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1

Critical behavior of the mixed-spin Ising model with two competing dynamics.

In this work we investigate the stationary states of a nonequilibrium mixed-spin Ising model on a square lattice. The model system consists of two interpenetrating sublattices of spins sigma=1/2 and S=1, and we take only nearest neighbor interactions between pairs of spins. The system is in contact with a heat bath at temperature T and subject to an external flux of energy. The contact with the heat bath is simulated by single spin flips according to the Metropolis rule, while the input of energy is mimicked by the simultaneous flipping of pairs of neighboring spins. We performed Monte Carlo simulations on this model in order to find its phase diagram in the plane of temperature T versus the competition parameter between one- and two-spin flips, p. The phase diagram of the model exhibits two ordered phases with sublattice magnetizations m(1), m(2)>0 and m(1)>0, m(2)<0. These phases are separated from the paramagnetic phase (m(1)=m(2)=0) by continuous transition lines. We found the static critical exponents along these lines and showed that this nonequilibrium model belongs to the universality class of the two-dimensional equilibrium Ising model. PMID:11863591

Godoy, Mauricio; Figueiredo, Wagner

2002-02-01

2

Spin glasses are magnetic systems with conflicting and random interactions between the individual spins. The dynamics of spin glasses, as of structural glasses, reflect their complexity. Both in experimental and numerical work the relaxation below the freezing temperature depends strongly on the annealing conditions (aging) and, above the freezing point, relaxation in equilibrium is slow and non-exponential. In this Forum,

I. A. Campbell; J. Hammann; H. Kawamura; R. H. McKenzie; P. Nordblad; R. Orbach; H. Takayama

1998-01-01

3

Quantum spin pumping for a system with competing exchange interactions

We study the quantum spin pumping of an antiferromagnetic spin-1/2 chain with competing exchange interactions. We show that spatially periodic potential modulated in space and time acts as a quantum spin pump. In our model system, an applied electric field causes a spin gap to its critical ground state by introducing bond-alternation exchange interactions.

Sarkar, Sujit [PoornaPrajn Institute of Scientific Research, 4 Sadashivanagar, Bangalore 5600 80 (India); Hu, C. D. [Department of Physics, National Taiwan University, Taipei 10617, Taiwan (China)

2008-04-24

4

NASA Astrophysics Data System (ADS)

Geometrically frustrated magnets (GFMs) are materials in which it is impossible to satisfy all exchange interactions due the geometry of the lattice. The frustration of interactions is the origin of many unique and interesting material properties. GFMs are typified by large ground state degeneracy and will undergo spin fluctuations down to temperatures well below theta W, where un-frustrated materials display long-range order. This results in the development of correlated magnetic states that are analogous to various structural phases of matter such as spin glasses and spin liquids. Very recently, another magnetic-structural analog has been discovered where the magnetic properties show distinct similarities with the structural properties of a common substance that has itself long perplexed scientists, water ice. The aptly named spin ice compounds have been shown to exhibit the same "ground state entropy" as water ice and to be well characterized by consideration in terms of the "ice model". In this thesis, we explore the low temperature dynamics of the spins in the spin ice compound Dy2Ti2O7 through measurements of the magnetization and ac susceptibility. We show that the ground state represents a unique form of glassiness in a dense magnetic system. Our results show the onset of irreversibility and the development of a metastable state where the dynamics are significantly slowed but no long-range order is achieved below Tirr ˜ 650 mK. The system is also shown to display unique properties at higher temperatures with a partial freezing of the ac susceptibility at T ˜ 16 K. This freezing is shown to be thermally activated in nature above Tcross ˜ 12 K below which it is driven by quantum tunneling until it assumes faster than activated behavior at T ice ˜ 4 K. The freezing is shown to occur over a very narrow range of relaxation time constants, similar to that seen in the dielectric constants of ice. Measurements of Dy2-xYxTi2O 7, where the J = 15/2 Dy3+ ions were replaced with non-magnetic Y ions, show the freezing above Tice to be single ion in nature and to likely result from strong single ion anisotropy created by the crystalline field.

Snyder, Joseph William

2003-07-01

5

Electron spin decoherence in nuclear spin baths and dynamical decoupling

We introduce the quantum theory of the electron spin decoherence in a nuclear spin bath and the dynamical decoupling approach for protecting the electron spin coherence. These theories are applied to various solid-state systems, such as radical spins in molecular crystals and NV centers in diamond.

Zhao, N.; Yang, W.; Ho, S. W.; Hu, J. L.; Wan, J. T. K.; Liu, R. B. [Department of Physics, Chinese University of Hong Kong, Shatin, New Territories (Hong Kong)

2011-12-23

6

Spin rectification induced by dynamical Hanle effect

NASA Astrophysics Data System (ADS)

Dynamic response of spin accumulation to a time-dependent magnetic field has been investigated in a ferromagnetic/nonmagnetic bilayer under ferromagnetic resonance. In this system, magnetization precession driven by a microwave generates direct-current (dc) and alternate-current (ac) spin accumulation in the nonmagnetic layer by the spin pumping. The ac spin accumulation is coupled with the microwave magnetic field through a dynamical Hanle spin precession, giving rise to rectified spin accumulation comparable with the dc spin accumulation directly generated by the spin pumping.

Sakimura, Hiroto; Matsumoto, Takahiko; Ando, Kazuya

2013-09-01

7

Dynamically triangulated Ising spins in flat space

A model describing Ising spins with short range interactions moving randomly in a plane is considered. In the presence ofa hard core repulsion, which prevents the Ising spins from overlapping, the model is analogous to a dynamically triangulatedIsing model with spins constrained to move on a flat surface. It is found that as a function of coupling strength and hardcore

Marco Vekic; Shao Liu; Herbert W. Hamber

1994-01-01

8

Spin-glass dynamics determined from muon spin-relaxation and neutron spin-echo measurements

Muon spin-relaxation (..mu..SR) and neutron spin-echo (NSE) measurements of magnetic-ion correlation times and correlation functions in the spin-glass systems CuMn, AgMn, and AuFe are compared. It is found that the ..mu..SR and NSE measurements are in excellent agreement both above and below the spin-glass freezing temperatures. The experimental results are compared to recent theories of spin-glass dynamics.

Heffner, R.H.; Leon, M.; MacLaughlin, D.E.

1983-01-01

9

Electrically Driven Spin Dynamics of Paramagnetic Impurities

NASA Astrophysics Data System (ADS)

The spin dynamics of dilute paramagnetic impurities embedded in a semiconductor GaAs channel of a conventional lateral spin valve has been investigated. It is observed that the electron spin of paramagnetic Mn atoms can be polarized electrically when driven by a spin valve in the antiparallel configuration. The transient current through the MnAs/GaAs/MnAs spin valve bears the signature of the underlying spin dynamics driven by the exchange interaction between the conduction band electrons in GaAs and the localized Mn electron spins. The time constant for this interaction is observed to be dependent on temperature and is estimated to be 80 ns at 15 K.

Saha, D.; Siddiqui, L.; Bhattacharya, P.; Datta, S.; Basu, D.; Holub, M.

2008-05-01

10

Numerical study of the three-state Ashkin-Teller model with competing dynamics

NASA Astrophysics Data System (ADS)

An open ferromagnetic Ashkin-Teller model with spin variables 0, ±1 is studied by standard Monte Carlo simulations on a square lattice in the presence of competing Glauber and Kawasaki dynamics. The Kawasaki dynamics simulates spin-exchange processes that continuously flow energy into the system from an external source. Our calculations reveal the presence, in the model, of tricritical points where first order and second order transition lines meet. Beyond that, several self-organized phases are detected when Kawasaki dynamics become dominant. Phase diagrams that comprise phase boundaries and stationary states have been determined in the model parameters' space. In the case where spin-phonon interactions are incorporated in the model Hamiltonian, numerical results indicate that the paramagnetic phase is stabilized and almost all of the self-organized phases are destroyed.

Ndizeye, Prosper; Hontinfinde, Felix; Kounouhewa, Basile; Bekhechi, Smaine

2014-04-01

11

Numerical study of the three-state Ashkin-Teller model with competing dynamics

NASA Astrophysics Data System (ADS)

An open ferromagnetic Ashkin-Teller model with spin variables 0, ±1 is studied by standard Monte Carlo simulations on a square lattice in the presence of competing Glauber and Kawasaki dynamics. The Kawasaki dynamics simulates spin-exchange processes that continuously flow energy into the system from an external source. Our calculations reveal the presence, in the model, of tricritical points where first order and second order transition lines meet. Beyond that, several self-organized phases are detected when Kawasaki dynamics become dominant. Phase diagrams that comprise phase boundaries and stationary states have been determined in the model parameters' space. In the case where spin-phonon interactions are incorporated in the model Hamiltonian, numerical results indicate that the paramagnetic phase is stabilized and almost all of the self-organized phases are destroyed.

Ndizeye, Prosper; Hontinfinde, Felix; Kounouhewa, Basile; Bekhechi, Smaine

2014-05-01

12

Scaling for domain growth in the Ising model with competing dynamics

NASA Astrophysics Data System (ADS)

We study the domain growth of the one-dimensional kinetic Ising model under the competing influence of Glauber dynamics at temperature T and Kawasaki dynamics with a configuration-independent rate. The scaling of the structure factor is shown to have the form for nonconserved dynamics with the corrections arising from the spin-exchange process, i.e., S(k,t)=Lg0(kL,t/?)+g1(kL,t/?)+..., and the corresponding scaling functions are calculated analytically. A correction to the Porod law at zero temperature is also given.

Huang, Zhi-Feng; Gu, Bing-Lin; Tang, Yun

1998-12-01

13

Parallel algorithm for spin and spin-lattice dynamics simulations

NASA Astrophysics Data System (ADS)

To control numerical errors accumulated over tens of millions of time steps during the integration of a set of highly coupled equations of motion is not a trivial task. In this paper, we propose a parallel algorithm for spin dynamics and the newly developed spin-lattice dynamics simulation [P. W. Ma , Phys. Rev. B 78, 024434 (2008)]. The algorithm is successfully tested in both types of dynamic calculations involving a million spins. It shows good stability and numerical accuracy over millions of time steps (˜1ns) . The scheme is based on the second-order Suzuki-Trotter decomposition (STD). The usage can avoid numerical energy dissipation despite the trajectory and machine errors. The mathematical base of the symplecticity, for properly decomposed evolution operators, is presented. Due to the noncommutative nature of the spin in the present STD scheme, a unique parallel algorithm is needed. The efficiency and stability are tested. It can attain six to seven times speed up when eight threads are used. The run time per time step is linearly proportional to the system size.

Ma, Pui-Wai; Woo, C. H.

2009-04-01

14

Parallel algorithm for spin and spin-lattice dynamics simulations.

To control numerical errors accumulated over tens of millions of time steps during the integration of a set of highly coupled equations of motion is not a trivial task. In this paper, we propose a parallel algorithm for spin dynamics and the newly developed spin-lattice dynamics simulation [P. W. Ma, Phys. Rev. B 78, 024434 (2008)]. The algorithm is successfully tested in both types of dynamic calculations involving a million spins. It shows good stability and numerical accuracy over millions of time steps (approximately 1 ns) . The scheme is based on the second-order Suzuki-Trotter decomposition (STD). The usage can avoid numerical energy dissipation despite the trajectory and machine errors. The mathematical base of the symplecticity, for properly decomposed evolution operators, is presented. Due to the noncommutative nature of the spin in the present STD scheme, a unique parallel algorithm is needed. The efficiency and stability are tested. It can attain six to seven times speed up when eight threads are used. The run time per time step is linearly proportional to the system size. PMID:19518376

Ma, Pui-Wai; Woo, C H

2009-04-01

15

Advanced computational methods for nonlinear spin dynamics

NASA Astrophysics Data System (ADS)

We survey methods for the accurate computation of the dynamics of spin in general nonlinear accelerator lattices. Specifically, we show how it is possible to compute high-order nonlinear spin transfer maps in SO(3) or SU(2) representations in parallel with the corresponding orbit transfer maps. Specifically, using suitable invariant subspaces of the coupled spin-orbit dynamics, it is possible to develop a differential algebraic flow operator in a similar way as in the symplectic case of the orbit dynamics. The resulting high-order maps can be utilized for a variety of applications, including long-term spin-orbit tracking under preservation of the symplectic-orthonormal structure and the associated determination of depolarization rates. Using normal form methods, it is also possible to determine spin-orbit invariants of the motion, in particular the nonlinear invariant axis as well as the associated spin-orbit tune shifts. The methods are implemented in the code COSY INFINITY [1] and available for spin-orbit computations for general accelerator lattices, including conventional particle optical elements including their fringe fields, as well as user specified field arrangements.

Berz, Martin; Makino, Kyoko

2011-05-01

16

Magnetic Suspension for Dynamic Spin Rig

NASA Technical Reports Server (NTRS)

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.

Johnson, Dexter

1998-01-01

17

Dynamically triangulated Ising spins in flat space

NASA Astrophysics Data System (ADS)

A model describing Ising spins with short range interactions moving randomly in a plane is considered. In the presence ofa hard core repulsion, which prevents the Ising spins from overlapping, the model is analogous to a dynamically triangulatedIsing model with spins constrained to move on a flat surface. It is found that as a function of coupling strength and hardcore repulsion the model exhibits multicritical behavior, with first and second order transition lines terminating at a tricriticalpoint. The thermal and magnetic exponents computed at the tricritical point are consistent with the exact two-matrix modelsolution of the random Ising model, introduced previously to describe the effects of fluctuating geometries.

Veki?, Marco; Liu, Shao; Hamber, Herbert W.

1994-06-01

18

Kinetic Ashkin-Teller model with competing dynamics.

We study a two-dimensional nonequilibrium Ashkin-Teller model based on competing dynamics induced by contact with a heat bath at temperature T, and subject to an external source of energy. The dynamics of the system is simulated by two competing stochastic processes: a Glauber dynamics with probability p, which simulates the contact with the heat bath; and a Kawasaki dynamics with probability 1-p, which takes into account the flux of energy into the system. Monte Carlo simulations were employed to determine the phase diagram for the stationary states of the model and the corresponding critical exponents. The phase diagrams of the model exhibit a self-organization phenomenon for certain values of the fourth coupling interaction strength. On the other hand, from exponent calculations, the equilibrium critical behavior is preserved when nonequilibrium conditions are applied. PMID:11461358

Bekhechi, S; Benyoussef, A; Ettaki, B; Loulidi, M; El Kenz, A; Hontinfinde, F

2001-07-01

19

Vanishing spin gap in a competing spin-liquid phase in the kagome Heisenberg antiferromagnet

NASA Astrophysics Data System (ADS)

We provide strong numerical evidence, using improved variational wave functions, for a ground state with vanishing spin gap in the spin-1/2 quantum Heisenberg model on the kagome lattice. Starting from the algebraic U (1) Dirac spin liquid state proposed by Ran et al. [Phys. Rev. Lett. 98, 117205 (2007), 10.1103/PhysRevLett.98.117205] and iteratively applying a few Lanczos steps, we compute the lowest S =2 excitation constructed by exciting spinons close to the Dirac nodes. Our results are compatible with a vanishing spin gap in the thermodynamic limit and in consonance with a power-law decay of long distance spin-spin correlations in real space. The competition with a gapped (topological) spin liquid is discussed.

Iqbal, Yasir; Poilblanc, Didier; Becca, Federico

2014-01-01

20

Two competing species in super-diffusive dynamical regimes

NASA Astrophysics Data System (ADS)

The dynamics of two competing species within the framework of the generalized Lotka-Volterra equations, in the presence of multiplicative ?-stable Lévy noise sources and a random time dependent interaction parameter, is studied. The species dynamics is characterized by two different dynamical regimes, exclusion of one species and coexistence of both, depending on the values of the interaction parameter, which obeys a Langevin equation with a periodically fluctuating bistable potential and an additive ?-stable Lévy noise. The stochastic resonance phenomenon is analyzed for noise sources asymmetrically distributed. Finally, the effects of statistical dependence between multiplicative noise and additive noise on the dynamics of the two species are studied.

La Cognata, A.; Valenti, D.; Spagnolo, B.; Dubkov, A. A.

2010-09-01

21

Set-valued dynamic treatment regimes for competing outcomes.

Dynamic treatment regimes (DTRs) operationalize the clinical decision process as a sequence of functions, one for each clinical decision, where each function maps up-to-date patient information to a single recommended treatment. Current methods for estimating optimal DTRs, for example Q-learning, require the specification of a single outcome by which the "goodness" of competing dynamic treatment regimes is measured. However, this is an over-simplification of the goal of clinical decision making, which aims to balance several potentially competing outcomes, for example, symptom relief and side-effect burden. When there are competing outcomes and patients do not know or cannot communicate their preferences, formation of a single composite outcome that correctly balances the competing outcomes is not possible. This problem also occurs when patient preferences evolve over time. We propose a method for constructing DTRs that accommodates competing outcomes by recommending sets of treatments at each decision point. Formally, we construct a sequence of set-valued functions that take as input up-to-date patient information and give as output a recommended subset of the possible treatments. For a given patient history, the recommended set of treatments contains all treatments that produce non-inferior outcome vectors. Constructing these set-valued functions requires solving a non-trivial enumeration problem. We offer an exact enumeration algorithm by recasting the problem as a linear mixed integer program. The proposed methods are illustrated using data from the CATIE schizophrenia study. PMID:24400912

Laber, Eric B; Lizotte, Daniel J; Ferguson, Bradley

2014-03-01

22

Dynamical behavior of two predators competing over a single prey.

Dynamical behavior of a food web comprising two predators competing over a single prey has been investigated. The analysis of the food web model shows that the persistence is not possible for two competing predators sharing a single prey species in the cases when any one of the boundary prey-predator planes has a stable equilibrium point. The principle of competitive exclusion holds in such cases. However, numerical simulations exhibit persistence in the presence of periodic solutions in the boundary planes. The system exhibits quasi-periodic behavior in the positive octant. The co-existence in the form of a limit cycle is also possible in some cases. PMID:17574733

Gakkhar, Sunita; Singh, Brahampal; Naji, Raid Kamel

2007-01-01

23

Theory of Dynamical Behaviors of Ferromagnetic Spins

The dynamical behavior of ferromagnetic spins is studied on the basis of the statistical mechanics of irreversible processes. A macroscopic equation determining the change in time of an inhomogeneous magnetization is derived with explicit expressions for the frequency spectrum and damping constant. With the use of the general expressions thus obtained, the following problems are discussed on the basis of

Hazime Mori; Kyozi Kawasaki

1962-01-01

24

Magnetic monopole dynamics in spin ice.

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. PMID:21471628

Jaubert, L D C; Holdsworth, P C W

2011-04-27

25

Communication: Quantum dynamics in classical spin baths

NASA Astrophysics Data System (ADS)

A formalism for studying the dynamics of quantum systems embedded in classical spin baths is introduced. The theory is based on generalized antisymmetric brackets and predicts the presence of open-path off-diagonal geometric phases in the evolution of the density matrix. The weak coupling limit of the equation can be integrated by standard algorithms and provides a non-Markovian approach to the computer simulation of quantum systems in classical spin environments. It is expected that the theory and numerical schemes presented here have a wide applicability.

Sergi, Alessandro

2013-07-01

26

Interfacial spin glass state and exchange bias in manganite bilayers with competing magnetic orders

NASA Astrophysics Data System (ADS)

The magnetic properties of manganite bilayers composed of G-type antiferromagnetic (AFM) SrMnO3 and double-exchange ferromagnetic (FM) La0.7Sr0.3MnO3 are studied. A spin-glass state is observed as a result of competing magnetic orders and spin frustration at the La0.7Sr0.3MnO3/SrMnO3 interface. The dependence of the irreversible temperature on the cooling magnetic field follows the Almeida-Thouless line. Although an ideal G-type AFM SrMnO3 is featured with a compensated spin configuration, the bilayers exhibit exchange bias below the spin glass freezing temperature, which is much lower than the Néel temperature of SMO, indicating that the exchange bias is strongly correlated with the spin glass state. The results indicate that the spin frustration that originates from the competition between the AFM super-exchange and the FM double-exchange interactions can induce a strong magnetic anisotropy at the La0.7Sr0.3MnO3/SrMnO3 interface.

Ding, J. F.; Lebedev, O. I.; Turner, S.; Tian, Y. F.; Hu, W. J.; Seo, J. W.; Panagopoulos, C.; Prellier, W.; Van Tendeloo, G.; Wu, T.

2013-02-01

27

Dynamics of spin charge carriers in polyaniline

NASA Astrophysics Data System (ADS)

The review summarizes the results of the study of emeraldine forms of polyaniline by multifrequency (9.7-140 GHz, 3-cm and 2-mm) wavebands Electron Paramagnetic Resonance (EPR) spectroscopy combined with the spin label and probe, steady-state saturation of spin-packets, and saturation transfer methods. Spin excitations formed in emeraldine form of polyaniline govern structure, magnetic resonance, and electronic properties of the polymer. Conductivity in neutral or weakly doped samples is defined mainly by interchain charge tunneling in the frames of the Kivelson theory. As the doping level increases, this process is replaced by a charge thermal activation transport by molecular-lattice polarons. In heavily doped polyaniline, the dominating is the Mott charge hopping between well-conducting crystalline ravels embedded into amorphous polymer matrix. The main properties of polyaniline are described in the first part. The theoretical background of the magnetic, relaxation, and dynamics study of nonlinear spin carriers transferring a charge in polyaniline is briefly explicated in the second part. An original data obtained in the EPR study of the nature, relaxation, and dynamics of polarons as well as the mechanism of their transfer in polyaniline chemically modified by sulfuric, hydrochloric, camphorsulfonic, 2-acrylamido-2-methyl-1-propanesulfonic, and para-toluenesulfonic acids up to different doping levels are analyzed in the third part. Some examples of utilization of polyaniline in molecular electronics and spintronics are described.

Krinichnyi, V. I.

2014-06-01

28

Competing effective interactions of Dirac electrons in the Spin-Fermion system

NASA Astrophysics Data System (ADS)

Recently discovered advanced materials, such as heavy fermions, frequently exhibit a rich phase diagram suggesting the presence of different competing interactions. A unified description of the origin of these multiple interactions, albeit very important for the comprehension of such materials is, in general not available. It would be therefore very useful to have a simple model where the common source of different interactions could be possibly traced back. In this work we consider a system consisting in a set of localized spins on a square lattice with antiferromagnetic nearest neighbors interactions and itinerant electrons, which are assumed to be Dirac-like and interact with the localized spins through a Kondo magnetic interaction. This system is conveniently described by the Spin-Fermion model, which we use in order to determine the effective interactions among the itinerant electrons. By integrating out the localized degrees of freedom we obtain a set of different interactions, which includes: a BCS-like superconducting term, a Nambu-Jona-Lasinio-like, excitonic term and a spin-spin magnetic term. The resulting phase diagram is investigated by evaluation of the mean-field free-energy as a function of the relevant order parameters. This shows the competition of the above interactions, depending on the temperature, chemical potential and coupling constants.

Marino, E. C.; Nunes, Lizardo H. C. M.

2014-01-01

29

Dissipative dynamics of a spin in a spin environment with non-uniform coupling

NASA Astrophysics Data System (ADS)

We investigate the reduced dynamics of a central spin coupled to a spin environment with non-uniform coupling. Through using the method of time-dependent density-matrix renormalization group (t-DMRG), we nonperturbatively show the dissipative dynamics of the central spin beyond the case of uniform coupling between the central spin and the environment spins. It is shown that only when the system-environment coupling is weak enough, the central spin system shows Markovian effect and will finally reach the steady state; otherwise, the reduced dynamics is non-Markovian and exhibits a quasi-periodic oscillation. The frequency spectrum and the correlation between the central spin system and the environment are also studied to elucidate the dissipative dynamics of the central spin system for different coupling strengths.

Guo, Y.; Wang, Z. H.; Zhou, D. L.

2014-05-01

30

Entanglement Dynamics of Two Spin Qubits in a Spin Environment with Nonuniform Coupling

NASA Astrophysics Data System (ADS)

We investigate the entanglement dynamics of a two-spin-qubit system coupled to a spin environment with nonuniform coupling through using the time-dependent density-matrix renormalization group method. We show that the entanglement generation and decay depend on the number of environment spins, the coupling strength between the central spin system and the environment, and the initial state of the central spin system.

Guo, Yu; Deng, Hong-Liang

2014-05-01

31

Epoch Lifetimes in the Dynamics of a Competing Population

NASA Astrophysics Data System (ADS)

We propose a dynamical model of a competing population whose agents have a tendency to balance their decisions in time. The model is applicable to financial markets in which the agents trade with finite capital, or other multiagent systems such as routers in communication networks attempting to transmit multiclass traffic in a fair way. We find an oscillatory behavior due to the segregation of agents into two groups. Each group remains winning over epochs. The aggregation of smart agents is able to explain the lifetime distribution of epochs to 8 decades of probability. The existence of the super agents further refines the lifetime distribution of short epochs.

Yeung, C. H.; Ma, Y. P.; Wong, K. Y. Michael

32

Dynamic susceptibility and dynamic correlations in spin ice

NASA Astrophysics Data System (ADS)

Here we calculate the dynamic susceptibility and dynamic correlation function in spin ice using the model of emergent magnetic monopoles. Calculations are based on a method originally suggested for the description of dynamic processes in water ice (non-equilibrium thermodynamics approach). We show that for T\\rightarrow 0 the dynamic correlation function reproduces the transverse dipole correlations (static correlation function) characteristic of spin ice in its ground state and explains in what sense spin ice is non-ergodic. At non-zero temperatures the dynamic correlation function includes an additional longitudinal component which decreases as the temperature decreases. Both terms (transverse and longitudinal) exhibit identical Debye-like dependences on frequency but with different relaxation times: the magnetic Coulomb interaction of monopoles reduces the longitudinal relaxation time with respect to the transverse one. We calculate the dielectric function analogue for the magnetic monopole gas and discuss how the non-equilibrium thermodynamics approach exposes corrections to the Debye-Hückel theory of magnetic monopoles and the concept of “entropic charge”.

Ryzhkin, M. I.; Ryzhkin, I. A.; Bramwell, S. T.

2013-11-01

33

Spin dynamics under local gauge fields in chiral spin-orbit coupling systems

NASA Astrophysics Data System (ADS)

We present a theoretical description of local spin dynamics in magnetic systems with a chiral spin texture and finite spin-orbit coupling (SOC). Spin precession about the relativistic effective magnetic field in a SOC system gives rise to a non-Abelian SU(2) gauge field reminiscent of the Yang-Mills field. In addition, the adiabatic relaxation of electron spin along the local spin yields an U(1) ? U(1) topological gauge (Berry) field. We derive the corresponding equation of motion i.e. modified Landau-Lifshitz-Gilbert (LLG) equation, for the local spin under the influence of these effects. Focusing on the SU(2) gauge, we obtain the spin torque magnitude, and the amplitude and frequency of spin oscillations in this system. Our theoretical estimates indicate significant spin torque and oscillations in systems with large spin-orbit coupling, which may be utilized in technological applications such as current-induced magnetization-switching and tunable microwave oscillators.

Tan, S. G.; Jalil, M. B. A.; Fujita, T.; Liu, X. J.

2011-02-01

34

Spin dynamics simulation of electron spin relaxation in Ni(2 +)(aq).

The ability to quantitatively predict and analyze the rate of electron spin relaxation of open-shell systems is important for electron paramagnetic resonance and paramagnetic nuclear magnetic resonance spectroscopies. We present a combined molecular dynamics (MD), quantum chemistry (QC), and spin dynamics simulation method for calculating such spin relaxation rates. The method is based on the sampling of a MD trajectory by QC calculations, to produce instantaneous parameters of the spin Hamiltonian used, in turn, to numerically solve the Liouville-von Neumann equation for the time evolution of the spin density matrix. We demonstrate the approach by simulating the relaxation of electron spin in an aqueous solution of Ni(2 +) ion. The spin-lattice (T1) and spin-spin (T2) relaxation rates are extracted directly from the simulations of the time dependence of the longitudinal and transverse magnetization, respectively. Good agreement with the available, indirectly obtained experimental data is obtained by our method. PMID:25005279

Rantaharju, Jyrki; Mareš, Ji?í; Vaara, Juha

2014-07-01

35

Dynamically generated pure spin current in single-layer graphene

NASA Astrophysics Data System (ADS)

The conductance mismatch problem limits the spin-injection efficiency significantly, and spin injection into graphene usually requires high-quality tunnel barriers to circumvent the conductance mismatch. We introduce an approach which enables the generation of pure spin current into single-layer graphene (SLG) that is free from electrical conductance mismatch by using dynamical spin injection. An experimental demonstration of spin-pumping-induced spin current generation and spin transport in SLG at room temperature was successfully achieved, and the spin coherence length was estimated to be 1.36 ?m by using a conventional theoretical model based on the Landau-Lifshitz-Gilbert equation. The spin coherence length is proportional to the quality of SLG, which indicates that spin relaxation in SLG is governed by the Elliot-Yafet mechanism, as was reported.

Tang, Zhenyao; Shikoh, Eiji; Ago, Hiroki; Kawahara, Kenji; Ando, Yuichiro; Shinjo, Teruya; Shiraishi, Masashi

2013-04-01

36

Spinning compact binary inspiral. II. Conservative angular dynamics

We establish the evolution equations of the set of independent variables characterizing the 2PN rigorous conservative dynamics of a spinning compact binary, with the inclusion of the leading order spin-orbit, spin-spin, and mass quadrupole-mass monopole effects, for generic (noncircular, nonspherical) orbits. More specifically, we give a closed system of first order ordinary differential equations for the orbital elements of the osculating ellipse and for the angles characterizing the spin orientations with respect to the osculating orbit. We also prove that (i) the relative angle of the spins stays constant for equal mass black holes, irrespective of their orientation, and (ii) the special configuration of equal mass black holes with equal, but antialigned spins, both laying in the plane of motion (leading to the largest recoil found in numerical simulations) is preserved at 2PN level of accuracy, with leading order spin-orbit, spin-spin, and mass quadrupolar contributions included.

Gergely, Laszlo Arpad [Department of Theoretical Physics, University of Szeged, Tisza Lajos krt 84-86, Szeged 6720 (Hungary); Department of Experimental Physics, University of Szeged, Dom ter 9, Szeged 6720 (Hungary)

2010-11-15

37

Generalized competing Glauber-type dynamics and Kawasaki-type dynamics

NASA Astrophysics Data System (ADS)

In this paper, we have given a systematic formulation of a generalized competing mechanism: The Glauber-type single-spin transition mechanism, with probability p, simulates the contact of the system with the heat bath, and the Kawasaki-type spin-pair redistribution mechanism, with probability 1-p, simulates an external energy flux. These two mechanisms are natural generalizations of Glauber's single-spin flipping mechanism and Kawasaki's spin-pair exchange mechanism respectively. On the one hand, the proposed mechanism is, in principle, applicable to arbitrary systems, while on the other hand, our formulation is able to contain a mechanism that just directly combines single-spin flipping and spin-pair exchange in their original form. Compared with the conventional mechanism, the proposed mechanism does not assume the simplified version and leads to a greater influence of temperature. The fact, order for lower temperature and disorder for higher temperature, will be universally true. In order to exemplify this difference, we applied the mechanism to the one-dimensional Ising model and obtained analytical results. We also applied this mechanism to the kinetic Gaussian model and found that above the critical point there will be only paramagnetic phase, while below the critical point, the self-organization as a result of the energy flux will lead the system to an interesting heterophase, instead of the initially guessed antiferromagnetic phase. We studied this process in details.

Zhu, Han; Zhu, Jian-Yang; Zhou, Yang

2002-09-01

38

Generalized competing Glauber-type dynamics and Kawasaki-type dynamics.

In this paper, we have given a systematic formulation of a generalized competing mechanism: The Glauber-type single-spin transition mechanism, with probability p, simulates the contact of the system with the heat bath, and the Kawasaki-type spin-pair redistribution mechanism, with probability 1-p, simulates an external energy flux. These two mechanisms are natural generalizations of Glauber's single-spin flipping mechanism and Kawasaki's spin-pair exchange mechanism respectively. On the one hand, the proposed mechanism is, in principle, applicable to arbitrary systems, while on the other hand, our formulation is able to contain a mechanism that just directly combines single-spin flipping and spin-pair exchange in their original form. Compared with the conventional mechanism, the proposed mechanism does not assume the simplified version and leads to a greater influence of temperature. The fact, order for lower temperature and disorder for higher temperature, will be universally true. In order to exemplify this difference, we applied the mechanism to the one-dimensional Ising model and obtained analytical results. We also applied this mechanism to the kinetic Gaussian model and found that above the critical point there will be only paramagnetic phase, while below the critical point, the self-organization as a result of the energy flux will lead the system to an interesting heterophase, instead of the initially guessed antiferromagnetic phase. We studied this process in details. PMID:12366183

Zhu, Han; Zhu, Jian-Yang; Zhou, Yang

2002-09-01

39

Models for ? + depolarization in spin glasses reflecting dynamical processes

The muon spin depolarization function is calculated for different dynamical processes. Muon diffusion is shown to cause motional narrowing at high temperatures (T»Tf=freezing temperature of the spin glass) as well as at low temperatures (Tf), where the static line is essentially lorentzian due to the randomness of the spin distribution of the dilute system. Different models for µ+ depolarization reflecting

K. Emmerich

1982-01-01

40

Spin-Lattice Dynamics Simulations of Ferromagnetic Iron

NASA Astrophysics Data System (ADS)

We develop a Spin-Lattice Dynamics (SLD) simulation model for ferromagnetic iron where atoms are treated as classical particles with spins. The atoms interact via many-body forces as well as via spin-orientation-dependent forces of the Heisenberg form. The coupling between the lattice and the spin degrees of freedom is described by a coordinate-dependent exchange function. An algorithm for integrating the spin-lattice dynamics equations of motion is based on the 2nd order Suzuki-Trotter decomposition for the non-commuting Liouville evolution operators for atomic coordinates and spins. The notions of the spin thermostat and the spin temperature are introduced through a combined application of the Langevin spin dynamics and the fiuctuation-dissipation theorem. Several applications of the new method described in the paper illustrate the significant effect of the spin degrees of freedom on the dynamics of atomic motion in iron and iron-based alloys, and confirm that the Spin-Lattice Dynamics approach provides a viable framework for performing realistic large-scale simulations of magnetic materials.

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

2008-04-01

41

Dynamic spin fluctuations at T ?0 in a spin-1/2 ferromagnetic kagome lattice

NASA Astrophysics Data System (ADS)

We report magnetization, electron-spin resonance (ESR), and muon-spin relaxation (?SR) measurements on single crystals of the S =1/2 (Cu+2) kagome compound Cu(1,3-benzendicarboxylate). The ?SR is carried to temperatures as low as 45 mK. The spin-Hamiltonian parameters are determined from the analysis of the magnetization and ESR data. We find that this compound has anisotropic ferromagnetic interactions. Nevertheless, no spin freezing is observed even at temperatures two orders of magnitude lower than the coupling constants. In light of this finding, the relation between persistent spin dynamics and spin liquids on kagome lattices is reexamined.

Ofer, Oren; Marcipar, Lital; Ravi Chandra, V.; Gazit, Snir; Podolsky, Daniel; Arovas, Daniel P.; Keren, Amit

2014-05-01

42

Spin Dynamics of a Trapped Spin1 Bose Gas above the Bose-Einstein Transition Temperature

We study collective spin oscillations in a trapped spin-1 Bose gas above the Bose-Einstein transition temperature. Starting\\u000a from the Heisenberg equation of motion, we derive a kinetic equation describing the dynamics of a thermal gas with the spin-1\\u000a internal degree of freedom. Applying the moment method to the kinetic equation, we study spin-wave collective modes with dipole\\u000a symmetry. The dipole

Yuki Endo; Tetsuro Nikuni

2008-01-01

43

In this Letter, we report a new spin ice--Pr2Sn2O7--which appears to have enhanced residual entropy due to the dynamic nature of the spins. Neutron scattering experiments show that at 200 mK, there is a significant amount of magnetic diffuse scattering which can be fit to the dipolar spin-ice model. However, these short-ranged ordered spins have a quasielastic response that is atypical of the canonical spin ices, and suggests that the ground state is dynamic (i.e., composed of locally ordered two-in-two-out spin configurations that can tunnel between energetically equivalent orientations). We report this as an example of a dynamic spin ice down to 200 mK. PMID:19113519

Zhou, H D; Wiebe, C R; Janik, J A; Balicas, L; Yo, Y J; Qiu, Y; Copley, J R D; Gardner, J S

2008-11-28

44

Spin dynamics in tunneling decay of a metastable state

NASA Astrophysics Data System (ADS)

We analyze spin dynamics in the tunneling decay of a metastable localized state in the presence of spin-orbit coupling. We find that the spin polarization at short-time scale is affected by the initial state, while at long-time scale both the probability and the spin density exhibit diffraction-in-time phenomenon. We find that in addition to the tunneling time the tunneling in general can be characterized by a new parameter, the tunneling length. Although the tunneling length is independent of the spin-orbit coupling, it can be accessed by the spin rotation measurement.

Ban, Yue; Sherman, E. Ya.

2012-05-01

45

Spin dynamics of chromium. II. Incommensurate alloys

Since magnetic moments of transition-metal antiferromagnets are created by electron-hole pairs, the spin dynamics of Cr alloys are associated with quasiparticle transitions. This paper uses random-phase approximation to investigate spin dynamics about two different spin-density-wave (SDW) states of incommensurate ({ital I}) alloys with wave vectors {ital Q}{sub {+-}}{sup {prime}}=(2{pi}/{ital a})(0,0,1{+-} {partial_derivative} {prime}). Because of the more complex quasiparticle energies, {ital I} alloys have a richer spectrum of collective excitations than the commensurate ({ital C}) alloys studied previously. Associated with the free energy`s rotational invariance are transverse spin-wave (SW) modes which evolve from each satellite wave vector {ital Q}{sub {+-}}{sup {prime}} with the same temperature-independent mode velocity {ital c}={ital v}{sub {ital F}}/{radical}(3) as in the {ital C} regime. The translational invariance of the ISDW state is responsible for longitudinal phason modes which evolve from the satellite wave vectors and are damped for any nonzero frequency. As {ital T}{r_arrow}{ital T}{sub {ital N}}, the phason mode velocity approaches {ital c}. Together with a related longitudinal damped excitation, the phason modes tilt the SW cones towards {bold G}/2=(2{pi}/{ital a}) (0,0,1) and produce a peak in the {bold G}/2 cross section at 60 meV, as observed experimentally. High-frequency amplitude modes, both transverse and longitudinal, lie near the pair-breaking edge for each satellite, which is about 40{percent} lower than in the {ital C} case. Undamped collective modes called wavons are associated with fluctuations of the SDW wave vectors {ital Q}{sub {plus_minus}}{sup {prime}} about their equilibrium values. Wavon modes were recently observed as peaks in the satellite cross sections between 15 and 20 meV. Our model predicts the temperature and doping dependences of the phason and wavon peaks. {copyright} {ital 1996 The American Physical Society.}

Fishman, R.S. [Solid State Division, Oak Ridge National Lab, Oak Ridge, Tennessee 37831-6032 (United States)] [Solid State Division, Oak Ridge National Lab, Oak Ridge, Tennessee 37831-6032 (United States); [Department of Physics, North Dakota State University, Fargo, North Dakota 58105-5566 (United States); Liu, S.H. [Department of Physics, University of California, San Diego, California 92093 (United States)] [Department of Physics, University of California, San Diego, California 92093 (United States)

1996-09-01

46

Self-consistent treatment of spin and magnetization dynamic effect in spin transfer switching

NASA Astrophysics Data System (ADS)

The effect of itinerant spin moment ( m) dynamic in spin transfer switching has been ignored in most previous theoretical studies of the magnetization ( M) dynamics. Thus in this paper, we proposed a more refined micromagnetic model of spin transfer switching that takes into account in a self-consistent manner of the coupled m and M dynamics. The numerical results obtained from this model further shed insight on the switching profiles of m and M, both of which show particular sensitivity to parameters such as the anisotropy field, the spin torque field, and the initial deviation between m and M.

Guo, Jie; Tan, Seng Ghee; Jalil, Mansoor Bin Abdul; Koh, Dax Enshan; Han, Guchang; Meng, Hao

2011-01-01

47

In this presentation, we report a new spin ice - Pr2Sn2O7 - which appears to have enhanced residual entropy due to the dynamic nature of the spins. Neutron scattering experiments show that at 200 mK, there is a significant amount of magnetic diffuse scattering which can be fit to the dipolar spin ice model. However, these short-ranged ordered spins have

Christopher Wiebe; Haidong Zhou; John Janik; Luis Balicas; Youn-Joon Jo; Yiming Qiu; John Copley; Jason Gardner

2009-01-01

48

In this Letter, we report a new spin ice---Pr2Sn2O7---which appears to have enhanced residual entropy due to the dynamic nature of the spins. Neutron scattering experiments show that at 200 mK, there is a significant amount of magnetic diffuse scattering which can be fit to the dipolar spin-ice model. However, these short-ranged ordered spins have a quasielastic response that is

H. D. Zhou; C. R. Wiebe; J. A. Janik; L. Balicas; Y. J. Yo; Y. Qiu; J. R. D. Copley; J. S. Gardner

2008-01-01

49

Mechanical analogues of spin Hamiltonians and dynamics

NASA Astrophysics Data System (ADS)

Bloch et al. mapped the precession of the spin-half in a magnetic field of variable magnitude and direction to the rotations of a rigid sphere rolling on a curved surface utilizing SU(2)–SO(3) isomorphism. This formalism is extended to study the behaviour of spin–orbit interactions and the mechanical analogy for Rashba–Dresselhauss spin–orbit interaction in two dimensions is presented by making its spin states isomorphic to the rotations of a rigid sphere rolling on a ring. The change in phase of spin is represented by the angle of rotation of sphere after a complete revolution. In order to develop the mechanical analogy for the spin filter, we find that perfect spin filtration of down spin makes the sphere to rotate at some unique angles and the perfect spin filtration of up spin causes the rotations with certain discrete frequencies.

Kaur, Harjeet; Jain, Sudhir R.; Malik, Sham S.

2014-01-01

50

Spin dynamics in atomically assembled antiferromagnets

NASA Astrophysics Data System (ADS)

Antiferromagnetic materials possess ordered magnetic states that have vanishing magnetization. We used a low-temperature scanning tunneling microscope to construct few-atom antiferromagnets. Even-numbered arrays of antiferromagnetically coupled atoms were found to have no net spin. Their shapes can be defined precisely by atom manipulation avoiding uncompensated magnetic moments at the nanoparticle's edge. We use such spin-compensated atomic arrays to study the intrinsic dynamics of nanoscale antiferromagnets [1]. For chains of more than four atoms we observe two Neel-ordered ground states and frequent switching between them. The spontaneous switching rates depend strongly on the number of coupled atoms and we observed magnetic tunneling of the Neel vector for the smallest structures. In arrays with ten or more atoms the residence time in each state can exceed many hours but current-induced switching proceeds at nanosecond speed. These properties enable a model demonstration of dense magnetic data storage that uses antiferromagnets as memory elements. [1] S. Loth, S. Baumann, C. P. Lutz, D. M. Eigler and A. J. Heinrich, Science 335, 196 (2012).

Loth, Sebastian

2013-03-01

51

Scaling of Dynamical Decoupling for Spin Qubits

NASA Astrophysics Data System (ADS)

We investigate the scaling of coherence time T2 with the number of ? pulses n? in a singlet-triplet spin qubit using Carr-Purcell-Meiboom-Gill (CPMG) and concatenated dynamical decoupling (CDD) pulse sequences. For an even numbers of CPMG pulses, we find a power law T2?(n?)?e, with ?e=0.72±0.01, essentially independent of the envelope function used to extract T2. From this surprisingly robust value, a power-law model of the noise spectrum of the environment, S(?)˜?-?, yields ?=?e/(1-?e)=2.6±0.1. Model values for T2n? using ?=2.6 for CPMG with both even and odd n? up to 32 and CDD orders 3 through 6 compare very well with the experiment.

Medford, J.; Cywi?ski, ?.; Barthel, C.; Marcus, C. M.; Hanson, M. P.; Gossard, A. C.

2012-02-01

52

Lattice Instability and Competing Spin Structures in the Double Perovskite Insulator Sr2FeOsO6

NASA Astrophysics Data System (ADS)

The semiconductor Sr2FeOsO6, depending on temperature, adopts two types of spin structures that differ in the spin sequence of ferrimagnetic iron-osmium layers along the tetragonal c axis. Neutron powder diffraction experiments, Fe57 Mössbauer spectra, and density functional theory calculations suggest that this behavior arises because a lattice instability resulting in alternating iron-osmium distances fine-tunes the balance of competing exchange interactions. Thus, Sr2FeOsO6 is an example of a double perovskite, in which the electronic phases are controlled by the interplay of spin, orbital, and lattice degrees of freedom.

Paul, Avijit Kumar; Reehuis, Manfred; Ksenofontov, Vadim; Yan, Binghai; Hoser, Andreas; Többens, Daniel M.; Abdala, Paula M.; Adler, Peter; Jansen, Martin; Felser, Claudia

2013-10-01

53

Lattice instability and competing spin structures in the double perovskite insulator Sr2FeOsO6.

The semiconductor Sr2FeOsO6, depending on temperature, adopts two types of spin structures that differ in the spin sequence of ferrimagnetic iron-osmium layers along the tetragonal c axis. Neutron powder diffraction experiments, 57Fe Mössbauer spectra, and density functional theory calculations suggest that this behavior arises because a lattice instability resulting in alternating iron-osmium distances fine-tunes the balance of competing exchange interactions. Thus, Sr2FeOsO6 is an example of a double perovskite, in which the electronic phases are controlled by the interplay of spin, orbital, and lattice degrees of freedom. PMID:24182298

Paul, Avijit Kumar; Reehuis, Manfred; Ksenofontov, Vadim; Yan, Binghai; Hoser, Andreas; Többens, Daniel M; Abdala, Paula M; Adler, Peter; Jansen, Martin; Felser, Claudia

2013-10-18

54

Spin dynamics of isoelectronic bound excitons in ZnO

NASA Astrophysics Data System (ADS)

Time-resolved optical spin orientation is employed to study spin dynamics of I* and I1* excitons bound to isoelectronic centers in bulk ZnO. It is found that spin orientation at the exciton ground state can be generated using resonant excitation via a higher lying exciton state located at about 4 meV from the ground state. Based on the performed rate equation analysis of the measured spin dynamics, characteristic times of subsequent hole, electron, and direct exciton spin flips in the exciton ground state are determined as being ?hs = 0.4 ns, ?es? 15 ns, and ?ehs? 15 ns, respectively. This relatively slow spin relaxation of the isoelectronic bound excitons is attributed to combined effects of (i) weak e-h exchange interaction, (ii) restriction of the exciton movement due to its binding at the isoelectronic center, and (iii) suppressed spin-orbit coupling for the tightly bound hole.

Chen, S. L.; Chen, W. M.; Buyanova, I. A.

2014-06-01

55

Molecular dynamics, spin dynamics study of phonon-magnon interactions in BCC iron

NASA Astrophysics Data System (ADS)

By combining an atomistic many-body potential (Finnis-Sinclair) with a classical Heisenberg-like spin Hamiltonian, we perform combined molecular and spin dynamics simulations to investigate phonon-magnon interactions in BCC iron. The coupling between atomic and spin degrees of freedom is established via a distance dependent exchange interaction derived from first principles electronic structure calculations. Coupled equations of motion are integrated using a second order Suzuki-Trotter decomposition of the exponential time evolution operator. To investigate the effect of lattice vibrations on spin wave spectrum, we calculate spin-spin and density-density dynamic structure factors S(q, ?), and compare that to the results obtained from pure spin dynamics simulations performed on a rigid lattice. In the presence of lattice vibrations, we observe an additional peak in the longitudinal spin-spin dynamic structure factor which coincides with the peak position in density-density dynanmic structure factor.

Perera, Dilina; Landau, David P.; Stocks, G. Malcolm; Nicholson, Don; Eisenbach, Markus; Yin, Junqi

2013-03-01

56

Coherent Spin Dynamics in Semiconductor Nanostructures

Manipulation of coherent spins in semiconductors without laboratory AC (or in some cases DC) magnetic fields can be driven with the electronic spin-orbit interaction. This relativistic effect produces ``pseudomagnetic'' fields surpassing plausible laboratory magnetic fields by orders of magnitude. The theory of two principal examples will be described here: the coupling between light fields and electron spin in quantum dots,

Michael E. Flatté

2004-01-01

57

NASA Astrophysics Data System (ADS)

We investigate the dynamic nuclear spin polarization in an n-GaAs lateral channel induced by electrical spin injection from a (Ga,Mn)As/n-GaAs spin Esaki diode. Signatures of nuclear spin polarization are studied in both three-terminal and non-local voltage signals, where a strong electron spin depolarization feature is observed close to zero magnetic field. This is due to the large nuclear field induced in the channel through hyperfine interaction between injected electron spins and localized nuclear spins. We study the time evolution of the dynamic nuclear spin polarization and evaluate polarization and relaxation times of nuclear spins in the channel.

Shiogai, J.; Ciorga, M.; Utz, M.; Schuh, D.; Arakawa, T.; Kohda, M.; Kobayashi, K.; Ono, T.; Wegscheider, W.; Weiss, D.; Nitta, J.

2012-11-01

58

ULTRAFAST ELECTRON SPIN DYNAMICS OF AS-GROWN Ga1-xMnxAs WITH APPROPRIATE Mn DOPING

NASA Astrophysics Data System (ADS)

The electron spin dynamics in the as-grown Ga1-xMnxAs films with appropriate Mn doping of x 2-5% is studied using time-resolved magneto-optical Kerr effect measurements. Due to the existence of Mn interstitials, the s-d exchange scattering is found to play an important role for the as-grown Ga1-xMnxAs, and compete with p-d exchange coupling to dominate the electron spin relaxation process. The contribution of electron-electron Coulomb scattering to the electron spin dynamics for the as-grown Ga1-x MnxAs appears to be as important as that of the annealed ones. Our findings are fundamentally important for better understanding the electron spin dynamics in Ga1-xMnxAs for its future spintronic applications.

Yue, Han

2013-06-01

59

Nonlinear dynamics of spin and charge in spin-Calogero model

The fully nonlinear dynamics of spin and charge in spin-Calogero model is studied. The latter is an integrable one-dimensional model of quantum spin-1/2 particles interacting through inverse-square interaction and exchange. Classical hydrodynamic equations of motion are written for this model in the regime where gradient corrections to the exact hydrodynamic formulation of the theory may be neglected. In this approximation variables separate in terms of dressed Fermi momenta of the model. Hydrodynamic equations reduce to a set of decoupled Riemann-Hopf (or inviscid Burgers') equations for the dressed Fermi momenta. We study the dynamics of some nonequilibrium spin-charge configurations for times smaller than the time scale of the gradient catastrophe. We find an interesting interplay between spin and charge degrees of freedom. In the limit of large coupling constant the hydrodynamics reduces to the spin hydrodynamics of the Haldane-Shastry model.

Kulkarni, Manas [Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794-3800 (United States); Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, New York 11973 (United States); Franchini, Fabio [Abdus Salam ICTP, Strada Costiera 11, Trieste 34100 (Italy); Abanov, Alexander G. [Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794-3800 (United States)

2009-10-15

60

Electrical control of single spin dynamics

NASA Astrophysics Data System (ADS)

Over ten years ago, Daniel Loss and David DiVincenzo proposed using the spin of a single electron as a quantum bit. At the time of the proposal, it was not possible to trap a single electron in a device and measure its spin, let alone demonstrate control of quantum coherence. In this talk I will describe recent progress in the field, focusing on two new methods for single spin control that have been developed by my group at Princeton. The first method is based on quantum interference and implements spin-interferometry on a chip. The second method utilizes the strong spin-orbit coupling of InAs. By shifting the orbital position of the electronic wavefunction at gigahertz frequencies, we can control the orientation of a single electron spin and measure the full g-tensor, which exhibits a large anisotropy due to spin-orbit interactions. Both methods for single spin control are orders of magnitude faster than conventional electron spin resonance and allow investigations of single spin coherence in the presence of fluctuating nuclear and spin-orbit fields. I will also describe recent efforts to transfer these methods to silicon quantum dots, where the effects of fluctuating nuclear fields are much smaller.

Petta, Jason

2012-02-01

61

Spin dynamics under local gauge fields in chiral spin-orbit coupling systems

Research Highlights: > We derive a modified LLG equation in magnetic systems with spin-orbit coupling (SOC). > Our results are applied to magnetic multilayers, and DMS and magnetic Rashba systems. > SOC mediated magnetization switching is predicted in rare earth metals (large SOC). > The magnetization trajectory and frequency can be modulated by applied voltage. > This facilitates potential application as tunable microwave oscillators. - Abstract: We present a theoretical description of local spin dynamics in magnetic systems with a chiral spin texture and finite spin-orbit coupling (SOC). Spin precession about the relativistic effective magnetic field in a SOC system gives rise to a non-Abelian SU(2) gauge field reminiscent of the Yang-Mills field. In addition, the adiabatic relaxation of electron spin along the local spin yields an U(1) x U(1) topological gauge (Berry) field. We derive the corresponding equation of motion i.e. modified Landau-Lifshitz-Gilbert (LLG) equation, for the local spin under the influence of these effects. Focusing on the SU(2) gauge, we obtain the spin torque magnitude, and the amplitude and frequency of spin oscillations in this system. Our theoretical estimates indicate significant spin torque and oscillations in systems with large spin-orbit coupling, which may be utilized in technological applications such as current-induced magnetization-switching and tunable microwave oscillators.

Tan, S.G., E-mail: TAN_Seng_Ghee@dsi.a-star.edu.sg [Data Storage Institute, A-STAR (Agency for Science, Technology and Research), DSI Building, 5 Engineering Drive 1, Singapore 117608 (Singapore); Computational Nanoelectronics and Nano-device Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Jalil, M.B.A. [Information Storage Materials Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Computational Nanoelectronics and Nano-device Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Fujita, T. [Information Storage Materials Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Data Storage Institute, A-STAR (Agency for Science, Technology and Research), DSI Building, 5 Engineering Drive 1, Singapore 117608 (Singapore); Computational Nanoelectronics and Nano-device Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Liu, X.J. [Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542 (Singapore)

2011-02-15

62

Nodal trajectories of spin observables and kaon photoproduction dynamics

NASA Astrophysics Data System (ADS)

Spin observables for the reaction ?p-->K+? are examined using three recent dynamical models and are compared to the general features of such observables deduced earlier by Fasano, Tabakin, and Saghai. These general features, such as the energy dependence of spin observables and the location of nodes in their angle dependence, are realized. Several instructive surprises, which occur in this comparison to the conjectures of Fasano et al., are then discussed. The sensitivity of spin observables to isobar and t-channel dynamics is analyzed and suggestions for selecting experiments which provide important dynamical information are presented.

Saghai, Bijan; Tabakin, Frank

1996-01-01

63

Models for mu+ depolarization in spin glasses reflecting dynamical processes

The muon spin depolarization function is calculated for different dynamical processes. Muon diffusion is shown to cause motional narrowing at high temperatures (T≫Tf=freezing temperature of the spin glass) as well as at low temperatures (T

K. Emmerich

1982-01-01

64

Dynamic spin reorientation in orthoferrites irradiated by a laser pulse

NASA Astrophysics Data System (ADS)

A theory of dynamic spin reorientation in an antiferromagnet irradiated by a femtosecond laser pulse has been developed taking into account both the nonthermal effect of the pulse due to the inverse Faraday effect and the thermal effect of the pulse. It has been shown that even a weak heating of the spin subsystem by the pulse can significantly enhance the reorientation effect. The possibility of applying this effect to increase the efficiency of the excitation of the spin oscillations has been considered.

Galkina, E. G.; Mikhailov, I. Yu.; Ivanov, B. A.

2011-08-01

65

Spin dynamics for wave packets in Rashba systems

NASA Astrophysics Data System (ADS)

We explore the spin dynamics of wave packets inside Rashba systems using a spin propagator approach. A spin propagator gives conditional probability amplitude between two points in position and spin space at a time interval [1]. We derive and apply the Rashba spin propagator to localized spin wave packets. We observe several interesting features, such asspin separation, persistent spin helix, bamboo-shooting structure, ripple formation structure, and others [2]. We discuss these features which depend critically on the choice of both the width of the wavepacket and the Rashba coupling strength quantitatively with realistic experimental data. [1].B. C. Hsu and J.-F. S. Van Huele, J. Phys. A: Math. Theor., 42, 475304 (2009). [2]B. C. Hsu and J.-F. S. Van Huele, Phys. Rev. B, 80 , 19XXXX (2009).

Hsu, Bailey C.; van Huele, Jean-Francois S.

2010-03-01

66

Dynamics of Magnetic Charges in Artificial Spin Ice

Artificial spin ice has been recently implemented in two-dimensional arrays of mesoscopic magnetic wires. We propose a theoretical model of magnetization dynamics in artificial spin ice under the action of an applied magnetic field. Magnetization reversal is mediated by domain walls carrying two units of magnetic charge. They are emitted by lattice junctions when the local field exceeds a critical

Paula Mellado; Olga Petrova; Yichen Shen; Oleg Tchernyshyov

2010-01-01

67

Self-quenching of nuclear spin dynamics in the central spin problem

NASA Astrophysics Data System (ADS)

We consider, in the framework of the central spin s =1/2 model, driven dynamics of two electrons in a double quantum dot subject to hyperfine interaction with nuclear spins and spin-orbit coupling. The nuclear subsystem dynamically evolves in response to Landau-Zener singlet-triplet transitions of the electronic subsystem controlled by external gate voltages. Without noise and spin-orbit coupling, subsequent Landau-Zener transitions die out after about 104 sweeps, the system self-quenches, and nuclear spins reach one of the numerous glassy dark states. We present an analytical model that captures this phenomenon. We also account for the multi-nuclear-specie content of the dots and numerically determine the evolution of around 107 nuclear spins in up to 2×105 Landau-Zener transitions. Without spin-orbit coupling, self-quenching is robust and sets in for arbitrary ratios of the nuclear spin precession times and the waiting time between Landau-Zener sweeps as well as under moderate noise. In the presence of spin-orbit coupling of a moderate magnitude, and when the waiting time is in resonance with the precession time of one of the nuclear species, the dynamical evolution of nuclear polarization results in stroboscopic screening of spin-orbit coupling. However, small deviations from the resonance or strong spin-orbit coupling destroy this screening. We suggest that the success of the feedback loop technique for building nuclear gradients is based on the effect of spin-orbit coupling.

Brataas, Arne; Rashba, Emmanuel I.

2014-01-01

68

Coherent dynamics of a single spin interacting with an adjustable spin bath.

Phase coherence is a fundamental concept in quantum mechanics. Understanding the loss of coherence is paramount for future quantum information processing. We studied the coherent dynamics of a single central spin (a nitrogen-vacancy center) coupled to a bath of spins (nitrogen impurities) in diamond. Our experiments show that both the internal interactions of the bath and the coupling between the central spin and the bath can be tuned in situ, allowing access to regimes with surprisingly different behavior. The observed dynamics are well explained by analytics and numerical simulations, leading to valuable insight into the loss of coherence in spin systems. These measurements demonstrate that spins in diamond provide an excellent test bed for models and protocols in quantum information. PMID:18339902

Hanson, R; Dobrovitski, V V; Feiguin, A E; Gywat, O; Awschalom, D D

2008-04-18

69

Dynamics of a Many-Spin System including Relaxation Effects

NASA Astrophysics Data System (ADS)

The Heisenberg model constitutes an essential stepping stone to understand ferromagnetism and anti-ferromagnetism in magnetic materials. The basic idea is that individual two-spin short-range interactions of atomic magnetic dipoles can give rise to coherent long-range behavior in a lattice structure. These ``classical spins'' are free to rotate and can arrange themselves in a parallel or anti parallel configuration in the ordered state. The local magnetic field acting on the spin arises as the result of the addition of nearest neighbors (NN) spins. In our present project we study the dynamics of N 3-d spins in a two-dimensional square lattice with a NN constant exchange interaction. An additional dissipative Gilbert term is included to allow for the relaxation to the (anti-)ferromagnetic global state. We have developed a Matlab code that preserves the individual spin magnitudes at each time step in the dynamics using a symplectic integration second-order method. We present our results in terms of plots and animations of the spin-behavior on the lattice. In addition we have allowed for a time dependence of the Gilbert term considered as a driving force. The spin domain formation appears as a metastable state in the ferromagnetic case and we are able to follow the corresponding dynamics.

Jung, Soyoung; Berrondo, Manuel

2011-10-01

70

Dynamics, synchronization, and quantum phase transitions of two dissipative spins

We analyze the static and dynamic properties of two Ising-coupled quantum spins embedded in a common bosonic bath as an archetype of dissipative quantum mechanics. First, we elucidate the ground-state phase diagram for an Ohmic and a sub-Ohmic bath using a combination of bosonic numerical renormalization group (NRG), analytical techniques, and intuitive arguments. Second, by employing the time-dependent NRG we investigate the system's rich dynamical behavior arising from the complex interplay between spin-spin and spin-bath interactions. Interestingly, spin oscillations can synchronize due to the proximity of the common non-Markovian bath and the system displays highly entangled steady states for certain nonequilibrium initial preparations. We complement our nonperturbative numerical results by exact analytical solutions when available and provide quantitative limits on the applicability of the perturbative Bloch-Redfield approach at weak coupling.

Orth, Peter P.; Le Hur, Karyn [Department of Physics, Yale University, New Haven, Connecticut 06520 (United States); Roosen, David; Hofstetter, Walter [Institut fuer Theoretische Physik, Johann Wolfgang Goethe-Universitaet, 60438 Frankfurt/Main (Germany)

2010-10-01

71

Optimized dynamical control of state transfer through noisy spin chains

NASA Astrophysics Data System (ADS)

We propose a method of optimally controlling the tradeoff of speed and fidelity of state transfer through a noisy quantum channel (spin-chain). This process is treated as qubit state-transfer through a fermionic bath. We show that dynamical modulation of the boundary-qubits levels can ensure state transfer with the best tradeoff of speed and fidelity. This is achievable by dynamically optimizing the transmission spectrum of the channel. The resulting optimal control is robust against both static and fluctuating noise in the channel?s spin–spin couplings. It may also facilitate transfer in the presence of diagonal disorder (on site energy noise) in the channel.

Zwick, Analia; Álvarez, Gonzalo A.; Bensky, Guy; Kurizki, Gershon

2014-06-01

72

NMR with generalized dynamics of spin and spatial coordinates

This work is concerned with theoretical and experimental aspects of the generalized dynamics of nuclear spin and spatial coordinates under magnetic-field pulses and mechanical motions. The main text begins with an introduction to the concept of ''fictitious'' interactions. A systematic method for constructing fictitious spin-1/2 operators is given. The interaction of spins with a quantized-field is described. The concept of the fictitious interactions under the irradiation of multiple pulses is utilized to design sequences for selectively averaging linear and bilinear operators. Relations between the low-field sequences and high-field iterative schemes are clarified. These relations and the transformation properties of the spin operators are exploited to develop schemes for heteronuclear decoupling of multi-level systems. The resulting schemes are evaluated for heteronuclear decoupling of a dilute spin-1/2 from a spin-1 in liquid crystal samples and from a homonuclear spin-1/2 pair in liquids. A relation between the spin and the spatial variables is discussed. The transformation properties of the spin operators are applied to spatial coordinates and utilized to develop methods for removing the orientational dependence responsible for line broadening in a powder sample. Elimination of the second order quadrupole effects, as well as the first order anisotropies is discussed. It is shown that various sources of line broadening can effectively be eliminated by spinning and/or hopping the sample about judiciously chosen axes along with appropriate radio-frequency pulse sequences.

Lee, Chang Jae

1987-11-01

73

Coherent Spin Dynamics in Semiconductor Nanostructures

NASA Astrophysics Data System (ADS)

Manipulation of coherent spins in semiconductors without laboratory AC (or in some cases DC) magnetic fields can be driven with the electronic spin-orbit interaction. This relativistic effect produces ``pseudomagnetic'' fields surpassing plausible laboratory magnetic fields by orders of magnitude. The theory of two principal examples will be described here: the coupling between light fields and electron spin in quantum dots, and the use of DC electric fields to manipulate spin coherence times in quantum wells. We find that intense coherent optical illumination of quantum dots can generate ultrafast ˜ 1000 Tesla pseudomagnetic fields suitable for electron spin rotation. These effective fields are roughly spherically symmetric for colloidal quantum dots, but for structurally aspherical quantum dots (such as self-assembled dots during molecular beam epitaxy growth) these pseudomagnetic fields are highly anisotropic - large parallel to the growth direction and often a factor of five or ten smaller along perpendicular directions. The structural anisotropy also leads to very anisotropic selection rules for light emission in quantum dot spin-light-emitting-diodes. For the second principal example, manipulation of spin coherence times in quantum wells, the zero-field spin coherence times and the tuning ranges depend strongly on the crystalline orientation of the growth axis. Near room temperature in (110)-grown structures for applied electric fields of 10-100 kV/cm, the tuning range can exceed several orders of magnitude. This work was done in collaboration with W. H. Lau and C. E. Pryor and was supported by DARPA/ARO and an ARO MURI.

Flatté, Michael E.

2004-03-01

74

Dynamics of polarization buildup by spin filtering

NASA Astrophysics Data System (ADS)

There has been much recent research into polarizing an antiproton beam, instigated by the recent proposal from the PAX (Polarized Antiproton eXperiment) project at GSI Darmstadt. It plans to polarize an antiproton beam by repeated interaction with a polarized internal target in a storage ring. The method of polarization by spin filtering requires many of the beam particles to remain within the ring after scattering off the polarized internal target via electromagnetic and hadronic interactions. We present and solve sets of differential equations which describe the buildup of polarization by spin filtering in many different scenarios of interest to projects planning to produce high-intensity polarized beams. These scenarios are: 1) spin filtering of a fully stored beam; 2) spin filtering while the beam is being accumulated, i.e. unpolarized particles are continuously being fed into the beam; 3) the particle input rate is equal to the rate at which particles are being lost due to scattering beyond the ring acceptance angle, the beam intensity remaining constant; 4) increasing the initial polarization of a stored beam by spin filtering; 5) the input of particles into the beam is stopped after a certain amount of time, but spin filtering continues. The rate of depolarization of a stored polarized beam on passing through an electron cooler is also shown to be negligible.

Buttimore, N. H.; O'Brien, D. S.

2008-01-01

75

Dynamics of artificial spin ice: a continuous honeycomb network

We model the dynamics of magnetization in an artificial analogue of spin ice specializing to the case of a honeycomb network of connected magnetic nanowires. The inherently dissipative dynamics is mediated by the emission and absorption of domain walls in the sites of the lattice, and their propagation in its links. These domain walls carry two natural units of magnetic

Yichen Shen; Olga Petrova; Paula Mellado; Stephen Daunheimer; John Cumings; Oleg Tchernyshyov

2012-01-01

76

Gigahertz dynamics of a strongly driven single quantum spin.

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. PMID:19965386

Fuchs, G D; Dobrovitski, V V; Toyli, D M; Heremans, F J; Awschalom, D D

2009-12-11

77

The spin-temperature theory of dynamic nuclear polarization and nuclear spin-lattice relaxation

NASA Technical Reports Server (NTRS)

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.

Byvik, C. E.; Wollan, D. S.

1974-01-01

78

Spin Polarized Electron Scattering from and Spin Dynamics of Ultrathin Magnetic Films

NASA Astrophysics Data System (ADS)

Polarized electron beams interacting with the surface via exchange and spin orbit coupling established themselves as a unique tool for studying magnetic and electronic surface properties. We use the multiple scattering theory of the spin polarized low energy electron diffraction (SPLEED) to study the structural and magnetic properties of Fe bilayer on W(001) substrate. We find the spin orbit asymmetry--a measure of the spin orbit coupling--to be very sensitive to the position of the surface ions. On the other hand, the exchange asymmetry--a measure of the exchange coupling between the beam and substrate electrons--proves to be far less sensitive to changes in magnetic properties of the film. Inelastic electron scattering accompanied by the flip of the incoming beam spin is a potentially powerful probe of magnetic excitations in ultrathin films. We have investigated the spin flip component of the diffuse scattering near the bulk critical temperature of an antiferromagnetically ordered surface. Within the Landau-Ginzburg theory we explore the static correlation function. For Cr(110), we then calculate the intensity of both the diffuse peak near T_{c} and the half -order beams. We find the intensities are within the reach of the state of the art experimental techniques. While the total rate of inelastic scattering integrated over the energy loss is controlled by the static correlation function, the energy resolved loss spectrum requires the knowledge of the spin dynamics. There is currently very little understanding of the spin dynamics of itinerant electron magnetic films. We use the one band Hubbard model to study the transverse dynamic susceptibility of films consisting of magnetic layers with ferromagnetic order within the layers parallel to the surface. The coupling between the layers is arbitrary. The nature of the spin waves and Stoner spectrum is investigated and discussed. It is shown that the SPEELS spectrum contains information about the local magnetic properties of the surface layer.

Plihal, Martin

1995-01-01

79

Ultrafast photo-induced spin and charge dynamics in correlated electron system

NASA Astrophysics Data System (ADS)

Photo-induced phenomena in correlated electron system are one of the attractive themes in recent solid state physics. One of the well known examples is manganites with the perovskite crystal structure. The charge ordered insulating state associated with the antiferromagnetic (AFM) long-range order competes with the ferromagnetic metallic phase. After introduction of the pump photon into the charge-ordered insulating phase, dramatic changes in the optical reflectivity and in the optical Kerr rotation are observed. These results imply that the charge and magnetic structures are changed cooperatively by the photo-irradiation. We present a theoretical study of photo-induced dynamics in a correlated electron system where electronic charge couples with spin and lattice. The generalized double exchange model is analyzed by utilizing the two complementary methods, the exact diagonalization and inhomogeneous Hartree-Fock methods. Time evolutions of the optical absorption spectra, spin correlation, and charge correlation are calculated. There are two time scales in the photo-induced dynamics; the charge and AFM spin orders are collapsed within a short time scale corresponding to 10-100 fs, and the long-range FM spin correlation appears in a long time scale corresponding to a few ps.

Ishihara, Sumio; Kanamori, Yu; Matsueda, Hiroaki

2009-03-01

80

Development of Competence in Dynamic Learning Environments. No. 79.

ERIC Educational Resources Information Center

Perspective Text Analysis is a way to measure competence by measuring the strategy of synthesizing, which intelligence tests or questionnaires cannot measure. This paper proposes the use of Perspective Text Analysis in the study of instructional materials. Perspective Text Analysis has been applied in various learning environments, and the results…

Bierschenk, Inger

81

Spin tunnelling dynamics for spin-1 Bose Einstein condensates in a swept magnetic field

We investigate the spin tunnelling of spin-1 Bose-Einstein condensates in a linearly swept magnetic field with a mean-field treatment. We focus on the two typical alkali Bose atoms 87Rb and 23Na condensates and study their tunnelling dynamics according to the sweep rates of the external magnetic fields. In the adiabatic (i.e. slowly sweeping) and sudden (i.e. fast sweeping) limits, no

Guan-Fang Wang; Li-Bin Fu; Jie Liu

2008-01-01

82

We study the enhancement of spin coherence with periodic, concatenated, or Uhrig dynamical decoupling N-pulse sequences in a spin-1 Bose-Einstein condensate, where the intrinsic dynamical instability in such a ferromagnetically interacting condensate causes spin decoherence and eventually leads to a multiple spatial-domain structure or a spin texture. Our results show that all three sequences successfully enhance the spin coherence by pushing the wave vector of the most unstable mode in the condensate to a larger value. Among the three sequences with the same number of pulses, the concatenated one shows the best performance in preserving the spin coherence. More interestingly, we find that all three sequences exactly follow the same enhancement law, k{sub -}T{sup 1/2}=c, with k{sub -} the wave vector of the most unstable mode, T the sequence period, and c a sequence-dependent constant. Such a law between k{sub -} and T is also derived analytically for an attractive scalar Bose-Einstein condensate subjected to a periodic dynamical decoupling sequence.

Ning Boyuan; Zhuang Jun; Zhang Wenxian [Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Department of Optical Science and Engineering, Fudan University, Shanghai 200433 (China); You, J. Q. [Department of Physics, Fudan University, Shanghai 200433 (China)

2011-07-15

83

Spin dynamics in the generalized ferromagnetic Kondo model for manganites

We calculate the dynamic spin susceptibility in the generalized Kondo model describing the interaction between the band eg electrons and the localized t2g electrons coupled via the antiferromagnetic exchange. We show that the spin-wave spectrum in the ferromagnetic phase has\\u000a acoustic and optical branches in the mean-field approximation. We evaluate the self-energy corrections to the spectrum and\\u000a estimate the damping

N. B. Perkins; N. M. Plakida

1999-01-01

84

Spin dynamics in the generalized ferromagnetic Kondo model for manganites

Dynamical spin susceptibility is calculated for the generalized ferromagnetic Kondo model which describes itinerant $e_{g}$ electrons interacting with localized $t_{2g}$ electrons with antiferromagnetic coupling. The calculations done in the mean field approximation show that the spin-wave spectrum of the system in ferromagnetic state has two branches, acoustic and optic ones. Self-energy corrections to the spectrum are considered and the acoustic

N. B. Perkins; N. M. Plakida

1999-01-01

85

Effects of Spin-polarized Current on Magnetization Dynamics

For the current perpendicular to the plane of the layer in a magnetic multilayer, one needs to add a non-equilibrium spin torque and a non-equilibrium bias magnetic field to the standard Landau-Lifshitz-Gilbert equation for the modeling of magnetization dynamics and hysteresis. The presence of the torque leads to several unique features: 1) the spin torque effectively makes the damping parameter

Shufeng Zhang; Zhanjie Li

2002-01-01

86

Voltage controlled electron spin dynamics in resonant tunnelling devices

NASA Astrophysics Data System (ADS)

We investigate the electron spin dynamics in a p-type GaAs/AlAs resonant tunnelling device by measuring the time- and polarized-resolved photoluminescence (PL) from the GaAs quantum well under a high magnetic field (15 T). The voltage dependence of the PL transients have revealed various tunnelling processes with different time constants that give rise to distinct spin-polarized carriers injected into the double-barrier structure.

Galeti, H. V. A.; Brasil, M. J. S. P.; Gobato, Y. Galv ao; Henini, M.

2014-04-01

87

LETTER TO THE EDITOR: Dynamical crossover in 'hot' spin ice

The magnetic dynamics of the spin ice material Ho2Ti2O7 in its paramagnetic ('hot') phase have been investigated by a combination of neutron spin echo and ac-susceptibility techniques. Relaxation at high temperatures (T > 15 K) is proved to occur by a thermally activated single-ion process that is distinct from the process that dominates at lower temperatures (1 K < T

G. Ehlers; A. L. Cornelius; M. Orendác; M. Kajnaková; T. Fennell; S. T. Bramwell; J. S. Gardner

2003-01-01

88

Preserving electron spin coherence in solids by optimal dynamical decoupling

NASA Astrophysics Data System (ADS)

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 50K to room temperature [1]. Using a seven-pulse optimal dynamical decoupling sequence, we prolonged the spin coherence time to about 30 ms; it would otherwise be about 0.04 ms without control or 6.2 ms under one-pulse control. By comparing experiments with microscopic theories, we have identified the relevant electron spin decoherence mechanisms in the solid. Recently, we demonstrate experimentally that dynamical decoupling can preserve bipartite pseudo-entanglement in phosphorous donors in a silicon system [2]. In particular, the lifetime of pseudo entangled states is extended from 0.4 us in the absence of decoherence control to 30 us in the presence of a two-flip dynamical decoupling sequence. [4pt] [1]. Jiangfeng Du, Xing Rong, Nan Zhao, Ya Wang, Jiahui Yang and R. B. Liu, Preserving electron spin coherence in solids by optimal dynamical decoupling, Nature 461, 1265-1268 (2009). [0pt] [2] Ya Wang, Xing Rong, Pengbo Feng, Wanjie Xu, Bo Chong, Ji-Hu Su, Jiangbin Gong, and Jiangfeng Du, Preservation of bipartite pseudo-entanglement in solids using dynamical decoupling, submitted to Phys. Rev. Lett.

Du, Jiangfeng

2011-03-01

89

Spin dynamics in a two-dimensional quantum gas

NASA Astrophysics Data System (ADS)

We have investigated spin dynamics in a two-dimensional quantum gas. Through spin-changing collisions, two clouds with opposite spin orientations are spontaneously created in a Bose-Einstein condensate. After ballistic expansion, both clouds acquire ring-shaped density distributions with superimposed angular density modulations. The density distributions depend on the applied magnetic field and are well explained by a simple Bogoliubov model. We show that the two clouds are anticorrelated in momentum space. The observed momentum correlations pave the way towards the creation of an atom source with nonlocal Einstein-Podolsky-Rosen entanglement.

Pedersen, Poul L.; Gajdacz, Miroslav; Deuretzbacher, Frank; Santos, Luis; Klempt, Carsten; Sherson, Jacob F.; Hilliard, Andrew J.; Arlt, Jan J.

2014-05-01

90

Configurational Dependence of the Magnetization Dynamics in Spin Valve Systems

NASA Astrophysics Data System (ADS)

Spin current related phenomena in F1/N/F2 spin valve heterostructures, where F is a ferromagnetic layer and N is a nonmagnetic metal layer, are important in modern magnetism. Spin valve theory predicts a spin pumping effect with a precessional relaxation rate that depends on the configuration of F1 and F2 [1]. Using time-resolved x-ray resonant magnetic scattering we report on the precessional dynamics of spin valve systems with parallel (P) and antiparallel (AP) orientation. We observe in Co/Cu/Py spin valve systems an increase of the magnetic damping parameter in Py with changing magnetization direction of Py and Co layers from P to AP orientation [2]. Furthermore we studied the temperature dependence of the spin pumping effect and possible other causes for the configurational dependence of the damping parameter, such as domain wall induced coupling or magnetic dipole coupling [3]. The main focus is on Co/Cu/Py and on Co2MnGe/V/Py trilayers with spin valve properties.[4pt] [1] J.-V. Kim, C. Chappert, JMMM 286, 56 (2005)[0pt] [2] R. Salikhov et al., APL 99, 092509 (2011)[0pt] [3] R. Salikhov et al., PRB 86, 144422 (2012)

Salikhov, Ruslan; Abrudan, Radu; Bruessing, Frank; Westerholt, Kurt; Zabel, Hartmut; Radu, Florin; Garifullin, Ilgiz A.

2013-03-01

91

Nodal trajectories of spin observables and kaon photoproduction dynamics

Spin observables for the reaction {gamma}{ital p}{r_arrow}{ital K}{sup +}{Lambda} are examined using three recent dynamical models and are compared to the general features of such observables deduced earlier by Fasano, Tabakin, and Saghai. These general features, such as the energy dependence of spin observables and the location of nodes in their angle dependence, are realized. Several instructive surprises, which occur in this comparison to the conjectures of Fasano {ital et} {ital al}., are then discussed. The sensitivity of spin observables to isobar and {ital t}-channel dynamics is analyzed and suggestions for selecting experiments which provide important dynamical information are presented. {copyright} {ital 1996 The American Physical Society.}

Saghai, B. [Service de Physique Nucleaire, CEA/DSM/DAPNIA, Centre dEtudes de Saclay, F-91191 Gif-sur-Yvette (France)] [Service de Physique Nucleaire, CEA/DSM/DAPNIA, Centre dEtudes de Saclay, F-91191 Gif-sur-Yvette (France); Tabakin, F. [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States)] [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States)

1996-01-01

92

Dynamics and hysteresis in square lattice artificial spin ice

NASA Astrophysics Data System (ADS)

Dynamical effects under geometrical frustration are considered in a model for artificial spin ice on a square lattice in two dimensions. Each island of the spin ice has a three-component Heisenberg-like dipole moment subject to shape anisotropies that influence its direction. The model has real dynamics, including rotation of the magnetic degrees of freedom, going beyond the Ising-type models of spin ice. The dynamics is studied using a Langevin equation solved via a second-order Heun algorithm. Thermodynamic properties such as the specific heat are presented for different couplings. A peak in specific heat is related to a type of melting-like phase transition present in the model. Hysteresis in an applied magnetic field is calculated for model parameters where the system is able to reach thermodynamic equilibrium.

Wysin, G. M.; Moura-Melo, W. A.; Mól, L. A. S.; Pereira, A. R.

2013-04-01

93

Tunable nonequilibrium dynamics of field quenches in spin ice

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.

Mostame, Sarah; Castelnovo, Claudio; Moessner, Roderich; Sondhi, Shivaji L.

2014-01-01

94

Tunable nonequilibrium dynamics of field quenches in spin ice.

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

Mostame, Sarah; Castelnovo, Claudio; Moessner, Roderich; Sondhi, Shivaji L

2014-01-14

95

Dynamic Advertising Strategies of Competing Durable Good Producers

This work develops a diffusion model which incorporates word-of-mouth and advertising effects for two firms introducing competing brands of a new durable product. The competition between the two firms is formulated as a two-player, nonzero sum Markovian game. The firms are assumed to behave noncooperatively in choosing their advertising strategies and the solution concept is a Nash noncooperative equilibrium. Optimal

Dan Horsky; Karl Mate

1988-01-01

96

Investigating the Problem Solving Competency of Pre Service Teachers in Dynamic Geometry Environment

ERIC Educational Resources Information Center

This study investigated the problem-solving competency of four secondary pre service teachers (PSTs) of University of London as they explored geometry problems in dynamic geometry environment (DGE) in 2004. A constructivist experiment was designed in which dynamic software Cabri-Geometre II (hereafter Cabri) was used as an interactive medium.…

Haja, Shajahan

2005-01-01

97

Dynamics of spinning spacecraft during the deployment of flexible boom

NASA Technical Reports Server (NTRS)

The effect of flexibility on the dynamics of a spinning symmetrical spacecraft during the extension (or retraction) of boom-type appendages is treated by modeling the appendages as compound spherical pendula with varying lengths. Both boom stiffness and structural damping are included. For constant boom length the resulting linearized equations of motion contain periodic coefficients involving the spin frequency. A bounded transformation converts this system into a kinematically equivalent one (with only constant coefficients), whose stability is analyzed using the Kelvin-Tait-Chetaev theorem. The dynamics during extension is predicted by numerical simulation of the nonlinear equations.

James, P. K.; Beinum, P. M.

1978-01-01

98

Magnetic monopole dynamics in spin ice

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

L. D. C. Jaubert; P. C. W. Holdsworth

2011-01-01

99

Dynamics of spin torque switching in all-perpendicular spin valve nanopillars

NASA Astrophysics Data System (ADS)

We present a systematic experimental study of the spin-torque-induced magnetic switching statistics at room temperature, using all-perpendicularly magnetized spin-valves as a model system. Three physical regimes are distinguished: a short-time ballistic limit below a few nanoseconds, where spin-torque dominates the reversal dynamics from a thermal distribution of initial conditions; a long time limit, where the magnetization reversal probability is determined by spin-torque-amplified thermal activation; and a cross-over regime, where the spin-torque and thermal agitation both contribute. For a basic quantitative understanding of the physical processes involved, an analytical macrospin model is presented which contains both spin-torque dynamics and finite temperature effects. The latter was treated rigorously using a Fokker-Plank formalism, and solved numerically for specific sets of parameters relevant to the experiments to determine the switching probability behavior in the short-time and cross-over regimes. This analysis shows that thermal fluctuations during magnetization reversal greatly affect the switching probability over all the time scales studied, even in the short-time limit.

Liu, H.; Bedau, D.; Sun, J. Z.; Mangin, S.; Fullerton, E. E.; Katine, J. A.; Kent, A. D.

2014-05-01

100

Quantum dynamics of two-spin-qubit systems.

The aim of this topical review is a systematic and concise presentation of the results of a series of theoretical works on the quantum dynamics of two-spin-qubit systems towards the elaboration of a physical mechanism of the quantum information transfer between two spin-qubits. For this purpose the main attention is paid to exactly solvable models of two-spin-qubit systems, since the analytical expressions of the elements of their reduced density matrices explicitly exhibit the mutual dependence of the quantum information encoded into the spin-qubits. The treatment of their decoherence due to the interaction with the environment is performed in the Markovian approximation. Rate equations for axially symmetric systems of two coupled spin-qubits non-interacting, as well as interacting, with the environment are exactly solved. It is shown how the solutions of rate equations demonstrate the physical mechanism of the quantum information exchange between the spin-qubits. This mechanism holds also in all two-spin-qubit systems whose rate equations can be solved only by means of numerical calculations. Exact solutions of rate equations for two uncoupled spin-qubits interacting with two separate environments reveal an interesting physical phenomenon in the time evolution of the qubit-qubit entanglement generated by their interaction with the environments: the entanglement sudden death and revival. A two-spin-qubit system with an asymptotically decoherence free subspace was also explicitly constructed. The presented calculations and reasonings can be extended for application to the study of spin-qubit chains or networks. PMID:21828484

Nguyen, Van Hieu

2009-07-01

101

NASA Astrophysics Data System (ADS)

Solid-state spin qubits are promising candidates for quantum computation and quantum communication applications, for which long coherence times are a prerequisite. In the case of single Nitrogen-Vacancy (NV) centers, the coherence times are often limited by interactions with the surrounding nuclear environment. In this poster we present recent experimental results demonstrating the detection of individual nuclear spins weakly coupled to single electronic spin defects beyond the ``T2-star'' limit using dynamical decoupling pulse sequences. We take advantage of the coherent nature of the hyperfine interaction to probe the nuclear environment of individual NV centers, and to identify the nearby nuclear spins and determine their coupling strengths and relative positions to the NV. We observe coupling strengths ranging from 2 MHz down to 46 kHz, well below the limit imposed by ``T2-star,'' and observe multiple nuclei coupled to a single NV. We discuss potential applications of this technique in magnetometry and quantum information science.

Unterreithmeier, Quirin; Kolkowitz, Shimon; Bennett, Steven; Lukin, Mikhail

2012-06-01

102

Spin dynamics of chromium. I. Formalism and commensurate alloys

The spin dynamics of chromium alloys are produced by the fluctuations about a spin-density wave (SDW) consisting of bound electron-hole pairs. While commensurate ({ital C}) alloys have a single SDW with wave vector {ital G}/2=2{pi}/{ital a}, incommensurate ({ital I}) alloys have two SDW{close_quote}s with wave vectors on either side of {ital G}/2. Spin fluctuations with frequency {omega} and wave vector {ital q} correspond to possible quasiparticle transitions between the two ({ital C}) or three ({ital I}) bands of hybridized electron and hole energies with energy change {omega} and momentum change {ital q}. This paper develops the random-phase approximation for the spin dynamics of both {ital C} and {ital I} alloys. The collective excitations of {ital C} alloys consist of a transverse spin-wave (SW) mode with linear dispersion and a longitudinal amplitude mode. Incoherent spin fluctuations lie above the amplitude mode frequency and below the SW frequency. While the SW mode involves the rigid rotation of the local magnetic moments, the amplitude mode involves the oscillation of the SDW amplitude, which decays in time according to a power law. {copyright} {ital 1996 The American Physical Society.}

Fishman, R.S. [Solid State Division, Oak Ridge National Lab, Oak Ridge, Tennessee 37831-6032 (United States)] [Solid State Division, Oak Ridge National Lab, Oak Ridge, Tennessee 37831-6032 (United States); [Department of Physics, North Dakota State University, Fargo, North Dakota 58105-5566 (United States); Liu, S.H. [Department of Physics, University of California, San Diego, California 92093 (United States)] [Department of Physics, University of California, San Diego, California 92093 (United States)

1996-09-01

103

Spinor dynamics in an antiferromagnetic spin-1 thermal Bose gas.

We present experimental observations of coherent spin-population oscillations in a cold thermal, Bose gas of spin-1 23Na atoms. The population oscillations in a multi-spatial-mode thermal gas have the same behavior as those observed in a single-spatial-mode antiferromagnetic spinor Bose-Einstein condensate. We demonstrate this by showing that the two situations are described by the same dynamical equations, with a factor of 2 change in the spin-dependent interaction coefficient, which results from the change to particles with distinguishable momentum states in the thermal gas. We compare this theory to the measured spin population evolution after times up to a few hundreds of ms, finding quantitative agreement with the amplitude and period. We also measure the damping time of the oscillations as a function of magnetic field. PMID:23889412

Pechkis, H K; Wrubel, J P; Schwettmann, A; Griffin, P F; Barnett, R; Tiesinga, E; Lett, P D

2013-07-12

104

Coherent spin dynamics of polaritons in semiconductor microcavities

NASA Astrophysics Data System (ADS)

The influence of the strong light-matter coupling in semiconductor III-V microcavities on polariton spin dynamics is studied in the spontaneous emission regime. Under resonant pulsed excitation, we observe a quenching of spin and alignment relaxation when the polariton is photon-like. These behaviours are attributed to the very small value of the long-range electron-hole exchange term of Coulomb interaction within the excitonic component of the quasi-particle and to the weakness of polariton-polariton Coulomb scattering via the inter-exciton short-range exchange interaction. We investigate then the polariton coherent spin dynamics. Coherence decay occurs in two steps: at short time delay, the polariton keeps the phase memory of the excitation pulse. We show that it is thus possible to manipulate the polariton spin and alignment within the optical dephasing time T2 using the temporal coherent control technique. In a second step (t > T2), optical coherence vanishes, but spin coherences survive and spin quantum beats experiments can be performed within the spin relaxation time under transverse magnetic field. We observe an electron-hole spin correlation within the excitonic component of the quasi-particle under resonant excitation; an increase of the absolute value of the electron effective transverse Landé g-factor with the excitonic character of polaritons is evidenced, which is the consequence of the strong coupling regime. The main experimental features are well accounted by a model taking into account only two classes of excitations in the lower polariton branch.

Renucci, P.; Amand, T.; Marie, X.

2003-10-01

105

Spin dynamics simulations for a nanoscale Heisenberg antiferromagnet

NASA Astrophysics Data System (ADS)

Thermoinduced magnetization(TiM) is a novel response which was predicted to occur in nanoscale antiferromagnetic materials. Extensive Monte Carlo simulations footnotetextG. Brown, A. Janotti, M. Eisenbach, and G. M. Stocks, Phys.Rev.B 72, 140405(2005) have shown that TiM is an intrinsic property of the antiferromagnetic classical Heisenberg model below the Neel temperature. To obtain a fundamental understanding of TiM, spin dynamics(SD) simulations are performed to study the spin wave behavior, which seems to be the cause of TiM. A classical Heisenberg model with an antiferromagnetic nearest-neighbor exchange interaction and uniaxial single-site anisotropy is studied. Simple-cubic lattices with free boundary conditions are used. We employed the fast spin dynamics algorithms with fourth-order Suzuki-Trotter decompositions of the exponential operator. Additional small excitation peaks due to surface effects are found in transverse S(q,w).

Hou, Zhuofei; Landau, D. P.; Brown, G.; Stocks, G. M.

2010-03-01

106

Controlling the quantum dynamics of a mesoscopic spin bath in diamond

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.

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

2012-01-01

107

Coherent and Dissipative Spin Dynamics in N Electron Systems

We investigate the ensemble averaged evolution of N-electron systems dynamically coupled to a statistical environment. The electrons are characterized by their spatial and by their spin properties. While the Hilbert space for single electrons is given by the tensor product of the Hilbert spaces associated with both properties, the corresponding Hilbert space for N-electron systems cannot be factorized. Consequently, quantum

F. A. Reuse; V. de Coulon; K. Maschke

2004-01-01

108

Coherent and Dissipative Spin Dynamics in N-Electron Systems

We investigate the ensemble averaged evolution of N-electron systems dynamically coupled to a statistical environment. The electrons are characterized by their spatial and by their spin properties. While the Hilbert space for single electrons is given by the tensor product of the Hilbert spaces associated with both properties, the corresponding Hilbert space for N-electron systems cannot be factorized. Consequently, quantum

F. A. Reuse; V. de Coulon; K. Maschke

2004-01-01

109

Dynamics of quantum discord under decoherence from a spin environment

The effect of decoherence from a spin environment on quantum discord of two-qubit states is investigated. Our results imply that the dynamics of quantum discord depend not only on the white noise in the Werner state, the coupling strength, and the number of the freedom degrees of the environment but also on the tunneling elements of the environment and the

Xiao San Ma; Guang Xing Zhao; Jia Yan Zhang; An Min Wang

2011-01-01

110

Dynamics of carrions in the spin-fermion model.

National Technical Information Service (NTIS)

The spectrum of hole quasiparticles (carrions) and the role of magnetic correlations has been considered in the framework of spin-fermion (Kondo-Heisenberg) model by means of the equation-of-motion method. The hole quasiparticle dynamics has been discusse...

A. L. Kuzemskij D. Marvakov

1996-01-01

111

Dynamics of nanospheres: Spin waves and collective plasmons

This work investigates the dynamic response of nanospheres. We explore two seemingly different, but nonetheless conceptually related areas. Our first studies were directed toward the microwave response of nanoscale ferromagnetic spheres and arrays of such spheres, where spin excitations are of interest. Then we turn our attention to the collective plasmons of nanoscale metallic structures, and their influence on important

Ping Chu

2007-01-01

112

Vertex Dynamics in Finite Two-Dimensional Square Spin Ices

Local magnetic ordering in artificial spin ices is discussed from the point of view of how geometrical frustration controls dynamics and the approach to steady state. We discuss the possibility of using a particle picture based on vertex configurations to interpret the time evolution of magnetic configurations. Analysis of possible vertex processes allows us to anticipate different behaviors for open

Zoe Budrikis; Paolo Politi; R. L. Stamps

2010-01-01

113

Dynamics of magnetization in artificial spin ice on kagome

We model magnetization dynamics in artificial spin ice on kagome under an applied magnetic field. Magnetization reversal is mediated by domain walls carrying two units of magnetic charge emitted from and absorbed by lattice junctions and propagating along the wires. The Coulomb interaction between magnetic charges induces avalanches in magnetization reversal. Distributions of avalanche lengths for various angles between the

Olga Petrova; Yichen Shen; Paula Mellado; Oleg Tchernyshyov

2011-01-01

114

Optimal Controller Tested for a Magnetically Suspended Five-Axis Dynamic Spin Rig.

National Technical Information Service (NTIS)

NASA Glenn Research Center's Structural Mechanics and Dynamics Branch has developed a fully suspended magnetic bearing system for their Dynamic Spin Rig, which performs vibration tests of turbomachinery blades and components under spinning conditions in a...

B. B. Choi

2003-01-01

115

NASA Astrophysics Data System (ADS)

We investigate the effect of ring exchange on the ground-state properties and magnetic excitations of the S =1/2 Heisenberg model on the anisotropic triangular lattice with ring exchange at T =0 using linear spin-wave theory. Classically, we find stable Néel, spiral and collinear magnetically ordered phases. Upon including quantum fluctuations to the model, linear spin-wave theory shows that ring exchange induces a large quantum disordered region in the phase diagram, completely wiping out the classically stable collinear phase. Analysis of the spin-wave spectra for each of these three models demonstrates that the large spin-liquid phase observed in the full model is a direct manifestation of competing classical orders. To understand the origin of these competing phases, we introduce models where either the four spin contributions from ring exchange, or the renormalization of the Heisenberg terms due to ring exchange are neglected. We find that these two terms favor rather different physics.

Holt, Michael; Powell, Ben J.; Merino, Jaime

2014-05-01

116

Spin dynamics of paramagnetic centers with anisotropic g tensor and spin of 1/2

NASA Astrophysics Data System (ADS)

The influence of g tensor anisotropy on spin dynamics of paramagnetic centers having real or effective spin of 1/2 is studied. The g anisotropy affects both the excitation and the detection of EPR signals, producing noticeable differences between conventional continuous-wave (cw) EPR and pulsed EPR spectra. The magnitudes and directions of the spin and magnetic moment vectors are generally not proportional to each other, but are related to each other through the g tensor. The equilibrium magnetic moment direction is generally parallel to neither the magnetic field nor the spin quantization axis due to the g anisotropy. After excitation with short microwave pulses, the spin vector precesses around its quantization axis, in a plane that is generally not perpendicular to the applied magnetic field. Paradoxically, the magnetic moment vector precesses around its equilibrium direction in a plane exactly perpendicular to the external magnetic field. In the general case, the oscillating part of the magnetic moment is elliptically polarized and the direction of precession is determined by the sign of the g tensor determinant (g tensor signature). Conventional pulsed and cw EPR spectrometers do not allow determination of the g tensor signature or the ellipticity of the magnetic moment trajectory. It is generally impossible to set a uniform spin turning angle for simple pulses in an unoriented or 'powder' sample when g tensor anisotropy is significant.

Maryasov, Alexander G.; Bowman, Michael K.

2012-08-01

117

Spin dynamics of paramagnetic centers with anisotropic g tensor and spin of 1/2.

The influence of g tensor anisotropy on spin dynamics of paramagnetic centers having real or effective spin of 1/2 is studied. The g anisotropy affects both the excitation and the detection of EPR signals, producing noticeable differences between conventional continuous-wave (cw) EPR and pulsed EPR spectra. The magnitudes and directions of the spin and magnetic moment vectors are generally not proportional to each other, but are related to each other through the g tensor. The equilibrium magnetic moment direction is generally parallel to neither the magnetic field nor the spin quantization axis due to the g anisotropy. After excitation with short microwave pulses, the spin vector precesses around its quantization axis, in a plane that is generally not perpendicular to the applied magnetic field. Paradoxically, the magnetic moment vector precesses around its equilibrium direction in a plane exactly perpendicular to the external magnetic field. In the general case, the oscillating part of the magnetic moment is elliptically polarized and the direction of precession is determined by the sign of the g tensor determinant (g tensor signature). Conventional pulsed and cw EPR spectrometers do not allow determination of the g tensor signature or the ellipticity of the magnetic moment trajectory. It is generally impossible to set a uniform spin turning angle for simple pulses in an unoriented or 'powder' sample when g tensor anisotropy is significant. PMID:22743542

Maryasov, Alexander G; Bowman, Michael K

2012-08-01

118

Spin dynamics of paramagnetic centers with anisotropic g tensor and spin of 1/2

The influence of g tensor anisotropy on spin dynamics of paramagnetic centers having real or effective spin of 1/2 is studied. The g anisotropy affects both the excitation and the detection of EPR signals, producing noticeable differences between conventional continuous-wave (cw) EPR and pulsed EPR spectra. The magnitudes and directions of the spin and magnetic moment vectors are generally not proportional to each other, but are related to each other through the g tensor. The equilibrium magnetic moment direction is generally parallel to neither the magnetic field nor the spin quantization axis due to the g anisotropy. After excitation with short microwave pulses, the spin vector precesses around its quantization axis, in a plane that is generally not perpendicular to the applied magnetic field. Paradoxically, the magnetic moment vector precesses around its equilibrium direction in a plane exactly perpendicular to the external magnetic field. In the general case, the oscillating part of the magnetic moment is elliptically polarized and the direction of precession is determined by the sign of the g tensor determinant (g tensor signature). Conventional pulsed and cw EPR spectrometers do not allow determination of the g tensor signature or the ellipticity of the magnetic moment trajectory. It is generally impossible to set a uniform spin turning angle for simple pulses in an unoriented or ‘powder’ sample when g tensor anisotropy is significant.

Maryasov, Alexander G.

2012-01-01

119

SPIN DYNAMICS IN AGS AND RHIC.

A fundamental aspect of particle physics is the spin of the particles. With polarized beams, the internal structure of the proton may be probed in ways that are unattainable with unpolarized beams. The Relativistic Heavy Ion Collider (RHIC) has the unique capability of colliding protons with both transverse and longitudinal polarization at center-of-mass energies up to 500 GeV. In this paper we examine the methods used to accelerate and manipulate polarized proton beams in RHIC and its injectors. Special techniques include the use of a partial Siberian snake and an ac dipole in the AGS. In RHIC we use four superconducting helical Siberian snakes (two per ring) for acceleration, and eight superconducting helical rotators for independent control of polarization directions at two interaction regions.

Mackay, W W; Bai, M; Courant, E D; Brown, K; Glenn, W; Huang, H; Luccio, A; Ptitsyn, V; Roser, T; Satogata, T; Ltepikian, S; Tsoupas, N

2003-05-12

120

Spin dynamics of a tetrahedral cluster magnet

NASA Astrophysics Data System (ADS)

We study the magnetism of a lattice of coupled tetrahedral spin-1/2 clusters which might be of relevance to the tellurate compounds Cu2Te2O5X2, with X=Cl, Br. Using the flow equation method we perform a series expansion in terms of the inter-tetrahedral exchange couplings starting from the quadrumer limit. Results will be given for the magnetic instabilities of the quadrumer phase and the dispersion of elementary triplet excitations. In limiting cases of our model of one- or two-dimensional character we show our results to be consistent with findings on previously investigated decoupled tetrahedral chains and the Heisenberg model on the 1/5-depleted square lattice.

Brenig, Wolfram

2003-02-01

121

muSR investigation of spin dynamics in the spin-ice material Dy2Ti2O7

We present a detailed muon spin relaxation (mu+SR) study of the spin-ice material Dy2Ti2O7. Polycrystalline samples of this material have been studied in the temperature range 0.02 K

J. Lago; S. J. Blundell; C. Baines

2007-01-01

122

Ultrafast coherent control of Spin- and magnetization dynamics

NASA Astrophysics Data System (ADS)

The manipulating of the electron spin is not only relevant for magnetic storage but may also lead to the development of novel electronic devices with new characteristics (so-called spintronics). Therefore, the investigations of the physical mechanisms underlying the manipulation of electron spin in ferromagnets, semiconductors and hybrid ferromagnet/semiconductor structures constitute at present an exciting area of research. Due to the fact that in antiferromagnets no angular momentum is associated with the order parameter, spin dynamics in these materials is intrinsically much faster than in ferromagnets, expanding the area of spin-dynamics even more ^[1]. Femto-second laser excitation opens the way to excite magnetic systems on a time scale much shorter than fundamental time scales such as spin-lattice relaxation or precession times. This has already lead to surprising and exciting results like changes in magnetization on a sub-picoscond time scale ^[2]. Fs laser pulses can also be used to generate short magnetic field pulses, that allow coherent control of the magnetization dynamics ^[3] . Recent progress in this area will be discussed, demonstrating in particular the use of time resolved magneto-optical methods to investigate the static and dynamic properties of magnetically ordered structures and the possibility of direct spin manipulation with optical fields^[4,5]. [1] A. V. Kimel, A. Kirilyuk, A. Tsvetkov, R. V. Pisarev, and Th. Rasing, Nature 429 850 (2004). [2] Spin Dynamics in Confined Magnetic Structures I-II, edited by B. Hillebrands and K. Ounadjela (Springer-Verlag, Berlin, 2002-2003). [3] Th. Gerrits, H. A. M. van den Berg, J. Hohlfeld, L. Bär, and Th. Rasing, Nature 418, 509 (2002). [4] A. Kimel, A. Kirilyuk, P.A. Usachev, R.V. Pisarev, A.M. Balbashov and Th. Rasing, Nature 435, 655 (2005) [5] F. Hansteen, A.V. Kimel, A. Kirilyuk and Th. Rasing, PRL 95, 047402-1 (2005). Acknowledgements This work was partially supported by the European IST network SPINOSA, the RTN network DYNAMICS, the Russian Foundation for Basic Research (RFBR), Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) as well as Stichting voor Fundamenteel Onderzoek der Materie (FOM).

Rasing, Theo

2006-03-01

123

On the Spin-axis Dynamics of a Moonless Earth

NASA Astrophysics Data System (ADS)

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 coefficient 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.

Li, Gongjie; Batygin, Konstantin

2014-07-01

124

Global attractors and extinction dynamics of cyclically competing species.

Transitions to absorbing states are of fundamental importance in nonequilibrium physics as well as ecology. In ecology, absorbing states correspond to the extinction of species. We here study the spatial population dynamics of three cyclically interacting species. The interaction scheme comprises both direct competition between species as in the cyclic Lotka-Volterra model, and separated selection and reproduction processes as in the May-Leonard model. We show that the dynamic processes leading to the transient maintenance of biodiversity are closely linked to attractors of the nonlinear dynamics for the overall species' concentrations. The characteristics of these global attractors change qualitatively at certain threshold values of the mobility and depend on the relative strength of the different types of competition between species. They give information about the scaling of extinction times with the system size and thereby the stability of biodiversity. We define an effective free energy as the negative logarithm of the probability to find the system in a specific global state before reaching one of the absorbing states. The global attractors then correspond to minima of this effective energy landscape and determine the most probable values for the species' global concentrations. As in equilibrium thermodynamics, qualitative changes in the effective free energy landscape indicate and characterize the underlying nonequilibrium phase transitions. We provide the complete phase diagrams for the population dynamics and give a comprehensive analysis of the spatio-temporal dynamics and routes to extinction in the respective phases. PMID:23767569

Rulands, Steffen; Zielinski, Alejandro; Frey, Erwin

2013-05-01

125

Global attractors and extinction dynamics of cyclically competing species

NASA Astrophysics Data System (ADS)

Transitions to absorbing states are of fundamental importance in nonequilibrium physics as well as ecology. In ecology, absorbing states correspond to the extinction of species. We here study the spatial population dynamics of three cyclically interacting species. The interaction scheme comprises both direct competition between species as in the cyclic Lotka-Volterra model, and separated selection and reproduction processes as in the May-Leonard model. We show that the dynamic processes leading to the transient maintenance of biodiversity are closely linked to attractors of the nonlinear dynamics for the overall species’ concentrations. The characteristics of these global attractors change qualitatively at certain threshold values of the mobility and depend on the relative strength of the different types of competition between species. They give information about the scaling of extinction times with the system size and thereby the stability of biodiversity. We define an effective free energy as the negative logarithm of the probability to find the system in a specific global state before reaching one of the absorbing states. The global attractors then correspond to minima of this effective energy landscape and determine the most probable values for the species’ global concentrations. As in equilibrium thermodynamics, qualitative changes in the effective free energy landscape indicate and characterize the underlying nonequilibrium phase transitions. We provide the complete phase diagrams for the population dynamics and give a comprehensive analysis of the spatio-temporal dynamics and routes to extinction in the respective phases.

Rulands, Steffen; Zielinski, Alejandro; Frey, Erwin

2013-05-01

126

Atomistic spin dynamics of low-dimensional magnets

NASA Astrophysics Data System (ADS)

We investigate the magnetic properties of a range of low-dimensional ferromagnets using a combination of first-principles calculations and atomistic spin dynamics simulations. This approach allows us to evaluate the ground state and finite temperature properties of experimentally well characterized systems such as Co/Cu(111), Co/Cu(001), Fe/Cu(001) and Fe/W(110), for different thicknesses of the magnetic layer. We compare our calculated spin wave spectra with experimental data available in the literature, and find a good quantitative agreement. We also predict magnon spectra for systems for which no experimental data exist at the moment, and estimate the role of temperature effects.

Bergqvist, Lars; Taroni, Andrea; Bergman, Anders; Etz, Corina; Eriksson, Olle

2013-04-01

127

Dynamics of magnetic charges in artificial spin ice.

Artificial spin ice has been recently implemented in two-dimensional arrays of mesoscopic magnetic wires. We propose a theoretical model of magnetization dynamics in artificial spin ice under the action of an applied magnetic field. Magnetization reversal is mediated by domain walls carrying two units of magnetic charge. They are emitted by lattice junctions when the local field exceeds a critical value Hc required to pull apart magnetic charges of opposite sign. Positive feedback from Coulomb interactions between magnetic charges induces avalanches in magnetization reversal. PMID:21231135

Mellado, Paula; Petrova, Olga; Shen, Yichen; Tchernyshyov, Oleg

2010-10-29

128

Effects of Spin-polarized Current on Magnetization Dynamics

NASA Astrophysics Data System (ADS)

For the current perpendicular to the plane of the layer in a magnetic multilayer, one needs to add a non-equilibrium spin torque and a non-equilibrium bias magnetic field to the standard Landau-Lifshitz-Gilbert equation for the modeling of magnetization dynamics and hysteresis. The presence of the torque leads to several unique features: 1) the spin torque effectively makes the damping parameter vary with time, magnetic field and the current density, 2) the spin torque can control the precession frequencies during the magnetization reversal, and 3) there is new phase boundaries where the solutions are precessional, i.e., as if the system has no damping at all. By using the micromagnetic modeling, we quantitatively calculate I-H (I is the current and H is the external magnetic field) phase boundaries and hysteresis for a magnetic trilayer structure. The possible experimental consequences will be discussed. Research supported by DARPA-MURI.

Zhang, Shufeng; Li, Zhanjie

2002-03-01

129

Long-term orbital and spin dynamics of Mars

NASA Technical Reports Server (NTRS)

This review of the long-term dynamical behavior of Mars covers secular variations of the orbit, oscillations of the obliquity, and polar wandering. Calculations of the large-scale obliquity oscillations of Mars are updated using the most recent orbit theory and contrasted with the earth. The motion for Mars is characterized by about 100,000-yr oscillations driven by differential spin axis and orbit plane precession rates during which the obliquity may change by as much as about 20 deg. The possible role of spin-orbit secular resonances to the spin axis histories of the earth and Mars is also considered. Numerical integrations of the equations of motion indicate that Mars may have passed through resonance as little as 5 Myr ago and that obliquities approaching about 45 deg could have been achieved during such an event.

Ward, William R.

1992-01-01

130

Ultrafast spin dynamics in half-metallic ferromagnetic thin film

NASA Astrophysics Data System (ADS)

Manipulation of electron spins by optical means is anticipated to play a key role in future high-density magnetic storage technology. The ability to maneuver spins beyond thermal excitation regime is of great interests because of its potential in breaking the "bottle neck" in current magnetic recording speed. Scientifically, initial studies of spin dynamics in ferromagnetic materials by ultrafast laser pulses have revealed many intriguing phenomena, but such studies have been mostly limited to conventional transition metals and many novel materials still remain unexplored. CrO2 has provided us such a good model system. The availability of high-quality single-crystal CrO2 film has stimulated extensive studies of the properties of this material in the last few years and revealed that it is a ferromagnetic half metal, namely, the spins are highly polarized in vicinity of the Fermi surface. The transient spin dynamics study has given us an opportunity to look at CrO2 from another aspect, which has never be seen before. In this thesis, transient magneto-optic Kerr measurement utilizing ultrafast laser pulse excitation and detection has been performed to study the spin dynamics in epitaxial CrO2 films. Different microscopic contributions leading to incoherent spin thermalization and relaxation on distinct time scales have been identified in a modified three-temperature model by taking into account the nonthermal electrons, which has been mostly neglected in previous studies. Interestingly, the spins and thermalized electrons seemed to have been decoupled in these measurements, which could be attributed to the half-metallic nature of the material. Coherent magnetization precession directly triggered by photoexcitation was also found to be present in CrO2, when an external magnetic field of proper strength was applied to the magnetic hard axis of the film. Furthermore, coherent phase control of these oscillations could be achieved by employing two temporally separated excitation pulses. The above findings can be very well described by a simple model based on Landau-Lifshitz-Gilbert (LLG) equation. In this model, the driving force of the coherent magnetization rotation was provided by the optically modulated magnetocrystalline anisotropy. Direct experimental evidence of the magnetic anisotropy relaxation was provided.

Zhang, Qiang

131

Competing orders and spin density wave instabilities in FeAs-based systems

The discovery of superconductivity with Tc up to 55 K in layered FeAs-based compounds has generated tremendous interest in the scientific community. Except for relatively high Tc, the Fe pnictides display many interesting properties. Among others, the presence of competing orders is one of the most intriguing phenomena. In the early stage of our study on the compounds, we identified

Nan Lin Wang

2009-01-01

132

Dynamic-angle spinning and double rotation of quadrupolar nuclei

Nuclear magnetic resonance (NMR) spectroscopy of quadrupolar nuclei is complicated by the coupling of the electric quadrupole moment of the nucleus to local variations in the electric field. The quadrupolar interaction is a useful source of information about local molecular structure in solids, but it tends to broaden resonance lines causing crowding and overlap in NMR spectra. Magic- angle spinning, which is routinely used to produce high resolution spectra of spin-{1/2} nuclei like carbon-13 and silicon-29, is incapable of fully narrowing resonances from quadrupolar nuclei when anisotropic second-order quadrupolar interactions are present. Two new sample-spinning techniques are introduced here that completely average the second-order quadrupolar coupling. Narrow resonance lines are obtained and individual resonances from distinct nuclear sites are identified. In dynamic-angle spinning (DAS) a rotor containing a powdered sample is reoriented between discrete angles with respect to high magnetic field. Evolution under anisotropic interactions at the different angles cancels, leaving only the isotropic evolution of the spin system. In the second technique, double rotation (DOR), a small rotor spins within a larger rotor so that the sample traces out a complicated trajectory in space. The relative orientation of the rotors and the orientation of the larger rotor within the magnetic field are selected to average both first- and second-order anisotropic broadening. The theory of quadrupolar interactions, coherent averaging theory, and motional narrowing by sample reorientation are reviewed with emphasis on the chemical shift anisotropy and second-order quadrupolar interactions experienced by half-odd integer spin quadrupolar nuclei. The DAS and DOR techniques are introduced and illustrated with application to common quadrupolar systems such as sodium-23 and oxygen-17 nuclei in solids.

Mueller, K.T. (Lawrence Berkeley Lab., CA (United States) California Univ., Berkeley, CA (United States). Dept. of Chemistry)

1991-07-01

133

Spin dynamics in CeB6 studied by muon spin relaxation

NASA Astrophysics Data System (ADS)

The dynamics of magnetic fluctuations in the paramagnetic and antiferroquadrupolarly (AFQ) ordered phases of single crystal CeB6 was investigated by means of muon spin relaxation experiments. Applied magnetic fields up to 2.5 T were used. Since in the AFQ phase the contact hyperfine coupling that contributes to the fluctuating field amplitudes at the three d -type interstitial muon sites strongly depends on the temperature and the applied field, as shown by the corresponding Knight-shift results, this feature was taken into account in determining the magnetic fluctuation rates. The extracted correlation time ?c of the magnetic fluctuations depends only weakly on the applied field, its temperature dependence demonstrates an accelerated slowing down of the spin dynamics in parallel with the development of the AFQ order.

Gygax, F. N.; Schenck, A.; Solt, G.; Zaharko, O.

2010-03-01

134

Spin dynamics simulations for a nanoscale Heisenberg antiferromagnetic film

NASA Astrophysics Data System (ADS)

Thermoinduced magnetization(TiM) is a novel response predicted to occur in nanoscale antiferromagnetic (AF) materials. Extensive Monte Carlo simulationsootnotetextG. Brown, A. Janotti, M. Eisenbach, and G. M. Stocks, Phys.Rev.B 72, 140405(2005) have shown that TiM is an intrinsic property of the AF classical Heisenberg model. To obtain a fundamental understanding of TiM, spin dynamics (SD) simulations are performed to study the spin wave behavior, which seems to be the cause of TiM. A classical Heisenberg model with an AF nearest-neighbor exchange interaction and uniaxial single-site anisotropy is studied. Simple-cubic lattices with two free-surfaces and periodic boundaries parallel to the surfaces are used. We applied fast SD algorithms with 4th-order Suzuki-Trotter decompositions of the exponential operator. Discrete spin wave modes due to spin wave confinementootnotetextSpin Wave Confinement, edited by S. O Demokritov (Pan Stanford Publishing, Singapore, 2008) are found in transverse S(q,,?) in the perpendicular direction to free surfaces.

Hou, Zhuofei; Landau, David; Stocks, G. Malcolm

2011-03-01

135

Chaos and dynamics of spinning particles in Kerr spacetime

NASA Astrophysics Data System (ADS)

We study chaos dynamics of spinning particles in Kerr spacetime of rotating black holes use the Papapetrou equations by numerical integration. Because of spin, this system exists many chaos solutions, and exhibits some exceptional dynamic character. We investigate the relations between the orbits chaos and the spin magnitude S, pericenter, polar angle and Kerr rotation parameter a by means of a kind of brand new Fast Lyapulov Indicator (FLI) which is defined in general relativity. The classical definition of Lyapulov exponent (LE) perhaps fails in curve spacetime. And we emphasize that the Poincaré sections cannot be used to detect chaos for this case. Via calculations, some new interesting conclusions are found: though chaos is easier to emerge with bigger S, but not always depends on S monotonically; the Kerr parameter a has a contrary action on the chaos occurrence. Furthermore, the spin of particles can destroy the symmetry of the orbits about the equatorial plane. And for some special initial conditions, the orbits have equilibrium points.

Han, Wenbiao

2008-09-01

136

Spin Dynamics and Spin-flop transition in Magnetoelectric Effect LiMnPO4

Neutron scattering techniques were used to study the magnetic phase transition and spin dynamics in single crystal LiMnPO4 both with and without magnetic field. Elastic scattering confirmed that LiMnPO4 has a collinear antiferromagnetic ground state with moments along a-axis in zero-field. The temperature dependent order parameter, calculated from the integrated intensity of the (010) magnetic reflection, was fit to a

J. Li; W. Tian; Y. Chen; J. L. Zarestky; D. Vaknin; J. W. Lynn

2008-01-01

137

Spin dynamics of the reentrant spin glass Fe_0.7Al_0.3

The magnetic excitation spectrum of Fe_0.7Al_0.3 has been studied by inelastic neutron scattering in a single crystal near the (111) Bragg peak. In the ferromagnetic phase, three enrgy scales clearly participate to the scattering cross section. An elatice, resolution limited central peakcharacteristic of the frozen configuration of spin glass compounds is observed. The dynamics consists of two entities: paramagnetic scattering

S. Shapiro; W. Bao; S. Raymond; K. Motoya

1998-01-01

138

Dynamical Encoding by Networks of Competing Neuron Groups: Winnerless Competition

Following studies of olfactory processing in insects and fish, we investigate neural networks whose dynamics in phase space is represented by orbits near the heteroclinic connections between saddle regions (fixed points or limit cycles). These networks encode input information as trajectories along the heteroclinic connections. If there are N neurons in the network, the capacity is approximately e(N-1)! , i.e., much larger than that of most traditional network structures. We show that a small winnerless competition network composed of FitzHugh-Nagumo spiking neurons efficiently transforms input information into a spatiotemporal output.

Rabinovich, M.; Volkovskii, A.; Lecanda, P.; Huerta, R.; Abarbanel, H. D. I.; Laurent, G.

2001-08-06

139

Competing mechanism for generating high spin excitations in ?-soft nuclei: the 136Nd case

NASA Astrophysics Data System (ADS)

High-spin structures in 136Nd have been investigated via the 110Pd( 30Si,4n) reaction at 125 MeV using the GASP array. Several bands consisting of stretched quadrupole transitions were identified. Two of them reach spins comparable to those of the highly-deformed (HD) band in 136Nd, which is based on a neutron i {13}/{2}- {h {9}/{2}}/{f {7}/{2}} configuration. Total routhian surface (TRS) calculations indicate that regular high-spin excitations in this ?-soft nucleus, can be also generated through successive pairs of h {11}/{2} protons and neutrons coupled to a stable small-deformation triaxial core. The previously reported ?-ray transitions of an excited HD band, identical to the yrast HD band, are not confirmed by our data.

Petrache, C. M.; Bazzacco, D.; Lunardi, S.; Rossi Alvarez, C.; Venturelli, R.; Bucurescu, D.; Ur, C. A.; De Acuña, D.; Maron, G.; Napoli, D. R.; Medina, N. H.; Oliveira, J. R. B.; Wyss, R.

1996-02-01

140

Dipolar broadening of nuclear spin resonance under dynamical pumping

NASA Astrophysics Data System (ADS)

We study the polarization dependence of the homogeneously broadened nuclear spin resonance in a crystal. We employ a combinatorial method to restrict the nuclear states to a fixed polarization and show that the center of the resonance is shifted linearly with the nuclear polarization by up to the zero polarization line width. The width shrinks from its maximum value at zero polarization to zero at full polarization. This suggests to use the line shape as a direct measure of nuclear polarization reached under dynamical pumping. In the limit of single quantum of excitation above the fully ferromagnetic state, we provide an explicit solution to the problem of nuclear spin dynamics which links a bound on the fastest decay rate to the observable width of the resonance line.

Tsyplyatyev, O.; Whittaker, D. M.

2012-03-01

141

Planar Spin-Transfer Device with a Dynamic Polarizer.

NASA Astrophysics Data System (ADS)

In planar nano-magnetic devices magnetization direction is kept close to a given plane by the large easy-plane magnetic anisotropy (e.g. by shape anisotropy in a thin film). In conventional micromagnetics it is known that in this case the magnetization motion is effectively in-plane with only one angle required for its description, and can become overdamped even for small values of the Gilbert damping. We extend the equations of the effective in-plane dynamics to include the spin-transfer torques. The simplifications achieved in the overdamped regime allow us to study systems with several dynamic magnetic pieces (``free layers''). A transition from a spin-transfer device with a static polarizer to a device with two equivalent magnets is observed: when the size difference between the magnets is less than critical, the device does not exhibit switching, but goes directly into the ``windmill'' precession state.

Bazaliy, Yaroslaw; Olaosebikan, Debo; Jones, Barbara

2007-03-01

142

Chiral pion nucleon dynamics in finite nuclei: Spin isospin excitations

NASA Astrophysics Data System (ADS)

The nuclear density functional framework, based on chiral dynamics and the symmetry breaking pattern of low-energy QCD, is extended to the description of collective nuclear excitations. Starting from the relativistic point-coupling Lagrangian introduced in [P. Finelli, N. Kaiser, D. Vretenar, W. Weise, Nucl. Phys. A 770 (2006) 1], the proton-neutron (quasiparticle) random phase approximation is formulated and applied to investigate the role of chiral pion-nucleon dynamics in excitation modes involving spin and isospin degrees of freedom, e.g. isobaric analog states and Gamow-Teller resonances.

Finelli, P.; Kaiser, N.; Vretenar, D.; Weise, W.

2007-07-01

143

Competing superfluid orders in spin-orbit-coupled fermionic cold-atom optical lattices

NASA Astrophysics Data System (ADS)

The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase, a superconducting state with nonzero total momentum Cooper pairs in a large magnetic field, was first predicted about 50 years ago and has since become an important concept in many branches of physics. Despite an intensive search in various materials, unambiguous experimental evidence for the FFLO phase is still lacking in experiments. In this paper we show that both Fulde-Ferrell (FF) (a uniform order parameter with a plane-wave phase) and Larkin-Ovchinnikov (LO) phases (a spatially varying order parameter amplitude) can be observed using fermionic cold atoms in spin-orbit-coupled optical lattices. The increasing spin-orbit coupling enhances the FF phase over the LO phase. The coexistence of superfluid and magnetic orders is also found in the normal BCS phase. The pairing mechanism for different phases is understood by visualizing superfluid pairing densities in different spin-orbit bands. The possibility of observing similar physics using spin-orbit-coupled superconducting ultrathin films is also discussed.

Xu, Yong; Qu, Chunlei; Gong, Ming; Zhang, Chuanwei

2014-01-01

144

Competing antiferromagnetic and spin-glass phases in a hollandite structure

NASA Astrophysics Data System (ADS)

We introduce a simple lattice model with Ising spins as a zeroth-order approximation of the hollandite-type magnetic compounds. We argue that geometrical frustration of the lattice in combination with nearest-neighbor antiferromagnetic (AFM) interactions are responsible for the appearance of a spin-glass phase in presence of disorder. We investigate this system numerically using parallel tempering. The model reproduces magnetic transitions present in some oxides with hollandite structure and displays a rich phenomenology: in the absence of disorder we have identified five different ground states, depending on the relative strength and sign of the interactions: one ferromagnetically ordered, three antiferromagnetically ordered, and one disordered, macroscopically degenerate ground state. Remarkably, for the sets of AFM couplings having an AFM ground state in the clean system, there exists a critical value of the disorder above which the ground state becomes a spin glass while maintaining all the couplings antiferromagnetically. This model presents this kind of transition with nearest-neighbor frustrated AFM interactions. We argue that this model is useful for understanding the relation between AFM coupling, disorder, and appearance of spin-glass phases.

Crespo, Y.; Andreanov, A.; Seriani, N.

2013-07-01

145

Competing Jahn-Teller and spin Jahn-Teller ordering in ACr2O4 spinels

NASA Astrophysics Data System (ADS)

Magnetic ordering is strongly linked to structural distortions in the frustrated antiferromagnets ZnCr2O4 and MgCr2O4. These systems undergo spin Jahn-Teller distortions at the onset of magnetic order. The addition of magnetic A site cations in ACr2O4 spinels can relieve frustration. High-resolution variable-temperature synchrotron powder X-ray diffraction, detailed magnetic studies, and heat capacity measurements show that dilute amounts of Jahn-Teller active Cu^2+ or Co^2+ on the A sites of these spinels have different effects on structure but similar effects on magnetism. Partial replacement of A by Cu^2+ generates Jahn-Teller distortions at temperatures above the endmember Neel temperatures, yet spin interactions remain frustrated to ˜ 12 K. This contrasts with Co^2+ substitution which also maintains frustration, but results in a suppression of spin Jahn-Teller ordering in ZnCr2O4. We report decoupled Jahn-Teller and spin Jahn-Teller ordering in the canonical frustrated systems ZnCr2O4 and MgCr2O4 that is tunable by varying the identity of the magnetic A site substituent.

Kemei, Moureen; Moffitt, Stephanie; Suchomel, Matthew; Shoemaker, Daniel; Seshadri, Ram

2013-03-01

146

Current-driven spin dynamics in spin-orbit coupled superconductors

NASA Astrophysics Data System (ADS)

The study of the interplay between spin-orbit coupling (SOC) and superconductivity in two-dimensional electron gases (2DEG) has recently gained impetus following the discovery of i) 2DEGs in InAs or GaAs semiconductor heterostructures that are proximized by ordinary s-wave superconducting leads -- a class of systems which plays a key role in the quest for Majorana fermions -- and ii) 2DEGs that form at interfaces between complex oxides such as LaAlO3 and SrTiO3, which display tunable SOC and, under appropriate conditions, superconductivity. Motivated by this body of experimental and theoretical literature, we investigate the collective spin dynamics of an archetypical 2DEG model Hamiltonian with Rashba SOC in the presence of repulsive electron-electron (e-e) interactions. In the absence of superconductivity a Rashba 2DEG exhibits spin oscillations, which, at long wavelength and for weak repulsive interactions, have a frequency 2 ?kF, ? being the strength of SOC and kF the usual 2D Fermi wavenumber in the absence of SOC. These oscillations, however, are damped and quickly decay due to the emission of (double) electron-hole pairs, which, in the normal phase, are present at arbitrary low energies. In the presence of superconductivity, collective spin oscillations continue to exist in a wide range of parameters, because the Cooper pairs are mixtures of singlet and triplet components. Further, these excitations are undamped because they lie inside the superconducting gap where no other excitation exists. These spin oscillations can be excited by the application of a magnetic field or a supercurrent and can be used to realize persistent spin oscillators operating in the frequency range of 10 GHz - 1 THz.[4pt] Work supported by EU FP7 Programme Grant No. 215368-SEMISPINNET, No. 234970- NANOCTM and No. 248629-SOLID, and by NSF DMR-0705460.

Vignale, Giovanni

2012-02-01

147

The impact of competing zealots on opinion dynamics

NASA Astrophysics Data System (ADS)

An individual’s opinion on an issue is greatly impacted by others in his or her social network. Most people are open-minded and ready to change their opinion when presented evidence; however, some are zealots or inflexibles, that is, individuals who refuse to change their opinion while staunchly advocating an opinion in hopes of convincing others. Zealotry is present in opinions of significant personal investment, such as political, religious or corporate affiliation; it tends to be less commonplace in opinions involving rumors or fashion trends. In this paper, we examine the effect that zealots have in a population whose opinion dynamics obey the naming game model. We present numerical and analytical results about the number and nature of steady state solutions, demonstrating the existence of a bifurcation in the space of zealot fractions. Our analysis indicates conditions under which a minority zealot opinion ultimately prevails, and conditions under which neither opinion attains a majority. We also present numerical and simulation analysis of finite populations and on networks with partial connectivity.

Verma, Gunjan; Swami, Ananthram; Chan, Kevin

2014-02-01

148

Spin Transfer Driven Magnetization Dynamics in Spin Valves and Magnetic Tunnel Junctions

NASA Astrophysics Data System (ADS)

This thesis describes experimental studies of magnetization dynamics in both spin valves (SVs) and magnetic tunnel junctions (MTJs) subject to spin-polarized currents. A spin-polarized electrical current can transfer its angular momentum to a ferromagnet through a spin-transfer torque (STT), resulting in intriguing magnetization dynamics such as the reversal of the magnetization direction, precession and relaxation. The ferromagnetic systems investigated were nanopillars, tens to hundreds of nanometers in cross section and a few nanometers in thickness, which were further integrated into SV or MTJ structures. The magnetization switching and relaxation studies were performed on all-perpendicularly magnetized SVs. The switching probabilities were investigated for different pulse conditions at room temperature, where thermal fluctuations can play an important role. The pulse duration was varied over 10 orders of magnitude, from the fundamental timescales of magnetization precessional dynamics, 50 ps, to 1 s. Three switching regimes were found at different timescales. In the short-time regime, the switching probability was mainly determined by the angular momentum transfer between the current and the magnetization. In the long-time regime, the switching becomes thermal activation over an effective energy barrier modified by the STT. In the crossover regime, both spin-transfer and thermal effects are important. The magnetization relaxation was studied by a two-pulse correlation method, where the relaxation time is measured by the interval between the two pulses. The thermal effects were shown to be important even at nanosecond time scales. The switching and precession of magnetization were also studied in structures where a perpendicular spin polarizing layer is employed with an in-plane magnetized MTJ. When subject to pulses, the initial STT from the polarizer to the free layer is perpendicular to the free layer plane. For a large enough STT, this tilts the free layer magnetization out of the plane to create a large demagnetization field, typically at tens or hundreds of millitesla. This demagnetization field then becomes the dominant magnetic field acting on the free layer, leading to the precession of its magnetization. This magnetization precession was observed through real-time device resistance measurements, where precessions with hundreds of picoseconds are found from single current pulse stimuli.

Liu, Huanlong

149

Dynamics of a Single Spin-1/2 Coupled to x- and y-Spin Baths: Algorithm and Results

NASA Astrophysics Data System (ADS)

The real-time dynamics of a single spin-1/2 particle, called the central spin, coupled to the x(y)-components of the spins of one or more baths is simulated. The bath Hamiltonians contain interactions of x(y)-components of the bath spins only but are general otherwise. An efficient algorithm is described which allows solving the time-dependent Schr’odinger equation for the central spin, even if the x(y) baths contain hundreds of spins. The algorithm requires storage for 2 × 2 matrices only, no matter how many spins are in the baths. We calculate the expectation value of the central spin, as well as its von Neumann entropy S(t), the quantum purity P(t), and the off-diagonal elements of the quantum density matrix. In the case of coupling the central spin to both x- and y- baths the relaxation of S(t) and P(t) with time is a power law, compared to an exponential if the central spin is only coupled to an x-bath. The effect of different initial states for the central spin and bath is studied. Comparison with more general spin baths is also presented.

Novotny, M. A.; Guerra, Marta L.; De Raedt, Hans; Michielsen, Kristel; Jin, Fengping

150

Quantum gravity and spin-1/2 particle effective dynamics

NASA Astrophysics Data System (ADS)

Quantum gravity phenomenology opens up the possibility of probing Planck scale physics. Thus, by exploiting the generic properties that a semiclassical state of the compound system fermions plus gravity should have, an effective dynamics of spin-1/2 particles is obtained within the framework of loop quantum gravity. Namely, at length scales much larger than Planck length lP˜10-33 cm and below the wavelength of the fermion, the spin-1/2 dynamics in flat spacetime includes Planck scale corrections. In particular we obtain modified dispersion relations in vacuo for fermions. These corrections yield a time of arrival delay of the spin-1/2 particles with respect to a light signal and, in the case of neutrinos, a novel flavor oscillation. To detect these effects the corresponding particles must be highly energetic and should travel long distances. Hence neutrino bursts accompanying gamma ray bursts or ultrahigh energy cosmic rays could be considered. Remarkably, future neutrino telescopes may be capable of testing such effects. This paper provides a detailed account of the calculations and elaborates on results previously reported in a Letter. These are further amended by introducing a real parameter ? aimed at encoding our lack of knowledge of scaling properties of the gravitational degrees of freedom.

Alfaro, Jorge; Morales-Técotl, Hugo A.; Urrutia, Luis F.

2002-12-01

151

Dynamical Quantum Phase Transitions in Random Spin Chains

NASA Astrophysics Data System (ADS)

Using a renormalization group approach, we solve the time evolution of random Ising spin chains with generic interactions starting from initial states of arbitrary energy. As a function of the Hamiltonian parameters, the system is tuned through a dynamical transition, similar to the ground-state critical point, at which the local spin correlations establish true long-range temporal order. In the state with a dominant transverse field, a spin that starts in an up state loses its orientation with time, while in the "ordered" state it never does. As in ground-state quantum phase transitions, the dynamical transition has unique signatures in the entanglement properties of the system. When the system is initialized in a product state, the entanglement entropy grows as log(t) in the two "phases," while at the critical point it grows as log?(t), with ? a universal number. This universal entanglement growth requires generic ("integrability breaking") interactions to be added to the pure transverse field Ising model.

Vosk, Ronen; Altman, Ehud

2014-05-01

152

\\u000a In the paper measures of classifier competence and diversity using a probabilistic model are proposed. The multiple classifier\\u000a system (MCS) based on dynamic ensemble selection scheme was constructed using both measures developed. The performance of\\u000a proposed MCS was compared against three multiple classifier systems using six databases taken from the UCI Machine Learning\\u000a Repository and the StatLib statistical dataset. The

Rafal Lysiak; Marek Kurzynski; Tomasz Woloszynski

153

Planar spin-transfer device with dynamical polarizer and analizer

NASA Astrophysics Data System (ADS)

The behavior of the planar spin-transfer devices with monodomain magnetic layers can be described by the macrospin Landau-Lifshitz-Gilbert (LLG) equation with spin-transfer terms. The LLG description of a device with two layers is simplified after applying the overdamped, large easy-plane anisotropy approximation. A decrease of the magnetic layer thickness asymmetry creates a transition from the conventional polarizer-analizer ("fixed layer -- free layer") operation regime to the regime of the nearly identical magnets. Here electric current leads to a "Slonczewski windmill" dynamic state, rather than producing the magnetic switching. The "windmill" precession state of a device with two free layers was investigated by numerical solution of the LLG equation.

Bazaliy, Yaroslaw; Kravchenko, Anton

2011-03-01

154

Influence of the particle number on the spin dynamics of ultracold atoms

We study the dependency of the quantum spin dynamics on the particle number in a system of ultracold spin-1 atoms within the single-spatial-mode approximation. We find, for all strengths of the spin-dependent interaction, convergence toward the mean-field dynamics in the thermodynamic limit. The convergence is, however, particularly slow when the spin-changing collisional energy and the quadratic Zeeman energy are equal; that is, deviations between quantum and mean-field spin dynamics may be extremely large under these conditions. Our estimates show that quantum corrections to the mean-field dynamics may play a relevant role in experiments with spinor Bose-Einstein condensates. This is especially the case in the regime of few atoms, which may be accessible in optical lattices. Here, spin dynamics is modulated by a beat note at large magnetic fields due to the significant influence of correlated many-body spin states.

Heinze, Jannes; Pfannkuche, Daniela [I. Institut fuer Theoretische Physik, Universitaet Hamburg, Jungiusstrasse 9, D-20355 Hamburg (Germany); Deuretzbacher, Frank [Institut fuer Theoretische Physik, Leibniz Universitaet Hannover, Appelstrasse 2, D-30167, Hannover (Germany)

2010-08-15

155

Dynamic switching of the spin circulation in tapered magnetic nanodisks.

Magnetic vortices are characterized by the sense of in-plane magnetization circulation and by the polarity of the vortex core. With each having two possible states, there are four possible stable magnetization configurations that can be utilized for a multibit memory cell. Dynamic control of vortex core polarity has been demonstrated using both alternating and pulsed magnetic fields and currents. Here, we show controlled dynamic switching of spin circulation in vortices using nanosecond field pulses by imaging the process with full-field soft X-ray transmission microscopy. The dynamic reversal process is controlled by far-from-equilibrium gyrotropic precession of the vortex core, and the reversal is achieved at significantly reduced field amplitudes when compared with static switching. We further show that both the field pulse amplitude and duration required for efficient circulation reversal can be controlled by appropriate selection of the disk geometry. PMID:23603985

Uhlí?, V; Urbánek, M; Hladík, L; Spousta, J; Im, M-Y; Fischer, P; Eibagi, N; Kan, J J; Fullerton, E E; Sikola, T

2013-05-01

156

Large-scale simulation of the spin-lattice dynamics in ferromagnetic iron

NASA Astrophysics Data System (ADS)

We develop a dynamical simulation model for magnetic iron where atoms are treated as classical particles with intrinsic spins. The atoms interact via scalar many-body forces as well as via spin orientation dependent forces of the Heisenberg form. The coupling between the lattice and spin degrees of freedom is described by a coordinate-dependent exchange function where the spin orientation dependent forces are proportional to the gradient of this function. The spin-lattice dynamics simulation approach extends the existing magnetic potential treatment to the case where the energy of interaction between the atoms depends on the relative noncollinear orientations of spins. An algorithm for integrating the linked spin-coordinate equations of motion is based on the second-order Suzuki-Trotter decomposition for noncommuting operators of evolution for coordinate and spin variables. The notions of the spin thermostat and the spin temperature are introduced through the combined application of the Langevin spin dynamics and the fluctuation-dissipation theorem. We investigate several applications of the method, performing microcanonical ensemble simulations of adiabatic spin-lattice relaxation of periodic arrays of 180° domain walls, and isothermal-isobaric ensemble dynamical simulations of thermally equilibrated homogeneous systems at various temperatures. The predicted isothermal magnetization curve agrees well with the experimental data for a broad range of temperatures. The equilibrium as well as time-correlation functions of spin orientations exhibit the presence of short-range magnetic order above the Curie temperature. Furthermore, short-range order spin fluctuations are shown to contribute to the thermal expansion of the material. Our analysis illustrates the significant part played by the spin degrees of freedom in the dynamics of motion of atoms in magnetic iron and iron-based alloys. It also shows that the spin-lattice dynamics algorithm developed in this paper offers a viable way of performing large-scale dynamical atomistic simulations of magnetic materials.

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

2008-07-01

157

Magnetism and spin dynamics of nanoscale FeOOH particles

The nature of magnetism and electron paramagnetic resonance (EPR) spin dynamics in 30 A particles of FeOOH have been investigated in the range 5--350 K. X-ray diffraction shows that the particles are neither [alpha]-Fe[sub 2]O[sub 3] nor [alpha]-FeOOH based and they convert to Fe[sub 3]O[sub 4] ([alpha]-Fe[sub 2]O[sub 3]) on heating to 800 K in vacuum (air). Magnetization [ital M] vs [ital T] data show a blocking temperature [ital T][sub [ital B

Ibrahim, M.M.; Edwards, G.; Seehra, M.S. (Physics Department, West Virginia University, P. O. Box 6315, Morgantown, West Virginia 26506-6315 (United States)); Ganguly, B.; Huffman, G.P. (Consortium for Fossil Fuel Liquefaction Science, 233 Mining and Mineral Resources Building, University of Kentucky, Lexington, Kentucky 40506 (United States))

1994-05-15

158

Spin dynamics of the giant polyoxometalate molecule {Mn40W224} studied by NMR

NASA Astrophysics Data System (ADS)

7Li nuclear magnetic resonance (NMR) studies have been performed to investigate magnetic properties and spin dynamics of Mn3+ (S = 2) spins in the giant polyoxometalate molecule {Mn40W224}. The 7Li-NMR line width is proportional to the external magnetic field H as expected in a paramagnetic state above 3 K. Below this temperature the line width shows a sudden increase and is almost independent of H, which indicates freezing of the local Mn3+ spins. The temperature dependence of T1 for both 1H and 7Li reveals slow spin dynamics at low temperatures, consistent with spin freezing. The slow spin dynamics is also evidenced by the observation of a peak of 1/T2 around 3 K, where the fluctuation frequency of spins is of the order of ?200 kHz. An explicit form of the temperature dependence of the fluctuation frequency of Mn3+ spins is derived from the nuclear relaxation data.

Furukawa, Y.; Fang, X.; Kögerler, P.

2014-05-01

159

Electrical control of spin dynamics in finite one-dimensional systems

NASA Astrophysics Data System (ADS)

We investigate the possibility of the electrical control of spin transfer in monoatomic chains incorporating spin impurities. Our theoretical framework is the mixed quantum-classical (Ehrenfest) description of the spin dynamics, in the spirit of the s-d model, where the itinerant electrons are described by a tight-binding model while localized spins are treated classically. Our main focus is on the dynamical exchange interaction between two well-separated spins. This can be quantified by the transfer of excitations in the form of transverse spin oscillations. We systematically study the effect of an electrostatic gate bias Vg on the interconnecting channel and we map out the long-range dynamical spin transfer as a function of Vg. We identify regions of Vg giving rise to significant amplification of the spin transmission at low frequencies and relate this to the electronic structure of the channel.

Pertsova, A.; Stamenova, M.; Sanvito, S.

2011-10-01

160

Spin Dynamics and Spin-flop transition in Magnetoelectric Effect LiMnPO4

NASA Astrophysics Data System (ADS)

Neutron scattering techniques were used to study the magnetic phase transition and spin dynamics in single crystal LiMnPO4 both with and without magnetic field. Elastic scattering confirmed that LiMnPO4 has a collinear antiferromagnetic ground state with moments along a-axis in zero-field. The temperature dependent order parameter, calculated from the integrated intensity of the (010) magnetic reflection, was fit to a power law equation, yielding a transition temperature TN = 33.8 K. By applying magnetic field along the a-axis, the moments rotate from a-axis to the c-axis at a critical field of 3.5 Tesla at 5 K. The field dependent (100) and (001) intensities indicate a complicated intermediate state between the ground state and the spin-flop state. The critical field increased from 3.5 Tesla at 5 K to 4.5 Tesla near the transition TN. Spin-wave dispersion curves along the three principal axes were measured in the antiferromagnetic state at 4.5 K in zero magnetic field and were analyzed using a 3D Heisenberg model.

Li, J.; Tian, W.; Chen, Y.; Zarestky, J. L.; Vaknin, D.; Lynn, J. W.

2008-03-01

161

NASA Astrophysics Data System (ADS)

We show that the quadratic interaction of fundamental and second harmonics in a bulk dispersive medium, combined with self-defocusing cubic nonlinearity, gives rise to completely localized spatiotemporal solitons (vortex tori) with vorticity s=1. There is no threshold necessary for the existence of these solitons. They are found to be stable if their energy exceeds a certain critical value, so that the stability domain occupies about 10% of the existence region of the solitons. On the contrary to spatial vortex solitons in the same model, the spatiotemporal ones with s=2 are never stable. These results might open the way for experimental observation of spinning three-dimensional solitons in optical media.

Mihalache, D.; Mazilu, D.; Crasovan, L.-C.; Towers, I.; Malomed, B. A.; Buryak, A. V.; Torner, L.; Lederer, F.

2002-07-01

162

Experimental investigation of the dynamics of spinning tethered bodies

NASA Astrophysics Data System (ADS)

Ground based experiments are conducted as a part of the OEDIPUS-C sounding rocket mission, scheduled for launch in the winter of 1995. Here OEDIPUS stands for Observation of Electrified Distribution in Ionospheric Plasma—a Unique Strategy. The OEDIPUS-C configuration consists of two spinning bodies connected by a 1 km long tether (the spin axis is nominally along the tether line). The objective is to assess dynamic behaviour of the tether and the payload. The test configuration consists of an end-body supported by a tether. The test procedure involves slow spin-up of the system and identifying the speeds corresponding to onset of the tether modes or the large amplitude end-body coning. This is referred to as the critical speed and corresponds to the stability boundary of the system. Experimental results are obtained for four different bodies to study the system stability over a wide range of mass and geometric parameters. Effect of offset of the tether attachment from the end-body centre of mass is also investigated. The observed critical speeds are compared with those given by the linear theory. The test results are generally in very good agreement with the theory, however several transient phenomena observed during the test suggest that system nonlinearities cannot be ignored when modelling such a complex system.

Modi, V. J.; Pradhan, S.; Chu, M.; Tyc, G.; Misra, A. K.

1996-10-01

163

Emergent magnetic monopoles and their dynamics in artificial spin ice

NASA Astrophysics Data System (ADS)

Electrically charged particles such as electrons are common in our world. In contrast, no elementary particles with a net magnetic charge have ever been observed. After a recent discovery that magnetic monopoles can emerge in a system of magnetic dipoles [1], much attention has been paid to the behavior of magnetic monopoles in artificial spin ice, arrays of nano-scale magnetic islands or wires that mimic the behavior of geometrically frustrated materials [2]. We have developed a theoretical model of magnetization dynamics in artificial spin ice under the action of an external magnetic field [3]. Magnetization reversal is mediated by the creation, propagation and absorption of domain walls carrying two units of magnetic. Domain walls are emitted from lattice junctions when the local field becomes large enough to overcome the Coulomb attraction between the magnetic charges of the domain wall and the junction. This interaction is also responsible for a positive feedback that triggers magnetic avalanches observed experimentally in artificial spin ice. [4pt] [1] C. Castelnovo, R. Moessner, and S. L. Sondhi, Nature 451, 42 (2008). [0pt] [2] O. Tchernyshyov, Nat. Phys. 6, 323 (2010). [0pt] [3] P. Mellado, O. Petrova, Y. Shen, and O. Tchernyshyov, Phys. Rev. Lett. 105, 187206 (2010).

Shen, Yichen; Petrova, Olga; Mellado, Paula; Tchernyshyov, Oleg

2011-03-01

164

Phonon-magnon interactions in body centered cubic iron: A combined molecular and spin dynamics study

NASA Astrophysics Data System (ADS)

Combining an atomistic many-body potential with a classical spin Hamiltonian parameterized by first principles calculations, molecular-spin dynamics computer simulations were performed to investigate phonon-magnon interactions in body centered cubic iron. Results obtained for spin-spin and density-density dynamic structure factors show that noticeable softening and damping of magnon modes occur due to the presence of lattice vibrations. Furthermore, as a result of the phonon-magnon coupling, additional longitudinal spin wave excitations are observed, with the same frequencies as the longitudinal phonon modes.

Perera, Dilina; Landau, David P.; Nicholson, Don M.; Malcolm Stocks, G.; Eisenbach, Markus; Yin, Junqi; Brown, Gregory

2014-05-01

165

Non-diffusive spin dynamics in a two-dimensional electron gas

We describe measurements of spin dynamics in the two-dimensional electron gas in GaAs/GaAlAs quantum wells. Optical techniques, including transient spin-grating spectroscopy, are used to probe the relaxation rates of spin polarization waves in the wavevector range from zero to 6 x 10{sup 4} cm{sup -1}. We find that the spin polarization lifetime is maximal at nonzero wavevector, in contrast with expectation based on ordinary spin diffusion, but in quantitative agreement with recent theories that treat diffusion in the presence of spin-orbit coupling.

Weber, C.P.

2010-04-28

166

Spin dynamics in relativistic ionization with highly charged ions in super-strong laser fields

NASA Astrophysics Data System (ADS)

Spin dynamics and induced spin effects in above-threshold ionization of hydrogenlike highly charged ions in super-strong laser fields are investigated. Spin-resolved ionization rates in the tunnelling regime are calculated by employing two versions of a relativistic Coulomb-corrected strong-field approximation (SFA). An intuitive simpleman model is developed which explains the derived scaling laws for spin flip and spin asymmetry effects. The intuitive model as well as our ab initio numerical simulations support the analytical results for the spin effects obtained in the dressed SFA where the impact of the laser field on the electron spin evolution in the bound state is taken into account. In contrast, the standard SFA is shown to fail in reproducing spin effects in ionization even at a qualitative level. The anticipated spin-effects are expected to be measurable with modern laser techniques combined with an ion storage facility.

Klaiber, Michael; Yakaboylu, Enderalp; Müller, Carsten; Bauke, Heiko; Paulus, Gerhard G.; Hatsagortsyan, Karen Z.

2014-03-01

167

Spin-Entry Characteristics of a Large Supersonic Bomber as Determined by Dynamic Model Tests

NASA Technical Reports Server (NTRS)

An investigation has been conducted in the Langley spin tunnel and at a catapult launch facility of a 1/60-scale dynamic model to determine the spin-entry characteristics of a large supersonic bomber. Catapult tests indicated that spin-entry motions were obtainable for a center-of-gravity location of 0.21 mean aerodynamic chord but were not obtainable at a center-of-gravity location of 0.25 mean aerodynamic chord. Deflected ailerons were effective in promoting or preventing the spin- entry motion and this effect was qualitatively the same as it was for the fully developed spin. Varying the configuration had little significant effect on the spin-entry characteristics. Brief tests conducted with the model in the Langley spin tunnel indicated that fully developed spins were obtainable at the forward center-of-gravity location and that spins were highly unlikely at the rearward center-of-location.

Bowman, James S.

1965-01-01

168

Solid effect in magic angle spinning dynamic nuclear polarization.

For over five decades, the solid effect (SE) has been heavily utilized as a mechanism for performing dynamic nuclear polarization (DNP). Nevertheless, it has not found widespread application in contemporary, high magnetic field DNP experiments because SE enhancements display an ?(0)(-2) field dependence. In particular, for nominally forbidden zero and double quantum SE transitions to be partially allowed, it is necessary for mixing of adjacent nuclear spin states to occur, and this leads to the observed field dependence. However, recently we have improved our instrumentation and report here an enhancement of ? = 91 obtained with the organic radical trityl (OX063) in magic angle spinning experiments performed at 5 T and 80 K. This is a factor of 6-7 higher than previous values in the literature under similar conditions. Because the solid effect depends strongly on the microwave field strength, we attribute this large enhancement to larger microwave field strengths inside the sample volume, achieved with more efficient coupling of the gyrotron to the sample chamber. In addition, we develop a theoretical model to explain the dependence of the buildup rate of enhanced nuclear polarization and the steady-state enhancement on the microwave power. Buildup times and enhancements were measured as a function of (1)H concentration for both trityl and Gd-DOTA. Comparison of the results indicates that for trityl the initial polarization step is the slower, rate-determining step. However, for Gd-DOTA the spread of nuclear polarization via homonuclear (1)H spin diffusion is rate-limiting. Finally, we discuss the applicability of the solid effect at fields > 5 T and the requirements to address the unfavorable field dependence of the solid effect. PMID:22894339

Corzilius, Björn; Smith, Albert A; Griffin, Robert G

2012-08-01

169

Population Dynamics of a Spin1 Bose Gas at Finite Temperatures

We study population dynamics of a trapped spin-1 Bose gas above the Bose-Einstein transition temperature. Starting from the\\u000a semiclassical kinetic equation for a spin-1 gas, we derive coupled rate equations for the populations of internal states.\\u000a Solving the rate equations, we study the dynamical evolution of spin populations. We also estimate the characteristic timescale\\u000a in which the system reaches equilibrium.

Yuki Endo; Tetsuro Nikuni

2010-01-01

170

NASA Astrophysics Data System (ADS)

We theoretically study the nuclear spin dynamics driven by electron transport and hyperfine interaction in an electrically defined double quantum dot in the Pauli-blockade regime. We derive a master-equation-based framework and show that the coupled electron-nuclear system displays an instability towards the buildup of large nuclear spin polarization gradients in the two quantum dots. In the presence of such inhomogeneous magnetic fields, a quantum interference effect in the collective hyperfine coupling results in sizable nuclear spin entanglement between the two quantum dots in the steady state of the evolution. We investigate this effect using analytical and numerical techniques, and demonstrate its robustness under various types of imperfections.

Schuetz, M. J. A.; Kessler, E. M.; Vandersypen, L. M. K.; Cirac, J. I.; Giedke, G.

2014-05-01

171

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

NASA Technical Reports Server (NTRS)

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.

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

1984-01-01

172

Imaging intracellular protein dynamics by spinning disk confocal microscopy

The palette of fluorescent proteins has grown exponentially over the last decade, and as a result live imaging of cells expressing fluorescently tagged proteins is becoming more and more main stream. Spinning disk confocal microscopy (SDC) is a high speed optical sectioning technique, and a method of choice to observe and analyze intracellular fluorescent protein dynamics at high spatial and temporal resolution. In an SDC system, a rapidly rotating pinhole disk generates thousands of points of light that scan the specimen simultaneously, which allows direct capture of the confocal image with low noise scientific grade cooled charged-coupled device (CCD) cameras, and can achieve frame rates of up 1000 frames per second. In this chapter we describe important components of a state-of-the-art spinning disk system optimized for live cell microscopy, and provide a rationale for specific design choices. We also give guidelines how other imaging techniques such as total internal reflection (TIRF) microscopy or spatially controlled photoactivation can be coupled with SDC imaging, and provide a short protocol on how to generate cell lines stably expressing fluorescently tagged proteins by lentivirus-mediated transduction.

Stehbens, Samantha; Pemble, Hayley; Murrow, Lindsay; Wittmann, Torsten

2012-01-01

173

Imaging intracellular protein dynamics by spinning disk confocal microscopy.

The palette of fluorescent proteins (FPs) has grown exponentially over the past decade, and as a result, live imaging of cells expressing fluorescently tagged proteins is becoming more and more mainstream. Spinning disk confocal (SDC) microscopy is a high-speed optical sectioning technique and a method of choice to observe and analyze intracellular FP dynamics at high spatial and temporal resolution. In an SDC system, a rapidly rotating pinhole disk generates thousands of points of light that scan the specimen simultaneously, which allows direct capture of the confocal image with low-noise scientific grade-cooled charge-coupled device cameras, and can achieve frame rates of up to 1000 frames per second. In this chapter, we describe important components of a state-of-the-art spinning disk system optimized for live cell microscopy and provide a rationale for specific design choices. We also give guidelines of how other imaging techniques such as total internal reflection microscopy or spatially controlled photoactivation can be coupled with SDC imaging and provide a short protocol on how to generate cell lines stably expressing fluorescently tagged proteins by lentivirus-mediated transduction. PMID:22264541

Stehbens, Samantha; Pemble, Hayley; Murrow, Lyndsay; Wittmann, Torsten

2012-01-01

174

The dynamics of a generalized Heisenberg ferromagnetic spin chain.

We introduce a generalized Heisenberg ferromagnetic spin chain with a four-dimensional target space, and investigate its continuous limit, the generalized continuous Heisenberg model (GCHM). We reduce the dynamics of the GCHM to a nonlinear evolution of space curves in four dimensions. The space curve evolution is expressed in terms of a system of coupled nonlinear equations for the three curvatures, k(1)(x),k(2)(x),k(3)(x), of a curve in R(4). Applying the Painleve analysis to the stationary equations, we conclude that GCHM, in general, is not integrable, unless k(1) is constant. We obtain explicit solutions of the resulting stationary system under the latter condition. (c) 1995 American Institute of Physics. PMID:12780198

Daniel, M.; Gutkin, Eugene

1995-06-01

175

Spin-boson dynamics beyond conventional perturbation theories

NASA Astrophysics Data System (ADS)

A generalized approximation scheme is proposed to describe the dynamics of the spin-boson problem. Being nonperturbative in the coupling strength nor in the tunneling frequency, it gives reliable results over a wide regime of temperatures and coupling strength to the thermal environment for a large class of bath spectral densities. We use a path-integral approach and start from the exact solution for the two-level system population difference in the form of a generalized master equation (GME). Then, we approximate interblip and blip-sojourn interactions up to linear order, while retaining all intrablip correlations to find the kernels entering the GME in analytical form. Our approximation scheme, which we call weakly interacting blip approximation, fully agrees with conventional perturbative approximations in the tunneling matrix element (noninteracting-blip approximation) or in the system-bath coupling strength in the proper parameter regime.

Nesi, Francesco; Paladino, Elisabetta; Thorwart, Michael; Grifoni, Milena

2007-10-01

176

A key role for unusual spin dynamics in ferropnictides

NASA Astrophysics Data System (ADS)

The discovery of high-Tc ferropnictides introduced a new family of superconductors, and has already revealed a complicated and often contradictory picture of the structural and magnetic properties. An almost unprecedented sensitivity of the calculated magnetism and Fermi surface to structural details prevents correspondence to experiment. Experimental probes of the order parameter are in surprisingly strong disagreement, even considering the relative immaturity of the field. We outline various and seemingly contradictory evidence, both theoretical and experimental, and show it can be rectified by assuming a large-moment spin density wave, well defined but with magnetic twin and antiphase boundaries, dynamic on the experimental timescale. Under this assumption, calculations can accurately reproduce even very fine details of the structure, and a natural explanation for the temperature separation of structural and magnetic transitions is provided. Thus, our theory restores agreement between experiment and theory in crucial areas, making further cooperative progress possible on both fronts.

Mazin, I. I.; Johannes, M. D.

2009-02-01

177

Dynamic clustering and dispersion of lipid rafts contribute to fusion competence of myogenic cells

Recent research indicates that the leading edge of lamellipodia of myogenic cells (myoblasts and myotubes) contains presumptive fusion sites, yet the mechanisms that render the plasma membrane fusion-competent remain largely unknown. Here we show that dynamic clustering and dispersion of lipid rafts contribute to both cell adhesion and plasma membrane union during myogenic cell fusion. Adhesion-complex proteins including M-cadherin, {beta}-catenin, and p120-catenin accumulated at the leading edge of lamellipodia, which contains the presumptive fusion sites of the plasma membrane, in a lipid raft-dependent fashion prior to cell contact. In addition, disruption of lipid rafts by cholesterol depletion directly prevented the membrane union of myogenic cell fusion. Time-lapse recording showed that lipid rafts were laterally dispersed from the center of the lamellipodia prior to membrane fusion. Adhesion proteins that had accumulated at lipid rafts were also removed from the presumptive fusion sites when lipid rafts were laterally dispersed. The resultant lipid raft- and adhesion complex-free area at the leading edge fused with the opposing plasma membrane. These results demonstrate a key role for dynamic clustering/dispersion of lipid rafts in establishing fusion-competent sites of the myogenic cell membrane, providing a novel mechanistic insight into the regulation of myogenic cell fusion.

Mukai, Atsushi [Department of Regenerative Medicine, National Institute for Longevity Sciences, National Center for Geriatrics and Gerontology, 36-3 Gengo, Morioka, Oobu, Aichi 474-8522 (Japan)] [Department of Regenerative Medicine, National Institute for Longevity Sciences, National Center for Geriatrics and Gerontology, 36-3 Gengo, Morioka, Oobu, Aichi 474-8522 (Japan); Kurisaki, Tomohiro [Department of Growth Regulation, Institute for Frontier Medical Sciences, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507 (Japan)] [Department of Growth Regulation, Institute for Frontier Medical Sciences, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507 (Japan); Sato, Satoshi B. [Research Center for Low Temperature and Material Sciences, Kyoto University, Yoshida-honmachi, Kyoto 606-8501 (Japan)] [Research Center for Low Temperature and Material Sciences, Kyoto University, Yoshida-honmachi, Kyoto 606-8501 (Japan); Kobayashi, Toshihide [Lipid Biology Laboratory, Discovery Research Institute, RIKEN, Wako, Saitama 351-0198 (Japan)] [Lipid Biology Laboratory, Discovery Research Institute, RIKEN, Wako, Saitama 351-0198 (Japan); Kondoh, Gen [Laboratory of Animal Experiments for Regeneration, Institute for Frontier Medical Sciences, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507 (Japan)] [Laboratory of Animal Experiments for Regeneration, Institute for Frontier Medical Sciences, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507 (Japan); Hashimoto, Naohiro, E-mail: nao@nils.go.jp [Department of Regenerative Medicine, National Institute for Longevity Sciences, National Center for Geriatrics and Gerontology, 36-3 Gengo, Morioka, Oobu, Aichi 474-8522 (Japan)] [Department of Regenerative Medicine, National Institute for Longevity Sciences, National Center for Geriatrics and Gerontology, 36-3 Gengo, Morioka, Oobu, Aichi 474-8522 (Japan)

2009-10-15

178

Dynamical Properties of Spins and Holes in Carrier Doped Quantum Haldane Chain

NASA Astrophysics Data System (ADS)

Quantum spins in one-dimensional (1D) chains exhibit characteristic features such as the Haldane gap (S=1) and the spin-Peierls state (S=1/2). Recently multi degrees of freedom in cooperation with quantum spins are focused. We present here spin dynamics in the lightly hole doped Nd2-xCaxBaNiO5 (x=0.035), 1D Haldane system by means of pulsed neutron inelastic scattering method. One-magnon band with a spin gap (Haldane gap) was visible with the decrease of the zone boundary energy to 60 meV. In contrast, the spin gap slightly increases. Dynamical structures inside spin gap upon carrier doping showing incommensurate structure centered at the magnetic zone center was newly observed which is possibly originating from the doped holes in Haldane chains.

Yokoo, T.; Itoh, S.; Kawana, D.; Yoshizawa, H.; Akimitsu, J.

2014-04-01

179

Controllable spin-dynamics cycles and ERASE functionality on quasilinear molecular ions

NASA Astrophysics Data System (ADS)

We present an ab initio investigation of the ?-process-based ultrafast spin manipulation on positively charged two-magnetic-center molecular ions with a nonmagnetic bridging atom O in-between. Multiple spin-switching and spin-transfer scenarios are derived on the quasilinear structure [Fe-O-Co]+, which are used to build two closed, irreversible spin-dynamics cycles with respect to the spin localization and orientation. A mechanism addressing the "ERASE" functionality is proposed by properly exploiting the irreversibility of some laser-induced spin-manipulation scenarios, and the resulting Shannon entropy change is analyzed. Such controllable spin-dynamics cycles and logic functionality demonstrate promising applications in the design of spintronic devices.

Li, Chun; Zhang, Shaobin; Jin, Wei; Lefkidis, Georgios; Hübner, Wolfgang

2014-05-01

180

The recently isolated TiSc(2)N@C(80) was used to study the spin state of a Ti(3+) ion in a mixed metal nitride cluster in a fullerene cage. The electronic state of the new clusterfullerene is characterized starting with the redox behavior of this structure. It differs markedly from that of homometallic nitride clusterfullerenes in giving reversible one-electron transfers even on the cathodic scale. Both oxidation and reduction of TiSc(2)N@C(80) occur at the endohedral cluster changing the valence state of Ti from Ti(II) in anion to Ti(IV) in cation. The unpaired electron in TiSc(2)N@C(80) is largely fixed at the Ti ion as shown by low temperature ESR measurements. Isotropic g-factor 1.9454 points to the significant spin-orbit coupling with an unquenched orbital momentum of the 3d electron localized on Ti. Measurements with the frozen solution also point to the strong anisotropy of the g-tensor. DFT computations show that the cluster can adopt several nearly isoenergetic configurations. DFT-based Born-Oppenheimer molecular dynamics (BOMD) simulations reveal that, unlike in Sc(3)N@C(80), the cluster dynamics in TiSc(2)N@C(80) cannot be described as a 3D rotation. The cluster rotates around the Ti-N axis, while the Ti atom oscillates in one position around the pentagon/hexagon edge. Evolution of the spin populations along the BOMD trajectory has shown that the spin distribution in the cluster is very flexible, and both an intracluster and cluster-cage spin flows take place. Fourier transformation of the time dependencies of the spin populations results in the spin-flow vibrational spectra, which reveal the major spin-flow channels. It is shown that the cluster-cage spin flow is selectively coupled to one vibrational mode, thus, pointing to the utility of the clusterfullerene for the molecular spin transport. Spin-flow vibrational spectroscopy is thus shown to be a useful method for characterization of the spin dynamics in radicals with flexible spin density distribution. PMID:20731461

Popov, Alexey A; Chen, Chuanbao; Yang, Shangfeng; Lipps, Ferdinand; Dunsch, Lothar

2010-08-24

181

NMR time reversal as a probe of incipient turbulent spin dynamics.

We demonstrate time reversal of nuclear spin dynamics in highly magnetized dilute liquid (3)He-(4)He mixtures through effective inversion of long-range dipolar interactions. These experiments, which involve using magic sandwich NMR pulse sequences to generate spin echoes, probe the spatiotemporal development of turbulent spin dynamics and promise to serve as a versatile tool for the study and control of dynamic magnetization instabilities. We also show that a repeated magic sandwich pulse sequence can be used to dynamically stabilize modes of nuclear precession that are otherwise intrinsically unstable. To date, we have extended the effective precession lifetimes of our magnetized samples by more than three orders of magnitude. PMID:17930637

Hayden, M E; Baudin, E; Tastevin, G; Nacher, P J

2007-09-28

182

Using Markov models to simulate electron spin resonance spectra from molecular dynamics trajectories

Simulating electron spin resonance (ESR) spectra directly from molecular dynamics simulations of a spin labeled protein necessitates a large number (hundreds or thousands) of relatively long (hundreds of ns) trajectories. To meet this challenge, we explore the possibility of constructing accurate stochastic models of the spin label dynamics from atomistic trajectories. A systematic, two-step procedure, based on the probabilistic framework of hidden Markov models, is developed to build a discrete-time Markov chain process that faithfully captures the internal spin label dynamics on time scales longer than about 150 ps. The constructed Markov model is used both to gain insight into the long-lived conformations of the spin label and to generate the stochastic trajectories required for the simulation of ESR spectra. The methodology is illustrated with an application to the case of a spin labeled poly-alanine alpha helix in explicit solvent.

Sezer, Deniz; Freed, Jack H.; Roux, Benoit

2008-01-01

183

Spinning Black Hole Pairs: Dynamics and Gravitational Waves

NASA Astrophysics Data System (ADS)

Black hole binaries will be an important source of gravitational radiation for both ground-based and future space-based gravitational wave detectors. The study of such systems will offer a unique opportunity to test the dynamical predictions of general relativity when gravity is very strong. To date, most investigations of black hole binary dynamics have focused attention on restricted scenarios in which the black holes do not spin (and thus are confined to move in a plane) and/or in which they stay on quasi-circular orbits. However, spinning black hole pairs in eccentric orbits are now understood to be astrophysically equally important. These spinning binaries exhibit a range of complicated dynamical behaviors, even in the absence of radiation reaction. Their conservative dynamics is complicated by extreme perihelion precession compounded by spin-induced precession. Although the motion seems to defy simple decoding, we are able to quantitatively define and describe the fully three-dimensional motion of arbitrary mass-ratio binaries with at least one black hole spinning and expose an underlying simplicity. To do so, we untangle the dynamics by constructing an instantaneous orbital plane and showing that the motion captured in that plane obeys elegant topological rules. In this thesis, we apply the above prescription to two formal systems used to model black hole binaries. The first is defined by the conservative 3PN Hamiltonian plus spin-orbit coupling and is particularly suitable to comparable-mass binaries. The second is defined by geodesics of the Kerr metric and is used exclusively for extreme mass-ratio binaries. In both systems, we define a complete taxonomy for fully three-dimensional orbits. More than just a naming system, the taxonomy provides unambiguous and quantitative descriptions of the orbits, including a determination of the zoom-whirliness of any given orbit. Through a correspondence with the rational numbers, we are able to show that all of the qualitative features of the well-studied equatorial geodesic motion around Schwarzschild and Kerr black holes are also present in more general black hole binary systems. This includes so-called zoom-whirl behavior, which turns out to be unexpectedly prevalent in comparable-mass binaries in the strong-field regime just as it is for extreme mass-ratio binaries. In each case we begin by thoroughly cataloging the constant radius orbits which generally lie on the surface of a sphere and have acquired the name "spherical orbits". The spherical orbits are significant as they energetically frame the distribution of all orbits. In addition, each unstable spherical orbit is asymptotically approached by an orbit that whirls an infinite number of times, known as a homoclinic orbit. We further catalog the homoclinic trajectories, each of which is the infinite whirl limit of some part of the zoom-whirl spectrum and has a further significance as the separatrix between inspiral and plunge for eccentric orbits. We then show that there exists a discrete set of orbits that are geometrically closed n-leaf clovers in a precessing orbital plane. When viewed in the full three dimensions, these orbits do not close, but they are nonetheless periodic when projected into the orbital plane. Each n-leaf clover is associated with a rational number, q, that measures the degree of perihelion precession in the precessing orbital plane. The rational number q varies monotonically with the orbital energy and with the orbital eccentricity. Since any bound orbit can be approximated as near one of these periodic n-leaf clovers, this special set offers a skeleton that illuminates the structure of all bound orbits in both systems, in or out of the equatorial plane. A first significant conclusion that can be drawn from this analysis is that all generic orbits in the final stages of inspiral under gravitational radiation losses are characterized by precessing clovers with few leaves, and that no orbit will behave like the tightly precessing ellipse of Mercury. We close with a practical applicati

Grossman, Rebecca

184

Spin-lattice coupling in molecular dynamics simulation of ferromagnetic iron

NASA Astrophysics Data System (ADS)

A model for magnetic iron where atoms are treated as classical particles with intrinsic spins is developed. The atoms interact via scalar many-body forces as well as via spin-dependent forces of the Heisenberg form. The coupling between the lattice and spin degrees of freedom is described by a coordinate-dependent exchange function, where the spin-orientation-dependent forces are proportional to the gradient of this function. A spin-lattice dynamics simulation approach extends the existing magnetic-potential treatment to the case where the strength of interaction between the atoms depends on the relative non-collinear orientations of their spins. An algorithm for integrating the linked spin-coordinate equations of motion is based on the 2nd order Suzuki-Trotter decomposition for the non-commuting evolution operators for both coordinates and spins. The notions of the spin thermostat and the spin temperature are introduced through the combined application of the Langevin spin dynamics and the fluctuation-dissipation theorem. We investigate several applications of the method, performing microcanonical ensemble simulations of adiabatic spin-lattice relaxation of periodic arrays of 180° domain-walls, and isothermal-isobaric ensemble dynamical simulations of thermally equilibrated homogeneous systems at various temperatures. The isothermal magnetization curve evaluated using the spin-lattice dynamics algorithm is well described by the mean-field approximation and agrees satisfactorily with the experimental data for a broad range of temperatures. The equilibrium time-correlation functions of spin orientations exhibit the presence of short-range magnetic order above the Curie temperature. Short-range order spin fluctuations are shown to contribute to the thermal expansion of the material. Simulations on thermal expansion and elastic response of bulk bcc iron, and magnetization in bcc iron thin films are also performed and the results discussed. Our analysis illustrates the significant part played by the spin directional degrees of freedom in the dynamics of atomic motion in magnetic iron and iron-based alloys, and shows that the spin-lattice dynamics algorithm provides a viable way of performing realistic large-scale dynamical simulations of magnetic materials.

Ma, Pui Wai

185

Tracking excited-state charge and spin dynamics in iron coordination complexes.

Crucial to many light-driven processes in transition metal complexes is the absorption and dissipation of energy by 3d electrons. But a detailed understanding of such non-equilibrium excited-state dynamics and their interplay with structural changes is challenging: a multitude of excited states and possible transitions result in phenomena too complex to unravel when faced with the indirect sensitivity of optical spectroscopy to spin dynamics and the flux limitations of ultrafast X-ray sources. Such a situation exists for archetypal polypyridyl iron complexes, such as [Fe(2,2'-bipyridine)3](2+), where the excited-state charge and spin dynamics involved in the transition from a low- to a high-spin state (spin crossover) have long been a source of interest and controversy. Here we demonstrate that femtosecond resolution X-ray fluorescence spectroscopy, with its sensitivity to spin state, can elucidate the spin crossover dynamics of [Fe(2,2'-bipyridine)3](2+) on photoinduced metal-to-ligand charge transfer excitation. We are able to track the charge and spin dynamics, and establish the critical role of intermediate spin states in the crossover mechanism. We anticipate that these capabilities will make our method a valuable tool for mapping in unprecedented detail the fundamental electronic excited-state dynamics that underpin many useful light-triggered molecular phenomena involving 3d transition metal complexes. PMID:24805234

Zhang, Wenkai; Alonso-Mori, Roberto; Bergmann, Uwe; Bressler, Christian; Chollet, Matthieu; Galler, Andreas; Gawelda, Wojciech; Hadt, Ryan G; Hartsock, Robert W; Kroll, Thomas; Kjær, Kasper S; Kubi?ek, Katharina; Lemke, Henrik T; Liang, Huiyang W; Meyer, Drew A; Nielsen, Martin M; Purser, Carola; Robinson, Joseph S; Solomon, Edward I; Sun, Zheng; Sokaras, Dimosthenis; van Driel, Tim B; Vankó, György; Weng, Tsu-Chien; Zhu, Diling; Gaffney, Kelly J

2014-05-15

186

Tracking excited-state charge and spin dynamics in iron coordination complexes

NASA Astrophysics Data System (ADS)

Crucial to many light-driven processes in transition metal complexes is the absorption and dissipation of energy by 3d electrons. But a detailed understanding of such non-equilibrium excited-state dynamics and their interplay with structural changes is challenging: a multitude of excited states and possible transitions result in phenomena too complex to unravel when faced with the indirect sensitivity of optical spectroscopy to spin dynamics and the flux limitations of ultrafast X-ray sources. Such a situation exists for archetypal polypyridyl iron complexes, such as [Fe(2,2'-bipyridine)3]2+, where the excited-state charge and spin dynamics involved in the transition from a low- to a high-spin state (spin crossover) have long been a source of interest and controversy. Here we demonstrate that femtosecond resolution X-ray fluorescence spectroscopy, with its sensitivity to spin state, can elucidate the spin crossover dynamics of [Fe(2,2'-bipyridine)3]2+ on photoinduced metal-to-ligand charge transfer excitation. We are able to track the charge and spin dynamics, and establish the critical role of intermediate spin states in the crossover mechanism. We anticipate that these capabilities will make our method a valuable tool for mapping in unprecedented detail the fundamental electronic excited-state dynamics that underpin many useful light-triggered molecular phenomena involving 3d transition metal complexes.

Zhang, Wenkai; Alonso-Mori, Roberto; Bergmann, Uwe; Bressler, Christian; Chollet, Matthieu; Galler, Andreas; Gawelda, Wojciech; Hadt, Ryan G.; Hartsock, Robert W.; Kroll, Thomas; Kjær, Kasper S.; Kubi?ek, Katharina; Lemke, Henrik T.; Liang, Huiyang W.; Meyer, Drew A.; Nielsen, Martin M.; Purser, Carola; Robinson, Joseph S.; Solomon, Edward I.; Sun, Zheng; Sokaras, Dimosthenis; van Driel, Tim B.; Vankó, György; Weng, Tsu-Chien; Zhu, Diling; Gaffney, Kelly J.

2014-05-01

187

Spin dynamics in (III,Mn)V ferromagnetic semiconductors: the role of correlations.

We address the role of correlations between spin and charge degrees of freedom on the dynamical properties of ferromagnetic systems governed by the magnetic exchange interaction between itinerant and localized spins. For this we introduce a general theory that treats quantum fluctuations beyond the random phase approximation based on a correlation expansion of the Green's function equations of motion. We calculate the spin susceptibility, spin-wave excitation spectrum, and magnetization precession damping. We find that correlations strongly affect the magnitude and carrier concentration dependence of the spin stiffness and magnetization Gilbert damping. PMID:18851650

Kapetanakis, M D; Perakis, I E

2008-08-29

188

Dynamical self-quenching of spin pumping into double quantum dots.

Nuclear spin polarization can be pumped into spin-blockaded quantum dots by multiple Landau-Zener passages through singlet-triplet anticrossings. By numerical simulations of realistic systems with 10(7) nuclear spins during 10(5) sweeps, we uncover a mechanism of dynamical self-quenching which results in a fast saturation of the nuclear polarization under stationary pumping. This is caused by screening the random field of the nuclear spins. For moderate spin-orbit coupling, self-quenching persists but its patterns are modified. Our finding explains low polarization levels achieved experimentally and calls for developing new protocols that break the self-quenching limitations. PMID:23368239

Brataas, Arne; Rashba, Emmanuel I

2012-12-01

189

Low temperature spin dynamics of the geometrically frustrated antiferromagnetic garnet Gd3Ga5O12

The low temperature spin dynamics of the geometrically frustrated antiferromagnet Gd 3Ga 5O (12) (GGG) have been investigated using muon spin relaxation. No evidence for static order is seen down to a temperature of 25 mK or a few percent of the Curie-Weiss temperature. Instead there is a linear decrease in the Gd spin fluctuation rate below 1 K which extrapolates to a small but finite value of 2 GHz at zero temperature. In terms of the spin fluctuations the system appears essentially to remain dynamic at low temperatures (T>0.02 K) and magnetic fields up to 1.8 T. PMID:11030932

Dunsiger; Gardner; Chakhalian; Cornelius; Jaime; Kiefl; Movshovich; MacFarlane; Miller; Sonier; Gaulin

2000-10-16

190

Simulating the Dynamics and Orientations of Spin Labeled Side Chains in a Protein-DNA Complex

Site-directed spin labeling, wherein a nitroxide side chain is introduced into a protein at a selected mutant site, is increasingly employed to investigate biological systems by electron spin resonance (ESR) spectroscopy. An understanding of the packing and dynamics of the spin label is needed to extract the biologically relevant information about the macromolecule from ESR measurements. In this work, molecular dynamics (MD) simulations were performed on the spin labeled restriction endonuclease, EcoRI in complex with DNA. Mutants of this homodimeric enzyme were previously constructed and distance measurements were performed using the Double Electron Electron Resonance experiment. These correlated distance constraints have been leveraged with MD simulations to learn about side chain packing and preferred conformers of the spin label on sites in an ?-helix and a ?-strand. We found three dihedral angles of the spin label side chain to be most sensitive to the secondary structure where the spin label was located. Conformers sampled by the spin label differed between secondary structures as well. C?-C? distance distributions were constructed and used to extract details about the protein backbone mobility at the two spin labeled sites. These simulation studies enhance our understanding of the behavior of spin labels in proteins and thus expand the ability of ESR spectroscopy to contribute to knowledge of protein structure and dynamics.

Sarver, Jessica L.; Townsend, Jacqueline E.; Rajapakse, Gayathri; Jen-Jacobson, Linda; Saxena, Sunil

2012-01-01

191

Dynamic magnetic hysteresis behavior and dynamic phase transition in the spin-1 Blume-Capel model

NASA Astrophysics Data System (ADS)

The nature (time variation) of response magnetization m( wt) of the spin-1 Blume-Capel model in the presence of a periodically varying external magnetic field h( wt) is studied by employing the effective-field theory (EFT) with correlations as well as the Glauber-type stochastic dynamics. We determine the time variations of m( wt) and h( wt) for various temperatures, and investigate the dynamic magnetic hysteresis behavior. We also investigate the temperature dependence of the dynamic magnetization, hysteresis loop area and correlation near the transition point in order to characterize the nature (first- or second-order) of the dynamic transitions as well as obtain the dynamic phase transition temperatures. The hysteresis loops are obtained for different reduced temperatures and we find that the areas of the loops are decreasing with the increasing of the reduced temperatures. We also present the dynamic phase diagrams and compare the results of the EFT with the results of the dynamic mean-field approximation. The phase diagrams exhibit many dynamic critical points, such as tricritical (•), zero-temperature critical (Z), triple (TP) and multicritical (A) points. According to values of Hamiltonian parameters, besides the paramagnetic (P), ferromagnetic (F) fundamental phases, one coexistence or mixed phase region, (F+P) and the reentrant behavior exist in the system. The results are in good agreement with some experimental and theoretical results.

Deviren, Bayram; Keskin, Mustafa

2012-03-01

192

Spin dynamics and diffusion in GaMnAs

NASA Astrophysics Data System (ADS)

We use an ultrafast transient spin grating to measure the lifetime and diffusion coefficient of optically oriented spins in (Ga,Mn)As. We measure films with nominal doping of 5%, 6%, and 7% Mn. Both below and above the Curie temperature we observe a spin lifetime of about 8 ps. The spins diffuse at nearly the same rate as do electrons (about 70 cm^2/s), allowing us to identify our signal as the spins of mobile, photoexcited electrons. The rapidity of the spin diffusion indicates that spin Coulomb drag (SCD), due to electron-electron collisions, is weak. We attribute this weakness to screening of the Coulomb interaction by holes. SCD appears to have comparable strength in both the ferromagnetic and normal states.

Weber, Chris; Mattia, Kassandra; Kittlaus, Eric; Liu, Xinyu; Furdyna, Jacek

2013-03-01

193

Controlling coherent and incoherent spin dynamics by steering the photoinduced energy flow

NASA Astrophysics Data System (ADS)

We present a femtosecond spectroscopic magneto-optical investigation of the coherent and incoherent spin dynamics in the antiferromagnetic dielectric KNiF3. The pathways of the photoinduced energy flow to spins were controlled by tuning the pump photon energy. In particular, we demonstrate that laser pulses, with photon energy tuned to a nearly-zero-absorption region, excite the spin system without any signatures of heating of electrons or phonons. In this regime the ultrafast excitation of coherent spin waves is followed by a gradual increase of the spin temperature solely due to decoherence of the laser-generated magnons, as revealed by our simultaneous measurement of both the transversal and the longitudinal component of the spin dynamics.

Bossini, D.; Kalashnikova, A. M.; Pisarev, R. V.; Rasing, Th.; Kimel, A. V.

2014-02-01

194

Dynamics of the collective modes of an inhomogeneous spin ensemble in a cavity

We study the excitation dynamics of an inhomogeneously broadened spin ensemble coupled to a single cavity mode. The collective excitations of the spin ensemble can be described in terms of generalized spin waves, and, in the absence of the cavity, the free evolution of the spin ensemble can be described as a drift in the wavenumber without dispersion. In this article we show that the dynamics in the presence of coupling to the cavity mode can be described solely by a modified time evolution of the wavenumbers. In particular, we show that collective excitations with a well-defined wavenumber pass without dispersion from negative to positive-valued wavenumbers without populating the zero wavenumber spin wave mode. The results are relevant for multimode collective quantum memories where qubits are encoded in different spin waves.

Wesenberg, Janus H. [Centre for Quantum Technologies, National University of Singapore, Singapore 117543 (Singapore); Kurucz, Zoltan; Moelmer, Klaus [Lundbeck Foundation Theoretical Center for Quantum System Research, Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark)

2011-02-15

195

Two-Dimensional Monopole Dynamics in the Dipolar Spin Ice Dy2Ti2O7

NASA Astrophysics Data System (ADS)

The spin dynamics of the dipolar spin-ice Dy2Ti2O7 under a dc magnetic field (Bdc) along the [111] direction has been investigated using ac susceptibility (?ac), which enables us to study two-dimensional monopole motion in an ac magnetic field perpendicular to Bdc. We have observed the slowing down of monopole dynamics in the kagomé spin-ice regime (Bdc˜ 0.4 T) and the extreme speeding up under Bdc close to the critical point (Bdc˜ 0.93 T). An analysis using a Monte Carlo simulation suggests that the dynamics changes from a random walk of monopoles to a collective motion as Bdc increases.

Takatsu, Hiroshi; Goto, Kazuki; Otsuka, Hiromi; Higashinaka, Ryuji; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya; Kadowaki, Hiroaki

2013-07-01

196

Spin echo dynamics under an applied drift field in graphene nanoribbon superlattices

NASA Astrophysics Data System (ADS)

We investigate the evolution of spin dynamics in graphene nanoribbon superlattices (GNSLs) with armchair and zigzag edges in the presence of a drift field. We determine the exact evolution operator and show that it exhibits spin echo phenomena due to rapid oscillations of the quantum states along the ribbon. The evolution of the spin polarization is accompanied by strong beating patterns. We also provide detailed analysis of the band structure of GNSLs with armchair and zigzag edges.

Prabhakar, Sanjay; Melnik, Roderick; Bonilla, Luis L.; Raynolds, James E.

2013-12-01

197

Spin echo dynamics under an applied drift field in graphene nanoribbon superlattices

We investigate the evolution of spin dynamics in graphene nanoribbon superlattices (GNSLs) with armchair and zigzag edges in the presence of a drift field. We determine the exact evolution operator and show that it exhibits spin echo phenomena due to rapid oscillations of the quantum states along the ribbon. The evolution of the spin polarization is accompanied by strong beating patterns. We also provide detailed analysis of the band structure of GNSLs with armchair and zigzag edges.

Prabhakar, Sanjay, E-mail: sprabhakar@wlu.ca [M 2NeT Laboratory, Wilfrid Laurier University, 75 University Avenue West, Waterloo, Ontario N2L 3C5 (Canada)] [M 2NeT Laboratory, Wilfrid Laurier University, 75 University Avenue West, Waterloo, Ontario N2L 3C5 (Canada); Melnik, Roderick [M 2NeT Laboratory, Wilfrid Laurier University, 75 University Avenue West, Waterloo, Ontario N2L 3C5 (Canada) [M 2NeT Laboratory, Wilfrid Laurier University, 75 University Avenue West, Waterloo, Ontario N2L 3C5 (Canada); Gregorio Millan Institute, Universidad Carlos III de Madrid, 28911 Leganes (Spain); Bonilla, Luis L. [Gregorio Millan Institute, Universidad Carlos III de Madrid, 28911 Leganes (Spain)] [Gregorio Millan Institute, Universidad Carlos III de Madrid, 28911 Leganes (Spain); Raynolds, James E. [Drinker Biddle and Reath LLP, Washington, DC 20005 (United States)] [Drinker Biddle and Reath LLP, Washington, DC 20005 (United States)

2013-12-02

198

Investigation of dynamical magnetic properties in spin ice pyrochlore Dy2Ti2O7

The frequency and temperature dependence of the spin relaxation processes were studied, to understand the dynamics of the spin interactions in typical spin ice compound Dy2Ti2O7. Two transition peaks were found in ac susceptibilities for frequencies higher than 150 Hz at temperatures around 15 K and 2 K. However, the relaxation times and activation energies were different at corresponding transition

H. M. Wu; P. Y. Chen; R. C. Hong; S. L. Cheng; J. G. Lin

2005-01-01

199

Electron-Nuclear Spin Dynamics in a Mesoscopic Solid-State Quantum Computer

We numerically simulate the process of nuclear spin measurement in Kane's quantum computer. For this purpose, we model the quantum dynamics of two coupled nuclear spins located on {sup 31}P donors implanted in Si. We estimate the minimum time of measurement necessary for the reliable transfer of quantum information from the nuclear spin subsystem to the electronic one and the probability of error for typical values of external noise.

Berman, G.P.; Campbell, D.K.; Doolen, G.D.; Nagaev, K.E.

1998-12-07

200

Detection and Measurement of Spin-Dependent Dynamics in Random Telegraph Signals

NASA Astrophysics Data System (ADS)

A quantum point contact was used to observe single-electron fluctuations of a quantum dot in a GaAs heterostructure. The resulting random telegraph signals (RTS) contain statistical information about the electron spin state if the tunneling dynamics are spin dependent. We develop a statistical method to extract information about spin-dependent dynamics from RTS and use it to demonstrate that these dynamics can be studied in the thermal energy regime. The tunneling rates of each spin state are independently measured in a finite external magnetic field. We confirm previous findings of a decrease in overall tunneling rates for the spin excited state compared to the ground state as an external magnetic field is increased.

House, M. G.; Xiao, Ming; Guo, GuoPing; Li, HaiOu; Cao, Gang; Rosenthal, M. M.; Jiang, HongWen

2013-09-01

201

Dynamics of magnetization in artificial spin ice on kagome

NASA Astrophysics Data System (ADS)

We model magnetization dynamics in artificial spin ice on kagome under an applied magnetic field. Magnetization reversal is mediated by domain walls carrying two units of magnetic charge emitted from and absorbed by lattice junctions and propagating along the wires. The Coulomb interaction between magnetic charges induces avalanches in magnetization reversal. Distributions of avalanche lengths for various angles between the initial magnetization and the applied magnetic field were considered. We used a Gaussian distribution in the magnitude of the links' critical fields to mimic disorder in a real system [1]. An asymmetric distribution of topological defects at a wire junction gives rise to an offset angle ? in the reversal field H(?)=Hc/(?+?) where ? is the angle between the link and the applied magnetic field [2]. The model reproduces the salient features of magnetization reversal curves observed experimentally. [4pt] [1] Y. Qi, T. Brintlinger, and J. Cumings, Phys. Rev. B 77, 094418 (2008). [0pt] [2] P. Mellado, O. Petrova, Y. Shen, and O. Tchernyshyov, Phys. Rev. Lett. 105, 187206 (2010).

Petrova, Olga; Shen, Yichen; Mellado, Paula; Tchernyshyov, Oleg

2011-03-01

202

Optimal control of coupled spin dynamics in the presence of relaxation

In this thesis, we study methods for optimal manipulation of coupled spin dynamics in the presence of relaxation. We use these methods to compute analytical upper bounds for the efficiency of coherence and polarization transfer between coupled nuclear spins in multidimensional nuclear magnetic resonance (NMR) experiments, under the presence of relaxation. We derive relaxation optimized pulse sequences which achieve or

Dionisis Stefanatos

2005-01-01

203

Dynamical passage to approximate equilibrium shapes for spinning, gravitating rubble asteroids

Many asteroids are thought to be particle aggregates held together principally by self-gravity. Here we study — for static and dynamical situations — the equilibrium shapes of spinning asteroids that are permitted for rubble piles. As in the case of spinning fluid masses, not all shapes are compatible with a granular rheology. We take the asteroid to always be an

Ishan Sharma; James T. Jenkins; Joseph A. Burns

2009-01-01

204

Dynamical passage to approximate equilibrium shapes for spinning, gravitating rubble asteroids

Many asteroids are thought to be particle aggregates held together principally by self-gravity. Here we study --- for static and dynamical situations --- the equilibrium shapes of spinning asteroids that are permitted for rubble piles. As in the case of spinning fluid masses, not all shapes are compatible with a granular rheology. We take the asteroid to always be an

Ishan Sharma; James T. Jenkins; Joseph A. Burns

2009-01-01

205

Quantum phases and dynamics of geometric phase in a quantum spin chain under linear quench

NASA Astrophysics Data System (ADS)

We study the quantum phases of anisotropic XY spin chain in presence and absence of adiabatic quench. A connection between geometric phase and criticality is established from the dynamical behavior of the geometric phase for a quench induced quantum phase transition in a quantum spin chain. We predict XX criticality associated with a sequence of non-contractible geometric phases.

Sarkar, S.; Basu, B.

2012-12-01

206

NASA Astrophysics Data System (ADS)

We have investigated numerically the square planer model of Klemm, Thomann, and Johnston assuming the orthorhombic symmetry-breaking energy is large enough, so that the spin interactions are Ising-like. Monte Carlo computations yield ground states generally exhibiting long-range order. The excited states often contain pairs of spins that are flipped relative to the ground state.

Fay, D.; Klemm, R. A.; Monien, H.

1988-06-01

207

Charge and Spin Dynamics of the Hubbard Chains

NASA Technical Reports Server (NTRS)

We calculate the local correlation functions of charge and spin for the one-chain and two-chain Hubbard model using density matrix renormalization group method and the recursion technique. Keeping only finite number of states we get good accuracy for the low energy excitations. We study the charge and spin gaps, bandwidths and weights of the spectra for various values of the on-site Coulomb interaction U and the electron filling. In the low energy part, the local correlation functions are different for the charge and spin. The bandwidths are proportional to t for the charge and J for the spin respectively.

Park, Youngho; Liang, Shoudan

1999-01-01

208

We have studied the spin relaxation in diluted spin ice Ho2-xYxTi2O7 by means of neutron spin echo spectroscopy and ac susceptibility measurements. Remarkably, the geometrical frustration is not relieved by doping with nonmagnetic Y, and the dynamics of the freezing is unaltered in the spin echo time window up to x~=1.6 . At higher doping with nonmagnetic Y (x>=1.6) a

G. Ehlers; J. S. Gardner; C. H. Booth; M. Daniel; K. C. Kam; A. K. Cheetham; D. Antonio; H. E. Brooks; A. L. Cornelius; S. T. Bramwell; J. Lago; W. Häussler; N. Rosov

2006-01-01

209

The dynamics of diluted Ho spin ice Ho2-xYxTi2O7 studied byneutron spin echo spectroscopy

We have studied the spin relaxation in diluted spin ice Ho{sub 2-x} Yâ TiâOâ by means of neutron spin echo spectroscopy. Remarkably, the geometrical frustration is not relieved by doping with non-magnetic Y, and the dynamics of the freezing is unaltered in the spin echo time window up to x â 1.6. At higher doping with non-magnetic Y (x â¥

G. Ehlers; J. S. Gardner; C. H. Booth; M. Daniel; K. C. Kam; A. K. Cheetham; D. Antonio; H. E. Brooks; A. L. Cornelius; S. T. Bramwell; J. Lago; W. Haussler; N. Rosov

2006-01-01

210

Dynamic spin correlations in 'stuffed' spin ice Ho(2+x)Ti(2-x)O(7-d)

The magnetic correlations in 'stuffed' spin ice Ho{sub 2+x}Ti{sub 2-x}O{sub 7-{delta}} have been characterized using quasielastic neutron scattering. At temperatures above 1K , these correlations are short ranged in nature and dynamic on a picosecond to nanosecond time scale. As for the case of pure spin ice Ho{sub 2+x}Ti{sub 2-x}O{sub 7}, one can identify, above the freezing temperature, a quantum relaxation regime which is enhanced as it persists to even higher temperatures, T{approx}30-40K , than in the parent compound.

Ehlers, Georg [ORNL

2008-01-01

211

The multiple quantum (MQ) NMR dynamics in the system of equivalent spins with the dipolar ordered initial state is considered. The high symmetry of the Hamiltonian responsible for the MQ NMR dynamics (the MQ Hamiltonian) is used to develop analytic and numerical methods for the investigation of the MQ NMR dynamics in systems consisting of hundreds of spins from the 'first principles.' We obtain the dependence of the intensities of the MQ NMR coherences on their orders (profiles of the MQ NMR coherences) for systems of 200-600 spins. It is shown that these profiles may be well approximated by exponential distribution functions. We also compare the MQ NMR dynamics in the systems of equivalent spins having two different initial states, the dipolar ordered state and the thermal equilibrium state in a strong external magnetic field.

Doronin, S. I.; Fel'dman, E. B.; Zenchuk, A. I., E-mail: zenchuk@itp.ac.ru [Russian Academy of Sciences, Institute of Problems of Chemical Physics (Russian Federation)

2011-09-15

212

Spin and Charge Dynamics in Atomic Fermions Loaded on Optical Lattice

NASA Astrophysics Data System (ADS)

We study spin and charge dynamics of trapped two-component fermions loaded on an optical lattice by using the time dependent density matrix renormalization group (TDDMRG) method. The present target issue is dynamics of spin and charge in Mott state recently realized experimentally by [1]. Firstly, we simply shake a trapped potential superposed onto an optical lattice and observe the charge dynamics on the Mott state by using TDDMRG. Secondly, we do the same thing on a trapped potential which works only on a pseudo-spin species and observe the spin density dynamics. These results are compared with non-trapped case with an open boundary condition. Also, we compare one-dimensional chain like cases with those of n-legs square and triangular ladder systems. References [1] U. Schneider, L. Hackermuller, S. Will, Th. Best, I. Bloch, T. A. Costi, R. W. Helmes, D. Rasch, A. Rosch, arXiv:0809.1464.

Okumura, Masahiko; Onishi, Hiroaki; Yamada, Susumu; Machida, Masahiko

2009-03-01

213

NASA Astrophysics Data System (ADS)

We report measurements of slow magnetization fluctuations in an ultrathin Au/Co/Au system that exhibits a spin reorientation phase transition as a function of temperature. The intermediate scattering function is well described by a stretched exponential that is indicative of cooperative motion throughout the temperature range of 150 - 300 K. The decay times were found to exhibit a maximum at the transition temperature. The slowdown has been explained as due to formation of a shallow double well in the energy landscape by the different competing interactions. Our results show that slow dynamics in the mesoscopic length scale can provide valuable insights into the nature of magnetic phase transitions. Work at LBNL is supported by DOE.

Roy, S.; Seu, K. A.; Parks, D.; Su, R.; Turner, J. J.; Park, S.; Falco, C. M.; Kevan, S. D.

2010-03-01

214

Next-to-leading order gravitational spin(1)-spin(2) dynamics in Hamiltonian form

Based on recent developments by the authors a next-to-leading order spin(1)-spin(2) Hamiltonian is derived for the first time. The result is obtained within the canonical formalism of Arnowitt, Deser, and Misner (ADM) utilizing their generalized isotropic coordinates. A comparison with other methods is given.

Steinhoff, Jan; Hergt, Steven; Schaefer, Gerhard [Theoretisch-Physikalisches Institut, Friedrich-Schiller-Universitaet, Max-Wien-Pl. 1, 07743 Jena (Germany)

2008-04-15

215

Dynamic neutron scattering on incoherent systems using efficient resonance spin flip techniques

NASA Astrophysics Data System (ADS)

We have performed numerical ray-tracing Monte-Carlo-simulations of incoherent dynamic neutron scattering experiments. We intend to optimize the efficiency of incoherent measurements depending on the fraction of neutrons scattered without and with spin flip at the sample. In addition to conventional spin echo, we have numerically and experimentally studied oscillating intensity techniques. The results point out the advantages of these different spin echo variants and are an important prerequisite for neutron resonance spin echo instruments like RESEDA (FRM II, Munich), to choose the most efficient technique depending on the scattering vector range and the properties of the sample system under study.

Häussler, Wolfgang; Kredler, Lukas

2014-05-01

216

Spin-exchange dynamical structure factor of the S=1/2 Heisenberg chain.

We determine the spin-exchange dynamical structure factor of the Heisenberg spin chain, as is measured by indirect resonant inelastic x-ray scattering (RIXS). We find that two-spin RIXS excitations nearly entirely fractionalize into two-spinon states. These share the same continuum lower bound as single-spin neutron scattering excitations, even if the relevant final states belong to orthogonal symmetry sectors. The RIXS spectral weight is mainly carried by higher-energy excitations, and is beyond the reach of the low-energy effective theories of Luttinger liquid type. PMID:21568610

Klauser, Antoine; Mossel, Jorn; Caux, Jean-Sébastien; van den Brink, Jeroen

2011-04-15

217

Neutron scattering study of spin dynamics in superconducting (Tl,Rb)2Fe4Se5

NASA Astrophysics Data System (ADS)

We observed in superconducting (Tl,Rb)2Fe4Se5 spin-wave branches that span an energy range from 6.5 to 209 meV. Spin dynamics are successfully described by a Heisenberg localized spin model whose dominant in-plane interactions include only the nearest (J1 and J1') and next nearest neighbor (J2 and J2') exchange terms within and between the tetramer spin blocks, respectively. These experimentally determined exchange constants would crucially constrain the theoretical viewpoints on magnetism and superconductivity in the Fe-based materials.

Chi, Songxue; Ye, Feng; Bao, Wei; Fang, Minghu; Wang, H. D.; Dong, C. H.; Savici, A. T.; Granroth, G. E.; Stone, M. B.; Fishman, R. S.

2013-03-01

218

Spin Crossover in Ferropericlase From First-Principles Molecular Dynamics Simulations

NASA Astrophysics Data System (ADS)

Ferropericlase is believed to be the second-most abundant mineral of the lower mantle of the Earth. It is experimentally known that with increasing pressure, the iron ions in the mineral begin to collapse from a high-spin to low-spin state. This spin crossover looks certain to have geophysical effects, and hence a good theoretical understanding of the phenomenon is necessary. Using first-principles molecular dynamics simulations in conjunction with thermodynamic integration, we construct a phase diagram of the spin crossover as a function of pressure and temperature. In addition, we predict that the mineral loses its electrically insulating character within the lower mantle.

Holmstrom, E.; Stixrude, L. P.

2013-12-01

219

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) 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.

Damour, Thibault; Jaranowski, Piotr; Schaefer, Gerhard [Institut des Hautes Etudes Scientifiques, 91440 Bures-sur-Yvette (France); Faculty of Physics, University of Bialystok, Lipowa 41, 15-424 Bialystok (Poland); Theoretisch-Physikalisches Institut, Friedrich-Schiller-Universitaet, Max-Wien-Pl. 1, 07743 Jena (Germany)

2008-07-15

220

Studies of quantum fluctuations and competing orders on vortex dynamics in cuprate superconductors

NASA Astrophysics Data System (ADS)

The existence of competing orders (CO) and the proximity to quantum criticality (QC) in cuprate superconductors create unconventional low energy excitations and significant quantum fluctuations (QF) which can alter the low temperature vortex dynamics of cuprates. We report studies on the effect of QF and CO on vortex dynamics in cuprates at low temperatures, focusing on the four-layer, hole-doped HgBa2Ca3Cu4Ox (Hg-1234). Hg-1234 has two underdoped inner layers that are anti-ferromagnetic and two optimally doped outer layers that are superconducting. Vortex phase diagrams, derived from 3^rd harmonic AC hall probe and high-field DC cantilever magnetization measurements, allow comparison of Hg-1234 with other cuprates such as YBa2Cu3O7-x and La0.1Sr0.9CuO2. Comparison plots of the ab-plane reduced fields (normalized by the paramagnetic field, Hpara), hirr.(t)=Hirr.(t)/Hpara and hC2(t)=HC2(t)/Hpara versus reduced temperature, t, demonstrate that QF and CO indeed affect Hg-1234 more than other cuprates, with Hg-1234 having the smallest extrapolated value of h*? hirr.(0) 0.12, indicating its closest proximity to QC.

Beyer, A. D.; Zapf, V. S.; Park, M.-S.

2005-03-01

221

Ultrafast spin dynamics in half-metallic ferromagnetic thin film

Manipulation of electron spins by optical means is anticipated to play a key role in future high-density magnetic storage technology. The ability to maneuver spins beyond thermal excitation regime is of great interests because of its potential in breaking the \\

Qiang Zhang

2005-01-01

222

Spin dynamics of the giant polyoxometalate molecule {Mn40W224} studied by NMR.

(7)Li nuclear magnetic resonance (NMR) studies have been performed to investigate magnetic properties and spin dynamics of Mn(3+) (S = 2) spins in the giant polyoxometalate molecule {Mn40W224}. The (7)Li-NMR line width is proportional to the external magnetic field H as expected in a paramagnetic state above 3 K. Below this temperature the line width shows a sudden increase and is almost independent of H, which indicates freezing of the local Mn(3+) spins. The temperature dependence of T1 for both (1)H and (7)Li reveals slow spin dynamics at low temperatures, consistent with spin freezing. The slow spin dynamics is also evidenced by the observation of a peak of 1/T2 around 3 K, where the fluctuation frequency of spins is of the order of ?200 kHz. An explicit form of the temperature dependence of the fluctuation frequency of Mn(3+) spins is derived from the nuclear relaxation data. PMID:24762855

Furukawa, Y; Fang, X; Kögerler, P

2014-05-14

223

Spin ordering and dynamics in the frustrated antiferromagnet YBaCo4O7.1

NASA Astrophysics Data System (ADS)

The stoichiometric 114-layered material YBaCo4O7 exhibits long-range antiferromagnetic order below a Néel temperature of 106 K. Nonstoichiometric YBaCo4O7.1, which contains a relatively small amount (1.4%) of interstitial oxygen, has recently been shown to have drastically modified magnetic properties compared to the parent compound. The present experiments have used magnetization, ac susceptibility, and zero applied field NMR to study the spin configuration and spin dynamics in a single crystal of YBaCo4O7.1 as a function of temperature below 100 K. Evidence has been obtained for a magnetic transition at 80 K corresponding to some form of spin freeze-out. Based on previous results for the stoichiometric material, it is likely that the freezing process involves spins in the triangular layers in this frustrated antiferromagnet. At lower temperatures, dynamic effects persist and below 50 K a fraction of the spins, located primarily in the kagome layers, constitute what may be termed a viscous spin liquid component. For T < 10 K, a disordered or glasslike spin structure, with a large distribution of spin correlation times, emerges as the low-temperature state of the spin system.

Yuan, S.; Hu, X.; Kuhns, P. L.; Reyes, A. P.; Brooks, J. S.; Besara, T.; Siegrist, T.; Zheng, H.; Mitchell, J. F.; Hoch, M. J. R.

2014-03-01

224

Computation of dynamical correlation functions of the spin-1 Babujan–Takhtajan chain

NASA Astrophysics Data System (ADS)

The dynamical structure factor of the Babujan–Takhtajan antiferromagnetic spin-1 chain is computed numerically at zero temperature and zero magnetic field, using the higher spin generalization of an algebraic Bethe ansatz-based method previously used for spin-1/2 integrable chains. This method, which consists in the explicit construction of eigenstates and the summation of the Lehmann representation of the correlator, is particularly challenging to implement here in view of the presence of strongly deviated string solutions to the Bethe equations. We show that a careful treatment of these deviations makes it possible to obtain perfect saturation of sum rules for small system sizes, and extremely good saturation for large system sizes where the dynamical structure factor is computed by including all two-spinon and four-spinon contributions. The real-space spin–spin correlation, obtained by Fourier transforming our results, displays asymptotics fitting predictions from conformal field theory.

Vlijm, Rogier; Caux, Jean-Sébastien

2014-05-01

225

Unified dynamics of electrons and photons via Zitterbewegung and spin-orbit interaction

NASA Astrophysics Data System (ADS)

We show that when an electron or photon propagates in a cylindrically symmetric waveguide, it experiences both a Zitterbewegung effect and a spin-orbit interaction leading to identical propagation dynamics for both particles. Applying a unified perturbative approach to both particles simultaneously, we find that to first order in perturbation theory, their Hamiltonians each contain identical Darwin (Zitterbewegung) and spin-orbit terms, resulting in the unification of their dynamics. The presence of the Zitterbewegung effect may be interpreted physically as the delocalization of the electron on the scale of its Compton wavelength, or the delocalization of the photon on the scale of its wavelength in the waveguide. The presence of the spin-orbit interaction leads to the prediction of several rotational effects: the spatial or time evolution of either particle's spin or polarization vector is controlled by the sign of its orbital angular momentum quantum number or, conversely, its spatial wave function is controlled by its spin angular momentum.

Leary, C. C.; Smith, Karl H.

2014-02-01

226

Relaxation Dynamics of an Isolated Large-Spin Fermi Gas Far from Equilibrium

NASA Astrophysics Data System (ADS)

A fundamental question in many-body physics is how closed quantum systems reach equilibrium. We address this question experimentally and theoretically in an ultracold large-spin Fermi gas where we find a complex interplay between internal and motional degrees of freedom. The fermions are initially prepared far from equilibrium with only a few spin states occupied. The subsequent dynamics leading to redistribution among all spin states is observed experimentally and simulated theoretically using a kinetic Boltzmann equation with full spin coherence. The latter is derived microscopically and provides good agreement with experimental data without any free parameters. We identify several collisional processes that occur on different time scales. By varying density and magnetic field, we control the relaxation dynamics and are able to continuously tune the character of a subset of spin states from an open to a closed system.

Ebling, Ulrich; Krauser, Jasper Simon; Fläschner, Nick; Sengstock, Klaus; Becker, Christoph; Lewenstein, Maciej; Eckardt, André

2014-04-01

227

NASA Astrophysics Data System (ADS)

We analytically derive deterministic equations of order parameters such as spontaneous magnetization in infinite-range quantum spin systems obeying quantum Monte Carlo dynamics. By means of the Trotter decomposition, we consider the transition probability of Glauber-type dynamics of microscopic states for the corresponding classical system. Under the static approximation, differential equations with respect to macroscopic order parameters are explicitly obtained from the master equation that describes the microscopic-law. We discuss several possible applications of our approach to disordered spin systems for statistical-mechanical informatics. Especially, we argue the ground state searching for infinite-range random spin systems via quantum adiabatic evolution.

Inoue, Jun-Ichi

2011-03-01

228

Quantum Nondemolition Measurement of Large-Spin Ensembles by Dynamical Decoupling

NASA Astrophysics Data System (ADS)

Quantum nondemolition (QND) measurement of collective variables by off-resonant optical probing has the ability to create entanglement and squeezing in atomic ensembles. Until now, this technique has been applied to real or effective spin one-half systems. We show theoretically that the buildup of Raman coherence prevents the naive application of this technique to larger spin atoms, but that dynamical decoupling can be used to recover the ideal QND behavior. We experimentally demonstrate dynamical decoupling by using a two-polarization probing technique. The decoupled QND measurement achieves a sensitivity 5.7(6) dB better than the spin projection noise.

Koschorreck, M.; Napolitano, M.; Dubost, B.; Mitchell, M. W.

2010-08-01

229

Quantum nondemolition measurement of large-spin ensembles by dynamical decoupling.

Quantum nondemolition (QND) measurement of collective variables by off-resonant optical probing has the ability to create entanglement and squeezing in atomic ensembles. Until now, this technique has been applied to real or effective spin one-half systems. We show theoretically that the buildup of Raman coherence prevents the naive application of this technique to larger spin atoms, but that dynamical decoupling can be used to recover the ideal QND behavior. We experimentally demonstrate dynamical decoupling by using a two-polarization probing technique. The decoupled QND measurement achieves a sensitivity 5.7(6) dB better than the spin projection noise. PMID:20868158

Koschorreck, M; Napolitano, M; Dubost, B; Mitchell, M W

2010-08-27

230

Magnon softening in a ferromagnetic monolayer: A first-principles spin dynamics study

NASA Astrophysics Data System (ADS)

We study the Fe/W(110) monolayer system through a combination of first-principles calculations and atomistic spin dynamics simulations. We focus on the dispersion of the spin-waves parallel to the [001] direction. Our results compare favorably with the experimental data of Prokop [Phys. Rev. Lett. 102, 177206 (2009)] and correctly capture a drastic softening of the magnon spectrum, with respect to bulk bcc Fe. The suggested shortcoming of the itinerant electron model, in particular that given by density functional theory, is refuted. We also demonstrate that finite-temperature effects are significant, and that atomistic spin dynamics simulations represent a powerful tool with which to include these.

Bergman, Anders; Taroni, Andrea; Bergqvist, Lars; Hellsvik, Johan; Hjörvarsson, Björgvin; Eriksson, Olle

2010-04-01

231

Perfusion measurements using dynamic susceptibility contrast imaging provide additional information about the mean vessel size of microvasculature when supplemented with a dual gradient echo (GE) - spin echo (SE) contrast. Dynamic increase in the corresponding transverse relaxation rate constant changes, ?R2GE and ?R2SE , forms a loop on the (? R2SE3/2, ?R2GE ) plane, rather than a reversible line. The shape of the loop and the direction of its passage differentiate between healthy brain and pathological tissue, such as tumour and ischemic tissue. By considering a tree model of microvasculature, the direction of the loop is found to be influenced mainly by the relative arterial and venous blood volume, as well as the tracer bolus dispersion. A parameter ? is proposed to characterize the direction and shape of the loop, which might be considered as a novel imaging marker for describing the pathology of cerebrovascular network. PMID:22611004

Xu, Chao; Kiselev, Valerij G; Möller, Harald E; Fiebach, Jochen B

2013-04-01

232

Voltage control of the spin dynamics of an exciton in a semiconductor quantum dot.

We report the observation of a spin-flip process in a quantum dot whereby a dark exciton with total angular momentum L = 2 becomes a bright exciton with L = 1. The spin-flip process is revealed in the decay dynamics following nongeminate excitation. We are able to control the spin-flip rate by more than an order of magnitude simply with a dc voltage. The spin-flip mechanism involves a spin exchange with the Fermi sea in the back contact of our device and corresponds to the high temperature Kondo regime. We use the Anderson Hamiltonian to calculate a spin-flip rate, and we find excellent agreement with the experimental results. PMID:16090209

Smith, J M; Dalgarno, P A; Warburton, R J; Govorov, A O; Karrai, K; Gerardot, B D; Petroff, P M

2005-05-20

233

Dynamics of laser-induced spin reorientation in Co/SmFeO3 heterostructure

NASA Astrophysics Data System (ADS)

Ultrafast control of a ferromagnet (FM) via exchange coupling with an antiferromagnet (AFM) is demonstrated in a Co/SmFeO3 heterostructure. Employing time-resolved photoemission electron microscopy combined with x-ray magnetic circular dichroism, a sub-100-ps change of the Co spins orientation by up to 10? driven by the ultrafast heating of the SmFeO3 orthoferrite substrate through its spin reorientation phase transition is revealed. Numerical modeling of the ultrafast-laser-induced heat profile in the heterostructure, and the subsequent coupled spins dynamics and equilibration of the spin systems suggest that the localized laser-induced spin reorientation is hindered compared with the static case. Moreover, numerical simulations show that a relatively small Co/SmFeO3 exchange interaction could be sufficient to induce a complete and fast spin reorientation transition (SRT).

Le Guyader, L.; Kleibert, A.; Nolting, F.; Joly, L.; Derlet, P. M.; Pisarev, R. V.; Kirilyuk, A.; Rasing, Th.; Kimel, A. V.

2013-02-01

234

Brownian motion and quantum dynamics of magnetic monopoles in spin ice

NASA Astrophysics Data System (ADS)

Spin ice illustrates many unusual magnetic properties, including zero point entropy, emergent monopoles and a quasi liquid-gas transition. To reveal the quantum spin dynamics that underpin these phenomena is an experimental challenge. Here we show how crucial information is contained in the frequency dependence of the magnetic susceptibility and in its high frequency or adiabatic limit. The typical response of Dy2Ti2O7 spin ice indicates that monopole diffusion is Brownian but is underpinned by spin tunnelling and is influenced by collective monopole interactions. The adiabatic response reveals evidence of driven monopole plasma oscillations in weak applied field, and unconventional critical behaviour in strong applied field. Our results clarify the origin of the relatively high frequency response in spin ice. They disclose unexpected physics and establish adiabatic susceptibility as a revealing characteristic of exotic spin systems.

Bovo, L.; Bloxsom, J. A.; Prabhakaran, D.; Aeppli, G.; Bramwell, S. T.

2013-02-01

235

Brownian motion and quantum dynamics of magnetic monopoles in spin ice.

Spin ice illustrates many unusual magnetic properties, including zero point entropy, emergent monopoles and a quasi liquid-gas transition. To reveal the quantum spin dynamics that underpin these phenomena is an experimental challenge. Here we show how crucial information is contained in the frequency dependence of the magnetic susceptibility and in its high frequency or adiabatic limit. The typical response of Dy(2)Ti(2)O(7) spin ice indicates that monopole diffusion is Brownian but is underpinned by spin tunnelling and is influenced by collective monopole interactions. The adiabatic response reveals evidence of driven monopole plasma oscillations in weak applied field, and unconventional critical behaviour in strong applied field. Our results clarify the origin of the relatively high frequency response in spin ice. They disclose unexpected physics and establish adiabatic susceptibility as a revealing characteristic of exotic spin systems. PMID:23443563

Bovo, L; Bloxsom, J A; Prabhakaran, D; Aeppli, G; Bramwell, S T

2013-01-01

236

NASA Astrophysics Data System (ADS)

Using time-resolved x-ray resonant magnetic scattering we report on the precessional dynamics of spin valve systems with parallel (P) and antiparallel (AP) orientation of the ferromagnetic layers separated by a nonmagnetic spacer layers. Previously we observed in Co/Cu/Ni81Fe19(Py) spin valve systems an increase of the magnetic damping parameter in Py with changing magnetization direction of Py and Co layers from P to AP orientation [Salikhov , Appl. Phys. Lett.APPLAB0003-695110.1063/1.3633115 99, 092509 (2011)]. We attributed this finding to the configurational dependence of the spin pumping effect [Kim and Chappert, J. Magn. Magn. Mater.JMMMDC0304-885310.1016/j.jmmm.2004.09.036 286, 56 (2005)]. Here we extend our earlier findings by investigating the temperature dependence of the spin pumping effect and possible other causes for the configurational dependence of the damping parameter, such as domain wall induced coupling or magnetic dipole coupling. The main focus is on Co/Cu/Py trilayers and on Co2MnGe/V/Py trilayers with spin valve properties.

Salikhov, R.; Abrudan, R.; Brüssing, F.; Gross, K.; Luo, C.; Westerholt, K.; Zabel, H.; Radu, F.; Garifullin, I. A.

2012-10-01

237

Electron spin dynamics in Fe-doped InP

NASA Astrophysics Data System (ADS)

We have used time-resolved Kerr rotation to investigate carrier spin relaxation in bulk InP:Fe from 80 K to room temperature. We observe several coexisting mechanisms contributing to spin relaxation with different time scales, as well as a rich but intricate dependence on the illumination frequency and intensity. In particular, we find indications of strong many-body interactions that result in a slower relaxation rate with increasing excitation intensity and that, possibly, generate spin level splitting in the absence of magnetic fields.

Li, Bo; Tamargo, Maria C.; Meriles, Carlos A.

2007-11-01

238

Entanglement dynamics of spin systems in pure states

NASA Astrophysics Data System (ADS)

We investigate numerically the appearance and evolution of entanglement in spin systems prepared initially in a pure state. We consider the dipolar coupling spin systems of different molecular structures: benzene C6H6 , cyclopentane C5H10 , sodium butyrate CH3(CH2)2CO2Na , and calcium hydroxyapatite Ca5(OH)(PO4)3 . Numerical simulations show that the close relationship exists between the intensity of second order (2Q) coherences and concurrences of nearest spins in a cyclopentane molecule.

Furman, G. B.; Meerovich, V. M.; Sokolovsky, V. L.

2009-09-01

239

Dynamical spectra of quantum strings in quantum spin ice

NASA Astrophysics Data System (ADS)

String-like excitations in quantum spin-ice are a fascinating manifestation of quantum fluctuations and may be observable in materials such as Yb2Ti2O7 and Pr2Zr2O7. We study quantum spin-ice under external magnetic fields on both the checkerboard and pyrochlore lattice for experimentally relevant conditions. We show that excitations in quantum spin ice may be string-like, and that stronger quantum fluctuations reduce string tension and lead to deconfined monopoles. Additionally, we discuss the crossover from strings to magnons in the high-field regime. We provide predictions for observing strings via inelastic neutron scattering and THz spectroscopy.

Fuhrman, Wesley; Wan, Yuan; Tchernyshyov, Oleg

2013-03-01

240

Cavity Exciton-Polaritons, Bose Einstein Condensation and Spin Dynamics

An introduction giving elementary properties of cavity exciton-polariton will be given. The condition of occurrence of the polariton lasing effect and of the polariton Bose Eintein condensation will be discussed. The impact of the structural disorder on the superfluid behavior of polariton condensates will be analysed. The spin properties of polariton condensates will be discussed. I will show how the anisotropy of the polariton-polariton interaction leads to the suppression of zeeman splitting for polariton condensates (spin Meissner effects). I will show how the combined impact of disorder and spin Meissner effect can lead to the formation of a new condense phase. I will show how these phenomena can allow for the realization of a polaritonic Datta Das spin transistor.

Malpuech, Guillaume; Solnyshkov, Dmitry [LASMEA, CNRS and University Blaise Pascal Clermont Ferrand (France); Shelykh, Ivan [Science Institute University of Reykjavik, Reykjavik (Iceland); St. Petersburg State Polytechnical University, St. Petersburg (Russian Federation)

2009-10-07

241

Noncompact dynamical symmetry of a spin-orbit-coupled oscillator

NASA Astrophysics Data System (ADS)

We explain the finite as well as infinite degeneracy in the spectrum of a particular system of spin-1/2 fermions with spin-orbit coupling in three spatial dimensions. Starting from a generalized Runge-Lenz vector, we explicitly construct a complete set of symmetry operators, which span a noncompact SO(3,2) algebra. The degeneracy of the physical spectrum only involves an infinite, so-called singleton representation. In the branch where orbital and spin angular momentum are aligned, the full representation appears, constituting a three-dimensional analog of Landau levels. Antialigning the spin leads to a finite degeneracy due to a truncation of the singleton representation. We conclude the paper by constructing the spectrum generating algebra of the problem.

Haaker, S. M.; Bais, F. A.; Schoutens, K.

2014-03-01

242

Chaotic Dynamics of Stellar Spin in Binaries and the Production of Misaligned Hot Jupiters. Part II

NASA Astrophysics Data System (ADS)

Secular Kozai oscillations, induced by a distant stellar companion and acting in concert with tidal dissipation, is one of the major channels for the production of hot Jupiters (extrasolar gas giants in 1-5 day orbits) and close stellar binaries. This mechanism is particularly attractive due to the high degree of misalignment between the stellar spin and planet/binary orbital angular momentum axes that has been observed in many systems. In the typical Kozai picture, this misalignment is thought to be the result of large variation in the planet's orbital axis, while the stellar spin orientation remains mostly fixed. Here we demonstrate that gravitational interaction between the stellar spin and the planetary orbit can induce a variety of dynamical behaviors for the stellar spin evolution during the Kozai cycle. In particular, in systems hosting giant planets, the stellar spin exhibits rich, often strongly chaotic dynamics, with Lyapunov times as short as $10 Myr. This arises from secular spin-orbit resonances and resonance overlaps. We construct Poincar\\'{e} surfaces of section to demonstrate thechaotic behavior. As the system parameters (such as planet mass) vary, ``periodic islands'' can appear in largely chaotic domains, in a manner reminiscent of the logistic map or Lorenz chaos. We show that in the presence of tidal dissipation, the memory of chaotic spin evolution can be preserved, leaving an imprint on the final spin-orbit misalignment angles.

Anderson, Kassandra R.; Lai, Dong

2014-05-01

243

Chaotic Dynamics of Stellar Spin in Binaries and the Production of Misaligned Hot Jupiters

NASA Astrophysics Data System (ADS)

Secular Kozai oscillation, induced by a distant stellar companion and acting in concert with tidal dissipation, is one of the major channels for the production of hot Jupiters (extrasolar gas giants in 1-5 day orbits) and close stellar binaries. This mechanism is particularly attractive due to the high degree of misalignment between the stellar spin and planet/binary orbital angular momentum axes that has been observed in many systems. In the typical Kozai picture, this misalignment is thought to be the result of large variation in the planet’s orbital axis, while the stellar spin orientation remains mostly fixed. Here we demonstrate that gravitational interaction between the stellar spin and the planetary orbit can induce a variety of dynamical behaviors for the stellar spin evolution during the Kozai cycle. In particular, in systems hosting giant planets, the stellar spin exhibits rich, often strongly chaotic dynamics, with Lyapunov times as short as 10 Myr. This arises from secular spin-orbit resonances and resonance overlaps. We construct Poincare surfaces of section to demonstrate the chaotic behavior. As the system parameters (such as planet mass) vary, “periodic islands” can appear in largely chaotic domains, in a manner reminiscent of the logistic map or Lorenz chaos. We show that in the presence of tidal dissipation, the memory of chaotic spin evolution can be preserved, leaving an imprint on the final spin-orbit misalignment angles.

Storch, Natalia I; Lai, Dong

2014-05-01

244

Molecular dynamics simulations (MD) were carried out to model the miscibility behavior of blends of poly(p-dioxanone) (PPDO) with poly(vinylphenol) (PVPh). The Hildebrand solubility parameters of the pure polymers and the Flory-Huggins interaction parameters of the blends at different compositions were computed. Negative interaction parameters were found across the whole range of compositions, suggesting the miscibility of the system, in agreement with the experimental results. The interaction parameter obtained from melting point depression studies was also found to be in good agreement with the value computed from the simulations. The repeat unit of PPDO contains one ether and one ester group, and both can act as hydrogen bond acceptors. The radial distribution functions (RDFs) between those groups and the hydroxyl groups of PVPh were computed to investigate the competence between the acceptor groups for the specific interactions. The RDFs indicate that interassociation occurs mainly with the ester groups, which is detrimental to the ether groups. This result was also corroborated by the analysis of the hydroxyl stretching region of the blends using Fourier transform infrared spectroscopy (FTIR). The good overall agreement found between the simulated and the experimental data reveals the importance of the molecular modeling techniques in the analysis of the miscibility behavior of polymer blends. PMID:23249364

Martínez de Arenaza, Inger; Hernandez-Montero, Natalia; Meaurio, Emilio; Sarasua, Jose-Ramon

2013-01-17

245

NASA Astrophysics Data System (ADS)

We have investigated numerically the model of Klemm, Thomann, and Johnston for La2-zCuO4-y. We assume for computational simplicity that the orthorhombic symmetry-breaking energy is large, implying Ising-like spin interactions predominate. Monte Carlo calculations suggest that the ground states exhibit quasi-long-range order in the orthorhombic c-axis direction, but are frustrated (or incommensurate) in the a-axis direction. The excited states often exhibit triplet pairs of spins that are flipped relative to the ground state.

Fay, D.; Klemm, R. A.; Monien, H.

1988-06-01

246

Low energy spin dynamics in the spin ice Ho2Sn2O7.

The magnetic properties of Ho(2)Sn(2)O(7) have been investigated and compared to other spin ice compounds. Although the lattice has expanded by 3% relative to the better studied Ho(2)Ti(2)O(7) spin ice, no significant changes were observed in the high temperature properties, T is more or approximately equal to 20 K. As the temperature is lowered and correlations develop, Ho(2)Sn(2)O(7) enters its quantum phase at a slightly higher temperature than Ho(2)Ti(2)O(7) and is more antiferromagnetic in character. Below 80 K a weak inelastic mode associated with the holmium nuclear spin system has been measured. The hyperfine field at the holmium nucleus was found to be ?700 T. PMID:22293128

Ehlers, G; Huq, A; Diallo, S O; Adriano, C; Rule, K C; Cornelius, A L; Fouquet, P; Pagliuso, P G; Gardner, J S

2012-02-22

247

National Technical Information Service (NTIS)

The extended Peierls-Hubbard model is used to study the competition of the spin-density-wave (SDW) and charge-density-wave (CDW) states as well as the attendant localized excitations in quasi-one-dimensional systems like MX-chains. The ground state proper...

W. Wang Z. Su L. Yu C. Wang

1992-01-01

248

Direct Dynamical Evidence for the Spin Glass Lower Critical Dimension 2

NASA Astrophysics Data System (ADS)

A dynamical method is introduced to study the effect of dimensionality on phase transitions. Direct experimental measurements for the lower critical dimension for spin glasses is provided as an example. The method makes use of the spin glass correlation length ?(t,T). Once nucleated, it can become comparable to sample dimensions in convenient time and temperature ranges. Thin films of amorphous Ge:Mn alloys were prepared with thickness L ?15.5 nm. Conventional behavior is observed as long as ?(t,T)

Guchhait, Samaresh; Orbach, Raymond

2014-03-01

249

Exact out-of-equilibrium central spin dynamics from integrability

NASA Astrophysics Data System (ADS)

We consider a Gaudin magnet (central spin model) with a time-dependent exchange couplings. We explicitly show that the Schrödinger equation is analytically solvable in terms of generalized hypergeometric functions for particular choices of the time dependence of the coupling constants. Our method establishes a new link between this system and the SU\\left( 2 \\right) Wess-Zumino-Witten model, and sheds new light on the implications of integrability in out-of-equilibrium quantum physics. As an application, a driven four-spin system is studied in detail.

Fioretto, Davide; Caux, Jean-Sébastien; Gritsev, Vladimir

2014-04-01

250

Experimental test of the new analytic matrix formalism for spin dynamics

We recently started testing Chao's proposed new matrix formalism for describing the spin dynamics due to a single spin resonance. The Chao formalism is probably the first fundamental improvement of the Froissart-Stora equation in that it allows analytic calculations of the beam polarization's behavior inside a resonance. We tested the Chao formalism using a 1.85GeV\\/c polarized deuteron beam stored in

V. S. Morozov; A. W. Chao; A. D. Krisch; M. A. Leonova; R. S. Raymond; D. W. Sivers; V. K. Wong; R. Gebel; A. Lehrach; B. Lorentz; R. Maier; D. Prasuhn; H. Stockhorst; F. Hinterberger; K. Ulbrich; A. Schnase

2007-01-01

251

Edge exponent in the dynamic spin structure factor of the Yang-Gaudin model

NASA Astrophysics Data System (ADS)

The dynamic spin structure factor S(k,?) of a system of spin-1/2 bosons is investigated at arbitrary strength of the interparticle repulsion. As a function of ? it is shown to exhibit a power-law singularity at the threshold frequency defined by the energy of a magnon at given k . The power-law exponent is found exactly using a combination of the Bethe ansatz solution and an effective-field theory approach.

Zvonarev, M. B.; Cheianov, V. V.; Giamarchi, T.

2009-11-01

252

Decay of Rabi Oscillations by Dipolar-Coupled Dynamical Spin Environments

We study the Rabi oscillations decay of a spin decohered by a spin bath whose internal dynamics is caused by dipolar coupling between the bath spins. The form and rate of decay as a function of the intrabath coupling is obtained analytically, and confirmed numerically. The complex form of decay smoothly varies from power law to exponential, and the rate changes nonmonotonically with the intrabath coupling, decreasing for both slow and fast baths. The form and rate of Rabi oscillations decay can be used to experimentally determine the intrabath coupling strength for a broad class of solid-state systems.

Dobrovitski, V.V.; Feiguin, A.E.; Hanson, R.; Awschalom, D.D.

2009-06-09

253

Low temperature spin dynamics in Cr7Ni-Cu-Cr7Ni coupled molecular rings

NASA Astrophysics Data System (ADS)

Proton Nuclear Magnetic Resonance (NMR) relaxation measurements have been performed down to very low temperature (50 mK) to determine the effect of coupling two Cr7Ni molecular rings via a Cu2+ ion. No difference in the spin dynamics was found from nuclear spin lattice relaxation down to 1.5 K. At lower temperature, the 1H-NMR line broadens dramatically indicating spin freezing. From the plot of the line width vs. magnetization, it is found that the freezing temperature is higher (260 mK) in the coupled ring with respect to the single Cr7Ni ring (140 mK).

Bordonali, L.; Furukawa, Y.; Mariani, M.; Sabareesh, K. P. V.; Garlatti, E.; Carretta, S.; Lascialfari, A.; Timco, G.; Winpenny, R. E. P.; Borsa, F.

2014-05-01

254

Spin-Fermion Models for Manganites and Diluted Magnetic Semiconductors: A Dynamical Mean Field Study

NASA Astrophysics Data System (ADS)

Using Dynamical Mean Field Theory (DMFT) we derive general expressions for the Curie Temperature (Tc) of a spin-fermion model for any coupling constant J and any concentration of localized spins x. In the case of manganites, we compare these results with those obtained previously for the case of an infinite Hund's coupling JH. In the case of diluted magnetic semiconductors (DMS) we discuss the dependence of Tc on model parameters and the effect of the inclusion of a more realistic band structure. We show that DMFT is a powerful tool to study spin-fermion models for DMS in the weak coupling regime.

Popescu, Florentin; Alvarez, Gonzalo; Dagotto, Elbio

2005-03-01

255

Large-amplitude spin dynamics driven by a THz pulse in resonance with an electromagnon.

Multiferroics have attracted strong interest for potential applications where electric fields control magnetic order. The ultimate speed of control via magnetoelectric coupling, however, remains largely unexplored. Here, we report an experiment in which we drove spin dynamics in multiferroic TbMnO3 with an intense few-cycle terahertz (THz) light pulse tuned to resonance with an electromagnon, an electric-dipole active spin excitation. We observed the resulting spin motion using time-resolved resonant soft x-ray diffraction. Our results show that it is possible to directly manipulate atomic-scale magnetic structures with the electric field of light on a sub-picosecond time scale. PMID:24603154

Kubacka, T; Johnson, J A; Hoffmann, M C; Vicario, C; de Jong, S; Beaud, P; Grübel, S; Huang, S-W; Huber, L; Patthey, L; Chuang, Y-D; Turner, J J; Dakovski, G L; Lee, W-S; Minitti, M P; Schlotter, W; Moore, R G; Hauri, C P; Koohpayeh, S M; Scagnoli, V; Ingold, G; Johnson, S L; Staub, U

2014-03-21

256

Impurity and boundary effects on magnetic monopole dynamics in spin ice

NASA Astrophysics Data System (ADS)

Using a SQUID magnetometer, we measure the time-dependent magnetic relaxation in Dy2Ti2O7 and find that it decays with a stretched exponential followed by a very slow long-time tail. In a Monte Carlo simulation governed by Metropolis dynamics we find that surface effects and a very low level of stuffed spins (0.30%) - magnetic Dy ions substituted for non-magnetic Ti ions - can explain these signatures in the relaxation. We find that the additional spins trap the magnetic monopole excitations and provide the first example of how defects in a spin-ice material can obstruct the flow of monopoles.

Kycia, J. B.; Revell, H. M.; Yaraskavitch, L. R.; Mason, J. D.; Ross, K. A.; Noad, H. M. L.; Dabkowska, H. A.; Gaulin, B. D.; Henelius, P.

2013-03-01

257

Laser-induced ultrafast spin dynamics in ErFeO3

NASA Astrophysics Data System (ADS)

Using 100-fs optical laser pulses, we have been able to excite and probe spin dynamics in the rare-earth orthoferrite ErFeO3. The investigation was performed in a broad temperature range with the focus on the vicinities of the compensation point Tcomp?47K and the spin reorientation transition region in the interval 86K?T?99K. Spin precession excited by the laser pulse was present in a large part of the investigated temperature range, but was especially strong near the spin reorientation region. In this region the laser pulse also caused an ultrafast spin reorientation. By changing the laser pulse fluence, we could vary both the reorientation amplitude and the reorientation speed. We show that the laser-induced spin dynamics in ErFeO3 is caused in part by heating and in part by the inverse Faraday effect. Comparing to the results of similar experiments in other rare-earth orthoferrites, we found the speed of the laser-induced spin reorientation to be significantly lower. We attribute this finding to the weaker electron-phonon coupling of the Er3+ 4f electrons with the lattice.

de Jong, J. A.; Kimel, A. V.; Pisarev, R. V.; Kirilyuk, A.; Rasing, Th.

2011-09-01

258

Oscillatory Dyakonov-Perel spin dynamics in two-dimensional electron gases

NASA Astrophysics Data System (ADS)

Optical pump-probe measurements of spin dynamics at temperatures down to 1.5K are described for a series of (001)-oriented GaAs/AlGaAs quantum well samples containing high mobility two-dimensional electron gases (2DEGs). For well widths ranging from 5to20nm and 2DEG sheet densities from 1.75×1011to3.5×1011cm-2 , the evolution of a small injected spin population is found to be a damped oscillation rather than an exponential relaxation, consistent with the quasi-collision-free regime of the Dyakonov-Perel spin dynamics. A Monte Carlo simulation method is used to extract the spin-orbit-induced electron spin precession frequency ??(kF)? and electron momentum scattering time ?p* at the Fermi wave vector. The spin decay time passes through a minimum at a temperature corresponding to the transition from collision-free to collision-dominated regimes and ?p* is found to be close to the ensemble momentum scattering time ?p obtained from Hall measurements of electron mobility. The values of ??(kF)? give the Dresselhaus or bulk inversion asymmetry (BIA) coefficient of spin-orbit interaction as a function of electron confinement energy in the quantum wells and show, qualitatively, the behavior expected from k•p theory.

Leyland, W. J. H.; Harley, R. T.; Henini, M.; Shields, A. J.; Farrer, I.; Ritchie, D. A.

2007-11-01

259

Topological excitations and the dynamic structure factor of spin liquids on the kagome lattice

NASA Astrophysics Data System (ADS)

Recent neutron scattering experiments on the spin-1/2 kagome lattice antiferromagnet ZnCu3(OH)6Cl2 (Herbertsmithite) provide the first evidence of fractionalized excitations in a quantum spin liquid state in two spatial dimensions. In contrast to existing theoretical models of both gapped and gapless spin liquids, which give rise to sharp dispersing features in the dynamic structure factor, the measured dynamic structure factor reveals an excitation continuum that is remarkably flat as a function of frequency. Here we show that many experimentally observed features can be explained by the presence of topological vison excitations in a Z2 spin liquid. These visons form flat bands on the kagome lattice, and thus act as a momentum sink for spin-carrying excitations that are probed by neutron scattering. We compute the dynamic structure factor for two different Z2 spin liquids and find that our results for one of them are in qualitative agreement with the neutron scattering experiments above a very low energy cutoff, below which the structure factor is probably dominated by impurities.

Punk, Matthias; Chowdhury, Debanjan; Sachdev, Subir

2014-04-01

260

Computational Fluid Dynamics of Liquid Filled Spinning Shells.

National Technical Information Service (NTIS)

A fully implicit, three-dimensional finite difference simulation of the incompressible Navier-Stokes equations has been cast using upwind operators. A non-inertial coordinate system was used to simulate the fluid motion in a processing and spinning cylind...

J. L. Steger S. R. Chakravarthy

1983-01-01

261

Dynamical magnetic anisotropy in spin--1 molecular systems

NASA Astrophysics Data System (ADS)

We study electronic transport through a deformable spin-1 molecular system in a break junction setup, under the influence of a local vibrational mode. Our study shows that the magnetic anisotropy, which arises due to stretching along the transport axis[Science 328 1370 (2010)], is renormalized by the interactions with vibrations. The coupling induces additional spin--asymmetric hybridizations that contribute to the net molecular anisotropy. We show that the low temperature physics of such device can be described by an anisotropic Kondo model (J> J), with a magnetic anisotropy term, ANetSz^2, negative at zero stretching. A quantum phase transition (QPT) is explored by stretching the molecule, driving ANet into positive values, and changing the character of the device from a non--Fermi--liquid (NFL) to a Fermi liquid (FL) ground state. This transition can be directly observed through the zero--bias conductance, which we find to be finite for negative anisotropy, zero for positive anisotropy, and to reach the unitary limit at ANet 0. At that point, an underscreened spin-1 Kondo ground state appears due to the restitution of the spin-1 triplet degeneracy.

Ruiz-Tijerina, David; Cornaglia, Pablo; Balseiro, Carlos; Ulloa, Sergio

2012-02-01

262

Spin glasses and fragile glasses: Statics, dynamics, and complexity

In this paper I will briefly review some theoretical results that have been obtained in recent years for spin glasses and fragile glasses. I will concentrate my attention on the predictions coming from the so called broken replica symmetry approach and on their experimental verifications. I will also mention the relevance or these results for other fields, and in general for complex systems.

Parisi, Giorgio

2006-01-01

263

Emergent magnetic monopoles and their dynamics in artificial spin ice

Electrically charged particles such as electrons are common in our world. In contrast, no elementary particles with a net magnetic charge have ever been observed. After a recent discovery that magnetic monopoles can emerge in a system of magnetic dipoles [1], much attention has been paid to the behavior of magnetic monopoles in artificial spin ice, arrays of nano-scale magnetic

Yichen Shen; Olga Petrova; Paula Mellado; Oleg Tchernyshyov

2011-01-01

264

Two-level system in spin baths: Non-adiabatic dynamics and heat transport.

We study the non-adiabatic dynamics of a two-state subsystem in a bath of independent spins using the non-interacting blip approximation, and derive an exact analytic expression for the relevant memory kernel. We show that in the thermodynamic limit, when the subsystem-bath coupling is diluted (uniformly) over many (infinite) degrees of freedom, our expression reduces to known results, corresponding to the harmonic bath with an effective, temperature-dependent, spectral density function. We then proceed and study the heat current characteristics in the out-of-equilibrium spin-spin-bath model, with a two-state subsystem bridging two thermal spin-baths of different temperatures. We compare the behavior of this model to the case of a spin connecting boson baths, and demonstrate pronounced qualitative differences between the two models. Specifically, we focus on the development of the thermal diode effect, and show that the spin-spin-bath model cannot support it at weak (subsystem-bath) coupling, while in the intermediate-strong coupling regime its rectifying performance outplays the spin-boson model. PMID:24784256

Segal, Dvira

2014-04-28

265

Two-level system in spin baths: Non-adiabatic dynamics and heat transport

NASA Astrophysics Data System (ADS)

We study the non-adiabatic dynamics of a two-state subsystem in a bath of independent spins using the non-interacting blip approximation, and derive an exact analytic expression for the relevant memory kernel. We show that in the thermodynamic limit, when the subsystem-bath coupling is diluted (uniformly) over many (infinite) degrees of freedom, our expression reduces to known results, corresponding to the harmonic bath with an effective, temperature-dependent, spectral density function. We then proceed and study the heat current characteristics in the out-of-equilibrium spin-spin-bath model, with a two-state subsystem bridging two thermal spin-baths of different temperatures. We compare the behavior of this model to the case of a spin connecting boson baths, and demonstrate pronounced qualitative differences between the two models. Specifically, we focus on the development of the thermal diode effect, and show that the spin-spin-bath model cannot support it at weak (subsystem-bath) coupling, while in the intermediate-strong coupling regime its rectifying performance outplays the spin-boson model.

Segal, Dvira

2014-04-01

266

Competing quantum effects in the dynamics of a flexible water model.

Numerous studies have identified large quantum mechanical effects in the dynamics of liquid water. In this paper, we suggest that these effects may have been overestimated due to the use of rigid water models and flexible models in which the intramolecular interactions were described using simple harmonic functions. To demonstrate this, we introduce a new simple point charge model for liquid water, q-TIP4P/F, in which the O-H stretches are described by Morse-type functions. We have parametrized this model to give the correct liquid structure, diffusion coefficient, and infrared absorption frequencies in quantum (path integral-based) simulations. The model also reproduces the experimental temperature variation of the liquid density and affords reasonable agreement with the experimental melting temperature of hexagonal ice at atmospheric pressure. By comparing classical and quantum simulations of the liquid, we find that quantum mechanical fluctuations increase the rates of translational diffusion and orientational relaxation in our model by a factor of around 1.15. This effect is much smaller than that observed in all previous simulations of empirical water models, which have found a quantum effect of at least 1.4 regardless of the quantum simulation method or the water model employed. The small quantum effect in our model is a result of two competing phenomena. Intermolecular zero point energy and tunneling effects destabilize the hydrogen-bonding network, leading to a less viscous liquid with a larger diffusion coefficient. However, this is offset by intramolecular zero point motion, which changes the average water monomer geometry resulting in a larger dipole moment, stronger intermolecular interactions, and a slower diffusion. We end by suggesting, on the basis of simulations of other potential energy models, that the small quantum effect we find in the diffusion coefficient is associated with the ability of our model to produce a single broad O-H stretching band in the infrared absorption spectrum. PMID:19603998

Habershon, Scott; Markland, Thomas E; Manolopoulos, David E

2009-07-14

267

A theoretical analysis of the optically driven spin dynamics of a single Mn atom in a quantum dot in the presence of magnetic fields in different geometries is presented. When a magnetic field in Faraday configuration is applied, the Mn spin can be flipped from its initial state into each of its six spin eigenstates via optical excitation and manipulation

D. E. Reiter; T. Kuhn; V. M. Axt; P. Machnikowski

2009-01-01

268

Optimal Controller Tested for a Magnetically Suspended Five-Axis Dynamic Spin Rig

NASA Technical Reports Server (NTRS)

NASA Glenn Research Center's Structural Mechanics and Dynamics Branch has developed a fully suspended magnetic bearing system for their Dynamic Spin Rig, which performs vibration tests of turbomachinery blades and components under spinning conditions in a vacuum. Two heteropolar radial magnetic bearings and a thrust magnetic bearing and the associated control system were integrated into the Dynamic Spin Rig to provide magnetic excitation as well as noncontact magnetic suspension of the 35-lb vertical rotor with blades to induce turbomachinery blade vibration (ref. 1). The new system can provide longer run times at higher speeds and larger vibration amplitudes for rotating blades. Also, it was proven that bearing mechanical life was substantially extended and flexibility was increased in the excitation orientation (direction and phasing).

Choi, Benjamin B.

2003-01-01

269

NASA Astrophysics Data System (ADS)

To exploit the quantum coherence of electron spins in solids in future technologies such as quantum manipulating, it's first vital to overcome the problem of spin decoherence due to their coupling the noisy environment. Dynamical decoupling is a particularly promising strategy for combating decoherence. I will briefly introduce the roadmap for dynamical decoupling and show our experimental research on the field in detail. We first applied the optimal dynamical decoupling scheme [1] on electron spins of ensemble sample [2]. Based on the technology, the dynamical decoupling sequence was used to observe the anomalous coherence effect and of single electron spin based on nitrogen-vacancy defect center in diamond [3]. For application, combined the dynamical decoupling together with quantum metrology protocol, the phase estimation was enhanced [4]. Instead of pulsed model, continuous dynamical decoupling was realized in our experiment and applied to protect quantum gate [5]. The next step, we will apply multi flip pulses to enhance the magnetic field sensitivity of NV center towards to the micro-scale magnetic resonance and single molecular imaging. [1] G. S. Uhrig, Phys. Rev. Lett. 98, 100504 (2007) [2] J. Du, et al., Nature 461, 1265 (2009) [3] P. Huang, et al., Nature Communications, 2, 570 (2011) [4] X. Rong, et al., Europhys. Lett. 95, 60005 (2011) [5] X. Xu, et al., Phys. Rev. Lett. 109, 070502 (2012)

Du, Jiangfeng

2013-03-01

270

Nanosecond Scanning Tunneling Microscopy: resolving spin dynamics at the atomic scale

NASA Astrophysics Data System (ADS)

With the advent of nanoelectronics, functional electronic elements advance towards atomic dimensions and analysis techniques need to keep pace. Scanning tunneling microscopes (STM) have evolved into standard tools to measure the static electronic properties of nanostructures, molecules and atoms. Here we show how the STM can be used to access the equally important dynamical properties on time scales ranging from pico- to nanoseconds. We combine inelastic electron tunneling spectroscopy (IETS) with an all-electronic pump-probe measurement scheme and record the dynamical evolution of magnetic atoms on surfaces in the time domain [1]. We focus on the dynamics of electron spin relaxation in transition metal atoms placed onto a copper nitride decoupling layer on Cu(100). On this surface Fe atoms experience large magneto-crystalline anisotropy [2] that enables long spin lifetimes. At the same time the quantum mechanical nature of the discrete spin states allows for an additional path of spin relaxation: quantum tunneling of magnetization. We probe the dynamic behavior associated with this process and find that placing a Cu atom close to a Fe atom boosts the uniaxial anisotropy energy and creates a long-lived spin state with relaxation times in excess of 200 ns. The ability to probe individual nanostructures with atomic spatial and nanosecond temporal resolution opens a new avenue to explore spin dynamics and other dynamical phenomena on the intrinsic length scale of the underlying interactions. [4pt] [1] S. Loth, M. Etzkorn, C. P. Lutz, D. M. Eigler, A. J. Heinrich, Science 329 1628 (2010). [0pt] [2] C.F. Hirjibehedin, et al., Science 317, 1199 (2007).

Loth, Sebastian

2011-03-01

271

Spin dynamics and spin freezing in the triangular lattice antiferromagnets FeGa2S4 and NiGa2S4

NASA Astrophysics Data System (ADS)

Magnetic susceptibility and muon spin relaxation (?SR) experiments have been carried out on the quasi-2D triangular-lattice spin S=2 antiferromagnet FeGa2S4. The ?SR data indicate a sharp onset of a frozen or nearly frozen spin state at T*=31(2) K, twice the spin-glass-like freezing temperature Tf=16(1) K. The susceptibility becomes field dependent below T*, but no sharp anomaly is observed in any bulk property. A similar transition is observed in ?SR data from the spin-1 isomorph NiGa2S4. In both compounds the dynamic muon spin relaxation rate ?d(T) above T* agrees well with a calculation of spin-lattice relaxation by Chubukov, Sachdev, and Senthil in the renormalized classical regime of a 2D frustrated quantum antiferromagnet. There is no firm evidence for other mechanisms. At low temperatures, ?d(T) becomes temperature independent in both compounds, indicating persistence of spin dynamics. Scaling of ?d(T) between the two compounds is observed from ˜Tf to ˜1.5T*. Although the ?SR data by themselves cannot exclude a truly static spin component below T*, together with the susceptibility data they are consistent with a slowly fluctuating “spin gel” regime between Tf and T*. Such a regime and the absence of a divergence in ?d(T) at T* are features of two unconventional mechanisms: (1) binding/unbinding of Z2 vortex excitations, and (2) impurity spins in a nonmagnetic spin-nematic ground state. The absence of a sharp anomaly or history dependence at T* in the susceptibility of FeGa2S4, and the weakness of such phenomena in NiGa2S4, strongly suggest transitions to low-temperature phases with unconventional dynamics.

Zhao, Songrui; Dalmas de Réotier, P.; Yaouanc, A.; MacLaughlin, D. E.; Mackie, J. M.; Bernal, O. O.; Nambu, Y.; Higo, T.; Nakatsuji, S.

2012-08-01

272

We consider spin dynamics for implementation in an atomistic framework and we address the feasibility of capturing processes in the femtosecond regime by inclusion of moment of inertia. In the spirit of an s-d-like interaction between the magnetization and electron spin, we derive a generalized equation of motion for the magnetization dynamics in the semiclassical limit, which is nonlocal in both space and time. Using this result we retain a generalized Landau-Lifshitz-Gilbert equation, also including the moment of inertia, and demonstrate how the exchange interaction, damping, and moment of inertia, all can be calculated from first principles. PMID:22400957

Bhattacharjee, Satadeep; Nordström, Lars; Fransson, Jonas

2012-02-01

273

We present the results of a large-scale numerical study of the equilibrium three-dimensional Edwards-Anderson Ising spin glass with Gaussian disorder. Using parallel tempering (replica exchange) Monte Carlo we measure various static, as well as dynamical quantities, such as the autocorrelation times and round-trip times for the parallel tempering Monte Carlo method. The correlation between static and dynamic observables for 5000 disorder realizations and up to 1000 spins down to temperatures at 20% of the critical temperature is examined. Our results show that autocorrelation times are directly correlated with the roughness of the free-energy landscape. PMID:23410280

Yucesoy, Burcu; Machta, Jonathan; Katzgraber, Helmut G

2013-01-01

274

Element-specific probing of ultrafast spin dynamics in multisublattice magnets with visible light.

We demonstrate the feasibility of element-specific probing of ultrafast spin dynamics in the multisublattice magnet TbFe in the visible spectral range. In particular, we show that one can selectively study the dynamics of Tb and Fe sublattices choosing the wavelength of light below and above 610 nm, respectively. We observe that, despite their antiferromagnetic coupling in the ground state, the Tb and Fe spins temporarily align ferromagnetically after excitation with an intense 55-fs laser pulse, after which they relax to their initial states due to the strong anisotropy in Tb. PMID:23521292

Khorsand, A R; Savoini, M; Kirilyuk, A; Kimel, A V; Tsukamoto, A; Itoh, A; Rasing, Th

2013-03-01

275

Attitude dynamic of spin-stabilized satellites with flexible appendages

NASA Technical Reports Server (NTRS)

Equations of motion and computer programs have been developed for analyzing the motion of a spin-stabilized spacecraft having long, flexible appendages. Stability charts were derived, or can be redrawn with the desired accuracy for any particular set of design parameters. Simulation graphs of variables of interest are readily obtainable on line using program FLEXAT. Finally, applications to actual satellites, such as UK-4 and IMP-1 have been considered.

Renard, M. L.

1973-01-01

276

RosettaEPR: Rotamer Library for Spin Label Structure and Dynamics

An increasingly used parameter in structural biology is the measurement of distances between spin labels bound to a protein. One limitation to these measurements is the unknown position of the spin label relative to the protein backbone. To overcome this drawback, we introduce a rotamer library of the methanethiosulfonate spin label (MTSSL) into the protein modeling program Rosetta. Spin label rotamers were derived from conformations observed in crystal structures of spin labeled T4 lysozyme and previously published molecular dynamics simulations. Rosetta’s ability to accurately recover spin label conformations and EPR measured distance distributions was evaluated against 19 experimentally determined MTSSL labeled structures of T4 lysozyme and the membrane protein LeuT and 73 distance distributions from T4 lysozyme and the membrane protein MsbA. For a site in the core of T4 lysozyme, the correct spin label conformation (?1 and ?2) is recovered in 99.8% of trials. In surface positions 53% of the trajectories agree with crystallized conformations in ?1 and ?2. This level of recovery is on par with Rosetta performance for the 20 natural amino acids. In addition, Rosetta predicts the distance between two spin labels with a mean error of 4.4 Å. The width of the experimental distance distribution, which reflects the flexibility of the two spin labels, is predicted with a mean error of 1.3 Å. RosettaEPR makes full-atom spin label modeling available to a wide scientific community in conjunction with the powerful suite of modeling methods within Rosetta.

Alexander, Nathan S.; Stein, Richard A.; Koteiche, Hanane A.; Kaufmann, Kristian W.; Mchaourab, Hassane S.; Meiler, Jens

2013-01-01

277

Position-dependent dynamics of electronic spin-subband entanglement in a Rashba nanoloop

NASA Astrophysics Data System (ADS)

In this paper, as a complementation to our previous reports, we study the position dependency of the electronic spin-subband entanglement for different spin initial conditions in a quasi-one-dimensional Rashba nanoloop acted upon by a strong perpendicular magnetic field. We compute the von Neumann entropy, a measure of entanglement, as a function of time by explicitly including the confining potential and the Rashba spin-orbit (SO) coupling into the Hamiltonian. An analysis of the von Neumann entropy demonstrates that, due to a fictitious magnetic field arising from Rashba SO coupling, the spin-subband entanglement strongly depends upon the location of electron within the loop. Moreover, it is shown that the position dependency of entanglement dynamics depends upon the spin initial state. When the initial state is a pure one formed by a subband excitation and the z-component of spin states, the entanglement exhibits periodic oscillations with just one local minimum in each oscillation. On the other hand, when the initial state is formed by the subband states and a coherent superposition of spin states, the entanglement still periodically oscillates either with two local minima in each oscillation at ? ? 0, ? or without local minima at ? = 0, ?. The physical reasons behind such behavior are also discussed.

Safaiee, R.; Golshan, M. M.

2013-08-01

278

Electron-nuclei spin dynamics in II-VI semiconductor quantum dots

NASA Astrophysics Data System (ADS)

We report on the dynamics of optically induced nuclear spin polarization in individual CdTe/ZnTe quantum dots loaded with one electron by modulation doping. The fine structure of the hot trion (charged exciton X- with an electron in the P shell) is identified in photoluminescence excitation spectra. A negative polarization rate of the photoluminescence, optical pumping of the resident electron, and the built up of dynamic nuclear spin polarization (DNSP) are observed in time-resolved optical pumping experiments when the quantum dot is excited at higher energy than the hot trion triplet state. The time and magnetic field dependence of the polarization rate of the X- emission allows us to probe the dynamics of formation of the DNSP in the optical pumping regime. We demonstrate using time-resolved measurements that the creation of a DNSP at B=0 T efficiently prevents longitudinal spin relaxation of the electron caused by fluctuations of the nuclear spin bath. The DNSP is built in the microsecond range at high excitation intensity. A relaxation time of the DNSP in about 10 ?m is observed at B=0 T and significantly increases under a magnetic field of a few milli-Tesla. We discuss mechanisms responsible for the fast initialization and relaxation of the diluted nuclear spins in this system.

Le Gall, C.; Brunetti, A.; Boukari, H.; Besombes, L.

2012-05-01

279

Dynamics of a two-level system coupled to a bath of spins

NASA Astrophysics Data System (ADS)

The dynamics of a two-level system coupled to a spin bath is investigated via the numerically exact multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) theory. Consistent with the previous work on linear response approximation [N. Makri, J. Phys. Chem. B 103, 2823 (1999)], it is demonstrated numerically that this spin-spin-bath model can be mapped onto the well-known spin-boson model if the system-bath coupling strength obeys an appropriate scaling behavior. This linear response mapping, however, may require many bath spin degrees of freedom to represent the practical continuum limit. To clarify the discrepancies resulted from different approximate treatments of this model, the population dynamics of the central two-level system has been investigated near the transition boundary between the coherent and incoherent motions via the ML-MCTDH method. It is found that increasing temperature favors quantum coherence in the nonadiabatic limit of this model, which corroborates the prediction in the previous work [J. Shao and P. Hanggi, Phys. Rev. Lett. 81, 5710 (1998)] based on the non-interacting blip approximation (NIBA). However, the coherent-incoherent boundary obtained by the exact ML-MCTDH simulation is slightly different from the approximate NIBA results. Quantum dynamics in other physical regimes are also discussed.

Wang, Haobin; Shao, Jiushu

2012-12-01

280

Dynamics of a two-level system coupled to a bath of spins.

The dynamics of a two-level system coupled to a spin bath is investigated via the numerically exact multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) theory. Consistent with the previous work on linear response approximation [N. Makri, J. Phys. Chem. B 103, 2823 (1999)], it is demonstrated numerically that this spin-spin-bath model can be mapped onto the well-known spin-boson model if the system-bath coupling strength obeys an appropriate scaling behavior. This linear response mapping, however, may require many bath spin degrees of freedom to represent the practical continuum limit. To clarify the discrepancies resulted from different approximate treatments of this model, the population dynamics of the central two-level system has been investigated near the transition boundary between the coherent and incoherent motions via the ML-MCTDH method. It is found that increasing temperature favors quantum coherence in the nonadiabatic limit of this model, which corroborates the prediction in the previous work [J. Shao and P. Hanggi, Phys. Rev. Lett. 81, 5710 (1998)] based on the non-interacting blip approximation (NIBA). However, the coherent-incoherent boundary obtained by the exact ML-MCTDH simulation is slightly different from the approximate NIBA results. Quantum dynamics in other physical regimes are also discussed. PMID:23249041

Wang, Haobin; Shao, Jiushu

2012-12-14

281

Spin crossover in ferropericlase from first-principles molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Ferropericlase is the second-most abundant mineral of the lower mantle of the Earth. It is experimentally known that with increasing pressure, the iron ions in the mineral begin to collapse from a high-spin to low-spin state. This spin crossover alters various properties of the material, and hence a good theoretical understanding of the phenomenon is necessary. Using first-principles molecular dynamics simulations in conjunction with thermodynamic integration, we construct a phase diagram of the spin crossover as a function of pressure and temperature. In addition, we present the thermal equation of state of the mineral up to 140 GPa and 4000 K, and predict that the electrical conductivity of ferropericlase reaches semi-metallic values within the lower mantle.

Holmstrom, Eero; Stixrude, Lars

2014-05-01

282

Persistent spin dynamics intrinsic to amplitude-modulated long-range magnetic order.

An incommensurate elliptical helical magnetic structure in the frustrated coupled-spin-chain system FeTe(2)O(5)Br is surprisingly found to persist down to 53(3) mK (T/T(N)~1/200), according to neutron scattering and muon spin relaxation. In this state, finite spin fluctuations at T?0 are evidenced by muon depolarization, which is in agreement with specific-heat data indicating the presence of both gapless and gapped excitations. We thus show that the amplitude-modulated magnetic order intrinsically accommodates contradictory persistent spin dynamics and long-range order and can serve as a model structure to investigate their coexistence. PMID:23368156

Pregelj, M; Zorko, A; Zaharko, O; Ar?on, D; Komelj, M; Hillier, A D; Berger, H

2012-11-30

283

From coherent motion to localization: dynamics of the spin-boson model at zero temperature

NASA Astrophysics Data System (ADS)

The dynamics of the spin-boson model at zero temperature is investigated using the multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) method. This method allows a numerically exact description of the dynamics of the spin-boson model in a broad range of coupling strengths. The results show the transition of the dynamics from weakly damped coherent motion to incoherent decay and finally to localization upon increase of the system bath coupling strength. A detailed analysis of the incoherent decay for stronger coupling reveals that multiple timescales are involved in the dynamics. Furthermore, the applicability of the scaling limit for large characteristic frequencies of the bath as well as the validity of the non-interacting blip approximation are studied in some detail.

Wang, Haobin; Thoss, Michael

2008-11-01

284

Dynamics of a spinning spacecraft during extension of flexible appendages

NASA Astrophysics Data System (ADS)

This paper addresses the problem of analyzing the deployment of flexible appendages from a central rigid hub of a spinning spacecraft. The rigorous mathematical modeling of mass flow and changing structural configuration of the spacecraft during deployment, while the vehicle experiences small elastic deflection and small angular rate, is presented. The equations of motion are obtained in terms of integro-partial differential equations. An approximate solution for the equations of motion is obtained by using a Raleigh-Ritz method and numerical results are presented for several deployment strategies. For every instantaneous physical configuration of the spacecraft, that extension rate which will lead to unstable behavior is also determined.

Turner, J.; Keat, J.; Messac, A.

1984-05-01

285

Modulating electron dynamics: Modified spin-boson approach

NASA Astrophysics Data System (ADS)

Vibrationally modulated electron transfer in polar media is considered in the framework of a modified spin-boson approach when modulation and solvation degrees of freedom are independent of each other. The transition probability is presented in terms of the infinite series of multidimensional integrals. The solution is rigorously derived in the noninteracting blip approximation for symmetric electron transfer. It is proved that in this approximation the procedure of the direct averaging of the rate constant over modulation bath appears to be correct. Possible applications in molecular electronics, vibrational coherence, long range electron transfer, and solar cells are discussed.

Dahnovsky, Yuri

2006-04-01

286

Simulation of the dynamics of many-body quantum spin systems using phase-space techniques

NASA Astrophysics Data System (ADS)

We reformulate the full quantum dynamics of spin systems using a phase-space representation based on SU(2) coherent states which generates an exact mapping of the dynamics of any spin system onto a set of stochastic differential equations. This representation is superior in practice to an earlier phase-space approach based on Schwinger bosons, with the numerical effort scaling only linearly with system size. By also implementing extrapolation techniques from quasiclassical equations to the full quantum limit, we are able to extend useful simulation times severalfold. This approach is applicable in any dimension including cases where frustration is present in the spin system. The method is demonstrated by simulating quenches in the transverse-field Ising model in one and two dimensions.

Ng, Ray; Sørensen, Erik S.; Deuar, Piotr

2013-10-01

287

Real-time energy dynamics in spin-(1)\\/(2) Heisenberg chains

We study the real-time dynamics of the local energy density in the spin-1\\/2 XXZ chain starting from initial states with an inhomogeneous profile of bond energies. Numerical simulations of the dynamics of the initial states are carried out using the adaptive time-dependent density matrix renormalization group method. We analyze the time dependence of the spatial variance associated with the local

Stephan Langer; Markus Heyl; Ian P. McCulloch; Fabian Heidrich-Meisner

2011-01-01

288

Controlling chaotic behaviour for spin generator and Rossler dynamical systems with feedback control

Different methods are proposed to control chaotic behaviour of the Nuclear Spin Generator (NSG) and Rossler continuous dynamical systems. Linear and nonlinear feedback control techniques are used to suppress chaos. The stabilization of unstable fixed point or unstable periodic solution of chaotic behaviour is achieved. The controlled system is stable under some conditions on the parameters of the system. Stability

A. Hegazi; H. N. Agiza; M. M. El-Dessoky

2001-01-01

289

Lattice-Site-Specific Spin Dynamics in Double Perovskite Sr2CoOsO6

NASA Astrophysics Data System (ADS)

Magnetic properties and spin dynamics have been studied for the structurally ordered double perovskite Sr2CoOsO6. Neutron diffraction, muon-spin relaxation, and ac-susceptibility measurements reveal two antiferromagnetic (AFM) phases on cooling from room temperature down to 2 K. In the first AFM phase, with transition temperature TN1=108 K, cobalt (3d7, S =3/2) and osmium (5d2, S =1) moments fluctuate dynamically, while their average effective moments undergo long-range order. In the second AFM phase below TN2=67 K, cobalt moments first become frozen and induce a noncollinear spin-canted AFM state, while dynamically fluctuating osmium moments are later frozen into a randomly canted state at T ?5 K. Ab initio calculations indicate that the effective exchange coupling between cobalt and osmium sites is rather weak, so that cobalt and osmium sublattices exhibit different ground states and spin dynamics, making Sr2CoOsO6 distinct from previously reported double-perovskite compounds.

Yan, Binghai; Paul, Avijit Kumar; Kanungo, Sudipta; Reehuis, Manfred; Hoser, Andreas; Többens, Daniel M.; Schnelle, Walter; Williams, Robert C.; Lancaster, Tom; Xiao, Fan; Möller, Johannes S.; Blundell, Stephen J.; Hayes, William; Felser, Claudia; Jansen, Martin

2014-04-01

290

Lattice-site-specific spin dynamics in double perovskite Sr2CoOsO6.

Magnetic properties and spin dynamics have been studied for the structurally ordered double perovskite Sr2CoOsO6. Neutron diffraction, muon-spin relaxation, and ac-susceptibility measurements reveal two antiferromagnetic (AFM) phases on cooling from room temperature down to 2 K. In the first AFM phase, with transition temperature TN1=108??K, cobalt (3d7, S=3/2) and osmium (5d2, S=1) moments fluctuate dynamically, while their average effective moments undergo long-range order. In the second AFM phase below TN2=67??K, cobalt moments first become frozen and induce a noncollinear spin-canted AFM state, while dynamically fluctuating osmium moments are later frozen into a randomly canted state at T?5??K. Ab initio calculations indicate that the effective exchange coupling between cobalt and osmium sites is rather weak, so that cobalt and osmium sublattices exhibit different ground states and spin dynamics, making Sr2CoOsO6 distinct from previously reported double-perovskite compounds. PMID:24766007

Yan, Binghai; Paul, Avijit Kumar; Kanungo, Sudipta; Reehuis, Manfred; Hoser, Andreas; Többens, Daniel M; Schnelle, Walter; Williams, Robert C; Lancaster, Tom; Xiao, Fan; Möller, Johannes S; Blundell, Stephen J; Hayes, William; Felser, Claudia; Jansen, Martin

2014-04-11

291

Spin dynamics in magnetic thin films and eletromagnetic properties of metamaterials

In this work, I have investigated the high frequency magnetic properties of a variety of novel materials by using the microwave techniques. The work consists of two parts: (1) spin dynamics study in magnetic multilayer thin films, (2) fabrication and characterization of novel magnetic materials. In the first part, we have observed nonlinear behaviors of the normal Gilbert damping G0

Rong Cao

2009-01-01

292

Effects of ruthenium seed layer on the microstructure and spin dynamics of thin permalloy films

The spin dynamics and microstructure properties of a sputtered 12 nm Ni{sub 81}Fe{sub 19} thin film have been enhanced by the use of a ruthenium seed layer. Both the ferromagnetic resonance field and linewidth are enhanced dramatically as the thickness of ruthenium seed layer is increased. The surface anisotropy energy constant can also be largely tailored from 0.06 to 0.96 erg/cm{sup -2} by changing the seed layer thickness. The changes to the dynamics magnetization properties are caused by both ruthenium seed layer induced changes in the Ni{sub 81}Fe{sub 19} structure properties and surface topography properties. Roughness induced inhomogeneous linewidth broadening is also seen. The damping constant is highly tunable via the ruthenium thickness. This approach can be used to tailor both the structure and spin dynamic properties of thin Ni{sub 81}Fe{sub 19} films over a wide range. And it may benefit the applications of spin dynamics and spin current based devices.

Jin Lichuan; Zhang Huaiwu; Tang Xiaoli; Bai Feiming; Zhong Zhiyong [State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054 (China)

2013-02-07

293

Dynamics of Artificial Kagome `Spin Ice' In Geometrically Frustrated Permalloy Nano Structures

Thin films of ferro-magnetic material with lithographically designed geometries can be used as an analog for the study of spin ice or frustrated systems. Here we study the magnetic structure and magnetization dynamics of permalloy thin films in a frustrated, hexagonal geometry using Transmission Lorentz Microscopy. The permalloy films are evaporated through patterns defined by conventional electron beam lithography to

Yi Qi; Todd Brintlinger; John Cumings

2007-01-01

294

Two approaches to the description of spin dynamics of electron-nuclear system in quantum dots are compared: the quantum-mechanical one is based on direct diagonalization of the model Hamiltonian and semiclassical one is based on coupled equations for precession of mean electron spin and mean spin of nuclear spin fluctuations. The comparison was done for a model problem describing periodic excitation of electron-nuclear system by optical excitation. The computation results show that scattering of parameters related to fluctuation of the nuclear spin system leads to appearance of an ordered state in the system caused by periodic excitation and to the effect of electron-spin mode locking in an external magnetic field. It is concluded that both models can qualitatively describe the mode-locking effect, however give significantly different quantitative results. This may indicate the limited applicability of the precession model for describing the spin dynamics in quantum dots in the presence of optical pumping.

Petrov, M. Yu., E-mail: m.petrov@spbu.ru; Yakovlev, S. V. [Saint Petersburg State University (Russian Federation)

2012-08-15

295

NASA Astrophysics Data System (ADS)

We show that spin-density separation in a Bose gas is not restricted to 1D but also occurs in higher dimensions. The ratio (?) of the intraspecies atom-atom interaction strength to the interspecies interaction strength strongly influences the dynamics of spin-density separation and the elementary excitations. The density wave is phononlike for all values of ?. For ?<1, the spin wave is also phononlike. The spin waves have a quadratic dispersion in the ?=1 coupling regime, while in the phase separated regime (?>1) the spin waves are found to be damped. The dynamical structure factor reveals two distinct peaks corresponding to the density and spin waves for ??1. For ?>1 there is only one dynamical structure factor peak corresponding to the density wave.

Chung, M.-C.; Bhattacherjee, A. B.

2008-08-01

296

Competing Orders in Strongly Correlated Systems

NASA Astrophysics Data System (ADS)

Systems with competing orders are of great interest in condensed matter physics. When two phases have comparable energies, novel interplay effects such can be induced by tuning an appropriate parameter. In this thesis, we study two problems of competing orders - (i) ultracold atom gases with competing superfluidity and Charge Density Wave (CDW) orders, and (ii) low dimensional antiferromagnets with Neel order competing against various disordered ground states. In the first part of the thesis, we study the attractive Hubbard model which could soon be realized in ultracold atom experiments. Close to half-filling, the superfluid ground state competes with a low-lying CDW phase. We study the collective excitations of the superfluid using the Generalized Random Phase Approximation (GRPA) and strong-coupling spin wave analysis. The competing CDW phase manifests as a roton-like excitation. We characterize the collective mode spectrum, setting benchmarks for experiments. We drive competition between orders by imposing superfluid flow. Superflow leads to various instabilities: in particular, we find a dynamical instability associated with CDW order. We also find a novel dynamical incommensurate instability analogous to exciton condensation in semiconductors. In the second part, inspired by experiments on Bi3Mn 4O12(NO3)(BMNO), we first study the interlayer dimer state in spin-S bilayer antiferromagnets. At a critical bilayer coupling strength, condensation of triplet excitations leads to Neel order. In describing this transition, bond operator mean field theory suffers from systematic deviations. We bridge these deviations by taking into account corrections arising from higher spin excitations. The interlayer dimer state shows a field induced Neel transition, as seen in BMNO. Our results are relevant to the quantitative modelling of spin-S dimerized systems. We then study the J1 - J2 model on the honeycomb lattice with frustrating next-nearest neighbour exchange. For J2 >J1/6, quantum and thermal fluctuations lead to lattice nematic states. For S=1/2, this lattice nematic takes the form of a valence bond solid. With J2

Ramachandran, Ganesh

297

The resource-based perspective has done much to identify idiosyncratic firm attributes that may be a principal source of competitive advantages. Unfortunately, there has been little systematic industry evidence to support the strategic importance of core competence, nor has there been much work on the temporal or cumulative nature of core capabilities within an industrial setting. Further, little or no research

Steven T. Walsh; Robert L. Boylan; Chris McDermott; Al Paulson

2005-01-01

298

Academic Freedom, the First Amendment and Competing Stakeholders: The Dynamics of a Changing Balance

ERIC Educational Resources Information Center

The Supreme Court first affirmed the importance of academic freedom in 1957. Yet in subsequent cases, First Amendment precedent has displaced the concept of academic freedom to resolve disputes among competing interests on public campuses, primarily in favor of institutions. This paper draws on the concepts of path dependence and policy space to…

Jorgensen, James D.; Helms, Lelia B.

2008-01-01

299

Domain Wall Dynamics under Nonlocal Spin-Transfer Torque

NASA Astrophysics Data System (ADS)

We study spin-diffusion effects within a continuously variable magnetization distribution, integrating with micromagnetics the diffusive model of Zhang and Li [Phys. Rev. Lett. 93, 127204 (2004)PRLTAO0031-900710.1103/PhysRevLett.93.127204]. Current-driven wall motion is, in the steady velocity regime, shown to be adequately described by an effective nonlocal nonadiabatic parameter. This parameter is found to be 20% larger than its local counterpart for a vortex wall in a NiFe nanostrip and hardly modified for a transverse wall. This may account for the yet unexplained experimental evidence that vortex walls move more easily under current when compared with transverse walls. It is shown that this effective parameter can be derived from the domain wall structure at rest.

Claudio-Gonzalez, David; Thiaville, André; Miltat, Jacques

2012-06-01

300

Magnetic properties and spin dynamics in magnetic molecule {Mn3}

NASA Astrophysics Data System (ADS)

We report dc magnetization and nuclear magnetic resonance (NMR) measurements in a trinuclear manganese compound, {Mn3}, with formula [Mn3O(O2CCH3)6(C5H5N)3].C5H5N. The magnetic properties are characterized by two antiferromagnetic (AF) coupling constants, J=-7.9 K and J'=-27.6 K. 1H NMR linewidth strongly depends on both the magnetic field and temperature, and is quantitatively explained by the dipolar interaction between proton nuclei and Mn ion spins. The strong enhancement of T1-1 at low temperatures is ascribed to the slowing down of magnetic fluctuations resulting from building up of AF correlations. From the T dependence of T1-1 at low T, we obtained the gap ?NMR=19 K, in qualitative agreement with the gap ??12 K obtained from susceptibility ?.

Suh, B. J.; Procissi, D.; Jung, J. K.; Bud'Ko, S.; Jeon, W. S.; Kim, Y. J.; Jung, D.-Y.

2003-05-01

301

Domain wall dynamics under nonlocal spin-transfer torque.

We study spin-diffusion effects within a continuously variable magnetization distribution, integrating with micromagnetics the diffusive model of Zhang and Li [Phys. Rev. Lett. 93, 127204 (2004)]. Current-driven wall motion is, in the steady velocity regime, shown to be adequately described by an effective nonlocal nonadiabatic parameter. This parameter is found to be 20% larger than its local counterpart for a vortex wall in a NiFe nanostrip and hardly modified for a transverse wall. This may account for the yet unexplained experimental evidence that vortex walls move more easily under current when compared with transverse walls. It is shown that this effective parameter can be derived from the domain wall structure at rest. PMID:23003651

Claudio-Gonzalez, David; Thiaville, André; Miltat, Jacques

2012-06-01

302

Advances and applications of dynamic-angle spinning nuclear magnetic resonance

This dissertation describes nuclear magnetic resonance experiments and theory which have been developed to study quadrupolar nuclei (those nuclei with spin greater than one-half) in the solid state. Primarily, the technique of dynamic-angle spinning (DAS) is extensively reviewed and expanded upon in this thesis. Specifically, the improvement in both the resolution (two-dimensional pure-absorptive phase methods and DAS angle choice) and sensitivity (pulse-sequence development), along with effective spinning speed enhancement (again through choice of DAS conditions or alternative multiple pulse schemes) of dynamic-angle spinning experiment was realized with both theory and experimental examples. The application of DAS to new types of nuclei (specifically the {sup 87}Rb and {sup 85}Rb nuclear spins) and materials (specifically amorphous solids) has also greatly expanded the possibilities of the use of DAS to study a larger range of materials. This dissertation is meant to demonstrate both recent advances and applications of the DAS technique, and by no means represents a comprehensive study of any particular chemical problem.

Baltisberger, J.H.

1993-06-01

303

Dynamic nuclear spin polarization of liquids and gases in contact with nanostructured diamond.

Optical pumping of spin polarization can produce almost complete spin order but its application is restricted to select atomic gases and condensed matter systems. Here, we theoretically investigate a novel route to nuclear spin hyperpolarization in arbitrary fluids in which target molecules are exposed to polarized paramagnetic centers located near the surface of a host material. We find that adsorbed nuclear spins relax to positive or negative polarization depending on the average paramagnetic center depth and nanoscale surface topology. For the particular case of optically pumped nitrogen-vacancy centers in diamond, we calculate strong nuclear spin polarization at moderate magnetic fields provided the crystal surface is engineered with surface roughness in the few-nanometer range. The equilibrium nuclear spin temperature depends only weakly on the correlation time describing the molecular adsorption dynamics and is robust in the presence of other, unpolarized paramagnetic centers. These features could be exploited to polarize flowing liquids or gases, as we illustrate numerically for the model case of a fluid brought in contact with an optically pumped diamond nanostructure. PMID:24754755

Abrams, Daniel; Trusheim, Matthew E; Englund, Dirk R; Shattuck, Mark D; Meriles, Carlos A

2014-05-14

304

Competing magnetic interactions and interfacial frozen spin in Ni-NiO core-shell nano-rods

NASA Astrophysics Data System (ADS)

This work investigates the complex interfacial magnetism of free- standing Ni-NiO core-shell rods fabricated by electroless plating and an anodic aluminum oxide template. Vertical magnetization shift, arising from opposite field cooling conditions, suggests frozen spin (FS) at the Ni-NiO interface. The FS was related to the pinning effects of the NiO on the Ni, which mediated the interfacial antiferromagnetic (AFM)-ferromagnetic (FM) coupling, leading to the temperature-dependent properties of the rods. The FS was evident below 100 K, at which point the NiO-AFM dominated the properties with a suppressed coercive field and non-saturated magnetization. Above 100 K, however, the Ni-FM dominated and the FM phase was restored, due to the disappearance of the FS.

Tseng, Yuan-Chieh; Hsu, Hao-Chun; Lo, Chih-Chieh

2012-02-01

305

Dynamical transition in the D =3 Edwards-Anderson spin glass in an external magnetic field

NASA Astrophysics Data System (ADS)

We study the off-equilibrium dynamics of the three-dimensional Ising spin glass in the presence of an external magnetic field. We have performed simulations both at fixed temperature and with an annealing protocol. Thanks to the Janus special-purpose computer, based on field-programmable gate array (FPGAs), we have been able to reach times equivalent to 0.01 s in experiments. We have studied the system relaxation both for high and for low temperatures, clearly identifying a dynamical transition point. This dynamical temperature is strictly positive and depends on the external applied magnetic field. We discuss different possibilities for the underlying physics, which include a thermodynamical spin-glass transition, a mode-coupling crossover, or an interpretation reminiscent of the random first-order picture of structural glasses.

Baity-Jesi, M.; Baños, R. A.; Cruz, A.; Fernandez, L. A.; Gil-Narvion, J. M.; Gordillo-Guerrero, A.; Iñiguez, D.; Maiorano, A.; Mantovani, F.; Marinari, E.; Martin-Mayor, V.; Monforte-Garcia, J.; Muñoz Sudupe, A.; Navarro, D.; Parisi, G.; Perez-Gaviro, S.; Pivanti, M.; Ricci-Tersenghi, F.; Ruiz-Lorenzo, J. J.; Schifano, S. F.; Seoane, B.; Tarancon, A.; Tripiccione, R.; Yllanes, D.; Janus Collaboration

2014-03-01

306

Dynamical transition in the D=3 Edwards-Anderson spin glass in an external magnetic field.

We study the off-equilibrium dynamics of the three-dimensional Ising spin glass in the presence of an external magnetic field. We have performed simulations both at fixed temperature and with an annealing protocol. Thanks to the Janus special-purpose computer, based on field-programmable gate array (FPGAs), we have been able to reach times equivalent to 0.01 s in experiments. We have studied the system relaxation both for high and for low temperatures, clearly identifying a dynamical transition point. This dynamical temperature is strictly positive and depends on the external applied magnetic field. We discuss different possibilities for the underlying physics, which include a thermodynamical spin-glass transition, a mode-coupling crossover, or an interpretation reminiscent of the random first-order picture of structural glasses. PMID:24730822

Baity-Jesi, M; Baños, R A; Cruz, A; Fernandez, L A; Gil-Narvion, J M; Gordillo-Guerrero, A; Iñiguez, D; Maiorano, A; Mantovani, F; Marinari, E; Martin-Mayor, V; Monforte-Garcia, J; Muñoz Sudupe, A; Navarro, D; Parisi, G; Perez-Gaviro, S; Pivanti, M; Ricci-Tersenghi, F; Ruiz-Lorenzo, J J; Schifano, S F; Seoane, B; Tarancon, A; Tripiccione, R; Yllanes, D

2014-03-01

307

Carrier and Spin Dynamics in InAsP Ternary Alloys

NASA Astrophysics Data System (ADS)

The recent rapid progress in the field of spintronics involves extensive measurements of carrier and spin relaxation dynamics in III-V semiconductors. In addition, as the switching rates in electronic and optoelectronic devices are pushed to higher frequencies, it is important to understand carrier dynamic phenomena in semiconductors on femtosecond time-scales. In this work, we employed time and polarization-resolved differential transmission measurements in near and mid-infrared, to probe carrier and spin relaxation times in several InAsP ternary alloys. Our results demonstrate the unique and complex dynamics in this material system that can be important for electronic and optoelectronic devices. We present our experimental observations and compare them with the observations in InAs and InP.

Meeker, Michael; McCutcheon, Kelly; Bhowmick, Mithun; Magill, Brenden; Khodaparast, Giti A.; Tischler, Joe G.; Choi, Sukgeun G.; Palmstrøm, Chris J.

2013-03-01

308

Deployment dynamics of a simplified spinning IKAROS solar sail via absolute coordinate based method

NASA Astrophysics Data System (ADS)

The spinning solar sail of large scale has been well developed in recent years. Such a solar sail can be considered as a rigid-flexible multibody system mainly composed of a spinning central rigid hub, a number of flexible thin tethers, sail membranes, and tip masses. A simplified interplanetary kite-craft accelerated by radiation of the Sun (IKAROS) model is established in this study by using the absolute-coordinate-based (ACB) method that combines the natural coordinate formulation (NCF) describing the central rigid hub and the absolute nodal coordinate formulation (ANCF) describing flexible parts. The initial configuration of the system in the second-stage deployment is determined through both dynamic and static analyses. The huge set of stiff equations of system dynamics is solved by using the generalized-alpha method, and thus the deployment dynamics of the system can be well understood.

Zhao, Jiang; Tian, Qiang; Hu, Hai-Yan

2013-02-01

309

Spin dynamics of the LAGEOS satellite in support of a measurement of the Earth's gravitomagnetism

LAGEOS is an accurately tracked, dense spherical satellite covered with 426 retroreflectors. Ciufolini has suggested the launch of an additional satellite (LAGEOS-3) into an orbit supplementary to that of the 1976-launched LAGEOS-1. In addition to providing a more accurate real-time measurement of the Earth's length of day and polar wobble, this paired-satellite experiment would provide the first direct measurement of the general relativistic frame-dragging effect. Of the five dominant error sources in this experiment, the largest one involves surface forces on the satellite, and their consequent impact on the orbital nodal precession. The surface forces are a function of the spin dynamics of the satellite. Consequently, we undertake here a theoretical effort to model the spin dynamics of LAGEOS. In this paper we derive, and solve numerically, a set of Euler equations that evolve the angular momentum vector for a slightly oblate spheroid of brass orbiting an Earth-like mass, idealized as being a perfect sphere and having a perfect polar-oriented dipole magnetic field. We have identified three phases of the rotational dynamics---a fast spin phase, a spin-orbit resonance phase, and an asymptotic (tidally locked) phase. From our numerical runs we give analytic expressions for this tidally locked phase.

Habib, S. (Theoretical Astrophysics Group (T-6, MS B288), Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)); Holz, D.E. (Department of Physics, Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637 (United States) Theoretical Astrophysics Group (T-6, MS B288), Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)); Kheyfets, A. (Department of Mathematics, North Carolina State University, Raleigh, North Carolina 27695-8205 (United States)); Matzner, R.A. (Center for Relativity and Physics Department, The University of Texas at Austin, Austin, Texas 78712-1081 (United States) Applied Research Laboratories, The University of Texas at Austin, P.O. Box 8029, Austin, Texas 78713-8209 (United States)); Miller, W.A. (Theoretical Astrophysics Group (T-6, MS B288), Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States) Astrodynamics Bran

1994-11-15

310

NASA Astrophysics Data System (ADS)

Antiferromagnetic (AFM) materials with zero or vanishingly small macroscopic magnetization are nowadays the constituent elements of spintronic devices. However, the possibility to use them as active elements that show nontrivial and controllable magnetic dynamics is still discussible. In the present paper we extend the phenomenologic theory [Andreev and Marchenko, Sov. Phys. Usp.SOPUAP0038-567010.1070/PU1980v023n01ABEH004859 23, 21 (1980)] of macroscopic dynamics in AFM materials for the cases typical for spin-valve devices. In particular, we consider the solidlike magnetic dynamics of AFM materials with strong exchange coupling in the presence of a spin-polarized current and give the general expression for the current-induced Rayleigh dissipation function in terms of the rotation vector for different types of AFMs. Based on the analysis of linearized equations of motion we predict the current-induced spin reorientation and AFM resonance, and find the values of critical currents in terms of AFMR frequencies and damping constants. The possibility of a current-induced spin-diode effect and second-harmonic generation in the AFM layer is also shown.

Gomonay, Helen V.; Kunitsyn, Roman V.; Loktev, Vadim M.

2012-04-01

311

Multiple-pulse NQR dynamics of spin systems with strong heteronuclear coupling

NASA Astrophysics Data System (ADS)

The results are presented of a theoretical consideration of the nuclear quadrupole resonance (NQR) and spin—spin relaxation for a paramagnetic body containing nuclei of two different sorts coupled by the strong homonuclear and heteronuclear dipole—dipole interactions and influenced by an external multiple-pulse radiofrequency magnetic field acting only on nuclei of one sort. Kinetic equations were obtained giving the possibility of finding the time dependence of the magnetization of the body and the kinetic coefficients calculated as a function of the multiple-pulse field parameters. The possibilities of using the results in question for molecular structure and molecular dynamics investigations are briefly surveyed.

Furman, G. B.; Shaposhnikov, I. G.

1994-05-01

312

NASA Astrophysics Data System (ADS)

We provide a complete and exact theoretical study of the dynamical structure factor of a two-dimensional quantum spin liquid in gapless and gapped phases, as realized in Kitaev's honeycomb model. We show that there are direct signatures—qualitative and quantitative—of the Majorana fermions and gauge fluxes emerging in this model. These include counterintuitive manifestations of quantum number fractionalization, such as a neutron scattering response with a gap even in the presence of gapless excitations, and a sharp component despite the fractionalization of electron spin. Our analysis identifies new varieties of the venerable x-ray edge problem and explores connections to the physics of quantum quenches.

Knolle, J.; Kovrizhin, D. L.; Chalker, J. T.; Moessner, R.

2014-05-01

313

Dynamical properties of three terminal magnetic tunnel junctions: Spintronics meets spin-orbitronics

This Letter introduces a micromagnetic model able to characterize the magnetization dynamics in three terminal magnetic tunnel junctions, where the effects of spin-transfer torque and spin-orbit torque are taken into account. Our results predict that the possibility to separate electrically those two torque sources is very promising from a technological point of view for both next generation of nanoscale spintronic oscillators and microwave detectors. A scalable synchronization scheme based on the parallel connection of those three terminal devices is also proposed.

Tomasello, R. [Department of Computer Science, Modeling, Electronics and System Science, University of Calabria, Rende (CS) (Italy)] [Department of Computer Science, Modeling, Electronics and System Science, University of Calabria, Rende (CS) (Italy); Carpentieri, M., E-mail: m.carpentieri@poliba.it [Department of Electrical and Information Engineering, Politecnico of Bari, via E. Orabona 4, I-70125 Bari (Italy); Finocchio, G. [Department of Electronic Engineering, Industrial Chemistry and Engineering, University of Messina, C.da di Dio, I-98166 Messina (Italy)] [Department of Electronic Engineering, Industrial Chemistry and Engineering, University of Messina, C.da di Dio, I-98166 Messina (Italy)

2013-12-16

314

Steady-State Entanglement in the Nuclear Spin Dynamics of a Double Quantum Dot

NASA Astrophysics Data System (ADS)

We propose a scheme for the deterministic generation of steady-state entanglement between the two nuclear spin ensembles in an electrically defined double quantum dot. Due to quantum interference in the collective coupling to the electronic degrees of freedom, the nuclear system is actively driven into a two-mode squeezed-like target state. The entanglement build-up is accompanied by a self-polarization of the nuclear spins towards large Overhauser field gradients. Moreover, the feedback between the electronic and nuclear dynamics leads to multi-stability and criticality in the steady-state solutions.

Schuetz, M. J. A.; Kessler, E. M.; Vandersypen, L. M. K.; Cirac, J. I.; Giedke, G.

2013-12-01

315

High-field dynamic nuclear polarization with high-spin transition metal ions.

We report the dynamic nuclear polarization of (1)H spins in magic-angle-spinning spectra recorded at 5 T and 84 K via the solid effect using Mn(2+) and Gd(3+) complexes as polarizing agents. We show that the magnitude of the enhancements can be directly related to the effective line width of the central (m(S) = -1/2 ? +1/2) EPR transition. Using a Gd(3+) complex with a narrow central transition EPR line width of 29 MHz, we observed a maximum enhancement of ?13, which is comparable to previous results on the narrow-line-width trityl radical. PMID:21446700

Corzilius, Björn; Smith, Albert A; Barnes, Alexander B; Luchinat, Claudio; Bertini, Ivano; Griffin, Robert G

2011-04-20

316

High Field Dynamic Nuclear Polarization with High-Spin Transition Metal Ions

We report the dynamic nuclear polarization of 1H spins in magic angle spinning spectra recorded at 5 T and 84K via the solid effect using Mn2+ and Gd3+ complexes as polarizing agents. We show that the magnitude of the enhancements can be directly related to the effective linewidth of the central (MS = ?1/2 ?+1/2) EPR transition. Using a Gd3+ complex with a narrow central transition EPR linewidth of 29 MHz, a maximum enhancement of ~13 is observed, which is comparable to previous results on the narrow linewidth trityl radical.

Corzilius, Bjorn; Smith, Albert A.; Barnes, Alexander B.; Luchinat, Claudio; Bertini, Ivano; Griffin, Robert G.

2011-01-01

317

Dynamical properties of three terminal magnetic tunnel junctions: Spintronics meets spin-orbitronics

NASA Astrophysics Data System (ADS)

This Letter introduces a micromagnetic model able to characterize the magnetization dynamics in three terminal magnetic tunnel junctions, where the effects of spin-transfer torque and spin-orbit torque are taken into account. Our results predict that the possibility to separate electrically those two torque sources is very promising from a technological point of view for both next generation of nanoscale spintronic oscillators and microwave detectors. A scalable synchronization scheme based on the parallel connection of those three terminal devices is also proposed.

Tomasello, R.; Carpentieri, M.; Finocchio, G.

2013-12-01

318

Homoclinic solutions and motion chaotization in attitude dynamics of a multi-spin spacecraft

NASA Astrophysics Data System (ADS)

The attitude dynamics of the multi-spin spacecraft (MSSC) and the torque-free angular motion of the multi-rotor system are considered. Some types of homoclinic and general solutions are obtained in hyperbolic and elliptic functions. The local homoclinic chaos in the MSSC angular motion is investigated under the influence of polyharmonic perturbations. Some possible applications of the multi-rotor system are indicated, including gyrostat-satellites, dual-spin spacecraft, roll-walking robots, and also the inertialess method of the spacecraft attitude (angular) reorientation/control.

Doroshin, Anton V.

2014-07-01

319

Our current work in modeling reaction center dynamics has resulted in the observation of each major spin-dependent photochemical pathway that is observed in reaction centers. The development of new, simpler model systems has permitted us to probe deeply into the mechanistic issues that drive these dynamics. Based on these results we have returned to biomimetic chlorophyll-based electron donors to mimic these dynamics. Future studies will focus on the details of electronic structure and energetic of both the donor-acceptor molecules and their surrounding environment that dictate the mechanistic pathways and result in efficient photosynthetic charge separation.

Wasielewski, M. R.

1998-08-27

320

Spin dynamics in magnetic thin films and eletromagnetic properties of metamaterials

NASA Astrophysics Data System (ADS)

In this work, I have investigated the high frequency magnetic properties of a variety of novel materials by using the microwave techniques. The work consists of two parts: (1) spin dynamics study in magnetic multilayer thin films, (2) fabrication and characterization of novel magnetic materials. In the first part, we have observed nonlinear behaviors of the normal Gilbert damping G0 and the effective spin-mixing conductance g?? in Pt/NiFe/Pt thin films when the incident microwave power is above a critical ac field hrf of 1.6 Oe. Both G0 and g?? are affected by the coupling between spin coherent precession and spin wave modes. Our work is the first experimental demonstration of nonlinear behavior of the effective spin-mixing conductance g?? . It suggests the nonlinear spin wave modes excited at high incident microwave power is detrimental to the spin pumping effect and should be avoided in future spin battery design. We have also studied the magnetization dynamic in IrMn/FeCo/Cu/NiFe/Cu spin valve through the Gilbert damping. Our results show that the Gilbert damping constant of NiFe is enhanced in antiparallel configuration when the magnetizations of both FM layers are precessing. This enhancement is induced by the dynamic exchange between the magnetizations of NiFe and FeCo layers. We have observed the dc voltage generation across the tunneling barrier while the spin precession is excited in the ferromagnetic free layer by the microwave field. The magnitude of the dc voltage peak is around few muVs with AlOx tunneling barrier. Our results directly indicate that spin current can be pumped through the tunneling barrier thus generates the dc voltage across the barrier. The results raise an important question about the role of the F/I barrier interface in spin pumping mechanism. More detailed experiment and theory studies are certainly needed, especially in MgO barrier based MTJ that could become a good candidate for realizing spin battery device. In the second part, we have experimentally observed, in addition to conventional PBG from Bragger scattering, two groups of magnetically tunable PBGs in 2D magnetic photonic crystals due to magnetic surface plasmon and spin-wave resonance bands, respectively. The former is particularly interesting because of its analogy to surface plasmon in metals. Simulations on transmission coefficients are in a good agreement with experimental results. Our results thus provide a first demonstation of the concept of the magnetic SP bands and illustrate the fundamental mechanism for EM propogation at subwavelength confinement via surface plasmons. We have also experimentally studied the high frequency properties of the novel metamaterials, including NiFex/Polymer 100-x nanocomposites and magnetic left-handed materials (m-LHMs). In the nanocomposites study, we found the microwave transmission in NiFe x/Polymer100-x nanocomposites can be improved in the presence of an external magnetic field. It provides us a potential method to make a controllable microwave absorber for wave transmission at microwave frequency, which has various applications in microwave devices and communication. In m-LHM study, we have theoretically investigated the possibility of realizing LHM in metallic magnetic system. We have found that these thin magnetic films consist of metallic entities that may exhibit left-handed behaviors near the vicinity of the ferromagnetic resonant frequency o0. Experimentally, we observed the thickness dependent peak shifts in both multilayer [NiFe(10nm)/SiO2(2nm)]N thin films and granular Fe 30(SiO2)70 thin films. This suggests a negative refraction index.

Cao, Rong

321

Alamethicin F50/5 is a hydrophobic peptide that is devoid of charged residues and that induces voltage-dependent ion channels in lipid membranes. The peptide backbone is likely to be involved in the ion conduction pathway. Electron spin-echo spectroscopy of alamethicin F50/5 analogs in which a selected Aib residue (at position n = 1, 8, or 16) is replaced by the TOAC amino-acid spin label was used to study torsional dynamics of the peptide backbone in association with phosphatidylcholine bilayer membranes. Rapid librational motions of limited angular amplitude were observed at each of the three TOAC sites by recording echo-detected spectra as a function of echo delay time, 2?. Simulation of the time-resolved spectra, combined with conventional EPR measurements of the librational amplitude, shows that torsional fluctuations of the peptide backbone take place on the subnanosecond to nanosecond timescale, with little temperature dependence. Associated fluctuations in polar fields from the peptide could facilitate ion permeation.

Bartucci, Rosa; Guzzi, Rita; De Zotti, Marta; Toniolo, Claudio; Sportelli, Luigi; Marsh, Derek

2008-01-01

322

Competing magnetic interactions and interfacial frozen-spins in Ni-NiO core-shell nano-rods

NASA Astrophysics Data System (ADS)

This paper investigates the subtle interfacial magnetism of highly-aligned, free-standing Ni-NiO core-shell rods on a Si substrate, fabricated by electroless-plating and an anodic aluminum oxide template. Transmission electron microscopy found that the NiO shell was uniformly present along the entire rod. Vertical magnetization shift, arising from opposite field cooling conditions, suggests frozen spins (FS) at the Ni-NiO interface. The FS were related to the pinning effects of the NiO on the Ni. The pinning strength depended on the NiO thickness, displaying a tunable fashion from 6 to 10 nano-meters with thermal annealing. The FS mediated the antiferromagnetic (AFM)-ferromagnetic (FM) interfacial coupling, leading to the temperature-dependent properties of the rods. FS were evident below 100 K, at which the NiO-AFM dominated the properties with a suppressed coercive field and non-saturated magnetization. At 100 K, however, the Ni-FM was superior to the NiO-AFM with a restored FM phase. Meanwhile, the interfacial magnetic frustration occurred due to the disappearance of FS. These two factors resulted in the coercivity enhancement at 100 K. The uniqueness of the structure opens opportunities to tailoring the properties of the rods by manipulating the core-shell inter-dependency, as well as inspiring further researches concerning its applications in spintronics.

Hsu, Hao-Chun; Lo, Chih-Chieh; Tseng, Yuan-Chieh

2012-03-01

323

The hydrated ternary lamellar lipid mixture of dipalmitoyl-PC/dilauroyl-PC/cholesterol (DPPC/DLPC/Chol) has been studied by electron spin resonance (ESR) to reveal the dynamic structure on a molecular level of the different phases that exist and coexist over virtually the full range of composition. The spectra for more than 100 different compositions at room temperature were analyzed by nonlinear least-squares fitting to provide the rotational diffusion rates and order parameters of the end-chain labeled phospholipid 16-PC. The ESR spectra exhibit substantial variation as a function of composition, even though the respective phases generally differ rather modestly from each other. The L? and L? phases are clearly distinguished, with the former exhibiting substantially lower ordering and greater motional rates, whereas the well-defined Lo phase exhibits the greatest ordering and relatively fast motional rates. Typically, smaller variations occur within a given phase. The ESR spectral analysis also yields phase boundaries and coexistence regions which are found to be consistent with previous results from fluorescence methods, although new features are found. Phase coexistence regions were in some cases confirmed by observing the existence of isosbestic points in the absorption mode ESR spectra from the phases. The dynamic structural properties of the DPPC-rich L? and DLPC-rich L? phases, within their two-phase coexistence region do not change with composition along a tie-line, but the ratio of the two phases follows the lever rule in accordance with thermodynamic principles. The analysis shows that 16-PC spin-label partitions nearly equally between the L? and L? phases, making it a useful probe for studying such coexisting phases. Extensive study of two-phase coexistence regions requires the determination of tie-lines, which were approximated in this study. However, a method is suggested to accurately determine the tie-lines by ESR.

Chiang, Yun-Wei; Shimoyama, Yuhei; Feigenson, Gerald W.; Freed, Jack H.

2004-01-01

324

Magnetic field dependence of the dynamics of 87 Rb spin-2 Bose-Einstein condensates

NASA Astrophysics Data System (ADS)

We experimentally studied the spin-dependent collision dynamics of 87 Rb spin-2 Bose-Einstein condensates confined in an optical trap. The condensed atoms were initially populated in the ? F=2, mF =0 > state, and their time evolutions in the trap were measured in the presence of external magnetic field strengths ranging from 0.1 to 3.0 G . The atom loss rate due to inelastic two-body collisions was found to be 1.4 (2) × 10-13 cm3 s-1 . Spin mixing in the F=2 manifold developed dramatically for the first few tens of milliseconds, and the oscillations in the population distribution between different magnetic components were observed over a limited range of magnetic field strengths. The antiferromagnetic property of this system was deduced from the magnetic field dependence on the evolution of relative populations for each mF component.

Kuwamoto, T.; Araki, K.; Eno, T.; Hirano, T.

2004-06-01

325

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

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.

Veshtort, Mikhail; Griffin, Robert G.

2011-01-01

326

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

NASA Astrophysics Data System (ADS)

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 A?. 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.

Veshtort, Mikhail; Griffin, Robert G.

2011-10-01

327

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

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 (R(2)). 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 (13)C nuclei and about ten (1)H 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 (R(3)-PDSD) experiments performed in three model compounds, where magnetization exchange occurred over distances up to 4.9 A?. 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 R(2) spin dynamics. The conventional semi-phenomenological treatment of relxation in R(2) 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 R(2) 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 R(2) dynamics in the few simple model systems we considered. PMID:21992326

Veshtort, Mikhail; Griffin, Robert G

2011-10-01

328

Dynamics of entanglement in a two-dimensional spin system

We consider the time evolution of entanglement in a finite two-dimensional transverse Ising model. The model consists of a set of seven localized spin-(1/2) particles in a two-dimensional triangular lattice coupled through nearest-neighbor exchange interaction in the presence of an external time-dependent magnetic field. The magnetic field is applied in different function forms: step, exponential, hyperbolic, and periodic. We found that the time evolution of the entanglement shows an ergodic behavior under the effect of the time-dependent magnetic fields. Also, we found that while the step magnetic field causes great disturbance to the system, creating rapid oscillations, the system shows great controllability under the effects of the other magnetic fields where the entanglement profile follows closely the shape of the applied field even with the same frequency for periodic fields. This follow-up trend breaks down as the strength of the field, the transition constant for the exponential and hyperbolic forms, or the frequency for periodic field increase leading to rapid oscillations. We observed that the entanglement is very sensitive to the initial value of the applied periodic field: the smaller the initial value is, the less distorted the entanglement profile is. Furthermore, the effect of thermal fluctuations is very devastating to the entanglement, which decays very rapidly as the temperature increases. Interestingly, although a large value of the magnetic field strength may yield a small entanglement, the magnetic field strength was found to be more persistent against thermal fluctuations than the small field strengths.

Xu Qing [Department of Physics, Purdue University, West Lafayette, Indiana 47907 (United States); Sadiek, Gehad [Department of Physics, King Saud University, Riyadh 11451 (Saudi Arabia); Department of Physics, Ain Shams University, Cairo 11566 (Egypt); Kais, Sabre [Department of Physics, King Saud University, Riyadh 11451 (Saudi Arabia); Department of Chemistry and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907 (United States)

2011-06-15

329

We study the dynamics of an electron confined in a one-dimensional double-well potential in the presence of driving external magnetic fields. The orbital motion of the electron is coupled to the spin dynamics by spin-orbit interaction of the Dresselhaus type. We derive an effective time-dependent model Hamiltonian for the orbital motion of the electron and obtain a condition for synchronization of the orbital and the spin dynamics. We find an analytical expression for the Arnold 'tongue' and propose an experimental scheme for realizing the proposed synchronization. PMID:22634490

Chotorlishvili, L; Toklikishvili, Z; Komnik, A; Berakdar, J

2012-06-27

330

Effects of Spin Transition and Partitioning of Iron on Mantle Dynamics

NASA Astrophysics Data System (ADS)

Experimental studies at the pressure and temperature conditions of the Earth's lower mantle, have shown that iron in ferropericlase (Fp) and in magnesium silicate perovskite (Pv) undergoes a spin state transition, whereby modifying important mineral properties. Of particular interest are the increase in density caused by the spin state transition in Fp and the change of iron partitioning between Pv and Fp, for which there is still debate on the range of values most appropriate for the Earth's mantle. Here we use numerical simulations to explore the effect on mantle dynamics of the variation of mineral properties induced by the spin state transition. We consider two end-member mantle composition, one without aluminum and one with ~5wt % aluminum in Pv. Al increases ferric iron in perovskite, and hence the magnitude of effect of the spin state transition in ferrous iron. We build two models of iron partitioning, one for the Al-free case (based on experiments by Auzende et al. [2008], Sakai et al. [2009]), and one for the Al-bearing case (based on experiments by Irifune et al. [2010]). We also consider two cases with constant partition coefficients. We follow the theoretical model of Sturhahn et al. [2005] to model the effect of spin state transition on density. The result is a dramatic increase in density through the lower mantle (between 1% and 2.5%). The density models are then included in StagYY, the numerical code by Paul Tackley (Tackley [2008]), that can be used in cartesian or in spherical geometry. We find multiple dynamical effects, among which enhanced plume upwelling velocities and a reduction of slab downwelling velocities in the denser lower mantle (due to spin state), and we quantify their dependence on the considered models. The results of our study bear implications on mantle mixing, on entrainment of lower mantle materials in plumes and on stability of Large Low Shear Velocity Province (LLSVP).

Vilella, K.; Shim, S.; Farnetani, C. G.; Badro, J.

2013-12-01

331

Stochastic Resonance in Chaotic Spin-Wave Dynamics

NASA Astrophysics Data System (ADS)

We report the first experimental observation of noise-free stochastic resonance by utilizing the intrinsic chaotic dynamics of the system. To this end we have investigated the effect of an external periodic modulation on intermittent signals observed by high power ferromagnetic resonance in yttrium iron garnet spheres. Both the signal-to-noise ratio and the residence time distributions show the characteristic features of stochastic resonance. The phenomena can be explained by means of a one-dimensional intermittent map. We present analytical results as well as computer simulations.

Reibold, Ekkehard; Just, Wolfram; Becker, Jens; Benner, Hartmut

1997-04-01

332

Finite Temperature Dynamics of the Spin-1/2 Heisenberg Chain.

NASA Astrophysics Data System (ADS)

We report on our recent studies of the finite temperature (T) dynamics of the isotropic antiferromagnetic S=1/2 Heisenberg chain for all values of the ratio T/J (J is the nearest-neighbor exchange). (A) Dynamics in the low-T region (T/J << 1) is studied via a simple ansatz taking into account marginally irrelevant operator which describes Umklapp scattering between right- and left-moving spinons (O. A. Starykh, R. R. P. Singh, A. W. Sandvik, Phys. Rev. Lett.) 78, 539 (1997). This operator is found to produce (i) logarithmic T-dependent corrections to the scaling dimension of the spin operator, and (ii) multiple logarithmic corrections to the spin correlation function, in agreement with previous renormalization group and thermal Bethe-ansatz studies. As a result, the staggered spin susceptibility \\chi(q,?) shows deviations from the quantum-critical scaling behavior expected for the model with critical correlations in the ground state. Our quantum Monte Carlo (QMC) and high-temperature expansions (HTE) studies provide striking quantitative confirmation of this behavior. We also demonstrate that these logarithmic corrections are essential for the quantitative comparison with the measured spin-lattice (1/T_1) and Gaussian spin-echo (1/T_2G) NMR decay rates of Sr_2CuO3 (M. Takigawa, O. A. Starykh. A. W. Sandvik, R. R. P. Singh, Phys. Rev. B) 56, 13681 (1997). (B) Spin dynamics in the intermediate and high-T regions (T/J >= 0.5) is studied by combining HTE with the recursion method, and QMC with the maximum entropy method. We find that the spectral weight of the dynamic structure factor S(k,?) gradually transfers from a diffusive long-wavelenght modes (k ~ 0) at T >> J to a propagating antiferromagnetic ones (k ~ ?) at intermediate temperatures (T ~ J). We extract the NMR 1/T1 rate from the ? arrow 0 limit of S(k,?), and also discuss temperature scaling of the structure factor and staggered spin susceptibility ( O. A. Starykh, A. W. Sandvik, R. R. P. Singh, Phys. Rev. B) 55, 14953 (1997).

Starykh, Oleg A.

1998-03-01

333

Dynamical modelling and control of a spacecraft-mounted manipulator capturing a spinning satellite

NASA Astrophysics Data System (ADS)

Issues associated with the modelling and control of a spacecraft-mounted manipulator capturing a spinning satellite are presented. The Lagrangian formulation is used to derive the dynamical equations of the system immediately following the capture. The formulation is carried out by writing Lagrange's equations for the individual bodies, and then assembling them to obtain the constrained dynamical equations of the system. The non-working constraint forces/torques are then eliminated by using the natural orthogonal complement which produces a set of independent dynamical equations. A control algorithm whose objective is to produce a set of feedback-linearized, homogeneous and uncoupled equations is designed and implemented. The initial conditions of the state variables needed to achieve smooth berthing of the satellite are computed, and the dynamics simulation of both the controlled and uncontrolled systems is carried out. The manipulator's structural flexibility is included in the dynamics simulation model.

Cyril, Xavier; Jaar, Gilbert J.; Misra, Arun K.

1995-01-01

334

Topological insulators possess completely different spin-orbit coupled bulk and surface electronic spectra that are each predicted to exhibit exotic responses to light. Here we report time-resolved fundamental and second harmonic optical pump-probe measurements on the topological insulator Bi(2)Se(3) to independently measure its photoinduced charge and spin dynamics with bulk and surface selectivity. Our results show that a transient net spin density can be optically induced in both the bulk and surface, which may drive spin transport in topological insulators. By utilizing a novel rotational anisotropy analysis we are able to separately resolve the spin depolarization, intraband cooling, and interband recombination processes following photoexcitation, which reveal that spin and charge degrees of freedom relax on very different time scales owing to strong spin-orbit coupling. PMID:21902428

Hsieh, D; Mahmood, F; McIver, J W; Gardner, D R; Lee, Y S; Gedik, N

2011-08-12

335

Trapping membrane proteins in the confines of a crystal lattice obscures dynamic modes essential for interconversion between multiple conformations in the functional cycle. Moreover, lattice forces could conspire with detergent solubilization to stabilize a minor conformer in an ensemble thus confounding mechanistic interpretation. Spin labeling in conjunction with electron paramagnetic resonance (EPR) spectroscopy offers an exquisite window into membrane protein dynamics in the native–like environment of a lipid bilayer. Systematic application of spin labeling and EPR identifies sequence-specific secondary structures, defines their topology and their packing in the tertiary fold. Long range distance measurements (60-80Å) between pairs of spin labels enable quantitative analysis of equilibrium dynamics and triggered conformational changes. This review highlights the contribution of spin labeling to bridging structure and mechanism. Efforts to develop methods for determining structures from EPR restraints and to increase sensitivity and throughput promise to expand spin labeling applications in membrane protein structural biology.

Mchaourab, Hassane S.; Steed, P. Ryan; Kazmier, Kelli

2011-01-01

336

A Multifrequency Electron Spin Resonance Study of the Dynamics of Spin Labeled T4 Lysozyme

An extensive set of ESR spectra was obtained over a wide range of frequencies (9, 95, 170 and 240 GHz) and temperatures (2 to 32°C) to explore the dynamic modes of nitroxide-labeled T4 lysozyme in solution. A commonly used nitroxide side chain (R1), or a methylated analogue with hindered internal motion (R2), was substituted for the native side chain at solvent-exposed helical sites, 72 or 131. The spectra at all four frequencies were simultaneously fit with the slowly relaxing local structure (SRLS) model. Good fits were achieved at all the temperatures. Two principle dynamic modes are included in the SRLS model: the global tumbling of the protein and the internal motion consisting of backbone fluctuations and side chain isomerizations. Three distinct spectral components were required for R1 and two for R2 to account for the spectra at all temperatures. One is a highly ordered and slow motional component, which is observed in the spectra of both R1 and R2; it may correspond to conformers stabilized by interaction with the protein surface. The fraction of this component decreases with increasing temperature, and is more populated in the R2 spectra, possibly arising from stronger interaction of the nitroxide ring with the protein surface due to the additional methyl group. The other two components of R1 and the second component of R2, are characterized by fast anisotropic diffusion and relatively low ordering, most likely corresponding to conformers having little or no interactions with nearby residues. Ficoll of different concentrations was added to increase the solution viscosity, thereby slowing down the global tumbling of the protein. A significant effect of Ficoll on the internal motion of an immobilized component was apparent in R2 but not in R1. The ability of such multifrequency studies to separate the effects of faster internal modes of motion from slower overall motions is clearly demonstrated, and its utility in future studies is considered.

Zhang, Ziwei; Fleissner, Mark R.; Tipikin, Dmitriy; Liang, Zhichun; Moscicki, Jozef K.; Earle, Keith; Hubbell, Wayne

2010-01-01

337

Spin dynamics in two-dimensional arrays of quantum dots with different shapes

NASA Astrophysics Data System (ADS)

Electron paramagnetic resonance and spin echo methods are used to probe the spin dynamics in two-dimensional quantum dot (QD) arrays with different shape of nanoclusters. Two types of QD structures were investigated: 1) with single shaped QDs (hut-clusters, having the ratio of height h to lateral size l, h/l = 0.1), and 2) with two groups of QDs, hut- and dome-clusters (h/l = 0.2). Both types of structures demonstrate the EPR signals from electrons localized in QD layers.The orientation dependence of EPR line width for first type structures is well described by model of spin relaxation through precession in the effective magnetic field, arising during tunneling between QDs due to structure-inversion-asymmetry. In the experiments on structures with dome-clusters the additional peculiarity, which can not be explained in the framework of precession model, is observed. The different orientation dependencies can be explained by different localization degree of electrons in investigated structures. Spin echo measurements give the longest spin decoherence time for structures with single shaped QDs.

Zinovieva, A. F.; Lyubin, A. S.; Stepina, N. P.; Koptev, E. S.; Nikiforov, A. I.; Dvurechenskii, A. V.; Sobolev, N. A.; Carmo, M. C.

2010-09-01

338

Spin dynamics in frustrated magnets: from edge- to corner-sharing geometries

NASA Astrophysics Data System (ADS)

Our work in the past few years has been focused on local NMR (nuclear magnetic resonance) and ?SR (muon spin resonance) studies of pure Heisenberg isotropic triangular lattices with nearest neighbour couplings, a prerequisite for reaching the ideal spin liquid case. In the case of chromates, although S = 3/2, the combination of the weakness of the Cr3+ single-ion anisotropy and that of an exchange interaction resulting from a direct overlap of the Cr3+ orbitals allows us to tackle these properties. We were recently able to single out, in the triangular compound NaCrO2, an original dynamical crossover regime in a broad range of T between the peak in specific heat and a low T static ground state. Moving to the corner-sharing geometry of Kagome bilayers (Ba2Sn2ZnGa10-7pCr7pO22 and SrCr9pGa12-9pO19), we illustrate all the potential of local studies (NMR and ?SR) for revealing some key aspects of the physics of these compounds, namely T\\rightarrow 0 fluctuations, susceptibility, the impact of dilution defects which generate an extended response of the spin lattice as well as their puzzling spin glass state. These results are compared to the case of volborthite which features S = 1/2 spins on a corner-sharing, probably anisotropic, antiferromagnetic Kagome lattice.

Mendels, P.; Olariu, A.; Bert, F.; Bono, D.; Limot, L.; Collin, G.; Ueland, B.; Schiffer, P.; Cava, R. J.; Blanchard, N.; Duc, F.; Trombe, J. C.

2007-04-01

339

Quantum dynamical simulations for nuclear spin selective laser control of ortho- and para-fulvene

NASA Astrophysics Data System (ADS)

In the present paper we explore the prospects for laser control of the photoinduced nonadiabatic dynamics of para- and ortho-fulvene with the help of quantum dynamical simulations. Previous investigations [Bearpark et al., J. Am. Chem. Soc. 118, 5253 (1996); Alfalah et al., J. Chem. Phys. 130, 124318 (2009)] show that photoisomerization of fulvene is hindered by ultrafast radiationless decay through a conical intersection at planar configuration. Here, we demonstrate that photoisomerization can nevertheless be initiated by damping unfavorable nuclear vibrations with properly designed laser pulses. Moreover, we show that the resulting intramolecular torsion is nuclear spin selective. The selectivity of the photoexcitation with respect to the nuclear spin isomers can be further enhanced by applying an optimized sequence of two laser pulses.

Belz, S.; Grohmann, T.; Leibscher, M.

2009-07-01

340

Dynamic spin correlations in the frustrated cubic phase of MnV2O4

NASA Astrophysics Data System (ADS)

The ferrimagnetic spinel MnV2O4 undergoes an orbital-induced cubic-to-tetragonal distortion at TYK=58 K, below which noncollinear commensurate ferrimagnetic ordering occurs. Using inelastic neutron scattering, we investigated low-energy dynamics in its cubic phase above TYK. We observed two types of coexisting short-range magnetic excitations: the dispersive spin waves centered around the Brillouin-zone centers, k0 = (0, 0, 0), and quasielastic spin fluctuations centered at incommensurate wave vectors, kincom = (?, ?, 0). The coexistence of the two distinct features can be understood as a dynamic realization of the conical spiral order observed in cubic spinels such as CoCr2O4.

Chung, Jae-Ho; Song, Young-Sang; Kim, J.-H.; Suzuki, T.; Katsufuji, T.; Matsuda, M.; Lee, S.-H.

2013-09-01

341

Magnetic Phase Transition and Spin Dynamics in Magnetoelectric Effect LiMnPO4

Elastic and inelastic neutron scattering techniques were used to study the magnetic phase transition and spin dynamics in single crystal LiMnPO4. In this mulitiferroic, antiferromagnetism coexists with induced ferroelectricity below the Neel temperature. Elastic neutron scattering technique confirmed that LiMnPO4 has a collinear antiferromagnetic ground state with magnetic moments oriented along the a-axis. The temperature dependent order parameter, calculated from

J. Li; W. Tain; J. L. Zarestky; D. Vaknin; Y. Chen; J. W. Lynn

2007-01-01

342

Magnetic soft x-ray microscopy-imaging fast spin dynamics inmagnetic nanostructures

Magnetic soft X-ray microscopy combines 15nm spatial resolution with 70ps time resolution and elemental sensitivity. Fresnel zone plates are used as X-ray optics and X-ray magnetic circular dichroism serves as magnetic contrast mechanism. Thus scientifically interesting and technologically relevant low dimensional nanomagnetic systems can be imaged at fundamental length and ultrafast time scales in a unique way. Studies include magnetization reversal in magnetic multilayers, nanopatterned systems, vortex dynamics in nanoelements and spin current induced phenomena.

Fischer, Peter; Kim, Dong-Hyun; Mesler, Brooke L.; Chao, Weilun; Sakdinawat, Anne E.; Anderson, Erik H.

2007-06-01

343

Lipid chain dynamics in stratum corneum studied by spin label electron paramagnetic resonance

The lipid chain motions in stratum corneum (SC) membranes have been studied through electron paramagnetic resonance (EPR) spectroscopy of stearic acid spin-labeled at the 5th, 12th and 16th carbon atom positions of the acyl chain. Lipids have been extracted from SC with a series of chloroform\\/methanol mixtures, in order to compare the molecular dynamics and the thermotropic behavior in intact

Antonio Alonso; Nilce C Meirelles; Marcel Tabak

2000-01-01

344

Effective spin-glass Hamiltonian for the anomalous dynamics of the HMF model

We discuss an effective spin-glass Hamiltonian which can be used to study the glassy-like dynamics observed in the metastable states of the Hamiltonian mean field (HMF) model. By means of the Replica formalism, we were able to find a self-consistent equation for the glassy order parameter which reproduces, in a restricted energy region below the phase transition, the microcanonical simulations

Alessandro Pluchino; Vito Latora; Andrea Rapisarda

2006-01-01

345

New Dynamic Spin Rig Capabilities Used to Determine Rotating Blade Dynamics

NASA Technical Reports Server (NTRS)

The Dynamic Spin Rig Facility at the NASA Glenn Research Center is used to determine the structural response of rotating engine components without the effects of aerodynamic loading. Recently, this rig's capabilities were enhanced through the replacement of grease-lubricated ball bearings with magnetic bearings. Magnetic bearings offer a number of advantages--the most important here being that they not only fully support the rotor system, but excite it as well. Three magnetic bearings support the rotor and provide five axes of controlled motion: an x- and y-axis translation at each of two radial bearings and a z-axis translation in the vertical or axial direction. Sinusoidal excitation (most commonly used) can be imparted on the rotor through the radial magnetic bearings in either a fixed or rotating frame of reference. This excitation is added directly to the magnetic bearing control output. Since the rotor is fully levitated, large translations and rotations of the rotor system can be achieved. Some of the capabilities of this excitation system were determined and reported. The accelerations obtained at the tip of a titanium flat plate test article versus the swept sine excitation sent to both radial bearings in phase and perpendicular to the plane containing the two blades are shown. Recent tests required the excitation of fundamental bending and torsional blade resonances at rotor speeds up to 10,000 rpm. Successful fixed synchronous rotation of the excitation signal provided the best detectable blade resonant vibrations at excitation frequencies up to 1100 Hz for the particular blades of interest. A noncontacting laser measurement system was used to collect blade-tip motions. From these data, the amplitude and frequency of the motion could be determined as well as the blade damping properties. Damping could be determined using two methods: (1) free decay and (2) curve fitting the vibration amplitude as a function of frequency in and around the resonance of interest and using the half-power method. The free decay of a composite blade vibrating at its first bending resonance while rotating at 3000 rp is shown. This new system is currently being used to support the Efficient Low-Noise Fan project at Glenn. The damping properties of prototype hollow composite blades specially designed to reduce fan noise are currently being determined.

Provenza, Andrew J.

2004-01-01

346

Supercurrent and dynamical instability of spin-orbit-coupled ultracold Bose gases

NASA Astrophysics Data System (ADS)

We investigate the stability of supercurrents in a Bose-Einstein condensate with one-dimensional spin-orbit and Raman couplings. The consequence of the lack of Galilean invariance is explicitly discussed. We show that in the plane-wave phase, characterized by a uniform density, the supercurrent state can become dynamically unstable, the instability being associated with the occurrence of a complex sound velocity, in a region where the effective mass is negative. We also discuss the emergence of energetic instability in these supercurrent states. We argue that both the dynamical and the energetic instabilities in these systems can be generated experimentally through excitation of the collective dipole oscillation.

Ozawa, Tomoki; Pitaevskii, Lev P.; Stringari, Sandro

2013-06-01

347

Cumulative quantum work-deficit versus entanglement in the dynamics of an infinite spin chain

NASA Astrophysics Data System (ADS)

We find that the dynamical phase transition (DPT) in nearest-neighbor bipartite entanglement of time-evolved states of the anisotropic infinite quantum XY spin chain, in a transverse time-dependent magnetic field, can be quantitatively characterized by the dynamics of an information-theoretic quantum correlation measure, namely, quantum work-deficit (QWD). We show that only those nonequilibrium states exhibit entanglement resurrection after death, on changing the field parameter during the DPT, for which the cumulative bipartite QWD is above a threshold. The results point to an interesting inter-relation between two quantum correlation measures that are conceptualized from different perspectives.

Dhar, Himadri Shekhar; Ghosh, Rupamanjari; Sen(De), Aditi; Sen, Ujjwal

2014-03-01

348

The dynamics of diluted Ho spin ice Ho2-xYxTi2O7 studied byneutron spin echo spectroscopy

We have studied the spin relaxation in diluted spin ice Ho{sub 2-x} Y{sub x} Ti{sub 2}O{sub 7} by means of neutron spin echo spectroscopy. Remarkably, the geometrical frustration is not relieved by doping with non-magnetic Y, and the dynamics of the freezing is unaltered in the spin echo time window up to x {approx_equal} 1.6. At higher doping with non-magnetic Y (x {ge} 1.6) a new relaxation process at relatively high temperature (up to at least T {approx_equal} 55 K) appears which is more than 10 times faster than the thermally activated main relaxation process. We find evidence that over the whole range of composition all Ho spins participate in the dynamics. These results are compared to a.c. susceptibility measurements of the diluted Ho and Dy spin ice systems. X-ray absorption fine structure (EXAFS) spectra and x-ray diffraction show that the samples are structurally well ordered.

Ehlers, G.; Gardner, J.S.; Booth, C.H.; Daniel, M.; Kam, K.C.; Cheetham, A.K.; Antonio, D.; Brooks, H.E.; Cornelius, A.L.; Bramwell,S.T.; Lago, J.; Haussler, W.; Rosov, N.

2006-02-27

349

Spin-labeled lipids are commonly used as fluorescence quenchers in studies of membrane penetration of dye-labeled proteins and peptides using depth-dependent quenching. Accurate calculations of depth of the fluorophore rely on the use of several spin labels placed in the membrane at various positions. The depth of the quenchers (spin probes) has to be determined independently, however; experimental determination of transverse distributions of spin probe depths is difficult. In this article, we use molecular dynamics (MD) simulations to study the membrane behavior and depth distributions of spin–labeled phospholipids in a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer. To probe different depths within the bilayer, a series containing five Doxyl-labeled lipids (n-Doxyl PC) has been studied, in which a spin moiety was covalently attached to n–th carbon atoms (where n=5, 7, 10, 12 and 14) of the sn-2 stearoyl chain of the host phospholipid. Our results demonstrate that the chain–attached spin labels are broadly distributed across the model membrane and their environment is characterized by a high degree of mobility and structural heterogeneity. Despite the high thermal disorder, the depth distributions of the Doxyl labels were found to correlate well with their attachment positions, indicating that the distribution of the spin label within the model membrane is dictated by the depth of the n–th lipid carbon atom and not by intrinsic properties of the label. In contrast, a much broader and heterogeneous distribution was observed for a headgroup–attached Tempo spin label of Tempo–PC lipids. MD simulations reveal that, due to the hydrophobic nature, a Tempo moiety favors partitioning from the headgroup region deeper into the membrane. Depending on the concentration of Tempo-PC lipids, the probable depth of the Tempo moiety could span a range from 14.4 Å to 18.2 Å from the membrane center. Comparison of the MD–estimated immersion depths of Tempo and n-Doxyl labels with their suggested experimental depth positions allows us to review critically the possible sources of error in depth-dependent fluorescence quenching studies.

Kyrychenko, Alexander; Ladokhin, Alexey S.

2013-01-01

350

Dynamic Model Investigation of a 1/20 Scale Gemini Spacecraft in the Langley Spin Tunnel

NASA Technical Reports Server (NTRS)

Dynamic Model Investigation of a 1/20 Scale Gemini Spacecraft in the Langley Spin Tunnel. The investigation was conducted in the Langley spin tunnel. The tunnel is an atmospheric wind tunnel with a vertically rising airstream in the test section and a maximum airspeed of approximately 90 feet per second. For this investigation, the model was hand launched into the vertically rising airstream. At times the model, both with and without a drogue parachute, was launched gently with as little disturbance as possible to determine what motions of the spacecraft were self-excited. At other times, the spacecraft with pre-deployed drogue parachute was launched into various spinning motions to determine the effectiveness of the drogue parachute in terminating these spinning motions. During drogue-parachute deployment tests, the spacecraft was launched into various spinning and tumbling motions and the drogue parachute was deployed. The motions of the model were photographed with a motion-picture camera, and some of the film records were read to obtain typical time histories of the model motion. The angles of attack indicated in the time histories presented are believed to be accurate within +/-1 degree. The mass and dimensional characteristics of the dynamic model are believed to be measured to an accuracy of: +/-1 percent for the weight, +/-1 percent for z(sub cg)/d, +/-15 percent for x (sub cg), and +/-5 percent for the moments of inertia. The towline and bridle-line lengths were simulated to an accuracy of +/-1 foot full scale. [Entire movie available on DVD from CASI as Doc ID 20070030985. Contact help@sti.nasa.gov

1963-01-01

351

Inelastic neutron scattering studies of the spin and lattice dynamics in iron arsenide compounds.

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 initio 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.

Osborn, R.; Rosenkranz, S.; Goremychkin, E. A.; Christianson, A. D. (Materials Science Division); (ORNL)

2009-03-20

352

Inelastic Neutron Scattering Studies of the Spin and Lattice Dynamics inIron Arsenide Compounds

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 initio 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.

Christianson, Andrew D [ORNL; Osborn, R. [Argonne National Laboratory (ANL); Rosenkranz, Stephen [Argonne National Laboratory (ANL); Goremychkin, E. A. [ISIS Facility, Rutherford Appleton Laboratory

2009-01-01

353

A Slave Spin Impurity Solver for Non Equilibrium Dynamical Mean Field Theory

NASA Astrophysics Data System (ADS)

The non equilibrium dynamics of strongly correlated electronic systems represents a challenging theoretical problem in condensed matter physics with applications ranging from pump probe experiments in correlated materials to dynamics in ultracold atomic gases. Dynamical Mean Field Theory (DMFT) has emerged in recent years as a powerful theoretical framework to deal with strong correlations in a non pertubative way. Its extension to the out of equilibrium case requires the solution of an auxiliary quantum impurity model in a non equilibrium bath. Here we present an impurity solver for Non Equilibrium DMFT based on a slave spin representation of the fermionic degrees of freedom. We apply this method to study the quench dynamics in the single band fermionic Hubbard model and compare the results with the time dependent Gutzwiller method.

Schiro, Marco

2012-02-01

354

We present time-resolved studies of the spin polarization dynamics during and after initialization through pulsed electrical spin injection into InGaAs quantum dots embedded in a p-i-n-type spin-injection light-emitting diode. Experiments are performed with pulse widths in the nanosecond range and a time-resolved single photon counting setup is used to detect the subsequent electroluminescence. We find evidence that the achieved spin polarization shows an unexpected temporal behavior, attributed mainly to many-carrier and non-equilibrium effects in the device.

Asshoff, P.; Loeffler, W.; Fluegge, H.; Zimmer, J.; Mueller, J.; Westenfelder, B.; Hu, D. Z.; Schaadt, D. M.; Kalt, H.; Hetterich, M. [Institut fuer Angewandte Physik and DFG Center for Functional Nanostructures (CFN), Universitaet Karlsruhe, 76131 Karlsruhe (Germany)

2010-01-04

355

The dynamics of the soft x-ray induced excited spin state trapping (SOXIESST) effect of Fe(phen){sub 2}(NCS){sub 2} (Fe-phen) powder have been investigated by x-ray absorption spectroscopy (XAS) using the total electron yield method, in a wide temperature range. The low-spin (LS) state is excited into the metastable high-spin (HS) state at a rate that depends on the intensity of the x-ray illumination it receives, and both the temperature and the intensity of the x-ray illumination will affect the maximum HS proportion that is reached. We find that the SOXIESST HS spin state transforms back to the LS state at a rate that is similar to that found for the light induced excited spin state trapping (LIESST) effect. We show that it is possible to use the SOXIESST effect in combination with the LIESST effect to investigate the influence of cooperative behavior on the dynamics of both effects. To investigate the impact of molecular cooperativity, we compare our results on Fe-phen with those obtained for Fe([Me{sub 2}Pyrz]{sub 3}BH){sub 2} (Fe-pyrz) powder, which exhibits a similar thermal transition temperature but with a hysteresis. We find that, while the time constant of the dynamic is identical for both molecules, the SOXIESST effect is less efficient at exciting the HS state in Fe-pyrz than in Fe-phen.

Davesne, V.; Gruber, M. [Institut de Physique et de Chimie des Matériaux de Strasbourg, Université de Strasbourg, CNRS UMR 7504 23 rue du Loess, 67034 Strasbourg (France) [Institut de Physique et de Chimie des Matériaux de Strasbourg, Université de Strasbourg, CNRS UMR 7504 23 rue du Loess, 67034 Strasbourg (France); Physikalisches Institut, Karlsruhe Institut of Technology, Wolfgang-Gaede-Str. 1, 76131 Karlsruhe (Germany); Miyamachi, T. [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwashi, Chiba 277-8581 (Japan)] [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwashi, Chiba 277-8581 (Japan); Da Costa, V.; Boukari, S.; Scheurer, F.; Joly, L.; Bowen, M.; Beaurepaire, E. [Institut de Physique et de Chimie des Matériaux de Strasbourg, Université de Strasbourg, CNRS UMR 7504 23 rue du Loess, 67034 Strasbourg (France)] [Institut de Physique et de Chimie des Matériaux de Strasbourg, Université de Strasbourg, CNRS UMR 7504 23 rue du Loess, 67034 Strasbourg (France); Ohresser, P.; Otero, E.; Choueikani, F. [Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, BP48, 91192 Gif-sur-Yvette (France)] [Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, BP48, 91192 Gif-sur-Yvette (France); Gaspar, A. B.; Real, J. A. [Institut of Molecular Science, Universitat de València, Edifici de Instituts de Paterna, Apartat de Correus 22085, 46071 València (Spain)] [Institut of Molecular Science, Universitat de València, Edifici de Instituts de Paterna, Apartat de Correus 22085, 46071 València (Spain); Wulfhekel, W. [Physikalisches Institut, Karlsruhe Institut of Technology, Wolfgang-Gaede-Str. 1, 76131 Karlsruhe (Germany)] [Physikalisches Institut, Karlsruhe Institut of Technology, Wolfgang-Gaede-Str. 1, 76131 Karlsruhe (Germany)

2013-08-21

356

Zero-temperature attenuation and transverse spin dynamics in fermi liquids. II. Dilute fermi systems

NASA Astrophysics Data System (ADS)

This is the second in a series of papers on a consistent microscopic theory of transverse dynamics in spin-polarized or binary Fermi liquids. We demonstrate when and how the exact theory of Ref. 1 reduces to the conventional theory of highly polarized degenerate low-density Fermi liquids and gases. In the lowest approximations, i.e. for an ideal polarized Fermi gas and in the first (Born) order, our theory assumes the standard form. In the next order in density and/or interaction, the main equations still have a fairly conventional form, though they already contain the peculiar zero-temperature attenuation which is missing in the standard theory. This attenuation can be incorporated into the standard Fermi liquid formalism by adding an imaginary part to a mixed spin component of the Landau interaction function. The source of this imaginary contribution at T = 0 is a pole in the integral expression for the Landau interaction function (the situation is very similar to the case of collisionless Landau damping). In the next order, the standard theory fails completely, and even the form of the equations of transverse dynamics becomes very unconventional. We calculated explicitly the parameters of transverse spin dynamics and the spectrum of spin waves, including the zero-temperature attenuation, and, as a by-product, the polarization dependencies of thermodynamic parameters. The calculation includes a possible non-locality of the interaction. An application of the results to3He?-4He mixtures covers the non-locality in the direct interaction channel as well as the non-locality and retardation associated with a phonon-mediated part of particles' interaction.

Meyerovich, A. E.; Musaelian, K. A.

1994-02-01

357

Site-directed spin labeling with continuous wave electron paramagnetic resonance (EPR) spectroscopy was utilized to characterize dynamic features of the kink-turn motif formed through a leader-linker interaction in the Vibrio cholerae glycine riboswitch. Efficient incorporation of spin-labels into select sites within the phosphate backbone of the leader-linker region proceeded via splinted ligation of chemically synthesized spin-labeled oligonucleotides to in vitro transcribed larger RNA fragments. The resultant nitroxide EPR line shapes have spectral characteristics consistent with a kink-turn motif and reveal differential backbone dynamics that are modulated by the presence of magnesium, potassium, and glycine. PMID:24849816

Esquiaqui, Jackie M; Sherman, Eileen M; Ionescu, Sandra A; Ye, Jing-Dong; Fanucci, Gail E

2014-06-10

358

Relevance of electron spin dissipative processes to dynamic nuclear polarization via thermal mixing.

The available theoretical approaches aiming at describing Dynamic Nuclear spin Polarization (DNP) in solutions containing molecules of biomedical interest and paramagnetic centers are not able to model the behaviour observed upon varying the concentration of trityl radicals or the polarization enhancement caused by moderate addition of gadolinium complexes. In this manuscript, we first show experimentally that the nuclear steady state polarization reached in solutions of pyruvic acid with 15 mM trityl radicals is substantially independent on the average internuclear distance. This evidences a leading role of electron (over nuclear) spin relaxation processes in determining the ultimate performances of DNP. Accordingly, we have devised a variant of the Thermal Mixing model for inhomogenously broadened electron resonance lines which includes a relaxation term describing the exchange of magnetic anisotropy energy of the electron spin system with the lattice. Thanks to this additional term, the dependence of the nuclear polarization on the electron concentration can be properly accounted for. Moreover, the model predicts a strong increase of the final polarization upon shortening the electron spin-lattice relaxation time, providing a possible explanation for the effect of gadolinium doping. PMID:24270353

Serra, Sonia Colombo; Filibian, Marta; Carretta, Pietro; Rosso, Alberto; Tedoldi, Fabio

2014-01-14

359

Evidence of impurity and boundary effects on magnetic monopole dynamics in spin ice

NASA Astrophysics Data System (ADS)

Electrical resistance is a crucial and well-understood property of systems ranging from computer microchips to nerve impulse propagation in the human body. Here we study the motion of magnetic charges in spin ice and find that extra spins inserted in Dy2Ti2O7 trap magnetic monopole excitations and provide the first example of how defects in a spin-ice material obstruct the flow of monopoles--a magnetic version of residual resistance. We measure the time-dependent magnetic relaxation in Dy2Ti2O7 and show that it decays with a stretched exponential followed by a very slow long-time tail. In a Monte Carlo simulation governed by Metropolis dynamics we show that surface effects and a very low level of stuffed spins (0.30%)--magnetic Dy ions substituted for non-magnetic Ti ions--cause these signatures in the relaxation. In addition, we find evidence that the rapidly diverging experimental timescale is due to a temperature-dependent attempt rate proportional to the monopole density.

Revell, H. M.; Yaraskavitch, L. R.; Mason, J. D.; Ross, K. A.; Noad, H. M. L.; Dabkowska, H. A.; Gaulin, B. D.; Henelius, P.; Kycia, J. B.

2013-01-01

360

Ultrafast electron dynamics in a metallic quantum well nanofilm with spin splitting

NASA Astrophysics Data System (ADS)

Using time- and angle-resolved two-photon photoemission spectroscopy, we investigate the energy- and momentum-dependent ultrafast electron dynamics in the Rashba spin-split quantum-well nanofilm Bi/Cu(111). We find an expected increase of electron lifetimes towards the band bottom due to a competition of intra- and interband scattering processes. In addition, we find an unexpected peculiar decrease of the lifetimes around the intersection of the split bands. We compare the experimental results with calculated lifetimes due to electron-electron scattering in a model system of a 2D electron gas including a Rashba interaction term and an effective statically screened Coulomb interaction. Although the Rashba model reproduces the increase of lifetimes towards the band bottom well, there is no indication of the experimentally observed decrease around the intersection point in this simple model system. To investigate spin-orbit coupling effects, beyond those contained in a pure Rashba model, we introduce a phenomenological k-dependent spin mixing that leads to a “spin hot spot.” It is shown that such a mixing would strongly increase the electron-electron scattering rate around the band intersection and thus improves the agreement with experiment.

Ruffing, A.; Vollmar, S.; Jakobs, S.; Kaltenborn, S.; Baral, A.; Cinchetti, M.; Mathias, S.; Schneider, H. C.; Aeschlimann, M.

2013-08-01

361

Resonant dynamics of Dirac monopoles and strings in an artificial spin-ice lattice

NASA Astrophysics Data System (ADS)

Spin ices can occur in atomic structures, in which the magnetic interaction with neighboring vertices cannot be simultaneously minimized at each atomic vertex, leading to frustration. Artificial spin-ice lattices are arrays of patterned elements geometrically arranged to mimic the frustration in such atomic lattices, and have the advantage that their properties are directly observable using microscopy techniques. Artificial spin-ices can support topological defects, such as Dirac monopoles and Dirac strings connecting the monopoles. We present micromagnetic simulations of the resonant dynamics of a square spin-ice lattice. The simulations predict that topological defects give rise to specific signatures in the excitation spectrum of the lattice and that, moreover, the amplitude of a defect-specific resonant peak increases linearly with the number of defects or length of the Dirac line. A measured spectrum therefore allows to both identify the defects in an array as well as to determine their number. In addition, we observe that the main bulk-like FMR spectral peak is split in the presence of defects in the lattice, compared to a defect-free reference state. This splitting is caused by Dirac strings, in which the FMR frequency is increased due to the different magnetostatic coupling of the elements within a string as compared to the rest of the lattice.

Heinonen, Olle; Gliga, Sebastian; Kakay, Attila; Hertel, Riccardo

2013-03-01

362

Dynamics of the Spin Liquid Phase of Cs2CuCl4

NASA Astrophysics Data System (ADS)

The dynamics of a spin-liquid phase of an antiferromagnet on the anisotropic triangular lattice and in a magnetic field are studied with a combination of Gutzwiller-projected wavefunctions and mean-field theory. Candidate ground states that support fermionic gapless spinon excitations include four different U(1) spin liquidsootnotetextY. Zhou, X. G. Wen, cond-mat/0210662 (2003).. The lattice and the states interpolate between limiting cases of 1D decoupled chains (J/J^' = 0) and the isotropic 2D square lattice (J/J^'= ?). Parameters of the mean field theory are chosen to minimize the ground state energy of the corresponding Gutzwiller-projected wavefunction. The spin-lattice relaxation rate 1/T1, calculated within the mean-field approximation, is compared to NMR measurementsootnotetextM. A. Vachon, O. Ma, J. B. Marston, V. F. Mitrovi'c, unpublished (2007). in the spin liquid phase of Cs2CuCl4ootnotetextY. Tokiwa, T. Radu, R. Coldea, H. Wilhelm, Z. Tylczynski, F. Steglich, PRB 73, 134414 (2006)..

Ma, Ookie; Vachon, Marc-Andre; Mitrovi{?}, Vesna F.; Marston, Brad

2008-03-01

363

NASA Astrophysics Data System (ADS)

Dynamic magnetic properties of spins from Mn ions doped in semiconductor nanocrystals (Cd1-xMnxSe) have been studied using an electron paramagnetic resonance method based on two different crystalline sizes and a series of Mn concentrations. By decreasing the size of the quantum dots, the electron spin-nuclear spin interactions are reduced due to enhanced magnetic interactions between Mn ions. A linewidth analysis was also carried out, showing longer spin relaxation times and supporting the enhancement of spin coherence. We suggest that the enhancement of Mn-Mn interactions results from the quantized electrons which have longer coherence length in quantum dots. Quantum size effects may benefit to control and manipulation of spins in a semiconductor nanocrystalline system in which the magnetic ions are incorporated.

Jian, W. B.; Fang, Jiye; Ji, Tianhao; He, Jibao

2003-10-01

364

Numerical Investigations of Post-Newtonian Hamiltonian Dynamics for Spinning Compact Binaries

NASA Astrophysics Data System (ADS)

Spinning compact binaries, consisting of neutron stars or black holes, not only have rich dynamic phenomena of resonance and chaos, but also are the most promising source for detecting gravitational waves. There should be a certain relation between the dynamics of the gravitational bodies and the gravitational waveforms. Based on the least-squares correction, several manifold correction schemes like the single-scaling method and the dual-scaling method are designed to suppress numerical errors from 6 integrals of motion in a conservative post-Newtonian (PN) Hamiltonian of spinning compact binaries. Taking a fifth order Runge-Kutta algorithm as a basic integrator, we wonder whether the PN contributions, the spin effects, and the classification of orbits exert some influences on these correction schemes and the Nacozy's approach. It is found that they are almost the same in correcting the integrals for the pure Kepler problem. Once the third-order PN contributions are added to the pure orbital part, there are explicit differences of correction effectiveness among these methods. As an interesting case, the efficiency of correction is better for chaotic eccentric orbits than for quasicircular regular ones. In all cases tested, the new momentum-position dual-scaling scheme does always have the optimal performance. It costs a little but not much expensive additional computational cost when the spin effects exist, and several time-saving techniques are used. The corrected numerical results are more accurate than the uncorrected ones, so that chaos from the numerical errors can be avoided. See Phys. Rev. D 81, 104037 (2010) for more details. Lubich et al. (Phys. Rev. D 81, 104025 (2010)) presented a noncanonically symplectic integrator for the PN Hamiltonian of a spinning compact binary. However, the Euler mixed integrator is problematic because of its bad numerical stability.We improved the work by constructing the second-order and the fourth-order fixed symplectic integrators, where the second-order symplectic implicit midpoint rule and its symmetric compositions are together used to integrate a PN Hamiltonian with the canonical spin variables of Wu and Xie (Phys. Rev. D 81, 084045 (2010)). Many numerical tests show that the mixed leapfrog integrator is always superior to the midpoint rule in the accuracy, while both of them are almost equivalent in the computational efficiency. Particularly, the optimized fourth-order algorithm compared with the mixed leapfrog scheme provides a good precision and needs no expensive additional computational time. The chaoticity of the system can lead to fast iterative convergence and improve the computational efficiency. Because symplectic integrators have no secular change in the energy errors, can give more reliable dynamical information from gravitational waves. See Phys. Rev. D 82, 124040 (2010) for more information. In sum, we have confirmed that the dynamics of the spinning compact binaries can not be determined uniquely by the dynamical parameters, initial conditions, and initial spin angles. Instead, a combination of them is a sourse for causing chaos. These support the results of Wu and Xie (Phys. Rev. D 77, 103012 (2008)).Finally, the gravitational waveforms from chaotic orbits are proved to be stochastic.

Zhong, S. Y.

2012-03-01

365

Dynamic susceptibility evidence of surface spin freezing in ultrafine NiFe2O4 nanoparticles.

We investigated the dynamic behavior of ultrafine NiFe2O4 nanoparticles (average size D = 3.5 nm) that exhibit anomalous low temperature magnetic properties such as low saturation magnetization and high-field irreversibility in both M(H) and ZFC-FC processes. Besides the expected blocking of the superspin, observed at T1 approximately 45 K, the system undergoes a magnetic transition at T2 approximately 6 K. For the latter, frequency- and temperature-resolved dynamic susceptibility data reveal characteristics that are unambiguously related to collective spin freezing: the relative variation (per frequency decade) of the in-phase susceptibility peak temperature is approximately 0.025, critical dynamics analysis yields an exponent znu = 9.6 and a zero-field freezing temperature T(F) = 5.8 K, and, in a magnetic field, T(F)(H) is excellently described by the de Almeida-Thouless line delta T(F) = 1 - T(F)(H)/T(F) alpha H(2/3). Moreover, out-of-phase susceptibility versus temperature datasets collected at different frequencies collapse on a universal dynamic scaling curve. All these observations indicate the existence of a spin-glass-like surface layer that surrounds the superparamagnetic core and undergoes a transition to a frozen state upon cooling below 5.8 K. PMID:19809109

Tackett, Ronald J; Bhuiya, Abdul W; Botez, Cristian E

2009-11-01

366

Dynamic susceptibility evidence of surface spin freezing in ultrafine NiFe2O4 nanoparticles

NASA Astrophysics Data System (ADS)

We investigated the dynamic behavior of ultrafine NiFe2O4 nanoparticles (average size langDrang = 3.5 nm) that exhibit anomalous low temperature magnetic properties such as low saturation magnetization and high-field irreversibility in both M(H) and ZFC-FC processes. Besides the expected blocking of the superspin, observed at T1?45 K, the system undergoes a magnetic transition at T2?6 K. For the latter, frequency- and temperature-resolved dynamic susceptibility data reveal characteristics that are unambiguously related to collective spin freezing: the relative variation (per frequency decade) of the in-phase susceptibility peak temperature is ~0.025, critical dynamics analysis yields an exponent z? = 9.6 and a zero-field freezing temperature TF = 5.8 K, and, in a magnetic field, TF(H) is excellently described by the de Almeida-Thouless line \\delta T_{\\mathrm {F}}= 1-T_{\\mathrm {F}}(H)/T_{\\mathrm {F}} \\propto H^{2 / 3} . Moreover, out-of-phase susceptibility versus temperature datasets collected at different frequencies collapse on a universal dynamic scaling curve. All these observations indicate the existence of a spin-glass-like surface layer that surrounds the superparamagnetic core and undergoes a transition to a frozen state upon cooling below 5.8 K.

Tackett, Ronald J.; Bhuiya, Abdul W.; Botez, Cristian E.

2009-11-01

367

Time-resolved x-ray imaging of magnetization dynamics in spin-transfer torque devices

Time-resolved x-ray imaging techniques have recently demonstrated the capability to probe the magnetic switching of nanoscale devices. This technique has enabled, for example, the direct observation of the nonuniform intermediate states assumed by the magnetic free layer during reversal by a spin-polarized current. These experiments have shown an interesting size-dependent behavior associated with the motion of vortices to mediate the magnetization reversal which cannot be explained by the macrospin picture of spin-torque switching. In this paper we present both experimental and analytical results which show the origin of the complex switching behavior. We use time-resolved x-ray microscopy to further study the switching behavior of samples with 45{sup o} angle between the free and polarizing magnetic layers. A model is developed in terms of a linearized Landau-Lifshitz-Gilbert equation showing that the initial dynamics is dominated by the balance between the Oersted field and thermal fluctuations. The spin torque amplifies this dynamics, leading to a strong sensitivity to sample size, angle, and temperature. The model is in good agreement with current and previous experimental observations.

Chembrolu, V.

2010-02-24

368

Optical analogue of quantum spin and dynamic localization in optical waveguides arrays

NASA Astrophysics Data System (ADS)

We have discovered an optical analogue of quantum spin in optical waveguides arrays. Quantum-optical analogy is recently a hot topic. By using special configuration of optical devices, some optical analogues of quantum systems can be realized. Stefano Longhi and coworkers proposed some classical realization of quantum phenomena like the two-site Fermi-Hubbard system [1] and Rabi oscillation [2]. In this work, we propose an optical waveguides arrays system with evanescent couplings according a symmetrized Kac matrix. The system can mimic the quantum spin under different operators like the rotation operator. Also by adding a suitable time-dependent applied potential to the system, dynamic localization of optical signal can be realized along the signal propagation. The system can be extended to mimic any arbitrary angular momentum by increasing the number of optical waveguides arrays. The occurrences of spin under rotation operator and dynamic localization are simulated by a field-evolution analysis using an input Gaussian beam.[4pt] [1] S. Longhi, G. Della Valle, V. Foglietti, arXiv:1111.3460 (November 2011)[0pt] [2] Ivan L. Garanovich, Stefano Longhi, Andrey A. Sukhorukov, Yuri S. Kivshar, Physics Reports, Volume 518, Issues 1-2, September 2012, Pages 1-7

Yeung, Kin Chung Au; Yu, Kin Wah

2013-03-01

369

Competing Thermodynamic and Dynamic Factors Select Molecular Assemblies on a Gold Surface

NASA Astrophysics Data System (ADS)

Controlling the self-assembly of surface-adsorbed molecules into nanostructures requires understanding physical mechanisms that act across multiple length and time scales. By combining scanning tunneling microscopy with hierarchical ab initio and statistical mechanical modeling of 1,4-substituted benzenediamine (BDA) molecules adsorbed on a gold (111) surface, we demonstrate that apparently simple nanostructures are selected by a subtle competition of thermodynamics and dynamics. Of the collection of possible BDA nanostructures mechanically stabilized by hydrogen bonding, the interplay of intermolecular forces, surface modulation, and assembly dynamics select at low temperature a particular subset: low free energy oriented linear chains of monomers and high free energy branched chains.

Haxton, Thomas K.; Zhou, Hui; Tamblyn, Isaac; Eom, Daejin; Hu, Zonghai; Neaton, Jeffrey B.; Heinz, Tony F.; Whitelam, Stephen

2013-12-01

370

Competing thermodynamic and dynamic factors select molecular assemblies on a gold surface.

Controlling the self-assembly of surface-adsorbed molecules into nanostructures requires understanding physical mechanisms that act across multiple length and time scales. By combining scanning tunneling microscopy with hierarchical ab initio and statistical mechanical modeling of 1,4-substituted benzenediamine (BDA) molecules adsorbed on a gold (111) surface, we demonstrate that apparently simple nanostructures are selected by a subtle competition of thermodynamics and dynamics. Of the collection of possible BDA nanostructures mechanically stabilized by hydrogen bonding, the interplay of intermolecular forces, surface modulation, and assembly dynamics select at low temperature a particular subset: low free energy oriented linear chains of monomers and high free energy branched chains. PMID:24483804

Haxton, Thomas K; Zhou, Hui; Tamblyn, Isaac; Eom, Daejin; Hu, Zonghai; Neaton, Jeffrey B; Heinz, Tony F; Whitelam, Stephen

2013-12-27

371

Ultrafast infrared studies of the role of spin states in organometallic reaction dynamics.

The importance of spin state changes in organometallic reactions is a topic of significant interest, as an increasing number of reaction mechanisms involving changes of spin state are consistently being uncovered. The potential influence of spin state changes on reaction rates can be difficult to predict, and thus this class of reactions remains among the least well understood in organometallic chemistry. Ultrafast time-resolved infrared (TRIR) spectroscopy provides a powerful tool for probing the dynamics of spin state changes in organometallic catalysis, as such processes often occur on the picosecond to nanosecond time scale and can readily be monitored in the infrared via the absorptions of carbonyl reporter ligands. In this Account, we summarize recent work from our group directed toward identifying trends in reactivity that can be used to offer predictive insight into the dynamics of coordinatively unsaturated organometallic reaction intermediates. In general, coordinatively unsaturated 16-electron (16e) singlets are able to coordinate to solvent molecules as token ligands to partially stabilize the coordinatively unsaturated metal center, whereas 16e triplets and 17-electron (17e) doublets are not, allowing them to diffuse more rapidly through solution than their singlet counterparts. Triplet complexes typically (but not always) undergo spin crossover prior to solvent coordination, whereas 17e doublets do not coordinate solvent molecules as token ligands and cannot relax to a lower spin state to do so. 16e triplets are typically able to undergo facile spin crossover to yield a 16e singlet where an associative, exothermic reaction pathway exists. The combination of facile spin crossover with faster diffusion through solution for triplets can actually lead to faster catalytic reactivity than for singlets, despite the forbidden nature of these reactions. We summarize studies on odd-electron complexes in which 17e doublets were found to display varying behavior with regard to their tendency to react with 2-electron donor ligands to form 19-electron (19e) adducts. The ability of 19e adducts to serve as reducing agents in disproportionation reactions depends on whether the excess electron density localized at the metal center or at a ligand site. The reactivity of both 16e and 17e complexes toward a widely used organic nitroxyl radical (TEMPO) are reviewed, and both classes of complexes generally react similarly via an associative mechanism with a low barrier to these reactions. We also describe recent work targeted at unraveling the photoisomerization mechanism of a thermal-solar energy storage complex in which spin state changes were found to play a crucial role. Although a key triplet intermediate was found to be required for this photoisomerization mechanism to proceed, the details of why this triplet is formed in some complexes (those based on ruthenium) and not others (those based on iron, molybdenum, or tungsten) remains uncertain, and further exploration in this area may lead to a better understanding of the factors that influence intramolecular and excited state spin state changes. PMID:24819619

Lomont, Justin P; Nguyen, Son C; Harris, Charles B

2014-05-20

372

Spin dynamics and implications for superconductivity: Some problems with the d-wave scenario

We review the spin dynamics of the normal state of the cuprates with special emphasis on neutron data in both the YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} and La{sub 2-x}Sr{sub x}CuO{sub 4} systems. When realistic models of the Fermi surface shapes are incorporated, along with a moderate degree of spin fluctuations, we find good semi-quantiative agreement with experiment for both cuprates. Building on the success of this Fermi-liquid-based scheme, we explore the implications for d-wave pairing from a number of vantage points. We conclude that our present experimental and theoretical understanding is inadequate to confirm or refute the d-wave scenario.

Levin, K.; Zha, Y.; Radtke, R.J. [Chicago Univ., IL (United States). Dept. of Physics; Si, Q. [Rutgers Univ., Piscataway, NJ (United States). Serin Physics Lab.; Norman, M.R. [Argonne National Lab., IL (United States); Schuttler, H.B. [Georgia Univ., Athens, GA (United States). Dept. of Physics and Astronomy

1993-09-01

373

Implementation of Dynamically Corrected Gates on a Single Electron Spin in Diamond

NASA Astrophysics Data System (ADS)

Precise control of an open quantum system is critical to quantum information processing but is challenging due to inevitable interactions between the quantum system and the environment. We demonstrated experimentally a type of dynamically corrected gates using only bounded-strength pulses on the nitrogen-vacancy centers in diamond. The infidelity of quantum gates caused by a nuclear-spin bath is reduced from being the second order to the sixth order of the noise-to-control-field ratio, which offers greater efficiency in reducing infidelity. The quantum gates have been protected to the limit essentially set by the spin-lattice relaxation time T1. Our work marks an important step towards fault-tolerant quantum computation in realistic systems.

Rong, Xing; Geng, Jianpei; Wang, Zixiang; Zhang, Qi; Ju, Chenyong; Shi, Fazhan; Duan, Chang-Kui; Du, Jiangfeng

2014-02-01

374

A Comparison Study of Magnetic Bearing Controllers for a Fully Suspended Dynamic Spin Rig

NASA Technical Reports Server (NTRS)

NASA Glenn Research Center (GRC) has developed a fully suspended magnetic bearing system for the Dynamic Spin Rig (DSR) that is used to perform vibration tests of turbomachinery blades and components under spinning conditions in a vacuum. Two heteropolar radial magnetic bearings and a thrust bearing and the associated control system were integrated into the DSR to provide noncontact magnetic suspension and mechanical excitation of the 35 lb vertical rotor with blades to induce turbomachinery blade vibration. A simple proportional-integral-derivative (PID) controller with a special feature for multidirectional radial excitation worked very well to both support and shake the shaft with blades. However, more advanced controllers were developed and successfully tested to determine the optimal controller in terms of sensor and processing noise reduction, smaller rotor orbits, and energy savings for the system. The test results of a variety of controllers we demonstrated up to the rig's maximum allowable speed of 10,000 rpm are shown.

Choi, Benjamin; Johnson, Dexter; Morrison, Carlos; Mehmed, Oral; Huff, Dennis (Technical Monitor)

2002-01-01

375

Langevin spin dynamics based on ab initio calculations: numerical schemes and applications.

A method is proposed to study the finite-temperature behaviour of small magnetic clusters based on solving the stochastic Landau-Lifshitz-Gilbert equations, where the effective magnetic field is calculated directly during the solution of the dynamical equations from first principles instead of relying on an effective spin Hamiltonian. Different numerical solvers are discussed in the case of a one-dimensional Heisenberg chain with nearest-neighbour interactions. We performed detailed investigations for a monatomic chain of ten Co atoms on top of a Au(0?0?1) surface. We found a spiral-like ground state of the spins due to Dzyaloshinsky-Moriya interactions, while the finite-temperature magnetic behaviour of the system was well described by a nearest-neighbour Heisenberg model including easy-axis anisotropy. PMID:24806308

Rózsa, L; Udvardi, L; Szunyogh, L

2014-05-28

376

Dynamic generation of spin-squeezed states in bosonic Josephson junctions

NASA Astrophysics Data System (ADS)

We analyze the formation of squeezed states in a condensate of ultracold bosonic atoms confined by a double-well potential. The emphasis is set on the dynamical formation of such states from initially coherent many-body quantum states. Two cases are described: the squeezing formation in the evolution of the system around the stable point, and in the short-time evolution in the vicinity of an unstable point. The latter is shown to produce highly squeezed states on very short times. On the basis of a semiclassical approximation to the Bose-Hubbard Hamiltonian, we are able to predict the amount of squeezing, its scaling with N, and the speed of coherent spin formation with simple analytical formulas which successfully describe the numerical Bose-Hubbard results. This method of producing highly squeezed spin states in systems of ultracold atoms is compared to other standard methods in the literature.

Juliá-Díaz, B.; Zibold, T.; Oberthaler, M. K.; Melé-Messeguer, M.; Martorell, J.; Polls, A.

2012-08-01

377

Implementation of dynamically corrected gates on a single electron spin in diamond.

Precise control of an open quantum system is critical to quantum information processing but is challenging due to inevitable interactions between the quantum system and the environment. We demonstrated experimentally a type of dynamically corrected gates using only bounded-strength pulses on the nitrogen-vacancy centers in diamond. The infidelity of quantum gates caused by a nuclear-spin bath is reduced from being the second order to the sixth order of the noise-to-control-field ratio, which offers greater efficiency in reducing infidelity. The quantum gates have been protected to the limit essentially set by the spin-lattice relaxation time T1. Our work marks an important step towards fault-tolerant quantum computation in realistic systems. PMID:24580578

Rong, Xing; Geng, Jianpei; Wang, Zixiang; Zhang, Qi; Ju, Chenyong; Shi, Fazhan; Duan, Chang-Kui; Du, Jiangfeng

2014-02-01

378

Dynamical Splayed Ferromagnetic Ground State in the Quantum Spin Ice Yb2Sn2O7

NASA Astrophysics Data System (ADS)

From magnetic, specific heat, Yb170 Mössbauer effect, neutron diffraction, and muon spin relaxation measurements on polycrystalline Yb2Sn2O7, we show that below the first order transition at 0.15 K all of the Yb3+ ions are long-range magnetically ordered and each has a moment of 1.1?B which lies at ?10° to a common fourfold cubic axis. The four sublattice moments have four different directions away from this axis and are therefore noncoplanar. We term this arrangement splayed ferromagnetism. This ground state has a dynamical component with a fluctuation rate in the megahertz range. The net ferromagnetic exchange interaction has an anisotropy that favors the local threefold axis. We discuss our results in terms of the phase diagram proposed by Savary and Balents [Phys. Rev. Lett. 108, 037202 (2012)PRLTAO0031-9007] for a pyrochlore lattice of Kramers 1/2 effective spins.

Yaouanc, A.; Dalmas de Réotier, P.; Bonville, P.; Hodges, J. A.; Glazkov, V.; Keller, L.; Sikolenko, V.; Bartkowiak, M.; Amato, A.; Baines, C.; King, P. J. C.; Gubbens, P. C. M.; Forget, A.

2013-03-01

379

Quantum dynamics of a spin chain in the presence of engineered collective noise

NASA Astrophysics Data System (ADS)

We experimentally and theoretically investigate the effect of engineered collective noise on the quantum dynamics of a spin chain evolving under the double-quantum Hamiltonian. This Hamiltonian is related by a similarity transformation to the isotropic XX Hamiltonian, and is experimentally accessible in solid-state NMR using coherent averaging techniques. In the absence of noise, a localized magnetic moment is observed to move down the chain at a constant velocity. We show that this transport is disrupted by the presence of collective z-noise, and that the magnetic moment becomes localized at the initial site as the strength of the noise increases. The relevance to quantum information transport in spin chains is also discussed.

Zeitler, Christopher; Anderson, Laurel E.; Viola, Lorenza; Ramanathan, Chandrasekhar

2013-03-01

380

Interplay of spin and charge dynamics in Sr14-xCaxCu24O41

NASA Astrophysics Data System (ADS)

In single crystals of intrinsically hole-doped Sr14-xCaxCu24O41 a strong electron spin resonance (ESR) signal has been observed and studied as a function of temperature and Ca concentration (x=0-12). Since the spin ladders show a large spin gap of about 400-500 K, the dominant contribution to the ESR signal below 300 K is attributed to the CuO2 spin-1/2 chains. For all values of x the data reveal a remarkable influence of the hole dynamics on the Cu-spin relaxation. This enables us to identify the onset of charge order in the chains for x=0 and 2 at 200 and 170 K, respectively. A further increase of x rapidly destroys the charge ordered state. A transition to an antiferromagnetically ordered state is observed at 2.5 K for x=12. However, the ESR signal shows critical broadening already for x>=8 at low temperatures, which indicates the development of magnetic order for values of x smaller than 12. For comparison we show ESR data of La1Sr13Cu24O41 and La2Ca12Cu24O41, in which the hole concentration is reduced. The whole set of ESR data can be understood in terms of a transfer of only a small amount of holes from the chains to the ladders with increasing x in Sr14-xCaxCu24O41 and a simultaneous crossover from independent dimers to antiferromagnetically coupled chains, which order at low temperatures due to weak interchain interactions.

Kataev, V.; Choi, K.-Y.; Grüninger, M.; Ammerahl, U.; Büchner, B.; Freimuth, A.; Revcolevschi, A.

2001-09-01

381

The Study of Competence-Anxiety Relations within Social Interaction: A Dynamic Systems Approach.

ERIC Educational Resources Information Center

This study presents a dynamic systems model that suggests that social behavior emerges from the self-organization of cognition-emotion relationships and becomes stable through a process of positive feedback and coupling of components over time. Five 10- to 12-year-old children identified as anxious in evaluative situations by their teacher were…

Phillips, Sian

382

Analysis of Work: Describing Competences through a Dynamic Approach to Jobs.

ERIC Educational Resources Information Center

Human resources management personnel have been encouraged to develop a job analysis approach capable of grasping work situations that are more complex, less defined, and in a state of flux. In France, this perspective has given rise to Emploi Type Etudie dans sa Dynamique (ETED) or "typical job studied in its dynamic," an approach that reflects…

Mandon, Nicole; Sulzer, Emmanuel

1998-01-01

383

In order to balance the tensions of the concepts of organizational core competencies and dynamic capability we introduce social knowledge networks as a strategic means from a knowledge management perspective. A facilitator for the development of the respective framework is the precise distinction between explicit and non-explicit knowledge. Social knowledge networks are informal with regard to their very character but

Harald F. O. Von Kortzfleisch; Ines Mergel; Christian Proll

2007-01-01

384

Spin Dynamics Simulations of Multiple Echo Spacing Pulse Sequences in Grossly Inhomogeneous Fields

Pulse sequences with multiple lengths of echo spacings are used in oilfield NMR logging for diffusion-based NMR applications such as rock and fluid characterization. One specific implementation is the so-called diffusion editing sequence comprising two long echo spacings followed by a standard CPMG at a shorter echo spacing. The echoes in the CPMG portion contain signal from both the direct and stimulated echoes.Modern oilfield NMR logging tools are designed for continuous depth logging of earth formations by projecting both the static (B{sub 0}) and dynamic (B{sub 1}) fields into the formation. Both B{sub 0} and B{sub 1} profiles are grossly inhomogeneous which results in non-steady-state behavior in the early echoes. The spin dynamics effects present a challenge for processing the echo amplitudes to measure porosity (amplitude extrapolated to zero time) and attenuations for fluid or pore size characterization.In this work we describe a calculation of the spin dynamics of the diffusion editing sequence with two long echo spacings. The calculation takes into account full B{sub 1} and B{sub 0} field maps, and comparisons will be made for sensors and parameters typical of oilfield logging tools and environments.

Heidler, R.; Bachman, H. N.; Johansen, Y. [Schlumberger Oilfield Services, Sugar Land, TX 77478 (United States)

2008-12-05

385

Optimal pulse spacing for dynamical decoupling in the presence of a purely dephasing spin bath

Maintaining quantum coherence is a crucial requirement for quantum computation; hence protecting quantum systems against their irreversible corruption due to environmental noise is an important open problem. Dynamical decoupling (DD) is an effective method for reducing decoherence with a low control overhead. It also plays an important role in quantum metrology, where, for instance, it is employed in multiparameter estimation. While a sequence of equidistant control pulses [the Carr-Purcell-Meiboom-Gill (CPMG) sequence] has been ubiquitously used for decoupling, Uhrig recently proposed that a nonequidistant pulse sequence [the Uhrig dynamic decoupling (UDD) sequence] may enhance DD performance, especially for systems where the spectral density of the environment has a sharp frequency cutoff. On the other hand, equidistant sequences outperform UDD for soft cutoffs. The relative advantage provided by UDD for intermediate regimes is not clear. In this paper, we analyze the relative DD performance in this regime experimentally, using solid-state nuclear magnetic resonance. Our system qubits are {sup 13}C nuclear spins and the environment consists of a {sup 1}H nuclear spin bath whose spectral density is close to a normal (Gaussian) distribution. We find that in the presence of such a bath, the CPMG sequence outperforms the UDD sequence. An analogy between dynamical decoupling and interference effects in optics provides an intuitive explanation as to why the CPMG sequence performs better than any nonequidistant DD sequence in the presence of this kind of environmental noise.

Ajoy, Ashok [Fakultaet Physik, Technische Universitaet Dortmund, D-44221 Dortmund (Germany); Birla Institute of Technology and Science, Pilani, Zuarinagar, Goa 403726 (India); NMR Research Centre, Indian Institute of Science, Bangalore 560012 (India); Alvarez, Gonzalo A.; Suter, Dieter [Fakultaet Physik, Technische Universitaet Dortmund, D-44221 Dortmund (Germany)

2011-03-15

386

An intriguing aspect of unconventional superconductivity is that it always appears in the vicinity of other competing phases, whose suppression brings the full emergence of superconductivity. In the iron pnictides, these competing phases are marked by a tetragonal-to-orthorhombic structural transition and a collinear spin-density wave (SDW) transition. There has been macroscopic evidence for competition between these phases and superconductivity as the magnitude of both the orthorhombicity and magnetic moment are suppressed in the superconducting state. Here, using angle-resolved photoemission spectroscopy on detwinned underdoped Ba(1-x)K(x)Fe2As2, we observe a coexistence of both the SDW gap and superconducting gap in the same electronic structure. Furthermore, our data reveal that following the onset of superconductivity, the SDW gap decreases in magnitude and shifts in a direction consistent with a reduction of the orbital anisotropy. This observation provides direct spectroscopic evidence for the dynamic competition between superconductivity and both SDW and electronic nematic orders in these materials. PMID:24762657

Yi, M; Zhang, Y; Liu, Z-K; Ding, X; Chu, J-H; Kemper, A F; Plonka, N; Moritz, B; Hashimoto, M; Mo, S-K; Hussain, Z; Devereaux, T P; Fisher, I R; Wen, H H; Shen, Z-X; Lu, D H

2014-01-01

387

NASA Astrophysics Data System (ADS)

An intriguing aspect of unconventional superconductivity is that it always appears in the vicinity of other competing phases, whose suppression brings the full emergence of superconductivity. In the iron pnictides, these competing phases are marked by a tetragonal-to-orthorhombic structural transition and a collinear spin-density wave (SDW) transition. There has been macroscopic evidence for competition between these phases and superconductivity as the magnitude of both the orthorhombicity and magnetic moment are suppressed in the superconducting state. Here, using angle-resolved photoemission spectroscopy on detwinned underdoped Ba1?xKxFe2As2, we observe a coexistence of both the SDW gap and superconducting gap in the same electronic structure. Furthermore, our data reveal that following the onset of superconductivity, the SDW gap decreases in magnitude and shifts in a direction consistent with a reduction of the orbital anisotropy. This observation provides direct spectroscopic evidence for the dynamic competition between superconductivity and both SDW and electronic nematic orders in these materials.

Yi, M.; Zhang, Y.; Liu, Z.-K.; Ding, X.; Chu, J.-H.; Kemper, A. F.; Plonka, N.; Moritz, B.; Hashimoto, M.; Mo, S.-K.; Hussain, Z.; Devereaux, T. P.; Fisher, I. R.; Wen, H. H.; Shen, Z.-X.; Lu, D. H.

2014-04-01

388

Subnanosecond radical pair (RP) formation by electron transfer from an excited singlet state or by bond breaking produces two correlated spins coupled by their spin-spin exchange (J) and magnetic dipole (D) interactions. In the high magnetic field limit, the two-spin system can be described by a singlet state (S) and three triplet states (T0, T+1, T-1). When J is small relative to the electron Zeeman interaction, |T0? is the only triplet state that is populated by coherent spin mixing with the |S? state because the |T+1? and |T-1? states are well-separated from |S? by a large energy gap. Herein, we describe the spin dynamics for RPs having restricted geometries in which J is similar in magnitude to the electron Zeeman interaction and does not fluctuate significantly. Under these circumstances, depending on the sign of J, the energies of |T+1? or |T-1? are close to that of |S? so that weak isotropic electron-nuclear hyperfine coupling leads to population of |T+1? or |T-1?. An approximate relationship for the triplet quantum yield is developed for a RP in the large J regime, where one or both electrons interact with nearby spin-1/2 nuclei. This relationship also yields the net spin polarization transfer to the nuclear spins. PMID:24870373

Zarea, Mehdi; Carmieli, Raanan; Ratner, Mark A; Wasielewski, Michael R

2014-06-19

389

Spin Dynamics in Two-Dimensional Arrays of Quantum Dots with Local Ordering of Nanoclusters

NASA Astrophysics Data System (ADS)

Electron paramagnetic resonance (EPR) is used to probe the spin dynamics in two-dimensional (2D) quantum dot (QD) arrays with local ordering of nanoclusters. A careful examination of EPR line shape, width and g-factor values allow us to attribute this signal to the electrons localized in the strain-induced potential wells in Si in the vicinity of the Ge dots. The strong orientation dependence of EPR line width is defined by changing localization degree of electrons at different magnetic field directions. The theoretical approximation of orientation dependence of EPR line width allows estimating the effective radius of electron localization, as ~80 nm.

Zinovieva, A. F.; Dvurechenskii, A. V.; Stepina, N. P.; Nikiforov, A. I.; Lyubin, A. S.; Sobolev, N.; Carmo, M. C.

2011-12-01

390

Chaos and its avoidance in spinup dynamics of an axial dual-spin spacecraft

NASA Astrophysics Data System (ADS)

Attitude dynamics of a dual-spin spacecraft (DSSC) and a torque-free angular motion of a coaxial bodies system are considered. Some regimes of the heteroclinic chaos are described. The local chaotization of the DSSC is investigated at the presence of polyharmonic perturbations and small nutation restoring/overturning torques on the base of the Melnikov method and Poincaré Maps. Reasons of the chaotic regimes initiation at the spinup maneuver realization are studied. An approach for the local heteroclinic chaos escape/avoidance at the modification of the classical spinup maneuver is suggested.

Doroshin, Anton V.

2014-02-01

391

Dynamic control of quantum geometric heat flux in a nonequilibrium spin-boson model

NASA Astrophysics Data System (ADS)

We study the quantum geometric heat flux in the nonequilibrium spin-boson model. By adopting the noninteracting-blip approximation that is able to accommodate the strong system-bath coupling, we show that there exists a nonzero geometric heat flux only when the two-level system is nondegenerate. Moreover, the pumping, no pumping, and dynamic control of geometric heat flux are discussed in detail, compared to the results with Redfield weak-coupling approximation. In particular, the geometric energy transfer induced by modulation of two system-bath couplings is identified, which is exclusive to quantum transport in the strong system-bath coupling regime.

Chen, Tian; Wang, Xiang-Bin; Ren, Jie

2013-04-01

392

Quantum states, symmetry and dynamics in degenerate spin s=1 magnets

NASA Astrophysics Data System (ADS)

The paper deals with spin s=1 magnets. The symmetry conditions for normal and degenerate equilibrium states are defined and types of magnetic ordering were found out. For each type of symmetry breaking the structure of source in the Gibbs statistical operator has been obtained and additional thermodynamic parameters have been introduced. The algebra of Poisson bracket for magnetic degrees of freedom has been established and nonlinear dynamic equations have been derived. Using the models of the exchange interaction, we have calculated the spectra of collective excitations for two degenerate states whose order parameters have different signatures under the time reversal transformation.

Kovalevsky, M. Y.; Glushchenko, A. V.

2014-04-01

393

We investigate the effects of lattice distortions and anisotropy on the non-collinear ground state and spin dynamics of the multiferroic phase of doped CuFeO2. Using a Holstein-Primakoff expansion, we evaluate the change in the spin dynamics as lattice distortions and anisotropy distort the simple incommensurate helix. Distinct features in the spin dynamics that are created by lattice distortions and anisotropy have recently been observed in Ga-doped CuFeO2.

Haraldsen, Jason T [ORNL; Fishman, Randy Scott [ORNL

2010-01-01

394

Magnetic Phase Transition and Spin Dynamics in Magnetoelectric Effect LiMnPO4

NASA Astrophysics Data System (ADS)

Elastic and inelastic neutron scattering techniques were used to study the magnetic phase transition and spin dynamics in single crystal LiMnPO4. In this mulitiferroic, antiferromagnetism coexists with induced ferroelectricity below the Neel temperature. Elastic neutron scattering technique confirmed that LiMnPO4 has a collinear antiferromagnetic ground state with magnetic moments oriented along the a-axis. The temperature dependent order parameter, calculated from the integrated intensity of the (010) magnetic reflection, was fit to a power law equation, yielding a transition temperature TN = 33.7 K and a critical exponent of ? = 0.114. Above the Neel temperature, in the paramagnetic phase, unusually strong magnetic fluctuations were observed to temperatures as high as 60 K. The correlation lengths in the MnO layer and between the layers were also determined. The spin-wave dispersion curves along a- and b-axis were measured in the antiferromagnetic state at 4.5 K and the system was shown to be quasi-2D by analyzing the dispersion curves using a 3D Heisenberg model from linear spin wave theory.

Li, J.; Tain, W.; Zarestky, J. L.; Vaknin, D.; Chen, Y.; Lynn, J. W.

2007-03-01

395

NASA Astrophysics Data System (ADS)

In this paper, we combine thermal effects with Landau-Zener (LZ) quantum tunneling effects in a dynamical Monte Carlo (DMC) framework to produce satisfactory magnetization curves of single-molecule magnet (SMM) systems. We use the giant spin approximation for SMM spins and consider regular lattices of SMMs with magnetic dipolar interactions (MDIs). We calculate spin-reversal probabilities from thermal-activated barrier hurdling, direct LZ tunneling, and thermal-assisted LZ tunnelings in the presence of sweeping magnetic fields. We do systematical DMC simulations for Mn12 systems with various temperatures and sweeping rates. Our simulations produce clear step structures in low-temperature magnetization curves, and our results show that the thermally activated barrier hurdling becomes dominating at high temperature near 3 K and the thermal-assisted tunnelings play important roles at intermediate temperature. These are consistent with corresponding experimental results on good Mn12 samples (with less disorders) in the presence of little misalignments between the easy axis and applied magnetic fields, and therefore our magnetization curves are satisfactory. Furthermore, our DMC results show that the MDI, with the thermal effects, have important effects on the LZ tunneling processes, but both the MDI and the LZ tunneling give place to the thermal-activated barrier hurdling effect in determining the magnetization curves when the temperature is near 3 K. This DMC approach can be applicable to other SMM systems and could be used to study other properties of SMM systems.

Liu, Gui-Bin; Liu, Bang-Gui

2010-10-01

396

Random variable approach to dissipative spin dynamics and Landau-Zener transitions

NASA Astrophysics Data System (ADS)

We present a random variable approach to solve for the dynamics of a dissipative two-state system. Based on an exact functional integral description, our method reformulates the problem as that of non-unitary time evolution of a quantum state vector under a Hamiltonian containing random noise fields. This non-perturbative formalism goes beyond the frequently used Non-Interacting Blip Approximation (NIBA) and is particularly well suited to treat an explicitly time-dependent Hamiltonian. As an example, we consider the renowned Landau-Zener problem in the presence of an Ohmic bath with a large bath cutoff frequency ?c. We identify an intermediate time regime where the energy separation of the two spin states is much larger than their tunneling coupling ?, but still smaller than ?c such that bath mediated spin transitions still occur. Such a situation can for example be realized with a cold atomic quantum dot setup. We also derive an approximate analytical expression for the decay of the upper spin state population in this regime, which agrees well with our numerical results.

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

2010-03-01

397

Silicon spin chains at finite temperature: Dynamics of Si(553)-Au

NASA Astrophysics Data System (ADS)

When gold is deposited on Si(553), the surface self-assembles to form a periodic array of steps with nearly perfect structural order. In scanning tunneling microscopy these steps resemble quasi-one-dimensional atomic chains. At temperatures below ˜50 K the chains develop a tripled periodicity. We recently predicted, on the basis of density-functional theory calculations at T=0, that this tripled periodicity arises from the complete polarization of the electron spin on every third silicon atom along the step; in the ground state these linear chains of silicon spins are antiferromagnetically ordered. Here we explore, using ab initio molecular dynamics and kinetic Monte Carlo simulations, the behavior of silicon spin chains on Si(553)-Au at finite temperature. Thermodynamic phase transitions at T>0 in one-dimensional systems are prohibited by the Mermin-Wagner theorem. Nevertheless we find that a surprisingly sharp onset occurs upon cooling—at about 30 K for perfect surfaces and at higher temperature for surfaces with defects—to a well-ordered phase with tripled periodicity, in good agreement with experiment.

Erwin, Steven C.; Snijders, Paul C.

2013-06-01

398

Rotating Frame Spin dynamics of a Single Nitrogen Vacancy Center in Diamond Nanocrystal

NASA Astrophysics Data System (ADS)

We investigate the spin dynamics of a nitrogen-vacancy (NV) center contained in individual diamond nanocrystals with an average diameter of 70 ± 20 nm in the presence of continuous microwave excitation. Upon periodic reversal of the microwave phase, we observe a train of rotary (Solomon) echoes that effectively extends the system coherence lifetime to reach several tens of microseconds, depending on the microwave power and phase inversion rate [1]. Starting from a model where the NV center interacts with a bath of paramagnetic defects on the nanocrystal surface, we use average Hamiltonian theory to compute the signal envelope from its amplitude at the echo maxima. A comparison between the effective Rabi and Solomon propagators shows that the observed response can be understood as a form of higher-order decoupling from the spin bath. The observed rotary echoes can be thought of as the rotating frame analog of Hahn's spin echoes, implying that the present scheme may find use for nanodiamond-based magnetic sensing. [1] A. Laraoui, C. A. Meriles, Phys. Rev. B 84, 161403(R) (2011).

Laraoui, Abdelghani; Meriles, Carlos

2012-02-01

399

Spin Dynamics and Quantum Tunneling in Fe8 Nanomagnet and in AFM Rings by NMR

In this thesis, our main interest has been to investigate the spin dynamics and quantum tunneling in single molecule magnets (SMMs), For this we have selected two different classes of SMMs: a ferrimagnetic total high spin S = 10 cluster Fe8 and antiferromagnetic (AFM) ring-type clusters. For Fe8, our efforts have been devoted to the investigation of the quantum tunneling of magnetization in the very low temperature region. The most remarkable experimental finding in Fe8 is that the nuclear spin-lattice relaxation rate (1/T{sub l}) at low temperatures takes place via strong collision mechanism, and thus it allows to measure directly the tunneling rate vs T and H for the first time. For AFM rings, we have shown that 1/T{sub l} probes the thermal fluctuations of the magnetization in the intermediate temperature range. We find that the fluctuations are dominated by a single characteristic frequency which has a power law T-dependence indicative of fluctuations due to electron-acoustic phonon interactions.

Seung-Ho-Baek

2004-12-19

400

The population transfer to the spin-sublevels of the unique quartet (S = 3/2) high-spin state of the strongly exchange-coupled (SC) radical-triplet pair (for example, an Acceptor-Donor-Radical triad (A-D-R)) via a doublet-quartet quantum-mixed (QM) state is theoretically investigated by a stochastic Liouville equation. In this work, we have treated the loss of the quantum coherence (de-coherence) due to the de-phasing during the population transfer and neglected the effect of other de-coherence mechanisms. The dependences on the magnitude of the exchange coupling or the fine-structure parameter of the QM state are investigated. The dependence on the velocity of the population transfer (by the electron transfer or the energy-transfer) from the QM state to the SC quartet state is also clarified. It is revealed that the de-coherence during the population transfer mainly originates from the fine-structure term of the QM state in the doublet-triplet exchange coupled systems. This de-coherence leads to the unique dynamic electron polarization (DEP) on the high-field spin sublevels of the SC state, which is similar to the unique DEP pattern of the photo-excited triplet states of the reaction centers of photosystems I and II. The magnetic field dependence of the population transfer leading to the populations of the spin-sublevels of the SC states is also calculated. The possibility of the control of energy transport, spin transport and information technology by using the QM state is discussed based on these results. The knowledge obtained in this work is useful in the spin dynamics of any doublet-triplet exchange coupled systems. PMID:22717738

Matsumoto, Takafumi; Teki, Yoshio

2012-08-01

401

The dynamics of neutralization of electron-spin-polarized (4)He(+) ions at surfaces

NASA Astrophysics Data System (ADS)

Ion Neutralization Spectroscopy (INS) is a well known probe of surface electronic structure with unparalleled surface specificity. In INS, a beam of singly-charged low-energy rare gas ions is directed at a target surface, and electrons ejected as a result of ion neutralization are analyzed. The use of spin-labeling techniques in INS provides a powerful tool for understanding the nature of the ion neutralization process. In the current research a spin polarized He+ ion source has been developed and used to study the dynamics of ion-surface interactions. The He+ ions are produced in a weak rf- excited discharge by Penning ionization reactions between helium metastable atoms. The He(2 3S) metastable atoms are electron-spin-polarized by optical pumping on the D1 transition with 1083nm radiation. Spin conservation in Penning ionization reactions produces spin-polarized ions, which are extracted from the discharge and focused onto the target surface using a series of electrostatic lenses. The impact energy can be varied from ~10eV to ~600eV with beam currents of ~0.3nA and typical beam polarizations of 10-15%. Measurements of the polarization of electrons ejected from an Au(100) surface as a result of Auger neutralization of polarized ions reveal a net spin correlation which increases dramatically at high electron energies. The net correlation is explained as resulting from interference effects between different neutralization channels; and the increase at high electron energies is explained by considering the local perturbation in the surface electronic structure induced by the presence of the polarized He+ ion. Electrons ejected during neutralization of polarized He+ ions at a Xe film were also studied. These reveal a low-energy feature in the electron energy distribution (EED) that was previously observed with metastable deexcitation spectroscopy (MDS). The presence of this feature in the EED for ion neutralization supports the hypotheses put forth to explain the previous results. Improvements to the polarized He+ ion source are currently being explored and a number of new targets are being considered.

Bixler, David Lynn

1999-10-01

402

Dynamical passage to approximate equilibrium shapes for spinning, gravitating rubble asteroids

NASA Astrophysics Data System (ADS)

Many asteroids are thought to be particle aggregates held together principally by self-gravity. Here we study — for static and dynamical situations — the equilibrium shapes of spinning asteroids that are permitted for rubble piles. As in the case of spinning fluid masses, not all shapes are compatible with a granular rheology. We take the asteroid to always be an ellipsoid with an interior modeled as a rigid-plastic, cohesion-less material with a Drucker-Prager yield criterion. Using an approximate volume-averaged procedure, based on the classical method of moments, we investigate the dynamical process by which such objects may achieve equilibrium. We first collapse our dynamical approach to its statical limit to derive regions in spin-shape parameter space that allow equilibrium solutions to exist. At present, only a graphical illustration of these solutions for a prolate ellipsoid following the Drucker-Prager failure law is available [Sharma, I., Jenkins, J.T., Burns, J.A., 2005a. Bull. Am. Astron. Soc. 37, 643; Sharma, I., Jenkins, J.T., Burns, J.A., 2005b. Equilibrium shapes of ellipsoidal soil asteroids. In: García-Rojo, R., Hermann, H.J., McNamara, S. (Eds.), Proceedings of the 5th International Conference on Micromechanics of Granular Media, vol. 1. A.A. Balkema, UK; Holsapple, K.A., 2007. Icarus 187, 500-509]. Here, we obtain the equilibrium landscapes for general triaxial ellipsoids, as well as provide the requisite governing formulae. In addition, we demonstrate that it may be possible to better interpret the results of Richardson et al. [Richardson, D.C., Elankumaran, P., Sanderson, R.E., 2005. Icarus 173, 349-361] within the context of a Drucker-Prager material. The graphical result for prolate ellipsoids in the static limit is the same as those of Holsapple [Holsapple, K.A., 2007. Icarus 187, 500-509] because, when worked out, his final equations will match ours. This is because, though the formalisms to reach these expressions differ, in statics, at the lowest level of approximation, volume-averaging and the approach of Holsapple [Holsapple, K.A., 2007. Icarus 187, 500-509] coincide. We note that the approach applied here was obtained independently [Sharma, I., Jenkins, J.T., Burns, J.A., 2003. Bull. Am. Astron. Soc. 35, 1034; Sharma, I., 2004. Rotational Dynamics of Deformable Ellipsoids with Applications to Asteroids. Ph.D. thesis, Cornell University] and it provides a general, though approximate, framework that is amenable to systematic improvements and is flexible enough to incorporate the dynamical effects of a changing shape, different rheologies and complex rotational histories. To demonstrate our technique, we investigate the non-equilibrium dynamics of rigid-plastic, spinning, prolate asteroids to examine the simultaneous histories of shape and spin rate for rubble piles. We have succeeded in recovering most results of Richardson et al. [Richardson, D.C., Elankumaran, P., Sanderson, R.E., 2005. Icarus 173, 349-361], who obtained equilibrium shapes by studying numerically the passage into equilibrium of aggregates containing discrete, interacting, frictionless, spherical particles. Our mainly analytical approach aids in understanding and quantifying previous numerical simulations.

Sharma, Ishan; Jenkins, James T.; Burns, Joseph A.

2009-03-01

403

We study the dynamics of quantum discord and entanglement for two spin qubits coupled to a spin chain with Dzyaloshinsky-Moriya (DM) interaction. We numerically and analytically investigate the time evolution of quantum discord and entanglement for two-qubit initially prepared in a class of $X-$structure state. In the case of evolution from a pure state, quantum correlations decay to zero in

Yi-ying Yan; Li-jun Tian; Li-guo Qin

2011-01-01

404

NASA Astrophysics Data System (ADS)

We report a new experimental technique that integrates high frequency surface acoustic waves (SAWs) with high frequency electron paramagnetic resonance (HFEPR) spectroscopy in order to measure spin dynamics on fast time scales in single-molecule magnets. After driving the system out of equilibrium by triggering magnetic avalanches, or simply by heating with short SAW pulses, the evolution of the spin populations within fixed energy levels is measured using HFEPR spectroscopy.

Hill, Stephen; Lawrence, Jonathan; Macia, Ferran; Hernandez, Joan Manel; Tejada, Javier; Santos, Paulo; Lampropoulos, Christos; Christou, George

2008-03-01

405

NASA Astrophysics Data System (ADS)

We report an experimental technique that integrates high-frequency surface acoustic waves (SAWs) with high-frequency electron paramagnetic resonance (HFEPR) spectroscopy in order to measure spin dynamics on fast time scales in single-molecule magnets. After the system is driven out of equilibrium by triggering magnetic avalanches, or simply by heating with short SAW pulses, the evolution of the spin populations within fixed energy levels is measured using HFEPR spectroscopy.

Macià, F.; Lawrence, J.; Hill, S.; Hernandez, J. M.; Tejada, J.; Santos, P. V.; Lampropoulos, C.; Christou, G.

2008-01-01

406

We have used saturation transfer electron paramagnetic resonance (ST-EPR) to study the rotational dynamics of spin-labeled regulatory light chain (RLC) in scallop ( Placopecten magellanicus) muscle fibers. The single cysteine (Cys 51) in isolated clam (Mercenaria) RLC was labeled with an indanedione spin label (InVSL). RLC was completely and specifically extracted from scallop striated muscle fibers, eliminating the Ca sensitivity

Osha Roopnarine; Andrew G. Szent-Györgyi; David D. Thomas

1998-01-01

407

Dynamic phase transitions in the kinetic spin-1 Blume-Capel model on the Bethe lattice

NASA Astrophysics Data System (ADS)

The stationary states of the kinetic spin-1 Blume-Capel (BC) model on the Bethe lattice are analyzed in detail in terms of recursion relations. The model is described using a Glauber-type stochastic dynamics in the presence of a time-dependent oscillating external magnetic field ( h) and crystal field ( D) interactions. The dynamic order parameter, the hysteresis loop area and the dynamic correlation are calculated. It is found that the magnetization oscillates around nonzero values at low temperatures ( T) for the ferromagnetic (F) phase while it only oscillates around zero values at high temperatures for the paramagnetic (P) phase. There are regions of the phase space where the two solutions coexist. The dynamic phase diagrams are obtained on the (kT/J,h/J) and (kT/J,D/J) planes for the coordination number q=4. In addition to second-order and first-order phase transitions, dynamical tricritical points and triple points are also observed.

Deviren, Seyma Akkaya; Albayrak, Erhan

2011-10-01

408

Structural analysis of protein dynamics by MD simulations and NMR spin-relaxation

Molecular dynamics (MD) simulations and nuclear magnetic resonance spin-relaxation measurements provide detailed insights into ps-ns structural dynamics of proteins. An analysis of discrepancies between the two methods is presented for the B3 immunoglobulin-binding domain of streptococcal protein G. MD simulations using three MD force fields (OPLS-AA, AMBER ff99SB, and AMBER ff03) overestimate the flexibility of backbone N—H vectors at the borders of secondary structure and in loops when compared with experimentally determined backbone amide generalized order parameters (Hall and Fushman, J Am Chem Soc 2006; 12:7855–7870). Comparison with a previous study of residual dipolar coupling constants (Bouvignies et al., Proc Natl Acad Sci USA 2005;102:13885–13890) indicates that slower timescale motions do not account for the discrepancies. Structural analysis reveals that relative imbalance between the description of hydrogen bonding and other terms of modern force fields may be responsible for disagreement.

Trbovic, Nikola; Kim, Byungchan; Friesner, Richard A.; Palmer, Arthur G.

2009-01-01

409

Off-equilibrium dynamics at very low temperatures in three-dimensional spin glasses

NASA Astrophysics Data System (ADS)

We present a high-statistic systematic study of the overlap correlation function well below the critical temperature in the three-dimensional Gaussian spin glass. The off-equilibrium correlation function has been studied confirming the power law behaviour for the dynamical correlation length. In particular, we have computed the dynamical critical exponent z in a wide range of temperatures, 0.35icons/Journals/Common/le" ALT="le" ALIGN="TOP"/> Ticons/Journals/Common/le" ALT="le" ALIGN="TOP"/> 0.9, obtaining a dependence z (T ) = 6.2/T in very good agreement with recent experiments. Moreover, we report a study of the violation of the fluctuation-dissipation theorem for very low temperatures T = 0.5 and 0.35. All our numerical results avoid a droplet model interpretation even when T is as low as T = 0.35.

Marinari, Enzo; Parisi, Giorgio; Ricci-Tersenghi, Federico; Ruiz-Lorenzo, Juan J.

2000-03-01

410

Dynamics of the sub-Ohmic spin-boson model: A time-dependent variational study

The Dirac-Frenkel time-dependent variation is employed to probe the dynamics of the zero temperature sub-Ohmic spin-boson model with strong friction utilizing the Davydov D{sub 1} ansatz. It is shown that initial conditions of the phonon bath have considerable influence on the dynamics. Counterintuitively, even in the very strong coupling regime, quantum coherence features still manage to survive under the polarized bath initial condition, while such features are absent under the factorized bath initial condition. In addition, a coherent-incoherent transition is found at a critical coupling strength {alpha} Almost-Equal-To 0.1 for s= 0.25 under the factorized bath initial condition. We quantify how faithfully our ansatz follows the Schroedinger equation, finding that the time-dependent variational approach is robust for strong dissipation and deep sub-Ohmic baths (s Much-Less-Than 1).

Wu Ning; Duan Liwei; Zhao Yang [School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Li Xin [School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Institute of High Energy Physics, Theoretical Physics Center for Science Facilities, Chinese Academy of Sciences, 100049 Beijing (China)

2013-02-28

411

Spin dynamics in oxide glass of Fe 2O 3-Bi 2O 3-B 2O 3 system

NASA Astrophysics Data System (ADS)

We have investigated magnetic aging and memory effects in the magnetically ordered phase of 32Fe 2O 3·48Bi 2O 3·20B 2O 3 (mol%) glass, which exhibits a spin glass-like transition at about 15 K ( Tsg) and a superparam