Application Of Current Pulses Research Articles

Mechanisms of Electrical Switching of Ultrathin CoO/Pt Bilayers.

We study current-induced switching of the Néel vector in CoO/Pt bilayers to understand the underlying antiferromagnetic switching mechanism. Surprisingly, we find that for ultrathin CoO/Pt bilayers electrical pulses along the same path can lead to an increase or decrease of the spin Hall magnetoresistance signal, depending on the current density of the pulse. By comparing these results to XMLD-PEEM imaging of the antiferromagnetic domain structure before and after the application of current pulses, we reveal the details of the reorientation of the Néel vector in ultrathin CoO(4 nm). This allows us to understand how opposite resistance changes can result from a thermomagnetoelastic switching mechanism. Importantly, our spatially resolved imaging shows that regions where the current pulses are applied and regions further away exhibit different switched spin structures, which can be explained by a spin-orbit torque-based switching mechanism that can dominate in very thin films.

A Platform for Addressing Individual Magnetite Islands Grown Epitaxially on Ru(0001) and Manipulating Their Magnetic Domains.

We have grown high-quality magnetite micrometric islands on ruthenium stripes on sapphire through a combination of magnetron sputtering (Ru film), high-temperature molecular beam epitaxy (oxide islands), and optical lithography. The samples have been characterized by atomic force microscopy, Raman spectroscopy, X-ray absorption and magnetic circular dichroism in a photoemission microscope. The magnetic domains on the magnetite islands can be modified by the application of current pulses through the Ru stripes in combination with magnetic fields. The modification of the magnetic domains is explained by the Oersted field generated by the electrical current flowing through the stripes underneath the magnetite nanostructures. The fabrication method is applicable to a wide variety of rock salt and spinel oxides.

The effect of pulsed electric current on the structural and mechanical behavior of 6016 aluminium alloy in different states of hardening

This study presents the effect of high current pulses on the structural and mechanical behavior of the 6016 aluminium alloy in three different states of hardening: naturally aged, super saturated, and annealed. The 6016 aluminium alloy was used for the first time in terms of electrically-assisted forming. The influence of the application of different current parameters on the material behavior was conducted. The study of electrically-assisted tensile tests showed that the application of current pulses results in a distinct response of the material, depending on the hardening state. Although in a hardened state, the mechanical properties and plasticity are deteriorated, in the solution treated state, they are improved. For the changes of the material properties is responsible the interaction of the flowing current with the precipitates and the aging process. The new parameters were proposed to describe the distinctions in the material properties between the different states of hardening of the aluminium alloy during the electrically-assisted tension. The material examination was conducted using light and scanning electron microscopy, using also electron backscattered diffraction methods. The application of, for example, the grain orientation spread parameter demonstrated the presence of recrystallized grains, in electrically-assisted specimens.

Evaluation of mass transfer behaviour of sulfamethoxazole species at ion–exchange membranes by chronopotentiometry for electrodialytic processes

In recent years, electrodialysis has been often considered as an appropriate method to treat industrial and/or municipal wastewater containing pharmaceutically active compounds. However, the scarcity of information on the ion transport mechanisms through the membranes, especially concerning occurrence of possible sorption phenomena, has limited the process implementation in practice. The present work aims to evaluate, by chronopotentiometry, the transport of sulfamethoxazole (SMX) through a cation- (CEM) and anion-exchange membrane (AEM) using synthetic solutions at different concentrations (0.001–0.1 g/L) and pH conditions (1.6 for CEM and 9 for AEM). The dominant mechanism of mass transfer under overlimiting current conditions at each membrane/solution system was determined. The potential drop profile measured during and after application of current pulses, as well as the transition times obtained from the curves, showed that sorption occurs at/in both membranes, especially for the AEM. Besides, this phenomenon was reversible for the CEM and irreversible for the AEM under the conditions evaluated herein. The chronopotentiograms of the AEM showed that the intense occurrence of water dissociation with the most diluted solution caused chemical equilibrium shifts in the membrane/electrolyte system, leading to formation of neutral SMX species that can impair the electrodialysis performance. The results obtained are useful for optimizing the electrodialytic treatment of SMX-containing solutions as well as of other compounds with similar physicochemical properties.

Efficient current-driven magnetization switching owing to isotropic magnetism in a highly symmetric 111-oriented Mn4N epitaxial single layer

We investigated in-plane current-induced magnetization switching in a Mn4N epitaxial single layer. Efficient magnetization switching was detected via the measurement of anomalous Hall resistivity after the application of current pulses, with a duration of 1 s, to the 111-oriented Mn4N film compared with a reference 001-oriented Mn4N film. The threshold current density of magnetization switching with 0.5 s pulse durations, Jc ≈ 1 MA/cm2, was relatively low compared with that reported for magnetic tunnel junctions and/or ferromagnet/heavy metal bilayer systems. The relatively low Jc in the 111-oriented film was attributed to the low magnetic anisotropy on the (111) plane of Mn4N owing to the isotropic crystal symmetry as revealed by x-ray diffraction and transmission electron microscopy as a reduced switching barrier boosts the probability of magnetization switching. It was concluded that manipulation of the magnetic anisotropy based on the crystal orientation is one of the promising approaches to develop materials suitable for application in highly efficient switching devices with Mn4N layers.

Mechanism of Néel Order Switching in Antiferromagnetic Thin Films Revealed by Magnetotransport and Direct Imaging.

We probe the current-induced magnetic switching of insulating antiferromagnet-heavy-metal systems, by electrical spin Hall magnetoresistance measurements and direct imaging, identifying a reversal occurring by domain wall (DW) motion. We observe switching of more than one-third of the antiferromagnetic domains by the application of current pulses. Our data reveal two different magnetic switching mechanisms leading together to an efficient switching, namely, the spin-current induced effective magnetic anisotropy variation and the action of the spin torque on the DWs.

Deterministic creation and deletion of a single magnetic skyrmion observed by direct time-resolved X-ray microscopy

Spintronic devices based on magnetic skyrmions are a promising candidate for next-generation memory applications due to their nanometre-size, topologically-protected stability and efficient current-driven dynamics. Since the recent discovery of room-temperature magnetic skyrmions, there have been reports of current-driven skyrmion displacement on magnetic tracks and demonstrations of current pulse-driven skyrmion generation. However, the controlled annihilation of a single skyrmion at room temperature has remained elusive. Here we demonstrate the deterministic writing and deleting of single isolated skyrmions at room temperature in ferrimagnetic GdFeCo films with a device-compatible stripline geometry. The process is driven by the application of current pulses, which induce spin-orbit torques, and is directly observed using a time resolved nanoscale X-ray imaging technique. We provide a current-pulse profile for the efficient and deterministic writing and deleting process. Using micromagnetic simulations, we also reveal the microscopic mechanism of the topological fluctuations that occur during this process.

Spin-orbit torque-driven skyrmion dynamics revealed by time-resolved X-ray microscopy

Magnetic skyrmions are topologically protected spin textures with attractive properties suitable for high-density and low-power spintronic device applications. Much effort has been dedicated to understanding the dynamical behaviours of the magnetic skyrmions. However, experimental observation of the ultrafast dynamics of this chiral magnetic texture in real space, which is the hallmark of its quasiparticle nature, has so far remained elusive. Here, we report nanosecond-dynamics of a 100nm-diameter magnetic skyrmion during a current pulse application, using a time-resolved pump-probe soft X-ray imaging technique. We demonstrate that distinct dynamic excitation states of magnetic skyrmions, triggered by current-induced spin–orbit torques, can be reliably tuned by changing the magnitude of spin–orbit torques. Our findings show that the dynamics of magnetic skyrmions can be controlled by the spin–orbit torque on the nanosecond time scale, which points to exciting opportunities for ultrafast and novel skyrmionic applications in the future.

Automated and manual patch clamp data of human induced pluripotent stem cell-derived dopaminergic neurons

Human induced pluripotent stem cells can be differentiated into dopaminergic neurons (Dopa.4U). Dopa.4U neurons expressed voltage-gated NaV and KV channels and showed neuron-like spontaneous electrical activity. In automated patch clamp measurements with suspended Dopa.4U neurons, delayed rectifier K+ current (delayed KV) and rapidly inactivating A-type K+ current (fast KV) were identified. Examination of the fast KV current with inhibitors yielded IC50 values of 0.4 mM (4-aminopyridine) and 0.1 mM (tetraethylammonium). In manual patch clamp measurements with adherent Dopa.4U neurons, fast KV current could not be detected, while the delayed KV current showed an IC50 of 2 mM for 4-aminopyridine. The NaV channels in adherent and suspended Dopa.4U neurons showed IC50 values for tetrodotoxin of 27 and 2.9 nM, respectively. GABA-induced currents that could be observed in adherent Dopa.4U neurons could not be detected in suspended cells. Application of current pulses induced action potentials in approx. 70 % of the cells. Our results proved the feasibility of automated electrophysiological characterization of neuronal cells.

Avoiding the side effects of electric current pulse application to electroporated cells in disposable small volume cuvettes assures good cell survival

BackgroundThe harmful side effects of electroporation to cells due to local changes in pH, the appearance of toxic electrode products, temperature increase, and the heterogeneity of the electric field acting on cells in the cuvettes used for electroporation were observed and discussed in several laboratories. If cells are subjected to weak electric fields for prolonged periods, for example in experiments on cell electrophoresis or galvanotaxis the same effects are seen. In these experiments investigators managed to reduce or eliminate the harmful side effects of electric current application.MethodsFor the experiments, disposable 20 μl cuvettes with two walls made of dialysis membranes were constructed and placed in a locally focused electric field at a considerable distance from the electrodes. Cuvettes were mounted into an apparatus for horizontal electrophoresis and the cells were subjected to direct current electric field (dcEF) pulses from a commercial pulse generator of exponentially declining pulses and from a custom-made generator of double and single rectangular pulses.ResultsMore than 80% of the electroporated cells survived the dcEF pulses in both systems. Side effects related to electrodes were eliminated in both the flow through the dcEF and in the disposable cuvettes placed in the focused dcEFs. With a disposable cuvette system, we also confirmed the sensitization of cells to a dcEF using procaine by observing the loading of AT2 cells with calceine and using a square pulse generator, applying 50 ms single rectangular pulses.ConclusionsWe suggest that the same methods of avoiding the side effects of electric current pulse application as in cell electrophoresis and galvanotaxis should also be used for electroporation. This conclusion was confirmed in our electroporation experiments performed in conditions assuring survival of over 80% of the electroporated cells. If the amplitude, duration, and shape of the dcEF pulse are known, then electroporation does not depend on the type of pulse generator. This knowledge of the characteristics of the pulse assures reproducibility of electroporation experiments using different equipment.

Electroplastic effect in nanocrystal and amorphous alloys

The influence of the structural and phase state in nanocrystalline and amorphous alloys, as well as the pulsed current modes, on the electroplastic effect is studied under their tension. The decreasing grain size to nanoscale, the emergence of secondary phases, and amorphization in alloys cause the attenuation or disappearance of the electroplastic effect. The application of current pulses upon tension of alloys with a reversible thermoelastic martensitic transformation suppresses the step down of stress on the tensile diagrams caused by the electroplastic effects, but activates the jump up of stress attributed to the shape memory effect.

MODELING THE HEALING OF MICROCRACKS IN METAL STIMULATED BY A PULSED HIGH-ENERGY ELECTROMAGNETIC FIELD. PART II

The article investigates the processes of transformation and interaction of defects, such as plane microcracks with linear dimension of the order of 10 μm that occur in materials when metal samples are treated by short-term pulses of high-density electric current. The investigation is made numerically based on a coupled model of intense electromagnetic field impact on a predamaged thermoelastoplastic material with defects. The model allows for melting and evaporation of metal as well as the dependence of all physicomechanical properties of it on temperature, as was presented in Part I of this article. The solution of the resultant system of equations is sought by the finite-element method on moving meshes, using a arbitrary Euler–Lagrange method. The calculations showed that as a result of simultaneous decrease of the length, release of the molten metal to the crack, and closing of the edges, the crack edges begin contacting the jet of molten metal and, at the end of these processes, the jet is fully enclosed by the crack edges. Thus, the application of current pulses leads to the welding of the crack and the healing of microdefects. In the present work we consider the problems of choosing the preferable integration domains and the conditions at their boundaries when the above processes are simulated. The way in which the processes under consideration depend on the boundary conditions that can be used in the model is investigated. The effect of the distance between the microcracks and of their mutual position relative to each other on the processes of their healing is studied. Numerical simulation showed that in studying the processes microcrack healing it is possible to restrict oneself, without loss of accuracy, to consideration of one representative cell as the integration domain (or one-fourth of the symmetric representative cell) by specifying at its boundaries, that are not the axes of symmetry, the difference of potentials determined for the cell without defect (in the state "unperturbed" by the presence of a microcrack). In such case, the conditions of symmetry can be selected as the mechanical boundary conditions. When the distances between the cracks exceed 5–6 lengths of the cracks, the processes of healing will occur identically, irrespective of whether they are simulated in the integration domain composed of one or several representative cells. Decreasing the distances between the cracks to 1–2 linear dimension of the cracks (taking into account changes in their mutual position) does not change qualitatively the described process of healing; however, this results in substantial slowing down of the process: the release of the molten material to the crack continues, but the decrease of the crack reduces significantly, especially in the lateral direction.

Current-induced domain wall motion and magnetization dynamics in CoFeB/Cu/Co nanostripes

Current-induced domain wall motion and magnetization dynamics in the CoFeB layer of CoFeB/Cu/Co nanostripes were studied using photoemission electron microscopy combined with x-ray magnetic circular dichroism (XMCD-PEEM). Quasi-static measurements show that current-induced domain wall motion in the CoFeB layer is similar to the one observed in the NiFe layer of NiFe/Cu/Co trilayers, although the threshold current densities for domain wall depinning are lower. Time-resolved XMCD-PEEM measurements are used as an efficient probe of domain wall depinning statistics. They also reveal that, during the application of current pulses, the CoFeB magnetization rotates in the direction transverse to the nanostripe. The corresponding tilt angles have been quantified and compared to analytical and micromagnetic calculations, highlighting the influence of magnetostatic interactions between the two magnetic layers on the magnetization rotation.

Mixed bi-material electrodes based on LiMn 2O 4 and activated carbon for hybrid electrochemical energy storage devices

The performance of mixed bi-material electrodes composed of the battery material, LiMn 2O 4, and the electrochemical capacitor material, activated carbon, for hybrid electrochemical energy storage devices is investigated by galvanostatic charge/discharge and pulsed discharge experiments. Both, a high and a low conductivity lithium-containing electrolyte are used. The specific charge of the bi-material electrode is the linear combination of the specific charges of LiMn 2O 4 and activated carbon according to the electrode composition at low discharge rates. Thus, the specific charge of the bi-material electrode falls between the specific charge of the activated carbon electrode and the LiMn 2O 4 battery electrode. The bi-material electrodes have better rate capability than the LiMn 2O 4 battery electrode. For high current pulsed applications the bi-material electrodes typically outperform both the battery and the capacitor electrode.

Control of magnetic domain wall displacement using spin current in small in-plane magnetic field in Permalloy nanowires

We microscopically investigate the magnetic domain wall motion induced by current pulse application in a small in-plane magnetic field in U-shaped Permalloy wires by means of Lorentz microscopy together with simultaneous transport measurement. An in-plane magnetic field less than 7 Oe parallel to the wire direction in U-shaped geometry effectively works to impede bidirectional motion of the domain wall induced by current pulse application, i.e. to suppress the stochastic nature of the domain wall displacement. The present finding will provide practical and reliable ways of controlling and manipulating the domain wall dynamics, which are widely applicable in spintronic devices, especially when stochastic nature causes serious problems in device operation. Reliable manipulation of the magnetic state is discussed using the current-driven domain wall motion and domain nucleation in the magnetic wire device.

Low temperature electric pulse induced resistance switching in Na0.5−δCoO2

We have been able to control the resistance state of the NaxCoO2 system for the x=0.5−δ sample at low temperatures by the application of current pulses. We can reversibly commute between two resistance states, controlling the amplitude and polarity of the applied pulses. We also studied the resistance temperature dependence of the different state and we interpret the switching effect in term of the displacement of Na+ ions induced by current.

The electroplastic effect in the cold-drawing of copper wires for the automotive industry

The paper presents a comparison between conventional cold wire drawing and wire drawing combined with the application of high-density electric current pulses. The investigations were carried out having in mind the manufacture of copper wire for cables used in the automotive industry. A specially built experimental stand is described. The experiments showed a decrease in the pull force for wire drawing combined with the application of current pulses. The material properties of the drawn wires were tested. It was found that the plastic properties of the wire and its surface quality improved in the case of wire drawing combined with current pulses. The proposed technique of wire drawing is highly promising and potentially can replace the conventional on-line continuous annealing of the material.

Detection of current‐driven magnetic domain wall deformation using anisotropic magnetoresistance effect

AbstractWe report on an electrical detection of current driven domain wall (DW) deformation induced by a current pulse injection in arc‐shaped permalloy (Py) submicron wires. Current polarity and pulse length dependence were investigated under an assisting external magnetic field. Initial DW states prepared by an application of a large magnetic field were distributed to two distinct DW states. A current pulse application promoted transition between them. In addition, the third DW state was established only by an application of the short pulses (<50 ns). This result suggests the possibility of the high‐speed control of the DW dynamics. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Intrinsic metastability of low doped manganites: La0.8Ca0.2MnO3 case

Transport properties of phase separated La0.8Ca0.2MnO3 crystals in the aged highly resistive metastable state were studied. It was found that the coexistence of different ferromagnetic phases at low temperatures is sensitive to electric current/field. In a contrast with the previously studied low resistivity metastable states the high resistivity state exhibits positive magnetoresistance and significant current dependence of the resistivity even at temperatures much higher than the Curie temperature. Application of current pulses results in appearance of zero bias anomaly in the current dependent conductivity. Similarly to the low resistivity metastable states the memory of the resistivity can be erased only after heating of the sample to Te ≈360 K. After one year storage at room temperature the La0.8Ca0.2MnO3 samples show clear signatures of aging. The aged samples spontaneously evolute towards high resistivity states. The results are discussed in the context of a coexistence of two ferromagnetic phases with different orbital order and different conductivity. The metallic ferromagnetic phase seems to be less stable giving rise to the experimentally observed electric field effects and aging.

Current-Driven Magnetization Reversal in a Ferromagnetic Semiconductor(Ga,Mn)As/GaAs/(Ga,Mn)AsTunnel Junction

Current-driven magnetization reversal in a ferromagnetic semiconductor based (Ga,Mn)As/GaAs/(Ga,Mn)As magnetic tunnel junction is demonstrated at 30 K. Magnetoresistance measurements combined with current pulse application on a rectangular 1.5 x 0.3 microm2 device revealed that magnetization switching occurs at low critical current densities of 1.1-2.2 x 10(5) A/cm2 despite the presence of spin-orbit interaction in the p-type semiconductor system. Possible mechanisms responsible for the effect are discussed.