Metal Spacer Research Articles

Resonant enhancement of thermal spin-transfer torque in asymmetric double-barrier tunnel junctions

Charge current and thermal spin-transfer torque (TSTT) in asymmetric double-barrier magnetic tunnel junctions (DBMTJs) with a non-magnetic metal (NM) spacer as CoFeB/MgO/NM/MgO/LSMO are studied by non-equilibrium Green’s function (NEGF) formalism. It is found that the results show oscillatory behavior with an increase of the NM spacer thickness due to the resonant tunneling effect through the DBMTJs structures. About the dependence of the temperature difference and angle between the magnetizations, the charge current and TSTT are larger at the specific thicknesses (resonant positions) of the NM spacer than the others. The results also illustrate a magnitude enhancement for asymmetric DBMTJs compared with asymmetric single-barrier MTJs (SBMTJs). Therefore, it is possible to achieve a large TSTT for magnetization dynamics by new asymmetric DBMTJs.

Electrically conductive spacers for self-cleaning membrane surfaces via periodic electrolysis

The use of an electrically conductive membrane has attracted significant interest in water treatment technology due to remarkable performance in fouling mitigation domain. In electrochemical systems, when external potential is applied, water electrolysis occurs and the generated gases efficiently clean the membrane surface. However, fabricating and integrating conductive membranes in current water treatment modules are challenging. The present work applies, for the first time, the electrolysis concept at the spacer component of the module rather than the membrane. Two types of materials were tested, a titanium metal spacer and a polymeric spacer. The polymeric spacer was made conductive via coating with a carbon-based ink comprised of graphene nanoplates (GNPs). A membrane system composed of the carbon coated/titanium metal spacer attached to the surface of a polyvinylidene fluoride (PVDF) microfiltration membrane and was assembled to the case of membrane module. The conductive spacers worked as an electrode (cathode) in electrochemical set-up. The membrane system was subjected to fouling and then exposed to periodic electrolysis, wherein in-situ cleaning of membrane surface by hydrogen bubbles generation at the spacer is applied.

Asymmetric Magnetoimpedance in Ferromagnetic Biphase Films: Effects of Magnetostatic Coupling and Number of Layers

A model to describe the asymmetric magnetoimpedance in biphase soft/hard magnetic multilayered film is proposed. It is shown that a magnetostatic coupling changes the magnetization distribution in soft magnetic layers and leads to asymmetry in the field dependence of the impedance. The influence of the number of the repetitions of the base three-layered film structure having the soft and hard magnetic layers separated by non-ferromagnetic metallic spacer on the asymmetric magnetoimpedance is analyzed. The results of modelling describe main features of the asymmetric magnetoimpedance effect observed in bimagnetic multilayered films. The analysis shows that the multilayers may be attractive for use in miniature sensors of a weak magnetic field.

Control of the Oscillatory Interlayer Exchange Interaction with Terahertz Radiation.

The oscillatory interlayer exchange interaction between two magnetic layers separated by a metallic spacer is one of the few coherent quantum phenomena that persists at room temperature. Here, we show that this interaction can be controlled dynamically by illuminating the sample (e.g., a spin valve) with radiation in the 10-100THz range. We predict that the exchange interaction can be changed from ferromagnetic to antiferromagnetic (and vice versa) by tuning the amplitude and/or the frequency of the radiation. Our chief theoretical result is an expression that relates the dynamical exchange interaction to the static one that has already been extensively measured.

Transport in ferromagnet/superconductor spin valves

We consider charge transport properties in realistic, fabricable, Ferromagnet/Superconductor spin valves having a layered structure $F_1/N/F_2/S$, where $F_1$ and $F_2$ denote the ferromagnets, $S$ the superconductor, and $N$ the normal metal spacer usually inserted in actual devices. Our calculation is fully self-consistent, as required to ensure that conservation laws are satisfied. We include the effects of scattering at all the interfaces. We obtain results for the device conductance $G$, as a function of bias voltage, for all values of the angle $\phi$ between the magnetizations of the $F_1$ and $F_2$ layers and a range of realistic values for the material and geometrical parameters in the sample. We discuss, in the context of our results for $G$, the relative influence of all parameters on the spin valve properties. We study also the spin current and the corresponding spin transfer torque in $F_1/F_2/S$ structures.

Temperature Gradient Effects on Spin Torque in Double Barrier Magnetic Tunnel Junctions with a Non-magnetic Metal Spacer

Temperature gradient effects on spin torque (ST) are studied in MgO-based double-barrier magnetic tunnel junctions (DBMTJs) with a non-magnetic metal (NM) spacer. Using non-equilibrium Green’s function (NEGF) formalism, it is found that the thermal ST (TST) show oscillatory behavior with an increase of theNM spacer thickness. The results also show a magnitude enhancement of the TST in a DBMTJ compared with a single-barrier MTJ (SBMTJ). Such behavior is related to the existence of the quantum well states inside the NM spacer and resonant tunneling effect. Therefore, a faster magnetization switching is possible by TST in a DBMTJ without any bias voltage.

Enhancement of thermal spin transfer torque by double-barrier magnetic tunnel junctions with a nonmagnetic metal spacer

Enhancement of thermal spin transfer torque in a double-barrier magnetic tunnel junction with a nonmagnetic-metal spacer is proposed in this study. The results indicate that, given the same temperature difference, thermal spin transfer torque and charge current density for the proposed double barrier magnetic tunnel junction configuration can be approximately twice as much as that of the traditional single-barrier magnetic tunnel junctions. This enhancement can be attributed to the resonant tunneling mechanism in the double-barrier structure.

Co/Fe multilayers with ultra-low damping and large negative anisotropy as the free layer for spin torque oscillator

We have investigated the characteristic properties of Co/Fe multilayers sputtered on Ru underlayer as the field generation layer (FGL) of spin torque oscillator (STO) for microwave assisted magnetic recording. The Co/Fe multilayers exhibit large uniaxial negative anisotropy (up to ∼8.7 × 106 erg/cm3), ultra-low damping constant (∼0.008), and small in plane coercivity Hc (∼5 Oe) that are required for stable STO precession over a wide range of applied magnetic fields and injected spin currents. The importance of Ru underlayer to achieve the above parameters has been addressed. We further show through theoretical calculations that a frequency of 30+ GHz is realistic using Co/Fe multilayers as the field generation layer in a STO comprising a perpendicularly magnetized polarizer and a planar FGL (10-nm Co/Fe multilayers) separated by a metallic spacer.

Spin-Josephson effects in exchange coupled antiferromagnetic insulators

The energy of exchange coupled antiferromagnetic insulators (AFMIs) is a periodic function of the relative in-plane orientation of the N\'{e}el vector fields. We show that this leads to oscillations in the relative magnetization of exchange coupled AFMIs separated by a thin metallic barrier. These oscillations pump a spin current ($I_{S}$) through the metallic spacer that is proportional to the rate of change of the relative in-plane orientation of the N\'{e}el vector fields. By considering spin-transfer torque induced by a spin chemical potential ($V_{S}$) at one of the interfaces, we predict non-Ohmic $I_{S}$-$V_{S}$ characteristics of AFMI exchange coupled hetero-structures, which leads to a non-local voltage across a spin-orbit coupled metallic spacer.

Superconductivity and Dirac fermions in 112‐phase pnictides

AbstractThis article reviews the current research on the 112‐phase of pnictides. The 112‐phase has gained augmented attention due to the recent discovery of high‐temperature superconductivity in with a maximum critical temperature upon Sb substitution. The structural, magnetic, and electronic properties of bear some similarities with other superconducting pnictide phases, however, the different valence states of the pnictogen and the presence of a metallic spacer layer are unique features of the 112‐system. Low‐temperature superconductivity which coexists with antiferromagnetic order was observed in transition metal (Ni, Pd) deficient 112‐compounds like , , , . Besides superconductivity, the presence of naturally occurring anisotropic Dirac Fermionic states were observed in the layered 112‐compounds SrMnBi2, CaMnBi2, LaAgBi2 which are of significant interest for future nanoelectronics as an alternative to graphene. In these compounds, the linear energy dispersion resulted in a high magnetoresistance that stayed unsaturated even at the highest applied magnetic fields. Here, we describe various 112‐type materials systems combining experimental results and theoretical predictions to stimulate further research on this less well‐known member of the pnictide family.

Electromagnetic properties of a new microwave plasma torch with double resonance configuration

In order to obtain a stable plasma and improve the performance of the torch for atomic emission spectroscopy( AES), the structure of microwave plasma torch(MPT) was analyzed. The transmission and distribution characteristics of the electromagnetic field of the torch configuration with two or three concentric tubes, as well as the metal spacer between inner and intermediate tubes with different depths were simulated with electromagnetic simulation software and verified by experiments. The results indicate that the inner tube of MPT plays an important role in strengthening the electric field intensity at the opening end of the MPT and redistributing the electromagnetic field in the whole torch by forming a double resonance configuration, and contributes to enhancing the macroscopic stability and the self-sustainment of the plasma. The stability of the plasma is proved to be excellent when the metal spacer between the inner and intermediate tubes is located at a place 20—30 mm away from the top opening of the torch. A proper location of the spacer can also avoid the formation of a static filament plasma or a rotating plasma rooted from the outer wall of the inner tube. With the help of morphological analysis, the underlying reason why MPT possesses a great tolerance to wet aerosols and air introduction was clearly made, that is, the formation region of the plasma formed with MPT is apparently separated from the reaction zone of it.

A New Reactive Thermoplastic Spacer with Excellent Durable Energy Efficiency for Structural Glazing Façades

For the use in structural glazing (SSG) applications a new generation of warm edge system has been developed. This new technology is a spacer system based on polyisobutylene, especially designed for silicone sealed units, which replaces the conventional edge seal components: metal or plastic spacer, desiccant and primary sealant. In contrast to these components, this hot applied spacer system is an integrated polymer matrix incorporating the desiccant, which meets the high requirements regarding long term stability and in particular the demands for noble gas tightness of insulating glass units (IGUs) with silicone secondary sealant. In contrast to rigid spacer frames, this new spacer generation utilizes the whole inner gap size of the IGU to absorb movements caused by environmental stresses and allows full flexibility in shape of IGU. Excellent durability of the edge seal is insured by a chemical bond of the spacer matrix to glass and silicone secondary sealants. Due to the computer controlled application and the low permeability of the spacer the IGUs fulfil the requirements of the EN 1279-3 (gas tightness) even under standard mass production process conditions. This allows for an especially easy production even of triple IGUs, large formats and free shape designs with outstanding accuracy. The innovative reactive thermoplastic spacer is a new milestone in IGU technology with excellent durable energy efficiency for facades and contributes a significant step towards energy sustainability in building envelopes.

Wide-band polarization independent perfect metamaterial absorber based on concentric rings topology for solar cells application

Since the discovery of metamaterial absorber to the present days, several designs were proposed which display single-, dual-, and multiple-bands absorption responses in almost all regions of solar spectrum. However, little work has been done for wide-band metamaterial absorber in the visible frequency range. Hence, a novel wide-band metamaterial perfect absorber (MPA) based on concentric Circular Ring Resonator (CRR) topology is proposed for the application to improve the absorbance of solar photovoltaic cells for the visible frequency region. The proposed design consists of three basic components as resonators, ground metal, and dielectric spacer. The geometrical parametric study is conducted in order to investigate the flexibility of the proposed MPA structure. The design flexibility also analyzed by the polarization angle insensitivity character, in which the proposed design provides the perfect absorption for different angles of the incident electromagnetic wave as well as for TE and TM polarized waves.

Thermally driven spin torques in layered magnetic insulators

Thermally-driven spin-transfer torques have recently been reported in electrically insulating ferromagnet$|$normal-metal heterostructures. In this paper, we propose two physically distinct mechanisms for such torques. The first is a local effect: out-of-equilibrium, thermally-activated magnons in the ferromagnet, driven by a spin Seebeck effect, exert a torque on the magnetization via magnon-magnon scattering with coherent dynamics. The second is a nonlocal effect which requires an additional magnetic layer to provide the symmetry breaking necessary to realize a thermal torque. The simplest structure in which to induce a nonlocal thermal torque is a spin valve composed of two insulating magnets separated by a normal metal spacer; there, a thermal flux generates a pure spin current through the spin valve, which results in a torque when the magnetizations of the layers are misaligned.

Enhanced spin-torque in double tunnel junctions using a nonmagnetic-metal spacer

This study proposes an enhancement in the spin-transfer torque of a magnetic tunnel junction (MTJ) designed with double-barrier layer structure using a nonmagnetic metal spacer, as a replacement for the ferromagnetic material, which is traditionally used in these double-barrier stacks. Our calculation results show that the spin-transfer torque and charge current density of the proposed double-barrier MTJ can be as much as two orders of magnitude larger than the traditional double-barrier one. In other words, the proposed double-barrier MTJ has a spin-transfer torque that is three orders larger than that of the single-barrier stack. This improvement may be attributed to the quantum-well states that are formed in the nonmagnetic metal spacer and the resonant tunneling mechanism that exists throughout the system.

Trabecular metal spacers as standalone or with pedicle screw augmentation, in posterior lumbar interbody fusion: a prospective, randomized controlled trial.

This prospective randomized comparative trial compared radiological and clinical outcome of Trabecular Metal™ (TM) spacers in PLIF, used as standalone (SA) devices, to TM spacers in PLIF with pedicle screw fixation (PF), in patients with single-level degenerative disc disease (DDD). Patients (n = 80) with chronic low back pain and single-level degenerative disc were randomly assigned to the SA PLIF (n = 40) or PLIF with PF (n = 40). The primary radiological outcome was the evaluation of a long-term (±6 years; range 6.0-7.7 years) stable construct measured by dynamic X-rays. CT scan does not allow judging the bony bridging between vertebrae, because of Tantalum artefacts. The clinical evaluation (6 weeks, 6, 12 and 24 months) consisted of the Oswestry Disability Index (ODI) score, intensity of low back pain (Visual Analogue Scale) and quality of life (Short Form-36). At 6-year follow-up, X-rays showed a stable construct in 94 % of patients treated by SA TM-500 spacers and in 97 % of those with additional PF. Neither subsidence nor migration was observed in either the SA or the PF group. The average improvement in ODI scores at 24-month clinical follow-up was 14.4 and 13.8 for the SA and PF group, respectively. The VAS score showed an average improvement of 6.4 (SA) and 6.7 (PF), 2 years after implantation. No significant difference between groups was observed at all the evaluation points. In this study, TM spacers were found to provide a solid construct at more than 6-year follow-up after PLIF for DDD both with and without additional pedicle fixation. The clinical, but also radiological results were not significantly different between both cohorts. Future studies focusing on the differences of SA and PF at L4/5 level should be powered to study differences in post-surgery stability at the long term.

Current-perpendicular-to-the-plane magnetoresistance from large interfacial spin-dependent scattering between Co50Fe50 magnetic layer and In-Zn-O conductive oxide spacer layer

We have investigated electrically conductive indium-zinc-oxide (IZO) deposited by magnetron sputtering as spacer layer for current-perpendicular-to-the-plane giant magnetoresistance sensor devices. Spin-valves with a Co50Fe50/IZO/Co50Fe50 trilayer showed resistance-area product (RA) ranging from 110 to 250 mΩ μm2, significantly larger than all-metal structures with Ag or Cu spacers (∼40 mΩ μm2). Magnetoresistance ratios (ΔR/R) of 2.5% to 5.5% depending on the IZO spacer thickness (1.5–6.0 nm), corresponding to ΔRA values from 3 to 13 mΩ μm2, were obtained. The values of ΔRA with the IZO spacers and Co50Fe50 magnetic layers were significantly larger than those with conventional metal spacers and Co50Fe50 magnetic layers (∼1–2 mΩ μm2). The dependence of ΔRA on the magnetic layer thickness suggests that the larger ΔRA obtained with IZO spacer is due to a large interfacial spin-dependent scattering caused by the large specific resistance at the Co50Fe50/IZO interface. From structural characterization by TEM and the observed dependence of the RA dispersion on device size, the electric current flowing through the IZO spacer is thought to be laterally uniform, similar to normal metal spacers.

Magnetoresistance effects and spin-valve like behavior of an arrangement of two MnAs nanoclusters

We report on magnetotransport measurements on a MnAs nanocluster arrangement consisting of two elongated single-domain clusters connected by a metal spacer. The arrangement was grown on GaAs(111)B-substrates by selective-area metal organic vapor phase epitaxy. Its structural properties were investigated using scanning-electron microscopy and atomic-force microscopy, while its magnetic domain structure was analyzed by magnetic-force microscopy. The magnetoresistance of the arrangement was investigated at 120 K for two measurement geometries with the magnetic field oriented in the sample plane. For both geometries, discrete jumps of the magnetoresistance of the MnAs nanocluster arrangement were observed. These jumps can be explained by magnetic-field induced switching of the relative orientation of the magnetizations of the two clusters which affects the spin-dependent scattering in the interface region between the clusters. For a magnetic field orientation parallel to the nanoclusters' elongation direction a spin-valve like behavior was observed, showing that ferromagnetic nanoclusters may be suitable building blocks for planar magnetoelectronic devices.

Enhanced Signal-to-Noise Ratio in Current-Perpendicular-to-Plane Giant-Magnetoresistance Sensors by Suppression of Spin-Torque Effects

We report a ~4 dB enhancement in signal-to-noise ratio of current-perpendicular-to-the-plane giant magnetoresistance sensors with Heusler alloy magnetic layers due to insertion of an In-Zn-O electrically conductive oxide into an Ag-based metallic spacer layer. Signal and noise device characterization at various magnetic bias conditions shows that this enhancement arises from an increase in magnetoresistance signal at higher bias currents without spin-torque-induced magnetic instability. The best obtained signal-to-noise, over 30 dB for 1 GHz bandwidth, promises application of these sensors in magnetic recording heads for hard-disk drives at recording densities above 1 Tbit/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Spin-dependent transport in antiferromagnetic tunnel junctions

We investigate the behaviour of spin transfer torque (STT) and tunnelling magnetoresistance (TMR) in epitaxial antiferromagnetic-based tunnel junctions using tight binding calculations in the framework of the Keldysh formalism. We find that the STT out-of-plane component exhibits a staggered spatial distribution similar to its in-plane component. This behaviour is specific to the use of a tunnel barrier and significantly differs from the out-of-plane torques reported in previous works using a metallic spacer. Additionally, we show that unlike conventional ferromagnetic-based tunnel junctions, the TMR can increase with applied bias and reach values comparable to typical magnetoresistances found for usual spin valves.