APS March Meeting 2015
1This work is supported by ARO MURI W911NF 14 1 0016. 5:18PM W28.00013 Effects of heat current on magnetization dynamics FRANCESCO ANTONIO VETRO, SYLVAIN BRECHET, JEAN PHILIPPE ANSERMET, Ecole Polytechnique Federale de Lausanne, IPMC, station 3, 1015 Lausanne, Switzerland The work is aimed at investigating the interplay between spin dynamics and heat currents in single crystal Yttrium Iron Garnet (YIG) The irreversible thermodynamics for a continuous medium [1] predicts that a thermal gradient, in the presence of magnetization waves, produces a magnetic induction field, thus a magnetic analog of the well known Seebeck effect. Time resolved transmission measurements revealed a change in the attenuation of magnetization waves propagating along the thermal gradient when the gradient is reversed. This magnetic damping change can be accounted for by the Magnetic Seebeck effect [2] In order to characterize this effect further, we have conducted studies on magnetization dynamic in YIG single crystal samples placed in various geometrical configurations, e.g. with YIG disks in which magnetic vortices might be present. Various magnetic resonance schemes were used, e.g. local probes and cavities. [1] S. D. Brechet and J. P. Ansermet, Eur. Phys. J. B, vol. 86, no. 7, pp. 1 19, Jul. 2013. [2] S. D. Brechet, F. A. Vetro, E. Papa, S. E. Barnes and J. P. Ansermet, Physical Review Letters 111, 8, 087205, Aug. 2013. Thursday, March 5, 2015 2:30PM 5:18PM Session W29 GMAG DMP: Focus Session: Spin Dependent Physics in Carbon Based Materials 206A Olaf vant Erve, Naval Research Laboratory 2:30PM W29.00001 Extrinsic spin Hall effect in graphene1 TATIANA RAPPOPORT, Universidade Federal do Rio de Janeiro The intrinsic spin orbit coupling in graphene is extremely weak, making it a promising spin conductor for spintronic devices. In addition, many applications also require the generation of spin currents in graphene. Theoretical predictions and recent experimental results suggest one can engineer the spin Hall effect in graphene by greatly enhancing the spin orbit coupling in the vicinity of an impurity. The extrinsic spin Hall effect then results from the spin dependent skew scattering of electrons by impurities in the presence of spin orbit interaction. This effect can be used to efficiently convert charge currents into spin polarized currents. I will discuss recent experimental results on spin Hall effect in graphene decorated with adatoms and metallic cluster [1,2] and show that a large spin Hall effect can appear due to skew scattering. While this spin orbit coupling is small if compared with what it is found in metals, the effect is strongly enhanced in the presence of resonant scattering, giving rise to robust spin Hall angles. I will present our single impurity scattering calculations done with exact partial wave expansions [3] and complement the analysis with numerical results from a novel real space implementation of the Kubo formalism for tight binding Hamiltonians [4] [1] J. Balakrishnan et al. Nat. Phys. 9, 284 (2013) [2] J. Balakrishnan et al. Nat. Commun. 5, 4748 (2014) [3] A. Ferreira, T. G. Rappoport, M. A. Cazalilla, A. H. Castro Neto, Phys. Rev. Lett. 112, 066601 (2014) [4] Jose H. Garcia, Lucian Covaci and Tatiana G. Rappoport, arXiv:1410.8140. 1The author acknowledges the Brazilian agencies CNPq, CAPES, FAPERJ and INCT de Nanoestruturas de Carbono for financial support 3:06PM W29.00002 Inverse Spin Hall Voltage in Organic Semiconductors with Tunable SpinOrbit Coupling DALI SUN, KIPP VAN SCHOOTEN, HANS MALISSA, MARZIEH KAVAND, CHUANG ZHANG, CHRISTOPH BOEHME, Z. VALY VARDENY, Department of Physics Astronomy, University of Utah, Salt Lake City, UT, 84112, USA Spin current in organic semiconductors that are generated via the process of 'spin pumping' from FM substrates subjected to resonant microwave absorption has attracted recently great interest, since this scheme circumvents the impedance mismatch that exists in the "spin injection" technique between the organic semiconductors and FM injector. Because of the weak spin orbit coupling (SOC) in most organic semiconductors (OSECs) the obtained inverse spin Hall effect (ISHE) in these materials is very subtle. In this work we measured ISHE in a variety of OSECs having tunable SOC ranging from strong SOC (pi conjugated polymers that contain intrachain Pt atoms) to weak SOC polymers (such as DOO PPV) We found that the ISHE response in these compounds increases with the SOC, in spite of the decrease in the spin diffusion length. 3:18PM W29.00003 Neutral currents probed by non local transport in graphene with 5 d metal adatoms1 YILIN WANG, XINGHAN CAI, SHUDONG XIAO, WENZHONG BAO, JANICE REUTT ROBEY, University of Maryland, College Park, MICHAEL FUHRER, School of Physics, Monash University, Victoria, Australia Adsorption of adatoms on graphene has been theoretically proposed as an effective means to enhance spin orbit coupling in graphene. Here we use the non local measurement geometry to detect neutral currents (spin, valley, energy) through their Hall and inverse Hall effects. Single layer graphene devices are probed in situ in ultra high vacuum while depositing 5d heavy metal atoms (Ir, Au) at a temperature of 7 K. Surprisingly, we detect a non local signal in pristine devices as well as metal atom modified devices, with a consistent dependence of the signal on length and gate voltage for several devices. Changes in the non local signal upon deposition of 5d metal atoms appear governed by charge carrier mobility (reduced with increasing metal atom concentration) and are difficult to understand with spin Hall/inverse spin Hall effects alone due to increased spin orbit coupling in graphene. We will discuss other possible origins of the non local signal. 1This work was supported by the U.S. ONR MURI. MSF was supported by an ARC Laureate Fellowship. 3:30PM W29.00004 Theory of spin relaxation in bilayer graphene.1 DENIS KOCHAN, SUSANNE IRMER, MARTIN GMITRA, JAROSLAV FABIAN, University of Regensburg We present a new spin relaxation mechanism based on resonant scattering off local magnetic moments. We apply this mechanism to mono [1] and bilayer graphene and show that it can account for the ultrafast spin relaxation observed in spin injection experiments. In particular, the model explains the opposite dependence of the spin relaxation on the carrier density in mono and in bilayer graphene. We also show that for bilayer graphene the model explains the observed temperature induced changes in the carrier density dependence. [1] D. Kochan, M. Gmitra, J. Fabian; Phys. Rev. Lett. 112, 116602 (2014) 1This work has been supported by the SFB 689, GRK 1570, and European Union Seventh Framework Programme under Grant Agreement No. 604391