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Nonlinear Magnetic Damping and Parametric Excitation of Magnetization in Nanomagnets

2017
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Release : 2017
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Book Rating : 908/5 ( reviews)

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Book Synopsis Nonlinear Magnetic Damping and Parametric Excitation of Magnetization in Nanomagnets by : Han Kyu Lee

Download or read book Nonlinear Magnetic Damping and Parametric Excitation of Magnetization in Nanomagnets written by Han Kyu Lee. This book was released on 2017. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation explores the study of magnetization dynamics in a ferromagnetic thin film and nanoscale ferromagnets. In bulk ferromagnets, nonlinear interactions generally couple each spin wave eigenmode to a continuum of other available modes through multi-magnon scattering. The multi-magnon scattering can potentially limit an achievable amplitude of spin wave modes by pumping energy into other energy-degenerate modes. For example, two-magnon scattering process in the presence of impurities and defects is known to act as a channel of magnetic damping in ferromagnetic thin films. I present an observation of the two-magnon scattering in epitaxial La0.7Sr0.3MnO3 (LSMO) and LSMO/Pt thin films, investigate its impact on the evaluation of low magnetic damping in LSMO, and properties of spin transport through the LSMO/Pt interface for potential nanodevice applications.Magnetic damping is a critical parameter that determines the speed and energy efficiency of the magnetic nanodevice such as spin-torque memory and oscillators. In a nanomagnet, the geometric confinement breaks translational invariance of the system and discretizes the spin wave spectrum, which helps to suppress the kinematically allowed multi-magnon scattering. The suppression of multi-magnon scattering enables an unusual type of nonlinear interactions and excitation processes in nanoscale ferromagnets that are qualitatively different from that in bulk ferromagnets. In this regard, I report an observation of nonlinear resonant three-magnon scattering and its effect in the damping of nanoscale magnetic tunneling junctions (MTJs). The spectral lineshape of a spin wave resonance undergoing three-magnon scattering exhibits a minimum at the resonance frequency in sharp contrast to the amplitude maximum seen in the linear resonance regime. This unusual behavior arises because the damping parameter of a spin wave ceases to be frequency-independent and itself becomes a resonant function of the excitation frequency. Also, such resonant nonlinear damping dramatically alters the response of a nanomagnet to antidamping spin-torque in a counterintuitive way - the antidamping torque can increase the damping of a spin wave mode that undergoes the nonlinear resonant scattering.Lastly, I present an experimental demonstration of electric-field driven parametric excitation of a spin wave eigenmode in nanoscale MTJ. This work shows that the microwave electric field applied across the MTJ electrode efficiently couples to the out-of-plane component of oscillating magnetization via voltage-controlled magnetic anisotropy (VCMA) in the system. The threshold voltage of parametric excitation is found to be well below 1 Volt, which makes it attractive for magnonic nanodevices such as spin wave logic. The electric-field driven parametric excitation of magnetization is a versatile method for generating short-wavelength spin wave and thus results in this work pave the way towards energy-efficient excitation of magnetization dynamics in thin films of metallic ferromagnets and nanodevices based on magnetic multilayers.

Nonlinear Magnetization Dynamics in Nanosystems

2009-04-20 Mathematics
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Release : 2009-04-20
Genre : Mathematics
Kind : eBook
Book Rating : 792/5 ( reviews)

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Book Synopsis Nonlinear Magnetization Dynamics in Nanosystems by : Isaak D. Mayergoyz

Download or read book Nonlinear Magnetization Dynamics in Nanosystems written by Isaak D. Mayergoyz. This book was released on 2009-04-20. Available in PDF, EPUB and Kindle. Book excerpt: As data transfer rates increase within the magnetic recording industry, improvements in device performance and reliability crucially depend on the thorough understanding of nonlinear magnetization dynamics at a sub-nanoscale level. This book offers a modern, stimulating approach to the subject of nonlinear magnetization dynamics by discussing important aspects such as the Landau-Lifshitz-Gilbert (LLG) equation, analytical solutions, and the connection between the general topological and structural aspects of dynamics. An advanced reference for the study and understanding of nonlinear magnetization dynamics, it addresses situations such as the understanding of spin dynamics in short time scales and device performance and reliability in magnetic recording. Topics covered include nonlinear magnetization dynamics and the Landau-Lifshitz-Gilbert equation, nonlinear dynamical systems, spin waves, ferromagnetic resonance and pulsed magnetization switching. The book explains how to derive exact analytical solutions for the complete nonlinear problem and emphasises the connection between the general topological and structural aspects of nonlinear magnetization dynamics and the discretization schemes better suited to its numerical study. It is an exceptional research tool providing an advanced understanding of the study of magnetization dynamics in situations of fundamental and technological interest.

Handbook of Nanomagnetism

2015-10-06 Science
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Release : 2015-10-06
Genre : Science
Kind : eBook
Book Rating : 053/5 ( reviews)

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Book Synopsis Handbook of Nanomagnetism by : Rosa A. Lukaszew

Download or read book Handbook of Nanomagnetism written by Rosa A. Lukaszew. This book was released on 2015-10-06. Available in PDF, EPUB and Kindle. Book excerpt: This unique handbook compiles and details cutting-edge research in nanomagnetism and its applications in spintronics, magnetoplasmonics, and nonlinear magneto-optics. Fundamental aspects of magnetism relevant to nanodevices and new spin-transfer torque random-access memory (STT-RAM), current-induced domain wall motion memory, and spin torque oscill

Non-collinear Spin-torque Driven Excitation in Nanomagnets

2013
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Release : 2013
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Book Synopsis Non-collinear Spin-torque Driven Excitation in Nanomagnets by : Ouk Jae Lee

Download or read book Non-collinear Spin-torque Driven Excitation in Nanomagnets written by Ouk Jae Lee. This book was released on 2013. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation summarizes my investigations in non-collinear spin-transfertorque (ST) effects on nanomagnets. The Slonczewksi-like ST mostly competes with the damping torque in a device structure where the spin polarization (SP) is collinear to the magnetic moment of a free layer (FL) at equilibrium. Contrarily the ST has both (anti- )damping and an equivalent field torque effects in non-collinear configurations in which the SP is close to perpendicular to the FL. The additional field effect of the ST shifts the equilibrium or dynamic offset angle of the FL and thereby changes the characteristics of the excitations. In my first study, I demonstrated the ST-driven ultrafast nanomagnet switching in nanopillar spin-valve devices incorporating both an out-of-plane spinpolarizer and an in-plane polarizer/analyzer, with pulse widths down to 50 ps. I also explained the physical origin of the observed asymmetric threshold currents as functions of the switching direction and the pulse polarity, which is beneficial for a non-toggle write operation. In addition I proposed methods to suppress the magnetic ringing that occurs after the ballistic switching. In my second study, I discovered quasi-linear behavior of a spin-torque nano-oscillator under an external hard axis magnetic field that controls the precession axis of the FL and its offset angle from the SP. The observed linewidth (~ 5 MHz) was very close to the fundamental limit determined by thermal driven noise. The quasi-linearity, or the cancellation of the nonlinear coupling between the amplitude fluctuation and phase noise, was achieved by obtaining a small frequency agility together with a negative feedback effect from the ST causing the enhancement of the dynamical damping. In my third study, I investigated perpendicularly magnetized Co nanodot switching via spin-Hall-induced spin currents. In the thermally activated reversal regime I estimated the current-induced effective field (H s) that has a magnitude within the predicted range due to the large spin-Hall angle in Pt when the Joule heating effect is taken into account for the magnetic system. In addition an excitation of a subvolume drove the entire magnetization switching, thus even a small but heat-assisted H s was able to reverse such a Co dot with a strong perpendicular magnetic anisotropy.

Parametric Resonance of Magnetization Excited by Electric Field

2016
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Release : 2016
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Book Rating : 403/5 ( reviews)

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Book Synopsis Parametric Resonance of Magnetization Excited by Electric Field by : Yu-Jin Chen

Download or read book Parametric Resonance of Magnetization Excited by Electric Field written by Yu-Jin Chen. This book was released on 2016. Available in PDF, EPUB and Kindle. Book excerpt: This thesis describes the experiments that demonstrate the ability to efficiently excite magnetization parametrically by electric field. The experiments are done with nanoscale magnetic tunnel junctions, which are multilayer thin film devices patterned into nanopillar shape. One of the layers possesses strong perpendicular magnetic anisotropy and exhibits strong voltage-controlled magnetic anisotropy. This magneto-electric effect allows one to modulate the perpendicular magnetic anisotropy of the layer and parametrically excite large-amplitude oscillations of the magnetization. The results of this experiment show that it is possible to parametrically excite resonance in a magnetic nanostructure using electric field and that the threshold voltage for this process is low: it is found to be well below 1Volt. This paves the way towards developing energy-efficient spintronic devices based on parametric excitation of magnetization by electric field.

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