Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session E24: Spin Orbit Torques and Spin WavesInvited
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Sponsoring Units: GMAG Chair: Chris Hammel, Ohio State University Room: New Orleans Theater C |
Tuesday, March 14, 2017 8:00AM - 8:36AM |
E24.00001: A reconfigurable waveguide for energy-efficient transmission and local manipulation of information in a nanomagnetic device Invited Speaker: Adekunle Adeyeye In the last few years, interest in propagating-spin-wave based devices has grown largely due to advances in nanotechnology which allows shapes of geometrically confined magnonic elements to be fabricated, the development of new advanced experimental techniques for studying high-frequency magnetization dynamics and the potential use of spin waves as information carriers in spintronic applications. The first part of this talk will focus on design and fabrication strategies for synthesizing nanomagnetic networks with deterministic magnetic ground states [1]. Reliable reconfiguration between ferromagnetic (FM), antiferromagnetic (AFM) and ferrimagnetic ground magnetic states will be shown in rhomboid nanomagnets which stabilize to unique ground states upon field initialized along their short axis [2]. In the second part, a new waveguide consisting of dipolar coupled rhombic shaped nanomagnetic chain that eliminate the requirement of a stand-by power during operation will be presented [3]. The sizes of the nanomagnets are small enough to retain their correct magnetic states once initialized. It will be shown that our waveguide could be used to send spin wave signal around a corner without any stand-by power. Another important parameter for device operation is the manipulation of the output signal, which is similar to a gating operation in a transistor. In our design, gating operation is demonstrated by switching the magnetization of single/multiple nanomagnets in the waveguides in order to manipulate the spin wave amplitude at the output. [1] A. Haldar and A. O. Adeyeye, ACS Nano 10, 1690-1698 (2016). [2] A. Haldar and A. O. Adeyeye, Appl. Phys. Lett. 108, 022405 (2016). [3] A. Haldar, D. Kumar and A. O. Adeyeye, Nature Nanotech 11,437-443 (2016). [Preview Abstract] |
Tuesday, March 14, 2017 8:36AM - 9:12AM |
E24.00002: Excitation of propagating spin waves by pure spin current Invited Speaker: Sergej Demokritov Recently it was demonstrated that pure spin currents can be utilized to excite coherent magnetization dynamics, which enables development of novel magnetic nano-oscillators. Such oscillators do not require electric current flow through the active magnetic layer, which can help to reduce the Joule power dissipation and electromigration. In addition, this allows one to use insulating magnetic materials and provides an unprecedented geometric flexibility. The pure spin currents can be produced by using the spin-Hall effect (SHE). However, SHE devices have a number of shortcomings. In particular, efficient spin Hall materials exhibit a high resistivity, resulting in the shunting of the driving current through the active magnetic layer and a significant Joule heating. These shortcomings can be eliminated in devices that utilize spin current generated by the nonlocal spin-injection (NLSI) mechanism. Here we review our recent studies of excitation of magnetization dynamics and propagating spin waves by using NLSI. We show that NLSI devices exhibit highly-coherent dynamics resulting in the oscillation linewidth of a few MHz at room temperature. Thanks to the geometrical flexibility of the NLSI oscillators, one can utilize dipolar fields in magnetic nano-patterns to convert current-induced localized oscillations into propagating spin waves. The demonstrated systems exhibit efficient and controllable excitation and directional propagation of coherent spin waves characterized by a large decay length. The obtained results open new perspectives for the future-generation electronics using electron spin degree of freedom for transmission and processing of information on the nanoscale. References: V. E. Demidov et al., Nature Materials 11, 1028 (2012); V. E. Demidov et al., Sci. Rep. 5, 8578 (2015); V. E. Demidov et al., \quad Appl. Phys. Lett. 107, 202402 (2015); V. E. Demidov et al., Nat. Commun. 7, 10446 (2016). [Preview Abstract] |
Tuesday, March 14, 2017 9:12AM - 9:48AM |
E24.00003: Magnon Condensates in Spin-Transfer Torque Nanocontacts Invited Speaker: Andrew D. Kent In ferromagnets with uniaxial magnetic anisotropy there is an attractive interaction between spin-wave excitations or magnons. This can lead to the formation of a magnon condensate, predicted in the late 1970s---also known as a magnetic droplet soliton [1]. Only recently has it been possible to realize this state experimentally by creating a non-equilibrium magnon population using spin-transfer torques from a spin-polarized current. Experiments are conducted using a nanocontact to a thin film with perpendicular magnetic anisotropy [3-6]. DC and high frequency transport measurements demonstrate that magnetic droplet solitons exhibit a strong hysteretic response to field and current, showing the existence of bistable states: droplet and non-droplet states [4]. We also present the first direct observation of droplet solitons using scanning transmission x-ray microscopy (SXTM) [5]. Element resolved x-ray magnetic circular dichroism images show an abrupt onset of magnetic solitons at a threshold current, as predicted by theory [2]. The amplitude of the excitation, however, is far less than predicted. A possible origin of this discrepancy is a resonant drift instability, whereby the droplet periodically moves out of the contact region, annihilates and renucleates in the nanocontact [6,7]. Our recent measurements of the time scale for droplet generation and annihilation with pulsed currents show that annihilation takes several ns but the generation time is much longer, $\sim$ 100 ns. These recent results will be presented along with a prespective on future experiments with magnon condensates.\\ \\ 1. A. Ivanov and A. M. Kosevich JETP {\bf 45}, 1050 (1978) \\ 2. M. A. Hoefer, T. J. Silva, and M. W. Keller, PRB {\bf 82}, 054432 (2010)\\ 3. M. Mohseni {\it et al.}, Science {\bf 339}, 1295 (2013)\\ 4. F. Macia, D. Backes and A. D. Kent, Nat. Nano. {\bf 9}, 992 (2014)\\ 5. D. Backes, F. Macia, S. Bonetti, R. Kukreja, H. Ohldag and A. D. Kent, PRL {\bf 115}, 127205 (2015)\\ 6. S. Lendnez, N. Statuto, D. Backes A. D. Kent and F. Macia, PRB {\bf 92}, 174426 (2015)\\ 7. P. Wills, E. Iacocca, and M. A. Hoefer, PRB {\bf 93}, 144408 (2016)\\ [Preview Abstract] |
Tuesday, March 14, 2017 9:48AM - 10:24AM |
E24.00004: Neuromorphic computing with spin-torque nano-oscillators Invited Speaker: Julie Grollier The brain displays many features typical of non-linear dynamical networks, such as synchronization or complex transient behaviour. These observations have inspired a whole class of models that harness the power of complex non-linear dynamical networks for computing. In this framework, neurons are modeled as non-linear oscillators, and synapses as the coupling between oscillators. These abstract models are very good at processing waveforms for pattern recognition. However there are very few hardware implementations of these systems, because large numbers of interacting non-linear oscillators are indeed. Magnetic nano-devices, and in particular spin-torque oscillators are interesting in this context because of their tunability combined with their small size, CMOS compatibility, endurance and speed \footnote{J. Grollier, D. Querlioz, M.D. Stiles, “Spintronic nanodevices for bioinspired computing”, PIEEE 104, 2024 (2016)}. In this talk, I will show different ways of leveraging the non-linear dynamics of spin-torque nano-oscillators for neuromorphic computing, and present our first experimental results of speech recognition. [Preview Abstract] |
Tuesday, March 14, 2017 10:24AM - 11:00AM |
E24.00005: Long-range mutual synchronization of spin Hall nano-oscillators. Invited Speaker: Johan Akerman We present the first experimental demonstration of mutual synchronization of up to nine nano-constriction based spin Hall nano-oscillators (SHNOs) [1]. The mutual synchronization is observed both as a strong increase in the power and coherence of the electrically measured microwave signal. The mutual synchronization is also optically probed using scanning micro-focused Brillouin light scattering microscopy ($\mu $-BLS), providing the first direct imaging of synchronized nano-magnetic oscillators. Through tailoring of the region connecting two SHNOs, we are able to extend the synchronization range to 4 $\mu$ m. Given the design flexibility of nano-constriction SHNOs [2], and the very long synchronization range, we argue that our results open up many research and application opportunities where coherent phase locking is believed to be advantageous, e.g. for energy efficient spin wave computing on the nanoscale. [1] A. A. Awad, P. D\"{u}rrenfeld, A. Houshang, M. Dvornik, E. Iacocca, R. K. Dumas, and J. {\AA}kerman, Nature Physics, 10.1038/nphys3927 (2016). [2] V. E. Demidov, S. Urazhdin, A. Zholud, A. V. Sadovnikov, and S. O. Demokritov, Appl. Phys. Lett. 105, 172410 (2014) [Preview Abstract] |
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