Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session K47: Magnons and Magnonic DevicesFocus
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Sponsoring Units: GMAG DMP FIAP Chair: Sergei Urazhdin, Emory University Room: 394 |
Wednesday, March 15, 2017 8:00AM - 8:12AM |
K47.00001: Phase Detection of Propagating Magnetostatic Spin Waves: From Damon-Eschbach to Backward Volume Modes Jonathan Trossman, Jinho Lim, Wonbae Bang, John Ketterson, C. C. Tsai We report experiments which characterize spin wave propagation in a thin (3.05 micron) (111) YIG film for arbitrary angles between the in-plane magnetic field and the mode wavevectors. By measuring the magnetic field evolution of the phase of the wave traveling across the film we deduce the frequency dependence of the wavevector, the dispersion relation, from which the mode velocity follows. Additionally, we observe multiple nodes in the regime of the propagating Damon-Eschbach mode; these arise from avoided crossings associated quantization of the higher backward volume modes along the film normal together with the exchange energy. This, in turn, allows a determination of the exchange energy. [Preview Abstract] |
Wednesday, March 15, 2017 8:12AM - 8:24AM |
K47.00002: Spin waves propagation in structured magnetic films with perpendicular magnetic anisotropy Cody Kellogg, Kasuni Nanayakkara, Alexander Kozhanov Spin wave based signal processing and logic devices have a long history of development and exploration. Typically, structures with in-plane magnetization are used. The shape and dimensions of the structures define the spin wave dispersion. It was shown that spin wave propagation in complex structures like spin waveguide bends, T-, Y- and cross junctions is strongly dependent on the spin wave mode coupling between different parts of the structure. Spin wave scattering and interference processes define the wave propagation in these structures. In this work we perform numeric simulations to investigate spin wave propagation in structures based on magnetic films with perpendicular magnetic anisotropy (PMA). We analyze spin wave propagation in spin waveguide bends, T, and cross junctions while varying their dimensions. We demonstrate that forward volume magnetostatic spin wave modes supported by films with PMA can propagate in complex structures with geometry-controlled scattering. We show that varying a uniform out-of-plane external magnetic field results in the spin wave frequency shift while not affecting the overall wave propagation. We analyze local standing spin wave modes and discuss the structure shape variation effect on the wave propagation. [Preview Abstract] |
Wednesday, March 15, 2017 8:24AM - 8:36AM |
K47.00003: Nanopatterned reconfigurable spin-textures for magnonics E. Albisetti, D. Petti, M. Pancaldi, M. Madami, S. Tacchi, J. Curtis, W. P. King, A. Papp, G. Csaba, W. Porod, P. Vavassori, E. Riedo, R. Bertacco The control of spin-waves holds the promise to enable energy-efficient information transport and wave-based computing. Conventionally, the engineering of spin-waves is achieved via physically patterning magnetic structures such as magnonic crystals and micro-nanowires. We demonstrate a new concept for creating reconfigurable magnonic nanostructures, by crafting at the nanoscale the magnetic anisotropy landscape of a ferromagnet exchange-coupled to an antiferromagnet. By performing a highly localized field cooling with the hot tip of a scanning probe microscope, magnetic structures, with arbitrarily oriented magnetization and tunable unidirectional anisotropy, are patterned without modifying the film chemistry and topography. We demonstrate that, in such structures, the spin-wave excitation and propagation can be spatially controlled at remanence, and can be tuned by external magnetic fields.[1] This opens the way to the use of nanopatterned spin-textures, such as domains and domain walls, for exciting and manipulating magnons in reconfigurable nanocircuits. [1] E. Albisetti \textit{et al.}, Nat. Nanotechnol. 11, 545--551 (2016). [Preview Abstract] |
Wednesday, March 15, 2017 8:36AM - 8:48AM |
K47.00004: Overcoming thermal noise in non-volatile spin wave logic Sourav Dutta, Dmitri Nikonov, Sasikanth Manipatruni, Ian Young, Azad Naeemi Spin waves are propagating disturbances in magnetically ordered materials. To compete as a promising candidate for beyond-CMOS application, the all-magnon based computing system must undergo the essential steps of careful selection of materials and demonstrate robustness with respect to thermal noise/variability. Here, we identify suitable materials and investigate two viable options for translating the theoretical idea of phase-dependent switching of the spin wave detector to a practical realization of a thermally reliable magnonic device by - (a) using the built-in strain in the ME cell, arising from the lattice mismatch and/or thermal expansion coefficient mismatch between the film and the substrate, for compensation of the demagnetization, and (b) using an exchange-spring structure that exhibits a strong exchange-coupling between the ME cell and PMA SWB and provides a modification of the energy landscape of the ME cell magnet. A high switching success and error-free logic functionality can be ensured if the amplitude of the detected spin wave ($<\theta>$) remains higher than a threshold value of around 6$^o$ and the detected phase falls within the window from 280$^o$ through 0 to 20$^o$ or from 100$^o$ to 200$^o$ with a maximum allowable $\phi$ range of around 100$^o$. [Preview Abstract] |
Wednesday, March 15, 2017 8:48AM - 9:00AM |
K47.00005: Developing magnonic architectures in circuit QED Alexy Karenowska, Arjan van Loo, Richard Morris, Sandoko Kosen The development of low-temperature experiments aimed at exploring and exploiting magnonic systems at the quantum level is rapidly becoming a highly active and innovative area of microwave magnetics research. Magnons are easily excited over the microwave frequency range typical of established solid-state quantum circuit technology, and couple readily to electromagnetic fields. These facts, in combination with the highly tunable dispersion of the excitations, make them a particularly interesting proposition in the context of quantum device design. In this talk, we survey recent progress made in our group in the area of the hybridization of planar superconducting circuit technology (circuit-QED) with magnon systems. We discuss the technical requirements of successful experiments, including the choice of suitable materials. We go on to describe the results of investigations including the study spin-wave propagation in magnetic waveguides at the single magnon level [1, 2], the investigation of magnon modes in spherical magnetic resonators [3], and the development of systems incorporating Josephson-junction based qubits. [1] A. Karenowska et al., arXiv:1502.06263 (2014). [2] A. van Loo et al., arXiv:1610.08402 (2016). [3] R. Morris et al., arXiv:1610.09963 (2016). [Preview Abstract] |
Wednesday, March 15, 2017 9:00AM - 9:36AM |
K47.00006: Magnon-mediated current drag across a magnetic insulator Invited Speaker: Jing Shi Electric current transmission can occur in a magnetic insulator via spin current inter-conversions at heavy metal/magnetic insulator interfaces. In magnetic insulators, spin current is carried by spin wave excitations or their quanta, magnons. This marvelous phenomenon was first theoretically predicted and dubbed as the magnon-mediated current drag in 2012 by Zhang et al. (1, 2). Following a breakthrough in materials growth, i.e. yttrium iron garnet films or YIG ranging from 30 to 80 nm in thickness sandwiched between two heavy metal films (3), we successfully showed the nonlocal DC current transmission in such sandwich structures via spin current rather than charge current (4). To exclude the leakage effect, the experiments are conducted at temperatures below 250 K where the resistance between the metal layers exceeds 20 Gohms. In addition, by replacing the top Pt electrode with beta-Ta which is known to reverse the sign in the spin Hall angle, we found that the nonlocal signal reverses the polarity, which is a direct demonstration of the spin current nature. Furthermore, the temperature dependence of the nonlocal signal confirms the role of magnons in this effect. \begin{enumerate} \item S. S.-L. Zhang {\&} S. Zhang, Magnon Mediated Electric Current Drag across a Ferromagnetic Insulator Layer. Phys. Rev. Lett. 109, 096603 (2012). \item S. S.-L. Zhang {\&} S. Zhang, Spin convertance at magnetic interfaces. Phys. Rev. B 86, 214424 (2012). \item Mohammed Aldosary, Junxue Li, Chi Tang, Yadong Xu, Jian-Guo Zheng, Krassimir N. Bozhilov, and Jing Shi, Platinum/yttrium iron garnet inverted structures for spin current transport, Appl. Phys. Lett. 108, 242401 (2016); DOI: 10.1063/1.4953454. \item J.X. Li, Y.D. Xu, M. Aldosary, C. Tang, Z.S. Lin, S.F. Zhang, R. Lake, and Jing Shi, Observation of magnon-mediated current drag in Pt/yttrium iron garnet/Pt(Ta) trilayer. Nat. Comm. 7, 10858 (2016); DOI: 10.1038/ncomms10858. \end{enumerate} [Preview Abstract] |
Wednesday, March 15, 2017 9:36AM - 9:48AM |
K47.00007: Coupled electron-magnon spin transport in magnetic heterostructure Yihong Cheng, Kai Chen, Shufeng Zhang Both conduction electrons and magnons are angular momentum carriers that are capable of propagating spin information in magnetic multilayers. In conducting ferromagnets or antiferromagnets, conduction electron spin currents are correlated with magnon currents through strong exchange coupling between itinerant spins and localized moments. Here we develop a theory of angular momentum transport by explicitly taking into account the electron-magnon coupling. In our Boltzmann approaches, the distribution functions for electrons and magnons are mutually dependent, and thus, the electron spin current would drag a magnon current and vice versa. To determine these distributions, we investigate the roles of different scattering terms, including the electron spin diffusion and magnon diffusion. We find that relative strengths of the spin and magnon currents depend not only on the spin-magnon coupling, but also on the relative relaxation times of the non-equilibrium magnons and electron spins. A coupled spin-magnon diffusion equation has been constructed and the effective spin-magnon diffusion lengths are obtained. We predict the temperature and spatial dependence of the total angular momentum current for a number of layered structures by explicitly solving the spin-magnon diffusion equations. We discuss possible experimental realizations of our predictions. [Preview Abstract] |
Wednesday, March 15, 2017 9:48AM - 10:00AM |
K47.00008: Nonlocal magnon spin transport in a ferrimagnetic insulator Juan Shan, Ludo Cornelissen, Jing Liu, Nynke Vlietstra, Timo Kuschel, Jamal Ben Youssef, Rembert Duine, Bart van Wees Magnons recently entered the field of spintronics as novel, long-distance spin information carriers. In this talk, I will show the experimental demonstration of the diffusive magnon transport in yttrium iron garnet (YIG), a ferrimagnetic insulator [1]. Magnons can be excited in two ways simultaneously: electrical injection as a result of the spin Hall effect in an adjacent heavy metal, and thermal generation due to the bulk spin Seebeck effect. Magnons excited in both methods can be described by diffusive transport over a magnon relaxation length, around 10 $\backslash $mu m at room temperature [2]. We studied the transport behavior of both types of magnons as a function of magnetic field, YIG thickness and temperature [3][4]. However, the study of magnon transport in different YIG thickness shows quantitative disagreement with the magnon diffusion model, suggesting more complex processes. [1] Cornelissen \textit{et al., Nature Phys}. \textbf{11},1022 (2015) [2] Cornelissen \textit{et al.}, \textit{Phys. Rev. B} \textbf{94}, 014412 (2016) [3] Cornelissen \textit{et al., Phys. Rev. B }\textbf{93}, 020403 (R) (2016); \textit{Phys. Rev. B }\textbf{94}, 180402(R) (2016) [4] Shan \textit{et al}., \textit{Phys. Rev. B }in press, arxiv:1608.01178; J. Shan \textit{et al}., in preparation [Preview Abstract] |
Wednesday, March 15, 2017 10:00AM - 10:12AM |
K47.00009: Finite-element modeling of thermal and condensed magnon transport Roberto Myers, Zihao Yang Understanding the interaction between spin and heat fluxes is crucial to uncover the physics of existing spin caloritronic phenomena and to predict new ones. Along these lines, Flebus et. al. proposed that a magnon Bose-Einstein condensate (BEC) would form in an easy-plane magnetic insulator in the presence of a thermal gradient [1]. That theory used hydrodynamic transport equations for spin and heat which can be solved using finite-element method (FEM). Here, we use FEM to solve the normal magnon and heat transport equations with and without magnon condensation in a Pt/YIG/Cu structure [1]. First, the effect of a heating laser on normal magnons is modeled. The magnon spin current decays away from the laser heating source. The modeled decay and its temperature dependence are compared to the recent non-local spin transport studies in YIG[2][3]. The heating laser is shown to induce a magnon BEC along with the normal magnons. The BEC velocity, condensed magnon current, and condensate frequency are calculated as a function of temperature and magnetic field. This work is supported by ARO MURI W911NF-14-1-0016. [1]Flebus et. al. PRL, 116, 117201 (2016) [2]Giles et. al. PRB 92, 224415 (2015) [3]Cornelissen el. al. PRB 94, 180402(R) (2016) [Preview Abstract] |
Wednesday, March 15, 2017 10:12AM - 10:24AM |
K47.00010: Temperature Dependence of Lateral magnon spin diffusion in Yttrium Iron Garnet bulk crystals and films Brandon Giles, Zihao Yang, John Jamison, Roberto Myers We present measurements of the spin diffusion length of thermally generated magnons in bulk single crystal and epitaxial films of yttrium iron garnet (YIG). A focused 980 nm laser is used to thermally inject a flux of magnons beneath a Pt absorption pad that is sputter deposited onto YIG bulk single crystals or liquid phase epitaxy films. The thermally injected magnons that diffuse laterally are measured non-locally through an electrically and thermally isolated Pt detection pad via the inverse spin hall effect. Such a configuration allows for an accurate measurement of the spin diffusion length by modeling the decay profile of the lateral spin current as a function of the distance between the excitation laser spot and the detector [1]. The diffusion profiles in bulk and epitaxial YIG films are measured from 10K to 350K. Multidimensional finite element method (FEM) calculations of the magnon diffusion based on hydrodynamic transport equations are used to model the magnon spin diffusion process$_{\mathrm{\thinspace }}$and determine the temperature dependent magnon spin conductivity. [1] Giles et al. \textit{PRB} \textbf{92,} 224415 (2015). [Preview Abstract] |
Wednesday, March 15, 2017 10:24AM - 10:36AM |
K47.00011: Magnon Temperature Sensing in YIG and Permalloy using Brillouin Light Scattering Kevin Olsson, Kyongmo An, Xin Ma, Sean Sullivan, Vijay Venu, Maxim Tsoi, Jianshi Zhou, Li Shi, Xiaoqin Li In spin caloritronics, many phenomena crucially on knowledge the magnon temperature. We investigate Brillouin light scattering (BLS) as a method for measuring magnon temperature. The magnon BLS spectra offer three temperature dependent parameters: peak frequency, linewidth, and integrated intensity. The BLS spectra of magnons in a ferrimagnetic insulator (yttrium iron garnet or YIG) and a ferromagnetic metal (permalloy or Py) are measured at different temperatures under uniform heating. The contributions to the temperature dependence of the three BLS spectra parameters are discussed and the temperature precision of each parameter is determined. We find the BLS integrated intensity has opposite temperature dependence between YIG and Py, due to magneto-optics effects. This finding indicates the BLS integrated intensity must be corrected for these effects before the intensity can be used as a direct measurement of magnon population. [Preview Abstract] |
Wednesday, March 15, 2017 10:36AM - 10:48AM |
K47.00012: Topologically protected unidirectional edge spin waves Xiang Rong Wang, Xiansi Wang, Ying Su Magnetic materials are highly correlated spin systems that do not respect the time-reversal symmetry. The low-energy excitations of magnetic materials are spin waves whose quanta are magnons. Like electronic materials that can be topologically nontrivial, a magnetic material can also be topologically nontrivial with topologically protected unidirectional edge states. These edge states should be superb channels of processing and manipulating spin waves because they are robust against perturbations and geometry changes, unlike the normal spin wave states that are very sensitive to the system changes and geometry. Therefore, the magnetic topological matter is of fundamental interest and technologically useful in magnonics. Here, we show that ferromagnetically interacting spins on a two-dimensional honeycomb lattice with nearest-neighbour interactions and governed by the Landau-Lifshitz-Gilbert equation, can be topologically nontrivial with gapped bulk spin waves and gapless edge spin waves. These edge spin waves are indeed very robust against defects under topological protection. Because of the unidirectional nature of these topologically protected edge spin waves, an interesting functional magnonic device called beam splitter can be made out of a domain wall in a strip. It is shown that an in-coming spin wave beam along one edge splits into two spin wave beams propagating along two opposite directions on the other edge after passing through a domain wall. [Preview Abstract] |
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