Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session E41: Spin Hall effectsFocus

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Sponsoring Units: GMAG Chair: Hailong Wang, Massachusetts Institute of Technology Room: BCEC 209 
Tuesday, March 5, 2019 8:00AM  8:36AM 
E41.00001: Unidirectional spinHall and Rashba−Edelstein magnetoresistance in topological insulatorferromagnet layer heterostructures Invited Speaker: Yang Lv The large spin−orbit coupling in topological insulators results in helical spintextured Dirac surface states that are attractive for topological spintronics. These states generate an efficient spin−orbit torque on proximal magnetic moments. However, memory or logic spin devices based upon such switching require a nonoptimal threeterminal geometry, with two terminals for the writing current and one for reading the state of the device. An alternative twoterminal device geometry is now possible by exploiting the recent discovery of the unidirectional spin Hall magnetoresistance in heavy metal/ferromagnet bilayers and unidirectional magnetoresistance in magnetic topological insulators. Here, we report the observation of such unidirectional magnetoresistance in a technologically relevant device geometry that combines a topological insulator with a conventional ferromagnetic metal. Our devices show a figure of merit (magnetoresistance per current density per total resistance) that is more than twice as large as the highest reported values in allmetal Ta/Co bilayers. 
Tuesday, March 5, 2019 8:36AM  8:48AM 
E41.00002: Giant Spin Hall Effect in Magnetron sputtered W_{3}Ta thin films Mohsin Zamir Minhas, Ilya Kostanovskiy, Stuart S Parkin, Mazhar Nawaz Ali The spin Hall effect (SHE), in nonmagnetic (NM) metals with strong spinorbit coupling (SOC) has received much attention due to potential technological applications like magnetic randomaccess memory (MRAM) and spinlogic devices. Large spin Hall angles (SHA, the ratio of J_{s}/J_{c}) have been observed in materials like Pt and βW (a.k.a. W_{3}W in the A15structure), particularly when doped with oxygen reaching a peak value of 0.45. Recently, W_{3}Ta (and other A15 compounds) was theoretically predicted to host an even larger intrinsic SHE than βW, originating from the large spin Berry curvature of its electronic band structure. Here we present experimental results on magnetron sputtered W_{3}Ta thin films, fabricated in Hall bar geometries using standard lithography and deposition techniques. The SHA was measured using STFMR on films of various thicknesses. Also, SHAs of various W_{4x}Ta_{x} compositions will be presented and compared with theoretical predictions. 
Tuesday, March 5, 2019 8:48AM  9:00AM 
E41.00003: Giant intrinsic orbital Hall effects in weakly spinorbit coupled metals Daegeun Jo, Dongwook Go, HyunWoo Lee Recently, it was proposed that the intrinsic orbital Hall effect (OHE) can emerge from momentumspace orbital texture in centrosymmetric materials [1]. In searching for real materials with strong OHE, we investigate the intrinsic OHE in metals with small spinorbit coupling (SOC) in facecentered cubic (Al, Mn, and Ni) and bodycentered cubic structures (Li, V, Cr, and Mn). We find that these materials can have the giant orbital Hall conductivities (OHCs) ∼ 10^{3} − 10^{4} (h/e)(Ω cm)^{1}, which are comparable or larger than spin Hall conductivity (SHC) of Pt. We also show SHCs in these materials are sizable and the spin Hall angles may be of the order of 0.1, although SHCs are smaller than OHCs due to small SOC. We discuss implications on recent spincharge interconversion experiments on materials having small SOC. 
Tuesday, March 5, 2019 9:00AM  9:12AM 
E41.00004: Ab initio calculation of intrinsic anomalous and spin Hall conductivity using localized pseudoatomic orbitals Juwon Oh, Hyoung Joon Choi For firstprinciples calculation of intrinsic anomalous Hall conductivity (AHC) and spin Hall conductivity (SHC), we implemented AHC and SHC formulas into the SIESTA code, which uses localized pseudoatomic orbitals to expand electronic wavefunctions. We calculate AHC from the Brillouin zone integration of the Berry curvature, and SHC by replacing a velocity operator in the AHC formula with a symmetrized product of spin and velocity operators. For AHC and SHC calculations, it is crucial to perform noncollinearspin calculations including the spinorbit coupling. We conduct AHC calculations of Fe, Co and SHC calculations of Pd, Pt and Ta. We compare our calculations with experimental results. We also investigate Berry curvature along high symmetry k points and the energy dependence of AHC and SHC. 
Tuesday, March 5, 2019 9:12AM  9:24AM 
E41.00005: Realspace Picture of the Intrinsic Anomalous Hall Effect Fei Xue, Paul Haney The intrinsic anomalous Hall effect is commonly expressed as the integral of Berry curvature in the reciprocal space. It has been shown that this intrinsic effect can also be computed in real space for systems which lack periodicity (e.g finite or open systems). Motivated by this, we study a tightbinding toy model to show that the intrinsic anomalous Hall effect could be interpreted in terms of an electric fieldinduced change in the charge quadropole moment. We additionally present a firstprinciple calculation of bcc Fe and demonstrate how the charge quadrupole moments changes in the presence of electric field. We also consider a real space interpretation of intrinsic antidamping torques in a ferromagnet/heavy metal bilayer system. 
Tuesday, March 5, 2019 9:24AM  9:36AM 
E41.00006: Intrinsic spin Hall effect in nonmagnetic compounds Yang Zhang, Qiunan Xu, Jakub Zelezny, Tomas Jungwirth, Claudia Felser, Jeroen Van den Brink, Yan Sun The spin Hall effect (SHE), i.e., conversion of charge current to spin current without magnetic moment, has gained intensive interests over the last decade since the study of its intrinsic mechanism and the observation of it in experiments. Owing to its natural functions of spin current generation, detection, and manipulation, SHE meets the fundamental requirements for the spintronics. In this work, we performed an extensive study of the intrinsic SHE for all the existing nonmagnetic materials, and provide an intrinsic SHC database including approximately 20000 compounds. From this database, we extracted a universal origin for strong SHE, the mirror symmetry protected nodal lines that are gapped out by spinorbit coupling. This extensive study of intrinsic SHE in materials via numerical predictions offers a good platform to experimental design strong SHE, and it is helpful for the comprehensive understanding of the SHE via statistical analysis. 
Tuesday, March 5, 2019 9:36AM  9:48AM 
E41.00007: Large spin Hall conductivity in Pt as measured with noncontact microwave spectroscopy Andrew Berger, Eric Edwards, Hans T. Nembach, Alexy Karenowska, Mathias Weiler, Olof Karis, Mark Keller, Thomas Silva By use of microwave spectroscopy, we have measured the spin Hall effect (SHE) and spin transparency in bilayers of Ni80Fe20/Pt. The method uses a phasesensitive amplitude analysis of FMR spectra with unpatterned thin films that are proximate to, but not electrically connected with a coplanar waveguide [1]. Both SHE and iSHE are measured simultaneously, as mandated by Onsager reciprocity. The method does not require the samples to have an easy axis, nor knowledge of the precession angle. Damping is simultaneously measured, permitting selfconsistent fitting of the SHE and spin pumping signals [2]. In agreement with previous reports [3], the spin transport efficiency between Ni80Fe20 and Pt is << 1, presumably due to interfacial spin memory loss. Also, the transparency is a strong function of deposition order, with a 3x reduction when Ni80Fe20 is grown on Pt. While the effective SHE signal and spin diffusion length are comparable to previous reports [4], substantial spin memory loss implies a larger value for the intrinsic SHE ratio of Pt (~ 0.4) than previously reported. [1] Berger, A. J., et al. (2018). PRB 97 094407. [2] Berger, A. J., et al. (2018). PRB 98 024402. [3] RojasSánchez, J.C., et al. (2014). PRL 112 106602. [4] Nguyen, M.H., et al. (2016). PRL 116 126601 
Tuesday, March 5, 2019 9:48AM  10:00AM 
E41.00008: Anisotropic and spin Hall magnetoresistance in FeRh/Pt bilayers Joseph Sklenar, Hilal Saglam, Junseok Oh, Greg Hamilton, Yi Li, Wei Zhang, Matthew Gilbert, Axel F Hoffmann, Nadya Mason We have sputtered epitaxial films of BCC FeRh with thicknesses between 7.535 nm on (100) MgO, capped with 5nm Pt. Magnetometry and magnetotransport measurements indicate a firstorder transition from ferromagnetic to antiferromagnetic order below room temperature. We have structured lithographically the films into Hall bars and nanowires, such that the current is directed along different crystalline orientations. The angulardependent magnetoresistance of all devices is measured in both the ferromagnetic and antiferromagnetic phase, and there is evidence for both intrinsic anisotropic magnetoresistance as well as spin Hall magnetoresistance contributing to the measured signal. In the antiferromagnetic phase we measure drastically different angular signals depending on whether the current is along the (100) or (110) direction. 
Tuesday, March 5, 2019 10:00AM  10:12AM 
E41.00009: Spin hall effect in SrIrO_{3} measured by spin torque ferromagnetic resonance_{ } Xiaoxi Huang, Arnoud Everhardt, Mahendra DC, Christoph Klewe, R Ramesh, Jianping Wang A lot of research focus on spin Hall effect for the use of spintronic devices has been put on heavy metals such as Pt and topological insulators but there is rare research on spin Hall effect in complex oxide systems with strong spin orbit coupling effects. Complex oxides such as SrIrO_{3} with strong spin orbit coupling effects have drawn considerable research interest. We have studied spin torque ferromagnetic resonance (STFMR) induced by spin Hall effect in SrIrO_{3}. Spin Hall angle of SrIrO_{3} as large as 0.36 is determined by STFMR, which is almost the same order as Ta. More interestingly, as thickness of SrIrO_{3} increases, spin Hall angle of SrIrO_{3} increases, while resistivity decreases. 
Tuesday, March 5, 2019 10:12AM  10:24AM 
E41.00010: Detecting end states of topological quantum paramagnets via spin Hall noise spectroscopy Darshan G. Joshi, Andreas P Schnyder, So Takei We theoretically study the equilibrium spin current fluctuations and the corresponding charge noise generated by the inverse spin Hall effect (ISHE) in a metal with strong spinorbit coupling deposited on top of a quantum paramagnet. It is shown that the charge noise power spectra measured along different spatial axes can directly probe the different spin components of the boundary dynamic spin correlations of the quantum paramagnet. We report the utility of this ISHEfacilitated spin noise probe as a tool to unambiguously detect topological phase transitions in an S = 1/2 quantum spin ladder that hosts a trivial ground state of singlet product states, but topologically protected fractional spin excitations localized at its ends. Our work demonstrates the general usefulness of ISHEmediated spin noise spectroscopy for the detection of topological phases in quantum paramagnets. 
Tuesday, March 5, 2019 10:24AM  10:36AM 
E41.00011: Electrical detection of Spin Hall effect in Tungsten films using a compact device geometry Arpita Mandal, Soumik Aon, Partha Mitra Direct detection of Spin Hall Effect (SHE) using electrical schemes continues to be an experimental challenge as there is no electrical voltage associated with the accumulation of electron spins of opposite signs at the edges of a standard Hall bar sample. We present a simple yet elegant measurement scheme that allows detection of spin accumulation using the well known concepts of nonlocal detection proposed by Johnson and Silsbee. We fabricated devices with pairs of voltage leads consisting of a ferromagnet (FM: Co or Py) and a normal metal (NM: Cu) suitably placed in contact with one of the spin accumulation edge of Tungsten (W) bar shaped films, so that other competing effects like ordinary Hall effect and magnetoresistance are minimised. We show that voltage difference measured between the FM and NM leads are a manifestation of the spin accumulation due to SHE. We present detailed temperature and magnetic field dependent study of the spin Hall conductivity extracted from the spin accumulation voltage. 
Tuesday, March 5, 2019 10:36AM  10:48AM 
E41.00012: Temperature dependence of sidejump contribution to anomalous/spin Hall conductivities Cong Xiao, Yi Liu, Zhe Yuan, Shengyuan Yang, Qian Niu The sidejump contribution to anomalous/spin Hall conductivities is conventionally understood 
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