negative index had been obtained. The correlation between the left‐handed feature with the local dielectric response has been established. The ‘natural' double negative behaviour is attributed to the intrinsic domain structure of Fe‐based ferromagnetic wires. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural, magnetic and conduction properties of 3d-metal monoatomic wires

From density functional theory calculations, we study the structure, magnetism and conduction properties of monoatomic wires made of all the 3d elements (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu). Wires with equidistant and alternating bond lengths are considered. Both magnetism and structure are found to play an important role for the conduction properties of the wires. Ferromagnetic wires are found to present a spin filtering effect which is not directly related with the magnitude of their magnetic moment. On the other hand, the main effect of bond length alternation is to partially destroy the transmission around the Fermi level, especially from the d bands. Ni wires are found to present particularly interesting spin filtering properties, meanwhile Cr wires present promising magnetoresistive effects.

Crack Detection Using Fluxgate Magnetic Field Sensor

In this study, the variation of the magnetic ux distribution in a magnetised ferromagnetic material which has in homogeneity as a crack is studied. An orthogonal uxgate magnetic eld sensor was used in the inspection of cracks. In the uxgate sensor, the sensing element (Co0.94Fe0.06)72.5Si12.5B15 amorphous ferromagnetic wire was placed inside a pickup coil winding with 50 μm copper wire and connected to a signal generator and the output from pick-up coil was detected using a lock-in ampli er. The surface pro le of magnetic materials with a crack was obtained using a specially designed 3-dimensional moving system. A large decrease in the output voltage of the sensor was observed when the sensor was moved on the top of the crack, after the further movement of the sensor the output voltage came back to the previous value.

An on-chip RT-PCR microfluidic device, that integrates mRNA extraction, cDNA synthesis, and gene amplification

This paper presents an on-chip integrated reverse transcriptase polymerase chain reaction (RT-PCR) microchip, which integrates the genetic functionalities of messenger ribonucleic acid (mRNA) extraction, complementary deoxyribonucleic acid (cDNA) synthesis, and gene amplification. The proposed RT-PCR microchip consists of a RNA microchannel for extracting mRNA from lysate biological samples, and a DNA microchamber for synthesizing cDNA and amplifying the target gene. As magnetic oligo-dT beads are passed through the RNA microchannel, mRNA bound to the beads was extracted within 1 min by a ferromagnetic wire array inlaid in the RNA microchannel. In the DNA microchamber, the extracted bound mRNA was used for direct synthesis of cDNA followed by amplification of the target gene. To evaluate the performance of the RT-PCR microchip, RT-PCR analyses were performed using various volumes of blood and numbers of breast cancer cells. Additionally, to verify the feasibility of the RT-PCR microchip for clinical applications, it was used for detection of virus-specific genes from specimens of patients infected with respiratory viruses. The continuous and integrated mRNA extraction, cDNA synthesis, and gene amplification process enabled by the proposed RT-PCR microchip suggests its use for high-precision genetic assays with small sample quantities.

Assessing the MR compatibility of dental retainer wires at 7 Tesla

To determine the MR compatibility of common dental retainer wires at 7 Tesla in terms of potential RF heating and magnetic susceptibility effects. Electromagnetic simulations and experimental results were compared for dental retainer wires placed in tissue-mimicking phantoms. Simulations were then performed for a human model with wire in place. Finally, image quality was assessed for different scanning protocols and wires. Simulations and experimental data in phantoms agreed well, with the length of the wire correlating to maximum heating in phantoms being approximately 47 mm. Even in this case, no substantial heating occurs when scanning within the specific absorption rate (SAR) guidelines for the head. Image distortions from the most ferromagnetic dental wire were not significant for any brain region. Dental retainer wires appear to be MR compatible at 7 Tesla.

On the Magnetic Susceptibility of Fractal Magnetic Wires

With the reasonable measure introduced the algorithm for computing the longitudinal component of the magnetic susceptibility of ferromagnetic fractal wire.

Gold shunt pads as a chirality filter for current-driven 360° domain wall motion in a ferromagnetic wire

A non-magnetic conductive pad on top of a ferromagnetic nanowire will both shunt the current injected into the nanowire and generate an in-plane Oersted field perpendicular to the wire. Micromagnetic simulations have shown that a current-driven 360° transverse domain wall (DW) can annihilate, pass through, or be pinned at the shunt pad depending on the magnitude of the driving spin current and the geometry of the pad. The response of the 360° DW to the Oersted field depends on the chirality of the DW, enabling the shunt pad to function as a chirality filter for 360° DWs, which may be useful in DW-based memory devices.

Oscillatory transformative domain wall inner structure of the depinning domain wall around a notched ferromagnetic wire

We have investigated the domain wall (DW) depinning behavior around the symmetric notches in ferromagnetic nanowires by means of a micromagnetic simulation. We observed that the depinning field decreases as the size of the notch increases. The change in the ratio of the height to the length of the bottom of the triangular notch is also considered, and a relatively insensitive variation of the depinning field is observed with for ratios greater than 2. When the depinning field strength is varied, the DW internal structure is found to change during the depinning process. At a lower depinning field ( 4 mT), the DW is depinned with a transformation of the inner structure with an antivortex soon after the DW has escaped from the notch due to the Walker breakdown phenomenon. Very interestingly, with any external field, the depinned DW with antivortex inner structure is observed to move back to the original notch position. This is explainable because the notch acts as an attractive pinning potential for the DW.

Nanocomposite Pattern-Mediated Magnetic Interactions for Localized Deposition of Nanomaterials

We present a method to create, align, and locate magnetic wires throughout and on the surface of patterned polymer matrices, following the magnetophoretic transport and self-assembly of ferromagnetic nanoparticles under a static magnetic field during laser photopolymerization of monomer/nanoparticle casted solutions. The resulting films have the ability to attract and immobilize small quantities of magnetic nanomaterials locally on the ferromagnetic wires, as proved by a detailed topography study. Magnetic studies on the films before and after the spontaneous deposition, demonstrate that the deposited nanomaterials alter significantly the magnetic character of the system, making thus possible their macroscopic identification. This offers the possibility to realize sensing devices based on hybrid materials with magnetic properties.

Ferromagnetic sandwich-like wires constructed with transition metals and anthracene

Properties of one-dimensional sandwich-like organometallic wires, [TM2(Ant)]∞, constructed with transition metals (TM = Sc, Ti, V, Cr, Mn, and Fe) and anthracene (Ant = C14H10) are systematically investigated by first-principles calculations. Our results show that the properties of [TM2(Ant)]∞ are mainly determined by charge transfer and the magnetic properties in [TM2(Ant)]∞ are much more diverse than those in [TM(Bz)]∞ due to the fact that HOMO-LUMO gap of Ant is much smaller than that of benzene (Bz = C6H6). In particular, [V2(Ant)]∞ and [Cr2(Ant)]∞ are found to be half-metallic ferromagnets, indicating that they are better than [TM(Bz)]∞ for spintronic devices due to high conductivity and stability. Furthermore, because the HOMO-LUMO gap of graphene flakes decreases with increasing size, the charge transfer effect may also manifest in sandwich-like wires based on graphene flakes and TM, which are also proposed to be potential candidates for spin transport.

Magnetic Separation of Malaria-Infected Red Blood Cells in Various Developmental Stages

Malaria is a serious disease that threatens the public health, especially in developing countries. Various methods have been developed to separate malaria-infected red blood cells (i-RBCs) from blood samples for clinical diagnosis and biological and epidemiological research. In this study, we propose a simple and label-free method for separating not only late-stage but also early-stage i-RBCs on the basis of their paramagnetic characteristics due to the malaria byproduct, hemozoin, by using a magnetic field gradient. A polydimethylsiloxane (PDMS) microfluidic channel was fabricated and integrated with a ferromagnetic wire fixed on a glass slide. To evaluate the performance of the microfluidic device containing the ferromagnetic wire, lateral displacement of NaNO2-treated RBCs, which also have paramagnetic characteristics, was observed at various flow rates. The results showed excellent agreement with theoretically predicted values. The same device was applied to separate i-RBCs. Late-stage i-RBCs (trophozoites and schizonts), which contain optically visible black dots, were separated with a recovery rate of approximately 98.3%. In addition, using an optimal flow rate, early-stage (ring-stage) i-RBCs, which had been difficult to separate because of their low paramagnetic characteristics, were successfully separated with a recovery rate of 73%. The present technique, using permanent magnets and ferromagnetic wire in a microchannel, can effectively separate i-RBCs in various developmental stages so that it could provide a potential tool for studying the invasion mechanism of the malarial parasite, as well as performing antimalarial drug assays.

Magnon Mediated Domain Wall Heat Conductance in Ferromagnetic Wires

A theoretical study of magnon-mediated heat transport in electrically insulating 1D ferromagnetic wires containing a domain wall is presented. In the regime of validity of continuum micromagnetism a domain wall is found to have no effect on the heat conductance. However, spin waves are found to be reflected by domain walls with widths of a few lattice spacings, which is associated with emergence of an additional spin wave bound state. We also discuss the role of dipolar interactions in high dimensions to generalize the argument in our previous work. The resulting reduction of the heat conductance due to a DW should be significant for thin wires of Yttrium Iron Garnet with sharply defined magnetic domains.

Microwires fabricated by glass-coated melt spinning

The glass-coated melt spinning method offers a route for the manufacture of metal filaments with a few micrometers in diameter in a single operation directly from the melt. Cobalt-based amorphous wires, Cu-15.0 atomic percent (at. %) Sn shape-memory wires, and Ni2MnGa (atomic percent) ferromagnetic wires were successfully produced by this method. The cobalt-based amorphous wire is flexible, and Cu-15.0 at. % Sn shape-memory wires have the tensile elongation of 14%. However, because of chemical reaction with glass and oxidation, it is hard to make Cu-Al-Ni shape-memory wires and Ni-Nb-Sn amorphous wires. Conditions for preparing these materials were summarized, and the differences of the solidification processes among glass-coated amorphous cobalt-based wires, Cu-15.0 at. % Sn shape-memory wires, and Ni2MnGa wires were analyzed and discussed.

Giant magneto-impedance effect in amorphous ferromagnetic wire with a weak helical anisotropy: Theory and experiment

An adequate description of the results of experimental measurement of both diagonal and off-diagonal Giant magneto-impedance (GMI) components has been obtained for Co-rich amorphous microwire at moderate frequencies assuming the existence of a small off-diagonal tensor component of the residual quenching stress. The latter is the origin of a weak helical anisotropy of amorphous microwire. The micromagnetic simulation of the magnetization reversal process in the microwire under the influence of the applied magnetic field and dc bias current has been carried out. It is shown that due to the influence of the magneto–elastic interaction in a wire with a weak helical anisotropy, the behavior of the longitudinal and circular magnetization components is significantly correlated. Namely, the change of the sign of the longitudinal magnetization component under the influence of the axial magnetic field leads to a subsequent jump of the circular magnetization component at some critical value of the applied magnetic field. As a result of the jump of the circular magnetization, the off-diagonal GMI component also changes sign during the wire magnetization reversal. This effect is confirmed experimentally for a Co-rich wire with a small negative magnetostriction. It is also shown that the jump of the circular magnetization can be eliminated by a circular magnetic field of a weak dc bias current flowing along the wire. This effect allows one to design sensitive magnetic field sensor based on the measurement of the off-diagonal GMI component.

Detection of edge magnetic state by a ballistic bend resistance measurement

We have investigated a magnetization process of a permalloy nanowire by using a ballistic micro-Hall sensor consisting of GaAs/AlGaAs two-dimensional electron gas. Although a conventional bi-stable hysteresis loop with a rectangular shape was observed in the Hall resistance measurement, unexpected extra resistance changes were observed in a bend resistance measurement. These unconventional features are quantitatively explained by the magnetic transitions among the meta-stable edge-domain structures in the ferromagnetic wire. The geometrical dependence of these resistance changes and their application possibility for the multiple-valued memory were also discussed.