31 research outputs found
Nanowire Spin Torque Oscillator Driven by Spin Orbit Torques
Spin torque from spin current applied to a nanoscale region of a ferromagnet
can act as negative magnetic damping and thereby excite self-oscillations of
its magnetization. In contrast, spin torque uniformly applied to the
magnetization of an extended ferromagnetic film does not generate
self-oscillatory magnetic dynamics but leads to reduction of the saturation
magnetization. Here we report studies of the effect of spin torque on a system
of intermediate dimensionality - a ferromagnetic nanowire. We observe coherent
self-oscillations of magnetization in a ferromagnetic nanowire serving as the
active region of a spin torque oscillator driven by spin orbit torques. Our
work demonstrates that magnetization self-oscillations can be excited in a
one-dimensional magnetic system and that dimensions of the active region of
spin torque oscillators can be extended beyond the nanometer length scale.Comment: The link to the published version is
http://www.nature.com/ncomms/2014/141205/ncomms6616/full/ncomms6616.htm
Chiral charge pumping in graphene deposited on a magnetic insulator
We demonstrate that a sizable chiral charge pumping can be achieved at room
temperature in graphene/Yttrium Iron Garnet (YIG) bilayer systems. The effect,
which cannot be attributed to the ordinary spin pumping, reveals itself in the
creation of a dc electric field/voltage in graphene as a response to the
dynamic magnetic excitations (spin waves) in an adjacent out-of-plane
magnetized YIG film. We show that the induced voltage changes its sign when the
orientation of the static magnetization is reversed, clearly indicating the
broken spatial inversion symmetry in the studied system. The strength of effect
shows a non-monotonous dependence on the spin-wave frequency, in agreement with
the proposed theoretical model.Comment: 8 pages, 5 figure
Degenerate and non-degenerate parametric excitation in YIG nanostructures
We study experimentally the processes of parametric excitation in microscopic
magnetically saturated disks of nanometer-thick Yttrium Iron Garnet. We show
that, depending on the relative orientation between the parametric pumping
field and the static magnetization, excitation of either degenerate or
non-degenerate magnon pairs is possible. In the latter case, which is
particularly important for applications associated with the realization of
computation in the reciprocal space, a single-frequency pumping can generate
pairs of magnons whose frequencies correspond to different eigenmodes of the
disk. We show that, depending on the size of the disk and the modes involved,
the frequency difference in a pair can vary in the range 0.1-0.8 GHz. We
demonstrate that in this system, one can easily realize a practically important
situation where several magnon pairs share the same mode. We also observe the
simultaneous generation of up to six different modes using a fixed-frequency
monochromatic pumping. Our experimental findings are supported by numerical
calculations that allow us to unambiguously identify the excited modes. Our
results open new possibilities for the implementation of reciprocal-space
computing making use of low damping magnetic insulators.Comment: 18 pages, 4 figure
Zeroing neural networks for computing quaternion linear matrix equation with application to color restoration of images
The importance of quaternions in a variety of fields, such as physics, engineering and computer science, renders the effective solution of the time-varying quaternion matrix linear equation (TV-QLME) an equally important and interesting task. Zeroing neural networks (ZNN) have seen great success in solving TV problems in the real and complex domains, while quaternions and matrices of quaternions may be readily represented as either a complex or a real matrix, of magnified size. On that account, three new ZNN models are developed and the TV-QLME is solved directly in the quaternion domain as well as indirectly in the complex and real domains for matrices of arbitrary dimension. The models perform admirably in four simulation experiments and two practical applications concerning color restoration of images
Effect of spin-polarized electric current on spin-wave radiation by spin-valve nanocontacts
Demidov VE, Demokritov SO, Reiss G, Rott K. Effect of spin-polarized electric current on spin-wave radiation by spin-valve nanocontacts. APPLIED PHYSICS LETTERS. 2007;90(17):172508.Using a spatially resolved microfocus Brillouin light scattering technique with spatial resolution of 250 nm, the authors have studied radiation of spin waves by a spin-valve nanocontact into a continuous underlying magnetic film. They have found that a spin-polarized electric current flowing through the contact affects the intensity of radiated spin waves. They show that for one of the directions of the current, the spin-wave intensity is noticeably increased, whereas for the other direction, spin waves are suppressed. They associate the findings with an amplification of spin waves due to spin-torque-transfer phenomena. (c) 2007 American Institute of Physics
Nano-optics with spin waves at microwave frequencies
Demidov VE, Demokritov SO, Rott K, Krzysteczko P, Reiss G. Nano-optics with spin waves at microwave frequencies. APPLIED PHYSICS LETTERS. 2008;92(23):232503.With the recent development in nanoscale patterning techniques, the potential of practical applications of nanometer-size structures for signal processing has been growing continuously. Experimental findings on the manipulation of optical signals in nanostructures have recently given rise to a widely addressed scientific area-subwavelength nano-optics. Here, we demonstrate that spin waves in microscopic ferromagnetic film structures represent a superb object for realization of the principles of nano-optics in the microwave frequency range. We show experimentally that by using the unique properties of spin waves, one can easily channelize, split, and manipulate submicrometer-width spin-wave beams propagating in microscopic magnetic-film waveguides. (C) 2008 American Institute of Physics
Mode interference and periodic self-focusing of spin waves in permalloy microstripes
Demidov VE, Demokritov SO, Rott K, Krzysteczko P, Reiss G. Mode interference and periodic self-focusing of spin waves in permalloy microstripes. PHYSICAL REVIEW B. 2008;77(6): 064406.We have studied propagation of spin waves in transversally magnetized permalloy microstripes. Our findings show that the interference of spin-wave modes quantized in the direction perpendicular to the stripe axis leads to a spatial pattern characterized by a periodic concentration of the spin-wave energy in the middle of the stripe, which can also be considered as a periodic self-focusing of spin waves. We present a simple model connecting the spatial period of the interference pattern with the width of the stripe and the spin-wave frequency. The studied phenomenon can be used for efficient transmission and processing of microwave-frequency signals by means of spin waves on the nanometer scale