Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session R11: Spin-Hall IVFocus Session
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Sponsoring Units: GMAG DMP FIAP Chair: Igor Barsukov, UC Irvine Room: 307 |
Thursday, March 17, 2016 8:00AM - 8:36AM |
R11.00001: Magnonic charge-pumping and spin-orbit torques in conducting ferromagnets Invited Speaker: Arne Brataas In conducting ferromagnets, the spin-transfer torque and spin-motive force are known to exhibit a reciprocal relationship. Recent works on ferromagnets with strong spin-orbit coupling have revealed a rich complexity of the interaction between itinerant charge carriers and magnetization. As a result, currents can also induce magnetization excitations via spin-orbit torques, sometimes in more efficient ways than via spin-transfer torques. The reciprocal phenomenon of spin-orbit torques is magnonic charge-pumping. We will discuss how the material symmetry governs spin-orbit torques and magnonic charge-pumping. We will also relate magnonic charge pumping and spin-orbit torques via the Onsager reciprocal relations. Finally, we will give examples for important classes of systems including isotropic ferromagnets with nonuniform magnetization. [Preview Abstract] |
Thursday, March 17, 2016 8:36AM - 8:48AM |
R11.00002: The Spin Hall Effect in Rare Earth Thin Films Neal Reynolds, Jonathan Gibbons, John Heron, Darrell Schlom, Daniel Ralph The spin Hall effect results in a spin current which flows transverse to an applied electric field in non-magnetic materials. We report measurements of the strength of the spin Hall effect in a series of lanthanide rare earth materials in order to determine whether the large spin and orbital moments in f-electron materials might enhance the spin Hall effect. To ensure trustworthy results, we compare the results of several complementary measurement techniques: off-resonant electrical and optical second harmonic detection of current-induced magnetic tilting, spin-torque ferromagnetic resonance, and spin pumping. We compare the results to ab-initio calculations of the intrinsic Berry curvature contribution to spin Hall effect. [Preview Abstract] |
Thursday, March 17, 2016 8:48AM - 9:00AM |
R11.00003: Towards brain-inspired computing with spin-torque nano-oscillators Julie Grollier, Jacob Torrejon, Mathieu Riou, Vincent Cros, Damien Querlioz, Sumito Tsunegi, Akio Fukushima, Hitoshi Kubota, Shinji Yuasa, Guru Khalsa, Mark D. Stiles The brain displays many features typical of non-linear dynamical networks, such as synchronization or chaotic behaviour. These observations have inspired a whole class of models that harness the power of complex non-linear dynamical networks for computing. In this framework, neurons are modeled as non-linear oscillators, and synapses as the coupling between oscillators. These abstract models are very good at processing waveforms for pattern recognition or at generating precise time sequences useful for robotic motion. However there are very few hardware implementations of these systems, because large numbers of interacting non-linear oscillators are indeed. In this talk, I will show that coupled spin-torque nano-oscillators are very promising for realizing cognitive computing at the nanometer and nanosecond scale, and will present our first results in this direction. [Preview Abstract] |
Thursday, March 17, 2016 9:00AM - 9:12AM |
R11.00004: Oscillatory spin transport in spin Hall multilayers Igor Barsukov, A. M. Gonçalves, P. Soledade, C. A. C. Passos, M. Costa, N. M. Souza-Neto, F. Garcia, H. K. Lee, A. Smith, O. Tretiakov, I. N. Krivorotov, L. C. Sampaio We study multilayers of sputtered Pt/(d)Cu/Py as a function of the Cu thickness d using ferromagnetic resonance (FMR). The FMR linewidth reveals a linear dependence on the frequency with negligible inhomogeneous contribution. The Gilbert damping falls smoothly with increasing d, but presents a strong superimposed oscillation with a period of \textasciitilde 1.5nm. We attribute this behavior to RKKY-like spin transport in the confinement of the Cu layer. The induced perpendicular anisotropy due to the proximity effect shows a similar behavior. We evaluate the induced magnetic moment on Pt using x-ray magnetic circular dichroism and find that it decreases with increasing Cu thickness smoothly. Again, we see oscillations of the magnetic moment and show that the oscillatory spin transport affects proximity induced magnetism in Pt. We extend our study to multilayer systems with increased oxidation levels and with out-of-plane crystal texture, in order to investigate the effects of disorder and electron's k-vectors that are responsible for the oscillatory spin transport. [Preview Abstract] |
Thursday, March 17, 2016 9:12AM - 9:24AM |
R11.00005: Magnon emission and radiation induced by spin--polarized current. Andrei Zholud, Ryan Freeman, Rongxing Cao, Sergei Urazhdin The spin-torque effect due to spin injection into ferromagnets can affect their effective dynamical damping, and modify the magnon populations. The latter leads to the onset of nonlinear damping that can prevent spontaneous current-induced magnetization oscillations. It has been argued that these nonlinear processes can be eliminate by the radiation of magnons excited by local spin injection in extended magnetic films. To test these effects, studied of the effects of spin injection on the magnon populations in nanoscale spin valves and magnetic point contacts. Measurements of the giant magnetoresistance show a significant resistance component that is antisymmetric in current, and linearly dependent on temperature T. This component is significantly larger for the nanopatterned ferromagnets than for point contacts. We interpret our observations in terms of stimulated generation of magnons by the spin current, and their radiation in point contacts. 1. V.E. Demidov, S. Urazhdin, H. Ulrichs, V. Tiberkevich, A. Slavin, D. Baither, G. Schmitz, and S. O. Demokritov, Nature Mater., \textbf{11}, 1028-1031 (2012) [Preview Abstract] |
Thursday, March 17, 2016 9:24AM - 9:36AM |
R11.00006: Electric probe for spin transition and fluctuation Zhiyong Qiu, Jia Li, Dazhi Hou, Elke Arenholz, Alpha T. N’Diaye, Ali Tan, Ken-ichi Uchida, Koji Sato, Yaroslov Tserkovnyak, Z. Q. Qiu, Eiji Saitoh Spin fluctuation and transition have always been one of central topics of magnetism and condense matter science. To probe them, neutron scatterings have been used as powerful tools. A part of neutrons injected into a sample is scattered by spin fluctuation inside the sample. This process transcribes the spin fluctuation onto scattering intensity, which is commonly represented by dynamical magnetic susceptibility of the sample and is maximized at magnetic phase transitions. Importantly, a neutron carries spin without electric charge, and it thus can bring spin into a sample without being disturbed by electric energy: an advantage of neutrons, although large facilities such as a nuclear reactor is necessary. Here we show that spin pumping, frequently used in nanoscale spintronic devices, provides a desktop micro probe for spin fluctuation and transition; not only a neutron beam, spin current is also a flux of spin without an electric charge and its transport reflects spin fluctuation in a sample. We demonstrate detection of anti-ferromagnetic transition in ultra-thin CoO films via frequency dependent spin-current transmission measurements. [Preview Abstract] |
Thursday, March 17, 2016 9:36AM - 9:48AM |
R11.00007: Electrical manipulation of a ferromagnet by an antiferromagnet V Tshitoyan, C Ciccarelli, A P Mihai, M Ali, A C Irvine, T A Moore, T Jungwirth, A J Ferguson Several recent studies of antiferromagnetic (AFM) spintronics have focused on transmission and detection of spin-currents in AFMs. Efficient spin transmission through AFMs was inferred from experiments in FM/AFM/NM (normal metal) structures. Measurements in FM/AFM bilayers have demonstrated that a metallic AFM can also act as an efficient ISHE detector of the spin-current, with spin-Hall angles comparable to heavy NMs. Here we demonstrate that an antiferromagnet can be employed for a highly efficient electrical manipulation of a ferromagnet. We use an all-electrical excitation and detection technique of ferromagnetic resonance in a NiFe/IrMn bilayer. We observe antidamping-like spin torque acting on the NiFe generated by the in-plane current driven through the IrMn antiferromagnet. A large enhancement of the torque, characterized by an effective spin-Hall angle exceeding most heavy transition metals, correlates with the presence of the exchange-bias field at the NiFe/IrMn interface. It highlights that, in addition to strong spin-orbit coupling, the AFM order in IrMn governs the observed phenomenon. [Preview Abstract] |
Thursday, March 17, 2016 9:48AM - 10:00AM |
R11.00008: Spin pumping and inverse spin Hall effects in heavy metal/antiferromagnet/Permalloy trilayers Hilal Saglam, Wei Zhang, M. Benjamin Jungfleisch, Wanjun Jiang, John E. Pearson, Axel Hoffmann Recent work shows efficient spin transfer via spin waves in insulating antiferromagnets (AFMs) [1], suggesting that AFMs can play a more active role in the manipulation of ferromagnets. We use spin pumping and inverse spin Hall effect experiments on heavy metal (Pt and W)/AFMs/Py (Ni$_{80}$Fe$_{20})$ trilayer structures, to examine the possible spin transfer phenomenon in metallic AFMs, $i.e.$, FeMn and PdMn. Previous work has studied electronic effects of the spin transport in these materials, yielding short spin diffusion length on the order of 1 nm [2]. However, the work did not examine whether besides diffusive spin transport by the conduction electrons, there are additional spin transport contributions from spin wave excitations [1]. We clearly observe spin transport from the Py spin reservoir to the heavy metal layer through the sandwiched AFMs with thicknesses well above the previously measured spin diffusion lengths, indicating that spin transport by spin waves may lead to non-negligible contributions. [1] H.~Wang, et al., Phys. Rev. Lett. \textbf{113}, 097202 (2014). [2] W. Zhang et al., Phys. Rev. Lett. \textbf{113}, 196602 (2014). [Preview Abstract] |
Thursday, March 17, 2016 10:00AM - 10:12AM |
R11.00009: Phase-sensitive inductive detection of ac currents due to spin-pumping/inverse spin Hall effect in unpatterned Permalloy/Pt bilayers Thomas Silva, Hans Nembach, Justin Shaw, Alexy Karenowska, Mathias Weiler We present a new method to measure the ac inverse spin Hall effect at GHz frequencies. Unlike previous methods [1-3], our does not rely on any patterning or electrical contacts. We utilize phase-sensitive, broad-band, perpendicular-field ferromagnetic resonance to detect the ac current by the inverse spin Hall effect (iSHE) in Py/Pt bilayers. The iSHE component of the signal is non-linear in the excitation frequency; while the inductive FMR response scales linearly with frequency, the iSHE signal scales quadratically because the iSHE current itself is proportional to dm/dt. This differential gain affords us detection of previously unreported higher order contributions to the iSHE signal. We compare FMR measurements with a control samples that do not include the high spin-orbit layer, e.g. Pt. Data sets with and without Pt are normalized by the complex Polder susceptibility, which nullifies any effects due to differences in line-width and anisotropy. The complex ratio of the normalized inductive amplitudes is analyzed with a simple model that considers how the ac currents generated by the iSHE couple inductively back into the excitations waveguide. The linear iSHE signal agrees with previous reported values. The nonlinear iSHE signal is 3-4 orders of magnitude weaker, but is easily detected over the frequency range of 5-45 GHz. [1] M. Weiler, et al., PRL 113, 157204 (2014), [2] C. Hahn, et al., PRL 111, 217204 (2013) [3] D. Wei, et al., Nat. Comm. 5, (2014) [Preview Abstract] |
Thursday, March 17, 2016 10:12AM - 10:24AM |
R11.00010: Extrinsic Spin Hall effect of AuW alloys Piotr Laczkowski, Juan Carlos Rojas-Sánchez, Williams Savero-Torres, Nicolas Reyren, Cyril Deranlot, Jean-Marie George, Henri JAFFRES, Cyril Beigné, Lucien Notin, Sophie Collin, Alain Marty, Jean-Philippe Attané, Laurent VILA, FREDERIC PETROFF, Albert FERT The spin Hall effect (SHE) allows a reciprocal conversion between charge and spin currents using spin orbit interactions. Large Spin Hall angle have been reported in transition metals (Pt, W, Beta-Ta) and in alloys made of heavy metals [1]. We will report on SHA in AuW alloys [2] exhibiting a non-monotonic relation with W content. In this regime, it suggests a skew-scattering to side-jump dominant contribution to the spin Hall resistivity, thus allowing precise tuning of SHA vs. W content. We will present experiments by using Lateral Spin Valves with refined spin-absorption model adapted to strong spin-orbit interactions. By using complementary FMR/Spin-Pumping techniques, we demonstrate very large SHA of the order of 15~{\%} at rather high W concentration in rather good agreement with the previous method. [1] \textit{PRL} \textbf{109, }156602 (2012), \textit{PRB} \textbf{89,} 054401 (2014), [2] P. Laczkowski \textit{et al.}, \textit{APL} \textbf{104}, 142403 (2014) . [Preview Abstract] |
Thursday, March 17, 2016 10:24AM - 11:00AM |
R11.00011: Chiral damping in magnetic domain walls dynamics Invited Speaker: Emilie Ju\'e Domain wall (DW) motion in materials with structural inversion asymmetry (SIA) and high spin-orbit coupling has attracted much interest in the recent years due to the discovery of unexpected physical mechanisms. Especially, it has been shown that the DW dynamics in such materials can be explained by chiral DWs with (partly or fully) N\'{e}el structure, whose stability derives from an interfacial Dzyaloshinskii-Moriya interaction (DMI) [1]. In this work, we show that DMI is not the only effect inducing chiral dynamics and demonstrate the existence of a chiral damping. This result is supported by the study of the asymmetry induced by an in-plane magnetic field on field induced domain wall motion in perpendicularly magnetized asymmetric Pt/Co/Pt trilayers. Using time reversal properties, we show that this asymmetry cannot be attributed to an effective field but originates from a purely dissipative mechanism. The observation of chiral damping, not only enriches the spectrum of physical phenomena engendered by the SIA, but since it can coexist with DMI it is essential for conceiving DW and skyrmion devices. [1] A. Thiaville, et al., EPL 100, 57002 (2012) [Preview Abstract] |
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