Dynamic nuclear polarization enhanced nuclear magnetic resonance and electron spin resonance studies of hydration and local water dynamics in micelle and vesicle assemblies.

PubMed

McCarney, Evan R; Armstrong, Brandon D; Kausik, Ravinath; Han, Songi

2008-09-16

We present a unique analysis tool for the selective detection of local water inside soft molecular assemblies (hydrophobic cores, vesicular bilayers, and micellar structures) suspended in bulk water. Through the use of dynamic nuclear polarization (DNP), the (1)H NMR signal of water is amplified, as it interacts with stable radicals that possess approximately 658 times higher spin polarization. We utilized stable nitroxide radicals covalently attached along the hydrophobic tail of stearic acid molecules that incorporate themselves into surfactant-based micelle or vesicle structures. Here, we present a study of local water content and fluid viscosity inside oleate micelles and vesicles and Triton X-100 micelles to serve as model systems for soft molecular assemblies. This approach is unique because the amplification of the NMR signal is performed in bulk solution and under ambient conditions with site-specific spin labels that only detect the water that is directly interacting with the localized spin labels. Continuous wave (cw) electron spin resonance (ESR) analysis provides rotational dynamics of the spin-labeled molecular chain segments and local polarity parameters that can be related to hydration properties, whereas we show that DNP-enhanced (1)H NMR analysis of fluid samples directly provides translational water dynamics and permeability of the local environment probed by the spin label. Our technique therefore has the potential to become a powerful analysis tool, complementary to cw ESR, to study hydration characteristics of surfactant assemblies, lipid bilayers, or protein aggregates, where water dynamics is a key parameter of their structure and function. In this study, we find that there is significant penetration of water inside the oleate micelles with a higher average local water viscosity (approximately 1.8 cP) than in bulk water, and Triton X-100 micelles and oleate vesicle bilayers mostly exclude water while allowing for considerable surfactant chain motion and measurable water permeation through the soft structure.

Self-sustaining dynamical nuclear polarization oscillations in quantum dots.

PubMed

Rudner, M S; Levitov, L S

2013-02-22

Early experiments on spin-blockaded double quantum dots revealed robust, large-amplitude current oscillations in the presence of a static (dc) source-drain bias. Despite experimental evidence implicating dynamical nuclear polarization, the mechanism has remained a mystery. Here we introduce a minimal albeit realistic model of coupled electron and nuclear spin dynamics which supports self-sustained oscillations. Our mechanism relies on a nuclear spin analog of the tunneling magnetoresistance phenomenon (spin-dependent tunneling rates in the presence of an inhomogeneous Overhauser field) and nuclear spin diffusion, which governs dynamics of the spatial profile of nuclear polarization. The proposed framework naturally explains the differences in phenomenology between vertical and lateral quantum dot structures as well as the extremely long oscillation periods.

All-Electrical Measurement of Interfacial Dzyaloshinskii-Moriya Interaction Using Collective Spin-Wave Dynamics.

PubMed

Lee, Jong Min; Jang, Chaun; Min, Byoung-Chul; Lee, Seo-Won; Lee, Kyung-Jin; Chang, Joonyeon

2016-01-13

Dzyaloshinskii-Moriya interaction (DMI), which arises from the broken inversion symmetry and spin-orbit coupling, is of prime interest as it leads to a stabilization of chiral magnetic order and provides an efficient manipulation of magnetic nanostructures. Here, we report all-electrical measurement of DMI using propagating spin wave spectroscopy based on the collective spin wave with a well-defined wave vector. We observe a substantial frequency shift of spin waves depending on the spin chirality in Pt/Co/MgO structures. After subtracting the contribution from other sources to the frequency shift, it is possible to quantify the DMI energy in Pt/Co/MgO systems. The result reveals that the DMI in Pt/Co/MgO originates from the interfaces, and the sign of DMI corresponds to the inversion asymmetry of the film structures. The electrical excitation and detection of spin waves and the influence of interfacial DMI on the collective spin-wave dynamics will pave the way to the emerging field of spin-wave logic devices.

Low field domain wall dynamics in artificial spin-ice basis structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kwon, J.; School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798; Goolaup, S.

2015-10-28

Artificial magnetic spin-ice nanostructures provide an ideal platform for the observation of magnetic monopoles. The formation of a magnetic monopole is governed by the motion of a magnetic charge carrier via the propagation of domain walls (DWs) in a lattice. To date, most experiments have been on the static visualization of DW propagation in the lattice. In this paper, we report on the low field dynamics of DW in a unit spin-ice structure measured by magnetoresistance changes. Our results show that reversible DW propagation can be initiated within the spin-ice basis. The initial magnetization configuration of the unit structure stronglymore » influences the direction of DW motion in the branches. Single or multiple domain wall nucleation can be induced in the respective branches of the unit spin ice by the direction of the applied field.« less

Recent Advances in Heliogyro Solar Sail Structural Dynamics, Stability, and Control Research

NASA Technical Reports Server (NTRS)

Wilkie, W. Keats; Warren, Jerry E.; Horta, Lucas G.; Lyle, Karen H.; Juang, Jer-Nan; Gibbs, S. Chad; Dowell, Earl H.; Guerrant, Daniel V.; Lawrence, Dale

2015-01-01

Results from recent NASA sponsored research on the structural dynamics, stability, and control characteristics of heliogyro solar sails are summarized. Specific areas under investigation include coupled nonlinear finite element analysis of heliogyro membrane blade with solar radiation pressure effects, system identification of spinning membrane structures, and solarelastic stability analysis of heliogyro solar sails, including stability during blade deployment. Recent results from terrestrial 1-g blade dynamics and control experiments on "rope ladder" membrane blade analogs, and small-scale in vacuo system identification experiments with hanging and spinning high-aspect ratio membranes will also be presented. A low-cost, rideshare payload heliogyro technology demonstration mission concept is used as a mission context for these heliogyro structural dynamics and solarelasticity investigations, and is also described. Blade torsional dynamic response and control are also shown to be significantly improved through the use of edge stiffening structural features or inclusion of modest tip masses to increase centrifugal stiffening of the blade structure. An output-only system identification procedure suitable for on-orbit blade dynamics investigations is also developed and validated using ground tests of spinning sub-scale heliogyro blade models. Overall, analytical and experimental investigations to date indicate no intractable stability or control issues for the heliogyro solar sail concept.

Out-of-plane chiral domain wall spin-structures in ultrathin in-plane magnets

DOE PAGES

Chen, Gong; Kang, Sang Pyo; Ophus, Colin; ...

2017-05-19

Chiral spin textures in ultrathin films, such as skyrmions or chiral domain walls, are believed to offer large performance advantages in the development of novel spintronics technologies. While in-plane magnetized films have been studied extensively as media for current- and field-driven domain wall dynamics with applications in memory or logic devices, the stabilization of chiral spin textures in in-plane magnetized films has remained rare. Here we report a phase of spin structures in an in-plane magnetized ultrathin film system where out-of-plane spin orientations within domain walls are stable. Moreover, while domain walls in in-plane films are generally expected to bemore » non-chiral, we show that right-handed spin rotations are strongly favoured in this system, due to the presence of the interfacial Dzyaloshinskii-Moriya interaction. These results constitute a platform to explore unconventional spin dynamics and topological phenomena that may enable high-performance in-plane spin-orbitronics devices.« less

Dynamic magnetic hysteresis properties of two-dimensional ferrimagnetic structures containing high-spin (S = 5/2) and low-spin (S = 1/2)

NASA Astrophysics Data System (ADS)

Batı, Mehmet; Ertaş, Mehmet

2017-09-01

The dynamic hysteresis behaviors of a containing high spin-5/2 and low spin-1/2 Ising ferrimagnetic system on a square lattice are studied by using the dynamic mean-field approximation. The influences of the temperature, the single-ion anisotropy and the frequency on dynamic hysteresis behaviors are investigated in detail. Somewhat characteristic behaviors are found, such as the presence of triple hysteresis loop for appropriate values of the crystal field or temperature. Besides, we observed that, hysteresis loop area and phase transition points are very sensitive to changes in frequency and thus have profound importance in device application.

Dynamical spin structure factors of α-RuCl3

NASA Astrophysics Data System (ADS)

Suzuki, Takafumi; Suga, Sei-ichiro

2018-03-01

Honeycomb-lattice magnet α-RuCl3 is considered to be a potential candidate of realizing Kitaev spin liquid, although this material undergoes a phase transition to the zigzag magnetically ordered state at T N ∼ 7 K. Quite recently, inelastic neutron-scattering experiments using single crystal α-RuCl3 have unveiled characteristic dynamical properties. We calculate dynamical spin structure factors of three ab-initio models for α-RuCl3 with an exact numerical diagonalization method. We also calculate temperature dependences of the specific heat by employing thermal pure quantum states. We compare our numerical results with the experiments and discuss characteristics obtained by using three ab-initio models.

Imaging Magnetization Structure and Dynamics in Ultrathin Y3Fe5O12/Pt Bilayers with High Sensitivity Using the Time-Resolved Longitudinal Spin Seebeck Effect

NASA Astrophysics Data System (ADS)

Bartell, Jason M.; Jermain, Colin L.; Aradhya, Sriharsha V.; Brangham, Jack T.; Yang, Fengyuan; Ralph, Daniel C.; Fuchs, Gregory D.

2017-04-01

We demonstrate an instrument for time-resolved magnetic imaging that is highly sensitive to the in-plane magnetization state and dynamics of thin-film bilayers of yttrium iron garnet [Y3Fe5O12(YIG )]/Pt : the time-resolved longitudinal spin Seebeck (TRLSSE) effect microscope. We detect the local in-plane magnetic orientation within the YIG by focusing a picosecond laser to generate thermally driven spin current from the YIG into the Pt by the spin Seebeck effect and then use the inverse spin Hall effect in the Pt to transduce this spin current to an output voltage. To establish the time resolution of TRLSSE, we show that pulsed optical heating of patterned YIG (20 nm )/Pt (6 nm )/Ru (2 nm ) wires generates a magnetization-dependent voltage pulse of less than 100 ps. We demonstrate TRLSSE microscopy to image both static magnetic structure and gigahertz-frequency magnetic resonance dynamics with submicron spatial resolution and a sensitivity to magnetic orientation below 0.3 °/√{H z } in ultrathin YIG.

Breaking Symmetry in Time-Dependent Electronic Structure Theory to Describe Spectroscopic Properties of Non-Collinear and Chiral Molecules

NASA Astrophysics Data System (ADS)

Goings, Joshua James

Time-dependent electronic structure theory has the power to predict and probe the ways electron dynamics leads to useful phenomena and spectroscopic data. Here we report several advances and extensions of broken-symmetry time-dependent electronic structure theory in order to capture the flexibility required to describe non-equilibrium spin dynamics, as well as electron dynamics for chiroptical properties and vibrational effects. In the first half, we begin by discussing the generalization of self-consistent field methods to the so-called two-component structure in order to capture non-collinear spin states. This means that individual electrons are allowed to take a superposition of spin-1/2 projection states, instead of being constrained to either spin-up or spin-down. The system is no longer a spin eigenfunction, and is known a a spin-symmetry broken wave function. This flexibility to break spin symmetry may lead to variational instabilities in the approximate wave function, and we discuss how these may be overcome. With a stable non-collinear wave function in hand, we then discuss how to obtain electronic excited states from the non-collinear reference, along with associated challenges in their physical interpretation. Finally, we extend the two-component methods to relativistic Hamiltonians, which is the proper setting for describing spin-orbit driven phenomena. We describe the first implementation of the explicit time propagation of relativistic two-component methods and how this may be used to capture spin-forbidden states in electronic absorption spectra. In the second half, we describe the extension of explicitly time-propagated wave functions to the simulation of chiroptical properties, namely circular dichroism (CD) spectra of chiral molecules. Natural circular dichroism, that is, CD in the absence of magnetic fields, originates in the broken parity symmetry of chiral molecules. This proves to be an efficient method for computing circular dichroism spectra for high density-of-states chiral molecules. Next, we explore the impact of allowing nuclear motion on electronic absorption spectra within the context of mixed quantum-classical dynamics. We show that nuclear motion modulates the electronic response, and this gives rise to infrared absorption as well as Raman scattering phenomena in the computed dynamic polarizability. Finally, we explore the accuracy of several perturbative approximations to the equation-of-motion coupled-cluster methods for the efficient and accurate prediction of electronic absorption spectra.

Spin dynamics of counterrotating Kitaev spirals via duality

NASA Astrophysics Data System (ADS)

Kimchi, Itamar; Coldea, Radu

2016-11-01

Incommensurate spiral order is a common occurrence in frustrated magnetic insulators. Typically, all magnetic moments rotate uniformly, through the same wavevector. However the honeycomb iridates family Li2IrO3 shows an incommensurate order where spirals on neighboring sublattices are counterrotating, giving each moment a different local environment. Theoretically describing its spin dynamics has remained a challenge: The Kitaev interactions proposed to stabilize this state, which arise from strong spin-orbit effects, induce magnon umklapp scattering processes in spin-wave theory. Here we propose an approach via a (Klein) duality transformation into a conventional spiral of a frustrated Heisenberg model, allowing a direct derivation of the dynamical structure factor. We analyze both Kitaev and Dzyaloshinskii-Moriya based models, both of which can stabilize counterrotating spirals, but with different spin dynamics, and we propose experimental tests to identify the origin of counterrotation.

Rapid characterizing of ferromagnetic materials using spin rectification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fan, Xiaolong, E-mail: fanxiaolong@lzu.edu.cn; Wang, Wei; Wang, Yutian

2014-12-29

Spin rectification is a powerful tool for dc electric detections of spin dynamics and electromagnetic waves. Technically, elaborately designed on-chip microwave devices are needed in order to realize that effect. In this letter, we propose a rapid characterizing approach based on spin rectification. By directly sending dynamic current into ferromagnetic films with stripe shape, resonant dc voltages can be detected along the longitudinal or transversal directions. As an example, Fe (010) films with precise crystalline structure and magnetic parameters were used to testify the reliability of such method. We investigated not only the dynamic parameters and the precise anisotropy constantsmore » of the Fe crystals but also the principle of spin rectification in this method.« less

Magnon Splitting Induced by Charge Transfer in the Three-Orbital Hubbard Model

NASA Astrophysics Data System (ADS)

Wang, Yao; Huang, Edwin W.; Moritz, Brian; Devereaux, Thomas P.

2018-06-01

Understanding spin excitations and their connection to unconventional superconductivity have remained central issues since the discovery of cuprates. Direct measurement of the dynamical spin structure factor in the parent compounds can provide key information on important interactions relevant in the doped regime, and variations in the magnon dispersion have been linked closely to differences in crystal structure between families of cuprate compounds. Here, we elucidate the relationship between spin excitations and various controlling factors thought to be significant in high-Tc materials by systematically evaluating the dynamical spin structure factor for the three-orbital Hubbard model, revealing differences in the spin dispersion along the Brillouin zone axis and the diagonal. Generally, we find that the absolute energy scale and momentum dependence of the excitations primarily are sensitive to the effective charge-transfer energy, while changes in the on-site Coulomb interactions have little effect on the details of the dispersion. In particular, our result highlights the splitting between spin excitations along the axial and diagonal directions in the Brillouin zone. This splitting decreases with increasing charge-transfer energy and correlates with changes in the apical oxygen position, and general structural variations, for different cuprate families.

Structural Effects on the Spin Dynamics of Potential Molecular Qubits.

PubMed

Atzori, Matteo; Benci, Stefano; Morra, Elena; Tesi, Lorenzo; Chiesa, Mario; Torre, Renato; Sorace, Lorenzo; Sessoli, Roberta

2018-01-16

Control of spin-lattice magnetic relaxation is crucial to observe long quantum coherence in spin systems at reasonable temperatures. Such a control is most often extremely difficult to achieve, because of the coexistence of several relaxation mechanisms, that is direct, Raman, and Orbach. These are not always easy to relate to the energy states of the investigated system, because of the contribution to the relaxation of additional spin-phonon coupling phenomena mediated by intramolecular vibrations. In this work, we have investigated the effect of slight changes on the molecular structure of four vanadium(IV)-based potential spin qubits on their spin dynamics, studied by alternate current (AC) susceptometry. The analysis of the magnetic field dependence of the relaxation time correlates well with the low-energy vibrational modes experimentally detected by time-domain THz spectroscopy. This confirms and extends our preliminary observations on the role played by spin-vibration coupling in determining the fine structure of the spin-lattice relaxation time as a function of the magnetic field, for S = 1 / 2 potential spin qubits. This study represents a step forward in the use of low-energy vibrational spectroscopy as a prediction tool for the design of molecular spin qubits with long-lived quantum coherence. Indeed, quantum coherence times of ca. 4.0-6.0 μs in the 4-100 K range are observed for the best performing vanadyl derivatives identified through this multitechnique approach.

Coherent structural trapping through wave packet dispersion during photoinduced spin state switching

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lemke, Henrik T.; Kjær, Kasper S.; Hartsock, Robert

The description of ultrafast nonadiabatic chemical dynamics during molecular photo-transformations remains challenging because electronic and nuclear configurations impact each other and cannot be treated independently. Here we gain experimental insights, beyond the Born–Oppenheimer approximation, into the light-induced spin-state trapping dynamics of the prototypical [Fe(bpy)3]2+ compound by time-resolved X-ray absorption spectroscopy at sub-30-femtosecond resolution and high signal-to-noise ratio. The electronic decay from the initial optically excited electronic state towards the high spin state is distinguished from the structural trapping dynamics, which launches a coherent oscillating wave packet (265 fs period), clearly identified as molecular breathing. Throughout the structural trapping, the dispersionmore » of the wave packet along the reaction coordinate reveals details of intramolecular vibronic coupling before a slower vibrational energy dissipation to the solution environment. These findings illustrate how modern time-resolved X-ray absorption spectroscopy can provide key information to unravel dynamic details of photo-functional molecules.« less

Coherent structural trapping through wave packet dispersion during photoinduced spin state switching

DOE PAGES

Lemke, Henrik T.; Kjær, Kasper S.; Hartsock, Robert; ...

2017-05-24

The description of ultrafast nonadiabatic chemical dynamics during molecular photo-transformations remains challenging because electronic and nuclear configurations impact each other and cannot be treated independently. Here we gain experimental insights, beyond the Born–Oppenheimer approximation, into the light-induced spin-state trapping dynamics of the prototypical [Fe(bpy)3]2+ compound by time-resolved X-ray absorption spectroscopy at sub-30-femtosecond resolution and high signal-to-noise ratio. The electronic decay from the initial optically excited electronic state towards the high spin state is distinguished from the structural trapping dynamics, which launches a coherent oscillating wave packet (265 fs period), clearly identified as molecular breathing. Throughout the structural trapping, the dispersionmore » of the wave packet along the reaction coordinate reveals details of intramolecular vibronic coupling before a slower vibrational energy dissipation to the solution environment. These findings illustrate how modern time-resolved X-ray absorption spectroscopy can provide key information to unravel dynamic details of photo-functional molecules.« less

Coherent structural trapping through wave packet dispersion during photoinduced spin state switching

NASA Astrophysics Data System (ADS)

Lemke, Henrik T.; Kjær, Kasper S.; Hartsock, Robert; van Driel, Tim B.; Chollet, Matthieu; Glownia, James M.; Song, Sanghoon; Zhu, Diling; Pace, Elisabetta; Matar, Samir F.; Nielsen, Martin M.; Benfatto, Maurizio; Gaffney, Kelly J.; Collet, Eric; Cammarata, Marco

2017-05-01

The description of ultrafast nonadiabatic chemical dynamics during molecular photo-transformations remains challenging because electronic and nuclear configurations impact each other and cannot be treated independently. Here we gain experimental insights, beyond the Born-Oppenheimer approximation, into the light-induced spin-state trapping dynamics of the prototypical [Fe(bpy)3]2+ compound by time-resolved X-ray absorption spectroscopy at sub-30-femtosecond resolution and high signal-to-noise ratio. The electronic decay from the initial optically excited electronic state towards the high spin state is distinguished from the structural trapping dynamics, which launches a coherent oscillating wave packet (265 fs period), clearly identified as molecular breathing. Throughout the structural trapping, the dispersion of the wave packet along the reaction coordinate reveals details of intramolecular vibronic coupling before a slower vibrational energy dissipation to the solution environment. These findings illustrate how modern time-resolved X-ray absorption spectroscopy can provide key information to unravel dynamic details of photo-functional molecules.

Quantum model of a solid-state spin qubit: Ni cluster on a silicon surface by the generalized spin Hamiltonian and X-ray absorption spectroscopy investigations

NASA Astrophysics Data System (ADS)

Farberovich, Oleg V.; Mazalova, Victoria L.; Soldatov, Alexander V.

2015-11-01

We present here the quantum model of a Ni solid-state electron spin qubit on a silicon surface with the use of a density-functional scheme for the calculation of the exchange integrals in the non-collinear spin configurations in the generalized spin Hamiltonian (GSH) with the anisotropic exchange coupling parameters linking the nickel ions with a silicon substrate. In this model the interaction of a spin qubit with substrate is considered in GSH at the calculation of exchange integrals Jij of the nanosystem Ni7-Si in the one-electron approach taking into account chemical bonds of all Si-atoms of a substrate (environment) with atoms of the Ni7-cluster. The energy pattern was found from the effective GSH Hamiltonian acting in the restricted spin space of the Ni ions by the application of the irreducible tensor operators (ITO) technique. In this paper we offer the model of the quantum solid-state N-spin qubit based on the studying of the spin structure and the spin-dynamics simulations of the 3d-metal Ni clusters on the silicon surface. The solution of the problem of the entanglement between spin states in the N-spin systems is becoming more interesting when considering clusters or molecules with a spectral gap in their density of states. For quantifying the distribution of the entanglement between the individual spin eigenvalues (modes) in the spin structure of the N-spin system we use the density of entanglement (DOE). In this study we have developed and used the advanced high-precision numerical techniques to accurately assess the details of the decoherence process governing the dynamics of the N-spin qubits interacting with a silicon surface. We have studied the Rabi oscillations to evaluate the N-spin qubits system as a function of the time and the magnetic field. We have observed the stabilized Rabi oscillations and have stabilized the quantum dynamical qubit state and Rabi driving after a fixed time (0.327 μs). The comparison of the energy pattern with the anisotropic exchange models conventionally used for the analysis of this system and, with the results of the experimental XANES spectra, shows that our complex investigations provide a good description of the pattern of the spin levels and the spin structures of the nanomagnetic Ni7 qubit. The results are discussed in the view of the general problem of the solid-state spin qubits and the spin structure of the Ni cluster.

Spin-charge coupled dynamics driven by a time-dependent magnetization

NASA Astrophysics Data System (ADS)

Tölle, Sebastian; Eckern, Ulrich; Gorini, Cosimo

2017-03-01

The spin-charge coupled dynamics in a thin, magnetized metallic system are investigated. The effective driving force acting on the charge carriers is generated by a dynamical magnetic texture, which can be induced, e.g., by a magnetic material in contact with a normal-metal system. We consider a general inversion-asymmetric substrate/normal-metal/magnet structure, which, by specifying the precise nature of each layer, can mimic various experimentally employed setups. Inversion symmetry breaking gives rise to an effective Rashba spin-orbit interaction. We derive general spin-charge kinetic equations which show that such spin-orbit interaction, together with anisotropic Elliott-Yafet spin relaxation, yields significant corrections to the magnetization-induced dynamics. In particular, we present a consistent treatment of the spin density and spin current contributions to the equations of motion, inter alia, identifying a term in the effective force which appears due to a spin current polarized parallel to the magnetization. This "inverse-spin-filter" contribution depends markedly on the parameter which describes the anisotropy in spin relaxation. To further highlight the physical meaning of the different contributions, the spin-pumping configuration of typical experimental setups is analyzed in detail. In the two-dimensional limit the buildup of dc voltage is dominated by the spin-galvanic (inverse Edelstein) effect. A measuring scheme that could isolate this contribution is discussed.

Dynamical structure factor of the J1-J2 Heisenberg model in one dimension: The variational Monte Carlo approach

NASA Astrophysics Data System (ADS)

Ferrari, Francesco; Parola, Alberto; Sorella, Sandro; Becca, Federico

2018-06-01

The dynamical spin structure factor is computed within a variational framework to study the one-dimensional J1-J2 Heisenberg model. Starting from Gutzwiller-projected fermionic wave functions, the low-energy spectrum is constructed from two-spinon excitations. The direct comparison with Lanczos calculations on small clusters demonstrates the excellent description of both gapless and gapped (dimerized) phases, including incommensurate structures for J2/J1>0.5 . Calculations on large clusters show how the intensity evolves when increasing the frustrating ratio and give an unprecedented accurate characterization of the dynamical properties of (nonintegrable) frustrated spin models.

Dynamics of a quantum spin liquid beyond integrability: The Kitaev-Heisenberg-Γ model in an augmented parton mean-field theory

NASA Astrophysics Data System (ADS)

Knolle, Johannes; Bhattacharjee, Subhro; Moessner, Roderich

2018-04-01

We present an augmented parton mean-field theory which (i) reproduces the exact ground state, spectrum, and dynamics of the quantum spin-liquid phase of Kitaev's honeycomb model, and (ii) is amenable to the inclusion of integrability breaking terms, allowing a perturbation theory from a controlled starting point. Thus, we exemplarily study dynamical spin correlations of the honeycomb Kitaev quantum spin liquid within the K -J -Γ model, which includes Heisenberg and symmetric-anisotropic (pseudodipolar) interactions. This allows us to trace changes of the correlations in the regime of slowly moving fluxes, where the theory captures the dominant deviations when integrability is lost. These include an asymmetric shift together with a broadening of the dominant peak in the response as a function of frequency, the generation of further-neighbor correlations and their structure in real and spin space, and a resulting loss of an approximate rotational symmetry of the structure factor in reciprocal space. We discuss the limitations of this approach and also view the neutron-scattering experiments on the putative proximate quantum spin-liquid material α -RuCl3 in the light of the results from this extended parton theory.

Resolving the role of femtosecond heated electrons in ultrafast spin dynamics.

PubMed

Mendil, J; Nieves, P; Chubykalo-Fesenko, O; Walowski, J; Santos, T; Pisana, S; Münzenberg, M

2014-02-05

Magnetization manipulation is essential for basic research and applications. A fundamental question is, how fast can the magnetization be reversed in nanoscale magnetic storage media. When subject to an ultrafast laser pulse, the speed of the magnetization dynamics depends on the nature of the energy transfer pathway. The order of the spin system can be effectively influenced through spin-flip processes mediated by hot electrons. It has been predicted that as electrons drive spins into the regime close to almost total demagnetization, characterized by a loss of ferromagnetic correlations near criticality, a second slower demagnetization process takes place after the initial fast drop of magnetization. By studying FePt, we unravel the fundamental role of the electronic structure. As the ferromagnet Fe becomes more noble in the FePt compound, the electronic structure is changed and the density of states around the Fermi level is reduced, thereby driving the spin correlations into the limit of critical fluctuations. We demonstrate the impact of the electrons and the ferromagnetic interactions, which allows a general insight into the mechanisms of spin dynamics when the ferromagnetic state is highly excited, and identifies possible recording speed limits in heat-assisted magnetization reversal.

Spin Resonance in the New-Structure-Type Iron-Based Superconductor CaKFe4As4

NASA Astrophysics Data System (ADS)

Iida, Kazuki; Ishikado, Motoyuki; Nagai, Yuki; Yoshida, Hiroyuki; Christianson, Andrew D.; Murai, Naoki; Kawashima, Kenji; Yoshida, Yoshiyuki; Eisaki, Hiroshi; Iyo, Akira

2017-09-01

The dynamical spin susceptibility in the new-structure-type iron-based superconductor CaKFe4As4 was investigated by using a combination of inelastic neutron scattering (INS) measurements and random phase approximation (RPA) calculations. Powder INS measurements show that the spin resonance at Qres = 1.17(1) Å-1, corresponding to the (π ,π ) nesting wave vector in tetragonal notation, evolves below Tc. The characteristic energy of the spin resonance Eres = 12.5 meV is smaller than twice the size of the superconducting gap (2Δ). The broad energy feature of the dynamical susceptibility of the spin resonance can be explained by the RPA calculations, in which the different superconducting gaps on different Fermi surfaces are taken into account. Our INS and PRA studies demonstrate that the superconducting pairing nature in CaKFe4As4 is the s± symmetry.

Competition between dynamic and structural disorder in a doped triangular antiferromagnet RbFe(MoO4)2

NASA Astrophysics Data System (ADS)

Smirnov, A. I.; Soldatov, T. A.; Petrenko, O. A.; Takata, A.; Kida, T.; Hagiwara, M.; Zhitomirsky, M. E.; Shapiro, A. Ya

2018-03-01

Magnetisation measurements and electron spin resonance (ESR) spectra of a doped quasi two dimensional (2D) antiferromagnet on a triangular lattice Rb1 ‑ x K x Fe(MoO4)2 reveal a crucial change of the ground state spin configuration and a disappearance of a characteristic 1/3-magnetisation plateau at x = 0.15. According to theory for triangular antiferromagnets with a weak random modulation of the exchange bonds, this is a result of the competition between the structural and dynamic disorders. The dynamic zero-point or thermal fluctuations are known to lift the degeneracy of the mean field ground state of a triangular antiferromagnet and cause the spin configuration to be the most collinear, while the static disorder provides another selection of the ground state, with the least collinear structure. Low-level doping (x ≤ 0.15) was found to decrease the Néel temperature and saturation field by only few percent, while the magnetisation plateau disappears completely and the spin configuration is drastically changed. ESR spectra confirm an impurity-induced change of the so-called Y-type structure to an inverted Y-structure for x = 0.15. For x = 0.075 the intermediate regime with the decrease of width and weakening of flattening of 1/3-plateau was found.

Combining EPR spectroscopy and X-ray crystallography to elucidate the structure and dynamics of conformationally constrained spin labels in T4 lysozyme single crystals.

PubMed

Consentius, Philipp; Gohlke, Ulrich; Loll, Bernhard; Alings, Claudia; Heinemann, Udo; Wahl, Markus C; Risse, Thomas

2017-08-09

Electron paramagnetic resonance (EPR) spectroscopy in combination with site-directed spin labeling is used to investigate the structure and dynamics of conformationally constrained spin labels in T4 lysozyme single crystals. Within a single crystal, the oriented ensemble of spin bearing moieties results in a strong angle dependence of the EPR spectra. A quantitative description of the EPR spectra requires the determination of the unit cell orientation with respect to the sample tube and the orientation of the spin bearing moieties within the crystal lattice. Angle dependent EPR spectra were analyzed by line shape simulations using the stochastic Liouville equation approach developed by Freed and co-workers and an effective Hamiltonian approach. The gain in spectral information obtained from the EPR spectra of single crystalline samples taken at different frequencies, namely the X-band and Q-band, allows us to discriminate between motional models describing the spectra of isotropic solutions similarly well. In addition, it is shown that the angle dependent single crystal spectra allow us to identify two spin label rotamers with very similar side chain dynamics. These results demonstrate the utility of single crystal EPR spectroscopy in combination with spectral line shape simulation techniques to extract valuable dynamic information not readily available from the analysis of isotropic systems. In addition, it will be shown that the loss of electron density in high resolution diffraction experiments at room temperature does not allow us to conclude that there is significant structural disorder in the system.

Current-driven second-harmonic domain wall resonance in ferromagnetic metal/nonmagnetic metal bilayers: A field-free method for spin Hall angle measurements

NASA Astrophysics Data System (ADS)

Hajiali, M. R.; Hamdi, M.; Roozmeh, S. E.; Mohseni, S. M.

2017-10-01

We study the ac current-driven domain wall motion in bilayer ferromagnetic metal (FM)/nonmagnetic metal (NM) nanowires. The solution of the modified Landau-Lifshitz-Gilbert equation including all the spin transfer torques is used to describe motion of the domain wall in the presence of the spin Hall effect. We show that the domain wall center has a second-harmonic frequency response in addition to the known first-harmonic excitation. In contrast to the experimentally observed second-harmonic response in harmonic Hall measurements of spin-orbit torque in magnetic thin films, this second-harmonic response directly originates from spin-orbit torque driven domain wall dynamics. Based on the spin current generated by domain wall dynamics, the longitudinal spin motive force generated voltage across the length of the nanowire is determined. The second-harmonic response introduces additionally a practical field-free and all-electrical method to probe the effective spin Hall angle for FM/NM bilayer structures that could be applied in experiments. Our results also demonstrate the capability of utilizing FM/NM bilayer structures in domain wall based spin-torque signal generators and resonators.

Anomalous magnetic structure and spin dynamics in magnetoelectric LiFePO 4

DOE PAGES

Toft-Petersen, Rasmus; Reehuis, Manfred; Jensen, Thomas B. S.; ...

2015-07-06

We report significant details of the magnetic structure and spin dynamics of LiFePO 4 obtained by single-crystal neutron scattering. Our results confirm a previously reported collinear rotation of the spins away from the principal b axis, and they determine that the rotation is toward the a axis. In addition, we find a significant spin-canting component along c. Furthermore, the possible causes of these components are discussed, and their significance for the magnetoelectric effect is analyzed. Inelastic neutron scattering along the three principal directions reveals a highly anisotropic hard plane consistent with earlier susceptibility measurements. While using a spin Hamiltonian, wemore » show that the spin dimensionality is intermediate between XY- and Ising-like, with an easy b axis and a hard c axis. As a result, it is shown that both next-nearest neighbor exchange couplings in the bc plane are in competition with the strongest nearest neighbor coupling.« less

Spin squeezing as an indicator of quantum chaos in the Dicke model.

PubMed

Song, Lijun; Yan, Dong; Ma, Jian; Wang, Xiaoguang

2009-04-01

We study spin squeezing, an intrinsic quantum property, in the Dicke model without the rotating-wave approximation. We show that the spin squeezing can reveal the underlying chaotic and regular structures in phase space given by a Poincaré section, namely, it acts as an indicator of quantum chaos. Spin squeezing vanishes after a very short time for an initial coherent state centered in a chaotic region, whereas it persists over a longer time for the coherent state centered in a regular region of the phase space. We also study the distribution of the mean spin directions when quantum dynamics takes place. Finally, we discuss relations among spin squeezing, bosonic quadrature squeezing, and two-qubit entanglement in the dynamical processes.

Electron spin resonance modes in a strong-leg ladder in the Tomonaga-Luttinger liquid phase

NASA Astrophysics Data System (ADS)

Ozerov, M.; Maksymenko, M.; Wosnitza, J.; Honecker, A.; Landee, C. P.; Turnbull, M. M.; Furuya, S. C.; Giamarchi, T.; Zvyagin, S. A.

2015-12-01

Magnetic excitations in the strong-leg quantum spin ladder compound (C7H10N) 2CuBr4 (known as DIMPY) in the field-induced Tomonaga-Luttinger spin-liquid phase are studied by means of high-field electron spin resonance (ESR) spectroscopy. The presence of a gapped ESR mode with unusual nonlinear frequency-field dependence is revealed experimentally. Using a combination of analytic and exact-diagonalization methods, we compute the dynamical structure factor and identify this mode with longitudinal excitations in the antisymmetric channel. We argue that these excitations constitute a fingerprint of the spin dynamics in a strong-leg spin-1/2 Heisenberg antiferromagnetic ladder and owe their ESR observability to the uniform Dzyaloshinskii-Moriya interaction.

Computer studies of multiple-quantum spin dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murdoch, J.B.

The excitation and detection of multiple-quantum (MQ) transitions in Fourier transform NMR spectroscopy is an interesting problem in the quantum mechanical dynamics of spin systems as well as an important new technique for investigation of molecular structure. In particular, multiple-quantum spectroscopy can be used to simplify overly complex spectra or to separate the various interactions between a nucleus and its environment. The emphasis of this work is on computer simulation of spin-system evolution to better relate theory and experiment.

Dynamical quadrupole structure factor of frustrated ferromagnetic chain

NASA Astrophysics Data System (ADS)

Onishi, Hiroaki

2018-05-01

We investigate the dynamical quadrupole structure factor of a spin-1/2 J1-J2 Heisenberg chain with competing ferromagnetic J1 and antiferromagnetic J2 in a magnetic field by exploiting density-matrix renormalization group techniques. In a field-induced spin nematic regime, we observe gapless excitations at q = π according to quasi-long-range antiferro-quadrupole correlations. The gapless excitation mode has a quadratic form at the saturation, while it changes into a linear dispersion as the magnetization decreases.

Effect of the spin-twist structure on the spin-wave dynamics in Fe{sub 55}Pt{sub 45}/Ni{sub 80}Fe{sub 20} exchange coupled bi-layers with varying Ni{sub 80}Fe{sub 20} thickness

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pal, Semanti; Barman, Saswati, E-mail: saswati@bose.res.in; Barman, Anjan, E-mail: abarman@bose.res.in

2014-05-07

We have investigated optically induced ultrafast magnetization dynamics of a series of Fe{sub 55}Pt{sub 45}/Ni{sub 80}Fe{sub 20} exchange spring bi-layers with varying Ni{sub 80}Fe{sub 20} thickness. Rich spin-wave spectra are observed; whose frequency shows a strong dependence on the Ni{sub 80}Fe{sub 20} layer thickness. Micromagnetic simulations based on a simplified magnetic microstructure were able to reproduce the experimental data qualitatively. The spin twist structure introduced in the Ni{sub 80}Fe{sub 20} layer gives rise to new modes in the composite system as opposed to the bare Ni{sub 80}Fe{sub 20} films.

All-electrical detection of spin dynamics in magnetic antidot lattices by the inverse spin Hall effect

DOE PAGES

Jungfleisch, Matthias B.; Zhang, Wei; Ding, Junjia; ...

2016-02-03

The understanding of spin dynamics in laterally confined structures on sub-micron length scales has become a significant aspect of the development of novel magnetic storage technologies. Numerous ferromagnetic resonance measurements, optical characterization by Kerr microscopy and Brillouin light scattering spectroscopy and x-ray studies were carried out to detect the dynamics in patterned magnetic antidot lattices. Here, we investigate Oersted-field driven spin dynamics in rectangular Ni80Fe20/Pt antidot lattices with different lattice parameters by electrical means. When the system is driven to resonance, a dc voltage across the length of the sample is detected that changes its sign upon field reversal, whichmore » is in agreement with a rectification mechanism based on the inverse spin Hall effect. Furthermore, we show that the voltage output scales linearly with the applied microwave drive in the investigated range of powers. Lastly, our findings have direct implications on the development of engineered magnonics applications and devices.« less

Spin-motive Force Induced by Domain Wall Dynamics in the Antiferromagnetic Spin Valve

NASA Astrophysics Data System (ADS)

Sugano, Ryoko; Ichimura, Masahiko; Takahashi, Saburo; Maekawa, Sadamichi; Crest Collaboration

2014-03-01

In spite of no net magnetization in antiferromagnetic (AF) textures, the local magnetic properties (Neel magnetization) can be manipulated in a similar fashion to ferromagnetic (F) ones. It is expected that, even in AF metals, spin transfer torques (STTs) lead to the domain wall (DW) motion and that the DW motion induces spin-motive force (SMF). In order to study the Neel magnetization dynamics and the resultant SMF, we treat the nano-structured F1/AF/F2 junction. The F1 and F2 leads behave as a spin current injector and a detector, respectively. Each F lead is fixed in the different magnetization direction. Torsions (DW in AF) are introduced reflecting the fixed magnetization of two F leads. We simulated the STT-induced Neel magnetization dynamics with the injecting current from F1 to F2 and evaluate induced SMF. Based on the adiabatic electron dynamics in the AF texture, Langevin simulations are performed at finite temperature. This research was supported by JST, CREST, Japan.

Anisotropic magnetic interactions and spin dynamics in the spin-chain compound Cu (py) 2Br2 : An experimental and theoretical study

NASA Astrophysics Data System (ADS)

Zeisner, J.; Brockmann, M.; Zimmermann, S.; Weiße, A.; Thede, M.; Ressouche, E.; Povarov, K. Yu.; Zheludev, A.; Klümper, A.; Büchner, B.; Kataev, V.; Göhmann, F.

2017-07-01

We compare theoretical results for electron spin resonance (ESR) properties of the Heisenberg-Ising Hamiltonian with ESR experiments on the quasi-one-dimensional magnet Cu (py) 2Br2 (CPB). Our measurements were performed over a wide frequency and temperature range giving insight into the spin dynamics, spin structure, and magnetic anisotropy of this compound. By analyzing the angular dependence of ESR parameters (resonance shift and linewidth) at room temperature, we show that the two weakly coupled inequivalent spin-chain types inside the compound are well described by Heisenberg-Ising chains with their magnetic anisotropy axes perpendicular to the chain direction and almost perpendicular to each other. We further determine the full g tensor from these data. In addition, the angular dependence of the linewidth at high temperatures gives us access to the exponent of the algebraic decay of a dynamical correlation function of the isotropic Heisenberg chain. From the temperature dependence of static susceptibilities, we extract the strength of the exchange coupling (J /kB=52.0 K ) and the anisotropy parameter (δ ≈-0.02 ) of the model Hamiltonian. An independent compatible value of δ is obtained by comparing the exact prediction for the resonance shift at low temperatures with high-frequency ESR data recorded at 4 K . The spin structure in the ordered state implied by the two (almost) perpendicular anisotropy axes is in accordance with the propagation vector determined from neutron scattering experiments. In addition to undoped samples, we study the impact of partial substitution of Br by Cl ions on spin dynamics. From the dependence of the ESR linewidth on the doping level, we infer an effective decoupling of the anisotropic component J δ from the isotropic exchange J in these systems.

Micromagnetic computer simulations of spin waves in nanometre-scale patterned magnetic elements

NASA Astrophysics Data System (ADS)

Kim, Sang-Koog

2010-07-01

Current needs for further advances in the nanotechnologies of information-storage and -processing devices have attracted a great deal of interest in spin (magnetization) dynamics in nanometre-scale patterned magnetic elements. For instance, the unique dynamic characteristics of non-uniform magnetic microstructures such as various types of domain walls, magnetic vortices and antivortices, as well as spin wave dynamics in laterally restricted thin-film geometries, have been at the centre of extensive and intensive researches. Understanding the fundamentals of their unique spin structure as well as their robust and novel dynamic properties allows us to implement new functionalities into existing or future devices. Although experimental tools and theoretical approaches are effective means of understanding the fundamentals of spin dynamics and of gaining new insights into them, the limitations of those same tools and approaches have left gaps of unresolved questions in the pertinent physics. As an alternative, however, micromagnetic modelling and numerical simulation has recently emerged as a powerful tool for the study of a variety of phenomena related to spin dynamics of nanometre-scale magnetic elements. In this review paper, I summarize the recent results of simulations of the excitation and propagation and other novel wave characteristics of spin waves, highlighting how the micromagnetic computer simulation approach contributes to an understanding of spin dynamics of nanomagnetism and considering some of the merits of numerical simulation studies. Many examples of micromagnetic modelling for numerical calculations, employing various dimensions and shapes of patterned magnetic elements, are given. The current limitations of continuum micromagnetic modelling and of simulations based on the Landau-Lifshitz-Gilbert equation of motion of magnetization are also discussed, along with further research directions for spin-wave studies.

Structural and mechanical properties of cardiolipin lipid bilayers determined using neutron spin echo, small angle neutron and X-ray scattering, and molecular dynamics simulations

DOE PAGES

Pan, Jianjun; Cheng, Xiaolin; Sharp, Melissa; ...

2014-10-29

We report that the detailed structural and mechanical properties of a tetraoleoyl cardiolipin (TOCL) bilayer were determined using neutron spin echo (NSE) spectroscopy, small angle neutron and X-ray scattering (SANS and SAXS, respectively), and molecular dynamics (MD) simulations. We used MD simulations to develop a scattering density profile (SDP) model, which was then utilized to jointly refine SANS and SAXS data. In addition to commonly reported lipid bilayer structural parameters, component distributions were obtained, including the volume probability, electron density and neutron scattering length density.

Online SAXS investigations of polymeric hollow fibre membranes.

PubMed

Pranzas, P Klaus; Knöchel, Arndt; Kneifel, Klemens; Kamusewitz, Helmut; Weigel, Thomas; Gehrke, Rainer; Funari, Sérgio S; Willumeit, Regine

2003-07-01

Polymeric membranes are used in industrial and analytical separation techniques. In this study small-angle X-ray scattering (SAXS) with synchrotron radiation has been applied for in-situ characterisation during formation of polymeric membranes. The spinning of a polyetherimide (PEI) hollow fibre membrane was chosen for investigation of dynamic aggregation processes during membrane formation, because it allows the measurement of the dynamic equilibrium at different distances from the spinning nozzle. With this system it is possible to resolve structural changes in the nm-size range which occur during membrane formation on the time-scale of milliseconds. Integral structural parameters, like radius of gyration and pair-distance distribution, were determined. Depending on the chosen spinning parameters, e.g. the flow ratio between polymer solution and coagulant water, significant changes in the scattering curves have been observed. The data are correlated with the distance from the spinning nozzle in order to get information about the kinetics of membrane formation which has fundamental influence on structure and properties of the membrane.

Decoherence and fluctuation dynamics of the quantum dot nuclear spin bath probed by nuclear magnetic resonance

NASA Astrophysics Data System (ADS)

Chekhovich, Evgeny A.

2017-06-01

Dynamics of nuclear spin decoherence and nuclear spin flip-flops in self-assembled InGaAs/GaAs quantum dots are studied experimentally using optically detected nuclear magnetic resonance (NMR). Nuclear spin-echo decay times are found to be in the range 1-4 ms. This is a factor of ~3 longer than in strain-free GaAs/AlGaAs structures and is shown to result from strain-induced quadrupolar effects that suppress nuclear spin flip-flops. The correlation times of the flip-flops are examined using a novel frequency-comb NMR technique and are found to exceed 1 s, a factor of ~1000 longer than in strain-free structures. These findings complement recent studies of electron spin coherence and reveal the paradoxical dual role of the quadrupolar effects in self-assembled quantum dots: large increase of the nuclear spin bath coherence and at the same time significant reduction of the electron spin-qubit coherence. Approaches to increasing electron spin coherence are discussed. In particular the nanohole filled GaAs/AlGaAs quantum dots are an attractive option: while their optical quality matches the self-assembled dots the quadrupolar effects measured in NMR spectra are a factor of 1000 smaller.

Ultrafast Band Engineering and Transient Spin Currents in Antiferromagnetic Oxides

NASA Astrophysics Data System (ADS)

Gu, Mingqiang; Rondinelli, James M.

2016-04-01

We report a dynamic structure and band engineering strategy with experimental protocols to induce indirect-to-direct band gap transitions and coherently oscillating pure spin-currents in three-dimensional antiferromagnets (AFM) using selective phononic excitations. In the Mott insulator LaTiO3, we show that a photo-induced nonequilibrium phonon mode amplitude destroys the spin and orbitally degenerate ground state, reduces the band gap by 160 meV and renormalizes the carrier masses. The time scale of this process is a few hundreds of femtoseconds. Then in the hole-doped correlated metallic titanate, we show how pure spin-currents can be achieved to yield spin-polarizations exceeding those observed in classic semiconductors. Last, we demonstrate the generality of the approach by applying it to the non-orbitally degenerate AFM CaMnO3. These results advance our understanding of electron-lattice interactions in structures out-of-equilibrium and establish a rational framework for designing dynamic phases that may be exploited in ultrafast optoelectronic and optospintronic devices.

Ultrafast Band Engineering and Transient Spin Currents in Antiferromagnetic Oxides.

PubMed

Gu, Mingqiang; Rondinelli, James M

2016-04-29

We report a dynamic structure and band engineering strategy with experimental protocols to induce indirect-to-direct band gap transitions and coherently oscillating pure spin-currents in three-dimensional antiferromagnets (AFM) using selective phononic excitations. In the Mott insulator LaTiO3, we show that a photo-induced nonequilibrium phonon mode amplitude destroys the spin and orbitally degenerate ground state, reduces the band gap by 160 meV and renormalizes the carrier masses. The time scale of this process is a few hundreds of femtoseconds. Then in the hole-doped correlated metallic titanate, we show how pure spin-currents can be achieved to yield spin-polarizations exceeding those observed in classic semiconductors. Last, we demonstrate the generality of the approach by applying it to the non-orbitally degenerate AFM CaMnO3. These results advance our understanding of electron-lattice interactions in structures out-of-equilibrium and establish a rational framework for designing dynamic phases that may be exploited in ultrafast optoelectronic and optospintronic devices.

Ultrafast band engineering and transient spin currents in antiferromagnetic oxides

DOE PAGES

Gu, Mingqiang; Rondinelli, James M.

2016-04-29

Here, we report a dynamic structure and band engineering strategy with experimental protocols to induce indirect-to-direct band gap transitions and coherently oscillating pure spin-currents in three-dimensional antiferromagnets (AFM) using selective phononic excitations. In the Mott insulator LaTiO 3, we show that a photo-induced nonequilibrium phonon mode amplitude destroys the spin and orbitally degenerate ground state, reduces the band gap by 160 meV and renormalizes the carrier masses. The time scale of this process is a few hundreds of femtoseconds. Then in the hole-doped correlated metallic titanate, we show how pure spin-currents can be achieved to yield spin-polarizations exceeding those observedmore » in classic semiconductors. Last, we demonstrate the generality of the approach by applying it to the non-orbitally degenerate AFM CaMnO 3. These results advance our understanding of electron-lattice interactions in structures out-of-equilibrium and establish a rational framework for designing dynamic phases that may be exploited in ultrafast optoelectronic and optospintronic devices.« less

Ultrafast Band Engineering and Transient Spin Currents in Antiferromagnetic Oxides

PubMed Central

Gu, Mingqiang; Rondinelli, James M.

2016-01-01

We report a dynamic structure and band engineering strategy with experimental protocols to induce indirect-to-direct band gap transitions and coherently oscillating pure spin-currents in three-dimensional antiferromagnets (AFM) using selective phononic excitations. In the Mott insulator LaTiO3, we show that a photo-induced nonequilibrium phonon mode amplitude destroys the spin and orbitally degenerate ground state, reduces the band gap by 160 meV and renormalizes the carrier masses. The time scale of this process is a few hundreds of femtoseconds. Then in the hole-doped correlated metallic titanate, we show how pure spin-currents can be achieved to yield spin-polarizations exceeding those observed in classic semiconductors. Last, we demonstrate the generality of the approach by applying it to the non-orbitally degenerate AFM CaMnO3. These results advance our understanding of electron-lattice interactions in structures out-of-equilibrium and establish a rational framework for designing dynamic phases that may be exploited in ultrafast optoelectronic and optospintronic devices. PMID:27126354

Dynamical modeling and free vibration analysis of spinning pipes conveying fluid with axial deployment

NASA Astrophysics Data System (ADS)

Liang, Feng; Yang, Xiao-Dong; Zhang, Wei; Qian, Ying-Jing

2018-03-01

In this paper, a dynamical model of simply-supported spinning pipes conveying fluid with axial deployment is proposed and the transverse free vibration and stability for such a doubly gyroscopic system involving time-dependent parameters are investigated. The partial differential equations of motion are derived by the extended Hamilton principle and then truncated by the Galerkin technique. The time-variant frequencies, mode shapes and responses to initial conditions are comprehensively investigated to reveal the dynamical essence of the system. It is indicated that the qualitative stability evolution of the system mainly depends on the effect of fluid-structure interaction (FSI), while the spinning motion will enhance the pipe rigidity and eliminate the buckling instability. The dynamical evolution of a retracting pipe is almost inverse to that of the deploying one. The pipe possesses different mode configurations of spatial curves as the pipe length increases and some modal and response characteristics of the present system are found rather distinct from those of deploying cantilevered structures.

Spin dynamics and magnetoelectric coupling mechanism of C o4N b2O9

NASA Astrophysics Data System (ADS)

Deng, Guochu; Cao, Yiming; Ren, Wei; Cao, Shixun; Studer, Andrew J.; Gauthier, Nicolas; Kenzelmann, Michel; Davidson, Gene; Rule, Kirrily C.; Gardner, Jason S.; Imperia, Paolo; Ulrich, Clemens; McIntyre, Garry J.

2018-02-01

Neutron powder diffraction experiments reveal that C o4N b2O9 forms a noncollinear in-plane magnetic structure with C o2 + moments lying in the a b plane. The spin-wave excitations of this magnet were measured by using inelastic neutron scattering and soundly simulated by a dynamic model involving nearest- and next-nearest-neighbor exchange interactions, in-plane anisotropy, and the Dzyaloshinskii-Moriya interaction. The in-plane magnetic structure of C o4N b2O9 is attributed to the large in-plane anisotropy, while the noncollinearity of the spin configuration is attributed to the Dzyaloshinskii-Moriya interaction. The high magnetoelectric coupling effect of C o4N b2O9 in fields can be explained by its special in-plane magnetic structure.

Spin Transport in Nondegenerate Si with a Spin MOSFET Structure at Room Temperature

NASA Astrophysics Data System (ADS)

Sasaki, Tomoyuki; Ando, Yuichiro; Kameno, Makoto; Tahara, Takayuki; Koike, Hayato; Oikawa, Tohru; Suzuki, Toshio; Shiraishi, Masashi

2014-09-01

Spin transport in nondegenerate semiconductors is expected to pave the way to the creation of spin transistors, spin logic devices, and reconfigurable logic circuits, because room-temperature (RT) spin transport in Si has already been achieved. However, RT spin transport has been limited to degenerate Si, which makes it difficult to produce spin-based signals because a gate electric field cannot be used to manipulate such signals. Here, we report the experimental demonstration of spin transport in nondegenerate Si with a spin metal-oxide-semiconductor field-effect transistor (MOSFET) structure. We successfully observe the modulation of the Hanle-type spin-precession signals, which is a characteristic spin dynamics in nondegenerate semiconductors. We obtain long spin transport of more than 20 μm and spin rotation greater than 4π at RT. We also observe gate-induced modulation of spin-transport signals at RT. The modulation of the spin diffusion length as a function of a gate voltage is successfully observed, which we attribute to the Elliott-Yafet spin relaxation mechanism. These achievements are expected to lead to the creation of practical Si-based spin MOSFETs.

Dynamical pairwise entanglement and two-point correlations in the three-ligand spin-star structure

NASA Astrophysics Data System (ADS)

Motamedifar, M.

2017-10-01

We consider the three-ligand spin-star structure through homogeneous Heisenberg interactions (XXX-3LSSS) in the framework of dynamical pairwise entanglement. It is shown that the time evolution of the central qubit ;one-particle; state (COPS) brings about the generation of quantum W states at periodical time instants. On the contrary, W states cannot be generated from the time evolution of a ligand ;one-particle; state (LOPS). We also investigate the dynamical behavior of two-point quantum correlations as well as the expectation values of the different spin-components for each element in the XXX-3LSSS. It is found that when a W state is generated, the same value of the concurrence between any two arbitrary qubits arises from the xx and yy two-point quantum correlations. On the opposite, zz quantum correlation between any two qubits vanishes at these time instants.

Confinement and Diffusion Effects in Dynamical Nuclear Polarization in Low Dimensional Nanostructures

NASA Astrophysics Data System (ADS)

Henriksen, Dan; Tifrea, Ionel

2012-02-01

We investigate the dynamic nuclear polarization as it results from the hyperfine coupling between nonequilibrium electronic spins and nuclear spins in semiconductor nanostructures. The natural confinement provided by low dimensional nanostructures is responsible for an efficient nuclear spin - electron spin hyperfine coupling [1] and for a reduced value of the nuclear spin diffusion constant [2]. In the case of optical pumping, the induced nuclear spin polarization is position dependent even in the presence of nuclear spin diffusion. This effect should be measurable via optically induced nuclear magnetic resonance or time-resolved Faraday rotation experiments. We discuss the implications of our calculations for the case of GaAs quantum well structures.[4pt] [1] I. Tifrea and M. E. Flatt'e, Phys. Rev. B 84, 155319 (2011).[0pt] [2] A. Malinowski and R. T. Harley, Solid State Commun. 114, 419 (2000).

Probing equilibrium by nonequilibrium dynamics: Aging in Co/Cr superlattices

NASA Astrophysics Data System (ADS)

Binek, Christian

2013-03-01

Magnetic aging phenomena are investigated in a structurally ordered Co/Cr superlattice through measurements of magnetization relaxation, magnetic susceptibility, and hysteresis at various temperatures above and below the onset of collective magnetic order. We take advantage of the fact that controlled growth of magnetic multilayer thin films via molecular beam epitaxy allows tailoring the intra and inter-layer exchange interaction and thus enables tuning of magnetic properties including the spin-fluctuation spectra. Tailored nanoscale periodicity in Co/Cr multilayers creates mesoscopic spatial magnetic correlations with slow relaxation dynamics when quenching the system into a nonequilibrium state. Magnetization relaxation in weakly correlated spin systems depends on the microscopic spin-flip time of about 10 ns and is therefore a fast process. The spin correlations in our Co/Cr superlattice bring the magnetization dynamics to experimentally better accessible time scales of seconds or hours. In contrast to spin-glasses, where slow dynamics due to disorder and frustration is a well-known phenomenon, we tune and increase relaxation times in ordered structures. This is achieved by increasing spin-spin correlation between mesoscopically correlated regions rather than individual atomic spins, a concept with some similarity to block spin renormalization. Magnetization transients are measured after exposing the Co/Cr heterostructure to a magnetic set field for various waiting times. Scaling analysis reveals an asymptotic power-law behavior in accordance with a full aging scenario. The temperature dependence of the relaxation exponent shows pronounced anomalies at the equilibrium phase transitions of the antiferromagnetic superstructure and the ferromagnetic to paramagnetic transition of the Co layers. The latter leaves only weak fingerprints in the equilibrium magnetic behavior but gives rise to a prominent change in nonequilibrium properties. Our findings suggest that scaling analysis of nonequilibrium data can serve as a probe for weak equilibrium phase transitions. Financial support by NRI, and NSF through EPSCoR, and MRSEC 0820521 is greatly acknowledged.

Structural Refinement of Membrane Proteins by Restrained Molecular Dynamics and Solvent Accessibility Data

PubMed Central

Sompornpisut, Pornthep; Roux, Benoît; Perozo, Eduardo

2008-01-01

We present an approach for incorporating solvent accessibility data from electron paramagnetic resonance experiments in the structural refinement of membrane proteins through restrained molecular dynamics simulations. The restraints have been parameterized from oxygen (ΠO2) and nickel-ethylenediaminediacetic acid (ΠNiEdda) collision frequencies, as indicators of lipid or aqueous exposed spin-label sites. These are enforced through interactions between a pseudoatom representation of the covalently attached Nitroxide spin-label and virtual “solvent” particles corresponding to O2 and NiEdda in the surrounding environment. Interactions were computed using an empirical potential function, where the parameters have been optimized to account for the different accessibilities of the spin-label pseudoatoms to the surrounding environment. This approach, “pseudoatom-driven solvent accessibility refinement”, was validated by refolding distorted conformations of the Streptomyces lividans potassium channel (KcsA), corresponding to a range of 2–30 Å root mean-square deviations away from the native structure. Molecular dynamics simulations based on up to 58 electron paramagnetic resonance restraints derived from spin-label mutants were able to converge toward the native structure within 1–3 Å root mean-square deviations with minimal computational cost. The use of energy-based ranking and structure similarity clustering as selection criteria helped in the convergence and identification of correctly folded structures from a large number of simulations. This approach can be applied to a variety of integral membrane protein systems, regardless of oligomeric state, and should be particularly useful in calculating conformational changes from a known reference crystal structure. PMID:18676641

Dynamic generation of spin-wave currents in hybrid structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lyapilin, I. I.; Okorokov, M. S., E-mail: Okorokovmike@gmail.com

2016-11-15

Spin transport through the interface in a semiconductor/ferromagnetic insulator hybrid structure is studied by the nonequilibrium statistical operator method under conditions of the spin Seebeck effect. The effective parameter approach in which each examined subsystem (conduction electrons, magnons, phonons) is characterized by its specific effective temperature is considered. The effect of the resonant (electric dipole) excitation of the spin electronic subsystem of conduction electrons on spin-wave current excitation in a ferromagnetic insulator is considered. The macroscopic equations describing the spin-wave current caused by both resonant excitation of the spin system of conduction electrons and the presence of a nonuniform temperaturemore » field in the ferromagnetic insulator are derived taking into account both the resonance-diffusion propagation of magnons and their relaxation processes. It is shown that spin-wave current excitation is also of resonant nature under the given conditions.« less

Superaging and Subaging Phenomena in a Nonequilibrium Critical Behavior of the Structurally Disordered Two-Dimensional XY Model

NASA Astrophysics Data System (ADS)

Prudnikov, V. V.; Prudnikov, P. V.; Popov, I. S.

2018-03-01

A Monte Carlo numerical simulation of the specific features of nonequilibrium critical behavior is carried out for the two-dimensional structurally disordered XY model during its evolution from a low-temperature initial state. On the basis of the analysis of the two-time dependence of autocorrelation functions and dynamic susceptibility for systems with spin concentrations of p = 1.0, 0.9, and 0.6, aging phenomena characterized by a slowing down of the relaxation system with increasing waiting time and the violation of the fluctuation-dissipation theorem (FDT) are revealed. The values of the universal limiting fluctuation-dissipation ratio (FDR) are obtained for the systems considered. As a result of the analysis of the two-time scaling dependence for spin-spin and connected spin autocorrelation functions, it is found that structural defects lead to subaging phenomena in the behavior of the spin-spin autocorrelation function and superaging phenomena in the behavior of the connected spin autocorrelation function.

Dynamic origins of fermionic D -terms

NASA Astrophysics Data System (ADS)

Hudson, Jonathan; Schweitzer, Peter

2018-03-01

The D -term is defined through matrix elements of the energy-momentum tensor, similarly to mass and spin, yet this important particle property is experimentally not known any fermion. In this work we show that the D -term of a spin 1/2 fermion is of dynamical origin: it vanishes for a free fermion. This is in pronounced contrast to the bosonic case where already a free spin-0 boson has a non-zero intrinsic D -term. We illustrate in two simple models how interactions generate the D -term of a fermion with an internal structure, the nucleon. All known matter is composed of elementary fermions. This indicates the importance to study this interesting particle property in more detail, which will provide novel insights especially on the structure of the nucleon.

Electric-field tunable spin diode FMR in patterned PMN-PT/NiFe structures

NASA Astrophysics Data System (ADS)

Zietek, Slawomir; Ogrodnik, Piotr; Skowroński, Witold; Stobiecki, Feliks; van Dijken, Sebastiaan; Barnaś, Józef; Stobiecki, Tomasz

2016-08-01

Dynamic properties of NiFe thin films on PMN-PT piezoelectric substrate are investigated using the spin-diode method. Ferromagnetic resonance (FMR) spectra of microstrips with varying width are measured as a function of magnetic field and frequency. The FMR frequency is shown to depend on the electric field applied across the substrate, which induces strain in the NiFe layer. Electric field tunability of up to 100 MHz per 1 kV/cm is achieved. An analytical model based on total energy minimization and the Landau-Lifshitz-Gilbert equation, taking into account the magnetostriction effect, is used to explain the measured dynamics. Based on this model, conditions for optimal electric-field tunable spin diode FMR in patterned NiFe/PMN-PT structures are derived.

Structure and dynamics of spin-labeled insulin entrapped in a silica matrix by the sol-gel method.

PubMed

Vanea, E; Gruian, C; Rickert, C; Steinhoff, H-J; Simon, V

2013-08-12

The structure and conformational dynamics of insulin entrapped into a silica matrix was monitored during the sol to maturated-gel transition by electron paramagnetic resonance (EPR) spectroscopy. Insulin was successfully spin-labeled with iodoacetamide and the bifunctional nitroxide reagent HO-1944. Room temperature continuous wave (cw) EPR spectra of insulin were recorded to assess the mobility of the attached spin labels. Insulin conformation and its distribution within the silica matrix were studied using double electron-electron resonance (DEER) and low-temperature cw-EPR. A porous oxide matrix seems to form around insulin molecules with pore diameters in the order of a few nanometers. Secondary structure of the encapsulated insulin investigated by Fourier transform infrared spectroscopy proved a high structural integrity of insulin even in the dried silica matrix. The results show that silica encapsulation can be used as a powerful tool to effectively isolate and functionally preserve biomolecules during preparation, storage, and release.

Control of Spin Wave Dynamics in Spatially Twisted Magnetic Structures

DTIC Science & Technology

2017-06-27

realize high-performance spintronic and magnetic storage devices. 15. SUBJECT TERMS nano- electronics , spin, wave, magnetic, multi-functional, device 16... electronics has required us to develop high-performance and multi-functional electronic devices driven with extremely low power consumption...Spintronics”, simultaneously utilizing the charge and the spin of electrons , provides us with solutions to essential problems for semiconductor-based

RVB signatures in the spin dynamics of the square-lattice Heisenberg antiferromagnet

NASA Astrophysics Data System (ADS)

Ghioldi, E. A.; Gonzalez, M. G.; Manuel, L. O.; Trumper, A. E.

2016-03-01

We investigate the spin dynamics of the square-lattice spin-\\frac{1}{2} Heisenberg antiferromagnet by means of an improved mean-field Schwinger boson calculation. By identifying both, the long-range Néel and the RVB-like components of the ground state, we propose an educated guess for the mean-field magnetic excitation consisting on a linear combination of local and bond spin flips to compute the dynamical structure factor. Our main result is that when this magnetic excitation is optimized in such a way that the corresponding sum rule is fulfilled, we recover the low- and high-energy spectral weight features of the experimental spectrum. In particular, the anomalous spectral weight depletion at (π,0) found in recent inelastic neutron scattering experiments can be attributed to the interference of the triplet bond excitations of the RVB component of the ground state. We conclude that the Schwinger boson theory seems to be a good candidate to adequately interpret the dynamic properties of the square-lattice Heisenberg antiferromagnet.

Studying Dynamics by Magic-Angle Spinning Solid-State NMR Spectroscopy: Principles and Applications to Biomolecules

PubMed Central

Schanda, Paul; Ernst, Matthias

2016-01-01

Magic-angle spinning solid-state NMR spectroscopy is an important technique to study molecular structure, dynamics and interactions, and is rapidly gaining importance in biomolecular sciences. Here we provide an overview of experimental approaches to study molecular dynamics by MAS solid-state NMR, with an emphasis on the underlying theoretical concepts and differences of MAS solid-state NMR compared to solution-state NMR. The theoretical foundations of nuclear spin relaxation are revisited, focusing on the particularities of spin relaxation in solid samples under magic-angle spinning. We discuss the range of validity of Redfield theory, as well as the inherent multi-exponential behavior of relaxation in solids. Experimental challenges for measuring relaxation parameters in MAS solid-state NMR and a few recently proposed relaxation approaches are discussed, which provide information about time scales and amplitudes of motions ranging from picoseconds to milliseconds. We also discuss the theoretical basis and experimental measurements of anisotropic interactions (chemical-shift anisotropies, dipolar and quadrupolar couplings), which give direct information about the amplitude of motions. The potential of combining relaxation data with such measurements of dynamically-averaged anisotropic interactions is discussed. Although the focus of this review is on the theoretical foundations of dynamics studies rather than their application, we close by discussing a small number of recent dynamics studies, where the dynamic properties of proteins in crystals are compared to those in solution. PMID:27110043

Effective model with strong Kitaev interactions for α -RuCl3

NASA Astrophysics Data System (ADS)

Suzuki, Takafumi; Suga, Sei-ichiro

2018-04-01

We use an exact numerical diagonalization method to calculate the dynamical spin structure factors of three ab initio models and one ab initio guided model for a honeycomb-lattice magnet α -RuCl3 . We also use thermal pure quantum states to calculate the temperature dependence of the heat capacity, the nearest-neighbor spin-spin correlation function, and the static spin structure factor. From the results obtained from these four effective models, we find that, even when the magnetic order is stabilized at low temperature, the intensity at the Γ point in the dynamical spin structure factors increases with increasing nearest-neighbor spin correlation. In addition, we find that the four models fail to explain heat-capacity measurements whereas two of the four models succeed in explaining inelastic-neutron-scattering experiments. In the four models, when temperature decreases, the heat capacity shows a prominent peak at a high temperature where the nearest-neighbor spin-spin correlation function increases. However, the peak temperature in heat capacity is too low in comparison with that observed experimentally. To address these discrepancies, we propose an effective model that includes strong ferromagnetic Kitaev coupling, and we show that this model quantitatively reproduces both inelastic-neutron-scattering experiments and heat-capacity measurements. To further examine the adequacy of the proposed model, we calculate the field dependence of the polarized terahertz spectra, which reproduces the experimental results: the spin-gapped excitation survives up to an onset field where the magnetic order disappears and the response in the high-field region is almost linear. Based on these numerical results, we argue that the low-energy magnetic excitation in α -RuCl3 is mainly characterized by interactions such as off-diagonal interactions and weak Heisenberg interactions between nearest-neighbor pairs, rather than by the strong Kitaev interactions.

Ultrafast spintronics roadmap: from femtosecond spin current pulses to terahertz non-uniform spin dynamics via nano-confined spin transfer torques (Conference Presentation)

NASA Astrophysics Data System (ADS)

Melnikov, Alexey; Razdolski, Ilya; Alekhin, Alexandr; Ilin, Nikita; Meyburg, Jan; Diesing, Detlef; Roddatis, Vladimir; Rungger, Ivan; Stamenova, Maria; Sanvito, Stefano; Bovensiepen, Uwe

2016-10-01

Further development of spintronics requires miniaturization and reduction of characteristic timescales of spin dynamics combining the nanometer spatial and femtosecond temporal ranges. These demands shift the focus of interest towards the fundamental open question of the interaction of femtosecond spin current (SC) pulses with a ferromagnet (FM). The spatio-temporal properties of the spin transfer torque (STT) exerted by ultrashort SC pulses on the FM open the time domain for studying STT fingerprint on spatially non-uniform magnetization dynamics. Using the sensitivity of magneto-induced second harmonic generation to SC, we develop technique for SC monitoring. With 20 fs resolution, we demonstrate the generation of 250 fs-long SC pulses in Fe/Au/Fe/MgO(001) structures. Their temporal profile indicates (i) nearly-ballistic hot electron transport in Au and (ii) that the pulse duration is primarily determined by the thermalization time of laser-excited hot carriers in Fe. Together with strongly spin-dependent Fe/Au interface transmission calculated for these carriers, this suggests the non-thermal spin-dependent Seebeck effect dominating the generation of ultrashort SC pulses. The analysis of SC transmission/reflection at the Au/Fe interface shows that hot electron spins orthogonal to the Fe magnetization rotate gaining huge parallel (anti-parallel) projection in transmitted (reflected) SC. This is accompanied by a STT-induced perturbation of the magnetization localized at the interface, which excites the inhomogeneous high-frequency spin dynamics in the FM. Time-resolved magneto-optical studies reveal the excitation of several standing spin wave modes in the Fe film with their spectrum extending up to 0.6 THz and indicating the STT spatial confinement to 2 nm.

Geometric representation of spin correlations and applications to ultracold systems

NASA Astrophysics Data System (ADS)

Mukherjee, Rick; Mirasola, Anthony E.; Hollingsworth, Jacob; White, Ian G.; Hazzard, Kaden R. A.

2018-04-01

We provide a one-to-one map between the spin correlations and certain three-dimensional shapes, analogous to the map between single spins and Bloch vectors, and demonstrate its utility. Much as one can reason geometrically about dynamics using a Bloch vector—e.g., a magnetic field causes it to precess and dissipation causes it to shrink—one can reason similarly about the shapes we use to visualize correlations. This visualization demonstrates its usefulness by unveiling the hidden structure in the correlations. For example, seemingly complex correlation dynamics can be described as simple motions of the shapes. We demonstrate the simplicity of the dynamics, which is obscured in conventional analyses, by analyzing several physical systems of relevance to cold atoms.

Non-Born-Oppenheimer molecular dynamics of the spin-forbidden reaction O(3P) + CO(X 1Σ+) → CO2(tilde X{}^1Σ _g^ +)

NASA Astrophysics Data System (ADS)

Jasper, Ahren W.; Dawes, Richard

2013-10-01

The lowest-energy singlet (1 1A') and two lowest-energy triplet (1 3A' and 1 3A″) electronic states of CO2 are characterized using dynamically weighted multireference configuration interaction (dw-MRCI+Q) electronic structure theory calculations extrapolated to the complete basis set (CBS) limit. Global analytic representations of the dw-MRCI+Q/CBS singlet and triplet surfaces and of their CASSCF/aug-cc-pVQZ spin-orbit coupling surfaces are obtained via the interpolated moving least squares (IMLS) semiautomated surface fitting method. The spin-forbidden kinetics of the title reaction is calculated using the coupled IMLS surfaces and coherent switches with decay of mixing non-Born-Oppenheimer molecular dynamics. The calculated spin-forbidden association rate coefficient (corresponding to the high pressure limit of the rate coefficient) is 7-35 times larger at 1000-5000 K than the rate coefficient used in many detailed chemical models of combustion. A dynamical analysis of the multistate trajectories is presented. The trajectory calculations reveal direct (nonstatistical) and indirect (statistical) spin-forbidden reaction mechanisms and may be used to test the suitability of transition-state-theory-like statistical methods for spin-forbidden kinetics. Specifically, we consider the appropriateness of the "double passage" approximation, of assuming statistical distributions of seam crossings, and of applications of the unified statistical model for spin-forbidden reactions.

Changes in the electronic structure and spin dynamics across the metal-insulator transition in LaLa 1-xSr xCoO 3

DOE PAGES

Smith, R. X.; Hoch, M. J. R.; Moulton, W. G.; ...

2016-01-25

The magnetoelectronic properties of La 1-xSr xCoO 3, which include giant magnetoresistance, are strongly dependent on the level of hole doping. The system evolves, with increasing x, from a spin glass insulator to a metallic ferromagnet with a metal-insulator (MI) transition at x C ~ 0.18. Nanoscale phase separation occurs in the insulating phase and persists, to some extent, into the just-metallic phase. The present experiments at 4.2 K have used 139La NMR to investigate the transition from hopping dynamics for x < x C to Korringa-like ferromagnetic metal behavior for x > x C. A marked decrease in themore » spin-lattice relaxation rate is found in the vicinity of x C as the MI transition is crossed. Lastly, this behavior is accounted for in terms of the evolution of the electronic structure and dynamics with cluster size.« less

Dynamics of a magnetic skyrmionium driven by spin waves

NASA Astrophysics Data System (ADS)

Li, Sai; Xia, Jing; Zhang, Xichao; Ezawa, Motohiko; Kang, Wang; Liu, Xiaoxi; Zhou, Yan; Zhao, Weisheng

2018-04-01

A magnetic skyrmionium is a skyrmion-like structure, but carries a zero net skyrmion number which can be used as a building block for non-volatile information processing devices. Here, we study the dynamics of a magnetic skyrmionium driven by propagating spin waves. It is found that the skyrmionium can be effectively driven into motion by spin waves showing a tiny skyrmion Hall effect, whose mobility is much better than that of the skyrmion at the same condition. We also show that the skyrmionium mobility depends on the nanotrack width and the damping coefficient and can be controlled by an external out-of-plane magnetic field. In addition, we demonstrate that the skyrmionium motion driven by spin waves is inertial. Our results indicate that the skyrmionium is a promising building block for building spin-wave spintronic devices.

Time evolution of a pair of distinguishable interacting spins subjected to controllable and noisy magnetic fields

NASA Astrophysics Data System (ADS)

Grimaudo, R.; Belousov, Yu.; Nakazato, H.; Messina, A.

2018-05-01

The quantum dynamics of a Jˆ2 =(jˆ1 +jˆ2) 2-conserving Hamiltonian model describing two coupled spins jˆ1 and jˆ2 under controllable and fluctuating time-dependent magnetic fields is investigated. Each eigenspace of Jˆ2 is dynamically invariant and the Hamiltonian of the total system restricted to any one of such (j1 +j2) - |j1 -j2 | + 1 eigenspaces, possesses the SU(2) structure of the Hamiltonian of a single fictitious spin acted upon by the total magnetic field. We show that such a reducibility holds regardless of the time dependence of the externally applied field as well as of the statistical properties of the noise, here represented as a classical fluctuating magnetic field. The time evolution of the joint transition probabilities of the two spins jˆ1 and jˆ2 between two prefixed factorized states is examined, bringing to light peculiar dynamical properties of the system under scrutiny. When the noise-induced non-unitary dynamics of the two coupled spins is properly taken into account, analytical expressions for the joint Landau-Zener transition probabilities are reported. The possibility of extending the applicability of our results to other time-dependent spin models is pointed out.

Anomalous quantum critical spin dynamics in YFe2Al10

NASA Astrophysics Data System (ADS)

Huang, K.; Tan, C.; Zhang, J.; Ding, Z.; MacLaughlin, D. E.; Bernal, O. O.; Ho, P.-C.; Baines, C.; Wu, L. S.; Aronson, M. C.; Shu, L.

2018-04-01

We report results of a muon spin relaxation (μ SR ) study of YFe2Al10 , a quasi-two-dimensional (2D) nearly ferromagnetic metal in which unconventional quantum critical behavior is observed. No static Fe2 + magnetism, with or without long-range order, is found down to 19 mK. The dynamic muon spin relaxation rate λ exhibits power-law divergences in temperature and magnetic field, the latter for fields that are too weak to affect the electronic spin dynamics directly. We attribute this to the proportionality of λ (ωμ,T ) to the dynamic structure factor S (ωμ,T ) , where ωμ≈105-107s-1 is the muon Zeeman frequency. These results suggest critical divergences of S (ωμ,T ) in both temperature and frequency. Power-law scaling and a 2D dissipative quantum XY model both yield forms for S (ω ,T ) that agree with neutron scattering data (ω ≈1012s-1 ). Extrapolation to μ SR frequencies agrees semiquantitatively with the observed temperature dependence of λ (ωμ,T ) , but predicts frequency independence for ωμ≪T , in extreme disagreement with experiment. We conclude that the quantum critical spin dynamics of YFe2Al10 is not well understood at low frequencies.

Spin Transfer torques in Antiferromagnets

NASA Astrophysics Data System (ADS)

Saidaoui, Hamed; Waintal, Xavier; Manchon, Aurelien; Spsms, Cea, Grenoble France Collaboration

2013-03-01

Spin Transfer Torque (STT) has attracted tremendously growing interest in the past two decades. Consisting on the transfer of spin angular momentum of a spin polarized current to local magnetic moments, the STT gives rise to a complex dynamics of the magnetization. Depending on the the structure, the STT shows a dominated In plane component for spin valves, whereas both components coexist for magnetic tunneling junctions (MTJ). For latter case the symmetry of the structure is considered to be decisive in identifying the nature and behavior of the torque. In the present study we are interested in magnetic structures where we substitute either one or both of the magnetic layers by antiferromagnets (AF). We use Non-equilibrium Green's function formalism applied on a tight-binding model to investigate the nature of the spin torque. We notice the presence of two types of torque exerted on (AF), a torque which tends to rotate the order parameter and another one that competes with the exchange interaction. We conclude by comparison with previous works.

Extracting full-field dynamic strain response of a rotating wind turbine using photogrammetry

NASA Astrophysics Data System (ADS)

Baqersad, Javad; Poozesh, Peyman; Niezrecki, Christopher; Avitabile, Peter

2015-04-01

Health monitoring of wind turbines is typically performed using conventional sensors (e.g. strain-gages and accelerometers) that are usually mounted to the nacelle or gearbox. Although many wind turbines stop operating due to blade failures, there are typically few to no sensor mounted on the blades. Placing sensors on the rotating parts of the structure is a challenge due to the wiring and data transmission constraints. Within the current work, an approach to monitor full-field dynamic response of rotating structures (e.g. wind turbine blades or helicopter rotors) is developed and experimentally verified. A wind turbine rotor was used as the test structure and was mounted to a block and horizontally placed on the ground. A pair of bearings connected to the rotor shaft allowed the turbine to freely spin along the shaft. Several optical targets were mounted to the blades and a pair of high-speed cameras was used to monitor the dynamics of the spinning turbine. Displacements of the targets during rotation were measured using three-dimensional point tracking. The point tracking technique measured both rigid body displacement and flexible deformation of the blades at target locations. While the structure is rotating, only flap displacements of optical targets (displacements out of the rotation plane) were used in strain prediction process. The measured displacements were expanded and applied to the finite element model of the turbine to extract full-field dynamic strain on the structure. The proposed approach enabled the prediction of dynamic response on the outer surface as well as within the inner points of the structure where no other sensor could be easily mounted. In order to validate the proposed approach, the predicted strain was compared to strain measured at four locations on the spinning blades using a wireless strain-gage system.

Electric-field tunable spin diode FMR in patterned PMN-PT/NiFe structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ziętek, Slawomir, E-mail: zietek@agh.edu.pl; Skowroński, Witold; Stobiecki, Tomasz

Dynamic properties of NiFe thin films on PMN-PT piezoelectric substrate are investigated using the spin-diode method. Ferromagnetic resonance (FMR) spectra of microstrips with varying width are measured as a function of magnetic field and frequency. The FMR frequency is shown to depend on the electric field applied across the substrate, which induces strain in the NiFe layer. Electric field tunability of up to 100 MHz per 1 kV/cm is achieved. An analytical model based on total energy minimization and the Landau-Lifshitz-Gilbert equation, taking into account the magnetostriction effect, is used to explain the measured dynamics. Based on this model, conditions formore » optimal electric-field tunable spin diode FMR in patterned NiFe/PMN-PT structures are derived.« less

1 / f α noise and generalized diffusion in random Heisenberg spin systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Agarwal, Kartiek; Demler, Eugene; Martin, Ivar

2015-11-01

We study the “flux-noise” spectrum of random-bond quantum Heisenberg spin systems using a real-space renormalization group (RSRG) procedure that accounts for both the renormalization of the system Hamiltonian and of a generic probe that measures the noise. For spin chains, we find that the dynamical structure factor Sq (f ), at finite wave vector q, exhibits a power-law behavior both at high and low frequencies f , with exponents that are connected to one another and to an anomalous dynamical exponent through relations that differ at T = 0 and T =∞. The low-frequency power-law behavior of the structure factormore » is inherited by any generic probe with a finite bandwidth and is of the form 1/f α with 0.5 < α < 1. An analytical calculation of the structure factor, assuming a limiting distribution of the RG flow parameters (spin size, length, bond strength) confirms numerical findings.More generally, we demonstrate that this form of the structure factor, at high temperatures, is a manifestation of anomalous diffusionwhich directly follows from a generalized spin-diffusion propagator.We also argue that 1/f -noise is intimately connected to many-body-localization at finite temperatures. In two dimensions, the RG procedure is less reliable; however, it becomes convergent for quasi-one-dimensional geometries where we find that one-dimensional 1/f α behavior is recovered at low frequencies; the latter configurations are likely representative of paramagnetic spin networks that produce 1/f α noise in SQUIDs.« less

A combined EPR and MD simulation study of a nitroxyl spin label with restricted internal mobility sensitive to protein dynamics.

PubMed

Oganesyan, Vasily S; Chami, Fatima; White, Gaye F; Thomson, Andrew J

2017-01-01

EPR studies combined with fully atomistic Molecular Dynamics (MD) simulations and an MD-EPR simulation method provide evidence for intrinsic low rotameric mobility of a nitroxyl spin label, Rn, compared to the more widely employed label MTSL (R1). Both experimental and modelling results using two structurally different sites of attachment to Myoglobin show that the EPR spectra of Rn are more sensitive to the local protein environment than that of MTSL. This study reveals the potential of using the Rn spin label as a reporter of protein motions. Copyright © 2016 Elsevier Inc. All rights reserved.

Analysis of the transient response of nuclear spins in GaAs with/without nuclear magnetic resonance

NASA Astrophysics Data System (ADS)

Rasly, Mahmoud; Lin, Zhichao; Yamamoto, Masafumi; Uemura, Tetsuya

2016-05-01

As an alternative to studying the steady-state responses of nuclear spins in solid state systems, working within a transient-state framework can reveal interesting phenomena. The response of nuclear spins in GaAs to a changing magnetic field was analyzed based on the time evolution of nuclear spin temperature. Simulation results well reproduced our experimental results for the transient oblique Hanle signals observed in an all-electrical spin injection device. The analysis showed that the so called dynamic nuclear polarization can be treated as a cooling tool for the nuclear spins: It works as a provider to exchange spin angular momentum between polarized electron spins and nuclear spins through the hyperfine interaction, leading to an increase in the nuclear polarization. In addition, a time-delay of the nuclear spin temperature with a fast sweep of the external magnetic field produces a possible transient state for the nuclear spin polarization. On the other hand, the nuclear magnetic resonance acts as a heating tool for a nuclear spin system. This causes the nuclear spin temperature to jump to infinity: i.e., the average nuclear spins along with the nuclear field vanish at resonant fields of 75As, 69Ga and 71Ga, showing an interesting step-dip structure in the oblique Hanle signals. These analyses provide a quantitative understanding of nuclear spin dynamics in semiconductors for application in future computation processing.

Temperature for a dynamic spin ensemble

NASA Astrophysics Data System (ADS)

Ma, Pui-Wai; Dudarev, S. L.; Semenov, A. A.; Woo, C. H.

2010-09-01

In molecular dynamics simulations, temperature is evaluated, via the equipartition principle, by computing the mean kinetic energy of atoms. There is no similar recipe yet for evaluating temperature of a dynamic system of interacting spins. By solving semiclassical Langevin spin-dynamics equations, and applying the fluctuation-dissipation theorem, we derive an equation for the temperature of a spin ensemble, expressed in terms of dynamic spin variables. The fact that definitions for the kinetic and spin temperatures are fully consistent is illustrated using large-scale spin dynamics and spin-lattice dynamics simulations.

Recent advancements in 2D-materials interface based magnetic junctions for spintronics

NASA Astrophysics Data System (ADS)

Iqbal, Muhammad Zahir; Qureshi, Nabeel Anwar; Hussain, Ghulam

2018-07-01

Two-dimensional (2D) materials comprising of graphene, hexagonal boron nitride (hBN) and transition metal dichalcogenides (TMDs) have revealed fascinating properties in various spintronic architectures. Here, we review spin valve effect in lateral and vertical magnetic junctions incorporating 2D materials as non-magnetic layer between ferromagnetic (FM) electrodes. The magnetic field dependent spin transport properties are studied by measuring non-local resistance (RNL) and relative magnetoresistance ratio (MR) for lateral and vertical structures, respectively. The review consists of (i) studying spin lifetimes and spin diffusion length thereby exploring the effect of tunneling and transparent contacts in lateral spin valve structures, temperature dependence, gate tunability and contrasting mechanisms of spin relaxation in single layer graphene (SLG) and bilayer graphene (BLG) devices. (ii) Perpendicular spin valve devices are thoroughly investigated thereby studying the role of different 2D materials in vertical spin dynamics. The dependence of spin valve signal on interface quality, temperature and various other parameters is also investigated. Furthermore, the spin reversal in graphene-hBN hybrid system is examined on the basis of Julliere model.

Correlation between spin structure oscillations and domain wall velocities

PubMed Central

Bisig, André; Stärk, Martin; Mawass, Mohamad-Assaad; Moutafis, Christoforos; Rhensius, Jan; Heidler, Jakoba; Büttner, Felix; Noske, Matthias; Weigand, Markus; Eisebitt, Stefan; Tyliszczak, Tolek; Van Waeyenberge, Bartel; Stoll, Hermann; Schütz, Gisela; Kläui, Mathias

2013-01-01

Magnetic sensing and logic devices based on the motion of magnetic domain walls rely on the precise and deterministic control of the position and the velocity of individual magnetic domain walls in curved nanowires. Varying domain wall velocities have been predicted to result from intrinsic effects such as oscillating domain wall spin structure transformations and extrinsic pinning due to imperfections. Here we use direct dynamic imaging of the nanoscale spin structure that allows us for the first time to directly check these predictions. We find a new regime of oscillating domain wall motion even below the Walker breakdown correlated with periodic spin structure changes. We show that the extrinsic pinning from imperfections in the nanowire only affects slow domain walls and we identify the magnetostatic energy, which scales with the domain wall velocity, as the energy reservoir for the domain wall to overcome the local pinning potential landscape. PMID:23978905

Atomic-Scale Nuclear Spin Imaging Using Quantum-Assisted Sensors in Diamond

NASA Astrophysics Data System (ADS)

Ajoy, A.; Bissbort, U.; Lukin, M. D.; Walsworth, R. L.; Cappellaro, P.

2015-01-01

Nuclear spin imaging at the atomic level is essential for the understanding of fundamental biological phenomena and for applications such as drug discovery. The advent of novel nanoscale sensors promises to achieve the long-standing goal of single-protein, high spatial-resolution structure determination under ambient conditions. In particular, quantum sensors based on the spin-dependent photoluminescence of nitrogen-vacancy (NV) centers in diamond have recently been used to detect nanoscale ensembles of external nuclear spins. While NV sensitivity is approaching single-spin levels, extracting relevant information from a very complex structure is a further challenge since it requires not only the ability to sense the magnetic field of an isolated nuclear spin but also to achieve atomic-scale spatial resolution. Here, we propose a method that, by exploiting the coupling of the NV center to an intrinsic quantum memory associated with the nitrogen nuclear spin, can reach a tenfold improvement in spatial resolution, down to atomic scales. The spatial resolution enhancement is achieved through coherent control of the sensor spin, which creates a dynamic frequency filter selecting only a few nuclear spins at a time. We propose and analyze a protocol that would allow not only sensing individual spins in a complex biomolecule, but also unraveling couplings among them, thus elucidating local characteristics of the molecule structure.

High-Frequency Dynamics Modulated by Collective Magnetization Reversal in Artificial Spin Ice

NASA Astrophysics Data System (ADS)

Jungfleisch, Matthias B.; Sklenar, Joseph; Ding, Junjia; Park, Jungsik; Pearson, John E.; Novosad, Valentine; Schiffer, Peter; Hoffmann, Axel

2017-12-01

Spin-torque ferromagnetic resonance arises in heavy metal-ferromagnet heterostructures when an alternating charge current is passed through the bilayer stack. The methodology to detect the resonance is based on the anisotropic magnetoresistance, which is the change in the electrical resistance due to different orientations of the magnetization. In connected networks of ferromagnetic nanowires, known as artificial spin ice, the magnetoresistance is rather complex owing to the underlying collective behavior of the geometrically frustrated magnetic domain structure. Here, we demonstrate spin-torque ferromagnetic resonance investigations in a square artificial spin-ice system and correlate our observations to magnetotransport measurements. The experimental findings are described using a simulation approach that highlights the importance of the correlated dynamics response of the magnetic system. Our results open the possibility of designing reconfigurable microwave oscillators and magnetoresistive devices based on connected networks of nanomagnets.

High-Frequency Dynamics Modulated by Collective Magnetization Reversal in Artificial Spin Ice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jungfleisch, Matthias B.; Sklenar, Joseph; Ding, Junjia

Spin-torque ferromagnetic resonance arises in heavy metal-ferromagnet heterostructures when an alternating charge current is passed through the bilayer stack. The methodology to detect the resonance is based on the anisotropic magnetoresistance, which is the change in the electrical resistance due to different orientations of the magnetization. In connected networks of ferromagnetic nanowires, known as artificial spin ice, the magnetoresistance is rather complex owing to the underlying collective behavior of the geometrically frustrated magnetic domain structure. Here, we demonstrate spin-torque ferromagnetic resonance investigations in a square artificial spin-ice system and correlate our observations to magneto-transport measurements. The experimental findings are describedmore » using a simulation approach that highlights the importance of the correlated dynamics response of the magnetic system. Our results open the possibility of designing reconfigurable microwave oscillators and magnetoresistive devices based on connected networks of nanomagnets.« less

Dissipative structure in the photo-induced phase under steady light irradiation in the spin crossover complex.

PubMed

Nishihara, Taishi; Bousseksou, Azzdine; Tanaka, Koichiro

2013-12-16

We report the spatial and temporal dynamics of the photo-induced phase in the iron (II) spin crossover complex Fe(ptz)(6)(BF(4))(2) studied by image measurement under steady light irradiation and transient absorption measurement. The dynamic factors are derived from the spatial and temporal fluctuation of the image in the steady state under light irradiation between 65 and 100 K. The dynamic factors clearly indicate that the fluctuation has a resonant frequency that strongly depends on the temperature, and is proportional to the relaxation rate of the photo-induced phase. This oscillation of the speckle pattern under steady light irradiation is ascribed to the nonlinear interaction between the spin state and the lattice volume at the surface.

Plasmonic diabolo cavity enhanced spin pumping

NASA Astrophysics Data System (ADS)

Qian, Jie; Gou, Peng; Gui, Y. S.; Hu, C. M.; An, Zhenghua

2017-09-01

Low spin-current generation efficiency has impeded further progress in practical spin devices, especially in the form of wireless excitation. To tackle this problem, a unique Plasmonic Diabolo Cavity (PDC) is proposed to enhance the spin pumping (SP) signal. The SP microwave photovoltage is enhanced ˜22-fold by PDC at ferromagnetic resonance (FMR). This improvement owes to the localization of the microwave magnetic field, which drives the spin precession process to more effectively generate photovoltage at the FMR condition. The in-plane anisotropy of spin pumping is found to be suppressed by PDC. Our work suggests that metamaterial resonant structures exhibit rich interactions with spin dynamics and could potentially be applied in future high-frequency spintronics.

Structure-dependent magnetoresistance and spin-transfer torque in antiferromagnetic Fe |MgO |FeMn |Cu tunnel junctions

NASA Astrophysics Data System (ADS)

Jia, Xingtao; Tang, Huimin; Wang, Shizhuo; Qin, Minghui

2017-02-01

We predict large magnetoresistance (MR) and spin transfer torque (STT) in antiferromagnetic Fe |MgO |FeMn |Cu tunnel junctions based on first-principles scattering theory. MR as large as ˜100 % is found in one junction. Magnetic dynamic simulations show that STT acting on the antiferromagnetic order parameter dominates the spin dynamics, and an electronic bias of order 10-1mV and current density of order 105Acm-2 can switches a junction of three-layer MgO, they are about one order smaller than that in Fe |MgO |Fe junction with the same barrier thickness, respectively. The multiple scattering in the antiferromagnetic region is considered to be responsible for the enhanced spin torque and smaller switching current density.

Coherent spin dynamics of carriers in ferromagnetic semiconductor heterostructures with an Mn δ layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zaitsev, S. V., E-mail: szaitsev@issp.ac.ru; Akimov, I. A.; Langer, L.

2016-09-15

The coherent spin dynamics of carriers in the heterostructures that contain an InGaAs/GaAs quantum well (QW) and an Mn δ layer, which are separated by a narrow GaAs spacer 2–10 nm thick, is comprehensively studied by the magnetooptical Kerr effect method at a picosecond time resolution. The exchange interaction of photoexcited electrons in QW with the ferromagnetic Mn δ layer manifests itself in magnetic-field and temperature dependences of the Larmor precession frequency of electron spins and is found to be very weak (several microelectron volts). Two nonoscillating components related to holes exist apart from an electron contribution to the Kerrmore » signal of polarization plane rotation. At the initial stage, a fast relaxation process, which corresponds to the spin relaxation of free photoexcited holes, is detected in the structures with a wide spacer. The second component is caused by the further spin dephasing of energyrelaxed holes, which are localized at strong QW potential fluctuations in the structures under study. The decay of all contributions to the Kerr signal in time increases substantially when the spacer thickness decreases, which correlates with the enhancement of nonradiative recombination in QW.« less

Spin wave nonreciprocity for logic device applications

NASA Astrophysics Data System (ADS)

Jamali, Mahdi; Kwon, Jae Hyun; Seo, Soo-Man; Lee, Kyung-Jin; Yang, Hyunsoo

2013-11-01

The utilization of spin waves as eigenmodes of the magnetization dynamics for information processing and communication has been widely explored recently due to its high operational speed with low power consumption and possible applications for quantum computations. Previous proposals of spin wave Mach-Zehnder devices were based on the spin wave phase, a delicate entity which can be easily disrupted. Here, we propose a complete logic system based on the spin wave amplitude utilizing the nonreciprocal spin wave behavior excited by microstrip antennas. The experimental data reveal that the nonreciprocity of magnetostatic surface spin wave can be tuned by the bias magnetic field. Furthermore, engineering of the device structure could result in a high nonreciprocity factor for spin wave logic applications.

Spin wave nonreciprocity for logic device applications

PubMed Central

Jamali, Mahdi; Kwon, Jae Hyun; Seo, Soo-Man; Lee, Kyung-Jin; Yang, Hyunsoo

2013-01-01

The utilization of spin waves as eigenmodes of the magnetization dynamics for information processing and communication has been widely explored recently due to its high operational speed with low power consumption and possible applications for quantum computations. Previous proposals of spin wave Mach-Zehnder devices were based on the spin wave phase, a delicate entity which can be easily disrupted. Here, we propose a complete logic system based on the spin wave amplitude utilizing the nonreciprocal spin wave behavior excited by microstrip antennas. The experimental data reveal that the nonreciprocity of magnetostatic surface spin wave can be tuned by the bias magnetic field. Furthermore, engineering of the device structure could result in a high nonreciprocity factor for spin wave logic applications. PMID:24196318

Spin-wave dynamics and exchange interactions in multiferroic NdFe3(BO3)4 explored by inelastic neutron scattering

NASA Astrophysics Data System (ADS)

Golosovsky, I. V.; Ovsyanikov, A. K.; Aristov, D. N.; Matveeva, P. G.; Mukhin, A. A.; Boehm, M.; Regnault, L.-P.; Bezmaternykh, L. N.

2018-04-01

Magnetic excitations and exchange interactions in multiferroic NdFe3(BO3)4 were studied by inelastic neutron scattering in the phase with commensurate antiferromagnetic structure. The observed spectra were analyzed in the frame of the linear spin-wave theory. It was shown that only the model, which includes the exchange interactions within eight coordination spheres, describes satisfactorily all observed dispersion curves. The calculation showed that the spin-wave dynamics is governed by the strongest antiferromagnetic intra-chain interaction and three almost the same inter-chain interactions. Other interactions, including ferromagnetic exchange, appeared to be insignificant. The overall energy balance of the antiferromagnetic inter-chain exchange interactions, which couple the moments from the adjacent ferromagnetic layers as well as within a layer, stabilizes ferromagnetic arrangement in the latter. It demonstrates that the pathway geometry plays a crucial role in forming of the magnetic structure.

Core structure and dynamics of non-Abelian vortices in a biaxial nematic spinor Bose-Einstein condensate

NASA Astrophysics Data System (ADS)

Borgh, Magnus O.; Ruostekoski, Janne

2016-05-01

We demonstrate that multiple interaction-dependent defect core structures as well as dynamics of non-Abelian vortices can be realized in the biaxial nematic (BN) phase of a spin-2 atomic Bose-Einstein condensate (BEC). An experimentally simple protocol may be used to break degeneracy with the uniaxial nematic phase. We show that a discrete spin-space symmetry in the core may be reflected in a breaking of its spatial symmetry. The discrete symmetry of the BN order parameter leads to non-commuting vortex charges. We numerically simulate reconnection of non-Abelian vortices, demonstrating formation of the obligatory rung vortex. In addition to atomic BECs, non-Abelian vortices are theorized in, e.g., liquid crystals and cosmic strings. Our results suggest the BN spin-2 BEC as a prime candidate for their realization. We acknowledge financial support from the EPSRC.

Semiclassical dynamics of spin density waves

NASA Astrophysics Data System (ADS)

Chern, Gia-Wei; Barros, Kipton; Wang, Zhentao; Suwa, Hidemaro; Batista, Cristian D.

2018-01-01

We present a theoretical framework for equilibrium and nonequilibrium dynamical simulation of quantum states with spin-density-wave (SDW) order. Within a semiclassical adiabatic approximation that retains electron degrees of freedom, we demonstrate that the SDW order parameter obeys a generalized Landau-Lifshitz equation. With the aid of an enhanced kernel polynomial method, our linear-scaling quantum Landau-Lifshitz dynamics (QLLD) method enables dynamical SDW simulations with N ≃105 lattice sites. Our real-space formulation can be used to compute dynamical responses, such as the dynamical structure factor, of complex and even inhomogeneous SDW configurations at zero or finite temperatures. Applying the QLLD to study the relaxation of a noncoplanar topological SDW under the excitation of a short pulse, we further demonstrate the crucial role of spatial correlations and fluctuations in the SDW dynamics.

14 CFR 25.473 - Landing load conditions and assumptions.

Code of Federal Regulations, 2010 CFR

2010-01-01

... presence of systems or procedures significantly affects the lift. (c) The method of analysis of airplane... dynamic characteristics. (2) Spin-up and springback. (3) Rigid body response. (4) Structural dynamic response of the airframe, if significant. (d) The landing gear dynamic characteristics must be validated by...

Room Temperature Spin Mediated Coupling in Hybrid Magnetic, Organic, and Oxide Structures and Devices

DTIC Science & Technology

2015-12-07

doi: Ran Lin, Fujian Wang, Markus Wohlgenannt, Chunyong He, Xiaofang Zhai, Yuri Suzuki. Organic spin- valves based on fullerene C60, Synthetic Metals...is likely incorrect, given that other groups have been able to dynamically tune LAO/STO samples along this anticorrelation curve. These dynamic...For jBj. Bp, the energy difference between the split peaks increases linearly (Zeeman- like ) with magnetic field –0.4 0 0.4 V 2 3 (m V) 100 50 0 dI

Room-Temperature Spin-Mediated Coupling in Hybrid Magnetic, Organic, and Oxide Structures and Devices

DTIC Science & Technology

2015-12-07

doi: Ran Lin, Fujian Wang, Markus Wohlgenannt, Chunyong He, Xiaofang Zhai, Yuri Suzuki. Organic spin- valves based on fullerene C60, Synthetic Metals...is likely incorrect, given that other groups have been able to dynamically tune LAO/STO samples along this anticorrelation curve. These dynamic...For jBj. Bp, the energy difference between the split peaks increases linearly (Zeeman- like ) with magnetic field –0.4 0 0.4 V 2 3 (m V) 100 50 0 dI

Spin-orbit torque induced magnetic vortex polarity reversal utilizing spin-Hall effect

NASA Astrophysics Data System (ADS)

Li, Cheng; Cai, Li; Liu, Baojun; Yang, Xiaokuo; Cui, Huanqing; Wang, Sen; Wei, Bo

2018-05-01

We propose an effective magnetic vortex polarity reversal scheme that makes use of spin-orbit torque introduced by spin-Hall effect in heavy-metal/ferromagnet multilayers structure, which can result in subnanosecond polarity reversal without endangering the structural stability. Micromagnetic simulations are performed to investigate the spin-Hall effect driven dynamics evolution of magnetic vortex. The mechanism of magnetic vortex polarity reversal is uncovered by a quantitative analysis of exchange energy density, magnetostatic energy density, and their total energy density. The simulation results indicate that the magnetic vortex polarity is reversed through the nucleation-annihilation process of topological vortex-antivortex pair. This scheme is an attractive option for ultra-fast magnetic vortex polarity reversal, which can be used as the guidelines for the choice of polarity reversal scheme in vortex-based random access memory.

Fast Auroral Snapshot performance using a multi-body dynamic simulation

NASA Technical Reports Server (NTRS)

Zimbelman, Darrell; Walker, Mary

1993-01-01

This paper examines the complex dynamic interaction between two 2.6 m long stacer booms, four 30 m long flexible wire booms and the attitude control system of the Fast Auroral SnapshoT (FAST) spacecraft. The FAST vehicle will nominally operate as a negative orbit spinner, positioned in a 83 deg inclination, 350 x 4200 km orbit. For this study, a three-axis, non-linear, seven body dynamic simulation is developed using the TREETOPS software package. The significance of this approach is the ability to model each component of the FAST spacecraft as an individual member and connect them together in order to better understand the dynamic coupling between structures and the control system. Both the wire and stacer booms are modeled as separate bodies attached to a rigid central body. The wire booms are oriented perpendicular to the spin axis at right angles relative to each other, whereas the stacer booms are aligned with the spin axis. The analysis consists of a comparison between the simulated in-plane and out-of-plane boom motions with theoretically derived frequencies, and an examination of the dynamic coupling between the control system and boom oscillations. Results show that boom oscillations of up to 0.36 deg are acceptable in order to meet the performance requirements. The dynamic motion is well behaved when the precession coil is operating, however, activation of the spin coil produces an erratic trend in the spin rate which approaches the spin rate requirement.

All-atom molecular dynamics simulations of spin labelled double and single-strand DNA for EPR studies.

PubMed

Prior, C; Danilāne, L; Oganesyan, V S

2018-05-16

We report the first application of fully atomistic molecular dynamics (MD) simulations to the prediction of electron paramagnetic resonance (EPR) spectra of spin labelled DNA. Models for two structurally different DNA spin probes with either the rigid or flexible position of the nitroxide group in the base pair, employed in experimental studies previously, have been developed. By the application of the combined MD-EPR simulation methodology we aimed at the following. Firstly, to provide a test bed against a sensitive spectroscopic technique for the recently developed improved version of the parmbsc1 force field for MD modelling of DNA. The predicted EPR spectra show good agreement with the experimental ones available from the literature, thus confirming the accuracy of the currently employed DNA force fields. Secondly, to provide a quantitative interpretation of the motional contributions into the dynamics of spin probes in both duplex and single-strand DNA fragments and to analyse their perturbing effects on the local DNA structure. Finally, a combination of MD and EPR allowed us to test the validity of the application of the Model-Free (M-F) approach coupled with the partial averaging of magnetic tensors to the simulation of EPR spectra of DNA systems by comparing the resultant EPR spectra with those simulated directly from MD trajectories. The advantage of the M-F based EPR simulation approach over the direct propagation techniques is that it requires motional and order parameters that can be calculated from shorter MD trajectories. The reported MD-EPR methodology is transferable to the prediction and interpretation of EPR spectra of higher order DNA structures with novel types of spin labels.

Spin-current emission governed by nonlinear spin dynamics.

PubMed

Tashiro, Takaharu; Matsuura, Saki; Nomura, Akiyo; Watanabe, Shun; Kang, Keehoon; Sirringhaus, Henning; Ando, Kazuya

2015-10-16

Coupling between conduction electrons and localized magnetization is responsible for a variety of phenomena in spintronic devices. This coupling enables to generate spin currents from dynamical magnetization. Due to the nonlinearity of magnetization dynamics, the spin-current emission through the dynamical spin-exchange coupling offers a route for nonlinear generation of spin currents. Here, we demonstrate spin-current emission governed by nonlinear magnetization dynamics in a metal/magnetic insulator bilayer. The spin-current emission from the magnetic insulator is probed by the inverse spin Hall effect, which demonstrates nontrivial temperature and excitation power dependences of the voltage generation. The experimental results reveal that nonlinear magnetization dynamics and enhanced spin-current emission due to magnon scatterings are triggered by decreasing temperature. This result illustrates the crucial role of the nonlinear magnon interactions in the spin-current emission driven by dynamical magnetization, or nonequilibrium magnons, from magnetic insulators.

Spin-current emission governed by nonlinear spin dynamics

PubMed Central

Tashiro, Takaharu; Matsuura, Saki; Nomura, Akiyo; Watanabe, Shun; Kang, Keehoon; Sirringhaus, Henning; Ando, Kazuya

2015-01-01

Coupling between conduction electrons and localized magnetization is responsible for a variety of phenomena in spintronic devices. This coupling enables to generate spin currents from dynamical magnetization. Due to the nonlinearity of magnetization dynamics, the spin-current emission through the dynamical spin-exchange coupling offers a route for nonlinear generation of spin currents. Here, we demonstrate spin-current emission governed by nonlinear magnetization dynamics in a metal/magnetic insulator bilayer. The spin-current emission from the magnetic insulator is probed by the inverse spin Hall effect, which demonstrates nontrivial temperature and excitation power dependences of the voltage generation. The experimental results reveal that nonlinear magnetization dynamics and enhanced spin-current emission due to magnon scatterings are triggered by decreasing temperature. This result illustrates the crucial role of the nonlinear magnon interactions in the spin-current emission driven by dynamical magnetization, or nonequilibrium magnons, from magnetic insulators. PMID:26472712

Analysis of the transient response of nuclear spins in GaAs with/without nuclear magnetic resonance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rasly, Mahmoud; Lin, Zhichao; Yamamoto, Masafumi

As an alternative to studying the steady-state responses of nuclear spins in solid state systems, working within a transient-state framework can reveal interesting phenomena. The response of nuclear spins in GaAs to a changing magnetic field was analyzed based on the time evolution of nuclear spin temperature. Simulation results well reproduced our experimental results for the transient oblique Hanle signals observed in an all-electrical spin injection device. The analysis showed that the so called dynamic nuclear polarization can be treated as a cooling tool for the nuclear spins: It works as a provider to exchange spin angular momentum between polarizedmore » electron spins and nuclear spins through the hyperfine interaction, leading to an increase in the nuclear polarization. In addition, a time-delay of the nuclear spin temperature with a fast sweep of the external magnetic field produces a possible transient state for the nuclear spin polarization. On the other hand, the nuclear magnetic resonance acts as a heating tool for a nuclear spin system. This causes the nuclear spin temperature to jump to infinity: i.e., the average nuclear spins along with the nuclear field vanish at resonant fields of {sup 75}As, {sup 69}Ga and {sup 71}Ga, showing an interesting step-dip structure in the oblique Hanle signals. These analyses provide a quantitative understanding of nuclear spin dynamics in semiconductors for application in future computation processing.« less

Mismatch in cation size causes rapid anion dynamics in solid electrolytes: the role of the Arrhenius pre-factor.

PubMed

Breuer, Stefan; Wilkening, Martin

2018-03-28

Crystalline ion conductors exhibiting fast ion dynamics are of utmost importance for the development of, e.g., sensors or rechargeable batteries. In some layer-structured or nanostructured compounds fluorine ions participate in remarkably fast self-diffusion processes. As has been shown earlier, F ion dynamics in nanocrystalline, defect-rich BaF 2 is much higher than that in the coarse-grained counterpart BaF 2 . The thermally metastable fluoride (Ba,Ca)F 2 , which can be prepared by joint high-energy ball milling of the binary fluorides, exhibits even better ion transport properties. While long-range ion dynamics has been studied recently, less information is known about local ion hopping processes to which 19 F nuclear magnetic resonance (NMR) spin-lattice relaxation is sensitive. The present paper aims at understanding ion dynamics in metastable, nanocrystalline (Ba,Ca)F 2 by correlating short-range ion hopping with long-range transport properties. Variable-temperature NMR line shapes clearly indicate fast and slow F spin reservoirs. Surprisingly, from an atomic-scale point of view increased ion dynamics at intermediate values of composition is reflected by increased absolute spin-lattice relaxation rates rather than by a distinct minimum in activation energy. Hence, the pre-factor of the underlying Arrhenius relation, which is determined by the number of mobile spins, the attempt frequency and entropy effects, is identified as the parameter that directly enhances short-range ion dynamics in metastable (Ba,Ca)F 2 . Concerted ion migration could also play an important role to explain the anomalies seen in NMR spin-lattice relaxation.

Characterization of KCNE1 inside Lipodisq Nanoparticles for EPR Spectroscopic Studies of Membrane Proteins.

PubMed

Sahu, Indra D; Zhang, Rongfu; Dunagan, Megan M; Craig, Andrew F; Lorigan, Gary A

2017-06-01

EPR spectroscopic studies of membrane proteins in a physiologically relevant native membrane-bound state are extremely challenging due to the complexity observed in inhomogeneity sample preparation and dynamic motion of the spin-label. Traditionally, detergent micelles are the most widely used membrane mimetics for membrane proteins due to their smaller size and homogeneity, providing high-resolution structure analysis by solution NMR spectroscopy. However, it is often difficult to examine whether the protein structure in a micelle environment is the same as that of the respective membrane-bound state. Recently, lipodisq nanoparticles have been introduced as a potentially good membrane mimetic system for structural studies of membrane proteins. However, a detailed characterization of a spin-labeled membrane protein incorporated into lipodisq nanoparticles is still lacking. In this work, lipodisq nanoparticles were used as a membrane mimic system for probing the structural and dynamic properties of the integral membrane protein KCNE1 using site-directed spin labeling EPR spectroscopy. The characterization of spin-labeled KCNE1 incorporated into lipodisq nanoparticles was carried out using CW-EPR titration experiments for the EPR spectral line shape analysis and pulsed EPR titration experiment for the phase memory time (T m ) measurements. The CW-EPR titration experiment indicated an increase in spectral line broadening with the addition of the SMA polymer which approaches close to the rigid limit at a lipid to polymer weight ratio of 1:1, providing a clear solubilization of the protein-lipid complex. Similarly, the T m titration experiment indicated an increase in T m values with the addition of SMA polymer and approaches ∼2 μs at a lipid to polymer weight ratio of 1:2. Additionally, CW-EPR spectral line shape analysis was performed on six inside and six outside the membrane spin-label probes of KCNE1 in lipodisq nanoparticles. The results indicated significant differences in EPR spectral line broadening and a corresponding inverse central line width between spin-labeled KCNE1 residues located inside and outside of the membrane for lipodisq nanoparticle samples when compared to lipid vesicle samples. These results are consistent with the solution NMR structure of KCNE1. This study will be beneficial for researchers working on studying the structural and dynamic properties of membrane proteins.

Intramolecular and Lattice Dynamics in V6-nIVVnV O7(OCH3)12 Crystal

NASA Astrophysics Data System (ADS)

Yablokov, Yu. V.; Augustyniak-Jabłokow, M. A.; Borshch, S.; Daniel, C.; Hartl, H.

2006-08-01

Multi-nuclear mixed-valence clusters V4IVV2VO7(OCH3)12 were studied by X-band EPR in the temperature range 4.2-300 K. An isotropic exchange interactions between four VIV ions with individual spin Si=1/2 determine the energy levels structure of the compound with the total spin states S=0, 1, and 2, which are doubled and split due to the extra electron transfer. The spin-Hamiltonian approach was used for the analysis of the temperature dependences of the EPR spectra parameters and the cluster dynamics. Two types of the electron transfer are assumed: the single jump transfer leading to the splitting of the total spin states by intervals comparable in magnitude with the exchange parameter J≈100-150cm-1 and the double jump one resulting in dynamics. The dependence of the transition ratesνtr on the energy of the total spin states was observed. In particular, in the range 300-220 K the νtr ≈0.7×1010 cm-1 and below 180 K the νtr≈1×1010 cm-1 was estimated. The g-factors of the spin states were shown to depend on the values of the intermediate spins. A phase transition in the T-range 210-180 K leading to the change in the initial VIV ions localization was discovered.

Second order nonlinear equations of motion for spinning highly flexible line-elements. [for spacecraft solar sail

NASA Technical Reports Server (NTRS)

Salama, M.; Trubert, M.

1979-01-01

A formulation is given for the second order nonlinear equations of motion for spinning line-elements having little or no intrinsic structural stiffness. Such elements have been employed in recent studies of structural concepts for future large space structures such as the Heliogyro solar sailer. The derivation is based on Hamilton's variational principle and includes the effect of initial geometric imperfections (axial, curvature, and twist) on the line-element dynamics. For comparison with previous work, the nonlinear equations are reduced to a linearized form frequently found in the literature. The comparison has revealed several new spin-stiffening terms that have not been previously identified and/or retained. They combine geometric imperfections, rotary inertia, Coriolis, and gyroscopic terms.

Interplay of stereoelectronic and enviromental effects in tuning the structural and magnetic properties of a prototypical spin probe: further insights from a first principle dynamical approach.

PubMed

Pavone, Michele; Cimino, Paola; De Angelis, Filippo; Barone, Vincenzo

2006-04-05

The nitrogen isotropic hyperfine coupling constant (hcc) and the g tensor of a prototypical spin probe (di-tert-butyl nitroxide, DTBN) in aqueous solution have been investigated by means of an integrated computational approach including Car-Parrinello molecular dynamics and quantum mechanical calculations involving a discrete-continuum embedding. The quantitative agreement between computed and experimental parameters fully validates our integrated approach. Decoupling of the structural, dynamical, and environmental contributions acting onto the spectral observables allows an unbiased judgment of the role played by different effects in determining the overall experimental observables and highlights the importance of finite-temperature vibrational averaging. Together with their intrinsic interest, our results pave the route toward more reliable interpretations of EPR parameters of complex systems of biological and technological relevance.

Lesion-induced DNA weak structural changes detected by pulsed EPR spectroscopy combined with site-directed spin labelling.

PubMed

Sicoli, Giuseppe; Mathis, Gérald; Aci-Sèche, Samia; Saint-Pierre, Christine; Boulard, Yves; Gasparutto, Didier; Gambarelli, Serge

2009-06-01

Double electron-electron resonance (DEER) was applied to determine nanometre spin-spin distances on DNA duplexes that contain selected structural alterations. The present approach to evaluate the structural features of DNA damages is thus related to the interspin distance changes, as well as to the flexibility of the overall structure deduced from the distance distribution. A set of site-directed nitroxide-labelled double-stranded DNA fragments containing defined lesions, namely an 8-oxoguanine, an abasic site or abasic site analogues, a nick, a gap and a bulge structure were prepared and then analysed by the DEER spectroscopic technique. New insights into the application of 4-pulse DEER sequence are also provided, in particular with respect to the spin probes' positions and the rigidity of selected systems. The lesion-induced conformational changes observed, which were supported by molecular dynamics studies, confirm the results obtained by other, more conventional, spectroscopic techniques. Thus, the experimental approaches described herein provide an efficient method for probing lesion-induced structural changes of nucleic acids.

A quantum spin-probe molecular microscope

NASA Astrophysics Data System (ADS)

Perunicic, V. S.; Hill, C. D.; Hall, L. T.; Hollenberg, L. C. L.

2016-10-01

Imaging the atomic structure of a single biomolecule is an important challenge in the physical biosciences. Whilst existing techniques all rely on averaging over large ensembles of molecules, the single-molecule realm remains unsolved. Here we present a protocol for 3D magnetic resonance imaging of a single molecule using a quantum spin probe acting simultaneously as the magnetic resonance sensor and source of magnetic field gradient. Signals corresponding to specific regions of the molecule's nuclear spin density are encoded on the quantum state of the probe, which is used to produce a 3D image of the molecular structure. Quantum simulations of the protocol applied to the rapamycin molecule (C51H79NO13) show that the hydrogen and carbon substructure can be imaged at the angstrom level using current spin-probe technology. With prospects for scaling to large molecules and/or fast dynamic conformation mapping using spin labels, this method provides a realistic pathway for single-molecule microscopy.

Ultrafast Study of Dynamic Exchange Coupling in Ferromagnet/Oxide/Semiconductor Heterostructures

NASA Astrophysics Data System (ADS)

Ou, Yu-Sheng

Spintronics is the area of research that aims at utilizing the quantum mechanical spin degree of freedom of electrons in solid-state materials for information processing and data storage application. Since the discovery of the giant magnetoresistance, the field of spintronics has attracted lots of attention for its numerous potential advantages over contemporary electronics, such as less power consumption, high integration density and non-volatility. The realization of a spin battery, defined by the ability to create spin current without associated charge current, has been a long-standing goal in the field of spintronics. The demonstration of pure spin current in ferromagnet/nonmagnetic material hybrid structures by ferromagnetic resonance spin pumping has defined a thrilling direction for this field. As such, this dissertation targets at exploring the spin and magnetization dynamics in ferromagnet/oxide/semiconductor heterostructures (Fe/MgO/GaAs) using time-resolved optical pump-probe spectroscopy with the long-range goal of understanding the fundamentals of FMR-driven spin pumping. Fe/GaAs heterostructures are complex systems that contain multiple spin species, including paramagnetic spins (GaAs electrons), nuclear spins (Ga and As nuclei) and ferromagnetic spins (Fe). Optical pump-probe studies on their interplay have revealed a number of novel phenomena that has not been explored before. As such they will be the major focus of this dissertation. First, I will discuss the effect of interfacial exchange coupling on the GaAs free-carrier spin relaxation. Temperature- and field-dependent spin-resolved pump-probe studies reveal a strong correlation of the electron spin relaxation with carrier freeze-out, in quantitative agreement with a theoretical interpretation that at low temperatures the free-carrier spin lifetime is dominated by inhomogeneity in the local hyperfine field due to carrier localization. Second, we investigate the impact of tunnel barrier thickness on GaAs electron spin dynamics in Fe/MgO/GaAs heterostructures. Comparison of the Larmor frequency between samples with thick and thin MgO barriers reveals a four-fold variation in exchange coupling strength, and investigation of the spin lifetimes argues that inhomogeneity in the local hyperfine field dominates free-carrier spin relaxation across the entire range of barrier thickness. These results provide additional evidence to support the theory of hyperfine-dominated spin relaxation in GaAs. Third, we investigated the origin and dynamics of an emergent spin population by pump power and magnetic field dependent spin-resolved pump-probe studies. Power dependent study confirms its origin to be filling of electronic states in GaAs, and further field dependent studies reveal the impact of contact hyperfine coupling on the dynamics of electron spins occupying distinct electronic states. Beyond above works, we also pursue optical detection of dynamic spin pumping in Fe/MgO/GaAs heterostructures in parallel. I will discuss the development and progress that we have made toward this goal. This project can be simply divided into two phases. In the first phase, we focused on microwave excitation and optical detection of spin pumping. In the second phase, we focused on all-optical excitation and detection of spin pumping. A number of measurement strategies have been developed and executed in both stages to hunt for a spin pumping signal. I will discuss the preliminary data based upon them.

Imaging Magnetic Vortices Dynamics Using Lorentz Electron Microscopy with GHz Excitations

NASA Astrophysics Data System (ADS)

Zhu, Yimei

2015-03-01

Magnetic vortices in thin films are naturally formed spiral spin configurations with a core polarization pointing out of the film plane. They typically represent ground states with high structural and thermal stability as well as four different chirality-polarity combinations, offering great promise in the development of spin-based devices. For applications to spin oscillators, non-volatile memory and logic devices, the fundamental understanding and precise control of vortex excitations and dynamic switching behavior are essential. The compact dimensionality and fast spin dynamics set grand challenges for direct imaging technologies. Recently, we have developed a unique method to directly visualize the dynamic magnetic vortex motion using advanced Lorentz electron microscopy combined with GHz electronic excitations. It enables us to map the orbit of a magnetic vortex core in a permalloy square with <5nm resolution and to reveal subtle changes of the gyrotropic motion as the vortex is driven through resonance. Further, in multilayer spin-valve disks, we probed the strongly coupled coaxial vortex motion in the dipolar- and indirect exchange-coupled regimes and unraveled the underlying coherence and modality. Our approach is complementary to X-ray magnetic circular dichroism and is of general interest to the magnetism community as it paves a way to study fundamental spin phenomena with unprecedented resolution and accuracy. Collaborations with S.D. Pollard, J.F. Pulecio, D.A. Arena and K.S. Buchanan are acknowledged. Work supported by DOE-BES, Material Sciences and Engineering Division, under Contract No. DE-AC02-98CH10886.

Interaction modifiers in artificial spin ices

DOE PAGES

Ostman, Erik; Stopfel, Henry; Chioar, Ioan -Augustin; ...

2018-02-12

The modification of geometry and interactions in two-dimensional magnetic nanosystems has enabled a range of studies addressing the magnetic order, collective low-energy dynamics and emergent magnetic properties in, for example, artificial spin-ice structures. The common denominator of all these investigations is the use of Ising-like mesospins as building blocks, in the form of elongated magnetic islands. Here, we introduce a new approach: single interaction modifiers, using slave mesospins in the form of discs, within which the mesospin is free to rotate in the disc plane1. We show that by placing these on the vertices of square artificial spin-ice arrays andmore » varying their diameter, it is possible to tailor the strength and the ratio of the interaction energies. We demonstrate the existence of degenerate ice-rule-obeying states in square artificial spin-ice structures, enabling the exploration of thermal dynamics in a spin-liquid manifold. Furthermore, we even observe the emergence of flux lattices on larger length scales, when the energy landscape of the vertices is reversed. In conclusion, the work highlights the potential of a design strategy for two-dimensional magnetic nano-architectures, through which mixed dimensionality of mesospins can be used to promote thermally emergent mesoscale magnetic states.« less

Interaction modifiers in artificial spin ices

NASA Astrophysics Data System (ADS)

Ã-stman, Erik; Stopfel, Henry; Chioar, Ioan-Augustin; Arnalds, Unnar B.; Stein, Aaron; Kapaklis, Vassilios; Hjörvarsson, Björgvin

2018-04-01

The modification of geometry and interactions in two-dimensional magnetic nanosystems has enabled a range of studies addressing the magnetic order1-6, collective low-energy dynamics7,8 and emergent magnetic properties5, 9,10 in, for example, artificial spin-ice structures. The common denominator of all these investigations is the use of Ising-like mesospins as building blocks, in the form of elongated magnetic islands. Here, we introduce a new approach: single interaction modifiers, using slave mesospins in the form of discs, within which the mesospin is free to rotate in the disc plane11. We show that by placing these on the vertices of square artificial spin-ice arrays and varying their diameter, it is possible to tailor the strength and the ratio of the interaction energies. We demonstrate the existence of degenerate ice-rule-obeying states in square artificial spin-ice structures, enabling the exploration of thermal dynamics in a spin-liquid manifold. Furthermore, we even observe the emergence of flux lattices on larger length scales, when the energy landscape of the vertices is reversed. The work highlights the potential of a design strategy for two-dimensional magnetic nano-architectures, through which mixed dimensionality of mesospins can be used to promote thermally emergent mesoscale magnetic states.

Interaction modifiers in artificial spin ices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ostman, Erik; Stopfel, Henry; Chioar, Ioan -Augustin

The modification of geometry and interactions in two-dimensional magnetic nanosystems has enabled a range of studies addressing the magnetic order, collective low-energy dynamics and emergent magnetic properties in, for example, artificial spin-ice structures. The common denominator of all these investigations is the use of Ising-like mesospins as building blocks, in the form of elongated magnetic islands. Here, we introduce a new approach: single interaction modifiers, using slave mesospins in the form of discs, within which the mesospin is free to rotate in the disc plane1. We show that by placing these on the vertices of square artificial spin-ice arrays andmore » varying their diameter, it is possible to tailor the strength and the ratio of the interaction energies. We demonstrate the existence of degenerate ice-rule-obeying states in square artificial spin-ice structures, enabling the exploration of thermal dynamics in a spin-liquid manifold. Furthermore, we even observe the emergence of flux lattices on larger length scales, when the energy landscape of the vertices is reversed. In conclusion, the work highlights the potential of a design strategy for two-dimensional magnetic nano-architectures, through which mixed dimensionality of mesospins can be used to promote thermally emergent mesoscale magnetic states.« less

ESR modes in a Strong-Leg Ladder in the Tomonaga-Luttinger Liquid Phase

NASA Astrophysics Data System (ADS)

Zvyagin, S.; Ozerov, M.; Maksymenko, M.; Wosnitza, J.; Honecker, A.; Landee, C. P.; Turnbull, M.; Furuya, S. C.; Giamarchi, T.

Magnetic excitations in the strong-leg quantum spin ladder compound (C7H10N)2CuBr4 (known as DIMPY) in the field-induced Tomonaga-Luttinger spin liquid phase are studied by means of high-field electron spin resonance (ESR) spectroscopy. The presence of a gapped ESR mode with unusual non-linear frequency-field dependence is revealed experimentally. Using a combination of analytic and exact diagonalization methods, we compute the dynamical structure factor and identify this mode with longitudinal excitations in the antisymmetric channel. We argue that these excitations constitute a fingerprint of the spin dynamics in a strong-leg spin-1/2 Heisenberg antiferromagnetic ladder and owe its ESR observability to the uniform Dzyaloshinskii-Moriya interaction. This work was partially supported by the DFG and Helmholtz Gemeinschaft (Germany), Swiss SNF under Division II, and ERC synergy UQUAM project. We acknowledge the support of the HLD at HZDR, member of the European Magnetic Field Laboratory (EMFL).

Nonlocal and local magnetization dynamics excited by an RF magnetic field in magnetic multilayers

NASA Astrophysics Data System (ADS)

Moriyama, Takahiro

A microwave study in spintronic devices has been actively pursued in the past several years due to the fertile physics and potential applications. On one hand, a passive use of microwave can be very helpful to analyze and understand the magnetization dynamics in spintronic devices. Examples include ferromagnetic resonance (FMR) measurements, and various microwave spectrum analyses in ferromagnetic materials. The most important chrematistic parameter for the phenomenological analysis on the magnetization dynamics is, so called, the Gilbert damping constant. In this work, a relatively new measurement technique, a flip-chip FMR measurement, to conduct the ferromagnetic resonance measurements has been developed. The measurement technique is equally comparable to a conventional FMR measurement. The Gilbert damping constants were extracted for single ferromagnetic layer, spin vale structures, and magnetic tunnel junctions (MTJs). On the other hand, an active use of microwave yields a great potential for interesting phenomena which give new functionalities into spintronic devices. For instance, a spin wave excitation by an rf field can be used to reduce the switching field of a ferromagnet, i.e. microwave assisted magnetization reversal, which could be a potential application in advanced recording media. More interestingly, a precessing magnetization driven by an rf field can generate a pure spin current into a neighboring layer, i.e. spin pumping effect, which is one of the candidates for generating a pure spin current. A ferromagnetic tunnel junction (MTJ) is one of the important devices in spintronics, which is also the key device to investigate the local and nonlocal magnetization dynamics in this work. Therefore, it is also important to develop high quality MTJs. My work starts from the development of MTJ with AlOx and MgO tunnel barriers where it was found it is crucial to find the proper condition for forming a few nanometers thick tunnel barrier. After obtaining quality MTJs, we proceeded to the study on magnetization dynamics using the MTJs. First interesting phenomenon found in this work is the microwave assisted magnetization reversal (MAMR). It is found that magnetization reversal can be achieved efficiently by an appropriate power and frequency microwave. Moreover, there is a mutual relationship between microwave power and frequency for achieving a maximum switching field reduction. This effect can be very useful in magnetic data storage device which essentially needs to reduce the "effective" coercivity field. In the study of nonlocal magnetization dynamics, we tried to detect the spin accumulation induced by spin pumping effect in FM/NM/I/FM, FM/I/NM and FM/I/FM structures with a microwave excitation (FM: ferromagnetic material, NM: nonmagnetic material, and I: tunnel barrier). Interestingly, in the FM/I/NM and FM/I/FM structures, we observed ˜muV dc voltage due to the precessing magnetizations. It is found that the dc voltage we observed is much larger than the current the spin pumping theory predicts. Therefore we speculated a new mechanism to explain the results. Although we discussed only a portion of the magnetization dynamics involving nonlinear and nonequilibrium phenomena, it reveals that there is still a fertile physics which has not yet been investigated or explained.

On the spin-axis dynamics of a Moonless Earth

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Gongjie; Batygin, Konstantin, E-mail: gli@cfa.harvard.edu

2014-07-20

The variation of a planet's obliquity is influenced by the existence of satellites with a high mass ratio. For instance, Earth's obliquity is stabilized by the Moon and would undergo chaotic variations in the Moon's absence. In turn, such variations can lead to large-scale changes in the atmospheric circulation, rendering spin-axis dynamics a central issue for understanding climate. The relevant quantity for dynamically forced climate change is the rate of chaotic diffusion. Accordingly, here we re-examine the spin-axis evolution of a Moonless Earth within the context of a simplified perturbative framework. We present analytical estimates of the characteristic Lyapunov coefficientmore » as well as the chaotic diffusion rate and demonstrate that even in absence of the Moon, the stochastic change in Earth's obliquity is sufficiently slow to not preclude long-term habitability. Our calculations are consistent with published numerical experiments and illustrate the putative system's underlying dynamical structure in a simple and intuitive manner.« less

Phase diagram and quench dynamics of the cluster-XY spin chain

NASA Astrophysics Data System (ADS)

Montes, Sebastián; Hamma, Alioscia

2012-08-01

We study the complete phase space and the quench dynamics of an exactly solvable spin chain, the cluster-XY model. In this chain, the cluster term and the XY couplings compete to give a rich phase diagram. The phase diagram is studied by means of the quantum geometric tensor. We study the time evolution of the system after a critical quantum quench using the Loschmidt echo. The structure of the revivals after critical quantum quenches presents a nontrivial behavior depending on the phase of the initial state and the critical point.

Phase diagram and quench dynamics of the cluster-XY spin chain.

PubMed

Montes, Sebastián; Hamma, Alioscia

2012-08-01

We study the complete phase space and the quench dynamics of an exactly solvable spin chain, the cluster-XY model. In this chain, the cluster term and the XY couplings compete to give a rich phase diagram. The phase diagram is studied by means of the quantum geometric tensor. We study the time evolution of the system after a critical quantum quench using the Loschmidt echo. The structure of the revivals after critical quantum quenches presents a nontrivial behavior depending on the phase of the initial state and the critical point.

Femtosecond manipulation of spins, charges, and ions in nanostructures, thin films, and surfaces

PubMed Central

Carbone, F.; Hengsberger, M.; Castiglioni, L.; Osterwalder, J.

2017-01-01

Modern ultrafast techniques provide new insights into the dynamics of ions, charges, and spins in photoexcited nanostructures. In this review, we describe the use of time-resolved electron-based methods to address specific questions such as the ordering properties of self-assembled nanoparticles supracrystals, the interplay between electronic and structural dynamics in surfaces and adsorbate layers, the light-induced control of collective electronic modes in nanowires and thin films, and the real-space/real-time evolution of the skyrmion lattice in topological magnets. PMID:29308416

Lattice dynamics and metastability of fcc metals in the hcp structure and the crucial role of spin-orbit coupling in platinum

NASA Astrophysics Data System (ADS)

Schönecker, Stephan; Li, Xiaoqing; Richter, Manuel; Vitos, Levente

2018-06-01

We investigate the lattice dynamical properties of Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au in the nonequilibrium hcp structure by means of density-functional simulations, wherein spin-orbit coupling (SOC) was considered for Ir, Pt, and Au. The determined dynamical properties reveal that all eight elements possess a metastable hcp phase at zero temperature and pressure. The hcp Ni, Cu, Rh, Pd, and Au previously observed in nanostructures support this finding. We make evident that the inclusion of SOC is mandatory for an accurate description of the phonon dispersion relations and dynamical stability of hcp Pt. The underlying sensitivity of the interatomic force constants is ascribed to a SOC-induced splitting of degenerate band states accompanied by a pronounced reduction of electronic density of states at the Fermi level. To give further insight into the importance of SOC in Pt, we (i) focus on phase stability and examine a lattice transformation related to optical phonons in the hcp phase and (ii) focus on the generalized stacking fault energy (GSFE) of the fcc phase pertinent to crystal plasticity. We show that the intrinsic stable and unstable fault energies of the GSFE scale as in other common fcc metals, provided that the spin-orbit interaction is taken into account.

Software package for modeling spin-orbit motion in storage rings

NASA Astrophysics Data System (ADS)

Zyuzin, D. V.

2015-12-01

A software package providing a graphical user interface for computer experiments on the motion of charged particle beams in accelerators, as well as analysis of obtained data, is presented. The software package was tested in the framework of the international project on electric dipole moment measurement JEDI (Jülich Electric Dipole moment Investigations). The specific features of particle spin motion imply the requirement to use a cyclic accelerator (storage ring) consisting of electrostatic elements, which makes it possible to preserve horizontal polarization for a long time. Computer experiments study the dynamics of 106-109 particles in a beam during 109 turns in an accelerator (about 1012-1015 integration steps for the equations of motion). For designing an optimal accelerator structure, a large number of computer experiments on polarized beam dynamics are required. The numerical core of the package is COSY Infinity, a program for modeling spin-orbit dynamics.

Homogeneous microwave field emitted propagating spin waves: Direct imaging and modeling

NASA Astrophysics Data System (ADS)

Lohman, Mathis; Mozooni, Babak; McCord, Jeffrey

2018-03-01

We explore the generation of propagating dipolar spin waves by homogeneous magnetic field excitation in the proximity of the boundaries of magnetic microstructures. Domain wall motion, precessional dynamics, and propagating spin waves are directly imaged by time-resolved wide-field magneto-optical Kerr effect microscopy. The aspects of spin wave generation are clarified by micromagnetic calculations matching the experimental results. The region of dipolar spin wave formation is confined to the local resonant excitation due to non-uniform internal demagnetization fields at the edges of the patterned sample. Magnetic domain walls act as a border for the propagation of plane and low damped spin waves, thus restraining the spin waves within the individual magnetic domains. The findings are of significance for the general understanding of structural and configurational magnetic boundaries for the creation, the propagation, and elimination of spin waves.

A study of structural concepts for ultralightweight spacecraft

NASA Technical Reports Server (NTRS)

Miller, R. K.; Knapp, K.; Hedgepeth, J. M.

1984-01-01

Structural concepts for ultralightweight spacecraft were studied. Concepts for ultralightweight space structures were identified and the validity of heir potential application in advanced spacecraft was assessed. The following topics were investigated: (1) membrane wrinkling under pretensioning; (2) load-carrying capability of pressurized tubes; (3) equilibrium of a precompressed rim; (4) design of an inflated reflector spacecraft; (5) general instability of a rim; and (6) structural analysis of a pressurized isotensoid column. The design approaches for a paraboloidal reflector spacecraft included a spin-stiffened design, both inflated and truss central columns, and to include both deep truss and rim-stiffened geodesic designs. The spinning spacecraft analysis is included, and the two truss designs are covered. The performances of four different approaches to the structural design of a paraboloidal reflector spacecraft are compared. The spinning and inflated configurations result in very low total masses and some concerns about their performance due to unresolved questions about dynamic stability and lifetimes, respectively.

Quantum memory enhanced nuclear magnetic resonance of nanometer-scale samples with a single spin in diamond

NASA Astrophysics Data System (ADS)

Aslam, Nabeel; Pfender, Matthias; Zaiser, Sebastian; Favaro de Oliveira, Felipe; Momenzadeh, S. Ali; Denisenko, Andrej; Isoya, Junichi; Neumann, Philipp; Wrachtrup, Joerg

Recently nuclear magnetic resonance (NMR) of nanoscale samples at ambient conditions has been achieved with nitrogen-vacancy (NV) centers in diamond. So far the spectral resolution in the NV NMR experiments was limited by the sensor's coherence time, which in turn prohibited revealing the chemical composition and dynamics of the system under investigation. By entangling the NV electron spin sensor with a long-lived memory spin qubit we increase the spectral resolution of NMR measurement sequences for the detection of external nuclear spins. Applying the latter sensor-memory-couple it is particularly easy to track diffusion processes, to identify the molecules under study and to deduce the actual NV center depth inside the diamond. We performed nanoscale NMR on several liquid and solid samples exhibiting unique NMR response. Our method paves the way for nanoscale identification of molecule and protein structures and dynamics of conformational changes.

Theoretical Study of Gilbert Damping and Spin Dynamics in Spintronic Devices

NASA Astrophysics Data System (ADS)

Qu, Tao

The determination of damping mechanisms is one of the most fundamental problems of magnetism. It represents the elimination of the magnetic energy and thus has broad impact in both science and technology. The dynamic time scale in spintronic devices is controlled by the damping and the consumed power depends on the damping constant squared. In recent years, the interest in high perpendicular anisotropy materials and thin film structures have increased considerably, owing to their stability over a wide temperature range when scaling devices to nanometer length scales. However, the conventional measurement method-Ferromagnetic resonance (FMR) can not produce accurate damping results in the high magnetic crystalline anisotropy materials/structures, and the intrinsic damping reported experimentally diverges among investigators, probably due to the varying fabrication techniques. This thesis describes the application of the Kambersky torque correlation technique, within the tight binding method, to multiple materials with high perpendicular magnetic anisotropy ( 10 7 erg/cm3), in both bulk and thin film structures. The impact of the inevitable experimental defects on the energy dissipation is identified and the experimental damping divergence among investigators due to the material degree of order is explained. It is demonstrated that this corresponds to an enhanced DOS at the Fermi level, owing to the rounding of the DOS with loss of long-range order. The consistency of the predicted damping constant with experimental measurement is demonstrated and the interface contribution to the energy damping constant in potential superlattices and heterostructures for spintronic devices is explored. An optimized structure will be a tradeoff involving both anisotropy and damping. The damping related spin dynamics in spintronic devices for different applications is investigated. One device is current perpendicular to planes(CPP) spin valve. Incoherent scattering matrices are applied to calculate the angle dependent magnetoresistantce and obtain analytic expressions for the spin valve. The non-linearity of magnetoresistance can be quantitatively explained by reflected electrons using only experimental spin polarization as input. The other device is a spin-transfer-torque nano-oscillator. The Landau-Lifshitz-Gilbert equation is applied and the synchronization requirement for experimentally fabricated non-identical multi spintronic oscillators is explored. Power enhancement and noise decrease for the synchronized state is demonstrated in a temperature range. Through introducing combined electric and magnetic coupling effect, a design for an optimized feasible nanopillar structure suitable for thin-film deposition is developed.

Site-directed spin labeling reveals a conformational switch in the phosphorylation domain of smooth muscle myosin.

PubMed

Nelson, Wendy D; Blakely, Sarah E; Nesmelov, Yuri E; Thomas, David D

2005-03-15

We have used site-directed spin labeling and EPR spectroscopy to detect structural changes within the regulatory light chain (RLC) of smooth muscle myosin upon phosphorylation. Smooth muscle contraction is activated by phosphorylation of S19 on RLC, but the structural basis of this process is unknown. There is no crystal structure containing a phosphorylated RLC, and there is no crystal structure for the N-terminal region of any RLC. Therefore, we have prepared single-Cys mutations throughout RLC, exchanged each mutant onto smooth muscle heavy meromyosin, verified normal regulatory function, and used EPR to determine dynamics and solvent accessibility at each site. A survey of spin-label sites throughout the RLC revealed that only the N-terminal region (first 24 aa) shows a significant change in dynamics upon phosphorylation, with most of the first 17 residues showing an increase in rotational amplitude. Therefore, we focused on this N-terminal region. Additional structural information was obtained from the pattern of oxygen accessibility along the sequence. In the absence of phosphorylation, little or no periodicity was observed, suggesting a lack of secondary structural order in this region. However, phosphorylation induced a strong helical pattern (3.6-residue periodicity) in the first 17 residues, while increasing accessibility throughout the first 24 residues. We have identified a domain within RLC, the N-terminal phosphorylation domain, in which phosphorylation increases helical order, internal dynamics, and accessibility. These results support a model in which this disorder-to-order transition within the phosphorylation domain results in decreased head-head interactions, activating myosin in smooth muscle.

Elucidating the design principles of photosynthetic electron-transfer proteins by site-directed spin labeling EPR spectroscopy.

PubMed

Ishara Silva, K; Jagannathan, Bharat; Golbeck, John H; Lakshmi, K V

2016-05-01

Site-directed spin labeling electron paramagnetic resonance (SDSL EPR) spectroscopy is a powerful tool to determine solvent accessibility, side-chain dynamics, and inter-spin distances at specific sites in biological macromolecules. This information provides important insights into the structure and dynamics of both natural and designed proteins and protein complexes. Here, we discuss the application of SDSL EPR spectroscopy in probing the charge-transfer cofactors in photosynthetic reaction centers (RC) such as photosystem I (PSI) and the bacterial reaction center (bRC). Photosynthetic RCs are large multi-subunit proteins (molecular weight≥300 kDa) that perform light-driven charge transfer reactions in photosynthesis. These reactions are carried out by cofactors that are paramagnetic in one of their oxidation states. This renders the RCs unsuitable for conventional nuclear magnetic resonance spectroscopy investigations. However, the presence of native paramagnetic centers and the ability to covalently attach site-directed spin labels in RCs makes them ideally suited for the application of SDSL EPR spectroscopy. The paramagnetic centers serve as probes of conformational changes, dynamics of subunit assembly, and the relative motion of cofactors and peptide subunits. In this review, we describe novel applications of SDSL EPR spectroscopy for elucidating the effects of local structure and dynamics on the electron-transfer cofactors of photosynthetic RCs. Because SDSL EPR Spectroscopy is uniquely suited to provide dynamic information on protein motion, it is a particularly useful method in the engineering and analysis of designed electron transfer proteins and protein networks. This article is part of a Special Issue entitled Biodesign for Bioenergetics--the design and engineering of electronic transfer cofactors, proteins and protein networks, edited by Ronald L. Koder and J.L. Ross Anderson. Copyright © 2016. Published by Elsevier B.V.

Motion of spin label side chains in cellular retinol-binding protein: correlation with structure and nearest-neighbor interactions in an antiparallel beta-sheet.

PubMed

Lietzow, Michael A; Hubbell, Wayne L

2004-03-23

A goal in the development of site-directed spin labeling in proteins is to correlate the motion of a nitroxide side chain with local structure, interactions, and dynamics. Significant progress toward this goal has been made using alpha-helical proteins of known structure, and the present study is the first step in a similar exploration of a beta-sheet protein, cellular retinol-binding protein (CRBP). Nitroxide side chains were introduced along both interior and edge strands. At sites in interior strands, the side-chain motion is strongly influenced by interactions with side chains of neighboring strands, giving rise to a rich variety of dynamic modes (weakly ordered, strongly ordered, immobilized) and complex electron paramagnetic resonance spectra that are modulated by strand twist. The interactions giving rise to the dynamic modes are explored using mutagenesis, and the results demonstrate the particular importance of the non-hydrogen-bonded neighbor residue in giving rise to highly ordered states. Along edge strands of the beta-sheet, the motion of the side chain is simple and weakly ordered, resembling that at solvent-exposed surfaces of an alpha-helix. A simple working model is proposed that can account for the wide variety of dynamic modes encountered. Collectively, the results suggest that the nitroxide side chain is an effective probe of side-chain interactions, and that site-directed spin labeling should be a powerful means of monitoring conformational changes that involve changes in beta-sheet topology.

Fingerprints of electronic, spin and structural dynamics from resonant inelastic soft X-ray scattering in transient photo-chemical species

DOE PAGES

Norell, Jesper; Jay, Raphael M.; Hantschmann, Markus; ...

2018-02-20

Here, we describe how inversion symmetry separation of electronic state manifolds in resonant inelastic soft X-ray scattering (RIXS) can be applied to probe excited-state dynamics with compelling selectivity. In a case study of Fe L 3-edge RIXS in the ferricyanide complex Fe(CN) 6 3-, we demonstrate with multi-configurational restricted active space spectrum simulations how the information content of RIXS spectral fingerprints can be used to unambiguously separate species of different electronic configurations, spin multiplicities, and structures, with possible involvement in the decay dynamics of photo-excited ligand-to-metal charge-transfer. Specifically, we propose that this could be applied to confirm or reject themore » presence of a hitherto elusive transient Quartet species. Thus, RIXS offers a particular possibility to settle a recent controversy regarding the decay pathway, and we expect the technique to be similarly applicable in other model systems of photo-induced dynamics.« less

Fingerprints of electronic, spin and structural dynamics from resonant inelastic soft X-ray scattering in transient photo-chemical species

DOE Office of Scientific and Technical Information (OSTI.GOV)

Norell, Jesper; Jay, Raphael M.; Hantschmann, Markus

Here, we describe how inversion symmetry separation of electronic state manifolds in resonant inelastic soft X-ray scattering (RIXS) can be applied to probe excited-state dynamics with compelling selectivity. In a case study of Fe L 3-edge RIXS in the ferricyanide complex Fe(CN) 6 3-, we demonstrate with multi-configurational restricted active space spectrum simulations how the information content of RIXS spectral fingerprints can be used to unambiguously separate species of different electronic configurations, spin multiplicities, and structures, with possible involvement in the decay dynamics of photo-excited ligand-to-metal charge-transfer. Specifically, we propose that this could be applied to confirm or reject themore » presence of a hitherto elusive transient Quartet species. Thus, RIXS offers a particular possibility to settle a recent controversy regarding the decay pathway, and we expect the technique to be similarly applicable in other model systems of photo-induced dynamics.« less

Spin-orbit-torque-induced skyrmion dynamics for different types of spin-orbit coupling

NASA Astrophysics Data System (ADS)

Lee, Seung-Jae; Kim, Kyoung-Whan; Lee, Hyun-Woo; Lee, Kyung-Jin

2018-06-01

We investigate current-induced skyrmion dynamics in the presence of Dzyaloshinskii-Moriya interaction and spin-orbit spin-transfer torque corresponding to various types of spin-orbit coupling. We determine the symmetries of Dzyaloshinskii-Moriya interaction and spin-orbit spin-transfer torque based on linear spin-orbit coupling model. We find that like interfacial Dzyaloshinskii-Moriya interaction (Rashba spin-orbit coupling) and bulk Dzyaloshinskii-Moriya interaction (Weyl spin-orbit coupling), Dresselhaus spin-orbit coupling also has a possibility for stabilizing skyrmion and current-induced skyrmion dynamics.

Quenching of dynamic nuclear polarization by spin-orbit coupling in GaAs quantum dots.

PubMed

Nichol, John M; Harvey, Shannon P; Shulman, Michael D; Pal, Arijeet; Umansky, Vladimir; Rashba, Emmanuel I; Halperin, Bertrand I; Yacoby, Amir

2015-07-17

The central-spin problem is a widely studied model of quantum decoherence. Dynamic nuclear polarization occurs in central-spin systems when electronic angular momentum is transferred to nuclear spins and is exploited in quantum information processing for coherent spin manipulation. However, the mechanisms limiting this process remain only partially understood. Here we show that spin-orbit coupling can quench dynamic nuclear polarization in a GaAs quantum dot, because spin conservation is violated in the electron-nuclear system, despite weak spin-orbit coupling in GaAs. Using Landau-Zener sweeps to measure static and dynamic properties of the electron spin-flip probability, we observe that the size of the spin-orbit and hyperfine interactions depends on the magnitude and direction of applied magnetic field. We find that dynamic nuclear polarization is quenched when the spin-orbit contribution exceeds the hyperfine, in agreement with a theoretical model. Our results shed light on the surprisingly strong effect of spin-orbit coupling in central-spin systems.

Technological advances in site-directed spin labeling of proteins.

PubMed

Hubbell, Wayne L; López, Carlos J; Altenbach, Christian; Yang, Zhongyu

2013-10-01

Molecular flexibility over a wide time range is of central importance to the function of many proteins, both soluble and membrane. Revealing the modes of flexibility, their amplitudes, and time scales under physiological conditions is the challenge for spectroscopic methods, one of which is site-directed spin labeling EPR (SDSL-EPR). Here we provide an overview of some recent technological advances in SDSL-EPR related to investigation of structure, structural heterogeneity, and dynamics of proteins. These include new classes of spin labels, advances in measurement of long range distances and distance distributions, methods for identifying backbone and conformational fluctuations, and new strategies for determining the kinetics of protein motion. Copyright © 2013 Elsevier Ltd. All rights reserved.

Spin structure in high energy processes: Proceedings

DOE Office of Scientific and Technical Information (OSTI.GOV)

DePorcel, L.; Dunwoodie, C.

1994-12-01

This report contains papers as the following topics: Spin, Mass, and Symmetry; physics with polarized Z{sup 0}s; spin and precision electroweak physics; polarized electron sources; polarization phenomena in quantum chromodynamics; polarized lepton-nucleon scattering; polarized targets in high energy physics; spin dynamics in storage rings and linear accelerators; spin formalism and applications to new physics searches; precision electroweak physics at LEP; recent results on heavy flavor physics from LEP experiments using 1990--1992 data; precise measurement of the left-right cross section asymmetry in Z boson production by electron-positron collisions; preliminary results on heavy flavor physics at SLD; QCD tests with SLD andmore » polarized beams; recent results from TRISTAN at KEK; recent B physics results from CLEO; searching for the H dibaryon at Brookhaven; recent results from the compton observatory; the spin structure of the deuteron; spin structure of the neutron ({sup 3}HE) and the Bjoerken sum rule; a consumer`s guide to lattice QCD results; top ten models constrained by b {yields} sy; a review of the Fermilab fixed target program; results from the D0 experiment; results from CDF at FNAL; quantum-mechanical suppression of bremsstrahlung; report from the ZEUS collaboration at HERA; physics from the first year of H1 at HERA, and hard diffraction. These papers have been cataloged separately elsewhere.« less

Quantum spin dynamics at terahertz frequencies in 2D hole gases and improper ferroelectrics

NASA Astrophysics Data System (ADS)

Lloyd-Hughes, J.

2015-08-01

Terahertz time-domain spectroscopy permits the excitations of novel materials to be examined with exquisite precision. Improper ferroelectric materials such as cupric oxide (CuO) exhibit complex magnetic ground states. CuO is antiferromagnetic below 213K, but has an incommensurate cycloidal magnetic phase between 213K and 230K. Remarkably, the cycloidal magnetic phase drives ferroelectricity, where the material becomes polar. Such improper multiferroics are of great contemporary interest, as a better understanding of the science of magnetoelectric materials may lead to their application in actuators, sensors and solid state memories. Improper multiferroics also have novel quasiparticle excitations: electromagnons form when spin-waves become electric-dipole active. By examining the dynamic response of spins as they interact with THz radiation we gain insights into the underlying physics of multi-ferroics. In contrast to improper ferroelectrics, where magnetism drives structural inversion asymmetry (SIA), two-dimensional electronic systems can exhibit non-degenerate spin states as a consequence of SIA created by strain and/or electric fields. We identify and explore the influence of the Rashba spin-orbit interaction upon cyclotron resonance at terahertz frequencies in high-mobility 2D hole gases in germanium quantum wells. An enhanced Rashba spin-orbit interaction can be linked to the strain of the quantum well, while a time-frequency decomposition method permitted the dynamical formation and decay of spin-split cyclotron resonances to be tracked on picosecond timescales. Long spin-decoherence times concurrent with high hole mobilities highlight the potential of Ge quantum wells in spintronics.

State-Resolved Metal Nanoparticle Dynamics Viewed through the Combined Lenses of Ultrafast and Magneto-optical Spectroscopies.

PubMed

Zhao, Tian; Herbert, Patrick J; Zheng, Hongjun; Knappenberger, Kenneth L

2018-06-19

Electronic carrier dynamics play pivotal roles in the functional properties of nanomaterials. For colloidal metals, the mechanisms and influences of these dynamics are structure dependent. The coherent carrier dynamics of collective plasmon modes for nanoparticles (approximately 2 nm and larger) determine optical amplification factors that are important to applied spectroscopy techniques. In the nanocluster domain (sub-2 nm), carrier coupling to vibrational modes affects photoluminescence yields. The performance of photocatalytic materials featuring both nanoparticles and nanoclusters also depends on the relaxation dynamics of nonequilibrium charge carriers. The challenges for developing comprehensive descriptions of carrier dynamics spanning both domains are multifold. Plasmon coherences are short-lived, persisting for only tens of femtoseconds. Nanoclusters exhibit discrete carrier dynamics that can persist for microseconds in some cases. On this time scale, many state-dependent processes, including vibrational relaxation, charge transfer, and spin conversion, affect carrier dynamics in ways that are nonscalable but, rather, structure specific. Hence, state-resolved spectroscopy methods are needed for understanding carrier dynamics in the nanocluster domain. Based on these considerations, a detailed understanding of structure-dependent carrier dynamics across length scales requires an appropriate combination of spectroscopic methods. Plasmon mode-specific dynamics can be obtained through ultrafast correlated light and electron microscopy (UCLEM), which pairs interferometric nonlinear optical (INLO) with electron imaging methods. INLO yields nanostructure spectral resonance responses, which capture the system's homogeneous line width and coherence dynamics. State-resolved nanocluster dynamics can be obtained by pairing ultrafast with magnetic-optical spectroscopy methods. In particular, variable-temperature variable-field (VTVH) spectroscopies allow quantification of transient, excited states, providing quantification of important parameters such as spin and orbital angular momenta as well as the energy gaps that separate electronic fine structure states. Ultrafast two-dimensional electronic spectroscopy (2DES) can be used to understand how these details influence state-to-state carrier dynamics. In combination, VTVH and 2DES methods can provide chemists with detailed information regarding the structure-dependent and state-specific flow of energy through metal nanoclusters. In this Account, we highlight recent advances toward understanding structure-dependent carrier dynamics for metals spanning the sub-nanometer to tens of nanometers length scale. We demonstrate the use of UCLEM methods for arresting interband scattering effects. For sub-nanometer thiol-protected nanoclusters, we discuss the effectiveness of VTVH for distinguishing state-specific radiative recombination originating from a gold core versus organometallic protecting layers. This state specificity is refined further using femtosecond 2DES and two-color methods to isolate so-called superatom state dynamics and vibrationally mediated spin-conversion and emission processes. Finally, we discuss prospects for merging VTVH and 2DES methods into a single platform.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gupta, J. B.; Hamilton, J. H.

The change in the structure of the collective levels with spin angular momentum in atomic nuclei is often expressed in terms of the classical concepts of the kinematic and the dynamic moments of inertia varying with spin. For the well deformed even-even nuclei the kinematic moment of inertia increases with spin up to 10%-20%, at say I{sup {pi}} = 12{sup +}. However, for the shape transitional nuclei, or almost spherical nuclei, it increases with spin much faster. The pitfalls of using the rotor model form of kinematic moment of inertia in such cases are pointed out here. Alternative methods ofmore » extracting the nuclear structure information are explored. The important role of the ground state deformation is illustrated. The use of the power index formula for evaluating the effective moment of inertia, free from the assumption of the rotor model, is described.« less

Direct Prediction of EPR Spectra from Lipid Bilayers: Understanding Structure and Dynamics in Biological Membranes.

PubMed

Catte, Andrea; White, Gaye F; Wilson, Mark R; Oganesyan, Vasily S

2018-06-02

Of the many biophysical techniques now being brought to bear on studies of membranes, electron paramagnetic resonance (EPR) of nitroxide spin probes was the first to provide information about both mobility and ordering in lipid membranes. Here, we report the first prediction of variable temperature EPR spectra of model lipid bilayers in the presence and absence of cholesterol from the results of large scale fully atomistic molecular dynamics (MD) simulations. Three types of structurally different spin probes were employed in order to study different parts of the bilayer. Our results demonstrate very good agreement with experiment and thus confirm the accuracy of the latest lipid force fields. The atomic resolution of the simulations allows the interpretation of the molecular motions and interactions in terms of their impact on the sensitive EPR line shapes. Direct versus indirect effects of cholesterol on the dynamics of spin probes are analysed. Given the complexity of structural organisation in lipid bilayers, the advantage of using a combined MD-EPR simulation approach is two-fold. Firstly, prediction of EPR line shapes directly from MD trajectories of actual phospholipid structures allows unambiguous interpretation of EPR spectra of biological membranes in terms of complex motions. Secondly, such an approach provides an ultimate test bed for the up-to-date MD simulation models employed in the studies of biological membranes, an area that currently attracts great attention. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Variable-Structure Control of a Model Glider Airplane

NASA Technical Reports Server (NTRS)

Waszak, Martin R.; Anderson, Mark R.

2008-01-01

A variable-structure control system designed to enable a fuselage-heavy airplane to recover from spin has been demonstrated in a hand-launched, instrumented model glider airplane. Variable-structure control is a high-speed switching feedback control technique that has been developed for control of nonlinear dynamic systems.

Variable Structure Control of a Hand-Launched Glider

NASA Technical Reports Server (NTRS)

Anderson, Mark R.; Waszak, Martin R.

2005-01-01

Variable structure control system design methods are applied to the problem of aircraft spin recovery. A variable structure control law typically has two phases of operation. The reaching mode phase uses a nonlinear relay control strategy to drive the system trajectory to a pre-defined switching surface within the motion state space. The sliding mode phase involves motion along the surface as the system moves toward an equilibrium or critical point. Analysis results presented in this paper reveal that the conventional method for spin recovery can be interpreted as a variable structure controller with a switching surface defined at zero yaw rate. Application of Lyapunov stability methods show that deflecting the ailerons in the direction of the spin helps to insure that this switching surface is stable. Flight test results, obtained using an instrumented hand-launched glider, are used to verify stability of the reaching mode dynamics.

Controlling the quantum dynamics of a mesoscopic spin bath in diamond

PubMed Central

de Lange, Gijs; van der Sar, Toeno; Blok, Machiel; Wang, Zhi-Hui; Dobrovitski, Viatcheslav; Hanson, Ronald

2012-01-01

Understanding and mitigating decoherence is a key challenge for quantum science and technology. The main source of decoherence for solid-state spin systems is the uncontrolled spin bath environment. Here, we demonstrate quantum control of a mesoscopic spin bath in diamond at room temperature that is composed of electron spins of substitutional nitrogen impurities. The resulting spin bath dynamics are probed using a single nitrogen-vacancy (NV) centre electron spin as a magnetic field sensor. We exploit the spin bath control to dynamically suppress dephasing of the NV spin by the spin bath. Furthermore, by combining spin bath control with dynamical decoupling, we directly measure the coherence and temporal correlations of different groups of bath spins. These results uncover a new arena for fundamental studies on decoherence and enable novel avenues for spin-based magnetometry and quantum information processing. PMID:22536480

The classical and quantum dynamics of molecular spins on graphene.

PubMed

Cervetti, Christian; Rettori, Angelo; Pini, Maria Gloria; Cornia, Andrea; Repollés, Ana; Luis, Fernando; Dressel, Martin; Rauschenbach, Stephan; Kern, Klaus; Burghard, Marko; Bogani, Lapo

2016-02-01

Controlling the dynamics of spins on surfaces is pivotal to the design of spintronic and quantum computing devices. Proposed schemes involve the interaction of spins with graphene to enable surface-state spintronics and electrical spin manipulation. However, the influence of the graphene environment on the spin systems has yet to be unravelled. Here we explore the spin-graphene interaction by studying the classical and quantum dynamics of molecular magnets on graphene. Whereas the static spin response remains unaltered, the quantum spin dynamics and associated selection rules are profoundly modulated. The couplings to graphene phonons, to other spins, and to Dirac fermions are quantified using a newly developed model. Coupling to Dirac electrons introduces a dominant quantum relaxation channel that, by driving the spins over Villain's threshold, gives rise to fully coherent, resonant spin tunnelling. Our findings provide fundamental insight into the interaction between spins and graphene, establishing the basis for electrical spin manipulation in graphene nanodevices.

The classical and quantum dynamics of molecular spins on graphene

NASA Astrophysics Data System (ADS)

Cervetti, Christian; Rettori, Angelo; Pini, Maria Gloria; Cornia, Andrea; Repollés, Ana; Luis, Fernando; Dressel, Martin; Rauschenbach, Stephan; Kern, Klaus; Burghard, Marko; Bogani, Lapo

2016-02-01

Controlling the dynamics of spins on surfaces is pivotal to the design of spintronic and quantum computing devices. Proposed schemes involve the interaction of spins with graphene to enable surface-state spintronics and electrical spin manipulation. However, the influence of the graphene environment on the spin systems has yet to be unravelled. Here we explore the spin-graphene interaction by studying the classical and quantum dynamics of molecular magnets on graphene. Whereas the static spin response remains unaltered, the quantum spin dynamics and associated selection rules are profoundly modulated. The couplings to graphene phonons, to other spins, and to Dirac fermions are quantified using a newly developed model. Coupling to Dirac electrons introduces a dominant quantum relaxation channel that, by driving the spins over Villain’s threshold, gives rise to fully coherent, resonant spin tunnelling. Our findings provide fundamental insight into the interaction between spins and graphene, establishing the basis for electrical spin manipulation in graphene nanodevices.

Observation of multicellular spinning behavior of Proteus mirabilis by atomic force microscopy and multifunctional microscopy.

PubMed

Liu, Yanxia; Deng, Yuanxin; Luo, Shuxiu; Deng, Yu; Guo, Linming; Xu, Weiwei; Liu, Lei; Liu, Junkang

2014-01-01

This study aimed to observe the multicellular spinning behavior of Proteus mirabilis by atomic force microscopy (AFM) and multifunctional microscopy in order to understand the mechanism underlying this spinning movement and its biological significance. Multifunctional microscopy with charge-coupled device (CCD) and real-time AFM showed changes in cell structure and shape of P. mirabilis during multicellular spinning movement. Specifically, the morphological characteristics of P. mirabilis, multicellular spinning dynamics, and unique movement were observed. Our findings indicate that the multicellular spinning behavior of P. mirabilis may be used to collect nutrients, perform colonization, and squeeze out competitors. The movement characteristics of P. mirabilis are vital to the organism's biological adaptability to the surrounding environment. Copyright © 2013 Elsevier Ltd. All rights reserved.

Resonantly enhanced spin-lattice relaxation of Mn2 + ions in diluted magnetic (Zn,Mn)Se/(Zn,Be)Se quantum wells

NASA Astrophysics Data System (ADS)

Debus, J.; Ivanov, V. Yu.; Ryabchenko, S. M.; Yakovlev, D. R.; Maksimov, A. A.; Semenov, Yu. G.; Braukmann, D.; Rautert, J.; Löw, U.; Godlewski, M.; Waag, A.; Bayer, M.

2016-05-01

The dynamics of spin-lattice relaxation in the magnetic Mn2 + ion system of (Zn,Mn)Se/(Zn,Be)Se quantum-well structures are studied using optical methods. Pronounced cusps are found in the giant Zeeman shift of the quantum-well exciton photoluminescence at specific magnetic fields below 10 T, when the Mn spin system is heated by photogenerated carriers. The spin-lattice relaxation time of the Mn ions is resonantly accelerated at the cusp magnetic fields. Our theoretical analysis demonstrates that a cusp occurs at a spin-level mixing of single Mn2 + ions and a quick-relaxing cluster of nearest-neighbor Mn ions, which can be described as intrinsic cross-relaxation resonance within the Mn spin system.

Floquet spin states in graphene under ac-driven spin-orbit interaction

NASA Astrophysics Data System (ADS)

López, A.; Sun, Z. Z.; Schliemann, J.

2012-05-01

We study the role of periodically driven time-dependent Rashba spin-orbit coupling (RSOC) on a monolayer graphene sample. After recasting the originally 4×4 system of dynamical equations as two time-reversal related two-level problems, the quasienergy spectrum and the related dynamics are investigated via various techniques and approximations. In the static case, the system is gapped at the Dirac point. The rotating wave approximation (RWA) applied to the driven system unphysically preserves this feature, while the Magnus-Floquet approach as well as a numerically exact evaluation of the Floquet equation show that this gap is dynamically closed. In addition, a sizable oscillating pattern of the out-of-plane spin polarization is found in the driven case for states that are completely unpolarized in the static limit. Evaluation of the autocorrelation function shows that the original uniform interference pattern corresponding to time-independent RSOC gets distorted. The resulting structure can be qualitatively explained as a consequence of the transitions induced by the ac driving among the static eigenstates, i.e., these transitions modulate the relative phases that add up to give the quantum revivals of the autocorrelation function. Contrary to the static case, in the driven scenario, quantum revivals (suppressions) are correlated to spin-up (down) phases.

Lattice Waves, Spin Waves, and Neutron Scattering

DOE R&D Accomplishments Database

Brockhouse, Bertram N.

1962-03-01

Use of neutron inelastic scattering to study the forces between atoms in solids is treated. One-phonon processes and lattice vibrations are discussed, and experiments that verified the existence of the quantum of lattice vibrations, the phonon, are reviewed. Dispersion curves, phonon frequencies and absorption, and models for dispersion calculations are discussed. Experiments on the crystal dynamics of metals are examined. Dispersion curves are presented and analyzed; theory of lattice dynamics is considered; effects of Fermi surfaces on dispersion curves; electron-phonon interactions, electronic structure influence on lattice vibrations, and phonon lifetimes are explored. The dispersion relation of spin waves in crystals and experiments in which dispersion curves for spin waves in Co-Fe alloy and magnons in magnetite were obtained and the reality of the magnon was demonstrated are discussed. (D.C.W)

Dual nature of 3 d electrons in YbT 2 Zn 20 (T = Co; Fe) evidenced by electron spin resonance

DOE PAGES

Ivanshin, V. A.; Litvinova, T. O.; Gimranova, K.; ...

2015-03-18

The electron spin resonance experiments were carried out in the single crystals YbFe 2Zn 20. The observed spin dynamics is compared with that in YbCo 2Zn 20 and Yb 2Co 12P 7 as well as with the data of inelastic neutron scattering and electronic band structure calculations. Our results provide direct evidence that 3d electrons are itinerant in YbFe 2Zn 20 and localized in YbCo 2Zn 20. Possible connection between spin paramagnetism of dense heavy fermion systems, quantum criticality effects, and ESR spectra is discussed.

Stable spin domains in a nondegenerate ultracold gas

NASA Astrophysics Data System (ADS)

Graham, S. D.; Niroomand, D.; Ragan, R. J.; McGuirk, J. M.

2018-05-01

We study the stability of two-domain spin structures in an ultracold gas of magnetically trapped 87Rb atoms above quantum degeneracy. Adding a small effective magnetic field gradient stabilizes the domains via coherent collective spin rotation effects, despite negligibly perturbing the potential energy relative to the thermal energy. We demonstrate that domain stabilization is accomplished through decoupling the dynamics of longitudinal magnetization, which remains in time-independent domains, from transverse magnetization, which undergoes a purely transverse spin wave trapped within the domain wall. We explore the effect of temperature and density on the steady-state domains, and compare our results to a hydrodynamic solution to a quantum Boltzmann equation.

A practical approach to calculate the time evolutions of magnetic field effects on photochemical reactions in nano-structured materials.

PubMed

Yago, Tomoaki; Wakasa, Masanobu

2015-04-21

A practical method to calculate time evolutions of magnetic field effects (MFEs) on photochemical reactions involving radical pairs is developed on the basis of the theory of the chemically induced dynamic spin polarization proposed by Pedersen and Freed. In theory, the stochastic Liouville equation (SLE), including the spin Hamiltonian, diffusion motions of the radical pair, chemical reactions, and spin relaxations, is solved by using the Laplace and the inverse Laplace transformation technique. In our practical approach, time evolutions of the MFEs are successfully calculated by applying the Miller-Guy method instead of the final value theorem to the inverse Laplace transformation process. Especially, the SLE calculations are completed in a short time when the radical pair dynamics can be described by the chemical kinetics consisting of diffusions, reactions and spin relaxations. The SLE analysis with a short calculation time enables one to examine the various parameter sets for fitting the experimental date. Our study demonstrates that simultaneous fitting of the time evolution of the MFE and of the magnetic field dependence of the MFE provides valuable information on the diffusion motions of the radical pairs in nano-structured materials such as micelles where the lifetimes of radical pairs are longer than hundreds of nano-seconds and the magnetic field dependence of the spin relaxations play a major role for the generation of the MFE.

Role of internal demagnetizing field for the dynamics of a surface-modulated magnonic crystal

NASA Astrophysics Data System (ADS)

Langer, M.; Röder, F.; Gallardo, R. A.; Schneider, T.; Stienen, S.; Gatel, C.; Hübner, R.; Bischoff, L.; Lenz, K.; Lindner, J.; Landeros, P.; Fassbender, J.

2017-05-01

This work aims to demonstrate and understand the key role of local demagnetizing fields in hybrid structures consisting of a continuous thin film with a stripe modulation on top. To understand the complex spin dynamics of these structures, the magnonic crystal was reconstructed in two different ways—performing micromagnetic simulations based on the structural shape as well as based on the internal demagnetizing field, which both are mapped on the nanoscale using electron holography. The simulations yield the frequency-field dependence as well as the angular dependence revealing the governing role of the internal field landscape around the backward-volume geometry. Simple rules for the propagation vector and the mode localization are formulated in order to explain the calculated mode profiles. Treating internal demagnetizing fields equivalent to anisotropies, the complex angle-dependent spin-wave behavior is described for an in-plane rotation of the external field.

How far in-silico computing meets real experiments. A study on the structure and dynamics of spin labeled vinculin tail protein by molecular dynamics simulations and EPR spectroscopy

PubMed Central

2013-01-01

Background Investigation of conformational changes in a protein is a prerequisite to understand its biological function. To explore these conformational changes in proteins we developed a strategy with the combination of molecular dynamics (MD) simulations and electron paramagnetic resonance (EPR) spectroscopy. The major goal of this work is to investigate how far computer simulations can meet the experiments. Methods Vinculin tail protein is chosen as a model system as conformational changes within the vinculin protein are believed to be important for its biological function at the sites of cell adhesion. MD simulations were performed on vinculin tail protein both in water and in vacuo environments. EPR experimental data is compared with those of the simulated data for corresponding spin label positions. Results The calculated EPR spectra from MD simulations trajectories of selected spin labelled positions are comparable to experimental EPR spectra. The results show that the information contained in the spin label mobility provides a powerful means of mapping protein folds and their conformational changes. Conclusions The results suggest the localization of dynamic and flexible regions of the vinculin tail protein. This study shows MD simulations can be used as a complementary tool to interpret experimental EPR data. PMID:23445506

Ultrafast optical excitation of magnetic skyrmions

NASA Astrophysics Data System (ADS)

Ogawa, N.; Seki, S.; Tokura, Y.

2015-04-01

Magnetic skyrmions in an insulating chiral magnet Cu2OSeO3 were studied by all-optical spin wave spectroscopy. The spins in the conical and skyrmion phases were excited by the impulsive magnetic field from the inverse-Faraday effect, and resultant spin dynamics were detected by using time-resolved magneto-optics. Clear dispersions of the helimagnon were observed, which is accompanied by a distinct transition into the skyrmion phase, by sweeping temperature and magnetic field. In addition to the collective excitations of skyrmions, i.e., rotation and breathing modes, several spin precession modes were identified, which would be specific to optical excitation. The ultrafast, nonthermal, and local excitation of the spin systems by photons would lead to the efficient manipulation of nano-magnetic structures.

Activation of coherent lattice phonon following ultrafast molecular spin-state photo-switching: A molecule-to-lattice energy transfer

PubMed Central

Marino, A.; Cammarata, M.; Matar, S. F.; Létard, J.-F.; Chastanet, G.; Chollet, M.; Glownia, J. M.; Lemke, H. T.; Collet, E.

2015-01-01

We combine ultrafast optical spectroscopy with femtosecond X-ray absorption to study the photo-switching dynamics of the [Fe(PM-AzA)2(NCS)2] spin-crossover molecular solid. The light-induced excited spin-state trapping process switches the molecules from low spin to high spin (HS) states on the sub-picosecond timescale. The change of the electronic state (<50 fs) induces a structural reorganization of the molecule within 160 fs. This transformation is accompanied by coherent molecular vibrations in the HS potential and especially a rapidly damped Fe-ligand breathing mode. The time-resolved studies evidence a delayed activation of coherent optical phonons of the lattice surrounding the photoexcited molecules. PMID:26798836

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, S. L., E-mail: shuch@ist.hokudai.ac.jp; Takayama, J.; Murayama, A.

Power-dependent time-resolved optical spin orientation measurements were performed on In{sub 0.1}Ga{sub 0.9}As quantum well (QW) and In{sub 0.5}Ga{sub 0.5}As quantum dot (QD) tunnel-coupled structures with an 8-nm-thick GaAs barrier. A fast transient increase of electron spin polarization was observed at the QW ground state after circular-polarized pulse excitation. The temporal maximum of polarization increased with increasing pumping fluence owing to enhanced spin blocking in the QDs, yielding a highest amplification of 174% with respect to the initial spin polarization. Further elevation of the laser power gradually quenched the polarization dynamics, which was induced by saturated spin filling of both themore » QDs and the QW phase spaces.« less

Semiclassical theory for liquidlike behavior of the frustrated magnet Ca10Cr7O28

NASA Astrophysics Data System (ADS)

Biswas, Sounak; Damle, Kedar

2018-03-01

We identify the low energy effective Hamiltonian that is expected to describe the low temperature properties of the frustrated magnet Ca10Cr7O28 . Motivated by the fact that this effective Hamiltonian has S =3 /2 effective moments as its degrees of freedom, we use semiclassical spin-wave theory to study the T =0 physics of this effective model and argue that singular spin-wave fluctuations destabilize the spiral order favored by the exchange couplings of this effective Hamiltonian. We also use a combination of classical Monte-Carlo simulations and molecular dynamics, as well as analytical approximations, to study the physics at low, nonzero temperatures. The results of these nonzero temperature calculations capture the liquidlike structure factors observed in the temperature range accessed by recent experiments. Additionally, at still lower temperatures, they predict that a transition to nematic order in the bond energies reflects itself in the spin channel in the form of a crossover to a regime with large but finite correlation length for spiral spin correlations and a corresponding slowing down of spin dynamics.

μ SR study of NaCaNi2F7 in zero field and applied longitudinal magnetic field

NASA Astrophysics Data System (ADS)

Cai, Yipeng; Wilson, Murray; Hallas, Alannah; Liu, Lian; Frandsen, Benjamin; Dunsiger, Sarah; Krizan, Jason; Cava, Robert; Uemura, Yasutomo; Luke, Graeme

Rich physics of abundant magnetic ground states has been realized in the A2B2X7 geometrically frustrated magnetic pyrochlores. Recently, a new spin-1 Ni2+ pyrochlore, NaCaNi2F7, was synthesized and shown to have spin freezing at 3.6 K with a frustration index of f 36 and antiferromagnetic exchange interactions [1] . This structure has chemical disorder on the A site caused by randomly distributed Ca and Na ions, which causes bond disorder around the magnetic Ni sites. We present Zero Field (ZF) and Longitudinal Field (LF) muon spin rotation (μSR) measurements on this single crystal pyrochlore. Our data shows that the Ni2+ spins start freezing around 4 K giving a static local field of 140 G. The data show no oscillations down to 75 mK which indicates no long range magnetic order. They are well described by the dynamic Gaussian Kubo-Toyabe function with a non-zero hopping rate that is not easily decoupled with an applied longitudinal field, which implies persistent spin dynamics down to 75 mK.

Numerically exploring the 1D-2D dimensional crossover on spin dynamics in the doped Hubbard model

DOE PAGES

Kung, Y. F.; Bazin, C.; Wohlfeld, K.; ...

2017-11-02

Using determinant quantum Monte Carlo (DQMC) simulations, we systematically study the doping dependence of the crossover from one to two dimensions and its impact on the magnetic properties of the Hubbard model. A square lattice of chains is used, in which the dimensionality can be tuned by varying the interchain coupling t ⊥. The dynamical spin structure factor and static quantities, such as the static spin susceptibility and nearest-neighbor spin correlation function, are characterized in the one- and two-dimensional limits as a benchmark. When the dimensionality is tuned between these limits, the magnetic properties, while evolving smoothly from one tomore » two dimensions, drastically change regardless of the doping level. This suggests that the spin excitations in the two-dimensional Hubbard model, even in the heavily doped case, cannot be explained using the spinon picture known from one dimension. In conclusion, the DQMC calculations are complemented by cluster perturbation theory studies to form a more complete picture of how the crossover occurs as a function of doping and how doped holes impact magnetic order.« less

Monte Carlo generators for studies of the 3D structure of the nucleon

DOE PAGES

Avakian, Harut; D'Alesio, U.; Murgia, F.

2015-01-23

In this study, extraction of transverse momentum and space distributions of partons from measurements of spin and azimuthal asymmetries requires development of a self consistent analysis framework, accounting for evolution effects, and allowing control of systematic uncertainties due to variations of input parameters and models. Development of realistic Monte-Carlo generators, accounting for TMD evolution effects, spin-orbit and quark-gluon correlations will be crucial for future studies of quark-gluon dynamics in general and 3D structure of the nucleon in particular.

Spin dynamics in the stripe-ordered buckled honeycomb lattice antiferromagnet Ba 2 NiTeO 6

DOE PAGES

Asai, Shinichiro; Soda, Minoru; Kasatani, Kazuhiro; ...

2017-09-01

We carried out inelastic neutron scattering experiments on a buckled honeycomb lattice antiferromagnet Ba 2NiTeO 6 exhibiting a stripe structure at a low temperature. Magnetic excitations are observed in the energy range of ℏω≲10 meV having an anisotropy gap of 2 meV at 2 K. We perform spin-wave calculations to identify the spin model. The obtained microscopic parameters are consistent with the location of the stripe structure in the classical phase diagram. Furthermore, the Weiss temperature independently estimated from a bulk magnetic susceptibility is consistent with the microscopic parameters. The results reveal that a competition between the nearest-neighbor and next-nearest-neighbormore » interactions that together with a relatively large single-ion magnetic anisotropy stabilize the stripe magnetic structure.« less

Spin dynamics in the stripe-ordered buckled honeycomb lattice antiferromagnet Ba 2 NiTeO 6

DOE Office of Scientific and Technical Information (OSTI.GOV)

Asai, Shinichiro; Soda, Minoru; Kasatani, Kazuhiro

We carried out inelastic neutron scattering experiments on a buckled honeycomb lattice antiferromagnet Ba 2NiTeO 6 exhibiting a stripe structure at a low temperature. Magnetic excitations are observed in the energy range of ℏω≲10 meV having an anisotropy gap of 2 meV at 2 K. We perform spin-wave calculations to identify the spin model. The obtained microscopic parameters are consistent with the location of the stripe structure in the classical phase diagram. Furthermore, the Weiss temperature independently estimated from a bulk magnetic susceptibility is consistent with the microscopic parameters. The results reveal that a competition between the nearest-neighbor and next-nearest-neighbormore » interactions that together with a relatively large single-ion magnetic anisotropy stabilize the stripe magnetic structure.« less

Structural Refinement of Proteins by Restrained Molecular Dynamics Simulations with Non-interacting Molecular Fragments.

PubMed

Shen, Rong; Han, Wei; Fiorin, Giacomo; Islam, Shahidul M; Schulten, Klaus; Roux, Benoît

2015-10-01

The knowledge of multiple conformational states is a prerequisite to understand the function of membrane transport proteins. Unfortunately, the determination of detailed atomic structures for all these functionally important conformational states with conventional high-resolution approaches is often difficult and unsuccessful. In some cases, biophysical and biochemical approaches can provide important complementary structural information that can be exploited with the help of advanced computational methods to derive structural models of specific conformational states. In particular, functional and spectroscopic measurements in combination with site-directed mutations constitute one important source of information to obtain these mixed-resolution structural models. A very common problem with this strategy, however, is the difficulty to simultaneously integrate all the information from multiple independent experiments involving different mutations or chemical labels to derive a unique structural model consistent with the data. To resolve this issue, a novel restrained molecular dynamics structural refinement method is developed to simultaneously incorporate multiple experimentally determined constraints (e.g., engineered metal bridges or spin-labels), each treated as an individual molecular fragment with all atomic details. The internal structure of each of the molecular fragments is treated realistically, while there is no interaction between different molecular fragments to avoid unphysical steric clashes. The information from all the molecular fragments is exploited simultaneously to constrain the backbone to refine a three-dimensional model of the conformational state of the protein. The method is illustrated by refining the structure of the voltage-sensing domain (VSD) of the Kv1.2 potassium channel in the resting state and by exploring the distance histograms between spin-labels attached to T4 lysozyme. The resulting VSD structures are in good agreement with the consensus model of the resting state VSD and the spin-spin distance histograms from ESR/DEER experiments on T4 lysozyme are accurately reproduced.

Polarized targets in high energy physics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cates, G.D. Jr.

1994-12-01

Various approaches are discussed for producing polarized nuclear targets for high energy physics experiments. As a unifying theme, examples are drawn from experiments to measure spin dependent structure functions of nucleons in deep inelastic scattering. This single physics goal has, over roughly two decades, been a driving force in advances in target technology. Actual or planned approaches have included solid targets polarized by dynamic nuclear polarization (DNP), several types of internal targets for use in storage rings, and gaseous {sup 3}He targets polarized by spin-exchange optical pumping. This last approach is the type of target adopted for SLAC E-142, anmore » experiment to measure the spin structure function of the neutron, and is described in detail.« less

Shape coexistence in the N = 19 neutron-rich nucleus 31Mg explored by β-γ spectroscopy of spin-polarized 31Na

NASA Astrophysics Data System (ADS)

Nishibata, H.; Shimoda, T.; Odahara, A.; Morimoto, S.; Kanaya, S.; Yagi, A.; Kanaoka, H.; Pearson, M. R.; Levy, C. D. P.; Kimura, M.

2017-04-01

The structure of excited states in the neutron-rich nucleus 31Mg, which is in the region of the ;island of inversion; associated with the neutron magic number N = 20, is studied by β-γ spectroscopy of spin-polarized 31Na. Among the 31Mg levels below the one neutron separation energy of 2.3 MeV, the spin values of all five positive-parity levels are unambiguously determined by observing the anisotropic β decay. Two rotational bands with Kπ = 1 /2+ and 1 /2- are proposed based on the spins and energies of the levels. Comparison on a level-by-level basis is performed between the experimental results and theoretical calculations by the antisymmetrized molecular dynamics (AMD) plus generator coordinate method (GCM). It is found that various nuclear structures coexist in the low excitation energy region in 31Mg.

New type of quantum spin Hall insulators in hydrogenated PbSn thin films

PubMed Central

Liu, Liang; Qin, Hongwei; Hu, Jifan

2017-01-01

The realization of a quantum spin Hall (QSH) insulator working at high temperature is of both scientific and technical interest since it supports spin-polarized and dssipationless edge states. Based on first-principle calculations, we predicted that the two-dimensional (2D) binary compound of lead and tin (PbSn) in a buckled honeycomb framework can be tuned into a topological insulator with huge a band gap and structural stability via hydrogenation or growth on special substrates. This heavy-element-based structure is sufficiently ductile to survive the 18 ps molecular dynamics (MD) annealing to 400 K, and the band gap opened by strong spin-orbital-coupling (SOC) is as large as 0.7 eV. These characteristics indicate that hydrogenated PbSn (H-PbSn) is an excellent platform for QSH realization at high temperature. PMID:28218297

Single-spin observables and orbital structures in hadronic distributions

NASA Astrophysics Data System (ADS)

Sivers, Dennis

2006-11-01

Single-spin observables in scattering processes (either analyzing powers or polarizations) are highly constrained by rotational invariance and finite symmetries. For example, it is possible to demonstrate that all single-spin observables are odd under the finite transformation O=PAτ where P is parity and Aτ is a finite symmetry that can be designated “artificial time reversal”. The operators P, O and Aτ all have eigenvalues ±1 so that all single-spin observables can be classified into two distinct categories: (1) P-odd and Aτ-even, (2) P-even and Aτ-odd. Within the light-quark sector of the standard model, P-odd observables are generated from pointlike electroweak processes while Aτ-odd observables (neglecting quark mass parameters) come from dynamic spin-orbit correlations within hadrons or within larger composite systems, such as nuclei. The effects of Aτ-odd dynamics can be inserted into transverse-momentum dependent constituent distribution functions and, in this paper, we construct the contribution from an orbital quark to the Aτ-odd quark parton distribution ΔNGq/p↑front(x,kTN;μ2). Using this distribution, we examine the crucial role of initial- and final-state interactions in the observation of the scattering asymmetries in different hard-scattering processes. This construction provides a geometrical and dynamical interpretation of the Collins conjugation relation between single-spin asymmetries in semi-inclusive deep inelastic scattering and the asymmetries in Drell-Yan production. Finally, our construction allows us to display a significant difference between the calculation of a spin asymmetry generated by a hard-scattering mechanism involving color-singlet exchange (such as a photon) and a calculation of an asymmetry with a hard-scattering exchange involving gluons. This leads to an appreciation of the process-dependence inherent in measurements of single-spin observables.

Spin-flip transitions and departure from the Rashba model in the Au(111) surface

NASA Astrophysics Data System (ADS)

Ibañez-Azpiroz, Julen; Bergara, Aitor; Sherman, E. Ya.; Eiguren, Asier

2013-09-01

We present a detailed analysis of the spin-flip excitations induced by a periodic time-dependent electric field in the Rashba prototype Au(111) noble metal surface. Our calculations incorporate the full spinor structure of the spin-split surface states and employ a Wannier-based scheme for the spin-flip matrix elements. We find that the spin-flip excitations associated with the surface states exhibit an strong dependence on the electron momentum magnitude, a feature that is absent in the standard Rashba model [E. I. Rashba, Sov. Phys. Solid State 2, 1109 (1960)]. Furthermore, we demonstrate that the maximum of the calculated spin-flip absorption rate is about twice the model prediction. These results show that, although the Rashba model accurately describes the spectrum and spin polarization, it does not fully account for the dynamical properties of the surface states.

Element-selective investigation of domain structure in CoPd and FePd alloys using small-angle soft X-ray scattering

NASA Astrophysics Data System (ADS)

Weier, C.; Adam, R.; Frömter, R.; Bach, J.; Winkler, G.; Kobs, A.; Oepen, H. P.; Grychtol, P.; Kapteyn, H. C.; Murnane, M. M.; Schneider, C. M.

2014-03-01

Recent optical pump-probe experiments on magnetic multilayers and alloys identified perpendicular spin superdiffusion as one of possible mechanisms responsible for femtosecond magnetization dynamics. On the other hand, no strong evidence for the ultrafast lateral spin transport has been reported, so far. To address this question, we studied magnetic domain structure of CoPd and FePd thin films using small-angle scattering of soft X-rays. By tuning the synchrotron-generated X-rays to the absorption edges of Fe or Co we recorded Fourier images of the magnetic domain structure corresponding to a chosen element. Applying in - situ magnetic fields resulted in pronounced rearrangement of domain structure that was clearly observed in scattering images. Our analysis of both the stand-alone, as well as magnetically coupled CoPd/FePd layers provides insight into the formation of domains under small magnetic field perturbations and pave the way to better understanding of transient changes expected in magneto-dynamic measurements.

Magnetic structure and excitation spectrum of the hyperhoneycomb Kitaev magnet β -Li2IrO3

NASA Astrophysics Data System (ADS)

Ducatman, Samuel; Rousochatzakis, Ioannis; Perkins, Natalia B.

2018-03-01

We present a theoretical study of the static and dynamical properties of the three-dimensional, hyperhoneycomb Kitaev magnet β -Li2IrO3 . We argue that the observed incommensurate order can be understood in terms of a long-wavelength twisting of a nearby commensurate period-3 state, with the same key qualitatively features. The period-3 state shows very different structure when either the Kitaev interaction K or the off-diagonal exchange anisotropy Γ is dominant. A comparison of the associated static spin structure factors with reported scattering experiments in zero and finite fields gives strong evidence that β -Li2IrO3 lies in the regime of dominant Kitaev coupling, and that the Heisenberg exchange J is much weaker than both K and Γ . Our predictions for the magnon excitation spectra, the dynamical spin structure factors, and their polarization dependence provide additional distinctive fingerprints that can be checked experimentally.

The classical and quantum dynamics of molecular spins on graphene

PubMed Central

Cervetti, Christian; Rettori, Angelo; Pini, Maria Gloria; Cornia, Andrea; Repollés, Ana; Luis, Fernando; Dressel, Martin; Rauschenbach, Stephan; Kern, Klaus; Burghard, Marko; Bogani, Lapo

2015-01-01

Controlling the dynamics of spins on surfaces is pivotal to the design of spintronic1 and quantum computing2 devices. Proposed schemes involve the interaction of spins with graphene to enable surface-state spintronics3,4, and electrical spin-manipulation4-11. However, the influence of the graphene environment on the spin systems has yet to be unraveled12. Here we explore the spin-graphene interaction by studying the classical and quantum dynamics of molecular magnets13 on graphene. While the static spin response remains unaltered, the quantum spin dynamics and associated selection rules are profoundly modulated. The couplings to graphene phonons, to other spins, and to Dirac fermions are quantified using a newly-developed model. Coupling to Dirac electrons introduces a dominant quantum-relaxation channel that, by driving the spins over Villain’s threshold, gives rise to fully-coherent, resonant spin tunneling. Our findings provide fundamental insight into the interaction between spins and graphene, establishing the basis for electrical spin-manipulation in graphene nanodevices. PMID:26641019

Theoretical study of dynamic electron-spin-polarization via the doublet-quartet quantum-mixed state and time-resolved ESR spectra of the quartet high-spin state.

PubMed

Teki, Yoshio; Matsumoto, Takafumi

2011-04-07

The mechanism of the unique dynamic electron polarization of the quartet (S = 3/2) high-spin state via a doublet-quartet quantum-mixed state and detail theoretical calculations of the population transfer are reported. By the photo-induced electron transfer, the quantum-mixed charge-separate state is generated in acceptor-donor-radical triad (A-D-R). This mechanism explains well the unique dynamic electron polarization of the quartet state of A-D-R. The generation of the selectively populated quantum-mixed state and its transfer to the strongly coupled pure quartet and doublet states have been treated both by a perturbation approach and by exact numerical calculations. The analytical solutions show that generation of the quantum-mixed states with the selective populations after de-coherence and/or accompanying the (complete) dephasing during the charge-recombination are essential for the unique dynamic electron polarization. Thus, the elimination of the quantum coherence (loss of the quantum information) is the key process for the population transfer from the quantum-mixed state to the quartet state. The generation of high-field polarization on the strongly coupled quartet state by the charge-recombination process can be explained by a polarization transfer from the quantum-mixed charge-separate state. Typical time-resolved ESR patterns of the quantum-mixed state and of the strongly coupled quartet state are simulated based on the generation mechanism of the dynamic electron polarization. The dependence of the spectral pattern of the quartet high-spin state has been clarified for the fine-structure tensor and the exchange interaction of the quantum-mixed state. The spectral pattern of the quartet state is not sensitive towards the fine-structure tensor of the quantum-mixed state, because this tensor contributes only as a perturbation in the population transfer to the spin-sublevels of the quartet state. Based on the stochastic Liouville equation, it is also discussed why the selective population in the quantum-mixed state is generated for the "finite field" spin-sublevels. The numerical calculations of the elimination of the quantum coherence (de-coherence and/or dephasing) are demonstrated. A new possibility of the enhanced intersystem crossing pathway in solution is also proposed.

Magnetic Excitations and Continuum of a Possibly Field-Induced Quantum Spin Liquid in α -RuCl3

NASA Astrophysics Data System (ADS)

Wang, Zhe; Reschke, S.; Hüvonen, D.; Do, S.-H.; Choi, K.-Y.; Gensch, M.; Nagel, U.; Rõõm, T.; Loidl, A.

2017-12-01

We report on terahertz spectroscopy of quantum spin dynamics in α -RuCl3 , a system proximate to the Kitaev honeycomb model, as a function of temperature and magnetic field. We follow the evolution of an extended magnetic continuum below the structural phase transition at Ts 2=62 K . With the onset of a long-range magnetic order at TN=6.5 K , spectral weight is transferred to a well-defined magnetic excitation at ℏω1=2.48 meV , which is accompanied by a higher-energy band at ℏω2=6.48 meV . Both excitations soften in a magnetic field, signaling a quantum phase transition close to Bc=7 T , where a broad continuum dominates the dynamical response. Above Bc, the long-range order is suppressed, and on top of the continuum, emergent magnetic excitations evolve. These excitations follow clear selection rules and exhibit distinct field dependencies, characterizing the dynamical properties of a possibly field-induced quantum spin liquid.

Magnetic stray-field studies of a single Cobalt nanoelement as a component of the building blocks of artificial square spin ice

NASA Astrophysics Data System (ADS)

Pohlit, Merlin; Porrati, Fabrizio; Huth, Michael; Ohno, Yuzo; Ohno, Hideo; Müller, Jens

2016-02-01

We use Focused Electron Beam Deposition (FEBID) to directly write Cobalt magnetic nanoelements onto a micro-Hall magnetometer, which allows for high-sensitivity measurements of the magnetic stray field emanating from the samples. In a previous study [M. Pohlit et al., J. Appl. Phys. 117 (2015) 17C746] [21] we investigated thermal dynamics of an individual building block (nanocluster) of artificial square spin ice. In this work, we compare the results of this structure with interacting elements to the switching of a single nanoisland. By analyzing the survival function of the repeatedly prepared state in a given temperature range, we find thermally activated switching dynamics. A detailed analysis of the hysteresis loop reveals a metastable microstate preceding the overall magnetization reversal of the single nanoelement, also found in micromagnetic simulations. Such internal degrees of freedom may need to be considered, when analyzing the thermal dynamics of larger spin ice configurations on different lattice types.

Competition between Bose-Einstein Condensation and Spin Dynamics.

PubMed

Naylor, B; Brewczyk, M; Gajda, M; Gorceix, O; Maréchal, E; Vernac, L; Laburthe-Tolra, B

2016-10-28

We study the impact of spin-exchange collisions on the dynamics of Bose-Einstein condensation by rapidly cooling a chromium multicomponent Bose gas. Despite relatively strong spin-dependent interactions, the critical temperature for Bose-Einstein condensation is reached before the spin degrees of freedom fully thermalize. The increase in density due to Bose-Einstein condensation then triggers spin dynamics, hampering the formation of condensates in spin-excited states. Small metastable spinor condensates are, nevertheless, produced, and they manifest in strong spin fluctuations.

Magic Angle Spinning NMR of Viruses

PubMed Central

Quinn, Caitlin; Lu, Manman; Suiter, Christopher L.; Hou, Guangjin; Zhang, Huilan; Polenova, Tatyana

2015-01-01

Viruses, relatively simple pathogens, are able to replicate in many living organisms and to adapt to various environments. Conventional atomic-resolution structural biology techniques, X-ray crystallography and solution NMR spectroscopy provided abundant information on the structures of individual proteins and nucleic acids comprising viruses; however, viral assemblies are not amenable to analysis by these techniques because of their large size, insolubility, and inherent lack of long-range order. In this article, we review the recent advances in magic angle spinning NMR spectroscopy that enabled atomic-resolution analysis of structure and dynamics of large viral systems and give examples of several exciting case studies. PMID:25919197

Ultrafast intersystem-crossing in platinum containing π-conjugated polymers with tunable spin-orbit coupling.

PubMed

Sheng, C-X; Singh, S; Gambetta, A; Drori, T; Tong, M; Tretiak, S; Vardeny, Z V

2013-01-01

The development of efficient organic light-emitting diodes (OLED) and organic photovoltaic cells requires control over the dynamics of spin sensitive excitations. Embedding heavy metal atoms in π-conjugated polymer chains enhances the spin-orbit coupling (SOC), and thus facilitates intersystem crossing (ISC) from the singlet to triplet manifolds. Here we use various nonlinear optical spectroscopies such as two-photon absorption and electroabsorption in conjunction with electronic structure calculations, for studying the energies, emission bands and ultrafast dynamics of spin photoexcitations in two newly synthesized π-conjugated polymers that contain intrachain platinum (Pt) atoms separated by one (Pt-1) or three (Pt-3) organic spacer units. The controllable SOC in these polymers leads to a record ISC time of <~1 ps in Pt-1 and ~6 ps in Pt-3. The tunable ultrafast ISC rate modulates the intensity ratio of the phosphorescence and fluorescence emission bands, with potential applications for white OLEDs.

Ab initio modeling of CW-ESR spectra of the double spin labeled peptide Fmoc-(Aib-Aib-TOAC)2-Aib-OMe in acetonitrile.

PubMed

Zerbetto, Mirco; Carlotto, Silvia; Polimeno, Antonino; Corvaja, Carlo; Franco, Lorenzo; Toniolo, Claudio; Formaggio, Fernando; Barone, Vincenzo; Cimino, Paola

2007-03-15

In this work we address the interpretation, via an ab initio integrated computational approach, of the CW-ESR spectra of the double spin labeled, 310-helical, peptide Fmoc-(Aib-Aib-TOAC)2-Aib-OMe dissolved in acetonitrile. Our approach is based on the determination of geometric and local magnetic parameters of the heptapeptide by quantum mechanical density functional calculations taking into account solvent and, when needed, vibrational averaging contributions. The system is then described by a stochastic Liouville equation for the two electron spins interacting with each other and with two 14N nuclear spins, in the presence of diffusive rotational dynamics. Parametrization of the diffusion rotational tensor is provided by a hydrodynamic model. CW-ESR spectra are simulated with minimal resorting to fitting procedures, proving that the combination of sensitive ESR spectroscopy and sophisticated modeling can be highly helpful in providing 3D structural and dynamic information on molecular systems.

Dynamic localization in optical and Zeeman lattices in the presence of spin-orbit coupling

NASA Astrophysics Data System (ADS)

Kartashov, Yaroslav V.; Konotop, Vladimir V.; Zezyulin, Dmitry A.; Torner, Lluis

2016-12-01

The dynamic localization of a two-level atom in a periodic potential under the action of spin-orbit coupling and a weak harmonically varying linear force is studied. We consider optical and Zeeman potentials that are either in phase or out of phase in two spinor components, respectively. The expectation value for the position of the atom after one oscillation period of the linear force is recovered in authentic resonances or in pseudoresonances. The frequencies of the linear force corresponding to authentic resonances are determined by the band structure of the periodic potential and are affected by the spin-orbit coupling. The width or dispersion of the wave packet in authentic resonances is usually minimal. The frequencies corresponding to pseudoresonances do not depend on the type of potential and on the strength of the spin-orbit coupling, while the evolution of excitations at the corresponding frequencies is usually accompanied by significant dispersion. Pseudoresonances are determined by the initial phase of the linear force and by the quasimomentum of the wave packet. Due to the spinor nature of the system, the motion of the atom is accompanied by periodic, but not harmonic, spin oscillations. Under the action of spin-orbit coupling the oscillations of the wave packet can be nearly completely suppressed in optical lattices. Dynamic localization in Zeeman lattices is characterized by doubling of the resonant oscillation periods due to band crossing at the boundary of the Brillouin zone. We also show that higher harmonics in the Fourier expansion of the energy band lead to effective dispersion, which can be strong enough to prevent dynamic localization of the Bloch wave packet.

Magnon Polarons in the Spin Seebeck Effect.

PubMed

Kikkawa, Takashi; Shen, Ka; Flebus, Benedetta; Duine, Rembert A; Uchida, Ken-Ichi; Qiu, Zhiyong; Bauer, Gerrit E W; Saitoh, Eiji

2016-11-11

Sharp structures in the magnetic field-dependent spin Seebeck effect (SSE) voltages of Pt/Y_{3}Fe_{5}O_{12} at low temperatures are attributed to the magnon-phonon interaction. Experimental results are well reproduced by a Boltzmann theory that includes magnetoelastic coupling. The SSE anomalies coincide with magnetic fields tuned to the threshold of magnon-polaron formation. The effect gives insight into the relative quality of the lattice and magnetization dynamics.

Voltage-Driven Magnetization Switching and Spin Pumping in Weyl Semimetals

NASA Astrophysics Data System (ADS)

Kurebayashi, Daichi; Nomura, Kentaro

2016-10-01

We demonstrate electrical magnetization switching and spin pumping in magnetically doped Weyl semimetals. The Weyl semimetal is a three-dimensional gapless topological material, known to have nontrivial coupling between the charge and the magnetization due to the chiral anomaly. By solving the Landau-Lifshitz-Gilbert equation for a multilayer structure of a Weyl semimetal, an insulator and a metal while taking the charge-magnetization coupling into account, magnetization dynamics is analyzed. It is shown that the magnetization dynamics can be driven by the electric voltage. Consequently, switching of the magnetization with a pulsed electric voltage can be achieved, as well as precession motion with an applied oscillating electric voltage. The effect requires only a short voltage pulse and may therefore be energetically favorable for us in spintronics devices compared to conventional spin-transfer torque switching.

Overhauser shift and dynamic nuclear polarization on carbon fibers

NASA Astrophysics Data System (ADS)

Herb, Konstantin; Denninger, Gert

2018-06-01

We report on the first experimental magnetic resonance determination of the coupling between electrons and nuclear spins (1H, 13C) in carbon fibers. Our results strongly support the assumption that the electronic spins are delocalized on graphene like structures in the fiber. The coupling between these electrons and the nuclei of the lattice results in dynamic nuclear polarization of the nuclei (DNP), enabling very sensitive NMR experiments on these nuclear spins. For possible applications of graphene in spintronics devices the coupling between nuclei and electrons is essential. We were able to determine the interactions down to 30 × 10-9(30 ppb) . We were even able to detect the coupling of the electrons to 13C (in natural abundance). These experiments open the way for a range of new double resonance investigations with possible applications in the field of material science.

Dynamical spin accumulation in large-spin magnetic molecules

NASA Astrophysics Data System (ADS)

Płomińska, Anna; Weymann, Ireneusz; Misiorny, Maciej

2018-01-01

The frequency-dependent transport through a nanodevice containing a large-spin magnetic molecule is studied theoretically in the Kondo regime. Specifically, the effect of magnetic anisotropy on dynamical spin accumulation is of primary interest. Such accumulation arises due to finite components of frequency-dependent conductance that are off diagonal in spin. Here, employing the Kubo formalism and the numerical renormalization group method, we demonstrate that the dynamical transport properties strongly depend on the relative orientation of spin moments in electrodes of the device, as well as on intrinsic parameters of the molecule. In particular, the effect of dynamical spin accumulation is found to be greatly affected by the type of magnetic anisotropy exhibited by the molecule, and it develops for frequencies corresponding to the Kondo temperature. For the parallel magnetic configuration of the device, the presence of dynamical spin accumulation is conditioned by the interplay of ferromagnetic-lead-induced exchange field and the Kondo correlations.

Strong Enhancement of the Spin Hall Effect by Spin Fluctuations near the Curie Point of FexPt1 -x Alloys

NASA Astrophysics Data System (ADS)

Ou, Yongxi; Ralph, D. C.; Buhrman, R. A.

2018-03-01

Robust spin Hall effects (SHE) have recently been observed in nonmagnetic heavy metal systems with strong spin-orbit interactions. These SHE are either attributed to an intrinsic band-structure effect or to extrinsic spin-dependent scattering from impurities, namely, side jump or skew scattering. Here we report on an extraordinarily strong spin Hall effect, attributable to spin fluctuations, in ferromagnetic FexPt1 -x alloys near their Curie point, tunable with x . This results in a dampinglike spin-orbit torque being exerted on an adjacent ferromagnetic layer that is strongly temperature dependent in this transition region, with a peak value that indicates a lower bound 0.34 ±0.02 for the peak spin Hall ratio within the FePt. We also observe a pronounced peak in the effective spin-mixing conductance of the FM /FePt interface, and determine the spin diffusion length in these FexPt1 -x alloys. These results establish new opportunities for fundamental studies of spin dynamics and transport in ferromagnetic systems with strong spin fluctuations, and a new pathway for efficiently generating strong spin currents for applications.

Orbital and spin dynamics of intraband electrons in quantum rings driven by twisted light.

PubMed

Quinteiro, G F; Tamborenea, P I; Berakdar, J

2011-12-19

We theoretically investigate the effect that twisted light has on the orbital and spin dynamics of electrons in quantum rings possessing sizable Rashba spin-orbit interaction. The system Hamiltonian for such a strongly inhomogeneous light field exhibits terms which induce both spin-conserving and spin-flip processes. We analyze the dynamics in terms of the perturbation introduced by a weak light field on the Rasha electronic states, and describe the effects that the orbital angular momentum as well as the inhomogeneous character of the beam have on the orbital and the spin dynamics.

EDITORIAL: Ultrafast magnetization processes

NASA Astrophysics Data System (ADS)

Hillebrands, Burkard

2008-09-01

This Cluster Issue of Journal of Physics D: Applied Physics is devoted to ultrafast magnetization processes. It reports on the scientific yield of the Priority Programme 1133 'Ultrafast Magnetization Processes' which was funded by the Deutsche Forschungsgemeinschaft in the period 2002-2008 in three successive two-year funding periods, supporting research of 17-18 groups in Germany. Now, at the end of this Priority Programme, the members feel that the achievements made in the course of the programme merit communication to the international scientific community in a concerted way. Therefore, each of the projects of the last funding period presents a key result in a published contribution to this Cluster Issue. The purpose of the funding by a Priority Programme is to advance knowledge in an emerging field of research through collaborative networked support over several locations. Priority Programmes are characterized by their enhanced quality of research through the use of new methods and forms of collaboration in emerging fields, by added value through interdisciplinary cooperation, and by networking. The aim of the Priority Programme 1133 'Ultrafast Magnetization Processes' may be well characterized by the call for projects in June 2001 after the programme was approved by the Deutsche Forschungsgemeinschaft: 'The aim of the priority programme is the achievement of a basic understanding of the temporal evolution of fast magnetization processes in magnetically ordered films, multilayers and micro-structured systems. The challenge lies in the advancement of the field of ultrafast magnetization processes into the regime of a few femtoseconds to nanoseconds, a topic not yet well explored. A general aim is to understand the fundamental mechanisms needed for applications in ultrafast magneto-electronic devices. The fundamental topic to be addressed is the response of the magnetization of small structures upon the application of pulsed magnetic fields, laser pulses or injected spin-polarized electron pulses on short time scales, ranging from a small disturbance of the system up to the reversal of the magnetization direction.' Now, seven years later, the subject of ultrafast magnetization processes has grown into a mainstream research direction in modern magnetism. The major international conferences on magnetism, such as the Annual Conference on Magnetism and Magnetic Materials (MMM), the INTERMAG, the International Conference of Magnetism, as well as many regional conferences, schedule dedicated sessions to ultrafast magnetization processes, very often several of them. The large share in research in this field from German scientists has been made possible by this Priority Programme. Since its beginning, new developments have been picked up by the Priority Programme 1133 and addressed by projects. Spin torque phenomena in spin dynamics, although foreseen at the time of establishing the Priority Programme, have been taken up. The field of dissipation has been addressed and extended by several groups, with contributions both from theoretical and experimental groups. A first set of contributions addresses ultrafast dynamics and materials. T Roth et al [article 164001] in this issue] study the dynamics of coercivity in ultrafast pump-probe experiments on the femtosecond time scale. They show that an all optical pump-probe technique is, in general, not suitable for gaining access to the time-dependent behaviour of the coercivity, since the switching in a fixed external field is an irreversible process. They comment on the possible mechanisms leading to the observed reduction of the coercivity with increasing pump power and propose a potential solution to clarify the origin of such a behaviour. B Heitkamp et al [164002] discuss the femtosecond spin dynamics of ferromagnetic CoPt thin films and nanodots, which they probe using spin-polarized photoemission electron microscopy. They show by photoelectron spin analysis, that enhanced optical near fields can be used to induce a local demagnetization of the sample following femtosecond laser excitation. A B Schmidt et al [164003] report a new access to the surface electronic structure of fcc Co films combining spin-resolved one- and two-photon photoemission. The knowledge of surface states is important for interpreting time-resolved measurements of ultrafast magnetization dynamics in this material. An extension of ultrafast dynamics has been made by several groups. A Melnikov et al [164004] report on the ultrafast dynamics at lanthanide surfaces such as Gd(0001) and Tb(0001) using time-resolved second-harmonic generation and photoelectron spectroscopy. These surfaces exhibit a rich dynamics including a collective response of the crystal lattice and the magnetization. Effects of phonon-magnon scattering are discussed. M Fiebig et al [164005] report on experiments of ultrafast magnetization dynamics in antiferromagnetic compounds, and show that the magnetization dynamics in these systems differs noticeably from that of ferromagnetic compounds. They use optical second-harmonic generation and linear reflection to monitor the evolution of the antiferromagnetic order parameter subsequent to an intense optical excitation. In a theory paper, the local light-induced spin manipulation in two-magnetic-centre metallic chains is studied by T Hardenstein et al [164006] using highly correlational ab initio calculations. They show that, as an example of local spin manipulation, the spin on the iron side of a Co-Na-Fe cluster can be switched. S Halm et al [164007] present evidence to manipulate spin states in a diluted magnetic semiconductor on a submicrometer length scale via the magnetic fringe fields of micro-structured magnets. By optically switching the magnetization of the ferromagnet, the magnetization in the semiconductor is manipulated and the limits of a dynamical interaction between the spin states in the ferromagnet and the magnetic semiconductor are discussed. A second set of contributions addresses the field of spin waves and dynamic spin torque phenomena. C W Sandweg et al [164008] discuss the modification of the thermal spin wave spectrum by a domain wall in a narrow stripe and report the observation of a localized mode near the domain wall using the new technique of Brillouin light scattering microscopy. Time-resolved measurements are often made using a stroboscopic approach, thus missing non-periodic responses. P Möhrke et al [164009] report single-shot Kerr magnetometer measurements to observe the real time-domain wall motion in permalloy nanowires. The dynamics in magnetic disks is studied by I Neudecker et al [164010] using in-plane magnetic microwave fields for excitation. The effect of current-induced magnetization dynamics in single and double layer magnetic nanopillars is reported by N Müsgens et al [164011]. A spin-polarized charge current can modify the damping properties of spin waves in magnetic nanostructures. This is reported by V E Demidov et al [164012] using space-resolved Brillouin light scattering. They also present results regarding nonlinear spin-wave propagation and mode coupling in magnetic stripes and squares. D V Berkov and N L Gorn [164013] report on their results of nonlinear magnetization dynamics in nanodevices induced by a spin-polarized current using micromagnetic simulation. A third set of contributions focuses on dissipation phenomena ranging from a phenomenological description to the investigation of the microscopic origin(s). In a theory paper, M Fähnle et al [164014] revisit the Gilbert equation and discuss anisotropic and non-local damping of the magnetization dynamics. They derive their results by a combination of the breathing Fermi surface model with a variant of the ab initio density functional electron theory given by the magnetic force theorem. On the experimental side, S Serrano-Guisan et al [164015] address Gilbert damping in Ni81Fe19 thin films and microstructures using anisotropic magnetoresistance and pulsed inductive microwave magnetometry to measure the time-resolved precessional magnetization dynamics. The intrinsic and non-local Gilbert damping in polycrystalline Ni films is also addressed by J Walowski et al [164016] using femtosecond laser pulses. Several spin-wave modes are observed and their dissipation is studied. Non-local damping by spin currents emitted into a non-magnetic metallic layer of either vanadium, palladium or dysprosium is studied. Dissipation in small magnetic Ni81Fe19 rings is studied using Brillouin light scattering microscopy by H Schultheiss et al [164017]. They investigate the spatial profiles and the decay constants of spin-wave quasi-eigenmodes. We hope that this cluster of papers will help to stimulate and advance a better understanding of this very interesting field of ultrafast magnetization processes.

Dynamical characteristics of an electromagnetic field under conditions of total reflection

NASA Astrophysics Data System (ADS)

Bekshaev, Aleksandr Ya

2018-04-01

The dynamical characteristics of electromagnetic fields include energy, momentum, angular momentum (spin) and helicity. We analyze their spatial distributions near the planar interface between two transparent and non-dispersive media, when the incident monochromatic plane wave with arbitrary polarization is totally reflected, and an evanescent wave is formed in the medium with lower optical density. Based on the recent arguments in favor of the Minkowski definition of the electromagnetic momentum in a material medium (Philbin 2011 Phys. Rev. A 83 013823; Philbin and Allanson 2012 86 055802; Bliokh et al 2017 Phys. Rev. Lett. 119 073901), we derive the explicit expressions for the dynamical characteristics in both media, with special attention to their behavior at the interface. In particular, the ‘extraordinary’ spin and momentum components orthogonal to the plane of incidence are described, and a canonical (spin-orbital) momentum decomposition is performed that contains no singular terms. The field energy, helicity, the spin momentum and orbital momentum components are everywhere regular but experience discontinuities at the interface; the spin components parallel to the interface appear to be continuous, which testifies to the consistency of the adopted Minkowski picture. The results supply a meaningful example of the electromagnetic momentum decomposition, with separation of spatial and polarization degrees of freedom, in inhomogeneous media, and can be used in engineering the structured fields designed for optical sorting, dispatching and micromanipulation.

Three-Dimensional Spin Texture in Hybrid Perovskites and Its Impact on Optical Transitions

DOE PAGES

Zhang, Xie; Shen, Jimmy -Xuan; Van de Walle, Chris G.

2018-05-15

Hybrid perovskites such as MAPbI 3 (MA = CH 3NH 3) exhibit a unique spin texture. The spin texture (as calculated within the Rashba model) has been suggested to be responsible for a suppression of radiative recombination due to a mismatch of spins at the band edges. Here we compute the spin texture from first principles and demonstrate that it does not suppress recombination. The exact spin texture is dominated by the inversion asymmetry of the local electrostatic potential, which is determined by the structural distortion induced by the MA molecule. In addition, the rotation of the MA molecule atmore » room temperature leads to a dynamic spin texture in MAPbI 3. Furthermore these insights call for a reconsideration of the scenario that radiative recombination is suppressed and provide an in-depth understanding of the origin of the spin texture in hybrid perovskites, which is crucial for designing spintronic devices.« less

Three-Dimensional Spin Texture in Hybrid Perovskites and Its Impact on Optical Transitions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Xie; Shen, Jimmy -Xuan; Van de Walle, Chris G.

Hybrid perovskites such as MAPbI 3 (MA = CH 3NH 3) exhibit a unique spin texture. The spin texture (as calculated within the Rashba model) has been suggested to be responsible for a suppression of radiative recombination due to a mismatch of spins at the band edges. Here we compute the spin texture from first principles and demonstrate that it does not suppress recombination. The exact spin texture is dominated by the inversion asymmetry of the local electrostatic potential, which is determined by the structural distortion induced by the MA molecule. In addition, the rotation of the MA molecule atmore » room temperature leads to a dynamic spin texture in MAPbI 3. Furthermore these insights call for a reconsideration of the scenario that radiative recombination is suppressed and provide an in-depth understanding of the origin of the spin texture in hybrid perovskites, which is crucial for designing spintronic devices.« less

Quantum dynamics of nuclear spins and spin relaxation in organic semiconductors

NASA Astrophysics Data System (ADS)

Mkhitaryan, V. V.; Dobrovitski, V. V.

2017-06-01

We investigate the role of the nuclear-spin quantum dynamics in hyperfine-induced spin relaxation of hopping carriers in organic semiconductors. The fast-hopping regime, when the carrier spin does not rotate much between subsequent hops, is typical for organic semiconductors possessing long spin coherence times. We consider this regime and focus on a carrier random-walk diffusion in one dimension, where the effect of the nuclear-spin dynamics is expected to be the strongest. Exact numerical simulations of spin systems with up to 25 nuclear spins are performed using the Suzuki-Trotter decomposition of the evolution operator. Larger nuclear-spin systems are modeled utilizing the spin-coherent state P -representation approach developed earlier. We find that the nuclear-spin dynamics strongly influences the carrier spin relaxation at long times. If the random walk is restricted to a small area, it leads to the quenching of carrier spin polarization at a nonzero value at long times. If the random walk is unrestricted, the carrier spin polarization acquires a long-time tail, decaying as 1 /√{t } . Based on the numerical results, we devise a simple formula describing the effect quantitatively.

Electrical detection of magnetization dynamics via spin rectification effects

NASA Astrophysics Data System (ADS)

Harder, Michael; Gui, Yongsheng; Hu, Can-Ming

2016-11-01

The purpose of this article is to review the current status of a frontier in dynamic spintronics and contemporary magnetism, in which much progress has been made in the past decade, based on the creation of a variety of micro and nanostructured devices that enable electrical detection of magnetization dynamics. The primary focus is on the physics of spin rectification effects, which are well suited for studying magnetization dynamics and spin transport in a variety of magnetic materials and spintronic devices. Intended to be intelligible to a broad audience, the paper begins with a pedagogical introduction, comparing the methods of electrical detection of charge and spin dynamics in semiconductors and magnetic materials respectively. After that it provides a comprehensive account of the theoretical study of both the angular dependence and line shape of electrically detected ferromagnetic resonance (FMR), which is summarized in a handbook format easy to be used for analysing experimental data. We then review and examine the similarity and differences of various spin rectification effects found in ferromagnetic films, magnetic bilayers and magnetic tunnel junctions, including a discussion of how to properly distinguish spin rectification from the spin pumping/inverse spin Hall effect generated voltage. After this we review the broad applications of rectification effects for studying spin waves, nonlinear dynamics, domain wall dynamics, spin current, and microwave imaging. We also discuss spin rectification in ferromagnetic semiconductors. The paper concludes with both historical and future perspectives, by summarizing and comparing three generations of FMR spectroscopy which have been developed for studying magnetization dynamics.

The indispensable role of the transversal spin fluctuations mechanism in laser-induced demagnetization of Co/Pt multilayers with nanoscale magnetic domains.

PubMed

Zhang, Wei; He, Wei; Peng, Li-Cong; Zhang, Ying; Cai, Jian-Wang; Evans, Richard F L; Zhang, Xiang-Qun; Cheng, Zhao-Hua

2018-07-06

The switching of magnetic domains induced by an ultrashort laser pulse has been demonstrated in nanostructured ferromagnetic films. This leads to the dawn of a new era in breaking the ultimate physical limit for the speed of magnetic switching and manipulation, which is relevant to current and future information storage. However, our understanding of the interactions between light and spins in magnetic heterostructures with nanoscale domain structures is still lacking. Here, both time-resolved magneto-optical Kerr effect experiments and atomistic simulations are carried out to investigate the dominant mechanism of laser-induced ultrafast demagnetization in [Co/Pt] 20 multilayers with nanoscale magnetic domains. It is found that the ultrafast demagnetization time remains constant with various magnetic configurations, indicating that the domain structures play a minor role in laser-induced ultrafast demagnetization. In addition, both in experiment and atomistic simulations, we find a dependence of ultrafast demagnetization time τ M on the laser fluence, which is in contrast to the observations of spin transport within magnetic domains. The remarkable agreement between experiment and atomistic simulations indicates that the local dissipation of spin angular momentum is the dominant demagnetization mechanism in this system. More interestingly, we made a comparison between the atomistic spin dynamic simulation and the longitudinal spin flip model, highlighting that the transversal spin fluctuations mechanism is responsible for the ultrafast demagnetization in the case of inhomogeneous magnetic structures. This is a significant advance in clarifying the microscopic mechanism underlying the process of ultrafast demagnetization in inhomogeneous magnetic structures.

Output-only cyclo-stationary linear-parameter time-varying stochastic subspace identification method for rotating machinery and spinning structures

NASA Astrophysics Data System (ADS)

Velazquez, Antonio; Swartz, R. Andrew

2015-02-01

Economical maintenance and operation are critical issues for rotating machinery and spinning structures containing blade elements, especially large slender dynamic beams (e.g., wind turbines). Structural health monitoring systems represent promising instruments to assure reliability and good performance from the dynamics of the mechanical systems. However, such devices have not been completely perfected for spinning structures. These sensing technologies are typically informed by both mechanistic models coupled with data-driven identification techniques in the time and/or frequency domain. Frequency response functions are popular but are difficult to realize autonomously for structures of higher order, especially when overlapping frequency content is present. Instead, time-domain techniques have shown to possess powerful advantages from a practical point of view (i.e. low-order computational effort suitable for real-time or embedded algorithms) and also are more suitable to differentiate closely-related modes. Customarily, time-varying effects are often neglected or dismissed to simplify this analysis, but such cannot be the case for sinusoidally loaded structures containing spinning multi-bodies. A more complex scenario is constituted when dealing with both periodic mechanisms responsible for the vibration shaft of the rotor-blade system and the interaction of the supporting substructure. Transformations of the cyclic effects on the vibrational data can be applied to isolate inertial quantities that are different from rotation-generated forces that are typically non-stationary in nature. After applying these transformations, structural identification can be carried out by stationary techniques via data-correlated eigensystem realizations. In this paper, an exploration of a periodic stationary or cyclo-stationary subspace identification technique is presented here for spinning multi-blade systems by means of a modified Eigensystem Realization Algorithm (ERA) via stochastic subspace identification (SSI) and linear parameter time-varying (LPTV) techniques. Structural response is assumed to be stationary ambient excitation produced by a Gaussian (white) noise within the operative range bandwidth of the machinery or structure in study. ERA-OKID analysis is driven by correlation-function matrices from the stationary ambient response aiming to reduce noise effects. Singular value decomposition (SVD) and eigenvalue analysis are computed in a last stage to identify frequencies and complex-valued mode shapes. Proposed assumptions are carefully weighted to account for the uncertainty of the environment. A numerical example is carried out based a spinning finite element (SFE) model, and verified using ANSYS® Ver. 12. Finally, comments and observations are provided on how this subspace realization technique can be extended to the problem of modal-parameter identification using only ambient vibration data.

Comparison of the Supercooled Spin Liquid States in the Pyrochlore Magnets Dy2Ti2O7 and Ho2Ti2O7

NASA Astrophysics Data System (ADS)

Eyal, Anna; Eyvazov, Azar B.; Dusad, Ritika; Munsie, Timothy J. S.; Luke, Graeme M.; Davis, J. C. Séamus

Despite a well-ordered crystal structure and strong magnetic interactions between the Dy or Ho ions, no long-range magnetic order has been detected in the pyrochlore titanates Ho2Ti2O7 and Dy2Ti2O7. The low temperature state in these materials is governed by spin-ice rules. These constrain the Ising like spins in the materials, yet does not result in a global broken symmetry state. To explore the actual magnetic phases, we simultaneously measure the time- and frequency-dependent magnetization dynamics of Dy2Ti2O7 and Ho2Ti2O7 using toroidal, boundary-free magnetization transport techniques. We demonstrate a distinctive behavior of the magnetic susceptibility of both compounds, that is indistinguishable in form from the permittivity of supercooled dipolar liquids. Moreover, we show that the microscopic magnetic relaxation times for both materials increase along a super-Arrhenius trajectory also characteristic of supercooled glass-forming liquids. Both materials therefore exhibit characteristics of a supercooled spin liquid. Strongly-correlated dynamics of loops of spins is suggested as a possible mechanism which could account for these findings. Potential connections to many-body spin localization will also be discussed.

Frequency swept microwaves for hyperfine decoupling and time domain dynamic nuclear polarization

PubMed Central

Hoff, Daniel E.M.; Albert, Brice J.; Saliba, Edward P.; Scott, Faith J.; Choi, Eric J.; Mardini, Michael; Barnes, Alexander B.

2015-01-01

Hyperfine decoupling and pulsed dynamic nuclear polarization (DNP) are promising techniques to improve high field DNP NMR. We explore experimental and theoretical considerations to implement them with magic angle spinning (MAS). Microwave field simulations using the high frequency structural simulator (HFSS) software suite are performed to characterize the inhomogeneous phase independent microwave field throughout a 198 GHz MAS DNP probe. Our calculations show that a microwave power input of 17 W is required to generate an average EPR nutation frequency of 0.84 MHz. We also present a detailed calculation of microwave heating from the HFSS parameters and find that 7.1% of the incident microwave power contributes to dielectric sample heating. Voltage tunable gyrotron oscillators are proposed as a class of frequency agile microwave sources to generate microwave frequency sweeps required for the frequency modulated cross effect, electron spin inversions, and hyperfine decoupling. Electron spin inversions of stable organic radicals are simulated with SPINEVOLUTION using the inhomogeneous microwave fields calculated by HFSS. We calculate an electron spin inversion efficiency of 56% at a spinning frequency of 5 kHz. Finally, we demonstrate gyrotron acceleration potentials required to generate swept microwave frequency profiles for the frequency modulated cross effect and electron spin inversions. PMID:26482131

Frequency swept microwaves for hyperfine decoupling and time domain dynamic nuclear polarization.

PubMed

Hoff, Daniel E M; Albert, Brice J; Saliba, Edward P; Scott, Faith J; Choi, Eric J; Mardini, Michael; Barnes, Alexander B

2015-11-01

Hyperfine decoupling and pulsed dynamic nuclear polarization (DNP) are promising techniques to improve high field DNP NMR. We explore experimental and theoretical considerations to implement them with magic angle spinning (MAS). Microwave field simulations using the high frequency structural simulator (HFSS) software suite are performed to characterize the inhomogeneous phase independent microwave field throughout a 198GHz MAS DNP probe. Our calculations show that a microwave power input of 17W is required to generate an average EPR nutation frequency of 0.84MHz. We also present a detailed calculation of microwave heating from the HFSS parameters and find that 7.1% of the incident microwave power contributes to dielectric sample heating. Voltage tunable gyrotron oscillators are proposed as a class of frequency agile microwave sources to generate microwave frequency sweeps required for the frequency modulated cross effect, electron spin inversions, and hyperfine decoupling. Electron spin inversions of stable organic radicals are simulated with SPINEVOLUTION using the inhomogeneous microwave fields calculated by HFSS. We calculate an electron spin inversion efficiency of 56% at a spinning frequency of 5kHz. Finally, we demonstrate gyrotron acceleration potentials required to generate swept microwave frequency profiles for the frequency modulated cross effect and electron spin inversions. Copyright © 2015 Elsevier Inc. All rights reserved.

Jump events in a 3D Edwards-Anderson spin glass

NASA Astrophysics Data System (ADS)

Mártin, Daniel A.; Iguain, José Luis

2017-11-01

The statistical properties of infrequent particle displacements, greater than a certain distance, are known as jump dynamics in the context of structural glass formers. We generalize the concept of a jump to the case of a spin glass, by dividing the system into small boxes, and considering the infrequent cooperative spin flips in each box. Jumps defined this way share similarities with jumps in structural glasses. We perform numerical simulations for the 3D Edwards-Anderson model, and study how the properties of these jumps depend on the waiting time after a quench. Similar to the results for structural glasses, we find that while jump frequency depends strongly on time, the jump duration and jump length are roughly stationary. At odds with some results reported on studies of structural glass formers, at long enough times, the rest time between jumps varies as the inverse of jump frequency. We give a possible explanation for this discrepancy. We also find that our results are qualitatively reproduced by a fully-connected trap model.

Role of Entropy and Structural Parameters in the Spin State Transition of LaCoO3

NASA Astrophysics Data System (ADS)

Chakrabarti, Bismayan; Birol, Turan; Haule, Kristjan

The spin state transition in LaCoO3 has eluded description for decades despite concerted theoretical and experimental effort. In this study, we approach this problem using fully charge consistent Density Functional Theory + Dynamical Mean Field Theory (DFT+DMFT). We show, from first principles, that LaCoO3 cannot be described by a single, pure spin state at any temperature, but instead shows a gradual change in the population of higher spin multiples as temperature is increased. We explicitly elucidate the critical role of the lattice expansion and oxygen octahedral rotations in the spin state transition. We also show that the spin state transition and the metal-insulator transition in the compound occur at different temperatures. In addition, our results shed light on the importance of electronic entropy, which has so far been ignored in all first principles studies of this material.

Immense Magnetic Response of Exciplex Light Emission due to Correlated Spin-Charge Dynamics

NASA Astrophysics Data System (ADS)

Wang, Yifei; Sahin-Tiras, Kevser; Harmon, Nicholas J.; Wohlgenannt, Markus; Flatté, Michael E.

2016-01-01

As carriers slowly move through a disordered energy landscape in organic semiconductors, tiny spatial variations in spin dynamics relieve spin blocking at transport bottlenecks or in the electron-hole recombination process that produces light. Large room-temperature magnetic-field effects (MFEs) ensue in the conductivity and luminescence. Sources of variable spin dynamics generate much larger MFEs if their spatial structure is correlated on the nanoscale with the energetic sites governing conductivity or luminescence such as in coevaporated organic blends within which the electron resides on one molecule and the hole on the other (an exciplex). Here, we show that exciplex recombination in blends exhibiting thermally activated delayed fluorescence produces MFEs in excess of 60% at room temperature. In addition, effects greater than 4000% can be achieved by tuning the device's current-voltage response curve by device conditioning. Both of these immense MFEs are the largest reported values for their device type at room temperature. Our theory traces this MFE and its unusual temperature dependence to changes in spin mixing between triplet exciplexes and light-emitting singlet exciplexes. In contrast, spin mixing of excitons is energetically suppressed, and thus spin mixing produces comparatively weaker MFEs in materials emitting light from excitons by affecting the precursor pairs. Demonstration of immense MFEs in common organic blends provides a flexible and inexpensive pathway towards magnetic functionality and field sensitivity in current organic devices without patterning the constituent materials on the nanoscale. Magnetic fields increase the power efficiency of unconditioned devices by 30% at room temperature, also showing that magnetic fields may increase the efficiency of the thermally activated delayed fluorescence process.

Immense Magnetic Response of Exciplex Light Emission due to Correlated Spin-Charge Dynamics

DOE PAGES

Wang, Yifei; Sahin-Tiras, Kevser; Harmon, Nicholas J.; ...

2016-02-05

As carriers slowly move through a disordered energy landscape in organic semiconductors, tiny spatial variations in spin dynamics relieve spin blocking at transport bottlenecks or in the electron-hole recombination process that produces light. Large room-temperature magnetic-field effects (MFEs) ensue in the conductivity and luminescence. Sources of variable spin dynamics generate much larger MFEs if their spatial structure is correlated on the nanoscale with the energetic sites governing conductivity or luminescence such as in coevaporated organic blends within which the electron resides on one molecule and the hole on the other (an exciplex). Here, we show that exciplex recombination in blendsmore » exhibiting thermally activated delayed fluorescence produces MFEs in excess of 60% at room temperature. In addition, effects greater than 4000% can be achieved by tuning the device’s current-voltage response curve by device conditioning. Both of these immense MFEs are the largest reported values for their device type at room temperature. Our theory traces this MFE and its unusual temperature dependence to changes in spin mixing between triplet exciplexes and light-emitting singlet exciplexes. In contrast, spin mixing of excitons is energetically suppressed, and thus spin mixing produces comparatively weaker MFEs in materials emitting light from excitons by affecting the precursor pairs. Demonstration of immense MFEs in common organic blends provides a flexible and inexpensive pathway towards magnetic functionality and field sensitivity in current organic devices without patterning the constituent materials on the nanoscale. In conclusion, magnetic fields increase the power efficiency of unconditioned devices by 30% at room temperature, also showing that magnetic fields may increase the efficiency of the thermally activated delayed fluorescence process.« less

Charge and spin in low-dimensional cuprates

NASA Astrophysics Data System (ADS)

Maekawa, Sadamichi; Tohyama, Takami

2001-03-01

One of the central issues in the study of high-temperature superconducting cuprates which are composed of two-dimensional (2D) CuO2 planes is whether the 2D systems with strong electron correlation behave as a Fermi liquid or a non-Fermi-liquid-like one-dimensional (1D) system with electron correlation. In this article, we start with the detailed examination of the electronic structure in cuprates and study theoretically the spin and charge dynamics in 1D and 2D cuprates. The theoretical background of spin-charge separation in the 1D model systems including the Hubbard and t-J models is presented. The first direct observation of collective modes of spin and charge excitations in a 1D cuprate, which are called spinons and holons respectively, in angle-resolved photoemission spectroscopy (ARPES) experiments is reviewed in the light of the theoretical results based on the numerically exact-diagonalization method. The charge and spin dynamics in 1D insulating cuprates is also discussed in connection with the spin-charge separation. The arguments are extended to the 2D cuprates, and the unique aspects of the electronic properties of high-temperature superconductors are discussed. Special emphasis is placed on the d-wave-like excitations in insulating 2D cuprates observed in ARPES experiments. We explain how the excitations are caused by the spin-charge separation. The charge stripes observed in the underdoped cuprates are examined in connection with spin-charge separation in real space.

Slow dynamics in the geometrically frustrated magnet ZnFe2O4: Universal features of aging phenomena in spin glasses

NASA Astrophysics Data System (ADS)

Mamiya, H.; Tsujii, N.; Terada, N.; Nimori, S.; Kitazawa, H.; Hoshikawa, A.; Ishigaki, T.

2014-07-01

To clarify the universal features of spin glasses, we carefully studied slow dynamics in a geometrically frustrated magnet ZnFe2O4 with slight disorders, regarded as an "unconventional" Heisenberg spin glass, using time-resolved neutron diffractometry and magnetometry. The results indicate that "aging" can be attributed not to growth of the short-range order detected by a diffuse scattering but to aging of a hidden aperiodic correlation, as expected from theories for spin glasses. Concerning aging, peculiar behavior was found; the decay of thermoremanent magnetization is extremely accelerated if the sample is heated/cooled briefly midway through the isothermal slow relaxation. Conversely, magnetization surprisingly increases despite the absence of a magnetic field when the temperature returns after the brief heating/cooling. The behavior can be explained as a destabilization of the aged spin configuration due to the thermal perturbations and subsequent spontaneous restoration of the original spin configuration after the destabilization. Whereas such destabilization and restoration do not occur during freezing into numerous metastable states in a fixed energy landscape, these are possible in an energy landscape with a temperature-sensitive funnel-like structure. These features, consistent with the ghost domain scenario of the droplet picture, are the same as for conventional Heisenberg spin glasses such as dilute magnetic alloys and dilute magnetic semiconductors. In other words, they are universal features in Heisenberg spin glasses including unconventional ones.

NMR contributions to structural dynamics studies of intrinsically disordered proteins☆

PubMed Central

Konrat, Robert

2014-01-01

Intrinsically disordered proteins (IDPs) are characterized by substantial conformational plasticity. Given their inherent structural flexibility X-ray crystallography is not applicable to study these proteins. In contrast, NMR spectroscopy offers unique opportunities for structural and dynamic studies of IDPs. The past two decades have witnessed significant development of NMR spectroscopy that couples advances in spin physics and chemistry with a broad range of applications. This article will summarize key advances in basic physical-chemistry and NMR methodology, outline their limitations and envision future R&D directions. PMID:24656082

Investigation of Local Structures in Cation-ordered Microwave Dielectric A Solid-state NMR and First Principle Calculation Study

NASA Astrophysics Data System (ADS)

Kalfarisi, Rony G.

Solid-state Nuclear Magnetic Resonance (ssNMR) spectroscopy has proven to be a powerful method to probe the local structure and dynamics of a system. In powdered solids, the nuclear spins experience various anisotropic interactions which depend on the molecular orientation. These anisotropic interactions make ssNMR very useful as they give a specific appearance to the resonance lines of the spectra. The position and shape of these resonance lines can be related to local structure and dynamics of the system under study. My research interest has focused around studying local structures and dynamics of quadrupolar nuclei in materials using ssNMR spectroscopy. 7Li and 93Nb ssNMR magic angle spinning (MAS) spectra, acquired at 17.6 and 7.06 T, have been used to evaluate the structural and dynamical properties of cation-ordered microwave dielectric materials. Microwave dielectric materials are essential in the application of wireless telecommunication, biomedical engineering, and other scientific and industrial implementations that use radio and microwave signals. The study of the local environment with respect to average structure, such as X-ray diffraction study, is essential for the better understanding of the correlations between structures and properties of these materials. The investigation for short and medium range can be performed with the use of ssNMR techniques. Even though XRD results show cationic ordering at the B-site (third coordination sphere), NMR spectra show a presence of disorder materials. This was indicated by the observation of a distribution in NMR parameters derived from experimental . {93}Nb NMR spectraand supported by theoretical calculations.

Dynamical time-reversal symmetry breaking and photo-induced chiral spin liquids in frustrated Mott insulators

DOE PAGES

Claassen, Martin; Jiang, Hong -Chen; Moritz, Brian; ...

2017-10-30

The search for quantum spin liquids in frustrated quantum magnets recently has enjoyed a surge of interest, with various candidate materials under intense scrutiny. However, an experimental confirmation of a gapped topological spin liquid remains an open question. Here, we show that circularly polarized light can provide a knob to drive frustrated Mott insulators into a chiral spin liquid, realizing an elusive quantum spin liquid with topological order. We find that the dynamics of a driven Kagome Mott insulator is well-captured by an effective Floquet spin model, with heating strongly suppressed, inducing a scalar spin chirality S i · (Smore » j × S k) term which dynamically breaks time-reversal while preserving SU(2) spin symmetry. We fingerprint the transient phase diagram and find a stable photo-induced chiral spin liquid near the equilibrium state. Furthermore, the results presented suggest employing dynamical symmetry breaking to engineer quantum spin liquids and access elusive phase transitions that are not readily accessible in equilibrium.« less

Higher-order spin and charge dynamics in a quantum dot-lead hybrid system.

PubMed

Otsuka, Tomohiro; Nakajima, Takashi; Delbecq, Matthieu R; Amaha, Shinichi; Yoneda, Jun; Takeda, Kenta; Allison, Giles; Stano, Peter; Noiri, Akito; Ito, Takumi; Loss, Daniel; Ludwig, Arne; Wieck, Andreas D; Tarucha, Seigo

2017-09-22

Understanding the dynamics of open quantum systems is important and challenging in basic physics and applications for quantum devices and quantum computing. Semiconductor quantum dots offer a good platform to explore the physics of open quantum systems because we can tune parameters including the coupling to the environment or leads. Here, we apply the fast single-shot measurement techniques from spin qubit experiments to explore the spin and charge dynamics due to tunnel coupling to a lead in a quantum dot-lead hybrid system. We experimentally observe both spin and charge time evolution via first- and second-order tunneling processes, and reveal the dynamics of the spin-flip through the intermediate state. These results enable and stimulate the exploration of spin dynamics in dot-lead hybrid systems, and may offer useful resources for spin manipulation and simulation of open quantum systems.

[Hyperfine structure analysis in magnetic resonance spectroscopy: from astrophysical measurements towards endogenous biosensors in human tissue].

PubMed

Schröder, Leif

2007-01-01

The hyperfine interaction of two spins is a well studied effect in atomic systems. Magnetic resonance experiments demonstrate that the detectable dipole transitions are determined by the magnetic moments of the constituents and the external magnetic field. Transferring the corresponding quantum mechanics to molecular bound nuclear spins allows for precise prediction of NMR spectra obtained from metabolites in human tissue. This molecular hyperfine structure has been neglected so far in in vivo NMR spectroscopy but contains useful information, especially when studying molecular dynamics. This contribution represents a review of the concept of applying the Breit-Rabi formalism to coupled nuclear spins and discusses the immobilization of different metabolites in anisotropic tissue revealed by 1H NMR spectra of carnosine, phosphocreatine and taurine. Comparison of atomic and molecular spin systems allows for statements on the biological constraints for direct spin-spin interactions. Moreover, the relevance of hyperfine effects on the line shapes of multiplets of indirectly-coupled spin systems with more than two constituents can be predicted by analyzing quantum mechanical parameters. As an example, the superposition of eigenstates of the A MX system of adenosine 5'-triphosphate and its application for better quantification of 31P-NMR spectra will be discussed.

Resonant Spin-Transfer-Torque Nano-Oscillators

NASA Astrophysics Data System (ADS)

Sharma, Abhishek; Tulapurkar, Ashwin A.; Muralidharan, Bhaskaran

2017-12-01

Spin-transfer-torque nano-oscillators are potential candidates for replacing the traditional inductor-based voltage-controlled oscillators in modern communication devices. Typical oscillator designs are based on trilayer magnetic tunnel junctions, which have the disadvantages of low power outputs and poor conversion efficiencies. We theoretically propose using resonant spin filtering in pentalayer magnetic tunnel junctions as a possible route to alleviate these issues and present viable device designs geared toward a high microwave output power and an efficient conversion of the dc input power. We attribute these robust qualities to the resulting nontrivial spin-current profiles and the ultrahigh tunnel magnetoresistance, both of which arise from resonant spin filtering. The device designs are based on the nonequilibrium Green's-function spin-transport formalism self-consistently coupled with the stochastic Landau-Lifshitz-Gilbert-Slonczewski equation and Poisson's equation. We demonstrate that the proposed structures facilitate oscillator designs featuring a large enhancement in microwave power of around 1150% and an efficiency enhancement of over 1100% compared to typical trilayer designs. We rationalize the optimum operating regions via an analysis of the dynamic and static device resistances. We also demonstrate the robustness of our structures against device design fluctuations and elastic dephasing. This work sets the stage for pentalyer spin-transfer-torque nano-oscillator device designs that ameliorate major issues associated with typical trilayer designs.

Hyperpolarization of Frozen Hydrocarbon Gases by Dynamic Nuclear Polarization at 1.2 K.

PubMed

Vuichoud, Basile; Canet, Estel; Milani, Jonas; Bornet, Aurélien; Baudouin, David; Veyre, Laurent; Gajan, David; Emsley, Lyndon; Lesage, Anne; Copéret, Christophe; Thieuleux, Chloé; Bodenhausen, Geoffrey; Koptyug, Igor; Jannin, Sami

2016-08-18

We report a simple and general method for the hyperpolarization of condensed gases by dynamic nuclear polarization (DNP). The gases are adsorbed in the pores of structured mesoporous silica matrices known as HYPSOs (HYper Polarizing SOlids) that have paramagnetic polarizing agents covalently bound to the surface of the mesopores. DNP is performed at low temperatures and moderate magnetic fields (T = 1.2 K and B0 = 6.7 T). Frequency-modulated microwave irradiation is applied close to the electron spin resonance frequency (f = 188.3 GHz), and the electron spin polarization of the polarizing agents of HYPSO is transferred to the nuclear spins of the frozen gas. A proton polarization as high as P((1)H) = 70% can be obtained, which can be subsequently transferred to (13)C in natural abundance by cross-polarization, yielding up to P((13)C) = 27% for ethylene.

Glitches as probes of neutron star internal structure and dynamics: Effects of the superfluid-superconducting core

NASA Astrophysics Data System (ADS)

Gügercinoğlu, Erbil

2017-12-01

Glitches, sudden spin-up of pulsars with subsequent recovery, provide us with a unique opportunity to investigate various physical processes, including the crust-core coupling, distribution of reservoir angular momentum within different internal layers, spin-up in neutral and charged superfluids and constraining the equation of state of the neutron star (NS) matter. In this work, depending on the dynamic interaction between the vortex lines and the nuclei in the inner crust, and between the vortex lines and the magnetic flux tubes in the outer core, various types of relaxation behavior are obtained and confronted with the observations. It is shown that the glitches have strong potential to deduce information about the cooling behavior and interior magnetic field configuration of NSs. Some implications of the relative importance of the external spin-down torques and the superfluid internal torques for recently observed unusual glitches are also discussed.

The dynamics and optimal control of spinning spacecraft with movable telescoping appendages. Part C: Effect of flexibility during boom deployment

NASA Technical Reports Server (NTRS)

Bainum, P. M.; James, P. K.

1977-01-01

The dynamics of a spinning symmetrical spacecraft system during the deployment (or retraction) of flexible boom-type appendages were investigated. The effect of flexibility during boom deployment is treated by modelling the deployable members as compound spherical pendula of varying length (according to a control law). The orientation of the flexible booms with respect to the hub, is described by a sequence of two Euler angles. The boom members contain a flexural stiffness which can be related to an assumed effective restoring linear spring constant, and structural damping which effects the entire system. Linearized equations of motion for this system, when the boom length is constant, involve periodic coefficients with the frequency of the hub spin. A bounded transformation is found which converts this system into a kinematically equivalent one involving only constant coefficients.

Neutron scattering investigations of frustated magnets

NASA Astrophysics Data System (ADS)

Fennell, Tom

This thesis describes the experimental investigation of frustrated magnetic systems based on the pyrochlore lattice of corner-sharing tetrahedra. Ho2Ti207 and Dy2Ti207 are examples of spin ices, in which the manifold of disordered magnetic groundstates maps onto that of the proton positions in ice. Using single crystal neutron scattering to measure Bragg and diffuse scattering, the effect of applying magnetic fields along different directions in the crystal was investigated. Different schemes of degeneracy removal were observed for different directions. Long and short range order, and the coexistence of both could be observed by this technique.The field and temperature dependence of magnetic ordering was studied in Ho2Ti207 and Dy2Ti207. Ho2Ti2()7 has been more extensively investigated. The field was applied on [00l], [hh0], [hhh] and [hh2h]. Dy2Ti207 was studied with the field applied on [00l] and [hho] but more detailed information about the evolution of the scattering pattern across a large area of reciprocal space was obtained.With the field applied on [00l] both materials showed complete degeneracy removal. A long range ordered structure was formed. Any magnetic diffuse scattering vanished and was entirely replaced by strong magnetic Bragg scattering. At T =0.05 K both materials show unusual magnetization curves, with a prominent step and hysteresis. This was attributed to the extremely slow dynamics of spin ice materials at this temperature.Both materials were studied in greatest detail with the field applied on [hh0]. The coexistence of long and short range order was observed when the field was raised at T = 0.05 K. The application of a field in this direction separated the spin system into two populations. One could be ordered by the field, and one remained disordered. However, via spin-spin interactions, the field restricted the degeneracy of the disordered spin population. The neutron scattering pattern of Dy2Ti207 shows that the spin system was separated into two populations of spin chains, one set ordered and the other only partly so. Cycling the field induced dynamics in these chains, again via spin-spin interactions, as the field acted on the ordered si)in chains. These field regulated dynamics were particularly noted in Ho2Ti207 where a full field cycle was executed. Raising the temperature in an applied field also activated the dynamics of the partially ordered spin chains. The continued evolution of the spin system toward a more ordered state, when dynamics can be induced, suggested that a spin ice does indeed have an energetic groundstate.The remaining two directions probed in Ho2Ti20y both have two populations of spins with different Zeeman energies. The competition of the field and the spin- spin interactions was used to investigate the onset of the ice rules regime (field on [hh2h] and the breaking of the ice rules by a strong field (field on [hhh]). It was shown that the behavior of Ho2Ti207 with field on [hhh] was consistent with the "kagome ice" hypothesis.

Tunable two-dimensional arrays of single Rydberg atoms for realizing quantum Ising models

NASA Astrophysics Data System (ADS)

Labuhn, Henning; Barredo, Daniel; Ravets, Sylvain; de Léséleuc, Sylvain; Macrì, Tommaso; Lahaye, Thierry; Browaeys, Antoine

2016-06-01

Spin models are the prime example of simplified many-body Hamiltonians used to model complex, strongly correlated real-world materials. However, despite the simplified character of such models, their dynamics often cannot be simulated exactly on classical computers when the number of particles exceeds a few tens. For this reason, quantum simulation of spin Hamiltonians using the tools of atomic and molecular physics has become a very active field over the past years, using ultracold atoms or molecules in optical lattices, or trapped ions. All of these approaches have their own strengths and limitations. Here we report an alternative platform for the study of spin systems, using individual atoms trapped in tunable two-dimensional arrays of optical microtraps with arbitrary geometries, where filling fractions range from 60 to 100 per cent. When excited to high-energy Rydberg D states, the atoms undergo strong interactions whose anisotropic character opens the way to simulating exotic matter. We illustrate the versatility of our system by studying the dynamics of a quantum Ising-like spin-1/2 system in a transverse field with up to 30 spins, for a variety of geometries in one and two dimensions, and for a wide range of interaction strengths. For geometries where the anisotropy is expected to have small effects on the dynamics, we find excellent agreement with ab initio simulations of the spin-1/2 system, while for strongly anisotropic situations the multilevel structure of the D states has a measurable influence. Our findings establish arrays of single Rydberg atoms as a versatile platform for the study of quantum magnetism.

Spin dynamics of qqq wave function on light front in high momentum limit of QCD: Role of qqq force

NASA Astrophysics Data System (ADS)

Mitra, A. N.

2008-04-01

The contribution of a spin-rich qqq force (in conjunction with pairwise qq forces) to the analytical structure of the qqq wave function is worked out in the high momentum regime of QCD where the confining interaction may be ignored, so that the dominant effect is Coulombic. A distinctive feature of this study is that the spin-rich qqq force is generated by a ggg vertex (a genuine part of the QCD Lagrangian) wherein the 3 radiating gluon lines end on as many quark lines, giving rise to a (Mercedes-Benz type) Y-shaped diagram. The dynamics is that of a Salpeter-like equation (3D support for the kernel) formulated covariantly on the light front, a la Markov-Yukawa Transversality Principle (MYTP) which warrants a 2-way interconnection between the 3D and 4D Bethe-Salpeter (BSE) forms for 2 as well as 3 fermion quarks. With these ingredients, the differential equation for the 3D wave function ϕ receives well-defined contributions from the qq and qqq forces. In particular a negative eigenvalue of the spin operator iσ1 · σ2 × σ3 which is an integral part of the qqq force, causes a characteristic singularity in the differential equation, signalling the dynamical effect of a spin-rich qqq force not yet considered in the literature. The potentially crucial role of this interesting effect vis-a-vis the so-called 'spin anomaly' of the proton, is a subject of considerable physical interest.

Stochastic formation of magnetic vortex structures in asymmetric disks triggered by chaotic dynamics

DOE PAGES

Im, Mi-Young; Lee, Ki-Suk; Vogel, Andreas; ...

2014-12-17

The non-trivial spin configuration in a magnetic vortex is a prototype for fundamental studies of nanoscale spin behaviour with potential applications in magnetic information technologies. Arrays of magnetic vortices interfacing with perpendicular thin films have recently been proposed as enabler for skyrmionic structures at room temperature, which has opened exciting perspectives on practical applications of skyrmions. An important milestone for achieving not only such skyrmion materials but also general applications of magnetic vortices is a reliable control of vortex structures. However, controlling magnetic processes is hampered by stochastic behaviour, which is associated with thermal fluctuations in general. Here we showmore » that the dynamics in the initial stages of vortex formation on an ultrafast timescale plays a dominating role for the stochastic behaviour observed at steady state. Our results show that the intrinsic stochastic nature of vortex creation can be controlled by adjusting the interdisk distance in asymmetric disk arrays.« less

Dynamical multiferroicity

NASA Astrophysics Data System (ADS)

Juraschek, Dominik M.; Fechner, Michael; Balatsky, Alexander V.; Spaldin, Nicola A.

2017-06-01

An appealing mechanism for inducing multiferroicity in materials is the generation of electric polarization by a spatially varying magnetization that is coupled to the lattice through the spin-orbit interaction. Here we describe the reciprocal effect, in which a time-dependent electric polarization induces magnetization even in materials with no existing spin structure. We develop a formalism for this dynamical multiferroic effect in the case for which the polarization derives from optical phonons, and compute the strength of the phonon Zeeman effect, which is the solid-state equivalent of the well-established vibrational Zeeman effect in molecules, using density functional theory. We further show that a recently observed behavior—the resonant excitation of a magnon by optically driven phonons—is described by the formalism. Finally, we discuss examples of scenarios that are not driven by lattice dynamics and interpret the excitation of Dzyaloshinskii-Moriya-type electromagnons and the inverse Faraday effect from the viewpoint of dynamical multiferroicity.

Asymmetric and Stochastic Behavior in Magnetic Vortices Studied by Soft X-ray Microscopy

NASA Astrophysics Data System (ADS)

Im, Mi-Young

Asymmetry and stochasticity in spin processes are not only long-standing fundamental issues but also highly relevant to technological applications of nanomagnetic structures to memory and storage nanodevices. Those nontrivial phenomena have been studied by direct imaging of spin structures in magnetic vortices utilizing magnetic transmission soft x-ray microscopy (BL6.1.2 at ALS). Magnetic vortices have attracted enormous scientific interests due to their fascinating spin structures consisting of circularity rotating clockwise (c = + 1) or counter-clockwise (c = -1) and polarity pointing either up (p = + 1) or down (p = -1). We observed a symmetry breaking in the formation process of vortex structures in circular permalloy (Ni80Fe20) disks. The generation rates of two different vortex groups with the signature of cp = + 1 and cp =-1 are completely asymmetric. The asymmetric nature was interpreted to be triggered by ``intrinsic'' Dzyaloshinskii-Moriya interaction (DMI) arising from the spin-orbit coupling due to the lack of inversion symmetry near the disk surface and ``extrinsic'' factors such as roughness and defects. We also investigated the stochastic behavior of vortex creation in the arrays of asymmetric disks. The stochasticity was found to be very sensitive to the geometry of disk arrays, particularly interdisk distance. The experimentally observed phenomenon couldn't be explained by thermal fluctuation effect, which has been considered as a main reason for the stochastic behavior in spin processes. We demonstrated for the first time that the ultrafast dynamics at the early stage of vortex creation, which has a character of classical chaos significantly affects the stochastic nature observed at the steady state in asymmetric disks. This work provided the new perspective of dynamics as a critical factor contributing to the stochasticity in spin processes and also the possibility for the control of the intrinsic stochastic nature by optimizing the design of asymmetric disk arrays. This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, by Leading Foreign Research Institute Recruitment Program through the NRF.

Spin Dynamics in Novel Materials Systems

NASA Astrophysics Data System (ADS)

Yu, Howard

Spintronics and organic electronics are fields that have made considerable advances in recent years, both in fundamental research and in applications. Organic materials have a number of attractive properties that enable them to complement applications traditionally fulfilled by inorganic materials, while spintronics seeks to take advantage of the spin degree of freedom to produce new applications. My research is aimed at combining these two fields to develop organic materials for spintronics use. My thesis is divided into three primary projects centered around an organic-based semiconducting ferrimagnet, vanadium tetracyanoethylene. First, we investigated the transport characteristics of a hybrid organic-inorganic heterostructure. Semiconductors form the basis of the electronics industry, and there has been considerable effort put forward to develop organic semiconductors for applications like organic light-emitting diodes and organic thin film transistors. Working with hybrid organic-inorganic semiconductor device structures allows us to potentially take advantage of the infrastructure that has already been developed for silicon and other inorganic semiconductors. This could potentially pave the way for a new class of active hybrid devices with multifunctional behavior. Second, we investigated the magnetic resonance characteristics of V[TCNE]x, in multiple measurement schemes and exploring the effect of temperature, frequency, and chemical tuning. Recently, the spintronics community has shifted focus from static electrical spin injection to various dynamic processes, such as spin pumping and thermal effects. Spin pumping in particular is an intriguing way to generate pure spin currents via magnetic resonance that has attracted a high degree of interest, with the FMR linewidth being an important metric for spin injection. Furthermore, we can potentially use these measurements to probe the magnetic properties as we change the physical properties of the materials by chemically tuning the organic ligand. We are therefore interested in exploring the resonance properties of this materials system to lay the groundwork for future spin pumping applications. Third, we have made preliminary measurements of spin pumping in hybrid and all-organic bilayer structures. As mentioned above, FMR-driven spin pumping is method for generating pure spin currents with no associated charge motion. This can be detected in a number of ways, one of which is monitoring the FMR characteristics of two ferromagnets in close contact, where spins injected from one magnet into the other changes the linewidth. In conjunction with the magnetic resonance measurements, we have started to investigate the FMR properties of these bilayer systems.

Longitudinal spin dynamics in nickel fluorosilicate

NASA Astrophysics Data System (ADS)

Galkina, E. G.; Ivanov, B. A.; Butrim, V. I.

2014-07-01

The presence of single-ion anisotropy leads to the appearance of the effect of quantum spin reduction. As a consequence, purely longitudinal magnetization dynamics arises, which involves coupled oscillations of the mean spin modulus and the quadrupole mean values constructed on spin operators. In nickel fluorosilicate, the effect of quantum spin reduction may be controlled by changing pressure. The study of nonlinear longitudinal spin dynamics and the analysis of possible photomagnetic effects showed that this compound is a convenient model system to implement switching of the magnetization direction by femtosecond laser pulses.

First-principles approach to the dynamic magnetoelectric couplings for the non-reciprocal directional dichroism in BiFeO 3

DOE PAGES

Kezsmarki, I.; Fishman, Randy Scott

2016-04-18

Due to the complicated magnetic and crystallographic structures of BiFeO 3, its magnetoelectric (ME) couplings and microscopic model Hamiltonian remain poorly understood. By employing a firstprinciples approach, we uncover all possibleMEcouplings associated with the spin-current (SC) and exchange-striction (ES) polarizations, and construct an appropriate Hamiltonian for the long-range spin-cycloid in BiFeO 3. First-principles calculations are used to understand the microscopic origins of theMEcouplings.Wefind that inversion symmetries broken by ferroelectric and antiferroelectric distortions induce the SC and the ES polarizations, which cooperatively produce the dynamicME effects in BiFeO 3. A model motivated by first principles reproduces the absorption difference of counter-propagatingmore » light beams called non-reciprocal directional dichroism. The current paper focuses on the spin-driven (SD) polarizations produced by a dynamic electric field, i.e. the dynamic MEcouplings. Due to the inertial properties of Fe, the dynamic SD polarizations differ significantly from the static SD polarizations. Our systematic approach can be generally applied to any multiferroic material, laying the foundation for revealing hiddenMEcouplings on the atomic scale and for exploiting opticalMEeffects in the next generation of technological devices such as optical diodes.« less

Transverse spin structure of the nucleon from lattice-QCD simulations.

PubMed

Göckeler, M; Hägler, Ph; Horsley, R; Nakamura, Y; Pleiter, D; Rakow, P E L; Schäfer, A; Schierholz, G; Stüben, H; Zanotti, J M

2007-06-01

We present the first calculation in lattice QCD of the lowest two moments of transverse spin densities of quarks in the nucleon. They encode correlations between quark spin and orbital angular momentum. Our dynamical simulations are based on two flavors of clover-improved Wilson fermions and Wilson gluons. We find significant contributions from certain quark helicity flip generalized parton distributions, leading to strongly distorted densities of transversely polarized quarks in the nucleon. In particular, based on our results and recent arguments by Burkardt [Phys. Rev. D 72, 094020 (2005)], we predict that the Boer-Mulders function h(1/1), describing correlations of transverse quark spin and intrinsic transverse momentum of quarks, is large and negative for both up and down quarks.

Quasiclassical Theory of Spin Dynamics in Superfluid ^3He: Kinetic Equations in the Bulk and Spin Response of Surface Majorana States

NASA Astrophysics Data System (ADS)

Silaev, M. A.

2018-06-01

We develop a theory based on the formalism of quasiclassical Green's functions to study the spin dynamics in superfluid ^3He. First, we derive kinetic equations for the spin-dependent distribution function in the bulk superfluid reproducing the results obtained earlier without quasiclassical approximation. Then, we consider spin dynamics near the surface of fully gapped ^3He-B-phase taking into account spin relaxation due to the transitions in the spectrum of localized fermionic states. The lifetimes of longitudinal and transverse spin waves are calculated taking into account the Fermi-liquid corrections which lead to a crucial modification of fermionic spectrum and spin responses.

Preserving electron spin coherence in solids by optimal dynamical decoupling.

PubMed

Du, Jiangfeng; Rong, Xing; Zhao, Nan; Wang, Ya; Yang, Jiahui; Liu, R B

2009-10-29

To exploit the quantum coherence of electron spins in solids in future technologies such as quantum computing, it is first vital to overcome the problem of spin decoherence due to their coupling to the noisy environment. Dynamical decoupling, which uses stroboscopic spin flips to give an average coupling to the environment that is effectively zero, is a particularly promising strategy for combating decoherence because it can be naturally integrated with other desired functionalities, such as quantum gates. Errors are inevitably introduced in each spin flip, so it is desirable to minimize the number of control pulses used to realize dynamical decoupling having a given level of precision. Such optimal dynamical decoupling sequences have recently been explored. The experimental realization of optimal dynamical decoupling in solid-state systems, however, remains elusive. Here we use pulsed electron paramagnetic resonance to demonstrate experimentally optimal dynamical decoupling for preserving electron spin coherence in irradiated malonic acid crystals at temperatures from 50 K to room temperature. Using a seven-pulse optimal dynamical decoupling sequence, we prolonged the spin coherence time to about 30 mus; it would otherwise be about 0.04 mus without control or 6.2 mus under one-pulse control. By comparing experiments with microscopic theories, we have identified the relevant electron spin decoherence mechanisms in the solid. Optimal dynamical decoupling may be applied to other solid-state systems, such as diamonds with nitrogen-vacancy centres, and so lay the foundation for quantum coherence control of spins in solids at room temperature.

Disparate ultrafast dynamics of itinerant and localized magnetic moments in gadolinium metal

PubMed Central

Frietsch, B.; Bowlan, J.; Carley, R.; Teichmann, M.; Wienholdt, S.; Hinzke, D.; Nowak, U.; Carva, K.; Oppeneer, P. M.; Weinelt, M.

2015-01-01

The Heisenberg–Dirac intra-atomic exchange coupling is responsible for the formation of the atomic spin moment and thus the strongest interaction in magnetism. Therefore, it is generally assumed that intra-atomic exchange leads to a quasi-instantaneous aligning process in the magnetic moment dynamics of spins in separate, on-site atomic orbitals. Following ultrashort optical excitation of gadolinium metal, we concurrently record in photoemission the 4f magnetic linear dichroism and 5d exchange splitting. Their dynamics differ by one order of magnitude, with decay constants of 14 versus 0.8 ps, respectively. Spin dynamics simulations based on an orbital-resolved Heisenberg Hamiltonian combined with first-principles calculations explain the particular dynamics of 5d and 4f spin moments well, and corroborate that the 5d exchange splitting traces closely the 5d spin-moment dynamics. Thus gadolinium shows disparate dynamics of the localized 4f and the itinerant 5d spin moments, demonstrating a breakdown of their intra-atomic exchange alignment on a picosecond timescale. PMID:26355196

Tracking protein dynamics with photoconvertible Dendra2 on spinning disk confocal systems.

PubMed

Woods, Elena; Courtney, Jane; Scholz, Dimitri; Hall, William W; Gautier, Virginie W

2014-12-01

Understanding the dynamic properties of cellular proteins in live cells and in real time is essential to delineate their function. In this context, we introduce the Fluorescence Recovery After Photobleaching-Photoactivation unit (Andor) combined with the Nikon Eclipse Ti E Spinning Disk (Andor) confocal microscope as an advantageous and robust platform to exploit the properties of the Dendra2 photoconvertible fluorescent protein (Evrogen) and analyse protein subcellular trafficking in living cells. A major advantage of the spinning disk confocal is the rapid acquisition speed, enabling high temporal resolution of cellular processes. Furthermore, photoconversion and imaging are less invasive on the spinning disk confocal as the cell exposition to illumination power is reduced, thereby minimizing photobleaching and increasing cell viability. We have tested this commercially available platform using experimental settings adapted to track the migration of fast trafficking proteins such as UBC9, Fibrillarin and have successfully characterized their differential motion between subnuclear structures. We describe here step-by-step procedures, with emphasis on cellular imaging parameters, to successfully perform the dynamic imaging and photoconversion of Dendra2-fused proteins at high spatial and temporal resolutions necessary to characterize the trafficking pathways of proteins. © 2014 The Authors. Journal of Microscopy published by John Wiley & Sons, Ltd on behalf of Royal Microscopical Society.

Generalized GW+Boltzmann Approach for the Description of Ultrafast Electron Dynamics in Topological Insulators.

PubMed

Battiato, Marco; Aguilera, Irene; Sánchez-Barriga, Jaime

2017-07-17

Quantum-phase transitions between trivial insulators and topological insulators differ from ordinary metal-insulator transitions in that they arise from the inversion of the bulk band structure due to strong spin-orbit coupling. Such topological phase transitions are unique in nature as they lead to the emergence of topological surface states which are characterized by a peculiar spin texture that is believed to play a central role in the generation and manipulation of dissipationless surface spin currents on ultrafast timescales. Here, we provide a generalized G W +Boltzmann approach for the description of ultrafast dynamics in topological insulators driven by electron-electron and electron-phonon scatterings. Taking the prototypical insulator Bi 2 Te 3 as an example, we test the robustness of our approach by comparing the theoretical prediction to results of time- and angle-resolved photoemission experiments. From this comparison, we are able to demonstrate the crucial role of the excited spin texture in the subpicosecond relaxation of transient electrons, as well as to accurately obtain the magnitude and strength of electron-electron and electron-phonon couplings. Our approach could be used as a generalized theory for three-dimensional topological insulators in the bulk-conducting transport regime, paving the way for the realization of a unified theory of ultrafast dynamics in topological materials.

Femtosecond optical reflectivity measurements of lattice-mediated spin repulsions in photoexcited LaCoO3 thin films

NASA Astrophysics Data System (ADS)

Bielecki, J.; Rata, A. D.; Börjesson, L.

2014-01-01

We present results on the temperature dependence of ultrafast electron and lattice dynamics, measured with pump-probe transient reflectivity experiments, of an epitaxially grown LaCoO3 thin film under tensile strain. Probing spin-polarized transitions into the antibonding eg band provides a measure of the low-spin fraction, both as a function of temperature and time after photoexcitation. It is observed that femtosecond laser pulses destabilize the constant low-spin fraction (˜63%-64%) in equilibrium into a thermally activated state, driven by a subpicosecond change in spin gap Δ. From the time evolution of the low-spin fraction, it is possible to disentangle the thermal and lattice contributions to the spin state. A lattice mediated spin repulsion, identified as the governing factor determining the equilibrium spin state in thin-film LaCoO3, is observed. These results suggests that time-resolved spectroscopy is a sensitive probe of the spin state in LaCoO3 thin films, with the potential to bring forward quantitative insight into the complicated interplay between structure and spin state in LaCoO3.

Nonlocal Polarization Feedback in a Fractional Quantum Hall Ferromagnet.

PubMed

Hennel, Szymon; Braem, Beat A; Baer, Stephan; Tiemann, Lars; Sohi, Pirouz; Wehrli, Dominik; Hofmann, Andrea; Reichl, Christian; Wegscheider, Werner; Rössler, Clemens; Ihn, Thomas; Ensslin, Klaus; Rudner, Mark S; Rosenow, Bernd

2016-04-01

In a quantum Hall ferromagnet, the spin polarization of the two-dimensional electron system can be dynamically transferred to nuclear spins in its vicinity through the hyperfine interaction. The resulting nuclear field typically acts back locally, modifying the local electronic Zeeman energy. Here we report a nonlocal effect arising from the interplay between nuclear polarization and the spatial structure of electronic domains in a ν=2/3 fractional quantum Hall state. In our experiments, we use a quantum point contact to locally control and probe the domain structure of different spin configurations emerging at the spin phase transition. Feedback between nuclear and electronic degrees of freedom gives rise to memristive behavior, where electronic transport through the quantum point contact depends on the history of current flow. We propose a model for this effect which suggests a novel route to studying edge states in fractional quantum Hall systems and may account for so-far unexplained oscillatory electronic-transport features observed in previous studies.

Spin Hall effects

NASA Astrophysics Data System (ADS)

Sinova, Jairo; Valenzuela, Sergio O.; Wunderlich, J.; Back, C. H.; Jungwirth, T.

2015-10-01

Spin Hall effects are a collection of relativistic spin-orbit coupling phenomena in which electrical currents can generate transverse spin currents and vice versa. Despite being observed only a decade ago, these effects are already ubiquitous within spintronics, as standard spin-current generators and detectors. Here the theoretical and experimental results that have established this subfield of spintronics are reviewed. The focus is on the results that have converged to give us the current understanding of the phenomena, which has evolved from a qualitative to a more quantitative measurement of spin currents and their associated spin accumulation. Within the experimental framework, optical-, transport-, and magnetization-dynamics-based measurements are reviewed and linked to both phenomenological and microscopic theories of the effect. Within the theoretical framework, the basic mechanisms in both the extrinsic and intrinsic regimes are reviewed, which are linked to the mechanisms present in their closely related phenomenon in ferromagnets, the anomalous Hall effect. Also reviewed is the connection to the phenomenological treatment based on spin-diffusion equations applicable to certain regimes, as well as the spin-pumping theory of spin generation used in many measurements of the spin Hall angle. A further connection to the spin-current-generating spin Hall effect to the inverse spin galvanic effect is given, in which an electrical current induces a nonequilibrium spin polarization. This effect often accompanies the spin Hall effect since they share common microscopic origins. Both can exhibit the same symmetries when present in structures comprising ferromagnetic and nonmagnetic layers through their induced current-driven spin torques or induced voltages. Although a short chronological overview of the evolution of the spin Hall effect field and the resolution of some early controversies is given, the main body of this review is structured from a pedagogical point of view, focusing on well-established and accepted physics. In such a young field, there remains much to be understood and explored, hence some of the future challenges and opportunities of this rapidly evolving area of spintronics are outlined.

Ising model with conserved magnetization on the human connectome: Implications on the relation structure-function in wakefulness and anesthesia

NASA Astrophysics Data System (ADS)

Stramaglia, S.; Pellicoro, M.; Angelini, L.; Amico, E.; Aerts, H.; Cortés, J. M.; Laureys, S.; Marinazzo, D.

2017-04-01

Dynamical models implemented on the large scale architecture of the human brain may shed light on how a function arises from the underlying structure. This is the case notably for simple abstract models, such as the Ising model. We compare the spin correlations of the Ising model and the empirical functional brain correlations, both at the single link level and at the modular level, and show that their match increases at the modular level in anesthesia, in line with recent results and theories. Moreover, we show that at the peak of the specific heat (the critical state), the spin correlations are minimally shaped by the underlying structural network, explaining how the best match between the structure and function is obtained at the onset of criticality, as previously observed. These findings confirm that brain dynamics under anesthesia shows a departure from criticality and could open the way to novel perspectives when the conserved magnetization is interpreted in terms of a homeostatic principle imposed to neural activity.

A New Method for Determining Structure Ensemble: Application to a RNA Binding Di-Domain Protein.

PubMed

Liu, Wei; Zhang, Jingfeng; Fan, Jing-Song; Tria, Giancarlo; Grüber, Gerhard; Yang, Daiwen

2016-05-10

Structure ensemble determination is the basis of understanding the structure-function relationship of a multidomain protein with weak domain-domain interactions. Paramagnetic relaxation enhancement has been proven a powerful tool in the study of structure ensembles, but there exist a number of challenges such as spin-label flexibility, domain dynamics, and overfitting. Here we propose a new (to our knowledge) method to describe structure ensembles using a minimal number of conformers. In this method, individual domains are considered rigid; the position of each spin-label conformer and the structure of each protein conformer are defined by three and six orthogonal parameters, respectively. First, the spin-label ensemble is determined by optimizing the positions and populations of spin-label conformers against intradomain paramagnetic relaxation enhancements with a genetic algorithm. Subsequently, the protein structure ensemble is optimized using a more efficient genetic algorithm-based approach and an overfitting indicator, both of which were established in this work. The method was validated using a reference ensemble with a set of conformers whose populations and structures are known. This method was also applied to study the structure ensemble of the tandem di-domain of a poly (U) binding protein. The determined ensemble was supported by small-angle x-ray scattering and nuclear magnetic resonance relaxation data. The ensemble obtained suggests an induced fit mechanism for recognition of target RNA by the protein. Copyright © 2016 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Stern-Gerlach dynamics with quantum propagators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hsu, Bailey C.; Berrondo, Manuel; Van Huele, Jean-Francois S.

2011-01-15

We study the quantum dynamics of a nonrelativistic neutral particle with spin in inhomogeneous external magnetic fields. We first consider fields with one-dimensional inhomogeneities, both unphysical and physical, and construct the corresponding analytic propagators. We then consider fields with two-dimensional inhomogeneities and develop an appropriate numerical propagation method. We propagate initial states exhibiting different degrees of space localization and various initial spin configurations, including both pure and mixed spin states. We study the evolution of their spin densities and identify characteristic features of spin density dynamics, such as the spatial separation of spin components, and spin localization or accumulation. Wemore » compare our approach and our results with the coverage of the Stern-Gerlach effect in the literature, and we focus on nonstandard Stern-Gerlach outcomes, such as radial separation, spin focusing, spin oscillation, and spin flipping.« less

Correlation effects in fcc-Fe(x)Ni(1-x) alloys investigated by means of the KKR-CPA.

PubMed

Minár, J; Mankovsky, S; Šipr, O; Benea, D; Ebert, H

2014-07-09

The electronic structure and magnetic properties of the disordered alloy system fcc-FexNi1-x (fcc: face centered cubic) have been investigated by means of the KKR-CPA (Korringa-Kohn-Rostoker coherent potential approximation) band structure method. To investigate the impact of correlation effects, the calculations have been performed on the basis of the LSDA (local spin density approximation), the LSDA + U as well as the LSDA + DMFT (dynamical mean field theory). It turned out that the inclusion of correlation effects hardly changed the spin magnetic moments and the related hyperfine fields. The spin-orbit induced orbital magnetic moments and hyperfine fields, on the other hand, show a pronounced and element-specific enhancement. These findings are in full accordance with the results of a recent experimental study.

Influence of anisotropic dipolar interaction on the spin dynamics of Ni80Fe20 nanodot arrays arranged in honeycomb and octagonal lattices

NASA Astrophysics Data System (ADS)

Mondal, Sucheta; Barman, Saswati; Choudhury, Samiran; Otani, Yoshichika; Barman, Anjan

2018-07-01

Ultrafast spin dynamics in ferromagnetic nanodot arrays with dot diameter 100 nm and thickness 20 nm arranged in honeycomb and octagonal lattice symmetries are studied to explore the tunability of the collective magnetization dynamics. By varying the inter-dot separation between 30 nm and 300 nm drastic variation in the precessional dynamics from strongly collective to completely isolated regime has been observed by using all-optical time-resolved magneto-optical Kerr microscope. Micromagnetic simulation is exploited to gain insights about the resonant mode profiles and magnetic coupling between the nanodots. A significant spectral and spatial variation in the resonant mode with increasing dipolar interaction is demonstrated with increasing inter-dot separation. The spins driven by effective field inside single nanodots are prone to precess independently, generating two self-standing centre and edge modes in the array that are influenced by the relative orientation between the inter-dot coupling direction and bias magnetic field. The anisotropic behavior of dipolar field is rigorously investigated here. Splitting of the centre mode in case of octagonal lattice is experimentally observed here as a consequence of the anisotropic dipolar field between the nanodot pairs coupled horizontally and vertically, which is not found in the honeycomb lattice. In addition, proper understanding of the modification of dynamic mode profile by neighboring dipolar interaction built up here, is imperative for further control of the dynamic dipolar interaction and the corresponding collective excitation in magnonic crystals. The usage of nanodot lattices with complex basis structures can be advantageous for the designing of high density magnetic recording media, spin-wave filter and logic devices.

Clustering Effects on Dynamics in Ionomer Solutions: A Neutron Spin Echo Insight

NASA Astrophysics Data System (ADS)

Perahia, Dvora; Wijesinghe, Sidath; Senanayake, Manjula; Wickramasinghe, Anuradhi; Mohottalalage, Supun S.; Ohl, Michael

Ionizable blocks in ionomers associate into aggregates serving as physical cross-links and concurrently form transport pathways. The dynamics of ionomers underline their functionality. Incorporating small numbers of ionic groups into polymers significantly constraint their dynamics. Recent computational studies demonstrated a direct correlation between ionic cluster morphology and polymer dynamics. Here using neutron spin echo, we probe the segmental dynamics of polystyrene sulfonate (PSS) as the degree of sulfonation of the PSS and the solution dielectrics are varied. Specifically, 20Wt% PSS of 11,000 g/mol with polydispersity of 1.02 with 3% and 9% sulfonation were studies in toluene (dielectric constant ɛ = 2.8), a good solvent for polystyrene, and with 5Wt% of ethanol (ɛ = 24.3l) added. The dynamic structure factor S(q,t) was analyzed with a single exponential except for a limited q range where two time constants associated with constraint and mobile segments were detected. S(q,t) exhibits several distinctive time and length scales for the dynamics with a crossover appearing at the length scale of the ionic clusters. NSF DMR 1611136.

Dynamic Stabilization of a Quantum Many-Body Spin System

NASA Astrophysics Data System (ADS)

Hoang, T. M.; Gerving, C. S.; Land, B. J.; Anquez, M.; Hamley, C. D.; Chapman, M. S.

2013-08-01

We demonstrate dynamic stabilization of a strongly interacting quantum spin system realized in a spin-1 atomic Bose-Einstein condensate. The spinor Bose-Einstein condensate is initialized to an unstable fixed point of the spin-nematic phase space, where subsequent free evolution gives rise to squeezing and quantum spin mixing. To stabilize the system, periodic microwave pulses are applied that rotate the spin-nematic many-body fluctuations and limit their growth. The stability diagram for the range of pulse periods and phase shifts that stabilize the dynamics is measured and compares well with a stability analysis.

Spin-exchange interaction between transition metals and metalloids in soft-ferromagnetic metallic glasses

NASA Astrophysics Data System (ADS)

Das, Santanu; Choudhary, Kamal; Chernatynskiy, Aleksandr; Choi Yim, Haein; Bandyopadhyay, Asis K.; Mukherjee, Sundeep

2016-06-01

High-performance magnetic materials have immense industrial and scientific importance in wide-ranging electronic, electromechanical, and medical device technologies. Metallic glasses with a fully amorphous structure are particularly suited for advanced soft-magnetic applications. However, fundamental scientific understanding is lacking for the spin-exchange interaction between metal and metalloid atoms, which typically constitute a metallic glass. Using an integrated experimental and molecular dynamics approach, we demonstrate the mechanism of electron interaction between transition metals and metalloids. Spin-exchange interactions were investigated for a Fe-Co metallic glass system of composition [(Co1-x Fe x )0.75B0.2Si0.05]96Cr4. The saturation magnetization increased with higher Fe concentration, but the trend significantly deviated from simple rule of mixtures. Ab initio molecular dynamics simulation was used to identify the ferromagnetic/anti-ferromagnetic interaction between the transition metals and metalloids. The overlapping band-structure and density of states represent ‘Stoner type’ magnetization for the amorphous alloys in contrast to ‘Heisenberg type’ in crystalline iron. The enhancement of magnetization by increasing iron was attributed to the interaction between Fe 3d and B 2p bands, which was further validated by valence-band study.

Spin-tunnel investigation of a 1/25-scale model of the General Dynamics F-16XL airplane

NASA Technical Reports Server (NTRS)

Whipple, R. D.; White, W. L.

1984-01-01

A spin-tunnel investigation of the spin and recovery characteristics of a 1/25-scale model to the General Dynamics F-16XL aircraft was conducted in the Langley Spin Tunnel. Tests included erect and inverted spins at various symmetric and asymmetric loading conditions. The required size of an emergency spin-recovery parachute was determined.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schäfer, Gerhard

The current knowledge in the post-Newtonian (PN) dynamics and motion of non-spinning and spinning compact binaries will be presented based on the Arnowitt-Deser-Misner Hamiltonian approach to general relativity. The presentation will cover the binary dynamics with non-spinning components up to the 4PN order and for spinning binaries up to the next-to-next-to-leading order in the spin-orbit and spin-spin couplings. Radiation reaction will be treated for both non-spinning and spinning binaries. Explicit analytic expressions for the motion will be given, innermost stable circular orbits will be discussed.

Studying lipid-protein interactions with electron paramagnetic resonance spectroscopy of spin-labeled lipids.

PubMed

Páli, Tibor; Kóta, Zoltán

2013-01-01

Spin label electron paramagnetic resonance (EPR) of lipid-protein interactions reveals crucial features of the structure and assembly of integral membrane proteins. Spin label EPR spectroscopy is the technique of choice to characterize the protein-solvating lipid shell in its highly dynamic nature, because the EPR spectra of lipids that are spin labeled close to the terminal methyl end of their acyl chains display two spectral components, those corresponding to lipids directly contacting the protein and those corresponding to lipids in the bulk fluid bilayer regions of the membrane. In this chapter, typical spin label EPR procedures are presented that allow determination of the stoichiometry of interaction of spin-labeled lipids with the intra-membranous region of membrane proteins or polypeptides, as well as the association constant of the spin-labeled lipid with respect to the host lipid. The lipids giving rise to the so-called immobile spectral component in the EPR spectrum of such samples are identified as the motionally restricted first-shell lipids solvating membrane proteins in biomembranes. Stoichiometry and selectivity are directly related to the structure of the intra-membranous sections of membrane-associated proteins or polypeptides and can be used to study the state of assembly of such proteins in the membrane. Since these characteristics of lipid-protein interactions are discussed in detail in the literature [see Marsh (Eur Biophys J 39:513-525, 2010) for a most recent review], here we focus more on how to spin label model and biomembranes and how to measure and analyze the two-component EPR spectra of spin-labeled lipids in phospholipid bilayers that contain proteins or polypeptides. After a description of how to prepare spin-labeled model and native biological membranes, we present the reader with computational procedures for determining the molar fraction of motionally restricted lipids when both, one, or none of the pure isolated-mobile or immobile-spectral components are available. With these topics, this chapter complements a recent methodological paper [Marsh (Methods 46:83-96, 2008)]. The interpretation of the data is discussed briefly, as well as other relevant and recent spin label EPR techniques for studying lipid-protein interactions, not only from the point of view of lipid chain dynamics.

Proton-driven spin diffusion in rotating solids via reversible and irreversible quantum dynamics

PubMed Central

Veshtort, Mikhail; Griffin, Robert G.

2011-01-01

Proton-driven spin diffusion (PDSD) experiments in rotating solids have received a great deal of attention as a potential source of distance constraints in large biomolecules. However, the quantitative relationship between the molecular structure and observed spin diffusion has remained obscure due to the lack of an accurate theoretical description of the spin dynamics in these experiments. We start with presenting a detailed relaxation theory of PDSD in rotating solids that provides such a description. The theory applies to both conventional and radio-frequency-assisted PDSD experiments and extends to the non-Markovian regime to include such phenomena as rotational resonance (R2). The basic kinetic equation of the theory in the non-Markovian regime has the form of a memory function equation, with the role of the memory function played by the correlation function. The key assumption used in the derivation of this equation expresses the intuitive notion of the irreversible dissipation of coherences in macroscopic systems. Accurate expressions for the correlation functions and for the spin diffusion constants are given. The theory predicts that the spin diffusion constants governing the multi-site PDSD can be approximated by the constants observed in the two-site diffusion. Direct numerical simulations of PDSD dynamics via reversible Liouville-von Neumann equation are presented to support and compliment the theory. Remarkably, an exponential decay of the difference magnetization can be observed in such simulations in systems consisting of only 12 spins. This is a unique example of a real physical system whose typically macroscopic and apparently irreversible behavior can be traced via reversible microscopic dynamics. An accurate value for the spin diffusion constant can be usually obtained through direct simulations of PDSD in systems consisting of two 13C nuclei and about ten 1H nuclei from their nearest environment. Spin diffusion constants computed by this method are in excellent agreement with the spin diffusion constants obtained through equations given by the relaxation theory of PDSD. The constants resulting from these two approaches were also in excellent agreement with the results of 2D rotary resonance recoupling proton-driven spin diffusion (R3-PDSD) experiments performed in three model compounds, where magnetization exchange occurred over distances up to 4.9 Å. With the methodology presented, highly accurate internuclear distances can be extracted from such data. Relayed transfer of magnetization between distant nuclei appears to be the main (and apparently resolvable) source of uncertainty in such measurements. The non-Markovian kinetic equation was applied to the analysis of the R2 spin dynamics. The conventional semi-phenomenological treatment of relxation in R2 has been shown to be equivalent to the assumption of the Lorentzian spectral density function in the relaxatoin theory of PDSD. As this assumption is a poor approximation in real physical systems, the conventional R2 treatment is likely to carry a significant model error that has not been recognized previously. The relaxation theory of PDSD appears to provide an accurate, parameter-free alternative. Predictions of this theory agreed well with the full quantum mechanical simulations of the R2 dynamics in the few simple model systems we considered. PMID:21992326

Role of entropy and structural parameters in the spin-state transition of LaCoO3

NASA Astrophysics Data System (ADS)

Chakrabarti, Bismayan; Birol, Turan; Haule, Kristjan

2017-11-01

The spin-state transition in LaCoO3 has eluded description for decades despite concerted theoretical and experimental effort. In this study, we approach this problem using fully charge self-consistent density functional theory + embedded dynamical mean field theory (DFT+DMFT). We show from first principles that LaCoO3 cannot be described by a single, pure spin state at any temperature. Instead, we observe a gradual change in the population of higher-spin multiplets with increasing temperature, with the high-spin multiplets being excited at the onset of the spin-state transition followed by the intermediate-spin multiplets being excited at the metal-insulator-transition temperature. We explicitly elucidate the critical role of lattice expansion and oxygen octahedral rotations in the spin-state transition. We also reproduce, from first principles, that the spin-state transition and the metal-insulator transition in LaCoO3 occur at different temperature scales. In addition, our results shed light on the importance of electronic entropy in driving the spin-state transition, which has so far been ignored in all first-principles studies of this material.

Chiral symmetry breaking and the spin content of hadrons

NASA Astrophysics Data System (ADS)

Glozman, L. Ya.; Lang, C. B.; Limmer, M.

2012-04-01

From the parton distributions in the infinite momentum frame, one finds that only about 30% of the nucleon spin is carried by spins of the valence quarks, which gave rise to the term “spin crisis”. Similar results hold for the lowest mesons, as it follows from the lattice simulations. We define the spin content of a meson in the rest frame and use a complete and orthogonal q¯q chiral basis and a unitary transformation from the chiral basis to the 2LJ basis. Then, given a mixture of different allowed chiral representations in the meson wave function at a given resolution scale, one can obtain its spin content at this scale. To obtain the mixture of the chiral representations in the meson, we measure in dynamical lattice simulations a ratio of couplings of interpolators with different chiral structure. For the ρ meson, we obtain practically the 3S1 state with no trace of the spin crisis. Then a natural question arises: which definition does reflect the spin content of a hadron?

Finite-temperature spin dynamics in a perturbed quantum critical Ising chain with an E₈ symmetry.

PubMed

Wu, Jianda; Kormos, Márton; Si, Qimiao

2014-12-12

A spectrum exhibiting E₈ symmetry is expected to arise when a small longitudinal field is introduced in the transverse-field Ising chain at its quantum critical point. Evidence for this spectrum has recently come from neutron scattering measurements in cobalt niobate, a quasi-one-dimensional Ising ferromagnet. Unlike its zero-temperature counterpart, the finite-temperature dynamics of the model has not yet been determined. We study the dynamical spin structure factor of the model at low frequencies and nonzero temperatures, using the form factor method. Its frequency dependence is singular, but differs from the diffusion form. The temperature dependence of the nuclear magnetic resonance (NMR) relaxation rate has an activated form, whose prefactor we also determine. We propose NMR experiments as a means to further test the applicability of the E₈ description for CoNb₂O₆.

Spin valley and giant quantum spin Hall gap of hydrofluorinated bismuth nanosheet.

PubMed

Gao, Heng; Wu, Wei; Hu, Tao; Stroppa, Alessandro; Wang, Xinran; Wang, Baigeng; Miao, Feng; Ren, Wei

2018-05-09

Spin-valley and electronic band topological properties have been extensively explored in quantum material science, yet their coexistence has rarely been realized in stoichiometric two-dimensional (2D) materials. We theoretically predict the quantum spin Hall effect (QSHE) in the hydrofluorinated bismuth (Bi 2 HF) nanosheet where the hydrogen (H) and fluorine (F) atoms are functionalized on opposite sides of bismuth (Bi) atomic monolayer. Such Bi 2 HF nanosheet is found to be a 2D topological insulator with a giant band gap of 0.97 eV which might host room temperature QSHE. The atomistic structure of Bi 2 HF nanosheet is noncentrosymmetric and the spontaneous polarization arises from the hydrofluorinated morphology. The phonon spectrum and ab initio molecular dynamic (AIMD) calculations reveal that the proposed Bi 2 HF nanosheet is dynamically and thermally stable. The inversion symmetry breaking together with spin-orbit coupling (SOC) leads to the coupling between spin and valley in Bi 2 HF nanosheet. The emerging valley-dependent properties and the interplay between intrinsic dipole and SOC are investigated using first-principles calculations combined with an effective Hamiltonian model. The topological invariant of the Bi 2 HF nanosheet is confirmed by using Wilson loop method and the calculated helical metallic edge states are shown to host QSHE. The Bi 2 HF nanosheet is therefore a promising platform to realize room temperature QSHE and valley spintronics.

Dynamical instability of a spin spiral in an interacting Fermi gas as a probe of the Stoner transition

NASA Astrophysics Data System (ADS)

Conduit, G. J.; Altman, E.

2010-10-01

We propose an experiment to probe ferromagnetic phenomena in an ultracold Fermi gas, while alleviating the sensitivity to three-body loss and competing many-body instabilities. The system is initialized in a small pitch spin spiral, which becomes unstable in the presence of repulsive interactions. To linear order the exponentially growing collective modes exhibit critical slowing down close to the Stoner transition point. Also, to this order, the dynamics are identical on the paramagnetic and ferromagnetic sides of the transition. However, we show that scattering off the exponentially growing modes qualitatively alters the collective mode structure. The critical slowing down is eliminated and in its place a new unstable branch develops at large wave vectors. Furthermore, long-wavelength instabilities are quenched on the paramagnetic side of the transition. We study the experimental observation of the instabilities, specifically addressing the trapping geometry and how phase-contrast imaging will reveal the emerging domain structure. These probes of the dynamical phenomena could allow experiments to detect the transition point and distinguish between the paramagnetic and ferromagnetic regimes.

Dynamics of influence on hierarchical structures

NASA Astrophysics Data System (ADS)

Fotouhi, Babak; Rabbat, Michael G.

2013-08-01

Dichotomous spin dynamics on a pyramidal hierarchical structure (the Bethe lattice) are studied. The system embodies a number of classes, where a class comprises nodes that are equidistant from the root (head node). Weighted links exist between nodes from the same and different classes. The spin (hereafter state) of the head node is fixed. We solve for the dynamics of the system for different boundary conditions. We find necessary conditions so that the classes eventually repudiate or acquiesce in the state imposed by the head node. The results indicate that to reach unanimity across the hierarchy, it suffices that the bottommost class adopts the same state as the head node. Then the rest of the hierarchy will inevitably comply. This also sheds light on the importance of mass media as a means of synchronization between the topmost and bottommost classes. Surprisingly, in the case of discord between the head node and the bottommost classes, the average state over all nodes inclines towards that of the bottommost class regardless of the link weights and intraclass configurations. Hence the role of the bottommost class is signified.

Electronic, structural, and thermodynamic properties of mixed actinide dioxides (U, Pu, Am) O2 from hybrid density functional theory

NASA Astrophysics Data System (ADS)

Ma, Li; Ray, Asok K.

2010-03-01

As a continuation of our studies of pure actinide metals using hybrid density functional theory,footnotetextR. Atta-Fynn and A. K. Ray, Europhysics Letters, 85, 27008-p1- p6 (2009); Chemical Physics Letters, 482, 223-227 (2009). we present here a systematic study of the electronic and geometric structure properties of mixed actinide dioxides, U0.5Pu0.5O2, U0.5Am0.5O2, Pu0.5Am0.5 O2 and U0.8Pu0.2O2. The fraction of exact Hartree-Fock exchange used was 40%. To investigate the effect of spin-orbit coupling on the ground state electronic and geometric structure properties, computations have been carried out at two theoretical levels, one at the scalar-relativistic level with no spin-orbit coupling and one at the fully relativistic level with spin-orbit coupling. Thermodynamic properties have been calculated by a coupling of first-principles calculation and lattice dynamics.

Low temperature and high field regimes of connected kagome artificial spin ice: the role of domain wall topology.

PubMed

Zeissler, Katharina; Chadha, Megha; Lovell, Edmund; Cohen, Lesley F; Branford, Will R

2016-07-22

Artificial spin ices are frustrated magnetic nanostructures where single domain nanobars act as macrosized spins. In connected kagome artificial spin ice arrays, reversal occurs along one-dimensional chains by propagation of ferromagnetic domain walls through Y-shaped vertices. Both the vertices and the walls are complex chiral objects with well-defined topological edge-charges. At room temperature, it is established that the topological edge-charges determine the exact switching reversal path taken. However, magnetic reversal at low temperatures has received much less attention and how these chiral objects interact at reduced temperature is unknown. In this study we use magnetic force microscopy to image the magnetic reversal process at low temperatures revealing the formation of quite remarkable high energy remanence states and a change in the dynamics of the reversal process. The implication is the breakdown of the artificial spin ice regime in these connected structures at low temperatures.

Thermodynamic glass transition in a spin glass without time-reversal symmetry

PubMed Central

Baños, Raquel Alvarez; Cruz, Andres; Fernandez, Luis Antonio; Gil-Narvion, Jose Miguel; Gordillo-Guerrero, Antonio; Guidetti, Marco; Iñiguez, David; Maiorano, Andrea; Marinari, Enzo; Martin-Mayor, Victor; Monforte-Garcia, Jorge; Muñoz Sudupe, Antonio; Navarro, Denis; Parisi, Giorgio; Perez-Gaviro, Sergio; Ruiz-Lorenzo, Juan Jesus; Schifano, Sebastiano Fabio; Seoane, Beatriz; Tarancon, Alfonso; Tellez, Pedro; Tripiccione, Raffaele; Yllanes, David

2012-01-01

Spin glasses are a longstanding model for the sluggish dynamics that appear at the glass transition. However, spin glasses differ from structural glasses in a crucial feature: they enjoy a time reversal symmetry. This symmetry can be broken by applying an external magnetic field, but embarrassingly little is known about the critical behavior of a spin glass in a field. In this context, the space dimension is crucial. Simulations are easier to interpret in a large number of dimensions, but one must work below the upper critical dimension (i.e., in d < 6) in order for results to have relevance for experiments. Here we show conclusive evidence for the presence of a phase transition in a four-dimensional spin glass in a field. Two ingredients were crucial for this achievement: massive numerical simulations were carried out on the Janus special-purpose computer, and a new and powerful finite-size scaling method. PMID:22493229

Electrical detection of nuclear spins in organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Malissa, H.; Kavand, M.; Waters, D. P.; Lupton, J. M.; Vardeny, Z. V.; Saam, B.; Boehme, C.

2014-03-01

We present pulsed combined electrically detected electron paramagnetic and nuclear magnetic resonance experiments on MEH-PPV OLEDs. Spin dynamics in these structures are governed by hyperfine interactions between charge carriers and the surrounding hydrogen nuclei, which are abundant in these materials. Hyperfine coupling has been observed by monitoring the device current during coherent spin excitation. Electron spin echoes (ESEs) are detected by applying one additional readout pulse at the time of echo formation. This allows for the application of high-resolution spectroscopy based on ESE detection, such as electron spin echo envelope modulation (ESEEM) and electron nuclear double resonance (ENDOR) available for electrical detection schemes. We conduct electrically detected ESEEM and ENDOR experiments and show how hyperfine interactions in MEH-PPV with and without deuterated polymer side groups can be observed by device current measurements. We acknowledge support by the Department of Energy, Office of Basic Energy Sciences under Award #DE-SC0000909.

Quantum Spin Glasses, Annealing and Computation

NASA Astrophysics Data System (ADS)

Chakrabarti, Bikas K.; Inoue, Jun-ichi; Tamura, Ryo; Tanaka, Shu

2017-05-01

List of tables; List of figures, Preface; 1. Introduction; Part I. Quantum Spin Glass, Annealing and Computation: 2. Classical spin models from ferromagnetic spin systems to spin glasses; 3. Simulated annealing; 4. Quantum spin glass; 5. Quantum dynamics; 6. Quantum annealing; Part II. Additional Notes: 7. Notes on adiabatic quantum computers; 8. Quantum information and quenching dynamics; 9. A brief historical note on the studies of quantum glass, annealing and computation.

Electromagnetic pulse-driven spin-dependent currents in semiconductor quantum rings.

PubMed

Zhu, Zhen-Gang; Berakdar, Jamal

2009-04-08

We investigate the non-equilibrium charge and spin-dependent currents in a quantum ring with a Rashba spin-orbit interaction (SOI) driven by two asymmetric picosecond electromagnetic pulses. The equilibrium persistent charge and persistent spin-dependent currents are investigated as well. It is shown that the dynamical charge and the dynamical spin-dependent currents vary smoothly with a static external magnetic flux and the SOI provides a SU(2) effective flux that changes the phases of the dynamic charge and the dynamic spin-dependent currents. The period of the oscillation of the total charge current with the delay time between the pulses is larger in a quantum ring with a larger radius. The parameters of the pulse fields control to a certain extent the total charge and the total spin-dependent currents. The calculations are applicable to nanometre rings fabricated in heterojunctions of III-V and II-VI semiconductors containing several hundreds of electrons.

Twist of generalized skyrmions and spin vortices in a polariton superfluid

PubMed Central

Donati, Stefano; Dominici, Lorenzo; Dagvadorj, Galbadrakh; Ballarini, Dario; De Giorgi, Milena; Bramati, Alberto; Gigli, Giuseppe; Rubo, Yuri G.; Szymańska, Marzena Hanna; Sanvitto, Daniele

2016-01-01

We study the spin vortices and skyrmions coherently imprinted into an exciton–polariton condensate on a planar semiconductor microcavity. We demonstrate that the presence of a polarization anisotropy can induce a complex dynamics of these structured topologies, leading to the twist of their circuitation on the Poincaré sphere of polarizations. The theoretical description of the results carries the concept of generalized quantum vortices in two-component superfluids, which are conformal with polarization loops around an arbitrary axis in the pseudospin space. PMID:27965393

Twist of generalized skyrmions and spin vortices in a polariton superfluid.

PubMed

Donati, Stefano; Dominici, Lorenzo; Dagvadorj, Galbadrakh; Ballarini, Dario; De Giorgi, Milena; Bramati, Alberto; Gigli, Giuseppe; Rubo, Yuri G; Szymańska, Marzena Hanna; Sanvitto, Daniele

2016-12-27

We study the spin vortices and skyrmions coherently imprinted into an exciton-polariton condensate on a planar semiconductor microcavity. We demonstrate that the presence of a polarization anisotropy can induce a complex dynamics of these structured topologies, leading to the twist of their circuitation on the Poincaré sphere of polarizations. The theoretical description of the results carries the concept of generalized quantum vortices in two-component superfluids, which are conformal with polarization loops around an arbitrary axis in the pseudospin space.

Landau Levels of Majorana Fermions in a Spin Liquid.

PubMed

Rachel, Stephan; Fritz, Lars; Vojta, Matthias

2016-04-22

Majorana fermions, originally proposed as elementary particles acting as their own antiparticles, can be realized in condensed-matter systems as emergent quasiparticles, a situation often accompanied by topological order. Here we propose a physical system which realizes Landau levels-highly degenerate single-particle states usually resulting from an orbital magnetic field acting on charged particles-for Majorana fermions. This is achieved in a variant of a quantum spin system due to Kitaev which is distorted by triaxial strain. This strained Kitaev model displays a spin-liquid phase with charge-neutral Majorana-fermion excitations whose spectrum corresponds to that of Landau levels, here arising from a tailored pseudomagnetic field. We show that measuring the dynamic spin susceptibility reveals the Landau-level structure by a remarkable mechanism of probe-induced bound-state formation.

Redox Thermodynamics of High-Spin and Low-Spin Forms of Chlorite Dismutases with Diverse Subunit and Oligomeric Structures

PubMed Central

2012-01-01

Chlorite dismutases (Clds) are heme b-containing oxidoreductases that convert chlorite to chloride and dioxygen. In this work, the thermodynamics of the one-electron reduction of the ferric high-spin forms and of the six-coordinate low-spin cyanide adducts of the enzymes from Nitrobacter winogradskyi (NwCld) and Candidatus “Nitrospira defluvii” (NdCld) were determined through spectroelectrochemical experiments. These proteins belong to two phylogenetically separated lineages that differ in subunit (21.5 and 26 kDa, respectively) and oligomeric (dimeric and pentameric, respectively) structure but exhibit similar chlorite degradation activity. The E°′ values for free and cyanide-bound proteins were determined to be −119 and −397 mV for NwCld and −113 and −404 mV for NdCld, respectively (pH 7.0, 25 °C). Variable-temperature spectroelectrochemical experiments revealed that the oxidized state of both proteins is enthalpically stabilized. Molecular dynamics simulations suggest that changes in the protein structure are negligible, whereas solvent reorganization is mainly responsible for the increase in entropy during the redox reaction. Obtained data are discussed with respect to the known structures of the two Clds and the proposed reaction mechanism. PMID:23126649

Superlattice Structures, Electronic Properties, and Spin Dynamics of the Partially Cu-Extracted Phase for the Composite Crystal System CuxV4O11

NASA Astrophysics Data System (ADS)

Onoda, Masashige; Tamura, Asato

2017-02-01

The crystal structures, electronic properties, and spin dynamics of CuxV4O11 with 1.2 ≤ x < 2, classified as the partially Cu-extracted phase for the composite crystal system, are explored through measurements of x-ray four-circle diffraction, electrochemistry, electrical resistivity, thermoelectric power, magnetization, and electron paramagnetic resonance. This system has superlattice structures mainly ascribed to the partial ordering of Cu ions. Cu1.78V4O11 is triclinic with space group Pbar{1} and the double supercell of the V4O11 substructure of the composite crystal. The significantly Cu-extracted crystal Cu1.40V4O11 has a quadruple supercell with space group P1. The electron transport for V ions is nonmetallic owing to the polaronic nature and/or phonon softening and to the random potential of Cu ions. The Curie-Weiss-type paramagnetism basically originates from the Cu2+ chain coordinated octahedrally, and the EPR relaxation at low temperatures is understood through the exchange mechanism for the dipole-dipole and anisotropic exchange interactions. The near absence of paramagnetic behaviors of V4+ ions might be due to the spin-singlet ladder model or alternating-exchange chain model depending on the superlattice structure and valence distribution. The electrochemical performance of Li rechargeable batteries using this superlattice system is about 300 A h kg-1 at voltages above 2 V.

Quantum approach of mesoscopic magnet dynamics with spin transfer torque

NASA Astrophysics Data System (ADS)

Wang, Yong; Sham, L. J.

2013-05-01

We present a theory of magnetization dynamics driven by spin-polarized current in terms of the quantum master equation. In the spin coherent state representation, the master equation becomes a Fokker-Planck equation, which naturally includes the spin transfer and quantum fluctuation. The current electron scattering state is correlated to the magnet quantum states, giving rise to quantum correction to the electron transport properties in the usual semiclassical theory. In the large-spin limit, the magnetization dynamics is shown to obey the Hamilton-Jacobi equation or the Hamiltonian canonical equations.

All optical detection of picosecond spin-wave dynamics in 2D annular antidot lattice

NASA Astrophysics Data System (ADS)

Porwal, Nikita; Mondal, Sucheta; Choudhury, Samiran; De, Anulekha; Sinha, Jaivardhan; Barman, Anjan; Datta, Prasanta Kumar

2018-02-01

Novel magnetic structures with precisely controlled dimensions and shapes at the nanoscale have potential applications in spin logic, spintronics and other spin-based communication devices. We report the fabrication of 2D bi-structure magnonic crystal in the form of embedded nanodots in a periodic Ni80Fe20 antidot lattice structure (annular antidot) by focused ion-beam lithography. The spin-wave spectra of the annular antidot sample, studied for the first time by a time-resolved magneto-optic Kerr effect microscopy show a remarkable variation with bias field, which is important for the above device applications. The optically induced spin-wave spectra show multiple modes in the frequency range 14.7 GHz-3.5 GHz due to collective interactions between the dots and antidots as well as the annular elements within the whole array. Numerical simulations qualitatively reproduce the experimental results, and simulated mode profiles reveal the spatial distribution of the spin-wave modes and internal magnetic fields responsible for these observations. It is observed that the internal field strength increases by about 200 Oe inside each dot embedded within the hole of annular antidot lattice as compared to pure antidot lattice and pure dot lattice. The stray field for the annular antidot lattice is found to be significant (0.8 kOe) as opposed to the negligible values of the same for the pure dot lattice and pure antidot lattice. Our findings open up new possibilities for development of novel artificial crystals.

Frequency-dependent dynamic magnetic properties of the Ising bilayer system consisting of spin-3/2 and spin-5/2 spins

NASA Astrophysics Data System (ADS)

Keskin, Mustafa; Ertaş, Mehmet

2018-04-01

Dynamic magnetic properties of the Ising bilayer system consisting of the mixed (3/2, 5/2) Ising spins with a crystal-field interaction in an oscillating field on a two-layer square lattice is studied by the use of dynamic mean-field theory based on the Glauber-type stochastic. Dynamic phase transition temperatures are obtained and dynamic phase diagrams are presented in three different planes. The frequency dependence of dynamic hysteresis loops is also investigated in detail. We compare the results with some available theoretical and experimental works and observe a quantitatively good agreement with some theoretical and experimental results.

Rényi information flow in the Ising model with single-spin dynamics.

PubMed

Deng, Zehui; Wu, Jinshan; Guo, Wenan

2014-12-01

The n-index Rényi mutual information and transfer entropies for the two-dimensional kinetic Ising model with arbitrary single-spin dynamics in the thermodynamic limit are derived as functions of ensemble averages of observables and spin-flip probabilities. Cluster Monte Carlo algorithms with different dynamics from the single-spin dynamics are thus applicable to estimate the transfer entropies. By means of Monte Carlo simulations with the Wolff algorithm, we calculate the information flows in the Ising model with the Metropolis dynamics and the Glauber dynamics, respectively. We find that not only the global Rényi transfer entropy, but also the pairwise Rényi transfer entropy, peaks in the disorder phase.

Quantum spin liquid signatures in Kitaev-like frustrated magnets

NASA Astrophysics Data System (ADS)

Gohlke, Matthias; Wachtel, Gideon; Yamaji, Youhei; Pollmann, Frank; Kim, Yong Baek

2018-02-01

Motivated by recent experiments on α -RuCl3 , we investigate a possible quantum spin liquid ground state of the honeycomb-lattice spin model with bond-dependent interactions. We consider the K -Γ model, where K and Γ represent the Kitaev and symmetric-anisotropic interactions between spin-1/2 moments on the honeycomb lattice. Using the infinite density matrix renormalization group, we provide compelling evidence for the existence of quantum spin liquid phases in an extended region of the phase diagram. In particular, we use transfer-matrix spectra to show the evolution of two-particle excitations with well-defined two-dimensional dispersion, which is a strong signature of a quantum spin liquid. These results are compared with predictions from Majorana mean-field theory and used to infer the quasiparticle excitation spectra. Further, we compute the dynamical structure factor using finite-size cluster computations and show that the results resemble the scattering continuum seen in neutron-scattering experiments on α -RuCl3 . We discuss these results in light of recent and future experiments.

Research Reports: 1983 NASA/ASEE Summer Faculty Fellowship Program

NASA Technical Reports Server (NTRS)

Karr, G. R.; Dozier, J. B.; Osborn, L.; Freeman, M.

1983-01-01

Thirty-five technical reports contain results of investigations in information and electronic systems; materials and processing; systems dynamics; structures and propulsion; and space sciences. Ecology at KSC, satellite de-spin, and the X-ray source monitor were also studied.

Signatures of a quantum dynamical phase transition in a three-spin system in presence of a spin environment

NASA Astrophysics Data System (ADS)

Álvarez, Gonzalo A.; Levstein, Patricia R.; Pastawski, Horacio M.

2007-09-01

We have observed an environmentally induced quantum dynamical phase transition in the dynamics of a two-spin experimental swapping gate [G.A. Álvarez, E.P. Danieli, P.R. Levstein, H.M. Pastawski, J. Chem. Phys. 124 (2006) 194507]. There, the exchange of the coupled states |↑,↓> and |↓,↑> gives an oscillation with a Rabi frequency b/ℏ (the spin-spin coupling). The interaction, ℏ/τSE with a spin-bath degrades the oscillation with a characteristic decoherence time. We showed that the swapping regime is restricted only to bτSE≳ℏ. However, beyond a critical interaction with the environment the swapping freezes and the system enters to a Quantum Zeno dynamical phase where relaxation decreases as coupling with the environment increases. Here, we solve the quantum dynamics of a two-spin system coupled to a spin-bath within a Liouville-von Neumann quantum master equation and we compare the results with our previous work within the Keldysh formalism. Then, we extend the model to a three interacting spin system where only one is coupled to the environment. Beyond a critical interaction the two spins not coupled to the environment oscillate with the bare Rabi frequency and relax more slowly. This effect is more pronounced when the anisotropy of the system-environment (SE) interaction goes from a purely XY to an Ising interaction form.

Superconductivity and spin excitations in orbitally ordered FeSe

NASA Astrophysics Data System (ADS)

Kreisel, Andreas; Mukherjee, Shantanu; Hirschfeld, P. J.; Andersen, B. M.

We provide a band-structure with low-energy properties consistent with recent photoemission and quantum oscillations measurements on the Fe-based superconductor FeSe, including a mean-field like orbital ordering in the dxz /dyz channel, and show that this model also accounts for the temperature dependence of the measured Knight shift and the spin-relaxation rate. An RPA calculation of the dynamical spin susceptibility yields spin excitations which are peaked at wave vector (π , 0) in the 1-Fe Brillouin zone, with a broad maximum at energies of order a few meV. Furthermore, the superconducting gap structure obtained from spin fluctuation theory exhibits nodes on the electron pockets, consistent with the 'V'-shaped density of states measured by tunneling spectroscopy on this material. The redistribution of spectral weight in the superconducting state creates a (π , 0) ''neutron resonance'' as seen in recent experiments. Comparing to various experimental results, we give predictions for further studies A.K. and B.M.A. acknowledge financial support from a Lundbeckfond fellowship (Grant No. A9318). P.J.H. was partially supported by the Department of Energy under Grant No. DE-FG02-05ER46236.

Quantum group spin nets: Refinement limit and relation to spin foams

NASA Astrophysics Data System (ADS)

Dittrich, Bianca; Martin-Benito, Mercedes; Steinhaus, Sebastian

2014-07-01

So far spin foam models are hardly understood beyond a few of their basic building blocks. To make progress on this question, we define analogue spin foam models, so-called "spin nets," for quantum groups SU(2)k and examine their effective continuum dynamics via tensor network renormalization. In the refinement limit of this coarse-graining procedure, we find a vast nontrivial fixed-point structure beyond the degenerate and the BF phase. In comparison to previous work, we use fixed-point intertwiners, inspired by Reisenberger's construction principle [M. P. Reisenberger, J. Math. Phys. (N.Y.) 40, 2046 (1999)] and the recent work [B. Dittrich and W. Kaminski, arXiv:1311.1798], as the initial parametrization. In this new parametrization fine-tuning is not required in order to flow to these new fixed points. Encouragingly, each fixed point has an associated extended phase, which allows for the study of phase transitions in the future. Finally we also present an interpretation of spin nets in terms of melonic spin foams. The coarse-graining flow of spin nets can thus be interpreted as describing the effective coupling between two spin foam vertices or space time atoms.

Spatiotemporal dynamics of the spin transition in [Fe (HB(tz)3) 2] single crystals

NASA Astrophysics Data System (ADS)

Ridier, Karl; Rat, Sylvain; Shepherd, Helena J.; Salmon, Lionel; Nicolazzi, William; Molnár, Gábor; Bousseksou, Azzedine

2017-10-01

The spatiotemporal dynamics of the spin transition have been thoroughly investigated in single crystals of the mononuclear spin-crossover (SCO) complex [Fe (HB (tz )3)2] (tz = 1 ,2 ,4-triazol-1-yl) by optical microscopy. This compound exhibits an abrupt spin transition centered at 334 K with a narrow thermal hysteresis loop of ˜1 K (first-order transition). Most single crystals of this compound reveal exceptional resilience upon repeated switching (several hundred cycles), which allowed repeatable and quantitative measurements of the spatiotemporal dynamics of the nucleation and growth processes to be carried out. These experiments revealed remarkable properties of the thermally induced spin transition: high stability of the thermal hysteresis loop, unprecedented large velocities of the macroscopic low-spin/high-spin phase boundaries up to 500 µm/s, and no visible dependency on the temperature scan rate. We have also studied the dynamics of the low-spin → high-spin transition induced by a local photothermal excitation generated by a spatially localized (Ø = 2 μ m ) continuous laser beam. Interesting phenomena have been evidenced both in quasistatic and dynamic conditions (e.g., threshold effects and long incubation periods, thermal activation of the phase boundary propagation, stabilization of the crystal in a stationary biphasic state, and thermal cutoff frequency). These measurements demonstrated the importance of thermal effects in the transition dynamics, and they enabled an accurate determination of the thermal properties of the SCO compound in the framework of a simple theoretical model.

Probing the impact of magnetic interactions on the lattice dynamics of two-dimensional Ti2X (X = C, N) MXenes.

PubMed

Sternik, Małgorzata; Wdowik, Urszula D

2018-03-14

Dynamical properties of the two-dimensional Ti 2 C and Ti 2 N MXenes were investigated using density functional theory and discussed in connection with their structures and electronic properties. To elucidate the influence of magnetic interactions on the fundamental properties of these systems, the nonmagnetic, ferromagnetic and three distinct antiferromagnetic spin arrangements on titanium sublattice were considered. Each magnetic configuration was also studied at two directions of the spin magnetic moment with respect to the MXene layer. The zero-point energy motion, following from the phonon calculations, was taken into account while analyzing the energetic stability of the magnetic phases against the nonmagnetic solution. This contribution was found not to change a sequence of the energetic stability of the considered magnetic structures of Ti 2 X (X = C, N) MXenes. Both Ti 2 X (X = C, N) systems are shown to prefer antiferromagnetic arrangement of spins between Ti layers and the ferromagnetic order within each layer. This energetically privileged phase is semiconducting for Ti 2 C and metallic for Ti 2 N. The type of magnetic order as well as the in-plane or out-of-plane spin polarizations have a relatively small impact on the structural parameters, Ti-X bonding length, force constants and phonon spectra of both Ti 2 X systems, leading to observable differences only between the nonmagnetic and any other magnetic configurations. Nonetheless, a noticeable effect of the spin orientation on degeneracy of the Ti-3d orbitals is encountered. The magnetic interactions affect to a great extent the positions and intensities of the Raman-active modes, and hence one could exploit this effect for experimental verification of the theoretically predicted magnetic state of Ti 2 X monolayers. Theoretical phonon spectra of Ti 2 X (X = C, N) MXenes exhibit a linear dependence on energy in the long-wavelength limit, which is typical for a 2D system.

Y{sub 3}Fe{sub 5}O{sub 12} spin pumping for quantitative understanding of pure spin transport and spin Hall effect in a broad range of materials (invited)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Du, Chunhui; Wang, Hailong; Hammel, P. Chris

2015-05-07

Using Y{sub 3}Fe{sub 5}O{sub 12} (YIG) thin films grown by our sputtering technique, we study dynamic spin transport in nonmagnetic, ferromagnetic, and antiferromagnetic (AF) materials by ferromagnetic resonance spin pumping. From both inverse spin Hall effect and damping enhancement, we determine the spin mixing conductance and spin Hall angle in many metals. Surprisingly, we observe robust spin conduction in AF insulators excited by an adjacent YIG at resonance. This demonstrates that YIG spin pumping is a powerful and versatile tool for understanding spin Hall physics, spin-orbit coupling, and magnetization dynamics in a broad range of materials.

Relevance of Internal Friction and Structural Constraints for the Dynamics of Denatured Bovine Serum Albumin.

PubMed

Ameseder, Felix; Radulescu, Aurel; Holderer, Olaf; Falus, Peter; Richter, Dieter; Stadler, Andreas M

2018-05-17

A general property of disordered proteins is their structural expansion that results in a high molecular flexibility. The structure and dynamics of bovine serum albumin (BSA) denatured by guanidinium hydrochloride (GndCl) were investigated using small-angle neutron scattering (SANS) and neutron spin-echo spectroscopy (NSE). SANS experiments demonstrated the relevance of intrachain interactions for structural expansion. Using NSE experiments, we observed a high internal flexibility of denatured BSA in addition to center-of-mass diffusion detected by dynamic light scattering. Internal motions measured by NSE were described using concepts based on polymer theory. The contribution of residue-solvent friction was accounted for using the Zimm model including internal friction (ZIF). Disulfide bonds forming loops of amino acids of the peptide backbone have a major impact on internal dynamics that can be interpreted with a reduced set of Zimm modes.

Spin-vibronic quantum dynamics for ultrafast excited-state processes.

PubMed

Eng, Julien; Gourlaouen, Christophe; Gindensperger, Etienne; Daniel, Chantal

2015-03-17

Ultrafast intersystem crossing (ISC) processes coupled to nuclear relaxation and solvation dynamics play a central role in the photophysics and photochemistry of a wide range of transition metal complexes. These phenomena occurring within a few hundred femtoseconds are investigated experimentally by ultrafast picosecond and femtosecond transient absorption or luminescence spectroscopies, and optical laser pump-X-ray probe techniques using picosecond and femtosecond X-ray pulses. The interpretation of ultrafast structural changes, time-resolved spectra, quantum yields, and time scales of elementary processes or transient lifetimes needs robust theoretical tools combining state-of-the-art quantum chemistry and developments in quantum dynamics for solving the electronic and nuclear problems. Multimode molecular dynamics beyond the Born-Oppenheimer approximation has been successfully applied to many small polyatomic systems. Its application to large molecules containing a transition metal atom is still a challenge because of the nuclear dimensionality of the problem, the high density of electronic excited states, and the spin-orbit coupling effects. Rhenium(I) α-diimine carbonyl complexes, [Re(L)(CO)3(N,N)](n+) are thermally and photochemically robust and highly flexible synthetically. Structural variations of the N,N and L ligands affect the spectroscopy, the photophysics, and the photochemistry of these chromophores easily incorporated into a complex environment. Visible light absorption opens the route to a wide range of applications such as sensors, probes, or emissive labels for imaging biomolecules. Halide complexes [Re(X)(CO)3(bpy)] (X = Cl, Br, or I; bpy = 2,2'-bipyridine) exhibit complex electronic structure and large spin-orbit effects that do not correlate with the heavy atom effects. Indeed, the (1)MLCT → (3)MLCT intersystem crossing (ISC) kinetics is slower than in [Ru(bpy)3](2+) or [Fe(bpy)3](2+) despite the presence of a third-row transition metal. Counterintuitively, singlet excited-state lifetime increases on going from Cl (85 fs) to Br (128 fs) and to I (152 fs). Moreover, correlation between the Re-X stretching mode and the rate of ISC is observed. In this Account, we emphasize on the role of spin-vibronic coupling on the mechanism of ultrafast ISC put in evidence in [Re(Br)(CO)3(bpy)]. For this purpose, we have developed a model Hamiltonian for solving an 11 electronic excited states multimode problem including vibronic and SO coupling within the linear vibronic coupling (LVC) approximation and the assumption of harmonic potentials. The presence of a central metal atom coupled to rigid ligands, such as α-diimine, ensures nuclear motion of small amplitudes and a priori justifies the use of the LVC model. The simulation of the ultrafast dynamics by wavepacket propagations using the multiconfiguration time-dependent Hartree (MCTDH) method is based on density functional theory (DFT), and its time-dependent extension to excited states (TD-DFT) electronic structure data. We believe that the interplay between time-resolved experiments and these pioneering simulations covering the first picoseconds and including spin-vibronic coupling will promote a number of quantum dynamical studies that will contribute to a better understanding of ultrafast processes in a wide range of organic and inorganic chromophores easily incorporated in biosystems or supramolecular devices for specific functions.

Spin pumping and inverse spin Hall voltages from dynamical antiferromagnets

NASA Astrophysics Data System (ADS)

Johansen, Øyvind; Brataas, Arne

2017-06-01

Dynamical antiferromagnets can pump spins into adjacent conductors. The high antiferromagnetic resonance frequencies represent a challenge for experimental detection, but magnetic fields can reduce these resonance frequencies. We compute the ac and dc inverse spin Hall voltages resulting from dynamical spin excitations as a function of a magnetic field along the easy axis and the polarization of the driving ac magnetic field perpendicular to the easy axis. We consider the insulating antiferromagnets MnF2,FeF2, and NiO. Near the spin-flop transition, there is a significant enhancement of the dc spin pumping and inverse spin Hall voltage for the uniaxial antiferromagnets MnF2 and FeF2. In the uniaxial antiferromagnets it is also found that the ac spin pumping is independent of the external magnetic field when the driving field has the optimal circular polarization. In the biaxial NiO, the voltages are much weaker, and there is no spin-flop enhancement of the dc component.

Ultrafast Photoinduced Multimode Antiferromagnetic Spin Dynamics in Exchange-Coupled Fe/RFeO3 (R = Er or Dy) Heterostructures.

PubMed

Tang, Jin; Ke, Yajiao; He, Wei; Zhang, Xiangqun; Zhang, Wei; Li, Na; Zhang, Yongsheng; Li, Yan; Cheng, Zhaohua

2018-05-25

Antiferromagnetic spin dynamics is important for both fundamental and applied antiferromagnetic spintronic devices; however, it is rarely explored by external fields because of the strong exchange interaction in antiferromagnetic materials. Here, the photoinduced excitation of ultrafast antiferromagnetic spin dynamics is achieved by capping antiferromagnetic RFeO 3 (R = Er or Dy) with an exchange-coupled ferromagnetic Fe film. Compared with antiferromagnetic spin dynamics of bare RFeO 3 orthoferrite single crystals, which can be triggered effectively by ultrafast laser heating just below the phase transition temperature, the ultrafast photoinduced multimode antiferromagnetic spin dynamic modes, for exchange-coupled Fe/RFeO 3 heterostructures, including quasiferromagnetic resonance, impurity, coherent phonon, and quasiantiferromagnetic modes, are observed in a temperature range of 10-300 K. These experimental results not only offer an effective means to trigger ultrafast antiferromagnetic spin dynamics of rare-earth orthoferrites, but also shed light on the ultrafast manipulation of antiferromagnetic magnetization in Fe/RFeO 3 heterostructures. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A Low Spin Manganese(IV) Nitride Single Molecule Magnet

PubMed Central

Ding, Mei; Cutsail, George E.; Aravena, Daniel; Amoza, Martín; Rouzières, Mathieu; Dechambenoit, Pierre; Losovyj, Yaroslav; Pink, Maren

2016-01-01

Structural, spectroscopic and magnetic methods have been used to characterize the tris(carbene)borate compound PhB(MesIm)3Mn≡N as a four-coordinate manganese(IV) complex with a low spin (S = 1/2) configuration. The slow relaxation of the magnetization in this complex, i.e. its single-molecule magnet (SMM) properties, is revealed under an applied dc field. Multireference quantum mechanical calculations indicate that this SMM behavior originates from an anisotropic ground doublet stabilized by spin-orbit coupling. Consistent theoretical and experiment data show that the resulting magnetization dynamics in this system is dominated by ground state quantum tunneling, while its temperature dependence is influenced by Raman relaxation. PMID:27746891

Heisenberg operator approach for spin squeezing dynamics

NASA Astrophysics Data System (ADS)

Bhattacherjee, Aranya Bhuti; Sharma, Deepti; Pelster, Axel

2017-12-01

We reconsider the one-axis twisting Hamiltonian, which is commonly used for generating spin squeezing, and treat its dynamics within the Heisenberg operator approach. To this end we solve the underlying Heisenberg equations of motion perturbatively and evaluate the expectation values of the resulting time-dependent Heisenberg operators in order to determine approximately the dynamics of spin squeezing. Comparing our results with those originating from exact numerics reveals that they are more accurate than the commonly used frozen spin approximation.

Lattice dynamics and thermal transport in multiferroic CuCrO2

NASA Astrophysics Data System (ADS)

Bansal, Dipanshu; Niedziela, Jennifer L.; May, Andrew F.; Said, Ayman; Ehlers, Georg; Abernathy, Douglas L.; Huq, Ashfia; Kirkham, Melanie; Zhou, Haidong; Delaire, Olivier

2017-02-01

Inelastic neutron and x-ray scattering measurements of phonons and spin waves were performed in the delafossite compound CuCrO2 over a wide range of temperature, and complemented with first-principles lattice dynamics simulations. The phonon dispersions and density of states are well reproduced by our density functional calculations, and reveal a strong anisotropy of Cu vibrations, which exhibit low-frequency modes of large amplitude parallel to the basal plane of the layered delafossite structure. The low frequency in-plane modes also show a systematic temperature dependence of neutron and x-ray scattering intensities. In addition, we find that spin fluctuations persist above 300 K, far above the Néel temperature for long-range antiferromagnetic order, TN≃24 K . Our modeling of the thermal conductivity, based on our phonon measurements and simulations, reveals a significant anisotropy and indicates that spin fluctuations above TN constitute an important source of phonon scattering, considerably suppressing the thermal conductivity compared to that of the isostructural but nonmagnetic compound CuAlO2.

Target and double spin asymmetries for {rvec e} {rvec p} {yields} e{prime} p {pi}{sup 0}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Angela Biselli

2004-03-01

An extensive experimental program to measure the spin structure of the nucleons is carried out in Hall B with the CLAS detector at Jefferson Lab using a polarized electron beam incident on a polarized target. Spin degrees of freedom offer the possibility to test, in an independent way, existing models of resonance electroproduction. The present analysis selects the exclusive channel {rvec p}({rvec e}, e{prime}, p){pi}{sup 0} from data taken in 2000-2001, to extract single and double asymmetries in a Q{sup 2} range from 0.2 to 0.75 GeV{sup 2} and W range from 1.1 to 1.6 GeV/c{sup 2}. Results of themore » asymmetries will be presented as a function of the center of mass decay angles of the {pi}{sup 0} and compared with the unitary isobar model MAID, the dynamic model by Sato and Lee and the dynamic model DMT.« less

Correlated lateral phase separations in stacks of lipid membranes

NASA Astrophysics Data System (ADS)

Hoshino, Takuma; Komura, Shigeyuki; Andelman, David

2015-12-01

Motivated by the experimental study of Tayebi et al. [Nat. Mater. 11, 1074 (2012)] on phase separation of stacked multi-component lipid bilayers, we propose a model composed of stacked two-dimensional Ising spins. We study both its static and dynamical features using Monte Carlo simulations with Kawasaki spin exchange dynamics that conserves the order parameter. We show that at thermodynamical equilibrium, due to strong inter-layer correlations, the system forms a continuous columnar structure for any finite interaction across adjacent layers. Furthermore, the phase separation shows a faster dynamics as the inter-layer interaction is increased. This temporal behavior is mainly due to an effective deeper temperature quench because of the larger value of the critical temperature, Tc, for larger inter-layer interaction. When the temperature ratio, T/Tc, is kept fixed, the temporal growth exponent does not increase and even slightly decreases as a function of the increased inter-layer interaction.

Dynamics for a 2-vertex quantum gravity model

NASA Astrophysics Data System (ADS)

Borja, Enrique F.; Díaz-Polo, Jacobo; Garay, Iñaki; Livine, Etera R.

2010-12-01

We use the recently introduced U(N) framework for loop quantum gravity to study the dynamics of spin network states on the simplest class of graphs: two vertices linked with an arbitrary number N of edges. Such graphs represent two regions, in and out, separated by a boundary surface. We study the algebraic structure of the Hilbert space of spin networks from the U(N) perspective. In particular, we describe the algebra of operators acting on that space and discuss their relation to the standard holonomy operator of loop quantum gravity. Furthermore, we show that it is possible to make the restriction to the isotropic/homogeneous sector of the model by imposing the invariance under a global U(N) symmetry. We then propose a U(N)-invariant Hamiltonian operator and study the induced dynamics. Finally, we explore the analogies between this model and loop quantum cosmology and sketch some possible generalizations of it.

Dynamical control of Mn spin-system cooling by photogenerated carriers in a (Zn,Mn)Se/BeTe heterostructure

NASA Astrophysics Data System (ADS)

Debus, J.; Maksimov, A. A.; Dunker, D.; Yakovlev, D. R.; Tartakovskii, I. I.; Waag, A.; Bayer, M.

2010-08-01

The magnetization dynamics of the Mn spin system in an undoped (Zn,Mn)Se/BeTe type-II quantum well was studied by a time-resolved pump-probe photoluminescence technique. The Mn spin temperature was evaluated from the giant Zeeman shift of the exciton line in an external magnetic field of 3 T. The relaxation dynamics of the Mn spin temperature to the equilibrium temperature of the phonon bath after the pump-laser-pulse heating can be accelerated by the presence of free electrons. These electrons, generated by a control laser pulse, mediate the spin and energy transfer from the Mn spin system to the lattice and bypass the relatively slow direct spin-lattice relaxation of the Mn ions.

Orbital effects in cobaltites by neutron scattering

NASA Astrophysics Data System (ADS)

Louca, Despina

2005-03-01

The orbital degree of freedom can play a central role in the physics of transition metal perovskite oxides because of its intricate coupling with other degrees of freedom such as spin, charge and lattice. In this talk the case of La1-xSrxCoO3 will be presented. Using elastic and inelastic neutron scattering, we investigated the thermal evolution of the local atomic structure and lattice dynamics in the pure sample and with the addition of charge carriers as the system crosses over from a paramagnetic insulator to a ferromagnetic metal. In LaCoO3, the thermal activation of the Co ions from a nonmagnetic ground state to an intermediate spin state gives rise to orbital degeneracy. This leads to Jahn-Teller distortions that are dynamical in nature. Doping stabilizes the intermediate spin configuration of the Co ions in the paramagnetic insulating phase. Evidence for local static Jahn-Teller distortions is observed but without long-range ordering. The size of the JT lattice is proportional to the amount of charge. However, with cooling to the metallic phase, static JT distortions disappear for x <= 30 %, the percolation limit. This coincides with narrowing of two modes at φ=22,nd,4,eV in the phonon spectrum in which we argue is due to localized dynamical JT fluctuations^1. The implications of the orbital effects to the structural and magnetic properties will be discussed. ^1D. Louca and J. L. Sarrao, Phys. Rev. Lett. 91, 155501 (2003).

Spin-1/2 Heisenberg antiferromagnet on an anisotropic triangular lattice

NASA Astrophysics Data System (ADS)

Starykh, Oleg

2007-03-01

The Triangular lattice spin-1/2 Heisenberg AntiFerromagnet (TAF) is a prototypical model of frustrated quantum magnetism. While it is believed to exhibit long-range order in the isotropic limit, changes such as spatial anisotropy can alter the delicate balance amongst competing ground states. I will describe the static and dynamic properties of the spatially anisotropic TAF, with inter-chain diagonal exchange J' much weaker than the intrachain exchange J. Treating J' as a perturbation of decoupled Heisenberg spin-1/2 chains, I find that the ground state is spontaneously dimerized in a four-fold degenerate zig-zag pattern. This dimerization instability is driven by quantum fluctuations, which are dramatically enhanced here by the frustrated nature of inter-chain exchange. A magnetic field partially relieves frustration, by canting the spins along the field direction, and causes a quantum phase transition into a magnetically-ordered spin-density-wave phase. This is followed by cone and, finally, fully polarized (saturated) phases, as a function of increasing magnetic field. I show that many of these features are in fact observed in experiments on the celebrated material Cs2CuCl4 (J'/J =1/3). I will also discuss the significant modification of the phase diagram by symmetry-breaking anisotropic Dzyaloshinskii-Moriya (DM) interactions, present in this interesting magnet. In addition to static and thermodynamic properties, the proposed ``one-dimensional'' approach offers a compelling explanation of the unusual experimentally measured dynamical structure factor of Cs2CuCl4 in terms of descendants of one-dimensional spinons. Quite generally, I find characteristic features of a momentum-dependent spinon bound state and a dispersing incoherent excitation in the structure factor, in agreement with experiments.

SD-CAS: Spin Dynamics by Computer Algebra System.

PubMed

Filip, Xenia; Filip, Claudiu

2010-11-01

A computer algebra tool for describing the Liouville-space quantum evolution of nuclear 1/2-spins is introduced and implemented within a computational framework named Spin Dynamics by Computer Algebra System (SD-CAS). A distinctive feature compared with numerical and previous computer algebra approaches to solving spin dynamics problems results from the fact that no matrix representation for spin operators is used in SD-CAS, which determines a full symbolic character to the performed computations. Spin correlations are stored in SD-CAS as four-entry nested lists of which size increases linearly with the number of spins into the system and are easily mapped into analytical expressions in terms of spin operator products. For the so defined SD-CAS spin correlations a set of specialized functions and procedures is introduced that are essential for implementing basic spin algebra operations, such as the spin operator products, commutators, and scalar products. They provide results in an abstract algebraic form: specific procedures to quantitatively evaluate such symbolic expressions with respect to the involved spin interaction parameters and experimental conditions are also discussed. Although the main focus in the present work is on laying the foundation for spin dynamics symbolic computation in NMR based on a non-matrix formalism, practical aspects are also considered throughout the theoretical development process. In particular, specific SD-CAS routines have been implemented using the YACAS computer algebra package (http://yacas.sourceforge.net), and their functionality was demonstrated on a few illustrative examples. Copyright © 2010 Elsevier Inc. All rights reserved.

Spin dynamics in helical molecules with nonlinear interactions

NASA Astrophysics Data System (ADS)

Díaz, E.; Albares, P.; Estévez, P. G.; Cerveró, J. M.; Gaul, C.; Diez, E.; Domínguez-Adame, F.

2018-04-01

It is widely admitted that the helical conformation of certain chiral molecules may induce a sizable spin selectivity observed in experiments. Spin selectivity arises as a result of the interplay between a helicity-induced spin–orbit coupling (SOC) and electric dipole fields in the molecule. From the theoretical point of view, different phenomena might affect the spin dynamics in helical molecules, such as quantum dephasing, dissipation and the role of metallic contacts. With a few exceptions, previous studies usually neglect the local deformation of the molecule about the carrier, but this assumption seems unrealistic to describe charge transport in molecular systems. We introduce an effective model describing the electron spin dynamics in a deformable helical molecule with weak SOC. We find that the electron–lattice interaction allows the formation of stable solitons such as bright solitons with well defined spin projection onto the molecule axis. We present a thorough study of these bright solitons and analyze their possible impact on the spin dynamics in deformable helical molecules.

Switching of chiral magnetic skyrmions by picosecond magnetic field pulses via transient topological states

PubMed Central

Heo, Changhoon; Kiselev, Nikolai S.; Nandy, Ashis Kumar; Blügel, Stefan; Rasing, Theo

2016-01-01

Magnetic chiral skyrmions are vortex like spin structures that appear as stable or meta-stable states in magnetic materials due to the interplay between the symmetric and antisymmetric exchange interactions, applied magnetic field and/or uniaxial anisotropy. Their small size and internal stability make them prospective objects for data storage but for this, the controlled switching between skyrmion states of opposite polarity and topological charge is essential. Here we present a study of magnetic skyrmion switching by an applied magnetic field pulse based on a discrete model of classical spins and atomistic spin dynamics. We found a finite range of coupling parameters corresponding to the coexistence of two degenerate isolated skyrmions characterized by mutually inverted spin structures with opposite polarity and topological charge. We demonstrate how for a wide range of material parameters a short inclined magnetic field pulse can initiate the reliable switching between these states at GHz rates. Detailed analysis of the switching mechanism revealed the complex path of the system accompanied with the excitation of a chiral-achiral meron pair and the formation of an achiral skyrmion. PMID:27273157

Switching of chiral magnetic skyrmions by picosecond magnetic field pulses via transient topological states.

PubMed

Heo, Changhoon; Kiselev, Nikolai S; Nandy, Ashis Kumar; Blügel, Stefan; Rasing, Theo

2016-06-08

Magnetic chiral skyrmions are vortex like spin structures that appear as stable or meta-stable states in magnetic materials due to the interplay between the symmetric and antisymmetric exchange interactions, applied magnetic field and/or uniaxial anisotropy. Their small size and internal stability make them prospective objects for data storage but for this, the controlled switching between skyrmion states of opposite polarity and topological charge is essential. Here we present a study of magnetic skyrmion switching by an applied magnetic field pulse based on a discrete model of classical spins and atomistic spin dynamics. We found a finite range of coupling parameters corresponding to the coexistence of two degenerate isolated skyrmions characterized by mutually inverted spin structures with opposite polarity and topological charge. We demonstrate how for a wide range of material parameters a short inclined magnetic field pulse can initiate the reliable switching between these states at GHz rates. Detailed analysis of the switching mechanism revealed the complex path of the system accompanied with the excitation of a chiral-achiral meron pair and the formation of an achiral skyrmion.

Low-energy spin dynamics of orthoferrites AFeO3 (A  =  Y, La, Bi)

NASA Astrophysics Data System (ADS)

Park, Kisoo; Sim, Hasung; Leiner, Jonathan C.; Yoshida, Yoshiyuki; Jeong, Jaehong; Yano, Shin-ichiro; Gardner, Jason; Bourges, Philippe; Klicpera, Milan; Sechovský, Vladimír; Boehm, Martin; Park, Je-Geun

2018-06-01

YFeO3 and LaFeO3 are members of the rare-earth orthoferrites family with Pbnm space group. Using inelastic neutron scattering, the low-energy spin excitations have been measured around the magnetic Brillouin zone center. Splitting of magnon branches and finite magnon gaps (∼2 meV) are observed for both compounds, where the Dzyaloshinsky–Moriya interactions account for most of this gap with some additional contribution from single-ion anisotropy. We also make comparisons with multiferroic BiFeO3 (R3c space group), in which similar behavior was observed. By taking into account all relevant local Dzyaloshinsky–Moriya interactions, our analysis allows for the precise determination of all experimentally observed parameters in the spin-Hamiltonian. We find that different properties of the Pbnm and R3c space group lead to the stabilization of a spin cycloid structure in the latter case but not in the former, which explains the difference in the levels of complexity of magnon band structures for the respective compounds.

Effect of spin-orbit and on-site Coulomb interactions on the electronic structure and lattice dynamics of uranium monocarbide

NASA Astrophysics Data System (ADS)

Wdowik, U. D.; Piekarz, P.; Legut, D.; Jagło, G.

2016-08-01

Uranium monocarbide, a potential fuel material for the generation IV reactors, is investigated within density functional theory. Its electronic, magnetic, elastic, and phonon properties are analyzed and discussed in terms of spin-orbit interaction and localized versus itinerant behavior of the 5 f electrons. The localization of the 5 f states is tuned by varying the local Coulomb repulsion interaction parameter. We demonstrate that the theoretical electronic structure, elastic constants, phonon dispersions, and their densities of states can reproduce accurately the results of x-ray photoemission and bremsstrahlung isochromat measurements as well as inelastic neutron scattering experiments only when the 5 f states experience the spin-orbit interaction and simultaneously remain partially localized. The partial localization of the 5 f electrons could be represented by a moderate value of the on-site Coulomb interaction parameter of about 2 eV. The results of the present studies indicate that both strong electron correlations and spin-orbit effects are crucial for realistic theoretical description of the ground-state properties of uranium carbide.

Helical waves in easy-plane antiferromagnets

NASA Astrophysics Data System (ADS)

Semenov, Yuriy G.; Li, Xi-Lai; Xu, Xinyi; Kim, Ki Wook

2017-12-01

Effective spin torques can generate the Néel vector oscillations in antiferromagnets (AFMs). Here, it is theoretically shown that these torques applied at one end of a normal AFM strip can excite a helical type of spin wave in the strip whose properties are drastically different from characteristic spin waves. An analysis based on both a Néel vector dynamical equation and the micromagnetic simulation identifies the direction of magnetic anisotropy and the damping factor as the two key parameters determining the dynamics. Helical wave propagation requires the hard axis of the easy-plane AFM to be aligned with the traveling direction, while the damping limits its spatial extent. If the damping is neglected, the calculation leads to a uniform periodic domain wall structure. On the other hand, finite damping decelerates the helical wave rotation around the hard axis, ultimately causing stoppage of its propagation along the strip. With the group velocity staying close to spin-wave velocity at the wave front, the wavelength becomes correspondingly longer away from the excitation point. In a sufficiently short strip, a steady-state oscillation can be established whose frequency is controlled by the waveguide length as well as the excitation energy or torque.

Dynamics of Proton Spin: Role of qqq Force

NASA Astrophysics Data System (ADS)

Mitra, A. N.

The analytic structure of the qqq wave function, obtained recently in the high momentum regime of QCD, is employed for the formulation of baryonic transition amplitudes via quark loops. A new aspect of this study is the role of a direct (Y -shaped, Mercedes-Benz type) qqq force in generating the qqq wave function The dynamics is that of a Salpeter-like equation (3D support for the kernel) formulated covariantly on the light front, a la Markov-Yukawa Transversality Principle (MYTP) which warrants a 2-way interconnection between the 3D and 4D Bethe-Salpeter (BSE) forms for 2 as well as 3 fermion quarks. The dynamics of this 3-body force shows up through a characteristic singularity in the hypergeometric differential equation for the 3D wave function ϕ, corresponding to a negative eigenvalue of the spin operator iσ1·σ2 × σ3 which is an integral part of the qqq force. As a first application of this wave function to the problem of the proton spin anomaly, the two-gluon contribution to the anomaly yields an estimate of the right sign, although somewhat smaller in magnitude.

Understanding Unimer Exchange Processes in Block Copolymer Micelles using NMR Diffusometry, Time-Resolved NMR, and SANS

NASA Astrophysics Data System (ADS)

Madsen, Louis; Kidd, Bryce; Li, Xiuli; Miller, Katherine; Cooksey, Tyler; Robertson, Megan

Our team seeks to understand dynamic behaviors of block copolymer micelles and their interplay with encapsulated cargo molecules. Quantifying unimer and cargo exchange rates micelles can provide critical information for determining mechanisms of unimer exchange as well as designing systems for specific cargo release dynamics. We are exploring the utility of NMR spectroscopy and diffusometry techniques as complements to existing SANS and fluorescence methods. One promising new method involves time-resolved NMR spin relaxation measurements, wherein mixing of fully protonated and 2H-labeled PEO-b-PCL micelles solutions shows an increase in spin-lattice relaxation time (T1) with time after mixing. This is due to a weakening in magnetic environment surrounding 1H spins as 2H-bearing unimers join fully protonated micelles. We are measuring time constants for unimer exchange of minutes to hours, and we expect to resolve times of <1 min. This method can work on any solution NMR spectrometer and with minimal perturbation to chemical structure (as in dye-labelled fluorescence methods). Multimodal NMR can complement existing characterization tools, expanding and accelerating dynamics measurements for polymer micelle, nanogel, and nanoparticle developers.

Effect of spin traps on charge transport in low-bandgap copolymer:fullerene composites

NASA Astrophysics Data System (ADS)

Krinichnyi, Victor I.; Yudanova, Evgeniya I.; Bogatyrenko, Victor R.

2017-12-01

Light-Induced EPR study of magnetic, relaxation and dynamic parameters of spin charge carriers background photoinduced in bulk heterojunctions of composites formed by poly[2,7-(9,9-dioctylfluorene)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PFO-DBT) and poly[N-9‧-heptadecanyl-2,7-carbazole-alt-5,5-(4‧,7‧-di-2-thienyl-2‧,1‧,3‧-benzothiadiazole)] (PCDTBT) with methanofullerene [6,6]-phenyl-C61-butyric acid methyl ester is described. A part of polarons is captured by deep spin traps whose number and energy depth are governed by the structure, morphology of a copolymer matrix and also by the photon energy. Both the composites exhibit photo-response within photon energy/wavelength 1.32-3.14 eV/940-395 nm region which is wider than that of other polymer composites. Magnetic, relaxation and dynamics parameters of spin charge carriers were shown to be governed by their exchange interaction and photon energy. Specific morphology of the composites causes selectivity of these parameters to the photon energy. It was shown that the anisotropy of spin mobility through bulk heterojunctions reflects the system dimensionality and is governed by the photon properties. The replacement of the PFO-DBT backbone by the PCDTBT matrix leads increases the ordering of a copolymer, decreases the number of spin traps and changes a mechanism of charge recombination. The decay of free charge carriers was interpreted in terms of the trapping-detrapping spin diffusion in bulk heterojunctions.

X-ray imaging of spin currents and magnetisation dynamics at the nanoscale

NASA Astrophysics Data System (ADS)

Bonetti, Stefano

2017-04-01

Understanding how spins move in time and space is the aim of both fundamental and applied research in modern magnetism. Over the past three decades, research in this field has led to technological advances that have had a major impact on our society, while improving the understanding of the fundamentals of spin physics. However, important questions still remain unanswered, because it is experimentally challenging to directly observe spins and their motion with a combined high spatial and temporal resolution. In this article, we present an overview of the recent advances in x-ray microscopy that allow researchers to directly watch spins move in time and space at the microscopically relevant scales. We discuss scanning x-ray transmission microscopy (STXM) at resonant soft x-ray edges, which is available at most modern synchrotron light sources. This technique measures magnetic contrast through the x-ray magnetic circular dichroism (XMCD) effect at the resonant absorption edges, while focusing the x-ray radiation at the nanometre scale, and using the intrinsic pulsed structure of synchrotron-generated x-rays to create time-resolved images of magnetism at the nanoscale. In particular, we discuss how the presence of spin currents can be detected by imaging spin accumulation, and how the magnetisation dynamics in thin ferromagnetic films can be directly imaged. We discuss how a direct look at the phenomena allows for a deeper understanding of the the physics at play, that is not accessible to other, more indirect techniques. Finally, we present an overview of the exciting opportunities that lie ahead to further understand the fundamentals of novel spin physics, opportunities offered by the appearance of diffraction limited storage rings and free electron lasers.

X-ray imaging of spin currents and magnetisation dynamics at the nanoscale.

PubMed

Bonetti, Stefano

2017-04-05

Understanding how spins move in time and space is the aim of both fundamental and applied research in modern magnetism. Over the past three decades, research in this field has led to technological advances that have had a major impact on our society, while improving the understanding of the fundamentals of spin physics. However, important questions still remain unanswered, because it is experimentally challenging to directly observe spins and their motion with a combined high spatial and temporal resolution. In this article, we present an overview of the recent advances in x-ray microscopy that allow researchers to directly watch spins move in time and space at the microscopically relevant scales. We discuss scanning x-ray transmission microscopy (STXM) at resonant soft x-ray edges, which is available at most modern synchrotron light sources. This technique measures magnetic contrast through the x-ray magnetic circular dichroism (XMCD) effect at the resonant absorption edges, while focusing the x-ray radiation at the nanometre scale, and using the intrinsic pulsed structure of synchrotron-generated x-rays to create time-resolved images of magnetism at the nanoscale. In particular, we discuss how the presence of spin currents can be detected by imaging spin accumulation, and how the magnetisation dynamics in thin ferromagnetic films can be directly imaged. We discuss how a direct look at the phenomena allows for a deeper understanding of the the physics at play, that is not accessible to other, more indirect techniques. Finally, we present an overview of the exciting opportunities that lie ahead to further understand the fundamentals of novel spin physics, opportunities offered by the appearance of diffraction limited storage rings and free electron lasers.

Probing ultrafast spin dynamics through a magnon resonance in the antiferromagnetic multiferroic HoMnO 3

DOE PAGES

Bowlan, P.; Trugman, S. A.; Bowlan, J.; ...

2016-09-26

Here, we demonstrate an approach for directly tracking antiferromagnetic (AFM) spin dynamics by measuring ultrafast changes in a magnon resonance. We also test this idea on the multiferroic HoMnO 3 by optically photoexciting electrons, after which changes in the spin order are probed with a THz pulse tuned to a magnon resonance. This reveals a photoinduced change in the magnon line shape that builds up over 5–12 picoseconds, which we show to be the spin-lattice thermalization time, indicating that electrons heat the spins via phonons. We compare our results to previous studies of spin-lattice thermalization in ferromagnetic manganites, giving insightmore » into fundamental differences between the two systems. Finally, our work sheds light on the microscopic mechanism governing spin-phonon interactions in AFMs and demonstrates a powerful approach for directly monitoring ultrafast spin dynamics.« less

Probing ultrafast spin dynamics through a magnon resonance in the antiferromagnetic multiferroic HoMnO 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bowlan, P.; Trugman, S. A.; Bowlan, J.

Here, we demonstrate an approach for directly tracking antiferromagnetic (AFM) spin dynamics by measuring ultrafast changes in a magnon resonance. We also test this idea on the multiferroic HoMnO 3 by optically photoexciting electrons, after which changes in the spin order are probed with a THz pulse tuned to a magnon resonance. This reveals a photoinduced change in the magnon line shape that builds up over 5–12 picoseconds, which we show to be the spin-lattice thermalization time, indicating that electrons heat the spins via phonons. We compare our results to previous studies of spin-lattice thermalization in ferromagnetic manganites, giving insightmore » into fundamental differences between the two systems. Finally, our work sheds light on the microscopic mechanism governing spin-phonon interactions in AFMs and demonstrates a powerful approach for directly monitoring ultrafast spin dynamics.« less

Dynamical control of a quantum Kapitza pendulum in a spin-1 BEC

NASA Astrophysics Data System (ADS)

Hoang, Thai; Gerving, Corey; Land, Ben; Anquez, Martin; Hamley, Chris; Chapman, Michael

2013-05-01

We demonstrate dynamic stabilization of an unstable strongly interacting quantum many-body system by periodic manipulation of the phase of the collective states. The experiment employs a spin-1 atomic Bose condensate that has spin dynamics analogous to a non-rigid pendulum in the mean-field limit. The condensate spin is initialized to an unstable (hyperbolic) fixed point of the phase space, where subsequent free evolution gives rise to spin-nematic squeezing and quantum spin mixing. To stabilize the system, periodic microwave pulses are applied that manipulate the spin-nematic fluctuations and limit their growth. The range of pulse periods and phase shifts with which the condensate can be stabilized is measured and compares well with a linear stability analysis of the problem. C.D. Hamley, et al., ``Spin-Nematic Squeezed Vacuum in a Quantum Gas,'' Nature Physics 8, 305-308 (2012).

NMR investigations of molecular dynamics

NASA Astrophysics Data System (ADS)

Palmer, Arthur

2011-03-01

NMR spectroscopy is a powerful experimental approach for characterizing protein conformational dynamics on multiple time scales. The insights obtained from NMR studies are complemented and by molecular dynamics (MD) simulations, which provide full atomistic details of protein dynamics. Homologous mesophilic (E. coli) and thermophilic (T. thermophilus) ribonuclease H (RNase H) enzymes serve to illustrate how changes in protein sequence and structure that affect conformational dynamic processes can be monitored and characterized by joint analysis of NMR spectroscopy and MD simulations. A Gly residue inserted within a putative hinge between helices B and C is conserved among thermophilic RNases H, but absent in mesophilic RNases H. Experimental spin relaxation measurements show that the dynamic properties of T. thermophilus RNase H are recapitulated in E. coli RNase H by insertion of a Gly residue between helices B and C. Additional specific intramolecular interactions that modulate backbone and sidechain dynamical properties of the Gly-rich loop and of the conserved Trp residue flanking the Gly insertion site have been identified using MD simulations and subsequently confirmed by NMR spin relaxation measurements. These results emphasize the importance of hydrogen bonds and local steric interactions in restricting conformational fluctuations, and the absence of such interactions in allowing conformational adaptation to substrate binding.

NMR Studies of Mass Transport in New Conducting Media for Fuel Cells

DTIC Science & Technology

2009-01-01

PEM films, for example those containing phosphoric acid and ionic liquids . Dynamical processes are probed at the short range by spin-lattice...structural environments of muticomponent PEM films, for example those containing phosphoric acid and ionic liquids . Dynamical processes are probed at the...correlation between water diffusivity and proton conductivity in the nanocomposites Transport properties of several ionic liquids (IL’s) and membranes

Equations of motion of test particles for solving the spin-dependent Boltzmann–Vlasov equation

DOE PAGES

Xia, Yin; Xu, Jun; Li, Bao-An; ...

2016-06-16

A consistent derivation of the equations of motion (EOMs) of test particles for solving the spin-dependent Boltzmann–Vlasov equation is presented. The resulting EOMs in phase space are similar to the canonical equations in Hamiltonian dynamics, and the EOM of spin is the same as that in the Heisenburg picture of quantum mechanics. Considering further the quantum nature of spin and choosing the direction of total angular momentum in heavy-ion reactions as a reference of measuring nucleon spin, the EOMs of spin-up and spin-down nucleons are given separately. The key elements affecting the spin dynamics in heavy-ion collisions are identified. Themore » resulting EOMs provide a solid foundation for using the test-particle approach in studying spin dynamics in heavy-ion collisions at intermediate energies. Future comparisons of model simulations with experimental data will help to constrain the poorly known in-medium nucleon spin–orbit coupling relevant for understanding properties of rare isotopes and their astrophysical impacts.« less

The influence of gyroscopic forces on the dynamic behavior and flutter of rotating blades

NASA Technical Reports Server (NTRS)

Sisto, F.; Chang, A. T.

1983-01-01

The structural dynamics of a cantilever turbomachine blade mounted on a spinning and precessing rotor are investigated. Both stability and forced vibration are considered with a blade model that increases in complexity (and verisimilitude) from a spring-restrained point mass, to a uniform cantilever, to a twisted uniform cantilever turbomachine blade mounted on a spinning and precessing rotor are investigated. Both stability and forced vibration are considered with a blade model that increases in complexity (and verisimilitude) from a spring-restrained point mass, to a uniform cantilever, to a twisted uniform cantilever, to a tapered twisted cantilever of arbitrary cross-section. In every instance the formulation is from first principles using a finite element based on beam theory. Both ramp-type and periodic-type precessional angular displacements are considered. In concluding, forced vibrating and flutter are studied using the final and most sophisticated structural model. The analysis of stability is presented and a number of numerical examples are worked out.

Theoretical approach to resonant inelastic x-ray scattering in iron-based superconductors at the energy scale of the superconducting gap

PubMed Central

Marra, Pasquale; van den Brink, Jeroen; Sykora, Steffen

2016-01-01

We develop a phenomenological theory to predict the characteristic features of the momentum-dependent scattering amplitude in resonant inelastic x-ray scattering (RIXS) at the energy scale of the superconducting gap in iron-based super-conductors. Taking into account all relevant orbital states as well as their specific content along the Fermi surface we evaluate the charge and spin dynamical structure factors for the compounds LaOFeAs and LiFeAs, based on tight-binding models which are fully consistent with recent angle-resolved photoemission spectroscopy (ARPES) data. We find a characteristic intensity redistribution between charge and spin dynamical structure factors which discriminates between sign-reversing and sign-preserving quasiparticle excitations. Consequently, our results show that RIXS spectra can distinguish between s± and s++ wave gap functions in the singlet pairing case. In addition, we find that an analogous intensity redistribution at small momenta can reveal the presence of a chiral p-wave triplet pairing. PMID:27151253

Phenomenological study of decoherence in solid-state spin qubits due to nuclear spin diffusion

NASA Astrophysics Data System (ADS)

Biercuk, Michael J.; Bluhm, Hendrik

2011-06-01

We present a study of the prospects for coherence preservation in solid-state spin qubits using dynamical decoupling protocols. Recent experiments have provided the first demonstrations of multipulse dynamical decoupling sequences in this qubit system, but quantitative analyses of potential coherence improvements have been hampered by a lack of concrete knowledge of the relevant noise processes. We present calculations of qubit coherence under the application of arbitrary dynamical decoupling pulse sequences based on an experimentally validated semiclassical model. This phenomenological approach bundles the details of underlying noise processes into a single experimentally relevant noise power spectral density. Our results show that the dominant features of experimental measurements in a two-electron singlet-triplet spin qubit can be replicated using a 1/ω2 noise power spectrum associated with nuclear spin flips in the host material. Beginning with this validation, we address the effects of nuclear programming, high-frequency nuclear spin dynamics, and other high-frequency classical noise sources, with conjectures supported by physical arguments and microscopic calculations where relevant. Our results provide expected performance bounds and identify diagnostic metrics that can be measured experimentally in order to better elucidate the underlying nuclear spin dynamics.

Ion dynamics in a new class of materials: nanoglassy lithium alumosilicates

NASA Astrophysics Data System (ADS)

Stanje, B.; Bottke, P.; Breuer, S.; Hanzu, I.; Heitjans, P.; Wilkening, M.

2018-03-01

In many cases nanocrystalline materials, prepared through high-energy ball milling, reveal enhanced ion dynamics when compared to the situation in the coarse-grained analogues. This effect, which has particularly been seen for lithium alumosilicates, has been ascribed to structural disorder, i.e., the introduction of defect sites during mechanical treatment. Much less is, however, known about ion transport in nanostructured amorphous materials, e.g., nanoglassy compounds, which are regarded as a new class of functional materials. Following earlier studies on nanoglassy lithium alumosilicates and borates, here we studied ion dynamics in nanoglassy petalite LiAlSi4O10. While conductivity spectroscopy unequivocally reveals that long-range ion dynamics in nanoglassy LiAlSi4O10 decreases upon milling, local dynamics, sensed by 7Li nuclear magnetic resonance (NMR) spin-lattice relaxation, points to enhanced Li ion mobility compared to the non-treated glass. Most likely, as for nanocrystalline ceramics also for nanoglassy samples a heterogeneous structure, consisting of bulk and interfacial regions, is formed. For LiAlSi4O10 these interfacial regions, characterized by a higher degree of free volume, might act as hosts for spins experiencing fast longitudinal NMR relaxation. Obviously, these regions do not form a through-going network, which would allow the ions to move over long distances as quickly as in the unmilled glass.

Surface hopping trajectory simulations with spin-orbit and dynamical couplings

NASA Astrophysics Data System (ADS)

Granucci, Giovanni; Persico, Maurizio; Spighi, Gloria

2012-12-01

In this paper we consider the inclusion of the spin-orbit interaction in surface hopping molecular dynamics simulations to take into account spin forbidden transitions. Two alternative approaches are examined. The spin-diabatic one makes use of eigenstates of the spin-free electronic Hamiltonian and of hat{S}^2 and is commonly applied when the spin-orbit coupling is weak. We point out some inconsistencies of this approach, especially important when more than two spin multiplets are coupled. The spin-adiabatic approach is based on the eigenstates of the total electronic Hamiltonian including the spin-orbit coupling. Advantages and drawbacks of both strategies are discussed and illustrated with the help of two model systems.

Spin-orbit torque-driven skyrmion dynamics revealed by time-resolved X-ray microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Woo, Seonghoon; Song, Kyung Mee; Han, Hee-Sung

Magnetic skyrmions are topologically protected spin textures with attractive properties suitable for high-density and low-power spintronic device applications. Much effort has been dedicated to understanding the dynamical behaviours of the magnetic skyrmions. However, experimental observation of the ultrafast dynamics of this chiral magnetic texture in real space, which is the hallmark of its quasiparticle nature, has so far remained elusive. Here, we report nanosecond-dynamics of a 100nm-diameter magnetic skyrmion during a current pulse application, using a time-resolved pump-probe soft X-ray imaging technique. We demonstrate that distinct dynamic excitation states of magnetic skyrmions, triggered by current-induced spin-orbit torques, can be reliablymore » tuned by changing the magnitude of spin-orbit torques. Our findings show that the dynamics of magnetic skyrmions can be controlled by the spin-orbit torque on the nanosecond time scale, which points to exciting opportunities for ultrafast and novel skyrmionic appl ications in the future.« less

Spin-orbit torque-driven skyrmion dynamics revealed by time-resolved X-ray microscopy

DOE PAGES

Woo, Seonghoon; Song, Kyung Mee; Han, Hee-Sung; ...

2017-05-24

Magnetic skyrmions are topologically protected spin textures with attractive properties suitable for high-density and low-power spintronic device applications. Much effort has been dedicated to understanding the dynamical behaviours of the magnetic skyrmions. However, experimental observation of the ultrafast dynamics of this chiral magnetic texture in real space, which is the hallmark of its quasiparticle nature, has so far remained elusive. Here, we report nanosecond-dynamics of a 100nm-diameter magnetic skyrmion during a current pulse application, using a time-resolved pump-probe soft X-ray imaging technique. We demonstrate that distinct dynamic excitation states of magnetic skyrmions, triggered by current-induced spin-orbit torques, can be reliablymore » tuned by changing the magnitude of spin-orbit torques. Our findings show that the dynamics of magnetic skyrmions can be controlled by the spin-orbit torque on the nanosecond time scale, which points to exciting opportunities for ultrafast and novel skyrmionic appl ications in the future.« less

Lorentzian symmetry predicts universality beyond scaling laws

NASA Astrophysics Data System (ADS)

Watson, Stephen J.

2017-06-01

We present a covariant theory for the ageing characteristics of phase-ordering systems that possess dynamical symmetries beyond mere scalings. A chiral spin dynamics which conserves the spin-up (+) and spin-down (-) fractions, μ+ and μ- , serves as the emblematic paradigm of our theory. Beyond a parabolic spatio-temporal scaling, we discover a hidden Lorentzian dynamical symmetry therein, and thereby prove that the characteristic length L of spin domains grows in time t according to L = \\fracβ{\\sqrt{1 - σ^2}}t\\frac{1{2}} , where σ:= μ+ - μ- (the invariant spin-excess) and β is a universal constant. Furthermore, the normalised length distributions of the spin-up and the spin-down domains each provably adopt a coincident universal (σ-independent) time-invariant form, and this supra-universal probability distribution is empirically verified to assume a form reminiscent of the Wigner surmise.

High Performance Nuclear Magnetic Resonance Imaging Using Magnetic Resonance Force Microscopy

DTIC Science & Technology

2013-12-12

Micron- Size Ferromagnet . Physical Review Letters, 92(3) 037205 (2004) [22] A. Z. Genack and A. G. Redeld. Theory of nuclear spin diusion in a...perform spatially resolved scanned probe studies of spin dynamics in nanoscale ensembles of few electron spins of varying size . Our research culminated...perform spatially resolved scanned probe studies of spin dynamics in nanoscale ensembles of few electron spins of varying size . Our research culminated

Coevolution of Glauber-like Ising dynamics and topology

NASA Astrophysics Data System (ADS)

Mandrà, Salvatore; Fortunato, Santo; Castellano, Claudio

2009-11-01

We study the coevolution of a generalized Glauber dynamics for Ising spins with tunable threshold and of the graph topology where the dynamics takes place. This simple coevolution dynamics generates a rich phase diagram in the space of the two parameters of the model, the threshold and the rewiring probability. The diagram displays phase transitions of different types: spin ordering, percolation, and connectedness. At variance with traditional coevolution models, in which all spins of each connected component of the graph have equal value in the stationary state, we find that, for suitable choices of the parameters, the system may converge to a state in which spins of opposite sign coexist in the same component organized in compact clusters of like-signed spins. Mean field calculations enable one to estimate some features of the phase diagram.

Dipolar Spin Ice States with a Fast Monopole Hopping Rate in CdEr2X4 (X =Se , S)

NASA Astrophysics Data System (ADS)

Gao, Shang; Zaharko, O.; Tsurkan, V.; Prodan, L.; Riordan, E.; Lago, J.; Fâk, B.; Wildes, A. R.; Koza, M. M.; Ritter, C.; Fouquet, P.; Keller, L.; Canévet, E.; Medarde, M.; Blomgren, J.; Johansson, C.; Giblin, S. R.; Vrtnik, S.; Luzar, J.; Loidl, A.; Rüegg, Ch.; Fennell, T.

2018-03-01

Excitations in a spin ice behave as magnetic monopoles, and their population and mobility control the dynamics of a spin ice at low temperature. CdEr2 Se4 is reported to have the Pauling entropy characteristic of a spin ice, but its dynamics are three orders of magnitude faster than the canonical spin ice Dy2 Ti2 O7 . In this Letter we use diffuse neutron scattering to show that both CdEr2 Se4 and CdEr2 S4 support a dipolar spin ice state—the host phase for a Coulomb gas of emergent magnetic monopoles. These Coulomb gases have similar parameters to those in Dy2 Ti2 O7 , i.e., dilute and uncorrelated, and so cannot provide three orders faster dynamics through a larger monopole population alone. We investigate the monopole dynamics using ac susceptometry and neutron spin echo spectroscopy, and verify the crystal electric field Hamiltonian of the Er3 + ions using inelastic neutron scattering. A quantitative calculation of the monopole hopping rate using our Coulomb gas and crystal electric field parameters shows that the fast dynamics in CdEr2X4 (X =Se , S) are primarily due to much faster monopole hopping. Our work suggests that CdEr2X4 offer the possibility to study alternative spin ice ground states and dynamics, with equilibration possible at much lower temperatures than the rare earth pyrochlore examples.

High temperature spin dynamics in linear magnetic chains, molecular rings, and segments by nuclear magnetic resonance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adelnia, Fatemeh; Lascialfari, Alessandro; Dipartimento di Fisica, Università degli Studi di Pavia and INSTM, Pavia

2015-05-07

We present the room temperature proton nuclear magnetic resonance (NMR) nuclear spin-lattice relaxation rate (NSLR) results in two 1D spin chains: the Heisenberg antiferromagnetic (AFM) Eu(hfac){sub 3}NITEt and the magnetically frustrated Gd(hfac){sub 3}NITEt. The NSLR as a function of external magnetic field can be interpreted very well in terms of high temperature spin dynamics dominated by a long time persistence of the decay of the two-spin correlation function due to the conservation of the total spin value for isotropic Heisenberg chains. The high temperature spin dynamics are also investigated in Heisenberg AFM molecular rings. In both Cr{sub 8} closed ringmore » and in Cr{sub 7}Cd and Cr{sub 8}Zn open rings, i.e., model systems for a finite spin segment, an enhancement of the low frequency spectral density is found consistent with spin diffusion but the high cut-off frequency due to intermolecular anisotropic interactions prevents a detailed analysis of the spin diffusion regime.« less

Modulation of spin dynamics via voltage control of spin-lattice coupling in multiferroics

DOE PAGES

Zhu, Mingmin; Zhou, Ziyao; Peng, Bin; ...

2017-02-03

Our work aims at magnonics manipulation by the magnetoelectric coupling effect and is motivated by the most recent progresses in both magnonics (spin dynamics) and multiferroics fields. Here, voltage control of magnonics, particularly the surface spin waves, is achieved in La 0.7Sr 0.3MnO 3/0.7Pb(Mg 1/3Nb 2/3)O 3-0.3PbTiO 3 multiferroic heterostructures. With the electron spin resonance method, a large 135 Oe shift of surface spin wave resonance (≈7 times greater than conventional voltage-induced ferromagnetic resonance shift of 20 Oe) is determined. A model of the spin-lattice coupling effect, i.e., varying exchange stiffness due to voltage-induced anisotropic lattice changes, has been establishedmore » to explain experiment results with good agreement. In addition, an “on” and “off” spin wave state switch near the critical angle upon applying a voltage is created. The modulation of spin dynamics by spin-lattice coupling effect provides a platform for realizing energy-efficient, tunable magnonics devices.« less

Manifestations of Dynamical Localization in the Disordered XXZ Spin Chain

NASA Astrophysics Data System (ADS)

Elgart, Alexander; Klein, Abel; Stolz, Günter

2018-04-01

We study disordered XXZ spin chains in the Ising phase exhibiting droplet localization, a single cluster localization property we previously proved for random XXZ spin chains. It holds in an energy interval I near the bottom of the spectrum, known as the droplet spectrum. We establish dynamical manifestations of localization in the energy window I, including non-spreading of information, zero-velocity Lieb-Robinson bounds, and general dynamical clustering. Our results do not rely on knowledge of the dynamical characteristics of the model outside the droplet spectrum. A byproduct of our analysis is that for random XXZ spin chains this droplet localization can happen only inside the droplet spectrum.

Fast domain wall motion in the vicinity of the angular momentum compensation temperature of ferrimagnets

NASA Astrophysics Data System (ADS)

Kim, Kab-Jin; Kim, Se Kwon; Hirata, Yuushou; Oh, Se-Hyeok; Tono, Takayuki; Kim, Duck-Ho; Okuno, Takaya; Ham, Woo Seung; Kim, Sanghoon; Go, Gyoungchoon; Tserkovnyak, Yaroslav; Tsukamoto, Arata; Moriyama, Takahiro; Lee, Kyung-Jin; Ono, Teruo

2017-12-01

Antiferromagnetic spintronics is an emerging research field which aims to utilize antiferromagnets as core elements in spintronic devices. A central motivation towards this direction is that antiferromagnetic spin dynamics is expected to be much faster than its ferromagnetic counterpart. Recent theories indeed predicted faster dynamics of antiferromagnetic domain walls (DWs) than ferromagnetic DWs. However, experimental investigations of antiferromagnetic spin dynamics have remained unexplored, mainly because of the magnetic field immunity of antiferromagnets. Here we show that fast field-driven antiferromagnetic spin dynamics is realized in ferrimagnets at the angular momentum compensation point TA. Using rare earth-3d-transition metal ferrimagnetic compounds where net magnetic moment is nonzero at TA, the field-driven DW mobility is remarkably enhanced up to 20 km s-1 T-1. The collective coordinate approach generalized for ferrimagnets and atomistic spin model simulations show that this remarkable enhancement is a consequence of antiferromagnetic spin dynamics at TA. Our finding allows us to investigate the physics of antiferromagnetic spin dynamics and highlights the importance of tuning of the angular momentum compensation point of ferrimagnets, which could be a key towards ferrimagnetic spintronics.

Measure synchronization in a spin-orbit-coupled bosonic Josephson junction

NASA Astrophysics Data System (ADS)

Wang, Wen-Yuan; Liu, Jie; Fu, Li-Bin

2015-11-01

We present measure synchronization (MS) in a bosonic Josephson junction with spin-orbit coupling. The two atomic hyperfine states are coupled by a Raman dressing scheme, and they are regarded as two orientations of a pseudo-spin-1 /2 system. A feature specific to a spin-orbit-coupled (SOC) bosonic Josephson junction is that the transition from non-MS to MS dynamics can be modulated by Raman laser intensity, even in the absence of interspin atomic interaction. A phase diagram of non-MS and MS dynamics as functions of Raman laser intensity and Josephson tunneling amplitude is presented. Taking into account interspin atomic interactions, the system exhibits MS breaking dynamics resulting from the competition between intraspin and interspin atomic interactions. When interspin atomic interactions dominate in the competition, the system always exhibits MS dynamics. For interspin interaction weaker than intraspin interaction, a window for non-MS dynamics is present. Since SOC Bose-Einstein condensates provide a powerful platform for studies on physical problems in various fields, the study of MS dynamics is valuable in researching the collective coherent dynamical behavior in a spin-orbit-coupled bosonic Josephson junction.

Propagation of electromagnetic soliton in a spin polarized current driven weak ferromagnetic nanowire

NASA Astrophysics Data System (ADS)

Senthil Kumar, V.; Kavitha, L.; Gopi, D.

2017-11-01

We investigate the nonlinear spin dynamics of a spin polarized current driven anisotropic ferromagnetic nanowire with Dzyaloshinskii-Moriya interaction (DMI) under the influence of electromagnetic wave (EMW) propagating along the axis of the nanowire. The magnetization dynamics and electromagnetic wave propagation in the ferromagnetic nanowire with weak anti-symmetric interaction is governed by a coupled vector Landau-Lifshitz-Gilbert and Maxwell's equations. These coupled nonlinear vector equations are recasted into the extended derivative nonlinear Schrödinger (EDNLS) equation in the framework of reductive perturbation method. As it is well known, the modulational instability is a precursor for the emergence of localized envelope structures of various kinds, we compute the instability criteria for the weak ferromagnetic nanowire through linear stability analysis. Further, we invoke the homogeneous balance method to construct kink and anti-solitonic like electromagnetic (EM) soliton profiles for the EDNLS equation. We also explore the appreciable effect of the anti-symmetric weak interaction on the magnetization components of the propagating EM soliton. We find that the combination of spin-polarized current and the anti-symmetric DMI have a profound effect on the propagating EMW in a weak ferromagnetic nanowire. Thus, the anti-symmetric DMI in a spin polarized current driven ferromagnetic nanowire supports the lossless propagation of EM solitons, which may have potential applications in magnetic data storage devices.

Long-range dynamical magnetic order and spin tunneling in the cooperative paramagnetic states of the pyrochlore analogous spinel antiferromagnets CdYb2X4 (X =S or Se)

NASA Astrophysics Data System (ADS)

Dalmas de Réotier, P.; Marin, C.; Yaouanc, A.; Ritter, C.; Maisuradze, A.; Roessli, B.; Bertin, A.; Baker, P. J.; Amato, A.

2017-10-01

Magnetic systems with spins sitting on a lattice of corner sharing regular tetrahedra have been particularly prolific for the discovery of new magnetic states for the last two decades. The pyrochlore compounds have offered the playground for these studies, while little attention has been comparatively devoted to other compounds where the rare earth R occupies the same sublattice, e.g., the spinel chalcogenides Cd R2X4 (X =S or Se ). Here, we report measurements performed on powder samples of this series with R =Yb using specific heat, magnetic susceptibility, neutron diffraction, and muon-spin-relaxation measurements. The two compounds are found to be magnetically similar. They long-range order into structures described by the Γ5 irreducible representation. The magnitude of the magnetic moment at low temperature is 0.77 (1) and 0.62 (1) μB for X =S and Se , respectively. Persistent spin dynamics is present in the ordered states. The spontaneous field at the muon site is anomalously small, suggesting magnetic moment fragmentation. A double spin-flip tunneling relaxation mechanism is suggested in the cooperative paramagnetic state up to 10 K. The magnetic space groups into which magnetic moments of systems of corner-sharing regular tetrahedra order are provided for a number of insulating compounds characterized by null propagation wave vectors.

Distinguishing magnetic blocking and surface spin-glass freezing in nickel ferrite nanoparticles

NASA Astrophysics Data System (ADS)

Nadeem, K.; Krenn, H.; Traussing, T.; Letofsky-Papst, I.

2011-01-01

Nickel ferrite nanoparticles dispersed in SiO2 matrix have been synthesized by sol-gel method. Structural analysis has been performed by using x-ray diffraction and transmission electron microscopy. Magnetic properties have been investigated by using superconducting quantum interference device magnetometry. In addition to the average blocking temperature peak at TB=120 K measured by a zero field cooled temperature scan of the dc susceptibility, an additional hump near 15 K is observed. Temperature dependent out-of-phase ac susceptibility shows the same features: one broad peak at high temperature and a second narrow peak at low temperature. The high temperature peak corresponds to magnetic blocking of individual nanoparticles, while the low temperature peak is attributed to surface spin-glass freezing which becomes dominant for decreasing particle diameter. To prove the dynamics of the spin (dis)order in both regimes of freezing and blocking, the frequency dependent ac susceptibility is investigated under a biasing dc field. The frequency shift in the "frozen" low-temperature ac susceptibility peak is fitted to a dynamic scaling law with a critical exponent zv=7.5, which indicates a spin-glass phase. Exchange bias is turned on at low temperature which signifies the existence of a strong core-shell interaction. Aging and memory effects are further unique fingerprints of a spin-glass freezing on the surface of isolated magnetic nanoparticles.

Determination of the proton spin structure functions for 0.05

NASA Astrophysics Data System (ADS)

Fersch, R. G.; Guler, N.; Bosted, P.; Deur, A.; Griffioen, K.; Keith, C.; Kuhn, S. E.; Minehart, R.; Prok, Y.; Adhikari, K. P.; Adhikari, S.; Akbar, Z.; Amaryan, M. J.; Anefalos Pereira, S.; Asryan, G.; Avakian, H.; Ball, J.; Balossino, I.; Baltzell, N. A.; Battaglieri, M.; Bedlinskiy, I.; Biselli, A. S.; Briscoe, W. J.; Brooks, W. K.; Bültmann, S.; Burkert, V. D.; Thanh Cao, Frank; Carman, D. S.; Careccia, S.; Celentano, A.; Chandavar, S.; Charles, G.; Chetry, T.; Ciullo, G.; Clark, L.; Colaneri, L.; Cole, P. L.; Compton, N.; Contalbrigo, M.; Cortes, O.; Crede, V.; D'Angelo, A.; Dashyan, N.; De Vita, R.; De Sanctis, E.; Djalali, C.; Dodge, G. E.; Dupre, R.; Egiyan, H.; El Alaoui, A.; El Fassi, L.; Elouadrhiri, L.; Eugenio, P.; Fanchini, E.; Fedotov, G.; Filippi, A.; Fleming, J. A.; Forest, T. A.; Garçon, M.; Gavalian, G.; Ghandilyan, Y.; Gilfoyle, G. P.; Giovanetti, K. L.; Girod, F. X.; Gleason, C.; Golovatch, E.; Gothe, R. W.; Guidal, M.; Guo, L.; Hafidi, K.; Hakobyan, H.; Hanretty, C.; Harrison, N.; Hattawy, M.; Heddle, D.; Hicks, K.; Holtrop, M.; Hughes, S. M.; Ilieva, Y.; Ireland, D. G.; Ishkhanov, B. S.; Isupov, E. L.; Jenkins, D.; Joo, K.; Keller, D.; Khachatryan, G.; Khachatryan, M.; Khandaker, M.; Kim, A.; Kim, W.; Klein, A.; Klein, F. J.; Kubarovsky, V.; Lagerquist, V. G.; Lanza, L.; Lenisa, P.; Livingston, K.; Lu, H. Y.; McKinnon, B.; Meyer, C. A.; Mirazita, M.; Mokeev, V.; Montgomery, R. A.; Movsisyan, A.; Munoz Camacho, C.; Murdoch, G.; Nadel-Turonski, P.; Niccolai, S.; Niculescu, G.; Niculescu, I.; Osipenko, M.; Ostrovidov, A. I.; Paolone, M.; Paremuzyan, R.; Park, K.; Pasyuk, E.; Phelps, W.; Pierce, J.; Pisano, S.; Pogorelko, O.; Price, J. W.; Protopopescu, D.; Raue, B. A.; Ripani, M.; Riser, D.; Rizzo, A.; Rosner, G.; Rossi, P.; Roy, P.; Sabatié, F.; Salgado, C.; Schumacher, R. A.; Sharabian, Y. G.; Simonyan, A.; Skorodumina, Iu.; Smith, G. D.; Sokhan, D.; Sparveris, N.; Stankovic, I.; Stepanyan, S.; Strakovsky, I. I.; Strauch, S.; Taiuti, M.; Tian, Ye; Torayev, B.; Ungaro, M.; Voskanyan, H.; Voutier, E.; Walford, N. K.; Watts, D. P.; Wei, X.; Weinstein, L. B.; Zachariou, N.; Zhang, J.; CLAS Collaboration

2017-12-01

We present the results of our final analysis of the full data set of g1p(Q2) , the spin structure function of the proton, collected using CLAS at Jefferson Laboratory in 2000-2001. Polarized electrons with energies of 1.6, 2.5, 4.2, and 5.7 GeV were scattered from proton targets (NH153 dynamically polarized along the beam direction) and detected with CLAS. From the measured double spin asymmetries, we extracted virtual photon asymmetries A1p and A2p and spin structure functions g1p and g2p over a wide kinematic range (0.05 GeV2

Nonperturbative stochastic method for driven spin-boson model

NASA Astrophysics Data System (ADS)

Orth, Peter P.; Imambekov, Adilet; Le Hur, Karyn

2013-01-01

We introduce and apply a numerically exact method for investigating the real-time dissipative dynamics of quantum impurities embedded in a macroscopic environment beyond the weak-coupling limit. We focus on the spin-boson Hamiltonian that describes a two-level system interacting with a bosonic bath of harmonic oscillators. This model is archetypal for investigating dissipation in quantum systems, and tunable experimental realizations exist in mesoscopic and cold-atom systems. It finds abundant applications in physics ranging from the study of decoherence in quantum computing and quantum optics to extended dynamical mean-field theory. Starting from the real-time Feynman-Vernon path integral, we derive an exact stochastic Schrödinger equation that allows us to compute the full spin density matrix and spin-spin correlation functions beyond weak coupling. We greatly extend our earlier work [P. P. Orth, A. Imambekov, and K. Le Hur, Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.82.032118 82, 032118 (2010)] by fleshing out the core concepts of the method and by presenting a number of interesting applications. Methodologically, we present an analogy between the dissipative dynamics of a quantum spin and that of a classical spin in a random magnetic field. This analogy is used to recover the well-known noninteracting-blip approximation in the weak-coupling limit. We explain in detail how to compute spin-spin autocorrelation functions. As interesting applications of our method, we explore the non-Markovian effects of the initial spin-bath preparation on the dynamics of the coherence σx(t) and of σz(t) under a Landau-Zener sweep of the bias field. We also compute to a high precision the asymptotic long-time dynamics of σz(t) without bias and demonstrate the wide applicability of our approach by calculating the spin dynamics at nonzero bias and different temperatures.

Focus: Two-dimensional electron-electron double resonance and molecular motions: The challenge of higher frequencies.

PubMed

Franck, John M; Chandrasekaran, Siddarth; Dzikovski, Boris; Dunnam, Curt R; Freed, Jack H

2015-06-07

The development, applications, and current challenges of the pulsed ESR technique of two-dimensional Electron-Electron Double Resonance (2D ELDOR) are described. This is a three-pulse technique akin to 2D Exchange Nuclear Magnetic Resonance, but involving electron spins, usually in the form of spin-probes or spin-labels. As a result, it required the extension to much higher frequencies, i.e., microwaves, and much faster time scales, with π/2 pulses in the 2-3 ns range. It has proven very useful for studying molecular dynamics in complex fluids, and spectral results can be explained by fitting theoretical models (also described) that provide a detailed analysis of the molecular dynamics and structure. We discuss concepts that also appear in other forms of 2D spectroscopy but emphasize the unique advantages and difficulties that are intrinsic to ESR. Advantages include the ability to tune the resonance frequency, in order to probe different motional ranges, while challenges include the high ratio of the detection dead time vs. the relaxation times. We review several important 2D ELDOR studies of molecular dynamics. (1) The results from a spin probe dissolved in a liquid crystal are followed throughout the isotropic → nematic → liquid-like smectic → solid-like smectic → crystalline phases as the temperature is reduced and are interpreted in terms of the slowly relaxing local structure model. Here, the labeled molecule is undergoing overall motion in the macroscopically aligned sample, as well as responding to local site fluctuations. (2) Several examples involving model phospholipid membranes are provided, including the dynamic structural characterization of the boundary lipid that coats a transmembrane peptide dimer. Additionally, subtle differences can be elicited for the phospholipid membrane phases: liquid disordered, liquid ordered, and gel, and the subtle effects upon the membrane, of antigen cross-linking of receptors on the surface of plasma membrane, vesicles can be observed. These 2D ELDOR experiments are performed as a function of mixing time, Tm, i.e., the time between the second and third π/2 pulses, which provides a third dimension. In fact, a fourth dimension may be added by varying the ESR frequency/magnetic field combination. Therefore, (3) it is shown how continuous-wave multifrequency ESR studies enable the decomposition of complex dynamics of, e.g., proteins by virtue of their respective time scales. These studies motivate our current efforts that are directed to extend 2D ELDOR to higher frequencies, 95 GHz in particular (from 9 and 17 GHz), in order to enable multi-frequency 2D ELDOR. This required the development of quasi-optical methods for performing the mm-wave experiments, which are summarized. We demonstrate state-of-the-art 95 GHz 2D ELDOR spectroscopy through its ability to resolve the two signals from a spin probe dissolved in both the lipid phase and the coexisting aqueous phase. As current 95 GHz experiments are restricted by limited spectral coverage of the π/2 pulse, as well as the very short T2 relaxation times of the electron spins, we discuss how these limitations are being addressed.

Focus: Two-dimensional electron-electron double resonance and molecular motions: The challenge of higher frequencies

NASA Astrophysics Data System (ADS)

Franck, John M.; Chandrasekaran, Siddarth; Dzikovski, Boris; Dunnam, Curt R.; Freed, Jack H.

2015-06-01

The development, applications, and current challenges of the pulsed ESR technique of two-dimensional Electron-Electron Double Resonance (2D ELDOR) are described. This is a three-pulse technique akin to 2D Exchange Nuclear Magnetic Resonance, but involving electron spins, usually in the form of spin-probes or spin-labels. As a result, it required the extension to much higher frequencies, i.e., microwaves, and much faster time scales, with π/2 pulses in the 2-3 ns range. It has proven very useful for studying molecular dynamics in complex fluids, and spectral results can be explained by fitting theoretical models (also described) that provide a detailed analysis of the molecular dynamics and structure. We discuss concepts that also appear in other forms of 2D spectroscopy but emphasize the unique advantages and difficulties that are intrinsic to ESR. Advantages include the ability to tune the resonance frequency, in order to probe different motional ranges, while challenges include the high ratio of the detection dead time vs. the relaxation times. We review several important 2D ELDOR studies of molecular dynamics. (1) The results from a spin probe dissolved in a liquid crystal are followed throughout the isotropic → nematic → liquid-like smectic → solid-like smectic → crystalline phases as the temperature is reduced and are interpreted in terms of the slowly relaxing local structure model. Here, the labeled molecule is undergoing overall motion in the macroscopically aligned sample, as well as responding to local site fluctuations. (2) Several examples involving model phospholipid membranes are provided, including the dynamic structural characterization of the boundary lipid that coats a transmembrane peptide dimer. Additionally, subtle differences can be elicited for the phospholipid membrane phases: liquid disordered, liquid ordered, and gel, and the subtle effects upon the membrane, of antigen cross-linking of receptors on the surface of plasma membrane, vesicles can be observed. These 2D ELDOR experiments are performed as a function of mixing time, Tm, i.e., the time between the second and third π/2 pulses, which provides a third dimension. In fact, a fourth dimension may be added by varying the ESR frequency/magnetic field combination. Therefore, (3) it is shown how continuous-wave multifrequency ESR studies enable the decomposition of complex dynamics of, e.g., proteins by virtue of their respective time scales. These studies motivate our current efforts that are directed to extend 2D ELDOR to higher frequencies, 95 GHz in particular (from 9 and 17 GHz), in order to enable multi-frequency 2D ELDOR. This required the development of quasi-optical methods for performing the mm-wave experiments, which are summarized. We demonstrate state-of-the-art 95 GHz 2D ELDOR spectroscopy through its ability to resolve the two signals from a spin probe dissolved in both the lipid phase and the coexisting aqueous phase. As current 95 GHz experiments are restricted by limited spectral coverage of the π/2 pulse, as well as the very short T2 relaxation times of the electron spins, we discuss how these limitations are being addressed.

Structural, Electronic and Dynamical Properties of Curium Monopnictides: Density Functional Calculations

NASA Astrophysics Data System (ADS)

Roondhe, Basant; Upadhyay, Deepak; Som, Narayan; Pillai, Sharad B.; Shinde, Satyam; Jha, Prafulla K.

2017-03-01

The structural, electronic, dynamical and thermodynamical properties of CmX (X = N, P, As, Sb, and Bi) compounds are studied using first principles calculations within density functional theory. The Perdew-Burke-Ernzerhof spin polarized generalized gradient approximation and Perdew-Wang (PW) spin polarized local density approximation as the exchange correlational functionals are used in these calculations. There is a good agreement between the present and previously reported data. The calculated electronic density of states suggests that the curium monopnictides are metallic in nature, which is consistent with earlier studies. The significant values of magnetic moment suggest their magnetic nature. The phonon dispersion curves and phonon density of states are also calculated, which depict the dynamical stability of these compounds. There is a significant separation between the optical and acoustical phonon branches. The temperature dependence of the thermodynamical functions are also calculated and discussed. Internal energy and vibrational contribution to the Helmholtz free energy increases and decreases, respectively, with temperature. The entropy increases with temperature. The specific heat at constant volume and Debye temperature obey Debye theory. The temperature variation of the considered thermodynamical functions is in line with those of other crystalline solids.

Nanoscale cluster dynamics in the martensitic phase of Ni-Mn-Sn shape-memory alloys

NASA Astrophysics Data System (ADS)

Hoch, Michael; Yuan, Shaojie; Kuhns, Phillip; Reyes, Arneil; Brooks, James; Phelan, Daniel; Srivastava, Vijay; James, Richard; Leighton, Chris

2015-03-01

The martensitic phases of Ni-Mn-Sn magnetic shape memory alloys exhibit interesting low temperature magnetic properties, including intrinsic superparamagnetism and exchange bias effects, which have previously been rationalized in terms of spin clusters. We show here that spin-echo NMR, involving 55Mn hyperfine fields, permits ferromagnetic and antiferromagnetic nanoregions to be directly identified in these materials and yields estimates of their size distributions. Nuclear relaxation rate measurements, made as a function of temperature, provide information on both the dynamics and on the electronic structure of the nanoregions. The relaxation rates are analyzed using a combination of Redfield and Korringa mechanisms, the Korringa procedure providing information on the density of states at the Fermi level. Results will be presented for a number of these alloys. DMR-1309463.

Far-from-Equilibrium Field Theory of Many-Body Quantum Spin Systems: Prethermalization and Relaxation of Spin Spiral States in Three Dimensions

NASA Astrophysics Data System (ADS)

Babadi, Mehrtash; Demler, Eugene; Knap, Michael

2015-10-01

We study theoretically the far-from-equilibrium relaxation dynamics of spin spiral states in the three-dimensional isotropic Heisenberg model. The investigated problem serves as an archetype for understanding quantum dynamics of isolated many-body systems in the vicinity of a spontaneously broken continuous symmetry. We present a field-theoretical formalism that systematically improves on the mean field for describing the real-time quantum dynamics of generic spin-1 /2 systems. This is achieved by mapping spins to Majorana fermions followed by a 1 /N expansion of the resulting two-particle-irreducible effective action. Our analysis reveals rich fluctuation-induced relaxation dynamics in the unitary evolution of spin spiral states. In particular, we find the sudden appearance of long-lived prethermalized plateaus with diverging lifetimes as the spiral winding is tuned toward the thermodynamically stable ferro- or antiferromagnetic phases. The emerging prethermalized states are characterized by different bosonic modes being thermally populated at different effective temperatures and by a hierarchical relaxation process reminiscent of glassy systems. Spin-spin correlators found by solving the nonequilibrium Bethe-Salpeter equation provide further insight into the dynamic formation of correlations, the fate of unstable collective modes, and the emergence of fluctuation-dissipation relations. Our predictions can be verified experimentally using recent realizations of spin spiral states with ultracold atoms in a quantum gas microscope [S. Hild et al., Phys. Rev. Lett. 113, 147205 (2014), 10.1103/PhysRevLett.113.147205].

Atomic-resolution structure of the CAP-Gly domain of dynactin on polymeric microtubules determined by magic angle spinning NMR spectroscopy.

PubMed

Yan, Si; Guo, Changmiao; Hou, Guangjin; Zhang, Huilan; Lu, Xingyu; Williams, John Charles; Polenova, Tatyana

2015-11-24

Microtubules and their associated proteins perform a broad array of essential physiological functions, including mitosis, polarization and differentiation, cell migration, and vesicle and organelle transport. As such, they have been extensively studied at multiple levels of resolution (e.g., from structural biology to cell biology). Despite these efforts, there remain significant gaps in our knowledge concerning how microtubule-binding proteins bind to microtubules, how dynamics connect different conformational states, and how these interactions and dynamics affect cellular processes. Structures of microtubule-associated proteins assembled on polymeric microtubules are not known at atomic resolution. Here, we report a structure of the cytoskeleton-associated protein glycine-rich (CAP-Gly) domain of dynactin motor on polymeric microtubules, solved by magic angle spinning NMR spectroscopy. We present the intermolecular interface of CAP-Gly with microtubules, derived by recording direct dipolar contacts between CAP-Gly and tubulin using double rotational echo double resonance (dREDOR)-filtered experiments. Our results indicate that the structure adopted by CAP-Gly varies, particularly around its loop regions, permitting its interaction with multiple binding partners and with the microtubules. To our knowledge, this study reports the first atomic-resolution structure of a microtubule-associated protein on polymeric microtubules. Our approach lays the foundation for atomic-resolution structural analysis of other microtubule-associated motors.

Non-local detection of spin dynamics via spin rectification effect in yttrium iron garnet/SiO{sub 2}/NiFe trilayers near simultaneous ferromagnetic resonance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soh, Wee Tee, E-mail: a0046479@u.nus.edu; Ong, C. K.; Peng, Bin

2015-08-15

The spin rectification effect (SRE), a phenomenon that generates dc voltages from ac microwave fields incident onto a conducting ferromagnet, has attracted widespread attention due to its high sensitivity to ferromagnetic resonance (FMR) as well as its relevance to spintronics. Here, we report the non-local detection of yttrium iron garnet (YIG) spin dynamics by measuring SRE voltages from an adjacent conducting NiFe layer up to 200 nm thick. In particular, we detect, within the NiFe layer, SRE voltages stemming from magnetostatic surface spin waves (MSSWs) of the adjacent bulk YIG which are excited by a shorted coaxial probe. These non-localmore » SRE voltages within the NiFe layer that originates from YIG MSSWs are present even in 200 nm-thick NiFe films with a 50 nm thick SiO{sub 2} spacer between NiFe and YIG, thus strongly ruling out the mechanism of spin-pumping induced inverse spin Hall effect in NiFe as the source of these voltages. This long-range influence of YIG dynamics is suggested to be mediated by dynamic fields generated from YIG spin precession near YIG/NiFe interface, which interacts with NiFe spins near the simultaneous resonance of both spins, to generate a non-local SRE voltage within the NiFe layer.« less

Coulomb correlations in 4d and 5d oxides from first principles—or how spin-orbit materials choose their effective orbital degeneracies

NASA Astrophysics Data System (ADS)

Martins, C.; Aichhorn, M.; Biermann, S.

2017-07-01

The interplay of spin-orbit coupling and Coulomb correlations has become a hot topic in condensed matter theory and is especially important in 4d and 5d transition metal oxides, like iridates or rhodates. Here, we review recent advances in dynamical mean-field theory (DMFT)-based electronic structure calculations for treating such compounds, introducing all necessary implementation details. We also discuss the evaluation of Hubbard interactions in spin-orbit materials. As an example, we perform DMFT calculations on insulating strontium iridate (Sr2IrO4) and its 4d metallic counterpart, strontium rhodate (Sr2RhO4). While a Mott-insulating state is obtained for Sr2IrO4 in its paramagnetic phase, the spectral properties and Fermi surfaces obtained for Sr2RhO4 show excellent agreement with available experimental data. Finally, we discuss the electronic structure of these two compounds by introducing the notion of effective spin-orbital degeneracy as the key quantity that determines the correlation strength. We stress that effective spin-orbital degeneracy introduces an additional axis into the conventional picture of a phase diagram based on filling and on the ratio of interactions to bandwidth, analogous to the degeneracy-controlled Mott transition in d1 perovskites.

Coulomb correlations in 4d and 5d oxides from first principles-or how spin-orbit materials choose their effective orbital degeneracies.

PubMed

Martins, C; Aichhorn, M; Biermann, S

2017-07-05

The interplay of spin-orbit coupling and Coulomb correlations has become a hot topic in condensed matter theory and is especially important in 4d and 5d transition metal oxides, like iridates or rhodates. Here, we review recent advances in dynamical mean-field theory (DMFT)-based electronic structure calculations for treating such compounds, introducing all necessary implementation details. We also discuss the evaluation of Hubbard interactions in spin-orbit materials. As an example, we perform DMFT calculations on insulating strontium iridate (Sr 2 IrO 4 ) and its 4d metallic counterpart, strontium rhodate (Sr 2 RhO 4 ). While a Mott-insulating state is obtained for Sr 2 IrO 4 in its paramagnetic phase, the spectral properties and Fermi surfaces obtained for Sr 2 RhO 4 show excellent agreement with available experimental data. Finally, we discuss the electronic structure of these two compounds by introducing the notion of effective spin-orbital degeneracy as the key quantity that determines the correlation strength. We stress that effective spin-orbital degeneracy introduces an additional axis into the conventional picture of a phase diagram based on filling and on the ratio of interactions to bandwidth, analogous to the degeneracy-controlled Mott transition in d 1 perovskites.

Nitrogen-vacancy-assisted magnetometry of paramagnetic centers in an individual diamond nanocrystal.

PubMed

Laraoui, Abdelghani; Hodges, Jonathan S; Meriles, Carlos A

2012-07-11

Semiconductor nanoparticles host a number of paramagnetic point defects and impurities, many of them adjacent to the surface, whose response to external stimuli could help probe the complex dynamics of the particle and its local, nanoscale environment. Here, we use optically detected magnetic resonance in a nitrogen-vacancy (NV) center within an individual diamond nanocrystal to investigate the composition and spin dynamics of the particle-hosted spin bath. For the present sample, a ∼45 nm diamond crystal, NV-assisted dark-spin spectroscopy reveals the presence of nitrogen donors and a second, yet-unidentified class of paramagnetic centers. Both groups share a common spin lifetime considerably shorter than that observed for the NV spin, suggesting some form of spatial clustering, possibly on the nanoparticle surface. Using double spin resonance and dynamical decoupling, we also demonstrate control of the combined NV center-spin bath dynamics and attain NV coherence lifetimes comparable to those reported for bulk, Type Ib samples. Extensions based on the experiments presented herein hold promise for applications in nanoscale magnetic sensing, biomedical labeling, and imaging.

Time-resolved nonlinear optics in strongly correlated insulators

NASA Astrophysics Data System (ADS)

Dodge, J. Steven

2000-03-01

Transition metal oxides form the basis for much of our understanding of Mott insulators, and have enjoyed a renaissance of interest since the discovery of high temperature superconductivity in the cuprates. They are characterized by complex interactions among spin, lattice, orbital and charge degrees of freedom, which lead to dynamical behavior on time scales ranging from femtoseconds to microseconds. We have applied time resolved nonlinear optical spectroscopy to probe these dynamics. In one well-studied antiferromagnetic insulator, Cr_2O_3, we observed spin-wave dynamics on a picosecond time scale by performing pump-probe spectroscopy of the exciton-magnon transition(J. S. Dodge, et al.), Phys. Rev. Lett. 83, 4650 (1999).. At excitation densities ~ 10-3/Cr, a lineshape associated with the exciton-magnon absorption appears in the pump-probe spectrum. We assign this nonlinearity to a time-dependent renormalization of the magnon band structure, which in turn modifies the lineshape of the exciton-magnon transition. At long time delays, this assignment agrees semiquantitatively with calculations based on spin-wave theory. However, the initial population at the zone-boundary induces surprisingly little renormalization effect, indicating that spin-wave theory is insufficient to describe our observations in this regime. The renormalization lineshape grows on a time scale of ~ 50 ps, which we associate with the decay of the photoexcited, nonequilibrium population of zone-boundary spin-waves into a thermalized population of zone-center spin-waves. We have also performed a study of the linear and nonlinear optical properties of Sr_2CuO_2Cl_2, an insulating, two-dimensional cuprate. In the nonlinear optical experiments, we have performed pump-probe spectroscopy over a 1 eV spectral range, varying both the pump and the probe energy. We observe a pump-probe lineshape which varies considerably as a function of pump energy and temperature, and which differs sharply from those typically observed in band insulators. At low-temperatures, in particular, we observe an overall increase of spectral weight in our probe range, indicating that states are shifting over an energy scale larger than 1 eV. We attribute this behavior to the strongly correlated nature of the electronic structure in this material. Studies of the elementary excitations in other magnetic oxides, currently in progress, will be discussed.

Study of translational dynamics in molten polymer by variation of gradient pulse-width of PGSE.

PubMed

Stepišnik, Janez; Lahajnar, Gojmir; Zupančič, Ivan; Mohorič, Aleš

2013-11-01

Pulsed gradient spin echo is a method of measuring molecular translation. Changing Δ makes it sensitive to diffusion spectrum. Spin translation effects the buildup of phase structure during the application of gradient pulses as well. The time scale of the self-diffusion measurement shortens if this is taken into account. The method of diffusion spectrometry with variable δ is also less sensitive to artifacts caused by spin relaxation and internal gradient fields. Here the method is demonstrated in the case of diffusion spectrometry of molten polyethylene. The results confirm a model of constraint release in a system of entangled polymer chains as a sort of tube Rouse motion. Copyright © 2013 Elsevier Inc. All rights reserved.

Using polarized muons as ultrasensitive spin labels in free radical chemistry

NASA Astrophysics Data System (ADS)

McKenzie, Iain; Roduner, Emil

2009-08-01

In a chemical sense, the positive muon is a light proton. It is obtained at the ports of accelerators in beams with a spin polarization of 100%, which makes it a highly sensitive probe of matter. The muonium atom is a light hydrogen isotope, nine times lighter than H, with a muon as its nucleus. It reacts the same way as H, and by addition to double bonds it is implemented in free radicals in which the muon serves as a fully polarized spin label. It is reviewed here how the muon can be used to obtain information about muonium and radical reaction rates, radical structure, dynamics, and local environments. It can even tell us what a fragrance molecule does in a shampoo.

The Kubo-Greenwood spin-dependent electrical conductivity of 2D transition-metal dichalcogenides and group-IV materials: A Green's function study

NASA Astrophysics Data System (ADS)

Hoi, Bui Dinh; Yarmohammadi, Mohsen

2018-04-01

The spin-dependent electrical conductivity of counterparts of graphene, transition-metal dichalcogenides (TMDs) and group-IV nanosheets, have investigated by a magnetic exchange field (MEF)-induction to gain the electronic transport properties of charge carriers. We have implemented a k.p Hamiltonian model through the Kubo-Greenwood formalism in order to address the dynamical behavior of correlated Dirac fermions. Tuning the MEF enables one to control the effective mass of carriers in group-IV and TMDs, differently. We have found the Dirac-like points in a new quantum anomalous Hall (QAH) state at strong MEFs for both structures. For both cases, a broad peak in electrical conductivity originated from the scattering rate and entropy is observed. Spin degeneracy at some critical MEFs is another remarkable point. We have found that in the limit of zero or uniform MEFs with respect to the spin-orbit interaction, the large resulting electrical conductivity depends on the spin sub-bands in group-IV and MLDs. Featuring spin-dependent electronic transport properties, one can provide a new scenario for future possible applications.

Dynamic nuclear spin polarization in the resonant laser excitation of an InGaAs quantum dot.

PubMed

Högele, A; Kroner, M; Latta, C; Claassen, M; Carusotto, I; Bulutay, C; Imamoglu, A

2012-05-11

Resonant optical excitation of lowest-energy excitonic transitions in self-assembled quantum dots leads to nuclear spin polarization that is qualitatively different from the well-known optical orientation phenomena. By carrying out a comprehensive set of experiments, we demonstrate that nuclear spin polarization manifests itself in quantum dots subjected to finite external magnetic field as locking of the higher energy Zeeman transition to the driving laser field, as well as the avoidance of the resonance condition for the lower energy Zeeman branch. We interpret our findings on the basis of dynamic nuclear spin polarization originating from noncollinear hyperfine interaction and find excellent agreement between experiment and theory. Our results provide evidence for the significance of noncollinear hyperfine processes not only for nuclear spin diffusion and decay, but also for buildup dynamics of nuclear spin polarization in a coupled electron-nuclear spin system.

Electrical manipulation of dynamic magnetic impurity and spin texture of helical Dirac fermions

NASA Astrophysics Data System (ADS)

Wang, Rui-Qiang; Zhong, Min; Zheng, Shi-Han; Yang, Mou; Wang, Guang-Hui

2016-05-01

We have theoretically investigated the spin inelastic scattering of helical electrons off a high-spin nanomagnet absorbed on a topological surface. The nanomagnet is treated as a dynamic quantum spin and driven by the spin transfer torque effect. We proposed a mechanism to electrically manipulate the spin texture of helical Dirac fermions rather than by an external magnetic field. By tuning the bias voltage and the direction of impurity magnetization, we present rich patterns of spin texture, from which important fingerprints exclusively associated with the spin helical feature are obtained. Furthermore, it is found that the nonmagnetic potential can create the resonance state in the spin density with different physics as the previously reported resonance of charge density.

Charge and spin control of ultrafast electron and hole dynamics in single CdSe/ZnSe quantum dots

NASA Astrophysics Data System (ADS)

Hinz, C.; Gumbsheimer, P.; Traum, C.; Holtkemper, M.; Bauer, B.; Haase, J.; Mahapatra, S.; Frey, A.; Brunner, K.; Reiter, D. E.; Kuhn, T.; Seletskiy, D. V.; Leitenstorfer, A.

2018-01-01

We study the dynamics of photoexcited electrons and holes in single negatively charged CdSe/ZnSe quantum dots with two-color femtosecond pump-probe spectroscopy. An initial characterization of the energy level structure is performed at low temperatures and magnetic fields of up to 5 T. Emission and absorption resonances are assigned to specific transitions between few-fermion states by a theoretical model based on a configuration interaction approach. To analyze the dynamics of individual charge carriers, we initialize the quantum system into excited trion states with defined energy and spin. Subsequently, the time-dependent occupation of the trion ground state is monitored by spectrally resolved differential transmission measurements. We observe subpicosecond dynamics for a hole excited to the D shell. The energy dependence of this D -to-S shell intraband transition is investigated in quantum dots of varying size. Excitation of an electron-hole pair in the respective p shells leads to the formation of singlet and triplet spin configurations. Relaxation of the p -shell singlet is observed to occur on a time scale of a few picoseconds. Pumping of p -shell triplet transitions opens up two pathways with distinctly different scattering times. These processes are shown to be governed by the mixing of singlet and triplet states due to exchange interactions enabling simultaneous electron and hole spin flips. To isolate the relaxation channels, we align the spin of the residual electron by a magnetic field and employ laser pulses of defined helicity. This step provides ultrafast preparation of a fully inverted trion ground state of the quantum dot with near unity probability, enabling deterministic addition of a single photon to the probe pulse. Therefore our experiments represent a significant step towards using single quantum emitters with well-controled inversion to manipulate the photon statistics of ultrafast light pulses.

Short-range magentic correlations and dynamic orbital ordering in the thermally activated spin state of LaCoO3

NASA Astrophysics Data System (ADS)

Rosenkranz, S.; Phelan, D.; Louca, D.; Lee, S. H.; Chupas, P. J.; Osborn, R.; Zheng, H.; Mitchell, J. F.

2006-03-01

The cobalt perovskites La1-xSrxCoO3 show intriguing spin, lattice, and orbital properties similar to the ones observed in colossal magnetoresistive manganites. The x=0 parent compound is a non-magnetic insulator at low temperatures, but shows evidence of a spin-state transition of the cobalt ions above 50K from a low-spin to an intermediate or high-spin configuration. Using high resolution, inelastic neutron scattering, we observe a distinct low energy excitation at 0.6meV coincident with the thermally induced spin state transition observed in susceptibility measurements. The thermal activation of this excited spin state also leads to short-range, dynamic ferro- and antiferromagnetic correlations. These observations are consistent with the activation of a zero-field split intermediate spin state as well as the presence of dynamic orbital ordering of these excited states. Work supported by US DOE BES-DMS W-31-109-ENG-38 and NSF DMR-0454672

General theory of feedback control of a nuclear spin ensemble in quantum dots

NASA Astrophysics Data System (ADS)

Yang, Wen; Sham, L. J.

2013-12-01

We present a microscopic theory of the nonequilibrium nuclear spin dynamics driven by the electron and/or hole under continuous-wave pumping in a quantum dot. We show the correlated dynamics of the nuclear spin ensemble and the electron and/or hole under optical excitation as a quantum feedback loop and investigate the dynamics of the many nuclear spins as a nonlinear collective motion. This gives rise to three observable effects: (i) hysteresis, (ii) locking (avoidance) of the pump absorption strength to (from) the natural resonance, and (iii) suppression (amplification) of the fluctuation of weakly polarized nuclear spins, leading to prolonged (shortened) electron-spin coherence time. A single nonlinear feedback function is constructed which determines the different outcomes of the three effects listed above depending on the feedback being negative or positive. The general theory also helps to put in perspective the wide range of existing theories on the problem of a single electron spin in a nuclear spin bath.

Surface Plasmon-Mediated Nanoscale Localization of Laser-Driven sub-Terahertz Spin Dynamics in Magnetic Dielectrics

NASA Astrophysics Data System (ADS)

Chekhov, Alexander L.; Stognij, Alexander I.; Satoh, Takuya; Murzina, Tatiana V.; Razdolski, Ilya; Stupakiewicz, Andrzej

2018-05-01

Ultrafast all-optical control of spins with femtosecond laser pulses is one of the hot topics at the crossroads of photonics and magnetism with a direct impact on future magnetic recording. Unveiling light-assisted recording mechanisms for an increase of the bit density beyond the diffraction limit without excessive heating of the recording medium is an open challenge. Here we show that surface plasmon-polaritons in hybrid metal-dielectric structures can provide spatial confinement of the inverse Faraday effect, mediating the excitation of localized coherent spin precession with 0.41 THz frequency. We demonstrate a two orders of magnitude enhancement of the excitation efficiency at the surface plasmon resonance within the 100 nm layer in dielectric garnet. Our findings broaden the horizons of ultrafast spin-plasmonics and open pathways towards non-thermal opto-magnetic recording at the nano-scale.

Microwave-Assisted Cross-Polarization of Nuclear Spin Ensembles from Optically Pumped Nitrogen-Vacancy Centers in Diamond.

PubMed

Shagieva, F; Zaiser, S; Neumann, P; Dasari, D B R; Stöhr, R; Denisenko, A; Reuter, R; Meriles, C A; Wrachtrup, J

2018-06-13

The ability to optically initialize the electronic spin of the nitrogen-vacancy (NV) center in diamond has long been considered a valuable resource to enhance the polarization of neighboring nuclei, but efficient polarization transfer to spin species outside the diamond crystal has proven challenging. Here we demonstrate variable-magnetic-field, microwave-enabled cross-polarization from the NV electronic spin to protons in a model viscous fluid in contact with the diamond surface. Further, slight changes in the cross-relaxation rate as a function of the wait time between successive repetitions of the transfer protocol suggest slower molecular dynamics near the diamond surface compared to that in bulk. This observation is consistent with present models of the microscopic structure of a fluid and can be exploited to estimate the diffusion coefficient near a solid-liquid interface, of importance in colloid science.

Spin polarization transfer by the radical pair mechanism

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zarea, Mehdi, E-mail: m-zarea@northwestern.edu; Ratner, Mark A.; Wasielewski, Michael R.

2015-08-07

In a three-site representation, we study a spin polarization transfer from radical pair spins to a nearby electron or nuclear spin. The quantum dynamics of the radical pair spins is governed by a constant exchange interaction between the radical pair spins which have different Zeeman frequencies. Radical pair spins can recombine to the singlet ground state or to lower energy triplet states. It is then shown that the coherent dynamics of the radical pair induces spin polarization on the nearby third spin in the presence of a magnetic field. The spin polarization transfer depends on the difference between Zeeman frequencies,more » the singlet and triplet recombination rates, and on the exchange and dipole-dipole interactions between the different spins. In particular, the sign of the polarization depends on the exchange coupling between radical pair spins and also on the difference between singlet and triplet recombination rate constants.« less

Ab-initio study of high temperature lattice dynamics of BCC zirconium (β-Zr) and uranium (γ-U)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ghosh, Partha S., E-mail: parthasarathi13@gmail.com; Arya, A., E-mail: parthasarathi13@gmail.com; Dey, G. K., E-mail: parthasarathi13@gmail.com

2014-04-24

Using self consistent ab-initio lattice dynamics calculations, we show that bcc structures of Zr and U phases become stable at high temperature by phonon-phonon interactions. The calculated temperature dependent phonon dispersion curve (PDC) of β-Zr match excellently with experimental PDC. But the calculated PDC for γ-U shows negative phonon frequencies even at solid to liquid transition temperature. We show that this discrepancy is due to an overestimation of instability depth of bcc U phase which is removed by incorporation of spin-orbit coupling in the electronic structure calculations.

MAS NMR of HIV-1 protein assemblies

NASA Astrophysics Data System (ADS)

Suiter, Christopher L.; Quinn, Caitlin M.; Lu, Manman; Hou, Guangjin; Zhang, Huilan; Polenova, Tatyana

2015-04-01

The negative global impact of the AIDS pandemic is well known. In this perspective article, the utility of magic angle spinning (MAS) NMR spectroscopy to answer pressing questions related to the structure and dynamics of HIV-1 protein assemblies is examined. In recent years, MAS NMR has undergone major technological developments enabling studies of large viral assemblies. We discuss some of these evolving methods and technologies and provide a perspective on the current state of MAS NMR as applied to the investigations into structure and dynamics of HIV-1 assemblies of CA capsid protein and of Gag maturation intermediates.

Design and Experimental Study on Spinning Solid Rocket Motor

NASA Astrophysics Data System (ADS)

Xue, Heng; Jiang, Chunlan; Wang, Zaicheng

The study on spinning solid rocket motor (SRM) which used as power plant of twice throwing structure of aerial submunition was introduced. This kind of SRM which with the structure of tangential multi-nozzle consists of a combustion chamber, propellant charge, 4 tangential nozzles, ignition device, etc. Grain design, structure design and prediction of interior ballistic performance were described, and problem which need mainly considered in design were analyzed comprehensively. Finally, in order to research working performance of the SRM, measure pressure-time curve and its speed, static test and dynamic test were conducted respectively. And then calculated values and experimental data were compared and analyzed. The results indicate that the designed motor operates normally, and the stable performance of interior ballistic meet demands. And experimental results have the guidance meaning for the pre-research design of SRM.

Evolution of magnetic Dirac bosons in a honeycomb lattice

NASA Astrophysics Data System (ADS)

Boyko, D.; Balatsky, A. V.; Haraldsen, J. T.

2018-01-01

We examine the presence and evolution of magnetic Dirac nodes in the Heisenberg honeycomb lattice. Using linear spin theory, we evaluate the collinear phase diagram as well as the change in the spin dynamics with various exchange interactions. We show that the ferromagnetic structure produces bosonic Dirac and Weyl points due to the competition between the interactions. Furthermore, it is shown that the criteria for magnetic Dirac nodes are coupled to the magnetic structure and not the overall crystal symmetry, where the breaking of inversion symmetry greatly affects the antiferromagnetic configurations. The tunability of the nodal points through variation of the exchange parameters leads to the possibility of controlling Dirac symmetries through an external manipulation of the orbital interactions.

Enhanced spin wave propagation in magnonic rings by bias field modulation

NASA Astrophysics Data System (ADS)

Venkat, G.; Venkateswarlu, D.; Joshi, R. S.; Franchin, M.; Fangohr, H.; Anil Kumar, P. S.; Prabhakar, A.

2018-05-01

We simulate the spin wave (SW) dynamics in ring structures and obtain the ω - k dispersion relations corresponding to the output waveguide. Different bias field configurations affect the transfer of SW power from one arm of the structure to the other arm. To this end, we show that circular or radial bias fields are more suitable for energy transfer across the ring than the conventional horizontal bias field Hx. The SW dispersion shows that modes excited, when the bias field is along the ring radius, are almost 10 dB higher in power when compared to the modal power in the case of Hx. This is also corroborated by the SW energy density in the receiving stub.

Spin-orbit torque induced magnetization anisotropy modulation in Pt/(Co/Ni)4/Co/IrMn heterostructure

NASA Astrophysics Data System (ADS)

Engel, Christian; Goolaup, Sarjoosing; Luo, Feilong; Gan, Weiliang; Lew, Wen Siang

2017-04-01

In this work, we show that domain wall (DW) dynamics within a system provide an alternative platform to characterizing spin-orbit torque (SOT) effective fields. In perpendicularly magnetized wires with a Pt/(Co/Ni)4/Co/IrMn stack structure, differential Kerr imaging shows that the magnetization switching process is via the nucleation of the embryo state followed by domain wall propagation. By probing the current induced DW motion in the presence of in-plane field, the SOT effective fields are obtained using the harmonic Hall voltage scheme. The effective anisotropy field of the structure decreases by 12% due to the SOT effective fields, as the in-plane current in the wire is increased.

Two-dimensional topological photonics

NASA Astrophysics Data System (ADS)

Khanikaev, Alexander B.; Shvets, Gennady

2017-12-01

Originating from the studies of two-dimensional condensed-matter states, the concept of topological order has recently been expanded to other fields of physics and engineering, particularly optics and photonics. Topological photonic structures have already overturned some of the traditional views on wave propagation and manipulation. The application of topological concepts to guided wave propagation has enabled novel photonic devices, such as reflection-free sharply bent waveguides, robust delay lines, spin-polarized switches and non-reciprocal devices. Discrete degrees of freedom, widely used in condensed-matter physics, such as spin and valley, are now entering the realm of photonics. In this Review, we summarize the latest advances in this highly dynamic field, with special emphasis on the experimental work on two-dimensional photonic topological structures.

Spin-orbit-coupled fermions in an optical lattice clock

NASA Astrophysics Data System (ADS)

Kolkowitz, S.; Bromley, S. L.; Bothwell, T.; Wall, M. L.; Marti, G. E.; Koller, A. P.; Zhang, X.; Rey, A. M.; Ye, J.

2017-02-01

Engineered spin-orbit coupling (SOC) in cold-atom systems can enable the study of new synthetic materials and complex condensed matter phenomena. However, spontaneous emission in alkali-atom spin-orbit-coupled systems is hindered by heating, limiting the observation of many-body effects and motivating research into potential alternatives. Here we demonstrate that spin-orbit-coupled fermions can be engineered to occur naturally in a one-dimensional optical lattice clock. In contrast to previous SOC experiments, here the SOC is both generated and probed using a direct ultra-narrow optical clock transition between two electronic orbital states in 87Sr atoms. We use clock spectroscopy to prepare lattice band populations, internal electronic states and quasi-momenta, and to produce spin-orbit-coupled dynamics. The exceptionally long lifetime of the excited clock state (160 seconds) eliminates decoherence and atom loss from spontaneous emission at all relevant experimental timescales, allowing subsequent momentum- and spin-resolved in situ probing of the SOC band structure and eigenstates. We use these capabilities to study Bloch oscillations, spin-momentum locking and Van Hove singularities in the transition density of states. Our results lay the groundwork for using fermionic optical lattice clocks to probe new phases of matter.

On the interpretation of continuous wave electron spin resonance spectra of tempo-palmitate in 5-cyanobiphenyl.

PubMed

Zerbetto, Mirco; Polimeno, Antonino; Cimino, Paola; Barone, Vincenzo

2008-01-14

Electron spin resonance (ESR) measurements are highly informative on the dynamic behavior of molecules, which is of fundamental importance to understand their stability, biological functions and activities, and catalytic action. The wealth of dynamic information which can be extracted from a continuous wave electron spin resonance (cw-ESR) spectrum can be inferred by a basic theoretical approach defined within the stochastic Liouville equation formalism, i.e., the direct inclusion of motional dynamics in the form of stochastic (Fokker-Planck/diffusive) operators in the super Hamiltonian H governing the time evolution of the system. Modeling requires the characterization of magnetic parameters (e.g., hyperfine and Zeeman tensors) and the calculation of ESR observables in terms of spectral densities. The magnetic observables can be pursued by the employment of density functional theory which is apt, provided that hybrid functionals are employed, for the accurate computation of structural properties of molecular systems. Recently, an ab initio integrated computational approach to the in silico interpretation of cw-ESR spectra of multilabeled systems in isotropic fluids has been discussed. In this work we present the extension to the case of nematic liquid crystalline environments by performing simulations of the ESR spectra of the prototypical nitroxide probe 4-(hexadecanoyloxy)-2,2,6,6-tetramethylpiperidine-1-oxy in isotropic and nematic phases of 5-cyanobiphenyl. We first discuss the basic ingredients of the integrated approach, i.e., (1) determination of geometric and local magnetic parameters by quantum-mechanical calculations, taking into account the solvent and, when needed, the vibrational averaging contributions; (2) numerical solution of a stochastic Liouville equation in the presence of diffusive rotational dynamics, based on (3) parameterization of diffusion rotational tensor provided by a hydrodynamic model. Next we present simulated spectra with minimal resorting to fitting procedures, proving that the combination of sensitive ESR spectroscopy and sophisticated modeling can be highly helpful in providing three-dimensional structural and dynamic information on molecular systems in anisotropic environments.

Gigahertz dynamics of a strongly driven single quantum spin.

PubMed

Fuchs, G D; Dobrovitski, V V; Toyli, D M; Heremans, F J; Awschalom, D D

2009-12-11

Two-level systems are at the core of numerous real-world technologies such as magnetic resonance imaging and atomic clocks. Coherent control of the state is achieved with an oscillating field that drives dynamics at a rate determined by its amplitude. As the strength of the field is increased, a different regime emerges where linear scaling of the manipulation rate breaks down and complex dynamics are expected. By calibrating the spin rotation with an adiabatic passage, we have measured the room-temperature "strong-driving" dynamics of a single nitrogen vacancy center in diamond. With an adiabatic passage to calibrate the spin rotation, we observed dynamics on sub-nanosecond time scales. Contrary to conventional thinking, this breakdown of the rotating wave approximation provides opportunities for time-optimal quantum control of a single spin.

Structurally Dynamic Spin Market Networks

NASA Astrophysics Data System (ADS)

Horváth, Denis; Kuscsik, Zoltán

The agent-based model of stock price dynamics on a directed evolving complex network is suggested and studied by direct simulation. The stationary regime is maintained as a result of the balance between the extremal dynamics, adaptivity of strategic variables and reconnection rules. The inherent structure of node agent "brain" is modeled by a recursive neural network with local and global inputs and feedback connections. For specific parametric combination the complex network displays small-world phenomenon combined with scale-free behavior. The identification of a local leader (network hub, agent whose strategies are frequently adapted by its neighbors) is carried out by repeated random walk process through network. The simulations show empirically relevant dynamics of price returns and volatility clustering. The additional emerging aspects of stylized market statistics are Zipfian distributions of fitness.

Lattice dynamics of the rare-earth element samarium

NASA Astrophysics Data System (ADS)

Bauder, Olga; Piekarz, Przemysław; Barla, Alessandro; Sergueev, Ilya; Rüffer, Rudolf; ŁaŻewski, Jan; Baumbach, Tilo; Parlinski, Krzysztof; Stankov, Svetoslav

2013-12-01

The lattice dynamics of samarium is determined by in situ low-temperature nuclear inelastic scattering on a single crystalline (0001)Sm film, a polycrystalline Sm foil, and by first-principles theory. The ab initio calculated phonon dispersion relations and phonon density of states for the Sm-type structure and the double hexagonal-close-packed (dhcp) lattice, characteristic for light lanthanides, are compared. The dhcp unit cell, which is a factor of 2.24 smaller in height, exhibits more pronounced vibrational anisotropy in comparison to the Sm-type structure. The analysis reveals a minor influence of the spin-orbit coupling in the Sm atom on the lattice dynamics. A broadening of the longitudinal peak, not found in the calculations, suggests the influence of electron correlations on lattice dynamics in metallic samarium.

Parity-time symmetry breaking in magnetic systems

DOE PAGES

Galda, Alexey; Vinokur, Valerii M.

2016-07-14

The understanding of out-of-equilibrium physics, especially dynamic instabilities and dynamic phase transitions, is one of the major challenges of contemporary science, spanning the broadest wealth of research areas that range from quantum optics to living organisms. By focusing on nonequilibrium dynamics of an open dissipative spin system, we introduce a non-Hermitian Hamiltonian approach, in which non-Hermiticity reflects dissipation and deviation from equilibrium. The imaginary part of the proposed spin Hamiltonian describes the effects of Gilbert damping and applied Slonczewski spin-transfer torque. In the classical limit, our approach reproduces Landau-Lifshitz-Gilbert-Slonczewski dynamics of a large macrospin. Here, we reveal the spin-transfer torque-drivenmore » parity-time symmetry-breaking phase transition corresponding to a transition from precessional to exponentially damped spin dynamics. Micromagnetic simulations for nanoscale ferromagnetic disks demonstrate the predicted effect. These findings can pave the way to a general quantitative description of out-of-equilibrium phase transitions driven by spontaneous parity-time symmetry breaking.« less

Inelastic Neutron Scattering Studies of the Spin and Lattice Dynamics inIron Arsenide Compounds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Christianson, Andrew D; Osborn, R.; Rosenkranz, Stephen

2009-01-01

Although neutrons do not couple directly to the superconducting order parameter, they have nevertheless played an important role in advancing our understanding of the pairing mechanism and the symmetry of the superconducting energy gap in the iron arsenide compounds. Measurements of the spin and lattice dynamics have been performed on non-superconducting 'parent' compounds based on the LaFeAsO ('1111') and BaFe{sub 2}As{sub 2} ('122') crystal structures, and on electron and hole-doped superconducting compounds, using both polycrystalline and single crystal samples. Neutron measurements of the phonon density-of-state, subsequently supported by single crystal inelastic X-ray scattering, are in good agreement with ab initiomore » calculations, provided the magnetism of the iron atoms is taken into account. However, when combined with estimates of the electron-phonon coupling, the predicted superconducting transition temperatures are less than 1 K, making a conventional phononic mechanism for superconductivity highly unlikely. Measurements of the spin dynamics within the spin density wave phase of the parent compounds show evidence of strongly dispersive spin waves with exchange interactions consistent with the observed magnetic order and a large anisotropy gap. Antiferromagnetic fluctuations persist in the normal phase of the superconducting compounds, but they are more diffuse. Below T{sub c}, there is evidence in three '122' compounds that these fluctuations condense into a resonant spin excitation at the antiferromagnetic wavevector with an energy that scales with T{sub c}. Such resonances have been observed in the high-T{sub c} copper oxides and a number of heavy fermion superconductors, where they are considered to be evidence of d-wave symmetry. In the iron arsenides, they also provide evidence of unconventional superconductivity, but a comparison with ARPES and other measurements, which indicate that the gaps are isotropic, suggests that the symmetry is more likely to be extended-s{sub {+-}} wave in character.« less

Inelastic neutron scattering studies of the spin and lattice dynamics in iron arsenide compounds.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Osborn, R.; Rosenkranz, S.; Goremychkin, E. A.

2009-03-20

Although neutrons do not couple directly to the superconducting order parameter, they have nevertheless played an important role in advancing our understanding of the pairing mechanism and the symmetry of the superconducting energy gap in the iron arsenide compounds. Measurements of the spin and lattice dynamics have been performed on non-superconducting 'parent' compounds based on the LaFeAsO ('1111') and BaFe{sub 2}As{sub 2} ('122') crystal structures, and on electron and hole-doped superconducting compounds, using both polycrystalline and single crystal samples. Neutron measurements of the phonon density-of-state, subsequently supported by single crystal inelastic X-ray scattering, are in good agreement with ab initiomore » calculations, provided the magnetism of the iron atoms is taken into account. However, when combined with estimates of the electron-phonon coupling, the predicted superconducting transition temperatures are less than 1 K, making a conventional phononic mechanism for superconductivity highly unlikely. Measurements of the spin dynamics within the spin density wave phase of the parent compounds show evidence of strongly dispersive spin waves with exchange interactions consistent with the observed magnetic order and a large anisotropy gap. Antiferromagnetic fluctuations persist in the normal phase of the superconducting compounds, but they are more diffuse. Below T{sub c}, there is evidence in three '122' compounds that these fluctuations condense into a resonant spin excitation at the antiferromagnetic wavevector with an energy that scales with T{sub c}. Such resonances have been observed in the high-T{sub c} copper oxides and a number of heavy fermion superconductors, where they are considered to be evidence of d-wave symmetry. In the iron arsenides, they also provide evidence of unconventional superconductivity, but a comparison with ARPES and other measurements, which indicate that the gaps are isotropic, suggests that the symmetry is more likely to be extended-s{sub {+-}} wave in character.« less

Selective Tuning of Gilbert Damping in Spin-Valve Trilayer by Insertion of Rare-Earth Nanolayers.

PubMed

Zhang, Wen; Zhang, Dong; Wong, Ping Kwan Johnny; Yuan, Honglei; Jiang, Sheng; van der Laan, Gerrit; Zhai, Ya; Lu, Zuhong

2015-08-12

Selective tuning of the Gilbert damping constant, α, in a NiFe/Cu/FeCo spin-valve trilayer has been achieved by inserting different rare-earth nanolayers adjacent to the ferromagnetic layers. Frequency dependent analysis of the ferromagnetic resonances shows that the initially small magnitude of α in the NiFe and FeCo layers is improved by Tb and Gd insertions to various amounts. Using the element-specific technique of X-ray magnetic circular dichroism, we find that the observed increase in α can be attributed primarily to the orbital moment enhancement of Ni and Co, rather than that of Fe. The amplitude of the enhancement depends on the specific rare-earth element, as well as on the lattice and electronic band structure of the transition metals. Our results demonstrate an effective way for individual control of the magnetization dynamics in the different layers of the spin-valve sandwich structures, which will be important for practical applications in high-frequency spintronic devices.

Structural Biology of Supramolecular Assemblies by Magic Angle Spinning NMR Spectroscopy

PubMed Central

Quinn, Caitlin M.; Polenova, Tatyana

2017-01-01

In recent years, exciting developments in instrument technology and experimental methodology have advanced the field of magic angle spinning (MAS) NMR to new heights. Contemporary MAS NMR yields atomic-level insights into structure and dynamics of an astounding range of biological systems, many of which cannot be studied by other methods. With the advent of fast magic angle spinning, proton detection, and novel pulse sequences, large supramolecular assemblies, such as cytoskeletal proteins and intact viruses, are now accessible for detailed analysis. In this review, we will discuss the current MAS NMR methodologies that enable characterization of complex biomolecular systems and will present examples of applications to several classes of assemblies comprising bacterial and mammalian cytoskeleton as well as HIV-1 and bacteriophage viruses. The body of work reviewed herein is representative of the recent advancements in the field, with respect to the complexity of the systems studied, the quality of the data, and the significance to the biology. PMID:28093096

Using RIXS to uncover elementary charge and spin excitations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jia, Chunjing; Wohlfeld, Krzysztof; Wang, Yao

2016-05-13

Despite significant progress in resonant inelastic x-ray scattering (RIXS) experiments on cuprates at the Cu L-edge, a theoretical understanding of the cross section remains incomplete in terms of elementary excitations and the connection to both charge and spin structure factors. Here, we use state-of-the-art, unbiased numerical calculations to study the low-energy excitations probed by RIXS in the Hubbard model, relevant to the cuprates. The results highlight the importance of scattering geometry, in particular, both the incident and scattered x-ray photon polarization, and they demonstrate that on a qualitative level the RIXS spectral shape in the cross-polarized channel approximates that ofmore » the spin dynamical structure factor. Furthermore, in the parallel-polarized channel, the complexity of the RIXS process beyond a simple two-particle response complicates the analysis and demonstrates that approximations and expansions that attempt to relate RIXS to less complex correlation functions cannot reproduce the full diversity of RIXS spectral features.« less

Spinon dynamics in quantum integrable antiferromagnets

NASA Astrophysics Data System (ADS)

Vlijm, R.; Caux, J.-S.

2016-05-01

The excitations of the Heisenberg antiferromagnetic spin chain in zero field are known as spinons. As pairwise-created fractionalized excitations, spinons are important in the understanding of inelastic neutron scattering experiments in (quasi-)one-dimensional materials. In the present paper, we consider the real space-time dynamics of spinons originating from a local spin flip on the antiferromagnetic ground state of the (an)isotropic Heisenberg spin-1/2 model and the Babujan-Takhtajan spin-1 model. By utilizing algebraic Bethe ansatz methods at finite system size to compute the expectation value of the local magnetization and spin-spin correlations, spinons are visualized as propagating domain walls in the antiferromagnetic spin ordering with anisotropy dependent behavior. The spin-spin correlation after the spin flip displays a light cone, satisfying the Lieb-Robinson bound for the propagation of correlations at the spinon velocity.

Effective one body approach to the dynamics of two spinning black holes with next-to-leading order spin-orbit coupling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Damour, Thibault; Jaranowski, Piotr; Schaefer, Gerhard

2008-07-15

Using a recent, novel Hamiltonian formulation of the gravitational interaction of spinning binaries, we extend the effective one body (EOB) description of the dynamics of two spinning black holes to next-to-leading order (NLO) in the spin-orbit interaction. The spin-dependent EOB Hamiltonian is constructed from four main ingredients: (i) a transformation between the 'effective' Hamiltonian and the 'real' one; (ii) a generalized effective Hamilton-Jacobi equation involving higher powers of the momenta; (iii) a Kerr-type effective metric (with Pade-resummed coefficients) which depends on the choice of some basic 'effective spin vector' S{sub eff}, and which is deformed by comparable-mass effects; and (iv)more » an additional effective spin-orbit interaction term involving another spin vector {sigma}. As a first application of the new, NLO spin-dependent EOB Hamiltonian, we compute the binding energy of circular orbits (for parallel spins) as a function of the orbital frequency, and of the spin parameters. We also study the characteristics of the last stable circular orbit: binding energy, orbital frequency, and the corresponding dimensionless spin parameter a{sub LSO}{identical_to}cJ{sub LSO}/(G(H{sub LSO}/c{sup 2}){sup 2}). We find that the inclusion of NLO spin-orbit terms has a significant 'moderating' effect on the dynamical characteristics of the circular orbits for large and parallel spins.« less

Laser-Induced Ultrafast Demagnetization: Femtomagnetism, a New Frontier?

NASA Astrophysics Data System (ADS)

Zhang, Guoping; Huebner, Wolfgang; Beaurepaire, Eric; Bigot, Jean-Yves

The conventional demagnetization process (spin precession, magnetic domain motion and rotation) is governed mainly by spin-lattice, magnetic dipole and Zeeman, and spin-spin interactions. It occurs on a timescale of nanoseconds. Technologically, much faster magnetization changes are always in great demand to improve data processing speed. Unfortunately, the present speed of magnetic devices is already at the limit of the conventional mechanism with little room left. Fortunately and unprecedentedly, recent experimental investigations have evidenced much faster magnetization dynamics which occurs on a femtosecond time scale: femtomagnetism. This novel spin dynamics has not been well-understood until now. This article reviews the current status of ultrafast spin dynamics and presents a perspective for future experimental and theoretical investigations.Present address: Department of Physics and Astronomy, The University of Tennessee at Knoxville, TN 37996-1200, USA; gpzhang@utk.edu

The spin-temperature theory of dynamic nuclear polarization and nuclear spin-lattice relaxation

NASA Technical Reports Server (NTRS)

Byvik, C. E.; Wollan, D. S.

1974-01-01

A detailed derivation of the equations governing dynamic nuclear polarization (DNP) and nuclear spin lattice relaxation by use of the spin temperature theory has been carried to second order in a perturbation expansion of the density matrix. Nuclear spin diffusion in the rapid diffusion limit and the effects of the coupling of the electron dipole-dipole reservoir (EDDR) with the nuclear spins are incorporated. The complete expression for the dynamic nuclear polarization has been derived and then examined in detail for the limit of well resolved solid effect transitions. Exactly at the solid effect transition peaks, the conventional solid-effect DNP results are obtained, but with EDDR effects on the nuclear relaxation and DNP leakage factor included. Explicit EDDR contributions to DNP are discussed, and a new DNP effect is predicted.

Collective dynamics in atomistic models with coupled translational and spin degrees of freedom

DOE PAGES

Perera, Dilina; Nicholson, Don M.; Eisenbach, Markus; ...

2017-01-26

When using an atomistic model that simultaneously treats the dynamics of translational and spin degrees of freedom, we perform combined molecular and spin dynamics simulations to investigate the mutual influence of the phonons and magnons on their respective frequency spectra and lifetimes in ferromagnetic bcc iron. Furthermore, by calculating the Fourier transforms of the space- and time-displaced correlation functions, the characteristic frequencies and the linewidths of the vibrational and magnetic excitation modes were determined. A comparison of the results with that of the stand-alone molecular dynamics and spin dynamics simulations reveals that the dynamic interplay between the phonons and magnonsmore » leads to a shift in the respective frequency spectra and a decrease in the lifetimes. Moreover, in the presence of lattice vibrations, additional longitudinal magnetic excitations were observed with the same frequencies as the longitudinal phonons.« less

Effects of Cd vacancies and unconventional spin dynamics in the Dirac semimetal Cd3As2

NASA Astrophysics Data System (ADS)

Koumoulis, Dimitrios; Taylor, Robert E.; McCormick, Jeffrey; Ertas, Yavuz N.; Pan, Lei; Che, Xiaoyu; Wang, Kang L.; Bouchard, Louis-S.

2017-08-01

Cd3As2 is a Dirac semimetal that is a 3D analog of graphene. We investigated the local structure and nuclear-spin dynamics in Cd3As2 via 113Cd NMR. The wideline spectrum of the static sample at 295 K is asymmetric and its features are well described by a two-site model with the shielding parameters extracted via Herzfeld-Berger analysis of the magic-angle spinning spectrum. Surprisingly, the 113Cd spin-lattice relaxation time (T1) is extremely long (T1 = 95 s at 295 K), in stark contrast to conductors and the effects of native defects upon semiconductors; but it is similar to that of 13C in graphene (T1 = 110 s). The temperature dependence of 1/T1 revealed a complex bipartite mechanism that included a T2 power-law behavior below 330 K and a thermally activated process above 330 K. In the high-temperature regime, the Arrhenius behavior is consistent with a field-dependent Cd atomic hopping relaxation process. At low temperatures, a T2 behavior consistent with a spin-1/2 Raman-like process provides evidence of a time-dependent spin-rotation magnetic field caused by angular oscillations of internuclear vectors due to lattice vibrations. The observed mechanism does not conform to the conventional two-band model of semimetals, but is instead closer to a mechanism observed in high-Z element ionic solids with large magnetorotation constant [A. J. Vega et al., Phys. Rev. B 74, 214420 (2006)].

Integrated dynamic analysis simulation of space stations with controllable solar array

NASA Technical Reports Server (NTRS)

Heinrichs, J. A.; Fee, J. J.

1972-01-01

A methodology is formulated and presented for the integrated structural dynamic analysis of space stations with controllable solar arrays and non-controllable appendages. The structural system flexibility characteristics are considered in the dynamic analysis by a synthesis technique whereby free-free space station modal coordinates and cantilever appendage coordinates are inertially coupled. A digital simulation of this analysis method is described and verified by comparison of interaction load solutions with other methods of solution. Motion equations are simulated for both the zero gravity and artificial gravity (spinning) orbital conditions. Closed loop controlling dynamics for both orientation control of the arrays and attitude control of the space station are provided in the simulation by various generic types of controlling systems. The capability of the simulation as a design tool is demonstrated by utilizing typical space station and solar array structural representations and a specific structural perturbing force. Response and interaction load solutions are presented for this structural configuration and indicate the importance of using an integrated type analysis for the predictions of structural interactions.

Long-lived nanosecond spin relaxation and spin coherence of electrons in monolayer MoS 2 and WS 2

DOE PAGES

Yang, Luyi; Sinitsyn, Nikolai A.; Chen, Weibing; ...

2015-08-03

The recently discovered monolayer transition metal dichalcogenides (TMDCs) provide a fertile playground to explore new coupled spin–valley physics. Although robust spin and valley degrees of freedom are inferred from polarized photoluminescence (PL) experiments PL timescales are necessarily constrained by short-lived (3–100 ps) electron–hole recombination9, 10. Direct probes of spin/valley polarization dynamics of resident carriers in electron (or hole)-doped TMDCs, which may persist long after recombination ceases, are at an early stage. Here we directly measure the coupled spin–valley dynamics in electron-doped MoS 2 and WS 2 monolayers using optical Kerr spectroscopy, and reveal very long electron spin lifetimes, exceeding 3more » ns at 5 K (2-3 orders of magnitude longer than typical exciton recombination times). In contrast with conventional III–V or II–VI semiconductors, spin relaxation accelerates rapidly in small transverse magnetic fields. Supported by a model of coupled spin–valley dynamics, these results indicate a novel mechanism of itinerant electron spin dephasing in the rapidly fluctuating internal spin–orbit field in TMDCs, driven by fast inter-valley scattering. Additionally, a long-lived spin coherence is observed at lower energies, commensurate with localized states. These studies provide insight into the physics underpinning spin and valley dynamics of resident electrons in atomically thin TMDCs.« less

Critical Spin Superflow in a Spinor Bose-Einstein Condensate

NASA Astrophysics Data System (ADS)

Kim, Joon Hyun; Seo, Sang Won; Shin, Y.

2017-11-01

We investigate the critical dynamics of spin superflow in an easy-plane antiferromagnetic spinor Bose-Einstein condensate. Spin-dipole oscillations are induced in a trapped condensate by applying a linear magnetic field gradient and we observe that the damping rate increases rapidly as the field gradient increases above a certain critical value. The onset of dissipation is found to be associated with the generation of dark-bright solitons due to the modulation instability of the counterflow of two spin components. Spin turbulence emerges as the solitons decay because of their snake instability. We identify another critical point for spin superflow, in which transverse magnon excitations are dynamically generated via spin-exchanging collisions, which leads to the transient formation of axial polar spin domains.

Comparison of spin transfer mechanisms in three terminal spin-torque-oscillators

NASA Astrophysics Data System (ADS)

Jue, Emilie; Rippard, William; Pufall, Matthew; Evarts, Eric R.; Quantum Electromagnetics Division Team

The manipulation of magnetization by electric current is one of the most active field of spintronics due to its interests for memory and logic applications. This control can be achieved through the transfer of angular momentum via a spin polarized current (the mechanism of spin-transfer torque - STT) or through a direct transfer of angular momentum from the crystal lattice through the spin-orbit interaction (the mechanism of spin-orbit torque - SOT). Over the five past years, SOT gained a lot of attention especially for the new possibilities that it offers for data storage application. However, the quantification and the comparison of both mechanisms' efficiencies remains uncertain. In this work, we compare for the first time the STT and SOT efficiencies in individual devices. For this, we created 3-terminal spin-torque oscillators (STO) composed of spin-valves (SV) on top of a Pt wires. The devices can be excited either by STT or by SOT depending on whether the current is applied through the SV or through the Pt wire. By varying the Pt width and the dimensions of the SV, we tune the SOT and STT and compare their efficiencies. We will discuss the complexity of such a structure and the differences in the magnetization dynamics induced by the different excitation mechanisms.

Ultrafast spin dynamics and switching via spin transfer torque in antiferromagnets with weak ferromagnetism

PubMed Central

Kim, Tae Heon; Grünberg, Peter; Han, Song Hee; Cho, Beongki

2016-01-01

The spin-torque driven dynamics of antiferromagnets with Dzyaloshinskii-Moriya interaction (DMI) were investigated based on the Landau-Lifshitz-Gilbert-Slonczewski equation with antiferromagnetic and ferromagnetic order parameters (l and m, respectively). We demonstrate that antiferromagnets including DMI can be described by a 2-dimensional pendulum model of l. Because m is coupled with l, together with DMI and exchange energy, close examination of m provides fundamental understanding of its dynamics in linear and nonlinear regimes. Furthermore, we discuss magnetization reversal as a function of DMI and anisotropy energy induced by a spin current pulse. PMID:27713522

Aging dynamics of quantum spin glasses of rotors

NASA Astrophysics Data System (ADS)

Kennett, Malcolm P.; Chamon, Claudio; Ye, Jinwu

2001-12-01

We study the long time dynamics of quantum spin glasses of rotors using the nonequilibrium Schwinger-Keldysh formalism. These models are known to have a quantum phase transition from a paramagnetic to a spin-glass phase, which we approach by looking at the divergence of the spin-relaxation rate at the transition point. In the aging regime, we determine the dynamical equations governing the time evolution of the spin response and correlation functions, and show that all terms in the equations that arise solely from quantum effects are irrelevant at long times under time reparametrization group (RPG) transformations. At long times, quantum effects enter only through the renormalization of the parameters in the dynamical equations for the classical counterpart of the rotor model. Consequently, quantum effects only modify the out-of-equilibrium fluctuation-dissipation relation (OEFDR), i.e. the ratio X between the temperature and the effective temperature, but not the form of the classical OEFDR.

Spin Interactions and Spin Dynamics in Electronic Nanostructures

DTIC Science & Technology

2006-08-31

in Semiconductor Nanostructures,” D. D. Awschalom, Plenary Speaker, 36th International Symposium on Compound Semiconductors, San Diego, CA, August 25...Electrical Manipulation of Spin Orientation in Compound Semiconductors”, M. E. Flatté, W. H. Lau, C. E. Pryor, and I. Tifrea, International Symposium...on Compound Semiconductors 2003, San Diego, August 25, 2003. 73. “Spin Dynamics in Semiconductors”, M. E. Flatté, SPINTECH II: 2nd International

Tetragonal bismuth bilayer: A stable and robust quantum spin hall insulator

DOE PAGES

Kou, Liangzhi; Tan, Xin; Ma, Yandong; ...

2015-11-23

In this study, topological insulators (TIs) exhibit novel physics with great promise for new devices, but considerable challenges remain to identify TIs with high structural stability and large nontrivial band gap suitable for practical applications. Here we predict by first-principles calculations a two-dimensional (2D) TI, also known as a quantum spin Hall (QSH) insulator, in a tetragonal bismuth bilayer (TB-Bi) structure that is dynamically and thermally stable based on phonon calculations and finite-temperature molecular dynamics simulations. Density functional theory and tight-binding calculations reveal a band inversion among the Bi-p orbits driven by the strong intrinsic spin–orbit coupling, producing a largemore » nontrivial band gap, which can be effectively tuned by moderate strains. The helical gapless edge states exhibit a linear dispersion with a high Fermi velocity comparable to that of graphene, and the QSH phase remains robust on a NaCl substrate. These remarkable properties place TB-Bi among the most promising 2D TIs for high-speed spintronic devices, and the present results provide insights into the intriguing QSH phenomenon in this new Bi structure and offer guidance for its implementation in potential applications.« less

Evidence for a dynamical ground state in the frustrated pyrohafnate Tb2Hf2O7

NASA Astrophysics Data System (ADS)

Anand, V. K.; Opherden, L.; Xu, J.; Adroja, D. T.; Hillier, A. D.; Biswas, P. K.; Herrmannsdörfer, T.; Uhlarz, M.; Hornung, J.; Wosnitza, J.; Canévet, E.; Lake, B.

2018-03-01

We report the physical properties of Tb2Hf2O7 based on ac magnetic susceptibility χac(T ) , dc magnetic susceptibility χ (T ) , isothermal magnetization M (H ) , and heat capacity Cp(T ) measurements combined with muon spin relaxation (μ SR ) and neutron powder diffraction measurements. No evidence for long-range magnetic order is found down to 0.1 K. However, χac(T ) data present a frequency-dependent broad peak (near 0.9 K at 16 Hz) indicating slow spin dynamics. The slow spin dynamics is further evidenced from the μ SR data (characterized by a stretched exponential behavior) which show persistent spin fluctuations down to 0.3 K. The neutron powder diffraction data collected at 0.1 K show a broad peak of magnetic origin (diffuse scattering) but no magnetic Bragg peaks. The analysis of the diffuse scattering data reveals a dominant antiferromagnetic interaction in agreement with the negative Weiss temperature. The absence of long-range magnetic order and the presence of slow spin dynamics and persistent spin fluctuations together reflect a dynamical ground state in Tb2Hf2O7 .

Dynamical systems approach to the study of a sociophysics agent-based model

NASA Astrophysics Data System (ADS)

Timpanaro, André M.; Prado, Carmen P. C.

2011-03-01

The Sznajd model is a Potts-like model that has been studied in the context of sociophysics [1,2] (where spins are interpreted as opinions). In a recent work [3], we generalized the Sznajd model to include assymetric interactions between the spins (interpreted as biases towards opinions) and used dynamical systems techniques to tackle its mean-field version, given by the flow: ησ = ∑ σ' = 1Mησησ'(ησρσ'→σ-σ'ρσ→σ'). Where hs is the proportion of agents with opinion (spin) σ', M is the number of opinions and σ'→σ' is the probability weight for an agent with opinion σ being convinced by another agent with opinion σ'. We made Monte Carlo simulations of the model in a complex network (using Barabási-Albert networks [4]) and they displayed the same attractors than the mean-field. Using linear stability analysis, we were able to determine the mean-field attractor structure analytically and to show that it has connections with well known graph theory problems (maximal independent sets and positive fluxes in directed graphs). Our dynamical systems approach is quite simple and can be used also in other models, like the voter model.

Generalized GW+Boltzmann Approach for the Description of Ultrafast Electron Dynamics in Topological Insulators

PubMed Central

Battiato, Marco; Sánchez-Barriga, Jaime

2017-01-01

Quantum-phase transitions between trivial insulators and topological insulators differ from ordinary metal-insulator transitions in that they arise from the inversion of the bulk band structure due to strong spin–orbit coupling. Such topological phase transitions are unique in nature as they lead to the emergence of topological surface states which are characterized by a peculiar spin texture that is believed to play a central role in the generation and manipulation of dissipationless surface spin currents on ultrafast timescales. Here, we provide a generalized GW+Boltzmann approach for the description of ultrafast dynamics in topological insulators driven by electron–electron and electron–phonon scatterings. Taking the prototypical insulator Bi2Te3 as an example, we test the robustness of our approach by comparing the theoretical prediction to results of time- and angle-resolved photoemission experiments. From this comparison, we are able to demonstrate the crucial role of the excited spin texture in the subpicosecond relaxation of transient electrons, as well as to accurately obtain the magnitude and strength of electron–electron and electron–phonon couplings. Our approach could be used as a generalized theory for three-dimensional topological insulators in the bulk-conducting transport regime, paving the way for the realization of a unified theory of ultrafast dynamics in topological materials. PMID:28773171

Dynamical systems approach to the study of a sociophysics agent-based model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Timpanaro, Andre M.; Prado, Carmen P. C.

2011-03-24

The Sznajd model is a Potts-like model that has been studied in the context of sociophysics [1,2](where spins are interpreted as opinions). In a recent work [3], we generalized the Sznajd model to include assymetric interactions between the spins (interpreted as biases towards opinions) and used dynamical systems techniques to tackle its mean-field version, given by the flow: {eta}{sub {sigma}} = {Sigma}{sub {sigma}}'{sup M} = 1{eta}{sub {sigma}}{eta}{sigma}'({eta}{sub {sigma}}{rho}{sigma}'{yields}{sigma}-{sigma}'{rho}{sigma}{yields}{sigma}').Where hs is the proportion of agents with opinion (spin){sigma}', M is the number of opinions and {sigma}'{yields}{sigma}' is the probability weight for an agent with opinion {sigma} being convinced by another agentmore » with opinion {sigma}'. We made Monte Carlo simulations of the model in a complex network (using Barabasi-Albert networks [4]) and they displayed the same attractors than the mean-field. Using linear stability analysis, we were able to determine the mean-field attractor structure analytically and to show that it has connections with well known graph theory problems (maximal independent sets and positive fluxes in directed graphs). Our dynamical systems approach is quite simple and can be used also in other models, like the voter model.« less

Effect of clathrate hydrate formation and decomposition on NMR parameters in THF-D2O solution.

PubMed

Rousina-Webb, Alexander; Leek, Donald M; Ripmeester, John

2012-06-28

The NMR spin-lattice relaxation time (T(1)), spin-spin relaxation time (T(2)) and the diffusion coefficient D were measured for (1)H in a 1:17 mol % solution of tetrahydrofuran (THF) in D(2)O. The aim of the work was to clarify some earlier points raised regarding the utility of these measurements to convey structural information on hydrate formation and reformation. A number of irregularities in T(1) and T(2) measurements during hydrate processes reported earlier are explained in terms of the presence of interfaces and possible temperature gradients. We observe that T(1) and T(2) in solution are exactly the same before and after hydrate formation, thus confirming that the solution is isotropic. This is inconsistent with the presence of memory effects, at least those that may affect the dynamics to which T(1) and T(2) are sensitive. The measurement of the diffusion coefficient for a number of hours in the subcooled solution before nucleation proved invariant with time, again suggesting that the solution remains isotropic without affecting the guest dynamics and diffusion.

Quasiparticle dynamics and spin-orbital texture of the SrTiO3 two-dimensional electron gas.

PubMed

King, P D C; McKeown Walker, S; Tamai, A; de la Torre, A; Eknapakul, T; Buaphet, P; Mo, S-K; Meevasana, W; Bahramy, M S; Baumberger, F

2014-02-27

Two-dimensional electron gases (2DEGs) in SrTiO3 have become model systems for engineering emergent behaviour in complex transition metal oxides. Understanding the collective interactions that enable this, however, has thus far proved elusive. Here we demonstrate that angle-resolved photoemission can directly image the quasiparticle dynamics of the d-electron subband ladder of this complex-oxide 2DEG. Combined with realistic tight-binding supercell calculations, we uncover how quantum confinement and inversion symmetry breaking collectively tune the delicate interplay of charge, spin, orbital and lattice degrees of freedom in this system. We reveal how they lead to pronounced orbital ordering, mediate an orbitally enhanced Rashba splitting with complex subband-dependent spin-orbital textures and markedly change the character of electron-phonon coupling, co-operatively shaping the low-energy electronic structure of the 2DEG. Our results allow for a unified understanding of spectroscopic and transport measurements across different classes of SrTiO3-based 2DEGs, and yield new microscopic insights on their functional properties.

Chevrons, filaments, spinning clusters and phase coexistence: emergent dynamics of 2- and 3-d particle suspensions driven by multiaxial magnetic fields

DOE PAGES

Solis, Kyle J.; Martin, James E.

2017-07-06

In recent years a rich variety of emergent phenomena have been observed when suspensions of magnetic particles are subjected to alternating magnetic fields. These particle assemblies often exhibit vigorous dynamics due to the injection of energy from the field. These include surface and interface phenomena, such as highly organized, segmented “snakes” that can be induced to swim by structural symmetry breaking, and “asters” and “anti-asters,” particle assemblies that can be manipulated to capture and transport cargo. In bulk suspensions of magnetic platelets subjected to multiaxial alternating fields, advection lattices and even vortex lattices have been created, and a variety ofmore » biomimetic dynamics – serpents, bees and amoebas – have been discovered in magnetic fluids suspended in an immiscible liquid. In this paper several new driven phases are presented, including flying chevrons, dense spinning clusters, filaments, and examples of phase coexistence in driven phases. These observations broaden the growing field of driven magnetic suspensions and present new challenges to those interested in simulating the dynamics of these complex systems.« less

Enhancing coherence in molecular spin qubits via atomic clock transitions

NASA Astrophysics Data System (ADS)

Shiddiq, Muhandis; Komijani, Dorsa; Duan, Yan; Gaita-Ariño, Alejandro; Coronado, Eugenio; Hill, Stephen

2016-03-01

Quantum computing is an emerging area within the information sciences revolving around the concept of quantum bits (qubits). A major obstacle is the extreme fragility of these qubits due to interactions with their environment that destroy their quantumness. This phenomenon, known as decoherence, is of fundamental interest. There are many competing candidates for qubits, including superconducting circuits, quantum optical cavities, ultracold atoms and spin qubits, and each has its strengths and weaknesses. When dealing with spin qubits, the strongest source of decoherence is the magnetic dipolar interaction. To minimize it, spins are typically diluted in a diamagnetic matrix. For example, this dilution can be taken to the extreme of a single phosphorus atom in silicon, whereas in molecular matrices a typical ratio is one magnetic molecule per 10,000 matrix molecules. However, there is a fundamental contradiction between reducing decoherence by dilution and allowing quantum operations via the interaction between spin qubits. To resolve this contradiction, the design and engineering of quantum hardware can benefit from a ‘bottom-up’ approach whereby the electronic structure of magnetic molecules is chemically tailored to give the desired physical behaviour. Here we present a way of enhancing coherence in solid-state molecular spin qubits without resorting to extreme dilution. It is based on the design of molecular structures with crystal field ground states possessing large tunnelling gaps that give rise to optimal operating points, or atomic clock transitions, at which the quantum spin dynamics become protected against dipolar decoherence. This approach is illustrated with a holmium molecular nanomagnet in which long coherence times (up to 8.4 microseconds at 5 kelvin) are obtained at unusually high concentrations. This finding opens new avenues for quantum computing based on molecular spin qubits.

Rattleback dynamics and its reversal time of rotation.

PubMed

Kondo, Yoichiro; Nakanishi, Hiizu

2017-06-01

A rattleback is a rigid, semielliptic toy which exhibits unintuitive behavior; when it is spun in one direction, it soon begins pitching and stops spinning, then it starts to spin in the opposite direction, but in the other direction, it seems to spin just steadily. This puzzling behavior results from the slight misalignment between the principal axes for the inertia and those for the curvature; the misalignment couples the spinning with the pitching and the rolling oscillations. It has been shown that under the no-slip condition and without dissipation the spin can reverse in both directions, and Garcia and Hubbard obtained the formula for the time required for the spin reversal t_{r} [Proc. R. Soc. Lond. A 418, 165 (1988)1364-502110.1098/rspa.1988.0078]. In this work, we reformulate the rattleback dynamics in a physically transparent way and reduce it to a three-variable dynamics for spinning, pitching, and rolling. We obtain an expression of the Garcia-Hubbard formula for t_{r} by a simple product of four factors: (1) the misalignment angle, (2) the difference in the inverses of inertia moment for the two oscillations, (3) that in the radii for the two principal curvatures, and (4) the squared frequency of the oscillation. We perform extensive numerical simulations to examine validity and limitation of the formula, and find that (1) the Garcia-Hubbard formula is good for both spinning directions in the small spin and small oscillation regime, but (2) in the fast spin regime especially for the steady direction, the rattleback may not reverse and shows a rich variety of dynamics including steady spinning, spin wobbling, and chaotic behavior reminiscent of chaos in a dissipative system.

Rattleback dynamics and its reversal time of rotation

NASA Astrophysics Data System (ADS)

Kondo, Yoichiro; Nakanishi, Hiizu

2017-06-01

A rattleback is a rigid, semielliptic toy which exhibits unintuitive behavior; when it is spun in one direction, it soon begins pitching and stops spinning, then it starts to spin in the opposite direction, but in the other direction, it seems to spin just steadily. This puzzling behavior results from the slight misalignment between the principal axes for the inertia and those for the curvature; the misalignment couples the spinning with the pitching and the rolling oscillations. It has been shown that under the no-slip condition and without dissipation the spin can reverse in both directions, and Garcia and Hubbard obtained the formula for the time required for the spin reversal tr [Proc. R. Soc. Lond. A 418, 165 (1988), 10.1098/rspa.1988.0078]. In this work, we reformulate the rattleback dynamics in a physically transparent way and reduce it to a three-variable dynamics for spinning, pitching, and rolling. We obtain an expression of the Garcia-Hubbard formula for tr by a simple product of four factors: (1) the misalignment angle, (2) the difference in the inverses of inertia moment for the two oscillations, (3) that in the radii for the two principal curvatures, and (4) the squared frequency of the oscillation. We perform extensive numerical simulations to examine validity and limitation of the formula, and find that (1) the Garcia-Hubbard formula is good for both spinning directions in the small spin and small oscillation regime, but (2) in the fast spin regime especially for the steady direction, the rattleback may not reverse and shows a rich variety of dynamics including steady spinning, spin wobbling, and chaotic behavior reminiscent of chaos in a dissipative system.

Spin-orbit torques in magnetic bilayers

NASA Astrophysics Data System (ADS)

Haney, Paul

2015-03-01

Spintronics aims to utilize the coupling between charge transport and magnetic dynamics to develop improved and novel memory and logic devices. Future progress in spintronics may be enabled by exploiting the spin-orbit coupling present at the interface between thin film ferromagnets and heavy metals. In these systems, applying an in-plane electrical current can induce magnetic dynamics in single domain ferromagnets, or can induce rapid motion of domain wall magnetic textures. There are multiple effects responsible for these dynamics. They include spin-orbit torques and a chiral exchange interaction (the Dzyaloshinskii-Moriya interaction) in the ferromagnet. Both effects arise from the combination of ferromagnetism and spin-orbit coupling present at the interface. There is additionally a torque from the spin current flux impinging on the ferromagnet, arising from the spin hall effect in the heavy metal. Using a combination of approaches, from drift-diffusion to Boltzmann transport to first principles methods, we explore the relative contributions to the dynamics from these different effects. We additionally propose that the transverse spin current is locally enhanced over its bulk value in the vicinity of an interface which is oriented normal to the charge current direction.

Lanczos algorithm with matrix product states for dynamical correlation functions

NASA Astrophysics Data System (ADS)

Dargel, P. E.; Wöllert, A.; Honecker, A.; McCulloch, I. P.; Schollwöck, U.; Pruschke, T.

2012-05-01

The density-matrix renormalization group (DMRG) algorithm can be adapted to the calculation of dynamical correlation functions in various ways which all represent compromises between computational efficiency and physical accuracy. In this paper we reconsider the oldest approach based on a suitable Lanczos-generated approximate basis and implement it using matrix product states (MPS) for the representation of the basis states. The direct use of matrix product states combined with an ex post reorthogonalization method allows us to avoid several shortcomings of the original approach, namely the multitargeting and the approximate representation of the Hamiltonian inherent in earlier Lanczos-method implementations in the DMRG framework, and to deal with the ghost problem of Lanczos methods, leading to a much better convergence of the spectral weights and poles. We present results for the dynamic spin structure factor of the spin-1/2 antiferromagnetic Heisenberg chain. A comparison to Bethe ansatz results in the thermodynamic limit reveals that the MPS-based Lanczos approach is much more accurate than earlier approaches at minor additional numerical cost.

Molecular dynamics simulations reveal a disorder-to-order transition on phosphorylation of smooth muscle myosin.

PubMed

Espinoza-Fonseca, L Michel; Kast, David; Thomas, David D

2007-09-15

We have performed molecular dynamics simulations of the phosphorylated (at S-19) and the unphosphorylated 25-residue N-terminal phosphorylation domain of the regulatory light chain (RLC) of smooth muscle myosin to provide insight into the structural basis of regulation. This domain does not appear in any crystal structure, so these simulations were combined with site-directed spin labeling to define its structure and dynamics. Simulations were carried out in explicit water at 310 K, starting with an ideal alpha-helix. In the absence of phosphorylation, large portions of the domain (residues S-2 to K-11 and R-16 through Y-21) were metastable throughout the simulation, undergoing rapid transitions among alpha-helix, pi-helix, and turn, whereas residues K-12 to Q-15 remained highly disordered, displaying a turn motif from 1 to 22.5 ns and a random coil pattern from 22.5 to 50 ns. Phosphorylation increased alpha-helical order dramatically in residues K-11 to A-17 but caused relatively little change in the immediate vicinity of the phosphorylation site (S-19). Phosphorylation also increased the overall dynamic stability, as evidenced by smaller temporal fluctuations in the root mean-square deviation. These results on the isolated phosphorylation domain, predicting a disorder-to-order transition induced by phosphorylation, are remarkably consistent with published experimental data involving site-directed spin labeling of the intact RLC bound to the two-headed heavy meromyosin. The simulations provide new insight into structural details not revealed by experiment, allowing us to propose a refined model for the mechanism by which phosphorylation affects the N-terminal domain of the RLC of smooth muscle myosin.

Magnetic Suspension for Dynamic Spin Rig

NASA Technical Reports Server (NTRS)

Johnson, Dexter

1998-01-01

NASA Lewis Research Center's Dynamic Spin Rig, located in Building 5, Test Cell CW-18, is used to test turbomachinery blades and components by rotating them in a vacuum chamber. A team from Lewis' Machine Dynamics Branch successfully integrated a magnetic bearing and control system into the Dynamic Spin Rig. The magnetic bearing worked very well both to support and shake the shaft. It was demonstrated that the magnetic bearing can transmit more vibrational energy into the shaft and excite some blade modes to larger amplitudes than the existing electromagnetic shakers can.

Interfacial exchange interactions and magnetism of Ni2MnAl /Fe bilayers

NASA Astrophysics Data System (ADS)

Yanes, R.; Simon, E.; Keller, S.; Nagyfalusi, B.; Khmelevsky, S.; Szunyogh, L.; Nowak, U.

2017-08-01

Based on multiscale calculations combining ab initio methods with spin dynamics simulations, we perform a detailed study of the magnetic behavior of Ni2MnAl /Fe bilayers. Our simulations show that such a bilayer exhibits a small exchange bias effect when the Ni2MnAl Heusler alloy is in a disordered B2 phase. Additionally, we present an effective way to control the magnetic structure of the Ni2MnAl antiferromagnet, in the pseudo-ordered B2-I as well as the disordered B2 phases, via a spin-flop coupling to the Fe layer.

Beam and spin dynamics in the fast ramping storage ring ELSA: Concepts and measures to increase beam energy, current and polarization

NASA Astrophysics Data System (ADS)

Hillert, Wolfgang; Balling, Andreas; Boldt, Oliver; Dieckmann, Andreas; Eberhardt, Maren; Frommberger, Frank; Heiliger, Dominik; Heurich, Nikolas; Koop, Rebecca; Klarner, Fabian; Preisner, Oliver; Proft, Dennis; Pusch, Thorsten; Roth, André; Sauerland, Dennis; Schedler, Manuel; Schmidt, Jan Felix; Switka, Michael; Thiry, Jens-Peter; Wittschen, Jürgen; Zander, Sven

2017-01-01

The electron accelerator facility ELSA has been operated for almost 30 years serving nuclear physics experiments investigating the sub-nuclear structure of matter. Within the 12 years funding period of the collaborative research center SFB/TR 16, linearly and circularly polarized photon beams with energies up to more than 3 GeV were successfully delivered to photoproduction experiments. In order to fulfill the increasing demands on beam polarization and intensity, a comprehensive research and upgrade program has been carried out. Beam and spin dynamics have been studied theoretically and experimentally, and sophisticated new devices have been developed and installed. The improvements led to a significant increase of the available beam polarization and intensity. A further increase of beam energy seems feasible with the implementation of superconducting cavities.

Multiscale modeling of current-induced switching in magnetic tunnel junctions using ab initio spin-transfer torques

NASA Astrophysics Data System (ADS)

Ellis, Matthew O. A.; Stamenova, Maria; Sanvito, Stefano

2017-12-01

There exists a significant challenge in developing efficient magnetic tunnel junctions with low write currents for nonvolatile memory devices. With the aim of analyzing potential materials for efficient current-operated magnetic junctions, we have developed a multi-scale methodology combining ab initio calculations of spin-transfer torque with large-scale time-dependent simulations using atomistic spin dynamics. In this work we introduce our multiscale approach, including a discussion on a number of possible schemes for mapping the ab initio spin torques into the spin dynamics. We demonstrate this methodology on a prototype Co/MgO/Co/Cu tunnel junction showing that the spin torques are primarily acting at the interface between the Co free layer and MgO. Using spin dynamics we then calculate the reversal switching times for the free layer and the critical voltages and currents required for such switching. Our work provides an efficient, accurate, and versatile framework for designing novel current-operated magnetic devices, where all the materials details are taken into account.

Tunable Spin dependent beam shift by simultaneously tailoring geometric and dynamical phases of light in inhomogeneous anisotropic medium

PubMed Central

Pal, Mandira; Banerjee, Chitram; Chandel, Shubham; Bag, Ankan; Majumder, Shovan K.; Ghosh, Nirmalya

2016-01-01

Spin orbit interaction and the resulting Spin Hall effect of light are under recent intensive investigations because of their fundamental nature and potential applications. Here, we report an interesting manifestation of spin Hall effect of light and demonstrate its tunability in an inhomogeneous anisotropic medium exhibiting spatially varying retardance level. In our system, the beam shift occurs only for one circular polarization mode keeping the other orthogonal mode unaffected, which is shown to arise due to the combined spatial gradients of the geometric phase and the dynamical phase of light. The constituent two orthogonal circular polarization modes of an input linearly polarized light evolve in different trajectories, eventually manifesting as a large and tunable spin separation. The spin dependent beam shift and the demonstrated principle of simultaneously tailoring space-varying geometric and dynamical phase of light for achieving its tunability (of both magnitude and direction), may provide an attractive route towards development of spin-optical devices. PMID:28004825

Electron-spin dynamics in Mn-doped GaAs using time-resolved magneto-optical techniques

NASA Astrophysics Data System (ADS)

Akimov, I. A.; Dzhioev, R. I.; Korenev, V. L.; Kusrayev, Yu. G.; Zhukov, E. A.; Yakovlev, D. R.; Bayer, M.

2009-08-01

We study the electron-spin dynamics in p -type GaAs doped with magnetic Mn acceptors by means of time-resolved pump-probe and photoluminescence techniques. Measurements in transverse magnetic fields show a long spin-relaxation time of 20 ns that can be uniquely related to electrons. Application of weak longitudinal magnetic fields above 100 mT extends the spin-relaxation times up to microseconds which is explained by suppression of the Bir-Aronov-Pikus spin relaxation for the electron on the Mn acceptor.

Dynamic spin injection into a quantum well coupled to a spin-split bound state

NASA Astrophysics Data System (ADS)

Maslova, N. S.; Rozhansky, I. V.; Mantsevich, V. N.; Arseyev, P. I.; Averkiev, N. S.; Lähderanta, E.

2018-05-01

We present a theoretical analysis of dynamic spin injection due to spin-dependent tunneling between a quantum well (QW) and a bound state split in spin projection due to an exchange interaction or external magnetic field. We focus on the impact of Coulomb correlations at the bound state on spin polarization and sheet density kinetics of the charge carriers in the QW. The theoretical approach is based on kinetic equations for the electron occupation numbers taking into account high order correlation functions for the bound state electrons. It is shown that the on-site Coulomb repulsion leads to an enhanced dynamic spin polarization of the electrons in the QW and a delay in the carriers tunneling into the bound state. The interplay of these two effects leads to nontrivial dependence of the spin polarization degree, which can be probed experimentally using time-resolved photoluminescence experiments. It is demonstrated that the influence of the Coulomb interactions can be controlled by adjusting the relaxation rates. These findings open a new way of studying the Hubbard-like electron interactions experimentally.

Quasi-two-dimensional spin correlations in the triangular lattice bilayer spin glass LuCoGaO 4

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fritsch, Katharina; Ross, Kathyrn A.; Granroth, Garrett E.

Here we present a single-crystal time-of-flight neutron scattering study of the static and dynamic spin correlations in LuCoGaO 4, a quasi-two-dimensional dilute triangular lattice antiferromagnetic spin-glass material. This system is based on Co 2+ ions that are randomly distributed on triangular bilayers within the YbFe 2O 4 type, hexagonal crystal structure. Antiferromagnetic short-range two-dimensional correlations at wave vectors Q = (1/3,1/3, L) develop within the bilayers at temperatures as high as |Θ CW| ~100 K and extend over roughly five unit cells at temperatures below T g = 19 K. These two-dimensional static correlations are observed as diffuse rods ofmore » neutron scattering intensity along c * and display a continuous spin freezing process in their energy dependence. Aside from exhibiting these typical spin-glass characteristics, this insulating material reveals a novel gapped magnetic resonant spin excitation at ΔE ~12 meV localized around Q = (1 / 3, 1 / 3,L) . The temperature dependence of the spin gap associated with this two-dimensional excitation correlates with the evolution of the static correlations into the spin-glass state ground state. Lastly, we associate it with the effect of the staggered exchange field acting on the S eff = 1/2 Ising-like doublet of the Co 2+ moments.« less

Quasi-two-dimensional spin correlations in the triangular lattice bilayer spin glass LuCoGaO 4

DOE PAGES

Fritsch, Katharina; Ross, Kathyrn A.; Granroth, Garrett E.; ...

2017-09-13

Here we present a single-crystal time-of-flight neutron scattering study of the static and dynamic spin correlations in LuCoGaO 4, a quasi-two-dimensional dilute triangular lattice antiferromagnetic spin-glass material. This system is based on Co 2+ ions that are randomly distributed on triangular bilayers within the YbFe 2O 4 type, hexagonal crystal structure. Antiferromagnetic short-range two-dimensional correlations at wave vectors Q = (1/3,1/3, L) develop within the bilayers at temperatures as high as |Θ CW| ~100 K and extend over roughly five unit cells at temperatures below T g = 19 K. These two-dimensional static correlations are observed as diffuse rods ofmore » neutron scattering intensity along c * and display a continuous spin freezing process in their energy dependence. Aside from exhibiting these typical spin-glass characteristics, this insulating material reveals a novel gapped magnetic resonant spin excitation at ΔE ~12 meV localized around Q = (1 / 3, 1 / 3,L) . The temperature dependence of the spin gap associated with this two-dimensional excitation correlates with the evolution of the static correlations into the spin-glass state ground state. Lastly, we associate it with the effect of the staggered exchange field acting on the S eff = 1/2 Ising-like doublet of the Co 2+ moments.« less

Dynamical Negative Differential Resistance in Antiferromagnetically Coupled Few-Atom Spin Chains

NASA Astrophysics Data System (ADS)

Rolf-Pissarczyk, Steffen; Yan, Shichao; Malavolti, Luigi; Burgess, Jacob A. J.; McMurtrie, Gregory; Loth, Sebastian

2017-11-01

We present the appearance of negative differential resistance (NDR) in spin-dependent electron transport through a few-atom spin chain. A chain of three antiferromagnetically coupled Fe atoms (Fe trimer) was positioned on a Cu2 N /Cu (100 ) surface and contacted with the spin-polarized tip of a scanning tunneling microscope, thus coupling the Fe trimer to one nonmagnetic and one magnetic lead. Pronounced NDR appears at the low bias of 7 mV, where inelastic electron tunneling dynamically locks the atomic spin in a long-lived excited state. This causes a rapid increase of the magnetoresistance between the spin-polarized tip and Fe trimer and quenches elastic tunneling. By varying the coupling strength between the tip and Fe trimer, we find that in this transport regime the dynamic locking of the Fe trimer competes with magnetic exchange interaction, which statically forces the Fe trimer into its high-magnetoresistance state and removes the NDR.

Precise determination of the deuteron spin structure at low to moderate Q2 with CLAS and extraction of the neutron contribution

NASA Astrophysics Data System (ADS)

Guler, N.; Fersch, R. G.; Kuhn, S. E.; Bosted, P.; Griffioen, K. A.; Keith, C.; Minehart, R.; Prok, Y.; Adhikari, K. P.; Adikaram, D.; Amaryan, M. J.; Anderson, M. D.; Anefalos Pereira, S.; Avakian, H.; Ball, J.; Battaglieri, M.; Batourine, V.; Bedlinskiy, I.; Biselli, A.; Briscoe, W. J.; Brooks, W. K.; Bültmann, S.; Burkert, V. D.; Carman, D. S.; Celentano, A.; Chandavar, S.; Charles, G.; Colaneri, L.; Cole, P. L.; Contalbrigo, M.; Crabb, D.; Crede, V.; D'Angelo, A.; Dashyan, N.; Deur, A.; Djalali, C.; Dodge, G. E.; Dupre, R.; Alaoui, A. El; El Fassi, L.; Elouadrhiri, L.; Eugenio, P.; Fedotov, G.; Fegan, S.; Filippi, A.; Fleming, J. A.; Forest, T. A.; Garillon, B.; Garçon, M.; Gevorgyan, N.; Gilfoyle, G. P.; Giovanetti, K. L.; Girod, F. X.; Goetz, J. T.; Golovatch, E.; Gothe, R. W.; Guidal, M.; Guo, L.; Hafidi, K.; Hakobyan, H.; Harrison, N.; Hattawy, M.; Hicks, K.; Ho, D.; Holtrop, M.; Hughes, S. M.; Hyde, C. E.; Ireland, D. G.; Ishkhanov, B. S.; Isupov, E. L.; Jo, H. S.; Joo, K.; Joosten, S.; Keller, D.; Khandaker, M.; Kim, A.; Kim, W.; Klein, A.; Klein, F. J.; Kubarovsky, V.; Kuleshov, S. V.; Livingston, K.; Lu, H. Y.; Mayer, M.; MacGregor, I. J. D.; McKinnon, B.; Mirazita, M.; Mokeev, V.; Montgomery, R. A.; Movsisyan, A.; Munoz Camacho, C.; Nadel-Turonski, P.; Net, L. A.; Niculescu, I.; Osipenko, M.; Ostrovidov, A. I.; Park, K.; Pasyuk, E.; Pisano, S.; Pogorelko, O.; Price, J. W.; Procureur, S.; Ripani, M.; Rizzo, A.; Rosner, G.; Rossi, P.; Roy, P.; Sabatié, F.; Salgado, C.; Schott, D.; Schumacher, R. A.; Seder, E.; Simonyan, A.; Skorodumina, Iu.; Sokhan, D.; Sparveris, N.; Strakovsky, I. I.; Strauch, S.; Sytnik, V.; Tian, Ye; Tkachenko, S.; Ungaro, M.; Voutier, E.; Walford, N. K.; Wei, X.; Weinstein, L. B.; Wood, M. H.; Zachariou, N.; Zana, L.; Zhang, J.; Zhao, Z. W.; Zonta, I.; CLAS Collaboration

2015-11-01

We present the final results for the deuteron spin structure functions obtained from the full data set collected in 2000-2001 with Jefferson Lab's continuous electron beam accelerator facility (CEBAF) using the CEBAF large acceptance spectrometer (CLAS). Polarized electrons with energies of 1.6, 2.5, 4.2, and 5.8 GeV were scattered from deuteron (15ND3 ) targets, dynamically polarized along the beam direction, and detected with CLAS. From the measured double-spin asymmetry, the virtual photon absorption asymmetry A1d and the polarized structure function g1d were extracted over a wide kinematic range (0.05 GeV2

Precise determination of the deuteron spin structure at low to moderate Q 2 with CLAS and extraction of the neutron contribution

DOE PAGES

Guler, N.; Fersch, R. G.; Kuhn, S. E.; ...

2015-11-02

In this study, we present the final results for the deuteron spin structure functions obtained from the full data set collected with Jefferson Lab's CLAS in 2000-2001. Polarized electrons with energies of 1.6, 2.5, 4.2 and 5.8 GeV were scattered from deuteron ( 15ND 3) targets, dynamically polarized along the beam direction, and detected with CLAS. From the measured double spin asymmetry, the virtual photon absorption asymmetry A d 1 and the polarized structure function g d 1 were extracted over a wide kinematic range (0.05 GeV2 < Q2 < 5 GeV2 and 0.9 GeV < W < 3 GeV).more » We use an unfolding procedure and a parametrization of the corresponding proton results to extract from these data the polarized structure functions A n 1 and g 1 n of the (bound) neutron, which are so far unknown in the resonance region, W < 2 GeV. We compare our final results, including several moments of the deuteron and neutron spin structure functions, with various theoretical models and expectations as well as parametrizations of the world data. The unprecedented precision and dense kinematic coverage of these data can aid in future extractions of polarized parton distributions, tests of perturbative QCD predictions for the quark polarization at large x, a better understanding of quark-hadron duality, and more precise values for higher-twist matrix elements in the framework of the Operator Product Expansion.« less

Dynamics of a Cr spin in a semiconductor quantum dot: Hole-Cr flip-flops and spin-phonon coupling

NASA Astrophysics Data System (ADS)

Lafuente-Sampietro, A.; Utsumi, H.; Sunaga, M.; Makita, K.; Boukari, H.; Kuroda, S.; Besombes, L.

2018-04-01

A detailed analysis of the photoluminescence (PL) intensity distribution in singly Cr-doped CdTe/ZnTe quantum dots (QDs) is performed. First of all, we demonstrate that hole-Cr flip-flops induced by an interplay of the hole-Cr exchange interaction and the coupling with acoustic phonons are the main source of spin relaxation within the exciton-Cr complex. This spin flip mechanism appears in the excitation power dependence of the PL of the exciton as well as in the intensity distribution of the resonant PL. The resonant optical pumping of the Cr spin which was recently demonstrated can also be explained by these hole-Cr flip-flops. Despite the fast exciton-Cr spin dynamics, an analysis of the PL intensity under magnetic field shows that the hole-Cr exchange interaction in CdTe/ZnTe QDs is antiferromagnetic. In addition to the Cr spin dynamics induced by the interaction with carriers' spin, we finally demonstrate using time resolved optical pumping measurements that a Cr spin interacts with nonequilibrium acoustic phonons generated during the optical excitation inside or near the QD.

Microscopic observation of magnon bound states and their dynamics.

PubMed

Fukuhara, Takeshi; Schauß, Peter; Endres, Manuel; Hild, Sebastian; Cheneau, Marc; Bloch, Immanuel; Gross, Christian

2013-10-03

The existence of bound states of elementary spin waves (magnons) in one-dimensional quantum magnets was predicted almost 80 years ago. Identifying signatures of magnon bound states has so far remained the subject of intense theoretical research, and their detection has proved challenging for experiments. Ultracold atoms offer an ideal setting in which to find such bound states by tracking the spin dynamics with single-spin and single-site resolution following a local excitation. Here we use in situ correlation measurements to observe two-magnon bound states directly in a one-dimensional Heisenberg spin chain comprising ultracold bosonic atoms in an optical lattice. We observe the quantum dynamics of free and bound magnon states through time-resolved measurements of two spin impurities. The increased effective mass of the compound magnon state results in slower spin dynamics as compared to single-magnon excitations. We also determine the decay time of bound magnons, which is probably limited by scattering on thermal fluctuations in the system. Our results provide a new way of studying fundamental properties of quantum magnets and, more generally, properties of interacting impurities in quantum many-body systems.

Dynamical Jahn-Teller effect of fullerene anions

NASA Astrophysics Data System (ADS)

Liu, Dan; Iwahara, Naoya; Chibotaru, Liviu F.

2018-03-01

The dynamical Jahn-Teller effect of C60n - anions (n =1 -5) is studied using the numerical diagonalization of the linear pn⊗8 d Jahn-Teller Hamiltonian with the currently established coupling parameters. It is found that in all anions the Jahn-Teller effect stabilizes the low-spin states, resulting in the violation of Hund's rule. The energy gain due to the Jahn-Teller dynamics is found to be comparable to the static Jahn-Teller stabilization. The Jahn-Teller dynamics influences the thermodynamic properties via strong variation of the density of vibronic states with energy. Thus the large vibronic entropy in the low-spin states enhances the effective spin gap of C603 - quenching the spin crossover. From the calculations of the effective spin gap as a function of the Hund's rule coupling, we found that the latter should amount 40 ±5 meV in order to cope with the violation of Hund's rule and to reproduce the large spin gap. With the obtained numerical solutions, the matrix elements of electronic operators for the low-lying vibronic levels and the vibronic reduction factors are calculated for all anions.

Solution of the Lindblad equation for spin helix states.

PubMed

Popkov, V; Schütz, G M

2017-04-01

Using Lindblad dynamics we study quantum spin systems with dissipative boundary dynamics that generate a stationary nonequilibrium state with a nonvanishing spin current that is locally conserved except at the boundaries. We demonstrate that with suitably chosen boundary target states one can solve the many-body Lindblad equation exactly in any dimension. As solution we obtain pure states at any finite value of the dissipation strength and any system size. They are characterized by a helical stationary magnetization profile and a ballistic spin current which is independent of system size, even when the quantum spin system is not integrable. These results are derived in explicit form for the one-dimensional spin-1/2 Heisenberg chain and its higher-spin generalizations, which include the integrable spin-1 Zamolodchikov-Fateev model and the biquadratic Heisenberg chain.

Mechanism of the high transition temperature for the 1111-type iron-based superconductors R FeAsO (R =rare earth ): Synergistic effects of local structures and 4 f electrons

NASA Astrophysics Data System (ADS)

Zhang, Lifang; Meng, Junling; Liu, Xiaojuan; Yao, Fen; Meng, Jian; Zhang, Hongjie

2017-07-01

Among the iron-based superconductors, the 1111-type Fe-As-based superconductors REFeAs O1 -xFx (RE = rare earth) exhibit high transition temperatures (Tc) above 40 K. We perform first-principles calculations based on density functional theory with the consideration of both electronic correlations and spin-orbit couplings on rare earths and Fe ions to study the underlying mechanism as the microscopic structural distortions in REFeAsO tuned by both lanthanide contraction and external strain. The electronic structures evolve similarly in both cases. It is found that there exist an optimal structural regime that will not only initialize but also optimize the orbital fluctuations due to the competing Fe-As and Fe-Fe crystal fields. We also find that the key structural features in REFeAsO, such as As-Fe-As bond angle, intrinsically induce the modification of the Fermi surface and dynamic spin fluctuation. These results suggest that the superconductivity is mediated by antiferromagnetic spin fluctuations. Simultaneously, we show that the rare-earth 4 f electrons play important roles on the high transition temperature whose behavior might be analogous to that of the heavy-fermion superconductors. The superconductivity of these 1111-type iron-based superconductors with high-Tc is considered to originate from the synergistic effects of local structures and 4 f electrons.

EDITORIAL: Focus on Quantum Dissipation in Unconventional Environments FOCUS ON QUANTUM DISSIPATION IN UNCONVENTIONAL ENVIRONMENTS

NASA Astrophysics Data System (ADS)

Grifoni, Milena; Paladino, Elisabetta

2008-11-01

Quantum dissipation has been the object of study within the physics and chemistry communities for many years. Despite this, the field is in constant evolution, largely due to the fact that novel systems where the understanding of dissipation and dephasing processes is of crucial importance have become experimentally accessible in recent years. Among the ongoing research themes, we mention the defeat of decoherence in solid state-based quantum bits (qubits) (e.g. superconducting qubits or quantum dot based qubits), or dissipation due to non-equilibrium Fermi reservoirs, as is the case for quantum transport through meso- and nanoscale structures. A close inspection of dissipation in such systems reveals that one has to deal with 'unconventional' environments, where common assumptions of, for example, linearity of the bath and/or equilibrium reservoir have to be abandoned. Even for linear baths at equilibrium it might occur that the bath presents some internal structure, due, for example, to the presence of localized bath modes. A large part of this focus issue is devoted to topics related to the rapidly developing fields of quantum computation and information with solid state nanodevices. In these implementations, single and two-qubit gates as well as quantum information transmission takes place in the presence of broadband noise that is typically non-Markovian and nonlinear. On both the experimental and theory side, understanding and defeating such noise sources has become a crucial step towards the implementation of efficient nanodevices. On a more fundamental level, electron and spin transport through quantum dot nanostructures may suffer from 'unconventional' dissipation mechanisms such as the simultaneous presence of spin relaxation and fermionic dissipation, or may represent themselves out of equilibrium baths for nearby mesoscopic systems. Finally, although not expected from the outset, the present collection of articles has revealed that different 'unconventional' questions were still open on the standard harmonic oscillator and spin baths. This includes both fundamental issues, such as the possibility of estimating the specific heat for a free particle in the presence of dissipation, and the development of methods suitable to dealing with long range correlations at zero temperature and with quantum chaotic environments. We believe that the present focus issue on Quantum Dissipation in Unconventional Environments, although certainly not exhaustive, provides an important open-access resource that presents the latest state of the art of research in this field along its different lines. Focus on Quantum Dissipation in Unconventional Environments Contents Dephasing by electron-electron interactions in a ballistic Mach-Zehnder interferometer Clemens Neuenhahn and Florian Marquardt Quantum frustration of dissipation by a spin bath D D Bhaktavatsala Rao, Heiner Kohler and Fernando Sols A random matrix theory of decoherence T Gorin, C Pineda, H Kohler and T H Seligman Dissipative dynamics of a biased qubit coupled to a harmonic oscillator: analytical results beyond the rotating wave approximation Johannes Hausinger and Milena Grifoni Dissipative dynamics of a two-level system resonantly coupled to a harmonic mode Frederico Brito and Amir O Caldeira Spin correlations in spin blockade Rafael Sánchez, Sigmund Kohler and Gloria Platero Landau-Zener tunnelling in dissipative circuit QED David Zueco, Peter Hänggi and Sigmund Kohler Quantum oscillations in the spin-boson model: reduced visibility from non-Markovian effects and initial entanglement F K Wilhelm Dynamics of dissipative coupled spins: decoherence, relaxation and effects of a spin-boson bath P Nägele, G Campagnano and U Weiss Spin chain model for correlated quantum channels Davide Rossini, Vittorio Giovannetti and Simone Montangero Finite quantum dissipation: the challenge of obtaining specific heat Peter Hänggi, Gert-Ludwig Ingold and Peter Talkner Dynamics of large anisotropic spin in a sub-ohmic dissipative environment close to a quantum-phase transition Frithjof B Anders Effects of low-frequency noise cross-correlations in coupled superconducting qubits A D'Arrigo, A Mastellone, E Paladino and G Falci From coherent motion to localization: dynamics of the spin-boson model at zero temperature Haobin Wang and Michael Thoss Phonon distributions of a single-bath mode coupled to a quantum dot F Cavaliere, G Piovano, E Paladino and M Sassetti

Determination of the proton spin structure functions for 0.05 < Q 2 < 5 GeV 2 using CLAS

DOE PAGES

Fersch, R. G.; Guler, N.; Bosted, P.; ...

2017-12-27

In this work, we present the results of our final analysis of the full data set of gmore » $$p\\atop{1}$$ (Q 2), the spin structure function of the proton, collected using CLAS at Jefferson Laboratory in 2000–2001. Polarized electrons with energies of 1.6, 2.5, 4.2, and 5.7 GeV were scattered from proton targets ( 15NH 3 dynamically polarized along the beam direction) and detected with CLAS. From the measured double spin asymmetries, we extracted virtual photon asymmetries A$$p\\atop{1}$$ and A$$p\\atop{2}$$ and spin structure functions g$$p\\atop{1}$$ and g$$p\\atop{2}$$ over a wide kinematic range (0.05 GeV 2 < Q 2 < 5 GeV 2 and 1.08 GeV < W < 3 GeV) and calculated moments of g$$p\\atop{1}$$. We compare our final results with various theoretical models and expectations, as well as with parametrizations of the world data. Lastly, our data, with their precision and dense kinematic coverage, are able to constrain fits of polarized parton distributions, test pQCD predictions for quark polarizations at large x, offer a better understanding of quark-hadron duality, and provide more precise values of higher twist matrix elements in the framework of the operator product expansion.« less

A unified stochastic formulation of dissipative quantum dynamics. II. Beyond linear response of spin baths

NASA Astrophysics Data System (ADS)

Hsieh, Chang-Yu; Cao, Jianshu

2018-01-01

We use the "generalized hierarchical equation of motion" proposed in Paper I [C.-Y. Hsieh and J. Cao, J. Chem. Phys. 148, 014103 (2018)] to study decoherence in a system coupled to a spin bath. The present methodology allows a systematic incorporation of higher-order anharmonic effects of the bath in dynamical calculations. We investigate the leading order corrections to the linear response approximations for spin bath models. Two kinds of spin-based environments are considered: (1) a bath of spins discretized from a continuous spectral density and (2) a bath of localized nuclear or electron spins. The main difference resides with how the bath frequency and the system-bath coupling parameters are distributed in an environment. When discretized from a continuous spectral density, the system-bath coupling typically scales as ˜1 /√{NB } where NB is the number of bath spins. This scaling suppresses the non-Gaussian characteristics of the spin bath and justifies the linear response approximations in the thermodynamic limit. For the nuclear/electron spin bath models, system-bath couplings are directly deduced from spin-spin interactions and do not necessarily obey the 1 /√{NB } scaling. It is not always possible to justify the linear response approximations in this case. Furthermore, if the spin-spin Hamiltonian is highly symmetrical, there exist additional constraints that generate highly non-Markovian and persistent dynamics that is beyond the linear response treatments.

Magic-angle spinning NMR of intact bacteriophages: Insights into the capsid, DNA and their interface

NASA Astrophysics Data System (ADS)

Abramov, Gili; Morag, Omry; Goldbourt, Amir

2015-04-01

Bacteriophages are viruses that infect bacteria. They are complex macromolecular assemblies, which are composed of multiple protein subunits that protect genomic material and deliver it to specific hosts. Various biophysical techniques have been used to characterize their structure in order to unravel phage morphogenesis. Yet, most bacteriophages are non-crystalline and have very high molecular weights, in the order of tens of MegaDaltons. Therefore, complete atomic-resolution characterization on such systems that encompass both capsid and DNA is scarce. In this perspective article we demonstrate how magic-angle spinning solid-state NMR has and is used to characterize in detail bacteriophage viruses, including filamentous and icosahedral phage. We discuss the process of sample preparation, spectral assignment of both capsid and DNA and the use of chemical shifts and dipolar couplings to probe the capsid-DNA interface, describe capsid structure and dynamics and extract structural differences between viruses.

Quantum spin chains with multiple dynamics

NASA Astrophysics Data System (ADS)

Chen, Xiao; Fradkin, Eduardo; Witczak-Krempa, William

2017-11-01

Many-body systems with multiple emergent time scales arise in various contexts, including classical critical systems, correlated quantum materials, and ultracold atoms. We investigate such nontrivial quantum dynamics in a different setting: a spin-1 bilinear-biquadratic chain. It has a solvable entangled ground state, but a gapless excitation spectrum that is poorly understood. By using large-scale density matrix renormalization group simulations, we find that the lowest excitations have a dynamical exponent z that varies from 2 to 3.2 as we vary a coupling in the Hamiltonian. We find an additional gapless mode with a continuously varying exponent 2 ≤z <2.7 , which establishes the presence of multiple dynamics. In order to explain these striking properties, we construct a continuum wave function for the ground state, which correctly describes the correlations and entanglement properties. We also give a continuum parent Hamiltonian, but show that additional ingredients are needed to capture the excitations of the chain. By using an exact mapping to the nonequilibrium dynamics of a classical spin chain, we find that the large dynamical exponent is due to subdiffusive spin motion. Finally, we discuss the connections to other spin chains and to a family of quantum critical models in two dimensions.

Design of one-kilometer-long antenna sticks and support structure for a geosynchronous satellite

NASA Astrophysics Data System (ADS)

Freeman, Janet Elizabeth

This study develops a preliminary structural design for three one-kilometer-long antenna sticks and an antenna support structure for a geosynchronous earth-imaging satellite. On each of the antenna sticks is mounted a linear array of over 16,000 antenna elements. The antenna sticks are parallel to each other, and are spaced 1 km apart so that they form the corners of an imaginary triangular tube. This tube is spinning about its long axis. Antenna performance requires that the position of each antenna element be known to an accuracy of 0.5 cm, and that the spacecraft's spin axis be parallel to the earth's spin axis within one degree. Assuming that the position of each joint on each antenna stick is known, the antenna sticks are designed as beams under a uniformly distributed acceleration (due to spacecraft spin) to meet the displacement accuracy requirements for the antenna elements. Both a thin-walled round tube and a three-longeron double-laced truss are considered for the antenna stick structure. A spacecraft spinrate is chosen by considering the effects of environmental torques on the precession of a simplified spacecraft. A preliminary truss-like support structure configuration is chosen, and analyzed in quasi-static equilibrium with control thrusters firing to estimate the axial loads in the structural members. The compressive loads found by this analysis are used to design the support structure members to be buckling-critical three-longeron double-laced truss columns. Some tension-only members consisting of Kevlar cord are included in the design to eliminate the need for bulkier members. The lateral vibration modes of the individual structural members are found by conventional analysis -- the fundamental frequencies are as low as 0.0066 Hz. Finite element dynamic analyses of the structure in free vibration confirm that simplified models of the structure and members can be used to determine the structural modes and natural frequencies for design purposes.

Investigations of quantum pendulum dynamics in a spin-1 BEC

NASA Astrophysics Data System (ADS)

Hoang, Thai; Gerving, Corey; Land, Ben; Anquez, Martin; Hamley, Chris; Chapman, Michael

2013-05-01

We investigate the quantum spin dynamics of a spin-1 BEC initialized to an unstable critical point of the dynamical phase space. The subsequent evolution of the collective states of the system is analogous to an inverted simple pendulum in the quantum limit and yields non-classical states with quantum correlations. For short evolution times in the low depletion limit, we observe squeezed states and for longer times beyond the low depletion limit we observe highly non-Gaussian distributions. C.D. Hamley, C.S. Gerving, T.M. Hoang, E.M. Bookjans, and M.S. Chapman, ``Spin-Nematic Squeezed Vacuum in a Quantum Gas,'' Nature Physics 8, 305-308 (2012).

Bias field tunable magnetic configuration and magnetization dynamics in Ni80Fe20 nano-cross structures with varying arm length

NASA Astrophysics Data System (ADS)

Adhikari, K.; Choudhury, S.; Mandal, R.; Barman, S.; Otani, Y.; Barman, A.

2017-01-01

Ferromagnetic nano-cross structures promise exotic static magnetic configurations and very rich and tunable magnetization dynamics leading towards potential applications in magnetic logic and communication devices. Here, we report an experimental study of external magnetic field tunable static magnetic configurations and magnetization dynamics in Ni80Fe20 nano-cross structures with varying arm lengths (L). Broadband ferromagnetic resonance measurements showed a strong variation in the number of spin-wave (SW) modes and mode frequencies (f) with bias field magnitude (H). Simulated static magnetic configurations and SW mode profiles explain the rich variation of the SW spectra, including mode softening, mode crossover, mode splitting, and mode merging. Such variation of SW spectra is further modified by the size of the nano-cross. Remarkably, with decreasing arm length of nano-cross structures, the onion magnetization ground state becomes more stable. Calculated magnetostatic field distributions support the above observations and revealed the non-collective nature of the dynamics in closely packed nano-cross structures. The latter is useful for their possible applications in magnetic storage and memory devices.

Lattice dynamic properties of Rh2XAl (X=Fe and Y) alloys

NASA Astrophysics Data System (ADS)

Al, Selgin; Arikan, Nihat; Demir, Süleyman; Iyigör, Ahmet

2018-02-01

The electronic band structure, elastic and vibrational spectra of Rh2FeAl and Rh2YAl alloys were computed in detail by employing an ab-initio pseudopotential method and a linear-response technique based on the density-functional theory (DFT) scheme within a generalized gradient approximation (GGA). Computed lattice constants, bulk modulus and elastic constants were compared. Rh2YAl exhibited higher ability to resist volume change than Rh2FeAl. The elastic constants, shear modulus, Young modulus, Poisson's ratio, B/G ratio electronic band structure, total and partial density of states, and total magnetic moment of alloys were also presented. Rh2FeAl showed spin up and spin down states whereas Rh2YAl showed none due to being non-magnetic. The calculated total densities of states for both materials suggest that both alloys are metallic in nature. Full phonon spectra of Rh2FeAl and Rh2YA1 alloys in the L21 phase were collected using the ab-initio linear response method. The obtained phonon frequencies were in the positive region indicating that both alloys are dynamically stable.

Spin dynamics and frequency dependence of magnetic damping study in soft ferromagnetic FeTaC film with a stripe domain structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Samantaray, B., E-mail: iitg.biswanath@gmail.com; Ranganathan, R.; Mandal, P.

Perpendicular magnetic anisotropy (PMA) and low magnetic damping are the key factors for the free layer magnetization switching by spin transfer torque technique in magnetic tunnel junction devices. The magnetization precessional dynamics in soft ferromagnetic FeTaC thin film with a stripe domain structure was explored in broad band frequency range by employing micro-strip ferromagnetic resonance technique. The polar angle variation of resonance field and linewidth at different frequencies have been analyzed numerically using Landau-Lifshitz-Gilbert equation by taking into account the total free energy density of the film. The numerically estimated parameters Landé g-factor, PMA constant, and effective magnetization are foundmore » to be 2.1, 2 × 10{sup 5} erg/cm{sup 3} and 7145 Oe, respectively. The frequency dependence of Gilbert damping parameter (α) is evaluated by considering both intrinsic and extrinsic effects into the total linewidth analysis. The value of α is found to be 0.006 at 10 GHz and it increases monotonically with decreasing precessional frequency.« less

Focus: Two-dimensional electron-electron double resonance and molecular motions: The challenge of higher frequencies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Franck, John M.; Chandrasekaran, Siddarth; Dzikovski, Boris

2015-06-07

The development, applications, and current challenges of the pulsed ESR technique of two-dimensional Electron-Electron Double Resonance (2D ELDOR) are described. This is a three-pulse technique akin to 2D Exchange Nuclear Magnetic Resonance, but involving electron spins, usually in the form of spin-probes or spin-labels. As a result, it required the extension to much higher frequencies, i.e., microwaves, and much faster time scales, with π/2 pulses in the 2-3 ns range. It has proven very useful for studying molecular dynamics in complex fluids, and spectral results can be explained by fitting theoretical models (also described) that provide a detailed analysis ofmore » the molecular dynamics and structure. We discuss concepts that also appear in other forms of 2D spectroscopy but emphasize the unique advantages and difficulties that are intrinsic to ESR. Advantages include the ability to tune the resonance frequency, in order to probe different motional ranges, while challenges include the high ratio of the detection dead time vs. the relaxation times. We review several important 2D ELDOR studies of molecular dynamics. (1) The results from a spin probe dissolved in a liquid crystal are followed throughout the isotropic → nematic → liquid-like smectic → solid-like smectic → crystalline phases as the temperature is reduced and are interpreted in terms of the slowly relaxing local structure model. Here, the labeled molecule is undergoing overall motion in the macroscopically aligned sample, as well as responding to local site fluctuations. (2) Several examples involving model phospholipid membranes are provided, including the dynamic structural characterization of the boundary lipid that coats a transmembrane peptide dimer. Additionally, subtle differences can be elicited for the phospholipid membrane phases: liquid disordered, liquid ordered, and gel, and the subtle effects upon the membrane, of antigen cross-linking of receptors on the surface of plasma membrane, vesicles can be observed. These 2D ELDOR experiments are performed as a function of mixing time, T{sub m}, i.e., the time between the second and third π/2 pulses, which provides a third dimension. In fact, a fourth dimension may be added by varying the ESR frequency/magnetic field combination. Therefore, (3) it is shown how continuous-wave multifrequency ESR studies enable the decomposition of complex dynamics of, e.g., proteins by virtue of their respective time scales. These studies motivate our current efforts that are directed to extend 2D ELDOR to higher frequencies, 95 GHz in particular (from 9 and 17 GHz), in order to enable multi-frequency 2D ELDOR. This required the development of quasi-optical methods for performing the mm-wave experiments, which are summarized. We demonstrate state-of-the-art 95 GHz 2D ELDOR spectroscopy through its ability to resolve the two signals from a spin probe dissolved in both the lipid phase and the coexisting aqueous phase. As current 95 GHz experiments are restricted by limited spectral coverage of the π/2 pulse, as well as the very short T{sub 2} relaxation times of the electron spins, we discuss how these limitations are being addressed.« less

Muon spin relaxation study of spin dynamics in the extended kagome systems YBaCo 4 O 7 + δ   ( δ = 0 , 0.1 )

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, S.; Lee, Wonjun; Lee, K. J.

Here, we present muon spin relaxation (μSR) measurements of the extended kagome systems YBaCo 4O 7+δ (δ = 0,0.1), comprising two interpenetrating kagome sublattice of Co(I) 3+ (S = 3/2) and a triangle sublattice of Co(II) 2+ (S = 2). The zero- and longitudinal-field μ SR spectra of the stoichiometric compound YBaCo 4O 7 unveil that the triangular subsystem orders at TN = 101 K. In contrast, the muon spin relaxation rate pertaining to the kagome subsystem shows persistent spin dynamics down to T = 20 K and then a sublinear decrease λ(T ) ~ T 0.66(5) on cooling towardsmore » T = 4 K. In addition, the introduction of interstitial oxygen (δ = 0.1) is found to drastically affect the magnetism. For the fast-cooling experiment (>10 K/min), YBaCo 4O 7.1 enters a regime characterized by persistent spin dynamics below 90 K. For the slow-cooling experiment (1 K/min), evidence is obtained for the phase separation into interstitial oxygen-poor and oxygen-rich regions with distinct correlation times. The observed temperature, cooling rate, and oxygen content dependencies of spin dynamics are discussed in terms of a broad range of spin-spin correlation times, relying on a different degree of frustration between the kagome and triangle sublattices as well as of oxygen migration.« less

Isotropic and anisotropic regimes of the field-dependent spin dynamics in Sr 2 IrO 4 : Raman scattering studies

DOE PAGES

Gim, Y.; Sethi, A.; Zhao, Q.; ...

2016-01-11

A major focus of experimental interest in Sr 2IrO 4 has been to clarify how the magnetic excitations of this strongly spin-orbit coupled system differ from the predictions of an isotropic 2D spin-1/2 Heisenberg model and to explore the extent to which strong spin-orbit coupling affects the magnetic properties of iridates. Here, we present a high-resolution inelastic light (Raman) scattering study of the low energy magnetic excitation spectrum of Sr 2IrO 4 and doped Eu-doped Sr 2IrO 4 as functions of both temperature and applied magnetic field. We show that the high-field (H > 1.5 T) in-plane spin dynamics ofmore » Sr 2IrO 4 are isotropic and governed by the interplay between the applied field and the small in-plane ferromagnetic spin components induced by the Dzyaloshinskii-Moriya interaction. However, the spin dynamics of Sr 2IrO 4 at lower fields (H < 1.5 T) exhibit important effects associated with interlayer coupling and in-plane anisotropy, including a spin-flop transition at Hc in Sr 2IrO 4 that occurs either discontinuously or via a continuous rotation of the spins, depending upon the in-plane orientation of the applied field. Furthermore, these results show that in-plane anisotropy and interlayer coupling effects play important roles in the low-field magnetic and dynamical properties of Sr 2IrO 4.« less

Muon spin relaxation study of spin dynamics in the extended kagome systems YBaCo 4 O 7 + δ   ( δ = 0 , 0.1 )

DOE PAGES

Lee, S.; Lee, Wonjun; Lee, K. J.; ...

2018-03-15

Here, we present muon spin relaxation (μSR) measurements of the extended kagome systems YBaCo 4O 7+δ (δ = 0,0.1), comprising two interpenetrating kagome sublattice of Co(I) 3+ (S = 3/2) and a triangle sublattice of Co(II) 2+ (S = 2). The zero- and longitudinal-field μ SR spectra of the stoichiometric compound YBaCo 4O 7 unveil that the triangular subsystem orders at TN = 101 K. In contrast, the muon spin relaxation rate pertaining to the kagome subsystem shows persistent spin dynamics down to T = 20 K and then a sublinear decrease λ(T ) ~ T 0.66(5) on cooling towardsmore » T = 4 K. In addition, the introduction of interstitial oxygen (δ = 0.1) is found to drastically affect the magnetism. For the fast-cooling experiment (>10 K/min), YBaCo 4O 7.1 enters a regime characterized by persistent spin dynamics below 90 K. For the slow-cooling experiment (1 K/min), evidence is obtained for the phase separation into interstitial oxygen-poor and oxygen-rich regions with distinct correlation times. The observed temperature, cooling rate, and oxygen content dependencies of spin dynamics are discussed in terms of a broad range of spin-spin correlation times, relying on a different degree of frustration between the kagome and triangle sublattices as well as of oxygen migration.« less

Investigation of Kibble-Zurek Quench Dynamics in a Spin-1 Ferromagnetic BEC

NASA Astrophysics Data System (ADS)

Anquez, Martin; Robbins, Bryce; Hoang, Thai; Yang, Xiaoyun; Land, Benjamin; Hamley, Christopher; Chapman, Michael

2014-05-01

We study the temporal evolution of spin populations in small spin-1 87Rb condensates following a slow quench. A ferromagnetic spin-1 BEC exhibits a second-order gapless (quantum) phase transition due to a competition between the magnetic and collisional spin interaction energies. The dynamics of slow quenches through the critical point are predicted to exhibit universal power-law scaling as a function of quench speed. In spatially extended condensates, these excitations are revealed as spatial spin domains. In small condensates, the excitations are manifest in the temporal evolution of the spin populations, illustrating a Kibble-Zurek type scaling. We will present the results of our investigation and compare them to full quantum simulations of the system.

High-frequency polarization dynamics in spin-lasers: pushing the limits

NASA Astrophysics Data System (ADS)

Gerhardt, Nils C.; Lindemann, Markus; Pusch, Tobias; Michalzik, Rainer; Hofmann, Martin R.

2017-09-01

While the high-frequency performance of conventional lasers is limited by the coupled carrier-photon dynamics, spin-polarized lasers have a high potential to overcome this limitation and to push the direct modulation bandwidth beyond 100 GHz. The key is to utilize the ultrafast polarization dynamics in spin-polarized vertical cavity surface-emitting lasers (spin-VCSELs) which is decoupled from the intensity dynamics and its fundamental limitations. The polarization dynamics in such devices, characterized by the polarization oscillation resonance frequency, is mainly determined by the amount of birefringence in the cavity. Using an approach for manipulating the birefringence via mechanical strain we were able to increase the polarization dynamics to resonance frequencies of more than 40 GHz. Up to now these values are only limited by the setup to induce birefringence and do not reflect any fundamental limitations. Taking our record results for the birefringence-induced mode splitting of more than 250 GHz into account, the concept has the potential to provide polarization modulation in spin-VCSELs with modulation frequencies far beyond 100 GHz. This makes them ideal devices for next-generation fast optical interconnects. In this paper we present experimental results for ultrafast polarization dynamics up to 50 GHz and compare them to numerical simulations.

Approche Kaluza-Klein et Supersymetrie de Jauge

NASA Astrophysics Data System (ADS)

Pare, Jean-Pierre

This thesis presents a non-Abelian gauge-supersymmetric Kaluza-Klein approach for charged spinning particles and strings in a background of gravitational and Yang-Mills fields. In the classical Kaluza-Klein approach, the basic mathematical structure is a principal bundle of which the base manifold is space-time. This principal bundle is endowed with a pseudo-Riemannian metric, invariant under the action of the structural group of the bundle, and a connection. Geodesic equations on the bundle lead to the Maxwell-Lorentz equation for curved space-time and Yang -Mills fields, and to a conservation law of a non-Abelian (bosonic) charge. This conservation law originates from the invariance of the free-particle action on the bundle under the action of the structural group of the bundle (gauge group). Firstly, we generalize this approach for a spinning particle. The spin of the particle is described by Grassmannian variables added to the principal bundle. This supersymmetrization gives rise, in addition to the bosonic non-Abelian charge, a fermionic one. This leads to a search for a supergroup action on the superprincipal bundle which leaves invariant the action of the spinning particle. The invariance of this action would lead to the conservation of a non-Abelian super-charge, generalizing the conservation law obtained for particles without spin. We present Lagrangian and Hamiltonian formulations, both invariant under a super -group action. The equations of motion are derived and discussed. Different terms in these equations are well known in the literature. The invariance of these formulations under a supergroup action leads to a conservation law of a non-Abelian supercharge. The bosonic part of this supercharge corresponds to the non-Abelian (bosonic) charge obtained for a particle without spin. The fermionic part is a non -physical charge. It turns out in the supersymmetric case that this decouples from all other dynamical variables, and hence it does not influence trajectories of spinning particles. It is interesting to mention how this gauge -supersymmetry is introduced in the dynamics. It arises by choosing the unique metric connection on the principal bundle with torsion given by the Chern-Simons 3-form. We then proceed to extend these formulations for spinning strings. We present Lagrangian and Hamiltonian gauge-supersymmetric formulations in a superloop space setting. The same connection corresponding to the Chern -Simons 3-form is used here. Equations of motion are derived and discussed. In the appendix, we discuss the effect of using this connection in a non-Abelian Kaluza-Klein field theory. Using the same connection, we present a non-Abelian Kaluza-Klein approach leading to a zero cosmological constant.

The effect of engine spin direction on the dynamics of powered two wheelers

NASA Astrophysics Data System (ADS)

Massaro, Matteo; Marconi, Edoardo

2018-04-01

The effect of engine spin direction on the dynamics of powered two wheelers is investigated in terms of steady-state points (equilibria), vibration modes (stability), manoeuvre time (performance/manoeuvrability) and handling. The goal is to assess and quantify the advantage sometimes claimed for the 'counter-rotating' engine configuration, where the engine spins in the opposite direction with respect to wheels, against the 'conventional' configuration, where the engine spins in the same direction of wheels.

Phase locking of vortex cores in two coupled magnetic nanopillars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Qiyuan; Liu, Xianyin; Zheng, Qi

2014-11-15

Phase locking dynamics of the coupled vortex cores in two identical magnetic spin valves induced by spin-polarized current are studied by means of micromagnetic simulations. Our results show that the available current range of phase locking can be expanded significantly by the use of constrained polarizer, and the vortices undergo large orbit motions outside the polarization areas. The effects of polarization areas and dipolar interaction on the phase locking dynamics are studied systematically. Phase locking parameters extracted from simulations are discussed by theoreticians. The dynamics of vortices influenced by spin valve geometry and vortex chirality are discussed at last. Thismore » work provides deeper insights into the dynamics of phase locking and the results are important for the design of spin-torque nano-oscillators.« less

Driving magnetization dynamics with interfacial spin-orbit torques (Conference Presentation)

NASA Astrophysics Data System (ADS)

Hoffmann, Axel F.; Zhang, Wei; Sklenar, Joseph; Jungfleisch, Matthias Benjamin; Jiang, Wanjun; Hsu, Bo; Xiao, Jiao; Pearson, John E.; Fradin, Frank Y.; Liu, Yaohua; Ketterson, John B.; Yang, Zheng

2016-10-01

Bulk spin Hall effects are well know to provide spin orbit torques, which can be used to drive magnetization dynamics [1]. But one of the reoccurring questions is to what extend spin orbit torques may also originate at the interface between materials with strong spin orbit coupling and the ferromagnets. Using spin torque driven ferromagnetic resonance we show for two systems, where interfacial torques dominate, that they can be large enough to be practically useful. First, we show spin transfer torque driven magnetization dynamics based on Rashba-Edelstein effects at the Bi/Ag interface [2]. Second, we will show that combining permalloy with monolayer MoS2 gives rise to sizable spin-orbit torques. Given the monolayer nature of MoS2 it is clear that bilk spin Hall effects are negligible and therefore the spin transfer torques are completely interfacial in nature. Interestingly the spin orbit torques with MoS2 show a distinct dependence on the orientation of the magnetization in the permalloy, and become strongly enhanced, when the magnetization is pointing perpendicular to the interfacial plane. This work was supported by the U.S. Department of Energy, Office of Science, Materials Science and Engineering Division. [1] A. Hoffmann, IEEE Trans. Mag. 49, 5172 (2013). [2] W. Zhang et al., J. Appl. Phys. 117, 17C727 (2015). [3] M. B. Jungfleisch et al., arXiv:1508.01410.

Molecular, dynamic, and structural origin of inhomogeneous magnetization transfer in lipid membranes.

PubMed

Swanson, Scott D; Malyarenko, Dariya I; Fabiilli, Mario L; Welsh, Robert C; Nielsen, Jon-Fredrik; Srinivasan, Ashok

2017-03-01

To elucidate the dynamic, structural, and molecular properties that create inhomogeneous magnetization transfer (ihMT) contrast. Amphiphilic lipids, lamellar phospholipids with cholesterol, and bovine spinal cord (BSC) specimens were examined along with nonlipid systems. Magnetization transfer (MT), enhanced MT (eMT, obtained with double-sided radiofrequency saturation), ihMT (MT - eMT), and dipolar relaxation, T 1D , were measured at 2.0 and 11.7 T. The amplitude of ihMT ratio (ihMTR) is positively correlated with T 1D values. Both ihMTR and T 1D increase with increasing temperature in BSC white matter and in phospholipids and decrease with temperature in other lipids. Changes in ihMTR with temperature arise primarily from alterations in MT rather than eMT. Spectral width of MT, eMT, and ihMT increases with increasing carbon chain length. Concerted motions of phospholipids in white matter decrease proton spin diffusion leading to increased proton T 1D times and increased ihMT amplitudes, consistent with decoupling of Zeeman and dipolar spin reservoirs. Molecular specificity and dynamic sensitivity of ihMT contrast make it a suitable candidate for probing myelin membrane disorders. Magn Reson Med 77:1318-1328, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

Universality, maximum radiation, and absorption in high-energy collisions of black holes with spin.

PubMed

Sperhake, Ulrich; Berti, Emanuele; Cardoso, Vitor; Pretorius, Frans

2013-07-26

We explore the impact of black hole spins on the dynamics of high-energy black hole collisions. We report results from numerical simulations with γ factors up to 2.49 and dimensionless spin parameter χ=+0.85, +0.6, 0, -0.6, -0.85. We find that the scattering threshold becomes independent of spin at large center-of-mass energies, confirming previous conjectures that structure does not matter in ultrarelativistic collisions. It has further been argued that in this limit all of the kinetic energy of the system may be radiated by fine tuning the impact parameter to threshold. On the contrary, we find that only about 60% of the kinetic energy is radiated for γ=2.49. By monitoring apparent horizons before and after scattering events we show that the "missing energy" is absorbed by the individual black holes in the encounter, and moreover the individual black-hole spins change significantly. We support this conclusion with perturbative calculations. An extrapolation of our results to the limit γ→∞ suggests that about half of the center-of-mass energy of the system can be emitted in gravitational radiation, while the rest must be converted into rest-mass and spin energy.

Neutron-scattering measurements of spin excitations in LaFeAsO and Ba(Fe 0.953Co 0.047)2As 2: Evidence for a sharp enhancement of spin fluctuations by nematic order [Sharp enhancement of spin fluctuations by nematic order in iron pnictides

DOE PAGES

Zhang, Qiang; Fernandes, Rafael M.; Lamsal, Jagat; ...

2015-02-04

Inelastic neutron scattering is employed to investigate the impact of electronic nematic order on the magnetic spectra of LaFeAsO and Ba(Fe 0.953Co 0.047) 2As 2. These materials are ideal to study the paramagnetic-nematic state, since the nematic order, signaled by the tetragonal-to-orthorhombic transition at T S, sets in well above the stripe antiferromagnetic ordering at T N. We find that the temperature-dependent dynamic susceptibility displays an anomaly at T S followed by a sharp enhancement in the spin-spin correlation length, revealing a strong feedback effect of nematic order on the low-energy magnetic spectrum. As a result, our findings can bemore » consistently described by a model that attributes the structural or nematic transition to magnetic fluctuations, and unveils the key role played by nematic order in promoting the long-range stripe antiferromagnetic order in iron pnictides.« less

Neutron-scattering measurements of spin excitations in LaFeAsO and Ba(Fe 0.953Co 0.047)2As 2: Evidence for a sharp enhancement of spin fluctuations by nematic order [Sharp enhancement of spin fluctuations by nematic order in iron pnictides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Qiang; Fernandes, Rafael M.; Lamsal, Jagat

Inelastic neutron scattering is employed to investigate the impact of electronic nematic order on the magnetic spectra of LaFeAsO and Ba(Fe 0.953Co 0.047) 2As 2. These materials are ideal to study the paramagnetic-nematic state, since the nematic order, signaled by the tetragonal-to-orthorhombic transition at T S, sets in well above the stripe antiferromagnetic ordering at T N. We find that the temperature-dependent dynamic susceptibility displays an anomaly at T S followed by a sharp enhancement in the spin-spin correlation length, revealing a strong feedback effect of nematic order on the low-energy magnetic spectrum. As a result, our findings can bemore » consistently described by a model that attributes the structural or nematic transition to magnetic fluctuations, and unveils the key role played by nematic order in promoting the long-range stripe antiferromagnetic order in iron pnictides.« less

A LDA + U study of the photoemission spectra of the double hexagonal close packed phases of Am and Cm

NASA Astrophysics Data System (ADS)

Islam, M. Fhokrul; Ray, Asok K.

2010-05-01

We have investigated the photoemission spectra and other electronic structure properties such as equilibrium volume and bulk modulus of double hexagonal close packed (dhcp) americium and the density of states (DOS) and magnetic properties of dhcp curium using the LDA+U method. Our calculations show that spin polarized americium is energetically favorable but spin degenerate configuration produces experimental quantities significantly better than those calculated using the spin polarized configuration. The density of states calculated using LDA+U with both non-magnetic and spin polarized configurations is compared and the non-magnetic DOS is shown to be in good agreement with experimental photoemission spectra when U=4.5 eV. In spin polarized case, the onsite interaction parameter, U, is observed to increase the splitting between occupied and unoccupied bands by enhancing the Stoner parameter. The DOS of both non-magnetic americium and anti-ferromagnetic curium are shown to be in good agreement with that calculated using dynamical mean field theory for these two heavy actinides. For curium exchange interaction appears to play a dominant role in magnetic stability.

Simultaneous control of magnetic topologies for reconfigurable vortex arrays

DOE PAGES

Im, Mi-Young; Fischer, Peter; Han, Hee-Sung; ...

2017-02-10

The topological spin textures in magnetic vortices in confined magnetic elements offer a platform for understanding the fundamental physics of nanoscale spin behavior and the potential of harnessing their unique spin structures for advanced magnetic technologies. For magnetic vortices to be practical, an effective reconfigurability of the two topologies of magnetic vortices, that is, the circularity and the polarity, is an essential prerequisite. The reconfiguration issue is highly relevant to the question of whether both circularity and polarity are reliably and efficiently controllable. In this work, we report the first direct observation of simultaneous control of both circularity and polaritymore » by the sole application of an in-plane magnetic field to arrays of asymmetrically shaped permalloy disks. Our investigation demonstrates that a high degree of reliability for control of both topologies can be achieved by tailoring the geometry of the disk arrays. We also propose a new approach to control the vortex structures by manipulating the effect of the stray field on the dynamics of vortex creation. The current study is expected to facilitate complete and effective reconfiguration of magnetic vortex structures, thereby enhancing the prospects for technological applications of magnetic vortices.« less

Simultaneous control of magnetic topologies for reconfigurable vortex arrays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Im, Mi-Young; Fischer, Peter; Han, Hee-Sung

The topological spin textures in magnetic vortices in confined magnetic elements offer a platform for understanding the fundamental physics of nanoscale spin behavior and the potential of harnessing their unique spin structures for advanced magnetic technologies. For magnetic vortices to be practical, an effective reconfigurability of the two topologies of magnetic vortices, that is, the circularity and the polarity, is an essential prerequisite. The reconfiguration issue is highly relevant to the question of whether both circularity and polarity are reliably and efficiently controllable. In this work, we report the first direct observation of simultaneous control of both circularity and polaritymore » by the sole application of an in-plane magnetic field to arrays of asymmetrically shaped permalloy disks. Our investigation demonstrates that a high degree of reliability for control of both topologies can be achieved by tailoring the geometry of the disk arrays. We also propose a new approach to control the vortex structures by manipulating the effect of the stray field on the dynamics of vortex creation. The current study is expected to facilitate complete and effective reconfiguration of magnetic vortex structures, thereby enhancing the prospects for technological applications of magnetic vortices.« less

On Dynamics of Spinning Structures

NASA Technical Reports Server (NTRS)

Gupta, K. K.; Ibrahim, A.

2012-01-01

This paper provides details of developments pertaining to vibration analysis of gyroscopic systems, that involves a finite element structural discretization followed by the solution of the resulting matrix eigenvalue problem by a progressive, accelerated simultaneous iteration technique. Thus Coriolis, centrifugal and geometrical stiffness matrices are derived for shell and line elements, followed by the eigensolution details as well as solution of representative problems that demonstrates the efficacy of the currently developed numerical procedures and tools.

Selective coupling of individual electron and nuclear spins with integrated all-spin coherence protection

NASA Astrophysics Data System (ADS)

Terletska, Hanna; Dobrovitski, Viatcheslav

2015-03-01

The electron spin of the NV center in diamond is a promising platform for spin sensing. Applying the dynamical decoupling, the NV electron spin can be used to detect the individual weakly coupled carbon-13 nuclear spins in diamond and employ them for small-scale quantum information processing. However, the nuclear spins within this approach remain unprotected from decoherence, which ultimately limits the detection and restricts the fidelity of the quantum operation. Here we investigate possible schemes for combining the resonant decoupling on the NV spin with the decoherence protection of the nuclear spins. Considering several schemes based on pulse and continuous-wave decoupling, we study how the joint electron-nuclear spin dynamics is affected. We identify regimes where the all-spin coherence protection improves the detection and manipulation. We also discuss potential applications of the all-spin decoupling for detecting spins outside diamond, with the purpose of implementing the nanoscale NMR. This work was supported by the US Department of Energy Basic Energy Sciences (Contract No. DE-AC02-07CH11358).

A spin rotator model for Heisenberg helimagnet

NASA Astrophysics Data System (ADS)

Felcy, A. Ludvin; Latha, M. M.

2018-02-01

We study the dynamics of a helimagnetic spin system by proposing a spin rotator model taking into account bilinear, twist interplane and anisotropic interactions in the continuum limit. The dynamical equations of motion are obtained and studied numerically. The influence of different types of inhomogeneities is also analysed. Similar studies are carried out for the system including biquadratic type interactions.

Quantum nonunital dynamics of spin-bath-assisted Fisher information

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hao, Xiang, E-mail: haoxiang-edu198126@163.com; Wu, Yinzhong

2016-04-15

The nonunital non-Markovian dynamics of qubits immersed in a spin bath is studied without any Markovian approximation. The environmental effects on the precisions of quantum parameter estimation are taken into account. The time-dependent transfer matrix and inhomogeneity vector are obtained for the description of the open dynamical process. The dynamical behaviour of one qubit coupled to a spin bath is geometrically described by the Bloch vector. It is found out that the nonunital non-Markovian effects can engender the improvement of the precision of quantum parameter estimation. This result contributes to the environment-assisted quantum information theory.

Investigation of the Dynamics of Magnetic Vortices and Antivortices Using Micromagnetic Simulations

NASA Astrophysics Data System (ADS)

Asmat-Uceda, Martin Antonio

This thesis is focused on investigating the dynamic properties of spin textures in patterned magnetic structures by using micromagnetic simulations. These textures become particularly relevant at sub-micron length scales where the interplay between magnetostatic and exchange energy leads to unique properties that are of great interest both from a fundamental perspective and for the development of new technologies. Two different systems, a magnetic antivortex (AV) stabilized in the intersection of perpendicular microwires, and three interacting vortices in an equilateral arrangement, were considered for this study. For the first system, the AV, the formation process and the excitation spectra were investigated. Since the AV is a metastable state, the design of a host structure capable of stabilizing it requires careful consideration and it is desirable to have general guidelines that could help to optimize the AV formation rate. The role of the shape anisotropy and the field dependence of the AV formation process is discussed in detail. Micromagnetic simulations along with magneto-optical Kerr effect and magnetic force microscopy measurements demonstrated that the asymmetry in the structure can be used to promote the formation of such AV's and that regions with lower shape anisotropy lead the reversal process, while simulations of the dynamic response show that when the system is excited with in-plane and out-of-plane external magnetic fields, normal modes with azimuthal and radial characteristics are found, respectively, in addition to the low frequency gyrotropic mode. The modes are influenced by the spin texture in the intersection, which offers additional possibilities for manipulating spin waves (SW). For the second system, three interacting vortices are simulated and compared with a simple analytical model that considers only dipolar interactions. It was found that when a fitting parameter is introduced to the model, the main features of the simulations are captured better than more complex models, which suggest that this simple framework can be used to accurately model more complex vortex networks.

Dynamics of a spin-boson model with structured spectral density

NASA Astrophysics Data System (ADS)

Kurt, Arzu; Eryigit, Resul

2018-05-01

We report the results of a study of the dynamics of a two-state system coupled to an environment with peaked spectral density. An exact analytical expression for the bath correlation function is obtained. Validity range of various approximations to the correlation function for calculating the population difference of the system is discussed as function of tunneling splitting, oscillator frequency, coupling constant, damping rate and the temperature of the bath. An exact expression for the population difference, for a limited range of parameters, is derived.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deb, Marwan, E-mail: marwan.deb@ipcms.unistra.fr; Vomir, Mircea; Rehspringer, Jean-Luc

Controlling the magnetization dynamics on the femtosecond timescale is of fundamental importance for integrated opto-spintronic devices. For industrial perspectives, it requires to develop simple growth techniques for obtaining large area magneto-optical materials having a high amplitude ultrafast Faraday or Kerr response. Here we report on optical pump probe studies of light induced spin dynamics in high quality bismuth doped iron garnet polycrystalline film prepared by the spin coating method. We demonstrate an ultrafast non-thermal optical control of the spin dynamics using both circularly and linearly polarized pulses.

Role of Orbital Dynamics in Spin Relaxation and Weak Antilocalization in Quantum Dots

NASA Astrophysics Data System (ADS)

Zaitsev, Oleg; Frustaglia, Diego; Richter, Klaus

2005-01-01

We develop a semiclassical theory for spin-dependent quantum transport to describe weak (anti)localization in quantum dots with spin-orbit coupling. This allows us to distinguish different types of spin relaxation in systems with chaotic, regular, and diffusive orbital classical dynamics. We find, in particular, that for typical Rashba spin-orbit coupling strengths, integrable ballistic systems can exhibit weak localization, while corresponding chaotic systems show weak antilocalization. We further calculate the magnetoconductance and analyze how the weak antilocalization is suppressed with decreasing quantum dot size and increasing additional in-plane magnetic field.

Magnetic droplet solitons generated by pure spin currents

NASA Astrophysics Data System (ADS)

Divinskiy, B.; Urazhdin, S.; Demidov, V. E.; Kozhanov, A.; Nosov, A. P.; Rinkevich, A. B.; Demokritov, S. O.

2017-12-01

Magnetic droplets are dynamical solitons that can be generated by locally suppressing the dynamical damping in magnetic films with perpendicular anisotropy. To date, droplets have been observed only in nanocontact spin-torque oscillators operated by spin-polarized electrical currents. Here, we experimentally demonstrate that magnetic droplets can be nucleated and sustained by pure spin currents in nanoconstriction-based spin Hall devices. Micromagnetic simulations support our interpretation of the data, and indicate that in addition to the stationary droplets, propagating solitons can be also generated in the studied system, which can be utilized for the information transmission in spintronic applications.

Magnetic monopole dynamics in spin ice.

PubMed

Jaubert, L D C; Holdsworth, P C W

2011-04-27

One of the most remarkable examples of emergent quasi-particles is that of the 'fractionalization' of magnetic dipoles in the low energy configurations of materials known as 'spin ice' into free and unconfined magnetic monopoles interacting via Coulomb's 1/r law (Castelnovo et al 2008 Nature 451 42-5). Recent experiments have shown that a Coulomb gas of magnetic charges really does exist at low temperature in these materials and this discovery provides a new perspective on otherwise largely inaccessible phenomenology. In this paper, after a review of the different spin ice models, we present detailed results describing the diffusive dynamics of monopole particles starting both from the dipolar spin ice model and directly from a Coulomb gas within the grand canonical ensemble. The diffusive quasi-particle dynamics of real spin ice materials within the 'quantum tunnelling' regime is modelled with Metropolis dynamics, with the particles constrained to move along an underlying network of oriented paths, which are classical analogues of the Dirac strings connecting pairs of Dirac monopoles.

Spin-controlled ultrafast vertical-cavity surface-emitting lasers

NASA Astrophysics Data System (ADS)

Höpfner, Henning; Lindemann, Markus; Gerhardt, Nils C.; Hofmann, Martin R.

2014-05-01

Spin-controlled semiconductor lasers are highly attractive spintronic devices providing characteristics superior to their conventional purely charge-based counterparts. In particular, spin-controlled vertical-cavity surface emitting lasers (spin-VCSELs) promise to offer lower thresholds, enhanced emission intensity, spin amplification, full polarization control, chirp control and ultrafast dynamics. Most important, the ability to control and modulate the polarization state of the laser emission with extraordinarily high frequencies is very attractive for many applications like broadband optical communication and ultrafast optical switches. We present a novel concept for ultrafast spin-VCSELs which has the potential to overcome the conventional speed limitation for directly modulated lasers by the relaxation oscillation frequency and to reach modulation frequencies significantly above 100 GHz. The concept is based on the coupled spin-photon dynamics in birefringent micro-cavity lasers. By injecting spin-polarized carriers in the VCSEL, oscillations of the coupled spin-photon system can by induced which lead to oscillations of the polarization state of the laser emission. These oscillations are decoupled from conventional relaxation oscillations of the carrier-photon system and can be much faster than these. Utilizing these polarization oscillations is thus a very promising approach to develop ultrafast spin-VCSELs for high speed optical data communication in the near future. Different aspects of the spin and polarization dynamics, its connection to birefringence and bistability in the cavity, controlled switching of the oscillations, and the limitations of this novel approach will be analysed theoretically and experimentally for spin-polarized VCSELs at room temperature.

Excitation of propagating spin waves by pure spin current

NASA Astrophysics Data System (ADS)

Demokritov, Sergej

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.

Recent NASA Research on Aerodynamic Modeling of Post-Stall and Spin Dynamics of Large Transport Airplanes

NASA Technical Reports Server (NTRS)

Murch, Austin M.; Foster, John V.

2007-01-01

A simulation study was conducted to investigate aerodynamic modeling methods for prediction of post-stall flight dynamics of large transport airplanes. The research approach involved integrating dynamic wind tunnel data from rotary balance and forced oscillation testing with static wind tunnel data to predict aerodynamic forces and moments during highly dynamic departure and spin motions. Several state-of-the-art aerodynamic modeling methods were evaluated and predicted flight dynamics using these various approaches were compared. Results showed the different modeling methods had varying effects on the predicted flight dynamics and the differences were most significant during uncoordinated maneuvers. Preliminary wind tunnel validation data indicated the potential of the various methods for predicting steady spin motions.

Theory of dynamic spin susceptibility in terms of the t-J-V model: Comparison with neutron scattering data for Pr0.88LaCe0.12CuO4 - x and La2 - x Sr x CuO4

NASA Astrophysics Data System (ADS)

Andreev, A. I.; Eremin, I. M.; Eremin, M. V.

2009-01-01

A formula for the dynamic spin susceptibility is derived in terms of the t-J-V model. This formula makes it possible to explain the main features of recent experiments on neutron scattering in the electron-doped superconductor Pr0.88LaCe0.12CuO4 - x . In particular, the proposed theory reproduces well a V-shaped relief in the frequency behavior of the imaginary part χ″( Q, ω) of the susceptibility of the Pr0.88LaCe0.12CuO4 - x compound in the vicinity of the wave vector Q = (π,π) and the scaling behavior of the position of the maxima in the dependence of the function χ″( Q, ω) T on the quantity ω/ T. The magnetism of the high-temperature superconductors is dual. These materials contain charge carriers, on the one hand, and localized spins in the copper ion sublattice, on the other hand. Both these systems are strongly coupled to each other. The mode of collective oscillations is common. The magnetism of localized spins “freezes” with the appearance of the superconducting gap. The recently revealed double-peak structure of the imaginary part χ″( Q, ω) of the susceptibility in superconductors of the La1.84Sr0.16CuO4 type is explained. The low-frequency absorption peak is located within the superconducting gap and interpreted as a manifestation of the branch of spin excitons, and the high-frequency absorption peak predominantly corresponds to renormalized collective oscillations of localized spins.

Optical Orientation of Mn2+ Ions in GaAs in Weak Longitudinal Magnetic Fields

NASA Astrophysics Data System (ADS)

Akimov, I. A.; Dzhioev, R. I.; Korenev, V. L.; Kusrayev, Yu. G.; Sapega, V. F.; Yakovlev, D. R.; Bayer, M.

2011-04-01

We report on optical orientation of Mn2+ ions in bulk GaAs subject to weak longitudinal magnetic fields (B≤100mT). A manganese spin polarization of 25% is directly evaluated by using spin-flip Raman scattering. The dynamical Mn2+ polarization occurs due to the s-d exchange interaction with optically oriented conduction band electrons. Time-resolved photoluminescence reveals a nontrivial electron spin dynamics, where the oriented Mn2+ ions tend to stabilize the electron spins.

Optical orientation of Mn2+ ions in GaAs in weak longitudinal magnetic fields.

PubMed

Akimov, I A; Dzhioev, R I; Korenev, V L; Kusrayev, Yu G; Sapega, V F; Yakovlev, D R; Bayer, M

2011-04-08

We report on optical orientation of Mn2+ ions in bulk GaAs subject to weak longitudinal magnetic fields (B≤100  mT). A manganese spin polarization of 25% is directly evaluated by using spin-flip Raman scattering. The dynamical Mn2+ polarization occurs due to the s-d exchange interaction with optically oriented conduction band electrons. Time-resolved photoluminescence reveals a nontrivial electron spin dynamics, where the oriented Mn2+ ions tend to stabilize the electron spins.

Novel spin dynamics in ferrimagnetic molecular chains from 1H NMR and μSR spin-lattice relaxation measurements

NASA Astrophysics Data System (ADS)

Micotti, E.; Lascialfari, A.; Rigamonti, A.; Aldrovandi, S.; Caneschi, A.; Gatteschi, D.; Bogani, L.

2004-05-01

The spin dynamics in the helical chain Co(hfac) 2NITPhOMe has been investigated by 1H NMR and μSR relaxation. In the temperature range 15

Faithful Solid State Optical Memory with Dynamically Decoupled Spin Wave Storage

NASA Astrophysics Data System (ADS)

Lovrić, Marko; Suter, Dieter; Ferrier, Alban; Goldner, Philippe

2013-07-01

We report a high fidelity optical memory in which dynamical decoupling is used to extend the storage time. This is demonstrated in a rare-earth doped crystal in which optical coherences were transferred to nuclear spin coherences and then protected against environmental noise by dynamical decoupling, leading to storage times of up to 4.2 ms. An interference experiment shows that relative phases of input pulses are preserved through the whole storage and retrieval process with a visibility ≈1, demonstrating the usefulness of dynamical decoupling for extending the storage time of quantum memories. We also show that dynamical decoupling sequences insensitive to initial spin coherence increase retrieval efficiency.

Faithful solid state optical memory with dynamically decoupled spin wave storage.

PubMed

Lovrić, Marko; Suter, Dieter; Ferrier, Alban; Goldner, Philippe

2013-07-12

We report a high fidelity optical memory in which dynamical decoupling is used to extend the storage time. This is demonstrated in a rare-earth doped crystal in which optical coherences were transferred to nuclear spin coherences and then protected against environmental noise by dynamical decoupling, leading to storage times of up to 4.2 ms. An interference experiment shows that relative phases of input pulses are preserved through the whole storage and retrieval process with a visibility ≈1, demonstrating the usefulness of dynamical decoupling for extending the storage time of quantum memories. We also show that dynamical decoupling sequences insensitive to initial spin coherence increase retrieval efficiency.

Bose-Fermi mapping and a multibranch spin-chain model for strongly interacting quantum gases in one dimension: Dynamics and collective excitations

NASA Astrophysics Data System (ADS)

Yang, Li; Pu, Han

2016-09-01

We show that the wave function in one spatial sector x1

Experimental and theoretical investigation of the magnetization dynamics of an artificial square spin ice cluster

NASA Astrophysics Data System (ADS)

Pohlit, Merlin; Stockem, Irina; Porrati, Fabrizio; Huth, Michael; Schröder, Christian; Müller, Jens

2016-10-01

We study the magnetization dynamics of a spin ice cluster which is a building block of an artificial square spin ice fabricated by focused electron-beam-induced deposition both experimentally and theoretically. The spin ice cluster is composed of twelve interacting Co nanoislands grown directly on top of a high-resolution micro-Hall sensor. By employing micromagnetic simulations and a macrospin model, we calculate the magnetization and the experimentally investigated stray field emanating from a single nanoisland. The parameters determined from a comparison with the experimental hysteresis loop are used to derive an effective single-dipole macrospin model that allows us to investigate the dynamics of the spin ice cluster. Our model reproduces the experimentally observed non-deterministic sequences in the magnetization curves as well as the distinct temperature dependence of the hysteresis loop.

Femtosecond Measurements Of Size-Dependent Spin Crossover In FeII(pyz)Pt(CN)4 Nanocrystals

DOE PAGES

Sagar, D. M.; Baddour, Frederick G.; Konold, Patrick; ...

2016-01-07

We report a femtosecond time-resolved spectroscopic study of size-dependent dynamics in nanocrystals (NCs) of Fe(pyz)Pt(CN) 4. We observe that smaller NCs (123 or 78 nm cross section and < 25 nm thickness) exhibit signatures of spin crossover (SCO) with time constants of ~ 5-10 ps whereas larger NCs with 375 nm cross section and 43 nm thickness exhibit a weaker SCO signature accompanied by strong spectral shifting on a ~20 ps time scale. For the small NCs, the fast dynamics appear to result from thermal promotion of residual low-spin states to high-spin states following nonradiative decay, and the size dependencemore » is postulated to arise from differing high-spin vs low-spin fractions in domains residing in strained surface regions. The SCO is less efficient in larger NCs owing to their larger size and hence lower residual LS/HS fractions. Our results suggest that size-dependent dynamics can be controlled by tuning surface energy in NCs with dimensions below ~25 nm for use in energy harvesting, spin switching, and other applications.« less

Spin-Mechanical Inertia in Antiferromagnet

NASA Astrophysics Data System (ADS)

Cheng, Ran; Wu, Xiaochuan; Xiao, Di

Interplay between spin dynamics and mechanical motions is responsible for numerous striking phenomena, which has shaped a rapidly expanding field known as spin-mechanics. The guiding principle of this field has been the conservation of angular momentum that involves both quantum spins and classical mechanical rotations. However, in an antiferromagnet, the macroscopic magnetization vanishes while the order parameter (Néel order) does not carry an angular momentum. It is therefore not clear whether the order parameter dynamics has any mechanical consequence as its ferromagnetic counterparts. Here we demonstrate that the Néel order dynamics affects the mechanical motion of a rigid body by modifying its inertia tensor in the presence of strong magnetocrystalline anisotropy. This effect depends on temperature when magnon excitations are considered. Such a spin-mechanical inertia can produce measurable consequences at nanometer scales. Our discovery establishes spin-mechanical inertia as an essential ingredient to properly describe spin-mechanical effects in AFs, which supplements the known governing physics from angular momentum conservation. This work was supported by the DOE, Basic Energy Sciences, Grant No. DE-SC0012509. D.X. also acknowledges support from a Research Corporation for Science Advancement Cottrell Scholar Award.

Theoretical model of dynamic spin polarization of nuclei coupled to paramagnetic point defects in diamond and silicon carbide

NASA Astrophysics Data System (ADS)

Ivády, Viktor; Szász, Krisztián; Falk, Abram L.; Klimov, Paul V.; Christle, David J.; Janzén, Erik; Abrikosov, Igor A.; Awschalom, David D.; Gali, Adam

2015-09-01

Dynamic nuclear spin polarization (DNP) mediated by paramagnetic point defects in semiconductors is a key resource for both initializing nuclear quantum memories and producing nuclear hyperpolarization. DNP is therefore an important process in the field of quantum-information processing, sensitivity-enhanced nuclear magnetic resonance, and nuclear-spin-based spintronics. DNP based on optical pumping of point defects has been demonstrated by using the electron spin of nitrogen-vacancy (NV) center in diamond, and more recently, by using divacancy and related defect spins in hexagonal silicon carbide (SiC). Here, we describe a general model for these optical DNP processes that allows the effects of many microscopic processes to be integrated. Applying this theory, we gain a deeper insight into dynamic nuclear spin polarization and the physics of diamond and SiC defects. Our results are in good agreement with experimental observations and provide a detailed and unified understanding. In particular, our findings show that the defect electron spin coherence times and excited state lifetimes are crucial factors in the entire DNP process.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lafuente-Sampietro, A.; CNRS, Institut Néel, F-38000 Grenoble; Institute of Materials Science, University of Tsukuba, 305-8573 Tsukuba

We studied the spin dynamics of a Cr atom incorporated in a II-VI semiconductor quantum dot using photon correlation techniques. We used recently developed singly Cr-doped CdTe/ZnTe quantum dots to access the spin of an individual magnetic atom. Auto-correlation of the photons emitted by the quantum dot under continuous wave optical excitation reveals fluctuations of the localized spin with a timescale in the 10 ns range. Cross-correlation gives quantitative transfer time between Cr spin states. A calculation of the time dependence of the spin levels population in Cr-doped quantum dots shows that the observed spin dynamics is dominated by the exciton-Crmore » interaction. These measurements also provide a lower bound in the 20 ns range for the intrinsic Cr spin relaxation time.« less

Electron Tunneling in Lithium Ammonia Solutions Probed by Frequency-Dependent Electron-Spin Relaxation Studies

PubMed Central

Maeda, Kiminori; Lodge, Matthew T.J.; Harmer, Jeffrey; Freed, Jack H.; Edwards, Peter P.

2012-01-01

Electron transfer or quantum tunneling dynamics for excess or solvated electrons in dilute lithium-ammonia solutions have been studied by pulse electron paramagnetic resonance (EPR) spectroscopy at both X- (9.7 GHz) and W-band (94 GHz) frequencies. The electron spin-lattice (T1) and spin-spin (T2) relaxation data indicate an extremely fast transfer or quantum tunneling rate of the solvated electron in these solutions which serves to modulate the hyperfine (Fermi-contact) interaction with nitrogen nuclei in the solvation shells of ammonia molecules surrounding the localized, solvated electron. The donor and acceptor states of the solvated electron in these solutions are the initial and final electron solvation sites found before, and after, the transfer or tunneling process. To interpret and model our electron spin relaxation data from the two observation EPR frequencies requires a consideration of a multi-exponential correlation function. The electron transfer or tunneling process that we monitor through the correlation time of the nitrogen Fermi-contact interaction has a time scale of (1–10)×10−12 s over a temperature range 230–290K in our most dilute solution of lithium in ammonia. Two types of electron-solvent interaction mechanisms are proposed to account for our experimental findings. The dominant electron spin relaxation mechanism results from an electron tunneling process characterized by a variable donor-acceptor distance or range (consistent with such a rapidly fluctuating liquid structure) in which the solvent shell that ultimately accepts the transferring electron is formed from random, thermal fluctuations of the liquid structure in, and around, a natural hole or Bjerrum-like defect vacancy in the liquid. Following transfer and capture of the tunneling electron, further solvent-cage relaxation with a timescale of ca. 10−13 s results in a minor contribution to the electron spin relaxation times. This investigation illustrates the great potential of multi-frequency EPR measurements to interrogate the microscopic nature and dynamics of ultra fast electron transfer or quantum-tunneling processes in liquids. Our results also impact on the universal issue of the role of a host solvent (or host matrix, e.g. a semiconductor) in mediating long-range electron transfer processes and we discuss the implications of our results with a range of other materials and systems exhibiting the phenomenon of electron transfer. PMID:22568866

Dynamics of bright-bright solitons in Bose-Einstein condensate with Raman-induced one-dimensional spin-orbit coupling

NASA Astrophysics Data System (ADS)

Wen, Lin; Zhang, Xiao-Fei; Hu, Ai-Yuan; Zhou, Jing; Yu, Peng; Xia, Lei; Sun, Qing; Ji, An-Chun

2018-03-01

We investigate the dynamics of bright-bright solitons in one-dimensional two-component Bose-Einstein condensates with Raman-induced spin-orbit coupling, via the variational approximation and the numerical simulation of Gross-Pitaevskii equations. For the uniform system without trapping potential, we obtain two population balanced stationary solitons. By performing the linear stability analysis, we find a Goldstone eigenmode and an oscillation eigenmode around these stationary solitons. Moreover, we derive a general dynamical solution to describe the center-of-mass motion and spin evolution of the solitons under the action of spin-orbit coupling. The effects of a harmonic trap have also been discussed.

EDITORIAL: Spin-transfer-torque-induced phenomena Spin-transfer-torque-induced phenomena

NASA Astrophysics Data System (ADS)

Hirohata, Atsufumi

2011-09-01

This cluster, consisting of five invited articles on spin-transfer torque, offers the very first review covering both magnetization reversal and domain-wall displacement induced by a spin-polarized current. Since the first theoretical proposal on spin-transfer torque—reported by Berger and Slonczewski independently—spin-transfer torque has been experimentally demonstrated in both vertical magnetoresistive nano-pillars and lateral ferromagnetic nano-wires. In the former structures, an electrical current flowing vertically in the nano-pillar exerts spin torque onto the thinner ferromagnetic layer and reverses its magnetization, i.e., current-induced magnetization switching. In the latter structures, an electrical current flowing laterally in the nano-wire exerts torque onto a domain wall and moves its position by rotating local magnetic moments within the wall, i.e., domain wall displacement. Even though both phenomena are induced by spin-transfer torque, each phenomenon has been investigated separately. In order to understand the physical meaning of spin torque in a broader context, this cluster overviews both cases from theoretical modellings to experimental demonstrations. The earlier articles in this cluster focus on current-induced magnetization switching. The magnetization dynamics during the reversal has been calculated by Kim et al using the conventional Landau--Lifshitz-Gilbert (LLG) equation, adding a spin-torque term. This model can explain the dynamics in both spin-valves and magnetic tunnel junctions in a nano-pillar form. This phenomenon has been experimentally measured in these junctions consisting of conventional ferromagnets. In the following experimental part, the nano-pillar junctions with perpendicularly magnetized FePt and half-metallic Heusler alloys are discussed from the viewpoint of efficient magnetization reversal due to a high degree of spin polarization of the current induced by the intrinsic nature of these alloys. Such switching can be further operated at high frequency resulting in an oscillator, as shown in the article by Sulka et al. These results provide fundamental elements for magnetic random access memories. The later articles discuss domain-wall displacement. Again this phenomenon is also described by Shibata et al based on the LLG equation with spin-torque terms. This analytical model can explain the details of the depinning mechanism and a critical current for the displacement. Experimental observation is presented in the subsequent article by Malinowski et al, showing the depinning processes for the cases of intrinsic and extrinsic pinning sites. Here, the detailed magnetic moment configurations within the wall hold the dominant control over the critical current. These results can be used for future 3-dimensional magnetic memories, such as racetrack memory proposed by IBM. We sincerely hope this cluster offers an up-to-date understanding of macroscopic behaviour induced by spin-transfer torque and contributes to further advancement in this exciting research field. We are grateful to all the authors for spending their precious time and knowledge submitting to this cluster. We would also like to thank Professor Kevin O'Grady for his kind offer of the opportunity to make this review accessible to a general audience.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kung, Y. F.; Bazin, C.; Wohlfeld, K.

Using determinant quantum Monte Carlo (DQMC) simulations, we systematically study the doping dependence of the crossover from one to two dimensions and its impact on the magnetic properties of the Hubbard model. A square lattice of chains is used, in which the dimensionality can be tuned by varying the interchain coupling t ⊥. The dynamical spin structure factor and static quantities, such as the static spin susceptibility and nearest-neighbor spin correlation function, are characterized in the one- and two-dimensional limits as a benchmark. When the dimensionality is tuned between these limits, the magnetic properties, while evolving smoothly from one tomore » two dimensions, drastically change regardless of the doping level. This suggests that the spin excitations in the two-dimensional Hubbard model, even in the heavily doped case, cannot be explained using the spinon picture known from one dimension. In conclusion, the DQMC calculations are complemented by cluster perturbation theory studies to form a more complete picture of how the crossover occurs as a function of doping and how doped holes impact magnetic order.« less

Finite-temperature dynamic structure factor of the spin-1 XXZ chain with single-ion anisotropy

NASA Astrophysics Data System (ADS)

Lange, Florian; Ejima, Satoshi; Fehske, Holger

2018-02-01

Improving matrix-product state techniques based on the purification of the density matrix, we are able to accurately calculate the finite-temperature dynamic response of the infinite spin-1 XXZ chain with single-ion anisotropy in the Haldane, large-D , and antiferromagnetic phases. Distinct thermally activated scattering processes make a significant contribution to the spectral weight in all cases. In the Haldane phase, intraband magnon scattering is prominent, and the on-site anisotropy causes the magnon to split into singlet and doublet branches. In the large-D phase response, the intraband signal is separated from an exciton-antiexciton continuum. In the antiferromagnetic phase, holons are the lowest-lying excitations, with a gap that closes at the transition to the Haldane state. At finite temperatures, scattering between domain-wall excitations becomes especially important and strongly enhances the spectral weight for momentum transfer π .

Lattice dynamics of BaFe 2 X 3 ( X = S , Se ) compounds

DOE PAGES

Popović, Z. V.; Šćepanović, M.; Lazarević, N.; ...

2015-02-27

We present the Raman scattering spectra of the S=2 spin ladder compounds BaFe₂X₃ (X=S,Se) in a temperature range between 20 and 400 K. Although the crystal structures of these two compounds are both orthorhombic and very similar, they are not isostructural. The unit cell of BaFe₂S₃ (BaFe₂Se₃) is base-centered Cmcm (primitive Pnma), giving 18 (36) modes to be observed in the Raman scattering experiment. We have detected almost all Raman active modes, predicted by factor group analysis, which can be observed from the cleavage planes of these compounds. Assignment of the observed Raman modes of BaFe₂S(Se)₃ is supported by themore » lattice dynamics calculations. The antiferromagnetic long-range spin ordering in BaFe₂Se₃ below T N=255K leaves a fingerprint both in the A 1g and B 3g phonon mode linewidth and energy.« less

First principles molecular dynamics study of nitrogen vacancy complexes in boronitrene

NASA Astrophysics Data System (ADS)

Ukpong, A. M.; Chetty, N.

2012-07-01

We present the results of first principles molecular dynamics simulations of nitrogen vacancy complexes in monolayer hexagonal boron nitride. The threshold for local structure reconstruction is found to be sensitive to the presence of a substitutional carbon impurity. We show that activated nitrogen dynamics triggers the annihilation of defects in the layer through formation of Stone-Wales-type structures. The lowest energy state of nitrogen vacancy complexes is negatively charged and spin polarized. Using the divacancy complex, we show that their formation induces spontaneous magnetic moments, which is tunable by electron or hole injection. The Fermi level s-resonant defect state is identified as a unique signature of the ground state of the divacancy complex. Due to their ability to enhance structural cohesion, only the divacancy and the nitrogen vacancy carbon-antisite complexes are able to suppress the Fermi level resonant defect state to open a gap between the conduction and valence bands.

Towards Efficient and Accurate Description of Many-Electron Problems: Developments of Static and Time-Dependent Electronic Structure Methods

NASA Astrophysics Data System (ADS)

Ding, Feizhi

Understanding electronic behavior in molecular and nano-scale systems is fundamental to the development and design of novel technologies and materials for application in a variety of scientific contexts from fundamental research to energy conversion. This dissertation aims to provide insights into this goal by developing novel methods and applications of first-principle electronic structure theory. Specifically, we will present new methods and applications of excited state multi-electron dynamics based on the real-time (RT) time-dependent Hartree-Fock (TDHF) and time-dependent density functional theory (TDDFT) formalism, and new development of the multi-configuration self-consist field theory (MCSCF) for modeling ground-state electronic structure. The RT-TDHF/TDDFT based developments and applications can be categorized into three broad and coherently integrated research areas: (1) modeling of the interaction between moleculars and external electromagnetic perturbations. In this part we will first prove both analytically and numerically the gauge invariance of the TDHF/TDDFT formalisms, then we will present a novel, efficient method for calculating molecular nonlinear optical properties, and last we will study quantum coherent plasmon in metal namowires using RT-TDDFT; (2) modeling of excited-state charge transfer in molecules. In this part, we will investigate the mechanisms of bridge-mediated electron transfer, and then we will introduce a newly developed non-equilibrium quantum/continuum embedding method for studying charge transfer dynamics in solution; (3) developments of first-principles spin-dependent many-electron dynamics. In this part, we will present an ab initio non-relativistic spin dynamics method based on the two-component generalized Hartree-Fock approach, and then we will generalized it to the two-component TDDFT framework and combine it with the Ehrenfest molecular dynamics approach for modeling the interaction between electron spins and nuclear motion. All these developments and applications will open up new computational and theoretical tools to be applied to the development and understanding of chemical reactions, nonlinear optics, electromagnetism, and spintronics. Lastly, we present a new algorithm for large-scale MCSCF calculations that can utilize massively parallel machines while still maintaining optimal performance for each single processor. This will great improve the efficiency in the MCSCF calculations for studying chemical dissociation and high-accuracy quantum-mechanical simulations.

Microscopic studies of nonlocal spin dynamics and spin transport (invited)

NASA Astrophysics Data System (ADS)

Adur, Rohan; Du, Chunhui; Cardellino, Jeremy; Scozzaro, Nicolas; Wolfe, Christopher S.; Wang, Hailong; Herman, Michael; Bhallamudi, Vidya P.; Pelekhov, Denis V.; Yang, Fengyuan; Hammel, P. Chris

2015-05-01

Understanding the behavior of spins coupling across interfaces in the study of spin current generation and transport is a fundamental challenge that is important for spintronics applications. The transfer of spin angular momentum from a ferromagnet into an adjacent normal material as a consequence of the precession of the magnetization of the ferromagnet is a process known as spin pumping. We find that, in certain circumstances, the insertion of an intervening normal metal can enhance spin pumping between an excited ferromagnetic magnetization and a normal metal layer as a consequence of improved spin conductance matching. We have studied this using inverse spin Hall effect and enhanced damping measurements. Scanned probe magnetic resonance techniques are a complementary tool in this context offering high resolution magnetic resonance imaging, localized spin excitation, and direct measurement of spin lifetimes or damping. Localized magnetic resonance studies of size-dependent spin dynamics in the absence of lithographic confinement in both ferromagnets and paramagnets reveal the close relationship between spin transport and spin lifetime at microscopic length scales. Finally, detection of ferromagnetic resonance of a ferromagnetic film using the photoluminescence of nitrogen vacancy spins in neighboring nanodiamonds demonstrates long-range spin transport between insulating materials, indicating the complexity and generality of spin transport in diverse, spatially separated, material systems.

Microscopic studies of nonlocal spin dynamics and spin transport (invited)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adur, Rohan; Du, Chunhui; Cardellino, Jeremy

2015-05-07

Understanding the behavior of spins coupling across interfaces in the study of spin current generation and transport is a fundamental challenge that is important for spintronics applications. The transfer of spin angular momentum from a ferromagnet into an adjacent normal material as a consequence of the precession of the magnetization of the ferromagnet is a process known as spin pumping. We find that, in certain circumstances, the insertion of an intervening normal metal can enhance spin pumping between an excited ferromagnetic magnetization and a normal metal layer as a consequence of improved spin conductance matching. We have studied this usingmore » inverse spin Hall effect and enhanced damping measurements. Scanned probe magnetic resonance techniques are a complementary tool in this context offering high resolution magnetic resonance imaging, localized spin excitation, and direct measurement of spin lifetimes or damping. Localized magnetic resonance studies of size-dependent spin dynamics in the absence of lithographic confinement in both ferromagnets and paramagnets reveal the close relationship between spin transport and spin lifetime at microscopic length scales. Finally, detection of ferromagnetic resonance of a ferromagnetic film using the photoluminescence of nitrogen vacancy spins in neighboring nanodiamonds demonstrates long-range spin transport between insulating materials, indicating the complexity and generality of spin transport in diverse, spatially separated, material systems.« less

Dynamic bending of bionic flexible body driven by pneumatic artificial muscles(PAMs) for spinning gait of quadruped robot

NASA Astrophysics Data System (ADS)

Lei, Jingtao; Yu, Huangying; Wang, Tianmiao

2016-01-01

The body of quadruped robot is generally developed with the rigid structure. The mobility of quadruped robot depends on the mechanical properties of the body mechanism. It is difficult for quadruped robot with rigid structure to achieve better mobility walking or running in the unstructured environment. A kind of bionic flexible body mechanism for quadruped robot is proposed, which is composed of one bionic spine and four pneumatic artificial muscles(PAMs). This kind of body imitates the four-legged creatures' kinematical structure and physical properties, which has the characteristic of changeable stiffness, lightweight, flexible and better bionics. The kinematics of body bending is derived, and the coordinated movement between the flexible body and legs is analyzed. The relationship between the body bending angle and the PAM length is obtained. The dynamics of the body bending is derived by the floating coordinate method and Lagrangian method, and the driving force of PAM is determined. The experiment of body bending is conducted, and the dynamic bending characteristic of bionic flexible body is evaluated. Experimental results show that the bending angle of the bionic flexible body can reach 18°. An innovation body mechanism for quadruped robot is proposed, which has the characteristic of flexibility and achieve bending by changing gas pressure of PAMs. The coordinated movement of the body and legs can achieve spinning gait in order to improve the mobility of quadruped robot.

Environment overwhelms both nature and nurture in a model spin glass

NASA Astrophysics Data System (ADS)

Middleton, A. Alan; Yang, Jie

We are interested in exploring what information determines the particular history of the glassy long term dynamics in a disordered material. We study the effect of initial configurations and the realization of stochastic dynamics on the long time evolution of configurations in a two-dimensional Ising spin glass model. The evolution of nearest neighbor correlations is computed using patchwork dynamics, a coarse-grained numerical heuristic for temporal evolution. The dependence of the nearest neighbor spin correlations at long time on both initial spin configurations and noise histories are studied through cross-correlations of long-time configurations and the spin correlations are found to be independent of both. We investigate how effectively rigid bond clusters coarsen. Scaling laws are used to study the convergence of configurations and the distribution of sizes of nearly rigid clusters. The implications of the computational results on simulations and phenomenological models of spin glasses are discussed. We acknowledge NSF support under DMR-1410937 (CMMT program).

Magnon and phonon dispersion, lifetime, and thermal conductivity of iron from spin-lattice dynamics simulations

NASA Astrophysics Data System (ADS)

Wu, Xufei; Liu, Zeyu; Luo, Tengfei

2018-02-01

In recent years, the fundamental physics of spin-lattice (e.g., magnon-phonon) interaction has attracted significant experimental and theoretical interests given its potential paradigm-shifting impacts in areas like spin-thermoelectrics, spin-caloritronics, and spintronics. Modelling studies of the transport of magnons and phonons in magnetic crystals are very rare. In this paper, we use spin-lattice dynamics (SLD) simulations to model ferromagnetic crystalline iron, where the spin and lattice systems are coupled through the atomic position-dependent exchange function, and thus the interaction between magnons and phonons is naturally considered. We then present a method combining SLD simulations with spectral energy analysis to calculate the magnon and phonon harmonic (e.g., dispersion, specific heat, and group velocity) and anharmonic (e.g., scattering rate) properties, based on which their thermal conductivity values are calculated. This work represents an example of using SLD simulations to understand the transport properties involving coupled magnon and phonon dynamics.

Microscopic description of orbital-selective spin ordering in BaMn2As2

NASA Astrophysics Data System (ADS)

Craco, L.; Carara, S. S.

2018-05-01

Using generalized gradient approximation+dynamical mean-field theory, we provide a microscopic description of orbital-selective spin ordering in the tetragonal manganese pnictide BaMn2As2 . We demonstrate the coexistence of local moments and small band-gap electronic states in the parent compound. We also explore the role played by electron/hole doping, showing that the Mott insulating state is rather robust to small removal of electron charge carriers similar to cuprate oxide superconductors. Good qualitative accord between theory and angle-resolved photoemission as well as electrical transport provides support to our view of orbital-selective spin ordering in BaMn2As2 . Our proposal is expected to be an important step to understanding the emergent correlated electronic structure of materials with persisting ordered localized moments coexisting with Coulomb reconstructed nonmagnetic electronic states.

Magnetic order and spin dynamics in La2O2Fe2OSe2 probed by 57Fe Mössbauer, 139La NMR, and muon-spin relaxation spectroscopy

NASA Astrophysics Data System (ADS)

Günther, M.; Kamusella, S.; Sarkar, R.; Goltz, T.; Luetkens, H.; Pascua, G.; Do, S.-H.; Choi, K.-Y.; Zhou, H. D.; Blum, C. G. F.; Wurmehl, S.; Büchner, B.; Klauss, H.-H.

2014-11-01

We present a detailed local probe study of the magnetic order in the oxychalcogenide La2O2Fe2OSe2 utilizing 57Fe Mössbauer, 139La NMR, and muon-spin relaxation spectroscopy. This system can be regarded as an insulating reference system of the Fe arsenide and chalcogenide superconductors. From the combination of the local probe techniques we identify a noncollinear magnetic structure similar to Sr2F2Fe2OS2 . The analysis of the magnetic order parameter yields an ordering temperature TN=90.1 K and a critical exponent of β =0.133 , which is close to the two-dimensional Ising universality class as reported in the related oxychalcogenide family.

Nicholas Metropolis Award for Outstanding Doctoral Thesis Work in Computational Physics Lecture: The Janus computer, a new window into spin-glass physics

NASA Astrophysics Data System (ADS)

Yllanes, David

2013-03-01

Spin glasses are a longstanding model for the sluggish dynamics that appears at the glass transition. They enjoy a privileged status in this context, as they provide the simplest model system both for theoretical and experimental studies of glassy dynamics. However, in spite of forty years of intensive investigation, spin glasses still pose a formidable challenge to theoretical, computational and experimental physics. The main difficulty lies in their incredibly slow dynamics. A recent breakthrough has been made possible by our custom-built computer, Janus, designed and built in a collaboration formed by five universities in Spain and Italy. By employing a purpose-driven architecture, capable of fully exploiting the parallelization possibilities intrinsic to these simulations, Janus outperforms conventional computers by several orders of magnitude. After a brief introduction to spin glasses, the talk will focus on the new physics unearthed by Janus. In particular, we recall our numerical study of the nonequilibrium dynamics of the Edwards-Anderson Ising Spin Glass, for a time that spans eleven orders of magnitude, thus approaching the experimentally relevant scale (i.e. seconds). We have also studied the equilibrium properties of the spin-glass phase, with an emphasis on the quantitative matching between non-equilibrium and equilibrium correlation functions, through a time-length dictionary. Last but not least, we have clarified the existence of a glass transition in the presence of a magnetic field for a finite-range spin glass (the so-called de Almeida-Thouless line). We will finally mention some of the currently ongoing work of the collaboration, such as the characterization of the non-equilibrium dynamics in a magnetic field and the existence of a statics-dynamics dictionary in these conditions.

Spin stability of sounding rocket secondary payloads following high velocity ejections

NASA Astrophysics Data System (ADS)

Nelson, Weston M.

The Auroral Spatial Structures Probe (ASSP) mission is a sounding rocket mission studying solar energy input to space weather. ASSP requires the high velocity ejection (up to 50 m/s) of 6 secondary payloads, spin stabilized perpendicular to the ejection velocity. The proposed scientific instrumentation depends on a high degree of spin stability, requiring a maximum coning angle of less than 5°. It also requires that the spin axis be aligned within 25° of the local magnetic field lines. The maximum velocities of current ejection methods are typically less than 10m/s, and often produce coning angles in excess of 20°. Because of this they do not meet the ASSP mission requirements. To meet these requirements a new ejection method is being developed by NASA Wallops Flight Facility. Success of the technique in meeting coning angle and B-field alignment requirements is evaluated herein by modeling secondary payload dynamic behavior using a 6-DOF dynamic simulation employing state space integration written in MATLAB. Simulation results showed that secondary payload mass balancing is the most important factor in meeting stability requirements. Secondary mass payload properties will be measured using an inverted torsion pendulum. If moment of inertia measurement errors can be reduced to 0.5%, it is possible to achieve mean coning and B-field alignment angles of 2.16° and 2.71°, respectively.

An Update on Binary Formation by Rotational Fission

NASA Astrophysics Data System (ADS)

Tohline, Joel E.; Durisen, Richard H.

During the 1980s, numerical simulations showed that dynamic growth of a barlike mode in initially axisymmetric, equilibrium protostars does not lead to prompt binary formation, i. e., fission. Instead, such evolutions usually produce a dynamically stable, spinning barlike configuration. In recent years, this result has been confirmed by numerous groups using a variety of different hydrodynamical tools, and stability analyses have convincingly shown that fission does not occur in such systems because gravitational torques cause nonlinear saturation of the mode amplitude. Other possible routes to fission have been much less well scrutinized because they rely upon a detailed understanding of the structure and stability of initially nonaxisymmetric structures and/or evolutions that are driven by secular, rather than dynamic processes. Efforts are underway to examine these other fission scenarios.

Role of motive forces for the spin torque transfer for nano-structures

NASA Astrophysics Data System (ADS)

Barnes, Stewart

2009-03-01

Despite an announced imminent commercial realization of spin transfer random access memory (SPRAM) the current theory evolved from that of Slonczewski [1,2] does not conserve energy. Barnes and Maekawa [3] have shown, in order correct this defect, forces which originate from the spin rather than the charge of an electron must be accounted for, this leading to the concept of spin-motive-forces (smf) which must appear in Faraday's law and which significantly modifies the theory for spin-valves and domain wall devices [4]. A multi-channel theory in which these smf's redirect the spin currents will be described. In nano-structures it is now well known that the Kondo effect is reflected by conductance peaks. In essence, the spin degrees of freedom are used to enhance conduction. In a system with nano-magnets and a Coulomb blockade [5] the similar spin channels can be the only means of effective conduction. This results in a smf which lasts for minutes and an enormous magneto-resistance [5]. This implies the possibility of ``single electron memory'' in which the magnetic state is switched by a single electron. [4pt] [1] J. C. Slonczewski, Current-Driven Excitation of Magnetic Multilayers J. Magn. Magn. Mater. 159, L1 (1996). [0pt] [2] Y. Tserkovnyak, A. Brataas, G. E. W. Bauer, and B. I. Halperin, Nonlocal magnetization dynamics in ferromagnetic heterostructures, Rev. Mod. Phys. 77, 1375 (2005). [0pt] [3] S. E. Barnes and S. Maekawa, Generalization of Faraday's Law to Include Nonconservative Spin Forces Phys. Rev. Lett. 98, 246601 (2007); S. E. Barnes and S. Maekawa, Currents induced by domain wall motion in thin ferromagnetic wires. arXiv:cond-mat/ 0410021v1 (2004). [0pt] [4] S. E., Barnes, Spin motive forces, measurement, and spin-valves. J. Magn. Magn. Mat. 310, 2035-2037 (2007); S. E. Barnes, J. Ieda. J and S. Maekawa, Magnetic memory and current amplification devices using moving domain walls. Appl. Phys. Lett. 89, 122507 (2006). [0pt] [5] Pham-Nam Hai, Byung-Ho Yu, Shinobu Ohya, Masaaki Tanaka, Stewart E. Barnes and Sadamichi Maekawa, Electromotive force and huge magnetoresistance in magnetic tunnel junctions. Submitted Nature, August, (2008).

Coalescence of two spinning black holes: An effective one-body approach

NASA Astrophysics Data System (ADS)

Damour, Thibault

2001-12-01

We generalize to the case of spinning black holes a recently introduced ``effective one-body'' approach to the general relativistic dynamics of binary systems. We show how to approximately map the conservative part of the third post-Newtonian (3PN) dynamics of two spinning black holes of masses m1, m2 and spins S1, S2 onto the dynamics of a non-spinning particle of mass μ≡m1m2/(m1+m2) in a certain effective metric geffμν(xλM,ν,a) which can be viewed either as a spin deformation [with the deformation parameter a≡Seff/M] of the recently constructed 3PN effective metric geffμν(xλM,ν), or as a ν deformation [with the comparable-mass deformation parameter ν≡m1m2/(m1+m2)2] of a Kerr metric of mass M≡m1+m2 and (effective) spin Seff≡[1+3m2/(4m1)]S1+[1+3m1/(4m2)]S2. The combination of the effective one-body approach, and of a Padé definition of the crucial effective radial functions, is shown to define a dynamics with much improved post-Newtonian convergence properties, even for black hole separations of the order of 6 GM/c2. The complete (conservative) phase-space evolution equations of binary spinning black hole systems are written down and their exact and approximate first integrals are discussed. This leads to the approximate existence of a two-parameter family of ``spherical orbits'' (with constant radius), and of a corresponding one-parameter family of ``last stable spherical orbits'' (LSSO). These orbits are of special interest for forthcoming LIGO-VIRGO-GEO gravitational wave observations. The binding energy and total angular momentum of LSSO's are studied in some detail. It is argued that for most (but not all) of the parameter space of two spinning holes the approximate (leading-order) effective one-body approach introduced here gives a reliable analytical tool for describing the dynamics of the last orbits before coalescence. This tool predicts, in a quantitative way, how certain spin orientations increase the binding energy of the LSSO. This leads to a detection bias, in LIGO-VIRGO-GEO observations, favoring spinning black hole systems, and makes it urgent to complete the conservative effective one-body dynamics given here by adding (resummed) radiation reaction effects, and by constructing gravitational waveform templates that include spin effects. Finally, our approach predicts that the spin of the final hole formed by the coalescence of two arbitrarily spinning holes never approaches extremality.

Tunable nonequilibrium dynamics of field quenches in spin ice

PubMed Central

Mostame, Sarah; Castelnovo, Claudio; Moessner, Roderich; Sondhi, Shivaji L.

2014-01-01

We present nonequilibrium physics in spin ice as a unique setting that combines kinematic constraints, emergent topological defects, and magnetic long-range Coulomb interactions. In spin ice, magnetic frustration leads to highly degenerate yet locally constrained ground states. Together, they form a highly unusual magnetic state—a “Coulomb phase”—whose excitations are point-like defects—magnetic monopoles—in the absence of which effectively no dynamics is possible. Hence, when they are sparse at low temperature, dynamics becomes very sluggish. When quenching the system from a monopole-rich to a monopole-poor state, a wealth of dynamical phenomena occur, the exposition of which is the subject of this article. Most notably, we find reaction diffusion behavior, slow dynamics owing to kinematic constraints, as well as a regime corresponding to the deposition of interacting dimers on a honeycomb lattice. We also identify potential avenues for detecting the magnetic monopoles in a regime of slow-moving monopoles. The interest in this model system is further enhanced by its large degree of tunability and the ease of probing it in experiment: With varying magnetic fields at different temperatures, geometric properties—including even the effective dimensionality of the system—can be varied. By monitoring magnetization, spin correlations or zero-field NMR, the dynamical properties of the system can be extracted in considerable detail. This establishes spin ice as a laboratory of choice for the study of tunable, slow dynamics. PMID:24379372

Magic angle spinning NMR below 6 K with a computational fluid dynamics analysis of fluid flow and temperature gradients

NASA Astrophysics Data System (ADS)

Sesti, Erika L.; Alaniva, Nicholas; Rand, Peter W.; Choi, Eric J.; Albert, Brice J.; Saliba, Edward P.; Scott, Faith J.; Barnes, Alexander B.

2018-01-01

We report magic angle spinning (MAS) up to 8.5 kHz with a sample temperature below 6 K using liquid helium as a variable temperature fluid. Cross polarization 13C NMR spectra exhibit exquisite sensitivity with a single transient. Remarkably, 1H saturation recovery experiments show a 1H T1 of 21 s with MAS below 6 K in the presence of trityl radicals in a glassy matrix. Leveraging the thermal spin polarization available at 4.2 K versus 298 K should result in 71 times higher signal intensity. Taking the 1H longitudinal relaxation into account, signal averaging times are therefore predicted to be expedited by a factor of >500. Computer assisted design (CAD) and finite element analysis were employed in both the design and diagnostic stages of this cryogenic MAS technology development. Computational fluid dynamics (CFD) models describing temperature gradients and fluid flow are presented. The CFD models bearing and drive gas maintained at 100 K, while a colder helium variable temperature fluid stream cools the center of a zirconia rotor. Results from the CFD were used to optimize the helium exhaust path and determine the sample temperature. This novel cryogenic experimental platform will be integrated with pulsed dynamic nuclear polarization and electron decoupling to interrogate biomolecular structure within intact human cells.

Communication: a density functional with accurate fractional-charge and fractional-spin behaviour for s-electrons.

PubMed

Johnson, Erin R; Contreras-García, Julia

2011-08-28

We develop a new density-functional approach combining physical insight from chemical structure with treatment of multi-reference character by real-space modeling of the exchange-correlation hole. We are able to recover, for the first time, correct fractional-charge and fractional-spin behaviour for atoms of groups 1 and 2. Based on Becke's non-dynamical correlation functional [A. D. Becke, J. Chem. Phys. 119, 2972 (2003)] and explicitly accounting for core-valence separation and pairing effects, this method is able to accurately describe dissociation and strong correlation in s-shell many-electron systems. © 2011 American Institute of Physics

Current driven dynamics of magnetic domain walls in permalloy nanowires

NASA Astrophysics Data System (ADS)

Hayashi, Masamitsu

The significant advances in micro-fabrication techniques opened the door to access interesting properties in solid state physics. With regard to magnetic materials, geometrical confinement of magnetic structures alters the defining parameters that govern magnetism. For example, development of single domain nano-pillars made from magnetic multilayers led to the discovery of electrical current controlled magnetization switching, which revealed the existence of spin transfer torque. Magnetic domain walls (DWs) are boundaries in magnetic materials that divide regions with distinct magnetization directions. DWs play an important role in the magnetization reversal processes of both bulk and thin film magnetic materials. The motion of DW is conventionally controlled by magnetic fields. Recently, it has been proposed that spin polarized current passed across the DW can also control the motion of DWs. Current in most magnetic materials is spin-polarized, due to spin-dependent scattering of the electrons, and thus can deliver spin angular momentum to the DW, providing a "spin transfer" torque on the DW which leads to DW motion. In addition, owing to the development of micro-fabrication techniques, geometrical confinement of magnetic materials enables creation and manipulation of a "single" DW in magnetic nanostructures. New paradigms for DW-based devices are made possible by the direct manipulation of DWs using spin polarized electrical current via spin transfer torque. This dissertation covers research on current induced DW motion in magnetic nanowires. Fascinating effects arising from the interplay between DWs with spin polarized current will be revealed.

Polarized-neutron investigation of magnetic ordering and spin dynamics in BaCo2(AsO4)2 frustrated honeycomb-lattice magnet.

PubMed

Regnault, L-P; Boullier, C; Lorenzo, J E

2018-01-01

The magnetic properties of the cobaltite BaCo 2 (AsO 4 ) 2 , a good realization of the quasi two-dimensional frustrated honeycomb-lattice system with strong planar anisotropy, have been reinvestigated by means of spherical neutron polarimetry with CRYOPAD. From accurate measurements of polarization matrices both on elastic and inelastic contributions as a function of the scattering vector Q , we have been able to determine the low-temperature magnetic structure of BaCo 2 (AsO 4 ) 2 and reveal its puzzling in-plane spin dynamics. Surprisingly, the ground-state structure (described by an incommensurate propagation vector [Formula: see text], with [Formula: see text] and [Formula: see text]) appears to be a quasi-collinear structure, and not a simple helix, as previously determined. In addition, our results have revealed the existence of a non-negligible out-of-plane moment component [Formula: see text]/Co 2+ , representing about 10% of the in-plane component, as demonstrated by the presence of finite off-diagonal elements [Formula: see text] and [Formula: see text] of the polarization matrix, both on elastic and inelastic magnetic contributions. Despite a clear evidence of the existence of a slightly inelastic contribution of structural origin superimposed to the magnetic excitations at the scattering vectors [Formula: see text] and [Formula: see text] (energy transfer [Formula: see text] meV), no strong inelastic nuclear-magnetic interference terms could be detected so far, meaning that the nuclear and magnetic degrees of freedom have very weak cross-correlations. The strong inelastic [Formula: see text] and [Formula: see text] matrix elements can be understood by assuming that the magnetic excitations in BaCo 2 (AsO 4 ) 2 are spin waves associated with trivial anisotropic precessions of the magnetic moments involved in the canted incommensurate structure.

Simulation of spin label structure and its implication in molecular characterization

PubMed Central

Fajer, Piotr; Fajer, Mikolai; Zawrotny, Michael; Yang, Wei

2016-01-01

Interpretation of EPR from spin labels in terms of structure and dynamics requires knowledge of label behavior. General strategies were developed for simulation of labels used in EPR of proteins. The criteria for those simulations are: (a) exhaustive sampling of rotamer space; (b) consensus of results independent of starting points; (c) inclusion of entropy. These criteria are satisfied only when the number of transitions in any dihedral angle exceeds 100 and the simulation maintains thermodynamic equilibrium. Methods such as conventional MD do not efficiently cross energetic barriers, Simulated Annealing, Monte Carlo or popular Rotamer Library methodologies are potential energy based and ignore entropy (in addition to their specific shortcomings: environment fluctuations, fixed environment or electrostatics). Simulated Scaling method, avoids above flaws by modulating the forcefields between 0 (allowing crossing energy barriers) and full potential (sampling minima). Spin label diffuses on this surface while remaining in thermodynamic equilibrium. Simulations show that: (a) single conformation is rare, often there are 2–4 populated rotamers; (b) position of the NO varies up to 16Å. These results illustrate necessity for caution when interpreting EPR signals in terms of molecular structure. For example the 10–16Å distance change in DEER should not be interpreted as a large conformational change, it can well be a flip about Cα -Cβ bond. Rigorous exploration of possible rotamer structures of a spin label is paramount in signal interpretation. We advocate use of bifunctional labels, which motion is restricted 10,000-fold and the NO position is restricted to 2–5Å. PMID:26478501

Magnetic structure and dispersion relation of the S = 1 2 quasi-one-dimensional Ising-like antiferromagnet BaCo 2 V 2 O 8 in a transverse magnetic field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matsuda, M.; Onishi, H.; Okutani, A.

Here, BaCo 2V 2O 8 consists of Co chains in which a Co 2+ ion carries a fictitious spin 1/2 with Ising anisotropy. We performed elastic and inelastic neutron scattering experiments in BaCo 2V 2O 8 in a magnetic field perpendicular to the c axis which is the chain direction. With applying magnetic field along the a axis at 3.5 K, the antiferromagnetic order with the easy axis along the c axis, observed in zero magnetic field, is completely suppressed at 8 T, while the magnetic field gradually induces an antiferromagnetic order with the spin component along the b axis.more » We also studied magnetic excitations as a function of transverse magnetic field. The lower boundary of the spinon excitations splits gradually with increasing magnetic field. The overall feature of the magnetic excitation spectra in the magnetic field is reproduced by the theoretical calculation based on the spin 1/2 XXZ antiferromagnetic chain model, which predicts that the dynamic magnetic structure factor of the spin component along the chain direction is enhanced and that along the field direction has clear incommensurate correlations.« less

Magnetic structure and dispersion relation of the S = 1 2 quasi-one-dimensional Ising-like antiferromagnet BaCo 2 V 2 O 8 in a transverse magnetic field

DOE PAGES

Matsuda, M.; Onishi, H.; Okutani, A.; ...

2017-07-25

Here, BaCo 2V 2O 8 consists of Co chains in which a Co 2+ ion carries a fictitious spin 1/2 with Ising anisotropy. We performed elastic and inelastic neutron scattering experiments in BaCo 2V 2O 8 in a magnetic field perpendicular to the c axis which is the chain direction. With applying magnetic field along the a axis at 3.5 K, the antiferromagnetic order with the easy axis along the c axis, observed in zero magnetic field, is completely suppressed at 8 T, while the magnetic field gradually induces an antiferromagnetic order with the spin component along the b axis.more » We also studied magnetic excitations as a function of transverse magnetic field. The lower boundary of the spinon excitations splits gradually with increasing magnetic field. The overall feature of the magnetic excitation spectra in the magnetic field is reproduced by the theoretical calculation based on the spin 1/2 XXZ antiferromagnetic chain model, which predicts that the dynamic magnetic structure factor of the spin component along the chain direction is enhanced and that along the field direction has clear incommensurate correlations.« less