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Programmable delivery of biological matter is indispensable for the massive arrays of individual objects in biochemical and biomedical applications. Although a digital manipulation of single cells has been implemented by the integrated circuits of micromagnetophoretic patterns with current wires, the complex fabrication process and multiple current operation steps restrict its practical application for biomolecule arrays. Here, a convenient approach using multifarious transit gates is proposed, for digital manipulation of biofunctionalized microrobotic particles that can pass through the local energy barriers by a time-dependent pulsed magnetic field instead of multiple current wires. The multifarious transit gates including return, delay, and resistance linear gates, as well as dividing, reversed, and rectifying T-junction gates, are investigated theoretically and experimentally for the programmable manipulation of microrobotic particles. The results demonstrate that, a suitable angle of the gating field at a suitable time zone is crucial to implement digital operations at integrated multifarious transit gates along bifurcation paths to trap microrobotic particles in specific apartments, paving the way for flexible on-chip arrays of biomolecules and cells., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A novel method based on remotely controlled magnetic forces of bio-functionalized superparamagnetic colloids using micromagnet arrays was devised to measure frictional force at the sub-picoNewton (pN) scale for bio-nano-/micro-electromechanical system (bio-NEMS/MEMS) interfaces in liquid. The circumferential motion of the colloids with phase-locked angles around the periphery of the micromagnets under an in-plane rotating magnetic field was governed by a balance between tangential magnetic force and drag force, which consists of viscous and frictional forces. A model correlating the phase-locked angles of the steady colloid rotation was formulated and validated by measuring the angles under controlled magnetic forces. Hence, the frictional forces on the streptavidin/Teflon interface between the colloids and the micromagnet arrays were obtained using the magnetic forces at the phase-locked angles. The friction coefficient for the streptavidin/Teflon interface was estimated to be approximately 0.036 regardless of both vertical force in the range of a few hundred pN and velocity in the range of a few tenths of μm s(-1).

We investigated T 1 relaxations of ex-vivo cancer tissues at low magnetic fields in order to check the possibility of achieving a T 1 contrast higher than those obtained at high fields. The T 1 relaxations of fifteen pairs (normal and cancerous) of breast tissue samples were measured at three magnetic fields, 37, 62, and 122 μT, using our superconducting quantum interference device-based ultralow field nuclear magnetic resonance setup, optimally developed for ex-vivo tissue studies. A signal reconstruction based on Bayesian statistics for noise reduction was exploited to overcome the low signal-to-noise ratio. The ductal and lobular-type tissues did not exhibit meaningful T 1 contrast values between normal and cancerous tissues at the three different fields. On the other hand, an enhanced T 1 contrast was obtained for the mucinous cancer tissue.

This is the first report of significant energization (up to 7,000 eV) of low‐energy He+ ions, which occurred simultaneously with H‐band electromagnetic ion cyclotron (EMIC) wave activity, in a direction mostly perpendicular to the ambient magnetic field. The event was detected by the Arase satellite in the dayside plasmatrough region off the magnetic equator on 15 May 2019. The peak energy of the He+ flux enhancements is mostly above 1,000 eV. At some interval, the He+ ions are energized up to ∼7,000 eV. The H‐band waves are excited in a frequency band between the local crossover and helium gyrofrequencies and are close to a linear polarization state with weakly left‐handed or right‐handed polarization. The normal angle of the waves exhibits significant variation between 0° and 80°, indicating a non‐parallel propagation. We run a hybrid code with parameters estimated from the Arase observations to examine the He+ energization. The simulations show that cold He+ ions are energized up to more than 1,000 eV, similar to the spacecraft observations. From the analysis of the simulated wave fields and cold plasma motions, we found that the ratio of the wave frequency to He+ gyrofrequency is a primary factor for transverse energization of cold He+ ions. As a consequence of the numerical analysis, we suggest that the significant transverse energization of He+ ions observed by Arase is attributed to H‐band EMIC waves excited near the local helium gyrofrequency. Key Points: Strong H‐band EMIC waves were detected in the dayside plasmatrough region off the magnetic equator by the Arase spacecraftThe H‐band waves energize cold He+ ions to levels above ∼1,000 eV in the direction perpendicular to the background magnetic fieldSimulation indicates that the ratio of the wave frequency to He+ gyrofrequency is a primary factor in the strong energization of He+ ions [ABSTRACT FROM AUTHOR]

A nonvolatile magnetic switch is proposed by utilizing the unique properties of graphene-ferromagnet composite structures. The basic mechanism relies on the role of graphene in mediating and modulating the effective exchange bias between adjacent magnetic layers, which can lead to electrically controlled rotation of magnetic bits. Readout of magnetization states is also achieved electrically through the magnetoresistance effect in the graphene channel. The proposed switch can be used to realize both the memory and programmable logic elements. Theoretical estimates illustrate the feasibility of the concept as well as its potential advantage of low power consumption (∼10-19 J) for the intrinsic switching operation. [ABSTRACT FROM AUTHOR]

We fabricated spin light emitting diodes using oxide tunneling barriers between ferromagnetic materials (Ni0.8Fe0.2/Co0.9Fe0.1) and semiconductors (GaAs) and investigated the temperature-dependent carrier lifetime and spin relaxation time of the active GaAs layer. We observed the circular polarization of the free exciton from the electroluminescence spectra due to the spin injection from the ferromagnetic material, whereas the circular polarization of the conduction band to acceptor transition was negligible. From the temperature-dependent carrier lifetime and spin relaxation time of the active GaAs layer, we found that the spin injection efficiency was larger than 25% between 20 and 180 K, where the magnetic field dependence of the spin lifetime was ignored. [ABSTRACT FROM AUTHOR]

Interfacial engineering via nanoparticle substrate surface decoration has been extended to coated conductor templates. Preformed BaTiO3 and BaZrO3 nanoparticles were applied to substrate surfaces, prior to YBa2Cu3O7-δ (YBCO) deposition, by using a scalable and inexpensive technique of solution-based suspension. Compared to untreated reference samples, nanodecoration yields improved in-field critical current density (Jc) as well as strong correlated pinning along the c-axis direction of the YBCO film. Accordingly, a much reduced falloff of Jc with magnetic field strength was observed in all of the modified samples. In addition, scaling behavior of the normalized volume pinning force density (Fp) with respect to temperature provided insight as to the differences in flux pinning mechanisms dependent on the decoration technique. Finally, with these results our earlier proof-of-concept demonstrations on nanoparticle modified single crystal substrates were replicated on technological substrates, pointing to the versatility of this simple technique for realization of enhanced high temperature superconductor performance. [ABSTRACT FROM AUTHOR]

The magnetotransport properties of ferromagnetic Ga1-xMnxAs epilayers with Mn mole fractions in the range of x≈2.2%–4.4% were investigated using Hall effect measurements. The temperature-dependent Hall carrier concentration for a metallic sample with x≈2.2% was analyzed assuming an activation energy from two acceptor levels. It was found that the two acceptor levels with activation energies of 129.4 and 31.6 meV at B=0 Oe decreased to 87.6 and 30.7 meV, respectively, at B=5 kOe. The decrease in acceptor activation energy from 129.6 to 87.6 meV was due to the spin splitting of the Mn acceptor level in the ferromagnetic region, and was responsible for the increase in carrier concentration. From magnetic-field-dependent Hall resistance data, the Curie temperature was estimated to be TC=60 and 70 K for Ga1-xMnxAs samples with x≈2.2 and x≈4.4%, respectively. The magnetoresistance measurements confirmed that the anomalous Hall effect existed in these samples that showed metallic and insulating behavior, respectively. [ABSTRACT FROM AUTHOR]

Oxidation of an AlOx insulating barrier in a magnetic tunneling junction (MTJ) was carried out by a tilted-plasma oxidation method. It was found that the tilted-plasma oxidation induced a gradual change in the extent of oxidation of an insulating layer, which consequently led to a gradual change in the tunneling magnetoresistance (TMR) and specific junction resistance (RA) of the MTJ. We found a linear relation in the TMR versus RA curve with positive and negative slopes for less- and overoxidized junctions, respectively, and a parabolic relation for optimally oxidized junctions. The crossover in the TMR versus RA curves provides an effective and useful way to optimize (and monitor) the oxidation condition of a tunneling barrier in MTJs especially of a tunneling barrier less than 10 Å thick. The tunneling junctions were also investigated after thermal annealing at various temperatures. The observations after thermal annealing were found to be consistent with transmission electrons microscopy images and a scenario of the partial formation of an additional ultrathin tunneling barrier at the top surface of the bottom magnetic layer. [ABSTRACT FROM AUTHOR]

The influence of the structural disorder on the transport properties of Co[sub 0.50]Ti[sub 0.50] alloy films in a temperature range of 4.2-300 K has been investigated without and with a magnetic field of 0.5 T. The absence of translational invariance in a disordered state leads to an increase in the resistivity and causes a change from the positive to negative temperature coefficient of resistance. This fact is explained by the partial localization of electronic states near the Fermi level. It was established that a partial structural disordering enhances the role of the electron-phonon-vibrating impurity scattering in the transport properties and also makes the spin-diffusive scattering rather noticeable. The appearance of a low-temperature resistivity minimum for the disordered Co[sub 0.50]Ti[sub 0.50] alloy film arises from the quantum corrections to the electron-electron interactions in the presence of weak localization. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies striations in Czochralski silicon crystals grown under various axial magnetic field strengths. Method of the study; Results and discussion; Conclusion.

We have designed, fabricated, and demonstrated a novel system for translocation of magnetic beads at specific sites of the sensor surface on a single chip for biosensor applications. The soft NiFe elliptical (9×4×0.1 μm3) elements are arranged as magnetic pathways connected to the model sensor surface. The patterned NiFe elements can generate different stray magnetic fields when they are subjected to the external rotating magnetic field. The inhomogeneity in stray magnetic fields can govern the magnetic bead motion on the pathways. We demonstrated the motion of Dynabead® M-280 magnetic bead on patterned pathways by controlling the external rotating magnetic field in clockwise and counterclockwise directions. The magnetic beads that were placed on the magnetic elliptical pathways are shown to be transported to the sensor surface, as well as be pulled out away from the surface. This technique enables microtranslocation of the magnetic beads coated with biomolecules to the specific binding sites of the sensor surface and as well as drive off the nonspecific binding biomolecules from the surface in performing number of sequential bead detection experiments for future integrated lab-on-a-chip systems. [ABSTRACT FROM AUTHOR]

We report here the effect of ultrathin IrMn buffer layer on the magnetic and spin transport properties of spintronic structure for current-induced magnetization switching. The insertion of the ultrathin (∼1 nm) IrMn buffer layer drastically enhanced the coercive field of the fixed ferromagnetic layer from 36 to 215 Oe. Interestingly, the ultrathin IrMn buffer layer even enhanced the magnetoresistance ratio about 30%, and consequently the spin polarization effect was enhanced by reducing the critical current density of magnetization switching from 3.13×108 to 1.16×108 A/cm2. [ABSTRACT FROM AUTHOR]

This paper presents a wireless active finger rehabilitation method controlled magnetic forces within a three-axis coil system. The three-axis coils enhanced degree of freedom in hand positioning. The developed system includes three magnets for controlling one finger within the coil, thus, providing external force to the finger without the use of a complex mechanical structure. The proposed method is simple in configuration and operates wirelessly by magnetic interaction. The system generates three magnetic forces for flexion and extension of the finger. The proposed method can be used regardless of the position of the hand in the system. The combined influence of the three magnetic forces used to generate flexion and extension of the finger was verified through experimental analysis. [ABSTRACT FROM AUTHOR]

The measurements of voltage fluctuations at room temperature are performed for magnetic tunnel junction, patterned by photolithography to have 20 × 10 µm² in junction area. The observed noise power follows 1/f behavior for the whole applied magnetic field (H) range (-30 Oe≤H ≤30 Oe) and shows strong field dependence. The sharp increase in noise power spectral density is observed near a transition region from antiparallel to parallel magnetic state in two electrodes during field ramping down. In addition, the reduction of noise power density is accompanied by the reduction of magnetoresistance ratio after thermal annealing at 300°C for 700 s in the same junction. It is conjectured that the observed reduction of the noise level in our junction is due mainly to magnetic origin, such as thermally activated domain wall motion, rather than electrical origin. [ABSTRACT FROM AUTHOR]

Provides information on a study which investigated the magnetic relaxation phenomenon by using the pulse method for an alloy with nanoscale grain structure. Relationship between the microstructure and the magnitude of magnetic aftereffect in the nanocrystalline state; Change in the jumping field defined by the magnetic field; Features of Fe based nanocrystalline materials.

The dynamics of a magnetic domain wall (DW) under a transverse magnetic field Hy are investigated in two-dimensional (2D) Co/Ni microstrips, where an interfacial Dzyaloshinskii-Moriya interaction (DMI) exists with DMI vector D lying in +y direction. The DW velocity exhibits asymmetric behavior for ±Hy; that is, the DW velocity becomes faster when Hy is applied antiparallel to D. The key experimental results are reproduced in a 2D micromagnetic simulation, which reveals that the interfacial DMI suppresses the periodic change of the average DW angle φ even above the Walker breakdown and that Hy changes φ, resulting in a velocity asymmetry. This suggests that the 2D DW motion, despite its microscopic complexity, simply depends on the average angle of the DW and thus can be described using a one-dimensional soliton model. These findings provide insight into the magnetic DW dynamics in 2D systems, which are important for emerging spin-orbitronic applications. [ABSTRACT FROM AUTHOR]

Herein, we report a feasibility study for elimination of the screening current-induced field (SCIF) in fully insulated (INS) and no-insulation (NI) GdBCO coated conductor (CC) coils exposed to an external AC magnetic field generated by background solenoid copper coils. Prior to investigating the effects of external AC magnetic fields on SCIF in the GdBCO CC coils, the magnetic flux density ( B) was calculated using the equivalent circuit model and compared to the B obtained empirically to quantify the SCIF in the INS and NI coils. The value of the SCIF in the NI coil was smaller than that in the INS coil without the use of an external AC magnetic field, due to the current paths originating from the turn-to-turn and layer-to-layer contacts, suggesting that the screening current dissipated by contact resistance during charging. When the INS and NI coils were exposed to the external AC magnetic field, the B of the coils increased gradually, and eventually saturating to the calculated B values, indicating full removal of the SCIF. In addition, the SCIF of the NI coil could be removed under subjection to a lower external AC magnetic field compared to the INS coil, due to the lower SCIF occurring in the NI coil after charging. [ABSTRACT FROM AUTHOR]

We develop a nonlinear force-free field (NLFFF) extrapolation code based on the magnetohydrodynamic (MHD) relaxation method. We extend the classical MHD relaxation method in two important ways. First, we introduce an algorithm initially proposed by Dedner et al. to effectively clean the numerical errors associated with ∇ · B. Second, the multigrid type method is implemented in our NLFFF to perform direct analysis of the high-resolution magnetogram data. As a result of these two implementations, we successfully extrapolated the high resolution force-free field introduced by Low & Lou with better accuracy in a drastically shorter time. We also applied our extrapolation method to the MHD solution obtained from the flux-emergence simulation by Magara. We found that NLFFF extrapolation may be less effective for reproducing areas higher than a half-domain, where some magnetic loops are found in a state of continuous upward expansion. However, an inverse S-shaped structure consisting of the sheared and twisted loops formed in the lower region can be captured well through our NLFFF extrapolation method. We further discuss how well these sheared and twisted fields are reconstructed by estimating the magnetic topology and twist quantitatively. [ABSTRACT FROM AUTHOR]

We present studies of the transport properties of a superconducting film with an array of parallel nickel magnetic nanostripes (800 nm period) deposited on top of a germanium insulating layer covering the film surface. The critical current parallel to the stripes is larger than the critical current perpendicular to the stripes. Both critical currents demonstrate strong hysteresis and matching field effects. We have observed strong hysteresis in the resistance dependence on the magnetic field. [ABSTRACT FROM AUTHOR]

Studies of the transport properties of a superconducting film with several (1-7) parallel nickel magnetic nanostripes deposited on the top of a thin insulating layer covering the surface of the superconducting film are reported. Measurements of the dependence of the resistance on the in-plane magnetic field with two magnetic field orientations (parallel to the stripes direction and perpendicular to the stripes) and the temperature have been made. We have studied resistance versus in-plane magnetic field direction. Different types of strong hysteresis in the resistance dependence on the magnetic field for different magnetic field orientations were observed. [ABSTRACT FROM AUTHOR]

Studies of the transport properties of a PbBi superconducting film with an embedded triangular array of cobalt nanorods with a 300 nm period are reported. It is found that the critical current demonstrates strong hysteresis and maxima at magnetic field values corresponding to an integral number of flux quanta per unit cell of the array. The amplitude of the critical current is larger than for a control film without nanorods. The increase varies from several times to several orders of magnitude depending on the magnetic field and temperature. [ABSTRACT FROM AUTHOR]

GdBCO single-pancake coils wound with Kapton insulation every 3, 6, 9 turns, and without insulation, were characterized by charge-discharge and over-current tests. The magnetic field saturation at higher currents than the critical current was affected by the portion of the insulated turns that restricted the surplus current flow away from the azimuthal current path. The charge-discharge delay decreased with the increase of the portion of the insulated turns, which suggested that partial insulation winding may be effective for use in HTS power applications. Magnetic field loss of the coils with reduced insulation at excessive high currents was mainly affected by the decrease in ampere-turns due to the electrically shorted-circuits between the non-insulated turns, which resulted in the over-current flow bypass through the turn-to-turn contacts. [ABSTRACT FROM AUTHOR]

Controlling the position of a magnetic domain wall with electric current may allow for new types of non-volatile memory and logic devices. To be practical, however, the threshold current density necessary for domain wall motion must be reduced below present values. Intrinsic pinning due to magnetic anisotropy, as recently observed in perpendicularly magnetized Co/Ni nanowires, has been shown to give rise to an intrinsic current threshold Jth0. Here, we show that domain wall motion can be induced at current densities 40% below Jth0 when an external magnetic field of the order of the domain wall pinning field is applied. We observe that the velocity of the domain wall motion is the vector sum of current- and field-induced velocities, and that the domain wall can be driven against the direction of a magnetic field as large as 2,000 Oe, even at currents below Jth0. We show that this counterintuitive phenomenon is triggered by Walker breakdown, and that the additive velocities provide a unique way of simultaneously determining the spin polarization of current and the Gilbert damping constant. [ABSTRACT FROM AUTHOR]

This study examined the effects of external pressures on the thermal and electrical stabilities of stacked GdBCO CCs through quench tests. The minimum quench energies and two-dimensional normal zone propagation velocities of stacked GdBCO CCs connected electrically in series under various external pressures were examined. The quench test results showed that the minimum quench energy increased with increasing the external pressure. Longitudinal normal zone propagation velocities were greater than transverse normal zone propagation velocities. Moreover, normal zone propagation velocities increased with increasing applied pressure implying that applied pressure resulted in increased layer-to-layer thermal contact that allowed hot spots to dissipate more easily. [ABSTRACT FROM PUBLISHER]

A numerical study is performed to examine the heat transfer characteristics of natural convection past a vertical cone under the combined effects of magnetic field and thermal radiation. The surface of the cone is subjected to a variable surface heat flux. The fluid considered is a gray, absorbing-emitting radiation but a non-scattering medium. With approximate transformations, the boundary layer equations governing the flow are reduced to non-dimensional equations valid in the free convection regime. The dimensionless governing equations are solved by an implicit finite difference method of Crank-Nicolson type which is fast convergent, accurate, and unconditionally stable. Numerical results are obtained and presented for velocity, temperature, local and average wall shear stress, and local and average Nusselt number in air and water. The present results are compared with the previous published work and are found to be in excellent agreement. [ABSTRACT FROM AUTHOR]

A switchable beam pattern antenna composed of electric and magnetic radiators, i.e., a monopole and a loop, is proposed. The proposed antenna is designed to operate at 2 GHz for wireless communications. By controlling the state of the switch located at the junction between the dipole and the loop, the antenna can select one between two beam patterns. The simulated 10 dB frequency bandwidths are observed to be approximately 9.5% (1.87-2.06 GHz) and 10.0% (1.93-2.13 GHz) for on and off states, respectively. The simulated and measured results indicate that the proposed antenna operates at approximately the same frequencies, whereas it is clearly observed that the antenna's maximum beam direction is alternated depending on the switching states. [ABSTRACT FROM AUTHOR]

In this work, we report the results of our study on the magnetization-reversal properties in a bilayered magnetic antidot lattice (BMAL) system consisting of upper perforated thick Co layer of 40 nm and lower continuous thin Ni layer of 5 nm, probed by using a superconducting-quantum-interference-device (SQUID) magnetometer and by magnetic-force microscopy (MFM). Such a BMAL structure was fabricated by using photolithography and controlled wet-etching processes. A systematic study on the in-plane anisotropy, and the switching-field properties was carried out. The atomic-force-microscopy (AFM) image clearly indicated that the anti-dot array structures are well defined, and the local element composition was confirmed by using the energy dispersive spectra (EDS). The room-temperature hysteresis curves, taken along different directions of the applied magnetic-field, were proved to be useful to understand the magnetic anisotropy in the sample. A kind of uniaxial anisotropy with easy axis along 0^\circ and hard axis along 90^\circ of applied field direction was observed. To get a comprehensive knowledge about the domain configuration, we performed the MFM imaging along the easy and hard axis of the lattice. The MFM images revealed well-defined periodic domain networks which can be ascribed to the anisotropies such as magnetic uniaxial anisotropy, configurational anisotropy, etc. The observed changes in the magnetic properties are closely related to the patterning that pins the domains as well as to the magneto-anisotropic BMAL structure. [ABSTRACT FROM AUTHOR]

A network is frustrated when competing interactions between nodes prevent each bond from being satisfied. This compromise is central to the behaviour of many complex systems, from social and neural networks to protein folding and magnetism. Frustrated networks have highly degenerate ground states, with excess entropy and disorder even at zero temperature. In the case of quantum networks, frustration can lead to massively entangled ground states, underpinning exotic materials such as quantum spin liquids and spin glasses. Here we realize a quantum simulation of frustrated Ising spins in a system of three trapped atomic ions, whose interactions are precisely controlled using optical forces. We study the ground state of this system as it adiabatically evolves from a transverse polarized state, and observe that frustration induces extra degeneracy. We also measure the entanglement in the system, finding a link between frustration and ground-state entanglement. This experimental system can be scaled to simulate larger numbers of spins, the ground states of which (for frustrated interactions) cannot be simulated on a classical computer. [ABSTRACT FROM AUTHOR]

To detect quenches in the Poloidal Field (PF) magnet system is more difficult than the Toroidal Field (TF) magnet system due to excessively high inductive voltages generated by PF pulse-currents and plasma currents. According to reference scenarios being considered so far, the maximum voltage across the PF coils is inductively generated up to about 3.5 kV during the start of plasma (SoP) stage in a very short time period. The voltage measured by compensation of the inductive voltage should be below a certain level which is called as the quench voltage threshold. However, the compensated voltage might be higher than the threshold even with the well-designed compensation schemes. Accordingly, the quench voltage threshold and the quench protection delay time should be properly determined for the quench detection not to take a false action which could cause the fast energy discharge. From the quench simulation using the calculation of hot spot temperature and the resistive voltage growth as a function of time, the proper values of the quench detection parameters of the PF magnet system were derived for the maximum hot temperature rise to be limited within 150 K. [ABSTRACT FROM AUTHOR]

To achieve the first plasma of the Korea superconducting tokamak advanced research (KSTAR), the KSTAR superconducting coils were tested in advance. As they should operate in excessively low temperature of 4.5 K and high magnetic field environment of 7.5 T, it is crucial to monitor the cryogenic and the structural behaviors of KSTAR device during the commissioning period including a cool-down. The temperatures of the KSTAR toroidal field (TF) coil and the poloidal field (PF) coils were measured during the entire operating period. The mechanical stresses on the TF and PF structures were continuously monitored to check if they go beyond the limiting value calculated through the simulation. The alignment of the KSTAR device was checked by using displacement sensors. The TF coils were successfully supplied with 15 kA DC current for 8 hours, and the maximum 5 kA/s current variation of the PF coils were tested. For the main experiment, the interlock test of the quench detection system for the KSTAR coils was carried out at reduced currents of 1 kA. From these results the quench protection circuit, and the current-flow of the KSTAR superconducting coils proved to be well performed for the first plasma operation. [ABSTRACT FROM AUTHOR]

Titanium is a rare, secondary nucleus among Galactic cosmic rays. Using the Silicon matrix in the ATIC experiment, Titanium has been separated. The energy dependence of the Ti to Fe flux ratio in the energy region from 5 GeV per nucleon to about 500 GeV per nucleon is presented. [ABSTRACT FROM AUTHOR]

The metal organic deposition (MOD) of buffer layers on RABiTS substrates is considered a potential, low-cost approach to manufacturing high performance Second Generation (2G) high temperature superconducting (HTS) wires. The typical architecture used by American Superconductor in their 2G HTS wire consists of a Ni-W (5 at.%) substrate with a reactively sputtered Y2O3 seed layer, YSZ barrier layer and a CeO2 cap layer. This architecture supports critical currents of over 300 A/cm-width (77 K, self-field) with 0.8 μm YBCO films deposited by the TFA-MOD process. The main challenge in the development of the MOD buffers is to match or exceed the performance of the standard vacuum deposited buffer architecture. We have recently shown that the texture and properties of MOD - La2Zr2O7 (LZO) barrier layers can be improved by inserting a thin sputtered Y2O3 seed layer and prepared MOD deposited LZO layers followed by MOD or RF sputtered CeO2 cap layers that support MOD-YBCO films with Ic's of 200 and 255 A/cm-width, respectively. Detailed X-ray and microstructural characterizations indicated that MOD - CeO2 cap reacted completely with MOD YBCO. to form BaCeO3. However, sputtered CeO2 cap/MOD YBCO interface remains clean. By further optimizing the coating conditions and reducing the heat-treatment temperatures, we have demonstrated an Ic of 336 A/cm with improved LZO layers and sputtered CeO2 cap and exceeded the performance of that of standard vacuum deposited buffers. [ABSTRACT FROM AUTHOR]

In this paper we discuss the predictive analysis performed in support of the test program of the International Thermonuclear Experimental Reactor (ITER) Poloidal Field Conductor Insert (PFCI). A subset of the test program items was considered, with particular emphasis on DC performance and AC losses. The results and implications of the comparison of selected predictions from different laboratories will be presented. [ABSTRACT FROM AUTHOR]

We fabricated multichannel magnetocardiogram (MCG) systems of! magnetometer type and 2 planar gradiometer types, and compared the MCG data measured using different pickup coil systems. The magnetometer type is a 61-channel magnetometer system measuring vertical component of MCG fields. The magnetometers were integrated magnetometer structure with the pickup coil and SQUID fabricated on the same wafer. The two planar gradiometer systems are 64-channel planar gradiometer systems of first-order with a baseline of 4 cm, and of second-order with a baseline of 5 cm. The planar gradiometer systems are measuring field components tangential to the chest surface. The MCG waveforms and field distributions were measured on the same subject using the 3 MCG systems of different pickup coil types. The measured field distributions and waveforms were transformed into data of other pickup coil types, and the comparison between the measured and transformed results were done. [ABSTRACT FROM AUTHOR]

A 64-channel planar gradiometer system was developed to measure magnetocardiogram (MCG) signals. The planar gradiometers are second-order planar gradiometers with a baseline of 50 mm, fabricated from Nb thin films on Si wafers using thin film processes. The SQUIDs were fabricated from Nb/Al-oxide/Nb junctions, and a double relaxation oscillation SQUID (DROS) scheme was used to have a large flux-to-voltage transfer, typically about 1 mV/Φ0. The planar gradiometers were arranged to measure magnetic field components tangential to the chest surface, which has a field distribution peak just above the current dipole. The diameter of the sensor coverage area is 190 mm, which was proved to be large enough to provide MCG field distribution in a single measurement. Inside a thin-wall shield room, the white noise level of the planar gradiometer system is about 8 fT/√Hz. The 64-channel system was operated in a thin-wall shield room, and MCG signals were measured. [ABSTRACT FROM AUTHOR]

We have developed a new type of magnetocardiograph (MCG) system employing 6 high-Tc SQUID magnetometers. We have fabricated high performance YBCO SQUID devices for the system. The lightweight MCG system, requiring liquid nitrogen as a coolant, consists of 6-channel SQUID sensors and an adjustable patient bed with sliding motion. The MCG system showed stable operation in a room with moderate magnetic shielding. In normal operation with a moving subject, we could obtain 36-point and 48-point MCG mappings with high enough signal qualities for clinical trials. [ABSTRACT FROM AUTHOR]

The development of a high frequency, high harmonic gyrotron based on a superconducting magnet is described. A conduction-cooled superconducting magnet with the warm room of Φ 80 mm and the center field of 4 T was designed and fabricated. The superconducting magnet has two homogenous regions with length of 150 mm and 250 ram. The homogeneity of magnetic field is about ±0.25%. All the homogeneous regions are with the same starting point and the field is decayed to 1/6–1/7 from the front point of the homogeneous region to 195 mm. This paper describes the design and fabrication of the superconducting magnet for Gyrotron. [ABSTRACT FROM AUTHOR]

YBCO dc superconducting quantum interference device (SQUID) magnetometers based on bicrystal junctions have been fabricated for magnetocardiograph measurements. The pickup coil of the device was designed employing 16 parallel loops with 50-μm-wide lines. Noise performance was improved by applying a modification in the coupling line between pickup loop and SQUID washer. We could obtain optimized SQUID magnetometer design having magnetic field noise of about 38 fT/Hz1/2 at 1 Hz and about 20 fT/Hz1/2 at 100 Hz with an 1/f corner frequency of 2 Hz, measured inside a magnetically-Shielded room. Demonstration of magnetocardiograph measurements showed quite promising results with high signal-to-noise ratio of 82 with a moderate magnetic shielding. [ABSTRACT FROM AUTHOR]

The effect of an applied magnetic field on an inhomogeneous superconductor is studied and the value of the lower critical magnetic field Hc1 at which superconducting vortices appear is estimated. In addition, the authors locate the vortices of local minimizers, which depends on the inhomogeneous term a(x). [ABSTRACT FROM AUTHOR]

The limiting current has been derived for electron beams with gyromotion propagating down a waveguide immersed in an external guide magnetic field. It has been found that the maximum current is strongly dependent on the pitch angle parameter α, where α=v ???/v[sub 1], the ratio of the velocity associated with tile gyromotion and the velocity in the direction of propagation. The theory has been applied to the design of high power gyrotrons. [ABSTRACT FROM AUTHOR]

We consider transverse redistributions of the electrons and holes in intrinsic graphene ribbons under the influence of crossed electric and magnetic fields, i.e., the magnetoconcentration effect. The electron and hole transport is described from the Boltzmann kinetic equation assuming the local quasiequilibrium distributions of the carriers over energy states. The effective control of the carriers is achieved from deep depletion to accumulation modes depending on the properties of the ribbon edges, provided electron-hole recombination/generation rates at the edges are different from those inside the ribbon. The current-voltage characteristics reflect the behavior of the carrier redistributions across the ribbon. The obtained results suggest that interesting effects such as the population inversion in certain ranges of energies and the induced transparency are possible, which make them attractive for various optoelectronics applications in the terahertz spectral range. [ABSTRACT FROM AUTHOR]

We report measurements of the phase diagram and critical current of a PbBi superconducting film with an embedded square array of Ni nanorods. Strong hysteresis of the superconducting properties and an increase in the critical current which varies from several times to several orders of magnitude depending on the magnetic field and temperature is found. [ABSTRACT FROM AUTHOR]

An analysis of a magnetic field sensor based on a graphene spin capacitor is presented. The proposed device consists of graphene nanoribbons on top of an insulator material connected to a ferromagnetic source/drain. The time evolution of spin polarized electrons injected into the capacitor can be used for an accurate determination at room temperature of external magnetic fields. Assuming a spin relaxation time of 100 ns, magnetic fields on the order of ∼10 mOe may be detected at room temperature. The observational accuracy of this device depends on the density of magnetic defects and spin relaxation time that can be achieved. [ABSTRACT FROM AUTHOR]

The dynamic magnetization switching of a nanostructured exchange-coupled trilayer with a small thickness asymmetry is investigated by micromagnetic simulation. The magnetization switching initially occurs by coherent rotation, followed by magnetization oscillation. The switching time, which is about 9 ns at an applied field just above the switching field, is a factor of two longer than that observed for a single-layered thin film. A Fourier analysis of the magnetization oscillation shows multiple oscillation frequencies, the main frequency of which decreases as the applied magnetic field increases. [ABSTRACT FROM AUTHOR]

Variation in the quality of the interface in a CoFeB/MgO/CoFeB tunnel junction during thermal annealing was investigated using x-ray photoemission spectroscopy. The formation of B oxide and the reduction of Fe oxide at the bottom interface after thermal annealing near Ta=300 °C were found to enhance the tunneling magnetoresistance ratio significantly. At the same time, an asymmetry of the conductance (dV/dI) in the bias polarity and a local minimum of conductance in a positive bias state were measured which were attributed to the presence of a minority state at the bottom interface. The authors believe that the existence of the Bloch state was also responsible for the failure of the application of the Brinkman-Dynes-Rowell or Simmons models to the CoFeB/MgO/CoFeB junction. [ABSTRACT FROM AUTHOR]

The authors have investigated the magnetoresistance of ferromagnet-semiconductor devices in an InAs two-dimensional electron gas system in which the magnetic field has a sinusoidal profile. The magnetoresistance of their device is large. The longitudinal resistance has an additional contribution which is odd in applied magnetic field. It becomes even negative at low temperature where the transport is ballistic. Based on the numerical analysis, they confirmed that their data can be explained in terms of the local Hall effect due to the profile of negative and positive field regions. This device may be useful for future spintronic applications. [ABSTRACT FROM AUTHOR]