Local Spin Correlations in Heisenberg Antiferromagnets
Weihong, Zheng; Oitmaa, J.
2000-01-01
We use linked cluster series expansion methods to estimate the values of various short distance correlation functions in $S=1/2$ Heisenberg antiferromagnets at T=0, for dimension $d=1,2,3$. The method incorporates the possibility of spontaneous symmetry breaking, which is manifest in $d=2,3$. The results are important in providing a test for approximate theories of the antiferromagnetic ground state.
Antiferromagnetic phase transition and spin correlations in NiO
DEFF Research Database (Denmark)
Chatterji, Tapan; McIntyre, G.J.; Lindgård, Per-Anker
2009-01-01
We have investigated the antiferromagnetic (AF) phase transition and spin correlations in NiO by high-temperature neutron diffraction below and above TN. We show that AF phase transition is a continuous second-order transition within our experimental resolution. The spin correlations manifested by...... process. We determined the critical exponents =0.328±0.002 and =0.64±0.03 and the Néel temperature TN=530±1 K. These critical exponents suggest that NiO should be regarded as a 3dXY system...
International Nuclear Information System (INIS)
Magnetic correlations in all four phases of pure and doped vanadium sesquioxide (V2O3) have been examined by magnetic thermal-neutron scattering. Specifically, we have studied the antiferromagnetic and paramagnetic phases of metallic V2-yO3, the antiferromagnetic insulating and paramagnetic metallic phases of stoichiometric V2O3, and the antiferromagnetic and paramagnetic phases of insulating V1.944Cr0.056O3. While the antiferromagnetic insulator can be accounted for by a localized Heisenberg spin model, the long-range order in the antiferromagnetic metal is an incommensurate spin-density wave, resulting from a Fermi surface nesting instability. Spin dynamics in the strongly correlated metal are dominated by spin fluctuations with a open-quotes single lobeclose quotes spectrum in the Stoner electron-hole continuum. Furthermore, our results in metallic V2O3 represent an unprecedentedly complete characterization of the spin fluctuations near a metallic quantum critical point, and provide quantitative support for the self-consistent renormalization theory for itinerant antiferromagnets in the small moment limit. Dynamic magnetic correlations for ℎωBT in the paramagnetic insulator carry substantial magnetic spectral weight. However, they are extremely short-ranged, extending only to the nearest neighbors. The phase transition to the antiferromagnetic insulator, from the paramagnetic metal and the paramagnetic insulator, introduces a sudden switching of magnetic correlations to a different spatial periodicity which indicates a sudden change in the underlying spin Hamiltonian. To describe this phase transition and also the unusual short-range order in the paramagnetic state, it seems necessary to take into account the orbital degrees of freedom associated with the degenerate d orbitals at the Fermi level in V2O3. copyright 1998 The American Physical Society
On the second-neighbour correlator in 1D XXX quantum antiferromagnetic spin chain
International Nuclear Information System (INIS)
We have calculated the energy per site for the ground state of the antiferromagnetic quantum spin chain with variable range exchange h(j-k) ∝ sinh2 a sinh-2 a(j-k) in the framework of the asymptotic Bethe ansatz. By expanding it in powers of e-2a, we have confirmed the value of the second-neighbour correlator for the model with nearest-neighbour exchange obtained earlier in the atomic limit of the Hubbard chain. (author). Letter-to-the-editor
Antiferromagnetic spin-orbitronics
Manchon, Aurelien
2015-05-01
Antiferromagnets have long remained an intriguing and exotic state of matter, whose application has been restricted to enabling interfacial exchange bias in metallic and tunneling spin-valves [1]. Their role in the expanding field of applied spintronics has been mostly passive and the in-depth investigation of their basic properties mostly considered from a fundamental perspective.
Antiferromagnetic spin Seebeck effect.
Energy Technology Data Exchange (ETDEWEB)
Wu, Stephen M.; Zhang, Wei; KC, Amit; Borisov, Pavel; Pearson, John E.; Jiang, J. Samuel; Lederman, David; Hoffmann, Axel; Bhattacharya, Anand
2016-03-03
We report on the observation of the spin Seebeck effect in antiferromagnetic MnF2. A device scale on-chip heater is deposited on a bilayer of MnF2 (110) (30nm)/Pt (4 nm) grown by molecular beam epitaxy on a MgF2(110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF2 through the inverse spin Hall effect. The low temperature (2–80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop transition corresponding to the sudden rotation of antiferromagnetic spins out of the easy axis is observed in the spin Seebeck signal when large magnetic fields (>9T) are applied parallel to the easy axis of the MnF2 thin film. When the magnetic field is applied perpendicular to the easy axis, the spin-flop transition is absent, as expected.
Spin structures in antiferromagnetic nanoparticles
DEFF Research Database (Denmark)
Brok, Erik
In this thesis magnetic structures of antiferromagnetic nanoparticles are studied as a function of particle size and aggregation. In nanoparticles the magnetic structure can be different from that of the corresponding bulk system due to the following reasons: a) a significant surface contribution...... a detailed knowledge of it can be important for applications of antiferromagnetic nanoparticles for example combined with ferromagnetic nanoparticles in nanocomposite devices. In this thesis the magnetic structure, in particular the orientation of the spins in the antiferromagnetic sublattices......, is investigated in systems of magnetic nanoparticles using a variety of experimental techniques. The spin structure in systems with spin canting, due to magnetic atoms in low symmetry surroundings, is studied in a theoretical model that is able to quantitatively explain observations of anomalous temperature...
Spin Structure Analyses of Antiferromagnets
International Nuclear Information System (INIS)
We have synthesized series of powder sample of incommensurate antiferromagnetic multiferroics, (Mn, Co)WO4 and Al doped Ba0.5Sr1.5Zn2Fe12O22, incommensurate antiferromagnetic multiferroics. Their spin structure was studied by using the HRPD. In addition, we have synthesized series of crystalline samples of incommensurate multiferroics, (Mn, Co)WO4 and olivines. Their spin structure was investigated using neutron diffraction under high magnetic field. As a result, we were able to draw the phase diagram of (Mn, Co)WO4 as a function of composition and temperature. We learned the how the spin structure changes with increased ionic substitution. Finally we have drawn the phase diagram of the multicritical olivine Mn2SiS4/Mn2GeS4 as a function of filed and temperature through the spin structure studies
Antiferromagnetic noise correlations in optical lattices
DEFF Research Database (Denmark)
Bruun, Niels Bohr International Academy, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark, Georg Morten; Syljuåsen, F. T.; Pedersen, K. G. L.;
2009-01-01
We analyze how noise correlations probed by time-of-flight experiments reveal antiferromagnetic (AF) correlations of fermionic atoms in two-dimensional and three-dimensional optical lattices. Combining analytical and quantum Monte Carlo calculations using experimentally realistic parameters, we...... show that AF correlations can be detected for temperatures above and below the critical temperature for AF ordering. It is demonstrated that spin-resolved noise correlations yield important information about the spin ordering. Finally, we show how to extract the spin correlation length and the related...
International Nuclear Information System (INIS)
The spin correlations ωrz, r=1,2,3, and the probability pN of finding a system in the Neel state for the antiferromagnetic ring Fe6III (the so-called 'small ferric wheel') are calculated. States with magnetization M=0 and total spin 0≤S≤15, labeled by two (out of four) one-dimensional irreducible representations (irreps) of the point symmetry group D6, are taken into account. This choice follows from importance of these irreps in analyzing low-lying states in each S multiplet. Taking into account the Clebsch-Gordan coefficients for coupling total spins of sublattices (SA=SB=(15/2)) the global Neel probability pN* can be determined. Dependences of these quantities on state energy (per bond and in the units of exchange integral J) and the total spin S are analyzed. Providing we have determined pN(S), etc., for other antiferromagnetic rings (Fe10, for instance) we could try to approximate results for the largest synthesized ferric wheel Fe18. Since thermodynamic properties of Fe6 have been investigated recently, in the present considerations they are not discussed, but only used to verify obtained values of eigenenergies. Numerical results are calculated with high precision using two main tools: (i) thorough analysis of symmetry properties including methods of algebraic combinatorics and (ii) multiple precision arithmetic library GMP. The system considered yields more than 45 000 basic states (the so-called Ising configurations), but application of the method proposed reduces this problem to 20-dimensional eigenproblem for the ground state (S=0). The largest eigenproblem has to be solved for S=4; its dimension is 60. These two facts (high precision and small resultant eigenproblems) confirm the efficiency and usefulness of such an approach, so it is briefly discussed here
Antiferromagnetic Spin Wave Field-Effect Transistor
Cheng, Ran; Daniels, Matthew W.; Zhu, Jian-Gang; Xiao, Di
2016-04-01
In a collinear antiferromagnet with easy-axis anisotropy, symmetry dictates that the spin wave modes must be doubly degenerate. Theses two modes, distinguished by their opposite polarization and available only in antiferromagnets, give rise to a novel degree of freedom to encode and process information. We show that the spin wave polarization can be manipulated by an electric field induced Dzyaloshinskii-Moriya interaction and magnetic anisotropy. We propose a prototype spin wave field-effect transistor which realizes a gate-tunable magnonic analog of the Faraday effect, and demonstrate its application in THz signal modulation. Our findings open up the exciting possibility of digital data processing utilizing antiferromagnetic spin waves and enable the direct projection of optical computing concepts onto the mesoscopic scale.
Fujihala, M.; Zheng, X. G.; Oohara, Y.; Morodomi, H.; Kawae, T.; Matsuo, Akira; Kindo, Koichi
2012-01-01
Spin fluctuations and spin-liquid behaviors of frustrated kagome antiferromagnets have received intense recent attention. Although most severe frustration was predicted for an Ising kagome antiferromagnet, a real material system of undistorted kagome lattice has not been found so far. Here we report the frustrated magnetism of a new Ising kagome antiferromagnet, MgCo3(OH)6Cl2, which can be viewed as a Co version of the intensively researched quantum kagome antiferromagnet of Herbertsmithite ZnCu3(OH)6Cl2. Experiments of magnetization, heat capacity, μSR, and neutron scattering demonstrated a partially frozen state with persistent spin fluctuations below around T = 2.7 K. The present study has provided a real material system to study the Ising spin behaviors on undistorted kagome lattice.
Diffusive magnonic spin transport in antiferromagnetic insulators
Rezende, S. M.; Rodríguez-Suárez, R. L.; Azevedo, A.
2016-02-01
It has been shown recently that a layer of the antiferromagnetic insulator (AFI) NiO can be used to transport spin current between a ferromagnet (FM) and a nonmagnetic metal (NM). In the experiments one uses the microwave-driven ferromagnetic resonance in a FM layer to produce a spin pumped spin current that flows through an AFI layer and reaches a NM layer where it is converted into a charge current by means of the inverse spin Hall effect. Here we present a theory for the spin transport in an AFI that relies on the spin current carried by the diffusion of thermal antiferromagnetic magnons. The theory explains quite well the measured dependence of the voltage in the NM layer on the thickness of the NiO layer.
Transformation of spin current by antiferromagnetic insulators
Khymyn, Roman; Lisenkov, Ivan; Tiberkevich, Vasil S.; Slavin, Andrei N.; Ivanov, Boris A.
2015-01-01
It is demonstrated theoretically that a thin layer of an anisotropic antiferromagnetic (AFM) insulator can effectively conduct spin current by excitation of a pair of evanescent AFM spin wave modes. The spin current flowing through the AFM is not conserved due to the interaction between the excited AFM modes and the AFM lattice, and, depending on the excitation conditions, can be either attenuated or enhanced. When the phase difference between the excited evanescent modes is close to $\\pi/2$,...
Small antiferromagnetic spin systems-Sublattice Hamiltonians
International Nuclear Information System (INIS)
A few examples of four-spin Heisenberg systems with dominant antiferromagnetic couplings are considered. All systems can be described by the so-called sublattice Hamiltonian H=SA.SB or its modifications, where SX is the total spin of a sublattice X=A, B. In such a case (eigen)energies are simple functions of the total spin number S, total spins of sublattices SA, SB, and the Hamiltonian parameters (ratios of exchange integrals). Moreover, eigenstates are strictly determined by a coupling scheme assumed and the appropriate Clebsch-Gordan coefficients. In this sense the systems considered are classical ones.
Entanglement Perturbation Theory for Antiferromagnetic Heisenberg Spin Chains
Wang, Lihua; Chung, Sung Gong
2012-11-01
A recently developed numerical method, entanglement perturbation theory (EPT), is used to study the antiferromagnetic Heisenberg spin chains with z-axis anisotropy λ and magnetic field B. To demonstrate its accuracy, we first apply EPT to the isotropic spin-1/2 antiferromagnetic Heisenberg model, and find that EPT successfully reproduces the exact Bethe ansatz results for the ground state energy, the local magnetization, and the spin correlation functions (Bethe ansatz result is available for the first seven lattice separations). In particular, EPT confirms for the first time the asymptotic behavior of the spin correlation functions predicted by the conformal field theory, which realizes only for lattice separations larger than 1000. Next, turning on the z-axis anisotropy and the magnetic field, the 2- and 4-spin correlation functions are calculated, and the results are compared with those obtained by bosonization and density matrix renormalization group methods. Finally, for the spin-1 antiferromagnetic Heisenberg model, the ground state phase diagram in λ space is determined by Roomany--Wyld renormalization group (RG) finite size scaling. The results are in good agreement with those obtained by the level-spectroscopy method.
Terahertz Antiferromagnetic Spin Hall Nano-Oscillator
Cheng, Ran; Xiao, Di; Brataas, Arne
2016-05-01
We consider the current-induced dynamics of insulating antiferromagnets in a spin Hall geometry. Sufficiently large in-plane currents perpendicular to the Néel order trigger spontaneous oscillations at frequencies between the acoustic and the optical eigenmodes. The direction of the driving current determines the chirality of the excitation. When the current exceeds a threshold, the combined effect of spin pumping and current-induced torques introduces a dynamic feedback that sustains steady-state oscillations with amplitudes controllable via the applied current. The ac voltage output is calculated numerically as a function of the dc current input for different feedback strengths. Our findings open a route towards terahertz antiferromagnetic spin-torque oscillators.
Electron-phonon interaction and antiferromagnetic correlations
Sangiovanni, G.; Gunnarsson, O.; Koch, E.; Castellani, C.; M. Capone
2006-01-01
We study effects of the Coulomb repulsion on the electron-phonon interaction (EPI) in a model of cuprates at zero and finite doping. We find that antiferromagnetic correlations strongly enhance EPI effects on the electron Green's function with respect to the paramagnetic correlated system, but the net effect of the Coulomb interaction is a moderate suppression of the EPI. Doping leads to additional suppression, due to reduced antiferromagnetic correlations. In contrast, the Coulomb interactio...
High-field spin dynamics of antiferromagnetic quantum spin chains
DEFF Research Database (Denmark)
Enderle, M.; Regnault, L.P.; Broholm, C.;
2000-01-01
The characteristic internal order of macroscopic quantum ground states in one-dimensional spin systems is usually not directly accessible, but reflected in the spin dynamics and the field dependence of the magnetic excitations. In high magnetic fields quantum phase transitions are expected. We...... present recent work on the high-field spin dynamics of the S = I antiferromagnetic Heisenberg chains NENP (Haldane ground state) and CsNiCl3 (quasi-1D HAF close to the quantum critical point), the uniform S = 1/2 chain CTS, and the spin-Peierls system CuGeO3. (C) 2000 Elsevier Science B,V. All rights...
High-field spin dynamics of antiferromagnetic quantum spin chains
DEFF Research Database (Denmark)
Enderle, M.; Regnault, L.P.; Broholm, C.; Reich, D.; Zaliznyak, I.; Sieling, M.; Rønnow, H.M.; McMorrow, D.F.
The characteristic internal order of macroscopic quantum ground states in one-dimensional spin systems is usually not directly accessible, but reflected in the spin dynamics and the field dependence of the magnetic excitations. In high magnetic fields quantum phase transitions are expected. We...... present recent work on the high-field spin dynamics of the S = I antiferromagnetic Heisenberg chains NENP (Haldane ground state) and CsNiCl3 (quasi-1D HAF close to the quantum critical point), the uniform S = 1/2 chain CTS, and the spin-Peierls system CuGeO3. (C) 2000 Elsevier Science B,V. All rights...
Thermal Generation of Spin Current in an Antiferromagnet.
Seki, S; Ideue, T; Kubota, M; Kozuka, Y; Takagi, R; Nakamura, M; Kaneko, Y; Kawasaki, M; Tokura, Y
2015-12-31
The longitudinal spin Seebeck effect has been investigated for a uniaxial antiferromagnetic insulator Cr(2)O(3), characterized by a spin-flop transition under magnetic field along the c axis. We have found that a temperature gradient applied normal to the Cr(2)O(3)/Pt interface induces inverse spin Hall voltage of spin-current origin in Pt, whose magnitude turns out to be always proportional to magnetization in Cr(2)O(3). The possible contribution of the anomalous Nernst effect is confirmed to be negligibly small. The above results establish that an antiferromagnetic spin wave can be an effective carrier of spin current. PMID:26765011
A transverse Ising bilayer film with an antiferromagnetic spin configuration
Kaneyoshi, T.
2015-10-01
The phase diagrams and temperature dependences of magnetizations in a transverse Ising bilayer film with an antiferromagnetic spin configuration are studied by the uses of the effective-field theory (EFT) with correlations, in order to clarify whether the appearance of a compensation point is possible below the transition temperature in the system. From these investigations, we have found a lot of characteristic phenomena in these properties, when the value of an interlayer coupling takes a large value, such as the reentrant phenomenon free from the disorder-induced frustration and the novel types of magnetization curve with a compensation point.
Correlations in the Ising antiferromagnet on the anisotropic kagome lattice
International Nuclear Information System (INIS)
We study the correlation function of middle spins, i.e. of spins on intermediate sites between two adjacent parallel lattice axes, of the spatially anisotropic Ising antiferromagnet on the kagome lattice. It is given rigorously by a Toeplitz determinant. The large-distance behaviour of this correlation function is obtained by analytic methods. For shorter distances we evaluate the Toeplitz determinant numerically. The correlation function is found to vanish exactly on a line Jd(T) in the T − J (temperature versus coupling constant) phase diagram. This disorder line divides the phase diagram into two regions. For J d(T) the correlations display the features of an unfrustrated two-dimensional Ising magnet, whereas for J > Jd(T) the correlations between the middle spins are seen to be strongly influenced by the short-range antiferromagnetic order that prevails among the spins of the adjacent lattice axes. While for J d(T) there is a region with ferrimagnetic long-range order, the model remains disordered for J > Jd(T) down to T = 0
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...
Ultrafast Band Engineering and Transient Spin Currents in Antiferromagnetic Oxides
Gu, Mingqiang; Rondinelli, James M.
2016-01-01
We report a dynamic structure and band engineering strategy with experimental protocols to induce indirect-to-direct band gap transitions and coherently oscillating pure spin-currents in three-dimensional antiferromagnets (AFM) using selective phononic excitations. In the Mott insulator LaTiO3, we show that a photo-induced nonequilibrium phonon mode amplitude destroys the spin and orbitally degenerate ground state, reduces the band gap by 160 meV and renormalizes the carrier masses. The time scale of this process is a few hundreds of femtoseconds. Then in the hole-doped correlated metallic titanate, we show how pure spin-currents can be achieved to yield spin-polarizations exceeding those observed in classic semiconductors. Last, we demonstrate the generality of the approach by applying it to the non-orbitally degenerate AFM CaMnO3. These results advance our understanding of electron-lattice interactions in structures out-of-equilibrium and establish a rational framework for designing dynamic phases that may be exploited in ultrafast optoelectronic and optospintronic devices. PMID:27126354
Spin transfer torque in antiferromagnetic spin valves: From clean to disordered regimes
Saidaoui, Hamed Ben Mohamed
2014-05-28
Current-driven spin torques in metallic spin valves composed of antiferromagnets are theoretically studied using the nonequilibrium Green\\'s function method implemented on a tight-binding model. We focus our attention on G-type and L-type antiferromagnets in both clean and disordered regimes. In such structures, spin torques can either rotate the magnetic order parameter coherently (coherent torque) or compete with the internal antiferromagnetic exchange (exchange torque). We show that, depending on the symmetry of the spin valve, the coherent and exchange torques can either be in the plane, ∝n×(q×n) or out of the plane ∝n×q, where q and n are the directions of the order parameter of the polarizer and the free antiferromagnetic layers, respectively. Although disorder conserves the symmetry of the torques, it strongly reduces the torque magnitude, pointing out the need for momentum conservation to ensure strong spin torque in antiferromagnetic spin valves.
Electron spin resonance study of NiO antiferromagnetic nanoparticles
International Nuclear Information System (INIS)
The electron spin resonance (ESR) spectra of antiferromagnetic nanoparticle NiO specimens have been investigated as a function of temperature at x-band (microwave) frequencies. Below the nominal Neel temperature, the x-band resonances arising from the bulk antiferromagnets, including NiO particles with diameters greater than 100 A, all vanish due to the emergence of large molecular exchange fields. The ESR resonance signals of 60 A antiferromagnetic nanoparticles, however, persist to the lowest temperatures. These nanoparticle resonance lines shift to lower fields rapidly as the temperature is decreased, while the lineshapes broaden and distort
A quadrangular transverse Ising nanowire with an antiferromagnetic spin configuration
Kaneyoshi, T.
2015-11-01
The phase diagrams and the temperature dependences of magnetizations in a transverse Ising nanowire with an antiferromagnetic spin configuration are investigated by the use of the effective-field theory with correlations (EFT) and the core-shell concept. Many characteristic and unexpected behaviors are found for them, especially for thermal variation of total magnetization mT. The reentrant phenomenon induced by a transverse field in the core, the appearance of a compensation point, the non-monotonic variation with a compensation point, the reentrant phenomena with a compensation point and the existence of both a broad maximum and a compensation point have been found in the thermal variations of mT.
Mechanisms for spin supersolidity in S=(1/2) spin-dimer antiferromagnets
International Nuclear Information System (INIS)
Using perturbative expansions and the contractor renormalization (CORE) algorithm, we obtain effective hard-core bosonic Hamiltonians describing the low-energy physics of S=1/2 spin-dimer antiferromagnets known to display supersolid phases under an applied magnetic field. The resulting effective models are investigated by means of mean-field analysis and quantum Monte Carlo simulations. A ''leapfrog mechanism,'' through means of which extra singlets delocalize in a checkerboard-solid environment via correlated hoppings, is unveiled that accounts for the supersolid behavior
Spin waves in the block checkerboard antiferromagnetic phase
Institute of Scientific and Technical Information of China (English)
Lu Feng; Dai Xi
2012-01-01
Motivated by the discovery of a new family of 122 iron-based superconductors,we present the theoretical results on the ground state phase diagram,spin wave,and dynamic structure factor obtained from the extended J1-J2 Heisenberg model.In the reasonable physical parameter region of K2Fe4Ses,we find that the block checkerboard antiferromagnetic order phase is stable.There are two acoustic spin wave branches and six optical spin wave branches in the block checkerboard antiferromagnetic phase,which have analytic expressions at the high-symmetry points.To further compare the experimental data on neutron scattering,we investigate the saddlepoint structure of the magnetic excitation spectrum and the inelastic neutron scattering pattern based on linear spin wave theory.
Quantum phase competition in antiferromagnetic spin-1 ladders
International Nuclear Information System (INIS)
Motivated by recent chemical explorations into organic-radical-based higher-spin ladder systems, we study the ground-state properties of a wide class of antiferromagnetic spin-1 ladders. Numerical analysis featuring the level-spectroscopy technique reveals the rich phase diagram, correcting a preceding nonlinear-sigma-model prediction. A variational analysis well interprets the phase competition with particular emphasis on the re-entrant phase boundary on the way from single to coupled chains. (author)
The Berezinskii-Kosterlitz-Thouless transition and correlations in the XY kagome antiferromagnet
Cherepanov, V B; Podivilov, E V
2001-01-01
The problem of the Berezinskii-Kosterlitz-Thouless transition in the highly frustrated XY antiferromagnetic is solved. The transition temperature is found. It is shown that the spin correlation function exponentially decays with distance even in the low-temperature phase, in contrast to the order parameter correlation function, which decays algebraically with distance
Spin Hall effects in metallic antiferromagnets – perspectives for future spin-orbitronics
Directory of Open Access Journals (Sweden)
Joseph Sklenar
2016-05-01
Full Text Available We investigate angular dependent spin-orbit torques from the spin Hall effect in a metallic antiferromagnet using the spin-torque ferromagnetic resonance technique. The large spin Hall effect exists in PtMn, a prototypical CuAu-I-type metallic antiferromagnet. By applying epitaxial growth, we previously reported an appreciable difference in spin-orbit torques for c- and a-axis orientated samples, implying anisotropic effects in magnetically ordered materials. In this work we demonstrate through bipolar-magnetic-field experiments a small but noticeable asymmetric behavior in the spin-transfer-torque that appears as a hysteresis effect. We also suggest that metallic antiferromagnets may be good candidates for the investigation of various unidirectional effects related to novel spin-orbitronics phenomena.
Theory of the spin Seebeck effect in antiferromagnets
Rezende, S. M.; Rodríguez-Suárez, R. L.; Azevedo, A.
2016-01-01
The spin Seebeck effect (SSE) consists in the generation of a spin current by a temperature gradient applied in a magnetic film. The SSE is usually detected by an electric voltage generated in a metallic layer in contact with the magnetic film resulting from the conversion of the spin current into charge current by means of the inverse spin Hall effect. The SSE has been widely studied in bilayers made of the insulating ferrimagnet yttrium iron garnet (YIG) and metals with large spin-orbit coupling such as platinum. Recently the SSE has been observed in bilayers made of the antiferromagnet Mn F2 and Pt, revealing dependences of the SSE voltage on temperature and field very different from the ones observed in YIG/Pt. Here we present a theory for the SSE in structures with an antiferromagnetic insulator (AFI) in contact with a normal metal (NM) that relies on the bulk magnon spin current created by the temperature gradient across the thickness of the AFI/NM bilayer. The theory explains quite well the measured dependences of the SSE voltage on the sample temperature and on the applied magnetic field in Mn F2/Pt .
Long range anti-ferromagnetic spin model for prebiotic evolution
Energy Technology Data Exchange (ETDEWEB)
Nokura, Kazuo [Shonan Institute of Technology, Fujisawa 251-8511 (Japan)
2003-11-28
I propose and discuss a fitness function for one-dimensional binary monomer sequences of macromolecules for prebiotic evolution. The fitness function is defined by the free energy of polymers in the high temperature random coil phase. With repulsive interactions among the same kind of monomers, the free energy in the high temperature limit becomes the energy function of the one-dimensional long range anti-ferromagnetic spin model, which is shown to have a dynamical phase transition and glassy states.
Long range anti-ferromagnetic spin model for prebiotic evolution
International Nuclear Information System (INIS)
I propose and discuss a fitness function for one-dimensional binary monomer sequences of macromolecules for prebiotic evolution. The fitness function is defined by the free energy of polymers in the high temperature random coil phase. With repulsive interactions among the same kind of monomers, the free energy in the high temperature limit becomes the energy function of the one-dimensional long range anti-ferromagnetic spin model, which is shown to have a dynamical phase transition and glassy states
International Nuclear Information System (INIS)
By using the modified spin-wave and gauge invariant methods, we show that at zero temperature in the presence of an inhomogeneous magnetic field with magnitude B gives rise to a persistent magnetization current around a mesoscopic antiferromagnetic Heisenberg spin ring with the DM (Dzyaloshinskii–Moriya) interaction. The results show that the persistent magnetization current is vanishing at large Ds/J (Ds is reduced DM interaction and J is nearest exchange coupling) with α>1 (α is a constant describing the energy gap of the spin system). The result also shows that under the homogeneous magnetic field there exists a non-zero spin current in the spin ring. - Highlights: • Persistent spin current is calculated in anti-ferromagnetic ring. • Persistent magnetization current is vanishing at large Ds/J. • Under homogeneous magnetic field there exists a non-zero spin current in the ring
Spinor dynamics in an antiferromagnetic spin-1 thermal Bose gas
Pechkis, Hyewon K; Schwettmann, Arne; Griffin, Paul F; Barnett, Ryan; Tiesinga, Eite; Lett, Paul D
2013-01-01
We present experimental observations of coherent spin-population oscillations in a cold thermal, Bose gas of spin-1 sodium-23 atoms. The population oscillations in a multi-spatial-mode thermal gas have the same behavior as those observed in a single-spatial-mode antiferromagnetic spinor Bose Einstein condensate. We demonstrate this by showing that the two situations are described by the same dynamical equations, with a factor of two change in the spin-dependent interaction coefficient, which results from the change to particles with distinguishable momentum states in the thermal gas. We compare this theory to the measured spin population evolution after times up to a few hundreds of ms, finding quantitative agreement with the amplitude and period. We also measure the damping time of the oscillations as a function of magnetic field.
Mechanisms of Spin-Mixing Instabilities in Antiferromagnetic Molecular Wheels
Soncini, Alessandro; Chibotaru, Liviu F.
2007-08-01
The microscopic theory of field-induced spin-mixing instabilities in antiferromagnetic molecular wheels CsFe8 is proposed. The basic features of magnetic torque measurements [O. Waldmann , Phys. Rev. Lett. 96, 027206 (2006)PRLTAO0031-900710.1103/PhysRevLett.96.027206] are well explained by the interplay of three basic ingredients: the spin-mixing vibronic interaction with field-dependent vibronic constants, cooperative elastic interactions, and spin-mixing interactions independent from vibrations. The main contribution to spin mixing comes from second-order zero-field splitting mechanisms. At variance with previous interpretations, we find that the observed anomalies are not associated with a phase transition.
Spin wave acoustics of antiferromagnetic structures as magnetoacoustic metamaterials
Energy Technology Data Exchange (ETDEWEB)
Gulyaev, Yurii V; Tarasenko, Sergei V; Shavrov, Vladimir G
2011-06-30
This is a review of research results on conditions under which spatially restricted low-temperature antiferromagnets and their composites can be considered as a special class of acoustic magnetic metamaterials (magnetoacoustic metamaterials). In these, the dynamic magnetoacoustic interaction produces a number of effects that are acoustic analogs of polariton effects and which are currently intensively studied in nonmagnetic acoustic metamaterials. It is shown that the elastostatic approach to the analysis of the magnetoelastic dynamics of spatially restricted compensated magnetics is an effective tool in the search for new types of resonance acoustic anomalies, part of which are typical of the magnetostatic spin wave physics (elastostatic bulk and surface spin waves, nonuniform spin-spin resonances with their participation, etc.). (reviews of topical problems)
Spin wave acoustics of antiferromagnetic structures as magnetoacoustic metamaterials
International Nuclear Information System (INIS)
This is a review of research results on conditions under which spatially restricted low-temperature antiferromagnets and their composites can be considered as a special class of acoustic magnetic metamaterials (magnetoacoustic metamaterials). In these, the dynamic magnetoacoustic interaction produces a number of effects that are acoustic analogs of polariton effects and which are currently intensively studied in nonmagnetic acoustic metamaterials. It is shown that the elastostatic approach to the analysis of the magnetoelastic dynamics of spatially restricted compensated magnetics is an effective tool in the search for new types of resonance acoustic anomalies, part of which are typical of the magnetostatic spin wave physics (elastostatic bulk and surface spin waves, nonuniform spin-spin resonances with their participation, etc.). (reviews of topical problems)
Gu, Bo; Su, Gang; Gao, Song
2006-04-01
The magnetization process, the susceptibility, and the specific heat of the spin- 1/2 antiferromagnet (AF)-AF-ferromagnet (F) and F-F-AF trimerized quantum Heisenberg chains have been investigated by means of the transfer matrix renormalization group (TMRG) technique as well as the modified spin-wave (MSW) theory. A magnetization plateau at m=1/6 for both trimerized chains is observed at low temperature. The susceptibility and the specific heat show various behaviors for different ferromagnetic and antiferromagnetic interactions and in different magnetic fields. The TMRG results of susceptibility and the specific heat can be nicely fitted by a linear superposition of double two-level systems, where two fitting equations are proposed. Three branch excitations, one gapless excitation and two gapful excitations, for both systems are found within the MSW theory. It is observed that the MSW theory captures the main characteristics of the thermodynamic behaviors at low temperatures. The TMRG results are also compared with the possible experimental data.
Quantum kagome frustrated antiferromagnets: One route to quantum spin liquids
Mendels, Philippe; Bert, Fabrice
2016-03-01
After introducing the field of Highly Frustrated Magnetism through the quest for a quantum spin liquid in dimension higher than one, we focus on the emblematic case of the kagome network. From a theoretical point of view, the simple Heisenberg case for an antiferromagnetic kagome lattice decorated with quantum spins has been a long-standing problem, not solved yet. Experimental realizations have remained scarce for long until the discovery of herbertsmithite ZnCu3(OH)6Cl2 in 2005. This is one of the very few quantum kagome spin liquid candidates that triggered a burst of activity both on theory and experiment sides. We give a survey of theory outcomes on the "kagome" problem, review the experimental properties of that model candidate and shortly discuss them with respect to recent theoretical results. xml:lang="fr"
Spin waves in antiferromagnetically coupled bimetallic oxalates.
Reis, Peter L; Fishman, Randy S
2009-01-01
Bimetallic oxalates are molecule-based magnets with transition-metal ions M(II) and M(')(III) arranged on an open honeycomb lattice. Performing a Holstein-Primakoff expansion, we obtain the spin-wave spectrum of antiferromagnetically coupled bimetallic oxalates as a function of the crystal-field angular momentum L(2) and L(3) on the M(II) and M(')(III) sites. Our results are applied to the Fe(II)Mn(III), Ni(II)Mn(III) and V(II)V(III) bimetallic oxalates, where the spin-wave gap varies from 0 meV for quenched angular momentum to as high as 15 meV. The presence or absence of magnetic compensation appears to have no effect on the spin-wave gap. PMID:21817242
Spin-Flop Transition and a Tilted Canted Spin Structure in a Coupled Antiferromagnet
Shimahara, Hiroshi; Ito, Kazuhiro
2016-04-01
We study a uniaxial coupled Heisenberg antiferromagnet that consists of two subsystems of classical spins with small and large lengths and spin-flop transitions in a magnetic field parallel to the magnetic easy axis. It is proved that the anisotropy of inter-subsystem coupling stabilizes an asymmetric canted antiferromagnetic phase with a tilted direction of antiferromagnetism that is not perpendicular to the magnetic field. In contrast to the conventional first-order spin-flop transition, the spin-flop transition from the Néel phase to such a tilted canted antiferromagnetic (TCAF) phase is of the second order in the absence of simple anisotropic energies in the subsystems. The transition from the TCAF phase to the high-field saturated spin phase is of the second order in the strong coupling limit of the exchange interactions J1 between the small spins, whereas when J1 is finite, it becomes first-order. Therefore, in the former case, the TCAF phase converts the Néel phase continuously into the saturated phase. The transitions to the TCAF phase are accompanied by additional spontaneous symmetry breaking, causing the uniform magnetization to have a nonzero component perpendicular to the magnetic field.
International Nuclear Information System (INIS)
Highlights: • In a layered 2D cuprates the long-range order antiferromagnetism is driven mainly by the Van Hove singularity. • The long-range antiferromagnetism quickly disappear with doping away from the Van Hove singularity. • For pnictides the antiferromagnetism exists as a result of the nesting condition. • Since the doping steadily changes the nesting conditions, the antiferromagnetism and superconductivity may coexist. -- Abstract: We consider the Hubbard model in terms of the perturbative diagrammatic approach (UNF⩽1) where the interaction between two electrons with antiparallel spins in the lowest order of perturbation is described by the short-range repulsive contact (on-site) interaction (U>0). We argue that in layered 2D cuprates the long-range order antiferromagnetism is driven mainly by the Van Hove singularity, whereas in the case of pnictides the antiferromagnetism exists as a result of the nesting condition. We show that when the interaction is quite strong (UNF≈1) in the case of the Van Hove singularity the electron system undergoes the antiferromagnetic phase transition with the log-range order parameter and large insulating gap. The long-range antiferromagnetism quickly disappear, as shown, with the doping away from the Van Hove singularity, but the antiferromagnetic short-range correlation persists (UNF < 1) due to Coulomb repulsive interaction which is the mechanism for superconductivity in cuprates. We argue that in the case of pnictides the antiferromagnetism appears when the nesting conditions for the Fermi surface are met. Since the doping steadily changes the nesting conditions, the antiferromagnetism and superconductivity may coexist as has been observed in pnictides. We show that the proximity of the antiferromagnetism and superconductivity implies the repulsive interaction between electrons, which turns into attractive between quasiparticles as shown by the authors in the article published on the same issue as this one and
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Full text: In some low-dimensional quantum antiferromagnets a transition can occur between a Neel ordered ground state, characterised by gapless excitations and long range correlations, and a disordered ground state with a gap and short range correlations. The disordered phase is characterised by strong singlet formation on pairs of neighbouring spins. We have used a new analytic many body approach together with numerical series and exact diagonalisation methods to study such transitions in 1. a bilayer Heisenberg system 2. a spin analogue of the Kondo lattice model at half filling. A Letter on this work has been published. The analytic method is based on a 'bond operator' representation for spins which is used to transform the problem to an interacting Bose gas with a hardcore repulsion which is treated exactly. The results are in excellent agreement with numerical estimates, and represent a significant improvement on previous calculations
DEFF Research Database (Denmark)
Lindgård, Per-Anker
1984-01-01
The correlation theory is applied to a Heisenberg antiferromagnet in a magnetic field. Special cases covered are the ferromagnet and an anisotropic Heisenberg model. The theory includes selfconsistently correlation effects in static and dynamic properties. It is a generalization of the random......-phase approximation and is applicable to the quantum spin case for any dimension and temperature. The static susceptibilities and the excitation spectrum are calculated. Besides the spin-wave excitations a central peak is found which can be understood as coming from local longitudinal fluctuations. The results of the...... theory are exemplified by numerical calculations for the onedimensional S=1 quantum antiferromagnetic chain. Qualitative agreement is found with computer simulations on a classical chain....
Directory of Open Access Journals (Sweden)
P. Sahebsara
2006-09-01
Full Text Available The self-energy-functional approach is a powerful many-body tool to investigate different broken symmetry phases of strongly correlated electron systems. We use the variational cluster perturbation theory (also called the variational cluster approximation to investigate the interplay between the antiferromagnetism and d-wave superconductivity of κ-(ET2 X conductors. These compounds are described by the so-called dimer Hubbard model, with various values of the on-site repulsion U and diagonal hopping amplitude t. At strong coupling, our zero-temperature calculations show a transition from Néel antiferromagnetism to a spin-liquid phase with no long range order, at around t ~ 0.9. At lower values of U, we find d-wave superconductivity. Taking into account the point group symmetries of the lattice, we find a transition between dx2-y2 and dxy pairing symmetries, the latter happening for smaller values of U.
Barkhausen-like antiferromagnetic to ferromagnetic phase transition driven by spin polarized current
Energy Technology Data Exchange (ETDEWEB)
Suzuki, Ippei; Naito, Tomoyuki; Itoh, Mitsuru; Taniyama, Tomoyasu, E-mail: taniyama.t.aa@m.titech.ac.jp [Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan)
2015-08-24
We provide clear evidence for the effect of a spin polarized current on the antiferromagnetic to ferromagnetic phase transition of an FeRh wire at Co/FeRh wire junctions, where the antiferromagnetic ground state of FeRh is suppressed by injecting a spin polarized current. We find a discrete change in the current-voltage characteristics with increasing current density, which we attribute to the Barkhausen-like motion of antiferromagnetic/ferromagnetic interfaces within the FeRh wire. The effect can be understood via spin transfer, which exerts a torque to the antiferromagnetic moments of FeRh, together with non-equilibrium magnetic effective field at the interface. The conclusion is reinforced by the fact that spin unpolarized current injection from a nonmagnetic Cu electrode has no effects on the antiferromagnetic state of FeRh.
Barkhausen-like antiferromagnetic to ferromagnetic phase transition driven by spin polarized current
Suzuki, Ippei; Naito, Tomoyuki; Itoh, Mitsuru; Taniyama, Tomoyasu
2015-08-01
We provide clear evidence for the effect of a spin polarized current on the antiferromagnetic to ferromagnetic phase transition of an FeRh wire at Co/FeRh wire junctions, where the antiferromagnetic ground state of FeRh is suppressed by injecting a spin polarized current. We find a discrete change in the current-voltage characteristics with increasing current density, which we attribute to the Barkhausen-like motion of antiferromagnetic/ferromagnetic interfaces within the FeRh wire. The effect can be understood via spin transfer, which exerts a torque to the antiferromagnetic moments of FeRh, together with non-equilibrium magnetic effective field at the interface. The conclusion is reinforced by the fact that spin unpolarized current injection from a nonmagnetic Cu electrode has no effects on the antiferromagnetic state of FeRh.
Antiferromagnetically Spin Polarized Oxygen Observed in Magnetoelectric TbMn2O5
Beale, T. A. W.; Wilkins, S. B.; Johnson, R. D.; Bland, S. R.; Joly, Yves; Forrest, T. R.; McMorrow, D. F.; Yakhou, F.; Prabhakaran, D.; Boothroyd, A. T.; Hatton, P. D.
2010-01-01
We report the direct measurement of antiferromagnetic spin polarization at the oxygen sites in the multiferroic TbMn2O5, through resonant soft x-ray magnetic scattering. This supports recent theoretical models suggesting that the oxygen spin polarization is key to the magnetoelectric coupling mechanism. The spin polarization is observed through a resonantly enhanced diffraction signal at the oxygen K edge at the commensurate antiferromagnetic wave vector. Using the fdmnes code we have accurat...
Quantum entanglement in trimer spin-1/2 Heisenberg chains with antiferromagnetic coupling
Del Cima, O M; da Silva, S L L
2015-01-01
The quantum entanglement measure is determined, for the first time, for antiferromagnetic trimer spin-1/2 Heisenberg chains. The physical quantity proposed to measure the entanglement is the distance between states by adopting the Hilbert-Schmidt norm. The method is applied to the new magnetic Cu(II) trimer system, 2b.3CuCl_2.2H_2O, and to the trinuclear Cu(II) halide salt, (3MAP)_2Cu_2Cl_8. The decoherence temperature, above which the entanglement is suppressed, is determined for the both systems. A correlation among their decoherence temperatures and their respective exchange coupling constants is established.
Spin liquid nature in the Heisenberg J1-J2 triangular antiferromagnet
Iqbal, Yasir; Hu, Wen-Jun; Thomale, Ronny; Poilblanc, Didier; Becca, Federico
2016-04-01
We investigate the spin-1/2 Heisenberg model on the triangular lattice in the presence of nearest-neighbor J1 and next-nearest-neighbor J2 antiferromagnetic couplings. Motivated by recent findings from density-matrix renormalization group (DMRG) claiming the existence of a gapped spin liquid with signatures of spontaneously broken lattice point group symmetry [Zhu and White, Phys. Rev. B 92, 041105 (2015), 10.1103/PhysRevB.92.041105 and Hu, Gong, Zhu, and Sheng, Phys. Rev. B 92, 140403 (2015), 10.1103/PhysRevB.92.140403], we employ the variational Monte Carlo (VMC) approach to analyze the model from an alternative perspective that considers both magnetically ordered and paramagnetic trial states. We find a quantum paramagnet in the regime 0.08 ≲J2/J1≲0.16 , framed by 120∘ coplanar (stripe collinear) antiferromagnetic order for smaller (larger) J2/J1 . By considering the optimization of spin-liquid wave functions of a different gauge group and lattice point group content as derived from Abrikosov mean-field theory, we obtain the gapless U(1 ) Dirac spin liquid as the energetically most preferable state in comparison to all symmetric or nematic gapped Z2 spin liquids so far advocated by DMRG. Moreover, by the application of few Lanczos iterations, we find the energy to be the same as the DMRG result within error bars. To further resolve the intriguing disagreement between VMC and DMRG, we complement our methodological approach by the pseudofermion functional renormalization group (PFFRG) to compare the spin structure factors for the paramagnetic regime calculated by VMC, DMRG, and PFFRG. This model promises to be an ideal test bed for future numerical refinements in tracking the long-range correlations in frustrated magnets.
Spin-S kagome quantum antiferromagnets in a field with tensor networks
Picot, Thibaut; Ziegler, Marc; Orús, Román; Poilblanc, Didier
2016-02-01
Spin-S Heisenberg quantum antiferromagnets on the kagome lattice offer, when placed in a magnetic field, a fantastic playground to observe exotic phases of matter with (magnetic analogs of) superfluid, charge, bond, or nematic orders, or a coexistence of several of the latter. In this context, we have obtained the (zero-temperature) phase diagrams up to S =2 directly in the thermodynamic limit owing to infinite projected entangled pair states, a tensor network numerical tool. We find incompressible phases characterized by a magnetization plateau versus field and stabilized by spontaneous breaking of point group or lattice translation symmetry(ies). The nature of such phases may be semiclassical, as the plateaus at the 1/3th ,(1-2/9S)th, and (1-1/9S)th of the saturated magnetization (the latter followed by a macroscopic magnetization jump), or fully quantum as the spin-1/2 1/9 plateau exhibiting a coexistence of charge and bond orders. Upon restoration of the spin rotation U (1 ) symmetry, a finite compressibility appears, although lattice symmetry breaking persists. For integer spin values we also identify spin gapped phases at low enough fields, such as the S =2 (topologically trivial) spin liquid with no symmetry breaking, neither spin nor lattice.
Spin torque antiferromagnetic nanooscillator in the presence of magnetic noise
Directory of Open Access Journals (Sweden)
H. Gomonay
2012-12-01
Full Text Available Spin-torque effects in antiferromagnetic (AFM materials are of great interest due to the possible applications as high-speed spintronic devices. In the present paper we analyze the statistical properties of the current-driven AFM nanooscillator that result from the white Gaussian noise of magnetic nature. According to the peculiarities of deterministic dynamics, we derive the Langevin and Fokker-Planck equations in the energy representation of two normal modes. We find the stationary distribution function in the subcritical and overcritical regimes and calculate the current dependence of the average energy, energy fluctuation and their ratio (quality factor. The noncritical mode shows the Boltzmann statistics with the current-dependent effective temperature in the whole range of the current values. The effective temperature of the other, i.e., soft, mode critically depends on the current in the subcritical region. Distribution function of the soft mode follows the Gaussian law above the generation threshold. In the overcritical regime, the total average energy and the quality factor grow with the current value. This raises the AFM nanooscillators to the promising candidates for active spintronic components.
Probing Spatial Spin Correlations of Ultracold Gases by Quantum Noise Spectroscopy
Bruun, G.; Andersen, Brian; Sørensen, Anders; Demler, Eugene A.
2009-01-01
Spin noise spectroscopy with a single laser beam is demonstrated theoretically to provide a direct probe of the spatial correlations of cold fermionic gases. We show how the generic many-body phenomena of anti-bunching, pairing, antiferromagnetic, and algebraic spin liquid correlations can be revealed by measuring the spin noise as a function of laser width, temperature, and frequency.
Bootstrap equations and correlation functions for the Heisenberg XYZ antiferromagnet
Quano, Yas-Hiro
2002-01-01
Presented are two kinds of integral solutions to the quantum Knizhnik-Zamolodchikov equations for the 2n-point correlation functions of the Heisenberg XYZ antiferromagnet. Our first integral solution can be obtained from those for the cyclic SOS model by using the vertex-face correspondence. By the construction, the sum with respect to the local height variables k_0, k_1, >..., k_{2n} of the cyclic SOS model remains other than n-fold integral in the first solution. In order to perform those s...
International Nuclear Information System (INIS)
We investigate magnetism and quantum phase transitions in a one-dimensional system of integrable spin-1 bosons with strongly repulsive density-density interaction and antiferromagnetic spin-exchange interaction via the thermodynamic Bethe ansatz method. At zero temperature, the system exhibits three quantum phases: (i) a singlet phase of boson pairs when the external magnetic field H is less than the lower critical field Hc1; (ii) a ferromagnetic phase of atoms in the hyperfine state |F=1, mF=1> when the external magnetic field exceeds the upper critical field Hc2; and (iii) a mixed phase of singlet pairs and unpaired atoms in the intermediate region Hc1c2. At finite temperatures, the spin fluctuations affect the thermodynamics of the model through coupling the spin bound states to the dressed energy for the unpaired mF=1 bosons. However, such spin dynamics is suppressed by a sufficiently strong external field at low temperatures. Thus the singlet pairs and unpaired bosons may form a two-component Luttinger liquid in the strong coupling regime.
Antiferromagnetic Heisenberg Spin Chain of a Few Cold Atoms in a One-Dimensional Trap
Murmann, S.; Deuretzbacher, F.; Zürn, G.; Bjerlin, J.; Reimann, S. M.; Santos, L.; Lompe, T.; Jochim, S.
2015-11-01
We report on the deterministic preparation of antiferromagnetic Heisenberg spin chains consisting of up to four fermionic atoms in a one-dimensional trap. These chains are stabilized by strong repulsive interactions between the two spin components without the need for an external periodic potential. We independently characterize the spin configuration of the chains by measuring the spin orientation of the outermost particle in the trap and by projecting the spatial wave function of one spin component on single-particle trap levels. Our results are in good agreement with a spin-chain model for fermionized particles and with numerically exact diagonalizations of the full few-fermion system.
Nuclear spin-magnon relaxation in two-dimensional Heisenberg antiferromagnets
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Experiments are discussed of the dependence on temperature and magnetic field of the longitudinal relaxation time of single crystals of antiferromagnetically ordered insulators, i.e. in the temperature range below the Neel temperature and in fields up to the spin-flop transition. The experiments are done on 19F nuclei in the Heisenberg antiferromagnets K2MnF4 and K2NiF4, the magnetic structure of which is two-dimensional quadratic. (C.F.)
Frustration in a transverse Ising nanoisland with an antiferromagnetic spin configuration
Energy Technology Data Exchange (ETDEWEB)
Kaneyoshi, T., E-mail: kaneyosi@is.nagoya-u.ac.Jp
2015-09-01
The phase diagrams, saturation magnetizations and temperature dependences of magnetizations in a transverse Ising nanoisland with an antiferromagnetic spin configuration are studied by the uses of the effective-field theory with correlations (EFT) and the mean-field approximation (MFA), in order to clarify whether the MFA can be successfully applied to the theoretical discussions of naonoislands. From these investigations, we have found a lot of unexpected characteristic phenomena in these properties, when the value of an interlayer coupling takes a large value. We have also found that the applications of the MFA to the magnetic properties are extremely restricted for nanoislands, when the value of an interlayer coupling takes a large value, in contrast to a number of bulk studies.
DEFF Research Database (Denmark)
Kenzelmann, M.; Cowley, R.A.; Buyers, W.J.L.; Coldea, R.; Enderle, M.; McMorrow, D.F.
2002-01-01
We have mapped from the quantum to the classical limit the spin excitation spectrum of the antiferromagnetic spin-1 Heisenberg chain system CsNiCl3 in its paramagnetic phase from T=5 to 200 K. Neutron scattering shows that the excitations are resonant and dispersive up to at least T=70 Ksimilar o...... the experiment is not consistent with the random phase approximation for coupled quantum chains. At T=200 K, the structure factor and second energy moment of the excitation spectrum are in excellent agreement with the high-temperature series expansion.......We have mapped from the quantum to the classical limit the spin excitation spectrum of the antiferromagnetic spin-1 Heisenberg chain system CsNiCl3 in its paramagnetic phase from T=5 to 200 K. Neutron scattering shows that the excitations are resonant and dispersive up to at least T=70 Ksimilar or...... agreement with quantum Monte Carlo calculations for the spin-1 chain. xi is also consistent with the single mode approximation, suggesting that the excitations are short-lived single particle excitations. Below T=12 K where three-dimensional spin correlations are important, xi is shorter than predicted and...
Large inverse spin Hall effect in the antiferromagnetic metal Ir20Mn80
Mendes, J. B. S.; Cunha, R. O.; Alves Santos, O.; Ribeiro, P. R. T.; Machado, F. L. A.; Rodríguez-Suárez, R. L.; Azevedo, A.; Rezende, S. M.
2014-04-01
A spin current is usually detected by converting it into a charge current through the inverse spin Hall effect (ISHE) in thin layers of a nonmagnetic metal with large spin-orbit coupling, such as Pt, Pd, and Ta. Here we demonstrate that Ir20Mn80, a high-temperature antiferromagnetic metal that is commonly employed in spin-valve devices, exhibits a large inverse spin Hall effect, as recently predicted theoretically. We present results of experiments in which the spin currents are generated either by microwave spin pumping or by the spin Seebeck effect in bilayers of singe-crystal yttrium iron garnet (YIG)/Ir20Mn80 and compare them with measurements in YIG/Pt bilayers. The results of both measurements are consistent, showing that Ir20Mn80 has a spin Hall angle similar to Pt, and that it is an efficient spin-current detector.
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It has been proposed that antiferromagnetic Fe adatom spins on semiconductor Cu–N surfaces can be used to store information (Loth et al 2012 Science 335 196). Here, we investigate spin dynamics of such antiferromagnetic systems through Monte Carlo simulations. We find out the temperature and size laws of switching rates of Néel states and show that the Néel states can become stable enough for the information storage when the number of spins reaches one or two dozens of the Fe spins. We also explore promising methods for manipulating the Néel states. These could help realize information storage with such antiferromagnetic spin systems. (paper)
Energy Technology Data Exchange (ETDEWEB)
Deng, Xiao-Yan [Graduate School, Tianjin Polytechnic University, Tianjin 300387 (China); Dou, Jun-Ya [Department of Physics, Tianjin Polytechnic University, Tianjin 300387 (China); Liu, Guang-Hua, E-mail: liuguanghua@tjpu.edu.cn [Department of Physics, Tianjin Polytechnic University, Tianjin 300387 (China)
2015-10-15
The magnetization process of a spin-1/2 J{sub 1}–J{sub 1}–J{sub 2}–J{sub 2} tetrameric Heisenberg chain is investigated by the infinite time-evolving block decimation (iTEBD) method. A magnetization phase diagram including three different phases, i.e., a fully polarized (FP) phase, a 1/2 plateau phase, and a spin-fluid (SF) phase, is obtained. All the quantum phase transitions (QPTs) are determined to belong to the second-order category, and the central charge in the critical SF phase equals 1. In addition, a 1/2 plateau phase also exists in the classical J{sub 1}–J{sub 1}–J{sub 2}–J{sub 2} tetrameric Ising chain. The F–F–AF–AF (or AF–AF–F–F) type longitudinal correlation is found to be important and necessary for the appearance of the 1/2 plateau state in both quantum and classical cases. - Highlights: • 1/2 magnetization plateau can be realized in both quantum and classical cases. • 1/2 plateau is characterized by constant magnetization, entanglement and correlation. • Central charge of the spin-fluid phase is determined to be 1. • F–F–AF–AF correlation is important for the appearance of the 1/2 plateau.
Spin polaron in two-dimensional antiferromagnetics - from local singlet to compound quasi-particle
Barabanov, A F; Belemuk, A M
2002-01-01
The basic theoretical concepts, related to the spin polaron scenario for the charge excitations in the two-dimensional antiferromagnetics, are presented. The distinctive peculiarity of the developed approach consists in consideration of the local polaron as the zero approximation for the quasi-particles. On the following stage this excitation is coated into the antiferromagnetic spin waves and the radius intermediate polaron is formed. The method makes it possible to continuously describe the transition from the zero temperatures to the finite ones and to consider the wide doping range. The above approach explains basic results of the ARPES-experiments in the CuO sub 2 plane
Antiferromagnetic spin and twin domain walls govern hysteretic expressions of exchange anisotropy
Armstrong, Jason N.; Sullivan, Matthew R.; Chopra, Harsh Deep
2009-09-01
The present study shows that antiferromagnetic spin and twin domain walls govern the hysteretic expressions of exchange anisotropy at low and high fields, respectively, using annealed NiO single crystals and Co. In the presence of twin walls, spin walls are shown to be a geometrical necessity in the antiferromagnetic NiO. A threshold field (˜10000Oe) exists below which twin walls are frozen, and rotational hysteresis is dominated by losses due to spin walls. Above the threshold field, twin walls become mobile, resulting in a sharp increase in rotational hysteresis. Remarkably, rotational hysteresis associated with spin walls is similar to that of an ordinary ferromagnet—as the field strength increases, rotational hysteresis tends toward zero. However, unlike an ordinary ferromagnet where rotational hysteresis becomes zero above its saturation field, rotational hysteresis in antiferromagnet drops but then sharply increases once the threshold field for twin wall motion is exceeded. In crystals without spin walls, low-field rotational hysteresis is zero or negligible. Domain imaging of twin walls in antiferromagnet and Weiss walls in ferromagnet reveals a one-to-one spatial correlation even though twin walls are considered to have no net dipoles. This surprising result is explained by the fact that crystallographic interfaces in real crystals are not atomically sharp or ideal, and the defective interface invariably results in net moment across the finite width of the twin wall. The field dependence of domain walls in Co film exchange coupled to NiO shows global similarities to previously reported behavior of Co films deposited on nanocrystalline NiO [H. D. Chopra, D. X. Yang, P. J. Chen, H. J. Brown, L. J. Swartzendruber, and W. F. Egelhoff, Jr., Phys. Rev. B 61, 15312 (2000)]. In both cases, domain wall motion is not the dominant mode of magnetization reversal (wall motion is entirely absent in the present study while wall motion was only occasionally observed in
International Nuclear Information System (INIS)
Antiferromagnetic semiconductors gain increasing interest due to their possible application in spintronics. Using spin polarized scanning tunneling microscopy operating in a vector field, we mapped the noncollinear antiferromagnetic spin structure of a semiconducting hexagonal FeSe surface on the atomic scale. The surface possesses an in-plane compensated Néel structure which is further confirmed by first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Zhang, K. F.; Yang, Fang; Song, Y. R. [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Zhang, Xiaole [Institute of Natural Sciences, Shanghai Jiao Tong University, Shanghai 200240 (China); The State Key Laboratory of Advanced Optical Communication Systems and Networks, Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Chen, Xianfeng [The State Key Laboratory of Advanced Optical Communication Systems and Networks, Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Liu, Canhua; Qian, Dong; Gao, C. L., E-mail: clgao@sjtu.edu.cn; Jia, Jin-Feng [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing (China); Luo, Weidong, E-mail: wdluo@sjtu.edu.cn [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Institute of Natural Sciences, Shanghai Jiao Tong University, Shanghai 200240 (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing (China)
2016-02-08
Antiferromagnetic semiconductors gain increasing interest due to their possible application in spintronics. Using spin polarized scanning tunneling microscopy operating in a vector field, we mapped the noncollinear antiferromagnetic spin structure of a semiconducting hexagonal FeSe surface on the atomic scale. The surface possesses an in-plane compensated Néel structure which is further confirmed by first-principles calculations.
International Nuclear Information System (INIS)
The spin dynamics of an S = 1, two dimensional (2D) square lattice antiferromagnet, La2NiO4 was studied by neutron scattering experiments in wide energy (E N), the spin wave excitations of La2NiO4 are well described by a classical spin wave theory. The nearest-neighbor-exchange coupling constant, the in-plane and the out-of-plane anisotropy constants at 10 K were determined to be 28.7±0.7 meV, 0.10±0.02 meV and 1.26±0.12 meV, respectively. Above TN, the 2D spin fluctuation was observed over 600 K. The critical slowing down behavior of the fluctuation was observed in the enhancement of the low energy component toward TN. On the other hand, the high energy component is hardly affected by the three dimensional magnetic transition and still exists even at TN as observed in La2CuO4. The spin correlation length and the static structure factor at the 2D zone center were measured and compared with theoretical calculations for 2D Heisenberg antiferromagnets. (author)
Institute of Scientific and Technical Information of China (English)
JI An-Chun; TIAN Guang-Shan
2006-01-01
In the present paper, we calculate the Gaussian correction to the critical value Jc⊥ caused by quantum spin fluctuation in a two-dimensional spatially anisotropic Heisenberg antiferromagnet with integer spin S. Previously, someauthors computed this quantity by the mean-field theory based on the Schwinger boson representation of spin operators.However, for S = 1, their result is much less than the one derived by numerical calculations. By taking the effect ofquantum spin fluctuation into consideration, we are able to produce a greatly improved result.
Thermodynamic functions for a model antiferromagnet with identical coupling between all spins
International Nuclear Information System (INIS)
A model antiferromagnet consisting of N spins S=1/2, all interacting among themselves with equal strength, and with the external magnetic field H, was analysed, both for Ising spins and vector spins. Starting from the Hamiltonian, the partition function, specific heat and magnetic susceptibility vs temperature T have been calculated for both systems, for finite N (with the interspin coupling I < 0) and for N →∞ (with the coupling I/N < 0). For finite N one finds several relations between the features of the energy levels and the calculated plots, related especially to the number of spins being odd or even. The 1/(NT) behavior of the susceptibility at T→0 for odd N has been interpreted as due to the occurrence of a single frustrated spin pushing the whole system to behave like the free spin in the external magnetic field. For N→∞ (thermodynamic limit) the Kac procedure has been extended to include the effect of magnetic field, both for Ising spins and the vector spins. As compared with the ferromagnetic case, the evaluation of the partition function and related functions is in the case of antiferromagnetic coupling (I < 0) relatively straightforward. We have found the specific heat (per one spin) vs T at finite magnetic field to be proportional to the squared field, turning to zero at the absence of the field. The magnetic susceptibility (per one spin) shows a regular behavior of the paramagnetic type at all temperatures. (author)
19F spin-lattice relaxation in the cubic antiferromagnet KNiF3
Engelsberg, M.
1980-06-01
The temperature dependence of the 19F spin-lattice relaxation in the cubic quasi-isotropic antiferromagnet KNiF3 is studied experimentally and theoretically. Quantitative agreement with measured relaxation rates is obtained over a considerable temperature range by assuming a two-magnon relaxation process in the "domain-flopped" state.
Room temperature spin-polarizations of Mn-based antiferromagnetic nanoelectrodes
Energy Technology Data Exchange (ETDEWEB)
Yamada, Toyo Kazu, E-mail: toyoyamada@faculty.chiba-u.jp [Graduate School of Advanced Integration Science, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba-shi 263-8522, Chiba (Japan); Vazquez de Parga, Amadeo L. [Instituto Madrileño de Estudios Avanzados en Nanociencia IMDEA-Nanociencia and Dep. Fisica de la Materia Condensada, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid (Spain)
2014-11-03
Antiferromagnets produce no stray field, and therefore, a tip electrode made of antiferromagnetic material has been considered to be the most suitable choice to measure such as magnetoresistance (MR) through single isolated magnetic nanoparticles, molecules, and ultrathin films. Spin polarizations (P) of antiferromagnetic 3-nm, 6-nm, and annealed 3-nm Mn films grown on W tips with a bcc(110) apex as well as bulk-NiMn tips were obtained at 300 K by measuring MR in ultrahigh vacuum by means of spin-polarized scanning tunneling microscopy using a layerwise antiferromagnetically stacking bct-Mn(001) film electrode. The Mn-coated tips with coverages of 3 and 6 nm exhibited P values of 1 ± 1% and 3 ± 2%, respectively, which tips likely contain α- or strained Mn. With a thermal assist, the crystalline quality and the magnetic stability of the film could increase. The annealed tip exhibited P = 9 ± 2%. The bulk-NiMn tips exhibit spin polarizations of 0 or 6 ± 2% probably depending on the chemical species (Mn or Ni) present at the apex of the tip. Fe-coated W tips were used to estimate the bct-Mn(001) film spin polarization.
Soliton Confinement and the Excitation Spectrum of Spin-Peierls Antiferromagnets
Affleck, Ian
1997-01-01
The excitation spectrum of spin-Peierls antiferromagnets is discussed taking into acount phonon dynamics but treating inter-chain elastic couplings in mean field theory. This gives a ladder of soliton -anti-soliton boundstates, with no soliton continuum, until soliton deconfinement takes place at a transition into a non-dimerized phase.
Engelsberg, M.; Albino O. de Aguiar, J.
1985-04-01
The results of measurements on the magnetic field and temperature dependences of the 19F nuclear-spin lattice relaxation time T1 in KNiF3 for TKNiF3. Some similarities in the behavior of both systems suggest that a common mechanism may be responsible for spin-lattice relaxation in either case. We discuss the possibility that this mechanism may involve a diffusive mode below TN with a central peak in the relevant magnetic-ion spin correlation function.
Coffey, David; Diez-Ferrer, José Luis; Serrate, David; Ciria, Miguel; de la Fuente, César; Arnaudas, José Ignacio
2015-01-01
High-density magnetic storage or quantum computing could be achieved using small magnets with large magnetic anisotropy, a requirement that rare-earth iron alloys fulfill in bulk. This compelling property demands a thorough investigation of the magnetism in low dimensional rare-earth iron structures. Here, we report on the magnetic coupling between 4f single atoms and a 3d magnetic nanoisland. Thulium and lutetium adatoms deposited on iron monolayer islands pseudomorphically grown on W(110) have been investigated at low temperature with scanning tunneling microscopy and spectroscopy. The spin-polarized current indicates that both kind of adatoms have in-plane magnetic moments, which couple antiferromagnetically with their underlying iron islands. Our first-principles calculations explain the observed behavior, predicting an antiparallel coupling of the induced 5d electrons magnetic moment of the lanthanides with the 3d magnetic moment of iron, as well as their in-plane orientation, and pointing to a non-contribution of 4f electrons to the spin-polarized tunneling processes in rare earths. PMID:26333417
Simple model for non-Fermi-liquid behavior induced by antiferromagnetic spin fluctuations
International Nuclear Information System (INIS)
We consider a simple model for itinerant antiferromagnetism consisting of an electron pocket and a hole pocket separated by a wave vector Q. The nesting of the Fermi surfaces leads to a spin-density wave instability for repulsive Hubbard coupling and to charge-density waves for an attractive interaction. The order can gradually be suppressed by mismatching the nesting and a quantum critical point is obtained as TN→0. In the disordered phase perturbative corrections are logarithmic in the external frequency or the temperature. We investigate the renormalization-group flow of the model in leading and next-to-leading logarithmic order. The linear-response correlation functions for spin-density and charge-density waves are calculated. The specific-heat γ coefficient and the uniform magnetic-field susceptibility increase on a logarithmic scale when the temperature is lowered. The Wilson ratio is temperature dependent and nonuniversal. The Fermi-liquid picture breaks down at the ordering temperature TN or at a quantum critical point. Our results are valid in the disordered phase for weak and intermediate coupling, but not in the critical region. The results are discussed in the context of non-Fermi-liquid behavior found in some heavy fermion compounds (the two pockets are then part of the Fermi surface of the heavy electron bands). copyright 1999 The American Physical Society
Anomalous Curie response of an impurity in a quantum critical spin-1/2 Heisenberg antiferromagnet
Höglund, Kaj; Sandvik, Anders
2007-03-01
There is a disagreement concerning the low-temperature (T) magnetic susceptibility χ^zimp˜C/T of a spin-S impurity in a nearly quantum critical antiferromagnetic host. Field-theoretical work [1] predicted an anomalous Curie constant S^2/30 quantum Monte Carlo simulations in order to resolve the controversy. Our main result is for a vacancy in a quantum critical spin-1/2 Heisenberg antiferromagnet on a bilayer lattice. In our susceptibility data for the S=1/2 impurity we observe a Curie constant C=0.262(2). Although the value falls outside the predicted range, it should correspond to an anomalous impurity response, as proposed in Ref. [1]. [1] S. Sachdev, C. Buragohain, and M. Vojta, Science 286, 2479 (1999); M. Vojta, C. Buragohain, and S. Sachdev, Phys. Rev. B 61, 15152 (2000). [2] O. P. Sushkov, Phys. Rev. B 62, 12135 (2000). [3] M. Troyer, Prog. Theor. Phys. Supp. 145, 326 (2002).
LETTER TO THE EDITOR: Parity-broken ground state for the spin-1 pyrochlore antiferromagnet
Yamashita, Yasufumi; Ueda, Kazuo; Sigrist, Manfred
2001-12-01
The ground-state properties of the spin-1 pyrochlore antiferromagnet are studied by applying the VBS-like tetrahedron-unit decomposition to the original spin system. The symmetrization required on every vertex is taken into account by introducing a ferromagnetic coupling. The pairwise effective Hamiltonian between the adjacent tetrahedrons is obtained by considering the next nearest neighbour and the third neighbour exchange interactions. We find that the transverse component of the spin chirality exhibits a long-range order, breaking the parity symmetry of the tetrahedral group, while the chirality itself is not broken.
Spin squeezing and quantum correlations
Indian Academy of Sciences (India)
K S Mallesh; Swarnamala Sirsi; Mahmoud A A Sbaih; P N Deepak; G Ramachandran
2002-08-01
We discuss the notion of spin squeezing considering two mutually exclusive classes of spin- states, namely, oriented and non-oriented states. Our analysis shows that the oriented states are not squeezed while non-oriented states exhibit squeezing. We also present a new scheme for construction of spin- states using 2 spinors oriented along different axes. Taking the case of = 1, we show that the `non-oriented’ nature and hence squeezing arise from the intrinsic quantum correlations that exist among the spinors in the coupled state.
Antiferromagnetic order and spin glass behavior in Dy{sub 2}CuIn{sub 3}
Energy Technology Data Exchange (ETDEWEB)
Siouris, I.M., E-mail: jsiou@pme.duth.gr [Democritus University of Thrace (DUTH), Production and Management Engineering Department, Materials Laboratory, 67100 Xanthi (Greece); Kremer, R.K. [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, D-70569 Stuttgart (Germany); Hoelzel, M. [Technische Universitaet Muenchen, Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II), 85748 Garching (Germany)
2011-11-15
The magnetic properties of the intermetallic compound Dy{sub 2}CuIn{sub 3} have been investigated. Ac and dc-susceptibility measurements indicate an onset of antiferromagnetic ordering at T{sub N}=19.5 K and an additional frequency dependent transition at T{sub ds}{approx}9 K. Neutron diffraction studies confirm the ordered transition at 19.5{+-}1 K. The magnetic unit cell can be described by the propagation vector k=(0.25,0.25,0) with the magnetic moment {mu}=2.63(4){mu}{sub B}/Dy{sup 3+} parallel to the c-axis. Nevertheless, neutron diffraction reveals no additional magnetic phase transition around or below 9 K, which suggests that, at lower temperatures, a spin glass state may be formed in coexistence with the antiferromagnetic mode as a result of frustration and the antagonism between ferromagnetic and antiferromagnetic exchange interactions. - Highlights: > Dy{sub 2}CuIn{sub 3} is characterized by the dominance of antiferromagnetic (AF) interactions. > Geometric frustration and crystal field effects prevent the formation of the full magnetic moment on the Dy ions. > Two magnetic regimes are recognized: an AF state and a mixed AF-glassy state. > The antiferromagnetic structure of the compound has been determined.
Jungwirth, T.; Marti, X.; Wadley, P.; Wunderlich, J.
2016-03-01
Antiferromagnetic materials are internally magnetic, but the direction of their ordered microscopic moments alternates between individual atomic sites. The resulting zero net magnetic moment makes magnetism in antiferromagnets externally invisible. This implies that information stored in antiferromagnetic moments would be invisible to common magnetic probes, insensitive to disturbing magnetic fields, and the antiferromagnetic element would not magnetically affect its neighbours, regardless of how densely the elements are arranged in the device. The intrinsic high frequencies of antiferromagnetic dynamics represent another property that makes antiferromagnets distinct from ferromagnets. Among the outstanding questions is how to manipulate and detect the magnetic state of an antiferromagnet efficiently. In this Review we focus on recent works that have addressed this question. The field of antiferromagnetic spintronics can also be viewed from the general perspectives of spin transport, magnetic textures and dynamics, and materials research. We briefly mention this broader context, together with an outlook of future research and applications of antiferromagnetic spintronics.
Evidence for asymmetric rotation of spins in antiferromagnetic exchange-spring
Wang, Y. Y.; Song, C.; Wang, G. Y.; Zeng, F.; Pan, F.
2014-12-01
We demonstrate an asymmetric rotation of the antiferromagnetic (AFM) spins in the exchange-spring driven by perpendicularly magnetized Co/Pt. The static and dynamic behaviors of the twisted spin structure are directly revealed by a combination of element specific soft-x-ray absorption spectra and magnetoresistance measurements. X-ray magnetic linear dichroism spectra as a function of AFM thickness clarify the features of the whole exchange-spring, while the interfacial uncompensated spins are identified by the x-ray magnetic circular dichroism spectra. Moreover, the observed tunneling anisotropic magnetoresistance (TAMR) in AFM-based junctions based on this asymmetric rotation provides an electrical approach to monitoring the dynamic twist of the AFM spins. These investigations not only provide a deep insight into the spin structure of the exchange coupling layers but would also advance the development of AFM spintronics.
Evidence for asymmetric rotation of spins in antiferromagnetic exchange-spring
International Nuclear Information System (INIS)
We demonstrate an asymmetric rotation of the antiferromagnetic (AFM) spins in the exchange-spring driven by perpendicularly magnetized Co/Pt. The static and dynamic behaviors of the twisted spin structure are directly revealed by a combination of element specific soft-x-ray absorption spectra and magnetoresistance measurements. X-ray magnetic linear dichroism spectra as a function of AFM thickness clarify the features of the whole exchange-spring, while the interfacial uncompensated spins are identified by the x-ray magnetic circular dichroism spectra. Moreover, the observed tunneling anisotropic magnetoresistance (TAMR) in AFM-based junctions based on this asymmetric rotation provides an electrical approach to monitoring the dynamic twist of the AFM spins. These investigations not only provide a deep insight into the spin structure of the exchange coupling layers but would also advance the development of AFM spintronics. (paper)
International Nuclear Information System (INIS)
The competition among spin glass (SG), antiferromagnetism (AF) and local pairing superconductivity (PAIR) is studied in a two-sublattice fermionic Ising SG model with a local BCS pairing interaction in the presence of a transverse magnetic field Γ. The spins in different sublattices interact with Gaussian random couplings with an antiferromagnetic mean. The problem is formulated in a Grassmann path integral formalism. The static ansatz and the replica symmetry are used to obtain the half-filling thermodynamic potential. The results are shown in phase diagrams that exhibit a complex transition line separating the PAIR phase from the others. This line is second order at high temperature which ends in a tricritical point. The presence of Γ affects deeply the transition lines
Disorder effects in the S=1 antiferromagnetic spin ladder CaV2O4
Guitarra, S. R.; Caneiro, A.; Niebieskikwiat, D.
2015-10-01
We study the physical properties of the antiferromagnetic spin ladder CaV2O4 (CVO) and the Y-doped related compound Ca0.9Y0.1V2O4. In the latter, X-ray diffraction demonstrates the segregation of a small amount of a vanadium-perovskite impurity phase, leading to the formation of V vacancies within the main CVO-type structure. The 1D character of this calcium-vanadite enhances the influence of the vacancies on the electric and magnetic properties of Ca0.9Y0.1V2O4. Electrical transport is characterized by a variable-range hopping mechanism determined by the charging energy of nm-sized segments of V chains delimited by V vacancies, i.e. a Coulomb gap is formed at the Fermi level. These vacancies also locally affect the magnetic correlations, breaking the long-range AFM order observed in CaV2O4 and producing exchange bias when the Y-doped sample is cooled with an applied magnetic field.
Block-Spin Approach to Electron Correlations
Monthoux, P.
1997-01-01
We consider an expansion of the ground state wavefunction of quantum lattice many-body systems in a basis whose states are tensor products of block-spin wavefunctions. We demonstrate by applying the method to the antiferromagnetic spin-1/2 chain that by selecting the most important many-body states the technique affords a severe truncation of the Hilbert space while maintaining high accuracy.
Spinon dynamics in quantum integrable antiferromagnets
Vlijm, R.; Caux, J.-S.
2016-05-01
The excitations of the Heisenberg antiferromagnetic spin chain in zero field are known as spinons. As pairwise-created fractionalized excitations, spinons are important in the understanding of inelastic neutron scattering experiments in (quasi-)one-dimensional materials. In the present paper, we consider the real space-time dynamics of spinons originating from a local spin flip on the antiferromagnetic ground state of the (an)isotropic Heisenberg spin-1/2 model and the Babujan-Takhtajan spin-1 model. By utilizing algebraic Bethe ansatz methods at finite system size to compute the expectation value of the local magnetization and spin-spin correlations, spinons are visualized as propagating domain walls in the antiferromagnetic spin ordering with anisotropy dependent behavior. The spin-spin correlation after the spin flip displays a light cone, satisfying the Lieb-Robinson bound for the propagation of correlations at the spinon velocity.
Effect of next-nearest neighbor hopping on the spin dynamics in antiferromagnets
Morr, Dirk K.
1998-01-01
Recently, inelastic neutron scattering (INS) experiments on the insulating parent compounds of high-T_c materials were analyzed to extract the value of the superexchange constant $J$. Starting point of the analysis was the nearest-neighbor Heisenberg model. Motivated by recent ARPES experiments, we consider the effects of a next-nearest neighbor hopping, $t'$ in the strong coupling limit of the spin-density wave formalism, where it leads to an antiferromagnetic exchange $J'>0$ between next-ne...
Spin-Lattice-Coupled Order in Heisenberg Antiferromagnets on the Pyrochlore Lattice
Aoyama, Kazushi; Kawamura, Hikaru
2016-06-01
Effects of local lattice distortions on the spin ordering are investigated for the antiferromagnetic classical Heisenberg model on the pyrochlore lattice. It is found by Monte Carlo simulations that the spin-lattice coupling (SLC) originating from site phonons induces a first-order transition into two different types of collinear magnetic ordered states. The state realized at the stronger SLC is cubic symmetric characterized by the magnetic (1/2 ,1/2 ,1/2 ) Bragg peaks, while that at the weaker SLC is tetragonal symmetric characterized by the (1,1,0) ones, each accompanied by the commensurate local lattice distortions. Experimental implications to chromium spinels are discussed.
Spin frustration effects in an odd-member antiferromagnetic ring and the magnetic Mobius strip
Energy Technology Data Exchange (ETDEWEB)
Cador, Olivier [Laboratory of Molecular Magnetism, Department of Chemistry and UdR INSTM, Universita degli Studi di Firenze, Via Lastruccia n. 3, 50019 Sesto Fiorentino (Italy); Gatteschi, Dante [Laboratory of Molecular Magnetism, Department of Chemistry and UdR INSTM, Universita degli Studi di Firenze, Via Lastruccia n. 3, 50019 Sesto Fiorentino (Italy); Sessoli, Roberta [Laboratory of Molecular Magnetism, Department of Chemistry and UdR INSTM, Universita degli Studi di Firenze, Via Lastruccia n. 3, 50019 Sesto Fiorentino (Italy)]. E-mail: roberta.sessoli@unifi.it; Barra, Anne-Laure [Laboratoire des Champs Magnetiques Intenses-CNRS, F-38042 Grenoble Cede 9 (France); Timco, Grigore A. [Department of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL (United Kingdom); Winpenny, Richard E.P. [Department of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL (United Kingdom)
2005-04-15
The magnetic properties of the first odd-member antiferromagnetic ring comprising eight chromium(III) ions, S=32 spins, and one nickel(II) ion, S=1 spin, are investigated. The ring possesses an even number of unpaired electrons and a S=0 ground state but, due to competing AF interactions, the first excited spin states are close in energy. The spin frustrated ring is visualized by a Mobius strip. The 'knot' of the strip represents the region of the ring where the AF interactions are more frustrated. In the particular case of this bimetallic ring electron paramagnetic resonance (EPR) has unambiguously shown that the frustration is delocalized on the chromium chain, while the antiparallel alignment is more rigid at the nickel site.
Measuring spin correlations in optical lattices using superlattice potentials
DEFF Research Database (Denmark)
Pedersen, K.G.L.; Andersen, B.M.; Sørensen, A.S.; Bruun, G.M.; Syljuåsen, Olav Fredrik
2011-01-01
We suggest two experimental methods for probing both short- and long-range spin correlations of atoms in optical lattices using superlattice potentials. The first method involves an adiabatic doubling of the periodicity of the underlying lattice to probe neighboring singlet (triplet) correlations...... for fermions (bosons) by the occupation of the resulting vibrational ground state. The second method utilizes a time-dependent superlattice potential to generate spin-dependent transport by any number of prescribed lattice sites, and probes correlations by the resulting number of doubly occupied sites....... For experimentally relevant parameters, we demonstrate how both methods yield large signatures of antiferromagnetic correlations of strongly repulsive fermionic atoms in a single shot of the experiment. Lastly, we show how this method may also be applied to probe d-wave pairing, a possible ground...
Ground state and zero temperature phase diagrams of the XXZ antiferromagnetic spin- {1}/{2} chain
Zhou, P.
1990-05-01
An expression of the XXZ model is given from which the Ising, isotropic XY and Heisenberg models may be more properly obtained by varying only one anisotropy parameter. The ground state and spin configuration of the antiferromagnetic quasi-classical s = {1}/{2}XXZ chain in a magnetic field of arbitrary direction are studied. The phase diagrams with a longitudinal ( h⊥ = 0) and a transverse field ( h‖ = 0) are presented. Because we take into account an effect of anisotropy in the Zeeman interaction, the phase diagrams are quite different from those given by Kurmann, et al. [Physica A 112 (1982) 235]. A ferromagnetic-antiferromagnetic first order phase transition is indicated for the Ising case with h⊥=0.
Competing orders in spin-1 and spin-3/2 XXZ kagome antiferromagnets: A series expansion study
Oitmaa, J.; Singh, R. R. P.
2016-01-01
We study the competition between √{3 }×√{3 } (RT3) and q =0 (Q0) magnetic orders in spin-1 and spin-3/2 kagome-lattice XXZ antiferromagnets with varying XY anisotropy parameter Δ , using series expansion methods. The Hamiltonian is split into two parts: an H0 which favors the classical order in the desired pattern and an H1, which is treated in perturbation theory by a series expansion. We find that the ground state energy series for the RT3 and Q0 phases are identical up to sixth order in the expansion, but ultimately a selection occurs, which depends on spin and the anisotropy Δ . Results for ground state energy and the magnetization are presented. These results are compared with recent spin-wave theory and coupled-cluster calculations. The series results for the phase diagram are close to the predictions of spin-wave theory. For the spin-1 model at the Heisenberg point (Δ =1 ), our results are consistent with a vanishing order parameter, that is, an absence of a magnetically ordered phase. We also develop series expansions for the ground state energy of the spin-1 Heisenberg model in the trimerized phase. We find that the ground state energy in this phase is lower than those of magnetically ordered ones, supporting the existence of a spontaneously trimerized phase in this model.
Spin wave dynamics in Heisenberg ferromagnetic/antiferromagnetic single-walled nanotubes
Mi, Bin-Zhou
2016-09-01
The spin wave dynamics, including the magnetization, spin wave dispersion relation, and energy level splitting, of Heisenberg ferromagnetic/antiferromagnetic single-walled nanotubes are systematically calculated by use of the double-time Green's function method within the random phase approximation. The role of temperature, diameter of the tube, and wave vector on spin wave energy spectrum and energy level splitting are carefully analyzed. There are two categories of spin wave modes, which are quantized and degenerate, and the total number of independent magnon branches is dependent on diameter of the tube, caused by the physical symmetry of nanotubes. Moreover, the number of flat spin wave modes increases with diameter of the tube rising. The spin wave energy and the energy level splitting decrease with temperature rising, and become zero as temperature reaches the critical point. At any temperature, the energy level splitting varies with wave vector, and for a larger wave vector it is smaller. When pb=π, the boundary of first Brillouin zone, spin wave energies are degenerate, and the energy level splittings are zero.
Geometric phase of a central spin coupled to an antiferromagnetic environment
Yuan, Xiao-Zhong; Zhu, Ka-Di
2010-01-01
Using the spin-wave approximation, we study the geometric phase (GP) of a central spin (signal qubit) coupled to an antiferromagnetic (AF) environment under the application of an external global magnetic field. The external magnetic field affects the GP of the qubit directly and also indirectly through its effect on the AF environment. We find that when the applied magnetic field is increased to the critical magnetic field point, the AF environment undergoes a spin-flop transition, a first-order phase transition, and at the same time the GP of the qubit changes abruptly to zero. This sensitive change of the GP of a signal qubit to the parameter change of a many-body environment near its critical point may serve as another efficient tool or witness to study the many-body phase transition. The influences of the AF environment temperature and crystal anisotropy field on the GP are also investigated.
Tran, Minh-Tien; Kim, Ki-Seok
2010-01-01
We reveal that local interactions in graphene allow novel spin liquids between the semi-metal and antiferromagnetic Mott insulating phases, identified with algebraic spin liquid and Z$_{2}$ spin liquid, respectively. We argue that the algebraic spin liquid can be regarded as the two dimensional realization of one dimensional spin dynamics, where antiferromagnetic correlations show exactly the same power-law dependence as valence bond correlations. Nature of the Z$_{2}$ spin liquid turns out t...
Spin-Peierls States of Quantum Antiferromagnets on the CaV4O9 Lattice
International Nuclear Information System (INIS)
We discuss the quantum paramagnetic phases of Heisenberg antiferromagnets on the 1/5-depleted square lattice found in CaV4O9. The possible phases of the quantum dimer model on this lattice are obtained by a mapping to a quantum-mechanical height model. In addition to the open-quote open-quote decoupled close-quote close-quote phases found earlier, we find a possible intermediate spin-Peierls phase with spontaneously broken lattice symmetry. Experimental signatures of the different quantum paramagnetic phases are discussed. copyright 1996 The American Physical Society
Double-layer antiferromagnetic quantum spin-1/2 Heisenberg model: study of the ground state
International Nuclear Information System (INIS)
The crossover from two-dimensional to three-dimensional behavior in the quasi-two-dimensional quantum Heisenberg antiferromagnetic model in the presence of a magnetic field, at T=0 (ground state), is studied by using effective-field theory. In the model a nearest neighbour spin pair interacts with strength J in the xy-plane and with λJ (0=c is obtained as a function of parameter λ, where we have different values of the classical case (Ising model) Hc/J=4+2λ
Pu, Zhengguo; Zhang, Jun; Yi, Su; Wang, Dajun; Zhang, Wenxian
2016-05-01
We theoretically investigate four types of dynamical instability, in particular the periodic and oscillatory type IO, in an antiferromagnetic spin-1 Bose-Einstein condensate in a nonzero magnetic field, by employing the coupled-mode theory and numerical method. This is in sharp contrast to the dynamical stability of the same system in zero field. Remarkably, a pattern transition from a periodic dynamical instability IO to a uniform one IIIO occurs at a critical magnetic field. All four types of dynamical instability and the pattern transition are ready to be detected in 23Na condensates within the availability of the current experimental techniques.
A spin-valve-like magnetoresistance of an antiferromagnet-based tunnel junction
Czech Academy of Sciences Publication Activity Database
Park, B.G.; Wunderlich, Joerg; Martí, X.; Holý, V.; Kurosaki, Y.; Yamada, M.; Yamamoto, H.; Nishide, A.; Hayakawa, J.; Takahashi, H.; Shick, Alexander; Jungwirth, Tomáš
2011-01-01
Roč. 10, č. 5 (2011), s. 347-351. ISSN 1476-1122 R&D Projects: GA AV ČR KAN400100652; GA MŠk LC510; GA MŠk(CZ) 7E08087 EU Projects: European Commission(XE) 214499 - NAMASTE; European Commission(XE) 215368 - SemiSpinNet Grant ostatní: AVČR(CZ) Premium Academiae; 7 FP ERC Advanced Grant 0MSPIN(XE) 268066 Institutional research plan: CEZ:AV0Z10100521; CEZ:AV0Z10100520 Keywords : spintronic s * antiferromagnets Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 32.841, year: 2011
Yu, Rong; Roscilde, Tommaso; Haas, Stephan
2006-01-01
Site dilution of spin-gapped antiferromagnets leads to localized free moments, which can order antiferromagnetically in two and higher dimensions. Here we show how a weak magnetic field drives this order-by-disorder state into a novel disordered-free-moment phase, characterized by the formation of local singlets between neighboring moments and by localized moments aligned antiparallel to the field. This disordered phase is characterized by the absence of a gap, as it is the case in a Bose gla...
Disorder effects in the S=1 antiferromagnetic spin ladder CaV{sub 2}O{sub 4}
Energy Technology Data Exchange (ETDEWEB)
Guitarra, S.R. [Colegio de Ciencias e Ingeniería, Universidad San Francisco de Quito, Quito (Ecuador); Caneiro, A. [Instituto Balseiro - Centro Atómico Bariloche, 8400 Bariloche (Argentina); Niebieskikwiat, D., E-mail: dniebieskikwiat@usfq.edu.ec [Colegio de Ciencias e Ingeniería, Universidad San Francisco de Quito, Quito (Ecuador)
2015-10-15
We study the physical properties of the antiferromagnetic spin ladder CaV{sub 2}O{sub 4} (CVO) and the Y-doped related compound Ca{sub 0.9}Y{sub 0.1}V{sub 2}O{sub 4}. In the latter, X-ray diffraction demonstrates the segregation of a small amount of a vanadium–perovskite impurity phase, leading to the formation of V vacancies within the main CVO-type structure. The 1D character of this calcium–vanadite enhances the influence of the vacancies on the electric and magnetic properties of Ca{sub 0.9}Y{sub 0.1}V{sub 2}O{sub 4}. Electrical transport is characterized by a variable-range hopping mechanism determined by the charging energy of nm-sized segments of V chains delimited by V vacancies, i.e. a Coulomb gap is formed at the Fermi level. These vacancies also locally affect the magnetic correlations, breaking the long-range AFM order observed in CaV{sub 2}O{sub 4} and producing exchange bias when the Y-doped sample is cooled with an applied magnetic field. - Highlights: • We study disorder effects in the quasi-1D antiferromagnetic spin ladder CaV{sub 2}O{sub 4}. • V vacancies in CaV{sub 2}O{sub 4} lead to variable-range hopping electrical transport. • The charging energy of nm-sized V chains determine the transport mechanism exponents. • V vacancies break the long-range AFM order of CaV{sub 2}O{sub 4}. • Local magnetic correlations in the vicinity of the defects produce exchange bias.
Sadeghi, Azam; Alaei, Mojtaba; Shahbazi, Farhad; Gingras, Michel J. P.
2015-04-01
FeF3, with its half-filled Fe3 +3 d orbital, hence zero orbital angular momentum and S =5 /2 , is often put forward as a prototypical highly frustrated classical Heisenberg pyrochlore antiferromagnet. By employing ab initio density functional theory, we obtain an effective spin Hamiltonian for this material. This Hamiltonian contains nearest-neighbor antiferromagnetic Heisenberg, biquadratic, and Dzyaloshinskii-Moriya interactions as dominant terms and we use Monte Carlo simulations to investigate the nonzero temperature properties of this minimal model. We find that upon decreasing temperature, the system passes through a Coulomb phase, composed of short-range correlated coplanar states, before transforming into an "all-in/all-out" (AIAO) state via a very weakly first-order transition at a critical temperature Tc≈22 K, in good agreement with the experimental value for a reasonable set of Coulomb interaction U and Hund's coupling JH describing the material. Despite the transition being first order, the AIAO order parameter evolves below Tc with a power-law behavior characterized by a pseudo "critical exponent" β ≈0.18 in accord with experiment. We comment on the origin of this unusual β value.
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.
Magnetization switching by spin-orbit torque in an antiferromagnet-ferromagnet bilayer system
Fukami, Shunsuke; Zhang, Chaoliang; Duttagupta, Samik; Kurenkov, Aleksandr; Ohno, Hideo
2016-05-01
Spin-orbit torque (SOT)-induced magnetization switching shows promise for realizing ultrafast and reliable spintronics devices. Bipolar switching of the perpendicular magnetization by the SOT is achieved under an in-plane magnetic field collinear with an applied current. Typical structures studied so far comprise a nonmagnet/ferromagnet (NM/FM) bilayer, where the spin Hall effect in the NM is responsible for the switching. Here we show that an antiferromagnet/ferromagnet (AFM/FM) bilayer system also exhibits a SOT large enough to switch the magnetization of the FM. In this material system, thanks to the exchange bias of the AFM, we observe the switching in the absence of an applied field by using an antiferromagnetic PtMn and ferromagnetic Co/Ni multilayer with a perpendicular easy axis. Furthermore, tailoring the stack achieves a memristor-like behaviour where a portion of the reversed magnetization can be controlled in an analogue manner. The AFM/FM system is thus a promising building block for SOT devices as well as providing an attractive pathway towards neuromorphic computing.
Directory of Open Access Journals (Sweden)
R. L. Wang
2012-09-01
Full Text Available Effect of thermal cycle on the interfacial antiferromagnetic (AFM spin configuration and exchange bias in Ni50Mn36Sb14 alloy has been investigated. The results indicate thermal cycle can induce further martensitic transition from part of arrested FM phase to AFM phase, leading to the reconstruction of interfacial antiferromagnetic spin configuration. The shape of hysteresis loops at 5 K after cooling back can be tuned from a single-shifted loop to a nearly symmetric double-shifted loop gradually accompanied with exchange bias field increasing to peak value and then decreasing. The evolutions can be illustrated intuitively by a simple AFM bidomain model.
Spin-Jahn-Teller effect in the antiferromagnetic molecular wheel CsFe8
International Nuclear Information System (INIS)
Antiferromagnetic molecular wheels are ring-like arrangements of exchange-coupled magnetic metal ions. As a function of a magnetic field, the Zeeman splitting leads to a series of level-crossings (LCs) at characteristic fields, where the ground state changes from total spin S=0 to S=1, S=2, and so on. Previous magnetic torque and 1H-NMR measurements on CsFe8 single crystals demonstrated phase transitions at the LCs at low temperatures. They were explained by a field-induced spin-Jahn-Teller effect (JTE) due to a magneto-elastic coupling between the spins in the wheel and the lattice. Some models for this process were developed, but a full microscopic understanding is lacking. New high-field torque data were recorded, which provide a comprehensive picture of the angular as well as temperature dependence of the phase transition. A strong angle dependence of the critical fields and temperatures with two qualitatively different regimes was observed, which allows us to distinguish the relative contributions of zero-field splitting and Dzyaloshinsky-Moriya interactions to the spin-JTE.
Spin-Jahn-Teller effect in the antiferromagnetic molecular wheel CsFe{sub 8}
Energy Technology Data Exchange (ETDEWEB)
Lotze, Johannes; Waldmann, Oliver [Physikalisches Institut, Universitaet Freiburg (Germany); Chamayou, Anne-Christine; Janiak, Christoph [Institut fuer Anorganische und Analytische Chemie, Universitaet Freiburg (Germany); Ako, Ayuk M.; Powell, Annie K. [Institut fuer Anorganische Chemie, Universitaet Karlsruhe (Germany); Sheikin, Ilya [Grenoble High Magnetic Field Laboratory, CNRS, Grenoble (France)
2010-07-01
Antiferromagnetic molecular wheels are ring-like arrangements of exchange-coupled magnetic metal ions. As a function of a magnetic field, the Zeeman splitting leads to a series of level-crossings (LCs) at characteristic fields, where the ground state changes from total spin S=0 to S=1, S=2, and so on. Previous magnetic torque and {sup 1}H-NMR measurements on CsFe{sub 8} single crystals demonstrated phase transitions at the LCs at low temperatures. They were explained by a field-induced spin-Jahn-Teller effect (JTE) due to a magneto-elastic coupling between the spins in the wheel and the lattice. Some models for this process were developed, but a full microscopic understanding is lacking. New high-field torque data were recorded, which provide a comprehensive picture of the angular as well as temperature dependence of the phase transition. A strong angle dependence of the critical fields and temperatures with two qualitatively different regimes was observed, which allows us to distinguish the relative contributions of zero-field splitting and Dzyaloshinsky-Moriya interactions to the spin-JTE.
Magnetic correlations in the 2D S=5/2 honeycomb antiferromagnet MnPS3
DEFF Research Database (Denmark)
Rønnow, H.M.; Wildes, A.R.; Bramwell, S.T.
2000-01-01
MnPS3 is a quasi-2D S = 5/2 antiferromagnet on a honeycomb lattice. Using an energy integrating neutron scattering technique, we have measured the structure factor S(k) of the instantaneous magnetic fluctuations. The temperature dependence of the correlation length xi follows the Kosterlitz...
CIP spin torque effect in the spin valve pinned with an oxide antiferromagnetic layer
International Nuclear Information System (INIS)
Spin valve Ni0.85Co0.15O/Co85Fe15/Cu/Co85Fe15 was manufactured by a RF magnetron sputtering system. M(H) and R(H) characteristics of the spin valve were measured in CIP configuration at room temperature has a magnetoresistance ratio of about 8% and a high exchange bias at room temperature. The current density and angle between the applied magnetic field and injection current were changed in an aim to observe their effects on MR and exchange bias of the spin valve. The current density and angle strongly affect MR and exchange bias. Both MR and exchange bias clearly decrease in dependence of the current density and direction of the magnetic field. It is supposed to be related with a current-induced spin torque in device.
Soliton Lattice State of Spin-1/2 Antiferromagnetic Chain in an External Magnetic Field
Institute of Scientific and Technical Information of China (English)
WANG Zhi-Guo; ZHANG Yu-Mei; GAO Yang
2002-01-01
One-dimensional spin-1-2 anisotropic Heisenberg antiferromagnet in a longitudinal external magnetic field is studied using bosonization method and Gaussian wave functional techniques which take account of the spatial structure.The magnetization and the energy of the ground state which depend on the external magnetic field are calculated.For the case of anisotropic parameter △＞△0,increasing of the external magnetic field above the threshold value leads to the appearance of the soliton lattice state in the ground state,until to an another critical field where the ground state changes to the canted state phase.Therefore,with increasing external magnetic field,the ground state experiences four different phases successively,namely,antiferromagnetic Ising,soliton lattice state canted state,and magnetization saturated phases.When △＜△0,the soliton lattice state phase does not appear,with increasing external field,the paramagnetic phase smoothly evolves into the canted state phase,finally reaches magnetization saturated phase.
Spin liquid in a single crystal of the frustrated diamond lattice antiferromagnet CoAl2O4
DEFF Research Database (Denmark)
Zaharko, O.; Christensen, Niels Bech; Cervellino, A.;
2011-01-01
We study the evidence for spin liquid in the frustrated diamond lattice antiferromagnet CoAl2O4 by means of single-crystal neutron scattering in zero and applied magnetic fields. The magnetically ordered phase appearing below T-N = 8 K remains nonconventional down to 1.5 K. The magnetic Bragg pea...
Shinaoka, Hiroshi; Tomita, Yusuke; Motome, Yukitoshi
2014-10-01
Motivated by puzzling aspects of spin-glass behavior reported in frustrated magnetic materials, we theoretically investigate effects of magnetoelastic coupling in geometrically frustrated classical spin models. In particular, we consider bond-disordered Heisenberg antiferromagnets on a pyrochlore lattice coupled to local lattice distortions. By integrating out the lattice degree of freedom, we derive an effective spin-only model, the bilinear-biquadratic model with bond disorder. The effective model is analyzed by classical Monte Carlo simulations using an extended loop algorithm. First, we discuss the phase diagrams in detail by showing the comprehensive Monte Carlo data for thermodynamic and magnetic properties. We show that the spin-glass transition temperature Tf is largely enhanced by the spin-lattice coupling b in the weakly disordered regime. By considering the limit of strong spin-lattice coupling, this enhancement is ascribed to the suppression of thermal fluctuations in semidiscrete degenerate manifold formed in the presence of the spin-lattice coupling. We also find that, by increasing the strength of disorder Δ, the system shows a concomitant transition of the nematic order and spin glass at a temperature determined by b, being almost independent of Δ. This is due to the fact that the spin-glass transition is triggered by the spin collinearity developed by the nematic order. Although further-neighbor exchange interactions originating in the cooperative lattice distortions result in spin-lattice order in the weakly disordered regime, the concomitant transition remains robust with Tf almost independent of Δ. We find that the magnetic susceptibility shows hysteresis between the field-cooled and zero-field-cooled data below Tf, and that the nonlinear susceptibility shows a negative divergence at the transition. These features are common to conventional spin-glass systems. Meanwhile, we find that the specific heat exhibits a broad peak at Tf, and that the
Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr0.7Ca0.3MnO3
Energy Technology Data Exchange (ETDEWEB)
Zhou, S.Y.; Langner, M.C.; Zhu, Y.; Chuang, Y.-D.; Rini, M.; Glover, T.E.; Hertlein, M.P.; Gonzalez, A.G. Cruz; Tahir, N.; Tomioka, Y.; Tokura, Y.; Hussain, Z.; Schoenlein, R.W.
2014-01-16
Electronic orderings of charges, orbitals and spins are observed in many strongly correlated electron materials, and revealing their dynamics is a critical step toward understanding the underlying physics of important emergent phenomena. Here we use time-resolved resonant soft x-ray scattering spectroscopy to probe the dynamics of antiferromagnetic spin ordering in the manganite Pr0:7Ca0:3MnO3 following ultrafast photo-exitation. Our studies reveal a glass-like recovery of the spin ordering and a crossover in the dimensionality of the restoring interaction from quasi-1D at low pump fluence to 3D at high pump fluence. This behavior arises from the metastable state created by photo-excitation, a state characterized by spin disordered metallic droplets within the larger charge- and spin-ordered insulating domains. Comparison with time-resolved resistivity measurements suggests that the collapse of spin ordering is correlated with the insulator-to-metal transition, but the recovery of the insulating phase does not depend on the re-establishment of the spin ordering.
Role of the antiferromagnetic pinning layer on spin wave properties in IrMn/NiFe based spin-valves
Energy Technology Data Exchange (ETDEWEB)
Gubbiotti, G., E-mail: gubbiotti@fisica.unipg.it; Tacchi, S. [Istituto Officina dei Materiali del CNR (IOM-CNR), Unità di Perugia, I-06123 Perugia (Italy); Del Bianco, L. [Department of Physics and Astronomy, University of Bologna, I-40127 Bologna (Italy); Department of Physics and Earth Sciences and CNISM, University of Ferrara, I-44122 Ferrara (Italy); Bonfiglioli, E.; Giovannini, L.; Spizzo, F.; Zivieri, R. [Department of Physics and Earth Sciences and CNISM, University of Ferrara, I-44122 Ferrara (Italy); Tamisari, M. [Department of Physics and Earth Sciences and CNISM, University of Ferrara, I-44122 Ferrara (Italy); Dipartimento di Fisica e Geologia, Università di Perugia, I-06123 Perugia (Italy)
2015-05-07
Brillouin light scattering (BLS) was exploited to study the spin wave properties of spin-valve (SV) type samples basically consisting of two 5 nm-thick NiFe layers (separated by a Cu spacer of 5 nm), differently biased through the interface exchange coupling with an antiferromagnetic IrMn layer. Three samples were investigated: a reference SV sample, without IrMn (reference); one sample with an IrMn underlayer (10 nm thick) coupled to the bottom NiFe film; one sample with IrMn underlayer and overlayer of different thickness (10 nm and 6 nm), coupled to the bottom and top NiFe film, respectively. The exchange coupling with the IrMn, causing the insurgence of the exchange bias effect, allowed the relative orientation of the NiFe magnetization vectors to be controlled by an external magnetic field, as assessed through hysteresis loop measurements by magneto-optic magnetometry. Thus, BLS spectra were acquired by sweeping the magnetic field so as to encompass both the parallel and antiparallel alignment of the NiFe layers. The BLS results, well reproduced by the presented theoretical model, clearly revealed the combined effects on the spin dynamic properties of the dipolar interaction between the two NiFe films and of the interface IrMn/NiFe exchange coupling.
Search for the Heisenberg spin glass on rewired square lattices with antiferromagnetic interaction
Surungan, Tasrief; Bansawang B., J.; Tahir, Dahlang
2016-03-01
Spin glass (SG) is a typical magnetic system with frozen random spin orientation at low temperatures. The system exhibits rich physical properties, such as infinite number of ground states, memory effect, and aging phenomena. There are two main ingredients considered to be pivotal for the existence of SG behavior, namely, frustration and randomness. For the canonical SG system, frustration is led by the presence of competing interaction between ferromagnetic (FM) and antiferromagnetic (AF) couplings. Previously, Bartolozzi et al. [Phys. Rev. B73, 224419 (2006)], reported the SG properties of the AF Ising spins on scale free network (SFN). It is a new type of SG, different from the canonical one which requires the presence of both FM and AF couplings. In this new system, frustration is purely caused by the topological factor and its randomness is related to the irregular connectvity. Recently, Surungan et. al. [Journal of Physics: Conference Series, 640, 012001 (2015)] reported SG bahavior of AF Heisenberg model on SFN. We further investigate this type of system by studying an AF Heisenberg model on rewired square lattices. We used Replica Exchange algorithm of Monte Carlo Method and calculated the SG order parameter to search for the existence of SG phase.
Top Quark Spin Correlations at the Tevatron
Energy Technology Data Exchange (ETDEWEB)
Head, Tim; /Manchester U.
2010-07-01
Recent measurements of the correlation between the spin of the top and the spin of the anti-top quark produced in proton anti-proton scattering at a center of mass energy of {radical}s = 1.96 Tev by the CDF and D0 collaborations are discussed. using up to 4.3 fb{sup -1} of data taken with the CDF and D0 detectors the spin correlation parameter C, the degree to which the spins are correlated, is measured in dileptonic and semileptonic final states. The measurements are found to be in agreement with Standard Model predictions.
Wu, R.; Yun, C.; Ding, S. L.; Wen, X.; Liu, S. Q.; Wang, C. S.; Han, J. Z.; Du, H. L.; Yang, J. B.
2016-08-01
The motion of antiferromagnetic interfacial spins is investigated through the temperature evolution of training effect in a Co/CoO film with in-plane biaxial anisotropy. Significant differences in the training effect and its temperature dependence are observed in the magnetic easy axis and hard axis (HA) and ascribed to the different motion modes of antiferromagnetic interfacial spins, the collective spin cluster rotation (CSR) and the single spin reversal (SSR), caused by different magnetization reversal modes of ferromagnetic layer. These motion modes of antiferromagnetic spins are successfully separated using a combination of an exponential function and a classic n-1/2 function. A larger CSR to SSR ratio and a shorter lifetime of CSR found in the HA indicates that the domain rotation in the ferromagnetic layer tends to activate and accelerate a CSR mode in the antiferromagnetic spins.
Correlation Driven Transport Asymmetries Through Coupled Spins
Muenks, Matthias; Jacobson, Peter; Ternes, Markus; Kern, Klaus
2016-01-01
Correlation is a fundamental statistical measure of order in interacting quantum systems. In solids, electron correlations govern a diverse array of material classes and phenomena such as heavy fermion compounds, Hunds metals, high-Tc superconductors, and the Kondo effect. Spin-spin correlations, notably investigated by Kaufman and Onsager in the 1940s 6, are at the foundation of numerous theoretical models but are challenging to measure experimentally. Reciprocal space methods can map correl...
A frustrated spin-1 J1-J2 Heisenberg antiferromagnet: An anisotropic planar pyrochlore model
International Nuclear Information System (INIS)
The zero-temperature ground-state (GS) properties and phase diagram of a frustrated spin-1 J1-J2 Heisenberg model on the checkerboard square lattice are studied, using the coupled cluster method. We consider the case where the nearest-neighbour exchange bonds have strength J1 > 0 and the next-nearest-neighbour exchange bonds present (viz., in the checkerboard pattern of the planar pyrochlore) have strength J2 = κJ1 > 0. We find significant differences from both the spin-1/2 and classical versions of the model. We find that the spin-1 model has a first phase transition at κC1 ≈ 1.00 ± 0.01 (as does the classical model at κcl = 1) between two antiferromagnetic phases, viz., a quasiclassical Néel phase (for κ < κC1) and one of the infinitely degenerate family of quasiclassical phases (for k > κC1) that exists in the classical model for κ > κc1, which is now chosen by the order by disorder mechanism as (probably) the 'doubled Néel' (or Néel*) state. By contrast, none of this family survives quantum fluctuations to form a stable GS phase in the spin-1/2 case. We also find evidence for a second quantum critical point at κC2 ≈ 2.0 ± 0.5 in the spin-1 model, such that for κ > κC2 the quasiclassical (Néel*) ordering melts and a nonclassical phase appears, which, on the basis of preliminary evidence, appears unlikely to have crossed-dimer valence-bond crystalline (CDVBC) ordering, as in the spin-1/2 case. Unlike in the spin-1/2 case, where the Néel and CDVBC phases are separated by a phase with plaquette valence-bond crystalline (PVBC) ordering, we find very preliminary evidence for such a PVBC state in the spin-1 model for all κ > κC2.
Numerical simulations of strongly correlated electron and spin systems
Changlani, Hitesh Jaiprakash
Developing analytical and numerical tools for strongly correlated systems is a central challenge for the condensed matter physics community. In the absence of exact solutions and controlled analytical approximations, numerical techniques have often contributed to our understanding of these systems. Exact Diagonalization (ED) requires the storage of at least two vectors the size of the Hilbert space under consideration (which grows exponentially with system size) which makes it affordable only for small systems. The Density Matrix Renormalization Group (DMRG) uses an intelligent Hilbert space truncation procedure to significantly reduce this cost, but in its present formulation is limited to quasi-1D systems. Quantum Monte Carlo (QMC) maps the Schrodinger equation to the diffusion equation (in imaginary time) and only samples the eigenvector over time, thereby avoiding the memory limitation. However, the stochasticity involved in the method gives rise to the "sign problem" characteristic of fermion and frustrated spin systems. The first part of this thesis is an effort to make progress in the development of a numerical technique which overcomes the above mentioned problems. We consider novel variational wavefunctions, christened "Correlator Product States" (CPS), that have a general functional form which hopes to capture essential correlations in the ground states of spin and fermion systems in any dimension. We also consider a recent proposal to modify projector (Green's Function) Quantum Monte Carlo to ameliorate the sign problem for realistic and model Hamiltonians (such as the Hubbard model). This exploration led to our own set of improvements, primarily a semistochastic formulation of projector Quantum Monte Carlo. Despite their limitations, existing numerical techniques can yield physical insights into a wide variety of problems. The second part of this thesis considers one such numerical technique - DMRG - and adapts it to study the Heisenberg antiferromagnet
Spin dynamics of the 2D spin ½ quantum antiferromagnet copper deuteroformate tetradeuterate (CFTD)
DEFF Research Database (Denmark)
Rønnow, H.M.; McMorrow, D.F.; Coldea, R.; Harrison, A.; Youngson, I.D.; Perring, T.G.; Aeppli, G.; Syljuåsen, O.; Lefmann, K.; Rischel, C.
2001-01-01
energy is observed, which is attributed to a wave vector dependent quantum renormalization. At higher temperatures, spin-wavelike excitations persist, but are found to broaden and soften. By combining our data with numerical calculations, and with existing theoretical work, a consistent description of...
DEFF Research Database (Denmark)
Kawasaki, Yu; Gavilano, Jorge L.; Keller, Lukas; Schefer, Juerg; Christensen, Niels Bech; Amato, Alex; Ohno, Takashi; Kishimoto, Yutaka; He, Zhangzhen; Ueda, Yutaka; Itoh, Mitsuru
2011-01-01
,0,1), independent of external magnetic fields for fields below a critical value H-c(T). The ordered moments of 2.18 mu(B) per Co ion are aligned along the crystallographic c axis. Within the screw chains, along the c axis, the moments are arranged antiferromagnetically. In the basal planes the spins are arranged...
Triangular Ising antiferromagnets with quenched nonmagnetic impurities.
Tang, Huai-Lei; Zhu, Yi; Yang, Guo-Hong; Jiang, Ying
2010-05-01
In a random spin system, the cooperation of randomness and frustration will lead to a spin-glass phase. However, in geometrically frustrated spin systems, quenched nonmagnetic impurities lift frustration locally. This makes randomness and frustration in these systems as competitors rather than cooperators. By mapping the dilute triangular Ising antiferromagnetic system to elastic array of noncrossing strings, we find that the nonmagnetic impurities in the spin system play roles of pinning centers in the string system. Calculation shows that in the ground state of this system, the spin-glass correlation is power-law decayed, quite different from the standard behavior of spin glass in which spin-glass correlation between two spins at infinite distance tends to a finite value. This indicates that triangular Ising antiferromagnets with quenched nonmagnetic impurities cannot be a spin glass. Instead, in the ground states, they present properties of vortex glass. PMID:20866185
Yannouleas, Constantine; Brandt, Benedikt B.; Landman, Uzi
2016-07-01
Advances with trapped ultracold atoms intensified interest in simulating complex physical phenomena, including quantum magnetism and transitions from itinerant to non-itinerant behavior. Here we show formation of antiferromagnetic ground states of few ultracold fermionic atoms in single and double well (DW) traps, through microscopic Hamiltonian exact diagonalization for two DW arrangements: (i) two linearly oriented one-dimensional, 1D, wells, and (ii) two coupled parallel wells, forming a trap of two-dimensional, 2D, nature. The spectra and spin-resolved conditional probabilities reveal for both cases, under strong repulsion, atomic spatial localization at extemporaneously created sites, forming quantum molecular magnetic structures with non-itinerant character. These findings usher future theoretical and experimental explorations into the highly correlated behavior of ultracold strongly repelling fermionic atoms in higher dimensions, beyond the fermionization physics that is strictly applicable only in the 1D case. The results for four atoms are well described with finite Heisenberg spin-chain and cluster models. The numerical simulations of three fermionic atoms in symmetric DWs reveal the emergent appearance of coupled resonating 2D Heisenberg clusters, whose emulation requires the use of a t–J-like model, akin to that used in investigations of high T c superconductivity. The highly entangled states discovered in the microscopic and model calculations of controllably detuned, asymmetric, DWs suggest three-cold-atom DW quantum computing qubits.
Spin polarized STM imaging of the Fe3O4 (0 0 1) surface using antiferromagnetic tips
Jordan, K.; Mariotto, G.; Ceballos, S. F.; Murphy, S.; Shvets, I. V.
2005-04-01
Spin polarized STM is used to image the charge ordered Fe3O4 (0 0 1) surface, using antiferromagnetic MnNi probes. Such a surface is characterized by the presence of Fe- Fe and Fe- Fe dimers. These dimers have different spin configurations, which are resolved using a MnNi probe. The surface is also imaged with paramagnetic W tips, which do not distinguish between the dimers, providing further evidence for a spin polarized contribution to the tunnel current with MnNi tips.
Heavy-fermion, kondo, spin glass-like, and antiferromagnetic behavior in (Ce,Gd)Al/sub 3/
International Nuclear Information System (INIS)
We have found that Ce/sub 1-x/Gd/sub x/Al3 with x = 0.23 is a heavy-fermion system which undergoes a spin glass transition. The amplitude of the peak in the susceptibility that characterizes the spin glass transition passes through a sharp maximum at x = 0.5. For x = 0.635 and 0.77 the system undergoes a spin glass-like transition at 1000K and an antiferromagnetic transition at 200K
Spin excitations in the odd homonuclear antiferromagnetic molecular nanomagnet Fe{sub 9}
Energy Technology Data Exchange (ETDEWEB)
Konstantinidis, Nikolaos P.; Nehrkorn, Joscha; Stuiber, Stefan; Waldmann, Oliver [Physikalisches Institut, Universitaet Freiburg, 79104 Freiburg (Germany)
2011-07-01
The homonuclear ring Fe{sub 9} has an odd number of antiferromagnetically coupled Fe{sup I}II spin-5/2 centers, therefore frustration plays an important role in determining its magnetic properties. Molecular wheels of odd size have been known to possess a doubly-degenerate lowest level in each total spin S sector in the absence of magnetic anisotropy. We have performed inelastic neutron scattering measurements which produced very sharp peaks that located the transitions between the energy levels very accurately. Our magnetic susceptibility data also provided an estimate for the strength of the exchange interactions, while torque magnetometry reveals the presence of weak magnetic anisotropy. Different Hamiltonians are used to find the appropriate model for the magnetic properties of Fe{sub 9}, with the energy levels characterized by the symmetry of the Hamiltonian. Exchange interactions that respect the spatial symmetry of the molecule coupled with a uniform single-site anisotropy term can not reproduce the splitting of the lowest energy levels. Especially the lowest lying S=3/2 doublet is unexpectedly robust against perturbations. This particular nature of the theoretically generated low-energy spectrum will be discussed.
Makhfudz, Imam; Pujol, Pierre
We propose a mechanism for the protection against spin gapped states in doped antiferromagnets. It requires the presence of a Chern-Simons term that can be generated by a coupling between spin and an insulator.We first demonstrate that in the presence of this term the vortex loop excitations of the spin sector behave as anyons with fractional statistics. To generate such a term, the fermions should have a massive Dirac spectrum coupled to the emergent spin field of the spin sector. The Dirac spectrum can be realized by a planar spin configuration arising as the lowest-energy configuration of a square lattice antiferromagnet Hamiltonian involving a Dzyaloshinskii- Moriya interaction. The mass is provided by a combination of dimerization and staggered chemical potential.We finally showthat for realistic parameters, anyonic vortex loop condensationwill likely never occur and thus the spin gapped state is prevented.We also propose real magnetic materials for an experimental verification of our theory. Reference: Imam Makhfudz and Pierre Pujol,Phys.Rev. B 92, 144507 (2015).
DEFF Research Database (Denmark)
Jin, Zuanming; Mics, Zoltán; Ma, Guohong;
2013-01-01
We report on the coherent control of terahertz (THz) spin waves in a canted antiferromagnet yttrium orthoferrite, YFeO3, associated with a quasiferromagnetic (quasi-FM) spin resonance at a frequency of 0.3 THz, using a single-incident THz pulse. The spin resonance is excited impulsively by the ma...
Spin flop relaxation in the quasi-1d Heisenberg antiferromagnet CsMnBr 3 · 2H 2O
Chirwa, M.; Top, J.; Flokstra, J.
1983-12-01
The relaxation phenomena associated with the antiferromagnetic to spin-flop phase transition in the quasi one dimensional Heisenberg antiferromagnet CsMnBr 3 · 2H 2O have been determined in the temperature range 1.6-4.2 K using an automatic frequency-sweeping SQUID susceptometer. Below Tλ = 2.17 K the relaxation rate τ -1 displays an exponential temperature dependence given by τ-1 = ω0 exp(- E/ kT) where ω0 = 2.48 × 10 4 s -1 and E/ k = 3.62 K, the activation energy of the relaxation process. Above Tλ broadened absorption curves and flattened Argand diagrams are observed. The ratio K1/ K2 (=0.22 ± 0.02) of the orthorhombic anisotropy constants and a weak power-law temperature dependence of the critical spin-flop field Hcr were determined.
Energy Technology Data Exchange (ETDEWEB)
Ma, Q. L., E-mail: maqinli@gmail.com, E-mail: mizukami@wpi-aimr.tohoku.ac.jp; Miyazaki, T.; Mizukami, S., E-mail: maqinli@gmail.com, E-mail: mizukami@wpi-aimr.tohoku.ac.jp [WPI Advanced Institute for Materials Research, Tohoku University, 2-1-1, Katahira, 980-8577 Sendai (Japan); Iihama, S. [Department of Applied Physics, Tohoku University, 6-6-05 Aza-Aoba, Aramaki, Aoba-ku, Sendai 980-8579 (Japan); Zhang, X. M. [Key Laboratory for Anisotropy and Texture of Materials, Ministry of Education, Northeastern University, Shenyang 110819 (China)
2015-11-30
The laser-induced spin dynamics of FeCo in perpendicularly magnetized L1{sub 0}-MnGa/FeCo bilayers with ferromagnetic and antiferromagnetic interfacial exchange coupling (IEC) are examined using the time-resolved magneto-optical Kerr effect. We found a precessional phase reversal of the FeCo layer as the IEC changes from ferromagnetic to antiferromagnetic. Moreover, a precession-suspension window was observed when the magnetic field was applied in a certain direction for the bilayer with ferromagnetic IEC. Our observations reveal that the spin dynamics modulation is strongly dependent on the IEC type within the Landau-Lifshitz-Gilbert depiction. The IEC dependence of the precessional phase and amplitude suggests the interesting method for magnetization dynamics modulation.
International Nuclear Information System (INIS)
The laser-induced spin dynamics of FeCo in perpendicularly magnetized L10-MnGa/FeCo bilayers with ferromagnetic and antiferromagnetic interfacial exchange coupling (IEC) are examined using the time-resolved magneto-optical Kerr effect. We found a precessional phase reversal of the FeCo layer as the IEC changes from ferromagnetic to antiferromagnetic. Moreover, a precession-suspension window was observed when the magnetic field was applied in a certain direction for the bilayer with ferromagnetic IEC. Our observations reveal that the spin dynamics modulation is strongly dependent on the IEC type within the Landau-Lifshitz-Gilbert depiction. The IEC dependence of the precessional phase and amplitude suggests the interesting method for magnetization dynamics modulation
Spin correlations in percolating networks with fractal geometry
International Nuclear Information System (INIS)
Using neutron scattering techniques, the authors investigated the magnetic correlations in diluted antiferromagnets close to the percolation threshold in which the magnetic connectivity takes a fractal form. Recent experimental results concerning the self-similarity of the magnetic order, and magnetic excitations in two-dimensional Ising and three-dimensional Heisenberg antiferromagnets are presented
Spin correlations in percolating networks with fractal geometry
Energy Technology Data Exchange (ETDEWEB)
Ikeda, H.; Iwasa, K. [Keio Univ., Hiyoshi (Japan); Fernandez-Baca, J.A.; Nicklow, R.M. [Oak Ridge National Lab., TN (United States)
1994-07-28
Using neutron scattering techniques, the authors investigated the magnetic correlations in diluted antiferromagnets close to the percolation threshold in which the magnetic connectivity takes a fractal form. Recent experimental results concerning the self-similarity of the magnetic order, and magnetic excitations in two-dimensional Ising and three-dimensional Heisenberg antiferromagnets are presented.
International Nuclear Information System (INIS)
For one-dimensional quantum spin chain systems recent experimental and theoretical studies indicate unexpectedly large, in some cases diverging spin and heat transport coefficients. Local probes, like e.g. muon spin relaxation (μSR) can indirectly characterize the spin transport properties of low dimensional systems via the magnetic field dependence of the spin lattice relaxation rate λ(B). For diffusive spin transport λ∝B-0.5 is expected. For the ground state of the isotropic spin-1/2 antiferromagnetic Heisenberg chain the eigenstates of the Heisenberg Hamiltonian dominate the spin transport, which is then ballistic. Using the Mueller ansatz λ∝B-1 is expected in this case. For SrCuO2 we find λ∝B-0.9(3). This result is temperature independent for 5 K≤T ≤300 K. Within conformal field theory and using the Mueller ansatz we conclude ballistic spin transport in SrCuO2.
Energy Technology Data Exchange (ETDEWEB)
Guo, Y. M.; Ruan, M. Y.; Cheng, J. J.; Sun, Y. C. [Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074 (China); School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China); Ouyang, Z. W., E-mail: zwouyang@mail.hust.edu.cn; Xia, Z. C. [Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074 (China); Rao, G. H. [School of Materials Science and Engineering, Guilin University of Electronic Technology, Guilin 541004 (China)
2015-06-14
High-field electron spin resonance (ESR) has been employed to study the antiferromagnetic (AFM) ordering state (T < T{sub N} = 55 K) of spin-chain multiferroic Gd{sub 2}BaNiO{sub 5}. The spin reorientation at T{sub SR} = 24 K is well characterized by the temperature-dependent ESR spectra. The magnetization data evidence a field-induced spin-flop transition at 2 K. The frequency-field relationship of the ESR data can be explained by conventional AFM resonance theory with uniaxial anisotropy, in good agreement with magnetization data. Related discussion on zero-field spin gap is presented.
Institute of Scientific and Technical Information of China (English)
YAO Xiao-yan; LI Peng-lei; DONG Shuai; LIU Jun-ming
2007-01-01
A three-dimensional Ising-like model doped with anti-ferromagnetic (AFM) bonds is proposed to investigate the magnetic properties of a doped triangular spin-chain system by using a Monte-Carlo simulation. The simulated results indicate that a steplike magnetization behavior is very sensitive to the concentration of AFM bonds. A low concentration of AFM bonds can suppress the stepwise behavior considerably, in accordance with doping experiments on Ca3Co206. The analysis of spin snapshots demonstrates that the AFM bond doping not only breaks the ferromagnetic ordered linear spin chains along the hexagonal c-axis but also has a great influence upon the spin configuration in the ab-plane.
International Nuclear Information System (INIS)
High-spin-polarization materials are desired for the realization of high-performance spintronic devices. We combine recent experimental and theoretical findings to theoretically design several high-spin-polarization materials in binary D03-type Heusler alloys: gapless (zero-gap) half-metallic ferrimagnets of V3Si and V3Ge, half-metallic antiferromagnets of Mn3Al and Mn3Ga, half-metallic ferrimagnets of Mn3Si and Mn3Ge, and a spin gapless semiconductor of Cr3Al. The high spin polarization, zero net magnetic moment, zero energy gap, and slight disorder compared to the ternary and quaternary Heusler alloys make these binary materials promising candidates for spintronic applications. All results are obtained by the electronic structure calculations from first-principles
Inverse spin Hall effect of antiferromagnetic MnIr in exchange biased NiFe/MnIr films
International Nuclear Information System (INIS)
Antiferromagnetic Mn3Ir, which is widely employed in exchange-biased applications, has attracted much attention recently due to its predicted and subsequently observed large spin Hall effect, therefore increasing its potential for spintronic devices in place of conventional paramagnetic 5d spin Hall metals. (Pt, Ta and W) Via the electrical detection of ferromagnetic resonance, we study a series of exchange biased NiFe/MnIr films for various MnIr thicknesses. In these systems, spin-pumped spin currents from NiFe are converted into dc voltages within MnIr via the inverse spin Hall effect (ISHE), which mixes with spin rectification voltages generated from NiFe. Through angular measurements, we separate these different voltage contributions to qualitatively detect non-zero ISHE in MnIr, which coexists with a non-zero unidirectional anisotropy. We find significant extrinsic damping contributions which prevent the accurate quantification of spin pumping-induced ISHE in MnIr films. The results show that spin currents may propagate and dissipate in MnIr films through ISHE in the presence of exchange bias. (paper)
Incommensurate antiferromagnetism and magnetic correlations in CeCu6-xAux
DEFF Research Database (Denmark)
Stockert, O.; Lohneysen, H. von; Schröder, A.;
1997-01-01
Magnetic ordering and correlations in single crystals of the heavy-fermion alloys CeCu5.8Au0.2 and CeCu5.9Au0.1 were investigated by elastic and inelastic neutron scattering. CeCu5.8Au0.2 orders with an incommensurate magnetic structure and a wave vector q = (+/- 0.79 0 0). Only dynamic antiferro......Magnetic ordering and correlations in single crystals of the heavy-fermion alloys CeCu5.8Au0.2 and CeCu5.9Au0.1 were investigated by elastic and inelastic neutron scattering. CeCu5.8Au0.2 orders with an incommensurate magnetic structure and a wave vector q = (+/- 0.79 0 0). Only dynamic...... antiferromagnetic correlations along a* are observed in CeCu5.9Au0.1 which evolve into a static sine modulation in CeCu5.8Au0.2....
International Nuclear Information System (INIS)
For the integrable higher-spin XXX and XXZ spin chains we present multiple-integral representations for the correlation function of an arbitrary product of Hermitian elementary matrices in the massless ground state. We give a formula expressing it by a single term of multiple integrals. In particular, we explicitly derive the emptiness formation probability (EFP). We assume 2s-strings for the ground-state solution of the Bethe-ansatz equations for the spin-s XXZ chain, and solve the integral equations for the spin-s Gaudin matrix. In terms of the XXZ coupling Δ we define ζ by Δ=cosζ, and put it in a region 0≤ζ<π/2s of the gapless regime: -1<Δ≤1 (0≤ζ<π), where Δ=1 (ζ=0) corresponds to the antiferromagnetic point. We calculate the zero-temperature correlation functions by the algebraic Bethe-ansatz, introducing the Hermitian elementary matrices in the massless regime, and taking advantage of the fusion construction of the R-matrix of the higher-spin representations of the affine quantum group.
XXZ-spin chain with asymmetry parameter Δ = -1/2. Calculation of simplest correlators
International Nuclear Information System (INIS)
One studied final XXZ-spin chain with periodical boundary conditions and N odd number of nodes. It turns out that in case of special value of asymmetry parameters - Δ = -1/2 - the principal state of this system has E0 = -3N/2 energy. Though this state is of antiferromagnetic nature but one manages to derive the appropriate solution of the Bethe equations and to create Q(u) trigonometric polynomial of n = (N-1)/2 degree which zeros are the parameters of the Bethe wave function for the system principal state. Using the second independent solution of this equation one may find derivative of XXZ-chain principal state energy with respect to η crossing-parameter. This derivative is closely associated with one of spin-spin correlation functions. This correlation function offers the average number of spin strings for the principal state of the studied chain, that is, string> = (3/8)(N-1)/N
Institute of Scientific and Technical Information of China (English)
Jiang Xue-Fan; Liu Xian-Feng; Wu Yin-Zhong; Han Jiu-Rong
2012-01-01
The magnetic and electronic properties of the geometrically frustrated triangular antiferromagnet CuCrO2 are investigated by first principles through density functional theory calculations within the generalized gradient approximations (GGA)+U scheme.The spin exchange interactions up to the third nearest neighbours in the ab plane as well as the coupling between adjacent layers are calculated to examine the magnetism and spin frustration.It is found that CuCrO2 has a natural two-dimensional characteristic of the magnetic interaction.Using Monte-Carlo simulation,we obtain the Néel temperature to be 29.9 K,which accords well with the experimental value of 24 K.Based on noncollinear magnetic structure calculations,we verify that the incommensurate spiral-spin structure with (110) spiral plane is believable for the magnetic ground state,which is consistent with the experimental observations.Due to intra-layer geometric spin frustration,parallel helical-spin chains arise along the a,b,or a + b directions,each with a screw-rotation angle of about 120°.Our calculations of the density of states show that the spin frustration plays an important role in the change of d-p hybridization,while the spin-orbit coupling has a very limited influence on the electronic structure.
International Nuclear Information System (INIS)
In this work we study the critical behavior of the quantum spin-1/2 anisotropic Heisenberg antiferromagnet in the presence of a longitudinal field on a body centered cubic (bcc) lattice as a function of temperature, anisotropy parameter (Δ) and magnetic field (H), where Δ=0 and 1 correspond the isotropic Heisenberg and Ising models, respectively. We use the framework of the differential operator technique in the effective-field theory with finite cluster of N=4 spins (EFT-4). The staggered ms=(mA−mB)/2 and total m=(mA+mB)/2 magnetizations are numerically calculated, where in the limit of ms→0 the critical line TN(H,Δ) is obtained. The phase diagram in the T−H plane is discussed as a function of the parameter Δ for all values of H∈[0,Hc(Δ)], where Hc(Δ) correspond the critical field (TN=0). Special focus is given in the low temperature region, where a reentrant behavior is observed around of H=Hc(Δ)≥Hc(Δ=1)=8J in the Ising limit, results in accordance with Monte Carlo simulation, and also was observed for all values of Δ∈[0,1]. This reentrant behavior increases with increase of the anisotropy parameter Δ. In the limit of low field, our results for the Heisenberg limit are compared with series expansion values. - Highlights: ► In the lat decade there has been a great interest in the physics of the quantum phase transition in spins system. ► Effective-field theory in cluster with N=4 spins is generalized to treat the quantum spin-1/2 Heisenberg model. ► We have obtained phase diagram at finite temperature for the quantum spin-1/2 antiferromagnet Heisenberg model as a bcc lattice.
Directory of Open Access Journals (Sweden)
E Ghasemikhah
2012-03-01
Full Text Available This study investigated the electronic properties of antiferromagnetic UBi2 metal by using ab initio calculations based on the density functional theory (DFT, employing the augmented plane waves plus local orbital method. We used the exact exchange for correlated electrons (EECE method to calculate the exchange-correlation energy under a variety of hybrid functionals. Electric field gradients (EFGs at the uranium site in UBi2 compound were calculated and compared with the experiment. The EFGs were predicted experimentally at the U site to be very small in this compound. The EFG calculated by the EECE functional are in agreement with the experiment. The densities of states (DOSs show that 5f U orbital is hybrided with the other orbitals. The plotted Fermi surfaces show that there are two kinds of charges on Fermi surface of this compound.
The fishnet as anti-ferromagnetic phase of world sheet Ising spins
International Nuclear Information System (INIS)
We identify the strong coupling fishnet diagram with a certain Ising spin configuration in the light cone world sheet description of planar TrPHI3 field theory. Then, using a mean field formalism, we take the remaining planar diagrams into account in an average way. Since the fishnet spin configuration is regular but non-uniform, we introduce two mean fields phi,phi' where the fishnet diagram is the case phi=1, phi'=0. For general values of these fields, the system is then approximated as a light-cone quantized string with a field dependent effective string tension Teff(phi,phi'). We also calculate the world sheet energy density E(phi,phi'), and find the field values that minimize it in the presence of a transverse space infra-red cutoff ε>0. The criterion for string formation is that the tension in this minimum energy state remains non-zero as ε→0. In the most simple-minded implementation of the mean field method, which neglects all short range correlations of the Ising spins, we find, in this limit, that the tension vanishes for weak and moderate coupling, but for very large coupling does indeed stay non-zero. However, a more elaborate treatment, taking temporal correlations into account (but still neglecting spatial correlations), removes this 'phase transition' and the string tension of the minimum energy state vanishes for all values of the coupling when ε→0. Our mean field analysis thus suggests that the 'fishnet phase' of TrPHI3 theory is unstable, and there is no string formation for any value of the coupling. This is probably a reasonable outcome given the instability of the underlying theory. It is encouraging for our method, that an approach designed for a string description can predict, where appropriate, the absence of string formation within an intuitive and simple approximation
Ice rule correlations in stuffed spin ice
International Nuclear Information System (INIS)
Stuffed spin ice is a chemical variation of a spin ice material like Ho2Ti2O7 in which extra magnetic ions are inserted into the crystal structure. Previous studies have shown that the degree of stuffing has very little effect on the residual entropy in the system, which takes a value very close to the spin ice entropy. We argue, however, that the observation of this entropy does not imply long range coherence of the ice rules, that determine the local spin configurations. We have characterized deviations from the ice rules by means of a polarized neutron diffraction study of a single crystal of Ho2+δTi2−δO7−δ/2 with δ = 0.3. Our results demonstrate that the ice rules in stuffed spin ice are strictly valid only over a relatively short range, and that at longer range stuffed spin ice exhibits some characteristics of a ‘cluster glass’, with a tendency to more conventional ferromagnetic correlations. (paper)
Ghosh, Sayandip; Raghuvanshi, Nimisha; Mohapatra, Shubhajyoti; Kumar, Ashish; Singh, Avinash
2016-09-14
Effective spin couplings and spin fluctuation induced quantum corrections to sublattice magnetization are obtained in the [Formula: see text] AF state of a realistic three-orbital interacting electron model involving xz, yz and xy Fe 3d orbitals, providing insight into the multi-orbital quantum antiferromagnetism in iron pnictides. The xy orbital is found to be mainly responsible for the generation of strong ferromagnetic spin coupling in the b direction, which is critically important to fully account for the spin wave dispersion as measured in inelastic neutron scattering experiments. The ferromagnetic spin coupling is strongly suppressed as the xy band approaches half filling, and is ascribed to particle-hole exchange in the partially filled xy band. The strongest AF spin coupling in the a direction is found to be in the orbital off-diagonal sector involving the xz and xy orbitals. First order quantum corrections to sublattice magnetization are evaluated for the three orbitals, and yield a significant [Formula: see text] average reduction from the Hartree-Fock value. PMID:27406889
Palii, Andrei V; Reu, Oleg S; Ostrovsky, Sergei M; Klokishner, Sophia I; Tsukerblat, Boris S; Sun, Zhong-Ming; Mao, Jiang-Gao; Prosvirin, Andrey V; Zhao, Han-Hua; Dunbar, Kim R
2008-11-01
In this article we report for the first time experimental details concerning the synthesis and full characterization (including the single-crystal X-ray structure) of the spin-canted zigzag-chain compound [Co(H2L)(H2O)]infinity [L = 4-Me-C6H4-CH2N(CPO3H2)2], which contains antiferromagnetically coupled, highly magnetically anisotropic Co(II) ions with unquenched orbital angular momenta, and we also propose a new model to explain the single-chain magnet behavior of this compound. The model takes into account (1) the tetragonal crystal field and the spin-orbit interaction acting on each Co(II) ion, (2) the antiferromagnetic Heisenberg exchange between neighboring Co(II) ions, and (3) the tilting of the tetragonal axes of the neighboring Co units in the zigzag structure. We show that the tilting of the anisotropy axes gives rise to spin canting and consequently to a nonvanishing magnetization for the compound. In the case of a strong tetragonal field that stabilizes the orbital doublet of Co(II), the effective pseudo-spin-1/2 Hamiltonian describing the interaction between the Co ions in their ground Kramers doublet states is shown to be of the Ising type. An analytical expression for the static magnetic susceptibility of the infinite spin-canted chain is obtained. The model provides an excellent fit to the experimental data on both the static and dynamic magnetic properties of the chain. PMID:18839950
Mi, Bin-Zhou
2016-07-01
The thermodynamic properties of the frustrated arbitrary spin-S J1-J2 Heisenberg antiferromagnet on the body-centered-cubic lattice for Néel phase are systematically calculated by use of the double-time Green's function method within the random phase approximation (RPA). The role of spin quantum number and frustration strength on sublattice magnetization, Néel temperature, internal energy, and free energy are carefully analyzed. The curve of zero-temperature sublattice magnetization / S versus frustration strength J2/J1 values are almost flat at the larger spin quantum number S=10. With the increase of normalized temperature T/TN, the larger the spin quantum number S, the faster the / S drops, and the smaller influence of J2/J1 on the / S versus T/TN curve. Under the RPA approach, the Néel temperature TN /Sp and the internal energy E/Sp at the Néel point are independent of spin quantum number S. The numerical results show that the internal energy E/Sp at the Néel point seems independent of the frustration strength J2/J1. This indicates that thermodynamic quantities have universal characteristics for large spin quantum number.
Ghosh, Pratyay; Verma, Akhilesh Kumar; Kumar, Brijesh
2016-01-01
A spin-1 Heisenberg model on trimerized kagome lattice is studied by doing a low-energy bosonic theory in terms of plaquette triplons defined on its triangular unit cells. The model considered has an intratriangle antiferromagnetic exchange interaction J (set to 1) and two intertriangle couplings J'>0 (nearest neighbor) and J″ (next nearest neighbor; of both signs). The triplon analysis performed on this model investigates the stability of the trimerized singlet ground state (which is exact in the absence of intertriangle couplings) in the J'-J″ plane. It gives a quantum phase diagram that has two gapless antiferromagnetically ordered phases separated by the spin-gapped trimerized singlet phase. The trimerized singlet ground state is found to be stable on J″=0 line (the nearest-neighbor case), and on both sides of it for J″≠0 , in an extended region bounded by the critical lines of transition to the gapless antiferromagnetic phases. The gapless phase in the negative J″ region has a coplanar 120∘ antiferromagnetic order with √{3 }×√{3 } structure. In this phase, all the magnetic moments are of equal length, and the angle between any two of them on a triangle is exactly 120∘. The magnetic lattice in this case has a unit cell consisting of three triangles. The other gapless phase, in the positive J″ region, is found to exhibit a different coplanar antiferromagnetic order with ordering wave vector q =(0 ,0 ) . Here, two magnetic moments in a triangle are of the same magnitude, but shorter than the third. While the angle between two short moments is 120∘-2 δ , it is 120∘+δ between a short and the long one. Only when J″=J' , their magnitudes become equal and the relative angles 120∘. The magnetic lattice in this q =(0 ,0 ) phase has the translational symmetry of the kagome lattice with triangular unit cells of reduced (isosceles) symmetry. This reduction in the point-group symmetry is found to show up as a difference in the intensities of
Sandratskii, Leonid M.; Buczek, Paweł
2011-01-01
The study of the spin excitations in antiferromagnetic (AFM) and ferromagnetic (FM) phases of FeRh is reported. We demonstrate that although the Fe atomic moments are well defined there is a number of important phenomena absent in the Heisenberg description: Landau damping of spin waves, large Rh moments induced by the AFM magnons, the formation of the optical magnons terminated by Stoner excitations. We relate the properties of the spin-wave damping to the features of the Stoner continuum an...
Antiferromagnetic correlations near the lower edge of superconducting dome in YBCO6+x
International Nuclear Information System (INIS)
Neutron scattering from high-quality YBCO6.334 single crystals with a Tc of 8.4 K shows that there is no coexistence with long-range antiferromagnetic order at this very low, near-critical doping of ∼0.055, in contrast to claims based on local probe techniques. We find that the neutron resonance seen in optimally doped YBCO7 and underdoped YBCO6.5, has undergone large softening and damping. It appears that the overdamped resonance, with a relaxation rate of 2 meV, is coupled to a zero-energy central mode that grows with cooling and eventually saturates with no change at or below Tc. Although a similar qualitative behaviour is found for YBCO6.35, our study shows that the central mode is stronger in YBCO6.334 than YBCO6.35. The system remains subcritical with short-ranged three dimensional correlations
Disappearance of antiferromagnetic spin excitations in overdoped La2-xSrxCuO4.
Wakimoto, S; Yamada, K; Tranquada, J M; Frost, C D; Birgeneau, R J; Zhang, H
2007-06-15
Magnetic excitations for energies up to approximately 100 meV are studied for overdoped La(2-x)Sr(x)CuO(4) with x=0.25 and 0.30, using time-of-flight neutron spectroscopy. Comparison of spectra integrated over the width of an antiferromagnetic Brillouin zone demonstrates that the magnetic scattering at intermediate energies, 20 magnetism is not related to Fermi surface nesting, but rather is associated with a decreasing volume fraction of (probably fluctuating) antiferromagnetic bubbles. PMID:17677985
Energy Technology Data Exchange (ETDEWEB)
Adelnia, Fatemeh [Dipartimento di Fisica, Università degli Studi di Milano and INSTM, I-20133 Milano (Italy); Dipartimento di Fisica, Università degli Studi di Pavia and INSTM, I-27100 Pavia (Italy); Chiesa, Alessandro; Bordignon, Sara; Carretta, Stefano [Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Parma, I-43124 Parma (Italy); Ghirri, Alberto; Candini, Andrea [CNR Institute Nanosciences S3, I- 41125 Modena (Italy); Cervetti, Christian [Dipartimento di Scienze Fisiche, Informatiche, Matematiche, Università di Modena e Reggio Emilia, I-41125 Modena (Italy); Evangelisti, Marco [CNR Institute Nanosciences S3, I- 41125 Modena (Italy); Dipartimento di Scienze Fisiche, Informatiche, Matematiche, Università di Modena e Reggio Emilia, I-41125 Modena (Italy); Instituto de Ciencia de Materiales de Aragón and Departamento de Física de la Materia Condensada, CSIC-Universidad de Zaragoza, 50009 Zaragoza (Spain); Affronte, Marco [CNR Institute Nanosciences S3, I- 41125 Modena (Italy); Dipartimento di Scienze Fisiche, Informatiche, Matematiche, Università di Modena e Reggio Emilia, I-41125 Modena (Italy); Sheikin, Ilya [Grenoble High Magnetic Field Laboratory, CNRS-LNCMI, 25, B.P. 166, 38042 Grenoble Cedex 9 (France); Winpenny, Richard; Timco, Grigore [The Lewis Magnetism Laboratory, The University of Manchester, M13 9PL Manchester (United Kingdom); Borsa, Ferdinando [Dipartimento di Fisica, Università degli Studi di Pavia and INSTM, I-27100 Pavia (Italy); and others
2015-12-28
A detailed experimental investigation of the effects giving rise to the magnetic energy level structure in the vicinity of the level crossing (LC) at low temperature is reported for the open antiferromagnetic molecular ring Cr{sub 8}Zn. The study is conducted by means of thermodynamic techniques (torque magnetometry, magnetization and specific heat measurements) and microscopic techniques (nuclear magnetic resonance line width, nuclear spin lattice, and spin-spin relaxation measurements). The experimental results are shown to be in excellent agreement with theoretical calculations based on a minimal spin model Hamiltonian, which includes a Dzyaloshinskii-Moriya interaction. The first ground state level crossing at μ{sub 0}H{sub c1} = 2.15 T is found to be an almost true LC while the second LC at μ{sub 0}H{sub c2} = 6.95 T has an anti-crossing gap of Δ{sub 12} = 0.19 K. In addition, both NMR and specific heat measurements show the presence of a level anti-crossing between excited states at μ{sub 0}H = 4.5 T as predicted by the theory. In all cases, the fit of the experimental data is improved by introducing a distribution of the isotropic exchange couplings (J), i.e., using a J strain model. The peaks at the first and second LCs in the nuclear spin-lattice relaxation rate are dominated by inelastic scattering and a value of Γ ∼ 10{sup 10} rad/s is inferred for the life time broadening of the excited state of the open ring, due to spin phonon interaction. A loss of NMR signal (wipe-out effect) is observed for the first time at LC and is explained by the enhancement of the spin-spin relaxation rate due to the inelastic scattering.
International Nuclear Information System (INIS)
A detailed experimental investigation of the effects giving rise to the magnetic energy level structure in the vicinity of the level crossing (LC) at low temperature is reported for the open antiferromagnetic molecular ring Cr8Zn. The study is conducted by means of thermodynamic techniques (torque magnetometry, magnetization and specific heat measurements) and microscopic techniques (nuclear magnetic resonance line width, nuclear spin lattice, and spin-spin relaxation measurements). The experimental results are shown to be in excellent agreement with theoretical calculations based on a minimal spin model Hamiltonian, which includes a Dzyaloshinskii-Moriya interaction. The first ground state level crossing at μ0Hc1 = 2.15 T is found to be an almost true LC while the second LC at μ0Hc2 = 6.95 T has an anti-crossing gap of Δ12 = 0.19 K. In addition, both NMR and specific heat measurements show the presence of a level anti-crossing between excited states at μ0H = 4.5 T as predicted by the theory. In all cases, the fit of the experimental data is improved by introducing a distribution of the isotropic exchange couplings (J), i.e., using a J strain model. The peaks at the first and second LCs in the nuclear spin-lattice relaxation rate are dominated by inelastic scattering and a value of Γ ∼ 1010 rad/s is inferred for the life time broadening of the excited state of the open ring, due to spin phonon interaction. A loss of NMR signal (wipe-out effect) is observed for the first time at LC and is explained by the enhancement of the spin-spin relaxation rate due to the inelastic scattering
Adelnia, Fatemeh; Chiesa, Alessandro; Bordignon, Sara; Carretta, Stefano; Ghirri, Alberto; Candini, Andrea; Cervetti, Christian; Evangelisti, Marco; Affronte, Marco; Sheikin, Ilya; Winpenny, Richard; Timco, Grigore; Borsa, Ferdinando; Lascialfari, Alessandro
2015-12-01
A detailed experimental investigation of the effects giving rise to the magnetic energy level structure in the vicinity of the level crossing (LC) at low temperature is reported for the open antiferromagnetic molecular ring Cr8Zn. The study is conducted by means of thermodynamic techniques (torque magnetometry, magnetization and specific heat measurements) and microscopic techniques (nuclear magnetic resonance line width, nuclear spin lattice, and spin-spin relaxation measurements). The experimental results are shown to be in excellent agreement with theoretical calculations based on a minimal spin model Hamiltonian, which includes a Dzyaloshinskii-Moriya interaction. The first ground state level crossing at μ0Hc1 = 2.15 T is found to be an almost true LC while the second LC at μ0Hc2 = 6.95 T has an anti-crossing gap of Δ12 = 0.19 K. In addition, both NMR and specific heat measurements show the presence of a level anti-crossing between excited states at μ0H = 4.5 T as predicted by the theory. In all cases, the fit of the experimental data is improved by introducing a distribution of the isotropic exchange couplings (J), i.e., using a J strain model. The peaks at the first and second LCs in the nuclear spin-lattice relaxation rate are dominated by inelastic scattering and a value of Γ ˜ 1010 rad/s is inferred for the life time broadening of the excited state of the open ring, due to spin phonon interaction. A loss of NMR signal (wipe-out effect) is observed for the first time at LC and is explained by the enhancement of the spin-spin relaxation rate due to the inelastic scattering.
International Nuclear Information System (INIS)
Time-of-flight and polarized triple axis neutron scattering is used to probe the spin excitations of Cu(DCOO)2x4D2O and La2-xSrxCuO4. The first part of the thesis contains an investigation of the excitation spectrum of the square lattice S = 1/2 Heisenberg antiferromagnet Cu(DCOO)24D2O. Along the antiferromagnetic zone boundary a pronounced intensity variation is found for the dominant single-magnon excitations. This variation tracks an already known zone boundary dispersion. Using polarization analysis to separate the components of the excitation spectrum, a continuum of longitudinally polarized multimagnon excitations is discovered at energies above the single-magnon branch. At low energies, the findings are well described by linear spin wave theory. At high energies, linear spin wave theory fails and instead the data are very well accounted for by state-of-the-art Quantum Monte Carlo computations. In the second part of the thesis, the spin excitation spectra of the high temperature superconductors La1.90Sr0.10CuO4 and La1.84Sr0.16Cu characterized. The main discovery is that the excitations are dispersive at both doping levels. The dispersion strongly resembles that seen in other high-Tc superconductors. The presence of dispersive excitations does not require superconductivity to exist. For La1.84Sr0.16CuO4, but not for La1.90Sr0.10CuO4, the onset superconductivity gives rise to a spectral weight shift which displays qualitative and quantitative similarities to the resonance mode observed in other high-Tc superconductors. (au)
Energy Technology Data Exchange (ETDEWEB)
Bech Christensen, N
2005-01-01
Time-of-flight and polarized triple axis neutron scattering is used to probe the spin excitations of Cu(DCOO){sub 2}x4D{sub 2}O and La{sub 2-x}Sr{sub x}CuO{sub 4}. The first part of the thesis contains an investigation of the excitation spectrum of the square lattice S = 1/2 Heisenberg antiferromagnet Cu(DCOO){sub 2}4D{sub 2}O. Along the antiferromagnetic zone boundary a pronounced intensity variation is found for the dominant single-magnon excitations. This variation tracks an already known zone boundary dispersion. Using polarization analysis to separate the components of the excitation spectrum, a continuum of longitudinally polarized multimagnon excitations is discovered at energies above the single-magnon branch. At low energies, the findings are well described by linear spin wave theory. At high energies, linear spin wave theory fails and instead the data are very well accounted for by state-of-the-art Quantum Monte Carlo computations. In the second part of the thesis, the spin excitation spectra of the high temperature superconductors La{sub 1.90}Sr{sub 0.10}CuO{sub 4} and La{sub 1.84}Sr{sub 0.16}Cu characterized. The main discovery is that the excitations are dispersive at both doping levels. The dispersion strongly resembles that seen in other high-T{sub c} superconductors. The presence of dispersive excitations does not require superconductivity to exist. For La{sub 1.84}Sr{sub 0.16}CuO{sub 4}, but not for La{sub 1.90}Sr{sub 0.10}CuO{sub 4}, the onset superconductivity gives rise to a spectral weight shift which displays qualitative and quantitative similarities to the resonance mode observed in other high-T{sub c} superconductors. (au)
Li, Yuesheng; Liao, Haijun; Zhang, Zhen; Li, Shiyan; Jin, Feng; Ling, Langsheng; Zhang, Lei; Zou, Youming; Pi, Li; Yang, Zhaorong; Wang, Junfeng; Wu, Zhonghua; Zhang, Qingming
2015-11-01
Quantum spin liquid (QSL) is a novel state of matter which refuses the conventional spin freezing even at 0 K. Experimentally searching for the structurally perfect candidates is a big challenge in condensed matter physics. Here we report the successful synthesis of a new spin-1/2 triangular antiferromagnet YbMgGaO4 with symmetry. The compound with an ideal two-dimensional and spatial isotropic magnetic triangular-lattice has no site-mixing magnetic defects and no antisymmetric Dzyaloshinsky-Moriya (DM) interactions. No spin freezing down to 60 mK (despite θw ~ -4 K), the power-law temperature dependence of heat capacity and nonzero susceptibility at low temperatures suggest that YbMgGaO4 is a promising gapless (≤|θw|/100) QSL candidate. The residual spin entropy, which is accurately determined with a non-magnetic reference LuMgGaO4, approaches zero (<0.6%). This indicates that the possible QSL ground state (GS) of the frustrated spin system has been experimentally achieved at the lowest measurement temperatures.
Spin Dynamics and Critical Fluctuations in a Two-Dimensional Random Antiferromagnet
DEFF Research Database (Denmark)
Als-Nielsen, Jens Aage; Birgeneau, R. J.; Guggenheim, H. J.; Shirane, G.
1975-01-01
A comprehensive elastic- and inelastic-neutron-scattering study of the binary mixed antiferromagnet Rb2Mn0.5Ni0.5F4 has been carried out. The pure materials, Rb2MnF4 and Rb2NiF4 are [2d] near-Heisenberg antiferromagnets of the K2NiF4 type. Elastic-scattering experiments demonstrate that the Mn......++ and Ni++ ions are randomly distributed on a plane square lattice. At ∼ 64 K the system undergoes a second-order phase transition to two distinct [3d] antiferromagnetic structures, with both structures being composed of simple [2d] square antiferromagnetic arrays. All properties are found to be...... cluster model while the over-all dispersion is correctly given by the Walker mean-crystal model. The above calculations involve only interaction constants taken from the pure materials and JMn-Ni=(JMn-MnJNi-Ni)1/2 so that there are no adjustable parameters. At higher temperatures it is found that the gap...
Quantum Monte Carlo simulation of antiferromagnetic spin ladder (C5H12N)2CuBr4
Freitas, Augusto S.
2016-07-01
In this paper I present a Quantum Monte Carlo (QMC) study of the magnetic properties of an antiferromagnetic spin ladder (C5H12N)2CuBr4. This compound is the prototype of the Heisenberg model for a two leg spin ladder in the presence of an external magnetic field. The susceptibility phase diagram has a rounded peak in the vicinity of T=7.4 K, obeys Troyer's law for low temperatures, and Curie's law for high temperatures. I also study the susceptibility diagram in low temperatures and I found the spin gap Δ=9.26 K, in good concordance with the experimental value, 9.5 K. In high field, I present a diagram of magnetization as a function of temperature. In the vicinity of a critical field, Hci, the magnetization scales with T1/2 and this result was found also in the QMC simulation. In all the results, there is a very good concordance with the experimental data. I also show in this paper that the spin gap is null and the susceptibility is proportional to T for low temperatures when relatively high values of the ladders' coupling is taken in account.
Khuntia, P.; Bert, F.; Mendels, P.; Koteswararao, B.; Mahajan, A. V.; Baenitz, M.; Chou, F. C.; Baines, C.; Amato, A.; Furukawa, Y.
2016-03-01
PbCuTe2O6 is a rare example of a spin liquid candidate featuring a three-dimensional magnetic lattice. Strong geometric frustration arises from the dominant antiferromagnetic interaction that generates a hyperkagome network of Cu2 + ions although additional interactions enhance the magnetic lattice connectivity. Through a combination of magnetization measurements and local probe investigations by NMR and muon spin relaxation down to 20 mK, we provide robust evidence for the absence of magnetic freezing in the ground state. The local spin susceptibility probed by the NMR shift hardly deviates from the macroscopic one down to 1 K pointing to a homogeneous magnetic system with a low defect concentration. The saturation of the NMR shift and the sublinear power law temperature (T ) evolution of the 1 /T1 NMR relaxation rate at low T point to a nonsinglet ground state favoring a gapless fermionic description of the magnetic excitations. Below 1 K a pronounced slowing down of the spin dynamics is witnessed, which may signal a reconstruction of spinon Fermi surface. Nonetheless, the compound remains in a fluctuating spin liquid state down to the lowest temperature of the present investigation.
Khuntia, P; Bert, F; Mendels, P; Koteswararao, B; Mahajan, A V; Baenitz, M; Chou, F C; Baines, C; Amato, A; Furukawa, Y
2016-03-11
PbCuTe_{2}O_{6} is a rare example of a spin liquid candidate featuring a three-dimensional magnetic lattice. Strong geometric frustration arises from the dominant antiferromagnetic interaction that generates a hyperkagome network of Cu^{2+} ions although additional interactions enhance the magnetic lattice connectivity. Through a combination of magnetization measurements and local probe investigations by NMR and muon spin relaxation down to 20 mK, we provide robust evidence for the absence of magnetic freezing in the ground state. The local spin susceptibility probed by the NMR shift hardly deviates from the macroscopic one down to 1 K pointing to a homogeneous magnetic system with a low defect concentration. The saturation of the NMR shift and the sublinear power law temperature (T) evolution of the 1/T_{1} NMR relaxation rate at low T point to a nonsinglet ground state favoring a gapless fermionic description of the magnetic excitations. Below 1 K a pronounced slowing down of the spin dynamics is witnessed, which may signal a reconstruction of spinon Fermi surface. Nonetheless, the compound remains in a fluctuating spin liquid state down to the lowest temperature of the present investigation. PMID:27015508
Energy Technology Data Exchange (ETDEWEB)
Neto, Minos A., E-mail: minos@pq.cnpq.br [Departamento de Fisica, Universidade Federal do Amazonas, 3000, Japiim, Manaus, 69077-000 AM (Brazil); Roberto Viana, J., E-mail: vianafisica@bol.com.br [Departamento de Fisica, Universidade Federal do Amazonas, 3000, Japiim, Manaus, 69077-000 AM (Brazil); Ricardo de Sousa, J., E-mail: jsousa@edu.ufam.br [Departamento de Fisica, Universidade Federal do Amazonas, 3000, Japiim, Manaus, 69077-000 AM (Brazil); National Institute of Science and Technology for Complex Systems, 3000, Japiim, Manaus, 69077-000 AM (Brazil)
2012-08-15
In this work we study the critical behavior of the quantum spin-1/2 anisotropic Heisenberg antiferromagnet in the presence of a longitudinal field on a body centered cubic (bcc) lattice as a function of temperature, anisotropy parameter ({Delta}) and magnetic field (H), where {Delta}=0 and 1 correspond the isotropic Heisenberg and Ising models, respectively. We use the framework of the differential operator technique in the effective-field theory with finite cluster of N=4 spins (EFT-4). The staggered m{sub s}=(m{sub A}-m{sub B})/2 and total m=(m{sub A}+m{sub B})/2 magnetizations are numerically calculated, where in the limit of m{sub s}{yields}0 the critical line T{sub N}(H,{Delta}) is obtained. The phase diagram in the T-H plane is discussed as a function of the parameter {Delta} for all values of H Element-Of [0,H{sub c}({Delta})], where H{sub c}({Delta}) correspond the critical field (T{sub N}=0). Special focus is given in the low temperature region, where a reentrant behavior is observed around of H=H{sub c}({Delta}){>=}H{sub c}({Delta}=1)=8J in the Ising limit, results in accordance with Monte Carlo simulation, and also was observed for all values of {Delta} Element-Of [0,1]. This reentrant behavior increases with increase of the anisotropy parameter {Delta}. In the limit of low field, our results for the Heisenberg limit are compared with series expansion values. - Highlights: Black-Right-Pointing-Pointer In the lat decade there has been a great interest in the physics of the quantum phase transition in spins system. Black-Right-Pointing-Pointer Effective-field theory in cluster with N=4 spins is generalized to treat the quantum spin-1/2 Heisenberg model. Black-Right-Pointing-Pointer We have obtained phase diagram at finite temperature for the quantum spin-1/2 antiferromagnet Heisenberg model as a bcc lattice.
Unusual spin correlations in a nanomagnet
International Nuclear Information System (INIS)
We show how atomic-scale exchange phenomena can be controlled and exploited in nanoscale itinerant magnets to substantially improve magnetic properties. Cluster-deposition experiments, first-principle simulations, and analytical calculations are used to demonstrate the effect in Co2Si nanoclusters, which have average sizes varying from about 0.6 to 29.5 nm. The cluster-deposited nanoparticles exhibit average magnetic moments of up to 0.70 μB/Co at 10 K and 0.49 μB/Co at 300 K with appreciable magnetocrystalline anisotropies, in sharp contrast to the nearly vanishing bulk magnetization. The underlying spin correlations and associated cluster-size dependence of the magnetization are explained by a surface induced ferromagnetic spin polarization with a decay length of the order of 1 nm, much larger than the nearest-neighbor interatomic distance in the alloy
Sandratskii, Leonid M.; Buczek, Paweł
2012-01-01
The study of the spin excitations in antiferromagnetic (AFM) and ferromagnetic (FM) phases of FeRh is reported. We demonstrate that, although the Fe atomic moments are well defined, there is a number of important phenomena absent in the Heisenberg description: Landau damping of spin waves, large Rh moments induced by the AFM magnons, and the formation of the optical magnons terminated by Stoner excitations. We relate the properties of the spin-wave damping to the features of the Stoner continuum and compare the chirality of the spin excitations in AFM, FM, and paramagnetic systems.
Anisotropic inplane spin correlation in the parent and Co-doped BaFe2As2: A neutron scattering study
International Nuclear Information System (INIS)
Highlights: • Doping dependence study of inplane spin correlation in the normal states. • Anisotropy is larger for the higher doping level. • Temperature dependence of spin correlation in the parent compound is unusual. - Abstract: Antiferromagnetic spin fluctuations were investigated in the normal states of the parent (x = 0), under-doped (x = 0.04) and optimally-doped (x = 0.06) Ba(Fe1-xCox)2As2 single crystals using inelastic neutron scattering technique. For all the doping levels, quasi-two-dimensional antiferromagnetic fluctuations were observed as a broad peak localized at Q=(1/2,1/2,l). At lower energies, the peak shows an apparent anisotropy in the hk0 plane; longitudinal peak widths are considerably smaller than transverse widths. The anisotropy is larger for the higher doping level. These results are consistent with the random phase approximation (RPA) calculations taking account of the orbital character of the electronic bands, confirming that the anisotropic nature of the spin fluctuations in the normal states is mostly dominated by the nesting of Fermi surfaces. On the other hand, the quasi-two-dimensional spin correlations grow much rapidly for decreasing temperature in the x = 0 parent compound, compared to that expected for nearly antiferromagnetic metals. This may be another sign of the unconventional nature of the antiferromagnetic transition in BaFe2As2
Spin frustration and magnetic ordering in triangular lattice antiferromagnet Ca3CoNb2O9
Dai, Jia; Zhou, Ping; Wang, Peng-Shuai; Pang, Fei; Munsie, Tim J.; Luke, Graeme M.; Zhang, Jin-Shan; Yu, Wei-Qiang
2015-12-01
We synthesized a quasi-two-dimensional distorted triangular lattice antiferromagnet Ca3CoNb2O9, in which the effective spin of Co2+ is 1/2 at low temperatures, whose magnetic properties were studied by dc susceptibility and magnetization techniques. The x-ray diffraction confirms the quality of our powder samples. The large Weiss constant θCW˜ -55 K and the low Neel temperature TN˜ 1.45 K give a frustration factor f = | θCW/TN | ≈ 38, suggesting that Ca3CoNb2O9 resides in strong frustration regime. Slightly below TN, deviation between the susceptibility data under zero-field cooling (ZFC) and field cooling (FC) is observed. A new magnetic state with 1/3 of the saturate magnetization Ms is suggested in the magnetization curve at 0.46 K. Our study indicates that Ca3CoNb2O9 is an interesting material to investigate magnetism in triangular lattice antiferromagnets with weak anisotropy. Project supported by the National Natural Science Foundation of China (Grant Nos. 11374364 and 11222433), the National Basic Research Program of China (Grant No. 2011CBA00112). Research at McMaster University supported by the Natural Sciences and Engineering Research Council. Work at North China Electric Power University supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.
DEFF Research Database (Denmark)
Clarke, S.J.; Harrison, A.; Mason, T.E.; Visser, D.
1999-01-01
Copper(II) formate tetrahydrate (CFTH) is a model square S = 1/2 Heisenberg antiferromagnet with T-N = 16.54 +/- 0.05 K. The dispersion of spin-waves in the magnetic layers of a fully deuterated sample of this material has been mapped at 4.3 K by inelastic neutron scattering from the zone centre at...
International Nuclear Information System (INIS)
The structure, hyperfine interactions and magnetic properties of the series of multiferroic Bim+1Ti3Fem−3O3m+3 Aurivillius compounds with m=4–8 were studied using X-ray diffraction, 57Fe Mössbauer spectroscopy and vibrating sample magnetometry. Samples were prepared by the conventional solid-state sintering method. Bulk magnetic measurements showed that for m=4 the compound is paramagnetic down to 2 K while in the compound with m=5 the antiferromagnetic type transition was observed at 11 K. In the case of compounds with m=6–8 much more complex magnetic behavior was found. For these compounds a gradual spin freezing and antiferromagnetic spin glass-like ordering were observed on decreasing temperature. The temperature of spin glass freezing was determined as 260, 280 and 350 K for m=6, 7 and 8, respectively. Room-temperature Mössbauer spectra of all the compounds studied confirm their paramagnetic state. However, liquid nitrogen and liquid helium temperature measurements reveal magnetic ordering with a residual paramagnetic phase contribution for the compounds with m=5–8. - Highlights: • Aurivillius compounds prepared by solid-state sintering. • Coexistence of antiferromagnetic and paramagnetic phases seen by Mössbauer spectra. • Hyperfine interactions parameters of compounds determined. • Antiferromagnetic spin glass-like ordering observed down to 10 K
Spin-glass, antiferromagnetism and Kondo behavior in Ce2Au1-CoSi3 alloys
Indian Academy of Sciences (India)
Subham Majumdar; E V Sampathkumaran; St Berger; M Della Mea; H Michor; E Bauer; M Brando; J Hemberger; A Loidl
2002-05-01
Recently, the solid solution Ce2Au1-CoSi3 has been shown to exhibit many magnetic anomalies associated with the competition between magnetic ordering and the Kondo effect. Here we report high pressure electrical resistivity of Ce2AuSi3, ac susceptibility () and magnetoresistance of various alloys of this solid solution in order to gain better knowledge of the magnetism of these alloys. High pressure resistivity behavior is consistent with the proposal that Ce2AuSi3 lies at the left-hand side of the maximum in Doniach’s magnetic phase diagram. The ac data reveal that there are in fact two magnetic transitions, one at 2 K and the other at 3 K for this compound, both of which are spin-glass-like. However, as the Co concentration is increased, antiferromagnetism is stabilized for intermediate compositions before attaining non-magnetism for the Co end member.
Huang, Yi-Zhen; Xi, Bin; Chen, Xi; Li, Wei; Wang, Zheng-Chuan; Su, Gang
2016-06-01
The quantum phase transition, scaling behaviors, and thermodynamics in the spin-1/2 quantum Heisenberg model with antiferromagnetic coupling J >0 in the armchair direction and ferromagnetic interaction J'ratio Q2 and spin stiffness ρ in two directions for various coupling ratios α =J'/J under different lattice sizes, we found that a quantum phase transition from the dimerized phase to the stripe phase occurs at the quantum critical point αc=-0.93 . Through the finite-size scaling analysis on Q2, ρx, and ρy, we determined the critical exponent related to the correlation length ν to be 0.7212(8), implying that this transition falls into a classical Heisenberg O(3) universality. A zero magnetization plateau is observed in the dimerized phase, whose width decreases with increasing α . A phase diagram in the coupling ratio α -magnetic field h plane is obtained, where four phases, including dimerized, stripe, canted stripe, and polarized, are identified. It is also unveiled that the temperature dependence of the specific heat C (T ) for different α 's intersects precisely at one point, similar to that of liquid 3He under different pressures and several magnetic compounds under various magnetic fields. The scaling behaviors of Q2, ρ , and C (T ) are carefully analyzed. The susceptibility is compared with the experimental data to give the magnetic parameters of both compounds.
Exact ground and excited states of an antiferromagnetic quantum spin model
International Nuclear Information System (INIS)
A quasi-one-dimensional spin model which consists of a chain of octahedra of spins has been suggested for which a certain parameter regime of the Hamiltonian, the ground state, can be written down exactly. The ground state is highly degenerate and can be other than a singlet. Also, several excited states can be constructed exactly. The ground state is a local RVB state for which resonance is confined to rings of spins. Some exact numerical results for an octahedron of spins have also been reported. (author). 16 refs, 2 figs, 1 tab
Dugave, Maxime; Kozlowski, Karol K; Suzuki, Junji
2016-01-01
We use the form factors of the quantum transfer matrix in the zero-temperature limit in order to study the two-point ground-state correlation functions of the XXZ chain in the antiferromagnetic massive regime. We obtain novel form factor series representations of the correlation functions which differ from those derived either from the q-vertex-operator approach or from the algebraic Bethe Ansatz approach to the usual transfer matrix. We advocate that our novel representations are numerically more efficient and allow for a straightforward calculation of the large-distance asymptotic behaviour of the two-point functions. Keeping control over the temperature corrections to the two-point functions we see that these are of order $T^\\infty$ in the whole antiferromagnetic massive regime. The isotropic limit of our result yields a novel form factor series representation for the two-point correlation functions of the XXX chain at zero magnetic field.
On the ground state of antiferromagnets at zero temperature
Mayer, I.; Angelov, S. A.
1984-02-01
The wave function describing a perfect antiferromagnetic ordering of spins at 0 K (the singlet projection of the Néel function) was proved to be not an eigenfunction of the exchange Hamiltonian: the long-range order is reduced as to permit a higher correlation between the nearest-neighbour spins.
Mukai, Y; Yamamoto, T; Kageyama, H; Tanaka, K
2016-01-01
We report on the nonlinear magnetization dynamics of a HoFeO3 crystal induced by a strong terahertz magnetic field resonantly enhanced with a split ring resonator and measured with magneto-optical Kerr effect microscopy. The terahertz magnetic field induces a large change (~40%) in the spontaneous magnetization. The frequency of the antiferromagnetic resonance decreases in proportion to the square of the magnetization change. A modified Landau-Lifshitz-Gilbert equation with a phenomenological nonlinear damping term quantitatively reproduced the nonlinear dynamics.
Néel Temperature of Antiferromagnets for Phase Transitions Driven by Spin-wave Interactions
Ayuela, Andrés; Klein, Douglas J.; March, Norman H.
2013-01-01
In a recent article,1 a wide variety of phase transitions, with transition (t) temperature Tt , were shown to be usefully characterized by the form kBTt Echar exp1/ λ where λ measured the strength of the quasiparticle interactions driving the phase transition. The present article is concerned primarily with antiferromagnets (AFs) having Néel temperature TN. It is first argued that the characteristic energy Echar can be usefully represented by kBθ, where θ is the Curie-Weiss ...
Spin correlations due to Dyakonov-Perel and spin noise spectroscopy in semicoductor quantum wells
Energy Technology Data Exchange (ETDEWEB)
Hartenstein, Tobias; Krauss, Michael; Schneider, Hans Christian [Department of Physics and Research Center OPTIMAS, Kaiserslautern University of Technology (Germany)
2010-07-01
We present a theoretical investigation of dynamical electronic spin-spin correlations in quantum wells resulting from the Dyakonov-Perel mechanism due to electron-impurity interactions in the presence of external magnetic fields. We set up the coupled equations of motion for the different spin-spin correlation functions, and solve them numerically. Since spin-noise measurements are sensitive to the spin-spin correlation functions, our results provide a microcscopic basis for this measurement technique, but also allow us to study how the Dyakonov-Perel relaxation mechanism affects non-trivial electronic spin correlations and correlation waves that can be induced by the absorption of non-classical polarization-squeezed light.
International Nuclear Information System (INIS)
With a mean field approach, the heavy Fermi liquid in the two-dimensional Kondo lattice model is carefully considered in the presence of short-range antiferromagnetic correlations. As the ratio of the local Heisenberg superexchange coupling to the Kondo coupling increases, the Fermi surface structure changes dramatically. From the analysis of the ground state energy density, multiple Lifshitz type phase transitions occur at zero temperature.
Unusual spin correlations in a nanomagnet
Energy Technology Data Exchange (ETDEWEB)
Balasubramanian, Balamurugan, E-mail: bbalasubramanian2@unl.edu, E-mail: dsellmyer@unl.edu; Manchanda, Priyanka; Skomski, Ralph; Mukherjee, Pinaki; Das, Bhaskar; George, T. A.; Sellmyer, David J., E-mail: bbalasubramanian2@unl.edu, E-mail: dsellmyer@unl.edu [Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588 (United States); Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska 68588 (United States); Hadjipanayis, George C. [Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716 (United States)
2015-06-15
We show how atomic-scale exchange phenomena can be controlled and exploited in nanoscale itinerant magnets to substantially improve magnetic properties. Cluster-deposition experiments, first-principle simulations, and analytical calculations are used to demonstrate the effect in Co{sub 2}Si nanoclusters, which have average sizes varying from about 0.6 to 29.5 nm. The cluster-deposited nanoparticles exhibit average magnetic moments of up to 0.70 μ{sub B}/Co at 10 K and 0.49 μ{sub B}/Co at 300 K with appreciable magnetocrystalline anisotropies, in sharp contrast to the nearly vanishing bulk magnetization. The underlying spin correlations and associated cluster-size dependence of the magnetization are explained by a surface induced ferromagnetic spin polarization with a decay length of the order of 1 nm, much larger than the nearest-neighbor interatomic distance in the alloy.
Spintronics of antiferromagnetic systems
International Nuclear Information System (INIS)
Spintronics of antiferromagnetics is a new field that has developed in a fascinating research topic in physics of magnetism. Antiferromagnetics, like ferromagnetic materials experience the influence of spin-polarized current, even though they show no macroscopic magnetization. The mechanism of this phenomenon is related to spin-dependent interaction between free and localized electrons-sd-exchange. Due to the peculiarities of antiferromagnetic materials (complicated magnetic structure, essential role of the exchange interactions, lack of macroscopic magnetization) spintronics of antiferromagnets appeals to new theoretical and experimental approaches. The purpose of this review is to systemize and summarize the recent progress in this field. We start with a short introduction into the structure and dynamics of antiferromagnets and proceed with discussion of different microscopic and phenomenological theories for description of current-induced phenomena in ferro-/antiferromagnetic heterostructures. We also consider the problems of the reverse influence of antiferromagnetic ordering on current, and effectiveness of the fully antiferromagnetic spin valve. In addition, we shortly review and interpret the available experimental results.
Evolution from antiferromagnetic order to spin-glass state in Fe1.05−xCuxTe system
International Nuclear Information System (INIS)
Well understanding about the physical properties of FeTe compound, as a parent of superconducting Fe(Te, Se) system, is very important for exploring superconducting mechanism in the Fe-based superconductors. Here, based on the transport and magnetization measurements, we report the Cu doping effects on the physical properties of Fe1.05Te compound. We found that in the undoped sample, an antiferromagnetic (AFM) transition accompanying a semiconductor–metal transition occurs at 70 K. With the increase of Cu content x, the AFM transition temperature decreases monotonously at first. When x⩾0.05, both the metallic behavior and long-range AFM ordering disappear. Meanwhile, a spin-glass state emerges at low temperatures. The evolution of the transport and the magnetic properties with the Cu content x is summarized and a phase diagram is proposed. Our results indicate that a local spin picture may be more appropriate than an itinerant model for the Fe1.05Te compound.
A New Twist on Top Quark Spin Correlations
Baumgart, Matthew; Tweedie, Brock
2012-01-01
Top-antitop pairs produced at hadron colliders are largely unpolarized, but their spins are highly correlated. The structure of these correlations varies significantly over top production phase space, allowing very detailed tests of the Standard Model. Here, we explore top quark spin correlation measurement from a general perspective, highlighting the role of azimuthal decay angles. By taking differences and sums of these angles about the top-antitop production axis, the presence of spin corr...
Hu, Wen-Jun; Gong, Shou-Shu; Sheng, D. N.
2016-08-01
By using Gutzwiller projected fermionic wave functions and variational Monte Carlo technique, we study the spin-1 /2 Heisenberg model with the first-neighbor (J1), second-neighbor (J2), and additional scalar chiral interaction JχSi.(Sj×Sk) on the triangular lattice. In the nonmagnetic phase of the J1-J2 triangular model with 0.08 ≲J2/J1≲0.16 , recent density-matrix renormalization group (DMRG) studies [Zhu and White, Phys. Rev. B 92, 041105(R) (2015), 10.1103/PhysRevB.92.041105 and Hu, Gong, Zhu, and Sheng, Phys. Rev. B 92, 140403(R) (2015), 10.1103/PhysRevB.92.140403] find a possible gapped spin liquid with the signal of a competition between a chiral and a Z2 spin liquid. Motivated by the DMRG results, we consider the chiral interaction JχSi.(Sj×Sk) as a perturbation for this nonmagnetic phase. We find that with growing Jχ, the gapless U(1) Dirac spin liquid, which has the best variational energy for Jχ=0 , exhibits the energy instability towards a gapped spin liquid with nontrivial magnetic fluxes and nonzero chiral order. We calculate topological Chern number and ground-state degeneracy, both of which identify this flux state as the chiral spin liquid with fractionalized Chern number C =1 /2 and twofold topological degeneracy. Our results indicate a positive direction to stabilize a chiral spin liquid near the nonmagnetic phase of the J1-J2 triangular model.
Hu, Lin; Wu, Xiaojun; Yang, Jinlong
2016-07-14
To realize antiferromagnetic spintronics in the nanoscale, it is highly desirable to identify new nanometer-scale antiferromagnetic metals with both high Néel temperature and large spin-orbit coupling. In this work, on the basis of first-principles calculation and particle swarm optimization (PSO) global structure search, we demonstrate that a two-dimensional Mn2C monolayer is an antiferromagnetic metal with a Mn magnetic moment of ∼3μB. Mn2C monolayer has an anti-site structure of MoS2 sheet with carbon atoms hexagonally coordinated by neighboring Mn atoms. Remarkably, the in-plane carrier mobility of 2D Mn2C is highly anisotropic, amounting to about 47 000 cm(2) V(-1) s(-1) in the a' direction, which is much higher than that of MoS2 monolayer. The Néel temperature of Mn2C monolayer is high up to 720 K. Due to strong spin-orbit coupling in plane, the magnetic anisotropy energy of Mn2C monolayer is larger than those of pure metals, such as Fe, Co, and Ni. These advantages render 2D Mn2C sheet with great potential applications in nanometer-scale antiferromagnetic spintronics. PMID:27304676
International Nuclear Information System (INIS)
We have studied the dynamics of Tb spins in the intermetallic compound TbNiAl in the paramagnetic (pm) and ordered antiferromagnetic (afm) phases by means of neutron time-of-flight and spin-echo spectroscopy. It is a remarkable and very unusual characteristic of TbNiAl that its afm phase (below TN=47 K) contains regular long-range ordered spins as well as frustrated spins. The latter are identified by a strongly reduced moment measured by neutron diffraction. The new quasielastic measurements show that the frustrated moments relax on a time scale of 0.01 ns to 0.1 ns. Their autocorrelation function I(q,t) is q independent and exponential in time. While in the pm phase the spin relaxation is complete, i.e., I(q,t) goes to zero in the time range of the measurement, in the afm phase I(q,t) stays above zero
Correlation functions of the higher spin XXX chains
International Nuclear Information System (INIS)
Using the algebraic Bethe ansatz, we consider the correlation functions of the integrable higher spin chains. We apply a method recently developed for the spin 1/2 Heisenberg chain, based on the solution of the quantum inverse problem. We construct a representation for the correlation functions on a finite chain for arbitrary spin. Then we show how the string solutions of the Bethe equations can be considered in the framework of this approach in the thermodynamic limit. Finally, a multiple integral representation for the spin 1 zero-temperature correlation functions is obtained in the thermodynamic limit. (author)
Higher Point Spin Field Correlators in D=4 Superstring Theory
Haertl, D; Stieberger, S
2009-01-01
Calculational tools are provided allowing to determine general tree-level scattering amplitudes for processes involving bosons and fermions in heterotic and superstring theories in four space-time dimensions. We compute higher-point superstring correlators involving massless four-dimensional fermionic and spin fields. In D=4 these correlators boil down to a product of two pure spin field correlators of left- and right-handed spin fields. This observation greatly simplifies the computation of such correlators. The latter are basic ingredients to compute multi-fermion superstring amplitudes in D=4. Their underlying fermionic structure and the fermionic couplings in the effective action are determined by these correlators.
Energy Technology Data Exchange (ETDEWEB)
Parente, Walter E.F.; Pacobahyba, J.T.M.; Araújo, Ijanílio G. [Departamento de Física, Universidade Federal de Roraima, BR 174, Km 12. Bairro Monte Cristo. CEP: 69300-000 Boa Vista, Roraima (Brazil); Neto, Minos A., E-mail: minos@pq.cnpq.br [Universidade Federal do Amazonas, Departamento de Física, 3000, Japiim, 69077-000, Manaus-AM (Brazil); Ricardo de Sousa, J. [Universidade Federal do Amazonas, Departamento de Física, 3000, Japiim, 69077-000, Manaus-AM (Brazil); National Institute of Science and Technology for Complex Systems, 3000, Japiim, 69077-000, Manaus-AM (Brazil); Akinci, Ümit [Department of Physics, Dokuz Eylül University, Tr-35160 Izmir (Turkey)
2014-04-15
In this paper we study the quantum spin-1/2 anisotropic Heisenberg antiferromagnet model in the presence of a Dzyaloshinskii–Moriya interaction (D) and a uniform longitudinal (H) magnetic field. Using the effective-field theory with a finite cluster N=2 spin (EFT-2) we calculate the phase diagrams in the H−T and D−T planes on a simple cubic lattice (z=6). We have only observed second order phase transitions for values between Δ∈[0,1], where the cases were analysed: Ising (Δ=1), anisotropic Heisenberg (Δ=0.6) and isotropic Heisenberg (Δ=0). - Highlights: • Anisotropic Heisenberg antiferromagnet on a simple cubic lattice. • Effective-field theory. • Dzyaloshinskii–Moriya interaction.
International Nuclear Information System (INIS)
In this paper we study the quantum spin-1/2 anisotropic Heisenberg antiferromagnet model in the presence of a Dzyaloshinskii–Moriya interaction (D) and a uniform longitudinal (H) magnetic field. Using the effective-field theory with a finite cluster N=2 spin (EFT-2) we calculate the phase diagrams in the H−T and D−T planes on a simple cubic lattice (z=6). We have only observed second order phase transitions for values between Δ∈[0,1], where the cases were analysed: Ising (Δ=1), anisotropic Heisenberg (Δ=0.6) and isotropic Heisenberg (Δ=0). - Highlights: • Anisotropic Heisenberg antiferromagnet on a simple cubic lattice. • Effective-field theory. • Dzyaloshinskii–Moriya interaction
Akmaldinov, Kamil; Ducruet, Clarisse; Alvarez-Herault, Jeremy; Baltz, Vincent
2015-03-01
For thermally-assisted magnetic random access memories (TA-MRAM), lowering bit-cells dispersions of exchange bias is necessary. In this study, we prove that spin-glass-like phases (SG) spread over the ferromagnetic/antiferromagnetic (F/AF) storage layer are the main cause of such distributions once the film is nanofabricated into a device. In particular, we show that the less the SG, the lower the bit-cell dispersion. More precisely, the amount of SG was varied from sample to sample by sputtering various AFs: IrMn, FeMn and their alloys. Blocking temperature distributions were measured to quantify the amount of SG at the wafer level. The wafers were then patterned to obtain 1kb devices and all the cells were tested electrically. Finally, the resulting loop shift cumulative distribution functions accounting for the bit-cell dispersions were correlated to the initial amount of SG. In addition to bridging the gap between fundamental SG and a technological application, we also demonstrated that blocking temperature distributions are a versatile method to qualify TA-MRAM production batches before processing. Univ. Grenoble-Alpes/CNRS/INAC-CEA, 38000 Grenoble, France.
Random antiferromagnetic quantum spin chains: Exact results from scaling of rare regions
Igloi, F.; Juhasz, R.; Rieger, H.
1999-01-01
We study XY and dimerized XX spin-1/2 chains with random exchange couplings by analytical and numerical methods and scaling considerations. We extend previous investigations to dynamical properties, to surface quantities and operator profiles, and give a detailed analysis of the Griffiths phase. We present a phenomenological scaling theory of average quantities based on the scaling properties of rare regions, in which the distribution of the couplings follows a surviving random walk character...
Fisher Hartwig conjecture and the correlators in XY spin chain
Ovchinnikov, A. A.
2007-07-01
We apply the theorems from the theory of Toeplitz determinants to calculate the asymptotics of the correlators in the XY spin chain in the transverse magnetic field. The asymptotics of the correlators for the XX spin chain in the magnetic field are obtained.
Bogoliubov quasiparticles coupled to the antiferromagnetic spin mode in a vortex core
Berthod, C.
2015-12-01
In copper- and iron-based unconventional superconductors, the Bogoliubov quasiparticles interact with a spin resonance at momentum (π ,π ) . This interaction is revealed by specific signatures in the quasiparticle spectroscopies, like kinks in photoemission and dips in tunneling. We study these signatures, as they appear inside and around a vortex core in the local density of states (LDOS), a property accessible experimentally by scanning tunneling spectroscopy. Our model retains the whole nonlocal structure of the self-energy in space and time and is therefore not amenable to a Hamiltonian treatment using Bogoliubov-de Gennes equations. The interaction with the spin resonance does not suppress the zero-bias peak at the vortex center, although it reduces its spectral weight; neither does it smear out the vortex LDOS, but rather it adds structure to it. Some of the signatures we find may have been already measured in FeSe, but remained unnoticed. We compare the LDOS as a function of both energy and position with and without coupling to the spin resonance and observe, in particular, that the quasiparticle interference patterns around the vortex are strongly damped by the coupling. We study in detail the transfer of spectral weight induced both locally and globally by the interaction and also by the formation of the vortex. Finally, we introduce a new way of imaging the quasiparticles in real space, which combines locality and momentum-space sensitivity. This approach allows one to access quasiparticle properties that are not contained in the LDOS.
Unusual spin dynamics in the doped antiferromagnetic phase of YBa2(Cu0.98Zn0.02)3O6.39
International Nuclear Information System (INIS)
Inelastic neutron scattering experiments have been carried out on a YBa2(Cu0.98Zn0.02)3O6.39 single crystal to investigate the spin-excitation spectrum in the hole-doped antiferromagnetic state. New excitations are found at low energy as a consequence of electron-hole interactions, whereas standard magnons are recovered at sufficiently high energy. (orig.)
Kim, MinJae; Kim, Beom Hyun; Choi, Hong Chul; B. I. Min
2009-01-01
KO2 exhibits concomitant antiferromagnetic (AFM) and structural transitions, both of which originate from the open-shell 2p electrons of O$_{2}^{-}$ molecules. The structural transition is accompanied by the coherent tilting of O$_{2}^{-}$ molecular axes. The interplay among the spin-orbital-lattice degrees of freedom in KO2 is investigated by employing the first-principles electronic structure theory and the kinetic-exchange interaction scheme. We have shown that the insulating nature of the...
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The exactly integrable isotropic Heisenberg chain of N spins s is studied, and numerical solutions to the Bethe ansatz equations corresponding to the antiferromagnetic vacuum (for sN ≤ 128) and the simplest excitations have been obtained. For s = 1, a complete set of states for N = 6 is given, and the vacuum solution for finite N is estimated analytically. The deviations from the string picture at large N are discussed
Chakraborty, Subrata; Vijay, Amrendra
2016-04-01
Using a second-quantized many-electron Hamiltonian, we obtain (a) an effective Hamiltonian suitable for materials whose electronic properties are governed by a set of strongly correlated bands in a narrow energy range and (b) an effective spin-only Hamiltonian for magnetic materials. The present Hamiltonians faithfully include phonon and spin-related interactions as well as the external fields to study the electromagnetic response properties of complex materials and they, in appropriate limits, reduce to the model Hamiltonians due to Hubbard and Heisenberg. With the Hamiltonian for narrow-band strongly correlated materials, we show that the spin-orbit interaction provides a mechanism for metal-insulator transition, which is distinct from the Mott-Hubbard (driven by the electron correlation) and the Anderson mechanism (driven by the disorder). Next, with the spin-only Hamiltonian, we demonstrate the spin-orbit interaction to be a reason for the existence of antiferromagnetic phase in materials which are characterized by a positive isotropic spin-exchange energy. This is distinct from the Néel-VanVleck-Anderson paradigm which posits a negative spin-exchange for the existence of antiferromagnetism. We also find that the Néel temperature increases as the absolute value of the spin-orbit coupling increases.
Spinon, soliton, and breather in the spin-1/2 antiferromagnetic chain compound KCuGaF6
Umegaki, Izumi; Tanaka, Hidekazu; Kurita, Nobuyuki; Ono, Toshio; Laver, Mark; Niedermayer, Christof; Rüegg, Christian; Ohira-Kawamura, Seiko; Nakajima, Kenji; Kakurai, Kazuhisa
2015-11-01
Elementary excitations of the S =1/2 one-dimensional antiferromagnet KCuGaF6 were investigated by inelastic neutron scattering in zero and finite magnetic fields perpendicular to the (1 ,1 ,0 ) plane combined with specific heat measurements. KCuGaF6 exhibits no long-range magnetic ordering down to 50 mK despite the large exchange interaction J /kB=103 K. At zero magnetic field, well-defined spinon excitations were observed. The energy of the des Cloizeaux and Pearson [J. des Cloizeaux and J. J. Pearson, Phys. Rev. 128, 2131 (1962), 10.1103/PhysRev.128.2131] mode of the spinon excitations is somewhat larger than that calculated with the above exchange constant. This discrepancy is mostly ascribed to the effective X Y anisotropy arising from the large Dzyaloshinsky-Moriya [T. Moriya, Phys. Rev. 120, 91 (1960), 10.1103/PhysRev.120.91] interaction with an alternating D vector. KCuGaF6 in a magnetic field is represented by the quantum sine-Gordon model, for which low-energy elementary excitations are composed of solitons and antisolitons and their bound states called breathers. Unlike the theoretical prediction, it was found that the energy of a soliton is smaller than that of the first breather, although the energy of the first breather coincides with that observed in a previous electron spin resonance measurement.
Parente, Walter E. F.; Pacobahyba, J. T. M.; Araújo, Ijanílio G.; Neto, Minos A.; Ricardo de Sousa, J.
2015-11-01
We will study phase diagram the quantum spin-1/2 anisotropic Heisenberg antiferromagnet model in the presence of a Dzyaloshinskii-Moriya interaction (D) and a uniform longitudinal (H) magnetic field, where we have observed an anomaly at low temperatures. Using the effective-field theory with a finite cluster N=2 spin (EFT-2) we calculate the phase diagram in the H - D plane on a simple cubic lattice (z=6). We analyzed the cases: anisotropic Heisenberg - case I: (Δ = 1), anisotropic Heisenberg - case II: (Δ = 0.5) and anisotropic Heisenberg - case III: (Δ = 0), where only second order phase transitions are observed.
Spin–spin correlation length in a two-dimensional frustrated magnet and its relation to doping
International Nuclear Information System (INIS)
In a spherically symmetric self-consistent approach (SSSA), the spin-1/2 J1–J2 Heisenberg model on a two-dimensional square lattice is considered for two-time retarded spin–spin Green’s functions. The spin excitation spectrum, ω(q), and spin gaps at symmetric points are obtained for the entire J1–J2 diagram, i.e., for any ϕ, J1 = cosϕ, and J2 = sinϕ. The structure factor cq and the correlation length ξ at finite temperature are calculated in the entire range of parameters. A radical difference in the behavior of the system in the upper, frustrated (0 ⩽ ϕ ⩽ π), and the lower, nonfrustrated (π ⩽ ϕ ⩽ 2π), regions of the diagram is demonstrated. In the latter region, there is a first-order phase transition that is unique on the phase diagram. For a weakly frustrated antiferromagnet (J1 > J2 > 0), the results obtained are compared with the experimental dependence of ξ on temperature and doping level. A correspondence rule is proposed between frustration in a spin model and the doping of an antiferromagnet with holes
A New Twist on Top Quark Spin Correlations
Baumgart, Matthew
2012-01-01
Top-antitop pairs produced at hadron colliders are largely unpolarized, but their spins are highly correlated. The structure of these correlations varies significantly over top production phase space, allowing very detailed tests of the Standard Model. Here, we explore top quark spin correlation measurement from a general perspective, highlighting the role of azimuthal decay angles. By taking differences and sums of these angles about the top-antitop production axis, the presence of spin correlations can be seen as sinusoidal modulations resulting from the interference of different helicity channels. At the LHC, these modulations exhibit nontrivial evolution from near-threshold production into the boosted regime, where they become sensitive to almost the entire QCD correlation effect for centrally produced tops. We demonstrate that this form of spin correlation measurement is very robust under full kinematic reconstruction, and should already be observable with high significance using the current LHC data set...
Unusual Charge Transport and Spin Response of Doped Bilayer Triangular Antiferromagnets
Institute of Scientific and Technical Information of China (English)
LIANG Ying; MA Tian-Xing; FENG Shi-Ping
2003-01-01
Within the t-J model, the charge transport and spin response of the doped bilayer triangular antiferromagnetare studied by considering the bilayer interaction. Although the bilayer interaction leads to the band splitting in theelectronic structure, the qualitative behaviors of the physical properties are the same as in the single layer case. Theconductivity spectrum shows the low-energy peak and unusual midinfrared band, the temperature-dependent resistivityis characterized by the nonlinearity metallic-like behavior in the higher temperature range and the deviation from themetallic-like behavior in the lower temperature range and the commensurate neutron scattering peak near the half-fillingis split into six incommensurate peaks in the underdoped regime, with the incommensurability increasing with the holeconcentration at lower dopings, and saturating at higher dopings.
International Nuclear Information System (INIS)
Highlights: • Magnetic glassy state of Pr117Co54.5Sn115.2 freezes at ∼11 K. • Glassy state coexists with short range antiferromagnetic order. • Antiferromagnetic clusters developed at ∼11 K. • Negative temperature coefficient semiconductor-like resistivity from 2 to 300 K. - Abstract: The magnetic properties of Pr117Co54.5Sn115.2 – a member of a family of materials with a giant unit cell – have been investigated by dc magnetization, ac magnetic susceptibility, specific heat, and electrical resistivity measurements. A magnetic glassy state at freezing temperature of ∼11 K was determined from the magnetic susceptibility and specific heat data. The glassy state in Pr117Co54.5Sn115.2 is not the conventional spin glass with randomly oriented magnetic moments, but it is related to clusters of atoms that exist in the complex crystal lattice of the material. Furthermore, the glassy state coexists with short range antiferromagnetic order, leading to the development of antiferromagnetic clusters. A weak anomaly in the specific heat data centered around 11 K supports the formation of magnetic cluster glass state in Pr117Co54.5Sn115.2. Semiconductor-like resistivity with a negative temperature coefficient from 2 to 300 K is also observed in Pr117Co54.5Sn115.2
Drone-fermions in the two-dimensional antiferromagnet
Krivenko, S.; Khaliullin, G.
1995-02-01
Two different representations of spins - via the conventional fermions, or via the Mattis drone-fermions - are compared considering the planar antiferromagnetic Heisenberg model as an example. Mean-field spin correlation functions calculated for the uniform and flux RVB states show that the drone-fermion approach has an advantage in giving the lower energy and the enhanced AF correlations, because of the absence of unphysical spinless states in this representation.
Antiferromagnets at Low Temperatures
International Nuclear Information System (INIS)
The low-temperature properties of the Heisenberg antiferromagnet in 2+1 space-time dimensions are analyzed within the framework of effective Lagrangians. It is shown that the magnon-magnon interaction is very weak and repulsive, manifesting itself through a term proportional to five powers of the temperature in the pressure. The structure of the low-temperature series for antiferromagnets in 2+1 dimensions is compared with the structure of the analogous series for antiferromagnets in 3+1 dimensions. The model-independent and systematic effective field theory approach clearly proves to be superior to conventional condensed matter methods such as spin-wave theory.
Cross-correlation spin noise spectroscopy of heterogeneous interacting spin systems
International Nuclear Information System (INIS)
Interacting multi-component spin systems are ubiquitous in nature and in the laboratory. As such, investigations of inter-species spin interactions are of vital importance. Traditionally, they are studied by experimental methods that are necessarily perturbative: e.g., by intentionally polarizing or depolarizing one spin species while detecting the response of the other(s). Here, we describe and demonstrate an alternative approach based on multi-probe spin noise spectroscopy, which can reveal inter-species spin interactions - under conditions of strict thermal equilibrium - by detecting and cross-correlating the stochastic fluctuation signals exhibited by each of the constituent spin species. Specifically, we consider a two-component spin ensemble that interacts via exchange coupling, and we determine cross-correlations between their intrinsic spin fluctuations. The model is experimentally confirmed using 'two-color' optical spin noise spectroscopy on a mixture of interacting Rb and Cs vapors. Noise correlations directly reveal the presence of inter-species spin exchange, without ever perturbing the system away from thermal equilibrium. These non-invasive and noise-based techniques should be generally applicable to any heterogeneous spin system in which the fluctuations of the constituent components are detectable
Hu, Lin; Wu, Xiaojun; Yang, Jinlong
2016-06-01
To realize antiferromagnetic spintronics in the nanoscale, it is highly desirable to identify new nanometer-scale antiferromagnetic metals with both high Néel temperature and large spin-orbit coupling. In this work, on the basis of first-principles calculation and particle swarm optimization (PSO) global structure search, we demonstrate that a two-dimensional Mn2C monolayer is an antiferromagnetic metal with a Mn magnetic moment of ~3μB. Mn2C monolayer has an anti-site structure of MoS2 sheet with carbon atoms hexagonally coordinated by neighboring Mn atoms. Remarkably, the in-plane carrier mobility of 2D Mn2C is highly anisotropic, amounting to about 47 000 cm2 V-1 s-1 in the a' direction, which is much higher than that of MoS2 monolayer. The Néel temperature of Mn2C monolayer is high up to 720 K. Due to strong spin-orbit coupling in plane, the magnetic anisotropy energy of Mn2C monolayer is larger than those of pure metals, such as Fe, Co, and Ni. These advantages render 2D Mn2C sheet with great potential applications in nanometer-scale antiferromagnetic spintronics.To realize antiferromagnetic spintronics in the nanoscale, it is highly desirable to identify new nanometer-scale antiferromagnetic metals with both high Néel temperature and large spin-orbit coupling. In this work, on the basis of first-principles calculation and particle swarm optimization (PSO) global structure search, we demonstrate that a two-dimensional Mn2C monolayer is an antiferromagnetic metal with a Mn magnetic moment of ~3μB. Mn2C monolayer has an anti-site structure of MoS2 sheet with carbon atoms hexagonally coordinated by neighboring Mn atoms. Remarkably, the in-plane carrier mobility of 2D Mn2C is highly anisotropic, amounting to about 47 000 cm2 V-1 s-1 in the a' direction, which is much higher than that of MoS2 monolayer. The Néel temperature of Mn2C monolayer is high up to 720 K. Due to strong spin-orbit coupling in plane, the magnetic anisotropy energy of Mn2C monolayer is
Ferro- and antiferro-magnetism in (Np, Pu)BC
Czech Academy of Sciences Publication Activity Database
Klimczuk, T.; Shick, Alexander; Kozub, Agnieszka L.; Griveau, J.C.; Colineau, E.; Falmbigl, M.; Wastin, F.; Rogl, P.
2015-01-01
Roč. 3, č. 4 (2015), "041803-1"-"041803-9". ISSN 2166-532X R&D Projects: GA ČR GA15-07172S Institutional support: RVO:68378271 Keywords : ferromagetism * antiferromagnetism * magnetic anisotropy * strong electron correlations * spin-orbit coupling Subject RIV: BM - Solid Matter Physics ; Magnetism
An antiferromagnetic transverse Ising nanoisland; unconventional surface effects
Kaneyoshi, T.
2015-12-01
The phase diagrams and temperature dependences of magnetizations in a transverse Ising nanosisland with an antiferromagnetic spin configuration are studied by the use of the effective-field theory with correlations (EFT). Some novel features, such as the re-entrant phenomena with two compensation points being free from disorder induced frustration, are obtained for the magnetic properties in the system.
Jartych, E.; Pikula, T.; Mazurek, M.; Lisinska-Czekaj, A.; Czekaj, D.; Gaska, K.; Przewoznik, J.; Kapusta, C.; Surowiec, Z.
2013-09-01
The structure, hyperfine interactions and magnetic properties of the series of multiferroic Bim+1Ti3Fem-3O3m+3 Aurivillius compounds with m=4-8 were studied using X-ray diffraction, 57Fe Mössbauer spectroscopy and vibrating sample magnetometry. Samples were prepared by the conventional solid-state sintering method. Bulk magnetic measurements showed that for m=4 the compound is paramagnetic down to 2 K while in the compound with m=5 the antiferromagnetic type transition was observed at 11 K. In the case of compounds with m=6-8 much more complex magnetic behavior was found. For these compounds a gradual spin freezing and antiferromagnetic spin glass-like ordering were observed on decreasing temperature. The temperature of spin glass freezing was determined as 260, 280 and 350 K for m=6, 7 and 8, respectively. Room-temperature Mössbauer spectra of all the compounds studied confirm their paramagnetic state. However, liquid nitrogen and liquid helium temperature measurements reveal magnetic ordering with a residual paramagnetic phase contribution for the compounds with m=5-8.
Mikhak, B.; Zarkesh, A. M.
1993-01-01
Using the variational formula for operator product coefficients a method for perturbative calculation of the short-distance expansion of the Spin-Spin correlation function in the two dimensional Ising model is presented. Results of explicit calculation up to third order agree with known results from the scaling limit of the lattice calculation.
Spin excitations and correlations in scanning tunneling spectroscopy
Ternes, Markus
2015-06-01
In recent years inelastic spin-flip spectroscopy using a low-temperature scanning tunneling microscope has been a very successful tool for studying not only individual spins but also complex coupled systems. When these systems interact with the electrons of the supporting substrate correlated many-particle states can emerge, making them ideal prototypical quantum systems. The spin systems, which can be constructed by arranging individual atoms on appropriate surfaces or embedded in synthesized molecular structures, can reveal very rich spectral features. Up to now the spectral complexity has only been partly described. This manuscript shows that perturbation theory enables one to describe the tunneling transport, reproducing the differential conductance with surprisingly high accuracy. Well established scattering models, which include Kondo-like spin-spin and potential interactions, are expanded to enable calculation of arbitrary complex spin systems in reasonable time scale and the extraction of important physical properties. The emergence of correlations between spins and, in particular, between the localized spins and the supporting bath electrons are discussed and related to experimentally tunable parameters. These results might stimulate new experiments by providing experimentalists with an easily applicable modeling tool.
Energy Technology Data Exchange (ETDEWEB)
Amari, S., E-mail: siham_amari@yahoo.fr [Laboratoire de Modelisation et de Simulation en Sciences des Materiaux, Departement de Physique Universite Djillali Liabes, Sidi Bel-Abbes (Algeria); Mecabih, S.; Abbar, B.; Bouhafs, B. [Laboratoire de Modelisation et de Simulation en Sciences des Materiaux, Departement de Physique Universite Djillali Liabes, Sidi Bel-Abbes (Algeria)
2012-09-15
In this work, we aim to examine the spin-polarized electronic band structures, the local densities of states as well as the magnetism of Zn{sub 1-x}TM{sub x}Se (TM=Cr, Fe, Co and Ni) diluted magnetic semiconductors in the ferromagnetic (FM) and antiferromagnetic (AFM) phases, and with 25% of TM. The calculations are performed by the developed full-potential augmented plane wave plus local orbitals method within the spin density functional theory. As exchange-correlation potential we used the generalized gradient approximation (GGA) form. We treated the ferromagnetic and antiferromagnetic phases and we found that all compounds are stable in the ferromagnetic structure. Structural properties are computed after total energy minimization. Our results show that the cohesive energies of Zn{sub 0.75}TM{sub 0.25}Se are greater than that of zinc blende ZnSe. We discuss the electronic structures, total and partial densities of states, local moments and the p-d exchange splitting. Furthermore, we found that p-d hybridization reduces the local magnetic moment of TM and produces small local magnetic moments on the nonmagnetic Zn and Se sites. We found also that in the AFM phase the TM local magnetic moments are smaller than in the FM phase; this is due to the greater interaction of the TM d-up and d-down orbitals. - Highlights: Black-Right-Pointing-Pointer The calculation of the exchange constants of ZnTMSe (TM=Cr, Fe, Co and Ni). Black-Right-Pointing-Pointer Prediction of the spin-exchange splitting of ZnTMSe (TM=Cr, Fe, Co and Ni). Black-Right-Pointing-Pointer The study of ZnTMSe diluted magnetic semiconductors in the FM and AFM phases.
International Nuclear Information System (INIS)
The temperature variation of the sublattice magnetization of the quadratic double-layer antiferromagnet K3Mn2F7 has been determined by measuring the NMR frequency of the 19F nuclei adjacent to the Mn sites in the double-layer. The data have been analyzed in terms of a two-dimensional four-sublattice spin-wave theory with inclusion of temperature-dependent and temperature-independent renormalization as formulated by Oguchi, as well as temperature variation of the k = 0 energy gap, and with exact integration over the Brillouin zone
Spin-spin correlation functions of spin systems coupled to 2-d quantum gravity for 0 < c < 1.
Ambjørn, J.; Anagnostopoulos, K. N.; Magnea, U.; Thorleifsson, G.
1997-02-01
We perform Monte Carlo simulations of 2-d dynamically triangulated surfaces coupled to Ising and three-states Potts model matter. By measuring spin-spin correlation functions as a function of the geodesic distance we provide substantial evidence for a diverging correlation length at βc. The corresponding scaling exponents are directly related to the KPZ exponents of the matter fields as conjectured in [4].
Quantum Correlations and Teleportation in Heisenberg XX Spin Chain
Qin, Wan; Guo, Jin-Liang
2015-07-01
We investigate the thermal quantum correlations in the Heisenberg XX spin chain, and the teleportation of a two-qubit entangled state via the spin chain is analyzed. It is found that the effects of external magnetic field and three-site interaction on the thermal entanglement and quantum discord between the nearest or the next nearest neighbor qubits behave differently in various aspects. Special attention is paid to how to enhance the quantum correlations of the output state and the average fidelity of the teleportation. We find that quantum discord gives a better performance in the quantum correlations transmission, and the three-site interaction is necessary for a successful teleportation.
Spin-spin correlations of entangled qubit pairs in the Bohm interpretation of quantum mechanics
Ramsak, A
2012-01-01
A general entangled qubit pair is analyzed in the de Broglie-Bohm formalism corresponding to two spin-1/2 quantum rotors. Several spin-spin correlators of Bohm's hidden variables are analyzed numerically and a detailed comparison with results obtained by standard quantum mechanics is outlined. In addition to various expectation values the Bohm interpretation allows also a study of the corresponding probability distributions, which enables a novel understanding of entangled qubit dynamics. In particular, it is shown how the angular momenta of two qubits in this formalism can be viewed geometrically and characterized by their relative angles. For perfectly entangled pairs, for example, a compelling picture is given, where the qubits exhibit a unison precession making a constant angle between their angular momenta. It is also demonstrated that the properties of standard quantum mechanical spin-spin correlators responsible for the violation of Bell's inequalities are identical to their counterparts emerging from ...
Neutron scattering studies of three one-dimensional antiferromagnets
Kenzelmann, M
2001-01-01
observed in the disordered phase of spin-1/2 chains. The magnetic order of the one-dimensional spin-1/2 XY antiferromagnet Cs sub 2 CoCl sub 4 was investigated using neutron diffraction. The magnetic structure has an ordering wave-vector (0, 0.5, 0.5) for T < 217 mK and the magnetic structure is a non-linear structure with the magnetic moments at a small angle to the b axis. Above a field of H = 2.1 T the magnetic order collapses in an apparent first order phase transition, suggesting a transition to a spin-liquid phase. Low-dimensional magnets with low-spin quantum numbers are ideal model systems for investigating strongly interacting macroscopic quantum ground states and their non-linear spin excitations. This thesis describes neutron scattering experiments of three one-dimensional low-spin antiferromagnets where strong quantum fluctuations lead to highly-correlated ground states and unconventional cooperative spin excitations. The excitation spectrum of the antiferromagnetic spin-1 Heisenberg chain CsNi...
Antiferromagnetic crystalline topological insulators
LIU, CHAO-XING
2013-01-01
The gapless surface Dirac cone of time reversal invariant topological insulators is protected by time reversal symmetry due to the Kramers' theorem. Spin degree of freedom is usually required since Kramers' theorem only guarantees double degeneracy for spinful fermions, but not for spinless fermions. In this paper, we present an antiferromagnetic spinless model, which breaks time reversal symmetry. Similar to time reversal invariant topological insulators, this model possesses a topologically...
International Nuclear Information System (INIS)
In this paper, we do a complete classification of valence-bond crystals (VBCs) on the kagomé lattice based on general arguments of symmetry only and thus identify many new VBCs for different unit cell sizes. For the spin-1/2 Heisenberg antiferromagnet, we study the relative energetics of competing gapless spin liquids (SLs) and VBC phases within the class of Gutzwiller-projected fermionic wave functions using variational Monte Carlo techniques, hence implementing exactly the constraint of one fermion per site. By using a state-of-the-art optimization method, we conclusively show that the U(1) Dirac SL is remarkably stable towards dimerizing into all 6-, 12- and 36-site unit cell VBCs. This stability is also preserved on addition of a next-nearest-neighbor super-exchange coupling of both antiferromagnetic and ferromagnetic (FM) type. However, we find that a 36-site unit cell VBC is stabilized on addition of a very small next-nearest-neighbor FM super-exchange coupling, i.e. |J2| ≈ 0.045, and this VBC is the same in terms of space-group symmetry as that obtained in an effective quantum dimer model study. It breaks reflection symmetry, has a nontrivial flux pattern and is a strong dimerization of the uniform RVB SL. (paper)
A new twist on top quark spin correlations
Baumgart, Matthew; Tweedie, Brock
2013-03-01
Top-antitop pairs produced at hadron colliders are largely unpolarized, but their spins are highly correlated. The structure of these correlations varies significantly over top production phase space, allowing very detailed tests of the Standard Model. Here, we explore top quark spin correlation measurement from a general perspective, highlighting the role of azimuthal decay angles. By taking differences and sums of these angles about the top-antitop production axis, the presence of spin correlations can be seen as sinusoidal modulations resulting from the interference of different helicity channels. At the LHC, these modulations exhibit nontrivial evolution from near-threshold production into the boosted regime, where they become sensitive to almost the entire QCD correlation effect for centrally produced tops. We demonstrate that this form of spin correlation measurement is very robust under full kinematic reconstruction, and should already be observable with high significance using the current LHC data set. We also illustrate some novel ways that new physics can alter the azimuthal distributions. In particular, we estimate the power of our proposed measurements in probing for anomalous color-dipole operators, as well as for broad resonances with parity-violating couplings. Using these methods, the 2012 run of the LHC may be capable of setting simultaneous limits on the top quark's anomalous chromomagnetic and chromoelectric dipole moments at the level of 3 × 10-18 cm (0.03/ m t ).
Kontani, Hiroshi; Ohno, Masanori
2006-07-01
In nearly antiferromagnetic (AF) metals such as high- Tc superconductors (HTSCs), a single nonmagnetic impurity frequently causes nontrivial widespread change of the electronic states. To elucidate this long-standing issue, we study a Hubbard model with a strong onsite impurity potential based on an improved fluctuation-exchange (FLEX) approximation, which we call the GVI -FLEX method. This model corresponds to the HTSC with dilute nonmagnetic impurity concentration. We find that (i) both local and staggered susceptibilities are strongly enhanced around the impurity. By this reason, (ii) the quasiparticle lifetime as well as the local density of states are strongly suppressed in a wide area around the impurity (like a Swiss cheese hole), which causes the “huge residual resistivity” beyond the s -wave unitary scattering limit. We stress that the excess quasiparticle damping rate caused by impurities has strong k -dependence due to non- s -wave scatterings induced by many-body effects, so the structure of the “hot spot/cold spot” in the host system persists against impurity doping. This result could be examined by the ARPES measurements. In addition, (iii) only a few percent of impurities can cause a “Kondo-like” upturn of resistivity (dρ/dT<0) at low T when the system is very close to the AF quantum critical point. The results (i)-(iii) obtained in the present study, which cannot be derived by the simple FLEX approximation, naturally explain the main impurity effects in HTSCs. We also discuss the impurity effect in heavy fermion systems and organic superconductors.
International Nuclear Information System (INIS)
Spin torque ferromagnetic resonance (ST-FMR) in ferromagnetic metal (FM)/nonmagnetic metal (NM) bilayer films is one of the powerful methods to determine the spin Hall angle (SHA), conversion yield between charge and spin currents. Here we describe how to estimate the SHA and the spin diffusion length (SDL) from ST-FMR spectra. Although these two are fundamental parameters to characterize the spin Hall effect (SHE), there is still a heavy debate regarding their magnitudes even for platinum, which is the standard SHE material; reported values of SHA and SDL using FM/NM bilayer films vary very widely and there seems to be no correlation among SHA, SDL, and resistivity. In this work, we relate the three important physical quantities, i.e., SHA, SDL and resistivity, from their temperature dependences. (author)
Quantum dust magnetosonic waves with spin and exchange correlation effects
Energy Technology Data Exchange (ETDEWEB)
Maroof, R.; Qamar, A. [Department of Physics, University of Peshawar, Peshawar 25000 (Pakistan); Mushtaq, A. [Department of Physics, Abdul Wali Khan University, Mardan 23200 (Pakistan); National Center for Physics, Shahdra Valley Road, Islamabad 44000 (Pakistan)
2016-01-15
Dust magnetosonic waves are studied in degenerate dusty plasmas with spin and exchange correlation effects. Using the fluid equations of magnetoplasma with quantum corrections due to the Bohm potential, temperature degeneracy, spin magnetization energy, and exchange correlation, a generalized dispersion relation is derived. Spin effects are incorporated via spin force and macroscopic spin magnetization current. The exchange-correlation potentials are used, based on the adiabatic local-density approximation, and can be described as a function of the electron density. For three different values of angle, the dispersion relation is reduced to three different modes under the low frequency magnetohydrodynamic assumptions. It is found that the effects of quantum corrections in the presence of dust concentration significantly modify the dispersive properties of these modes. The results are useful for understanding numerous collective phenomena in quantum plasmas, such as those in compact astrophysical objects (e.g., the cores of white dwarf stars and giant planets) and in plasma-assisted nanotechnology (e.g., quantum diodes, quantum free-electron lasers, etc.)
Quantum dust magnetosonic waves with spin and exchange correlation effects
International Nuclear Information System (INIS)
Dust magnetosonic waves are studied in degenerate dusty plasmas with spin and exchange correlation effects. Using the fluid equations of magnetoplasma with quantum corrections due to the Bohm potential, temperature degeneracy, spin magnetization energy, and exchange correlation, a generalized dispersion relation is derived. Spin effects are incorporated via spin force and macroscopic spin magnetization current. The exchange-correlation potentials are used, based on the adiabatic local-density approximation, and can be described as a function of the electron density. For three different values of angle, the dispersion relation is reduced to three different modes under the low frequency magnetohydrodynamic assumptions. It is found that the effects of quantum corrections in the presence of dust concentration significantly modify the dispersive properties of these modes. The results are useful for understanding numerous collective phenomena in quantum plasmas, such as those in compact astrophysical objects (e.g., the cores of white dwarf stars and giant planets) and in plasma-assisted nanotechnology (e.g., quantum diodes, quantum free-electron lasers, etc.)
Propagation of nonclassical correlations across a quantum spin chain
International Nuclear Information System (INIS)
We study the transport of quantum correlations across a chain of interacting spin-1/2 particles. As a quantitative figure of merit, we choose a symmetric version of quantum discord and compare it with the transported entanglement, addressing various operating regimes of the spin medium. Discord turns out to be better transported for a wide range of working points and initial conditions of the system. We relate this behavior to the efficiency of propagation of a single excitation across the spin chain. Moreover, we point out the role played by a magnetic field in the dynamics of discord in the effective channel embodied by the chain. Our analysis can be interestingly extended to transport processes in more complex networks and the study of nonclassical correlations under general quantum channels.
Role of correlations on spin-polarized neutron matter
Vidana, Isaac; Durant, Victoria
2016-01-01
Using the Hellmann--Feynman theorem we analyze the contribution of the different terms of the nucleon-nucleon interaction to the spin symmetry energy of neutron matter. The analysis is performed within the microscopic Brueckner--Hartree--Fock approach using the Argonne V18 realistic potential plus the Urbana IX three-body force. The main contribution to the spin-symmetry energy of neutron matter comes from the S=0 channel, acting only in the non-polarized neutron matter, in particular the $^1S_0$ and the $^1D_2$ partial waves. The importance of correlations in spin-polarized neutron matter is estimated by evaluating the kinetic energy difference between the correlated system and the underlying Fermi sea.
Electric voltage generation by antiferromagnetic dynamics
Yamane, Yuta; Ieda, Jun'ichi; Sinova, Jairo
2016-05-01
We theoretically demonstrate dc and ac electric voltage generation due to spin motive forces originating from domain wall motion and magnetic resonance, respectively, in two-sublattice antiferromagnets. Our theory accounts for the canting between the sublattice magnetizations, the nonadiabatic electron spin dynamics, and the Rashba spin-orbit coupling, with the intersublattice electron dynamics treated as a perturbation. This work suggests a way to observe and explore the dynamics of antiferromagnetic textures by electrical means, an important aspect in the emerging field of antiferromagnetic spintronics, where both manipulation and detection of antiferromagnets are needed.
Coherent and correlated spin transport in nanoscale superconductors
Energy Technology Data Exchange (ETDEWEB)
Morten, Jan Petter
2008-03-15
the system varies from e.g. ballistic conductors or tunnel barriers. In the tunneling case, we calculate the magnetization-dependent full counting statistics, which determines all noise properties including the cross-correlations that can resolve the contributions due to crossed Andreev reflection and direct electron transport. We evaluate the magnetization-dependent two-particle probability that the constituents of spin-entangled pairs from crossed Andreev reflection flow into different ferromagnetic contacts. This probability implies violation of a Bell inequality, and determines the performance of a superconductor-ferromagnet entangler. (author). 105 refs., 13 figs
Dos Santos Lima, Leonardo
We study the two-dimensional Heisenberg antiferromagnetic model with ion single anisotropy in the square lattice in the presence of nonmagnetic impurities at T = 0 using the SU(3) Schwinger boson theory. In particular, we discuss the influence of site disorder on the quantum phase transition of this model at Dc that separates the Néel phase, D Dc . We find that the long-range order in D CNPq, FAPEMIG, CAPES.
Antiferromagnetic correlations in icosahedral R-Mg-Zn quasicrystals (R rare earth)
Energy Technology Data Exchange (ETDEWEB)
Charrier, B.; Schmitt, D. [Centre National de la Recherche Scientifique (CNRS), 38 - Grenoble (France); Ouladdiaf, B. [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France)
1997-04-01
Powder neutron-diffraction experiments performed on R-Mg-Zn quasicrystals have shown for the first time the existence of magnetic ordering of the rare earth in these systems at low temperature (T{sub c} {<=} 6.5 K depending on the rare earth). Both narrow and broad magnetic diffraction peaks have been observed showing the presence of two different scales of magnetic correlations. (author). 3 refs.
Correlation functions of the spin chains. Algebraic Bethe Ansatz approach
International Nuclear Information System (INIS)
Spin chains are the basic elements of integrable quantum models. These models have direct applications in condense matter theory, in statistical physics, in quantum optics, in field theory and even in string theory but they are also important because they enable us to solve, in an exact manner, non-perturbative phenomena that otherwise would stay unresolved. The method described in this work is based on the algebraic Bethe Ansatz. It is shown how this method can be used for the computation of null temperature correlation functions of the Heisenberg 1/2 spin chain. The important point of this approach is the solution of the inverse quantum problem given by the XXZ spin chain. This solution as well as a simple formulae for the scalar product of the Bethe states, have enabled us to get the most basic correlation functions under the form of multiple integrals. The formalism of multiple integrals open the way for asymptotic analysis for a few physical quantities like the probability of vacuum formation. It is worth noticing that this formalism can give exact results for two-point functions that are the most important correlation functions for applications. A relationship has been discovered between these multiple integrals and the sum of the form factors. The results have been extended to dynamical correlation functions. (A.C.)
Glass, S; Li, G; Adler, F; Aulbach, J; Fleszar, A; Thomale, R; Hanke, W; Claessen, R; Schäfer, J
2015-06-19
Two-dimensional (2D) atom lattices provide model setups with Coulomb correlations that induce competing ground states. Here, SiC emerges as a wide-gap substrate with reduced screening. We report the first artificial high-Z atom lattice on SiC(0001) by Sn adatoms, based on experimental realization and theoretical modeling. Density-functional theory of our triangular structure model closely reproduces the scanning tunneling microscopy. Photoemission data show a deeply gapped state (∼2 eV gap), and, based on our calculations including dynamic mean-field theory, we argue that this reflects a pronounced Mott-insulating scenario. We also find indications that the system is susceptible to antiferromagnetic superstructures. Such artificial lattices on SiC(0001) thus offer a novel platform for coexisting Coulomb correlations and spin-orbit coupling, with bearing for unusual magnetic phases and proposed topological quantum states of matter. PMID:26197013
Duan, T. F.; Ren, W. J.; Liu, W.; Zhang, Z. D.
2016-08-01
The magnetic structure of MnSn2 and magnetic phase transitions in this compound have been investigated by magnetic measurements on single crystals. The results show that two antiferromagnetic (AFM) states exist below 325 K and that a transition between these two phases occurs at 74 K. Applying a magnetic field (H) has great influence on the transition temperature. An anomalous magnetization process at low fields occurs when the magnetic field applied along the [110] direction, which is ascribed to the contribution of the basal anisotropy. Based on the data for the magnetization processes and the phase transition of the present single crystal, the H-T phase diagram has been established.
The Magnetism of Li doped La$_{2}$CuO$_4$: the antiferromagnetic spin-shard state
Sushkov, O. P.; Neto, A. H. Castro
2005-01-01
We study the dynamics of a single hole in Li and Sr doped La$_{2}$CuO$_4$ and its extension to a finite hole concentration. We compare the physics of La$_{2-x}$Sr$_x$CuO$_4$ and La$_{2}$Cu$_{1-x}$Li$_x$O$_4$ and explain why these systems are remarkably different. We demonstrate that holes in La$_{2}$Cu$_{1-x}$Li$_x$O$_4$ are always localized and that there is a critical concentration, $x_c\\approx 0.03$, above which the holes break the global antiferromagnetic state into an array of weakly cou...
Frustrated spin correlations in diluted spin ice Ho2-xLaxTi2O7
Energy Technology Data Exchange (ETDEWEB)
Ehlers, Georg; Ehlers, G.; Mamontov, E.; Zamponi, M.; Faraone, A.; Qiu, Y.; Cornelius, A.L.; Booth, C.H.; Kam, K.C.; Le Toquin, R.; Cheetham, A.K.; Gardner, J.S.
2008-04-30
We have studied the evolution of the structural properties as well as the static and dynamic spin correlations of spin ice Ho2Ti2O7, where Ho was partially replaced by non-magnetic La. The crystal structure of diluted samples Ho2-xLaxTi2O7 was characterized by x-ray and neutron diffraction and by Ho L-III-edge and Ti K-edge extended x-ray absorption fine structure (EXAFS) measurements. It is found that the pyrochlore structure remains intact until about x = 0.3, but a systematic increase in local disorder with increasing La concentration is observed in the EXAFS data, especially from the Ti K edge.Quasi-elastic neutron scattering and ac susceptibility measurements show that, in x<= 0.4 samples at temperatures above macroscopic freezing, the spin -spin correlations are short ranged and dynamic in nature. The main difference with pure spin ice in the dynamics is the appearance of a second, faster, relaxation process.
Zverev, M V; Clark, J W
2001-01-01
On the basis of analysis of the Landau-Pitaevskii one has determined that antiferromagnetic transition follows fermion condensation and rearrangement of single-particle degrees of freedom. It results in the spectrum of single-particle excitations. The derived results are used to explain structure of slit in the spectrum at T = 0 in two-dimensional high-temperature superconductors with a square lattice. They may be, as well, used to describe superfluid states of strongly correlated systems with fermion condensation
Cumulant approach to weakly doped antiferromagnets
International Nuclear Information System (INIS)
We present an approach to static and dynamical properties of holes and spins in weakly doped antiferromagnets in two dimensions. The calculations are based on a recently introduced cumulant approach to ground endash state properties of correlated electronic systems. The present method allows us to evaluate hole and spin-wave dispersion relations by considering hole or spin excitations of the ground state. Usually, these dispersions are found from time-dependent correlation functions. To demonstrate the ability of the approach we first derive the dispersion relation for the lowest single hole excitation at half-filling. However, the main purpose of this paper is to focus on the mutual influence of mobile holes and spin waves in the weakly doped system. It is shown that low-energy spin excitations strongly admix to the ground state. The coupling of spin waves and holes leads to a strong suppression of the staggered magnetization which cannot be explained by a simple rigid-band picture for the hole quasiparticles. Also the experimentally observed doping dependence of the spin-wave excitation energies can be understood within our formalism. copyright 1996 The American Physical Society
pp spin correlations at high p/sub T/
International Nuclear Information System (INIS)
New data are presented for measurements of the spin correlation in pp reactions with longitudinally polarized beam and target. Data were obtained at 11.75 GeV/c for both elastic scattering and for π+- and π--production at high p/sub T/ in pp reactions at 11.75 GeV/c. A comparison is made with recent predictions of quark-parton models
Spin-spin correlations in the reaction NN → NNπ at intermediate energies
International Nuclear Information System (INIS)
Spin-spin correlations and depolarisation parameters are predicted for the reaction pp → npπ+ in the geometry for exclusive, in-plane kinematics. Calculations are based on a relativistic and unitary three-body isobar model (described elsewhere). The partial-wave isobar amplitudes are found by solving coupled Blankenbecler-Sugar integral equations with one-pion-exchange driving terms. Results are presented for several proton-pion angle pairs at Tsub(lab) = 800 MeV and, for one angle pair, also at Tsub(lab) = 500 and 1200 MeV. (author)
Berger, Andrew J.; Page, Michael R.; Wen, Hua; McCreary, Kathleen M.; Bhallamudi, Vidya P.; Kawakami, Roland K.; Hammel, P. Chris
2015-01-01
Using simultaneous magnetic force microscopy (MFM) and transport measurements of a graphene spin valve, we correlate the non-local spin signal with the magnetization of the device electrodes. The imaged magnetization states corroborate the influence of each electrode within a one-dimensional spin transport model and provide evidence linking domain wall pinning to additional features in the transport signal.
International Nuclear Information System (INIS)
Using simultaneous magnetic force microscopy and transport measurements of a graphene spin valve, we correlate the non-local spin signal with the magnetization of the device electrodes. The imaged magnetization states corroborate the influence of each electrode within a one-dimensional spin transport model and provide evidence linking domain wall pinning to additional features in the transport signal
Energy Technology Data Exchange (ETDEWEB)
Berger, Andrew J., E-mail: berger.156@osu.edu; Page, Michael R.; Bhallamudi, Vidya P.; Chris Hammel, P. [Department of Physics, The Ohio State University, Columbus, Ohio 43210 (United States); Wen, Hua; Kawakami, Roland K. [Department of Physics, The Ohio State University, Columbus, Ohio 43210 (United States); Department of Physics and Astronomy, University of California, Riverside, California 92521 (United States); McCreary, Kathleen M. [United States Naval Research Laboratory, Washington, D.C. 20375 (United States)
2015-10-05
Using simultaneous magnetic force microscopy and transport measurements of a graphene spin valve, we correlate the non-local spin signal with the magnetization of the device electrodes. The imaged magnetization states corroborate the influence of each electrode within a one-dimensional spin transport model and provide evidence linking domain wall pinning to additional features in the transport signal.
Melnikov, N. B.; Reser, B. I.; Paradezhenko, G. V.
2016-08-01
To study the spin-density correlations in the ferromagnetic metals above the Curie temperature, we relate the spin correlator and neutron scattering cross-section. In the dynamic spin-fluctuation theory, we obtain explicit expressions for the effective and local magnetic moments and spatial spin-density correlator. Our theoretical results are demonstrated by the example of bcc Fe. The effective and local moments are found in good agreement with results of polarized neutron scattering experiment over a wide temperature range. The calculated short-range order is small (up to 4 Å) and slowly decreases with temperature.
Quantum critical behavior in a two-layer antiferromagnet
International Nuclear Information System (INIS)
We analyze quantum Monte Carlo data in the vicinity of the quantum transition between a Neel state and a quantum paramagnet in a two-layer, square-lattice spin-1/2 Heisenberg antiferromagnet. The real-space correlation function and the universal amplitude ratio of the structure factor and the dynamic susceptibility show clear evidence of quantum critical behavior at low temperatures. The numerical results are in good quantitative agreement with 1/N calculations for the O(N) nonlinear σ model. A discrepancy, reported earlier, between the critical properties of the antiferromagnet and the σ model is resolved. We also discuss the values of prefactors of the dynamic susceptibility and the structure factor in a single-layer antiferromagnet at low T
Li, Hai-Feng; Cao, Chongde; Wildes, Andrew; Schmidt, Wolfgang; Schmalzl, Karin; Hou, Binyang; Regnault, Louis-Pierre; Zhang, Cong; Meuffels, Paul; Löser, Wolfgang; Roth, Georg
2015-01-01
Identifying the nature of magnetism, itinerant or localized, remains a major challenge in condensed-matter science. Purely localized moments appear only in magnetic insulators, whereas itinerant moments more or less co-exist with localized moments in metallic compounds such as the doped-cuprate or the iron-based superconductors, hampering a thorough understanding of the role of magnetism in phenomena like superconductivity or magnetoresistance. Here we distinguish two antiferromagnetic modulations with respective propagation wave vectors at Q± = (H ± 0.557(1), 0, L ± 0.150(1)) and QC = (H ± 0.564(1), 0, L), where (H, L) are allowed Miller indices, in an ErPd2Si2 single crystal by neutron scattering and establish their respective temperature- and field-dependent phase diagrams. The modulations can co-exist but also compete depending on temperature or applied field strength. They couple differently with the underlying lattice albeit with associated moments in a common direction. The Q± modulation may be attributed to localized 4f moments while the QC correlates well with itinerant conduction bands, supported by our transport studies. Hence, ErPd2Si2 represents a new model compound that displays clearly-separated itinerant and localized moments, substantiating early theoretical predictions and providing a unique platform allowing the study of itinerant electron behavior in a localized antiferromagnetic matrix. PMID:25608949
DEFF Research Database (Denmark)
Jiang, Jianzhong; Mørup, Steen
1997-01-01
The influence of the particle size distribution on the ratio of the peak temperature, T-peak, to the blocking temperature, T-Bm, in zero field cooled (ZFD) magnetization curves has studied for both ferromagnetic and antiferromagnetic particle systems. In both systems the ratio beta=T-peak/T-Bm do...
Anomalous Magnetothermopower in a Metallic Frustrated Antiferromagnet
Arsenijević, Stevan; Ok, Jong Mok; Robinson, Peter; Ghannadzadeh, Saman; Katsnelson, Mikhail I.; Kim, Jun Sung; Hussey, Nigel E.
2016-02-01
We report the temperature T and magnetic field H dependence of the thermopower S of an itinerant triangular antiferromagnet PdCrO2 in high magnetic fields up to 32 T. In the paramagnetic phase, the zero-field thermopower is positive with a value typical of good metals with a high carrier density. In marked contrast to typical metals, however, S decreases rapidly with increasing magnetic field, approaching zero at the maximum field scale for T >70 K . We argue here that this profound change in the thermoelectric response derives from the strong interaction of the 4 d correlated electrons of the Pd ions with the short-range spin correlations of the Cr3 + spins that persist beyond the Néel ordering temperature due to the combined effects of geometrical frustration and low dimensionality.
Thermoinduced magnetization in nanoparticles of antiferromagnetic materials
DEFF Research Database (Denmark)
Mørup, Steen; Frandsen, Cathrine
2004-01-01
We show that there is a thermoinduced contribution to the magnetic moment of nanoparticles of antiferromagnetic materials. It arises from thermal excitations of the uniform spin-precession mode, and it has the unusual property that its magnitude increases with increasing temperature. This has...... the consequence that antiferromagnetism is nonexistent in nanoparticles at finite temperatures and it explains magnetic anomalies, which recently have been reported in a number of studies of nanoparticles of antiferromagnetic materials....
Global quantum correlations in finite-size spin chains
International Nuclear Information System (INIS)
We perform an extensive study of the properties of global quantum correlations in finite-size one-dimensional quantum spin models at finite temperature. By adopting a recently proposed measure for global quantum correlations (Rulli and Sarandy 2011 Phys. Rev. A 84 042109), called global discord, we show that critical points can be neatly detected even for many-body systems that are not in their ground state. We consider the transverse Ising model, the cluster-Ising model where three-body couplings compete with an Ising-like interaction, and the nearest-neighbor XX Hamiltonian in transverse magnetic field. These models embody our canonical examples showing the sensitivity of global quantum discord close to criticality. For the Ising model, we find a universal scaling of global discord with the critical exponents pertaining to the Ising universality class. (paper)
International Nuclear Information System (INIS)
We present first-principles density-functional-theory-based calculations to determine the effects of the strength of on-site electron correlation, magnetic ordering, pressure and Se vacancies on phonon frequencies and electronic structure of FeSe1-x. The theoretical equilibrium structure (lattice parameters) of FeSe depends sensitively on the value of the Hubbard parameter U of on-site correlation and magnetic ordering. Our results suggest that there is a competition between different antiferromagnetic states due to comparable magnetic exchange couplings between first- and second-neighbor Fe sites. As a result, a short range order of stripe antiferromagnetic type is shown to be relevant to the normal state of FeSe at low temperature. We show that there is a strong spin-phonon coupling in FeSe (comparable to its superconducting transition temperature) as reflected in large changes in the frequencies of certain phonons with different magnetic ordering, which is used to explain the observed hardening of a Raman-active phonon at temperatures (∼100 K) where magnetic ordering sets in. The symmetry of the stripe antiferromagnetic phase permits an induced stress with orthorhombic symmetry, leading to orthorhombic strain as a secondary order parameter at the temperature of magnetic ordering. The presence of Se vacancies in FeSe gives rise to a large peak in the density of states near the Fermi energy, which could enhance the superconducting transition temperature within the BCS-like picture.
Energy Technology Data Exchange (ETDEWEB)
Kumar, Anil; Waghmare, Umesh V [Theoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore-560064 (India); Kumar, Pradeep; Sood, A K [Department of Physics, Indian Institute of Science, Bangalore-560012 (India)
2010-09-29
We present first-principles density-functional-theory-based calculations to determine the effects of the strength of on-site electron correlation, magnetic ordering, pressure and Se vacancies on phonon frequencies and electronic structure of FeSe{sub 1-x}. The theoretical equilibrium structure (lattice parameters) of FeSe depends sensitively on the value of the Hubbard parameter U of on-site correlation and magnetic ordering. Our results suggest that there is a competition between different antiferromagnetic states due to comparable magnetic exchange couplings between first- and second-neighbor Fe sites. As a result, a short range order of stripe antiferromagnetic type is shown to be relevant to the normal state of FeSe at low temperature. We show that there is a strong spin-phonon coupling in FeSe (comparable to its superconducting transition temperature) as reflected in large changes in the frequencies of certain phonons with different magnetic ordering, which is used to explain the observed hardening of a Raman-active phonon at temperatures ({approx}100 K) where magnetic ordering sets in. The symmetry of the stripe antiferromagnetic phase permits an induced stress with orthorhombic symmetry, leading to orthorhombic strain as a secondary order parameter at the temperature of magnetic ordering. The presence of Se vacancies in FeSe gives rise to a large peak in the density of states near the Fermi energy, which could enhance the superconducting transition temperature within the BCS-like picture.
Tsuchimochi, Takashi
2015-10-14
Spin-flip approaches capture static correlation with the same computational scaling as the ordinary single reference methods. Here, we extend spin-flip configuration interaction singles (SFCIS) by projecting out intrinsic spin-contamination to make it spin-complete, rather than by explicitly complementing it with spin-coupled configurations. We give a general formalism of spin-projection for SFCIS, applicable to any spin states. The proposed method is viewed as a natural unification of SFCIS and spin-projected CIS to achieve a better qualitative accuracy at a low computational cost. While our wave function ansatz is more compact than previously proposed spin-complete SF approaches, it successfully offers more general static correlation beyond biradicals without sacrificing good quantum numbers. It is also shown that our method is invariant with respect to open-shell orbital rotations, due to the uniqueness of spin-projection. We will report benchmark calculations to demonstrate its qualitative performance on strongly correlated systems, including conical intersections that appear both in ground-excited and excited-excited degeneracies. PMID:26472370
Energy Technology Data Exchange (ETDEWEB)
Tsuchimochi, Takashi, E-mail: tsuchimochi@gmail.com [Department of Computational Science, Graduate School of System Informatics, Kobe University, Kobe 657-8501 (Japan)
2015-10-14
Spin-flip approaches capture static correlation with the same computational scaling as the ordinary single reference methods. Here, we extend spin-flip configuration interaction singles (SFCIS) by projecting out intrinsic spin-contamination to make it spin-complete, rather than by explicitly complementing it with spin-coupled configurations. We give a general formalism of spin-projection for SFCIS, applicable to any spin states. The proposed method is viewed as a natural unification of SFCIS and spin-projected CIS to achieve a better qualitative accuracy at a low computational cost. While our wave function ansatz is more compact than previously proposed spin-complete SF approaches, it successfully offers more general static correlation beyond biradicals without sacrificing good quantum numbers. It is also shown that our method is invariant with respect to open-shell orbital rotations, due to the uniqueness of spin-projection. We will report benchmark calculations to demonstrate its qualitative performance on strongly correlated systems, including conical intersections that appear both in ground-excited and excited-excited degeneracies.
International Nuclear Information System (INIS)
Spin-flip approaches capture static correlation with the same computational scaling as the ordinary single reference methods. Here, we extend spin-flip configuration interaction singles (SFCIS) by projecting out intrinsic spin-contamination to make it spin-complete, rather than by explicitly complementing it with spin-coupled configurations. We give a general formalism of spin-projection for SFCIS, applicable to any spin states. The proposed method is viewed as a natural unification of SFCIS and spin-projected CIS to achieve a better qualitative accuracy at a low computational cost. While our wave function ansatz is more compact than previously proposed spin-complete SF approaches, it successfully offers more general static correlation beyond biradicals without sacrificing good quantum numbers. It is also shown that our method is invariant with respect to open-shell orbital rotations, due to the uniqueness of spin-projection. We will report benchmark calculations to demonstrate its qualitative performance on strongly correlated systems, including conical intersections that appear both in ground-excited and excited-excited degeneracies
Becca, Federico; Iqbal, Yasir; Poilblanc, Didier
2012-02-01
Within the class of Gutzwiller projected fermionic wave functions, by using quantum variational Monte Carlo simulations, we investigated the energetics of all possible Z2 spin liquids that can potentially occur as ground states of the nearest-neighbor S=1/2 quantum Heisenberg model on the Kagome lattice [1]. We conclusively show that all gapped and gapless Z2 spin liquids are higher in energy compared to the U(1) gapless states in whose neighborhoods they lie. In particular, the most promising gapped Z2 spin liquid (the so-called Z2[0,π]β state), conjectured to describe the ground state [2], is always higher in energy compared to the U(1) Dirac spin liquid. We also extended the U(1) Dirac state and the uniform RVB spin liquid to include next-nearest-neighbor hopping terms, and studied its local and global stability towards various valence bond crystal patterns. We found that a non-trivial 36-site VBC is stabilized upon addition of a small ferromagnetic exchange coupling [3]. [4pt] [1] Y. Iqbal, F. Becca, and D. Poilblanc, Phys. Rev. B 84, 020407(R) (2011)[0pt] [2] Y.-M. Lu, Y. Ran, and P.A. Lee. Phys. Rev. B 83, 224413 (2011)[0pt] [3] Y. Iqbal, F. Becca, and D. Poilblanc, Phys. Rev. B 83, 100404(R) (2011)
International Nuclear Information System (INIS)
The ground-state properties of the spin-1/2 Ferromagnetic–Ferromagnetic–Antiferromagnetic (F–F–AF) trimerized chain are investigated by the infinite time-evolving block decimation (iTEBD) method. A ground-state phase diagram including three different phases, i.e., a fully polarized phase, a 1/3 plateau phase, and a non-plateau phase, is obtained. All the quantum phase transitions (QPTs) can be described well by the model independent bipartite entanglement. QPTs between the non-plateau phase and the other two phases belong to the second-order category. Doubly degenerate entanglement spectrum and nontrivial string order are observed in the 1/3 plateau phase, which can be used to distinguish it from the other phases. By the scaling behavior of the bipartite entanglement, the central charge of the critical non-plateau phase is determined to be c≃ 1. - Highlights: • A rich ground-state phase diagram is obtained. • QPTs can be well described by singular behavior of entanglement. • The 1/3 magnetization plateau is characterized by entanglement plateau. • Doubly degenerate entanglement spectrum is observed in the 1/3 plateau phase. • Nontrivial string order is observed in the 1/3 plateau phase
Energy Technology Data Exchange (ETDEWEB)
Liu, Guang-Hua, E-mail: liuguanghua@tjpu.edu.cn [Department of Physics, Tianjin Polytechnic University, Tianjin 300387 (China); Li, Wei [Department of Physics, Beihang University, Beijing 100191 (China); You, Wen-Long [School of Physical Science and Technology, Soochow University, Suzhou, Jiangsu 215006 (China); Su, Gang [Theoretical Condensed Matter Physics and Computational Materials Physics Laboratory, College of Physical Sciences, University of Chinese Academy of Sciences, P.O. Box 4588, Beijing 100049 (China); Tian, Guang-Shan [School of Physics, Peking University, Beijing 100871 (China)
2015-03-01
The ground-state properties of the spin-1/2 Ferromagnetic–Ferromagnetic–Antiferromagnetic (F–F–AF) trimerized chain are investigated by the infinite time-evolving block decimation (iTEBD) method. A ground-state phase diagram including three different phases, i.e., a fully polarized phase, a 1/3 plateau phase, and a non-plateau phase, is obtained. All the quantum phase transitions (QPTs) can be described well by the model independent bipartite entanglement. QPTs between the non-plateau phase and the other two phases belong to the second-order category. Doubly degenerate entanglement spectrum and nontrivial string order are observed in the 1/3 plateau phase, which can be used to distinguish it from the other phases. By the scaling behavior of the bipartite entanglement, the central charge of the critical non-plateau phase is determined to be c≃ 1. - Highlights: • A rich ground-state phase diagram is obtained. • QPTs can be well described by singular behavior of entanglement. • The 1/3 magnetization plateau is characterized by entanglement plateau. • Doubly degenerate entanglement spectrum is observed in the 1/3 plateau phase. • Nontrivial string order is observed in the 1/3 plateau phase.
Classical and quantum 'EPR'-spin correlations in the triplet state
International Nuclear Information System (INIS)
Quantum correlations and joint probabilities in the triplet state as well as the correlations of components of two correlated classical spin vectors, are evaluated. Correlations in the states with |Stotz|=1 are different from correlations in the state with Stotz=0 which may serve to distinguish different states of the triplet. As in the singlet case, we can reproduce quantum correlations by correlated classical spin vectors which also provide a precision of the notion of ''parallel spins''. Triplet state correlations could in principle be measured, for example, in the decay reaction J/ψ → e+e- for which there is a sufficiently large branching ratio. (author). 12 refs
International Nuclear Information System (INIS)
Electronic and magnetic properties of the three magnetic-sublattice double perovskite TbCu3Mn4O12 (TCMO) are investigated by performing first-principles density-functional theory calculations. Our electronic structure calculations show that TCMO is half-metallic and its half-metallicity can only be correctly described when the electron correlation on Tb3+ 4f8 electrons are considered. The energies of different magnetic configurations among the three magnetic sublattices are also calculated, revealing that the magnetic configuration with Mn and Cu spins in the antiparallel arrangement and with the Tb magnetic moments ferromagnetically/antiferromagnetically (FM/AFM) coupled to Cu/Mn spins (that is Tb↓Cu3↓Mn4↑O12) is the lowest energetic magnetic state, which is consistent with recent experimental results. The magnetic anisotropy is further calculated for the [1 1 1], [1 1 0], and [0 0 1] spin quantization directions. It is found that the [1 1 1]-direction is more stable than the [1 1 0]- and [0 0 1]-directions by 123 and 135 meV per formula unit, respectively, indicating a significant magnetic anisotropy. Our detailed projected partial density of states analysis finally shows that Cu and Mn are antiferromagnetically coupled by superexchange interaction and Tb is expected to interact FM with A-site Cu and AFM with B-site Mn sublattices by way of 4f-2p-3d.
Spin-correlations and magnetic structure in an Fe monolayer on 5d transition metal surfaces
International Nuclear Information System (INIS)
We present a detailed first principles study on the magnetic structure of an Fe monolayer on different surfaces of 5d transition metals. We use the spin-cluster expansion technique to obtain parameters of a spin model, and predict the possible magnetic ground state of the studied systems by employing the mean field approach and, in certain cases, by spin dynamics calculations. We point out that the number of shells considered for the isotropic exchange interactions plays a crucial role in the determination of the magnetic ground state. In the case of Ta substrate we demonstrate that the out-of-plane relaxation of the Fe monolayer causes a transition from ferromagnetic to antiferromagnetic ground state. We examine the relative magnitude of nearest neighbour Dzyaloshinskii–Moriya (D) and isotropic (J) exchange interactions in order to get insight into the nature of magnetic pattern formations. For the Fe/Os(0 0 0 1) system we calculate a very large D/J ratio, correspondingly, a spin spiral ground state. We find that, mainly through the leading isotropic exchange and Dzyaloshinskii–Moriya interactions, the inward layer relaxation substantially influences the magnetic ordering of the Fe monolayer. For the Fe/Re(0 0 0 1) system characterized by large antiferromagnetic interactions we also determine the chirality of the 120° Néel-type ground state. (paper)
Spin valves based on Mn{sub 75}Ir{sub 25} antiferromagnet with controllable functional parameters
Energy Technology Data Exchange (ETDEWEB)
Milyaev, M. A., E-mail: milyaev@imp.uran.ru; Naumova, L. I.; Kamenskii, I. Yu.; Ustinov, V. V. [Russian Academy of Sciences, Institute of Metal Physics, Ural Branch (Russian Federation)
2015-12-15
Using the example of spin valves of the Ta(50 Å)/Ni{sub 80}Fe{sub 20}(30 Å)/Co{sub 90}Fe{sub 10}(15 Å)/Cu(28 Å)/Co{sub 90}Fe{sub 10}(20 Å)/Mn{sub 75}Ir{sub 25}(50 Å)/Ta(20 Å) composition, factors controlling the hysteresis properties are studied for the case of macro- and microscopic sizes of an experimental sample. It is shown that a linear change in the magnetoresistance with small hysteresis while retaining the giant magnetoresistance effect at a level of 8% can be obtained in a micro-object (meander) using thermomagnetic treatment.
International Nuclear Information System (INIS)
The antiferromagnetic insulator La1.5Ca0.5CoO4 has been investigated by Co L2,3-edge and O K-edge X-ray absorption spectroscopy (XAS) measurements and Co L2,3-edge resonant soft X-ray magnetic scattering (RXMS) measurement to determine the Co electronic structures associated with magnetic ordering. Co L2,3-edge linear-dichroic XAS shows that Co2+ takes a high-spin (HS) state and Co3+ takes a low-spin (LS) state. Using Co L2,3-edge RXMS, we directly determined that an antiferromagnetic order is formed with a HS state of Co2+ ions. Moreover, the spin and orbital angular momenta of the Co2+ HS state are quantitatively estimated to be 1.1 ± 0.1 and 1.0 ± 0.1, respectively, and to align parallel in the ab plane by utilizing the cluster model calculation. The large orbital angular momentum of the Co2+ HS state originates from the small D4h-symmetry crystal field splitting of t2g levels, which is comparable with the spin-orbit coupling constant of the Co 3d orbital. (author)
Molecular orbital study on antiferromagnetic coupling mechanism in a silver (I) complex
Institute of Scientific and Technical Information of China (English)
ZHANG Guiqin; HUANG Jiangen; HUANG Yuanhe; FANG Decai; ZHANG Deqing
2005-01-01
The mechanism of antiferromagnetic coupling in an Ag (I) complex of nitronyl nitroxide is investigated by means of the broken-symmetry approach within the density functional method (DFT-BS). The magneto-structural correlation and the single-occupied molecular orbital (SOMO) analysis reveal the existence of the antiferromagnetic coupling pathway along nitronyl nitroxide units via Ag (I) ion, and that the Ag (I) ion plays an important bridge role. The spin population analysis also shows the existence of spin delocalization along the ONCNO-Ag-ONCNO chain. It is found that the non-typical covalent bonds with major ionic character between Ag (I) ions and oxygen atoms of nitronyl nitroxide units can be used to mediate the spin-spin interaction of nitronyl nitroxides.
Correlation between oxygen tension and spin-lattice relaxation rate in tumors
International Nuclear Information System (INIS)
The role of oxygen in influencing the spin-lattice and spin-spin relaxation mechanism in liquids has been known for decades. However, no concerted efforts has been made to find a correlation between relaxation rates and oxygen dissolved in cell water. A procedure has been developed that allows both in vitro and in vivo measurement of oxygen tension in tumors and helps to calculate spin-lattice relaxation rate. (orig.)
Calvo, Rafael; Sartoris, Rosana P.; Calvo, Hernán L.; Chagas, Edson F.; Rapp, Raul E.
2016-05-01
We study the spin chain behavior, a transition to 3D magnetic order and the magnitudes of the exchange interactions for the metal-amino acid complex Cu(D,L-alanine)2•H2O, a model compound to investigate exchange couplings supported by chemical paths characteristic of biomolecules. Thermal and magnetic data were obtained as a function of temperature (T) and magnetic field (B0). The magnetic contribution to the specific heat, measured between 0.48 and 30 K, displays above 1.8 K a 1D spin-chain behavior that can be fitted with an intrachain antiferromagnetic (AFM) exchange coupling constant 2J0=(-2.12±0.08) cm-1 (defined as ℋex(i,i+1) = -2J0SiṡSi+1), between neighbor coppers at 4.49 Å along chains connected by non-covalent and H-bonds. We also observe a narrow specific heat peak at 0.89 K indicating a phase transition to a 3D magnetically ordered phase. Magnetization curves at fixed T = 2, 4 and 7 K with B0 between 0 and 9 T, and at T between 2 and 300 K with several fixed values of B0 were globally fitted by an intrachain AFM exchange coupling constant 2J0=(-2.27±0.02) cm-1 and g = 2.091±0.005. Interchain interactions J1 between coppers in neighbor chains connected through long chemical paths with total length of 9.51 Å cannot be estimated from magnetization curves. However, observation of the phase transition in the specific heat data allows estimating the range 0.1≤|2J1|≤0.4 cm-1, covering the predictions of various approximations. We analyze the magnitudes of 2J0 and 2J1 in terms of the structure of the corresponding chemical paths. The main contribution in supporting the intrachain interaction is assigned to H-bonds while the interchain interactions are supported by paths containing H-bonds and carboxylate bridges, with the role of the H-bonds being predominant. We compare the obtained intrachain coupling with studies of compounds showing similar behavior and discuss the validity of the approximations allowing to calculate the interchain
Fisher-Hartwig conjecture and the correlators in XY spin chain
International Nuclear Information System (INIS)
We apply the theorems from the theory of Toeplitz determinants to calculate the asymptotics of the correlators in the XY spin chain in the transverse magnetic field. The asymptotics of the correlators for the XX spin chain in the magnetic field are obtained
Uranium nitride. A cubic antiferromagnet with anisotropic critical behaviour
International Nuclear Information System (INIS)
Highly anisotropic critical scattering associated with the transition at Tsub(N)=49.5K to the type-I antiferromagnetic structure has been observed in uranium nitride. The transverse susceptibility is found to be unobservably small. The longitudinal susceptibility diverges at Tsub(N) and its anisotropy shows that the spins within the (001) ferromagnetic sheets of the [001] domain are much more highly correlated than they are with the spins lying in adjacent (001) sheets. The correlation range within the sheets is much greater than that expected for a Heisenberg system with the same Tsub(N). The rod-like scattering extended along the spin and domain direction is reminiscent of two-dimensional behaviour. The results are inconsistent with a simple localized model and may reflect the itinerant nature of the 5f electrons. (author)
Spin-selective localization of correlated lattice fermions
Skolimowski, J.; Vollhardt, D.; Byczuk, K.
2015-09-01
The interplay between local, repulsive interactions and disorder acting only on one spin orientation of lattice fermions ("spin-dependent disorder") is investigated. The nonmagnetic disorder vs interaction phase diagram is computed using dynamical mean-field theory in combination with the geometric average over disorder. The latter determines the typical local density of states and is therefore sensitive to Anderson localization. The effect of spin-dependent disorder is found to be very different from that of conventional disorder. In particular, it destabilizes the metallic solution and leads to a spin-selective, localized phase at weak interactions and strong disorder.
Mediated entanglement and correlations in a star network of interacting spins
International Nuclear Information System (INIS)
We investigate analytically a star network of spins, in which all spins interact exclusively and continuously with a central spin through Heisenberg XX couplings of equal strength. We find that the central spin correlates and entangles the other spins at zero temperature to a degree that depends on the total number of spins. We find that the entanglement mediating capability of the central spin depends on the evenness or oddness of this number. In the limit of an infinite collection of spins, the difference between entanglement and correlations in terms of divisibility among multiple parties is clearly demonstrated. We also show that with a significant probability one can maximally entangle any two noncentral spins by measuring all the other spins (a process related to the recently introduced notion of localizable entanglement). This probability depends on the evenness and oddness of the total number of spins and remains substantial even for an infinite collection of spins. We show how symmetric multiparty states for optimal sharing and splitting of entanglement can be obtained as ground states of this system using a magnetic field. These states can then be mapped on to flying qubits for transmission to distant parties. We discuss a number of advantages of this mode of generation and distribution of entanglement over other standard methods
Spin-foam fermions: PCT symmetry, Dirac determinant and correlation functions
Han, Muxin; Rovelli, Carlo
2013-04-01
We discuss fermion coupling in the framework of spin-foam quantum gravity. We analyze the gravity-fermion spin-foam model and its fermion correlation functions. We show that there is a spin-foam analogue of PCT symmetry for the fermion fields on a spin-foam model, which is proved for spin-foam fermion correlation functions. We compute the determinant of the Dirac operator for the fermions, where two presentations of the Dirac determinant are given in terms of diagram expansions. We compute the fermion correlation functions and show that they can be given by Feynman diagrams on the spin-foams, where the Feynman propagators can be represented by a discretized path integral of a world-line action along the edges of the underlying 2-complex.
Gerasimova, Tatiana P.; Katsyuba, Sergey A.; Lavrenova, Ludmila G.; Pelmenschikov, Vladimir; Kaupp, Martin
2015-12-01
Combined IR spectroscopic/quantum-chemical analysis of a 4-propyl-1,2,4-triazole trinuclear Fe(II) complex capable of reversible thermal spin crossover has revealed mid-IR bands of the ligand sensitive to the Fe(II) spin state. The character of the correlations found between the intensity and peak position of the triazole bands and the spin state of the metal center depends neither on the identity of the metal nor on the nuclearity of the complex. The found spectral correlations therefore allow analysis of various similar complexes. This is illustrated by the example of experimental IR spectra reported earlier for Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes with triazole ligands. Quantum-chemical IR spectral simulations further suggest that certain ligand bands vary between the states with the same total molecular spin, but different distribution of the spin density between the metal centers. However these variations are too subtle to discriminate between the spin transitions of the central and peripheral Fe(II) ions. The experimentally revealed mid-IR markers are therefore conclusive only for the total molecular spin.
Constructing a magnetic handle for antiferromagnetic manganites
Glavic, Artur; Dixit, Hemant; Cooper, Valentino R.; Aczel, Adam A.
2016-04-01
An intrinsic property of antiferromagnetic materials is the compensation of the magnetic moments from the individual atoms that prohibits the direct interaction of the spin lattice with an external magnetic field. To overcome this limitation we have created artificial spin structures by heteroepitaxy between two bulk antiferromagnets SrMnO3 and NdMnO3. Here, we demonstrate that charge transfer at the interface results in the creation of thin ferromagnetic layers adjacent to A -type antiferromagnetism in thick NdMnO3 layers. A novel interference based neutron diffraction technique and polarized neutron reflectometry are used to confirm the presence of ferromagnetism in the SrMnO3 layers and to probe the relative alignment of antiferromagnetic spins induced by the coupling at the ferro- to antiferromagnet interface. A density functional theory analysis of the driving forces for the exchange reveals strong ferromagnetic interfacial coupling through quantifiable short range charge transfer. These results confirm a layer-by-layer control of magnetic arrangements that constitutes a promising step on a path towards isothermal magnetic control of antiferromagnetic arrangements as would be necessary in spin-based heterostructures like multiferroic devices.
Spin-spin critical point correlation functions for the 2D random bond Ising and Potts models
Dotsenko, V S; Pujol, P; Vladimir Dotsenko; Marco Picco; Pierre Pujol
1994-01-01
We compute the combined two and three loop order correction to the spin-spin correlation functions for the 2D Ising and q-states Potts model with random bonds at the critical point. The procedure employed is the renormalisation group approach for the perturbation series around the conformal field theories representing the pure models. We obtain corrections for the correlations functions which produce crossover in the amplitude but don't change the critical exponent in the case of the Ising model and which produce a shift in the critical exponent, due to randomness, in the case of the Potts model. Comparison with numerical data is discussed briefly.
Edge states in Open Antiferromagnetic Heisenberg Chains
Qin, Shaojin; Ng, Tai-Kai; Su, Zhao-Bin
1995-01-01
In this letter we report our results in investigating edge effects of open antiferromagnetic Heisenberg spin chains with spin magnitudes $S=1/2, 1,3/2,2$ using the density-matrix renormalization group (DMRG) method initiated by White. For integer spin chains, we find that edge states with spin magnitude $S_{edge}=S/2$ exist, in agreement with Valence-Bond-Solid model picture. For half-integer spin chains, we find that no edge states exist for $S=1/2$ spin chain, but edge state exists in $S=3/...
Immense magnetic response of exciplex light emission due to correlated spin-charge dynamics
Wang, Yifei; Sahin-Tiras, Kevser; Harmon, Nicholas J.; Wohlgenannt, Markus; Flatté, Michael E.
2016-01-01
As carriers slowly move through a disordered energy landscape in organic semiconductors, tiny spatial variations in spin dynamics relieve spin blocking at transport bottlenecks or in the electron-hole recombination process that produces light. Large room-temperature magnetic-field effects (MFE) ensue in the conductivity and luminescence. Sources of variable spin dynamics generate much larger MFE if their spatial structure is correlated on the nanoscale with the energetic sites governing condu...
Correlation energy in a spin polarized two dimensional electron liquid in the high density limit
Chesi, S; Giuliani, G. F.
2006-01-01
We have obtained an analytic expression for the ring diagram contribution to the correlation energy of a two-dimensional electron liquid as a function of the uniform fractional spin polarization. Our results can be used to improve the interpolation formulas which represent the basic ingredient for the construction of modern spin-density functionals in two dimensions.
Optimized resonating valence bond state in square lattice: correlations & excitations
Directory of Open Access Journals (Sweden)
Z Nourbakhsh
2009-09-01
Full Text Available We consider RVB state as a variational estimate for the ground state of Heisenberg antiferromagnet in square lattice. We present numerical calculation of energy, spin-spin correlation function and spin excitation spectrum. We show, that the quantum flactuations reduce of magnetization respect to Neel order. Our results are in good agreement with other methods such as spin-wave calculation and series expansions.
The Correlations of Jet Power with Black Hole Mass and Spin in Radio Loud Quasars
Xu, Zhang; Hao-jing, Zhang; Xiong, Zhang
2016-04-01
The formation of jets is closely related with the black hole mass and black hole spin, to study the correlations of jet power with the black hole mass and black hole spin is of significant importance for understanding the jet formation and structure. We have collected 65 radio loud quasars from the literature. The sample includes 35 Steep Spectrum Radio Quasars (SSRQs) and 30 Flat Spectrum Radio Quasars (FSRQs) with the redshifts ranging from about zero to two. We present here the correlation analysis of jet power with the black hole mass and back hole spin based on the sample data. Our conclusions are as follows: (1) The black hole mass has a strong correlation with the jet power; (2) The black hole spin is also strongly correlated with the jet power, especially for the magnetic field strength B = BEDD, where BEDD is the Eddington magnetic field strength, and the correlation coefficient is higher than that between black hole mass and jet power; (3) There are certain differences between the distributions of spin data of SSRQs and FSRQs; (4) This study has further confirmed that the jet energy is related not only with the black hole mass, but also with the spin energy of the black hole. The formation of black hole jet may be very possibly resulted by the joint effect of black hole mass and black hole spin. These results are consistent with the previous results obtained by other methods.
Asymptotics and functional form of correlators in the XX-spin chain of finite length
International Nuclear Information System (INIS)
We verify the functional form of the asymptotics of the spin-spin equal-time correlation function for the XX chain, predicted by the hypothesis of conformal invariance at large distances and by the bosonization procedure. We point out that the bosonization procedure also predicts the functional form of the correlators for the chains of finite length. We found the exact expression for the spin-spin equal-time correlator on a finite lattice. We find excellent agreement of the exact correlator with the prediction given by the leading asymptotics result up to very small distances. We also establish the correspondence between the value of the constant before the asymptotics for the XX chain with the expression for this constant proposed by Lukyanov and Zamolodchikov. We also evaluate the constant corresponding to the subleading term in the asymptotics in a way which is different from previous studies
Bond-centered, bond-ordered stripes in doped antiferromagnets
Wrobel, P.; Maciag, A; Eder, R.
2004-01-01
Motivated by recent inelastic neutron scattering experiments on cuprates, we discuss the formation of bond order in the stripe phase. We suggest that the spin Peierls order emerges in hole-rich domain walls (DWs) formed between hole-poor regions in which long-range antiferromagnetic (AF) correlations exist. On the example of a single stripe we analyze the stability of such structures. The motion of a hole inside the DW which takes the form of a bond ordered ladder is in principle unrestricted...
Quantum Effects in Higher-Order Correlators of a Quantum-Dot Spin Qubit
Bechtold, A.; Li, F.; Müller, K.; Simmet, T.; Ardelt, P.-L.; Finley, J. J.; Sinitsyn, N. A.
2016-07-01
We measure time correlators of a spin qubit in an optically active quantum dot beyond the second order. Such higher-order correlators are shown to be directly sensitive to pure quantum effects that cannot be explained within the classical framework. They allow direct determination of ensemble and quantum dephasing times, T2* and T2, using only repeated projective measurements and without the need for coherent spin control. Our method enables studies of purely quantum behavior in solid state systems, including tests of the Leggett-Garg type of inequalities that rule out local hidden variable interpretation of the quantum-dot spin dynamics.
Bett, Philip E.; Frenk, Carlos S.
2016-09-01
We expand our previous study on the relationship between changes in the orientation of the angular momentum vector of dark matter haloes (`spin flips') and changes in their mass, to cover the full range of halo masses in a simulation cube of length 100 h-1 Mpc. Since strong disturbances to a halo (such as might be indicated by a large change in the spin direction) are likely also to disturb the galaxy evolving within, spin flips could be a mechanism for galaxy morphological transformation without involving major mergers. We find that 35 per cent of haloes have, at some point in their lifetimes, had a spin flip of at least 45° that does not coincide with a major merger. Over 75 per cent of large spin flips coincide with non-major mergers; only a quarter coincide with major mergers. We find a similar picture for changes to the inner halo spin orientation, although here there is an increased likelihood of a flip occurring. Changes in halo angular momentum orientation, and other such measures of halo perturbation, are therefore very important quantities to consider, in addition to halo mergers, when modelling the formation and evolution of galaxies and confronting such models with observations.
Ferromagnetic response of a ``high-temperature'' quantum antiferromagnet
Wang, Xin
2014-03-01
We study the antiferromagnetic phase of the ionic Hubbard model at finite temperature using dynamical mean-field theory. We find that the ionic potential plays a dual role in determining the antiferromagnetic order. A small ionic potential (compared to the Hubbard repulsion) increases the super-exchange coupling, thereby implying an increase of the Neel temperature of the system, which should facilitate observation of antiferromagnetic ordering experimentally. On the other hand, for large ionic potential, the antiferromagnetic ordering is killed and the system becomes a charge density wave with electron occupancies alternating between 0 and 2. This novel way of degrading antiferromagnetism leads to spin polarization of the low energy single particle density of states. The dynamic response of the system thus mimics ferromagnetic behavior, although the system is still an antiferromagnet in terms of the static spin order. Work done in collaboration with Rajdeep Sensarma and Sankar Das Sarma, and supported by NSF-JQI-PFC, AFOSR MURI, and ARO MURI.
Vortical fluid and $\\Lambda$ spin correlations in high-energy heavy-ion collisions
Pang, Long-Gang; Wang, Qun; Wang, Xin-Nian
2016-01-01
Fermions become polarized in a vortical fluid due to spin-vorticity coupling. The spin polarization density is proportional to the local fluid vorticity at the next-to-leading order of a gradient expansion in a quantum kinetic theory. Spin correlations of two $\\Lambda$-hyperons can therefore reveal the vortical structure of the dense matter in high-energy heavy-ion collisions. We employ a (3+1)D viscous hydrodynamic model with event-by-event fluctuating initial conditions from A MultiPhase Transport (AMPT) model to calculate the vorticity distributions and $\\Lambda$ spin correlations. The azimuthal correlation of the transverse spin is shown to have a cosine form plus an offset due to a circular structure of the transverse vorticity around the beam direction and global spin polarization. The longitudinal spin correlation shows a structure of vortex-pairing in the transverse plane due to the convective flow of hot spots in the radial direction. The dependence on colliding energy, rapidity, centrality and sensi...
Heisenberg antiferromagnet on the Husimi lattice
Liao, H. J.; Xie, Z. Y.; Chen, J.; Han, X. J.; Xie, H. D.; Normand, B.; Xiang, T.
2016-02-01
We perform a systematic study of the antiferromagnetic Heisenberg model on the Husimi lattice using numerical tensor-network methods based on projected entangled simplex states. The nature of the ground state varies strongly with the spin quantum number S . For S =1/2 , it is an algebraic (gapless) quantum spin liquid. For S =1 , it is a gapped, nonmagnetic state with spontaneous breaking of triangle symmetry (a trimerized simplex-solid state). For S =2 , it is a simplex-solid state with a spin gap and no symmetry breaking; both integer-spin simplex-solid states are characterized by specific degeneracies in the entanglement spectrum. For S =3/2 , and indeed for all spin values S ≥5/2 , the ground states have 120∘ antiferromagnetic order. In a finite magnetic field, we find that, irrespective of the value of S , there is always a plateau in the magnetization at m =1/3 .
Magnetic interactions in strongly correlated systems: Spin and orbital contributions
International Nuclear Information System (INIS)
We present a technique to map an electronic model with local interactions (a generalized multi-orbital Hubbard model) onto an effective model of interacting classical spins, by requiring that the thermodynamic potentials associated to spin rotations in the two systems are equivalent up to second order in the rotation angles, when the electronic system is in a symmetry-broken phase. This allows to determine the parameters of relativistic and non-relativistic magnetic interactions in the effective spin model in terms of equilibrium Green’s functions of the electronic model. The Hamiltonian of the electronic system includes, in addition to the non-relativistic part, relativistic single-particle terms such as the Zeeman coupling to an external magnetic field, spin–orbit coupling, and arbitrary magnetic anisotropies; the orbital degrees of freedom of the electrons are explicitly taken into account. We determine the complete relativistic exchange tensors, accounting for anisotropic exchange, Dzyaloshinskii–Moriya interactions, as well as additional non-diagonal symmetric terms (which may include dipole–dipole interaction). The expressions of all these magnetic interactions are determined in a unified framework, including previously disregarded features such as the vertices of two-particle Green’s functions and non-local self-energies. We do not assume any smallness in spin–orbit coupling, so our treatment is in this sense exact. Finally, we show how to distinguish and address separately the spin, orbital and spin–orbital contributions to magnetism, providing expressions that can be computed within a tight-binding Dynamical Mean Field Theory
Cao, Chongde; Wildes, Andrew; Li, Haifeng; Schmidt, Wolfgang; Schmalzl, Karin; Hou, Binyang; Regnault, Louis-Pierre; Zhang, Cong; Meuffels, Paul; Löser, Wolfgang; Roth, Georg
2015-01-01
Identifying the nature of magnetism, itinerant or localized, remains a major challenge in condensed-matter science. Purely localized moments appear only in magnetic insulators, whereas itinerant moments more or less co-exist with localized moments in metallic compounds such as the doped-cuprate or the iron-based superconductors, hampering a thorough understanding of the role of magnetism in phenomena like superconductivity or magnetoresistance. Here we distinguish two antiferromagnetic modula...
Exchange bias in diluted-antiferromagnet/antiferromagnet bilayers
International Nuclear Information System (INIS)
The hysteresis-loop properties of a diluted-antiferromagnetic (DAF) layer exchange coupling to an antiferromagnetic (AF) layer are investigated by means of numerical simulations. Remarkable loop shift and coercivity enhancement are observed in such DAF/AF bilayers, while they are absent in the uncoupled DAF single layer. The influences of pinned domains, dilution, cooling field and DAF layer thickness on the loop shift are investigated systematically. The result unambiguously confirms an exchange bias (EB) effect in the DAF/AF bilayers. It also reveals that the EB effect originates from the pinned AF domains within the DAF layer. In contrast to conventional EB systems, frozen uncompensated spins are not found at the interface of the AF pinning layer. (paper)
Lee, H C
1998-01-01
First, we have investigated chiral edges of a quantum Hall liquids at filling factor nu=2. The separation of spin and charge degrees of freedom becomes manifest in the presence of long- range Coulomb interaction. Due to the spin-charge separation the tunneling density of states takes the form D(omega) approx ( -lnl omega l) sup 1 sup / sup 2. Experimentally, the spin-charge separation can be revealed in the temperature and voltage dependence of the tunneling current into Fermi liquid reservoir. Second, the charge and spin correlation functions of partially spin-polarized edge electrons of a quantum Hall bar are studied using effective Hamiltonian and bosonization techniques. In the presence of the Coulomb interaction between the edges with opposite chirality we find a different crossover behavior in spin and charge correlation functions. The crossover of the spin correlation function in the Coulomb dominated regime is characterized by an anomalous exponent, which originates from the finite value of the effect...
International Nuclear Information System (INIS)
A set of new NMR pulse sequences has been designed for the measurement of 13C relaxation rate constants in RNA and DNA bases: the spin-lattice relaxation rate constant R(Cz), the spin-spin relaxation rate constant R(C+), and the CSA-dipolar cross-correlated relaxation rate constant ΓC,CHxy. The use of spin-state selective correlation techniques provides increased sensitivity and spectral resolution. Sensitivity optimised C-C filters are included in the pulse schemes for the suppression of signals originating from undesired carbon isotopomers. The experiments are applied to a 15% 13C-labelled 33-mer RNA-theophylline complex. The measured R(C+)/ΓC,CHxy ratios indicate that 13C CSA tensors do not vary significantly for the same type of carbon (C2, C6, C8), but that they differ from one type to another. In addition, conformational exchange effects in the RNA bases are detected as a change in the relaxation decay of the narrow 13C doublet component when varying the spacing of a CPMG pulse train. This new approach allows the detection of small exchange effects with a higher precision compared to conventional techniques
Energy Technology Data Exchange (ETDEWEB)
Boisbouvier, Jerome; Brutscher, Bernhard; Simorre, Jean-Pierre; Marion, Dominique [C.N.R.S.-C.E.A., Institut de Biologie Structurale Jean-Pierre Ebel (France)
1999-07-15
A set of new NMR pulse sequences has been designed for the measurement of {sup 13}C relaxation rate constants in RNA and DNA bases: the spin-lattice relaxation rate constant R(C{sub z}), the spin-spin relaxation rate constant R(C{sub +}), and the CSA-dipolar cross-correlated relaxation rate constant {gamma}{sub C,CH}{sup xy}. The use of spin-state selective correlation techniques provides increased sensitivity and spectral resolution. Sensitivity optimised C-C filters are included in the pulse schemes for the suppression of signals originating from undesired carbon isotopomers. The experiments are applied to a 15% {sup 13}C-labelled 33-mer RNA-theophylline complex. The measured R(C{sub +})/{gamma}{sub C,CH}{sup xy} ratios indicate that {sup 13}C CSA tensors do not vary significantly for the same type of carbon (C{sub 2}, C{sub 6}, C{sub 8}), but that they differ from one type to another. In addition, conformational exchange effects in the RNA bases are detected as a change in the relaxation decay of the narrow {sup 13}C doublet component when varying the spacing of a CPMG pulse train. This new approach allows the detection of small exchange effects with a higher precision compared to conventional techniques.
Spin-spin correlations in proton-proton collisions at high energy and threshold enhancements
International Nuclear Information System (INIS)
The striking effects in the spin structure observed in elastic proton collisions and the Nuclear Transparency phenomenon recently discovered at BNL are described in terms of heavy quark threshold enhancements. The deviations from scaling laws and the broadening of the angular distributions at resonance are also consistent with the introduction of new degrees of freedom in the pp system. This implies new s-channel physics. Predictions are given for the spin effects in pp collisions near 18.5 GeV/c at large p/sub T/2 where new measurements are planned. 9 refs., 4 figs
Measurement of np elastic scattering spin-spin correlation parameters at 484, 634, and 788 MeV
Energy Technology Data Exchange (ETDEWEB)
Garnett, R.W.
1989-03-01
The spin-spin correlation parameters C/sub LL/ and C/sub SL/ were measured for np elastic scattering at the incident neutron kinetic energy of 634 MeV. Good agreement was obtained with previously measured data. Additionally, the first measurement of the correlation parameter C/sub SS/ was made at the three energies, 484, 634, and 788 MeV. It was found that the new values, in general, do not agree well with phase shift predictions. A study was carried out to determine which of the isospin-0 partial waves will be affected by this new data. It was found that the /sup 1/P/sub 1/ partial wave will be affected significantly at all three measurement energies. At 634 and 788 MeV, the /sup 3/S/sub 1/ phase shifts will also change. 29 refs., 21 figs., 16 tabs.
Measurement of np elastic scattering spin-spin correlation parameters at 484, 634, and 788 MeV
International Nuclear Information System (INIS)
The spin-spin correlation parameters C/sub LL/ and C/sub SL/ were measured for np elastic scattering at the incident neutron kinetic energy of 634 MeV. Good agreement was obtained with previously measured data. Additionally, the first measurement of the correlation parameter C/sub SS/ was made at the three energies, 484, 634, and 788 MeV. It was found that the new values, in general, do not agree well with phase shift predictions. A study was carried out to determine which of the isospin-0 partial waves will be affected by this new data. It was found that the 1P1 partial wave will be affected significantly at all three measurement energies. At 634 and 788 MeV, the 3S1 phase shifts will also change. 29 refs., 21 figs., 16 tabs
Inclusive Single-Spin Asymmetries, Quark-Photon, and Quark-Quark Correlations
Burkardt, Matthias
2016-01-01
We consider quark-photon correlations that have been proposed as a source for single-spin asymmetries in inclusive deep-inelastic scattering. A new sum rule for these correlators is derived and its phenomenological consequences are discussed. The results are interpreted within the context of an intuitive 'electrodynamic lensing' picture.
Quantum and classical thermal correlations in the XY spin-(1)/(2) chain
Maziero, J.; Guzman, H. C.; Céleri, L. C.; Sarandy, M. S.; Serra, R. M.
2010-07-01
We investigate pairwise quantum correlation as measured by the quantum discord as well as its classical counterpart in the thermodynamic limit of anisotropic XY spin-1/2 chains in a transverse magnetic field for both zero and finite temperatures. Analytical expressions for both classical and quantum correlations are obtained for spin pairs at any distance. In the case of zero temperature, it is shown that the quantum discord for spin pairs farther than second neighbors is able to characterize a quantum phase transition, even though pairwise entanglement is absent for such distances. For finite temperatures, we show that quantum correlations can be increased with temperature in the presence of a magnetic field. Moreover, in the XX limit, thermal quantum discord is found to be dominant over classical correlation while the opposite scenario takes place for the transverse field Ising model limit.
Quantum and classical thermal correlations in the XY spin-(1/2) chain
International Nuclear Information System (INIS)
We investigate pairwise quantum correlation as measured by the quantum discord as well as its classical counterpart in the thermodynamic limit of anisotropic XY spin-1/2 chains in a transverse magnetic field for both zero and finite temperatures. Analytical expressions for both classical and quantum correlations are obtained for spin pairs at any distance. In the case of zero temperature, it is shown that the quantum discord for spin pairs farther than second neighbors is able to characterize a quantum phase transition, even though pairwise entanglement is absent for such distances. For finite temperatures, we show that quantum correlations can be increased with temperature in the presence of a magnetic field. Moreover, in the XX limit, thermal quantum discord is found to be dominant over classical correlation while the opposite scenario takes place for the transverse field Ising model limit.
Study of f electron correlations in nonmagnetic Ce by means of spin resolved resonant photoemission
Energy Technology Data Exchange (ETDEWEB)
Yu, S; Komesu, T; Chung, B W; Waddill, G D; Morton, S A; Tobin, J G
2005-11-28
We have studied the spin-spin coupling between two f electrons of nonmagnetic Ce by means of spin resolved resonant photoemission using circularly polarized synchrotron radiation. The two f electrons participating in the 3d{sub 5/2} {yields} 4f resonance process are coupled in a singlet while the coupling is veiled in the 3d{sub 3/2} {yields} 4f process due to an additional Coster-Kronig decay channel. The identical singlet coupling is observed in the 4d {yields} 4f resonance process. Based on the Ce measurements, it is argued that spin resolved resonant photoemission is a unique approach to study the correlation effects, particularly in the form of spin, in the rare-earths and the actinides.
Pulsar Binary Birthrates with Spin-Opening Angle Correlations
O'Shaughnessy, Richard
2009-01-01
Empirical birthrate estimates for pulsar binaries depend on the fraction of sky subtended by the pulsar beam: the pulsar beaming fraction. This fraction depends on both the pulsar's opening angle and the misalignment angle between its spin and magnetic axes. Previous estimates use the average value for only two pulsars, i.e. PSRs B1913+16 and B1534+12. We explore how birthrate predictions depend on assumptions about opening angle and alignment, using empirically-motivated distributions to define an effective beaming correction factor, f_{b,eff}. For most known pulsars, we expect f_{b,eff} to be less than 6. We also calculate f_{b,eff} for PSRs J0737-3039A and J1141-6545, applying the currently available constraints for their beam geometry. Our median posterior birthrate predictions for tight PSR-NS binaries, wide PSR-NS binaries, and tight PSR-WD binaries are 89/Myr, 0.84/Myr, and 34/Myr, respectively. For pulsars with spin period between 10 ms and 100 ms, we marginalized our posterior birthrate distribution ...
Energy Technology Data Exchange (ETDEWEB)
Kitanine, N
2007-09-15
Spin chains are the basic elements of integrable quantum models. These models have direct applications in condense matter theory, in statistical physics, in quantum optics, in field theory and even in string theory but they are also important because they enable us to solve, in an exact manner, non-perturbative phenomena that otherwise would stay unresolved. The method described in this work is based on the algebraic Bethe Ansatz. It is shown how this method can be used for the computation of null temperature correlation functions of the Heisenberg 1/2 spin chain. The important point of this approach is the solution of the inverse quantum problem given by the XXZ spin chain. This solution as well as a simple formulae for the scalar product of the Bethe states, have enabled us to get the most basic correlation functions under the form of multiple integrals. The formalism of multiple integrals open the way for asymptotic analysis for a few physical quantities like the probability of vacuum formation. It is worth noticing that this formalism can give exact results for two-point functions that are the most important correlation functions for applications. A relationship has been discovered between these multiple integrals and the sum of the form factors. The results have been extended to dynamical correlation functions. (A.C.)
Spin-Momentum Correlations in Quasi-Elastic Electron Scattering from Deuterium
Energy Technology Data Exchange (ETDEWEB)
I. Passchier; L.D. van Buuren; D. Szczerba; R. Alarcon; Th.S. Bauer; D. Boersma; J.F.J. van den Brand; H.J. Bulten; R. Ent; M. Ferro-Luzzi; M. Harvey; P. Heimberg; D.W. Higinbotham; S. Klous; H. Kolster; J. Lang; B.L. Militsyn; D. Nikolenko; G.J.L. Nooren; B.E. Norum; H.R. Poolman; I. Rachek; M.C. Simani; E. Six; H. de Vries; K. Wang; Z.-L. Zhou
2002-02-25
We report on a measurement of spin-momentum correlations in quasi-elastic scattering of longitudinally polarized electrons with an energy of 720 MeV from vector-polarized deuterium. The spin correlation parameter A{sub ed}{sup V} was measured for the 2{rvec H}({rvec e},e{prime}p)n reaction for missing momenta up to 350 MeV/c at a four-momentum transfer squared of 0.21 (GeV/c){sup 2}. The data give detailed information about the spin structure of the deuteron, and are in good agreement with the predictions of microscopic calculations based on realistic nucleon-nucleon potentials and including various spin-dependent reaction mechanism effects. The experiment demonstrates in a most direct manner the effects of the D-state in the deuteron ground-state wave function and shows the importance of isobar configurations for this reaction.
Maximizing Spin Correlations in Top Quark Pair Production at the Tevatron
Mahlon, G; Mahlon, Gregory; Parke, Stephen
1997-01-01
A comparison is made between the off-diagonal and helicity spin bases for top quark pair production at the FNAL Tevatron. In the off-diagonal basis, 92% of the top quark pairs are in the spin configuration up-down plus down-up, whereas in the helicity basis only 70% are left-right plus right-left. The off-diagonal basis maximizes the spin asymmetry and hence the measured angular correlations between the decay products, which are more than twice as big in this basis as compared to the helicity basis. In addition, for the process q qbar --> t tbar, we give a very simple analytic expression for the matrix element squared which includes all spin correlations between the production and subsequent decay of the top quarks.
Improved Spin Basis for Angular Correlation Studies in Single Top Quark Production at the Tevatron
Mahlon, G; Mahlon, Gregory; Parke, Stephen
1997-01-01
We show in single top quark production that the spin of the top quark is correlated with the direction of the d-type quark in the event. For single top production in the W* channel, the d-type quark comes dominantly from the antiproton at the Tevatron, whereas for the W-gluon fusion channel the spectator jet is the d-type quark the majority of the time at this machine. Our results are that 98% of the top quarks from the W* process have their spins in the antiproton direction, and 95% of the top quarks in the W-gluon fusion process have their spins in the spectator jet direction. We also compare with the more traditional, but less effective, helicity basis. The direction of the top quark spin is reflected in angular correlations in its decay products.
International Nuclear Information System (INIS)
We review the main properties of spin waves condensation to a coherent quantum state, named homogeneously precessing domain (HPD). We describe the long range coherent transport of magnetization by spin supercurrent in antiferromagnetic superfluid He3. This quantum phenomenon was discovered 20 years ago. Since then, many magnetic extensions of superconductivity and superfluidity have been observed: spin Josephson phenomena, spin-current vortices, spin phase slippage, long distance magnetization transport by spin supercurrents, etc. Several new supercurrent phenomena have been discovered, like magnetically excited coherent quantum states, NMR in the molecular Landau field, spin-current turbulence, formation of stable non-topological solitons, etc
Quantum Correlations of Two Relativistic Spin-{1}/{2} Particles Under Noisy Channels
Mahdian, M.; Mojaveri, B.; Dehghani, A.; Makaremi, T.
2016-02-01
We study the quantum correlation dynamics of bipartite spin-{1}/{2} density matrices for two particles under Wigner rotations induced by Lorentz transformations which is transmitted through noisy channels. We compare quantum entanglement, geometric discord(GD), and quantum discord (QD) for bipartite relativistic spin-{1}/{2} states under noisy channels. We find out QD and GD tend to death asymptotically but a sudden change in the decay rate of the entanglement occurs under noisy channels. Also, bipartite relativistic spin density matrices are considered as a quantum channel for teleportation one-qubit state under the influence of depolarizing noise and compare fidelity for various velocities of observers.
Gangopadhyay, Shruba; Pickett, Warren E.
2016-04-01
High formal valence Os-based double perovskites are a focus of current interest because they display strong interplay of large spin-orbit coupling and strong electronic correlation. Here we present the electronic and magnetic characteristics of a sequence of three cubic Os based double perovskites Ba2A OsO6 (A =Na , Ca, Y), with formal valences of Os +7(d1) ,Os +6(d2) , and Os +5(d3) . For these first principles based calculations we apply an "exact exchange for correlated electrons" functional, with exact exchange applied in a hybrid fashion solely to the Os (5 d ) states. While Ba2NaOsO6 is a reported ferromagnetic Dirac-Mott insulator studied previously, the other two show antiferromagnetic ordering while all retain the undistorted cubic structure. For comparison purposes we have investigated only the ferromagnetic ordered phase. A metal-insulator transition is predicted to occur upon rotating the direction of magnetization in all three materials, reflecting the central role of spin-orbit coupling in these small gap osmates. Surprises arising from comparing formal charge states with the radial charge densities are discussed. Chemical shielding factors and orbital susceptibilities are provided for comparison with future nuclear magnetic resonance data.
Analyzing the correlations for spin-1/2 particles and singlet pairs
de Faria, Edson
2012-01-01
We revisit the computation of correlations of spin projections onto unit vectors for spin-1/2 particles in Quantum Mechanics. We then choose one of the Boole inequalities that, as we recall, must be obeyed by collections of sequences of normalized spin-spin-1/2 projections onto unit vectors that belong to, say, the plane that is orthogonal to the classical trajectory or to the three dimensional space. Next we define the concept of being a-p for i-indexed sequences of spin-1/2 particles: it turns out that a sequence of spin-spin-1/2 particles is a-p if and only if the particles behave as if they had indeed been prepared (in the usual sense) to have definite spins +1 or -1 along the axis a, the sequence of signs being pre-determined. The a-p property is formulated in a way abstract enough to let one generalize it and we define the concept of being a-p and b-p. However, using our chosen Boole inequality we prove that no particle sequence can be both a-p and b-p when a and b are not co-linear. We next consider tw...
Transverse spin and momentum correlations in quantum chromodynamics
Indian Academy of Sciences (India)
Leonard P Gamberg
2009-01-01
The naive time reversal odd (`T-odd') parton distribution and fragmentation functions are explored. We use the spectator model framework to study flavour dependence of the Boer–Mulders $(h_{1}^{⊥})$ and Sivers $(f_{1\\text{T}}^{⊥})$ functions as well as the `T-even' but chiral odd function $h_{1\\text{L}}^{⊥}$. These transverse momentum-dependent parton distribution functions are of significance for the analysis of azimuthal asymmetries in semi-inclusive deep inelastic scattering, as well as for the overall physical understanding of the distribution of transversely polarized quarks in unpolarized hadrons. In this context we also consider the Collins mechanism and the fragmentation function $H_{1}^{⊥}$. As a by-product of this analysis we calculate the leading twist unpolarized cos(2) asymmetry, and sin(2) single spin asymmetry for a longitudinally polarized target in semi-inclusive deep inelastic scattering.
International Nuclear Information System (INIS)
The geometrically frustrated antiferromagnet Gd2Ti2O7 is an easy-planer anisotropic system in which single ion anisotropy mainly arises due to the considerable admixture of higher Russel-Saunders terms of Gd3+ ion to its ground term 8S. The g-value of the ground CF doublet becomes anisotropic, g parallel = 1.99, g perpendicular = 7.97, instead of the free-ion isotropic value 2. The ground multiplet 8S7/2 splits into 4 doublets with total splitting ∼16 K, thus exhibiting its characteristic specific heat feature below 5 K. (author)
Lattice distortion in disordered antiferromagnetic XY models
Institute of Scientific and Technical Information of China (English)
Li Peng-Fei; Cao Hai-Jing
2012-01-01
The behavior of lattice distortion in spin 1/2 antiferromagnetic XY models with random magnetic modulation is investigated with the consideration of spin-phonon coupling in the adiabatic limit.It is found that lattice distortion relies on the strength of the random modulation.For strong or weak enough spin-phonon couplings,the average lattice distortion may decrease or increase as the random modulation is strengthened.This may be the result of competition between the random magnetic modulation and the spin-phonon coupling.
Energy Technology Data Exchange (ETDEWEB)
Tsuchimochi, Takashi, E-mail: tsuchimochi@gmail.com; Ten-no, Seiichiro, E-mail: tenno@garnet.kobe-u.ac.jp [Graduate School of System Informatics, Kobe University, Kobe 657-8501 (Japan)
2016-01-07
We present single and double particle-hole excitations in the recently revived spin-projected Hartree-Fock. Our motivation is to treat static correlation with spin-projection and recover the residual correlation, mostly dynamic in nature, with simple configuration interaction (CI). To this end, we introduce the Wick theorem for nonorthogonal determinants, which enables an efficient implementation in conjunction with the direct CI scheme. The proposed approach, termed spin-extended CI with singles and doubles, achieves a balanced treatment between dynamic and static correlations. To approximately account for the quadruple excitations, we also modify the well-known Davidson correction. We report that our approaches yield surprisingly accurate potential curves for HF, H{sub 2}O, N{sub 2}, and a hydrogen lattice, compared to traditional single reference wave function methods at the same computational scaling as regular CI.
International Nuclear Information System (INIS)
We present single and double particle-hole excitations in the recently revived spin-projected Hartree-Fock. Our motivation is to treat static correlation with spin-projection and recover the residual correlation, mostly dynamic in nature, with simple configuration interaction (CI). To this end, we introduce the Wick theorem for nonorthogonal determinants, which enables an efficient implementation in conjunction with the direct CI scheme. The proposed approach, termed spin-extended CI with singles and doubles, achieves a balanced treatment between dynamic and static correlations. To approximately account for the quadruple excitations, we also modify the well-known Davidson correction. We report that our approaches yield surprisingly accurate potential curves for HF, H2O, N2, and a hydrogen lattice, compared to traditional single reference wave function methods at the same computational scaling as regular CI
Boosting spin-caloritronic effects by attractive correlations in molecular junctions
Weymann, Ireneusz
2016-01-01
In nanoscopic systems quantum confinement and interference can lead to an enhancement of thermoelectric properties as compared to conventional bulk materials. For nanostructures, such as molecules or quantum dots coupled to external leads, the thermoelectric figure of merit can reach or even exceed unity. Moreover, in the presence of external magnetic field or when the leads are ferromagnetic, an applied temperature gradient can generate a spin voltage and an associated spin current flow in the system, which makes such nanostructures particularly interesting for future thermoelectric applications. In this study, by using the numerical renormalization group method, we examine the spin-dependent thermoelectric transport properties of a molecular junction involving an orbital level with attractive Coulomb correlations coupled to ferromagnetic leads. We analyze how attractive correlations affect the spin-resolved transport properties of the system and find a nontrivial dependence of the conductance and tunnel magnetoresistance on the strength and sign of those correlations. We also demonstrate that attractive correlations can lead to an enhancement of the spin thermopower and the figure of merit, which can be controlled by a gate voltage.
Tricritical behavior of the frustrated XY antiferromagnet
Plumer, M. L.; Mailhot, A.; Caillé, A.
1994-01-01
Extensive histogram Monte-Carlo simulations of the XY antiferromagnet on a stacked triangular lattice reveal exponent estimates which strongly favor a scenario of mean-field tricritical behavior for the spin-order transition. The corresponding chiral-order transition occurs at the same temperature but appears to be decoupled from the spin-order. These results are relevant to a wide class of frustrated systems with planar-type order and serve to resolve a long-standing controversy regarding th...
DEFF Research Database (Denmark)
Enevoldsen, Thomas; Oddershede, Jens; Sauer, Stephan P. A.
1998-01-01
We present correlated calculations of the indirect nuclear spin-spin coupling constants of HD, HF, H2O, CH4, C2H2, BH, AlH, CO and N2 at the level of the second-order polarization propagator approximation (SOPPA) and the second-order polarization propagator approximation with coupled......-cluster singles and doubles amplitudes - SOPPA(CCSD). Attention is given to the effect of the so-called W 4 term, which has not been included in previous SOPPA spin-spin coupling constant studies of these molecules. Large sets of Gaussian basis functions, optimized for the calculation of indirect nuclear spin...
Energy transfer and correlation dynamics in a three-quasi-spin-pigment system
Institute of Scientific and Technical Information of China (English)
Zhang Yin-Ping; Li Hong-Rong; Fang Ai-Ping; Chen Hao; Li Fu-Li
2013-01-01
In this paper,the effects of quantum and classical correlations on the excitation energy transfer in a three-quasi-spin-pigment system are investigated.We first study the dependence of the energy transfer efficiency on various initial correlations of the donor pigments,and find that the initial concurrence is crucial to the efficiency no matter whether the initial states are pure or mixed.We then demonstrate the dynamics of correlations of the system and observe the appearance of sudden death of quantum correlations in the donor pigments.The relation between the energy transfer efficiency and the dynamics of correlations in the donor pigments is also discussed.
Angles and Daemons: Spin Correlations at the LHC
Energy Technology Data Exchange (ETDEWEB)
Tran, Nhan V. [Johns Hopkins Univ., Baltimore, MD (United States)
2011-09-01
The Large Hadron Collider has recently started collecting data, opening a new energy regime. This will allow us to probe further than ever before many of the current mysteries of the field. New physics beyond the Standard Model, the field's current paradigm, could manifest itself via new particles. In addition, the Higgs boson, hypothesized as a consequence of electroweak symmetry breaking, remains undiscovered. At the time of discovery, the properties of such particles will be unknown. In order to understand the nature of any new physics, it will be important to understand the properties of that new particle. Methods are presented for measuring its spin, parity and coupling to the Standard Model particles. These methods are implemented at the Compact Muon Solenoid experiment and an analysis is presented with the data collected during 2010 and 2011 running at the Large Hadron Collider. An application of these techniques is used to make a measurement of the weak mixing angle. A current status of the search for the Higgs boson is also presented.
Hard-spin mean-field theory: A systematic derivation and exact correlations in one dimension
International Nuclear Information System (INIS)
Hard-spin mean-field theory is an improved mean-field approach which has proven to give accurate results, especially for frustrated spin systems, with relatively little computational effort. In this work, the previous phenomenological derivation is supplanted by a systematic and generic derivation that opens the possibility for systematic improvements, especially for the calculation of long-range correlation functions. A first level of improvement suffices to recover the exact long-range values of the correlation functions in one dimension. (c) 2000 The American Physical Society
Comments on correlation functions of large spin operators and null polygonal Wilson loops
International Nuclear Information System (INIS)
We discuss the relation between correlation functions of twist-two large spin operators and expectation values of Wilson loops along light-like trajectories. After presenting some heuristic field theoretical arguments suggesting this relation, we compute the divergent part of the correlator in the limit of large 't Hooft coupling and large spins, using a semi-classical world-sheet which asymptotically looks like a GKP rotating string. We show this diverges as expected from the expectation value of a null Wilson loop, namely, as (lnμ−2)2, μ being a cut-off of the theory.
Influence of Z' boson on top quark spin correlations at the LHC
Arai, Masato; Okada, Nobuchika; Smolek, Karel; Simak, Vladislav
2008-01-01
We study top-antitop pair production and top spin correlations in a model with an electrically neutral massive gauge boson, Z', at the Large Hadron Collider. In addition to the Standard Model processes, the Z' contributes to the top-antitop pair production process in the s-channel. Choosing a kinematical region of top invariant mass around the Z' resonance pole, we find sizable deviations of the top-antitop pair production cross section and the top spin correlations from those of the Standard...
Measurement of Spin Correlation coefficients in \\vec p \\vec p --> d pi^+
Przewoski, B.V.; Balewski, J. T.; Doskow, J.; Meyer, H. O.; Pollock, R. E.; Rinckel, T.; Thörngren-Engblom, P.; Wellinghausen, A.; W. Haeberli; Lorentz, B.; Rathmann, F.; Schwartz, B; Wise, T; Daehnick, W. W.; Saha, Swapan K.
1999-01-01
The spin correlation coefficent combinations A_{xx}+A_{yy} and A_{xx}-A_{yy}, the spin correlation coefficients A_{xz} and A_{zz}, and the analyzing power were measured for \\vec p \\vec p --> d pi^+ between center-of-mass angles 25 deg \\leq \\theta \\leq 65 deg at beam energies of 350.5, 375.0 and 400.0 MeV. The experiment was carried out with a polarized internal target and a stored, polarized beam. Non-vertical beam polarization needed for the measurement of A_{zz} was obtained by the use of s...
Ghorbani, Elaheh; Shahbazi, Farhad; Mosadeq, Hamid
2016-10-12
Using the modified spin wave method, we study the [Formula: see text] Heisenberg model with first and second neighbor antiferromagnetic exchange interactions. For a symmetric S = 1/2 model, with the same couplings for all the equivalent neighbors, we find three phases in terms of the frustration parameter [Formula: see text]: (1) a commensurate collinear ordering with staggered magnetization (Néel.I state) for [Formula: see text], (2) a magnetically gapped disordered state for [Formula: see text], preserving all the symmetries of the Hamiltonian and lattice, which by definition is a quantum spin liquid (QSL) state and (3) a commensurate collinear ordering in which two out of the three nearest neighbor magnetizations are antiparallel and the remaining pair are parallel (Néel.II state), for [Formula: see text]. We also explore the phase diagram of a distorted [Formula: see text] model with S = 1/2. Distortion is introduced as an inequality of one nearest neighbor coupling with the other two. This yields a richer phase diagram by the appearance of a new gapped QSL, a gapless QSL and also a valence bond crystal phase in addition to the previous three phases found for the undistorted model. PMID:27518832
Energy Technology Data Exchange (ETDEWEB)
Zhu, Jian-xin [Los Alamos National Laboratory; Dai, Jianhui [ZHEJIANG UNIV; Si, Qimiao [RICE UNIV
2009-01-01
Some of the high {Tc} iron pnictides contain rare-earth elements, raising the question of how the existence and tunability of a d-electron antiferromagnetic order influences the heavy fermion behavior of the f-moments. With CeOFeP and CeOFeAs in mind as prototypes, we derive an extended Anderson lattice model appropriate for these quaternary systems. We show that the Kondo screening of the f-moments are efficiently suppressed by the d-electron ordering. We also argue that, inside the d-electron ordered state (as in CeOFeAs), the f-moments provide a rare realization of a quantum frustrated magnet with competing J{sub 1}-J{sub 2}-J{sub 3} interactions in an effective square lattice. Implications ofr the heavy fermion physics in broader contexts are also discussed.
Correlation Functions of Sp(2n) Invariant Higher-Spin Systems
Skvortsov, Evgeny; Tsulaia, Mirian
2016-01-01
We study the general structure of correlation functions in an Sp(2n)-invariant formulation of systems of an infinite number of higher-spin fields. For n=4,8 and 16 these systems comprise the conformal higher-spin fields in space-time dimensions D=4,6 and 10, respectively, while when $n=2$, one deals with conventional D=3 conformal field theories of scalars and spinors. We show that for n>2 the Sp(2n) symmetry and current conservation makes the 3-point correlators of two (rank-one or rank-two) conserved currents with a scalar operator be that of free theory.This situation is analogous to the one in conventional conformal field theories, where conservation of higher-spin currents implies that the theories are free.
Von Przewoski, B; Doskow, J; Meyer, H O; Pollock, R E; Rinckel, T; Thörngren-Engblom, P; Wellinghausen, A; Haeberli, W; Lorentz, B; Rathmann, F; Schwartz, B; Wise, T; Daehnick, W W; Saha, S K; Pancella, P V; Saha, Swapan K.
2000-01-01
The spin correlation coefficent combinations A_{xx}+A_{yy} and A_{xx}-A_{yy}, the spin correlation coefficients A_{xz} and A_{zz}, and the analyzing power were measured for \\vec p \\vec p --> d pi^+ between center-of-mass angles 25 deg experiment was carried out with a polarized internal target and a stored, polarized beam. Non-vertical beam polarization needed for the measurement of A_{zz} was obtained by the use of solenoidal spin rotators. Near threshold, only a few partial waves contribute, and pion s- and p-waves dominate with a possible small admixture of d-waves. Certain combinations of the observables reported here are a direct measure of these d-waves. The d-wave contributions are found to be negligible even at 400.0 MeV.
Tobey, R. I.; Wall, S.; Foerst, M.; Bromberger, H.; Khanna, V.; Turner, J. J.; Schlotter, W.; Trigo, M.; Krupin, O.; Lee, W. S.; Chuang, Y. -D.; Moore, R.; Cavalieri, A. L.; Wilkins, S. B.; Zheng, H.; Mitchell, J. F.; Dhesi, S. S.; Cavalleri, A.; Hill, J.P.
2012-01-01
Using time-resolved resonant soft x-ray diffraction, we measure the evolution of the full three-dimensional scattering volume of the antiferromagnetic superlattice reflection in the single-layer manganite La0.5Sr1.5MnO4 on femtosecond time scales following photoexcitation. We find that the in-plane
Measurement of Spin Correlation in Top Quark Pair Production at ATLAS
McLaughlan, Thomas
2014-01-01
This thesis presents a study of spin correlation in tt ̄ production in the ATLAS detector, in proton-proton collisions, corresponding to an integrated luminosity of 4.7 fb$^{−1}$, with a centre of mass energy of $\\sqrt{s}$ = 7 TeV. Both the dilepton and single lepton channels are considered, the latter providing a greater challenge due to the neccessity to reconstruct the down-type quark resulting from the W boson decay. A simple technique is employed to reconstruct single lepton $t\\bar{t}$ events, with the transverse angle between the charged lepton and down-type quark used as a probe of the spin correlation. In the dilepton channel, the transverse angle between both charged leptons is used. The extracted value of spin correlation in each channel is consistent with Standard Model predictions, with the result in the eμ channel alone sufficient to exclude a model without spin correlation at 7.8$\\sigma$. Also described is the author’s contribution to the maintenance and development of the Atlantis Event D...
Effect of correlation energy on the stability of impurity spin models
International Nuclear Information System (INIS)
We apply density-functional theory to estimate the ground-state energy of the inhomogeneous Heisenberg model for nanoscale spin assemblies in the presence of boundaries or impurities. Correlations are shown to lift degeneracies present in the mean-field approximation
Spin correlations in amorphous Bi2Sr2CaCu2Ox
International Nuclear Information System (INIS)
Zero and longitudinal field μSR has been used to probe the magnetic state of amorphous Bi2Sr2CaCu2Ox prepared by rapid quenching from the melt. The results suggest quasi-static spin correlations between extremely dilute Cu2+ ions. (orig.)
Nuclear spin-orbit interaction and T-odd angular correlations in ternary fission
Barabanov, A L
2014-01-01
T-odd angular correlations in ternary fission of 233-U and 235-U nuclei by slow polarized neutrons are not related to TRI (time reversal invariance) violation, but are caused by an effective spin-orbit interaction in the final state.
DEFF Research Database (Denmark)
Andersen, Brian Møller; Graser, S.; Hirschfeld, P. J.
2012-01-01
Recent experimental and theoretical studies have highlighted the possible role of an electronic nematic liquid in underdoped cuprate superconductors. We calculate, within a model of d-wave superconductor with Hubbard correlations, the spin susceptibility in the case of a small explicitly broken...
Electrical control of antiferromagnetic metal up to 15 nm
Zhang, PengXiang; Yin, GuFan; Wang, YuYan; Cui, Bin; Pan, Feng; Song, Cheng
2016-08-01
Manipulation of antiferromagnetic (AFM) spins by electrical means is on great demand to develop the AFM spintronics with low power consumption. Here we report a reversible electrical control of antiferromagnetic moments of FeMn up to 15 nm, using an ionic liquid to exert a substantial electric-field effect. The manipulation is demonstrated by the modulation of exchange spring in [Co/Pt]/FeMn system, where AFM moments in FeMn pin the magnetization rotation of Co/Pt. By carrier injection or extraction, the magnetic anisotropy of the top layer in FeMn is modulated to influence the whole exchange spring and then passes its influence to the [Co/Pt]/FeMn interface, through a distance up to the length of exchange spring that fully screens electric field. Comparing FeMn to IrMn, despite the opposite dependence of exchange bias on gate voltages, the same correlation between carrier density and exchange spring stiffness is demonstrated. Besides the fundamental significance of modulating the spin structures in metallic AFM via all-electrical fashion, the present finding would advance the development of low-power-consumption AFM spintronics.
Magnetic Properties of Quantum Ferrimagnetic Spin Chains
Yamamoto, Shoji
1998-01-01
Magnetic susceptibilities of spin-$(S,s)$ ferrimagnetic Heisenberg chains are numerically investigated. It is argued how the ferromagnetic and antiferromagnetic features of quantum ferrimagnets are exhibited as functions of $(S,s)$. Spin-$(S,s)$ ferrimagnetic chains behave like combinations of spin-$(S-s)$ ferromagnetic and spin-$(2s)$ antiferromagnetic chains provided $S=2s$.
Golovenchits, E I
2001-01-01
One studied spin dynamics and dynamics of lattice in R sub 2 CuO sub 4 (R = Pr, Sm, and Eu) crystals within 20-250 GHz frequency range and within 50350 K temperature interval. One detected abrupt variation of absorption coefficient within wide range of frequencies above 120 GHz at 20, 80 and 150 K temperatures in R sub 2 CuO sub 4 (R = Pr, Sm, and Eu), respectively. Absorption jumpings result from structural phase transitions. Wide ranges of spin-wave excitations were observed in all examined crystals in high-temperature phase. Close to temperatures of phase transitions within wide range of frequencies including frequencies corresponding to ranges of spin-wave excitations one observed lines of a absorption caused by lattice dynamics
Observation of the orbital quantum dynamics in the spin-1/2 hexagonal antiferromagnet B a3CuS b2O9
Han, Yibo; Hagiwara, Masayuki; Nakano, Takehito; Nozue, Yasuo; Kimura, Kenta; Halim, Mario; Nakatsuji, Satoru
2015-11-01
We have studied orbital dynamics in the spin liquid candidate B a3CuS b2O9 using multifrequency electron-spin resonance. We prepared two high-quality single crystals. The crystal with a slight copper deficiency shows a structural phase transition at around 200 K due to the cooperative Jahn-Teller effect, accompanied with orbital ordering. In contrast, the crystal with almost perfect stoichiometry shows no orbital ordering down to the lowest temperature of 1.5 K. Dramatic change in the g factor anisotropy as a function of frequency and temperature demonstrates orbital quantum fluctuations at a nearly constant time scale of ˜100 ps below 20 K, evidencing the emergence of an orbital liquid state in this quantum spin liquid compound.
Order and disorder in two geometrically frustrated antiferromagnets
International Nuclear Information System (INIS)
2Ti2O7, by N. P. Raju, M. Dion, M. J. P. Gingras, T. E. Mason, and J. E. Greedan, Phys. Rev. B 59, 14489 (1999). Our second study, the results of which appear in Chapter 4, addresses the question of whether the ground state for the spin-1/2 nearest- neighbor antiferromagnetic Heisenberg model on a version of the pyrochlore lattice in 2D is ordered or disordered. We perform exact diagonalization calculations on small clusters of spins on this lattice. From an analysis of the low-lying energy levels in these systems, we find a large gap to spin excitations which does not appear to close in the thermodynamic limit. We see no order, as evidenced by measurements of ground state correlation functions and the structure of the low energy excitation spectrum. We find that spin-spin and spin-Peierls correlations decay rapidly with distance and that a large number of non-magnetic states fill the spin gap. Comparing our results to other exact diagonalization studies of the same model on the triangular and kagome lattices, we conclude that there is no Neel order in the ground state for this system. (author)
International Nuclear Information System (INIS)
It has been shown that the spin-density wave instability does not coexist with s-like anisotropic superconductivity in the molecular field approach to the nearly half-filled two-dimensional Hubbard model. The phase diagram of the interplay of normal state, spin density wave, d-wave and extended s-wave superconducting orderings has been constructed. The possibility of the first order transition from the normal state and the superconducting state to the SDW-phase has been discussed. (author). 14 refs, 2 figs
Spin correlation parameter Cyy of p+3He elastic backward scattering
International Nuclear Information System (INIS)
We measured the differential cross section and the spin correlation parameter Cyy of the p-vector+3He-vector elastic backward scattering at 200, 300, and 400 MeV at θ=180 deg. in the center-of-mass frame to study the mechanism of the reaction and to examine the validity of the 3He wave functions based on two different realistic two-body forces. This is the first measurement of the spin correlation parameter Cyy of the p-vector+3He-vector EBS at intermediate energies. The experimental results were compared with few-body calculations, including three reaction mechanisms: two-nucleon-pair exchange, pion exchange, and direct pp scattering. It was found that few-body calculations describe the differential cross-section data reasonably well. The spin correlation parameter Cyy shows clear evidence for the two-nucleon-pair exchange processes in the reaction, demonstrating that the spin observables are helpful for deeper understanding of the reaction mechanism
Uemura, Y. J.; Kossler, W. J.; Kempton, J. R.; Yu, X. H.; Schone, H. E.; Opie, D.; Stronach, C. E.; Brewer, J. H.; Kiefl, R. F.; Kreitzman, S. R.
1988-01-01
Muon spin rotation and neutron scattering studies on powder and single-crystal specimens of La2CuO(4-y) are compared. The apparent difference between the muon and neutron results for the ordered moment in the antiferromagnetic state is interpreted as the signature of increasingly short-ranged spatial spin correlations with increasing oxygen content.
Tsuchimochi, Takashi
2015-01-01
We introduce single and double particle-hole excitations in the recently revived spin-projected Hartree-Fock. Our motivation is to treat static correlation with spin-projection and recover the residual correlation, mostly dynamic in nature, with simple configuration interaction (CI). To this end, we introduce the Wick theorem for nonorhtogonal determinants, which enables an efficient implementation in conjunction with the direct CI scheme. The proposed approach, termed ECISD, achieves a balanced treatment between dynamic and static correlations. To approximately account for the quadruple excitations, we also modify the well-known Davidson correction. We report our approaches yield surprisingly accurate potential curves for HF, H2O, N2, and a hydrogen lattice, compared to traditional single reference wave function methods at the same computational scaling as regular CI.
Quantum and classical thermal correlations in the XY spin-1/2 chain
Maziero, J; Celeri, L C; Sarandy, M S; Serra, R M
2010-01-01
We investigate pairwise quantum correlations as measured by the quantum discord as well as its classical counterpart in the thermodynamic limit of anisotropic XY spin-1/2 chains in a transverse magnetic field for both zero and finite temperatures. In the case of zero temperature, it is shown that the quantum discord for spin pairs farther than second-neighbors is able to characterize a quantum phase transition, even though pairwise entanglement is absent for such distances. For finite temperatures, we show that quantum correlations can be increased with temperature in the presence of a magnetic field. Moreover, in the XX limit, the thermal quantum discord is found to be dominant over classical correlation while the opposite scenario takes place for the transverse field Ising model limit.
Dynamical correlation effects on structure factor of spin-polarized two-dimensional electron gas
International Nuclear Information System (INIS)
We report a theoretical study on static density structure factor S(q) of a spin-polarized two-dimensional electron gas over a wide range of electron number density rs. The electron correlations are treated within the dynamical version of the self-consistent mean-field theory of Singwi, Tosi, Land, and Sjolander, the so-called qSTLS approach. The calculated S(q) exhibits almost perfect agreement with the quantum Monte Carlo simulation data at rs=1. However, the extent of agreement somewhat diminishes with increasing rs, particularly for q around 2kF. Seen in conjunction with the success of qSTLS theory in dealing with correlations in the unpolarized phase, our study suggests that the otherwise celebrated qSTLS theory is not that good in treating the like-spin correlations
Macrospin dynamics in antiferromagnets triggered by sub-20 femtosecond injection of nanomagnons
Bossini, D.; Dal Conte, S.; Hashimoto, Y.; Secchi, A.; Pisarev, R. V.; Rasing, Th.; Cerullo, G.; Kimel, A. V.
2016-02-01
The understanding of how the sub-nanoscale exchange interaction evolves in macroscale correlations and ordered phases of matter, such as magnetism and superconductivity, requires to bridging the quantum and classical worlds. This monumental challenge has so far only been achieved for systems close to their thermodynamical equilibrium. Here we follow in real time the ultrafast dynamics of the macroscale magnetic order parameter in the Heisenberg antiferromagnet KNiF3 triggered by the impulsive optical generation of spin excitations with the shortest possible nanometre wavelength and femtosecond period. Our magneto-optical pump-probe experiments also demonstrate the coherent manipulation of the phase and amplitude of these femtosecond nanomagnons, whose frequencies are defined by the exchange energy. These findings open up opportunities for fundamental research on the role of short-wavelength spin excitations in magnetism and strongly correlated materials; they also suggest that nanospintronics and nanomagnonics can employ coherently controllable spin waves with frequencies in the 20 THz domain.
Spin correlations in the ΛΛ systems generated in relativistic heavy ion collisions
International Nuclear Information System (INIS)
Spin correlations for the ΛΛ and ΛΛ bar pairs, generated in relativistic heavy ion collisions, and related angular correlations at the joint registration of hadronic decays of two hyperons, in which space parity is not conserved, are analyzed. The correlation tensor components can be derived from the double angular distribution of products of two decays by the method of 'moments'. The properties of the 'trace' of the correlation tensor (a sum of three diagonal components), determining the relative fractions of the triplet states and singlet state of respective pairs, are discussed. Spin correlations for two identical particles (ΛΛ) and two non-identical particles (ΛΛbar) are considered from the viewpoint of the conventional model of one-particle sources. In the framework of this model, correlations vanish at sufficiently large relative momenta. However, under these conditions, in the case of two non-identical particles (ΛΛbar) a noticeable role is played by two-particle annihilation (two-quark, two-gluon) sources, which lead to the difference of the correlation tensor from zero. In particular, such a situation may arise when the system passes through the 'mixed phase'
Quantum spin Hall effect in a transition metal oxide Na2IrO3
Shitade, Atsuo; Katsura, Hosho; Kunes, Jan; Qi, Xiao-Liang; Zhang, Shou-Cheng; Nagaosa, Naoto
2008-01-01
We study theoretically the electronic states in a $5d$ transition metal oxide Na$_2$IrO$_3$, in which both the spin-orbit interaction and the electron correlation play crucial roles. Tight-binding model analysis together with the fisrt-principles band structure calculation predicts that this material is a layered quantum spin Hall system. Due to the electron correlation, an antiferromagnetic order first develops at the edge, and later inside the bulk at low temperatures.
Magnetizing and heating quantum spin ladders
Indian Academy of Sciences (India)
Andrey Zheludev
2008-11-01
Quasi-one-dimensional quantum spin liquids, such as weakly coupled even-legged S=1/2 spin ladders or spin tubes, have a singlet non-magnetic ground state and gap in the excitation spectrum. Their low-temperature properties can be described in terms of triplet massive quasiparticles. These magnons possess some unique features due to the peculiar topology of one dimension. For example, two-particle interactions totally destroy single-particle states for certain energy and momentum transfers, resulting in the so-called termination of the magnon spectrum. At high field a Bose–Einstein condensation of these magnons produces a `quantum spin solid' phase, where `conventional` antiferromagnetic order coexists with excitations that are totally outside conventional spin wave theory. At finite temperatures strong repulsion between quasiparticles leads to a universal renormalization of their masses and lifetimes. These diverse phenomena are best probed by neutron scattering experiments that directly measure the spin correlation functions and excitation spectra.
Spin–spin correlations of entangled qubit pairs in the Bohm interpretation of quantum mechanics
International Nuclear Information System (INIS)
A general entangled qubit pair is analyzed in the de Broglie–Bohm formalism corresponding to two spin-1/2 quantum rotors. Several spin–spin correlators of Bohm’s hidden variables are analyzed numerically and a detailed comparison with results obtained by standard quantum mechanics is outlined. In addition to various expectation values, the Bohm interpretation also allows a study of the corresponding probability distributions, which enables a novel understanding of entangled qubit dynamics. In particular, it is shown how the angular momenta of two qubits in this formalism can be viewed geometrically and characterized by their relative angles. For perfectly entangled pairs, for example, a compelling picture is given, where the qubits exhibit a unison precession making a constant angle between their angular momenta. It is also demonstrated that the properties of standard quantum mechanical spin-spin correlators responsible for the violation of Bell’s inequalities are identical to their counterparts emerging from the probability distributions obtained by the Bohmian approach. (paper)
Study on the energy dependence of spin-spin correlation in the range of diproton resonances
International Nuclear Information System (INIS)
Coefficients of polarization correlation Csub(NN) (90 deg) at 9 values of energy in the 550-950 MeV range with absolute error less than 0.05 are measured on the beams on JINR and LINP synchrocyclotrons. Csub(NN) values at the angles of 41 deg, 69 deg, 77 deg (T=550, 610, 630 MeV) and 50 deg at other energies have been obtained. The measurement results are presented together with predictions of the Arndt phase analysis and two variants of the Hoshizaki analysis conducted before and after publishing the results of the given experiment. Energy dependence of Csub(NN) (50 deg) does not reveal noticeable peculiarities and it well agrees with all the variants of the analysis. The considered total data do not substantiate certain conclusions on resonance character in pp interaction in the investigated energy range. The structure observed in respect to Csub(NN) (90 deg, p) is the consequence of different energy dependence of amplitudes of triplet and singlet scattering and it may be interpreted as a testify to presence of resonance or as a consequence of threshold phenomena in inelastic channels in the 550-750 MeV energy range
Antiferromagnetic coupling across silicon regulated by tunneling currents
Gareev, Rashid; Schmid, Maximilian; Vancea, Johann; Back, Christian; Schreiber, Reinert; Buergler, Daniel; Stromberg, Frank; Wende, Heiko
2012-02-01
We present the room temperature enhancement of antiferromagnetic coupling in epitaxial Fe(3 nm)/Si(2.4 nm)/Fe(3 nm) structures by voltage-driven spin-polarized tunneling currents. Using the ballistic electron magnetic microscopy we established that the saturation field for the collector current corresponding to parallel alignment of magnetizations rises up with the tunneling current, thus demonstrating stabilization of the antiparallel alignment and increase of antiferromagnetic coupling. We connect the enhancement of antiferromagnetic coupling with local dynamic spin torques mediated by spin-polarized tunneling electrons. Finally, in the antiparallel state the spin-polarized majority (minority) electrons exert dynamic torques in the bottom (upper) iron layer and, thus, additionally stabilize magnetization alignment.
Short distance correlators in the XXZ spin chain for arbitrary string distributions
International Nuclear Information System (INIS)
In this paper, we consider expectation values of local correlators in highly excited states of the spin-1/2 XXZ chain. Assuming that the string hypothesis holds we formulate the following conjecture: The correlation functions can be computed using the known factorized formulae of the finite temperature situation, if the building blocks are computed via certain linear integral equations using the string densities only. We prove this statement for the nearest neighbour z–z correlator for states with arbitrary string densities. Also, we check the conjecture numerically for other correlators in the finite temperature case. Our results pave the way towards the computation of the stationary values of correlators in non-equilibrium situations using the quench action approach. (paper)
Generalized parton correlation functions for a spin-1/2 hadron
Energy Technology Data Exchange (ETDEWEB)
Stephan Meissner, Andreas Metz, Marc Schlegel
2009-08-01
The fully unintegrated, off-diagonal quark-quark correlator for a spin-1/2 hadron is parameterized in terms of so-called generalized parton correlation functions. Such objects, in particular, can be considered as mother distributions of generalized parton distributions on the one hand and transverse momentum dependent parton distributions on the other. Therefore, our study provides new, model-independent insights into the recently proposed nontrivial relations between generalized and transverse momentum dependent parton distributions. We find that none of these relations can be promoted to a model-independent status. As a by-product we obtain the first complete classification of generalized parton distributions beyond leading twist. The present paper is a natural extension of our previous corresponding analysis for spin-0 hadrons.
Tchougréeff, A L
2009-01-01
We analyze the various approaches to construct exchange-correlation functionals which are able to describe states of definite spin multiplicity in the DFT realm and outline the characteristics of possible functionals consistent with the Kohn-Sham theory. To achieve this goal the unitary group technique is applied to label many-electron states of definite total spin and to calculate the corresponding analogs of the Roothaan coupling coefficients. The possibility of using range separated Coulomb potential of electron-electron interaction for constructing functionals discriminating multiplet states in the d-shells is explored and a tentative system of state-specific functionals, covering nontrivial correlations in d-shells of transition metal ions, is proposed for the Fe^{2+} ions.
Theoretical study of Coulomb correlations and spin-orbit coupling in SrIrO3
International Nuclear Information System (INIS)
Given that energy scales associated with crystal field splitting, spin orbit coupling and coulomb correlations in iridates are comparable, hence leading to exotic properties, we investigate the physical properties of orthorhombic SrIrO3 using density functional theory. Our calculations, however, show that SrIrO3 is a bad metal with no long range magnetic ordering, unlike its sister compounds Sr2IrO4 and Sr3Ir2O7. Moreover, despite having large band width, it appears conclusive that the larger resistivity in SrIrO3 is due to spin orbit interactions. Besides, the effects of electron-electron correlations on its electronic structure and magnetic properties are also discussed
Shiota, Takayoshi; Mukuda, Hidekazu; Uekubo, Masahiro; Engetsu, Fuko; Yashima, Mitsuharu; Kitaoka, Yoshio; Lai, Kwing To; Usui, Hidetomo; Kuroki, Kazuhiko; Miyasaka, Shigeki; Tajima, Setsuko
2016-05-01
We report on 31P-NMR studies of LaFe(As1‑xPx)(O1‑yFy) over wide compositions for 0 ≤ x ≤ 1 and 0 ≤ y ≤ 0.14, which provide clear evidence that antiferromagnetic spin fluctuations (AFMSFs) are one of the indispensable elements for enhancing Tc. Systematic 31P-NMR measurements revealed two types of AFMSFs in the temperature evolution, that is, one is the AFMSFs that develop rapidly down to Tc with low-energy characteristics, and the other, with relatively higher energy than the former, develops gradually upon cooling from high temperature. The low-energy AFMSFs in low y (electron doping) over a wide x (pnictogen height suppression) range are associated with the two orbitals of dxz/yz, whereas the higher-energy ones for a wide y region around low x originate from the three orbitals of dxy and dxz/yz. We remark that the nonmonotonic variation of Tc as a function of x and y in LaFe(As1‑xPx)(O1‑yFy) is attributed to these multiple AFMSFs originating from degenerated multiple 3d orbitals inherent to Fe-pnictide superconductors.
Brant, Jacilynn A; dela Cruz, Clarina; Yao, Jinlei; Douvalis, Alexios P; Bakas, Thomas; Sorescu, Monica; Aitken, Jennifer A
2014-12-01
Li2FeGeS4 (LIGS) and Li2FeSnS4 (LITS), which are among the first magnetic semiconductors with the wurtz-kesterite structure, exhibit antiferromagnetism with TN ≈ 6 and 4 K, respectively. Both compounds undergo a conventional metamagnetic transition that is accompanied by a hysteresis; a reversible spin-flop transition is dominant. On the basis of constant-wavelength neutron powder diffraction data, we propose that LIGS and LITS exhibit collinear magnetic structures that are commensurate and incommensurate with propagation vectors km = [1/2, 1/2, 1/2] and [0, 0, 0.546(1)], respectively. The two compounds exhibit similar magnetic phase diagrams, as the critical fields are temperature-dependent. The nuclear structures of the bulk powder samples were verified using time-of-flight neutron powder diffraction along with synchrotron X-ray powder diffraction. (57)Fe and (119)Sn Mössbauer spectroscopy confirmed the presence of Fe(2+) and Sn(4+) as well as the number of crystallographically unique positions. LIGS and LITS are semiconductors with indirect and direct bandgaps of 1.42 and 1.86 eV, respectively, according to optical diffuse-reflectance UV-vis-NIR spectroscopy. PMID:25397682
Pan, Bingying; Wang, Yang; Zhang, Lijuan; Li, Shiyan
2014-04-01
Single crystals of a metal organic complex (C5H12N)CuBr3 (C5H12N = piperidinium, pipH for short) have been synthesized, and the structure was determined by single-crystal X-ray diffraction. (pipH)CuBr3 crystallizes in the monoclinic group C2/c. Edging-sharing CuBr5 units link to form zigzag chains along the c axis, and the neighboring Cu(II) ions with spin-1/2 are bridged by bibromide ions. Magnetic susceptibility data down to 1.8 K can be well fitted by the Bonner-Fisher formula for the antiferromagnetic spin-1/2 chain, giving the intrachain magnetic coupling constant J ≈ -17 K. At zero field, (pipH)CuBr3 shows three-dimensional (3D) order below TN = 1.68 K. Calculated by the mean-field theory, the interchain coupling constant J' = -0.91 K is obtained and the ordered magnetic moment m0 is about 0.23 μB. This value of m0 makes (pipH)CuBr3 a rare compound suitable to study the 1D-3D dimensional cross-over problem in magnetism, since both 3D order and one-dimensional (1D) quantum fluctuations are prominent. In addition, specific heat measurements reveal two successive magnetic transitions with lowering temperature when external field μ0H ≥ 3 T is applied along the a' axis. The μ0H-T phase diagram of (pipH)CuBr3 is roughly constructed. PMID:24617285
International Nuclear Information System (INIS)
We discuss and analyze four magic-angle spinning solid-state NMR methods that can be used to measure internuclear distances and to obtain correlation spectra between a spin I = 1/2 and a half-integer spin S > 1/2 having a small quadrupolar coupling constant. Three of the methods are based on the heteronuclear multiple-quantum and single-quantum correlation experiments, that is, high rank tensors that involve the half spin and the quadrupolar spin are generated. Here, both zero and single-quantum coherence of the half spins are allowed and various coherence orders of the quadrupolar spin are generated, and filtered, via active recoupling of the dipolar interaction. As a result of generating coherence orders larger than one, the spectral resolution for the quadrupolar nucleus increases linearly with the coherence order. Since the formation of high rank tensors is independent of the existence of a finite quadrupolar interaction, these experiments are also suitable to materials in which there is high symmetry around the quadrupolar spin. A fourth experiment is based on the initial quadrupolar-driven excitation of symmetric high order coherences (up to p = 2S, where S is the spin number) and subsequently generating by the heteronuclear dipolar interaction higher rank (l + 1 or higher) tensors that involve also the half spins. Due to the nature of this technique, it also provides information on the relative orientations of the quadrupolar and dipolar interaction tensors. For the ideal case in which the pulses are sufficiently strong with respect to other interactions, we derive analytical expressions for all experiments as well as for the transferred echo double resonance experiment involving a quadrupolar spin. We show by comparison of the fitting of simulations and the analytical expressions to experimental data that the analytical expressions are sufficiently accurate to provide experimental 7Li–13C distances in a complex of lithium, glycine, and water. Discussion
Effects of impurities and vortices on the low-energy spin excitations in high-T_{c} materials
DEFF Research Database (Denmark)
Andersen, Brian Møller; Graser, S.; Schmid, M.; Kampf, A. F.; Hirschfeld, P.J.
2011-01-01
We review a theoretical scenario for the origin of the spin-glass phase of underdoped cuprate materials. In particular it is shown how disorder in a correlated d-wave superconductor generates a magnetic phase by inducing local droplets of antiferromagnetic order which eventually merge and form a ...... disorder and/or applied magnetic fields lead to a slowing down of the dynamical spin fluctuations in agreement with neutron scattering and muon spin rotation (mSR) experiments....
Top Quark Pair Properties - Spin Correlation, Charge Asymmetry, and Complex Final States - at ATLAS
Directory of Open Access Journals (Sweden)
Brost Elizabeth
2014-04-01
Full Text Available We present measurements of top quark pair properties performed with the ATLAS detector at the Large Hadron Collider in proton-proton collisions at a center-of-mass energy of √s = 7 TeV. The latest measurements of spin correlation and charge asymmetry in tt¯$t\\overline t $ events, as well as measurements of the cross section for tt¯$t\\overline t $ production in association with vector bosons, are presented.
Black-Schaffer, Annica M.; Doniach, Sebastian
2008-01-01
Using the self-consistent tight-binding Bogoliubov-de Gennes formalism we have studied the effect of nearest neighbor spin-singlet bond (SB) correlations on Josephson coupling and proximity effect in graphene SNS Josephson junctions with conventional s-wave superconducting contacts. Despite the s-wave superconducting state in the contacts, the SB pairing state inside the junction has d-wave symmetry and clean, sharp interface junctions resemble a 'bulk-meets-bulk' situation with very little i...
Recent progress on correlated electron systems with strong spin-orbit coupling.
Schaffer, Robert; Kin-Ho Lee, Eric; Yang, Bohm-Jung; Kim, Yong Baek
2016-09-01
The emergence of novel quantum ground states in correlated electron systems with strong spin-orbit coupling has been a recent subject of intensive studies. While it has been realized that spin-orbit coupling can provide non-trivial band topology in weakly interacting electron systems, as in topological insulators and semi-metals, the role of electron-electron interaction in strongly spin-orbit coupled systems has not been fully understood. The availability of new materials with significant electron correlation and strong spin-orbit coupling now makes such investigations possible. Many of these materials contain 5d or 4d transition metal elements; the prominent examples are iridium oxides or iridates. In this review, we succinctly discuss recent theoretical and experimental progress on this subject. After providing a brief overview, we focus on pyrochlore iridates and three-dimensional honeycomb iridates. In pyrochlore iridates, we discuss the quantum criticality of the bulk and surface states, and the relevance of the surface/boundary states in a number of topological and magnetic ground states, both in the bulk and thin film configurations. Experimental signatures of these boundary and bulk states are discussed. Domain wall formation and strongly-direction-dependent magneto-transport are also discussed. In regard to the three-dimensional honeycomb iridates, we consider possible quantum spin liquid phases and unusual magnetic orders in theoretical models with strongly bond-dependent interactions. These theoretical ideas and results are discussed in light of recent resonant x-ray scattering experiments on three-dimensional honeycomb iridates. We also contrast these results with the situation in two-dimensional honeycomb iridates. We conclude with the outlook on other related systems. PMID:27540689
Quantum correlation approach to criticality in the XX spin chain with multiple interaction
International Nuclear Information System (INIS)
We investigate the quantum critical behavior in the XX spin chain with a XZY-YZX type multiple interaction by means of quantum correlation (Concurrence C, quantum discord DQ and geometric discord DG). Around the critical point, the values of these quantum correlations and corresponding derivatives are investigated numerically and analytically. The results show that the non-analyticity property of the concurrence cannot signal well the quantum phase transition, but both the quantum discord and geometric discord can characterize the critical behavior in such model exactly.
Single spin optical read-out in CdTe/ZnTe quantum dot studied by photon correlation spectroscopy
Suffczynski, J.; K. Kowalik(The Andrzej Soltan Institute for Nuclear Studies); Kazimierczuk, T.; Trajnerowicz, A.; Goryca, M.; Kossacki, P.; Golnik, A.; Nawrocki, M.; Gaj, J. A.
2008-01-01
Spin dynamics of a single electron and an exciton confined in CdTe/ZnTe quantum dot is investigated by polarization-resolved correlation spectroscopy. Spin memory effects extending over at least a few tens of nanoseconds have been directly observed in magnetic field and described quantitatively in terms of a simple rate equation model. We demonstrate an effective (68%) all-optical read-out of the single carrier spin state through probing the degree of circular polarization of exciton emission...
Elantkowska, Magdalena; Ruczkowski, Jarosław; Dembczyński, Jerzy
2016-02-01
The continuation of the previous series of papers related to the construction of the energy matrix for complex atoms is presented. The contributions from the second-order perturbation theory concerning electrostatically correlated spin-orbit interactions (CSO), as well as electrostatically correlated hyperfine interactions (CHFS) to the atomic structure of nlN, nlNn1l1^{N_1} and nlNn1l1^{N_1}n2l2^{N_2} configurations, are considered. This theory assumes that the electron excitation n0l0→ nl affects spin-orbit splitting and magnetic dipole and electric quadrupole hyperfine structure in the same way which will be discussed below. Part I of the series presented, in general terms, a method allowing the analysis of complex electronic systems. Parts II, III and IV provided a description of an electrostatic interaction up to second-order perturbation theory; they constitute the basis for the design of an efficient computer program package for large-scale calculations of accurate wave functions. Analyses presented in the entire series of our papers clearly demonstrate that obtaining the precise wave functions is impossible without considering the contribution from the second-order effects into fine and hyperfine atomic structure.
Chen, Wei; Wang, Z. D.; Shen, R.; D. Y. Xing
2013-01-01
We propose an entanglement detector composed of two quantum spin Hall insulators and a side gate deposited on one of the edge channels. For an ac gate voltage, the differential noise contributed from the entangled electron pairs exhibits the nontrivial step structures, from which the spin entanglement concurrence can be easily obtained. The possible spin dephasing effects in the quantum spin Hall insulators are also included.
Investigation of spin correlations in top-pair production with the CMS detector at the LHC
Energy Technology Data Exchange (ETDEWEB)
Davids, Martina
2011-02-25
In spring 2010 the Large Hadron Collider (LHC) started its operation with a center-of-mass energy of 7 TeV, that will be increased up to 14 TeV in the following years. Considering a medium energy of {radical}(s)=10 TeV and a luminosity of L=10{sup 33} cm{sup -2}s{sup -1} some million top quarks are produced per year. This offers the opportunity to investigate spin-correlations between the top quarks from pair production. As the spinconfiguration of the top-quark pair depends on the production mechanism, a measurement of such effects is a unique tool to study the contributions of the production processes and spin effects. This allows to test the Standard Model. This thesis investigates dileptonic top-pair decays at the Compact Muon Solenoid based on simulated events. A quantitative measure of spin correlations is the asymmetry A, that manifests itself in the angular distribution of the two leptons. A full kinematic reconstruction of the top pair is necessary to determine this distribution. The MC generators Pythia, MC rate at NLO, and TopReX are tested with respect to their treatment of spin-correlations. Pythia is used to generate uncorrelated samples. MC rate at NLO reproduces the Standard Model prediction. These samples are used to determine the sensitivity of the present analysis. Due to an incorrect implementation of the helicity states, TopReX is not usable. A full event selection and reconstruction are adapted. The reconstructed angular distribution shows a significant distortion. A template method is implemented to determine the asymmetry. Here, the angular distribution is decomposed into a flat, a completely asymmetric, and a background part, that are fitted by a binned {chi}{sup 2} approach to toy-data. An ensemble study is performed to estimate the statistical uncertainty. As the main systematic uncertainties, generator effects, the jet energy scale and uncertainties in the cross sections or selection efficiency are investigated. Considering an integrated
Space-Time Parity Violation and Magnetoelectric Interactions in Antiferromagnets
Kadomtseva, A.M.; Zvezdin, A. K.; Popov, Yu. F.; Pyatakov, A. P.; Vorob'ev, G. P.
2004-01-01
The properties of antiferromagnetic materials with violated space-time parity are considered. Particular attention is given to the bismuth ferrite BiFeO3 ferroelectric magnet. This material is distinguished from other antiferromagnets in that the inversion center is absent in its crystal and magnetic structures. This circumstance gives rise to the diversified and unusual properties, namely, to the appearance of a spatially modulated spin structure and to the unique possibility of the linear m...
Quantum fluctuations of the antiferro-antiferromagnetic double-layer
Institute of Scientific and Technical Information of China (English)
Jiang Wei; Zhu Cheng-Bo; Yu Gui-Hong; Lo Veng-Cheong
2009-01-01
This paper stuides the magnetization and quantum fluctuations of an antiferro-antiferromagnetic (AF-AF) doublelayer at zero temperature.It is found that the exchanges and anisotropy constants affect the quantum fluctuations of spins. If the anisotropy exists,there will be no acoustic energy branch in the system. The anisotropy constant,antiferromagnetic intralayer and interlayer coupling have important roles in a balance of the quantum competition.
Ordered Phase in the Fermionized Heisenberg Antiferromagnet
Azakov, S.; Dilaver, M.; Oztas, A. M.
1999-01-01
Thermal properties of the ordered phase of the spin 1/2 isotropic Heisenberg Antiferromagnet on a d-dimensional hypercubical lattice are studied within the fermionic representation when the constraint of single occupancy condition is taken into account by the method suggested by Popov and Fedotov. Using saddle point approximation in path integral approach we discuss not only the leading order but also the fluctuations around the saddle point at one-loop level. The influence of taking into acc...
Phase separation of holes in antiferromagnets
International Nuclear Information System (INIS)
It is shown that dilute holes in an antiferromagnet are unstable against phase separation into a hole-rich phase and a no-hole phase. When the spin exchange interaction J exceeds a critical value Jc, one phase consists of all holes, the other all electrons. The argument is presented in detail for the t--J model but evidence of phase separation in other models is mentioned. 11 refs
Spin dynamics of the high-Tc system YBa2Cu3O6+x
International Nuclear Information System (INIS)
The contribution explains experiments with inelastic neutron scattering at monocrystals of the system YBa2Cu3O6+x. The spin dynamics is examined systematically in characteristic areas, as there are: the pure and doped antiferromagnetic states, (x=0.15; 0.37), the less doped states, (x=0.45; 0.51), the strongly doped (x=0.69; 0.92), and the overdoped, metallic states (x=1), which all exhibit a superconducting ground state. Doping with holes has a strong effect on the antiferromagnetic ordering; in the metallic state, however, there still are dynamic antiferromagnetic correlations. The spin excitation spectrum reveals a band gap in all superconducting samples, but the band gap gets weaker when approaching the insulator-metal transition. In addition, a quite unusual dependence of the spin excitation spectrum on the temperature is found. (orig.)
Pan, B. Y.; Wang, Y.; Zhang, L J; Li, S. Y.
2013-01-01
Single crystals of a metal organic complex \\ce{(C5H12N)CuBr3} (\\ce{C5H12N} = piperidinium, pipH for short) have been synthesized and the structure was determined by single-crystal X-ray diffraction. \\ce{(pipH)CuBr3} crystallizes in the monoclinic group $C$2/$c$. Edging-sharing \\ce{CuBr5} units link to form zigzag chains along the $c$ axis and the neighboring Cu(II) ions with spin-1/2 are bridged by bi-bromide ions. Magnetic susceptibility data down to 1.8 K can be well fitted by the Bonner-Fi...
Spin-reorientation and weak ferromagnetism in antiferromagnetic TbMn{sub 0.5}Fe{sub 0.5}O{sub 3}
Energy Technology Data Exchange (ETDEWEB)
Nhalil, Hariharan, E-mail: hariharan@physics.iisc.ernet.in, E-mail: hariharan.nhalil@gmail.com; Sanathkumar, R.; Elizabeth, Suja [Department of Physics, Indian Institute of Science, Bangalore 560012 (India); Nair, Harikrishnan S. [Highly Correlated Matter Research Group, Physics Department, University of Johannesburg, P.O. Box 524, Auckland Park 2006 (South Africa); Strydom, André M. [Highly Correlated Matter Research Group, Physics Department, University of Johannesburg, P.O. Box 524, Auckland Park 2006 (South Africa); Max Planck Institute for Chemical Physics of Solids (MPICPfS), Nöthnitzerstraße 40, 01187 Dresden (Germany)
2015-05-07
Orthorhombic single crystals of TbMn{sub 0.5}Fe{sub 0.5}O{sub 3} are found to exhibit spin-reorientation, magnetization reversal, and weak ferromagnetism. Strong anisotropy effects are evident in the temperature dependent magnetization measurements along the three crystallographic axes a, b, and c. A broad magnetic transition is visible at T{sub N}{sup Fe/Mn}=286 K due to paramagnetic to A{sub x}G{sub y}C{sub z} ordering. A sharp transition is observed at T{sub SR}{sup Fe/Mn}=28 K, which is pronounced along c axis in the form of a sharp jump in magnetization where the spins reorient to G{sub x}A{sub y}F{sub z} configuration. The negative magnetization observed below T{sub SR}{sup Fe/Mn} along c axis is explained in terms of domain wall pinning. A component of weak ferromagnetism is observed in field-scans along c-axis but below 28 K. Field-induced steps-like transitions are observed in hysteresis measurement along b axis below 28 K. It is noted that no sign of Tb-order is discernible down to 2 K. TbMn{sub 0.5}Fe{sub 0.5}O{sub 3} could be highlighted as a potential candidate to evaluate its magneto-dielectric effects across the magnetic transitions.
International Nuclear Information System (INIS)
We are developing the technique of spin-polarized photoelectron spectroscopy as a probe of electron correlation with the ultimate goal of resolving the Pu electronic structure controversy. Over the last several years, we have demonstrated the utility of spin polarized photoelectron spectroscopy for determining the fine details of the electronic structure in complex systems such as those shown in the paper.
What can the nuclear high-spin properties tell us about the decrease of the pair-correlation energy
International Nuclear Information System (INIS)
Pair-correlation energies at high spins are studied in cranking-HFB calculations under several model assumptions. The results are compared with experimental high-spin data: a) yrastlines of even-even nuclei b) systematics of rotational bands of odd-N nuclei and c) routhians of odd-N nuclei relative to corresponding routhians of neighbouring even-N isotopes. (author)
Lv, Yi-Fei; Xiang, Jian-Yong; Wen, Fu-Sheng; Lv, Wei-Ming; Hu, Wen-Tao; Liu, Zhong-Yuan
2015-03-01
Single phase of Fe3+-doped α-Ga2-xFexO3 (α-GFxO, x = 0.1, 0.2, 0.3, 0.4) is synthesized by treating the β-Ga2-xFexO3 (β-GFxO) precursors at high temperatures and high pressures. Rietveld refinements of the X-ray diffraction data show that the lattice constants increase monotonically with the increase of Fe3+ content. Calorimetric measurements show that the temperature of the phase transition from α-GFxO to β-GFxO increases, while the associated enthalpy change decreases upon increasing Fe3+ content. The optical energy gap deduced from the reflectance measurement is found to decrease monotonically with the increase in Fe3+ content. From the measurements of magnetic field-dependent magnetization and temperature-dependent inverse molar susceptibility, we find that the superexchange interaction between Fe3+ ions is antiferromagnetic. Remnant magnetization is observed in the Fe3+-doped α-GFxO and is attributed to the spin glass in the magnetic sublattice. At high Fe3+ doping level (x = 0.4), two evident peaks are observed in the image part of the AC susceptibility . The frequency dependence in intensity of these two peaks as well as two spin freezing temperatures observed in the DC magnetization measurements of α-GF0.4O is suggested to be the behavior of two spin glasses. Project supported by the National Basic Research Program of China (Grant No. 2010CB731605), the National Science Fund for Distinguished Young Scholars of China (Grant No. 51025103), the National Natural Science Foundation of China (Grant Nos. 51172198 and 51102206), the Natural Science Foundation of Hebei Province, China (Grant No. E2014203144), the Science Foundation for the Excellent Youth Scholars from Universities and Colleges of Hebei Province, China (Grant No. YQ2014009), and the Research Program of the College Science & Technology of Hebei Province, China (Grant No. QN2014047).
A nonmagnetic impurity in a 2D quantum critical antiferromagnet
Troyer, Matthias
2003-03-01
We compute the properties of a mobile hole and a static impurity injected into a two-dimensional antiferromagnet or superconductor in the vicinity of a magnetic quantum critical point. A static S=1/2 impurity doped into a quantum-disordered spin gap system induces a local moment with spin S=1/2 and a corresponding Curie-like impurity susceptibility, while the same impurity in a Néel ordered state only gives a finite impurity susceptibility. For the quantum critical system however an interesting field-theoretical prediction has been made that there the impurity spin susceptibility still has a Curie-like divergence, but with a universal effective spin that is neither an integer nor a half-odd integer [1]. In large-scale quantum Monte Carlo (QMC) simulations using the loop algorithm we calculate the impurity susceptibility and find that, unfortunately, this effect is not observable since the renormalization of the effective spin away from S=1/2 is minimal. Other predictions of the field theory, such as a new critical exponent η' describing the time-dependent impurity spin correlations can however be confirmed [2]. Next we compute the spectral function of a hole injected into a 2D antiferromagnet or superconductor in the vicinity of a magnetic quantum critical point [3]. We show that, near van Hove singularities, the problem maps onto that of a static vacancy. This allows the calculation of the spectral function in a QMC simulation without encountering the negative sign problem. We find a vanishing quasiparticle residue at the critical point, a new exponent η_h0.080.04 describing the frequency dependence of the spectral function G_h(ω)(ɛ_0-ω)-1+ηh and discuss possible relevance to photoemission spectra of cuprate superconductors near the antinodal points. ^1 S. Sachdev, C. Buragohain and M. Vojta, Science 286, 2479 (1999). ^2 M. Troyer, in Prog. Theor. Phys. Suppl. 145 (2002); M. Körner and M. Troyer, ibid. ^3 S. Sachdev, M. Troyer, and M. Vojta, Phys. Rev
Classical and quantum anisotropic Heisenberg antiferromagnets
Directory of Open Access Journals (Sweden)
W. Selke
2009-01-01
Full Text Available We study classical and quantum Heisenberg antiferromagnets with exchange anisotropy of XXZ-type and crystal field single-ion terms of quadratic and quartic form in a field. The magnets display a variety of phases, including the spin-flop (or, in the quantum case, spin-liquid and biconical (corresponding, in the quantum lattice gas description, to supersolid phases. Applying ground-state considerations, Monte Carlo and density matrix renormalization group methods, the impact of quantum effects and lattice dimension is analysed. Interesting critical and multicritical behaviour may occur at quantum and thermal phase transitions.
Ivanov, Dmitri A; Abanov, Alexander G
2013-02-01
We propose to describe correlations in classical and quantum systems in terms of full counting statistics of a suitably chosen discrete observable. The method is illustrated with two exactly solvable examples: the classical one-dimensional Ising model and the quantum spin-1/2 XY chain. For the one-dimensional Ising model, our method results in a phase diagram with two phases distinguishable by the long-distance behavior of the Jordan-Wigner strings. For the anisotropic spin-1/2 XY chain in a transverse magnetic field, we compute the full counting statistics of the magnetization and use it to classify quantum phases of the chain. The method, in this case, reproduces the previously known phase diagram. We also discuss the relation between our approach and the Lee-Yang theory of zeros of the partition function. PMID:23496467
Measurement of the neutrino-spin correlation parameter B neutron decay using ultracold neutrons
Energy Technology Data Exchange (ETDEWEB)
Wilburn, Wesley S [Los Alamos National Laboratory
2009-01-01
We present a new approach to measuring the neutrino-spin correlation parameter B in neutron decay. The approach combines the technology of large-area ion-implanted silicon detectors being developed for the abBA experiment, with an ultracold neutron source to provide more precise neutron polarimetry. The technique detects both proton and electron from the neutron decay in coincidence. B is determined from an electron-energy-dependent measurement of the proton spin asymmetry. This approach will provide a statistical precision of 1 x 10-4 . The systematic precision is still being evaluated, but is expected to be below 1 x 10-3 , and could approach 1 x 10-4 . A measurement of B with this precision would place constraints on supersymmetric extensions to the Standard Model.
Uniqueness, Spatial Mixing, and Approximation for Ferromagnetic 2-Spin Systems
Guo, Heng; Lu, Pinyan
2015-01-01
For anti-ferromagnetic 2-spin systems, a beautiful connection has been established, namely that the following three notions align perfectly: the uniqueness in infinite regular trees, the decay of correlations (also known as spatial mixing), and the approximability of the partition function. The uniqueness condition implies spatial mixing, and an FPTAS for the partition function exists based on spatial mixing. On the other hand, non-uniqueness implies some long range correlation, based on whic...
The role of three-gluon correlation functions in the single spin asymmetry
Directory of Open Access Journals (Sweden)
Beppu Hiroo
2015-01-01
Full Text Available We study the twist-3 three-gluon contribution to the single spin asymmetry in the light-hadron production in pp collision in the framework of the collinear factorization. We derive the corresponding cross section formula in the leading order with respect to the QCD coupling constant. We also present a numerical calculation of the asymmetry at the RHIC energy, using a model for the three-gluon correlation functions suggested by the asymmetry for the D-meson production at RHIC. We found that the asymmetries for the light-hadron and the jet productions are very useful to constrain the magnitude and form of the correlation functions. Since the three-gluon correlation functions shift the asymmetry for all kinds of hadrons in the same direction, it is unlikely that they become a main source of the asymmetry.
Vertex functions at finite momentum: Application to antiferromagnetic quantum criticality
Wölfle, Peter; Abrahams, Elihu
2016-02-01
We analyze the three-point vertex function that describes the coupling of fermionic particle-hole pairs in a metal to spin or charge fluctuations at nonzero momentum. We consider Ward identities, which connect two-particle vertex functions to the self-energy, in the framework of a Hubbard model. These are derived using conservation laws following from local symmetries. The generators considered are the spin density and particle density. It is shown that at certain antiferromagnetic critical points, where the quasiparticle effective mass is diverging, the vertex function describing the coupling of particle-hole pairs to the spin density Fourier component at the antiferromagnetic wave vector is also divergent. Then we give an explicit calculation of the irreducible vertex function for the case of three-dimensional antiferromagnetic fluctuations, and show that it is proportional to the diverging quasiparticle effective mass.
DMRG Study of the S >= 1 quantum Heisenberg Antiferromagnet on a Kagome-like lattice without loops
Lamberty, R. Zach; Changlani, Hitesh J.; Henley, Christopher L.
2013-03-01
The Kagome quantum Heisenberg antiferromagnet, for spin up to S = 1 and perhaps S = 3 / 2 , is a prime candidate to realize a quantum spin liquid or valence bond crystal state, but theoretical or computational studies for S > 1 / 2 are difficult and few. We consider instead the same interactions and S >= 1 on the Husimi Cactus, a graph of corner sharing triangles whose centers are vertices of a Bethe lattice, using a DMRG procedure tailored for tree graphs. Since both lattices are locally identical, properties of the Kagome antiferromagnet dominated by nearest-neighbor spin correlations should also be exhibited on the Cactus, whereas loop-dependent effects will be absent on the loopless Cactus. Our study focuses on the possible transition(s) that must occur with increasing S for the Cactus antiferromagnet. (It has a disordered valence bond state at S = 1 / 2 but a 3-sublattice coplanar ordered state in the large S limit). We also investigate the phase diagram of the S = 1 quantum XXZ model with on-site anisotropy, which we expect to have three-sublattice and valence-bond-crystal phases similar to the kagome case. This work is supported by the National Science Foundation through a Graduate Research Fellowship to R. Zach Lamberty, as well as grant DMR-
Bihrle, W., Jr.
1976-01-01
A correlation study was conducted to determine the ability of current analytical spin prediction techniques to predict the flight motions of a current fighter airplane configuration during the spin entry, the developed spin, and the spin recovery motions. The airplane math model used aerodynamics measured on an exact replica of the flight test model using conventional static and forced-oscillation wind-tunnel test techniques and a recently developed rotation-balance test apparatus capable of measuring aerodynamics under steady spinning conditions. An attempt was made to predict the flight motions measured during stall/spin flight testing of an unpowered, radio-controlled model designed to be a 1/10 scale, dynamically-scaled model of a current fighter configuration. Comparison of the predicted and measured flight motions show that while the post-stall and spin entry motions were not well-predicted, the developed spinning motion (a steady flat spin) and the initial phases of the spin recovery motion are reasonably well predicted.
Neutron-proton spin-correlation parameter Azz at 68 MeV
International Nuclear Information System (INIS)
We report a first measurement of the spin-correlation parameter Azz in neutron-proton scattering at 67.5 MeV. The results, obtained in the angular range 105 degree ≤θc.m.≤170 degree with typical accuracies of 0.008, are highly sensitive to the 3S1-3D1 mixing parameter ε1. A phase-shift analysis based on the current world data yields a value of ε1 significantly higher than predicted by modern potential models
Edén, Mattias
2010-05-01
Three two-dimensional (2D) NMR homonuclear correlation techniques invoking double-quantum (2Q) filtration of the central transitions of half-integer spins are evaluated numerically and experimentally. They correlate directly detected single-quantum (1Q) coherences in the t(2) domain with either of 1Q, two-spin 2Q or single-spin multiple-quantum coherence-evolutions in the indirect (t(1)) dimension. We employ experimental (23)Na and (27)Al NMR on sodium sulfite and the natural mineral sillimanite (SiAl(2)O(5)), in conjunction with simulated 2D spectra from pairs of dipolar-recoupled spins-3/2 and 5/2 at different external magnetic fields, to compare the correlation strategies from the viewpoints of 2D spectral resolution, signal sensitivity, implementational aspects and their relative merits for establishing internuclear proximities and quadrupolar tensor orientations. PMID:20202872
Control of antiferromagnetic domain distribution via polarization-dependent optical annealing.
Higuchi, Takuya; Kuwata-Gonokami, Makoto
2016-01-01
The absence of net magnetization inside antiferromagnetic domains has made the control of their spatial distribution quite challenging. Here we experimentally demonstrate an optical method for controlling antiferromagnetic domain distributions in MnF2. Reduced crystalline symmetry can couple an order parameter with non-conjugate external stimuli. In the case of MnF2, time-reversal symmetry is macroscopically broken reflecting the different orientations of the two magnetic sublattices. Thus, it exhibits different absorption coefficients between two orthogonal linear polarizations below its antiferromagnetic transition temperature under an external magnetic field. Illumination with linearly polarized laser light under this condition selectively destructs the formation of a particular antiferromagnetic order via heating. As a result, the other antiferromagnetic order is favoured inside the laser spot, achieving spatially localized selection of an antiferromagnetic order. Applications to control of interface states at antiferromagnetic domain boundaries, exchange bias and control of spin currents are expected. PMID:26911337
Interplay of spin-orbit coupling and superconducting correlations in germanium telluride thin films
Energy Technology Data Exchange (ETDEWEB)
Narayan, Vijay; Nguyen, Thuy-Anh; Mansell, Rhodri; Ritchie, David [Cavendish Laboratory, Department of Physics, University of Cambridge, J. J. Thomson Avenue, Cambridge, CB3 0HE (United Kingdom); Mussler, Gregor [Peter Gruenberg Institute (PGI-9), Forschungszentrum Juelich, 52425, Juelich (Germany)
2016-03-15
There is much current interest in combining superconductivity and spin-orbit coupling in order to induce the topological superconductor phase and associated Majorana-like quasiparticles which hold great promise towards fault-tolerant quantum computing. Experimentally these effects have been combined by the proximity-coupling of super-conducting leads and high spin-orbit materials such as InSb and InAs, or by controlled Cu-doping of topological insu-lators such as Bi{sub 2}Se{sub 3}. However, for practical purposes, a single-phase material which intrinsically displays both these effects is highly desirable. Here we demonstrate coexisting superconducting correlations and spin-orbit coupling in molecular-beam-epitaxy-grown thin films of GeTe. The former is evidenced by a precipitous low-temperature drop in the electrical resistivity which is quelled by a magnetic field, and the latter manifests as a weak antilocalisation (WAL) cusp in the magnetotransport. Our studies reveal several other intriguing features such as the presence of two-dimensional rather than bulk transport channels below 2 K, possible signatures of topological superconductivity, and unexpected hysteresis in the magnetotransport. Our work demonstrates GeTe to be a potential host of topological SC and Majorana-like excitations, and to be a versatile platform to develop quantum information device architectures. (copyright 2016 The Authors. Phys. Status Solidi RRL published by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Bond-Dilution-Induced Quantum Phase Transitions in Heisenberg Antiferromagnets
Yasuda, Chitoshi; Todo, Synge; Takayama, Hajime
2006-01-01
Bond-dilution effects on the ground state of the square-lattice antiferromagnetic Heisenberg model, consisting of coupled bond-alternating chains, are investigated by means of the quantum Monte Carlo simulation. It is found that, when the ground state of the non-diluted system is a non-magnetic state with a finite spin gap, a sufficiently weak bond dilution induces a disordered state with a mid gap in the original spin gap, and under a further stronger bond dilution an antiferromagnetic long-...
Spin-density functional for exchange anisotropic Heisenberg model
Energy Technology Data Exchange (ETDEWEB)
Prata, G.N.; Penteado, P.H.; Souza, F.C. [Departamento de Fisica e Informatica, Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, CP 369, Sao Carlos - SP (Brazil); Libero, Valter L., E-mail: valter@if.sc.usp.b [Departamento de Fisica e Informatica, Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, CP 369, Sao Carlos - SP (Brazil)
2009-10-15
Ground-state energies for antiferromagnetic Heisenberg models with exchange anisotropy are estimated by means of a local-spin approximation made in the context of the density functional theory. Correlation energy is obtained using the non-linear spin-wave theory for homogeneous systems from which the spin functional is built. Although applicable to chains of any size, the results are shown for small number of sites, to exhibit finite-size effects and allow comparison with exact-numerical data from direct diagonalization of small chains.
Spin-density functional for exchange anisotropic Heisenberg model
International Nuclear Information System (INIS)
Ground-state energies for antiferromagnetic Heisenberg models with exchange anisotropy are estimated by means of a local-spin approximation made in the context of the density functional theory. Correlation energy is obtained using the non-linear spin-wave theory for homogeneous systems from which the spin functional is built. Although applicable to chains of any size, the results are shown for small number of sites, to exhibit finite-size effects and allow comparison with exact-numerical data from direct diagonalization of small chains.
Energy Technology Data Exchange (ETDEWEB)
Eliav, U., E-mail: amirgo@tau.ac.il, E-mail: eliav@tau.ac.il; Haimovich, A.; Goldbourt, A., E-mail: amirgo@tau.ac.il, E-mail: eliav@tau.ac.il [School of Chemistry, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv, 69978 Tel Aviv (Israel)
2016-01-14
We discuss and analyze four magic-angle spinning solid-state NMR methods that can be used to measure internuclear distances and to obtain correlation spectra between a spin I = 1/2 and a half-integer spin S > 1/2 having a small quadrupolar coupling constant. Three of the methods are based on the heteronuclear multiple-quantum and single-quantum correlation experiments, that is, high rank tensors that involve the half spin and the quadrupolar spin are generated. Here, both zero and single-quantum coherence of the half spins are allowed and various coherence orders of the quadrupolar spin are generated, and filtered, via active recoupling of the dipolar interaction. As a result of generating coherence orders larger than one, the spectral resolution for the quadrupolar nucleus increases linearly with the coherence order. Since the formation of high rank tensors is independent of the existence of a finite quadrupolar interaction, these experiments are also suitable to materials in which there is high symmetry around the quadrupolar spin. A fourth experiment is based on the initial quadrupolar-driven excitation of symmetric high order coherences (up to p = 2S, where S is the spin number) and subsequently generating by the heteronuclear dipolar interaction higher rank (l + 1 or higher) tensors that involve also the half spins. Due to the nature of this technique, it also provides information on the relative orientations of the quadrupolar and dipolar interaction tensors. For the ideal case in which the pulses are sufficiently strong with respect to other interactions, we derive analytical expressions for all experiments as well as for the transferred echo double resonance experiment involving a quadrupolar spin. We show by comparison of the fitting of simulations and the analytical expressions to experimental data that the analytical expressions are sufficiently accurate to provide experimental {sup 7}Li–{sup 13}C distances in a complex of lithium, glycine, and water
Spin correlations in $\\vec{p}\\vec{p}\\to pn\\pi^{+}$ pion production near threshold
Daehnick, W W; Flammang, R W; Meyer, H O; Balewski, J T; Pollock, R E; Von Przewoski, B; Rinckel, T; Thörngren-Engblom, P; Wellinghausen, A; Lorentz, B; Rathmann, F; Schwartz, B; Wise, T; Pancella, P V; Saha, Swapan K.; Wise, and T.
2002-01-01
A first measurement of longitudinal as well as transverse spin correlation coefficients for the reaction $\\vec{p}\\vec{p}\\to pn\\pi^+$ was made using a polarized proton target and a polarized proton beam. We report kinematically complete measurements for this reaction at 325, 350, 375 and 400 MeV beam energy. The spin correlation coefficients $A_{xx}+A_{yy}, A_{xx}-A_{yy}, A_{zz}, A_{xz},$ and the analyzing power $A_{y},$ as well as angular distributions for $\\sigma(\\theta_{\\pi})$ and the polarization observables $A_{ij}(\\theta_{\\pi})$ were extracted. Partial wave cross sections for dominant transition channels were obtained from a partial wave analysis that included the transitions with final state angular momenta of $l\\leq 1$. The measurements of the ${\\vec{p}\\vec{p}\\to pn\\pi^{+}}$ polarization observables are compared with the predictions from the J\\"ulich meson exchange model. The agreement is very good at 325 MeV, but it deteriorates increasingly for the higher energies. At all energies agreement with the ...
Nanoparticles of antiferromagnetic materials
DEFF Research Database (Denmark)
Madsen, Daniel Esmarch
2008-01-01
I denne Ph.D. afhandling studeres forskellige egenskaber ved antiferromagnetiske nanopartikler. I en ideel antiferromagnet er spinnene orienteret således at der ikke er et resulterende magnetisk moment. I nanopartikler af antiferromagnetiske materialer er denne kompensation på grund af forskellig...
Alemany, Lawrence B.; Malloy, Thomas B.; Nunes, Megan M.; Zaibaq, Nicholas G.
2012-09-01
In a continuation of our initial investigation of the complex 13C and 19F spectra exhibited by two simple organofluorine compounds, additional organofluorine compounds expected to exhibit a wide range of spectral complexity were studied. Spectral simulations are critical for analyzing the more complex spin systems, in particular, A3B3X and A6B3X. Cross-correlated relaxation is commonly observed; examples of 13Csbnd 19F cross-correlated relaxation are shown with the signals for each nucleus exhibiting unequal relaxation rates. Higher order effects are particularly noticeable in the spectra of perfluoro-t-butyl alcohol because of a large 4JFF value in the (13CF3)(12CF3)212COH isotopomer. The many additional transitions in an A3B3X spin system compared to an ABX spin system result in much more complex 19F (A3 and B3) and 13C (X) spectra, even though only three types of nuclei are involved in each spin system. The corresponding protio compounds typically constitute a much simpler A3M3X spin system because the long-range nJHH coupling (n ⩾ 4) is much smaller than the corresponding long-range nJFF coupling. Spectra previously published for ethane-1-13C (A3B3X) and hexafluoroethane-1-13C (A3M3X) are notable exceptions and are discussed.
Sil, Debangsu; Bhowmik, Susovan; Khan, Firoz Shah Tuglak; Rath, Sankar Prasad
2016-04-01
The synthesis, structure, and properties of a new family of five ethane-bridged dimanganese(III) μ-hydroxo bisporphyrins with the same core structure but different counteranions are reported here. Additions of 10% Brønsted acids such as HI, HBF4, HSbF6, HPF6, and HClO4 to a dichloromethane solution of the dichloro dimanganese(III) bisporphyrin produces complexes having a remarkably bent μ-hydroxo group with I3(-), BF4(-), SbF6(-), PF6(-), and ClO4(-) as counteranions, respectively. The X-ray structures of all complexes have been determined, which have revealed the presence of two equivalent high-spin manganese(III) centers with equally distorted porphyrin rings in the complexes, in sharp contrast with the case for the diiron(III) μ-hydroxo bisporphyrin analogues. (1)H NMR spectra have shown highly deshielded meso resonances, unlike the case for the diiron(III) analogues, where the meso resonances are highly shielded. The variable-temperature magnetic data have been subjected to a least-squares fit which provides a moderate antiferromagnetic coupling through the hydroxo bridge between two zero-field split Mn(III) centers with coupling constant (J) values ranging from -29.5 to -38.6 cm(-1). Fairly good correlations are observed for J with Mn-O(H) distances and Mn-O(H)-Mn angles for all the complexes except for that having an I3(-) counteranion. DFT calculations support the stabilization of two equivalent high-spin Mn(III) porphyrin cores in the complexes and have also explored the role of metal spin in controlling porphyrin ring deformation. Unlike diiron(III) μ-hydroxo bisporphyrin complexes, the dimanganese(III) analogues do not have easily accessible spin states of the metal attainable by subtle environmental perturbations and, therefore, can only stabilize the high-spin state with a variety of counteranions. PMID:27002790
International Nuclear Information System (INIS)
We investigate the long distance asymptotics of various correlation functions for the one-dimensional spin-1/2 Fermi gas with attractive interactions using the dressed charge formalism. In the spin polarized phase, these correlation functions exhibit spatial oscillations with a power-law decay whereby their critical exponents are found through conformal field theory. We show that spatial oscillations of the leading terms in the pair correlation function and the spin correlation function solely depend on ΔkF and 2ΔkF, respectively. Here ΔkF=π(n↑-n↓) denotes the mismatch between the Fermi surfaces of spin-up and spin-down fermions. Such spatial modulations are characteristics of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. Our key observation is that backscattering among the Fermi points of bound pairs and unpaired fermions results in a one-dimensional analog of the FFLO state and displays a microscopic origin of the FFLO nature. Furthermore, we show that the pair correlation function in momentum space has a peak at the point of mismatch between both Fermi surfaces k=ΔkF, which has recently been observed in numerous numerical studies.
Fisher–Hartwig expansion for the transverse correlation function in the XX spin-1/2 chain
International Nuclear Information System (INIS)
Motivated by the recent results on the asymptotic behavior of Toeplitz determinants with Fisher–Hartwig singularities, we develop an asymptotic expansion for transverse spin correlations in the XX spin-1/2 chain. The coefficients of the expansion can be calculated to any given order using the relation to discrete Painlevé equations. We present explicit results up to the 11th order and compare them with a numerical example. (paper)
Evidence for correlation between spin and charge dynamics in La2Cu1-xLixO4
Park, Eunsung; Park, Tuson; Sarrao, J. L.; Thompson, J. D.
2009-04-01
From ac magnetic susceptibility measurements on Li-doped La2CuO4, with Hac parallel and perpendicular to the CuO plane, we find frequency-dependent behavior below a spin-glass temperature (TSG). TSG obtained from magnetic susceptibility is higher than the charge-glass temperature TCG obtained from dielectric constant measurements, indicating that spin freezes first and drives charge freezing at a lower temperature. Similar frequency dependence of the two characteristic freezing temperatures underlines that charge and spin dynamics are strongly correlated in this cuprate compound.
Wuyts, Floris; Clement, Gilles; Naumov, Ivan; Kornilova, Ludmila; Glukhikh, Dmitriy; Hallgren, Emma; MacDougall, Hamish; Migeotte, Pierre-Francois; Delière, Quentin; Weerts, Aurelie; Moore, Steven; Diedrich, Andre
In 13 cosmonauts, the vestibulo-autonomic reflex was investigated before and after 6 months duration spaceflight. Cosmonauts were rotated on the mini-centrifuge VVIS, which is installed in Star City. Initially, this mini-centrifuge flew on board of the Neurolab mission (STS-90), and served to generate intermittent artificial gravity during that mission, with apparent very positive effects on the preservation of the orthostatic tolerance upon return to earth in the 4 crew members that were subjected to the rotations in space. The current experiments SPIN and GAZE-SPIN are control experiments to test the hypothesis that intermittent artificial gravity in space can serve as a counter measure against several deleterious effects of microgravity. Additionally, the effect of microgravity on the gaze holding system is studied as well. Cosmonauts from a long duration stay in the International Space Station were tested on the VVIS (1 g centripetal interaural acceleration; consecutive right-ear-out anti-clockwise and left-ear-out clockwise measurement) on 5 different days. Two measurements were scheduled about one month and a half prior to launch and the remaining three immediately after their return from space (typically on R+2, R+4, R+9; R = return day from space). The ocular counter roll (OCR) as a measure of otolith function was measured on before, during and after the rotation in the mini centrifuge, using infrared video goggles. The perception of verticality was monitored using an ultrasound system. Gaze holding was tested before, during and after rotation. After the centrifugation part, the crew was installed on a tilt table, and instrumented with several cardiovascular recording equipment (ECG, continuous blood pressure monitoring, respiratory monitoring), as well as with impedance measurement devices to investigate fluid redistribution throughout the operational tilt test. To measure heart rate variability parameters, imposed breathing periods were included in the
International Nuclear Information System (INIS)
In order to improve existing I=0 phase shift solutions, the spin correlation parameter, ANN, and the analyzing powers, A0N and AN0, have been measured in n-p elastic scattering over an angular range of 50 degrees -150 degrees (c.m.) at three neutron energies, 220, 325 and 425 MeV to an absolute accuracy of ±0.03. The data have a profound effect on various phase parameters, particularly the 1P1, 3D2 and ε1 phase parameters which in some cases change by almost a degree. With exception of the highest energy, the data support the predictions of the latest version of the Bonn potential. Also the analyzing power data (A0N and AN0) measured at 477 MeV in a different experiment over a limited angular range (60 degrees - 80 degrees (c.m.)) are reported here. (Author) 30 refs., 10 figs., 5 tabs
Spin and orbital angular momentum correlations in parametric downconversion of Bessel beams
International Nuclear Information System (INIS)
We present a full vectorial analysis of the parametric downconversion process using a pump Bessel beam and a photon description based on Bessel wavefunctions. We find that, under the considered geometry, optical angular momentum is conserved but the crystal induces a coupling between the optical spin angular momentum (SAM) and the optical orbital angular momentum (OAM) ruled by the nonlinear properties of the crystal via the second order susceptibility tensor χijk(2). This leads to nontrivial correlations between the expected values of the SAM and OAM of the resulting two-photon states. Distributions of orbital angular momentum of the downconverted photons are evaluated in detail for a specific set-up
Spin-state selection for increased confidence in cross-correlation rates measurements
Energy Technology Data Exchange (ETDEWEB)
Vasos, Paul R.; Hall, Jennifer B.; Fushman, David [University of Maryland, Department of Chemistry and Biochemistry, Center for Biomolecular Structure and Organization (United States)], E-mail: fushman@umd.edu
2005-02-15
A new approach is described for measuring chemical shift anisotropy (CSA)/dipolar cross-correlated relaxation (CCR) rates based on the selection of the individual {sup 15}N doublet components prior to the relaxation period. The method uses the spin-state-selective element (S{sup 3}E) of Sorensen and co-authors [Meissner et al. (1997) J. Mag. Reson., 128, 92-97]. The main advantage of the new method compared to other J-resolved experiments is that it does not create problems of additional signal overlap encountered in coupled spectra. At the same time, this approach allows a simpler control of magnetization pathways than the indirect methods. The method is demonstrated for the B3 domain of protein G.
Spin-state selection for increased confidence in cross-correlation rates measurements
International Nuclear Information System (INIS)
A new approach is described for measuring chemical shift anisotropy (CSA)/dipolar cross-correlated relaxation (CCR) rates based on the selection of the individual 15N doublet components prior to the relaxation period. The method uses the spin-state-selective element (S3E) of Sorensen and co-authors [Meissner et al. (1997) J. Mag. Reson., 128, 92-97]. The main advantage of the new method compared to other J-resolved experiments is that it does not create problems of additional signal overlap encountered in coupled spectra. At the same time, this approach allows a simpler control of magnetization pathways than the indirect methods. The method is demonstrated for the B3 domain of protein G
Analysing powers and spin correlations in deuteron–proton charge exchange at 726 MeV
Directory of Open Access Journals (Sweden)
S. Dymov
2015-05-01
Full Text Available The charge exchange of vector polarised deuterons on a polarised hydrogen target has been studied in a high statistics experiment at the COSY-ANKE facility at a deuteron beam energy of Td=726 MeV. By selecting two fast protons at low relative energy Epp, the measured analysing powers and spin correlations are sensitive to interference terms between specific neutron–proton charge-exchange amplitudes at a neutron kinetic energy of Tn≈12Td=363 MeV. An impulse approximation calculation, which takes into account corrections due to the angular distribution in the diproton, describes reasonably the dependence of the data on both Epp and the momentum transfer. This lends broad support to the current neutron–proton partial wave solution that was used in the estimation.
Analysing powers and spin correlations in deuteron-proton charge exchange at 726 MeV
Dymov, S; Bagdasarian, Z; Barsov, S; Carbonell, J; Chiladze, D; Engels, R; Gebel, R; Grigoryev, K; Hartmann, M; Kacharava, A; Khoukaz, A; Komarov, V; Kulessa, P; Kulikov, A; Kurbatov, V; Lomidze, N; Lorentz, B; Macharashvili, G; Mchedlishvili, D; Merzliakov, S; Mielke, M; Mikirtychyants, M; Mikirtychyants, S; Nioradze, M; Ohm, H; Prasuhn, D; Rathmann, F; Serdyuk, V; Seyfarth, H; Shmakova, V; Ströher, H; Tabidze, M; Trusov, S; Tsirkov, D; Uzikov, Yu; Valdau, Yu; Weidemann, C; Wilkin, C
2015-01-01
The charge exchange of vector polarised deuterons on a polarised hydrogen target has been studied in a high statistics experiment at the COSY-ANKE facility at a deuteron beam energy of Td = 726 MeV. By selecting two fast protons at low relative energy E_{pp}, the measured analysing powers and spin correlations are sensitive to interference terms between specific neutron-proton charge-exchange amplitudes at a neutron kinetic energy of Tn ~ 1/2 Td =363 MeV. An impulse approximation calculation, which takes into account corrections due to the angular distribution in the diproton, describes reasonably the dependence of the data on both E_{pp} and the momentum transfer. This lends broad support to the current neutron-proton partial-wave solution that was used in the estimation.
Substrate-tuning of correlated spin-orbit oxides revealed by optical conductivity calculations
Kim, Bongjae; Kim, Beom Hyun; Kim, Kyoo; Min, B. I.
2016-06-01
We have systematically investigated substrate-strain effects on the electronic structures of two representative Sr-iridates, a correlated-insulator Sr2IrO4 and a metal SrIrO3. Optical conductivities obtained by the ab initio electronic structure calculations reveal that the tensile strain shifts the optical peak positions to higher energy side with altered intensities, suggesting the enhancement of the electronic correlation and spin-orbit coupling (SOC) strength in Sr-iridates. The response of the electronic structure upon tensile strain is found to be highly correlated with the direction of magnetic moment, the octahedral connectivity, and the SOC strength, which cooperatively determine the robustness of Jeff = 1/2 ground states. Optical responses are analyzed also with microscopic model calculation and compared with corresponding experiments. In the case of SrIrO3, the evolution of the electronic structure near the Fermi level shows high tunability of hole bands, as suggested by previous experiments.
International Nuclear Information System (INIS)
Conventional theories of nuclear interactions predict a net increase in the distribution of virtual pions in nuclei relative to free nucleons. Analysis of data from several nuclear experiments has led to claims of evidence against such a pion excess. These conclusions are usually based on a collective theory [random-phase approximation (RPA)] of the pions, which may be inadequate. The issue is the energy dependence of the nuclear response, which differs for theories with strong NN correlations from the RPA predictions. In the present paper, information about the energy dependence is extracted from sum rules, which are calculated for such a correlated, noncollective nuclear theory. The results lead to much reduced sensitivity of nuclear reactions to the correlations that are responsible for the pion excess. The primary example is (rvec p,rvec n) spin transfer, for which the expected effects are found to be smaller than the experimental uncertainties. The analysis has consequences for deep inelastic scattering experiments as well. copyright 1998 The American Physical Society
Enhancement of nearest neighbor spin-singlet correlations in d-wave SNS graphene Josephson junctions
Black-Schaffer, Annica; Doniach, Sebastian
2009-03-01
Using the self-consistent tight-binding Bogoliubov-de Gennes (BdG) formalism we investigate the effect of nearest neighbor spin-singlet bond (SB) correlations in a graphene SNS Josephson junction with d-wave superconducting contacts. All pπ-bonded planar organic molecules, of which graphene is the infinite extension, show a preference for SB over polar configurations, as originally captured by Pauling's idea of resonating valence bonds. At strong enough coupling and/or high doping levels, these correlations will give rise to a d-wave superconducting state. However, the estimated coupling strength in graphene would require a doping level not currently experimentally achievable by a gating bias. We demonstrate that by creating a graphene SNS Josephson junction with d-wave contacts, for example by depositing a high-Tc cuprate on top of the graphene, it should be possible to enhance the effect of the SB correlations and see clear signatures of d-wave pairing in proximity effect, superconducting decay length, and supercurrent.
Superconductivity and Antiferromagnetism in Quasi-one-dimensional Organic Conductors
Dupuis, N.; Bourbonnais, C.; Nickel, J. C.
2005-01-01
We review the current understanding of superconductivity in the quasi-one-dimensional organic conductors of the Bechgaard and Fabre salt families. We discuss the interplay between superconductivity, antiferromagnetism, and charge-density-wave fluctuations. The connection to recent experimental observations supporting unconventional pairing and the possibility of a triplet-spin order parameter for the superconducting phase is also presented.
Observation of Antiferromagnetic Resonance in an Organic Superconductor
DEFF Research Database (Denmark)
Torrance, J. B.; Pedersen, H. J.; Bechgaard, K.
1982-01-01
Anomalous microwave absorption has been observed in the organic superconductor TMTSF2AsF6 (TMTSF: tetramethyltetraselenafulvalene) below its metal-nonmetal transition near 12 K. This absorption is unambiguously identified as antiferromagnetic resonance by the excellent agreement between a spin...
Coupling the valley degree of freedom to antiferromagnetic order
Li, Xiao; Cao, Ting; Niu, Qian; Shi, Junren; Feng, Ji
2013-01-01
Conventional electronics are based invariably on the intrinsic degrees of freedom of an electron, namely, its charge and spin. The exploration of novel electronic degrees of freedom has important implications in both basic quantum physics and advanced information technology. Valley as a new electronic degree of freedom has received considerable attention in recent years. In this paper, we develop the theory of spin and valley physics of an antiferromagnetic honeycomb lattice. We show that by ...
Prospect for antiferromagnetic spintronics
Czech Academy of Sciences Publication Activity Database
Martí, Xavier; Fina, I.; Jungwirth, Tomáš
2015-01-01
Roč. 51, č. 4 (2015), s. 2900104. ISSN 0018-9464 R&D Projects: GA MŠk(CZ) LM2011026; GA ČR GB14-37427G Grant ostatní: ERC Advanced Grant 0MSPIN(XE) 268066 Institutional support: RVO:68378271 Keywords : spintronics * antiferromagnets Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.386, year: 2014
Nematic antiferromagnetic states in bulk FeSe
Liu, Kai; Lu, Zhong-Yi; Xiang, Tao
2016-05-01
The existence of nematic order, which breaks the lattice rotational symmetry with nonequivalent a and b axes in iron-based superconductors, is a well-established experimental fact. An antiferromagnetic (AFM) transition is accompanying this order, observed in nearly all parent compounds, except bulk FeSe. The absence of the AFM order in FeSe casts doubt on the magnetic mechanism of iron-based superconductivity, since the nematic order is believed to be driven by the same interaction that is responsible for the superconducting pairing in these materials. Here we show, through systematic first-principles electronic structure calculations, that the ground state of FeSe is in fact strongly AFM correlated but without developing a magnetic long-range order. Actually, there are a series of staggered n -mer AFM states with corresponding energies below that of the single stripe AFM state, which is the ground state for the parent compounds of most iron-based superconductors. Here, the staggered n -mer (n any integer >1 ) means a set of n adjacent parallel spins on a line along the b axis with antiparallel spins between n -mers along both a and b axes. Moreover, different n -mers can antiparallelly mix with each other to coexist. Among all the states, we find that the lowest energy states formed by the staggered dimer, staggered trimer, and their random antiparallel aligned spin states along the b axis are quasidegenerate. The thermal average of these states does not show any magnetic long-range order, but it does possess a hidden one-dimensional AFM order along the a axis, which can be detected by elastic neutron scattering measurements. Our finding gives a natural account for the absence of long-range magnetic order and suggests that the nematicity is driven predominantly by spin fluctuations even in bulk FeSe, providing a unified description on the phase diagram of iron-based superconductors.
Howarth, James William
2013-01-01
This thesis presents measurements of the the spin correlation strength in top anti-top quark pair production at the LHC using the ATLAS detector. The data used corresponds to 4.6 fb−1 of integrated luminosity taken during 2011 at the LHC at a center of mass energy of 7 TeV. The spin correlation is studied utilising different observables with different sensitivities to the production mechanism, in particular to gluon-gluon fusion in the like or unlike helicity state, quark anti- quark annihila...
The spin bag mechanism of high temperature superconductivity
Schrieffer, J. R.; Wen, X.-G.; Zhang, S.-C.
1989-01-01
In oxide superconductors the local suppression of antiferromagnetic correlations in the vicinity of a hole lowers the energy of the system. This quasi two-dimensional bag of weakened spin order follows the hole in its motion. In addition, holes prefer to share a bag, leading to a strong pairing attraction and a high Tc superconductivity. There are many experimental consequences of this mechanism for both the superconducting and normal phases.
Characterization of the Dilute Ising Antiferromagnet
Energy Technology Data Exchange (ETDEWEB)
Wiener, T.
2000-09-12
A spin glass is a magnetic ground state in which ferromagnetic and antiferromagnetic exchange interactions compete, thereby creating frustration and a multidegenerate state with no long range order. An Ising system is a system where the spins are constrained to lie parallel or antiparallel to a primary axis. There has been much theoretical interest in the past ten years in the effects of applying a magnetic field transverse to the primary axis in an Ising spin glass at low temperatures and thus study phase transitions at the T=0 limit. The focus of this study is to search for and characterize a new Ising spin glass system. This is accomplished by site diluting yttrium for terbium in the crystalline material TbNi{sub 2}Ge{sub 2}. The first part of this work gives a brief overview of the physics of rare earth magnetism and an overview of experimental characteristics of spin glasses. This is followed by the methodology used to manufacture the large single crystals used in this study, as well as the measurement techniques used. Next, a summary of the results of magnetic measurements on across the dilution series from pure terbium to pure yttrium is presented. This is followed by detailed measurements on particular dilutions which demonstrate spin glass behavior. Pure TbNi{sub 2}Ge{sub 2} is an Ising antiferromagnet with a several distinct metamagnetic states below 17 K. As the terbium is alloyed with yttrium, these magnetic states are weakened in a consistent manner, as is seen in measurements of the transition temperatures and analysis of Curie-Weiss behavior at high temperature. At low concentrations of terbium, below 35%, long range order is no longer present and a spin-glass-like state emerges. This state is studied through various measurements, dc and ac susceptibility, resistivity, and specific heat. This magnetic behavior was then compared to that of other well characterized spin glasses. It is concluded that there is a region of concentration s for which a spin
Switching of antiferromagnetic chains with magnetic pulses
Tao, Kun; Polyakov, Oleg P.; Stepanyuk, Valeri S.
2016-04-01
Recent experimental studies have demonstrated the possibility of information storage in short antiferromagnetic chains on an insulator substrate [S. Loth et al., Science 335, 196 (2012), 10.1126/science.1214131]. Here, using the density functional theory and atomistic spin dynamics simulations, we show that a local magnetic control of such chains with a magnetic tip and magnetic pulses can be used for fast switching of their magnetization. Furthermore, by changing the position of the tip one can engineer the magnetization dynamics of the chains.
Antiferromagnetic topological insulators in cold atomic gases
Essin, Andrew M.; Gurarie, Victor
2011-01-01
We propose a spin-dependent optical lattice potential that realizes a three-dimensional antiferromagnetic topological insulator in a gas of cold, two-state fermions such as alkaline earths, as well as a model that describes the tight-binding limit of this potential. We discuss the physically observable responses of the gas that can verify the presence of this phase. We also point out how this model can be used to obtain two-dimensional flat bands with nonzero Chern number.
The electronic structure of antiferromagnetic chromium
DEFF Research Database (Denmark)
Skriver, Hans Lomholt
1981-01-01
The author has used the local spin density formalism to perform self-consistent calculations of the electronic structure of chromium in the non-magnetic and commensurate antiferromagnetic phases, as a function of the lattice parameter. A change of a few per cent in the atomic radius brings...... the calculated ground state properties into agreement with experiment. The magnetisation is studied as function of volume in several models, and it is shown that a Stoner picture provides an extremely accurate description of the full calculation provided the sp-d hybridisation is taken into account. It is found...
Khanh, Nguyen Quoc; Totsuji, Hiroo
2004-01-01
Applying the classical-map hypernetted-chain method (CHNC) developed recently by Dharma-wardana and Perrot, we have studied the temperature and spin-polarization effects on electron correlation in the uniform quantum two-dimensional gas (2DEG) over a wide range of temperature T and spin-polarization ζ. The quantum fluid at the temperature T is mapped to a classical fluid at the temperature Tcf given by Tcf2= T2+ Tq2, where the quantum temperature Tq is determined by comparing the calculated correlation energy to that of Monte Carlo results for the fully spin-polarized quantum system at zero temperature. By the iterative solution of the modified HNC equation and the Ornstein-Zernike equation, we have obtained the pair distribution function (PDF) and correlation energy for the two-component classical 2DEG with a classical fluid temperature Tcf. The anti-parallel bridge function B12( r) appearing in the modified HNC equation is determined by using the Monte Carlo correlation energy at T=0 or STLS (Singwi-Tosi-Land-Sjölander) result at T>0 and the numerical solution to the Percus-Yevick (PY) equation for the system of hard disks. By calculating the Pauli potential, the bridge function, PDFs, structure factors and correlation energy, we have shown that in some cases, the properties of the uniform quantum 2DEG depend remarkably on the temperature and spin-polarization.
An effective correlated mean-field theory applied in the spin-1/2 Ising ferromagnetic model
Energy Technology Data Exchange (ETDEWEB)
Roberto Viana, J.; Salmon, Octávio R. [Universidade Federal do Amazonas – UFAM, Manaus 69077-000, AM (Brazil); Ricardo de Sousa, J. [Universidade Federal do Amazonas – UFAM, Manaus 69077-000, AM (Brazil); National Institute of Science and Technology for Complex Systems, Universidade Federal do Amazonas, 3000, Japiim, 69077-000 Manaus, AM (Brazil); Neto, Minos A.; Padilha, Igor T. [Universidade Federal do Amazonas – UFAM, Manaus 69077-000, AM (Brazil)
2014-11-15
We developed a new treatment for mean-field theory applied in spins systems, denominated effective correlated mean-field (ECMF). We apply this theory to study the spin-1/2 Ising ferromagnetic model with nearest-neighbor interactions on a square lattice. We use clusters of finite sizes and study the criticality of the ferromagnetic system, where we obtain a convergence of critical temperature for the value k{sub B}T{sub c}/J≃2.27905±0.00141. Also the behavior of magnetic and thermodynamic properties, using the condition of minimum energy of the physical system is obtained. - Highlights: • We developed spin models to study real magnetic systems. • We study the thermodynamic and magnetic properties of the ferromagnetism. • We enhanced a mean-field theory applied in spins models.
An effective correlated mean-field theory applied in the spin-1/2 Ising ferromagnetic model
International Nuclear Information System (INIS)
We developed a new treatment for mean-field theory applied in spins systems, denominated effective correlated mean-field (ECMF). We apply this theory to study the spin-1/2 Ising ferromagnetic model with nearest-neighbor interactions on a square lattice. We use clusters of finite sizes and study the criticality of the ferromagnetic system, where we obtain a convergence of critical temperature for the value kBTc/J≃2.27905±0.00141. Also the behavior of magnetic and thermodynamic properties, using the condition of minimum energy of the physical system is obtained. - Highlights: • We developed spin models to study real magnetic systems. • We study the thermodynamic and magnetic properties of the ferromagnetism. • We enhanced a mean-field theory applied in spins models
International Nuclear Information System (INIS)
While it was recently found that La2VTcO6 and La2VCuO6 are promising candidates for half-metallic antiferromagnets (HM-AFM), the search continues for other potential candidates of HM-AFM in the double perovskites structure La2BB'O6 (B, B'=transition metal). La2VReO6 is found to be a nearly HM-AFM. Furthermore, considering correlation and spin-orbital coupling (SOC) effects in transition metals, it is still nearly a HM-AFM after generalized gradient approximation with correction of on-site Coulomb interaction and SOC calculations, as reported herein.
Correlations between spin accumulation and degree of time-inverse breaking for electron gas in solid
Zayets, Vadym
2013-01-01
It is shown that the electron spin may not be conserved after a spin-independent scattering. This fact strongly limits the validity of the classical model of spin-up/spin-down bands, which has been used for description of magnetic properties of conduction electrons. It is shown that it is possible to divide all conduction electrons into two group distinguished by their symmetry for time reversal. The number of electrons in each group is conserved after a spin-independent scattering. This make...
International Nuclear Information System (INIS)
We study the influence of the spin-orbit interaction on the electronic transport through quantum dots and quantum wires of correlated electrons. Starting with a one-dimensional infinite continuum model without Coulomb interaction, we analyze the interplay of the spin-orbit interaction, an external magnetic field, and an external potential leading to currents with significant spin-polarization in appropriate parameter regimes. Since lattice models are known to often be superior to continuum models in describing the experimental situation of low-dimensional mesoscopic systems, we construct a lattice model which exhibits the same low-energy physics in terms of energy dispersion and spin expectation values. Confining the lattice to finite length and connecting it to two semi-infinite noninteracting Fermi liquid leads, we calculate the zero temperature linear conductance using the Landauer-Bttiker formalism and show that spin-polarization effects also evolve for the lattice model by adding an adequate potential structure and can be controlled by tuning the overall chemical potential of the system (quantum wire and leads). Next, we allow for a finite Coulomb interaction and use the functional renormalization group (fRG) method to capture correlation effects induced by the Coulomb interaction. The interacting system is thereby transformed into a noninteracting system with renormalized system parameters. For short wires (∝100 lattice sites), we show that the energy regime in which spin polarization is found is strongly affected by the Coulomb interaction. For long wires (>1000 lattice sites), we find the power-law suppression of the total linear conductance on low energy scales typical for inhomogeneous Luttinger liquids while the degree of spin polarization stays constant. Considering quantum dots which consist of two lattice sites, we observe the well-known Kondo effect and analyze, how the Kondo temperature is affected by the spin-orbit interaction. Moreover, we show
Energy Technology Data Exchange (ETDEWEB)
Birkholz, Jens Eiko
2008-10-06
We study the influence of the spin-orbit interaction on the electronic transport through quantum dots and quantum wires of correlated electrons. Starting with a one-dimensional infinite continuum model without Coulomb interaction, we analyze the interplay of the spin-orbit interaction, an external magnetic field, and an external potential leading to currents with significant spin-polarization in appropriate parameter regimes. Since lattice models are known to often be superior to continuum models in describing the experimental situation of low-dimensional mesoscopic systems, we construct a lattice model which exhibits the same low-energy physics in terms of energy dispersion and spin expectation values. Confining the lattice to finite length and connecting it to two semi-infinite noninteracting Fermi liquid leads, we calculate the zero temperature linear conductance using the Landauer-Bttiker formalism and show that spin-polarization effects also evolve for the lattice model by adding an adequate potential structure and can be controlled by tuning the overall chemical potential of the system (quantum wire and leads). Next, we allow for a finite Coulomb interaction and use the functional renormalization group (fRG) method to capture correlation effects induced by the Coulomb interaction. The interacting system is thereby transformed into a noninteracting system with renormalized system parameters. For short wires ({proportional_to}100 lattice sites), we show that the energy regime in which spin polarization is found is strongly affected by the Coulomb interaction. For long wires (>1000 lattice sites), we find the power-law suppression of the total linear conductance on low energy scales typical for inhomogeneous Luttinger liquids while the degree of spin polarization stays constant. Considering quantum dots which consist of two lattice sites, we observe the well-known Kondo effect and analyze, how the Kondo temperature is affected by the spin-orbit interaction
Spin correlation parameters Axx and Ayy measurements in p-p scattering from 11 to 26 MeV
International Nuclear Information System (INIS)
The Axx and Ayy spin correlation coefficients of the proton-proton scattering have been measured at the laboratory energies of 11,40 - 19,15 - 23,45 and 26,50 MeV for the center of mass scattering angle 90 degrees. These measurements have been made by scattering a polarized proton beam on a polarized proton target. (authors)
Holes in a two-dimensional quantum antiferromagnet
International Nuclear Information System (INIS)
A brief review is presented on the studies of the hole motion in a two-dimensional quantum antiferromagnetic. An extended introduction is given to cover the background of the problem. The quantum Bogoliubov-de Gennes formalism which treats the local distortion of the spin configuration and the quantum renormalization process on an equal footing, is outlined. The latest development on the central issue, whether a hole can freely propagate on an antiferromagnetic background, is overviewed. (author). 108 refs, 11 figs, 1 tab
Relativistic Néel-Order Fields Induced by Electrical Current in Antiferromagnets
Železný, J.
2014-10-06
We predict that a lateral electrical current in antiferromagnets can induce nonequilibrium Néel-order fields, i.e., fields whose sign alternates between the spin sublattices, which can trigger ultrafast spin-axis reorientation. Based on microscopic transport theory calculations we identify staggered current-induced fields analogous to the intraband and to the intrinsic interband spin-orbit fields previously reported in ferromagnets with a broken inversion-symmetry crystal. To illustrate their rich physics and utility, we consider bulk Mn2Au with the two spin sublattices forming inversion partners, and a 2D square-lattice antiferromagnet with broken structural inversion symmetry modeled by a Rashba spin-orbit coupling. We propose an antiferromagnetic memory device with electrical writing and reading.
Sun, Shih-Jye; Chung, Chung-Hou; Chang, Yung-Yeh; Tsai, Wei-Feng; Zhang, Fu-Chun
2016-01-01
There has been growing interest in searching for exotic self-conjugate, charge-neutral low-energy fermionic quasi-particles, known as Majorana fermions (MFs) in solid state systems. Their signatures have been proposed and potentially observed at edges of topological superconcuctors with non-trivial topological invariant in the bulk electronic band structure. Much effort have been focused on realizing MFs in odd-parity superconductors made of strong spin-orbit coupled materials in proximity to conventional superconductors. In this paper, we propose a novel mechanism for realizing MFs in 2D spin-singlet topological superconducting state induced by doping a correlated quantum spin Hall (Kane-Mele) insulator. Via a renormalized mean-field approach, the system is found to exhibits time-reversal symmetry (TRS) breaking -wave (chiral d-wave) superconductivity near half-filling in the limit of large on-site repulsion. Surprisingly, however, at large spin-orbit coupling, the system undergoes a topological phase transition and enter into a new topological phase protected by a pseudo-spin Chern number, which can be viewed as a persistent extension of the quantum spin Hall phase upon doping. From bulk-edge correspondence, this phase is featured by the presence of two pairs of counter-propagating helical Majorana modes per edge, instead of two chiral propagating edge modes in the d + id' superconductors. PMID:27064108
Dynamic rotor mode in antiferromagnetic nanoparticles
DEFF Research Database (Denmark)
Lefmann, Kim; Jacobsen, H.; Garde, J.;
2015-01-01
We present experimental, numerical, and theoretical evidence for an unusual mode of antiferromagnetic dynamics in nanoparticles. Elastic neutron scattering experiments on 8-nm particles of hematite display a loss of diffraction intensity with temperature, the intensity vanishing around 150 K....... However, the signal from inelastic neutron scattering remains above that temperature, indicating a magnetic system in constant motion. In addition, the precession frequency of the inelastic magnetic signal shows an increase above 100 K. Numerical Langevin simulations of spin dynamics reproduce all...... measured neutron data and reveal that thermally activated spin canting gives rise to an unusual type of coherent magnetic precession mode. This "rotor" mode can be seen as a high-temperature version of superparamagnetism and is driven by exchange interactions between the two magnetic sublattices. The...
Ising antiferromagnet on the Archimedean lattices
Yu, Unjong
2015-06-01
Geometric frustration effects were studied systematically with the Ising antiferromagnet on the 11 Archimedean lattices using the Monte Carlo methods. The Wang-Landau algorithm for static properties (specific heat and residual entropy) and the Metropolis algorithm for a freezing order parameter were adopted. The exact residual entropy was also found. Based on the degree of frustration and dynamic properties, ground states of them were determined. The Shastry-Sutherland lattice and the trellis lattice are weakly frustrated and have two- and one-dimensional long-range-ordered ground states, respectively. The bounce, maple-leaf, and star lattices have the spin ice phase. The spin liquid phase appears in the triangular and kagome lattices.
Quantum Phase Transitions in Antiferromagnets and Superfluids
Sachdev, Subir
2000-03-01
A general introduction to the non-zero temperature dynamic and transport properties of low-dimensional systems near a quantum phase transition shall be presented. Basic results will be reviewed in the context of experiments on the spin-ladder compounds. Recent large N computations (M. Vojta and S. Sachdev, Phys. Rev. Lett. 83), 3916 (1999) on an extended t-J model motivate a global scenario of the quantum phases and transitions in the high temperature superconductors, and connections will be made to numerous experiments. A universal theory (S. Sachdev, C. Buragohain, and M. Vojta, Science, in press M. Vojta, C. Buragohain, and S. Sachdev, cond- mat/9912020) of quantum impurities in spin-gap antiferromagnets near a magnetic ordering transition will be compared quantitatively to experiments on Zn doped Y Ba2 Cu3 O7 (Fong et al.), Phys. Rev. Lett. 82, 1939 (1999)
Antiferromagnetic proximity effect in epitaxial CoO/NiO/MgO(001) systems.
Li, Q; Liang, J H; Luo, Y M; Ding, Z; Gu, T; Hu, Z; Hua, C Y; Lin, H-J; Pi, T W; Kang, S P; Won, C; Wu, Y Z
2016-01-01
Magnetic proximity effect between two magnetic layers is an important focus of research for discovering new physical properties of magnetic systems. Antiferromagnets (AFMs) are fundamental systems with magnetic ordering and promising candidate materials in the emerging field of antiferromagnetic spintronics. However, the magnetic proximity effect between antiferromagnetic bilayers is rarely studied because detecting the spin orientation of AFMs is challenging. Using X-ray linear dichroism and magneto-optical Kerr effect measurements, we investigated antiferromagnetic proximity effects in epitaxial CoO/NiO/MgO(001) systems. We found the antiferromagnetic spin of the NiO underwent a spin reorientation transition from in-plane to out-of-plane with increasing NiO thickness, with the existence of vertical exchange spring spin alignment in thick NiO. More interestingly, the Néel temperature of the CoO layer was greatly enhanced by the adjacent NiO layer, with the extent of the enhancement closely dependent on the spin orientation of NiO layer. This phenomenon was attributed to different exchange coupling strengths at the AFM/AFM interface depending on the relative spin directions. Our results indicate a new route for modifying the spin configuration and ordering temperature of AFMs through the magnetic proximity effect near room temperature, which should further benefit the design of AFM spintronic devices. PMID:26932164
Antiferromagnetic proximity effect in epitaxial CoO/NiO/MgO(001) systems
Li, Q.; Liang, J. H.; Luo, Y. M.; Ding, Z.; Gu, T.; Hu, Z.; Hua, C. Y.; Lin, H.-J.; Pi, T. W.; Kang, S. P.; Won, C.; Wu, Y. Z.
2016-03-01
Magnetic proximity effect between two magnetic layers is an important focus of research for discovering new physical properties of magnetic systems. Antiferromagnets (AFMs) are fundamental systems with magnetic ordering and promising candidate materials in the emerging field of antiferromagnetic spintronics. However, the magnetic proximity effect between antiferromagnetic bilayers is rarely studied because detecting the spin orientation of AFMs is challenging. Using X-ray linear dichroism and magneto-optical Kerr effect measurements, we investigated antiferromagnetic proximity effects in epitaxial CoO/NiO/MgO(001) systems. We found the antiferromagnetic spin of the NiO underwent a spin reorientation transition from in-plane to out-of-plane with increasing NiO thickness, with the existence of vertical exchange spring spin alignment in thick NiO. More interestingly, the Néel temperature of the CoO layer was greatly enhanced by the adjacent NiO layer, with the extent of the enhancement closely dependent on the spin orientation of NiO layer. This phenomenon was attributed to different exchange coupling strengths at the AFM/AFM interface depending on the relative spin directions. Our results indicate a new route for modifying the spin configuration and ordering temperature of AFMs through the magnetic proximity effect near room temperature, which should further benefit the design of AFM spintronic devices.
Top Quark Polarization and Spin Correlation in the Littlest Higgs Model with T-Parity at the ILC
Institute of Scientific and Technical Information of China (English)
YANG Bing-Fang; LI Xiang-Dong
2013-01-01
In the framework of the littlest Higgs model with T-parity (LHT),we study the top quark spin correlation and polarization at the International Linear Collider (ILC).We find that the top quark polarization asymmetry δPt and the left-right asymmetry δALR car respectively reach-35％ and-37.5％ for √s =500 GeV and √s =1000 GeV via e+e-collision,which can reach the observable level at the ILC.By contrast,the spin correlation δC is smaller.The correlation behaviors of these observables at the e+ e-collision and the γγ collision will be helpful to distinguish different models and test the LHT model at the ILC.
Nachtmann, Otto
2014-01-01
We review ideas on the structure of the QCD vacuum which had served as motivation for the discussion of various non-standard QCD effects in high-energy reactions in articles from 1984 to 1995. These effects include, in particular, transverse-momentum and spin correlations in the Drell-Yan process and soft photon production in hadron-hadron collisions. We discuss the relation of the approach introduced in the above-mentioned articles to the approach, developed later, using transverse-momentum-dependent parton distributions (TDMs). The latter approach is a special case of our more general one which allows for parton entanglement in high-energy reactions. We discuss signatures of parton entanglement in the Drell-Yan reaction. Also for Higgs-boson production in pp collisions via gluon-gluon annihilation effects of entanglement of the two gluons are discussed and are found to be potentially important. These effects can be looked for in the current LHC experiments. In our opinion studying parton-entanglement effect...
International Nuclear Information System (INIS)
We review ideas on the structure of the QCD vacuum which had served as motivation for the discussion of various non-standard QCD effects in high-energy reactions in articles from 1984 to 1995. These effects include, in particular, transverse-momentum and spin correlations in the Drell–Yan process and soft photon production in hadron–hadron collisions. We discuss the relation of the approach introduced in the above-mentioned articles to the approach, developed later, using transverse-momentum-dependent parton distributions (TDMs). The latter approach is a special case of our more general one which allows for parton entanglement in high-energy reactions. We discuss signatures of parton entanglement in the Drell–Yan reaction. Also for Higgs-boson production in pp collisions via gluon–gluon annihilation effects of entanglement of the two gluons are discussed and are found to be potentially important. These effects can be looked for in the current LHC experiments. In our opinion studying parton-entanglement effects in high-energy reactions is, on the one hand, very worthwhile by itself and, on the other hand, it allows to perform quantitative tests of standard factorisation assumptions. Clearly, the experimental observation of parton-entanglement effects in the Drell–Yan reaction and/or in Higgs-boson production would have a great impact on our understanding how QCD works in high-energy collisions
Muon Beam Tracking and Spin-Orbit Correlations for Precision g-2 Measurements
Energy Technology Data Exchange (ETDEWEB)
Tarazona, David [Michigan State U., East Lansing (main); Berz, Martin [Michigan State U., East Lansing (main); Hipple, Robert [Michigan State U., East Lansing (main); Makino, Kyoko [Michigan State U., East Lansing (main); Syphers, Michael [Fermilab
2016-06-01
The main goal of the Muon g-2 Experiment (g-2) at Fermilab is to measure the muon anomalous magnetic moment to unprecedented precision. This new measurement will allow to test the completeness of the Standard Model (SM) and to validate other theoretical models beyond the SM. The close interplay of the understanding of particle beam dynamics and the preparation of the beam properties with the experimental measurement is tantamount to the reduction of systematic errors in the determination of the muon anomalous magnetic moment. We describe progress in developing detailed calculations and modeling of the muon beam delivery system in order to obtain a better understanding of spin-orbit correlations, nonlinearities, and more realistic aspects that contribute to the systematic errors of the g-2 measurement. Our simulation is meant to provide statistical studies of error effects and quick analyses of running conditions for when g-2 is taking beam, among others. We are using COSY, a differential algebra solver developed at Michigan State University that will also serve as an alternative to compare results obtained by other simulation teams of the g-2 Collaboration.
Quantum Phase Transitions in d-wave Superconductors and Antiferromagnetic Kagome Lattices
Huh, Yejin
Strongly correlated systems are of interest due to their exotic collective behavior. In this thesis we study low energy effective theory and quantum phase transitions of d-wave superconductors and spin liquids. First we examine the quantum theory of the spontaneous breaking of lattice rotation symmetry in d-wave superconductors on the square lattice. This is described by a field theory of an Ising nematic order parameter coupled to the gapless fermionic quasiparticles. We determine the structure of the renormalization group to all orders in a 1/Nf expansion, where Nf is the number of fermion spin components. Asymptotically exact results are obtained for the quantum critical theory in which, as in the large Nf theory, the nematic order has a large anomalous dimension, and the fermion spectral functions are highly anisotropic. Next we study quantum phase transitions in antiferromagnetic kagome lattices. Due to the high geometric frustration, this system poses as a good candidate for a spin liquid with exotic excitations. Here we look at physics of the spinon and vison sector. In the spinon sector, we investigate the zero-temperature phase diagram of the nearest-neighbor kagome antiferromagnet in the presence of Dzyaloshinksii-Moriya interaction. We develop a theory for the transition between Z 2 spin liquids with bosonic spinons and a phase with antiferromagnetic long-range order. Connections to recent numerical studies and experiments are discussed. Finally in the vison sector, we present a projective symmetry group (PSG) analysis of the spinless excitations of Z2 spin liquids on the kagome lattice. In the simplest case, vortices carrying Z2 magnetic flux ('visons') are shown to transform under the 48 element group GL(2, Z3 ). Alternative exchange couplings can also lead to a second case with visons transforming under 288 element group GL(2, Z3 ) x D3. We study the quantum phase transition in which visons condense into confining states with valence bond solid order
Electrical switching of an antiferromagnet
Wadley, P.; Howells, B.; Železný, J.; Andrews, C.; Hills, V.; Campion, R. P.; Novák, V.; Olejník, K.; Maccherozzi, F.; Dhesi, S. S.; Martin, S. Y.; Wagner, T.; Wunderlich, J.; Freimuth, F.; Mokrousov, Y.; Kuneš, J.; Chauhan, J. S.; Grzybowski, M. J.; Rushforth, A. W.; Edmonds, K. W.; Gallagher, B. L.; Jungwirth, T.
2016-02-01
Antiferromagnets are hard to control by external magnetic fields because of the alternating directions of magnetic moments on individual atoms and the resulting zero net magnetization. However, relativistic quantum mechanics allows for generating current-induced internal fields whose sign alternates with the periodicity of the antiferromagnetic lattice. Using these fields, which couple strongly to the antiferromagnetic order, we demonstrate room-temperature electrical switching between stable configurations in antiferromagnetic CuMnAs thin-film devices by applied current with magnitudes of order 106 ampere per square centimeter. Electrical writing is combined in our solid-state memory with electrical readout and the stored magnetic state is insensitive to and produces no external magnetic field perturbations, which illustrates the unique merits of antiferromagnets for spintronics.
Spin glass behaviour in URh2Ge2
International Nuclear Information System (INIS)
URh2Ge2 occupies an extraordinary position among the 122 heavy-electron compounds. Its physical properties strongly deviate from those of the other members of this materials class by exhibiting some previously unidentified form of magnetic correlations at low temperatures, instead of the usual antiferromagnetic ground state. Here, we present new results of AC-susceptibility and neutron diffraction measurements on single-crystalline as-grown URh2Ge2. These data clearly indicate that crystallographic disorder on a local scale produces spin-glass behaviour in the sample. We therefore conclude that URh2Ge2 is a random-bond, heavy-fermion spin glass. (orig.)
Spin Glass Behavior in URh2Ge2
International Nuclear Information System (INIS)
URh2Ge2 occupies an extraordinary position among the heavy-electron 122 compounds, by exhibiting a previously unidentified form of magnetic correlations at low temperatures instead of the usual antiferromagnetism. Here we present new results of ac and dc susceptibilities, specific heat, and neutron diffraction on single-crystalline as-grown URh2Ge2. These data clearly indicate that crystallographic disorder on a local scale produces spin glass behavior in the sample. We therefore conclude that URh2Ge2 is a 3D Ising-like, random-bond, heavy-fermion spin glass. copyright 1997 The American Physical Society
Spin-bag mechanism of high-temperature superconductivity
Schrieffer, J. R.; Wen, X.-G.; Zhang, S.-C.
1988-01-01
A new approach to the theory of high-temperature superconductivity is proposed, based on the two-dimensional antiferromagnetic spin correlations observed in these materials over distances large compared to the lattice spacing. The spin ordering produces an electronic pseudogap which is locally suppressed by the addition of a hole. This suppression forms a bag inside which the hole is self-consistently trapped. Two holes are attracted by sharing a common bag. The resulting pairing interaction leads to a superconducting energy gap which is nodeless over the Femri surface.
Observation of magnetic fragmentation in spin ice
Petit, S.; Lhotel, E.; Canals, B.; Ciomaga Hatnean, M.; Ollivier, J.; Mutka, H.; Ressouche, E.; Wildes, A. R.; Lees, M. R.; Balakrishnan, G.
2016-08-01
Fractionalized excitations that emerge from a many-body system have revealed rich physics and concepts, from composite fermions in two-dimensional electron systems, revealed through the fractional quantum Hall effect, to spinons in antiferromagnetic chains and, more recently, fractionalization of Dirac electrons in graphene and magnetic monopoles in spin ice. Even more surprising is the fragmentation of the degrees of freedom themselves, leading to coexisting and a priori independent ground states. This puzzling phenomenon was recently put forward in the context of spin ice, in which the magnetic moment field can fragment, resulting in a dual ground state consisting of a fluctuating spin liquid, a so-called Coulomb phase, on top of a magnetic monopole crystal. Here we show, by means of neutron scattering measurements, that such fragmentation occurs in the spin ice candidate Nd2Zr2O7. We observe the spectacular coexistence of an antiferromagnetic order induced by the monopole crystallization and a fluctuating state with ferromagnetic correlations. Experimentally, this fragmentation manifests itself through the superposition of magnetic Bragg peaks, characteristic of the ordered phase, and a pinch point pattern, characteristic of the Coulomb phase. These results highlight the relevance of the fragmentation concept to describe the physics of systems that are simultaneously ordered and fluctuating.
Spin correlations near the ferromagnetic-spin glass crossover in Eu/sub x/Sr/sub 1-x/S
International Nuclear Information System (INIS)
Bulk susceptibility and high-resolution neutron-diffraction measurements have been performed on single crystals of Eu/sub x/Sr/sub 1-x/S for x = 0.52 and 0.54 near the ferromagnet (FM) - spin glass (SG) crossover. A reentrant phase is established, which is induced by random-field effects. As the temperature is reduced the FM correlation length xi passes through a resolution-limited maximum where a frustrated FM phase is observed. In the SG at lower temperature xi decreases again and a coexisting FM component can be excluded. 6 figures
International Nuclear Information System (INIS)
We analyze the spin and charge susceptibilities of a spin-polarized electron gas subject to a weak space-and time-dependent electromagnetic field coupled to the electronic spins, with main attention to the case of space dimensionality D = 2. The effects of exchange and correlation are incorporated into the dynamic susceptibilities by introducing spin-dependent local-field factors Gσ±(q, ω). For an arbitrary degree of spin polarization we determine the exact analytic expressions of Gσ±(q, ω) in two limiting cases: (i) the limit of large wave-number q at finite frequency ω, already considered in D = 3 by D. C. Marinescu and J. J. Quinn [Phys. Rev. B 56 (1997) 1114]; and (ii) the static limit at small wave-number. In the latter case we obtain thermodynamic sum rules of general validity in both dimensionalities. Our work gives new insight into many-body vertex corrections and basic information for calculations of the effects of the electron-electron interactions on physical properties. (author)
Universality in antiferromagnetic strange metals
Maier, Stefan A.; Strack, Philipp
2016-04-01
We propose a theory of metals at the spin-density-wave quantum-critical point in spatial dimension d =2 . We provide a first estimate of the full set of critical exponents (dynamical exponent z =2.13 , correlation length ν =1.02 , spin susceptibility γ =0.96 , electronic non-Fermi liquid ητf=0.53 , spin-wave Landau damping ητb=1.06 ), which determine the universal power laws in thermodynamics and response functions in the quantum-critical regime relevant for experiments in heavy-fermion systems and iron pnictides. We present approximate numerical and analytical solutions of Polchinski-Wetterich-type flow equations with soft frequency regulators for an effective action of electrons coupled to spin-wave bosons. Performing the renormalization group in frequency instead of momentum space allows to track changes of the Fermi-surface shape and to capture Landau damping during the flow. The technique is easily generalizable from models retaining only patches of the Fermi surface to full, compact Fermi surfaces.
Balint-Kurti, Gabriel G; Vasyutinskii, Oleg S
2009-12-31
A general reactive collision of the type A + B --> C + D is considered where both the collision partners (A and B) or the products (C and D) may possess internal, i.e., spin, orbital or rotational, angular momenta. Compact expressions are derived using a rigorous quantum mechanical analysis for the angular momentum anisotropy of either of the products (C or D) arising from an initially polarized distribution of the reactant angular momentum. The angular momentum distribution of the product is expressed in terms of canonical spherical tensors multiplied by anisotropy-transforming coefficients c(K(i)q(k))(K)(K(r),L). These coefficients act as transformation coefficients between the angular momentum anisotropy of the reactants and that of the product. They are independent of scattering angle but depend on the details of the scattering dynamics. The relationship between the coefficients c(K(i)q(k))(K)(K(r),L) and the body-fixed scattering S matrix is given and the methodology for the quantum mechanical calculation of the anisotropy-transforming coefficients is clearly laid out. The anisotropy-transforming coefficients are amenable to direct experimental measurement in a similar manner to vector correlation and alignment parameters in photodissociation processes. A key aspect of the theory is the use of projections of both reactant and product angular momenta onto the product recoil vector direction. An important new conservation rule is revealed through the analysis, namely that if the state multipole for reactant angular momentum distribution has a projection q(k) onto the product recoil vector the state multipoles for the product angular momentum distribution all have this same projection. Expressions are also presented for the distribution of the product angular momentum when its components are evaluated relative to the space-fixed Z-axis. Notes with detailed derivations of all the formulas are available as Supporting Information. PMID:19642631
Spin polarized induction of quantum correlations_entanglement using a 2 MeV proton beam channeling
Berec, Vesna
2013-01-01
In solid_state hybrid electron_nuclear spin systems quantum entanglement plays vital role in allowing accessible transfer of information between subatomic particles, regardless of the host lattice coordination spatial geometry, revealing the powerful resource for nuclear quantum states engineering. Here we present study of 2 MeV superfocused channeled proton (SCP) beam induced polarization of atom_photon correlated states, established in isotopically purified silicon nanocrystal. Two level entangling interaction which couples an initial quantum state to two possible light_matter states via silicon nanocrystal interface is presented. The anisotropic hyperfine coupling is demonstrated by strong mixing of quantum states within the control mechanism of the coherent proton pulse sequence. Obtained results reveal the mutual predictable correlation of particles of energy_matter, by using the fully broadcastable and precise hybrid electron_nuclear spin qubit manipulations which can be exploited for the speed_superior...
Ground-state and low-lying excitations of the Heisenberg antiferromagnet
International Nuclear Information System (INIS)
Monte Carlo methods are used to determine the exact ground-state energy of the spin-1/2 Heisenberg antiferromagnet on two-dimensional square periodic lattices up to size 32 x 32. The extrapolated ground-state energy for infinite lattice size is -0.33459+-0.000 05. In addition, splittings between the ground state and the lowest spin-1 and -2 excitations are determined as a function of lattice size. The scaling of both the ground-state energy and the gap are in agreement with that predicted by spin-wave theory over a wide range of lattice sizes. In particular, numerical results demonstrate convincingly the lack of a gap for infinite systems, and that the gap for finite systems scales with the inverse volume of the lattice. Finally, we present results for the ground-state spin-correlation function. Our approximate results for larger lattices indicate that the staggered magnetization is 0.34+-0.01 units where the saturated value is
Energy Technology Data Exchange (ETDEWEB)
Mao, Kanmi [Iowa State Univ., Ames, IA (United States)
2011-01-01
The development of fast magic angle spinning (MAS) opened up an opportunity for the indirect detection of insensitive low-γ nuclei (e.g., ^{13}C and ^{15}N) via the sensitive high-{gamma} nuclei (e.g., ^{1}H and ^{19}F) in solid-state NMR, with advanced sensitivity and resolution. In this thesis, new methodology utilizing fast MAS is presented, including through-bond indirectly detected heteronuclear correlation (HETCOR) spectroscopy, which is assisted by multiple RF pulse sequences for ^{1}H-^{1}H homonuclear decoupling. Also presented is a simple new strategy for optimization of ^{1}H-^{1}H homonuclear decoupling. As applications, various classes of materials, such as catalytic nanoscale materials, biomolecules, and organic complexes, are studied by combining indirect detection and other one-dimensional (1D) and two-dimensional (2D) NMR techniques. Indirectly detected through-bond HETCOR spectroscopy utilizing refocused INEPT (INEPTR) mixing was developed under fast MAS (Chapter 2). The time performance of this approach in ^{1}H detected 2D ^{1}H{l_brace}^{13}C{r_brace} spectra was significantly improved, by a factor of almost 10, compared to the traditional ^{13}C detected experiments, as demonstrated by measuring naturally abundant organic-inorganic mesoporous hybrid materials. The through-bond scheme was demonstrated as a new analytical tool, which provides complementary structural information in solid-state systems in addition to through-space correlation. To further benefit the sensitivity of the INEPT transfer in rigid solids, the combined rotation and multiple-pulse spectroscopy (CRAMPS) was implemented for homonuclear ^{1}H decoupling under fast MAS (Chapter 3). Several decoupling schemes (PMLG5_{m}^{$\\bar{x}$}, PMLG5_{mm}^{$\\bar{x}$x} and SAM3) were analyzed to maximize the performance of through-bond transfer based
DEFF Research Database (Denmark)
Eltschka, M.; Klaui, M.; Rudiger, U;
2008-01-01
The correlation between magnetic spin structure and geometry in nanoscale chemically synthesized Fe3O4 rings has been investigated by transmission electron microscopy. We find primarily the flux closure vortex states but in rings with thickness variations, an effective stray field occurs. Using t...... interaction between exchange coupled rings leads to antiparallel vortex states and extended onion states. (c) 2008 American Institute of Physics....
International Nuclear Information System (INIS)
We introduce a class of spin models with long-range interactions—in the sense that they extend significantly beyond their nearest neighbors—whose ground states can be constructed analytically and that have a simple matrix product state representation. This enables the detailed study of ground state properties, such as correlation functions and entanglement, in the thermodynamic limit. The spin models presented here are closely related to lattice gases of strongly interacting polar molecules, or Rydberg atoms that feature an excluded volume or blockade interaction. While entanglement is only present between spins that are separated by no more than a blockade length, we show that non-classical correlations can extend much further, and we analyze them through quantum discord. We furthermore identify a set of seemingly critical points where the ground state approaches a crystalline state with a filling fraction that is given by the inverse of the blockade length. We analyze the scaling properties in the vicinity of this parameter region and show that the correlation length possesses a non-trivial dependence on the blockade length. (paper)
Energy Technology Data Exchange (ETDEWEB)
Grabowski, Ireneusz, E-mail: ig@fizyka.umk.pl; Śmiga, Szymon; Buksztel, Adam [Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun (Poland); Fabiano, Eduardo [National Nanotechnology Laboratory, Istituto Nanoscienze–CNR, Via per Arnesano, I-73100 Lecce (Italy); Teale, Andrew M. [School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD (United Kingdom); Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo (Norway); Sala, Fabio Della [National Nanotechnology Laboratory, Istituto Nanoscienze–CNR, Via per Arnesano, I-73100 Lecce (Italy); Center for Biomolecular Nanotechnologies @UNILE, Istituto Italiano di Tecnologia (IIT), Via Barsanti, 73010 Arnesano (LE) (Italy)
2014-07-14
The performance of correlated optimized effective potential (OEP) functionals based on the spin-resolved second-order correlation energy is analysed. The relative importance of singly- and doubly- excited contributions as well as the effect of scaling the same- and opposite- spin components is investigated in detail comparing OEP results with Kohn–Sham (KS) quantities determined via an inversion procedure using accurate ab initio electronic densities. Special attention is dedicated in particular to the recently proposed scaled-opposite–spin OEP functional [I. Grabowski, E. Fabiano, and F. Della Sala, Phys. Rev. B 87, 075103 (2013)] which is the most advantageous from a computational point of view. We find that for high accuracy, a careful, system dependent, selection of the scaling coefficient is required. We analyse several size-extensive approaches for this selection. Finally, we find that a composite approach, named OEP2-SOSh, based on a post-SCF rescaling of the correlation energy can yield high accuracy for many properties, being comparable with the most accurate OEP procedures previously reported in the literature but at substantially reduced computational effort.
Spin Excitations and Phonon Anomaly in Quasi-1D Spiral Magneti CuBr2
Li, Yuan; Wang, Chong; Yu, Daiwei; Wang, Lichen; Wang, Fa; Iida, Kazuki; Kamazawa, Kazuya; Wakimoto, Shuichi
CuBr2 can be considered as a model quasi-one-dimensional (quasi-1D) spin-1/2 magnet, in which the frustrating ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor exchange interactions give rise to a cycloidal magnetic order below TN = 73 K. The removal of inversion symmetry by the magnetic order also makes the material a type-II multiferroic system with a remarkably simple crystal structure. Using time-of-flight inelastic neutron scattering spectroscopy, we have determined the spin-wave as well as phonon spectra throughout the entire Brillouin zone. The spin-wave spectrum exhibits pronounced anisotropy and magnon damping, consistent with the material's quasi-1D nature and the non-colinear spin structure. The phonon spectrum exhibits dramatic discontinuities in the dispersion across the quasi-1D magnetic wave vector, indicative of strong magnetoelastic coupling and possibly of a spin-orbital texture that comes along with the spin correlations.
Boosting spin-caloritronic effects by attractive correlations in molecular junctions
Ireneusz Weymann
2016-01-01
In nanoscopic systems quantum confinement and interference can lead to an enhancement of thermoelectric properties as compared to conventional bulk materials. For nanostructures, such as molecules or quantum dots coupled to external leads, the thermoelectric figure of merit can reach or even exceed unity. Moreover, in the presence of external magnetic field or when the leads are ferromagnetic, an applied temperature gradient can generate a spin voltage and an associated spin current flow in t...
Magnetic correlation, excitation and slow dynamics in concentrated spin-glass alloys
Indian Academy of Sciences (India)
Kiyoichiro Motoya
2004-07-01
Three kinds of neutron scattering experiments have been performed to clarify the role of magnetic clusters on the various properties of re-entrant spin-glasses. The presence of two kinds of spin-wave excitations, the limitations of magnetic phase diagrams and the mechanism of slow dynamics have been discussed based on the results of in-elastic scattering, diffuse scattering and time-resolved small-angle scattering experiments, respectively.
Quantum spin Hall effect in a transition metal oxide Na2IrO3
Energy Technology Data Exchange (ETDEWEB)
Shitade, Atsuo
2010-05-26
We study theoretically the electronic states in a 5d transition metal oxide Na{sub 2}I{sub r}O{sub 3}, in which both the spin-orbit interaction and the electron correlation play crucial roles. Tight-binding model analysis together with the fisrt-principles band structure calculation predicts that this material is a layered quantum spin Hall system. Due to the electron correlation, an antiferromagnetic order first develops at the edge, and later inside the bulk at low temperatures.
Correlation between the spin Hall angle and the structural phases of early 5d transition metals
Energy Technology Data Exchange (ETDEWEB)
Liu, Jun; Ohkubo, Tadakatsu; Mitani, Seiji; Hono, Kazuhiro; Hayashi, Masamitsu, E-mail: hayashi.masamitsu@nimsgo.jp [National Institute for Materials Science, Tsukuba 305-0047 (Japan)
2015-12-07
We have studied the relationship between the structure and the spin Hall angle of the early 5d transition metals in X/CoFeB/MgO (X = Hf, Ta, W, and Re) heterostructures. Spin Hall magnetoresistance (SMR) is used to characterize the spin Hall angle of the heavy metals. Transmission electron microscopy images show that all underlayers are amorphous-like when their thicknesses are small, however, crystalline phases emerge as the thickness is increased for certain elements. We find that the heavy metal layer thickness dependence of the SMR reflects these changes in structure. The largest spin Hall angle |θ{sub SH}| of Hf, Ta, W, and Re (∼0.11, 0.10, 0.23, and 0.07, respectively) is found when the dominant phase is amorphous-like. We find that the amorphous-like phase not only possesses large resistivity but also exhibits sizeable spin Hall conductivity, which both contribute to the emergence of the large spin Hall angle.
Correlation between the spin Hall angle and the structural phases of early 5d transition metals
International Nuclear Information System (INIS)
We have studied the relationship between the structure and the spin Hall angle of the early 5d transition metals in X/CoFeB/MgO (X = Hf, Ta, W, and Re) heterostructures. Spin Hall magnetoresistance (SMR) is used to characterize the spin Hall angle of the heavy metals. Transmission electron microscopy images show that all underlayers are amorphous-like when their thicknesses are small, however, crystalline phases emerge as the thickness is increased for certain elements. We find that the heavy metal layer thickness dependence of the SMR reflects these changes in structure. The largest spin Hall angle |θSH| of Hf, Ta, W, and Re (∼0.11, 0.10, 0.23, and 0.07, respectively) is found when the dominant phase is amorphous-like. We find that the amorphous-like phase not only possesses large resistivity but also exhibits sizeable spin Hall conductivity, which both contribute to the emergence of the large spin Hall angle
Resonating Valence Bond states for low dimensional S=1 antiferromagnets
Liu, Zheng-Xin; Zhou, Yi; Ng, Tai-Kai
2014-03-01
We study S = 1 spin liquid states in low dimensions. We show that the resonating-valence-bond (RVB) picture of S = 1 / 2 spin liquid state can be generalized to S = 1 case. For S = 1 system, a many-body singlet (with even site number) can be decomposed into superposition of products of two-body singlets. In other words, the product states of two-body singlets, called the singlet pair states (SPSs), are over complete to span the Hilbert space of many-body singlets. Furthermore, we generalized fermionic representation and the corresponding mean field theory and Gutzwiller projected stats to S = 1 models. We applied our theory to study 1D anti-ferromagnetic bilinear-biquadratic model and show that both the ground states (including the phase transition point) and the excited states can be understood excellently well within the framework. Our method can be applied to 2D S = 1 antiferromagnets.
International Nuclear Information System (INIS)
Nuclear resonance investigations on the 23Na and the 139La nuclei in filled skutterudites MFe4Sb12 (M=Na, La) are reported. In contrast to NaFe4Sb12 for the La compound the effective magnetic moment is remarkably lower and the Curie-Weiss temperature is negative which indicates antiferromagnetic correlations. The spin-lattice relaxation rates 1/T1 exhibit a qualitatively different temperature behavior which provides clear evidence for dissimilar types of itinerant magnetism in the two compounds. For NaFe4Sb12 1/T1 vs. T indicates itinerant ferromagnetism with ordering at Tc=85K, whereas for the La0.9Fe4Sb12 weak itinerant antiferromagnetism with no ordering is found. 1/T1 is analyzed in terms of Moriya's self-consistent renormalization theory (SCR) for itinerant magnetic materials
Hybrid Spin Noise Spectroscopy and the Spin Hall Effect
Slipko, V. A.; Sinitsyn, N. A.; Pershin, Y. V.
2013-01-01
Here we suggest a novel hybrid spin noise spectroscopy technique, which is sensitive to the spin Hall effect. It is shown that, while the standard spin-spin correlation function is not sensitive to the spin Hall effect, spin-transverse voltage and transverse voltage-voltage correlation functions provide the missing sensitivity being linear and quadratic in the spin Hall coefficient, respectively. The correlation between transverse voltage and spin fluctuations appears as a result of spin-char...
Quantum discord in spin-cluster materials
Yurischev, M A
2011-01-01
The total quantum correlation (discord) in Heisenberg dimers is expressed via the spin-spin correlation function, internal energy, specific heat or magnetic susceptibility. This allows one to indirectly measure the discord through neutron scattering, as well as calorimetric or magnetometric experiments. Using the available experimental data, we found the discord for a number of binuclear Heisenberg substances with both antiferro- and ferromagnetic interactions. For the dimerized antiferromagnet copper nitrate Cu(NO_3)_2*2.5H_2O, the three independent experimental methods named above lead to a discord of approximately 0.2-0.3 bit/dimer at a temperature of 4 K. We also determined the temperature behavior of discord for hydrated and anhydrous copper acetates, as well as for the ferromagnetic binuclear copper acetate complex [Cu_2L(OAc)]*6H_2O, where L is a ligand.
International Nuclear Information System (INIS)
Several schemes to avoid the double counting of correlations in methods that merge multireference wavefunctions with density functional theory (DFT) are studied and here adapted to a combination of spin-projected Hartree-Fock (SUHF) and DFT. The advantages and limitations of the new method, denoted SUHF+fcDFT, are explored through calculations on benchmark sets in which the accounting of correlations is challenging for pure SUHF or DFT. It is shown that SUHF+fcDFT can greatly improve the description of certain molecular properties (e.g., singlet-triplet energy gaps) which are not improved by simple addition of DFT dynamical correlation to SUHF. However, SUHF+fcDFT is also shown to have difficulties dissociating certain types of bonds and describing highly charged ions with static correlation. Possible improvements to the current SUHF+fcDFT scheme are discussed in light of these results
Energy Technology Data Exchange (ETDEWEB)
Garza, Alejandro J.; Jiménez-Hoyos, Carlos A. [Department of Chemistry, Rice University, Houston, Texas 77251-1892 (United States); Scuseria, Gustavo E. [Department of Chemistry and Department of Physics and Astronomy, Rice University, Houston, Texas 77251-1892, USA and Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia)
2014-06-28
Several schemes to avoid the double counting of correlations in methods that merge multireference wavefunctions with density functional theory (DFT) are studied and here adapted to a combination of spin-projected Hartree-Fock (SUHF) and DFT. The advantages and limitations of the new method, denoted SUHF+f{sub c}DFT, are explored through calculations on benchmark sets in which the accounting of correlations is challenging for pure SUHF or DFT. It is shown that SUHF+f{sub c}DFT can greatly improve the description of certain molecular properties (e.g., singlet-triplet energy gaps) which are not improved by simple addition of DFT dynamical correlation to SUHF. However, SUHF+f{sub c}DFT is also shown to have difficulties dissociating certain types of bonds and describing highly charged ions with static correlation. Possible improvements to the current SUHF+f{sub c}DFT scheme are discussed in light of these results.
Zou, L. K.; Zhang, Y.; Gu, L.; Cai, J. W.; Sun, L.
2016-02-01
Angular-dependent magnetoresistance (MR) is considered to be intrinsic to spintronic materials, represented by the classical anisotropic MR (AMR) phenomenon and the recently emerged spin Hall MR (SMR). So far, isotropic AMR, AMR with geometric size effect and interfacial effect, and SMR have been treated separately to explain distinct MR correlations observed in various systems. Current study shows all four types of MR correlations can be reproduced in Fe thin films depending on the film thickness, texture, interface, and morphology. Results suggest previous explanations of the thin-film MR correlations are incomplete and it is inappropriate to use a specific MR angular-dependent correlation as the sole criterion in determining the origin of AMR or ascertaining the exclusive existence of SMR.
Garza, Alejandro J; Jiménez-Hoyos, Carlos A; Scuseria, Gustavo E
2014-06-28
Several schemes to avoid the double counting of correlations in methods that merge multireference wavefunctions with density functional theory (DFT) are studied and here adapted to a combination of spin-projected Hartree-Fock (SUHF) and DFT. The advantages and limitations of the new method, denoted SUHF+fcDFT, are explored through calculations on benchmark sets in which the accounting of correlations is challenging for pure SUHF or DFT. It is shown that SUHF+fcDFT can greatly improve the description of certain molecular properties (e.g., singlet-triplet energy gaps) which are not improved by simple addition of DFT dynamical correlation to SUHF. However, SUHF+fcDFT is also shown to have difficulties dissociating certain types of bonds and describing highly charged ions with static correlation. Possible improvements to the current SUHF+fcDFT scheme are discussed in light of these results. PMID:24985613
International Nuclear Information System (INIS)
Starting from a quantum kinetic theory for the spin dynamics in diluted magnetic semiconductors, we derive simplified equations that effectively describe the spin transfer between carriers and magnetic impurities for an arbitrary initial impurity magnetization. Taking the Markov limit of these effective equations, we obtain good quantitative agreement with the full quantum kinetic theory for the spin dynamics in bulk systems at high magnetic doping. In contrast, the standard rate description where the carrier–dopant interaction is treated according to Fermi’s golden rule, which involves the assumption of a short memory as well as a perturbative argument, has been shown previously to fail if the impurity magnetization is non-zero. The Markov limit of the effective equations is derived, assuming only a short memory, while higher order terms are still accounted for. These higher order terms represent the precession of the carrier–dopant correlations in the effective magnetic field due to the impurity spins. Numerical calculations show that the Markov limit of our effective equations reproduces the results of the full quantum kinetic theory very well. Furthermore, this limit allows for analytical solutions and for a physically transparent interpretation. (paper)
Multicritical points in the three-dimensional XXZ antiferromagnet with single-ion anisotropy
Selke, Walter
2013-01-01
The classical Heisenberg antiferromagnet with uniaxial exchange anisotropy, the XXZ model, and competing planar single-ion anisotropy in a magnetic field on a simple cubic lattice is studied with the help of extensive Monte Carlo simulations. The biconical (supersolid) phase, bordering the antiferromagnetic and spin-flop phases, is found to become thermally unstable well below the onset of the disordered, paramagnetic phase, leading to interesting multicritical points.
Magnetic structure of Cu in antiferromagnetic REBa sub 2 Cu sub 3 O sub y
Energy Technology Data Exchange (ETDEWEB)
Luetgemeier, H.; Brand, R.A.; Sauer, C.; Rupp, B.; Meuffels, P.M.; Zinn, W. (Inst. fuer Festkoerperforschung, KFA Juelich (Germany, F.R.))
1989-12-01
The NQR spectra of Cu and the Moessbauer effect spectra of Fe in oxygen deficient antiferromagnetic 123 compounds have been investigated. A transition from the high temperature anti-ferromagnetic spin structure of the magnetic moments at the Cu(2) sites with the stacking sequence + - + - to another one at low temperature (+ + - -) is induced by a small amount (about 1%) of magnetic impurities at the Cu(1) sites. The Cu(1) ions themselves carry no magnetic moments. (orig.).
Magnetic structure of Cu in antiferromagnetic reba2Cu3Oy
International Nuclear Information System (INIS)
This paper reports an investigation of the NQR spectra of Cu and the Mossbauer effect spectra of Fe in oxygen deficient antiferromagnetic 123 compounds. A transition from the high temperature antiferromagnetic spin structure of the magnetic moments at the Cu(2) sites with the stacking sequence + - + - to another one at low temperature (+ + - -) is induced by a small amount (about 1%) of magnetic impurities at the Cu(1) sites. The Cu(1) ions themselves carry no magnetic moments
Quantum order by disorder in frustrated diamond lattice antiferromagnets
Bernier, Jean-Sebastien; Lawler, Michael J.; Kim, Yong Baek
2008-01-01
We present a quantum theory of frustrated diamond lattice antiferromagnets. Considering quantum fluctuations as the predominant mechanism relieving spin frustration, we find a rich phase diagram comprising of six phases with coplanar spiral ordering in addition to the N\\'eel phase. By computing the specific heat of these ordered phases, we obtain a remarkable agreement between $(k,k,0)$-spiral ordering and the experimental specific heat data for the diamond lattice spinel compounds MnSc$_2$S$...
Polarized Neutron Reflectivity Simulation of Ferromagnet/ Antiferromagnet Thin Films
International Nuclear Information System (INIS)
This report investigates the current simulating and fitting programs capable of calculating the polarized neutron reflectivity of the exchange-biased ferromagnet/antiferromagnet magnetic thin films. The adequate programs are selected depending on whether nonspin flip and spin flip reflectivities of magnetic thin films and good user interface are available or not. The exchange-biased systems such as Fe/Cr, Co/CoO, CoFe/IrMn/Py thin films have been simulated successfully with selected programs
Singular field response and singular screening of vacancies in antiferromagnets.
Wollny, Alexander; Andrade, Eric C; Vojta, Matthias
2012-10-26
For isolated vacancies in ordered local-moment antiferromagnets we show that the magnetic-field linear-response limit is generically singular: The magnetic moment associated with a vacancy in zero field is different from that in a finite field h in the limit h→0(+). The origin is a universal and singular screening cloud, which moreover leads to perfect screening as h→0(+) for magnets which display spin-flop bulk states in the weak-field limit. PMID:23215218
Chan, Bun; Song, Jong-Won; Kawashima, Yukio; Hirao, Kimihiko
2016-05-30
In the present study, we have investigated two significant features of the OP correlation functional, namely the incorporation of the exchange functional into itself, and the inclusion of only opposite-spin (OS) effects. To explore the latter feature, we have compared OP with B95 and a new functional introduced in the present study - the OPB method that combines OP with the same-spin (SS) component of B95. In general, we find that B95 and OPB perform comparably. Our comparisons of the various DFT procedures suggest that the incorporation of a meta-GGA (e.g., TPSS) into OP and OPB does not necessarily lead to a chemically more accurate procedure than the use of a related GGA (e.g., PBE). An important finding is the more notable (and somewhat more consistent) improvement in performance with the incorporation of SS correlation, particularly for longer-range chemical properties. Nonetheless, on average across our test sets of over 800 systems, the difference between the performances of OP versus B95 or OPB is not exceedingly large. By drawing a parallel between these DFT methods and the wavefunction scaled-MP2-type methods, we reason that one can further develop the OP functional, and perhaps a wider range of correlation functionals by combining it with the technique of range separation. © 2016 Wiley Periodicals, Inc. PMID:26931189
Numerical investigation of correlation functions for the UqSU(2) invariant spin-1/2 Heisenberg chain
International Nuclear Information System (INIS)
We consider the UqSU(2) invariant spin-1/2 XXZ quantum spin chain at the roots of unity q=exp(i π/(m+1)), corresponding to different minimal models of conformal field theory. We conduct a numerical investigation of the correlation functions of UqSU(2) scalar two-point operators in order to find which operators in the minimal models they correspond to. Using graphical representations of the Temperley-Lieb algebra we are able to deal with chains of up to 28 sites. Depending on q, the correlation functions show different characteristics and finite-size behaviour. For m=2/3, which corresponds to the Lee-Yang edge singularity, we find the surface and bulk critical exponent -1/5. Together with the known result in the case m=3 (Ising model) this indicates that in the continuum limit the two-point operators involve conformal fields of spin-m-1/m+1. For other roots of unity q the chains are too short to determine the surface and bulk critical exponents. (author)
Sum rules for four-spinon exact dynamic structure function in antiferromagnetic XXX model
International Nuclear Information System (INIS)
In this work, we continue the description of the exact four-spinon dynamic structure factor S4in the antiferromagnetic Heisenberg spin chain started in a previous work. We compute for S4a number of sum rules the total dynamic structure factor S is known to satisfy exactly. The sum rules for S2 have been evaluated in the literature. We want to know by how much the sum rules for S2 + S4 correct that of S the total dynamic structure function. The sum rules we consider are those related to the static susceptibility, the integrated intensity, the total integrated intensity, the first frequency moment and the nearest-neighbor correlation function. We find that for each sum rule, S4 corrects only by a small amount the contribution from the two-spinon dynamic structure factor S2. (author)
Directory of Open Access Journals (Sweden)
V. G. Kravets
2012-01-01
Full Text Available We present the experimental results on magnetorefractive effect (MRE in ferromagnetic metal-metal and metal-insulator multilayer films of different composition and different type of magnetoresistive effects. The shape and magnitude of the MRE dependences are found to be very sensitive to the spin-dependent scattering parameters and the effective polarization of the electron density of state around the Fermi level. A study of an MRE in multilayered films is shown to be sufficient for direct extracting of the spin-dependent relaxation times of electron (for GMR-like samples and energy dependence of the tunnel spin-polarization density of states near the Fermi level for layered TMR films. It is proposed to use the magnetorefractive effect as a noncontact probe of magnetoresistive effects in thin magnetic films through investigations of the field-dependent reflection behaviors of multilayered films in the IR region.
Energy Technology Data Exchange (ETDEWEB)
Lu, Xingyu, E-mail: luxingyu@udel.edu; Guo, Changmiao, E-mail: cmguo@udel.edu; Hou, Guangjin, E-mail: hou@udel.edu; Polenova, Tatyana, E-mail: tpolenov@udel.edu [University of Delaware, Department of Chemistry and Biochemistry (United States)
2015-01-15
Fast magic angle spinning (MAS) NMR spectroscopy is emerging as an essential analytical and structural biology technique. Large resolution and sensitivity enhancements observed under fast MAS conditions enable structural and dynamics analysis of challenging systems, such as large macromolecular assemblies and isotopically dilute samples, using only a fraction of material required for conventional experiments. Homonuclear dipolar-based correlation spectroscopy constitutes a centerpiece in the MAS NMR methodological toolbox, and is used essentially in every biological and organic system for deriving resonance assignments and distance restraints information necessary for structural analysis. Under fast MAS conditions (rotation frequencies above 35–40 kHz), dipolar-based techniques that yield multi-bond correlations and non-trivial distance information are ineffective and suffer from low polarization transfer efficiency. To overcome this limitation, we have developed a family of experiments, CORD–RFDR. These experiments exploit the advantages of both zero-quantum RFDR and spin-diffusion based CORD methods, and exhibit highly efficient and broadband dipolar recoupling across the entire spectrum, for both short-range and long-range correlations. We have verified the performance of the CORD–RFDR sequences experimentally on a U-{sup 13}C,{sup 15}N-MLF tripeptide and by numerical simulations. We demonstrate applications of 2D CORD–RFDR correlation spectroscopy in dynein light chain LC8 and HIV-1 CA tubular assemblies. In the CORD–RFDR spectra of LC8 acquired at the MAS frequency of 40 kHz, many new intra- and inter-residue correlations are detected, which were not observed with conventional dipolar recoupling sequences. At a moderate MAS frequency of 14 kHz, the CORD–RFDR experiment exhibits excellent performance as well, as demonstrated in the HIV-1 CA tubular assemblies. Taken together, the results indicate that CORD–RFDR experiment is beneficial in a
Energy Technology Data Exchange (ETDEWEB)
Rossat-Mignod, J. (Lab. Leon Brillouin, CEA-CNRS, CE Saclay, 91 - Gif-sur-Yvette (France) CEN, DRFM/MDN 38 - Grenoble (France))
The contribution explains experiments with inelastic neutron scattering at monocrystals of the system YBa[sub 2]Cu[sub 3]O[sub 6+x]. The spin dynamics is examined systematically in characteristic areas, as there are: the pure and doped antiferromagnetic states, (x=0.15; 0.37), the less doped states, (x=0.45; 0.51), the strongly doped (x=0.69; 0.92), and the overdoped, metallic states (x=1), which all exhibit a superconducting ground state. Doping with holes has a strong effect on the antiferromagnetic ordering; in the metallic state, however, there still are dynamic antiferromagnetic correlations. The spin excitation spectrum reveals a band gap in all superconducting samples, but the band gap gets weaker when approaching the insulator-metal transition. In addition, a quite unusual dependence of the spin excitation spectrum on the temperature is found. (orig.).
Antiferromagnetic Exchange Interactions from Hybrid Density Functional Theory
Martin, Richard L.; Illas, Francesc
1997-08-01
A hybrid theory which combines the full nonlocal ``exact'' exchange interaction with the local spin-density approximation of density-functional theory is shown to lead to marked improvement in the description of antiferromagnetically coupled systems. Semiquantitative agreement with experiment is found for the magnitude of the coupling constant in La2CuO4, KNiF3, and K2NiF4. The magnitude of the unpaired spin population on the metal site is in excellent agreement with experiment for La2CuO4.
Antiferromagnetic exchange interactions from hybrid density functional theory
Martin, Richard L.; Illas i Riera, Francesc
1997-01-01
A hybrid theory which combines the full nonlocal ¿exact¿ exchange interaction with the local spin-density approximation of density-functional theory is shown to lead to marked improvement in the description of antiferromagnetically coupled systems. Semiquantitative agreement with experiment is found for the magnitude of the coupling constant in La2CuO4, KNiF3, and K2NiF4. The magnitude of the unpaired spin population on the metal site is in excellent agreement with experiment for La2CuO4.
Antiferromagnetic Exchange Interactions from Hybrid Density Functional Theory
International Nuclear Information System (INIS)
A hybrid theory which combines the full nonlocal open-quotes exactclose quotes exchange interaction with the local spin-density approximation of density-functional theory is shown to lead to marked improvement in the description of antiferromagnetically coupled systems. Semiquantitative agreement with experiment is found for the magnitude of the coupling constant in La2CuO 4 , KNiF3 , and K2NiF 4 . The magnitude of the unpaired spin population on the metal site is in excellent agreement with experiment for La2CuO 4 . copyright 1997 The American Physical Society
Angle-dependent loop shifts in antiferromagnetic nanoparticles
Mao, Zhongquan; Zhan, Xiaozhi; Chen, Xi
2016-08-01
Experimentally hysteresis loop shifts have been widely observed in antiferromagnetic (AF) nanoparticles. Here numerical investigations show that this effect is dependent on the angle between the easy axis of the AF spins and the applied magnetic field in uncompensated nanoparticles. In contrast, the loop shifts disappear in compensated nanoparticles. The results suggest that the uncompensated spins and field directions are essential ingredients to generate loop shifts in AF nanoparticle systems. The present study hints at a possible way to optimize the magnetic performance of AF nanostructures.
Magnetic correlations in half-doped manganates
International Nuclear Information System (INIS)
The coupled ordering of charge orbital and spin degrees of freedom in the manganates constitutes a key element to understand the mechanism of colossal magneto resistivity, which consists in switching from the antiferromagnetically ordered insulating state into the ferromagnetic metallic phase. Starting with the half doped layered material La0.5Sr1.5MnO4 we have analysed the magnon dispersion as well as the temperature dependence of the magnetic correlations in several compounds with a Mn4+:Mn3+ ratio close to half doping. In slightly over-doped La0.4Sr1.6MnO4 we find a coupling of incommensurate ordering of orbitals, charges and Mn3+ spins combined with commensurate ordering of Mn4+ spins. We further discuss the magnetic correlations in Pr0.5Ca1.5MnO4 and in Nd0.5Sr0.5MnO3.
Conductance of ferro- and antiferro-magnetic single-atom contacts: A first-principles study
International Nuclear Information System (INIS)
We present a first-principles study on the spin dependent conductance of five single-atom magnetic junctions consisting of a magnetic tip and an adatom adsorbed on a magnetic surface, i.e., the Co-Co/Co(001) and Ni-X/Ni(001) (X = Fe, Co, Ni, Cu) junctions. When their spin configuration changes from ferromagnetism to anti-ferromagnetism, the spin-up conductance increases while the spin-down one decreases. For the junctions with a magnetic adatom, there is nearly no spin valve effect as the decreased spin-down conductance counteracts the increased spin-up one. For the junction with a nonmagnetic adatom (Ni-Cu/Ni(001)), a spin valve effect is obtained with a variation of 22% in the total conductance. In addition, the change in spin configuration enhances the spin filter effect for the Ni-Fe/Ni(001) junction but suppresses it for the other junctions
Waeber, A. M.; Hopkinson, M.; Farrer, I.; Ritchie, D. A.; Nilsson, J.; Stevenson, R. M.; Bennett, A. J.; Shields, A. J.; Burkard, G.; Tartakovskii, A. I.; Skolnick, M. S.; Chekhovich, E. A.
2016-07-01
One of the key challenges in spectroscopy is the inhomogeneous broadening that masks the homogeneous spectral lineshape and the underlying coherent dynamics. Techniques such as four-wave mixing and spectral hole-burning are used in optical spectroscopy, and spin-echo in nuclear magnetic resonance (NMR). However, the high-power pulses used in spin-echo and other sequences often create spurious dynamics obscuring the subtle spin correlations important for quantum technologies. Here we develop NMR techniques to probe the correlation times of the fluctuations in a nuclear spin bath of individual quantum dots, using frequency-comb excitation, allowing for the homogeneous NMR lineshapes to be measured without high-power pulses. We find nuclear spin correlation times exceeding one second in self-assembled InGaAs quantum dots--four orders of magnitude longer than in strain-free III-V semiconductors. This observed freezing of the nuclear spin fluctuations suggests ways of designing quantum dot spin qubits with a well-understood, highly stable nuclear spin bath.
International Nuclear Information System (INIS)
Neutron scattering measurements have been performed on a single-crystal sample of CsCo0.83Mg0.17Br3, a quasi-one-dimensional, Ising-like antiferromagnet. Residual three- dimensional interactions between the dilute magnetic chains precipitate a phase transition to long-range order at TN∼9.0 K, and short-range correlations persist as high as 40 K. Relatively high-energy inelastic scattering from both ''bulk'' spin-wave modes and ''end'' modes is observed from the finite chains. The low-energy inelastic spectrum is dominated by soliton scattering due to antiphase domain walls propagating along the finite chains
Doping dependence of spin fluctuations and electron correlations in iron pnictides
Czech Academy of Sciences Publication Activity Database
Ikeda, H.; Arita, R.; Kuneš, Jan
2010-01-01
Roč. 82, č. 2 (2010), 024508/1-024508/6. ISSN 1098-0121 Institutional research plan: CEZ:AV0Z10100521 Keywords : iron pnicitdes * dynamic spin susceptibility * fluctuation- exchange approximation Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.772, year: 2010 http://prb.aps.org/abstract/PRB/v82/i2/e024508