Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session S47: Magnetization Dynamics II, Metals and InsulatorsFocus

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Sponsoring Units: GMAG DMP FIAP Chair: Rolando Valdes Aguilar, Ohio State University Room: 394 
Thursday, March 16, 2017 11:15AM  11:27AM 
S47.00001: Spin circuit representation of spintorque ferromagnetic resonance Kuntal Roy Earlier we developed equivalent circuit (spin and charge circuits) representation for spin pumping from metallic ferromagnets (e.g., Py) into an adjacent material (e.g., Pt, topological insulators) possessing spin orbit coupling, detected as inverse spin Hall voltage [1]. Here, we extend such development for magnetic insulators such as yttriumirongarnet (YIG), for which the imaginary part of spin mixing conductance is considerable and spin Hall magnetoresistance (SMR), i.e., the dependence of electrical resistance of Pt on the magnetization direction of YIG, has been observed. In spintorque ferromagnetic resonance (STFMR) experiments, an inplane alternating current in Pt drives the magnetization precession in the magnet via direct spin Hall effect and it pumps spins into the Pt layer detected as a charge voltage via inverse spin Hall effect. We construct the corresponding spin circuit representation and analyze the available experimental results. Such equivalent circuit models developed here can be utilized to analyze and evaluate more complex devices. [1] K. Roy, in APS March Meeting, Y28.12 (2015), K18.4 (2016); in EMN Meeting on Magnetic Materials (invited), and on Spintronics (invited), (2016). [Preview Abstract] 
Thursday, March 16, 2017 11:27AM  11:39AM 
S47.00002: Spin dynamics in Ni$_{80}$Fe$_{20}$/Pt bilayer antidot lattices Matthias Benjamin Jungfleisch, Junjia Ding, John E. Pearson, Axel Hoffmann, Wei Zhang, Wanjun Jiang, Joseph Sklenar, John B. Ketterson The understanding of spin dynamics in laterally confined structures on submicron length scales has become a significant aspect of the development of novel magnetic storage technologies. Many different aspects of dynamics in patterned magnetic antidot lattices were studied by numerous techniques ranging from optical to $rf$ characterization methods. Here, we investigate Oerstedfield driven spin dynamics in rectangular Ni$_{80}$Fe$_{20}$/Pt antidot lattices with different lattice parameters by dc electrical means and compare them to micromagnetic simulations\footnote{M. B. Jungfleisch et al., Appl. Phys. Lett. \textbf{108}, 052403 (2016).}. We find a dc voltage signal across the length of the sample when the system is driven to resonance. The observed signal flips sign upon magnetic field reversal. Furthermore, we show that the voltage output scales linearly with the applied microwave power. We have also taken initial steps towards the exploration of spintorque ferromagnetic resonance in these kind of bilayer antidot lattices. Our findings have direct implications on the development of engineered magnonics applications and devices.\newline This work was supported by the U.S. Department of Energy, Office of Science, Materials Science and Engineering Division. [Preview Abstract] 
Thursday, March 16, 2017 11:39AM  11:51AM 
S47.00003: Spin Pumping Oscillator Coupled Logic for PhaseBased Boolean Computing Shaloo Rakheja In this work, we demonstrate the dynamics of a spin pumping oscillator coupled (SPOC) device in which the magnetization dynamics are driven by spin pumping current generated from a ferromagnet precessing at rf frequencies. In this work, we specifically use the transverse oscillating ac component of the spin pumping current to encode information for implementing phasebased Boolean logic. The advantage of phasebased SPOC device is that switching between logic values does not, in principle, involve energy expenditure. The latency of the SPOC device is primarily limited by the setup time of oscillations in the ferromagnet, which is lower than that required for full magnetization reversal. As such, the SPOC device offers advantages in terms of energy dissipation and latency when compared against other nanoscale devices for beyondCMOS computing. The major highlights of this work include evaluation of the performance metrics  energy, delay, and power  of the SPOC device using physicsbased models of spin oscillators and spin pumping. We also identify a set of material and geometrical parameters of the SPOC device to achieve correct logic functionality, while also minimizing the overall energy per bit and power dissipation. [Preview Abstract] 
Thursday, March 16, 2017 11:51AM  12:27PM 
S47.00004: Applications of the scattering theory of magnetization damping Invited Speaker: Paul J. Kelly Magnetization (or Gilbert) damping results from a combination of spinorbit coupling and disorder. I review a scattering theoretical formulation of magnetization damping [1] implemented without parameters in density functional theory with a very efficient basis of tightbinding muffin tin orbitals [2]. By being able to handle scattering regions containing in excess of 10,000 atoms, the influence of various types of disorder can be studied, including temperatureinduced lattice and spin disorder [3]. I discuss applications to the important itinerant ferromagnets Fe, Co and Ni [4,5] as well as to the binary substitutional ferromagnetic alloys Fe$_x$Ni$_{1x}$, Fe$_x$Co$_{1x}$, and Co$_x$Ni$_{1x}$ [2,5] where the prediction of a very low damping in the Fe$_x$Co$_{1x}$ system was recently confirmed by experiment [6]. Studies of damping in structurally [7] and magnetically [8] inhomogeneous systems of great current interest lead to a number of new insights and predictions. \newline \newline [1] A. Brataas, Y. Tserkovnyak, and G. E.W. Bauer, PRL\textbf{101}, 037207 (2008); PRB\textbf{84}, 054416 (2011).\newline [2] A.A. Starikov, P.J. Kelly, A. Brataas, Y.Tserkovnyak, and G. E.W. Bauer, PRL\textbf{105}, 236601 (2010).\newline [3] Y. Liu, Z. Yuan, R.J.H. Wesselink, A.A. Starikov, M. van Schilfgaarde and P.J. Kelly, PRB\textbf{91}, 220405 (2015).\newline [4] Y. Liu, A.A. Starikov, Z. Yuan and P.J. Kelly, PRB\textbf{84}, 014412 (2011).\newline [5] H. Ebert, S. Mankovsky, D. Koedderitzsch and P.J. Kelly, PRL\textbf{107}, 066603 (2011).\newline [6] M.A.W. Schoen, D. Thonig, M.L. Schneider, T.J. Silva, H.T. Nembach, O. Eriksson, O. Karis, and J.M. Shaw, Nat. Phys. (2016).\newline [7] Y. Liu, Z. Yuan, R.J.H. Wesselink, A.A. Starikov, and P.J. Kelly, PRL\textbf{113}, 207202 (2014).\newline [8] Z. Yuan, K.M.D. Hals, Y. Liu, A.A. Starikov, A. Brataas and P.J. Kelly, PRL\textbf{113}, 266603 (2014). [Preview Abstract] 
Thursday, March 16, 2017 12:27PM  12:39PM 
S47.00005: A Phenomenological Model For The Spin Stiffness Of A Halfmetallic Ferromagnet Raul Chura, Kevin Bedell By using the Fermi Liquid Theory for Spin Polarized Systems, more specifically, by using the linearized form of Landau Silin Kinetic Equation, and after considering an appropriate approximation, we have obtained the dispersion relationships describing the collective modes for the spin waves in a Half Metallic Ferromagnetic (HMF) material. Our results predict the existence of a gapless mode for the spin dynamics of a HMF, in agreement with experiment. In addition, our calculations allowed us to get a phenomenological formula for the spin stiffness of HMF materials, which being entirely in terms of band theory and Landau interaction parameters, allowed us to test that formula for those HMF materials for which we were able to find, in the available literature, the required data. For these materials our model is consistent with experiment. [Preview Abstract] 
Thursday, March 16, 2017 12:39PM  12:51PM 
S47.00006: Mechanical readout of ferromagnetic resonance via the Wiedemann effect Sung Un Cho, Myung Rae Cho, Seondo Park, Yun Daniel Park We demonstrate a mechanical readout method of ferromagnetic resonance (FMR) as coupled to the mechanical flexural mode of a Py(NiFe)/Pt bilayer strip. Magnetoelastic interaction between the longitudinal and torsional strain arising from the Wiedemann effect [1] manifests as dispersive shifts of mechanical resonance frequencies sympathetic to FMR. Under external magnetic field, rfcurrent is applied through the mechanical beam to drive magnetization precession and piezoresistivity of Pt enables the mechanical resonance measurement in all electromechanical manner at room temperature [2]. We also characterize the FMR using spintorque FMR measurement technique [3] which well follows the Kittel formula. Additionally, spintransfer torque contribution to the mechanical reaction by spin Hall effect in the Pt layer is discussed with our numerical expectation. Our all electromechancial scheme guarantees the scalability to downscale for low power driving of FMR and is suitable applying nanoscale spintronics architecture for realization of integrating circuit. [1] G. Wiedemann, Annalen der Physik 179, 563577 (1858). [2] H. Bhaskaran et al., Appl. Phys. Lett. 98, 013502 (2011). [3] L. Liu et al., Phys. Rev. Lett. 106, 036601 (2011). [Preview Abstract] 
Thursday, March 16, 2017 12:51PM  1:03PM 
S47.00007: Sensitive imaging of magnetization structure and dynamics using picosecond laser heating Jason Bartell, Colin Jermain, Sriharsha Aradhya, Jack Brangham, Fengyuan Yang, Daniel Ralph, Gregory Fuchs We demonstrate the timeresolved longitudinal spin Seebeck effect (TRLSSE) as the basis for an ultrafast, highresolution, and sensitive microscope for imaging ferromagnetic insulator/normal metal spintronic devices. By focusing a picosecond laser to 0.7 $\mu$m, we generate a sub100 ps electrical signal from the combination of the TRLSSE and the inverse spin Hall effect in yittrium iron garnet (YIG)/platinum (Pt) bilayers. This signal is a spatiotemporal measurement of the local, inplane magnetic orientation of YIG with outstanding sensitivity – better than 0.3$^\circ/\sqrt{Hz}$ in samples with 20 nm of YIG. Static imaging of YIG/Pt devices reveals variations in the local magnetic anisotropy on a few micron scale. Phasesensitive ferromagnetic resonance imaging reveals corresponding variations in the resonance field, amplitude, phase, and linewidth. These results show the TRLSSE is a powerful tool for static and dynamic studies of spintronic devices made with ferromagnetic insulators. [Preview Abstract] 
Thursday, March 16, 2017 1:03PM  1:15PM 
S47.00008: Temperature dependence of the enhanced inverse spin Hall voltage in Pt/Antiferromagnetic/Y$_{\mathrm{3}}$Fe$_{\mathrm{5}}$O$_{\mathrm{12}}$ J. T. Brangham, A. J. Lee, Y. Cheng, S. S. Yu, S. R. Dunsiger, M. R. Page, P. C. Hammel, F. Y. Yang The generation, propagation, and detection of spin currents are of intense interest in the field of spintronics. Spin current generation by FMR spin pumping using Y$_{\mathrm{3}}$Fe$_{\mathrm{5}}$O$_{\mathrm{12}}$ (YIG) and spin current detection by the inverse spin Hall effect (ISHE) in metals such as Pt have been well studied. This is due to YIG's exceptionally low damping and insulating behavior and the large spin Hall angle of Pt. Previously, our group showed that the ISHE voltages are significantly enhanced by adding a thin intermediate layer of an antiferromagnet (AFM) between Pt and YIG at room temperature [1, 2]. Recent theoretical work predicts a mechanism for this enhancement as well as the temperature dependence of the ISHE voltages of metal/AFM/YIG trilayers [3]. The predictions show a maximum in the ISHE voltages for these systems near the magnetic phase transition temperature of the AFM. Here we present experimental results showing the temperature dependence for Pt/AFM/YIG structures with various AFMs. 1. H. L. Wang, et. al., Phys. Rev. Lett. 132, 097202 (2014). 2. H. L. Wang, et. al., Phys. Rev. B 91, 220410(R) (2015). 3. R. Khymyn, et. al., Phys. Rev. B 93, 224421 (2016). [Preview Abstract] 
Thursday, March 16, 2017 1:15PM  1:27PM 
S47.00009: Towards an alloptical FMR measurement using ultrafast magnetic fields excited at a Schottky interface Prerna Kabtiyal, Matthew Sheffield, Yu Sheng Ou, Patrick Odenthal, Jack Brangham, Fengyuan Yang, Roland Kawakami, Ezekiel JohnstonHalperin All optical timedomain ferromagnetic resonance (FMR) is an attractive technique for studying the dynamic behavior of magnetic materials as it avoids many of the technical challenges inherent in traditional microwave frequency measurements of magnetic resonance. For example, the excitation timescale is limited by the dynamics of photoexcited currents and the measurement timescale is limited by the time resolution of ultrafast optics (roughly 10’s of picoseconds and 100 femtoseconds, respectively). This allows an excitation bandwidth of 100 GHz and a measurement bandwidth from DC up to 10 THz without the need for sophisticated microwave engineering. Prior work has relied on direct deposition of a metallic ferromagnet (Fe) onto a GaAs Schottky diode [Acremann et al, Nature 414, 51 (2001)], but given that the excitation mechanism relies on transient Oersted fields to “tip” the magnetization, epitaxial contact between the ferromagnetic film and the diode is not clearly required. Here, we present work towards the development of a materialsgeneric approach to all optical FMR that exploits this flexibility to allow the ultrafast excitation and measurement of the magnetization dynamics of disparate materials that are not readily deposited onto semiconducting substrates. [Preview Abstract] 
Thursday, March 16, 2017 1:27PM  1:39PM 
S47.00010: PhaseResolved Detection of the Spin Hall Angle by Optical Ferromagnetic Resonance in Perpendicularly Magnetized Thin Films Amir Capua, Tianyu Wang, SeeHun Yang, Charles Rettner, Timothy Phung, Stuart Parkin Measurement of the spin Hall angle, especially for atomically thin systems with large magnetic anisotropies, is not straightforward. Here we demonstrate a hybrid phaseresolved opticalelectrical ferromagnetic resonance method that we show can robustly determine the spin Hall angle in heavymetal/ferromagnet bilayer systems with large perpendicular magnetic anisotropy. We present an analytical model of the ferromagnetic resonance spectrum in the presence of the spin Hall effect, in which the spin Hall angle can be directly determined from the changes in the amplitude response as a function of the spin current that is generated from a DC charge current passing through the heavymetal layer. Increased sensitivity to the spin current is achieved by operation under conditions for which the magnetic potential is shallowest at the ``Smit point''. Study of the phase response reveals that the spin Hall angle can be reliably extracted from a simplified measurement that does not require scanning over time or magnetic field but rather only on the DC current. The method is applied to the PtCo/Ni/Co system whose spin Hall angle was to date characterized only indirectly and that is especially relevant for spin orbit torque devices. [Preview Abstract] 
Thursday, March 16, 2017 1:39PM  1:51PM 
S47.00011: Spin pumping at quasionedimensional YIG/graphene interfaces Marta Anguera, Simranjeet Singh, Barbaros Ozyilmaz, Enrique del Barco We present a study of dynamical spin injection from a threedimensional ferromagnet into twodimensional singlelayer graphene. Comparative ferromagnetic resonance (FMR) studies of ferromagnet/graphene strips buried underneath the central line of a coplanar waveguide show that the FMR linewidth broadening is the largest when the graphene layer protrudes laterally away from the ferromagnetic strip, indicating that the spin current is injected into the graphene areas away from the area directly underneath the ferromagnet being excited. Our results confirm that the observed damping is indeed a signature of dynamical spin injection, wherein a pure spin current is pumped into the singlelayer graphene from the precessing magnetization of the ferromagnet. The observed spin pumping efficiency is difficult to reconcile with the expected backflow of spins according to the standard spin pumping theory and the characteristics of graphene, and constitutes an enigma for spin pumping in twodimensional structures. We will also discuss measurements of the inverse spin Hall effect aimed at identifying the source of spincurrent to chargecurrent interconversion at ferromagnet/graphene interfaces. [Preview Abstract] 
Thursday, March 16, 2017 1:51PM  2:03PM 
S47.00012: Spin Wave Propagation in an Yttrium Iron Garnet Film in an OutofPlane Magnetic Field Wonbae Bang$ ^{1}$, Jinho Lim$ ^{1}$, Jonathan Trossman$ ^{1}$, C. C. Tsai$ ^{2}$, J. B. Ketterson$ ^{1,3}$ We have studied the propagation of spin waves in a (111) thin film of Yttrium Iron Garnet (YIG) for magnetic fields inclined with respect to the plane of the sample. Waves are generated by a wire running parallel to one edge of the film and detected by a second wire positioned at the opposing edge of the film, which has been cut parallel to the first. By studying the evolution of the phase of the received signal with magnetic field one can determine frequency vs. wavevector relation, $\omega =\omega (k)$, of various propagating modes in the film. Data were taken with the magnetic field, \textbf{H}, lying in two principle planes. For the first \textbf{H} lies in the plane defined by the direction of \textbf{k} and the plane normal, with limiting forms corresponding to the backward (BV) and forward volume (FV) modes. The second principle plane is that for which \textbf{H} is perpendicular to\textbf{ k }with the limiting forms corresponding to the DamonEshbach (DE) and FV modes. In the DE and FV regimes avoided crossings are encountered when the propagating mode intersects the higher, exchange split, volume modes, leading to an extinction of the propagating mode; analysis of the resulting behavior allows a determination of the exchange parameter. [Preview Abstract] 
Thursday, March 16, 2017 2:03PM  2:15PM 
S47.00013: Strong coupling of magnons in a YIG sphere to photons in a planar superconducting resonator in the quantum limit Richard Morris, Arjan van Loo, Sandoko Kosen, Alexy Karenowska Magnonic systems have been studied for more than half a century but until recently most experimental investigations have been done at room temperature with high signal powers. Over the last few years, interest has grown in observing their behaviour at very low temperatures, where the thermal population of magnons is negligible and it becomes possible to observe quantum phenomena. With a view to enabling new hybrid systems and tools for studying the quantum physics of magnons, we investigate coupling of a superconducting coplanar waveguide resonator (CPWR) to a sphere of yttriumiron garnet at millikelvin temperatures. The nonuniform CPWR field allows us to excite a variety of magnon modes in the sphere, and we identify some of these modes based on their frequencies and relative coupling strengths. Strong coupling is observed to several modes, and the Kittel mode is seen even with, on average, less than one excitation in the CPWR. We also investigate the time response of the system to short square pulses, which shows oscillations at the mode splitting frequency. These results illustrate that planar superconducting components can be readily combined with magnonic systems, paving the way for new hybrid quantum devices. [Preview Abstract] 
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