Reversible ferromagnetic spin ordering governed by hydrogen in Co-doped ZnO semiconductor
Cho, Yong Chan; Kim, Sung-Jin; Lee, Seunghun; Kim, Su Jae; Cho, Chae Ryong; Nahm, Ho-Hyun; Park, Chul Hong; Jeong, Il Kyoung; Park, Sungkyun; Hong, Tae Eun; Kuroda, Shinji; Jeong, Se-Young
2009-10-26
We report a reversible manipulation of short-range spin ordering in Co-doped ZnO through hydrogenation and dehydrogenation processes. In both magnetic-circular dichroism and superconducting quantum interference device measurements, the ferromagnetism was clearly induced and removed by the injection and ejection of hydrogen, respectively. The x-ray photoelectron spectroscopy results and the first-principles electronic structure calculations consistently support the dependence of the ferromagnetism on the hydrogen position and the contribution of transition metal ions. The results suggest the ferromagnetic interaction between Co ions can be reversibly controlled by the hydrogen-mediated intrinsic spin ordering in Co doped ZnO.
Spin-current emission governed by nonlinear spin dynamics
Tashiro, Takaharu; Matsuura, Saki; Nomura, Akiyo; Watanabe, Shun; Kang, Keehoon; Sirringhaus, Henning; Ando, Kazuya
2015-01-01
Coupling between conduction electrons and localized magnetization is responsible for a variety of phenomena in spintronic devices. This coupling enables to generate spin currents from dynamical magnetization. Due to the nonlinearity of magnetization dynamics, the spin-current emission through the dynamical spin-exchange coupling offers a route for nonlinear generation of spin currents. Here, we demonstrate spin-current emission governed by nonlinear magnetization dynamics in a metal/magnetic insulator bilayer. The spin-current emission from the magnetic insulator is probed by the inverse spin Hall effect, which demonstrates nontrivial temperature and excitation power dependences of the voltage generation. The experimental results reveal that nonlinear magnetization dynamics and enhanced spin-current emission due to magnon scatterings are triggered by decreasing temperature. This result illustrates the crucial role of the nonlinear magnon interactions in the spin-current emission driven by dynamical magnetization, or nonequilibrium magnons, from magnetic insulators. PMID:26472712
Spin and Chiral Orderings of Frustrated Quantum Spin Chains
NASA Astrophysics Data System (ADS)
Kaburagi, Makoto; Kawamura, Hikaru; Hikihara, Toshiya
1999-10-01
The ordering offrustrated S=1/2 and 1 XY and Heisenberg spin chains with the competing nearest- and next-nearest-neighbor antiferromagneticcouplings is studied by the exact diagonalization and density-matrix renormalization-group methods. It is found that theS=1 XY chain exhibits both gapless and gapped `chiral' phases characterizedby the spontaneous breaking of parity, in which thelong-range order parameter is a chirality, κi=SixSi+1y-SiySi+1x, whereas the spin correlation decays either algebraically or exponentially. Such chiral phases are not realized in the S=1/2 XY chainor in the Heisenberg chains.
Spin Dynamics in an Ordered Stripe Phase
NASA Astrophysics Data System (ADS)
Tranquada, J. M.; Wochner, P.; Buttrey, D. J.
1997-09-01
Inelastic neutron scattering has been used to measure the low-energy spin excitations in the ordered charge-stripe phase of La2NiO4+δ with δ = 0.133. Spin-wave-like excitations disperse away from the incommensurate magnetic superlattice points with a velocity ~60% of that in the δ = 0 compound. Incommensurate inelastic peaks remain well resolved up to at least twice the magnetic ordering temperature. Paramagnetic scattering from a δ = 0.105 sample, which has a Néel-ordered ground state, shows anomalies suggestive of incipient stripe correlations. Similarities between these results and measurements on superconducting cuprates are discussed.
Real Space Observation of Helical Spin Order
NASA Astrophysics Data System (ADS)
Uchida, Masaya
2007-03-01
When a symmetry gets spontaneously broken in a phase transition, topological defects are routinely formed. There are numerous examples of topological defects in condensed matter systems, such as, vortices in superconductors, vortices in superfluid helium, monopoles and strings in liquid crystals, etc. A similar picture would emerge in helimagnets. It is therefore interesting to deepen our understanding of how, what kind of, and why magnetic defects form and how they evolve after formation in helimagnets. In recent years, there have been significant advances in the experiment [1] and in the theories [2] of phases and textures in helimagnets. This will have a significant impact on our understanding of not only the puzzling behavior of the helimagnet MnSi with non-Fermi-liquid transport properties [3], but also phase transitions and phase diagrams in different condensed matter systems. In this paper, we describe the current status of our experiments. To see the helical spin order and magnetic defects in metal silicides such as (Fe, Co)Si and FeGe in real space, we used Lorentz electron microscopy, combined with the transport of intensity equation (TIE) analysis or holographic interference microscopy. This method has allowed us to find the topological defect similar to atomic dislocations in the crystal lattice. Furthermore, by applying magnetic fields, we directly observed the deformation processes of the helical spin order, accompanied by nucleation, movement, and annihilation of the magnetic defects. [1] M. Uchida et al., Science 311, 359 (2006). [2] U. K. R"oßler, A. N. Bogdanov, and C. Pfleiderer, Nature 442, 797 (2006); B. Binz, A. Vishwanath, and V. Aji, Phys. Rev. Lett., 96, 207202 (2006); S. Tewari, D. Belitz, and T. R. Kirkpatric, Phys. Rev. Lett., 96, 47207 (2006). [3] C. Pfleiderer et al., Nature 427, 227 (2004).
Helical Spin Order from Topological Dirac and Weyl Semimetals
Sun, Xiao-Qi; Zhang, Shou-Cheng; Wang, Zhong
2015-08-14
In this paper, we study dynamical mass generation and the resultant helical spin orders in topological Dirac and Weyl semimetals, including the edge states of quantum spin Hall insulators, the surface states of weak topological insulators, and the bulk materials of Weyl semimetals. In particular, the helical spin textures of Weyl semimetals manifest the spin-momentum locking of Weyl fermions in a visible manner. Finally, the spin-wave fluctuations of the helical order carry electric charge density; therefore, the spin textures can be electrically controlled in a simple and predictable manner.
Higher order spin effects in inspiralling compact objects binaries
NASA Astrophysics Data System (ADS)
Marsat, Sylvain
2015-04-01
We present recent progress on higher order spin effects in the post-Newtonian dynamics of compact objects binaries. We present first an extension of a Lagrangian formalism for point particle with spins, where finite size effects are represented by an additional multipolar structure. When applied to the case of a spin-induced octupole, the formalism allows for the computation of the cubic-in-spin effects that enter at the order 3.5PN. We also report on results obtained for quadratic-in-spin effects at the next-to-leading order 3PN. In both cases, we recover existing results for the dynamics, and derive for the first time the gravitational wave energy flux and orbital phasing. These results will be useful for the data analysis of the upcoming generation of advanced detectors of gravitational waves. NASA Grant 11-ATP-046.
A spin crossover ferrous complex with ordered magnetic ferric anions.
Roubeau, Olivier; Evangelisti, Marco; Natividad, Eva
2012-08-07
The first tetrahaloferrate spin crossover compound, [Fe(Metz)(6)](FeBr(4))(2) (Metz = 1-methyltetrazole), is reported. The FeBr(4)(-) ions form ferromagnetically coupled 1D stacks and exhibit an antiferromagnetic order at 2.2 K, which coexists with the gradual spin crossover centred at 165 K.
Universal quantum computation with ordered spin-chain networks
Tserkovnyak, Yaroslav; Loss, Daniel
2011-09-15
It is shown that anisotropic spin chains with gapped bulk excitations and magnetically ordered ground states offer a promising platform for quantum computation, which bridges the conventional single-spin-based qubit concept with recently developed topological Majorana-based proposals. We show how to realize the single-qubit Hadamard, phase, and {pi}/8 gates as well as the two-qubit controlled-not (cnot) gate, which together form a fault-tolerant universal set of quantum gates. The gates are implemented by judiciously controlling Ising exchange and magnetic fields along a network of spin chains, with each individual qubit furnished by a spin-chain segment. A subset of single-qubit operations is geometric in nature, relying on control of anisotropy of spin interactions rather than their strength. We contrast topological aspects of the anisotropic spin-chain networks to those of p-wave superconducting wires discussed in the literature.
Higher-order spin-noise spectroscopy of atomic spins in fluctuating external fields
Li, Fuxiang; Crooker, S. A.; Sinitsyn, N. A.
2016-03-09
Here, we discuss the effect of external noisy magnetic fields on mesoscopic spin fluctuations that can be probed in semiconductors and atomic vapors by means of optical spin-noise spectroscopy. We also show that conventional arguments of the law of large numbers do not apply to spin correlations induced by external fields, namely, the magnitude of the 4th-order spin cumulant grows as ~N^{2} with the number N of observed spins, i.e., it is not suppressed in comparison to the 2nd-order cumulant. Moreover, this allows us to design a simple experiment to measure the 4th-order cumulant of spin fluctuations in an atomic system near thermodynamic equilibrium and develop a quantitative theory that explains all observations.
Higher-order spin-noise spectroscopy of atomic spins in fluctuating external fields
Li, Fuxiang; Crooker, S. A.; Sinitsyn, N. A.
2016-03-09
Here, we discuss the effect of external noisy magnetic fields on mesoscopic spin fluctuations that can be probed in semiconductors and atomic vapors by means of optical spin-noise spectroscopy. We also show that conventional arguments of the law of large numbers do not apply to spin correlations induced by external fields, namely, the magnitude of the 4th-order spin cumulant grows as ~N2 with the number N of observed spins, i.e., it is not suppressed in comparison to the 2nd-order cumulant. Moreover, this allows us to design a simple experiment to measure the 4th-order cumulant of spin fluctuations in an atomicmore » system near thermodynamic equilibrium and develop a quantitative theory that explains all observations.« less
New effective-one-body Hamiltonian with next-to-leading order spin-spin coupling
NASA Astrophysics Data System (ADS)
Balmelli, Simone; Damour, Thibault
2015-12-01
We present a new effective-one-body (EOB) Hamiltonian with next-to-leading order (NLO) spin-spin coupling for black hole binaries endowed with arbitrarily oriented spins. The Hamiltonian is based on the model for parallel spins and equatorial orbits developed in [Physical Review D 90, 044018 (2014)] but differs from it in several ways. In particular, the NLO spin-spin coupling is not incorporated by a redefinition of the centrifugal radius rc but by separately modifying certain sectors of the Hamiltonian, which are identified according to their dependence on the momentum vector. The gauge-fixing procedure we follow allows us to reduce the 25 different terms of the NLO spin-spin Hamiltonian in Arnowitt-Deser-Misner coordinates to only nine EOB terms. This is an improvement with respect to the EOB model recently proposed in [Physical Review D 91, 064011 (2015)], where 12 EOB terms were involved. Another important advantage is the remarkably simple momentum structure of the spin-spin terms in the effective Hamiltonian, which is simply quadratic up to an overall square root. Moreover, a Damour-Jaranowski-Schäfer-type gauge could be established, thus allowing one to concentrate, in the case of circular and equatorial orbits, the whole spin-spin interaction in a single radial potential.
Chen, Xiang-Bai; Hien, Nguyen Thi Minh; Han, Kiok; Nam, Ji-Yeon; Huyen, Nguyen Thi; Shin, Seong-Il; Wang, Xueyun; Cheong, S W; Lee, D; Noh, T W; Sung, N H; Cho, B K; Yang, In-Sang
2015-08-24
Spin-wave (magnon) scattering, when clearly observed by Raman spectroscopy, can be simple and powerful for studying magnetic phase transitions. In this paper, we present how to observe magnon scattering clearly by Raman spectroscopy, then apply the Raman method to study spin-ordering and spin-reorientation transitions of hexagonal manganite single crystal and thin films and compare directly with the results of magnetization measurements. Our results show that by choosing strong resonance condition and appropriate polarization configuration, magnon scattering can be clearly observed, and the temperature dependence of magnon scattering can be simple and powerful quantity for investigating spin-ordering as well as spin-reorientation transitions. Especially, the Raman method would be very helpful for investigating the weak spin-reorientation transitions by selectively probing the magnons in the Mn(3+) sublattices, while leaving out the strong effects of paramagnetic moments of the rare earth ions.
Spin liquid versus long-range magnetic order in the frustrated body-centered-tetragonal lattice
NASA Astrophysics Data System (ADS)
Farias, Carlene; Thomas, Christopher; Pépin, Catherine; Ferraz, Alvaro; Lacroix, Claudine; Burdin, Sébastien
2016-10-01
We show how spin-liquid (SL) states can be stabilized in a realistic three-dimensional model as a result of frustration. SU(n ) -symmetric generalization of the Heisenberg model for quantum spin S operators is used to investigate the frustrated body-centered tetragonal (BCT) lattice with antiferromagnetic interlayer coupling J1 and intralayer first and second-neighbor couplings J2 and J3. By using complementary representations of the spin operators, we study the phase diagram characterizing the ground state of this system. For small n , we find that the most stable solutions correspond to four different families of long-range magnetic orders that are governed by J1,J2, and J3. First, some possible instabilities of these phases are identified for n =2 , in large S expansions, up to the linear spin-wave corrections. Then, using a fermionic representation of the SU(n ) spin operators for S =1 /2 , we find that purely magnetic orders occur for n ≤3 while SL solutions are stabilized for n ≥10 . The SL solution governed by J1 breaks the lattice translation symmetry. The modulated SL is associated with a commensurate ordering wave vector (1 ,1 ,1 ) . For 4 ≤n ≤9 , we show how the competition between J1,J2, and J3 can turn the magnetically ordered ground state into a SL state. Finally, we discuss the relevance of this scenario for correlated systems with BCT crystal structure.
Next-to-leading order gravitational spin1-spin2 coupling with Kaluza-Klein reduction
Levi, Michele
2010-09-15
We use the recently proposed Kaluza-Klein (KK) reduction over the time dimension, within an effective field theory (EFT) approach, to calculate the next-to-leading order gravitational spin1-spin2 interaction between two spinning compact objects. It is shown here that to next-to-leading order in the spin1-spin2 interaction, the reduced KK action within the stationary approximation is sufficient to describe the gravitational interaction, and that it simplifies calculation substantially. We also find here that the gravitomagnetic vector field defined within the KK decomposition of the metric mostly dominates the mediation of the interaction. Our results coincide with those calculated in the Arnowitt-Deser-Misner Hamiltonian formalism, and we provide another explanation for the discrepancy with the result previously derived within the EFT approach, thus demonstrating clearly the equivalence of the Arnowitt-Deser-Misner Hamiltonian formalism and the EFT action approach.
Spin-Glass Model Governs Laser Multiple Filamentation.
Ettoumi, W; Kasparian, J; Wolf, J-P
2015-07-17
We show that multiple filamentation patterns in high-power laser beams can be described by means of two statistical physics concepts, namely, self-similarity of the patterns over two nested scales and nearest-neighbor interactions of classical rotators. The resulting lattice spin model perfectly reproduces the evolution of intense laser pulses as simulated by the nonlinear Schrödinger equation, shedding new light on multiple filamentation. As a side benefit, this approach drastically reduces the computing time by 2 orders of magnitude as compared to the standard simulation methods of laser filamentation.
Robust conversion of singlet spin order in coupled spin-1/2 pairs by adiabatically ramped RF-fields.
Pravdivtsev, Andrey N; Kiryutin, Alexey S; Yurkovskaya, Alexandra V; Vieth, Hans-Martin; Ivanov, Konstantin L
2016-12-01
We propose a robust and highly efficient NMR technique to create singlet spin order from longitudinal spin magnetization in coupled spin-½ pairs and to perform backward conversion (singlet order)→magnetization. In this method we exploit adiabatic ramping of an RF-field in order to drive transitions between the singlet state and the T± triplet states of a spin pair under study. We demonstrate that the method works perfectly for both strongly and weakly coupled spin pairs, providing a conversion efficiency between the singlet spin order and magnetization, which is equal to the theoretical maximum. We anticipate that the proposed technique is useful for generating long-lived singlet order, for preserving spin hyperpolarization and for analyzing singlet spin order in nearly equivalent spin pairs in specially designed molecules and in low-field NMR studies.
Topological spin ordering via Chern-Simons superconductivity
NASA Astrophysics Data System (ADS)
Sedrakyan, Tigran A.; Galitski, Victor M.; Kamenev, Alex
2017-03-01
We use the Chern-Simons (CS) fermion representation of s =1 /2 spin operators to construct topological, long-range magnetically ordered states of interacting two-dimensional (2D) quantum spin models. We show that the fermion-fermion interactions mediated by the dynamic CS flux attachment may give rise to Cooper pairing of the fermions. Specifically, in an X Y model on the honeycomb lattice, this construction leads to a "CS superconductor", which belongs to a topologically nontrivial in 2D symmetry class DIII, with particle-hole and time-reversal symmetries. It is shown that in the original spin language, this state corresponds to a symmetry protected topological state, which coexists with a magnetic long-range order. We discuss physical manifestations of the topological character of the corresponding state.
Algebraic spin liquid as the mother of many competing orders
NASA Astrophysics Data System (ADS)
Hermele, Michael; Senthil, T.; Fisher, Matthew P. A.
2005-09-01
We study the properties of a class of two-dimensional interacting critical states—dubbed algebraic spin liquids—that can arise in two-dimensional quantum magnets. A particular example that we focus on is the staggered flux spin liquid, which plays a key role in some theories of underdoped cuprate superconductors. We show that the low-energy theory of such states has much higher symmetry than the underlying microscopic spin system. This symmetry has remarkable consequences, leading in particular to the unification of a number of seemingly unrelated competing orders. The correlations of these orders—including, in the staggered flux state, the Néel vector, and the order parameter for the columnar and box valence-bond solid states—all exhibit the same slow power-law decay. Implications for experiments in the pseudogap regime of the cuprates and for numerical calculations on model systems are discussed.
Antiferromagnetic order and spin dynamics in iron-based superconductors
NASA Astrophysics Data System (ADS)
Dai, Pengcheng
2015-07-01
High-transition temperature (high-Tc) superconductivity in the iron pnictides or chalcogenides emerges from the suppression of the static antiferromagnetic order in their parent compounds, similar to copper oxide superconductors. This raises a fundamental question concerning the role of magnetism in the superconductivity of these materials. Neutron scattering, a powerful probe to study the magnetic order and spin dynamics, plays an essential role in determining the relationship between magnetism and superconductivity in high-Tc superconductors. The rapid development of modern neutron time-of-flight spectrometers allows a direct determination of the spin dynamical properties of iron-based superconductors throughout the entire Brillouin zone. In this paper, an overview is presented of the neutron scattering results on iron-based superconductors, focusing on the evolution of spin-excitation spectra as a function of electron and hole doping and isoelectronic substitution. Spin dynamical properties of iron-based superconductors are compared with those of copper oxide and heavy fermion superconductors and the common features of spin excitations in these three families of unconventional superconductors and their relationship with superconductivity are discussed.
Field-induced ordering in dipolar spin ice
NASA Astrophysics Data System (ADS)
Kao, Wen-Han; Holdsworth, Peter C. W.; Kao, Ying-Jer
2016-05-01
We present numerical studies of dipolar spin ice in the presence of a magnetic field slightly tilted away from the [111] axis. We find a first-order transition from a kagome ice to a q =X state when the external field is tilted toward the [11 2 ¯] direction. This is consistent with the anomalous critical scattering previously observed in the neutron scattering experiment on the spin ice material Ho2Ti2O7 in a tilted field [T. Fennell et al., Nat. Phys. 3, 566 (2007), 10.1038/nphys632]. We show that this ordering originates from the antiferromagnetic alignment of spin chains on the kagome planes. The residual entropy of the kagome ice is fully recovered. Our result captures the features observed in the experiments and points to the importance of the dipolar interaction in determining ordered states in the spin ice materials. We place our results in the context of recent susceptibility measurements on Dy2Ti2O7 , showing two features for a [111] field.
Superconductivity and spin excitations in orbitally ordered FeSe
NASA Astrophysics Data System (ADS)
Kreisel, Andreas; Mukherjee, Shantanu; Hirschfeld, P. J.; Andersen, B. M.
We provide a band-structure with low-energy properties consistent with recent photoemission and quantum oscillations measurements on the Fe-based superconductor FeSe, including a mean-field like orbital ordering in the dxz /dyz channel, and show that this model also accounts for the temperature dependence of the measured Knight shift and the spin-relaxation rate. An RPA calculation of the dynamical spin susceptibility yields spin excitations which are peaked at wave vector (π , 0) in the 1-Fe Brillouin zone, with a broad maximum at energies of order a few meV. Furthermore, the superconducting gap structure obtained from spin fluctuation theory exhibits nodes on the electron pockets, consistent with the 'V'-shaped density of states measured by tunneling spectroscopy on this material. The redistribution of spectral weight in the superconducting state creates a (π , 0) ''neutron resonance'' as seen in recent experiments. Comparing to various experimental results, we give predictions for further studies A.K. and B.M.A. acknowledge financial support from a Lundbeckfond fellowship (Grant No. A9318). P.J.H. was partially supported by the Department of Energy under Grant No. DE-FG02-05ER46236.
Plaquette order in a dimerized frustrated spin ladder
NASA Astrophysics Data System (ADS)
Shlagman, Ofer; Shimshoni, Efrat
2014-11-01
We study the effect of dimerization (due to, e.g., spin-Peierls instability) on the phase diagram of a frustrated antiferromagnetic spin-1/2 ladder, with weak transverse and diagonal rung coupling. Our analysis focuses on a one-dimensional version of the model (i.e., a single two-leg ladder) where we consider two forms of dimerization on the legs: columnar dimers (CDs) and staggered dimers (SDs). We examine in particular the regime of parameters (corresponding to an intermediate X X Z anisotropy) in which the leg dimerization and the rung coupling terms are equally relevant. In both the CD and SD cases, we find that the effective field theory describing the system is a self-dual sine-Gordon model, which favors ordering and the opening of a gap to excitations. The order parameter, which reflects the interplay between the leg and rung dimerization interactions, represents a crystal of 4-spin plaquettes on which longitudinal and transverse dimers are in a coherent superposition. Depending on the leg dimerization mode, these plaquettes are closed or open, however both types spontaneously break reflection symmetry across the ladder. The closed plaquettes are stable, while the open plaquette order is relatively fragile and the corresponding gap may be tuned to zero under extreme conditions. We further find that a first-order transition occurs from the plaquette order to a valence bond crystal (VBC) of dimers on the legs. This suggests that in a higher-dimensional version of this system, this variety of distinct VBC states with comparable energies leads to the formation of domains. Effectively one-dimensional gapless spinon modes on domain boundaries may account for the experimental observation of spin-liquid behavior in a physical realization of the model.
Magnetic order the iron spins in NdOFeAs
NASA Astrophysics Data System (ADS)
Chen, Ying; Lynn, J. W.; Li, J.; Li, G.; Chen, G. F.; Luo, J. L.; Wang, N. L.; Dai, Pengcheng; Dela Cruz, C.; Mook, H. A.
2009-03-01
Polarized and unpolarized powder neutron-diffraction measurements have been carried out to investigate the iron magnetic order in the parent compound of one of the highest Tc system, NdFeAsO. Antiferromagnetic order is observed below 141 K [1], which is in close proximity to the structural distortion observed in this material [2]. The magnetic structure consists of chains of parallel spins that are arranged antiparallel between chains, which is the same in-plane spin arrangement as observed in all the other iron oxypnictide materials. Nearest-neighbor spins along the c axis are antiparallel like LaFeAsO [3]. The ordered moment is 0.25 (7) μB, which is the smallest ordered moment found so far in these systems. [3pt] [1]Ying Chen, J. W. Lynn, J. Li, G. Li, G. F. Chen, J. L. Luo, N. L. Wang, Pengcheng Dai, C. dela Cruz and H. A. Mook, Phys. Rev. B 78, 064515 2008. [0pt] [2]Y. Qiu, W. Bao, Q. Huang, T. Yildirim, J. M. Simmons, M. A. Green, J.W. Lynn, Y.C. Gasparovic, J. Li, T. Wu, G. Wu, and X.H. Chen, arXiv:0806.2195 (Phys. Rev. Lett. accepted). [0pt] [3] C. dela Cruz, Q. Huang, J. W. Lynn, J. Li, W. Ratcliff II, J. L. Zarestky, H. A. Mook, G. F. Chen, J. L. Luo, N. L. Wang, and P. Dai, Nature 453, 899 (2008).
Phase ordering dynamics in spin-1 ferromagnetic condensates
NASA Astrophysics Data System (ADS)
Williamson, Lewis; Blakie, Peter
2016-05-01
Spinor Bose-Einstein condensates present rich phase diagrams for exploring phase transitions between states with different symmetry properties. In this work we simulate the approach to equilibrium of a spin-1 condensate quenched from an unmagnetised phase to three different ferromagnetic phases. The three ferromagnetic phases have Z2, SO(2) and SO(3) symmetries respectively and possess different conservation laws. Following the quench, domains of magnetization form, with each domain making an independent choice of the symmetry breaking order parameter. These domains grow and compete for the global equilibrium state. We find that this growth follows universal scaling laws and identify the dynamic universality class for each of the three quenches. Polar-core spin-vortices play a crucial role in the phase ordering of the SO(2) system and we identify fractal structures in the domain patterns of the SO(2) and SO(3) systems. We acknowledge support from the Marsden Fund of New Zealand.
Quantum dot spin coherence governed by a strained nuclear environment
NASA Astrophysics Data System (ADS)
Stockill, R.; Le Gall, C.; Matthiesen, C.; Huthmacher, L.; Clarke, E.; Hugues, M.; Atatüre, M.
2016-09-01
The interaction between a confined electron and the nuclei of an optically active quantum dot provides a uniquely rich manifestation of the central spin problem. Coherent qubit control combines with an ultrafast spin-photon interface to make these confined spins attractive candidates for quantum optical networks. Reaching the full potential of spin coherence has been hindered by the lack of knowledge of the key irreversible environment dynamics. Through all-optical Hahn echo decoupling we now recover the intrinsic coherence time set by the interaction with the inhomogeneously strained nuclear bath. The high-frequency nuclear dynamics are directly imprinted on the electron spin coherence, resulting in a dramatic jump of coherence times from few tens of nanoseconds to the microsecond regime between 2 and 3 T magnetic field and an exponential decay of coherence at high fields. These results reveal spin coherence can be improved by applying large magnetic fields and reducing strain inhomogeneity.
Quantum dot spin coherence governed by a strained nuclear environment
Stockill, R.; Le Gall, C.; Matthiesen, C.; Huthmacher, L.; Clarke, E.; Hugues, M.; Atatüre, M.
2016-01-01
The interaction between a confined electron and the nuclei of an optically active quantum dot provides a uniquely rich manifestation of the central spin problem. Coherent qubit control combines with an ultrafast spin–photon interface to make these confined spins attractive candidates for quantum optical networks. Reaching the full potential of spin coherence has been hindered by the lack of knowledge of the key irreversible environment dynamics. Through all-optical Hahn echo decoupling we now recover the intrinsic coherence time set by the interaction with the inhomogeneously strained nuclear bath. The high-frequency nuclear dynamics are directly imprinted on the electron spin coherence, resulting in a dramatic jump of coherence times from few tens of nanoseconds to the microsecond regime between 2 and 3 T magnetic field and an exponential decay of coherence at high fields. These results reveal spin coherence can be improved by applying large magnetic fields and reducing strain inhomogeneity. PMID:27615704
Chain-based order and quantum spin liquids in dipolar spin ice
NASA Astrophysics Data System (ADS)
McClarty, P. A.; Sikora, O.; Moessner, R.; Penc, K.; Pollmann, F.; Shannon, N.
2015-09-01
Recent experiments on the spin-ice material Dy2Ti2O7 suggest that the Pauling "ice entropy," characteristic of its classical Coulombic spin-liquid state, may be lost at low temperatures [Pomaranski et al., Nat. Phys. 9, 353 (2013), 10.1038/nphys2591]. However, despite nearly two decades of intensive study, the nature of the equilibrium ground state of spin ice remains uncertain. Here we explore how long-range dipolar interactions D , short-range exchange interactions, and quantum fluctuations combine to determine the ground state of dipolar spin ice. We identify the organizational principle that ordered ground states are selected from a set of "chain states" in which dipolar interactions are exponentially screened. Using both quantum and classical Monte Carlo simulation, we establish phase diagrams as a function of quantum tunneling g and temperature T , and find that only a very small gc≪D is needed to stabilize a quantum spin liquid ground state. We discuss the implications of these results for Dy2Ti2O7 .
Nematic spin order and spin-lattice coupling in Fe-based Superconductors
NASA Astrophysics Data System (ADS)
Hu, Jiangping; Fang, Chen; Tsai, Wei-Feng; Yao, Hong; Kivelson, Steve
2009-03-01
We show that the structure transitions observed in Fe-based superconductors are magnetically driven. A quantum Heisenberg model (J1-J2-Jz) exhibits a sequence of two phase transitions: from a high temperature symmetric phase to a narrow region of intermediate ``nematic'' phase, and then to a low temperature spin ordered phase when Jz is small. Identifying phases by their broken symmetries, these phases correspond precisely to the sequence of structural (tetragonal to monoclinic) and magnetic transitions that have been recently revealed in neutron scattering studies of 1111 series of Fe- based superconductors. The structural transition can thus be identified with the existence of incipient (``fluctuating'') magnetic order. We also discuss the effect of spin-lattice coupling on the phase diagram of the model. [3pt] Reference: Chen Fang, Hong Yao, Wei-Feng Tsai, JiangPing Hu and Steven A. Kivelson, Phys. Rev. B 77 224509 (2008).
Spin excitations of ferronematic order in underdoped cuprate superconductors
Seibold, G.; Di Castro, C.; Grilli, M.; Lorenzana, J.
2014-01-01
High-temperature superconductors exhibit a characteristic hourglass-shaped spectrum of magnetic fluctuations which most likely contribute to the pairing glue in the cuprates. Recent neutron scattering experiments in strongly underdoped compounds have revealed a significant low energy anisotropy of these fluctuations which we explain by a model in which topological defects of the antiferromagnet clump to producing domain wall segments with ferronematic order. This state does not invoke global charge order but breaks C4 rotational and inversion symmetry. The incommensurability of the low doping charge-disordered state is in good agreement with experiment and interpolates smoothly with the incommensurability of the stripe phase at higher doping. Within linear spin-wave theory the dynamic structure factor is in very good agreement with inelastic neutron scattering data and can account for the observed energy dependent anisotropy. PMID:24936723
Equilibrium pricing in an order book environment: Case study for a spin model
NASA Astrophysics Data System (ADS)
Meudt, Frederik; Schmitt, Thilo A.; Schäfer, Rudi; Guhr, Thomas
2016-07-01
When modeling stock market dynamics, the price formation is often based on an equilibrium mechanism. In real stock exchanges, however, the price formation is governed by the order book. It is thus interesting to check if the resulting stylized facts of a model with equilibrium pricing change, remain the same or, more generally, are compatible with the order book environment. We tackle this issue in the framework of a case study by embedding the Bornholdt-Kaizoji-Fujiwara spin model into the order book dynamics. To this end, we use a recently developed agent based model that realistically incorporates the order book. We find realistic stylized facts. We conclude for the studied case that equilibrium pricing is not needed and that the corresponding assumption of a "fundamental" price may be abandoned.
Vector-spin-chirality order in a dimerized frustrated spin-1/2 chain
NASA Astrophysics Data System (ADS)
Ueda, Hiroshi; Onoda, Shigeki
2014-01-01
A frustrated spin-1/2 XXZ chain model comprising a ferromagnetic nearest-neighbor coupling with the bond alternation, J1(1±δ)<0, and an antiferromagnetic second-neighbor exchange coupling J2>0 is studied at zero and weak magnetic fields by means of density-matrix renormalization-group calculations of order parameters, correlation functions, and the entanglement entropy, as well as an Abelian bosonization analysis. At zero magnetic field, the bond alternation δ >0 suppresses the gapless phase characterized by a vector-chiral (VC) long-range order (LRO) and a quasi-LRO of an incommensurate spin spiral, whereas this phase occupies a large region in the space of J1/J2 and the easy-plane exchange anisotropy for δ =0 [S. Furukawa et al., Phys. Rev. Lett. 105, 257205 (2010), 10.1103/PhysRevLett.105.257205]. Then, four gapped phases are found to appear as the exchange anisotropy varies from the SU(2)-symmetric case to the U(1)-symmetric case: the Haldane dimer (D+) phase with the same sign of the x ,y- and z-component dimer order parameters, two VC dimer (VCD+/VCD-) phases with the sign of the z-component dimer order parameter being unaltered/reversed, and the even-parity dimer (D-) phase. At small magnetic fields, a field-induced ring-exchange interaction, which is proportional to a staggered scalar chirality and a magnetic flux penetrating the associated triangle, drives a transition from the D- phase into a VC-Neel-dimer (VCND) phase, but not from the D+ phase. This VCND phase is stable up to the large magnetic field at which the Zeeman term closes the spin gap. A possible relevance to Rb2Cu2Mo3O12 is discussed.
Spin and orbital order separation in colossal magnetoresistive transition
NASA Astrophysics Data System (ADS)
Hossain, M. A.; Burkhardt, M. H.; Weschke, E.; Schierle, E.; Golden, M. S.; Tomioka, Y.; Tokura, Y.; StöHr, J.; D&üRr, H. A.
2013-03-01
Understanding the Colossal magnetoresistive (CMR) process in manganites is one of the grand challenges of modern physics. While the metallic ferromagnetic phase is relatively well understood, the triggering mechanism of the metal-insulator transition is not clear and it is believed that lattice strain in term of polarons play an important role in the mysterious insulating phase. Lattice strain occurs in the charge-orbitally ordered insulating phase via the Jahn-Teller type distortion and therefore, to understand the CMR it is critical to understand the interplay of ferromagnetism and orbital order during the CMR transition itself. In this letter, with high magnetic field dependent Resonant Soft X-ray Scattering measurements, we show that during the CMR process, an insulating antiferromagnetic phase, which is extremely susceptible to magnetic field and temperature, directly competes with metallic ferromagnetism while the robust CE type spin and orbitally ordered regions act as a catalyst to seed these antiferromagnetic regions. This allows us to construct a picture of the competing forces at the heart of CMR.
Spin-polarized photoelectron diffraction from magnetically-ordered solids and surfaces
NASA Astrophysics Data System (ADS)
Sinković, B.; Hermsmeier, B.; Fadley, C. S.
1986-02-01
We report the first experimental observation of Spin-Polarized Photoelectron Diffraction (SPPD), an effect which shows considerable promise for studying short-range order in magnetic solids and surfaces. The detection of photoelectron spin polarization in this experiment is provided by 3s-level multiplet splittings in 3d metals and their compounds; thus no external spin detector is required. Measurements on antiferromagnetic KMnF 3 show spin asymmetries of as high as 17% due to short-range order.
Double Charge Ordering States and Spin Ordering State Observed in a RFe2O4 System
Sun, Fei; Wang, Rui; Aku-Leh, C.; Yang, H. X.; He, Rui; Zhao, Jimin
2014-01-01
Charge, spin, and lattice degrees of orderings are of great interest in the layered quantum material RFe2O4 (R = Y, Er, Yb, Tm, and Lu) system. Recently many unique properties have been found using various experimental methods. However so far the nature of the two-dimensional (2D) charge ordering (CO) state is not clear and no observation of its fine structure in energy has been reported. Here we report unambiguous observation of double 2D CO states at relatively high temperature in a polycrystalline Er0.1Yb0.9Fe2O4 using Raman scattering. The energy gaps between the 3D and the double 2D states are 170 meV (41.2 THz) and 193 meV (46.6 THz), respectively. We also observed a spin ordering (SO) state at below 210 K with characteristic energy of 45 meV (10.7 THz). Our investigation experimentally identified new fine structures of quantum orders in the system, which also extends the capability of optical methods in investigating other layered quantum materials. PMID:25234133
Interaction induced staggered spin-orbit order in two-dimensional electron gas
Das, Tanmoy
2012-06-05
Decoupling spin and charge transports in solids is among the many prerequisites for realizing spin electronics, spin caloritronics, and spin-Hall effect. Beyond the conventional method of generating and manipulating spin current via magnetic knob, recent advances have expanded the possibility to optical and electrical method which are controllable both internally and externally. Yet, due to the inevitable presence of charge excitations and electrical polarizibility in these methods, the separation between spin and charge degrees of freedom of electrons remains a challenge. Here we propose and formulate an interaction induced staggered spin-orbit order as a new emergent phase of matter. We show that when some form of inherent spin-splitting via Rashba-type spin-orbit coupling renders two helical Fermi surfaces to become significantly nested, a Fermi surface instability arises. To lift this degeneracy, a spontaneous symmetry breaking spin-orbit density wave develops, causing a surprisingly large quasiparticle gapping with chiral electronic states, with no active charge excitations. Since the staggered spin-orbit order is associated with a condensation energy, quantified by the gap value, destroying such spin-orbit interaction costs sufficiently large perturbation field or temperature or de-phasing time. BiAg2 surface state is shown to be a representative system for realizing such novel spin-orbit interaction with tunable and large strength, and the spin-splitting is decoupled from charge excitations.
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2010-12-06
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Kim, Sang-Il; Seo, Min-Su; Park, Seung-Young; Kim, Dong-Jun; Park, Byong-Guk
2015-05-07
The dependence of the measured DC voltage on the non-magnetic material (NM) in NM/CoFeB and CoFeB/NM bilayers is studied under ferromagnetic resonance conditions in a TE{sub 011} resonant cavity. The directional change of the inverse spin Hall effect (ISHE) voltage V{sub ISHE} for the stacking order of the bilayer can separate the pure V{sub ISHE} and the anomalous Hall effect (AHE) voltage V{sub AHE} utilizing the method of addition and subtraction. The Ta and Ti NMs show a broad deviation of the spin Hall angle θ{sub ISH}, which originates from the AHE in accordance with the high resistivity of NMs. However, the Pt and Pd NMs show that the kinds of NMs with low resistivity are consistent with the previously reported θ{sub ISH} values. Therefore, the characteristics that NM should simultaneously satisfy to obtain a reasonable V{sub ISHE} value in bilayer systems are large θ{sub ISH} and low resistivity.
Dzyaloshinskii-Moriya Interaction and Spiral Order in Spin-orbit Coupled Optical Lattices
Gong, Ming; Qian, Yinyin; Yan, Mi; Scarola, V. W.; Zhang, Chuanwei
2015-01-01
We show that the recent experimental realization of spin-orbit coupling in ultracold atomic gases can be used to study different types of spin spiral order and resulting multiferroic effects. Spin-orbit coupling in optical lattices can give rise to the Dzyaloshinskii-Moriya (DM) spin interaction which is essential for spin spiral order. By taking into account spin-orbit coupling and an external Zeeman field, we derive an effective spin model in the Mott insulator regime at half filling and demonstrate that the DM interaction in optical lattices can be made extremely strong with realistic experimental parameters. The rich finite temperature phase diagrams of the effective spin models for fermions and bosons are obtained via classical Monte Carlo simulations. PMID:26014458
Critical competition between two distinct orbital-spin ordered states in perovskite vanadates
NASA Astrophysics Data System (ADS)
Fujioka, J.; Yasue, T.; Miyasaka, S.; Yamasaki, Y.; Arima, T.; Sagayama, H.; Inami, T.; Ishii, K.; Tokura, Y.
2010-10-01
We have investigated the spin/orbital phase diagram in the perovskite orthovanadate RVO3 ( R=Eu , Y, Dy, and Ho) by measurements of magnetization, dielectric constant, specific heat, Raman scattering spectra, and x-ray diffraction, focusing on the interplay between the V3d spin and the 4f moment of the R ion. The thermally induced phase transition between the C-type spin/G-type orbital ordered state and the G-type spin/C-type orbital ordered state is observed for Eu1-xYxVO3 (x=0-0.52) without 4f moment. By comparing this phase diagram with the spin/orbital ordering in TbVO3 , it is evident that the critical competition between the C-type spin/G-type orbital ordered phase and the G-type spin/C-type orbital ordered one depends not only on the GdFeO3 -type lattice distortion but also on the presence of the 4f moment of the R ion. The magnetic field induced phase transition of the spin/orbital ordering is achieved concomitantly with polarizing R4f moments for DyVO3 and HoVO3 . For DyVO3 , the G-type spin/C-type orbital ordered phase is switched to the C-type spin/G-type orbital ordered one by applying a moderate magnetic field around 3 T. By contrast, the G-type spin/C-type orbital ordering is rather favored under the magnetic field in HoVO3 . The results cannot be uniquely explained in terms of the exchange interaction between the V3d spin and the R -ion 4f moment. The coupling of the R4f moment polarization with the lattice distortion tied with the orbital ordering of the V3d sublattice may also be relevant to this field induced phase transition.
Ordering of the three-dimensional Heisenberg spin glass in magnetic fields.
Kawamura, H; Imagawa, D
2001-11-12
Spin and chirality orderings of the three-dimensional Heisenberg spin glass are studied under magnetic fields in light of the recently developed spin-chirality decoupling-recoupling scenario. It is found by Monte Carlo simulations that the chiral-glass transition and the chiral-glass ordered state, which are essentially of the same character as their zero-field counterparts, occur under magnetic fields. The implication to the experimental phase diagram is discussed.
Damped spin waves in the intermediate ordered phases in Ni3V2O8
Ehlers, Georg; Podlesnyak, Andrey A.; Frontzek, Matthias D.; ...
2015-06-09
Here, spin dynamics in the intermediate ordered phases (between 4 and 9 K) in Ni3V2O8 have been studied with inelastic neutron scattering. It is found that the spin waves are very diffuse, indicative of short lived correlations and the coexistence of paramagnetic moments with the long-range ordered state.
A method for solving exact-controllability problems governed by closed quantum spin systems
NASA Astrophysics Data System (ADS)
Ciaramella, G.; Salomon, J.; Borzì, A.
2015-04-01
The Liouville-von Neumann master equation models closed quantum spin systems that arise in nuclear magnetic resonance applications. In this paper, an efficient and robust computational framework to solve exact-controllability problems governed by the Liouville-von Neumann master equation is presented. The proposed control framework is based on a new optimisation formulation of exact-controllability quantum spin problems that allows the application of efficient computational techniques. This formulation results in an optimality system with four differential equations and an optimality condition. The differential equations are approximated with an appropriate modified Crank-Nicholson scheme and the resulting discretised optimality system is solved with a matrix-free Krylov-Newton scheme combined with a cascadic nonlinear conjugate gradient initialisation. Results of numerical experiments demonstrate the ability of the proposed framework to solve quantum spin exact-controllability control problems.
Zhai Hui; Zhou Fei
2005-07-01
We investigate the Zeeman-field-driven quantum phase transitions between singlet spin liquids and algebraically ordered O(2) nematic spin liquids of spin-one bosons in one-dimensional optical lattices. We find that the critical behavior is characterized by condensation of hardcore bosons instead of ideal magnons in high-dimensional lattices. Critical exponents are strongly renormalized by hardcore interactions and critical states are equivalent to the free Fermion model up to the Friedel oscillations. We also find that the algebraically ordered nematic spin liquids close to critical points are fully characterized by the Luttinger-liquid dynamics with Luttinger-liquid parameters magnetically tunable. The Bethe ansatz solution has been applied to determine the critical magnetization and nematic correlations.
Spatial confinement governs orientational order in patchy particles
Iwashita, Yasutaka; Kimura, Yasuyuki
2016-01-01
Orientational order in condensed matter plays a key role in determining material properties such as ferromagnetism, viscoelasticity or birefringence. We studied purely orientational ordering in closely-packed one-patch colloidal particles confined between flat substrates, where the particles can only rotate and are ordered via the sticky interaction between the patches. For the first time, we experimentally realized a rich variety of mesoscopic patterns through orientational ordering of colloids by controlling patch size and confinement thickness. The combination of experiment and numerical simulation reveals the decisive role of confinement: An ordered state(s) is selected from the (meta)stable options in bulk when it is commensurate with the system geometry and boundary conditions; otherwise, frustration induces a unique order. Our study offers a new means of systematic control over mesoscopic structures via orientational ordering in patchy particles. The system would also possess unique functionalities through the rotational response of the particles to external stimuli. PMID:27264521
Liu, Tao; Li, Wei; Su, Gang
2016-09-01
Three different tensor network (TN) optimization algorithms are employed to accurately determine the ground state and thermodynamic properties of the spin-3/2 kagome Heisenberg antiferromagnet. We found that the sqrt[3]×sqrt[3] state (i.e., the state with 120^{∘} spin configuration within a unit cell containing 9 sites) is the ground state of this system, and such an ordered state is melted at any finite temperature, thereby clarifying the existing experimental controversies. Three magnetization plateaus (m/m_{s}=1/3,23/27, and 25/27) were obtained, where the 1/3-magnetization plateau has been observed experimentally. The absence of a zero-magnetization plateau indicates a gapless spin excitation that is further supported by the thermodynamic asymptotic behaviors of the susceptibility and specific heat. At low temperatures, the specific heat is shown to exhibit a T^{2} behavior, and the susceptibility approaches a finite constant as T→0. Our TN results of thermodynamic properties are compared with those from high-temperature series expansion. In addition, we disclose a quantum phase transition between q=0 state (i.e., the state with 120^{∘} spin configuration within a unit cell containing three sites) and sqrt[3]×sqrt[3] state in a spin-3/2 kagome XXZ model at the critical point Δ_{c}=0.54. This study provides reliable and useful information for further explorations on high-spin kagome physics.
NASA Astrophysics Data System (ADS)
Liu, Tao; Li, Wei; Su, Gang
2016-09-01
Three different tensor network (TN) optimization algorithms are employed to accurately determine the ground state and thermodynamic properties of the spin-3/2 kagome Heisenberg antiferromagnet. We found that the √{3 }×√{3 } state (i.e., the state with 120° spin configuration within a unit cell containing 9 sites) is the ground state of this system, and such an ordered state is melted at any finite temperature, thereby clarifying the existing experimental controversies. Three magnetization plateaus (m /ms=1 /3 ,23 /27 , and 25/27) were obtained, where the 1/3-magnetization plateau has been observed experimentally. The absence of a zero-magnetization plateau indicates a gapless spin excitation that is further supported by the thermodynamic asymptotic behaviors of the susceptibility and specific heat. At low temperatures, the specific heat is shown to exhibit a T2 behavior, and the susceptibility approaches a finite constant as T →0 . Our TN results of thermodynamic properties are compared with those from high-temperature series expansion. In addition, we disclose a quantum phase transition between q =0 state (i.e., the state with 120° spin configuration within a unit cell containing three sites) and √{3 }×√{3 } state in a spin-3/2 kagome XXZ model at the critical point Δc=0.54 . This study provides reliable and useful information for further explorations on high-spin kagome physics.
Orbital driven impurity spin effect on the magnetic order of quasi-3D cupric oxide
NASA Astrophysics Data System (ADS)
Ganga, B. G.; Santhosh, P. N.; Nanda, B. R. K.
2017-04-01
Density functional calculations are performed to study the magnetic order of the severely distorted square planar cupric oxide (CuO) and local spin disorder in it in the presence of the transition metal impurities M (=Cr, Mn, Fe, Co and Ni). The distortion in the crystal structure, arisen to reduce the band energy by minimizing the covalent interaction, creates two crisscrossing zigzag spin-1/2 chains. From the spin dimer analysis we find that while the spin chain along ≤ft[1 0 \\bar{1}\\right] has strong Heisenberg type antiferromagnetic coupling (J ~ 127 meV), along ≤ft[1 0 1\\right] it exhibits weak, but robust, ferromagnetic coupling (J ~ 9 meV) mediated by reminiscent p-d covalent interactions. The impurity effect on the magnetic ordering is independent of M and purely orbital driven. If the given spin-state of M is such that the {{d}{{x2}-{{y}2}}} orbital is spin-polarized, then the original long-range ordering is maintained. However, if {{d}{{x2}-{{y}2}}} orbital is unoccupied, the absence of corresponding covalent interaction breaks the weak ferromagnetic coupling and a spin-flip takes place at the impurity site leading to breakdown of the long range magnetic ordering.
Orbital driven impurity spin effect on the magnetic order of quasi-3D cupric oxide.
Ganga, B G; Santhosh, P N; Nanda, B R K
2017-04-20
Density functional calculations are performed to study the magnetic order of the severely distorted square planar cupric oxide (CuO) and local spin disorder in it in the presence of the transition metal impurities M (=Cr, Mn, Fe, Co and Ni). The distortion in the crystal structure, arisen to reduce the band energy by minimizing the covalent interaction, creates two crisscrossing zigzag spin-1/2 chains. From the spin dimer analysis we find that while the spin chain along [Formula: see text] has strong Heisenberg type antiferromagnetic coupling (J ~ 127 meV), along [Formula: see text] it exhibits weak, but robust, ferromagnetic coupling (J ~ 9 meV) mediated by reminiscent p-d covalent interactions. The impurity effect on the magnetic ordering is independent of M and purely orbital driven. If the given spin-state of M is such that the [Formula: see text] orbital is spin-polarized, then the original long-range ordering is maintained. However, if [Formula: see text] orbital is unoccupied, the absence of corresponding covalent interaction breaks the weak ferromagnetic coupling and a spin-flip takes place at the impurity site leading to breakdown of the long range magnetic ordering.
Spain: government orders distribution of clean needles in prisons.
2002-03-01
In a previous issue of the Review we published an article about the positive results of the evaluation of the first needle exchange programs in Spanish prisons. Recently it was reported that Spain's Ministry of the Interior has ordered that sterile needles be distributed in prisons.
Two-body gravitational spin-orbit interaction at linear order in the mass ratio
NASA Astrophysics Data System (ADS)
Bini, Donato; Damour, Thibault
2014-07-01
We analytically compute, to linear order in the mass ratio, the "geodetic" spin-precession frequency of a small spinning body orbiting a large (nonspinning) body to the eight-and-a-half post-Newtonian order, thereby extending previous analytical knowledge which was limited to the third post-Newtonian level. These results are obtained applying analytical gravitational self-force theory to the first-derivative level generalization of Detweiler's gauge-invariant redshift variable. We compare our analytic results with strong-field numerical data recently obtained by Dolan et al. [Phys. Rev. D 89, 064011 (2014)]. Our new, high-post-Newtonian-order results capture the strong-field features exhibited by the numerical data. We argue that the spin precession will diverge as ≈-0.14/(1-3y) as the light ring is approached. We transcribe our kinematical spin-precession results into a corresponding improved analytic knowledge of one of the two (gauge-invariant) effective gyrogravitomagnetic ratios characterizing spin-orbit couplings within the effective-one-body formalism. We provide simple, accurate analytic fits both for spin precession and the effective gyrogravitomagnetic ratio. The latter fit predicts that the linear-in-mass-ratio correction to the gyrogravitomagnetic ratio changes sign before reaching the light ring. This strong-field prediction might be important for improving the analytic modeling of coalescing spinning binaries.
Initiation of Orderly Spinning Detonation Waves via Phased Sparking
NASA Astrophysics Data System (ADS)
Boening, Jacob A.
A Continuous Rotating Detonation Engine (CRDE) was tested with two unique features. First, the conventional pre-detonator was replaced by a novel detonation wave generator. This generator sequentially fired spark plugs at a speed near the acoustic speed of a reactant gas mixture thereby producing free radicals ready to partake in detonation. The generator produced high speed detonation waves traveling with homogenous direction in gaseous mixtures of H2 and O2. Detonation waves continued to spin in a self-sustained fashion after turning off the wave generator. The number of simultaneous sparks did not influence the number of detonation waves observed. Instead the number of observed detonation waves was a strong function of the mass flow rate of reactants. Second, the fuel and oxidizer were injected radially. To avoid the thrust-area loss of conventional axial injection, all injection holes were oriented along the annulus radially, thereby allowing the high pressure to work over the entire front end area. Furthermore, radial injection modulated the mixing of fuel and oxidizer to adjust the axial location of detonation zones avoiding damage to the wave generator.
Different growth rates for spin and superfluid order in a quenched spinor condensate
NASA Astrophysics Data System (ADS)
Bourges, Andréane; Blakie, P. B.
2017-02-01
In this paper we study the coarsening dynamics of a spinor condensate quenched into an easy-axis ferromagnetic phase by a sudden change in the quadratic Zeeman energy. We show that applying a spin rotation prior to changing the Zeeman energy accelerates the development of local order and reduces heating. We examine the longitudinal spin ordering and the superfluid ordering of the system and show that the respective order parameter correlation functions exhibit dynamic scaling in the late-time dynamics. Our results also demonstrate that these two types of order grow at different rates, i.e., with different dynamic critical exponents. The spin domain area distribution is calculated and is shown to have power-law scaling behavior expected from percolation theory.
String order and symmetries in quantum spin lattices.
Pérez-García, D; Wolf, M M; Sanz, M; Verstraete, F; Cirac, J I
2008-04-25
We show that the existence of string order in a given quantum state is intimately related to the presence of a local symmetry by proving that both concepts are equivalent within the framework of finitely correlated states. Once this connection is established, we provide a complete characterization of local symmetries in these states. The results allow us to understand in a straightforward way many of the properties of string order parameters, like their robustness or fragility under perturbations and their typical disappearance beyond strictly one-dimensional lattices. We propose and discuss an alternative definition, ideally suited for detecting phase transitions, and generalizations to two and more spatial dimensions.
Matis, Bernard R; Houston, Brian H; Baldwin, Jeffrey W
2016-04-26
We provide evidence that magnetic moments formed when hydrogen atoms are covalently bound to graphene exhibit spin glass ordering. We observe logarithmic time-dependent relaxations in the remnant magnetoresistance following magnetic field sweeps, as well as strong variances in the remnant magnetoresistance following field-cooled and zero-field-cooled scenarios, which are hallmarks of canonical spin glasses and provide experimental evidence for the hydrogenated graphene spin glass state. Following magnetic field sweeps, and over a relaxation period of several minutes, we measure changes in the resistivity that are more than 3 orders of magnitude larger than what has previously been reported for a two-dimensional spin glass. Magnetotransport measurements at the Dirac point, and as a function of hydrogen concentration, demonstrate that the spin glass state is observable as the zero-field resistivity reaches a value close to the quantum unit h/2e(2), corresponding to the point at which the system undergoes a transition from weak to strong localization. Our work sheds light on the critical magnetic-dopant density required to observe spin glass formation in two-dimensional systems. These findings have implications to the basic understanding of spin glasses as well the fields of two-dimensional magnetic materials and spintronics.
Next-to-leading order gravitational spin-orbit coupling in an effective field theory approach
Levi, Michele
2010-11-15
We use an effective field theory (EFT) approach to calculate the next-to-leading order (NLO) gravitational spin-orbit interaction between two spinning compact objects. The NLO spin-orbit interaction provides the most computationally complex sector of the NLO spin effects, previously derived within the EFT approach. In particular, it requires the inclusion of nonstationary cubic self-gravitational interaction, as well as the implementation of a spin supplementary condition (SSC) at higher orders. The EFT calculation is carried out in terms of the nonrelativistic gravitational field parametrization, making the calculation more efficient with no need to rely on automated computations, and illustrating the coupling hierarchy of the different gravitational field components to the spin and mass sources. Finally, we show explicitly how to relate the EFT derived spin results to the canonical results obtained with the Arnowitt-Deser-Misner (ADM) Hamiltonian formalism. This is done using noncanonical transformations, required due to the implementation of covariant SSC, as well as canonical transformations at the level of the Hamiltonian, with no need to resort to the equations of motion or the Dirac brackets.
Electron spin polarization by isospin ordering in correlated two-layer quantum Hall systems.
Tiemann, L; Wegscheider, W; Hauser, M
2015-05-01
Enhancement of the electron spin polarization in a correlated two-layer, two-dimensional electron system at a total Landau level filling factor of 1 is reported. Using resistively detected nuclear magnetic resonance, we demonstrate that the electron spin polarization of two closely spaced two-dimensional electron systems becomes maximized when interlayer Coulomb correlations establish spontaneous isospin ferromagnetic order. This correlation-driven polarization dominates over the spin polarizations of competing single-layer fractional quantum Hall states under electron density imbalances.
Spin-Lattice-Coupled Order in Heisenberg Antiferromagnets on the Pyrochlore Lattice.
Aoyama, Kazushi; Kawamura, Hikaru
2016-06-24
Effects of local lattice distortions on the spin ordering are investigated for the antiferromagnetic classical Heisenberg model on the pyrochlore lattice. It is found by Monte Carlo simulations that the spin-lattice coupling (SLC) originating from site phonons induces a first-order transition into two different types of collinear magnetic ordered states. The state realized at the stronger SLC is cubic symmetric characterized by the magnetic (1/2,1/2,1/2) Bragg peaks, while that at the weaker SLC is tetragonal symmetric characterized by the (1,1,0) ones, each accompanied by the commensurate local lattice distortions. Experimental implications to chromium spinels are discussed.
Spin-Lattice-Coupled Order in Heisenberg Antiferromagnets on the Pyrochlore Lattice
NASA Astrophysics Data System (ADS)
Aoyama, Kazushi; Kawamura, Hikaru
2016-06-01
Effects of local lattice distortions on the spin ordering are investigated for the antiferromagnetic classical Heisenberg model on the pyrochlore lattice. It is found by Monte Carlo simulations that the spin-lattice coupling (SLC) originating from site phonons induces a first-order transition into two different types of collinear magnetic ordered states. The state realized at the stronger SLC is cubic symmetric characterized by the magnetic (1/2 ,1/2 ,1/2 ) Bragg peaks, while that at the weaker SLC is tetragonal symmetric characterized by the (1,1,0) ones, each accompanied by the commensurate local lattice distortions. Experimental implications to chromium spinels are discussed.
NASA Astrophysics Data System (ADS)
Krempaský, J.; Muff, S.; Bisti, F.; Fanciulli, M.; Volfová, H.; Weber, A. P.; Pilet, N.; Warnicke, P.; Ebert, H.; Braun, J.; Bertran, F.; Volobuev, V. V.; Minár, J.; Springholz, G.; Dil, J. H.; Strocov, V. N.
2016-10-01
Entanglement of the spin-orbit and magnetic order in multiferroic materials bears a strong potential for engineering novel electronic and spintronic devices. Here, we explore the electron and spin structure of ferroelectric α-GeTe thin films doped with ferromagnetic Mn impurities to achieve its multiferroic functionality. We use bulk-sensitive soft-X-ray angle-resolved photoemission spectroscopy (SX-ARPES) to follow hybridization of the GeTe valence band with the Mn dopants. We observe a gradual opening of the Zeeman gap in the bulk Rashba bands around the Dirac point with increase of the Mn concentration, indicative of the ferromagnetic order, at persistent Rashba splitting. Furthermore, subtle details regarding the spin-orbit and magnetic order entanglement are deduced from spin-resolved ARPES measurements. We identify antiparallel orientation of the ferroelectric and ferromagnetic polarization, and altering of the Rashba-type spin helicity by magnetic switching. Our experimental results are supported by first-principles calculations of the electron and spin structure.
NASA Astrophysics Data System (ADS)
Schmitz, R.; Entin-Wohlman, O.; Aharony, A.; Müller-Hartmann, E.
2005-09-01
[Dedicated to Bernhard Mühlschlegel on the occasion ofhis 80th birthday]Using a point-charge calculation of the electrostatic crystal field, we determine the non-degenerate orbital ground state of the ferromagnetic Mott insulator YTiO3, which is found to agree perfectly with experiment. Based on the orbital order, we obtain by perturbation theory an effective spin Hamiltonian that describes the magnetic superexchange between nearest-neighbor Ti ions. The superexchange Hamiltonian includes, in addition to the isotropic Heisenberg coupling, antisymmetric (Dzyaloshinskii-Moriya) and symmetric anisotropy terms, caused by the spin-orbit interaction on the Ti ions. We find ferromagnetic Heisenberg couplings for Ti-Ti bonds in the crystallographic ab planes, but antiferromagnetic ones for Ti-Ti bonds between planes, in contradiction with experiment (which gives ferromagnetic couplings for both). Difficulties in calculating realistic values for the isotropic couplings of YTiO3 have been already reported in the literature. We discuss possible origins for these discrepancies. However, the much smaller values we obtain for the symmetric and antisymmetric anisotropies may be expected to be reliable. We therefore combine the experimentally-deduced isotropic coupling with the calculated anisotropic ones to determine the magnetic order of the Ti ions, which is found to be in satisfactory agreement with experiment. Based on this magnetic order, we derive the spin-wave spectrum. We find an acoustic branch with a very small zone-center gap and three optical spin-wave modes with sizeable zone-center gaps. The acoustic branch reproduces the one reported in experiment, and the optical ones are in a satisfactory agreement with experiment, upon a proper folding of the magnetic Brillouin zone.
NASA Astrophysics Data System (ADS)
Pürrer, Michael
2016-03-01
I provide a frequency domain reduced order model (ROM) for the aligned-spin effective-one-body model "SEOBNRv2" for data analysis with second- and third-generation ground-based gravitational wave (GW) detectors. SEOBNRv2 models the dominant mode of the GWs emitted by the coalescence of black hole binaries. The large physical parameter space (dimensionless spins -1 ≤χi≤0.99 and symmetric mass ratios 0.01 ≤η ≤0.25 ) requires sophisticated reduced order modeling techniques, including patching in the parameter space and in frequency. I find that the time window over which the inspiral-plunge and the merger-ringdown waveform in SEOBNRv2 are connected has a discontinuous dependence on the parameters when the spin parameter χ =0.8 or the symmetric mass ratio η ˜0.083 . This discontinuity increases resolution requirements for the ROM. The ROM can be used for compact binary systems with total masses of 2 M⊙ or higher for the Advanced LIGO design sensitivity and a 10 Hz lower cutoff frequency. The ROM has a worst mismatch against SEOBNRv2 of ˜1 %, but in general mismatches are better than ˜0.1 %. The ROM is crucial for key data analysis applications for compact binaries, such as GW searches and parameter estimation carried out within the LIGO Scientific Collaboration.
Hidden spin-order-induced room-temperature ferroelectricity in a peculiar conical magnetic structure
NASA Astrophysics Data System (ADS)
Shen, Shi-Peng; Liu, Xin-Zhi; Chai, Yi-Sheng; Studer, Andrew; Rule, Kirrily; Zhai, Kun; Yan, Li-Qin; Shang, Da-Shan; Klose, Frank; Liu, Yun-Tao; Chen, Dong-Feng; Sun, Young
2017-03-01
A novel mechanism of spin-induced ferroelectricity is unraveled in the alternating longitudinal conical (ALC) magnetic structure. Because the noncollinear ALC structure possesses a c -axis component with collinear ↑-↑-↓-↓ spin order, spin-driven ferroelectricity along the c axis due to the exchange striction mechanism is predicted. Our experiments verify this prediction in the Y-type hexaferrite B a0.3S r1.7C o2F e11Al O22 , where ferroelectricity along the c axis is observed up to room temperature. Neutron diffraction data clearly reveal the ALC phase and its evolution with magnetic fields. The c -axis electric polarization can be well modulated by applying either a b -plane or c -axis magnetic fields, even at 305 K. This kind of spin-induced ferroelectricity associated with the ALC magnetic structure provides a new resource of type II multiferroics.
3 CFR 13494 - Executive Order 13494 of January 30, 2009. Economy in Government Contracting
Code of Federal Regulations, 2010 CFR
2010-01-01
... 3 The President 1 2010-01-01 2010-01-01 false Executive Order 13494 of January 30, 2009. Economy... 13494 of January 30, 2009 EO 13494 Economy in Government Contracting By the authority vested in me as... promote economy and efficiency in Government contracting, certain costs that are not directly related...
Levi, Michele; Steinhoff, Jan E-mail: jan.steinhoff@ist.utl.pt
2014-12-01
The next-to-next-to-leading order spin1-spin2 potential for an inspiralling binary, that is essential for accuracy to fourth post-Newtonian order, if both components in the binary are spinning rapidly, has been recently derived independently via the ADM Hamiltonian and the Effective Field Theory approaches, using different gauges and variables. Here we show the complete physical equivalence of the two results, thereby we first prove the equivalence of the ADM Hamiltonian and the Effective Field Theory approaches at next-to-next-to-leading order with the inclusion of spins. The main difficulty in the spinning sectors, which also prescribes the manner in which the comparison of the two results is tackled here, is the existence of redundant unphysical spin degrees of freedom, associated with the spin gauge choice of a point within the extended spinning object for its representative worldline. After gauge fixing and eliminating the unphysical degrees of freedom of the spin and its conjugate at the level of the action, we arrive at curved spacetime generalizations of the Newton-Wigner variables in closed form, which can also be used to obtain further Hamiltonians, based on an Effective Field Theory formulation and computation. Finally, we make use of our validated result to provide gauge invariant relations among the binding energy, angular momentum, and orbital frequency of an inspiralling binary with generic compact spinning components to fourth post-Newtonian order, including all known sectors up to date.
Field-induced spin-density wave beyond hidden order in URu2Si2
Knafo, W.; Duc, F.; Bourdarot, F.; Kuwahara, K.; Nojiri, H.; Aoki, D.; Billette, J.; Frings, P.; Tonon, X.; Lelièvre-Berna, E.; Flouquet, J.; Regnault, L.-P.
2016-01-01
URu2Si2 is one of the most enigmatic strongly correlated electron systems and offers a fertile testing ground for new concepts in condensed matter science. In spite of >30 years of intense research, no consensus on the order parameter of its low-temperature hidden-order phase exists. A strong magnetic field transforms the hidden order into magnetically ordered phases, whose order parameter has also been defying experimental observation. Here, thanks to neutron diffraction under pulsed magnetic fields up to 40 T, we identify the field-induced phases of URu2Si2 as a spin-density-wave state. The transition to the spin-density wave represents a unique touchstone for understanding the hidden-order phase. An intimate relationship between this magnetic structure, the magnetic fluctuations and the Fermi surface is emphasized, calling for dedicated band-structure calculations. PMID:27762260
Field-induced spin-density wave beyond hidden order in URu2Si2
NASA Astrophysics Data System (ADS)
Knafo, W.; Duc, F.; Bourdarot, F.; Kuwahara, K.; Nojiri, H.; Aoki, D.; Billette, J.; Frings, P.; Tonon, X.; Lelièvre-Berna, E.; Flouquet, J.; Regnault, L.-P.
2016-10-01
URu2Si2 is one of the most enigmatic strongly correlated electron systems and offers a fertile testing ground for new concepts in condensed matter science. In spite of >30 years of intense research, no consensus on the order parameter of its low-temperature hidden-order phase exists. A strong magnetic field transforms the hidden order into magnetically ordered phases, whose order parameter has also been defying experimental observation. Here, thanks to neutron diffraction under pulsed magnetic fields up to 40 T, we identify the field-induced phases of URu2Si2 as a spin-density-wave state. The transition to the spin-density wave represents a unique touchstone for understanding the hidden-order phase. An intimate relationship between this magnetic structure, the magnetic fluctuations and the Fermi surface is emphasized, calling for dedicated band-structure calculations.
Magnetic-charge ordering and phase transitions in monopole-conserved square spin ice
Xie, Y.-L.; Du, Z.-Z.; Yan, Z.-B.; Liu, J.-M.
2015-01-01
Magnetic-charge ordering and corresponding magnetic/monopole phase transitions in spin ices are the emergent topics of condensed matter physics. In this work, we investigate a series of magnetic-charge (monopole) phase transitions in artificial square spin ice model using the conserved monopole density algorithm. It is revealed that the dynamics of low monopole density lattices is controlled by the effective Coulomb interaction and the Dirac string tension, leading to the monopole dimerization which is quite different from the dynamics of three-dimensional pyrochlore spin ice. The condensation of the monopole dimers into monopole crystals with staggered magnetic-charge order can be predicted clearly. For the high monopole density cases, the lattice undergoes two consecutive phase transitions from high-temperature paramagnetic/charge-disordered phase into staggered charge-ordered phase before eventually toward the long-range magnetically-ordered phase as the ground state which is of staggered charge order too. A phase diagram over the whole temperature-monopole density space, which exhibits a series of emergent spin and monopole ordered states, is presented. PMID:26511870
Spin-flop transition accompanied with changing the type of magnetic ordering
NASA Astrophysics Data System (ADS)
Syromyatnikov, A. V.
2017-03-01
We discuss theoretically rather rear example of spin-flop transition which is accompanied with changing the type of magnetic ordering and which seemingly has not been addressed yet. We demonstrate that changing the type of magnetic ordering can manifest itself in antiferromagnetic (AF) resonance experiments as an apparent peculiar switching of the anisotropy at the transition from the easy-axis type to the easy-plane one. We argue that this kind of spin-flop transition is observed recently by Povarov et al. (2013) [12] in Cu(pz)2(ClO4)2 (where pz denotes pyrazine), one of the best realizations of spin-1/2 Heisenberg AFs on square lattice having a very small anisotropy. We show that the magnetic ordering changes at the spin-flop transition in this material in the direction perpendicular to AF square planes. We examine the microscopic mechanism of such behavior in Cu(pz)2(ClO4)2 and find that dipolar forces and extremely small exchange coupling between spins from neighboring planes are responsible for it.
NASA Astrophysics Data System (ADS)
Elsässer, S.; Schiebl, M.; Mukhin, A. A.; Balbashov, A. M.; Pimenov, A.; Geurts, J.
2017-01-01
The orthorhombic rare-earth manganite compounds RMnO3 show a global magnetic order for T< {T}N, and several representatives are multiferroic with a cycloidal spin ground state order for T< {T}{{cycl}}< {T}N≈ 40 {{K}}. We deduce from the temperature dependence of spin-phonon coupling in Raman spectroscopy for a series of RMnO3 compounds that their spin order locally persists up to about twice T N . Along the same line, our observation of the persistence of the electromagnon in GdMnO3 up to T≈ 100 {{K}} is attributed to a local cycloidal spin order for T> {T}{{cycl}}, in contrast to the hitherto assumed incommensurate sinusoidal phase in the intermediate temperature range. The development of the magnetization pattern can be described in terms of an order-disorder transition at T cycl within a pseudospin model of localized spin cycloids with opposite chirality.
Coherent manipulation of non-thermal spin order in optical nuclear polarization experiments
NASA Astrophysics Data System (ADS)
Buntkowsky, Gerd; Ivanov, Konstantin L.; Zimmermann, Herbert; Vieth, Hans-Martin
2017-03-01
Time resolved measurements of Optical Nuclear Polarization (ONP) have been performed on hyperpolarized triplet states in molecular crystals created by light excitation. Transfer of the initial electron polarization to nuclear spins has been studied in the presence of radiofrequency excitation; the experiments have been performed with different pulse sequences using different doped molecular systems. The experimental results clearly demonstrate the dominant role of coherent mechanisms of spin order transfer, which manifest themselves in well pronounced oscillations. These oscillations are of two types, precessions and nutations, having characteristic frequencies, which are the same for the different molecular systems and the pulse sequences applied. Hence, precessions and nutations constitute a general feature of polarization transfer in ONP experiments. In general, coherent manipulation of spin order transfer creates a powerful resource for improving the performance of the ONP method, which paves the way to strong signal enhancement in nuclear magnetic resonance.
Coherent manipulation of non-thermal spin order in optical nuclear polarization experiments.
Buntkowsky, Gerd; Ivanov, Konstantin L; Zimmermann, Herbert; Vieth, Hans-Martin
2017-03-21
Time resolved measurements of Optical Nuclear Polarization (ONP) have been performed on hyperpolarized triplet states in molecular crystals created by light excitation. Transfer of the initial electron polarization to nuclear spins has been studied in the presence of radiofrequency excitation; the experiments have been performed with different pulse sequences using different doped molecular systems. The experimental results clearly demonstrate the dominant role of coherent mechanisms of spin order transfer, which manifest themselves in well pronounced oscillations. These oscillations are of two types, precessions and nutations, having characteristic frequencies, which are the same for the different molecular systems and the pulse sequences applied. Hence, precessions and nutations constitute a general feature of polarization transfer in ONP experiments. In general, coherent manipulation of spin order transfer creates a powerful resource for improving the performance of the ONP method, which paves the way to strong signal enhancement in nuclear magnetic resonance.
Pressure-tuned spin and charge ordering in an itinerant antiferromagnet.
Feng, Yejun; Jaramillo, R; Srajer, G; Lang, J C; Islam, Z; Somayazulu, M S; Shpyrko, O G; Pluth, J J; Mao, H-K; Isaacs, E D; Aeppli, G; Rosenbaum, T F
2007-09-28
Elemental chromium orders antiferromagnetically near room temperature, but the ordering temperature can be driven to zero by applying large pressures. We combine diamond anvil cell and synchrotron x-ray diffraction techniques to measure directly the spin and charge order in the pure metal at the approach to its quantum critical point. Both spin and charge order are suppressed exponentially with pressure, well beyond the region where disorder cuts off such a simple evolution, and they maintain a harmonic scaling relationship over decades in scattering intensity. By comparing the development of the order parameter with that of the magnetic wave vector, it is possible to ascribe the destruction of antiferromagnetism to the growth in electron kinetic energy relative to the underlying magnetic exchange interaction.
Stripe order of holes and spins in oxygen-doped nickelates
NASA Astrophysics Data System (ADS)
Wochner, P.; Tranquada, J. M.; Buttrey, D. J.; Sachan, V.
We present a detailed neutron-scattering study of the ordering of spins and holes in oxygen-doped La 2NiO 4.133. The temperature dependence of the stripe spacing, the width of the stripes and the extent of their pinning to the lattice are investigated.
Levi, Michele; Steinhoff, Jan E-mail: jan.steinhoff@aei.mpg.de
2016-01-01
The next-to-next-to-leading order spin-squared interaction potential for generic compact binaries is derived for the first time via the effective field theory for gravitating spinning objects in the post-Newtonian scheme. The spin-squared sector is an intricate one, as it requires the consideration of the point particle action beyond minimal coupling, and mainly involves the spin-squared worldline couplings, which are quite complex, compared to the worldline couplings from the minimal coupling part of the action. This sector also involves the linear in spin couplings, as we go up in the nonlinearity of the interaction, and in the loop order. Hence, there is an excessive increase in the number of Feynman diagrams, of which more are higher loop ones. We provide all the Feynman diagrams and their values. The beneficial ''nonrelativistic gravitational'' fields are employed in the computation. This spin-squared correction, which enters at the fourth post-Newtonian order for rapidly rotating compact objects, completes the conservative sector up to the fourth post-Newtonian accuracy. The robustness of the effective field theory for gravitating spinning objects is shown here once again, as demonstrated in a recent series of papers by the authors, which obtained all spin dependent sectors, required up to the fourth post-Newtonian accuracy. The effective field theory of spinning objects allows to directly obtain the equations of motion, and the Hamiltonians, and these will be derived for the potential obtained here in a forthcoming paper.
Longitudinal spin excitations and magnetic anisotropy in antiferromagnetically ordered BaFe2As2
NASA Astrophysics Data System (ADS)
Li, Yuan; Wang, Chong; Zhang, Rui; Luo, Huiqian; Wang, Fa; Dai, Pengcheng; Regnault, Louis-Pierre
2014-03-01
In the iron-based superconductors, there is an outstanding debate on the microscopic origin of the magnetism, whether it arises from local moments or itinerant electrons with Fermi-surface nesting. To answer this question, we performed a spin-polarized inelastic neutron scattering study of spin waves in the antiferromagnetically ordered state of BaFe2As2. Three distinct excitation components are identified, with spins fluctuating along the c-axis, perpendicular to the ordering direction in the ab -plane, and parallel to the ordering direction. While the first two ``transverse'' components can be described by a linear spin-wave theory with magnetic anisotropy and inter-layer coupling, the third ``longitudinal'' component is generically incompatible with the local moment picture. It points towards a contribution of itinerant electrons to the magnetism already in the parent compound of this family of Fe-based superconductors. (arXiv:1309.7553) Supported by the National Basic Research Program of China, the National Science Foundation of China, and the US National Science Foundation.
Spin frustration and magnetic ordering in the Mott insulating fcc-Cs3C60
NASA Astrophysics Data System (ADS)
Kasahara, Yuichi; Takeuchi, Yuki; Itou, Tatsuaki; Iwasa, Yoshihiro; Arcon, Denis; Rosseinsky, Matthew; Prassides, Kosmas
2014-03-01
The low-temperature magnetic state at ambient pressure has been investigated by specific heat and nuclear magnetic resonance (NMR) measurements in face-centered-cubic (fcc-) Cs3C60, which is characterized by a Mott insulating state with S = 1 / 2 spins in C603- anions and a geometrical spin frustration inherent in the fcc lattice. Specific heat exhibited no sharp anomaly down to 0.4 K, but both magnetic specific heat and NMR relaxation rate revealed a broad peak around 2.5 K, indicating that the reported antiferromagnetic ordering is accompanied by a gradual freezing of electronic spins with distributed transition temperatures. These results are unexpected in the conventional fcc antiferromagnets. Interplay of geometrical frustration, orientational disorder of C60 molecules, and weak Mottness gives rise to the unique magnetic ground state in fcc-Cs3C60.
First-order melting of a weak spin-orbit mott insulator into a correlated metal
Hogan, Tom; Yamani, Z.; Walkup, D.; Chen, Xiang; Dally, Rebecca; Ward, Thomas Zac; Dean, M. P. M.; Hill, John P.; Islam, Z.; Madhavan, Vidya; Wilson, Stephen D.
2015-06-25
Herein, the electronic phase diagram of the weak spin-orbit Mott insulator (Sr_{1-x}La_{x})_{3}Ir_{2}O_{7} is determined via an exhaustive experimental study. Upon doping electrons via La substitution, an immediate collapse in resistivity occurs along with a narrow regime of nanoscale phase separation comprised of antiferromagnetic, insulating regions and paramagnetic, metallic puddles persisting until x≈0.04. Continued electron doping results in an abrupt, first-order phase boundary where the Néel state is suppressed and a homogenous, correlated, metallic state appears with an enhanced spin susceptibility and local moments. In conclusion, as the metallic state is stabilized, a weak structural distortion develops and suggests a competing instability with the parent spin-orbit Mott state.
First-order melting of a weak spin-orbit mott insulator into a correlated metal
Hogan, Tom; Yamani, Z.; Walkup, D.; ...
2015-06-25
Herein, the electronic phase diagram of the weak spin-orbit Mott insulator (Sr1-xLax)3Ir2O7 is determined via an exhaustive experimental study. Upon doping electrons via La substitution, an immediate collapse in resistivity occurs along with a narrow regime of nanoscale phase separation comprised of antiferromagnetic, insulating regions and paramagnetic, metallic puddles persisting until x≈0.04. Continued electron doping results in an abrupt, first-order phase boundary where the Néel state is suppressed and a homogenous, correlated, metallic state appears with an enhanced spin susceptibility and local moments. In conclusion, as the metallic state is stabilized, a weak structural distortion develops and suggests a competingmore » instability with the parent spin-orbit Mott state.« less
Spin-charge order and excitonic effects in sawtooth-like graphene nanoribbons
NASA Astrophysics Data System (ADS)
Wu, Sha; Lu, Wengang; Qi, Jingshan
2016-09-01
In this paper we systematically study electronic structures and excitonic effects in one type of the sawtooth-like graphene nanoribbons. A main feature is that the local magnetism is developed for the certain width and changes with the increase of width. A variety of magnetic orders root in the competition of the short range interaction between the same spin-electrons and long range exchange interaction between opposite spin-electrons. For excitonic effects, the binding energy of degenerate spin-triplets T1 and T-1 is higher than that of T0 for all studied nanoribbons and is size dependent. We reveal the underlying physical mechanism from the charge distributions of excitons and its correlation with the spin-resolved charge density distributions in the ground state. We find that the electrons and holes in degenerate spin-triplets T1 and T-1 are closer together and thus the interaction between them is more strong, while the distribution of electrons and holes is relatively more disperse for T0, indicating the weaker interaction. We hope that these interesting results are able to be detected in the experiment and these multi-performance samples are better utilized in future device applications.
NASA Technical Reports Server (NTRS)
Uemura, Y. J.; Kossler, W. J.; Yu, X. H.; Schone, H. E.; Kempton, J. R.; Stronach, C. E.; Barth, S.; Gygax, F. N.; Hitti, B.; Schenck, A.
1988-01-01
Zero- and longitudinal-field muon spin relaxation measurements on a heavy fermion system CeCu2.1 Si2 have revealed an onset of static magnetic ordering below T(M) approximately 0.8 K, which coexists with superconductivity below T(c) = 0.7 K. The line shapes of the observed muon spin depolarization functions suggest an ordering in either spin glass or incommensurate spin-density-wave state, with a small averaged static moment of the order of 0.1 micro-B per formula unit at T approaches 0.
Sadhukhan, Debasis; Prabhu, R; Sen De, Aditi; Sen, Ujjwal
2016-03-01
We investigate the behavior of quantum correlations of paradigmatic quenched disordered quantum spin models, viz., the XY spin glass and random-field XY models. We show that quenched averaged quantum correlations can exhibit the order-from-disorder phenomenon for finite-size systems as well as in the thermodynamic limit. Moreover, we find that the order-from-disorder can become more pronounced in the presence of temperature by suitable tuning of the system parameters. The effects are found for entanglement measures as well as for information-theoretic quantum correlation ones, although the former show them more prominently. We also observe that the equivalence between the quenched averages and their self-averaged cousins--for classical and quantum correlations--is related to the quantum critical point in the corresponding ordered system.
NASA Astrophysics Data System (ADS)
Fadley, C. S.; Sinkovic, B.; Hermsmeier, B. D.; Osterwalder, J.
1988-04-01
It has recently been pointed out theoretically and subsequently observed experimentally that core-level multiplet splittings can be used to yield a spin-polarized form of photoelectron diffraction (SPPD). This internally referenced source of electrons that are highly polarized with both orientations of spin thus eliminates the need for an external spin detector, permits studying both ferromagnetic and antiferromagnetic specimens, and can, in principle, detect short-range magnetic or for temperatures above the Curie or Néel temperature. In the first measurements of this type on the antiferromagnet KMnF3, an abrupt loss of short-range order at a transition temperature considerably above the bulk Néel temperature of the material was observed. More recent theoretical diffraction calculations have pointed out several ways in which SPPD should permit deriving unique information on short-range spin-order structures at and near the surfaces of magnetic materials. New experimental results have also been obtained for the antiferromagnet MnO. This paper will discuss these new developments, will review the advantages and disadvantages of SPPD, and also will consider some interesting future directions of investigation.
Spin-orbital order in the undoped manganite LaMnO3 at finite temperature
NASA Astrophysics Data System (ADS)
Snamina, Mateusz; Oleś, Andrzej M.
2016-12-01
We investigate the evolution of spin and orbital order in undoped LaMnO3 under increasing temperature with a model including both superexchange and Jahn-Teller interactions. We used several cluster mean field calculation schemes and find coexisting A -type antiferromagnetic and C -type alternating orbital order at low temperature. The value of the Jahn-Teller coupling between strongly correlated eg orbitals is estimated from the orbital transition temperature at TOO≃780 K. By a careful analysis of onsite and on-bond correlations, we demonstrate that spin-orbital entanglement is rather weak. We have verified that the magnetic transition temperature is influenced by entangled spin-orbital operators as well as by entangled orbital operators on the bonds, but the errors introduced by decoupling such operators partly compensate each other. Altogether, these results justify why the commonly used disentangled spin-orbital model is so successful in describing the magnetic properties and the temperature dependence of the optical spectral weights for LaMnO3.
Transition from the Z2 spin liquid to antiferromagnetic order: Spectrum on the torus
NASA Astrophysics Data System (ADS)
Whitsitt, Seth; Sachdev, Subir
2016-08-01
We describe the finite-size spectrum in the vicinity of the quantum critical point between a Z2 spin liquid and a coplanar antiferromagnet on the torus. We obtain the universal evolution of all low-lying states in an antiferromagnet with global SU(2) spin rotation symmetry, as it moves from the fourfold topological degeneracy in a gapped Z2 spin liquid to the Anderson "tower-of-states" in the ordered antiferromagnet. Due to the existence of nontrivial order on either side of this transition, this critical point cannot be described in a conventional Landau-Ginzburg-Wilson framework. Instead, it is described by a theory involving fractionalized degrees of freedom known as the O (4) * model, whose spectrum is altered in a significant way by its proximity to a topologically ordered phase. We compute the spectrum by relating it to the spectrum of the O (4 ) Wilson-Fisher fixed point on the torus, modified with a selection rule on the states, and with nontrivial boundary conditions corresponding to topological sectors in the spin liquid. The spectrum of the critical O (2 N ) model is calculated directly at N =∞ , which then allows a reconstruction of the full spectrum of the O (2N ) * model at leading order in 1 /N . This spectrum is a unique characteristic of the vicinity of a fractionalized quantum critical point, as well as a universal signature of the existence of proximate Z2 topological and antiferromagnetically ordered phases, and can be compared with numerical computations on quantum antiferromagnets on two-dimensional lattices.
Second-order Peierls transition in the spin-orbital Kumar-Heisenberg model
NASA Astrophysics Data System (ADS)
Brzezicki, Wojciech; Hagymási, Imre; Dziarmaga, Jacek; Legeza, Örs
2015-05-01
We add a Heisenberg interaction term ∝λ in the one-dimensional SU(2 )⊗XY spin-orbital model introduced by Kumar. At λ =0 the spin and orbital degrees of freedom can be separated by a unitary transformation leading to an exact solution of the model. We show that a finite λ >0 leads to spontaneous dimerization of the system which in the thermodynamic limit becomes a smooth phase transition at λ →0 , whereas it remains discontinuous within the first-order perturbation approach. We present the behavior of the entanglement entropy, energy gap, and dimerization order parameter in the limit of λ →0 confirming the critical behavior. Finally, we show the evidence of another phase transition in the Heisenberg limit, λ →∞ , and give a qualitative analytical explanation of the observed dimerized states both in the limit of small and large λ .
Order and thermalized dynamics in Heisenberg-like square and Kagomé spin ices.
Wysin, G M; Pereira, A R; Moura-Melo, W A; de Araujo, C I L
2015-02-25
Thermodynamic properties of a spin ice model on a Kagomé lattice are obtained from dynamic simulations and compared with properties in square lattice spin ice. The model assumes three-component Heisenberg-like dipoles of an array of planar magnetic islands situated on a Kagomé lattice. Ising variables are avoided. The island dipoles interact via long-range dipolar interactions and are restricted in their motion due to local shape anisotropies. We define various order parameters and obtain them and thermodynamic properties from the dynamics of the system via a Langevin equation, solved by the Heun algorithm. Generally, a slow cooling from high to low temperature does not lead to a particular state of order, even for a set of coupling parameters that gives well thermalized states and dynamics. At very low temperature, however, square ice is more likely to reach states near the ground state than Kagomé ice, for the same island coupling parameters.
Formation of ordered microphase-separated pattern during spin coating of ABC triblock copolymer.
Huang, Weihuan; Luo, Chunxia; Zhang, Jilin; Han, Yanchun
2007-03-14
In this paper, the authors have systematically studied the microphase separation and crystallization during spin coating of an ABC triblock copolymer, polystyrene-b-poly(2-vinylpyridine)-b-poly(ethylene oxide) (PS-b-P2VP-b-PEO). The microphase separation of PS-b-P2VP-b-PEO and the crystallization of PEO blocks can be modulated by the types of the solvent and the substrate, the spinning speed, and the copolymer concentration. Ordered microphase-separated pattern, where PEO and P2VP blocks adsorbed to the substrate and PS blocks protrusions formed hexagonal dots above the P2VP domains, can only be obtained when PS-b-P2VP-b-PEO is dissolved in N,N-dimethylformamide and the films are spin coated onto the polar substrate, silicon wafers or mica. The mechanism of the formation of regular pattern by microphase separation is found to be mainly related to the inducement of the substrate (middle block P2VP wetting the polar substrate), the quick vanishment of the solvent during the early stage of the spin coating, and the slow evaporation of the remaining solvent during the subsequent stage. On the other hand, the probability of the crystallization of PEO blocks during spin coating decreases with the reduced film thickness. When the film thickness reaches a certain value (3.0 nm), the extensive crystallization of PEO is effectively prohibited and ordered microphase-separated pattern over large areas can be routinely prepared. When the film thickness exceeds another definite value (12.0 nm), the crystallization of PEO dominates the surface morphology. For films with thickness between these two values, microphase separation and crystallization can simultaneously occur.
Competing orders and spin density wave instabilities in FeAs-based systems
NASA Astrophysics Data System (ADS)
Wang, Nan Lin
2009-03-01
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 a spin-density-wave (SDW) ordered state for the parent compound with a stripe (or collinear) type spin structure based on the transport, specific heat, optical spectroscopy measurements and the first- principle calculations. The proposed spin structure from a nesting of the Fermi surfaces is confirmed by subsequent neutron experiments. However, it could also be explained by a local superexchange picture. In this talk I shall focus on our recent optical data on single crystal samples, trying to address the debating issue about itinerant or localized approaches to the SDW order. We found that the undoped compounds are quite metallic with relatively high plasma frequencies above TSDW. Upon entering the SDW ordered state, a large part of the Drude component is removed by the gapping of Fermi surfaces. Meanwhile, the carrier scattering rate is even more dramatically reduced. Those observations favor an itinerant description for the driving mechanism of SDW instability. Nevertheless, our experiments also indicate that Fe pnictides are not simple metals. A high energy gap-like feature is present even above TSDW, which seems to be linked with the antiferromagnetic spin fluctuations. For the superconducting samples, a superconducting pairing energy gap is clearly observed in the far-infrared reflectance measurement. The Ferrell-Glover- Tinkham sum rule is satisfied at a low energy scale. Work done in collaboration with: G. F. Chen, J. L. Luo, Z. Fang, X. Dai, W. Z. Hu, J. Dong, G. Li, Z. Li, P. Dai, J. Lynn, H. Q. Yuang, J. Singleton.
Magnetic ordering of defects in a molecular spin-Peierls system
NASA Astrophysics Data System (ADS)
Berlie, Adam; Terry, Ian; Cottrell, Stephen; Pratt, Francis L.; Szablewski, Marek
2017-01-01
With interest in charge transfer compounds growing steadily, it is important to understand all aspects of the underlying physics of these systems, including the properties of the defects and interfaces that are universally present in actual experimental systems. For the study of these defects and their interactions a spin-Peierls (SP) system provides a useful testing ground. This work presents an investigation within the SP phase of potassium TCNQF4 where anomalous features are observed in both the magnetic susceptibility and ESR spectra for temperatures between 60 K and 100 K. Muon spin spectroscopy measurements confirm the presence of these anomalous magnetic features, with low temperature zero-field data exhibiting the damped oscillatory form that is a characteristic signature of static magnetic order. This ordering is most likely due to the interaction between structurally correlated magnetic defects in the system. The critical behaviour of the temperature dependent muon spin rotation frequency indicates that a 2D Ising model is applicable to the magnetic ordering of these defects. We show that these observations can be explained by a simple model in which the magnetic defects are located at stacking faults, which provide them with a 2D structural framework to constrain their interactions.
Probing the antiferromagnetic long-range order with Glauber spin states
NASA Technical Reports Server (NTRS)
Cabrera, Guillermo G.
1994-01-01
It is well known that the ground state of low-dimensional antiferromagnets deviates from Neel states due to strong quantum fluctuations. Even in the presence of long-range order, those fluctuations produce a substantial reduction of the magnetic moment from its saturation value. Numerical simulations in anisotropic antiferromagnetic chains suggest that quantum fluctuations over Neel order appear in the form of localized reversal of pairs of neighboring spins. In this paper, we propose a coherent state representation for the ground state to describe the above situation. In the one-dimensional case, our wave function corresponds to a two-mode Glauber state, when the Neel state is used as a reference, while the boson fields are associated to coherent flip of spin pairs. The coherence manifests itself through the antiferromagnetic long-range order that survives the action of quantum fluctuations. The present representation is different from the standard zero-point spin wave state, and is asymptotically exact in the limit of strong anisotropy. The fermionic version of the theory, obtained through the Jordan-Wigner transformation, is also investigated.
NASA Astrophysics Data System (ADS)
Huang, Cheng-Yi; Tsai, Wei-Feng; Wang, Yung Jui; Lin, Hsin; Bansil, Arun
2014-03-01
We discuss spin reorientation phenomena, which may or may not yield gap formation, on the surface of topological crystalline insulators Pb1-xSnx(Te, Se) under various applied strains. The low-energy surface electrons on the (001) surface behave like massless Dirac particles with four Dirac points centered along the intersection of the mirror (xz or yz) plane and the surface plane. We use a four-band k.p model, which captures the spin and orbital texture of the surface states around surface X (or Y) point up to the energy around the Lifshitz transition, and systematically study effects of the applied strain. In contrast to the case without any strain, where the absence of the out-of-the-plane spin component is guaranteed by both the mirror and the time-reversal symmetries, we find that without time-reversal symmetry breaking, the hedgehog-like spin textures associated with a gap formation can be induced by the strain only, breaking the xz mirror symmetry. The other cases cannot induce a gap at Dirac points. We also investigate interaction-driven competing orders under the strain and obtain a phase diagram at the mean-field level to reveal the possible novel surface states in the system.
Topological order, symmetry, and Hall response of two-dimensional spin-singlet superconductors
NASA Astrophysics Data System (ADS)
Moroz, Sergej; Prem, Abhinav; Gurarie, Victor; Radzihovsky, Leo
2017-01-01
Fully gapped two-dimensional superconductors coupled to dynamical electromagnetism are known to exhibit topological order. In this work, we develop a unified low-energy description for spin-singlet paired states by deriving topological Chern-Simons field theories for s -wave, d +i d , and chiral higher even-wave superconductors. These theories capture the quantum statistics and fusion rules of Bogoliubov quasiparticles and vortices and incorporate global continuous symmetries—specifically, spin rotation and conservation of magnetic flux—present in all singlet superconductors. For all such systems, we compute the Hall response for these symmetries and investigate the physics at the edge. In particular, the weakly coupled phase of a chiral d +i d chiral state has a spin Hall coefficient νs=2 and a vanishing Hall response for the magnetic flux symmetry. We argue that the latter is a generic result for two-dimensional superconductors with gapped photons, thereby demonstrating the absence of a spontaneous magnetic field in the ground state of chiral superconductors. It is also shown that the Chern-Simons theories of chiral spin-singlet superconductors derived here fall into Kitaev's 16-fold classification of topological superconductors.
Geodesics for efficient creation and propagation of order along Ising spin chains
YuanHaidong; Glaser, Steffen J.; Khaneja, Navin
2007-07-15
Experiments in coherent nuclear and electron magnetic resonance, and optical spectroscopy correspond to control of quantum mechanical ensembles, guiding them from initial to final target states by unitary transformations. The control inputs (pulse sequences) that accomplish these unitary transformations should take as little time as possible so as to minimize the effects of relaxation and decoherence and to optimize the sensitivity of the experiments. Here we give efficient syntheses of various unitary transformations on Ising spin chains of arbitrary length. The efficient realization of the unitary transformations presented here is obtained by computing geodesics on a sphere under a special metric. We show that contrary to the conventional belief, it is possible to propagate a spin order along an Ising spin chain with coupling strength J (in units of Hz), significantly faster than (2J){sup -1} per step. The methods presented here are expected to be useful for immediate and future applications involving control of spin dynamics in coherent spectroscopy and quantum information processing.
Characterization of spin dynamics in stripe-ordered La2-xSrxNiO4
NASA Astrophysics Data System (ADS)
Woo, H.; Tranquada, J. M.; Boothroyd, A. T.; Nakajima, K.; Perring, T. G.; Frost, C.; Freeman, P. G.; Prabhakaran, D.; Yamada, K.
2004-03-01
Inelastic neutron scattering experiments at a spallation source have enabled us to measure the full momentum- and energy- dependent spectra of magnetic fluctuations in the charge- and spin-stripe ordered systems La_2-xSr_xNiO4 ( x=1/3 and x=0.275). Peaks in the dynamic magnetic response at incommensurate wavevectors and over a wide frequency range are commonly observed in the high-Tc superconductors YBa_2Cu_3O_6+x and La_2-xA_xCuO_4(A=Sr,Ba) , as well as in the static charge- and spin-striped system nickelates La_2-xSr_xNiO_4. High energy transfer up to 90meV with broad reciprocal spaces was observed. In addition to intrastripe and interstripe exchange interactions between neighboring Ni spins [1], exchange interactions between diagonal Ni spins (not through oxygen) are also considered. We will present a detailed measurement and analysis in the NiO2 plane. We acknowledge U.S.-DOE for financial support: contract # DE-AC02-98CH1088. [1] Boothroyd et al. Phys. Rev. B 67, 100407(R) (2003).
48 CFR 252.251-7000 - Ordering from Government supply sources.
Code of Federal Regulations, 2013 CFR
2013-10-01
... 48 Federal Acquisition Regulations System 3 2013-10-01 2013-10-01 false Ordering from Government supply sources. 252.251-7000 Section 252.251-7000 Federal Acquisition Regulations System DEFENSE ACQUISITION REGULATIONS SYSTEM, DEPARTMENT OF DEFENSE CLAUSES AND FORMS SOLICITATION PROVISIONS AND...
48 CFR 252.251-7000 - Ordering from Government supply sources.
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2012-10-01
... 48 Federal Acquisition Regulations System 3 2012-10-01 2012-10-01 false Ordering from Government supply sources. 252.251-7000 Section 252.251-7000 Federal Acquisition Regulations System DEFENSE ACQUISITION REGULATIONS SYSTEM, DEPARTMENT OF DEFENSE CLAUSES AND FORMS SOLICITATION PROVISIONS AND...
48 CFR 252.251-7000 - Ordering from Government supply sources.
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2014-10-01
... 48 Federal Acquisition Regulations System 3 2014-10-01 2014-10-01 false Ordering from Government supply sources. 252.251-7000 Section 252.251-7000 Federal Acquisition Regulations System DEFENSE ACQUISITION REGULATIONS SYSTEM, DEPARTMENT OF DEFENSE CLAUSES AND FORMS SOLICITATION PROVISIONS AND...
Nodal quasiparticles and the onset of spin-density-wave order in cuprate superconductors.
Pelissetto, Andrea; Sachdev, Subir; Vicari, Ettore
2008-07-11
We present a theory for the onset of spin-density-wave order in the superconducting ground state of the cuprates. We compute the scaling dimensions of allowed perturbations of a "relativistic" fixed point with O4 x O(3) symmetry, including those associated with the fermionic nodal Bogoliubov quasiparticles. Analyses of up to six loops show that all perturbations with square lattice symmetry are likely irrelevant. We demonstrate that the fermion spectral functions are primarily damped by the coupling to fluctuations of a composite field with Ising nematic order. A number of other experimental implications are also discussed.
Guo, Y. M.; Ruan, M. Y.; Cheng, J. J.; Sun, Y. C.; Ouyang, Z. W. Xia, Z. C.; Rao, G. H.
2015-06-14
High-field electron spin resonance (ESR) has been employed to study the antiferromagnetic (AFM) ordering state (T < T{sub N} = 55 K) of spin-chain multiferroic Gd{sub 2}BaNiO{sub 5}. The spin reorientation at T{sub SR} = 24 K is well characterized by the temperature-dependent ESR spectra. The magnetization data evidence a field-induced spin-flop transition at 2 K. The frequency-field relationship of the ESR data can be explained by conventional AFM resonance theory with uniaxial anisotropy, in good agreement with magnetization data. Related discussion on zero-field spin gap is presented.
Frequency-domain reduced order models for gravitational waves from aligned-spin compact binaries
NASA Astrophysics Data System (ADS)
Pürrer, Michael
2014-10-01
Black-hole binary coalescences are one of the most promising sources for the first detection of gravitational waves. Fast and accurate theoretical models of the gravitational radiation emitted from these coalescences are highly important for the detection and extraction of physical parameters. Spinning effective-one-body models for binaries with aligned-spins have been shown to be highly faithful, but are slow to generate and thus have not yet been used for parameter estimation (PE) studies. I provide a frequency-domain singular value decomposition-based surrogate reduced order model that is thousands of times faster for typical system masses and has a faithfulness mismatch of better than ˜0.1% with the original SEOBNRv1 model for advanced LIGO detectors. This model enables PE studies up to signal-to-noise ratios (SNRs) of 20 and even up to 50 for total masses below 50 {{M}⊙ }. This paper discusses various choices for approximations and interpolation over the parameter space that can be made for reduced order models of spinning compact binaries, provides a detailed discussion of errors arising in the construction and assesses the fidelity of such models.
Spin and orbital ordering in Y1-xLaxVO₃
Yan, J.-Q.; Zhou, J.-S.; Cheng, J. G.; ...
2011-12-02
The spin and orbital ordering in Y1-xLaxVO₃ (0.30 ≤ x ≤ 1.0) has been studied to map out the phase diagram over the whole doping range 0 ≤ x ≤ 1. The phase diagram is compared with that for RVO₃ (R = rare earth or Y) perovskites without A-site variance. For x > 0.20, no long-range orbital ordering was observed above the magnetic ordering temperature TN; the magnetic order is accompanied by a lattice anomaly at a Tt ≤ TN as in LaVO₃. The magnetic ordering below Tt ≤ TN is G type in the compositional range 0.20 ≤ xmore » ≤ 0.40 and C type in the range 0.738 ≤ x ≤ 1.0. Magnetization and neutron powder diffraction measurements point to the coexistence below TN of the two magnetic phases in the compositional range 0.4 < x < 0.738. Samples in the compositional range 0.20 < x ≤ 1.0 are characterized by an additional suppression of a glasslike thermal conductivity in the temperature interval TN < T < T* and a change in the slope of 1/χ(T). We argue that T* represents a temperature below which spin and orbital fluctuations couple together via λL∙S.« less
Study of spin-temperature effects using energy-ordered gamma-ray spectroscopy
Baktash, C.
1990-01-01
We investigated a new continuum {gamma}-ray spectroscopy technique which is based on the detection of all emitted {gamma} rays in a 4{pi} detector system, and ordering them according to their energies on an event-by-event basis. The technique allows determination of growth strength functions, and rotational damping width as a function of spin and temperature. Thus, it opens up the possibility of studying the onset of motional narrowing and the mapping of the evolution of nuclear collectivity with spin and temperature. Application of the technique for preferential entry-state population, exit-channel selection, and feeding of the discrete states via selective pathways will be discussed. 19 refs., 6 figs.
Levi, Michele; Steinhoff, Jan E-mail: jan.steinhoff@aei.mpg.de
2016-01-01
We implement the effective field theory for gravitating spinning objects in the post-Newtonian scheme at the next-to-next-to-leading order level to derive the gravitational spin-orbit interaction potential at the third and a half post-Newtonian order for rapidly rotating compact objects. From the next-to-next-to-leading order interaction potential, which we obtain here in a Lagrangian form for the first time, we derive straightforwardly the corresponding Hamiltonian. The spin-orbit sector constitutes the most elaborate spin dependent sector at each order, and accordingly we encounter a proliferation of the relevant Feynman diagrams, and a significant increase of the computational complexity. We present in detail the evaluation of the interaction potential, going over all contributing Feynman diagrams. The computation is carried out in terms of the ''nonrelativistic gravitational'' fields, which are advantageous also in spin dependent sectors, together with the various gauge choices included in the effective field theory for gravitating spinning objects, which also optimize the calculation. In addition, we automatize the effective field theory computations, and carry out the automated computations in parallel. Such automated effective field theory computations would be most useful to obtain higher order post-Newtonian corrections. We compare our Hamiltonian to the ADM Hamiltonian, and arrive at a complete agreement between the ADM and effective field theory results. Finally, we provide Hamiltonians in the center of mass frame, and complete gauge invariant relations among the binding energy, angular momentum, and orbital frequency of an inspiralling binary with generic compact spinning components to third and a half post-Newtonian order. The derivation presented here is essential to obtain further higher order post-Newtonian corrections, and to reach the accuracy level required for the successful detection of gravitational radiation.
Effect of random field disorder on the first order transition in p-spin interaction model
NASA Astrophysics Data System (ADS)
Sumedha; Singh, Sushant K.
2016-01-01
We study the random field p-spin model with Ising spins on a fully connected graph using the theory of large deviations in this paper. This is a good model to study the effect of quenched random field on systems which have a sharp first order transition in the pure state. For p = 2, the phase-diagram of the model, for bimodal distribution of the random field, has been well studied and is known to undergo a continuous transition for lower values of the random field (h) and a first order transition beyond a threshold, htp(≈ 0.439) . We find the phase diagram of the model, for all p ≥ 2, with bimodal random field distribution, using large deviation techniques. We also look at the fluctuations in the system by calculating the magnetic susceptibility. For p = 2, beyond the tricritical point in the regime of first order transition, we find that for htp < h < 0.447, magnetic susceptibility increases rapidly (even though it never diverges) as one approaches the transition from the high temperature side. On the other hand, for 0.447 < h ≤ 0.5, the high temperature behaviour is well described by the Curie-Weiss law. For all p ≥ 2, we find that for larger magnitudes of the random field (h >ho = 1 / p!), the system does not show ferromagnetic order even at zero temperature. We find that the magnetic susceptibility for p ≥ 3 is discontinuous at the transition point for h
Analytical high-order post-Newtonian expansions for spinning extreme mass ratio binaries
NASA Astrophysics Data System (ADS)
Kavanagh, Chris; Ottewill, Adrian C.; Wardell, Barry
2016-06-01
We present an analytic computation of Detweiler's redshift invariant for a point mass in a circular orbit around a Kerr black hole, giving results up to 8.5 post-Newtonian order while making no assumptions on the magnitude of the spin of the black hole. Our calculation is based on the functional series method of Mano, Suzuki and Takasugi, and employs a rigorous mode-sum regularization prescription based on the Detweiler-Whiting singular-regular decomposition. The approximations used in our approach are minimal; we use the standard self-force expansion to linear order in the mass ratio, and the standard post-Newtonian expansion in the separation of the binary. A key advantage of this approach is that it produces expressions that include contributions at all orders in the spin of the Kerr black hole. While this work applies the method to the specific case of Detweiler's redshift invariant, it can be readily extended to other gauge-invariant quantities and to higher post-Newtonian orders.
NASA Astrophysics Data System (ADS)
Ilker, Efe; Berker, A. Nihat
2014-04-01
In spin-glass systems, frustration can be adjusted continuously and considerably, without changing the antiferromagnetic bond probability p, by using locally correlated quenched randomness, as we demonstrate here on hypercubic lattices and hierarchical lattices. Such overfrustrated and underfrustrated Ising systems on hierarchical lattices in d =3 and 2 are studied. With the removal of just 51% of frustration, a spin-glass phase occurs in d =2. With the addition of just 33% frustration, the spin-glass phase disappears in d =3. Sequences of 18 different phase diagrams for different levels of frustration are calculated in both dimensions. In general, frustration lowers the spin-glass ordering temperature. At low temperatures, increased frustration favors the spin-glass phase (before it disappears) over the ferromagnetic phase and symmetrically the antiferromagnetic phase. When any amount, including infinitesimal, frustration is introduced, the chaotic rescaling of local interactions occurs in the spin-glass phase. Chaos increases with increasing frustration, as can be seen from the increased positive value of the calculated Lyapunov exponent λ, starting from λ =0 when frustration is absent. The calculated runaway exponent yR of the renormalization-group flows decreases with increasing frustration to yR=0 when the spin-glass phase disappears. From our calculations of entropy and specific-heat curves in d =3, it is shown that frustration lowers in temperature the onset of both long- and short-range order in spin-glass phases, but is more effective on the former. From calculations of the entropy as a function of antiferromagnetic bond concentration p, it is shown that the ground-state and low-temperature entropy already mostly sets in within the ferromagnetic and antiferromagnetic phases, before the spin-glass phase is reached.
Spin susceptibility of underdoped cuprate superconductors: Insights from a stripe-ordered crystal
NASA Astrophysics Data System (ADS)
Hücker, M.; Gu, G. D.; Tranquada, J. M.
2008-12-01
We report a detailed study of the temperature and magnetic-field dependence of the spin susceptibility for a single crystal of La1.875Ba0.125CuO4 . From a quantitative analysis, we find that the temperature-dependent anisotropy of the susceptibility, observed in both the paramagnetic and stripe-ordered phases, directly indicates that localized Cu moments dominate the magnetic response. A field-induced spin-flop transition provides further corroboration for the role of local moments. Contrary to previous analyses of data from polycrystalline samples, we find that a commonly assumed isotropic and temperature-independent contribution from free carriers, if present, must be quite small. Our conclusion is strengthened by extending the quantitative analysis to include crystals of La2-xBaxCuO4 with x=0.095 and 0.155. On the basis of our results, we present a revised interpretation of the temperature and doping dependence of the spin susceptibility in La2-x(Sr,Ba)xCuO4 .
Code of Federal Regulations, 2012 CFR
2012-01-01
... Property of Senior Officials of the Government of Syria 13573 Order 13573 Presidential Documents Executive Orders Executive Order 13573 of May 18, 2011 EO 13573 Blocking Property of Senior Officials of the... be a senior official of the Government of Syria; (ii) to be an agency or instrumentality of...
Majorana fermions in spin-singlet nodal superconductors with coexisting non-collinear magnetic order
NASA Astrophysics Data System (ADS)
Wang, Ziqiang; Lu, Yuan-Ming
2013-03-01
Realizations of Majorana fermions in solid state materials have attracted great interests recently in connection to topological order and quantum information processing. We propose a novel way to create Majorana fermions in superconductors. We show that an incipient non-collinear magnetic order turns a spin-singlet superconductor with nodes into a topological superconductor with a stable Majorana bound state (MBS) in the vortex core or on the edge. Moreover the topologically-stable point defect of non-collinear magnetic order also hosts a zero-energy MBS. We argue that such an exotic non-Abelian phase can be realized in extended t- J models on the triangular and square lattices. Our proposal suggests a new avenue for the search of Majorana fermions in correlated electron materials where nodal superconductivity and magnetism are two common caricatures.
Self Assembled Spin Coated and Bulk Films of a Novel Polydiacetylene as Second Order NLO Polymers
1994-05-31
T Code: 4132016 W.H. Kim, B. Bihari, R. Moody, N. B. Kodali , J.KumarS.K. Dr. JoAnn Milliken Tripathy. 7. PHI-OUHMING OFH-NIZATION NAMIE(S) AND...Self Assembled Spin Coated and Bulk Films of a Novel Polydiacetylene as Second Order NLO Polymers by W.H. Kim, B. Bihari, R. Moody, N. B. Kodali ...POLYMERS W. H. Kim, B. Bihari+, R. Moody+, N. B. Kodali , J. Kumar+, and S. K. Tripathy, University of Massachusetts-Lowell, Center for Advanced Materials
NASA Astrophysics Data System (ADS)
Derrida, Bernard; Hakim, Vincent; Zeitak, Reuven
1996-09-01
The fraction r\\(t\\) of spins which have never flipped up to time t is studied within a linear diffusion approximation to phase ordering. Numerical simulations show that r\\(t\\) decays with time like a power law with a nontrivial exponent θ which depends on the space dimension. The dynamics is a special case of a stationary Gaussian process of known correlation function. The exponent θ is given by the asymptotic decay of the probability distribution of intervals between consecutive zero crossings. An approximation based on the assumption that successive zero crossings are independent random variables gives values of θ in close agreement with the results of simulations.
Zhang, Wenliang; Park, J T; Lu, Xingye; Wei, Yuan; Ma, Xiaoyan; Hao, Lijie; Dai, Pengcheng; Meng, Zi Yang; Yang, Yi-Feng; Luo, Huiqian; Li, Shiliang
2016-11-25
The origin of nematic order remains one of the major debates in iron-based superconductors. In theories based on spin nematicity, one major prediction is that the spin-spin correlation length at (0,π) should decrease with decreasing temperature below the structural transition temperature T_{s}. Here, we report inelastic neutron scattering studies on the low-energy spin fluctuations in BaFe_{1.935}Ni_{0.065}As_{2} under uniaxial pressure. Both intensity and spin-spin correlation start to show anisotropic behavior at high temperature, while the reduction of the spin-spin correlation length at (0,π) happens just below T_{s}, suggesting the strong effect of nematic order on low-energy spin fluctuations. Our results favor the idea that treats the spin degree of freedom as the driving force of the electronic nematic order.
Federal Register 2010, 2011, 2012, 2013, 2014
2010-03-11
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Vestigial nematicity from spin and/or charge order in the cuprates
NASA Astrophysics Data System (ADS)
Nie, Laimei; Maharaj, Akash; Fradkin, Eduardo; Kivelson, Steven
Nematic order (C4 rotation symmetry breaking) has manifested itself in a variety of materials in the cuprates family, yet its origin remains debatable, with possible links to lattice, charge, and spin degrees of freedom across different doping regimes. We propose an effective field theory of a layered system with incommensurate, intertwined spin- and charge-density wave (SDW and CDW) orders, each of which consists of two components related by C4 rotations. Using a variational free energy approach, we study the growth of the associated nematicity from partially melting those density waves by either increasing temperature or adding quenched disorder. Under the assumption that the zero-disorder, zero-interaction SDW transition temperature is higher than CDW at small doping (and vice versa for large doping), we find that for the general case with finite disorder and interactions there is a universal nematic transition across the entire doping range, accompanied by SDW and CDW transitions (or strong fluctuations at large enough disorder) at lower temperatures. We also discuss the issues concerning the difference between La-based materials and the other hole-doped cuprates.
Second order formalism for spin (1/2) fermions and Compton scattering
Delgado-Acosta, E. G.; Napsuciale, Mauro; Rodriguez, Simon
2011-04-01
We develop a second order formalism for massive spin 1/2 fermions based on the projection over Poincare invariant subspaces in the ((1/2),0)+(0,(1/2)) representation of the homogeneous Lorentz group. Using the U(1){sub em} gauge principle we obtain a second order description for the electromagnetic interactions of a spin 1/2 fermion with two free parameters, the gyromagnetic factor g and a parameter {xi} related to odd-parity Lorentz structures. We calculate Compton scattering in this formalism. In the particular case g=2, {xi}=0, and for states with well-defined parity, we recover Dirac results. In general, we find the correct classical limit and a finite value r{sub c}{sup 2} for the forward differential cross section, independent of the photon energy and of the value of the parameters g and {xi}. The differential cross section vanishes at high energies for all g, {xi} except in the forward direction. The total cross section at high energies vanishes only for g=2, {xi}=0. We argue that this formalism is more convenient than Dirac theory in the description of low energy electromagnetic properties of baryons and illustrate the point with the proton case.
Stripe order of holes and spins in La_2NiO_4+δ
NASA Astrophysics Data System (ADS)
Wochner, P.; Tranquada, J. M.; Buttrey, D. J.; Sachan, V.
1997-03-01
We present a detailed neutron scattering study of the ordering of spins and holes in oxygen doped La_2NiO_4.133. The wave vector ɛ that characterizes the magnetic and charge satellite peaks shows pronounced lock-in transitions to rational fractions. The observed fractions are compatible with a Farey tree series. A competition between Coulomb and magnetic interactions as well as the oxygen interstitial potential can account for the observed strong temperature dependence of ɛ. Above the magnetic transition temperature of 110 K, purely charge order occurs with a wave vector ɛ = 1/3, controlled by the interstitial potential. This phase shows a local ferrimagnetic moment which can be driven into staggered magnetic order via an applied magnetic field. Our analysis shows that hole stripes are oxygen centered at high temperatures which changes to predominantly nickel centered stripes at low temperatures. The fact, that the charge orders before magnetic order occurs is also observed in La_2-xSr_xNiO4 and is consistent with the charge segregation concept of Emery and Kivelson in which local antiferromagnetic order can occur only after the charge has segregated into hole-rich and hole-poor regions.
Ge, Mingtao; Freed, Jack H
2009-06-17
A spin-labeling study of interactions of a fusion peptide from the hemagglutinin of the influenza virus, wt20, and a fusion-inactive mutant DeltaG1 with dimyristoylphosphatidylcholine (DMPC) and 1-palmitoyl-2-oleoyl-phosphatdylcholine bilayers was performed. We found that upon binding of wt20, the ordering of headgroups and the ordering of acyl chains near the headgroup increased significantly, in a manner consistent with a cooperative phenomenon. However, changes in the order at the end of the acyl chains were negligible. The ordering effect of wt20 on the headgroup was much stronger at pH 5 than at pH 7. No effect of DeltaG1 binding on the order of bilayers was evident. We also found that 1-palmitoyl-2-hydroxyl phosphatidylcholine, a membrane-fusion inhibitor, decreased the ordering of DMPC headgroups, whereas arachidonic acid, a membrane-fusion promoter, increased the ordering of DMPC headgroups. These results suggest that increases in headgroup ordering may be important for membrane fusion. We propose that upon binding of wt20, which is known to affect only the outer leaflet of the bilayer, this outer leaflet becomes more ordered, and thus more solid-like. Then the coupling between the hardened outer leaflet and the softer inner leaflet generates bending stresses in the bilayer, which tend to increase the negative curvature of the bilayer. We suggest that the increased ordering in the headgroup region enhances dipolar interactions and lowers electrostatic energy, which may provide an energy source for membrane fusion. Possible roles of bending stresses in promoting membrane fusion are discussed.
Spin polarized photons from an axially charged plasma at weak coupling: Complete leading order
Mamo, Kiminad A.; Yee, Ho-Ung
2016-03-24
In the presence of (approximately conserved) axial charge in the QCD plasma at finite temperature, the emitted photons are spin aligned, which is a unique P- and CP-odd signature of axial charge in the photon emission observables. We compute this “P-odd photon emission rate” in a weak coupling regime at a high temperature limit to complete leading order in the QCD coupling constant: the leading log as well as the constant under the log. As in the P-even total emission rate in the literature, the computation of the P-odd emission rate at leading order consists of three parts: (1) Compton and pair annihilation processes with hard momentum exchange, (2) soft t- and u-channel contributions with hard thermal loop resummation, (3) Landau-Pomeranchuk-Migdal resummation of collinear bremsstrahlung and pair annihilation. In conclusion, we present analytical and numerical evaluations of these contributions to our P-odd photon emission rate observable.
First-order transition and tricritical behavior of the transverse crystal field spin-1 Ising model
NASA Astrophysics Data System (ADS)
Costabile, Emanuel; Viana, J. Roberto; de Sousa, J. Ricardo; de Arruda, Alberto S.
2015-06-01
The phase diagram of the spin-1 Ising model in the presence of a transverse crystal-field anisotropy (Dx) is studied within the framework of an effective-field theory with correlation. The effect of the coordination number (z) on the phase diagram in the T -Dx plane is investigated. We observe only second-order transitions for coordination number z < 7, while that for z ≥ 7 we have first- and second-order transitions, with the presence of two tricritical points. The lower tricritical temperature (Tt) decreases monotonically with the increasing value of z, and in the limit of z → ∞ we found Tt = 0, corresponding to the mean-field solution [Ricardo de Sousa and Branco, Phys. Rev. E 77 (2008) 012104] with a single tricritical point in the phase diagram.
Spin polarized photons from an axially charged plasma at weak coupling: Complete leading order
NASA Astrophysics Data System (ADS)
Mamo, Kiminad A.; Yee, Ho-Ung
2016-03-01
In the presence of (approximately conserved) axial charge in the QCD plasma at finite temperature, the emitted photons are spin aligned, which is a unique P - and C P -odd signature of axial charge in the photon emission observables. We compute this "P -odd photon emission rate" in a weak coupling regime at a high temperature limit to complete leading order in the QCD coupling constant: the leading log as well as the constant under the log. As in the P -even total emission rate in the literature, the computation of the P -odd emission rate at leading order consists of three parts: (1) Compton and pair annihilation processes with hard momentum exchange, (2) soft t - and u -channel contributions with hard thermal loop resummation, (3) Landau-Pomeranchuk-Migdal resummation of collinear bremsstrahlung and pair annihilation. We present analytical and numerical evaluations of these contributions to our P -odd photon emission rate observable.
An alternative order-parameter for non-equilibrium generalized spin models on honeycomb lattices
NASA Astrophysics Data System (ADS)
Sastre, Francisco; Henkel, Malte
2016-04-01
An alternative definition for the order-parameter is proposed, for a family of non-equilibrium spin models with up-down symmetry on honeycomb lattices, and which depends on two parameters. In contrast to the usual definition, our proposal takes into account that each site of the lattice can be associated with a local temperature which depends on the local environment of each site. Using the generalised voter motel as a test case, we analyse the phase diagram and the critical exponents in the stationary state and compare the results of the standard order-parameter with the ones following from our new proposal, on the honeycomb lattice. The stationary phase transition is in the Ising universality class. Finite-size corrections are also studied and the Wegner exponent is estimated as ω =1.06(9).
Robust Takagi-Sugeno fuzzy control for fractional order hydro-turbine governing system.
Wang, Bin; Xue, Jianyi; Wu, Fengjiao; Zhu, Delan
2016-11-01
A robust fuzzy control method for fractional order hydro-turbine governing system (FOHGS) in the presence of random disturbances is investigated in this paper. Firstly, the mathematical model of FOHGS is introduced, and based on Takagi-Sugeno (T-S) fuzzy rules, the generalized T-S fuzzy model of FOHGS is presented. Secondly, based on fractional order Lyapunov stability theory, a novel T-S fuzzy control method is designed for the stability control of FOHGS. Thirdly, the relatively loose sufficient stability condition is acquired, which could be transformed into a group of linear matrix inequalities (LMIs) via Schur complement as well as the strict mathematical derivation is given. Furthermore, the control method could resist random disturbances, which shows the good robustness. Simulation results indicate the designed fractional order T-S fuzzy control scheme works well compared with the existing method.
Code of Federal Regulations, 2010 CFR
2010-10-01
....298 Are Self-Governance Tribes required to comply with Executive Orders to fulfill their environmental... 42 Public Health 1 2010-10-01 2010-10-01 false Are Self-Governance Tribes required to comply with Executive Orders to fulfill their environmental responsibilities under section 509 of the Act ?...
S =1/2 quantum critical spin ladders produced by orbital ordering in Ba2CuTeO6
NASA Astrophysics Data System (ADS)
Gibbs, A. S.; Yamamoto, A.; Yaresko, A. N.; Knight, K. S.; Yasuoka, H.; Majumder, M.; Baenitz, M.; Saines, P. J.; Hester, J. R.; Hashizume, D.; Kondo, A.; Kindo, K.; Takagi, H.
2017-03-01
The ordered hexagonal perovskite Ba2CuTeO6 hosts weakly coupled S =1/2 spin ladders produced by an orbital ordering of Cu2 +. The magnetic susceptibility χ (T ) of Ba2CuTeO6 is well described by that expected for isolated spin ladders with exchange coupling of J ≈ 86 K but shows a deviation from the expected thermally activated behavior at low temperatures below T*≈25 K . An anomaly in χ (T ) , indicative of magnetic ordering, is observed at Tmag=16 K . No clear signature of long-range ordering, however, is captured so far in NMR 1 /T1 , specific heat or neutron diffraction measurements at and below Tmag. The marginal magnetic transition, indicative of strong quantum fluctuations, is evidence that Ba2CuTeO6 is in very close proximity to a quantum critical point between magnetically ordered and spin-gapped phases controlled by interladder couplings.
NASA Astrophysics Data System (ADS)
Götze, Oliver; Richter, Johannes
2016-06-01
While the existence of a spin-liquid ground state of the spin-1/2 kagome Heisenberg antiferromagnet (KHAF) is well established, the discussion of the effect of an interlayer coupling (ILC) by controlled theoretical approaches is still lacking. Here we study this problem by using the coupled-cluster method to high orders of approximation. We consider a stacked KHAF with a perpendicular ILC J_\\perp , where we study ferro- as well as antiferromagnetic J_\\perp . We find that the spin-liquid ground state (GS) persists until relatively large strengths of the ILC. Only if the strength of the ILC exceeds about 15% of the intralayer coupling the spin-liquid phase gives way for q = 0 magnetic long-range order, where the transition between both phases is continuous and the critical strength of the ILC, |J^c_\\perp| , is almost independent of the sign of J_\\perp . Thus, by contrast to the quantum GS selection of the strictly two-dimensional KHAF at large spin s, the ILC leads first to a selection of the q = 0 GS. Only at larger |J_\\perp| the ILC drives a first-order transition to the \\sqrt{3}×\\sqrt{3} long-range ordered GS. As a result, the stacked spin-1/2 KHAF exhibits a rich GS phase diagram with two continuous and two discontinuous transitions driven by the ILC.
Spin and orbital ordering in TlMnO3: Neutron diffraction study
NASA Astrophysics Data System (ADS)
Khalyavin, Dmitry D.; Manuel, Pascal; Yi, Wei; Belik, Alexei A.
2016-10-01
Crystal and magnetic structures of the high-pressure stabilized perovskite phase of TlMnO3 have been studied by neutron powder diffraction. The crystal structure involves two types of primary structural distortions: a+b-b- octahedral tilting and antiferrodistortive type of orbital ordering, whose common action reduces the symmetry down to triclinic P 1 ¯ . The orbital pattern and the way it is combined with the octahedral tilting are different from the family of LnMnO3 (Ln = lanthanide or Y) manganites who share with TlMnO3 the same tilting scheme. The experimentally determined magnetic structure with the k =(1 /2 ,0 ,1 /2 ) propagation vector and PS1 ¯ symmetry implies anisotropic exchange interactions with a ferromagnetic coupling within the (1 ,0 ,1 ¯) planes and an antiferromagnetic one between them (A type). The spins in the primary magnetic mode were found to be confined close to the (1 ,0 ,1 ¯) plane, which underlines the predominant role of the single ion anisotropy with the local easy axes of Mn3 + following the Jahn-Teller distortions of the octahedra. In spite of the same octahedral tilting scheme in the perovskite structures of both LnMnO3 and TlMnO3 manganites, a coupling of the secondary ferromagnetic component to the primary A-type spin configuration through antisymmetric exchange interaction is allowed in the former and forbidden in the latter cases.
Magnetic ordering in PrBCO by MaxEnt Muon-Spin Research
NASA Astrophysics Data System (ADS)
Pham, H.; Rafik, L.; Boekema, C.
2007-03-01
Muon-Spin Research (μSR) is used to probe the magnetic ordering of PrBa2Cu3O7. The μSR PrBCO data are analyzed using the Maximum Entropy (ME) technique, a spectral analysis tool more sensitive than Fourier transformation. [1] At low temperature and zero applied field, muons are localized and their Larmor spin-precessions map the internal magnetic fields. For temperatures well below room temperature, ME-μSR analysis yields two unique frequencies (˜1.8 MHz and ˜2.4 MHz) corresponding to two different magnetic field regions (13 mT and 18 mT ) probed by the muon. Previous studies [2, 3] using Fourier analysis and curve fitting have shown only one broad frequency signal. We seek to confirm our new improved findings through dipole field search calculations and ME-μSR simulations at these near-zero μSR frequencies. [1] JC Lee et al, J Appl Phys 95 (2004) 6906; AIP/APS www: Virtual J Applications of Superconductivity, June 2004 V6 Iss11; S. Alves et al, Phys Rev Rapid Comm B49 (1994) 12396. [2] WK Dawson et al, J Appl Phys 69 (1991) 5385. [3] DW Cooke et al, Phys Rev B41 (1990) 4801.
On the zeroth-order hamiltonian for CASPT2 calculations of spin crossover compounds.
Vela, Sergi; Fumanal, Maria; Ribas-Ariño, Jordi; Robert, Vincent
2016-04-15
Complete active space self-consistent field theory (CASSCF) calculations and subsequent second-order perturbation theory treatment (CASPT2) are discussed in the evaluation of the spin-states energy difference (ΔH(elec)) of a series of seven spin crossover (SCO) compounds. The reference values have been extracted from a combination of experimental measurements and DFT + U calculations, as discussed in a recent article (Vela et al., Phys Chem Chem Phys 2015, 17, 16306). It is definitely proven that the critical IPEA parameter used in CASPT2 calculations of ΔH(elec), a key parameter in the design of SCO compounds, should be modified with respect to its default value of 0.25 a.u. and increased up to 0.50 a.u. The satisfactory agreement observed previously in the literature might result from an error cancellation originated in the default IPEA, which overestimates the stability of the HS state, and the erroneous atomic orbital basis set contraction of carbon atoms, which stabilizes the LS states.
Antiferromagnetic S=1/2 Spin Chain Driven by p-Orbital Ordering in CsO2
NASA Astrophysics Data System (ADS)
Riyadi, Syarif; Zhang, Baomin; de Groot, Robert A.; Caretta, Antonio; van Loosdrecht, Paul H. M.; Palstra, Thomas T. M.; Blake, Graeme R.
2012-05-01
We demonstrate, using a combination of experiment and density functional theory, that orbital ordering drives the formation of a one-dimensional (1D) S=1/2 antiferromagnetic spin chain in the 3D rocksalt structure of cesium superoxide (CsO2). The magnetic superoxide anion (O2-) exhibits degeneracy of its 2p-derived molecular orbitals, which is lifted by a structural distortion on cooling. A spin chain is then formed by zigzag ordering of the half-filled superoxide orbitals, promoting a superexchange pathway mediated by the pz orbitals of Cs+ along only one crystal direction. This scenario is analogous to the 3d-orbital-driven spin chain found in the perovskite KCuF3 and is the first example of an inorganic quantum spin system with unpaired p electrons.
NASA Astrophysics Data System (ADS)
Pathak, Anand; Sinha, Sitabhra
2015-09-01
Many complex systems can be represented as networks of dynamical elements whose states evolve in response to interactions with neighboring elements, noise and external stimuli. The collective behavior of such systems can exhibit remarkable ordering phenomena such as chimera order corresponding to coexistence of ordered and disordered regions. Often, the interactions in such systems can also evolve over time responding to changes in the dynamical states of the elements. Link adaptation inspired by Hebbian learning, the dominant paradigm for neuronal plasticity, has been earlier shown to result in structural balance by removing any initial frustration in a system that arises through conflicting interactions. Here we show that the rate of the adaptive dynamics for the interactions is crucial in deciding the emergence of different ordering behavior (including chimera) and frustration in networks of Ising spins. In particular, we observe that small changes in the link adaptation rate about a critical value result in the system exhibiting radically different energy landscapes, viz., smooth landscape corresponding to balanced systems seen for fast learning, and rugged landscapes corresponding to frustrated systems seen for slow learning.
Probing spin ordering in iron-platinum based antiferromagnetic films using neutron diffraction
NASA Astrophysics Data System (ADS)
Mani, Prakash
The antiferromagnetic properties of chemically ordered and epitaxial films of FexPt100-x grown on MgO(111) & MgO(100) and Fe50Pt50- xRhx grown on MgO(100) have been studied with neutron diffraction. Epitaxial films of FexPt 100-x (x = 25, 30) have two kinds of antiferromagnetic ordering. The Neel temperature of spin wave vector QA = (1/2 1/2 0) is T N = 160 K and QB = (1/2 0 0) is TN = 100 K, respectively. Neutron diffraction is used to determine the phase diagram of the antiferromagnetic ordering as a function of composition and temperature. The nature of antiferromagnetic ordering was found to be strongly related to the lattice strain present in the system. Lattice-matched antiferromagnetic/ferromagnetic films offer an ideal layered system to study exchange bias. The loop shifts in FePt3(AF)/CoPt 3(F) multilayers are correlated with rocking curve peak widths, and it has been shown that films with a narrower full-width-half-maximum have a smaller exchange bias. Neutron reflectivity is also applied to CoPt 3/FePt3 multilayers in order to probe layer-specific magnetizations owing to the significant difference in neutron scattering length density between Fe and Co. Fe50Pt50-xRh x (x˜10) exhibits a temperature dependent antiferromagnetic-ferromagnetic-paramagnetic triple point near 400 K. The temperature and composition dependent spin structure of Fe50Pt 50-xRhx alloy films grown on MgO(100) have been determined for the first time with neutron diffraction. Three types of antiferromagnetic orderings were observed: (0 0 1/2), (1/2 1/2 1/2), and (1/2 1/2 3/2). Future studies have been planned to explore a magnetic field induced antiferromagnetic to ferromagnetic transition in Fe50Pt50-xRh x alloy films.
Reentrant spin glass ordering in an Fe-based bulk metallic glass
Luo, Qiang; Shen, Jun
2015-02-07
We report the results of the complex susceptibility, temperature, and field dependence of DC magnetization and the nonequilibrium dynamics of a bulk metallic glass Fe{sub 40}Co{sub 8}Cr{sub 15}Mo{sub 14}C{sub 15}B{sub 6}Er{sub 2}. Solid indication of the coexistence of reentrant spin glass (SG) and ferromagnetic orderings is determined from both DC magnetization and AC susceptibility under different DC fields. Dynamics scaling of AC susceptibility indicates critical slowing down to a reentrant SG state with a static transition temperature T{sub s} = ∼17.8 K and a dynamic exponent zv = ∼7.3. The SG nature is further corroborated from chaos and memory effects, magnetic hysteresis, and aging behavior. We discuss the results in terms of the competition among random magnetic anisotropy and exchange interactions and compare them with simulation predictions.
NASA Astrophysics Data System (ADS)
Fernandes, R. M.; Kivelson, S. A.; Berg, E.
2016-01-01
Recent experiments in optimally hole-doped iron arsenides have revealed a novel magnetically ordered ground state that preserves tetragonal symmetry, consistent with either a charge-spin density wave (CSDW), which displays a nonuniform magnetization, or a spin-vortex crystal (SVC), which displays a noncollinear magnetization. Here we show that, similarly to the partial melting of the usual stripe antiferromagnet into a nematic phase, either of these phases can also melt in two stages. As a result, intermediate paramagnetic phases with vestigial order appears: a checkerboard charge density wave for the CSDW ground state, characterized by an Ising-like order parameter, and a remarkable spin-vorticity density wave for the SVC ground state—a triplet d -density wave characterized by a vector chiral order parameter. We propose experimentally detectable signatures of these phases, show that their fluctuations can enhance the superconducting transition temperature, and discuss their relevance to other correlated materials.
Theory of two-dimensional Fourier transform electron spin resonance for ordered and viscous fluids
NASA Astrophysics Data System (ADS)
Lee, Sanghyuk; Budil, David E.; Freed, Jack H.
1994-10-01
A comprehensive theory for interpreting two-dimensional Fourier transform (2D-FT) electron spin resonance (ESR) experiments that is based on the stochastic Liouville equation is presented. It encompasses the full range of motional rates from fast through very slow motions, and it also provides for microscopic as well as macroscopic molecular ordering. In these respects it is as sophisticated in its treatment of molecular dynamics as the theory currently employed for analyzing cw ESR spectra. The general properties of the pulse propagator superoperator, which describes the microwave pulses in Liouville space, are analyzed in terms of the coherence transfer pathways appropriate for COSY (correlation spectroscopy), SECSY (spin-echo correlation spectroscopy), and 2D-ELDOR (electron-electron double resonance) sequences wherein either the free-induction decay (FID) or echo decay is sampled. Important distinctions are made among the sources of inhomogeneous broadening, which include (a) incomplete spectral averaging in the slow-motional regime, (b) unresolved superhyperfine structure and related sources, and (c) microscopic molecular ordering but macroscopic disorder (MOMD). The differing effects these sources of inhomogeneous broadening have on the two mirror image coherence pathways observed in the dual quadrature 2D experiments, as well as on the auto vs crosspeaks of 2D-ELDOR, is described. The theory is applied to simulate experiments of nitroxide spin labels in complex fluids such as membrane vesicles, where the MOMD model applies and these distinctions are particularly relevant, in order to extract dynamic and ordering parameters. The recovery of homogeneous linewidths from FID-based COSY experiments on complex fluids with significant inhomogeneous broadening is also described. The theory is applied to the ultraslow motional regime, and a simple method is developed to determine rotational rates from the broadening of the autopeaks of the 2D-ELDOR spectra as a
Extracting order parameters from powder EPR lineshapes for spin-labelled lipids in membranes
NASA Astrophysics Data System (ADS)
Schorn, Karl; Marsh, Derek
1997-10-01
The corrections that must be made to the spectral separations of the hyperfine extrema in the pseudo-powder EPR lineshapes from lipid spin labels in randomly oriented membranes have been investigated by spectral simulations that include slow motional components. Using simulation parameters that are able to describe the corresponding experimental spectra rather well, it is found that any correction required to the outer hyperfine splitting, 2 Amax, is small, but that the correction to the inner splitting, 2 Amin, differs from that obtained previously from motional narrowing theory. Both Amax and Amin deduced from the simulated spectra are found to vary almost linearly with the molecular-frame order parameter, Szz. The corrections to Amin are used to obtain order parameters from the experimental line splittings. These are found to be in reasonable agreement with the order parameters derived from direct spectral simulation. The inclusion of slow motional components in the simulations represents an improvement over the correction to Amin that is routinely used for membrane systems and which is based on motional narrowing theory.
ERIC Educational Resources Information Center
Moran, K. D.
The author notes that two trends appear to be developing in litigation over the governance of the public schools. One trend is increasing participation of organized groups in suits against the schools. The other is a greater volume of litigation dealing with open meeting laws and freedom of information acts. Reflecting the second trend, the…
Disorder from order among anisotropic next-nearest-neighbor Ising spin chains in SrHo2O4
Wen, J. -J.; Tian, W.; Garlea, V. O.; ...
2015-02-26
In this study, we describe why Ising spin chains with competing interactions in SrHo2O4 segregate into ordered and disordered ensembles at low temperatures (T). Using elastic neutron scattering, magnetization, and specific heat measurements, the two distinct spin chains are inferred to have Néel (↑↓↑↓) and double-Néel (↑↑↓↓) ground states, respectively. Below TN = 0.68(2)K, the Néel chains develop three-dimensional long range order (LRO), which arrests further thermal equilibration of the double-Néel chains so they remain in a disordered incommensurate state for T below TS = 0.52(2)K. SrHo2O4 distills an important feature of incommensurate low dimensional magnetism: kinetically trapped topological defectsmore » in a quasi–d–dimensional spin system can preclude order in d + 1 dimensions.« less
Negi, D. S. E-mail: ranjan@jncasr.ac.in; Loukya, B.; Datta, R. E-mail: ranjan@jncasr.ac.in
2015-12-07
We report on the observation of Co vacancy (V{sub Co}) induced charge ordering and ferromagnetism in CoO epitaxial thin film. The ordering is associated with the coexistence of commensurate, incommensurate, and discommensurate electronic phases. Density functional theory calculation indicates the origin of ordering in Co atoms undergoing high spin to low spin transition immediately surrounding the V{sub Co(16.6 at. %)}. Electron magnetic chiral dichroism experiment confirms the ferromagnetic signal at uncompensated Co spins. Such a native defects induced coexistence of different electronic phases at room temperature in a simple compound CoO is unique and adds to the richness of the field with the possibility of practical device application.
Static magnetic ordering of CeCu2.1Si2 found by muon spin relaxation
NASA Technical Reports Server (NTRS)
Uemura, Y. J.; Kossler, W. J.; Yu, X. H.; Schone, H. E.; Kempton, J. R.; Stronach, C. E.; Barth, S.; Gygax, F. N.; Hitti, B.; Schenck, A.
1988-01-01
Zero- and longitudinal-field muon spin relaxation measurements on a polycrystal sample of a heavy fermion superconductor CeCu2.1 Si2 (T(c) = 0.7 K) have revealed an onset of static magnetic ordering below T approximately 0.8 K. The line shapes of the observed spectra in zero field indicate a wide distribution of static random local fields at muon sites, suggesting that the ordering is either spin glass or incommensurate spin-density-wave state. The observed width of the random local field at T = 0.05 K corresponds to a small averaged static moment of the order of 0.1 micro-B per formula unit.
Cu nuclear magnetic resonance study of charge and spin stripe order in La1.875Ba0.125CuO4
NASA Astrophysics Data System (ADS)
Pelc, D.; Grafe, H.-J.; Gu, G. D.; Požek, M.
2017-02-01
We present a Cu nuclear magnetic/quadrupole resonance study of the charge stripe ordered phase of LBCO, with detection of previously unobserved ("wiped-out") signal. We show that spin-spin and spin-lattice relaxation rates are strongly enhanced in the charge ordered phase, explaining the apparent signal decrease in earlier investigations. The enhancement is caused by magnetic, rather than charge fluctuations, conclusively confirming the long-suspected assumption that spin fluctuations are responsible for the wipeout effect. Observation of the full Cu signal enables insight into the spin and charge dynamics of the stripe-ordered phase, and measurements in external magnetic fields provide information on the nature and suppression of spin fluctuations associated with charge order. We find glassy spin dynamics, in agreement with previous work, and incommensurate static charge order with charge modulation amplitude similar to other cuprate compounds, suggesting that the amplitude of charge stripes is universal in the cuprates.
S. -H. Baek; Gu, G. D.; Utz, Y.; ...
2015-10-26
We report 139La nuclear magnetic resonance studies performed on a La1.875Ba0.125CuO4 single crystal. The data show that the structural phase transitions (high-temperature tetragonal → low-temperature orthorhombic → low-temperature tetragonal phase) are of the displacive type in this material. The 139La spin-lattice relaxation rate T–11 sharply upturns at the charge-ordering temperature TCO = 54 K, indicating that charge order triggers the slowing down of spin fluctuations. Detailed temperature and field dependencies of the T–11 below the spin-ordering temperature TSO=40 K reveal the development of enhanced spin fluctuations in the spin-ordered state for H ∥ [001], which are completely suppressed for largemore » fields along the CuO2 planes. Lastly, our results shed light on the unusual spin fluctuations in the charge and spin stripe ordered lanthanum cuprates.« less
Observation of correlated spin-orbit order in a strongly anisotropic quantum wire system.
Brand, C; Pfnür, H; Landolt, G; Muff, S; Dil, J H; Das, Tanmoy; Tegenkamp, Christoph
2015-09-10
Quantum wires with spin-orbit coupling provide a unique opportunity to simultaneously control the coupling strength and the screened Coulomb interactions where new exotic phases of matter can be explored. Here we report on the observation of an exotic spin-orbit density wave in Pb-atomic wires on Si(557) surfaces by mapping out the evolution of the modulated spin-texture at various conditions with spin- and angle-resolved photoelectron spectroscopy. The results are independently quantified by surface transport measurements. The spin polarization, coherence length, spin dephasing rate and the associated quasiparticle gap decrease simultaneously as the screened Coulomb interaction decreases with increasing excess coverage, providing a new mechanism for generating and manipulating a spin-orbit entanglement effect via electronic interaction. Despite clear evidence of spontaneous spin-rotation symmetry breaking and modulation of spin-momentum structure as a function of excess coverage, the average spin polarization over the Brillouin zone vanishes, indicating that time-reversal symmetry is intact as theoretically predicted.
Code of Federal Regulations, 2012 CFR
2012-01-01
.... Establishing a Coordinated Government-Wide Initiative to Promote Diversity and Inclusion in the Federal... EO 13583 Establishing a Coordinated Government-Wide Initiative to Promote Diversity and Inclusion in... opportunity, diversity, and inclusion, it is hereby ordered as follows: Section 1. Policy. Our Nation...
Code of Federal Regulations, 2013 CFR
2013-01-01
... Property of the Government of Iran and Iranian Financial Institutions 13599 Order 13599 Presidential... Government of Iran and Iranian Financial Institutions By the authority vested in me as President by the... Iran and other Iranian banks to conceal transactions of sanctioned parties, the deficiencies in...
ERIC Educational Resources Information Center
Mische, Patricia, Ed.
This proceedings focuses on religion and global governance, and addresses what kind of new world order will be present in the 21st century. Members of seven different religious traditions spoke from their perspectives on the contribution of religion to the development of ethical and humane systems of global governance, with special relevance to…
Spin polarized photons from an axially charged plasma at weak coupling: Complete leading order
Mamo, Kiminad A.; Yee, Ho-Ung
2016-03-24
In the presence of (approximately conserved) axial charge in the QCD plasma at finite temperature, the emitted photons are spin aligned, which is a unique P- and CP-odd signature of axial charge in the photon emission observables. We compute this “P-odd photon emission rate” in a weak coupling regime at a high temperature limit to complete leading order in the QCD coupling constant: the leading log as well as the constant under the log. As in the P-even total emission rate in the literature, the computation of the P-odd emission rate at leading order consists of three parts: (1) Comptonmore » and pair annihilation processes with hard momentum exchange, (2) soft t- and u-channel contributions with hard thermal loop resummation, (3) Landau-Pomeranchuk-Migdal resummation of collinear bremsstrahlung and pair annihilation. In conclusion, we present analytical and numerical evaluations of these contributions to our P-odd photon emission rate observable.« less
Order of magnitude improvement of nano-contact spin torque nano-oscillator performance.
Banuazizi, Seyed Amir Hossein; Sani, Sohrab R; Eklund, Anders; Naiini, Maziar M; Mohseni, Seyed Majid; Chung, Sunjae; Dürrenfeld, Philipp; Malm, B Gunnar; Åkerman, Johan
2017-02-02
Spin torque nano-oscillators (STNO) represent a unique class of nano-scale microwave signal generators and offer a combination of intriguing properties, such as nano sized footprint, ultrafast modulation rates, and highly tunable microwave frequencies from 100 MHz to close to 100 GHz. However, their low output power and relatively high threshold current still limit their applicability and must be improved. In this study, we investigate the influence of the bottom Cu electrode thickness (tCu) in nano-contact STNOs based on Co/Cu/NiFe GMR stacks and with nano-contact diameters ranging from 60 to 500 nm. Increasing tCu from 10 to 70 nm results in a 40% reduction of the threshold current, an order of magnitude higher microwave output power, and close to two orders of magnitude better power conversion efficiency. Numerical simulations of the current distribution suggest that these dramatic improvements originate from a strongly reduced lateral current spread in the magneto-dynamically active region.
Stoleriu, Laurentiu E-mail: cristian.enachescu@uaic.ro; Stancu, Alexandru; Enachescu, Cristian E-mail: cristian.enachescu@uaic.ro; Chakraborty, Pradip; Hauser, Andreas
2015-05-07
The recently obtained spin-crossover nanoparticles are possible candidates for applications in the recording media industry as materials for data storage, or as pressure and temperature sensors. For these applications, the intermolecular interactions and interactions between spin-crossover nanoparticles are extremely important, as they may be essential factors in triggering the transition between the two stable phases: the high-spin and low-spin ones. In order to find correlations between the distributions in size and interactions and the transition temperatures distribution, we apply the FORC (First Order Reversal Curves) method, using simulations based on a mechanoelastic model applied to 2D triangular lattices composed of molecules linked by springs and embedded in a surfactant. We consider two Gaussian distributions: one is the size of the nanoparticles and another is the elastic interactions between edge spin-crossover molecules and the surfactant molecules. In order to disentangle the kinetic and non-kinetic parts of the FORC distributions, we compare the results obtained for different temperature sweeping rates. We also show that the presence of few larger particles in a distribution centered around much smaller particles dramatically increases the hysteresis width.
An order-by-disorder process in the cyclic phase of spin-2 condensate with a weak magnetic field
Zheng, Gong-Ping; Xu, Lei-Kuan; Qin, Shuai-Feng; Jian, Wen-Tian; Liang, J.-Q.
2013-07-15
We present in this paper a model study on the “order-by-disorder” process in the cyclic phase of spin-2 condensate, which forms a family of incommensurable, spiral degenerate ground states. On the basis of the ordering mechanism of entropic splitting, it is demonstrated that the energy corrections resulting from quantum fluctuations of disorder lift the accidental degeneracy of the cyclic configurations and thus lead to an eventual spiral order called the cyclic order. The order-by-disorder phenomenon is then realized even if the magnetic field exists. Finally, we show that our theoretic observations can be verified experimentally by direct detection of the cyclic order in the {sup 87}Rb condensate of a spin-2 manifold with a weak magnetic field. -- Highlights: •A model for the order-by-disorder process in the cyclic phase of spin-2 condensate is presented. •The second-order quantum fluctuations of the mean-field states are studied. •The energy corrections lift the accidental degeneracy of the cyclic configurations. •The order-by-disorder phenomenon is realized even if a magnetic field exists. •The theoretic observations can be verified experimentally for {sup 87}Rb condensate.
NASA Astrophysics Data System (ADS)
Yuan, Dongna; Yuan, Jie; Huang, Yulong; Ni, Shunli; Feng, Zhongpei; Zhou, Huaxue; Mao, Yiyuan; Jin, Kui; Zhang, Guangming; Dong, Xiaoli; Zhou, Fang; Zhao, Zhongxian
2016-08-01
Superconducting FeSe single crystals of (001) orientation are synthesized via a hydrothermal ion-release route. An Ising spin-nematic order is identified by our systematic measurements of in-plane angular-dependent magnetoresistance (AMR) and static magnetization. The turn-on temperature of anisotropic AMR signifies the Ising spin-nematic ordering temperature Tsn, below which a twofold rotational symmetry is observed in the iron plane. A downward curvature appears below Tsn in the temperature dependence of static magnetization for the weak in-plane magnetic field as reported previously. Remarkably, we find a universal linear relationship between Tc and Tsn among various superconducting samples, indicating that the spin nematicity and the superconductivity in FeSe have a common microscopic origin.
Disappearance of static magnetic order and evolution of spin fluctuations in Fe1+δSexTe1-x
NASA Astrophysics Data System (ADS)
Xu, Zhijun; Wen, Jinsheng; Xu, Guangyong; Jie, Qing; Lin, Zhiwei; Li, Qiang; Chi, Songxue; Singh, D. K.; Gu, Genda; Tranquada, J. M.
2010-09-01
We report neutron-scattering studies on static magnetic orders and spin excitations in the Fe-based chalcogenide system Fe1+δSexTe1-x with different Fe and Se compositions. Short-range static magnetic order with an in-plane wave vector near the (0.5,0) (using the two-Fe unit cell), together with strong low-energy magnetic excitations is found in all nonsuperconducting samples for Se doping up to 45%. When the static order disappears and bulk superconductivity emerges, the spectral weight of the magnetic excitations shifts to the region of reciprocal space near the in-plane wave vector (0.5, 0.5), corresponding to “collinear” spin correlations. Our results suggest that there is a strong correlation between superconductivity and the character of the magnetic order/fluctuations in this system. Excess Fe appears to be important for stabilizing the magnetic order that competes with superconductivity.
NASA Astrophysics Data System (ADS)
Lai, Kwing To; Valldor, Martin
2017-03-01
We report on the syntheses and characterizations of single crystalline and polycrystalline Sr2Co3S2O3 with a novel crystal structure type. It contains Co–O 2-leg rectangular ladders and necklace ladders. The two ladders share common legs and construct a hybrid spin ladder. A rare meridional heteroleptic octahedral coordination is found for the Co2+ ions in the 2-leg ladder. Within the necklace ladders, the Co2+ ions are in trans-octahedral coordination. An antiferromagnetic order is observed at TN ~ 267 K, while a broad maximum in magnetic susceptibility is found below TN. This relatively high ordering temperature among Co-based ladder compounds is related to the highly anisotropic mer-coordination of the Co2+ ions. The trans-octahedrally coordinated Co2+ ions, on the other hand, corresponds to the possible short-range magnetic correlations through dimers with an effective . This results in a rare situation that spin ordering and spin dimers coexist down to 2 K.
Lai, Kwing To; Valldor, Martin
2017-01-01
We report on the syntheses and characterizations of single crystalline and polycrystalline Sr2Co3S2O3 with a novel crystal structure type. It contains Co–O 2-leg rectangular ladders and necklace ladders. The two ladders share common legs and construct a hybrid spin ladder. A rare meridional heteroleptic octahedral coordination is found for the Co2+ ions in the 2-leg ladder. Within the necklace ladders, the Co2+ ions are in trans-octahedral coordination. An antiferromagnetic order is observed at TN ~ 267 K, while a broad maximum in magnetic susceptibility is found below TN. This relatively high ordering temperature among Co-based ladder compounds is related to the highly anisotropic mer-coordination of the Co2+ ions. The trans-octahedrally coordinated Co2+ ions, on the other hand, corresponds to the possible short-range magnetic correlations through dimers with an effective . This results in a rare situation that spin ordering and spin dimers coexist down to 2 K. PMID:28256576
NASA Astrophysics Data System (ADS)
Kulić, Miodrag L.; Kulić, Igor M.
2003-08-01
The antagonistic interplay of antiferromagnetism (AF) and superconductivity (SC), recently discovered in high-temperature superconductors, is studied in the framework of a microscopic theory. We explain the surprisingly large increase of the magnetic Bragg peak intensity IQ at Q∼( π, π) in the magnetic field H≪ Hc2 at low temperatures 0< T≪ Tc, TAF in La 2- xSr xCuO 4. Good agreement with experimental results is found. The theory predicts large anisotropy of the relative intensity RQ( H)=( IQ( H)- IQ(0))/ IQ(0), i.e. R Q( H∥c -axis)≫R Q( H⊥c -axis) . The quantum ( T=0) phase diagram at H=0 is constructed. The theory also predicts: (i) that the magnetic field can induce the AF order in the SC state; (ii) that the spin-fluctuation (SF) effective coupling constant g<0.1 eV is small, which gives small SC critical temperature Tc (≪40 K)--thus questioning the SF mechanism of pairing in HTS oxides.
Order by disorder in spin-orbit-coupled Bose-Einstein condensates
NASA Astrophysics Data System (ADS)
Barnett, Ryan; Powell, Stephen; Graß, Tobias; Lewenstein, Maciej; Das Sarma, S.
2012-02-01
Motivated by recent experiments, we investigate the system of isotropically interacting bosons with Rashba spin-orbit coupling. At the noninteracting level, there is a macroscopic ground-state degeneracy due to the many ways bosons can occupy the Rashba spectrum. Interactions treated at the mean-field level restrict the possible ground-state configurations, but there remains an accidental degeneracy not corresponding to any symmetry of the Hamiltonian, indicating the importance of fluctuations. By finding analytical expressions for the collective excitations in the long-wavelength limit and through numerical solution of the full Bogoliubov-de Gennes equations, we show that the system condenses into a single-momentum state of the Rashba spectrum via the mechanism of order by disorder. We show that in three dimensions the quantum depletion for this system is small, while the thermal depletion has an infrared logarithmic divergence, which is removed for finite-size systems. In two dimensions, on the other hand, thermal fluctuations destabilize the system.
Order by Disorder in Spin-Orbit Coupled Bose-Einstein Condensates
NASA Astrophysics Data System (ADS)
Barnett, Ryan; Powell, Stephen; Grass, Tobias; Lewenstein, Maciej; Das Sarma, Sankar
2012-02-01
Motivated by recent experiments, we investigate the system of isotropically-interacting bosons with Rashba spin-orbit coupling. At the non-interacting level, there is a macroscopic ground-state degeneracy due to the many ways bosons can occupy the Rashba spectrum. Interactions treated at the mean-field level restrict the possible ground-state configurations, but there remains an accidental degeneracy not corresponding to any symmetry of the Hamiltonian, indicating the importance of fluctuations. By finding analytical expressions for the collective excitations in the long-wavelength limit and through numerical solution of the full Bogoliubov- de Gennes equations, we show that the system condenses into a single momentum state of the Rashba spectrum via the mechanism of order by disorder. We show that in 3D the quantum depletion for this system is small, while the thermal depletion has an infrared logarithmic divergence, which is removed for finite-size systems. In 2D, on the other hand, thermal fluctuations destabilize the system. This work is supported in part by JQI-PFC.
Order and dynamics inside H-PDLC nanodroplets: an ESR spin probe study.
Bacchiocchi, Corrado; Miglioli, Isabella; Arcioni, Alberto; Vecchi, Ilaria; Rai, Kashma; Fontecchio, Adam; Zannoni, Claudio
2009-04-23
We have performed a detailed study of the order and dynamics of the commercially available BL038 liquid crystal (LC) inside nanosized (50-300 nm) droplets of a reflection-mode holographic-polymer dispersed liquid crystal (H-PDLC) device where LC nanodroplet layers and polymer layers are alternately arranged, forming a diffraction grating. We have determined the configuration of the LC local director and derived a model of the nanodroplet organization inside the layers. To achieve this, we have taken advantage of the high sensitivity of the ESR spin probe technique to study a series of temperatures ranging from the nematic to the isotropic phase of the LC. Using also additional information on the nanodroplet size and shape distribution provided by SEM images of the H-PDLC cross section, the observed director configuration has been modeled as a bidimensional distribution of elongated nanodroplets whose long axis is, on the average, parallel to the layers and whose internal director configuration is a uniaxial quasi-monodomain aligned along the nanodroplet long axis. Interestingly, at room temperature the molecules tend to keep their average orientation even when the layers are perpendicular to the magnetic field, suggesting that the molecular organization is dictated mainly by the confinement. This result might explain, at least in part, (i) the need for switching voltages significantly higher and (ii) the observed faster turn-off times in H-PDLCs compared to standard PDLC devices.
Resonant Ultrasound studies of spin- and orbital ordering transitions in RVO3
NASA Astrophysics Data System (ADS)
Koehler, M.; Yan, J.-Q.; Ren, Y.; Sales, B. C.; Mandrus, D.; Keppens, V.
2013-03-01
RVO3 perovskites (R = rare earth) have been shown to undergo multiple spin and orbital transitions due to the Jahn-Teller active V3+ electrons. We have initiated a study of the elastic response of RVO3, (R = Dy, Gd, Ce) as well as Y1-xLaxVO3 (x = 0.05, 0.3, 1) using resonant ultrasound spectroscopy. The temperature-dependence of the elastic response is dominated by the ordering transitions, with transition temperatures that change with the size of the rare earth. For CeVO3 and LaVO3, two transitions are observed, separated by 17K and 2K, respectively. DyVO3 and Y0.95La0.05VO3 show three transitions below 220K while GdVO3 only shows one. The full elastic tensor of Y0 . 7 La0.3VO3 has also been determined from 300K to 50K, yielding the temperature dependence of the 9 orthorhombic elastic moduli. Work at ORNL was supported by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division.
NASA Astrophysics Data System (ADS)
Casanova, David; Rhee, Young Min; Head-Gordon, Martin
2008-04-01
Scaled opposite spin (SOS) second order perturbative corrections to single excitation configuration interaction (CIS) are extended to correctly treat quasidegeneracies between excited states. Two viable methods, termed as SOS-CIS(D0) and SOS-CIS(D1), are defined, implemented, and tested. Each involves one empirical parameter (plus a second for the SOS-MP2 ground state), has computational cost that scales with the fourth power of molecule size, and has storage requirements that are cubic, with only quantities of the rank of single excitations produced and stored during iterations. Tests on a set of low-lying adiabatic valence excitation energies and vertical Rydberg excitations of organic and inorganic molecules show that the empirical parameter can be acceptably transferred from the corresponding nondegenerate perturbation theories without any further fitting. Further tests on higher excited states show that the new methods correctly perform for surface crossings for which nondegenerate approaches fail. Numerical results show that SOS-CIS(D0) appears to treat Rydberg excitations in a more balanced way than SOS-CIS(D1) and is, therefore, likely to be the preferred approach. It should be useful for exploring excited state geometries, transition structures, and conical intersections for states of medium to large organic molecules that are dominated by single excitations.
The stability of steady motion of magnetic domain wall: Role of higher-order spin-orbit torques
He, Peng-Bin Yan, Han; Cai, Meng-Qiu; Li, Zai-Dong
2015-12-14
The steady motion of magnetic domain wall driven by spin-orbit torques is investigated analytically in the heavy/ferromagnetic metal nanowires for three cases with a current transverse to the in-plane and perpendicular easy axis, and along the in-plane easy axis. By the stability analysis of Walker wall profile, we find that if including the higher-order spin-orbit torques, the Walker breakdown can be avoided in some parameter regions of spin-orbit torques with a current transverse to or along the in-plane easy axis. However, in the case of perpendicular anisotropy, even considering the higher-order spin-orbit torques, the velocity of domain wall cannot be efficiently enhanced by the current. Furthermore, the direction of wall motion is dependent on the configuration and chirality of domain wall with a current along the in-plane easy axis or transverse to the perpendicular one. Especially, the direction of motion can be controlled by the initial chirality of domain wall. So, if only involving the spin-orbit mechanism, it is preferable to adopt the scheme of a current along the in-plane easy axis for enhancing the velocity and controlling the direction of domain wall.
ERIC Educational Resources Information Center
Zobl, Helmut
1986-01-01
A review of research about second language learning indicates that nonprimary acquisition is sensitive to the center-periphery distinction. There is clear evidence that this construct has reflexes in interlanguage word order with respect to the probability of native word order influence, difficulty, and order of emergence. (CB)
Tung, L. D.; Ivanov, A.; Schefer, J.; Lees, M. R.; Balakrishnan, G.; Paul, D. McK.
2008-08-01
We report the results of magnetization, heat capacity, and neutron scattering studies of LaVO{sub 3} single crystals. From the neutron-diffraction studies, it was found that the compound is magnetically ordered with a C-type antiferromagnetic spin structure at about 136 K. In the vicinity of the ordering temperature, we also observed hysteresis in the neutron-diffraction data measured on cooling and heating which indicates the first-order nature of the phase transition. In the antiferromagnetically ordered phase, the inelastic neutron scattering studies reveal the presence of a temperature independent c-axis spin-wave gap of about 6 meV which is similar to that previously reported for the sister compound YVO{sub 3}.
Magnetic ordering in the ultrapure site-diluted spin chain materials SrCu1 -xNixO2
NASA Astrophysics Data System (ADS)
Simutis, G.; Thede, M.; Saint-Martin, R.; Mohan, A.; Baines, C.; Guguchia, Z.; Khasanov, R.; Hess, C.; Revcolevschi, A.; Büchner, B.; Zheludev, A.
2016-06-01
The muon spin rotation technique is used to study magnetic ordering in ultrapure samples of SrCu1 -xNixO2 , an archetypical S =1 /2 antiferromagnetic Heisenberg chain system with a small number of S =1 defects. The ordered state in the parent compound is shown to be highly homogeneous, contrary to a previous report [M. Matsuda et al., Phys. Rev. B 55, R11953 (1997), 10.1103/PhysRevB.55.R11953]. Even a minute number of Ni impurities results in inhomogeneous order and a decrease of the transition temperature. At as little as 0.5 % Ni concentration, magnetic ordering is entirely suppressed. The results are compared to previous theoretical studies of weakly coupled spin chains with site defects.
Antiferromagnetic order in a semiconductor quantum well with spin-orbit coupling
NASA Astrophysics Data System (ADS)
Marinescu, D. C.
2015-05-01
An argument is made on the existence of a low-temperature itinerant antiferromagnetic (AF) spin alignment, rather than persistent helical (PH), in the ground state of a two dimensional electron gas in a semiconductor quantum well with linear spin-orbit Rashba-Dresselhaus interaction at equal coupling strengths, α. This result is obtained on account of the opposite-spin single-particle state degeneracy at k = 0 that makes the spin instability possible. A theory of the resulting magnetic phase is formulated within the Hartree-Fock approximation of the Coulomb interaction. In the AF state the direction of the fractional polarization is obtained to be aligned along the displacement vector of the single-particle states.
Exchange-Induced Negative-U Charge Order in N-Doped WO3: A Spin-Peierls-Like System
Huda, M. N.; Yan, Y.; Wei, S.-H.; Al-Jassim, M. M.
2009-01-01
An unconventional spin-Peierls-type distortion was found in a nonmagnetic atom N doped pseudo-one-dimensional WO{sub 3} system. The periodicity of the initial ferromagnetic WO{sub 3}:N is doubled in one direction, and the band gap opens up due to this distortion. The magnetic moment at the N site is asymmetric in the distorted system, and the interaction between the localized spin is very weak. We show that the large exchange interaction of the nitrogen 2p atomic orbital and the pseudo-one-dimensional W-O-W chain in monoclinic WO{sub 3} structure is the origin of this spin-Peierls-like transition that leads to the stabilization of an unusual negative-U charge-ordered system.
Ordering and spin waves in NaNi O2 : A stacked quantum ferromagnet
NASA Astrophysics Data System (ADS)
Lewis, M. J.; Gaulin, B. D.; Filion, L.; Kallin, C.; Berlinsky, A. J.; Dabkowska, H. A.; Qiu, Y.; Copley, J. R. D.
2005-07-01
Neutron scattering measurements on powder NaNiO2 reveal magnetic Bragg peaks and spin waves characteristic of strongly correlated s=1/2 magnetic moments arranged in ferromagnetic layers which are stacked antiferromagnetically. This structure lends itself to stacking sequence frustration in the presence of mixing between nickel and alkali metal sites, possibly providing a natural explanation for the enigmatic spin glass state of the isostructural compound, LiNiO2 .
NASA Astrophysics Data System (ADS)
Will, Clifford M.; Maitra, Matthew
2017-03-01
We derive the secular evolution of the orbital elements of a stellar-mass object orbiting a spinning massive black hole. We use the post-Newtonian (PN) approximation in harmonic coordinates, with test-body equations of motion for the conservative dynamics that are valid through 3PN order, including spin-orbit, quadrupole and (spin) 2 effects, and with radiation-reaction contributions linear in the mass of the body that are valid through 4.5PN order, including the 4PN damping effects of spin-orbit coupling. The evolution equations for the osculating orbit elements are iterated to high PN orders using a two-time-scale approach and averaging over orbital time scales. We derive a criterion for terminating the orbit when its Carter constant drops below a critical value, whereupon the body plunges across the event horizon at the next closest approach. The results are valid for arbitrary eccentricities and arbitrary inclinations. We then analyze numerically the orbits of objects injected into high-eccentricity orbits via interactions within a surrounding star cluster, obtaining the number of orbits and the elapsed time between injection and plunge, and the residual orbital eccentricity at plunge as a function of inclination. We derive an analytic approximation for the time to plunge in terms of initial orbital variables. We show that, if the black hole is spinning rapidly, the flux of gravitational radiation during the final orbit before plunge may be suppressed by as much as 3 orders of magnitude if the orbit is retrograde on the equatorial plane compared to its prograde counterpart.
ERIC Educational Resources Information Center
Parente, Roberto; Feola, Rosangela; Petrone, Michele
2011-01-01
This paper reports an investigation of governance issues in Italian academic spin-offs that arise from the need to balance the powers of two categories of partner: academic inventors and external investors (such as established companies and venture capital funds). The relationship between inventors and external investors, jointly pursuing a…
NASA Astrophysics Data System (ADS)
Buessen, Finn Lasse; Trebst, Simon
2016-12-01
Quantum magnets on kagome lattice geometries in two and three spatial dimensions are archetypal examples of spin systems in which geometric frustration inhibits conventional magnetic ordering and instead benefits the emergence of long-range entangled spin liquids at low temperature. Here we employ a recently developed pseudofermion functional renormalization group (pf-FRG) approach to study the low-temperature quantum magnetism of kagome and hyperkagome spin systems with exchange interactions beyond the nearest-neighbor coupling. We find that next-nearest-neighbor couplings stabilize a variety of magnetic orders as well as induce additional spin liquid regimes, giving rise to rather rich phase diagrams, which we characterize in detail. On a technical level, we find that the pf-FRG approach is in excellent quantitative agreement with high-temperature series expansions over their range of validity and it exhibits a systematic finite-size convergence in the temperature regime below. We discuss notable advantages and some current limitations of the pf-FRG approach in the ongoing search for unconventional forms of quantum magnetism.
Damped spin waves in the intermediate ordered phases in Ni_{3}V_{2}O_{8}
Ehlers, Georg; Podlesnyak, Andrey A.; Frontzek, Matthias D.; Pushkarev, A. V.; Shiryaev, Sergie V.; Barilo, Sergie
2015-06-09
Here, spin dynamics in the intermediate ordered phases (between 4 and 9 K) in Ni_{3}V_{2}O_{8} have been studied with inelastic neutron scattering. It is found that the spin waves are very diffuse, indicative of short lived correlations and the coexistence of paramagnetic moments with the long-range ordered state.
NASA Astrophysics Data System (ADS)
Jin, Fangzhou; Liu, Ying; Geng, Jianpei; Huang, Pu; Ma, Wenchao; Shi, Mingjun; Duan, Chang-Kui; Shi, Fazhan; Rong, Xing; Du, Jiangfeng
2017-01-01
As a fundamental postulate of quantum mechanics, Born's rule assigns probabilities to the measurement outcomes of quantum systems and excludes multiorder quantum interference. Here we report an experiment on a single spin in diamond to test Born's rule by inspecting the third-order quantum interference. The ratio of the third-order quantum interference to the second order in our experiment is bounded to the scale of 1 ×10-3 , which provides a stringent constraint on the potential breakdown of Born's rule.
Spin-orbital short-range order on a honeycomb-based lattice.
Nakatsuji, S; Kuga, K; Kimura, K; Satake, R; Katayama, N; Nishibori, E; Sawa, H; Ishii, R; Hagiwara, M; Bridges, F; Ito, T U; Higemoto, W; Karaki, Y; Halim, M; Nugroho, A A; Rodriguez-Rivera, J A; Green, M A; Broholm, C
2012-05-04
Frustrated magnetic materials, in which local conditions for energy minimization are incompatible because of the lattice structure, can remain disordered to the lowest temperatures. Such is the case for Ba(3)CuSb(2)O(9), which is magnetically anisotropic at the atomic scale but curiously isotropic on mesoscopic length and time scales. We find that the frustration of Wannier's Ising model on the triangular lattice is imprinted in a nanostructured honeycomb lattice of Cu(2+) ions that resists a coherent static Jahn-Teller distortion. The resulting two-dimensional random-bond spin-1/2 system on the honeycomb lattice has a broad spectrum of spin-dimer-like excitations and low-energy spin degrees of freedom that retain overall hexagonal symmetry.
Long-range orders and spin/orbital freezing in the two-band Hubbard model
NASA Astrophysics Data System (ADS)
Steiner, Karim; Hoshino, Shintaro; Nomura, Yusuke; Werner, Philipp
2016-08-01
We solve the orbitally degenerate two-band Hubbard model within dynamical mean field theory and map out the instabilities to various symmetry-broken phases based on an analysis of the corresponding lattice susceptibilities. Phase diagrams as a function of the Hund coupling parameter J are obtained both for the model with rotationally invariant interaction and for the model with Ising-type anisotropy. For negative J , an intraorbital spin-singlet superconducting phase appears at low temperatures, while the normal state properties are characterized by an orbital-freezing phenomenon. This is the negative-J analog of the recently discovered fluctuating-moment induced s -wave spin-triplet superconductivity in the spin-freezing regime of multiorbital models with J >0 .
Antiferromagnetic order in CeCoIn5 oriented by spin-orbital coupling
NASA Astrophysics Data System (ADS)
Mineev, V. P.
2017-01-01
An incommensurate spin-density wave (Q phase) confined inside the superconducting state at high basal plane magnetic field is an unique property of the heavy-fermion metal CeCoIn5. The neutron scattering experiments and the theoretical studies point out that this state come out from the soft mode condensation of magnetic resonance excitations. We show that the fixation of direction of antiferromagnetic modulations by a magnetic field reported by Gerber et al. [Nat. Phys. 10, 126 (2014)], is explained by spin-orbit coupling. This result, obtained on the basis of quite general phenomenological arguments, is supported by the microscopic derivation of the χ z z susceptibility dependence on the mutual orientation of the basal plane magnetic field and the direction of modulation of spin polarization in a multiband metal.
NASA Astrophysics Data System (ADS)
Bishop, R. F.; Li, P. H. Y.; Zinke, R.; Darradi, R.; Richter, J.; Farnell, D. J. J.; Schulenburg, J.
2017-04-01
We use the coupled cluster method (CCM) to study the ground-state properties and lowest-lying triplet excited state of the spin-half XXZ antiferromagnet on the square lattice. The CCM is applied to it to high orders of approximation by using an efficient computer code that has been written by us and which has been implemented to run on massively parallelized computer platforms. We are able therefore to present precise data for the basic quantities of this model over a wide range of values for the anisotropy parameter Δ in the range - 1 ≤ Δ < ∞ of interest, including both the easy-plane (- 1 < Δ < 1) and easy-axis (Δ > 1) regimes, where Δ → ∞ represents the Ising limit. We present results for the ground-state energy, the sublattice magnetization, the zero-field transverse magnetic susceptibility, the spin stiffness, and the triplet spin gap. Our results provide a useful yardstick against which other approximate methods and/or experimental studies of relevant antiferromagnetic square-lattice compounds may now compare their own results. We also focus particular attention on the behaviour of these parameters for the easy-axis system in the vicinity of the isotropic Heisenberg point (Δ = 1) , where the model undergoes a phase transition from a gapped state (for Δ > 1) to a gapless state (for Δ ≤ 1), and compare our results there with those from spin-wave theory (SWT). Interestingly, the nature of the criticality at Δ = 1 for the present model with spins of spin quantum number s =1/2 that is revealed by our CCM results seems to differ qualitatively from that predicted by SWT, which becomes exact only for its near-classical large-s counterpart.
NASA Astrophysics Data System (ADS)
Gudyma, Iurii V.; Maksymov, Artur I.
2012-01-01
In this work the macroscopic phenomenological model of spin-crossover compounds in term of relaxation rate in mean field approach have been comprehensive analyzed. It is given the more accurate description of spin-crossover model, which take into consideration environmental noise influence modeled as interaction with a heath bath. Also we have obtained the distribution of probability density function for different values of multiplicative and additive noise intensity. The correlation between the noises is considered. The calculations of mean first passage time of metastable state for correlated case have been performed.
NASA Astrophysics Data System (ADS)
Gudyma, Iurii V.; Maksymov, Artur I.
2011-09-01
In this work the macroscopic phenomenological model of spin-crossover compounds in term of relaxation rate in mean field approach have been comprehensive analyzed. It is given the more accurate description of spin-crossover model, which take into consideration environmental noise influence modeled as interaction with a heath bath. Also we have obtained the distribution of probability density function for different values of multiplicative and additive noise intensity. The correlation between the noises is considered. The calculations of mean first passage time of metastable state for correlated case have been performed.
Size-dependent magnetic ordering and spin-dynamics in DyPO4 and GdPO4 nanoparticles
Evangelisti, Marco; Sorop, Tibi G; Bakharev, Oleg N; Visser, Dirk; Hillier, Adrian D.; Alonso, Juan; Haase, Markus; Boatner, Lynn A; De Jongh, L. Jos
2011-01-01
Low-temperature magnetic susceptibility and heat capacity measurements on nanoparticles (d 2.6 nm) of the antiferromagnetic compounds DyPO4 (TN = 3:4 K) and GdPO4 (TN = 0:77 K) provide clear demonstrations of finite-size effects, which limit the divergence of the magnetic correlation lengths, thereby suppressing the bulk long-range magnetic ordering transitions. Instead, the incomplete antiferromagnetic order inside the particles leads to the formation of net magnetic moments on the particles. For the nanoparticles of Ising-type DyPO4 superparamagnetic blocking is found in the ac-susceptibility at 1 K, those of the XY-type GdPO4 analogue show a dipolar spin-glass transition at 0:2 K. Monte Carlo simulations for the magnetic heat capacities of both bulk and nanoparticle samples are in agreement with the experimental data. Strong size effects are also apparent in the Dy3+ and Gd3+ spin-dynamics, which were studied by zero-field SR relaxation and high-field 31P-NMR nuclear relaxation measurements. The freezing transitions observed in the ac-susceptibility of the nanoparticles also appear as peaks in the temperature dependence of the zero-field SR rates, but at slightly higher temperatures - as to be expected from the higher frequency of the muon probe. For both bulk and nanoparticles of GdPO4, the muon and 31P-NMR rates are for T 5 K dominated by exchange-narrowed hyperfine broadening arising from the electron spin-spin interactions inside the particles. The dipolar hyperfine interactions acting on the muons and the 31P are, however, much reduced in the nanoparticles. For the DyPO4 analogues the high-temperature rates appear to be fully determined by electron spin-lattice relaxation processes.
Evidence for two-dimensional spin-glass ordering in submonolayer Fe films on cleaved InAs surfaces.
Mochizuki, Toshimitsu; Masutomi, Ryuichi; Okamoto, Tohru
2008-12-31
Magnetotransport measurements have been performed on two-dimensional electron gases formed at InAs(110) surfaces covered with a submonolayer of Fe. Hysteresis in the magnetoresistance, a difference in remanent magnetoresistance between zero-field-cooling procedures and field-cooling procedures, and logarithmic time-dependent relaxation after magnetic field sweep are clearly observed at 1.7 K for a coverage of 0.42 monolayer. These features are associated with spin-glass ordering in the Fe film.
Ordering in Cs2 Cu Cl4 : Possibility of a proximate spin liquid
NASA Astrophysics Data System (ADS)
Isakov, S. V.; Senthil, T.; Kim, Yong Baek
2005-11-01
The layered spiral magnet Cs2CuCl4 displays several interesting properties that have been suggested as evidence of proximity to a two-dimensional quantum spin liquid. In this paper we study a concrete version of this proposal and suggest experiments that can potentially confirm it. We study universal critical properties of two-dimensional frustrated quantum magnets near the quantum phase transition between a spiral magnetic state and a spin liquid state with gapped bosonic spinons in the framework of an O(4)-invariant critical theory proposed earlier [A. Chubukov, T. Senthil, and S. Sachdev, Phys. Rev. Lett. 72, 2089 (1994)]. Direct numerical calculation of the anomalous exponent in spin correlations shows that the critical scattering has broad continua qualitatively similar to experiment. More remarkably we show that the enlarged O(4) symmetry leads to the same slow power-law decay for the vector spin chirality and the Néel correlations. We show how this may be observed through polarized-neutron scattering experiments. A number of other less dramatic consequences of the critical theory are outlined as well.
Spin dynamics, short range order and spin freezing in Y0.5Ca0.5BaCo4O7
Stewart, John Ross; Ehlers, Georg; Fouquet, Peter; Mutka, Hannu; Payen, Christophe; Lortz, Rolf
2011-01-01
Y0.5Ca0.5BaCo4O7 was recently introduced as a possible candidate for capturing some of the predicted classical spin kagome ground-state features. Stimulated by this conjecture, we have taken up a more complete study of the spin correlations in this compound with neutron scattering methods on a powder sample characterized with high-resolution neutron diffraction and the temperature dependence of magnetic susceptibility and specific heat. We have found that the frustrated near-neighbor magnetic correlations involve not only the kagome planes but concern the full Co sublattice, as evidenced by the analysis of the wave-vector dependence of the short-range order. We conclude from our results that the magnetic moments are located on the Co sublattice as a whole and that correlations extend beyond the two-dimensional kagome planes. We identify intriguing dynamical properties, observing high-frequency fluctuations with a Lorentzian linewidth G?20 meV at ambient temperature. On cooling a low-frequency ({approx}1 meV) dynamical component develops alongside the high-frequency fluctuations, which eventually becomes static at temperatures below T {approx} 50 K. The high-frequency response with an overall linewidth of {approx}10 meV prevails at T?2 K, coincident with a fully elastic short-range-ordered contribution.
NASA Astrophysics Data System (ADS)
Lewoczko, April D.
In part I, we investigate gold catalysis in the chemistry of organonitrogen compounds. We examine the adsorption of oxygen, nitrogen and sulfur atoms on the gold (111), (100) and (211) surfaces using density functional theory (DFT). Sulfur atoms bind most strongly, followed by oxygen and nitrogen atoms with stronger adsorption for greater coordination to the surface. We see a trend of stronger adsorption to undercoordinated gold, but find it is non-universal with the adsorption strength trend: (111) > (211) > (100). We consider the diffusion of oxygen, nitrogen and sulfur adatoms and find facile long-range diffusion of oxygen atoms on the (100) surface. Lastly, we compare the adsorption of methylamine on gold to that of a selection of alkylamines, methanol and methanethiol. In each case, the ontop site is preferred with stronger adsorption at low coordinated gold. At oxygen atom coverages of 0.125 -- 0.25 ML on Au (111), we find cooperative adsorption of methylamine and oxygen atoms. Energetic costs for adsorbate tilt from the surface normal and rotation about the gold-nitrogen bond are calculated. While methylamine rotation is barrierless on the (111) and (211) surfaces, it has a low energetic barrier for the 0.125 ML and 0.25 ML O atom pre-covered Au (111) surfaces. In part II, we interpret the experimental mass spectrum of small gas phase manganese sulfide clusters using DFT and elucidate the role of ionicity and spin ordering in sizes with special stability, i.e. magic clusters. We first consider nine low lying minima (MnS)6 structures and reveal antiferromagnetic (AFM) spin ordering with a ˜0.1 eV/pair AFM energy benefit and a ˜0.1 A shrinkage of average Mn-Mn distances over clusters with ferromagnetic (FM) spin ordering. We calculate energetic barriers for interconversion between the two lowest lying (MnS)6 isomers and predict an elevated cluster melting temperature due to increased configurational entropy in a pre-melted state. Second, we demonstrate the
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Spin-driven ordering of Cr in the equiatomic high entropy alloy NiFeCrCo
Niu, C.; Zaddach, A. J.; Oni, A. A.; Sang, X.; LeBeau, J. M.; Koch, C. C.; Irving, D. L.; Hurt, J. W.
2015-04-20
Spin-driven ordering of Cr in an equiatomic fcc NiFeCrCo high entropy alloy (HEA) was predicted by first-principles calculations. Ordering of Cr is driven by the reduction in energy realized by surrounding anti-ferromagnetic Cr with ferromagnetic Ni, Fe, and Co in an alloyed L1{sub 2} structure. The fully Cr-ordered alloyed L1{sub 2} phase was predicted to have a magnetic moment that is 36% of that for the magnetically frustrated random solid solution. Three samples were synthesized by milling or casting/annealing. The cast/annealed sample was found to have a low temperature magnetic moment that is 44% of the moment in the milled sample, which is consistent with theoretical predictions for ordering. Scanning transmission electron microscopy measurements were performed and the presence of ordered nano-domains in cast/annealed samples throughout the equiatomic NiFeCrCo HEA was identified.
Spin-driven ordering of Cr in the equiatomic high entropy alloy NiFeCrCo
NASA Astrophysics Data System (ADS)
Niu, C.; Zaddach, A. J.; Oni, A. A.; Sang, X.; Hurt, J. W.; LeBeau, J. M.; Koch, C. C.; Irving, D. L.
2015-04-01
Spin-driven ordering of Cr in an equiatomic fcc NiFeCrCo high entropy alloy (HEA) was predicted by first-principles calculations. Ordering of Cr is driven by the reduction in energy realized by surrounding anti-ferromagnetic Cr with ferromagnetic Ni, Fe, and Co in an alloyed L12 structure. The fully Cr-ordered alloyed L12 phase was predicted to have a magnetic moment that is 36% of that for the magnetically frustrated random solid solution. Three samples were synthesized by milling or casting/annealing. The cast/annealed sample was found to have a low temperature magnetic moment that is 44% of the moment in the milled sample, which is consistent with theoretical predictions for ordering. Scanning transmission electron microscopy measurements were performed and the presence of ordered nano-domains in cast/annealed samples throughout the equiatomic NiFeCrCo HEA was identified.
NASA Astrophysics Data System (ADS)
Kardash, Maria E.; Dzuba, Sergei A.
2014-12-01
Lipid-cholesterol interactions are responsible for different properties of biological membranes including those determining formation in the membrane of spatial inhomogeneities (lipid rafts). To get new information on these interactions, electron spin echo (ESE) spectroscopy, which is a pulsed version of electron paramagnetic resonance (EPR), was applied to study 3β-doxyl-5α-cholestane (DCh), a spin-labeled analog of cholesterol, in phospholipid bilayer consisted of equimolecular mixture of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and 1,2-dioleoyl-sn-glycero-3-phosphocholine. DCh concentration in the bilayer was between 0.1 mol.% and 4 mol.%. For comparison, a reference system containing a spin-labeled 5-doxyl-stearic acid (5-DSA) instead of DCh was studied as well. The effects of "instantaneous diffusion" in ESE decay and in echo-detected (ED) EPR spectra were explored for both systems. The reference system showed good agreement with the theoretical prediction for the model of spin labels of randomly distributed orientations, but the DCh system demonstrated remarkably smaller effects. The results were explained by assuming that neighboring DCh molecules are oriented in a correlative way. However, this correlation does not imply the formation of clusters of cholesterol molecules, because conventional continuous wave EPR spectra did not show the typical broadening due to aggregation of spin labels and the observed ESE decay was not faster than in the reference system. So the obtained data evidence that cholesterol molecules at low concentrations in biological membranes can interact via large distances of several nanometers which results in their orientational self-ordering.
Kardash, Maria E.; Dzuba, Sergei A.
2014-12-07
Lipid-cholesterol interactions are responsible for different properties of biological membranes including those determining formation in the membrane of spatial inhomogeneities (lipid rafts). To get new information on these interactions, electron spin echo (ESE) spectroscopy, which is a pulsed version of electron paramagnetic resonance (EPR), was applied to study 3β-doxyl-5α-cholestane (DCh), a spin-labeled analog of cholesterol, in phospholipid bilayer consisted of equimolecular mixture of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and 1,2-dioleoyl-sn-glycero-3-phosphocholine. DCh concentration in the bilayer was between 0.1 mol.% and 4 mol.%. For comparison, a reference system containing a spin-labeled 5-doxyl-stearic acid (5-DSA) instead of DCh was studied as well. The effects of “instantaneous diffusion” in ESE decay and in echo-detected (ED) EPR spectra were explored for both systems. The reference system showed good agreement with the theoretical prediction for the model of spin labels of randomly distributed orientations, but the DCh system demonstrated remarkably smaller effects. The results were explained by assuming that neighboring DCh molecules are oriented in a correlative way. However, this correlation does not imply the formation of clusters of cholesterol molecules, because conventional continuous wave EPR spectra did not show the typical broadening due to aggregation of spin labels and the observed ESE decay was not faster than in the reference system. So the obtained data evidence that cholesterol molecules at low concentrations in biological membranes can interact via large distances of several nanometers which results in their orientational self-ordering.
Coupling of Spin and Charge Ordering and Elastic Finescales in Complex Electronic Materials
NASA Astrophysics Data System (ADS)
Lookman, T.; Saxena, A.; Albers, R. C.; Bishop, A. R.; Shenoy, S. R.
2000-03-01
There has been an intense focus in the past decade on complex electronic/magnetic materials such as high temperature cuprate and bismuthate superconductors, colossal magnetoresistance manganites, martensitic (and shape memory) alloys, ferroelectric as well as relaxor titanates and zirconates. Various high-resolution microscopies probing spin, charge and lattice degrees of freedom have revealed new, intrinsically inhomogeneous phases, with complex multiscale patterning over hundreds of lattice spacings. We show that long-range anisotropic strain interactions arising from general elastic compatibility considerations, linking components of the strain tensor, can enable interfaces or atomic-scale defects, to induce global strain textures. Symmetry-allowed couplings between strains and electronic/magnetic variables can then generate effective strain-mediated long-range interactions between these variables. This provides a generic elastic mechanism for mutual multiscale texturing of spin, charge and microstructural variables in the above complex materials.
Federal Register 2010, 2011, 2012, 2013, 2014
2011-07-20
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Liberty and Order in Constitutional Government: Ideas and Issues in "The Federalist Papers."
ERIC Educational Resources Information Center
Patrick, John J.
This publication provides a brief introduction to core ideas of constitutional government in the United State as presented in "The Federalist" by Alexander Hamilton, James Madison, and John Jay. The first of "The Federalists" papers was written by Hamilton, who joined with Jay and Madison in this series of essays to refute the…
Observation of a second metastable spin-ordered state in ferrimagnet Cu2OSeO3
NASA Astrophysics Data System (ADS)
Huang, C. L.; Tseng, K. F.; Chou, C. C.; Mukherjee, S.; Her, J. L.; Matsuda, Y. H.; Kindo, K.; Berger, H.; Yang, H. D.
2011-02-01
dc and ac magnetization measurements were performed on single-crystal Cu2OSeO3 under magnetic field (H) and hydrostatic pressure (P) conditions. Increasing H shifts the ferrimagnetic transition observed at TC~60 K to a higher-temperature region. Moreover, the TC increases linearly and magnetization is enhanced with P. Features of the ladder in the M-vs-H curve or the peak in the dM/dH-vs-H curve are observed at HSF~0.5 kOe, suggesting a competing ordered state under magnetic fields below TC. Remarkably, a second shoulder is observed at ˜1 kOe in the dM/dH-vs-H curve, revealing another metastable spin-ordered state in Cu2OSeO3. This state is retained and enhanced by applying pressure. As H rises to 55 T, no further slope changes in the M-H curve are observed. These magnetic properties indicate a complex spin orientation in the geometrically spin-frustrated system Cu2OSeO3.
A second metastable spin-ordered state on ferrimagnetic single crystal Cu2 OSeO 3
NASA Astrophysics Data System (ADS)
Chou, Chih Chieh; Huang, C. L.; Tseng, K. F.; Mukherjee, S.; Her, J. L.; Matsuda, Y. H.; Kindo, K.; Berger, H.; Yang, H. D.
2011-03-01
DC and AC susceptibilities were executed on ferrimagnetic single crystal Cu 2 OSe O3 under magnetic field (H) and hydrostatic pressure (P) circumstance. With increasing H , the ferrimagnetic transition at TC ~ 60 K tends to a higher temperature. Furthermore, the TC rises with a linear slope and magnetization is enhanced with increasing P . Features of the ladder shown in the M vs. H curve or the peak observed in the d M / d H vs. H curve are noted at HSF ~ 0.5 kOe, exhibiting a competing ordered state in magnetic fields below TC . Remarkably, another shoulder is observed at ~ 1 kOe in the d M / d H vs. H curve, revealing a metastable spin ordered state in Cu 2 OSe O3 . In addition, the novel state is retained and enhanced by applied pressure. However, at H up to 55 T, there is no more observable slop change in magnetization. These magnetic properties suggest a complex spin orientation in the spin-frustrated system Cu 2 OSe O3 .
Spin and orbital ordering in Y_{1-x}La_{x}VO₃
Yan, J.-Q.; Zhou, J.-S.; Cheng, J. G.; Goodenough, J. B.; Ren, Y.; Llobet, A.; McQueeney, R. J.
2011-12-02
The spin and orbital ordering in Y_{1-x}La_{x}VO₃ (0.30 ≤ x ≤ 1.0) has been studied to map out the phase diagram over the whole doping range 0 ≤ x ≤ 1. The phase diagram is compared with that for RVO₃ (R = rare earth or Y) perovskites without A-site variance. For x > 0.20, no long-range orbital ordering was observed above the magnetic ordering temperature T_{N}; the magnetic order is accompanied by a lattice anomaly at a Tt ≤ T_{N} as in LaVO₃. The magnetic ordering below Tt ≤ T_{N} is G type in the compositional range 0.20 ≤ x ≤ 0.40 and C type in the range 0.738 ≤ x ≤ 1.0. Magnetization and neutron powder diffraction measurements point to the coexistence below T_{N} of the two magnetic phases in the compositional range 0.4 < x < 0.738. Samples in the compositional range 0.20 < x ≤ 1.0 are characterized by an additional suppression of a glasslike thermal conductivity in the temperature interval T_{N} < T < T* and a change in the slope of 1/χ(T). We argue that T* represents a temperature below which spin and orbital fluctuations couple together via λL∙S.
Competing nematic, antiferromagnetic, and spin-flux orders in the ground state of bilayer graphene
NASA Astrophysics Data System (ADS)
Lemonik, Y.; Aleiner, I.; Fal'ko, V. I.
2012-06-01
We analyze the phase diagram of bilayer graphene (BLG) at zero temperature and zero doping. Assuming that at high energies the electronic system of BLG can be described within a weak-coupling theory (consistent with the experimental evidence), we systematically study the evolution of the couplings with going from high to low energies. The divergences of the couplings at some energies indicate the tendency towards certain symmetry breakings. Carrying out this program, we found that the phase diagram is determined by microscopic couplings defined on the short distances (initial conditions). We explored all plausible space of these initial conditions and found that the three states have the largest phase volume of the initial couplings: nematic, antiferromagnetic, and spin flux (a.k.a. quantum spin Hall). In addition, ferroelectric and two superconducting phases appear only near the very limits of the applicability of the weak-coupling approach. The paper also contains the derivation and analysis of the renormalization group equations and the group theory classification of all the possible phases which might arise from the symmetry breakings of the lattice, spin rotation, and gauge symmetries of graphene.
NASA Astrophysics Data System (ADS)
Eills, James; Stevanato, Gabriele; Bengs, Christian; Glöggler, Stefan; Elliott, Stuart J.; Alonso-Valdesueiro, Javier; Pileio, Giuseppe; Levitt, Malcolm H.
2017-01-01
We have demonstrated two radiofrequency pulse methods which convert the nuclear singlet order of proton spin pairs into the magnetisation of nearby 13C nuclei. These irradiation schemes work well in the near-equivalence regime of the three-spin system, which applies when the difference in the two 1H-13C couplings is much smaller than the 1H-1H coupling. We use pulse sequences to generate thermally polarized singlet states in a reproducible manner, and study the singlet-to-magnetisation transfer step. Preliminary results demonstrate a parahydrogen-enhanced 13C polarization level of at least 9%, providing a signal enhancement factor of more than 9000, using 50% enriched parahydrogen.
Coupled Nd and B' spin ordering in the double perovskites Nd2NaB'O6 (B' = Ru, Os)
Aczel, Adam A; Bugaris, Dan; Yeon, Jeongho; Dela Cruz, Clarina R; Zur Loye, Hans-Conrad; Nagler, Stephen E
2013-01-01
We present a neutron powder diffraction study of the monoclinic double perovskite systems Nd$_2$NaB$'$O$_6$ (B$'$~$=$~Ru, Os), with magnetic atoms occupying both the A and B$'$ sites. Our measurements reveal coupled spin ordering between the Nd and B$'$ atoms with magnetic transition temperatures of 14~K for Nd$_2$NaRuO$_6$ and 16~K for Nd$_2$NaOsO$_6$. There is a Type I antiferromagnetic structure associated with the Ru and Os sublattices, with the ferromagnetic planes stacked along the c-axis and [110] direction respectively, while the Nd sublattices exhibit complex, canted antiferromagnetism with different spin arrangements in each system.
Low-temperature ordered phases of the spin-1/2 XXZ chain system Cs2CoCl4
NASA Astrophysics Data System (ADS)
Breunig, O.; Garst, M.; Rosch, A.; Sela, E.; Buldmann, B.; Becker, P.; Bohatý, L.; Müller, R.; Lorenz, T.
2015-01-01
In this study the magnetic order of the spin-1/2 XXZ chain system Cs2CoCl4 in a temperature range from 50 mK to 0.5 K and in applied magnetic fields up to 3.5 T is investigated by high-resolution measurements of the thermal expansion and the specific heat. Applying magnetic fields along a or c suppresses TN completely at about 2.1 T. In addition, we find an adjacent intermediate phase before the magnetization saturates close to 2.5 T. For magnetic fields applied along b , a surprisingly rich phase diagram arises. Two additional transitions are observed at critical fields μ0HS F 1≃0.25 T and μ0HS F 2≃0.7 T , which we propose to arise from a two-stage spin-flop transition.
Brünger, C; Assaad, F F; Capponi, S; Alet, F; Aristov, D N; Kiselev, M N
2008-01-11
We consider a spin-1/2 ladder with a ferromagnetic rung coupling J perpendicular and inequivalent chains. This model is obtained by a twist (theta) deformation of the ladder and interpolates between the isotropic ladder (theta=0) and the SU(2) ferromagnetic Kondo necklace model (theta = pi). We show that the ground state in the (theta, J perpendicular) plane has a finite string order parameter characterizing the Haldane phase. Twisting the chain introduces a new energy scale, which we interpret in terms of a Suhl-Nakamura interaction. As a consequence we observe a crossover in the scaling of the spin gap at weak coupling from delta/J parallel proportional, variant J perpendicular/J parallel for theta < theta c approximately 8 pi/9 to delta/J parallel proportional, variant (J perpendicular/J parallel)2 for theta > theta c. Those results are obtained on the basis of large scale quantum Monte Carlo calculations.
Uemura, Y.J.; Kossler, W.J.; Kempton, J.R.; Yu, X.H.; Schone, H.E.; Opie, D.; Stronach, C.E.; Brewer, J.H.; Kiefl, R.F.; Kreitzman, S.R.; Luke, G.M.; Riseman, T.; Williams, D.L.; Ansaldo, E.J.; Endoh, Y.; Kudo, E.; Yamada, K.; Johnston, D.C.; Alvarez, M.; Goshorn, D.P.; Hidaka, Y.; Oda, M; Enomoto, Y.; Suzuki, M.; Murakami, T.
1988-01-01
Muon spin rotation and neutron scattering studies on powder and single-crystal specimens of La/sub 2/CuO/sub 4-v/ are compared. The apparent difference between the muon and neutron results for the ordered moment in the antiferromagnetic state is interpreted as the signature of increasingly short-ranged spatial spin correlations with increasing oxygen content.
NASA Technical Reports Server (NTRS)
Uemura, Y. J.; Kossler, W. J.; Kempton, J. R.; Yu, X. H.; Schone, H. E.; Opie, D.; Stronach, C. E.; Brewer, J. H.; Kiefl, R. F.; Kreitzman, S. R.
1988-01-01
Muon spin rotation and neutron scattering studies on powder and single-crystal specimens of La2CuO(4-y) are compared. The apparent difference between the muon and neutron results for the ordered moment in the antiferromagnetic state is interpreted as the signature of increasingly short-ranged spatial spin correlations with increasing oxygen content.
Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr0.7Ca0.3MnO3
NASA Astrophysics Data System (ADS)
Zhou, S. Y.; Langner, M. C.; Zhu, Y.; Chuang, Y.-D.; Rini, M.; Glover, T. E.; Hertlein, M. P.; Gonzalez, A. G. Cruz; Tahir, N.; Tomioka, Y.; Tokura, Y.; Hussain, Z.; Schoenlein, R. W.
2014-02-01
Electronic orderings of charges, orbitals and spins are observed in many strongly correlated electron materials, and revealing their dynamics is a critical step toward undertsanding the underlying physics of important emergent phenomena. Here we use time-resolved resonant soft x-ray scattering spectroscopy to probe the dynamics of antiferromagnetic spin ordering in the manganite Pr0.7Ca0.3MnO3 following ultrafast photo-exitation. Our studies reveal a glass-like recovery of the spin ordering and a crossover in the dimensionality of the restoring interaction from quasi-1D at low pump fluence to 3D at high pump fluence. This behavior arises from the metastable state created by photo-excitation, a state characterized by spin disordered metallic droplets within the larger charge- and spin-ordered insulating domains. Comparison with time-resolved resistivity measurements suggests that the collapse of spin ordering is correlated with the insulator-to-metal transition, but the recovery of the insulating phase does not depend on the re-establishment of the spin ordering.
Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr₀.₇Ca₀.₃MnO₃.
Zhou, S Y; Langner, M C; Zhu, Y; Chuang, Y-D; Rini, M; Glover, T E; Hertlein, M P; Gonzalez, A G Cruz; Tahir, N; Tomioka, Y; Tokura, Y; Hussain, Z; Schoenlein, R W
2014-02-13
Electronic orderings of charges, orbitals and spins are observed in many strongly correlated electron materials, and revealing their dynamics is a critical step toward undertsanding the underlying physics of important emergent phenomena. Here we use time-resolved resonant soft x-ray scattering spectroscopy to probe the dynamics of antiferromagnetic spin ordering in the manganite Pr₀.₇Ca₀.₃MnO₃ following ultrafast photo-exitation. Our studies reveal a glass-like recovery of the spin ordering and a crossover in the dimensionality of the restoring interaction from quasi-1D at low pump fluence to 3D at high pump fluence. This behavior arises from the metastable state created by photo-excitation, a state characterized by spin disordered metallic droplets within the larger charge- and spin-ordered insulating domains. Comparison with time-resolved resistivity measurements suggests that the collapse of spin ordering is correlated with the insulator-to-metal transition, but the recovery of the insulating phase does not depend on the re-establishment of the spin ordering.
Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr0.7Ca0.3MnO3
Zhou, S. Y.; Langner, M. C.; Zhu, Y.; Chuang, Y. -D.; Rini, M.; Glover, T. E.; Hertlein, M. P.; Gonzalez, A.G. Cruz; Tahir, N.; Tomioka, Y.; Tokura, Y.; Hussain, Z.; Schoenlein, R. W.
2014-01-16
Electronic orderings of charges, orbitals and spins are observed in many strongly correlated electron materials, and revealing their dynamics is a critical step toward understanding the underlying physics of important emergent phenomena. Here we use time-resolved resonant soft x-ray scattering spectroscopy to probe the dynamics of antiferromagnetic spin ordering in the manganite Pr0:7Ca0:3MnO3 following ultrafast photo-exitation. Our studies reveal a glass-like recovery of the spin ordering and a crossover in the dimensionality of the restoring interaction from quasi-1D at low pump fluence to 3D at high pump fluence. This behavior arises from the metastable state created by photo-excitation, a state characterized by spin disordered metallic droplets within the larger charge- and spin-ordered insulating domains. Comparison with time-resolved resistivity measurements suggests that the collapse of spin ordering is correlated with the insulator-to-metal transition, but the recovery of the insulating phase does not depend on the re-establishment of the spin ordering.
Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr0.7Ca0.3MnO3
Zhou, S. Y.; Langner, M. C.; Zhu, Y.; Chuang, Y.-D.; Rini, M.; Glover, T. E.; Hertlein, M. P.; Gonzalez, A. G. Cruz; Tahir, N.; Tomioka, Y.; Tokura, Y.; Hussain, Z.; Schoenlein, R. W.
2014-01-01
Electronic orderings of charges, orbitals and spins are observed in many strongly correlated electron materials, and revealing their dynamics is a critical step toward undertsanding the underlying physics of important emergent phenomena. Here we use time-resolved resonant soft x-ray scattering spectroscopy to probe the dynamics of antiferromagnetic spin ordering in the manganite Pr0.7Ca0.3MnO3 following ultrafast photo-exitation. Our studies reveal a glass-like recovery of the spin ordering and a crossover in the dimensionality of the restoring interaction from quasi-1D at low pump fluence to 3D at high pump fluence. This behavior arises from the metastable state created by photo-excitation, a state characterized by spin disordered metallic droplets within the larger charge- and spin-ordered insulating domains. Comparison with time-resolved resistivity measurements suggests that the collapse of spin ordering is correlated with the insulator-to-metal transition, but the recovery of the insulating phase does not depend on the re-establishment of the spin ordering. PMID:24522173
Resonant soft X-ray scattering—a new probe of charge, spin and orbital ordering in the manganites
NASA Astrophysics Data System (ADS)
Hatton, P. D.; Wilkins, S. B.; Beale, T. A. W.; Johal, T. K.; Prabhakaran, D.; Boothroyd, A. T.
2005-04-01
Soft X-ray resonant diffraction is a new technique pioneered by our group. We have published examples of the huge resonant enhancements of charge and magnetic scattering that can be obtained at the L-edges of 3d transition metal oxides. In this paper we will also show how resonant soft X-ray scattering enables direct observation of orbital ordering. We have studied the low temperature phase of La0.5Sr1.5MnO4 that displays charge, spin and orbital ordering. We have employed resonant soft X-ray scattering at the manganese L edges which provide a direct measurement of the orbital ordering. Energy scans at constant wavevector have been compared to theoretical predictions and show that at all temperatures there are two separate contributions to the observed scattering, direct Goodenough orbital ordering and strong cooperative Jahn-Teller distortions of the Mn ions. Finally, we will show how that the spin and orbital degrees of freedom are strongly correlated in these materials.
Entanglement entropy and topological order in resonating valence-bond quantum spin liquids
NASA Astrophysics Data System (ADS)
Wildeboer, Julia; Seidel, Alexander; Melko, Roger G.
2017-03-01
On the triangular and kagome lattices, short-ranged resonating valence-bond wave functions can be sampled without the sign problem using a recently developed Pfaffian Monte Carlo scheme. In this Rapid Communication, we study the Renyi entanglement entropy in these wave functions using a replica-trick method. Using various spatial bipartitions, including the Levin-Wen construction, our finite-size scaled Renyi entropy gives a topological contribution consistent with γ =ln(2 ) , as expected for a gapped Z2 quantum spin liquid. We prove that the mutual statistics is consistent with the toric code anyon model and rule out any other quasiparticle statistics such as the double semion model.
NASA Astrophysics Data System (ADS)
Huang, Cheng-Yi; Lin, Hsin; Wang, Yung Jui; Bansil, Arun; Tsai, Wei-Feng
2016-05-01
We have investigated spin reorientation phenomena and interaction-driven effects under the presence of applied strains on the (001) surface of Pb1 -xSnx (Te, Se) topological crystalline insulators, which host multiple Dirac cones. Our analysis is based on a four-band k .p model, which captures the spin and orbital textures of the surface states at low energies around the X ¯ and Y ¯ points, including the Lifshitz transition. Even without breaking the time-reversal symmetry, we find that certain strains that break the mirror symmetry can induce a hedgehoglike spin texture associated with gap formation at the Dirac points. The Chern number of the gapped surface ground state is shown to be tunable through the interplay of strains and a perpendicular Zeeman field. We also consider the effects of strain in the presence of interactions in driving competing orders, and we obtain the associated phase diagram at the mean-field level. Potential applications of our results for low power consuming electronics are discussed.
NASA Astrophysics Data System (ADS)
Grabowski, Ireneusz; Fabiano, Eduardo; Teale, Andrew M.; Śmiga, Szymon; Buksztel, Adam; Della Sala, Fabio
2014-07-01
The performance of correlated optimized effective potential (OEP) functionals based on the spin-resolved second-order correlation energy is analysed. The relative importance of singly- and doubly- excited contributions as well as the effect of scaling the same- and opposite- spin components is investigated in detail comparing OEP results with Kohn-Sham (KS) quantities determined via an inversion procedure using accurate ab initio electronic densities. Special attention is dedicated in particular to the recently proposed scaled-opposite-spin OEP functional [I. Grabowski, E. Fabiano, and F. Della Sala, Phys. Rev. B 87, 075103 (2013)] which is the most advantageous from a computational point of view. We find that for high accuracy, a careful, system dependent, selection of the scaling coefficient is required. We analyse several size-extensive approaches for this selection. Finally, we find that a composite approach, named OEP2-SOSh, based on a post-SCF rescaling of the correlation energy can yield high accuracy for many properties, being comparable with the most accurate OEP procedures previously reported in the literature but at substantially reduced computational effort.
Grabowski, Ireneusz; Fabiano, Eduardo; Teale, Andrew M; Śmiga, Szymon; Buksztel, Adam; Della Sala, Fabio
2014-07-14
The performance of correlated optimized effective potential (OEP) functionals based on the spin-resolved second-order correlation energy is analysed. The relative importance of singly- and doubly- excited contributions as well as the effect of scaling the same- and opposite- spin components is investigated in detail comparing OEP results with Kohn-Sham (KS) quantities determined via an inversion procedure using accurate ab initio electronic densities. Special attention is dedicated in particular to the recently proposed scaled-opposite-spin OEP functional [I. Grabowski, E. Fabiano, and F. Della Sala, Phys. Rev. B 87, 075103 (2013)] which is the most advantageous from a computational point of view. We find that for high accuracy, a careful, system dependent, selection of the scaling coefficient is required. We analyse several size-extensive approaches for this selection. Finally, we find that a composite approach, named OEP2-SOSh, based on a post-SCF rescaling of the correlation energy can yield high accuracy for many properties, being comparable with the most accurate OEP procedures previously reported in the literature but at substantially reduced computational effort.
NASA Astrophysics Data System (ADS)
Bennett, Edmund; Mydosh, J. A.
2012-09-01
We summarize the development of strongly correlated electron physics (SCEP) stimu-lated from the 1930's when a strange upturn was found in the electrical resistivity at low temper-atures. It was only in 1965 that this effect was explained as a many-body, spin-flip, scattering of electrons from a magnetic impurity, i.e., the Kondo effect. This marked the beginning of SCEP. When the concentration of these impurities is increased so that they can randomly interact we have the spin glasses and their unconventional, yet classical phase transition. Spin glass physics formed the background know-how for the combination of two ferromagnetic layers separated by a non-magnetic spacer which generated the the giant magnetic resistance and it many applications in com-puter hardware. By fabricating a lattice of the magnetic species, viz., an intermetallic compound based upon certain rare-earth and actinide elements, we then create a heavy Fermi liquid that can support most unusual ground-state behavior, e.g., unconventional superconductivity. This leads to the mysterious and still unexplained "hidden order" phase transition of URu2Si2. Finally, since the heavy fermions commonly exhibit zero temperature phase transitions, aka, quantum phase transitions when tuned with pressure, magnetic field or doping, we are at the summit of today's SCEP - the prime topic of 2012 condensed matter physics.
Grabowski, Ireneusz Śmiga, Szymon; Buksztel, Adam; Fabiano, Eduardo; Teale, Andrew M.; Sala, Fabio Della
2014-07-14
The performance of correlated optimized effective potential (OEP) functionals based on the spin-resolved second-order correlation energy is analysed. The relative importance of singly- and doubly- excited contributions as well as the effect of scaling the same- and opposite- spin components is investigated in detail comparing OEP results with Kohn–Sham (KS) quantities determined via an inversion procedure using accurate ab initio electronic densities. Special attention is dedicated in particular to the recently proposed scaled-opposite–spin OEP functional [I. Grabowski, E. Fabiano, and F. Della Sala, Phys. Rev. B 87, 075103 (2013)] which is the most advantageous from a computational point of view. We find that for high accuracy, a careful, system dependent, selection of the scaling coefficient is required. We analyse several size-extensive approaches for this selection. Finally, we find that a composite approach, named OEP2-SOSh, based on a post-SCF rescaling of the correlation energy can yield high accuracy for many properties, being comparable with the most accurate OEP procedures previously reported in the literature but at substantially reduced computational effort.
Ordering and Spin Waves in NaNiO2: A Stacked Quantum Ferromagnet
NASA Astrophysics Data System (ADS)
Lewis, M. J.; Gaulin, B. D.; Dabkowska, H. A.; Qui, Y.; Copley, J. R. D.
2004-03-01
We have carried out time-of-flight neutron scattering measurements on NaNiO2 using the DCS spectrometer at the NIST Center for Neutron Research. NaNiO2 is made up of alternating triangular layers of NiO and NaO stacked along the c-direction. The conventional picture of the magnetism in this material has it arsing from s=1/2 moments originating from the Ni^3+ oxidation state. Our measurements reveal magnetic Bragg peaks and spin waves characteristic of strongly correlated s=1/2 magnetic moments arranged in ferromagnetic sheets and stacked in an antferromagnetic fashion. This structure lends itself very naturally to stacking sequence frustration in the presence of mixing of the Ni and alkali metal sublattice, a form of disorder known to occur at the 1-3% level in its isostructural sister compound LiNiO_2. We argue that these measurements provide a natural explanation for the enigmatic spin glass state observed in LiNiO_2, which has been a subject of speculation for nearly 20 years.
Ravi, Bolleddu; Chakraborty, Snigdha; Bhattacharjee, Mitradip; Mitra, Shirsendu; Ghosh, Abir; Gooh Pattader, Partho Sarathi; Bandyopadhyay, Dipankar
2017-01-11
Chemical pattern directed spin-dewetting of a macroscopic droplet composed of a dilute organic solution of liquid crystal (LC) formed an ordered array of micro- and nanoscale LC droplets. Controlled evaporation of the spin-dewetted droplets through vacuum drying could further miniaturize the size to the level of ∼90 nm. The size, periodicity, and spacing of these mesoscale droplets could be tuned with the variations in the initial loading of LC in the organic solution, the strength of the centripetal force on the droplet, and the duration of the evaporation. A simple theoretical model was developed to predict the spacing between the spin-dewetted droplets. The patterned LC droplets showed a reversible phase transition from nematic to isotropic and vice versa with the periodic exposure of a solvent vapor and its removal. A similar phase transition behavior was also observed with the periodic increase or reduction of temperature, suggesting their usefulness as vapor or temperature sensors. Interestingly, when the spin-dewetted droplets were confined between a pair of electrodes and an external electric field was applied, the droplets situated at the hydrophobic patches showed light-reflecting properties under the polarization microscopy highlighting their importance in the development of micro- or nanoscale LC displays. The digitized LC droplets, which were stationary otherwise, showed dielectrophoretic locomotion under the guidance of the external electric field beyond a threshold intensity of the field. Remarkably, the motion of these droplets could be restricted to the hydrophilic zones, which were confined between the hydrophobic patches of the chemically patterned surface. The findings could significantly contribute in the development of futuristic vapor or temperature sensors, light reflectors, and self-propellers using the micro- or nanoscale digitized LC droplets.
Gaffney, B J; Marsh, D
1998-10-27
The EPR spectra of spin-labeled lipid chains in fully hydrated bilayer membranes of dimyristoyl phosphatidylcholine containing 40 mol % of cholesterol have been studied in the liquid-ordered phase at a microwave radiation frequency of 94 GHz. At such high field strengths, the spectra should be optimally sensitive to lateral chain ordering that is expected in the formation of in-plane domains. The high-field EPR spectra from random dispersions of the cholesterol-containing membranes display very little axial averaging of the nitroxide g-tensor anisotropy for lipids spin labeled toward the carboxyl end of the sn-2 chain (down to the 8-C atom). For these positions of labeling, anisotropic 14N-hyperfine splittings are resolved in the gzz and gyy regions of the nonaxial EPR spectra. For positions of labeling further down the lipid chain, toward the terminal methyl group, the axial averaging of the spectral features systematically increases and is complete at the 14-C atom position. Concomitantly, the time-averaged
NASA Astrophysics Data System (ADS)
Terasaki, Ichiro; Igarashi, Taichi; Nagai, Takayuki; Tanabe, Kenji; Taniguchi, Hiroki; Matsushita, Taku; Wada, Nobuo; Takata, Atsushi; Kida, Takanori; Hagiwara, Masayuki; Kobayashi, Kensuke; Sagayama, Hajime; Kumai, Reiji; Nakao, Hironori; Murakami, Youichi
2017-03-01
We have discovered a novel candidate for a spin liquid state in a ruthenium oxide composed of dimers of S = 3/2 spins of Ru5+, Ba3ZnRu2O9. This compound lacks a long range order down to 37 mK, which is a temperature 5000-times lower than the magnetic interaction scale of around 200 K. Partial substitution for Zn can continuously vary the magnetic ground state from an antiferromagnetic order to a spin-gapped state through the liquid state. This indicates that the spin-liquid state emerges from a delicate balance of inter- and intra-dimer interactions, and the spin state of the dimer plays a vital role. This unique feature should realize a new type of quantum magnetism.
Antiferromagnetic interaction between A'-site Mn spins in A-site-ordered perovskite YMn3Al4O12.
Tohyama, Takenori; Saito, Takashi; Mizumaki, Masaichiro; Agui, Akane; Shimakawa, Yuichi
2010-03-01
The A-site-ordered perovskite YMn(3)Al(4)O(12) was prepared by high-pressure synthesis. Structural analysis with synchrotron powder X-ray diffraction data and the Mn L-edges X-ray absorption spectrum revealed that the compound has a chemical composition Y(3+)Mn(3+)(3)Al(3+)(4)O(2-)(12) with magnetic Mn(3+) at the A' site and non-magnetic Al(3+) at the B site. An antiferromagnetic interaction between the A'-site Mn(3+) spins is induced by the nearest neighboring Mn-Mn direct exchange interaction and causes an antiferromagnetic transition at 34.3 K.
Anomalous nuclear spin-lattice relaxation of 3He in contact with ordered Al2O3 aerogel
NASA Astrophysics Data System (ADS)
Alakshin, E. M.; Zakharov, M. Yu.; Klochkov, A. V.; Kuzmin, V. V.; Safiullin, K. R.; Stanislavovas, A. A.; Tagirov, M. S.
2016-09-01
Spin-lattice relaxation of 3He in contact with the ordered Al2O3 fiber aerogel has been studied at the temperature of 1.6 K in fields of 0.1-0.5 T by the pulsed nuclear magnetic resonance (NMR) method. An additional mechanism of the relaxation of 3He in aerogels is found and it is shown that this relaxation mechanism is not associated with the adsorbed layer. A hypothesis about the influence of intrinsic paramagnetic centers on the relaxation of gaseous 3He is proposed.
Spin dynamics in pressure-induced magnetically ordered phases in (C4H12N2)Cu2Cl6
Perren, G.; Möller, J. S.; Hüvonen, D.; ...
2015-08-07
In this paper, we present inelastic neutron-scattering experiments on the S=1/2 frustrated gapped quantum magnet piperazinium hexachlorodicuprate (PHCC) under applied hydrostatic pressure. These results show that at 9 kbar the magnetic triplet excitations in the system are gapless, contrary to what was previously reported. Our results are in agreement with recent muon-spin relaxation experiments which found magnetic order above a quantum-critical point at 4.3 kbar. Finally, we show that the changes in the excitation spectrum can be primarily attributed to the change in a single exchange pathway.
Development of High-Order Methods for Multi-Physics Problems Governed by Hyperbolic Equations
2010-10-01
the conservative variable state vector: U = ρ ρu ρv ρE , and F (U) is the inviscid flux tensor with vector components: f = ρu ρu2 + p ρuv...ρE + p )u , g = ρv ρuv ρv2 + p (ρE + p )v . The specific energy E is the sum of the specific internal energy e and the kinetic energy...the constitutive relations: e = CV T, p = (γ − 1) [ ρE − ρ 2 (u2 + v2) ] . 0.3 Discretization method The governing equations of fluid motion, given
Zhang, Qiang; Fernandes, Rafael M.; Lamsal, Jagat; ...
2015-02-04
Inelastic neutron scattering is employed to investigate the impact of electronic nematic order on the magnetic spectra of LaFeAsO and Ba(Fe0.953Co0.047)2As2. These materials are ideal to study the paramagnetic-nematic state, since the nematic order, signaled by the tetragonal-to-orthorhombic transition at TS, sets in well above the stripe antiferromagnetic ordering at TN. We find that the temperature-dependent dynamic susceptibility displays an anomaly at TS followed by a sharp enhancement in the spin-spin correlation length, revealing a strong feedback effect of nematic order on the low-energy magnetic spectrum. As a result, our findings can be consistently described by a model that attributesmore » the structural or nematic transition to magnetic fluctuations, and unveils the key role played by nematic order in promoting the long-range stripe antiferromagnetic order in iron pnictides.« less
Field-controlled spin-density-wave order and quantum critically in Sr3 Ru2 O7
NASA Astrophysics Data System (ADS)
Hayden, Stephen
The quasi-2D metamagnetic perovskite metal Sr3Ru2O7 has been an enigma for the last decade. The application of a large magnetic field of 8T parallel to the c-axis creates a new phase at low temperatures. This phase shows ``electronic nematic'' properties in that strong anisotropy its resistivity can be created by tilting the field away from the c-axis. In addition, measurement of transport and thermodynamic properties suggest that the phase is at the centre of a quantum critical region. Here we use neutron scattering to show that the magnetic field actually induces spin-density-wave magnetic order in the proximity of a metamagnetic critical endpoint. In fact, Sr3Ru2O7 can be tuned through two magnetically-ordered SDW states which exist over relatively small ranges in field (< 0.4 T). Their origin is probably due to the electronic fine structure near the Fermi energy. The magnetic field direction is shown to control the SDW domain populations which naturally explains the strong resistivity anisotropy or ''electronic nematic'' behaviour observed in this material. We find that Sr3Ru2O7 is also unique in that its the quantum critical region is controlled by overdamped incommensurate low-energy spin fluctuations with a diverging relaxation time. The low-energy electronic properties reflect the presence of these fluctuations and, in particular, the field-dependent low-temperature specific heat is proportional to the spin relaxation rate. [Based on C. Lester, S. Ramos, R. S. Perry at el. Natural Materials 14, 373 (2015).
Magnetic ordering and spin-reorientation transitions in TbCo{sub 3}B{sub 2}
Dubman, Moshe; Caspi, El'ad N.; Ettedgui, Hanania; Keller, Lukas; Melamud, Mordechai; Shaked, Hagai
2005-07-01
The magnetic structure of the compound TbCo{sub 3}B{sub 2} has been studied in the temperature range 1.5 K{<=}T{<=}300 K by means of neutron powder diffraction, magnetization, magnetic ac susceptibility, and heat capacity measurements. The compound is of hexagonal symmetry and is paramagnetic at 300 K, undergoes a magnetic Co-Co ordering transition at {approx}170 K, and a second magnetic Tb-Tb ordering transition at {approx}30 K. The latter induces a spin-reorientation transition, in which the magnetic axis rotates from the c axis toward the basal plane. Below this transition a symmetry decrease ({gamma} magnetostriction) sets in, leading to an orthorhombic distortion of the crystal lattice. The crystal and magnetic structures and interactions and their evolution with temperature are discussed using a microscopic physical model.
Nakajima, Yuya; Seino, Junji; Nakai, Hiromi
2013-12-28
In this study, the analytical energy gradient for the spin-free infinite-order Douglas-Kroll-Hess (IODKH) method at the levels of the Hartree-Fock (HF), density functional theory (DFT), and second-order Møller-Plesset perturbation theory (MP2) is developed. Furthermore, adopting the local unitary transformation (LUT) scheme for the IODKH method improves the efficiency in computation of the analytical energy gradient. Numerical assessments of the present gradient method are performed at the HF, DFT, and MP2 levels for the IODKH with and without the LUT scheme. The accuracies are examined for diatomic molecules such as hydrogen halides, halogen dimers, coinage metal (Cu, Ag, and Au) halides, and coinage metal dimers, and 20 metal complexes, including the fourth-sixth row transition metals. In addition, the efficiencies are investigated for one-, two-, and three-dimensional silver clusters. The numerical results confirm the accuracy and efficiency of the present method.
Maurice, Rémi; Réal, Florent; Gomes, André Severo Pereira; Vallet, Valérie; Montavon, Gilles; Galland, Nicolas
2015-03-07
The nature of chemical bonds in heavy main-group diatomics is discussed from the viewpoint of effective bond orders, which are computed from spin-orbit wave functions resulting from spin-orbit configuration interaction calculations. The reliability of the relativistic correlated wave functions obtained in such two-step spin-orbit coupling frameworks is assessed by benchmark studies of the spectroscopic constants with respect to either experimental data, or state-of-the-art fully relativistic correlated calculations. The I2, At2, IO(+), and AtO(+) species are considered, and differences and similarities between the astatine and iodine elements are highlighted. In particular, we demonstrate that spin-orbit coupling weakens the covalent character of the bond in At2 even more than electron correlation, making the consideration of spin-orbit coupling compulsory for discussing chemical bonding in heavy (6p) main group element systems.
NASA Astrophysics Data System (ADS)
Maurice, Rémi; Réal, Florent; Gomes, André Severo Pereira; Vallet, Valérie; Montavon, Gilles; Galland, Nicolas
2015-03-01
The nature of chemical bonds in heavy main-group diatomics is discussed from the viewpoint of effective bond orders, which are computed from spin-orbit wave functions resulting from spin-orbit configuration interaction calculations. The reliability of the relativistic correlated wave functions obtained in such two-step spin-orbit coupling frameworks is assessed by benchmark studies of the spectroscopic constants with respect to either experimental data, or state-of-the-art fully relativistic correlated calculations. The I2, At2, IO+, and AtO+ species are considered, and differences and similarities between the astatine and iodine elements are highlighted. In particular, we demonstrate that spin-orbit coupling weakens the covalent character of the bond in At2 even more than electron correlation, making the consideration of spin-orbit coupling compulsory for discussing chemical bonding in heavy (6p) main group element systems.
NMR probing of spin and charge order near odd-integer filling in the second Landau level
NASA Astrophysics Data System (ADS)
Rhone, T. D.; Tiemann, L.; Muraki, K.
2015-07-01
Studies of spin degrees of freedom near odd-integer filling ν =3 in the second Landau level have engendered conflicting accounts of the spin properties in this regime. Using resistively detected NMR as a probe of local spin density, we explore the nature of the ground state in the quantum Hall regime near ν =3 . Our Knight shift measurements reveal anomalies in NMR spectral line shapes near ν =3 , which demonstrate the presence of solid phases formed from charged quasiparticles, with maximal spin polarization (i.e., no additional spin flips) at each ν . The long nuclear spin relaxation times demonstrate the absence of Skyrmions, or spin textures, in this phase. On the basis of these observations, we attempt to reconcile conflicting reports on the quasiparticle properties and spin wave excitations at ν ˜3 , which may engender new paradigms for the understanding of spin excitations in a collinear ferromagnet with broken translational symmetry.
Spin-1/2 kagome XXZ model in a field: Competition between lattice nematic and solid orders
NASA Astrophysics Data System (ADS)
Kshetrimayum, Augustine; Picot, Thibaut; Orús, Román; Poilblanc, Didier
2016-12-01
We study numerically the spin-1/2 XXZ model in a field on an infinite kagome lattice. We use different algorithms based on infinite projected entangled pair states (iPEPSs) for this, namely, (i) an approach with simplex tensors and a 9-site unit cell, and (ii) an approach based on coarse-graining three spins in the kagome lattice and mapping it to a square-lattice model with local and nearest-neighbor interactions, with the usual PEPS tensors, 6- and 12-site unit cells. Similarly to our previous calculation at the SU(2)-symmetric point (Heisenberg Hamiltonian), for any anisotropy from the Ising limit to the XY limit, we also observe the emergence of magnetization plateaus as a function of the magnetic field, at mz=1/3 using 6-, 9-, and 12-site PEPS unit cells, and at mz=1/9 ,5/9 , and 7/9 using a 9-site PEPS unit cell, the latter setup being able to accommodate √{3 }×√{3 } solid order. We also find that, at mz=1/3 , (lattice) nematic and √{3 }×√{3 } VBC-order states are degenerate within the accuracy of the nine-site simplex method, for all anisotropy. The 6- and 12-site coarse-grained PEPS methods produce almost-degenerate nematic and 1 ×2 VBC-solid orders. We also find that, within our accuracy, the six-site coarse-grained PEPS method gives slightly lower energies, which can be explained by the larger amount of entanglement this approach can handle, even in cases where the PEPS unit cell is not commensurate with the expected ground-state unit cell. Furthermore, we do not observe chiral spin liquid behaviors at and close to the XY point, as has been recently proposed. Our results are the first tensor network investigations of the XXZ model in a field and reveal the subtle competition between nearby magnetic orders in numerical simulations of frustrated quantum antiferromagnets, as well as the delicate interplay between energy optimization and symmetry in tensor network numerical simulations.
Relaxation of antiferromagnetic order in spin-1/2 chains following a quantum quench.
Barmettler, Peter; Punk, Matthias; Gritsev, Vladimir; Demler, Eugene; Altman, Ehud
2009-04-03
We study the unitary time evolution of antiferromagnetic order in anisotropic Heisenberg chains that are initially prepared in a pure quantum state far from equilibrium. Our analysis indicates that the antiferromagnetic order imprinted in the initial state vanishes exponentially. Depending on the anisotropy parameter, oscillatory or nonoscillatory relaxation dynamics is observed. Furthermore, the corresponding relaxation time exhibits a minimum at the critical point, in contrast to the usual notion of critical slowing down, from which a maximum is expected.
Stripe order on the spin-1 stacked honeycomb lattice in Ba2Ni (PO4)2
NASA Astrophysics Data System (ADS)
Yogi, Arvind; Bera, A. K.; Maurya, Arvind; Kulkarni, Ruta; Yusuf, S. M.; Hoser, A.; Tsirlin, A. A.; Thamizhavel, A.
2017-01-01
We report a comprehensive investigation of the crystal structure and magnetic behavior of the S =1 compound Ba2Ni (PO4)2 with a honeycomblike topology of the spin lattice. Magnetic susceptibility and specific-heat data reveal two successive transitions at TN 1=5 K and TN 2=4.6 K . Additionally, these data demonstrate a broad peak at Tmax˜8 K , indicative of the short-range magnetic order above TN 1, whereas below TN 1 field-induced transitions around 4 and 10 T are identified from the magnetization measurements. Neutron diffraction in zero field establishes stripe antiferromagnetic order below TN 2 with the ordered moment of 1.75 (8 ) μB/Ni2 + at 1.5 K. Density-functional band-structure calculations reveal the leading interaction J3=3.5 K running perpendicular to the honeycomb planes, and weaker interactions J1=0.5 K and J4=1.8 K within the honeycomb planes, whereas the stripe order is stabilized by the diagonal interlayer interaction J2=1.3 K that frustrates J1. This is in contrast to the usually expected scenario where the competing second- and third-neighbor interactions on the honeycomb lattice stabilize the stripe order. The Ni2 + ions feature a sizable easy-plane anisotropy A ≃10.5 K , but the position of the easy plane changes from one atom to another, thus amplifying magnetic frustration.
Elastic Membrane Deformations Govern Interleaflet Coupling of Lipid-Ordered Domains
NASA Astrophysics Data System (ADS)
Galimzyanov, Timur R.; Molotkovsky, Rodion J.; Bozdaganyan, Marine E.; Cohen, Fredric S.; Pohl, Peter; Akimov, Sergey A.
2015-08-01
The mechanism responsible for domain registration in two membrane leaflets has thus far remained enigmatic. Using continuum elasticity theory, we show that minimum line tension is achieved along the rim between thicker (ordered) and thinner (disordered) domains by shifting the rims in opposing leaflets by a few nanometers relative to each other. Increasing surface tension yields an increase in line tension, resulting in larger domains. Because domain registration is driven by lipid deformation energy, it does not require special lipid components or interactions at the membrane midplane.
ELASTIC MEMBRANE DEFORMATIONS GOVERN INTERLEAFLET COUPLING OF LIPID-ORDERED DOMAINS
Galimzyanov, Timur R.; Molotkovsky, Rodion J.; Bozdaganyan, Marine E.; Cohen, Fredric S.; Pohl, Peter; Akimov, Sergey A.
2016-01-01
The mechanism responsible for domain registration in two membrane leaflets has thus far remained enigmatic. Using continuum elasticity theory, we show that minimum line tension is achieved along the rim between thicker (ordered) and thinner (disordered) domains by shifting the rims in opposing leaflets by a few nanometers relative to each other. Increasing surface tension yields an increase in line tension, resulting in larger domains. Because domain registration is driven by lipid deformation energy, it does not require special lipid components nor interactions at the membrane midplane. PMID:26340212
Stan, Raluca-Maria; Gaina, Roxana; Enachescu, Cristian E-mail: radu.tanasa@uaic.ro; Stancu, Alexandru; Tanasa, Radu E-mail: radu.tanasa@uaic.ro; Bronisz, Robert
2015-05-07
In this paper, we analyze two types of hysteresis in spin crossover molecular magnets compounds in the framework of the First Order Reversal Curve (FORC) method. The switching between the two stable states in these compounds is accompanied by hysteresis phenomena if the intermolecular interactions are higher than a threshold. We have measured the static thermal hysteresis (TH) and the kinetic light induced thermal hysteresis (LITH) major loops and FORCs for the polycrystalline Fe(II) spin crossover compound [Fe{sub 1−x}Zn{sub x}(bbtr){sub 3}](ClO{sub 4}){sub 2} (bbtr = 1,4-di(1,2,3-triazol-1-yl)butane), either in a pure state (x = 0) or doped with Zn ions (x = 0.33) considering different sweeping rates. Here, we use this method not only to infer the domains distribution but also to disentangle between kinetic and static components of the LITH and to estimate the changes in the intermolecular interactions introduced by dopants. We also determined the qualitative relationship between FORC distributions measured for TH and LITH.
Large-Gap Quantum Spin Hall State in MXenes: d-Band Topological Order in a Triangular Lattice.
Si, Chen; Jin, Kyung-Hwan; Zhou, Jian; Sun, Zhimei; Liu, Feng
2016-10-12
MXenes are a large family of two-dimensional (2D) early transition metal carbides that have shown great potential for a host of applications ranging from electrodes in supercapacitors and batteries to sensors to reinforcements in polymers. Here, on the basis of first-principles calculations, we predict that Mo2MC2O2 (M = Ti, Zr, or Hf), belonging to a recently discovered new class of MXenes with double transition metal elements in an ordered structure, are robust quantum spin Hall (QSH) insulators. A tight-binding (TB) model based on the dz(2)-, dxy-, and dx(2)-y(2)-orbital basis in a triangular lattice is also constructed to describe the QSH states in Mo2MC2O2. It shows that the atomic spin-orbit coupling (SOC) strength of M totally contributes to the topological gap at the Γ point, a useful feature advantageous over the usual cases where the topological gap is much smaller than the atomic SOC strength based on the classic Kane-Mele (KM) or Bernevig-Hughes-Zhang (BHZ) model. Consequently, Mo2MC2O2 show sizable gaps from 0.1 to 0.2 eV with different M atoms, sufficiently large for realizing room-temperature QSH effects. Another advantage of Mo2MC2O2 MXenes lies in their oxygen-covered surfaces which make them antioxidative and stable upon exposure to air.
Adaptive rheology and ordering of cell cytoskeleton govern matrix rigidity sensing
Gupta, Mukund; Sarangi, Bibhu Ranjan; Deschamps, Joran; Nematbakhsh, Yasaman; Callan-Jones, Andrew; Margadant, Felix; Mège, René-Marc; Lim, Chwee Teck; Voituriez, Raphaël; Ladoux, Benoît
2015-01-01
Matrix rigidity sensing regulates a large variety of cellular processes and has important implications for tissue development and disease. However, how cells probe matrix rigidity, and hence respond to it, remains unclear. Here, we show that rigidity sensing and adaptation emerge naturally from actin cytoskeleton remodeling. Our in vitro experiments and theoretical modeling demonstrate a bi-phasic rheology of the actin cytoskeleton, which transitions from fluid on soft substrates to solid on stiffer ones. Furthermore, we find that increasing substrate stiffness correlates with the emergence of an orientational order in actin stress fibers, which exhibit an isotropic to nematic transition that we characterize quantitatively in the framework of active matter theory. These findings imply mechanisms mediated by a large-scale reinforcement of actin structures under stress, which could be the mechanical drivers of substrate stiffness dependent cell shape changes and cell polarity. PMID:26109233
Matzen, S.; Moussy, J.-B.; Wei, P.; Gatel, C.; Cezar, J. C.; Arrio, M. A.; Sainctavit, Ph.; Moodera, J. S.
2014-05-05
NiFe{sub 2}O{sub 4}(111) ultrathin films (3–5 nm) have been grown by oxygen-assisted molecular beam epitaxy and integrated as effective spin-filter barriers. Structural and magnetic characterizations have been performed in order to investigate the presence of defects that could limit the spin filtering efficiency. These analyses have revealed the full strain relaxation of the layers with a cationic order in agreement with the inverse spinel structure but also the presence of antiphase boundaries. A spin-polarization up to +25% has been directly measured by the Meservey-Tedrow technique in Pt(111)/NiFe{sub 2}O{sub 4}(111)/γ-Al{sub 2}O{sub 3}(111)/Al tunnel junctions. The unexpected positive sign and relatively small value of the spin-polarization are discussed, in comparison with predictions and previous indirect tunnelling magnetoresistance measurements.
Incommensurate magnetic order in Ag2NiO2 studied with muon-spin-rotation and relaxation spectroscopy
NASA Astrophysics Data System (ADS)
Sugiyama, J.; Ikedo, Y.; Mukai, K.; Brewer, J. H.; Ansaldo, E. J.; Morris, G. D.; Chow, K. H.; Yoshida, H.; Hiroi, Z.
2006-06-01
The nature of the magnetic transition of the half-filled triangular antiferromagnet Ag2NiO2 with TN=56K was studied with positive muon-spin-rotation and relaxation (μ+SR) spectroscopy. Zero field μ+SR measurements indicate the existence of a static internal magnetic field at temperatures below TN . Two components with slightly different precession frequencies and wide internal-field distributions suggest the formation of an incommensurate antiferromagnetic order below 56K . This implies that the antiferromagnetic interaction is predominant in the NiO2 plane in contrast to the case of the related compound NaNiO2 . An additional transition was found at ˜22K by both μ+SR and susceptibility measurements. It was also clarified that the transition at ˜260K observed in the susceptibility of Ag2NiO2 is induced by a purely structural transition.
The local and long-range structural order of the spin-glass pyrochlore, Tb2Mo2O7
Ehlers, Georg; Jiang, Yu; Booth, Corwin H; Greedan, John E; Gardner, Jason; Huq, Ashfia
2011-01-01
To understand the origin of the spin-glass state in molybdate pyrochlores, the structure of Tb2Mo2O7 is investigated using two techniques: the long-range lattice structure was measured using neutron powder diffraction (NPD), and the local structure information was obtained from extended x-ray absorption fine structure (EXAFS) measurements. While the long-range structure appears well ordered, apart from some enhanced mean-squared site displacements, the local structure measurements indicate nearest-neighbor disorder exists, similar to that found in the related spinglass pyrochlore, Y2Mo2O7. Although the freezing temperature in Tb2Mo2O7, 25 K, is slightly higher than in Y2Mo2O7, 22 K, the degree of local bond disorder is actually less in Tb2Mo2O7. This apparaent contradiction is considered in light of the interactions involved in the freezing process.
NASA Astrophysics Data System (ADS)
Levchenko, A.; Vavilov, M. G.; Khodas, M.; Chubukov, A. V.
2013-04-01
Recent measurements of the doping dependence of the London penetration depth λ(x) at low T in clean samples of isovalent BaFe2(As1-xPx)2 at T≪Tc [Hashimoto et al., Science 336, 1554 (2012)SCIEAS0036-8075] revealed a peak in λ(x) near optimal doping x=0.3. The observation of the peak at T≪Tc, points to the existence of a quantum critical point beneath the superconducting dome. We associate such a quantum critical point with the onset of a spin-density-wave order and show that the renormalization of λ(x) by critical magnetic fluctuations gives rise to the observed feature. We argue that the case of pnictides is conceptually different from a one-component Galilean invariant Fermi liquid, for which correlation effects do not cause the renormalization of the London penetration depth at T=0.
Reversed Crystal-Field Splitting and Spin-Orbital Ordering in α-Sr2CrO4
NASA Astrophysics Data System (ADS)
Ishikawa, Takashi; Toriyama, Tatsuya; Konishi, Takehisa; Sakurai, Hiroya; Ohta, Yukinori
2017-03-01
The origin of successive phase transitions observed in the layered perovskite α-Sr2CrO4 is studied by the density-functional-theory-based electronic structure calculation and mean-field analysis of the proposed low-energy effective model. We find that, despite the fact that the CrO6 octahedron is elongated along the c-axis of the crystal structure, the crystal-field level of nondegenerate 3dxy orbitals of the Cr ion is lower in energy than that of doubly degenerate 3dyz and 3dxz orbitals, giving rise to the orbital degrees of freedom in the system with a 3d2 electron configuration. We show that the higher (lower) temperature phase transition is caused by the ordering of the orbital (spin) degrees of freedom.
Striped superconductors: how spin, charge and superconducting orders intertwine in the cuprates
NASA Astrophysics Data System (ADS)
Berg, Erez; Fradkin, Eduardo; Kivelson, Steven A.; Tranquada, John M.
2009-11-01
Recent transport experiments in the original cuprate high temperature superconductor, La2-xBaxCuO4, have revealed a remarkable sequence of transitions and crossovers that give rise to a form of dynamical dimensional reduction, in which a bulk crystal becomes essentially superconducting in two directions while it remains poorly metallic in the third. We identify these phenomena as arising from a distinct new superconducting state, the 'striped superconductor', in which the superconducting order is spatially modulated, so that its volume average value is zero. Here, in addition to outlining the salient experimental findings, we sketch the order parameter theory of the state, stressing some of the ways in which a striped superconductor differs fundamentally from an ordinary (uniform) superconductor, especially concerning its response to quenched randomness. We also present the results of density matrix renormalization group calculations on a model of interacting electrons in which sign oscillations of the superconducting order are established. Finally, we speculate concerning the relevance of this state to experiments in other cuprates, including recent optical studies of La2-xSrxCuO4 in a magnetic field, neutron scattering experiments in underdoped YBa2Cu3O6+x and a host of anomalies seen in STM and ARPES studies of Bi2Sr2CaCu2O8+δ.
NASA Astrophysics Data System (ADS)
Kaul, S. N.; Messala, Umasankar
2016-03-01
Weak itinerant-electron ferromagnet Ni3Al is driven to magnetic instability (quantum critical point, QCP, where the long-range ferromagnetic order of the bulk ceases to exist) by reducing the average crystallite size to d=50 nm. 'Zero-field' (H=0) linear and nonlinear ac-susceptibilities, measured on Ni3Al nanoparticle aggregates, with d=50 nm (S1) and d=5 nm (S2), provide strong evidence for two spin glass (SG)-like thermodynamic phase transitions: one at Ti(H = 0) ≃ 30 K (Ti† (H = 0) ≃ 230 K) and the other at a lower temperature Tp(H = 0) ≃ 8 K (Th(H = 0) ≃ 52 K) in S1 (S2). 'In-field' (H ≠ 0) linear ac-susceptibility and dc magnetization demonstrate that the thermodynamic nature of these transitions is preserved in finite fields. The presently determined H-T phase diagrams for the samples S1 and S2 are compared with those predicted by the Kotliar-Sompolinsky and Gabay-Toulouse mean-field models and Monte Carlo simulations, based on the chirality-driven spin glass (SG) ordering scenario, for a three-dimensional nearest-neighbor Heisenberg SG system with or without weak random anisotropy. Such a detailed comparison permits us to unambiguously identify various 'zero-field' and 'in-field' SG phase transitions as: (i) the simultaneous paramagnetic (PM)-chiral glass (CG) and PM-SG phase transitions at Ti(H), (ii) the PM-CG transition at Ti† (H), (iii) the replica symmetry-breaking SG transition at Tp(H), and (iv) the continuous spin-rotation symmetry-breaking SG transition at Th(H). In the presence of random anisotropy, magnetization fails to saturate even at 90 kOe in S1 whereas negligibly small anisotropy allows even fields as weak as 1 kOe to saturate magnetization and induce ferromagnetism in S2. Due to the proximity to CG/SG-QCP, magnetization and susceptibility both exhibit non-Fermi liquid behavior over a wide range at low temperatures.
Self Assembled Spin Coated and Bulk Films of a Novel Polydiacetylene as Second Order NLO Polymers
1994-05-31
NLO Polymers 6. AUTHOm(m) R&T Code: 4132016 W.H. Kim, B. Bihari, R. Moody, N. B. Kodali , J.Kumar,S.K. Dr. JoAnn MilUiken Tripathy. 7. PERFORMING...Polymers by W.H. Kim, B. Bihari, R. Moody, N. B. Kodali , J.Kumar,S.K. Tripathy. Submitted to Macromolecules University of Massachusetts Lowell Department...FILMS OF A NOVEL POLYDIACETYLENE AS SECOND ORDER NLO POLYMERS W. H. Kim, B. Bihari+, R. Moody+, N. B. Kodali , J. Kumar+, and S. K. Tripathy, University
Higgins, David; Tweedale, Geoffrey
2010-01-01
In the Lancashire cotton textile industry, mule spinners were prone to a chronic and sometimes fatal skin cancer (often affecting the groin). The disease had reached epidemic proportions by the 1920s, which necessitated action by the government, employers, and trade unions. In contrast to previous accounts, this article focuses on the government's reaction to mule spinners' cancer. Using official records in the National Archives, the slow introduction of health and safety measures by the government is explored in detail. Although obstructionism by the employers played a key role, one of the reasons for government inaction was the ambiguity of scientific research on engineering oils. On the other hand, prolonged scientific research suited a government policy that was framed around self regulation - a policy that had proved largely ineffective by the 1950s.
Modulation of electronic properties from stacking orders and spin-orbit coupling for 3R-type MoS2
Fan, Xiaofeng; Zheng, W. T.; Kuo, Jer-Lai; Singh, David J.; Sun, C.Q.; Zhu, W.
2016-01-01
Two-dimensional crystals stacked by van der Waals coupling, such as twisted graphene and coupled graphene-BN layers with unusual phenomena have been a focus of research recently. As a typical representative, with the modulation of structural symmetry, stacking orders and spin-orbit coupling, transitional metal dichalcogenides have shown a lot of fascinating properties. Here we reveal the effect of stacking orders with spin-orbit coupling on the electronic properties of few-layer 3R-type MoS2 by first principles methods. We analyze the splitting of states at the top of valence band and the bottom of conduction band, following the change of stacking order. We find that regardless of stacking orders and layers’ number, the spin-up and spin-down channels are evidently separated and can be as a basis for the valley dependent spin polarization. With a model Hamiltonian about the layer’s coupling, the band splitting can be effectively analyzed by the coupling parameters. It is found that the stacking sequences, such as abc and abca, have the stronger nearest-neighbor coupling which imply the popular of periodic abc stacking sequence in natural growth of MoS2. PMID:27053462
Defect-induced short-range-order from a spin-ice related state in deformed pyrochlore Co2(OH)3Cl
NASA Astrophysics Data System (ADS)
Zheng, X. G.; Hagihala, M.; Kawae, T.; Xu, C. N.
2008-01-01
Recently, we observed a kagome-ice-like partial ferromagnetic order with coexisting fluctuation in a deformed pyrochlore structure Co2(OH)3Cl . Here, we show that when lattice defects are present, the remaining fluctuating spins in this material further freeze at lower temperatures below T
NASA Astrophysics Data System (ADS)
Wen, Jinsheng; Xu, Z.; Xu, G.; Jie, Q.; Hucker, M.; Zheludev, A.; Tian, W.; Winn, B.; Zarestky, J.; Singh, D.; Hong, T.; Li, Q.; Gu, G.; Tranquada, J.
2011-03-01
We have performed susceptibility, thermal transport, and neutron scattering measurements to study the effect of Zn and magnetic field on the structure, spin-stripe order and superconductivity, and the interplay between them in La 1.905 Ba 0.095 Cu O4 with and without 1% Zn. It is shown that the bulk superconductivity is depressed by either the Zn doping or the magnetic field, spin stripe order is enhanced, and the structure is unaffected. For a range of magnetic field, the spin stripe order appears to stabilize a quasi-two-dimensional vortex glass phase. Supported by Office of Basic Energy Sciences, US DOE, under Contract No. DE-AC02-98CH10886.
Bishop, Christopher B.; Moreo, Adriana; Dagotto, Elbio
2016-09-08
The bicollinear antiferromagnetic order experimentally observed in FeTe is shown to be stabilized by the coupling g~12 between monoclinic lattice distortions and the spin-nematic order parameter with B2g symmetry, within a three-orbital spin-fermion model studied with Monte Carlo techniques. A finite but small value of g~12 is required, with a concomitant lattice distortion compatible with experiments, and a tetragonal-monoclinic transition strongly first order. Remarkably, the bicollinear state found here displays a planar resistivity with the reversed puzzling anisotropy discovered in transport experiments. Orthorhombic distortions are also incorporated, and phase diagrams interpolating between pnictides and chalcogenides are presented. Here, we concludemore » that the spin-lattice coupling we introduce is sufficient to explain the challenging properties of FeTe.« less
Bishop, Christopher B.; Moreo, Adriana; Dagotto, Elbio
2016-09-08
The bicollinear antiferromagnetic order experimentally observed in FeTe is shown to be stabilized by the coupling g^{~}_{12} between monoclinic lattice distortions and the spin-nematic order parameter with B_{2g} symmetry, within a three-orbital spin-fermion model studied with Monte Carlo techniques. A finite but small value of g^{~}_{12} is required, with a concomitant lattice distortion compatible with experiments, and a tetragonal-monoclinic transition strongly first order. Remarkably, the bicollinear state found here displays a planar resistivity with the reversed puzzling anisotropy discovered in transport experiments. Orthorhombic distortions are also incorporated, and phase diagrams interpolating between pnictides and chalcogenides are presented. Here, we conclude that the spin-lattice coupling we introduce is sufficient to explain the challenging properties of FeTe.
NASA Astrophysics Data System (ADS)
De, Santanu; Kumar, Kranti; Banerjee, A.; Chaddah, P.
2016-05-01
We have found that the geometrically frustrated spin chain compound Ca3Co2O6 belonging to Ising like universality class with uniaxial anisotropy shows kinetic arrest of first order intermediate phase (IP) to ferrimagnetic (FIM) transition. In this system, dc magnetization measurements followed by different protocols suggest the coexistence of high temperature IP with equilibrium FIM phase in low temperature. Formation of metastable state due to hindered first order transition has also been probed through cooling and heating in unequal field (CHUF) protocol. Kinetically arrested high temperature IP appears to persist down to almost the spin freezing temperature in this system.
NASA Astrophysics Data System (ADS)
Čisárová, Jana; Strečka, Jozef
2013-01-01
The spin-(1)/(2) Ising-Heisenberg model on two geometrically related triangles-in-triangles lattices is exactly solved through the generalized star-triangle transformation, which establishes a rigorous mapping correspondence with the effective spin-(1)/(2) Ising model on a triangular lattice. Basic thermodynamic quantities were exactly calculated within this rigorous mapping method along with the ground-state and finite-temperature phase diagrams. Apart from the classical ferromagnetic phase, both investigated models exhibit several unconventional quantum ordered and disordered ground states. A mutual competition between two ferromagnetic interactions of basically different character generically leads to the emergence of a quantum ferromagnetic phase, in which a symmetric quantum superposition of three up-up-down states of the Heisenberg trimers accompanies a perfect alignment of all Ising spins. In the highly frustrated regime, we have either found the disordered quantum paramagnetic phase with a substantial residual entropy or a similar but spontaneously ordered phase with a nontrivial criticality at finite temperatures. The latter quantum ground state exhibits a striking coexistence of imperfect spontaneous order with partial disorder, which is evidenced by a quantum reduction of the spontaneous magnetization of Heisenberg spins that indirectly causes a small reduction of the spontaneous magnetization of otherwise classical Ising spins.
Zhang, Qiang; Fernandes, Rafael M.; Lamsal, Jagat; Yan, Jiaqiang; Chi, Songxue; Tucker, Gregory S.; Pratt, Daniel K.; Lynn, Jeffrey W.; McCallum, R. W.; Canfield, Paul C.; Lograsso, Thomas A.; Goldman, Alan I.; Vaknin, David; McQueeney, Robert J.
2015-02-04
Inelastic neutron scattering is employed to investigate the impact of electronic nematic order on the magnetic spectra of LaFeAsO and Ba(Fe_{0.953}Co_{0.047})_{2}As_{2}. These materials are ideal to study the paramagnetic-nematic state, since the nematic order, signaled by the tetragonal-to-orthorhombic transition at T_{S}, sets in well above the stripe antiferromagnetic ordering at T_{N}. We find that the temperature-dependent dynamic susceptibility displays an anomaly at T_{S} followed by a sharp enhancement in the spin-spin correlation length, revealing a strong feedback effect of nematic order on the low-energy magnetic spectrum. As a result, our findings can be consistently described by a model that attributes the structural or nematic transition to magnetic fluctuations, and unveils the key role played by nematic order in promoting the long-range stripe antiferromagnetic order in iron pnictides.
Unstable spin-ice order in the stuffed metallic pyrochlore Pr2+xIr2-xO7-δ
MacLaughlin, D. E.; Bernal, O. O.; Shu, Lei; ...
2015-08-24
Specific heat, elastic neutron scattering, and muon spin rotation experiments have been carried out on a well-characterized sample of “stuffed” (Pr-rich) Pr2+xIr2-xO7-δ. Elastic neutron scattering shows the onset of long-range spin-ice “2-in/2-out” magnetic order at 0.93 kelvin, with an ordered moment of 1.7(1) Bohr magnetons per Pr ion at low temperatures. Approximate lower bounds on the correlation length and correlation time in the ordered state are 170 angstroms and 0.7 nanosecond, respectively. Muon spin rotation experiments yield an upper bound 2.6(7) milliteslas on the local field B4floc at the muon site, which is nearly two orders of magnitude smaller thanmore » the expected dipolar field for long-range spin-ice ordering of 1.7-Bohr magneton moments (120–270 milliteslas, depending on the muon site). This shortfall is due in part to splitting of the non-Kramers crystal-field ground-state doublets of near-neighbor Pr3+ ions by the positive-muon-induced lattice distortion. For this to be the only effect, however, ~160 Pr moments out to a distance of ~14 angstroms must be suppressed. An alternative scenario—one consistent with the observed reduced nuclear hyperfine Schottky anomaly in the specific heat—invokes slow correlated Pr-moment fluctuations in the ordered state that average B4floc on the μSR time scale (~10-7 second), but are static on the time scale of the elastic neutron scattering experiments (~10-9 second). In this picture, the dynamic muon relaxation suggests a Pr3+ 4f correlation time of a few nanoseconds, which should be observable in a neutron spin echo experiment.« less
Lochan, Rohini C.; Head-Gordon, Martin
2007-01-01
Coupled cluster methods based on Brueckner orbitals are well-known to resolve the problems of symmetry-breaking and spin-contamination that are often associated with Hartree-Fock orbitals. However their computational cost is large enough to prevent application to large molecules. Here they present a simple approximation where the orbitals are optimized with the mean-field energy plus a correlation energy taken as the opposite-spin component of the second order many-body correlation energy, scaled by an empirically chosen parameter (recommended as 1.2 for general applications). This optimized 2nd order opposite spin (abbreviated as O2) method requires fourth order computation on each orbital iteration. O2 is shown to yield predictions of structure and frequencies for closed shell molecules that are very similar to scaled second order Moller-Plesset methods. However it yields substantial improvements for open shell molecules, where problems with spin-contamination and symmetry breaking are shown to be greatly reduced.
Collinear order in the frustrated three-dimensional spin-1/2 antiferromagnet Li2CuW2O8
NASA Astrophysics Data System (ADS)
Ranjith, K. M.; Nath, R.; Skoulatos, M.; Keller, L.; Kasinathan, D.; Skourski, Y.; Tsirlin, A. A.
2015-09-01
Magnetic frustration in three dimensions (3D) manifests itself in the spin-1/2 insulator Li2CuW2O8 . Density-functional band-structure calculations reveal a peculiar spin lattice built of triangular planes with frustrated interplane couplings. The saturation field of 29 T contrasts with the susceptibility maximum at 8.5 K and a relatively low Néel temperature TN≃3.9 K . Magnetic order below TN is collinear with the propagation vector (0 ,1/2 ,0 ) and an ordered moment of 0.65(4) μB according to neutron diffraction data. This reduced ordered moment together with the low maximum of the magnetic specific heat (Cmax/R ≃0.35 ) pinpoint strong magnetic frustration in 3D. Collinear magnetic order suggests that quantum fluctuations play a crucial role in this system, where a noncollinear spiral state would be stabilized classically.
NASA Astrophysics Data System (ADS)
Oravova, Lucie; Zhang, Zhiying; Church, Nathan; Harrison, Richard J.; Howard, Christopher J.; Carpenter, Michael A.
2013-03-01
Hematite, Fe2O3, provides in principle a model system for multiferroic (ferromagnetic/ferroelastic) behavior at low levels of strain coupling. The elastic and anelastic behavior associated with magnetic phase transitions in a natural polycrystalline sample have therefore been studied by resonant ultrasound spectroscopy (RUS) in the temperature range from 11 to 1072 K. Small changes in softening and attenuation are interpreted in terms of weak but significant coupling of symmetry-breaking and non-symmetry-breaking strains with magnetic order parameters in the structural sequence R\\overline{3}c{1}^{\\prime}\\rightarrow C 2/c\\rightarrow R\\overline{3}c. The R\\overline{3}c{1}^{\\prime}\\rightarrow C 2/c transition at TN = 946 ± 1 K is an example of a multiferroic transition which has both ferromagnetic (from canting of antiferromagnetically ordered spin moments) and ferroelastic (rhombohedral → monoclinic) character. By analogy with the improper ferroelastic transition in Pb3(PO4)2, W and W‧ ferroelastic twin walls which are also 60° and 120° magnetic domain walls should develop. These have been tentatively identified from microstructures reported in the literature. The very low attenuation in the stability field of the C2/c structure in the polycrystalline sample used in the present study, in comparison with the strong acoustic dissipation reported for single crystal samples, implies, however, that the individual grains each consist of a single ferroelastic domain or that the twin walls are strongly pinned by grain boundaries. This absence of attenuation allows an intrinsic loss mechanism associated with the transition point to be seen and interpreted in terms of local coupling of shear strains with fluctuations which have relaxation times in the vicinity of ˜10-8 s. The first order C 2/c\\rightarrow R\\overline{3}c (Morin) transition occurs through a temperature interval of coexisting phases but the absence of an acoustic loss peak suggests that the
Willenberg, B; Schäpers, M; Wolter, A U B; Drechsler, S-L; Reehuis, M; Hoffmann, J-U; Büchner, B; Studer, A J; Rule, K C; Ouladdiaf, B; Süllow, S; Nishimoto, S
2016-01-29
Low-temperature neutron diffraction and NMR studies of field-induced phases in linarite are presented for magnetic fields H∥b axis. A two-step spin-flop transition is observed, as well as a transition transforming a helical magnetic ground state into an unusual magnetic phase with sine-wave-modulated moments ∥H. An effective J[over ˜]_{1}-J[over ˜]_{2} single-chain model with a magnetization-dependent frustration ratio α_{eff}=-J[over ˜]_{2}/J[over ˜]_{1} is proposed. The latter is governed by skew interchain couplings and shifted to the vicinity of the ferromagnetic critical point. It explains qualitatively the observation of a rich variety of exotic longitudinal collinear spin-density wave, SDW_{p}, states (9≥p≥2).
Revealing magnetic ordering and spin-phonon coupling in Y1‑x Tb x MnO3 (0.1 ⩽ x ⩽ 0.3) compounds
NASA Astrophysics Data System (ADS)
Chakraborty, Keka R.; Paul, Barnita; Shukla, R.; Krishna, P. S. R.; Kumar, Amit; Mukadam, M. D.; Mandal, B. P.; Roy, Anushree; Tyagi, A. K.; Yusuf, S. M.
2017-04-01
The structural and magnetic properties of the Y1‑x Tb x MnO3 (0.1 ⩽ x ⩽ 0.3) compounds were investigated. Neutron diffraction patterns for all three samples, recorded at room temperature (RT), were fitted to the nuclear structure confirming the paramagnetic nature of the compounds. At 2.8 K, for the x = 0.1 sample magnetic moments of the Tb3+ ionic as well as Mn3+ ionic were ordered. At 5 K for the x = 0.2 sample only the Mn3+ ionic magnetic moments were ordered. There were six sites for Mn atoms. Three on the z = 0 plane and three on the z = 0.5 plane (where z corresponds to +c axis).The Mn3+ionic moments were confined to the a-b plane with a net magnitude of 2.78(3) µ B, and 2.90(3) µ B for the x = 0.1 and the x = 0.2 samples. The Tb3+ionic moments had a magnitude of 1.36(4) µ B at 2.8 K and were aligned antiferromagnetically along the crystallographic c-axis for the x = 0.1 sample. The low moment in comparison with Mn3+ free ions has been attributed to crystalline electric fields similar to that found in the parent compound YMnO3 and also in another rare earth manganite viz HoMnO3. The x = 0.3 sample was found to be a canonical spin glass. To investigate the role of the above spin ordering in Y1‑x Tb x MnO3 in governing the phonon dynamics, temperature dependent Raman measurements were carried out. We observed the deviation of the phonon frequency near 685 cm‑1 and its line-width from the expected anharmonic behaviour around magnetic ordering temperature for Tb substituted compounds with x = 0.1 and 0.2. This was attributed to the spin-phonon coupling in these systems. The anomalous behaviour of this phonon mode in the canonical spin glass compound with x = 0.3, indicated that the coupling sustained even in the presence of only local magnetic ordering.
NASA Astrophysics Data System (ADS)
Moor, Andreas; Volkov, Anatoly F.; Efetov, Konstantin B.
2014-12-01
On the basis of coupled Ginzburg-Landau equations we study nonhomogeneous states in systems with two order parameters (OPs). Superconductors with a superconducting OP Δ and a charge- or spin-density wave with amplitude W are examples of such systems. When one OP, say Δ , has a form of a topological defect, like, e.g., a vortex or domain wall between the domains with the phases 0 and π , the other OP W is determined by the Gross-Pitaevskii equation and is localized at the center of the defect. We consider in detail the domain-wall defect for Δ and show that the shape of the associated solution for W depends on temperature and doping (or on the curvature of the Fermi surface) μ . It turns out that, provided the temperature or doping level is close to some discrete values Tn and μn, the spatial dependence of the function W (x ) is determined by the form of the eigenfunctions of the linearized Gross-Pitaevskii equation. The spatial dependence of W0 corresponding to the ground state has the form of a soliton, while other possible solutions Wn(x ) have nodes. The inverse situation when W (x ) has the form of a topological defect and Δ (x ) is localized at the center of this defect is also possible. In particular, we predict a surface or interfacial superconductivity in a system where a superconductor is in contact with a material that suppresses W . This superconductivity should have rather unusual temperature dependence existing only in certain intervals of temperature. Possible experimental realizations of such nonhomogeneous states of OPs are discussed.
Strečka, Jozef; Ekiz, Cesur
2015-05-01
The geometrically frustrated spin-1/2 Ising-Heisenberg model on triangulated Husimi lattices is exactly solved by combining the generalized star-triangle transformation with the method of exact recursion relations. The ground-state and finite-temperature phase diagrams are rigorously calculated along with both sublattice magnetizations of the Ising and Heisenberg spins. It is evidenced that the Ising-Heisenberg model on triangulated Husimi lattices with two or three interconnected triangles-in-triangles units displays in a highly frustrated region a quantum disorder irrespective of temperature, whereas the same model on triangulated Husimi lattices with a greater connectivity of triangles-in-triangles units exhibits at low enough temperatures an outstanding quantum order due to the order-by-disorder mechanism. The quantum reduction of both sublattice magnetizations in the peculiar quantum ordered state gradually diminishes upon increasing the coordination number of the underlying Husimi lattice.
NASA Astrophysics Data System (ADS)
Uchigaito, Hiroshi; Udagawa, Masafumi; Motome, Yukitoshi
2011-04-01
We present our theoretical results on the ground states in the layered triangular-lattice compounds ANiO2 (A = Na, Li, Ag). To describe the interplay between charge, spin, orbital, and lattice degrees of freedom in these materials, we study a doubly degenerate Hubbard model with electron--phonon couplings by the Hartree--Fock approximation combined with the adiabatic approximation. In a weakly correlated region, we find a metallic state accompanied by \\sqrt{3}×\\sqrt{3} charge ordering. On the other hand, we obtain an insulating phase with spin-ferro and orbital-ferro ordering in a wide range from intermediate to strong correlation. These phases share many characteristics with the low-temperature states of AgNiO2 and NaNiO2, respectively. The charge-ordered metallic phase is stabilized by a compromise between Coulomb repulsions and effective attractive interactions originating from the breathing-type electron--phonon coupling as well as the Hund's-rule coupling. The spin--orbital-ordered insulating phase is stabilized by the cooperative effect of electron correlations and the Jahn--Teller coupling, while the Hund'-rule coupling also plays a role in the competition with other orbital-ordered phases. The results suggest a unified way of understanding a variety of low-temperature phases in ANiO2. We also discuss a keen competition among different spin--orbital-ordered phases in relation to the puzzling behavior observed in LiNiO2.
Guguchia, Z; Khasanov, R; Bendele, M; Pomjakushina, E; Conder, K; Shengelaya, A; Keller, H
2014-08-01
Large negative oxygen-isotope (^{16}O and ^{18}O) effects (OIEs) on the static spin-stripe-ordering temperature T_{so} and the magnetic volume fraction V_{m} were observed in La_{2-x}Ba_{x}CuO_{4}(x=1/8) by means of muon-spin-rotation experiments. The corresponding OIE exponents were found to be α_{T_{so}}=-0.57(6) and α_{V_{m}}=-0.71(9), which are sign reversed to α_{T_{c}}=0.46(6) measured for the superconducting transition temperature T_{c}. This indicates that the electron-lattice interaction is involved in the stripe formation and plays an important role in the competition between bulk superconductivity and static stripe order in the cuprates.
Sergeicheva, E. G.; Sosin, S. S.; Prozorova, L. A.; ...
2017-01-18
We report on an electron spin resonance (ESR) study of a nearly one-dimensional (1D) spin-1/2 chain antiferromagnet, Sr2CuO3, with extremely weak magnetic ordering. The ESR spectra at T > TN, in the disordered Luttinger-spin-liquid phase, reveal nearly ideal Heisenberg-chain behavior with only a very small, field-independent linewidth, ~1/T. In the ordered state, below TN, we identify field-dependent antiferromagnetic resonance modes, which are well described by pseudo-Goldstone magnons in the model of a collinear biaxial antiferromagnet. Additionally, we observe a major resonant mode with unusual and strongly anisotropic properties, which is not anticipated by the conventional theory of Goldstone spin waves.more » Lastly, we propose that this unexpected magnetic excitation can be attributed to a field-independent magnon mode renormalized due to its interaction with the high-energy amplitude (Higgs) mode in the regime of weak spontaneous symmetry breaking.« less
NASA Astrophysics Data System (ADS)
Sarkar, Tanushree; Manna, Kaustuv; Elizabeth, Suja; Anil Kumar, P. S.
2017-02-01
We report the detailed experimental characteristics of LuMn0.5Fe0.5O3 synthesized by the wet chemical method and proclaim it as a new member of the multiferroic family. The compound stabilizes in P63cm crystal symmetry. It exhibits a spin re-orientation transition at TSR and an antiferromagnetic transition at TN. In addition, our magnetization vs. temperature data reveals an extra broad maximum close to room temperature; unseen in earlier studies. By invoking the compatible nature of the magnetic exchange path in P63cm symmetry, we have argued that the origin lies in the intraplane short-range spin ordering. Heat capacity is measured and analysed to elucidate the magnetic entropy. Though long-range antiferromagnetic ordering vanishes at TN ˜ 103 K, we find the experimental magnetic entropy calculated till 200 K is less by a significant amount from the value of theoretical spin randomization magnetic entropy; further supporting the existence of spin ordering beyond TN and even above 200 K. While the specific heat data and phonon modes of Raman spectra show a signature of spin-phonon coupling at TSR and TN both, dielectric anomaly indicating a magnetoelectric effect is seen only at TN. Piezoresponse force microscopy and ferroelectric hysteresis loop measurement confirm the room-temperature weak ferroelectricity with a saturation polarization value 0.007 μC/cm2 and low coercive field. Furthermore high-temperature dielectric characteristics reveal the ferroelectric transition at around 900 K and exhibit Maxwell-Wagner type relaxation. The present work serves as a bridge between h-RMnO3 and rare earth ferrite RFeO3. It assumes significance in the light of recent research developments in hexagonal RFeO3 (mainly h-LuFeO3) in the context of room-temperature multiferroicity and magnetoelectricity.
NASA Astrophysics Data System (ADS)
Banda Guzmán, V. M.; Kirchbach, M.
2016-09-01
A boson of spin j≥ 1 can be described in one of the possibilities within the Bargmann-Wigner framework by means of one sole differential equation of order twice the spin, which however is known to be inconsistent as it allows for non-local, ghost and acausally propagating solutions, all problems which are difficult to tackle. The other possibility is provided by the Fierz-Pauli framework which is based on the more comfortable to deal with second-order Klein-Gordon equation, but it needs to be supplemented by an auxiliary condition. Although the latter formalism avoids some of the pathologies of the high-order equations, it still remains plagued by some inconsistencies such as the acausal propagation of the wave fronts of the (classical) solutions within an electromagnetic environment. We here suggest a method alternative to the above two that combines their advantages while avoiding the related difficulties. Namely, we suggest one sole strictly D^{(j,0)oplus (0,j)} representation specific second-order differential equation, which is derivable from a Lagrangian and whose solutions do not violate causality. The equation under discussion presents itself as the product of the Klein-Gordon operator with a momentum-independent projector on Lorentz irreducible representation spaces constructed from one of the Casimir invariants of the spin-Lorentz group. The basis used is that of general tensor-spinors of rank 2 j.
NASA Astrophysics Data System (ADS)
Ghorbani, Elaheh; Tocchio, Luca F.; Becca, Federico
2016-02-01
By using variational wave functions and quantum Monte Carlo techniques, we investigate the complete phase diagram of the Heisenberg model on the anisotropic triangular lattice, where two out of three bonds have superexchange couplings J and the third one has instead J'. This model interpolates between the square lattice and the isotropic triangular one, for J'/J ≤1 , and between the isotropic triangular lattice and a set of decoupled chains, for J /J'≤1 . We consider all the fully symmetric spin liquids that can be constructed with the fermionic projective-symmetry group classification (Zhou and Wen, arXiv:cond-mat/0210662) and we compare them with the spiral magnetic orders that can be accommodated on finite clusters. Our results show that, for J'/J ≤1 , the phase diagram is dominated by magnetic orderings, even though a spin-liquid state may be possible in a small parameter window, i.e., 0.7 ≲J'/J ≲0.8 . In contrast, for J /J'≤1 , a large spin-liquid region appears close to the limit of decoupled chains, i.e., for J /J'≲0.6 , while magnetically ordered phases with spiral order are stabilized close to the isotropic point.
Neutron scattering study of spin ordering and stripe pinning in superconducting La1.93Sr0.07CuO4
NASA Astrophysics Data System (ADS)
Jacobsen, H.; Zaliznyak, I. A.; Savici, A. T.; Winn, B. L.; Chang, S.; Hücker, M.; Gu, G. D.; Tranquada, J. M.
2015-11-01
The relationships among charge order, spin fluctuations, and superconductivity in underdoped cuprates remain controversial. We use neutron scattering techniques to study these phenomena in La1.93Sr0.07CuO4 , a superconductor with a transition temperature of Tc=20 K. At T ≪Tc we find incommensurate spin fluctuations with a quasielastic energy spectrum and no sign of a gap within the energy range from 0.2 to 15 meV. A weak elastic magnetic component grows below ˜10 K, consistent with results from local probes. Regarding the atomic lattice, we have discovered unexpectedly strong fluctuations of the CuO6 octahedra about Cu-O bonds, which are associated with inequivalent O sites within the CuO2 planes. Furthermore, we observed a weak elastic (3 3 ¯0 ) superlattice peak that implies a reduced lattice symmetry. The presence of inequivalent O sites rationalizes various pieces of evidence for charge stripe order in underdoped La2 -xSrxCuO4 . The coexistence of superconductivity with quasistatic spin-stripe order suggests the presence of intertwined orders; however, the rotation of the stripe orientation away from the Cu-O bonds might be connected with evidence for a finite gap at the nodal points of the superconducting gap function.
Neutron scattering study of spin ordering and stripe pinning in superconducting La1.93Sr0.07CuO4
Jacobsen, H.; Zaliznyak, I. A.; Savici, A. T.; ...
2015-11-20
Tmore » he relationships among charge order, spin fluctuations, and superconductivity in underdoped cuprates remain controversial. We use neutron scattering techniques to study these phenomena in La1.93Sr0.07CuO4 a superconductor with a transition temperature of c = 20 K. At << c, we find incommensurate spin fluctuations with a quasielastic energy spectrum and no sign of a gap within the energy range from 0.2 to 15 meV. A weak elastic magnetic component grows below ~ 10 K, consistent with results from local probes. Regarding the atomic lattice, we have discovered unexpectedly strong fluctuations of the CuO6 octahedra about Cu-O bonds, which are associated with inequivalent O sites within the CuO2 planes. Moreover, we observed a weak elastic (3 ⁻30) superlattice peak that implies a reduced lattice symmetry. he presence of inequivalent O sites rationalizes various pieces of evidence for charge stripe order in underdoped La2-xSrxCuO4. he coexistence of superconductivity with quasi-static spin-stripe order suggests the presence of intertwined orders; however, the rotation of the stripe orientation away from the Cu-O bonds might be connected with evidence for a finite gap at the nodal points of the superconducting gap function.« less
NASA Astrophysics Data System (ADS)
Arai, Hiroko; Matsumoto, Rie; Yuasa, Shinji; Imamura, Hiroshi
2015-08-01
Spin-torque-induced magnetization dynamics in a nanopillar having a perpendicularly magnetized free layer with first- and second-order uniaxial anisotropy and an in-plane magnetized reference layer is studied theoretically on the basis of the macrospin model. It is shown that in the presence of second-order uniaxial anisotropy, self-oscillation is induced even at zero bias magnetic field. Analytical expressions for the threshold current, condition of the second-order anisotropy constant required for oscillation, and current dependence of the oscillation frequency are obtained.
Moderate positive spin Hall angle in uranium
Singh, Simranjeet; Anguera, Marta; Barco, Enrique del E-mail: cwmsch@rit.edu; Springell, Ross; Miller, Casey W. E-mail: cwmsch@rit.edu
2015-12-07
We report measurements of spin pumping and the inverse spin Hall effect in Ni{sub 80}Fe{sub 20}/uranium bilayers designed to study the efficiency of spin-charge interconversion in a super-heavy element. We employ broad-band ferromagnetic resonance on extended films to inject a spin current from the Ni{sub 80}Fe{sub 20} (permalloy) into the uranium layer, which is then converted into an electric field by the inverse spin Hall effect. Surprisingly, our results suggest a spin mixing conductance of order 2 × 10{sup 19} m{sup −2} and a positive spin Hall angle of 0.004, which are both merely comparable with those of several transition metals. These results thus support the idea that the electronic configuration may be at least as important as the atomic number in governing spin pumping across interfaces and subsequent spin Hall effects. In fact, given that both the magnitude and the sign are unexpected based on trends in d-electron systems, materials with unfilled f-electron orbitals may hold additional exploration avenues for spin physics.
Spin excitations in stripe-ordered La 2- xSr xNiO 4 ( x=0.275 and {1}/{3})
NASA Astrophysics Data System (ADS)
Boothroyd, A. T.; Freeman, P. G.; Prabhakaran, D.; Woo, H.; Nakajima, K.; Tranquada, J. M.; Yamada, K.; Frost, C. D.
2004-05-01
We report neutron scattering measurements of the spectrum of magnetic excitations in the stripe-ordered phase of La 2- xSr xNiO 4 ( x=0.275 and {1}/{3}). The propagating spin excitations follow a similar dispersion relation for the two compositions, but the line widths are broader for x=0.275 than for {1}/{3}.
Spin state and magnetic ordering of half-doped Nd0.5Sr0.5CoO3 cobaltite
NASA Astrophysics Data System (ADS)
Reis, M. S.; Rocco, D. L.; Caraballo Vivas, R. J.; Pimentel, B.; Checca, N. R.; Torrão, R.; Paixão, L.; dos Santos, A. M.
2017-01-01
Cobaltites show intriguing magnetic and transport properties, when compared with manganites for instance, as they exhibit an additional degree of freedom: the spin state of the Co ions. For Nd0.5Sr0.5CoO3 this spin configuration is not well-established, as well as the magnetic ordering below the Curie temperature. Thus, in the present effort, magnetization measurements and a mean-field theoretical model were developed in order to understand in detail these aspects of the half-doped Nd0.5Sr0.5CoO3 cobaltite. These results show that the Co and Nd magnetic sub-lattices couple antiferromagnetically below Curie temperature Tc=215 K down to very low temperature. These findings clarify the presence of the plateau observed at 80 K on M(T) curve, which is erroneously attributed, in the literature, to the onset of an antiferromagnetic ordering. Magnetization data also clearly shows that Co3+ and Co4+ are in an intermediate spin state. In addition, experimental and theoretical magnetic entropy changes were determined and a comparative analysis among these two leads to ratify the results above claimed. Finally, from all those results, a magnetic phase diagram for Nd0.5Sr0.5CoO3. could be drawn.
Strong enhancement of spin ordering by A -site magnetic ions in the ferrimagnet CaC u3F e2O s2O12
NASA Astrophysics Data System (ADS)
Deng, Hongshan; Liu, Min; Dai, Jianhong; Hu, Zhiwei; Kuo, Changyang; Yin, Yunyu; Yang, Junye; Wang, Xiao; Zhao, Qing; Xu, Yuanji; Fu, Zhaoming; Cai, Jianwang; Guo, Haizhong; Jin, Kuijuan; Pi, Tunwen; Soo, Yunliang; Zhou, Guanghui; Cheng, Jinguang; Chen, Kai; Ohresser, Philippe; Yang, Yi-feng; Jin, Changqing; Tjeng, Liu-Hao; Long, Youwen
2016-07-01
A B O3 perovskite is a kind of very important functional material with versatile physical properties. Although B -site chemical substitution with various magnetic ions has been widely investigated, the A -site doping with magnetic transition metal is little known. Here we report A A3'B2B2'O12 -type A - and B -site ordered ferrimagnet CaC u3F e2O s2O12 with magnetic transition metals occupying three different atomic sites (A', B , and B' sites). This compound is synthesized by a special high-pressure annealing process. It possesses a much higher Curie temperature TC of 580 K compared with that of the B -site-only ordered C a2FeOs O6 (TC=320 K ) without magnetic ion at the A site. First-principles numerical calculations reveal that this enhancement primarily originates from the additional spin interaction between the A'-site C u2 + and the B'-site O s5 + , generating a strong C u2 +(↑) F e3 +(↑) O s5 +(↓) ferrimagnetic spin coupling. This work opens up an alternative way for enhancing the spin ordering temperature by introducing A -site magnetic ions.
Disorder from order among anisotropic next-nearest-neighbor Ising spin chains in SrHo_{2}O_{4}
Wen, J. -J.; Tian, W.; Garlea, V. O.; Koohpayeh, S. M.; McQueen, T. M.; Li, H. -F.; Yan, J. -Q.; Rodriguez-Rivera, J. A.; Vaknin, D.; Broholm, C. L.
2015-02-26
In this study, we describe why Ising spin chains with competing interactions in SrHo_{2}O_{4} segregate into ordered and disordered ensembles at low temperatures (T). Using elastic neutron scattering, magnetization, and specific heat measurements, the two distinct spin chains are inferred to have Néel (↑↓↑↓) and double-Néel (↑↑↓↓) ground states, respectively. Below T_{N} = 0.68(2)K, the Néel chains develop three-dimensional long range order (LRO), which arrests further thermal equilibration of the double-Néel chains so they remain in a disordered incommensurate state for T below T_{S} = 0.52(2)K. SrHo_{2}O_{4} distills an important feature of incommensurate low dimensional magnetism: kinetically trapped topological defects in a quasi–d–dimensional spin system can preclude order in d + 1 dimensions.
NASA Astrophysics Data System (ADS)
Asih, Retno; Adam, Noraina; Sakinah Mohd-Tajudin, Saidah; Puspita Sari, Dita; Matsuhira, Kazuyuki; Guo, Hanjie; Wakeshima, Makoto; Hinatsu, Yukio; Nakano, Takehito; Nozue, Yasuo; Sulaiman, Shukri; Ismail Mohamed-Ibrahim, Mohamad; Biswas, Pabitra Kumar; Watanabe, Isao
2017-02-01
Magnetic-ordered states of the pyrochlore iridates Nd2Ir2O7 (Nd227) and Sm2Ir2O7 (Sm227), showing metal-insulator transitions at 33 and 117 K, respectively, were studied by both the muon-spin-relaxation (μSR) method and density functional theory (DFT) calculations. A long-range magnetic ordering of Ir moments appeared in conjunction with the metal insulator transition, and additional long-range-ordered states of Nd/Sm moments were confirmed at temperatures below about 10 K. We found that the all-in all-out spin structure most convincingly explained the present μSR results of both Nd227 and Sm227. Observed internal fields were compared with values derived from DFT calculations. The lower limits of the sizes of magnetic moments were estimated to be 0.12 μB and 0.2 μB for Ir and Nd moments in Nd227, and 0.3 μB and 0.1 μB for Ir and Sm moments in Sm227, respectively. Further analysis indicated that the spin coupling between Ir and Nd/Sm moments was ferromagnetic for Nd227 and antiferromagnetic for Sm227.
Prosdocimi, Francisco; Bittencourt, Daniela; da Silva, Felipe Rodrigues; Kirst, Matias; Motta, Paulo C.; Rech, Elibio L.
2011-01-01
Characterized by distinctive evolutionary adaptations, spiders provide a comprehensive system for evolutionary and developmental studies of anatomical organs, including silk and venom production. Here we performed cDNA sequencing using massively parallel sequencers (454 GS-FLX Titanium) to generate ∼80,000 reads from the spinning gland of Actinopus spp. (infraorder: Mygalomorphae) and Gasteracantha cancriformis (infraorder: Araneomorphae, Orbiculariae clade). Actinopus spp. retains primitive characteristics on web usage and presents a single undifferentiated spinning gland while the orbiculariae spiders have seven differentiated spinning glands and complex patterns of web usage. MIRA, Celera Assembler and CAP3 software were used to cluster NGS reads for each spider. CAP3 unigenes passed through a pipeline for automatic annotation, classification by biological function, and comparative transcriptomics. Genes related to spider silks were manually curated and analyzed. Although a single spidroin gene family was found in Actinopus spp., a vast repertoire of specialized spider silk proteins was encountered in orbiculariae. Astacin-like metalloproteases (meprin subfamily) were shown to be some of the most sampled unigenes and duplicated gene families in G. cancriformis since its evolutionary split from mygalomorphs. Our results confirm that the evolution of the molecular repertoire of silk proteins was accompanied by the (i) anatomical differentiation of spinning glands and (ii) behavioral complexification in the web usage. Finally, a phylogenetic tree was constructed to cluster most of the known spidroins in gene clades. This is the first large-scale, multi-organism transcriptome for spider spinning glands and a first step into a broad understanding of spider web systems biology and evolution. PMID:21738742
Prosdocimi, Francisco; Bittencourt, Daniela; da Silva, Felipe Rodrigues; Kirst, Matias; Motta, Paulo C; Rech, Elibio L
2011-01-01
Characterized by distinctive evolutionary adaptations, spiders provide a comprehensive system for evolutionary and developmental studies of anatomical organs, including silk and venom production. Here we performed cDNA sequencing using massively parallel sequencers (454 GS-FLX Titanium) to generate ∼80,000 reads from the spinning gland of Actinopus spp. (infraorder: Mygalomorphae) and Gasteracantha cancriformis (infraorder: Araneomorphae, Orbiculariae clade). Actinopus spp. retains primitive characteristics on web usage and presents a single undifferentiated spinning gland while the orbiculariae spiders have seven differentiated spinning glands and complex patterns of web usage. MIRA, Celera Assembler and CAP3 software were used to cluster NGS reads for each spider. CAP3 unigenes passed through a pipeline for automatic annotation, classification by biological function, and comparative transcriptomics. Genes related to spider silks were manually curated and analyzed. Although a single spidroin gene family was found in Actinopus spp., a vast repertoire of specialized spider silk proteins was encountered in orbiculariae. Astacin-like metalloproteases (meprin subfamily) were shown to be some of the most sampled unigenes and duplicated gene families in G. cancriformis since its evolutionary split from mygalomorphs. Our results confirm that the evolution of the molecular repertoire of silk proteins was accompanied by the (i) anatomical differentiation of spinning glands and (ii) behavioral complexification in the web usage. Finally, a phylogenetic tree was constructed to cluster most of the known spidroins in gene clades. This is the first large-scale, multi-organism transcriptome for spider spinning glands and a first step into a broad understanding of spider web systems biology and evolution.
NASA Astrophysics Data System (ADS)
Morita, Daichi; Kubo, Toshihiro; Tokura, Yasuhiro; Yamashita, Makoto
2016-06-01
We study the quantum walks of two interacting spin-1 bosons. We derive an exact solution for the time-dependent wave function, which describes the two-particle dynamics governed by the one-dimensional spin-1 Bose-Hubbard model. We show that propagation dynamics in real space and mixing dynamics in spin space are correlated via the spin-dependent interaction in this system. The spin-mixing dynamics has two characteristic frequencies in the limit of large spin-dependent interactions. One of the characteristic frequencies is determined by the energy difference between two bound states, and the other frequency relates to the cotunneling process of a pair of spin-1 bosons. Furthermore, we numerically analyze the growth of the spin correlations in quantum walks. We find that long-range spin correlations emerge showing a clear dependence on the sign of the spin-dependent interaction and the initial state.
Yoon, Jinhwan; Ree, Moonhor; Hwang, Yongtaek; Lee, Seung Woo; Lee, Byeongdu; Kim, Jong-Seong; Kim, Heesoo; Magonov, Sergei N
2004-02-03
Oligo(N(6)-carbobenzyloxy-L-lysine) (OCBL) with n = 8 (n is the number-average degree of polymerization) was synthesized by the n-propylamine-catalyzed ring-opening polymerization of N(6)-carbobenzyloxy-L-lysine N-carboxylic anhydride, which was derived from N(6)-carbobenzyloxy-L-lysine. The formation of two-dimensionally well-ordered strip array monolayer films of the OBCL oligopeptide on graphite substrates was first succeeded by a conventional solution spin-coating process. The ordered strip array monolayer structure was characterized in detail by atomic force microscopy, and its assembly mechanism was examined.
NASA Astrophysics Data System (ADS)
Herak, Mirta; Žilić, Dijana; Matković Čalogović, Dubravka; Berger, Helmuth
2015-05-01
The antiferromagnetically ordered state of the monoclinic quasi-one-dimensional S =1 /2 Heisenberg antiferromagnet CuSb2O6 was studied combining torque magnetometry with a phenomenological approach to magnetic anisotropy. This system is known to have a number of different twins in the monoclinic β phase, which differ in the orientation of the two CuO6 octahedra in the unit cell resulting in different orientation of magnetic axes with respect to crystal axes for each twin. We performed torque measurements in magnetic fields H ≤0.8 T on a sample where a certain type of twin was shown to be dominant by ESR spectroscopy. The measured data reveal that the easy axis is the crystallographic b axis for this sample. Phenomenological magnetocrystalline anisotropy energy invariant to crystal symmetry operations was used to model the spin axis direction in zero and finite magnetic fields. Our model reproduces the value of the spin-flop field HSF=1.25 T found in literature. A combination of this approach with our torque results shows that the spin axis will flop in the direction of the maximal value of measured g tensor when the magnetic field H >HSF is applied along the easy axis direction. Our analysis of magnetocrystalline anisotropy energy predicts two possibilities for the easy axis direction in this system, b or a , connected to different crystallographic twins that can be realized in CuSb2O6 . These results offer a possibility to reconcile the different reports of easy axis direction found in literature for this system and also nicely demonstrate how a combination of torque magnetometry and a phenomenological approach to magnetic anisotropy can be used to determine the value of the spin-flop field and the direction of spin axis in antiferromagnets in both H
Datta, Dipayan Gauss, Jürgen
2014-09-14
An analytic scheme is presented for the evaluation of first derivatives of the energy for a unitary group based spin-adapted coupled cluster (CC) theory, namely, the combinatoric open-shell CC (COSCC) approach within the singles and doubles approximation. The widely used Lagrange multiplier approach is employed for the derivation of an analytical expression for the first derivative of the energy, which in combination with the well-established density-matrix formulation, is used for the computation of first-order electrical properties. Derivations of the spin-adapted lambda equations for determining the Lagrange multipliers and the expressions for the spin-free effective density matrices for the COSCC approach are presented. Orbital-relaxation effects due to the electric-field perturbation are treated via the Z-vector technique. We present calculations of the dipole moments for a number of doublet radicals in their ground states using restricted open-shell Hartree-Fock (ROHF) and quasi-restricted HF (QRHF) orbitals in order to demonstrate the applicability of our analytic scheme for computing energy derivatives. We also report calculations of the chlorine electric-field gradients and nuclear quadrupole-coupling constants for the CCl, CH{sub 2}Cl, ClO{sub 2}, and SiCl radicals.
Datta, Dipayan; Gauss, Jürgen
2014-09-14
An analytic scheme is presented for the evaluation of first derivatives of the energy for a unitary group based spin-adapted coupled cluster (CC) theory, namely, the combinatoric open-shell CC (COSCC) approach within the singles and doubles approximation. The widely used Lagrange multiplier approach is employed for the derivation of an analytical expression for the first derivative of the energy, which in combination with the well-established density-matrix formulation, is used for the computation of first-order electrical properties. Derivations of the spin-adapted lambda equations for determining the Lagrange multipliers and the expressions for the spin-free effective density matrices for the COSCC approach are presented. Orbital-relaxation effects due to the electric-field perturbation are treated via the Z-vector technique. We present calculations of the dipole moments for a number of doublet radicals in their ground states using restricted open-shell Hartree-Fock (ROHF) and quasi-restricted HF (QRHF) orbitals in order to demonstrate the applicability of our analytic scheme for computing energy derivatives. We also report calculations of the chlorine electric-field gradients and nuclear quadrupole-coupling constants for the CCl, CH2Cl, ClO2, and SiCl radicals.
NASA Astrophysics Data System (ADS)
Li, P. H. Y.; Bishop, R. F.; Campbell, C. E.
2015-01-01
We use the coupled cluster method (CCM) to study the zero-temperature ground-state (GS) properties of a spin-1/2 J1-J2 Heisenberg antiferromagnet on a triangular lattice with competing nearest-neighbor and next-nearest-neighbor exchange couplings J1>0 and J2≡κ J1>0 , respectively, in the window 0 ≤κ <1 . The classical version of the model has a single GS phase transition at κcl=1/8 in this window from a phase with 3-sublattice antiferromagnetic (AFM) 120∘ Néel order for κ <κcl to an infinitely degenerate family of 4-sublattice AFM Néel phases for κ >κcl . This classical accidental degeneracy is lifted by quantum fluctuations, which favor a 2-sublattice AFM striped phase. For the quantum model we work directly in the thermodynamic limit of an infinite number of spins, with no consequent need for any finite-size scaling analysis of our results. We perform high-order CCM calculations within a well-controlled hierarchy of approximations, which we show how to extrapolate to the exact limit. In this way we find results for the case κ =0 of the spin-1/2 model for the GS energy per spin, E /N =-0.5521 (2 ) J1 , and the GS magnetic order parameter, M =0.198 (5 ) (in units where the classical value is Mcl=1/2), which are among the best available. For the spin-1/2 J1-J2 model we find that the classical transition at κ =κcl is split into two quantum phase transitions at κ1c=0.060 (10 ) and κ2c=0.165 (5 ) . The two quasiclassical AFM states (viz., the 120∘ Néel state and the striped state) are found to be the stable GS phases in the regime κ <κ1c and κ >κ2c , respectively, while in the intermediate regimes κ1c<κ <κ2c the stable GS phase has no evident long-range magnetic order.
Haidar, S. M. Iguchi, R.; Yagmur, A.; Lustikova, J.; Shiomi, Y.; Saitoh, E.
2015-05-14
We have investigated dc voltage generation induced by ferromagnetic resonance in a Co{sub 75}Fe{sub 25}/Pt film. In order to reduce rectification effects of anisotropic magnetoresistance and the planar Hall effect, which may be observed simultaneously with the inverse spin Hall effect, we selected Co{sub 75}Fe{sub 25} with extremely small anisotropic magnetoresistance as a spin injector. Using the difference in the spectral shape of voltage and in the angle dependence of in-plane magnetization among the effects, we demonstrated that the generated dc voltage is governed by the inverse spin Hall effect induced by spin pumping.
Mapping spin-wave dispersions in stripe-ordered La2-xSrxNiO4 ( x=0.275 , 0.333)
NASA Astrophysics Data System (ADS)
Woo, Hyungje; Boothroyd, A. T.; Nakajima, K.; Perring, T. G.; Frost, C. D.; Freeman, P. G.; Prabhakaran, D.; Yamada, K.; Tranquada, J. M.
2005-08-01
Using the MAPS spectrometer at the ISIS spallation source, we have measured the magnetic excitations of single-crystal samples of stripe-ordered La2-xSrxNiO4 with x=0.333 and 0.275. The full two-dimensional spin-wave dispersions were obtained using incident energies of 60 and 160 meV. To analyze the excitations, we have evaluated a spin-only Hamiltonian describing diagonal, site-centered stripes in the linear spin-wave approximation. Besides the superexchange energy J within antiferromagnetic domains, we have considered effective exchange couplings J1 and J2 across a charge stripe coupling second-neighbor Ni sites along Ni-O bond directions and along the plaquette diagonal, respectively. From least-squares fits of the model to the measurements on the x=1/3 sample at T=10K , we find that the dispersions are well described by a model using just J and J1 , but not J and J2 . Consistent with an analysis of previous measurements, we find that J is about 90% of the superexchange energy of undoped La2NiO4 and J1/J≈0.5 . The excitations observed for x=0.275 are surprisingly similar to those for x=1/3 , despite the differing magnetic-ordering wave vectors; the main difference is a broadening of the excitations for x=0.275 . For both samples, we find that one spin-wave branch has a gap of ˜20meV , confirming a previous observation for x=1/3 . We discuss the possible origin of this gap.
Kim, Youngjae; Yun, Won Seok; Lee, J. D.
2016-01-01
Functionalized X-Bi bilayers (X = Ga, In, and Tl) with halogens bonded on their both sides have been recently claimed to be the giant topological insulators due to the strong band inversion strengths. Employing the first-principles electronic structure calculation, we find the topological band order transition from the order p – p – s of the X-Bi bilayers with halogens on their both sides to the new order p – s – p of the bilayers (especially for X = Ga and In) with halogen on one side and hydrogen on the other side, where the asymmetric hydrogen bonding simulates the substrate. We further find that the p – s bulk band gap of the bilayer bearing the new order p – s – p sensitively depends on the electric field, which enables a meaningful engineering of the quantum spin Hall edge state by controlling the external electric field. PMID:27623710
Kim, Youngjae; Yun, Won Seok; Lee, J D
2016-09-14
Functionalized X-Bi bilayers (X = Ga, In, and Tl) with halogens bonded on their both sides have been recently claimed to be the giant topological insulators due to the strong band inversion strengths. Employing the first-principles electronic structure calculation, we find the topological band order transition from the order p - p - s of the X-Bi bilayers with halogens on their both sides to the new order p - s - p of the bilayers (especially for X = Ga and In) with halogen on one side and hydrogen on the other side, where the asymmetric hydrogen bonding simulates the substrate. We further find that the p - s bulk band gap of the bilayer bearing the new order p - s - p sensitively depends on the electric field, which enables a meaningful engineering of the quantum spin Hall edge state by controlling the external electric field.
Code of Federal Regulations, 2013 CFR
2013-01-01
... Extracted From Nuclear Weapons 13617 Order 13617 Presidential Documents Executive Orders Executive Order... to the Disposition of Highly Enriched Uranium Extracted From Nuclear Weapons By the authority vested... accumulation of a large volume of weapons-usable fissile material in the territory of the Russian...
NASA Astrophysics Data System (ADS)
Delgado Acosta, E. G.; Banda Guzmán, V. M.; Kirchbach, M.
2015-03-01
We propose a general method for the description of arbitrary single spin- j states transforming according to ( j, 0) ⊕ (0, j) carrier spaces of the Lorentz algebra in terms of Lorentz tensors for bosons, and tensor-spinors for fermions, and by means of second-order Lagrangians. The method allows to avoid the cumbersome matrix calculus and higher ∂2 j order wave equations inherent to the Weinberg-Joos approach. We start with reducible Lorentz tensor (tensor-spinor) representation spaces hosting one sole ( j, 0) ⊕ (0, j) irreducible sector and design there a representation reduction algorithm based on one of the Casimir invariants of the Lorentz algebra. This algorithm allows us to separate neatly the pure spin- j sector of interest from the rest, while preserving the separate Lorentz and Dirac indexes. However, the Lorentz invariants are momentum independent and do not provide wave equations. Genuine wave equations are obtained by conditioning the Lorentz tensors under consideration to satisfy the Klein-Gordon equation. In so doing, one always ends up with wave equations and associated Lagrangians that are of second order in the momenta. Specifically, a spin-3/2 particle transforming as (3/2, 0) ⊕ (0, 3/2) is comfortably described by a second-order Lagrangian in the basis of the totally anti-symmetric Lorentz tensor-spinor of second rank, Ψ [ μν]. Moreover, the particle is shown to propagate causally within an electromagnetic background. In our study of (3/2, 0) ⊕ (0, 3/2) as part of Ψ [ μν] we reproduce the electromagnetic multipole moments known from the Weinberg-Joos theory. We also find a Compton differential cross-section that satisfies unitarity in forward direction. The suggested tensor calculus presents itself very computer friendly with respect to the symbolic software FeynCalc.
NASA Astrophysics Data System (ADS)
Schönecker, Stephan; Li, Xiaoqing; Johansson, Börje; Vitos, Levente
2016-08-01
The strained Fe-Co alloy in body-centered tetragonal (bct) structure has raised considerable interest due to its giant uniaxial magnetocrystalline anisotropy energy. On the basis of the classical Heisenberg Hamiltonian with ab initio interatomic exchange interactions, we perform a theoretical study of fundamental finite temperature magnetic properties of Fe1 -xCox alloy films as a function of three variables: chemical composition 0.3 ≤x ≤0.8 , bct geometry [a ,c (a )] arising from in-plane strain and associated out-of-plane relaxation, and atomic long-range order (ALRO). The Curie temperatures TC(x ,a ) obtained from Monte Carlo simulations display a competition between a pronounced dependence on tetragonality, strong ferromagnetism in the Co-rich alloy, and the beginning instability of ferromagnetic order in the Fe-rich alloy when c /a →√{2 } . Atomic ordering enhances TC and arises mainly due to different distributions of atoms in neighboring coordination shells rather than altering exchange interactions significantly. We investigate the ordering effect on the shape of the adiabatic spin-wave spectrum for selected pairs (x ,a ) . Our results indicate that long-wavelength acoustic spin-wave excitations show dependencies on x , a , and ALRO similar to those of TC. The directional anisotropy of the spin-wave stiffness d (x ,a ) peaks in narrow ranges of composition and tetragonality. ALRO exhibits a strong effect on d for near equiconcentration Fe-Co. We also discuss our findings in the context of employing Fe-Co as perpendicular magnetic recording medium.
Spin relaxation through Kondo scattering in Cu/Py lateral spin valves
NASA Astrophysics Data System (ADS)
Batley, J. T.; Rosaond, M. C.; Ali, M.; Linfield, E. H.; Burnell, G.; Hickey, B. J.
Within non-magnetic metals it is reasonable to expect the Elliot-Yafet mechanism to govern spin-relaxation and thus the temperature dependence of the spin diffusion length might be inversely proportional to resistivity. However, in lateral spin valves, measurements have found that at low temperatures the spin diffusion length unexpectedly decreases. We have fabricated lateral spin valves from Cu with different concentrations of magnetic impurities. Through temperature dependent charge and spin transport measurements we present clear evidence linking the presence of the Kondo effect within Cu to the suppression of the spin diffusion length below 30 K. We have calculated the spin-relaxation rate and isolated the contribution from magnetic impurities. At very low temperatures electron-electron interactions play a more prominent role in the Kondo effect. Well below the Kondo temperature a strong-coupling regime exists, where the moments become screened and the magnetic dephasing rate is reduced. We also investigate the effect of this low temperature regime (>1 K) on a pure spin current. This work shows the dominant role of Kondo scattering, even in low concentrations of order 1 ppm, within pure spin transport.
NASA Astrophysics Data System (ADS)
Gálisová, Lucia; Strečka, Jozef
2015-02-01
A hybrid spin-electron system defined on a one-dimensional double-tetrahedral chain, in which the localized Ising spin regularly alternates with two mobile electrons delocalized over a triangular plaquette, is exactly solved with the help of generalized decoration-iteration transformation. It is shown that a macroscopic degeneracy of ferromagnetic and ferrimagnetic ground states arising from chiral degrees of freedom of the mobile electrons cannot be lifted by a magnetic field in contrast to a macroscopic degeneracy of the frustrated ground state, which appears due to a kinetically driven frustration of the localized Ising spins. An anomalous behavior of all basic thermodynamic quantities can be observed on account of massive thermal excitations, which mimic a temperature-driven first-order phase transition from the nondegenerate frustrated state to the highly degenerate ferrimagnetic state at nonzero magnetic fields. A substantial difference in the respective degeneracies is responsible for an immense low-temperature peak of the specific heat and very abrupt (almost discontinuous) thermal variations of the entropy and sublattice magnetizations.
S. -H. Baek; Gu, G. D.; Utz, Y.; Hucker, M.; Buchner, B.; Grafe, H. -J.
2015-10-26
We report ^{139}La nuclear magnetic resonance studies performed on a La_{1.875}Ba_{0.125}CuO_{4} single crystal. The data show that the structural phase transitions (high-temperature tetragonal → low-temperature orthorhombic → low-temperature tetragonal phase) are of the displacive type in this material. The ^{139}La spin-lattice relaxation rate T^{–1}_{1} sharply upturns at the charge-ordering temperature T_{CO} = 54 K, indicating that charge order triggers the slowing down of spin fluctuations. Detailed temperature and field dependencies of the T^{–1}_{1} below the spin-ordering temperature T_{SO}=40 K reveal the development of enhanced spin fluctuations in the spin-ordered state for H ∥ [001], which are completely suppressed for large fields along the CuO_{2} planes. Lastly, our results shed light on the unusual spin fluctuations in the charge and spin stripe ordered lanthanum cuprates.
Spin dynamics, short-range order, and spin freezing in Y{sub 0.5}Ca{sub 0.5}BaCo{sub 4}O{sub 7}
Stewart, J. R.; Ehlers, G.; Mutka, H.; Fouquet, P.; Payen, C.; Lortz, R.
2011-01-15
Y{sub 0.5}Ca{sub 0.5}BaCo{sub 4}O{sub 7} was recently introduced as a possible candidate for capturing some of the predicted classical spin kagome ground-state features. Stimulated by this conjecture, we have taken up a more complete study of the spin correlations in this compound with neutron scattering methods on a powder sample characterized with high-resolution neutron diffraction and the temperature dependence of magnetic susceptibility and specific heat. We have found that the frustrated near-neighbor magnetic correlations involve not only the kagome planes but concern the full Co sublattice, as evidenced by the analysis of the wave-vector dependence of the short-range order. We conclude from our results that the magnetic moments are located on the Co sublattice as a whole and that correlations extend beyond the two-dimensional kagome planes. We identify intriguing dynamical properties, observing high-frequency fluctuations with a Lorentzian linewidth {Gamma}{<=}20 meV at ambient temperature. On cooling a low-frequency ({approx}1 meV) dynamical component develops alongside the high-frequency fluctuations, which eventually becomes static at temperatures below T{approx_equal}50 K. The high-frequency response with an overall linewidth of {approx}10 meV prevails at T{<=}2 K, coincident with a fully elastic short-range-ordered contribution.
NASA Astrophysics Data System (ADS)
Minamidate, T.; Matsunaga, N.; Nomura, K.; Sasaki, T.
2016-08-01
Magnetoresistance and Hall resistance measurements were conducted in the field-induced spin-density-wave (FISDW) phase of (TMTSF)2ReO4 above 1.0 GPa, with an anion ordering specified by Q_\\text{AO}=(0, 1/2, 1/2) . The quantized Hall resistance shows the sequence N = 0, 1, 2, -2, 4, -4, -6, -8, \\cdots , with decreasing field that is successfully explained by the “extended standard model”. Consequently, we demonstrate that the difference between the chemical and hydrostatic pressures is linked to the appearance of the peculiar FISDW phase of the TMTSF salts with Q_\\text{AO}=(0, 1/2, *) .
NASA Astrophysics Data System (ADS)
Sakai, Yoshiya; Shibata, Maki; Yokoyama, Daisuke
2015-09-01
Molecular orientation in organic light-emitting diodes (OLEDs) is now regarded as an important factor that affects device efficiency. However, methods to quantitatively estimate the degree of molecular orientation in OLEDs are currently limited, and they require constructing a model of an optical structure. Here, we propose a simple model-free method to estimate the orientation order parameters (S) of molecules in amorphous OLED films from their absorption spectra using the randomization of molecular orientation induced by heating. This method is used to quantitatively estimate the S values of vacuum-deposited and spin-coated films and clearly demonstrate the random orientation in the latter.
Becher, Carsten; Voigt, Jörg; Schierle, Enrico; Weschke, Eugen; Fiebig, Manfred; Brückel, Thomas
2013-01-01
We demonstrate spin-spiral-induced ferroelectricity in epitaxial TbMnO3 films grown on YAlO3 substrates down to a film thickness of 6nm. The ferroelectric polarization is identified by optical second-harmonic generation. Using x-ray resonant magnetic scattering we directly prove the existence of a noncollinear magnetic structure in the ferroelectric phase and thus bulk-like multiferroicity. The electric-field-induced reversal of the magnetic domains along with the reversal of the ferroelectric polarization evidences the rigid coupling of magnetic and ferroelectric order and hence a giant magnetoelectric effect in the films.
NASA Astrophysics Data System (ADS)
Kärkkäinen, Leo; Rummukainen, Kari
1991-05-01
This paper summarizes the contents of two talks presented at the conference. We compute the interface tension αoo of the interface between two ordered domains having different Z(3) values in Nt = 2 lattice SU(3) gauge theory. The interface is created dynamically by a twist along one plane of the lattice. We also study the variation of the order parameter < L> and of thermodynamic quantities across the interface. The formation of the interface and its fluctuations in Monte Carlo time were shown in a video presented at the conference.
The essential role of spin-memory loss at 3d/5d metallic interfaces in spin pumping
NASA Astrophysics Data System (ADS)
Jaffres, Henri
2015-03-01
I will present a review of experiments and theory of spin-pumping in Co/(Cu)/Pt 3d/5d metallic systems in the ferromagnetic resonance (FMR) regime of spin injection. By combining i) FMR analyses of the resonance linewidth of the Co spectra in contact with the Pt (or Cu/Pt) reservoir and ii) detection of the inverse spin-hall effect signal vs. Pt thickness, we were able to evidence two different lengthscales for the spin-current profile generated or absorbed at the interfaces. The first lenghscale, extracted from FMR analyses and of the order of 2 nm, represents a typical interface length characteristic of a spin memory loss at the Co/Pt and Co/Cu/Pt interfaces. This represent a typical region of spin-current dissipation by which almost 60-70 % of the total current generated is lost before conversion in bulk Pt. The second lengthscale, roughly equal to 3.4 nm, like determined by Inverse Spin Hall Effect (ISHE) transverse voltage measurement, is more characteristic of the spin-diffusion length of the bulk Pt that governs a part of the spin-to-charge conversion efficiency by ISHE. After careful analyses, we determined a spin-hall angle of 5.6 % for Pt and an intrinsic spin hall conductivity of 3200 (Ohm.cm)-1 for our corresponding Pt resistivity. In the end, I will focus on the physical description of our experiments within a derived Valet-Fert model describing the spin transport/relaxation in a diffusive approach and using relevant boundary conditions for spin-pumping (constant spin accumulation in the ferromagnet). The origin of the spin-memory loss and spin-current discontinuity, also proposed in a very recent work, will be explained in terms of atomic intermixing at interfaces or possible Rashba-split states at Co/Pt interfaces.
NASA Astrophysics Data System (ADS)
Holder, Tobias; Metzner, Walter
2014-10-01
We analyze the influence of quantum critical fluctuations on single-particle excitations at the onset of incommensurate 2kF charge- or spin-density wave order in two-dimensional metals. The case of a single pair of hot spots at high symmetry positions on the Fermi surface needs to be distinguished from the case of two hot spot pairs. We compute the fluctuation propagator and the electronic self-energy perturbatively in leading order. The energy dependence of the single-particle decay rate at the hot spots obeys non-Fermi-liquid power laws, with an exponent 2/3 in the case of a single hot spot pair, and exponent one for two hot spot pairs. The prefactors of the linear behavior obtained in the latter case are not particle-hole symmetric.
Cassera, M B; Silber, A M; Gennaro, A M
2002-10-16
The purpose of this work is to analyze the effects of cholesterol modulation on acyl chain ordering in the membrane of human erythrocytes as a function of depth from the surface. Partial cholesterol depletion was achieved by incubation of erythrocytes with liposomes containing saturated phospholipids, or with methyl-beta-cyclodextrin (MbetaCD). Cholesterol enrichment was achieved by incubation with liposomes formed by phospholipids/cholesterol, or with the complex MbetaCD/cholesterol. Acyl chain order was studied with electron paramagnetic resonance spectroscopy (EPR) using spin labels that sense the lipid bilayer at different depths. It is shown that the increase in cholesterol stiffens acyl chains but decreases the interaction among lipid headgroups, while cholesterol depletion causes the opposite behavior. It is likely that the observed cholesterol effects are related to those stabilizing the cholesterol-rich detergent-insoluble membrane domains (rafts), recently shown to exist in erythrocytes.
NASA Astrophysics Data System (ADS)
Nishiwaki, Yoichi; Tokunaga, Masashi; Sakakura, Ryo; Takeyama, Shojiro; Kato, Tetsuya; Iio, Katsunori
2017-04-01
Magnetization and electric polarization are measured for RbCoBr3 in the presence of an applied high magnetic field. The saturation of magnetization is recognized in the magnetization curve. The g-value of pseudospin and the nearest-neighbor intrachain exchange interaction of RbCoBr3, which has the properties of a quasi-one-dimensional Ising antiferromagnet, are evaluated. The electric polarization parallel to the c-axis under a magnetic field alone and also under the simultaneous application of electric and magnetic fields along the c-axis is observed to increase around the magnetic phase transition point from the ferrimagnetic low-temperature phase to the partially disordered high-temperature phase. Experimental results indicate that the electric polarization is induced through the rearrangement of the spin structure accompanied by the magnetic phase transition under an applied magnetic field. A probable reason for the enhancement of electric polarization is given from the viewpoint of the interplay between the distortion of the triangular lattice and the interchain exchange interactions.
Thompson, Corey; Greedan, John; Garlea, Vasile O; Flacau, Roxana; Tan, Malinda; Derakhshan, Shahab
2014-01-01
The novel iron-based compound, BaYFeO4, crystallizes in the Pnma space group with two distinct Fe3+ sites, that are alternately corner-shared [FeO5]7 square pyramids and [FeO6]9 octahedra, forming into [Fe4O18]24 rings, which propagate as columns along the b-axis. A recent report shows two discernible antiferromagnetic (AFM) transitions at 36 and 48 K in the susceptibility, yet heat capacity measurements reveal no magnetic phase transitions at these temperatures. An upturn in the magnetic susceptibility measurements up to 400 K suggests the presence of shortrange magnetic behavior at higher temperatures. In this Article, variable-temperature neutron powder diffraction and hightemperature magnetic susceptibility measurements were performed to clarify the magnetic behavior. Neutron powder diffraction confirmed that the two magnetic transitions observed at 36 and 48 K are due to long-range magnetic order. Below 48 K, the magnetic structure was determined as a spin-density wave (SDW) with a propagation vector, k = (0, 0, 1/3), and the moments along the b-axis, whereas the structure becomes an incommensurate cycloid [k = (0, 0, 0.35)] below 36 K with the moments within the bc-plane. However, for both cases the ordered moments on Fe3+ are only of the order 3.0 B, smaller than the expected values near 4.5 B, indicating that significant components of the Fe moments remain paramagnetic to the lowest temperature studied, 6 K. Moreover, new high-temperature magnetic susceptibility measurements revealed a peak maximum at 550 K indicative of short-range spin correlations. It is postulated that most of the magnetic entropy is thus removed at high temperatures which could explain the absence of heat capacity anomalies at the long-range ordering temperatures. Published spin dimer calculations, which appear to suggest a k = (0, 0, 0) magnetic structure, and allow for neither low dimensionality nor geometric frustration, are inadequate to explain the observed complex magnetic
Thompson, Corey M; Greedan, John E; Garlea, V Ovidiu; Flacau, Roxana; Tan, Malinda; Nguyen, Phuong-Hieu T; Wrobel, Friederike; Derakhshan, Shahab
2014-01-21
The novel iron-based compound, BaYFeO4, crystallizes in the Pnma space group with two distinct Fe(3+) sites, that are alternately corner-shared [FeO5](7-) square pyramids and [FeO6](9-) octahedra, forming into [Fe4O18](24-) rings, which propagate as columns along the b-axis. A recent report shows two discernible antiferromagnetic (AFM) transitions at 36 and 48 K in the susceptibility, yet heat capacity measurements reveal no magnetic phase transitions at these temperatures. An upturn in the magnetic susceptibility measurements up to 400 K suggests the presence of short-range magnetic behavior at higher temperatures. In this Article, variable-temperature neutron powder diffraction and high-temperature magnetic susceptibility measurements were performed to clarify the magnetic behavior. Neutron powder diffraction confirmed that the two magnetic transitions observed at 36 and 48 K are due to long-range magnetic order. Below 48 K, the magnetic structure was determined as a spin-density wave (SDW) with a propagation vector, k = (0, 0, (1)/3), and the moments along the b-axis, whereas the structure becomes an incommensurate cycloid [k = (0, 0, ∼0.35)] below 36 K with the moments within the bc-plane. However, for both cases the ordered moments on Fe(3+) are only of the order ∼3.0 μB, smaller than the expected values near 4.5 μB, indicating that significant components of the Fe moments remain paramagnetic to the lowest temperature studied, 6 K. Moreover, new high-temperature magnetic susceptibility measurements revealed a peak maximum at ∼550 K indicative of short-range spin correlations. It is postulated that most of the magnetic entropy is thus removed at high temperatures which could explain the absence of heat capacity anomalies at the long-range ordering temperatures. Published spin dimer calculations, which appear to suggest a k = (0, 0, 0) magnetic structure, and allow for neither low dimensionality nor geometric frustration, are inadequate to explain the
Nonlinear spin control by terahertz-driven anisotropy fields
NASA Astrophysics Data System (ADS)
Baierl, S.; Hohenleutner, M.; Kampfrath, T.; Zvezdin, A. K.; Kimel, A. V.; Huber, R.; Mikhaylovskiy, R. V.
2016-11-01
Future information technologies, such as ultrafast data recording, quantum computation or spintronics, call for ever faster spin control by light. Intense terahertz pulses can couple to spins on the intrinsic energy scale of magnetic excitations. Here, we explore a novel electric dipole-mediated mechanism of nonlinear terahertz-spin coupling that is much stronger than linear Zeeman coupling to the terahertz magnetic field. Using the prototypical antiferromagnet thulium orthoferrite (TmFeO3), we demonstrate that resonant terahertz pumping of electronic orbital transitions modifies the magnetic anisotropy for ordered Fe3+ spins and triggers large-amplitude coherent spin oscillations. This mechanism is inherently nonlinear, it can be tailored by spectral shaping of the terahertz waveforms and its efficiency outperforms the Zeeman torque by an order of magnitude. Because orbital states govern the magnetic anisotropy in all transition-metal oxides, the demonstrated control scheme is expected to be applicable to many magnetic materials.
NASA Astrophysics Data System (ADS)
Tung, Shen-Lung; Juang, Yau-Tarng; Wu, Wei-Ying; Shieh, Wern-Yarng
2011-12-01
In this article, the problems of exponential stability analysis and stabilisation of linear time-varying systems described by a class of second-order vector differential equations are considered. Using bounding techniques on the trajectories of a linear time-varying system, the stability problem of the time-varying system is transformed to that of a time-invariant system and a new sufficient condition for the exponential stability is obtained. Moreover, the new criterion is proven to be superior to a test presented in the recent literature. Finally, the proposed criterion is applied to the exponential stabilisation problem via state feedback. The results are illustrated by several numerical examples.
Goldey, Matthew; Head-Gordon, Martin
2014-06-19
Spin-component-scaled (SCS) second-order Møller-Plesset perturbation theory (MP2) improves the treatment of thermochemistry and noncovalent interactions relative to MP2, although the optimal scaling coefficients are quite different for thermochemistry versus noncovalent interactions. This work reconciles these two different scaling regimes for SCS-MP2 by using two different length scales for electronic attenuation of the two spin components. The attenuation parameters and scaling coefficients are optimized in the aug-cc-pVTZ (aTZ) basis using the S66 database of intermolecular interactions and the W4-11 database of thermochemistry. Transferability tests are performed for atomization energies and barrier heights, as well as on further test sets for inter- and intramolecular interactions. SCS dual-attenuated MP2 in the aTZ basis, SCS-MP2(2terfc, aTZ), performs similarly to SCS-MP2/aTZ for thermochemistry while frequently outperforming MP2 at the complete basis set limit (CBS) for nonbonded interactions.
NASA Astrophysics Data System (ADS)
Lefrancois, Daniel; Rehn, Dirk R.; Dreuw, Andreas
2016-08-01
For the calculation of adiabatic singlet-triplet gaps (STG) in diradicaloid systems the spin-flip (SF) variant of the algebraic diagrammatic construction (ADC) scheme for the polarization propagator in third order perturbation theory (SF-ADC(3)) has been applied. Due to the methodology of the SF approach the singlet and triplet states are treated on an equal footing since they are part of the same determinant subspace. This leads to a systematically more accurate description of, e.g., diradicaloid systems than with the corresponding non-SF single-reference methods. Furthermore, using analytical excited state gradients at ADC(3) level, geometry optimizations of the singlet and triplet states were performed leading to a fully consistent description of the systems, leading to only small errors in the calculated STGs ranging between 0.6 and 2.4 kcal/mol with respect to experimental references.
Lefrancois, Daniel; Rehn, Dirk R; Dreuw, Andreas
2016-08-28
For the calculation of adiabatic singlet-triplet gaps (STG) in diradicaloid systems the spin-flip (SF) variant of the algebraic diagrammatic construction (ADC) scheme for the polarization propagator in third order perturbation theory (SF-ADC(3)) has been applied. Due to the methodology of the SF approach the singlet and triplet states are treated on an equal footing since they are part of the same determinant subspace. This leads to a systematically more accurate description of, e.g., diradicaloid systems than with the corresponding non-SF single-reference methods. Furthermore, using analytical excited state gradients at ADC(3) level, geometry optimizations of the singlet and triplet states were performed leading to a fully consistent description of the systems, leading to only small errors in the calculated STGs ranging between 0.6 and 2.4 kcal/mol with respect to experimental references.
Evidence of spin-density-wave order in RFeAsO1-xFx from measurements of thermoelectric power
NASA Astrophysics Data System (ADS)
Matusiak, M.; Plackowski, T.; Bukowski, Z.; Zhigadlo, N. D.; Karpinski, J.
2009-06-01
Data on the magnetothermopower and specific heat of three compounds belonging to “1111” oxypnictides family are reported. One specimen (SmAsFeO0.8F0.2) is a superconductor with Tc=53K , while two others (SmAsFeO and NdAsFeO) are nonsuperconducting parent compounds. Our results confirm that spin-density-wave (SDW) order is present in SmAsFeO and NdAsFeO. In these two samples a strict connection between the thermoelectric power and electronic specific heat is found in the vicinity of SDW transition, which indicates that the chemical potential of charge carriers strongly depends on temperature in this region. Low-temperature data suggest presence of significant contribution magnon drag to the thermoelectric power.
NASA Astrophysics Data System (ADS)
Sau, Jay D.; Tewari, Sumanta; Lutchyn, Roman M.; Stanescu, Tudor D.; Das Sarma, S.
2010-12-01
We show that an ordinary semiconducting thin film with spin-orbit coupling can, under appropriate circumstances, be in a quantum topologically ordered state supporting exotic Majorana excitations which follow non-Abelian statistics. The key to the quantum topological order is the coexistence of spin-orbit coupling with proximity-induced s -wave superconductivity and an externally induced Zeeman coupling of the spins. For the Zeeman coupling below a critical value, the system is a nontopological (proximity-induced) s -wave superconductor. However, for a range of Zeeman coupling above the critical value, the lowest energy excited state inside a vortex is a zero-energy Majorana fermion state. The system, thus, has entered into a non-Abelian s -wave superconducting state via a topological quantum phase transition (TQPT) tuned by the Zeeman coupling. In the topological phase, since the time-reversal symmetry is explicitly broken by the Zeeman term in the Hamiltonian, the edge of the film constitutes a chiral Majorana wire. Just like the s -wave superconductivity, the Zeeman coupling can also be proximity induced in the film by an adjacent magnetic insulator. We show this by an explicit model tight-binding calculation for both types of proximity effects in the heterostructure geometry. Here we show that the same TQPT can be accessed by varying the interface transparency between the film and the superconductor. For the transparency below (above) a critical value, the system is a topological (regular) s -wave superconductor. In the one-dimensional version of the same structure and for the Zeeman coupling above the critical value, there are localized Majorana zero-energy modes at the two ends of a semiconducting quantum nanowire. In this case, the Zeeman coupling can be induced more easily by an external magnetic field parallel to the wire, obviating the need for a magnetic insulator. We show that, despite the fact that the superconducting pair potential in the nanowire is
NASA Astrophysics Data System (ADS)
Kato, Hatsuhiro; Kato, Hatsuyoshi
2016-05-01
We proposed a new discretisation scheme for deriving a second-order difference equation from any system being formulated with the weak-form theory framework. The proposed scheme enables us to extend the application range of the recursive transfer method (RTM) and to express perfectly matching conditions for port boundaries in a discrete fashion under the RTM framework. To evaluate the accuracy and demonstrate the validity of the proposed scheme, we discussed the scattering problem governed by the fourth-order differential equation that was hitherto outside the RTM application range. The difference equation can play an important role in maintaining the balance of the bending moment and the shear force at the interface of two segments. Using the new port boundary condition, a quasi-localised wave was extracted and found to be related to the phase shift due to Fano resonance.
Hanle magnetoresistance: The role of edge spin accumulation and interfacial spin current
NASA Astrophysics Data System (ADS)
Wu, H.; Zhang, X.; Wan, C. H.; Tao, B. S.; Huang, L.; Kong, W. J.; Han, X. F.
2016-11-01
We report the Hanle magnetoresistance (HMR) due to the spin precession of edge spin accumulation and interfacial spin current. Because of spin-orbit coupling (SOC), an electric current is accompanied by a transverse spin current, which builds up the spin accumulation at surfaces of Pt and the spin current across the YIG/Pt interface. Once a magnetic field is applied, the precession of spins will decrease the edge spin accumulation and interfacial spin current, which leads to an increased resistance of Pt via ISHE. Spin relaxation governs the HMR from edge spin accumulation, while spin diffusion and spin conversion play important roles in the HMR from interfacial spin current. This work provides another method to investigate the spin-orbit coupling by electrical measurement.
Spin-Spin Coupling in Asteroidal Binaries
NASA Astrophysics Data System (ADS)
Batygin, Konstantin; Morbidelli, Alessandro
2015-11-01
Gravitationally bound binaries constitute a substantial fraction of the small body population of the solar system, and characterization of their rotational states is instrumental to understanding their formation and dynamical evolution. Unlike planets, numerous small bodies can maintain a perpetual aspheroidal shape, giving rise to a richer array of non-trivial gravitational dynamics. In this work, we explore the rotational evolution of triaxial satellites that orbit permanently deformed central objects, with specific emphasis on quadrupole-quadrupole interactions. Our analysis shows that in addition to conventional spin-orbit resonances, both prograde and retrograde spin-spin resonances naturally arise for closely orbiting, highly deformed bodies. Application of our results to the illustrative examples of (87) Sylvia and (216) Kleopatra multi-asteroid systems implies capture probabilities slightly below ~10% for leading-order spin-spin resonances. Cumulatively, our results suggest that spin-spin coupling may be consequential for highly elongated, tightly orbiting binary objects.
Spin Pumping and Measurement of Spin Currents in Optical Superlattices
NASA Astrophysics Data System (ADS)
Schweizer, C.; Lohse, M.; Citro, R.; Bloch, I.
2016-10-01
We report on the experimental implementation of a spin pump with ultracold bosonic atoms in an optical superlattice. In the limit of isolated double wells, it represents a 1D dynamical version of the quantum spin Hall effect. Starting from an antiferromagnetically ordered spin chain, we periodically vary the underlying spin-dependent Hamiltonian and observe a spin current without charge transport. We demonstrate a novel detection method to measure spin currents in optical lattices via superexchange oscillations emerging after a projection onto static double wells. Furthermore, we directly verify spin transport through in situ measurements of the spins' center-of-mass displacement.
Spin Pumping and Measurement of Spin Currents in Optical Superlattices.
Schweizer, C; Lohse, M; Citro, R; Bloch, I
2016-10-21
We report on the experimental implementation of a spin pump with ultracold bosonic atoms in an optical superlattice. In the limit of isolated double wells, it represents a 1D dynamical version of the quantum spin Hall effect. Starting from an antiferromagnetically ordered spin chain, we periodically vary the underlying spin-dependent Hamiltonian and observe a spin current without charge transport. We demonstrate a novel detection method to measure spin currents in optical lattices via superexchange oscillations emerging after a projection onto static double wells. Furthermore, we directly verify spin transport through in situ measurements of the spins' center-of-mass displacement.
The spin-temperature theory of dynamic nuclear polarization and nuclear spin-lattice relaxation
NASA Technical Reports Server (NTRS)
Byvik, C. E.; Wollan, D. S.
1974-01-01
A detailed derivation of the equations governing dynamic nuclear polarization (DNP) and nuclear spin lattice relaxation by use of the spin temperature theory has been carried to second order in a perturbation expansion of the density matrix. Nuclear spin diffusion in the rapid diffusion limit and the effects of the coupling of the electron dipole-dipole reservoir (EDDR) with the nuclear spins are incorporated. The complete expression for the dynamic nuclear polarization has been derived and then examined in detail for the limit of well resolved solid effect transitions. Exactly at the solid effect transition peaks, the conventional solid-effect DNP results are obtained, but with EDDR effects on the nuclear relaxation and DNP leakage factor included. Explicit EDDR contributions to DNP are discussed, and a new DNP effect is predicted.
The ac-magnetic susceptibility and dielectric response of complex spin ordering processes in Mn₃O₄
Thota, Subhash E-mail: wilfrid.prellier@ensicaen.fr; Singh, Kiran; Simon, Ch.; Prellier, Wilfrid E-mail: wilfrid.prellier@ensicaen.fr; Nayak, Sanjib; Kumar, Jitendra
2014-09-14
We report a meticulous study of the ac-magnetization dynamics (χ{sub ac}(T)), relative dielectric permittivity ε{sub r}(T), and magneto-dielectric (Δε{sub r}/ε{sub r}(H)) response of various complex magnetic transitions that occur below the ferrimagnetic Néel temperature T{sub N} of Mn₃O₄. Besides the known sequence of transitions at T{sub N}~42.75 K, T₁~39 K, and T₂~34 K, the existence of a new anomaly reported recently at 38 K (T*) has been successfully probed by χ{sub ac}(T) and ε{sub r}(T) measurements. The effect of external dc-bias fields (H{sub DC}) and driving frequency (f) on the above mentioned transitions has been investigated in consonance with the ε{sub r}(T) and Δε{sub r}/ε{sub r}(T,H) results. For the first time, we observed a clear hysteresis of about 5.15 K in the zero-field ε{sub r}(T) across the incommensurate-to-commensurate transition T₂~34 K, which provides evidence to the first-order nature of this transition. The Arrott plot (H/M vs. M²}) criterion has been used to distinguish the nature of all the sequential transitions that take place below T{sub N}.
NASA Astrophysics Data System (ADS)
Izsák, Róbert; Neese, Frank
2013-07-01
The 'chain of spheres' approximation, developed earlier for the efficient evaluation of the self-consistent field exchange term, is introduced here into the evaluation of the external exchange term of higher order correlation methods. Its performance is studied in the specific case of the spin-component-scaled third-order Møller--Plesset perturbation (SCS-MP3) theory. The results indicate that the approximation performs excellently in terms of both computer time and achievable accuracy. Significant speedups over a conventional method are obtained for larger systems and basis sets. Owing to this development, SCS-MP3 calculations on molecules of the size of penicillin (42 atoms) with a polarised triple-zeta basis set can be performed in ∼3 hours using 16 cores of an Intel Xeon E7-8837 processor with a 2.67 GHz clock speed, which represents a speedup by a factor of 8-9 compared to the previously most efficient algorithm. Thus, the increased accuracy offered by SCS-MP3 can now be explored for at least medium-sized molecules.
Arora, Priya; Moudgil, R. K.; Bhukal, Nisha
2015-05-15
Static density-density correlation function has been calculated for a spin-polarized two-dimensional quantum electron fluid by including the first-order exchange and self-energy corrections to the random-phase approximation (RPA). This is achieved by determining these corrections to the RPA linear density-density response function, obtained by solving the equation of motion for the single-particle Green’s function. Resulting infinite hierarchy of equations (involving higher-order Green’s functions) is truncated by factorizing the two-particle Green’s function as a product of the single-particle Green’s function and one-particle distribution function. Numerical results of correlation function are compared directly against the quantum Monte Carlo simulation data due to Tanatar and Ceperley for different coupling parameter (r{sub s}) values. We find almost exact agreement for r{sub s}=1, with a noticeable improvement over the RPA. Its quality, however, deteriorates with increasing r{sub s}, but correction to RPA is quite significant.
NASA Astrophysics Data System (ADS)
Adolph, C.; Alekseev, M. G.; Alexakhin, V. Yu.; Alexandrov, Yu.; Alexeev, G. D.; Amoroso, A.; Antonov, A. A.; Austregesilo, A.; Badełek, B.; Balestra, F.; Barth, J.; Baum, G.; Bedfer, Y.; Berlin, A.; Bernhard, J.; Bertini, R.; Bettinelli, M.; Bicker, K.; Bieling, J.; Birsa, R.; Bisplinghoff, J.; Bordalo, P.; Bradamante, F.; Braun, C.; Bravar, A.; Bressan, A.; Büchele, M.; Burtin, E.; Capozza, L.; Chiosso, M.; Chung, S. U.; Cicuttin, A.; Crespo, M. L.; Dalla Torre, S.; Das, S.; Dasgupta, S. S.; Dasgupta, S.; Denisov, O. Yu.; Dhara, L.; Donskov, S. V.; Doshita, N.; Duic, V.; Dünnweber, W.; Dziewiecki, M.; Efremov, A.; Elia, C.; Eversheim, P. D.; Eyrich, W.; Faessler, M.; Ferrero, A.; Filin, A.; Finger, M.; Finger, M., Jr.; Fischer, H.; Franco, C.; du Fresne von Hohenesche, N.; Friedrich, J. M.; Frolov, V.; Garfagnini, R.; Gautheron, F.; Gavrichtchouk, O. P.; Gerassimov, S.; Geyer, R.; Giorgi, M.; Gnesi, I.; Gobbo, B.; Goertz, S.; Grabmüller, S.; Grasso, A.; Grube, B.; Gushterski, R.; Guskov, A.; Guthörl, T.; Haas, F.; von Harrach, D.; Heinsius, F. H.; Herrmann, F.; Heß, C.; Hinterberger, F.; Horikawa, N.; Höppner, Ch.; d'Hose, N.; Huber, S.; Ishimoto, S.; Ivanov, O.; Ivanshin, Yu.; Iwata, T.; Jahn, R.; Jary, V.; Jasinski, P.; Joosten, R.; Kabuß, E.; Kang, D.; Ketzer, B.; Khaustov, G. V.; Khokhlov, Yu. A.; Kisselev, Yu.; Klein, F.; Klimaszewski, K.; Koblitz, S.; Koivuniemi, J. H.; Kolosov, V. N.; Kondo, K.; Königsmann, K.; Konorov, I.; Konstantinov, V. F.; Korzenev, A.; Kotzinian, A. M.; Kouznetsov, O.; Krämer, M.; Kroumchtein, Z. V.; Kunne, F.; Kurek, K.; Lauser, L.; Lednev, A. A.; Lehmann, A.; Levorato, S.; Lichtenstadt, J.; Liska, T.; Maggiora, A.; Magnon, A.; Makke, N.; Mallot, G. K.; Mann, A.; Marchand, C.; Martin, A.; Marzec, J.; Matsuda, T.; Meshcheryakov, G.; Meyer, W.; Michigami, T.; Mikhailov, Yu. V.; Morreale, A.; Mutter, A.; Nagaytsev, A.; Nagel, T.; Nerling, F.; Neubert, S.; Neyret, D.; Nikolaenko, V. I.; Nowak, W.-D.; Nunes, A. S.; Olshevsky, A. G.; Ostrick, M.; Padee, A.; Panknin, R.; Panzieri, D.; Parsamyan, B.; Paul, S.; Perevalova, E.; Pesaro, G.; Peshekhonov, D. V.; Piragino, G.; Platchkov, S.; Pochodzalla, J.; Polak, J.; Polyakov, V. A.; Pretz, J.; Quaresma, M.; Quintans, C.; Rajotte, J.-F.; Ramos, S.; Rapatsky, V.; Reicherz, G.; Rocco, E.; Rondio, E.; Rossiyskaya, N. S.; Ryabchikov, D. I.; Samoylenko, V. D.; Sandacz, A.; Sapozhnikov, M. G.; Sarkar, S.; Savin, I. A.; Sbrizzai, G.; Schiavon, P.; Schill, C.; Schlüter, T.; Schmidt, A.; Schmidt, K.; Schmitt, L.; Schmïden, H.; Schönning, K.; Schopferer, S.; Schott, M.; Shevchenko, O. Yu.; Silva, L.; Sinha, L.; Sissakian, A. N.; Slunecka, M.; Smirnov, G. I.; Sosio, S.; Sozzi, F.; Srnka, A.; Steiger, L.; Stolarski, M.; Sulc, M.; Sulej, R.; Suzuki, H.; Sznajder, P.; Takekawa, S.; Ter Wolbeek, J.; Tessaro, S.; Tessarotto, F.; Tkatchev, L. G.; Uhl, S.; Uman, I.; Vandenbroucke, M.; Virius, M.; Vlassov, N. V.; Wang, L.; Weisrock, T.; Wilfert, M.; Windmolders, R.; Wiślicki, W.; Wollny, H.; Zaremba, K.; Zavertyaev, M.; Zemlyanichkina, E.; Ziembicki, M.; Zhuravlev, N.; Zvyagin, A.
2013-03-01
The gluon polarization in the nucleon was measured using open charm production by scattering 160GeV/c polarized muons off longitudinally polarized protons or deuterons. The data were taken by the COMPASS Collaboration between 2002 and 2007. A detailed account is given of the analysis method that includes the application of neural networks. Several decay channels of D0 mesons are investigated. Longitudinal spin asymmetries of the D meson production cross sections are extracted in bins of D0 transverse momentum and energy. At leading order QCD accuracy, the average gluon polarization is determined as ⟨Δg/g⟩LO=-0.06±0.21(stat.)±0.08(syst.) at the scale ⟨μ2⟩≈13(GeV/c)2 and an average gluon momentum fraction ⟨x⟩≈0.11. The average gluon polarization is also obtained at next-to-leading order QCD accuracy as ⟨Δg/g⟩ NLO=-0.13±0.15(stat.)±0.15(syst.) at the scale ⟨μ2⟩≈13(GeV/c)2 and ⟨x⟩≈0.20.
Zheng, Yan-Zhen; Xue, Wei; Zhang, Wei-Xiong; Tong, Ming-Liang; Chen, Xiao-Ming; Grandjean, Fernande; Long, Gary J; Ng, Seik-Weng; Panissod, Pierre; Drillon, Marc
2009-03-02
A three-dimensional mixed-valent iron(II,III) trans-1,4-cyclohexanedicarboxylate, 1,4-chdc, coordination polymer, [Fe(II)Fe(III)(mu(4)-O)(1,4-chdc)(1.5)](infinity), 1, has been synthesized hydrothermally by mixing iron powder and 1,4-chdcH(2) and investigated by X-ray diffraction, dc and ac magnetic susceptibility, and iron-57 Mossbauer spectroscopy over a wide range of temperatures. Single-crystal X-ray diffraction studies of 1 at 90(2), 293(2), and 473(2) K reveal a tetrahedral [Fe(II)(2)(mu(4)-O)Fe(III)(2)(mu(4)-O)](6+) mixed-spin-chain structure with no change in the P1 space group but with subtle changes in the Fe-O and Fe...Fe distances with increasing temperature. These changes are associated with the electron delocalization observed by Mossbauer spectroscopy above 225 K. Magnetic studies reveal three different magnetic regimes in 1 between 2 and 320 K. Above 36 K 1 is a one-dimensional ferrimagnetic-like complex with frustration arising from competing exchange interactions between the iron(II) and iron(III) ions in the chains. Between 36 and 25 K the interchain interactions are non-negligible and 1 undergoes three-dimensional ordering at 32.16 K but with some residual fluctuations. Below 25 K the residual fluctuations slow and eventually freeze below 15 K; the small net moment of 0.22 mu(B) per mole of 1 observed below 15 K may be attributed to a non-collinear or canted spin structure of the spins of the four iron ions in the [Fe(II)(2)(mu(4)-O)Fe(III)(2)(mu(4)-O)](6+) chains. Below 32 K the Mossbauer spectra of 1 exhibit sharp sextets for both the iron(III) and iron(II) ions and are consistent with either a static long-range or a short-range magnetic ground state or a slow relaxation between two canted magnetic states that are indistinguishable at the observed spectral resolution. The 85 and 155 K spectra reveal no electron delocalization and correspond solely to fixed valence iron(II) and iron(III). Between 225 and 310 K the spectra reveal the onset of
NASA Astrophysics Data System (ADS)
Calvo, Rafael; Sartoris, Rosana P.; Calvo, Hernán L.; Chagas, Edson F.; Rapp, Raul E.
2016-05-01
We study the spin chain behavior, a transition to 3D magnetic order and the magnitudes of the exchange interactions for the metal-amino acid complex Cu(D,L-alanine)2•H2O, a model compound to investigate exchange couplings supported by chemical paths characteristic of biomolecules. Thermal and magnetic data were obtained as a function of temperature (T) and magnetic field (B0). The magnetic contribution to the specific heat, measured between 0.48 and 30 K, displays above 1.8 K a 1D spin-chain behavior that can be fitted with an intrachain antiferromagnetic (AFM) exchange coupling constant 2J0=(-2.12±0.08) cm-1 (defined as ℋex(i,i+1) = -2J0SiṡSi+1), between neighbor coppers at 4.49 Å along chains connected by non-covalent and H-bonds. We also observe a narrow specific heat peak at 0.89 K indicating a phase transition to a 3D magnetically ordered phase. Magnetization curves at fixed T = 2, 4 and 7 K with B0 between 0 and 9 T, and at T between 2 and 300 K with several fixed values of B0 were globally fitted by an intrachain AFM exchange coupling constant 2J0=(-2.27±0.02) cm-1 and g = 2.091±0.005. Interchain interactions J1 between coppers in neighbor chains connected through long chemical paths with total length of 9.51 Å cannot be estimated from magnetization curves. However, observation of the phase transition in the specific heat data allows estimating the range 0.1≤|2J1|≤0.4 cm-1, covering the predictions of various approximations. We analyze the magnitudes of 2J0 and 2J1 in terms of the structure of the corresponding chemical paths. The main contribution in supporting the intrachain interaction is assigned to H-bonds while the interchain interactions are supported by paths containing H-bonds and carboxylate bridges, with the role of the H-bonds being predominant. We compare the obtained intrachain coupling with studies of compounds showing similar behavior and discuss the validity of the approximations allowing to calculate the interchain
NASA Astrophysics Data System (ADS)
Boone, Carl; Emori, Satoru; Nan, Tianxiang; Sun, Nian
2015-03-01
Spin pumping from a ferromagnet (FM) to a normal metal (NM) and spin transfer torque (STT) generated in a FM from an injected spin current should be reciprocal processes governed by the spin mixing conductance. The same should be true for the spin Hall effect (SHE) and inverse SHE, which are used to generate and measure spin currents. Past experiments on multilayer thin films involving FM and NM interfaces have measured only spin pumping or spin injection, and have utilized incomplete modeling that results in different effective values for the same parameter such as the spin mixing conductance or spin Hall angle. This gives rise to a large range of values reported in the literature. Here we develop a complete model for spin flow in the FM/NM system including SHE, spin diffusion and spin pumping that allows us to determine the true values of the spin transport parameters. To explore the physcis we use STT-ferromagnetic resonance (FMR) experiments of NM/FM/NM trilayers, and FMR spectroscopy of FM/NM bilayers where we simultaneously measure damping changes due to spin pumping, voltage generated by the inverse SHE, and STT generated by the SHE. These experiments, combined with the complete modeling, allow us to test the reciprocity of spin pumping and STT plus the SHE and its inverse.
NASA Astrophysics Data System (ADS)
Hnybida, Jeff
2016-10-01
We formulate the spin foam representation of discrete SU(2) gauge theory as a product of vertex amplitudes each of which is the spin network generating function of the boundary graph dual to the vertex. In doing so the sums over spins have been carried out. The boundary data of each n-valent node is explicitly reduced with respect to the local gauge invariance and has a manifest geometrical interpretation as a framed polyhedron of fixed total area. Ultimately, sums over spins are traded for contour integrals over simple poles and recoupling theory is avoided using generating functions.
Spin waves in a persistent spin-current Fermi liquid
Feldmann, J. D.; Bedell, K. S.
2010-06-15
We report two theoretical results for transverse spin waves, which arise in a system with a persistent spin current. Using Fermi liquid theory, we introduce a spin current in the ground state of a polarized or unpolarized Fermi liquid, and we derive the resultant spin waves using the Landau kinetic equation. The resulting spin waves have a q{sup 1} and q{sup 1/2} dispersion to leading order for the polarized and unpolarized systems, respectively.
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
2014-04-25
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.
Hole-doping-induced melting of spin-state ordering in PrBaCo2O5.5 +x
NASA Astrophysics Data System (ADS)
Miao, Ping; Lin, Xiaohuan; Lee, Sanghyun; Ishikawa, Yoshihisa; Torii, Shuki; Yonemura, Masao; Ueno, Tetsuro; Inami, Nobuhito; Ono, Kanta; Wang, Yingxia; Kamiyama, Takashi
2017-03-01
The layered perovskite cobaltite R BaCo2O5.5 (R : rare-earth elements) exhibits an abrupt temperature-induced metal-insulator transition (MIT) that has been attributed to spin-state ordering (SSO) of Co3 + ions. Here we investigate the hole-doping member of PrBaCo2O5.5 +x (0 ≤x ≤0.24 ) with multiple techniques. The analysis of crystal and magnetic structures by electron and neutron diffraction confirm the SSO in the insulating phase of undoped PrBaCo2O5.5 , which is melted by increasing the temperature across the MIT. In addition, we discover that hole doping to PrBaCo2O5.5 also melts the SSO in conjunction with an insulator-metal transition. The experimental results from electron and neutron diffraction and soft-x-ray absorption spectroscopy (XAS) all lead to the conclusion that hole-doping-induced MIT occurs in the same manner as the temperature-induced MIT. Therefore, we propose a unified mechanism that dominates the temperature- and hole-doping-induced MIT in the PrBaCo2O5.5 +x system. Specifically, this mechanism involves symmetry breaking coupled with a SSO in the paramagnetic phase.
Liu, Guang-Hua; You, Wen-Long; Li, Wei; Su, Gang
2015-04-29
Quantum phase transitions (QPTs) and the ground-state phase diagram of the spin-1/2 Heisenberg-Ising alternating chain (HIAC) with uniform Dzyaloshinskii-Moriya (DM) interaction are investigated by a matrix-product-state (MPS) method. By calculating the odd- and even-string order parameters, we recognize two kinds of Haldane phases, i.e. the odd- and even-Haldane phases. Furthermore, doubly degenerate entanglement spectra on odd and even bonds are observed in odd- and even-Haldane phases, respectively. A rich phase diagram including four different phases, i.e. an antiferromagnetic (AF), AF stripe, odd- and even-Haldane phases, is obtained. These phases are found to be separated by continuous QPTs: the topological QPT between the odd- and even-Haldane phases is verified to be continuous and corresponds to conformal field theory with central charge c = 1; while the rest of the phase transitions in the phase diagram are found to be c = 1/2. We also revisit, with our MPS method, the exactly solvable case of HIAC model with DM interactions only on odd bonds and find that the even-Haldane phase disappears, but the other three phases, i.e. the AF, AF stripe and odd-Haldane phases, still remain in the phase diagram. We exhibit the evolution of the even-Haldane phase by tuning the DM interactions on the even bonds gradually.
2003-08-01
spectroscopy laboratory including high pulse power capabilities (regenerative amplifiers and optical parametric amplifiers ) and broad spectral range ...The data identify narrow ranges of doping concentrations where spin lifetimes in semiconductors are enhanced by orders of magnitude, culminating in... dynamic measurements in the 10 to 100 picoseconds (ps) range . • A second program, which will come to fruition within one to two years, has the name
2012-05-01
responses from Government forces. More philosophically, foreign forces should not give up their own national values in the name of supporting another...delineate the responsibilities of each Government agency to realise that policy.220 It could also usefully describe the future international environment...protect the population and key infrastructure; promote political processes and governance structures, which lead to a political settlement that
Tanasa, Radu; Stancu, Alexandru; Enachescu, Cristian; Laisney, Jérôme; Boillot, Marie-Laure
2014-01-20
We discuss the influence of the embedding matrix on the thermal hysteretic behavior of spin transition microparticles of Fe(phen){sub 2}(NCS){sub 2} by using a series of experimental first order reversal curves (FORCs). The shape of FORCs supports the hypothesis considering additional interactions between the spin-transition microparticles and the embedding matrix, which compares to a negative pressure on the particles. A mean-field approach based on negative variable external pressures, together with a cut off/switch on of particles-matrix interactions accounts for the experimental features.
Slow spin relaxation in dipolar spin ice.
NASA Astrophysics Data System (ADS)
Orendac, Martin; Sedlakova, Lucia; Orendacova, Alzbeta; Vrabel, Peter; Feher, Alexander; Pajerowski, Daniel M.; Cohen, Justin D.; Meisel, Mark W.; Shirai, Masae; Bramwell, Steven T.
2009-03-01
Spin relaxation in dipolar spin ice Dy2Ti2O7 and Ho2Ti2O7 was investigated using the magnetocaloric effect and susceptibility. The magnetocaloric behavior of Dy2Ti2O7 at temperatures where the orientation of spins is governed by ``ice rules`` (T < Tice) revealed thermally activated relaxation; however, the resulting temperature dependence of the relaxation time is more complicated than anticipated by a mere extrapolation of the corresponding high temperature data [1]. A susceptibility study of Ho2Ti2O7 was performed at T > Tice and in high magnetic fields, and the results suggest a slow relaxation of spins analogous to the behavior reported in a highly polarized cooperative paramagnet [2]. [1] J. Snyder et al., Phys. Rev. Lett. 91 (2003) 107201. [2] B. G. Ueland et al., Phys. Rev. Lett. 96 (2006) 027216.
Spin-orbital short-range order in the honeycomb-based quantum magnet Ba3CuSb2O9
NASA Astrophysics Data System (ADS)
Nakatsuji, Satoru
2013-03-01
The realization of quantum correlated matter beyond one dimension has been vigorously pursued in geometrically frustrated spin systems for decades. In frustrated magnetic materials, however, symmetry breaking of orbital and chemical origin is usually found to induce semi-classical spin freezing. In this talk, I present a contrast case where spins and possibly orbitals remain in a liquid state down to low temperature even in a highly disordered structure of 6H-perovskite Ba3CuSb2O9. Our comprehensive experimental analysis indicates that the geometrical frustration of Wannier's Ising antiferromagnet on a triangular lattice can be exploited to build a nano-structured bipartite honeycomb lattice from electric dipolar spin-1/2 molecules. Despite a strong local Jahn-Teller distortion about the Cu2+ ion, the resulting spin-orbital random bond lattice not only retains hexagonal symmetry averaged over time and space, but it supports a gapless excitation spectrum without spin freezing down to ultralow temperatures. This is the work based on the collaboration with K. Kuga, K. Kimura, R. Satake, N. Katayama, E. Nishibori, H. Sawa, R. Ishii, M. Hagiwara, F. Bridges, T. U. Ito, W. Higemoto, Y. Karaki, M. Halim, A. A. Nugroho, J. A. Rodriguez-Rivera, M. A. Green, C. Broholm. This work is partially supported by Grant-in-Aid for Scientific Research (No. 20340089,21684019) from JSPS, by Grant-in-Aid for Scientific Research on Priority Areas (No. 1951010,19052003) from MEXT, Japan.
Kawame, Yu Akushichi, Taiju; Shuto, Yusuke; Sugahara, Satoshi; Takamura, Yota
2015-05-07
We successfully fabricate a (100)-orientated B2-type-Co{sub 2}FeSi{sub 0.5}Al{sub 0.5} (CFSA)/MgO/Si(100) tunnel contact that is promising for an efficient spin injector for Si channels. The MgO barrier is formed by radical oxidation of an Mg thin film deposited on a Si(100) surface at room temperature and successive radical oxygen annealing at 400 °C. The CFSA electrode is grown on the MgO barrier at 400 °C by ultrahigh-vacuum molecular beam deposition, and it exhibits a (100)-orientated columnar polycrystalline structure with a high degree (63%) of B2-order. The MgO barrier near the interface of the CFSA/MgO junction is crystallized with the (100) orientation, i.e., the spin filter effect due to the MgO barrier could be expected for this junction. A three-terminal Si-channel spin-accumulation device with a CFSA/MgO/Si(100) spin injector is fabricated, and the Hanle effect of accumulated spin polarized electrons injected from this contact to the Si channel is observed.
Bowlan, P.; Trugman, S. A.; Bowlan, J.; ...
2016-09-26
Here, we demonstrate an approach for directly tracking antiferromagnetic (AFM) spin dynamics by measuring ultrafast changes in a magnon resonance. We also test this idea on the multiferroic HoMnO 3 by optically photoexciting electrons, after which changes in the spin order are probed with a THz pulse tuned to a magnon resonance. This reveals a photoinduced change in the magnon line shape that builds up over 5–12 picoseconds, which we show to be the spin-lattice thermalization time, indicating that electrons heat the spins via phonons. We compare our results to previous studies of spin-lattice thermalization in ferromagnetic manganites, giving insightmore » into fundamental differences between the two systems. Finally, our work sheds light on the microscopic mechanism governing spin-phonon interactions in AFMs and demonstrates a powerful approach for directly monitoring ultrafast spin dynamics.« less
Bozkaya, Uğur
2014-10-14
An efficient implementation of analytic energy gradients and spin multiplicities for the density-fitted orbital-optimized second-order perturbation theory (DF-OMP2) [Bozkaya, U. J. Chem. Theory Comput. 2014, 10, 2371-2378] is presented. The DF-OMP2 method is applied to a set of alkanes, conjugated dienes, and noncovalent interaction complexes to compare the cost of single point analytic gradient computations with the orbital-optimized MP2 with the resolution of the identity approach (OO-RI-MP2) [Neese, F.; Schwabe, T.; Kossmann, S.; Schirmer, B.; Grimme, S. J. Chem. Theory Comput. 2009, 5, 3060-3073]. Our results demonstrate that the DF-OMP2 method provides substantially lower computational costs for analytic gradients than OO-RI-MP2. On average, the cost of DF-OMP2 analytic gradients is 9-11 times lower than that of OO-RI-MP2 for systems considered. We also consider aromatic bond dissociation energies, for which MP2 provides poor reaction energies. The DF-OMP2 method exhibits a substantially better performance than MP2, providing a mean absolute error of 2.5 kcal mol(-1), which is more than 9 times lower than that of MP2 (22.6 kcal mol(-1)). Overall, the DF-OMP2 method appears very helpful for electronically challenging chemical systems such as free radicals or other cases where standard MP2 proves unreliable. For such problematic systems, we recommend using DF-OMP2 instead of the canonical MP2 as a more robust method with the same computational scaling.
Spin-orbit torques and anisotropic magnetization damping in skyrmion crystals
NASA Astrophysics Data System (ADS)
Hals, Kjetil M. D.; Brataas, Arne
2014-02-01
The length scale of the magnetization gradients in chiral magnets is determined by the relativistic Dzyaloshinskii-Moriya interaction. Thus, even conventional spin-transfer torques are controlled by the relativistic spin-orbit coupling in these systems, and additional relativistic corrections to the current-induced torques and magnetization damping become important for a complete understanding of the current-driven magnetization dynamics. We theoretically study the effects of reactive and dissipative homogeneous spin-orbit torques and anisotropic damping on the current-driven skyrmion dynamics in cubic chiral magnets. Our results demonstrate that spin-orbit torques play a significant role in the current-induced skyrmion velocity. The dissipative spin-orbit torque generates a relativistic Magnus force on the skyrmions, whereas the reactive spin-orbit torque yields a correction to both the drift velocity along the current direction and the transverse velocity associated with the Magnus force. The spin-orbit torque corrections to the velocity scale linearly with the skyrmion size, which is inversely proportional to the spin-orbit coupling. Consequently, the reactive spin-orbit torque correction can be the same order of magnitude as the nonrelativistic contribution. More importantly, the dissipative spin-orbit torque can be the dominant force that causes a deflected motion of the skyrmions if the torque exhibits a linear or quadratic relationship with the spin-orbit coupling. In addition, we demonstrate that the skyrmion velocity is determined by anisotropic magnetization damping parameters governed by the skyrmion size.
One-dimensional spinon spin currents
NASA Astrophysics Data System (ADS)
Hirobe, Daichi; Sato, Masahiro; Kawamata, Takayuki; Shiomi, Yuki; Uchida, Ken-Ichi; Iguchi, Ryo; Koike, Yoji; Maekawa, Sadamichi; Saitoh, Eiji
2017-01-01
Quantum spin fluctuation in a low-dimensional or frustrated magnet breaks magnetic ordering while keeping spin correlation. Such fluctuation has been a central topic in magnetism because of its relevance to high-Tc superconductivity and topological states. However, utilizing such spin states has been quite difficult. In a one-dimensional spin-1/2 chain, a particle-like excitation called a spinon is known to be responsible for spin fluctuation in a paramagnetic state. Spinons behave as a Tomonaga-Luttinger liquid at low energy, and the spin system is often called a quantum spin chain. Here we show that a quantum spin chain generates and carries spin current, which is attributed to spinon spin current. This is demonstrated by observing an anisotropic negative spin Seebeck effect along the spin chains in Sr2CuO3. The results show that spin current can flow even in an atomic channel owing to long-range spin fluctuation.
Scattering bottleneck for spin dynamics in metallic helical antiferromagnetic dysprosium
NASA Astrophysics Data System (ADS)
Langner, M. C.; Roy, S.; Kemper, A. F.; Chuang, Y.-D.; Mishra, S. K.; Versteeg, R. B.; Zhu, Y.; Hertlein, M. P.; Glover, T. E.; Dumesnil, K.; Schoenlein, R. W.
2015-11-01
Ultrafast studies of magnetization dynamics have revealed fundamental processes that govern spin dynamics, and the emergence of time-resolved x-ray techniques has extended these studies to long-range spin structures that result from interactions with competing symmetries. By combining time-resolved resonant x-ray scattering and ultrafast magneto-optical Kerr studies, we show that the dynamics of the core spins in the helical magnetic structure occur on much longer time scales than the excitation of conduction electrons in the lanthanide metal Dy. The observed spin behavior differs markedly from that observed in the ferromagnetic phase of other lanthanide metals or transition metals and is strongly dependent on temperature and excitation fluence. This unique behavior results from coupling of the real-space helical spin structure to the shape of the conduction electron Fermi surface in momentum space, which creates a bottleneck in spin scattering events that transfer the valence excitation to the core spins. The dependence of the dynamics on the intersite interactions renders the helical ordering much more robust to perturbations than simple ferromagnetic or antiferromagnetic ordering, where dynamics are driven primarily by on-site interactions.
NASA Astrophysics Data System (ADS)
Geng, Rugang; Roy, Anandi; Subedi, Ram; Locklin, Jason; Nguyen, Tho; Zhao, Wenbo; Li, Xiaoguang
Charge transport in amorphous organic semiconductors is governed by carriers hopping between localized states with small spin diffusion length. Furthermore, the spin interfacial resistance of organic spin valves (OSVs) is poorly controlled resulting in controversial reports of the magnetoresistance response. Here, we used surface initiated Kumada transfer polycondensation to covalently graft π-conjugated poly(3-methylthiophene) brushes from the La0.67Sr0.33MnO3 (LSMO) bottom electrode. The covalent attachment along with the brush morphology allows for more control over the LSMO/brush interfacial resistance and large spacer mobility. Remarkably, with 15 nm brush spacer layer, we observed an optimum magnetoresistance (MR) effect of 70% at cryogenic temperatures and a MR of 2.7% at 280K. The temperature dependence of the MR is nearly an order of magnitude weaker than that found in control OSVs made from spin-coated poly(3-hexylthiophene). Using a variety of different brush layer thicknesses, the thickness dependent MR at 20K was investigated. A spin diffusion length of 20 nm at 5 mV junction voltage rapidly increases to 55 nm at -280 mV. We acknowledge NSF (CHE 1412714 and DMR 0953112) (J.L.), the UGA start-up funds and Faculty Research Grant (T.N.), NSFC and NBRPC (2012CB922003 and 2015CB921201, X.G.L.) for funding this work.
Spin Hall effect and spin swapping in diffusive superconductors
NASA Astrophysics Data System (ADS)
Espedal, Camilla; Lange, Peter; Sadjina, Severin; Mal'shukov, A. G.; Brataas, Arne
2017-02-01
We consider the spin-orbit-induced spin Hall effect and spin swapping in diffusive superconductors. By employing the nonequilibrium Keldysh Green's function technique in the quasiclassical approximation, we derive coupled transport equations for the spectral spin and particle distributions and for the energy density in the elastic scattering regime. We compute four contributions to the spin Hall conductivity, namely, skew scattering, side jump, anomalous velocity, and the Yafet contribution. The reduced density of states in the superconductor causes a renormalization of the spin Hall angle. We demonstrate that all four of these contributions to the spin Hall conductivity are renormalized in the same way in the superconducting state. In its simplest manifestation, spin swapping transforms a primary spin current into a secondary spin current with swapped current and polarization directions. We find that the spin-swapping coefficient is not explicitly but only implicitly affected by the superconducting gap through the renormalized diffusion coefficients. We discuss experimental consequences for measurements of the (inverse) spin Hall effect and spin swapping in four-terminal geometries. In our geometry, below the superconducting transition temperature, the spin-swapping signal is increased an order of magnitude while changes in the (inverse) spin Hall signal are moderate.
BAI,M.; LEHRACH,A.; LUCCIO,A.; MACKAY,W.W.; ROSER,T.; TSOUPAS,N.
2001-06-18
At the Relativistic Heavy Ion Collider (RHIC), polarized protons will be accelerated and stored for spin physics experiments. Two full helical snakes will be used to eliminate the depolarization due to imperfection and intrinsic spin resonances. Since no resonances are crossed in RHIC, the beam polarization remains fixed through acceleration. However, in order to reduce systematic errors, the experiment often requires the polarization direction reversed. This paper presents a method of using an ac dipole to obtain a full spin flip in the presence of two full snakes [1]. A similar method of using an rf solenoid for spin flip was tested at IUCF [2,3].
Picosecond Spin Seebeck Effect
NASA Astrophysics Data System (ADS)
Kimling, Johannes; Choi, Gyung-Min; Brangham, Jack T.; Matalla-Wagner, Tristan; Huebner, Torsten; Kuschel, Timo; Yang, Fengyuan; Cahill, David G.
2017-02-01
We report time-resolved magneto-optic Kerr effect measurements of the longitudinal spin Seebeck effect in normal metal /Y3Fe5 O12 bilayers driven by an interfacial temperature difference between electrons and magnons. The measured time evolution of spin accumulation induced by laser excitation indicates transfer of angular momentum across normal metal /Y3Fe5 O12 interfaces on a picosecond time scale, too short for contributions from a bulk temperature gradient in an yttrium iron garnet. The product of spin-mixing conductance and the interfacial spin Seebeck coefficient determined is of the order of 108 A m-2 K-1 .
Soydaş, Emine; Bozkaya, Uğur
2013-03-12
An assessment of the OMP3 method and its spin-component and spin-scaled variants for thermochemistry and kinetics is presented. For reaction energies of closed-shell systems, the CCSD, SCS-MP3, and SCS-OMP3 methods show better performances than other considered methods, and no significant improvement is observed due to orbital optimization. For barrier heights, OMP3 and SCS-OMP3 provide the lowest mean absolute deviations. The MP3 method yields considerably higher errors, and the spin scaling approaches do not help to improve upon MP3, but worsen it. For radical stabilization energies, the CCSD, OMP3, and SCS-OMP3 methods exhibit noticeably better performances than MP3 and its variants. Our results demonstrate that if the reference wave function suffers from a spin-contamination, then the MP3 methods dramatically fail. On the other hand, the OMP3 method and its variants can tolerate the spin-contamination in the reference wave function. For overall evaluation, we conclude that OMP3 is quite helpful, especially in electronically challenged systems, such as free radicals or transition states where spin contamination dramatically deteriorates the quality of the canonical MP3 and SCS-MP3 methods. Both OMP3 and CCSD methods scale as n(6), where n is the number of basis functions. However, the OMP3 method generally converges in much fewer iterations than CCSD. In practice, OMP3 is several times faster than CCSD in energy computations. Further, the stationary properties of OMP3 make it much more favorable than CCSD in the evaluation of analytic derivatives. For OMP3, the analytic gradient computations are much less expensive than CCSD. For the frequency computation, both methods require the evaluation of the perturbed amplitudes and orbitals. However, in the OMP3 case there is still a significant computational time savings due to simplifications in the analytic Hessian expression owing to the stationary property of OMP3. Hence, the OMP3 method emerges as a very useful
Spin supplementary conditions for spinning compact binaries
NASA Astrophysics Data System (ADS)
Mikóczi, Balázs
2017-03-01
We consider different spin supplementary conditions (SSC) for a spinning compact binary with the leading-order spin-orbit (SO) interaction. The Lagrangian of the binary system can be constructed, but it is acceleration-dependent in two cases of SSC. We rewrite the generalized Hamiltonian formalism proposed by Ostrogradsky and compute the conserved quantities and the dissipative part of relative motion during the gravitational radiation of each SSC. We give the orbital elements and observed quantities of the SO dynamics, for instance, the energy and the orbital angular momentum losses and waveforms, and discuss their SSC dependence.
Unstable spin-ice order in the stuffed metallic pyrochlore Pr_{2+x}Ir_{2-x}O_{7-δ}
MacLaughlin, D. E.; Bernal, O. O.; Shu, Lei; Ishikawa, Jun; Matsumoto, Yosuke; Wen, Jia -Jia; Mourigal, Martin P.; Stock, C.; Ehlers, Georg; Broholm, C. L.; Machida, Yo; Kimura, Kenta; Nakatsuji, Satoru; Shimura, Yasuyuki; Sakakibara, Toshiro
2015-08-24
Specific heat, elastic neutron scattering, and muon spin rotation experiments have been carried out on a well-characterized sample of “stuffed” (Pr-rich) Pr_{2+x}Ir_{2-x}O_{7-δ}. Elastic neutron scattering shows the onset of long-range spin-ice “2-in/2-out” magnetic order at 0.93 kelvin, with an ordered moment of 1.7(1) Bohr magnetons per Pr ion at low temperatures. Approximate lower bounds on the correlation length and correlation time in the ordered state are 170 angstroms and 0.7 nanosecond, respectively. Muon spin rotation experiments yield an upper bound 2.6(7) milliteslas on the local field B^{4f}_{loc} at the muon site, which is nearly two orders of magnitude smaller than the expected dipolar field for long-range spin-ice ordering of 1.7-Bohr magneton moments (120–270 milliteslas, depending on the muon site). This shortfall is due in part to splitting of the non-Kramers crystal-field ground-state doublets of near-neighbor Pr^{3+} ions by the positive-muon-induced lattice distortion. For this to be the only effect, however, ~160 Pr moments out to a distance of ~14 angstroms must be suppressed. An alternative scenario—one consistent with the observed reduced nuclear hyperfine Schottky anomaly in the specific heat—invokes slow correlated Pr-moment fluctuations in the ordered state that average B^{4f}_{loc} on the μSR time scale (~10^{-7} second), but are static on the time scale of the elastic neutron scattering experiments (~10^{-9} second). In this picture, the dynamic muon relaxation suggests a Pr^{3+} 4f correlation time of a few nanoseconds, which should be observable in a neutron spin echo experiment.
Squeezed spin states: Squeezing the spin uncertainty relations
NASA Technical Reports Server (NTRS)
Kitagawa, Masahiro; Ueda, Masahito
1993-01-01
The notion of squeezing in spin systems is clarified, and the principle for spin squeezing is shown. Two twisting schemes are proposed as building blocks for spin squeezing and are shown to reduce the standard quantum noise, s/2, of the coherent S-spin state down to the order of S(sup 1/3) and 1/2. Applications to partition noise suppression are briefly discussed.
Solvent removal during synthetic and Nephila fiber spinning.
Kojic, Nikola; Kojic, Milos; Gudlavalleti, Sauri; McKinley, Gareth
2004-01-01
The process by which spiders make their mechanically superior fiber involves removal of solvent (water) from a concentrated protein solution while the solution flows through a progressively narrowing spinning canal. Our aim was to determine a possible mechanism of spider water removal by using a computational model. To develop appropriate computational techniques for modeling of solvent removal during fiber spinning, a study was first performed using a synthetic solution. In particular, the effect of solvent removal during elongational flow (also exhibited in the spinning canal of the spider) on fiber mechanical properties was examined. The study establishes a model for solvent removal during dry spinning of synthetic fibers, assuming that internal diffusion governs solvent removal and that convective resistance is small. A variable internal solvent diffusion coefficient, dependent on solvent concentration, is also taken into account in the model. An experimental setup for dry (air) spinning was used to make fibers whose diameter was on the order of those made by spiders (approximately 1 microm). Two fibers of different thickness, corresponding to different spinning conditions, were numerically modeled for solvent removal and then mechanically tested. These tests showed that the thinner fiber, which lost more solvent under elongational flow, had 5-fold better mechanical properties (elastic modulus of 100 MPa and toughness of 15 MJ/m3) than the thicker fiber. Even though the mechanical properties were far from those of dragline spider silk (modulus of 10 GPa and toughness of 150 MJ/m3), the experimental methodology and numerical principles developed for the synthetic case proved to be valuable when establishing a model for the Nephila spinning process. In this model, an assumption of rapid convective water removal at the spinning canal wall was made, with internal diffusion of water through the fiber as the governing process. Then the diffusion coefficient of water
Spin dynamics of polarons and polaron pairs in a random hyperfine field
NASA Astrophysics Data System (ADS)
Roundy, Robert C.
Spin-dependent recombination of polaron pairs and spin relaxation of a single polaron are the most fundamental processes are responsible for the performance of organic spintronics-based devices such as light-emitting diodes and organic spin valves. In organic materials, with no spin-orbit coupling, both processes are due to random hyperfine fields created by protons neighboring the polaron sites. The essence of spin-dependent recombination is that in order to recombine the pair must be in the singlet state. Hyperfine fields acting on the electron and hole govern the spin-dynamics of localized pairs during the waiting time for recombination. We demonstrate that for certain domain of trapping configurations of hyperfine fields, crossover to the singlet state is quenched. This leads to the blocking of current. The phenomenon of organic magnetoresistance (OMAR) is described by counting the weights of trapping configurations as a function of magnetic field. This explains the universality of the lineshapes of the OMAR curves. In finite samples incomplete averaging over the hyperfine fields gives rise to mesoscopic fluctuations of the current response. We also demonstrate that under the condition of magnetic resonance, new trapping configurations emerge. This leads to nontrivial evolution of current through the sample with microwave power. When discussing spin-relaxation two questions can be asked: (a) How does the local spin polarization decay as a function of distance from the spin-polarized injector? (b) How does the injected spin decay as a function of time after spatial averaging? With regard to (a), we demonstrate that, while decaying exponentially on average, local spin-polarization exhibits giant fluctuations from point to point. Concerning (b), we find that for a spin-carrier which moves diffusively in low dimensions the decay is faster than a simple exponent. The underlying physics for both findings is that in describing spin evolution it is necessary to add up
Spin-noise correlations and spin-noise exchange driven by low-field spin-exchange collisions
NASA Astrophysics Data System (ADS)
Dellis, A. T.; Loulakis, M.; Kominis, I. K.
2014-09-01
The physics of spin-exchange collisions have fueled several discoveries in fundamental physics and numerous applications in medical imaging and nuclear magnetic resonance. We report on the experimental observation and theoretical justification of spin-noise exchange, the transfer of spin noise from one atomic species to another. The signature of spin-noise exchange is an increase of the total spin-noise power at low magnetic fields, on the order of 1 mG, where the two-species spin-noise resonances overlap. The underlying physical mechanism is the two-species spin-noise correlation induced by spin-exchange collisions.
Disorder-Induced Quantum Spin Liquid in Spin Ice Pyrochlores
NASA Astrophysics Data System (ADS)
Savary, Lucile; Balents, Leon
2017-02-01
We propose that in a certain class of magnetic materials, known as non-Kramers "spin ice," disorder induces quantum entanglement. Instead of driving glassy behavior, disorder provokes quantum superpositions of spins throughout the system and engenders an associated emergent gauge structure and set of fractional excitations. More precisely, disorder transforms a classical phase governed by a large entropy, classical spin ice, into a quantum spin liquid governed by entanglement. As the degree of disorder is increased, the system transitions between (i) a "regular" Coulombic spin liquid, (ii) a phase known as "Mott glass," which contains rare gapless regions in real space, but whose behavior on long length scales is only modified quantitatively, and (iii) a true glassy phase for random distributions with large width or large mean amplitude.
Ewings, R. A.; Perring, T. G.; Sikora, O.; ...
2016-07-06
We have used time-of-flight inelastic neutron scattering to measure the spin wave spectrum of the canonical half-doped manganite Pr0.5Ca0.5MnO3 in its magnetic and orbitally ordered phase. Comparison of the data, which cover multiple Brillouin zones and the entire energy range of the excitations, with several different models shows that only the CE-type ordered state provides an adequate description of the magnetic ground state, provided interactions beyond nearest neighbor are included. We are able to rule out a ground state in which there exist pairs of dimerized spins which interact only with their nearest neighbors. The Zener polaron ground state, whichmore » comprises strongly bound magnetic dimers, can be ruled out on the basis of gross features of the observed spin wave spectrum. A model with weaker dimerization reproduces the observed dispersion but can be ruled out on the basis of subtle discrepancies between the calculated and observed structure factors at certain positions in reciprocal space. Adding further neighbor interactions results in almost no dimerization, i.e. interpolating back to the CE model. These results are consistent with theoretical analysis of the degenerate double exchange model for half-doping.« less
NASA Astrophysics Data System (ADS)
Woods, Justin; Bhat, Vinayak; Farmer, Barry; Sklenar, Joseph; Teipel, Eric; Ketterson, John; Hastings, J. Todd; de Long, Lance
2015-03-01
Artificial spin ice (ASI) systems are composed of nanoscale ferromagnetic segments whose shape anisotropy dictates they behave as mesoscopic Ising spins. Most ASI have segments patterned on periodic lattices and a single vertex topology. We have continuously distorted 2D honeycomb and square lattices such that the pattern vertex spacings follow a Fibonacci chain sequence along primitive lattice directions. The Fibonacci distortion is related to the aperiodic translational symmetry of 2D artificial quasicrystals1 that cannot be viewed as continuous distortions of periodic lattices due to their forbidden (e.g., fivefold) rotational symmetries. In contrast, Fibonacci distortions of 2D periodic lattices can be ``turned on'' by control of the ratio of two lattice parameters d1 and d2. Distortions alter film segments such that pattern vertices are no longer equivalent and traditional spin ice rules are no longer strictly valid. We have performed OOMMF simulations of magnetization reversal for samples having different levels of distortion, and found the magnetic reversal to be dramatically slowed by small distortions (d1/d2 ~ 1). Research at Kentucky is supported by U.S. DoE Grant DE-FG02-97ER45653 and NSF Grant EPS-0814194.
NASA Astrophysics Data System (ADS)
Cahill, David G.
The coupling of spin and heat, i.e., spin caloritronics, gives rise to new physical phenomena in nanoscale spin devices and new ways to manipulate local magnetization. Our work in this field takes advantage of recent advances in the measurement and understanding of heat transport at the nanoscale using ultrafast lasers. We use a picosecond duration pump laser pulses as a source of heat and picosecond duration probe laser pulses to detect changes in temperature, spin accumulation, and spin transfer torque using a combination of time-domain thermoreflectance and time-resolved magneto-optic Kerr effect Our pump-probe optical methods enable us to change the temperature of ferromagnetic layers on a picosecond time-scale and generate enormous heat fluxes on the order of 100 GW m-2 that persist for ~ 30 ps. Thermally-driven ultrafast demagnetization of a perpendicular ferromagnet leads to spin accumulation in a normal metal and spin transfer torque in an in-plane ferromagnet. The data are well described by models of spin generation and transport based on differences and gradients of thermodynamic parameters. The spin-dependent Seebeck effect of a perpendicular ferromagnetic layer converts a heat current into spin current, which in turn can be used to exert a spin transfer torque (STT) on a second ferromagnetic layer with in-plane magnetization. Using a [Co,Ni] multilayer as the source of spin, an energy fluence of ~ 4 J m-2 creates thermal STT sufficient to induce ~ 1 % tilting of the magnetization of a 2 nm-thick CoFeB layer.
Bowlan, P.; Trugman, S. A.; Bowlan, J.; Zhu, J. -X.; Hur, N. J.; Taylor, A. J.; Yarotski, D. A.; Prasankumar, R. P.
2016-09-26
Here, we demonstrate an approach for directly tracking antiferromagnetic (AFM) spin dynamics by measuring ultrafast changes in a magnon resonance. We also test this idea on the multiferroic HoMnO _{3} by optically photoexciting electrons, after which changes in the spin order are probed with a THz pulse tuned to a magnon resonance. This reveals a photoinduced change in the magnon line shape that builds up over 5–12 picoseconds, which we show to be the spin-lattice thermalization time, indicating that electrons heat the spins via phonons. We compare our results to previous studies of spin-lattice thermalization in ferromagnetic manganites, giving insight into fundamental differences between the two systems. Finally, our work sheds light on the microscopic mechanism governing spin-phonon interactions in AFMs and demonstrates a powerful approach for directly monitoring ultrafast spin dynamics.
NASA Astrophysics Data System (ADS)
García-Muñoz, José Luis; Padilla-Pantoja, Jessica; Torrelles, Xavier; Blasco, Javier; Herrero-Martín, Javier; Bozzo, Bernat; Rodríguez-Velamazán, José A.
2016-07-01
In half-doped P r0.50A0.50Co O3 metallic perovskites, the spin-lattice coupling brings about distinct magnetostructural transitions for A =Ca and A =Sr at temperatures close to ˜100 K. However, the ground magnetic properties of P r0.50S r0.50Co O3 (PSCO) strongly differ from P r0.50C a0.50Co O3 ones, where a partial P r3 + to P r4 + valence shift and Co spin transition makes the system insulating below the transition. This paper investigates and describes the relationship between the I m m a →I 4 /m c m symmetry change [Padilla-Pantoja, García-Muñoz, Bozzo, Jirák, and Herrero-Martín, Inorg. Chem. 53, 12297 (2014)] and the original magnetic behavior of PSCO versus temperature and external magnetic fields. The FM1 and FM2 ferromagnetic phases, above and below the magnetostructural transition (TS 1˜120 K ) have been investigated. The FM2 phase of PSCO is composed of [100] FM domains, with magnetic symmetry I m'm'a (mx≠0 , mz=0 ). The magnetic space group of the FM1 phase is F m'm'm (with mx=my ). Neutron data analyses in combination with magnetometry and earlier reports results agrees with a reorientation of the magnetization axis by 45∘ within the a b plane across the transition, in which the system retains its metallic character. The presence below TS 1 of conjugated magnetic domains, both of F m'm'm symmetry but having perpendicular spin orientations along the diagonals in the x y plane of the tetragonal unit cell, is at the origin of the anomalies observed in the macroscopic magnetization. A relatively small field μ0H [⊥ z ] ≳30 mT is able to reorient the magnetization within the a b plane, whereas a higher field (μ0H [∥z ] ≳1.2 T at 2 K) is necessary to align the Co moments perpendicular to the a b plane. Such a spin reorientation, in which the orbital and spin components of the Co moment rotate joined by 45∘, was not observed previously in analogous cobaltites without praseodymium.
Thompson, C M; Carlo, J P; Flacau, R; Aharen, T; Leahy, I A; Pollichemi, J R; Munsie, T J S; Medina, T; Luke, G M; Munevar, J; Cheung, S; Goko, T; Uemura, Y J; Greedan, J E
2014-07-30
The B-site ordered double perovskite Ba2CaOsO6 was studied by dc magnetic susceptibility, powder neutron diffraction and muon spin relaxation methods. The lattice parameter is a = 8.3619(6) Å at 280 K and cubic symmetry [Formula: see text] is retained to 3.5 K with a = 8.3462(7) Å. Curie-Weiss susceptibility behaviour is observed for T > 100 K and the derived constants are C = 0.3361(3) emu K mol(-1) and ΘCW = -156.2(3) K, in excellent agreement with literature values. This Curie constant is much smaller than the spin-only value of 1.00 emu K mol(-1) for a 5d(2) Os(6+) configuration, indicating a major influence of spin-orbit coupling. Previous studies had detected both susceptibility and heat capacity anomalies near 50 K but no definitive conclusion was drawn concerning the nature of the ground state. While no ordered Os moment could be detected by powder neutron diffraction, muon spin relaxation (µSR) data show clear long-lived oscillations indicative of a continuous transition to long-range magnetic order below TC = 50 K. An estimate of the ordered moment on Os(6+) is ∼ 0.2 μB, based upon a comparison with µSR data for Ba2YRuO6 with a known ordered moment of 2.2 μB. These results are compared with those for isostructural Ba2YReO6 which contains Re(5+), also 5d(2), and has a nearly identical unit cell constant, a = 8.36278(2) Å-a structural doppelgänger. In contrast, Ba2YReO6 shows ΘCW = - 616 K, and a complex spin-disordered and, ultimately, spin-frozen ground state below 50 K, indicating a much higher level of geometric frustration than in Ba2CaOsO6. The results on these 5d(2) systems are compared to recent theory, which predicts a variety of ferromagnetic and antiferromagnetic ground states. In the case of Ba2CaOsO6, our data indicate that a complex four-sublattice magnetic structure is likely. This is in contrast to the spin-disordered ground state in Ba2YReO6, despite a lack of evidence for structural disorder
Yan, J.-Q.; Cao, H. B.; McGuire, M. A.; Ren, Y.; Sales, B. C.; Mandrus, D. G.
2013-06-10
The spin and orbital ordering in Dy₁₋_{x}Tb_{x}VO₃ (x=0 and 0.2) was studied by measuring x-ray powder diffraction, magnetization, specific heat, and neutron single-crystal diffraction. The results show that G-OO/C-AF and C-OO/G-AF phases coexist in Dy_{0.8}Tb_{0.20}VO_{3} in the temperature range 2–60 K, and the volume fraction of each phase is temperature and field dependent. The ordering of Dy moments at T* = 12 K induces a transition from G-OO/C-AF to a C-OO/G-AF phase. Magnetic fields suppress the long-range order of Dy moments and thus the C-OO/G-AF phase below T*. The polarized moments induced at the Dy sublattice by external magnetic fields couple to the V 3d moments, and this coupling favors the G-OO/C-AF state. Also discussed is the effect of the Dy-V magnetic interaction and local structure distortion on the spin and orbital ordering in Dy₁₋_{x}Tb_{x}VO₃.
Yan, J.-Q.; Cao, H. B.; McGuire, M. A.; ...
2013-06-10
The spin and orbital ordering in Dy₁₋xTbxVO₃ (x=0 and 0.2) was studied by measuring x-ray powder diffraction, magnetization, specific heat, and neutron single-crystal diffraction. The results show that G-OO/C-AF and C-OO/G-AF phases coexist in Dy0.8Tb0.20VO3 in the temperature range 2–60 K, and the volume fraction of each phase is temperature and field dependent. The ordering of Dy moments at T* = 12 K induces a transition from G-OO/C-AF to a C-OO/G-AF phase. Magnetic fields suppress the long-range order of Dy moments and thus the C-OO/G-AF phase below T*. The polarized moments induced at the Dy sublattice by external magnetic fieldsmore » couple to the V 3d moments, and this coupling favors the G-OO/C-AF state. Also discussed is the effect of the Dy-V magnetic interaction and local structure distortion on the spin and orbital ordering in Dy₁₋xTbxVO₃.« less
NASA Astrophysics Data System (ADS)
Ruangsri, Uchupol; Vigeland, Sarah J.; Hughes, Scott A.
2016-08-01
A small body orbiting a black hole follows a trajectory that, at leading order, is a geodesic of the black hole spacetime. Much effort has gone into computing "self-force" corrections to this motion, arising from the small body's own contributions to the system's spacetime. Another correction to the motion arises from coupling of the small body's spin to the black hole's spacetime curvature. Spin-curvature coupling drives a precession of the small body, and introduces a "force" (relative to the geodesic) which shifts the small body's worldline. These effects scale with the small body's spin at leading order. In this paper, we show that the equations which govern spin-curvature coupling can be analyzed with a frequency-domain decomposition, at least to leading order in the small body's spin. We show how to compute the frequency of precession along generic orbits, and how to describe the small body's precession and motion in the frequency domain. We illustrate this approach with a number of examples. This approach is likely to be useful for understanding spin coupling effects in the extreme mass ratio limit, and may provide insight into modeling spin effects in the strong field for nonextreme mass ratios.
NASA Astrophysics Data System (ADS)
Dieny, B.; Sousa, R.; Prejbeanu, L.
2007-04-01
Conventional electronics has in the past ignored the spin on the electron, however things began to change in 1988 with the discovery of giant magnetoresistance in metallic thin film stacks which led to the development of a new research area, so called spin-electronics. In the last 10 years, spin-electronics has achieved a number of breakthroughs from the point of view of both basic science and application. Materials research has led to several major discoveries: very large tunnel magnetoresistance effects in tunnel junctions with crystalline barriers due to a new spin-filtering mechanism associated with the spin-dependent symmetry of the electron wave functions new magnetic tunnelling barriers leading to spin-dependent tunnelling barrier heights and acting as spin-filters magnetic semiconductors with increasingly high ordering temperature. New phenomena have been predicted and observed: the possibility of acting on the magnetization of a magnetic nanostructure with a spin-polarized current. This effect, due to a transfer of angular momentum between the spin polarized conduction electrons and the local magnetization, can be viewed as the reciprocal of giant or tunnel magnetoresistance. It can be used to switch the magnetization of a magnetic nanostructure or to generate steady magnetic excitations in the system. the possibility of generating and manipulating spin current without charge current by creating non-equilibrium local accumulation of spin up or spin down electrons. The range of applications of spin electronics materials and phenomena is expanding: the first devices based on giant magnetoresistance were the magnetoresistive read-heads for computer disk drives. These heads, introduced in 1998 with current-in plane spin-valves, have evolved towards low resistance tunnel magnetoresistice heads in 2005. Besides magnetic recording technology, these very sensitive magnetoresistive sensors are finding applications in other areas, in particular in biology. magnetic
NASA Astrophysics Data System (ADS)
Reynolds, Christopher S.
2015-08-01
Black hole spin is important in both the fundamental physics and astrophysics realms. In fundamental terms, many extensions and alternatives to General Relativity (GR) reveal themselves through effects related to (or at least of the same order as) spin. Astrophysically, spin is a fossil record of how black holes have grown and may, in addition, be an important source of energy (e.g., powering relativistic jets from black hole systems). I shall review recent progress on observational studies of black hole spin, especially those made in the X-ray waveband. We now have multiple techniques that can be applied in our search for black hole spin; I shall discuss the concordance (or, sometimes, lack thereof) between these techniques. Finally, I shall discuss what we can expect in the next few years with the launch of new X-ray instrumentation as well as the deployment of the Event Horizon Telescope.
ERIC Educational Resources Information Center
Whitlatch, Jo Bell
1979-01-01
Reviews recent federal publications on government information, particularly in the area of general informational services, public access to government information and privacy issues, coordination of government information systems, and congressional information needs. (Author)
Spin-Orbit Torques and Anisotropic Magnetization Damping in Skyrmion Crystals
NASA Astrophysics Data System (ADS)
Hals, Kjetil; Brataas, Arne
2014-03-01
We theoretically study the effects of reactive and dissipative homogeneous spin-orbit torques and anisotropic damping on the current-driven skyrmion dynamics in cubic chiral magnets. Our results demonstrate that spin-orbit torques play a significant role in the current-induced skyrmion velocity. The dissipative spin-orbit torque generates a relativistic Magnus force on the skyrmions, whereas the reactive spin-orbit torque yields a correction to both the drift velocity along the current direction and the transverse velocity associated with the Magnus force. The spin-orbit torque corrections to the velocity scale linearly with the skyrmion size, which is inversely proportional to the spin-orbit coupling. Consequently, the reactive spin-orbit torque correction can be the same order of magnitude as the non-relativistic contribution. More importantly, the dissipative spin-orbit torque can be the dominant force that causes a deflected motion of the skyrmions if the torque exhibits a linear or quadratic relationship with the spin-orbit coupling. In addition, we demonstrate that the skyrmion velocity is determined by anisotropic magnetization damping parameters governed by the skyrmion size.
NASA Astrophysics Data System (ADS)
Ewings, R. A.; Perring, T. G.; Sikora, O.; Abernathy, D. L.; Tomioka, Y.; Tokura, Y.
2016-07-01
We have used time-of-flight inelastic neutron scattering to measure the spin wave spectrum of the canonical half-doped manganite Pr0.5Ca0.5MnO3 in its magnetic and orbitally ordered phase. The data, which cover multiple Brillouin zones and the entire energy range of the excitations, are compared with several different models that are all consistent with CE-type magnetic order, but arise through different exchange coupling schemes. The Goodenough model, i.e., an ordered state comprising strong nearest-neighbor ferromagnetic interactions along zigzag chains with antiferromagnetic interchain coupling, provides the best description of the data, provided that further neighbor interactions along the chains are included. We are able to rule out a coupling scheme involving formation of strongly bound ferromagnetic dimers, i.e., Zener polarons, on the basis of gross features of the observed spin wave spectrum. A model with weaker dimerization reproduces the observed dispersion but can be ruled out on the basis of discrepancies between the calculated and observed structure factors at certain positions in reciprocal space. Adding further neighbor interactions results in almost no dimerization, i.e., recovery of the Goodenough model. These results are consistent with theoretical analysis of the degenerate double exchange model for half-doping, and provide a recipe for how to interpret future measurements away from half-doping, where degenerate double exchange models predict more complex ground states.
NASA Astrophysics Data System (ADS)
Nakatsuji, S.; Tonomura, H.; Onuma, K.; Nambu, Y.; Sakai, O.; Maeno, Y.; Macaluso, R. T.; Chan, Julia Y.
2007-10-01
Our single crystal study reveals that the single-layer S=2 triangular Heisenberg antiferromagnet FeGa2S4 forms a frozen spin-disordered state, similar to the S=1 isostructural magnet NiGa2S4. In this state, the magnetic specific heat CM is not only insensitive to the field, but shows a T2 dependence that scales to CM of NiGa2S4, suggesting the same underlying mechanism of the 2D coherent behavior. In contrast, the bilayer system Fe2Ga2S5 exhibits a 3D antiferromagnetic order.
Neutron-scattering study of stripe-phase order of holes and spins in La1.48Nd0.4Sr0.12CuO4
NASA Astrophysics Data System (ADS)
Tranquada, J. M.; Axe, J. D.; Ichikawa, N.; Nakamura, Y.; Uchida, S.; Nachumi, B.
1996-09-01
We present a neutron diffraction study of charge and spin order within the CuO2 planes of La1.48Nd0.4Sr0.12CuO4, a crystal in which superconductivity is anomalously suppressed. At low temperatures we observe elastic magnetic superlattice peaks of the type (1/2+/-ɛ,1/2,0) and charge-order peaks at (2+/-2ɛ,0,0), where ɛ=0.118. After cooling the crystal through the low-temperature-orthorhombic (LTO) to low-temperature-tetragonal (LTT) phase transition near 70 K, the charge-order peaks appear first at ~60 K, with the magnetic peaks appearing below 50 K. The magnetic peaks increase in intensity by an order of magnitude below 3 K due to ordering of the Nd ions. We show that the observed diffraction features are consistent with stripe-phase order, in which the dopant-induced holes collect in domain walls that separate antiferromagnetic antiphase domains. The Q dependence of the magnetic scattering indicates that the low-temperature correlation length within the planes is substantial (~170 Å), but only very weak correlations exist between next-nearest-neighbor planes. Correlations between nearest-neighbor layers are frustrated by pinning of the charge stripes to the lattice distortions of the LTT phase. The spin-density-wave amplitude corresponds to a Cu moment of 0.10+/-0.03 μB. The behavior of the electrical resistivity within the LTT phase is examined, and the significance of stripe-phase correlations for understanding the unusual transport properties of layered cuprates is discussed.
NASA Astrophysics Data System (ADS)
Champagne, Benoît; Kirtman, Bernard
Static longitudinal polarizabilities (α) and second hyperpolarizabilities (γ) of model H2 chains have been calculated at different ab initio levels to address the performance of the recently proposed spin-component-scaled MP2 (SCS-MP2) method (Grimme, J. Chem Phys 2003, 118, 9095). For both α and γ, the SCS-MP2 method improves over the MP2 results in comparison with reference values evaluated at the CCSD(T) level. Differences from the reference are in the range of 4-6% for α and 1-4% for γ. In the case of γ, the SCS-MP2 scheme improves not only over MP2 but also MP4 and CCSD. Further studies are needed on π-conjugated systems to evaluate the generality of these results.
Magnon Bose-Einstein condensation and spin superfluidity
NASA Astrophysics Data System (ADS)
Bunkov, Yuriy M.; Volovik, Grigory E.
2010-04-01
Bose-Einstein condensation (BEC) is a quantum phenomenon of formation of a collective quantum state in which a macroscopic number of particles occupy the lowest energy state and thus is governed by a single wavefunction. Here we highlight the BEC in a magnetic subsystem—the BEC of magnons, elementary magnetic excitations. The magnon BEC is manifested as the spontaneously emerging state of the precessing spins, in which all spins precess with the same frequency and phase even in an inhomogeneous magnetic field. The coherent spin precession was observed first in superfluid 3He-B and this domain was called the homogeneously precessing domain (HPD). The main feature of the HPD is the induction decay signal, which ranges over many orders of magnitude longer than is prescribed by the inhomogeneity of magnetic field. This means that spins precess not with a local Larmor frequency, but coherently with a common frequency and phase. This BEC can also be created and stabilized by continuous NMR pumping. In this case the NMR frequency plays the role of a magnon chemical potential, which determines the density of the magnon condensate. The interference between two condensates has also been demonstrated. It was shown that HPD exhibits all the properties of spin superfluidity. The main property is the existence of a spin supercurrent. This spin supercurrent flows separately from the mass current. Transfer of magnetization by the spin supercurrent by a distance of more than 1 cm has been observed. Also related phenomena have been observed: the spin current Josephson effect; the phase-slip processes at the critical current; and the spin current vortex—a topological defect which is the analog of a quantized vortex in superfluids and of an Abrikosov vortex in superconductors; and so on. It is important to mention that the spin supercurrent is a magnetic phenomenon, which is not directly related to the mass superfluidity of 3He: it is the consequence of a specific
NASA Astrophysics Data System (ADS)
Tatara, Gen; Nakabayashi, Noriyuki
2014-05-01
Emergent electromagnetic field which couples to electron's spin in ferromagnetic metals is theoretically studied. Rashba spin-orbit interaction induces spin electromagnetic field which is in the linear order in gradient of magnetization texture. The Rashba-induced effective electric and magnetic fields satisfy in the absence of spin relaxation the Maxwell's equations as in the charge-based electromagnetism. When spin relaxation is taken into account besides spin dynamics, a monopole current emerges generating spin motive force via the Faraday's induction law. The monopole is expected to play an important role in spin-charge conversion and in the integration of spintronics into electronics.
Tatara, Gen; Nakabayashi, Noriyuki
2014-05-07
Emergent electromagnetic field which couples to electron's spin in ferromagnetic metals is theoretically studied. Rashba spin-orbit interaction induces spin electromagnetic field which is in the linear order in gradient of magnetization texture. The Rashba-induced effective electric and magnetic fields satisfy in the absence of spin relaxation the Maxwell's equations as in the charge-based electromagnetism. When spin relaxation is taken into account besides spin dynamics, a monopole current emerges generating spin motive force via the Faraday's induction law. The monopole is expected to play an important role in spin-charge conversion and in the integration of spintronics into electronics.
Non-Abelian hydrodynamics and the flow of spin in spin orbit coupled substances
NASA Astrophysics Data System (ADS)
Leurs, B. W. A.; Nazario, Z.; Santiago, D. I.; Zaanen, J.
2008-04-01
Motivated by the heavy ion collision experiments there is much activity in studying the hydrodynamical properties of non-Abelian (quark-gluon) plasmas. A major question is how to deal with color currents. Although not widely appreciated, quite similar issues arise in condensed matter physics in the context of the transport of spins in the presence of spin-orbit coupling. The key insight is that the Pauli Hamiltonian governing the leading relativistic corrections in condensed matter systems can be rewritten in a language of SU(2) covariant derivatives where the role of the non-Abelian gauge fields is taken by the physical electromagnetic fields: the Pauli system can be viewed as Yang-Mills quantum-mechanics in a 'fixed frame', and it can be viewed as an 'analogous system' for non-Abelian transport in the same spirit as Volovik's identification of the He superfluids as analogies for quantum fields in curved space time. We take a similar perspective as Jackiw and coworkers in their recent study of non-Abelian hydrodynamics, twisting the interpretation into the 'fixed frame' context, to find out what this means for spin transport in condensed matter systems. We present an extension of Jackiw's scheme: non-Abelian hydrodynamical currents can be factored in a 'non-coherent' classical part, and a coherent part requiring macroscopic non-Abelian quantum entanglement. Hereby it becomes particularly manifest that non-Abelian fluid flow is a much richer affair than familiar hydrodynamics, and this permits us to classify the various spin transport phenomena in condensed matter physics in an unifying framework. The "particle based hydrodynamics" of Jackiw et al. is recognized as the high temperature spin transport associated with semiconductor spintronics. In this context the absence of faithful hydrodynamics is well known, but in our formulation it is directly associated with the fact that the covariant conservation of non-Abelian currents turns into a disastrous non
Spin excitations in fluctuating stripe phases of doped cuprate superconductors.
Vojta, Matthias; Vojta, Thomas; Kaul, Ribhu K
2006-09-01
Using a phenomenological lattice model of coupled spin and charge modes, we determine the spin susceptibility in the presence of fluctuating stripe charge order. We assume the charge fluctuations to be slow compared to those of the spins, and combine Monte Carlo simulations for the charge order parameter with exact diagonalization of the spin sector. Our calculations unify the spin dynamics of both static and fluctuating stripe phases and support the notion of a universal spin excitation spectrum in doped cuprate superconductors.
Characterization of spin relaxation anisotropy in Co using spin pumping
NASA Astrophysics Data System (ADS)
Li, Yi; Cao, Wei; Bailey, W. E.
2016-11-01
Ferromagnets are believed to exhibit strongly anisotropic spin relaxation, with relaxation lengths for spin longitudinal to the magnetization significantly longer than those for spin transverse to the magnetization. Here, we characterize the anisotropy of spin relaxation in Co using the spin pumping contribution to Gilbert damping in noncollinearly magnetized Py1 -xCux /Cu/Co trilayer structures. The static magnetization angle between Py1 -xCux and Co, adjusted under field bias perpendicular to film planes, controls the projections of longitudinal and transverse spin current pumped from Py1 -xCux into Co. We find nearly isotropic absorption of pure spin current in Co using this technique; fits to a diffusive transport model yield the longitudinal spin relaxation length <2 nm in Co. The longitudinal spin relaxation lengths found are an order of magnitude smaller than those determined by current-perpendicular-to-planes giant magnetoresistance measurements, but comparable with transverse spin relaxation lengths in Co determined by spin pumping.
NASA Astrophysics Data System (ADS)
Ke, Yougang; Liu, Zhenxing; Liu, Yachao; Zhou, Junxiao; Shu, Weixing; Luo, Hailu; Wen, Shuangchun
2016-10-01
In this letter, we propose and experimentally demonstrate a compact photonic spin filter formed by integrating a Pancharatnam-Berry phase lens (focal length of ±f ) into a conventional plano-concave lens (focal length of -f). By choosing the input port of the filter, photons with a desired spin state, such as the right-handed component or the left-handed one, propagate alone its original propagation direction, while the unwanted spin component is quickly diverged after passing through the filter. One application of the filter, sorting the spin-dependent components of vector vortex beams on higher-order Poincaré sphere, is also demonstrated. Our scheme provides a simple method to manipulate light, and thereby enables potential applications for photonic devices.
Picosecond Spin Seebeck Effect.
Kimling, Johannes; Choi, Gyung-Min; Brangham, Jack T; Matalla-Wagner, Tristan; Huebner, Torsten; Kuschel, Timo; Yang, Fengyuan; Cahill, David G
2017-02-03
We report time-resolved magneto-optic Kerr effect measurements of the longitudinal spin Seebeck effect in normal metal/Y_{3}Fe_{5}O_{12} bilayers driven by an interfacial temperature difference between electrons and magnons. The measured time evolution of spin accumulation induced by laser excitation indicates transfer of angular momentum across normal metal/Y_{3}Fe_{5}O_{12} interfaces on a picosecond time scale, too short for contributions from a bulk temperature gradient in an yttrium iron garnet. The product of spin-mixing conductance and the interfacial spin Seebeck coefficient determined is of the order of 10^{8} A m^{-2} K^{-1}.
NASA Astrophysics Data System (ADS)
Özyilmaz, Barbaros
2012-02-01
Conventional electronic transistors involve the control of electronic charge at the nanoscale to realize memory, logic and communication functions. All these electronic charges, however, also carry a spin that remains unutilized in present commercial devices. This has motivated the search for new materials that propagate spin-polarized currents over large distances. Among the most promising materials for spintronics has been graphene. Micron-scale spin relaxation lengths have been previously demonstrated in single-layer graphene. Recently, we showed that bilayer graphene is a far more interesting candidate for spintronics. By fabricating spin valves on bilayer graphene we have achieved at room temperature spin relaxation times up to 2 nanoseconds, which are an order of magnitude higher than for single layer graphene [1]. Furthermore, the spin-relaxation time scales inversely with the mobility of BLG sample. This indicates the importance of D'yakonov-Perel' spin scattering in BLG. Last not but least, the presence of an electric field tunable band gap in bilayer graphene makes it particularly appealing. Our work provides fundamental insight into the unique properties of bilayer graphene for spintronic applications. Remarkably, a similar difference between single layer and bilayer graphene is also observed in large area graphene grown by the CVD method on copper. These results demonstrate the potential of CVD graphene in realistic spintronics devices [2]. [4pt] [1] T - Y. Yang et al., Observation of Long Spin-Relaxation Times in Bilayer Graphene at Room Temperature, PRL (2011). [0pt] [2] A. Avsar et al., Towards Wafer Scale Fabrication of Graphene Based Spin Valve Devices, Nano Lett. (2011).
Hatanaka, Takashi; Yoshida, Sumito; Ojino, Mayo; Ishii, Masami
2014-12-01
This research was carried out from the perspective that the damage to the people of Fukushima and others from the Fukushima Daiichi Nuclear Power Station (NPS) accident was an "information disaster." It evaluated the critical problems raised by and actual condition analysis on the process of events in the Fukushima Daiichi NPS disaster and responses of the governments and others, notification of the occurrence of the accident and evacuation order by the national and local governments and the evacuation of residents, and guidance for distribution and intake of stable iodine tablets. The research aimed to provide a basis for the implementation of effective distribution and intake of stable iodine tablets and responses to the "information disaster" in the nuclear power disaster. On March 15 at the time that the most radioactive substances were dispersed, even when the average wind speed at the site area was 1.6 m/s, the radioactive substances had reached the outer boundary of Urgent Protective action planning Zone (UPZ, the region with a radius of 30 km) within about five hours. Because of this, every second counted in the provision of information about the accident and the issuance of evacuation orders. This study evaluated the actual condition of information provision by the national government and others from the perspective of this awareness of the importance of time. On the basis of the results of this kind of consideration, we come to the following recommendations: The Nuclear Emergency Response Guidelines and the system for communication of information to medical providers should be revised. The national government should make preparations for the effective advance distribution and intake of stable iodine tablets.
NASA Astrophysics Data System (ADS)
Rinaldi, C.; Bertoli, S.; Asa, M.; Baldrati, L.; Manzoni, C.; Marangoni, M.; Cerullo, G.; Bianchi, M.; Sordan, R.; Bertacco, R.; Cantoni, M.
2016-10-01
The measurement of the spin diffusion length and/or lifetime in semiconductors is a key issue for the realisation of spintronic devices, exploiting the spin degree of freedom of carriers for storing and manipulating information. In this paper, we address such parameters in germanium (0 0 1) at room temperature (RT) by three different measurement methods. Exploiting optical spin orientation in the semiconductor and spin filtering across an insulating MgO barrier, the dependence of the resistivity on the spin of photo-excited carriers in Fe/MgO/Ge spin photodiodes (spin-PDs) was electrically detected. A spin diffusion length of 0.9 ± 0.2 µm was obtained by fitting the photon energy dependence of the spin signal by a mathematical model. Electrical techniques, comprising non-local four-terminal and Hanle measurements performed on CoFeB/MgO/Ge lateral devices, led to spin diffusion lengths of 1.3 ± 0.2 µm and 1.3 ± 0.08 µm, respectively. Despite minor differences due to experimental details, the order of magnitude of the spin diffusion length is the same for the three techniques. Although standard electrical methods are the most employed in semiconductor spintronics for spin diffusion length measurements, here we demonstrate optical spin orientation as a viable alternative for the determination of the spin diffusion length in semiconductors allowing for optical spin orientation.
1988-05-01
manufacturers. The Navy has a major in- house design capability for ships; the government does not possess such a capability for aircraft or other weapon systems...the Coast Guard, government agencies acquire a wide variety of ships, ranging from sophisticated submarines and nuclear aircraft carriers to much...the initial phase a review was made of written material relating to government procedures in U.S. Government agencies for acquiring vessels, aircraft
1949-07-01
CGSC MG MILITARY GOVERNMENT LIBHARY ARI\\’IY WAR COLLEGE CJ\\RLISLE BARRACKS, PAa This text is approved for resident and extension-course...and functions · of ’ military government . It conforms ·substantially to the subject matter , of Field Manual 27-5, Civil Affairs/ Military Government ...Teaching experience at the Command and General Staff College has ···--·demonstrated the need for a military government text which brings to- gether
Zhu, Jian-xin; Dai, Jianhui; Si, Qimiao
2009-01-01
Some of the high {Tc} iron pnictides contain rare-earth elements, raising the question of how the existence and tunability of a d-electron antiferromagnetic order influences the heavy fermion behavior of the f-moments. With CeOFeP and CeOFeAs in mind as prototypes, we derive an extended Anderson lattice model appropriate for these quaternary systems. We show that the Kondo screening of the f-moments are efficiently suppressed by the d-electron ordering. We also argue that, inside the d-electron ordered state (as in CeOFeAs), the f-moments provide a rare realization of a quantum frustrated magnet with competing J{sub 1}-J{sub 2}-J{sub 3} interactions in an effective square lattice. Implications ofr the heavy fermion physics in broader contexts are also discussed.
ERIC Educational Resources Information Center
Mondale, Walter F.
1975-01-01
In order to deal successfully with the changes and pressures placed upon families, article considered the extent government policies are helping or hurting families, and what kind of support services are available. (Author/RK)
Jiang, Yu; Huq, Ashfia; Booth, Corwin H.; Ehlers, Georg; Greedan, John E.; Gardner, Jason S.
2011-02-11
To understand the origin of the spin-glass state in molybdate pyrochlores, the structure of Tb{sub 2}Mo{sub 2}O{sub 7} is investigated using two techniques: the long-range lattice structure was measured using neutron powder diffraction (NPD), and local structure information was obtained from the extended x-ray absorption fine structure (EXAFS) technique. While the long-range structure appears generally well ordered, enhanced mean-squared site displacements on the O(1) site and the lack of temperature dependence of the strongly anisotropic displacement parameters for both the Mo and O(1) sites indicate some disorder exists. Likewise, the local structure measurements indicate some Mo-Mo and Tb-O(1) nearest-neighbor disorder exists, similar to that found in the related spin-glass pyrochlore, Y{sub 2}Mo{sub 2}O{sub 7}. Although the freezing temperature in Tb{sub 2}Mo{sub 2}O{sub 7}, 25 K, is slightly higher than in Y{sub 2}Mo{sub 2}O{sub 7}, 22 K, the degree of local pair distance disorder is actually less in Tb{sub 2}Mo{sub 2}O{sub 7}. This apparent contradiction is considered in light of the interactions involved in the freezing process.
Spin Hall voltages from a.c. and d.c. spin currents
Wei, Dahai; Obstbaum, Martin; Ribow, Mirko; Back, Christian H.; Woltersdorf, Georg
2014-01-01
In spin electronics, the spin degree of freedom is used to transmit and store information. To this end the ability to create pure spin currents—that is, without net charge transfer—is essential. When the magnetization vector in a ferromagnet–normal metal junction is excited, the spin pumping effect leads to the injection of pure spin currents into the normal metal. The polarization of this spin current is time-dependent and contains a very small d.c. component. Here we show that the large a.c. component of the spin currents can be detected efficiently using the inverse spin Hall effect. The observed a.c.-inverse spin Hall voltages are one order of magnitude larger than the conventional d.c.-inverse spin Hall voltages measured on the same device. Our results demonstrate that ferromagnet–normal metal junctions are efficient sources of pure spin currents in the gigahertz frequency range. PMID:24780927
Kim, Inkoo; Lee, Yoon Sup
2014-10-28
We report the formulation and implementation of KRCASPT2, a two-component multi-configurational second-order perturbation theory based on Kramers restricted complete active space self-consistent field (KRCASSCF) reference function, in the framework of the spin-orbit relativistic effective core potential. The zeroth-order Hamiltonian is defined as the sum of nondiagonal one-electron operators with generalized two-component Fock matrix elements as scalar factors. The Kramers symmetry within the zeroth-order Hamiltonian is maintained via the use of a state-averaged density, allowing a consistent treatment of degenerate states. The explicit expressions are derived for the matrix elements of the zeroth-order Hamiltonian as well as for the perturbation vector. The use of a fully variational reference function and nondiagonal operators in relativistic multi-configurational perturbation theory is reported for the first time. A series of initial calculations are performed on the ionization potential and excitation energies of the atoms of the 6p-block; the results display a significant improvement over those from KRCASSCF, showing a closer agreement with experimental results. Accurate atomic properties of the superheavy elements of the 7p-block are also presented, and the electronic structures of the low-lying excited states are compared with those of their lighter homologues.
Shinohara, Takeshi; Ikawa, Shukuko; Iwasaki, Wakana; Hiraki, Toshiki; Hikima, Takaaki; Mikawa, Tsutomu; Arai, Naoto; Kamiya, Nobuo; Shibata, Takehiko
2015-01-01
In all organisms, RecA-family recombinases catalyze homologous joint formation in homologous genetic recombination, which is essential for genome stability and diversification. In homologous joint formation, ATP-bound RecA/Rad51-recombinases first bind single-stranded DNA at its primary site and then interact with double-stranded DNA at another site. The underlying reason and the regulatory mechanism for this conserved binding order remain unknown. A comparison of the loop L1 structures in a DNA-free RecA crystal that we originally determined and in the reported DNA-bound active RecA crystals suggested that the aspartate at position 161 in loop L1 in DNA-free RecA prevented double-stranded, but not single-stranded, DNA-binding to the primary site. This was confirmed by the effects of the Ala-replacement of Asp-161 (D161A), analyzed directly by gel-mobility shift assays and indirectly by DNA-dependent ATPase activity and SOS repressor cleavage. When RecA/Rad51-recombinases interact with double-stranded DNA before single-stranded DNA, homologous joint-formation is suppressed, likely by forming a dead-end product. We found that the D161A-replacement reduced this suppression, probably by allowing double-stranded DNA to bind preferentially and reversibly to the primary site. Thus, Asp-161 in the flexible loop L1 of wild-type RecA determines the preference for single-stranded DNA-binding to the primary site and regulates the DNA-binding order in RecA-catalyzed recombinase reactions. PMID:25561575
Spin noise in the anisotropic central spin model
NASA Astrophysics Data System (ADS)
Hackmann, Johannes; Anders, Frithjof B.
2014-01-01
Spin-noise measurements can serve as a direct probe for the microscopic decoherence mechanism of an electronic spin in semiconductor quantum dots (QDs). We have calculated the spin-noise spectrum in the anisotropic central spin model using a Chebyshev expansion technique which exactly accounts for the dynamics up to an arbitrary long but fixed time in a finite-size system. In the isotropic case, describing QD charge with a single electron, the short-time dynamics is in good agreement with quasistatic approximations for the thermodynamic limit. The spin-noise spectrum, however, shows strong deviations at low frequencies with a power-law behavior of ω-3/4 corresponding to a t-1/4 decay at intermediate and long times. In the Ising limit, applicable to QDs with heavy-hole spins, the spin-noise spectrum exhibits a threshold behavior of (ω-ωL)-1/2 above the Larmor frequency ωL=gμBB. In the generic anisotropic central spin model we have found a crossover from a Gaussian type of spin-noise spectrum to a more Ising-type spectrum with increasing anisotropy in a finite magnetic field. In order to make contact with experiments, we present ensemble averaged spin-noise spectra for QD ensembles charged with single electrons or holes. The Gaussian-type noise spectrum evolves to a more Lorentzian shape spectrum with increasing spread of characteristic time scales and g factors of the individual QDs.
Spin Funneling for Enhanced Spin Injection into Ferromagnets
NASA Astrophysics Data System (ADS)
Sayed, Shehrin; Diep, Vinh Q.; Camsari, Kerem Yunus; Datta, Supriyo
2016-07-01
It is well-established that high spin-orbit coupling (SOC) materials convert a charge current density into a spin current density which can be used to switch a magnet efficiently and there is increasing interest in identifying materials with large spin Hall angle for lower switching current. Using experimentally benchmarked models, we show that composite structures can be designed using existing spin Hall materials such that the effective spin Hall angle is larger by an order of magnitude. The basic idea is to funnel spins from a large area of spin Hall material into a small area of ferromagnet using a normal metal with large spin diffusion length and low resistivity like Cu or Al. We show that this approach is increasingly effective as magnets get smaller. We avoid unwanted charge current shunting by the low resistive NM layer utilizing the newly discovered phenomenon of pure spin conduction in ferromagnetic insulators via magnon diffusion. We provide a spin circuit model for magnon diffusion in FMI that is benchmarked against recent experiments and theory.
Spin Funneling for Enhanced Spin Injection into Ferromagnets
Sayed, Shehrin; Diep, Vinh Q.; Camsari, Kerem Yunus; Datta, Supriyo
2016-01-01
It is well-established that high spin-orbit coupling (SOC) materials convert a charge current density into a spin current density which can be used to switch a magnet efficiently and there is increasing interest in identifying materials with large spin Hall angle for lower switching current. Using experimentally benchmarked models, we show that composite structures can be designed using existing spin Hall materials such that the effective spin Hall angle is larger by an order of magnitude. The basic idea is to funnel spins from a large area of spin Hall material into a small area of ferromagnet using a normal metal with large spin diffusion length and low resistivity like Cu or Al. We show that this approach is increasingly effective as magnets get smaller. We avoid unwanted charge current shunting by the low resistive NM layer utilizing the newly discovered phenomenon of pure spin conduction in ferromagnetic insulators via magnon diffusion. We provide a spin circuit model for magnon diffusion in FMI that is benchmarked against recent experiments and theory. PMID:27374496
Spin polarization transfer by the radical pair mechanism.
Zarea, Mehdi; Ratner, Mark A; Wasielewski, Michael R
2015-08-07
In a three-site representation, we study a spin polarization transfer from radical pair spins to a nearby electron or nuclear spin. The quantum dynamics of the radical pair spins is governed by a constant exchange interaction between the radical pair spins which have different Zeeman frequencies. Radical pair spins can recombine to the singlet ground state or to lower energy triplet states. It is then shown that the coherent dynamics of the radical pair induces spin polarization on the nearby third spin in the presence of a magnetic field. The spin polarization transfer depends on the difference between Zeeman frequencies, the singlet and triplet recombination rates, and on the exchange and dipole-dipole interactions between the different spins. In particular, the sign of the polarization depends on the exchange coupling between radical pair spins and also on the difference between singlet and triplet recombination rate constants.
Spin polarization transfer by the radical pair mechanism
Zarea, Mehdi Ratner, Mark A.; Wasielewski, Michael R.
2015-08-07
In a three-site representation, we study a spin polarization transfer from radical pair spins to a nearby electron or nuclear spin. The quantum dynamics of the radical pair spins is governed by a constant exchange interaction between the radical pair spins which have different Zeeman frequencies. Radical pair spins can recombine to the singlet ground state or to lower energy triplet states. It is then shown that the coherent dynamics of the radical pair induces spin polarization on the nearby third spin in the presence of a magnetic field. The spin polarization transfer depends on the difference between Zeeman frequencies, the singlet and triplet recombination rates, and on the exchange and dipole-dipole interactions between the different spins. In particular, the sign of the polarization depends on the exchange coupling between radical pair spins and also on the difference between singlet and triplet recombination rate constants.
Antiferromagnetic long-range spin ordering in Fe- and NiF e2 -doped BaTi O3 multiferroic layers
NASA Astrophysics Data System (ADS)
Barbier, A.; Aghavnian, T.; Badjeck, V.; Mocuta, C.; Stanescu, D.; Magnan, H.; Rountree, C. L.; Belkhou, R.; Ohresser, P.; Jedrecy, N.
2015-01-01
We report on the Fe doping and on the comparative Ni-Fe codoping with composition close to NiF e2 of fully oxidized BaTi O3 layers (˜20 nm) elaborated by atomic oxygen plasma assisted molecular beam epitaxy; specifically any role of oxygen vacancies can be excluded in our films. Additionally to the classical in situ laboratory tools, the films were thoroughly characterized by synchrotron radiation x-ray diffraction and x-ray absorption spectroscopy. For purely Fe-doped layers, the native tetragonal perovskite structure evolves rapidly toward cubiclike up to 5% doping level above which the crystalline order disappears. On the contrary, low codoping levels (˜5 %NiF e2 ) fairly improve the thin film crystalline structure and surface smoothness; high levels (˜27%) lead to more crystallographically disordered films, although the tetragonal structure is preserved. Synchrotron radiation magnetic dichroic measurements reveal that metal clustering does not occur, that the Fe valence evolves from Fe2 + for low Fe doping levels to Fe3 + for high doping levels, and that the introduction of Ni favors the occurrence of the Fe2 + valence in the films. For the lower codoping levels it seems that Fe2 + substitutes Ba2 +, whereas Ni2 + always substitutes Ti4 +. Ferromagnetic long-range ordering can be excluded with great sensitivity in all samples as deduced from our x-ray magnetic absorption circular dichroic measurements. On the contrary, our linear dichroic x-ray absorption results support antiferromagnetic long-range ordering while piezoforce microscopy gives evidence of a robust ferroelectric long-range ordering showing that our films are excellent candidates for magnetic exchange coupled multiferroic applications.
Nakajima, Yuya; Seino, Junji; Nakai, Hiromi
2016-05-10
An analytical energy gradient for the spin-dependent general Hartree-Fock method based on the infinite-order Douglas-Kroll-Hess (IODKH) method was developed. To treat realistic systems, the local unitary transformation (LUT) scheme was employed both in energy and energy gradient calculations. The present energy gradient method was numerically assessed to investigate the accuracy in several diatomic molecules containing fifth- and sixth-period elements and to examine the efficiency in one-, two-, and three-dimensional silver clusters. To arrive at a practical calculation, we also determined the geometrical parameters of fac-tris(2-phenylpyridine)iridium and investigated the efficiency. The numerical results confirmed that the present method describes a highly accurate relativistic effect with high efficiency. The present method can be a powerful scheme for determining geometries of large molecules, including heavy-element atoms.
Spin manipulation in nanoscale superconductors.
Beckmann, D
2016-04-27
The interplay of superconductivity and magnetism in nanoscale structures has attracted considerable attention in recent years due to the exciting new physics created by the competition of these antagonistic ordering phenomena, and the prospect of exploiting this competition for superconducting spintronics devices. While much of the attention is focused on spin-polarized supercurrents created by the triplet proximity effect, the recent discovery of long range quasiparticle spin transport in high-field superconductors has rekindled interest in spin-dependent nonequilibrium properties of superconductors. In this review, the experimental situation on nonequilibrium spin injection into superconductors is discussed, and open questions and possible future directions of the field are outlined.
Prodi, A; Gilioli, E; Gauzzi, A; Licci, F; Marezio, M; Bolzoni, F; Huang, Q; Santoro, A; Lynn, J W
2004-01-01
Mixed-valence manganites with the ABO3 perovskite structure display a variety of magnetic and structural transitions, dramatic changes of electrical conductivity and magnetoresistance effects. The physical properties vary with the relative concentration of Mn3+ and Mn4+ in the octahedral corner-sharing network, and the proportion of these two cations is usually changed by doping the trivalent large A cation (for example, La3+) with divalent cations. As the dopant and the original cation have, in general, different sizes, and as they are distributed randomly in the structure, such systems are characterized by local distortions that make it difficult to obtain direct information about their crystallographic and physical properties. On the other hand, the double oxides of formula AA'3Mn4O12 contain a perovskite-like network of oxygen octahedra centred on the Mn cations, coupled with an ordered arrangement of the A and A' cations, whose valences control the proportion of Mn3+ and Mn4+ in the structure. The compound investigated in this work, (NaMn3+(3))(Mn3+(2)Mn4+(2))O12, contains an equal number of Mn3+ and Mn4+ in the octahedral sites. We show that the absence of disorder enables the unambiguous determination of symmetry, the direct observation of full, or nearly full, charge ordering of Mn3+ and Mn4+ in distinct crystallographic sites, and a nearly perfect orbital ordering of the Mn3+ octahedra.
Charge, orbital and spin ordering phenomena in the mixed valence manganite (NaMn3+3)(Mn3+2Mn4+2)O12
NASA Astrophysics Data System (ADS)
Prodi, A.; Gilioli, E.; Gauzzi, A.; Licci, F.; Marezio, M.; Bolzoni, F.; Huang, Q.; Santoro, A.; Lynn, J. W.
2004-01-01
Mixed-valence manganites with the ABO3 perovskite structure display a variety of magnetic and structural transitions, dramatic changes of electrical conductivity and magnetoresistance effects. The physical properties vary with the relative concentration of Mn3+ and Mn4+ in the octahedral corner-sharing network, and the proportion of these two cations is usually changed by doping the trivalent large A cation (for example, La3+) with divalent cations. As the dopant and the original cation have, in general, different sizes, and as they are distributed randomly in the structure, such systems are characterized by local distortions that make it difficult to obtain direct information about their crystallographic and physical properties. On the other hand, the double oxides of formula AA'3Mn4O12 contain a perovskite-like network of oxygen octahedra centred on the Mn cations, coupled with an ordered arrangement of the A and A' cations, whose valences control the proportion of Mn3+ and Mn4+ in the structure. The compound investigated in this work, (NaMn3+3)(Mn3+2Mn4+2)O12, contains an equal number of Mn3+ and Mn4+ in the octahedral sites. We show that the absence of disorder enables the unambiguous determination of symmetry, the direct observation of full, or nearly full, charge ordering of Mn3+ and Mn4+ in distinct crystallographic sites, and a nearly perfect orbital ordering of the Mn3+ octahedra.
Intrinsic spin dynamics in semiconductor quantum dots
NASA Astrophysics Data System (ADS)
Valín-Rodríguez, Manuel
2005-12-01
We investigate the characteristic spin dynamics corresponding to semiconductor quantum dots within the multiband envelope function approximation (EFA). By numerically solving an 8 × 8 k·p Hamiltonian we treat systems based on different III-V semiconductor materials. It is shown that, even in the absence of an applied magnetic field, these systems show intrinsic spin dynamics governed by intraband and interband transitions leading to characteristic spin frequencies ranging from THz to optical frequencies.
Biswas, Ayan K; Atulasimha, Jayasimha; Bandyopadhyay, Supriyo
2015-07-17
In artificial neural networks, neurons are usually implemented with highly dissipative CMOS-based operational amplifiers. A more energy-efficient implementation is a 'spin-neuron' realized with a magneto-tunneling junction (MTJ) that is switched with a spin-polarized current (representing weighted sum of input currents) that either delivers a spin transfer torque or induces domain wall motion in the soft layer of the MTJ to mimic neuron firing. Here, we propose and analyze a different type of spin-neuron in which the soft layer of the MTJ is switched with mechanical strain generated by a voltage (representing weighted sum of input voltages) and term it straintronic spin-neuron. It dissipates orders of magnitude less energy in threshold operations than the traditional current-driven spin neuron at 0 K temperature and may even be faster. We have also studied the room-temperature firing behaviors of both types of spin neurons and find that thermal noise degrades the performance of both types, but the current-driven type is degraded much more than the straintronic type if both are optimized for maximum energy-efficiency. On the other hand, if both are designed to have the same level of thermal degradation, then the current-driven version will dissipate orders of magnitude more energy than the straintronic version. Thus, the straintronic spin-neuron is superior to current-driven spin neurons.
NASA Astrophysics Data System (ADS)
Taddei, Keith M.
With nearly innumerable applications, superconductivity stands as a holy grail in the research of quantum phenomena. Understanding the mechanism that begets the fabled pairing of electrons which leads to zero resistance is the most significant undertaking in order to bring to fruition all of superconductivity's splendor. Yet the interaction which couples electrons in the most promising family of superconductors known as unconventional superconductors, which show the highest Tc's and largest upper critical fields remains a mystery. Intense study over the past several decades on the cuprate superconductors has allowed for the identification of several candidate mechanisms --- cardinal of which is magnetic fluctuations --- however as of yet the question still remains. Recently, the discovery of the iron-based superconductors has provided another fruitful avenue through which this mechanism can be probed. Excitingly in these materials superconductivity not only arises near a magnetic instability - a situation which is expected to be particularly suited for engendering superconductivity should magnetic fluctuations be the pairing mechanism - but also exhibit the microscopic co-existence of the two presumably adversarial phenomena. In the work presented here the powerful techniques of neutron and x-ray diffraction will be used to study two particularly interesting members of this family: the intercalated iron-selenide CsxFe 2--xSe2 and two members of the iron-arsenide 122 family (BaFe2(As1--xPx)2 and Sr1--xNaxFe2As 2). Though isostructural at high temperatures, these two materials behave remarkably differently and the idiosyncratic manifestations of superconductivity and ordered magnetism in either give clues as to how the latter might stabilize the former. The iron-selenides will be shown to exhibit a complex phase space with phase separation leading to stabilization of magnetism and superconductivity in separate phases. The structure, behavior and complex vacancy
Spin relaxation 1/f noise in graphene
NASA Astrophysics Data System (ADS)
Omar, S.; Guimarães, M. H. D.; Kaverzin, A.; van Wees, B. J.; Vera-Marun, I. J.
2017-02-01
We report the first measurement of 1/f type noise associated with electronic spin transport, using single layer graphene as a prototypical material with a large and tunable Hooge parameter. We identify the presence of two contributions to the measured spin-dependent noise: contact polarization noise from the ferromagnetic electrodes, which can be filtered out using the cross-correlation method, and the noise originated from the spin relaxation processes. The noise magnitude for spin and charge transport differs by three orders of magnitude, implying different scattering mechanisms for the 1/f fluctuations in the charge and spin transport processes. A modulation of the spin-dependent noise magnitude by changing the spin relaxation length and time indicates that the spin-flip processes dominate the spin-dependent noise.
Spin Susceptibility of Underdoped Cuprates: Insight from Stripe-Ordered La1.875Ba0.125CuO4
NASA Astrophysics Data System (ADS)
Hücker, Markus; Gu, Gen D.; Tranquada, John M.
2008-03-01
The low-temperature decrease of the bulk magnetic susceptibility in underdoped high-temperature superconductors has commonly been cited as evidence for a pseudogap; however, the interpretations range from a Fermi-liquid perspective, with the susceptibility being proportional to the density of free carriers, to strong coupling pictures, with the susceptibility resulting from antiferromagnetic correlations among local moments. Analysis of the susceptibility of a particular cuprate, the stripe ordered La1.875Ba0.125CuO4, sheds new light on this remarkable system and puts tight constraints on possible interpretations. The recently discovered magnetic transition in high magnetic fields will also be discussed.[1] M. Hücker, G. D. Gu, J. M. Tranquada, cond- mat/0503417v2.[2] Q. Li, M. Hücker, G. D. Gu, A. M. Tsvelik, J. M. Tranquada, Phys. Rev. Lett. 99, 067001 (2007).
Heisenberg ferromagnetic spin chain with bilinear and biquadratic interactions in (2 + 1) dimensions
NASA Astrophysics Data System (ADS)
Vasanthi, C. Christal; Latha, M. M.
2015-11-01
We study the nonlinear dynamics of (2 + 1) dimensional ferromagnetic (FM) spin system with bilinear and biquadratic interactions in the semiclassical limit and the dynamics is found to be governed by a new integrable fourth order nonlinear Schrödinger (NLS) equation in (2 + 1) dimensions. The integrability is identified by using Lax pair operators and soliton solutions are obtained using straightforward Darboux transformation (DT) technique. The model Hamiltonian representing (2 + 1) dimensional FM spin chain with varying bilinear and biquadratic interactions are also constructed and inhomogeneity effects are studied by performing a perturbation analysis. Moreover, the modulational instability (MI) aspects are discussed through analytical solutions and graphical illustrations.
Confined spin wave spectra of Kagome artificial spin ice arrays
NASA Astrophysics Data System (ADS)
Panagiotopoulos, I.
2017-01-01
The spin wave modes of elongated magnetic islands arranged in Kagome artificial spin-ice arrays are micromagnetically simulated in the frequency regime between 3 and 16 GHz. The edge modes are more suitable in order to detect the signatures of various types of local order of the spin-ice lattice as they are much more sensitive to the magnetic configurations of neighboring elements. The spectra of arrays consisting up to 30 elements can be decomposed to those originating from local magnetic states of their vertices.
Han, Tian-Heng; Isaacs, Eric D.; Schlueter, John A.; Singleton, John
2016-06-15
Despite decades-long fascination, the difficulty of maintaining high lattice symmetry in frustrated nonbipartite S = 1/2 materials that can also be made into high-quality single crystals has been a persistent challenge. Here we report magnetization studies of a single-crystal sample of barlowite, Cu-4(OH)_{6}FBr, which has a geometrically perfect kagome motif. At T ≤ 4.2 K and 35 ≤ mu H-0 ≤ 65 T, the interlayer spins are fully polarized, and the kagome-intrinsic magnetization is consistent with a Heisenberg model having J/k_{B} = -180 K. Several field-driven anomalies are observed, having varied scalings with temperature. At an applied field, kagome disorder caused by the interlayer spins is smaller than that in herbertsmithite. At T ≤ 15 K, the bulk magnetic moment comes from the interlayer spins. An almost coplanar spin order suggests that the magnitude of in-plane Dzyaloshinskii-Moriya interaction is smaller than 0.006(6) J. On the other hand, the possibility of a spin-liquid state in the kagome lattice coexisting with ordered interlayer spins is left open.
Chiral spin liquids in arrays of spin chains
NASA Astrophysics Data System (ADS)
Gorohovsky, Gregory; Pereira, Rodrigo G.; Sela, Eran
2015-06-01
We describe a coupled-chain construction for chiral spin liquids in two-dimensional spin systems. Starting from a one-dimensional zigzag spin chain and imposing SU(2) symmetry in the framework of non-Abelian bosonization, we first show that our approach faithfully describes the low-energy physics of an exactly solvable model with a three-spin interaction. Generalizing the construction to the two-dimensional case, we obtain a theory that incorporates the universal properties of the chiral spin liquid predicted by Kalmeyer and Laughlin: charge-neutral edge states, gapped spin-1/2 bulk excitations, and ground-state degeneracy on the torus signaling the topological order of this quantum state. In addition, we show that the chiral spin liquid phase is more easily stabilized in frustrated lattices containing corner-sharing triangles, such as the extended kagome lattice, than in the triangular lattice. Our field-theoretical approach invites generalizations to more exotic chiral spin liquids and may be used to assess the existence of the chiral spin liquid as the ground state of specific lattice systems.
Green, Emily C; Zhang, Yiying; Li, Heng; Minus, Marilyn L
2017-01-01
Synthetic gel-spun collagen and collagen/nano-carbon fibers were found to exhibit structural mimicry comparable to native tendons. X-ray scattering and microscopy analyses are used to characterize the molecular and fibrillar alignment in the synthetic fibers, where D-banding is observed throughout the spun fibers - consistent with native collagen. For the composite collagen/nano-carbon fibers, the morphology and dispersion quality of the nano-carbons within was found to play a significant role in influencing collagen molecular ordering and fibril alignment. Fibrillar and molecular alignment was also better preserved during elongation of the composites as compared to the control collagen fibers. These results show the structural influence of a rigid inclusion on the collagen fibril structure. Both dry- and wet-state tensile testing were performed on the collagen fibers, and these results show behavior comparable to the native materials. Dry-state tests also reveal interfacial interaction between the nano-fillers and the collagen fibrils through theoretical analysis. Wet-state tensile testing indicates the structure-property behavior of the mimetic hierarchical structure within the synthetic fibers.
NASA Astrophysics Data System (ADS)
Lyubutin, I. S.; Starchikov, S. S.; Gervits, N. E.; Korotkov, N. Yu.; Dmitrieva, T. V.; Lin, Chun-Rong; Tseng, Yaw-Teng; Shih, Kun-Yauh; Lee, Jiann-Shing; Wang, Cheng-Chien
2016-10-01
The functional polymer (PMA-co-MAA) latex microspheres were used as a core template to prepare magnetic hollow spheres consisting of CoFe2O4/SiO2 composites. The spinel type crystal structure of CoFe2O4 ferrite is formed under annealing, whereas the polymer cores are completely removed after annealing at 450 °C. Magnetic and Mössbauer spectroscopy measurements reveal very interesting magnetic properties of the CoFe2O4/SiO2 hollow spheres strongly dependent on the particle size which can be tuned by the annealing temperature. In the ground state of low temperatures, the CoFe2O4 nanoparticles are in antiferromagnetic state due to the canted magnetic structure. Under heating in the applied field, the magnetic structure gradually transforms from canted to collinear, which increases the magnetization. The Mössbauer data revealed that the small size CoFe2O4/SiO2 particles (2.2-4.3 nm) do not show superparamagnetic behavior but transit from the magnetic to the paramagnetic state by a jump-like magnetic transition of the first order This effect is a specific property of the magnetic nanoparticles isolated by inert material, and can be initiated by internal pressure creating at the particle surface. The suggested method of synthesis can be modified with various bio-ligands on the silane surface, and such materials can find many applications in diagnostics and bio-separation.
Spin resonance and spin fluctuations in a quantum wire
NASA Astrophysics Data System (ADS)
Pokrovsky, V. L.
2017-02-01
This is a review of theoretical works on spin resonance in a quantum wire associated with the spin-orbit interaction. We demonstrate that the spin-orbit induced internal "magnetic field" leads to a narrow spin-flip resonance at low temperatures in the absence of an applied magnetic field. An applied dc magnetic field perpendicular to and small compared with the spin-orbit field enhances the resonance absorption by several orders of magnitude. The component of applied field parallel to the spin-orbit field separates the resonance frequencies of right and left movers and enables a linearly polarized ac electric field to produce a dynamic magnetization as well as electric and spin currents. We start with a simple model of noninteracting electrons and then consider the interaction that is not weak in 1d electron system. We show that electron spin resonance in the spin-orbit field persists in the Luttinger liquid. The interaction produces an additional singularity (cusp) in the spin-flip channel associated with the plasma oscillation. As it was shown earlier by Starykh and his coworkers, the interacting 1d electron system in the external field with sufficiently large parallel component becomes unstable with respect to the appearance of a spin-density wave. This instability suppresses the spin resonance. The observation of the electron spin resonance in a thin wires requires low temperature and high intensity of electromagnetic field in the terahertz diapason. The experiment satisfying these two requirements is possible but rather difficult. An alternative approach that does not require strong ac field is to study two-time correlations of the total spin of the wire with an optical method developed by Crooker and coworkers. We developed theory of such correlations. We prove that the correlation of the total spin component parallel to the internal magnetic field is dominant in systems with the developed spin-density waves but it vanishes in Luttinger liquid. Thus, the
Development of an underwater spin facility for combined environment testing
Roach, D.P.; Nusser, M.A.
1991-01-01
In response to a request from the US Government, Sandia National Laboratories has developed an instrumentation system to monitor the conditions along an underwater, rotating drive shaft. It was desired to study the structural integrity and signal acquisition capabilities of the Shaft Instrumentation System (SIS) in an environment which closely simulates the actual deployment conditions. In this manner, the SIS response to ill-defined conditions, such as flow field turbulence or temperature fluctuations, could be determined. An Underwater Spin Facility was developed in order to verify the operation of the instrumentation and telemetric data acquisition system in a combined environment of external pressure, transient axial loads and centrifugal force. The main components of the Underwater Spin Facility are a large, five foot diameter pressure vessel, a dynamically sealed shaft, a drive train assembly and a shaker table interface which is used to apply the axial loads. This paper presents a detailed description of the design of the Underwater Spin Facility. It also discusses the SIS certification test program in order to demonstrate the successful performance of the Underwater Spin Facility. 8 refs., 10 figs.
Matouzenko, Galina S; Bousseksou, Azzedine; Borshch, Serguei A; Perrin, Monique; Zein, Samir; Salmon, Lionel; Molnar, Gabor; Lecocq, Sylvain
2004-01-12
The synthesis and detailed characterization of the new spin crossover mononuclear complex [Fe(II)(DAPP)(abpt)](ClO(4))(2), where DAPP = [bis(3-aminopropyl)(2-pyridylmethyl)amine] and abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole, are reported. Variable-temperature magnetic susceptibility measurements and Mössbauer spectroscopy have revealed the occurrence of an abrupt spin transition with a hysteresis loop. The hysteresis width derived from magnetic susceptibility measurements is 10 K, the transition being centered at T(c) downward arrow = 171 K for decreasing and T(c) upward arrow = 181 K for increasing temperatures. The crystal structure was resolved in the high-spin (293 and 183 K) and low-spin (123 K) states. Both spin-state structures belong to the monoclinic space group P2(1)/n (Z = 4). The thermal spin transition is accompanied by the shortening of the mean Fe-N distances by 0.177 A. The two main structural characteristics of [Fe(DAPP)(abpt)](ClO(4))(2) are a branched network of intermolecular links in the crystal lattice and the occurrence of two types of order-disorder transitions (in the DAPP ligand and in the perchlorate anions) accompanying the thermal spin change. These features are discussed relative to the magnetic properties of the complex. The electronic structure calculations show that the structural disorder in the DAPP ligand modulates the energy gap between the HS and LS states. In line with previous studies, the order-disorder phenomena and the spin transition in [Fe(DAPP)(abpt)](ClO(4))(2) are found to be interrelated.
Radu, I; Vahaplar, K; Stamm, C; Kachel, T; Pontius, N; Dürr, H A; Ostler, T A; Barker, J; Evans, R F L; Chantrell, R W; Tsukamoto, A; Itoh, A; Kirilyuk, A; Rasing, Th; Kimel, A V
2011-04-14
Ferromagnetic or antiferromagnetic spin ordering is governed by the exchange interaction, the strongest force in magnetism. Understanding spin dynamics in magnetic materials is an issue of crucial importance for progress in information processing and recording technology. Usually the dynamics are studied by observing the collective response of exchange-coupled spins, that is, spin resonances, after an external perturbation by a pulse of magnetic field, current or light. The periods of the corresponding resonances range from one nanosecond for ferromagnets down to one picosecond for antiferromagnets. However, virtually nothing is known about the behaviour of spins in a magnetic material after being excited on a timescale faster than that corresponding to the exchange interaction (10-100 fs), that is, in a non-adiabatic way. Here we use the element-specific technique X-ray magnetic circular dichroism to study spin reversal in GdFeCo that is optically excited on a timescale pertinent to the characteristic time of the exchange interaction between Gd and Fe spins. We unexpectedly find that the ultrafast spin reversal in this material, where spins are coupled antiferromagnetically, occurs by way of a transient ferromagnetic-like state. Following the optical excitation, the net magnetizations of the Gd and Fe sublattices rapidly collapse, switch their direction and rebuild their net magnetic moments at substantially different timescales; the net magnetic moment of the Gd sublattice is found to reverse within 1.5 picoseconds, which is substantially slower than the Fe reversal time of 300 femtoseconds. Consequently, a transient state characterized by a temporary parallel alignment of the net Gd and Fe moments emerges, despite their ground-state antiferromagnetic coupling. These surprising observations, supported by atomistic simulations, provide a concept for the possibility of manipulating magnetic order on the timescale of the exchange interaction.
Topologically protected unidirectional edge spin waves and beam splitter
NASA Astrophysics Data System (ADS)
Wang, X. S.; Su, Ying; Wang, X. R.
2017-01-01
Magnetic topological states are investigated theoretically and numerically. It is shown that ferromagnetically interacting spins on a two-dimensional honeycomb lattice with nearest-neighbor interactions, which is governed by the Landau-Lifshitz-Gilbert equation, can be topologically nontrivial with gapped bulk spin waves and topologically protected gapless edge spin waves. These edge spin waves are robust against defects and perturbations, and should be superb channels of processing and manipulating spin waves, in contrast to the normal spin waves that are very sensitive to defects as well as sample geometry. Because of the unidirectional nature of these topologically protected edge spin waves, a spin-wave beam splitter can be made out of a domain wall in a strip. It is shown that an incoming spin-wave beam along one edge splits into two spin-wave beams propagating along two opposite directions on the other edge after passing through a domain wall.
NASA Astrophysics Data System (ADS)
Yang, Jin-Wei; Gao, Yi-Tian; Wang, Qi-Min; Su, Chuan-Qi; Feng, Yu-Jie; Yu, Xin
2016-01-01
In this paper, a fourth-order variable-coefficient nonlinear Schrödinger equation is studied, which might describe a one-dimensional continuum anisotropic Heisenberg ferromagnetic spin chain with the octuple-dipole interaction or an alpha helical protein with higher-order excitations and interactions under continuum approximation. With the aid of auxiliary function, we derive the bilinear forms and corresponding constraints on the variable coefficients. Via the symbolic computation, we obtain the Lax pair, infinitely many conservation laws, one-, two- and three-soliton solutions. We discuss the influence of the variable coefficients on the solitons. With different choices of the variable coefficients, we obtain the parabolic, cubic, and periodic solitons, respectively. We analyse the head-on and overtaking interactions between/among the two and three solitons. Interactions between a bound state and a single soliton are displayed with different choices of variable coefficients. We also derive the quasi-periodic formulae for the three cases of the bound states.
Spin quasi-distribution functions
NASA Astrophysics Data System (ADS)
Scully, M. O.; Wódkiewicz, K.
1994-01-01
Two-classes of phase-space spin quasi-distribution functions are introduced and discussed. The first class of these distributions is based on the delta function construction. It is shown that such a construction can be carried out for an arbitrary spin s and an arbitrary ordering of the spin operators. The second class of the spin distributions is constructed with the help of the spin coherent states. The connection of the spin coherent states to the Stratonovich formalism is established and discussed. It is shown that the c-number phase-space description of quantum fluctuations provides a simple statistical picture of quantum fluctuations of spinoperators in terms of random directions on a unit sphere. For quantum states of the spin system the statistics of these random orientations is given by non-positive spin quasi-distribution functions. It is shown that the application of these spin quasi-distribution functions to the Einstein-Podolsky-Rosen correlations provide an insight into the quantum theory of measurement.
Spin transport in hydrogenated graphene
NASA Astrophysics Data System (ADS)
Soriano, David; Van Tuan, Dinh; M-M Dubois, Simon; Gmitra, Martin; Cummings, Aron W.; Kochan, Denis; Ortmann, Frank; Charlier, Jean-Christophe; Fabian, Jaroslav; Roche, Stephan
2015-06-01
In this review we discuss the multifaceted problem of spin transport in hydrogenated graphene from a theoretical perspective. The current experimental findings suggest that hydrogenation can either increase or decrease spin lifetimes, which calls for clarification. We first discuss the spin-orbit coupling induced by local σ -π re-hybridization and {s}{{{p}}3} C-H defect formation together with the formation of a local magnetic moment. First-principles calculations of hydrogenated graphene unravel the strong interplay of spin-orbit and exchange couplings. The concept of magnetic scattering resonances, recently introduced by Kochan et al (2014 Phys. Rev. Lett. 112 116602) is revisited by describing the local magnetism through the self-consistent Hubbard model in the mean field approximation in the dilute limit, while spin relaxation lengths and transport times are computed using an efficient real space order N wavepacket propagation method. Typical spin lifetimes on the order of 1 ns are obtained for 1 ppm of hydrogen impurities (corresponding to a transport time of about 50 ps), and the scaling of spin lifetimes with impurity density is described by the Elliott-Yafet mechanism. This reinforces the statement that local defect-induced magnetism can be at the origin of the substantial spin polarization loss in the clean graphene limit.
Topological Effects on Quantum Phase Slips in Superfluid Spin Transport.
Kim, Se Kwon; Tserkovnyak, Yaroslav
2016-03-25
We theoretically investigate effects of quantum fluctuations on superfluid spin transport through easy-plane quantum antiferromagnetic spin chains in the large-spin limit. Quantum fluctuations result in the decaying spin supercurrent by unwinding the magnetic order parameter within the easy plane, which is referred to as phase slips. We show that the topological term in the nonlinear sigma model for the spin chains qualitatively differentiates the decaying rate of the spin supercurrent between the integer versus half-odd-integer spin chains. An experimental setup for a magnetoelectric circuit is proposed, in which the dependence of the decaying rate on constituent spins can be verified by measuring the nonlocal magnetoresistance.
Spin dynamics of polarization inversion spin exchange at the magic angle in multiple spin systems.
Gan, Z
2000-03-01
Polarization inversion spin exchange at the magic angle (PISEMA) [J. Magn. Reson. A 109, 270 (1994)] is an important experiment in NMR structural characterization of membrane proteins in oriented lipid bilayers. This paper presents a theoretical and experimental study of the spin dynamics in PISEMA to investigate the line-narrowing mechanism. The study focuses on the effect of neighboring protons on the spin exchange of a strongly coupled spin pair. The spin exchange is solved analytically for simple spin systems and is numerically simulated for many-spin systems. The results show that the dipolar couplings from the neighboring protons of a strongly coupled spin pair perturb the spin exchange only in the second order, therefore it has little contribution to the linewidth of PISEMA spectra in comparison to the separated-local-field spectra. The effects from proton resonance offset and the mismatch of the Hartmann-Hahn condition are also discussed along with experimental results using model single-crystal samples.
Spin slush in an extended spin ice model
Rau, Jeffrey G.; Gingras, Michel J. P.
2016-01-01
We present a new classical spin liquid on the pyrochlore lattice by extending spin ice with further neighbour interactions. We find that this disorder-free spin model exhibits a form of dynamical heterogeneity with extremely slow relaxation for some spins, while others fluctuate quickly down to zero temperature. We thus call this state spin slush, in analogy to the heterogeneous mixture of solid and liquid water. This behaviour is driven by the structure of the ground-state manifold which extends the celebrated two-in/two-out ice states to include branching structures built from three-in/one-out, three-out/one-in and all-in/all-out tetrahedra defects. Distinctive liquid-like patterns in the magnetic correlations serve as a signature of this intermediate range order. Possible applications to materials as well the effects of quantum tunnelling are discussed. PMID:27470199
Mazziotti, David A.
2005-09-15
The energy and properties of a many-electron atom or molecule may be directly computed from a variational optimization of a two-electron reduced density matrix (2RDM) that is constrained to represent many-electron quantum systems. In this paper we implement a variational 2RDM method with a representability constraint, known as the T{sub 2} condition. The optimization of the 2RDM is performed with a first-order algorithm for semidefinite programming [D. A. Mazziotti, Phys. Rev. Lett. 93, 213001 (2004)] which, because of its lower computational cost in comparison to second-order methods, allows the treatment of larger basis sets. We also derive and implement a spin- and symmetry-adapted formulation of the T{sub 2} condition that significantly decreases the size of the largest block in the T{sub 2} matrix. The T{sub 2} condition, originally derived by Erdahl [Int. J. Quantum Chem. 13, 697 (1978)], was recently applied via a second-order algorithm to atoms and molecules [Z. Zhao et al., J. Chem. Phys. 120, 2095 (2004)]. While these calculations were restricted to molecules at equilibrium geometries in minimal basis sets, we apply the 2RDM method with the T{sub 2} condition to compute the electronic energies of molecules in both minimal and nonminimal basis sets at equilibrium as well as nonequilibrium geometries. Accurate potential energies curves are produced for BH, HF, and N{sub 2}. Results are compared with the 2RDM method without the T{sub 2} condition as well as several wave-function methods.
Spin diffusion and torques in disordered antiferromagnets
NASA Astrophysics Data System (ADS)
Manchon, Aurelien
2017-03-01
We have developed a drift-diffusion equation of spin transport in collinear bipartite metallic antiferromagnets. Starting from a model tight-binding Hamiltonian, we obtain the quantum kinetic equation within Keldysh formalism and expand it to the lowest order in spatial gradient using Wigner expansion method. In the diffusive limit, these equations track the spatio-temporal evolution of the spin accumulations and spin currents on each sublattice of the antiferromagnet. We use these equations to address the nature of the spin transfer torque in (i) a spin-valve composed of a ferromagnet and an antiferromagnet, (ii) a metallic bilayer consisting of an antiferromagnet adjacent to a heavy metal possessing spin Hall effect, and in (iii) a single antiferromagnet possessing spin Hall effect. We show that the latter can experience a self-torque thanks to the non-vanishing spin Hall effect in the antiferromagnet.
Spin diffusion and torques in disordered antiferromagnets.
Manchon, Aurelien
2017-03-15
We have developed a drift-diffusion equation of spin transport in collinear bipartite metallic antiferromagnets. Starting from a model tight-binding Hamiltonian, we obtain the quantum kinetic equation within Keldysh formalism and expand it to the lowest order in spatial gradient using Wigner expansion method. In the diffusive limit, these equations track the spatio-temporal evolution of the spin accumulations and spin currents on each sublattice of the antiferromagnet. We use these equations to address the nature of the spin transfer torque in (i) a spin-valve composed of a ferromagnet and an antiferromagnet, (ii) a metallic bilayer consisting of an antiferromagnet adjacent to a heavy metal possessing spin Hall effect, and in (iii) a single antiferromagnet possessing spin Hall effect. We show that the latter can experience a self-torque thanks to the non-vanishing spin Hall effect in the antiferromagnet.
Independent freezing of charge and spin dynamics in La1.5Sr0.5CoO4
Zaliznyak; Hill; Tranquada; Erwin; Moritomo
2000-11-13
We present elastic and quasielastic neutron scattering measurements characterizing peculiar short-range charge-orbital and spin order in the layered perovskite material La1.5Sr0.5CoO4. We find that below T(c) approximately 750 K holes introduced by Sr doping lose mobility and enter a statically ordered charge glass phase with loosely correlated checkerboard arrangement of empty and occupied d(3z(2)-r(2)) orbitals ( Co3+ and Co2+). The dynamics of the resultant mixed spin system is governed by the anisotropic nature of the crystal-field Hamiltonian and the peculiar exchange pattern produced by the orbital order. It undergoes a spin freezing transition at a much lower temperature, T(s) less, similar30 K.
Numerical Modeling of the Central Spin Problem Using the Spin-Coherent-State P Representation
Al Hassanieh, Khaled A; Dobrovitski, V. V.; Dagotto, Elbio R; Harmon, B. N.
2006-01-01
In this work, we consider decoherence of a central spin by a spin bath. In order to study the nonperturbative decoherence regimes, we develop an efficient mean-field-based method for modeling the spin-bath decoherence, based on the P representation of the central spin density matrix. The method can be applied to longitudinal and transverse relaxation at different external fields. In particular, by modeling large-size quantum systems (up to 16 000 bath spins), we make controlled predictions for the slow long-time decoherence of the central spin.
Andersen, John A.; Flanigan, John J.; Kindley, Robert J.
1978-01-01
The disclosure relates to an apparatus for spin ejecting a body having a flat plate base containing bosses. The apparatus has a base plate and a main ejection shaft extending perpendicularly from the base plate. A compressible cylindrical spring is disposed about the shaft. Bearings are located between the shaft and the spring. A housing containing a helical aperture releasably engages the base plate and surrounds the shaft bearings and the spring. A piston having an aperture follower disposed in the housing aperture is seated on the spring and is guided by the shaft and the aperture. The spring is compressed and when released causes the piston to spin eject the body.
Cyclotron dynamics of a Kondo singlet in a spin-orbit-coupled alkaline-earth-metal atomic gas
NASA Astrophysics Data System (ADS)
Jiang, Bo-Nan; Lv, Hao; Wang, Wen-Li; Du, Juan; Qian, Jun; Wang, Yu-Zhu
2014-11-01
We propose a scheme to investigate the interplay between the Kondo-exchange interaction and the quantum spin Hall effect with ultracold fermionic alkaline-earth-metal atoms trapped in two-dimensional optical lattices using ultracold collision and laser-assisted tunneling. In the strong Kondo-coupling regime, although the loop trajectory of the mobile atom disappears, collective dynamics of an atom pair in two clock states can exhibit an unexpected spin-dependent cyclotron orbit in a plaquette, realizing the quantum spin Hall effect of the Kondo singlet. We demonstrate that the collective cyclotron dynamics of the spin-zero Kondo singlet is governed by an effective Harper-Hofstadter model in addition to second-order diagonal tunneling.
Viet, Dao Xuan; Kawamura, Hikaru
2009-01-16
Ordering of the three-dimensional Heisenberg spin glass with Gaussian coupling is studied by extensive Monte Carlo simulations. The model undergoes successive chiral-glass and spin-glass transitions at nonzero temperatures T_{CG}>T_{SG}>0, exhibiting spin-chirality decoupling.
Spin decoherence and electron spin bath noise of a nitrogen-vacancy center in diamond
NASA Astrophysics Data System (ADS)
Wang, Zhi-Hui; Takahashi, Susumu
2013-03-01
We theoretically investigate spin decoherence of a single nitrogen-vacancy (NV) center in diamond. Using the spin coherent-state P-representation method, we simulate coherence evolution of the NV center coupled to surrounding nitrogen electron (N) spins. In the system, the strength of N-N coupling is the same order as that of NV-N coupling (the strong intrabath coupling regime). We find that spin decoherence time as well as free-induction decay of the NV center depend on the spatial configuration of N spins. Both the spin decoherence rate (1/T2) and dephasing rate (1/T2*) of the NV center increase linearly with the concentration of the N spins. Using the P-representation method, we also demonstrate extracting the noise spectrum of the N spin bath. The capability to calculate the noise spectrum will provide promising pathways to suppress decoherence of spin systems in the strong intrabath coupling regime.
Cross relaxation in nitroxide spin labels
NASA Astrophysics Data System (ADS)
Marsh, Derek
2016-11-01
Cross relaxation, and mI -dependence of the intrinsic electron spin-lattice relaxation rate We , are incorporated explicitly into the rate equations for the electron-spin population differences that govern the saturation behaviour of 14N- and 15N-nitroxide spin labels. Both prove important in spin-label EPR and ELDOR, particularly for saturation recovery studies. Neither for saturation recovery, nor for CW-saturation EPR and CW-ELDOR, can cross relaxation be described simply by increasing the value of We , the intrinsic spin-lattice relaxation rate. Independence of the saturation recovery rates from the hyperfine line pumped or observed follows directly from solution of the rate equations including cross relaxation, even when the intrinsic spin-lattice relaxation rate We is mI -dependent.
Zhao, Long; Liu, Wei Cao, Lixin; Su, Ge; Gao, Rongjie; Yang, Hongzhan
2015-11-15
A sanderite ferrous sulfate FeSO{sub 4}·2H{sub 2}O has been synthesized by the hydro/solvothermal method. Its crystal structure (Pccn, a=6.3160 Å, b=7.7550 Å, c=8.9880 Å, V=440.2 Å{sup 3}, Z=4) can be regarded as the condensation of alternately corner-shared FeO{sub 4}(H{sub 2}O){sub 2} octahedra and SO{sub 4} tetrahedra with a similar topology of PtS. By structural comparison with the known hydrated ferrous sulfates, the structural relation among them has been noted and discussed in detail. A variable temperature magnetic study shows a spin-canted long-range antiferromagnetic ordering in the low temperature regime, which might result from a possible phase transition during the cooling from the high temperature. - Graphical abstract: As a new number of ferrous sulfates, sanderite FeSO{sub 4}·2H{sub 2}O has been synthesized under hydro/solvothermal conditions, which exhibits a similar topology of PtS. - Highlights: • Sanderite ferrous sulfate has been synthesized. • The topology of its structure is similar to that of PtS. • A structural relation between these hydrated ferrous sulfates is discovered.
Transverse target spin asymmetry in inclusive DIS with two-photon exchange
Andrei Afanasev; Mark Strikman; Christian Weiss
2007-09-06
We study the transverse target spin dependence of the cross section for the inclusive electron-nucleon scattering with unpolarized beam. Such dependence is absent in the one-photon exchange approximation (Christ-Lee theorem) and arises only in higher orders of the QED expansion, from the interference of one-photon and absorptive two-photon exchange amplitudes as well as from real photon emission (bremsstrahlung). We demonstrate that the transverse spin-dependent two-photon exchange cross section is free of QED infrared and collinear divergences. We argue that in DIS kinematics the transverse spin dependence should be governed by a "parton-like" mechanism in which the two-photon exchange couples mainly to a single quark. We calculate the normal spin asymmetry in an approximation where the dominant contribution arises from quark helicity flip due to interactions with non-perturbative vacuum fields (constituent quark picture) and is proportional to the quark transversity distribution in the nucleon. Such helicity-flip processes are not significantly Sudakov-suppressed if the infrared scale for gluon emission in the photon-quark subprocess is of the order of the chiral symmetry breaking scale, mu^2_chiral>>Lambda^2_QCD. We estimate the asymmetry in the kinematics of the planned Jefferson Lab Hall A experiment to be of the order 10^-4, with different sign for proton and neutron. We also comment on the spin dependence in the limit of soft high-energy scattering.
Spin transport in nanoscale Si-based spin-valve devices
NASA Astrophysics Data System (ADS)
Hiep, Duong Dinh; Tanaka, Masaaki; Hai, Pham Nam
2016-12-01
We investigated the spin transport in nano-scale silicon (Si)-based spin-valve devices with Fe electrodes, MgO/Ge tunnel barriers, and a 20 nm-long Si channel. We observed a clear spin-valve effect when a magnetic field was applied in the film plane along and perpendicular to the Si channel transport direction. Systematic investigations of the bias voltage dependence, temperature dependence, and magnetic-field direction dependence of the magnetoresistance indicate that the observed spin-valve effect is governed by the spin transport through the nano-scale Si channel. The spin-valve effect remains observable up to 200 K. For the device with MgO/Ge tunnel barriers, with a bias voltage of 1.7 V at 50 K, the spin-dependent output voltage is 13 mV, which is among the highest values reported so far.
Random SU(2)-symmetric spin-S chains
NASA Astrophysics Data System (ADS)
Quito, V. L.; Hoyos, José A.; Miranda, E.
2016-08-01
We study the low-energy physics of a broad class of time-reversal invariant and SU(2)-symmetric one-dimensional spin-S systems in the presence of quenched disorder via a strong-disorder renormalization-group technique. We show that, in general, there is an antiferromagnetic phase with an emergent SU (2 S +1 ) symmetry. The ground state of this phase is a random singlet state in which the singlets are formed by pairs of spins. For integer spins, there is an additional antiferromagnetic phase which does not exhibit any emergent symmetry (except for S =1 ). The corresponding ground state is a random singlet one but the singlets are formed mostly by trios of spins. In each case the corresponding low-energy dynamics is activated, i.e., with a formally infinite dynamical exponent, and related to distinct infinite-randomness fixed points. The phase diagram has two other phases with ferromagnetic tendencies: a disordered ferromagnetic phase and a large spin phase in which the effective disorder is asymptotically finite. In the latter case, the dynamical scaling is governed by a conventional power law with a finite dynamical exponent.
Quantum Spin Liquids and Fractionalization
NASA Astrophysics Data System (ADS)
Misguich, Grégoire
This chapter discusses quantum antiferromagnets which do not break any symmetries at zero temperature - also called "spin liquids" - and focuses on lattice spin models with Heisenberg-like (i.e. SU(2)-symmetric) interactions in dimensions larger than one. We begin by discussing the Lieb-Schultz-Mattis theorem and its recent extension to D > 1 by Hastings (2004), which establishes an important distinction between spin liquids with an integer and with a half-integer spin per unit cell. Spin liquids of the first kind, "band insulators", can often be understood by elementary means, whereas the latter, "Mott insulators", are more complex (featuring "topological order") and support spin-1/2 excitations (spinons). The fermionic formalism (Affleck and Marston, 1988) is described and the effect of fluctuations about mean-field solutions, such as the possible creation of instabilities, is discussed in a qualitative way. In particular, we explain the emergence of gauge modes and their relation to fractionalization. The concept of the projective symmetry group (X.-G. Wen, 2002) is introduced, with the aid of some examples. Finally, we present the phenomenology of (gapped) short-ranged resonating-valence-bond spin liquids, and make contact with the fermionic approach by discussing their description in terms of a fluctuating Z 2 gauge field. Some recent references are given to other types of spin liquid, including gapless ones.
NASA Astrophysics Data System (ADS)
Zheng, X. G.; Hagihala, M.; Fujihala, M.; Kawae, T.
2009-01-01
Following the discovery of frustrated magnetism in deformed pyrochlore lattice Cu2(OH)3Cl and Co2(OH)3Cl we have extensively investigated the material series in the chemical formula of M2(OH)3X, with M = Cu, Co, Ni, Fe, Mn, and X = Cl, Br, or I. In atacamite-structure Ni2(OH)3Cl, strong geometric frustration and an exotic antiferromagnetic transition below 5 K was found. While neutron diffraction witnessed unambiguously an antiferromagnetic long-range order, the μSR method can't 'see' this order, instead, the detected local field behaved quite like a dynamically fluctuating one. For the system of Co2(OH)3Cl, the magnetic state is very sensitive to both the anion and cation substitution. While Co2(OH)3Cl behaves like a zero-field kagomé ice ferromagnet, a completely substituted version of Co2(OH)3Br becomes antiferromagnetic although there is little difference in the crystal structure. The antiferromagnetic Co2(OH)3Br showed complicated magnetic transitions. Meanwhile, partially substituted Co2(OH)3Cl1-xBrx transforms from ferromagnetic to antiferromagnetic with increasing the x ratio. The results suggest that the interaction on the kagome-lattice plane is antiferromagnetic while that on the triangular lattice plane is ferromagnetic. For the substituted series (Co1-xFex)2(OH)3Cl a spin glass state is observed.
Oscillatory spin transport in spin Hall multilayers
NASA Astrophysics Data System (ADS)
Barsukov, Igor; Gonçalves, A. M.; Soledade, P.; Passos, C. A. C.; Costa, M.; Souza-Neto, N. M.; Garcia, F.; Lee, H. K.; Smith, A.; Tretiakov, O.; Krivorotov, I. N.; Sampaio, L. C.
We study multilayers of sputtered Pt/(d)Cu/Py as a function of the Cu thickness d using ferromagnetic resonance (FMR). The FMR linewidth reveals a linear dependence on the frequency with negligible inhomogeneous contribution. The Gilbert damping falls smoothly with increasing d, but presents a strong superimposed oscillation with a period of ~1.5nm. We attribute this behavior to RKKY-like spin transport in the confinement of the Cu layer. The induced perpendicular anisotropy due to the proximity effect shows a similar behavior. We evaluate the induced magnetic moment on Pt using x-ray magnetic circular dichroism and find that it decreases with increasing Cu thickness smoothly. Again, we see oscillations of the magnetic moment and show that the oscillatory spin transport affects proximity induced magnetism in Pt. We extend our study to multilayer systems with increased oxidation levels and with out-of-plane crystal texture, in order to investigate the effects of disorder and electron's k-vectors that are responsible for the oscillatory spin transport.
Lagrangian geometrical optics of nonadiabatic vector waves and spin particles
Ruiz, D. E.; Dodin, I. Y.
2015-07-29
Linear vector waves, both quantum and classical, experience polarization-driven bending of ray trajectories and polarization dynamics that can be interpreted as the precession of the "wave spin". Here, both phenomena are governed by an effective gauge Hamiltonian vanishing in leading-order geometrical optics. This gauge Hamiltonian can be recognized as a generalization of the Stern-Gerlach Hamiltonian that is commonly known for spin-1/2 quantum particles. The corresponding reduced Lagrangians for continuous nondissipative waves and their geometrical-optics rays are derived from the fundamental wave Lagrangian. The resulting Euler-Lagrange equations can describe simultaneous interactions of N resonant modes, where N is arbitrary, and lead to equations for the wave spin, which happens to be an (N^{2} - 1)-dimensional spin vector. As a special case, classical equations for a Dirac particle (N = 2) are deduced formally, without introducing additional postulates or interpretations, from the Dirac quantum Lagrangian with the Pauli term. The model reproduces the Bargmann-Michel-Telegdi equations with added Stern-Gerlach force.
Lagrangian geometrical optics of nonadiabatic vector waves and spin particles
Ruiz, D. E.; Dodin, I. Y.
2015-07-29
Linear vector waves, both quantum and classical, experience polarization-driven bending of ray trajectories and polarization dynamics that can be interpreted as the precession of the "wave spin". Here, both phenomena are governed by an effective gauge Hamiltonian vanishing in leading-order geometrical optics. This gauge Hamiltonian can be recognized as a generalization of the Stern-Gerlach Hamiltonian that is commonly known for spin-1/2 quantum particles. The corresponding reduced Lagrangians for continuous nondissipative waves and their geometrical-optics rays are derived from the fundamental wave Lagrangian. The resulting Euler-Lagrange equations can describe simultaneous interactions of N resonant modes, where N is arbitrary, and leadmore » to equations for the wave spin, which happens to be an (N2 - 1)-dimensional spin vector. As a special case, classical equations for a Dirac particle (N = 2) are deduced formally, without introducing additional postulates or interpretations, from the Dirac quantum Lagrangian with the Pauli term. The model reproduces the Bargmann-Michel-Telegdi equations with added Stern-Gerlach force.« less
Spin Heat Accumulation Induced by Tunneling from a Ferromagnet
NASA Astrophysics Data System (ADS)
Vera-Marun, I. J.; van Wees, B. J.; Jansen, R.
2014-02-01
An electric current from a ferromagnet into a nonmagnetic material can induce a spin-dependent electron temperature. Here, it is shown that this spin heat accumulation, when created by tunneling from a ferromagnet, produces a non-negligible voltage signal that is comparable to that due to the coexisting electrical spin accumulation and can give a different Hanle spin precession signature. The effect is governed by the spin polarization of the Peltier coefficient of the tunnel contact, its Seebeck coefficient, and the spin heat resistance of the nonmagnetic material, which is related to the electrical spin resistance by a spin-Wiedemann-Franz law. Moreover, spin heat injection is subject to a heat conductivity mismatch that is overcome if the tunnel interface has a sufficiently large resistance.
Exchange anisotropy as mechanism for spin-stripe formation in frustrated spin chains
NASA Astrophysics Data System (ADS)
Pregelj, M.; Zaharko, O.; Herak, M.; Gomilšek, M.; Zorko, A.; Chapon, L. C.; Bourdarot, F.; Berger, H.; Arčon, D.
2016-08-01
We investigate the spin-stripe mechanism responsible for the peculiar nanometer modulation of the incommensurate magnetic order that emerges between the vector-chiral and the spin-density-wave phase in the frustrated zigzag spin-1/2 chain compound β -TeVO4 . A combination of magnetic-torque, neutron-diffraction, and spherical-neutron-polarimetry measurements is employed to determine the complex magnetic structures of all three ordered phases. Based on these results, we develop a simple phenomenological model, which exposes the exchange anisotropy as the key ingredient for the spin-stripe formation in frustrated spin systems.
Spin Orbit Interaction Engineering for beyond Spin Transfer Torque memory
NASA Astrophysics Data System (ADS)
Wang, Kang L.
Spin transfer torque memory uses electron current to transfer the spin torque of electrons to switch a magnetic free layer. This talk will address an alternative approach to energy efficient non-volatile spintronics through engineering of spin orbit interaction (SOC) and the use of spin orbit torque (SOT) by the use of electric field to improve further the energy efficiency of switching. I will first discuss the engineering of interface SOC, which results in the electric field control of magnetic moment or magneto-electric (ME) effect. Magnetic memory bits based on this ME effect, referred to as magnetoelectric RAM (MeRAM), is shown to have orders of magnitude lower energy dissipation compared with spin transfer torque memory (STTRAM). Likewise, interests in spin Hall as a result of SOC have led to many advances. Recent demonstrations of magnetization switching induced by in-plane current in heavy metal/ferromagnetic heterostructures have been shown to arise from the large SOC. The large SOC is also shown to give rise to the large SOT. Due to the presence of an intrinsic extraordinarily strong SOC and spin-momentum lock, topological insulators (TIs) are expected to be promising candidates for exploring spin-orbit torque (SOT)-related physics. In particular, we will show the magnetization switching in a chromium-doped magnetic TI bilayer heterostructure by charge current. A giant SOT of more than three orders of magnitude larger than those reported in heavy metals is also obtained. This large SOT is shown to come from the spin-momentum locked surface states of TI, which may further lead to innovative low power applications. I will also describe other related physics of SOC at the interface of anti-ferromagnetism/ferromagnetic structure and show the control exchange bias by electric field for high speed memory switching. The work was in part supported by ERFC-SHINES, NSF, ARO, TANMS, and FAME.
Spin pumping and spin Seebeck effect
NASA Astrophysics Data System (ADS)
Saitoh, Eiji
2012-02-01
Utilization of a spin current, a flow of electrons' spins in a solid, is the key technology in spintronics that will allow the achievement of efficient magnetic memories and computing devices. In this technology, generation and detection of spin currents are necessary. Here, we review inverse spin-Hall effect and spin-current-generation phenomena recently discovered both in metals and insulators: inverse spin-Hall effect, spin pumping, and spin Seebeck effect. (1)Spin pumping and spin torque in a Mott insulator system We found that spin pumping and spin torque effects appear also at an interface between Pt and an insulator YIG.. This means that we can connect a spin current carried by conduction electrons and a spin-wave spin current flowing in insulators. We demonstrate electric signal transmission by using these effects and interconversion of the spin currents [1]. (2) Spin Seebeck effect We have observed, by using the inverse spin-Hall effect [2], spin voltage generation from a heat current in a NiFe, named the spin-Seebeck effect [3]. Surprisingly, spin-Seebeck effect was found to appear even in insulators [4], a situation completely different from conventional charge Seebeck effect. The result implies an important role of elementary excitation in solids beside charge in the spin Seebeck effect. In the talk, we review the recent progress of the research on this effect. This research is collaboration with K. Ando, K. Uchida, Y. Kajiwara, S. Maekawa, G. E. W. Bauer, S. Takahashi, and J. Ieda. [4pt] [1] Y. Kajiwara and E. Saitoh et al. Nature 464 (2010) 262. [0pt] [2] E. Saitoh et al., Appl. Phys. Lett. 88 (2006) 182509. [0pt] [3] K. Uchida and E. Saitoh et al., Nature 455 (2008)778. [0pt] [4] K. Uchida and E. Saitoh et al.,Nature materials 9 (2010) 894 - 897.
Spin injection beyond the diffusive limit in the presence of spin-orbit coupling
NASA Astrophysics Data System (ADS)
Liefeith, Lennart-Knud; Tholapi, Rajkiran; Ishikura, Tomotsugu; Hänze, Max; Hartmann, Robert; Slobodskyy, Taras; Hansen, Wolfgang
2017-02-01
Spin injection from epitaxial iron into InGaAs/InAs quantum wells is observed using an all-electric nonlocal setup. From the choice of material, a significant spin-orbit interaction (SOI) is expected. The contact separation of the spin-valve devices is in the order of the mean free path so that the transport is at the transition between diffusive and ballistic. With an established purely diffusive model a spin-injection efficiency of 77 % is determined from the data. This value is very large compared to previous observations on diffusive spin-valve devices on similar material systems. Motivated by similar results on ballistic spin-valve devices in a material system with small spin-orbit coupling, a recent model was suggested in which a ballistic spin-dephasing length was pointed out to be the crucial length scale. With this model and an experimentally determined spin-orbit coupling parameter of α =4 ×10-12 eV m, very high spin-injection efficiencies are still determined in our quantum wells. We suggest that the spin-dephasing length to be used in the model must be larger due to the crystallographic anisotropy of the spin-orbit coupling, i.e., in our setup the SOI stabilizes the spin in the crystal direction of the spin-polarized current.
Novel effects of spin-orbit interaction in interacting electronic systems
NASA Astrophysics Data System (ADS)
Sun, Jianmin
Over the last several years there has been a remarkable growth in research activity in the physical properties of mesoscopic systems. Significant results, which were obtained by both theoretical and experimental studies, together with the enormous promise of nano-technology applications, contribute to this interest. In mesoscopic systems, there are 1023 or so electrons with strong Coulomb interaction. The length scale governing the electrons motion is small enough to cause quantization of the energy levels. In this work we study such quantum systems: quantum wires, quantum dots. During the last decade several experimental techniques have been developed for manufacturing both kinds of devices, which are currently an important tool for understanding low dimensions physics. The finite spin-orbit coupling is very natural, and, strictly speaking, unavoidable, in semiconducting quantum wires due to pronounced structural asymmetry inherent in the fabrication process. Thus the interplay between Coulomb interaction and spin-orbit coupling is important to investigate. The magnetic field also plays an important role which breaks the time-reversal symmetry of the Hamiltonian and splits the band of free electrons into two, corresponding to up-spin and down-spin electrons, reducing spin-rotational symmetry of the system from SU(2) to U(1). The dissertation takes account of the effect of the spin-orbit coupling interactions in the properties of mesoscopic systems. The manuscript is divided in four Chapters. In Chapter 1, the field theory in mesoscopic system is introduced. I present the relations between bosonic and fermionic operators in one dimension. These relations are used to bosonize spin 1/2 interaction fermion system. I show how to derive the RG equations around a fixed-point from the Operator Product Expansion (OPE). In Chapter 2, I present analysis of the interacting quantum wire problem in the presence of magnetic field and spin-orbital interaction. I show that an
Suppression of spin-exchange relaxation in tilted magnetic fields within the geophysical range
NASA Astrophysics Data System (ADS)
Scholtes, Theo; Pustelny, Szymon; Fritzsche, Stephan; Schultze, Volkmar; Stolz, Ronny; Meyer, Hans-Georg
2016-07-01
We present a detailed experimental and theoretical study on the relaxation of spin coherence due to the spin-exchange mechanism arising in the electronic ground states of alkali-metal vapor atoms. As opposed to the well-explored formation of a stretched state in a longitudinal geometry (magnetic field parallel to the laser propagation direction) we employ adapted hyperfine-selective optical pumping in order to suppress spin-exchange relaxation. By comparing measurements of the intrinsic relaxation rate of the spin coherence in the ground state of cesium atoms with detailed density-matrix simulations we show that the relaxation due to spin-exchange collisions can be reduced substantially even in a tilted magnetic field of geomagnetic strength, the major application case of scalar magnetic surveying. This explains the observed striking improvement in sensitivity and further deepens the understanding of the light-narrowed Mx magnetometer, which was presented recently. Additionally, new avenues for investigating the dynamics in alkali-metal atoms governed by the spin-exchange interaction and interacting with arbitrary external fields open up.
Critical spin-flip scattering at the helimagnetic transition of MnSi
NASA Astrophysics Data System (ADS)
Kindervater, J.; Häußler, W.; Janoschek, M.; Pfleiderer, C.; Böni, P.; Garst, M.
2014-05-01
We report spherical neutron polarimetry (SNP) and discuss the spin-flip scattering cross sections as well as the chiral fraction η close to the helimagnetic transition in MnSi. For our study we have developed a miniaturized SNP device that allows fast data collection when used in small angle scattering geometry with an area detector. Critical spin-flip scattering is found to be governed by chiral paramagnons that soften on a sphere in momentum space. Carefully accounting for the incoherent spin-flip background, we find that the resulting chiral fraction η decreases gradually above the helimagnetic transition reflecting a strongly renormalized chiral correlation length with a temperature dependence in excellent quantitative agreement with the Brazovskii theory for a fluctuation-induced first order transition.
Magnetic excitations in a bond-centered stripe phase: spin waves far from the semiclassical limit.
Vojta, Matthias; Ulbricht, Tobias
2004-09-17
Using a spin-only model, we compute spin excitation spectra in a bond-centered stripe state with long-range magnetic order. We employ a bond operator formalism, which naturally captures both dimerization and broken spin symmetry in a unified framework. At low energies, the spin excitations resemble spin waves, but at higher energies they are very similar to spin-one excitations of isolated spin ladders. Our theory does well describe neutron scattering data [Nature (London) 429, 534 (2004)
Time-optimal control of spin 1/2 particles in the presence of radiation damping and relaxation.
Zhang, Y; Lapert, M; Sugny, D; Braun, M; Glaser, S J
2011-02-07
We consider the time-optimal control of an ensemble of uncoupled spin 1/2 particles in the presence of relaxation and radiation damping effects, whose dynamics is governed by nonlinear equations generalizing the standard linear Bloch equations. For a single spin, the optimal control strategy can be fully characterized analytically. However, in order to take into account the inhomogeneity of the static magnetic field, an ensemble of isochromats at different frequencies must be considered. For this case, numerically optimized pulse sequences are computed and the dynamics under the corresponding optimal field is experimentally demonstrated using nuclear magnetic resonance techniques.
Spin transport through the metallic antiferromagnet FeMn
NASA Astrophysics Data System (ADS)
Saglam, H.; Zhang, W.; Jungfleisch, M. B.; Sklenar, J.; Pearson, J. E.; Ketterson, J. B.; Hoffmann, A.
2016-10-01
We investigate spin transport through metallic antiferromagnets using measurements based on spin pumping combined with inverse spin Hall effects in N i80F e20/FeMn /W trilayers. The relatively large magnitude and opposite sign of spin Hall effects in W compared to FeMn enable an unambiguous detection of spin currents transmitted through the entire FeMn layer thickness. Using this approach we can detect two distinctively different spin transport regimes, which we associate with electronic and magnonic spin currents, respectively. The latter can extend to relatively large distances (≈9 nm) and is enhanced when the antiferromagnetic ordering temperature is close to the measurement temperature.
Thermal spin current from a ferromagnet to silicon by Seebeck spin tunnelling.
Le Breton, Jean-Christophe; Sharma, Sandeep; Saito, Hidekazu; Yuasa, Shinji; Jansen, Ron
2011-06-29
Heat generation by electric current, which is ubiquitous in electronic devices and circuits, raises energy consumption and will become increasingly problematic in future generations of high-density electronics. The control and re-use of heat are therefore important topics for existing and emerging technologies, including spintronics. Recently it was reported that heat flow within a ferromagnet can produce a flow of spin angular momentum-a spin current-and an associated voltage. This spin Seebeck effect has been observed in metallic, insulating and semiconductor ferromagnets with temperature gradients across them. Here we describe and report the demonstration of Seebeck spin tunnelling-a distinctly different thermal spin flow, of purely interfacial nature-generated in a tunnel contact between electrodes of different temperatures when at least one of the electrodes is a ferromagnet. The Seebeck spin current is governed by the energy derivative of the tunnel spin polarization. By exploiting this in ferromagnet-oxide-silicon tunnel junctions, we observe thermal transfer of spins from the ferromagnet to the silicon without a net tunnel charge current. The induced spin accumulation scales linearly with heating power and changes sign when the temperature differential is reversed. This thermal spin current can be used by itself, or in combination with electrical spin injection, to increase device efficiency. The results highlight the engineering of heat transport in spintronic devices and facilitate the functional use of heat.
Thermal spin current from a ferromagnet to silicon by Seebeck spin tunnelling
NASA Astrophysics Data System (ADS)
Le Breton, Jean-Christophe; Sharma, Sandeep; Saito, Hidekazu; Yuasa, Shinji; Jansen, Ron
2011-07-01
Heat generation by electric current, which is ubiquitous in electronic devices and circuits, raises energy consumption and will become increasingly problematic in future generations of high-density electronics. The control and re-use of heat are therefore important topics for existing and emerging technologies, including spintronics. Recently it was reported that heat flow within a ferromagnet can produce a flow of spin angular momentum--a spin current--and an associated voltage. This spin Seebeck effect has been observed in metallic, insulating and semiconductor ferromagnets with temperature gradients across them. Here we describe and report the demonstration of Seebeck spin tunnelling--a distinctly different thermal spin flow, of purely interfacial nature--generated in a tunnel contact between electrodes of different temperatures when at least one of the electrodes is a ferromagnet. The Seebeck spin current is governed by the energy derivative of the tunnel spin polarization. By exploiting this in ferromagnet-oxide-silicon tunnel junctions, we observe thermal transfer of spins from the ferromagnet to the silicon without a net tunnel charge current. The induced spin accumulation scales linearly with heating power and changes sign when the temperature differential is reversed. This thermal spin current can be used by itself, or in combination with electrical spin injection, to increase device efficiency. The results highlight the engineering of heat transport in spintronic devices and facilitate the functional use of heat.
Thermal imaging of spin Peltier effect.
Daimon, Shunsuke; Iguchi, Ryo; Hioki, Tomosato; Saitoh, Eiji; Uchida, Ken-Ichi
2016-12-12
The Peltier effect modulates the temperature of a junction comprising two different conductors in response to charge currents across the junction, which is used in solid-state heat pumps and temperature controllers in electronics. Recently, in spintronics, a spin counterpart of the Peltier effect was observed. The 'spin Peltier effect' modulates the temperature of a magnetic junction in response to spin currents. Here we report thermal imaging of the spin Peltier effect; using active thermography technique, we visualize the temperature modulation induced by spin currents injected into a magnetic insulator from an adjacent metal. The thermal images reveal characteristic distribution of spin-current-induced heat sources, resulting in the temperature change confined only in the vicinity of the metal/insulator interface. This finding allows us to estimate the actual magnitude of the temperature modulation induced by the spin Peltier effect, which is more than one order of magnitude greater than previously believed.
Thermal imaging of spin Peltier effect
Daimon, Shunsuke; Iguchi, Ryo; Hioki, Tomosato; Saitoh, Eiji; Uchida, Ken-ichi
2016-01-01
The Peltier effect modulates the temperature of a junction comprising two different conductors in response to charge currents across the junction, which is used in solid-state heat pumps and temperature controllers in electronics. Recently, in spintronics, a spin counterpart of the Peltier effect was observed. The ‘spin Peltier effect' modulates the temperature of a magnetic junction in response to spin currents. Here we report thermal imaging of the spin Peltier effect; using active thermography technique, we visualize the temperature modulation induced by spin currents injected into a magnetic insulator from an adjacent metal. The thermal images reveal characteristic distribution of spin-current-induced heat sources, resulting in the temperature change confined only in the vicinity of the metal/insulator interface. This finding allows us to estimate the actual magnitude of the temperature modulation induced by the spin Peltier effect, which is more than one order of magnitude greater than previously believed. PMID:27941953
Thermal imaging of spin Peltier effect
NASA Astrophysics Data System (ADS)
Daimon, Shunsuke; Iguchi, Ryo; Hioki, Tomosato; Saitoh, Eiji; Uchida, Ken-Ichi
2016-12-01
The Peltier effect modulates the temperature of a junction comprising two different conductors in response to charge currents across the junction, which is used in solid-state heat pumps and temperature controllers in electronics. Recently, in spintronics, a spin counterpart of the Peltier effect was observed. The `spin Peltier effect' modulates the temperature of a magnetic junction in response to spin currents. Here we report thermal imaging of the spin Peltier effect; using active thermography technique, we visualize the temperature modulation induced by spin currents injected into a magnetic insulator from an adjacent metal. The thermal images reveal characteristic distribution of spin-current-induced heat sources, resulting in the temperature change confined only in the vicinity of the metal/insulator interface. This finding allows us to estimate the actual magnitude of the temperature modulation induced by the spin Peltier effect, which is more than one order of magnitude greater than previously believed.
Quantum spin liquids: a review
NASA Astrophysics Data System (ADS)
Savary, Lucile; Balents, Leon
2017-01-01
Quantum spin liquids may be considered ‘quantum disordered’ ground states of spin systems, in which zero-point fluctuations are so strong that they prevent conventional magnetic long-range order. More interestingly, quantum spin liquids are prototypical examples of ground states with massive many-body entanglement, which is of a degree sufficient to render these states distinct phases of matter. Their highly entangled nature imbues quantum spin liquids with unique physical aspects, such as non-local excitations, topological properties, and more. In this review, we discuss the nature of such phases and their properties based on paradigmatic models and general arguments, and introduce theoretical technology such as gauge theory and partons, which are conveniently used in the study of quantum spin liquids. An overview is given of the different types of quantum spin liquids and the models and theories used to describe them. We also provide a guide to the current status of experiments in relation to study quantum spin liquids, and to the diverse probes used therein.
spin pumping occurred under nonlinear spin precession
NASA Astrophysics Data System (ADS)
Zhou, Hengan; Fan, Xiaolong; Ma, Li; Zhou, Shiming; Xue, Desheng
Spin pumping occurs when a pure-spin current is injected into a normal metal thin layer by an adjacent ferromagnetic metal layer undergoing ferromagnetic resonance, which can be understood as the inverse effect of spin torque, and gives access to the physics of magnetization dynamics and damping. An interesting question is that whether spin pumping occurring under nonlinear spin dynamics would differ from linear case. It is known that nonlinear spin dynamics differ distinctly from linear response, a variety of amplitude dependent nonlinear effect would present. It has been found that for spin precession angle above a few degrees, nonlinear damping term would present and dominated the dynamic energy/spin-moment dissipation. Since spin pumping are closely related to the damping process, it is interesting to ask whether the nonlinear damping term could be involved in spin pumping process. We studied the spin pumping effect occurring under nonlinear spin precession. A device which is a Pt/YIG microstrip coupled with coplanar waveguide was used. High power excitation resulted in spin precession entering in a nonlinear regime. Foldover resonance lineshape and nonlinear damping have been observed. Based on those nonlinear effects, we determined the values of the precession cone angles, and the maximum cone angle can reach a values as high as 21.5 degrees. We found that even in nonlinear regime, spin pumping is still linear, which means the nonlinear damping and foldover would not affect spin pumping process.
NASA Astrophysics Data System (ADS)
Liu, Luqiao
2016-10-01
Spin orbit interactions give rise to interesting physics phenomena in solid state materials such as the spin Hall effect (SHE) and topological insulator surface states. Those effects have been extensively studied using various electrical detection methods. However, to date most experiments focus only on characterizing electrons near the Fermi surface, while spin-orbit interaction is expected to be energy dependent. Here we developed a tunneling spectroscopy technique to measure spin Hall materials and topological insulators under finite bias voltages. By electrically injecting spin polarized electrons into spin Hall metals or topological insulators using tunnel junctions and measuring the induced transverse voltage, we are able to study SHE in typical 5d transition metals and the spin momentum locking in topological insulators. For spin Hall effect metals, the magnitude of the spin Hall angle has been a highly controversial topic in previous studies. Results obtained from various techniques can differ by more than an order of magnitude. Our results from this transport measurement turned out to be consistent with the values obtained from spin Hall torque measurements, which can help to address the long debating issue. Besides the magnitude, the voltage dependent spectra from our experiment also provide useful information in distinguishing between different potential mechanisms. Finally, because of the impedance matching capability of tunnel junctions, the spin polarized tunneling technique can also be used as a powerful tool to measure resistive materials such as the topological insulators. Orders of magnitude improvement in the effective spin Hall angle was demonstrated through our measurement
Paramagnetic and Antiferromagnetic Spin Seebeck Effect
NASA Astrophysics Data System (ADS)
Wu, Stephen
We report on the observation of the longitudinal spin Seebeck effect in both antiferromagnetic and paramagnetic insulators. By using a microscale on-chip local heater, it is possible to generate a large thermal gradient confined to the chip surface without a large increase in the total sample temperature. This technique allows us to easily access low temperatures (200 mK) and high magnetic fields (14 T) through conventional dilution refrigeration and superconducting magnet setups. By exploring this regime, we detect the spin Seebeck effect through the spin-flop transition in antiferromagnetic MnF2 when a large magnetic field (>9 T) is applied along the easy axis direction. Using the same technique, we are also able to resolve a spin Seebeck effect from the paramagnetic phase of geometrically frustrated antiferromagnet Gd3Ga5O12 (gadolinium gallium garnet) and antiferromagnetic DyScO3 (DSO). Since these measurements occur above the ordering temperatures of these two materials, short-range magnetic order is implicated as the cause of the spin Seebeck effect in these systems. The discovery of the spin Seebeck effect in these two materials classes suggest that both antiferromagnetic spin waves and spin excitations from short range magnetic order may be used to generate spin current from insulators and that the spin wave spectra of individual materials are highly important to the specifics of the longitudinal spin Seebeck effect. Since insulating antiferromagnets and paramagnets are far more common than the typical insulating ferrimagnetic materials used in spin Seebeck experiments, this discovery opens up a large new class of materials for use in spin caloritronic devices. All authors acknowledge support of the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), Materials Sciences and Engineering Division. The use of facilities at the Center for Nanoscale Materials, was supported by the U.S. DOE, BES under Contract No. DE-AC02-06CH11357.
Afghanistan: Government Formation and Performance
2008-10-14
1 For text, see [http://www.un.org/News/dh/latest/afghan/afghan-agree.htm]. Order Code RS21922 Updated October 14, 2008 Afghanistan: Government ...However, ethnic disputes have been confined to political debate and competition, enabling Karzai to focus on improving governance , reversing security...deterioration and on his re-election bid in the fall of 2009. See CRS Report RL30588, Afghanistan: Post- War Governance , Security, and U.S. Policy, by
Interaction-driven exotic quantum phases in spin-orbit-coupled spin-1 bosons
NASA Astrophysics Data System (ADS)
Pixley, J. H.; Natu, Stefan S.; Spielman, I. B.; Das Sarma, S.
2016-02-01
We study the interplay between large-spin, spin-orbit coupling, and superfluidity for bosons in a two-dimensional optical lattice, focusing on the spin-1 spin-orbit-coupled system recently realized at the Joint Quantum Institute [Campbell et al., arXiv:1501.05984]. We find a rich quantum phase diagram where, in addition to the conventional phases—superfluid and insulator—contained in the spin-1 Bose-Hubbard model, there are new lattice symmetry breaking phases. For weak interactions, the interplay between two length scales, the lattice momentum and the spin-orbit wave vector, induce a phase transition from a uniform superfluid to a phase where bosons simultaneously condense at the center and edge of the Brillouin zone at a nonzero spin-orbit strength. This state is characterized by spin-density-wave order, which arises from the spin-1 nature of the system. Interactions suppress spin-density-wave order, and favor a superfluid only at the Brillouin zone edge. This state has spatially oscillating mean-field order parameters, but a homogeneous density. We show that the spin-density-wave superfluid phase survives in a two-dimensional harmonic trap, and thus establish that our results are directly applicable to experiments on 87Rb,7Li, and 41K.
NASA Astrophysics Data System (ADS)
Snyder, Joseph William
2003-07-01
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
Spin-crossover molecule based thermoelectric junction
Ghosh, Dibyajyoti; Parida, Prakash; Pati, Swapan K.
2015-05-11
Using ab-initio numerical methods, we explore the spin-dependent transport and thermoelectric properties of a spin-crossover molecule (i.e., iron complex of 2-(1H-pyrazol-1-yl)-6-(1H-tetrazole-5-yl)pyridine) based nano-junction. We demonstrate a large magnetoresistance, efficient conductance-switching, and spin-filter activity in this molecule-based two-terminal device. The spin-crossover process also modulates the thermoelectric entities. It can efficiently switch the magnitude as well as spin-polarization of the thermocurrent. We find that thermocurrent is changed by ∼4 orders of magnitude upon spin-crossover. Moreover, it also substantially affects the thermopower and consequently, the device shows extremely efficient spin-crossover magnetothermopower generation. Furthermore, by tuning the chemical potential of electrodes into a certain range, a pure spin-thermopower can be achieved for the high-spin state. Finally, the reasonably large values of figure-of-merit in the presence and absence of phonon demonstrate a large heat-to-voltage conversion efficiency of the device. We believe that our study will pave an alternative way of tuning the transport and thermoelectric properties through the spin-crossover process and can have potential applications in generation of spin-dependent current, information storage, and processing.
Spin-torque generator engineered by natural oxidation of Cu
NASA Astrophysics Data System (ADS)
An, Hongyu; Kageyama, Yuito; Kanno, Yusuke; Enishi, Nagisa; Ando, Kazuya
2016-10-01
The spin Hall effect is a spin-orbit coupling phenomenon, which enables electric generation and detection of spin currents. This relativistic effect provides a way for realizing efficient spintronic devices based on electric manipulation of magnetization through spin torque. However, it has been believed that heavy metals are indispensable for the spin-torque generation. Here we show that the spin Hall effect in Cu, a light metal with weak spin-orbit coupling, is significantly enhanced through natural oxidation. We demonstrate that the spin-torque generation efficiency of a Cu/Ni81Fe19 bilayer is enhanced by over two orders of magnitude by tuning the surface oxidation, reaching the efficiency of Pt/ferromagnetic metal bilayers. This finding illustrates a crucial role of oxidation in the spin Hall effect, opening a route for engineering the spin-torque generator by oxygen control and manipulating magnetization without using heavy metals.
Magnetic tetrastability in a spin chain
NASA Astrophysics Data System (ADS)
Pianet, Vivien; Urdampilleta, Matias; Colin, Thierry; Clérac, Rodolphe; Coulon, Claude
2016-08-01
Bistability in magnetism is extensively used, in particular for information storage. Here an alternative approach using tetrastable magnetic domains in one-dimensional (1D) spin systems is presented. Using numerical and analytical calculations, we show that a spin chain with a canting angle of π/4 possesses four energy-equivalent states. We discuss the static properties of this canted 1D system such as the profile and the energy of the domain walls as they govern the dynamics of the magnetization. The realization of this π/4 canted spin chain could enable the encoding of the information on four bits, which is a potential alternative toward the increase of storage density.
NASA Technical Reports Server (NTRS)
Lee, Seungwon; vonAllmen, Paul; Oyafuso, Fabiano; Klimeck, Gerhard; Whale, K. Birgitta
2004-01-01
Electron spin dephasing and decoherence by its interaction with nuclear spins in self-assembled quantum dots are investigated in the framework of the empirical tight-binding model. Electron spin dephasing in an ensemble of dots is induced by the inhomogeneous precession frequencies of the electron among dots, while electron spin decoherence in a single dot arises from the inhomogeneous precession frequencies of nuclear spins in the dot. For In(x)Ga(1-x) As self-assembled dots containing 30000 nuclei, the dephasing and decoherence times are predicted to be on the order of 100 ps and 1 (micro)s.
NASA Astrophysics Data System (ADS)
Alday, Luis F.; Bissi, Agnese; Lukowski, Tomasz
2015-11-01
Using conformal field theory (CFT) arguments we derive an infinite number of constraints on the large spin expansion of the anomalous dimensions and structure constants of higher spin operators. These arguments rely only on analyticity, unitarity, crossing-symmetry and the structure of the conformal partial wave expansion. We obtain results for both, perturbative CFT to all order in the perturbation parameter, as well as non-perturbatively. For the case of conformal gauge theories this provides a proof of the reciprocity principle to all orders in perturbation theory and provides a new "reciprocity" principle for structure constants. We argue that these results extend also to non-conformal theories.
Miyazaki, Yuji; Nakamoto, Tadahiro; Ikeuchi, Satoaki; Saito, Kazuya; Inaba, Akira; Sorai, Michio; Tojo, Takeo; Atake, Tooru; Matouzenko, Galina S; Zein, Samir; Borshch, Serguei A
2007-11-01
The spin crossover phenomenon of the recently described spin crossover complex [FeII(DAPP)(abpt)](ClO4)2 [DAPP = bis(3-aminopropyl)(2-pyridylmethyl)amine, abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole] accompanying an order-disorder phase transition of the ligand was investigated by adiabatic heat capacity calorimetry, far-IR, IR, and Raman spectroscopies, and normal vibrational mode calculation. A large heat capacity peak due to the spin crossover transition was observed at T(trs) = 185.61 K. The transition enthalpy and entropy amounted to Delta(trs)H = 15.44 kJ mol-1 and Delta(trs)S = 83.74 J K-1 mol-1, respectively. The transition entropy is larger than the expected value 60.66 J K-1 mol-1, which is contributed from the spin multiplicity (R ln 5; R: the gas constant), disordering of the carbon atom of the six-membered metallocycle in the DAPP ligand, and one of the two perchlorate anions (2R ln 2), and change of the normal vibrational modes between the high-spin (HS) and low-spin (LS) states (35.75 J K-1 mol-1). The remaining entropy would be ascribed to changes of the lattice vibrations and molecular librations between the HS and LS states. Furthermore, [Fe(DAPP)(abpt)](ClO4)2 crystals disintegrated and became smaller crystallites whenever they experienced the phase transition. This may be regarded as a successive self-grinding effect, evidenced by adiabatic calorimetry, DSC, magnetic susceptibility, and microscope observation. The relationship between the crystal size and the physical quantities is discussed.
SPINS OF LARGE ASTEROIDS: A HINT OF A PRIMORDIAL DISTRIBUTION IN THEIR SPIN RATES
Steinberg, Elad; Sari, Re’em
2015-04-15
The Asteroid Belt and the Kuiper Belt are relics from the formation of our solar system. Understanding the size and spin distribution of the two belts is crucial for a deeper understanding of the formation of our solar system and the dynamical processes that govern it. In this paper, we investigate the effect of collisions on the evolution of the spin distribution of asteroids and KBOs. We find that the power law nature of the impactors’ size distribution leads to a Lévy distribution of the spin rates. This results in a power law tail in the spin distribution, in stark contrast to the usually quoted Maxwellian distribution. We show that for bodies larger than 10 km, collisions alone lead to spin rates peaking at 0.15–0.5 revolutions per day. Comparing that to the observed spin rates of large asteroids (R > 50 km), we find that the spins of large asteroids, peaking at ∼1–2 revolutions per day, are dominated by a primordial component that reflects the formation mechanism of the asteroids. Similarly, the Kuiper Belt has undergone virtually no collisional spin evolution, assuming current densities. Collisions contribute a spin rate of ∼0.01 revolutions per day, thus the observed fast spin rates of KBOs are also primordial in nature.
Spin-bowling in cricket re-visited: model trajectories for various spin-vector angles
NASA Astrophysics Data System (ADS)
Robinson, Garry; Robinson, Ian
2016-08-01
In this paper we investigate, via the calculation of model trajectories appropriate to slow bowling in cricket, the effects on the flight path of the ball before pitching due to changes in the angle of the spin-vector. This was accomplished by allowing the spin-vector to vary in three ways. Firstly, from off-spin, where the spin-vector points horizontally and directly down the pitch, to top-spin where it points horizontally towards the off-side of the pitch. Secondly, from off-spin to side-spin where, for side-spin, the spin-vector points vertically upwards. Thirdly, where the spin-vector points horizontally and at 45° to the pitch (in the general direction of ‘point’, as viewed by the bowler), and is varied towards the vertical, while maintaining the 45° angle in the horizontal plane. It is found that, as is well known, top-spin causes the ball to dip in flight, side-spin causes the ball to move side-ways in flight and, perhaps most importantly, off-spin can cause the ball to drift to the off-side of the pitch late in its flight as it begins to fall. At a more subtle level it is found that, if the total spin is kept constant and a small amount of top-spin is added to the ball at the expense of some off-spin, there is little change in the side-ways drift. However, a considerable reduction in the length at which the ball pitches occurs, ˜25 cm, an amount that batsmen can ignore at their peril. On the other hand, a small amount of side-spin introduced to a top-spin delivery does not alter the point of pitching significantly, but produces a considerable amount of side-ways drift, ˜10 cm or more. For pure side-spin the side-ways drift is up to ˜30 cm. When a side-spin component is added to the spin of a ball bowled with a mixture of off-spin and top-spin in equal proportions, significant movement occurs in both the side-ways direction and in the point of pitching, of the order of a few tens of centimetres.
Spin superfluidity and coherent spin precession
NASA Astrophysics Data System (ADS)
Bunkov, Yuriy M.
2009-04-01
The spontaneous phase coherent precession of the magnetization in superfluid 3He-B was discovered experimentally in 1984 at the Institute for Physical Problems, Moscow by Borovik-Romanov, Bunkov, Dmitriev and Mukharsky and simultaneously explained theoretically by Fomin (Institut Landau, Moscow). Its formation is a direct manifestation of spin superfluidity. The latter is the magnetic counterpart of mass superfluidity and superconductivity. It is also an example of the Bose-Einstein condensation of spin-wave excitations (magnons). The coherent spin precession opened the way for investigations of spin supercurrent magnetization transport and other related phenomena, such as spin-current Josephson effect, process of phase slippage at a critical value of spin supercurrent, spin-current vortices, non-topological solitons (analogous to Q-balls in high energy physics) etc. New measuring techniques based on coherent spin precession made the investigation of mass counterflow and mass vortices possible owing to the spin-mass interaction. New phenomena were observed: mass-spin vortices, the Goldstone mode of the mass vortex with non-axisymmetric core, superfluid density anisotropy etc. Different types of coherent spin precession were later found in superfluid 3He-A and 3He-B confined in anisotropic aerogel, in the states with counterflow and in 3He with reduced magnetization. Finally, spin superfluidity investigations developed the basis for a modern investigation of electron spin supercurrent and spintronics.
Wong, Loke-Yuen; Png, Rui-Qi; Silva, F B Shanjeera; Chua, Lay-Lay; Repaka, D V Maheswar; Shi-Chen; Gao, Xing-Yu; Ke, Lin; Chua, Soo-Jin; Wee, Andrew T S; Ho, Peter K H
2010-10-05
The dependence of morphology and polymer-chain orientation of regioregular poly(3-hexylthiophene) (rrP3HT) thin films on processing conditions have been widely studied. However, their possible variation across the film thickness direction remains largely unknown. We report here a marked difference in the optical dielectric (n,k) spectra between the top and bottom interfaces of spin-cast (sc) rrP3HT films deposited from chlorobenzene solutions. These spectra were obtained from reflection variable-angle spectroscopic ellipsometry using a self-consistent graded optical model with self-imposed Kramers-Krönig consistency. The top interface shows a red-shifted absorption that is characteristic of better order than at the bottom, across a wide range of film thicknesses. This disparity diminishes in drop-cast (dc) and multipass inkjet-printed (ijp) films, and disappears in amorphous films such as those of polystyrene and of a green-emitting phenyl-substituted poly(p-phenylenevinylene). The (n,k) spectra also reveal that crystallinity increases across sc < dc < ijp films. This is supported by cross section scanning electron microscopy of the cleaved edges and measurement of the microroughness of both the film interfaces. Furthermore, optical anisotropy decreases across sc > dc > ijp films. Finally, near-edge X-ray absorption fine structure spectroscopy also shows the frontier chains in ijp and dc films are more isotropically oriented than those in sc films. These results suggest that semicrystalline conjugated polymer films can be produced far from equilibrium. This explains the marked variation in their (opto)electronic properties between the top and bottom surfaces that has sometimes been found depending on the film deposition method. In particular, an unusually pronounced crystallization is induced by ijp. We label this marked ijp-induced crystallization the "ijp morphology", which appears to be general, as it is found also in single-inkjet-droplet films. It appears
High spin isomer beam line at RIKEN
Kishida, T.; Ideguchi, E.; Wu, H.Y.
1996-12-31
Nuclear high spin states have been the subject of extensive experimental and theoretical studies. For the production of high spin states, fusion reactions are usually used. The orbital angular momentum brought in the reaction is changed into the nuclear spin of the compound nucleus. However, the maximum induced angular momentum is limited in this mechanism by the maximum impact parameter of the fusion reaction and by the competition with fission reactions. It is, therefore, difficult to populate very high spin states, and as a result, large {gamma}-detector arrays have been developed in order to detect subtle signals from such very high spin states. The use of high spin isomers in the fusion reactions can break this limitation because the high spin isomers have their intrinsic angular momentum, which can bring the additional angular momentum without increasing the excitation energy. There are two methods to use the high spin isomers for secondary reactions: the use of the high spin isomers as a target and that as a beam. A high spin isomer target has already been developed and used for several experiments. But this method has an inevitable shortcoming that only {open_quotes}long-lived{close_quotes} isomers can be used for a target: {sup 178}Hf{sup m2} (16{sup +}) with a half-life of 31 years in the present case. By developing a high spin isomer beam, the authors can utilize various short-lived isomers with a short half-life around 1 {mu}s. The high spin isomer beam line of RIKEN Accelerator Facility is a unique apparatus in the world which provides a high spin isomer as a secondary beam. The combination of fusion-evaporation reaction and inverse kinematics are used to produce high spin isomer beams; in particular, the adoption of `inverse kinematics` is essential to use short-lived isomers as a beam.
Zhang, Wei; Jungfleisch, Matthias B.; Freimuth, Frank; Jiang, Wanjun; Sklenar, Joseph; Pearson, John E.; Ketterson, John B.; Mokrousov, Yuri; Hoffmann, Axel
2015-10-06
We investigate spin-orbit torques of metallic CuAu-I-type antiferromagnets using spin-torque ferromagnetic resonance tuned by a dc-bias current. The observed spin torques predominantly arise from diffusive transport of spin current generated by the spin Hall effect. We find a growth-orientation dependence of the spin torques by studying epitaxial samples, which may be correlated to the anisotropy of the spin Hall effect. The observed anisotropy is consistent with first-principles calculations on the intrinsic spin Hall effect. Our work suggests large tunable spin-orbit effects in magnetically-ordered materials.
Tidal deformations of a spinning compact object
NASA Astrophysics Data System (ADS)
Pani, Paolo; Gualtieri, Leonardo; Maselli, Andrea; Ferrari, Valeria
2015-07-01
The deformability of a compact object induced by a perturbing tidal field is encoded in the tidal Love numbers, which depend sensibly on the object's internal structure. These numbers are known only for static, spherically-symmetric objects. As a first step to compute the tidal Love numbers of a spinning compact star, here we extend powerful perturbative techniques to compute the exterior geometry of a spinning object distorted by an axisymmetric tidal field to second order in the angular momentum. The spin of the object introduces couplings between electric and magnetic deformations and new classes of induced Love numbers emerge. For example, a spinning object immersed in a quadrupolar, electric tidal field can acquire some induced mass, spin, quadrupole, octupole and hexadecapole moments to second order in the spin. The deformations are encoded in a set of inhomogeneous differential equations which, remarkably, can be solved analytically in vacuum. We discuss certain subtleties in defining the tidal Love numbers in general relativity, which are due to the difficulty in separating the tidal field from the linear response of the object in the solution, even in the static case. By extending the standard procedure to identify the linear response in the static case, we prove analytically that the Love numbers of a Kerr black hole remain zero to second order in the spin. As a by-product, we provide the explicit form for a slowly-rotating, tidally-deformed Kerr black hole to quadratic order in the spin, and discuss its geodesic and geometrical properties.
Nuclear spin circular dichroism
Vaara, Juha; Rizzo, Antonio; Kauczor, Joanna; Norman, Patrick; Coriani, Sonia
2014-04-07
Recent years have witnessed a growing interest in magneto-optic spectroscopy techniques that use nuclear magnetization as the source of the magnetic field. Here we present a formulation of magnetic circular dichroism (CD) due to magnetically polarized nuclei, nuclear spin-induced CD (NSCD), in molecules. The NSCD ellipticity and nuclear spin-induced optical rotation (NSOR) angle correspond to the real and imaginary parts, respectively, of (complex) quadratic response functions involving the dynamic second-order interaction of the electron system with the linearly polarized light beam, as well as the static magnetic hyperfine interaction. Using the complex polarization propagator framework, NSCD and NSOR signals are obtained at frequencies in the vicinity of optical excitations. Hartree-Fock and density-functional theory calculations on relatively small model systems, ethene, benzene, and 1,4-benzoquinone, demonstrate the feasibility of the method for obtaining relatively strong nuclear spin-induced ellipticity and optical rotation signals. Comparison of the proton and carbon-13 signals of ethanol reveals that these resonant phenomena facilitate chemical resolution between non-equivalent nuclei in magneto-optic spectra.
Spin coupling in zigzag Wigner crystals.
Klironomos, A. D.; Meyer, J. S.; Hikihara, T.; Matveev, K. A.; Materials Science Division; Ohio State Univ.; Hokkaido Univ.
2007-08-01
We consider interacting electrons in a quantum wire in the case of a shallow confining potential and low electron density. In a certain range of densities, the electrons form a two-row (zigzag) Wigner crystal whose spin properties are determined by nearest and next-nearest neighbor exchange as well as by three- and four-particle ring exchange processes. The phase diagram of the resulting zigzag spin chain has regions of complete spin polarization and partial spin polarization in addition to a number of unpolarized phases, including antiferromagnetism and dimer order as well as a novel phase generated by the four-particle ring exchange.
The universal definition of spin current
An, Z.; Liu, F. Q.; Lin, Y.; Liu, C.
2012-01-01
The spin current, orbit angular momentum current and total angular momentum current in a tensor form have been universally defined according to the quantum electrodynamics. Their conservation quantities and the continuity equations have been discussed in different cases. Non-relativistic approximation forms are deduced in order to explain their physical meanings, and to analyze some experimental results. The spin current of helical edge states in HgTe/CdTe quantum wells is calculated to demonstrate the properties of the spin current of the two dimensional quantum spin-Hall system. A generalized spin-orbit coupling term in the semiconducting media is deduced based on the theory of the electrodynamics in the moving media. It is recommended to use the effective total angular momentum current instead of the pure spin current to describe the distribution of polarization and the transport properties in spintronics. PMID:22563522
Cavity cooling of an ensemble spin system.
Wood, Christopher J; Borneman, Troy W; Cory, David G
2014-02-07
We describe how sideband cooling techniques may be applied to large spin ensembles in magnetic resonance. Using the Tavis-Cummings model in the presence of a Rabi drive, we solve a Markovian master equation describing the joint spin-cavity dynamics to derive cooling rates as a function of ensemble size. Our calculations indicate that the coupled angular momentum subspaces of a spin ensemble containing roughly 10(11) electron spins may be polarized in a time many orders of magnitude shorter than the typical thermal relaxation time. The described techniques should permit efficient removal of entropy for spin-based quantum information processors and fast polarization of spin samples. The proposed application of a standard technique in quantum optics to magnetic resonance also serves to reinforce the connection between the two fields, which has recently begun to be explored in further detail due to the development of hybrid designs for manufacturing noise-resilient quantum devices.
Measurement of spin coherence using Raman scattering
NASA Astrophysics Data System (ADS)
Sun, Z.; Delteil, A.; Faelt, S.; Imamoǧlu, A.
2016-06-01
Ramsey interferometry provides a natural way to determine the coherence time of most qubit systems. Recent experiments on quantum dots, however, demonstrated that dynamical nuclear spin polarization can strongly influence the measurement process, making it difficult to extract the T2* coherence time using standard optical Ramsey pulses. Here, we demonstrate an alternative method for spin coherence measurement that is based on first-order coherence of photons generated in spin-flip Raman scattering. We show that if a quantum emitter is driven by a weak monochromatic laser, Raman coherence is determined exclusively by spin coherence, allowing for a direct determination of spin T2* time. When combined with coherence measurements on Rayleigh scattered photons, our technique enables us to identify coherent and incoherent contributions to resonance fluorescence, and to minimize the latter. We verify the validity of our technique by comparing our results to those determined from Ramsey interferometry for electron and heavy-hole spins.
Effects of Quantum Spin-1 /2 Impurities on the Magnetic Properties of Zigzag Spin Chains
NASA Astrophysics Data System (ADS)
Karmakar, Koushik; Skoulatos, Markos; Prando, Giacomo; Roessli, Bertran; Stuhr, Uwe; Hammerath, Franziska; Rüegg, Christian; Singh, Surjeet
2017-03-01
We investigate the effect of Co2 + (spin-1 /2 ) impurities on the magnetic ground state and low-lying spin excitations of the quasione-dimensional spin-1 /2 antiferromagnet SrCuO2 by means of neutron scattering, muon spin spectroscopy, and bulk (ac and dc) magnetic susceptibilities. We found that dilute Co doping induces an Ising-like anisotropy and enhances the magnetic ordering temperature rather significantly, but preserves the gapless nature of the spin excitations. These results are in apparent contradiction with the recent studies of Ni (spin-1) doped SrCuO2 . Low-temperature magnetic behavior of the Co-doped zigzag chains in SrCuO2 reveals the presence of a weak geometrical spin frustration.
Effects of Quantum Spin-1/2 Impurities on the Magnetic Properties of Zigzag Spin Chains.
Karmakar, Koushik; Skoulatos, Markos; Prando, Giacomo; Roessli, Bertran; Stuhr, Uwe; Hammerath, Franziska; Rüegg, Christian; Singh, Surjeet
2017-03-10
We investigate the effect of Co^{2+} (spin-1/2) impurities on the magnetic ground state and low-lying spin excitations of the quasione-dimensional spin-1/2 antiferromagnet SrCuO_{2} by means of neutron scattering, muon spin spectroscopy, and bulk (ac and dc) magnetic susceptibilities. We found that dilute Co doping induces an Ising-like anisotropy and enhances the magnetic ordering temperature rather significantly, but preserves the gapless nature of the spin excitations. These results are in apparent contradiction with the recent studies of Ni (spin-1) doped SrCuO_{2}. Low-temperature magnetic behavior of the Co-doped zigzag chains in SrCuO_{2} reveals the presence of a weak geometrical spin frustration.
The limit spin current in a time-dependent Rashba spin-orbit coupling system
NASA Astrophysics Data System (ADS)
Zhang, Shu-feng; Zhu, Wei
2013-02-01
The generation of spin current in a one dimensional electron gas (1DEG) system is studied, where the Rashba spin-orbit coupling (RSOC) is modulated by a time-varying gate voltage. With a simple unitary transformation, we show the appearance of an additional spin-dependent potential which results in a spin-dependent effective electric field. We include the scattering interaction by taking a relaxation approximation. The formula for the induced spin current is derived, the limit value accessible by time-varying RSOC is obtained and the order of magnitude is estimated. We find that the maximum of a pulsed spin current can reach that limit value. The results in 1DEG are extended to 2DEG. In addition, we study the spin current in a metal-quantum dot-metal system.
Spin qubit relaxation in a moving quantum dot
NASA Astrophysics Data System (ADS)
Huang, Peihao; Hu, Xuedong
2013-08-01
Long-range quantum communication for spin qubits is an important open problem. Here we study decoherence of an electron spin qubit that is being transported in a moving quantum dot. We focus on spin decoherence due to spin-orbit interaction and a random electric potential. We find that at the lowest order, the motion induces longitudinal spin relaxation, with a rate linear in the dot velocity. Our calculated spin relaxation time ranges from sub μs in GaAs to above ms in Si, making this relaxation a significant decoherence channel. Our results also give clear indications on how to reduce the decoherence effect of electron motion.
The role of spin exchange in charge transfer in low-bandgap polymer: Fullerene bulk heterojunctions
Krinichnyi, V. I. Yudanova, E. I.; Denisov, N. N.
2014-07-28
Formation, relaxation and dynamics of polarons and methanofullerene anion radicals photoinitiated in poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′, 3′-benzothiadiazole)]:-[6,6]-phenyl-C{sub 61}-butyric acid methyl ester (PCDTBT:PC{sub 61}BM) bulk heterojunctions were studied mainly by light-induced EPR (LEPR) spectroscopy in wide photon energy and temperature ranges. Some polarons are pinned by spin traps whose number and depth are governed by the composite morphology and photon energy. The proximity of the photon energy and the polymer bandgap reduces the number of such traps, inhibits recombination of mobile charge carriers, and facilitates their mobility in polymer network. Spin relaxation and charge carrier dynamics were studied by the steady-state saturation method at wide range of temperature and photon energy. These processes were shown to be governed by spin exchange as well as by the photon energy. Charge transfer in the composite is governed by the polaron scattering on the lattice phonons of crystalline domains embedded into amorphous polymer matrix and its activation hopping between polymer layers. The energy barrier required for polaron interchain hopping exceeds that of its intrachain diffusion. Anisotropy of polaron dynamics in the PCDTBT:PC61BM composite is less than that of poly(3-alkylthiophenes)-based systems that evidences for better ordering of the former. Lorentzian shape of LEPR lines of both charge carriers, lower concentration of spin traps as well as behaviours of the main magnetic resonance parameters were explained by layer ordered morphology of polymer matrix.
Spin waves in triple-q structures: Application to USb
Jensen, J.; Bak, P.
1981-06-01
The spin-wave spectrum in a system with triple-q magnetic structure is calculated. The spin waves differ distinctly from those in the corresponding single-q structure, but agree with the excitations observed by Lander and Stirling in uranium antimonide (USb). Their experiments thus directly verify that the spins in USb are ordered in the triple-q structure.
The spin Hall effect as a probe of nonlinear spin fluctuations.
Wei, D H; Niimi, Y; Gu, B; Ziman, T; Maekawa, S; Otani, Y
2012-01-01
The spin Hall effect and its inverse have key roles in spintronic devices as they allow conversion of charge currents to and from spin currents. The conversion efficiency strongly depends on material details, such as the electronic band structure and the nature of impurities. Here we show an anomaly in the inverse spin Hall effect in weak ferromagnetic NiPd alloys near their Curie temperatures with a shape independent of material details, such as Ni concentrations. By extending Kondo's model for the anomalous Hall effect, we explain the observed anomaly as originating from the second-order nonlinear spin fluctuation of Ni moments. This brings to light an essential symmetry difference between the spin Hall effect and the anomalous Hall effect, which reflects the first-order nonlinear fluctuations of local moments. Our finding opens up a new application of the spin Hall effect, by which a minuscule magnetic moment can be detected.
Ewings, R. A.; Perring, T. G.; Sikora, O.; Abernathy, D. L.; Tomioka, Y.; Tokura, Y.
2016-07-06
We have used time-of-flight inelastic neutron scattering to measure the spin wave spectrum of the canonical half-doped manganite Pr_{0.5}Ca_{0.5}MnO_{3} in its magnetic and orbitally ordered phase. Comparison of the data, which cover multiple Brillouin zones and the entire energy range of the excitations, with several different models shows that only the CE-type ordered state provides an adequate description of the magnetic ground state, provided interactions beyond nearest neighbor are included. We are able to rule out a ground state in which there exist pairs of dimerized spins which interact only with their nearest neighbors. The Zener polaron ground state, which comprises strongly bound magnetic dimers, can be ruled out on the basis of gross features of the observed spin wave spectrum. A model with weaker dimerization reproduces the observed dispersion but can be ruled out on the basis of subtle discrepancies between the calculated and observed structure factors at certain positions in reciprocal space. Adding further neighbor interactions results in almost no dimerization, i.e. interpolating back to the CE model. These results are consistent with theoretical analysis of the degenerate double exchange model for half-doping.
BAI,M.; ROSER, T.
2007-06-25
This paper proposes a new design of spin flipper for RHIC to obtain full spin flip with the spin tune staying at half integer. The traditional technique of using an rf dipole or solenoid as spin flipper to achieve full spin flip in the presence of full Siberian snake requires one to change the snake configuration to move the spin tune away from half integer. This is not practical for an operational high energy polarized proton collider like RHIC where beam lifetime is sensitive to small betatron tune change. The design of the new spin flipper as well as numerical simulations are presented.
Spin relaxation through Kondo scattering in Cu/Py lateral spin valves
NASA Astrophysics Data System (ADS)
Batley, J. T.; Rosamond, M. C.; Ali, M.; Linfield, E. H.; Burnell, G.; Hickey, B. J.
2015-12-01
The temperature dependence of the spin diffusion length typically reflects the scattering mechanism responsible for spin relaxation. Within nonmagnetic metals it is reasonable to expect the Elliot-Yafet mechanism to play a role and thus the temperature dependence of the spin diffusion length might be inversely proportional to resistivity. In lateral spin valves, measurements have found that at low temperatures the spin diffusion length unexpectedly decreases. By measuring the transport properties of lateral Py/Cu/Py spin valves, fabricated from Cu with magnetic impurities of <1 ppm and ˜4 ppm, we extract a spin diffusion length which shows this suppression below 30 K only in the presence of the Kondo effect. We have calculated the spin-relaxation rate and isolated the contribution from magnetic impurities. We find the spin-flip probability of a magnetic impurity to be 34%. Our analysis demonstrates the dominant role of Kondo scattering in spin relaxation, even in low concentrations of order 1 ppm, and hence illustrates its importance to the reduction in spin diffusion length observed by ourselves and others.
Time evolution of a single spin inhomogeneously coupled to an interacting spin environment.
Huang, Zhen; Sadiek, Gehad; Kais, Sabre
2006-04-14
We study the time evolution of a single spin coupled by exchange interaction to an environment of interacting spin bath modeled by the XY Hamiltonian. By evaluating the spin correlator of the single spin, we observed that the decay rate of the spin oscillations strongly depends on the relative magnitude of the exchange coupling between the single spin and its nearest neighbor J(') and coupling among the spins in the environment J. The decoherence time varies significantly based on the relative coupling magnitudes of J and J('). The decay rate law has a Gaussian profile when the two exchange couplings are of the same order J(') approximately J but converts to exponential and then a power law as we move to the regimes of J(')>J and J(')
Temperature Chaos in Some Spherical Mixed p-Spin Models
NASA Astrophysics Data System (ADS)
Chen, Wei-Kuo; Panchenko, Dmitry
2017-03-01
We give two types of examples of the spherical mixed even- p-spin models for which chaos in temperature holds. These complement some known results for the spherical pure p-spin models and for models with Ising spins. For example, in contrast to a recent result of Subag who showed absence of chaos in temperature in the spherical pure p-spin models for p≥3, we show that even a smaller order perturbation induces temperature chaos.
NASA Astrophysics Data System (ADS)
Saslow, Wayne; Li, Fuxiang; Taniguchi, Tomohiro
We extend the irreversible thermodynamics of uniform ferromagnets to include the non-equilibrium phenomenon of spin accumulation, both for conductors and for insulators. The dynamics of the quantization axis M& circ; is governed by the Landau-Lifshitz equation. The spin accumulation, whose longitudinal and transverse parts we label δM and m -->, is due to a non-equilibrium distribution of magnetic excitations. Its dynamics is governed by a Bloch equation that includes spin diffusion. We also consider transport across surfaces, including boundary conditions for M& circ;, δM , and m -->, and apply the results to the nature of the reciprocity between spin transfer torque and spin pumping.
Giant spin Seebeck effect in a non-magnetic material.
Jaworski, C M; Myers, R C; Johnston-Halperin, E; Heremans, J P
2012-07-11
The spin Seebeck effect is observed when a thermal gradient applied to a spin-polarized material leads to a spatially varying transverse spin current in an adjacent non-spin-polarized material, where it gets converted into a measurable voltage. It has been previously observed with a magnitude of microvolts per kelvin in magnetically ordered materials, ferromagnetic metals, semiconductors and insulators. Here we describe a signal in a non-magnetic semiconductor (InSb) that has the hallmarks of being produced by the spin Seebeck effect, but is three orders of magnitude larger (millivolts per kelvin). We refer to the phenomenon that produces it as the giant spin Seebeck effect. Quantizing magnetic fields spin-polarize conduction electrons in semiconductors by means of Zeeman splitting, which spin-orbit coupling amplifies by a factor of ∼25 in InSb. We propose that the giant spin Seebeck effect is mediated by phonon-electron drag, which changes the electrons' momentum and directly modifies the spin-splitting energy through spin-orbit interactions. Owing to the simultaneously strong phonon-electron drag and spin-orbit coupling in InSb, the magnitude of the giant spin Seebeck voltage is comparable to the largest known classical thermopower values.
Spin Tqfts and Fermionic Phases of Matter
NASA Astrophysics Data System (ADS)
Gaiotto, Davide; Kapustin, Anton
We study lattice constructions of gapped fermionic phases of matter. We show that the construction of fermionic Symmetry Protected Topological orders by Gu and Wen has a hidden dependence on a discrete spin structure on the Euclidean space-time. The spin structure is needed to resolve ambiguities which are otherwise present. An identical ambiguity is shown to arise in the fermionic analog of the string-net construction of 2D topological orders. We argue that the need for a spin structure is a general feature of lattice models with local fermionic degrees of freedom and is a lattice analog of the spinstatistics relation.
Magnons, Spin Current and Spin Seebeck Effect
NASA Astrophysics Data System (ADS)
Maekawa, Sadamichi
2012-02-01
When metals and semiconductors are placed in a temperature gradient, the electric voltage is generated. This mechanism to convert heat into electricity, the so-called Seebeck effect, has attracted much attention recently as the mechanism for utilizing wasted heat energy. [1]. Ferromagnetic insulators are good conductors of spin current, i.e., the flow of electron spins [2]. When they are placed in a temperature gradient, generated are magnons, spin current and the spin voltage [3], i.e., spin accumulation. Once the spin voltage is converted into the electric voltage by inverse spin Hall effect in attached metal films such as Pt, the electric voltage is obtained from heat energy [4-5]. This is called the spin Seebeck effect. Here, we present the linear-response theory of spin Seebeck effect based on the fluctuation-dissipation theorem [6-8] and discuss a variety of the devices. [4pt] [1] S. Maekawa et al, Physics of Transition Metal Oxides (Springer, 2004). [0pt] [2] S. Maekawa: Nature Materials 8, 777 (2009). [0pt] [3] Concept in Spin Electronics, eds. S. Maekawa (Oxford University Press, 2006). [0pt] [4] K. Uchida et al., Nature 455, 778 (2008). [0pt] [5] K. Uchida et al., Nature Materials 9, 894 (2010) [0pt] [6] H. Adachi et al., APL 97, 252506 (2010) and Phys. Rev. B 83, 094410 (2011). [0pt] [7] J. Ohe et al., Phys. Rev. B (2011) [0pt] [8] K. Uchida et al., Appl. Phys. Lett. 97, 104419 (2010).
Observation of unconventional quantum spin textures in topological insulators.
Hsieh, D; Xia, Y; Wray, L; Qian, D; Pal, A; Dil, J H; Osterwalder, J; Meier, F; Bihlmayer, G; Kane, C L; Hor, Y S; Cava, R J; Hasan, M Z
2009-02-13
A topologically ordered material is characterized by a rare quantum organization of electrons that evades the conventional spontaneously broken symmetry-based classification of condensed matter. Exotic spin-transport phenomena, such as the dissipationless quantum spin Hall effect, have been speculated to originate from a topological order whose identification requires a spin-sensitive measurement, which does not exist to this date in any system. Using Mott polarimetry, we probed the spin degrees of freedom and demonstrated that topological quantum numbers are completely determined from spin texture-imaging measurements. Applying this method to Sb and Bi(1-x)Sb(x), we identified the origin of its topological order and unusual chiral properties. These results taken together constitute the first observation of surface electrons collectively carrying a topological quantum Berry's phase and definite spin chirality, which are the key electronic properties component for realizing topological quantum computing bits with intrinsic spin Hall-like topological phenomena.
Switzner, Nathan; Henry, Dick
2009-03-20
In a second development order, spin-forming equipment was again evaluated using the test shape, a hemispherical shell. In this second development order, pure vanadium and alloy titanium (Ti-6Al-4V) were spin-formed, as well as additional copper and 21-6-9 stainless. In the first development order the following materials had been spin-formed: copper (alloy C11000 ETP), 6061 aluminum, 304L stainless steel, 21-6-9 stainless steel, and tantalum-2.5% tungsten. Significant challenges included properly adjusting the rotations-per-minute (RPM), cracking at un-beveled edges and laser marks, redressing of notches, surface cracking, non-uniform temperature evolution in the titanium, and cracking of the tailstock. Lessons learned were that 300 RPM worked better than 600 RPM for most materials (at the feed rate of 800 mm/min); beveling the edges to lower the stress reduces edge cracking; notches, laser marks, or edge defects in the preform doom the process to cracking and failure; coolant is required for vanadium spin-forming; increasing the number of passes to nine or more eliminates surface cracking for vanadium; titanium develops a hot zone in front of the rollers; and the tailstock should be redesigned to eliminate the cylindrical stress concentrator in the center.
Topological spin pumps coupled by a magnetic impurity
NASA Astrophysics Data System (ADS)
Ren, Y. J.; Sheng, L.; Xing, D. Y.
2016-05-01
The recently proposed topological spin pump is a full spin analogue to the famous Thouless charge pump, in the sense that it is protected by bulk band topology alone and independent of any symmetries. The previous works were however confined to a single one-dimensional (1D) pump with spin Chern number C{spin}=C\\uparrow-C \\downarrow= 2 or a series of such pumps in parallel without any interaction. In this paper, we investigate the influence of coupling between two 1D spin Chern pumps by a magnetic impurity potential, which also breaks the time-reversal symmetry, on the spin pumping effect. By using the Green's function and Born approximation, it is shown that the leading correction to the spin pumped per cycle due to the impurity scattering is of the second order in the impurity potential. For not very strong impurity potential, the spin pumped per cycle in units of \\hbar/2 stays near the quantized value determined by the total spin Chern number of the system C{spin} , for all the cases in which both, either or none of the two pumps are topologically nontrivial, corresponding to C{spin}=4 , 2 or 0, respectively. This result demonstrates that the topological spin pumps can be generally classified by different integer values of the total spin Chern number C{spin} .