Nonmagnetic Electrodes Research Articles

Enhancement of electrocatalysis through magnetic field effects on mass transport

Magnetic field effects on electrocatalysis have recently gained attention due to the substantial enhancement of the oxygen evolution reaction (OER) on ferromagnetic catalysts. When detecting an enhanced catalytic activity, the effect of magnetic fields on mass transport must be assessed. In this study, we employ a specifically designed magneto-electrochemical system and non-magnetic electrodes to quantify magnetic field effects. Our findings reveal a marginal enhancement in reactions with high reactant availability, such as the OER, whereas substantial boosts exceeding 50% are observed in diffusion limited reactions, exemplified by the oxygen reduction reaction (ORR). Direct visualization and quantification of the whirling motion of ions under a magnetic field underscore the importance of Lorentz forces acting on the electrolyte ions, and demonstrate that bubbles’ movement is a secondary phenomenon. Our results advance the fundamental understanding of magnetic fields in electrocatalysis and unveil new prospects for developing more efficient and sustainable energy conversion technologies.

Effect of lattice distortion on spin admixture and quantum transport in organic devices with spin–orbit coupling

Abstract With an extended Su–Schrieffer–Heeger model and Green’s function method, the spin–orbit coupling (SOC) effects on spin admixture of electronic states and quantum transport in organic devices are investigated. The role of lattice distortion induced by the strong electron–lattice interaction in organics is clarified in contrast with a uniform chain. The results demonstrate an enhanced SOC effect on the spin admixture of frontier eigenstates by the lattice distortion at a larger SOC, which is explained by the perturbation theory. The quantum transport under the SOC is calculated for both nonmagnetic and ferromagnetic electrodes. A more notable SOC effect on total transmission and current is observed for ferromagnetic electrodes, where spin filtering induced by spin-flipped transmission and suppression of magnetoresistance are obtained. Unlike the spin admixture, a stronger SOC effect on transmission exists for the uniform chain rather than the organic lattices with distortion. The reason is attributed to the modified spin-polarized conducting states in the electrodes by lattice configuration, and hence the spin-flip transmission, instead of the spin admixture of eigenstates. This work is helpful to understand the SOC effect in organic spin valves in the presence of lattice distortion.

Significant effects of magnetic electrodes on rhenium phthalocyanine molecules

The investigation focused on examining the spin polarization and thermal spin polarization transport characteristics of dual rhenium phthalocyanine (Re2PC2) molecular junctions. This analysis was conducted using first-principles density-functional theory and the non-equilibrium Green's function approach. Calculations were performed on molecular junctions in two configurations: one at a non-magnetic electrode (Au) and the other at a magnetic electrode (Ni). A comparison of the spin transport properties of the two electrodes shows significant differences. The magnetic electrode has a notable effect on the spin-polarization and thermal spin-polarization transport properties of the devices. In contrast, the nickel electrode bis-phthalocyanine rhenium molecular device exhibits perfect spin/thermal spin-filtering efficiencies in a parallel structure. The properties of the dual phthalocyanine rhenium molecular devices were significantly affected by the nature of the electrodes. This makes dual rhenium phthalocyanine molecular junctions have great potential for the development of high-performance multifunctional spintronic and spin caloritronic devices.

Magnetic molecules lose identity when connected to different combinations of magnetic metal electrodes in MTJ-based molecular spintronics devices (MTJMSD)

Understanding the magnetic molecules’ interaction with different combinations of metal electrodes is vital to advancing the molecular spintronics field. This paper describes experimental and theoretical understanding showing how paramagnetic single-molecule magnet (SMM) catalyzes long-range effects on metal electrodes and, in that process, loses its basic magnetic properties. For the first time, our Monte Carlo simulations, verified for consistency with regards to experimental studies, discuss the properties of the whole device and a generic paramagnetic molecule analog (GPMA) connected to the combinations of ferromagnet-ferromagnet, ferromagnet-paramagnet, and ferromagnet-antiferromagnet metal electrodes. We studied the magnetic moment vs. magnetic field of GPMA exchange coupled between two metal electrodes along the exposed side edge of cross junction-shaped magnetic tunnel junction (MTJ). We also studied GPMA-metal electrode interfaces’ magnetic moment vs. magnetic field response. We have also found that the MTJ dimension impacted the molecule response. This study suggests that SMM spin at the MTJ exposed sides offers a unique and high-yield method of connecting molecules to virtually endless magnetic and nonmagnetic electrodes and observing unprecedented phenomena in the molecular spintronics field.

Spin diode and spin valve based on an interacting quantum dot coupled with nonmagnetic electrodes

How to control the charge and spin in nanodevices is an important topic in spintronics. In this letter, we theoretically propose a spin diode and spin valve (SV) device controlled by all-electrical means, which is composed of a quantum dot (QD) coupled to a pair of nonmagnetic electrodes. When both electric charge bias and spin bias exist within the device, the I–V curves of this device exhibit an asymmetric distribution, and this asymmetry can be manipulated by the gate voltage. More interestingly, if we apply an external magnetic field on the QD, we can observe significant high- and low-resistance state switching with respect to the magnetic field, which can function as a SV device. This device scheme can be compatible with current technologies and has potential applications in spintronics or quantum processing.

Spin-selectivity effect of G-quadruplex DNA molecules.

Chirality-induced spin selectivity has been attracting extensive interest in recent years and is demonstrated in a variety of chiral molecules, all of which arise from inherent molecular chirality. Here, we first propose a theoretical model to study the spin-dependent electron transport along guanine-quadruplex (G4) DNA molecules, connected to two nonmagnetic electrodes, by considering the molecule-electrode contact and weak spin-orbit coupling. Our results indicate that the G4-DNA molecular junctions exhibit pronounced spin-selectivity effect, and the asymmetric contact-induced external chirality, instead of the inherent molecular chirality, dominates their spin filtration efficiency. Furthermore, the spin-selectivity effect is robust against the disorder and hold in a wide range of model parameters. These results could be checked by charge transport measurements and provide an alternative way to improve the spin-selectivity effect of chiral nanodevices.

Ameliorative and Renoprotective Effect of Electrical Stimulation on Blood Sugar, Blood Urea Nitrogen (BUN), Creatinine Levels, and the Islets of Langerhans Weight in Diabetic Mice.

Diabetes mellitus (DM) is a chronic metabolic disease or disorder characterized by high blood sugar levels as well as impaired carbohydrate, lipid, and protein metabolism due to insulin function insufficiency. Insulin deficiency can be caused by impaired or deficient insulin production by Langerhans beta cells in the pancreas or by a lack of responsiveness of the body's cells to insulin. This study aims to the effects of electrostimulation on the ameliorative (improves disease manifestations) or renoprotective (protects the kidneys) in a diabetic rat model using noninvasive (electrical stimulation with the magnetic and nonmagnetic electrode) and invasive (using needles) methods. This study used 25 female rats, with a normal control group (KN), a diabetes control group (KD), a needle treatment group (A), an electro-stimulator treatment group with a magnetic electrode (M), and an ES group with a nonmagnetic electrode (ES) (L). The electro-stimulator used AES-05 with a magnetic field strength of 90 mT at two acupoints, Pishu (BL20) and Shenshu (BL23). The treatment was administered 12 times in one month with a therapy time of 6.6 minutes per session. Body weight and blood sugar levels were compared before and after the treatment. After treatment, the diameter of the islets of Langerhans, as well as levels of creatinine and blood urea nitrogen (BUN), was measured. Furthermore, statistical analysis was performed (α = 0.05). The results of this study showed that electrical stimulation treatments with needle-invasive, noninvasive magnetic electrodes, and nonmagnetic electrodes significantly reduced diabetic rats' blood glucose levels before and after the treatment. The analysis of the diameter of the islets of Langerhans revealed a significant difference between the treatment groups. The analysis of creatinine levels revealed a significant difference between groups, but creatinine levels in the group with the magnetic electrode (0.58 ± 0.17 mg/dL) were not significantly different from the control group (0.58 ± 0.07 mg/dL). The BUN test results revealed a significant difference compared with the diabetic control group, but no significant difference with the magnetic electrode treatment group. Conclusion. Based on the results, the most effective therapy for diabetes is a noninvasive method with magnetic (M) electrodes.

Magnetic control of heat generation in a magnetic tunnel contact with spin accumulation

It is described how the heat generation by an electrical current in a ferromagnetic tunnel contact to a nonmagnetic material depends on the spin accumulation in the nonmagnetic electrode for both Joule and Peltier heating. This enables the control of the heating in the tunnel contact by an external applied magnetic field that induces spin precession of the spin accumulation. Thereby, a Hanle type of spin signal is imprinted in the heating power. We derive expressions for the magnitude and sign of the magnetic-field-dependent heating power for Joule and Peltier heating, and discuss the important parameters. For contacts with small resistance-area product, the spin accumulation provides the dominant contribution to the Joule heating power, which can therefore be modulated by more than a factor of 2 with a magnetic field. The described phenomenon can also produce genuine spin signals in various devices, including nonlocal lateral spin valves.

Fano effect in a thermally induced transport through a triple quantum dot within the Coulomb blockade regime

In the present work we theoretically study thermoelectric transport and heat transfer in a junction including a T-shaped double quantum dot coupled to nonmagnetic electrodes and supplemented with a third dot in a parallel configuration. We focus on the combined effect of Coulomb interactions and quantum interference occurring in the T-shaped portion of the considered triple quantum dot on the thermoelectric electron transport. The transport through the system is studied within the Coulomb blockade regime in the limit of strong intra-dot interactions between electrons beyond the linear response regime. It is shown that under these conditions both charge and heat transfer through the considered system may be significantly affected by the quantum interference and inter-dot Coulomb interactions.

Current-induced out-of-plane torques in a single permalloy layer with lateral structural asymmetry

We investigated current-induced torques in a single permalloy layer connected to nonmagnetic electrodes with lateral inversion asymmetry by spin-torque ferromagnetic resonance. Considering the symmetry of the spin-torque ferromagnetic resonance spectrum with respect to the magnetic field direction, we successfully separated various types of torque. In addition to in-plane damping-like and field-like torques, we detected two additional components of out-of-plane (OOP) torques, the symmetries of which with respect to the magnetic field direction correspond to an OOP field-like torque and an OOP damping-like torque. We obtained the OOP torques in particular by breaking a lateral inversion symmetry of the nonmagnetic electrodes, and the sign of the torques is reversed by inverting the electrode structure. The microwave frequency dependence of the OOP torques indicates that the OOP torques are not attributable to a spin current but to the Oersted field generated by a nonuniform charge current, ${B}_{\mathrm{Oersted}}$, and an inductive field, ${B}_{\mathrm{induc}.}$ (which originates from ${B}_{\mathrm{Oersted}}$). We propose an external field-free and fast magnetization switching of a ferromagnetic layer with perpendicular magnetic anisotropy by using ${B}_{\mathrm{induc}.}$, which can be achieved only by fabricating the electrodes asymmetrically.

Van der Waals Antiferroelectric Magnetic Tunnel Junction: A First-Principles Study of a CrSe2/CuInP2S6/CrSe2 Junction.

Magnetic tunnel junctions (MTJs), ferroelectric/antiferroelectric tunnel junctions (FTJs/AFTJs), and multiferroic tunnel junctions (MFTJs) have recently attracted significant interest for technological applications of nanoscale memory devices. Until now, most of them are based on perovskite oxide heterostructures with a relatively high resistance-area (RA) product and low resistance difference unfavorable for practical applications. The recent discovery of the two-dimensional (2D) van der Waals (vdW) ferroelectric (FE) and magnetic materials has opened a new route to realize tunnel junctions with high performance and atomic-scale dimensions. Here, using first-principles calculations, we propose a new type of 2D tunnel junction: an antiferroelectric magnetic tunnel junction (AFMTJ), which inherits the features of both MTJ and AFTJ. This AFMTJ is composed of monolayer CuInP2S6 (CIPS) sandwiched between 2D magnetic electrodes of CrSe2. The AFTJ with nonmagnetic electrodes of TiSe2 on both sides of CIPS and the asymmetric AFTJ with both CrSe2 and TiSe2 electrodes are also investigated. Based on quantum-mechanical modeling of the electronic transport, sizeable tunneling electroresistance effects and multiple nonvolatile resistance states are demonstrated. More importantly, a remarkably low RA product (less than 0.1 Ω·μm2) makes the proposed vdW AFMTJs superior to the conventional MFTJs in terms of their promising nonvolatile memory applications. Our calculations provide new guidance for the experiment and application of nanoscale memory devices.

Electrochemical Potential-Driven High-Throughput Molecular Electronic and Spintronic Devices: From Molecules to Applications.

Molecules are fascinating candidates for constructing tunable and electrically conducting devices by the assembly of either a single molecule or an ensemble of molecules between two electrical contacts followed by current-voltage (I-V) analysis, which is often termed "molecular electronics". Recently, there has been also an upsurge of interest in spin-based electronics or spintronics across the molecules, which offer additional scope to create ultrafast responsive devices with less power consumption and lower heat generation using the intrinsic spin property rather than electronic charge. Researchers have been exploring this idea of utilizing organic molecules, organometallics, coordination complexes, polymers, and biomolecules (proteins, enzymes, oligopeptides, DNA) in integrating molecular electronics and spintronics devices. Although several methods exist to prepare molecular thin-films on suitable electrodes, the electrochemical potential-driven technique has emerged as highly efficient. In this Review we describe recent advances in the electrochemical potential driven growth of nanometric various molecular films on technologically relevant substrates, including non-magnetic and magnetic electrodes to investigate the stimuli-responsive charge and spin transport phenomena.

Thermal Spin Torque in Double-Barrier Tunnel Junctions with Magnetic Insulators

The thermal spin torque induced by the spin-dependent Seebeck effect in double-barrier tunnel junctions is derived considering free-electron and tight-binding calculations. We show that in systems comprising ferromagnetic electrodes and nonmagnetic barriers, the in-plane component of the thermal spin torque is the dominant term, whereas in junctions comprising nonmagnetic electrodes and ferromagnetic barriers, both components, the in-plane and the out-of-plane, are comparable in magnitude. Moreover, larger torque amplitudes up to 3 orders of magnitude are obtained in the second system as a result of the spin-filtering effect; consequently, double-barrier tunnel junctions in the presence of magnetic insulators offer an enhanced thermal spin-torque mechanism for reliable applications. We propose taking advantage of quantum resonant tunneling through resonance states below the Fermi level in these structures that can pave a route toward achieving larger spin-torque efficiencies, even when considering smaller values of the exchange splitting. Furthermore, we identify the parameters needed to tune efficiently these resonant states.

Investigation of the thermal tolerance of silicon-based lateral spin valves

Improvement in the thermal tolerance of Si-based spin devices is realized by employing thermally stable nonmagnetic (NM) electrodes. For Au/Ta/Al electrodes, intermixing between Al atoms and Au atoms occurs at approximately 300 °C, resulting in the formation of a Au/Si interface. The Au–Si liquid phase is formed and diffuses mainly along an in-plane direction between the Si and AlN capping layers, eventually breaking the MgO layer of the ferromagnetic (FM) metal/MgO electrodes, which is located 7 µm away from the NM electrodes. By changing the layer structure of the NM electrode from Au/Ta/Al to Au/Ta, the thermal tolerance is clearly enhanced. Clear spin transport signals are obtained even after annealing at 400 °C. To investigate the effects of Mg insertion in FM electrodes on thermal tolerance, we also compare the thermal tolerance among Fe/Co/MgO, Fe/Co/Mg/MgO and Fe/Co/MgO/Mg contacts. Although a highly efficient spin injection has been reported by insertion of a thin Mg layer below or above the MgO layer, these thermal tolerances decrease obviously.

Magnetic field-controlled spin-dependent thermoelectric current in a single-molecule magnet transistor

Control of the charge, spin, and heat currents in thermoelectric devices is an interesting research field that is currently experiencing a burst of activity. In this work, a new type of spin-current generator is proposed that consists of a single-molecule magnet sandwiched between a pair of nonmagnetic electrodes. By applying an external magnetic field, this tunneling junction can generate a 100% spin-polarized current via thermoelectric effects, and the flow direction and spin polarization can be changed by adjusting the gate voltage or magnetic field. Moreover, regardless of whether the external magnetic field exists, the thermoelectric current is always highly spin polarized and can be switched by using different gate voltage windows. This molecular electrical device can be realized with current technologies and may have practical use in spin caloritronics and quantum information processing.

Pure spin-current diode based on interacting quantum dot tunneling junction* *Project supported by the National Natural Science Foundation of China (Grant No. 11404322) and the Natural Science Foundation of Huai’an (Grant No. HAB202150).

A magnetic field-controlled spin-current diode is theoretically proposed, which consists of a junction with an interacting quantum dot sandwiched between a pair of nonmagnetic electrodes. By applying a spin bias V S across the junction, a pure spin current can be obtained in a certain gate voltage regime,regardless of whether the Coulomb repulsion energy exists. More interestingly, if we applied an external magnetic field on the quantum dot, we observed a clear asymmetry in the spectrum of spin current I S as a function of spin bias, while the charge current always decays to zero in the Coulomb blockade regime. Such asymmetry in the current profile suggests a spin diode-like behavior with respect to the spin bias, while the net charge through the device is almost zero. Different from the traditional charge current diode, this design can change the polarity direction and rectifying ability by adjusting the external magnetic field, which is very convenient. This device scheme can be compatible with current technologies and has potential applications in spintronics or quantum processing.

Spinterfaces Manipulate Large Magnetic Field Effects in 3D and Quasi‐2D Organic–Inorganic Hybrid Perovskites

AbstractSpinterfaces are due to the orbital hybridization at an interface of a ferromagnet and a nonmagnetic semiconductor. Interfacial densities of states (i‐DOS) are spin‐dependent, which may offer the spin‐filter effect for enhancing spin‐polarized charge injection efficiency and magnetic field effects (MFEs). In the work, a prototypical perovskite spin valve (PeSV) comprising Ni/MAPbI3−xClx/Ni (MA = CH3NH3) is fabricated, showing a clear magnetic switching behavior in the ambient condition. It is further explored by studying the magnetophotocurrent (MPC) at the short‐circuit current density condition (magneto‐Jsc). Anomalously large magneto‐Jsc can be detected by comparing to devices with nonmagnetic Au electrodes. The effect can be more pronounced for the quasi‐2D perovskite such as (PEA)2(MA)3Pb4I13 (PEA = C6H5(CH2)2NH3). At low fields, the hyperfine field induced spin‐mixing shows remarkable magneto‐Jsc signals for it. In addition, the circularly and linearly polarized laser beam can effectively manipulate the magnitude of magneto‐Jsc for both MAPbI3−xClx and (PEA)2(MA)3Pb4I13. It is postulated that the formation of the spinterfaces may play a dominant role for the large and tunable magneto‐Jsc effect. These studies may pave the way for future experimental and theoretical studies in the field.

Spin-polarized electrical transport in transition metal encapsulated C20 fullerenes: A theoretical account

This work delves into the conductance property of transition metal (Ti, V, Cr, Mn, Fe, Co, Ni) encapsulated C20 endohedral metallofullerenes (EMFs), sandwiched between non-magnetic gold electrodes. DFT optimization of the designed systems casts the encapsulated metal at the center of the C20 cage irrespective of the system and spin states. Application of density functional theory coupled with non-equilibrium green function techniques on these EMFs results variant transport characteristics for different metal encapsulation, represented through transmission spectra at zero bias and current vs. voltage (I-V) plots. Spin-polarized electrical transport has been observed for the Mn, Fe, Co and Ni encapsulated C20, while no such spin polarization could be traced for Ti, V and Cr both in absence and presence of applied bias. The EMFs with Mn, Fe, Co and Ni display half-metallic behavior and significant spin-filtering efficiency, which reaches maximum value for the Fe encapsulated C20. Spin-resolved electrical conductance in the Mn/Fe/Co/Ni-EMFs are explained by density of states, projected density of states at zero bias and molecular orbital analyses, which reveal the contribution of C20 electrons towards the down-spin-polarized transmission for Fe/Co/Ni-EMFs, while for the Mn-EMF, the metal d-electrons mostly participate in the up-spin-polarized transmission. Taken these observations together, the present computational study showcases the importance of encapsulating transition metal inside carbon cages in inducing spin polarization and thus provides an aid to tailor suitable molecules for spintronic applications.

Acute Exercise Modulates Pain-induced Response on Sensorimotor Cortex ∼20 Hz Oscillation

Exercise affects positively on self-reported pain in musculoskeletal pain conditions possibly via top-down pain inhibitory networks. However, the role of cortical activity in these networks is unclear. The aim of the current exploratory study was to investigate the effects of acute exercise on cortical nociceptive processing and specifically the excitability in the human sensorimotor cortex. Five healthy adults (mean age 32.8 years) were recorded with a whole-head 306-channel magnetoencephalography (MEG, Elekta Neuromag® Triux™). Participant’s right hand third fingertip was stimulated electrically with an intracutaneous non-magnetic copper tip electrode before and immediately after an exercise task. Stimulus intensity was set individually so that the stimulation was subjectively rated as moderately painful, 6–7 on a visual analog scale. The acute exercise task was an isometric three-minute fatiguing left hand contraction with force-level at 30% of maximum voluntary contraction. Data analysis was conducted as event-related evoked field and frequency analysis. Early cortical activations after stimulation were localized in the primary and secondary somatosensory cortices. The main result demonstrated modulation of cortical nociceptive processing in the sensorimotor cortex ∼20 Hz rhythm immediately after the acute exercise. In conclusion, acute exercise may have an effect on nociceptive processing in the sensorimotor cortex on oscillatory level. Research on cortical oscillations analyzing interaction between nociception and exercise is limited. This study presents results indicating brain oscillatory activity as a feasible research target for examining mechanisms interacting between exercise and cortical nociceptive processing.

The spin-dependent transport properties of endohedral transition-metal-fullerene X@C66H4 (X=Fe, Co, Mn, Ni)

Inspired by recent experiments on the successful synthesis of hydrofullerene C66H4 in Tian et al. (2019) [12] with two negatively curved heptagons. Based on the density functional theory and nonequilibrium Green's function method, we report the spin-dependent transport through transition-metal-atom-encapsulated C66H4 hydrofullerene, i.e., X@C66H4(X=Fe, Co, Mn, Ni), contacted by single gold atoms via semi-infinite non-magnetic Au electrodes. It is found that, Mn- and Fe-doped systems show highly spin-polarized transmission as well as considerable magnetic moments whereas Ni-doped systems show completely spin-unpolarized transmission and nonmagnetic. Interestingly, Co-doped systems show two spin states, i.e., spin-polarized and spin-unpolarized ones. Further analysis shows that, for Mn-, Fe- and Ni-doped systems, the spin-polarized/unpolarized state is caused by the finite/(nearly-)zero magnetism of the encapsulated metal atom. While the magnetism in Co-doped systems is quenched for the top hexagonal doping case, but not for the side heptagonal doping one, which induces the spin-unpolarized/spin-polarized state. And the screening effect of electrodes on the magnetism of Co is the underlying physical mechanism. Our findings would be beneficial to the design of spintronics devices.