On induced action for conformal higher spins in curved background

Directory of Open Access Journals (Sweden)

Matteo Beccaria

2017-06-01

Full Text Available We continue the investigation of the structure of the action for a tower of conformal higher spin fields in non-trivial 4d background metric recently discussed in Grigoriev and Tseytlin (2016 [15]. The action is defined as an induced one from path integral of a conformal scalar field in curved background coupled to higher spin fields. We analyze in detail the dependence of the quadratic part of the induced action on the spin 1 and spin 3 fields, determining the presence of a curvature-dependent mixed spin 1–3 term. One consequence is that the pure spin 3 kinetic term cannot be gauge-invariant on its own beyond the leading term in small curvature expansion. We also compute the non-zero contribution of the 1–3 mixing term to the conformal anomaly c-coefficient. One is thus to determine all such mixing terms before addressing the question of possible vanishing of the total c-coefficient in the conformal higher spin theory.

Accurate potential energy curves, spectroscopic parameters, transition dipole moments, and transition probabilities of 21 low-lying states of the CO+ cation

Science.gov (United States)

Xing, Wei; Shi, Deheng; Zhang, Jicai; Sun, Jinfeng; Zhu, Zunlue

2018-05-01

This paper calculates the potential energy curves of 21 Λ-S and 42 Ω states, which arise from the first two dissociation asymptotes of the CO+ cation. The calculations are conducted using the complete active space self-consistent field method, which is followed by the valence internally contracted multireference configuration interaction approach with the Davidson correction. To improve the reliability and accuracy of the potential energy curves, core-valence correlation and scalar relativistic corrections, as well as the extrapolation of potential energies to the complete basis set limit are taken into account. The spectroscopic parameters and vibrational levels are determined. The spin-orbit coupling effect on the spectroscopic parameters and vibrational levels is evaluated. To better study the transition probabilities, the transition dipole moments are computed. The Franck-Condon factors and Einstein coefficients of some emissions are calculated. The radiative lifetimes are determined for a number of vibrational levels of several states. The transitions between different Λ-S states are evaluated. Spectroscopic routines for observing these states are proposed. The spectroscopic parameters, vibrational levels, transition dipole moments, and transition probabilities reported in this paper can be considered to be very reliable and can be used as guidelines for detecting these states in an appropriate spectroscopy experiment, especially for the states that were very difficult to observe or were not detected in previous experiments.

Antiferromagnetic spin phase transition in nuclear matter with effective Gogny interaction

International Nuclear Information System (INIS)

Isayev, A.A.; Yang, J.

2004-01-01

The possibility of ferromagnetic and antiferromagnetic phase transitions in symmetric nuclear matter is analyzed within the framework of a Fermi liquid theory with the effective Gogny interaction. It is shown that at some critical density nuclear matter with the D1S effective force undergoes a phase transition to the antiferromagnetic spin state (opposite directions of neutron and proton spins). The self-consistent equations of spin polarized nuclear matter with the D1S force have no solutions corresponding to ferromagnetic spin ordering (the same direction of neutron and proton spins) and, hence, the ferromagnetic transition does not appear. The dependence of the antiferromagnetic spin polarization parameter as a function of density is found at zero temperature

Condensate-induced transitions and critical spin chains

NARCIS (Netherlands)

Månsson, T.; Lahtinen, V.; Suorsa, J.; Ardonne, E.

2013-01-01

We show that condensate-induced transitions between two-dimensional topological phases provide a general framework to relate one-dimensional spin models at their critical points. We demonstrate this using two examples. First, we show that two well-known spin chains, namely, the XY chain and the

Percolation and spin glass transition

International Nuclear Information System (INIS)

Sadiq, A.; Tahir-Kheli, R.A.; Wortis, M.; Bhatti, N.A.

1980-10-01

The behaviour of clusters of curved and normal plaquette particles in a bond random, +-J, Ising model is studied in finite square and triangular lattices. Computer results for the concentration of antiferromagnetic bonds when percolating clusters first appears are found to be close to those reported for the occurrence and disappearance of spin glass phases in these systems. (author)

Tunable spin-charge conversion through topological phase transitions in zigzag nanoribbons

KAUST Repository

Li, Hang

2016-06-29

We study spin-orbit torques and charge pumping in magnetic quasi-one-dimensional zigzag nanoribbons with a hexagonal lattice, in the presence of large intrinsic spin-orbit coupling. Such a system experiences a topological phase transition from a trivial band insulator to a quantum spin Hall insulator by tuning of either the magnetization direction or the intrinsic spin-orbit coupling. We find that the spin-charge conversion efficiency (i.e., spin-orbit torque and charge pumping) is dramatically enhanced at the topological transition, displaying a substantial angular anisotropy.

Tunable spin-charge conversion through topological phase transitions in zigzag nanoribbons

KAUST Repository

Li, Hang; Manchon, Aurelien

2016-01-01

We study spin-orbit torques and charge pumping in magnetic quasi-one-dimensional zigzag nanoribbons with a hexagonal lattice, in the presence of large intrinsic spin-orbit coupling. Such a system experiences a topological phase transition from a trivial band insulator to a quantum spin Hall insulator by tuning of either the magnetization direction or the intrinsic spin-orbit coupling. We find that the spin-charge conversion efficiency (i.e., spin-orbit torque and charge pumping) is dramatically enhanced at the topological transition, displaying a substantial angular anisotropy.

Giant spin-orbit-induced spin splitting in two-dimensional transition-metal dichalcogenide semiconductors

KAUST Repository

Zhu, Zhiyong

2011-10-14

Fully relativistic first-principles calculations based on density functional theory are performed to study the spin-orbit-induced spin splitting in monolayer systems of the transition-metal dichalcogenides MoS2, MoSe2, WS2, and WSe2. All these systems are identified as direct-band-gap semiconductors. Giant spin splittings of 148–456 meV result from missing inversion symmetry. Full out-of-plane spin polarization is due to the two-dimensional nature of the electron motion and the potential gradient asymmetry. By suppression of the Dyakonov-Perel spin relaxation, spin lifetimes are expected to be very long. Because of the giant spin splittings, the studied materials have great potential in spintronics applications.

Giant spin-orbit-induced spin splitting in two-dimensional transition-metal dichalcogenide semiconductors

KAUST Repository

Zhu, Zhiyong; Cheng, Yingchun; Schwingenschlö gl, Udo

2011-01-01

Fully relativistic first-principles calculations based on density functional theory are performed to study the spin-orbit-induced spin splitting in monolayer systems of the transition-metal dichalcogenides MoS2, MoSe2, WS2, and WSe2. All these systems are identified as direct-band-gap semiconductors. Giant spin splittings of 148–456 meV result from missing inversion symmetry. Full out-of-plane spin polarization is due to the two-dimensional nature of the electron motion and the potential gradient asymmetry. By suppression of the Dyakonov-Perel spin relaxation, spin lifetimes are expected to be very long. Because of the giant spin splittings, the studied materials have great potential in spintronics applications.

Quantum phase transitions in random XY spin chains

International Nuclear Information System (INIS)

Bunder, J.E.; McKenzie, R.H.

2000-01-01

Full text: The XY spin chain in a transverse field is one of the simplest quantum spin models. It is a reasonable model for heavy fermion materials such as CeCu 6-x Au x . It has two quantum phase transitions: the Ising transition and the anisotropic transition. Quantum phase transitions occur at zero temperature. We are investigating what effect the introduction of randomness has on these quantum phase transitions. Disordered systems which undergo quantum phase transitions can exhibit new universality classes. The universality class of a phase transition is defined by the set of critical exponents. In a random system with quantum phase transitions we can observe Griffiths-McCoy singularities. Such singularities are observed in regions which have no long range order, so they are not classified as critical regions, yet they display phenomena normally associated with critical points, such as a diverging susceptibility. Griffiths-McCoy phases are due to rare regions with stronger than! average interactions and may be present far from the quantum critical point. We show how the random XY spin chain may be mapped onto a random Dirac equation. This allows us to calculate the density of states without making any approximations. From the density of states we can describe the conditions which should allow a Griffiths-McCoy phase. We find that for the Ising transition the dynamic critical exponent, z, is not universal. It is proportional to the disorder strength and inversely proportional to the energy gap, hence z becomes infinite at the critical point where the energy gap vanishes

Hysteretic behavior of spin-crossover noise driven system

Energy Technology Data Exchange (ETDEWEB)

Gudyma, Iurii [Department of General Physics, Chernivtsi National University, Chernivtsi 58012 (Ukraine); Maksymov, Artur, E-mail: maxyartur@gmail.com [Department of General Physics, Chernivtsi National University, Chernivtsi 58012 (Ukraine); Advanced Materials Research Institute, University of New Orleans, LA 70148 (United States); Dimian, Mihai [Department of Electrical and Computer Engineering, Howard University, Washington DC, 20059 (United States); Faculty of Electrical Engineering and Computer Science, Stefan cel Mare University, Suceava 720229 (Romania)

2016-04-01

The influence of white Gaussian noise on hysteretic behavior of spin-crossover system is analyzed in the framework of stochastic Langevin dynamics. Various stochastic simulations are performed and several important properties of spin-transition in spin-crossover system driven by noise are reproduced. The numerical results are tested against the stationary probability function and the associated dynamic potential obtained from Fokker–Planck equation corresponding to spin-crossover Langevin dynamics. The dependence of light-induced optical hysteresis width and non-hysteretic transition curve slope on the noise intensity is illustrated. The role of low-spin and high-spin phase stabilities in the hysteretic behavior of noise-driven spin-crossover system is discussed.

Integrable motion of curves in self-consistent potentials: Relation to spin systems and soliton equations

Energy Technology Data Exchange (ETDEWEB)

Myrzakulov, R.; Mamyrbekova, G.K.; Nugmanova, G.N.; Yesmakhanova, K.R. [Eurasian International Center for Theoretical Physics and Department of General and Theoretical Physics, Eurasian National University, Astana 010008 (Kazakhstan); Lakshmanan, M., E-mail: lakshman@cnld.bdu.ac.in [Centre for Nonlinear Dynamics, School of Physics, Bharathidasan University, Tiruchirapalli 620 024 (India)

2014-06-13

Motion of curves and surfaces in R{sup 3} lead to nonlinear evolution equations which are often integrable. They are also intimately connected to the dynamics of spin chains in the continuum limit and integrable soliton systems through geometric and gauge symmetric connections/equivalence. Here we point out the fact that a more general situation in which the curves evolve in the presence of additional self-consistent vector potentials can lead to interesting generalized spin systems with self-consistent potentials or soliton equations with self-consistent potentials. We obtain the general form of the evolution equations of underlying curves and report specific examples of generalized spin chains and soliton equations. These include principal chiral model and various Myrzakulov spin equations in (1+1) dimensions and their geometrically equivalent generalized nonlinear Schrödinger (NLS) family of equations, including Hirota–Maxwell–Bloch equations, all in the presence of self-consistent potential fields. The associated gauge equivalent Lax pairs are also presented to confirm their integrability. - Highlights: • Geometry of continuum spin chain with self-consistent potentials explored. • Mapping on moving space curves in R{sup 3} in the presence of potential fields carried out. • Equivalent generalized nonlinear Schrödinger (NLS) family of equations identified. • Integrability of identified nonlinear systems proved by deducing appropriate Lax pairs.

Sudden transition and sudden change from open spin environments

International Nuclear Information System (INIS)

Hu, Zheng-Da; Xu, Jing-Bo; Yao, Dao-Xin

2014-01-01

We investigate the necessary conditions for the existence of sudden transition or sudden change phenomenon for appropriate initial states under dephasing. As illustrative examples, we study the behaviors of quantum correlation dynamics of two noninteracting qubits in independent and common open spin environments, respectively. For the independent environments case, we find that the quantum correlation dynamics is closely related to the Loschmidt echo and the dynamics exhibits a sudden transition from classical to quantum correlation decay. It is also shown that the sudden change phenomenon may occur for the common environment case and stationary quantum discord is found at the high temperature region of the environment. Finally, we investigate the quantum criticality of the open spin environment by exploring the probability distribution of the Loschmidt echo and the scaling transformation behavior of quantum discord, respectively. - Highlights: • Sudden transition or sudden change from open spin baths are studied. • Quantum discord is related to the Loschmidt echo in independent open spin baths. • Steady quantum discord is found in a common open spin bath. • The probability distribution of the Loschmidt echo is analyzed. • The scaling transformation behavior of quantum discord is displayed

Quantum spin-glass transition in the two-dimensional electron gas

Indian Academy of Sciences (India)

Home; Journals; Pramana – Journal of Physics; Volume 58; Issue 2 ... Spin glasses; quantum phase transition; ferromagnetism; electron gas. ... We argue that a quantum transition involving the destruction of the spin-glass order in an applied in-plane magnetic field offers a natural explanation of some features of recent ...

The shape of the melting curve and phase transitions in the liquid state

International Nuclear Information System (INIS)

Yahel, Eyal

2014-01-01

The phase diagram of elemental liquids has been found to be surprisingly rich, including variations in the melting curve and transitions in the liquid phase. The effect of these transitions on the shape of the melting curve is reviewed and analyzed. First-order phase transitions intersecting the melting curve imply piecewise continuous melting curves, with solid-solid transitions generating upward kinks or minima and liquid-liquid transitions generating downward kinks or maxima

Spin-reorientation magnetic transitions in Mn-doped SmFeO3

Directory of Open Access Journals (Sweden)

Jian Kang

2017-09-01

Full Text Available Spin reorientation is a magnetic phase transition in which rotation of the magnetization vector with respect to the crystallographic axes occurs upon a change in the temperature or magnetic field. For example, SmFeO3 shows a magnetization rotation from the c axis above 480 K to the a axis below 450 K, known as the Γ4 → Γ2 transition. This work reports the successful synthesis of the new single-crystal perovskite SmFe0.75Mn0.25O3 and finds interesting spin reorientations above and below room temperature. In addition to the spin reorientation of the Γ4 → Γ2 magnetic phase transition observed at around TSR2 = 382 K, a new spin reorientation, Γ2 → Γ1, was seen at around TSR1 = 212 K due to Mn doping, which could not be observed in the parent rare earth perovskite compound. This unexpected spin configuration has complete antiferromagnetic order without any canting-induced weak ferromagnetic moment, resulting in zero magnetization in the low-temperature regime. M–T and M–H measurements have been made to study the temperature and magnetic-field dependence of the observed spin reorientation transitions.

Spin Properties of Transition-Metallorganic Self-Assembled Molecules

International Nuclear Information System (INIS)

Yu, Zhi Gang

2010-01-01

This report summarizes SRI's accomplishments on the project, 'Spin Properties of Transition-Metallorganic Self-Assembled Molecules' funded by the Office of Basic Energy Sciences, US Department of Energy. We have successfully carried out all tasks identified in our proposal and gained significant knowledge and understanding of spin-polarized electronic structure, spin relaxation, and spin-dependent transport in transition-metallorganic molecules and enhohedral fullerenes. These molecules contain integrated spin and charge components and will enable us to achieve sophisticated functions in spintronics and quantum computing at molecular level with simple circuitry and easy fabrication. We have developed microscopic theories that describe the underlying mechanisms of spin-dependent porcesses and constructed quantitative modeling tools that compute several important spin properties. These results represent the basic principles governing the spin-dependent behaviors in nanostructures containing such molecules. Based on these results we have shown that novel device functions, such as electrically controlled g-factor and noninvasive electrical detection of spin dynamics, can be achieved in these nanostructures. Some of our results have been published in peer-reviewed journals and presented at professional conferences. In addition, we have established a close collaboration with experimentalists at Oxford University, UK (Dr. J. Morton and Prof. G. Briggs), Princeton University (Dr. A. Tyryshkin and Prof. S. Lyon), University of Delaware (Prof. E. Nowak), and University of California (Profs. R. Kawakami and J. Shi), who have been studying related systems and supplying us with new experimental data. We have provided our understanding and physical insights to the experimentalists and helped analyze their experimental measurements. The collaboration with experimentalists has also broadened our research scope and helped us focus on the most relevant issues concerning these

Spin-flip transitions between Zeeman sublevels in semiconductor quantum dots

International Nuclear Information System (INIS)

Khaetskii, Alexander V.; Nazarov, Yuli V.

2001-01-01

We have studied spin-flip transitions between Zeeman sublevels in GaAs electron quantum dots. Several different mechanisms which originate from spin-orbit coupling are shown to be responsible for such processes. It is shown that spin-lattice relaxation for the electron localized in a quantum dot is much less effective than for the free electron. The spin-flip rates due to several other mechanisms not related to the spin-orbit interaction are also estimated

Spin Properties of Transition-Metallorganic Self-Assembled Molecules

Energy Technology Data Exchange (ETDEWEB)

Zhi Gang Yu

2010-06-30

This report summarizes SRI's accomplishments on the project, 'Spin Properties of Transition-Metallorganic Self-Assembled Molecules' funded by the Office of Basic Energy Sciences, US Department of Energy. We have successfully carried out all tasks identified in our proposal and gained significant knowledge and understanding of spin-polarized electronic structure, spin relaxation, and spin-dependent transport in transition-metallorganic molecules and enhohedral fullerenes. These molecules contain integrated spin and charge components and will enable us to achieve sophisticated functions in spintronics and quantum computing at molecular level with simple circuitry and easy fabrication. We have developed microscopic theories that describe the underlying mechanisms of spin-dependent porcesses and constructed quantitative modeling tools that compute several important spin properties. These results represent the basic principles governing the spin-dependent behaviors in nanostructures containing such molecules. Based on these results we have shown that novel device functions, such as electrically controlled g-factor and noninvasive electrical detection of spin dynamics, can be achieved in these nanostructures. Some of our results have been published in peer-reviewed journals and presented at professional conferences. In addition, we have established a close collaboration with experimentalists at Oxford University, UK (Dr. J. Morton and Prof. G. Briggs), Princeton University (Dr. A. Tyryshkin and Prof. S. Lyon), University of Delaware (Prof. E. Nowak), and University of California (Profs. R. Kawakami and J. Shi), who have been studying related systems and supplying us with new experimental data. We have provided our understanding and physical insights to the experimentalists and helped analyze their experimental measurements. The collaboration with experimentalists has also broadened our research scope and helped us focus on the most relevant issues

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

Science.gov (United States)

Chakrabarti, Bismayan; Birol, Turan; Haule, Kristjan

2017-11-01

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

Spin-orbit-induced spin splittings in polar transition metal dichalcogenide monolayers

KAUST Repository

Cheng, Yingchun

2013-06-01

The Rashba effect in quasi two-dimensional materials, such as noble metal surfaces and semiconductor heterostructures, has been investigated extensively, while interest in real two-dimensional systems has just emerged with the discovery of graphene. We present ab initio electronic structure, phonon, and molecular-dynamics calculations to study the structural stability and spin-orbit-induced spin splitting in the transition metal dichalcogenide monolayers MXY (M = Mo, W and X, Y = S, Se, Te). In contrast to the non-polar systems with X = Y, in the polar systems with X ≠ Y the Rashba splitting at the Γ-point for the uppermost valence band is caused by the broken mirror symmetry. An enhancement of the splitting can be achieved by increasing the spin-orbit coupling and/or the potential gradient. © Copyright EPLA, 2013.

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

Science.gov (United States)

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

2017-10-01

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

Quantum Phase Transition in a Cold Atomic Spin-Boson Mixture

Science.gov (United States)

Orth, Peter P.; Stanic, Ivan; Le Hur, Karyn

2008-03-01

We theoretically implement a spin array in a tunable bosonic environment using cold bosonic atoms with two (hyperfine) ground states, trapped by different potentials [1]. The first specie lies in a deep optical lattice with tightly confining wells and forms a spin array; spin-up/down corresponds to occupation by one/no atom at each site. The second specie forms a superfluid reservoir. Different species are coupled coherently via laser transitions and collisions. Whereas the laser coupling mimics a transverse field for the spins, the coupling to the reservoir phonons (sound modes) induces a ferromagnetic (Ising) coupling as well as dissipation. This results in a peculiar ferro-paramagnetic quantum phase transition where the effect of dissipation can be studied in a controllable manner. [1] Peter P. Orth, Ivan Stanic, and Karyn Le Hur, arXiv:0711.2309 [cond-mat.other].

Driven spin transitions in fluorinated single- and bilayer-graphene quantum dots

Science.gov (United States)

Żebrowski, D. P.; Peeters, F. M.; Szafran, B.

2017-06-01

Spin transitions driven by a periodically varying electric potential in dilute fluorinated graphene quantum dots are investigated. Flakes of monolayer graphene as well as electrostatic electron traps induced in bilayer graphene are considered. The stationary states obtained within the tight-binding approach are used as the basis for description of the system dynamics. The dilute fluorination of the top layer lifts the valley degeneracy of the confined states and attenuates the orbital magnetic dipole moments due to current circulation within the flake. The spin-orbit coupling introduced by the surface deformation of the top layer induced by the adatoms allows the spin flips to be driven by the AC electric field. For the bilayer quantum dots the spin flip times is substantially shorter than the spin relaxation. Dynamical effects including many-photon and multilevel transitions are also discussed.

Testing Environmental Kuznets Curve in the Selected Transition Economies with Panel Smooth Transition Regression Analysis

Directory of Open Access Journals (Sweden)

Mahmut Zortuk

2016-08-01

Full Text Available The Environmental Kuznets Curve (EKC introduces an inverted U-shaped relationship between environmental pollution and economic development. The inverted U-shaped curve is seen as complete pattern for developed economies. However, our study tests the EKC for developing transition economies of European Union, therefore, our results could make a significant contribution to the literature. In this paper, the relationship between carbon dioxide (CO2 emissions, gross domestic product (GDP, energy use and urban population is investigated in the Transition Economies (Bulgaria, Croatia, Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Romania, Slovakia and Slovenia. Environmental Kuznets Curve is tested by panel smooth transition regression for these economies for 1993 – 2010 periods. As a result of study, the null hypothesis of linearity was rejected and no-remaining nonlinearity test showed that there is a smooth transition exists between two regimes (below $5176 GDP per capita is first one and above $5176 GDP per capita is second one in the related period for these economies.

Hydrostatic-pressure and uniaxial-strain experiments for controlling the spin-Peierls transition

International Nuclear Information System (INIS)

Mito, Masaki; Deguchi, Hiroyuki; Fujita, Wataru; Kondo, Ryusuke; Kagoshima, Seiichi

2010-01-01

The spin-Peierls (SP) system is considered to be a quantum spin system strongly coupled with the lattice. We have succeeded in controlling SP transition by applying hydrostatic pressure and/or uniaxial strain. The observed phenomenon could be a typical example for understanding the SP transition based on the Hamiltonian. (author)

Spin glass transition in the rhombohedral LiNi1/3Mn1/3Co1/3O2

International Nuclear Information System (INIS)

Bie, Xiaofei; Yang, Xu; Han, Bing; Chen, Nan; Liu, Lina; Wei, Yingjin; Wang, Chunzhong; Chen, Hong; Du, Fei; Chen, Gang

2013-01-01

Highlights: •The Rietveld analysis of XRD data reveals a single phase with rhombohedral structure. •Dc susceptibility data suggest a spin glass behavior at low T in the 333 compound. •The ac susceptibility measurements have been observed in the typical SG system. •Three models have been employed to study the behavior of the spin glass state. •Both geometrical frustration and disorder play important role in the formation of SG. -- Abstract: Layered LiNi 1/3 Mn 1/3 Co 1/3 O 2 has been synthesized by co-precipitation method, and the magnetic properties were comprehensively studied by dc and ac susceptibilities. The dc magnetization curves show the irreversibility and spin freezing behavior at 109 K and 9 K. The evolution of real and imaginary part of ac susceptibility under different frequencies indicates a spin glass transition at low temperature. Three models (the Néel–Arrhenius law, the Vogel–Fulcher law, and the power law) have been employed to study the relaxation behavior of the spin glass state. Both frustration and disorder play important role in the formation of spin glass

Electron spin relaxation in a transition-metal dichalcogenide quantum dot

Science.gov (United States)

Pearce, Alexander J.; Burkard, Guido

2017-06-01

We study the relaxation of a single electron spin in a circular quantum dot in a transition-metal dichalcogenide monolayer defined by electrostatic gating. Transition-metal dichalcogenides provide an interesting and promising arena for quantum dot nano-structures due to the combination of a band gap, spin-valley physics and strong spin-orbit coupling. First we will discuss which bound state solutions in different B-field regimes can be used as the basis for qubits states. We find that at low B-fields combined spin-valley Kramers qubits to be suitable, while at large magnetic fields pure spin or valley qubits can be envisioned. Then we present a discussion of the relaxation of a single electron spin mediated by electron-phonon interaction via various different relaxation channels. In the low B-field regime we consider the spin-valley Kramers qubits and include impurity mediated valley mixing which will arise in disordered quantum dots. Rashba spin-orbit admixture mechanisms allow for relaxation by in-plane phonons either via the deformation potential or by piezoelectric coupling, additionally direct spin-phonon mechanisms involving out-of-plane phonons give rise to relaxation. We find that the relaxation rates scale as \\propto B 6 for both in-plane phonons coupling via deformation potential and the piezoelectric effect, while relaxation due to the direct spin-phonon coupling scales independant to B-field to lowest order but depends strongly on device mechanical tension. We will also discuss the relaxation mechanisms for pure spin or valley qubits formed in the large B-field regime.

Ab initio study of the RbSr electronic structure: Potential energy curves, transition dipole moments, and permanent electric dipole moments

Energy Technology Data Exchange (ETDEWEB)

Pototschnig, Johann V., E-mail: johann.pototschnig@tugraz.at; Krois, Günter; Lackner, Florian; Ernst, Wolfgang E., E-mail: wolfgang.ernst@tugraz.at [Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz (Austria)

2014-12-21

Excited states and the ground state of the diatomic molecule RbSr were calculated by post Hartree-Fock molecular orbital theory up to 22 000 cm{sup −1}. We applied a multireference configuration interaction calculation based on multiconfigurational self-consistent field wave functions. Both methods made use of effective core potentials and core polarization potentials. Potential energy curves, transition dipole moments, and permanent electric dipole moments were determined for RbSr and could be compared with other recent calculations. We found a good agreement with experimental spectra, which have been obtained recently by helium nanodroplet isolation spectroscopy. For the lowest two asymptotes (Rb (5s {sup 2}S) + Sr (5s4d {sup 3}P°) and Rb (5p {sup 2}P°) + Sr (5s{sup 2} {sup 1}S)), which exhibit a significant spin-orbit coupling, we included relativistic effects by two approaches, one applying the Breit-Pauli Hamiltonian to the multireference configuration interaction wave functions, the other combining a spin-orbit Hamiltonian and multireference configuration interaction potential energy curves. Using the results for the relativistic potential energy curves that correspond to the Rb (5s {sup 2}S) + Sr (5s4d {sup 3}P°) asymptote, we have simulated dispersed fluorescence spectra as they were recently measured in our lab. The comparison with experimental data allows to benchmark both methods and demonstrate that spin-orbit coupling has to be included for the lowest states of RbSr.

Ab initio study of the RbSr electronic structure: potential energy curves, transition dipole moments, and permanent electric dipole moments.

Science.gov (United States)

Pototschnig, Johann V; Krois, Günter; Lackner, Florian; Ernst, Wolfgang E

2014-12-21

Excited states and the ground state of the diatomic molecule RbSr were calculated by post Hartree-Fock molecular orbital theory up to 22 000 cm(-1). We applied a multireference configuration interaction calculation based on multiconfigurational self-consistent field wave functions. Both methods made use of effective core potentials and core polarization potentials. Potential energy curves, transition dipole moments, and permanent electric dipole moments were determined for RbSr and could be compared with other recent calculations. We found a good agreement with experimental spectra, which have been obtained recently by helium nanodroplet isolation spectroscopy. For the lowest two asymptotes (Rb (5s (2)S) + Sr (5s4d (3)P°) and Rb (5p (2)P°) + Sr (5s(2) (1)S)), which exhibit a significant spin-orbit coupling, we included relativistic effects by two approaches, one applying the Breit-Pauli Hamiltonian to the multireference configuration interaction wave functions, the other combining a spin-orbit Hamiltonian and multireference configuration interaction potential energy curves. Using the results for the relativistic potential energy curves that correspond to the Rb (5s (2)S) + Sr (5s4d (3)P°) asymptote, we have simulated dispersed fluorescence spectra as they were recently measured in our lab. The comparison with experimental data allows to benchmark both methods and demonstrate that spin-orbit coupling has to be included for the lowest states of RbSr.

Influence of longitudinal spin fluctuations on the phase transition features in chiral magnets

Science.gov (United States)

Belemuk, A. M.; Stishov, S. M.

2018-04-01

Using the classical Monte Carlo calculations, we investigate the effects of longitudinal spin fluctuations on the helimagnetic transition in a Heisenberg magnet with the Dzyaloshinskii-Moriya interaction. We use variable spin amplitudes in the framework of the spin-lattice Hamiltonian. It is this kind of fluctuations that naturally occur in an itinerant system. We show that the basic features of the helical phase transition are not changed much by the longitudinal spin fluctuations though the transition temperature Tc and the fluctuation hump seen in specific heat at T >Tc is significantly affected. We report thermodynamic and structural effects of these fluctuations. By increasing the system size in the Monte Carlo modeling, we are able to reproduce the ring shape scattering intensity above the helimagnetic transition temperature Tc, which transforms into the spiral spots seen below Tc in the neutron scattering experiments.

High temperature spin-glass-like transition in La0.67Sr0.33MnO3 nanofibers near the Curie point.

Science.gov (United States)

Lu, Ruie; Yang, Sen; Li, Yitong; Chen, Kaiyun; Jiang, Yun; Fu, Bi; Zhang, Yin; Zhou, Chao; Xu, Minwei; Zhou, Xuan

2017-06-28

The glassy transition of superparamagnetic (SPM) (r glass-like (SGL) behavior near the Curie point (T C ), i.e., T 0 = 330 K, in La 0.67 Sr 0.33 MnO 3 (LSMO) nanofibers (NFs) composed of nanoparticles beyond the SPM size (r ≫ r 0 ), resulting in a significant increase of the glass transition temperature. This SGL transition near the T C of bulk LSMO can be explained to be the scenario of locally ordered clusters embedded in a disordered host, in which the assembly of nanoparticles has a magnetic core-shell model driven by surface spin glass. The presence of a surface spin glass of nanoparticles was proved by the Almeida-Thouless line δT f ∝ H 2/3 , exchange bias, and reduced saturation magnetization of the NF system. Composite dynamics were found - that is, both the SPM and the super-spin-glass (SSG) behavior are found in such an NF system. The bifurcation of the zero-field-cooled (ZFC) and field-cooled (FC) magnetization vs. temperature curves at the ZFC peak, and the flatness of FC magnetization involve SSG, while the frequency-dependent ac susceptibility anomaly follows the Vogel-Fulcher law that implies weak dipole interactions of the SPM model. This finding can help us to find a way to search for high temperature spin glass materials.

Chiral-glass transition and replica symmetry breaking of a three-dimensional Heisenberg spin glass

OpenAIRE

Hukushima, K.; Kawamura, H.

2000-01-01

Extensive equilibrium Monte Carlo simulations are performed for a three-dimensional Heisenberg spin glass with the nearest-neighbor Gaussian coupling to investigate its spin-glass and chiral-glass orderings. The occurrence of a finite-temperature chiral-glass transition without the conventional spin-glass order is established. Critical exponents characterizing the transition are different from those of the standard Ising spin glass. The calculated overlap distribution suggests the appearance ...

Spherical 2+p spin-glass model: An exactly solvable model for glass to spin-glass transition

International Nuclear Information System (INIS)

Crisanti, A.; Leuzzi, L.

2004-01-01

We present the full phase diagram of the spherical 2+p spin-glass model with p≥4. The main outcome is the presence of a phase with both properties of full replica symmetry breaking phases of discrete models, e.g., the Sherrington-Kirkpatrick model, and those of one replica symmetry breaking. This phase has a finite complexity which leads to different dynamic and static properties. The phase diagram is rich enough to allow the study of different kinds of glass to spin glass and spin glass to spin glass phase transitions

Spin-flip transition of L10-type MnPt alloy single crystal studied by neutron scattering

International Nuclear Information System (INIS)

Hama, Hiroaki; Motomura, Ryo; Shinozaki, Tatsuya; Tsunoda, Yorihiko

2007-01-01

Magnetic structure, tetragonality, and the spin-flip transition for an L1 0 -type MnPt ordered alloy were studied by neutron scattering using a single-crystal specimen. Tetragonality of the lattice showed strong correlation with the spin-flip transition. Although the spin-flip transition looks like a gradual change of the easy axis in the temperature range between 580 and 770 K, two modes of magnon-gap peaks with different energies were observed in this transition temperature range. Thus, the crystal consists of two regions with different anisotropy energies and the volume fractions of these regions with different spin directions change gradually with temperature. The tetragonality and spin-flip transition are discussed using the hard-sphere model for atomic radii of Pt and Mn. The Invar effect of Mn atoms is proposed using high- and low-spin transitions of Mn moments in analogy with the two-γ model of Fe moments in FeNi Invar alloy

High-frequency EPR on high-spin transition-metal sites

NARCIS (Netherlands)

Mathies, Guinevere

2012-01-01

The electronic structure of transition-metal sites can be probed by electron-paramagnetic-resonance (EPR) spectroscopy. The study of high-spin transition-metal sites benefits from EPR spectroscopy at frequencies higher than the standard 9.5 GHz. However, high-frequency EPR is a developing field. In

Topological phase transition in anisotropic square-octagon lattice with spin-orbit coupling and exchange field

Science.gov (United States)

Yang, Yuan; Yang, Jian; Li, Xiaobing; Zhao, Yue

2018-03-01

We investigate the topological phase transitions in an anisotropic square-octagon lattice in the presence of spin-orbit coupling and exchange field. On the basis of the Chern number and spin Chern number, we find a number of topologically distinct phases with tuning the exchange field, including time-reversal-symmetry-broken quantum spin Hall phases, quantum anomalous Hall phases and a topologically trivial phase. Particularly, we observe a coexistent state of both the quantum spin Hall effect and quantum anomalous Hall effect. Besides, by adjusting the exchange filed, we find the phase transition from time-reversal-symmetry-broken quantum spin Hall phase to spin-imbalanced and spin-polarized quantum anomalous Hall phases, providing an opportunity for quantum spin manipulation. The bulk band gap closes when topological phase transitions occur between different topological phases. Furthermore, the energy and spin spectra of the edge states corresponding to different topological phases are consistent with the topological characterization based on the Chern and spin Chern numbers.

Dissipation-driven quantum phase transitions in collective spin systems

International Nuclear Information System (INIS)

Morrison, S; Parkins, A S

2008-01-01

We consider two different collective spin systems subjected to strong dissipation-on the same scale as interaction strengths and external fields-and show that either continuous or discontinuous dissipative quantum phase transitions can occur as the dissipation strength is varied. First, we consider a well-known model of cooperative resonance fluorescence that can exhibit a second-order quantum phase transition, and analyse the entanglement properties near the critical point. Next, we examine a dissipative version of the Lipkin-Meshkov-Glick interacting collective spin model, where we find that either first- or second-order quantum phase transitions can occur, depending only on the ratio of the interaction and external field parameters. We give detailed results and interpretation for the steady-state entanglement in the vicinity of the critical point, where it reaches a maximum. For the first-order transition we find that the semiclassical steady states exhibit a region of bistability. (fast track communication)

Spin-Driven Emergent Antiferromagnetism and Metal-Insulator Transition in Nanoscale p-Si

Science.gov (United States)

Lou, Paul C.; Kumar, Sandeep

2018-04-01

The entanglement of the charge, spin and orbital degrees of freedom can give rise to emergent behavior especially in thin films, surfaces and interfaces. Often, materials that exhibit those properties require large spin orbit coupling. We hypothesize that the emergent behavior can also occur due to spin, electron and phonon interactions in widely studied simple materials such as Si. That is, large intrinsic spin-orbit coupling is not an essential requirement for emergent behavior. The central hypothesis is that when one of the specimen dimensions is of the same order (or smaller) as the spin diffusion length, then non-equilibrium spin accumulation due to spin injection or spin-Hall effect (SHE) will lead to emergent phase transformations in the non-ferromagnetic semiconductors. In this experimental work, we report spin mediated emergent antiferromagnetism and metal insulator transition in a Pd (1 nm)/Ni81Fe19 (25 nm)/MgO (1 nm)/p-Si (~400 nm) thin film specimen. The spin-Hall effect in p-Si, observed through Rashba spin-orbit coupling mediated spin-Hall magnetoresistance behavior, is proposed to cause the spin accumulation and resulting emergent behavior. The phase transition is discovered from the diverging behavior in longitudinal third harmonic voltage, which is related to the thermal conductivity and heat capacity.

A new high-pressure phase of Fe2SiO4 and the relationship between spin and structural transitions

Science.gov (United States)

Yamanaka, T.; Kyono, A.; Nakamoto, Y.; Kharlamova, S. A.; Struzhkin, V. V.; Gramsch, S.; Mao, H.; Hemley, R. J.

2013-12-01

Structure transformation of Fe2SiO4 Angle-dispersive powder x-ray diffraction was carried out at beam line 16-BMD APS. Structure of a new high-pressure phase of I-Fe2SiO4 spinel was determined by Rietveld profile fitting of x-ray diffraction data up to 64GPa at ambient temperature. A structural transition from the cubic spinel to the new structure was observed at 34GPa. Diffraction patterns taken at 44.6GPa and 54.6GPa indicate a two-phase mixture of spinel and new high-pressure phase. Reversible transition from I-Fe2SiO4 to spinel was confirmed. Laser heating experiment at 1500K proved the decomposition of Fe2SiO4 spinel to two oxides of FeO and SiO2. Spin transition X-ray emission measurements of Fe2SiO4 were carried out up to 65GPa at ambient temperature at beam line 16-IDD APS. The spin transition exerts an influence to Fe2SiO4 spinel structure and triggers two distinct curves of the lattice constant in the spinel phase. Although the compression curve of the spinel is discontinuous at approximately 20 GPa, Fe Kβ emission measurements show that the transition from a high spin (HS) to an intermediate spin (IS) state begins at 17GPa in the spinel phase. The IS electronic state is gradually enhanced with pressure, which results in an isostructural phase transition. HS-to-LS transition of iron bearing spinels starts from 15.6GPa in Fe3O4 and 19.6GPa in Fe2TiO4. The transition is more capable due to Fe2+ in the octahedral site. The extremely shortened octahedral bonds result in a distortion of 6-fold cation site. New structure of Fe2SiO4 Monte Carlo method was applied to find candidates for the high-pressure phase using the diffraction intensities with fixed lattice constants determined by DICVOL. Rietveld profile fitting was then performed using the initial model. The new structure is a body centered orthorhombic phase (I-Fe2SiO4) with space group Imma and Z=4, with two crystallographically distinct FeO6 octahedra. Silicon exists in six-fold coordination in I-Fe2Si

Control of entanglement transitions in quantum spin clusters

Science.gov (United States)

Irons, Hannah R.; Quintanilla, Jorge; Perring, Toby G.; Amico, Luigi; Aeppli, Gabriel

2017-12-01

Quantum spin clusters provide a platform for the experimental study of many-body entanglement. Here we address a simple model of a single-molecule nanomagnet featuring N interacting spins in a transverse field. The field can control an entanglement transition (ET). We calculate the magnetization, low-energy gap, and neutron-scattering cross section and find that the ET has distinct signatures, detectable at temperatures as high as 5% of the interaction strength. The signatures are stronger for smaller clusters.

Photo-modulation of the spin Hall conductivity of mono-layer transition metal dichalcogenides

Energy Technology Data Exchange (ETDEWEB)

Sengupta, Parijat; Bellotti, Enrico [Department of Electrical and Computer Engineering, Boston University, Boston, MA 02215 (United States)

2016-05-23

We report on a possible optical tuning of the spin Hall conductivity in mono-layer transition metal dichalcogenides. Light beams of frequencies much higher than the energy scale of the system (the off-resonant condition) do not excite electrons but rearrange the band structure. The rearrangement is quantitatively established using the Floquet formalism. For such a system of mono-layer transition metal dichalcogenides, the spin Hall conductivity (calculated with the Kubo expression in presence of disorder) exhibits a drop at higher frequencies and lower intensities. Finally, we compare the spin Hall conductivity of the higher spin-orbit coupled WSe{sub 2} to MoS{sub 2}; the spin Hall conductivity of WSe{sub 2} was found to be larger.

Large magnetoresistance dips and perfect spin-valley filter induced by topological phase transitions in silicene

Science.gov (United States)

Prarokijjak, Worasak; Soodchomshom, Bumned

2018-04-01

Spin-valley transport and magnetoresistance are investigated in silicene-based N/TB/N/TB/N junction where N and TB are normal silicene and topological barriers. The topological phase transitions in TB's are controlled by electric, exchange fields and circularly polarized light. As a result, we find that by applying electric and exchange fields, four groups of spin-valley currents are perfectly filtered, directly induced by topological phase transitions. Control of currents, carried by single, double and triple channels of spin-valley electrons in silicene junction, may be achievable by adjusting magnitudes of electric, exchange fields and circularly polarized light. We may identify that the key factor behind the spin-valley current filtered at the transition points may be due to zero and non-zero Chern numbers. Electrons that are allowed to transport at the transition points must obey zero-Chern number which is equivalent to zero mass and zero-Berry's curvature, while electrons with non-zero Chern number are perfectly suppressed. Very large magnetoresistance dips are found directly induced by topological phase transition points. Our study also discusses the effect of spin-valley dependent Hall conductivity at the transition points on ballistic transport and reveals the potential of silicene as a topological material for spin-valleytronics.

Effective coupling constants for spin-flip and non spin-flip E1 transitions in A--90 nuclei

International Nuclear Information System (INIS)

Nakayama, Shintaro; Shibata, Tokushi; Kishimoto, Tadafumi; Sasao, Mamiko; Ejiri, Hiroyasu

1983-01-01

Radiative proton capture reactions through two isobaric analogue resonances (IAR) in 89 Y were studied, one was the 12.07 MeV 2dsub(5/2) state lying just above the neutron threshold energy Bsub(n) and another was the 14.48 MeV 2dsub(3/2) state lying well above Bsub(n). E1 transitions from these IAR's were studied for favoured cases with no spin-flip and no change of radial nodes, and for unfavoured cases spin-flip and/or change of radial nodes. At the 2dsub(3/2) IAR lying well above Bsub(n), the favoured transitions show the resonance feature, but the unfavoured ones not. At the 2dsub(5/2) IAR near Bsub(n), however, both the favoured and unfavoured transitions show the resonance feature. Anormalous resonant feature of the unfavoured transitions is interpreted mainly due to the compound process. Favoured transitions are all found to be reduced by factors -- 0.3 over the shell model values. (author)

Control of the Speed of a Light-Induced Spin Transition through Mesoscale Core-Shell Architecture.

Science.gov (United States)

Felts, Ashley C; Slimani, Ahmed; Cain, John M; Andrus, Matthew J; Ahir, Akhil R; Abboud, Khalil A; Meisel, Mark W; Boukheddaden, Kamel; Talham, Daniel R

2018-05-02

The rate of the light-induced spin transition in a coordination polymer network solid dramatically increases when included as the core in mesoscale core-shell particles. A series of photomagnetic coordination polymer core-shell heterostructures, based on the light-switchable Rb a Co b [Fe(CN) 6 ] c · mH 2 O (RbCoFe-PBA) as core with the isostructural K j Ni k [Cr(CN) 6 ] l · nH 2 O (KNiCr-PBA) as shell, are studied using temperature-dependent powder X-ray diffraction and SQUID magnetometry. The core RbCoFe-PBA exhibits a charge transfer-induced spin transition (CTIST), which can be thermally and optically induced. When coupled to the shell, the rate of the optically induced transition from low spin to high spin increases. Isothermal relaxation from the optically induced high spin state of the core back to the low spin state and activation energies associated with the transition between these states were measured. The presence of a shell decreases the activation energy, which is associated with the elastic properties of the core. Numerical simulations using an electro-elastic model for the spin transition in core-shell particles supports the findings, demonstrating how coupling of the core to the shell changes the elastic properties of the system. The ability to tune the rate of optically induced magnetic and structural phase transitions through control of mesoscale architecture presents a new approach to the development of photoswitchable materials with tailored properties.

Quantum spin/valley Hall effect and topological insulator phase transitions in silicene

KAUST Repository

Tahir, M.

2013-04-26

We present a theoretical realization of quantum spin and quantum valley Hall effects in silicene. We show that combination of an electric field and intrinsic spin-orbit interaction leads to quantum phase transitions at the charge neutrality point. This phase transition from a two dimensional topological insulator to a trivial insulating state is accompanied by a quenching of the quantum spin Hall effect and the onset of a quantum valley Hall effect, providing a tool to experimentally tune the topological state of silicene. In contrast to graphene and other conventional topological insulators, the proposed effects in silicene are accessible to experiments.

Quantum spin/valley Hall effect and topological insulator phase transitions in silicene

KAUST Repository

Tahir, M.; Manchon, Aurelien; Sabeeh, K.; Schwingenschlö gl, Udo

2013-01-01

We present a theoretical realization of quantum spin and quantum valley Hall effects in silicene. We show that combination of an electric field and intrinsic spin-orbit interaction leads to quantum phase transitions at the charge neutrality point. This phase transition from a two dimensional topological insulator to a trivial insulating state is accompanied by a quenching of the quantum spin Hall effect and the onset of a quantum valley Hall effect, providing a tool to experimentally tune the topological state of silicene. In contrast to graphene and other conventional topological insulators, the proposed effects in silicene are accessible to experiments.

Unconventional transformation of spin Dirac phase across a topological quantum phase transition

Science.gov (United States)

Xu, Su-Yang; Neupane, Madhab; Belopolski, Ilya; Liu, Chang; Alidoust, Nasser; Bian, Guang; Jia, Shuang; Landolt, Gabriel; Slomski, Batosz; Dil, J. Hugo; Shibayev, Pavel P.; Basak, Susmita; Chang, Tay-Rong; Jeng, Horng-Tay; Cava, Robert J.; Lin, Hsin; Bansil, Arun; Hasan, M. Zahid

2015-01-01

The topology of a topological material can be encoded in its surface states. These surface states can only be removed by a bulk topological quantum phase transition into a trivial phase. Here we use photoemission spectroscopy to image the formation of protected surface states in a topological insulator as we chemically tune the system through a topological transition. Surprisingly, we discover an exotic spin-momentum locked, gapped surface state in the trivial phase that shares many important properties with the actual topological surface state in anticipation of the change of topology. Using a spin-resolved measurement, we show that apart from a surface bandgap these states develop spin textures similar to the topological surface states well before the transition. Our results offer a general paradigm for understanding how surface states in topological phases arise from a quantum phase transition and are suggestive for the future realization of Weyl arcs, condensed matter supersymmetry and other fascinating phenomena in the vicinity of a quantum criticality. PMID:25882717

Magnetization relaxation in spin glasses above transition point

International Nuclear Information System (INIS)

Zajtsev, I.A.; Minakov, A.A.; Galonzka, R.R.

1988-01-01

Magnetization relaxation of Cd 0.6 Zn 0.4 Cr 2 Se 4 and Cd 0.6 Mn 0.4 Te monocrystalline samples with T g =21 K and T g =12 K respectively and magnetic colloid is investigated. It is shown that magnetization inexponential relaxation detected experimentally in spin and dipole glasses is essentially higher than T g temperature transition. It is found that at temperatures higher than T g the essential difference is observed in behaviour of spin glasses with different Z and disorder types

Spin glass transition in canonical AuFe alloys: A numerical study

International Nuclear Information System (INIS)

Zhang, Kai-Cheng; Li, Yong-Feng; Liu, Gui-Bin; Zhu, Yan

2012-01-01

Although spin glass transitions have long been observed in diluted magnetic alloys, e.g. AuFe and CuMn alloys, previous numerical studies are not completely consistent with the experiment results. The abnormal critical exponents of the alloys remain still puzzling. By employing parallel tempering algorithm with finite-size scaling analysis, we investigated the phase transitions in canonical AuFe alloys. Our results strongly support that spin glass transitions occur at finite temperatures in the alloys. The calculated critical exponents agree well with those obtained from experiments. -- Highlights: ► By simulation we investigated the abnormal critical exponents observed in canonical SG alloys. ► The critical exponents obtained from our simulations agree well with those measured from experiments. ► Our results strongly support that RKKY interactions lead to SG transitions at finite temperatures.

Study of thermal spin crossover in [Fe(II)(isoxazole)(6)](BF4)(2) with Mossbauer spectroscopy

NARCIS (Netherlands)

Bhattacharjee, A.; van Koningsbruggen, P. J.; Hibbs, W.; Miller, Joel S.; Guetlich, P.

2007-01-01

Fe-57 Mossbauer spectroscopy of the mononuclear [Fe( II)( isoxazole)(6)]( BF4)(2) compound has been studied to reveal the thermal spin crossover of Fe( II) between low- spin ( S = 0) and high- spin ( S = 2) states. A temperature-dependent spin transition curve has been constructed with the least-

Electronic structure and quantum spin fluctuations at the magnetic phase transition in MnSi

Science.gov (United States)

Povzner, A. A.; Volkov, A. G.; Nogovitsyna, T. A.

2018-05-01

The effect of spin fluctuations on the heat capacity and homogeneous magnetic susceptibility of the chiral magnetic MnSi in the vicinity of magnetic transition has been investigated by using the free energy functional of the coupled electron and spin subsystems and taking into account the Dzyaloshinsky-Moriya interaction. For helical ferromagnetic ordering, we found that zero-point fluctuations of the spin density are large and comparable with fluctuations of the non-uniform magnetization. The amplitude of zero-point spin fluctuations shows a sharp decrease in the region of the magnetic phase transition. It is shown that sharp decrease of the amplitude of the quantum spin fluctuations results in the lambda-like maxima of the heat capacity and the homogeneous magnetic susceptibility. Above the temperature of the lambda anomaly, the spin correlation radius becomes less than the period of the helical structure and chiral fluctuations of the local magnetization appear. It is shown that formation of a "shoulder" on the temperature dependence of the heat capacity is due to disappearance of the local magnetization. Our finding allows to explain the experimentally observed features of the magnetic phase transition of MnSi as a result of the crossover of quantum and thermodynamic phase transitions.

Abnormal Elasticity of Single-Crystal Magnesiosiderite across the Spin Transition in Earth's Lower Mantle

Science.gov (United States)

Fu, Suyu; Yang, Jing; Lin, Jung-Fu

2017-01-01

Brillouin light scattering and impulsive stimulated light scattering have been used to determine the full elastic constants of magnesiosiderite [(Mg0.35Fe0.65)CO3 ] up to 70 GPa at room temperature in a diamond-anvil cell. Drastic softening in C11 , C33 , C12 , and C13 elastic moduli associated with the compressive stress component and stiffening in C44 and C14 moduli associated with the shear stress component are observed to occur within the spin transition between ˜42.4 and ˜46.5 GPa . Negative values of C12 and C13 are also observed within the spin transition region. The Born criteria constants for the crystal remain positive within the spin transition, indicating that the mixed-spin state remains mechanically stable. Significant auxeticity can be related to the electronic spin transition-induced elastic anomalies based on the analysis of Poisson's ratio. These elastic anomalies are explained using a thermoelastic model for the rhombohedral system. Finally, we conclude that mixed-spin state ferromagnesite, which is potentially a major deep-carbon carrier, is expected to exhibit abnormal elasticity, including a negative Poisson's ratio of -0.6 and drastically reduced VP by 10%, in Earth's midlower mantle.

Study on the effect of transition curve to the dynamic characteristics of high-temperature superconducting maglev

International Nuclear Information System (INIS)

Qian, Nan; Zheng, Botian; Gou, Yanfeng; Chen, Ping; Zheng, Jun; Deng, Zigang

2015-01-01

Highlights: • Vibration of a HTS maglev model on two guideways was studied. • Simulation about vibration of HTS maglev on two guideways is accomplished. • Transition curve can weaken vibration of HTS maglev effectively when it running through curves. • Dynamic characteristics of HTS maglev can be enhanced with transition curve. - Abstract: High temperature superconducting (HTS) maglev technology is becoming more and more mature, and many key technologies have been deeply studied. However, the transition curve plays a key role in HTS maglev system, and related studies have not been carried out. In this paper series of simulations were conducted to test the lateral and vertical vibration of HTS maglev when passing through curves. Two magnetic guideways, of which one has transition curves but the other does not, are designed to test the vibration characteristics of a mini HTS maglev model running though curves. Results show that after adding transition curves between straight line and circular curve the vibration of HTS maglev model in lateral and vertical directions are all weakened in different degrees. It proves that adding transition curve into HTS maglev system is favorable and necessary.

Study on the effect of transition curve to the dynamic characteristics of high-temperature superconducting maglev

Energy Technology Data Exchange (ETDEWEB)

Qian, Nan [Applied Superconductivity Laboratory, State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031, P R China (China); Zheng, Botian [Applied Superconductivity Laboratory, State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031, P R China (China); School of Electrical Engineering, Southwest Jiaotong University, Chengdu 610031, P R China (China); Gou, Yanfeng [Applied Superconductivity Laboratory, State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031, P R China (China); Chen, Ping [Applied Superconductivity Laboratory, State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031, P R China (China); School of Electrical Engineering, Southwest Jiaotong University, Chengdu 610031, P R China (China); Zheng, Jun [Applied Superconductivity Laboratory, State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031, P R China (China); Deng, Zigang, E-mail: deng@swjtu.cn [Applied Superconductivity Laboratory, State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031, P R China (China)

2015-12-15

Highlights: • Vibration of a HTS maglev model on two guideways was studied. • Simulation about vibration of HTS maglev on two guideways is accomplished. • Transition curve can weaken vibration of HTS maglev effectively when it running through curves. • Dynamic characteristics of HTS maglev can be enhanced with transition curve. - Abstract: High temperature superconducting (HTS) maglev technology is becoming more and more mature, and many key technologies have been deeply studied. However, the transition curve plays a key role in HTS maglev system, and related studies have not been carried out. In this paper series of simulations were conducted to test the lateral and vertical vibration of HTS maglev when passing through curves. Two magnetic guideways, of which one has transition curves but the other does not, are designed to test the vibration characteristics of a mini HTS maglev model running though curves. Results show that after adding transition curves between straight line and circular curve the vibration of HTS maglev model in lateral and vertical directions are all weakened in different degrees. It proves that adding transition curve into HTS maglev system is favorable and necessary.

Evidence for a pressure-induced spin transition in olivine-type LiFePO4 triphylite

Science.gov (United States)

Núñez Valdez, Maribel; Efthimiopoulos, Ilias; Taran, Michail; Müller, Jan; Bykova, Elena; McCammon, Catherine; Koch-Müller, Monika; Wilke, Max

2018-05-01

We present a combination of first-principles and experimental results regarding the structural and magnetic properties of olivine-type LiFePO4 under pressure. Our investigations indicate that the starting P b n m phase of LiFePO4 persists up to 70 GPa. Further compression leads to an isostructural transition in the pressure range of 70-75 GPa, inconsistent with a former theoretical study. Considering our first-principles prediction for a high-spin to low-spin transition of Fe2 + close to 72 GPa, we attribute the experimentally observed isostructural transition to a change in the spin state of Fe2 + in LiFePO4. Compared to relevant Fe-bearing minerals, LiFePO4 exhibits the largest onset pressure for a pressure-induced spin state transition.

Spin-curvature interaction from curved Dirac equation: Application to single-wall carbon nanotubes

Science.gov (United States)

Zhang, Kai; Zhang, Erhu; Chen, Huawei; Zhang, Shengli

2017-06-01

The spin-curvature interaction (SCI) and its effects are investigated based on curved Dirac equation. Through the low-energy approximation of curved Dirac equation, the Hamiltonian of SCI is obtained and depends on the geometry and spinor structure of manifold. We find that the curvature can be considered as field strength and couples with spin through Zeeman-like term. Then, we use dimension reduction to derive the local Hamiltonian of SCI for cylinder surface, which implies that the effective Hamiltonian of single-wall carbon nanotubes results from the geometry and spinor structure of lattice and includes two types of interactions: one does not break any symmetries of the lattice and only shifts the Dirac points for all nanotubes, while the other one does and opens the gaps except for armchair nanotubes. At last, analytical expressions of the band gaps and the shifts of their positions induced by curvature are given for metallic nanotubes. These results agree well with experiments and can be verified experimentally.

Comparison of ductile-to-brittle transition curve fitting approaches

International Nuclear Information System (INIS)

Cao, L.W.; Wu, S.J.; Flewitt, P.E.J.

2012-01-01

Ductile-to-brittle transition (DBT) curve fitting approaches are compared over the transition temperature range for reactor pressure vessel steels with different kinds of data, including Charpy-V notch impact energy data and fracture toughness data. Three DBT curve fitting methods have been frequently used in the past, including the Burr S-Weibull and tanh distributions. In general there is greater scatter associated with test data obtained within the transition region. Therefore these methods give results with different accuracies, especially when fitting to small quantities of data. The comparison shows that the Burr distribution and tanh distribution can almost equally fit well distributed and large data sets extending across the test temperature range to include the upper and lower shelves. The S-Weibull distribution fit is poor for the lower shelf of the DBT curve. Overall for both large and small quantities of measured data the Burr distribution provides the best description. - Highlights: ► Burr distribution offers a better fit than that of a S-Weibull and tanh fit. ► Burr and tanh methods show similar fitting ability for a large data set. ► Burr method can fit sparse data well distributed across the test temperature. ► S-Weibull method cannot fit the lower shelf well and show poor fitting quality.

Quantum phase transitions in matrix product states of one-dimensional spin-1 chains

International Nuclear Information System (INIS)

Zhu Jingmin

2014-01-01

We present a new model of quantum phase transitions in matrix product systems of one-dimensional spin-1 chains and study the phases coexistence phenomenon. We find that in the thermodynamic limit the proposed system has three different quantum phases and by adjusting the control parameters we are able to realize any phase, any two phases equal coexistence and the three phases equal coexistence. At every critical point the physical quantities including the entanglement are not discontinuous and the matrix product system has long-range correlation and N-spin maximal entanglement. We believe that our work is helpful for having a comprehensive understanding of quantum phase transitions in matrix product states of one-dimensional spin chains and of certain directive significance to the preparation and control of one-dimensional spin lattice models with stable coherence and N-spin maximal entanglement. (author)

Optimal Charge-to-Spin Conversion in Graphene on Transition-Metal Dichalcogenides

Science.gov (United States)

Offidani, Manuel; Milletarı, Mirco; Raimondi, Roberto; Ferreira, Aires

2017-11-01

When graphene is placed on a monolayer of semiconducting transition metal dichalcogenide (TMD) its band structure develops rich spin textures due to proximity spin-orbital effects with interfacial breaking of inversion symmetry. In this work, we show that the characteristic spin winding of low-energy states in graphene on a TMD monolayer enables current-driven spin polarization, a phenomenon known as the inverse spin galvanic effect (ISGE). By introducing a proper figure of merit, we quantify the efficiency of charge-to-spin conversion and show it is close to unity when the Fermi level approaches the spin minority band. Remarkably, at high electronic density, even though subbands with opposite spin helicities are occupied, the efficiency decays only algebraically. The giant ISGE predicted for graphene on TMD monolayers is robust against disorder and remains large at room temperature.

Enhanced spin accumulation in Fe3O4 based spin injection devices below the Verwey transition

Science.gov (United States)

Bhat, Shwetha G.; Kumar, P. S. Anil

2016-12-01

Spin injection into GaAs and Si (both n and p-type) semiconductors using Fe3O4 is achieved with and without a tunnel barrier (MgO) via three-terminal electrical Hanle measurement. Interestingly, the magnitude of spin accumulation voltage (ΔV) in semiconductor is found to be associated with a drastic increment in ΔV in Fe3O4 based devices for temperature metal-to-insulator transition of Fe3O4 at T V. Observations from our elaborate investigations show that spin polarization of Fe3O4 has an explicit influence on the enhanced spin injection. It is argued that the theoretical prediction of half-metallicity of Fe3O4 above and below T V has to be reinvestigated.

Phase transitions and thermal entanglement of the distorted Ising-Heisenberg spin chain: topology of multiple-spin exchange interactions in spin ladders

Science.gov (United States)

Arian Zad, Hamid; Ananikian, Nerses

2017-11-01

We consider a symmetric spin-1/2 Ising-XXZ double sawtooth spin ladder obtained from distorting a spin chain, with the XXZ interaction between the interstitial Heisenberg dimers (which are connected to the spins based on the legs via an Ising-type interaction), the Ising coupling between nearest-neighbor spins of the legs and rungs spins, respectively, and additional cyclic four-spin exchange (ring exchange) in the square plaquette of each block. The presented analysis supplemented by results of the exact solution of the model with infinite periodic boundary implies a rich ground state phase diagram. As well as the quantum phase transitions, the characteristics of some of the thermodynamic parameters such as heat capacity, magnetization and magnetic susceptibility are investigated. We prove here that among the considered thermodynamic and thermal parameters, solely heat capacity is sensitive versus the changes of the cyclic four-spin exchange interaction. By using the heat capacity function, we obtain a singularity relation between the cyclic four-spin exchange interaction and the exchange coupling between pair spins on each rung of the spin ladder. All thermal and thermodynamic quantities under consideration should be investigated by regarding those points which satisfy the singularity relation. The thermal entanglement within the Heisenberg spin dimers is investigated by using the concurrence, which is calculated from a relevant reduced density operator in the thermodynamic limit.

Spin asymmetry calculations of the TMR-V curves in single and double-barrier magnetic tunnel junctions

KAUST Repository

Useinov, Arthur

2011-10-01

Spin-polarization asymmetry is the key parameter in asymmetric voltage behavior (AVB) of the tunnel magnetoresistance (TMR) in magnetic tunnel junctions. In this paper, we study the value of the TMR as a function of the applied voltage Va in the single as well as double barrier magnetic tunnel junctions (SMTJ & DMTJ, which are constructed from CoFeB/MgO interfaces) and numerically estimate the possible difference of the TMR-V a curves for negative and positive voltages in the homojunctions. As a result, we found that AVB may help to determine the exact values of Fermi wave vectors for minority and majority conducting spin sub-bands. Moreover, significant asymmetry of the experimental TMR-Va curves, which arises due to different annealing regimes, is explained by different heights of the tunnel barriers and values of the spin asymmetry. The numerical TMR-V a data are in good agreement with experimental ones. © 2011 IEEE.

Tuning magnetoresistance in molybdenum disulphide and graphene using a molecular spin transition.

Science.gov (United States)

Datta, Subhadeep; Cai, Yongqing; Yudhistira, Indra; Zeng, Zebing; Zhang, Yong-Wei; Zhang, Han; Adam, Shaffique; Wu, Jishan; Loh, Kian Ping

2017-09-22

Coupling spins of molecular magnets to two-dimensional (2D) materials provides a framework to manipulate the magneto-conductance of 2D materials. However, with most molecules, the spin coupling is usually weak and devices fabricated from these require operation at low temperatures, which prevents practical applications. Here, we demonstrate field-effect transistors based on the coupling of a magnetic molecule quinoidal dithienyl perylenequinodimethane (QDTP) to 2D materials. Uniquely, QDTP switches from a spin-singlet state at low temperature to a spin-triplet state above 370 K, and the spin transition can be electrically transduced by both graphene and molybdenum disulphide. Graphene-QDTP shows hole-doping and a large positive magnetoresistance ( ~ 50%), while molybdenum disulphide-QDTP demonstrates electron-doping and a switch to large negative magnetoresistance ( ~ 100%) above the magnetic transition. Our work shows the promise of spin detection at high temperature by coupling 2D materials and molecular magnets.Engineering a coupling between magnetic molecules and conducting materials at room temperature could help the development of spintronic devices. Loh et al. show that the spin state of QDTP molecules deposited on graphene and MoS 2 couples to their electronic structure, affecting magnetotransport.

Magnetic ordering of CoCl2-GIC, a spin ceramic: hierarchical successive transitions and the intermediate glassy phase

International Nuclear Information System (INIS)

Suzuki, Masatsugu; Suzuki, Itsuko S; Matsuura, Motohiro

2007-01-01

Stage-2 CoCl 2 -graphite intercalation compound (GIC) is a spin ceramic which shows hierarchical successive transitions at T cu (= 8.9 K) and T cl (= 7.0 K) from the paramagnetic phase into an intra-cluster (two-dimensional ferromagnetic) order with inter-cluster disorder and then to an inter-cluster (three-dimensional antiferromagnetic like) order over the whole system. The nature of the inter-cluster disorder was suggested to be of spin glass by nonlinear magnetic response analyses around T cu and by studies on dynamical aspects of ordering between T cu and T cl . Here, we present a further extensive examination of a series of time dependence of zero-field cooled magnetization M ZFC after the ageing protocol below T cu . The time dependence of the relaxation rates S ZFC (t) = (1/H) dM ZFC (t)/dlnt dramatically changes from the curves of simple spin glass ageing effect below T cl to those of two peaks above T cl . The characteristic relaxation behaviour apparently indicates that there coexist two different kinds of glassy correlated region below T cu

Unambiguously identifying spin states of transition-metal ions in the Earth (Invited)

Science.gov (United States)

Hsu, H.

2010-12-01

The spin state of a transition-metal ion in crystalline solids, defined by the number of unpaired electrons in the ion’s incomplete 3d shell, may vary with many factors, such as temperature, pressure, strain, and the local atomic configuration, to name a few. Such a phenomenon, known as spin-state crossover, plays a crucial role in spintronic materials. Recently, the pressure-induced spin-state crossover in iron-bearing minerals has been recognized to affect the minerals’ structural and elastic properties. However, the detailed mechanism of such crossover in iron-bearing magnesium silicate perovskite, the most abundant mineral in the Earth, remains unclear. A significant part of this confusion arises from the difficulty in reliably extracting the spin state from experiments. For the same reason, the thermally-induced spin-state crossover in lanthanum cobaltite (LaCoO3) has been controversial for more than four decades. In this talk, I will discuss how first-principle calculations can help clarifying these long-standing controversies. In addition to the total energy, equation of state, and elastic properties of each spin state, first-principle calculations also predict the electric field gradient (EFG) at the nucleus of each transition-metal ion. Our calculations showed that the nuclear EFG, a quantity that can be measured via Mössbauer or nuclear magnetic resonance (NMR) spectroscopy, depends primarily on the spin state, irrespective of the concentration or configuration of transition-metal ions. Such robustness makes EFG a unique fingerprint to identify the spin state. The combination of first-principle calculations and Mössbauer/NMR spectroscopy can therefore be a reliable and efficient approach in tackling spin-state crossover problems in the Earth. This work was primarily supported by the MRSEC Program of NSF under Awards Number DMR-0212302 and DMR-0819885, and partially supported by NSF under ATM-0428774 (V-Lab), EAR-1019853, and EAR-0810272. The

Study on the effect of transition curve to the dynamic characteristics of high-temperature superconducting maglev

Science.gov (United States)

Qian, Nan; Zheng, Botian; Gou, Yanfeng; Chen, Ping; Zheng, Jun; Deng, Zigang

2015-12-01

High temperature superconducting (HTS) maglev technology is becoming more and more mature, and many key technologies have been deeply studied. However, the transition curve plays a key role in HTS maglev system, and related studies have not been carried out. In this paper series of simulations were conducted to test the lateral and vertical vibration of HTS maglev when passing through curves. Two magnetic guideways, of which one has transition curves but the other does not, are designed to test the vibration characteristics of a mini HTS maglev model running though curves. Results show that after adding transition curves between straight line and circular curve the vibration of HTS maglev model in lateral and vertical directions are all weakened in different degrees. It proves that adding transition curve into HTS maglev system is favorable and necessary.

Phase transitions and multicritical points in the mixed spin-32 and spin-2 Ising system with a single-ion anisotropy

International Nuclear Information System (INIS)

Bobak, A.; Dely, J.

2007-01-01

The effect of a single-ion anisotropy on the phase diagram of the mixed spin-32 and spin-2 Ising system is investigated by the use of a mean-field theory based on the Bogoliubov inequality for the free energy. Topologically different kinds of phase diagrams are achieved by changing values of the parameter in the model Hamiltonian. Besides second-order transitions, lines of first-order transitions terminating either at a tricritical point or an isolated critical point, are found

Spin delocalization phase transition in a correlated electrons model

International Nuclear Information System (INIS)

Huerta, L.

1990-11-01

In a simplified one-site model for correlated electrons systems we show the existence of a phase transition corresponding to spin delocalization. The system becomes a solvable model and zero-dimensional functional techniques are used. (author). 7 refs, 3 figs

Spin Chern number and topological phase transition on the Lieb lattice with spin–orbit coupling

International Nuclear Information System (INIS)

Chen, Rui; Zhou, Bin

2017-01-01

We propose that quantum anomalous Hall effect may occur in the Lieb lattice, when Rashba spin–orbit coupling, spin-independent and spin-dependent staggered potentials are introduced into the lattice. It is found that spin Chern numbers of two degenerate flat bands change from 0 to ±2 due to Rashba spin–orbit coupling effect. The inclusion of Rashba spin–orbit coupling and two kinds of staggered potentials opens a gap between the two flat bands. The topological property of the gap is determined by the amplitudes of Rashba spin–orbit coupling and staggered potentials, and thus the topological phase transition from quantum anomalous Hall effect to normal insulator can occur. Finally, the topological phase transition from quantum spin Hall state to normal insulator is discussed when Rashba spin–orbit coupling and intrinsic spin–orbit coupling coexist in the Lieb lattice. - Highlights: • Spin Chern numbers of the bulk states on the Lieb lattice are calculated. • RSOC plays an important role on the topological phase transition on the Lieb lattice. • Quantum anomalous Hall effect can occur due to RSOC and staggered potentials. • Topological phase transition can occur when ISOC and RSOC coexist.

Exploring the dynamics about the glass transition by muon spin relaxation and muon spin rotation

International Nuclear Information System (INIS)

Bermejo, F J; Bustinduy, I; Cox, S F J; Lord, J S; Cabrillo, C; Gonzalez, M A

2006-01-01

The capability of muon spin rotation and muon spin relaxation to explore dynamics in the vicinity of the glass transition is illustrated by results pertaining to three materials exhibiting two different glass-forming abilities. Measurements under transverse magnetic fields enable us to monitor the dynamics of muonium-labelled closed-shell molecules within the microsecond range. The results display the onset of stochastic molecular motions taking place upon crossing from below the glass-transition temperature. In turn, the molecular dynamics of radicals formed by addition of atomic muonium to unsaturated organic molecules can also be explored up to far shorter times by means of relaxation measurements under longitudinal fields. The technique is then shown to be capable of singling out stochastic reorientational motions from others, which usually are strongly coupled to them and usually dominate the material response when measured using higher-frequency probes such as neutron and light scattering

Surface-environment effects in spin crossover solids

Energy Technology Data Exchange (ETDEWEB)

Gudyma, Iu., E-mail: yugudyma@gmail.com; Maksymov, A.

2017-06-15

Highlights: • The spin-crossover nanocrystals were described by modified Ising-like model. • The ligand field on the surface is a function of external fluctuations. • The thermal hysteresis with surface and bulk interactions of the lattice was studied. • The system behavior with fluctuating ligand field on the surface was examined. • The fluctuations enlarge the hysteresis, but smaller surface interaction narrows it. - Abstract: The impact of surface effects on thermal induced spin crossover phenomenon is a subject of a broad and current interest. Using the modified Ising-like model of spin crossover solids with the ligand field as function of the molecule’ positions and random component on surface by means of Metropolis Monte Carlo algorithm the thermal spin transition curves were calculated. The analysis of spin configuration during transition gives a general idea about contribution of molecules from the surface and inside the lattice into resulting magnetization of the systems. The behavior of hysteresis loop for various surface coupling and fluctuations strength has been described.

Investigation of a Spin Transition in a LaCoO3 Single Crystal by the Method of X-Ray Magnetic Circular Dichroism at the Cobalt K- and L 2,3-Edges

Science.gov (United States)

Sikolenko, V. V.; Troyanchuk, I. O.; Karpinsky, D. V.; Rogalev, A.; Wilhelm, F.; Rosenberg, R.; Prabhakaran, D.; Efimova, E. A.; Efimov, V. V.; Tiutiunnikov, S. I.; Bobrikov, I. A.

2018-02-01

Spin transitions of cobalt ions in LaCoO3 single crystals have been studied by the method of X-ray magnetic circular dichroism (XMCD) at the K- and L 2,3-edges of Co3+ ions. The orbital momentum of cobalt ions obtained for the K-edge at the 3 d level in the region of the spin transition in the temperature range from 25 to 120 K increases by a factor of approximately 1.6, whereas the slope of the magnetization curve value in the same temperature range and magnetic field increases by a factor of more than 10. XMCD experiments at the cobalt L 2,3-edges demonstrate gradual growth of the ratio of the orbital momentum to the spin one L/ S from 0.48 to 0.53 in the temperature range from 60 K to 120 K.

Spin relaxation and the Kondo effect in transition metal dichalcogenide monolayers

International Nuclear Information System (INIS)

Rostami, Habib; Moghaddam, Ali G; Asgari, Reza

2016-01-01

We investigate the spin relaxation and Kondo resistivity caused by magnetic impurities in doped transition metal dichalcogenide monolayers. We show that momentum and spin relaxation times, due to the exchange interaction by magnetic impurities, are much longer when the Fermi level is inside the spin-split region of the valence band. In contrast to the spin relaxation, we find that the dependence of Kondo temperature T K on the doping is not strongly affected by the spin–orbit induced splitting, although only one of the spin species are present at each valley. This result, which is obtained using both perturbation theory and the poor man’s scaling methods, originates from the intervalley spin-flip scattering in the spin-split region. We further demonstrate the decline in the conductivity with temperatures close to T K , which can vary with the doping. Our findings reveal the qualitative difference with the Kondo physics in conventional metallic systems and other Dirac materials. (paper)

Topological quantum phase transitions and edge states in spin-orbital coupled Fermi gases.

Science.gov (United States)

Zhou, Tao; Gao, Yi; Wang, Z D

2014-06-11

We study superconducting states in the presence of spin-orbital coupling and Zeeman field. It is found that a phase transition from a Fulde-Ferrell-Larkin-Ovchinnikov state to the topological superconducting state occurs upon increasing the spin-orbital coupling. The nature of this topological phase transition and its critical property are investigated numerically. Physical properties of the topological superconducting phase are also explored. Moreover, the local density of states is calculated, through which the topological feature may be tested experimentally.

Long Spin-Relaxation Times in a Transition-Metal Atom in Direct Contact to a Metal Substrate.

Science.gov (United States)

Hermenau, Jan; Ternes, Markus; Steinbrecher, Manuel; Wiesendanger, Roland; Wiebe, Jens

2018-03-14

Long spin-relaxation times are a prerequisite for the use of spins in data storage or nanospintronics technologies. An atomic-scale solid-state realization of such a system is the spin of a transition-metal atom adsorbed on a suitable substrate. For the case of a metallic substrate, which enables the direct addressing of the spin by conduction electrons, the experimentally measured lifetimes reported to date are on the order of only hundreds of femtoseconds. Here, we show that the spin states of iron atoms adsorbed directly on a conductive platinum substrate have a surprisingly long spin-relaxation time in the nanosecond regime, which is comparable to that of a transition metal atom decoupled from the substrate electrons by a thin decoupling layer. The combination of long spin-relaxation times and strong coupling to conduction electrons implies the possibility to use flexible coupling schemes to process the spin information.

Nuclear shape transitions and some properties of aligned-particle configurations at high spin

International Nuclear Information System (INIS)

Koo, T.L.; Chowdhury, P.; Emling, H.

1982-01-01

Two topics are addressed in this paper. First, we discuss the variation of shapes with spin and neutron number for nuclei in the N approx. = 88 transitional region. Second, we present comments on the feeding times of very high spin single-particle yrast states

Glass transition in the spin-density wave phase of (TMTSF)2PF6

DEFF Research Database (Denmark)

Lasjaunias, J.C.; Biljakovic, K.; Nad, F.

1994-01-01

We present the results of low frequency dielectric measurements and a detailed kinetic investigation of the specific heat anomaly in the spin-density wave phase of (TMTSF)(2)PF6 in the temperature range between 2 and 4 K. The dielectric relaxation shows a critical slowing down towards a ''static'......'' glass transition around 2 K. The jump in the specific heat in different controlled kinetic conditions shows all the characteristics of freezing in supercooled liquids. Both effects give direct evidence of a glass transition in the spin-density wave ground state....

Effect of stellar activity on the high precision transit light curve

Directory of Open Access Journals (Sweden)

Oshagh, M.

2015-01-01

Full Text Available Stellar activity features such as spots and plages can create difficulties in determining planetary parameters through spectroscopic and photometric observations. The overlap of a transiting planet and a stellar spot, for instance, can produce anomalies in the transit light curve that may lead to inaccurate estimation of the transit duration, depth, and timing. Such inaccuracies can affect the precise derivation of the planet’s radius. In this talk we will present the results of a quantitative study on the effects of stellar spots on high precision transit light curves. We show that spot anomalies can lead to the estimate of a planet radius that is 4% smaller than the real value. The effects on the transit duration can also be of the order of 4%, longer or shorter. Depending on the size and distribution of spots, anomalies can also produce transit timing variations with significant amplitudes. For instance, TTVs with signal amplitudes of 200 seconds can be produced by spots as large as the largest sunspot. Finally, we examine the impact of active regions on the transit depth measurements in different wavelengths, in order to probe the impact of this effect on transmission spectroscopy measurements. We show that significant (up to 10% underestimation/overestimation of the planet-to-star radius ratio can be measured, especially in the short wavelength regime.

Magnetic phase transitions in low dimension quantum spin systems

International Nuclear Information System (INIS)

Canevet, Emmanuel

2010-01-01

In this PhD thesis, three low dimensional spin systems are studied by means of elastic and inelastic neutron scattering. Macroscopic measurements in the DMACuCl 3 compound indicate the coexistence of two kinds of dimers: antiferromagnetic and ferromagnetic. The magnetic structure determined by our neutron diffraction survey at H = 0 shows irrevocably the existence of these two kinds of dimers. It has been shown that the Ising-like compound BaCo 2 V 2 O 8 should be the first realization of a system in which a longitudinal spin density wave (LSDW) magnetic order occurs when a magnetic field is applied. In a first time, we have determined the magnetic structure in zero magnetic field. Then, we focused on the effect of a magnetic field on the propagation vector, showing an entrance in the LSDW phase at H c = 3.9 T. The magnetic structure refined above this critical field confirms that BaCo 2 V 2 O 8 is the first compound in which occurs a LSDW phase. In the organic compound DF 5 PNN, it has been shown that this compound is well described at low temperature by spin chains with alternating couplings. However, the crystallographic structure determined at room temperature implies that the interactions are uniform. By means of neutron diffraction, we characterized a structural transition at low temperature (T c = 450 mK) making the system evolve from C2/c space group to Pc. This transition explains the alternating behavior of the interactions. We have also evidenced a field-induced structural transition (H c = 1.1 T). Above this field, the system is back to the C2/c space group, implying that the interactions are back to uniform. We have confirmed this by studying the magnetic excitations. (author) [fr

Period-doubling bifurcation cascade observed in a ferromagnetic nanoparticle under the action of a spin-polarized current

Energy Technology Data Exchange (ETDEWEB)

Horley, Paul P., E-mail: paul.horley@cimav.edu.mx [Centro de Investigación en Materiales Avanzados, S.C. (CIMAV), Chihuahua/Monterrey, 120 Avenida Miguel de Cervantes, 31109 Chihuahua (Mexico); Kushnir, Mykola Ya. [Yuri Fedkovych Chernivtsi National University, 2 Kotsyubynsky str., 58012 Chernivtsi (Ukraine); Morales-Meza, Mishel [Centro de Investigación en Materiales Avanzados, S.C. (CIMAV), Chihuahua/Monterrey, 120 Avenida Miguel de Cervantes, 31109 Chihuahua (Mexico); Sukhov, Alexander [Institut für Physik, Martin-Luther Universität Halle-Wittenberg, 06120 Halle (Saale) (Germany); Rusyn, Volodymyr [Yuri Fedkovych Chernivtsi National University, 2 Kotsyubynsky str., 58012 Chernivtsi (Ukraine)

2016-04-01

We report on complex magnetization dynamics in a forced spin valve oscillator subjected to a varying magnetic field and a constant spin-polarized current. The transition from periodic to chaotic magnetic motion was illustrated with bifurcation diagrams and Hausdorff dimension – the methods developed for dissipative self-organizing systems. It was shown that bifurcation cascades can be obtained either by tuning the injected spin-polarized current or by changing the magnitude of applied magnetic field. The order–chaos transition in magnetization dynamics can be also directly observed from the hysteresis curves. The resulting complex oscillations are useful for development of spin-valve devices operating in harmonic and chaotic modes.

Noise as a Probe of Ising Spin Glass Transitions

Science.gov (United States)

Chen, Zhi; Yu, Clare

2009-03-01

Noise is ubiquitous and and is often viewed as a nuisance. However, we propose that noise can be used as a probe of the fluctuations of microscopic entities, especially in the vicinity of a phase transition. In recent work we have used simulations to show that the noise increases in the vicinity of phase transitions of ordered systems. We have recently turned our attention to noise near the phase transitions of disordered systems. In particular, we are studying the noise near Ising spin glass transitions using Monte Carlo simulations. We monitor the system as a function of temperature. At each temperature, we obtain the time series of quantities characterizing the properties of the system, i.e., the energy and magnetization. We look at different quantities, such as the noise power spectrum and the second spectrum of the noise, to analyze the fluctuations.

Effect of Spin Transition onComposition and Seismic Structure of the Lower Mantle

Science.gov (United States)

Wu, Z.

2015-12-01

Spin transition of iron in ferropericlase (Fp) causes a significant softening in bulk modulus [e.g.,1,2], which leads to unusual dVP/dT>0. Because dVP/dT>0 in Fp cancels out with dVP/dTMao, Z., Marquardt, H., 2013. . Rev Geophys 51, 244-275 (2013). [3] Wu, Z.Q., Wentzcovitch, R.M., 2014. Spin crossover in ferropericlase and velocity heterogeneities in the lower mantle. Proc. Natl. Acad. Sci. U. S. A. 111, 10468-10472. [4] Zhao, D.P., 2007. Seismic images under 60 hotspots: Search for mantle plumes. Gondwana Res 12, 335-355. [5] van der Hilst, R.D., Karason, H., 1999. Science 283, 1885-1888. [6] Huang,C., Leng, W., Wu, Z. Q., 2015. Iron-spin transition controls structure and stability of LLSVPs in the lower mantle, Earth Planet. Sci. Lett. 423, 173-181.

PyTranSpot: A tool for multiband light curve modeling of planetary transits and stellar spots

Science.gov (United States)

Juvan, Ines G.; Lendl, M.; Cubillos, P. E.; Fossati, L.; Tregloan-Reed, J.; Lammer, H.; Guenther, E. W.; Hanslmeier, A.

2018-02-01

Several studies have shown that stellar activity features, such as occulted and non-occulted starspots, can affect the measurement of transit parameters biasing studies of transit timing variations and transmission spectra. We present PyTranSpot, which we designed to model multiband transit light curves showing starspot anomalies, inferring both transit and spot parameters. The code follows a pixellation approach to model the star with its corresponding limb darkening, spots, and transiting planet on a two dimensional Cartesian coordinate grid. We combine PyTranSpot with a Markov chain Monte Carlo framework to study and derive exoplanet transmission spectra, which provides statistically robust values for the physical properties and uncertainties of a transiting star-planet system. We validate PyTranSpot's performance by analyzing eleven synthetic light curves of four different star-planet systems and 20 transit light curves of the well-studied WASP-41b system. We also investigate the impact of starspots on transit parameters and derive wavelength dependent transit depth values for WASP-41b covering a range of 6200-9200 Å, indicating a flat transmission spectrum.

EXTRACTING PERIODIC TRANSIT SIGNALS FROM NOISY LIGHT CURVES USING FOURIER SERIES

Energy Technology Data Exchange (ETDEWEB)

Samsing, Johan [Department of Astrophysical Sciences, Princeton University, Peyton Hall, 4 Ivy Lane, Princeton, NJ 08544 (United States)

2015-07-01

We present a simple and powerful method for extracting transit signals associated with a known transiting planet from noisy light curves. Assuming the orbital period of the planet is known and the signal is periodic, we illustrate that systematic noise can be removed in Fourier space at all frequencies by only using data within a fixed time frame with a width equal to an integer number of orbital periods. This results in a reconstruction of the full transit signal, which on average is unbiased despite no prior knowledge of either the noise or the transit signal itself being used in the analysis. The method therefore has clear advantages over standard phase folding, which normally requires external input such as nearby stars or noise models for removing systematic components. In addition, we can extract the full orbital transit signal (360°) simultaneously, and Kepler-like data can be analyzed in just a few seconds. We illustrate the performance of our method by applying it to a dataset composed of light curves from Kepler with a fake injected signal emulating a planet with rings. For extracting periodic transit signals, our presented method is in general the optimal and least biased estimator and could therefore lead the way toward the first detections of, e.g., planet rings and exo-trojan asteroids.

Exact-exchange spin-density functional theory of Wigner localization and phase transitions in quantum rings.

Science.gov (United States)

Arnold, Thorsten; Siegmund, Marc; Pankratov, Oleg

2011-08-24

We apply exact-exchange spin-density functional theory in the Krieger-Li-Iafrate approximation to interacting electrons in quantum rings of different widths. The rings are threaded by a magnetic flux that induces a persistent current. A weak space and spin symmetry breaking potential is introduced to allow for localized solutions. As the electron-electron interaction strength described by the dimensionless parameter r(S) is increased, we observe-at a fixed spin magnetic moment-the subsequent transition of both spin sub-systems from the Fermi liquid to the Wigner crystal state. A dramatic signature of Wigner crystallization is that the persistent current drops sharply with increasing r(S). We observe simultaneously the emergence of pronounced oscillations in the spin-resolved densities and in the electron localization functions indicating a spatial electron localization showing ferrimagnetic order after both spin sub-systems have undergone the Wigner crystallization. The critical r(S)(c) at the transition point is substantially smaller than in a fully spin-polarized system and decreases further with decreasing ring width. Relaxing the constraint of a fixed spin magnetic moment, we find that on increasing r(S) the stable phase changes from an unpolarized Fermi liquid to an antiferromagnetic Wigner crystal and finally to a fully polarized Fermi liquid. © 2011 IOP Publishing Ltd

Spin transition diagram of (2Me-5Et-PyH)[Fe(Th-5Cl-Sa)2] studied by EPR

International Nuclear Information System (INIS)

Krupska, A.; Augustyniak-Jablokow, M.A.; Yablokov, V.Yu.; Zelentsov, V.V.

2005-01-01

The high-spin - low-spin transition in (2Me-5Et-PyH)[Fe(Th-5Cl-Sa) 2 ] was studied by EPR under hydrostatic pressure in the temperature range of 80-310 K. Two modifications of the low-spin complexes: low-pressure (LS-1) and high-pressure (S-2) ones were observed. The low-spin complexes are associated in domains. Under atmospheric pressure LS-1 appears or disappears at 220 K. The hydrostatic pressure shifts the transition to high temperatures. Above 410 MPa the abrupt changes of the g-factor and width ΔB of the EPR line is observed. The pressure-induced transition LS-1 - LS-2 is almost independent of T up to 275 K where under pressure 420 MPa a triple point is observed. When the pressure has been decreased the reverse transition from LS-2 to LS-1 or to high spin phase (at T > 260 K) occurs with a large hysteresis about 95 MPa. (author)

2-vertex Lorentzian spin foam amplitudes for dipole transitions

Science.gov (United States)

Sarno, Giorgio; Speziale, Simone; Stagno, Gabriele V.

2018-04-01

We compute transition amplitudes between two spin networks with dipole graphs, using the Lorentzian EPRL model with up to two (non-simplicial) vertices. We find power-law decreasing amplitudes in the large spin limit, decreasing faster as the complexity of the foam increases. There are no oscillations nor asymptotic Regge actions at the order considered, nonetheless the amplitudes still induce non-trivial correlations. Spin correlations between the two dipoles appear only when one internal face is present in the foam. We compute them within a mini-superspace description, finding positive correlations, decreasing in value with the Immirzi parameter. The paper also provides an explicit guide to computing Lorentzian amplitudes using the factorisation property of SL(2,C) Clebsch-Gordan coefficients in terms of SU(2) ones. We discuss some of the difficulties of non-simplicial foams, and provide a specific criterion to partially limit the proliferation of diagrams. We systematically compare the results with the simplified EPRLs model, much faster to evaluate, to learn evidence on when it provides reliable approximations of the full amplitudes. Finally, we comment on implications of our results for the physics of non-simplicial spin foams and their resummation.

Smoothed transitions in higher spin AdS gravity

International Nuclear Information System (INIS)

Banerjee, Shamik; Shenker, Stephen; Castro, Alejandra; Hellerman, Simeon; Hijano, Eliot; Lepage-Jutier, Arnaud; Maloney, Alexander

2013-01-01

We consider CFTs conjectured to be dual to higher spin theories of gravity in AdS 3 and AdS 4 . Two-dimensional CFTs with W N symmetry are considered in the λ = 0 (k → ∞) limit where they are conjectured to be described by continuous orbifolds. The torus partition function is computed, using reasonable assumptions, and equals that of a free-field theory. We find no phase transition at temperatures of order 1; the usual Hawking–Page phase transition is removed by the highly degenerate light states associated with conical defect states in the bulk. Three-dimensional Chern–Simons matter CFTs with vector-like matter are considered on T 3 , where the dynamics is described by an effective theory for the eigenvalues of the holonomies. Likewise, we find no evidence for a Hawking–Page phase transition at a large level k. (paper)

Dynamical phase transitions in spin models and automata

International Nuclear Information System (INIS)

Derrida, B.

1989-01-01

Some of the models and methods developed in the study of the dynamics of spin models and automata are described. Special attention is given to the distance method which consists of comparing the time evolution of two configurations. The method is used to obtain the phase boundary between a frozen and a chaotic phase in the case of deterministic models. For stochastic systems the method is used to obtain dynamical phase transitions

Analytical evidence for the absence of spin glass transition on self-dual lattices

International Nuclear Information System (INIS)

Ohzeki, Masayuki; Nishimori, Hidetoshi

2009-01-01

We show strong evidence for the absence of a finite-temperature spin glass transition for the random-bond Ising model on self-dual lattices. The analysis is performed by an application of duality relations, which enables us to derive a precise but approximate location of the multicritical point on the Nishimori line. This method can be systematically improved to presumably give the exact result asymptotically. The duality analysis, in conjunction with the relationship between the multicritical point and the spin glass transition point for the symmetric distribution function of randomness, leads to the conclusion of the absence of a finite-temperature spin glass transition for the case of symmetric distribution. The result is applicable to the random-bond Ising model with ±J or Gaussian distribution and the Potts gauge glass on the square, triangular and hexagonal lattices as well as the random three-body Ising model on the triangular and the Union-Jack lattices and the four-dimensional random plaquette gauge model. This conclusion is exact provided that the replica method is valid and the asymptotic limit of the duality analysis yields the exact location of the multicritical point. (fast track communication)

Spin reorientation transition in Co/Au multilayers

Energy Technology Data Exchange (ETDEWEB)

Quispe-Marcatoma, J., E-mail: jquispem@unmsm.edu.pe [Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro 22290-180 (Brazil); Facultad de Ciencias Físicas, Universidad Nacional Mayor de San Marcos, P.O. Box 14-0149, Lima 14, Perú (Peru); Tarazona, H. [Facultad de Ciencias Físicas, Universidad Nacional Mayor de San Marcos, P.O. Box 14-0149, Lima 14, Perú (Peru); Pandey, B. [Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro 22290-180 (Brazil); Department of Applied Science, Symbiosis Institute of Technology, SIU, Lavale, Pune 412 115, India. (India); Sousa, M.A. de [Instituto de Física, Universidade Federal de Goiás, Goiânia 74001-970 (Brazil); Carvalho, M. [Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro 22290-180 (Brazil); Landauro, C.V. [Facultad de Ciencias Físicas, Universidad Nacional Mayor de San Marcos, P.O. Box 14-0149, Lima 14, Perú (Peru); Pelegrini, F. [Instituto de Física, Universidade Federal de Goiás, Goiânia 74001-970 (Brazil); Baggio Saitovitch, E. [Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro 22290-180 (Brazil)

2014-10-01

We report a study about the spin reorientation transition (SRT) from perpendicular easy axis to in-plane easy axis of magnetization in Co/Au multilayers. A series of multilayers of Si/Au(100 Å)/{[Co(t_C_o)/Au(20 Å)]_2_0}/Au(50 Å) family were studied, with Co layer thickness varying between 6 Å to 30 Å. The thickness of the Au layer was chosen large enough in order to minimize the interlayer exchange coupling between Co layers. In such thick Au-layer samples the magnetic properties are mainly the result of competition between interlayer magnetostatic coupling due to stray field, perpendicular magnetic anisotropy and shape anisotropy. The effective anisotropy constant K{sub eff} and the second order anisotropy K{sub 2} were deduced from the fit of the resonant magnetic field obtained from out of plane dependence Ferromagnetic Resonance (FMR) experiments. To study the SRT, we have plotted the phase diagram between K{sub eff} and K{sub 2}. The results show that SRT occurs through the metastable region with K{sub 2} ≤ −½ K{sub eff}, (K{sub eff} > 0). It is interesting to note that FMR shows the coexistence of two modes with different anisotropy for small Co thickness, while for thick Co layers the modes have the same anisotropy. Moreover, in thick Co layer samples, volume and surface spin wave resonance (SWR) modes were also excited by the microwave field, around the perpendicular FMR geometry, giving a clear evidence of a magnetic coupling between the Co layers. - Highlights: • Co/Au multilayers with varying Co layer thickness are prepared by DC-magnetron sputtering. • The spin reorientation transition (SRT) and flipping of magnetic moment are studied. • Effective anisotropy constant (K) and 2nd order anisotropy constant (K{sub 2}) are calculated. • K Vs K{sub 2} plot showed that SRT occurs through the metastable region with K{sub 2} ≤ −½ K, (K > 0). • Ferromagnetic Resonance spectra showed the coexistence of two resonance modes.

Phase Transitions in Definite Total Spin States of Two-Component Fermi Gases.

Science.gov (United States)

Yurovsky, Vladimir A

2017-05-19

Second-order phase transitions have no latent heat and are characterized by a change in symmetry. In addition to the conventional symmetric and antisymmetric states under permutations of bosons and fermions, mathematical group-representation theory allows for non-Abelian permutation symmetry. Such symmetry can be hidden in states with defined total spins of spinor gases, which can be formed in optical cavities. The present work shows that the symmetry reveals itself in spin-independent or coordinate-independent properties of these gases, namely as non-Abelian entropy in thermodynamic properties. In weakly interacting Fermi gases, two phases appear associated with fermionic and non-Abelian symmetry under permutations of particle states, respectively. The second-order transitions between the phases are characterized by discontinuities in specific heat. Unlike other phase transitions, the present ones are not caused by interactions and can appear even in ideal gases. Similar effects in Bose gases and strong interactions are discussed.

Experimental and simulated beam-foil decay curves for some transitions in Zn II

International Nuclear Information System (INIS)

Hultberg, S.; Liljeby, L.; Mannervik, S.; Veje, E.; Lindgaard, A.

1980-01-01

Experimental beam-foil decay curves for the 4s-4p, 4p-4d, 4d-4f, and the 4p-5s transitions in Zn II are compared to decay curves synthesized from transition probabilities calculated in the numerical Coulomb approximation and either measured initial level populations or population models. Good agreement exists between experimental curves and those based on the measured initial level populations for the 5s, 4d, and 4f levels while certain deviations are noted for the 4p term. None of the applied population models reproduce all experimental curves satisfyingly well. In addition, lifetimes are determined experimentally for 7 terms in Zn II, and good agreement with the numerical Coulomb approximation lifetimes is generally found except for some p terms. Beam-foil excitation-mechanism results for zinc are presented and compared to previous results from light projectiles. (Auth.)

Spinning particle approach to higher spin field theory

International Nuclear Information System (INIS)

Corradini, Olindo

2011-01-01

We shortly review on the connection between higher-spin gauge field theories and supersymmetric spinning particle models. In such approach the higher spin equations of motion are linked to the first-class constraint algebra associated with the quantization of particle models. Here we consider a class of spinning particle models characterized by local O(N)-extended supersymmetry since these models are known to provide an alternative approach to the geometric formulation of higher spin field theory. We describe the canonical quantization of the models in curved target space and discuss the obstructions that appear in presence of an arbitrarily curved background. We then point out the special role that conformally flat spaces appear to have in such models and present a derivation of the higher-spin curvatures for maximally symmetric spaces.

Anderson Transition of Cold Atoms with Synthetic Spin-Orbit Coupling in Two-Dimensional Speckle Potentials

Science.gov (United States)

Orso, Giuliano

2017-03-01

We investigate the metal-insulator transition occurring in two-dimensional (2D) systems of noninteracting atoms in the presence of artificial spin-orbit interactions and a spatially correlated disorder generated by laser speckles. Based on a high order discretization scheme, we calculate the precise position of the mobility edge and verify that the transition belongs to the symplectic universality class. We show that the mobility edge depends strongly on the mixing angle between Rashba and Dresselhaus spin-orbit couplings. For equal couplings a non-power-law divergence is found, signaling the crossing to the orthogonal class, where such a 2D transition is forbidden.

Mean-Field Studies of a Mixed Spin-3/2 and Spin-2 and a Mixed Spin-3/2 and Spin-5/2 Ising System with Different Anisotropies

International Nuclear Information System (INIS)

Wei Guozhu; Miao Hailing

2009-01-01

The magnetic properties of a mixed spin-3/2 and spin-2 and a mixed spin-3/2 and spin-5/2 Ising ferromagnetic system with different anisotropies are studied by means of mean-field theory (MFT). The dependence of the phase diagram on single-ion anisotropy strengths is studied too. In the mixed spin-3/2 and spin-2 Ising model, besides the second-order phase transition, the first order-disorder phase transition and the tricritical line are found. In the mixed spin-3/2 and spin-5/2 Ising model, there is no first-order transition and tricritical line. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

k-asymmetric spin splitting at the interface between transition metal ferromagnets and heavy metals

KAUST Repository

Grytsiuk, Sergii

2016-05-23

We systematically investigate the spin-orbit coupling-induced band splitting originating from inversion symmetry breaking at the interface between a Co monolayer and 4d (Tc, Ru, Rh, Pd, and Ag) or 5d (Re, Os, Ir, Pt, and Au) transition metals. In spite of the complex band structure of these systems, the odd-in-k spin splitting of the bands displays striking similarities with the much simpler Rashba spin-orbit coupling picture. We establish a clear connection between the overall strength of the odd-in-k spin splitting of the bands and the charge transfer between the d orbitals at the interface. Furthermore, we show that the spin splitting of the Fermi surface scales with the induced orbital moment, weighted by the spin-orbit coupling.

k-asymmetric spin splitting at the interface between transition metal ferromagnets and heavy metals

KAUST Repository

Grytsyuk, Sergiy; Belabbes, Abderrezak; Haney, Paul M.; Lee, Hyun-Woo; Lee, Kyung-Jin; Stiles, M. D.; Schwingenschlö gl, Udo; Manchon, Aurelien

2016-01-01

We systematically investigate the spin-orbit coupling-induced band splitting originating from inversion symmetry breaking at the interface between a Co monolayer and 4d (Tc, Ru, Rh, Pd, and Ag) or 5d (Re, Os, Ir, Pt, and Au) transition metals. In spite of the complex band structure of these systems, the odd-in-k spin splitting of the bands displays striking similarities with the much simpler Rashba spin-orbit coupling picture. We establish a clear connection between the overall strength of the odd-in-k spin splitting of the bands and the charge transfer between the d orbitals at the interface. Furthermore, we show that the spin splitting of the Fermi surface scales with the induced orbital moment, weighted by the spin-orbit coupling.

Low to High Spin-State Transition Induced by Charge Ordering in Antiferromagnetic YBaCo2O5

International Nuclear Information System (INIS)

Vogt, T.; Woodward, P. M.; Karen, P.; Hunter, B. A.; Henning, P.; Moodenbaugh, A. R.

2000-01-01

The oxygen-deficient double perovskite YBaCo 2 O 5 , containing corner-linked CoO 5 square pyramids as principal building units, undergoes a paramagnetic to antiferromagnetic spin ordering at 330 K. This is accompanied by a tetragonal to orthorhombic distortion. Below 220 K orbital ordering and long-range Co 2+ /Co 3+ charge ordering occur as well as a change in the Co 2+ spin state from low to high spin. This transition is shown to be very sensitive to the oxygen content of the sample. To our knowledge this is the first observation of a spin-state transition induced by long-range orbital and charge ordering. (c) 2000 The American Physical Society

Spin-Polarization-Induced Preedge Transitions in the Sulfur K-Edge XAS Spectra of Open-Shell Transition-Metal Sulfates: Spectroscopic Validation of σ-Bond Electron Transfer.

Science.gov (United States)

Frank, Patrick; Szilagyi, Robert K; Gramlich, Volker; Hsu, Hua-Fen; Hedman, Britt; Hodgson, Keith O

2017-02-06

Sulfur K-edge X-ray absorption spectroscopy (XAS) spectra of the monodentate sulfate complexes [M II (itao)(SO 4 )(H 2 O) 0,1 ] (M = Co, Ni, Cu) and [Cu(Me 6 tren)(SO 4 )] exhibit well-defined preedge transitions at 2479.4, 2479.9, 2478.4, and 2477.7 eV, respectively, despite having no direct metal-sulfur bond, while the XAS preedge of [Zn(itao)(SO 4 )] is featureless. The sulfur K-edge XAS of [Cu(itao)(SO 4 )] but not of [Cu(Me 6 tren)(SO 4 )] uniquely exhibits a weak transition at 2472.1 eV, an extraordinary 8.7 eV below the first inflection of the rising K-edge. Preedge transitions also appear in the sulfur K-edge XAS of crystalline [M II (SO 4 )(H 2 O)] (M = Fe, Co, Ni, and Cu, but not Zn) and in sulfates of higher-valent early transition metals. Ground-state density functional theory (DFT) and time-dependent DFT (TDDFT) calculations show that charge transfer from coordinated sulfate to paramagnetic late transition metals produces spin polarization that differentially mixes the spin-up (α) and spin-down (β) spin orbitals of the sulfate ligand, inducing negative spin density at the sulfate sulfur. Ground-state DFT calculations show that sulfur 3p character then mixes into metal 4s and 4p valence orbitals and various combinations of ligand antibonding orbitals, producing measurable sulfur XAS transitions. TDDFT calculations confirm the presence of XAS preedge features 0.5-2 eV below the rising sulfur K-edge energy. The 2472.1 eV feature arises when orbitals at lower energy than the frontier occupied orbitals with S 3p character mix with the copper(II) electron hole. Transmission of spin polarization and thus of radical character through several bonds between the sulfur and electron hole provides a new mechanism for the counterintuitive appearance of preedge transitions in the XAS spectra of transition-metal oxoanion ligands in the absence of any direct metal-absorber bond. The 2472.1 eV transition is evidence for further radicalization from copper(II), which

Statistics from dynamics in curved spacetime

International Nuclear Information System (INIS)

Parker, L.; Wang, Y.

1989-01-01

We consider quantum fields of spin 0, 1/2, 1, 3/2, and 2 with a nonzero mass in curved spacetime. We show that the dynamical Bogolubov transformations associated with gravitationally induced particle creation imply the connection between spin and statistics: By embedding two flat regions in a curved spacetime, we find that only when one imposes Bose-Einstein statistics for an integer-spin field and Fermi-Dirac statistics for a half-integer-spin field in the first flat region is the same type of statistics propagated from the first to the second flat region. This derivation of the flat-spacetime spin-statistics theorem makes use of curved-spacetime dynamics and does not reduce to any proof given in flat spacetime. We also show in the same manner that parastatistics, up to the fourth order, are consistent with the dynamical evolution of curved spacetime

Spin-glass-like transition in the majority-vote model with anticonformists

Science.gov (United States)

Krawiecki, Andrzej

2018-03-01

Majority-vote model on scale-free networks and random graphs is investigated in which a randomly chosen fraction p of agents (called anticonformists) follows an antiferromagnetic update rule, i.e., they assume, with probability governed by a parameter q (0 transition from a disordered (paramagnetic) state to a spin-glass-like state, characterized by a non-zero value of the spin-glass order parameter measuring the overlap of agents' opinions in two replicas of the system, and simultaneously by the magnetization close to zero. In the case of the model on scale-free networks the critical value of the parameter q weakly depends on the details of the degree distribution. As p is decreased, the critical value of q falls quickly to zero and only the disordered phase is observed. On the other hand, for p close to zero for decreasing q the usual ferromagnetic transition is observed.

Searching for transits in the WTS with the difference imaging light curves

Science.gov (United States)

Zendejas Dominguez, Jesus

2013-12-01

The search for exo-planets is currently one of the most exiting and active topics in astronomy. Small and rocky planets are particularly the subject of intense research, since if they are suitably located from their host star, they may be warm and potentially habitable worlds. On the other hand, the discovery of giant planets in short-period orbits provides important constraints on models that describe planet formation and orbital migration theories. Several projects are dedicated to discover and characterize planets outside of our solar system. Among them, the Wide-Field Camera Transit Survey (WTS) is a pioneer program aimed to search for extra-solar planets, that stands out for its particular aims and methodology. The WTS has been in operation since August 2007 with observations from the United Kingdom Infrared Telescope, and represents the first survey that searches for transiting planets in the near-infrared wavelengths; hence the WTS is designed to discover planets around M-dwarfs. The survey was originally assigned about 200 nights, observing four fields that were selected seasonally (RA = 03, 07, 17 and 19h) during a year. The images from the survey are processed by a data reduction pipeline, which uses aperture photometry to construct the light curves. For the most complete field (19h-1145 epochs) in the survey, we produce an alternative set of light curves by using the method of difference imaging, which is a photometric technique that has shown important advantages when used in crowded fields. A quantitative comparison between the photometric precision achieved with both methods is carried out in this work. We remove systematic effects using the sysrem algorithm, scale the error bars on the light curves, and perform a comparison of the corrected light curves. The results show that the aperture photometry light curves provide slightly better precision for objects with J detect transits in the WTS light curves, we use a modified version of the box

Searching for transits in the Wide Field Camera Transit Survey with difference-imaging light curves

NARCIS (Netherlands)

Zendejas, Dominguez J.; Koppenhoefer, J.; Saglia, R.; Birkby, J.L.; Hodgkin, S.; Kovács, G.; Pinfield, D.; Sipocz, B.; Barrado, D.; Bender, R.; Burgo, del C.; Cappetta, M.; Martín, E.; Nefs, B.; Riffeser, A.; Steele, P.

2013-01-01

The Wide Field Camera Transit Survey is a pioneer program aiming at for searching extra-solar planets in the near-infrared. The images from the survey are processed by a data reduction pipeline, which uses aperture photometry to construct the light curves. We produce an alternative set of light

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

International Nuclear Information System (INIS)

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

2007-01-01

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

Orbital occupancy evolution across spin- and charge-ordering transitions in YBaFe2O5

Science.gov (United States)

Lindén, J.; Lindroos, F.; Karen, P.

2017-08-01

Thermal evolution of the Fe2+-Fe3+ valence mixing in YBaFe2O5 is investigated using Mössbauer spectroscopy. In this high-spin double-cell perovskite, the d6 and d5 Fe states differ by the single minority-spin electron which then controls all the spin- and charge-ordering transitions. Orbital occupancies can be extracted from the spectra in terms of the dxz , dz2 and either dx2-y2 (Main Article) or dxy (Supplement) populations of this electron upon conserving its angular momentum. At low temperatures, the minority-spin electrons fill up the ordered dxz orbitals of Fe2+, in agreement with the considerable orthorhombic distortion of the structure. Heating through the Verwey transition supplies 93% of the mixing entropy, at which point the predominantly mixing electron occupies mainly the dx2-y2 /dxy orbitals weakly bonding the two Fe atoms that face each other across the bases of their coordination pyramids. This might stabilize a weak coulombic checkerboard order suggested by McQueeney et alii in Phys. Rev. B 87(2013)045127. When the remaining 7% of entropy is supplied at a subsequent transition, the mixing electron couples the two Fe atoms predominantly via their dz2 orbitals. The valence mixing concerns more than 95% of the Fe atoms present in the crystalline solid; the rest is semi-quantitatively interpreted as domain walls and antiphase boundaries formed upon cooling through the Néel and Verwey-transition temperatures, respectively.

Marginalizing Instrument Systematics in HST WFC3 Transit Light Curves

Science.gov (United States)

Wakeford, H. R.; Sing, D. K.; Evans, T.; Deming, D.; Mandell, A.

2016-03-01

Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) infrared observations at 1.1-1.7 μm probe primarily the H2O absorption band at 1.4 μm, and have provided low-resolution transmission spectra for a wide range of exoplanets. We present the application of marginalization based on Gibson to analyze exoplanet transit light curves obtained from HST WFC3 to better determine important transit parameters such as Rp/R*, which are important for accurate detections of H2O. We approximate the evidence, often referred to as the marginal likelihood, for a grid of systematic models using the Akaike Information Criterion. We then calculate the evidence-based weight assigned to each systematic model and use the information from all tested models to calculate the final marginalized transit parameters for both the band-integrated and spectroscopic light curves to construct the transmission spectrum. We find that a majority of the highest weight models contain a correction for a linear trend in time as well as corrections related to HST orbital phase. We additionally test the dependence on the shift in spectral wavelength position over the course of the observations and find that spectroscopic wavelength shifts {δ }λ (λ ) best describe the associated systematic in the spectroscopic light curves for most targets while fast scan rate observations of bright targets require an additional level of processing to produce a robust transmission spectrum. The use of marginalization allows for transparent interpretation and understanding of the instrument and the impact of each systematic evaluated statistically for each data set, expanding the ability to make true and comprehensive comparisons between exoplanet atmospheres.

Spin canting and magnetic transition in NixZn1-xFe2O4 (x=0.0, 0.5 and 1.0) nanoparticles

Science.gov (United States)

Rani, Stuti; Raghav, Dharmendra Singh; Yadav, Prashant; Varma, G. D.

2018-04-01

Nanoparticles of NixZn1-xFe2O4(x=0.0, 0.5 and 1.0) have been synthesized via co-precipitation method and studied thestructural and magnetic properties. Rietveld refinement of X ray diffraction data of as synthesized samples revealthat the samples have mixed spinel structure with space group Fd-3m. The lattice parameter of the samples decreases as doping concentration of Ni ions increases. Magnetic measurements show paramagnetic to ferrimagnetic transition at room temperature on Ni doping in ZnFe2O4 nanoparticles. The magnetic measurements also show spin canting in samples possibly due to their nanocrystalline nature. The spin canting angles have been calculated with the help of Yafet-Kittel (Y-K) model. Furthermore, the Law of approach (LA) fitting of M-H curves indicates that the samples are highly anisotropicin nature. The Arrot plots of as synthesized samples also indicate the paramagnetic to ferrimagnetic transition. The correlation between the structural and observed magnetic properties of NixZn1-xFe2O4(x=0.0, 0.5 and 1.0) nanocrystals will be described and discussed in this paper.

Quantum discord and quantum phase transition in spin chains

OpenAIRE

Dillenschneider, Raoul

2008-01-01

Quantum phase transitions of the transverse Ising and antiferromagnetic XXZ spin S=1/2 chains are studied using quantum discord. Quantum discord allows the measure of quantum correlations present in many-body quantum systems. It is shown that the amount of quantum correlations increases close to the critical points. The observations are in agreement with the information provided by the concurrence which measures the entanglement of the many-body system.

The light-induced spin transition of tetranuclear spin crossover complex [Fe4(CN)4(bpy)4(tpa)2](PF6)4

International Nuclear Information System (INIS)

Nishihara, T; Tanaka, K; Nihei, M; Oshio, H

2009-01-01

We report on the light induced spin transition in the tetranuclear spin crossover complex [Fe 4 (CN) 4 (bpy) 4 (tpa) 2 ](PF 6 ) 4 . The photo-conversion occurs at the specific site (Fe2) of four Fe II ions. The red light irradiation (1.79 eV) gives rise to full conversion of Fe2 into the high spin state from the low spin state. The green light irradiation (2.33 eV) can convert only the half of Fe2 into the high spin state, though the photo-conversion rate in the beginning is much higher than that with the red light. We present a simple model in which the photo-conversion kinetics is controlled by a large background absorption due to remaining three Fe II ions (Fe1, Fe3 and Fe4).

Spin-polarized spin excitation spectroscopy

International Nuclear Information System (INIS)

Loth, Sebastian; Lutz, Christopher P; Heinrich, Andreas J

2010-01-01

We report on the spin dependence of elastic and inelastic electron tunneling through transition metal atoms. Mn, Fe and Cu atoms were deposited onto a monolayer of Cu 2 N on Cu(100) and individually addressed with the probe tip of a scanning tunneling microscope. Electrons tunneling between the tip and the substrate exchange energy and spin angular momentum with the surface-bound magnetic atoms. The conservation of energy during the tunneling process results in a distinct onset threshold voltage above which the tunneling electrons create spin excitations in the Mn and Fe atoms. Here we show that the additional conservation of spin angular momentum leads to different cross-sections for spin excitations depending on the relative alignment of the surface spin and the spin of the tunneling electron. For this purpose, we developed a technique for measuring the same local spin with a spin-polarized and a non-spin-polarized tip by exchanging the last apex atom of the probe tip between different transition metal atoms. We derive a quantitative model describing the observed excitation cross-sections on the basis of an exchange scattering process.

Photoinduced Coherent Spin Fluctuation in Primary Dynamics of Insulator to Metal Transition in Perovskite Cobalt Oxide

Directory of Open Access Journals (Sweden)

Arima T.

2013-03-01

Full Text Available Coherent spin fluctuation was detected in the photoinduced Mott insulator-metal transition in perovskite cobalt oxide by using 3 optical-cycle infrared pulse. Such coherent spin fluctuation is driven by the perovskite distortion changing orbital gap.

The urban health transition hypothesis: empirical evidence of an avian influenza Kuznets curve in Vietnam?

Science.gov (United States)

Spencer, James Herbert

2013-04-01

The literature on development has focused on the concept of transition in understanding the emergent challenges facing poor but rapidly developing countries. Scholars have focused extensively on the health and urban transitions associated with this change and, in particular, its use for understanding emerging infectious diseases. However, few have developed explicit empirical measures to quantify the extent to which a transitions focus is useful for theory, policy, and practice. Using open source data on avian influenza in 2004 and 2005 and the Vietnam Census of Population and Housing, this paper introduces the Kuznets curve as a tool for empirically estimating transition and disease. Findings suggest that the Kuznets curve is a viable tool for empirically assessing the role of transitional dynamics in the emergence of new infectious diseases.

STELLAR TRANSITS IN ACTIVE GALACTIC NUCLEI

International Nuclear Information System (INIS)

Béky, Bence; Kocsis, Bence

2013-01-01

Supermassive black holes (SMBHs) are typically surrounded by a dense stellar population in galactic nuclei. Stars crossing the line of site in active galactic nuclei (AGNs) produce a characteristic transit light curve, just like extrasolar planets do when they transit their host star. We examine the possibility of finding such AGN transits in deep optical, UV, and X-ray surveys. We calculate transit light curves using the Novikov-Thorne thin accretion disk model, including general relativistic effects. Based on the expected properties of stellar cusps, we find that around 10 6 solar mass SMBHs, transits of red giants are most common for stars on close orbits with transit durations of a few weeks and orbital periods of a few years. We find that detecting AGN transits requires repeated observations of thousands of low-mass AGNs to 1% photometric accuracy in optical, or ∼10% in UV bands or soft X-ray. It may be possible to identify stellar transits in the Pan-STARRS and LSST optical and the eROSITA X-ray surveys. Such observations could be used to constrain black hole mass, spin, inclination, and accretion rate. Transit rates and durations could give valuable information on the circumnuclear stellar clusters as well. Transit light curves could be used to image accretion disks with unprecedented resolution, allowing us to resolve the SMBH silhouette in distant AGNs.

Disentanglement of two qubits coupled to an XY spin chain: Role of quantum phase transition

International Nuclear Information System (INIS)

Yuan Zigang; Li Shushen; Zhang Ping

2007-01-01

We study the disentanglement evolution of two spin qubits which interact with a general XY spin-chain environment. The dynamical process of the disentanglement is numerically and analytically investigated in the vicinity of a quantum phase transition (QPT) of the spin chain in both weak and strong coupling cases. We find that the disentanglement of the two spin qubits may be greatly enhanced by the quantum critical behavior of the environmental spin chain. We give a detailed analysis to facilitate the understanding of the QPT-enhanced decaying behavior of the coherence factor. Furthermore, the scaling behavior in the disentanglement dynamics is also revealed and analyzed

Isotope enrichment by electron spin resonance transitions of the intermediate radical pair

International Nuclear Information System (INIS)

Okazaki, M.; Shiga, T.; Sakata, S.; Konaka, R.; Toriyama, K.

1988-01-01

Microwave effects on the spin adduct yield were observed in the photoreduction of menadione in micellar solutions with ordinary sodium dodecyl sulfate (SDS), deuterium-labeled SDS, and a mixture of them. A large isotope effect was found in the microwave modulation of the spin adduct yield, which is due to the ESR transitions of the transient radical pair in the reaction. It is demonstrated for the first time that the microwave field can be used to enrich one of the isotopes which coexist in the system

Many-body localization-delocalization transition in the quantum Sherrington-Kirkpatrick model

Science.gov (United States)

Mukherjee, Sudip; Nag, Sabyasachi; Garg, Arti

2018-04-01

We analyze the many-body localization- (MBL) to-delocalization transition in the Sherrington-Kirkpatrick (SK) model of Ising spin glass in the presence of a transverse field Γ . Based on energy-resolved analysis, which is of relevance for a closed quantum system, we show that the quantum SK model has many-body mobility edges separating the MBL phase, which is nonergodic and nonthermal, from the delocalized phase, which is ergodic and thermal. The range of the delocalized regime increases with an increase in the strength of Γ , and eventually for Γ larger than ΓCP the entire many-body spectrum is delocalized. We show that the Renyi entropy is almost independent of the system size in the MBL phase while the delocalized phase shows extensive Renyi entropy. We further obtain the spin-glass transition curve in the energy density ɛ -Γ plane from the collapse of the eigenstate spin susceptibility. We demonstrate that in most of the parameter regime, the spin-glass transition occurs close to the MBL transition, indicating that the spin-glass phase is nonergodic and nonthermal while the paramagnetic phase is delocalized and thermal.

Evidence for reentrant spin glass behavior in transition metal substituted Co-Ga alloys near critical concentration

Science.gov (United States)

Yasin, Sk. Mohammad; Srinivas, V.; Kasiviswanathan, S.; Vagadia, Megha; Nigam, A. K.

2018-04-01

In the present study magnetic and electrical transport properties of transition metal substituted Co-Ga alloys (near critical cobalt concentration) have been investigated. Analysis of temperature and field dependence of dc magnetization and ac susceptibility (ACS) data suggests an evidence of reentrant spin glass (RSG) phase in Co55.5TM3Ga41.5 (TM = Co, Cr, Fe, Cu). The magnetic transition temperatures (TC and Tf) are found to depend on the nature of TM element substitution with the exchange coupling strength Co-Fe > Co-Co > Co-Cu > Co-Cr. From magnetization dynamics precise transition temperatures for the glassy phases are estimated. It is found that characteristic relaxation times are higher than that of spin glasses with minimal spin-cluster formation. The RSG behavior has been further supported by the temperature dependence of magnetotransport studies. From the magnetic field and substitution effects it has been established that the magnetic and electrical transport properties are correlated in this system.

Signatures for isoscalar spin transitions excited in (d, d,) reactions

International Nuclear Information System (INIS)

Morlet, M.; Willis, A.; Van de Wiele, J.; Marty, N.; Guillot, J.; Langevin-Joliot, H.; Bimbot, L.; Rosier, L.; Djalali, C.; Duchazeaubeneix, J.C.

1990-01-01

Three different signatures for isoscalar spin transitions in nuclei have been tested in the 12 C(d, d , ) 12 C reaction at 400 MeV. These signatures have values of close to zero for the natural parity states, and values ranging from 0.22 to 0.50 for the ΔS=1 ΔT=0, 12.7 MeV state

Quantum phase transitions in effective spin-ladder models for graphene zigzag nanoribbons

Science.gov (United States)

Koop, Cornelie; Wessel, Stefan

2017-10-01

We examine the magnetic correlations in quantum spin models that were derived recently as effective low-energy theories for electronic correlation effects on the edge states of graphene nanoribbons. For this purpose, we employ quantum Monte Carlo simulations to access the large-distance properties, accounting for quantum fluctuations beyond mean-field-theory approaches to edge magnetism. For certain chiral nanoribbons, antiferromagnetic interedge couplings were previously found to induce a gapped quantum disordered ground state of the effective spin model. We find that the extended nature of the intraedge couplings in the effective spin model for zigzag nanoribbons leads to a quantum phase transition at a large, finite value of the interedge coupling. This quantum critical point separates the quantum disordered region from a gapless phase of stable edge magnetism at weak intraedge coupling, which includes the ground states of spin-ladder models for wide zigzag nanoribbons. To study the quantum critical behavior, the effective spin model can be related to a model of two antiferromagnetically coupled Haldane-Shastry spin-half chains with long-ranged ferromagnetic intrachain couplings. The results for the critical exponents are compared also to several recent renormalization-group calculations for related long-ranged interacting quantum systems.

Superconductor to spin-density-wave transition in quasi-one-dimensional metals with repulsive anisotropic interaction

International Nuclear Information System (INIS)

Rozhkov, A.V.

2007-01-01

A mechanism for superconductivity in a quasi-one-dimensional system with repulsive Ising-anisotropic interaction is studied. The Ising anisotropy opens the gap Δ s in the spin sector of the model. This gap allows the triplet superconductivity and the spin-density wave as the only broken symmetry phases. These phases are separated by the first order transition. The transport properties of the system are investigated in different parts of the phase diagram. The calculation of DC conductivity σ(T) in the high-temperature phase shows that the function σ(T) cannot be used as an indicator of a superconducting ground state: even if σ(T) is a decreasing function at high temperature, yet, the ground state may be insulating spin-density wave; the opposite is also true. The calculation of the spin dynamical structure factor S zz (q, ω) demonstrates that it is affected by the superconducting phase transition in a qualitative fashion: below T c the structure factor develops a gap with a coherent excitation inside this gap

Lattice architecture effect on the cooperativity of spin transition coordination polymers

Energy Technology Data Exchange (ETDEWEB)

Chiruta, Daniel [Faculty of Electrical Engineering and Computer Science and Advanced Materials and Nanotechnology Laboratory (AMNOL), Ştefan cel Mare University, Suceava 720229 (Romania); GEMaC, Université de Versailles Saint-Quentin-en-Yvelines, CNRS-UVSQ (UMR 8635), 78035 Versailles Cedex (France); LISV, Université de Versailles Saint-Quentin-en-Yvelines, 78140 Velizy (France); Jureschi, Catalin-Maricel; Rotaru, Aurelian, E-mail: jorge.linares@uvsq.fr, E-mail: rotaru@eed.usv.ro [Faculty of Electrical Engineering and Computer Science and Advanced Materials and Nanotechnology Laboratory (AMNOL), Ştefan cel Mare University, Suceava 720229 (Romania); Linares, Jorge, E-mail: jorge.linares@uvsq.fr, E-mail: rotaru@eed.usv.ro [GEMaC, Université de Versailles Saint-Quentin-en-Yvelines, CNRS-UVSQ (UMR 8635), 78035 Versailles Cedex (France); Garcia, Yann [Institute of Condensed Matter and Nanosciences, Molecules, Solids and Reactivity (IMCN/MOST), Université Catholique de Louvain, Place L. Pasteur, 1, 1348 Louvain-la-Neuve (Belgium)

2014-02-07

We have investigated in the framework of the Ising-like model, by means of Monte Carlo Metropolis method with open boundary condition, the architecture effect on the cooperativity of spin transition coordination polymers. We have analyzed the influence of several physical parameters (size, pressure, and edge effects) on different lattice architectures which were in good agreement with reported experimental data. We show that the cooperativity of a spin crossover system, characterized by the same number of molecules and the same short- and long-range interaction parameters, is progressively enhanced when going from a 1D chain to a 1D ladder type lattice and to a 2D square lattice.

Study of transitional Erbium nuclei (N=86) at very high spin. Highlight of dipolar transitions and medium livetimes in the continuum

International Nuclear Information System (INIS)

Bogaert, G.

1984-01-01

Average lifetimes and multipolarities of unresolved transitions deexciting very high spin states of the light Rare Earth nuclei (N approximately 86) have been determined by a measure of Doppler shift attenuation and their anisotropy. The spin selection is provided by the total energy spectrometer technique; great care was taken of the existence of many long lived isomeric states in the studied nuclei. The N approximately 86 nuclei have been formed in the 84 Kr(340 MeV) + 74 Ge → 158 Er* reactions using the 84 Kr beam of the Orsay ALICE facilities and targets of 74 Ge built at the PARIS Isotope separator of the CSNSM. NaI γ spectra have been thoroughly cleared of the discrete lines contribution through a carefull subtraction procedure synthetising NaI spectra from the Ge ones. At very high spin the continuum γ rays feed two well separated bumps with Esub(γ) approximately .65 MeV and Esub(γ) approximately 1.3 MeV. The 1.3 MeV transitions appear at I > 30 h and their energy does not vary with the increasing spin like expected in the rotational case of the well deformed nuclei; they are strongly collectively enhanced with B(E2) > 130 W.u. Below 1 MeV the anisotropy of transitions is R approximately 0.7, indicating their stretched dipole nature. Recent calculations of nuclear shape deformation (following Strutinsky shell correction method) reproduce the two bumps shape of the experimental spectra and the origin of the excitation is explained in terms of nuclear vibration (γ-vibration, wobbling motion) [fr

A Study of the Spin-State Transition and Phase Transformation in [Fe(bpp)(2)][CF(3)SO(3)](2).H(2)O and [Fe(bpp)(2)][BF(4)](2) Using Mn(2+) Electron Spin Resonance.

Science.gov (United States)

Sung, Raymond C. W.; McGarvey, Bruce R.

1999-08-09

X-band ESR powder studies have been done on the spin transition in Mn(2+)-doped [Fe(bpp)(2)][CF(3)SO(3)](2).H(2)O and [Fe(bpp)(2)][BF(4)](2) (bpp = 2,6-bis(pyrazol-3-yl) pyridine). The change in D value of Mn(2+) during the thermally induced high-spin (HS) low-spin (LS) transition shows that the spin transition is accompanied by a phase transformation involving a domain mechanism. Irradiation experiments at 77 K have shown that a LS --> HS spin change occurs without a change in the crystalline phase. The rate of the change from the HS phase to the LS phase in the vicinity of 100 K has been measured and is found to be the same as that measured for the corresponding spin change obtained from Mössbauer spectroscopy and magnetic susceptibility studies.

Role of nuclear penetration effects in spin assignments. [J, transitions, internal conversion

Energy Technology Data Exchange (ETDEWEB)

Sahota, H S [Punjabi Univ., Patiala (India). Dept. of Physics

1976-04-01

Nuclear penetrations have been found to affect the internal conversion process of the retarded magnetic dipole transitions. In all cases where the penetration coefficient has been found to be essentially different from unity the transition is 1-forbidden. This criterian has been applied to the case of 191 keV transition in /sup 197/Au where the spin of the 268 keV level could not be deduced uniquely by any of the existing methods. The result is that the 199 keV transition has a dynamic contribution to its internal conversion process with the penetration coefficient lambda = 5.5 +- 0.9. To illustrate the applicability of the criterian further two more cases namely that of the 92 keV transition in /sup 131/Cs and 182 keV transition in /sup 129/Cs are also included.

Phase Transition in the Density of States of Quantum Spin Glasses

Energy Technology Data Exchange (ETDEWEB)

Erdős, László, E-mail: lerdos@ist.ac.at [IST Austria (Austria); Schröder, Dominik, E-mail: schroeder.dominik@gmail.com [Ludwig-Maximilians-Universität München (Germany)

2014-12-15

We prove that the empirical density of states of quantum spin glasses on arbitrary graphs converges to a normal distribution as long as the maximal degree is negligible compared with the total number of edges. This extends the recent results of Keating et al. (2014) that were proved for graphs with bounded chromatic number and with symmetric coupling distribution. Furthermore, we generalise the result to arbitrary hypergraphs. We test the optimality of our condition on the maximal degree for p-uniform hypergraphs that correspond to p-spin glass Hamiltonians acting on n distinguishable spin- 1/2 particles. At the critical threshold p = n{sup 1/2} we find a sharp classical-quantum phase transition between the normal distribution and the Wigner semicircle law. The former is characteristic to classical systems with commuting variables, while the latter is a signature of noncommutative random matrix theory.

Inter-cluster coupling effects in high-spin molecular magnets

International Nuclear Information System (INIS)

Affronte, M.; Lasjaunias, J.C.; Wernsdorfer, W.; Sessoli, R.; Gatteschi, D.; Heath, S.L.; Fort, A.; Rettori, A.

2004-01-01

We report evidences of antiferromagnetic (AF) transition in Fe 19 metheidi, a new molecular nanomagnet with a total spin S=((33)/(2)), among the highest known so far. The temperature (T) dependence of specific heat (C) shows a λ-anomaly at 1.19 K and at the same temperature an anomaly is also observed in the low field (B<0.12 T) magnetization M-vs.-T curves. Since the dipolar interaction between clusters is estimated to be ∼190 mK, the origin of the AF transition is probably due to superexchange

Inter-cluster coupling effects in high-spin molecular magnets

Energy Technology Data Exchange (ETDEWEB)

Affronte, M.; Lasjaunias, J.C.; Wernsdorfer, W.; Sessoli, R.; Gatteschi, D.; Heath, S.L.; Fort, A. E-mail: fort@fi.infn.it; Rettori, A

2004-05-01

We report evidences of antiferromagnetic (AF) transition in Fe{sub 19}metheidi, a new molecular nanomagnet with a total spin S=((33)/(2)), among the highest known so far. The temperature (T) dependence of specific heat (C) shows a {lambda}-anomaly at 1.19 K and at the same temperature an anomaly is also observed in the low field (B<0.12 T) magnetization M-vs.-T curves. Since the dipolar interaction between clusters is estimated to be {approx}190 mK, the origin of the AF transition is probably due to superexchange.

The ferromagnetic-spin glass transition in PdMn alloys: symmetry breaking of ferromagnetism and spin glass studied by a multicanonical method.

Science.gov (United States)

Kato, Tomohiko; Saita, Takahiro

2011-03-16

The magnetism of Pd(1-x)Mn(x) is investigated theoretically. A localized spin model for Mn spins that interact with short-range antiferromagnetic interactions and long-range ferromagnetic interactions via itinerant d electrons is set up, with no adjustable parameters. A multicanonical Monte Carlo simulation, combined with a procedure of symmetry breaking, is employed to discriminate between the ferromagnetic and spin glass orders. The transition temperature and the low-temperature phase are determined from the temperature variation of the specific heat and the probability distributions of the ferromagnetic order parameter and the spin glass order parameter at different concentrations. The calculation results reveal that only the ferromagnetic phase exists at x glass phase exists at x > 0.04, and that the two phases coexist at intermediate concentrations. This result agrees semi-quantitatively with experimental results.

Unifying Exchange Sensitivity in Transition-Metal Spin-State Ordering and Catalysis through Bond Valence Metrics.

Science.gov (United States)

Gani, Terry Z H; Kulik, Heather J

2017-11-14

Accurate predictions of spin-state ordering, reaction energetics, and barrier heights are critical for the computational discovery of open-shell transition-metal (TM) catalysts. Semilocal approximations in density functional theory, such as the generalized gradient approximation (GGA), suffer from delocalization error that causes them to overstabilize strongly bonded states. Descriptions of energetics and bonding are often improved by introducing a fraction of exact exchange (e.g., erroneous low-spin GGA ground states are instead correctly predicted as high-spin with a hybrid functional). The degree of spin-splitting sensitivity to exchange can be understood based on the chemical composition of the complex, but the effect of exchange on reaction energetics within a single spin state is less well-established. Across a number of model iron complexes, we observe strong exchange sensitivities of reaction barriers and energies that are of the same magnitude as those for spin splitting energies. We rationalize trends in both reaction and spin energetics by introducing a measure of delocalization, the bond valence of the metal-ligand bonds in each complex. The bond valence thus represents a simple-to-compute property that unifies understanding of exchange sensitivity for catalytic properties and spin-state ordering in TM complexes. Close agreement of the resulting per-metal-organic-bond sensitivity estimates, together with failure of alternative descriptors demonstrates the utility of the bond valence as a robust descriptor of how differences in metal-ligand delocalization produce differing relative energetics with exchange tuning. Our unified description explains the overall effect of exact exchange tuning on the paradigmatic two-state FeO + /CH 4 reaction that combines challenges of spin-state and reactivity predictions. This new descriptor-sensitivity relationship provides a path to quantifying how predictions in transition-metal complex screening are sensitive to the

Pressure variation of Rashba spin splitting toward topological transition in the polar semiconductor BiTeI

Science.gov (United States)

Ideue, T.; Checkelsky, J. G.; Bahramy, M. S.; Murakawa, H.; Kaneko, Y.; Nagaosa, N.; Tokura, Y.

2014-10-01

BiTeI is a polar semiconductor with gigantic Rashba spin-split bands in bulk. We have investigated the effect of pressure on the electronic structure of this material via magnetotransport. Periods of Shubunikov-de Haas (SdH) oscillations originating from the spin-split outer Fermi surface and inner Fermi surface show disparate responses to pressure, while the carrier number derived from the Hall effect is unchanged with pressure. The associated parameters which characterize the spin-split band structure are strongly dependent on pressure, reflecting the pressure-induced band deformation. We find the SdH oscillations and transport response are consistent with the theoretically proposed pressure-induced band deformation leading to a topological phase transition. Our analysis suggests the critical pressure for the quantum phase transition near Pc=3.5 GPa.

Theoretical determination of transit time locus curves for ultrasonic pulse echo testing - ALOK. Pt. 4

International Nuclear Information System (INIS)

Grohs, B.

1983-01-01

The ALOK-technique allows the simultaneous detection of flaws and their evaluation with respect to type, location and dimension by interpretation of the transit time behaviour during scanning of the reflector. The accuracy of information obtained by means of this technique can be further improved both during interference elimination and reconstruction owing to the ability of exact calculation of possible transit time locus curves of given reflectors. The mathematical solution of transit time locus curve calculations refers here to pulse echo testing in consideration of the refraction of sound on the forward wedge/test object - interface. The method of solving the problem is equivalent to the Fermat's principle in optics. (orig.) [de

Double exchange model on triangular lattice: Non-coplanar spin configuration and phase transition near quarter filling

Energy Technology Data Exchange (ETDEWEB)

Zhang, G.P., E-mail: bugubird_zhang@hotmail.com [Department of Physics, Renmin University of China, Beijing 100872 (China); Zhang, Jian [3M Company, 3M Corporate Headquarters, 3M Center, St. Paul, MN 55144-1000 (United States); Zhang, Qi-Li [Data Center for High Energy Density Physics, Institute of Applied Physics and Computational Mathematics, Beijing 100094 (China); Zhou, Jiang-Tao [College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060 (China); Shangguan, M.H. [Department of Physics, Renmin University of China, Beijing 100872 (China)

2013-05-15

Unconventional anomalous Hall effect in frustrated pyrochlore oxides is originated from spin chirality of non-coplanar localized spins, which can also be induced by the competition between ferromagnetic (FM) double exchange interaction J{sub H} and antiferromagnetic superexchange interaction J{sub AF}. Here truncated polynomial expansion method and Monte Carlo simulation are adopted to investigate the above model on two-dimensional triangular lattice. We discuss the influence of the range of FM-type spin–spin correlation and strong electron–spin correlation on the truncation error of spin–spin correlation near quarter filling. Two peaks of the probability distribution of spin–spin correlation in non-coplanar spin configuration clearly show that non-coplanar spin configuration is an intermediate phase between FM and 120° spin phase. Near quarter filling, there is a phase transition from FM into non-coplanar and further into 120° spin phase when J{sub AF} continually increases. Finally the effect of temperature on the magnetic structure is discussed.

First-order phase transition in the quantum spin glass at T=0

Energy Technology Data Exchange (ETDEWEB)

Viana, J. Roberto; Nogueira, Yamilles; Sousa, J. Ricardo de

2003-05-26

The van Hemmen model with transverse and random longitudinal field is studied to analyze the tricritical behavior in the quantum Ising spin glass at T=0. The free energy and order parameter are calculated for two types of probability distributions: Gaussian and bimodal. We obtain the phase diagram in the {omega}-H plane, where {omega} and H are the transverse and random longitudinal fields, respectively. For the case of Gaussian distribution the phase transition is of second order, while the bimodal distribution we observe second-order transition for high-transverse field and first-order transition for small transverse field, with a tricritical point in the phase diagram.

First-order phase transition in the quantum spin glass at T=0

International Nuclear Information System (INIS)

Viana, J. Roberto; Nogueira, Yamilles; Sousa, J. Ricardo de

2003-01-01

The van Hemmen model with transverse and random longitudinal field is studied to analyze the tricritical behavior in the quantum Ising spin glass at T=0. The free energy and order parameter are calculated for two types of probability distributions: Gaussian and bimodal. We obtain the phase diagram in the Ω-H plane, where Ω and H are the transverse and random longitudinal fields, respectively. For the case of Gaussian distribution the phase transition is of second order, while the bimodal distribution we observe second-order transition for high-transverse field and first-order transition for small transverse field, with a tricritical point in the phase diagram

Direct measurement of the low temperature spin state transitions in La1-xSrxCoO3 (0.05 < x < 0.3)

Science.gov (United States)

Gulec, A.; Klie, R. F.

2014-12-01

Sr-doped LaCoO3 has a complex magnetic phase diagram, which is believed to be directly correlated to changes in the crystal structure and ordering of the Co3+ spin states. In this work, we study the low temperature Co3+-ion spin state transitions in Sr-doped LaCoO3 around the critical doping concentration where a metal to insulator transition has been observed using electron energy-loss spectroscopy of the O K-edge combined with the Co L-edge fine structure. We measure the local spin state of the Co3+-ions and we demonstrate that the Co3+ spin-state transition only occurs in La0.95Sr0.05CoO3 single-crystal materials in the temperature range accessible by LN2 in-situ cooling, while no structural symmetry change is observed. The presence of this low-temperature spin-state transition in La1-xSrxCoO3 (x < 0.17) has been proposed as the origin of the percolative magnetic ordering in doped LaCoO3.

Magneto-electronic properties and spin-resolved I-V curves of a Co/GeSe heterojunction diode: an ab initio study

Science.gov (United States)

Makinistian, Leonardo; Albanesi, Eduardo A.

2013-06-01

We present ab initio calculations of magnetoelectronic and transport properties of the interface of hcp Cobalt (001) and the intrinsic narrow-gap semiconductor germanium selenide (GeSe). Using a norm-conserving pseudopotentials scheme within DFT, we first model the interface with a supercell approach and focus on the spin-resolved densities of states and the magnetic moment (spin and orbital components) at the different atomic layers that form the device. We also report a series of cuts (perpendicular to the plane of the heterojunction) of the electronic and spin densities showing a slight magnetization of the first layers of the semiconductor. Finally, we model the device with a different scheme: using semiinfinite electrodes connected to the heterojunction. These latter calculations are based upon a nonequilibrium Green's function approach that allows us to explore the spin-resolved electronic transport under a bias voltage (spin-resolved I-V curves), revealing features of potential applicability in spintronics.

Generation of a third harmonic due to spin-flip transitions in non-symmetric heterostructures

CERN Document Server

Korovin, A V

2003-01-01

The third-order non-linear response due to spin-flip transitions of electrons in asymmetric narrow-gap quantum wells with a spin-split energy spectrum is calculated. The resonant spectral dependences and the gate-voltage dependences of the third-order susceptibility are obtained. The efficiency of up-conversion of the microwave pumping into submillimetre radiation in the multi-well structure is estimated and the dependences on the incidence angle and on the polarization of pumping are presented.

Vibration dependence of the tensor spin-spin and scalar spin-spin hyperfine interactions by precision measurement of hyperfine structures of 127I2 near 532 nm

International Nuclear Information System (INIS)

Hong Fenglei; Zhang Yun; Ishikawa, Jun; Onae, Atsushi; Matsumoto, Hirokazu

2002-01-01

Hyperfine structures of the R(87)33-0, R(145)37-0, and P(132)36-0 transitions of molecular iodine near 532 nm are measured by observing the heterodyne beat-note signal of two I 2 -stabilized lasers, whose frequencies are bridged by an optical frequency comb generator. The measured hyperfine splittings are fit to a four-term Hamiltonian, which includes the electric quadrupole, spin-rotation, tensor spin-spin, and scalar spin-spin interactions, with an accuracy of ∼720 Hz. High-accurate hyperfine constants are obtained from this fit. Vibration dependences of the tensor spin-spin and scalar spin-spin hyperfine constants are determined for molecular iodine, for the first time to our knowledge. The observed hyperfine transitions are good optical frequency references in the 532-nm region

Magnetic ordering and spin-reorientation transitions in TbCo3B2

International Nuclear Information System (INIS)

Dubman, Moshe; Caspi, El'ad N.; Ettedgui, Hanania; Keller, Lukas; Melamud, Mordechai; Shaked, Hagai

2005-01-01

The magnetic structure of the compound TbCo 3 B 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 ∼170 K, and a second magnetic Tb-Tb ordering transition at ∼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 (γ 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

Two-dimensional ferromagnet/semiconductor transition metal dichalcogenide contacts: p-type Schottky barrier and spin-injection control

KAUST Repository

Gan, Liyong; Cheng, Yingchun; Schwingenschlö gl, Udo; Zhang, Qingyun

2013-01-01

We study the ferromagnet/semiconductor contacts formed by transition metal dichalcogenide monolayers, focusing on semiconducting MoS2 and WS2 and ferromagnetic VS2. We investigate the degree of p-type doping and demonstrate tuning of the Schottky barrier height by vertical compressive pressure. An analytical model is presented for the barrier heights that accurately describes the numerical findings and is expected to be of general validity for all transition metal dichalcogenide metal/semiconductor contacts. Furthermore, magnetic proximity effects induce a 100% spin polarization at the Fermi level in the semiconductor where the spin splitting increases up to 0.70 eV for increasing pressure.

Two-dimensional ferromagnet/semiconductor transition metal dichalcogenide contacts: p-type Schottky barrier and spin-injection control

KAUST Repository

Gan, Liyong

2013-09-26

We study the ferromagnet/semiconductor contacts formed by transition metal dichalcogenide monolayers, focusing on semiconducting MoS2 and WS2 and ferromagnetic VS2. We investigate the degree of p-type doping and demonstrate tuning of the Schottky barrier height by vertical compressive pressure. An analytical model is presented for the barrier heights that accurately describes the numerical findings and is expected to be of general validity for all transition metal dichalcogenide metal/semiconductor contacts. Furthermore, magnetic proximity effects induce a 100% spin polarization at the Fermi level in the semiconductor where the spin splitting increases up to 0.70 eV for increasing pressure.

Spin glass transition in a thin-film NiO/permalloy bilayer

Science.gov (United States)

Ma, Tianyu; Urazhdin, Sergei

2018-02-01

We experimentally study magnetization aging in a thin-film NiO/permalloy bilayer. Aging characteristics are nearly independent of temperature below the exchange bias blocking temperature TB, but rapidly vary above it. The dependence on the magnetic history qualitatively changes across TB. The observed behaviors are consistent with the spin glass transition at TB, with significant implications for magnetism and magnetoelectronic phenomena in antiferromagnet/ferromagnet bilayers.

Linear perturbation renormalization group method for Ising-like spin systems

Directory of Open Access Journals (Sweden)

J. Sznajd

2013-03-01

Full Text Available The linear perturbation group transformation (LPRG is used to study the thermodynamics of the axial next-nearest-neighbor Ising model with four spin interactions (extended ANNNI in a field. The LPRG for weakly interacting Ising chains is presented. The method is used to study finite field para-ferrimagnetic phase transitions observed in layered uranium compounds, UAs1-xSex, UPd2Si2 or UNi2Si2. The above-mentioned systems are made of ferromagnetic layers and the spins from the nearest-neighbor and next-nearest-neighbor layers are coupled by the antiferromagnetic interactions J121-xSex the para-ferri phase transition is of the first order as expected from the symmetry reason, in UT2Si2 (T=Pd, Ni this transition seems to be a continuous one, at least in the vicinity of the multicritical point. Within the MFA, the critical character of the finite field para-ferrimagnetic transition at least at one isolated point can be described by the ANNNI model supplemented by an additional, e.g., four-spin interaction. However, in LPRG approximation for the ratio κ = J2/J1 around 0.5 there is a critical value of the field for which an isolated critical point also exists in the original ANNNI model. The positive four-spin interaction shifts the critical point towards higher fields and changes the shape of the specific heat curve. In the latter case for the fields small enough, the specific heat exhibits two-peak structure in the paramagnetic phase.

Multiple-Quantum Transitions and Charge-Induced Decoherence of Donor Nuclear Spins in Silicon

Science.gov (United States)

Franke, David P.; Pflüger, Moritz P. D.; Itoh, Kohei M.; Brandt, Martin S.

2017-06-01

We study single- and multiquantum transitions of the nuclear spins of an ensemble of ionized arsenic donors in silicon and find quadrupolar effects on the coherence times, which we link to fluctuating electrical field gradients present after the application of light and bias voltage pulses. To determine the coherence times of superpositions of all orders in the 4-dimensional Hilbert space, we use a phase-cycling technique and find that, when electrical effects were allowed to decay, these times scale as expected for a fieldlike decoherence mechanism such as the interaction with surrounding Si 29 nuclear spins.

Changing the cubic ferrimagnetic domain structure in temperature region of spin flip transition

International Nuclear Information System (INIS)

Djuraev, D.R.; Niyazov, L.N.; Saidov, K.S.; Sokolov, B.Yu.

2011-01-01

The transformation of cubic ferrimagnetic Tb 0.2 Y 2.8 Fe 5 O 12 domain structure has been studied by magneto optic method in the temperature region of spontaneous spin flip phase transition (SPT). It has been found that SPT occurs in a finite temperature interval where the coexistence of low- and high- temperature magnetic phase domains has observed. A character of domain structure evolution in temperature region of spin flip essentially depends on the presence of mechanical stresses in crystal. Interpretation of experimental results has been carried out within the framework of SPT theory for a cubic crystal. (authors)

Spin-chirality decoupling in Heisenberg spin glasses and related systems

OpenAIRE

Kawamura, Hikaru

2006-01-01

Recent studies on the spin and the chirality orderings of the three-dimensional Heisenberg spin glass and related systems are reviewed with particular emphasis on the possible spin-chirality decoupling phenomena. Chirality scenario of real spin-glass transition and its experimental consequence on the ordering of Heisenberg-like spin glasses are discussed.

Strain-induced phase transition and electron spin-polarization in graphene spirals.

Science.gov (United States)

Zhang, Xiaoming; Zhao, Mingwen

2014-07-16

Spin-polarized triangular graphene nanoflakes (t-GNFs) serve as ideal building blocks for the long-desired ferromagnetic graphene superlattices, but they are always assembled to planar structures which reduce its mechanical properties. Here, by joining t-GNFs in a spiral way, we propose one-dimensional graphene spirals (GSs) with superior mechanical properties and tunable electronic structures. We demonstrate theoretically the unique features of electron motion in the spiral lattice by means of first-principles calculations combined with a simple Hubbard model. Within a linear elastic deformation range, the GSs are nonmagnetic metals. When the axial tensile strain exceeds an ultimate strain, however, they convert to magnetic semiconductors with stable ferromagnetic ordering along the edges. Such strain-induced phase transition and tunable electron spin-polarization revealed in the GSs open a new avenue for spintronics devices.

Spin-dependent electronic transport properties of transition metal atoms doped α-armchair graphyne nanoribbons

Science.gov (United States)

Fotoohi, Somayeh; Haji-Nasiri, Saeed

2018-04-01

Spin-dependent electronic transport properties of single 3d transition metal (TM) atoms doped α-armchair graphyne nanoribbons (α-AGyNR) are investigated by non-equilibrium Green's function (NEGF) method combined with density functional theory (DFT). It is found that all of the impurity atoms considered in this study (Fe, Co, Ni) prefer to occupy the sp-hybridized C atom site in α-AGyNR, and the obtained structures remain planar. The results show that highly localized impurity states are appeared around the Fermi level which correspond to the 3d orbitals of TM atoms, as can be derived from the projected density of states (PDOS). Moreover, Fe, Co, and Ni doped α-AGyNRs exhibit magnetic properties due to the strong spin splitting property of the energy levels. Also for each case, the calculated current-voltage characteristic per super-cell shows that the spin degeneracy in the system is obviously broken and the current becomes strongly spin dependent. Furthermore, a high spin-filtering effect around 90% is found under the certain bias voltages in Ni doped α-AGyNR. Additionally, the structure with Ni impurity reveals transfer characteristic that is suitable for designing a spin current switch. Our findings provide a high possibility to design the next generation spin nanodevices with novel functionalities.

Influence of quantum phase transition on spin transport in the quantum antiferromagnet in the honeycomb lattice

Science.gov (United States)

Lima, L. S.

2017-06-01

We use the SU(3) Schwinger boson theory to study the spin transport properties of the two-dimensional anisotropic frustrated Heisenberg model in a honeycomb lattice at T = 0 with single ion anisotropy and third neighbor interactions. We have investigated the behavior of the spin conductivity for this model that presents exchange interactions J1 , J2 and J3 . We study the spin transport in the Bose-Einstein condensation regime where the bosons tz are condensed. Our results show an influence of the quantum phase transition point on the spin conductivity behavior. We also have made a diagrammatic expansion for the Green-function and did not obtain any significant change of the results.

WASP-36b: A NEW TRANSITING PLANET AROUND A METAL-POOR G-DWARF, AND AN INVESTIGATION INTO ANALYSES BASED ON A SINGLE TRANSIT LIGHT CURVE

Energy Technology Data Exchange (ETDEWEB)

Smith, A. M. S.; Anderson, D. R.; Hellier, C.; Maxted, P. F. L.; Smalley, B.; Southworth, J. [Astrophysics Group, Keele University, Staffordshire, ST5 5BG (United Kingdom); Collier Cameron, A. [SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, Fife, KY16 9SS (United Kingdom); Gillon, M.; Jehin, E. [Institut d' Astrophysique et de Geophysique, Universite de Liege, Allee du 6 Aout, 17 Bat. B5C, Liege 1 (Belgium); Lendl, M.; Queloz, D.; Triaud, A. H. M. J.; Pepe, F.; Segransan, D.; Udry, S. [Observatoire de Geneve, Universite de Geneve, 51 Chemin des Maillettes, 1290 Sauverny (Switzerland); West, R. G. [Department of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH (United Kingdom); Barros, S. C. C.; Pollacco, D. [Astrophysics Research Centre, School of Mathematics and Physics, Queen' s University, University Road, Belfast, BT7 1NN (United Kingdom); Street, R. A., E-mail: amss@astro.keele.ac.uk [Las Cumbres Observatory, 6740 Cortona Drive Suite 102, Goleta, CA 93117 (United States)

2012-04-15

We report the discovery, from WASP and CORALIE, of a transiting exoplanet in a 1.54 day orbit. The host star, WASP-36, is a magnitude V = 12.7, metal-poor G2 dwarf (T{sub eff} = 5959 {+-} 134 K), with [Fe/H] =-0.26 {+-} 0.10. We determine the planet to have mass and radius, respectively, 2.30 {+-} 0.07 and 1.28 {+-} 0.03 times that of Jupiter. We have eight partial or complete transit light curves, from four different observatories, which allow us to investigate the potential effects on the fitted system parameters of using only a single light curve. We find that the solutions obtained by analyzing each of these light curves independently are consistent with our global fit to all the data, despite the apparent presence of correlated noise in at least two of the light curves.

Spin inelastic electron tunneling spectroscopy on local spin adsorbed on surface.

Science.gov (United States)

Fransson, J

2009-06-01

The recent experimental conductance measurements taken on magnetic impurities on metallic surfaces, using scanning tunneling microscopy technique and suggesting occurrence of inelastic scattering processes, are theoretically addressed. We argue that the observed conductance signatures are caused by transitions between the spin states that have opened due to, for example, exchange coupling between the local spins and the tunneling electrons, and are directly interpretable in terms of inelastic transitions energies. Feasible measurements using spin-polarized scanning tunneling microscopy that would enable new information about the excitation spectrum of the local spins are discussed.

Spin-Spin Cross Relaxation in Single-Molecule Magnets

Science.gov (United States)

Wernsdorfer, W.; Bhaduri, S.; Tiron, R.; Hendrickson, D. N.; Christou, G.

2002-10-01

The one-body tunnel picture of single-molecule magnets (SMMs) is not always sufficient to explain the measured tunnel transitions. An improvement to the picture is proposed by including also two-body tunnel transitions such as spin-spin cross relaxation (SSCR) which are mediated by dipolar and weak superexchange interactions between molecules. A Mn4 SMM is used as a model system. At certain external fields, SSCRs lead to additional quantum resonances which show up in hysteresis loop measurements as well-defined steps. A simple model is used to explain quantitatively all observed transitions.

Spectroscopic parameters, vibrational levels, transition dipole moments and transition probabilities of the 9 low-lying states of the NCl+ cation

Science.gov (United States)

Yin, Yuan; Shi, Deheng; Sun, Jinfeng; Zhu, Zunlue

2018-03-01

This work calculates the potential energy curves of 9 Λ-S and 28 Ω states of the NCl+ cation. The technique employed is the complete active space self-consistent field method, which is followed by the internally contracted multireference configuration interaction approach with the Davidson correction. The Λ-S states are X2Π, 12Σ+, 14Π, 14Σ+, 14Σ-, 24Π, 14Δ, 16Σ+, and 16Π, which are yielded from the first two dissociation channels of NCl+ cation. The Ω states are generated from these Λ-S states. The 14Π, 14Δ, 16Σ+, and 16Π states are inverted with the spin-orbit coupling effect included. The 14Σ+, 16Σ+, and 16Π states are very weakly bound, whose well depths are only several-hundred cm- 1. One avoided crossing of PECs occurs between the 12Σ+ and 22Σ+ states. To improve the quality of potential energy curves, core-valence correlation and scalar relativistic corrections are included. The potential energies are extrapolated to the complete basis set limit. The spectroscopic parameters and vibrational levels are calculated. The transition dipole moments are computed. The Franck-Condon factors, Einstein coefficients, and radiative lifetimes of many transitions are determined. The spectroscopic approaches are proposed for observing these states according to the transition probabilities. The spin-orbit coupling effect on the spectroscopic and vibrational properties is evaluated. The spectroscopic parameters, vibrational levels, transition dipole moments, as well as transition probabilities reported in this paper could be considered to be very reliable.

Quasi-continuous transition from a Fermi liquid to a spin liquid in κ-(ET)2Cu2(CN)3.

Science.gov (United States)

Furukawa, Tetsuya; Kobashi, Kazuhiko; Kurosaki, Yosuke; Miyagawa, Kazuya; Kanoda, Kazushi

2018-01-22

The Mott metal-insulator transition-a manifestation of Coulomb interactions among electrons-is known as a discontinuous transition. Recent theoretical studies, however, suggest that the transition is continuous if the Mott insulator carries a spin liquid with a spinon Fermi surface. Here, we demonstrate the case of a quasi-continuous Mott transition from a Fermi liquid to a spin liquid in an organic triangular-lattice system κ-(ET) 2 Cu 2 (CN) 3 . Transport experiments performed under fine pressure tuning have found that as the Mott transition is approached, the Fermi liquid coherence temperature continuously falls to the scale of kelvins, with a divergent quasi-particle decay rate on the metal side, and the charge gap continuously closes on the insulator side. A Clausius-Clapeyron analysis provides thermodynamic evidence for the extremely weak first-order nature of the transition. These results provide additional support for the existence of a spinon Fermi surface, which becomes an electron Fermi surface when charges are delocalized.

The spectrum of a vertex model and related spin one chain sitting in a genus five curve

Directory of Open Access Journals (Sweden)

M.J. Martins

2017-11-01

Full Text Available We derive the transfer matrix eigenvalues of a three-state vertex model whose weights are based on a R-matrix not of difference form with spectral parameters lying on a genus five curve. We have shown that the basic building blocks for both the transfer matrix eigenvalues and Bethe equations can be expressed in terms of meromorphic functions on an elliptic curve. We discuss the properties of an underlying spin one chain originated from a particular choice of the R-matrix second spectral parameter. We present numerical and analytical evidences that the respective low-energy excitations can be gapped or massless depending on the strength of the interaction coupling. In the massive phase we provide analytical and numerical evidences in favor of an exact expression for the lowest energy gap. We point out that the critical point separating these two distinct physical regimes coincides with the one in which the weights geometry degenerate into union of genus one curves.

The spectrum of a vertex model and related spin one chain sitting in a genus five curve

Science.gov (United States)

Martins, M. J.

2017-11-01

We derive the transfer matrix eigenvalues of a three-state vertex model whose weights are based on a R-matrix not of difference form with spectral parameters lying on a genus five curve. We have shown that the basic building blocks for both the transfer matrix eigenvalues and Bethe equations can be expressed in terms of meromorphic functions on an elliptic curve. We discuss the properties of an underlying spin one chain originated from a particular choice of the R-matrix second spectral parameter. We present numerical and analytical evidences that the respective low-energy excitations can be gapped or massless depending on the strength of the interaction coupling. In the massive phase we provide analytical and numerical evidences in favor of an exact expression for the lowest energy gap. We point out that the critical point separating these two distinct physical regimes coincides with the one in which the weights geometry degenerate into union of genus one curves.

THE IMPACT OF THE CONVECTIVE BLUESHIFT EFFECT ON SPECTROSCOPIC PLANETARY TRANSITS

International Nuclear Information System (INIS)

Shporer, Avi; Brown, Tim

2011-01-01

We present here a small anomalous radial velocity (RV) signal expected to be present in RV curves measured during planetary transits. This signal is induced by the convective blueshift (CB) effect-a net blueshift emanating from the stellar surface, resulting from a larger contribution of rising hot and bright gas relative to the colder and darker sinking gas. Since the CB radial component varies across the stellar surface, the light blocked by the planet during a transit will have a varying RV component, resulting in a small shift of the measured RVs. The CB-induced anomalous RV curve is different than, and independent of, the well-known Rossiter-McLaughlin (RM) effect, where the latter is used for determining the sky-projected angle between the host star rotation axis and the planet's orbital angular momentum axis. The observed RV curve is the sum of the CB and RM signals, and they are both superposed on the orbital Keplerian curve. If not accounted for, the presence of the CB RV signal in the spectroscopic transit RV curve may bias the estimate of the spin-orbit angle. In addition, future very high precision RVs will allow the use of transiting planets to study the CB of their host stars.

Magnetic phase transitions and magnetization reversal in MnRuP

Science.gov (United States)

Lampen-Kelley, P.; Mandrus, D.

The ternary phosphide MnRuP is an incommensurate antiferromagnetic metal crystallizing in the non-centrosymmetric Fe2P-type crystal structure. Below the Neel transition at 250 K, MnRuP exhibits hysteretic anomalies in resistivity and magnetic susceptibility curves as the propagation vectors of the spiral spin structure change discontinuously across T1 = 180 K and T2 = 100 K. Temperature-dependent X-ray diffraction data indicate that the first-order spin reorientation occurs in the absence of a structural transition. A strong magnetization reversal (MR) effect is observed upon cooling the system through TN in moderate dc magnetic fields. Positive magnetization is recovered on further cooling through T1 and maintained in subsequent warming curves. The field dependence and training of the MR effect in MnRuP will be discussed in terms of the underlying magnetic structures and compared to anomalous MR observed in vanadate systems. This work is supported by the Gordon and Betty Moore Foundation GBMF4416 and U.S. DOE, Office of Science, BES, Materials Science and Engineering Division.

Electric dipole spin resonance in a quantum spin dimer system driven by magnetoelectric coupling

Science.gov (United States)

Kimura, Shojiro; Matsumoto, Masashige; Akaki, Mitsuru; Hagiwara, Masayuki; Kindo, Koichi; Tanaka, Hidekazu

2018-04-01

In this Rapid Communication, we propose a mechanism for electric dipole active spin resonance caused by spin-dependent electric polarization in a quantum spin gapped system. This proposal was successfully confirmed by high-frequency electron spin resonance (ESR) measurements of the quantum spin dimer system KCuCl3. ESR measurements by an illuminating linearly polarized electromagnetic wave reveal that the optical transition between the singlet and triplet states in KCuCl3 is driven by an ac electric field. The selection rule of the observed transition agrees with the calculation by taking into account spin-dependent electric polarization. We suggest that spin-dependent electric polarization is effective in achieving fast control of quantum spins by an ac electric field.

Elementary excitations and the phase transition in the bimodal Ising spin glass model

International Nuclear Information System (INIS)

Jinuntuya, N; Poulter, J

2012-01-01

We show how the nature of the phase transition in the two-dimensional bimodal Ising spin glass model can be understood in terms of elementary excitations. Although the energy gap with the ground state is expected to be 4J in the ferromagnetic phase, a gap 2J is in fact found if the finite lattice is wound around a cylinder of odd circumference L. This 2J gap is really a finite size effect that should not occur in the thermodynamic limit of the ferromagnet. The spatial influence of the frustration must be limited and not wrap around the system if L is large enough. In essence, the absence of 2J excitations defines the ferromagnetic phase without recourse to calculating the magnetization or investigating the system response to domain wall defects. This study directly investigates the response to temperature. We also estimate the defect concentration where the phase transition to the spin glass state occurs. The value p c = 0.1045(11) is in reasonable agreement with the literature

The algebraic curve of 1-loop planar N=4 SYM

International Nuclear Information System (INIS)

Schaefer-Nameki, S.

2004-12-01

The algebraic curve for the psu(2,2 vertical stroke 4) quantum spin chain is determined from the thermodynamic limit of the algebraic Bethe ansatz. The Hamiltonian of this spin chain has been identified with the planar 1-loop dilatation operator of N=4 SYM. In the dual AdS 5 x S 5 string theory, various properties of the data defining the curve for the gauge theory are compared to the ones obtained from semiclassical spinning-string configurations, in particular for the case of strings on AdS 5 x S 1 and the su(2,2) spin chain agreement of the curves is shown. (orig.)

Matrix-assisted relaxation in Fe(phen)2(NCS)2 spin-crossover microparticles, experimental and theoretical investigations

International Nuclear Information System (INIS)

Enachescu, Cristian; Stancu, Alexandru; Tanasa, Radu; Tissot, Antoine; Laisney, Jérôme; Boillot, Marie-Laure

2016-01-01

In this study, we present the influence of the embedding matrix on the relaxation of Fe(phen) 2 (NCS) 2 (phen = 1,10-phenanthroline) spin-transition microparticles as revealed by experiments and provide an explanation within the framework of an elastic model based on a Monte-Carlo method. Experiments show that the shape of the high-spin → low-spin relaxation curves is drastically changed when the particles are dispersed in glycerol. This effect was considered in the model by means of interactions between the microparticles and the matrix. A faster start of the relaxation for microparticles embedded in glycerol is due to an initial positive local pressure acting on the edge spin-crossover molecules from the matrix side. This local pressure diminishes and eventually becomes negative during relaxation, as an effect of the decrease of the volume of spin-crossover microparticles from high-spin to low-spin.

Spin transitions in La{sub 0.7} Ba{sub 0.3}CoO{sub 3} thin films revealed by combining Raman spectroscopy and X-ray diffraction

Energy Technology Data Exchange (ETDEWEB)

Othmen, Zied; Oueslati, Meherzi [Unité Nanomatériaux et Photonique, Faculty of Sciences of Tunis, Tunis El-Manar University, 2092 Tunis (Tunisia); Copie, Olivier; Gemeiner, Pascale; Dkhil, Brahim [Laboratoire Structures, Propriétés et Modélisation des Solides, Centrale Supélec, CNRS-UMR 8580, Université Paris-Saclay (France); Daoudi, Kais [Unité Nanomatériaux et Photonique, Faculty of Sciences of Tunis, Tunis El-Manar University, 2092 Tunis (Tunisia); Department of Applied Physics and Astronomy, College of Sciences, University of Sharjah, P.O. Box 27272, Sharjah (United Arab Emirates); Boudard, Michel [Univ. Grenoble Alpes, LMGP, F-38000 Grenoble (France)

2016-07-07

In cobaltite, the spin states transitions of Co{sup 3+/4+} ions govern the magnetic and electronic conduction properties. These transitions are strain-sensitive and can be varied using external parameters, including temperature, hydrostatic pressure, or chemical stresses through ionic substitutions. In this work, using temperature dependent Raman spectroscopy and X-ray diffraction, the epitaxial strain effects on both structural and vibrational properties of La{sub 0.7} Ba{sub 0.3} CoO{sub 3} (LBCO) cobaltite thin films are investigated. All Raman active phonon modes as well as the structure are found to be strongly affected. Both Raman modes and lattice parameter evolutions show temperature changes correlated with magnetic and electronic transitions properties. Combining Raman spectroscopy and X-ray diffraction appears as a powerful approach to probe the spin transition in thin film cobaltite. Our results provide insight into strong spin-charge-phonon coupling in LBCO thin film. This coupling manifests as vibrational transition with temperature in the Raman spectra near the ferromagnetic spin ordered transition at 220 K.

Recent advances of spin crossover research

NARCIS (Netherlands)

Gutlich, P; van Koningsbruggen, PJ; Renz, F; Schonherr, T

2004-01-01

Thermal spin transition (spin crossover), one of the most fascinating dynamic electronic structure phenomena occurring in coordination compounds of third row transition metal ions, mostly of iron(II), iron(III) and cobalt(II) with critical ligand field strengths competing with the spin pairing

Spin reorientation transition and hard magnetic properties of MnBi intermetallic compound

Science.gov (United States)

Suzuki, K.; Wu, X.; Ly, V.; Shoji, T.; Kato, A.; Manabe, A.

2012-04-01

The effects of mechanical grinding (MG) on the crystallite size, the spin reorientation transition temperature (TSR) and the hard magnetic properties in melt-spun low temperature phase (LTP) MnBi have been investigated in order to understand the origin of magnetic hardening induced by MG. The room-temperature coercive field (μ0Hcj) is enhanced dramatically from 0.08 T before MG to 1.5 T after MG for 43.2 ks while TSR is concurrently suppressed from 110 to 38 K. The coercive force exhibits positive temperature dependence approximately 50-60 K above TSR and the lowered TSR after MG could result in magnetic hardening at room temperature. The room-temperature coercive force of LTP-MnBi is highly dependent on the crystallite size (D) and is found to be described phenomenologically by the following relationship: μ0Hcj = μ0Ha(δ/D)n, where μ0Ha is ˜ 4 T, the Bloch wall width δ is 7 nm, and the exponent n is approximately 0.7. Our results suggest that the grain refinement is the primary origin of the hardening effect induced by MG with a possible minor hardening effect due to the suppression of the spin reorientation transition temperature.

The Nuclear Spin Nanomagnet

OpenAIRE

Korenev, V. L.

2007-01-01

Linearly polarized light tuned slightly below the optical transition of the negatively charged exciton (trion) in a single quantum dot causes the spontaneous nuclear spin polarization (self-polarization) at a level close to 100%. The effective magnetic field of spin-polarized nuclei brings the optical transition energy into resonance with photon energy. The resonantly enhanced Overhauser effect sustains the stability of the nuclear self-polarization even in the absence of spin polarization of...

Transitions in eigenvalue and wavefunction structure in (1+2) -body random matrix ensembles with spin.

Science.gov (United States)

Vyas, Manan; Kota, V K B; Chavda, N D

2010-03-01

Finite interacting Fermi systems with a mean-field and a chaos generating two-body interaction are modeled by one plus two-body embedded Gaussian orthogonal ensemble of random matrices with spin degree of freedom [called EGOE(1+2)-s]. Numerical calculations are used to demonstrate that, as lambda , the strength of the interaction (measured in the units of the average spacing of the single-particle levels defining the mean-field), increases, generically there is Poisson to GOE transition in level fluctuations, Breit-Wigner to Gaussian transition in strength functions (also called local density of states) and also a duality region where information entropy will be the same in both the mean-field and interaction defined basis. Spin dependence of the transition points lambda_{c} , lambdaF, and lambdad , respectively, is described using the propagator for the spectral variances and the formula for the propagator is derived. We further establish that the duality region corresponds to a region of thermalization. For this purpose we compared the single-particle entropy defined by the occupancies of the single-particle orbitals with thermodynamic entropy and information entropy for various lambda values and they are very close to each other at lambda=lambdad.

Characterization of type, position and dimension of flaws by transit time locus curves of ultrasonic inspections - ALOK. Pt. 2

International Nuclear Information System (INIS)

Grohs, B.; Barbian, O.A.; Kappes, W.; Paul, H.

1981-01-01

With automatic ultrasonic testing, flaws can be detected and described and thus characterized according to their type, position and dimensions. During scanning of a test object, the flaws are registered by many different pathways and many different acoustic irradiation directions. The transit time locus curve represents the distance between the relfecting points of a flaw and the source in dependence of the probe position; hence, information on flaw position and dimensions can be derived from this curve. If the sound velocity is known, the transit path can then be calculated from the transit time. This requires, above all, a constant sound velocity along the whole transit path. Various methods are presented for reconstructing the flaw border in the plane of incidence. (orig./RW) [de

Study of spin crossover nanoparticles thermal hysteresis using FORC diagrams on an Ising-like model

International Nuclear Information System (INIS)

Atitoaie, Alexandru; Tanasa, Radu; Stancu, Alexandru; Enachescu, Cristian

2014-01-01

Recent developments in the synthesis and characterization of spin crossover (SCO) nanoparticles and their prospects of switching at molecular level turned these bistable compounds into possible candidates for replacing the materials used in recording media industry for development of solid state pressure and temperature sensors or for bringing contributions in engineering. Compared to bulk samples with the same chemical structure, SCO nanoparticles display different characteristics of the hysteretic and relaxation properties like the shift of the transition temperature towards lower values along with decrease of the hysteresis width with nanoparticles size. Using an Ising-like model with specific boundary conditions within a Monte Carlo procedure, we here reproduce most of the hysteretic properties of SCO nanoparticles by considering the interaction between spin crossover edge molecules and embedding surfactant molecules and we propose a complex analysis concerning the effect of the interactions and sizes during the thermal transition in systems of SCO nanoparticles by using the First Order Reversal Curves diagram method and by comparison with similar effects in mixed crystal systems. - Highlights: • The influence of size effects in spin crossover nanoparticles is analyzed. • The environment shifts the hysteresis loop towards lower temperatures. • First Order Reversal Curves technique is employed. • One determines the distributions of switching temperatures. • One disentangles between kinetics and non-kinetic parts of the hysteresis

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

Science.gov (United States)

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

2016-06-01

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

In Situ AFM Imaging of Microstructural Changes Associated with The Spin Transition in [Fe(Htrz)₂(Trz)](Bf₄) Nanoparticles.

Science.gov (United States)

Manrique-Juárez, María D; Suleimanov, Iurii; Hernández, Edna M; Salmon, Lionel; Molnár, Gábor; Bousseksou, Azzedine

2016-06-30

Topographic images of [Fe(Htrz)₂(trz)](BF₄) nanoparticles were acquired across the first-order spin transition using variable-temperature atomic force microscopy (AFM) in amplitude modulation mode. These studies revealed a complex morphology of the particles consisting of aggregates of small nanocrystals, which expand, separate and re-aggregate due to the mechanical stress during the spin-state switching events. Both reversible (prompt or slow recovery) and irreversible effects (fatigue) on the particle morphology were evidenced and correlated with the spin crossover properties.

Control of electron spin decoherence in nuclear spin baths

Science.gov (United States)

Liu, Ren-Bao

2011-03-01

Nuclear spin baths are a main mechanism of decoherence of spin qubits in solid-state systems, such as quantum dots and nitrogen-vacancy (NV) centers of diamond. The decoherence results from entanglement between the electron and nuclear spins, established by quantum evolution of the bath conditioned on the electron spin state. When the electron spin is flipped, the conditional bath evolution is manipulated. Such manipulation of bath through control of the electron spin not only leads to preservation of the center spin coherence but also demonstrates quantum nature of the bath. In an NV center system, the electron spin effectively interacts with hundreds of 13 C nuclear spins. Under repeated flip control (dynamical decoupling), the electron spin coherence can be preserved for a long time (> 1 ms) . Thereforesomecharacteristicoscillations , duetocouplingtoabonded 13 C nuclear spin pair (a dimer), are imprinted on the electron spin coherence profile, which are very sensitive to the position and orientation of the dimer. With such finger-print oscillations, a dimer can be uniquely identified. Thus, we propose magnetometry with single-nucleus sensitivity and atomic resolution, using NV center spin coherence to identify single molecules. Through the center spin coherence, we could also explore the many-body physics in an interacting spin bath. The information of elementary excitations and many-body correlations can be extracted from the center spin coherence under many-pulse dynamical decoupling control. Another application of the preserved spin coherence is identifying quantumness of a spin bath through the back-action of the electron spin to the bath. We show that the multiple transition of an NV center in a nuclear spin bath can have longer coherence time than the single transition does, when the classical noises due to inhomogeneous broadening is removed by spin echo. This counter-intuitive result unambiguously demonstrates the quantumness of the nuclear spin bath

Spin-Orbit Misalignments of Three Jovian Planets via Doppler Tomography

Science.gov (United States)

Johnson, Marshall C.; Cochran, William D.; Addison, Brett C.; Tinney, Chris G.; Wright, Duncan J.

2017-10-01

We present measurements of the spin-orbit misalignments of the hot Jupiters HAT-P-41 b and WASP-79 b, and the aligned warm Jupiter Kepler-448 b. We obtain these measurements with Doppler tomography, where we spectroscopically resolve the line profile perturbation during the transit due to the Rossiter-McLaughlin effect. We analyze time series spectra obtained during portions of five transits of HAT-P-41 b, and find a value of the spin-orbit misalignment of λ =-{22.1}-6.0{+0.8^\\circ }. We reanalyze the radial velocity Rossiter-McLaughlin data on WASP-79 b obtained by Addison et al. using Doppler tomographic methodology. We measure λ =-{99.1}-3.9{+4.1^\\circ }, consistent with but more precise than the value found by Addison et al. For Kepler-448 b we perform a joint fit to the Kepler light curve, Doppler tomographic data, and a radial velocity data set from Lillo-Box et al. We find an approximately aligned orbit (λ =-{7.1}-2.8{+4.2^\\circ }), in agreement with the value found by Bourrier et al. Through analysis of the Kepler light curve we measure a stellar rotation period of {P}{rot}=1.27+/- 0.11 days, and use this to argue that the full three-dimensional spin-orbit misalignment is small, \\psi ˜ 0^\\circ . Based in part on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen.

Tweaking the spin-wave dispersion and suppressing the incommensurate phase in LiNiPO4 by iron substitution

DEFF Research Database (Denmark)

Li, Jiying; Jensen, Thomas Bagger Stibius; Andersen, Niels Hessel

2009-01-01

) indicates the instability of the Ising-type ground state that eventually evolves into the incommensurate phase as the temperature is raised. The pure LiNiPO4 system (x=0) undergoes a first-order magnetic phase transition from a long-range incommensurate phase to an antiferromagnetic (AFM) ground state at TN......Elastic and inelastic neutron-scattering studies of Li(Ni1−xFex)PO4 single crystals reveal anomalous spin-wave dispersions along the crystallographic direction parallel to the characteristic wave vector of the magnetic incommensurate phase. The anomalous spin-wave dispersion (magnetic soft mode......=20.8 K. At 20% Fe concentrations, although the AFM ground state is to a large extent preserved as that of the pure system, the phase transition is second order, and the incommensurate phase is completely suppressed. Analysis of the dispersion curves using a Heisenberg spin Hamiltonian that includes...

Matrix-assisted relaxation in Fe(phen){sub 2}(NCS){sub 2} spin-crossover microparticles, experimental and theoretical investigations

Energy Technology Data Exchange (ETDEWEB)

Enachescu, Cristian, E-mail: cristian.enachescu@uaic.ro; Stancu, Alexandru [Faculty of Physics, “Alexandru Ioan Cuza” University, 700506 Iasi (Romania); Tanasa, Radu [Faculty of Physics, “Alexandru Ioan Cuza” University, 700506 Iasi (Romania); Department of Engineering, University of Cambridge, CB2 1PZ Cambridge (United Kingdom); Tissot, Antoine [Institut de Chimie Moléculaire et des Matériaux d' Orsay, Université Paris Sud, Université Paris-Saclay, CNRS, 91405 Orsay (France); Institut Lavoisier de Versailles, UMR 8180, CNRS, Université de Versailles-Saint Quentin en Yvelines, 78035 Versailles (France); Laisney, Jérôme; Boillot, Marie-Laure, E-mail: marie-laure.boillot@u-psud.fr [Institut de Chimie Moléculaire et des Matériaux d' Orsay, Université Paris Sud, Université Paris-Saclay, CNRS, 91405 Orsay (France)

2016-07-18

In this study, we present the influence of the embedding matrix on the relaxation of Fe(phen){sub 2}(NCS){sub 2} (phen = 1,10-phenanthroline) spin-transition microparticles as revealed by experiments and provide an explanation within the framework of an elastic model based on a Monte-Carlo method. Experiments show that the shape of the high-spin → low-spin relaxation curves is drastically changed when the particles are dispersed in glycerol. This effect was considered in the model by means of interactions between the microparticles and the matrix. A faster start of the relaxation for microparticles embedded in glycerol is due to an initial positive local pressure acting on the edge spin-crossover molecules from the matrix side. This local pressure diminishes and eventually becomes negative during relaxation, as an effect of the decrease of the volume of spin-crossover microparticles from high-spin to low-spin.

Coexistence of ferromagnetism and spin glass behavior in antiferromagnetic Y2BaCuO5

International Nuclear Information System (INIS)

Zhu, Zhonghua; Gao, Daqiang; Zhang, Jing; Shi, Zhenhua; Gao, Hua; Yang, Zhaolong; Zhang, Zhipeng; Xue, Desheng

2013-01-01

Highlights: • Room temperature ferromagnetism is observed in ultrafine Y 2 BaCuO 5 particles. • The observed ferromagnetism originates from the oxygen defects. • A very interesting spin glass transition located at about 110 K is found. -- Abstract: We report the synthesis of a series of Y 2 BaCuO 5 samples by varying the annealing temperature with a citrate pyrolysis technique. X-ray diffraction patterns, scanning electron microscopy and transmission electron microscopy observation show the formation of a columnar Y 2 BaCuO 5 phase and these samples are composed of many irregular particles with different particle size. Magnetic measurements show that these samples exhibit room temperature ferromagnetism and the saturation magnetization decreases with increasing sintering temperature. Post-heating treatment under argon atmosphere can enhance the ferromagnetism greatly, suggesting that the magnetism is attributed to the surface oxygen defects. By measuring magnetization versus temperature curves after zero field cooling with various applied magnetic fields, two magnetic phase transitions located at about 11 and 110 K are revealed. The position of the peak at about 11 K is independent of the magnetic field; the other peak, however, becomes rounder and shifts to lower temperatures with increasing the magnetic field, showing a strong field dependence. In addition, the virgin magnetization curves with the measured temperature below 110 K display an S-type. These features are suggestive of an antiferromagnetic phase transition at about 11 K and a spin glass transition at about 110 K

Transit Timing Variation analysis with Kepler light curves of KOI 227 and Kepler 93b

Science.gov (United States)

Dulz, Shannon; Reed, Mike

2017-01-01

By searching for transit signals in approximately 150,000 stars, NASA’s Kepler Space telescope found thousands of exoplanets over its primary mission from 2009 to 2013 (Tenenbaum et al. 2014, ApJS, 211, 6). Yet, a detailed follow-up examination of Kepler light curves may contribute more evidence on system dynamics and planetary atmospheres of these objects. Kepler’s continuous observing of these systems over the mission duration produced light curves of sufficient duration to allow for the search for transit timing variations. Transit timing variations over the course of many orbits may indicate a precessing orbit or the existence of a non-transiting third body such as another exoplanet. Flux contributions of the planet just prior to secondary eclipse may provide a measurement of bond albedo from the day-side of the transiting planet. Any asymmetries of the transit shape may indicate thermal asymmetries which can measure upper atmosphere motion of the planet. These two factors can constrain atmospheric models of close orbiting exoplanets. We first establish our procedure with the well-documented TTV system, KOI 227 (Nesvorny et al. 2014, ApJ, 790, 31). Using the test case of KOI 227, we analyze Kepler-93b for TTVs and day-side flux contributions. Kepler-93b is likely a rocky planet with R = 1.50 ± 0.03 Earth Radii and M = 2.59 ± 2.0 Earth Masses (Marcy et al. 2014, ApJS, 210, 20). This research is funded by a NASA EPSCoR grant.

Evidence for two spin-glass transitions with magnetoelastic and magnetoelectric couplings in the multiferroic (B i1 -xB ax) (F e1 -xT ix ) O3 system

Science.gov (United States)

Kumar, Arun; Kaushik, S. D.; Siruguri, V.; Pandey, Dhananjai

2018-03-01

For disordered Heisenberg systems with small single ion anisotropy (D ), two spin-glass (SG) transitions below the long-range ordered (LRO) phase transition temperature (Tc) have been predicted theoretically for compositions close to the percolation threshold. Experimental verification of these predictions is still controversial for conventional spin glasses. We show that multiferroic spin-glass systems can provide a unique platform for verifying these theoretical predictions via a study of change in magnetoelastic and magnetoelectric couplings, obtained from an analysis of diffraction data, at the spin-glass transition temperatures (TSG). Results of macroscopic (dc M (H , T ), M(t ), ac susceptibility [χ (ω, T )], and specific heat (Cp)) and microscopic (x-ray and neutron scattering) measurements are presented on disordered BiFe O3 , a canonical Heisenberg system with small single ion anisotropy, which reveal appearance of two spin-glass phases, SG1 and SG2, in coexistence with the LRO phase below the Almeida-Thouless (A-T) and Gabey-Toulouse (G-T) lines. It is shown that the temperature dependence of the integrated intensity of the antiferromagnetic (AFM) peak shows dips with respect to the Brillouin function behavior around the SG1 and SG2 transition temperatures. The temperature dependence of the unit cell volume departs from the Debye-Grüneisen behavior below the SG1 transition and the magnitude of departure increases significantly with decreasing temperature up to the electromagnon driven transition temperature below which a small change of slope occurs followed by another similar change of slope at the SG2 transition temperature. The ferroelectric polarization also changes significantly at the two spin-glass transition temperatures. These results, obtained using microscopic techniques, clearly demonstrate that the SG1 and SG2 transitions occur on the same magnetic sublattice and are intrinsic to the system. We also construct a phase diagram showing all

Integer Quantum Magnon Hall Plateau-Plateau Transition in a Spin Ice Model

OpenAIRE

Xu, Baolong; Ohtsuki, Tomi; Shindou, Ryuichi

2016-01-01

Low-energy magnon bands in a two-dimensional spin ice model become integer quantum magnon Hall bands. By calculating the localization length and the two-terminal conductance of magnon transport, we show that the magnon bands with disorders undergo a quantum phase transition from an integer quantum magnon Hall regime to a conventional magnon localized regime. Finite size scaling analysis as well as a critical conductance distribution shows that the quantum critical point belongs to the same un...

Evidence for a temperature-induced spin-state transition of Co3+ in La2-xSrxCoO4

Science.gov (United States)

Hollmann, N.; Haverkort, M. W.; Benomar, M.; Cwik, M.; Braden, M.; Lorenz, T.

2011-05-01

We study the magnetic susceptibility of mixed-valent La2-xSrxCoO4 single crystals in the doping range of 0.5⩽x⩽0.8 for temperatures up to 1000 K. The magnetism below room temperature is described by paramagnetic Co2+ in the high-spin state and by Co3+ in the nonmagnetic low-spin state. At high temperatures, an increase in susceptibility is seen, which we attribute to a temperature-induced spin-state transition of Co3+. The susceptibility is analyzed by comparison to full-multiplet calculations for the thermal population of the high- and intermediate-spin states of Co3+.

Evidence of spin transition and charge order in cobalt substituted La sub 0 sub . sub 7 Ca sub 0 sub . sub 3 MnO sub 3

CERN Document Server

Srivastava, C M; Gundurao, T K; Nigam, A K; Bahadur, D

2003-01-01

The transport and magnetic studies of a series of compounds having the general formula La sub 0 sub . sub 7 Ca sub 0 sub . sub 3 Mn sub 1 sub - sub x Co sub x O sub 3 (0.1 = 0.25 there is a clear spin transition at low temperature from the high to the low spin state of trivalent cobalt and this leads to change in ferromagnetic (FM) and antiferromagnetic (AFM) phases. For x >= 0.25 there are two transitions for each value of x: the upper one gives the FM and AFM spin arrangement depending upon whether the DE or the SE dominates; the lower one is obtained due to the transition from the high to the low spin state of the trivalent cobalt ion.

Spin waves in antiferromagnetic FeF2

DEFF Research Database (Denmark)

Hutchings, M T; Rainford, B.D.; Guggenheim, H J

1970-01-01

Spin-wave dispersion in antiferromagnetic FeF2 has been investigated by inelastic neutron scattering using a chopper time-of-flight spectrometer. The single mode observed has a relatively flat dispersion curve rising from 53 cm-1 at the zone centre to 79 cm-1 at the zone boundary. A spin Hamilton......Spin-wave dispersion in antiferromagnetic FeF2 has been investigated by inelastic neutron scattering using a chopper time-of-flight spectrometer. The single mode observed has a relatively flat dispersion curve rising from 53 cm-1 at the zone centre to 79 cm-1 at the zone boundary. A spin...

Transit time corrected arterial spin labeling technique aids to overcome delayed transit time effect

International Nuclear Information System (INIS)

Yun, Tae Jin; Sohn, Chul-Ho; Yoo, Roh-Eul; Kang, Kyung Mi; Choi, Seung Hong; Kim, Ji-hoon; Park, Sun-Won; Hwang, Moonjung; Lebel, R.M.

2018-01-01

This study aimed to evaluate the usefulness of transit time corrected cerebral blood flow (CBF) maps based on multi-phase arterial spin labeling MR perfusion imaging (ASL-MRP). The Institutional Review Board of our hospital approved this retrospective study. Written informed consent was waived. Conventional and multi-phase ASL-MRPs and dynamic susceptibility contrast MR perfusion imaging (DSC-MRP) were acquired for 108 consecutive patients. Vascular territory-based volumes of interest were applied to CBF and time to peak (TTP) maps obtained from DSC-MRP and CBF maps obtained from conventional and multi-phase ASL-MRPs. The concordances between normalized CBF (nCBF) from DSC-MRP and nCBF from conventional and transition time corrected CBF maps from multi-phase ASL-MRP were evaluated using Bland-Altman analysis. In addition, the dependence of difference between nCBF (ΔnCBF) values obtained from DSC-MRP and conventional ASL-MRP (or multi-phase ASL-MRP) on TTP obtained from DSC-MRP was also analyzed using regression analysis. The values of nCBFs from conventional and multi-phase ASL-MRPs had lower values than nCBF based on DSC-MRP (mean differences, 0.08 and 0.07, respectively). The values of ΔnCBF were dependent on TTP values from conventional ASL-MRP technique (F = 5.5679, P = 0.0384). No dependency of ΔnCBF on TTP values from multi-phase ASL-MRP technique was revealed (F = 0.1433, P > 0.05). The use of transit time corrected CBF maps based on multi-phase ASL-MRP technique can overcome the effect of delayed transit time on perfusion maps based on conventional ASL-MRP. (orig.)

Transit time corrected arterial spin labeling technique aids to overcome delayed transit time effect

Energy Technology Data Exchange (ETDEWEB)

Yun, Tae Jin; Sohn, Chul-Ho; Yoo, Roh-Eul; Kang, Kyung Mi; Choi, Seung Hong; Kim, Ji-hoon [Seoul National University Medical Research Center, Institute of Radiation Medicine, Seoul (Korea, Republic of); Seoul National University Hospital, Department of Radiology, Seoul (Korea, Republic of); Park, Sun-Won [Seoul National University Medical Research Center, Institute of Radiation Medicine, Seoul (Korea, Republic of); Seoul National University Boramae Medical Center, Department of Radiology, Seoul (Korea, Republic of); Hwang, Moonjung [GE Healthcare Korea, Seoul (Korea, Republic of); Lebel, R.M. [GE Healthcare Canada, Calgary (Canada)

2018-03-15

This study aimed to evaluate the usefulness of transit time corrected cerebral blood flow (CBF) maps based on multi-phase arterial spin labeling MR perfusion imaging (ASL-MRP). The Institutional Review Board of our hospital approved this retrospective study. Written informed consent was waived. Conventional and multi-phase ASL-MRPs and dynamic susceptibility contrast MR perfusion imaging (DSC-MRP) were acquired for 108 consecutive patients. Vascular territory-based volumes of interest were applied to CBF and time to peak (TTP) maps obtained from DSC-MRP and CBF maps obtained from conventional and multi-phase ASL-MRPs. The concordances between normalized CBF (nCBF) from DSC-MRP and nCBF from conventional and transition time corrected CBF maps from multi-phase ASL-MRP were evaluated using Bland-Altman analysis. In addition, the dependence of difference between nCBF (ΔnCBF) values obtained from DSC-MRP and conventional ASL-MRP (or multi-phase ASL-MRP) on TTP obtained from DSC-MRP was also analyzed using regression analysis. The values of nCBFs from conventional and multi-phase ASL-MRPs had lower values than nCBF based on DSC-MRP (mean differences, 0.08 and 0.07, respectively). The values of ΔnCBF were dependent on TTP values from conventional ASL-MRP technique (F = 5.5679, P = 0.0384). No dependency of ΔnCBF on TTP values from multi-phase ASL-MRP technique was revealed (F = 0.1433, P > 0.05). The use of transit time corrected CBF maps based on multi-phase ASL-MRP technique can overcome the effect of delayed transit time on perfusion maps based on conventional ASL-MRP. (orig.)

Field induced phase transition in layered honeycomb spin system α-RuCl3 studied by thermal conductivity

Science.gov (United States)

Leahy, Ian; Bornstein, Alex; Choi, Kwang-Yong; Lee, Minhyea

α -RuCl3, a quasi -two-dimensional honeycomb lattice is known to be a candidate material to realize the Heisenberg-Kitaev spin model of a highly anisotropic bond-dependent exchange interaction. We investigate in-plane thermal conductivity (κ) as a function of temperature (T) and in-plane applied field (H). At H = 0 , the onset of a strong increase in κ marks the spontaneous long range ordering temperature, Tc = 6 . 5 K , corresponding to ``zigzag'' antiferromagnetic ordering. A broad peak appearing below Tc in κ was found to be suppressed significantly as H increases up to ~ 7 T , implying the system undergoes a field-induced transition from ordered to a new spin-disordered state analogous to the transverse-field Ising model. Further increasing H above 7 . 1 T , the large field seems to begin polarizing spins thus increasing the phonon mean free path, resulting in a significant rise in κ. This tendency is clearly shown in the field dependence of κ below Tc, which has a pronounced minimum at Hmin = 7 . 1 T . We will discuss our scaling analysis to characterize this field-induced phase transition and compare to the transverse-field Ising spin system. Work at the University of Colorado was supported by the US DOE Basic Energy Sciences under Award No. DE-SC0006888.

Mixed spin-3/2 and spin-5/2 Ising system on the Bethe lattice

International Nuclear Information System (INIS)

Albayrak, Erhan; Yigit, Ali

2006-01-01

In order to study the critical behaviors of the half-integer mixed spin-3/2 and spin-5/2 Blume-Capel Ising ferrimagnetic system, we have used the exact recursion relations on the Bethe lattice. The system was studied for the coordination numbers with q=3, 4, 5 and 6, and the obtained phase diagrams are illustrated on the (kT c /|J|,D A /|J|) plane for constant values of D B /|J|, the reduced crystal field of the sublattice with spin-5/2, and on the (kT c /|J|,D B /|J|) plane for constant values of D A /|J|, the reduced crystal field of the sublattice with spin-3/2, for q=3 only, since the cases corresponding to q=4, 5 and 6 reproduce results similar to the case for q=3. In addition we have also presented the phase diagram with equal strengths of the crystal fields for q=3, 4, 5 and 6. Besides the second- and first-order phase transitions, the system also exhibits compensation temperatures for appropriate values of the crystal fields. In this mixed spin system while the second-order phase transition lines never cut the reduced crystal field axes as in the single spin type spin-3/2 and spin-5/2 Ising models separately, the first-order phase transition lines never connect to the second-order phase transition lines and they end at the critical points, therefore the system does not give any tricritical points. In addition to this, this mixed-spin model exhibits one or two compensation temperatures depending on the values of the crystal fields, as a result the compensation temperature lines show reentrant behavior

Spin-waves in antiferromagnetic single crystal LiFePO$_4$

OpenAIRE

Li, Jiying; Garlea, Vasile O.; Zarestky, Jerel L.; Vaknin, David

2005-01-01

Spin-wave dispersions in the antiferromagnetic state of single crystal LiFePO$_4$ were determined by inelastic neutron scattering measurements. The dispersion curves measured from the (010) reflection along both {\\it a}$^\\ast$ and {\\it b}$^\\ast$ reciprocal-space directions reflect the anisotropic coupling of the layered Fe$^{2+}$ (S = 2) spin-system. The spin-wave dispersion curves were theoretically modeled using linear spin-wave theory by including in the spin-Hamiltonian in-plane nearest- ...

Structural anomalies, spin transitions and charge disproportionation in LnCoO.sub.3./sub..

Czech Academy of Sciences Publication Activity Database

Knížek, Karel; Jirák, Zdeněk; Hejtmánek, Jiří; Henry, P.; André, G.

2008-01-01

Roč. 103, č. 7 (2008), 07B703/1-07B703/3 ISSN 0021-8979 R&D Projects: GA ČR GA202/06/0051 Institutional research plan: CEZ:AV0Z10100521 Keywords : LnCoO 3 * neutron diffraction * thermal expansion * spin-state transition Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.201, year: 2008

Spin nematics next to spin singlets

Science.gov (United States)

Yokoyama, Yuto; Hotta, Chisa

2018-05-01

We provide a route to generate nematic order in a spin-1/2 system. Unlike the well-known magnon-binding mechanism, our spin nematics requires neither the frustration effect nor spin polarization in a high field or in the vicinity of a ferromagnet, but instead appears next to the spin singlet phase. We start from a state consisting of a quantum spin-1/2 singlet dimer placed on each site of a triangular lattice, and show that interdimer ring exchange interactions efficiently dope the SU(2) triplets that itinerate and interact, easily driving a stable singlet state to either Bose-Einstein condensates or a triplet crystal, some hosting a spin nematic order. A variety of roles the ring exchange serves includes the generation of a bilinear-biquadratic interaction between nearby triplets, which is responsible for the emergent nematic order separated from the singlet phase by a first-order transition.

Electron spin torque in atoms

International Nuclear Information System (INIS)

Hara, Takaaki; Senami, Masato; Tachibana, Akitomo

2012-01-01

The spin torque and zeta force, which govern spin dynamics, are studied by using monoatoms in their steady states. We find nonzero local spin torque in transition metal atoms, which is in balance with the counter torque, the zeta force. We show that d-orbital electrons have a crucial effect on these torques. Nonzero local chirality density in transition metal atoms is also found, though the electron mass has the effect to wash out nonzero chirality density. Distribution patterns of the chirality density are the same for Sc–Ni atoms, though the electron density distributions are different. -- Highlights: ► Nonzero local spin torque is found in the steady states of transition metal atoms. ► The spin steady state is realized by the existence of a counter torque, zeta force. ► D-orbital electrons have a crucial effect on the spin torque and zeta force. ► Nonzero local chiral density is found in spite of the washout by the electron mass. ► Chiral density distribution have the same pattern for Sc–Ni atoms.

A no-go theorem for the consistent quantization of the massive gravitino on Robertson-Walker spacetimes and arbitrary spin 3/2 fields on general curved spacetimes

Energy Technology Data Exchange (ETDEWEB)

Hack, Thomas-Paul; Makedonski, Mathias [Hamburg Univ. (Germany). II. Inst. fuer Theoretische Physik

2011-06-15

We first introduce a set of conditions which assure that a free spin (3)/(2) field with m{>=}0 can be consistently ('unitarily') quantized on all four-dimensional curved spacetimes, i.e. also on spacetimes which are not assumed to be solutions of the Einstein equations. We discuss a large - and, as we argue, exhaustive - class of spin (3)/(2) field equations obtained from the Rarita-Schwinger equation by the addition of non-minimal couplings and prove that no equation in this class fulfils all sufficient conditions. Afterwards, we investigate the situation in supergravity, where the curved background is usually assumed to satisfy the Einstein equations and, hence, detailed knowledge on the spacetime curvature is available. We provide a necessary condition for the unitary quantization of a spin (3)/(2) Majorana field and prove that this condition is not met by supergravity models in four-dimensional Robertson-Walker spacetimes if local supersymmetry is broken. Our proof is model-independent as we merely assume that the gravitino has the standard kinetic term. (orig.)

Electronic Structure from Iron L-edge Spectroscopy : An Example of Spin Transition Evidenced by Soft X-ray Absorption Spectroscopy

NARCIS (Netherlands)

Cartier dit Moulin, Ch.; Flank, A.M.; Rudolf, P.; Chen, C.T.

1993-01-01

Soft X-ray Absorption Spectroscopy at the transition metal L2,3 edges provides information about the 3d unoccupied states by dipole allowed transitions. We have recorded iron L2,3 edges in order to follow the reversible thermal spin interconversion (S=2 S=0) of the Fe(II)(o-phenantroline)2(NCS)2.

Understanding the spin-driven polarizations in Bi MO3 (M = 3 d transition metals) multiferroics

Science.gov (United States)

Kc, Santosh; Lee, Jun Hee; Cooper, Valentino R.

Bismuth ferrite (BiFeO3) , a promising multiferroic, stabilizes in a perovskite type rhombohedral crystal structure (space group R3c) at room temperature. Recently, it has been reported that in its ground state it possess a huge spin-driven polarization. To probe the underlying mechanism of this large spin-phonon response, we examine these couplings within other Bi based 3 d transition metal oxides Bi MO3 (M = Ti, V, Cr, Mn, Fe, Co, Ni) using density functional theory. Our results demonstrate that this large spin-driven polarization is a consequence of symmetry breaking due to competition between ferroelectric distortions and anti-ferrodistortive octahedral rotations. Furthermore, we find a strong dependence of these enhanced spin-driven polarizations on the crystal structure; with the rhombohedral phase having the largest spin-induced atomic distortions along [111]. These results give us significant insights into the magneto-electric coupling in these materials which is essential to the magnetic and electric field control of electric polarization and magnetization in multiferroic based devices. Research is supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division and the Office of Science Early Career Research Program (V.R.C) and used computational resources at NERSC.

Scaling of quantum Fisher information close to the quantum phase transition in the XY spin chain

Energy Technology Data Exchange (ETDEWEB)

Ye, En-Jia, E-mail: yeenjia@jiangnan.edu.cn [Jiangsu Provincial Research Center of Light Industrial Optoelectronic Engineering and Technology, School of Science, Jiangnan University, Wuxi 214122 (China); Hu, Zheng-Da [Jiangsu Provincial Research Center of Light Industrial Optoelectronic Engineering and Technology, School of Science, Jiangnan University, Wuxi 214122 (China); Wu, Wei [Zhejiang Institute of Modern Physics and Physics Department, Zhejiang University, Hangzhou 310027 (China)

2016-12-01

The quantum phase transition of an XY spin chain is investigated by employing the quantum Fisher information encoded in the ground state. It is shown that the quantum Fisher information is an effective tool for characterizing the quantum criticality. The quantum Fisher information, its first and second derivatives versus the transverse field display the phenomena of sudden transition, sudden jump and divergence, respectively. Besides, the analysis of finite size scaling for the second derivative of quantum Fisher information is performed.

Study on gamma-ray transitions induced in nuclear spin isomers by X-rays

International Nuclear Information System (INIS)

Yang Tianli; Hao Fanhua; Liu Xiaoya; Gong Jian

2005-10-01

The development of induced X-ray has been summarized for high spin isomer. the radiation model, transition mechanism and experiment plan have been introduced. The experiments about isomers 180m Ta and 178m2 Hf have been narrated in detail respectively, and the analysis between those results have been obtained. The reasonable theoretical frame and good experimental data have offered the powerful technique base for pumping γ-ray laser with low energy. (authors)

Pressure effect on hysteresis in spin-crossover solid materials

Energy Technology Data Exchange (ETDEWEB)

Gudyma, Iurii, E-mail: yugudyma@gmail.com [Department of General Physics, Chernivtsi National University, Chernivtsi 58012 (Ukraine); Ivashko, Victor [Department of General Physics, Chernivtsi National University, Chernivtsi 58012 (Ukraine); Dimian, Mihai [Department of Electrical and Computer Engineering, Howard University, Washington DC 20059 (United States); Faculty of Electrical Engineering and Computer Science & Integrated Center for Research, Development and Innovation in Advanced Materials, Nanotechnologies, and Distributed Systems for fabrication and control, Stefan cel Mare University, Suceava 720229 (Romania)

2016-04-01

A generalized microscopic Ising-like model is proposed to describe behavior of compressible spin-crossover solids with two states: low-spin and high-spin. The model was solved in mean-field approximation and shows hysteretic behavior at low energy difference between the states. We study the thermal transition between states under external hydrostatic pressure taking into account the changes in the volume of spin-crossover molecules in different states. Depending on the applied pressure, a spin-crossover system can have three types of behavior of molecular fraction in the high-spin state: hysteretic, second-order phase transition and no-phase transition. For the hysteretic regime, it is shown that the transition temperature under pressure is increased while the width of the hysteresis reduced.

Spin relaxation near the metal-insulator transition: dominance of the Dresselhaus spin-orbit coupling.

Science.gov (United States)

Intronati, Guido A; Tamborenea, Pablo I; Weinmann, Dietmar; Jalabert, Rodolfo A

2012-01-06

We identify the Dresselhaus spin-orbit coupling as the source of the dominant spin-relaxation mechanism in the impurity band of a wide class of n-doped zinc blende semiconductors. The Dresselhaus hopping terms are derived and incorporated into a tight-binding model of impurity sites, and they are shown to unexpectedly dominate the spin relaxation, leading to spin-relaxation times in good agreement with experimental values. This conclusion is drawn from two complementary approaches: an analytical diffusive-evolution calculation and a numerical finite-size scaling study of the spin-relaxation time.

On the possibility of contact-induced spin polarization in interfaces of armchair nanotubes with transition metal substrates

Energy Technology Data Exchange (ETDEWEB)

Kuzubov, Alexander A. [Siberian Federal University, 79 Svobodny Prospect, 660041 Krasnoyarsk (Russian Federation); Kirensky Institute of Physics, 50 Akademgorodok, 660036 Krasnoyarsk (Russian Federation); Kovaleva, Evgenia A., E-mail: kovaleva.evgeniya1991@mail.ru [Siberian Federal University, 79 Svobodny Prospect, 660041 Krasnoyarsk (Russian Federation); Kirensky Institute of Physics, 50 Akademgorodok, 660036 Krasnoyarsk (Russian Federation); Tomilin, Felix N.; Mikhaleva, Natalya S.; Kuklin, Artem V. [Siberian Federal University, 79 Svobodny Prospect, 660041 Krasnoyarsk (Russian Federation); Kirensky Institute of Physics, 50 Akademgorodok, 660036 Krasnoyarsk (Russian Federation)

2015-12-15

The interaction between armchair carbon and boron nitride nanotubes (NT) with ferromagnetic transition metal (TM) surfaces, namely, Ni(111) and Co(0001), was studied by means of density functional theory. Different configurations of composite compartments mutual arrangement were considered. Partial densities of states and spin density spatial distribution of optimized structures were investigated. Influence of ferromagnetic substrate on nanotubes’ electronic properties was discussed. The values of spin polarization magnitude at the Fermi level are also presented and confirm the patterns of spin density spatial distribution. - Highlights: • Interaction of armchair nanotubes with ferromagnetic metal surfaces was investigated. • Different configurations of nanotube's location were considered. • For all nanotubes the energy difference between configurations is negligible. • Nanotubes were found to be more or less spin-polarized regarding to the configuration. • BN nanotubes demonstrate vanishing of the band gap and contact-induced conductivity.

Spin Transition in the Lower Mantle: Deep Learning and Pattern Recognition of Superplumes from the Mid-mantle and Mid-mantle Slab Stagnation

Science.gov (United States)

Yuen, D. A.; Shahnas, M. H.; De Hoop, M. V.; Pysklywec, R.

2016-12-01

The broad, slow seismic anomalies under Africa and Pacific cannot be explained without ambiguity. There is no well-established theory to explain the fast structures prevalent globally in seismic tomographic images that are commonly accepted to be the remnants of fossil slabs at different depths in the mantle. The spin transition from high spin to low spin in iron in ferropericlase and perovskite, two major constituents of the lower mantle can significantly impact their physical properties. We employ high resolution 2D-axisymmetric and 3D-spherical control volume models to reconcile the influence of the spin transition-induced anomalies in density, thermal expansivity, and bulk modulus in ferropericlase and perovskite on mantle dynamics. The model results reveal that the spin transition effects increase the mixing in the lower regions of mantle. Depending on the changes of bulk modulus associated with the spin transition, these effects may also cause both stagnation of slabs and rising plumes at mid-mantle depths ( 1600 km). The stagnation may be followed by downward or upward penetration of cold or hot mantle material, respectively, through an avalanche process. The size of these mid-mantle plumes reaches 1500 km across with a radial velocity reaching 20 cm/yr near the seismic transition zone and plume heads exceeding 2500 km across. We will employ a deep-learning algorithm to formulate this challenge as a classification problem where modelling/computation aids in the learning stage for detecting the particular patterns.The parameters based on which the convection models are developed are poorly constrained. There are uncertainties in initial conditions, heterogeneities and boundary conditions in the simulations, which are nonlinear. Thus it is difficult to reconstruct the past configuration over long time scales. In order to extract information and better understand the parameters in mantle convection, we employ deep learning algorithm to search for different

Relaxation theory of spin-3/2 Ising system near phase transition temperatures

International Nuclear Information System (INIS)

Canko, Osman; Keskin, Mustafa

2010-01-01

Dynamics of a spin-3/2 Ising system Hamiltonian with bilinear and biquadratic nearest-neighbour exchange interactions is studied by a simple method in which the statistical equilibrium theory is combined with the Onsager's theory of irreversible thermodynamics. First, the equilibrium behaviour of the model in the molecular-field approximation is given briefly in order to obtain the phase transition temperatures, i.e. the first- and second-order and the tricritical points. Then, the Onsager theory is applied to the model and the kinetic or rate equations are obtained. By solving these equations three relaxation times are calculated and their behaviours are examined for temperatures near the phase transition points. Moreover, the z dynamic critical exponent is calculated and compared with the z values obtained for different systems experimentally and theoretically, and they are found to be in good agrement. (general)

Mixed spin Ising model with four-spin interaction and random crystal field

International Nuclear Information System (INIS)

Benayad, N.; Ghliyem, M.

2012-01-01

The effects of fluctuations of the crystal field on the phase diagram of the mixed spin-1/2 and spin-1 Ising model with four-spin interactions are investigated within the finite cluster approximation based on a single-site cluster theory. The state equations are derived for the two-dimensional square lattice. It has been found that the system exhibits a variety of interesting features resulting from the fluctuation of the crystal field interactions. In particular, for low mean value D of the crystal field, the critical temperature is not very sensitive to fluctuations and all transitions are of second order for any value of the four-spin interactions. But for relatively high D, the transition temperature depends on the fluctuation of the crystal field, and the system undergoes tricritical behaviour for any strength of the four-spin interactions. We have also found that the model may exhibit reentrance for appropriate values of the system parameters.

Heisenberg spin glass experiments and the chiral ordering scenario

International Nuclear Information System (INIS)

Campbell, Ian A.; Petit, Dorothee C.M.C.

2010-01-01

An overview is given of experimental data on Heisenberg spin glass materials so as to make detailed comparisons with numerical results on model Heisenberg spin glasses, with particular reference to the chiral driven ordering transition scenario due to Kawamura and collaborators. On weak anisotropy systems, experiments show critical exponents which are very similar to those estimated numerically for the model Heisenberg chiral ordering transition but which are quite different from those at Ising spin glass transitions. Again on weak anisotropy Heisenberg spin glasses, experimental torque data show well defined in-field transverse ordering transitions up to strong applied fields, in contrast to Ising spin glasses where fields destroy ordering. When samples with stronger anisotropies are studied, critical and in-field behavior tend progressively towards the Ising limit. It can be concluded that the essential physics of laboratory Heisenberg spin glasses mirrors that of model Heisenberg spin glasses, where chiral ordering has been demonstrated numerically. (author)

Large spin relaxation anisotropy and valley-Zeeman spin-orbit coupling in WSe2/graphene/h -BN heterostructures

Science.gov (United States)

Zihlmann, Simon; Cummings, Aron W.; Garcia, Jose H.; Kedves, Máté; Watanabe, Kenji; Taniguchi, Takashi; Schönenberger, Christian; Makk, Péter

2018-02-01

Large spin-orbital proximity effects have been predicted in graphene interfaced with a transition-metal dichalcogenide layer. Whereas clear evidence for an enhanced spin-orbit coupling has been found at large carrier densities, the type of spin-orbit coupling and its relaxation mechanism remained unknown. We show an increased spin-orbit coupling close to the charge neutrality point in graphene, where topological states are expected to appear. Single-layer graphene encapsulated between the transition-metal dichalcogenide WSe2 and h -BN is found to exhibit exceptional quality with mobilities as high as 1 ×105 cm2 V-1 s-1. At the same time clear weak antilocalization indicates strong spin-orbit coupling, and a large spin relaxation anisotropy due to the presence of a dominating symmetric spin-orbit coupling is found. Doping-dependent measurements show that the spin relaxation of the in-plane spins is largely dominated by a valley-Zeeman spin-orbit coupling and that the intrinsic spin-orbit coupling plays a minor role in spin relaxation. The strong spin-valley coupling opens new possibilities in exploring spin and valley degree of freedom in graphene with the realization of new concepts in spin manipulation.

Wetting and layering transitions of a spin-1/2 Ising model in a random transverse field

International Nuclear Information System (INIS)

Bahmad, L.; Benyoussef, A.; El-Kenz, A.; Ez-Zahraouy, H.

2000-09-01

The effect of a random transverse field (RTF) on the wetting and layering transitions of a spin-1/2 Ising model, in the presence of bulk and surface fields, is studied within an effective field theory by using the differential operator technique. Indeed, the dependencies of the wetting temperature and wetting transverse field on the probability of the presence of a transverse field are established. For specific values of the surface field we show the existence of a critical probability p, above which wetting and layering transitions disappear. (author)

Theory of relaxation phenomena in a spin-3/2 Ising system near the second-order phase transition temperature

International Nuclear Information System (INIS)

Keskin, Mustafa; Canko, Osman

2005-01-01

The relaxation behavior of the spin-3/2 Ising model Hamiltonian with bilinear and biquadratic interactions near the second-order phase transition temperature or critical temperature is studied by means of the Onsager's theory of irreversible thermodynamics or the Onsager reciprocity theorem (ORT). First, we give the equilibrium case briefly within the molecular-field approximation in order to study the relaxation behavior by using the ORT. Then, the ORT is applied to the model and the kinetic equations are obtained. By solving these equations, three relaxation times are calculated and examined for temperatures near the second-order phase transition temperature. It is found that one of the relaxation times goes to infinity near the critical temperature on either side, the second relaxation time makes a cusp at the critical temperature and third one behaves very differently in which it terminates at the critical temperature while approaching it, then showing a 'flatness' property and then decreases. We also study the influences of the Onsager rate coefficients on the relaxation times. The behavior of these relaxation times is discussed and compared with the spin-1/2 and spin-1 Ising systems

Transitional millisecond pulsars in the low-level accretion state

Science.gov (United States)

Jaodard, Amruta D.; Hessels, Jason W. T.; Archibald, Anne; Bogdanov, Slavko; Deller, Adam; Hernandez Santisteban, Juan; Patruno, Alessandro; D'Angelo, Caroline; Bassa, Cees; Amruta Jaodand

2018-01-01

In the canonical pulsar recycling scenario, a slowly spinning neutron star can be rejuvenated to rapid spin rates by the transfer of angular momentum and mass from a binary companion star. Over the last decade, the discovery of three transitional millisecond pulsars (tMSPs) has allowed us to study recycling in detail. These systems transition between accretion-powered (X-ray) and rotation-powered (radio) pulsar states within just a few days, raising questions such as: what triggers the state transition, when does the recycling process truly end, and what will the radio pulsar’s final spin rate be? Systematic multi-wavelength campaigns over the last decade have provided critical insights: multi-year-long, low-level accretion states showing coherent X-ray pulsations; extremely stable, bi-modal X-ray light curves; outflows probed by radio continuum emission; a surprising gamma-ray brightening during accretion, etc. In my thesis I am trying to bring these clues together to understand the low-level accretion process that recycles a pulsar. For example, recently we timed PSR J1023+0038 in the accretion state and found it to be spinning down ~26% faster compared to the non-accreting radio pulsar state. We are currently conducting simultaneous multi-wavelength campaigns (XMM, HST, Kepler and VLA) to understand the global variability of the accretion flow, as well as high-energy Fermi-LAT observations to probe the gamma-ray emission mechanism. I will highlight these recent developments, while also presenting a broad overview of tMSPs as exciting new laboratories to test low-level accretion onto magnetized neutron stars.

DISCOVERY OF GAMMA-RAY PULSATIONS FROM THE TRANSITIONAL REDBACK PSR J1227-4853

Energy Technology Data Exchange (ETDEWEB)

Johnson, T. J. [College of Science, George Mason University, Fairfax, VA 22030 (United States); Ray, P. S.; Cheung, C. C. [Space Science Division, Naval Research Laboratory, Washington, DC 20375-5352 (United States); Roy, J.; Bhattacharyya, B.; Stappers, B. W. [Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL (United Kingdom); Harding, A. K. [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Pletsch, H. J.; Fort, S. [Albert-Einstein-Institut, Max-Planck-Institut für Gravitationsphysik, D-30167 Hannover (Germany); Camilo, F. [Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States); Deneva, J. [National Research Council Research Associate, National Academy of Sciences, Washington, DC 20001 (United States); Kerr, M., E-mail: tyrel.j.johnson@gmail.com, E-mail: Paul.Ray@nrl.navy.mil, E-mail: jayanta.roy@manchester.ac.uk [CSIRO Astronomy and Space Science, Australia Telescope National Facility, Epping NSW 1710 (Australia)

2015-06-10

The 1.69 ms spin period of PSR J1227−4853 was recently discovered in radio observations of the low-mass X-ray binary XSS J12270−4859 following the announcement of a possible transition to a rotation-powered millisecond pulsar state, inferred from decreases in optical, X-ray, and gamma-ray flux from the source. We report the detection of significant (5σ) gamma-ray pulsations after the transition, at the known spin period, using ∼1 year of data from the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. The gamma-ray light curve of PSR J1227−4853 can be fit by one broad peak, which occurs at nearly the same phase as the main peak in the 1.4 GHz radio profile. The partial alignment of light-curve peaks in different wavebands suggests that at least some of the radio emission may originate at high altitude in the pulsar magnetosphere, in extended regions co-located with the gamma-ray emission site. We folded the LAT data at the orbital period, both pre- and post-transition, but find no evidence for significant modulation of the gamma-ray flux. Analysis of the gamma-ray flux over the mission suggests an approximate transition time of 2012 November 30. Continued study of the pulsed emission and monitoring of PSR J1227−4853, and other known redback systems, for subsequent flux changes will increase our knowledge of the pulsar emission mechanism and transitioning systems.

Observation of the anisotropic spin-glass transition and transverse spin ordering in pseudo-brookite through muon spin relaxation

NARCIS (Netherlands)

Boekema, C.; Brabers, V.A.M.; Lichti, R.L.; Denison, A.B.; Cooke, D.W.; Heffner, R.H.; Hutson, R.L.; Schillaci, M.E.; MacLaughlin, D.E.; Dodds, S.A.

1986-01-01

Zero-field longitudinal muon-spin-relaxation (µSR) experiments have been performed on single crystals of pseudo-brookite (Fe2-xTil+x O 5; x=0.25), an anisotropic spin-glass system. The spinglass temperature (Tg) is determined to be 44.0±0.5K. Above Tg, a distinct exponential muon-spin-relaxation

Quantum Monte Carlo studies of a metallic spin-density wave transition

Energy Technology Data Exchange (ETDEWEB)

Gerlach, Max Henner

2017-01-20

Plenty experimental evidence indicates that quantum critical phenomena give rise to much of the rich physics observed in strongly correlated itinerant electron systems such as the high temperature superconductors. A quantum critical point of particular interest is found at the zero-temperature onset of spin-density wave order in two-dimensional metals. The appropriate low-energy theory poses an exceptionally hard problem to analytic theory, therefore the unbiased and controlled numerical approach pursued in this thesis provides important contributions on the road to comprehensive understanding. After discussing the phenomenology of quantum criticality, a sign-problem-free determinantal quantum Monte Carlo approach is introduced and an extensive toolbox of numerical methods is described in a self-contained way. By the means of large-scale computer simulations we have solved a lattice realization of the universal effective theory of interest. The finite-temperature phase diagram, showing both a quasi-long-range spin-density wave ordered phase and a d-wave superconducting dome, is discussed in its entirety. Close to the quantum phase transition we find evidence for unusual scaling of the order parameter correlations and for non-Fermi liquid behavior at isolated hot spots on the Fermi surface.

Dynamic Phase Transitions In The Spin-2 Ising System Under An Oscillating Magnetic Field Within The Effective-Field Theory

International Nuclear Information System (INIS)

Ertas, Mehmet; Keskin, Mustafa; Deviren, Bayram

2010-01-01

The dynamic phase transitions are studied in the spin-2 Ising model under a time-dependent oscillating magnetic field by using the effective-field theory with correlations. The effective-field dynamic equation is derived by employing the Glauber transition rates and the phases in the system are obtained by solving this dynamic equation. The nature (first- or second-order) of the dynamic phase transition is characterized by investigating the thermal behavior of the dynamic order parameter and the dynamic phase transition temperatures are obtained. The dynamic phase diagrams are presented in (T/zJ, h/zJ) plane.

Analytical description of spin-Rabi oscillation controlled electronic transitions rates between weakly coupled pairs of paramagnetic states with S=(1)/(2)

Science.gov (United States)

Glenn, R.; Baker, W. J.; Boehme, C.; Raikh, M. E.

2013-04-01

We report on the theoretical and experimental study of spin-dependent electronic transition rates which are controlled by a radiation-induced spin-Rabi oscillation of weakly spin-exchange and spin-dipolar coupled paramagnetic states (S=(1)/(2)). The oscillation components [the Fourier content, F(s)] of the net transition rates within spin-pair ensembles are derived for randomly distributed spin resonances, with an account of a possible correlation between the two distributions corresponding to individual pair partners. Our study shows that when electrically detected Rabi spectroscopy is conducted under an increasing driving field B1, the Rabi spectrum, F(s), evolves from a single peak at s=ΩR, where ΩR=γB1 is the Rabi frequency (γ is the gyromagnetic ratio), to three peaks at s=ΩR, s=2ΩR, and low s≪ΩR. The crossover between the two regimes takes place when ΩR exceeds the expectation value δ0 of the difference in the Zeeman energies within the pairs, which corresponds to the broadening of the magnetic resonance by disorder caused by a hyperfine field or distributions of Landé g factors. We capture this crossover by analytically calculating the shapes of all three peaks at an arbitrary relation between ΩR and δ0. When the peaks are well developed their widths are Δs˜δ02/ΩR. We find a good quantitative agreement between the theory and experiment.

Effect of Noise on the Decoherence of a Central Electron Spin Coupled to an Antiferromagnetic Spin Bath

Directory of Open Access Journals (Sweden)

G. C. Fouokeng

2014-01-01

Full Text Available We analyze the influence of a two-state autocorrelated noise on the decoherence and on the tunneling Landau-Zener (LZ transitions during a two-level crossing of a central electron spin (CES coupled to a one dimensional anisotropic-antiferomagnetic spin, driven by a time-dependent global external magnetic field. The energy splitting of the coupled spin system is found through an approach that computes the noise-averaged frequency. At low magnetic field intensity, the decoherence (or entangled state of a coupled spin system is dominated by the noise intensity. The effects of the magnetic field pulse and the spin gap antiferromagnetic material used suggest to us that they may be used as tools for the direct observation of the tunneling splitting through the LZ transitions in the sudden limit. We found that the dynamical frequencies display basin-like behavior decay with time, with the birth of entanglement, while the LZ transition probability shows Gaussian shape.

Graphene on transition-metal dichalcogenides: a platform for proximity spin-orbit physics and optospintronics

OpenAIRE

Gmitra, Martin; Fabian, Jaroslav

2015-01-01

Hybrids of graphene and two dimensional transition metal dichalcogenides (TMDC) have the potential to bring graphene spintronics to the next level. As we show here by performing first-principles calculations of graphene on monolayer MoS$_2$, there are several advantages of such hybrids over pristine graphene. First, Dirac electrons in graphene exhibit a giant global proximity spin-orbit coupling, without compromising the semimetallic character of the whole system at zero field. Remarkably, th...

Position dependent spin wave spectrum in nanostrip magnonic waveguides

International Nuclear Information System (INIS)

Wang, Qi; Zhang, Huaiwu; Ma, Guokun; Liao, Yulong; Zhong, Zhiyong; Zheng, Yun

2014-01-01

The dispersion curves of propagating spin wave along different positions in nanostrip magnonic waveguides were studied by micromagnetic simulation. The results show that the modes of spin wave in the nanostrip magnonic waveguide are dependent on the position and the weak even modes of spin wave are excited even by symmetric excitation fields in a nanostrip magnonic waveguide. The reasons of the position dependent dispersion curve are explained by associating with geometrical confinement in the nanostrip magnonic waveguide

Magnetostriction anisotropy in the rare earth RCo5 compounds on spontaneous spin-orientation phase transitions

International Nuclear Information System (INIS)

Ahdreev, A.V.; Deryagin, A.V.; Zadvorkin, S.M.

1983-01-01

The temperature dependences of parameters a and c in the crystal lattice of RCo 5 compounds (R=Pr, Tb, Dy, Ho) are studied in an X-ray diffractometer the spin reorientation region. On the basis of these data the magnetostriction constants lambdasub(1)sup(α, 2) and lambdasub(2)sup(α, 2) are determined for temperatures corresponding to the middle of reorientation regions of the compounds mentioned above (excluding PrCo 5 ). The values of lambdasub(1)sup(α, 2) and lambdasub(2)sup(α, 2) at T=0 K are calculated on the basis of the single-ion model for all the compounds investigalted and also for some other intermetallides of the RCo 5 type in which spontaneous spin reorien tation transitions do not occur

Geometrically controlled snapping transitions in shells with curved creases.

Science.gov (United States)

Bende, Nakul Prabhakar; Evans, Arthur A; Innes-Gold, Sarah; Marin, Luis A; Cohen, Itai; Hayward, Ryan C; Santangelo, Christian D

2015-09-08

Curvature and mechanics are intimately connected for thin materials, and this coupling between geometry and physical properties is readily seen in folded structures from intestinal villi and pollen grains to wrinkled membranes and programmable metamaterials. While the well-known rules and mechanisms behind folding a flat surface have been used to create deployable structures and shape transformable materials, folding of curved shells is still not fundamentally understood. Shells naturally deform by simultaneously bending and stretching, and while this coupling gives them great stability for engineering applications, it makes folding a surface of arbitrary curvature a nontrivial task. Here we discuss the geometry of folding a creased shell, and demonstrate theoretically the conditions under which it may fold smoothly. When these conditions are violated we show, using experiments and simulations, that shells undergo rapid snapping motion to fold from one stable configuration to another. Although material asymmetry is a proven mechanism for creating this bifurcation of stability, for the case of a creased shell, the inherent geometry itself serves as a barrier to folding. We discuss here how two fundamental geometric concepts, creases and curvature, combine to allow rapid transitions from one stable state to another. Independent of material system and length scale, the design rule that we introduce here explains how to generate snapping transitions in arbitrary surfaces, thus facilitating the creation of programmable multistable materials with fast actuation capabilities.

Free-energy analysis of spin models on hyperbolic lattice geometries.

Science.gov (United States)

Serina, Marcel; Genzor, Jozef; Lee, Yoju; Gendiar, Andrej

2016-04-01

We investigate relations between spatial properties of the free energy and the radius of Gaussian curvature of the underlying curved lattice geometries. For this purpose we derive recurrence relations for the analysis of the free energy normalized per lattice site of various multistate spin models in the thermal equilibrium on distinct non-Euclidean surface lattices of the infinite sizes. Whereas the free energy is calculated numerically by means of the corner transfer matrix renormalization group algorithm, the radius of curvature has an analytic expression. Two tasks are considered in this work. First, we search for such a lattice geometry, which minimizes the free energy per site. We conjecture that the only Euclidean flat geometry results in the minimal free energy per site regardless of the spin model. Second, the relations among the free energy, the radius of curvature, and the phase transition temperatures are analyzed. We found out that both the free energy and the phase transition temperature inherit the structure of the lattice geometry and asymptotically approach the profile of the Gaussian radius of curvature. This achievement opens new perspectives in the AdS-CFT correspondence theories.

Mixed-Spin Diamond Chain Cu2FePO4F4(H2O)4 with a Noncollinear Spin Order and Possible Successive Phase Transitions.

Science.gov (United States)

Lu, Hongcheng; Hayashi, Naoaki; Matsumoto, Yuki; Takatsu, Hiroshi; Kageyama, Hiroshi

2017-08-07

A diamond spin chain system, one of the one-dimensional frustrated lattices, is known to exhibit novel properties, but experimental studies have been exclusively confined to materials with a single spin component. Here, we report on the synthesis, structure, and magnetic properties of a new diamond chain compound Cu 2 FePO 4 F 4 (H 2 O) 4 1 composed of mixed-spins of Cu 2+ (S = 1/2 × 2) and Fe 3+ (S = 5/2). Compound 1 crystallizes in the space group C2/c of the monoclinic crystal system with a = 7.7546(4) Å, b = 12.1290(6) Å, c = 9.9209(6) Å, β = 105.29(1)°, and Z = 4. DC magnetization, Mössbauer spectroscopy, and heat capacity measurements revealed an antiferromagnetic order at 11.3 K with a small ferromagnetic component. It is suggested that ferrimagnetic diamond chains are arranged in an antiferromagnetic fashion (i.e., [...Fe(↑)-2Cu(↓↓)-Fe(↑)...] and [...Fe(↓)-2Cu(↑↑)-Fe(↓)...]) within the ab plane to cancel net magnetization, and the spin orientation of the diamond chains changes alternately along the c axis due to the magnetic anisotropy, leading to a noncollinear spin order. Furthermore, another anomaly is observed in the heat capacity at around 3 K, suggesting a successive magnetic transition or crossover due to competing magnetic interactions.

Quantum Fidelity and Thermal Phase Transitions in a Two-Dimensional Spin System

International Nuclear Information System (INIS)

Wang Bo; Kou Su-Peng; Huang Hai-Lin; Sun Zhao-Yu

2012-01-01

We investigate the ability of quantum fidelity in detecting the classical phase transitions (CPTs) in a two-dimensional Heisenberg—Ising mixed spin model, which has a very rich phase diagram and is exactly soluble. For a two-site subsystem of the model, the reduced fidelity (including the operator fidelity and the fidelity susceptibility) at finite temperatures is calculated, and it is found that an extreme value presents at the critical temperature, thus shows a signal for the CPTs. In some parameter region, the signal becomes blurred. We propose to use the 'normalized fidelity susceptibility' to solve this problem

Massless fields in curved space-time: The conformal formalism

International Nuclear Information System (INIS)

Castagnino, M.A.; Sztrajman, J.B.

1986-01-01

A conformally invariant theory for massless quantum fields in curved space-time is formulated. We analyze the cases of spin-0, - 1/2 , and -1. The theory is developed in the important case of an ''expanding universe,'' generalizing the particle model of ''conformal transplantation'' known for spin-0 to spins- 1/2 and -1. For the spin-1 case two methods introducing new conformally invariant gauge conditions are stated, and a problem of inconsistency that was stated for spin-1 is overcome

Electron spin exchange of shallow donor muonium states

International Nuclear Information System (INIS)

Senba, Masayoshi

2005-01-01

Shallow donor muonium states with small hyperfine frequencies, recently observed in II-VI semiconductor compounds, have a number of unique features that present both opportunities and challenges in understanding muon spin dynamics in the presence of Heisenberg spin exchange. First, the shallow muonium state in CdSe with hyperfine frequency ω 0 /2π ∼ 0.1 MHz is already in the high field regime even in the earth's magnetic field, where only two precession frequencies are observable by the muon spin rotation (μSR) technique. Second, unlike in the case of more conventional muonium species with a larger hyperfine frequency, the μSR signal of shallow muonium states can be observed even in the transition region, between the slow spin-flip regime and the fast spin-flip regime, where the spin-flip rate and the hyperfine frequency are comparable. The muon spin dynamics in the transition region has not been theoretically explored previously, mainly because normal muonium in vacuum gives no observable signal in this region. Third, in the case of shallow muonium states, the incoherent process defined to be those spin-flip collisions that cause changes in muon spin precession frequencies, becomes crucially important in the transition region, where the incoherent process is entirely negligible in more conventional muonium species. By taking incoherent multiple collisions into account, an analytical expression for the time evolution of the muon spin polarization in Mu is derived, where Mu undergoes repeated spin-flip collisions. Comparisons with Monte Carlo calculations show that the analytical expression obtained in this work can reliably be used to analyse experimental data for shallow donor states not only in the slow spin-flip regime, but also in the transition region up to the onset of the fast regime. The present work confirms a recent experimental finding that, in the transition region, the initial phases of the two precession components of shallow donor states

Zero-Field Spin Structure and Spin Reorientations in Layered Organic Antiferromagnet, κ-(BEDT-TTF)2Cu[N(CN)2]Cl, with Dzyaloshinskii-Moriya Interaction

Science.gov (United States)

Ishikawa, Rui; Tsunakawa, Hitoshi; Oinuma, Kohsuke; Michimura, Shinji; Taniguchi, Hiromi; Satoh, Kazuhiko; Ishii, Yasuyuki; Okamoto, Hiroyuki

2018-06-01

Detailed magnetization measurements enabled us to claim that the layered organic insulator κ-(BEDT-TTF)2Cu[N(CN)2]Cl [BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene] with the Dzyaloshinskii-Moriya interaction has an antiferromagnetic spin structure with the easy axis being the crystallographic c-axis and the net canting moment parallel to the a-axis at zero magnetic field. This zero-field spin structure is significantly different from that proposed in the past studies. The assignment was achieved by arguments including a correction of the direction of the weak ferromagnetism, reinterpretations of magnetization behaviors, and reasoning based on known high-field spin structures. We suggest that only the contributions of the strong intralayer antiferromagnetic interaction, the moderately weak Dzyaloshinskii-Moriya interaction, and the very weak interlayer ferromagnetic interaction can realize this spin structure. On the basis of this model, characteristic magnetic-field dependences of the magnetization can be interpreted as consequences of intriguing spin reorientations. The first reorientation is an unusual spin-flop transition under a magnetic field parallel to the b-axis. Although the existence of this transition is already known, the interpretation of what happens at this transition has been significantly revised. We suggest that this transition can be regarded as a spin-flop phenomenon of the local canting moment. We also claim that half of the spins rotate by 180° at this transition, in contrast to the conventional spin flop transition. The second reorientation is the gradual rotation of the spins during the variation of the magnetic field parallel to the c-axis. In this process, all the spins rotate around the Dzyaloshinskii-Moriya vectors by 90°. The results of our simulation based on the classical spin model well reproduce these spin reorientation behaviors, which strongly support our claimed zero-field spin structure. The present study highlights the

Effect of spin structure transition in IrMn on the CoPd/IrMn perpendicular exchange biased system

Energy Technology Data Exchange (ETDEWEB)

Janjua, Muhammad Bilal; Guentherodt, Gernot [II. Physikalisches Institut A, RWTH Aachen University, Aachen (Germany)

2011-07-01

The exchange bias (EB) phenomenon is studied in MBE grown Pd(10 nm)/CoPd(x=8,16,30 nm)/IrMn(15 nm)/Pd(4 nm) samples, which exhibit a perpendicular anisotropy of Co22Pd78. These samples are field cooled along the out-of-plane direction and hysteresis loops are measured along both the out-of-plane and in-plane directions. It is observed that there is a transition temperature where the out-of-plane EB becomes greater than the in-plane EB. This behavior of EB is an evidence of the change in the spin structure of the given system, which is also revealed by the magnetization versus temperature measurements of the exchange biased and of the sole IrMn samples. It is found that with increasing temperature there is a spin structure transition in Ir25Mn75 (15nm) related to the 2Q to 3Q transition in the bulk, which is responsible for the increase in out-of-plane EB. A vertical shift in the hysteresis loop is also observed in these exchange biased samples at low temperatures (T<50 K).

Theoretical study on the low-lying excited states of the phosphorus monoiodide (PI) including the spin-orbit coupling

Science.gov (United States)

Zhang, Xiaomei; Liu, Xiaoting; Liang, Guiying; Li, Rui; Xu, Haifeng; Yan, Bing

2016-01-01

The potential energy curves (PECs) of the 22 Λ-S states of the phosphorus monoiodide (PI) molecule have been calculated at the level of MRCI+Q method with correlation-consistent quadruple-ζ quality basis set. The spectroscopic constants of the bound states are determined, which well reproduce the available measurements. The metastable a1Δ state has been reported for the first time, which lies between the X3Σ- and b1Σ+ states and have much deeper well than the ground state. The R-dependent spin-orbit (SO) matrix elements are calculated with the full-electron Breit-Pauli operator. Based on the SO matrix elements, the perturbations that the 23Π state may suffer from are analyzed in detail. The SOC effect makes the original Λ-S states split into 51 Ω states. In the zero-field splitting of the ground state X3Σ-, the spin-spin coupling contribution (2.23 cm-1) is found to be much smaller compared to the spin-orbit coupling contribution (50 cm-1). The avoided crossings between the Ω states lead to much shallower potential wells and the change of dissociation relationships of the states. The Ω-state wavefunctions are analyzed depending on their Λ-S compositions, showing the strong interactions among several quasidegenerate Λ-S states of the same total SO symmetry. The transition properties including electric dipole (E1), magnetic dipole (M1), and electric quadrupole (E2) transition moments (TMs), the Franck-Condon factors, the transition probabilities and the radiative lifetimes are computed for the transitions between Ω components of a1Δ and b1Σ+ states and ground state. The transition probabilities induced by the E1, E2, and M1 transitions are evaluated. The E2 makes little effect on transition probabilities. In contrast, the E1 transition makes the main contribution to the transition probability and the M1 transition also brings the influence that cannot be neglected. Finally, the radiative lifetimes are determined with the transition moments including E

Exact phase boundaries and topological phase transitions of the X Y Z spin chain

Science.gov (United States)

Jafari, S. A.

2017-07-01

Within the block spin renormalization group, we give a very simple derivation of the exact phase boundaries of the X Y Z spin chain. First, we identify the Ising order along x ̂ or y ̂ as attractive renormalization group fixed points of the Kitaev chain. Then, in a global phase space composed of the anisotropy λ of the X Y interaction and the coupling Δ of the Δ σzσz interaction, we find that the above fixed points remain attractive in the two-dimesional parameter space. We therefore classify the gapped phases of the X Y Z spin chain as: (1) either attracted to the Ising limit of the Kitaev-chain, which in turn is characterized by winding number ±1 , depending on whether the Ising order parameter is along x ̂ or y ̂ directions; or (2) attracted to the charge density wave (CDW) phases of the underlying Jordan-Wigner fermions, which is characterized by zero winding number. We therefore establish that the exact phase boundaries of the X Y Z model in Baxter's solution indeed correspond to topological phase transitions. The topological nature of the phase transitions of the X Y Z model justifies why our analytical solution of the three-site problem that is at the core of the present renormalization group treatment is able to produce the exact phase boundaries of Baxter's solution. We argue that the distribution of the winding numbers between the three Ising phases is a matter of choice of the coordinate system, and therefore the CDW-Ising phase is entitled to host appropriate form of zero modes. We further observe that in the Kitaev-chain the renormalization group flow can be cast into a geometric progression of a properly identified parameter. We show that this new parameter is actually the size of the (Majorana) zero modes.

Ferromagnetism and spin glass ordering in transition metal alloys (invited)

Science.gov (United States)

Crane, S.; Carnegie, D. W., Jr.; Claus, H.

1982-03-01

Magnetic properties of transition metal alloys near the percolation threshold are often complicated by metallurgical effects. Alloys like AuFe, VFe, CuNi, RhNi, and PdNi are in general not random solid solutions but have various degrees of atomic clustering or short-range order (SRO), depending on the heat treatment. First, it is shown how the magnetic ordering temperature of these alloys varies with the degree of clustering or SRO. Second, by systematically changing this degree of clustering or SRO, important information can be obtained about the magnetic phase diagram. In all these alloys below the percolation limit, the onset of ferromagnetic order is probably preceded by a spin glass-type ordering. However, details of the magnetic phase diagram near the critical point can be quite different alloy systems.

Quantum-Classical Phase Transition of the Escape Rate of Two-Sublattice Antiferromagnetic Large Spins

Science.gov (United States)

Owerre, Solomon Akaraka; Paranjape, M. B.

2014-11-01

The Hamiltonian of a two-sublattice antiferromagnetic spins, with single (hard-axis) and double ion anisotropies described by H = J {\\hat S}1...\\hatS 2-2Jz \\hat {S}1z\\hat {S}2z+K(\\hat {S}1z2 +\\hat {S}2z2) is investigated using the method of effective potential. The problem is mapped to a single particle quantum-mechanical Hamiltonian in terms of the relative coordinate and reduced mass. We study the quantum-classical phase transition of the escape rate of this model. We show that the first-order phase transition for this model sets in at the critical value Jc = (Kc+Jz, c)/2 while for the anisotropic Heisenberg coupling H = J(S1xS2x +S1yS2y) + JzS1zS2z + K(S1z2+ S2z2) we obtain Jc = (2Kc-Jz, c)/3. The phase diagrams of the transition are also studied.

Dynamic Algorithms for Transition Matrix Generation

Science.gov (United States)

Yevick, David; Lee, Yong Hwan

The methods of [D. Yevick, Int. J. Mod. Phys. C, 1650041] for constructing transition matrices are applied to the two dimensional Ising model. Decreasing the system temperature during the acquisition of the matrix elements yields a reasonably precise specific heat curve for a 32x32 spin system for a limited number (50-100M) of realizations. If the system is instead evolved to first higher and then lower energies within a restricted interval that is steadily displaced in energy as the computation proceeds, a modification which permits backward displacements up to a certain lower bound for each forward step ensures acceptable accuracy. Additional constraints on the transition rule are also investigated. The Natural Sciences and Engineering Research Council of Canada (NSERC) and CIENA are acknowledged for financial support.

Topological phase transition in the quench dynamics of a one-dimensional Fermi gas with spin-orbit coupling

Science.gov (United States)

Wang, Pei; Yi, Wei; Xianlong, Gao

2015-01-01

We study the quench dynamics of a one-dimensional ultracold Fermi gas with synthetic spin-orbit coupling. At equilibrium, the ground state of the system can undergo a topological phase transition and become a topological superfluid with Majorana edge states. As the interaction is quenched near the topological phase boundary, we identify an interesting dynamical phase transition of the quenched state in the long-time limit, characterized by an abrupt change of the pairing gap at a critical quenched interaction strength. We further demonstrate the topological nature of this dynamical phase transition from edge-state analysis of the quenched states. Our findings provide interesting clues for the understanding of topological phase transitions in dynamical processes, and can be useful for the dynamical detection of Majorana edge states in corresponding systems.

Some recent developments in spin glasses

Indian Academy of Sciences (India)

I give some experimental and theoretical background to spin glasses, and then discuss the nature of the phase transition in spin glasses with vector spins. Results of Monte Carlo simulations of the Heisenberg spin glass model in three dimensions are presented. A finite-size scaling analysis of the correlation length of the ...

Spin-flip tunneling in quantum dots

Energy Technology Data Exchange (ETDEWEB)

Schreiber, Lars; Braakman, Floris; Meunier, Tristan; Calado, Victor; Vandersypen, Lieven [Kavli Institute of NanoScience, Delft (Netherlands); Wegscheider, Werner [Institute for Experimental and Applied Physics, University of Regensburg (Germany)

2010-07-01

Electron spins in a gate-defined double quantum dot formed in a GaAs/(Al,Ga)As 2DEG are promising candidates for quantum information processing as coherent single spin rotation and spin swap has been demonstrated recently. In this system we investigate the two-electron spin dynamics in the presence of microwaves (5.20 GHz) applied to one side gate. During microwave excitation we observe characteristic photon assisted tunneling (PAT) peaks at the (1,1) to (0,2) charge transition. Some of the PAT peaks are attributed to photon tunneling events between the singlet S(0,2) and the singlet S(1,1) states, a spin-conserving transition. Surprisingly, other PAT peaks stand out by their different external magnetic field dependence. They correspond to tunneling involving a spin-flip, from the (0,2) singlet to a (1,1) triplet. The full spectrum of the observed PAT lines is captured by simulations. This process offers novel possibilities for 2-electron spin manipulation and read-out.

Holographic RG flows on curved manifolds and quantum phase transitions

Science.gov (United States)

Ghosh, J. K.; Kiritsis, E.; Nitti, F.; Witkowski, L. T.

2018-05-01

Holographic RG flows dual to QFTs on maximally symmetric curved manifolds (dS d , AdS d , and S d ) are considered in the framework of Einstein-dilaton gravity in d + 1 dimensions. A general dilaton potential is used and the flows are driven by a scalar relevant operator. The general properties of such flows are analyzed and the UV and IR asymptotics computed. New RG flows can appear at finite curvature which do not have a zero curvature counterpart. The so-called `bouncing' flows, where the β-function has a branch cut at which it changes sign, are found to persist at finite curvature. Novel quantum first-order phase transitions are found, triggered by a variation in the d-dimensional curvature in theories allowing multiple ground states.

Efficient spin transitions in inelastic electron tunneling spectroscopy.

Science.gov (United States)

Lorente, Nicolás; Gauyacq, Jean-Pierre

2009-10-23

The excitation of the spin degrees of freedom of an adsorbed atom by tunneling electrons is computed using strong coupling theory. Recent measurements [Heinrich, Science 306, 466 (2004)] reveal that electron currents in a magnetic system efficiently excite its magnetic moments. Our theory shows that the incoming electron spin strongly couples with that of the adsorbate so that memory of the initial spin state is lost, leading to large excitation efficiencies. First-principles transmissions are evaluated in quantitative agreement with the experiment.

Control over the magnetism and transition between high- and low-spin states of an adatom on trilayer graphene.

Science.gov (United States)

Zheng, Anmin; Gao, Guoying; Huang, Hai; Gao, Jinhua; Yao, Kailun

2017-05-31

Using density-functional theory, we investigate the electronic and magnetic properties of an adatom (Na, Cu and Fe) on ABA- and ABC-stacked (Bernal and rhombohedral) trilayer graphenes. In particular, we study the influence of an applied gate voltage on magnetism, as it modifies the electronic states of the trilayer graphene (TLG) as well as changes the adatom spin states. Our study performed for a choice of three different adatoms (Na, Cu, and Fe) shows that the nature of adatom-graphene bonding evolves from ionic to covalent in moving from an alkali metal (Na) to a transition metal (Cu or Fe). Applying an external electric field (EEF) to TLG systems with different stacking orders results in the transition between high- and low-spin states in the latter case (Cu, Fe) and induces a little of magnetism in the former (Na) without magnetism in the absence of an external electric field. Our study would be useful for controlled adatom magnetism and (organic) spintronic applications in nanotechnology.

Unusual metal-insulator transition in disordered ferromagnetic films

International Nuclear Information System (INIS)

Muttalib, K.A.; Wölfle, P.; Misra, R.; Hebard, A.F.

2012-01-01

We present a theoretical interpretation of recent data on the conductance near and farther away from the metal-insulator transition in thin ferromagnetic Gd films of thickness b≈2-10 nm. For increasing sheet resistances a dimensional crossover takes place from d=2 to d=3 dimensions, since the large phase relaxation rate caused by scattering of quasiparticles off spin wave excitations renders the dephasing length L φ ≲b at strong disorder. The conductivity data in the various regimes obey fractional power-law or logarithmic temperature dependence. One observes weak localization and interaction induced corrections at weaker disorder. At strong disorder, near the metal-insulator transition, the data show scaling and collapse onto two scaling curves for the metallic and insulating regimes. We interpret this unusual behavior as proof of two distinctly different correlation length exponents on both sides of the transition.

Spin-resolved electron waiting times in a quantum-dot spin valve

Science.gov (United States)

Tang, Gaomin; Xu, Fuming; Mi, Shuo; Wang, Jian

2018-04-01

We study the electronic waiting-time distributions (WTDs) in a noninteracting quantum-dot spin valve by varying spin polarization and the noncollinear angle between the magnetizations of the leads using the scattering matrix approach. Since the quantum-dot spin valve involves two channels (spin up and down) in both the incoming and outgoing channels, we study three different kinds of WTDs, which are two-channel WTD, spin-resolved single-channel WTD, and cross-channel WTD. We analyze the behaviors of WTDs in short times, correlated with the current behaviors for different spin polarizations and noncollinear angles. Cross-channel WTD reflects the correlation between two spin channels and can be used to characterize the spin-transfer torque process. We study the influence of the earlier detection on the subsequent detection from the perspective of cross-channel WTD, and define the influence degree quantity as the cumulative absolute difference between cross-channel WTDs and first-passage time distributions to quantitatively characterize the spin-flip process. We observe that influence degree versus spin-transfer torque for different noncollinear angles as well as different polarizations collapse into a single curve showing universal behaviors. This demonstrates that cross-channel WTDs can be a pathway to characterize spin correlation in spintronics system.

Spontaneous spin polarization in quantum wires

Energy Technology Data Exchange (ETDEWEB)

Vasilchenko, A.A., E-mail: a_vas2002@mail.ru

2015-12-04

The total energy of a quasi-one-dimensional electron system was calculated using the density functional theory. In the absence of a magnetic field, we have found that ferromagnetic state occurs in the quantum wires. The phase diagram of the transition into the spin-polarized state is constructed. The critical electron density below which electrons are in spin-polarized state is estimated analytically. - Highlights: • Density functional theory used to study a spin-polarized state in quantum wires. • The Kohn–Sham equation for quasi-one-dimensional electrons solved numerically. • The phase diagram of the transition into the spin-polarized state is constructed. • The electron density below which electrons are in a spin-polarized state was found. • The critical density of electrons was estimated analytically.

Spontaneous spin polarization in quantum wires

International Nuclear Information System (INIS)

Vasilchenko, A.A.

2015-01-01

The total energy of a quasi-one-dimensional electron system was calculated using the density functional theory. In the absence of a magnetic field, we have found that ferromagnetic state occurs in the quantum wires. The phase diagram of the transition into the spin-polarized state is constructed. The critical electron density below which electrons are in spin-polarized state is estimated analytically. - Highlights: • Density functional theory used to study a spin-polarized state in quantum wires. • The Kohn–Sham equation for quasi-one-dimensional electrons solved numerically. • The phase diagram of the transition into the spin-polarized state is constructed. • The electron density below which electrons are in a spin-polarized state was found. • The critical density of electrons was estimated analytically.

Distribution of spin dipole transition strength in the 15N(n,p)15C reaction

International Nuclear Information System (INIS)

Cellar, A.; Alford, W.P.; Helmer, R.; Abegg, R.; Frekers, D.; Haeusser, O.; Henderson, R.S.; Jackson, K.P.; Vetterli, M.; Yen, S.; Jeppesen, R.; Larson, B.; Mildenberger, J.; Pointon, B.W.; Trudel, A.

1990-08-01

The reaction 15 N(n,p) 15 C was studied at a neutron energy of 288 MeV using the TRIUMF (n,p) charge exchange facility and a high pressure gas target. The angular distributions for spin dipole (ΔL=1) transitions to the states in 15 C at energies 0 MeV and 0.740 MeV, as well as for higher excitation energies, were measured and the results were compared with DWIA calculations. The measured distribution of the spin dipole strength agrees well with shell model predictions, indicating that a rather simple model provides a satisfactory description of the 15 N ground state, and of positive parity states in 15 C up to about 18 MeV excitation. The magnitude of the peak cross sections (at ≅ 7 degrees) is described well by the calculations when the theoretical cross section is renormalized by a factor 0.7. The calculated cross sections near zero degrees are generally smaller than experimental data. It this is a general feature of ΔL=1 transitions, it suggests that estimates of GT strength based on a multipole decomposition of measured cross sections may be too high. (Author) (41 refs., 3 tabs., 14 figs.)

Exact solution of the mixed spin-1/2 and spin-S Ising-Heisenberg diamond chain

Directory of Open Access Journals (Sweden)

L. Čanová

2009-01-01

Full Text Available The geometric frustration in a class of the mixed spin-1/2 and spin-S Ising-Heisenberg diamond chains is investigated by combining three exact analytical techniques: Kambe projection method, decoration-iteration transformation and transfer-matrix method. The ground state, the magnetization process and the specific heat as a function of the external magnetic field are particularly examined for different strengths of the geometric frustration. It is shown that the increase of the Heisenberg spin value S raises the number of intermediate magnetization plateaux, which emerge in magnetization curves provided that the ground state is highly degenerate on behalf of a sufficiently strong geometric frustration. On the other hand, all intermediate magnetization plateaux merge into a linear magnetization versus magnetic field dependence in the limit of classical Heisenberg spin S → ∞. The enhanced magnetocaloric effect with cooling rate exceeding the one of paramagnetic salts is also detected when the disordered frustrated phase constitutes the ground state and the external magnetic field is small enough.

Detection of individual spin transitions of a single proton confined in a cryogenic Penning trap

Energy Technology Data Exchange (ETDEWEB)

Kracke, Holger

2013-02-27

The presented experiment for the determination of the magnetic moment of the proton is based on the measurement of the ratio of cyclotron frequency and Larmor frequency of a single proton confined in a cryogenic double-Penning trap. In the course of this thesis, the simultaneous non-destructive measurement of two of the three eigenfrequencies of the proton in thermal equilibrium with corresponding detection systems was demonstrated, which reduces the measurement time of the cyclotron frequency by a factor of two. Furthermore, this thesis presents the first detection of individual spin transitions of a single proton, which allows for the determination of the Larmor frequency. The continuous Stern-Gerlach effect is utilized to couple the magnetic moment to the axial mode of the trapped proton by means of a magnetic bottle. Thus, a spin flip causes a jump of the axial frequency, which can be measured non-destructively with highly-sensitive detection systems. However, not only the spin momentum is coupled to the axial motion but also the angular momentum. Thus, the main experimental challenge is the elimination of energy fluctuations in the radial modes in order to maintain spin flip resolution. Due to systematic studies on the stability of the axial frequency and a complete revision of the experimental setup, this goal was achieved. The spin state of the proton can be determined with very high fidelity for the very first time. Thus, this thesis represents an important step towards a high-precision determination of the magnetic moment of the proton.

Spin Flips versus Spin Transport in Nonthermal Electrons Excited by Ultrashort Optical Pulses in Transition Metals

Science.gov (United States)

Shokeen, V.; Sanchez Piaia, M.; Bigot, J.-Y.; Müller, T.; Elliott, P.; Dewhurst, J. K.; Sharma, S.; Gross, E. K. U.

2017-09-01

A joint theoretical and experimental investigation is performed to understand the underlying physics of laser-induced demagnetization in Ni and Co films with varying thicknesses excited by 10 fs optical pulses. Experimentally, the dynamics of spins is studied by determining the time-dependent amplitude of the Voigt vector, retrieved from a full set of magnetic and nonmagnetic quantities performed on both sides of films, with absolute time reference. Theoretically, ab initio calculations are performed using time-dependent density functional theory. Overall, we demonstrate that spin-orbit induced spin flips are the most significant contributors with superdiffusive spin transport, which assumes only that the transport of majority spins without spin flips induced by scattering does not apply in Ni. In Co it plays a significant role during the first ˜20 fs only. Our study highlights the material dependent nature of the demagnetization during the process of thermalization of nonequilibrium spins.

Quantum spin Hall effect and topological phase transition in InN x Bi y Sb1-x-y /InSb quantum wells

Science.gov (United States)

Song, Zhigang; Bose, Sumanta; Fan, Weijun; Zhang, Dao Hua; Zhang, Yan Yang; Shen Li, Shu

2017-07-01

Quantum spin Hall (QSH) effect, a fundamentally new quantum state of matter and topological phase transitions are characteristics of a kind of electronic material, popularly referred to as topological insulators (TIs). TIs are similar to ordinary insulator in terms of their bulk bandgap, but have gapless conducting edge-states that are topologically protected. These edge-states are facilitated by the time-reversal symmetry and they are robust against nonmagnetic impurity scattering. Recently, the quest for new materials exhibiting non-trivial topological state of matter has been of great research interest, as TIs find applications in new electronics and spintronics and quantum-computing devices. Here, we propose and demonstrate as a proof-of-concept that QSH effect and topological phase transitions can be realized in {{InN}}x{{Bi}}y{{Sb}}1-x-y/InSb semiconductor quantum wells (QWs). The simultaneous incorporation of nitrogen and bismuth in InSb is instrumental in lowering the bandgap, while inducing opposite kinds of strain to attain a near-lattice-matching conducive for lattice growth. Phase diagram for bandgap shows that as we increase the QW thickness, at a critical thickness, the electronic bandstructure switches from a normal to an inverted type. We confirm that such transition are topological phase transitions between a traditional insulator and a TI exhibiting QSH effect—by demonstrating the topologically protected edge-states using the bandstructure, edge-localized distribution of the wavefunctions and edge-state spin-momentum locking phenomenon, presence of non-zero conductance in spite of the Fermi energy lying in the bandgap window, crossover points of Landau levels in the zero-mode indicating topological band inversion in the absence of any magnetic field and presence of large Rashba spin-splitting, which is essential for spin-manipulation in TIs.

High-spin states in the transitional odd-odd nuclei 150Eu and 152Tb

International Nuclear Information System (INIS)

Barneoud, D.; Foin, C.; Pinston, J.A.; Monnand, E.

1983-06-01

The ( 7 Li, 5n) and ( 11 B, 5n) reactions have been used to study the high-spin states in the two odd-odd nuclei 150 Eu and 152 Tb. Three decoupled bands have been evidenced in each nucleus belonging to the same configurations [f 7/2]sub(n) [h 11/2]sub(p), [h 9/2]sub(n) [h 11/2 ]sub(p) and [i 13/2]sub(n) [h 11/2]sub(p). The latter one is well developped and improves our knowledge of this system between the spherical and deformed region. The analysis of the collective moment of inertia and transition ratios strongly suggests an increase of the deformation when the rotational frequency increases in these two transitional nuclei 150 Eu and 152 Tb

Electron Spin Resonance Studies of Carbonic Anhydrase: Transition Metal Ions and Spin-Labeled Sulfonamides*

Science.gov (United States)

Taylor, June S.; Mushak, Paul; Coleman, Joseph E.

1970-01-01

Electron spin resonance (esr) spectra of Cu(II) and Co(II) carbonic anhydrase, and a spin-labeled sulfonamide complex of the Zn(II) enzyme, are reported. The coordination geometry of Cu(II) bound in the enzyme appears to have approximately axial symmetry. Esr spectra of enzyme complexes with metal-binding anions also show axial symmetry and greater covalency, in the order ethoxzolamide cyanide complex suggests the presence of two, and probably three, equivalent nitrogen ligands from the protein. Esr spectra of the Co(II) enzyme and its complexes show two types of Co(II) environment, one typical of the native enzyme and the 1:1 CN- complex, and one typical of a 2:1 CN- complex. Co(II) in the 2:1 complex appears to be low-spin and probably has a coordination number of 5. Binding of a spin-labeled sulfonamide to the active center immobilizes the free radical. The similarity of the esr spectra of spin-labeled Zn(II) and Co(II) carbonic anhydrases suggests that the conformation at the active center is similar in the two metal derivatives. PMID:4320976

A Multi-year Search for Transits of Proxima Centauri. I. Light Curves Corresponding to Published Ephemerides

Science.gov (United States)

Blank, David L.; Feliz, Dax; Collins, Karen A.; White, Graeme L.; Stassun, Keivan G.; Curtis, Ivan A.; Hart, Rhodes; Kielkopf, John F.; Nelson, Peter; Relles, Howard; Stockdale, Christopher; Jayawardene, Bandupriya; Pennypacker, Carlton R.; Shankland, Paul; Reichart, Daniel E.; Haislip, Joshua B.; Kouprianov, Vladimir V.

2018-06-01

Proxima Centauri has become the subject of intense study since the radial-velocity (RV) discovery by Anglada-Escudé et al. of a planet orbiting this nearby M dwarf every ∼11.2 days. If Proxima Centauri b transits its host star, independent confirmation of its existence is possible, and its mass and radius can be measured in units of the stellar host mass and radius. To date, there have been three independent claims of possible transit-like event detections in light curve observations obtained by the MOST satellite (in 2014–15), the Bright Star Survey Telescope telescope in Antarctica (in 2016), and the Las Campanas Observatory (in 2016). The claimed possible detections are tentative, due in part to the variability intrinsic to the host star, and in the case of the ground-based observations, also due to the limited duration of the light curve observations. Here, we present preliminary results from an extensive photometric monitoring campaign of Proxima Centauri, using telescopes around the globe and spanning from 2006 to 2017, comprising a total of 329 observations. Considering our data that coincide directly and/or phased with the previously published tentative transit detections, we are unable to independently verify those claims. We do, however, verify the previously reported ubiquitous and complex variability of the host star. We discuss possible interpretations of the data in light of the previous claims, and we discuss future analyses of these data that could more definitively verify or refute the presence of transits associated with the RV-discovered planet.

Stochastic kinetics of photoinduced phase transitions in spin-crossover solids

Science.gov (United States)

Gudyma, Iurii; Maksymov, Artur; Dimian, Mihai

2013-10-01

We study the stochastic macroscopic kinetics of photoinduced phase transitions in spin-crossover compounds assisted by white and colored Ornstein-Uhlenbeck noise. By using a phenomenological master equation obtained in the mean-field approach, the phase diagram is constructed based on the associated Lyapunov function. The stochastic behavior is then analyzed in the Langevin framework and the corresponding Fokker-Planck equations. Both additive and multiplicative and white and colored types of noise are considered and the stationary probability densities are found along with the noise-assisted light induced hysteretic loops. By using the Kramers formalism, we also focus our attention on the escape time problem in these noise perturbed systems. A detailed study of the relative escape time dependence on various noise characteristics is performed and the main features are compared for different types of noise.

Quantum phase transitions in spin-1 X X Z chains with rhombic single-ion anisotropy

Science.gov (United States)

Ren, Jie; Wang, Yimin; You, Wen-Long

2018-04-01

We explore numerically the inverse participation ratios in the ground state of one-dimensional spin-1 X X Z chains with the rhombic single-ion anisotropy. By employing the techniques of density-matrix renormalization group, effects of the rhombic single-ion anisotropy on various information theoretical measures are investigated, such as the fidelity susceptibility, the quantum coherence, and the entanglement entropy. Their relations with the quantum phase transitions are also analyzed. The phase transitions from the Y -Néel phase to the large-Ex or the Haldane phase can be well characterized by the fidelity susceptibility. The second-order derivative of the ground-state energy indicates all the transitions are of second order. We also find that the quantum coherence, the entanglement entropy, the Schmidt gap, and the inverse participation ratios can be used to detect the critical points of quantum phase transitions. Results drawn from these quantum information observables agree well with each other. Finally we provide a ground-state phase diagram as functions of the exchange anisotropy Δ and the rhombic single-ion anisotropy E .

Lattice Waves, Spin Waves, and Neutron Scattering

Science.gov (United States)

Brockhouse, Bertram N.

1962-03-01

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

MRCI study on the spectroscopic parameters, transition dipole moments and transition probabilities of 16 low-lying states of the BeB radical

Science.gov (United States)

Zhou, Dan; Shi, Deheng; Sun, Jinfeng; Zhu, Zunlue

2018-03-01

In this work, we calculate the potential energy curves of 16 Λ-S and 36 Ω states of beryllium boride (BeB) radical using the complete active space self-consistent field method, followed by the valence internally contracted multireference configuration interaction approach with Davidson correction. The 16 Λ-S states are the X2Π, A2Σ+, B2Π, C2Δ, D2Ʃ-, E2Σ+, G2Π, I2Σ+, a4Σ-, b4Π, c4Σ-, d4Δ, e4Σ+, g4Π, h4Π, and 24Σ+, which are obtained from the first three dissociation channels of the BeB radical. The Ω states are obtained from the Λ-S states. Of the Λ-S states, the G2Π, I2Σ+, and h4Π states exhibit double well curves. The G2Π, b4Π, and g4Π states are inverted with the spin-orbit coupling effect included. The d4Δ, e4Σ+, and g4Π states as well as the second well of the h4Π state are very weakly bound. Avoided crossings exist between the G2Π and H2Π states, the A2Σ+ and E2Σ+ states, the c4Σ- and f4Σ- states, the g4Π and h4Π states, the I2Σ+ and 42Σ+ states, as well as the 24Σ+ and 34Σ+ states. To improve the quality of the potential energy curves, core-valence correlation and scalar relativistic corrections, as well as the extrapolation of the potential energies to the complete basis set limit, are included. The transition dipole moments are computed. Spectroscopic parameters and vibrational levels are determined along with Franck-Condon factors, Einstein coefficients, and radiative lifetimes of many electronic transitions. The transition probabilities are evaluated. The spin-orbit coupling effect on the spectroscopic parameters and vibrational levels is discussed. The spectroscopic parameters, vibrational levels, and transition probabilities reported in this paper can be considered very reliable and can be employed to predict these states in an appropriate spectroscopy experiment.

Spin-phonon induced magnetic order in magnetized Spin Ice systems

International Nuclear Information System (INIS)

Albarracín, F A Gómez; Cabra, D C; Rosales, H D; Rossini, G L

2014-01-01

We study the behavior of spin ice pyrochlore systems above the well known [111] 1/3 plateau, under slight deviations of the direction of the external field. We model the relevant degrees of freedom by Ising spins on the kagome lattice. We propose the inclusion of lattice deformations, which imply phononic degrees of freedom in the adiabatic limit. We use analytical calculations to estimate how these new degrees of freedom affect the short and long range spin interactions in the presence of an external magnetic field. We then obtain the magnetization curves, explore the phases and the ground states of this system in the presence of magnetic field by Monte Carlo simulations. We discuss comparisons with experimental results

Comparison of the order of magnetic phase transitions in several magnetocaloric materials using the rescaled universal curve, Banerjee and mean field theory criteria

Energy Technology Data Exchange (ETDEWEB)

Burrola-Gándara, L. A., E-mail: andres.burrola@gmail.com; Santillan-Rodriguez, C. R.; Rivera-Gomez, F. J.; Saenz-Hernandez, R. J.; Botello-Zubiate, M. E.; Matutes-Aquino, J. A. [Departamento de Física de Materiales, Centro de Investigación en Materiales Avanzados, S.C., Miguel de Cervantes 120, Complejo Industrial Chihuahua, Chihuahua 31109 (Mexico)

2015-05-07

Magnetocaloric materials with second order phase transition near the Curie temperature can be described by critical phenomena theory. In this theory, scaling, universality, and renormalization are key concepts from which several phase transition order criteria are derived. In this work, the rescaled universal curve, Banerjee and mean field theory criteria were used to make a comparison for several magnetocaloric materials including pure Gd, SmCo{sub 1.8}Fe{sub 0.2}, MnFeP{sub 0.46}As{sub 0.54}, and La{sub 0.7}Ca{sub 0.15}Sr{sub 0.15}MnO{sub 3}. Pure Gd, SmCo{sub 1.8}Fe{sub 0.2}, and La{sub 0.7}Ca{sub 0.15}Sr{sub 0.15}MnO{sub 3} present a collapse of the rescaled magnetic entropy change curves into a universal curve, which indicates a second order phase transition; applying Banerjee criterion to H/σ vs σ{sup 2} Arrot plots and the mean field theory relation |ΔS{sub M}| ∝ (μ{sub 0}H/T{sub c}){sup 2/3} for the same materials also determines a second order phase transition. However, in the MnFeP{sub 0.46}As{sub 0.54} sample, the Banerjee criterion applied to the H/σ vs σ{sup 2} Arrot plot indicates a first order magnetic phase transition, while the mean field theory prediction for a second order phase transition, |ΔS{sub M}| ∝ (μ{sub 0}H/T{sub c}){sup 2/3}, describes a second order behavior. Also, a mixture of first and second order behavior was indicated by the rescaled universal curve criterion. The diverse results obtained for each criterion in MnFeP{sub 0.46}As{sub 0.54} are apparently related to the magnetoelastic effect and to the simultaneous presence of weak and strong magnetism in Fe (3f) and Mn (3g) alternate atomic layers, respectively. The simultaneous application of the universal curve, the Banerjee and the mean field theory criteria has allowed a better understanding about the nature of the order of the phase transitions in different magnetocaloric materials.

Large magnetocaloric effect of NdGa compound due to successive magnetic transitions

Science.gov (United States)

Zheng, X. Q.; Xu, J. W.; Shao, S. H.; Zhang, H.; Zhang, J. Y.; Wang, S. G.; Xu, Z. Y.; Wang, L. C.; Chen, J.; Shen, B. G.

2018-05-01

The magnetic behavior and MCE property of NdGa compound were studied in detail. According to the temperature dependence of magnetization (M-T) curve at 0.01 T, two sharp changes were observed at 20 K (TSR) and 42 K (TC), respectively, corresponding to spin reorientation and FM-PM transition. Isothermal magnetization curves up to 5 T at different temperatures were measured and magnetic entropy change (ΔSM) was calculated based on M-H data. Temperature dependences of -ΔSM for a field change of 0-2 T and 0-5 T show that there are two peaks on the curves corresponding to TSR and TC, respectively. The value of the two peaks is 6.4 J/kg K and 15.5 J/kg K for the field change of 0-5 T. Since the two peaks are close, the value of -ΔSM in the temperature range between TSR and TC keeps a large value. The excellent MCE performance of NdGa compound benefits from the existence of two successive magnetic transitions.

Modulation Algorithms for Manipulating Nuclear Spin States

OpenAIRE

Liu, Boyang; Zhang, Ming; Dai, Hong-Yi

2013-01-01

We exploit the impact of exact frequency modulation on transition time of steering nuclear spin states from theoretical point of view. 1-stage and 2-stage Frequency-Amplitude-Phase modulation (FAPM) algorithms are proposed in contrast with 1-stage and 3-stage Amplitude-Phase modulation (APM) algorithms. The sufficient conditions are further present for transiting nuclear spin states within the specified time by these four modulation algorithms. It is demonstrated that transition time performa...

Spin-State Transition in La1-xSrxCoO3 Single Crystals

Science.gov (United States)

Bhardwaj, S.; Prabhakaran, D.; Awasthi, A. M.

2011-07-01

We present a study of the thermal conductivity (κ), specific heat (Cp) and Raman spectra of La1-xSrxCoO3 (x = 0,0.1) single crystals. Both the specimens have low thermal conductivity and board Raman peaks, arising from strong scattering of phonons by lattice disorder, produced by (and doping-enhanced) spin-states admixture of the Co3+ ions. The thermal conductivity anomalously deviates from ˜1/T behaviour at high (room) temperatures, expected of an insulator. High-temperature specific heat reveals large decrease in the metal-insulator (M-I) transition temperature with Sr-doping.

Irreversibility and self-organization in spin glasses. 1. Origin of irreversibility in spin glasses

International Nuclear Information System (INIS)

Kovrov, V.P.; Kurbatov, A.M.

1989-05-01

The origin of irreversibility in spin glasses is found out on the basis of the analytical study of the well-known TAP equations. Connection between irreversible jumpwise transitions and a positive feedback in spin glasses is discussed. (author). 7 refs, 4 figs

A signature for isoscalar-spin transitions in (d vector, d' vector) scattering at intermediate energy

International Nuclear Information System (INIS)

Morlet, M.; Bimbot, L.; Guillot, J.; Johnson, B.N.; Jourdan, F.; Langevin-Joliot, H.; Marty, N.; Rosier, L.; Wiele, J. van de; Willis, A.; Beatty, D.; Edwards, G.; Fergerson, R.W.; Glashausser, C.; Green, A.; Djalali, C.; Johnson, B.N.; Tomasi-Gustafsson, E.; Youn, M.Y.

1991-05-01

Three different signatures for isoscalar spin transitions in nuclei have been tested in the 12 C(d,d') 12 C reaction at 400 MeV. These signatures have values close to zero for the natural parity states, and range from 0.22 to 0.50 for the ΔS=1 ΔT=0, 12.7 MeV state. Preliminary results on 40 Ca(d,d') at 400 MeV are also presented. (author) 26 refs., 4 figs., 1 tab

Manipulation of the spin in single molecule magnets via Landau-Zener transitions

Science.gov (United States)

Palii, Andrew; Tsukerblat, Boris; Clemente-Juan, Juan M.; Gaita-Ariño, Alejandro; Coronado, Eugenio

2011-11-01

We theoretically investigate the effects of a magnetic pulse on a single-molecule magnet (SMM) initially magnetized by a dc field along the easy axis of magnetization. In the Landau-Zener (LZ) scheme, it is shown that the final spin state is a function of the shape and duration of the pulse, conditioned by the decoherence time of the SMM. In the case of coherent tunneling, the asymmetric pulses are shown to reverse the direction of the magnetization, while the symmetric pulses can only decrease the value of the initial magnetization. It is also demonstrated that the application of an external variable dc field in the hard plane of magnetization provides the possibility to tune the resulting magnetization due to quantum interference effects. The results and the conditions for the observation of the pulse-triggered LZ transitions are illustrated by the application of the proposed scheme to the well-studied single-molecule magnet Fe8. To put the results into perspective, some potential applications of SMMs experiencing pulse-induced LZ transitions, such as switching devices and qubits, are discussed.

Three-dimensional whole-brain perfusion quantification using pseudo-continuous arterial spin labeling MRI at multiple post-labeling delays: accounting for both arterial transit time and impulse response function.

Science.gov (United States)

Qin, Qin; Huang, Alan J; Hua, Jun; Desmond, John E; Stevens, Robert D; van Zijl, Peter C M

2014-02-01

Measurement of the cerebral blood flow (CBF) with whole-brain coverage is challenging in terms of both acquisition and quantitative analysis. In order to fit arterial spin labeling-based perfusion kinetic curves, an empirical three-parameter model which characterizes the effective impulse response function (IRF) is introduced, which allows the determination of CBF, the arterial transit time (ATT) and T(1,eff). The accuracy and precision of the proposed model were compared with those of more complicated models with four or five parameters through Monte Carlo simulations. Pseudo-continuous arterial spin labeling images were acquired on a clinical 3-T scanner in 10 normal volunteers using a three-dimensional multi-shot gradient and spin echo scheme at multiple post-labeling delays to sample the kinetic curves. Voxel-wise fitting was performed using the three-parameter model and other models that contain two, four or five unknown parameters. For the two-parameter model, T(1,eff) values close to tissue and blood were assumed separately. Standard statistical analysis was conducted to compare these fitting models in various brain regions. The fitted results indicated that: (i) the estimated CBF values using the two-parameter model show appreciable dependence on the assumed T(1,eff) values; (ii) the proposed three-parameter model achieves the optimal balance between the goodness of fit and model complexity when compared among the models with explicit IRF fitting; (iii) both the two-parameter model using fixed blood T1 values for T(1,eff) and the three-parameter model provide reasonable fitting results. Using the proposed three-parameter model, the estimated CBF (46 ± 14 mL/100 g/min) and ATT (1.4 ± 0.3 s) values averaged from different brain regions are close to the literature reports; the estimated T(1,eff) values (1.9 ± 0.4 s) are higher than the tissue T1 values, possibly reflecting a contribution from the microvascular arterial blood compartment

Low-spin electromagnetic transition probabilities in {sup 102,104}Cd

Energy Technology Data Exchange (ETDEWEB)

Jolie, J.; Dewald, A.; Fransen, C.; Linnemann, A.; Melon, B.; Moeller, O. [Inst. fuer Kernphysik, Univ. zu Koeln (Germany); Boelaert, N. [Inst. fuer Kernphysik, Univ. zu Koeln (Germany); Dept. of Subatomic and Radiation Physics, Gent Univ. (Belgium); Smirnova, N.; Heyde, K. [Dept. of Subatomic and Radiation Physics, Gent Univ. (Belgium)

2007-07-01

Lifetimes of low-lying states in {sup 102,104}Cd were determined by using the recoil distance Doppler shift technique with a plunger device and a Ge array consisting of five HP Ge detectors and one Euroball cluster detector. The experiments were carried out at the Cologne FN Tandem accelerator using the {sup 92,94}Mo({sup 12}C,2n){sup 102,104}Cd reactions. The differential decay curve method in coincidence mode was employed to derive the lifetime of the first excited 2{sup +} state in both nuclei and the first excited 4{sup +} state in {sup 104}Cd. The corresponding E2 transition probabilities agree well with large scale shell-model calculations. (orig.)

A combined DFT and restricted open-shell configuration interaction method including spin-orbit coupling: Application to transition metal L-edge X-ray absorption spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Roemelt, Michael; Maganas, Dimitrios; Neese, Frank [Max-Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, D-45470 Muelheim an der Ruhr (Germany); DeBeer, Serena [Max-Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, D-45470 Muelheim an der Ruhr (Germany); Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853 (United States)

2013-05-28

A novel restricted-open-shell configuration interaction with singles (ROCIS) approach for the calculation of transition metal L-edge X-ray absorption spectra is introduced. In this method, one first calculates the ground state and a number of excited states of the non-relativistic Hamiltonian. By construction, the total spin is a good quantum number in each of these states. For a ground state with total spin S excited states with spin S Prime = S, S - 1, and S + 1 are constructed. Using Wigner-Eckart algebra, all magnetic sublevels with M{sub S}= S, Horizontal-Ellipsis , -S for each multiplet of spin S are obtained. The spin-orbit operator is represented by a mean-field approximation to the full Breit-Pauli spin-orbit operator and is diagonalized over this N-particle basis. This is equivalent to a quasi-degenerate treatment of the spin-orbit interaction to all orders. Importantly, the excitation space spans all of the molecular multiplets that arise from the atomic Russell-Saunders terms. Hence, the method represents a rigorous first-principles approach to the complicated low-symmetry molecular multiplet problem met in L-edge X-ray absorption spectroscopy. In order to gain computational efficiency, as well as additional accuracy, the excitation space is restricted to single excitations and the configuration interaction matrix is slightly parameterized in order to account for dynamic correlation effects in an average way. To this end, it is advantageous to employ Kohn-Sham rather than Hartree-Fock orbitals thus defining the density functional theory/ROCIS method. However, the method can also be used in an entirely non-empirical fashion. Only three global empirical parameters are introduced and have been determined here for future application of the method to any system containing any transition metal. The three parameters were carefully calibrated using the L-edge X-ray absorption spectroscopy spectra of a test set of coordination complexes containing first row

Influence of the spin reorientation transition on the hysteresis characteristics of Nd-Fe-B film and bulk magnets

International Nuclear Information System (INIS)

Lileev, A.S.; Parilov, A.A.; Reissner, M.; Steiner, W.

2004-01-01

A comparison was made of the hysteresis characteristics of hard magnetic films with those of bulk samples based on Nd 2 Fe 14 B in the temperature range between 4.2 and 293 K. In both types of specimens characteristic 'dips' appear below 135 K in the demagnetisation curves which are caused by both the spin reorientation from easy axis to easy cone and the deviation from a perfect texture of the sample

Transition from Spin Dewetting to continuous film in spin coating of Liquid Crystal 5CB.

Science.gov (United States)

Dhara, Palash; Bhandaru, Nandini; Das, Anuja; Mukherjee, Rabibrata

2018-05-08

Spin dewetting refers to spontaneous rupture of the dispensed solution layer during spin coating, resulting in isolated but periodic, regular sized domains of the solute and is pre-dominant when the solute concentration (C n ) is very low. In this article we report how the morphology of liquid crystal (LC) 5CB thin films coated on flat and patterned PMMA substrate transform from spin dewetted droplets to continuous films with increase in C n . We further show that within the spin dewetted regime, with gradual increase in the solute concentration, periodicity of the isotropic droplets (λ D ) as well as their mean diameter (d D ), gradually decreases, till the film becomes continuous at a critical concentration (C n *). Interestingly, the trend that λ D reduces with increase in C n is exact opposite to what is observed in thermal/solvent vapor induced dewetting of a thin film. The spin dewetted droplets exhibit transient Radial texture, in contrast to Schlieren texture observed in elongated threads and continuous films of 5CB, which remains in the Nematic phase at room temperature. Finally we show that by casting the film on a grating patterned substrate it becomes possible to align the spin dewetted droplets along the contours substrate patterns.

Spins of superdeformed rotational bands in Tl isotopes

Energy Technology Data Exchange (ETDEWEB)

Dadwal, Anshul; Mittal, H.M. [Dr. B.R. Ambedkar National Institute of Technology, Jalandhar (India)

2017-01-15

The two-parameter model defined for even-even nuclei viz. soft-rotor formula is used to assign the band-head spin of the 17 rotational bands in Tl isotopes. The least-squares fitting method is employed to obtain the spins of these bands in the A ∝ 190 mass region. The calculated transition energies are found to depend sensitively on the proposed spin. Whenever a correct spin assignment is made, the calculated and experimental transition energies coincide very well. The dynamic moment of inertia is also calculated and its variation with rotational frequency is explored. (orig.)

Coupled spin and charge collective excitations in a spin polarized electron gas

International Nuclear Information System (INIS)

Marinescu, D.C.; Quinn, J.J.; Yi, K.S.

1997-01-01

The charge and longitudinal spin responses induced in a spin polarized quantum well by a weak electromagnetic field are investigated within the framework of the linear response theory. The authors evaluate the excitation frequencies for the intra- and inter-subband transitions of the collective charge and longitudinal spin density oscillations including many-body corrections beyond the random phase approximation through the spin dependent local field factors, G σ ± (q,ω). An equation-of-motion method was used to obtain these corrections in the limit of long wavelengths, and the results are given in terms of the equilibrium pair correlation function. The finite degree of spin polarization is shown to introduce coupling between the charge and spin density modes, in contrast with the result for an unpolarized system

Franck-Condon factors and potential curves for the combining states of the cesium dimer A 1Σ+u - X1Σ+g transition

International Nuclear Information System (INIS)

Smirnov, A.D.

1995-01-01

It is shown that the actual Cs 2 ground and first excited state potentials are better approximated by the Rydberg-Klein-Rees potential curve than by the Morse, Hulburt-Hirschfelder, Dunham, and perturbed Morse potentials. The Franck-Condon factors for the Cs 2 A-X transition (O ≤υ'≤35; 0 ≤υ double-prime ≤22) are calculated for the Rydberg,-Klein-Rees potential curves. The results of the calculations were used to determine the oscillator strength for the A-X transition of the Cs 2 molecule

Low-temperature structural transition in the quasi-one-dimensional spin-1/2 compound L i2C u2O (SO4) 2

Science.gov (United States)

Rousse, G.; Rodríguez-Carvajal, J.; Giacobbe, C.; Sun, M.; Vaccarelli, O.; Radtke, G.

2017-04-01

A thorough structural exploration has been made on the quasi-one-dimensional S =1 /2 compound L i2C u2O (SO4) 2 by neutron and synchrotron x-ray diffraction. It reveals the occurrence of a structural transition at 125 K, characterized by a lowering of symmetry from P 42/m to P 1 ¯ , which is possibly driven by an exchange striction mechanism. This transition involves a dimerization of some Cu in the edge-sharing tetrahedral Cu chains. A symmetry mode analysis indicates that one representation, Γ3+Γ4+ , dominates the structural transition. Interestingly, no intermediate structure with P 112 /m symmetry is observed experimentally. Lastly, temperature dependent magnetic susceptibility measurements and neutron diffraction reveal that the magnetic ground state of this compound is a spin-singlet with a spin gap, characterized by the absence of long-range magnetic order down to 1.7 K.

Spin-orbit coupling and electric-dipole spin resonance in a nanowire double quantum dot.

Science.gov (United States)

Liu, Zhi-Hai; Li, Rui; Hu, Xuedong; You, J Q

2018-02-02

We study the electric-dipole transitions for a single electron in a double quantum dot located in a semiconductor nanowire. Enabled by spin-orbit coupling (SOC), electric-dipole spin resonance (EDSR) for such an electron can be generated via two mechanisms: the SOC-induced intradot pseudospin states mixing and the interdot spin-flipped tunneling. The EDSR frequency and strength are determined by these mechanisms together. For both mechanisms the electric-dipole transition rates are strongly dependent on the external magnetic field. Their competition can be revealed by increasing the magnetic field and/or the interdot distance for the double dot. To clarify whether the strong SOC significantly impact the electron state coherence, we also calculate relaxations from excited levels via phonon emission. We show that spin-flip relaxations can be effectively suppressed by the phonon bottleneck effect even at relatively low magnetic fields because of the very large g-factor of strong SOC materials such as InSb.

Detection of a repeated transit signature in the light curve of the enigma star KIC 8462852: A possible 928-day period

Science.gov (United States)

Kiefer, F.; Lecavelier des Étangs, A.; Vidal-Madjar, A.; Hébrard, G.; Bourrier, V.; Wilson, P. A.

2017-12-01

As revealed by its peculiar Kepler light curve, the enigmatic star KIC 8462852 undergoes short and deep flux dimmings at a priori unrelated epochs. This star presents nonetheless all other characteristics of a quiet 1 Gyr old F3V star. These dimmings resemble the absorption features expected for the transit of dust cometary tails. The exocomet scenario is therefore most commonly advocated. We reanalysed the Kepler data and extracted a new high-quality light curve to allow for the search of shallow signatures of single or a few exocomets. We discovered that among the 22 flux dimming events that we identified, two events present a striking similarity. These events occurred 928.25 days apart and lasted for 4.4 days with a drop in the star brightness by 1000 ppm. We show that the light curve of these events is well explained by the occultation of the star by a giant ring system or by the transit of a string of half a dozen exocomets with a typical dust production rate of 105-106 kg s-1. Assuming that these two similar events are related to the transit of the same object, we derive a period of 928.25 days. The following transit was expected in March 2017 but bad weather prohibited us from detecting it from ground-based spectroscopy. We predict that the next event will occur between 3-8 October 2019.

A structural phase transition coupled to the Fe{sup 3+} spin-state crossover in anhydrous RbMn[Fe(CN){sub 6}

Energy Technology Data Exchange (ETDEWEB)

Rykov, A. I., E-mail: rykov3@yahoo.com; Wang, J., E-mail: wangjh@dicp.ac.cn; Zhang, T. [Chinese Academy of Sciences, Moessbauer Effect Data Center, Dalian Institute of Chemical Physics (China); Nomura, K. [University of Tokyo, Graduate School of Engineering (Japan)

2013-04-15

Linkage isomerism is the coexistence of iso-compositional molecules or solids differing by connectivity of the metal to a ligand. In a crystalline solid state, the rotation is possible for asymmetric ligands, e.g., for cyanide ligand. Here we report on our observation of a phase transition in anhydrous RbMn[Fe(CN){sub 6}] (nearly stoichiometric) and on the effect of linkage isomerism ensuing our interpretation of the results of Moessbauer study in which we observe the iron spin state crossover among two phases involved into this transition. The anhydrous RbMn[Fe(CN){sub 6}] can be prepared via prolonged thermal treatment (1 week at at 80 Degree-Sign C) of the as-synthesized hydrated RbMn[Fe(CN){sub 6}]{center_dot}H{sub 2}O. The latter compound famous for its charge-transfer phase transition is a precursor in our case. As the temperature is raising above 80 Degree-Sign C (remaining below 100 Degree-Sign C) we observe RbMn[Fe(CN){sub 6}] that inherited its F-43 m symmetry from RbMn[Fe(CN){sub 6}]{center_dot}H{sub 2}O transforming to a phase of the Fm-3 m symmetry. In the latter, more than half of Fe{sup 3 + } ions are in high-spin state. We suggest a plausible way to explain the spin-crossover that is to allow the linkage isomerism by rotation of the cyanide ligands.

Coherent spin transport through a 350 micron thick silicon wafer.

Science.gov (United States)

Huang, Biqin; Monsma, Douwe J; Appelbaum, Ian

2007-10-26

We use all-electrical methods to inject, transport, and detect spin-polarized electrons vertically through a 350-micron-thick undoped single-crystal silicon wafer. Spin precession measurements in a perpendicular magnetic field at different accelerating electric fields reveal high spin coherence with at least 13pi precession angles. The magnetic-field spacing of precession extrema are used to determine the injector-to-detector electron transit time. These transit time values are associated with output magnetocurrent changes (from in-plane spin-valve measurements), which are proportional to final spin polarization. Fitting the results to a simple exponential spin-decay model yields a conduction electron spin lifetime (T1) lower bound in silicon of over 500 ns at 60 K.

SOAP-T: a tool to study the light curve and radial velocity of a system with a transiting planet and a rotating spotted star

Science.gov (United States)

Oshagh, M.; Boisse, I.; Boué, G.; Montalto, M.; Santos, N. C.; Bonfils, X.; Haghighipour, N.

2013-01-01

We present an improved version of SOAP named "SOAP-T", which can generate the radial velocity variations and light curves for systems consisting of a rotating spotted star with a transiting planet. This tool can be used to study the anomalies inside transit light curves and the Rossiter-McLaughlin effect, to better constrain the orbital configuration and properties of planetary systems and the active zones of their host stars. Tests of the code are presented to illustrate its performance and to validate its capability when compared with analytical models and real data. Finally, we apply SOAP-T to the active star, HAT-P-11, observed by the NASA Kepler space telescope and use this system to discuss the capability of this tool in analyzing light curves for the cases where the transiting planet overlaps with the star's spots. The tool's public interface is available at http://www.astro.up.pt/resources/soap-t/

Field-induced phase transition in a metalorganic spin-dimer system-a potential model system to study Bose-Einstein condensation of magnons

International Nuclear Information System (INIS)

Tsui, Y.; Bruehl, A.; Removic-Langer, K.; Pashchenko, V.; Wolf, B.; Donath, G.; Pikul, A.; Kretz, T.; Lerner, H.-W.; Wagner, M.; Salguero, A.; Saha-Dasgupta, T.; Rahaman, B.; Valenti, R.; Lang, M.

2007-01-01

We report on the results obtained from studying electron spin resonance, magnetic susceptibility, specific heat and thermal expansion experiments on a metalorganic spin-dimer system, C 36 H 48 Cu 2 F 6 N 8 O 12 S 2 (TK91). According to the first principle Density Functional Theory calculations, the compound represents a 3D-coupled dimer system with intradimer coupling J 1 /k B ∼ 10K and interdimer couplings J 2 /k B ∼J 3 /k B ∼ 1K. The measurements have been performed on both pressed powder and single-crystal samples in external magnetic fields up to 12T and at low temperatures down to ∼ 0.2K. Susceptibility measurements reveal a spin-gap behavior consistent with the theoretical results. Furthermore, clear indications of a field-induced phase transition have been observed. A similar field-induced phase transition was also detected in an inorganic compound TlCuCl 3 and was interpreted as Bose-Einstein condensation (BEC) of magnons. The possibility of changing both the intradimer and interdimer couplings in TK91 by chemical substitutions makes the system a potentially good system to study BEC of magnons

Electromagnetic wave propagating along a space curve

Science.gov (United States)

Lai, Meng-Yun; Wang, Yong-Long; Liang, Guo-Hua; Wang, Fan; Zong, Hong-Shi

2018-03-01

By using the thin-layer approach, we derive the effective equation for the electromagnetic wave propagating along a space curve. We find intrinsic spin-orbit, extrinsic spin-orbit, and extrinsic orbital angular-momentum and intrinsic orbital angular-momentum couplings induced by torsion, which can lead to geometric phase, spin, and orbital Hall effects. And we show the helicity inversion induced by curvature that can convert a right-handed circularly polarized electromagnetic wave into a left-handed polarized one, vice versa. Finally, we demonstrate that the gauge invariance of the effective dynamics is protected by the geometrically induced gauge potential.

Cluster glass transition in Ca2-xLaxMnO4

International Nuclear Information System (INIS)

Manaka, H.; Mishima, K.; Okuda, T.

2007-01-01

We performed linear and nonlinear AC magnetic susceptibility measurements on Ca 2-x La x MnO 4 (x=0.03,0.07,0.10, and 0.14). In such manganites, coexistence or competition brings about various phenomena. We focus on a cluster glass state consisting of ferromagnetic clusters within an antiferromagnetic matrix because the coexistence of the ferromagnetic double exchange interaction and the antiferromagnetic superexchange interaction is closely associated with phase separation. As a result, temperature (T) dependence of a linear susceptibility (X 0 ' (T)) exhibits a sharp peak for x=0.03, and these peaks become broad with increasing x. The X 0 ' (T) curves for x=0.07 and 0.10 show a typical frequency dependence around the peaks, suggesting a cluster (spin) glass transition. Furthermore, a nonlinear susceptibility (X 2 ' (T)) for x=0.10 exhibits successive transitions: the ferromagnetic transition in each cluster occurs at ∼108K and the antiferromagnetic transition between the ferromagnetic clusters occurs at ∼89K. From the X 0 ' (T) and X 2 ' (T) curves for various values of x, we found the existence of the ferromagnetic clusters within the antiferromagnetic matrix, and the cluster glass state was realized for 0.07=< x=<0.14

Effect of spin reorientation on magnetocaloric and transport properties of NdAl{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Souza, M.V. de, E-mail: marcos_vinicios@hotmail.com [Núcleo de Pós-Graduação em Física, Campus Prof. José Aloísio de Campos, UFS, 49100-000 São Cristóvão, SE (Brazil); Silva, J.A. da [Núcleo de Pós-Graduação em Física, Campus Prof. José Aloísio de Campos, UFS, 49100-000 São Cristóvão, SE (Brazil); Silva, L.S. [Núcleo de Pós-Graduação em Física, Campus Prof. José Aloísio de Campos, UFS, 49100-000 São Cristóvão, SE (Brazil); Instituto Federal de Tocantins, IFTO – Campus Colinas do Tocantins, AV. Bernardo Sayao S/N, Chácara Raio de Sol, Setor Santa Maria, CEP 77760-000 Colinas do Tocantins, TO (Brazil)

2017-01-01

We report the magneto-thermal and resistive properties of rare-earth dialuminide NdAl{sub 2}, including spin reorientation transition. To this purpose, we used a theoretical model that considers the interactions of exchange and Zeeman, besides the anisotropy due to the electrical crystal field. The theoretical results obtained were compared to experimental data of the NdAl{sub 2} in single crystal and bulk forms. Explicitly, we have calculated the anisotropic variation of magnetic entropy with the magnetic field oriented along the three principal crystallographic directions: [100], [110], and [111] of NdAl{sub 2} single crystal, where a signature of the spin reorientation is observed in the [110] and [111] directions. Moreover, of magnetoresistivity we consider the applied magnetic field along the crystallographic directions [100] and [110]. In turn, for the polycrystalline form, the good agreement between theory and experiment confirms the presence of spin reorientation, which was predicted theoretically in magnetization curves. - Highlights: • Modeling of the thermodynamics quantities in NdAl{sub 2} single crystal and policrystal. • Modeling of the transport properties in NdAl{sub 2} single crystal. • Effect of reorientation of spin on caloric and transport properties.

Classical model of the Dirac electron in curved space

International Nuclear Information System (INIS)

Barut, A.O.; Pavsic, M.

1987-01-01

The action for the classical model of the electron exhibiting Zitterbewegung is generalized to curved space by introducing a spin connection. The dynamical equations and the symplectic structure are given for several different choices of the variables. In particular, we obtain the equation of motion for spin and compare it with the Papapetrou equation. (author)

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

Energy Technology Data Exchange (ETDEWEB)

Deviren, Bayram, E-mail: bayram.deviren@nevsehir.edu.tr [Department of Physics, Nevsehir University, 50300 Nevsehir (Turkey); Keskin, Mustafa [Department of Physics, Erciyes University, 38039 Kayseri (Turkey)

2012-03-15

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

Spontaneous spin-polarization and phase transition in the relativistic approach

International Nuclear Information System (INIS)

Maruyama, Tomoyuki; Tatsumi, Toshitaka

2001-01-01

We study the spin-polarization mechanism in the highly dense nuclear matter with the relativistic mean-field approach. In the relativistic Hartree-Fock framework we find that there are two kinds of spin-spin interaction channels, which are the axial-vector and tensor exchange ones. If each interaction is strong and different sign, the system loses the spherical symmetry and holds the spin-polarization in the high-density region. When the axial-vector interaction is negative enough, the system holds ferromagnetism. (author)

Spin crossover and high spin filtering behavior in Co-Pyridine and Co-Pyrimidine molecules

Science.gov (United States)

Wen, Zhongqian; Zhou, Liping; Cheng, Jue-Fei; Li, Shu-Jin; You, Wen-Long; Wang, Xuefeng

2018-03-01

We present a theoretical study on a series of cobalt complexes, which are constructed with cobalt atoms and pyridine/pyrimidine rings, using density functional theory. We investigate the structural and electric transport properties of spin crossover (SCO) Co complex with two spin states, namely low-spin configuration [LS] and high-spin configuration [HS]. Energy analyses of the two spin states imply that the SCO Co-Pyridine2 and Co-Pyrimidine2 complexes may display a spin transition process accompanied by a geometric modification driven by external stimuli. A nearly perfect spin filtering effect is observed in the Co-Pyrimidine2 complex with [HS] state. In addition, we also discover the contact-dependent transmission properties of Co-Pyridine2. These findings indicate that SCO Co complexes are promising materials for molecular spintronic devices.

Spin-flip scattering effect on the current-induced spin torque in ferromagnet-insulator-ferromagnet tunnel junctions

International Nuclear Information System (INIS)

Zhu Zhengang; Su Gang; Jin Biao; Zheng Qingrong

2003-01-01

We have investigated the current-induced spin transfer torque of a ferromagnet-insulator-ferromagnet tunnel junction by taking the spin-flip scatterings into account. It is found that the spin-flip scattering can induce an additional spin torque, enhancing the maximum of the spin torque and giving rise to an angular shift compared to the case when the spin-flip scatterings are neglected. The effects of the molecular fields of the left and right ferromagnets on the spin torque are also studied. It is found that τ Rx /I e (τ Rx is the spin-transfer torque acting on the right ferromagnet and I e is the tunneling electrical current) does vary with the molecular fields. At two certain angles, τ Rx /I e is independent of the molecular field of the right ferromagnet, resulting in two crossing points in the curve of τ Rx /I e versus the relevant orientation for different molecular fields

Novel spin transition between S = 5/2 and S = 3/2 in highly saddled iron(III) porphyrin complexes at extremely low temperatures.

Science.gov (United States)

Ohgo, Yoshiki; Chiba, Yuya; Hashizume, Daisuke; Uekusa, Hidehiro; Ozeki, Tomoji; Nakamura, Mikio

2006-05-14

A novel spin transition between S = 5/2 and S = 3/2 has been observed for the first time in five-coordinate, highly saddled iron(III) porphyrinates by EPR and SQUID measurements at extremely low temperatures.

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

Science.gov (United States)

Hoi, Bui Dinh; Yarmohammadi, Mohsen

2018-04-01

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

Spin-Glass Transition and Giant Paramagnetism in Heavily Hole-Doped Bi2Sr2Co2Oy

Science.gov (United States)

Hsu, Hung Chang; Lee, Wei-Li; Lin, Jiunn-Yuan; Young, Ben-Li; Kung, Hsiang-Hsi; Huang, Jian; Chou, Fang Cheng

2014-02-01

Hole-doped single crystals of misfit-layered cobaltate Bi2-xPbxSr2-zCo2Oy (x = 0-0.61, y = 8.28-8.62, and z = 0.01-0.22) have been successfully grown using the optical floating-zone method. Heavier hole doping has been achieved through both Pb substitution in the Bi site and the more effective Sr vacancy formation. The Co4+ : Co3+ ratio can be raised significantly from its original ˜1 : 1 to 4.5 : 1, as confirmed by iodometric titration. A spin-glass transition temperature of Tg ˜ 70 K is confirmed by ac susceptibility measurement when the Co4+ : Co3+ ratio becomes higher than 2 : 1, presumably owing to the significantly increased probability of triangular geometrical frustration among antiferromagnetically coupled localized Co4+ spins.

Nuclear Spin Nanomagnet in an Optically Excited Quantum Dot

Science.gov (United States)

Korenev, V. L.

2007-12-01

Linearly polarized light tuned slightly below the optical transition of the negatively charged exciton (trion) in a single quantum dot causes the spontaneous nuclear spin polarization (self-polarization) at a level close to 100%. The effective magnetic field of spin-polarized nuclei shifts the optical transition energy close to resonance with photon energy. The resonantly enhanced Overhauser effect sustains the stability of the nuclear self-polarization even in the absence of spin polarization of the quantum dot electron. As a result the optically selected single quantum dot represents a tiny magnet with the ferromagnetic ordering of nuclear spins—the nuclear spin nanomagnet.

Identification of high-spin states in 235U

International Nuclear Information System (INIS)

Lorenz, A.; Makarenko, V.E.; Chukreev, F.E.

1994-02-01

The results of a 235 U high spin states study are analysed. A new way to assign newly observed gamma ray transitions is proposed. Such assignments deals with low spin parts of the level scheme without introducing high spin level states. (author)

Spin polarized states in strongly asymmetric nuclear matter

International Nuclear Information System (INIS)

Isayev, A.A.; Yang, J.

2004-01-01

The possibility of appearance of spin polarized states in strongly asymmetric nuclear matter is analyzed within the framework of a Fermi liquid theory with the Skyrme effective interaction. The zero temperature dependence of the neutron and proton spin polarization parameters as functions of density is found for SLy4 and SLy5 effective forces. It is shown that at some critical density strongly asymmetric nuclear matter undergoes a phase transition to the state with the oppositely directed spins of neutrons and protons while the state with the same direction of spins does not appear. In comparison with neutron matter, even small admixture of protons strongly decreases the threshold density of spin instability. It is clarified that protons become totally polarized within a very narrow density domain while the density profile of the neutron spin polarization parameter is characterized by the appearance of long tails near the transition density

Direct observation of spin-quadrupolar excitations in Sr2CoGe2O7 by high-field electron spin resonance

Science.gov (United States)

Akaki, Mitsuru; Yoshizawa, Daichi; Okutani, Akira; Kida, Takanori; Romhányi, Judit; Penc, Karlo; Hagiwara, Masayuki

2017-12-01

Exotic spin-multipolar ordering in spin transition metal insulators has so far eluded unambiguous experimental observation. A less studied, but perhaps more feasible fingerprint of multipole character emerges in the excitation spectrum in the form of quadrupolar transitions. Such multipolar excitations are desirable as they can be manipulated with the use of light or electric field and can be captured by means of conventional experimental techniques. Here we study single crystals of multiferroic Sr2CoGe2O7 and observe a two-magnon spin excitation appearing above the saturation magnetic field in electron spin resonance (ESR) spectra. Our analysis of the selection rules reveals that this spin excitation mode does not couple to the magnetic component of the light, but it is excited by the electric field only, in full agreement with the theoretical calculations. Due to the nearly isotropic nature of Sr2CoGe2O7 , we identify this excitation as a purely spin-quadrupolar two-magnon mode.

Spin-waves in Antiferromagnetic Single-crystal LiFePO4

International Nuclear Information System (INIS)

Li, Jiying; Garlea, Vasile O.; Zarestky, Jarel; Vaknin, D.

2006-01-01

Spin-wave dispersions in the antiferromagnetic state of single-crystal LiFePO 4 were determined by inelastic neutron scattering measurements. The dispersion curves measured from the (0,1,0) reflection along both a* and b* reciprocal-space directions reflect the anisotropic coupling of the layered Fe 2+ (S=2) spin system. The spin-wave dispersion curves were theoretically modeled using linear spin-wave theory by including in the spin Hamiltonian in-plane nearest- and next-nearest-neighbor interactions (J 1 and J 2 ), inter-plane nearest-neighbor interactions (J(perpendicular)) and a single-ion anisotropy (D). A weak (0,1,0) magnetic peak was observed in elastic neutron scattering studies of the same crystal indicating that the ground state of the staggered iron moments is not along the (0,1,0) direction, as previously reported from polycrystalline samples studies, but slightly rotated away from this axis.

Spin interferometry in anisotropic spin-orbit fields

Science.gov (United States)

Saarikoski, Henri; Reynoso, Andres A.; Baltanás, José Pablo; Frustaglia, Diego; Nitta, Junsaku

2018-03-01

Electron spins in a two-dimensional electron gas can be manipulated by spin-orbit (SO) fields originating from either Rashba or Dresselhaus interactions with independent isotropic characteristics. Together, though, they produce anisotropic SO fields with consequences on quantum transport through spin interference. Here we study the transport properties of modeled mesoscopic rings subject to Rashba and Dresselhaus [001] SO couplings in the presence of an additional in-plane Zeeman field acting as a probe. By means of one- and two-dimensional quantum transport simulations we show that this setting presents anisotropies in the quantum resistance as a function of the Zeeman field direction. Moreover, the anisotropic resistance can be tuned by the Rashba strength up to the point to invert its response to the Zeeman field. We also find that a topological transition in the field texture that is associated with a geometric phase switching is imprinted in the anisotropy pattern. We conclude that resistance anisotropy measurements can reveal signatures of SO textures and geometric phases in spin carriers.

Dynamic selective switching in antiferromagnetically-coupled bilayers close to the spin reorientation transition

International Nuclear Information System (INIS)

Fernández-Pacheco, A.; Mansell, R.; Petit, D.; Lee, J. H.; Cowburn, R. P.; Ummelen, F. C.; Swagten, H. J. M.

2014-01-01

We have designed a bilayer synthetic antiferromagnet where the order of layer reversal can be selected by varying the sweep rate of the applied magnetic field. The system is formed by two ultra-thin ferromagnetic layers with different proximities to the spin reorientation transition, coupled antiferromagnetically using Ruderman-Kittel-Kasuya-Yosida interactions. The different dynamic magnetic reversal behavior of both layers produces a crossover in their switching fields for field rates in the kOe/s range. This effect is due to the different effective anisotropy of both layers, added to an appropriate asymmetric antiferromagnetic coupling between them. Field-rate controlled selective switching of perpendicular magnetic anisotropy layers as shown here can be exploited in sensing and memory applications.

Monte Carlo simulation and theory in Gaussian approximation of a phase transition in the nuclear spin system of a solid

Energy Technology Data Exchange (ETDEWEB)

Merkulov, I A; Papava, Y I; Ponomarenko, V V [Leningradskij Gosudarstvennyj Univ., Leningrad (Russian Federation); Vasiliev, S I [Carleton Univ., Ottawa, ON (Canada). Dept. of Physics

1988-02-01

A phase transition of the nuclear spin system of a solid with dipolar and indirect scalar interactions is considered. Monte Carlo simulations of the spin-system isothermic states and of the adiabatic demagnetization process have been made. The structures and energies of the ground states and the values of the critical temperatures, T[sub C], and minimal polarizations, [rho][sub C], at which adiabatic demagnetization leads to spontaneous spin ordering, calculated for the GaAs and CaF[sub 2] nuclear spin systems, are presented. The results of numerical simulations are compared with the experimental data for CaF[sub 2]. The Weiss-field model is extended to the case of adiabatic demagnetization. The fluctuations of the local field are taken into account in the Gaussian approximation. It is shown that the proposed approach allows one to obtain asymptotically correct results both for T >> T[sub C] and T << T[sub C]. The results of the calculations in the Gaussian approximation are compared with the numerical simulations. (10 refs., 9 figs., tab.).

Spin crossover and Mott—Hubbard transition under high pressure and high temperature in the low mantle of the Earth

Science.gov (United States)

Ovchinnikov, S. G.; Ovchinnikova, T. M.; Plotkin, V. V.; Dyad'kov, P. G.

2015-11-01

Effect of high pressure induced spin crossover on the magnetic, electronic and structural properties of the minerals forming the Earth's low mantle is discussed. The low temperature P, T phase diagram of ferropericlase has the quantum phase transition point Pc = 56 GPa at T = 0 confirmed recently by the synchrotron Mössbauer spectroscopy. The LDA+GTB calculated phase diagram describes the experimental data. Its extension to the high temperature resulted earlier in prediction of the metallic properties of the Earth's mantle at the depth 1400 km insulator transition and compare them with the experimental seismic and geomagnetic field data.

High-spin states and coexisting states in the Pt-Au transition region

International Nuclear Information System (INIS)

Riedinger, L.L.; Carpenter, M.P.; Courtney, L.H.; Janzen, V.P.; Schmitz, W.

1986-01-01

High-spin states in the N = 104 to 108 region have been studied by in-beam spectroscopy techniques in a number of Ir, Pt, and Au nuclei. These measurements have been performed at tandem Van de Graaff facilities at the Oak Ridge National Laboratory and at McMaster University. Through comparison of band crossings in a variety of odd-A and even-A nuclei, we are able to assign the first neutron and first proton alignment processes, which are nearly degenerate for 184 Pt. These measurements yield the trend of these crossing frequencies with N and Z in this region. Knowledge of this trend is important, since these crossing frequencies can give an estimate of how the shape parameters vary across this transitional region. 22 refs., 7 figs., 1 tab

Complex band structures of transition metal dichalcogenide monolayers with spin-orbit coupling effects

Science.gov (United States)

Szczęśniak, Dominik; Ennaoui, Ahmed; Ahzi, Saïd

2016-09-01

Recently, the transition metal dichalcogenides have attracted renewed attention due to the potential use of their low-dimensional forms in both nano- and opto-electronics. In such applications, the electronic and transport properties of monolayer transition metal dichalcogenides play a pivotal role. The present paper provides a new insight into these essential properties by studying the complex band structures of popular transition metal dichalcogenide monolayers (MX 2, where M  =  Mo, W; X  =  S, Se, Te) while including spin-orbit coupling effects. The conducted symmetry-based tight-binding calculations show that the analytical continuation from the real band structures to the complex momentum space leads to nonlinear generalized eigenvalue problems. Herein an efficient method for solving such a class of nonlinear problems is presented and yields a complete set of physically relevant eigenvalues. Solutions obtained by this method are characterized and classified into propagating and evanescent states, where the latter states manifest not only monotonic but also oscillatory decay character. It is observed that some of the oscillatory evanescent states create characteristic complex loops at the direct band gap of MX 2 monolayers, where electrons can directly tunnel between the band gap edges. To describe these tunneling currents, decay behavior of electronic states in the forbidden energy region is elucidated and their importance within the ballistic transport regime is briefly discussed.

Mechanisms of spin-flipping and metal-insulator transition in nano-Fe3O4

Science.gov (United States)

Dito Fauzi, Angga; Aziz Majidi, Muhammad; Rusydi, Andrivo

2017-04-01

Fe3O4 is a half-metallic ferrimagnet with {{T}\\text{C}}˜ 860 K exhibiting metal-insulator transition (MIT) at  ˜120 K. In bulk form, the saturation magnetization is 0.6 Tesla (˜471 emu cm-3). A recent experimental study has shown that the saturation magnetization of nano-Fe3O4 thin films can achieve up to  ˜760 emu cm-3, attributed to spin-flipping of Fe ions at tetrahedral sites assisted by oxygen vacancies (V O). Such a system has shown to have higher MIT temperature (˜150 K). The spin-flipping is a new phenomenon in Fe3O4, while the MIT is a long-standing one. Here, we propose a model and calculations to investigate the mechanisms of both phenomena. Our results show that, for the system without V O, the ferrimagnetic configuration is energetically favorable. Remakably, upon inclusion of V O, the ground-state configuration switches into ferromagnetic. As for the MIT, by proposing temperature dependences of some hopping integrals in the model, we demonstrate that the system without and with V O undergo the MIT in slightly different ways, leading to higher MIT temperature for the system with V O, in agreement with the experimental data. Our results also show that the MIT in both systems occur concomitantly with the redistribution of electrons among the three Fe ions in each Fe3O4 formula unit. As such temperature dependences of hopping integrals may arise due to dynamic Jahn-Teller effects, our phenomenological theory may provide a way to reconcile existing theories relating the MIT to the structural transition and the charge ordering.

Tuning the presence of dynamical phase transitions in a generalized XY spin chain.

Science.gov (United States)

Divakaran, Uma; Sharma, Shraddha; Dutta, Amit

2016-05-01

We study an integrable spin chain with three spin interactions and the staggered field (λ) while the latter is quenched either slowly [in a linear fashion in time (t) as t/τ, where t goes from a large negative value to a large positive value and τ is the inverse rate of quenching] or suddenly. In the process, the system crosses quantum critical points and gapless phases. We address the question whether there exist nonanalyticities [known as dynamical phase transitions (DPTs)] in the subsequent real-time evolution of the state (reached following the quench) governed by the final time-independent Hamiltonian. In the case of sufficiently slow quenching (when τ exceeds a critical value τ_{1}), we show that DPTs, of the form similar to those occurring for quenching across an isolated critical point, can occur even when the system is slowly driven across more than one critical point and gapless phases. More interestingly, in the anisotropic situation we show that DPTs can completely disappear for some values of the anisotropy term (γ) and τ, thereby establishing the existence of boundaries in the (γ-τ) plane between the DPT and no-DPT regions in both isotropic and anisotropic cases. Our study therefore leads to a unique situation when DPTs may not occur even when an integrable model is slowly ramped across a QCP. On the other hand, considering sudden quenches from an initial value λ_{i} to a final value λ_{f}, we show that the condition for the presence of DPTs is governed by relations involving λ_{i},λ_{f}, and γ, and the spin chain must be swept across λ=0 for DPTs to occur.

Quantum statistical metastability for a finite spin

Science.gov (United States)

Garanin, D. A.; Chudnovsky, E. M.

2001-01-01

We study quantum-classical escape-rate transitions for uniaxial and biaxial models with finite spins S=10 (such as Mn12Ac and Fe8) and S=100 by a direct numerical approach. At second-order transitions the level making a dominant contribution into thermally assisted tunneling changes gradually with temperature whereas at first-order transitions a group of levels is skipped. For finite spins, the quasiclassical boundaries between first- and second-order transitions are shifted, favoring a second-order transition: For Fe8 in zero field the transition should be first order according to a theory with S-->∞, but we show that there are no skipped levels at the transition. Applying a field along the hard axis in Fe8 makes transition the strongest first order. For the same model with S=100 we confirmed the existence of a region where a second-order transition is followed by a first-order transition [X. Martínes Hidalgo and E. M. Chudnovsky, J. Phys.: Condensed Matter 12, 4243 (2000)].

F(α) curves: Experimental results

International Nuclear Information System (INIS)

Glazier, J.A.; Gunaratne, G.; Libchaber, A.

1988-01-01

We study the transition to chaos at the golden and silver means for forced Rayleigh-Benard (RB) convection in mercury. We present f(α) curves below, at, and above the transition, and provide comparisons to the curves calculated for the one-dimensional circle map. We find good agreement at both the golden and silver means. This confirms our earlier observation that for low amplitude forcing, forced RB convection is well described by the one-dimensional circle map and indicates that the f(α) curve is a good measure of the approach to criticality. For selected subcritical experimental data sets we calculate the degree of subcriticality. We also present both experimental and calculated results for f(α) in the presence of a third frequency. Again we obtain agreement: The presence of random noise or a third frequency narrows the right-hand (negative q) side of the f(α) curve. Subcriticality results in symmetrically narrowed curves. We can also distinguish these cases by examining the power spectra and Poincare sections of the time series

Hysteresis, nucleation and growth phenomena in spin-crossover solids

Science.gov (United States)

Ridier, Karl; Molnár, Gábor; Salmon, Lionel; Nicolazzi, William; Bousseksou, Azzedine

2017-12-01

The observation and the study of first-order phase transitions in cooperative spin-crossover (SCO) solids exhibiting hysteresis behaviours are of particular interest and currently constitute a burgeoning area in the field of bistable molecular materials. The understanding and the control of the transition mechanisms (nucleation and growth processes) and their dynamics within the hysteresis region appear to be a general and appealing problem from a fundamental point of view and for technological applications as well. This review reports on the recent progresses and most important findings made on the spatiotemporal dynamics of the spin transition in SCO solids, particularly through the universal nucleation and growth process. Both thermally induced and light-induced spin transitions are discussed. We open up this review to the central question of the evolution of the transition mechanisms and dynamics in SCO nano-objects, which constitute promising systems to reach ultra-fast switching, and the experimental issues inherent to such studies at the micro- and nanometric scale.

Deformed Fredkin spin chain with extensive entanglement

Science.gov (United States)

Salberger, Olof; Udagawa, Takuma; Zhang, Zhao; Katsura, Hosho; Klich, Israel; Korepin, Vladimir

2017-06-01

We introduce a new spin chain which is a deformation of the Fredkin spin chain and has a phase transition between bounded and extensive entanglement entropy scaling. In this chain, spins have a local interaction of three nearest neighbors. The Hamiltonian is frustration-free and its ground state can be described analytically as a weighted superposition of Dyck paths that depends on a deformation parameter t. In the purely spin 1/2 case, whenever t\

Structural transition in Mo{sub 3}Sb{sub 7} probed by muon spin relaxation

Energy Technology Data Exchange (ETDEWEB)

Tabata, Y. [Department of Materials Science and Engineering, Kyoto University, Kyoto 606-8501 (Japan); Koyama, T.; Kohara, T. [Graduate School of Material Science, University of Hyogo, Kamigori, Ako-gun, Hyogo 678-1297 (Japan); Watanabe, I. [Advanced Meson Science Laboratory, RIKEN Nishina Center, Wako, Saitama 351-0198 (Japan); Nakamura, H., E-mail: h.nakamura@ht8.ecs.kyoto-u.ac.j [Department of Materials Science and Engineering, Kyoto University, Kyoto 606-8501 (Japan)

2009-04-15

Longitudinal-field muSR measurements have been made for Mo{sub 3}Sb{sub 7} focusing on the nature of the structural transition recently found at T{sub S}approx =50K. Taking account of a critical behavior of the relaxation rate lambda at approxT{sub S}, together with the motional narrowing of the nuclear dipolar field revealed in a zero-field experiment, and the tetragonal lattice symmetry lowering below T{sub S}, we propose long-range order of spin-singlet dimers, i.e., the formation of the valence bond crystal below T{sub S}. As a possible origin, the frustration in the interdimer antiferromagnetic interaction is suggested.

Electron spin-lattice relaxation in fractals

International Nuclear Information System (INIS)

Shrivastava, K.N.

1986-08-01

We have developed the theory of the spin-fracton interaction for paramagnetic ions in fractal structures. The interaction is exponentially damped by the self-similarity length of the fractal and by the range dimensionality d Φ . The relaxation time of the spin due to the absorption and emission of the fracton has been calculated for a general dimensionality called the Raman dimensionality d R , which for the fractons differs from the Hausdorff (fractal) dimensionality, D, as well as from the Euclidean dimensionality, d. The exponent of the energy level separation in the relaxation rate varies with d R d Φ /D. We have calculated the spin relaxation rate due to a new type of Raman process in which one fracton is absorbed to affect a spin transition from one electronic level to another and later another fracton is emitted along with a spin transition such that the difference in the energies of the two fractons is equal to the electronic energy level separation. The temperature and the dimensionality dependence of such a process has been found in several approximations. In one of the approximations where the van Vleck relaxation rate for a spin in a crystal is known to vary with temperature as T 9 , our calculated variation for fractals turns out to be T 6.6 , whereas the experimental value for Fe 3+ in frozen solutions of myoglobin azide is T 6.3 . Since we used d R =4/3 and the fracton range dimensionality d Φ =D/1.8, we expect to measure the dimensionalities of the problem by measuring the temperature dependence of the relaxation times. We have also calculated the shift of the paramagnetic resonance transition for a spin in a fractal for general dimensionalities. (author)

Spin critical opalescence in zero-temperature Bose-Einstein condensates

Science.gov (United States)

Santamore, D. H.; Timmermans, E.

2012-02-01

Cold-atom developments suggest the prospect of measuring scaling properties and long-range fluctuations of continuous phase transitions at zero temperature. We discuss the conditions for characterizing the phase separation of Bose-Einstein condensates of boson atoms in two distinct hyperfine spin states. The mean-field description breaks down as the system approaches the transition from the miscible side. An effective spin description clarifies the ferromagnetic nature of the transition. We show that a difference in the scattering lengths for the bosons in the same spin state leads to an effective internal magnetic field. The point at which the internal magnetic field vanishes (i.e., equal values of the like-boson scattering lengths) is a special point. We show that the long-range density fluctuations are suppressed near that point, while the effective spin exhibits the long-range fluctuations that characterize critical points. The zero-temperature system exhibits critical opalescence with respect to long-wavelength waves of impurity atoms that interact with the bosons in a spin-dependent manner.

The spin-Peierls chain revisited

International Nuclear Information System (INIS)

Hager, Georg; Weisse, Alexander; Wellein, Gerhard; Jeckelmann, Eric; Fehske, Holger

2007-01-01

We extend previous analytical studies of the ground-state phase diagram of a one-dimensional Heisenberg spin chain coupled to optical phonons, which for increasing spin-lattice coupling undergoes a quantum phase transition from a gapless to a gaped phase with finite lattice dimerisation. We check the analytical results against established four-block and new two-block density matrix renormalisation group (DMRG) calculations. Different finite-size scaling behaviour of the spin excitation gaps is found in the adiabatic and anti-adiabatic regimes

Unveiling multiple solid-state transitions in pharmaceutical solid dosage forms using multi-series hyperspectral imaging and different curve resolution approaches

DEFF Research Database (Denmark)

Alexandrino, Guilherme L; Amigo Rubio, Jose Manuel; Khorasani, Milad Rouhi

2017-01-01

Solid-state transitions at the surface of pharmaceutical solid dosage forms (SDF) were monitored using multi-series hyperspectral imaging (HSI) along with Multivariate Curve Resolution – Alternating Least Squares (MCR-ALS) and Parallel Factor Analysis (PARAFAC and PARAFAC2). First, the solid-stat...

Thermal hysteresis kinetic effects of spin crossover nanoparticulated systems studied by FORC diagram method on an Ising-like model

International Nuclear Information System (INIS)

Atitoaie, Alexandru; Stoleriu, Laurentiu; Tanasa, Radu; Stancu, Alexandru; Enachescu, Cristian

2016-01-01

The scientific community is manifesting a high research interest on spin crossover compounds and their recently synthesized nanoparticles, due to their various appealing properties, such as the bistability between a diamagnetic low spin state and a paramagnetic high spin state (HS), inter-switchable by temperature or pressure changes, light irradiation or magnetic field. The utility of these compounds showing hysteresis covers a broad area of applications, from the development of more efficient designs of temperature and pressure sensors to automotive and aeronautic industries and even a new type of molecular actuators. We are proposing in this work a study regarding the kinetic effects and the distribution of reversible and irreversible components on the thermal hysteresis of spin crossover nanoparticulated systems. We are considering here tridimensional systems with different sizes and also systems of nanoparticles with a Gaussian size distribution. The correlations between the kinetics of the thermal hysteresis, the distributions of sizes and intermolecular interactions and the transition temperature distributions were established by using the FORC (First Order Reversal Curves) method using a Monte Carlo technique within an Ising-like system.

Thermal hysteresis kinetic effects of spin crossover nanoparticulated systems studied by FORC diagram method on an Ising-like model

Energy Technology Data Exchange (ETDEWEB)

Atitoaie, Alexandru, E-mail: atitoaie@phys-iasi.ro [Department. of Physics, “Alexandru Ioan Cuza” University, 700506 Iasi (Romania); National Institute of Research and Development for Technical Physics, Iasi (Romania); Stoleriu, Laurentiu [Department. of Physics, “Alexandru Ioan Cuza” University, 700506 Iasi (Romania); Tanasa, Radu [Department. of Physics, “Alexandru Ioan Cuza” University, 700506 Iasi (Romania); Department of Engineering, University of Cambridge, CB2 1PZ Cambridge (United Kingdom); Stancu, Alexandru; Enachescu, Cristian [Department. of Physics, “Alexandru Ioan Cuza” University, 700506 Iasi (Romania)

2016-04-01

The scientific community is manifesting a high research interest on spin crossover compounds and their recently synthesized nanoparticles, due to their various appealing properties, such as the bistability between a diamagnetic low spin state and a paramagnetic high spin state (HS), inter-switchable by temperature or pressure changes, light irradiation or magnetic field. The utility of these compounds showing hysteresis covers a broad area of applications, from the development of more efficient designs of temperature and pressure sensors to automotive and aeronautic industries and even a new type of molecular actuators. We are proposing in this work a study regarding the kinetic effects and the distribution of reversible and irreversible components on the thermal hysteresis of spin crossover nanoparticulated systems. We are considering here tridimensional systems with different sizes and also systems of nanoparticles with a Gaussian size distribution. The correlations between the kinetics of the thermal hysteresis, the distributions of sizes and intermolecular interactions and the transition temperature distributions were established by using the FORC (First Order Reversal Curves) method using a Monte Carlo technique within an Ising-like system.

Universal spin dynamics in quantum wires

Energy Technology Data Exchange (ETDEWEB)

Fajardo, E. A.; Zülicke, U.; Winkler, R.

2017-10-01

We discuss the universal spin dynamics in quasi-one-dimensional systems including the real spin in narrow-gap semiconductors like InAs and InSb, the valley pseudospin in staggered single-layer graphene, and the combination of real spin and valley pseudospin characterizing single-layer transition metal dichalcogenides (TMDCs) such as MoS2, WS2, MoS2, and WSe2. All these systems can be described by the same Dirac-like Hamiltonian. Spin-dependent observable effects in one of these systems thus have counterparts in each of the other systems. Effects discussed in more detail include equilibrium spin currents, current-induced spin polarization (Edelstein effect), and spin currents generated via adiabatic spin pumping. Our work also suggests that a long-debated spin-dependent correction to the position operator in single-band models should be absent.

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

Science.gov (United States)

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

2014-07-01

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

Spin waves and the order-disorder transition in chromium

DEFF Research Database (Denmark)

Als-Nielsen, Jens Aage; Dietrich, O.W.

1969-01-01

The inelastic magnetic scattering of neutrons has been studied in Cr and Cr0.95-Mn0.05 both below and above the Neel temperature. The temperature dependence of the spin-wave velocity in the alloy has been measured below TN. The scattering above TN may also be interpreted in terms of spin-wavelike...

Experimental realization of a silicon spin field-effect transistor

OpenAIRE

Huang, Biqin; Monsma, Douwe J.; Appelbaum, Ian

2007-01-01

A longitudinal electric field is used to control the transit time (through an undoped silicon vertical channel) of spin-polarized electrons precessing in a perpendicular magnetic field. Since an applied voltage determines the final spin direction at the spin detector and hence the output collector current, this comprises a spin field-effect transistor. An improved hot-electron spin injector providing ~115% magnetocurrent, corresponding to at least ~38% electron current spin polarization after...

Possible evidence for spin-transfer torque induced by spin-triplet supercurrent

KAUST Repository

Li, Lailai

2017-10-04

Cooper pairs in superconductors are normally spin singlet. Nevertheless, recent studies suggest that spin-triplet Cooper pairs can be created at carefully engineered superconductor-ferromagnet interfaces. If Cooper pairs are spin-polarized they would transport not only charge but also a net spin component, but without dissipation, and therefore minimize the heating effects associated with spintronic devices. Although it is now established that triplet supercurrents exist, their most interesting property - spin - is only inferred indirectly from transport measurements. In conventional spintronics, it is well known that spin currents generate spin-transfer torques that alter magnetization dynamics and switch magnetic moments. The observation of similar effects due to spin-triplet supercurrents would not only confirm the net spin of triplet pairs but also pave the way for applications of superconducting spintronics. Here, we present a possible evidence for spin-transfer torques induced by triplet supercurrents in superconductor/ferromagnet/superconductor (S/F/S) Josephson junctions. Below the superconducting transition temperature T_c, the ferromagnetic resonance (FMR) field at X-band (~ 9.0 GHz) shifts rapidly to a lower field with decreasing temperature due to the spin-transfer torques induced by triplet supercurrents. In contrast, this phenomenon is absent in ferromagnet/superconductor (F/S) bilayers and superconductor/insulator/ferromagnet/superconductor (S/I/F/S) multilayers where no supercurrents pass through the ferromagnetic layer. These experimental observations are discussed with theoretical predictions for ferromagnetic Josephson junctions with precessing magnetization.

Transition currents in diagonal spin basis

International Nuclear Information System (INIS)

Rogalev, R.N.

1996-01-01

Scalar and pseudoscalar densities, vector, pseudovector and tensor currents are expressed in terms of momentum and spin vectors of the corresponding particles in an explicitly covariant way. The obtained expressions are free of singularities and make it possible to draw a number of identities, which relate axial-vector, vector and tensor currents to each other. 8 refs

Markov chain analysis of single spin flip Ising simulations

International Nuclear Information System (INIS)

Hennecke, M.

1997-01-01

The Markov processes defined by random and loop-based schemes for single spin flip attempts in Monte Carlo simulations of the 2D Ising model are investigated, by explicitly constructing their transition matrices. Their analysis reveals that loops over all lattice sites using a Metropolis-type single spin flip probability often do not define ergodic Markov chains, and have distorted dynamical properties even if they are ergodic. The transition matrices also enable a comparison of the dynamics of random versus loop spin selection and Glauber versus Metropolis probabilities

New type of ordering process with volume change of molecules in the spin-crossover transition, and its new aspects of dynamical processes

Science.gov (United States)

Miyashita, Seiji; Nishino, Masamichi; Konishi, Yusuke; Tokoro, Hiroko; Boukheddaden, Kamel; Varret, François; Rikvold, Per Arne

2009-02-01

Bistability between the high- and low-spin states in spin-crossover materials provides a complex temperature dependence of the ordering processes. Thermodynamic properties of the ordering phenomena were studied in a unified way, and a generic structure of the ordering processes was proposed. The origin of the interaction among the spins was also discussed, and a new mechanism based on an elastic interaction among distortions due to the volume of a molecule depending on its spin state was also proposed. With this mechanism, the typical pressure dependence of the ordering processes can be reproduced. Moreover, we studied the type of criticality of the phase transition and pointed out that the present model possesses critical behaviour belonging to the mean-field universality class. There, the spin-spin correlation function is constant at long distances and does not show an exponential decay in contrast to short-range models. It is also pointed out that the model with periodic boundary conditions does not show ordering clusters, even near the critical point or in the process of spinodal decomposition. This indicates that critical opalescence would not be observed in this model. No cluster appears, either in photo-excitation process from the low-spin state at low temperatures. On the other hand, with open boundary conditions, the system shows a cluster structure. The effects of the boundary conditions are also discussed.

Crystal growth of Sm0.3Tb0.7FeO3 and spin reorientation transition in Sm1−xTbxFeO3 orthoferrite

International Nuclear Information System (INIS)

Wu, Anhua; Wang, Bo; Zhao, Xiangyang; Xie, Tao; Man, Peiwen; Su, Liangbi; Kalashnikova, A.M.; Pisarev, R.V.

2017-01-01

In this work, Sm 0.3 Tb 0.7 FeO 3 single crystal was successfully grown by optical floating zone method. Sm 0.3 Tb 0.7 FeO 3 samples with a-, b-, and c-orientation were manufactured by means of Laue photograph. Magnetic properties of Sm 0.3 Tb 0.7 FeO 3 single crystals are studied over a wide temperature range from 2 to 400 K. Spin reorientation transition from Γ 2 to Γ 4 are observed by means of the temperature dependence of magnetization It indicated the reorientation transition temperature of Sm 1−x Tb x FeO 3 single crystals is lowered with the contents of Tb contents rising based on this work and our previous works, thus the spin reorientation transition temperature can be adjusted through changing the compound in orthoferrites materials, which means that we can get orthoferrites single crystals with high magnetism property in various temperature through material design. - Highlights: • Sm 0.3 Tb 0.7 FeO 3 single crystals with various compounds were successfully grown by optical floating zone method. • The relation between SRT temperature and composition in Sm 1−x Tb x FeO 3 orthoferrite was indicated. • The spin reorientation transition temperature of Sm 1−x Tb x FeO 3 single crystals can be adjusted through changing the compound in orthoferrites materials.

Rigorous spin-spin correlation function of Ising model on a special kind of Sierpinski Carpets

International Nuclear Information System (INIS)

Yang, Z.R.

1993-10-01

We have exactly calculated the rigorous spin-spin correlation function of Ising model on a special kind of Sierpinski Carpets (SC's) by means of graph expansion and a combinatorial approach and investigated the asymptotic behaviour in the limit of long distance. The result show there is no long range correlation between spins at any finite temperature which indicates no existence of phase transition and thus finally confirms the conclusion produced by the renormalization group method and other physical arguments. (author). 7 refs, 6 figs

A parity-breaking electronic nematic phase transition in the spin-orbit coupled correlated metal Cd2Re2O7

Science.gov (United States)

Harter, J. W.; Zhao, Z. Y.; Yan, J.-Q.; Mandrus, D. G.; Hsieh, D.

Strong interactions between electrons are known to drive metallic systems toward a variety of well-known symmetry-broken phases, including superconducting, electronic liquid crystalline, and charge- and spin-density wave ordered states. In contrast, the electronic instabilities of correlated metals with strong spin-orbit coupling have only recently begun to be explored. We uncover a novel multipolar nematic phase of matter in the metallic pyrochlore Cd2Re2O7 using spatially-resolved second-harmonic optical anisotropy measurements. Like previously discovered electronic liquid crystalline phases, this multipolar nematic phase spontaneously breaks rotational symmetry while preserving translational invariance. However, it has the distinguishing property of being odd under spatial inversion, which is allowed only in the presence of spin-orbit coupling. By examining the critical behavior of the multipolar nematic order parameter, we show that it drives the thermal phase transition near 200 K in Cd2Re2O7 and induces a parity-breaking lattice distortion as a secondary order parameter.

Dynamic compensation temperatures in a mixed spin-1 and spin-3/2 Ising system under a time-dependent oscillating magnetic field

Energy Technology Data Exchange (ETDEWEB)

Keskin, Mustafa, E-mail: keskin@erciyes.edu.t [Department of Physics, Erciyes University, 38039 Kayseri (Turkey); Kantar, Ersin [Institute of Science, Erciyes University, 38039 Kayseri (Turkey)

2010-09-15

We study the existence of dynamic compensation temperatures in the mixed spin-1 and spin-3/2 Ising ferrimagnetic system Hamiltonian with bilinear and crystal-field interactions in the presence of a time-dependent oscillating external magnetic field on a hexagonal lattice. We employ the Glauber transitions rates to construct the mean-field dynamic equations. We investigate the time dependence of an average sublattice magnetizations, the thermal behavior of the dynamic sublattice magnetizations and the total magnetization. From these studies, we find the phases in the system, and characterize the nature (continuous or discontinuous) of transitions as well as obtain the dynamic phase transition (DPT) points and the dynamic compensation temperatures. We also present dynamic phase diagrams, including the compensation temperatures, in the five different planes. A comparison is made with the results of the available mixed spin Ising systems.

Dynamic compensation temperatures in a mixed spin-1 and spin-3/2 Ising system under a time-dependent oscillating magnetic field

International Nuclear Information System (INIS)

Keskin, Mustafa; Kantar, Ersin

2010-01-01

We study the existence of dynamic compensation temperatures in the mixed spin-1 and spin-3/2 Ising ferrimagnetic system Hamiltonian with bilinear and crystal-field interactions in the presence of a time-dependent oscillating external magnetic field on a hexagonal lattice. We employ the Glauber transitions rates to construct the mean-field dynamic equations. We investigate the time dependence of an average sublattice magnetizations, the thermal behavior of the dynamic sublattice magnetizations and the total magnetization. From these studies, we find the phases in the system, and characterize the nature (continuous or discontinuous) of transitions as well as obtain the dynamic phase transition (DPT) points and the dynamic compensation temperatures. We also present dynamic phase diagrams, including the compensation temperatures, in the five different planes. A comparison is made with the results of the available mixed spin Ising systems.

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

Science.gov (United States)

Conduit, G. J.; Altman, E.

2010-10-01

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

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

International Nuclear Information System (INIS)

Conduit, G. J.; Altman, E.

2010-01-01

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

Exactly solvable spin-1 Ising–Heisenberg diamond chain with the second-neighbor interaction between nodal spins

International Nuclear Information System (INIS)

Hovhannisyan, V V; Ananikian, N S; Strečka, J

2016-01-01

The spin-1 Ising–Heisenberg diamond chain with the second-neighbor interaction between nodal spins is rigorously solved using the transfer-matrix method. In particular, exact results for the ground state, magnetization process and specific heat are presented and discussed. It is shown that further-neighbor interaction between nodal spins gives rise to three novel ground states with a translationally broken symmetry, but at the same time, does not increases the total number of intermediate plateaus in a zero-temperature magnetization curve compared with the simplified model without this interaction term. The zero-field specific heat displays interesting thermal dependencies with a single- or double-peak structure. (paper)

Dynamic phase transitions and dynamic phase diagrams of the spin-2 Blume-Capel model under an oscillating magnetic field within the effective-field theory

Energy Technology Data Exchange (ETDEWEB)

Ertas, Mehmet [Department of Physics, Erciyes University, 38039 Kayseri (Turkey); Institute of Science, Erciyes University, 38039 Kayseri (Turkey); Deviren, Bayram [Department of Physics, Nevsehir University, 50300 Nevsehir (Turkey); Keskin, Mustafa, E-mail: keskin@erciyes.edu.tr [Department of Physics, Erciyes University, 38039 Kayseri (Turkey)

2012-03-15

The dynamic phase transitions are studied in the kinetic spin-2 Blume-Capel model under a time-dependent oscillating magnetic field using the effective-field theory with correlations. The effective-field dynamic equation for the average magnetization is derived by employing the Glauber transition rates and the phases in the system are obtained by solving this dynamic equation. The nature (first- or second-order) of the dynamic phase transition is characterized by investigating the thermal behavior of the dynamic magnetization and the dynamic phase transition temperatures are obtained. The dynamic phase diagrams are constructed in the reduced temperature and magnetic field amplitude plane and are of seven fundamental types. Phase diagrams contain the paramagnetic (P), ferromagnetic-2 (F{sub 2}) and three coexistence or mixed phase regions, namely the F{sub 2}+P, F{sub 1}+P and F{sub 2}+F{sub 1}+P, which strongly depend on the crystal-field interaction (D) parameter. The system also exhibits the dynamic tricritical behavior. - Highlights: Black-Right-Pointing-Pointer Dynamic phase transitions are studied in spin-2 BC model using EFT. Black-Right-Pointing-Pointer Dynamic phase diagrams are constructed in (T/zJ, h/zJ) plane. Black-Right-Pointing-Pointer Seven fundamental types of dynamic phase diagrams are found in the system. Black-Right-Pointing-Pointer System exhibits dynamic tricritical behavior.

Large spin-valve effect in a lateral spin-valve device based on ferromagnetic semiconductor GaMnAs

Science.gov (United States)

Asahara, Hirokatsu; Kanaki, Toshiki; Ohya, Shinobu; Tanaka, Masaaki

2018-03-01

We investigate the spin-dependent transport properties of a lateral spin-valve device based on the ferromagnetic semiconductor GaMnAs. This device is composed of a GaMnAs channel layer grown on GaAs with a narrow trench across the channel. Its current-voltage characteristics show tunneling behavior. Large magnetoresistance (MR) ratios of more than ˜10% are obtained. These values are much larger than those (˜0.1%) reported for lateral-type spin metal-oxide-semiconductor field-effect transistors. The magnetic field direction dependence of the MR curve differs from that of the anisotropic magnetoresistance of GaMnAs, which confirms that the MR signal originates from the spin-valve effect between the GaMnAs electrodes.

Bandwidth broadening and asymmetric softening of collective spin waves in magnonic crystals

International Nuclear Information System (INIS)

Montoncello, F.; Giovannini, L.

2014-01-01

We investigate the dependence on the applied field of the frequency/wavevector dispersion relations of collective spin waves in arrays of dots, close to a magnetic transition. In particular, we focus on the low frequency “soft” modes in three different cases: end modes in the transition between two different saturated states in ellipses, fundamental mode in the saturated-to-vortex transition in disks, and gyrotropic mode in the vortex-to-saturated transition in disks. Noteworthy, the spin waves with nonzero Bloch wavevector along the direction of the applied field happen to soften earlier than spin waves with a Bloch wavevector along different directions, and this feature is responsible for an asymmetric broadening of the bandwidth along the different lattice directions. This is particularly useful in magnonic/spin-logic device research, if different binary digits are associated to modes with the same cell function but different propagation directions.

The role of binary and many-centre molecular interactions in spin crossover in the solid state. Part II. Non-ideality parameters defined via binary molecular potentials

International Nuclear Information System (INIS)

Koudriavtsev, A.B.; Linert, W.

2005-01-01

Parameters of the formalism [1-6] describing spin crossover in the solid state have been defined via molecular potentials in model systems of neutral and ionic complexes. In the first instance Lennard-Jones and electric dipole-dipole potentials have been used whereas in ionic systems Lennard-Jones and electric point-charge potentials have been used. Electric dipole-dipole interaction of neutral complexes brings about a positive excess energy controlled by the difference of electric dipole moments of HS and LS molecules. Differences of the order of Δμ = 1-2D cause an abrupt spin crossover in systems with T 1/2 = 100-150K. Magnetic coupling contributes both to the excess energy and excess entropy, however the overall effect is equivalent to a modest positive excess energy. Ionic systems in the absence of specific interactions are characterized by very small excess energies corresponding to practically linear van't Hoff plots. Detectable positive and negative excess energies in these systems may arise from interactions of ligands belonging to neighbouring complexes. The HOMO-LUMO overlap in HS-LS pairs can bring about a nontrivial variation of the shape of transition curves. Examples of regression analysis of experimental transition curves in terms of molecular potentials are given. (author)

Pure spin current manipulation in antiferromagnetically exchange coupled heterostructures

Science.gov (United States)

Avilés-Félix, L.; Butera, A.; González-Chávez, D. E.; Sommer, R. L.; Gómez, J. E.

2018-03-01

We present a model to describe the spin currents generated by ferromagnet/spacer/ferromagnet exchange coupled trilayer systems and heavy metal layers with strong spin-orbit coupling. By exploiting the magnitude of the exchange coupling (oscillatory RKKY-like coupling) and the spin-flop transition in the magnetization process, it has been possible to produce spin currents polarized in arbitrary directions. The spin-flop transition of the trilayer system originates pure spin currents whose polarization vector depends on the exchange field and the magnetization equilibrium angles. We also discuss a protocol to control the polarization sign of the pure spin current injected into the metallic layer by changing the initial conditions of magnetization of the ferromagnetic layers previously to the spin pumping and inverse spin Hall effect experiments. The small differences in the ferromagnetic layers lead to a change in the magnetization vector rotation that permits the control of the sign of the induced voltage components due to the inverse spin Hall effect. Our results can lead to important advances in hybrid spintronic devices with new functionalities, particularly, the ability to control microscopic parameters such as the polarization direction and the sign of the pure spin current through the variation of macroscopic parameters, such as the external magnetic field or the thickness of the spacer in antiferromagnetic exchange coupled systems.

Numerical Evidence for a Phase Transition in 4D Spin-Foam Quantum Gravity.

Science.gov (United States)

Bahr, Benjamin; Steinhaus, Sebastian

2016-09-30

Building on recent advances in defining Wilsonian renormalization group (RG) flows, and the notion of scales in particular, for background-independent theories, we present a first investigation of the renormalization of the 4D spin-foam path integral for quantum gravity, both analytically and numerically. Focusing on a specific truncation of the model using a hypercubic lattice, we compute the RG flow and find strong indications for a phase transition, as well as an interesting interplay between the different observed phases and the (broken) diffeomorphism symmetry of the model. Most notably, it appears that the critical point between the phases, which is a fixed point of the RG flow, is precisely where broken diffeomorphism symmetry is restored, which suggests that it might allow us to define a continuum limit of the quantum gravity theory.

Numerical Evidence for a Phase Transition in 4D Spin-Foam Quantum Gravity

Science.gov (United States)

Bahr, Benjamin; Steinhaus, Sebastian

2016-09-01

Building on recent advances in defining Wilsonian renormalization group (RG) flows, and the notion of scales in particular, for background-independent theories, we present a first investigation of the renormalization of the 4D spin-foam path integral for quantum gravity, both analytically and numerically. Focusing on a specific truncation of the model using a hypercubic lattice, we compute the RG flow and find strong indications for a phase transition, as well as an interesting interplay between the different observed phases and the (broken) diffeomorphism symmetry of the model. Most notably, it appears that the critical point between the phases, which is a fixed point of the RG flow, is precisely where broken diffeomorphism symmetry is restored, which suggests that it might allow us to define a continuum limit of the quantum gravity theory.

Calculation of the magnetic anisotropy energy and finite-temperature magnetic properties of transition-metal films

International Nuclear Information System (INIS)

Garibay-Alonso, R; Villasenor-Gonzalez, P; Dorantes-Davila, J; Pastor, G M

2004-01-01

The magnetic anisotropy energy at the interface (IMAE) of Co films deposited on the Pd(111) surface are determined in the framework of a self-consistent, real-space tight-binding method at zero temperature. Significant spin moments are induced at the Pd atoms at the interface which have an important influence on the observed reorientation transitions as a function of Co film thickness. Film-substrate hybridizations are therefore crucial for the magneto-anisotropic behaviour of thin transition-metal films deposited on metallic non-magnetic substrates. Furthermore, using a real-space recursive expansion of the local Green function and within the virtual-crystal approximation we calculate the magnetization curves and the Curie temperature T C for free-standing Fe films

Spin polarized and density modulated phases in symmetric electron-electron and electron-hole bilayers.

Science.gov (United States)

Kumar, Krishan; Moudgil, R K

2012-10-17

We have studied symmetric electron-electron and electron-hole bilayers to explore the stable homogeneous spin phase and the feasibility of inhomogeneous charge-/spin-density ground states. The former is resolved by comparing the ground-state energies in states of different spin polarizations, while the latter is resolved by searching for a divergence in the wavevector-dependent static charge/spin susceptibility. For this endeavour, we have used the dielectric approach within the self-consistent mean-field theory of Singwi et al. We find that the inter-layer interactions tend to change an abrupt spin-polarization transition of an isolated layer into a nearly gradual one, even though the partially spin-polarized phases are not clearly stable within the accuracy of our calculation. The transition density is seen to decrease with a reduction in layer spacing, implying a suppression of spin polarization by inter-layer interactions. Indeed, the suppression shows up distinctly in the spin susceptibility computed from the spin-polarization dependence of the ground-state energy. However, below a critical layer spacing, the unpolarized liquid becomes unstable against a charge-density-wave (CDW) ground state at a density preceding full spin polarization, with the transition density for the CDW state increasing on further reduction in the layer spacing. Due to attractive e-h correlations, the CDW state is found to be more pronounced in the e-h bilayer. On the other hand, the static spin susceptibility diverges only in the long-wavelength limit, which simply represents a transition to the homogeneous spin-polarized phase.

Electric-field effects in optically generated spin transport

International Nuclear Information System (INIS)

Miah, M. Idrish

2009-01-01

Transport of spin-polarized electrons in semiconductors is studied experimentally. Spins are generated by optical excitation because of the selection rules governing optical transitions from heavy-hole and light-hole states to conduction-band states. Experiments designed for the control of spins in semiconductors investigate the bias-dependent spin transport process and detect the spin-polarized electrons during transport. A strong bias dependence is observed. The electric-field effects on the spin-polarized electron transport are also found to be depended on the excitation photon energy and temperature. Based on a field-dependent spin relaxation mechanism, the electric-field effects in the transport process are discussed.

Electric-field effects in optically generated spin transport

Energy Technology Data Exchange (ETDEWEB)

Miah, M. Idrish [Nanoscale Science and Technology Centre and School of Biomolecular and Physical Sciences, Griffith University, Nathan, Brisbane, QLD 4111 (Australia); Department of Physics, University of Chittagong, Chittagong 4331 (Bangladesh)], E-mail: m.miah@griffith.edu.au

2009-05-25

Transport of spin-polarized electrons in semiconductors is studied experimentally. Spins are generated by optical excitation because of the selection rules governing optical transitions from heavy-hole and light-hole states to conduction-band states. Experiments designed for the control of spins in semiconductors investigate the bias-dependent spin transport process and detect the spin-polarized electrons during transport. A strong bias dependence is observed. The electric-field effects on the spin-polarized electron transport are also found to be depended on the excitation photon energy and temperature. Based on a field-dependent spin relaxation mechanism, the electric-field effects in the transport process are discussed.

Coupling a Surface Acoustic Wave to an Electron Spin in Diamond via a Dark State

Directory of Open Access Journals (Sweden)

D. Andrew Golter

2016-12-01

Full Text Available The emerging field of quantum acoustics explores interactions between acoustic waves and artificial atoms and their applications in quantum information processing. In this experimental study, we demonstrate the coupling between a surface acoustic wave (SAW and an electron spin in diamond by taking advantage of the strong strain coupling of the excited states of a nitrogen vacancy center while avoiding the short lifetime of these states. The SAW-spin coupling takes place through a Λ-type three-level system where two ground spin states couple to a common excited state through a phonon-assisted as well as a direct dipole optical transition. Both coherent population trapping and optically driven spin transitions have been realized. The coherent population trapping demonstrates the coupling between a SAW and an electron spin coherence through a dark state. The optically driven spin transitions, which resemble the sideband transitions in a trapped-ion system, can enable the quantum control of both spin and mechanical degrees of freedom and potentially a trapped-ion-like solid-state system for applications in quantum computing. These results establish an experimental platform for spin-based quantum acoustics, bridging the gap between spintronics and quantum acoustics.

Intrinsic spin polarized electronic structure of CrO2 epitaxial film revealed by bulk-sensitive spin-resolved photoemission spectroscopy

International Nuclear Information System (INIS)

Fujiwara, Hirokazu; Sunagawa, Masanori; Kittaka, Tomoko; Terashima, Kensei; Wakita, Takanori; Muraoka, Yuji; Yokoya, Takayoshi

2015-01-01

We have performed bulk-sensitive spin-resolved photoemission spectroscopy in order to clarify the intrinsic spin-resolved electronic states of half-metallic ferromagnet CrO 2 . We used CrO 2 epitaxial films on TiO 2 (100), which shows a peak at 1 eV with a clear Fermi edge, consistent with the bulk-sensitive PES spectrum for CrO 2 . In spin-resolved spectra at 40 K, while the Fermi edge was observed in the spin up (majority spin) state, no states at the Fermi level (E F ) with an energy gap of 0.5 eV below E F were observed in the spin down (minority spin) state. At 300 K, the gap in the spin down state closes. These results are consistent with resistivity measurements and magnetic hysteresis curves of the fabricated CrO 2 film, constituting spectroscopic evidence for the half-metallicity of CrO 2 at low temperature and reducing the spin polarization at room temperature. We also discuss the electron correlation effects of Cr 3d

Spin-flip effects on the supercurrent through mesoscopic superconducting junctions

International Nuclear Information System (INIS)

Pan Hui; Lin Tsunghan

2005-01-01

We investigate the spin-flip effects on the Andreev bound states and the supercurrent in a superconductor/quantum-dot/superconductor system, theoretically. The spin-flip scattering in the quantum dot can reverse the supercurrent flowing through the system, which results in a π-junction transition. By controlling the energy level of the quantum dot, the π-junction transition can be caused to occur again. The two mechanisms of the π-junction transitions are interpreted within the picture of Andreev bound states

One and two-phonon processes of the spin-flip relaxation in quantum dots: Spin-phonon coupling mechanism

Science.gov (United States)

Wang, Zi-Wu; Li, Shu-Shen

2012-07-01

We investigate the spin-flip relaxation in quantum dots using a non-radiation transition approach based on the descriptions for the electron-phonon deformation potential and Fröhlich interaction in the Pavlov-Firsov spin-phonon Hamiltonian. We give the comparisons of the electron relaxations with and without spin-flip assisted by one and two-phonon processes. Calculations are performed for the dependence of the relaxation time on the external magnetic field, the temperature and the energy separation between the Zeeman sublevels of the ground and first-excited state. We find that the electron relaxation time of the spin-flip process is more longer by three orders of magnitudes than that of no spin-flip process.

Upper critical fields and superconducting transition temperatures of some zirconium-base amorphous transition-metal alloys

International Nuclear Information System (INIS)

Karkut, M.G.; Hake, R.R.

1983-01-01

Superconducting upper critical fields H/sub c/2(T), transition temperatures T/sub c/, and normal-state electrical resistivities rho/sub n/ have been measured in the amorphous transition-metal alloy series Zr/sub 1-z/Co/sub x/, Zr/sub 1-x/Ni/sub x/, (Zr/sub 1-x/Ti/sub x/)/sub 0.78/Ni/sub 0.22/, and (Zr/sub 1-x/Nb/sub x/)/sub 0.78/Ni/sub 0.22/. Structural integrity of these melt-spun alloys is indicated by x-ray, density, bend-ductility, normal-state electrical resistivity, superconducting transition width, and mixed-state flux-pinning measurements. The specimens display T/sub c/ = 2.1--3.8 K, rho/sub n/ = 159--190 μΩ cm, and Vertical Bar(dH/sub c/2/dT)cVertical Bar = 28--36 kG/K. These imply electron mean free paths lroughly-equal2--6 A, zero-temperature Ginzburg-Landau coherence distances xi/sub G/0roughly-equal50--70 A, penetration depths lambda/sub G/0roughly-equal(7--10) x 10 3 A, and extremely high dirtiness parameters xi 0 /lroughly-equal300--1300. All alloys display H/sub c/2(T) curves with negative curvature and (with two exceptions) fair agreement with the standard dirty-limit theory of Werthamer, Helfand, Hohenberg, and Maki (WHHM) for physically reasonable values of spin-orbit-coupling induced, electron-spin-flip scattering time tau/sub so/. This is in contrast to the anomalously elevated H/sub c/2(T) behavior which is nearly linear in T that is observed by some, and the unphysically low-tau/sub so/ fits to WHHM theory obtained by others, for various amorphous alloys

New Topological Configurations in the Continuous Heisenberg Spin Chain: Lower Bound for the Energy

Directory of Open Access Journals (Sweden)

Rossen Dandoloff

2015-01-01

Full Text Available In order to study the spin configurations of the classical one-dimensional Heisenberg model, we map the normalized unit vector, representing the spin, on a space curve. We show that the total chirality of the configuration is a conserved quantity. If, for example, one end of the space curve is rotated by an angle of 2π relative to the other, the Frenet frame traces out a noncontractible loop in SO(3 and this defines a new class of topological spin configurations for the Heisenberg model.

Quaternary structure and spin state of human fetal methemoglobin

International Nuclear Information System (INIS)

Chevion, M.; Navok, T.; Ilan, Y.A.; Czapski, G.

1981-01-01

Using the pulse-radiolysis technique, solutions of fetal human methemoglobin were irradiated in order to reduce a single heme-iron within the protein tetramers. The valence-hybrids thus formed ere reacted wjth oxygen. Kinetics of the reactions were studied. The effects of p and inositol-hexaphosphate (IHP) were examined. The kinetics of the ligation of oxygen to stripped valence-hybrids showed a single-phase behaviour at the pH range 7-9. As the pH was lowered below 6.5, a second slower phase became apparent. This slow phase consisted of approximately 50% at pH 5.8. In the presence of IHP above pH 7.4, the kinetics of oxygen-binding was of a single-phase. As the pH was lowered a transition to a second, slower phase was noticed. Below pH 7 the slower phase was the only detectable one. The analysis of the relative contribution of the faster phase to the total reaction, as a function of the pH, showed a typical sigmoidal transition curve characterized by a pK = 7.2 and a Hill parameter n = 3.06. On this basis it is concluded that stripped, fetal human methemoglobin resides in an R quaternary structure while the presence of IHP stabilizes the T structure at pH below 7.2. The switch between the high spin aquomet- and the low spin hydroxymet-derivatives of adult and fetal human hemoglobins was studied optically in detail. These switches were found to be only slightly affected by IHP, and exhibited very low cooperativity (pK = 8.04; n = 1.1 and pK = 8.10; n = 1.3 for adult methemoglobin when stripped and in the presence of IHP, respectively; pK = 8.18; n = 1.11 and pK = 8.21; n = 1.28 for fetal methemoglobin when stripped and in the presence of IHP, respectively). These findings lead to the conclusion that the transition between quaternary structures in either human or fetal methemoglobins is not coupled to the switch of the spin state of the ferric heme. (author)

Transition probability spaces in loop quantum gravity

Science.gov (United States)

Guo, Xiao-Kan

2018-03-01

We study the (generalized) transition probability spaces, in the sense of Mielnik and Cantoni, for spacetime quantum states in loop quantum gravity. First, we show that loop quantum gravity admits the structures of transition probability spaces. This is exemplified by first checking such structures in covariant quantum mechanics and then identifying the transition probability spaces in spin foam models via a simplified version of general boundary formulation. The transition probability space thus defined gives a simple way to reconstruct the discrete analog of the Hilbert space of the canonical theory and the relevant quantum logical structures. Second, we show that the transition probability space and in particular the spin foam model are 2-categories. Then we discuss how to realize in spin foam models two proposals by Crane about the mathematical structures of quantum gravity, namely, the quantum topos and causal sites. We conclude that transition probability spaces provide us with an alternative framework to understand various foundational questions of loop quantum gravity.

Detecting the multi-spin interaction of an XY spin chain by the geometric phase of a coupled qubit

International Nuclear Information System (INIS)

Zhang, Xiu-xing; Zhang, Ai-ping; Li, Fu-li

2012-01-01

We investigate geometric phase (GP) of a qubit symmetrically coupled to a XY spin chain with three-spin interaction in a transverse magnetic field. An analytical expression for the GP is found in the weak coupling limit. It is shown that the GP displays a sharp peak or dip around the quantum phase transition point of the spin chain. Without the three-spin interaction, the GP has a peak or dip around the critical point λ=1. If the three-spin interaction exists, the peak or dip position is obviously shifted away from the original position. This result reveals that the GP may be taken as an observable to detect both the existence and strength of multi-spin interaction in a spin chain. -- Highlights: ► Analytical expression for geometric phase (GP) of a qubit coupled to a spin chain is obtained. ► Relation between GP and multi-spin interaction is investigated. ► Detection of multi-spin interaction by means of GP is proposed.

Measuring spin of black holes in the universe

Indian Academy of Sciences (India)

Table of contents. Measuring spin of black holes in the universe · What is black hole? Accretion Disk and Jet · What is black hole's spin? Accretion Disk · Black Hole's Potential · Light Curves: Photon Count Rate Vs Time · Quasi-Periodic Oscillation · Slide 9 · Model · Slide 11 · Slide 12 · Slide 13 · Summary.

Emerging Early Actions to Bend the Curve in Sub-Saharan Africa's Nutrition Transition.

Science.gov (United States)

Haggblade, Steven; Duodu, Kwaku G; Kabasa, John D; Minnaar, Amanda; Ojijo, Nelson K O; Taylor, John R N

2016-06-01

Sub-Saharan Africa is the last region to undergo a nutrition transition and can still avoid its adverse health outcomes. The article explores emerging responses to "bend the curve" in sub-Saharan Africa's nutrition transition to steer public health outcomes onto a healthier trajectory. Early responses in 3 countries at different stages of food system transformation are examined: South Africa-advanced, Ghana-intermediate, and Uganda-early. By comparing these with international experience, actions are proposed to influence nutrition and public health trajectories as Africa's food systems undergo rapid structural change. Arising from rapid urbanization and diet change, major public health problems associated with overweight are taking place, particularly in South Africa and among adult women. However, public health responses are generally tepid in sub-Saharan Africa. Only in South Africa have policy makers instituted extensive actions to combat overweight and associated noncommunicable diseases through regulation, education, and public health programs. Elsewhere, in countries in the early and middle stages of transition, public health systems continue to focus their limited resources primarily on undernutrition. Related pressures on the supply side of Africa's food systems are emerging that also need to be addressed. Three types of intervention appear most feasible: maternal and child health programs to simultaneously address short-term undernutrition problems while at the same time helping to reduce future tendencies toward overweigh; regulatory and fiscal actions to limit access to unhealthy foods; and modernization of Africa's agrifood food system through job skills training, marketing reforms, and food industry entrepreneurship. © The Author(s) 2016.

Anisotropic optical absorption induced by Rashba spin-orbit coupling in monolayer phosphorene

Science.gov (United States)

Li, Yuan; Li, Xin; Wan, Qi; Bai, R.; Wen, Z. C.

2018-04-01

We obtain the effective Hamiltonian of the phosphorene including the effect of Rashba spin-orbit coupling in the frame work of the low-energy theory. The spin-splitting energy bands show an anisotropy feature for the wave vectors along kx and ky directions, where kx orients to ΓX direction in the k space. We numerically study the optical absorption of the electrons for different wave vectors with Rashba spin-orbit coupling. We find that the spin-flip transition from the valence band to the conduction band induced by the circular polarized light closes to zero with increasing the x-component wave vector when ky equals to zero, while it can be significantly increased to a large value when ky gets a small value. When the wave vector varies along the ky direction, the spin-flip transition can also increase to a large value, however, which shows an anisotropy feature for the optical absorption. Especially, the spin-conserved transitions keep unchanged and have similar varying trends for different wave vectors. This phenomenon provides a novel route for the manipulation of the spin-dependent property of the fermions in the monolayer phosphorene.

Spin correlations in quantum wires

Science.gov (United States)

Sun, Chen; Pokrovsky, Valery L.

2015-04-01

We consider theoretically spin correlations in a one-dimensional quantum wire with Rashba-Dresselhaus spin-orbit interaction (RDI). The correlations of noninteracting electrons display electron spin resonance at a frequency proportional to the RDI coupling. Interacting electrons, upon varying the direction of the external magnetic field, transit from the state of Luttinger liquid (LL) to the spin-density wave (SDW) state. We show that the two-time total-spin correlations of these states are significantly different. In the LL, the projection of total spin to the direction of the RDI-induced field is conserved and the corresponding correlator is equal to zero. The correlators of two components perpendicular to the RDI field display a sharp electron-spin resonance driven by the RDI-induced intrinsic field. In contrast, in the SDW state, the longitudinal projection of spin dominates, whereas the transverse components are suppressed. This prediction indicates a simple way for an experimental diagnostic of the SDW in a quantum wire. We point out that the Luttinger model does not respect the spin conservation since it assumes the infinite Fermi sea. We propose a proper cutoff to correct this failure.

Nuclear spin bath effects in molecular nanomagnets: Direct quantum mechanical simulations

Science.gov (United States)

Sinitsyn, N. A.; Dobrovitski, V. V.

2004-11-01

We investigate the influence of nuclear spins on the electronic spin tunneling in magnetic molecules such as Fe8 , focusing on the role of the spin diffusion in the nuclear spin bath. We simulate the quantum spin dynamics by numerically solving the time-dependent Schrödinger equation for the compound system (the electronic spin plus the bath spins). Our results demonstrate that the effect of the spin bath cannot always be modeled as a randomly varying magnetic field acting on the electronic spin. We consider two dynamical regimes: the spin relaxation in a constant magnetic field, and the spin tunneling in the linearly varying magnetic field passing the avoided level crossing, so-called Landau-Zener-Stückelberg (LZS) transition. For the first regime, we confirmed that the hole in the magnetization distribution has the width of the hyperfine fields distribution. For the second regime, we found that the transition probability for moderately slow sweeps deviates from the standard LZS prediction, while for the fast sweeps the deviation is negligible.

Effects of hydrostatic pressure and uniaxial strain on spin-Peierls transition in an organic radical magnet, BBDTA·InCl4

International Nuclear Information System (INIS)

Mito, Masaki; Kawagoe, Seiichiro; Deguchi, Hiroyuki; Takagi, Seichi; Fujita, Wataru; Awaga, Kunio; Kondo, Ryusuke; Kagoshima, Seiichi

2009-01-01

We investigated the effects of hydrostatic pressure and uniaxial strain on the spin-Peierls (SP) transition of an organic radical magnet, benzo[1,2-d:4,5-d']bis[1,3,2]dithiazole(BBDTA)·InCl 4 . It has a one-dimensional coordination polymer structure along its c-axis and its SP transition occurs at 108 K. The SP transition temperature T SP decreased to 99 K at a hydrostatic pressure of 10 kbar, while it increased to 132 K at a uniaxial strain along the c-axis of 8 kbar. The pressure dependences of T SP under these two conditions were discussed by evaluating two parameters, namely, the intrachain interaction 2J/k B and the effective spin-lattice coupling parameter η, that are related to T SP by the equation T SP =1.6ηJ/k B . Under ambient pressure, the a- and c-axes of this material shortened monotonically with decreasing temperature, while the b-axis elongated below T SP . In this study, we found the correlation between η and the change in the lattice constant b. 2J/k B increased with increasing hydrostatic pressure and uniaxial strain, suggesting that the contraction along the c-axis does not depend on the manner of pressurization. From the evaluation of η, the observed variation in T SP is explained by the difference between the changes in b under the two pressurization conditions. (author)

Magnetic transitions and phases in random-anisotropy magnets

International Nuclear Information System (INIS)

Sellmyer, D.J.; Nafis, S.; O'Shea, M.J.

1988-01-01

The generality and universality of the Ising spin-glass-like phase transitions observed in several rare-earth, random-anisotropy magnets are discussed. Some uncertainties and practical problems in determining critical exponents are considered, and a comparison is made to insulating spin glasses and crystalline spin glasses where an apparent anisotropy-induced crossover from Heisenberg to Ising-like behavior is seen. The observation of a reentrant transition in a weak anisotropy system and its correlation with the theory of Chudnovsky, Saslow, and Serota [Phys. Rev. B 33, 251 (1986)] for the correlated spin glass is discussed

Magnetic transitions and phases in random-anisotropy magnets

Science.gov (United States)

Sellmyer, D. J.; Nafis, S.; O'Shea, M. J.

1988-04-01

The generality and universality of the Ising spin-glass-like phase transitions observed in several rare-earth, random-anisotropy magnets are discussed. Some uncertainties and practical problems in determining critical exponents are considered, and a comparison is made to insulating spin glasses and crystalline spin glasses where an apparent anisotropy-induced crossover from Heisenberg to Ising-like behavior is seen. The observation of a reentrant transition in a weak anisotropy system and its correlation with the theory of Chudnovsky, Saslow, and Serota [Phys. Rev. B 33, 251 (1986)] for the correlated spin glass is discussed.

Spin interferometry and phase relations in three level systems

International Nuclear Information System (INIS)

Mehring, M.; Stoll, M.E.; Wolff, E.K.

1978-01-01

The sign of the wavefunctions of deuterium, a spin-1 nucleus, under a 2π rotation (spinor character) has been studied with using a single crystal of 98% deuterated hexamethyl-benzene (HMB, C 6 (CD 3 ) 6 ). In a large magnetic fields, the three energy levels of the Zeeman hamiltonian have equal spacing, whereas unequivalent transition frequencies may occur if a suitable quadrupolar interaction is included. Three types of experiment are discussed. Simultaneous irradiation of both transitions with a field strength ω 1 in the x direction verified spin-locking, quadrature, or phase variation; consecutive irradiation at both transition with π-pulses showed coherence transfer from transition 1-2 to the forbidden transition 1-3; double quantum spinor behavior was demonstrated by applying rf field of strength ω 1 = γH 1 at the 'double quantum transition' frequency ω 0

Role of open boundary conditions on the hysteretic behaviour of one-dimensional spin crossover nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Chiruta, Daniel [GEMaC, Université de Versailles Saint-Quentin-en-Yvelines, CNRS-UVSQ (UMR 8635), 78035 Versailles Cedex (France); Faculty of Electrical Engineering and Computer Science, Stefan cel Mare University, Suceava 720229 (Romania); Linares, Jorge, E-mail: jorge.linares@uvsq.fr, E-mail: miya@spin.phys.s.u-tokyo.ac.jp; Boukheddaden, Kamel [GEMaC, Université de Versailles Saint-Quentin-en-Yvelines, CNRS-UVSQ (UMR 8635), 78035 Versailles Cedex (France); Miyashita, Seiji, E-mail: jorge.linares@uvsq.fr, E-mail: miya@spin.phys.s.u-tokyo.ac.jp [Department of Physics, Graduate School of Science, University of Tokyo, Bunkyo-Ku, Tokyo (Japan); CREST, JST, 4-1-8 Honcho Kawaguchi, Saitama 332-0012 (Japan)

2014-05-21

In order to explain clearly the role of the open boundary conditions (OBCs) on phase transition in one dimensional system, we consider an Ising model with both short-range (J) and long-range (G) interactions, which has allowed us to study the cooperative nature of spin-crossover (SCO) materials at the nanometer scale. At this end, we developed a transfer-matrix method for one-dimensional (1D) SCO system with free boundary conditions, and we give numerical evidences for how the thermal spin transition curves vary as a function of the physical parameters (J, G) or an applied pressure. Moreover for OBCs case, we have derived the bulk, surface and finite-size contributions to the free energy and we have investigated the variation of these energies as function of J and system size. We have found that the surface free energy behaves like J〈σ〉{sup 2}, where 〈σ〉 is the average magnetization per site. Since the properties of the nanometric scale are dramatically influenced by the system's size (N), our analytical outcomes for the size dependence represent a step to achieve new characteristic of the future devices and also a way to find various novel properties which are absent in the bulk materials.

Creating Spin-One Fermions in the Presence of Artificial Spin-Orbit Fields: Emergent Spinor Physics and Spectroscopic Properties

Science.gov (United States)

Kurkcuoglu, Doga Murat; de Melo, C. A. R. Sá

2018-05-01

We propose the creation and investigation of a system of spin-one fermions in the presence of artificial spin-orbit coupling, via the interaction of three hyperfine states of fermionic atoms to Raman laser fields. We explore the emergence of spinor physics in the Hamiltonian described by the interaction between light and atoms, and analyze spectroscopic properties such as dispersion relation, Fermi surfaces, spectral functions, spin-dependent momentum distributions and density of states. Connections to spin-one bosons and SU(3) systems is made, as well relations to the Lifshitz transition and Pomeranchuk instability are presented.

Field-induced negative differential spin lifetime in silicon.

Science.gov (United States)

Li, Jing; Qing, Lan; Dery, Hanan; Appelbaum, Ian

2012-04-13

We show that the electric-field-induced thermal asymmetry between the electron and lattice systems in pure silicon substantially impacts the identity of the dominant spin relaxation mechanism. Comparison of empirical results from long-distance spin transport devices with detailed Monte Carlo simulations confirms a strong spin depolarization beyond what is expected from the standard Elliott-Yafet theory even at low temperatures. The enhanced spin-flip mechanism is attributed to phonon emission processes during which electrons are scattered between conduction band valleys that reside on different crystal axes. This leads to anomalous behavior, where (beyond a critical field) reduction of the transit time between spin-injector and spin-detector is accompanied by a counterintuitive reduction in spin polarization and an apparent negative spin lifetime.

Entanglement and quantum phase transitions in matrix-product spin-1 chains

International Nuclear Information System (INIS)

Alipour, S.; Karimipour, V.; Memarzadeh, L.

2007-01-01

We consider a one-parameter family of matrix-product states of spin-1 particles on a periodic chain and study in detail the entanglement properties of such a state. In particular, we calculate exactly the entanglement of one site with the rest of the chain, and the entanglement of two distant sites with each other, and show that the derivative of both these properties diverge when the parameter g of the states passes through a critical point. Such a point can be called a point of quantum phase transition, since at this point the character of the matrix-product state, which is the ground state of a Hamiltonian, changes discontinuously. We also study the finite size effects and show how the entanglement depends on the size of the chain. This later part is relevant to the field of quantum computation where the problem of initial state preparation in finite arrays of qubits or qutrits is important. It is also shown that the entanglement of two sites have scaling behavior near the critical point

Trajectory phase transitions and dynamical Lee-Yang zeros of the Glauber-Ising chain.

Science.gov (United States)

Hickey, James M; Flindt, Christian; Garrahan, Juan P

2013-07-01

We examine the generating function of the time-integrated energy for the one-dimensional Glauber-Ising model. At long times, the generating function takes on a large-deviation form and the associated cumulant generating function has singularities corresponding to continuous trajectory (or "space-time") phase transitions between paramagnetic trajectories and ferromagnetically or antiferromagnetically ordered trajectories. In the thermodynamic limit, the singularities make up a whole curve of critical points in the complex plane of the counting field. We evaluate analytically the generating function by mapping the generator of the biased dynamics to a non-Hermitian Hamiltonian of an associated quantum spin chain. We relate the trajectory phase transitions to the high-order cumulants of the time-integrated energy which we use to extract the dynamical Lee-Yang zeros of the generating function. This approach offers the possibility to detect continuous trajectory phase transitions from the finite-time behavior of measurable quantities.

Giant magnetostriction effect near onset of spin reorientation in MnBi

Science.gov (United States)

Choi, Y.; Ryan, P. J.; McGuire, M. A.; Sales, B. C.; Kim, J.-W.

2018-05-01

In materials undergoing spontaneous symmetry breaking transitions, the emergence of multiple competing order parameters is pervasive. Employing in-field x-ray diffraction, we investigate the temperature and magnetic field dependence of the crystallographic structure of MnBi, elucidating the microscopic interplay between lattices and spin. The hexagonal phase of MnBi undergoes a spin reorientation transition (TSR), whereby the easy axis direction changes from the c axis to the basal plane. Across TSR, an abrupt symmetry change is accompanied by a clear sign change in the magnetostrictive coefficient, revealing that this transition corresponds to the onset of the spin reorientation. In the vicinity of TSR, a significantly larger in-plane magnetostrictive effect is observed, presenting the emergence of an intermediate phase that is highly susceptible to an applied magnetic field. X-ray linear dichroism shows that asymmetric Bi and Mn p orbitals do not play a role in the spin reorientation. This work suggests that the spin reorientation is caused by structural modification rather than changes in the local electronic configuration, providing a strategy for manipulating the magnetic anisotropy by external strain.

Phase diagrams of a nonequilibrium mixed spin-3/2 and spin-2 Ising system in an oscillating magnetic field

International Nuclear Information System (INIS)

Keskin, Mustafa; Polat, Yasin

2009-01-01

The phase diagrams of the nonequilibrium mixed spin-3/2 and spin-2 Ising ferrimagnetic system on square lattice under a time-dependent external magnetic field are presented by using the Glauber-type stochastic dynamics. The model system consists of two interpenetrating sublattices of spins σ=3/2 and S=2, and we take only nearest-neighbor interactions between pairs of spins. The system is in contact with a heat bath at absolute temperature T abs and the exchange of energy with the heat bath occurs via one-spin flip of the Glauber dynamics. First, we investigate the time variations of average order parameters to find the phases in the system and then the thermal behavior of the dynamic order parameters to obtain the dynamic phase transition (DPT) points as well as to characterize the nature (first- or second-order) phase transitions. The dynamic phase diagrams are presented in two different planes. Phase diagrams contain paramagnetic (p), ferrimagnetic (i 1 , i 2 , i 3 ) phases, and three coexistence or mixed phase regions, namely i 1 +p, i 2 +p and i 3 +p mixed phases that strongly depend on interaction parameters.

Phase diagrams of a nonequilibrium mixed spin-3/2 and spin-2 Ising system in an oscillating magnetic field

Energy Technology Data Exchange (ETDEWEB)

Keskin, Mustafa [Department of Physics, Erciyes University, 38039 Kayseri (Turkey)], E-mail: keskin@erciyes.edu.tr; Polat, Yasin [Institutes of Science, Erciyes University, 38039 Kayseri (Turkey)

2009-12-15

The phase diagrams of the nonequilibrium mixed spin-3/2 and spin-2 Ising ferrimagnetic system on square lattice under a time-dependent external magnetic field are presented by using the Glauber-type stochastic dynamics. The model system consists of two interpenetrating sublattices of spins {sigma}=3/2 and S=2, and we take only nearest-neighbor interactions between pairs of spins. The system is in contact with a heat bath at absolute temperature T{sub abs} and the exchange of energy with the heat bath occurs via one-spin flip of the Glauber dynamics. First, we investigate the time variations of average order parameters to find the phases in the system and then the thermal behavior of the dynamic order parameters to obtain the dynamic phase transition (DPT) points as well as to characterize the nature (first- or second-order) phase transitions. The dynamic phase diagrams are presented in two different planes. Phase diagrams contain paramagnetic (p), ferrimagnetic (i{sub 1}, i{sub 2}, i{sub 3}) phases, and three coexistence or mixed phase regions, namely i{sub 1}+p, i{sub 2}+p and i{sub 3}+p mixed phases that strongly depend on interaction parameters.

Dual descriptors within the framework of spin-polarized density functional theory.

Science.gov (United States)

Chamorro, E; Pérez, P; Duque, M; De Proft, F; Geerlings, P

2008-08-14

Spin-polarized density functional theory (SP-DFT) allows both the analysis of charge-transfer (e.g., electrophilic and nucleophilic reactivity) and of spin-polarization processes (e.g., photophysical changes arising from electron transitions). In analogy with the dual descriptor introduced by Morell et al. [J. Phys. Chem. A 109, 205 (2005)], we introduce new dual descriptors intended to simultaneously give information of the molecular regions where the spin-polarization process linking states of different multiplicity will drive electron density and spin density changes. The electronic charge and spin rearrangement in the spin forbidden radiative transitions S(0)-->T(n,pi(*)) and S(0)-->T(pi,pi(*)) in formaldehyde and ethylene, respectively, have been used as benchmark examples illustrating the usefulness of the new spin-polarization dual descriptors. These quantities indicate those regions where spin-orbit coupling effects are at work in such processes. Additionally, the qualitative relationship between the topology of the spin-polarization dual descriptors and the vertical singlet triplet energy gap in simple substituted carbene series has been also discussed. It is shown that the electron density and spin density rearrangements arise in agreement with spectroscopic experimental evidence and other theoretical results on the selected target systems.

Spin filter effect of hBN/Co detector electrodes in a 3D topological insulator spin valve

Science.gov (United States)

Vaklinova, Kristina; Polyudov, Katharina; Burghard, Marko; Kern, Klaus

2018-03-01

Topological insulators emerge as promising components of spintronic devices, in particular for applications where all-electrical spin control is essential. While the capability of these materials to generate spin-polarized currents is well established, only very little is known about the spin injection/extraction into/out of them. Here, we explore the switching behavior of lateral spin valves comprising the 3D topological insulator Bi2Te2Se as channel, which is separated from ferromagnetic Cobalt detector contacts by an ultrathin hexagonal boron nitride (hBN) tunnel barrier. The corresponding contact resistance displays a notable variation, which is correlated with a change of the switching characteristics of the spin valve. For contact resistances below ~5 kΩ, the hysteresis in the switching curve reverses upon reversing the applied current, as expected for spin-polarized currents carried by the helical surface states. By contrast, for higher contact resistances an opposite polarity of the hysteresis loop is observed, which is independent of the current direction, a behavior signifying negative spin detection efficiency of the multilayer hBN/Co contacts combined with bias-induced spin signal inversion. Our findings suggest the possibility to tune the spin exchange across the interface between a ferromagnetic metal and a topological insulator through the number of intervening hBN layers.

Spin-state responses to light impurity substitution in low-spin perovskite LaCoO3

Science.gov (United States)

Tomiyasu, Keisuke; Kubota, Yuuki; Shimomura, Saya; Onodera, Mitsugi; Koyama, Syun-Ichi; Nojima, Tsutomu; Ishihara, Sumio; Nakao, Hironori; Murakami, Youichi

2013-06-01

We studied the spin-state responses to light impurity substitution in low-spin perovskite LaCoO3 (Co3+: d6) through magnetization, x-ray fluorescence, and electrical resistivity measurements of single-crystal LaCo0.99M0.01O3 (M = Cr, Mn, Fe, Ni). In the magnetization curves measured at 1.8 K, a change in the spin-state was not observed for Cr, Mn, or Fe substitution but was observed for Ni substitution. Strong magnetic anisotropy was also found in the Ni-substituted sample. The fluorescence measurements revealed that the valences were roughly estimated to be Cr3+, Mn(4-δ)+, Fe(3+δ')+, and Ni3+. From the observed chemical trends, we propose that the chemical potential is a key factor in inducing the change of the low-spin state. By expanding a model of the ferromagnetic spin-state heptamer generated by hole doping [Podlesnyak , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.101.247603 101, 247603 (2008)], the emergence of highly anisotropic spin-state molecular ferromagnets induced by low-spin Ni3+ with Jahn-Teller activity is suggested. We also discuss applicability of the present results to other materials with Fe (d6).

Calogero-Sutherland system with two types interacting spins

Science.gov (United States)

Kharchev, S.; Levin, A.; Olshanetsky, M.; Zotov, A.

2017-08-01

We consider the classical Calogero-Sutherland system with two types of interacting spin variables. It can be reduced to the standard Calogero-Sutherland system, when one of the spin variables vanishes. We describe the model in the Hitchin approach and prove complete integrability of the system by constructing the Lax pair and the classical r-matrix with the spectral parameter on a singular curve.

Fermions in curved spacetimes

Energy Technology Data Exchange (ETDEWEB)

Lippoldt, Stefan

2016-01-21

In this thesis we study a formulation of Dirac fermions in curved spacetime that respects general coordinate invariance as well as invariance under local spin base transformations. We emphasize the advantages of the spin base invariant formalism both from a conceptual as well as from a practical viewpoint. This suggests that local spin base invariance should be added to the list of (effective) properties of (quantum) gravity theories. We find support for this viewpoint by the explicit construction of a global realization of the Clifford algebra on a 2-sphere which is impossible in the spin-base non-invariant vielbein formalism. The natural variables for this formulation are spacetime-dependent Dirac matrices subject to the Clifford-algebra constraint. In particular, a coframe, i.e. vielbein field is not required. We disclose the hidden spin base invariance of the vielbein formalism. Explicit formulas for the spin connection as a function of the Dirac matrices are found. This connection consists of a canonical part that is completely fixed in terms of the Dirac matrices and a free part that can be interpreted as spin torsion. The common Lorentz symmetric gauge for the vielbein is constructed for the Dirac matrices, even for metrics which are not linearly connected. Under certain criteria, it constitutes the simplest possible gauge, demonstrating why this gauge is so useful. Using the spin base formulation for building a field theory of quantized gravity and matter fields, we show that it suffices to quantize the metric and the matter fields. This observation is of particular relevance for field theory approaches to quantum gravity, as it can serve for a purely metric-based quantization scheme for gravity even in the presence of fermions. Hence, in the second part of this thesis we critically examine the gauge, and the field-parametrization dependence of renormalization group flows in the vicinity of non-Gaussian fixed points in quantum gravity. While physical

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

Science.gov (United States)

Silaev, M. A.

2018-06-01

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

A technique for measurement of vector and tensor polarization in solid spin one polarized targets

International Nuclear Information System (INIS)

Kielhorn, W.F.

1991-06-01

Vector and tensor polarizations are explicitly defined and used to characterize the polarization states of spin one polarized targets, and a technique for extracting these polarizations from nuclear magnetic resonance (NMR) data is developed. This technique is independent of assumptions about spin temperature, but assumes the target's crystal structure induces a quadrupole interaction with the spin one particles. Analysis of the NMR signals involves a computer curve fitting algorithm implemented with a fast Fourier transform method which speeds and simplifies curve fitting algorithms used previously. For accurate curve fitting, the NMR electronic circuit must be modeled by the fitting algorithm. Details of a circuit, its model, and data collected from this circuit are given for a solid deuterated ammonia target. 37 refs., 19 figs., 3 tabs

Chiral-glass transition in a diluted dipolar-interaction Heisenberg system

International Nuclear Information System (INIS)

Zhang Kaicheng; Liu Guibin; Zhu Yan

2011-01-01

Recently, numerical simulations reveal that a spin-glass transition can occur in the three-dimensional diluted dipolar system. By defining the chirality of triple spins in a diluted dipolar Heisenberg spin glass, we study the chiral ordering in the system using parallel tempering algorithm and heat bath method. The finite-size scaling analysis reveals that the system undergoes a chiral-glass transition at finite temperature. - Highlights: → We define the chirality in a diluted dipolar Heisenberg system. → The system undergoes a chiral-glass transition at finite temperature. → We extract the critical exponents of the chiral-glass transition.

Spin-crossover behavior of polymeric iron(III) complexes

International Nuclear Information System (INIS)

Maeda, Yonezo; Miyamoto, Makoto; Takashima, Yoshimasa; Oshio, Hiroaki

1989-01-01

Polymeric spin-crossover iron(III) complexes possessing poly(4-vinylpyridine), poly(N-vinylimidazole) or poly(octylmethacrylate-co-4-vinylpyridine) as ligand are prepared. In this experience enriched 57 Fe was used to get strong Moessbauer absorption. The enriched behavior of the complexes were examined by magnetic susceptibilities measurement, and Moessbauer and esr spectroscopies. Some of them show spin-state behavior over a wide range of temperature. Some of them show rapid spin-state interexchange compared to the Moessbauer time scale and others not. Spin-crossover behavior of polymeric complexes is characterized of wide spin-state transition temperature range

Spin-flip transitions in self-assembled quantum dots

Science.gov (United States)

Stavrou, V. N.

2017-12-01

Detailed realistic calculations of the spin-flip time (T 1) for an electron in a self-assembled quantum dot (SAQD) due to emission of an acoustic phonon, using only bulk properties with no fitting parameters, are presented. Ellipsoidal lens shaped Inx Ga1-x As quantum dots, with electronic states calculated using 8-band strain dependent {k \\cdot p} theory, are considered. The phonons are treated as bulk acoustic phonons coupled to the electron by both deformation potential and piezoelectric interactions. The dependence of T 1 on the geometry of SAQD, on the applied external magnetic field and on the lattice temperature is highlighted. The theoretical results are close to the experimental measurements on the spin-flip times for a single electron in QD.

Spin and orbital moments in actinide compounds

DEFF Research Database (Denmark)

Lebech, B.; Wulff, M.; Lander, G.H.

1991-01-01

The extended spatial distribution of both the transition-metal 3d electrons and the actinide 5f electrons results in a strong interaction between these electron states when the relevant elements are alloyed. A particular interesting feature of this hybridization, which is predicted by single...... experiments designed to determine the magnetic moments at the actinide and transition-metal sublattice sites in compounds such as UFe2, NpCo2, and PuFe2 and to separate the spin and orbital components at the actinide sites. The results show, indeed, that the ratio of the orbital to spin moment is reduced...

Spin-flip transition and Faraday effect in antiferromagnet KMnF3 in megagauss magnetic field

International Nuclear Information System (INIS)

Mukhin, A.A.; Plis, V.I.; Popov, A.I.; Zvezdin, A.K.; Platonov, V.; Tatsenko, O.M.

1998-01-01

Faraday effect in the antiferromagnet KMnF 3 has been investigated in pulse explosive fields up to 500 T at T=78 K. The laser wavelength 0.63 μm was used in the experiment. The magnetic field dependence of Faraday rotation in this antiferromagnet shows a unique feature of a lack of saturation effect in the fields up to 500 T whereas critical field of spin-flip transition is about 120 T. The theoretical analysis of microscopic nature of Faraday rotation, including the diamagnetic, magneto-dipole and paramagnetic mechanisms has been performed. The strong competition of these mechanisms is important to explain the extremely small value of the effect and its unusual magnetic field dependence

Erratum to: Quadrupole moments of low-lying baryons with spin ...

Indian Academy of Sciences (India)

physics pp. 1083. Erratum to: Quadrupole moments of low-lying baryons with spin-. 1. 2. +. , spin-. 3. 2. +. , and spin-. 3. 2. +. → 1. 2. + transitions. NEETIKA SHARMA and HARLEEN DAHIYA. ∗. Department of Physics, Dr. B.R. Ambedkar National Institute of Technology,. Jalandhar 144 011, India. ∗. Corresponding author.

Sign rules for anisotropic quantum spin systems

International Nuclear Information System (INIS)

Bishop, R. F.; Farnell, D. J. J.; Parkinson, J. B.

2000-01-01

We present exact ''sign rules'' for various spin-s anisotropic spin-lattice models. It is shown that, after a simple transformation which utilizes these sign rules, the ground-state wave function of the transformed Hamiltonian is positive definite. Using these results exact statements for various expectation values of off-diagonal operators are presented, and transitions in the behavior of these expectation values are observed at particular values of the anisotropy. Furthermore, the importance of such sign rules in variational calculations and quantum Monte Carlo calculations is emphasized. This is illustrated by a simple variational treatment of a one-dimensional anisotropic spin model

Spin-state studies with XES and RIXS: From static to ultrafast

International Nuclear Information System (INIS)

Vankó, György; Bordage, Amélie; Glatzel, Pieter; Gallo, Erik; Rovezzi, Mauro; Gawelda, Wojciech; Galler, Andreas; Bressler, Christian; Doumy, Gilles; March, Anne Marie; Kanter, Elliot P.; Young, Linda; Southworth, Stephen H.; Canton, Sophie E.; Uhlig, Jens; Smolentsev, Grigory; Sundström, Villy; Haldrup, Kristoffer; Brandt van Driel, Tim; Nielsen, Martin M.

2013-01-01

Highlights: ► We study light-induced spin-state transition of Fe(II) complexes in solution. ► Laser-pump-X-ray-probe spectroscopy is extended to MHz repetition rates. ► XES and RIXS compare well with the static spectra at thermal spin transition. ► The typical assumptions used in XES line shape analysis are validated. -- Abstract: We report on extending hard X-ray emission spectroscopy (XES) along with resonant inelastic X-ray scattering (RIXS) to study ultrafast phenomena in a pump-probe scheme at MHz repetition rates. The investigated systems include low-spin (LS) Fe II complex compounds, where optical pulses induce a spin-state transition to their (sub)nanosecond-lived high-spin (HS) state. Time-resolved XES clearly reflects the spin-state variations with very high signal-to-noise ratio, in agreement with HS–LS difference spectra measured at thermal spin crossover, and reference HS–LS systems in static experiments, next to multiplet calculations. The 1s2p RIXS, measured at the Fe 1s pre-edge region, shows variations after laser excitation, which are consistent with the formation of the HS state. Our results demonstrate that X-ray spectroscopy experiments with overall rather weak signals, such as RIXS, can now be reliably exploited to study chemical and physical transformations on ultrafast time scales

Nonequilibrium dynamics of a mixed spin-1/2 and spin-3/2 Ising ferrimagnetic system with a time dependent oscillating magnetic field source

Energy Technology Data Exchange (ETDEWEB)

Vatansever, Erol [Dokuz Eylül University, Graduate School of Natural and Applied Sciences, TR-35160 Izmir (Turkey); Polat, Hamza, E-mail: hamza.polat@deu.edu.tr [Department of Physics, Dokuz Eylül University, TR-35160 Izmir (Turkey)

2015-10-15

Nonequilibrium phase transition properties of a mixed Ising ferrimagnetic model consisting of spin-1/2 and spin-3/2 on a square lattice under the existence of a time dependent oscillating magnetic field have been investigated by making use of Monte Carlo simulations with a single-spin flip Metropolis algorithm. A complete picture of dynamic phase boundary and magnetization profiles have been illustrated and the conditions of a dynamic compensation behavior have been discussed in detail. According to our simulation results, the considered system does not point out a dynamic compensation behavior, when it only includes the nearest-neighbor interaction, single-ion anisotropy and an oscillating magnetic field source. As the next-nearest-neighbor interaction between the spins-1/2 takes into account and exceeds a characteristic value which sensitively depends upon values of single-ion anisotropy and only of amplitude of external magnetic field, a dynamic compensation behavior occurs in the system. Finally, it is reported that it has not been found any evidence of dynamically first-order phase transition between dynamically ordered and disordered phases, which conflicts with the recently published molecular field investigation, for a wide range of selected system parameters. - Highlights: • Spin-1/2 and spin-3/2 Ising ferrimagnetic model is examined. • The system is exposed to time-dependent magnetic field. • Kinetic Monte Carlo simulation technique is used. • Any evidence of first-order phase transition has not been found.

(Non-) Gibbsianness and Phase Transitions in Random Lattice Spin Models

NARCIS (Netherlands)

Külske, C.

1999-01-01

We consider disordered lattice spin models with finite-volume Gibbs measures µΛ[η](dσ). Here σ denotes a lattice spin variable and η a lattice random variable with product distribution P describing the quenched disorder of the model. We ask: when will the joint measures limΛ↑Zd P(dη)µΛ[η](dσ) be

Theoretical study of the low-lying electronic states of magnesium sulfide cation including spin-orbit interaction

Science.gov (United States)

Chen, Peng; Wang, Ning; Li, Song; Chen, Shan-Jun

2017-11-01

Highly correlated ab initio calculations have been performed for an accurate determination of electronic structures and spectroscopic features for the low-lying electronic states of the MgS+ cation. The potential energy curves for the four Λ-S states correlating to the lowest dissociation asymptote are studied for the first time. Four Λ-S states split into nine Ω states through the spin-orbit coupling effect. Accurate spectroscopic constants are deduced for all bound states. The spin-orbit couplings and the transition dipole moments, as well as the PECs, are utilized to calculate Franck-Condon factors and radiative lifetimes of the vibrational levels. To verify our computational accuracy, analogous calculations for the ground state of MgS are also carried out, and our derived results are in reasonable agreement with available experimental data. In addition, photoelectron spectrum of MgS has been simulated. The predictive results are anticipated to serve as guidelines for further researches such as assisting laboratorial detections and analyzing observed spectrum.

Observation of Spin Polarons in a Tunable Fermi Liquid of Ultracold Atoms

Science.gov (United States)

Zwierlein, Martin

2009-05-01

We have observed spin polarons, dressed spin down impurities in a spin up Fermi sea of ultracold atoms via tomographic RF spectroscopy. Feshbach resonances allow to freely tune the interactions between the two spin states involved. A single spin down atom immersed in a Fermi sea of spin up atoms can do one of two things: For strong attraction, it can form a molecule with exactly one spin up partner, but for weaker interaction it will spread its attraction and surround itself with a collection of majority atoms. This spin down atom dressed with a spin up cloud constitutes the spin- or Fermi polaron. We have observed a striking spectroscopic signature of this quasi-particle for various interaction strengths, a narrow peak in the spin down spectrum that emerges above a broad background. The spectra allow us to directly measure the polaron energy and the quasi-particle residue Z. The polarons are found to be only weakly interacting with each other, and can thus be identified with the quasi-particles of Landau's Fermi liquid theory. At a critical interaction strength, we observe a transition from spin one-half polarons to spin zero molecules. At this point the Fermi liquid undergoes a phase transition into a superfluid Bose liquid.

Asteroid (367943) 2012 DA14 Flyby Spin State Analysis

Science.gov (United States)

Benson, Conor; Scheeres, Daniel J.; Moskovitz, Nicholas

2017-10-01

On February 15, 2013 asteroid 2012 DA14 experienced an extremely close Earth encounter, passing within 27700 km altitude. This flyby gave observers the chance to directly detect flyby-induced changes to the asteroid’s spin state and physical properties. The strongest shape and spin state constraints were provided by Goldstone delay-Doppler radar and visible-wavelength photometry taken after closest approach. These data indicated a roughly 40 m x 20 m object in non-principal axis rotation. NPA states are described by two fundamental periods. Pφ is the average precession period of the long/short axis about the angular momentum vector and Pψ is the rotation period about the long/short axis.WindowCLEAN (Belton & Gandhi 1988) power spectrum analysis of the post flyby light curve showed three prominent frequencies, two of which were 1:2 multiples of each other. Mueller et al. (2002) suggest peaks with this relationship are 1/Pφ and 2/Pφ, implying that Pφ = 6.35 hr. Likely values for Pψ were then 8.72, 13.95, or 23.39 hr. These Pφ,Pψ pairs yielded six candidate spin states in total, one LAM and one SAM per pair.Second to fourth order, two-dimensional Fourier series fits to the light curve were best for periods of 6.359 and 8.724 hr. The two other candidate pairs were also in the top ten fits. Inertia constraints of a roughly 2:1 uniform density ellipsoid eliminated two of the three SAM states. Using JPL Horizons ephemerides and Lambertian ellipsoids, simulated light curves were generated. The simulated and observed power spectra were then compared for all angular momentum poles and reasonable ellipsoid elongations. Only the Pφ = 6.359 hr and Pψ = 8.724 hr LAM state produced light curves consistent with the observed frequency structure. All other states were clearly incompatible. With two well-fitting poles found, phasing the initial attitude and angular velocity yielded plausible matches to the observed light curve. Neglecting gravitational torques, neither

Electrical detection of spin transport in lateral ferromagnet-semiconductor devices

Science.gov (United States)

Lou, Xiaohua

2007-03-01

A fully electrical scheme of spin injection, transport, and detection in a single ferromagnet-semiconductor structure has been a long-standing goal in the field of spintronics. In this talk, we report on an experimental demonstration of such a scheme. The devices are fabricated from epitaxial Fe/GaAs (100) heterostructures with highly doped GaAs as a Schottky tunnel barrier. A set of closely spaced Fe contacts on the top of an n-GaAs channel are used as spin injectors and detectors. Reference electrodes are placed at the far ends of the channel, allowing for non-local spin detection [1]. The electro-chemical potential of the detector is sensitive to the relative magnetizations of the injector and detector. In spin-valve measurements, a magnetic field is applied along the Fe easy axis to switch the relative magnetizations of injector and detector from parallel to antiparallel, resulting in a voltage jump that is proportional to the non-equilibrium spin polarization in the channel. A more rigorous test of electrical spin detection is the observation of the Hanle effect, in which an out-of-plane magnetic field is used to modulate and dephase the spin polarization in the channel. The magnitudes of the observed Hanle curves agree with the results of the spin-valve measurements. The dependence of the Hanle curves on temperature and contact separation is studied in detail and is consistent with a drift-diffusion model incorporating spin precession and relaxation. The spin polarization generated by spin injection (reverse bias at the injector) or spin accumulation (forward bias at the injector) is measured using the magneto-optical Kerr effect and is found to be in good agreement with the spin-dependent non-local voltage. Both the transport and optical measurements show a non-linear relationship between the bias voltage at the injector and the spin polarization in the channel. [1] M. Johnson and R. H. Silsbee, Phys. Rev. Lett. 55, 1790 (1985).

Phase diagrams in mixed spin-3/2 and spin-2 Ising system with two alternative layers within the effective-field theory

International Nuclear Information System (INIS)

Deviren, Bayram; Polat, Yasin; Keskin, Mustafa

2011-01-01

The phase diagrams in the mixed spin-3/2 and spin-2 Ising system with two alternative layers on a honeycomb lattice are investigated and discussed by the use of the effective-field theory with correlations. The interaction of the nearest-neighbour spins of each layer is taken to be positive (ferromagnetic interaction) and the interaction of the adjacent spins of the nearest-neighbour layers is considered to be either positive or negative (ferromagnetic or anti-ferromagnetic interaction). The temperature dependence of the layer magnetizations of the system is examined to characterize the nature (continuous or discontinuous) of the phase transitions and obtain the phase transition temperatures. The system exhibits both second- and first-order phase transitions besides triple point (TP), critical end point (E), multicritical point (A), isolated critical point (C) and reentrant behaviour depending on the interaction parameters. We have also studied the temperature dependence of the total magnetization to find the compensation points, as well as to determine the type of behaviour, and N-type behaviour in Néel classification nomenclature existing in the system. The phase diagrams are constructed in eight different planes and it is found that the system also presents the compensation phenomena depending on the sign of the bilinear exchange interactions. (general)

Communication: Evaluating non-empirical double hybrid functionals for spin-state energetics in transition-metal complexes

Science.gov (United States)

Wilbraham, Liam; Adamo, Carlo; Ciofini, Ilaria

2018-01-01

The computationally assisted, accelerated design of inorganic functional materials often relies on the ability of a given electronic structure method to return the correct electronic ground state of the material in question. Outlining difficulties with current density functionals and wave function-based approaches, we highlight why double hybrid density functionals represent promising candidates for this purpose. In turn, we show that PBE0-DH (and PBE-QIDH) offers a significant improvement over its hybrid parent functional PBE0 [as well as B3LYP* and coupled cluster singles and doubles with perturbative triples (CCSD(T))] when computing spin-state splitting energies, using high-level diffusion Monte Carlo calculations as a reference. We refer to the opposing influence of Hartree-Fock (HF) exchange and MP2, which permits higher levels of HF exchange and a concomitant reduction in electronic density error, as the reason for the improved performance of double-hybrid functionals relative to hybrid functionals. Additionally, using 16 transition metal (Fe and Co) complexes, we show that low-spin states are stabilised by increasing contributions from MP2 within the double hybrid formulation. Furthermore, this stabilisation effect is more prominent for high field strength ligands than low field strength ligands.

Pressure-induced spin reorientation transition in layered ferromagnetic insulator Cr2Ge2Te6

Science.gov (United States)

Lin, Zhisheng; Lohmann, Mark; Ali, Zulfikhar A.; Tang, Chi; Li, Junxue; Xing, Wenyu; Zhong, Jiangnan; Jia, Shuang; Han, Wei; Coh, Sinisa; Beyermann, Ward; Shi, Jing

2018-05-01

The anisotropic magnetoresistance (AMR) of Cr2Ge2Te6 (CGT), a layered ferromagnetic insulator, is investigated under an applied hydrostatic pressure up to 2 GPa. The easy-axis direction of the magnetization is inferred from the AMR saturation feature in the presence and absence of an applied pressure. At zero applied pressure, the easy axis is along the c direction or perpendicular to the layer. Upon application of a hydrostatic pressure > 1 GPa, the uniaxial anisotropy switches to easy-plane anisotropy which drives the equilibrium magnetization from the c axis to the a b plane at zero magnetic field, which amounts to a giant magnetic anisotropy energy change (> 100%). As the temperature is increased across the Curie temperature, the characteristic AMR effect gradually decreases and disappears. Our first-principles calculations confirm the giant magnetic anisotropy energy change with moderate pressure and assign its origin to the increased off-site spin-orbit interaction of Te atoms due to a shorter Cr-Te distance. Such a pressure-induced spin reorientation transition is very rare in three-dimensional ferromagnets, but it may be common to other layered ferromagnets with similar crystal structures to CGT, and therefore offers a unique way to control magnetic anisotropy.

Pressure and Temperature Spin Crossover Sensors with Optical Detection

Science.gov (United States)

Linares, Jorge; Codjovi, Epiphane; Garcia, Yann

2012-01-01

Iron(II) spin crossover molecular materials are made of coordination centres switchable between two states by temperature, pressure or a visible light irradiation. The relevant macroscopic parameter which monitors the magnetic state of a given solid is the high-spin (HS) fraction denoted nHS, i.e., the relative population of HS molecules. Each spin crossover material is distinguished by a transition temperature T1/2 where 50% of active molecules have switched to the low-spin (LS) state. In strongly interacting systems, the thermal spin switching occurs abruptly at T1/2. Applying pressure induces a shift from HS to LS states, which is the direct consequence of the lower volume for the LS molecule. Each material has thus a well defined pressure value P1/2. In both cases the spin state change is easily detectable by optical means thanks to a thermo/piezochromic effect that is often encountered in these materials. In this contribution, we discuss potential use of spin crossover molecular materials as temperature and pressure sensors with optical detection. The ones presenting smooth transitions behaviour, which have not been seriously considered for any application, are spotlighted as potential sensors which should stimulate a large interest on this well investigated class of materials. PMID:22666041

A technique for measurement of vector and tensor polarization in solid spin one polarized targets

Energy Technology Data Exchange (ETDEWEB)

Kielhorn, W.F.

1991-06-01

Vector and tensor polarizations are explicitly defined and used to characterize the polarization states of spin one polarized targets, and a technique for extracting these polarizations from nuclear magnetic resonance (NMR) data is developed. This technique is independent of assumptions about spin temperature, but assumes the target's crystal structure induces a quadrupole interaction with the spin one particles. Analysis of the NMR signals involves a computer curve fitting algorithm implemented with a fast Fourier transform method which speeds and simplifies curve fitting algorithms used previously. For accurate curve fitting, the NMR electronic circuit must be modeled by the fitting algorithm. Details of a circuit, its model, and data collected from this circuit are given for a solid deuterated ammonia target. 37 refs., 19 figs., 3 tabs.

Supersymmetries and constants of motion in spinning spaces

International Nuclear Information System (INIS)

Visinescu, Mihai

1999-01-01

The models of relativistic particles with spin have been proposed for a long time. The first published work concerning the Lagrangian description of the relativistic particle with spin was the paper by Frenkel which appeared in 1926. After that the literature on the particle with spin grew vast. The models involving only conventional coordinates are called the classical models while the models involving anticommuting (Grassmann) coordinates are generally called pseudo-classical. We shall confine ourselves to discuss the relativistic spin one half particle models involving anticommuting vectorial degrees of freedom which are usually called spinning particles. Spinning particles are in some sense the classical limit of the Dirac particles. After the first quantization these new anticommuting variables are mapped into the Dirac matrices and they disappear from the theory. We investigate the motion of pseudo-classical spinning point particles in curved spaces. The generalized Killing equations for the configuration space of spinning particles (spinning space) are analyzed and the solutions are expressed in terms of Killing-Yano tensors. The general results are applied to the case of the four-dimensional Euclidean Taub-NUT spinning space. (author)