Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session P42: Spin Transport in GrapheneFocus
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Sponsoring Units: GMAG DMP DCOMP FIAP Chair: Olaf van 't Erve, Naval Research Laboratory Room: 389 |
Wednesday, March 15, 2017 2:30PM - 2:42PM |
P42.00001: Spintronics in high-quality graphene heterostructures via 1D contacts. Victor Guarochico, Jose Sambricio, Irina Grigorieva, Ivan Vera We report the first observation of nonlocal pure spin currents in high-quality graphene channels that are fully encapsulated by hexagonal boron nitride (hBN) layers. Our heterostructure devices prevent residual contamination from the fabrication process, routinely allowing high-quality channels with mobilities up to 100000 cm$^2$/Vs. This architecture is enabled by creating spin injectors based on edge one-dimensional (1D) contacts\footnote{ Wang, L. et al. Science {\bf 2013}, 342 (6158), 614-617.}, which avoid any significant charge doping from the contacts in the center of the channel. We present evidence for spin transport both at room and low temperatures. Spin injection through 1D contacts into uniform high-quality graphene gives us access to explore spintronics in the quantum transport regime, where we exploit quantum interference to enhance the nonlocal spin signals. [Preview Abstract] |
Wednesday, March 15, 2017 2:42PM - 2:54PM |
P42.00002: Interfacial Spin Dephasing and Spin Absorption in Graphene Probed by Pure Spin Current Walid Amamou, Gordon Stecklein, Tiancong Zhu, Simranjeet Singh, Jyoti Katoch, Serol Turkyilmaz, Cengiz Ozkan, Steven Koester, Paul Crowell, Roland Kawakami In order to understand the limiting factors for achieving magnetization switching using graphene, we study the spin absorption of a Fe nanomagnet deposited on a graphene spin valve. A pure spin current is injected into the graphene channel via electrical spin injection through a Co(80nm)/SrO(1nm) tunnel barrier junction. The generated pure spin current inside the graphene spin channel is partly absorbed by a nanomagnet grown on top of the spin channel allowing a direct determination of the absorbed spin current. We perform non-local magnetoresistance (MR) and Hanle spin precession measurement as we gradually deposit Fe in-situ inside an MBE chamber. We observe a rapid decrease of the non-local MR signal for a thickness ranging from 0 {\AA} to 1{\AA} followed by slower decrease and a saturation of the spin signal above 1 nm of Fe.Using 2D finite element modeling of the spatial distribution of the spin accumulation in the graphene channel, we extract an absorbed spin current of 2.9 x 10$^{\mathrm{6}}$~A/m$^{\mathrm{2}}$. By introducing a Cu spacer between the Fe and Graphene, we are able to decrease this rapid decay and observe a clear exponential decay due to the spin absorption into the Fe island. These results provide the first demonstration of interfacial spin dephasing in Graphene. [Preview Abstract] |
Wednesday, March 15, 2017 2:54PM - 3:06PM |
P42.00003: Spin transport in the $\nu=0$ quantum Hall state of graphene So Takei, Amir Yacoby, Bertrand Halperin, Yaroslav Tserkovnyak The ground state of neutral monolayer graphene in a strong perpendicular magnetic field is believed to be the so-called canted antiferromagnetic $\nu=0$ quantum Hall state. This state is an insulator for charge transport, but it should behave like a superfluid for transport of the spin component parallel to the magnetic field. Here, we have proposed an experiment to demonstrate this effect. [Preview Abstract] |
Wednesday, March 15, 2017 3:06PM - 3:18PM |
P42.00004: Quantum Hall Nematic States in Graphene Derrick Boone, Aaron Sharpe, Wenmin Yang, Arthur Barnard, David Goldhaber-Gordon, Rakashi Taniguchi, Kenji Watanabe In the quantum Hall effect at millikelvin temperatures, specific half-filled Landau levels in gallium arsenide show striking anisotropy in magnetotransport. Theoretical predictions and scanning gate microscopy measurements suggest these states are quantum Hall nematics: the partitioning of what is on average a half-filled Landau level into periodic stripes of integer-filled landau levels with long-range directional order. While this transport anisotropy has been observed in high-mobility GaAs two-dimensional electron gases, there is no clear evidence of quantum hall nematic states in graphene. Here, we discuss transport measurements of graphene at half-filling with geometries designed to identify transport anisotropy that is the signature of the quantum Hall nematic state. [Preview Abstract] |
Wednesday, March 15, 2017 3:18PM - 3:30PM |
P42.00005: Probing magnetic noise from currents and spins in 2d layered materials using diamond NV centers Javier Sanchez-Yamagishi, Bo Dwyer, Trond Andersen, Hongkun Park, Mikhail Lukin Diamond NV centers are ultra-sensitive magnetometers which can be read out optically and operate from room to cryogenic temperatures. I will discuss our recent progress using NV centers to measure local magnetic noise emanating from spins and electrical currents in 2d layered materials. By fabricating high-quality graphene devices on the diamond surface, we can probe the local structure of the graphene electrical conductivity by monitoring the magnetic noise due to thermal fluctuations in the electron sea as we vary both the electron temperature and chemical potential. I will discuss how this measurement technique can be used to study electronic behavior in the ballistic, diffusive and hydrodynamic transport regimes. [Preview Abstract] |
Wednesday, March 15, 2017 3:30PM - 3:42PM |
P42.00006: Charge and spin transport in metal-graphene-metal vertical junctions Enrique Cobas, Olaf van 't Erve, Shu-Fan Cheng, James Culbertson, Glenn Jernigan, Konrad Bussman, Berry Jonker We observe negative magnetoresistance(MR) in metallic NiFe(111)\textbar multi-layer graphene\textbar Fe heterostructures[1] consistent with minority spin filtering[2]. The MR is -5 percent at room temperature and -12 percent at 10 K. The transport properties and temperature dependence are metallic. We further investigate the out-of-plane (c-axis) resistivity and magnetoresistance of multi-layer graphene between metal surfaces. We fabricate various metal-graphene-metal vertical heterostructures via chemical vapor deposition directly on lattice-matched crystalline metal films including NiFe(111) and Co(0002) and in-situ electron beam evaporation of NiFe, Co, Ni, Fe, Cu and Au. [1] Cobas, E.D., van 't Erve, O.M.J., Cheng, S-F., Culbertson, J.C., Jernigan, G.G., Bussman, K., and Jonker, B.T, Room Temperature Spin Filtering in Metallic Ferromagnet-Multilayer Graphene-Ferromagnet Junctions, ACS Nano ASAP 2 Nov 2016. [2] Karpan, V.M., Giovannetti, G., Khomyakov, P.A., Talanana, M., Starikov, A.A., Zwierzycki, M., van der Brink, J., Brocks G. and Kelly, P.J., Graphite and graphene as perfect spin filters, Phys. Rev. Lett. (2007) 99, 176602. [Preview Abstract] |
Wednesday, March 15, 2017 3:42PM - 3:54PM |
P42.00007: Modeling the negative magnetoresistance of Ferromagnet-Graphene-Ferromagnet junctions Olaf Van T Erve, Enrique Cobas, Berend Jonker Ferromagnet -- multilayer graphene -- ferromagnet junctions are predicted to yield low resistance devices with a high magnetoresistance (MR) due to a metallic minority spin transport channel [1]. We fabricated arrays of such junctions via chemical vapor deposition of graphene on lattice-matched single-crystal NiFe(111) films with a bcc-Fe top contact. The junctions exhibit negative MR and metallic transport behavior attributed to minority spin filtering, and low resistance. Existing models fail to predict the negative MR observed in our metallic junctions. Here we develop a model based on the Mott two spin current approximation where the two spin channels are treated independently. The model incorporates spin current conversion, the minority spin filtering predicted for the high quality lattice matched NiFe(111) /graphene interface, as well as a diffusive interface for the graphene / e-beam deposited bcc-Fe layer that is not expected to result in spin filtering. This model correctly predicts the observed negative MR and gives a lower bound for the minority spin polarization, exceeding 80{\%} at low temperatures, for junctions that exhibit an MR of -12{\%} at 10K. The model quantitatively predicts the dependence of the MR on the RA product at room temperature, and is consistent with the high minority spin polarization inside the graphene junction as predicted by Karpan. [1] Karpan, V. M. et al. \textit{Phys. Rev. Lett.} 99, 176602 (2007). [Preview Abstract] |
Wednesday, March 15, 2017 3:54PM - 4:06PM |
P42.00008: Spin transport in polycrystalline graphene and in graphene/TMDC heterostructures Aron W. Cummings, Jose Garcia, Stephan Roche Owing to its small spin-orbit coupling (SOC) and negligible hyperfine interaction, graphene is predicted to be an efficient carrier of spin-based information, and is thus promising for spintronics applications. While measured spin lifetimes are quite satisfactory, in the nanosecond range, there is still room for optimization of spin transport in this material. In addition, some applications, such as those relying on the spin Hall effect or spin orbit torque, require a large SOC. In this talk I will present numerical studies of spin transport in two graphene systems: polycrystalline graphene, and graphene on transition metal dichalcogenides (TMDCs). In polycrystalline graphene, grain boundaries impede charge transport and are generally unfavorable. However, numerical simulations indicate that under the right conditions grain boundaries may actually be beneficial to spin transport. Meanwhile, proximity to a TMDC can significantly enhance the SOC in graphene, making it potentially useful for applications requiring large SOC while also taking advantage of its superior charge transport properties. I will present numerical simulations detailing the impact of this enhanced SOC on the spin lifetime, as well as on phenomena such as weak antilocalization and the spin Hall effect. [Preview Abstract] |
Wednesday, March 15, 2017 4:06PM - 4:18PM |
P42.00009: Collective charge and spin excitations in graphene with in-plane magnetic fields Matthew Anderson, Carsten Ullrich Plasmonics in graphene is a subject of much current interest, with many prospects for novel applications. However, the dynamics of collective spin excitations and spin waves in graphene has been much less explored. Here, we study the collective excitations of doped graphene in the presence of in-plane magnetic fields. These excitations can be divided into spin-conserving and spin-flip channels. We calculate the dispersions of charge and spin plasmons using time-dependent density-functional methods within a standard tight-binding approach. The effects of spin-orbit coupling on the spin excitations will be discussed. [Preview Abstract] |
Wednesday, March 15, 2017 4:18PM - 4:30PM |
P42.00010: Gate dependent non-local spin resistance in an Au-patched graphene. Jungmin Park, Hyungduk Yun, Mi-Jin Jin, Junhyeon Jo, Inseon Oh, Vijayakumar Modepalli, Soon-Yong Kwon, Jung-Woo Yoo Enhanced spin-orbit coupling in grapheme can induce spin Hall effect, which can be adapted to electrically generate or detect a spin current in the spin logic device without a ferromagnet. Recently, spin Hall effect in decorated graphenes has been experimentally observed by non-local transport studies. However, results on the non-local measurements in graphene hall bar devices exploiting spin Hall effect have been under controversy. In this study, we introduced an ultra-thin Au-patch on a graphene surface to enhance the spin-orbit coupling, and employed an H-bar type device to probe the nonlocal spin signal induced by spin Hall effect. The geometry of the studied H-bar devices has channels of 1 $\mu $m width and 5.6 $\mu $m length. An ultra-thin Au patch (\textasciitilde 1 nm) was deposited by a thermal evaporation. And in-plane field dependent spin precession signature can be observed at particular gate voltage. At that point, the spin hall angle and the spin relaxation length of the Au-patch graphene device were $\gamma $ \textasciitilde 8.8 {\%} and $\lambda $s \textasciitilde 2.2 $\mu $m at 2 K, respectively. The estimated spin relaxation rates were proportional to square of temperature, suggesting an Elliott-Yafet spin relaxation mechanism. [Preview Abstract] |
Wednesday, March 15, 2017 4:30PM - 4:42PM |
P42.00011: Crossover to the anomalous quantum regime in the extrinsic spin Hall effect of graphene Aires Ferreira, Mirco Milletari Recent reports of spin-orbit coupling enhancement in chemically modified graphene have opened doors to studies of the spin Hall effect with massless chiral fermions. Here, we theoretically investigate the interaction and impurity density dependence of the extrinsic spin Hall effect in spin-orbit coupled graphene. We present a nonperturbative quantum diagrammatic calculation of the spin Hall response function in the strong-coupling regime that incorporates skew scattering and anomalous impurity density-independent contributions on equal footing. The spin Hall conductivity dependence on Fermi energy and electron-impurity interaction strength reveals the existence of experimentally accessible regions where anomalous quantum processes dominate. Our findings suggest that spin-orbit-coupled graphene is an ideal model system for probing the competition between semiclassical and bona fide quantum scattering mechanisms underlying the spin Hall effect. [Preview Abstract] |
Wednesday, March 15, 2017 4:42PM - 4:54PM |
P42.00012: Magnetism of substitutional sp-element impurities in graphene and silicene: energetics and concentration dependence J. Hern\'andez-Tecorralco, L. Meza-Montes, M.E. Cifuentes-Quintal, R. de Coss It has been predicted from ab-initio calculations that a finite spin magnetic moment may result in sp-element substitutional impurities in two-dimensional materials. Particularly, phosphorus-doped graphene and nitrogen-doped silicene for 3.2\% concentrations (supercell 4x4) have been reported to present this effect. In this work, we have performed a structural, electronic, magnetic, and energetics properties systematic study of substitutional impurities for P@graphene and N@silicene as a function of doping concentration, by means of first principles calculations. We have calculated the electronic and magnetic properties for different supercell sizes, from 3x3 to 8x8. The energetics and the magnetic moment for the studied systems were obtained with the Fixed-Spin Moment Method. We found that the magnetic moment in P@graphene practically remains constant for supercell sizes from 3x3 to 8x8, however the exchange energy gained by the spin-polarization is strongly reduced as the concentration decreases. In contrast, N@silicene showed a magnetic moment around 0.8 $\mu_B$ for the 3x3 and 4x4 supercells, but for lower concentrations the system becomes non-magnetic. Finally, the results are analyzed in terms of the charge and spin density distributions in the $\sigma$ and $\pi$ orbitals. [Preview Abstract] |
Wednesday, March 15, 2017 4:54PM - 5:06PM |
P42.00013: Orientation control of graphene flakes by magnetic field: broad device applications of macroscopically aligned graphene. Feng Lin, Zhuan Zhu, Xufeng Zhou, Wenlan Qiu, Chao Niu, Jonathan Hu, Keshab Daha, Yanan Wang, Zhenhuan Zhao, Zhifeng Ren, Dimitri Litvinov, Zhaoping Liu, Zhiming M. Wang, Jiming Bao We demonstrate the orientation control of graphene flakes by a weak magnetic field and subsequently show two examples of novel device applications of macroscopically aligned graphene. The control is made possible by a large diamagnetic susceptibility of exfoliated graphene. A liquid suspension of graphene flakes is first used for magnetic field sensing and display with sensitivity and spatial resolution higher than traditional iron filings or particles. The graphene suspension is then packaged as a writing and/or display board that can be controlled by magnets or magnetic field. Both applications require no external lighting or polarizing optics because they utilize macroscopic alignment and anisotropic optical properties of graphene. The macroscopic control and alignment of graphene can not only transfer unique properties of graphene from microscopic to macroscopic scale, but also be used to align other nanomaterials.. [Preview Abstract] |
Wednesday, March 15, 2017 5:06PM - 5:18PM |
P42.00014: Spin transport through molecules of graphene fragments Partha Mitra, Semanti Pal, Arpita Mandal, Arindam Mukherkee A variety of molecular structures that are essentially fragments of a graphene layer can be synthesized chemically. One such structure is 9-hydroxyphenalenone(PLY) that consist of three fused benzene rings and has one unpaired electron delocalised over the entire planner ring. Various molecules with PLY ligands and metal centers are previously reported showing interesting properties including spin filtering effect. We showcase a new molecule, denoted as Mn-PLY, where three PLY ligands are coordinated with one Mn(III) ion . Bulk susceptibility measurement exhibits paramagnetic behaviour down to 40K and onset of ferromagnetism thereafter. Crystal packing arrangement shows that PLY from two neighboring molecules stack on top of one another with separation $\sim 3.7 \AA$. Thus, Mn-PLY is a promising material where injected spins can be envisaged to travel between molecules. Mn-PLY thin films were prepared by controlled thermal evaporation using effusion cells and fabricated device structures using lithography techniques. Distinct spin valve effect signals were observed from trilayer structures of Cobalt/ Mn-PLY(5-20nm) /Permalloy with MR ratio $\sim 2\%$ at room temperature. Detailed studies of spin valve effect and non-local measurements to probe Hanle effect will be presented. [Preview Abstract] |
Wednesday, March 15, 2017 5:18PM - 5:30PM |
P42.00015: Tunable magnetic states of 5}\textbf{\textit{d}}\textbf{ metal adsorbed nanoporous graphene Pankaj Kumar, Vinit Sharma, Fernando Reboredo, Pushpa Raghani Magnetic nanostructures derived from graphene have got a lot of attention for future data storage and spintronic devices. Here, using density functional theory, we investigated the electronic and magnetic properties of 5$d$ metal adsorbed di and tri-vacancy fluorinated graphene and studied the effect of external electric field. We find an induced magnetic moment in these systems, which range from 1-7 $\mu_{\mathrm{{\rm B}}}$. For W adsorbed tri-vacancy fluorinated graphene, we find a huge magnetic moment of 7 $\mu_{\mathrm{{\rm B}}}$ along with high magneto-crystalline anisotropy energy (MAE). Furthermore, the system changes from high spin to low spin under the effect of electric field along with change in MAE. Our study suggests that the defect engineering and external electric field both can be used as a probe to control the magnetic states and magnetic properties of the system. Our results provide a promising way to develop the hybrid materials and control their properties for future spintronic and non-volatile memory devices. [Preview Abstract] |
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