Spin injection and accumulation in mesoscopic metal device structures

The spin injection and accumulation in metallic lateral spin valves with transparent interfaces are studied using dc injection current. Unlike ac-based techniques, this allows the investigation of the effects of the direction and magnitude of the injected current. We find that the spin accumulation is reversed by changing the direction of the injected current, whereas its magnitude does not change. The injection mechanism for both current directions is thus perfectly symmetric, leading to the same spin injection efficiency for both spin types. This result is accounted for by a spin-dependent diffusion model. Joule heating increases considerably the local temperature in the spin valves when high-current densities are injected ($\ensuremath{\sim}80--105\text{ }\text{K}$ for $1--2\ifmmode\times\else\texttimes\fi{}{10}^{7}\text{ }\text{A}\text{ }{\text{cm}}^{\ensuremath{-}2}$), strongly affecting the spin accumulation.

We investigate the influence of Au capping layer on the spin accumulation in a lateral spin valve consisting of Permalloy and Cu wires. The nonlocal spin valve measurements show that the Au capping significantly suppresses the spin accumulation in the Cu wire, although it improves the electrical conductivity. This is understood as a result of the small spin-flip resistance of Au whereby absorbed spins are successively flipped.

Efficient generation and detection of the spin current is a crucial issue for the application of spintronic devices. In addition, integrating spintronic circuit with conventional semiconductor devices is another important milestone for the practical application of the spin devices. Recently, the interplay between the heat and spin has attracted great attention because the temperature gradient is found to generate the spin current [1]. Since the heat can generate and propagate without electricity, this novel approach using the heat may open a new avenue for simplifying integration of spin devices. The precise estimation of the spin-dependent Seebeck coefficient (S s ), which is one of the important factors for the efficient generation of the thermal spin current, is indispensable to develop and optimize the spin device structure using the heat. However, it is still a hard nut to crack for the conventional ferromagnet because of its small magnitude and tiny related spin signal. Moreover, the related spin signal is smeared out by the spurious signals induced by classical thermoelectric effects especially at room temperature. Recently, we have shown that both the electrically and thermally driven spin injection efficiencies have been dramatically enhanced by the CoFeAl electrodes because of the excellent property for the thermal spin injection and electrical spin detection of CoFeAl [2]. In this presentation, by using the excellent CoFeAl, we develop the precise evaluation method for the thermal spin injection properties of Permalloy (Py)/Cu hybrid in lateral spin valve structure.

We have investigated the effect of annealing on the nonlocal spin valve signal in lateral spin valves with permalloy/MgO/Ag junctions. The results show that annealing up to 400 °C pushes up the spin polarization of the MgO interface to 38%, resulting in an increase in the nonlocal spin valve signal of up to 77.2 mΩ. Further increase in the annealing temperature up to 500 °C causes a decrease in the spin valve signal of 48.0 mΩ. However, the high spin polarization of 55% could be advantageous for the enhancement of the spin accumulation in lateral spin valves.

Organic–inorganic hybrid perovskites (OIHPs) have been explosively investigated mainly due to their potential applications in optoelectronics. Despite the electronic charge transport, phenomena regarding the spin‐polarized electronic transport in OIHPs‐based spintronic devices and the role of ferromagnet/OIHP spinterfaces remain unclear. In this work, the spin injection, accumulation, transport, and detection at room temperature for a vertical perovskite spin valve (PeSV) consisting of Ni/CH3NH3PbI3−xClx/Ni is reported. An in‐plane anisotropic magnetoresistance (AMR) and a PeSV related magnetoresistance (MR) show remarkable magnetic switching behaviors due to the formation of Ni/CH3NH3PbI3−xClx spinterfaces, and the ferromagnetic coupling between two spin quantization axes of the spinterfaces. With assists of capacitance–frequency (C − − f) measurements under magnetic fields, the spin accumulation that occurs at the Ni/CH3NH3PbI3−xClx interface can be detected at the spin parallel (↑↑) and antiparallel (↑↓) configurations. Owing to a strong orbital interaction at the Ni/CH3NH3PbI3−xClx hybrid interface, the spin‐sensitive electron paramagnetic spectroscopy (EPR) reveals significant change of the magnetic moment (µ). It is believed that the solution processed CH3NH3PbI3−xClx and the formation of the Ni/CH3NH3PbI3−xClx spinterface may hold an exceptionally important role for future hybrid optospintronic applications.

The nonlocal spin valve configuration consists of two ferromagnetic and nonmagnetic channels, which is an effective configuration for determining spin injection and accumulation. Here, we report that a reversed nonlocal spin signal was detected by changing the voltage probe configurations in graphene (Py/MgO/graphene/MgO/Py) lateral spin valves. The abnormal reversed spin-dependent nonlocal voltage is attributed to the nonuniform pinhole at the interface of the low-resistance tunnel barrier, which makes the charge current flow through the detection electrode and return to the graphene channel. We demonstrate that the channel-width induced spin-polarized current inhomogeneity significantly contributes to nonlocal resistance. A detailed description and simulated results of the tunnel junctions provide evidence for the reversal of the nonlocal voltage sign induced by the low-resistance tunnel barriers. Our work sheds light on the understanding of the spatial distribution of the spin current and the effect of the tunnel barrier, which are essential for the development of spintronic devices.

We investigated Co/Cu lateral spin valves by means of high-resolution transmission soft x-ray microscopy with magnetic contrast that utilizes x-ray magnetic circular dichroism (XMCD). No magnetic XMCD contrast was observed at the Cu L$_3$ absorption edge, which should directly image the spin accumulation in Cu. Although electrical transport measurements in a non-local geometry clearly detected the spin accumulation in Cu, which remained unchanged during illumination with circular polarized x-rays at the Co and Cu L$_3$ absorption edges.

25pPSA-32 The Effect of Ferromagnetic Layer Thickness on Spin Accumulation / Injection Efficiency in Lateral Spin Valves

We study spin accumulation in dual-injection lateral spin valves (DLSVs) with Ni80Fe20(/MgO)/Ag or Co50Fe50/MgO/Ag junctions. In Ohmic NiFe/Ag junctions, there is negligible enhancement in the spin accumulation for the dual scheme compared with the conventional single scheme. In contrast, large spin valve signals of 233 and 480 m Ω are observed for DLSVs with NiFe/MgO/Ag and CoFe/MgO/Ag junctions, respectively. The experimental results are analyzed with a one-dimensional spin diffusion model, taking into account the junctions and their structures. The efficient generation of a pure spin current IS/IC up to 0.55 is realized.

Electrical creation of spin accumulation in [formula omitted]-type germanium

We report on features in charge transport and spin injection in an oxide semiconductor, Nb-doped SrTiO3. This is demonstrated using electrically tunable spin injection contacts which exploit the large electric field at the interface and its interplay with the relative permittivity of the semiconductor. We realize spin accumulation in Nb-doped SrTiO3 which displays a unique dependence of the spin lifetime with bias polarity. These findings suggest a strong influence of the interface electric field on the charge transport as well as on spin accumulation unlike in conventional semiconductors and opens up promising avenues in oxide spintronics.

We reexamined curve-fitting analysis for spin-accumulation signals observed in Si-channel spin-accumulation devices, employing widely-used Lorentz functions and a new formula developed from the spin diffusion equation. A Si-channel spin-accumulation device with a high quality ferromagnetic spin injector was fabricated, and its observed spin-accumulation signals were verified. Experimentally obtained Hanle-effect signals for spin accumulation were not able to be fitted by a single Lorentz function and were reproduced by the newly developed formula. Our developed formula can represent spin-accumulation signals and thus analyze Hanle-effect signals.

Using fully self consistent methods, we study spin transport in realistic,\nfabricable experimental spin valve systems consisting of two magnetic layers, a\nsuperconducting layer, and a spacer normal layer between the ferromagnets. Our\nmethods ensure that the proper relations between spin current gradients and\nspin transfer torques are satisfied. We present results as a function of\ngeometrical parameters, interfacial barrier values, misalignment angle between\nthe ferromagnets, and bias voltage. Our main results are for the spin current\nand spin accumulation as functions of position within the spin valve structure.\nWe see precession of the spin current about the exchange fields within the\nferromagnets, and penetration of the spin current into the superconductor for\nbiases greater than the critical bias, defined in the text. The spin\naccumulation exhibits oscillating behavior in the normal metal, with a strong\ndependence on the physical parameters both as to the structure and formation of\nthe peaks. We also study the bias dependence of the spatially averaged spin\ntransfer torque and spin accumulation. We examine the critical bias effect of\nthese quantities, and their dependence on the physical parameters. Our results\nare predictive of the outcome of future experiments, as they take into account\nimperfect interfaces and a realistic geometry.\n

Spin-torque critical current of graphene-based lateral spin valves

Introduction Historical Overview: From Electron Transport in Magnetic Materials to Spintronics Albert Fert Spin Transport and Magnetism in Magnetic Metallic Multilayers Basics of Nano-Thin Film Magnetism Bretislav Heinrich Micromagnetism as a Prototype for Complexity. Anthony S. Arrott Giant Magnetoresistance: Experiment Jack Bass Giant Magnetoresistance: Theory Evgeny Y. Tsymbal, D.G. Pettifor, and Sadamichi Maekawa Spin Injection, Accumulation, and Relaxation in Metals Mark Johnson Spin Torque Effects: Experiment Maxim Tsoi Spin Torque in Magnetic Systems: Theory A. Manchon and Shufeng Zhang Hot Carrier Spin Transport Ron Jansen Spin Transport and Magnetism in Magnetic Tunnel Junctions Tunneling Magnetoresistance: Experiment (Non-MgO) Patrick R. LeClair and Jagadeesh S. Moodera Tunnel Magnetoresistance in MgO-Based Magnetic Tunnel JunctionsExperiment Shinji Yuasa Tunneling Magnetoresistance: Theory Kirill D. Belashchenko and Evgeny Y. Tsymbal Spin-Filter Tunneling Tiffany S. Santos and Jagadeesh S. Moodera Spin Torques in Magnetic Tunnel Junctions. Yoshishige Suzuki and Hitoshi Kubota Multiferroic Tunnel Junctions Manuel Bibes and Agnes Barthelemy Spin Transport and Magnetism in Semiconductors Spin Relaxation and Spin Dynamics in Semiconductors Jaroslav Fabian and M.W. Wu Electrical Spin Injection and Transport in Semiconductors Berend T. Jonker Spin-Polarized Ballistic Hot-Electron Injection and Detection in Hybrid Metal Semiconductor Devices Ian Appelbaum Magnetic Semiconductors: IIIV Semiconductors Carsten Timm Magnetism of Dilute Oxides J.M.D. Coey Tunneling Magnetoresistance and Spin Transfer with (Ga,Mn)As H. Jaffres and Jean Marie George Spin Transport in Organic Semiconductors Valentin Dediu, Luis E. Hueso, and Ilaria Bergenti Spin Transport in Ferromagnet/IIIV Semiconductor Heterostructures Paul A. Crowell and Scott A. Crooker Spin Polarization by Current Sergey D. Ganichev, Maxim Trushin, and John Schliemann Anomalous and Spin-Injection Hall Effects Jairo Sinova, Jorg Wunderlich, and Tomas Jungwirth Spin Transport and Magnetism at the Nanoscale Spin-Polarized Scanning Tunneling Microscopy Matthias Bode Point Contact Andreev Ref lection Spectroscopy Boris E. Nadgorny Ballistic Spin Transport. Bernard Doudin and N.T. Kemp Graphene Spintronics Csaba Jozsa and Bart J. van Wees Magnetism and Transport in Diluted Magnetic Semiconductor Quantum Dots Joaquin Fernandez Rossier and R. Aguado Spin Transport in Hybrid Nanostructures Saburo Takahashi and Sadamichi Maekawa Nonlocal Spin Valves in Metallic Nanostructures Yoshichika Otani and Takashi Kimura Molecular Spintronics Stefano Sanvito Applications Magnetoresistive Sensors Based on Magnetic Tunneling Junctions Gang Xiao Magnetoresistive Random Access Memory. Johan Akerman Emerging Spintronics Memories. Stuart Parkin, Masamitsu Hayashi, Luc Thomas, Xin Jiang, Rai Moriya, and William Gallagher GMR Spin-Valve Biosensors Drew A. Hall, Richard S. Gaster, and Shan X. Wang Semiconductor Spin-Lasers Rafal Oszwaldowski, Christian Gothgen, Jeongsu Lee, and Igor Zutic Spin Logic Devices Hanan Dery