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Spin-orbit torque driven chiral magnetization reversal in ultrathin nanostructures  [PDF]
N. Mikuszeit,O. Boulle,I. M. Miron,K. Garello,P. Gambardella,G. Gaudin,L. D. Buda-Prejbeanu
Physics , 2015, DOI: 10.1103/PhysRevB.92.144424
Abstract: We show that the spin-orbit torque induced magnetization switching in nanomagnets presenting Dzyaloshinskii-Moriya (DMI) interaction is governed by a chiral domain nucleation at the edges. The nucleation is induced by the DMI and the applied in-plane magnetic field followed by domain wall propagation. Our micromagnetic simulations show that the DC switching current can be defined as the edge nucleation current, which decreases strongly with increasing amplitude of the DMI. This description allows us to build a simple analytical model to quantitatively predict the switching current. We find that domain nucleation occurs down to a lateral size of 15 nm, defined by the length-scale of the DMI, beyond which the reversal mechanism approaches a macrospin behavior. The switching is deterministic and bipolar.
Non-equilibrium magnetization dynamics of ferromagnetically coupled Kondo spins  [PDF]
Andreas Hackl,Stefan Kehrein,Matthias Vojta
Physics , 2009, DOI: 10.1103/PhysRevB.80.195117
Abstract: An analytical description of non-equilibrium phenomena in interacting quantum systems is rarely possible. Here we present one example where such a description can be achieved, namely the ferromagnetic Kondo model. In equilibrium, this model is tractable via perturbative renormalization-group techniques. We employ a recently developed extension of the flow-equation method to calculate the non-equilibrium decay of the local magnetization at zero temperature. The flow equations admit analytical solutions which become exact at short and long times, in the latter case revealing that the system always retains a memory of its initial state.
Real-time simulation of non-equilibrium transport of magnetization in large open quantum spin systems driven by dissipation  [PDF]
Debasish Banerjee,Florian Hebenstreit,Fu-Jiun Jiang,Uwe-Jens Wiese
Physics , 2015, DOI: 10.1103/PhysRevB.92.121104
Abstract: Using quantum Monte Carlo, we study the non-equilibrium transport of magnetization in large open strongly correlated quantum spin $\frac{1}{2}$ systems driven by purely dissipative processes that conserve the uniform or staggered magnetization. We prepare both a low-temperature Heisenberg ferromagnet and an antiferromagnet in two parts of the system that are initially isolated from each other. We then bring the two subsystems in contact and study their real-time dissipative dynamics for different geometries. The flow of the uniform or staggered magnetization from one part of the system to the other is described by a diffusion equation that can be derived analytically.
Magnetization dynamics driven by angle-dependent spin-orbit spin transfer torque  [PDF]
Seo-Won Lee,Kyung-Jin Lee
Physics , 2015,
Abstract: Spin-orbit spin transfer torque allows an efficient control of magnetization by an in-plane current. Recent experiments found that the spin-orbit torque has strong dependence on the magnetization angle [Garello et al., Nature Nanotechnol. 8, 587 (2013); Qiu et al., Sci. Rep. 4, 4491 (2014)]. We theoretically investigate magnetization switching and domain wall motion in a perpendicularly magnetized layer, induced by angle-dependent spin-orbit torque. We obtain analytic expressions of the switching current and domain wall velocity, in agreement with numerical results. Based on the expressions, we find that the spin-orbit torque increasing with the polar angle of magnetization is beneficial for both switching and domain wall motion. Our result will serve as a guideline to design and interpret switching and domain wall experiments based on spin-orbit torque.
Chaos-driven dynamics in spin-orbit coupled atomic gases  [PDF]
Jonas Larson,Brandon Anderson,Alexander Altland
Physics , 2012, DOI: 10.1103/PhysRevA.87.013624
Abstract: The dynamics, appearing after a quantum quench, of a trapped, spin-orbit coupled, dilute atomic gas is studied. The characteristics of the evolution is greatly influenced by the symmetries of the system, and we especially compare evolution for an isotropic Rashba coupling and for an anisotropic spin-orbit coupling. As we make the spin-orbit coupling anisotropic, we break the rotational symmetry and the underlying classical model becomes chaotic; the quantum dynamics is affected accordingly. Within experimentally relevant time-scales and parameters, the system thermalizes in a quantum sense. The corresponding equilibration time is found to agree with the Ehrenfest time, i.e. we numerically verify a ~log(1/h) scaling. Upon thermalization, we find the equilibrated distributions show examples of quantum scars distinguished by accumulation of atomic density for certain energies. At shorter time-scales we discuss non-adiabatic effects deriving from the spin-orbit coupled induced Dirac point. In the vicinity of the Dirac point, spin fluctuations are large and, even at short times, a semi-classical analysis fails.
Spin-wave instabilities in spin-transfer-driven magnetization dynamics  [PDF]
G. Bertotti,R. Bonin,M. d'Aquino,C. Serpico,I. D. Mayergoyz
Physics , 2010,
Abstract: We study the stability of magnetization precessions induced in spin-transfer devices by the injection of spin-polarized electric currents. Instability conditions are derived by introducing a generalized, far-from-equilibrium interpretation of spin-waves. It is shown that instabilities are generated by distinct groups of magnetostatically coupled spin-waves. Stability diagrams are constructed as a function of external magnetic field and injected spin-polarized current. These diagrams show that applying larger fields and currents has a stabilizing effect on magnetization precessions. Analytical results are compared with numerical simulations of spin-transfer-driven magnetization dynamics.
Spin-orbit torque-driven magnetization switching and thermal effects studied in Ta\CoFeB\MgO nanowires  [PDF]
R. Lo Conte,A. Hrabec,A. P. Mihai,T. Schulz,S. -J. Noh,C. H. Marrows,T. A. Moore,M. Kl?ui
Physics , 2014, DOI: 10.1063/1.4896225
Abstract: We demonstrate magnetization switching in out-of-plane magnetized Ta\CoFeB\MgO nanowires by current pulse injection along the nanowires, both with and without a constant and uniform magnetic field collinear to the current direction. We deduce that an effective torque arising from spin-orbit effects in the multilayer drives the switching mechanism. While the generation of a component of the magnetization along the current direction is crucial for the switching to occur, we observe that even without a longitudinal field thermally generated magnetization fluctuations can lead to switching. Analysis using a generalized N\'eel-Brown model enables key parameters of the thermally induced spin-orbit torques switching process to be estimated, such as the attempt frequency and the effective energy barrier.
Soliton Magnetization Dynamics in Spin-Orbit Coupled Bose-Einstein Condensates  [PDF]
O. Fialko,J. Brand,U. Zülicke
Physics , 2012, DOI: 10.1103/PhysRevA.85.051605
Abstract: Ring-trapped Bose-Einstein condensates subject to spin-orbit coupling support localized dark soliton excitations that show periodic density dynamics in real space. In addition to the density feature, solitons also carry a localized pseudo-spin magnetization that exhibits a rich and tunable dynamics. Analytic results for Rashba-type spin-orbit coupling and spin-invariant interactions predict a conserved magnitude and precessional motion for the soliton magnetization that allows for the simulation of spin-related geometric phases recently seen in electronic transport measurements.
Interaction driven exotic quantum phases in spin-orbit coupled spin$-1$ bosons  [PDF]
J. H. Pixley,Stefan S. Natu,I. B. Spielman,S. Das Sarma
Physics , 2015,
Abstract: We study the interplay among large-spin, spin orbit coupling, and superfluidity for bosons in a two dimensional optical lattice, focusing on the spin-1 spin-orbit coupled system recently realized at the Joint Quantum Institute [Campbell et. al., arXiv:1501.05984]. We find a rich quantum phase diagram, where, in addition to the conventional phases -superfluid and insulator- contained in the spin-$1$ Bose-Hubbard model, there are new symmetry broken spin-orbit driven exotic phases where bosons condense at single or multiple points in momentum space, that have no analog in the continuum. In the lattice, increasing the spin-orbit coupling strength induces a robust spin density wave superfluid with broken translation symmetry where a non-zero condensate fraction occurs both at the center and edge of the Brillouin zone. For strong interactions, spin density wave order is suppressed concomitantly with the condensate at zero momentum leading to a continuous transition into a superfluid only at the Brillouin zone edge. We show that the spin density wave superfluid phase survives in a two dimensional harmonic trap, and thus establish that our results are directly applicable to experiments on $^{87}$Rb, $^7$Li, and $^{41}$K.
Electric-field driven long-lived spin excitations on a cylindrical surface with spin-orbit interaction  [PDF]
P. Kleinert
Physics , 2008,
Abstract: Based on quantum-kinetic equations, coupled spin-charge drift-diffusion equations are derived for a two-dimensional electron gas on a cylindrical surface. Besides the Rashba and Dresselhaus spin-orbit interaction, the elastic scattering on impurities, and a constant electric field are taken into account. From the solution of the drift-diffusion equations, a long-lived spin excitation is identified for spins coupled to the Rashba term on a cylinder with a given radius. The electric-field driven weakly damped spin waves are manifest in the components of the magnetization and have the potential for non-ballistic spin-device applications.
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