Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Q29: Focus Session: Spin-waves and Magnetizion Dynamics |
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Sponsoring Units: GMAG DMP FIAP Chair: Vassilios Kapaklis, University of Uppsala Room: 206A |
Wednesday, March 4, 2015 2:30PM - 2:42PM |
Q29.00001: Excitation and detection of propagating spin waves at the single magnon level. Alexy Karenowska, Andrew Patterson, Michael Peterer, Einar Magn\'usson, Peter Leek The fields of spin-wave dynamics and magnonics have made substantial contributions to our understanding of fundamental magnetism, and are increasingly widely acknowledged to be areas of solid-state physics with significant technological potential. To date however, experimental activity has focused on the study and possible application of room-temperature systems operating within classical limits. Here, we report a series of experiments in which we demonstrate, for the first time, the excitation and detection of propagating spin waves at the single magnon level. Our results, which have been obtained at cryogenic temperatures using an yttrium iron garnet spin-wave waveguide, serve as evidence that the experimental tools now exist to permit us to create microwave (i.e. GHz frequency) quantum circuits incorporating dispersive magnon systems. This allows us to anticipate the possibility both of exploring quantum aspects of magnon physics with new experimental clarity, and of examining how this physics --- in particular, the magnon's highly tunable dispersion, its readily accessible nonlinearity, and its capacity to couple to optical excitations and electron-based spintronic systems --- might have a role to play in new microwave quantum technologies. [Preview Abstract] |
Wednesday, March 4, 2015 2:42PM - 2:54PM |
Q29.00002: Surface Acoustic Waves for Traveling Spin-Wave Resonance Spectroscopy Praveen Gowtham, Takahiro Moriyama, Daniel Ralph, Robert Buhrman Gigahertz frequency surface acoustic waves (SAWs) can, via the magnetoelastic interaction, generate effective RF pump fields that can resonantly excite spin waves in a thin-film ferromagnet. SAWs provide a powerful means to study spin waves because the pump field excites traveling spin waves with a definite nonzero wave-vector \textbf{q}. This enables studies, at fixed \textbf{q}, of the spin-wave self-interaction energies and damping. Here we report measurements of the angular dependence of SAW-induced magnetic resonance in Al(10)\textbar AlOx(2)\textbar Ni(10)\textbar Pt(15) structures (thicknesses in nm). We characterize the resonances by measurement of both the acoustical transmission loss in a SAW delay line and the inverse spin Hall voltage generated in the Pt layer by spin pumping. The measurements allow quantitative determinations of the effective RF field generated by the SAW, the magnetoelastic coupling, and damping. The angular dependence reveals that, within the range of \textbf{q} studied, the spin-wave self-interactions are dominated by dipolar fields rather than exchange. [Preview Abstract] |
Wednesday, March 4, 2015 2:54PM - 3:06PM |
Q29.00003: Control of Spin Wave Band Structure and Propagation in Two-Dimensional Magnonic Crystals Glade Sietsema, Michael E. Flatt\'e We have studied the properties of spin waves in two-dimensional magnonic crystals consisting of a magnetic material arranged in a lattice of cylinders and embedded in a second magnetic material. Dispersion curves, linewidths, and spin wave propagation patterns were obtained from the Landau-Lifshitz-Gilbert equation using the plane wave expansion method[1]. We have examined how these results are affected by various parameters including the shape of the cylinders, the lattice structure, the material properties, and the spin-orbit interaction. Adjusting these values can open or close band gaps and drastically shift the frequency range of the band structure. The spin wave propagation patterns were found to exhibit high directionality dependent on the excitation frequency and can also be modified with the aforementioned parameters.\\[4pt] [1]arXiv:1111.2506 [Preview Abstract] |
Wednesday, March 4, 2015 3:06PM - 3:18PM |
Q29.00004: Spin Wave Directional Coupler Kasuni Nanayakkara, Alexander Kozhanov Spin wave based logic devices are evolved as promising candidates for information processing due to potential in scaling and low power consumption. An element performing directional energy transfer between spin waveguides is required in order to implement existing proposed spin wave logic devices. Optical waveguide couplers are well studied and widely utilized in integrated and fiber optics applications. In this work we apply the concept of optical directional coupler to design and investigate the spin wave directional coupler comprised of the two ferromagnetic stripes separated by a nanometer scale air gap. Micromagnetic simulations and experimental spin wave energy transfer investigations using propagating spin wave spectroscopy were carried out. Spin waves are generated at one of the ends of the input waveguide while detected at remaining three ends of both spin waveguides. Spin wave coupling is investigated as the coupler geometry, biasing magnetic field amplitude and orientation and the spin wavelength are varied. Results are modeled as coupled backward volume magnetostatic spin wave modes. [Preview Abstract] |
Wednesday, March 4, 2015 3:18PM - 3:30PM |
Q29.00005: Electric-Field Control over Spin-Wave and Current Induced Domain Wall Motion and Magnonic Torques in Multiferroics Iryna Kulagina, Jacob Linder We discover that the way spin-waves exert magnetic torques in multiferroic materials can cause not only domain wall motion, but also magnetization dynamics for homogeneous magnetization textures. Interestingly, the domain wall motion can be controlled via purely electrical means with the spin-waves being generated by an ac electric field E while the direction of the wall motion also is sensitive to an applied dc E field. Moreover, we determine the interaction between spin-transfer torque from an electric current and a magnetic domain wall in multiferroics and show that the Walker breakdown threshold scales with the magnitude of a perpendicular electric field, offering a way to control the properties of domain wall propagation via electric gating. [Preview Abstract] |
Wednesday, March 4, 2015 3:30PM - 3:42PM |
Q29.00006: Generalized stochastic Landau-Lifshitz-Gilbert equation for yttrium-iron garnet films Andreas R\"{u}ckriegel, Peter Kopietz We derive a generalization of the well-known stochastic Landau-Lifshitz-Gilbert equation starting from a microscopic Heisenberg model coupled to the lattice degrees of freedom. By integrating out the phonons we obtain a non-Markovian, stochastic equation of motion for the spin degrees of freedom satisfying a Fluctuation-Dissipation theorem. We apply our theory to study the parametric pumping and thermalization of spin excitations in thin yttrium-iron garnet films. [Preview Abstract] |
Wednesday, March 4, 2015 3:42PM - 3:54PM |
Q29.00007: Angle-dependent 2D domain wall motion with Dzyaloshinskii-Moriya interaction Jin Lan, Jiang Xiao, Ruqian Wu We explore the dependence of the 2D domain wall motion on the incident angle of magnons (spin waves), in the presence of the Dzyaloshinskii-Moriya interaction (DMI). It is found that the domain wall may either be dragged toward or be pushed away from the magnon source, depending on the incident angle of the magnons. This is mainly contributed by the linear momentum absorbed or released by the DMI when magnons pass through the domain wall. In addition, the total internal reflection of magnons beyond a critical incident angle from one side also contributes to the pushing effect. This adds a new mechanism for the magnetic domain wall motion. [Preview Abstract] |
Wednesday, March 4, 2015 3:54PM - 4:06PM |
Q29.00008: ABSTRACT WITHDRAWN |
Wednesday, March 4, 2015 4:06PM - 4:18PM |
Q29.00009: Field- and current- induced domain wall creep motions in Tb-based ferrimagnetic alloys with varying compositions Michael Quinsat, Shiho Nakamura, Takuya Shimada, Yasuaki Ootera, Hirofumi Morise, Tsuyoshi Kondo Due to their tunable magnetization (Ms), Tb-based ferrimagnetic alloys are expected as promising materials for spintronic devices utilizing current-induced domain wall motion (CIDWM) with low current-density. On this material system, we have investigated domain wall motions (DWM) induced by magnetic field $H$ or electric current $J$ in creep regime. We fabricated 2-$\mu $m-wide and 9-nm-thick wires made of Tb-based alloys of various composition ratios Tb/CoFe, resulting in Ms of 35-150 emu/cc. From the DW velocities $v$ - $H$ characteristics for the wires, we obtained creep exponents between 1 and 1/4 suggesting strong potential-disorder for DW in the samples[1]. In CIDWM experiments, we also identified creep with $J$ ranging from 5 to 20 MA/cm$^{\mathrm{2}}$. It is found that the creep driven by $J$ is impeded more seriously by increasing the DW pinning strength observed in the creep by $H$, while the J-induced DW motion is in the electrons' flow. We infer that the observed DW motion by $J$ for the present samples is interfered with the potential disorders, unlike to the case of Co/Ni wires in a literature[2]. [1] A.B. Kolton et al., Phys. Rev. Lett. 94, 047002 (2005). [2] T. Koyama et al., Nature Materials 10, 194 (2011). [Preview Abstract] |
Wednesday, March 4, 2015 4:18PM - 4:30PM |
Q29.00010: Comparison of Current and Field Driven Domain Wall Motion in Beaded Permalloy Nanowires Enno Lage, Sumit Dutta, Caroline A. Ross Domain wall based devices are promising candidates for non-volatile memory devices with no static power consumption. A common approach is the use of (field assisted) current driven domain wall motion in magnetic nanowires. In such systems local variations in linewidth act as obstacles for propagating domain walls. In this study we compare simulated field driven and current driven domain wall motion in permalloy nanowires with anti-notches. The simulations were obtained using the Object Oriented MicroMagnetics Framework (OOMMF). The wires with a constant thickness of 8 nm exhibit linewidths ranging from 40 nm to 300 nm. Circular shaped anti-notches extend the linewidth locally by 10\% to 30\% and raise information about the domain wall propagation in such beaded nanowires. The results are interpreted in terms of the observed propagation behavior and summarized in maps indicating ranges of different ability to overcome the pinning caused by anti-notches of different sizes. Furthermore, regimes of favored domain wall type (transverse walls or vortex walls) and complex propagation effects like walker breakdown behavior or dynamic change between domain wall structures are identified [Preview Abstract] |
Wednesday, March 4, 2015 4:30PM - 4:42PM |
Q29.00011: Direct X-Ray Imaging of Transient Spin Accumulation near a Ferromagnet/Nonmagnet Interface Zhao Chen, Roopali Kukreja, Stefano Bonetti, Dirk Backes, Andrew Kent, Jordan Katine, Hermann Durr, Hendrik Ohldag, Joachim Stohr The physics of spin transport across a ferromagnet/nonmagnet interface is not well understood, even though such interfaces are common in spintronic devices. We use time-resolved x-ray spectro-microscopy to directly image transient spin accumulation in a Cu film caused by an injected spin current from an adjacent Co film. The measurement uses element-specific, circularly polarized x-rays detected via a scanning transmission x-ray microscope (STXM) in conjunction with 1.28MHz temporal modulation for remarkably increased x-ray sensitivity to spin signals. The transient moments per atom within the spin diffusion length from the interface were measured to be 8 x $10^{-5}\mu_B$ per Cu atom and 1.5 x $10^{-4}\mu_B$ per Co atom. The transient spin signal in Cu is found to be confined to states at the Fermi level, as expected, but we also observe a second peak of the same spin polarization in the spin accumulation signal that is 0.7eV higher than Fermi. The transient moments in the 28nm thick Cu layer exhibit the same spin sign as both the hybridization-induced static spins in Cu at the Cu/Co interface and the spins in the Co film. In contrast, the transient moments in the Co layer have the opposite sign, consistent with magnetization depleting from the Co polarizing layer. [Preview Abstract] |
Wednesday, March 4, 2015 4:42PM - 4:54PM |
Q29.00012: Spin transport and dynamics in the F/N junction Hua Li, Kevin Bedell We study the spin transport in the low temperature regime (often referred to as the precession-dominated regime) between a ferromagnetic Fermi liquid (FFL) and a normal metal metallic Fermi liquid (NFL), the F/N junction, which is considered one of the basic spintronic devices. In particular, we explore the propagation of spin waves and transport of magnetization through the interface of the F/N junction where non-equilibrium spin polarization is created on the normal metal side of the junction by spin injection. We calculate the probable spin wave modes in the precession-dominated regime on both sides of the junction especially on the NFL side where the system is out of equilibrium. Proper boundary conditions at the interface are introduced to establish the transport of the spin properties through the F/N junction. In the end, a possible transmission conduction electron spin resonance experiment is suggested on the F/N junction to see if the predicted spin wave modes could propagate through the junction. [Preview Abstract] |
Wednesday, March 4, 2015 4:54PM - 5:06PM |
Q29.00013: Current-induced spin polarization in transition metals and Bi/Ag bilayers observed by spin-polarized positron beam Hongjun Zhang, Shunya Yamamoto, Yuki Fukaya, Masaki Maekawa, Hui Li, Atsuo Kawasuso, Takeshi Seki, Eiji Saitoh, Koki Takanashi Current-induced spin polarization (CISP) on the outermost surfaces of Au, Cu, Pt, Pd, Ta, and W films were studied by spin-polarized positron beam (SPPB). The Au and Cu surfaces showed no significant CISP. In contrast, the Pt, Pd, Ta, and W films exhibited large CISP (3 $\sim$ 15\% per charge current of $10^{5}$ A/cm$^{2}$) and the CISP of Ta and W were opposite to those of Pt and Pd. The sign of the CISP obeys the same rule in spin Hall effect suggesting that the spin-orbit coupling is mainly responsible for the CISP.\footnote{H. J. Zhang \emph{et al}., Scientific Reports {\bf4}, 4844 (2014).} The outermost spin poalrization of Bi/Ag/Al$_{2}$O$_{3}$ and Ag/Bi/Al$_{2}$O$_{3}$ (charge currents directly connected to Ag layers) were probed by SPPB. The opposite outermost spin polarization of Bi/Ag/Al$_{2}$O$_{3}$ and Ag/Bi/Al$_{2}$O$_{3}$ clarified the charge-to-spin conversion in Bi/Ag bilayers. Nevertheless, the magnitudes of the outermost spin polarization of Bi(0.3$\sim$5)/Ag(25)/Al$_{2}$O$_{3}$ (numbers in parentheses denote thickness in nm) and Ag(25$\sim$500)/Bi(8)/Al$_{2}$O$_{3}$ decrease exponentially with increasing Bi thickness and Ag thickness, respectively. This provides probably the first direct evidence for spin diffusion mechanism. [Preview Abstract] |
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