Spin Transmission Research Articles

Thermal Spin Injection and Inverse Edelstein Effect of the Two-Dimensional Electron Gas at EuO-KTaO3 Interfaces.

With the help of the two-dimensional electron gas (2DEG) at the LaAlO3-SrTiO3 interface, spin and charge currents can be interconverted. However, the conversion efficiency has been strongly depressed by LaAlO3, which blocks spin transmission. It is therefore highly desired to explore 2DEGs sandwiched between ferromagnetic insulators that are transparent for magnons. By constructing epitaxial heterostructure with ferromagnetic EuO, which is conducting for spin current but insulating for electric current, and KTaO3, we successfully obtained the 2DEGs, which can receive thermally injected spin current directly from EuO and convert the spin current to charge current via inverse Edelstein effect of the interface. Strong dependence of the spin Seebeck coefficient on the layer thickness of EuO is further observed and the propagation length for non-equilibrium magnons in EuO has been determined. The present work demonstrates the great potential of the 2DEGs formed by ferromagnetic oxides for spin caloritronics.

Spin-dependent electron transmission model for chiral molecules in mesoscopic devices

Various device-based experiments have indicated that electron transfer in certain chiral molecules may be spin-dependent, a phenomenon known as the Chiral Induced Spin Selectivity (CISS) effect. However, due to the complexity of these devices and a lack of theoretical understanding, it is not always clear to what extent the chiral character of the molecules actually contributes to the magnetic-field-dependent signals in these experiments. To address this issue, we report here an electron transmission model that evaluates the role of the CISS effect in two-terminal and multi-terminal linear-regime electron transport experiments. Our model reveals that for the CISS effect, the chirality-dependent spin transmission is accompanied by a spin-flip electron reflection process. Furthermore, we show that more than two terminals are required in order to probe the CISS effect in the linear regime. In addition, we propose two types of multi-terminal nonlocal transport measurements that can distinguish the CISS effect from other magnetic-field-dependent signals. Our model provides an effective tool to review and design CISS-related transport experiments, and to enlighten the mechanism of the CISS effect itself.

Self-assembled chitosan-zirconium phosphate nanostructures for adsorption of chromium and degradation of dyes

Nano zirconium phosphate (ZrP) was synthesized hydrothermally using an autoclave and was further self-assembled with chitosan to form bionanocomposite CZrP. The structural characteristics of ZrP and CZrP were investigated by Fourier Transform Infrared (FT-IR), X-Ray Diffraction (XRD), Energy Dispersive X-Ray (EDX), X-Ray Photelectron Spectroscopy (XPS), Electron Spin Resonance (ESR), Raman spectroscopy and Transmission Electron Microscopy (TEM) techniques. During the course of characterization, unique surface defects and superoxide anions stabilized on ZrP and CZrP were observed for the first time. The potential of the synthesized nanocomposite was investigated for adsorption of Cr(VI), a copper phthalocynanine dye- Reactive blue-21 (RB-21), azo dye- Reactive Red 141 (RR-141), a xanthene dye-Rhodamine-6G as well as binary mixtures of the dyes. Further the potential of CZRP as catalyst for the hydrogen peroxide degradation of dyes was investigated. The dyes were degraded in ˜10 min and CZrP exhibited stability during multiple runs of degradation of the dyes.

Spin-polarized transport in a quasi-1D wire with Rashba dots

A numerical study on spin-polarized transport properties in a quasi-one-dimensional wire with Rashba quantum dots is presented. The ballistic spin transmission probability and spin density profiles are obtained using the quantum transmitting boundary method. The Fano-Rashba effect on the spin transmission is analyzed as a function of the Rashba spin-orbit coupling strength for single dot and double dot systems. The spin density profiles show the localized states that contribute to the backscattering and spin-flip processes in the Rashba dots. The results enlighten us on the Fano-Rashba effect caused by local Rashba spin-orbit coupling and provide concrete ideas for modeling a system with spin-polarized transport for future applications.

A comprehensive compact model for the design of all-spin-logic based circuits

By relying on pure spin transmission, low-frequency charge-spin conversion, and neuron-like mechanism, All Spin Logic (ASL) has the potential to outperform CMOS technology in logic design and especially in neuromorphic computing, with improved fabrication process and material technology in the future. As ASL technology is gaining in maturity, compact models are needed to fill the gap between application requirements and circuit fabrication. However, defining such a model is a tedious task due to the numerous physical parameters to consider and the need for flexibility to explore design tradeoffs. In this paper, we propose an accurate, generic, scalable, and easy-to-use compact model for ASL devices. The model has been validated by comparing with experimental results, which allows investigating the impact of device characteristics such as channel length and channel width on the propagation delay. The model has been implemented in Cadence using in Verilog-A, which allows running transient simulations and comparing the implementations of 4-bit adder and multiplier circuits regarding the area, energy and delay metrics.

Characteristics of electronic and spin-independent linear conductance in conjugated aromatic polymer based molecular device

Using the non-equilibrium Green's function formalism combined with density-functional theory, we performed a theoretical research to study the electronic and spin-dependent electron transport of a molecular device constructed from a 2-TBQP, 1D-conjugated aromatic polymer(CAP) and 1D-CAP with dihedral angle being 180° sandwiched between two semiinfinite zigzag-edged graphene nanoribbon (zGNR) electrodes. Results show that the proposed 1D-CAP model exhibits an interesting linear conductive behavior, which is much larger than other two models. The intriguing linear current-voltage characteristic can be explained by the well delocalized spatial distribution of frontier orbitals and the separation of electron transmission pathways. Moreover, it's also shown that the spin-charge transport can be modulated by performing the magnetic configuration in zGNR electrodes. The proposed models show many spin related behaviors, such as single spin conductance, dual spin filter and spin-independent linear conductance. The corresponding mechanisms of the above mentioned spin-resolved results can be analyzed and discussed in terms of the spin transmission spectra and the separation of isosurfaces of spin density of these systems.

Input Interface for all Spin Logic

We propose an input interface circuit that can provide input signals for the emerging all spin logic (ASL) devices. It consists of metal wires that are used for the transmission of electrical signals and magnetic tunnel junction that are used to transform electrical signals into input signals of ASL devices. The operation of input interface is validated by using a coupled spin-transport/magneto-dynamics model. A salient advantage of the proposed input interface is its ability to shorten the length of spin channel for spin transmission and avoid the complex fan-out structure when multiple identical input signals are needed. This input interface is especially useful for the design of large scale ASL circuits, in which many identical units are needed.

Controllable spin-dependent transport in silicene superlattice

Based on the transfer-matrix method, we theoretically investigate the spin-dependent transport properties in magnetic silicene superlattice in the presence of extrinsic Rashba spin–orbit interaction (RSOI). It is found that the spin transmission probability and spin conductivities can be efficiently controlled by the number of magnetic barriers. As the number of magnetic barriers increases, spin conductivities strongly decrease, and reduce to zero in the large on-site potential difference between A and B sublattices (Δz) region. The results indicate that a magnetic silicene superlattice exhibits a remarkable wavevector-dependent spin filtering effect. Also, the magnetoresistance (MR) ratio exhibits an oscillatory behavior with the Fermi energy. The MR ratio can be tuned by the Fermi energy, number of magnetic barriers and extrinsic RSOI. Specifically, in the presence of magnetic field the spin polarization can be observed, and increases by increasing the magnetic field.

Tunable long-distance spin transport in a crystalline antiferromagnetic iron oxide.

Spintronics uses spins, the intrinsic angular momentum of electrons, as an alternative for the electron charge. Its long-term goal is to develop beyond-Moore, low-dissipation technology devices, recently demonstrating long-distance transport of spin signals across ferromagnetic insulators1. Antiferromagnetically ordered materials, the most common class of magnetic materials, have several crucial advantages over ferromagnetic systems2. Antiferromagnets exhibit no net magnetic moment, rendering them stable and impervious to external fields. Additionally, they can be operated at THz frequencies3. Although their properties bode well for spin transport4–7, previous indirect observations indicate that spin transmission through antiferromagnets is limited to only a few nanometers8–10. Here we demonstrate the long-distance propagation of spin-currents through single-crystalline hematite (α-Fe2O3)11, the most common antiferromagnetic iron oxide, exploiting the spin Hall effect for spin injection. We control the spin-current flow by the interfacial spin-bias, tuning the antiferromagnetic resonance frequency with an external magnetic field12. This simple antiferromagnetic insulator conveys spin information parallel to the Néel order over distances exceeding tens of micrometers. This newly-discovered mechanism transports spin as efficiently as the net magnetic moments in the best-suited complex ferromagnets1. Our results pave the way to ultra-fast, low-power antiferromagnet-insulator-based spin-logic devices6,13 that operate, without magnetic fields, at room temperature.

Engineering magnetic heterostructures to obtain large spin Hall efficiency for spin-orbit torque devices

By sandwiching a CoFeB ferromagnetic layer between Ta and Pt heavy metals with an opposite spin Hall angle, spin currents of the same polarity are transmitted from both interfaces of the Ta/CoFeB/Pt trilayer to the CoFeB layer simultaneously. Here, we investigated the spin-orbit torque, magnetization dynamics, and interface spin transmission efficiency of the trilayer heterostructure by spin-torque ferromagnetic resonance. A large effective spin Hall angle, substantially larger than both Ta and Pt, was obtained in the Ta/CoFeB/Pt stack. The thickness-dependence study showed that with the reducing of CoFeB thickness, Gilbert damping enhances by spin pumping and spin Hall angle increases by the spin Hall effect and the Rashba effect. Furthermore, the spin transparency derived from effective spin mixing conductance was 0.63 ± 0.07 and 0.48 ± 0.02 at the CoFeB/Pt and Ta/CoFeB interfaces, respectively. Hence, the spin Hall angle could be further enhanced by improving the spin transmission efficiency at the interface. Our method of increasing spin-orbit torque through stack engineering would have potential applications in domain wall racetrack memory, logic gates, and magnetic tunnel junctions.

Spin-orbit torque and spin pumping in YIG/Pt with interfacial insertion layers

We experimentally investigate spin-orbit torque and spin pumping in Y3Fe5O12 (YIG)/Pt bilayers with ultrathin insertion layers at the interface. An insertion layer of Cu suppresses both spin-orbit torque and spin pumping, whereas an insertion layer of Ni80Fe20 (permalloy, Py) enhances them in a quantitatively consistent manner with the reciprocity of the two spin transmission processes. However, we observe a large enhancement of Gilbert damping with the insertion of Py that cannot be accounted for solely by spin pumping, suggesting significant spin-memory loss due to the interfacial magnetic layer. Our findings indicate that the magnetization at the YIG-metal interface strongly influences the transmission and depolarization of pure spin current.

Spin-orbit torques associated with ferrimagnetic order in Pt/GdFeCo/MgO layers

We investigate spin orbit torque (SOT) efficiencies and magnetic properties of Pt/GdFeCo/MgO multilayers by varying the thicknesses of GdFeCo and MgO layers. Our studies indicate that the ferrimagnetism in the GdFeCo alloy is considerably influenced by both thicknesses due to the diffusion of Gd atoms toward the MgO layer. Comparing to conventional Pt/ferromagnet/MgO structures, the Pt/GdFeCo/MgO exhibits a lower efficiency of SOTs associated with ferrimagnetic order and a similar magnitude of magnetic damping. The previous models that have been developed for rigid ferromagnets are inappropriate to analyze our experimental data, leading to an unphysical consequence of spin transmission larger than unity. Our results imply that the heavy-metal/ferrimagnet system is quite different from heavy-metal/ferromagnet systems in terms of magnetic dynamical modes, spin angular momentum transfer, and relaxation processes.

Study on spin filtering and switching action in a double-triangular network chain

Spin transport properties of a double-triangular quantum network with local magnetic moment on backbones and magnetic flux penetrating the network plane are studied. Numerical simulation results show that such a quantum network will be a good candidate for spin filter and spin switch. Local dispersion and density of states are considered in the framework of tight-binding approximation. Transmission coefficients are calculated by the method of transfer matrix. Spin transmission is regulated by substrate magnetic moment and magnetic flux piercing those triangles. Experimental realization of such theoretical research will be conducive to designing of new spintronic devices.

Spin Polarization Efficiency in a Diluted Magnetic Nano-Semiconductor Quantum Well System

Diluted magnetic semiconductors (DMS) in which a fraction of non-magnetic cation is replaced by any transition metal ions. They are considered to have wide potential applications for magneto-optic devices. In the present work, the magnetic field is applied externally in a diluted magnetic semiconductor quantum well to investigate spin transmission properties. The material taken for the study is ZnMnSe/ZnSe quantum well. Rashba spin orbit interaction on the resonant spin polarized transport in this heterostructure quantum well is studied. The plane wave function of the electron is applied to obtain the energy eigen values. The mean field approximation is employed to investigate the interaction of the host electron and the localized magnetic impurities. The large polarization occurs in DMS due to the exchange interaction between the local magnetic impurity and the electrons and this effect lifts the degeneracy of spin-up and spin down electron states. The obtained results, on spindependent tunneling, may be used in the spin based devices especially in the spin field effect transistors.

Humic-based bionanocomposites containing stable paramagnetic gold nanoparticles for prospective use in pharmaceuticals

ABSTRACTStructural peculiarities and supramolecular organization of medicinally promising nanocomposites, synthesized from humic substances, which essentially differ depending on decomposition degree, have been studied using electron spin resonance, transmission electron, and confocal laser scanning microscopy techniques and some other modern physical–chemical methods. It is shown that stable zero-valent gold nanoparticle of about 10–17 nm in size are formed in a natural macromolecular matrix. The nanocomposites obtained turn out to be stable in aggregative state for a long time and preserve their properties that are extremely important for prospective medicinal substances.

The effects of Rashba spin-orbit coupling on spin-polarized transport in hexagonal graphene nano-rings and flakes

Quantum transport properties and spin polarization in hexagonal graphene nanostructures with zigzag edges and different sizes were investigated in the presence of Rashba spin-orbit interaction (RSOI). The nanostructure was considered as a channel to which two semi-infinite armchair graphene nanoribbons were coupled as input and output leads. Spin transmission and spin polarization in x, y, and z directions were calculated through applying Landauer-Buttiker formalism with tight binding model and the Green's function to the system. In these quantum structures it is shown that changing the size of system, induce and control the spin polarized currents. In short, these graphene systems are typical candidates for electrical spintronic devices as spin filtering.

Room-Temperature Giant Charge-to-Spin Conversion at the SrTiO3-LaAlO3 Oxide Interface.

The two-dimensional electron gas (2DEG) formed at the interface between SrTiO3 (STO) and LaAlO3 (LAO) insulating layer is supposed to possess strong Rashba spin-orbit coupling. To date, the inverse Edelstein effect (i.e., spin-to-charge conversion) in the 2DEG layer is reported. However, the direct effect of charge-to-spin conversion, an essential ingredient for spintronic devices in a current-induced spin-orbit torque scheme, has not been demonstrated yet. Here we show, for the first time, a highly efficient spin generation with the efficiency of ∼6.3 in the STO/LAO/CoFeB structure at room temperature by using spin torque ferromagnetic resonance. In addition, we suggest that the spin transmission through the LAO layer at a high temperature range is attributed to the inelastic tunneling via localized states in the LAO band gap. Our findings may lead to potential applications in the oxide insulator based spintronic devices.

Spin Hall magnetoresistance in heavy-metal/metallic-ferromagnet multilayer structures

We investigate spin Hall magnetoresistance (SMR) in heavy-metal (HM)/metallic-ferromagnet (FM) multilayers as a function of the FM thickness. We observe that the SMR is considerably modified when the FM layer is thinner than \ensuremath{\sim}1.5 nm, which is a critical thickness of a FM for the absorption or reflection of spin current generated from the spin Hall effect in a HM. Moreover, the FM thickness dependence of the SMR in HM/FM/HM trilayer structures relies on the relative signs of the spin Hall angle in HMs, indicating that there is non-negligible interaction between the accumulated spins at each HM/FM interface. We propose an analytical model of the SMR in a HM/FM/HM trilayer by incorporating the spin transmission through the HM/FM interfaces and the resultant interaction in the FM layer, which can explain the variation of the SMR with the relative signs of the spin Hall angle in HMs.

Reduction of in-plane field required for spin-orbit torque magnetization reversal by insertion of Au spacer in Pt/Au/Co/Ni/Co/Ta

Spin-orbit torques and current-induced switching are studied in perpendicularly magnetized Pt/Au/(Co/Ni/Co) films as a function of Au insertion layer thickness tAu. By simultaneously varying the ferromagnet layer thickness, a parametric series of samples with nearly constant anisotropy were prepared. On this series, spin orbit torques were characterized by harmonic voltage and hysteresis loop shift measurements, and current-induced switching was examined as a function of the in-plane bias field. Little variation is seen for tAu < 0.5 nm, whereas for tAu > 0.5 nm, a series of well-correlated effects appear. Both the loop shift efficiency and the Slonczewski-like spin-orbit torque effective field double, while the in-plane field required to saturate the loop shift efficiency decreases by a factor of ∼10. Correspondingly, the current and in-plane field required for spin-orbit torque switching are reduced by about 90%. These results suggest that a thin Au insertion layer reduces the Dzyaloshinskii-Moriya interaction strength and improves spin transmission at the spin Hall metal/ferromagnet interface, substantially reducing the in-plane field and currents for spin orbit torque switching.

Spin wave propagation detected over [formula omitted] in half-metallic Heusler alloy Co2MnSi

The field of magnon spintronics offers a charge current free way of information transportation by using spin waves (SWs). Compared to forward volume spin waves for example, Damon-Eshbach (DE) SWs need a relatively weak external magnetic field which is suitable for small spintronic devices. In this work we study DE SWs in Co2MnSi, a half-metallic Heusler alloy with significant potential for magnonics. Thin films have been produced by pulsed laser deposition. Integrated coplanar waveguide (CPW) antennas with different distances between emitter and detection antenna have been prepared on a Co2MnSi film. We used a vector network analyzer to measure spin wave reflection and transmission. We observe spin wave propagation up to 100μm, a new record for half-metallic Heusler thin films.