Final Report Summary - SPINTORQOSC (Spin torque oscillators with applications in non digital computing science and communications.) SpinTorqOsc aimed at studying spin-wave excitations in ferromagnetic thin films and implementing biological inspired computations in nano-structures, likely in terms of spin waves in ferromagnetic films. The project joined Prof. F.C. Hoppensteadt’s research in mathematical neuroscience and Prof. A.D. Kent's group expertise on experimental nanomagnetism both at New York University. Dr. F. Macià has lead the effort on this multidisciplinary team and he brought the scientific outcome and expertise to the Magnetics Lab at University of Barcelona with Prof. J. Tejada and Dr. J. M. Hernandez.Specifically, the project main objectives were i) direct imaging and study of spin-wave excitations produce by nanocontacts (spin torque oscillators, STOs) in ferromagnetic films and ii) modeling and implementing wavefront computations using spin-waves. Achievement of main objectives required a multidisciplinary approach involving research activities such as study of ferromagnetic thin films, nanofabrication of nanopoint contacts, mathematical modeling of the physical implementations, electric and magnetic characterization of fabricated devices and X-ray synchrotron studies.In the first stages of the project we modeled spin-wave excitations from STOs and we have proposed a model for implementing biological inspired computations with wave-fronts in nano structures [1,2]. We have built a proposal for a system capable of computing with waves, similarly to what the brain does [3] and further we suggested other utilities for the arrays os STNOs [14]. Briefly, the proposal consists in a medium, the ferromagnetic thin films where spin waves propagate and interfere, and the transponders, STOs (point contacts to the ferromagnetic thin films) that can excite magnetization dynamics and, at the same time, sense any incoming spin wave. The proposed system works at the nanometer scale and with gigahertz frequencies. STNOs can synchronize and create diffusive spin-wave patterns in the ferromagnetic thin films [14]. The STNOs themselves may be used as well as detectors of spin wave activity and thus as readers of information. Experimentally, we have studied what would be the best materials to use as ferromagnetic thin films. We have fabricated, measured, optimized and imaged in two different synchrotrons: (some at Brookhaven National Lab with Dr. D. A. Arena and some at Lawrence National Lab with Dr. P. Fischer). The results are summarized in [4]. We have succeeded at fabricating STO devices on the desired ferromagnetic thin films. Electrical measurements on fabricated STOs have shown spin-wave activity. We have imaged spin-wave activity at the beamline at SLAC (synchrotron at Stanford) after several runs that forced us to modify our sample’s design to fit with the synchrotron needs. The results of these experiments are still being considered for publication and they will appear soon.We have explored complementary approaches to both imaging/controlling spin waves in ferromagnetic thin films and modeling spin-wave activity. One direction we followed is the use of organic semiconductors to sense the spin-wave activity. We first coupled a ferromagnetic thin film with an organic film and designed an experiment that studied the effect of magnetic domains—as a means of creating a distribution of fringe fields as would happen in the case of spin waves—on the organic material conductance [5]. We continued experiments on the coupling between the magnetic thin films and the organic semiconductors [6,7] and we discovered a new effect that consists in transduction of a magnetic signal (magnetic domains) into an optical signal (electroluminescence in the organic semiconductor) [15]. Another complementary approach we followed to study spin dynamics on ferromagnetic thin films was to study ferromagnetic resonance on LSMO manganites and how to control its magnonic behavior [8,9,10]. This was done in collaboration with Erik Wahlström from Institutt for Fysikk in Trondheim, Norway.In order to strengthen the collaboration between the outgoing and the returning groups, a graduate student from the Magnetism Lab at Universitat de Barcelona (returning institution) has spent 3+1 months at NYU and we have designed an experiment to study and control spin reversing in molecule magnets; this process consist in a spin-wave front that propagates mediated by phonons. We have shown how to control the onset of magnetic deflagration in a molecule magnet [11,13]. Our published manuscript has been highlighted by the American Physical Society (APS) with a viewpoint article [12]. In the returning phase of the project we continued with the planned experiment of imaging spin-waves in ferromagnetic thin films; we have produced a considerable number of STO devices to study. We found a new regime of excitations in the STNOs—droplet solitons [16]. And we imaged them in the synchrotron [17]References[1] Ferran Macià, Andrew D. Kent and Frank C. Hoppensteadt. Spin-wave interference patterns created by spin-torque nano-oscillators for memory and computation. NANOTECHNOLOGY Volume: 22 Issue:9 Article Number: 095301 (2011)[2] Ferran Macià, Andrew D. Kent and Frank C. Hoppensteadt. Anisotropic spin-wave patterns generated by spin-torque nano-oscillators. JOURNAL OF APPLIED PHYSICS 109, 07C733 (2011). [3] Ferran Macià, Andrew D. Kent and Frank C. Hoppensteadt. Aggregated spin-torque nano-oscillators. Patent Application Number PCT/US2011/044790.[4] F. Macià, P. Warnicke, D. Bedau, M.-Y. Im, P. Fischer, D. A. Arena, and A. D. Kent. Perpendicular magnetic anisotropy in ultrathin Co|Ni multilayer films studied with ferromagnetic resonance and magnetic x-ray microspectroscopy. JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS. 324 (2012) 3629–3632 [5] Fujian Wang, Ferran Macià, Markus Wohlgenannt, Andrew D. Kent, and Michael E. Flatté. Magnetic fringe field control of electronic transport in an organic film. PHYSICS REVIEW X, 2, 021013 (2012)[6] F. Macià, F. Wang, N. J. Harmon, M. Wohlgenannt, A. D. Kent, and M. E. Flatté. Hysteretic control of organic conductance due to remanent magnetic fringe fields. APPLIED PHYSICS LETTERS 102, 042408 (2013)[7] N. J. Harmon, F. Macià, F. Wang, M. Wohlgenannt, A. D. Kent and M. E. Flatté. Including fringe fields from a nearby ferromagnet in a percolation theory of organic magnetoresistance. PHYSICAL REVIEW B 87, 121203(R) (2013)[8] E. Wahlström, Ferran Macià, Jos E. Boschker, Asmund Monsen, Per Nordblad, Roland Mathieu, Andrew Kent and Thomas Tybell. Perovskite manganite magnonic crystals - growth control of dynamic magnetic properties of La0.7Sr0.3MnO3/SrTiO3(001) thin films. (In prepeartion)[9] F. Macià, E. Wahlström, and A. D. Kent. Exchange bias control of magnetization dynamics–directional damping and temperature effects in the Py/IrMn system. (In prepeartion)[10] Asmund Monsen, Jos E. Boschker, Ferran Macià, Justin Wells, Per Nordblad, Andrew Kent, Roland Mathieu, Thomas Tybell, and Erik Wahlström. Thickness dependence of dynamic and static magnetic properties of pulsed laser deposited La0.7Sr0.3MnO3 films on SrTiO3(001). Jour. of Mag. and Mag. Mat. 369, 197 (2014)[11] P. Subedi, S. Vélez, F. Macià, S. Li, M. P. Sarachik, J. Tejada, S. Mukherjee, G. Christou, and A. D. Kent. Onset of a Propagating Self-Sustained Spin Reversal Front in a Magnetic System. PHYSICS REVIEW LETTERS 110, 207203 (2013)[12] Je-Geun Park and Carley Paulsen. Viewpoint: Fire in a Quantum Mechanical Forest. Physics 6, 55 (2013)[13] P. Subedi, S. Vélez, F. Macià, S. Li, M. P. Sarachik, J. Tejada, S. Mukherjee, G. Christou, and A. D. Kent. Magnetic field control of magnetic deflagration. Phys. Rev. B, 89, 144408, (2014)[14] Ferran Macià, Frank C. Hoppensteadt and Andrew D. Kent. Spin wave excitation patterns generated by spin torque oscillators. NANOTECHNOLOGY Volume: 25 Issue:4 Article Number: 045303 (2014)[15] Ferran Macià, Fujian Wang, Nicholas J. Harmon, Andrew D. Kent, Markus Wohlgenannt and Michael E. Flatté. Organic magnetoelectroluminescence for room temperature transduction between magnetic and optical information. Nature Communications, 5, 3609, (2014)[16] Ferran Macià, Dirk Backes and Andrew D. Kent Stable Magnetic Droplet Solitons in Spin Transfer Nanocontacts (submitted to Nat. Nanotechology) [17] Dirk Backes, Ferran Macià and Andrew D. Kent. Imaging of droplet solitons with xrays (in preparation) Related documents final1-publishable-summary.pdf
