Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session M8: Focus Session: Spin Hall Effect and Related Phenomenon |
Hide Abstracts |
Sponsoring Units: GMAG DMP FIAP Chair: Luqiao Liu, IBM TJ Watson Research Center Room: 104 |
Wednesday, March 5, 2014 11:15AM - 11:51AM |
M8.00001: Inverse Spin Hall Effect in a Ferromagnetic Metal Invited Speaker: Bingfeng Miao Recently, intense attention has been focused on the generation, detection, and exploitation of pure spin current. Only few mechanisms, among them spin Hall effect (SHE) [1], lateral spin valve [2], spin pumping [3] and spin Seebeck effect (SSE) [4], can generate a pure spin current. Once generated, a pure spin current cannot be detected electrically but by the inverse spin Hall effect (ISHE) that converts it back into a charge current. To date, ISHE has been observed only in non-magnetic metals, such as Pt and Au, with a strong spin-orbit coupling. We report the observation of ISHE in a ferromagnetic metal permalloy (Py) on ferromagnetic insulator yttrium iron garnet (YIG) [5]. Through controlling the spin current injection by altering the Py/YIG interface, we have isolated the spin current contribution and demonstrated the ISHE in a ferromagnetic metal, the reciprocal phenomenon of anomalous Hall effect. A large spin Hall angle in Py, determined from Py thin films of different thicknesses, indicates many other ferromagnetic metals may be exploited as superior pure spin current detectors and for applications in spin current.\\[4pt] [1] Hirsch, J. E. Spin Hall Effect. Phys. Rev. Lett., 83, 1834-1837 (1999).\\[0pt] [2] Valenzuela, S. O., Tinkham, M. Direct electronic measurement of the spin Hall effect. Nature, 442, 176-179 (2006).\\[0pt] [3] Saitoh, E., Ueda, M., Miyajima, H., Tatara, G. Conversion of spin current into charge current at room temperature: Inverse spin-Hall effect. Appl. Phys. Lett., 88, 182509-182503 (2006).\\[0pt] [4] Uchida, K., Xiao, J., Adachi, H., Ohe, J., Takahashi, S., Ieda, J., et al. Spin Seebeck insulator. Nature Mater, 9, 894-897 (2010). \\[0pt] [5] Miao, B. F., Huang, S. Y., Qu, D. R., Chien, C. L. Inverse spin Hall effect in a ferromagnetic metal. Phys. Rev. Lett., 111, 066602 (2013). [Preview Abstract] |
Wednesday, March 5, 2014 11:51AM - 12:03PM |
M8.00002: Spin Hall effect tunneling spectroscopy Luqiao Liu, Ching-tzu Chen, Jonathan Sun, Guohan Hu, Daniel Worledge The spin Hall effect (SHE) has attracted a lot research interest recently. Up to now, almost all of the experimental efforts related to the SHE have been focused on utilizing or characterizing electrons at the Fermi surface (FS). In this talk, we will report a technique with which one can determine the magnitude of the SHE under finite bias voltage. In our study, the spin Hall effect (SHE) was measured by injecting a spin polarized current from a ferromagnet electrode into SHE materials through an insulating tunnel barrier. By applying a combination of DC and AC current across the tunnel barrier, we were able to probe the SHE under finite biases via measuring the generated transverse voltage. Two different materials, Ta and Pt were examined with this technique. Under zero bias, the obtained SH angles agree well with previous results determined through the SHE induced switching and oscillation experiments, while below and above the FS, the SHE in those two materials shows different voltage dependences. The experimentally determined voltage dependence of the SHE can be used to check the validity of various types of band structure calculations and it also provides a guideline on further increasing the magnitude the SHE via electronic structure engineering. [Preview Abstract] |
Wednesday, March 5, 2014 12:03PM - 12:15PM |
M8.00003: ABSTRACT WITHDRAWN |
Wednesday, March 5, 2014 12:15PM - 12:27PM |
M8.00004: The spin Hall effect in single-crystal platinum Gregory M. Stiehl, John T. Heron, Neal Reynolds, Alex Mellnik, Robert A. Buhrman, Darrell G. Schlom, Daniel C. Ralph We have developed a process to grow thin films of single-crystal platinum by DC magnetron sputtering at elevated temperatures with post growth annealing. We have incorporated these films into bilayers with polycrystalline permalloy (Ni$_{\mathrm{80}}$Fe$_{\mathrm{20}})$ for measurements of the spin transfer torque generated by the spin Hall effect in the platinum. We will compare measurements of the strength of the spin Hall effect, the spin diffusion length, and the Pt/permalloy spin mixing conductance between these samples and samples containing a polycrystalline Pt layer. With these studies we hope to understand better how disorder may affect the generation of spin currents by the spin Hall effect and the transmission of spin currents from a spin Hall metal to a ferromagnet. [Preview Abstract] |
Wednesday, March 5, 2014 12:27PM - 12:39PM |
M8.00005: The spin Hall effect and spin-orbit torques in SH-metal/normal metal/ferromagnetic trilayers Minh-Hai Nguyen, Chi-Feng Pai, Daniel C. Ralph, Robert A. Buhrman The spin Hall effect (SHE) in ferromagnet/transition metal bilayer structures has been demonstrated to be a powerful means for producing pure spin currents and for exerting spin-orbit damping-like and field-like torques on the ferromagnetic layer. Large spin Hall angles have been reported for Pt, $\beta$-Ta and $\beta$-W films and have been utilized to achieve magnetic switching of in-plane and out-of-plane magnetized nanomagnets, spin torque auto-oscillators, and the control of high velocity domain wall motion. In general the spin orbit torques and the effective damping are predicted to depend directly on the spin-mixing conductance of the SHE/ferromagnet interface. This opens up the possibility of tuning these properties with the insertion of a very thin layer of another metal between the SH metal and the ferromagnet. Here we will report on experiments with such trilayer structures where we have studied the variation of the effective spin Hall angle and the effective damping constant with the choice and thickness of the insertion layer. Our results indicate that there is considerable opportunity to optimize the effectiveness and energy efficiency of the damping-like torque through engineering of such trilayer structures. [Preview Abstract] |
Wednesday, March 5, 2014 12:39PM - 12:51PM |
M8.00006: Determination of the spin diffusion length via spin pumping and spin Hall effects Wei Zhang, Vincent Vlaminck, John Pearson, Ralu Divan, Samuel Bader, Axel Hoffmann We present an experimental approach for determining the spin diffusion length of various metals by using spin pumping -- spin Hall effect via a coplanar waveguide ferromagnetic resonance (CPW-FMR) broadband technique. By studying the ratio of two voltage components (anisotropic magnetoresistance and inverse spin Hall effect) as a function of the metal layer thickness, the spin diffusion length of the material can be directly extracted. As examples, we determined spin diffusion lengths for paramagnetic Pt (1.2 nm), Pd (5 nm), Ir (0.5 nm), and antiferromagnetic IrMn (0.75 nm) at room temperature. In addition, temperature-dependent measurements show only weak dependence of these lengths with temperature. This approach for determining the spin diffusion length at any temperatures has the advantage that it does not require knowing the resistivity value of the metal layer, which changes with both thickness and temperature. Finally, the ratio of the two voltage components can also be used to probe the temperature-dependent proximity effect for metals such as Pt. [Preview Abstract] |
Wednesday, March 5, 2014 12:51PM - 1:03PM |
M8.00007: Sign change of spin Hall effect due to electron correlation in CuIr alloys Zhuo Xu, Bo Gu, Michiyasu Mori, Tim Ziman, Sadamichi Maekawa Recently the predominant extrinsic skew scattering mechanism with a positive spin Hall angle (SHA) was experimentally observed in nonmagnetic CuIr alloys [Niimi et al., Phys. Rev. Lett. 106, 126601 (2011)], while the negative SHA was obtained by ab initio simulation if the consistent definition of SHA is used [Fedorov et al., Phys. Rev. B 88, 085116 (2013)]. We reconsider the SHA in CuIr alloys by the quantum Monte Carlo method, where the Coulomb correlation U in 5d orbitals of Ir impurities is properly included. It indicates that the SHA is negative without electron correlation (U=0), and becomes positive when an electron correlation of U=0.5 eV is included, which is consistent with the experiment. It opens a way to control the sign of SHA by electron correlation in novel spintronic devices. [Preview Abstract] |
Wednesday, March 5, 2014 1:03PM - 1:15PM |
M8.00008: Manipulation of Magnetic Insulators Using Spin Torque from the Spin Hall Effect Colin Jermain, Hanjong Paik, John Heron, Sriharsha Aradhya, Darrell Schlom, Dan Ralph We will report the growth and fabrication of devices incorporating thin films of the magnetic insulators yttrium iron garnet and lutetium iron garnet with thicknesses less than 20 nm. We perform the growth using oxide MBE, achieving high-quality films with magnetic damping parameters for single 5 nm films as small as 0.00036. We use electron beam lithography and ion milling to pattern the films into device structures with sizes ranging from 100 nm to above 1 micron, integrated with Ta contacts so that we can use the spin Hall effect to apply spin-transfer torque to the magnetic materials. We will use these devices to study how the spin Hall torque affects the effective magnetic damping parameter of isolated magnetic insulator devices, and whether spin Hall torque can be used to drive reliable magnetic switching in these materials at low current levels. [Preview Abstract] |
Wednesday, March 5, 2014 1:15PM - 1:27PM |
M8.00009: Spin-cluster Formation and Spin-Hall Effect in a Pyrochlore Magnet Hiroaki Ishizuka, Yukitoshi Motome Metallic magnets with interacting localized moments and itinerant electrons are known to be the source of various fascinating phenomena. Recent theoretical studies on the spin-charge coupled systems have shown that the presence of frustration further gives rise to nontrivial magnetic states as well as transport phenomena. These situations are expected to be realized in pyrochlore and triangular metallic magnets, which have gained much interest due to their peculiar magnetism and transport properties. In this study, to explore novel phases and transport phenomena that may take place in the frustrated spin-charge coupled systems, we studied a double-exchange model on a pyrochlore lattice with spin-ice type localized moments [1]. By using a Monte Carlo technique, we show that the model shows peculiar spin-cluster formation induced by competition between the double-exchange interaction and the super-exchange interaction between the localized moments. Furthermore, we show that the peculiar intermediate phase accompanies an unconventional spin-Hall effect which originates from noncollinear spin configurations. [1] H. Ishizuka and Y. Motome, PRB 88 100402 (2013). [Preview Abstract] |
Wednesday, March 5, 2014 1:27PM - 1:39PM |
M8.00010: Electrical spin manipulation in spin-orbit coupling systems Akihito Takeuchi, Naoto Nagaosa Generation of spin by applying as electric current in a spin-orbit coupling system has been investigated with much theoretical and experimental attention in spintronics. Although the electronic spin is the well-defined quantity, the spin is not conserved in the presence of spin-orbit interaction and therefore the theoretical definition of spin current is not uniquely given. To resolve this ambiguity in the definition, the non-Abelian gauge theory is one of the possible solutions. By associating the spin-orbit interaction with the non-Abelian vector potential, a proper definition of spin current is given on the basis of the SU(2) gauge invariance and the electronic spin is covariantly conserved. In this context, we present theoretically a general form of spin polarization in terms of an effective Yang-Mills field corresponding to the spin-orbit interaction and usual U(1) Maxwell electromagnetic field. In particular, we focus on a purely electrical spin manipulation, and we find that both of the spin Hall effect and the inverse of the spin galvanic effect arise from the same origin, i.e., the SU(2)$\times$U(1) Hall effect. [Preview Abstract] |
Wednesday, March 5, 2014 1:39PM - 1:51PM |
M8.00011: Driving a uniform magnetization to a metastable, mixed state by Spin Hall Effect Spin Torque Debanjan Bhowmik, Mark Nowakowski, Long You, David Keating, Mark Wong, Jeffrey Bokor, Sayeef Salahuddin Spin Hall effect based magnetic switching and domain wall motion have recently attracted a lot of attention both from a fundamental and an application perspective [1,2,3]. In that context it is important to understand how spin Hall current acts on a uniform magnetization in the absence of external magnetic field. We observe that in Hall bars made from a thin film stack of Ta (10 nm)/CoFeB (1 nm)/MgO (1 nm)/Ta (10 nm) a current pulse of magnitude 5x10$^6$ A/sq. cm. drives a uniformly polarized magnet to a metastable mixed state of up and down polarized domains. We have experimentally confirmed the mixed state through anomalous Hall effect measurement and magneto-optic Kerr effect imaging. The magnet breaks into domains due to nucleation of domain walls followed by free domain wall motion as a result of depinning of the domain walls from defects by the spin Hall torque.\\[4pt] [1] Liu, L. \textit{et al. Science }\textbf{336,} 555-558 (2012).\\[0pt] [2] Bhowmik, D. \textit{et al.} Nature Nanotechnology (2013), DOI:10.1038/nnano.2013.241.\\[0pt] [3] Emori, S. \textit{et al. }Nature Materials \textbf{12}, 611-616 (2013). [Preview Abstract] |
Wednesday, March 5, 2014 1:51PM - 2:03PM |
M8.00012: Spin Hall effect excited parametric resonance in permalloy/platinum nanowires Liu Yang, Zheng Duan, Andrew Smith, Brian Youngblood, Ilya Krivorotov We report measurement of Spin Hall effect excited parametric resonance of spin wave modes in Permalloy (Py) / Platinum (Pt) bilayer nanowires. The excitation of the parametric resonance is assisted by spin torque from direct Spin Hall current generated in the Pt layer, which acts like effective negative magnetic damping on Py magnetization. A saturating in-plane magnetic field is applied perpendicular to the wire axis. We simultaneously apply a direct and a microwave current to the nanowire and measure voltage as a function of magnetic field. At approximately twice the frequency of the spin wave eigenmodes in the Py wire in the field range used in the experiment, peaks in voltage versus field are observed above a threshold value of the ac current. The double frequency of the drive and the threshold character of the excitation demonstrate the parametric nature of the excited resonance. We also measured the dependence of the voltage peak amplitude on the microwave current amplitude measured for several values of the direct current bias applied to the nanowire. It's found that the threshold ac current shifts to lower values at higher dc bias, indicating that dc spin Hall current injected from Pt into Py reduces the effective damping in the Py layer. [Preview Abstract] |
Wednesday, March 5, 2014 2:03PM - 2:15PM |
M8.00013: Dependence of the spin Hall effect in platinum / ferromagnet bilayers on the composition of the ferromagnet Weifeng Zhang, Wei Han, Xin Jiang, Stuart Parkin The spin Hall effect (SHE) provides a mechanism by which charge current is converted to a pure spin current via spin--orbit interactions. These spin currents can be used to manipulate magnetization via diffusion of the spin current into neighboring magnetic layers, and, conversely, the change in the magnetization in the presence of such spin currents can be used to infer the magnitude and sign of the spin accumulation generated via the SHE. Recently, it has been recognized that large spin currents are generated in platinum layers via the SHE and that these strongly influence the current induced motion of domain walls in coupled magnetic layers. A variety of experimental techniques have been used to measure the SHE in Pt but these give inconsistent results. We have studied the SHE in Pt layers that are coupled to several different ferromagnetic layers, including, permalloy (Py), Ni, Co, and CoFeB alloys. The spin Hall angle is characterized using the spin torque ferromagnetic resonance technique. We find that there is a strong dependence of the spin Hall angle in Pt on the ferromagnetic layer to which it is coupled. The interface between the ferromagnetic layer and Pt plays a central role in determining the magnitude of the SHE which will be the focus of this talk. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700