Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session X39: Magnons, Spin Waves, and Magnetic DynamicsFocus

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Sponsoring Units: GMAG DMP Chair: Thomas Silva, National Institute of Standards and Technology Boulder Room: BCEC 207 
Friday, March 8, 2019 8:00AM  8:12AM 
X39.00001: Topological magnons on a kagome lattice Ranjani Seshadri, Diptiman Sen A system of spins on a kagome lattice interacting via the nearestneighbor XXZ interaction (anisotropy ratio △) and DzyaloshinskiiMoriya interaction (strength D) is found to have a very rich phase diagram. In the classical limit, five distinct phases with different groundstate spin configurations are found by varying the two interaction parameters. In some of these phases, spinwave theory using the HolsteinPrimakoff transformations is used to find the bulk energy bands of the magnons. In the ferromagnetic phase, where all the spins point along the +z direction, the bulk bands are separated from each other by finite energy gaps. Finding the Chern numbers here, one finds that there are four topologically distinct phases sharing the same ground state spinconfiguration. Hence an infinite strip of the system hosts robust edge states which are directly related to the Chern number of the bands. The other phases, however, are found to have gapless magnon bands. 
Friday, March 8, 2019 8:12AM  8:24AM 
X39.00002: Spin waves in doped graphene with inplane magnetic fields Matthew Anderson, Carsten Ullrich Plasmonics in graphene and related 2D materials has attracted much interest, with many prospects for novel applications. However, the dynamics of collective spin excitations and spin waves in 2D materials has been much less explored. Here, we study the spinwave excitations of itinerant electrons in doped graphene in the presence of inplane magnetic fields. We calculate the spinwave dispersions using timedependent densityfunctional methods within a standard tightbinding approach. Dynamical exchangecorrelation effects are treated using the SingwiTosiLandSjolander (STLS) approach, generalized for systems with noncollinear spins. 
Friday, March 8, 2019 8:24AM  8:36AM 
X39.00003: Relation between unidirectional magnetoresistance and magnon generation by spin current Igor Borisenko, Vladislav Demidov, Sergei Urazhdin, Sergej Demokritov Ferromagnet/spin Hall effect (SHE) material bialyers are central to modern active nanomagnetic devices. The unidirectional magnetoresistance (UMR) observed in such structures – the asymmetry of resistance with respect to the current direction – has been explained in terms of spindependent electronic transport [1], or alternatively the effects of SHEinduced magnon generation [2]. 
Friday, March 8, 2019 8:36AM  9:12AM 
X39.00004: How to generate whispering gallery magnons Invited Speaker: Katrin Schultheiss One of the most fascinating topics in current quantum physics are hybridized systems, in which resonators of different quantum systems are strongly coupled. Prominent examples are circular resonators with high quality factors that allow the coupling of optical whispering gallery modes to microwave cavities or magnon resonances. However, the coupling to magnons with finite wave vectors has not yet been achieved due to the lack of efficient excitation schemes. 
Friday, March 8, 2019 9:12AM  9:24AM 
X39.00005: Spin and Charge Pumping and Spin Wave Emission by Magnetic Domain Wall Annihilation: QuantumClassical Micromagnetics Approach Marko Petrovic, Petr Petr Plechac, Branislav Nikolic Recent experiments on magnetic domain wall collisions [1] showed their importance in generating shortlived spin wave bursts, lowpower signals which can be used in future spintronics devices. Using a new, timedependent method to propagate the nonequilibrium density matrix (the TDNEGF method) combined with the classical LandauLifshitzGilbert (LLG) equation [2], we analyze spin and charge currents produced by an annihilation of two colliding domain walls in a magnetic material coupled to two electron reservoirs. The advantage of this approach is in its selfconsistent coupling between quantum electron spin and classical magnetic moments which gives rise to a dynamical Gilbert damping and allows for calculation of the exact charge current pumped out of the system, in contrast to an approximate solution given by the perturbative spin motive force formula combined with the LLG equation [3]. The pumped currents provide enough information to indirectly determine details of the annihilation event. 
Friday, March 8, 2019 9:24AM  9:36AM 
X39.00006: Magnon Damping in Yttrium Iron Garnet Films at Millikelvin Temperatures Sandoko Kosen, Arjan F. Van Loo, Laura Mihalceanu, Dmitry Bozhko, Alexander Serga, Alexy Karenowska Magnonbased quantum devices require low damping materials to maintain coherence. One of the most promising candidates is yttrium iron garnet (YIG). A ferrimagnetic insulator, YIG has the narrowest known linewidth of any practical material at room temperature. Bulk YIG has been shown to have low damping at millikelvin (mK) temperatures. However, there is some debate about whether this is the case in YIG films. Much of the uncertainty centres around the fact that the lowtemperature magnetic behaviour of the substrate upon which highquality samples are grown  gadolinium gallium garnet (GGG)  is not fully understood. 
Friday, March 8, 2019 9:36AM  9:48AM 
X39.00007: Nonlinear parallel pump FMR studies in magnetic insulators Aneesh Venugopal, Tao Qu, Randall Victora Nonlinear magnetic response of magnetic insulator materials is often used in the realization of radiofrequency (RF) devices. Although in use, there exists physical aspects that still need investigation for such devices. Here, we use high performance parallel computing based CUDA simulations and a theoretical model for magnon scattering to explore the direct and parametric generation of magnons, excited by microwaves in parallel pumped configurations. The sample is 10100s of um and the response is largely dominated by the demagnetization fields in the sample. The DC applied magnetic field is inplane and the RF field is linearly polarized and 
Friday, March 8, 2019 9:48AM  10:00AM 
X39.00008: Magnon transport in quasitwodimensional van der Waals antiferromagnets Wenyu Xing, Luyi Qiu, Xirui Wang, Yunyan Yao, Yang Ma, Ranran Cai, Shuang Jia, Xincheng Xie, Wei Han The recent emergence of 2D van der Waals magnets down to atomic layer thickness provides an exciting platform for exploring quantum magnetism and spintronics applications. However, the potential of 2D van der Waals magnets for magnonics, has not been explored yet. In this talk, we will present the experimental observation of long distance magnon transport over several micrometers in quasi2D van der Waals antiferromagnet MnPS_{3}. Experimentally, we exfoliated mechanically MnPS_{3} flakes down to a few nanometers, and then fabricated the devices of nonlocal geometry where MnPS_{3} is the transport channel of magnon. Then magnon is injected via thermal method and detected based on inverse spin Hall effect of platinum. As the quasi2D MnPS_{3} thickness decreases, a shorter magnon diffusion length is observed, which could be attributed to the surfaceimpurityinduced magnon scattering. 
Friday, March 8, 2019 10:00AM  10:12AM 
X39.00009: Spinwave Confinement and Coupling in OrganicBased Magnetic Nanostructures Michael Chilcote, Megan Harberts, Bodo Fuhrmann, Katrin Lehmann, Yu Lu, Andrew Franson, Howard Yu, Na Zhu, Hong X Tang, Georg Schmidt, Ezekiel JohnstonHalperin We present the synthesis of a new class of organicbased magnetic nanostructures consisting of nanowires of V[TCNE]_{x} that assemble along the ridges of a grooved substrate. These nanowires exhibit uniaxial magnetic anisotropy in direct contrast to the isotropic inplane response of typical thinfilms. When different magnon modes excited in these structures are brought into resonance by varying the orientation of an inplane magnetic field, we observe anticrossing behavior, indicating strong coherent coupling between excitations. Furthermore, micromagnetic simulations using real nanowire profiles extracted from crosssectional scanning electron microscopy faithfully reproduce the experimentally measured spectra without any free parameters, including spinwave and other higherorder modes. These results introduce a new degree of freedom for organicbased magnetism and spintronics, and together with recent demonstration of encapsulation technologies and demonstrated functional microwave devices that exhibit high quality factors across a frequency range, suggest future promising applications in microwave electronics and quantum magnonics. 
Friday, March 8, 2019 10:12AM  10:24AM 
X39.00010: Revisiting the Einsteinde Haas Effect Michael G Dunsmore, Kayte Mori, Miro Belov, John Thibault, Vincent T.K. Sauer, Joseph E Losby, Mark Freeman The Einsteinde Haas (EdH) effect manifests the intrinsic connection between magnetic moment and mechanical angular momentum. In the original experiment [1], angular momentum changes induced in an iron cylinder by fielddriven changes in the net magnetic moment were detected via resonant motion of a torsion pendulum. The miniaturization of torque sensors [2], combined with ultrasensitive optical detection, enables routine measurements of EdH effects. Millimeter to nanometerscale sensors affixed to yttrium iron garnet structures were fabricated to explore the frequencydependence of the EdH effect. Described are experimental methods for distinguishing EdH and conventional magnetic torques simultaneously. 
Friday, March 8, 2019 10:24AM  10:36AM 
X39.00011: Observation of Ultrastrong MagnonMagnon Coupling in YFeO_{3} in High Magnetic Fields Gary Noe, Motoaki Bamba, Xinwei Li, Ning Yuan, Jiashu Zhang, Zuanming Jin, Wei Ren, Guohong Ma, Shixun Cao, Dmitry Turchinovich, Junichiro Kono There is currently much interest in exploring resonant lightmatter interaction in the ultrastrongcoupling (USC) regime where light and matter mix to an extreme degree and a variety of new phenomena emerge [1]. Recently, we have extended the concept of USC to a magnetic context in the form of mattermatter interaction [2]. Specifically, the exchange interaction of paramagnetic Er^{3+} spins with an Fe^{3+} magnon field in ErFeO_{3} exhibited a large vacuum Rabi splitting. Here, we report another type of mattermatter USC between two magnon modes in YFeO_{3}. In rareearth orthoferrite materials, there are ferromagnetic (FM) and antiferromagnetic (AFM) modes of magnons in the terahertz (THz) frequency range. By performing singleshot THz timedomain spectroscopy with a tabletop pulsed magnet [3], we have investigated the magnetic field dependent magnon frequency and discovered anticrossing behavior for the FM and AFM magnon modes in high magnetic fields. The magnitude of the vacuum Rabi splitting suggests USC strength between the magnon modes when applying high magnetic fields at certain finite angles with respect to the crystallographic axes of bulk YFeO_{3}. 
Friday, March 8, 2019 10:36AM  10:48AM 
X39.00012: Magnonphoton coupling in orthoferrites Marcin Bialek, Arnaud Magrez, JeanPhilippe Ansermet We study the magnonphoton coupling at THz frequencies [1]. The Purcell effect and magnonpolaritons were shown in ferromagnetic materials [2, 3]. It is interesting to observe these interactions in antiferromagnetic materials due to their highfrequency magnetic resonances. We report on an magnonphonon coupling in hightemperature antiferromagnets, bismuth ferrite BiFeO_{3} (BFO) and dysprosium ferrite DyFeO_{3 }(DFO). We investigated polycrystaline samples of different thicknesses, thus having different sets of FabryPerrottype cavity modes. We measured transmission spectra in 200350 GHz frequency band at 300600 K temperature range using frequency extenders to a vector network analyzer. Magneticresonance frequencies soften with rising temperature and cross with cavity modes. In BFO samples, we found that the width of the resonant line broadens at these crossings, consistent with the Purcell effect. In DFO samples, our data show avoided crossings of resonances with cavity modes, which is an indication of magnonpolaritons. 
Friday, March 8, 2019 10:48AM  11:00AM 
X39.00013: Spin Waves Across 3Dimensional, ClosePacked Nanoparticles Kathryn Krycka, James J Rhyne, Samuel D Oberdick, Ahmed M Abdelgawad, Julie Borchers, Yumi Ijiri, Sara Majetich, Jeffrey W Lynn While there is much practical and theoretical interest in characterizing magnons within 3dimensional selfassembled nanoscale systems, few experimental techniques are appropriate. Here inelastic neutron scattering, although intensity limited, is utilized to measure internanoparticle spin waves, or magnons, which arise from coupling between 8.4 nm manganese ferrite nanoparticles that are selfassembled into a closepacked lattice, yet physically separated by oleic acid surfactant. The observed magnons are dispersive, respond to an applied magnetic field, and display the expected temperaturedependent Bose population factor. Moreover, the dispersion yields a nonnegative energy gap only when the effective Q is reduced by the interparticle spacing, confirming that it is a collective excitation between the nanoparticles, rather than originating within individual nanoparticles. The experimental results are well explained by a limited parameter model which treats the 3dimensional ordered, magnetic nanoparticles as dipolarcoupled superspins. 
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