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Sample records for antiferromagnetic spin correlations

  1. Spin correlations in the dipolar pyrochlore antiferromagnet Gd2Sn2O7

    NASA Astrophysics Data System (ADS)

    Paddison, Joseph A. M.; Ehlers, Georg; Petrenko, Oleg A.; Wildes, Andrew R.; Gardner, Jason S.; Stewart, J. Ross

    2017-04-01

    We investigate spin correlations in the dipolar Heisenberg antiferromagnet Gd2Sn2O7 using polarised neutron-scattering measurements in the correlated paramagnetic regime. Using Monte Carlo methods, we show that our data are sensitive to weak further-neighbour exchange interactions of magnitude  ∼0.5% of the nearest-neighbour interaction, and are compatible with either antiferromagnetic next-nearest-neighbour interactions, or ferromagnetic third-neighbour interactions that connect spins across hexagonal loops. Calculations of the magnetic scattering intensity reveal rods of diffuse scattering along [1 1 1] reciprocal-space directions, which we explain in terms of strong antiferromagnetic correlations parallel to the set of < 1 1 0> directions that connect a given spin with its nearest neighbours. Finally, we demonstrate that the spin correlations in Gd2Sn2O7 are highly anisotropic, and correlations parallel to third-neighbour separations are particularly sensitive to critical fluctuations associated with incipient long-range order.

  2. Antiferromagnetic spin Seebeck effect.

    SciTech Connect

    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.

  3. Antiferromagnetic Spin Seebeck Effect.

    PubMed

    Wu, Stephen M; Zhang, Wei; Kc, Amit; Borisov, Pavel; Pearson, John E; Jiang, J Samuel; Lederman, David; Hoffmann, Axel; Bhattacharya, Anand

    2016-03-04

    We report on the observation of the spin Seebeck effect in antiferromagnetic MnF_{2}. A device scale on-chip heater is deposited on a bilayer of MnF_{2} (110) (30  nm)/Pt (4 nm) grown by molecular beam epitaxy on a MgF_{2} (110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF_{2} 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 (>9  T) are applied parallel to the easy axis of the MnF_{2} thin film. When the magnetic field is applied perpendicular to the easy axis, the spin-flop transition is absent, as expected.

  4. Antiferromagnetic Spin Seebeck Effect

    NASA Astrophysics Data System (ADS)

    Wu, Stephen M.; Zhang, Wei; KC, Amit; Borisov, Pavel; Pearson, John E.; Jiang, J. Samuel; Lederman, David; Hoffmann, Axel; Bhattacharya, Anand

    2016-03-01

    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) (30 nm )/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 (>9 T ) 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.

  5. Spin dynamics and magnetic correlation length in two-dimensional quantum heisenberg antiferromagnets

    PubMed

    Carretta; Ciabattoni; Cuccoli; Mognaschi; Rigamonti; Tognetti; Verrucchi

    2000-01-10

    The correlated spin dynamics and temperature dependence of the correlation length xi(T) in two-dimensional quantum (S = 1/2) Heisenberg antiferromagnets (2DQHAF) on a square lattice are discussed in light of experimental results of proton spin lattice relaxation in copper formiate tetradeuterate. In this compound the exchange constant is much smaller than the one in recently studied 2DQHAF, such as La2CuO4 and Sr2CuO2Cl2. Thus the spin dynamics can be probed in detail over a wider temperature range. The NMR relaxation rates turn out to be in excellent agreement with a theoretical mode-coupling calculation. The deduced temperature behavior of xi(T) is in agreement with high-temperature expansions, quantum Monte Carlo simulations, and the pure quantum self-consistent harmonic approximation. Contrary to the predictions of the theories based on the nonlinear sigma model, no evidence of crossover between different quantum regimes is observed.

  6. Spin reorientation via antiferromagnetic coupling

    SciTech Connect

    Ranjbar, M.; Sbiaa, R.; Dumas, R. K.; Åkerman, J.; Piramanayagam, S. N.

    2014-05-07

    Spin reorientation in antiferromagnetically coupled (AFC) Co/Pd multilayers, wherein the thickness of the constituent Co layers was varied, was studied. AFC-Co/Pd multilayers were observed to have perpendicular magnetic anisotropy even for a Co sublayer thickness of 1 nm, much larger than what is usually observed in systems without antiferromagnetic coupling. When similar multilayer structures were prepared without antiferromagnetic coupling, this effect was not observed. The results indicate that the additional anisotropy energy contribution arising from the antiferromagnetic coupling, which is estimated to be around 6 × 10{sup 6} ergs/cm{sup 3}, induces the spin-reorientation.

  7. Spin diffusion and torques in disordered antiferromagnets

    NASA Astrophysics Data System (ADS)

    Manchon, Aurelien

    2017-03-01

    We have developed a drift-diffusion equation of spin transport in collinear bipartite metallic antiferromagnets. Starting from a model tight-binding Hamiltonian, we obtain the quantum kinetic equation within Keldysh formalism and expand it to the lowest order in spatial gradient using Wigner expansion method. In the diffusive limit, these equations track the spatio-temporal evolution of the spin accumulations and spin currents on each sublattice of the antiferromagnet. We use these equations to address the nature of the spin transfer torque in (i) a spin-valve composed of a ferromagnet and an antiferromagnet, (ii) a metallic bilayer consisting of an antiferromagnet adjacent to a heavy metal possessing spin Hall effect, and in (iii) a single antiferromagnet possessing spin Hall effect. We show that the latter can experience a self-torque thanks to the non-vanishing spin Hall effect in the antiferromagnet.

  8. Spin diffusion and torques in disordered antiferromagnets.

    PubMed

    Manchon, Aurelien

    2017-03-15

    We have developed a drift-diffusion equation of spin transport in collinear bipartite metallic antiferromagnets. Starting from a model tight-binding Hamiltonian, we obtain the quantum kinetic equation within Keldysh formalism and expand it to the lowest order in spatial gradient using Wigner expansion method. In the diffusive limit, these equations track the spatio-temporal evolution of the spin accumulations and spin currents on each sublattice of the antiferromagnet. We use these equations to address the nature of the spin transfer torque in (i) a spin-valve composed of a ferromagnet and an antiferromagnet, (ii) a metallic bilayer consisting of an antiferromagnet adjacent to a heavy metal possessing spin Hall effect, and in (iii) a single antiferromagnet possessing spin Hall effect. We show that the latter can experience a self-torque thanks to the non-vanishing spin Hall effect in the antiferromagnet.

  9. Antiferromagnetic spin flop and exchange bias

    NASA Astrophysics Data System (ADS)

    Nogués, J.; Morellon, L.; Leighton, C.; Ibarra, M. R.; Schuller, Ivan K.

    2000-03-01

    The effect of the antiferromagnetic spin flop on exchange bias has been investigated in antiferromagnetic (MnF2)-ferromagnetic (Fe) bilayers. Cooling and measuring in fields larger than the antiferromagnetic spin-flop field, HSF, causes an irreversible reduction of the magnitude of the exchange bias field, HE. This indicates that, contrary to what is normally assumed, the interface spin structure does not remain ``frozen in'' below TN if large enough fields are applied.

  10. Spin-transfer torque induced spin waves in antiferromagnetic insulators

    SciTech Connect

    Daniels, Matthew W.; Guo, Wei; Stocks, George Malcolm; Xiao, Di; Xiao, Jiang

    2015-01-01

    We explore the possibility of exciting spin waves in insulating antiferromagnetic films by injecting spin current at the surface. We analyze both magnetically compensated and uncompensated interfaces. We find that the spin current induced spin-transfer torque can excite spin waves in insulating antiferromagnetic materials and that the chirality of the excited spin wave is determined by the polarization of the injected spin current. Furthermore, the presence of magnetic surface anisotropy can greatly increase the accessibility of these excitations.

  11. Paramagnetic and Antiferromagnetic Spin Seebeck Effect

    NASA Astrophysics Data System (ADS)

    Wu, Stephen

    We report on the observation of the longitudinal spin Seebeck effect in both antiferromagnetic and paramagnetic insulators. By using a microscale on-chip local heater, it is possible to generate a large thermal gradient confined to the chip surface without a large increase in the total sample temperature. This technique allows us to easily access low temperatures (200 mK) and high magnetic fields (14 T) through conventional dilution refrigeration and superconducting magnet setups. By exploring this regime, we detect the spin Seebeck effect through the spin-flop transition in antiferromagnetic MnF2 when a large magnetic field (>9 T) is applied along the easy axis direction. Using the same technique, we are also able to resolve a spin Seebeck effect from the paramagnetic phase of geometrically frustrated antiferromagnet Gd3Ga5O12 (gadolinium gallium garnet) and antiferromagnetic DyScO3 (DSO). Since these measurements occur above the ordering temperatures of these two materials, short-range magnetic order is implicated as the cause of the spin Seebeck effect in these systems. The discovery of the spin Seebeck effect in these two materials classes suggest that both antiferromagnetic spin waves and spin excitations from short range magnetic order may be used to generate spin current from insulators and that the spin wave spectra of individual materials are highly important to the specifics of the longitudinal spin Seebeck effect. Since insulating antiferromagnets and paramagnets are far more common than the typical insulating ferrimagnetic materials used in spin Seebeck experiments, this discovery opens up a large new class of materials for use in spin caloritronic devices. All authors acknowledge support of the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), Materials Sciences and Engineering Division. The use of facilities at the Center for Nanoscale Materials, was supported by the U.S. DOE, BES under Contract No. DE-AC02-06CH11357.

  12. Antiferromagnetic Spin Ice Correlations at (1/2,1/2,1/2) in the Ground State of the Pyrochlore Magnet Tb2Ti2O7

    NASA Astrophysics Data System (ADS)

    Fritsch, K.; Ross, K. A.; Qiu, Y.; Copley, J. R. D.; Guidi, T.; Bewley, R. I.; Dabkowska, H. A.; Gaulin, B. D.

    2013-03-01

    The ground state of the candidate spin liquid pyrochlore magnet Tb2Ti2O7 (TTO) has been long debated. Despite theoretical expectations of magnetic order below 1K based on classical Ising-like Tb spins, muSR and neutron scattering experiments show no long range order down to 50mK. Two theoretical scenarios have been put forward to account for this: the quantum spin ice scenario and a non-magnetic singlet ground state, but no clear consensus has been reached. We present neutron scattering measurements on TTO at 70mK that reveal elastic scattering intensity at (1/2,1/2,1/2) positions in reciprocal space. The corresponding spin configuration can be modeled as a short-range antiferromagnetically ordered spin ice, in which spins obey a variant of the ice rules in each unit cell, and flip directions between adjacent cells. At low temperatures, this elastic scattering is separated from low-lying magnetic inelastic scattering by ~0.05meV. The elastic signal disappears under the application of small magnetic fields and upon elevating temperature. Pinch-point-like elastic diffuse scattering is observed, which together with the elastic spin ice correlations strongly supports the quantum spin ice picture for TTO.

  13. Antiferromagnetic Spin Wave Field-Effect Transistor

    DOE PAGES

    Cheng, Ran; Daniels, Matthew W.; Zhu, Jian-Gang; ...

    2016-04-06

    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. In conclusion, our findings open up the exciting possibilitymore » of digital data processing utilizing antiferromagnetic spin waves and enable the direct projection of optical computing concepts onto the mesoscopic scale.« less

  14. Antiferromagnetic Spin Wave Field-Effect Transistor

    SciTech Connect

    Cheng, Ran; Daniels, Matthew W.; Zhu, Jian-Gang; Xiao, Di

    2016-04-06

    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. In conclusion, 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.

  15. Antiferromagnetic Spin Wave Field-Effect Transistor

    PubMed Central

    Cheng, Ran; Daniels, Matthew W.; Zhu, Jian-Gang; Xiao, Di

    2016-01-01

    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. PMID:27048928

  16. Antiferromagnetic domain wall motion driven by spin-orbit torques

    PubMed Central

    Shiino, Takayuki; Oh, Se-Hyeok; Haney, Paul M.; Lee, Seo-Won; Go, Gyungchoon; Park, Byong-Guk; Lee, Kyung-Jin

    2016-01-01

    We theoretically investigate dynamics of antiferromagnetic domain walls driven by spin-orbit torques in antiferromagnet/heavy metal bilayers. We show that spin-orbit torques drive antiferromagnetic domain walls much faster than ferromagnetic domain walls. As the domain wall velocity approaches the maximum spin-wave group velocity, the domain wall undergoes Lorentz contraction and emits spin-waves in the terahertz frequency range. The interplay between spin-orbit torques and the relativistic dynamics of antiferromagnetic domain walls leads to the efficient manipulation of antiferromagnetic spin textures and paves the way for the generation of high frequency signals from antiferromagnets. PMID:27588878

  17. Magnon Spin Nernst Effect in Antiferromagnets

    NASA Astrophysics Data System (ADS)

    Zyuzin, Vladimir A.; Kovalev, Alexey A.

    2016-11-01

    We predict that a temperature gradient can induce a magnon-mediated spin Hall response in an antiferromagnet with nontrivial magnon Berry curvature. We develop a linear response theory which gives a general condition for a Hall current to be well defined, even when the thermal Hall response is forbidden by symmetry. We apply our theory to a honeycomb lattice antiferromagnet and discuss a role of magnon edge states in a finite geometry.

  18. Spin transfer in antiferromagnets (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Moriyama, Takahiro

    2016-10-01

    Since antiferromagnets (AFMs) have no spontaneous magnetization unlike ferromagnetic materials, it is not easy to manipulate the magnetic moments in AFMs by external magnetic field. However, recent theoretical studies suggest that it is possible to manipulate the magnetization in AFMs by spin-transfer-torque in a similar manner to ferromagnetic materials. In this study, we perform spin-toque ferromagnetic resonance (ST-FMR) measurements on FeNi/NiO/Pt multilayers to experimentally investigate the interaction between the spin current and the magnetic moments of antiferromagnetic NiO. The spin current is injected to the NiO by the spin Hall effect in Pt. The monotonous change in the FMR linewidth of this system with respect to the spin current can be interpreted in a way that the spin current is transferred through the NiO and interacts with the FeNi. This intriguing spin current transport can be explained by the angular momentum transfer mediated by the antiferromagnetic magnons. The results assure that the spin current exerts a torque on the NiO magnetic moments and excites their dynamics. In the talk, recent results will be also discussed.

  19. Excitations in a four-leg antiferromagnetic Heisenberg spin tube

    SciTech Connect

    Garlea, Vasile O; Zheludev, Andrey I; Regnault, L.-P.; Chung, J.-H.; Qiu, Y.; Boehm, Martin; Habicht, Klaus; Meissner, Michael

    2008-01-01

    Inelastic neutron scattering is used to investigate magnetic excitations in the quasi-one-dimensional quantum spin-liquid system Cu$_2$Cl$_{4}\\cdot$ D$_8$C$_4$SO$_2$. Contrary to previously conjectured models that relied on bond-alternating nearest neighbor interactions in the spin chains, the dominant interactions are actually next-nearest-neighbor in-chain antiferromagnetic couplings. The appropriate Heisenberg Hamiltonian is equivalent to that of a $S=1/2$ 4-leg spin-tube with almost perfect one dimensionality and no bond alternation. A partial geometric frustration of rung interactions induces a small incommensurability of short-range spin correlations.

  20. Excitations in a Four-Leg Antiferromagnetic Heisenberg Spin Tube,

    SciTech Connect

    Garlea, Vasile O; Zheludev, Andrey I; Regnault, L.-P.; Chung, J.-H.; Qiu, Y.; Boehm, Martin; Habicht, Klaus; Meissner, Michael; Fernandez-Baca, Jaime A

    2008-01-01

    Inelastic neutron scattering is used to investigate magnetic excitations in the quasi-one-dimensional quantum spin-liquid system Cu2Cl4 D8C4SO2. Contrary to previously conjectured models that relied on bond-alternating nearest-neighbor interactions in the spin chains, the dominant interactions are actually next-nearest-neighbor in-chain antiferromagnetic couplings. The appropriate Heisenberg Hamiltonian is equivalent to that of a S 1=2 4-leg spin-tube with almost perfect one dimensionality and no bond alternation. A partial geometric frustration of rung interactions induces a small incommensurability of short-range spin correlations.

  1. Excitations in a four-leg antiferromagnetic Heisenberg spin tube.

    PubMed

    Garlea, V O; Zheludev, A; Regnault, L-P; Chung, J-H; Qiu, Y; Boehm, M; Habicht, K; Meissner, M

    2008-01-25

    Inelastic neutron scattering is used to investigate magnetic excitations in the quasi-one-dimensional quantum spin-liquid system Cu(2)Cl(4).D(8)C(4)SO(2). Contrary to previously conjectured models that relied on bond-alternating nearest-neighbor interactions in the spin chains, the dominant interactions are actually next-nearest-neighbor in-chain antiferromagnetic couplings. The appropriate Heisenberg Hamiltonian is equivalent to that of a S=1/2 4-leg spin-tube with almost perfect one dimensionality and no bond alternation. A partial geometric frustration of rung interactions induces a small incommensurability of short-range spin correlations.

  2. High-Tc spin superfluidity in antiferromagnets.

    PubMed

    Bunkov, Yu M; Alakshin, E M; Gazizulin, R R; Klochkov, A V; Kuzmin, V V; L'vov, V S; Tagirov, M S

    2012-04-27

    We report the observation of the unusual behavior of induction decay signals in antiferromagnetic monocrystals with Suhl-Nakamura interactions. The signals show the formation of the Bose-Einstein condensation (BEC) of magnons and the existence of spin supercurrent, in complete analogy with the spin superfluidity in the superfluid (3)He and the atomic BEC of quantum gases. In the experiments described here, the temperature of the magnon BEC is a thousand times larger than in the superfluid (3)He. It opens a possibility to apply the spin supercurrent for various magnetic spintronics applications.

  3. Coexistence of antiferromagnetic and ferromagnetic spin correlations in SrCo2As2 revealed by 59Co and 75As NMR

    DOE PAGES

    Wiecki, P.; Ogloblichev, V.; Pandey, Abhishek; ...

    2015-06-15

    In nonsuperconducting, metallic paramagnetic SrCo2As2, inelastic neutron scattering measurements have revealed strong stripe-type q=(π,0) antiferromagnetic (AFM) spin correlations. Using nuclear magnetic resonance (NMR) measurements on 59Co and 75As nuclei, we demonstrate that stronger ferromagnetic (FM) spin correlations coexist in SrCo2As2. Our NMR data are consistent with density functional theory (DFT) calculations which show enhancements at both q=(π,0) and the in-plane FM q=0 wave vectors in static magnetic susceptibility χ(q). We suggest that the strong FM fluctuations prevent superconductivity in SrCo2As2, despite the presence of stripe-type AFM fluctuations. Since DFT calculations have consistently revealed similar enhancements of the χ(q) at bothmore » q=(π,0) and q=0 in the iron-based superconductors and parent compounds, our observation of FM correlations in SrCo2As2 calls for detailed studies of FM correlations in the iron-based superconductors.« less

  4. Antiferromagnetic spin correlations and pseudogaplike behavior in Ca(Fe1-xCox)2As2 studied by 75As nuclear magnetic resonance and anisotropic resistivity

    DOE PAGES

    Cui, J.; Roy, B.; Tanatar, M. A.; ...

    2015-11-06

    We report 75As nuclear magnetic resonance (NMR) measurements of single-crystalline Ca(Fe1–xCox)2As2 (x=0.023, 0.028, 0.033, and 0.059) annealed at 350°C for 7 days. From the observation of a characteristic shape of 75As NMR spectra in the stripe-type antiferromagnetic (AFM) state, as in the case of x=0 (TN=170 K), clear evidence for the commensurate AFM phase transition with the concomitant structural phase transition is observed in x=0.023 (TN=106 K) and x=0.028 (TN=53 K). Through the temperature dependence of the Knight shifts and the nuclear spin lattice relaxation rates (1/T1), although stripe-type AFM spin fluctuations are realized in the paramagnetic state as inmore » the case of other iron pnictide superconductors, we found a gradual decrease of the AFM spin fluctuations below a crossover temperature T* that was nearly independent of Co-substitution concentration, and it is attributed to a pseudogaplike behavior in the spin excitation spectra of these systems. The T* feature finds correlation with features in the temperature-dependent interplane resistivity, ρc(T), but not with the in-plane resistivity ρa(T). The temperature evolution of anisotropic stripe-type AFM spin fluctuations is tracked in the paramagnetic and pseudogap phases by the 1/T1 data measured under magnetic fields parallel and perpendicular to the c axis. As a result, based on our NMR data, we have added a pseudogaplike phase to the magnetic and electronic phase diagram of Ca(Fe1–xCox)2As2.« less

  5. Spin Seebeck Effect Signals from Antiferromagnets

    NASA Astrophysics Data System (ADS)

    Prakash, Arati; Brangham, Jack; Yang, Fengyuan; Heremans, Joseph

    The Longitudinal Spin Seebeck Effect (LSSE), in which a heat current stimulates spin propagation across an interface between a magnetic material and a normal metal, is well established and observed in ferromagnetic systems. Data have been presented indicating that antiferromagnetic systems could also give rise to LSSE signals. We report here on LSSE signal measured on the Pt/NiO/YIG structure, where NiO is an antiferromagnet. This system is reported to exhibit antiferromagnonic transport. We explore the dependence of the signal on the thickness of the NiO and YIG layers. We also report its temperature dependence, which was not explored before. The results are interpreted in terms of the temperature dependence of the magnon density of states. It appears that magnon modes with energies below about 40 K are most involved in the process, as was the case to the LSSE on YIG itself. Preliminary results using other antiferromagnets and other inverse spin-Hall layers look promising and will also be reported Work supported by ARO- MURI W911NF-14-1-0016.

  6. Spin supercurrent in the canted antiferromagnetic phase

    NASA Astrophysics Data System (ADS)

    Hama, Yusuke; Tsitsishvili, George; Ezawa, Zyun F.

    2013-03-01

    The spin and layer (pseudospin) degrees of freedom are entangled coherently in the canted antiferromagnetic phase of the bilayer quantum Hall system at the filling factor ν=2. A complex Goldstone mode emerges describing such a combined degree of freedom. In the zero tunneling-interaction limit (ΔSAS→0), its phase field provokes a supercurrent carrying both spin and charge within each layer. The Hall resistance is predicted to become anomalous precisely as in the ν=1 bilayer system in the counterflow and drag experiments. Furthermore, it is shown that the total current flowing in the bilayer system is a supercurrent carrying solely spins in the counterflow geometry. It is intriguing that all these phenomena occur only in imbalanced bilayer systems.

  7. Nonequilibrium antiferromagnetic mixed-spin Ising model.

    PubMed

    Godoy, Mauricio; Figueiredo, Wagner

    2002-09-01

    We studied an antiferromagnetic mixed-spin Ising model on the square lattice subject to two competing stochastic processes. The model system consists of two interpenetrating sublattices of spins sigma=1/2 and S=1, and we take only nearest neighbor interactions between pairs of spins. The system is in contact with a heat bath at temperature T, and the exchange of energy with the heat bath occurs via one-spin flip (Glauber dynamics). Besides, the system interacts with an external agency of energy, which supplies energy to it whenever two nearest neighboring spins are simultaneously flipped. By employing Monte Carlo simulations and a dynamical pair approximation, we found the phase diagram for the stationary states of the model in the plane temperature T versus the competition parameter between one- and two-spin flips p. We observed the appearance of three distinct phases, that are separated by continuous transition lines. We also determined the static critical exponents along these lines and we showed that this nonequilibrium model belongs to the universality class of the two-dimensional equilibrium Ising model.

  8. Spin Seebeck effect through antiferromagnetic NiO

    NASA Astrophysics Data System (ADS)

    Prakash, Arati; Brangham, Jack; Yang, Fengyuan; Heremans, Joseph P.

    2016-07-01

    We report temperature-dependent spin Seebeck measurements on Pt/YIG bilayers and Pt/NiO/YIG trilayers, where YIG (yttrium iron garnet, Y3F e5O12 ) is an insulating ferrimagnet and NiO is an antiferromagnet at low temperatures. The thickness of the NiO layer is varied from 0 to 10 nm. In the Pt/YIG bilayers, the temperature gradient applied to the YIG stimulates dynamic spin injection into the Pt, which generates an inverse spin Hall voltage in the Pt. The presence of a NiO layer dampens the spin injection exponentially with a decay length of 2 ± 0.6 nm at 180 K. The decay length increases with temperature and shows a maximum of 5.5 ± 0.8 nm at 360 K. The temperature dependence of the amplitude of the spin Seebeck signal without NiO shows a broad maximum of 6.5 ± 0.5 μV/K at 20 K. In the presence of NiO, the maximum shifts sharply to higher temperatures, likely correlated to the increase in decay length. This implies that NiO is most transparent to magnon propagation near the paramagnet-antiferromagnet transition. We do not see the enhancement in spin current driven into Pt reported in other papers when 1-2 nm NiO layers are sandwiched between Pt and YIG.

  9. Spin-dynamics simulations of the antiferromagnetic triangular XY model*

    NASA Astrophysics Data System (ADS)

    Nho, Kwangsik; Landau, D. P.

    2002-03-01

    Using Monte Carlo and spin-dynamics methods, we have simulated the dynamic behavior of the classical, antiferromagnetic XY model on a triangular lattice. The temporal evolutions of spin configurations were obtained by solving numerically the coupled equations of motion for each spin using fourth-order Suzuki-Trotter decompositions of exponential operators. From space-and time-displaced spin-spin correlation functions and their space-time Fourier transforms we obtained the dynamic structure factor S(q,w) for momentum q and frequency w. Below T_c, where long-range order appears in the staggered chirality[1], S(q,w) exhibits very strong and sharp spin-wave peaks in the in-plane-component S^xx. We also observe two-spin-wave peaks at low w and an almost dispersionless domain-wall peak at high w. Above T_c, a weak spin-wave peak persists but the domain-wall peak disappears for all q. We have calculated the dispersion relation and the linewidth of the spin-wave peak in S^xx by fitting the line shape to simple Lorentzians. *Supported by NSF [1] D.H. Lee, J.D. Joannopoulos, J.W. Negele, and D.P. Landau, Phys. Rev. Lett. 52, 433 (1984)

  10. Spin transport through the metallic antiferromagnet FeMn

    NASA Astrophysics Data System (ADS)

    Saglam, H.; Zhang, W.; Jungfleisch, M. B.; Sklenar, J.; Pearson, J. E.; Ketterson, J. B.; Hoffmann, A.

    2016-10-01

    We investigate spin transport through metallic antiferromagnets using measurements based on spin pumping combined with inverse spin Hall effects in N i80F e20/FeMn /W trilayers. The relatively large magnitude and opposite sign of spin Hall effects in W compared to FeMn enable an unambiguous detection of spin currents transmitted through the entire FeMn layer thickness. Using this approach we can detect two distinctively different spin transport regimes, which we associate with electronic and magnonic spin currents, respectively. The latter can extend to relatively large distances (≈9 nm) and is enhanced when the antiferromagnetic ordering temperature is close to the measurement temperature.

  11. All electrical manipulation of magnetization dynamics in a ferromagnet by antiferromagnets with anisotropic spin Hall effects.

    SciTech Connect

    Zhang, Wei; Jungfleisch, Matthias B.; Freimuth, Frank; Jiang, Wanjun; Sklenar, Joseph; Pearson, John E.; Ketterson, John B.; Mokrousov, Yuri; Hoffmann, Axel

    2015-10-06

    We investigate spin-orbit torques of metallic CuAu-I-type antiferromagnets using spin-torque ferromagnetic resonance tuned by a dc-bias current. The observed spin torques predominantly arise from diffusive transport of spin current generated by the spin Hall effect. We find a growth-orientation dependence of the spin torques by studying epitaxial samples, which may be correlated to the anisotropy of the spin Hall effect. The observed anisotropy is consistent with first-principles calculations on the intrinsic spin Hall effect. Our work suggests large tunable spin-orbit effects in magnetically-ordered materials.

  12. Dynamics of antiferromagnetic skyrmion driven by the spin Hall effect

    NASA Astrophysics Data System (ADS)

    Jin, Chendong; Song, Chengkun; Wang, Jianbo; Liu, Qingfang

    2016-10-01

    Magnetic skyrmion moved by the spin-Hall effect is promising for the application of the generation racetrack memories. However, the Magnus force causes a deflected motion of skyrmion, which limits its application. Here, we create an antiferromagnetic skyrmion by injecting a spin-polarized pulse in the nanostripe and investigate the spin Hall effect-induced motion of antiferromagnetic skyrmion by micromagnetic simulations. In contrast to ferromagnetic skyrmion, we find that the antiferromagnetic skyrmion has three evident advantages: (i) the minimum driving current density of antiferromagnetic skyrmion is about two orders smaller than the ferromagnetic skyrmion; (ii) the velocity of the antiferromagnetic skyrmion is about 57 times larger than the ferromagnetic skyrmion driven by the same value of current density; (iii) antiferromagnetic skyrmion can be driven by the spin Hall effect without the influence of Magnus force. In addition, antiferromagnetic skyrmion can move around the pinning sites due to its property of topological protection. Our results present the understanding of antiferromagnetic skyrmion motion driven by the spin Hall effect and may also contribute to the development of antiferromagnetic skyrmion-based racetrack memories.

  13. Chiral Magnetic Effect and Anomalous Hall Effect in Antiferromagnetic Insulators with Spin-Orbit Coupling.

    PubMed

    Sekine, Akihiko; Nomura, Kentaro

    2016-03-04

    We search for dynamical magnetoelectric phenomena in three-dimensional correlated systems with spin-orbit coupling. We focus on the antiferromagnetic insulator phases where the dynamical axion field is realized by the fluctuation of the antiferromagnetic order parameter. It is shown that the dynamical chiral magnetic effect, an alternating current generation by magnetic fields, emerges due to such time dependences of the order parameter as antiferromagnetic resonance. It is also shown that the anomalous Hall effect arises due to such spatial variations of the order parameter as antiferromagnetic domain walls. Our study indicates that spin excitations in antiferromagnetic insulators with spin-orbit coupling can result in nontrivial charge responses. Moreover, observing the chiral magnetic effect and anomalous Hall effect in our system is equivalent to detecting the dynamical axion field in condensed matter.

  14. Observation of antiferromagnetic correlations in UBe 13

    NASA Astrophysics Data System (ADS)

    Neumann, K. U.; Capellmann, H.; Fisk, Z.; Smith, J. L.; Ziebeck, K. R. A.

    1986-11-01

    The wavevector and energy dependence of the paramagnetic response in the normal phase of the Heavy Fermion system UBe 13 has been investigated between 10 K and 300 K using polarized neutrons and polarization analysis. At 10 K the response was found to be enhanced at non zero wave-vectors indicating the presence of strong antiferromagnetic correlations. The peaks in the scattering occured at positions expected for incipient type G antiferromagnetism of the simple cubic uranium sublattice. At room temperature the spatial correlations completely disappeared and the response was wave vector independent. Constant Q scans carried out at 10 K confirmed the Lorentzian dependence proposed by Goldman et al. [1].

  15. Spin Nernst Effect of Magnons in Collinear Antiferromagnets

    NASA Astrophysics Data System (ADS)

    Cheng, Ran; Okamoto, Satoshi; Xiao, Di

    2016-11-01

    In a collinear antiferromagnet with easy-axis anisotropy, symmetry guarantees that the spin wave modes are doubly degenerate. The two modes carry opposite spin angular momentum and exhibit opposite chirality. Using a honeycomb antiferromagnet in the presence of the Dzyaloshinskii-Moriya interaction, we show that a longitudinal temperature gradient can drive the two modes to opposite transverse directions, realizing a spin Nernst effect of magnons with vanishing thermal Hall current. We find that magnons around the Γ point and the K point contribute oppositely to the transverse spin transport, and their competition leads to a sign change of the spin Nernst coefficient at finite temperature. Possible material candidates are discussed.

  16. Spin liquids and spin dynamics in kagome antiferromagnets

    NASA Astrophysics Data System (ADS)

    Mendels, Philippe

    2006-03-01

    Among all the corner sharing highly frustrated magnets, only a few experimental systems are good candidates for a low-T fluctuating state, ie fulfilling the important conditions of the pure Heisenberg lattice with nn couplings. The combination of the weakness of the single-ion anisotropy and of a direct overlap antiferromagnetic exchange are certainly the major advantages of the chromate S=3/2 kagome bilayer Ba2Sn2ZnGa10-7pCr7pO22- BSZCGO(p)- and the long studied SrCr9pGa12-9pO19 - SCGO(p). Beyond the absence of ordering well below the Curie-Weiss temperature, the unusual large value of the specific heat unveils a high density of low lying excitations and its field independence suggests that the excited states are mostly singlets. Moreover, their ground state is found essentially fluctuating although an intrinsic spin glass (SG) signature is observed in susceptibility measurements. Through a review of our past years work, I'll illustrate all the potential of local studies (NMR and μSR) to reveal some key aspects of the physics of these compounds: susceptibility, fluctuations, impact of dilution defects which generate an extended response of the spin-lattice ... as well as the puzzling spin-glass state. More recently we also investigated new series of compounds, among them volborthite and delafossites which feature S=1/2 spins on a corner sharing antiferromagnetic lattice. I'll introduce these compounds and shortly discuss their relation to ideal Hamiltonians and novel features. - D. Bono et al.Phys. Rev. Lett. 93, 187201 (2004), 92, 217202 (2004) ; Cond-mat/0503496. F. Bert et al. Phys. Rev. Lett., 95, 087203 (2005). L. Limot, et al., Phys. Rev. B, 65, 132403 (2002). P. Mendels et al. Phys. Rev. Lett., 85, 3496 (2000).

  17. Thermalization of a dimerized antiferromagnetic spin chain.

    PubMed

    Konstantinidis, N P

    2016-01-20

    Thermalization is investigated for the one-dimensional anisotropic antiferromagnetic Heisenberg model with dimerized nearest-neighbor interactions that break integrability. For this purpose the time evolution of local operator expectation values after an interacting quench is calculated directly with the Chebyshev polynomial expansion, and the deviation of the diagonal from the canonical thermal ensemble value is calculated for increasing system size for these operators. The spatial and spin symmetries of the Hamiltonian are taken into account to divide it into symmetry subsectors. The rate of thermalization is found to weaken with the dimerization parameter as the Hamiltonian evolves between two integrable limits, the non-dimerized and the fully dimerized where the chain breaks up into isolated dimers. This conclusion is supported by the distribution of the local operator off-diagonal elements between the eigenstates of the Hamiltonian with respect to their energy difference, which determines the strength of temporal fluctuations. The off-diagonal elements have a low-energy peak for small dimerization which facilitates thermalization, and originates in the reduction of spatial symmetry with respect to the non-dimerized limit. For increasing dimerization their distribution changes and develops a single low-energy maximum that relates to the fully dimerized limit and slows down thermalization.

  18. Spin excitations in the antiferromagnet NaNiO2

    NASA Astrophysics Data System (ADS)

    de Brion, S.; Darie, C.; Holzapfel, M.; Talbayev, D.; Mihály, L.; Simon, F.; Jánossy, A.; Chouteau, G.

    2007-03-01

    In NaNiO2 , Ni3+ ions form a quasi-two-dimensional triangular lattice of S=1/2 spins. The magnetic order observed below 20K has been described as an A type antiferromagnet with ferromagnetic layers weakly coupled antiferromagnetically. We studied the magnetic excitations with the electron spin resonance for frequencies 1-20cm-1 , in magnetic fields up to 14T . The bulk of the results are interpreted in terms of a phenomenological model involving biaxial anisotropy for the spins: a strong easy-plane term, and a weaker anisotropy within the plane.

  19. Spin Excitations in the Antiferromagnet NaNiO2

    SciTech Connect

    de Brion,S.; Darie, C.; Holzapfel, M.; Talbayev, D.; Mihaly, L.; Simon, F.; Janossy, A.; Chouteau, G.

    2007-01-01

    In NaNiO2 , Ni3+ ions form a quasi-two-dimensional triangular lattice of S=1/2 spins. The magnetic order observed below 20K has been described as an A type antiferromagnet with ferromagnetic layers weakly coupled antiferromagnetically. We studied the magnetic excitations with the electron spin resonance for frequencies 1 20cm-1 , in magnetic fields up to 14T . The bulk of the results are interpreted in terms of a phenomenological model involving biaxial anisotropy for the spins: a strong easy-plane term, and a weaker anisotropy within the plane

  20. Magnetization damping in noncollinear spin valves with antiferromagnetic interlayer couplings

    NASA Astrophysics Data System (ADS)

    Chiba, Takahiro; Bauer, Gerrit E. W.; Takahashi, Saburo

    2015-08-01

    We study the magnetic damping in the simplest of synthetic antiferromagnets, i.e., antiferromagnetically exchange-coupled spin valves, in the presence of applied magnetic fields that enforce noncolliear magnetic configurations. We formulate the dynamic exchange of spin currents in a noncollinear texture based on the spin-diffusion theory with quantum mechanical boundary conditions at the ferrromagnet/normal-metal interfaces and derive the Landau-Lifshitz-Gilbert equations coupled by the interlayer static and dynamic exchange interactions. We predict noncollinearity-induced additional damping that is modulated by an applied magnetic field. We compare theoretical results with published experiments.

  1. Spin excitations and thermodynamics of the antiferromagnetic Heisenberg model on the layered honeycomb lattice

    NASA Astrophysics Data System (ADS)

    Vladimirov, Artem A.; Ihle, Dieter; Plakida, Nikolay M.

    2017-03-01

    We present a spin-rotation-invariant Green-function theory for the dynamic spin susceptibility in the spin-1/2 antiferromagnetic Heisenberg model on a stacked honeycomb lattice. Employing a generalized mean-field approximation for arbitrary temperatures, the thermodynamic quantities (two-spin correlation functions, internal energy, magnetic susceptibility, staggered magnetization, Néel temperature, correlation length) and the spin-excitation spectrum are calculated by solving a coupled system of self-consistency equations for the correlation functions. The temperature dependence of the magnetic (uniform static) susceptibility is ascribed to antiferromagnetic short-range order. The Néel temperature is calculated for arbitrary interlayer couplings. Our results are in a good agreement with numerical computations for finite clusters and with available experimental data on the β-Cu2V2O2 compound.

  2. Ultrafast band engineering and transient spin currents in antiferromagnetic oxides

    DOE PAGES

    Gu, Mingqiang; Rondinelli, James M.

    2016-04-29

    Here, we report a dynamic structure and band engineering strategy with experimental protocols to induce indirect-to-direct band gap transitions and coherently oscillating pure spin-currents in three-dimensional antiferromagnets (AFM) using selective phononic excitations. In the Mott insulator 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 inmore » 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.« less

  3. Ultrafast Band Engineering and Transient Spin Currents in Antiferromagnetic Oxides

    PubMed Central

    Gu, Mingqiang; Rondinelli, James M.

    2016-01-01

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

  4. Ultrafast Band Engineering and Transient Spin Currents in Antiferromagnetic Oxides

    NASA Astrophysics Data System (ADS)

    Gu, Mingqiang; Rondinelli, James M.

    2016-04-01

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

  5. Ultrafast band engineering and transient spin currents in antiferromagnetic oxides

    SciTech Connect

    Gu, Mingqiang; Rondinelli, James M.

    2016-04-29

    Here, we report a dynamic structure and band engineering strategy with experimental protocols to induce indirect-to-direct band gap transitions and coherently oscillating pure spin-currents in three-dimensional antiferromagnets (AFM) using selective phononic excitations. In the Mott insulator 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.

  6. Spin injection and absorption in antiferromagnets (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Frangou, Lamprini; Merodio, Pablo; Ghosh, Abhijit; Oyarzun, Simon; Auffret, Stephane; Ebels, Ursula; Chshiev, Mair; Bea, Helene; Vila, Laurent; Bailey, William E.; Gambarelli, Serge; Baltz, Vincent

    2016-10-01

    The antiferromagnetic order is expected to have a high potential in next-generation spintronic applications. It is resistant to perturbation by magnetic fields, produces no stray fields, displays ultrafast dynamics and may generate large magneto-transport effects. In spintronic materials, spin currents are key to unravelling spin dependent transport phenomena. Here, spin pumping results from the non-equilibrium magnetization dynamics of a ferromagnetic spin injector, which pumps a spin current into an adjacent spin sink. This spin sink absorbs the current to an extent which depends on its spin-dependent properties. The properties of the spin sink can be recorded either through the changes induced in ferromagnetic damping or through direct electrical means, such as by measuring the inverse spin Hall voltage. In this talk, we will deal with the injection of a spin current in thin antiferromagnetic sinks. Measurements of the spin penetration depths and absorption mechanisms were obtained for polycrystalline Ir20Mn80 and Fe50Mn50 films (Appl. Phys. Lett. 104, 032406 (2014)). More interestingly, spins propagate more efficiently in layers where the magnetic order is fluctuating rather than static. The experimental data were compared to some of the recently developed theories and converted into interfacial spin mixing conductance enhancements. These findings help us progress towards the development of more efficient spin sources, while also providing an alternative method to probe magnetic phase transitions (Phys. Rev. Lett. in press (2016)). This type of alternative method is particularly needed to deal with the case of thin materials with no net magnetic moments, such as thin antiferromagnets.

  7. Spin dynamics simulations for a nanoscale Heisenberg antiferromagnet

    NASA Astrophysics Data System (ADS)

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

    2010-03-01

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

  8. Spin Nernst effect of magnons in collinear antiferromagnets

    DOE PAGES

    Cheng, Ran; Okamoto, Satoshi; Xiao, Di

    2016-11-15

    In a collinear antiferromagnet with easy-axis anisotropy, symmetry guarantees that the spin wave modes are doubly degenerate. The two modes carry opposite spin angular momentum and exhibit opposite chirality. Using a honeycomb antiferromagnet in the presence of the Dzyaloshinskii-Moriya interaction, we show that a longitudinal temperature gradient can drive the two modes to opposite transverse directions, realizing a spin Nernst effect of magnons with vanishing thermal Hall current. We find that magnons around themore » $$\\Gamma$$ point and the $K$ point contribute oppositely to the transverse spin transport, and their competition leads to a sign change of the spin Nernst coefficient at finite temperature. As a result, possible material candidates are discussed.« less

  9. Spin Nernst effect of magnons in collinear antiferromagnets

    SciTech Connect

    Cheng, Ran; Okamoto, Satoshi; Xiao, Di

    2016-11-15

    In a collinear antiferromagnet with easy-axis anisotropy, symmetry guarantees that the spin wave modes are doubly degenerate. The two modes carry opposite spin angular momentum and exhibit opposite chirality. Using a honeycomb antiferromagnet in the presence of the Dzyaloshinskii-Moriya interaction, we show that a longitudinal temperature gradient can drive the two modes to opposite transverse directions, realizing a spin Nernst effect of magnons with vanishing thermal Hall current. We find that magnons around the $\\Gamma$ point and the $K$ point contribute oppositely to the transverse spin transport, and their competition leads to a sign change of the spin Nernst coefficient at finite temperature. As a result, possible material candidates are discussed.

  10. Spin superconductivity in the frustrated two-dimensional antiferromagnet in the square lattice

    NASA Astrophysics Data System (ADS)

    Lima, L. S.

    2017-02-01

    We use the SU(2) Schwinger boson formalism to study the spin transport in the two-dimensional S = 1 / 2 frustrated Heisenberg antiferromagnet in a square lattice, considering the second-neighbors interactions in the diagonal. We have obtained a spin superfluid behavior for the spin transport to this system similar to obtained recently to the triangular lattice. We consider an antiferromagnetic inter-chain coupling on the diagonal, J2 > 0 , and the nearest-neighbor coupling antiferromagnetic J1 > 0 . We also have in the critical temperature T0, where the correlation length ξ → 0 , that the system suffers a transition from an ordered ground state to a disordered ground state.

  11. Theory of spin transport in antiferromagnets (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Manchon, Aurélien; Saidaoui, Hamed; Akosa, Collins

    2016-10-01

    Antiferromagnets (AF) have long remained an intriguing and exotic state of matter, their application being restricted to enabling interfacial exchange bias in spin-valves. Their role in the expanding field of applied spintronics has been mostly passive and the in-depth investigation of their basic properties considered as fundamental condensed matter physics. A conceptual breakthrough was achieved ten years ago with the proposal that spin transfer torque could be used to electrically control the direction of the order parameter of AF spin valves, henceforth making these materials potential candidates for low energy spin devices. In spite of substantial theoretical efforts and experimental attempts to observe such a torque, the difficulty to independently detect the direction of the AF order parameter has remained a major obstacle. In this talk, I will first introduce the original concept of spin transfer torque in AF spin-valves, demonstrating that it is strongly limited by the spin decoherence and dramatically vanishes in the presence of disorder, leaving little hope to observe this effect experimentally. Then, I will present the newly proposed concept of spin-orbit torque that utilizes bulk or interfacial the spin-orbit coupling in non-centrosymmetric magnets to directly generate a torque on the AF order parameter. This torque, being local, is much more robust against impurities, as will be demonstrated for the specific case of interfacial Rashba spin-orbit coupling. Finally, I will discuss about spin motive force and torques in antiferromagnetic textures, intriguing effects that remained to be experimentally observed.

  12. Distinct spin liquids and their transitions in spin-1/2 XXZ kagome antiferromagnets.

    PubMed

    He, Yin-Chen; Chen, Yan

    2015-01-23

    By using the density matrix renormalization group approach, we study spin-liquid phases of spin-1/2 XXZ kagome antiferromagnets. We find that the emergence of the spin-liquid phase is independent of the anisotropy of the XXZ interaction. In particular, the two extreme limits-the Ising (a strong S^{z} interaction) and the XY (zero S^{z} interaction)-host the same spin-liquid phases as the isotropic Heisenberg model. Both a time-reversal-invariant spin liquid and a chiral spin liquid with spontaneous time-reversal symmetry breaking are obtained. We show that they evolve continuously into each other by tuning the second- and the third-neighbor interactions. And last, we discuss possible implications of our results for the nature of spin liquid in nearest-neighbor XXZ kagome antiferromagnets, including the nearest-neighbor spin-1/2 kagome antiferromagnetic Heisenberg model.

  13. Mechanisms for spin supersolidity in S=(1/2) spin-dimer antiferromagnets

    SciTech Connect

    Picon, J.-D.; Albuquerque, A. F.; Schmidt, K. P.; Laflorencie, N.; Troyer, M.; Mila, F.

    2008-11-01

    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.

  14. Strong correlation induced charge localization in antiferromagnets

    PubMed Central

    Zhu, Zheng; Jiang, Hong-Chen; Qi, Yang; Tian, Chushun; Weng, Zheng-Yu

    2013-01-01

    The fate of a hole injected in an antiferromagnet is an outstanding issue of strongly correlated physics. It provides important insights into doped Mott insulators closely related to high-temperature superconductivity. Here, we report a systematic numerical study of t-J ladder systems based on the density matrix renormalization group. It reveals a surprising result for the single hole's motion in an otherwise well-understood undoped system. Specifically, we find that the common belief of quasiparticle picture is invalidated by the self-localization of the doped hole. In contrast to Anderson localization caused by disorders, the charge localization discovered here is an entirely new phenomenon purely of strong correlation origin. It results from destructive quantum interference of novel signs picked up by the hole, and since the same effect is of a generic feature of doped Mott physics, our findings unveil a new paradigm which may go beyond the single hole doped system. PMID:24002668

  15. Muon Spin Relaxation Evidence for the U(1) Quantum Spin-Liquid Ground State in the Triangular Antiferromagnet YbMgGaO_{4}.

    PubMed

    Li, Yuesheng; Adroja, Devashibhai; Biswas, Pabitra K; Baker, Peter J; Zhang, Qian; Liu, Juanjuan; Tsirlin, Alexander A; Gegenwart, Philipp; Zhang, Qingming

    2016-08-26

    Muon spin relaxation (μSR) experiments on single crystals of the structurally perfect triangular antiferromagnet YbMgGaO_{4} indicate the absence of both static long-range magnetic order and spin freezing down to 0.048 K in a zero field. Below 0.4 K, the μ^{+} spin relaxation rates, which are proportional to the dynamic correlation function of the Yb^{3+} spins, exhibit temperature-independent plateaus. All these μSR results unequivocally support the formation of a gapless U(1) quantum spin liquid ground state in the triangular antiferromagnet YbMgGaO_{4}.

  16. Coexistence of antiferromagnetic and ferromagnetic spin correlations in SrCo2As2 revealed by 59Co and 75As NMR

    SciTech Connect

    Wiecki, P.; Ogloblichev, V.; Pandey, Abhishek; Johnston, D. C.; Furukawa, Y.

    2015-06-15

    In nonsuperconducting, metallic paramagnetic SrCo2As2, inelastic neutron scattering measurements have revealed strong stripe-type q=(π,0) antiferromagnetic (AFM) spin correlations. Using nuclear magnetic resonance (NMR) measurements on 59Co and 75As nuclei, we demonstrate that stronger ferromagnetic (FM) spin correlations coexist in SrCo2As2. Our NMR data are consistent with density functional theory (DFT) calculations which show enhancements at both q=(π,0) and the in-plane FM q=0 wave vectors in static magnetic susceptibility χ(q). We suggest that the strong FM fluctuations prevent superconductivity in SrCo2As2, despite the presence of stripe-type AFM fluctuations. Since DFT calculations have consistently revealed similar enhancements of the χ(q) at both q=(π,0) and q=0 in the iron-based superconductors and parent compounds, our observation of FM correlations in SrCo2As2 calls for detailed studies of FM correlations in the iron-based superconductors.

  17. Ultrafast spin dynamics and switching via spin transfer torque in antiferromagnets with weak ferromagnetism

    PubMed Central

    Kim, Tae Heon; Grünberg, Peter; Han, Song Hee; Cho, Beongki

    2016-01-01

    The spin-torque driven dynamics of antiferromagnets with Dzyaloshinskii-Moriya interaction (DMI) were investigated based on the Landau-Lifshitz-Gilbert-Slonczewski equation with antiferromagnetic and ferromagnetic order parameters (l and m, respectively). We demonstrate that antiferromagnets including DMI can be described by a 2-dimensional pendulum model of l. Because m is coupled with l, together with DMI and exchange energy, close examination of m provides fundamental understanding of its dynamics in linear and nonlinear regimes. Furthermore, we discuss magnetization reversal as a function of DMI and anisotropy energy induced by a spin current pulse. PMID:27713522

  18. Ultrafast spin dynamics and switching via spin transfer torque in antiferromagnets with weak ferromagnetism

    NASA Astrophysics Data System (ADS)

    Kim, Tae Heon; Grünberg, Peter; Han, Song Hee; Cho, Beongki

    2016-10-01

    The spin-torque driven dynamics of antiferromagnets with Dzyaloshinskii-Moriya interaction (DMI) were investigated based on the Landau-Lifshitz-Gilbert-Slonczewski equation with antiferromagnetic and ferromagnetic order parameters (l and m, respectively). We demonstrate that antiferromagnets including DMI can be described by a 2-dimensional pendulum model of l. Because m is coupled with l, together with DMI and exchange energy, close examination of m provides fundamental understanding of its dynamics in linear and nonlinear regimes. Furthermore, we discuss magnetization reversal as a function of DMI and anisotropy energy induced by a spin current pulse.

  19. Spin pumping and inverse spin Hall effect in antiferromagnetic exchange coupled [Co/Ru/Co]/Pt heterostructures

    NASA Astrophysics Data System (ADS)

    Avilés-Félix, L.; Butera, A.; Gómez, J. E.

    2017-01-01

    We report the observation of spin pumping and inverse spin Hall effects in antiferromagnetically coupled [Co/Ru/Co]/Pt heterostructures. The "spin-flop" magnetization process observed in antiferromagnetically exchange coupled Co layers combined with spin pumping and inverse spin Hall effects allowed us to detect both transversal and longitudinal charge accumulations. By controlling the exchange coupling strength and the spin flop transition in the magnetization process, it was possible to produce spin currents polarized in different directions.

  20. Persistent spin excitations in doped antiferromagnets revealed by resonant inelastic light scattering

    NASA Astrophysics Data System (ADS)

    Jia, C. J.; Nowadnick, E. A.; Wohlfeld, K.; Kung, Y. F.; Chen, C.-C.; Johnston, S.; Tohyama, T.; Moritz, B.; Devereaux, T. P.

    2014-02-01

    How coherent quasiparticles emerge by doping quantum antiferromagnets is a key question in correlated electron systems, whose resolution is needed to elucidate the phase diagram of copper oxides. Recent resonant inelastic X-ray scattering (RIXS) experiments in hole-doped cuprates have purported to measure high-energy collective spin excitations that persist well into the overdoped regime and bear a striking resemblance to those found in the parent compound, challenging the perception that spin excitations should weaken with doping and have a diminishing effect on superconductivity. Here we show that RIXS at the Cu L3-edge indeed provides access to the spin dynamical structure factor once one considers the full influence of light polarization. Further we demonstrate that high-energy spin excitations do not correlate with the doping dependence of Tc, while low-energy excitations depend sensitively on doping and show ferromagnetic correlations. This suggests that high-energy spin excitations are marginal to pairing in cuprate superconductors.

  1. Theory of the spin Seebeck effect in antiferromagnets

    NASA Astrophysics Data System (ADS)

    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 .

  2. Effects of random fields in an antiferromagnetic Ising spin glass

    PubMed

    Vieira; Nobre; Yokoi

    2000-05-01

    The effects of random fields on the two-sublattice infinite-ranged Ising spin-glass model are investigated. This model is expected to be appropriate as a mean-field description of antiferromagnetic spin glasses such as FexMn1-xTiO3. Within replica-symmetric calculations, we study the influence of Gaussian and bimodal random fields on the phase transitions and phase diagrams. It is shown that, in the presence of random fields, the first-order transitions are weakened and may become continuous. Also, the antiferromagnetic phases are always destroyed by sufficiently strong random fields. A qualitative comparison with existing experimental results and the limitations of the present calculations are discussed.

  3. Terahertz-Driven Nonlinear Spin Response of Antiferromagnetic Nickel Oxide

    NASA Astrophysics Data System (ADS)

    Baierl, S.; Mentink, J. H.; Hohenleutner, M.; Braun, L.; Do, T.-M.; Lange, C.; Sell, A.; Fiebig, M.; Woltersdorf, G.; Kampfrath, T.; Huber, R.

    2016-11-01

    Terahertz magnetic fields with amplitudes of up to 0.4 Tesla drive magnon resonances in nickel oxide while the induced dynamics is recorded by femtosecond magneto-optical probing. We observe distinct spin-mediated optical nonlinearities, including oscillations at the second harmonic of the 1 THz magnon mode. The latter originate from coherent dynamics of the longitudinal component of the antiferromagnetic order parameter, which are probed by magneto-optical effects of second order in the spin deflection. These observations allow us to dynamically disentangle electronic from lattice-related contributions to magnetic linear birefringence and dichroism—information so far only accessible by ultrafast THz spin control. The nonlinearities discussed here foreshadow physics that will become essential in future subcycle spin switching.

  4. Antiferromagnetic molecular nanomagnets with odd-numbered coupled spins

    NASA Astrophysics Data System (ADS)

    Owerre, S. A.; Nsofini, J.

    2015-05-01

    In recent years, studies on cyclic molecular nanomagnets have captivated the attention of researchers. These magnets are finite in size and contain very large spins. They are interesting because they possess macroscopic quantum tunneling of Néel vectors. For antiferromagnetic molecular nanomagnets with finite number of even-numbered coupled spins, tunneling involves two classical localized Néel ground states separated by a magnetic energy barrier. The question is: can such phenomena be observed in nanomagnets with odd number of magnetic ions? The answer is not directly obvious because cyclic chains with odd-numbered coupled spins are frustrated as one cannot obtain a perfect Néel order. These frustrated spins can indeed be observed experimentally, so they are of interest. In this letter, we theoretically investigate macroscopic quantum tunneling in this odd spin system with arbitrary spins s, in the presence of a magnetic field applied along the plane of the magnet. In contrast to systems with an even-numbered coupled spins, the ground state of the cyclic odd-spin system contains a topological soliton due to spin frustration. Thus, the classical ground state is 2N-fold degenerate as the soliton can be placed anywhere along the ring with total S_z=+/- s . Small quantum fluctuations delocalize the soliton with a formation of an energy band. We obtain this energy band using degenerate perturbation theory at order 2s. We show that the soliton ground state is chiral for half-odd integer spins and non-chiral for integer spins. From the structure of the energy band we infer that as the value of the spin increases the inelastic polarized neutron-scattering intensity may increase or decrease depending on the strengths of the parameters of the Hamiltonian.

  5. Resonant spin tunneling in small antiferromagnetic particles

    NASA Astrophysics Data System (ADS)

    Luis, F.; del Barco, E.; Hernández, J. M.; Remiro, E.; Bartolomé, J.; Tejada, J.

    1999-05-01

    The paper reports a detailed experimental study on magnetic relaxation of natural horse-spleen ferritin. ac susceptibility measurements performed on three samples of different concentration show that dipole-dipole interactions between uncompensated moments play no significant role. Furthermore, the distribution of relaxation times in these samples has been obtained from a scaling of experimental χ'' data, obtained at different frequencies. The average uncompensated magnetic moment per protein is compatible with a disordered arrangement of atomic spins throughout the core, rather than with surface disorder. The observed field dependence of the blocking temperature suggests that magnetic relaxation is faster at zero field than at intermediate field values. This is confirmed by the fact that the magnetic viscosity peaks at zero field, too. Using the distribution of relaxation times obtained independently, we show that these results cannot be explained in terms of classical relaxation theory. The most plausible explanation of these results is the existence, near zero field, of resonant magnetic tunneling between magnetic states of opposite orientation, which are thermally populated.

  6. Striped spin liquid crystal ground state instability of kagome antiferromagnets.

    PubMed

    Clark, Bryan K; Kinder, Jesse M; Neuscamman, Eric; Chan, Garnet Kin-Lic; Lawler, Michael J

    2013-11-01

    The Dirac spin liquid ground state of the spin 1/2 Heisenberg kagome antiferromagnet has potential instabilities. This has been suggested as the reason why it does not emerge as the ground state in large-scale numerical calculations. However, previous attempts to observe these instabilities have failed. We report on the discovery of a projected BCS state with lower energy than the projected Dirac spin liquid state which provides new insight into the stability of the ground state of the kagome antiferromagnet. The new state has three remarkable features. First, it breaks spatial symmetry in an unusual way that may leave spinons deconfined along one direction. Second, it breaks the U(1) gauge symmetry down to Z(2). Third, it has the spatial symmetry of a previously proposed "monopole" suggesting that it is an instability of the Dirac spin liquid. The state described herein also shares a remarkable similarity to the distortion of the kagome lattice observed at low Zn concentrations in Zn-paratacamite and in recently grown single crystals of volborthite suggesting it may already be realized in these materials.

  7. Scattering bottleneck for spin dynamics in metallic helical antiferromagnetic dysprosium

    NASA Astrophysics Data System (ADS)

    Langner, M. C.; Roy, S.; Kemper, A. F.; Chuang, Y.-D.; Mishra, S. K.; Versteeg, R. B.; Zhu, Y.; Hertlein, M. P.; Glover, T. E.; Dumesnil, K.; Schoenlein, R. W.

    2015-11-01

    Ultrafast studies of magnetization dynamics have revealed fundamental processes that govern spin dynamics, and the emergence of time-resolved x-ray techniques has extended these studies to long-range spin structures that result from interactions with competing symmetries. By combining time-resolved resonant x-ray scattering and ultrafast magneto-optical Kerr studies, we show that the dynamics of the core spins in the helical magnetic structure occur on much longer time scales than the excitation of conduction electrons in the lanthanide metal Dy. The observed spin behavior differs markedly from that observed in the ferromagnetic phase of other lanthanide metals or transition metals and is strongly dependent on temperature and excitation fluence. This unique behavior results from coupling of the real-space helical spin structure to the shape of the conduction electron Fermi surface in momentum space, which creates a bottleneck in spin scattering events that transfer the valence excitation to the core spins. The dependence of the dynamics on the intersite interactions renders the helical ordering much more robust to perturbations than simple ferromagnetic or antiferromagnetic ordering, where dynamics are driven primarily by on-site interactions.

  8. Quantum kagome frustrated antiferromagnets: One route to quantum spin liquids

    NASA Astrophysics Data System (ADS)

    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.

  9. Quantum critical behavior of low-dimensional spin 1/2 Heisenberg antiferromagnets

    NASA Astrophysics Data System (ADS)

    Stone, Matthew Brandon

    In this dissertation, experiments on four different insulating antiferromagnetic spin 1/2 Heisenberg systems are presented and described. Copper pyrazine dinitrate is a linear chain spin 1/2 (S = 1/2) Heisenberg antiferromagnet. In an applied magnetic field, the continuum splits into multiple continua including incommensurate gapless excitations. The inelastic neutron scattering measurements presented represent the first complete experimental study of the S = 1/2 linear chain excitation spectrum in an applied magnetic field. Copper nitrate is a S = 1/2 alternating chain Heisenberg antiferromagnet. This system is near the isolated dimer limit, such that perturbation theory based on weakly coupled spin pairs accurately describes the excitation spectrum. Inelastic neutron scattering measurements were performed as a function of applied magnetic field. The data presented here represent the first such measure in all portions of the magnetic phase diagram of a gapped quantum magnet. Piperazinium hexachlorodicuprate is a two-dimensional S = 1/2 Heisenberg antiferromagnet. It is shown in this work that the structure consists of a collection of coupled spins in the crystalline ac plane. Multiple spin-spin interactions are important in this material. This has consequences for the nature of the dominant interactions and causes there to be significant spin frustration in this system. The spectrum consists of coherent dispersive singlet-triplet excitations describable in terms of multiple significant exchange interactions with geometrical frustration. Thermodynamic and inelastic neutron scattering measurements are presented which characterize the magnetic excitations as a function of temperature and applied magnetic field. In addition, the full magnetic phase diagram including a gapless disordered phase and a reentrant phase transition is presented. Cu2(1,4-diazacycloheptane)2Cl4 was widely believed to be a S = 1/2 Heisenberg spin-ladder material. Neutron scattering measurements

  10. Using the ground state of an antiferromagnetic spin-1 atomic condensate for Heisenberg-limited metrology

    NASA Astrophysics Data System (ADS)

    Wu, Ling-Na; You, L.

    2016-03-01

    We show that the ground state of a spin-1 atomic condensate with antiferromagnetic interactions constitutes a useful resource for quantum metrology upon approaching the Heisenberg limit. Unlike a ferromagnetic condensate state where individual atomic spins are aligned in the same direction, the antiferromagnetic ground-state condensate is a condensate of spin-singlet atom pairs. The inherent correlation between paired atoms allows for parameter estimation at precisions beyond the standard quantum limit (SQL) for uncorrelated atoms. The degree of improvement over the SQL is measured by the scaled quantum Fisher information (QFI), whose dependence on the ratio of linear Zeeman shift p to spin-dependent atomic interaction c is studied. At a typical value of p =0.4 c , which corresponds to a magnetic field of 28.6 μ G for c =50 h Hz (for 23Na atom condensate in the F =1 state at a typical density of ˜1014cm-3 ), the scaled QFI can reach ˜0.48 N , which approaches the limit of 0.5 N for the twin-Fock state |N/2 > +|N/2 > - . Our work encourages experimental efforts to reach the ground state of an antiferromagnetic condensate at a extremely low magnetic field.

  11. The ground state of a spin-1 anti-ferromagnetic atomic condensate for Heisenberg limited metrology

    NASA Astrophysics Data System (ADS)

    Wu, Ling-Na; You, Li

    2016-05-01

    The ground state of a spin-1 atomic condensate with anti-ferromagnetic interaction can be applied to quantum metrology approaching the Heisenberg limit. Unlike a ferromagnetic condensate state where individual atomic spins are aligned in the same direction, atoms in an anti-ferromagnetic ground state condensate exist as spin singlet pairs, whose inherent correlation promises metrological precisions beyond the standard quantum limit (SQL) for uncorrelated atoms. The degree of improvement over the SQL is measured by quantum Fisher information (QFI), whose dependence on the ratio of linear Zeeman shift p to spin-dependent atomic interaction c is studied. At a typical value of p = 0 . 4 c corresponding to a magnetic field of 28 . 6 μ G with c = h × 50 Hz (for 23 Na atom condensate in the F = 1 state at a typical density of ~1014cm-3), the scaled QFI can reach ~ 0 . 48 N , which is close to the limits of N for NooN state, or 0 . 5 N for twin-Fock state. We hope our work will stimulate experimental efforts towards reaching the anti-ferromagnetic condensate ground state at extremely low magnetic fields.

  12. Photo-induced Spin Angular Momentum Transfer into Antiferromagnetic Insulator

    NASA Astrophysics Data System (ADS)

    Fang, Fan; Fan, Yichun; Ma, Xin; Zhu, J.; Li, Q.; Ma, T. P.; Wu, Y. Z.; Chen, Z. H.; Zhao, H. B.; Luepke, Gunter; College of William and Mary Team; Department of Physics, Fudan University Team; Department of Optical Science and Engineering, Fudan University Team

    2014-03-01

    Spin angular momentum transfer into antiferromagnetic(AFM) insulator is observed in single crystalline Fe/CoO/MgO(001) heterostructure by time-resolved magneto-optical Kerr effect (TR-MOKE). The transfer process is mediated by the Heisenberg exchange coupling between Fe and CoO spins. Below the Neel temperature(TN) of CoO, the fact that effective Gilbert damping parameter α is independent of external magnetic field and it is enhanced with respect to the intrinsic damping in Fe/MgO, indicates that the damping process involves both the intrinsic spin relaxation and the transfer of Fe spin angular momentum to CoO spins via FM-AFM exchange coupling and then into the lattice by spin-orbit coupling. The work at the College of William and Mary was sponsored by the Office of Naval Research. The work at Department of Physics, Fudan, was supported by NSFC. The work at Department of Optical Science and Engineering, Fudan was supported by NSFC and NCET.

  13. Valence bond distribution and correlation in bipartite Heisenberg antiferromagnets

    NASA Astrophysics Data System (ADS)

    Schwandt, David; Alet, Fabien; Oshikawa, Masaki

    2014-03-01

    Every singlet state of a quantum spin-1/2 system can be decomposed into a linear combination of valence bond basis states. The range of valence bonds within this linear combination as well as the correlations between them can reveal the nature of the singlet state and are key ingredients in variational calculations. In this work, we study the bipartite valence bond distributions and their correlations within the ground state of the Heisenberg antiferromagnet on bipartite lattices. In terms of field theory, this problem can be mapped to correlation functions near a boundary. In dimension d ≥2, a nonlinear σ model analysis reveals that at long distances the probability distribution P (r) of valence bond lengths decays as |r|-d-1 and that valence bonds are uncorrelated. By a bosonization analysis, we also obtain P(r )∝|r|-d-1 in d =1 despite the different mechanism. On the other hand, we find that correlations between valence bonds are important even at large distances in d =1, in stark contrast to d ≥2. The analytical results are confirmed by high-precision quantum Monte Carlo simulations in d =1, 2, and 3. We develop a single-projection loop variant of the valence bond projection algorithm, which is well designed to compute valence bond probabilities and for which we provide algorithmic details.

  14. Spin-dynamics simulations of the triangular antiferromagnetic XY model*

    NASA Astrophysics Data System (ADS)

    Nho, Kwangsik; Landau, D. P.

    2003-03-01

    Using Monte Carlo and spin-dynamics methods, we have studied the dynamic behavior of the classical, antiferromagnetic XY model on a triangular lattice. The temporal evolutions of spin configurations were obtained by solving numerically the coupled equations of motion for each spin using fourth-order Suzuki-Trotter decompositions of exponential operators. We calculated the dynamic structure factor S(q,w) for momentum q and frequency w. Below T_KT (Kosteritz-Thouless transition), both the in-plane (S^xx) and out-of-plane (S^zz) components exhibit very strong and sharp spin-wave peaks. Well above T_KT, S^xx and S^zz apparently display a central peak, and spin-wave signatures are still seen in S^zz. In addition, we also observed an almost dispersionless domain-wall peak at high w below Tc (Ising transition), where long-range order appears in the staggered chirality[1]. We found that our results demonstrate the consistency of the dynamic finite-size scaling theory for the characteristic frequency wm and S(q,w). *Supported by NSF [1] D.H. Lee, J.D. Joannopoulos, J.W. Negele, and D.P. Landau, Phys. Rev. Lett. 52, 433 (1984)

  15. Surface spin-flop and discommensuration transitions in antiferromagnets

    NASA Astrophysics Data System (ADS)

    Micheletti, C.; Griffiths, R. B.; Yeomans, J. M.

    1999-03-01

    Phase diagrams as a function of anisotropy D and magnetic field H are obtained for discommensurations and surface states for an antiferromagnet in which H is parallel to the easy axis, by modeling it using the ground states of a one-dimensional chain of classical XY spins. A surface spin-flop phase exists for all D, but the interval in H over which it is stable becomes extremely small as D goes to zero. First-order transitions, separating different surface states and ending in critical points, exist inside the surface spin-flop region. They accumulate at a field H' (depending on D) significantly less than the value HSF for a bulk spin-flop transition. For H'spin-flop phase in the strict sense; instead, the surface restructures by, in effect, producing a discommensuration infinitely far away in the bulk. The results are used to explain in detail the phase transitions occurring in systems consisting of a finite, even number of layers.

  16. Antiferromagnetic order and spin dynamics in iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Dai, Pengcheng

    2015-07-01

    High-transition temperature (high-Tc) superconductivity in the iron pnictides or chalcogenides emerges from the suppression of the static antiferromagnetic order in their parent compounds, similar to copper oxide superconductors. This raises a fundamental question concerning the role of magnetism in the superconductivity of these materials. Neutron scattering, a powerful probe to study the magnetic order and spin dynamics, plays an essential role in determining the relationship between magnetism and superconductivity in high-Tc superconductors. The rapid development of modern neutron time-of-flight spectrometers allows a direct determination of the spin dynamical properties of iron-based superconductors throughout the entire Brillouin zone. In this paper, an overview is presented of the neutron scattering results on iron-based superconductors, focusing on the evolution of spin-excitation spectra as a function of electron and hole doping and isoelectronic substitution. Spin dynamical properties of iron-based superconductors are compared with those of copper oxide and heavy fermion superconductors and the common features of spin excitations in these three families of unconventional superconductors and their relationship with superconductivity are discussed.

  17. Spin-Flop Phenomenon of Two-Dimensional Frustrated Antiferromagnets without Anisotropy in Spin Space

    NASA Astrophysics Data System (ADS)

    Nakano, Hiroki; Sakai, Tôru; Hasegawa, Yasumasa

    2014-08-01

    Motivated by a recent finding of a spin-flop phenomenon in a system without anisotropy in spin space reported in the S = 1/2 Heisenberg antiferromagnet on the square-kagome lattice, we study the S = 1/2 Heisenberg antiferromagnets on two other lattices composed of vertex-sharing triangles by the numerical diagonalization method. One is a novel lattice including a shuriken shape with four teeth; the other is the kagome lattice with √{3} × √{3} -structure distortion, which includes a shuriken shape with six teeth. We find in the magnetization processes of these systems that a magnetization jump accompanied by a spin-flop phenomenon occurs at the higher-field-side edge of the magnetization plateau at one-third the height of saturation. This finding indicates that the spin-flop phenomenon found in the isotropic system on the square-kagome lattice is not an exceptional case.

  18. Probing spin ordering in iron-platinum based antiferromagnetic films using neutron diffraction

    NASA Astrophysics Data System (ADS)

    Mani, Prakash

    The antiferromagnetic properties of chemically ordered and epitaxial films of FexPt100-x grown on MgO(111) & MgO(100) and Fe50Pt50- xRhx grown on MgO(100) have been studied with neutron diffraction. Epitaxial films of FexPt 100-x (x = 25, 30) have two kinds of antiferromagnetic ordering. The Neel temperature of spin wave vector QA = (1/2 1/2 0) is T N = 160 K and QB = (1/2 0 0) is TN = 100 K, respectively. Neutron diffraction is used to determine the phase diagram of the antiferromagnetic ordering as a function of composition and temperature. The nature of antiferromagnetic ordering was found to be strongly related to the lattice strain present in the system. Lattice-matched antiferromagnetic/ferromagnetic films offer an ideal layered system to study exchange bias. The loop shifts in FePt3(AF)/CoPt 3(F) multilayers are correlated with rocking curve peak widths, and it has been shown that films with a narrower full-width-half-maximum have a smaller exchange bias. Neutron reflectivity is also applied to CoPt 3/FePt3 multilayers in order to probe layer-specific magnetizations owing to the significant difference in neutron scattering length density between Fe and Co. Fe50Pt50-xRh x (x˜10) exhibits a temperature dependent antiferromagnetic-ferromagnetic-paramagnetic triple point near 400 K. The temperature and composition dependent spin structure of Fe50Pt 50-xRhx alloy films grown on MgO(100) have been determined for the first time with neutron diffraction. Three types of antiferromagnetic orderings were observed: (0 0 1/2), (1/2 1/2 1/2), and (1/2 1/2 3/2). Future studies have been planned to explore a magnetic field induced antiferromagnetic to ferromagnetic transition in Fe50Pt50-xRh x alloy films.

  19. Spin-flop states in a synthetic antiferromagnet and variations of unidirectional anisotropy in FeMn-based spin valves

    NASA Astrophysics Data System (ADS)

    Milyaev, M. A.; Naumova, L. I.; Chernyshova, T. A.; Proglyado, V. V.; Kulesh, N. A.; Patrakov, E. I.; Kamenskii, I. Yu.; Ustinov, V. V.

    2016-12-01

    Spin valves with a synthetic antiferromagnet have been prepared by magnetron sputtering. Regularities of the formation of single- and two-phase spin-flop states in the synthetic antiferromagnet have been studied using magnetoresistance measurements and imaging the magnetic structure. A thermomagnetic treatment of spin valve in a field that corresponds to the single-phase spin-flop state of synthetic antiferromagnet was shown to allow us to obtain a magnetically sensitive material characterized by hysteresis-free field dependence of the magnetoresistance.

  20. Electron spin resonance shifts in S=1 antiferromagnetic chains

    NASA Astrophysics Data System (ADS)

    Furuya, Shunsuke C.; Maeda, Yoshitaka; Oshikawa, Masaki

    2013-03-01

    We discuss electron spin resonance (ESR) shifts in spin-1 Heisenberg antiferromagnetic chains with a weak single-ion anisotropy, based on several effective field theories: the O(3) nonlinear sigma model (NLSM) in the Haldane phase, free-fermion theories around the lower and the upper critical fields. In the O(3) NLSM, the single-ion anisotropy corresponds to a composite operator which creates two magnons at the same time and position. Therefore, even inside a parameter range where free magnon approximation is valid for thermodynamics, we have to take interactions among magnons into account in order to include the single-ion anisotropy as a perturbation. Although the O(3) NLSM is only valid in the Haldane phase, an appropriate translation of Faddeev-Zamolodchikov operators of the O(3) NLSM to fermion operators enables one to treat ESR shifts near the lower critical field in a similar manner to discussions in the Haldane phase. Our theory gives quantitative agreements with a numerical evaluation using quantum Monte Carlo simulation, and also with recent ESR experimental results on a spin-1 chain compound Ni(C5H14N2)2N3(PF6).

  1. Qubit teleportation and transfer across antiferromagnetic spin chains.

    PubMed

    Campos Venuti, L; Degli Esposti Boschi, C; Roncaglia, M

    2007-08-10

    We explore the capability of spin-1/2 chains to act as quantum channels for both teleportation and transfer of qubits. Exploiting the emergence of long-distance entanglement in low-dimensional systems [Phys. Rev. Lett. 96, 247206 (2006)10.1103/Phys.Rev.Lett.96, 247206(2006)], here we show how to obtain high communication fidelities between distant parties. An investigation of protocols of teleportation and state transfer is presented, in the realistic situation where temperature is included. Basing our setup on antiferromagnetic rotationally invariant systems, both protocols are represented by pure depolarizing channels. We propose a scheme where channel fidelity close to 1 can be achieved on very long chains at moderately small temperature.

  2. Antiferromagnetic spin correlations between corner-shared [FeO5]7- and [FeO6]9- units, in the novel iron-based compound: BaYFeO4.

    PubMed

    Wrobel, Friederike; Kemei, Moureen C; Derakhshan, Shahab

    2013-03-04

    A novel quaternary compound in the Ba-Y-Fe-O phase diagram was synthesized by solid-state reaction and its crystal structure was characterized using powder X-ray diffraction. The crystal structure of BaYFeO4 consists of a unique arrangement of Fe(3+) magnetic ions, which is based on alternate corner-shared units of [FeO5](7-) square pyramids and [FeO6](9-) octahedra. This results in the formation of stairwise channels of FeO polyhedra along the b crystallographic axis. The structure is described in an orthorhombic crystal system in the space group Pnma with lattice parameters a = 13.14455(1) Å, b = 5.694960(5) Å, and c = 10.247630(9) Å. The temperature-dependent magnetic susceptibility data reveal two antiferromagnetic (AFM) transitions at 33 and 48 K. An upturn in the magnetic susceptibility data above these transitions is observed, which does not reach its maximum even at 390 K. The field-dependent magnetization data at both 2 and 300 K show a nearly linear dependence and do not exhibit significant hysteresis. Heat capacity measurements between 2 and 200 K reveal only a broad anomaly without any indication of long-range ordering. The latter data set is not in good agreement with the magnetic susceptibility data, which makes it difficult to exactly determine the magnetic ground state of BaYFeO4. Accordingly, a temperature-dependent neutron diffraction study is in order, which will enable resolving this issue. The theoretical study of the relative strengths of magnetic exchange interactions along various possible pathways, using extended Hückel spin dimer analysis, shows that only interactions between square pyramidal and octahedral centers are significant, and among them, the intrachannel correlations are stronger than interchannel interactions. This is the first physical property study in such a magnetic ion substructure.

  3. Barkhausen-like antiferromagnetic to ferromagnetic phase transition driven by spin polarized current

    SciTech Connect

    Suzuki, Ippei; Naito, Tomoyuki; Itoh, Mitsuru; Taniyama, Tomoyasu

    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.

  4. Barkhausen-like antiferromagnetic to ferromagnetic phase transition driven by spin polarized current

    NASA Astrophysics Data System (ADS)

    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.

  5. Emergent incommensurate correlations in frustrated ferromagnetic spin-1 chains

    NASA Astrophysics Data System (ADS)

    Lee, Hyeong Jun; Choi, MooYoung; Jeon, Gun Sang

    2017-01-01

    We study frustrated ferromagnetic spin-1 chains, where the ferromagnetic nearest-neighbor coupling competes with the antiferromagnetic next-nearest-neighbor coupling. We use the density-matrix renormalization group to obtain the ground states. Through the analysis of spin-spin correlations we identify the double Haldane phase as well as the ferromagnetic phase. It is shown that the ferromagnetic coupling leads to incommensurate correlations in the double Haldane phase. Such short-range correlations transform continuously into the ferromagnetic instability at the transition to the ferromagnetic phase. We also compare the results with the spin-1/2 and classical spin systems and discuss the string orders in the system.

  6. Correlations and Werner states in finite spin linear arrays

    NASA Astrophysics Data System (ADS)

    Wells, P. R.; Chaves, C. M.; d'Albuquerque e Castro, J.; Koiller, Belita

    2013-10-01

    Pairwise quantum correlations in the ground state of an N-spins antiferromagnetic Heisenberg chain are investigated. By varying the exchange coupling between two neighboring sites, it is possible to reversibly drive spins from entangled to disentangled states. For even N, the two-spin density matrix is written in the form of a Werner state, allowing identification of its single parameter with the usual spin-spin correlation function. The N = 4 chain is identified as a promising system for practical demonstrations of non-classical correlations and the realization of Werner states in familiar condensed matter systems. Fabrication and measurement ingredients are within current capabilities.

  7. Fermionic algebraic quantum spin liquid in an octa-kagome frustrated antiferromagnet

    NASA Astrophysics Data System (ADS)

    Peng, Cheng; Ran, Shi-Ju; Liu, Tao; Chen, Xi; Su, Gang

    2017-02-01

    We investigate the ground state and finite-temperature properties of the spin-1/2 Heisenberg antiferromagnet on an infinite octa-kagome lattice by utilizing state-of-the-art tensor network-based numerical methods. It is shown that the ground state has a vanishing local magnetization and possesses a 1 /2 -magnetization plateau with an up-down-up-up spin configuration. A quantum phase transition at the critical coupling ratio Jd/Jt=0.6 is found. When 0 spin excitation; when Jd/Jt>0.6 , the system exhibits a gapless excitation, in which the dimer-dimer correlation is found decaying in a power law, while the spin-spin and chiral-chiral correlation functions decay exponentially. At the isotropic point (Jd/Jt=1 ), we unveil that at low temperature T , the specific heat depends linearly on T , and the susceptibility tends to a constant for T →0 , giving rise to a Wilson ratio around unity, implying that the system under interest is a fermionic algebraic quantum spin liquid.

  8. Topological Phases of the Spin-1/2 Ferromagnetic--Antiferromagnetic Alternating Heisenberg Chain with Frustrated Next-Nearest-Neighbour Interaction

    NASA Astrophysics Data System (ADS)

    Hida, Kazuo; Takano, Ken'ichi; Suzuki, Hidenori

    2013-06-01

    The spin-1/2 ferromagnetic--antiferromagnetic alternating Heisenberg chain with ferromagnetic next-nearest-neighbour (NNN) interaction is investigated. The ground state is the Haldane phase for weak NNN interaction, and is the ferromagnetic phase for weak antiferromagnetic interaction. We find a series of topologically distinct spin-gap phases with various magnitudes of edge spins for strong NNN interaction. The phase boundaries between these phases are determined on the basis of the DMRG calculation with additional spins that compensate the edge spins. It is found that each of the exact solutions with short-range antiferromagnetic correlation on the ferromagnetic--nonmagnetic phase boundary is representative of each spin gap phase.

  9. Spin liquid nature in the Heisenberg J1-J2 triangular antiferromagnet

    NASA Astrophysics Data System (ADS)

    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.

  10. Excitation spectra of generalized antiferromagnetic Heisenberg spin chains (abstract)

    NASA Astrophysics Data System (ADS)

    Parkinson, J. B.; Bonner, J. C.

    1988-04-01

    We compare the excitation spectra in the presence of a magnetic field of a number of integrable (exactly solvable) and nonintegrable quantum spin chains of various spin value s. The archetypal Bethe-ansatz integrable model is the s= 1/2 Heisenberg antiferromagnet (HB AFM). The excitation spectra are characterized by a soft mode which tracks across the Brillouin zone as the field increases to its saturation value. A class of Bethe-ansatz integrable models with SU(2) symmetry and the general spin s display excitation spectra qualitatively similar to the spin- 1/2 model above, for all s. A second class of Bethe-ansatz integrable models has SU(n) symmetry, where n=2s+1. Like the SU(2) integrable chains, these models have gapless excitation spectra, but the basic Brillouin zone changes from k=±2π/(2s+1)a. Studies show that periodicity of the SU(3) member of the class changes (increases) as the field increases to saturation. For both classes of integrable models, there is a single type of excitation pattern which is generically similar for all s. In the case of the other models, on the other hand, numerical studies show that the excitations divide into at least two distinct classes. In the case of the s=1 HB AFM, at high fields (corresponding to SzT=N,N-1, . . .,N/2) the excitations map approximately onto the complete set of excitations for s= 1/2 , whereas at low fields (SzT=N/2,N/2-1,. . .,0) the excitations have notable classical character. In the case of the s=1 model with pure biquadratic exchange, one set of excitations, corresponding to SzT even (SzT=N,N-2,. . .,2,0), again shows an approximate mapping to the complete excitation set for s= 1/2 . The second class of excitations, corresponding to SzT odd, are very different. They are symmetric about k=±π/2a for all SzT, i.e., correspond to a basic Brillouin zone of ±π/2a.

  11. Wall-like spin excitations in A-type antiferromagnetic CaCo2As2

    NASA Astrophysics Data System (ADS)

    Sapkota, A.; Ueland, B. G.; Pandey, Abhishek; Johnston, D. C.; Kreyssig, A.; McQueeney, R. J.; Goldman, A. I.; Anand, V. K.; Niedziela, J. L.; Abernathy, D. L.

    The ACo2As2 (A = Ca, Sr, Ba) compounds are structurally and chemically similar to AFe2As2 and possess some interesting similarities and differences in their magnetism. We recently discovered that SrCo2As2 has stripe antiferromagnetic (AFM) spin correlations similar to stripe-ordered AFe2As2. On the other hand, CaCo2As2 orders in an A-type AFM structure with ferromagnetic correlation of the spins in the square-lattice Co-layer and AFM correlations between layers. Despite the A-type order, our recent inelastic neutron scattering measurements show that spin excitations in CaCo2As2 are not associated with either the A-type or stripe-type order. Instead, we observe broad excitations that extend longitudinally (along (1,1,0) in reciprocal space), but remain sharply defined in the transverse direction. These excitations seem to be best characterized as a ``wall'' of scattering and suggest that CaCo2As2 has quasi-one-dimensional spin dynamics very different than in AFe2As2 and SrCo2As2. Work at Ames Laboratory was supported by US DOE, Basic Energy Sciences, Division of Materials Sciences and Engineering, under Contract No. DE-AC02-07CH11358. Work at ORNL was supported by US DOE, Office of Basic Energy Sciences, Scientific User Facilities Division.

  12. Quantum Monte Carlo study of the itinerant-localized model of strongly correlated electrons: Spin-spin correlation functions

    NASA Astrophysics Data System (ADS)

    Ivantsov, Ilya; Ferraz, Alvaro; Kochetov, Evgenii

    2016-12-01

    We perform quantum Monte Carlo simulations of the itinerant-localized periodic Kondo-Heisenberg model for the underdoped cuprates to calculate the associated spin correlation functions. The strong electron correlations are shown to play a key role in the abrupt destruction of the quasi-long-range antiferromagnetic order in the lightly doped regime.

  13. Spin-transfer torques in antiferromagnetic textures: Efficiency and quantification method

    NASA Astrophysics Data System (ADS)

    Yamane, Yuta; Ieda, Jun'ichi; Sinova, Jairo

    2016-08-01

    We formulate a theory of spin-transfer torques in textured antiferromagnets, which covers the small to large limits of the exchange coupling energy relative to the kinetic energy of the intersublattice electron dynamics. Our theory suggests a natural definition of the efficiency of spin-transfer torques in antiferromagnets in terms of well-defined material parameters, revealing that the charge current couples predominantly to the antiferromagnetic order parameter and the sublattice-canting moment in, respectively, the limits of large and small exchange coupling. The effects can be quantified by analyzing the antiferromagnetic spin-wave dispersions in the presence of charge current: in the limit of large exchange coupling the spin-wave Doppler shift always occurs, whereas, in the opposite limit, the only spin-wave modes to react to the charge current are ones that carry a pronounced sublattice-canting moment. The findings offer a framework for understanding and designing spin-transfer torques in antiferromagnets belonging to different classes of sublattice structures such as, e.g., bipartite and layered antiferromagnets.

  14. Spin-orbit torque in two-dimensional antiferromagnetic topological insulators

    NASA Astrophysics Data System (ADS)

    Ghosh, S.; Manchon, A.

    2017-01-01

    We investigate spin transport in two-dimensional ferromagnetic (FTI) and antiferromagnetic (AFTI) topological insulators. In the presence of an in-plane magnetization AFTI supports zero energy modes, which enables topologically protected edge conduction at low energy. We address the nature of current-driven spin torque in these structures and study the impact of spin-independent disorder. Interestingly, upon strong disorder the spin torque develops an antidamping component (i.e., even upon magnetization reversal) along the edges, which could enable current-driven manipulation of the antiferromagnetic order parameter. This antidamping torque decreases when increasing the system size and when the system enters the trivial insulator regime.

  15. Single-component molecular material hosting antiferromagnetic and spin-gapped Mott subsystems

    NASA Astrophysics Data System (ADS)

    Takagi, Rina; Hamai, Takamasa; Gangi, Hiro; Miyagawa, Kazuya; Zhou, Biao; Kobayashi, Akiko; Kanoda, Kazushi

    2017-03-01

    We investigated a system based solely on a single molecular species, Cu(tmdt) 2, accommodating d and π orbitals within the molecule. 13C nuclear magnetic resonance measurements captured singlet-triplet excitations of π spins indicating the existence of a π -electron-based spin-gapped Mott insulating subsystem, which has been hidden by the large magnetic susceptibility exhibited by the d spins forming antiferromagnetic chains. The present results demonstrate a unique hybrid Mott insulator composed of antiferromagnetic and spin-singlet Mott subsystems with distinctive dimensionalities.

  16. Noncollinear antiferromagnetism of coupled spins and pseudospins in the double perovskite La2CuIrO6

    NASA Astrophysics Data System (ADS)

    Manna, Kaustuv; Sarkar, R.; Fuchs, S.; Onykiienko, Y. A.; Bera, A. K.; Cansever, G. Aslan; Kamusella, S.; Maljuk, A.; Blum, C. G. F.; Corredor, L. T.; Wolter, A. U. B.; Yusuf, S. M.; Frontzek, M.; Keller, L.; Iakovleva, M.; Vavilova, E.; Grafe, H.-J.; Kataev, V.; Klauss, H.-H.; Inosov, D. S.; Wurmehl, S.; Büchner, B.

    2016-10-01

    We report the structural, magnetic, and thermodynamic properties of the double perovskite compound La2CuIrO6 from x-ray, neutron diffraction, neutron depolarization, dc magnetization, ac susceptibility, specific heat, muon-spin-relaxation (μ SR ), electron-spin-resonance (ESR) and nuclear magnetic resonance (NMR) measurements. Below ˜113 K, short-range spin-spin correlations occur within the Cu2 + sublattice. With decreasing temperature, the Ir4 + sublattice is progressively involved in the correlation process. Below T =74 K, the magnetic sublattices of Cu (spin s =1/2 ) and Ir (pseudospin j =1/2 ) in La2CuIrO6 are strongly coupled and exhibit an antiferromagnetic phase transition into a noncollinear magnetic structure accompanied by a small uncompensated transverse moment. A weak anomaly in ac susceptibility as well as in the NMR and μ SR spin lattice relaxation rates at 54 K is interpreted as a cooperative ordering of the transverse moments which is influenced by the strong spin-orbit coupled 5 d ion Ir4 +. We argue that the rich magnetic behavior observed in La2CuIrO6 is related to complex magnetic interactions between the strongly correlated spin-only 3 d ions with the strongly spin-orbit coupled 5 d transition ions where a combination of the spin-orbit coupling and the low symmetry of the crystal lattice plays a special role for the spin structure in the magnetically ordered state.

  17. Evidence of exchange bias effect originating from the interaction between antiferromagnetic core and spin glass shell

    SciTech Connect

    Zhang, X. K. Yuan, J. J.; Yu, H. J.; Zhu, X. R.; Xie, Y. M.; Tang, S. L.; Xu, L. Q.

    2014-07-14

    Spin glass behavior and exchange bias effect have been observed in antiferromagnetic SrMn{sub 3}O{sub 6−x} nanoribbons synthesized via a self-sacrificing template process. The magnetic field dependence of thermoremanent magnetization and isothermal remanent magnetization shows that the sample is good correspondence to spin glass and diluted antiferromagnetic system for the applied field H < 2 T and H > 2 T, respectively. By detailed analysis of training effect using Binek's model, we argue that the observed exchange bias effect in SrMn{sub 3}O{sub 6−x} nanoribbons arises entirely from an interface exchange coupling between the antiferromagnetic core and spin glass shell. The present study is useful for understanding the nature of shell layer and the origin of exchange bias effect in other antiferromagnetic nanosystems as well.

  18. Probing Spatial Spin Correlations of Ultracold Gases by Quantum Noise Spectroscopy

    SciTech Connect

    Bruun, G. M.; Andersen, Brian M.; Demler, Eugene; Soerensen, Anders S.

    2009-01-23

    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 antibunching, pairing, antiferromagnetic, and algebraic spin liquid correlations can be revealed by measuring the spin noise as a function of laser width, temperature, and frequency.

  19. Persistent nonequilibrium dynamics of the thermal energies in the spin and phonon systems of an antiferromagnet.

    PubMed

    von Reppert, A; Pudell, J; Koc, A; Reinhardt, M; Leitenberger, W; Dumesnil, K; Zamponi, F; Bargheer, M

    2016-09-01

    We present a temperature and fluence dependent Ultrafast X-Ray Diffraction study of a laser-heated antiferromagnetic dysprosium thin film. The loss of antiferromagnetic order is evidenced by a pronounced lattice contraction. We devise a method to determine the energy flow between the phonon and spin system from calibrated Bragg peak positions in thermal equilibrium. Reestablishing the magnetic order is much slower than the cooling of the lattice, especially around the Néel temperature. Despite the pronounced magnetostriction, the transfer of energy from the spin system to the phonons in Dy is slow after the spin-order is lost.

  20. Persistent nonequilibrium dynamics of the thermal energies in the spin and phonon systems of an antiferromagnet

    PubMed Central

    von Reppert, A.; Pudell, J.; Koc, A.; Reinhardt, M.; Leitenberger, W.; Dumesnil, K.; Zamponi, F.; Bargheer, M.

    2016-01-01

    We present a temperature and fluence dependent Ultrafast X-Ray Diffraction study of a laser-heated antiferromagnetic dysprosium thin film. The loss of antiferromagnetic order is evidenced by a pronounced lattice contraction. We devise a method to determine the energy flow between the phonon and spin system from calibrated Bragg peak positions in thermal equilibrium. Reestablishing the magnetic order is much slower than the cooling of the lattice, especially around the Néel temperature. Despite the pronounced magnetostriction, the transfer of energy from the spin system to the phonons in Dy is slow after the spin-order is lost. PMID:27679803

  1. Continuous spin reorientation transition in epitaxially grown antiferromagnetic NiO thin films

    SciTech Connect

    Li, J.; Arenholz, E.; Meng, Y.; Tan, A.; Park, J.; Jin, E.; Son, H.; Wu, J.; Jenkins, C. A.; Scholl, A.; Hwang, Chanyong; Qiu, Z. Q.

    2011-03-01

    Fe/NiO/MgO/Ag(001) films were grown epitaxially, and the Fe and NiO spin orientations were determined using x-ray magnetic dichroism. We find that the NiO spins are aligned perpendicularly to the in-plane Fe spins. Analyzing both the in-plane and out-of-plane spin components of the NiO layer, we demonstrate unambiguously that the antiferromagnetic NiO spins undergo a continuous spin reorientation transition from the in-plane to out-of-plane directions with increasing of the MgO thickness.

  2. Giant facet-dependent spin-orbit torque and spin Hall conductivity in the triangular antiferromagnet IrMn3

    PubMed Central

    Zhang, Weifeng; Han, Wei; Yang, See-Hun; Sun, Yan; Zhang, Yang; Yan, Binghai; Parkin, Stuart S. P.

    2016-01-01

    There has been considerable interest in spin-orbit torques for the purpose of manipulating the magnetization of ferromagnetic elements for spintronic technologies. Spin-orbit torques are derived from spin currents created from charge currents in materials with significant spin-orbit coupling that propagate into an adjacent ferromagnetic material. A key challenge is to identify materials that exhibit large spin Hall angles, that is, efficient charge-to-spin current conversion. Using spin torque ferromagnetic resonance, we report the observation of a giant spin Hall angle θSHeff of up to ~0.35 in (001)-oriented single-crystalline antiferromagnetic IrMn3 thin films, coupled to ferromagnetic permalloy layers, and a θSHeff that is about three times smaller in (111)-oriented films. For (001)-oriented samples, we show that the magnitude of θSHeff can be significantly changed by manipulating the populations of various antiferromagnetic domains through perpendicular field annealing. We identify two distinct mechanisms that contribute to θSHeff: the first mechanism, which is facet-independent, arises from conventional bulk spin-dependent scattering within the IrMn3 layer, and the second intrinsic mechanism is derived from the unconventional antiferromagnetic structure of IrMn3. Using ab initio calculations, we show that the triangular magnetic structure of IrMn3 gives rise to a substantial intrinsic spin Hall conductivity that is much larger for the (001) than for the (111) orientation, consistent with our experimental findings. PMID:27704044

  3. Giant facet-dependent spin-orbit torque and spin Hall conductivity in the triangular antiferromagnet IrMn3.

    PubMed

    Zhang, Weifeng; Han, Wei; Yang, See-Hun; Sun, Yan; Zhang, Yang; Yan, Binghai; Parkin, Stuart S P

    2016-09-01

    There has been considerable interest in spin-orbit torques for the purpose of manipulating the magnetization of ferromagnetic elements for spintronic technologies. Spin-orbit torques are derived from spin currents created from charge currents in materials with significant spin-orbit coupling that propagate into an adjacent ferromagnetic material. A key challenge is to identify materials that exhibit large spin Hall angles, that is, efficient charge-to-spin current conversion. Using spin torque ferromagnetic resonance, we report the observation of a giant spin Hall angle [Formula: see text] of up to ~0.35 in (001)-oriented single-crystalline antiferromagnetic IrMn3 thin films, coupled to ferromagnetic permalloy layers, and a [Formula: see text] that is about three times smaller in (111)-oriented films. For (001)-oriented samples, we show that the magnitude of [Formula: see text] can be significantly changed by manipulating the populations of various antiferromagnetic domains through perpendicular field annealing. We identify two distinct mechanisms that contribute to [Formula: see text]: the first mechanism, which is facet-independent, arises from conventional bulk spin-dependent scattering within the IrMn3 layer, and the second intrinsic mechanism is derived from the unconventional antiferromagnetic structure of IrMn3. Using ab initio calculations, we show that the triangular magnetic structure of IrMn3 gives rise to a substantial intrinsic spin Hall conductivity that is much larger for the (001) than for the (111) orientation, consistent with our experimental findings.

  4. Spin-density-wave antiferromagnetism of Cr in Fe/Cr(001) superlattices

    SciTech Connect

    Fullerton, E.E.; Bader, S.D.; Robertson, J.L.

    1996-10-01

    The antiferromagnetic spin-density-wave (SDW) order of Cr layers in Fe/Cr(001) superlattices was investigated by neutron scattering. For Cr thickness 51-190 {Angstrom}, a transverse SDW is formed for all temperatures below Neel temperature with a single wavevector Q normal to the layers. A coherent magnetic structure forms with the nodes of the SDW near the Fe-Cr interfaces. For thinner Cr layers, the magnetic scattering can be described by commensurate antiferromagnetic order.

  5. Evidence for a gapped spin-liquid ground state in a kagome Heisenberg antiferromagnet

    DOE PAGES

    Fu, Mingxuan; Imai, Takahashi; Han, Tian -Heng; ...

    2015-11-06

    Here, the kagome Heisenberg antiferromagnet is a leading candidate in the search for a spin system with a quantum spin-liquid ground state. The nature of its ground state remains a matter of active debate. We conducted oxygen-17 single-crystal nuclear magnetic resonance (NMR) measurements of the spin-1/2 kagome lattice in herbertsmithite [ZnCu3(OH)6Cl2], which is known to exhibit a spinon continuum in the spin excitation spectrum. We demonstrated that the intrinsic local spin susceptibility χkagome, deduced from the oxygen-17 NMR frequency shift, asymptotes to zero below temperatures of 0.03J, where J ~ 200 kelvin is the copper-copper superexchange interaction. Combined with themore » magnetic field dependence of χkagome that we observed at low temperatures, these results imply that the kagome Heisenberg antiferromagnet has a spin-liquid ground state with a finite gap.« less

  6. Evidence for a gapped spin-liquid ground state in a kagome Heisenberg antiferromagnet.

    PubMed

    Fu, Mingxuan; Imai, Takashi; Han, Tian-Heng; Lee, Young S

    2015-11-06

    The kagome Heisenberg antiferromagnet is a leading candidate in the search for a spin system with a quantum spin-liquid ground state. The nature of its ground state remains a matter of active debate. We conducted oxygen-17 single-crystal nuclear magnetic resonance (NMR) measurements of the spin-1/2 kagome lattice in herbertsmithite [ZnCu3(OH)6Cl2], which is known to exhibit a spinon continuum in the spin excitation spectrum. We demonstrated that the intrinsic local spin susceptibility χ(kagome), deduced from the oxygen-17 NMR frequency shift, asymptotes to zero below temperatures of 0.03J, where J ~ 200 kelvin is the copper-copper superexchange interaction. Combined with the magnetic field dependence of χ(kagome) that we observed at low temperatures, these results imply that the kagome Heisenberg antiferromagnet has a spin-liquid ground state with a finite gap.

  7. Magnetic excitations in the spin-1/2 triangular-lattice antiferromagnet Cs2CuBr4

    DOE PAGES

    Zvyagin, S. A.; Ozerov, M.; Kamenskyi, D.; ...

    2015-11-27

    We present on high- field electron spin resonance (ESR) studies of magnetic excitations in the spin- 1/2 triangular-lattice antiferromagnet Cs2CuBr4. Frequency- field diagrams of ESR excitations are measured for different orientations of magnetic fields up to 25 T. We show that the substantial zero- field energy gap, Δ ≈ 9.5 K, observed in the low-temperature excitation spectrum of Cs2CuBr4 [Zvyagin et al:, Phys. Rev. Lett. 112, 077206 (2014)], is present well above TN. Noticeably, the transition into the long-range magnetically ordered phase does not significantly affect the size of the gap, suggesting that even below TN the high-energy spin dynamicsmore » in Cs2CuBr4 is determined by short-range-order spin correlations. The experimental data are compared with results of model spin-wave-theory calculations for spin-1/2 triangle-lattice antiferromagnet.« less

  8. Boundary-induced spin-density waves in linear Heisenberg antiferromagnetic spin chains with S ≥1

    NASA Astrophysics Data System (ADS)

    Dey, Dayasindhu; Kumar, Manoranjan; Soos, Zoltán G.

    2016-10-01

    Linear Heisenberg antiferromagnets (HAFs) are chains of spin-S sites with isotropic exchange J between neighbors. Open and periodic boundary conditions return the same ground-state energy per site in the thermodynamic limit, but not the same spin SG when S ≥1 . The ground state of open chains of N spins has SG=0 or S , respectively, for even or odd N . Density-matrix renormalization-group calculations with different algorithms for even and odd N are presented up to N =500 for the energy and spin densities ρ (r ,N ) of edge states in HAFs with S =1 , 3/2, and 2. The edge states are boundary-induced spin density waves (BI-SDWs) with ρ (r ,N ) ∝(-1) r -1 for r =1 ,2 ,...,N . The SDWs are in phase when N is odd, are out of phase when N is even, and have finite excitation energy Γ (N ) that decreases exponentially with N for integer S and faster than 1 /N for half integer S . The spin densities and excitation energy are quantitatively modeled for integer S chains longer than 5 ξ spins by two parameters, the correlation length ξ and the SDW amplitude, with ξ =6.048 for S =1 and 49.0 for S =2 . The BI-SDWs of S =3 /2 chains are not localized and are qualitatively different for even and odd N . Exchange between the ends for odd N is mediated by a delocalized effective spin in the middle that increases |Γ (N )| and weakens the size dependence. The nonlinear sigma model (NL σ M ) has been applied to the HAFs, primarily to S =1 with even N , to discuss spin densities and exchange between localized states at the ends as Γ (N ) ∝(-1) Nexp(-N /ξ ) . S =1 chains with odd N are fully consistent with the NL σ M ; S =2 chains have two gaps Γ (N ) with the same ξ as predicted whose ratio is 3.45 rather than 3; the NL σ M is more approximate for S =3 /2 chains with even N and is modified for exchange between ends for odd N .

  9. Incommensurate antiferromagnetism in a pure spin system via cooperative organization of local and itinerant moments

    PubMed Central

    Feng, Yejun; Wang, Jiyang; Silevitch, D. M.; Mihaila, B.; Kim, J. W.; Yan, J.-Q.; Schulze, R. K.; Woo, Nayoon; Palmer, A.; Ren, Y.; van Wezel, Jasper; Littlewood, P. B.; Rosenbaum, T. F.

    2013-01-01

    Materials with strong correlations are prone to spin and charge instabilities, driven by Coulomb, magnetic, and lattice interactions. In materials that have significant localized and itinerant spins, it is not obvious which will induce order. We combine electrical transport, X-ray magnetic diffraction, and photoemission studies with band structure calculations to characterize successive antiferromagnetic transitions in GdSi. GdSi has both sizable local moments and a partially nested Fermi surface, without confounding contributions from orbital effects. We identify a route to incommensurate order where neither type of moment dominates, but is rooted in cooperative feedback between them. The nested Fermi surface of the itinerant electrons induces strong interactions between local moments at the nesting vector, whereas the ordered local moments in turn provide the necessary coupling for a spin-density wave to form among the itinerant electrons. This mechanism echoes the cooperative interactions between electrons and ions in charge-density–wave materials, and should be germane across a spectrum of transition-metal and rare-earth intermetallic compounds. PMID:23401555

  10. Spin-Chirality-Driven Ferroelectricity on a Perfect Triangular Lattice Antiferromagnet

    DOE PAGES

    Mitamura, H.; Watanuki, R.; Kaneko, Koji; ...

    2014-10-01

    Magnetic field (B) variation of the electrical polarization Pc ( ∥c) of the perfect triangular lattice antiferromagnet RbFe(MoO4)2 is examined up to the saturation point of the magnetization for B⊥c. Pc is observed only in phases for which chirality is predicted in the in-plane magnetic structures. No strong anomaly is observed in Pc at the field at which the spin modulation along the c axis, and hence the spin helicity, exhibits a discontinuity to the commensurate state. These results indicate that the ferroelectricity in this compound originates predominantly from the spin chirality, the explanation of which would require a newmore » mechanism for magnetoferroelectricity. Lastly, the obtained field-temperature phase diagrams of ferroelectricity well agree with those theoretically predicted for the spin chirality of a Heisenberg spin triangular lattice antiferromagnet.« less

  11. Spin-Chirality-Driven Ferroelectricity on a Perfect Triangular Lattice Antiferromagnet

    SciTech Connect

    Mitamura, H.; Watanuki, R.; Kaneko, Koji; Onozaki, N.; Amou, Y.; Kittaka, S.; Kobayashi, Riki; Shimura, Y.; Yamamoto, I.; Suzuki, K.; Chi, Songxue; Sakakibara, T.

    2014-10-01

    Magnetic field (B) variation of the electrical polarization Pc ( ∥c) of the perfect triangular lattice antiferromagnet RbFe(MoO4)2 is examined up to the saturation point of the magnetization for B⊥c. Pc is observed only in phases for which chirality is predicted in the in-plane magnetic structures. No strong anomaly is observed in Pc at the field at which the spin modulation along the c axis, and hence the spin helicity, exhibits a discontinuity to the commensurate state. These results indicate that the ferroelectricity in this compound originates predominantly from the spin chirality, the explanation of which would require a new mechanism for magnetoferroelectricity. Lastly, the obtained field-temperature phase diagrams of ferroelectricity well agree with those theoretically predicted for the spin chirality of a Heisenberg spin triangular lattice antiferromagnet.

  12. Antiferromagnetically Spin Polarized Oxygen Observed in Magneto-electric TbMn2O5

    SciTech Connect

    Wilkins, S.B.; Beale, T.A.W.; Johnson, R.D.; Bland, S.R.; Joly, Y.; Forrest, T.R.; McMorrow, D.F.; Yakhou, F.; Prabhakaran, D.; Boothroyd, A.T.; Hatton, P.D.

    2010-08-18

    We report the direct measurement of antiferromagnetic spin polarization at the oxygen sites in the multiferroic TbMn{sub 2}O{sub 5}, 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 accurately reproduced the experimental data. We have established that the resonance arises through the spin polarization on the oxygen sites hybridized with the square based pyramid Mn{sup 3+} ions. Furthermore we have discovered that the position of the Mn{sup 3+} ion directly influences the oxygen spin polarization.

  13. Vectorial mapping of noncollinear antiferromagnetic structure of semiconducting FeSe surface with spin-polarized scanning tunneling microscopy

    SciTech Connect

    Zhang, K. F.; Yang, Fang; Song, Y. R.; Zhang, Xiaole; Chen, Xianfeng; Liu, Canhua; Qian, Dong; Gao, C. L. Jia, Jin-Feng; Luo, Weidong

    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.

  14. Spin-orbit torques in locally and globally noncentrosymmetric crystals: Antiferromagnets and ferromagnets

    NASA Astrophysics Data System (ADS)

    Železný, J.; Gao, H.; Manchon, Aurélien; Freimuth, Frank; Mokrousov, Yuriy; Zemen, J.; Mašek, J.; Sinova, Jairo; Jungwirth, T.

    2017-01-01

    One of the main obstacles that prevents practical applications of antiferromagnets is the difficulty of manipulating the magnetic order parameter. Recently, following the theoretical prediction [J. Železný et al., Phys. Rev. Lett. 113, 157201 (2014)], 10.1103/PhysRevLett.113.157201, the electrical switching of magnetic moments in an antiferromagnet was demonstrated [P. Wadley et al., Science 351, 587 (2016)], 10.1126/science.aab1031. The switching is due to the so-called spin-orbit torque, which has been extensively studied in ferromagnets. In this phenomena a nonequilibrium spin-polarization exchange coupled to the ordered local moments is induced by current, hence exerting a torque on the order parameter. Here we give a general systematic analysis of the symmetry of the spin-orbit torque in locally and globally noncentrosymmetric crystals. We study when the symmetry allows for a nonzero torque, when is the torque effective, and its dependence on the applied current direction and orientation of magnetic moments. For comparison, we consider both antiferromagnetic and ferromagnetic orders. In two representative model crystals we perform microscopic calculations of the spin-orbit torque to illustrate its symmetry properties and to highlight conditions under which the spin-orbit torque can be efficient for manipulating antiferromagnetic moments.

  15. Antiferromagnetic domains and the spin-flop transition of MnF2

    NASA Astrophysics Data System (ADS)

    Felcher, G. P.; Kleb, R.

    1996-11-01

    In antiferromagnetic MnF2 the magnetic moments of manganese are aligned along the tetragonal axis of the rutile structure. In a magnetic field HSF along that axis (9.27 T at 4.2 K) the antiferromagnetic moments flop in the basal plane. Polarized neutron diffraction measurements showed that at about HSF the entire crystal becomes aligned in a single antiferromagnetic domain, which persists even after the field is suppressed. The effect is due to a minute misalignment (a fraction of degree) of the applied field with the tetragonal axis of the crystal. The ensuing breakdown of symmetry at the spin-flop transition provides a way to control domains in this type of antiferromagnet.

  16. Transient ferromagnetic-like state mediating ultrafast reversal of antiferromagnetically coupled spins.

    PubMed

    Radu, I; Vahaplar, K; Stamm, C; Kachel, T; Pontius, N; Dürr, H A; Ostler, T A; Barker, J; Evans, R F L; Chantrell, R W; Tsukamoto, A; Itoh, A; Kirilyuk, A; Rasing, Th; Kimel, A V

    2011-04-14

    Ferromagnetic or antiferromagnetic spin ordering is governed by the exchange interaction, the strongest force in magnetism. Understanding spin dynamics in magnetic materials is an issue of crucial importance for progress in information processing and recording technology. Usually the dynamics are studied by observing the collective response of exchange-coupled spins, that is, spin resonances, after an external perturbation by a pulse of magnetic field, current or light. The periods of the corresponding resonances range from one nanosecond for ferromagnets down to one picosecond for antiferromagnets. However, virtually nothing is known about the behaviour of spins in a magnetic material after being excited on a timescale faster than that corresponding to the exchange interaction (10-100 fs), that is, in a non-adiabatic way. Here we use the element-specific technique X-ray magnetic circular dichroism to study spin reversal in GdFeCo that is optically excited on a timescale pertinent to the characteristic time of the exchange interaction between Gd and Fe spins. We unexpectedly find that the ultrafast spin reversal in this material, where spins are coupled antiferromagnetically, occurs by way of a transient ferromagnetic-like state. Following the optical excitation, the net magnetizations of the Gd and Fe sublattices rapidly collapse, switch their direction and rebuild their net magnetic moments at substantially different timescales; the net magnetic moment of the Gd sublattice is found to reverse within 1.5 picoseconds, which is substantially slower than the Fe reversal time of 300 femtoseconds. Consequently, a transient state characterized by a temporary parallel alignment of the net Gd and Fe moments emerges, despite their ground-state antiferromagnetic coupling. These surprising observations, supported by atomistic simulations, provide a concept for the possibility of manipulating magnetic order on the timescale of the exchange interaction.

  17. Role of the antiferromagnetic bulk spins in exchange bias

    NASA Astrophysics Data System (ADS)

    Schuller, Ivan K.; Morales, Rafael; Batlle, Xavier; Nowak, Ulrich; Güntherodt, Gernot

    2016-10-01

    This "Critical Focused Issue" presents a brief review of experiments and models which describe the origin of exchange bias in epitaxial or textured ferromagnetic/antiferromagnetic bilayers. Evidence is presented which clearly indicates that inner, uncompensated, pinned moments in the bulk of the antiferromagnet (AFM) play a very important role in setting the magnitude of the exchange bias. A critical evaluation of the extensive literature in the field indicates that it is useful to think of this bulk, pinned uncompensated moments as a new type of a ferromagnet which has a low total moment, an ordering temperature given by the AFM Néel temperature, with parallel aligned moments randomly distributed on the regular AFM lattice.

  18. Robust picosecond writing of a layered antiferromagnet by staggered spin-orbit fields

    NASA Astrophysics Data System (ADS)

    Roy, P. E.; Otxoa, R. M.; Wunderlich, J.

    2016-07-01

    Ultrafast electrical switching by current-induced staggered spin-orbit fields, with minimal risk of overshoot is shown in layered easy-plane antiferromagnets with basal-plane anisotropies. Reliable switching is due to the fieldlike torque, relaxing stringent requirements with respect to precision in the duration of the excitation pulse. Focus is put on a system with weak planar biaxial anisotropy. We investigate the switching as a function of the spin-orbit field strength, pulse duration, rise and fall times, and damping using atomistic spin dynamics simulations and an effective equation for the antiferromagnetic order parameter. The critical spin-orbit field strength required for switching a biaxial system is determined, and we show that writing is possible at feasible current magnitudes. Finally, we discuss switching of systems exhibiting a dominant uniaxial basal-plane anisotropy.

  19. Quantum spin fluctuations and ellipticity for a triangular-lattice antiferromagnet

    NASA Astrophysics Data System (ADS)

    Fishman, Randy S.

    2011-08-01

    The effects of quantum spin fluctuations are investigated for the three-sublattice spin configurations of a geometrically frustrated triangular-lattice antiferromagnet in a magnetic field with easy-axis anisotropy. Because quantum fluctuations reduce the tilt of the spins toward the easy axis, the predicted distortion of the noncollinear state at zero field is too small to explain the ellipticity reported for the multiferroic state of CuCrO2. Due to the change in spin angles, quantum fluctuations shift the boundaries between the collinear and noncollinear phases and open a gap in field between the two types of noncollinear phases.

  20. Adiabatic demagnetization of the antiferromagnetic spin-1/2 Heisenberg hexagonal cluster

    NASA Astrophysics Data System (ADS)

    Deb, Moumita; Ghosh, Asim Kumar

    2016-05-01

    Exact analytic expressions of eigenvalues of the antiferromagnetic spin-1/2 Heisenberg hexagon in the presence of uniform magnetic field have been obtained. Magnetization process, nature of isentrops and properties of magneto caloric effect in terms of adiabatic demagnetization have been investigated. Theoretical results have been used to study the magneto caloric effect of the spin-1/2 Heisenberg hexagonal compound Cu3WO6.

  1. Room temperature spin-polarizations of Mn-based antiferromagnetic nanoelectrodes

    SciTech Connect

    Yamada, Toyo Kazu; Vazquez de Parga, Amadeo L.

    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.

  2. Antiferromagnetic Spin Coupling between Rare Earth Adatoms and Iron Islands Probed by Spin-Polarized Tunneling

    PubMed Central

    Coffey, David; Diez-Ferrer, José Luis; Serrate, David; Ciria, Miguel; Fuente, César de la; 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

  3. High Antiferromagnetic Domain Wall Velocity Induced by Néel Spin-Orbit Torques

    NASA Astrophysics Data System (ADS)

    Gomonay, O.; Jungwirth, T.; Sinova, J.

    2016-07-01

    We demonstrate the possibility to drive an antiferromagnetic domain wall at high velocities by fieldlike Néel spin-orbit torques. Such torques arise from current-induced local fields that alternate their orientation on each sublattice of the antiferromagnet and whose orientation depends primarily on the current direction, giving them their fieldlike character. The domain wall velocities that can be achieved by this mechanism are 2 orders of magnitude greater than the ones in ferromagnets. This arises from the efficiency of the staggered spin-orbit fields to couple to the order parameter and from the exchange-enhanced phenomena in antiferromagnetic texture dynamics, which leads to a low domain wall effective mass and the absence of a Walker breakdown limit. In addition, because of its nature, the staggered spin-orbit field can lift the degeneracy between two 180° rotated states in a collinear antiferromagnet, and it provides a force that can move such walls and control the switching of the states.

  4. Instanton paths and coherent quantum tunneling in antiferromagnetic spin clusters subject to a strong magnetic field

    SciTech Connect

    Ivanov, B. A. Kireev, V. E.

    2008-09-15

    The coherent quantum tunneling effects in antiferromagnets in the presence of a strong external magnetic field parallel to the easy axis have been investigated using the instanton formalism. In a wide field range including the region of the phase spin-flop transition, the tunneling is described by 180{sup o} instantons for which the Euclidean action is real and destructive interference is absent. At the transition point, 90{sup o} instantons describing the tunneling between the collinear and spin-flop states appear. The Euclidean action decreases, whereas the tunneling probability and tunneling level splitting in both phases increase significantly in the immediate vicinity of the spin-flop transition point. The possibility of observing the coherent tunneling effects for artificial small particles (magnetic dots) made of antiferromagnets is discussed.

  5. Spin-1/2 Heisenberg Antiferromagnet on the Spatially Anisotropic Kagome Lattice

    NASA Astrophysics Data System (ADS)

    Schnyder, Andreas; Starykh, Oleg; Balents, Leon

    2008-03-01

    We study the quasi-one-dimensional limit of the Spin-1/2 quantum antiferromagnet on the Kagome lattice, a model Hamiltonian that might be of relevance for the mineral volborthite [1,2]. The lattice is divided into antiferromagnetic spin-chains (exchange J) that are weakly coupled via intermediate ``dangling'' spins (exchange J'). Using bosonization, renormalization group methods, and current algebra techniques we determine the ground state as a function of J'/J. The case of a strictly one-dimensional Kagome strip is also discussed. [1] Z. Hiroi, M. Hanawa, N. Kobayashi, M. Nohara, Hidenori Takagi, Y. Kato, and M. Takigawa, J. Phys. Soc. Japan 70, 3377 (2001). [2] F. Bert, D. Bono, P. Mendels, F. Ladieu, F. Duc, J.-C. Trumbe, and P. Millet, Phys. Rev. Lett. 95, 087203 (2005).

  6. Electric Control of Dirac Quasiparticles by Spin-Orbit Torque in an Antiferromagnet

    NASA Astrophysics Data System (ADS)

    Šmejkal, L.; Železný, J.; Sinova, J.; Jungwirth, T.

    2017-03-01

    Spin orbitronics and Dirac quasiparticles are two fields of condensed matter physics initiated independently about a decade ago. Here we predict that Dirac quasiparticles can be controlled by the spin-orbit torque reorientation of the Néel vector in an antiferromagnet. Using CuMnAs as an example, we formulate symmetry criteria allowing for the coexistence of topological Dirac quasiparticles and Néel spin-orbit torques. We identify the nonsymmorphic crystal symmetry protection of Dirac band crossings whose on and off switching is mediated by the Néel vector reorientation. We predict that this concept verified by minimal model and density functional calculations in the CuMnAs semimetal antiferromagnet can lead to a topological metal-insulator transition driven by the Néel vector and to the topological anisotropic magnetoresistance.

  7. Transition from the Z2 spin liquid to antiferromagnetic order: Spectrum on the torus

    NASA Astrophysics Data System (ADS)

    Whitsitt, Seth; Sachdev, Subir

    2016-08-01

    We describe the finite-size spectrum in the vicinity of the quantum critical point between a Z2 spin liquid and a coplanar antiferromagnet on the torus. We obtain the universal evolution of all low-lying states in an antiferromagnet with global SU(2) spin rotation symmetry, as it moves from the fourfold topological degeneracy in a gapped Z2 spin liquid to the Anderson "tower-of-states" in the ordered antiferromagnet. Due to the existence of nontrivial order on either side of this transition, this critical point cannot be described in a conventional Landau-Ginzburg-Wilson framework. Instead, it is described by a theory involving fractionalized degrees of freedom known as the O (4) * model, whose spectrum is altered in a significant way by its proximity to a topologically ordered phase. We compute the spectrum by relating it to the spectrum of the O (4 ) Wilson-Fisher fixed point on the torus, modified with a selection rule on the states, and with nontrivial boundary conditions corresponding to topological sectors in the spin liquid. The spectrum of the critical O (2 N ) model is calculated directly at N =∞ , which then allows a reconstruction of the full spectrum of the O (2N ) * model at leading order in 1 /N . This spectrum is a unique characteristic of the vicinity of a fractionalized quantum critical point, as well as a universal signature of the existence of proximate Z2 topological and antiferromagnetically ordered phases, and can be compared with numerical computations on quantum antiferromagnets on two-dimensional lattices.

  8. Directly probing spin dynamics in insulating antiferromagnets using ultrashort terahertz pulses

    SciTech Connect

    Bowlan, Pamela Renee; Trugman, Stuart Alan; Wang, X.; Dai, Yaomin; Cheong, S.-W.; Bauer, Eric Dietzgen; Taylor, Antoinette Jane; Yarotski, Dmitry Anatolievitch; Prasankumar, Rohit Prativadi

    2016-11-22

    We investigate spin dynamics in the antiferromagnetic (AFM) multiferroic TbMnO3 using opticalpump, terahertz (THz)-probe spectroscopy. Photoexcitation results in a broadband THz transmission change, with an onset time of 25 ps at 6 K that becomes faster at higher temperatures. We attribute this time constant to spin-lattice thermalization. The excellent agreement between our measurements and previous ultrafast resonant x-ray diffraction measurements on the same material confirms that our THz pulse directly probes spin order. We suggest that this could be the case in general for insulating AFM materials, if the origin of the static absorption in the THz spectral range is magnetic.

  9. Spin transport of the frustrated quasi-two-dimensional XY-like antiferromagnet

    NASA Astrophysics Data System (ADS)

    Lima, L. S.

    2017-01-01

    We use the Self Consistent Harmonic Approximation together with the Kubo formalism of the Linear Response Theory to study the spin transport in the two-dimensional frustrated Heisenberg antiferromagnet in a square lattice with easy-plane ion single anisotropy. The regular part of the spin conductivity σreg(ω) is determined for several values of the critical ion single parameter Dc, that separates the low D region from the large D quantum paramagnetic phase. We have obtained an abrupt change in the spin conductivity in the discontinuity points of the graphic Dc vs. η, where the system presents a quantum phase transition.

  10. Competing antiferromagnetic and spin-glass phases in a hollandite structure

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

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

  11. Magnetic Correlations in the Triangular Antiferromagnet TbInO3

    NASA Astrophysics Data System (ADS)

    Sala, Gabriele; Clark, Lucy; Maharaj, Dalini; Stone, Matthew B.; Knight, Kevin S.; Cheong, Sang-Wook; Gaulin, Bruce D.

    TbInO3 crystallizes with a hexagonal P63 cm structure in which layers of edge-sharing triangles of magnetic Tb3+ ions are separated by non-magnetic [InO5]7- units. TbInO3, therefore, realizes an excellent opportunity to explore the behavior of a two-dimensional magnetic triangular lattice, a canonical model of geometric frustration. Here we present our study of a polycrystalline sample of TbInO3. Our high resolution powder neutron diffraction data (HRPD, ISIS) of TbInO3 confirm that the triangular layers of Tb3+ remain undistorted to at least 0 . 46 K. Magnetic susceptibility data follow Curie-Weiss behavior over a wide range of T with θ = - 17 . 19 (3) K indicating the dominance of antiferromagnetic correlations. The susceptibility data also show an absence of conventional long-range spin order down to at least 0 . 55 K, reflecting the frustrated nature of TbInO3. Elastic magnetic diffuse neutron scattering (SEQUOIA, SNS) is observed below ~ 15 K, due to the presence of static two-dimensional spin correlations. The spectrum of crystal field excitations in TbInO3 appears to have an exotic form due to the existence of two crystallographically distinct Tb3+ sites and leads to a strong Ising anisotropy of the spin symmetry.

  12. Spin-polarized valley Hall effect in ultrathin silicon nanomembrane via interlayer antiferromagnetic coupling

    NASA Astrophysics Data System (ADS)

    Sun, Jia-Tao; Wang, Zhengfei; Meng, S.; Du, Shixuan; Liu, F.; Gao, H.-J.

    2016-09-01

    Fundamental understanding of two-dimensional materials has spurred a surge in the search for topological quantum phase associated with the valley degree of freedom (VDOF). We discuss a spin-polarized version to the VDOF in which spin degeneracy is broken by the antiferromagnetic exchange coupling (LAFM) between opposite layers of the quasi-two-dimensional silicon nanomembrane (SiNM). Based on first principles calculations, we found that the LAFM state in SiNM can lead to metal-insulator transition (MIT). The broken degeneracy of spin degree of freedom in this insulating state of ultrathin SiNM may differ for different valleys, so that the SiNM can be exploited to produce the spatially separated spin and valley currents. We propose that the tunable spin-polarized valley photocurrents can be generated in an experimentally feasible ellipsometry setup. Our work shows promise for the development of spintronic and valleytronic devices compatible with current silicon industry.

  13. Spin waves in the fcc lattice antiferromagnet: competing interactions, frustration, and instabilities in the Hubbard model

    NASA Astrophysics Data System (ADS)

    Singh, Avinash; Mohapatra, Shubhajyoti; Ziman, Timothy; Chatterji, Tapan

    2017-02-01

    Spin waves in the type-III ordered antiferromagnetic state of the frustrated t- t ' Hubbard model on the face-centred-cubic (fcc) lattice are calculated to investigate finite-U-induced competing interaction and frustration effects on magnetic excitations and instabilities. Particularly strong competing interactions generated due to the interplay of fcc lattice geometry and magnetic order result in significant spin wave softening. The calculated spin wave dispersion is found to be in qualitative agreement with the measured spin wave dispersion in the pyrite mineral MnS2 obtained from inelastic neutron scattering experiments. Instabilities to other magnetic orders (type I, type II, spiral, non-collinear), as signalled by spin wave energies turning negative, are also discussed.

  14. Field-dependent spin-wave damping in ferromagnet/antiferromagnet bilayers

    NASA Astrophysics Data System (ADS)

    Moradi, H.

    2006-04-01

    Damon Eshbach mode is used to explain the dependence of spin-wave frequency of ferromagnetic layer in thin ferromagnetic (FM)/antiferromagnetic bilayer (FM/AFM) (Fe/FeF2) as a function of external field. We show that the exchange bias changes as a function of external field. Field-dependent spin-wave damping is calculated by Born approximation. A random field, due to roughness at interface, is invoked to explain the large broadening of the spin-wave mode when the AFM layer is present. In this calculation, the broadening of the spin-wave mode depends on the square of linewidth random fields. To explain the broadening of the spin-wave mode with observed results, the linewidth random fields should decrease with external field. For a magnitude of external field, we have a peak in broadening that can also be observed in experimental results.

  15. Antiferromagnetic spintronics.

    PubMed

    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.

  16. Pairing Correlations at High Spins

    NASA Astrophysics Data System (ADS)

    Ma, Hai-Liang; Dong, Bao-Guo; Zhang, Yan; Fan, Ping; Yuan, Da-Qing; Zhu, Shen-Yun; Zhang, Huan-Qiao; Petrache, C. M.; Ragnarsson, I.; Carlsson, B. G.

    The pairing correcting energies at high spins in 161Lu and 138Nd are studied by comparing the results of the cranked-Nilsson-Strutinsky (CNS) and cranked-Nilsson-Strutinsky-Bogoliubov (CNSB) models. It is concluded that the Coriolis effect rather than the rotational alignment effect plays a major role in the reduction of the pairing correlations in the high spin region. Then we proposed an average pairing correction method which not only better reproduces the experimental data comparing with the CNS model but also enables a clean-cut tracing of the configurations thus the full-spin-range discussion on the various rotating bands.

  17. Spin dynamics near a putative antiferromagnetic quantum critical point in Cu-substituted BaFe2As2 and its relation to high-temperature superconductivity

    DOE PAGES

    Kim, M. G.; Wang, M.; Tucker, G. S.; ...

    2015-12-02

    We present the results of elastic and inelastic neutron scattering measurements on nonsuperconducting Ba(Fe0.957Cu0.043)2As2, a composition close to a quantum critical point between antiferromagnetic (AFM) ordered and paramagnetic phases. By comparing these results with the spin fluctuations in the low-Cu composition as well as the parent compound BaFe2As2 and superconducting Ba(Fe1–xNix)2As2 compounds, we demonstrate that paramagnon-like spin fluctuations are evident in the antiferromagnetically ordered state of Ba(Fe0.957Cu0.043)2As2, which is distinct from the AFM-like spin fluctuations in the superconducting compounds. Our observations suggest that Cu substitution decouples the interaction between quasiparticles and the spin fluctuations. In addition, we show that themore » spin-spin correlation length ξ(T) increases rapidly as the temperature is lowered and find ω/T scaling behavior, the hallmark of quantum criticality, at an antiferromagnetic quantum critical point.« less

  18. Evidence for a gapped spin-liquid ground state in a kagome Heisenberg antiferromagnet

    SciTech Connect

    Fu, Mingxuan; Imai, Takahashi; Han, Tian -Heng; Lee, Young S.

    2015-11-06

    Here, the kagome Heisenberg antiferromagnet is a leading candidate in the search for a spin system with a quantum spin-liquid ground state. The nature of its ground state remains a matter of active debate. We conducted oxygen-17 single-crystal nuclear magnetic resonance (NMR) measurements of the spin-1/2 kagome lattice in herbertsmithite [ZnCu3(OH)6Cl2], which is known to exhibit a spinon continuum in the spin excitation spectrum. We demonstrated that the intrinsic local spin susceptibility χkagome, deduced from the oxygen-17 NMR frequency shift, asymptotes to zero below temperatures of 0.03J, where J ~ 200 kelvin is the copper-copper superexchange interaction. Combined with the magnetic field dependence of χkagome that we observed at low temperatures, these results imply that the kagome Heisenberg antiferromagnet has a spin-liquid ground state with a finite gap.

  19. Quantized antiferromagnetic spin waves in the molecular Heisenberg ring CsFe8

    NASA Astrophysics Data System (ADS)

    Dreiser, J.; Waldmann, O.; Dobe, C.; Carver, G.; Ochsenbein, S. T.; Sieber, A.; Güdel, H. U.; van Duijn, J.; Taylor, J.; Podlesnyak, A.

    2010-01-01

    We report on inelastic neutron-scattering (INS) measurements on the molecular spin ring CsFe8 , in which eight spin-5/2 Fe(III) ions are coupled by nearest-neighbor antiferromagnetic Heisenberg interaction. We have recorded INS data on a nondeuterated powder sample up to high energies at the time-of-flight spectrometers FOCUS at PSI and MARI at ISIS, which clearly show the excitation of spin waves in the ring. Due to the small number of spin sites, the spin-wave dispersion relation is not continuous but quantized. Furthermore, the system exhibits a gap between the ground state and the first excited state. We have modeled our data using exact diagonalization of a Heisenberg-exchange Hamiltonian together with a small single-ion anisotropy term. Due to the molecule’s symmetry, only two parameters J and D are needed to obtain excellent agreement with the data. The results can be well described within the framework of the rotational-band model as well as antiferromagnetic spin-wave theories.

  20. Pressure-tuned spin and charge ordering in an itinerant antiferromagnet.

    PubMed

    Feng, Yejun; Jaramillo, R; Srajer, G; Lang, J C; Islam, Z; Somayazulu, M S; Shpyrko, O G; Pluth, J J; Mao, H-K; Isaacs, E D; Aeppli, G; Rosenbaum, T F

    2007-09-28

    Elemental chromium orders antiferromagnetically near room temperature, but the ordering temperature can be driven to zero by applying large pressures. We combine diamond anvil cell and synchrotron x-ray diffraction techniques to measure directly the spin and charge order in the pure metal at the approach to its quantum critical point. Both spin and charge order are suppressed exponentially with pressure, well beyond the region where disorder cuts off such a simple evolution, and they maintain a harmonic scaling relationship over decades in scattering intensity. By comparing the development of the order parameter with that of the magnetic wave vector, it is possible to ascribe the destruction of antiferromagnetism to the growth in electron kinetic energy relative to the underlying magnetic exchange interaction.

  1. Susceptibility of the 2D spin-1 / 2 Heisenberg antiferromagnet with an impurity.

    PubMed

    Höglund, Kaj H; Sandvik, Anders W

    2003-08-15

    We use a quantum Monte Carlo method (stochastic series expansion) to study the effects of a magnetic or nonmagnetic impurity on the magnetic susceptibility of the two-dimensional Heisenberg antiferromagnet. At low temperatures, we find a log-divergent contribution to the transverse susceptibility. We also introduce an effective few-spin model that can quantitatively capture the differences between magnetic and nonmagnetic impurities at high and intermediate temperatures.

  2. Probing the antiferromagnetic long-range order with Glauber spin states

    NASA Technical Reports Server (NTRS)

    Cabrera, Guillermo G.

    1994-01-01

    It is well known that the ground state of low-dimensional antiferromagnets deviates from Neel states due to strong quantum fluctuations. Even in the presence of long-range order, those fluctuations produce a substantial reduction of the magnetic moment from its saturation value. Numerical simulations in anisotropic antiferromagnetic chains suggest that quantum fluctuations over Neel order appear in the form of localized reversal of pairs of neighboring spins. In this paper, we propose a coherent state representation for the ground state to describe the above situation. In the one-dimensional case, our wave function corresponds to a two-mode Glauber state, when the Neel state is used as a reference, while the boson fields are associated to coherent flip of spin pairs. The coherence manifests itself through the antiferromagnetic long-range order that survives the action of quantum fluctuations. The present representation is different from the standard zero-point spin wave state, and is asymptotically exact in the limit of strong anisotropy. The fermionic version of the theory, obtained through the Jordan-Wigner transformation, is also investigated.

  3. Antiferromagnetism of La2CuO(4-y) studied by muon-spin rotation

    NASA Technical Reports Server (NTRS)

    Uemura, Y. J.; Kossler, W. J.; Yu, X. H.; Kempton, J. R.; Schone, H. E.

    1987-01-01

    Zero-field spin precession of positive muons has been observed in the antiferromagnetic state of La2CuO(4-y). Sharp onsets of the sublattice magnetization are found at temperatures close to those of the susceptibility maxima of different specimens. The long-lived precession signal indicates a microscopically homogeneous distribution of spin density at each Cu atom below the Neel temperature. A combination of the present results and neutron-scattering studies indicates the ordered moment per Cu atom to be significantly less than 1 mu(B).

  4. Spin-Lattice-Coupled Order in Heisenberg Antiferromagnets on the Pyrochlore Lattice.

    PubMed

    Aoyama, Kazushi; Kawamura, Hikaru

    2016-06-24

    Effects of local lattice distortions on the spin ordering are investigated for the antiferromagnetic classical Heisenberg model on the pyrochlore lattice. It is found by Monte Carlo simulations that the spin-lattice coupling (SLC) originating from site phonons induces a first-order transition into two different types of collinear magnetic ordered states. The state realized at the stronger SLC is cubic symmetric characterized by the magnetic (1/2,1/2,1/2) Bragg peaks, while that at the weaker SLC is tetragonal symmetric characterized by the (1,1,0) ones, each accompanied by the commensurate local lattice distortions. Experimental implications to chromium spinels are discussed.

  5. Spin-Lattice-Coupled Order in Heisenberg Antiferromagnets on the Pyrochlore Lattice

    NASA Astrophysics Data System (ADS)

    Aoyama, Kazushi; Kawamura, Hikaru

    2016-06-01

    Effects of local lattice distortions on the spin ordering are investigated for the antiferromagnetic classical Heisenberg model on the pyrochlore lattice. It is found by Monte Carlo simulations that the spin-lattice coupling (SLC) originating from site phonons induces a first-order transition into two different types of collinear magnetic ordered states. The state realized at the stronger SLC is cubic symmetric characterized by the magnetic (1/2 ,1/2 ,1/2 ) Bragg peaks, while that at the weaker SLC is tetragonal symmetric characterized by the (1,1,0) ones, each accompanied by the commensurate local lattice distortions. Experimental implications to chromium spinels are discussed.

  6. Correlation-driven transport asymmetries through coupled spins in a tunnel junction

    NASA Astrophysics Data System (ADS)

    Muenks, Matthias; Jacobson, Peter; Ternes, Markus; Kern, Klaus

    2017-01-01

    Spin-spin correlations can be the driving force that favours certain ground states and are key in numerous models that describe the behaviour of strongly correlated materials. While the sum of collective correlations usually lead to a macroscopically measurable change in properties, a direct quantification of correlations in atomic scale systems is difficult. Here we determine the correlations between a strongly hybridized spin impurity on the tip of a scanning tunnelling microscope and its electron bath by varying the coupling to a second spin impurity weakly hybridized to the sample surface. Electronic transport through these coupled spins reveals an asymmetry in the differential conductance reminiscent of spin-polarized transport in a magnetic field. We show that at zero field, this asymmetry can be controlled by the coupling strength and is related to either ferromagnetic or antiferromagnetic spin-spin correlations in the tip.

  7. Thermal evolution of antiferromagnetic correlations and tetrahedral bond angles in superconducting FeTe1-xSex

    NASA Astrophysics Data System (ADS)

    Xu, Guangyong; Xu, Zhijun; Schneeloch, John; Wen, Jinsheng; Bozin, Emil; Winn, Barry; Feygenson, M.; Birgeneau, R. J.; Gu, Genda; Zaliznyak, Igor; Tranquada, John

    We will present neutron scattering measurements of low energy magnetic excitations from superconducting FeTe1-xSex samples. A model with short-range correlated spin plaquettes characterized by particular antiferromagnetic wave vectors is used to describe the measured magnetic scattering data in the (HK0) plane. We show that the characteristic antiferromagnetic wave vector evolves from that characteristic of the bicollinear structure characteristic of FeTe1-xSex (at high temperature) to that associated with the stripe structure of antiferromagnetic iron arsenides (at low temperature). We also present powder neutron diffraction results for lattice parameters in FeTe1-xSex indicating that the tetrahedral bond angle tends to increase towards the ideal value on cooling, with a corresponding reduction in crystal-field splitting of the Fe 3d orbitals. We suggest that the thermal change in spin correlations implies a relative change among the exchange couplings, and that this is associated with changes in orbital occupancies. Finally, while the magnitude of the low energy magnetic spectral weight is substantial at all temperatures, it actually weakens somewhat at low temperature, where the charge carriers become more itinerant.

  8. Antiferromagnetic order in a semiconductor quantum well with spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Marinescu, D. C.

    2015-05-01

    An argument is made on the existence of a low-temperature itinerant antiferromagnetic (AF) spin alignment, rather than persistent helical (PH), in the ground state of a two dimensional electron gas in a semiconductor quantum well with linear spin-orbit Rashba-Dresselhaus interaction at equal coupling strengths, α. This result is obtained on account of the opposite-spin single-particle state degeneracy at k = 0 that makes the spin instability possible. A theory of the resulting magnetic phase is formulated within the Hartree-Fock approximation of the Coulomb interaction. In the AF state the direction of the fractional polarization is obtained to be aligned along the displacement vector of the single-particle states.

  9. Heisenberg antiferromagnetic chain with multiple spin 1/2 particles of different flavors per site

    NASA Astrophysics Data System (ADS)

    Duki, Solomon F.; Yu, Yi-Kuo

    Motivated by the discoveries of quasi-1D magnetic systems, we studied a quantum mechanical spin lattice system consisting of a one-dimensional antiferromagnetic Heisenberg chain. In this system we considered M spin 1/2 particles of different flavors per site, and the low-lying states, ground state included, of the Hamiltonian was solved numerically using the exact diagonalization method for finite cluster sizes. We have also obtained the corresponding solutions for systems of the same chain length but with one spin M/2 particle per site. The low energy spectra of both systems are then compared. For M = 2 and M =3, our result shows that the two spin chain systems (one spin M/2 per site vs. M spin 1/2 of different flavors per site) have the same excitation spectra at low energy and the number of overlapped states increases as the size of the cluster increases. The observed overlap also indicates that low energy excitations of the M flavored spin 1/2 chain system selects the high spin states, effectively satisfying the Hund's Rule even though the system does not possess the orbital angular momentum. This work was supported by the Intramural Research Program of the National Library of Medicine at the National Institutes of Health.

  10. Antiferromagnetic Ising spin glass competing with BCS pairing interaction in a transverse field

    NASA Astrophysics Data System (ADS)

    Magalhães, S. G.; Zimmer, F. M.; Kipper, C. J.; Calegari, E. J.

    2006-07-01

    The competition among spin glass (SG), antiferromagnetism (AF) and local pairing superconductivity (PAIR) is studied in a two-sublattice fermionic Ising spin glass model with a local BCS pairing interaction in the presence of an applied magnetic transverse field Γ. In the present approach, spins in different sublattices interact with a Gaussian random coupling with an antiferromagnetic mean J0 and standard deviation J. The problem is formulated in the path integral formalism in which spin operators are represented by bilinear combinations of Grassmann variables. The saddle-point Grand Canonical potential is obtained within the static approximation and the replica symmetric ansatz. The results are analysed in phase diagrams in which the AF and the SG phases can occur for small g (g is the strength of the local superconductor coupling written in units of J), while the PAIR phase appears as unique solution for large g. However, there is a complex line transition separating the PAIR phase from the others. It is second order at high temperature that ends in a tricritical point. The quantum fluctuations affect deeply the transition lines and the tricritical point due to the presence of Γ.

  11. Observation of antiferromagnetic correlations in the Hubbard model with ultracold atoms

    NASA Astrophysics Data System (ADS)

    Hart, Russell A.; Duarte, Pedro M.; Yang, Tsung-Lin; Liu, Xinxing; Paiva, Thereza; Khatami, Ehsan; Scalettar, Richard T.; Trivedi, Nandini; Huse, David A.; Hulet, Randall G.

    2015-03-01

    Ultracold atoms in optical lattices have great potential to contribute to a better understanding of some of the most important issues in many-body physics, such as high-temperature superconductivity. The Hubbard model--a simplified representation of fermions moving on a periodic lattice--is thought to describe the essential details of copper oxide superconductivity. This model describes many of the features shared by the copper oxides, including an interaction-driven Mott insulating state and an antiferromagnetic (AFM) state. Optical lattices filled with a two-spin-component Fermi gas of ultracold atoms can faithfully realize the Hubbard model with readily tunable parameters, and thus provide a platform for the systematic exploration of its phase diagram. Realization of strongly correlated phases, however, has been hindered by the need to cool the atoms to temperatures as low as the magnetic exchange energy, and also by the lack of reliable thermometry. Here we demonstrate spin-sensitive Bragg scattering of light to measure AFM spin correlations in a realization of the three-dimensional Hubbard model at temperatures down to 1.4 times that of the AFM phase transition. This temperature regime is beyond the range of validity of a simple high-temperature series expansion, which brings our experiment close to the limit of the capabilities of current numerical techniques, particularly at metallic densities. We reach these low temperatures using a compensated optical lattice technique, in which the confinement of each lattice beam is compensated by a blue-detuned laser beam. The temperature of the atoms in the lattice is deduced by comparing the light scattering to determinant quantum Monte Carlo simulations and numerical linked-cluster expansion calculations. Further refinement of the compensated lattice may produce even lower temperatures which, along with light scattering thermometry, would open avenues for producing and characterizing other novel quantum states of

  12. Thermal evolution of antiferromagnetic correlations and tetrahedral bond angles in superconducting FeTe1 -xSex

    NASA Astrophysics Data System (ADS)

    Xu, Zhijun; Schneeloch, J. A.; Wen, Jinsheng; Božin, E. S.; Granroth, G. E.; Winn, B. L.; Feygenson, M.; Birgeneau, R. J.; Gu, Genda; Zaliznyak, I. A.; Tranquada, J. M.; Xu, Guangyong

    2016-03-01

    It has recently been demonstrated that dynamical magnetic correlations measured by neutron scattering in iron chalcogenides can be described with models of short-range correlations characterized by particular choices of four-spin plaquettes, where the appropriate choice changes as the parent material is doped towards superconductivity. Here we apply such models to describe measured maps of magnetic scattering as a function of two-dimensional wave vectors obtained for optimally superconducting crystals of FeTe1 -xSex . We show that the characteristic antiferromagnetic wave vector evolves from that of the bicollinear structure found in underdoped chalcogenides (at high temperature) to that associated with the stripe structure of antiferromagnetic iron arsenides (at low temperature); these can both be described with the same local plaquette, but with different interplaquette correlations. While the magnitude of the low-energy magnetic spectral weight is substantial at all temperatures, it actually weakens somewhat at low temperature, where the charge carriers become more itinerant. The observed change in spin correlations is correlated with the dramatic drop in the electronic scattering rate and the growth of the bulk nematic response upon cooling. Finally, we also present powder neutron diffraction results for lattice parameters in FeTe1 -xSex indicating that the tetrahedral bond angle tends to increase towards the ideal value upon cooling, in agreement with the increased screening of the crystal field by more itinerant electrons and the correspondingly smaller splitting of the Fe 3 d orbitals.

  13. Influence of the antiferromagnetic spin density wave on the magnetoresistance of Cr

    NASA Astrophysics Data System (ADS)

    Soh, Yeong-Ah; Kummamuru, Ravi

    2007-03-01

    We have performed magnetotransport measurements on Cr films that are 350, 56, 43 and 18 nm thick. The magnetoresistance with the field perpendicular to the film plane shows a clear increase below the Neel temperature and is accompanied by an anomalous negative magnetoresistance at the Neel temperature. The orbital magnetoresistance satisfies the Kohler's rule in the paramagnetic state but violates it in the Neel state. The Hall resistance shows temperature dependence in the paramagnetic state, which was previously suggested to be indicative of a pseudogap [1]. We explain the above phenomena by the evolution of the electronic structure due to the formation of antiferromagnetic spin density wave, the influence of antiferromagnetic domain walls, and the existence of more than one scattering time. [1] ``Quantum phase transition in a common metal'', A. Yeh, Y-A. Soh, J. Brooke, G. Aeppli, T. F. Rosenbaum, and S. M. Hayden, Nature (London) 419, 459 (2002).

  14. Spin wave dynamics in Heisenberg ferromagnetic/antiferromagnetic single-walled nanotubes

    NASA Astrophysics Data System (ADS)

    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.

  15. Antiferromagnetic spin correlations and pseudogaplike behavior in Ca(Fe1-xCox)2As2 studied by 75As nuclear magnetic resonance and anisotropic resistivity

    SciTech Connect

    Cui, J.; Roy, B.; Tanatar, M. A.; Ran, S.; Bud'ko, S. L.; Prozorov, R.; Canfield, P. C.; Furukawa, Y.

    2015-11-06

    We report 75As nuclear magnetic resonance (NMR) measurements of single-crystalline Ca(Fe1–xCox)2As2 (x=0.023, 0.028, 0.033, and 0.059) annealed at 350°C for 7 days. From the observation of a characteristic shape of 75As NMR spectra in the stripe-type antiferromagnetic (AFM) state, as in the case of x=0 (TN=170 K), clear evidence for the commensurate AFM phase transition with the concomitant structural phase transition is observed in x=0.023 (TN=106 K) and x=0.028 (TN=53 K). Through the temperature dependence of the Knight shifts and the nuclear spin lattice relaxation rates (1/T1), although stripe-type AFM spin fluctuations are realized in the paramagnetic state as in the case of other iron pnictide superconductors, we found a gradual decrease of the AFM spin fluctuations below a crossover temperature T* that was nearly independent of Co-substitution concentration, and it is attributed to a pseudogaplike behavior in the spin excitation spectra of these systems. The T* feature finds correlation with features in the temperature-dependent interplane resistivity, ρc(T), but not with the in-plane resistivity ρa(T). The temperature evolution of anisotropic stripe-type AFM spin fluctuations is tracked in the paramagnetic and pseudogap phases by the 1/T1 data measured under magnetic fields parallel and perpendicular to the c axis. As a result, based on our NMR data, we have added a pseudogaplike phase to the magnetic and electronic phase diagram of Ca(Fe1–xCox)2As2.

  16. Directly probing spin dynamics in insulating antiferromagnets using ultrashort terahertz pulses

    DOE PAGES

    Bowlan, Pamela Renee; Trugman, Stuart Alan; Wang, X.; ...

    2016-11-22

    We investigate spin dynamics in the antiferromagnetic (AFM) multiferroic TbMnO3 using opticalpump, terahertz (THz)-probe spectroscopy. Photoexcitation results in a broadband THz transmission change, with an onset time of 25 ps at 6 K that becomes faster at higher temperatures. We attribute this time constant to spin-lattice thermalization. The excellent agreement between our measurements and previous ultrafast resonant x-ray diffraction measurements on the same material confirms that our THz pulse directly probes spin order. We suggest that this could be the case in general for insulating AFM materials, if the origin of the static absorption in the THz spectral range ismore » magnetic.« less

  17. Antiferromagnetic order in CeCoIn5 oriented by spin-orbital coupling

    NASA Astrophysics Data System (ADS)

    Mineev, V. P.

    2017-01-01

    An incommensurate spin-density wave (Q phase) confined inside the superconducting state at high basal plane magnetic field is an unique property of the heavy-fermion metal CeCoIn5. The neutron scattering experiments and the theoretical studies point out that this state come out from the soft mode condensation of magnetic resonance excitations. We show that the fixation of direction of antiferromagnetic modulations by a magnetic field reported by Gerber et al. [Nat. Phys. 10, 126 (2014)], is explained by spin-orbit coupling. This result, obtained on the basis of quite general phenomenological arguments, is supported by the microscopic derivation of the χ z z susceptibility dependence on the mutual orientation of the basal plane magnetic field and the direction of modulation of spin polarization in a multiband metal.

  18. Reentrant spin glass behavior in antiferromagnetic single crystalline Ba 6Mn 24O 48 nanoribbons

    NASA Astrophysics Data System (ADS)

    Zhang, Xianke; Tang, Shaolong; Li, Yulong; Du, Youwei

    2010-04-01

    Single crystalline Ba 6Mn 24O 48 nanoribbons with diameters ranging from one hundred nanometers to a few hundred nanometers and length up to tens of microns are synthesized via a facile molten salt method. These nanoribbons are characterized by a range of methods including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). The magnetic properties of Ba 6Mn 24O 48 nanoribbons are investigated by the zero-field-cooled (ZFC), field-cooled (FC) magnetization, and ac susceptibility. Upon cooling, we find the reentrant spin glass (RSG) behavior in these nanoribbons, i.e., paramagnetic (PM), antiferromagnetic (AFM), and spin glass (SG). The RSG behavior might be due to the surface spin disorder, geometrical frustration and Mn 3+/Mn 4+ mixture in Ba 6Mn 24O 48 nanoribbons.

  19. Spin-Ice State of the Quantum Heisenberg Antiferromagnet on the Pyrochlore Lattice

    NASA Astrophysics Data System (ADS)

    Huang, Yuan; Chen, Kun; Deng, Youjin; Prokof'ev, Nikolay; Svistunov, Boris

    2016-04-01

    We study the low-temperature physics of the SU(2)-symmetric spin-1 /2 Heisenberg antiferromagnet on a pyrochlore lattice and find "fingerprint" evidence for the thermal spin-ice state in this frustrated quantum magnet. Our conclusions are based on the results of bold diagrammatic Monte Carlo simulations, with good convergence of the skeleton series down to the temperature T /J =1 /6 . The identification of the spin-ice state is done through a remarkably accurate microscopic correspondence for the static structure factor between the quantum Heisenberg, classical Heisenberg, and Ising models at all accessible temperatures, and the characteristic bowtie pattern with pinch points observed at T /J =1 /6 . The dynamic structure factor at real frequencies (obtained by the analytic continuation of numerical data) is consistent with diffusive spinon dynamics at the pinch points.

  20. Spin-Ice State of the Quantum Heisenberg Antiferromagnet on the Pyrochlore Lattice.

    PubMed

    Huang, Yuan; Chen, Kun; Deng, Youjin; Prokof'ev, Nikolay; Svistunov, Boris

    2016-04-29

    We study the low-temperature physics of the SU(2)-symmetric spin-1/2 Heisenberg antiferromagnet on a pyrochlore lattice and find "fingerprint" evidence for the thermal spin-ice state in this frustrated quantum magnet. Our conclusions are based on the results of bold diagrammatic Monte Carlo simulations, with good convergence of the skeleton series down to the temperature T/J=1/6. The identification of the spin-ice state is done through a remarkably accurate microscopic correspondence for the static structure factor between the quantum Heisenberg, classical Heisenberg, and Ising models at all accessible temperatures, and the characteristic bowtie pattern with pinch points observed at T/J=1/6. The dynamic structure factor at real frequencies (obtained by the analytic continuation of numerical data) is consistent with diffusive spinon dynamics at the pinch points.

  1. Inverse freezing in a cluster Ising spin-glass model with antiferromagnetic interactions.

    PubMed

    Silva, C F; Zimmer, F M; Magalhaes, S G; Lacroix, C

    2012-11-01

    Inverse freezing is analyzed in a cluster spin-glass (SG) model that considers infinite-range disordered interactions between magnetic moments of different clusters (intercluster interaction) and short-range antiferromagnetic coupling J(1) between Ising spins of the same cluster (intracluster interaction). The intercluster disorder J is treated within a mean-field theory by using a framework of one-step replica symmetry breaking. The effective model obtained by this treatment is computed by means of an exact diagonalization method. With the results we build phase diagrams of temperature T/J versus J(1)/J for several sizes of clusters n(s) (number of spins in the cluster). The phase diagrams show a second-order transition from the paramagnetic phase to the SG order at the freezing temperature T(f) when J(1)/J is small. The increase in J(1)/J can then destroy the SG phase. It decreases T(f)/J and introduces a first-order transition. In addition, inverse freezing can arise at a certain range of J(1)/J and large enough n(s). Therefore, the nontrivial frustration generated by disorder and short-range antiferromagnetic coupling can introduce inverse freezing spontaneously.

  2. Anomalous Curie response of an impurity in a quantum critical spin-1/2 Heisenberg antiferromagnet

    NASA Astrophysics Data System (ADS)

    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).

  3. Observation of Spin-flop Transition in Antiferromagnetic Organic Molecular Conductors using AFM Micro-cantilever

    NASA Astrophysics Data System (ADS)

    Tokumoto, Madoka; Otsuka, Takeo; Kobayashi, Akiko

    2005-03-01

    A series of (BETS)2Fe1-xGaxCl1-yBry salts is a good candidate for a systematic study of π-d interaction between the conduction electrons and local magnetic moments in organic conductors. Some of them show antiferromagnetic ground state at low temperatures. A torque magnetometry is useful for precise determination of the easy axis as well as the spin-flop field. In this work we will report on the measurements of spin-flop transitions in antiferromagnetic organic molecular conductors including λ-(BETS)2FeCl4[1], using a commercial self-sensing piezo-resistive microcantilever for Atomic Force Microscopy (AFM) developed by Seiko Instruments Inc. We have succeeded in observation of spin-flop transitions of tiny single crystals including λ-(BETS)2FeCl4 as small as less than 1μg[2]. The results are consistent with the capacitive magnetic torque study[3]. [1] M. Tokumoto et al. Synth. Metals 86, 2161 (1997). [2] M. Tokumoto et al., ICMM2004, Polyhedron in press. [3] T. Sasaki et al., Synth. Metals 120, 759 (2001).

  4. Spin-ordered ground state and thermodynamic behaviors of the spin-3/2 kagome Heisenberg antiferromagnet.

    PubMed

    Liu, Tao; Li, Wei; Su, Gang

    2016-09-01

    Three different tensor network (TN) optimization algorithms are employed to accurately determine the ground state and thermodynamic properties of the spin-3/2 kagome Heisenberg antiferromagnet. We found that the sqrt[3]×sqrt[3] state (i.e., the state with 120^{∘} spin configuration within a unit cell containing 9 sites) is the ground state of this system, and such an ordered state is melted at any finite temperature, thereby clarifying the existing experimental controversies. Three magnetization plateaus (m/m_{s}=1/3,23/27, and 25/27) were obtained, where the 1/3-magnetization plateau has been observed experimentally. The absence of a zero-magnetization plateau indicates a gapless spin excitation that is further supported by the thermodynamic asymptotic behaviors of the susceptibility and specific heat. At low temperatures, the specific heat is shown to exhibit a T^{2} behavior, and the susceptibility approaches a finite constant as T→0. Our TN results of thermodynamic properties are compared with those from high-temperature series expansion. In addition, we disclose a quantum phase transition between q=0 state (i.e., the state with 120^{∘} spin configuration within a unit cell containing three sites) and sqrt[3]×sqrt[3] state in a spin-3/2 kagome XXZ model at the critical point Δ_{c}=0.54. This study provides reliable and useful information for further explorations on high-spin kagome physics.

  5. Spin-ordered ground state and thermodynamic behaviors of the spin-3/2 kagome Heisenberg antiferromagnet

    NASA Astrophysics Data System (ADS)

    Liu, Tao; Li, Wei; Su, Gang

    2016-09-01

    Three different tensor network (TN) optimization algorithms are employed to accurately determine the ground state and thermodynamic properties of the spin-3/2 kagome Heisenberg antiferromagnet. We found that the √{3 }×√{3 } state (i.e., the state with 120° spin configuration within a unit cell containing 9 sites) is the ground state of this system, and such an ordered state is melted at any finite temperature, thereby clarifying the existing experimental controversies. Three magnetization plateaus (m /ms=1 /3 ,23 /27 , and 25/27) were obtained, where the 1/3-magnetization plateau has been observed experimentally. The absence of a zero-magnetization plateau indicates a gapless spin excitation that is further supported by the thermodynamic asymptotic behaviors of the susceptibility and specific heat. At low temperatures, the specific heat is shown to exhibit a T2 behavior, and the susceptibility approaches a finite constant as T →0 . Our TN results of thermodynamic properties are compared with those from high-temperature series expansion. In addition, we disclose a quantum phase transition between q =0 state (i.e., the state with 120° spin configuration within a unit cell containing three sites) and √{3 }×√{3 } state in a spin-3/2 kagome XXZ model at the critical point Δc=0.54 . This study provides reliable and useful information for further explorations on high-spin kagome physics.

  6. Elemental analysis and magnetism of hydronium jarosites--model kagome antiferromagnets and topological spin glasses.

    PubMed

    Wills, A S; Bisson, W G

    2011-04-27

    The jarosites are the most studied examples of kagome antiferromagnets. Research into them has inspired new directions in magnetism, such as the role of the Dzyaloshinsky-Moriya interaction in symmetry breaking, kagome spin ice, and whether spin glass-like phases can exist in the disorder-free limit. This last point is based around the observation of unconventional thermodynamic and kinetic responses in hydronium jarosite, H(3)OFe(3)(SO(4))(2)(OH)(6), that have led to its classification as a 'topological' spin glass, reflecting the defining role that the underlying geometry of the kagome lattice plays in the formation of the spin glass state. In this paper we explore one of the fundamental questions concerning the frustrated magnetism in hydronium jarosite: whether the spin glass phase is the result of chemical disorder and concomitant randomness in the exchange interactions. Confirming previous crystallographic studies, we use elemental analysis to show that the nature of the low temperature magnetic state is not a simple function of chemical disorder and provide evidence to support the hypothesis that anisotropies drive the spin glass transition.

  7. Enhancement of spin-wave nonreciprocity in magnonic crystals via synthetic antiferromagnetic coupling

    PubMed Central

    Di, K.; Feng, S. X.; Piramanayagam, S. N.; Zhang, V. L.; Lim, H. S.; Ng, S. C.; Kuok, M. H.

    2015-01-01

    Spin-wave nonreciprocity arising from dipole-dipole interaction is insignificant for magnon wavelengths in the sub-100 nm range. Our micromagnetic simulations reveal that for the nanoscale magnonic crystals studied, such nonreciprocity can be greatly enhanced via synthetic antiferromagnetic coupling. The nonreciprocity is manifested as highly asymmetric magnon dispersion curves of the magnonic crystals. Furthermore, based on the study of the dependence of the nonreciprocity on an applied magnetic field, the antiparallel alignment of the magnetizations is shown to be responsible for the enhancement. Our findings would be useful for magnonic and spintronics applications. PMID:25950082

  8. Electrical Detection of Spin Backflow from an Antiferromagnetic Insulator/Y3Fe5O12 Interface

    NASA Astrophysics Data System (ADS)

    Lin, Weiwei; Chien, C. L.

    2017-02-01

    Spin Hall magnetoresistance (SMR) has been observed in Pt /NiO /Y3Fe5O12 (YIG) heterostructures with characteristics very different from those in Pt /YIG . This phenomenon indicates that a spin current generated by the spin Hall effect in Pt transmits through the insulating NiO and is reflected from the NiO /YIG interface. The SMR in Pt /NiO /YIG shows a strong temperature dependence dominated by effective spin conductance, due to antiferromagnetic magnons and spin fluctuation. Inverted SMR has been observed below a temperature which increases with the NiO thickness, suggesting a spin-flip reflection from the antiferromagnetic NiO exchange coupled with the YIG.

  9. Spin waves in a two-sublattice antiferromagnet. A self-similar solution of the Landau-Lifshitz equation

    NASA Astrophysics Data System (ADS)

    Gorobets, Y. I.; Gorobets, Y.; Kulish, V. V.

    2017-01-01

    In the paper, spin waves in a uniaxial two-sublattice antiferromagnet are investigated. A new class of self-similar solutions of the Landau-Lifshitz equation is obtained and, therefore, a new type of spin waves is described. Examples of solutions of the found class are presented. New type of solution admits both linear and non-linear spin waves, including solitons. Space transformations used in the solution are mathematically analogous to the relativistic transformations.

  10. Optical conductivity of cuprates in the pseudogap state: Yang-Rice-Zhang model and antiferromagnetic spin waves

    SciTech Connect

    Singh, Navinder; Sharma, Raman

    2015-05-15

    In the underdoped regime of the cuprate phase diagram, the modified version of the Resonance Valence Bond (RVB) model by Yang, Rice and Zhang (YRZ) captures the strong electronic correlation effects very well as corroborated by the ARPES and many other experiments. However, under a non-equilibrium transport setting, YRZ says nothing about the scattering mechanisms of the charge carriers. In the present investigation we include, in a very simplified way, the scattering of charge carriers due to antiferromagnetic type spin waves (ASW). The effect of ASW excitations on conductivity has been studied by changing combined life times of the included process. It has been found that there is a qualitative change in the conductivity in the right direction. The theoretical conductivity reproduces qualitatively the experimental one.

  11. Magnetic excitations in the spin-1/2 triangular-lattice antiferromagnet Cs2CuBr4

    SciTech Connect

    Zvyagin, S. A.; Ozerov, M.; Kamenskyi, D.; Wosnitza, J.; Krzystek, J.; Yoshizawa, D.; Hagiwara, M.; Hu, Rongwei; Ryu, Hyejin; Petrovic, C.; Zhitomirsky, M. E.

    2015-11-27

    We present on high- field electron spin resonance (ESR) studies of magnetic excitations in the spin- 1/2 triangular-lattice antiferromagnet Cs2CuBr4. Frequency- field diagrams of ESR excitations are measured for different orientations of magnetic fields up to 25 T. We show that the substantial zero- field energy gap, Δ ≈ 9.5 K, observed in the low-temperature excitation spectrum of Cs2CuBr4 [Zvyagin et al:, Phys. Rev. Lett. 112, 077206 (2014)], is present well above TN. Noticeably, the transition into the long-range magnetically ordered phase does not significantly affect the size of the gap, suggesting that even below TN the high-energy spin dynamics in Cs2CuBr4 is determined by short-range-order spin correlations. The experimental data are compared with results of model spin-wave-theory calculations for spin-1/2 triangle-lattice antiferromagnet.

  12. Correlation-driven transport asymmetries through coupled spins in a tunnel junction

    PubMed Central

    Muenks, Matthias; Jacobson, Peter; Ternes, Markus; Kern, Klaus

    2017-01-01

    Spin–spin correlations can be the driving force that favours certain ground states and are key in numerous models that describe the behaviour of strongly correlated materials. While the sum of collective correlations usually lead to a macroscopically measurable change in properties, a direct quantification of correlations in atomic scale systems is difficult. Here we determine the correlations between a strongly hybridized spin impurity on the tip of a scanning tunnelling microscope and its electron bath by varying the coupling to a second spin impurity weakly hybridized to the sample surface. Electronic transport through these coupled spins reveals an asymmetry in the differential conductance reminiscent of spin-polarized transport in a magnetic field. We show that at zero field, this asymmetry can be controlled by the coupling strength and is related to either ferromagnetic or antiferromagnetic spin–spin correlations in the tip. PMID:28074832

  13. Superconductivity, antiferromagnetism, and neutron scattering

    NASA Astrophysics Data System (ADS)

    Tranquada, John M.; Xu, Guangyong; Zaliznyak, Igor A.

    2014-01-01

    High-temperature superconductivity in both the copper-oxide and the iron-pnictide/chalcogenide systems occurs in close proximity to antiferromagnetically ordered states. Neutron scattering has been an essential technique for characterizing the spin correlations in the antiferromagnetic phases and for demonstrating how the spin fluctuations persist in the superconductors. While the nature of the spin correlations in the superconductors remains controversial, the neutron scattering measurements of magnetic excitations over broad ranges of energy and momentum transfers provide important constraints on the theoretical options. We present an overview of the neutron scattering work on high-temperature superconductors and discuss some of the outstanding issues.

  14. Padé approximations for the magnetic susceptibilities of Heisenberg antiferromagnetic spin chains for various spin values.

    PubMed

    Law, J M; Benner, H; Kremer, R K

    2013-02-13

    The temperature dependence of the spin susceptibilities of S = 1, 3/2, 2, 5/2 and 7/2 Heisenberg antiferromagnetic 1D spins chains with nearest-neighbor coupling was simulated via quantum Monte Carlo calculations, within the reduced temperature range of 0.005 ≤ T* ≤ 100, and fitted to a Padé approximation with deviations between the simulated and fitted data of the same order of magnitude as or smaller than the quantum Monte Carlo simulation error. To demonstrate the practicality of our theoretical findings, we compare these results with the susceptibility of the well known 1D chain compound TMMC ([(CH(3))(4)N[MnCl(3)

  15. Local moments and suppression of antiferromagnetism in correlated Zr4Fe4Si7

    SciTech Connect

    Simonson, Jack; Pezzoli, M; Garlea, Vasile O; Aronson, M.

    2013-01-01

    We report magnetic, transport, and neutron diffraction measurements as well as a doping study of the V-phase compound Zr4Fe4Si7. This compound exhibits collinear antiferromagnetic order below TN = 98 1 K with a staggered moment of 0.57(3) B/Fe as T 0. The magnetic order can be quenched with Co substitution to the Fe site, but even then a 1.5 B/Fe paramagnetic moment remains. The resistivity and heat capacity of Zr4Fe4Si7 are Fermi-liquid-like below 16 and 7 K, respectively, and reveal correlations on the scale of those observed in superconducting Fe pnictides and chalcogenides. Electronic structure calculations overestimate the ordered moment, suggesting the importance of dynamical effects. The existence of magnetic order, electronic correlations, and spin fluctuations make Zr4Fe4Si7 distinct from the majority of Fe-Si compounds, fostering comparison instead with the parent compounds of Fe-based superconductors.

  16. Controlling the canted state in antiferromagnetically coupled magnetic bilayers close to the spin reorientation transition

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

    Canted magnetization is obtained in ultrathin, antiferromagnetically coupled magnetic bilayers with thicknesses around the spin reorientation transition. The canting angle is controlled by both the magnetic layer thickness and interlayer coupling strength, which are tuned independently. Hysteresis loops are obtained, where magnetization components parallel and transverse to the applied field are measured, and analyzed by comparison to micromagnetic simulations. This enables the canting angle to be extracted and the behavior of the individual layers to be distinguished. Two types of canted systems are obtained with either single-layer reversal or complex, coupled two-layer reversal, under moderate external magnetic fields. Controlling the magnetization canting and reversal behavior of ultra-thin layers is relevant for the development of magnetoresistive random-access memory and spin-torque oscillator devices.

  17. Spin-flop transition in the easy-plane antiferromagnet nickel oxide

    NASA Astrophysics Data System (ADS)

    Machado, F. L. A.; Ribeiro, P. R. T.; Holanda, J.; Rodríguez-Suárez, R. L.; Azevedo, A.; Rezende, S. M.

    2017-03-01

    NiO is a room-temperature antiferromagnetic (AF) insulator with important applications in AF spintronics. Although it is considered a prototypical AF material with a simple magnetic structure with two sublattice spins aligned in easy planes and having small in-plane magnetic anisotropy, its critical behavior has not been studied in detail. Here we present an experimental investigation of the critical magnetic field for the transition from the AF to the spin-flop (SF) phase obtained with magnetization and susceptibility measurements. The measured temperature dependence of the AF-SF critical field can be quite well explained by the instability of the low-lying magnon mode with energy renormalized by four-magnon interactions.

  18. Spin-waves in Antiferromagnetic Single-crystal LiFePO4

    SciTech Connect

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

    2006-01-01

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

  19. Competing Antiferromagnetic and Spin-Glass phases in a hollandite structure

    NASA Astrophysics Data System (ADS)

    Crespo Hernandez, Yanier; Andreanov, Alexei; Seriani, Nicola

    2013-03-01

    We introduce a simple model to explain recent experimental results on spin freezing in a hollandite-type structure. We argue that geometrical frustration of the lattice with antiferromagnetic (AFM) interactions is responsible for the appearance of a spin-glass phase in presence of disorder. We check our predictions numerically using parallel tempering on a model that considers Ising spins and nearest-neighbor AFM interactions. The proposed model presents a rich phenomenology: in absence of disorder two ground states are possible, depending on the strength of the interactions, namely an AFM or a geometrically frustrated phase. Remarkably for any set of AFM couplings having an AFM ground state in the clean system, there exist a critical value of the disorder for which the ground state is replaced by a spin-glass one while maintaining all couplings AFM. To the best of our knowledge in the literature there is not a model that presents this kind of transition considering just short-range AFM interactions. Therefore we argue that this model would be useful to understand the relation between AFM coupling, disorder and the appearance of spin glasses phase.

  20. Barlowite: A Spin-1/2 Antiferromagnet with a Geometrically Perfect Kagome Motif.

    PubMed

    Han, Tian-Heng; Singleton, John; Schlueter, John A

    2014-11-28

    We present thermodynamic studies of a new spin-1/2 antiferromagnet containing undistorted kagome lattices-barlowite Cu_{4}(OH)_{6}FBr. Magnetic susceptibility gives θ_{CW}=-136  K, while long-range order does not happen until T_{N}=15  K with a weak ferromagnetic moment μ<0.1μ_{B}/Cu. A 60 T magnetic field induces a moment less than 0.5μ_{B}/Cu at T=0.6  K. Specific-heat measurements have observed multiple phase transitions at T≪∣θ_{CW}∣. The magnetic entropy of these transitions is merely 18% of k_{B}ln2 per Cu spin. These observations suggest that nontrivial spin textures are realized in barlowite with magnetic frustration. Comparing with the leading spin-liquid candidate herbertsmithite, the superior interkagome environment of barlowite sheds light on new spin-liquid compounds with minimum disorder. The robust perfect geometry of the kagome lattice makes charge doping promising.

  1. Electrical switching of antiferromagnets via strongly spin-orbit coupled materials

    NASA Astrophysics Data System (ADS)

    Li, Xi-Lai; Duan, Xiaopeng; Semenov, Yuriy G.; Kim, Ki Wook

    2017-01-01

    Electrically controlled ultra-fast switching of an antiferromagnet (AFM) is shown to be realizable by interfacing it with a material of strong spin-orbit coupling. The proximity interaction between the sublattice magnetic moments of a layered AFM and the spin-polarized free electrons at the interface offers an efficient way to manipulate antiferromagnetic states. A quantitative analysis, using the combination with a topological insulator as an example, demonstrates highly reliable 90° and 180° rotations of AFM magnetic states under two different mechanisms of effective torque generation at the interface. The estimated switching speed and energy requirement are in the ps and aJ ranges, respectively, which are about two-three orders of magnitude better than the ferromagnetic counterparts. The observed differences in the magnetization dynamics may explain the disparate characteristic responses. Unlike the usual precessional/chiral motions in the ferromagnets, those of the AFMs can essentially be described as a damped oscillator with a more direct path. The impact of random thermal fluctuations is also examined.

  2. Raman spectroscopic study of the frustrated spin 1/2 antiferromagnet clinoatacamite

    NASA Astrophysics Data System (ADS)

    Liu, Xiao-Dong; Zheng, Xu-Guang; Meng, Dong-Dong; Xu, Xing-Liang; Guo, Qi-Xin

    2013-06-01

    Raman spectroscopy is a valuable and complementary tool for studying geometrically frustrated magnetic systems due to the intrinsic spin-phonon coupling. Here, we report on a Raman spectroscopic study of the geometrically frustrated spin 1/2 antiferromagnet microcrystalline clinoatacamite Cu2(OH)3Cl, focusing on the anomalous transition into the intermediate phase at Tc1 = 18.1 K. By measuring the temperature-dependent (295-4 K) full spectral profiles and main representative modes in spectral regions from 4000 to 95 cm-1, we observed probable signatures of successive magnetic transitions near Tc1 = 18 K and Tc2 = 6.4 K in the Raman band frequencies and peak widths of the representative modes. Further, we observed a pronounced Raman spectroscopy background featuring a broad continuum at all temperatures. A quantitative analysis reveals that spin fluctuations may exist on a picosecond time scale in the intermediate phase. The short time scale falls out of the μSR time window; therefore, in the intermediate phase, the μSR study as reported in (2005 Phys. Rev. Lett. 95 057201) apparently only probed the local field of the ordered spins but overlooked the quickly fluctuating ones. This is likely to give a reasonable explanation of the fact that only a small entropy release occurs at Tc1 = 18 K although a long-range order is formed.

  3. Longitudinal optical and spin Hall conductivities of Rashba conducting strips coupled to ferromagnetic and antiferromagnetic layers

    NASA Astrophysics Data System (ADS)

    Riera, José A.

    2017-01-01

    A system composed of a conducting planar strip with Rashba spin-orbit coupling (RSOC), magnetically coupled to a layer of localized magnetic moments, at equilibrium, is studied within a microscopic Hamiltonian with numerical techniques at zero temperature in the clean limit. In particular, transport properties for the cases of ferromagnetic (FM) and antiferromagnetic (AFM) coupled layers are computed in linear response on strips of varying width. Some behaviors observed for these properties are consistent with the ones observed for the corresponding Rashba helical currents. The case of uncoupled Rashba strips is also studied for comparison. In the case of Rashba strips coupled to an AFM localized order, results for the longitudinal dc conductivity, for small strip widths, suggest the proximity to a metal-insulator transition. More interesting, in the proximity of this transition, and in general at intermediate values of the RSOC, a large spin Hall conductivity is observed that is two orders of magnitude larger than the one for the FM order for the same values of the RSOC and strip widths. There are clearly two different regimes for small and for large RSOC, which is also present in the behavior of Rashba helical currents. Different contributions to the optical and the spin Hall conductivities, according to a new classification of inter- or intraband origin proposed for planar strips in the clean limit, or coming from the hopping or spin-orbit terms of the Hamiltonian, are examined. Finally, the effects of different orientation of the coupled magnetic moments will be also studied.

  4. Search for the Heisenberg spin glass on rewired cubic lattices with antiferromagnetic interaction

    NASA Astrophysics Data System (ADS)

    Surungan, Tasrief

    2016-10-01

    Spin glass (SG) is a typical magnetic system which is mainly characterized by a frozen random spin orientation at low temperatures. Frustration and randomness are considered to be the key ingredients for the existence of SGs. Previously, Bartolozzi et al. [Phys. Rev. B73, 224419 (2006)] found that the antiferromagnetic (AF) Ising spins on scale free network (SFN) exhibited SG behavior. This is purely AF system, 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 due to a topological factor and its randomness is brought by irregular connectivity. Recently, it was reported that the AF Heisenberg model on SFN exhibited SG behavior [Surungan et al., JPCS, 640, 012005 (2015)/doi:10.1088/1742-6596/640/1/012005]. In order to accommodate the notion of spatial dimension, we further investigated this type of system by studying an AF Heisenberg model on rewired cubic lattices, constructed by adding one extra bond randomly connecting each spin to one of its next-nearest neighbors. We used Replica Exchange algorithm of Monte Carlo Method and calculated the SG order parameter to search for the existence of SG phase.

  5. Longitudinal spin excitations and magnetic anisotropy in antiferromagnetically ordered BaFe2As2

    NASA Astrophysics Data System (ADS)

    Li, Yuan; Wang, Chong; Zhang, Rui; Luo, Huiqian; Wang, Fa; Dai, Pengcheng; Regnault, Louis-Pierre

    2014-03-01

    In the iron-based superconductors, there is an outstanding debate on the microscopic origin of the magnetism, whether it arises from local moments or itinerant electrons with Fermi-surface nesting. To answer this question, we performed a spin-polarized inelastic neutron scattering study of spin waves in the antiferromagnetically ordered state of BaFe2As2. Three distinct excitation components are identified, with spins fluctuating along the c-axis, perpendicular to the ordering direction in the ab -plane, and parallel to the ordering direction. While the first two ``transverse'' components can be described by a linear spin-wave theory with magnetic anisotropy and inter-layer coupling, the third ``longitudinal'' component is generically incompatible with the local moment picture. It points towards a contribution of itinerant electrons to the magnetism already in the parent compound of this family of Fe-based superconductors. (arXiv:1309.7553) Supported by the National Basic Research Program of China, the National Science Foundation of China, and the US National Science Foundation.

  6. Low-temperature spectrum of correlation lengths of the XXZ chain in the antiferromagnetic massive regime

    NASA Astrophysics Data System (ADS)

    Dugave, Maxime; Göhmann, Frank; Kozlowski, Karol K.; Suzuki, Junji

    2015-08-01

    We consider the spectrum of correlation lengths of the spin-\\displaystyle \\frac{1}{2} XXZ chain in the antiferromagnetic massive regime. These are given as ratios of eigenvalues of the quantum transfer matrix of the model. The eigenvalues are determined by integrals over certain auxiliary functions and by their zeros. The auxiliary functions satisfy nonlinear integral equations. We analyse these nonlinear integral equations in the low-temperature limit. In this limit we can determine the auxiliary functions and the expressions for the eigenvalues as functions of a finite number of parameters which satisfy finite sets of algebraic equations, the so-called higher-level Bethe ansatz equations. The behaviour of these equations, if we send the temperature T to zero, is different for zero and non-zero magnetic field h. If h is zero the situation is much like in the case of the usual transfer matrix. Non-trivial higher-level Bethe ansatz equations remain which determine certain complex excitation parameters as functions of hole parameters which are free on a line segment in the complex plane. If h is non-zero, on the other hand, a remarkable restructuring occurs, and all parameters which enter the description of the quantum transfer matrix eigenvalues can be interpreted entirely in terms of particles and holes which are freely located on two curves when T goes to zero. Dedicated to Professor Baxter on the occasion of his 75th birthday.

  7. Coexistence of antiferromagnetism and d+id superconducting correlations in the graphene bilayer

    NASA Astrophysics Data System (ADS)

    Milovanović, M. V.; Predin, S.

    2012-11-01

    We discuss the t-J-U model on a honeycomb monolayer that has the same low-energy description of the kinetic term as the graphene bilayer, and in particular study coexistence of antiferromagnetism and superconducting correlations that originate from Cooper pairs without phase coherence. We show that the model is relevant for the description of the graphene bilayer and that the presence of the d+id superconducting correlations with antiferromagnetism can lead to quadratic dependence in small magnetic fields of the gap of the effective monolayer consistent with the transport measurements of Velasco on the graphene bilayer.

  8. Effect of the phase transition to the ferroquadrupolar phase on spin transport in the biquadratic antiferromagnet of the triangular lattice

    NASA Astrophysics Data System (ADS)

    Lima, L. S.

    2017-04-01

    We use the SU(N) Schwinger boson formalism to study the spin transport in the S=1 biquadratic frustrated Heisenberg antiferromagnetic model in the triangular lattice, considering the next-nearest-neighbors interactions J2. We have obtained a jump in the spin conductivity in the point of cusp of the phase diagram - η vs. - α of the model at T=0, which represents the force of the biquadratic coupling versus the next-nearest-neighbor coupling (K vs. J2). We have obtained also a superfluid behavior for the spin transport in the DC limit for this system similar to ones recently obtained for other two-dimensional frustrated spin systems. We consider all the couplings, first and second couplings as antiferromagnetic.

  9. Characterization of Topological Phases of Spin-1/2 Frustrated Ferromagnetic-Antiferromagnetic Alternating Heisenberg Chains by Entanglement Spectrum

    NASA Astrophysics Data System (ADS)

    Hida, Kazuo

    2016-02-01

    The topological classification of a series of frustration-induced spin-gap phases in the spin-1/2 ferromagnetic-antiferromagnetic alternating Heisenberg chain with next-nearest-neighbour interaction reported in J. Phys. Soc. Jpn. 82, 064703 (2013) is confirmed using two kinds of entanglement spectra defined by different divisions of the whole chain. For the numerical calculation, the iDMRG method is used. The results are consistent with the valence bond solid picture proposed in the previous paper.

  10. Effect of magnetoelastic coupling on spin-glass behavior in Heisenberg pyrochlore antiferromagnets with bond disorder

    NASA Astrophysics Data System (ADS)

    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

  11. Coordinate Bethe ansatz computation for low temperature behavior of a triangular lattice of a spin-1 Heisenberg antiferromagnet

    SciTech Connect

    Shuaibu, A.; Rahman, M. M.

    2014-03-05

    We study the low temperature behavior of a triangular lattice quantum spin-1 Heisenberg antiferromagnet with single-site anisotropy by using coordinate Bethe ansatz method. We compute the standard two-particle Hermitian Hamiltonian, and obtain the eigenfunctions and eigenvalue of the system. The obtained results show a number of advantages in comparison with many results.

  12. Role of the antiferromagnetic pinning layer on spin wave properties in IrMn/NiFe based spin-valves

    NASA Astrophysics Data System (ADS)

    Gubbiotti, G.; Tacchi, S.; Del Bianco, L.; Bonfiglioli, E.; Giovannini, L.; Tamisari, M.; Spizzo, F.; Zivieri, R.

    2015-05-01

    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.

  13. Role of the antiferromagnetic pinning layer on spin wave properties in IrMn/NiFe based spin-valves

    SciTech Connect

    Gubbiotti, G. Tacchi, S.; Del Bianco, L.; Bonfiglioli, E.; Giovannini, L.; Spizzo, F.; Zivieri, R.; Tamisari, M.

    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.

  14. Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr0.7Ca0.3MnO3

    NASA Astrophysics Data System (ADS)

    Zhou, S. Y.; Langner, M. C.; Zhu, Y.; Chuang, Y.-D.; Rini, M.; Glover, T. E.; Hertlein, M. P.; Gonzalez, A. G. Cruz; Tahir, N.; Tomioka, Y.; Tokura, Y.; Hussain, Z.; Schoenlein, R. W.

    2014-02-01

    Electronic orderings of charges, orbitals and spins are observed in many strongly correlated electron materials, and revealing their dynamics is a critical step toward undertsanding the underlying physics of important emergent phenomena. Here we use time-resolved resonant soft x-ray scattering spectroscopy to probe the dynamics of antiferromagnetic spin ordering in the manganite Pr0.7Ca0.3MnO3 following ultrafast photo-exitation. Our studies reveal a glass-like recovery of the spin ordering and a crossover in the dimensionality of the restoring interaction from quasi-1D at low pump fluence to 3D at high pump fluence. This behavior arises from the metastable state created by photo-excitation, a state characterized by spin disordered metallic droplets within the larger charge- and spin-ordered insulating domains. Comparison with time-resolved resistivity measurements suggests that the collapse of spin ordering is correlated with the insulator-to-metal transition, but the recovery of the insulating phase does not depend on the re-establishment of the spin ordering.

  15. Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr₀.₇Ca₀.₃MnO₃.

    PubMed

    Zhou, S Y; Langner, M C; Zhu, Y; Chuang, Y-D; Rini, M; Glover, T E; Hertlein, M P; Gonzalez, A G Cruz; Tahir, N; Tomioka, Y; Tokura, Y; Hussain, Z; Schoenlein, R W

    2014-02-13

    Electronic orderings of charges, orbitals and spins are observed in many strongly correlated electron materials, and revealing their dynamics is a critical step toward undertsanding the underlying physics of important emergent phenomena. Here we use time-resolved resonant soft x-ray scattering spectroscopy to probe the dynamics of antiferromagnetic spin ordering in the manganite Pr₀.₇Ca₀.₃MnO₃ following ultrafast photo-exitation. Our studies reveal a glass-like recovery of the spin ordering and a crossover in the dimensionality of the restoring interaction from quasi-1D at low pump fluence to 3D at high pump fluence. This behavior arises from the metastable state created by photo-excitation, a state characterized by spin disordered metallic droplets within the larger charge- and spin-ordered insulating domains. Comparison with time-resolved resistivity measurements suggests that the collapse of spin ordering is correlated with the insulator-to-metal transition, but the recovery of the insulating phase does not depend on the re-establishment of the spin ordering.

  16. Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr0.7Ca0.3MnO3

    SciTech Connect

    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.

  17. Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr0.7Ca0.3MnO3

    PubMed Central

    Zhou, S. Y.; Langner, M. C.; Zhu, Y.; Chuang, Y.-D.; Rini, M.; Glover, T. E.; Hertlein, M. P.; Gonzalez, A. G. Cruz; Tahir, N.; Tomioka, Y.; Tokura, Y.; Hussain, Z.; Schoenlein, R. W.

    2014-01-01

    Electronic orderings of charges, orbitals and spins are observed in many strongly correlated electron materials, and revealing their dynamics is a critical step toward undertsanding the underlying physics of important emergent phenomena. Here we use time-resolved resonant soft x-ray scattering spectroscopy to probe the dynamics of antiferromagnetic spin ordering in the manganite Pr0.7Ca0.3MnO3 following ultrafast photo-exitation. Our studies reveal a glass-like recovery of the spin ordering and a crossover in the dimensionality of the restoring interaction from quasi-1D at low pump fluence to 3D at high pump fluence. This behavior arises from the metastable state created by photo-excitation, a state characterized by spin disordered metallic droplets within the larger charge- and spin-ordered insulating domains. Comparison with time-resolved resistivity measurements suggests that the collapse of spin ordering is correlated with the insulator-to-metal transition, but the recovery of the insulating phase does not depend on the re-establishment of the spin ordering. PMID:24522173

  18. Thermal evolution of antiferromagnetic correlations and tetrahedral bond angles in superconducting FeTe1-xSex

    DOE PAGES

    Xu, Zhijun; Xu, Guangyong; Schneeloch, J. A.; ...

    2016-03-14

    It has recently been demonstrated that dynamical magnetic correlations measured by neutron scattering in iron chalcogenides can be described with models of short-range correlations characterized by particular choices of four-spin plaquettes, where the appropriate choice changes as the parent material is doped towards superconductivity. Here we apply such models to describe measured maps of magnetic scattering as a function of two-dimensional wave vectors obtained for optimally superconducting crystals of FeTe1–xSex. We show that the characteristic antiferromagnetic wave vector evolves from that of the bicollinear structure found in underdoped chalcogenides (at high temperature) to that associated with the stripe structure ofmore » antiferromagnetic iron arsenides (at low temperature); these can both be described with the same local plaquette, but with different interplaquette correlations. While the magnitude of the low-energy magnetic spectral weight is substantial at all temperatures, it actually weakens somewhat at low temperature, where the charge carriers become more itinerant. The observed change in spin correlations is correlated with the dramatic drop in the electronic scattering rate and the growth of the bulk nematic response upon cooling. Lastly, we also present powder neutron diffraction results for lattice parameters in FeTe1–xSex indicating that the tetrahedral bond angle tends to increase towards the ideal value upon cooling, in agreement with the increased screening of the crystal field by more itinerant electrons and the correspondingly smaller splitting of the Fe 3d orbitals.« less

  19. Thermal evolution of antiferromagnetic correlations and tetrahedral bond angles in superconducting FeTe1₋xSex

    DOE PAGES

    Xu, Zhijun; Schneeloch, J. A.; Wen, Jinsheng; ...

    2016-03-14

    Imore » t has recently been demonstrated that dynamical magnetic correlations measured by neutron scattering in iron chalcogenides can be described with models of short-range correlations characterized by particular choices of four-spin plaquettes, where the appropriate choice changes as the parent material is doped towards superconductivity. Here we apply such models to describe measured maps of magnetic scattering as a function of two-dimensional wave vectors obtained for optimally superconducting crystals of FeTe1₋xSex. We show that the characteristic antiferromagnetic wave vector evolves from that of the bicollinear structure found in underdoped chalcogenides (at high temperature) to that associated with the stripe structure of antiferromagnetic iron arsenides (at low temperature); these can both be described with the same local plaquette, but with different interplaquette correlations. While the magnitude of the low-energy magnetic spectral weight is substantial at all temperatures, it actually weakens somewhat at low temperature, where the charge carriers become more itinerant. The observed change in spin correlations is correlated with the dramatic drop in the electronic scattering rate and the growth of the bulk nematic response upon cooling. n conclusion, we also present powder neutron diffraction results for lattice parameters in FeTe1₋xSex indicating that the tetrahedral bond angle tends to increase towards the ideal value upon cooling, in agreement with the increased screening of the crystal field by more itinerant electrons and the correspondingly smaller splitting of the Fe 3d orbitals.« less

  20. Search for the Heisenberg spin glass on rewired square lattices with antiferromagnetic interaction

    NASA Astrophysics Data System (ADS)

    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.

  1. Competing nematic, antiferromagnetic, and spin-flux orders in the ground state of bilayer graphene

    NASA Astrophysics Data System (ADS)

    Lemonik, Y.; Aleiner, I.; Fal'ko, V. I.

    2012-06-01

    We analyze the phase diagram of bilayer graphene (BLG) at zero temperature and zero doping. Assuming that at high energies the electronic system of BLG can be described within a weak-coupling theory (consistent with the experimental evidence), we systematically study the evolution of the couplings with going from high to low energies. The divergences of the couplings at some energies indicate the tendency towards certain symmetry breakings. Carrying out this program, we found that the phase diagram is determined by microscopic couplings defined on the short distances (initial conditions). We explored all plausible space of these initial conditions and found that the three states have the largest phase volume of the initial couplings: nematic, antiferromagnetic, and spin flux (a.k.a. quantum spin Hall). In addition, ferroelectric and two superconducting phases appear only near the very limits of the applicability of the weak-coupling approach. The paper also contains the derivation and analysis of the renormalization group equations and the group theory classification of all the possible phases which might arise from the symmetry breakings of the lattice, spin rotation, and gauge symmetries of graphene.

  2. A separation of antiferromagnetic spin motion modes in the training effect of exchange biased Co/CoO film with in-plane anisotropy

    NASA Astrophysics Data System (ADS)

    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.

  3. Probing ultrafast spin dynamics through a magnon resonance in the antiferromagnetic multiferroic HoMnO3

    DOE PAGES

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

    2016-09-26

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

  4. Top Quark Spin Correlations at the Tevatron

    SciTech Connect

    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.

  5. Antiferromagnetic interaction between A'-site Mn spins in A-site-ordered perovskite YMn3Al4O12.

    PubMed

    Tohyama, Takenori; Saito, Takashi; Mizumaki, Masaichiro; Agui, Akane; Shimakawa, Yuichi

    2010-03-01

    The A-site-ordered perovskite YMn(3)Al(4)O(12) was prepared by high-pressure synthesis. Structural analysis with synchrotron powder X-ray diffraction data and the Mn L-edges X-ray absorption spectrum revealed that the compound has a chemical composition Y(3+)Mn(3+)(3)Al(3+)(4)O(2-)(12) with magnetic Mn(3+) at the A' site and non-magnetic Al(3+) at the B site. An antiferromagnetic interaction between the A'-site Mn(3+) spins is induced by the nearest neighboring Mn-Mn direct exchange interaction and causes an antiferromagnetic transition at 34.3 K.

  6. Spin-glass transition in bond-disordered Heisenberg antiferromagnets coupled with local lattice distortions on a pyrochlore lattice.

    PubMed

    Shinaoka, Hiroshi; Tomita, Yusuke; Motome, Yukitoshi

    2011-07-22

    Motivated by puzzling characteristics of spin-glass transitions widely observed in pyrochlore-based frustrated materials, we investigate the effects of coupling to local lattice distortions in a bond-disordered antiferromagnet on the pyrochlore lattice by extensive Monte Carlo simulations. We show that the spin-glass transition temperature T(f) is largely enhanced by the spin-lattice coupling and, furthermore, becomes almost independent of Δ in a wide range of the disorder strength Δ. The critical property of the spin-glass transition is indistinguishable from that of the canonical Heisenberg spin glass in the entire range of Δ. These peculiar behaviors are ascribed to a modification of the degenerate manifold from a continuous to semidiscrete one by spin-lattice coupling.

  7. Field-induced spin density wave and spiral phases in a layered antiferromagnet

    DOE PAGES

    Stone, Matthew B.; Lumsden, Mark D.; Garlea, Vasile O.; ...

    2015-07-28

    Here we determine the low-field ordered magnetic phases of the S=1 dimerized antiferromagnet Ba3Mn2O8 using single crystal neutron diffraction. We find that for magnetic fields between μ0H=8.80 T and 10.56 T applied along themore » $$1\\bar{1}0$$ direction the system exhibits spin density wave order with incommensurate wave vectors of type (η,η,ε). For μ0H > 10.56 T, the magnetic order changes to a spiral phase with incommensurate wave vectors only along the [hh0] direction. For both field induced ordered phases, the magnetic moments are lying in the plane perpendicular to the field direction. Finally, the nature of these two transitions is fundamentally different: the low-field transition is a second order transition to a spin-density wave ground state, while the one at higher field, toward the spiral phase, is of first order.« less

  8. Field-induced spin density wave and spiral phases in a layered antiferromagnet

    SciTech Connect

    Stone, Matthew B.; Lumsden, Mark D.; Garlea, Vasile O.; Grenier, B.; Ressouche, E.; Samulon, Eric C.; Fisher, Ian R.

    2015-07-28

    Here we determine the low-field ordered magnetic phases of the S=1 dimerized antiferromagnet Ba3Mn2O8 using single crystal neutron diffraction. We find that for magnetic fields between μ0H=8.80 T and 10.56 T applied along the $1\\bar{1}0$ direction the system exhibits spin density wave order with incommensurate wave vectors of type (η,η,ε). For μ0H > 10.56 T, the magnetic order changes to a spiral phase with incommensurate wave vectors only along the [hh0] direction. For both field induced ordered phases, the magnetic moments are lying in the plane perpendicular to the field direction. Finally, the nature of these two transitions is fundamentally different: the low-field transition is a second order transition to a spin-density wave ground state, while the one at higher field, toward the spiral phase, is of first order.

  9. Antiferromagnetic THz-frequency Josephson-like Oscillator Driven by Spin Current

    PubMed Central

    Khymyn, Roman; Lisenkov, Ivan; Tiberkevich, Vasyl; Ivanov, Boris A.; Slavin, Andrei

    2017-01-01

    The development of compact and tunable room temperature sources of coherent THz-frequency signals would open a way for numerous new applications. The existing approaches to THz-frequency generation based on superconductor Josephson junctions (JJ), free electron lasers, and quantum cascades require cryogenic temperatures or/and complex setups, preventing the miniaturization and wide use of these devices. We demonstrate theoretically that a bi-layer of a heavy metal (Pt) and a bi-axial antiferromagnetic (AFM) dielectric (NiO) can be a source of a coherent THz signal. A spin-current flowing from a DC-current-driven Pt layer and polarized along the hard AFM anisotropy axis excites a non-uniform in time precession of magnetizations sublattices in the AFM, due to the presence of a weak easy-plane AFM anisotropy. The frequency of the AFM oscillations varies in the range of 0.1–2.0 THz with the driving current in the Pt layer from 108 A/cm2 to 109 A/cm2. The THz-frequency signal from the AFM with the amplitude exceeding 1 V/cm is picked up by the inverse spin-Hall effect in Pt. The operation of a room-temperature AFM THz-frequency oscillator is similar to that of a cryogenic JJ oscillator, with the energy of the easy-plane magnetic anisotropy playing the role of the Josephson energy. PMID:28262731

  10. Antiferromagnetic THz-frequency Josephson-like Oscillator Driven by Spin Current

    NASA Astrophysics Data System (ADS)

    Khymyn, Roman; Lisenkov, Ivan; Tiberkevich, Vasyl; Ivanov, Boris A.; Slavin, Andrei

    2017-03-01

    The development of compact and tunable room temperature sources of coherent THz-frequency signals would open a way for numerous new applications. The existing approaches to THz-frequency generation based on superconductor Josephson junctions (JJ), free electron lasers, and quantum cascades require cryogenic temperatures or/and complex setups, preventing the miniaturization and wide use of these devices. We demonstrate theoretically that a bi-layer of a heavy metal (Pt) and a bi-axial antiferromagnetic (AFM) dielectric (NiO) can be a source of a coherent THz signal. A spin-current flowing from a DC-current-driven Pt layer and polarized along the hard AFM anisotropy axis excites a non-uniform in time precession of magnetizations sublattices in the AFM, due to the presence of a weak easy-plane AFM anisotropy. The frequency of the AFM oscillations varies in the range of 0.1–2.0 THz with the driving current in the Pt layer from 108 A/cm2 to 109 A/cm2. The THz-frequency signal from the AFM with the amplitude exceeding 1 V/cm is picked up by the inverse spin-Hall effect in Pt. The operation of a room-temperature AFM THz-frequency oscillator is similar to that of a cryogenic JJ oscillator, with the energy of the easy-plane magnetic anisotropy playing the role of the Josephson energy.

  11. CP observables with spin spin correlations in chargino production

    NASA Astrophysics Data System (ADS)

    Bartl, A.; Hohenwarter-Sodek, K.; Kernreiter, T.; Kittel, O.; Terwort, M.

    2008-10-01

    We study the CP-violating terms of the spin-spin correlations in chargino production ee→χ˜1±χ˜2∓, and their subsequent two-body decays into sneutrinos plus leptons. We propose novel CP-sensitive observables with the help of T-odd products of the spin-spin terms. These terms depend on the polarizations of both charginos, with one polarization perpendicular to the production plane. We identify two classes of CP-sensitive observables; one requires the reconstruction of the production plane, the other not. Our framework is the Minimal Supersymmetric Standard Model with complex parameters.

  12. Direct manipulation of the uncompensated antiferromagnetic spins in exchange coupled system by GeV ion irradiation

    SciTech Connect

    Paul, Amitesh; Boeni, P.; Paul, N.; Hoepfner, Britta; Lauermann, Iver; Lux-Steiner, M.; Trautmann, C.; Mattauch, S.

    2012-06-18

    Incident ion energy to matrix electrons of a material is dissipated within a narrow cylinder surrounding the swift heavy ion path. The temperature of the lattice exceeds the melting point and upon quenching causes nanometric modifications. We present here a unique ex situ approach in manipulating the uncompensated spins in antiferromagnetic layers of ferro-/antiferromagnetic exchange coupled systems on a nanometric scale. We use the impact of relativistic heavy ion (1-2 GeV) irradiation on such systems. We find an increase in the bias field and a restoration of the reversal via domain nucleation in the trained state. These are identified as plausible results of ion-induced antiferromagnetic ordering with little or no effect on the layer structure. This study demonstrates, therefore, the possibility of nanoscale tailoring of exchange coupled systems that survive even in the trained state.

  13. Spin reorientation and Ce-Mn coupling in antiferromagnetic oxypnictide CeMnAsO

    SciTech Connect

    Zhang, Qiang; Tian, Wei; Peterson, Spencer G.; Dennis, Kevin W.; Vaknin, David

    2015-02-18

    Structure and magnetic properties of high-quality polycrystlline CeMnAsO, a parent compound of the “1111”-type oxypnictides, have been investigated using neutron powder diffraction and magnetization measurements. We find that CeMnAsO undergoes a C-type antiferromagnetic order with Mn2+(S = 5/2) moments pointing along the c axis below a relatively high Néel temperature of TN = 347(1) K. Below TSR = 35 K, two simultaneous transitions occur where the Mn moments reorient from the c axis to the ab plane preserving the C-type magnetic order, and Ce moments undergo long-range AFM ordering with antiparallel moments pointing in the ab plane. Another transition to a noncollinear magnetic structure occurs below 7 K. The ordered moments of Mn and Ce at 2 K are 3.32(4) μB and 0.81(4)μB, respectively. We find that CeMnAsO primarily falls into the category of a local-moment antiferromagnetic insulator in which the nearest-neighbor interaction (J1) is dominant with J2 < J1/2 in the context of J1 – J2 – Jc model. The spin reorientation transition driven by the coupling between Ce and the transition metal seems to be common to Mn, Fe, and Cr ions, but not to Co and Ni ions in the isostructural oxypnictides. As a result, a schematic illustration of magnetic structures in Mn and Ce sublattices in CeMnAsO is presented.

  14. Spin reorientation and Ce-Mn coupling in antiferromagnetic oxypnictide CeMnAsO

    DOE PAGES

    Zhang, Qiang; Tian, Wei; Peterson, Spencer G.; ...

    2015-02-18

    Structure and magnetic properties of high-quality polycrystlline CeMnAsO, a parent compound of the “1111”-type oxypnictides, have been investigated using neutron powder diffraction and magnetization measurements. We find that CeMnAsO undergoes a C-type antiferromagnetic order with Mn2+(S = 5/2) moments pointing along the c axis below a relatively high Néel temperature of TN = 347(1) K. Below TSR = 35 K, two simultaneous transitions occur where the Mn moments reorient from the c axis to the ab plane preserving the C-type magnetic order, and Ce moments undergo long-range AFM ordering with antiparallel moments pointing in the ab plane. Another transition tomore » a noncollinear magnetic structure occurs below 7 K. The ordered moments of Mn and Ce at 2 K are 3.32(4) μB and 0.81(4)μB, respectively. We find that CeMnAsO primarily falls into the category of a local-moment antiferromagnetic insulator in which the nearest-neighbor interaction (J1) is dominant with J2 < J1/2 in the context of J1 – J2 – Jc model. The spin reorientation transition driven by the coupling between Ce and the transition metal seems to be common to Mn, Fe, and Cr ions, but not to Co and Ni ions in the isostructural oxypnictides. As a result, a schematic illustration of magnetic structures in Mn and Ce sublattices in CeMnAsO is presented.« less

  15. Antiferromagnetic Spin Correlations Between Corner-Shared [FeO5]7- and [FeO6]9- Units, in the Novel Iron-Based Compound: BaYFeO4

    SciTech Connect

    Wrobel, Friederike; Kemei, Moureen C; Derakhshan, Shahab

    2013-02-25

    A novel quaternary compound in the Ba–Y–Fe-O phase diagram was synthesized by solid-state reaction and its crystal structure was characterized using powder X-ray diffraction. The crystal structure of BaYFeO4 consists of a unique arrangement of Fe3+ magnetic ions, which is based on alternate corner-shared units of [FeO5]7– square pyramids and [FeO6]9– octahedra. This results in the formation of stairwise channels of FeO polyhedra along the b crystallographic axis. The structure is described in an orthorhombic crystal system in the space group Pnma with lattice parameters a = 13.14455(1) Å, b = 5.694960(5) Å, and c = 10.247630(9) Å. The temperature-dependent magnetic susceptibility data reveal two antiferromagnetic (AFM) transitions at 33 and 48 K. An upturn in the magnetic susceptibility data above these transitions is observed, which does not reach its maximum even at 390 K. The field-dependent magnetization data at both 2 and 300 K show a nearly linear dependence and do not exhibit significant hysteresis. Heat capacity measurements between 2 and 200 K reveal only a broad anomaly without any indication of long-range ordering. The latter data set is not in good agreement with the magnetic susceptibility data, which makes it difficult to exactly determine the magnetic ground state of BaYFeO4. Accordingly, a temperature-dependent neutron diffraction study is in order, which will enable resolving this issue. The theoretical study of the relative strengths of magnetic exchange interactions along various possible pathways, using extended Hückel spin dimer analysis, shows that only interactions between square pyramidal and octahedral centers are significant, and among them, the intrachannel correlations are stronger than interchannel interactions. This is the first physical property study in such a magnetic ion substructure.

  16. Direct measurement of voltage-controlled reversal of the antiferromagnetic spin structure in magnetoelectric Cr2O3

    NASA Astrophysics Data System (ADS)

    Wang, Junlei; Binek, Christian

    The frequency dependence of the electric field induced magneto-optical Faraday effect is investigated in the magnetoelectric antiferromagnet chromia. Two electrically induced Faraday signals superimpose in proportion to the linear magnetoelectric susceptibility and the antiferromagnetic order parameter. The relative strength of these contributions is determined by the frequency of the probing light beam. It allows tuning the Faraday signal between extreme characteristics which follow the temperature dependence of the magnetoelectric susceptibility or solely that of the antiferromagnetic order parameter. The frequency dependence is analyzed in terms of electric dipole transitions of perturbed Cr3 + crystal-field states. The results lead to a table-top set-up allowing to measure voltage-controlled selection and temperature dependence of the antiferromagnetic order parameter. The Faraday rotation per applied voltage is independent of the sample thickness making the method scalable and versatile for thin film investigations. Scalability, compactness, and simplicity of the data analysis combined with low photon flux requirements make the Faraday approach advantageous for the investigation of the otherwise difficult to access voltage-controlled switching of antiferromagnetic domain states in magnetoelectric thin films. This project is supported by NRI via CNFD through tasks SRC 2398.001 and 2587.001, by C-SPIN, a SRC program, sponsored by MARCO and DARPA, and by NSF through Nebraska MRSEC DMR-1420645.

  17. Gapless quantum spin liquid ground state behavior in the rare-earth triangular antiferromagnet YbMgGaO4

    NASA Astrophysics Data System (ADS)

    Li, Yuesheng; Zhang, Qingming; Chen, Gang

    The ground state of a spin-orbit coupled insulator with an odd number of electrons per unit cell must be exotic as long as the time reversal symmetry is preserved according to the recent theoretical advances. We present a new structurally perfect triangular quantum spin liquid (QSL) candidate YbMgGaO4 with spin-orbit entangled effective spin-1/2 for Yb3+. Due to the spin-orbit entanglement, the neighboring spin interaction is highly anisotropic in the spin space. We carried out the thermodynamic and the electron spin resonance measurements for YbMgGaO4 single-crystals to quantitatively determine the anisotropic couplings. Despite the antiferromagnetic couplings (~4K), no spin freezing was observed at least down to 60mK. The magnetic heat capacity of YbMgGaO4 clearly behaves as Cv ~ Tγ (γ ~ 2/3) from about 1K down to 60mK, suggesting a probable gapless QSL. Almost zero residual spin entropy (<0.6% of Rln2) at 60mK, indicates the system accesses the ground state property. Our results shed new light on the search for QSLs in strong spin-orbit coupled insulators.

  18. Antiferromagnetism in chromium

    NASA Astrophysics Data System (ADS)

    Jaramillo, Rafael

    I present two experimental studies of the spin density wave antiferromagnetic order in elemental Chromium. The first addresses the response of the magnetic ground state to applied pressure. The spin and charge order parameters are probed at high pressure and low temperature in a diamond anvil cell using monochromatic X-ray diffraction. We find that the magnetism is suppressed exponentially with pressure, providing a canonical example of a weak-coupling, mean-field ground state, before terminating at a quantum phase transition. We confirm the harmonic relationship between the spin and charge degrees of freedom in the low temperature regime, and we identify the microscopic coupling between pressure and magnetism. The discovery of the long-sought-after quantum critical regime sets the stage for a complete study of antiferromagnetic quantum criticality in this clean model system. The second study addresses the thermodynamics and transport properties of antiferromagnetic domain structure. We find a robust thermal hysteresis in the longitudinal and Hall resistivities of sub-mm bulk Cr samples. The temperature limits of the hysteresis are correlated with domain wall fluctuations and freezing. The persistent sign of the hysteresis and the macroscopic return point memory warrant a new understanding of domain wall energetics. By combining electrical transport and X-ray microdiffraction measurements we are able to pinpoint the effects of antiferromagnetic domain walls on electron transport.

  19. Variational Monte Carlo study of a gapless spin liquid in the spin-1/2 XXZ antiferromagnetic model on the kagome lattice

    NASA Astrophysics Data System (ADS)

    Hu, Wen-Jun; Gong, Shou-Shu; Becca, Federico; Sheng, D. N.

    2015-11-01

    By using the variational Monte Carlo technique, we study the spin-1/2 XXZ antiferromagnetic model (with easy-plane anisotropy) on the kagome lattice. A class of Gutzwiller projected fermionic states with a spin Jastrow factor is considered to describe either spin liquids [with U (1 ) or Z2 symmetry] or magnetically ordered phases [with q =(0 ,0 ) or q =(4 π /3 ,0 ) ]. We find that the magnetic states are not stable in the thermodynamic limit. Moreover, there is no energy gain to break the gauge symmetry from U (1 ) to Z2 within the spin-liquid states, as previously found in the Heisenberg model. The best variational wave function is therefore the U (1 ) Dirac state, supplemented by the spin Jastrow factor. Furthermore, a vanishing S =2 spin gap is obtained at the variational level, in the whole regime from the X Y to the Heisenberg model.

  20. Observation of pure inverse spin Hall effect in ferromagnetic metals via ferromagnetic/antiferromagnetic exchange-bias structures

    NASA Astrophysics Data System (ADS)

    Wu, H.; Wan, C. H.; Yuan, Z. H.; Zhang, X.; Jiang, J.; Zhang, Q. T.; Wen, Z. C.; Han, X. F.

    2015-08-01

    We report that the spin current generated by the spin Seebeck effect (SSE) in yttrium iron garnet (YIG) can be detected by a ferromagnetic metal (NiFe). By using the ferromagnetic/antiferromagnetic (FM/AFM) exchange bias structure (NiFe/IrMn), the inverse spin Hall effect (ISHE) and planar Nernst effect (PNE) of NiFe can be unambiguously separated, allowing us to observe a pure ISHE signal. After eliminating the in-plane temperature gradient in NiFe, we can even observe a pure ISHE signal without PNE from NiFe itself. It is worth noting that a large spin Hall angle (0.098) of NiFe is obtained, which is comparable with Pt. This work provides a kind of FM/AFM exchange bias structure to detect the spin current by charge signals, and highlights that ISHE in ferromagnetic metals can be used in spintronic research and applications.

  1. The route to magnetic order in the spin-1/2 kagome Heisenberg antiferromagnet: The role of interlayer coupling

    NASA Astrophysics Data System (ADS)

    Götze, Oliver; Richter, Johannes

    2016-06-01

    While the existence of a spin-liquid ground state of the spin-1/2 kagome Heisenberg antiferromagnet (KHAF) is well established, the discussion of the effect of an interlayer coupling (ILC) by controlled theoretical approaches is still lacking. Here we study this problem by using the coupled-cluster method to high orders of approximation. We consider a stacked KHAF with a perpendicular ILC J_\\perp , where we study ferro- as well as antiferromagnetic J_\\perp . We find that the spin-liquid ground state (GS) persists until relatively large strengths of the ILC. Only if the strength of the ILC exceeds about 15% of the intralayer coupling the spin-liquid phase gives way for q = 0 magnetic long-range order, where the transition between both phases is continuous and the critical strength of the ILC, |J^c_\\perp| , is almost independent of the sign of J_\\perp . Thus, by contrast to the quantum GS selection of the strictly two-dimensional KHAF at large spin s, the ILC leads first to a selection of the q = 0 GS. Only at larger |J_\\perp| the ILC drives a first-order transition to the \\sqrt{3}×\\sqrt{3} long-range ordered GS. As a result, the stacked spin-1/2 KHAF exhibits a rich GS phase diagram with two continuous and two discontinuous transitions driven by the ILC.

  2. Spin dynamics induced by ultrafast heating with ferromagnetic/antiferromagnetic interfacial exchange in perpendicularly magnetized hard/soft bilayers

    SciTech Connect

    Ma, Q. L. E-mail: mizukami@wpi-aimr.tohoku.ac.jp; Miyazaki, T.; Mizukami, S. E-mail: mizukami@wpi-aimr.tohoku.ac.jp; Iihama, S.; Zhang, X. M.

    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.

  3. Spin dynamics induced by ultrafast heating with ferromagnetic/antiferromagnetic interfacial exchange in perpendicularly magnetized hard/soft bilayers

    NASA Astrophysics Data System (ADS)

    Ma, Q. L.; Iihama, S.; Zhang, X. M.; Miyazaki, T.; Mizukami, S.

    2015-11-01

    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.

  4. Quantification of magnetic domain disorder and correlations in antiferromagnetically coupled multilayers by neutron reflectometry

    PubMed

    Langridge; Schmalian; Marrows; Dekadjevi; Hickey

    2000-12-04

    The in-plane correlation lengths and angular dispersion of magnetic domains in a transition metal multilayer have been studied using off-specular neutron reflectometry techniques. A theoretical framework considering both structural and magnetic disorder has been developed, quantitatively connecting the observed scattering to the in-plane correlation length and the dispersion of the local magnetization vector about the mean macroscopic direction. The antiferromagnetic domain structure is highly vertically correlated throughout the multilayer. We are easily able to relate the neutron determined magnetic domain dispersion to magnetization and magnetoresistance experiments.

  5. High- Tc superconductors with antiferromagnetic order: limitations on spin-fluctuation pairing mechanism

    NASA Astrophysics Data System (ADS)

    Kulić, Miodrag L.; Kulić, Igor M.

    2003-08-01

    The antagonistic interplay of antiferromagnetism (AF) and superconductivity (SC), recently discovered in high-temperature superconductors, is studied in the framework of a microscopic theory. We explain the surprisingly large increase of the magnetic Bragg peak intensity IQ at Q∼( π, π) in the magnetic field H≪ Hc2 at low temperatures 0< T≪ Tc, TAF in La 2- xSr xCuO 4. Good agreement with experimental results is found. The theory predicts large anisotropy of the relative intensity RQ( H)=( IQ( H)- IQ(0))/ IQ(0), i.e. R Q( H∥c -axis)≫R Q( H⊥c -axis) . The quantum ( T=0) phase diagram at H=0 is constructed. The theory also predicts: (i) that the magnetic field can induce the AF order in the SC state; (ii) that the spin-fluctuation (SF) effective coupling constant g<0.1 eV is small, which gives small SC critical temperature Tc (≪40 K)--thus questioning the SF mechanism of pairing in HTS oxides.

  6. Magnetic properties of uniaxial synthetic antiferromagnets for spin-valve applications

    NASA Astrophysics Data System (ADS)

    Zhao, Zhiya; Mani, P.; Mankey, G. J.; Gubbiotti, G.; Tacchi, S.; Spizzo, F.; Lee, W.-T.; Yu, C. T.; Pechan, M. J.

    2005-03-01

    The magnetic properties of synthetic antiferromagnetic Si(100)/Ta(5nm)/Co(t1)/Ru(0.65nm)/Co(t2)/Ta(10nm) with an obliquely sputtered Ta underlayer are reported as a function of the top Co layer thickness, t2 . The morphological origin of the large in-plane magnetic anisotropy created by the obliquely sputtered Ta underlayer is revealed by atomic force microscopy. The magnetic anisotropy of the base Co layer is determined by measuring the dispersion of the Damon-Eshbach spin-wave mode with Brillouin light scattering. Ferromagnetic resonance measurements and hysteresis loops reveal that both the anisotropy and the saturation field of the trilayer system decrease with increasing top Co layer thickness. The dependence of the saturation field on layer thickness is fitted to an energy minimization equation that contains both bilinear and biquadratic exchange coupling constants. Magnetoresistance and polarized neutron reflectometry results both confirm that the magnetic reversal process of the system is through magnetic domain formation followed by rotation.

  7. Spin glass behavior of the antiferromagnetic Heisenberg model on scale free network

    NASA Astrophysics Data System (ADS)

    Surungan, Tasrief; Zen, Freddy P.; Williams, Anthony G.

    2015-09-01

    Randomness and frustration are considered to be the key ingredients for the existence of spin glass (SG) phase. In a canonical system, these ingredients are realized by the random mixture of ferromagnetic (FM) and antiferromagnetic (AF) couplings. The study by Bartolozzi et al. [Phys. Rev. B73, 224419 (2006)] who observed the presence of SG phase on the AF Ising model on scale free network (SFN) is stimulating. It is a new type of SG system where randomness and frustration are not caused by the presence of FM and AF couplings. To further elaborate this type of system, here we study Heisenberg model on AF SFN and search for the SG phase. The canonical SG Heisenberg model is not observed in d-dimensional regular lattices for (d ≤ 3). We can make an analogy for the connectivity density (m) of SFN with the dimensionality of the regular lattice. It should be plausible to find the critical value of m for the existence of SG behaviour, analogous to the lower critical dimension (dl) for the canonical SG systems. Here we study system with m = 2, 3, 4 and 5. We used Replica Exchange algorithm of Monte Carlo Method and calculated the SG order parameter. We observed SG phase for each value of m and estimated its corersponding critical temperature.

  8. Two-dimensional-lattice spin models with long-range antiferromagnetic interactions

    NASA Astrophysics Data System (ADS)

    Romano, S.

    1991-10-01

    We consider a classical system, consisting of m-component unit vectors (m=2,3), associated with a two-dimensional lattice \\{uk||k∈openZ2\\} and interacting via translationally and rotationally invariant antiferromagnetic pair potentials of the long-range form W=Wjk=ɛ||xj-xk||-puj.uk, p>2, where ɛ is a positive quantity, setting energy and temperature scales (i.e., T*=kBT/ɛ), and xk are the coordinates of the lattice sites. A spin-wave approach predicts orientational disorder (in the thermodynamic limit) at all finite temperatures and for all p>2 this agrees with available rigorous results for p>=4, whereas no such theorems are known in the literature when 22.

  9. Quantum Monte-Carlo simulation of spin-one antiferromagnets with single-ion anisotropy

    NASA Astrophysics Data System (ADS)

    Kato, Yasuyuki; Wierschem, Keola; Nishida, Yusuke; Batista, Cristian; Sengupta, Pinaki

    2013-03-01

    We study a spin-one Heisenberg model with uniaxial single-ion anisotropy, D, and Zeeman coupling to a magnetic field, B, parallel to the symmetry axis. We compute the (D / J , B / J) quantum phase diagram for square and simple cubic lattices by combining analytical and Quantum Monte Carlo approaches, and find a transition between XY-antiferromagnetic and ferronematic phases that spontaneously break the U(1) symmetry of the model. In the language of bosonic gases, this is a transition between a Bose-Einstein condensate (BEC) of single bosons and a BEC of pairs. For the efficient simulation of ferronematic phase, we developed and implemented a new multi-discontinuity algorithm based on the directed-loop algorithm. The ordinary quantum Monte-Carlo methods fall into freezing problems when we apply them to this system at large D / J and finite B / J ~ 1 . The new method does not suffer from the freezing problems. This research used resources of the NERSCC (DOE Contract No. DE-AC02-05CH11231). Work at LANL was performed under the auspices of a J. Robert Oppenheimer Fellowship and the U.S. DOE contract No. DE-AC52-06NA25396 through the LDRD program.

  10. CaMn2Sb2: Spin waves on a frustrated antiferromagnetic honeycomb lattice

    DOE PAGES

    McNally, D. E.; Simonson, J. W.; Kistner-Morris, J. J.; ...

    2015-05-22

    We present inelastic neutron scattering measurements of the antiferromagnetic insulator CaMn2Sb2:, which consists of corrugated honeycomb layers of Mn. The dispersion of magnetic excitations has been measured along the H and L directions in reciprocal space, with a maximum excitation energy of ≈ 24 meV. These excitations are well described by spin waves in a Heisenberg model, including first and second neighbor exchange interactions, J1 and J2, in the Mn plane and also an exchange interaction between planes. The determined ratio J2/J1 ≈ 1/6 suggests that CaMn2Sb2: is the first example of a compound that lies very close to themore » mean field tricritical point, known for the classical Heisenberg model on the honeycomb lattice, where the N´eel phase and two different spiral phases coexist. The magnitude of the determined exchange interactions reveal a mean field ordering temperature ≈ 4 times larger than the reported N´eel temperature TN = 85 K, suggesting significant frustration arising from proximity to the tricritical point.« less

  11. Antiferromagnetic ordering in spin-chain multiferroic Gd{sub 2}BaNiO{sub 5} studied by electronic spin resonance

    SciTech Connect

    Guo, Y. M.; Ruan, M. Y.; Cheng, J. J.; Sun, Y. C.; Ouyang, Z. W. Xia, Z. C.; Rao, G. H.

    2015-06-14

    High-field electron spin resonance (ESR) has been employed to study the antiferromagnetic (AFM) ordering state (T < T{sub N} = 55 K) of spin-chain multiferroic Gd{sub 2}BaNiO{sub 5}. The spin reorientation at T{sub SR} = 24 K is well characterized by the temperature-dependent ESR spectra. The magnetization data evidence a field-induced spin-flop transition at 2 K. The frequency-field relationship of the ESR data can be explained by conventional AFM resonance theory with uniaxial anisotropy, in good agreement with magnetization data. Related discussion on zero-field spin gap is presented.

  12. Spin correlations in percolating networks with fractal geometry

    SciTech Connect

    Ikeda, H.; Iwasa, K.; Fernandez-Baca, J.A.; Nicklow, R.M.

    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.

  13. Coexistence of antiferromagnetic and ferromagnetic spin correlations in Ca(Fe1-xCox)2As2 revealed by As75 nuclear magnetic resonance

    SciTech Connect

    Cui, J.; Wiecki, P.; Ran, S.; Bud'ko, S. L.; Canfield, P. C.; Furukawa, Y.

    2016-11-22

    Recent nuclear magnetic resonance (NMR) measurements revealed the coexistence of stripe-type antiferromagnetic (AFM) and ferromagnetic (FM) spin correlations in both the hole- and electron-doped BaFe 2 As 2 families of iron-pnictide superconductors by a Korringa ratio analysis. Motivated by the NMR work, we investigate the possible existence of FM fluctuations in another iron-pnictide superconducting family, Ca ( Fe 1 - x Co x ) 2 As 2 . We reanalyzed our previously reported data in terms of the Korringa ratio and found clear evidence for the coexistence of stripe-type AFM and FM spin correlations in the electron-doped CaFe 2 As 2 system. These NMR data indicate that FM fluctuations exist in general in iron-pnictide superconducting families and thus must be included to capture the phenomenology of the iron pnictides.

  14. Antiferromagnetic half-metals, gapless half-metals, and spin gapless semiconductors: The D0{sub 3}-type Heusler alloys

    SciTech Connect

    Gao, G. Y. Yao, Kai-Lun

    2013-12-02

    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 D0{sub 3}-type Heusler alloys: gapless (zero-gap) half-metallic ferrimagnets of V{sub 3}Si and V{sub 3}Ge, half-metallic antiferromagnets of Mn{sub 3}Al and Mn{sub 3}Ga, half-metallic ferrimagnets of Mn{sub 3}Si and Mn{sub 3}Ge, and a spin gapless semiconductor of Cr{sub 3}Al. 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.

  15. Antiferromagnetic S=1/2 Spin Chain Driven by p-Orbital Ordering in CsO2

    NASA Astrophysics Data System (ADS)

    Riyadi, Syarif; Zhang, Baomin; de Groot, Robert A.; Caretta, Antonio; van Loosdrecht, Paul H. M.; Palstra, Thomas T. M.; Blake, Graeme R.

    2012-05-01

    We demonstrate, using a combination of experiment and density functional theory, that orbital ordering drives the formation of a one-dimensional (1D) S=1/2 antiferromagnetic spin chain in the 3D rocksalt structure of cesium superoxide (CsO2). The magnetic superoxide anion (O2-) exhibits degeneracy of its 2p-derived molecular orbitals, which is lifted by a structural distortion on cooling. A spin chain is then formed by zigzag ordering of the half-filled superoxide orbitals, promoting a superexchange pathway mediated by the pz orbitals of Cs+ along only one crystal direction. This scenario is analogous to the 3d-orbital-driven spin chain found in the perovskite KCuF3 and is the first example of an inorganic quantum spin system with unpaired p electrons.

  16. Antiferromagnetic skyrmions

    NASA Astrophysics Data System (ADS)

    Tretiakov, Oleg; Barker, Joseph

    Skyrmions are topologically protected entities in magnetic materials which have the potential to be used in spintronics for information storage and processing. However, skyrmions in ferromagnets have some intrinsic difficulties which must be overcome to use them for spintronic applications, such as the inability to move straight along current. We show that skyrmions can also be stabilized and manipulated in antiferromagnetic materials. An antiferromagnetic skyrmion is a compound topological object with a similar but of opposite sign spin texture on each sublattice, which e.g. results in a complete cancelation of the Magnus force. We find that the composite nature of antiferromagnetic skyrmions gives rise to different dynamical behavior, both due to an applied current and temperature effects. O.A.T. and J.B. acknowledge support by the Grants-in-Aid for Scientific Research (Nos. 25800184, 25247056, 25220910 and 15H01009) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan and SpinNet.

  17. Zigzag antiferromagnetic ground state with anisotropic correlation lengths in the quasi-two-dimensional honeycomb lattice compound N a2C o2Te O6

    NASA Astrophysics Data System (ADS)

    Bera, A. K.; Yusuf, S. M.; Kumar, Amit; Ritter, C.

    2017-03-01

    The crystal structure, magnetic ground state, and the temperature-dependent microscopic spin-spin correlations of the frustrated honeycomb lattice antiferromagnet N a2C o2Te O6 have been investigated by powder neutron diffraction. A long-range antiferromagnetic (AFM) ordering has been found below TN˜24.8 K . The magnetic ground state, determined to be zigzag antiferromagnetic and characterized by a propagation vector k =(1 /2 0 0 ) , occurs due to the competing exchange interactions up to third-nearest neighbors within the honeycomb lattice. The exceptional existence of a limited magnetic correlation length along the c axis (perpendicular to the honeycomb layers in the a b planes) has been found even at 1.8 K, well below the TN˜24.8 K . The observed limited correlation along the c axis is explained by the disorder distribution of the Na ions within the intermediate layers between honeycomb planes. The reduced ordered moments mCo (1 )=2.77 (3 ) μB/C o2 + and mCo (2 )=2.45 (2 ) μB/C o2 + at 1.8 K reflect the persistence of spin fluctuations in the ordered state. Above TN˜24.8 K , the presence of short-range magnetic correlations, manifested by broad diffuse magnetic peaks in the diffraction patterns, has been found. Reverse Monte Carlo analysis of the experimental diffuse magnetic scattering data reveals that the spin correlations are mainly confined within the two-dimensional honeycomb layers (a b plane) with a correlation length of ˜12 Å at 25 K. The nature of the spin arrangements is found to be similar in both the short-range and long-range ordered magnetic states. This implies that the short-range correlation grows with decreasing temperature and leads to the zigzag AFM ordering at T ≤TN . The present study provides a comprehensive picture of the magnetic correlations over the temperature range above and below the TN and their relation to the crystal structure. The role of intermediate soft Na layers on the magnetic coupling between honeycomb planes is

  18. Large magnetic cooling power involving frustrated antiferromagnetic spin-glass state in R2NiSi3(R =Gd ,Er )

    NASA Astrophysics Data System (ADS)

    Pakhira, Santanu; Mazumdar, Chandan; Ranganathan, R.; Giri, S.; Avdeev, Maxim

    2016-09-01

    The ternary intermetallic compounds Gd2NiSi3 and Er2NiSi3 are synthesized in chemically single phase, which are characterized using dc magnetization, ac magnetic susceptibility, heat capacity, and neutron diffraction studies. Neutron diffraction and heat capacity studies confirm that long-range magnetic ordering coexists with the frustrated glassy magnetic components for both compounds. The static and dynamical features of dc magnetization and frequency-dependent ac susceptibility data reveal that Gd2NiSi3 is a canonical spin-glass system, while Er2NiSi3 is a reentrant spin cluster-glass system. The spin freezing temperature merges with the long-range antiferromagnetic ordering temperature at 16.4 K for Gd2NiSi3 . Er2NiSi3 undergoes antiferromagnetic ordering at 5.4 K, which is slightly above the spin freezing temperature at 3 K. The detailed studies of nonequilibrium dynamical behavior, viz., the memory effect and relaxation behavior using different protocols, suggest that both compounds favor the hierarchical model over the droplet model. A large magnetocaloric effect is observed for both compounds. Maximum values of isothermal entropy change (-Δ SM ) and relative cooling power (RCP) are found to be 18.4 J/kg K and 525 J/kg for Gd2NiSi3 and 22.6 J/kg K and 540 J/kg for Er2NiSi3 , respectively, for a change in field from 0 to 70 kOe. The values of RCP are comparable to those of the promising refrigerant materials. A correlation between large RCP and magnetic frustration is discussed for developing new magnetic refrigerant materials.

  19. Off-easy-plane antiferromagnetic spin canting in coupled FePt/NiO bilayer structure with perpendicular exchange bias

    NASA Astrophysics Data System (ADS)

    Gao, Tenghua; Itokawa, Nobuhide; Wang, Jian; Yu, Youxing; Harumoto, Takashi; Nakamura, Yoshio; Shi, Ji

    2016-08-01

    We report on the investigation of perpendicular exchange bias in FePt (001 ) /NiO (1 ¯1 ¯1 ) orthogonal exchange couple with FePt partially L 10 ordered. From initial magnetization curve measurement and magnetic domain imaging, we find that, for the as-grown bilayer structure, the FePt layer experiences a small-angle magnetization rotation when it is magnetized near to saturation in film normal direction. After field cooling, the bilayer structure shows a significant enhancement of perpendicular magnetic anisotropy, indicating the field mediated coupling between the spins across the FePt/NiO interface. According to Koon's theoretical calculation on the basis of lowest energy ferromagnetic/antiferromagnetic coupling configuration for compensated spins at antiferromagnetic side, we consider slightly slanted Ni spins at the interface off the (1 ¯1 ¯1 ) easy plane can stabilize the spin coupling between FePt and NiO and result in the observed exchange bias in this paper. This consideration was further confirmed by stripe domain width calculation.

  20. Correlated impurities and intrinsic spin-liquid physics in the kagome material herbertsmithite

    NASA Astrophysics Data System (ADS)

    Han, Tian-Heng; Norman, M. R.; Wen, J.-J.; Rodriguez-Rivera, Jose A.; Helton, Joel S.; Broholm, Collin; Lee, Young S.

    2016-08-01

    Low energy inelastic neutron scattering on single crystals of the kagome spin-liquid compound ZnCu3(OD) 6Cl2 (herbertsmithite) reveals antiferromagnetic correlations between impurity spins for energy transfers ℏ ω <0.8 meV (˜J /20 ). The momentum dependence differs significantly from higher energy scattering which arises from the intrinsic kagome spins. The low energy fluctuations are characterized by diffuse scattering near wave vectors (100) and (00 3/2 ), which is consistent with antiferromagnetic correlations between pairs of nearest-neighbor Cu impurities on adjacent triangular (Zn) interlayers. The corresponding impurity lattice resembles a simple cubic lattice in the dilute limit below the percolation threshold. Such an impurity model can describe prior neutron, NMR, and specific heat data. The low energy neutron data are consistent with the presence of a small spin gap (Δ ˜0.7 meV ) in the kagome layers, similar to that recently observed by NMR. The ability to distinguish the scattering due to Cu impurities from that of the planar kagome Cu spins provides an important avenue for probing intrinsic spin-liquid physics.

  1. Doping dependence of spin excitations and its correlations with high-temperature superconductivity in iron pnictides.

    PubMed

    Wang, Meng; Zhang, Chenglin; Lu, Xingye; Tan, Guotai; Luo, Huiqian; Song, Yu; Wang, Miaoyin; Zhang, Xiaotian; Goremychkin, E A; Perring, T G; Maier, T A; Yin, Zhiping; Haule, Kristjan; Kotliar, Gabriel; Dai, Pengcheng

    2013-01-01

    High-temperature superconductivity in iron pnictides occurs when electrons and holes are doped into their antiferromagnetic parent compounds. Since spin excitations may be responsible for electron pairing and superconductivity, it is important to determine their electron/hole-doping evolution and connection with superconductivity. Here we use inelastic neutron scattering to show that while electron doping to the antiferromagnetic BaFe₂As₂ parent compound modifies the low-energy spin excitations and their correlation with superconductivity (<50 meV) without affecting the high-energy spin excitations (>100 meV), hole-doping suppresses the high-energy spin excitations and shifts the magnetic spectral weight to low-energies. In addition, our absolute spin susceptibility measurements for the optimally hole-doped iron pnictide reveal that the change in magnetic exchange energy below and above T(c) can account for the superconducting condensation energy. These results suggest that high-T(c) superconductivity in iron pnictides is associated with both the presence of high-energy spin excitations and a coupling between low-energy spin excitations and itinerant electrons.

  2. Doping dependence of spin excitations and its correlations with high-temperature superconductivity in iron pnictides

    PubMed Central

    Wang, Meng; Zhang, Chenglin; Lu, Xingye; Tan, Guotai; Luo, Huiqian; Song, Yu; Wang, Miaoyin; Zhang, Xiaotian; Goremychkin, E.A.; Perring, T.G.; Maier, T.A.; Yin, Zhiping; Haule, Kristjan; Kotliar, Gabriel; Dai, Pengcheng

    2013-01-01

    High-temperature superconductivity in iron pnictides occurs when electrons and holes are doped into their antiferromagnetic parent compounds. Since spin excitations may be responsible for electron pairing and superconductivity, it is important to determine their electron/hole-doping evolution and connection with superconductivity. Here we use inelastic neutron scattering to show that while electron doping to the antiferromagnetic BaFe2As2 parent compound modifies the low-energy spin excitations and their correlation with superconductivity (<50 meV) without affecting the high-energy spin excitations (>100 meV), hole-doping suppresses the high-energy spin excitations and shifts the magnetic spectral weight to low-energies. In addition, our absolute spin susceptibility measurements for the optimally hole-doped iron pnictide reveal that the change in magnetic exchange energy below and above Tc can account for the superconducting condensation energy. These results suggest that high-Tc superconductivity in iron pnictides is associated with both the presence of high-energy spin excitations and a coupling between low-energy spin excitations and itinerant electrons. PMID:24301219

  3. Effects of frustration and cyclic exchange on the spin-1/2 Heisenberg antiferromagnet within the self-consistent spin-wave theory

    NASA Astrophysics Data System (ADS)

    Rutonjski, Milica S.; Pavkov-Hrvojević, Milica V.; Berović, Maja B.

    2016-12-01

    The relevance of the quasi-two-dimensional spin-1/2 frustrated quantum antiferromagnet (AFM) due to its possibility of modeling the high-temperature superconducting parent compounds has resulted in numerous theoretical and experimental studies. This paper presents a detailed research of the influence of the varying exchange interactions on the model magnetic properties within the framework of self-consistent spin-wave theory based on Dyson-Maleev (DM) representation. Beside the nearest neighbor (NN) interaction within the plane, the planar frustration up to the third NNs, cyclic interaction and the interlayer coupling are taken into account. The detailed description of the elementary spin excitations, staggered magnetization, spin-wave velocity renormalization factor and ground state energy is given. The results are compared to the predictions of the linear spin-wave theory and when possible also to the second-order perturbative spin-wave expansion results. Finally, having at our disposal improved experimental results for the in-plane spin-wave dispersion in high-Tc copper oxide La2CuO4, the self-consistent spin-wave theory (SCSWT) is applied to that compound in order to correct earlier obtained set of exchange parameters and high-temperature spin-wave dispersion.

  4. Relaxation of a Classical Spin Coupled to a Strongly Correlated Electron System

    NASA Astrophysics Data System (ADS)

    Sayad, Mohammad; Rausch, Roman; Potthoff, Michael

    2016-09-01

    A classical spin which is antiferromagnetically coupled to a system of strongly correlated conduction electrons is shown to exhibit unconventional real-time dynamics which cannot be described by Gilbert damping. Depending on the strength of the local Coulomb interaction U , the two main electronic dissipation channels, namely transport of excitations via correlated hopping and via excitations of correlation-induced magnetic moments, become active on largely different time scales. We demonstrate that correlations can lead to a strongly suppressed relaxation which so far has been observed in purely electronic systems only and which is governed here by proximity to the divergent magnetic time scale in the infinite-U limit.

  5. Electronic structure reconstruction across the antiferromagnetic transition in TaFe₁̣₂₃Te₃ spin ladder

    DOE PAGES

    Xu, Min; Wang, Li -Min; Peng, Rui; ...

    2015-02-01

    With angle-resolved photoemission spectroscopy, we studied the electronic structure of TaFe₁̣₂₃Te₃, a two-leg spin ladder compound with a novel antiferromagnetic ground state. Quasi-two-dimensional Fermi surface is observed, with sizable inter-ladder hopping. Moreover, instead of observing an energy gap at the Fermi surface in the antiferromagnetic state, we observed the shifts of various bands. Combining these observations with density-functional-theory calculations, we propose that the large scale reconstruction of the electronic structure, caused by the interactions between coexisting itinerant electrons and local moments, is most likely the driving force of the magnetic transition. Thus TaFe₁̣₂₃Te₃ serves as a simpler platform that containsmore » similar ingredients as the parent compounds of iron-based superconductors.« less

  6. Spin-flip transition and Faraday effect in antiferromagnet KMnF 3 in megagauss magnetic field

    NASA Astrophysics Data System (ADS)

    Mukhin, A. A.; Platonov, V.; Plis, V. I.; Popov, A. I.; Tatsenko, O. M.; Zvezdin, A. K.

    1998-05-01

    Faraday effect in the antiferromagnet KMnF 3 has been investigated in pulse explosive fields up to 500 T at T=78 K. The laser wavelength 0.63 μm was used in the experiment. The magnetic field dependence of Faraday rotation in this antiferromagnet shows a unique feature of a lack of saturation effect in the fields up to 500 T whereas critical field of spin-flip transition is about 120 T. The theoretical analysis of microscopic nature of Faraday rotation, including the diamagnetic, magneto-dipole and paramagnetic mechanisms has been performed. The strong competition of these mechanisms is important to explain the extremely small value of the effect and its unusual magnetic field dependence.

  7. Electronic structure reconstruction across the antiferromagnetic transition in TaFe₁̣₂₃Te₃ spin ladder

    SciTech Connect

    Xu, Min; Wang, Li -Min; Peng, Rui; Ge, Qing -Qin; Chen, Fei; Ye, Zi -Rong; Zhang, Yan; Chen, Su -Di; Xia, Miao; Liu, Rong -Hua; Arita, M.; Shimada, K.; Namatame, H.; Taniguchi, M.; Matsunami, M.; Kimura, S.; Shi, Ming; Chen, Xian -Hui; Yin, Wei -Guo; Ku, Wei; Xie, Bin -Ping; Feng, Dong -Lai

    2015-02-01

    With angle-resolved photoemission spectroscopy, we studied the electronic structure of TaFe₁̣₂₃Te₃, a two-leg spin ladder compound with a novel antiferromagnetic ground state. Quasi-two-dimensional Fermi surface is observed, with sizable inter-ladder hopping. Moreover, instead of observing an energy gap at the Fermi surface in the antiferromagnetic state, we observed the shifts of various bands. Combining these observations with density-functional-theory calculations, we propose that the large scale reconstruction of the electronic structure, caused by the interactions between coexisting itinerant electrons and local moments, is most likely the driving force of the magnetic transition. Thus TaFe₁̣₂₃Te₃ serves as a simpler platform that contains similar ingredients as the parent compounds of iron-based superconductors.

  8. Spin-Orbit-Coupled Correlated Metal Phase in Kondo Lattices: An Implementation with Alkaline-Earth Atoms

    NASA Astrophysics Data System (ADS)

    Isaev, L.; Schachenmayer, J.; Rey, A. M.

    2016-09-01

    We show that an interplay between quantum effects, strong on-site ferromagnetic exchange interaction, and antiferromagnetic correlations in Kondo lattices can give rise to an exotic spin-orbit coupled metallic state in regimes where classical treatments predict a trivial insulating behavior. This phenomenon can be simulated with ultracold alkaline-earth fermionic atoms subject to a laser-induced magnetic field by observing dynamics of spin-charge excitations in quench experiments.

  9. Spin flop transition of the diluted antiferromagnet Mn xMg 1- xTiO 3

    NASA Astrophysics Data System (ADS)

    Fukaya, Atsuko; Tobo, Aya; Ito, Atsuko; Aruga Katori, Hiroko; Goto, Tsuneaki

    1994-07-01

    Magnetization measurements were made for the diluted antiferromagnet Mn xMg 1- xTiO 3 up to high-field region. The critical field of the spin-flop-like transition HSF approaches zero at x ∼ 0.6 and the magnetization curve becomes not to depend on directions of the applied field indicating that the x ≤ 0.6 samples are magnetically isotropic. It is considered that the critical concentration of x ∼ 0.6 giving HSF = 0 is connected with the crossover phenomenon from random-field behavior to spin-glass behavior observed around x = 0.6. A small but anomalous hysteresis is observed at the spin-flop-like transition of Mn xMg 1- xTiO 3 ( x <1.0). This hysteresis is attributed to the random-field effect.

  10. Exclusive processes in QCD and spin-spin correlations

    SciTech Connect

    de Teramond, G.F.

    1988-09-01

    The unexpected spin behavior observed in hard proton-proton collisions is described in terms of new degrees of freedom associated with the onset of strange and charmed thresholds. The deviation from dimensional scaling laws, the anomalous broadening of angular distributions, and the unusual energy dependence of pp quasielastic scattering in nuclear targets are also consistent with the onset of highly inelastic contributions to elastic pp amplitudes interfering with a perturbative QCD background. The model predicts significant charm production above 12 GeV/c and a relaxation of the spin correlation parameters to their scaling values at higher energies. 13 refs., 3 figs.

  11. The spin-half XXZ antiferromagnet on the square lattice revisited: A high-order coupled cluster treatment

    NASA Astrophysics Data System (ADS)

    Bishop, R. F.; Li, P. H. Y.; Zinke, R.; Darradi, R.; Richter, J.; Farnell, D. J. J.; Schulenburg, J.

    2017-04-01

    We use the coupled cluster method (CCM) to study the ground-state properties and lowest-lying triplet excited state of the spin-half XXZ antiferromagnet on the square lattice. The CCM is applied to it to high orders of approximation by using an efficient computer code that has been written by us and which has been implemented to run on massively parallelized computer platforms. We are able therefore to present precise data for the basic quantities of this model over a wide range of values for the anisotropy parameter Δ in the range - 1 ≤ Δ < ∞ of interest, including both the easy-plane (- 1 < Δ < 1) and easy-axis (Δ > 1) regimes, where Δ → ∞ represents the Ising limit. We present results for the ground-state energy, the sublattice magnetization, the zero-field transverse magnetic susceptibility, the spin stiffness, and the triplet spin gap. Our results provide a useful yardstick against which other approximate methods and/or experimental studies of relevant antiferromagnetic square-lattice compounds may now compare their own results. We also focus particular attention on the behaviour of these parameters for the easy-axis system in the vicinity of the isotropic Heisenberg point (Δ = 1) , where the model undergoes a phase transition from a gapped state (for Δ > 1) to a gapless state (for Δ ≤ 1), and compare our results there with those from spin-wave theory (SWT). Interestingly, the nature of the criticality at Δ = 1 for the present model with spins of spin quantum number s =1/2 that is revealed by our CCM results seems to differ qualitatively from that predicted by SWT, which becomes exact only for its near-classical large-s counterpart.

  12. Relaxation of antiferromagnetic order in spin-1/2 chains following a quantum quench.

    PubMed

    Barmettler, Peter; Punk, Matthias; Gritsev, Vladimir; Demler, Eugene; Altman, Ehud

    2009-04-03

    We study the unitary time evolution of antiferromagnetic order in anisotropic Heisenberg chains that are initially prepared in a pure quantum state far from equilibrium. Our analysis indicates that the antiferromagnetic order imprinted in the initial state vanishes exponentially. Depending on the anisotropy parameter, oscillatory or nonoscillatory relaxation dynamics is observed. Furthermore, the corresponding relaxation time exhibits a minimum at the critical point, in contrast to the usual notion of critical slowing down, from which a maximum is expected.

  13. Coupled antiferromagnetic spin- 12 chains in green dioptase Cu6[Si6O18]·6H2O

    DOE PAGES

    Podlesnyak, Andrey A; Larry M. Anovitz; Kolesnikov, Alexander I; ...

    2016-02-01

    Inmore » this paper, we report inelastic neutron scattering measurements of the magnetic excitations of green dioptase Cu6[Si6O18]∙6H2O. The observed spectrum contains two magnetic modes and a prominent spin gap that is consistent with the ordered ground state of Cu moments coupled antiferromagnetically in spiral chains along the c axis and ferromagnetically in ab planes on the hexagonal cell. The data are in excellent agreement with a spin- 12Hamiltonian that includes antiferromagnetic nearest-neighbor intrachain coupling Jc=10.6(1) meV, ferromagnetic interchain coupling Jab=₋1.2 (1) meV, and exchange anisotropy ΔJc=0.14(1) meV. We calculated the sublattice magnetization to be strongly reduced, ~0.39μB. This appears compatible with a reduced Néel temperature, TN=14.5Kspin fluctuations« less

  14. Spin Correlations and Excitations in the Quasi-2D Triangular Bilayer Spin Glass LuCoGaO4

    NASA Astrophysics Data System (ADS)

    Fritsch, K.; Granroth, G. E.; Savici, A. T.; Noad, H. M. L.; Dabkowska, H. A.; Gaulin, B. D.

    2012-02-01

    LuCoGaO4 is a layered magnetic-bilayer material wherein Co2+ magnetic moments and nonmagnetic Ga3+ ions are randomly distributed on planar triangular bilayers. This makes it an ideal case to study the interplay between geometric frustration, site disorder and low dimensionality and its influence on the magnetic ground of the system. This novel material has been grown for the first time in single crystal form at McMaster University. We have performed magnetization measurements, revealing a previously identified spin glass transition near Tf˜19K, and a Curie Weiss temperature of Tcw˜-96K, consistent with antiferromagnetic interactions[1]. We discuss time-of-flight neutron scattering measurements using SEQUOIA at SNS which elucidate the evolution of the static and dynamic spin correlations in LuCoGaO4 over a range of temperatures from T<< Tf to T>Tcw. We observe quasielastic scattering at (1/3,1/3,L) positions in reciprocal space and rods of scattering along the c*-direction, consistent with short range antiferromagnetic correlations within decoupled bilayers, and which comfirm the 2-dimensional character of this system. Inelastic scattering measurements show a gapped ˜ 12 meV spin excitation which softens and broadens in energy, filling in the gap on a temperature scale of ˜ Tcw/2. [1] Cava et al., J. Solid State Chem. 140, 337 (1998).

  15. Refining the spin Hamiltonian in the spin-1/2 kagome lattice antiferromagnet ZnCu3(OH)6Cl2 using single crystals.

    PubMed

    Han, Tianheng; Chu, Shaoyan; Lee, Young S

    2012-04-13

    We report thermodynamic measurements of the S=1/2 kagome lattice antiferromagnet ZnCu3(OH)6Cl2, a promising candidate system with a spin-liquid ground state. Using single crystal samples, the magnetic susceptibility both perpendicular and parallel to the kagome plane has been measured. A small, temperature-dependent anisotropy has been observed, where χ(z)/χ(p)>1 at high temperatures and χ(z)/χ(p)<1 at low temperatures. Fits of the high-temperature data to a Curie-Weiss model also reveal an anisotropy. By comparing with theoretical calculations, the presence of a small easy-axis exchange anisotropy can be deduced as the primary perturbation to the dominant Heisenberg nearest neighbor interaction. These results have great bearing on the interpretation of theoretical calculations based on the kagome Heisenberg antiferromagnet model to the experiments on ZnCu3(OH)6Cl2.

  16. Thermodynamic properties of frustrated arbitrary spin-S J1-J2 quantum Heisenberg antiferromagnet on the body-centered-cubic lattice in random phase approximation

    NASA Astrophysics Data System (ADS)

    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.

  17. Critical spin dynamics of the 2D quantum Heisenberg antiferromagnets Sr2CuO2Cl2 and Sr2Cu3O4Cl2.

    PubMed

    Kim, Y J; Birgeneau, R J; Chou, F C; Erwin, R W; Kastner, M A

    2001-04-02

    We report a neutron scattering study of the long-wavelength dynamic spin correlations in the model two-dimensional S = 1/2 square lattice Heisenberg antiferromagnets Sr2CuO2Cl2 and Sr2Cu3O4Cl2. The characteristic energy scale, omega(0)(T/J), is determined by measuring the quasielastic peak width in the paramagnetic phase over a wide range of temperature ( 0.2 less similarT/J less similar0.7). The obtained values for omega(0)(T/J) agree quantitatively between the two compounds and also with values deduced from quantum Monte Carlo simulations. The combined data show scaling behavior, omega approximately xi(-z), over the entire temperature range with z = 1.0(1), in agreement with dynamic scaling theory.

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

  19. Low temperature magnetic properties and spin dynamics in single crystals of Cr{sub 8}Zn antiferromagnetic molecular rings

    SciTech Connect

    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; 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.

  20. Low temperature magnetic properties and spin dynamics in single crystals of Cr8Zn antiferromagnetic molecular rings

    NASA Astrophysics Data System (ADS)

    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.

  1. Magnetic coupling between Sm3+ and the canted spin in an antiferromagnetic SmFeO3 single crystal

    NASA Astrophysics Data System (ADS)

    Marshall, L. G.; Cheng, J.-G.; Zhou, J.-S.; Goodenough, J. B.; Yan, J.-Q.; Mandrus, D. G.

    2012-08-01

    The perovskite SmFeO3 exhibits type-G antiferromagnetic ordering at TN ≈ 670 K and an easy axis rotation transition at TSR ≈ 480 K. Owing to the peculiar site anisotropy of rare-earth Sm3+, the moment on Sm3+ is oriented antiparallel to the canted spin from the Fe+ sublattice along the a axis at T < TSR. The development of the magnetic moment on Sm3+ as temperature decreases makes it possible to balance the two magnetic moments at Tcomp. The application of a moderate external magnetic field along the a axis can trigger an abrupt reversal of the moment on Sm3+ and the canted spin relative to the external field at a temperature around Tcomp. We report here a study of the field-induced magnetic-moment reversal in a single crystal SmFeO3 by measuring the magnetization and specific heat with the external field along different crystallographic axes.

  2. The magnetic properties of three-dimensional spin-1 easy-axis single-ion anisotropic antiferromagnets

    NASA Astrophysics Data System (ADS)

    Hu, Ai-Yuan; Wang, Qin

    2010-05-01

    The ordered and disordered phases of spin-1 Heisenberg and Ising antiferromagnets with easy-axis single-ion anisotropy on a three-dimensional lattice are studied. By using of the double-time Green's function method within the Tyablikov decoupling for the exchange anisotropy and Callen's approximation for the single-ion anisotropy, the Néel temperature, magnetization and susceptibility are investigated. Their relations with the temperature and anisotropic parameter are analyzed over the entire range of temperature. It is found that our results agree well with spin wave theory results at low temperature, agree with the high temperature series results at high temperature, and compare reasonably well with the linked-cluster series approach and ratio method results at intermediate temperature.

  3. Antiferromagnetic spin cantings as a driving force of ferroelectricity in multiferroic Cu2OSeO3

    NASA Astrophysics Data System (ADS)

    Chizhikov, Viacheslav A.; Dmitrienko, Vladimir E.

    2017-04-01

    Ferroelectric properties of cubic chiral magnet Cu2OSeO3 can emerge due to the spin noncollinearity induced by antiferromagnetic cantings. The cantings are the result of the Dzyaloshinskii–Moriya interaction and in many ways similar to the ferromagnetic cantings in weak ferromagnets. An expression for the local electric polarization is derived, including terms with gradients of magnetization \\mathbf{M}≤ft(\\mathbf{r}\\right) . When averaged over the crystal the electric polarization has a non-vanishing part associated with the anisotropy of the crystal point group 23. In the framework of the microscopic theory, it is shown that both scalar and vector products of spins, ≤ft({{\\mathbf{s}}1}\\cdot {{\\mathbf{s}}2}\\right) and ≤ft[{{\\mathbf{s}}1}× {{\\mathbf{s}}2}\\right] , can give contributions of the same order of magnitude into the electric polarization.

  4. Spin-Hall-Effect-Assisted Electroresistance in Antiferromagnets via 105 A/cm2 dc Current

    PubMed Central

    Han, Jiahao; Wang, Yuyan; Pan, Feng; Song, Cheng

    2016-01-01

    Antiferromagnet (AFM) spintronics with reduced electrical current is greatly expected to process information with high integration and low power consumption. In Pt/FeMn and Ta/FeMn hybrids, we observe significant resistance variation (up to 7% of the total resistance) manipulated by 105 A/cm2 dc current. We have excluded the contribution of isotropic structural effects, and confirmed the critical role of the spin Hall injection from Pt (or Ta) to FeMn. This electrical current-manipulated resistance (i.e. electroresistance) is proposed to be attributed to the spin-Hall-effect-induced spin-orbit torque in FeMn. Similar results have also been detected in plain IrMn films, where the charge current generates spin current via the spin Hall effect with the existence of Ir atoms. All the measurements are free from external magnetic fields and ferromagnets. Our findings present an interesting step towards high-efficiency spintronic devices. PMID:27546199

  5. Magnetism and thermodynamics of the anisotropic frustrated spin-1 Heisenberg antiferromagnet on a body-centered cubic lattice

    NASA Astrophysics Data System (ADS)

    Mi, Bin-Zhou

    2017-02-01

    The magnetic and thermodynamic properties of anisotropic frustrated spin-1 Heisenberg antiferromagnet on a body-centered cubic lattice for Néel phase (the region of weak frustration) are systematically investigated by use of the double-time Green's function method within the random phase approximation and the Anderson and Callen's decoupling. The zero-temperature sublattice magnetization and Néel temperature increase with spin anisotropy strength and single-ion anisotropy strength, and decrease with frustration strength. This indicates that quantum fluctuation is suppressed by spin anisotropy and single-ion anisotropy, by contrast, is strengthened by frustration. It is possible to tune the quantum fluctuations by the competition of anisotropy strength and frustration strength to change the ground state properties of magnetic materials. Although we find that both the spin anisotropy and the single-ion anisotropy suppress the quantum fluctuations, but their respective effects on the thermodynamic quantities, especially the internal energy and free energy, are different at zero temperature and finite temperature. Furthermore, when these two kinds of anisotropic coexist, the effect of the spin anisotropy on the sublattice magnetization and internal energy is larger than that of the single-ion anisotropy.

  6. Spin-Hall-Effect-Assisted Electroresistance in Antiferromagnets via 10(5) A/cm(2) dc Current.

    PubMed

    Han, Jiahao; Wang, Yuyan; Pan, Feng; Song, Cheng

    2016-08-22

    Antiferromagnet (AFM) spintronics with reduced electrical current is greatly expected to process information with high integration and low power consumption. In Pt/FeMn and Ta/FeMn hybrids, we observe significant resistance variation (up to 7% of the total resistance) manipulated by 10(5) A/cm(2) dc current. We have excluded the contribution of isotropic structural effects, and confirmed the critical role of the spin Hall injection from Pt (or Ta) to FeMn. This electrical current-manipulated resistance (i.e. electroresistance) is proposed to be attributed to the spin-Hall-effect-induced spin-orbit torque in FeMn. Similar results have also been detected in plain IrMn films, where the charge current generates spin current via the spin Hall effect with the existence of Ir atoms. All the measurements are free from external magnetic fields and ferromagnets. Our findings present an interesting step towards high-efficiency spintronic devices.

  7. Disappearance of antiferromagnetic spin excitations in overdoped La2-xSrxCuO4.

    PubMed

    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 antiferromagnetic bubbles.

  8. Gapless quantum spin liquid ground state in the two-dimensional spin-1/2 triangular antiferromagnet YbMgGaO4

    PubMed Central

    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

    2015-01-01

    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. PMID:26552727

  9. Quantum Monte Carlo simulation of antiferromagnetic spin ladder (C5H12N)2CuBr4

    NASA Astrophysics Data System (ADS)

    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.

  10. Pairing correlations in high-spin isomers

    SciTech Connect

    Odahara, A.; Gono, Y.; Fukuchi, T.; Wakabayashi, Y.; Sagawa, H.; Satula, W.; Nazarewicz, W.

    2005-12-15

    High-spin isomers with J{sup {pi}}=49/2{sup +} and 27{sup +} have been systematically observed in a number of N=83 isotones with 60{<=}Z{<=}67 at excitation energies {approx}9 MeV. Based on experimental excitation energies, an odd-even binding energy staggering has been extracted for the first time for these multi-quasiparticle states. Surprisingly, the magnitude of the odd-even effect in high-spin isomers turned out to be very close to that in ground states, thus challenging conventional wisdom that pairing correlations are reduced in highly excited states. Theoretical analysis based on mean-field theory explains the observed proton number dependence of the odd-even effect as a manifestation of strong pairing correlations in the highly excited states. Mean-field effects and the proton-neutron residual interaction on the odd-even staggering are also examined.

  11. Evidence for spin correlation in tt production

    DOE PAGES

    Abazov, Victor Mukhamedovich

    2012-01-19

    We present a measurement of the ratio of events with correlated t and t spins to the total number of tt events. This ratio f is evaluated using a matrix-element-based approach in 729 tt candidate events with a single lepton ℓ (electron or muon) and at least four jets. The analyzed pp collisions data correspond to an integrated luminosity of 5.3 fb-1 and were collected with the D0 detector at the Fermilab Tevatron collider operating at a center-of-mass energy \\(\\sqrt{s}=1.96\\) TeV. Combining this result with a recent measurement of f in dileptonic final states, we find f in agreement withmore » the standard model. In addition, the combination provides evidence for the presence of spin correlation in tt events with a significance of more than 3 standard deviations.« less

  12. Anomalous Hall effect and spin-orbit torques in MnGa/IrMn films: Modification from strong spin Hall effect of the antiferromagnet

    NASA Astrophysics Data System (ADS)

    Meng, K. K.; Miao, J.; Xu, X. G.; Wu, Y.; Zhao, X. P.; Zhao, J. H.; Jiang, Y.

    2016-12-01

    We report systematic measurements of anomalous Hall effect (AHE) and spin-orbit torques (SOTs) in MnGa/IrMn films, in which a single L 10-MnGa epitaxial layer reveals obvious orbital two-channel Kondo (2CK) effect. As increasing the thickness of the antiferromagnet IrMn, the strong spin Hall effect (SHE) has gradually suppressed the orbital 2CK effect and modified the AHE of MnGa. A scaling involving multiple competing scattering mechanisms has been used to distinguish different contributions to the modified AHE. Finally, the sizeable SOT in the MnGa/IrMn films induced by the strong SHE of IrMn have been investigated. The IrMn layer also supplies an in-plane exchange bias field and enables nearly field-free magnetization reversal.

  13. Spin Liquid State in the 3D Frustrated Antiferromagnet PbCuTe_{2}O_{6}: NMR and Muon Spin Relaxation Studies.

    PubMed

    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.

  14. Spin liquid state in the 3D frustrated antiferromagnet PbCuTe2O6: NMR and muon spin relaxation studies

    DOE PAGES

    Khuntia, P.; Bert, F.; Mendels, P.; ...

    2016-03-11

    In this study, 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 homogeneousmore » 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.« less

  15. Thermal evolution of antiferromagnetic correlations and tetrahedral bond angles in superconducting FeTe1-xSex

    SciTech Connect

    Xu, Zhijun; Xu, Guangyong; Schneeloch, J. A.; Wen, Jinsheng; Bozin, E. S.; Granroth, G. E.; Winn, B. L.; Feygenson, M.; Birgeneau, R. J.; Gu, Genda; Zaliznyak, I. A.; Tranquada, J. M.

    2016-03-14

    It has recently been demonstrated that dynamical magnetic correlations measured by neutron scattering in iron chalcogenides can be described with models of short-range correlations characterized by particular choices of four-spin plaquettes, where the appropriate choice changes as the parent material is doped towards superconductivity. Here we apply such models to describe measured maps of magnetic scattering as a function of two-dimensional wave vectors obtained for optimally superconducting crystals of FeTe1–xSex. We show that the characteristic antiferromagnetic wave vector evolves from that of the bicollinear structure found in underdoped chalcogenides (at high temperature) to that associated with the stripe structure of antiferromagnetic iron arsenides (at low temperature); these can both be described with the same local plaquette, but with different interplaquette correlations. While the magnitude of the low-energy magnetic spectral weight is substantial at all temperatures, it actually weakens somewhat at low temperature, where the charge carriers become more itinerant. The observed change in spin correlations is correlated with the dramatic drop in the electronic scattering rate and the growth of the bulk nematic response upon cooling. Lastly, we also present powder neutron diffraction results for lattice parameters in FeTe1–xSex indicating that the tetrahedral bond angle tends to increase towards the ideal value upon cooling, in agreement with the increased screening of the crystal field by more itinerant electrons and the correspondingly smaller splitting of the Fe 3d orbitals.

  16. Quantum Spin Fluctuations and magnons in antiferromagnetically coupled bilayers with tuneable intra-bilayer exchange - the case of Cr2W(Te)O6

    NASA Astrophysics Data System (ADS)

    Majumdar, Kingshuk; Mahanti, S. D.

    Recent neutron diffraction studies have shown that in Cr2(W,Te)O6 systems, which consist of bilayers with strong antiferromagnetic inter-bilayer coupling between Cr moments, the intra-bilayer coupling between the Cr moments can be tuned from ferro (for W) to antiferro (for Te). Ab initio density functional calculations provide a microscopic understanding of the magnetic structure but cannot explain the magnitude of the ordered Cr3+ moments. In order to understand the reduction of the ordered moment (ROM) caused by quantum spin fluctuations we have studied the magnon dispersion and ROM using a two parameter quantum Heisenberg spin Hamiltonian with tunable intra-(j) and antiferromagnetic inter- (J) bilayer couplings. The magnon dispersion and sublattice magnetization have been calculated using non-linear spin wave theory up to second-order corrections in spin S. We acknowledge the use of HPC cluster at GVSU, supported by the National Science Foundation Grant No. CNS-1228291.

  17. Relaxation mechanism in NiFe thin films driven by spin angular momentum absorption throughout the antiferromagnetic phase transition in native surface oxides

    NASA Astrophysics Data System (ADS)

    Frangou, L.; Forestier, G.; Auffret, S.; Gambarelli, S.; Baltz, V.

    2017-02-01

    We report an alternative mechanism for the physical origin of the temperature-dependent ferromagnetic relaxation observed in bare permalloy (NiFe) thin films. Through spin-pumping experiments, we demonstrate that the peak in the temperature dependence of NiFe damping can be understood in terms of enhanced absorption of spin angular momentum at the magnetic phase transition in native antiferromagnetic surface-oxidized layers. These results suggest some avenues for the investigation of an incompletely understood phenomenon in physics.

  18. (A neutron scattering experiment to study the high-energy spin dynamics of the itinerant antiferromagnet Mn sub 90 Cu sub 10 )

    SciTech Connect

    Fernandez-Baca, J.A.

    1990-10-26

    The traveler performed a neutron scattering experiment to study the high-energy spin dynamics of the itinerant antiferromagnet. This experiment was conducted at a unique instrument located at the hot-neutron source at the ILL. The traveler also held various scientific discussions with ILL research staff members and visiting scientists.

  19. Charge stripes and spin correlations in copper-oxide superconductors

    NASA Astrophysics Data System (ADS)

    Tranquada, J. M.

    1997-08-01

    Recent neutron diffraction studies have yielded evidence that, in a particular cuprate family, holes doped into the CuO 2 planes segregate into stripes that separate antiferromagnetic domains. Here it is shown that such a picture provides a quantitatively consistent interpretation of the spin fluctuations measured by neutron diffraction in La 1.85Sr 0.15CuO 4 and YBa 2Cu 3O 6+ x.

  20. First-order melting of a weak spin-orbit mott insulator into a correlated metal

    SciTech Connect

    Hogan, Tom; Yamani, Z.; Walkup, D.; Chen, Xiang; Dally, Rebecca; Ward, Thomas Zac; Dean, M. P. M.; Hill, John P.; Islam, Z.; Madhavan, Vidya; Wilson, Stephen D.

    2015-06-25

    Herein, the electronic phase diagram of the weak spin-orbit Mott insulator (Sr1-xLax)3Ir2O7 is determined via an exhaustive experimental study. Upon doping electrons via La substitution, an immediate collapse in resistivity occurs along with a narrow regime of nanoscale phase separation comprised of antiferromagnetic, insulating regions and paramagnetic, metallic puddles persisting until x≈0.04. Continued electron doping results in an abrupt, first-order phase boundary where the Néel state is suppressed and a homogenous, correlated, metallic state appears with an enhanced spin susceptibility and local moments. In conclusion, as the metallic state is stabilized, a weak structural distortion develops and suggests a competing instability with the parent spin-orbit Mott state.

  1. First-order melting of a weak spin-orbit mott insulator into a correlated metal

    DOE PAGES

    Hogan, Tom; Yamani, Z.; Walkup, D.; ...

    2015-06-25

    Herein, the electronic phase diagram of the weak spin-orbit Mott insulator (Sr1-xLax)3Ir2O7 is determined via an exhaustive experimental study. Upon doping electrons via La substitution, an immediate collapse in resistivity occurs along with a narrow regime of nanoscale phase separation comprised of antiferromagnetic, insulating regions and paramagnetic, metallic puddles persisting until x≈0.04. Continued electron doping results in an abrupt, first-order phase boundary where the Néel state is suppressed and a homogenous, correlated, metallic state appears with an enhanced spin susceptibility and local moments. In conclusion, as the metallic state is stabilized, a weak structural distortion develops and suggests a competingmore » instability with the parent spin-orbit Mott state.« less

  2. Topological Phases of Spin-1/2 Ferromagnetic-Antiferromagnetic Alternating Heisenberg Chains with Alternating Next-Nearest-Neighbour Interaction

    NASA Astrophysics Data System (ADS)

    Hida, Kazuo

    2016-12-01

    A series of symmetry-protected topological (SPT) and trivial spin-gap phases in the spin-1/2 ferromagnetic-antiferromagnetic alternating Heisenberg chain with alternating next-nearest-neighbour interaction are investigated using two kinds of entanglement spectra defined by different divisions of the whole chain. In case one of the next-nearest-neighbor interactions vanishes, the model reduces to the Δ-chain in which a series of spin-gap phases are found, as shown in J. Phys. Soc. Jpn. 77, 044707 (2008). From the degeneracy of the entanglement spectra, these phases are identified as the SPT and trivial phases. It is found that the ground-state phase boundaries are insensitive to the strength of the alternation in the next-nearest-neighbor interaction. These results are consistent with the analysis based on the nonlinear σ model and exact solution on the ferromagnetic-nonmagnetic phase boundary.

  3. Direct Observation of Localized Spin Antiferromagnetic Transition in PdCrO2 by Angle-Resolved Photoemission Spectroscopy

    NASA Astrophysics Data System (ADS)

    Noh, Han-Jin; Jeong, Jinwon; Chang, Bin; Jeong, Dahee; Moon, Hyun Sook; Cho, En-Jin; Ok, Jong Mok; Kim, Jun Sung; Kim, Kyoo; Min, B. I.; Lee, Han-Koo; Kim, Jae-Young; Park, Byeong-Gyu; Kim, Hyeong-Do; Lee, Seongsu

    2014-03-01

    We report the first case of the successful measurements of a localized spin antiferromagnetic transition in delafossite-type PdCrO2 by angle-resolved photoemission spectroscopy (ARPES). This demonstrates how to circumvent the shortcomings of ARPES for investigation of magnetism involved with localized spins in limited size of two-dimensional crystals or multi-layer thin films that neutron scattering can hardly study due to lack of bulk compared to surface. Also, our observations give direct evidence for the spin ordering pattern of Cr3+ ions in PdCrO2 suggested by neutron diffraction and quantum oscillation measurements, and provide a strong constraint that has to be satisfied by a microscopic mechanism for the unconventional anomalous Hall effect recently reported in this system. This work was supported by the National Research Foundation (NRF) of Korea Grant funded by the Korean Government (MEST) (Nos. 2010-0010771 and 2012M2B2A4029607). K.K. and B.I.M. acknowledge the support of NRF (Nos. 2009-0079947 and 2011-0025237) and KISTI.

  4. Device-size dependence of field-free spin-orbit torque induced magnetization switching in antiferromagnet/ferromagnet structures

    NASA Astrophysics Data System (ADS)

    Kurenkov, A.; Zhang, C.; DuttaGupta, S.; Fukami, S.; Ohno, H.

    2017-02-01

    We study spin-orbit torque induced magnetization switching in devices consisting of an antiferromagnetic PtMn and ferromagnetic Co/Ni multilayer with sizes ranging from 5 μm to 50 nm. As the size decreases, switching behavior changes from analogue-like to stepwise with several intermediate levels. The number of intermediate levels decreases with the decreasing size and finally evolves into a binary mode below a certain threshold. The results are found to be explained by a unique reversal process of this system, where ferromagnetic domains comprising a number of polycrystalline grains reverse individually and among the domains both out-of-plane and in-plane components of exchange bias vary.

  5. Phase transition in the spin- 3 / 2 Blume-Emery-Griffiths model with antiferromagnetic second neighbor interactions

    NASA Astrophysics Data System (ADS)

    Yezli, M.; Bekhechi, S.; Hontinfinde, F.; EZ-Zahraouy, H.

    2016-04-01

    Two nonperturbative methods such as Monte-Carlo simulation (MC) and Transfer-Matrix Finite-Size-Scaling calculations (TMFSS) have been used to study the phase transition of the spin- 3 / 2 ​Blume-Emery-Griffiths model (BEG) with quadrupolar and antiferromagnetic next-nearest-neighbor exchange interactions. Ground state and finite temperature phase diagrams are obtained by means of these two methods. New degenerate phases are found and only second order phase transitions occur for all values of the parameter interactions. No sign of the intermediate phase is found from both methods. Critical exponents are also obtained from TMFSS calculations. Ising criticality and nonuniversal behaviors are observed depending on the strength of the second neighbor interaction.

  6. Magnetic Raman Scattering in Two-Dimensional Spin-1/2 Heisenberg Antiferromagnets: Explanation of the Spectral Shape Anomaly

    NASA Astrophysics Data System (ADS)

    Nori, F.; Merlin, R.; Haas, S.; Sandvick, A.; Dagotto, E.

    1996-03-01

    We calculate(F. Nori, R.Merlin, S. Haas, A.W. Sandvik, and E. Dagotto, Physical Review Letters) 75, 553 (1995). the Raman spectrum of the two-dimensional (2D) spin-1/2 Heisenberg antiferromagnet by exact diagonalization and quantum Monte Carlo techniques on clusters of up to 144 sites. On a 16-site cluster, we consider the phonon-magnon interaction which leads to random fluctuations of the exchange integral. Results are in good agreement with experiments on various high-Tc precursors, such as La_2CuO4 and YBa_2Cu_3O_6.2. In particular, our calculations reproduce the broad lineshape of the two-magnon peak, the asymmetry about its maximum, the existence of spectral weight at high energies, and the observation of nominally forbidden A_1g scattering.

  7. Geometric frustration effects in the spin-1 antiferromagnetic Ising model on the kagome-like recursive lattice: exact results

    NASA Astrophysics Data System (ADS)

    Jurčišinová, E.; Jurčišin, M.

    2016-09-01

    The antiferromagnetic spin-1 Ising model is studied on the Husimi lattice constructed from elementary triangles with coordination number z  =  4. It is found that the model has a unique solution for arbitrary values of the magnetic field as well as for all temperatures. A detailed analysis of the magnetization is performed and it is shown that in addition to the standard plateau-like ground states, the model also contains well-defined single-point ground states related to definite values of the magnetic field. Exact values of the residual entropies for all ground states are found. The properties of the susceptibility and the specific heat of the model are also discussed. The existence of the Schottky-type behavior of the specific heat and the strong magnetocaloric effect for low enough temperatures and for the external magnetic field close to the values at which the single-point ground states exist are identified.

  8. Probing ultrafast spin dynamics through a magnon resonance in the antiferromagnetic multiferroic HoMnO3

    SciTech Connect

    Bowlan, P.; Trugman, S. A.; Bowlan, J.; Zhu, J. -X.; Hur, N. J.; Taylor, A. J.; Yarotski, D. A.; Prasankumar, R. P.

    2016-09-26

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

  9. Site-resolved measurement of the spin-correlation function in the Fermi-Hubbard model

    NASA Astrophysics Data System (ADS)

    Parsons, Maxwell F.; Mazurenko, Anton; Chiu, Christie S.; Ji, Geoffrey; Greif, Daniel; Greiner, Markus

    2016-09-01

    Exotic phases of matter can emerge from strong correlations in quantum many-body systems. Quantum gas microscopy affords the opportunity to study these correlations with unprecedented detail. Here, we report site-resolved observations of antiferromagnetic correlations in a two-dimensional, Hubbard-regime optical lattice and demonstrate the ability to measure the spin-correlation function over any distance. We measure the in situ distributions of the particle density and magnetic correlations, extract thermodynamic quantities from comparisons to theory, and observe statistically significant correlations over three lattice sites. The temperatures that we reach approach the limits of available numerical simulations. The direct access to many-body physics at the single-particle level demonstrated by our results will further our understanding of how the interplay of motion and magnetism gives rise to new states of matter.

  10. Origin of anomalously high exchange field in antiferromagnetically coupled magnetic structures: Spin reorientation versus interface anisotropy

    NASA Astrophysics Data System (ADS)

    Ranjbar, M.; Piramanayagam, S. N.; Wong, S. K.; Sbiaa, R.; Song, W.; Tan, H. K.; Gonzaga, L.; Chong, T. C.

    2011-11-01

    Magnetization reorientation from in-plane to perpendicular direction, observed in Co thin film coupled antiferromagnetically to high perpendicular magnetic anisotropy (Co/Pd) multilayers, is studied systematically for Co thickness ranging from 0 to 2.4 nm. The sample with 0.75 nm thick Co showed an exchange coupling field (Hex) exceeding 15 kOe at room temperature and 17.2 kOe at 5 K. With an increase of Co thickness, Hex decreased as expected and beyond certain thickness, magnetization reorientation was not observed. Indeed, three regions were observed in the thickness dependence of magnetization of the thin layer; one in which the thin layer (in the thickness range up to 0.8 nm) had a perpendicular magnetic anisotropy due to interface effects and antiferromagnetic coupling, another in which the thin layer (0.9-1.2 nm) magnetization had no interface or crystallographic anisotropy but was reoriented in the perpendicular direction due to antiferromagnetic coupling, and the third (above 1.2 nm) in which the magnetization was in-plane. In addition, Hall effect measurements were carried out to observe the anomalous and planar Hall voltages and to quantify the perpendicular and in-plane components of magnetization. The sample with thicker Co layer (2.4 nm) showed an in-plane component of magnetization, whereas the sample with 0.75 nm Co showed no in-plane component. The high value of Hex observed in 0.75 nm Co samples can have important implications in spintronics and bit patterned media.

  11. Phase diagram and spin correlations of the Kitaev-Heisenberg model: Importance of quantum effects

    NASA Astrophysics Data System (ADS)

    Gotfryd, Dorota; Rusnačko, Juraj; Wohlfeld, Krzysztof; Jackeli, George; Chaloupka, Jiří; Oleś, Andrzej M.

    2017-01-01

    We explore the phase diagram of the Kitaev-Heisenberg model with nearest neighbor interactions on the honeycomb lattice using the exact diagonalization of finite systems combined with the cluster mean field approximation, and supplemented by the insights from analytic approaches: the linear spin-wave and second-order perturbation theories. This study confirms that by varying the balance between the Heisenberg and Kitaev term, frustrated exchange interactions stabilize in this model either one of four phases with magnetic long range order: Néel phase, ferromagnetic phase, and two other phases with coexisting antiferromagnetic and ferromagnetic bonds, zigzag and stripy phase, or one of two distinct spin-liquid phases. Out of these latter disordered phases, the one with ferromagnetic Kitaev interactions has a substantially broader range of stability as the neighboring competing ordered phases, ferromagnetic and stripy, have very weak quantum fluctuations. Focusing on the quantum spin-liquid phases, we study spatial spin correlations and dynamic spin structure factor of the model by the exact diagonalization technique, and discuss the evolution of gapped low-energy spin response across the quantum phase transitions between the disordered spin liquid and phases with long range magnetic order.

  12. Pair correlation function for spin glasses

    NASA Astrophysics Data System (ADS)

    Fernández, Julio F.; Alonso, Juan J.

    2012-10-01

    We extract a pair correlation function (PCF) from probability distributions of the spin-overlap parameter q. The distributions come from Monte Carlo simulations. A measure, w, of the thermal fluctuations of magnetic patterns follows from the PCFs. We also obtain rms deviations (over different system samples) δp away from average probabilities for q. For the linear system sizes L that we have studied, w and δp are independent of L in the Edwards-Anderson model but scale as 1/L and L, respectively, in the Sherrington-Kirkpatrick model.

  13. Spin waves and phonons in a paraelectric antiferromagnet EuTiO3

    NASA Astrophysics Data System (ADS)

    Cao, Huibo; Hong, Jiawang; Delaire, Olivier; Hahn, Steven; Ehlers, Georg; Chi, Songxue; Garlea, Vasile; Fernandez-Baca, Jaime; Chakoumakos, Bryan; Yan, Jiaqiang; Sales, Brian

    2015-03-01

    Perovskite titanates ATiO3 (A=Ba,Pb,Sr,Ca,Cd,or Eu) are widely studied for their interesting instabilities and broad applications. A ferroelectric (FE) transition occurs in Ba, Pb, and Cd titanates, but not in SrTiO3 (STO) or EuTiO3 (ETO). In the case of STO, fluctuations yield a quantum paraelectric state, but whether ETO is quantum paraelectric remains an open question. Despite a number of similarities with well-studied STO, ETO is also unique owing to the magnetic Eu ions. By applying a tuning parameter, such as bi-axial tension, ETO can be turned into a FE ferromagnet, the ideal multiferroic. [J. H. Lee, et al., Nature 466, 954 (2010)] Studies of spin-spin and spin-lattice couplings in ETO are of great interest not only from a fundamental standpoint, but also for technological applications. We successfully grew a large, high-quality isotopically-enriched ETO crystal for neutron scattering. The crystal and magnetic structures were characterized with single crystal diffraction at HB-3A at HFIR at ORNL. The spin waves and phonons were measured in the temperature range of 1.5-400 K with CNCS at SNS and HB-3 at HFIR at ORNL. In this presentation, we will discuss structural instabilities, spin-spin interactions, and spin-phonon couplings in ETO. This work was supported by Office of Basic Energy Sciences, U.S. Department of Energy.

  14. Spin-noise correlations and spin-noise exchange driven by low-field spin-exchange collisions

    NASA Astrophysics Data System (ADS)

    Dellis, A. T.; Loulakis, M.; Kominis, I. K.

    2014-09-01

    The physics of spin-exchange collisions have fueled several discoveries in fundamental physics and numerous applications in medical imaging and nuclear magnetic resonance. We report on the experimental observation and theoretical justification of spin-noise exchange, the transfer of spin noise from one atomic species to another. The signature of spin-noise exchange is an increase of the total spin-noise power at low magnetic fields, on the order of 1 mG, where the two-species spin-noise resonances overlap. The underlying physical mechanism is the two-species spin-noise correlation induced by spin-exchange collisions.

  15. Ferrimagnetic and Long Period Antiferromagnetic Phases in High Spin Heisenberg Chains with D-Modulation

    NASA Astrophysics Data System (ADS)

    Hida, Kazuo

    2007-02-01

    The ground state properties of the high spin Heisenberg chains with alternating single site anisotropy are investigated by means of the numerical exact daigonaization and DMRG method. It is found that the ferrimagnetic state appears between the Haldane phase and period doubled Néel phase for the integer spin chains. On the other hand, the transition from the Tomonaga-Luttinger liquid state into the ferrimagnetic state takes place for the half-odd-integer spin chains. In the ferrimagnetic phase, the spontaneous magnetization varies continuously with the modulation amplitude of the single site anisotropy. Eventually, the magnetization is locked to fractional values of the saturated magnetization. These fractional values satisfy the Oshikawa-Yamanaka-Affleck condition. The local spin profile is calculated to reveal the physical nature of each state. In contrast to the case of frustration induced ferrimagnetism, no incommensurate magnetic superstructure is found.

  16. Stripe Antiferromagnetic Spin Fluctuations in SrCo2As2

    SciTech Connect

    Jayasekara, W.; Lee, Y; Pandey, Abishek; Tucker, G. S.; Sapkota, A; Lamsal, Jagat; Calder, Stuart A; Abernathy, Douglas L; Niedziela, Jennifer L; Harmon, B N; Kreyssig, A.; Vaknin, D; Johnston, D C; Goldman, A. I.; McQueeney, R. J.

    2013-01-01

    Inelastic neutron scattering measurements of paramagnetic SrCo2As2 at T = 5 K reveal antifer- romagnetic (AFM) spin fluctuations that are peaked at a wavevector of QAFM = (1/2, 1/2, 1) and possess a large energy scale. These stripe spin fluctuations are similar to those found in AFe2As2 compounds, where spin-density wave AFM is driven by Fermi surface nesting between electron and hole pockets separated by QAFM. SrCo2As2 has a more complex Fermi surface and band structure calculations indicate a potential instability towards either a ferromagnetic or stripe AFM ground state. The results suggest that stripe AFM magnetism is a general feature of both iron and cobalt- based arsenides and the search for spin fluctuation-induced unconventional superconductivity should be expanded to include cobalt-based compounds.

  17. Spin entanglement loss by local correlation transfer to the momentum

    SciTech Connect

    Lamata, Lucas; Leon, Juan; Salgado, David

    2006-05-15

    We show the decrease of spin-spin entanglement between two s=(1/2) fermions or two photons due to local transfer of correlations from the spin to the momentum degree of freedom of one of the two particles. We explicitly show how this phenomenon operates in the case where one of the two fermions (photons) passes through a local homogeneous magnetic field (optically active medium), losing its spin correlations with the other particle.

  18. Ground States of Spin-1/2 Heisenberg Antiferromagnets with Frustration on a Diamond-Like-Decorated Square Lattice

    NASA Astrophysics Data System (ADS)

    Hirose, Yuhei; Oguchi, Akihide; Fukumoto, Yoshiyuki

    2017-01-01

    We study the ground-state phase diagram of a Heisenberg model with spin S = 1/2 on a diamond-like-decorated square lattice. A diamond unit has two types of antiferromagnetic exchange interactions, and the ratio λ of the length of the diagonal bond to that of the other four edges determines the strength of frustration. It has been pointed out [J. Phys. Soc. Jpn 85, 033705 (2016)] that the so-called tetramer-dimer states, which are expected to be stabilized in an intermediate region of λc < λ < 2, are identical to the square-lattice dimer-covering states, which ignited renewed interest in high-dimensional diamond-like-decorated lattices. In order to determine the phase boundary λc, we employ the modified spin wave method to estimate the energy of the ferrimagnetic state and obtain λc = 0.974. Furthermore, our numerical diagonalization study suggests that other cluster states do not appear in the ground-state phase diagram.

  19. Stripe Correlations of Spins and Holes in Cuprate Superconductors

    NASA Astrophysics Data System (ADS)

    Tranquada, John M.

    1996-03-01

    Several different theoretical approaches have suggested that holes doped into a CuO2 plane might segregate. In particular, a stripe phase has been proposed in which hole-rich stripes alternate periodically with antiferromagnetic domains. Such a phase was first properly identified in the insulating model compounds La_2NiO_4+δ and La_2-xSr_xNiO4 by neutron diffraction studies.(J. M. Tranquada, D. J. Buttrey, V. Sachan, and J. E. Lorenzo, Phys. Rev. Lett. 73), 1003 (1994); V. Sachan, D. J. Buttrey, J. M. Tranquada, J. E. Lorenzo, and G. Shirane, Phys. Rev. B 51, 12742 (1995). That work led to an experiment(J. M. Tranquada, B. J. Sternlieb, J. D. Axe, Y. Nakamura, and S. Uchida, Nature 375), 561 (1995). which revealed evidence for static spin and charge stripes in La_1.6-xNd_0.4Sr_xCuO4 with x=0.12, a cuprate in which superconductivity is anomalously suppressed.(J. D. Axe and M. K. Crawford, J. Low Temp. Phys. 95), 271 (1994); Y. Nakamura and S. Uchida, Phys. Rev. B 46, 5841 (1992). In contrast to the nickelates, where the stripes run diagonally within a plane with one hole per site along a domain wall, the stripes in the cuprate run horizontally (or vertically) with a charge density of half a hole per site. In both cases the order appears to be driven by the charge rather than the magnetism. The magnetic scattering observed in the cuprate is closely related to the purely inelastic magnetic signal found in superconducting La_1.85Sr_0.15CuO_4, thus justifying the inference that dynamical stripe correlations occur in the superconductors. The static order found in the x=0.12 sample can be explained by pinning of the charge modulation by a well known lattice distortion, and is correlated with the suppression of superconductivity.

  20. Correlated cluster mean-field theory for spin-glass systems

    NASA Astrophysics Data System (ADS)

    Zimmer, F. M.; Schmidt, M.; Magalhaes, S. G.

    2014-06-01

    The competition between cluster spin glass (CSG) and ferromagnetism or antiferromagnetism is studied in this work. The model considers clusters of spins with short-range ferromagnetic or antiferromagnetic (FE-AF) interactions (J0) and long-range disordered couplings (J) between clusters. The problem is treated by adapting the correlated cluster mean-field theory of D. Yamamoto [Phys. Rev. B 79, 144427 (2009), 10.1103/PhysRevB.79.144427]. Phase diagrams T /J×J0/J are obtained for different cluster sizes ns. The results show that the CSG phase is found below the freezing temperature Tf for lower intensities of J0/J. The increase of short-range FE interaction can favor the CSG phase, while the AF one reduces the CSG region by decreasing the Tf. However, there are always critical values of J0 where AF or FE orders become stable. The results also indicate a strong influence of the cluster size in the competition of magnetic phases. For AF cluster, the increase of ns diminishes Tf reducing the CSG phase region, which indicates that the cluster surface spins can play an important role in the CSG arising.

  1. Anomalous curie response of impurities in quantum-critical spin-1/2 Heisenberg antiferromagnets.

    PubMed

    Höglund, Kaj H; Sandvik, Anders W

    2007-07-13

    We consider a magnetic impurity in two different S=1/2 Heisenberg bilayer antiferromagnets at their respective critical interlayer couplings separating Néel and disordered ground states. We calculate the impurity susceptibility using a quantum Monte Carlo method. With intralayer couplings in only one of the layers (Kondo lattice), we observe an anomalous Curie constant C*, as predicted on the basis of field-theoretical work [S. Sachdev, Science 286, 2479 (1999)10.1126/science.286.5449.2479]. The value C* = 0.262 +/- 0.002 is larger than the normal Curie constant C=S(S+1)/3. Our low-temperature results for a symmetric bilayer are consistent with a universal C*.

  2. Variational Monte Carlo study of chiral spin liquid in quantum antiferromagnet on the triangular lattice

    NASA Astrophysics Data System (ADS)

    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.

  3. J1-J2 square-lattice Heisenberg antiferromagnets with 4 d1 spins: A MoOP O4Cl (A =K ,Rb )

    NASA Astrophysics Data System (ADS)

    Ishikawa, Hajime; Nakamura, Nanako; Yoshida, Makoto; Takigawa, Masashi; Babkevich, Peter; Qureshi, Navid; Rønnow, Henrik M.; Yajima, Takeshi; Hiroi, Zenji

    2017-02-01

    Magnetic properties of A MoOP O4Cl (A =K ,Rb ) with M o5 + ions in the 4 d1 electronic configuration are investigated by magnetization, heat capacity, and nuclear magnetic resonance (NMR) measurements on single crystals, combined with powder neutron diffraction experiments. The magnetization measurements reveal that they are good model compounds for the spin-1/2 J1-J2 square-lattice magnet with the first and second nearest-neighbor interactions. Magnetic transitions are observed at around 6 and 8 K in the K and Rb compounds, respectively. In contrast to the normal Néel-type antiferromagnetic order, the NMR and neutron diffraction experiments find a columnar antiferromagnetic order for each compound, which is stabilized by a dominant antiferromagnetic J2. Both compounds realize the unusual case of two interpenetrating J2 square lattices weakly coupled to each other by J1.

  4. Spin-wave approach for entanglement entropies of the J1-J2 Heisenberg antiferromagnet on the square lattice

    NASA Astrophysics Data System (ADS)

    Laflorencie, Nicolas; Luitz, David J.; Alet, Fabien

    2015-09-01

    Using a modified spin-wave theory which artificially restores zero sublattice magnetization on finite lattices, we investigate the entanglement properties of the Néel ordered J1-J2 Heisenberg antiferromagnet on the square lattice. Different kinds of subsystem geometries are studied, either corner-free (line, strip) or with sharp corners (square). Contributions from the nG=2 Nambu-Goldstone modes give additive logarithmic corrections with a prefactor nG/2 independent of the Rényi index. On the other hand, π /2 corners lead to additional (negative) logarithmic corrections with a prefactor lqc which does depend on both nG and the Rényi index q , in good agreement with scalar field theory predictions. By varying the second neighbor coupling J2 we also explore universality across the Néel ordered side of the phase diagram of the J1-J2 antiferromagnet, from the frustrated side 0

  5. Slow and static spin correlations in Dy(2+x)Ti(2-x)O(7-d)

    SciTech Connect

    Gardner, Jason; Ehlers, Georg; Fouquet, Peter; Farago, Bela; Stewart, John Ross

    2011-01-01

    The static and dynamic spin correlations in the spin ices Dy{sub 2.3}Ti{sub 1.7}O{sub 6.85} and Dy{sub 2}Ti{sub 2}O{sub 7} have been studied in polarized neutron diffraction and neutron spin echo experiments. The measurements reveal that, below 100 mK, the magnetic scattering braodens and shifts to higher |Q| upon stuffing the pyrochlore lattice with additional Dy{sup 3+} ions. These observations can be related, by means of reverse Monte Carlo simulation, to the modified distribution of near-neighbour distances and an overall more antiferromagnetic character of the near-neighbour couplings. The dynamic measurements show that the spin correlations are slower in the stuffed system. These results will be discussed and compared to the holmium analogues.

  6. Unusual magnetic excitations in the weakly ordered spin- 12 chain antiferromagnet Sr2CuO3: Possible evidence for Goldstone magnon coupled with the amplitude mode

    DOE PAGES

    Sergeicheva, E. G.; Sosin, S. S.; Prozorova, L. A.; ...

    2017-01-18

    We report on an electron spin resonance (ESR) study of a nearly one-dimensional (1D) spin-1/2 chain antiferromagnet, Sr2CuO3, with extremely weak magnetic ordering. The ESR spectra at T > TN, in the disordered Luttinger-spin-liquid phase, reveal nearly ideal Heisenberg-chain behavior with only a very small, field-independent linewidth, ~1/T. In the ordered state, below TN, we identify field-dependent antiferromagnetic resonance modes, which are well described by pseudo-Goldstone magnons in the model of a collinear biaxial antiferromagnet. Additionally, we observe a major resonant mode with unusual and strongly anisotropic properties, which is not anticipated by the conventional theory of Goldstone spin waves.more » Lastly, we propose that this unexpected magnetic excitation can be attributed to a field-independent magnon mode renormalized due to its interaction with the high-energy amplitude (Higgs) mode in the regime of weak spontaneous symmetry breaking.« less

  7. Strong anisotropic anomalous Hall effect and spin Hall effect in the chiral antiferromagnetic compounds Mn3X (X =Ge , Sn, Ga, Ir, Rh, and Pt)

    NASA Astrophysics Data System (ADS)

    Zhang, Yang; Sun, Yan; Yang, Hao; Železný, Jakub; Parkin, Stuart P. P.; Felser, Claudia; Yan, Binghai

    2017-02-01

    We have carried out a comprehensive study of the intrinsic anomalous Hall effect and spin Hall effect of several chiral antiferromagnetic compounds Mn3X (X = Ge, Sn, Ga, Ir, Rh and Pt) by ab initio band structure and Berry phase calculations. These studies reveal large and anisotropic values of both the intrinsic anomalous Hall effect and spin Hall effect. The Mn3X materials exhibit a noncollinear antiferromagnetic order which, to avoid geometrical frustration, forms planes of Mn moments that are arranged in a Kagome-type lattice. With respect to these Kagome planes, we find that both the anomalous Hall conductivity (AHC) and the spin Hall conductivity (SHC) are quite anisotropic for any of these materials. Based on our calculations, we propose how to maximize AHC and SHC for different materials. The band structures and corresponding electron filling, that we show are essential to determine the AHC and SHC, are compared for these different compounds. We point out that Mn3Ga shows a large SHC of about 600 (ℏ /e ) (Ωcm) -1 . Our work provides insights into the realization of strong anomalous Hall effects and spin Hall effects in chiral antiferromagnetic materials.

  8. Variational Monte Carlo study of chiral spin liquid in quantum antiferromagnet on the triangular lattice

    NASA Astrophysics Data System (ADS)

    Hu, Wenjun; Gong, Shoushu; Sheng, Donna; Donna Sheng Team

    We investigate the Heisenberg model with chiral coupling on the triangular lattice by using Gutzwiller projected fermionic states and the variational Monte Carlo technique. As the chiral coupling grows, a gapped spin liquid with non-trivial magnetic fluxes and nonzero chiral order is stabilized. Furthermore, we calculate the topological Chern number and the degeneracy of the ground state, both of which lead us to identify this flux state as the chiral spin liquid with C = 1 / 2 fractionalized Chern number. Finally, we add spatial anisotropy in the model to study the effects for the chiral order.

  9. Spin dynamics near a putative antiferromagnetic quantum critical point in Cu-substituted BaFe2As2 and its relation to high-temperature superconductivity

    SciTech Connect

    Kim, M. G.; Wang, M.; Tucker, G. S.; Valdivia, P. N.; Abernathy, D. L.; Chi, Songxue; Christianson, A. D.; Aczel, A. A.; Hong, T.; Heitmann, T. W.; Ran, S.; Canfield, P. C.; Bourret-Courchesne, E. D.; Kreyssig, A.; Lee, D. H.; Goldman, A. I.; McQueeney, R. J.; Birgeneau, R. J.

    2015-12-02

    We present the results of elastic and inelastic neutron scattering measurements on nonsuperconducting Ba(Fe0.957Cu0.043)2As2, a composition close to a quantum critical point between antiferromagnetic (AFM) ordered and paramagnetic phases. By comparing these results with the spin fluctuations in the low-Cu composition as well as the parent compound BaFe2As2 and superconducting Ba(Fe1–xNix)2As2 compounds, we demonstrate that paramagnon-like spin fluctuations are evident in the antiferromagnetically ordered state of Ba(Fe0.957Cu0.043)2As2, which is distinct from the AFM-like spin fluctuations in the superconducting compounds. Our observations suggest that Cu substitution decouples the interaction between quasiparticles and the spin fluctuations. In addition, we show that the spin-spin correlation length ξ(T) increases rapidly as the temperature is lowered and find ω/T scaling behavior, the hallmark of quantum criticality, at an antiferromagnetic quantum critical point.

  10. Spin correlations and topological entanglement entropy in a non-Abelian spin-one spin liquid

    NASA Astrophysics Data System (ADS)

    Wildeboer, Julia; Bonesteel, N. E.

    2016-07-01

    We analyze the properties of a non-Abelian spin-one chiral spin liquid state proposed by Greiter and Thomale [Phys. Rev. Lett. 102, 207203 (2009), 10.1103/PhysRevLett.102.207203] using Monte Carlo. In this state the bosonic ν =1 Moore-Read Pfaffian wave function is used to describe a gas of bosonic spin flips on a square lattice with one flux quantum per plaquette. For toroidal geometries there is a three-dimensional space of these states corresponding to the topological degeneracy of the bosonic Moore-Read state on the torus. We show that spin correlations for different states in this space become indistinguishable for large system size. We also calculate the Renyi entanglement entropy for different system partitions to extract the topological entanglement entropy and provide evidence that the topological order of the lattice spin-liquid state is the same as that of the continuum Moore-Read state from which it is constructed.

  11. Direct observation of impurity-induced magnetism in a spin-(1/2) antiferromagnetic Heisenberg two-leg spin ladder.

    PubMed

    Casola, F; Shiroka, T; Wang, S; Conder, K; Pomjakushina, E; Mesot, J; Ott, H-R

    2010-08-06

    Nuclear magnetic resonance and magnetization measurements were used to probe the magnetic features of single-crystalline Bi(Cu(1-x)Zn(x))(2)PO(6) with 00 and we present clear evidence for a temperature-dependent variation of the local magnetization close to the Zn sites. The generic nature of this observation is indicated by results of model calculations on appropriate spin systems of limited size employing quantum Monte Carlo methods.

  12. Electric Polarization Induced by Spin Ordering under Magnetic Fields in Distorted Triangular Lattice Antiferromagnet RbCoBr3

    NASA Astrophysics Data System (ADS)

    Nishiwaki, Yoichi; Tokunaga, Masashi; Sakakura, Ryo; Takeyama, Shojiro; Kato, Tetsuya; Iio, Katsunori

    2017-04-01

    Magnetization and electric polarization are measured for RbCoBr3 in the presence of an applied high magnetic field. The saturation of magnetization is recognized in the magnetization curve. The g-value of pseudospin and the nearest-neighbor intrachain exchange interaction of RbCoBr3, which has the properties of a quasi-one-dimensional Ising antiferromagnet, are evaluated. The electric polarization parallel to the c-axis under a magnetic field alone and also under the simultaneous application of electric and magnetic fields along the c-axis is observed to increase around the magnetic phase transition point from the ferrimagnetic low-temperature phase to the partially disordered high-temperature phase. Experimental results indicate that the electric polarization is induced through the rearrangement of the spin structure accompanied by the magnetic phase transition under an applied magnetic field. A probable reason for the enhancement of electric polarization is given from the viewpoint of the interplay between the distortion of the triangular lattice and the interchain exchange interactions.

  13. CaMn2Sb2: Spin waves on a frustrated antiferromagnetic honeycomb lattice

    SciTech Connect

    McNally, D. E.; Simonson, J. W.; Kistner-Morris, J. J.; Smith, G. J.; Hassinger, J. E.; DeBeer-Schmidt, L.; Kolesnikov, A. I.; Zaliznyak, I.; Aronson, M. C.

    2015-05-22

    We present inelastic neutron scattering measurements of the antiferromagnetic insulator CaMn2Sb2:, which consists of corrugated honeycomb layers of Mn. The dispersion of magnetic excitations has been measured along the H and L directions in reciprocal space, with a maximum excitation energy of ≈ 24 meV. These excitations are well described by spin waves in a Heisenberg model, including first and second neighbor exchange interactions, J1 and J2, in the Mn plane and also an exchange interaction between planes. The determined ratio J2/J1 ≈ 1/6 suggests that CaMn2Sb2: is the first example of a compound that lies very close to the mean field tricritical point, known for the classical Heisenberg model on the honeycomb lattice, where the N´eel phase and two different spiral phases coexist. The magnitude of the determined exchange interactions reveal a mean field ordering temperature ≈ 4 times larger than the reported N´eel temperature TN = 85 K, suggesting significant frustration arising from proximity to the tricritical point.

  14. Quantum phase transition, universality, and scaling behaviors in the spin-1/2 Heisenberg model with ferromagnetic and antiferromagnetic competing interactions on a honeycomb lattice

    NASA Astrophysics Data System (ADS)

    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'<0 in the zigzag direction on a honeycomb lattice are systematically studied using the continuous-time quantum Monte Carlo method. By calculating the Binder 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.

  15. Quantum phase transition, universality, and scaling behaviors in the spin-1/2 Heisenberg model with ferromagnetic and antiferromagnetic competing interactions on a honeycomb lattice.

    PubMed

    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^{'}<0 in the zigzag direction on a honeycomb lattice are systematically studied using the continuous-time quantum Monte Carlo method. By calculating the Binder ratio Q_{2} 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 α_{c}=-0.93. Through the finite-size scaling analysis on Q_{2}, ρ_{x}, and ρ_{y}, 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 ^{3}He under different pressures and several magnetic compounds under various magnetic fields. The scaling behaviors of Q_{2}, ρ, and C(T) are carefully analyzed. The susceptibility is compared with the experimental data to give the magnetic parameters of both compounds.

  16. Interdot Coulomb correlation effects and spin-orbit coupling in two carbon nanotube quantum dots

    SciTech Connect

    Wang, Zhen-Hua; Kuang, Xiao-Yu Zhong, Ming-Min; Shao, Peng; Li, Hui

    2014-01-28

    Transport properties of the two-level Kondo effect involving spin, orbital, and pseudospin degrees of freedom are examined in a parallel carbon nanotube double quantum dot with a sufficient interdot Coulomb interaction and small interdot tunneling. The interdot Coulomb correlation effects are taken into account, and it plays an important role in forming bonding and antibonding states. Attached to ferromagnetic leads, the Kondo effect is observed at the interdot Coulomb blockade region with degeneracy of spin, orbital, and pseudospin degrees of freedom. A crossover from a two-level Kondo state involving the fivefold degeneracy of the double quantum dots to an SU(4) spin-orbit Kondo state and to an SU(2) spin-Kondo effect is demonstrated. At finite magnetic field, the splitting of the spin, orbital, and pseudospin Kondo resonance can be restored. For finite intradot Coulomb interaction U, there is a competition between the single-dot Kondo effect and the antiferromagnetic exchange coupling J{sub AFM}, resulting in the suppression of the Kondo resonance. Moreover, both the J{sub AFM} and the Zeeman interactions compete, leading to need a much higher value of the magnetic field to compensate for the Kondo splitting.

  17. Similarity between the superconductivity in the graphene with the spin transport in the two-dimensional antiferromagnet in the honeycomb lattice

    NASA Astrophysics Data System (ADS)

    Lima, L. S.

    2017-02-01

    We have used the Dirac's massless quasi-particles together with the Kubo's formula to study the spin transport by electrons in the graphene monolayer. We have calculated the electric conductivity and verified the behavior of the AC and DC currents of this system, that is a relativistic electron plasma. Our results show that the AC conductivity tends to infinity in the limit ω → 0 , similar to the behavior obtained for the spin transport in the two-dimensional frustrated antiferromagnet in the honeycomb lattice. We have made a diagrammatic expansion for the Green's function and we have not gotten significative change in the results.

  18. Effective Hamiltonians for correlated narrow energy band systems and magnetic insulators: Role of spin-orbit interactions in metal-insulator transitions and magnetic phase transitions.

    PubMed

    Chakraborty, Subrata; Vijay, Amrendra

    2016-04-14

    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.

  19. Torque magnetometry study of magnetically ordered state and spin reorientation in the quasi-one-dimensional S =1/2 Heisenberg antiferromagnet CuSb2O6

    NASA Astrophysics Data System (ADS)

    Herak, Mirta; Žilić, Dijana; Matković Čalogović, Dubravka; Berger, Helmuth

    2015-05-01

    The antiferromagnetically ordered state of the monoclinic quasi-one-dimensional S =1 /2 Heisenberg antiferromagnet CuSb2O6 was studied combining torque magnetometry with a phenomenological approach to magnetic anisotropy. This system is known to have a number of different twins in the monoclinic β phase, which differ in the orientation of the two CuO6 octahedra in the unit cell resulting in different orientation of magnetic axes with respect to crystal axes for each twin. We performed torque measurements in magnetic fields H ≤0.8 T on a sample where a certain type of twin was shown to be dominant by ESR spectroscopy. The measured data reveal that the easy axis is the crystallographic b axis for this sample. Phenomenological magnetocrystalline anisotropy energy invariant to crystal symmetry operations was used to model the spin axis direction in zero and finite magnetic fields. Our model reproduces the value of the spin-flop field HSF=1.25 T found in literature. A combination of this approach with our torque results shows that the spin axis will flop in the direction of the maximal value of measured g tensor when the magnetic field H >HSF is applied along the easy axis direction. Our analysis of magnetocrystalline anisotropy energy predicts two possibilities for the easy axis direction in this system, b or a , connected to different crystallographic twins that can be realized in CuSb2O6 . These results offer a possibility to reconcile the different reports of easy axis direction found in literature for this system and also nicely demonstrate how a combination of torque magnetometry and a phenomenological approach to magnetic anisotropy can be used to determine the value of the spin-flop field and the direction of spin axis in antiferromagnets in both H HSF by performing measurements in fields significantly smaller than HSF.

  20. Spin–spin correlation length in a two-dimensional frustrated magnet and its relation to doping

    SciTech Connect

    Mikheyenkov, A. V.; Valiullin, V. E.; Shvartsberg, A. V.; Barabanov, A. F.

    2015-09-15

    In a spherically symmetric self-consistent approach (SSSA), the spin-1/2 J{sub 1}–J{sub 2} 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 J{sub 1}–J{sub 2} diagram, i.e., for any ϕ, J{sub 1} = cosϕ, and J{sub 2} = sinϕ. The structure factor c{sub q} 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 (J{sub 1} > J{sub 2} > 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.

  1. Superconducting transition temperatures and coherence length in non-s-wave pairing materials correlated with spin-fluctuation mediated interaction

    NASA Astrophysics Data System (ADS)

    Angilella, G. G.; March, N. H.; Pucci, R.

    2002-03-01

    Following earlier work on electron or hole liquids flowing through assemblies with magnetic fluctuations, we have recently exposed a marked correlation of the superconducting temperature Tc, for non-s-wave pairing materials, with coherence length ξ and effective mass m*. The very recent study of Abanov et al. [Europhys. Lett. 54, 488 (2001)] and the prior investigation of Monthoux and Lonzarich [Phys. Rev. B 59, 14 598 (1999)] have each focused on the concept of a spin-fluctuation temperature Tsf, which again is intimately related to Tc. For the d-wave pairing via antiferromagnetic spin fluctuations in the cuprates, these studies are brought into close contact with our own work, and the result is that kBTsf~ħ2/m*ξ2. This demonstrates that ξ is also determined by such antiferromagnetic spin-fluctuation mediated pair interaction. The coherence length in units of the lattice spacing is then essentially given in the cuprates as the square root of the ratio of two characteristic energies, namely, the kinetic energy of localization of a charge carrier of mass m* in a specified magnetic correlation length to the hopping energy. The quasi-two-dimensional ruthenate Sr2RuO4, with Tc~1.3 K, has p-wave spin-triplet pairing and so is also briefly discussed here.

  2. Cross-correlation spin noise spectroscopy of heterogeneous interacting spin systems

    SciTech Connect

    Roy, Dibyendu; Yang, Luyi; Crooker, Scott A.; Sinitsyn, Nikolai A.

    2015-04-30

    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.

  3. Evidence for stripe correlations of spins and holes in copper oxide superconductors

    NASA Astrophysics Data System (ADS)

    Tranquada, J. M.; Sternlieb, B. J.; Axe, J. D.; Nakamura, Y.; Uchida, S.

    1995-06-01

    ONE of the long-standing mysteries associated with the high-temperature copper oxide superconductors concerns the anomalous suppression1 of superconductivity in La2-xBaxCuO4 (and certain related compounds) when the hole concentration x is near ⅛. Here we examine the possibility that this effect is related to dynamical two-dimensional spin correlations, incommensurate with the crystal lattice, that have been observed in La2-xSrxCuO4 by neutron scattering2 4. A possible explanation for the incommensurability involves a coupled, dynamical modulation of spin and charge in which antiferromagnetic 'stripes' of copper spins are separated by periodically spaced domain walls to which the holes segregate5 9. An ordered stripe phase of this type has recently been observed in hole-doped La2NiO4 (refs 10 12). We present evidence from neutron diffraction that in the copper oxide material La1.6-xNd0.4SrxCuO4, with x = 0.12, a static analogue of the dynamical stripe phase is present, and is associated with an anomalous suppression of superconductivity13,14. Our results thus provide an explanation of the '⅛' conundrum, and also support the suggestion15 that spatial modulations of spin and charge density are related to superconductivity in the copper oxides.

  4. Mn2C monolayer: a 2D antiferromagnetic metal with high Néel temperature and large spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    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

  5. Femtosecond switching of magnetism via strongly correlated spin-charge quantum excitations.

    PubMed

    Li, Tianqi; Patz, Aaron; Mouchliadis, Leonidas; Yan, Jiaqiang; Lograsso, Thomas A; Perakis, Ilias E; Wang, Jigang

    2013-04-04

    The technological demand to push the gigahertz (10(9) hertz) switching speed limit of today's magnetic memory and logic devices into the terahertz (10(12) hertz) regime underlies the entire field of spin-electronics and integrated multi-functional devices. This challenge is met by all-optical magnetic switching based on coherent spin manipulation. By analogy to femtosecond chemistry and photosynthetic dynamics--in which photoproducts of chemical and biochemical reactions can be influenced by creating suitable superpositions of molecular states--femtosecond-laser-excited coherence between electronic states can switch magnetic order by 'suddenly' breaking the delicate balance between competing phases of correlated materials: for example, manganites exhibiting colossal magneto-resistance suitable for applications. Here we show femtosecond (10(-15) seconds) photo-induced switching from antiferromagnetic to ferromagnetic ordering in Pr0.7Ca0.3MnO3, by observing the establishment (within about 120 femtoseconds) of a huge temperature-dependent magnetization with photo-excitation threshold behaviour absent in the optical reflectivity. The development of ferromagnetic correlations during the femtosecond laser pulse reveals an initial quantum coherent regime of magnetism, distinguished from the picosecond (10(-12) seconds) lattice-heating regime characterized by phase separation without threshold behaviour. Our simulations reproduce the nonlinear femtosecond spin generation and underpin fast quantum spin-flip fluctuations correlated with coherent superpositions of electronic states to initiate local ferromagnetic correlations. These results merge two fields, femtosecond magnetism in metals and band insulators, and non-equilibrium phase transitions of strongly correlated electrons, in which local interactions exceeding the kinetic energy produce a complex balance of competing orders.

  6. Direct measurement of antiferromagnetic domain fluctuations.

    PubMed

    Shpyrko, O G; Isaacs, E D; Logan, J M; Feng, Yejun; Aeppli, G; Jaramillo, R; Kim, H C; Rosenbaum, T F; Zschack, P; Sprung, M; Narayanan, S; Sandy, A R

    2007-05-03

    Measurements of magnetic noise emanating from ferromagnets owing to domain motion were first carried out nearly 100 years ago, and have underpinned much science and technology. Antiferromagnets, which carry no net external magnetic dipole moment, yet have a periodic arrangement of the electron spins extending over macroscopic distances, should also display magnetic noise. However, this must be sampled at spatial wavelengths of the order of several interatomic spacings, rather than the macroscopic scales characteristic of ferromagnets. Here we present a direct measurement of the fluctuations in the nanometre-scale superstructure of spin- and charge-density waves associated with antiferromagnetism in elemental chromium. The technique used is X-ray photon correlation spectroscopy, where coherent X-ray diffraction produces a speckle pattern that serves as a 'fingerprint' of a particular magnetic domain configuration. The temporal evolution of the patterns corresponds to domain walls advancing and retreating over micrometre distances. This work demonstrates a useful measurement tool for antiferromagnetic domain wall engineering, but also reveals a fundamental finding about spin dynamics in the simplest antiferromagnet: although the domain wall motion is thermally activated at temperatures above 100 K, it is not so at lower temperatures, and indeed has a rate that saturates at a finite value-consistent with quantum fluctuations-on cooling below 40 K.

  7. A correlation between spin parameter and dark matter halo mass

    NASA Astrophysics Data System (ADS)

    Knebe, A.; Power, C.

    2011-01-01

    Using a set of high-resolution dark matter only cosmological simulations we found a correlation between the dark matter halo mass M and its spin parameter λ for objects forming at redshifts z > 10: the spin parameter decreases with increasing mass. However, halos forming at later times do not exhibit such a strong correlation, in agreement with the findings of previous studies. While we presented such a correlation in a previous study using the Bullock et al. (2001) spin parameter defintion we now defer to the classical definition showing that the results are independent of the definition.

  8. Thermal form factor approach to the ground-state correlation functions of the XXZ chain in the antiferromagnetic massive regime

    NASA Astrophysics Data System (ADS)

    Dugave, Maxime; Göhmann, Frank; Kozlowski, Karol K.; Suzuki, Junji

    2016-09-01

    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}∞ 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. Dedicated to the memory of Petr Petrovich Kulish.

  9. Static and dynamical properties of the spin-1/2 equilateral triangular-lattice antiferromagnet Ba3CoSb2O9

    DOE PAGES

    Ma, Jie; Kamiya, Yoshitomo; Hong, Tao; ...

    2016-02-24

    We present single-crystal neutron scattering measurements of the spin-1/2 equilateral triangular-lattice antiferromagnet Ba3CoSb2O9. Besides confirming that the Co2+ magnetic moments lie in the ab plane for zero magnetic field and then determining all the exchange parameters of the minimal quasi-2D spin Hamiltonian, we provide conclusive experimental evidence of magnon decay through observation of intrinsic line broadening. Through detailed comparisons with the linear and nonlinear spin-wave theories, we also point out that the large-S approximation, which is conventionally employed to predict magnon decay in noncollinear magnets, is inadequate to explain our experimental observation. Hence, our results call for a new theoreticalmore » framework for describing excitation spectra in low-dimensional frustrated magnets under strong quantum effects.« less

  10. Non-linear spin wave theory results for the frustrated [Formula: see text] Heisenberg antiferromagnet on a body-centered cubic lattice.

    PubMed

    Majumdar, Kingshuk; Datta, Trinanjan

    2009-10-07

    At zero temperature the sublattice magnetization of the quantum spin- 1/2 Heisenberg antiferromagnet on a body-centered cubic lattice with competing first and second neighbor exchange (J(1) and J(2)) is investigated using the non-linear spin wave theory. The zero temperature phases of the model consist of a two sublattice Néel phase for small J(2) (AF(1)) and a collinear phase at large J(2) (AF(2)). We show that quartic corrections due to spin wave interactions enhance the sublattice magnetization in both the AF(1) and the AF(2) phase. The magnetization corrections are prominent near the classical transition point of the model and in the J(2)>J(1) regime. The ground state energy with quartic interactions is also calculated. It is found that up to quartic corrections the first order phase transition (previously observed in this model) between the AF(1) and the AF(2) phase survives.

  11. Bicollinear antiferromagnetic order, monoclinic distortion, and reversed resistivity anisotropy in FeTe as a result of spin-lattice coupling

    DOE PAGES

    Bishop, Christopher B.; Moreo, Adriana; Dagotto, Elbio

    2016-09-08

    The bicollinear antiferromagnetic order experimentally observed in FeTe is shown to be stabilized by the coupling g~12 between monoclinic lattice distortions and the spin-nematic order parameter with B2g symmetry, within a three-orbital spin-fermion model studied with Monte Carlo techniques. A finite but small value of g~12 is required, with a concomitant lattice distortion compatible with experiments, and a tetragonal-monoclinic transition strongly first order. Remarkably, the bicollinear state found here displays a planar resistivity with the reversed puzzling anisotropy discovered in transport experiments. Orthorhombic distortions are also incorporated, and phase diagrams interpolating between pnictides and chalcogenides are presented. Here, we concludemore » that the spin-lattice coupling we introduce is sufficient to explain the challenging properties of FeTe.« less

  12. Bicollinear antiferromagnetic order, monoclinic distortion, and reversed resistivity anisotropy in FeTe as a result of spin-lattice coupling

    SciTech Connect

    Bishop, Christopher B.; Moreo, Adriana; Dagotto, Elbio

    2016-09-08

    The bicollinear antiferromagnetic order experimentally observed in FeTe is shown to be stabilized by the coupling g~12 between monoclinic lattice distortions and the spin-nematic order parameter with B2g symmetry, within a three-orbital spin-fermion model studied with Monte Carlo techniques. A finite but small value of g~12 is required, with a concomitant lattice distortion compatible with experiments, and a tetragonal-monoclinic transition strongly first order. Remarkably, the bicollinear state found here displays a planar resistivity with the reversed puzzling anisotropy discovered in transport experiments. Orthorhombic distortions are also incorporated, and phase diagrams interpolating between pnictides and chalcogenides are presented. Here, we conclude that the spin-lattice coupling we introduce is sufficient to explain the challenging properties of FeTe.

  13. Duality in spin fluctuation in correlated electron systems

    NASA Astrophysics Data System (ADS)

    Yanagisawa, Takashi; Hase, Izumi

    2016-11-01

    An origin of high-temperature superconductivity for cuprate superconductors is investigated on the basis of the two-dimensional Hubbard model. The Coulomb interaction is a candidate that can bring about high-temperature superconductivity because its characteristic energy is of the order of eV. It is not trivial whether the on-site Coulomb interaction U leads to a pairing interaction between two electrons. We argue that the antiferromagnetic fluctuation and the kinetic charge fluctuation are responsible for high-temperature superconductivity. The kinetic charge fluctuation is induced by large U to get the kinetic energy gain in the strongly correlated region. We consider electron correlation beyond the Gutzwiller ansatz, by taking account of inter-site correlation such as doublon-holon correlation and kinetic correlation. We show that high-temperature superconductivity is possible in the strongly correlated region, where U is greater than the bandwidth, by using the variational Monte Carlo method.

  14. Quantification of quantum discord in a antiferromagnetic Heisenberg compound

    SciTech Connect

    Singh, H. Chakraborty, T. Mitra, C.

    2014-04-24

    An experimental quantification of concurrence and quantum discord from heat capacity (C{sub p}) measurement performed over a solid state system has been reported. In this work, thermodynamic measurements were performed on copper nitrate (CN, Cu(NO{sub 3}){sub 2}⋅2.5H{sub 2}O) single crystals which is an alternating antiferromagnet Heisenberg spin 1/2 system. CN being a weak dimerized antiferromagnet is an ideal system to investigate correlations between spins. The theoretical expressions were used to obtain concurrence and quantum discord curves as a function of temperature from heat capacity data of a real macroscopic system, CN.

  15. Cross-correlation spin noise spectroscopy of heterogeneous interacting spin systems

    DOE PAGES

    Roy, Dibyendu; Yang, Luyi; Crooker, Scott A.; ...

    2015-04-30

    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 spinmore » 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.« less

  16. Universal scaling of Néel temperature, staggered magnetization density, and spin-wave velocity of three-dimensional disordered and clean quantum antiferromagnets

    NASA Astrophysics Data System (ADS)

    Tan, D.-R.; Jiang, F.-J.

    2017-02-01

    The Néel temperature, staggered magnetization density, as well as the spin-wave velocity of a three-dimensional (3D) quantum Heisenberg model with antiferromagnetic disorder (randomness) are calculated using first-principles nonperturbative quantum Monte Carlo simulations. In particular, we examine the validity of universal scaling relations that are related to these three studied physical quantities. These relations are relevant to experimental data and are firmly established for clean (regular) 3D dimerized spin-1/2 Heisenberg models. Remarkably, our numerical results show that the considered scaling relations remain true for the investigated model with the introduced disorder. In addition, while the presence of disorder may change the physical properties of regular dimerized models, hence leading to different critical theories, both the obtained data of Néel temperature and staggered magnetization density in our study are fully compatible with the expected critical behavior for clean dimerized systems. As a result, it is persuasive to conclude that the related quantum phase transitions of the considered disordered model and its clean analogues are governed by the same critical theory, which is not always the case in general. Finally, we also find smooth scaling curves even emerging when both the data of the investigated disordered model as well as its associated clean system are taken into account concurrently. This in turn implies that, while in a restricted sense, the considered scaling relations for 3D spin-1/2 antiferromagnets are indeed universal.

  17. Effect of grain size on charge and spin correlations in Bi0.5Ca0.5MnO3 manganite nanoparticles

    NASA Astrophysics Data System (ADS)

    Ade, Ramesh; Singh, Rajender

    2016-11-01

    In this work we report the electron spin resonance (ESR) and magnetization (M) studies to understand the effect of grain size (GS) on the charge ordering and spin correlations in Bi0.5Ca0.5MnO3 manganite synthesized by sol-gel method. The suppression of charge ordering (CO), long-range antiferromagnetic (AFM) state, shifting of ferromagnetic (FM)-cluster glass (CG) transition towards higher temperatures and evolution of different magnetic correlations with decrease in GS are discussed in view of the changes in surface to volume ratio of nano-grains.

  18. Competing magnetic fluctuations in iron pnictide superconductors: Role of ferromagnetic spin correlations revealed by NMR

    SciTech Connect

    Wiecki, P.; Roy, B.; Johnston, D. C.; Bud’ko, S. L.; Canfield, P. C.; Furukawa, Y.

    2015-09-22

    In the iron pnictide superconductors, theoretical calculations have consistently shown enhancements of the static magnetic susceptibility at both the stripe-type antiferromagnetic and in-plane ferromagnetic (FM) wave vectors. However, the possible existence of FM fluctuations has not yet been examined from a microscopic point of view. Here, using 75As NMR data, we provide clear evidence for the existence of FM spin correlations in both the hole- and electron-doped BaFe2As2 families of iron-pnictide superconductors. Furthermore, these FM fluctuations appear to compete with superconductivity and are thus a crucial ingredient to understanding the variability of Tc and the shape of the superconducting dome in these and other iron-pnictide families.

  19. Competing magnetic fluctuations in iron pnictide superconductors: Role of ferromagnetic spin correlations revealed by NMR

    DOE PAGES

    Wiecki, P.; Roy, B.; Johnston, D. C.; ...

    2015-09-22

    In the iron pnictide superconductors, theoretical calculations have consistently shown enhancements of the static magnetic susceptibility at both the stripe-type antiferromagnetic and in-plane ferromagnetic (FM) wave vectors. However, the possible existence of FM fluctuations has not yet been examined from a microscopic point of view. Here, using 75As NMR data, we provide clear evidence for the existence of FM spin correlations in both the hole- and electron-doped BaFe2As2 families of iron-pnictide superconductors. Furthermore, these FM fluctuations appear to compete with superconductivity and are thus a crucial ingredient to understanding the variability of Tc and the shape of the superconducting domemore » in these and other iron-pnictide families.« less

  20. Spin diffusion in the low-dimensional molecular quantum Heisenberg antiferromagnet Cu (pyz ) (NO3)2 detected with implanted muons

    NASA Astrophysics Data System (ADS)

    Xiao, F.; Möller, J. S.; Lancaster, T.; Williams, R. C.; Pratt, F. L.; Blundell, S. J.; Ceresoli, D.; Barton, A. M.; Manson, J. L.

    2015-04-01

    We present the results of muon-spin relaxation measurements of spin excitations in the one-dimensional quantum Heisenberg antiferromagnet Cu (pyz ) (NO3)2 . Using density-functional theory we propose muon sites and assess the degree of perturbation the muon probe causes on the system. We identify a site involving the muon forming a hydroxyl-type bond with an oxygen on the nitrate group that is sensitive to the characteristic spin dynamics of the system. Our measurements of the spin dynamics show that in the temperature range TNspin relaxation is characteristic of diffusive transport of spin excitations over a wide range of applied fields. We also identify a possible crossover at higher applied fields in the muon probe's response to the fluctuation spectrum, to a regime where the muon detects early-time transport with a ballistic character. This behavior is contrasted with that found for T >J and that in the related two-dimensional system Cu (pyz) 2(ClO4)2 .

  1. Quantum-spin-liquid states in the two-dimensional kagome antiferromagnets ZnxCu4-x(OD)6Cl2.

    PubMed

    Lee, S-H; Kikuchi, H; Qiu, Y; Lake, B; Huang, Q; Habicht, K; Kiefer, K

    2007-11-01

    A three-dimensional system of interacting spins typically develops static long-range order when it is cooled. If the spins are quantum (S=1/2), however, novel quantum paramagnetic states may appear. The most highly sought state among them is the resonating-valence-bond state, in which every pair of neighbouring quantum spins forms an entangled spin singlet (valence bonds) and these singlets are quantum mechanically resonating among themselves. Here we provide an experimental indication for such quantum paramagnetic states existing in frustrated antiferromagnets, Zn(x)Cu(4-x)(OD)(6)Cl(2), where the S=1/2 magnetic Cu2+ moments form layers of a two-dimensional kagome lattice. We find that in Cu(4)(OD)(6)Cl(2), where distorted kagome planes are weakly coupled, a dispersionless excitation mode appears in the magnetic excitation spectrum below approximately 20 K, whose characteristics resemble those of quantum spin singlets in a solid state, known as a valence-bond solid, that breaks translational symmetry. Doping with non-magnetic Zn2+ ions reduces the distortion of the kagome lattice, and weakens the interplane coupling but also dilutes the magnetic occupancy of the kagome lattice. The valence-bond-solid state is suppressed, and for ZnCu(3)(OD)(6)Cl(2), where the kagome planes are undistorted and 90% occupied by the Cu2+ ions, the low-energy spin fluctuations become featureless.

  2. FractionalSzExcitation and Its Boundstate for theS=1/2 Antiferromagnetic Zigzag Spin Chain in a Magnetic Field

    NASA Astrophysics Data System (ADS)

    Okunishi, Kouichi; Tonegawa, Takashi

    2005-01-01

    We demonstrate that domain-wall type excitations carrying the fractional magnetization $S^z=\\pm1/3$ and their bound state describe the low-energy physics around the 1/3 plateau of the antiferromagnetic zigzag spin chain in the strongly frustrated region. In particular we discuss the relevance of such domain-wall excitations to the characteristic properties of the magnetization curves: the 1/3 plateau accompanying the spontaneous symmetry breaking of the translation, the cusp singularities above and/or below the plateau, and the even-odd effect in the magnetization curve.

  3. Electron interactions, spin-orbit coupling, and intersite correlations in pyrochlore iridates

    NASA Astrophysics Data System (ADS)

    Wang, Runzhi; Go, Ara; Millis, Andrew J.

    2017-01-01

    We perform combined density functional and dynamical mean-field calculations to study the pyrochlore iridates Lu2Ir2O7 , Y2Ir2O7 , and Eu2Ir2O7 . Both single-site and cluster dynamical mean-field calculations are performed and spin-orbit coupling is included. Paramagnetic metallic phases, antiferromagnetic metallic phases with tilted Weyl cones, and antiferromagnetic insulating phases are found. The magnetic phases display all-in/all-out magnetic ordering, consistent with previous studies. Unusually for electronically three-dimensional materials, the single-site dynamical mean-field approximation fails to reproduce qualitative material trends, predicting in particular that the paramagnetic phase properties of Y2Ir2O7 and Eu2Ir2O7 are almost identical, although in experiments the Y compound has a much higher resistance than the Eu compound. This qualitative failure is attributed to the importance of intersite magnetic correlations in the physics of these materials.

  4. Ultrafast dynamics in the presence of antiferromagnetic correlations in electron-doped cuprate La2 -xCexCuO4 ±δ

    NASA Astrophysics Data System (ADS)

    Vishik, I. M.; Mahmood, F.; Alpichshev, Z.; Gedik, N.; Higgins, J.; Greene, R. L.

    2017-03-01

    We used femtosecond optical pump-probe spectroscopy to study the photoinduced change in reflectivity of thin films of the electron-doped cuprate La2 -xCexCuO4 (LCCO) with dopings of x =0.08 (underdoped) and x =0.11 (optimally doped). Above Tc, we observe fluence-dependent relaxation rates that begin at a temperature similar to the one where transport measurements first show signatures of antiferromagnetic correlations. Upon suppressing superconductivity with a magnetic field, it is found that the fluence and temperature dependence of relaxation rates are consistent with bimolecular recombination of electrons and holes across a gap (2 ΔAF ) originating from antiferromagnetic correlations which comprise the pseudogap in electron-doped cuprates. This can be used to learn about coupling between electrons and high-energy (ω >2 ΔAF ) excitations in these compounds and set limits on the time scales on which antiferromagnetic correlations are static.

  5. Quantum and classical correlations in electron-nuclear spin echo

    SciTech Connect

    Zobov, V. E.

    2014-11-15

    The quantum properties of dynamic correlations in a system of an electron spin surrounded by nuclear spins under the conditions of free induction decay and electron spin echo have been studied. Analytical results for the time evolution of mutual information, classical part of correlations, and quantum part characterized by quantum discord have been obtained within the central-spin model in the high-temperature approximation. The same formulas describe discord in both free induction decay and spin echo although the time and magnetic field dependences are different because of difference in the parameters entering into the formulas. Changes in discord in the presence of the nuclear polarization β{sub I} in addition to the electron polarization β{sub S} have been calculated. It has been shown that the method of reduction of the density matrix to a two-spin electron-nuclear system provides a qualitatively correct description of pair correlations playing the main role at β{sub S} ≈ β{sub I} and small times. At large times, such correlations decay and multispin correlations ensuring nonzero mutual information and zero quantum discord become dominant.

  6. CP-sensitive spin-spin correlations in neutralino production at the ILC

    NASA Astrophysics Data System (ADS)

    Bartl, A.; Hohenwarter-Sodek, K.; Kernreiter, T.; Kittel, O.; Terwort, M.

    2009-07-01

    We study the CP-violating terms of the spin-spin correlations in neutralino production and their subsequent two-body decays into sleptons plus leptons at the ILC. We analyze CP-sensitive observables with the help of T-odd products of the spin-spin terms. These terms depend on the polarizations of both neutralinos, with one polarization perpendicular to the production plane. We present a detailed numerical study of the CP-sensitive observables, cross sections, and neutralino branching ratios in the Minimal Supersymmetric Standard Model with complex parameters.

  7. Spin excitations and correlations in scanning tunneling spectroscopy

    NASA Astrophysics Data System (ADS)

    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.

  8. Spin-liquid polymorphism in a correlated electron system on the threshold of superconductivity.

    PubMed

    Zaliznyak, Igor; Savici, Andrei T; Lumsden, Mark; Tsvelik, Alexei; Hu, Rongwei; Petrovic, Cedomir

    2015-08-18

    We report neutron scattering measurements which reveal spin-liquid polymorphism in an "11" iron chalcogenide superconductor. It occurs when a poorly metallic magnetic state of FeTe is tuned toward superconductivity by substitution of a small amount of tellurium with isoelectronic sulfur. We observe a liquid-like magnetic response, which is described by the coexistence of two disordered magnetic phases with different local structures whose relative abundance depends on temperature. One is the ferromagnetic (FM) plaquette phase observed in undoped, nonsuperconducting FeTe, which preserves the C4 symmetry of the underlying square lattice and is favored at high temperatures, whereas the other is the antiferromagnetic plaquette phase with broken C4 symmetry, which emerges with doping and is predominant at low temperatures. These findings suggest the coexistence of and competition between two distinct liquid states, and a liquid-liquid phase transformation between these states, in the electronic spin system of FeTe(1-x)(S,Se)(x). We have thus discovered the remarkable physics of competing spin-liquid polymorphs in a correlated electron system approaching superconductivity. Our results facilitate an understanding of large swaths of recent experimental data in unconventional superconductors. In particular, the phase with lower C2 local symmetry, whose emergence precedes superconductivity, naturally accounts for a propensity for forming electronic nematic states which have been observed experimentally, in cuprate and iron-based superconductors alike.

  9. Determination of magnetic and structural properties in solids containing antiferromagnetically coupled metal centers using NMR methods. Magneto-structural correlations in anhydrous copper(II) n-butyrate

    SciTech Connect

    Campbell, G.C.; Haw, J.F.

    1988-10-19

    A new approach to the investigation of magneto-structural correlations in solids containing antiferromagnetically coupled transition-metal centers is described that illustrates the potential of NMR spectroscopy in such work. The results of a variable-temperature (VT) /sup 13/C cross-polarization magic-angle-spinning (CP/MAS) NMR investigation of anhydrous copper(II) n-butyrate, (Cu(C/sub 3/H/sub 7/COO)/sub 2/)/sub 2/ are reported. Isotropic shifts are found to be primarily contact in origin, and a statistical analysis of their temperature dependence allows the calculation of singlet-triplet energy level separations (-2J), diamagnetic shifts (delta/sub dia/), and electron-nucleus hyperfine coupling constants (A), which are shown to give insight into the mechanisms of electron delocalization along the superexchange pathway. Signal multiplicity can be related to compound structure, which was determined by using x-ray crystallography. The title compound is triclinic and has a space group of P/anti 1/ with a = 9.035 (2) /angstrom/, b = 5.192 (2) /angstrom/, c = 11.695 (3) /angstrom/, ..cap alpha.. = 85.88 (2)/degrees/, ..gamma.. = 109.32 (2)/degrees/, Z = 1, and V = 515.2 (3) /angstrom//sup 3/; the final weighted R value for 2169 reflections was 0.048. 21 references, 4 figures, 4 tables.

  10. Spin correlations and spin-wave excitations in Dirac-Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Araki, Yasufumi; Nomura, Kentaro

    We study correlations among magnetic dopants in three-dimensional Dirac and Weyl semimetals. Effective field theory for localized magnetic moments is derived by integrating out the itinerant electron degrees of freedom. We find that spin correlation in the spatial direction parallel to local magnetization is more rigid than that in the perpendicular direction, reflecting spin-momentum locking nature of the Dirac Hamiltonian. Such an anisotropy becomes stronger for Fermi level close to the Dirac points, due to Van Vleck paramagnetism triggered by spin-orbit coupling. One can expect topologically nontrivial spin textures under this anisotropy, such as a hedgehog around a single point, or a radial vortex around an axis, as well as a uniform ferromagnetic order. We further investigate the characteristics of spin waves in the ferromagnetic state. Spin-wave dispersion also shows a spatial anisotropy, which is less dispersed in the direction transverse to the magnetization than that in the longitudinal direction. The spin-wave dispersion anisotropy can be traced back to the rigidity and flexibility of spin correlations discussed above. This work was supported by Grant-in-Aid for Scientific Research (Grants No.15H05854, No.26107505, and No.26400308) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

  11. Magnetic phase diagram and multiferroicity of Ba3MnNb2O9 : A spin -52 triangular lattice antiferromagnet with weak easy-axis anisotropy

    DOE PAGES

    Lee, M.; Choi, E. S.; Huang, X.; ...

    2014-12-01

    Here we have performed magnetic, electric, thermal and neutron powder diffraction (NPD) experiments as well as density functional theory (DFT) calculations on Ba3MnNb2 O9. All results suggest that Ba3MnNb2 O9 is a spin-5/2 triangular lattice antiferromagnet (TLAF) with weak easy-axis anisotropy. At zero field, we observed a narrow two-step transition at TN1 = 3.4 K and TN2 = 3.0 K. The neutron diffraction measurement and the DFT calculation indicate a 120 spin structure in ab plane with out-of-plane canting at low temperatures. With increasing magnetic field, the 120 spin structure evolves into up-up-down (uud) and oblique phases showing successive magneticmore » phase transitions, which fits well to the theoretical prediction for the 2D Heisenberg TLAF with classical spins. Ultimately, multiferroicity is observed when the spins are not collinear but suppressed in the uud and oblique phases.« less

  12. Strong magnetic correlations to 900 K in single crystals of the trigonal antiferromagnetic insulators SrMn2As2 and CaMn2As2

    DOE PAGES

    Sangeetha, N. S.; Pandey, Abhishek; Benson, Zackery A.; ...

    2016-09-15

    Crystallographic, electronic transport, thermal, and magnetic properties are reported for SrMn2As2 and CaMn2As2 single crystals grown using Sn flux. Rietveld refinements of powder x-ray diffraction data show that the two compounds are isostructural and crystallize in the trigonal CaAl2Si2-type structure (space groupmore » $$P\\bar{3}$$ m1), in agreement with the literature. Electrical resistivity ρ versus temperature T measurements demonstrate insulating ground states for both compounds with activation energies of 85 meV for SrMn2As2 and 61 meV for CaMn2As2. In a local-moment picture, the Mn+2 3d5 ions are expected to have high-spin S=5/2 with spectroscopic splitting factor g≈2. Magnetic susceptibility χ and heat capacity Cp measurements versus T reveal antiferromagnetic (AFM) transitions at TN=120(2) K and 62(3) K for SrMn2As2 and CaMn2As2, respectively. The anisotropic χ(T≤TN) data indicate that the hexagonal c axis is the hard axis and hence that the ordered Mn moments are aligned in the ab plane. Finally, the χ(T) data for both compounds and the Cp(T) for SrMn2As2 show strong dynamic short-range AFM correlations from TN up to at least 900 K, likely associated with quasi-two-dimensional connectivity of strong AFM exchange interactions between the Mn spins within the corrugated honeycomb Mn layers parallel to the ab plane.« less

  13. Spin-correlation function of the fully frustrated Ising model and ± J Ising spin glass on a square lattice

    NASA Astrophysics Data System (ADS)

    M, Y. Ali; J, Poulter

    2013-06-01

    In this work we study the correlation function of the ground state of a two-dimensional fully frustrated Ising model as well as spin glass. The Pfaffian method is used to calculate free energy and entropy as well as the correlation function. We estimate the exponent of spin correlation function for the fully frustrated model and spin glass. In this paper an overview of the latest results on the spin correlation function is presented.

  14. Entropy and correlation functions of a driven quantum spin chain

    SciTech Connect

    Cherng, R. W.; Levitov, L. S.

    2006-04-15

    We present an exact solution for a quantum spin chain driven through its critical points. Our approach is based on a many-body generalization of the Landau-Zener transition theory, applied to a fermionized spin Hamiltonian. The resulting nonequilibrium state of the system, while being a pure quantum state, has local properties of a mixed state characterized by finite entropy density associated with Kibble-Zurek defects. The entropy and the finite spin correlation length are functions of the rate of sweep through the critical point. We analyze the anisotropic XY spin-1/2 model evolved with a full many-body evolution operator. With the help of Toeplitz determinant calculus, we obtain an exact form of correlation functions. The properties of the evolved system undergo an abrupt change at a certain critical sweep rate, signaling the formation of ordered domains. We link this phenomenon to the behavior of complex singularities of the Toeplitz generating function.

  15. Effects of Quantum Fluctuations and Short-Ranged Spin Correlations on the Magnetic Phase transitions in insulating vanadium oxide

    NASA Astrophysics Data System (ADS)

    de Silva, Theja; Ma, Michael; Zhang, Fu-Chun

    2002-03-01

    We study the magnetic phase transition of insulating vanadium oxide using the recently proposed S=2 bond model (1). In this model, the anomalous spin ordering of V_2O3 (RS) is due to a coupling of spin-spin correlations to orbitals. It was shown using single-site mean field theory (SSMFT) that the model also explains the unusual phase transition properities qualitatively (2). We use a modified MF approach to study the effects of quantum fluctuations and short range spin correlations which were neglected in the SSMFT calculation. The key results are i) Similar to SSMFT, at T=0, the ground state undergoes a transition from conventional antiferromagnetic (AS) ordering to ferro-orbital RS (FORS) ordering as the strength of the spin-orbital is increased relative to the bare spin-spin coupling. However, fluctuations tend to stabilize the FORS phase relative to the AS phase. ii) In contrast to SSMFT, which gave a weak first order transition, the paramagnetic to FORS transition is strongly first order. iii) The system can first become AS as T is lowered and then undergoes a second transition into either the FORS phase or a FO phase with short-ranged RS correlations. The last case corresponds to an orbital driven spin-Peirels transition. 1. F.Mila,R.Shiina,F.C.Zhang,A.Joshi,M.Ma,V.Anisimov, and T.M.Rice,Phys,Rev,Lett,85,1714(2000) 2. A.Joshi,M.Ma,and F.C.Zhang,Phys,Rev,Lett,86,5743(2001)

  16. Unconventional Transport of Spin Bipolarons on an Antiferromagnetic buckled hexagonal lattice of half-filled d-band Mn2+ ions

    NASA Astrophysics Data System (ADS)

    Thorsmolle, Verner; Ignatov, Alexander; Pezzoli, Maria; Haule, Kristjan; Kolchmeyer, David; Lee, Alexander; Simonson, Jack; Aronson, Meigan; Blumberg, Girsh

    2013-03-01

    CaMn2Sb2 presents a magnetic system with a buckled hexagonal lattice of half-filled d-band Mn2+ ions. AC resistivity and susceptibility exhibit non-monotonic temperature dependence at 85-210 K. Below 85 K it has an antiferromagnetic (AF) phase with an activation energy of 28 meV, and above 210 K a paramagnetic phase. Using Raman spectroscopy we find a mode at 32 meV which develops below the AF transition. We attribute this excitation to the activation energy associated with the motion of spin bipolarons. Here, hybridization between Sb and Mn results in extra electrons for the Mn 3 d-shells. It is energetically favorable for these extra carriers to form spin-singlets. These spin-bipolarons cover two Mn sites with a binding energy of ~80 meV and conduction proceed via photo-assisted hopping with an activation energy of ~32 meV. This spin bipolaron model explains the spectroscopic features providing a self-consistent picture of this conductivity mechanism that also clarifies reported unusual temperature-dependent magnetic and transport data. VKT, AI, DK, AL and GB acknowledge support by NSF DMR-1104884 and by U.S. DOE, Office of BES, Award DE-SC0005463. MEP and JWS acknowledge support by NSSEFF, administrative by the AFOSR.

  17. A new twist on top quark spin correlations

    NASA Astrophysics Data System (ADS)

    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 ).

  18. Electrical manipulation of a ferromagnet by an antiferromagnet

    NASA Astrophysics Data System (ADS)

    Tshitoyan, V.; Ciccarelli, C.; Mihai, A. P.; Ali, M.; Irvine, A. C.; Moore, T. A.; Jungwirth, T.; Ferguson, A. J.

    Several recent studies of antiferromagnetic (AFM) spintronics have focused on transmission and detection of spin-currents in AFMs. Efficient spin transmission through AFMs was inferred from experiments in FM/AFM/NM (normal metal) structures. Measurements in FM/AFM bilayers have demonstrated that a metallic AFM can also act as an efficient ISHE detector of the spin-current, with spin-Hall angles comparable to heavy NMs. Here we demonstrate that an antiferromagnet can be employed for a highly efficient electrical manipulation of a ferromagnet. We use an all-electrical excitation and detection technique of ferromagnetic resonance in a NiFe/IrMn bilayer. We observe antidamping-like spin torque acting on the NiFe generated by the in-plane current driven through the IrMn antiferromagnet. A large enhancement of the torque, characterized by an effective spin-Hall angle exceeding most heavy transition metals, correlates with the presence of the exchange-bias field at the NiFe/IrMn interface. It highlights that, in addition to strong spin-orbit coupling, the AFM order in IrMn governs the observed phenomenon.

  19. Quantum dust magnetosonic waves with spin and exchange correlation effects

    SciTech Connect

    Maroof, R.; Qamar, A.; Mushtaq, A.

    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.)

  20. Critical behavior of AC antiferromagnetic and ferromagnetic susceptibilities of a spin-1/2 > metamagnetic Ising system

    NASA Astrophysics Data System (ADS)

    Gulpinar, Gul; Vatansever, Erol

    2012-03-01

    In this study, the temperature variations of the equilibrium and the non-equilibrium antiferromagnetic and ferromagnetic susceptibilities of a metamagnetic system are examined near the critical point. The kinetic equations describing the time dependencies of the total and staggered magnetizations are derived by utilizing linear response theory. In order to obtain dynamic magnetic relaxation behavior of the system, the stationary solutions of the kinetic equations in existence of sinusoidal staggered and physical external magnetic fields are performed. In addition, the static and dynamical mean field critical exponents are calculated in order to formulate the critical behavior of antiferromagnetic and ferromagnetic magnetic response of a metamagnetic system. Finally, a comparison of the findings of this study with previous theoretical and experimental studies is represented and it is shown that a good agreement is found with our results.

  1. Giant spin gap and magnon localization in the disordered Heisenberg antiferromagnet Sr2Ir1 -xRuxO4

    NASA Astrophysics Data System (ADS)

    Cao, Yue; Liu, X.; Xu, Wenhu; Yin, Wei-Guo; Meyers, D.; Kim, Jungho; Casa, Diego; Upton, M. H.; Gog, Thomas; Berlijn, Tom; Alvarez, Gonzalo; Yuan, Shujuan; Terzic, Jasminka; Tranquada, J. M.; Hill, John P.; Cao, Gang; Konik, Robert M.; Dean, M. P. M.

    2017-03-01

    We study the evolution of magnetic excitations in the disordered two-dimensional antiferromagnet Sr2Ir1 -xRuxO4 . The maximum energy of the magnetic excitation remains robust up to x =0.77 , with a gap opening at low dopings and increasing to over 150 meV at x =0.77 . At these higher Ru concentrations, the dispersive magnetic excitations in Sr2IrO4 are rendered essentially momentum independent. Up to a Ru concentration of x =0.77 , both experiments and first-principles calculations show the Ir Jeff=1 /2 state remains intact. The magnetic gap arises from the local interaction anisotropy in the proximity of the Ru disorder. Under the coherent potential approximation, we reproduce the experimental magnetic excitations using the disordered Heisenberg antiferromagnetic model with suppressed next-nearest-neighbor ferromagnetic coupling.

  2. Giant spin gap and magnon localization in the disordered Heisenberg antiferromagnet Sr2Ir1-xRuxO4

    DOE PAGES

    Cao, Yue; Liu, X.; Xu, Wenhu; ...

    2017-03-06

    Here, we study the evolution of magnetic excitations in the disordered two-dimensional antiferromagnet Sr2Ir1–xRuxO4. The maximum energy of the magnetic excitation remains robust up to x = 0.77, with a gap opening at low dopings and increasing to over 150 meV at x = 0.77. At these higher Ru concentrations, the dispersive magnetic excitations in Sr2IrO4 are rendered essentially momentum independent. Up to a Ru concentration of x = 0.77, both experiments and first-principles calculations show the Ir Jeff = 1/2 state remains intact. The magnetic gap arises from the local interaction anisotropy in the proximity of the Ru disorder.more » Under the coherent potential approximation, we reproduce the experimental magnetic excitations using the disordered Heisenberg antiferromagnetic model with suppressed next-nearest-neighbor ferromagnetic coupling.« less

  3. Temperature and magnetic field dependence of spin-ice correlations in the pyrochlore magnet Tb2Ti2O7

    NASA Astrophysics Data System (ADS)

    Fritsch, K.; Kermarrec, E.; Ross, K. A.; Qiu, Y.; Copley, J. R. D.; Pomaranski, D.; Kycia, J. B.; Dabkowska, H. A.; Gaulin, B. D.

    2014-07-01

    We present a parametric study of the diffuse magnetic scattering at (1/2,1/2,1/2) positions in reciprocal space, ascribed to a frozen antiferromagnetic spin ice state in single-crystalline Tb2Ti2O7. Our high-resolution neutron scattering measurements show that the elastic (-0.02 meV correlates with the opening of a spin gap of ≈0.06 to 0.08 meV over most of the Brillouin zone. The nature of the transition at 275 mK has many characteristics of spin glass behavior, consistent with ac-susceptibility measurements. The application of a magnetic field of 0.075 T applied along the [11¯0] direction destroys the (1/2,1/2,1/2) elastic scattering, revealing the fragility of this short-range ordered ground state. We construct a refined H-T phase diagram for Tb2Ti2O7 and [11¯0] fields which incorporates this frozen spin ice regime and the antiferromagnetic long-range order previously known to be induced in relatively large fields. Specific heat measurements on the same crystal reveal a sharp anomaly at Tc≈ 450 mK and no indication of a transition near ≈275 mK. We conclude that the higher temperature specific heat peak is not related to the magnetic ordering but is likely a signal of other, nonmagnetic dipole correlations.

  4. Propagation of nonclassical correlations across a quantum spin chain

    SciTech Connect

    Campbell, S.; Apollaro, T. J. G.; Di Franco, C.; Banchi, L.; Cuccoli, A.; Vaia, R.; Plastina, F.; Paternostro, M.

    2011-11-15

    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.

  5. Quasiclassical magnetic order and its loss in a spin-1/2 Heisenberg antiferromagnet on a triangular lattice with competing bonds

    NASA Astrophysics Data System (ADS)

    Li, P. H. Y.; Bishop, R. F.; Campbell, C. E.

    2015-01-01

    We use the coupled cluster method (CCM) to study the zero-temperature ground-state (GS) properties of a spin-1/2 J1-J2 Heisenberg antiferromagnet on a triangular lattice with competing nearest-neighbor and next-nearest-neighbor exchange couplings J1>0 and J2≡κ J1>0 , respectively, in the window 0 ≤κ <1 . The classical version of the model has a single GS phase transition at κcl=1/8 in this window from a phase with 3-sublattice antiferromagnetic (AFM) 120∘ Néel order for κ <κcl to an infinitely degenerate family of 4-sublattice AFM Néel phases for κ >κcl . This classical accidental degeneracy is lifted by quantum fluctuations, which favor a 2-sublattice AFM striped phase. For the quantum model we work directly in the thermodynamic limit of an infinite number of spins, with no consequent need for any finite-size scaling analysis of our results. We perform high-order CCM calculations within a well-controlled hierarchy of approximations, which we show how to extrapolate to the exact limit. In this way we find results for the case κ =0 of the spin-1/2 model for the GS energy per spin, E /N =-0.5521 (2 ) J1 , and the GS magnetic order parameter, M =0.198 (5 ) (in units where the classical value is Mcl=1/2), which are among the best available. For the spin-1/2 J1-J2 model we find that the classical transition at κ =κcl is split into two quantum phase transitions at κ1c=0.060 (10 ) and κ2c=0.165 (5 ) . The two quasiclassical AFM states (viz., the 120∘ Néel state and the striped state) are found to be the stable GS phases in the regime κ <κ1c and κ >κ2c , respectively, while in the intermediate regimes κ1c<κ <κ2c the stable GS phase has no evident long-range magnetic order.

  6. Correlation inequalities for quantum spin systems with quenched centered disorder

    NASA Astrophysics Data System (ADS)

    Contucci, Pierluigi; Lebowitz, Joel L.

    2010-02-01

    It is shown that random quantum spin systems with centered disorder satisfy correlation inequalities previously proved [P. Contucci and J. Lebowitz, Ann. Henri Poincare 8, 1461 (2007)] in the classical case. Consequences include monotone approach of pressure and ground state energy to the thermodynamic limit. Signs and bounds on the surface pressures for different boundary conditions are also derived for finite range potentials.

  7. Influence of spin correlations on band structure of magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Sinkkonen, J.

    1981-06-01

    A perturbation treatment of the s-f interaction in ferromagnetic semiconductors is presented. The many-spin correlation functions are expressed in terms of connected correlation functions which are constructed by the meanfield theory. For the self-energy an integral equation is obtained which includes correlation effects. The method of calculation is closely connected with the coherent-potential approximation. As an application the density of states is shown in various cases by allowing the bandwidth to vary from broad- to narrow-band regime. The calculation is limited to the paramagnetic phase. Correlation effects are seen as temperature-dependent changes in the density of states.

  8. Numerical evidence for a chiral spin liquid in the XXZ antiferromagnetic Heisenberg model on the kagome lattice at m =2/3 magnetization

    NASA Astrophysics Data System (ADS)

    Kumar, Krishna; Changlani, Hitesh J.; Clark, Bryan K.; Fradkin, Eduardo

    2016-10-01

    We perform an exact-diagonalization study of the spin-1/2 XXZ Heisenberg antiferromagnet on the kagome lattice at finite magnetization m =2/3 with an emphasis on the X Y point (Jz=0 ) and in the presence of a small chiral term. Recent analytic work by Kumar et al. [K. Kumar, K. Sun, and E. Fradkin, Phys. Rev. B 90, 174409 (2014), 10.1103/PhysRevB.90.174409] on the same model, using a newly developed flux attachment transformation, predicts a plateau at this value of the magnetization described by a chiral spin liquid (CSL) with a spin Hall conductance of σx y=1/2 . Such a state is topological in nature, has a ground-state degeneracy, and exhibits fractional excitations. We analyze the degeneracy structure in the low-energy manifold, identify the candidate topological states, and use them to compute the modular matrices and Chern numbers, all of which strongly agree with expected theoretical behavior for the σx y=1/2 CSL. In the limit of zero chirality, we find on most (not all) clusters that the topological invariants are still those of a CSL.

  9. Magnetic Excitations and Electronic Interactions in Sr2 CuTeO6 : A Spin-1 /2 Square Lattice Heisenberg Antiferromagnet

    NASA Astrophysics Data System (ADS)

    Babkevich, P.; Katukuri, Vamshi M.; Fâk, B.; Rols, S.; Fennell, T.; Pajić, D.; Tanaka, H.; Pardini, T.; Singh, R. R. P.; Mitrushchenkov, A.; Yazyev, O. V.; Rønnow, H. M.

    2016-12-01

    Sr2 CuTeO6 presents an opportunity for exploring low-dimensional magnetism on a square lattice of S =1 /2 Cu2 + ions. We employ ab initio multireference configuration interaction calculations to unravel the Cu2 + electronic structure and to evaluate exchange interactions in Sr2 CuTeO6 . The latter results are validated by inelastic neutron scattering using linear spin-wave theory and series-expansion corrections for quantum effects to extract true coupling parameters. Using this methodology, which is quite general, we demonstrate that Sr2 CuTeO6 is an almost ideal realization of a nearest-neighbor Heisenberg antiferromagnet but with relatively weak coupling of 7.18(5) meV.

  10. Pressure-induced superconductivity in the antiferromagnet κ - (ET) 2C F3S O3 with quasi-one-dimensional triangular spin lattice

    NASA Astrophysics Data System (ADS)

    Ito, Hiroshi; Asai, Takayuki; Shimizu, Yasuhiro; Hayama, Hiromi; Yoshida, Yukihiro; Saito, Gunzi

    2016-07-01

    We report an antiferromagnetic (AF) ordering at ambient pressure and a superconducting transition under pressure for κ - (ET) 2C F3S O3 [ ET =bis (ethylenedithio)tetrathiafulvalene], which has a two-dimensional electronic system with quasi-one-dimensional triangular spin lattice. At ambient pressure, AF ordering was detected at TN=2.5 K by 1H NMR, subsequent to two structural phase transitions at 230 and 190 K. Under hydrostatic pressures, metallic behavior appeared above ˜1.1 GPa, and a superconducting transition (maximum onset Tc=4.8 K at ˜1.3 GPa) was observed up to 2.2 GPa. Superconductivity was also found under c -axis strain, which reduced t'/t , but was absent under b -axis strain which increased t'/t .

  11. The quantum spin-1/2 J1-J2 antiferromagnet on a stacked square lattice: a study of effective-field theory in a finite cluster.

    PubMed

    Nunes, Wagner A; de Sousa, J Ricardo; Viana, J Roberto; Richter, J

    2010-04-14

    The ground state phase diagram of the quantum spin-1/2 Heisenberg antiferromagnet in the presence of nearest-neighbor (J(1)) and next-nearest-neighbor (J(2)) interactions (J(1)-J(2) model) on a stacked square lattice, where we introduce an interlayer coupling through nearest-neighbor bonds of strength J(), is studied within the framework of the differential operator technique. The Hamiltonian is solved by effective-field theory in a cluster with N=4 spins (EFT-4). We obtain the sublattice magnetization m(A) for the ordered phases: antiferromagnetic (AF) and collinear (CAF-collinear antiferromagnetic). We propose a functional for the free energy Ψ(μ)(m(μ)) (μ=A, B) to obtain the phase diagram in the λ-α plane, where λ=J()/J(1) and α=J(2)/J(1). Depending on the values of λ and α, we found different ordered states (AF and CAF) and a disordered state (quantum paramagnetic (QP)). For an intermediate region α(1c)(λ) < α < α(2c)(λ) we observe a QP phase that disappears for λ below some critical value λ(1)≈0.67. For α < α(1c)(λ) and α > α(2c)(λ), and below λ(1), we have the AF and CAF semi-classically ordered states, respectively. At α=α(1c)(λ) a second-order transition between the AF and QP states occurs and at α=α(2c)(λ) a first-order transition between the AF and CAF phases takes place. The boundaries between these ordered phases merge at the critical end point CEP≡(λ(1), α(c)), where α(c)≈0.56. Above this CEP there is again a direct first-order transition between the AF and CAF phases, with a behavior described by the point α(c) independent of λ ≥ λ(1).

  12. A two-dimensional iron(II) carboxylate linear chain polymer that exhibits a metamagnetic spin-canted antiferromagnetic to single-chain magnetic transition.

    PubMed

    Zheng, Yan-Zhen; Xue, Wei; Tong, Ming-Liang; Chen, Xiao-Ming; Grandjean, Fernande; Long, Gary J

    2008-05-19

    A two-dimensional iron(II) carboxylate coordination polymer, [Fe(pyoa)2]infinity, where pyoa is 2-(pyridin-3-yloxy)acetate, has been prepared by hydrothermal synthesis. Its crystal structure reveals a single iron(II) site with an elongated octahedral coordination environment containing four equatorial carboxylate oxygens and two axial pyridyl nitrogens; the iron(II) sites are linked by syn-anti micro-carboxylates to form chains along the b axis that have an Fe...Fe separation of 4.910 A. The shortest interchain and interlayer Fe...Fe distances are 6.453 and 11.125 A, respectively. The 4.2-295 K Mössbauer spectra of [Fe(pyoa) 2] infinity consist of a single paramagnetic high-spin iron(II) quadrupole doublet. The axial Fe-N bond direction defines the Jahn-Teller axis at an iron(II) site and, consequently, the orientation of the single-ion magnetic anisotropy. Thus, along the b axis in a given chain, the spins are collinear and parallel to the Jahn-Teller axis. The Jahn-Teller axes of adjacent intralayer chains have different orientations with an angle of 79.2 degrees between the axes in adjacent chains in a bc layer. [Fe(pyoa)2]infinity exhibits field-induced metamagnetic behavior such that, in an applied field smaller than the critical field, the iron(II) spin-canted moments experience intrachain ferromagnetic interactions and weak interchain antiferromagnetic interactions; the spin canting yields weak ferromagnetism. In an applied field larger than the critical field, the weak antiferromagnetic interchain interactions are overwhelmed to yield superparamagnetic-like slow-magnetic relaxation with an energy barrier of 23(3) K. Single-crystal magnetic studies reveal a quasi-uniaxial magnetic anisotropy with the a axis as the easy-magnetic axis and the b axis as the hard-magnetic axis; the susceptibility measured along the easy a axis may be fit with the Glauber model to yield an effective intrachain exchange coupling constant of 2.06(8) K. A dynamic analysis of the

  13. Role of correlations in spin-polarized neutron matter

    NASA Astrophysics Data System (ADS)

    Vidaña, Isaac; Polls, Artur; Durant, Victoria

    2016-11-01

    Background: The possible existence of a phase transition to a ferromagnetic state in neutron matter as origin of the extremely high magnetic fields of neutron stars is still an open issue. Whereas many phenomenological interactions predict this transition at densities accessible in neutron stars, microscopic calculations based on realistic interactions show no indication of it. The existence or non-existence of this transition is a consequence of the different role of nucleon-nucleon correlations in polarized and unpolarized neutron matter. Therefore, to give a definite answer to this issue it is necessary to analyze the behavior of these correlations. Purpose: 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 with the purpose of identifying the nature and role of correlations in polarized and unpolarized neutron matter. Methods: The analysis is performed within the microscopic Brueckner-Hartree-Fock approach using the Argonne V18 realistic potential plus the Urbana IX three-body force. Results: Our results show no indication of a ferromagnetic transition as the spin symmetry energy of neutron matter is always an increasing function of density. They show also that the main contribution to it comes from the S =0 channel, acting only in non-polarized neutron matter, in particular from the 1S0 and the 1D2 partial waves. Three-body forces are found to play a secondary role in the determination of the spin symmetry energy. Conclusions: By evaluating the kinetic energy difference between the correlated system and the underlying Fermi sea to estimate the importance of correlations in spin-polarized neutron matter, we conclude that non-polarized neutron matter is more correlated than totally polarized one.

  14. Correlation between spin structure oscillations and domain wall velocities

    PubMed Central

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

    2013-01-01

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

  15. Correlation between spin structure oscillations and domain wall velocities.

    PubMed

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

    2013-01-01

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

  16. Correlations and dynamics of spins in an XY-like spin-glass (N i0.4M n0.6) Ti O3 single-crystal system

    NASA Astrophysics Data System (ADS)

    Solanki, R. S.; Hsieh, S.-H.; Du, C. H.; Deng, G.; Wang, C. W.; Gardner, J. S.; Tonomoto, H.; Kimura, T.; Pong, W. F.

    2017-01-01

    Elastic and inelastic neutron scattering (ENS and INS) experiments were performed on a single crystal of (N i0.4M n0.6) Ti O3 (NMTO) to study the spatial correlations and dynamics of spins in the XY-like spin-glass (SG) state. Magnetization measurements reveal signatures of SG behavior in NMTO with a freezing temperature of TSG˜9.1 K . The ENS experiments indicate that the intensity of magnetic diffuse scattering starts to increase around 12 K, which is close to TSG. Also, spin-spin correlation lengths (ξ ) at 1.5 K are approximately (21 ±1 ) and (73 ±2 )Å in the interlayer and the in-plane directions, respectively, demonstrating that magnetic correlations in NMTO exhibit quasi-two-dimensional antiferromagnetic order. In addition, critical exponent (β ) is determined to be 0.37 ±0.02 from the intensity of magnetic diffuse scattering confirms the XY-like SG state of NMTO. INS results show quasielastic neutron scattering (QENS) profiles below TSG. The lifetime of dynamic correlations τ ˜ℏ /ΓL , obtained from the half-width at half-maximum of the Lorentzian (ΓL) QENS profiles, are approximately (16 ±1 ) and (16 ±2 ) ps at 10 K for two positions (0.00, 0.00, 1.52) and (0.01, 0.01, 1.50), respectively. Therefore, our experimental findings demonstrate that short-range-ordered antiferromagnetic clusters with short-lived spin correlations are present in the XY-like SG state of NMTO.

  17. Effects of coexisting spin disorder and antiferromagnetism on the magnetic behavior of nanostructured (Fe{sub 79}Mn{sub 21}){sub 1−x}Cu{sub x} alloys

    SciTech Connect

    Mizrahi, M. E-mail: cabrera@fisica.unlp.edu.ar; Cabrera, A. F. E-mail: cabrera@fisica.unlp.edu.ar; Desimoni, J.; Stewart, S. J.

    2014-06-07

    We report a magnetic study on nanostructured (Fe{sub 79}Mn{sub 21}){sub 1−x}Cu{sub x} (0.00 ≤ x ≤ 0.30) alloys using static magnetic measurements. The alloys are mainly composed by an antiferromagnetic fcc phase and a disordered region that displays a spin-glass-like behavior. The interplay between the antiferromagnetic and magnetically disordered phases establishes an exchange anisotropy that gives rise to a loop shift at temperatures below the freezing temperature of moments belonging to the disordered region. The loop shift is more noticeable as the Cu content increases, which also enhances the spin-glass-like features. Further, in the x = 0.30 alloy the alignment imposed by applied magnetic fields higher than 4 kOe prevail over the configuration determined by the frustration mechanism that characterizes the spin glass-like phase.

  18. Triangular Spin-Orbit-Coupled Lattice with Strong Coulomb Correlations: Sn Atoms on a SiC(0001) Substrate.

    PubMed

    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.

  19. Spin Disorder and Order in Quasi-2D Triangular Heisenberg Antiferromagnets: Comparative Study of FeGa2S4, Fe2Ga2S5, and NiGa2S4

    NASA Astrophysics Data System (ADS)

    Nakatsuji, S.; Tonomura, H.; Onuma, K.; Nambu, Y.; Sakai, O.; Maeno, Y.; Macaluso, R. T.; Chan, Julia Y.

    2007-10-01

    Our single crystal study reveals that the single-layer S=2 triangular Heisenberg antiferromagnet FeGa2S4 forms a frozen spin-disordered state, similar to the S=1 isostructural magnet NiGa2S4. In this state, the magnetic specific heat CM is not only insensitive to the field, but shows a T2 dependence that scales to CM of NiGa2S4, suggesting the same underlying mechanism of the 2D coherent behavior. In contrast, the bilayer system Fe2Ga2S5 exhibits a 3D antiferromagnetic order.

  20. Frustrated spin correlations in diluted spin ice Ho2-xLaxTi2O7

    SciTech Connect

    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.

  1. Electron spin polarization transfer from photogenerated spin-correlated radical pairs to a stable radical observer spin.

    PubMed

    Colvin, Michael T; Carmieli, Raanan; Miura, Tomoaki; Richert, Sabine; Gardner, Daniel M; Smeigh, Amanda L; Dyar, Scott M; Conron, Sarah M; Ratner, Mark A; Wasielewski, Michael R

    2013-06-27

    A series of donor-chromophore-acceptor-stable radical (D-C-A-R(•)) molecules having well-defined molecular structures were synthesized to study the factors affecting electron spin polarization transfer from the photogenerated D(+•)-C-A(-•) spin-correlated radical pair (RP) to the stable radical R(•). Theory suggests that the magnitude of this transfer depends on the spin-spin exchange interaction (2JDA) of D(+•)-C-A(-•). Yet, the generality of this prediction has never been demonstrated. In the D-C-A-R(•) molecules described herein, D is 4-methoxyaniline (MeOAn), 2,3-dihydro-1,4-benzodioxin-6-amine (DioxAn), or benzobisdioxole aniline (BDXAn), C is 4-aminonaphthalene-1,8-dicarboximide, and A is naphthalene-1,8:4,5-bis(dicarboximide) (1A,B-3A,B) or pyromellitimide (4A,B-6A,B). The terminal imide of the acceptors is functionalized with either a hydrocarbon (1A-6A) or a 2,2,6,6-tetramethyl-1-piperidinyloxyl radical (R(•)) (1B-6B). Photoexcitation of C with 416-nm laser pulses results in two-step charge separation to yield D(+•)-C-A(-•)-(R(•)). Time-resolved electron paramagnetic resonance (TREPR) spectroscopy using continuous-wave (CW) microwaves at both 295 and 85 K and pulsed microwaves at 85 K (electron spin-echo detection) was used to probe the initial formation of the spin-polarized RP and the subsequent polarization of the attached R(•) radical. The TREPR spectra show that |2JDA| for D(+•)-C-A(-•) decreases in the order MeOAn(+•) > DioxAn(+•) > BDXAn(+•) as a result of their spin density distributions, whereas the spin-spin dipolar interaction (dDA) remains nearly constant. Given this systematic variation in |2JDA|, electron spin-echo-detected EPR spectra of 1B-6B at 85 K show that the magnitude of the spin polarization transferred from the RP to R(•) depends on |2JDA|.

  2. Pressure effect on the competition between ferromagnetic and antiferromagnetic spin fluctuations in TmTe investigated by 125Te-NMR

    NASA Astrophysics Data System (ADS)

    Yamamoto, A.; Wada, S.; Matsumura, T.

    2007-03-01

    To elucidate from a microscopic point of view the initial evolution of spin fluctuations in TmTe from the semiconducting state at ambient pressure with an antiferroquadrupole ordering (TQ=1.8 K) to the intermediate-valence metallic state at high pressures P⩾2 GPa with a ferromagnetic (FM) ordering (TC≃14 K), we have carried out 125Te-NMR study at pressures P=0 and 0.9 GPa. The spin-lattice relaxation rate measurements revealed a pronounced increase of the staggered susceptibility below T*≃14 K, in addition to the Curie-Weiss-type increase of the uniform susceptibility. Below ˜T*, a wipe-out decrease of the NMR intensity and the finding of an unconventional NMR signal around ˜10 MHz that is insensitive to applied field lead to the conclusion that a field-induced short-range FM ordering caused by the competition of FM and antiferromagnetic fluctuations takes place. Pressure of 0.9 GPa hardly affects the anomalous NMR behaviors below ˜T*, leading to speculate that the short-range FM ordering in the semiconducting state shares the origin with the long-range FM ordering at ≃14 K in the high-pressure metallic state.

  3. Correlating spin transport and electrode magnetization in a graphene spin valve: Simultaneous magnetic microscopy and non-local measurements

    SciTech Connect

    Berger, Andrew J. Page, Michael R.; Bhallamudi, Vidya P.; Chris Hammel, P.; Wen, Hua; Kawakami, Roland K.; McCreary, Kathleen M.

    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.

  4. Generalized parton correlation functions for a spin-0 hadron

    SciTech Connect

    Meissner, Stephan; Metz, Andreas; Schlegel, Marc; Goeke, Klaus

    2008-08-01

    The fully unintegrated, off-diagonal quark-quark correlator for a spin-0 hadron is parameterized in terms of so-called generalized parton correlation functions. Such objects are of relevance for the phenomenology of certain hard exclusive reactions. In particular, they 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. As a by-product we obtain the first complete classification of generalized parton distributions beyond leading twist.

  5. Antiferromagnetic spin fluctuations and unconventional nodeless superconductivity in an iron-based new superconductor (Ca4Al2O(6-y))(Fe2As2): 75As nuclear quadrupole resonance study.

    PubMed

    Kinouchi, H; Mukuda, H; Yashima, M; Kitaoka, Y; Shirage, P M; Eisaki, H; Iyo, A

    2011-07-22

    We report 75As nuclear quadrupole resonance studies on (Ca4Al2O(6-y))(Fe2As2) with T(c) = 27  K. Measurement of nuclear-spin-relaxation rate 1/T1 has revealed a significant development of two-dimensional antiferromagnetic spin fluctuations down to T(c) in association with the smallest As-Fe-As bond angle. Below T(c), the temperature dependence of 1/T1 without any trace of the coherence peak is well accounted for by a nodeless s(±)-wave multiple-gaps model. From the fact that its T(c) is comparable to T(c) = 28  K in the optimally doped LaFeAsO(1-y) in which antiferromagnetic spin fluctuations are not dominant, we remark that antiferromagnetic spin fluctuations are not a unique factor for enhancing T(c) among Fe-based superconductors, but a condition for optimizing superconductivity should be addressed from the lattice structure point of view.

  6. Distinct itinerant spin-density waves and local-moment antiferromagnetism in an intermetallic ErPd2Si2 single crystal

    PubMed Central

    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

  7. Huge positive magnetoresistance in antiferromagnetic double perovskite metals.

    PubMed

    Singh, Viveka Nand; Majumdar, Pinaki

    2014-07-23

    Metals with large positive magnetoresistance are rare. We demonstrate that antiferromagnetic metallic states, as have been predicted for the double perovskites, are excellent candidates for huge positive magnetoresistance. An applied field suppresses long range antiferromagnetic order leading to a state with short range antiferromagnetic correlations and strong electronic scattering. The field induced resistance ratio can be more than tenfold, at moderate field, in a structurally ordered system, and continues to be almost twofold even in systems with ∼ 25% antisite disorder. Although our explicit demonstration is in the context of a two- dimensional spin-fermion model of the double perovskites, the mechanism we uncover is far more general, complementary to the colossal negative magnetoresistance process, and would operate in other local moment metals that show a field driven suppression of non-ferromagnetic order.

  8. Unveiling the origin of the basal-plane antiferromagnetism in the spin-orbit Mott insulator Ba2IrO4: a density functional and model Hamiltonian study

    NASA Astrophysics Data System (ADS)

    Hou, Y. S.; Xiang, H. J.; Gong, X. G.

    2016-04-01

    Based on the density functional theory and model Hamiltonian, we studied the basal-plane antiferromagnetism in the spin-orbit Mott insulator Ba2IrO4. By comparing the magnetic properties of the bulk Ba2IrO4 with those of the single-layer Ba2IrO4, we demonstrate unambiguously that the basal-plane antiferromagnetism is caused by the intralyer magnetic interactions rather than by the previously proposed interlayer ones. Aiming at revealing the origin of the basal-plane antiferromagnetism, we add the single ion anisotropy and pseudo-quadrupole interactions into the general bilinear pseudo-spin Hamiltonian. The obtained magnetic interaction parameters indicate that the single ion anisotropy and pseudo-quadrupole interactions are unexpectedly strong. Systematical Monte Carlo simulations demonstrate that the basal-plane antiferromagnetism is caused by isotropic Heisenberg, bond-dependent Kitaev and pseudo-quadrupole interactions. On the basis of this study the single ion anisotropy and pseudo-quadrupole interactions could play a role in explaining magnetic interactions in other iridates.

  9. Towards spin-polarized two-dimensional electron gas at a surface of an antiferromagnetic insulating oxide

    NASA Astrophysics Data System (ADS)

    Mishra, Rohan; Kim, Young-Min; He, Qian; Huang, Xing; Kim, Seong Keun; Susner, Michael A.; Bhattacharya, Anand; Fong, Dillon D.; Pantelides, Sokrates T.; Borisevich, Albina Y.

    2016-07-01

    The surfaces of transition-metal oxides with the perovskite structure are fertile grounds for the discovery of novel electronic and magnetic phenomena. In this article, we combine scanning transmission electron microscopy (STEM) with density functional theory (DFT) calculations to obtain the electronic and magnetic properties of the (001) surface of a (LaFeO3) 8/(SrFeO3) 1 superlattice film capped with four layers of LaFe O3 . Simultaneously acquired STEM images and electron-energy-loss spectra reveal the surface structure and a reduction in the oxidation state of iron from F e3 + in the bulk to F e2 + at the surface, extending over several atomic layers, which signals the presence of oxygen vacancies. The DFT calculations confirm the reduction in terms of oxygen vacancies and further demonstrate the stabilization of an exotic phase in which the surface layer is half metallic and ferromagnetic, while the bulk remains antiferromagnetic and insulating. Based on the calculations, we predict that the surface magnetism and conductivity can be controlled by tuning the partial pressure of oxygen.

  10. Towards spin-polarized two-dimensional electron gas at a surface of an antiferromagnetic insulating oxide

    SciTech Connect

    Mishra, Rohan; Kim, Young -Min; He, Qian; Huang, Xing; Kim, Seong Keun; Susner, Michael A.; Bhattacharya, Anand; Fong, Dillon D.; Pantelides, Sokrates T.; Borisevich, Albina Y.

    2016-07-18

    Here, the surfaces of transition-metal oxides with the perovskite structure are fertile grounds for the discovery of novel electronic and magnetic phenomena. In this article, we combine scanning transmission electron microscopy (STEM) with density functional theory (DFT) calculations to obtain the electronic and magnetic properties of the (001) surface of a (LaFeO3)8/(SrFeO3)1 superlattice film capped with four layers of LaFeO3. Simultaneously acquired STEM images and electron-energy-loss spectra reveal the surface structure and a reduction in the oxidation state of iron from Fe3+ in the bulk to Fe2+ at the surface, extending over several atomic layers, which signals the presence of oxygen vacancies. The DFT calculations confirm the reduction in terms of oxygen vacancies and further demonstrate the stabilization of an exotic phase in which the surface layer is half metallic and ferromagnetic, while the bulk remains antiferromagnetic and insulating. Based on the calculations, we predict that the surface magnetism and conductivity can be controlled by tuning the partial pressure of oxygen.

  11. Towards spin-polarized two-dimensional electron gas at a surface of an antiferromagnetic insulating oxide

    DOE PAGES

    Mishra, Rohan; Kim, Young -Min; He, Qian; ...

    2016-07-18

    Here, the surfaces of transition-metal oxides with the perovskite structure are fertile grounds for the discovery of novel electronic and magnetic phenomena. In this article, we combine scanning transmission electron microscopy (STEM) with density functional theory (DFT) calculations to obtain the electronic and magnetic properties of the (001) surface of a (LaFeO3)8/(SrFeO3)1 superlattice film capped with four layers of LaFeO3. Simultaneously acquired STEM images and electron-energy-loss spectra reveal the surface structure and a reduction in the oxidation state of iron from Fe3+ in the bulk to Fe2+ at the surface, extending over several atomic layers, which signals the presence ofmore » oxygen vacancies. The DFT calculations confirm the reduction in terms of oxygen vacancies and further demonstrate the stabilization of an exotic phase in which the surface layer is half metallic and ferromagnetic, while the bulk remains antiferromagnetic and insulating. Based on the calculations, we predict that the surface magnetism and conductivity can be controlled by tuning the partial pressure of oxygen.« less

  12. Exploring the correlated phase behavior and electronic properties of parent and doped spin-orbit Mott phases

    NASA Astrophysics Data System (ADS)

    Wilson, Stephen

    2014-03-01

    An unusual manifestation of Mott physics dependent on strong spin-orbit interactions has recently been identified in a growing number of classes of 5d transition metal oxides built from Ir4+ ions. Instead of the naively expected increased itinerancy of these iridates due to the larger orbital extent of their 5d valence electrons, the interplay between the amplified relativistic spin-orbit interaction (intrinsic to large Z iridium cations) and their residual on-site Coulomb interaction U, conspires to stabilize a novel class of spin-orbit assisted Mott insulators with a proposed Jeff = 1/2 ground state wavefunction. The identification of this novel spin-orbit Mott state has been the focus of recent interest due to its potential of hosting a variety of new phases driven by correlated electron phenomena (such as high temperature superconductivity or enhanced ferroic behavior) in a strongly spin-orbit coupled setting. Currently, however, there remains very little understanding of how spin-orbit Mott phases respond to carrier doping and, more specifically, how relevant U remains for the charge carriers of a spin-orbit Mott phase once the bandwidth is increased. Here I will present our group's recent experimental work exploring carrier doping and the resulting electronic phase behavior in one such spin-orbit driven Mott material, Sr3Ir2O7, with the ultimate goal of determining the relevance of U and electron correlation effects within the doped system's ground state. Our results reveal the stabilization of an electronically phase separated ground state in B-site doped Sr3Ir2O7, suggestive of an extended regime of localization of in-plane doped carriers within the spin-orbit Mott phase. This results in a percolative metal-to-insulator transition with a novel, global, antiferromagnetic order. The electronic response of B-site doping in Sr3Ir2O7will then be compared with recent results exploring A-site doping if time permits. Supported by NSF CAREER Award DMR-1056625.

  13. Randomness-Induced Quantum Spin Liquid Behavior in the s = 1/2 Random J1-J2 Heisenberg Antiferromagnet on the Honeycomb Lattice

    NASA Astrophysics Data System (ADS)

    Uematsu, Kazuki; Kawamura, Hikaru

    2017-04-01

    We investigate the ground-state and finite-temperature properties of the bond-random s = 1/2 Heisenberg model on a honeycomb lattice with frustrated nearest- and next-nearest-neighbor antiferromagnetic interactions, J1 and J2, by the exact diagonalization and the Hams-de Raedt methods. The ground-state phase diagram of the model is constructed in the randomness versus the frustration (J2/J1) plane, with the aim of clarifying the effects of randomness and frustration in stabilizing a variety of distinct phases. We find that the randomness induces the gapless quantum spin liquid (QSL)-like state, the random-singlet state, in a wide range of parameter space. The observed robustness of the random-singlet state suggests that the gapless QSL-like behaviors might be realized in a wide class of frustrated quantum magnets possessing a certain amount of randomness or inhomogeneity, without fine-tuning the interaction parameters. Possible implications to recent experiments on the honeycomb-lattice magnets Ba3CuSb2O9 and 6HB-Ba3NiSb2O9 exhibiting the gapless QSL-like behaviors are discussed.

  14. TheS=1/2 Heisenberg antiferromagnet on the triangular lattice: Exact results and spin-wave theory for finite cells

    NASA Astrophysics Data System (ADS)

    Deutscher, R.; Everts, H. U.

    1993-03-01

    We study the ground state properties of the S=$\\frac{1}{2}$ Heisenberg antiferromagnet (HAF) on the triangular lattice with nearest-neighbour ($J$) and next-nearest neighbour ($\\alpha J$) couplings. Classically, this system is known to be ordered in a $120^\\circ$ N\\'eel type state for values $-\\infty<\\alpha\\le 1/8$ of the ratio $\\alpha$ of these couplings and in a collinear state for $1/8<\\alpha<1$. The order parameter ${\\cal M}$ and the helicity $\\chi$ of the $120^\\circ$ structure are obtained by numerical diagonalisation of finite periodic systems of up to $N=30$ sites and by applying the spin-wave (SW) approximation to the same finite systems. We find a surprisingly good agreement between the exact and the SW results in the entire region $-\\infty<\\alpha< 1/8$. It appears that the SW theory is still valid for the simple triangular HAF ($\\alpha=0$) although the sublattice magnetisation ${\\cal M}$ is substantially reduced from its classical value by quantum fluctuations. Our numerical results for the order parameter ${\\cal N}$ of the collinear order support the previous conjecture of a first order transition between the $120^\\circ$ and the collinear order at $\\alpha \\simeq 1/8$.

  15. Investigation of short range charge and spin correlation in Pr{sub 0.67}Ca{sub 0.33}MnO{sub 3} nanoparticles

    SciTech Connect

    Shukla, Vinay Kumar Mukhopadhyay, Soumik

    2015-06-24

    The particle size effects on charge and spin correlation were studied for Pr{sub 0.67}Ca{sub 0.33}MnO{sub 3}(PCMO) by Electron Paramagnetic Resonance spectroscopy. Magnetization measurements suggests long range charge/orbital ordering (CO/OO) in bulk Pr{sub 0.67}Ca{sub 0.33}MnO{sub 3} at T ∼230 K and antiferromagnetic (AFM) ordering at T∼140K. With the reduction of particle size, CO is suppressed, AFM ordering gives way to ferromagnetic (FM) ordering. We find that with the reduction of particle size in Pr{sub 0.67}Ca{sub 0.33}MnO{sub 3} nanoparticles, the short range correlation in charge and associated spin degrees of freedom also gets suppressed.

  16. Spin-flip configuration interaction singles with exact spin-projection: Theory and applications to strongly correlated systems

    SciTech Connect

    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.

  17. Spin-flip configuration interaction singles with exact spin-projection: Theory and applications to strongly correlated systems

    NASA Astrophysics Data System (ADS)

    Tsuchimochi, Takashi

    2015-10-01

    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.

  18. Numerical study of magnetization plateaus in the spin-1/2 Heisenberg antiferromagnet on the checkerboard lattice

    NASA Astrophysics Data System (ADS)

    Capponi, Sylvain

    2017-01-01

    We present numerical evidence that the spin-1/2 Heisenberg model on the two-dimensional checkerboard lattice exhibits several magnetization plateaus for m =0 , 1 /4 , 1 /2 , and 3 /4 , where m is the magnetization normalized by its saturation value. These incompressible states correspond to somewhat similar valence-bond crystal phases that break lattice symmetries, though they are different from the already established plaquette phase for m =0 . Our results are based on exact diagonalization as well as density-matrix renormalization-group large-scale simulations and interpreted in terms of simple parameter-free trial wave functions.

  19. Quantum Disordered State without Frustration in the Double Layer Heisenberg Antiferromagnet —Dimer Expansion and Projector Monte Carlo Study—

    NASA Astrophysics Data System (ADS)

    Hida, Kazuo

    1992-03-01

    The quantum disordered state (QDOS) of the spin 1/2 double layer square lattice Heisenberg antiferromagnet is studied. Using the dimer expansion from the limit of the large interlayer coupling J', the staggered susceptibility χ, the antiferromagnetic structure factor Sπ and the antiferromagnetic correlation length ξ are calculated up to the 6-th order in the intralayer coupling J. The ratio analysis shows that the QDOS becomes unstable against the Néel ordering at J'/J≃2.56. The critical exponents are not inconsistent with the universality class of the 3-dimensional classical Heisenberg model, suggesting that our QDOS corresponds to that expected in the 2-dimensional square lattice Heisenberg antiferromagnet with unphysically small spin (<0.276). The results of the projector Monte Carlo simulation also confirms the dimer expansion results.

  20. Spin-reorientation and weak ferromagnetism in antiferromagnetic TbMn0.5Fe0.5O3

    NASA Astrophysics Data System (ADS)

    Nhalil, Hariharan; Nair, Harikrishnan S.; Sanathkumar, R.; Strydom, André M.; Elizabeth, Suja

    2015-05-01

    Orthorhombic single crystals of TbMn0.5Fe0.5O3 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 TN Fe / Mn = 286 K due to paramagnetic to AxGyCz ordering. A sharp transition is observed at TS R Fe / Mn = 28 K , which is pronounced along c axis in the form of a sharp jump in magnetization where the spins reorient to GxAyFz configuration. The negative magnetization observed below TS R 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. TbMn0.5Fe0.5O3 could be highlighted as a potential candidate to evaluate its magneto-dielectric effects across the magnetic transitions.

  1. Correlated Exciton Transport in Rydberg-Dressed-Atom Spin Chains.

    PubMed

    Schempp, H; Günter, G; Wüster, S; Weidemüller, M; Whitlock, S

    2015-08-28

    We investigate the transport of excitations through a chain of atoms with nonlocal dissipation introduced through coupling to additional short-lived states. The system is described by an effective spin-1/2 model where the ratio of the exchange interaction strength to the reservoir coupling strength determines the type of transport, including coherent exciton motion, incoherent hopping, and a regime in which an emergent length scale leads to a preferred hopping distance far beyond nearest neighbors. For multiple impurities, the dissipation gives rise to strong nearest-neighbor correlations and entanglement. These results highlight the importance of nontrivial dissipation, correlations, and many-body effects in recent experiments on the dipole-mediated transport of Rydberg excitations.

  2. Gapless spin liquid ground state in the S = 1/2 vanadium oxyfluoride kagome antiferromagnet [NH4]2[C7H14N][V7O6F18].

    PubMed

    Clark, L; Orain, J C; Bert, F; De Vries, M A; Aidoudi, F H; Morris, R E; Lightfoot, P; Lord, J S; Telling, M T F; Bonville, P; Attfield, J P; Mendels, P; Harrison, A

    2013-05-17

    The vanadium oxyfluoride [NH(4)](2)[C(7)H(14)N][V(7)O(6)F(18)] (DQVOF) is a geometrically frustrated magnetic bilayer material. The structure consists of S = 1/2 kagome planes of V(4+) d(1) ions with S = 1 V(3+) d(2) ions located between the kagome layers. Muon spin relaxation measurements demonstrate the absence of spin freezing down to 40 mK despite an energy scale of 60 K for antiferromagnetic exchange interactions. From magnetization and heat capacity measurements we conclude that the S = 1 spins of the interplane V(3+) ions are weakly coupled to the kagome layers, such that DQVOF can be viewed as an experimental model for S = 1/2 kagome physics, and that it displays a gapless spin liquid ground state.

  3. Sub-Shot-Noise Magnetometry with a Correlated Spin-Relaxation Dominated Alkali-Metal Vapor

    SciTech Connect

    Kominis, I. K.

    2008-02-22

    Spin noise sets fundamental limits to the precision of measurements using spin-polarized atomic vapors, such as performed with sensitive atomic magnetometers. Spin squeezing offers the possibility to extend the measurement precision beyond the standard quantum limit of uncorrelated atoms. Contrary to current understanding, we show that, even in the presence of spin relaxation, spin squeezing can lead to a significant reduction of spin noise, and hence an increase in magnetometric sensitivity, for a long measurement time. This is the case when correlated spin relaxation due to binary alkali-atom collisions dominates independently acting decoherence processes, a situation realized in thermal high atom-density magnetometers and clocks.

  4. Spin valves based on Mn{sub 75}Ir{sub 25} antiferromagnet with controllable functional parameters

    SciTech Connect

    Milyaev, M. A. Naumova, L. I.; Kamenskii, I. Yu.; Ustinov, V. V.

    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.

  5. Correlation between electron spin resonance spectra and oil yield in eastern oil shales

    USGS Publications Warehouse

    Choudhury, M.; Rheams, K.F.; Harrell, J.W.

    1986-01-01

    Organic free radical spin concentrations were measured in 60 raw oil shale samples from north Alabama and south Tennessee and compared with Fischer assays and uranium concentrations. No correlation was found between spin concentration and oil yield for the complete set of samples. However, for a 13 sample set taken from a single core hole, a linear correlation was obtained. No correlation between spin concentration and uranium concentration was found. ?? 1986.

  6. Spin-Singlet Ground State of Two-Dimensional Quantum Spin Antiferromagnet (CuCl)Ca2Nb3O10

    NASA Astrophysics Data System (ADS)

    Tsujimoto, Yoshihiro; Kitada, Atsushi; Nishi, Masakazu; Narumi, Yasuo; Kindo, Koichi; Goko, Tatsuo; Uemura, Yasutomo J.; Aczel, Adam A.; Williams, Travis J.; Luke, Graeme M.; Ajiro, Yoshitami; Kageyama, Hiroshi

    2014-07-01

    We report structural and magnetic properties of the triple-layered perovskite (CuCl)Ca2Nb3O10 with a spin-1/2 CuCl layer, investigated by transmission electron microscopy, magnetic susceptibility, high-field magnetization, specific heat, µSR, and inelastic neutron scattering measurements. The results show that (CuCl)Ca2Nb3O10 has a spin-singlet ground state with a gap of Δ/kB = 11 K. The observation of a 2 × 2 superstructure suggests a coherent distortion of the CuCl square lattice as in the double-layered (CuCl)LaNb2O7 with Δ/kB = 14 K. The low-temperature magnetization exhibits a jump to saturation above the critical field of Hc = 7.8 T, in marked contrast to the case of (CuCl)LaNb2O7, where the magnetization slowly increases above Hc. The observed magnetic properties are discussed in terms of the ferromagnetic Shastry-Sutherland model.

  7. Antiferromagnetic spin chain behavior and a transition to 3D magnetic order in Cu(D,L-alanine)2: Roles of H-bonds

    NASA Astrophysics Data System (ADS)

    Calvo, Rafael; Sartoris, Rosana P.; Calvo, Hernán L.; Chagas, Edson F.; Rapp, Raul E.

    2016-05-01

    We study the spin chain behavior, a transition to 3D magnetic order and the magnitudes of the exchange interactions for the metal-amino acid complex Cu(D,L-alanine)2•H2O, a model compound to investigate exchange couplings supported by chemical paths characteristic of biomolecules. Thermal and magnetic data were obtained as a function of temperature (T) and magnetic field (B0). The magnetic contribution to the specific heat, measured between 0.48 and 30 K, displays above 1.8 K a 1D spin-chain behavior that can be fitted with an intrachain antiferromagnetic (AFM) exchange coupling constant 2J0=(-2.12±0.08) cm-1 (defined as ℋex(i,i+1) = -2J0SiṡSi+1), between neighbor coppers at 4.49 Å along chains connected by non-covalent and H-bonds. We also observe a narrow specific heat peak at 0.89 K indicating a phase transition to a 3D magnetically ordered phase. Magnetization curves at fixed T = 2, 4 and 7 K with B0 between 0 and 9 T, and at T between 2 and 300 K with several fixed values of B0 were globally fitted by an intrachain AFM exchange coupling constant 2J0=(-2.27±0.02) cm-1 and g = 2.091±0.005. Interchain interactions J1 between coppers in neighbor chains connected through long chemical paths with total length of 9.51 Å cannot be estimated from magnetization curves. However, observation of the phase transition in the specific heat data allows estimating the range 0.1≤|2J1|≤0.4 cm-1, covering the predictions of various approximations. We analyze the magnitudes of 2J0 and 2J1 in terms of the structure of the corresponding chemical paths. The main contribution in supporting the intrachain interaction is assigned to H-bonds while the interchain interactions are supported by paths containing H-bonds and carboxylate bridges, with the role of the H-bonds being predominant. We compare the obtained intrachain coupling with studies of compounds showing similar behavior and discuss the validity of the approximations allowing to calculate the interchain

  8. Field-Induced Multiple Reentrant Quantum Phase Transitions in Randomly Dimerized Antiferromagnetic S=1/2 Heisenberg Chains

    NASA Astrophysics Data System (ADS)

    Hida, Kazuo

    2006-07-01

    The multiple reentrant quantum phase transitions in the S=1/2 antiferromagnetic Heisenberg chains with random bond alternation in the magnetic field are investigated by the density matrix renormalization group method combined with interchain mean field approximation. It is assumed that odd numbered bonds are antiferromagnetic with strength J and even numbered bonds can take the values JS and JW (JS > J > JW > 0) randomly with the probabilities p and 1- p, respectively. The pure version ( p=0 and 1) of this model has a spin gap but exhibits a field-induced antiferromagnetism in the presence of interchain coupling if Zeeman energy due to the magnetic field exceeds the spin gap. For 0 < p < 1, antiferromagnetism is induced by randomness at the small field region where the ground state is disordered due to the spin gap in the pure version. At the same time, this model exhibits randomness-induced plateaus at several values of magnetization. The antiferromagnetism is destroyed on the plateaus. As a consequence, we find a series of reentrant quantum phase transitions between transverse antiferromagnetic phases and disordered plateau phases with the increase of magnetic field for a moderate strength of interchain coupling. Above the main plateaus, the magnetization curve consists of a series of small plateaus and jumps between them. It is also found that antiferromagnetism is induced by infinitesimal interchain coupling at the jumps between the small plateaus. We conclude that this antiferromagnetism is supported by the mixing of low-lying excited states by the staggered interchain mean field even though the spin correlation function is short ranged in the ground state of each chain.

  9. Intrinsic magnetization of antiferromagnetic textures

    NASA Astrophysics Data System (ADS)

    Tveten, Erlend G.; Müller, Tristan; Linder, Jacob; Brataas, Arne

    2016-03-01

    Antiferromagnets (AFMs) exhibit intrinsic magnetization when the order parameter spatially varies. This intrinsic spin is present even at equilibrium and can be interpreted as a twisting of the homogeneous AFM into a state with a finite spin. Because magnetic moments couple directly to external magnetic fields, the intrinsic magnetization can alter the dynamics of antiferromagnetic textures under such influence. Starting from the discrete Heisenberg model, we derive the continuum limit of the free energy of AFMs in the exchange approximation and explicitly rederive that the spatial variation of the antiferromagnetic order parameter is associated with an intrinsic magnetization density. We calculate the magnetization profile of a domain wall and discuss how the intrinsic magnetization reacts to external forces. We show conclusively, both analytically and numerically, that a spatially inhomogeneous magnetic field can move and control the position of domain walls in AFMs. By comparing our model to a commonly used alternative parametrization procedure for the continuum fields, we show that the physical interpretations of these fields depend critically on the choice of parametrization procedure for the discrete-to-continuous transition. This can explain why a significant amount of recent studies of the dynamics of AFMs, including effective models that describe the motion of antiferromagnetic domain walls, have neglected the intrinsic spin of the textured order parameter.

  10. Static and dynamical properties of the spin-1/2 equilateral triangular-lattice antiferromagnet Ba3CoSb2O9

    SciTech Connect

    Ma, Jie; Kamiya, Yoshitomo; Hong, Tao; Cao, H. B.; Ehlers, Georg; Tian, Wei; Batista, C. D.; Dun, Z. L.; Zhou, H. D.; Matsuda, Masaaki

    2016-02-24

    We present single-crystal neutron scattering measurements of the spin-1/2 equilateral triangular-lattice antiferromagnet Ba3CoSb2O9. Besides confirming that the Co2+ magnetic moments lie in the ab plane for zero magnetic field and then determining all the exchange parameters of the minimal quasi-2D spin Hamiltonian, we provide conclusive experimental evidence of magnon decay through observation of intrinsic line broadening. Through detailed comparisons with the linear and nonlinear spin-wave theories, we also point out that the large-S approximation, which is conventionally employed to predict magnon decay in noncollinear magnets, is inadequate to explain our experimental observation. Hence, our results call for a new theoretical framework for describing excitation spectra in low-dimensional frustrated magnets under strong quantum effects.

  11. Remarkably robust and correlated coherence and antiferromagnetism in (Ce1-xLax)Cu2Ge2

    DOE PAGES

    Hodovanets, H.; Bud’ko, S. L.; Straszheim, W. E.; ...

    2015-06-08

    We present magnetic susceptibility, resistivity, specific heat, and thermoelectric power measurements on (Ce1-xLax)Cu2Ge2 single crystals (0 ≤ x ≤ 1). With La-substitution, the antiferromagnetic temperature TN is suppressed in an almost linear fashion and moves below 0.36 K, the base temperature of our measurements for x > 0.8. Surprisingly, in addition to robust antiferromagnetism, the system also shows low temperature coherent scattering below Tcoh up to ~0.9 of La, indicating a small percolation limit ~9% of Ce. Tcoh as a function of magnetic field was found to have different behavior for x < 0.9 and x > 0.9. Remarkably, (Tcoh)2more » at H = 0 was found to be linearly proportional to TN. In conclusion, the jump in the magnetic specific heat δCm at TN as a function of TK/TN for (Ce1-xLax)Cu2Ge2 follows the theoretical prediction based on the molecular field calculation for the S = 1/2 resonant level model.« less

  12. Spin-orbit coupling, strong correlation, and insulator-metal transitions: The Jeff=32 ferromagnetic Dirac-Mott insulator Ba2NaOsO6

    DOE PAGES

    Gangopadhyay, Shruba; Pickett, Warren E.

    2015-01-15

    The double perovskite Ba2NaOsO6 (BNOO), an exotic example of a very high oxidation state (heptavalent) osmium d1 compound and also uncommon by being a ferromagnetic open d-shell (Mott) insulator without Jahn-Teller (JT) distortion, is modeled using a density functional theory based hybrid functional incorporating exact exchange for correlated electronic orbitals and including the large spin-orbit coupling (SOC). The experimentally observed narrow-gap ferromagnetic insulating ground state is obtained, but only when including spin-orbit coupling, making this a Dirac-Mott insulator. The calculated easy axis along [110] is in accord with experiment, providing additional support that this approach provides a realistic method formore » studying this system. The predicted spin density for [110] spin orientation is nearly cubic (unlike for other directions), providing an explanation for the absence of JT distortion. An orbital moment of –0.4μB strongly compensates the +0.5μB spin moment on Os, leaving a strongly compensated moment more in line with experiment. Remarkably, the net moment lies primarily on the oxygen ions. An insulator-metal transition, by rotating the magnetization direction with an external field under moderate pressure, is predicted as one consequence of strong SOC, and metallization under moderate pressure is predicted. In conclusion, a comparison is made with the isostructural, isovalent insulator Ba2LiOsO6, which, however, orders antiferromagnetically.« less

  13. μ SR insight into the impurity problem in quantum kagome antiferromagnets

    NASA Astrophysics Data System (ADS)

    Gomilšek, M.; Klanjšek, M.; Pregelj, M.; Luetkens, H.; Li, Y.; Zhang, Q. M.; Zorko, A.

    2016-07-01

    Impurities, which are unavoidable in real materials, may play an important role in the magnetism of frustrated spin systems with a spin-liquid ground state. We address the impurity issue in quantum kagome antiferromagnets by investigating ZnCu3(OH) 6SO4 (Zn-brochantite) by means of muon spin spectroscopy. We show that muons dominantly couple to impurities, originating from Cu-Zn intersite disorder, and that the impurity spins are highly correlated with the kagome spins, allowing us to probe the host kagome physics via a Kondo-like effect. The low-temperature plateau in the impurity susceptibility suggests that the kagome spin-liquid ground state is gapless. The corresponding spin fluctuations exhibit an unconventional spectral density and a nontrivial field dependence.

  14. Unusual ferromagnetic critical behavior owing to short-range antiferromagnetic correlations in antiperovskite Cu1-xNMn3+x (0.1 ≤ x ≤ 0.4)

    PubMed Central

    Lin, Jianchao; Tong, Peng; Cui, Dapeng; Yang, Cheng; Yang, Jie; Lin, Shuai; Wang, Bosen; Tong, Wei; Zhang, Lei; Zou, Youming; Sun, Yuping

    2015-01-01

    For ferromagnets, varying from simple metals to strongly correlated oxides,the critical behaviors near the Curie temperature (TC) can be grouped into several universal classes. In this paper, we report an unusual critical behavior in manganese nitrides Cu1-xNMn3+x (0.1 ≤ x ≤ 0.4). Although the critical behavior below TC can be well described by mean field (MF) theory, robust critical fluctuations beyond the expectations of any universal classes are observed above TC in x = 0.1. The critical fluctuations become weaker when x increases, and the MF-like critical behavior is finally restored at x = 0.4. In addition, the paramagnetic susceptibility of all the samples deviates from the Curie-Weiss (CW) law just above TC. This deviation is gradually smeared as x increases. The short-range antiferromagnetic ordering above TC revealed by our electron spin resonance measurement explains both the unusual critical behavior and the breakdown of the CW law. PMID:25604754

  15. Skew Scattering from Correlated Systems: Impurities and Collective Excitations in the Spin Hall Effect

    NASA Astrophysics Data System (ADS)

    Ziman, Timothy; Gu, Bo; Maekawa, Sadamichi

    2017-01-01

    The spin Hall effect is affected by the Coulomb interaction as well as spin-spin correlations in metals. Here we examine the enhancement in the effect caused by resonant skew scattering induced by electron correlations. For single-impurity scattering, local Coulomb correlations may significantly change the observed spin Hall angle. There may be additional effects because of the special atomic environment close to a surface — extra degeneracies compared to the bulk, enhanced correlations that move the relative d- or f-levels, and interference effects coming from the lower local dimension. Our results may explain the very large spin Hall angle observed in CuBi alloys. We discuss the impact on the spin Hall effect from cooperative effects, firstly in an itinerant ferromagnet where there is an anomaly near the Curie temperature originating from high-order spin fluctuations. The second case considered is a metallic spin glass, where exchange via slowly fluctuating magnetic moments may lead to the precession of an injected spin current. This decreases the net spin-charge conversion from skew scattering at temperatures below a value three or four times the freezing temperature.

  16. Magnetostructural correlations in the antiferromagnetic Co{sub 2-x} Cu{sub x}(OH)AsO{sub 4} (x=0 and 0.3) phases

    SciTech Connect

    Pedro, I. de; Rojo, J.M.; Arriortua, M.I.

    2011-08-15

    , spectroscopic characterization and magnetic properties. > Unusual dependence on the magnetic field for antiferromagnetic transitions. > Incommensurate magnetic structure at low temperature. > Magnetostructural correlations in cobalt-based M{sub 2}(OH)XO{sub 4} (M=Co and Cu) insulation compounds.

  17. The ? - ? antiferromagnet on the square lattice with Dzyaloshinskii - Moriya interaction: an exact diagonalization study

    NASA Astrophysics Data System (ADS)

    Voigt, Andreas; Richter, Johannes

    1996-07-01

    We examine the influence of an anisotropic interaction term of Dzyaloshinskii - Moriya (DM) type on the ground state ordering of the 0953-8984/8/27/015/img3 - 0953-8984/8/27/015/img4 spin-0953-8984/8/27/015/img5 Heisenberg antiferromagnet on the square lattice. For the DM term we consider several symmetries corresponding to different crystal structures. For the pure 0953-8984/8/27/015/img3 - 0953-8984/8/27/015/img4 model there are strong indications for a quantum spin liquid in the region of 0953-8984/8/27/015/img8. We find that a DM interaction influences the breakdown of the conventional antiferromagnetic order by (i) shifting the spin-liquid region, (ii) changing the isotropic character of the ground state towards anisotropic correlations and (iii) creating for certain symmetries a net ferromagnetic moment.

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

    SciTech Connect

    Ehlers, Georg

    2008-02-01

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

  19. Thermal evolution of antiferromagnetic correlations and tetrahedral bond angles in superconducting FeTe1xSex

    SciTech Connect

    Xu, Zhijun; Schneeloch, J. A.; Wen, Jinsheng; Božin, E. S.; Granroth, G. E.; Winn, B. L.; Feygenson, M.; Birgeneau, R. J.; Gu, Genda; Zaliznyak, I. A.; Tranquada, J. M.; Xu, Guangyong

    2016-03-14

    It has recently been demonstrated that dynamical magnetic correlations measured by neutron scattering in iron chalcogenides can be described with models of short-range correlations characterized by particular choices of four-spin plaquettes, where the appropriate choice changes as the parent material is doped towards superconductivity. Here we apply such models to describe measured maps of magnetic scattering as a function of two-dimensional wave vectors obtained for optimally superconducting crystals of FeTe1xSex. We show that the characteristic antiferromagnetic wave vector evolves from that of the bicollinear structure found in underdoped chalcogenides (at high temperature) to that associated with the stripe structure of antiferromagnetic iron arsenides (at low temperature); these can both be described with the same local plaquette, but with different interplaquette correlations. While the magnitude of the low-energy magnetic spectral weight is substantial at all temperatures, it actually weakens somewhat at low temperature, where the charge carriers become more itinerant. The observed change in spin correlations is correlated with the dramatic drop in the electronic scattering rate and the growth of the bulk nematic response upon cooling. In conclusion, we also present powder neutron diffraction results for lattice parameters in FeTe1xSex indicating that the tetrahedral bond angle tends to increase towards the ideal value upon cooling, in agreement with the increased screening of the crystal field by more itinerant electrons and the correspondingly smaller splitting of the Fe 3d orbitals.

  20. Spin-dependent Electron Correlations of a System with Broken Spin Symmetry

    NASA Astrophysics Data System (ADS)

    Yi, K. S.; Kim, J. I.; Kim, J. S.

    2001-04-01

    The spin-dependent local field corrections Gσ, σ'/ (q, ω) of a spin-polarized electron gas(SPEG) are examined within a genralized RPA. Numerical results of Gσ, σ/ (q, 0) for both the majority and minority spin electrons of SPEG show a complicated but interesting behavior as one varies the spin polarization ζ of the SPEG. A pronounced maximum in Gσ, σ/ (q, 0) is observed and the location of the peaks are found to depend strongly on the values of ζ. We also show some numerical results of the mixed susceptibilities χem and χme, which are finite and not identical in SPEG.

  1. Classical Antiferromagnetism in Kinetically Frustrated Electronic Models

    NASA Astrophysics Data System (ADS)

    Sposetti, C. N.; Bravo, B.; Trumper, A. E.; Gazza, C. J.; Manuel, L. O.

    2014-05-01

    We study, by means of the density matrix renormalization group, the infinite U Hubbard model—with one hole doped away from half filling—in triangular and square lattices with frustrated hoppings, which invalidate Nagaoka's theorem. We find that these kinetically frustrated models have antiferromagnetic ground states with classical local magnetization in the thermodynamic limit. We identify the mechanism of this kinetic antiferromagnetism with the release of the kinetic energy frustration, as the hole moves in the established antiferromagnetic background. This release can occur in two different ways: by a nontrivial spin Berry phase acquired by the hole, or by the effective vanishing of the hopping amplitude along the frustrating loops.

  2. Interactions of spins and electrons in highly correlated systems

    NASA Astrophysics Data System (ADS)

    Husmann, Anke

    In this thesis, we have been interested in two particular systems. NiSsb2 is a Mott-Hubbard system in which strong electron-electron interactions split the half-filled conduction band and open up a gap, which can be suppressed by substituting Se for S and/or by applying hydrostatic pressure. At finite temperature, it is well established that the metal-insulator transition in Mott-Hubbard systems is of first order, as can be seen in many systems. However, when the transition temperature is suppressed to zero (the so-called quantum phase transition), the nature of the phase transition as a function of the electron-electron interactions is not known. The challenge in characterising this quantum phase transition lies in the difficulty of finding a suitable experimental system. The constraints on the system are rather stringent, and Ni(S,Se)sb2 is (to date) the only known Mott-Hubbard system which can be used for the study of critical behaviour. The perovskite manganites, such as LaMnOsb3, are the prototype of materials where the double exchange mechanism couples the conduction electrons strongly to the magnetic ordering of the background lattice. This leads to a variety of differently ordered ground states, such as ferromagnetic metals and insulators, antiferromagnetic insulators, and also charge ordered antiferromagnets. These materials can be tuned in many ways. We are interested in only a small subset of this rich phase space. Prsb{0.5}Srsb{0.5}MnOsb3 and Ndsb{0.5}Srsb{0.5}MnOsb3 undergo two magnetic phase transitions as a function of decreasing temperature: the second order Curie (ferromagnetic ordering) temperature, TsbC, is followed by the first order Neel (antiferromagnetic ordering) temperature, TsbN, which coincides in Ndsb{0.5}Srsb{0.5}MnOsb3 with the charge ordering temperature, TsbCO. The peculiarity in these two materials is that TsbN can be suppressed to zero by applying a magnetic field. The nature of the charge degrees of freedom at low temperatures as

  3. Electron spin polarization by isospin ordering in correlated two-layer quantum Hall systems.

    PubMed

    Tiemann, L; Wegscheider, W; Hauser, M

    2015-05-01

    Enhancement of the electron spin polarization in a correlated two-layer, two-dimensional electron system at a total Landau level filling factor of 1 is reported. Using resistively detected nuclear magnetic resonance, we demonstrate that the electron spin polarization of two closely spaced two-dimensional electron systems becomes maximized when interlayer Coulomb correlations establish spontaneous isospin ferromagnetic order. This correlation-driven polarization dominates over the spin polarizations of competing single-layer fractional quantum Hall states under electron density imbalances.

  4. Entanglement entropy and massless phase in the antiferromagnetic three-state quantum chiral clock model

    NASA Astrophysics Data System (ADS)

    Dai, Yan-Wei; Cho, Sam Young; Batchelor, Murray T.; Zhou, Huan-Qiang

    2017-01-01

    The von Neumann entanglement entropy is used to estimate the critical point hc/J ≃0.143 (3 ) of the mixed ferro-antiferromagnetic three-state quantum Potts model H =∑i[J (XiXi+1 2+Xi2Xi +1) -h Ri] , where Xi and Ri are standard three-state Potts spin operators and J >0 is the antiferromagnetic coupling parameter. This critical point value gives improved estimates for two Kosterlitz-Thouless transition points in the antiferromagnetic (β <0 ) region of the Δ -β phase diagram of the three-state quantum chiral clock model, where Δ and β are, respectively, the chirality and coupling parameters in the clock model. These are the transition points βc≃-0.143 (3 ) at Δ =1/2 between incommensurate and commensurate phases and βc≃-7.0 (1 ) at Δ =0 between disordered and incommensurate phases. The von Neumann entropy is also used to calculate the central charge c of the underlying conformal field theory in the massless phase h ≤hc . The estimate c ≃1 in this phase is consistent with the known exact value at the particular point h /J =-1 corresponding to the purely antiferromagnetic three-state quantum Potts model. The algebraic decay of the Potts spin-spin correlation in the massless phase is used to estimate the continuously varying critical exponent η .

  5. An itinerant antiferromagnetic metal without magnetic constituents

    SciTech Connect

    Svanidze, E.; Wang, Jiakui K.; Besara, T.; Liu, L.; Huang, Q.; Siegrist, T.; Frandsen, B.; Lynn, J. W.; Nevidomskyy, Andriy H.; Gamża, Monika B.; Aronson, M. C.; Uemura, Y. J.; Morosan, E.

    2015-07-13

    The origin of magnetism in metals has been traditionally discussed in two diametrically opposite limits: itinerant and local moments. Surprisingly, there are very few known examples of materials that are close to the itinerant limit, and their properties are not universally understood. In the case of the two such examples discovered several decades ago, the itinerant ferromagnets ZrZn2 and Sc3In, the understanding of their magnetic ground states draws on the existence of 3d electrons subject to strong spin fluctuations. Similarly, in Cr, an elemental itinerant antiferromagnet with a spin density wave ground state, its 3d electron character has been deemed crucial to it being magnetic. Here, we report evidence for an itinerant antiferromagnetic metal with no magnetic constituents: TiAu. Antiferromagnetic order occurs below a Néel temperature of 36 K, about an order of magnitude smaller than in Cr, rendering the spin fluctuations in TiAu more important at low temperatures. In conclusion, this itinerant antiferromagnet challenges the currently limited understanding of weak itinerant antiferromagnetism, while providing insights into the effects of spin fluctuations in itinerant–electron systems.

  6. An itinerant antiferromagnetic metal without magnetic constituents

    DOE PAGES

    Svanidze, E.; Wang, Jiakui K.; Besara, T.; ...

    2015-07-13

    The origin of magnetism in metals has been traditionally discussed in two diametrically opposite limits: itinerant and local moments. Surprisingly, there are very few known examples of materials that are close to the itinerant limit, and their properties are not universally understood. In the case of the two such examples discovered several decades ago, the itinerant ferromagnets ZrZn2 and Sc3In, the understanding of their magnetic ground states draws on the existence of 3d electrons subject to strong spin fluctuations. Similarly, in Cr, an elemental itinerant antiferromagnet with a spin density wave ground state, its 3d electron character has been deemedmore » crucial to it being magnetic. Here, we report evidence for an itinerant antiferromagnetic metal with no magnetic constituents: TiAu. Antiferromagnetic order occurs below a Néel temperature of 36 K, about an order of magnitude smaller than in Cr, rendering the spin fluctuations in TiAu more important at low temperatures. In conclusion, this itinerant antiferromagnet challenges the currently limited understanding of weak itinerant antiferromagnetism, while providing insights into the effects of spin fluctuations in itinerant–electron systems.« less

  7. Spin-orbit coupling and electron correlation in relativistic configuration interaction and coupled-cluster methods

    NASA Astrophysics Data System (ADS)

    Kim, Inkoo; Park, Young Choon; Kim, Hyungjun; Lee, Yoon Sup

    2012-02-01

    We studied convergence characteristics of relativistic effective core potential (RECP) based configuration interaction (CI) and coupled-cluster (CC) schemes in terms of spin-orbit coupling and electron correlation. The relativistic correlated methods can be divided into Kramers restricted (KR) and spin-orbit (SO) methods which differ by the stage of spin-orbit treatment: the KR method employs two-component Kramers restricted Hartree-Fock (HF) spinors as the one-electron basis in which spin-orbit coupling is included, whereas the SO method is based on one-component molecular orbitals generated from scalar relativistic HF and the spin-orbit interaction is then entered in post-HF step. The KR method is usually superior to the SO method for molecules containing heavy elements since spin-orbit coupling is included from the HF step. A performance calibration of the SO method against the KR method is performed by computations of the ground state energies and equilibrium bond lengths of MH (M = Tl, Pb, Bi, Po, and At). Spin-orbit coupling of each molecule was systematically increased by adjusting the spin-orbit operator of RECP to investigate its impact on the SO method. Although KRCI and SOCI converged to the same full-CI limit, for the strong spin-orbit coupling SOCI required higher levels of correlation compared to KRCI to account for the orbital relaxation effect. SOCC, in contrast, was able to recover both spin-orbit interaction and electron correlation in CC steps regardless of the spin-orbit strength, implying that SOCC could be the reliable and efficient relativistic ab initio method for moderate sized molecules containing heavy elements.

  8. Frustrated spin correlations in diluted spin ice Ho(2-x)La(x)Ti2O7

    SciTech Connect

    Ehlers, Georg

    2008-01-01

    We have studied the evolution of the structural properties as well as the static and dynamic spin correlations of spin ice Ho{sub 2}Ti{sub 2}O{sub 7}, where Ho was partially replaced by non-magnetic La. The crystal structure of diluted samples Ho{sub 2-x}La{sub x}Ti{sub 2}O{sub 7} was characterized by x-ray and neutron diffraction and by Ho LIII-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{le}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.

  9. Giant spin gap and magnon localization in the disordered Heisenberg antiferromagnet Sr2Ir1−xRuxO4

    DOE PAGES

    Cao, Yue; Liu, X.; Xu, Wenhu; ...

    2017-03-06

    Here, we study the evolution of magnetic excitations in the disordered two-dimensional antiferromagnet Sr2Ir1–xRuxO4. The maximum energy of the magnetic excitation remains robust up to x = 0.77, with a gap opening at low dopings and increasing to over 150 meV at x = 0.77. At these higher Ru concentrations, the dispersive magnetic excitations in Sr2IrO4 are rendered essentially momentum independent. Up to a Ru concentration of x = 0.77, both experiments and first-principles calculations show the Ir Jeff = 1/2 state remains intact. The magnetic gap arises from the local interaction anisotropy in the proximity of the Ru disorder.more » Under the coherent potential approximation, we reproduce the experimental magnetic excitations using the disordered Heisenberg antiferromagnetic model with suppressed next-nearest-neighbor ferromagnetic coupling.« less

  10. First-principles determination of Heisenberg Hamiltonian parameters for the spin-(1)/(2) kagome antiferromagnet ZnCu3(OH)6Cl2

    NASA Astrophysics Data System (ADS)

    Jeschke, Harald O.; Salvat-Pujol, Francesc; Valentí, Roser

    2013-08-01

    Herbertsmithite [ZnCu3(OH)6Cl2] is often discussed as the best realization of the highly frustrated antiferromagnetic kagome lattice known so far. We employ density functional theory (DFT) calculations to determine eight exchange coupling constants of the underlying Heisenberg Hamiltonian. We find the nearest-neighbor coupling J1 to exceed all other couplings by far. However, next-nearest-neighbor kagome layer couplings of 0.019J1 and interlayer couplings of up to -0.035J1 slightly modify the perfect antiferromagnetic kagome Hamiltonian. Interestingly, the largest interlayer coupling is ferromagnetic, even without Cu impurities in the Zn layer. In addition, we validate our DFT approach by applying it to kapellasite, a polymorph of herbertsmithite, which is known experimentally to exhibit competing exchange interactions.

  11. Study of quantum spin correlations of relativistic electron pairs - Testing nonlocality of relativistic quantum mechanics

    SciTech Connect

    Bodek, K.; Rozpędzik, D.; Zejma, J.; Caban, P.; Rembieliński, J.; Włodarczyk, M.; Enders, J.; Köhler, A.; Kozela, A.

    2013-11-07

    The Polish-German project QUEST aims at studying relativistic quantum spin correlations of the Einstein-Rosen-Podolsky-Bohm type, through measurement of the correlation function and the corresponding probabilities for relativistic electron pairs. The results will be compared to theoretical predictions obtained by us within the framework of relativistic quantum mechanics, based on assumptions regarding the form of the relativistic spin operator. Agreement or divergence will be interpreted in the context of non-uniqueness of the relativistic spin operator in quantum mechanics as well as dependence of the correlation function on the choice of observables representing the spin. Pairs of correlated electrons will originate from the Mo/ller scattering of polarized 15 MeV electrons provided by the superconducting Darmstadt electron linear accelerator S-DALINAC, TU Darmstadt, incident on a Be target. Spin projections will be determined using the Mott polarimetry technique. Measurements (starting 2013) are planned for longitudinal and transverse beam polarizations and different orientations of the beam polarization vector w.r.t. the Mo/ller scattering plane. This is the first project to study relativistic spin correlations for particles with mass.

  12. Study of quantum spin correlations of relativistic electron pairs - Testing nonlocality of relativistic quantum mechanics

    NASA Astrophysics Data System (ADS)

    Bodek, K.; Caban, P.; Ciborowski, J.; Enders, J.; Köhler, A.; Kozela, A.; Rembieliński, J.; Rozpedzik, D.; Włodarczyk, M.; Zejma, J.

    2013-11-01

    The Polish-German project QUEST aims at studying relativistic quantum spin correlations of the Einstein-Rosen-Podolsky-Bohm type, through measurement of the correlation function and the corresponding probabilities for relativistic electron pairs. The results will be compared to theoretical predictions obtained by us within the framework of relativistic quantum mechanics, based on assumptions regarding the form of the relativistic spin operator. Agreement or divergence will be interpreted in the context of non-uniqueness of the relativistic spin operator in quantum mechanics as well as dependence of the correlation function on the choice of observables representing the spin. Pairs of correlated electrons will originate from the Mo/ller scattering of polarized 15 MeV electrons provided by the superconducting Darmstadt electron linear accelerator S-DALINAC, TU Darmstadt, incident on a Be target. Spin projections will be determined using the Mott polarimetry technique. Measurements (starting 2013) are planned for longitudinal and transverse beam polarizations and different orientations of the beam polarization vector w.r.t. the Mo/ller scattering plane. This is the first project to study relativistic spin correlations for particles with mass.

  13. Quasiparticle bandstructure of antiferromagnetic EuTe

    NASA Astrophysics Data System (ADS)

    Mathi Jaya, S.; Nolting, W.

    1997-11-01

    The temperature-dependent electronic quasiparticle spectrum of the antiferromagnetic semiconductor EuTe is derived by use of a combination of a many-body model procedure with a tight-binding - `linear muffin tin orbital' (TB - LMTO) band structure calculation. The central part is the d - f model for a single band electron (`test electron') being exchange coupled to the antiferromagnetically ordered localized moments of the Eu ions. The single-electron Bloch energies of the d - f model are taken from a TB - LMTO calculation for paramagnetic EuTe. The d - f model is evaluated by a recently proposed moment conserving Green function technique to get the temperature-dependent sublattice - quasiparticle bandstructure (S - QBS) and sublattice - quasiparticle density of states (S - QDOS) of the unoccupied 5d - 6s energy bands. Unconventional correlation effects and the appearance of characteristic quasiparticles (`magnetic polarons') are worked out in detail. The temperature dependence of the S - QDOS and S - QBS is mainly provoked by the spectral weights of the energy dispersions. Minority- and majority-spin spectra coincide for all temperatures but with different densities of states. Upon cooling from 0953-8984/9/47/012/img1 to T = 0 K the lower conduction band edge exhibits a small blue shift of -0.025 eV in accordance with the experiment. Quasiparticle damping manifesting itself in a temperature-dependent broadening of the spectral density peaks arises from spin exchange processes between (5d - 6s) conduction band electrons and localized 4f moments.

  14. Magnetic interactions in strongly correlated systems: Spin and orbital contributions

    SciTech Connect

    Secchi, A.; Lichtenstein, A.I.; Katsnelson, M.I.

    2015-09-15

    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.

  15. Evidence for Intertwining of Superconductivity and Antiferromagnetism in a Cuprate

    NASA Astrophysics Data System (ADS)

    Tranquada, John; Xu, Zhijun; Stock, C.; Chi, S. X.; Kolesnikov, A. I.; Xu, G. Y.; Gu, G. D.

    2014-03-01

    We have used inelastic neutron scattering to measure the low-energy, incommensurate antiferromagnetic spin excitations both above and below the superconducting transition temperature (Tc = 32 K) of La1.905Ba0.095CuO4. While the magnetic excitations in optimally-doped cuprates typically show the development of a spin gap and magnetic resonance below Tc, our sample shows no such effect. Instead strong, gapless spin excitations coexist with bulk superconductivity. To understand this, we note that previous transport measurements have shown that the superconducting layers are decoupled by a magnetic field applied along the c-axis, resulting in a state with frustrated interlayer Josephson coupling, similar to LBCO with x = 1 / 8 , where it has been proposed that pair-density-wave superconductivity occurs. This suggests that, in a similar fashion, the spatially modulated antiferromagnetic correlations (which we see directly in the x = 0 . 095 sample) are intertwined with a spatially modulated superconducting pair wave function. Work at BNL supported by Office of Basic Energy Sciences, US DOE, under Contract No. DE-AC02-98CH10886.

  16. Measurement of np elastic scattering spin-spin correlation parameters at 484, 634, and 788 MeV

    SciTech Connect

    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.

  17. Ultra-fast photo-carrier relaxation in Mott insulators with short-range spin correlations

    PubMed Central

    Eckstein, Martin; Werner, Philipp

    2016-01-01

    Ultra-fast spectroscopy can reveal the interplay of charges with low energy degrees of freedom, which underlies the rich physics of correlated materials. As a potential glue for superconductivity, spin fluctuations in Mott insulators are of particular interest. A theoretical description of the coupled spin and charge degrees of freedom is challenging, because magnetic order is often only short-lived and short-ranged. In this work we theoretically investigate how the spin-charge interactions influence the relaxation of a two-dimensional Mott-Hubbard insulator after photo-excitation. We use a nonequilibrium variant of the dynamical cluster approximation, which, in contrast to single-site dynamical mean-field theory, captures the effect of short-range correlations. The relaxation time is found to scale with the strength of the nearest-neighbor spin correlations, and can be 10–20 fs in the cuprates. Increasing the temperature or excitation density decreases the spin correlations and thus implies longer relaxation times. This may help to distinguish the effect of spin-fluctuations on the charge relaxation from the influence of other bosonic modes in the solid. PMID:26883536

  18. Ultra-fast photo-carrier relaxation in Mott insulators with short-range spin correlations

    NASA Astrophysics Data System (ADS)

    Eckstein, Martin; Werner, Philipp

    2016-02-01

    Ultra-fast spectroscopy can reveal the interplay of charges with low energy degrees of freedom, which underlies the rich physics of correlated materials. As a potential glue for superconductivity, spin fluctuations in Mott insulators are of particular interest. A theoretical description of the coupled spin and charge degrees of freedom is challenging, because magnetic order is often only short-lived and short-ranged. In this work we theoretically investigate how the spin-charge interactions influence the relaxation of a two-dimensional Mott-Hubbard insulator after photo-excitation. We use a nonequilibrium variant of the dynamical cluster approximation, which, in contrast to single-site dynamical mean-field theory, captures the effect of short-range correlations. The relaxation time is found to scale with the strength of the nearest-neighbor spin correlations, and can be 10–20 fs in the cuprates. Increasing the temperature or excitation density decreases the spin correlations and thus implies longer relaxation times. This may help to distinguish the effect of spin-fluctuations on the charge relaxation from the influence of other bosonic modes in the solid.

  19. Femtosecond optomagnetism in dielectric antiferromagnets

    NASA Astrophysics Data System (ADS)

    Bossini, D.; Rasing, Th

    2017-02-01

    Optical femtosecond manipulation of magnetic order is attractive for the development of new concepts for ultrafast magnetic recording. Theoretical and experimental investigations in this research area aim at establishing a physical understanding of magnetic media in light-induced non-equilibrium states. Such a quest requires one to adjust the theory of magnetism, since the thermodynamical concepts of elementary excitations and spin alignment determined by the exchange interaction are not applicable on the femtosecond time-scale after the photo-excitation. Here we report some key milestones concerning the femtosecond optical control of spins in dielectric antiferromagnets, whose spin dynamics is by nature faster than that of ferromagnets and can be triggered even without any laser heating. The recent progress of the opto-magnetic effect in the sub-wavelength regime makes this exciting research area even more promising, in terms of both fundamental breakthroughs and technological perspectives.

  20. Correlation Analysis between Spin, Velocity Shear, and Vorticity of Baryonic and Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Liu, L. L.

    2016-05-01

    Using cosmological hydrodynamic simulations, we investigate the alignments between velocity shear, vorticity, and the spin of dark matter halos, and study the correlation between baryonic and dark matter. We find that (1) mis-alignment between vorticity of baryonic and dark matter would develop on scales < 0.2h-1 Mpc; (2) the vorticity of baryonic matter exhibits stronger alignment/anti-alignment with the eigenvectors of velocity shear than that of dark matter; (3) small/massive halos spinning parallel/perpendicular to the host filaments are sensitive to the identification of cosmic web, simulation box size, and resolution. These factors might complicate the connection between the spins of dark matter halos and galaxies, and affect the correlation signal of the alignments of galaxy spin with nearby large-scale structures.

  1. Cross-Correlation Effects Involving Curie Spin Relaxation in Methyl Groups

    NASA Astrophysics Data System (ADS)

    Madhu, P. K.; Mandal, Pravat K.; Müller, Norbert

    2002-03-01

    Cross-correlation effects arising in methyl protons due to the simultaneous presence of dipole-dipole, chemical shift anisotropy, and Curie spin relaxation mechanisms in paramagnetic systems are analyzed. We assess the potential of obtaining structural constraints from the cross-correlation of Curie spin relaxation with dipolar relaxation mechanisms among methyl proton spins. By theoretical analysis and numerical simulations we characterize the transfer functions describing the interconversion processes of different ranks of multispin order. The time dependence of these processes contains a new type of structural information, the orientation of the methyl C3-axis with respect to the electron center. Experimental confirmation is found for selected methyl groups in low spin Fe3+ sperm whale myoglobin.

  2. Spin-Momentum Correlations in Quasi-Elastic Electron Scattering from Deuterium

    SciTech Connect

    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.

  3. Influence of the local-spin-density correlation functional on the stability of bcc ferromagnetic iron

    NASA Astrophysics Data System (ADS)

    Singh, D.; Clougherty, D. P.; MacLaren, J. M.; Albers, R. C.; Wang, C. S.

    1991-10-01

    The influence of local-spin-dependent correlation effects on the predicted stable ground-state phase of iron is reexamined with use of general-potential linearized augmented-plane-wave calculations. Differences in the form of the Vosko-Wilk-Nusair (VWN) local-spin-density functional used in previous studies are noted, since in previous studies significant additional approximations were made with respect to those of Vosko, Wilk, and Nusan [Can. J. Phys. 58, 1200 (1980)] and of MacLaren, Clougherty, and Albers [Phys. Rev. B 42, 3205 (1990)]. While the results of previous linear muffin-tin orbital calculations using the VWN functional predict a bcc ferromagnetic ground state, the present calculations show that the VWN spin-correlation effects fail to stabilize a bcc ground state. Considerable sensitivity to the form of the spin interpolation is found.

  4. Long-range spin-triplet correlations and edge spin currents in diffusive spin-orbit coupled SNS hybrids with a single spin-active interface

    NASA Astrophysics Data System (ADS)

    Alidoust, Mohammad; Halterman, Klaus

    2015-06-01

    Utilizing a SU(2) gauge symmetry technique in the quasiclassical diffusive regime, we theoretically study finite-sized two-dimensional intrinsic spin-orbit coupled superconductor/normal-metal/superconductor (S/N/S) hybrid structures with a single spin-active interface. We consider intrinsic spin-orbit interactions (ISOIs) that are confined within the N wire and absent in the s-wave superconducting electrodes (S). Using experimentally feasible parameters, we demonstrate that the coupling of the ISOIs and spin moment of the spin-active interface results in maximum singlet-triplet conversion and accumulation of spin current density at the corners of the N wire nearest the spin-active interface. By solely modulating the superconducting phase difference, we show how the opposing parities of the charge and spin currents provide an effective venue to experimentally examine pure edge spin currents not accompanied by charge currents. These effects occur in the absence of externally imposed fields and moreover are insensitive to the arbitrary orientations of the interface spin moment. The experimental implementation of these robust edge phenomena are also discussed.

  5. Interplay between charge density wave and antiferromagnetic order in GdNiC2

    NASA Astrophysics Data System (ADS)

    Hanasaki, N.; Shimomura, S.; Mikami, K.; Nogami, Y.; Nakao, H.; Onodera, H.

    2017-02-01

    The correlation between the charge density wave (CDW) and f local moments is observed in GdNiC2 by means of x-ray diffraction in a magnetic field. Various kinds of electronic states exist in the magnetic field. The intensity of the CDW peak changes in the successive transitions and the commensurate-incommensurate transition of the CDW takes place as well. The successive transitions are explained in terms of a cooperative effect of the Peierls instability and the spin Friedel oscillation, in which the antiferromagnetic order of the f local moments is coupled to the spin density wave coexisting with the CDW of the conduction electron.

  6. Resonant magnetic exciton mode in the heavy-fermion antiferromagnet CeB₆.

    PubMed

    Friemel, G; Li, Yuan; Dukhnenko, A V; Shitsevalova, N Y; Sluchanko, N E; Ivanov, A; Filipov, V B; Keimer, B; Inosov, D S

    2012-05-15

    Resonant magnetic excitations are recognised as hallmarks of unconventional superconductivity in copper oxides, iron pnictides and heavy-fermion compounds. Model calculations have related these modes to the microscopic properties of the pair wave function, but the mechanisms of their formation are still debated. Here we report the discovery of a similar resonant mode in the non-superconducting antiferromagnetic heavy-fermion metal CeB(6). Unlike conventional magnons, the mode is non-dispersive and is sharply peaked around a wave vector separate from those characterising the antiferromagnetic order. It is likely associated with a co-existing order parameter of the unusual antiferro-quadrupolar phase of CeB(6), which has long remained hidden to neutron-scattering probes. The mode energy increases continuously below the onset temperature for antiferromagnetism, in parallel to the opening of a nearly isotropic spin gap throughout the Brillouin zone. These attributes are similar to those of the resonant modes in unconventional superconductors. This unexpected commonality between the two disparate ground states indicates the dominance of itinerant spin dynamics in the ordered low-temperature phases of CeB(6) and throws new light on the interplay between antiferromagnetism, superconductivity and 'hidden' order parameters in correlated-electron materials.

  7. Thermodynamic properties of correlated fermions in lattices with spin-dependent disorder

    NASA Astrophysics Data System (ADS)

    Makuch, K.; Skolimowski, J.; Chakraborty, P. B.; Byczuk, K.; Vollhardt, D.

    2013-04-01

    Motivated by the rapidly growing possibilities for experiments with ultracold atoms in optical lattices, we investigate the thermodynamic properties of correlated lattice fermions in the presence of an external spin-dependent random potential. The corresponding model, a Hubbard model with spin-dependent local random potentials, is solved within dynamical mean-field theory. This allows us to present a comprehensive picture of the thermodynamic properties of this system. In particular, we show that for a fixed total number of fermions spin-dependent disorder induces a magnetic polarization. The magnetic response of the polarized system differs from that of a system with conventional disorder.

  8. Interplay between spin-orbit coupling and strong correlation effects: Comparison of the three osmate double perovskites Ba2A OsO6 (A =Na , Ca, Y)

    NASA Astrophysics Data System (ADS)

    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.

  9. New insights into electron spin dynamics in the presence of correlated noise.

    PubMed

    Spezia, S; Adorno, D Persano; Pizzolato, N; Spagnolo, B

    2012-02-08

    The changes in the spin depolarization length in zinc-blende semiconductors when an external component of correlated noise is added to a static driving electric field are analyzed for different values of field strength, noise amplitude and correlation time. Electron dynamics is simulated by a Monte Carlo procedure which takes into account all the possible scattering phenomena of the hot electrons in the medium and includes the evolution of spin polarization. Spin depolarization is studied by examining the decay of the initial spin polarization of the conduction electrons through the D'yakonov-Perel process, the only relevant relaxation mechanism in III-V crystals. Our results show that, for electric field amplitudes lower than the Gunn field, the dephasing length shortens with increasing noise intensity. Moreover, a nonmonotonic behavior of spin depolarization length with the noise correlation time is found, characterized by a maximum variation for values of noise correlation time comparable with the dephasing time. Instead, in high field conditions, we find that, critically depending on the noise correlation time, external fluctuations can positively affect the relaxation length. The influence of the inclusion of the electron-electron scattering mechanism is also shown and discussed.

  10. The nucleonic matter spin-orbit and tensor correlations in the LOCV framework

    NASA Astrophysics Data System (ADS)

    Tafrihi, A.; Modarres, M.

    2017-02-01

    The nucleonic matter operator-dependent correlation functions in the coupled channels, i.e. the S31-D31 and the P32-F32 channels, for the Av18 interaction, are obtained by the use of lowest order constrained variational (LOCV) method. While, in the S31-D31 channel, only, the tensor-dependent correlation function is considered; in the P32-F32 channel, the spin-obit-dependent correlation function is included as well. It is demonstrated that the S31-D31 channel tensor-dependent correlation function is dominant in the symmetric nuclear matter (SNM). In other words, the P32-F32 channel tensor- and spin-orbit-dependent correlation functions do not play any significant role in the SNM. Whereas, it is shown that the spin-orbit-dependent correlation function notably declines the LOCV pure neutron matter (PNM) energy, especially at high densities. Finally, it should be declared that, generally, the spin-orbit-dependent correlation functions are short-range in comparison with those of tensor-dependent.

  11. Breakdown of antiferromagnetism and the Coulomb phase for RVB states on anisotropic three-dimensional lattices

    NASA Astrophysics Data System (ADS)

    Beach, K. S. D.

    2015-03-01

    Nearest-neighbor (NN) resonating-valence-bond (RVB) wave functions often serve as prototype ground states for various frustrated models in two dimensions because of their lack of long-range magnetic correlations. In three dimensions, these states are generally not featureless, and their tendency is toward antiferromagnetic order. On the cubic and diamond lattices, for example, the NN RVB state exhibits both antiferromagnetism and power law dimer correlations characteristic of the ``Coulomb phase'' (in analogy with classical hardcore dimer models). The introduction of strong spatial anisotropy, however, leads to the destruction of these long-range and algebraic correlations, leaving behind an apparent short-range spin liquid state. We characterize the critical exponents at the phase boundaries for wave functions built from products of SU(2) singlets as well as their SU(N) generalizations and discuss attempts to construct a field theory that describes the transitions.

  12. Communication: Configuration interaction combined with spin-projection for strongly correlated molecular electronic structures

    SciTech Connect

    Tsuchimochi, Takashi Ten-no, Seiichiro

    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.

  13. Top Quarks Spin Correlations with Graviton in ADD and RS Models at the Large Hadron Collider

    NASA Astrophysics Data System (ADS)

    Arai, Masato; Okada, Nobuchika; Smolek, Karel; Šimák, Vladislav

    2008-03-01

    In LHC physics we study the spin correlation of top-antitop pairs production to investigate the production mechanism of heavy quarks[F. Hubard et al. Eur. Phys. J. C 44 (2006) 13]. The s-channel process mediated by graviton Kaluza-Klein modes in ADD model with several extra dimensions[N. Arkani-Hamed, S. Dimopoulos and G. Dvali, Phys. Lett. 429B (1998) 263, hep-ph/9803315] or in the Randall-Sundrum model with only one extra dimension[L. Randall and R. Sundrum, Phys. Rev. Lett. 83 (1999) 3370 hep-ph/9905221] contribute to the top-antitop pair production and affects the resulting top spin correlations. We calculated the full density matrix for the top-antitop pair production. We find a sizable deviation of the top spin correlations from the Standard.

  14. Ba8CoNb6O24 : A spin-1/2 triangular-lattice Heisenberg antiferromagnet in the two-dimensional limit

    NASA Astrophysics Data System (ADS)

    Rawl, R.; Ge, L.; Agrawal, H.; Kamiya, Y.; Dela Cruz, C. R.; Butch, N. P.; Sun, X. F.; Lee, M.; Choi, E. S.; Oitmaa, J.; Batista, C. D.; Mourigal, M.; Zhou, H. D.; Ma, J.

    2017-02-01

    The perovskite Ba8CoNb6O24 comprises equilateral effective spin-1/2 Co2 + triangular layers separated by six nonmagnetic layers. Susceptibility, specific heat, and neutron scattering measurements combined with high-temperature series expansions and spin-wave calculations confirm that Ba8CoNb6O24 is basically a two-dimensional magnet with no detectable spin anisotropy and no long-range magnetic ordering down to 0.06 K. In other words, Ba8CoNb6O24 is very close to be a realization of the paradigmatic spin-1/2 triangular Heisenberg model, which is not expected to exhibit symmetry breaking at finite temperatures according to the Mermin and Wagner theorem.

  15. Boosting spin-caloritronic effects by attractive correlations in molecular junctions

    PubMed Central

    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. PMID:26805591

  16. Boosting spin-caloritronic effects by attractive correlations in molecular junctions

    NASA Astrophysics Data System (ADS)

    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.

  17. Electron spin-flip correlations due to nuclear dynamics in driven GaAs double dots

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

    We present experimental data and associated theory for correlations in a series of experiments involving repeated Landau-Zener sweeps through the crossing point of a singlet state and a spin-aligned triplet state in a GaAs double quantum dot containing two conduction electrons, which are loaded in the singlet state before each sweep, and the final spin is recorded after each sweep. The experiments reported here measure correlations on time scales from 4 μ s to 2 ms. When the magnetic field is aligned in a direction such that spin-orbit coupling cannot cause spin flips, the correlation spectrum has prominent peaks centered at zero frequency and at the differences of the Larmor frequencies of the nuclei, on top of a frequency-independent background. When the spin-orbit field is relevant, there are additional peaks, centered at the frequencies of the individual species. A theoretical model which neglects the effects of high-frequency charge noise correctly predicts the positions of the observed peaks, and gives a reasonably accurate prediction of the size of the frequency-independent background, but gives peak areas that are larger than the observed areas by a factor of 2 or more. The observed peak widths are roughly consistent with predictions based on nuclear dephasing times of the order of 60 μ s . However, there is extra weight at the lowest observed frequencies, which suggests the existence of residual correlations on the scale of 2 ms. We speculate on the source of these discrepancies.

  18. Time-domain shape of electron spin echo signal of spin-correlated radical pairs in polymer/fullerene blends.

    PubMed

    Popov, Alexander A; Lukina, Ekaterina A; Rapatskiy, Leonid; Kulik, Leonid V

    2017-03-01

    Temporal shape of electron spin echo (ESE) signal of photoinduced spin-correlated radical pairs (SCRP) in composite of conductive polymer P3HT and substituted fullerene PCBM is studied in details. ESE signals of radical pairs (RP) P3HT(+)/PCBM(-) are calculated in realistic model, taking into account finite microwave pulse length. Inhomogeneous broadening of resonant lines and interradical distance distribution are included. Experimentally observed ESE time-domain shape was found to contradict predictions of conventional SCRP theory, which would be valid in the case of very fast electron transfer. Thus, instantaneous formation of singlet SCRP is not the case for P3HT(+)/PCBM(-) pair, and spin system has enough time to evolve coherently during sequential electron transfer. While it is impossible to reproduce experimental data within simple singlet SCRP model, assumption of presence of additional - with respect to what is predicted by singlet SCRP theory - AE (absorption/emission) spin polarization gives convincing accordance with the experiment. Density matrix of RP P3HT(+)/PCBM(-) is a superposition of two contributions, namely the parts reflecting (i) antiphase polarization of original singlet-born SCRP and (ii) additional AE-polarization which is generated during initial stage of charge separation. AE-polarization affects experimental ESEEM (electron spin echo envelope modulation) traces, as well as ESE shape, making impossible their interpretation via simple singlet SCRP model. However, this effect can be eliminated by averaging of ESEEM traces over EPR spectral positions. Finally, choosing the optimal gate for ESE time-domain integration and proper microwave detection phase tuning are considered.

  19. Time-domain shape of electron spin echo signal of spin-correlated radical pairs in polymer/fullerene blends

    NASA Astrophysics Data System (ADS)

    Popov, Alexander A.; Lukina, Ekaterina A.; Rapatskiy, Leonid; Kulik, Leonid V.

    2017-03-01

    Temporal shape of electron spin echo (ESE) signal of photoinduced spin-correlated radical pairs (SCRP) in composite of conductive polymer P3HT and substituted fullerene PCBM is studied in details. ESE signals of radical pairs (RP) P3HT+/PCBM- are calculated in realistic model, taking into account finite microwave pulse length. Inhomogeneous broadening of resonant lines and interradical distance distribution are included. Experimentally observed ESE time-domain shape was found to contradict predictions of conventional SCRP theory, which would be valid in the case of very fast electron transfer. Thus, instantaneous formation of singlet SCRP is not the case for P3HT+/PCBM- pair, and spin system has enough time to evolve coherently during sequential electron transfer. While it is impossible to reproduce experimental data within simple singlet SCRP model, assumption of presence of additional - with respect to what is predicted by singlet SCRP theory - AE (absorption/emission) spin polarization gives convincing accordance with the experiment. Density matrix of RP P3HT+/PCBM- is a superposition of two contributions, namely the parts reflecting (i) antiphase polarization of original singlet-born SCRP and (ii) additional AE-polarization which is generated during initial stage of charge separation. AE-polarization affects experimental ESEEM (electron spin echo envelope modulation) traces, as well as ESE shape, making impossible their interpretation via simple singlet SCRP model. However, this effect can be eliminated by averaging of ESEEM traces over EPR spectral positions. Finally, choosing the optimal gate for ESE time-domain integration and proper microwave detection phase tuning are considered.

  20. PULSAR BINARY BIRTHRATES WITH SPIN-OPENING ANGLE CORRELATIONS

    SciTech Connect

    O'Shaughnessy, Richard; Kim, Chunglee E-mail: ckim@astro.lu.s

    2010-05-20

    One ingredient in an empirical birthrate estimate for pulsar binaries is 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. The current estimates for pulsar binary birthrates are based on an average value of beaming fractions for only two pulsars, i.e., PSRs B1913+16 and B1534+12. In this paper, we revisit the observed pulsar binaries to examine the sensitivity of birthrate predictions to different assumptions regarding opening angle and alignment. Based on empirical estimates for the relative likelihood of different beam half-opening angles and misalignment angles between the pulsar rotation and magnetic axes, we calculate an effective beaming correction factor, f{sub b,eff}, whose reciprocal is equivalent to the average fraction of all randomly selected pulsars that point toward us. For those pulsars without any direct beam geometry constraints, we find that f{sub b,eff} is likely to be smaller than 6, a canonically adopted value when calculating birthrates of Galactic pulsar binaries. We calculate f{sub b,eff} for PSRs J0737-3039A and J1141-6545, applying the currently available constraints for their beam geometry. As in previous estimates of the posterior probability density function P(R) for pulsar binary birthrates R, PSRs J0737-3039A and J1141-6545 still significantly contribute to, if not dominate, the Galactic birthrate of tight pulsar-neutron star (NS) and pulsar-white dwarf (WD) binaries, respectively. Our median posterior present-day birthrate predictions for tight PSR-NS binaries, wide PSR-NS binaries, and tight PSR-WD binaries given a preferred pulsar population model and beaming geometry are 89 Myr{sup -1}, 0.5 Myr{sup -1}, and 34 Myr{sup -1}, respectively. For long-lived PSR-NS binaries, these estimates include a weak (x1.6) correction for slowly decaying star formation in the galactic disk. For pulsars

  1. Correlations between the dynamics of parallel tempering and the free-energy landscape in spin glasses

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

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

  2. Angles and Daemons: Spin Correlations at the LHC

    SciTech Connect

    Tran, Nhan V.

    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.

  3. The f-spin physics of rare-earth iron pnictides: influence of d-electron antiferromagnetic order on heavy fermion phase diagram

    SciTech Connect

    Zhu, Jian-xin; Dai, Jianhui; Si, Qimiao

    2009-01-01

    Some of the high {Tc} iron pnictides contain rare-earth elements, raising the question of how the existence and tunability of a d-electron antiferromagnetic order influences the heavy fermion behavior of the f-moments. With CeOFeP and CeOFeAs in mind as prototypes, we derive an extended Anderson lattice model appropriate for these quaternary systems. We show that the Kondo screening of the f-moments are efficiently suppressed by the d-electron ordering. We also argue that, inside the d-electron ordered state (as in CeOFeAs), the f-moments provide a rare realization of a quantum frustrated magnet with competing J{sub 1}-J{sub 2}-J{sub 3} interactions in an effective square lattice. Implications ofr the heavy fermion physics in broader contexts are also discussed.

  4. Spin liquid state in the 3D frustrated antiferromagnet PbCuTe2O6: NMR and muon spin relaxation studies

    SciTech Connect

    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

    In this study, 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.

  5. Nearest neighbor correlations in perpendicular artificial spin ice arrays in the presence of an applied field

    NASA Astrophysics Data System (ADS)

    Kempinger, Susan; Fraleigh, Robert; Lammert, Paul; Crespi, Vincent; Samarth, Nitin; Schiffer, Peter

    By studying the field dependent magnetization switching process in perpendicular artificial spin ice arrays arrays, we hope to gain insight in to the dynamical properties of interacting spin systems. To this end, we have used diffraction-limited Kerr imaging to study lithographically patterned arrays of single domain, nanoscale islands of Co/Pt multilayers. We can tune the interaction strength and introduce geometric frustration in to the patterned systems by changing the lattice spacing and geometry of the arrays. Using MOKE microscopy we are able to optically resolve, spatially isolate, and extract the switching field of each island in an array in the presence of an external field. These switching fields allow us to calculate the magnetization and nearest neighbor spin-spin correlation throughout a hysteresis loop. These quantities help us determine the effect of increased interactions and geometric frustration on the switching process of dipole coupled arrays. Funded by DOE.

  6. Electron correlations and the minority-spin band gap in half-metallic Heusler alloys.

    PubMed

    Chioncel, L; Arrigoni, E; Katsnelson, M I; Lichtenstein, A I

    2006-04-07

    Electron-electron correlations affect the band gap of half-metallic ferromagnets by introducing nonquasiparticle states just above the Fermi level. In contrast with the spin-orbit coupling, a large asymmetric nonquasiparticle spectral weight is present in the minority-spin channel, leading to a peculiar finite-temperature spin depolarization effects. Using recently developed first-principle dynamical mean-field theory, we investigate these effects for the half-metallic ferrimagnetic Heusler compound FeMnSb. We discuss depolarization effects in terms of strength of local Coulomb interaction U and temperature in FeMnSb. We propose Ni(1-x)Fe(x)MnSb alloys as a perspective materials to be used in spin-valve structures and for experimental search of nonquasiparticle states in half-metallic materials.

  7. Critical dynamics of the classical anisotropic BCC Heisenberg antiferromagnet.

    NASA Astrophysics Data System (ADS)

    Tsai, Shan-Ho; Bunker, Alex; Landau, D. P.

    2001-03-01

    Large-scale spin-dynamics simulations have been used to investigate the dynamic behavior of the classical Heisenberg antiferromagnet with single-site uniaxial anisotropy, in bcc lattices. Time evolutions of spin configurations were determined numerically from coupled equations of motion for individual spins using an algorithm implemented by Krech et al [1], which is based on fourth-order Suzuki-Trotter decompositions of exponential operators. The dynamic structure factor S(q,ω) was calculated from the space- and time-displaced spin-spin correlation function. Preliminary results for the transverse and the longitudinal components of S(q,ω) show that while the former is propagative, with a relatively short time scale, the latter is diffusive and its computation requires very long time integrations. Because of difficulties for experiments to probe the critical region, experimental data have not yet been able to distinguish between competing theories. While limited by finite lattice size and finite integration time, simulations offer the hope of shedding light on the differences between theories and experiment. [1] M. Krech, A. Bunker, D.P. Landau, Comput. Phys. Commun. 111, 1 (1998). Supported by NSF and SDSC

  8. A novel method for measurement of the spin correlation function for relativistic electron pairs produced in Møller scattering

    NASA Astrophysics Data System (ADS)

    Bodek, K.; Kępka, D.; Rozpędzik, D.; Zejma, J.; Kozela, A.

    2017-04-01

    A self-calibrating double-Mott polarimeter is proposed for measurement of the spin correlation function of relativistic electron pairs produced in Møller scattering. The polarization of outgoing electrons (appearing when the beam is polarized) is utilized for calibration of effective analyzing powers in the secondary Mott scattering used for spin analysis. The experiment will measure the newly introduced relative spin correlation function. This new observable can be measured with a significantly better accuracy than the regular spin correlation function in a small scale experiment. It is shown that both the spin correlation function and the relative spin correlation function are theoretically equivalent. A specific experimental data analysis scenario is proposed, which effectively eliminates the systematic effects related to the imperfect geometry and detector efficiency.

  9. An hour-glass magnetic spectrum in an insulating, hole-doped antiferromagnet.

    PubMed

    Boothroyd, A T; Babkevich, P; Prabhakaran, D; Freeman, P G

    2011-03-17

    Superconductivity in layered copper oxide compounds emerges when charge carriers are added to antiferromagnetically ordered CuO(2) layers. The carriers destroy the antiferromagnetic order, but strong spin fluctuations persist throughout the superconducting phase and are intimately linked to superconductivity. Neutron scattering measurements of spin fluctuations in hole-doped copper oxides have revealed an unusual 'hour-glass' feature in the momentum-resolved magnetic spectrum that is present in a wide range of superconducting and non-superconducting materials. There is no widely accepted explanation for this feature. One possibility is that it derives from a pattern of alternating spin and charge stripes, and this idea is supported by measurements on stripe-ordered La(1.875)Ba(0.125)CuO(4) (ref. 15). Many copper oxides without stripe order, however, also exhibit an hour-glass spectrum. Here we report the observation of an hour-glass magnetic spectrum in a hole-doped antiferromagnet from outside the family of superconducting copper oxides. Our system has stripe correlations and is an insulator, which means that its magnetic dynamics can conclusively be ascribed to stripes. The results provide compelling evidence that the hour-glass spectrum in the copper oxide superconductors arises from fluctuating stripes.

  10. Possible ground states and parallel magnetic-field-driven phase transitions of collinear antiferromagnets

    NASA Astrophysics Data System (ADS)

    Li, Hai-Feng

    2016-10-01

    Understanding the nature of all possible ground states and especially magnetic-field-driven phase transitions of antiferromagnets represents a major step towards unravelling the real nature of interesting phenomena such as superconductivity, multiferroicity or magnetoresistance in condensed-matter science. Here a consistent mean-field calculation endowed with antiferromagnetic (AFM) exchange interaction (J), easy axis anisotropy (γ), uniaxial single-ion anisotropy (D) and Zeeman coupling to a magnetic field parallel to the AFM easy axis consistently unifies the AFM state, spin-flop (SFO) and spin-flip transitions. We reveal some mathematically allowed exotic spin states and fluctuations depending on the relative coupling strength of (J, γ and D). We build the three-dimensional (J, γ and D) and two-dimensional (γ and D) phase diagrams clearly displaying the equilibrium phase conditions and discuss the origins of various magnetic states as well as their transitions in different couplings. Besides the traditional first-order type one, we unambiguously confirm an existence of a second-order type SFO transition. This study provides an integrated theoretical model for the magnetic states of collinear antiferromagnets with two interpenetrating sublattices and offers a practical approach as an alternative to the estimation of magnetic exchange parameters (J, γ and D), and the results may shed light on nontrivial magnetism-related properties of bulks, thin films and nanostructures of correlated electron systems.

  11. Effect of frustration on spin-wave excitation spectra and ground-state properties of the quasi-one-dimensional antiferromagnetic chain with asymmetrical sublattices

    NASA Astrophysics Data System (ADS)

    Jiang, Jian-Jun; Liu, Yong-Jun; Zhang, Song-Jun; Yang, Cui-Hong

    2009-10-01

    We investigate the effect of frustration on spin-wave excitation spectra and the properties of the quasi-one-dimensional Heisenberg chain using a spin-wave-wave analysis, the exact diagonalization method and the density matrix renormalization group method. The results show that frustration can cause the softening of the acoustic excitation spectrum ω3, as well as the hardening of the optical excitation spectrum ω1. As a function of the frustration parameter α, the phase diagram exhibits a ferromagnetic phase, a narrow canted phase and a singlet phase. The results obtained from numerical methods show that the spin gap obviously opens and the tetramer-dimer state dominates the properties of the ground state in the singlet phase.

  12. First example of a high-level correlated calculation of the indirect spin-spin coupling constants involving tellurium: tellurophene and divinyl telluride.

    PubMed

    Rusakov, Yury Yu; Krivdin, Leonid B; Østerstrøm, Freja F; Sauer, Stephan P A; Potapov, Vladimir A; Amosova, Svetlana V

    2013-08-21

    This paper documents the very first example of a high-level correlated calculation of spin-spin coupling constants involving tellurium taking into account relativistic effects, vibrational corrections and solvent effects for medium sized organotellurium molecules. The (125)Te-(1)H spin-spin coupling constants of tellurophene and divinyl telluride were calculated at the SOPPA and DFT levels, in good agreement with experimental data. A new full-electron basis set, av3z-J, for tellurium derived from the "relativistic" Dyall's basis set, dyall.av3z, and specifically optimized for the correlated calculations of spin-spin coupling constants involving tellurium was developed. The SOPPA method shows a much better performance compared to DFT, if relativistic effects calculated within the ZORA scheme are taken into account. Vibrational and solvent corrections are next to negligible, while conformational averaging is of prime importance in the calculation of (125)Te-(1)H spin-spin couplings. Based on the performed calculations at the SOPPA(CCSD) level, a marked stereospecificity of geminal and vicinal (125)Te-(1)H spin-spin coupling constants originating in the orientational lone pair effect of tellurium has been established, which opens a new guideline in organotellurium stereochemistry.

  13. Electrical control of antiferromagnetic metal up to 15 nm

    NASA Astrophysics Data System (ADS)

    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.

  14. Collective dynamics in the Heisenberg pyrochlore antiferromagnet Gd2Sn2O7

    NASA Astrophysics Data System (ADS)

    Stewart, J. R.; Gardner, J. S.; Qiu, Y.; Ehlers, G.

    2008-10-01

    Gd2Sn2O7 is believed to be a good approximation to a Heisenberg antiferromagnet on a pyrochlore lattice with exchange and dipole-dipole interactions. The system is known to enter a long-range ordered ground state (the “Palmer Chalker” state) below Tc=1K with kord=(000) . However, persistent electronic spin fluctuations have been observed as T→0 . Using inelastic neutron scattering, we have studied the buildup of short-range spin-spin correlations as the temperature is lowered, and the eventual formation of a gapped long-range ordered state that is able to sustain spin waves below Tc . As a magnetic field is applied, new magnetic phases develop and the gap widens. These measurements show that Gd2Sn2O7 completely relieves itself of frustration, but the self-selected ground state is very delicate.

  15. Controlling and detecting spin correlations of ultracold atoms in optical lattices.

    PubMed

    Trotzky, Stefan; Chen, Yu-Ao; Schnorrberger, Ute; Cheinet, Patrick; Bloch, Immanuel

    2010-12-31

    We report on the controlled creation of a valence bond state of delocalized effective-spin singlet and triplet dimers by means of a bichromatic optical superlattice. We demonstrate a coherent coupling between the singlet and triplet states and show how the superlattice can be employed to measure the singlet-fraction employing a spin-blockade effect. Our method provides a reliable way to detect and control nearest-neighbor spin correlations in many-body systems of ultracold atoms. Being able to measure these correlations is an important ingredient in studying quantum magnetism in optical lattices. We furthermore employ a SWAP operation between atoms which are part of different triplets, thus effectively increasing their bond-length. Such a SWAP operation provides an important step towards the massively parallel creation of a multiparticle entangled state in the lattice.

  16. Quantum correlations in quenched disordered spin models: Enhanced order from disorder by thermal fluctuations.

    PubMed

    Sadhukhan, Debasis; Prabhu, R; Sen De, Aditi; Sen, Ujjwal

    2016-03-01

    We investigate the behavior of quantum correlations of paradigmatic quenched disordered quantum spin models, viz., the XY spin glass and random-field XY models. We show that quenched averaged quantum correlations can exhibit the order-from-disorder phenomenon for finite-size systems as well as in the thermodynamic limit. Moreover, we find that the order-from-disorder can become more pronounced in the presence of temperature by suitable tuning of the system parameters. The effects are found for entanglement measures as well as for information-theoretic quantum correlation ones, although the former show them more prominently. We also observe that the equivalence between the quenched averages and their self-averaged cousins--for classical and quantum correlations--is related to the quantum critical point in the corresponding ordered system.

  17. Comparison between muon spin rotation and neutron scattering studies on the 3-dimensional magnetic ordering of La/sub 2/CuO/sub 4-y/

    SciTech Connect

    Uemura, Y.J.; Kossler, W.J.; Kempton, J.R.; Yu, X.H.; Schone, H.E.; Opie, D.; Stronach, C.E.; Brewer, J.H.; Kiefl, R.F.; Kreitzman, S.R.; Luke, G.M.; Riseman, T.; Williams, D.L.; Ansaldo, E.J.; Endoh, Y.; Kudo, E.; Yamada, K.; Johnston, D.C.; Alvarez, M.; Goshorn, D.P.; Hidaka, Y.; Oda, M; Enomoto, Y.; Suzuki, M.; Murakami, T.

    1988-01-01

    Muon spin rotation and neutron scattering studies on powder and single-crystal specimens of La/sub 2/CuO/sub 4-v/ are compared. The apparent difference between the muon and neutron results for the ordered moment in the antiferromagnetic state is interpreted as the signature of increasingly short-ranged spatial spin correlations with increasing oxygen content.

  18. Comparison between muon spin rotation and neutron scattering studies on the 3-dimensional magnetic ordering of La2CuO(4-y)

    NASA Technical Reports Server (NTRS)

    Uemura, Y. J.; Kossler, W. J.; Kempton, J. R.; Yu, X. H.; Schone, H. E.; Opie, D.; Stronach, C. E.; Brewer, J. H.; Kiefl, R. F.; Kreitzman, S. R.

    1988-01-01

    Muon spin rotation and neutron scattering studies on powder and single-crystal specimens of La2CuO(4-y) are compared. The apparent difference between the muon and neutron results for the ordered moment in the antiferromagnetic state is interpreted as the signature of increasingly short-ranged spatial spin correlations with increasing oxygen content.

  19. Mixing antiferromagnets to tune NiFe-[IrMn/FeMn] interfacial spin-glasses, grains thermal stability, and related exchange bias properties

    SciTech Connect

    Akmaldinov, K.; Ducruet, C.; Portemont, C.; Joumard, I.; Prejbeanu, I. L.; Dieny, B.; Baltz, V.

    2014-05-07

    Spintronics devices and in particular thermally assisted magnetic random access memories require a wide range of ferromagnetic/antiferromagnetic (F/AF) exchange bias (EB) properties and subsequently of AF materials to fulfil diverse functionality requirements for the reference and storage. For the reference layer, large EB energies and high blocking temperature (T{sub B}) are required. In contrast, for the storage layer, mostly moderate T{sub B} are needed. One of the present issues is to find a storage layer with properties intermediate between those of IrMn and FeMn and in particular: (i) with a T{sub B} larger than FeMn for better stability at rest-T but lower than IrMn to reduce power consumption at write-T and (ii) with improved magnetic interfacial quality, i.e., with reduced interfacial glassy character for lower properties dispersions. To address this issue, the EB properties of F/AF based stacks were studied for various mixed [IrMn/FeMn] AFs. In addition to EB loop shifts, the F/AF magnetic interfacial qualities and the AF grains thermal stability are probed via measurements of the low- and high-temperature contributions to the T{sub B} distributions, respectively. A tuning of the above three parameters is observed when evolving from IrMn to FeMn via [IrMn/FeMn] repetitions.

  20. Experimental estimation of discord in an antiferromagnetic Heisenberg compound

    NASA Astrophysics Data System (ADS)

    Singh, H.; Chakraborty, T.; Panigrahi, P. K.; Mitra, C.

    2015-03-01

    Temperature-dependent static magnetic susceptibility and heat capacity data were employed to quantify quantum discord in copper nitrate which is a spin 1/2 antiferromagnetic Heisenberg system. With the help of existing theoretical formulations, quantum discord, mutual information, and purely classical correlation were estimated as a function of temperature using the experimental data. The experimentally quantified correlations estimated from susceptibility and heat capacity data are consistent with each other, and they exhibit a good match with theoretical predictions. Violation of Bell's inequality was also checked using the static magnetic susceptibility as well as heat capacity data. Quantum discord estimated from magnetic susceptibility as well as heat capacity data is found to be present in the thermal states of the system even when the system is in a separable state.

  1. Large spin Hall magnetoresistance and its correlation to the spin-orbit torque in W/CoFeB/MgO structures

    PubMed Central

    Cho, Soonha; Baek, Seung-heon Chris; Lee, Kyeong-Dong; Jo, Younghun; Park, Byong-Guk

    2015-01-01

    The phenomena based on spin-orbit interaction in heavy metal/ferromagnet/oxide structures have been investigated extensively due to their applicability to the manipulation of the magnetization direction via the in-plane current. This implies the existence of an inverse effect, in which the conductivity in such structures should depend on the magnetization orientation. In this work, we report a systematic study of the magnetoresistance (MR) of W/CoFeB/MgO structures and its correlation with the current-induced torque to the magnetization. We observe that the MR is independent of the angle between the magnetization and current direction but is determined by the relative magnetization orientation with respect to the spin direction accumulated by the spin Hall effect, for which the symmetry is identical to that of so-called the spin Hall magnetoresistance. The MR of ~1% in W/CoFeB/MgO samples is considerably larger than those in other structures of Ta/CoFeB/MgO or Pt/Co/AlOx, which indicates a larger spin Hall angle of W. Moreover, the similar W thickness dependence of the MR and the current-induced magnetization switching efficiency demonstrates that MR in a non-magnet/ferromagnet structure can be utilized to understand other closely correlated spin-orbit coupling effects such as the inverse spin Hall effect or the spin-orbit spin transfer torques. PMID:26423608

  2. Collinear order in the frustrated three-dimensional spin-1/2 antiferromagnet Li2CuW2O8

    NASA Astrophysics Data System (ADS)

    Ranjith, K. M.; Nath, R.; Skoulatos, M.; Keller, L.; Kasinathan, D.; Skourski, Y.; Tsirlin, A. A.

    2015-09-01

    Magnetic frustration in three dimensions (3D) manifests itself in the spin-1/2 insulator Li2CuW2O8 . Density-functional band-structure calculations reveal a peculiar spin lattice built of triangular planes with frustrated interplane couplings. The saturation field of 29 T contrasts with the susceptibility maximum at 8.5 K and a relatively low Néel temperature TN≃3.9 K . Magnetic order below TN is collinear with the propagation vector (0 ,1/2 ,0 ) and an ordered moment of 0.65(4) μB according to neutron diffraction data. This reduced ordered moment together with the low maximum of the magnetic specific heat (Cmax/R ≃0.35 ) pinpoint strong magnetic frustration in 3D. Collinear magnetic order suggests that quantum fluctuations play a crucial role in this system, where a noncollinear spiral state would be stabilized classically.

  3. Antiferromagnetic domains in epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Scholl, Andreas

    2002-03-01

    Interface and surface effects play a central role in modern magnet structures. Magnetic exchange coupling and bias, spin injection across the boundary between magnetic and non-magnetic layers, and the surface and interface anisotropy in multilayers are examples for interface phenomena that are utilized in magneto-electronics. In particular, the microscopic origin of exchange bias at ferromagnet/antiferromagnet interfaces is still an unsolved problem despite of intense research, driven by the important application of exchange bias in hard disk read-heads and magnetic RAM. Knowledge of the microscopic magnetic structure in antiferromagnetic thin films and surfaces is of crucial importance for a better understanding of the exchange bias effect. Microscopic experiments on magnetically coupled ferromagnet/antiferromagnet layers using X-ray Photoemission Electron Microscopy (X-PEEM) now provide a new insight into the microscopic processes at this important interface. Using a combination of x-ray magnetic dichroism (XMD) contrast and microscopic electron yield detection we have resolved the magnetic domain structure in LaFeO3 and NiO thin films and crystals. The antiferromagnetic domain structure is linked to the crystallographic structure of the material and vanishes approaching the magnetic ordering temperature. Ferromagnetic films grown on the antiferromagnetic substrate show a corresponding ferromagnetic domain structure, an uniaxial exchange anistropy and a local bias which increases with decreasing domain size, suggesting a statistical origin of the bias effect. The role of uncompensated interface spins will also be discussed. We will present first experiments on magnetic interlayer coupling across metallic antiferromagnets, which suggest a similar origin of bias in full-metallic exchange bias system. A. Scholl et al., Science 287, 1014 (2000), F. Nolting et al., Nature 405, 767 (2000), H. Ohldag et al., Phys. Rev. Lett. 86, 2878 (2001)

  4. Quasi-one-dimensional spin-orbit-coupled correlated insulator in a multinuclear coordinated organometallic crystal

    NASA Astrophysics Data System (ADS)

    Merino, J.; Jacko, A. C.; Khosla, A. L.; Powell, B. J.

    2016-11-01

    We show how quasi-one-dimensional correlated insulating states arise at two-thirds filling in organometallic multinuclear coordination complexes described by layered decorated honeycomb lattices. The interplay of spin-orbit coupling and electronic correlations leads to pseudospin-one moments arranged in weakly coupled chains with highly anisotropic exchange and a large trigonal splitting. We show that the in-plane exchange coupling is very different from the interlayer coupling; in particular the latter is much larger, despite the underlying hopping integrals being close to isotropic. Surprisingly, the effective dimensionality of the pseudospin model is strongly dependent on the strength of the electronic correlations: With increasing Hubbard U the pseudospin-one model becomes increasingly one dimensional, even though the crystal is almost isotropic. We predict that the trigonal splitting leads to a quantum phase transition from a Haldane phase to a topologically trivial phase as the relative strength of the spin-orbit coupling increases.

  5. Dynamical correlation effects on structure factor of spin-polarized two-dimensional electron gas

    SciTech Connect

    Singh, Gurvinder; Moudgil, R. K.; Kumar, Krishan; Garg, Vinayak

    2015-06-24

    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 r{sub s}. 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 r{sub s}=1. However, the extent of agreement somewhat diminishes with increasing r{sub s}, particularly for q around 2k{sub F}. 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.

  6. Antiferromagnetic long-range spin ordering in Fe- and NiF e2 -doped BaTi O3 multiferroic layers

    NASA Astrophysics Data System (ADS)

    Barbier, A.; Aghavnian, T.; Badjeck, V.; Mocuta, C.; Stanescu, D.; Magnan, H.; Rountree, C. L.; Belkhou, R.; Ohresser, P.; Jedrecy, N.

    2015-01-01

    We report on the Fe doping and on the comparative Ni-Fe codoping with composition close to NiF e2 of fully oxidized BaTi O3 layers (˜20 nm) elaborated by atomic oxygen plasma assisted molecular beam epitaxy; specifically any role of oxygen vacancies can be excluded in our films. Additionally to the classical in situ laboratory tools, the films were thoroughly characterized by synchrotron radiation x-ray diffraction and x-ray absorption spectroscopy. For purely Fe-doped layers, the native tetragonal perovskite structure evolves rapidly toward cubiclike up to 5% doping level above which the crystalline order disappears. On the contrary, low codoping levels (˜5 %NiF e2 ) fairly improve the thin film crystalline structure and surface smoothness; high levels (˜27%) lead to more crystallographically disordered films, although the tetragonal structure is preserved. Synchrotron radiation magnetic dichroic measurements reveal that metal clustering does not occur, that the Fe valence evolves from Fe2 + for low Fe doping levels to Fe3 + for high doping levels, and that the introduction of Ni favors the occurrence of the Fe2 + valence in the films. For the lower codoping levels it seems that Fe2 + substitutes Ba2 +, whereas Ni2 + always substitutes Ti4 +. Ferromagnetic long-range ordering can be excluded with great sensitivity in all samples as deduced from our x-ray magnetic absorption circular dichroic measurements. On the contrary, our linear dichroic x-ray absorption results support antiferromagnetic long-range ordering while piezoforce microscopy gives evidence of a robust ferroelectric long-range ordering showing that our films are excellent candidates for magnetic exchange coupled multiferroic applications.

  7. Magnetic correlations in a classic Mott system

    SciTech Connect

    Bao, W.; Broholm, C.; Aeppli, G.; Carter, S.A.; Dai, D.; Frost, C.D.; Honig, J.M.; Metcalf, P.

    1997-07-01

    The metal-insulator transition in V{sub 2}O{sub 3} causes a fundamental change in its magnetism. While the antiferromagnetic insulator (AFI) is a Heisenberg localized spin system, the antiferromagnetism in the strongly correlated metal is determined by a Fermi surface instability. Paramagnetic fluctuations in the metal and insulator represent similar spatial spin correlations, but are unrelated to the long range order in the AFI. The phase transition to the AFI induces an abrupt switching of magnetic correlations to a different magnetic wave vector. The AFI transition, therefore, is not a conventional spin order-disorder transition. Instead it is accounted for by an ordering in the occupation of the two degenerate d-orbitals at the Fermi level.

  8. A new member of ferrous sulfates, FeSO{sub 4}·2H{sub 2}O with PtS topology showing spin-canted long-range antiferromagnetic ordering

    SciTech Connect

    Zhao, Long; Liu, Wei Cao, Lixin; Su, Ge; Gao, Rongjie; Yang, Hongzhan

    2015-11-15

    A sanderite ferrous sulfate FeSO{sub 4}·2H{sub 2}O has been synthesized by the hydro/solvothermal method. Its crystal structure (Pccn, a=6.3160 Å, b=7.7550 Å, c=8.9880 Å, V=440.2 Å{sup 3}, Z=4) can be regarded as the condensation of alternately corner-shared FeO{sub 4}(H{sub 2}O){sub 2} octahedra and SO{sub 4} tetrahedra with a similar topology of PtS. By structural comparison with the known hydrated ferrous sulfates, the structural relation among them has been noted and discussed in detail. A variable temperature magnetic study shows a spin-canted long-range antiferromagnetic ordering in the low temperature regime, which might result from a possible phase transition during the cooling from the high temperature. - Graphical abstract: As a new number of ferrous sulfates, sanderite FeSO{sub 4}·2H{sub 2}O has been synthesized under hydro/solvothermal conditions, which exhibits a similar topology of PtS. - Highlights: • Sanderite ferrous sulfate has been synthesized. • The topology of its structure is similar to that of PtS. • A structural relation between these hydrated ferrous sulfates is discovered.

  9. Origin of Light-Induced Spin-Correlated Radical Pairs in Cryptochrome

    PubMed Central

    Weber, Stefan; Biskup, Till; Okafuji, Asako; Marino, Anthony R.; Berthold, Thomas; Link, Gerhard; Hitomi, Kenichi; Getzoff, Elizabeth D.; Schleicher, Erik; Norris, James R.

    2012-01-01

    Blue-light excitation of cryptochromes and homologs uniformly triggers electron transfer (ET) from the protein surface to the flavin-adenine dinucleotide (FAD) cofactor. A cascade of three conserved tryptophan residues has been considered to be critically involved in this photoreaction. If the FAD is initially in its fully oxidized (diamagnetic) redox state, light-induced ET via the tryptophan triad generates a series of short-lived spin-correlated radical pairs comprising an FAD radical and a tryptophan radical. Coupled doublet-pair species of this type have been proposed as the basis, e.g., of a biological magnetic compass in migratory birds, and were found critical for some cryptochrome functions in vivo. In this contribution, a cryptochrome-like protein (CRYD) derived from Xenopus laevis has been examined as a representative system. The terminal radical-pair state FAD•⋯W324• of X. laevis CRYD has been characterized in detail by time-resolved electron-paramagnetic resonance (TREPR) at X-band microwave frequency (9.68 GHz) and magnetic fields around 345 mT, and at Q-band (34.08 GHz) at around 1215 mT. Different precursor states – singlet versus triplet – of radical-pair formation have been considered in spectral simulations of the experimental electron-spin polarized TREPR signals. Conclusively, we present evidence for a singlet-state precursor of FAD•⋯W324• radical-pair generation because at both magnetic fields, where radical pairs were studied by TREPR, net-zero electron-spin polarization has been detected. Neither a spin-polarized triplet precursor nor a triplet at thermal equilibrium can explain such an electron-spin polarization. It turns out that a two-microwave-frequency TREPR approach is essential to draw conclusions on the nature of the precursor electronic states in light-induced spin-correlated radical pair formations. PMID:20684534

  10. Spin Structures of Textured and Isotropic Nd-Fe-B-Based Nanocomposites: Evidence for Correlated Crystallographic and Spin Textures

    NASA Astrophysics Data System (ADS)

    Michels, A.; Weber, R.; Titov, I.; Mettus, D.; Périgo, É. A.; Peral, I.; Vallcorba, O.; Kohlbrecher, J.; Suzuki, K.; Ito, M.; Kato, A.; Yano, M.

    2017-02-01

    We report the results of a comparative study of the magnetic microstructure of textured and isotropic Nd2Fe14B /α -Fe nanocomposites using magnetometry, transmission electron microscopy, synchrotron x-ray diffraction, and, in particular, magnetic small-angle neutron scattering (SANS). Analysis of the magnetic neutron data of the textured specimen and computation of the correlation function of the spin-misalignment SANS cross section suggests the existence of inhomogeneously magnetized regions on an intraparticle nanometer length scale, about 40-50 nm in the remanent state. Possible origins for this spin disorder are discussed: it may originate in thin-grain-boundary layers (where the material parameters are different than in the Nd2Fe14B grains), or it may reflect the presence of crystal defects (introduced via hot pressing), or the dispersion in the orientation distribution of the magnetocrystalline anisotropy axes of the Nd2Fe14B grains. X-ray powder diffraction data reveal a crystallographic texture in the direction perpendicular to the pressing direction—a finding which might be related to the presence of a texture in the magnetization distribution, as inferred from the magnetic SANS data.

  11. Tailoring exchange couplings in magnetic topological-insulator/antiferromagnet heterostructures

    NASA Astrophysics Data System (ADS)

    He, Qing Lin; Kou, Xufeng; Grutter, Alexander J.; Yin, Gen; Pan, Lei; Che, Xiaoyu; Liu, Yuxiang; Nie, Tianxiao; Zhang, Bin; Disseler, Steven M.; Kirby, Brian J.; Ratcliff, William, II; Shao, Qiming; Murata, Koichi; Zhu, Xiaodan; Yu, Guoqiang; Fan, Yabin; Montazeri, Mohammad; Han, Xiaodong; Borchers, Julie A.; Wang, Kang L.

    2017-01-01

    Magnetic topological insulators such as Cr-doped (Bi,Sb)2Te3 provide a platform for the realization of versatile time-reversal symmetry-breaking physics. By constructing heterostructures exhibiting Néel order in an antiferromagnetic CrSb and ferromagnetic order in Cr-doped (Bi,Sb)2Te3, we realize emergent interfacial magnetic phenomena which can be tailored through artificial structural engineering. Through deliberate geometrical design of heterostructures and superlattices, we demonstrate the use of antiferromagnetic exchange coupling in manipulating the magnetic properties of magnetic topological insulators. Proximity effects are shown to induce an interfacial spin texture modulation and establish an effective long-range exchange coupling mediated by antiferromagnetism, which significantly enhances the magnetic ordering temperature in the superlattice. This work provides a new framework on integrating topological insulators with antiferromagnetic materials and unveils new avenues towards dissipationless topological antiferromagnetic spintronics.

  12. Spin correlation tensor for measurement of quantum entanglement in electron–electron scattering

    NASA Astrophysics Data System (ADS)

    Tsurikov, D. E.; Samarin, S. N.; Williams, J. F.; Artamonov, O. M.

    2017-04-01

    We consider the problem of correct measurement of a quantum entanglement in the two-body electron–electron scattering. An expression is derived for a spin correlation tensor of a pure two-electron state. A geometric measure of a quantum entanglement as the distance between two forms of this tensor in entangled and separable cases is presented. Due to such definition, one does not need to look for the closest separable state to the analyzed state. We prove that introduced measure satisfies properties of a valid entanglement measure: nonnegativity, discriminance, normalization, non-growth under local operations and classical communication. This measure is calculated for a problem of electron–electron scattering. We prove that it does not depend on the azimuthal rotation angle of the second electron spin relative to the first electron spin before scattering. We specify how to find a spin correlation tensor and the related measure of a quantum entanglement in an experiment with electron–electron scattering. Finally, the introduced measure is extended to the mixed states.

  13. Generalized parton correlation functions for a spin-1/2 hadron

    SciTech Connect

    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.

  14. Correlated spin currents generated by resonant-crossed Andreev reflections in topological superconductors.

    PubMed

    He, James J; Wu, Jiansheng; Choy, Ting-Pong; Liu, Xiong-Jun; Tanaka, Y; Law, K T

    2014-01-01

    Topological superconductors, which support Majorana fermion excitations, have been the subject of intense studies due to their novel transport properties and their potential applications in fault-tolerant quantum computations. Here we propose a new type of topological superconductors that can be used as a novel source of correlated spin currents. We show that inducing superconductivity on a AIII class topological insulator wire, which respects a chiral symmetry and supports protected fermionic end states, will result in a topological superconductor. This topological superconductor supports two topological phases with one or two Majorana fermion end states, respectively. In the phase with two Majorana fermions, the superconductor can split Cooper pairs efficiently into electrons in two spatially separated leads due to Majorana-induced resonant-crossed Andreev reflections. The resulting currents in the leads are correlated and spin-polarized. Importantly, the proposed topological superconductors can be realized using quantum anomalous Hall insulators in proximity to superconductors.

  15. High-pressure ultrasonic study of the commensurate-incommensurate spin-density-wave transition in an antiferromagnetic Cr-0.3 at. % Ru alloy single crystal

    NASA Astrophysics Data System (ADS)

    Cankurtaran, M.; Saunders, G. A.; Wang, Q.; Ford, P. J.; Alberts, H. L.

    1992-12-01

    A comprehensive experimental study has been made of the elastic and nonlinear acoustic behavior of a dilute Cr alloy as it undergoes a commensurate (C)-incommensurate (I) spin-density-wave transition. Simultaneous measurements of the temperature dependence of ultrasonic wave velocity and attenuation of longitudinal and shear 10-MHz ultrasonic waves propagated along both the [100] and the [110] direction of Cr-0.3 at. % Ru alloy single crystal have been made in the temperature range 200-300 K. The temperature dependence of ultrasonic attenuation for each mode is characterized by a spikelike peak centered at TCI (=238.6 K) (on cooling) and at TIC (=255.6 K) (on warming). The velocities of both longitudinal and shear ultrasonic waves exhibit a large and steep increase at TCI on cooling and a similar drop at TIC on warming with a pronounced hysteresis between TIC and TCI. These observations show that the transition between the commensurate and incommensurate phases is first order. Measurements of the effects of hydrostatic pressure (up to 0.15 GPa) on the velocities of ultrasonic waves, which were made at several fixed temperatures between 248 and 297 K, show similar features: a steep increase at PCI (increasing pressure) and a similar drop at PIC (decreasing pressure) with a well-defined hysteresis. Both TCI and TIC increase strongly and approximately linearly with pressure, the mean values of dTCI/dP and dTIC/dP being (333+/-3) K/GPa and (277+/-5) K/GPa, respectively. The pressure and temperature dependencies of the anomalies in the ultrasonic wave velocity have been used to locate both the C-I and I-C boundaries on the magnetic P-T phase diagram. There is a triple point (at about 315 K and 0.22 GPa) where the paramagnetic, commensurate, and incommensurate spin-density-wave phases coexist. Results for the complete sets of the elastic stiffness tensor components and their hydrostatic pressure derivatives have been used to evaluate the acoustic-mode Gr

  16. Random Ising antiferromagnet on Bethe-like lattices with triangular loops

    NASA Astrophysics Data System (ADS)

    Yokota, Terufumi

    2016-04-01

    Phase diagrams for a random Ising antiferromagnet on Bethe-like lattices with triangular loops are obtained. Triangular loops cause strong geometrical frustration for the Ising antiferromagnet. Spin glass states appear by introducing randomness in the interaction between Ising spins. The random Ising antiferromagnet is studied by the replica method using global order parameter. The phase diagrams are compared with those for the corresponding random Ising ferromagnet to see the effects of the geometrical frustration. Antiferromagnetic phase does not appear for M ≤ 4 where M is the number of the corner sharing triangles on the Bethe-like lattices. In these cases, spin glass phase appears with a reentrant behavior. Spin glass phase in the random antiferromagnet appears for much weaker randomness than that in the corresponding random ferromagnet.

  17. Preparation of Entangled and Antiferromagnetic States by Dissipative Rydberg Pumping

    NASA Astrophysics Data System (ADS)

    Carr, A. W.; Saffman, M.

    2013-07-01

    We propose and analyze an approach for preparation of high fidelity entanglement and antiferromagnetic states using Rydberg mediated interactions with dissipation. Using asymmetric Rydberg interactions the two-atom Bell singlet is a dark state of the Rydberg pumping process. Master equation simulations demonstrate Bell singlet preparation fidelity F=0.998. Antiferromagnetic states are generated on a four-spin plaquette in agreement with results found from diagonalization of the transverse field Ising Hamiltonian.

  18. Peculiarities of stochastic motion in antiferromagnetic nanoparticles

    NASA Astrophysics Data System (ADS)

    Gomonay, H.; Loktev, V.

    2013-01-01

    Antiferromagnetic (AFM) materials are widely used in spintronic devices as passive elements (for stabilization of ferromagnetic layers) and as active elements (for information coding). In both cases the switching between different AFM states, to a great extent depends on the environmental noise. In the present paper we derive stochastic Langevian equations for an AFM vector and a corresponding Fokker-Plank equation for a distribution function in the phase space of generalised coordinate and momentum. Thermal noise is modelled by a random delta-correlated magnetic field that interacts with the dynamic magnetisation of AFM particle. We scrupulously analyse a particular case of a collinear compensated AFM in the presence of spin-polarised current. The energy distribution function is found for normal modes in the vicinity of two equilibrium states (static and stationary) in sub- and super-critical regimes. It is shown that the noise-induced dynamics of AFM vector has some pecuilarities compared to the dynamics of magnetisation vector in ferromagnets.

  19. Piezo-antiferromagnetic effect of sawtooth-like graphene nanoribbons

    NASA Astrophysics Data System (ADS)

    Zhao, Shangqian; Lu, Yan; Zhang, Yuchun; Lu, Wengang; Liang, Wenjie; Wang, Enge

    2014-05-01

    A type of sawtooth-like graphene nanoribbon (SGNR) with piezo-antiferromagnetic effect is studied numerically. The ground state of the studied SGNR changes from nonmagnetic state to antiferromagnetic state with uniaxial strain. The changes of the spin-charge distributions during the stretching are investigated. The Hubbard model reveals that the hopping integrals between the π-orbitals of the carbon atoms are responsible to the piezo-antiferromagnetic effect. The study sheds light on the application of graphene-based structures to nanosensors and spintronic devices.

  20. Double spin-glass-like behavior and antiferromagnetic superexchange interaction between Fe3+ ions in α-Ga2-xFexO3 (0 ≤ x ≤ 0.4)

    NASA Astrophysics Data System (ADS)

    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).