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## Voltage-driven spintronic logic gates in graphene nanoribbons

Zhang, WenXing
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
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27.2%
Electronic devices lose efficacy due to quantum effect when the line-width of gate decreases to sub-10 nm. Spintronics overcome this bottleneck and logic gates are building blocks of integrated circuits. Thus, it is essential to control electronic transport of opposite spins for designing a spintronic logic gate, and spin-selective semiconductors are natural candidates such as zigzag graphene nanoribbons (ZGNR) whose edges are ferromagnetically ordered and antiferromagnetically coupled with each other. Moreover, it is necessary to sandwich ZGNR between two ferromagnetic electrodes for making a spintronic logic gate and also necessary to apply magnetic field to change the spin orientation for modulating the spin transport. By first principle calculations, we propose a method to manipulate the spin transport in graphene nanoribbons with electric field only, instead of magnetic field. We find that metal gates with specific bias nearby edges of ZGNR build up an in-plane inhomogeneous electric field which modulates the spin transport by localizing the spin density in device. The specific manipulation of spin transport we have proposed doesn't need spin-charge conversion for output and suggests a possible base for designing spintronic integrated circuit in atomic scale.

## Probing the electronic and spintronic properties of buried interfaces by extremely low energy photoemission spectroscopy

Fetzer, Roman; Stadtmüller, Benjamin; Ohdaira, Yusuke; Naganuma, Hiroshi; Oogane, Mikihiko; Ando, Yasuo; Taira, Tomoyuki; Uemura, Tetsuya; Yamamoto, Masafumi; Aeschlimann, Martin; Cinchetti, Mirko
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.04%
Ultraviolet photoemission spectroscopy (UPS) is a powerful tool to study the electronic spin and symmetry features at both surfaces and interfaces to ultrathin top layers. However, the very low mean free path of the photoelectrons usually prevents a direct access to the properties of buried interfaces. The latter are of particular interest since they crucially influence the performance of spintronic devices like magnetic tunnel junctions (MTJs). Here, we introduce spin-resolved extremely low energy photoemission spectroscopy (ELEPS) to provide a powerful way for overcoming this limitation. We apply ELEPS to the interface formed between the half-metallic Heusler compound Co2MnSi and the insulator MgO, prepared as in state-of-the-art Co2MnSi/MgO-based MTJs. The high accordance between the spintronic fingerprint of the free Co2MnSi surface and the Co2MnSi/MgO interface buried below up to 4 nm MgO provides clear evidence for the high interface sensitivity of ELEPS to buried interfaces. Although the absolute values of the interface spin polarization are well below 100%, the now accessible spin- and symmetry-resolved wave functions are in line with the predicted existence of non-collinear spin moments at the Co2MnSi/MgO interface, one of the mechanisms evoked to explain the controversially discussed performance loss of Heusler-based MTJs at room temperature.

## Entanglement of Electron Spin and Orbital States in Spintronic Quantum Transport

Nikolic, Branislav K.
Tipo: Artigo de Revista Científica
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27.04%
An electron within a mesoscopic (quantum-coherent) spintronic structure is described by a single wave function which, in the presence of both charge scattering and spin-orbit coupling, encodes an information about {\em entanglement} of its spin and orbital degrees of freedom. The quantum state--an {\em improper} mixture--of experimentally detectable spin subsystem is elucidated by evaluating quantum information theory measures of entanglement in the scattering states which determine {\em quantum transport} properties of spin-polarized electrons injected into a two-dimensional disordered Rashba spin-split conductor that is attached to the ferromagnetic source and drain electrodes. Thus, the Landauer transmission matrix, traditionally evaluated to obtain the spin-resolved conductances, also yields the reduced spin density operator allowing us to extract quantum-mechanical measures of the detected electron spin-polarization and spin-coherence, thereby pointing out how to avoid detrimental {\em decoherence} effects on spin-encoded information transport through semiconductor spintronic devices.; Comment: 5 pages, 2 color EPS figures; one new figure and discussion of some conceptual issues related to spin-polarization in quantum transport

## Reconfigurable nanoelectronics using graphene based spintronic logic gates

Dery, Hanan; Wu, Hui; Ciftcioglu, Berkehan; Huang, Michael; Song, Yang; Kawakami, Roland; Shi, Jing; Krivorotov, Ilya; Telesca, Donald A.; Zutic, Igor; Sham, Lu J.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.04%
This paper presents a novel design concept for spintronic nanoelectronics that emphasizes a seamless integration of spin-based memory and logic circuits. The building blocks are magneto-logic gates based on a hybrid graphene/ferromagnet material system. We use network search engines as a technology demonstration vehicle and present a spin-based circuit design with smaller area, faster speed, and lower energy consumption than the state-of-the-art CMOS counterparts. This design can also be applied in applications such as data compression, coding and image recognition. In the proposed scheme, over 100 spin-based logic operations are carried out before any need for a spin-charge conversion. Consequently, supporting CMOS electronics requires little power consumption. The spintronic-CMOS integrated system can be implemented on a single 3-D chip. These nonvolatile logic circuits hold potential for a paradigm shift in computing applications.; Comment: 14 pages (single column), 6 figures

## Power dissipation in spintronic devices out of thermodynamic equilibrium

Nikonov, Dmitri E.; Bourianoff, George I.; Gargini, Paolo
Tipo: Artigo de Revista Científica
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27.04%
Quantum limits of power dissipation in spintronic computing are estimated. A computing element composed of a single electron in a quantum dot is considered. Dynamics of its spin due to external magnetic field and interaction with adjacent dots is described via the Bloch equations. Spin relaxation due to magnetic noise from various sources is described as coupling to a reservoir. Resulting dissipation of energy is calculated and is shown to be much less than the thermal limit, ~kT per bit, if the rate of spin relaxation is much slower than the switching rate. Clues on how to engineer an energy efficient spintronic device are provided.; Comment: 31 pages, 7 figures

## Power dissipation in spintronic devices: A general perspective

Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.04%
Champions of spintronics often claim that spin based signal processing devices will vastly increase speed and/or reduce power dissipation compared to traditional charge based electronic devices. Yet, not a single spintronic device exists today that can lend credence to this claim. Here, I show that no spintronic device that clones conventional electronic devices, such as field effect transistors and bipolar junction transistors, is likely to reduce power dissipation significantly. For that to happen, spin-based devices must forsake the transistor paradigm of switching states by physical movement of charges, and instead, switch states by flipping spins of stationary charges. An embodiment of this approach is the single spin logic idea proposed more than 10 years ago. Here, I revisit that idea and present estimates of the switching speed and power dissipation. I show that the Single Spin Switch is far superior to the Spin Field Effect Transistor (or any of its clones) in terms of power dissipation. I also introduce the notion of matrix element engineering which will allow one to switch devices without raising and lowering energy barriers between logic states, thereby circumventing the kTln2 limit on energy dissipation. Finally, I briefly discuss single spin implementations of classical reversible (adiabatic) logic.; Comment: To appear in Journal of Nanoscience and Nanotechnology

## Hybrid CMOS-MQCA Logic Architectures using Multi-Layer Spintronic Devices

Das, Jayita; Alam, Syed M.; Rajaram, Srinath; Bhanja, Sanjukta
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.04%
We present a novel hybrid CMOS-MQCA architecture using multi-layer Spintronic devices as computing elements. A feasibility study is presented with 22nm CMOS where new approaches for spin transfer torque induced clocking and read-out scheme for variability-tolerance are introduced. A first-of-its-kind Spintronic device model enables circuit simulation using existing CAD infrastructure. Approximately 70% reduction in energy consumption is observed when compared against conventional field-induced clocking scheme.; Comment: The paper has been withdrawn

## Ab initio investigation of FeAs/GaAs heterostructures for potential spintronic and superconducting applications

Griffin, Sinéad M.; Spaldin, Nicola A.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.04%
Ultra-thin FeAs is of interest both as the active component in the newly identified pnictide superconductors, and in spintronic applications at the interface between ferromagnetic Fe and semiconducting GaAs. Here we use first-principles density functional theory to investigate the properties of FeAs/GaAs heterostructures. We find that the Fermi surface is modified from that characteristic of the pnictide superconductors by interactions between the FeAs layer and the As atoms in the GaAs layers. Regardless of the number of FeAs layers, the Fe to As ratio, or the strain state, the lowest energy magnetic ordering is always antiferromagnetic, suggesting that such heterostructures are not promising spintronic systems, and offering an explanation for the failure of spin injection across Fe/GaAs interfaces.; Comment: 8 pages, 12 figures

Seifert, T.; Jaiswal, S.; Martens, U.; Hannegan, J.; Braun, L.; Maldonado, P.; Freimuth, F.; Kronenberg, A.; Henrizi, J.; Radu, I.; Beaurepaire, E.; Mokrousov, Y.; Oppeneer, P. M.; Jourdan, M.; Jakob, G.; Turchinovich, D.; Hayden, L. M.; Wolf, M.; Münzen
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.04%
Terahertz electromagnetic radiation is extremely useful for numerous applications such as imaging and spectroscopy. Therefore, it is highly desirable to have an efficient table-top emitter covering the 1-to-30-THz window whilst being driven by a low-cost, low-power femtosecond laser oscillator. So far, all solid-state emitters solely exploit physics related to the electron charge and deliver emission spectra with substantial gaps. Here, we take advantage of the electron spin to realize a conceptually new terahertz source based on tailored fundamental spintronic/photonic phenomena in magnetic metal multilayers: a spin-dependent generalization of the photo-Dember effect, the inverse spin-Hall effect and a broadband Fabry-P\'erot resonance. Guided by an analytical model, such spintronic route offers unique possibilities for systematic optimization. We find that a 5.8-nm-thick W/CoFeB/Pt trilayer generates ultrashort THz pulses fully covering the 1-to-30-THz range. Our novel source outperforms standard emitters such as ZnTe(110) crystals in terms of bandwidth, conversion efficiency, flexibility, scalability and cost.; Comment: 11 pages, 4 figures

## Automotion of Domain Walls for Spintronic Interconnects

Nikonov, Dmitri E.; Manipatruni, Sasikanth; Young, Ian A.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.04%
We simulate automotion, the spontaneous transport of a magnetic domain wall under the influence of demagnetization and magnetic anisotropy, in nanoscale spintronic interconnects. In contrast to spin transfer driven magnetic domain wall motion, the proposed interconnects operate with only a transient current pulse and provide favorable scaling down to the 20nm scale. Cases of both in-plane and perpendicular magnetization are considered. Analytical dependence of the velocity of domain walls on the angle of magnetization are compared with full micromagnetic simulations. Deceleration, disappearance, and reflection of domain walls are demonstrated. Dependences of the magnetization angle on the current pulse parameters are studied. The energy and delay analysis suggests that automotion is an attractive option for spintronic logic interconnects.; Comment: 9 figures, 25 pages

## Circuit Theory for SPICE of Spintronic Integrated Circuits

Manipatruni, Sasikanth; Nikonov, Dmitri E.; Young, Ian A.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.04%
We present a theoretical and a numerical formalism for analysis and design of spintronic integrated circuits (SPINICs). The formalism encompasses a generalized circuit theory for spintronic integrated circuits based on nanomagnetic dynamics and spin transport. We propose an extension to the Modified Nodal Analysis technique for the analysis of spin circuits based on the recently developed spin conduction matrices. We demonstrate the applicability of the framework using an example spin logic circuit described using spin Netlists.; Comment: 14 pages, 11 figures; added fig. 2; added citations; modified title to emphasize SPICE; Results unchanged

## Spin Polarization Dependence of Carrier Effective Mass in Semiconductor Structures: Spintronic Effective Mass

Zhang, Ying; Sarma, S. Das
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.04%
We introduce the concept of a spintronic effective mass for spin-polarized carriers in semiconductor structures, which arises from the strong spin-polarization dependence of the renormalized effective mass in an interacting spin-polarized electron system. The majority-spin many-body effective mass renormalization differs by more than a factor of 2 at rs=5 between the unpolarized and the fully polarized two-dimensional system, whereas the polarization dependence (~15%) is more modest in three dimensions around metallic densities (rs~5). The spin-polarization dependence of the carrier effective mass is of significance in various spintronic applications.; Comment: Final version

## Roadmap for Emerging Materials for Spintronic Device Applications

Hirohata, Atsufumi; Sukegawa, Hiroaki; Yanagihara, Hideto; Žutić, Igor; Seki, Takeshi; Mizukami, Shigemi; Swaminathan, Raja
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.31%
The Technical Committee of the IEEE Magnetics Society has selected 7 research topics to develop their roadmaps, where major developments should be listed alongside expected timelines; (i) hard disk drives, (ii) magnetic random access memories, (iii) domain-wall devices, (iv) permanent magnets, (v) sensors and actuators, (vi) magnetic materials and (vii) organic devices. Among them, magnetic materials for spintronic devices have been surveyed as the first exercise. In this roadmap exercise, we have targeted magnetic tunnel and spin-valve junctions as spintronic devices. These can be used for example as a cell for a magnetic random access memory and spin-torque oscillator in their vertical form as well as a spin transistor and a spin Hall device in their lateral form. In these devices, the critical role of magnetic materials is to inject spin-polarised electrons efficiently into a non-magnet. We have accordingly identified 2 key properties to be achieved by developing new magnetic materials for future spintronic devices: (1) Half-metallicity at room temperature (RT); (2) Perpendicular anisotropy in nano-scale devices at RT. For the first property, 5 major magnetic materials are selected for their evaluation for future magnetic/spintronic device applications: Heusler alloys...

## Hybrid Spintronic-CMOS Spiking Neural Network With On-Chip Learning: Devices, Circuits and Systems

Sengupta, Abhronil; Banerjee, Aparajita; Roy, Kaushik
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.2%
Over the past decade Spiking Neural Networks (SNN) have emerged as one of the popular architectures to emulate the brain. In SNN, information is temporally encoded and communication between neurons is accomplished by means of spikes. In such networks, spike-timing dependent plasticity mechanisms require the online programming of synapses based on the temporal information of spikes transmitted by spiking neurons. In this work, we propose a spintronic synapse with decoupled spike transmission and programming current paths. The spintronic synapse consists of a ferromagnet-heavy metal heterostructure where programming current through the heavy metal generates spin-orbit torque to modulate the device conductance. Ultra-low programming energy and fast programming times demonstrate the efficacy of the proposed device as a nanoelectronic synapse. We demonstrate the interfacing of such spintronic synapses with CMOS neurons and learning circuits operating in transistor sub-threshold region to form a network of spiking neurons that can be utilized for pattern recognition problems.

## Spintronic magnetic anisotropy

Misiorny, Maciej; Hell, Michael; Wegewijs, Maarten R.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.04%
An attractive feature of magnetic adatoms and molecules for nanoscale applications is their superparamagnetism, the preferred alignment of their spin along an easy axis preventing undesired spin reversal. The underlying magnetic anisotropy barrier --a quadrupolar energy splitting-- is internally generated by spin-orbit interaction and can nowadays be probed by electronic transport. Here we predict that in a much broader class of quantum-dot systems with spin larger than one-half, superparamagnetism may arise without spin-orbit interaction: by attaching ferromagnets a spintronic exchange field of quadrupolar nature is generated locally. It can be observed in conductance measurements and surprisingly leads to enhanced spin filtering even in a state with zero average spin. Analogously to the spintronic dipolar exchange field, responsible for a local spin torque, the effect is susceptible to electric control and increases with tunnel coupling as well as with spin polarization.; Comment: 6 pages with 4 figures + 26 pages of Supplementary Information

## Direct epitaxial integration of the ferromagnetic semiconductor EuO with silicon for spintronic applications

Averyanov, Dmitry V.; Teterin, Peter E.; Sadofyev, Yuri G.; Tokmachev, Andrey M.; Primenko, Alexey E.; Likhachev, Igor A.; Storchak, Vyacheslav G.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.04%
Materials in which charge and spin degrees of freedom interact strongly offer applications known as spintronics. Following a remarkable success of metallic spintronics based on the giant-magnetoresistive effect, tremendous efforts have been invested into the less developed semiconductor spintronics, in particular, with the aim to produce three-terminal spintronic devices, e.g. spin transistors. One of the most important prerequisites for such a technology is an effective injection of spin-polarized carriers from a ferromagnetic semiconductor into a nonmagnetic semiconductor, preferably one of those currently used for industrial applications such as Si - a workhorse of modern electronics. Ferromagnetic semiconductor EuO is long believed to be the best candidate for integration of magnetic semiconductor with Si. Although EuO proved to offer optimal conditions for effective spin injection into silicon and in spite of considerable efforts, the direct epitaxial stabilization of stoichiometric EuO thin films on Si without any buffer layer has not been demonstrated to date. Here we report a new technique for control of EuO/Si interface on submonolayer level which may have general implications for the growth of functional oxides on Si. Using this technique we solve a long-standing problem of direct epitaxial growth on silicon of thin EuO films which exhibit structural and magnetic properties of EuO bulk material. This result opens up new possibilities in developing all-semiconductor spintronic devices.; Comment: 22 pages...

## Spintronic devices from bilayer graphene in contact to ferromagnetic insulators

Michetti, Paolo; Recher, Patrik
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.04%
Graphene-based materials show promise for spintronic applications due to their potentially large spin coherence length. On the other hand, because of their small intrinsic spin-orbit interaction, an external magnetic source is desirable in order to perform spin manipulation. Because of the flat nature of graphene, the proximity interaction with a ferromagnetic insulator (FI) surface seems a natural way to introduce magnetic properties into graphene. Exploiting the peculiar electronic properties of bilayer graphene coupled with FIs, we show that it is possible to devise very efficient gate-tunable spin-rotators and spin-filters in a parameter regime of experimental feasibility. We also analyze the composition of the two spintronic building blocks in a spin-field-effect transistor.; Comment: 9 pages, 7 figures, revised version, a figure added

## Spintronic properties and stability of the half-Heusler alloys LiMnZ (Z=N, P, Si)

Damewood, L.; Busemeyer, B.; Shaughnessy, M.; Fong, C. Y.; Yang, L. H.; Felser, C.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.04%
Li-based half-Heusler alloys have attracted much attention due to their potential applications in optoelectronics and because they carry the possibility of exhibiting large magnetic moments for spintronic applications. Due to their similarities to metastable zinc blende half-metals, the half-Heusler alloys $\beta$-LiMnZ (Z = N, P and Si) were systematically examined for their electric, magnetic and stability properties at optimized lattice constants and strained lattice constants that exhibit half-metallic properties. Other phases of the half-Heusler structure ($\alpha$ and $\gamma$) are also reported here, but they are unlikely to be grown. The magnetic moments of these stable Li-based alloys are expected to reach as high as 4 $\mu_{\mathrm{B}}$ per unit cell when Z = Si and 5 $\mu_{\mathrm{B}}$ per unit cell when Z = N and P, however the antiferromagnetic spin configuration is energetically favored when Z is a pnictogen. $\beta$-LiMnSi at a lattice constant 14\% larger than its equilibrium lattice constant is a promising half-metal for spintronic applications due to its large magnetic moment and vibrational stability. The modified Slater--Pauling rule for these alloys is determined. Finally, a plausible method for developing half-metallic Li$_x$MnZ at equilibrium...

## Lithium doped graphene as spintronic devices

Tipo: Artigo de Revista Científica