Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session S40: Invited Session: Spin Current and Magnetization Dynamics--Pure Spin Current Generation and Transport |
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Sponsoring Units: GMAG Chair: Paul Crowell, University of Minnesota Room: Mile High Ballroom 2B-3B |
Thursday, March 6, 2014 8:00AM - 8:36AM |
S40.00001: The Spin Hall Effect, Spin Currents and Spin Orbit Torques in Ferromagnetic/Normal Metal Multilayer Nanostructures Invited Speaker: Robert Buhrman In the spin Hall effect (SHE) the passage of a charge current through a non-ferromagnetic metal (NM) film generates a transverse pure spin current that when it impinges onto an adjacent ferromagnetic (FM) film will exert both a damping-like torque and a field-like torque on the FM, with the former arising from the absorption of the transverse component of the incident spin current and the latter due to spin rotation during the reflection of a portion of the incident spin current. Certain NMs (e.g. Pt, Ta, and W) have been found to exhibit a strong SHE and the damping-like torque that can be exerted in this manner on thin film magnetic materials has significant potential for spintronics in that it has been demonstrated to be capable of reversibly switching the magnetization direction of both in-plane and out-of-plane magnetized nanomagnets, to induce persistent microwave magnetic oscillations, and to facilitate the high-speed manipulation of domain walls in magnetic nanostrips. I will report some recent results from our SHE studies, including investigations into the fundamental role that the interfacial spin-mixing conductance plays in determining the effectiveness of the SHE for exerting strong anti-damping spin torques on the adjacent ferromagnet, and experiments which demonstrate that both the damping-like torque and a strong field-like torque can arise from the ``bulk'' SHE. [Preview Abstract] |
Thursday, March 6, 2014 8:36AM - 9:12AM |
S40.00002: Enhanced pure spin current emission by spin-lattice coupling Invited Speaker: Sergej Demokritov |
Thursday, March 6, 2014 9:12AM - 9:48AM |
S40.00003: \textit{g}-Factor Anisotropy Driven Spin Relaxation in Germanium Invited Speaker: Pengke Li In semiconductors possessing more than a single conduction band valley, g-factor anisotropy opens a new channel of electron spin relaxation. This unusual mechanism arises in a magnetic field because the effective Zeeman field is tilted along the valley axis, and is randomized when electrons undergo intervalley scattering. This fluctuation depolarizes electron spins [1], similar to the Dyakonov-Perel mechanism in noncentrosymmetric semiconductors where spin relaxation is driven by a wavevector dependent magnetic field. We study the unique nature of g-factor anisotropy spin relaxation by spin transport measurements from long-distance germanium devices in a magnetic field aligned to the initial spin orientation [2]. The confluence of electron-phonon scattering (leading to Elliott-Yafet spin flips) and this previously unobserved physics enables the extraction of spin lifetime solely from spin-valve measurements. We find spin lifetimes in Ge up to several hundreds of ns at low temperature, far beyond any other available experimental results. Electric field and magnetic field are used to manipulate the spin signal by accelerating the spin polarized electrons and generating carrier heating, or by inducing Hanle spin precession. \\[4pt] [1] J.-N. Chazalviel, J. Phys. Chem. Solids 36, 387 (1975)\\[0pt] [2] Pengke Li, Jing Li, Lan Qing, Hanan Dery, and Ian Appelbaum, Phys. Rev. Lett. (2013) [Preview Abstract] |
Thursday, March 6, 2014 9:48AM - 10:24AM |
S40.00004: Exchange Coupling with Exponential Decay in Y$_3$Fe$_5$O$_{12}$/Barrier/Pt Heterostructures Invited Speaker: Yong Pu Understanding the mechanism of spin pumping is essential for advancing this exciting field and realizing potential applications of pure spin currents. It is believed that exchange interaction between the ferromagnet and nonmagnetic material is responsible for this phenomenon. We have grown high-crystalline quality Y$_3$Fe$_5$O$_{12}$ epitaxial thin films by off-axis sputtering and observed millivolt–level inverse spin Hall effect (ISHE) voltages in Y$_3$Fe$_5$O$_{12}$/Pt bilayer excited by an FMR cavity. By inserting an insulating barrier between Y$_3$Fe$_5$O$_{12}$ and Pt, we detect an exponential decay of the ISHE voltages over three orders of magnitude for four different barrier materials, including SrTiO$_3$, Sr$_2$GaTaO$_6$, Sr$_2$CrNbO$_6$, and Si. Exponential decay lengths of 0.16, 0.19, and 0.23 nm are extracted for Sr$_2$GaTaO$_6$, SrTiO$_3$, and Sr$_2$CrNbO$_6$ with band gaps of 2.36, 3.40, and 4.91 eV, respectively. The exponential dependence of spin pumping on barrier thicknesses can be explained by quantum tunneling of the conduction electrons in Pt through the barrier and coupling with the precessing magnetization of Y$_3$Fe$_5$O$_{12}$ through exchange interaction to acquire spin polarization. [Preview Abstract] |
Thursday, March 6, 2014 10:24AM - 11:00AM |
S40.00005: Issues related to YIG spintronics - thin film growth, spin pumping efficiency, and spin current generation Invited Speaker: Mingzhong Wu If a magnetic field is applied to a magnetic material, the field produces a torque on the magnetization of the material and drives it to precess. This precession is similar to the motion of a spinning top where the gravitational field produces a torque, instead of the magnetic field. It turns out that magnetization precession in yttrium iron garnets (YIG) decays slower than in any other known magnetic materials. This fact gives rise to the recent birth of a new paradigm in the discipline of spintronics -- ``spintronics using YIG.'' This talk will touch on several topics related to YIG spintronics. The first part will demonstrate the feasibility of the use of pulsed laser deposition and magnetron sputtering to grow low-damping, nanometer-thick YIG films. The second part will address the efficiency of spin angular momentum transfer across YIG/normal metal interfaces. The last part will report on the use of YIG thin films to produce pure spin currents; Detailed discussions will be provided on the comparison between spin current generations using traveling spin waves and uniform ferromagnetic resonance modes, the field dependence of spin current generation, and spin current enhancement in YIG/Pt structures via the use of a thin Cu spacer. [Preview Abstract] |
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