Spin transport in proximity-induced ferromagnetic graphene (original) (raw)
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Magnetic Insulator-Induced Proximity Effects in Graphene: Spin Filtering and Exchange Splitting Gaps
2012
We report on first-principles calculations of spin-dependent properties in graphene induced by its interaction with a nearby magnetic insulator (Europium oxide, EuO). The magnetic proximity effect results in spin polarization of graphene π orbitals by up to 24 %, together with large exchange splitting bandgap of about 36 meV. The position of the Dirac cone is further shown to depend strongly on the graphene-EuO interlayer. These findings point towards the possible engineering of spin gating by proximity effect at relatively high temperature, which stands as a hallmark for future all-spin information processing technologies.
Physical Review Letters, 2013
We report on first-principles calculations of spin-dependent properties in graphene induced by its interaction with a nearby magnetic insulator (europium oxide, EuO). The magnetic proximity effect results in spin polarization of graphene orbitals by up to 24%, together with a large exchange-splitting band gap of about 36 meV. The position of the Dirac cone is further shown to depend strongly on the graphene-EuO interlayer. These findings point toward the possible engineering of spin gating by the proximity effect at a relatively high temperature, which stands as a hallmark for future all-spin information processing technologies.
Spintronics devices from bilayer graphene in contact to ferromagnetic insulators
Physical Review B, 2011
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. 72.80.Vp, 85.75.Mm, Graphene with its high mobility 1 and potentially long spin lifetimes, is an attractive material for spintronics. In particular, spin relaxation lengths on the order of micrometers have been observed 2 , together with spin relaxation times of hundreds of picoseconds, which are still believed to be limited by extrinsic impurities 3,4 . More recent experiments reported the measurement of a spin lifetime up to 1 ns in graphene and even of several nanoseconds in bilayer graphene (BG) 5,6 . Moreover, tunnel-injection of spin into graphene has been recently achieved using Co ferromagnets, with the observation of the largest non-local magnetoresistance of any material 7 . Graphene quantum dots have been also identified as an ideal host for spin qubits 8 .
Transverse Spin Transport in Graphene
International Journal of Modern Physics B, 2009
In this paper we report transverse spin transport properties of graphene in a device, where for the first time a mono-atomically thin atomic fabric was sandwiched between magnetic thin films. We found that a single layer graphene flake was sufficient to break the exchange coupling between magnetic films and also to enhance the magnetoresistance effect.
Physical review letters, 2017
Two-dimensional materials provide a unique platform to explore the full potential of magnetic proximity-driven phenomena, which can be further used for applications in next-generation spintronic devices. Of particular interest is to understand and control spin currents in graphene by the magnetic exchange field of a nearby ferromagnetic material in graphene-ferromagnetic-insulator (FMI) heterostructures. Here, we present the experimental study showing the strong modulation of spin currents in graphene layers by controlling the direction of the exchange field due to FMI magnetization. Owing to clean interfaces, a strong magnetic exchange coupling leads to the experimental observation of complete spin modulation at low externally applied magnetic fields in short graphene channels. Additionally, we discover that the graphene spin current can be fully dephased by randomly fluctuating exchange fields. This is manifested as an unusually strong temperature dependence of the nonlocal spin s...
Magnetic Insulators-Induced Proximity Effects in Graphene
2013
We report on first-principles calculations of spin-dependent properties in graphene induced by its interaction with a nearby magnetic insulator (Europium oxide, EuO). The magnetic proximity effect results in spin polarization of graphene π orbitals by up to 24 %, together with large exchange splitting bandgap of about 36 meV. The position of the Dirac cone is further shown to depend strongly on the graphene-EuO interlayer. These findings point towards the possible engineering of spin gating by proximity effect at relatively high temperature, which stands as a hallmark for future all-spin information processing technologies.
Spin-polarized transport through a domain wall in magnetized graphene
Physical Review B, 2009
Atomically thin two-dimensional layer of honeycomb crystalline carbon known as graphene is a promising system for electronics. It has a point-like Fermi surface, which is very sensitive to external potentials. In particular, Zeeman magnetic field parallel to the graphene layer splits electron bands and creates fully spin-polarized and geometrically congruent circular Fermi surfaces of particle and hole type. In the presence of electric field, particles and holes with opposite spins drift in opposite direction. These phenomena are likely to be of interest for developing graphene-based spintronic devices. A domain wall (DW) separating regions with opposite spin polarizations is a basic element of such a device. Here we consider a ballistic passage of spin-polarized charge carriers through DW in graphene. We also discuss the analogy between the generation of spin currents in graphene and in relativistic quark-gluon plasma, where the spin-polarized current is responsible for the phenomenon of charge separation studied recently at RHIC.
Spin-dependent transport for armchair-edge graphene nanoribbons between ferromagnetic leads
Journal of Physics: Condensed Matter, 2011
We theoretically investigate the spin-dependent transport for the system of an armchair-edge graphene nanoribbon (AGNR) between two ferromagnetic (FM) leads with arbitrary polarization directions at low temperatures, where a magnetic insulator is deposited on the AGNR to induce an exchange splitting between spin-up and-down carriers. By using the standard nonequilibrium Green's function (NGF) technique, it is demonstrated that, the spin-resolved transport property for the system depends sensitively on both the width of AGNR and the polarization strength of FM leads. The tunneling magnetoresistance (TMR) around zero bias voltage possesses a pronounced plateau structure for system with semiconducting 7-AGNR or metallic 8-AGNR in the absence of exchange splitting, but this plateau structure for 8-AGNR system is remarkably broader than that for 7-AGNR one. Interestingly, the increase of exchange splitting ∆ suppresses the amplitude of the structure for 7-AGNR system. However, the TMR is enhanced much for 8-AGNR system under the bias amplitude comparable to splitting strength. Further, the current-induced spin transfer torque (STT) for 7-AGNR system is systematically larger than that for 8-AGNR one. The findings here suggest the design of GNR-based spintronic devices by using a metallic AGNR, but it is more favorable to fabricate a current-controlled magnetic memory element by using a semiconducting AGNR.
Spin transfer torque and anisotropic conductance in spin orbit coupled graphene
2021
We theoretically study spin transfer torque (STT) in a graphene system with spin orbit coupling (SOC). We consider a graphene-based junction where the spin orbit coupled region is sandwiched between two ferromagnetic (F) segments. The magnetization in each ferromagnetic segment can possess arbitrary orientations. Our results show that the presence of SOC results in anisotropically modified STT, magnetoresistance, and charge conductance as a function of relative magnetization misalignment in the F regions. We have found that within the Klein regime, where particles hit the interfaces perpendicularly, the spin-polarized Dirac fermions transmit perfectly through the boundaries of a F-F junction (i.e., with zero reflection), regardless of the relative magnetization misalignment and exert zero STT. In the presence of SOC, however, due to band structure modification, a nonzero STT reappears. Our findings can be exploited for experimentally examining proximity-induced SOC into a graphene s...
Graphene spintronics: puzzling controversies and challenges for spin manipulation
Journal of Physics D: Applied Physics, 2014
This article presents the current puzzling controversy between theory and experimental results concerning the magnitude and mechanisms leading to spin relaxation in graphene-based materials. On the experimental side, it is surprising that regardless of the quality of the graphene monolayer, which is characterized by the carrier mobility, the typical Hanle precession measurements yield spin diffusion times (τ s) in the order of τ s ∼ 0.1 − 1ns (at low temperatures), which is several orders of magnitude below the theoretical estimates based on the expected low intrinsic spinorbit coupling in graphene. The results are weakly dependent on whether graphene is deposited onto SiO 2 or boron-nitride substrates or suspended, with the mobility spanning 3 orders of magnitude. On the other hand, extraction from two-terminal magnetoresistance measurements, accounting for contact effects result in τ s ∼ 0.1µs, and corresponding diffusion lengths of about 100 µm up to room temperature. Such discrepancy jeopardizes further progress towards spin manipulation on a lateral graphene two-dimensional platform. After a presentation of basic concepts, we here discuss state-of-the-art literature and the limits of all known approaches to describe spin transport in massless-Dirac Fermions, in which the effects of strong local spinorbit coupling ceases to be accessible with perturbative approaches. We focus on the limits of conventional views of spin transport in graphene and offer novel perspectives for further progress.