Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Y28: Focus Session: SpinHall Effect III 
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Sponsoring Units: GMAG DMP FIAP Chair: Luqiao Liu, IBM Yorktown Heights Room: 205 
Friday, March 6, 2015 8:00AM  8:12AM 
Y28.00001: Spin pumping by magnetopolaritons Yunshan Cao, Peng Yan, Hans Huebl, Sebastian Goennenwein, Gerrit Bauer Recent experiments report the strong coupling of microwaves to the magnetic insulator yttrium iron garnet with weakly damped magnetization dynamics [1]. We developed a scattering approach to study the coupled magnetization and microwave cavities beyond the paramagnetic/macrospin and rotating wave approximations that are implicit in the TavisCummings model [2]. To this end we solve the coupled LandauLifshitzGilbert and Maxwell's equations for a thin film magnet in a microwave cavity, leading to rich ferromagnetic spin wave resonance spectra of the transmitted or absorbed microwaves. Our method is valid for the full parameter range spanning the weak to strong coupling limits. We demonstrate strong coupling achievement not only for the FMR mode but also for standing spin waves, although the lowest excitation has a decisive leading role for coupling strength. Spin pumping in FI\textbar N bilayers as detected by inverse spin Hall voltages provides additional access to study strong coupling electrically.\\[4pt] [1] H. Huebl et al., PRL 111, 127003 (2013); G. Stenning et al., Opt. Express 21, 1456 (2013);Y. Tabuchi et al., PRL 113, 083603 (2014); X. Zhang et al., PRL 113, 156401 (2014).\\[0pt] [2] J. M. Fink et al., PRL 103, 083601 (2009). [Preview Abstract] 
Friday, March 6, 2015 8:12AM  8:24AM 
Y28.00002: Spin Transport in Insulators Mediated by Magnetic Correlations Probed by Y$_{3}$Fe$_{5}$O$_{12}$based Spin Pumping Chunhui Du, Hailong Wang, P. Chris Hammel, Fengyuan Yang Spin currents carried by mobile charges in ferromagnetic (FM) and nonmagnetic (NM) materials have been the central focus of spintronics, while spin transport in insulators is largely unexplored. FMR spin pumping has awakened intense interest in magnonmediated spin currents in both conducting and insulating FMs and in antiferromagnets (AF). Building on the large spin pumping signals enabled by our Y$_{3}$Fe$_{5}$O$_{12}$ (YIG) films, we report a systematic study of spin transport in six series of Pt/insulator/YIG trilayers where the insulators include one diamagnet, one paramagnet and four AFs. We observe remarkably robust spin transport in the AFs and a distinct linear relationship between the spin decay length in the insulator and the damping enhancement in the YIG, suggesting the critical role of magnetic correlations in AF insulators for spin transport. Strikingly, the insertion of a thin NiO layer between YIG and Pt significantly enhances the spin currents driven into Pt, suggesting exceptionally high spin transfer efficiency in YIG/NiO/Pt structures. [Preview Abstract] 
Friday, March 6, 2015 8:24AM  8:36AM 
Y28.00003: Spin pumping by timedependent gate without magnetic field in a nanowire LuYao Wang, ChonSaar Chu We theoretically study that spin pumping by smooth profile time dependent gate in a Rashba type nanowire without magnetic field.The time dependent gate produces both spin dependent and spinindependent potentials.The spin dependent temporary potential inducing a dynamic Rashba coupling constant combining with the static Rashba coupling constant generate asymmetry spin dependent transmission.Such spin pumping can be enhanced by spin independent temporary potential. [Preview Abstract] 
Friday, March 6, 2015 8:36AM  8:48AM 
Y28.00004: Manipulation of Magnetic Insulators Using Spin Torque from the Spin Hall Effect Colin Jermain, Aaron Rosenberg, Hanjong Paik, Sriharsha Aradhya, Hailong Wang, John Heron, Katja Nowack, John Kirtley, Darrell Schlom, Kathryn Moler, Fengyuan Yang, Dan Ralph We are exploring the possibility of currentinduced switching driven by spin torque from the spin Hall effect for micron and nanoscale devices made from the magnetic insulators yttrium iron garnet (YIG) and lutetium iron garnet (LuIG). We will report on the fabrication of devices incorporating thin films of YIG or LuIG with thickness less than 20 nm and inplane magnetization. We use electron beam lithography and ion milling to pattern the films into device structures with sizes ranging from 50 nm to 4 microns, integrated with a Ta or Pt layer so that we can use the spin Hall effect to apply spintransfer torque to the magnetic materials. With scanning SQUID magnetometry we measure the inplane dipole orientation of the device magnetic moment at 4 K. By examining the magnetic orientation as a function of applied current we investigate whether the spin Hall torque can be used to drive reliable magnetic switching at low current levels. [Preview Abstract] 
Friday, March 6, 2015 8:48AM  9:00AM 
Y28.00005: Spin Torque Arising from the Spin Hall Effect within Ferromagnets Jonathan Gibbons, Robert Buhrman, Daniel Ralph Recent spinpumping measurements have indicated that ferromagnetic materials such as permalloy can possess a significant inverse spin Hall effect, by which they convert an applied spin current to a charge current. We report experimental investigations of the inverse phenomenon, using the direct spin Hall effect within a ferromagnetic material to generate a spin current that can be used to apply a spin transfer torque to another nearby magnetic layer. Specifically, we measure spinorbitinduced torques generated by an inplane current in pinned ferromagnet/spacer/free ferromagnet multilayer structures. We quantify the strength of the torque using both nonresonant second harmonic magnetization tilting measurements and spintorque ferromagnetic resonance. We focus on the dependence of the direction and strength of the spin torque on the relative orientation of the fixedlayer magnetization and the current. [Preview Abstract] 
Friday, March 6, 2015 9:00AM  9:12AM 
Y28.00006: Coupled spincharge transport in twodimensional electron gases from weak to strong spinorbit couplings Yasufumi Araki, Allan H. MacDonald We investigate the magnetoelectric response of twodimensional electron gases with spinorbit interactions of arbitrary strength. Rashba or Dresselhaus spinorbit coupling in twodimensional systems gives rise to the coupling of spin and charge transport, which may appear as spin Hall effect, spinorbit induced torque, direct and inverse Edelstein effects, etc. We derive the diffusion equation for spin and charge densities microscopically with spinindependent disorder scattering and two types of spinorbit interactions of arbitrary strength, and analyze the crossover in the coupled spincharge transport from weak to strong spinorbit coupling regimes. Our calculation connects the traditional perturbative treatment of the spinorbit coupling in the weak spinorbit coupling regime, where two spin states are nearly degenerate, to the relaxation time approximation estimate in the strong spinorbit coupling regime, where the degeneracy is strongly lifted. The crossover becomes nontrivial when the Rashba and Dresselhaus spinorbit interactions are comparable. Based on those calculations, we will give some comments on the spinorbit induced torques induced in the heterostructure of ferromagnets and heavy metals. [Preview Abstract] 

Y28.00007: ABSTRACT WITHDRAWN 
Friday, March 6, 2015 9:24AM  9:36AM 
Y28.00008: Testing Reciprocity of Spin Pumping and Spin Transfer Torque in Ferromagnet/SpinOrbit Metal Heterostructures Carl Boone, Satoru Emori, Tianxiang Nan, Nian Sun Spin pumping from a ferromagnet (FM) to a normal metal (NM) and spin transfer torque (STT) generated in a FM from an injected spin current should be reciprocal processes governed by the spin mixing conductance. The same should be true for the spin Hall effect (SHE) and inverse SHE, which are used to generate and measure spin currents. Past experiments on multilayer thin films involving FM and NM interfaces have measured only spin pumping or spin injection, and have utilized incomplete modeling that results in different effective values for the same parameter such as the spin mixing conductance or spin Hall angle. This gives rise to a large range of values reported in the literature. Here we develop a complete model for spin flow in the FM/NM system including SHE, spin diffusion and spin pumping that allows us to determine the true values of the spin transport parameters. To explore the physcis we use STTferromagnetic resonance (FMR) experiments of NM/FM/NM trilayers, and FMR spectroscopy of FM/NM bilayers where we simultaneously measure damping changes due to spin pumping, voltage generated by the inverse SHE, and STT generated by the SHE. These experiments, combined with the complete modeling, allow us to test the reciprocity of spin pumping and STT plus the SHE and its inverse. [Preview Abstract] 
Friday, March 6, 2015 9:36AM  9:48AM 
Y28.00009: Spin pumping with interface spinorbit coupling Kai Chen, Shufeng Zhang The spin pumping has been formulated via a mixing conductance which characterizes the spindependent reflection coefficients [1]. The ``mixing conductance'' never mixes the spin at the interface, i.e., no spinflip processes have been taken into account up till now. We have recently reformulated the spin pumping via linear response approach in which the interface spinorbit coupling as well as spindiffusion driven backflow can be explicitly included. In some limiting cases, our formulation reduces to that of the previous theory. In the presence of the interface spinorbit coupling, the electron spin traveling through an interface will receive a spinorbit torque that rotates and absorbs the spin angular momentum. Among many distinctions with the previous theory [1], we predict a spatial dependent spin current in both magnetic and nonmagnetic layers, an anisotropic enhanced damping parameter, and a plausible resolution on the controversial experimental results obtained by different methods such as the inverse spin Hall signal and the broadening of ferromagnetic resonance linewidth. This work is supported by NSFECSS.\\[4pt] [1] Y. Tserkovnyak, A. Brataas and G. E. W. Bauer, Phys. Rev. Lett. 88, 117601 (2002). [Preview Abstract] 
Friday, March 6, 2015 9:48AM  10:24AM 
Y28.00010: Quantifying Spin Hall and Rashba effect contributions to spinorbit toque in magnetic bilayers Invited Speaker: John Q. Xiao Electrical control of magnetism has been energized by recent observation of spinorbit torques in magnetic bilayers made of a heavy metal (HM) and ferromagnet (FM). It has been demonstrated that the spinorbit torques driven by an inplane current can switch magnetization, manipulate magnetic domains and excite magnetization autooscillation. However, the microscopic mechanism for the spinorbit torques is still under debate. The question being whether the dominating spinorbit coupling (SOC) arises from the HM/FM interface due to the Rashba effect or arises in the bulk of HM due to the spin Hall effect, or a combination of the two. It has been theoretically demonstrated that both the Rashba effect and the spin Hall effect generate a fieldlike torque (T$_{\mathrm{SOF}})$ and dampinglike torque (T$_{\mathrm{SOT}})$ on the magnetization, with only quantitative differences. Therefore, an accurate method to determine the T$_{\mathrm{SOF}}$ and T$_{\mathrm{SOT}}$ with various thicknesses of the FM and HM are needed. We present a newly developed, magnetoopticKerreffect based spinorbit torque magnetometer that measures both T$_{\mathrm{SOF}}$ and T$_{\mathrm{SOT}}$, which can have both spatial and time resolution. We observed both T$_{\mathrm{SOF}}$ and T$_{\mathrm{SOT}}$ are nonlocal and does not require direct contact between FM and HM ...[1, 2]. By engineering the interface which modifies the Rashba interaction, we are able to show the coexistence of spin Hall and Rashba effect as well as quantify both contributions to spinorbit torques [1].\\[4pt] [1] Fan, X., H. Celik, J. Wu, C. Ni, K.J. Lee, V.O. Lorenz, and J.Q. Xiao, \textit{Quantifying interface and bulk contributions to spinorbit torque in magnetic bilayers.} Nature Communication, 2014. \textbf{January 9}: p. ncomms4042.\\[0pt] [2] Fan, X., J. Wu, Y.P. Chen, M.J. Jerry, H.W. Zhang, and J.Q. Xiao, \textit{Observation of the nonlocal spinorbital effective field.} Nature Communications, 2013. \textbf{4, April 30}. [Preview Abstract] 
Friday, March 6, 2015 10:24AM  10:36AM 
Y28.00011: Magnonic Charge Pumping via SpinOrbit Coupling Chiara Ciccarelli, Kjetil Hals, Andrew Irvine, Vit Novak, Yaroslav Tserkovnyak, Hidekazu Kurebayashi, Arne Brataas, Andrew Ferguson The interplay between spin, charge and orbital degrees of freedom has led to the development of spintronic devices such as spintorque oscillators and spintransfer torque MRAM. In this development, spin pumping represents a convenient way to electrically detect magnetization dynamics. The effect originates from direct conversion of lowenergy quantized spin waves in the magnet, known as magnons, into a flow of spins from the precessing magnet to adjacent leads. In this case, a secondary spincharge conversion element, such as heavy metals with large spin Hall angle~or multilayer layouts, is required to convert the spin current into a charge signal. Here, we report the observation of charge pumping in which a precessing ferromagnet pumps a charge current, demonstrating direct conversion of magnons into highfrequency currents via spinorbit interaction. The generated electric current, unlike spin currents generated by spinpumping, can be directly detected without the need of any additional spincharge conversion mechanism. The chargepumping phenomenon is generic and gives a deeper understanding of its reciprocal effect, the spin orbit torque, which is currently attracting interest for their potential in manipulating magnetic information. [Preview Abstract] 
Friday, March 6, 2015 10:36AM  10:48AM 
Y28.00012: Spin Circuit Representation for Spin Pumping Phenomena Kuntal Roy, Supriyo Datta There has been enormous progress in the field of spintronics and nanomagnetics in recent years with the discovery of many new materials and phenomena and it remains a formidable challenge to integrate these phenomena into functional devices and evaluate their potential. To facilitate this process a modular approach has been proposed whereby different phenomena are represented by spin circuit components [1]. Unlike ordinary circuit components, these spin circuit components are characterized by 4component voltages and currents (one for charge and three for spin). In this talk we will (1) present a spin circuit representation for spin pumping phenomena, (2) combine it with a spin circuit representation for the spin Hall effect [2] to show that it reproduces established results obtained earlier by other means, and finally (3) use it to propose a possible method for enhancing the spin pumping efficiency by an order of magnitude through the addition of a spin sink layer. [1] Kerem Camsari, Samiran Ganguly and Supriyo Datta, Modular Approach to Spintronics, https://nanohub.org/groups/spintronics [2] Seokmin Hong, Shehrin Sayed and Supriyo Datta, Spin Circuit Representation for the Spin Hall Effect, in review. [Preview Abstract] 
Friday, March 6, 2015 10:48AM  11:00AM 
Y28.00013: Dependence of the Spin Hall Torque Efficiency on the Transparency of PtFerromagnetic Layer Interfaces ChiFeng Pai, Yongxi Ou, Daniel C. Ralph, Robert A. Buhrman We report that spin current transport across Ptferromagnet (FM) interfaces is strongly dependent on the type and the thickness of the FM layer and on postdeposition processing protocols. By employing both harmonic voltage response measurements and spintorque ferromagnetic resonance measurements on various PtCo and PtCoFe magnetic heterostructures, we find that the efficiency of the Pt spin Hall effect in exerting a dampinglike spin torque on the FM ranges from $<$ 0.05 to $>$ 0.10 under different interfacial conditions. We also show that the temperature dependence of the spin torque efficiencies for both the dampinglike torque and fieldlike torque is dependent upon the details of the PtFM interface. The ``internal'' spin Hall angle of the Pt thin films used in this study, after taking the interfacial spin transmission factor that is derived from the spin mixing conductance into account, is estimated to be $\sim $0.20. This suggests that a careful engineering of PtFM interfaces can improve the spinHalltorque efficiency of Ptbased spintronic devices. [Preview Abstract] 
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