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Sample records for antiferromagnetic spin correlations

  1. Spin- and density-resolved microscopy of antiferromagnetic correlations in Fermi-Hubbard chains.

    PubMed

    Boll, Martin; Hilker, Timon A; Salomon, Guillaume; Omran, Ahmed; Nespolo, Jacopo; Pollet, Lode; Bloch, Immanuel; Gross, Christian

    2016-09-16

    The repulsive Hubbard Hamiltonian is one of the foundational models describing strongly correlated electrons and is believed to capture essential aspects of high-temperature superconductivity. Ultracold fermions in optical lattices allow for the simulation of the Hubbard Hamiltonian with control over kinetic energy, interactions, and doping. A great challenge is to reach the required low entropy and to observe antiferromagnetic spin correlations beyond nearest neighbors, for which quantum gas microscopes are ideal. Here, we report on the direct, single-site resolved detection of antiferromagnetic correlations extending up to three sites in spin-1/2 Hubbard chains, which requires entropies per particle well below s* = ln(2). The simultaneous detection of spin and density opens the route toward the study of the interplay between magnetic ordering and doping in various dimensions. Copyright © 2016, American Association for the Advancement of Science.

  2. 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.

  3. Third-neighbor correlators of a one-dimensional spin-1/2 Heisenberg antiferromagnet.

    PubMed

    Sakai, Kazumitsu; Shiroishi, Masahiro; Nishiyama, Yoshihiro; Takahashi, Minoru

    2003-06-01

    We exactly evaluate the third-neighbor correlator S(z)(j)S(z)(j+3) and all the possible nonzero correlators S(alpha)(j)S(beta)(j+1)S(gamma;)(j+2)S(delta)(j+3) of the one-dimensional spin-1/2 Heisenberg XXX antiferromagnet in the ground state without magnetic field. All the correlators are expressed in terms of certain combinations of logarithm ln 2, the Riemann zeta function zeta(3), zeta(5) with rational coefficients. The results accurately coincide with the numerical ones obtained by the density-matrix renormalization group method and the numerical diagonalization.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Spin Hall Effects in Metallic Antiferromagnets

    SciTech Connect

    Zhang, Wei; Jungfleisch, Matthias B.; Jiang, Wanjun; Pearson, John E.; Hoffmann, Axel; Freimuth, Frank; Mokrousov, Yuriy

    2014-11-04

    In this paper, we investigate four CuAu-I-type metallic antiferromagnets for their potential as spin current detectors using spin pumping and inverse spin Hall effect. Nontrivial spin Hall effects were observed for FeMn, PdMn, and IrMn while a much higher effect was obtained for PtMn. Using thickness-dependent measurements, we determined the spin diffusion lengths of these materials to be short, on the order of 1 nm. The estimated spin Hall angles of the four materials follow the relationship PtMn > IrMn > PdMn > FeMn, highlighting the correlation between the spin-orbit coupling of nonmagnetic species and the magnitude of the spin Hall effect in their antiferromagnetic alloys. These experiments are compared with first-principles calculations. Finally, engineering the properties of the antiferromagnets as well as their interfaces can pave the way for manipulation of the spin dependent transport properties in antiferromagnet-based spintronics.

  10. Spin Hall Effects in Metallic Antiferromagnets

    DOE PAGES

    Zhang, Wei; Jungfleisch, Matthias B.; Jiang, Wanjun; ...

    2014-11-04

    In this paper, we investigate four CuAu-I-type metallic antiferromagnets for their potential as spin current detectors using spin pumping and inverse spin Hall effect. Nontrivial spin Hall effects were observed for FeMn, PdMn, and IrMn while a much higher effect was obtained for PtMn. Using thickness-dependent measurements, we determined the spin diffusion lengths of these materials to be short, on the order of 1 nm. The estimated spin Hall angles of the four materials follow the relationship PtMn > IrMn > PdMn > FeMn, highlighting the correlation between the spin-orbit coupling of nonmagnetic species and the magnitude of the spinmore » Hall effect in their antiferromagnetic alloys. These experiments are compared with first-principles calculations. Finally, engineering the properties of the antiferromagnets as well as their interfaces can pave the way for manipulation of the spin dependent transport properties in antiferromagnet-based spintronics.« less

  11. Spin pumping torque in antiferromagnets

    NASA Astrophysics Data System (ADS)

    Semenov, Yuriy G.; Kim, Ki Wook

    2017-05-01

    A currentless, magnetic-field free mechanism for the Néel vector rotation in an antiferromagnet is proposed. An efficient torque is induced by spin pumping through charging/discharging of spin filtered electrons via a ferromagnetic layer in a spin capacitor structure consisting of the two heterogenous magnetic materials. The relatively long electron spin relaxation time in the antiferromagnet enables the electron spin polarizations to retain the exchange effective field sufficiently long to modulate the local magnetic moments and subsequently the magnetic state of the material. Precession of the sublattice magnetization is modeled based on the Néel vector formulation, theoretically demonstrating the feasibility of the physical mechanism (such as the reversal) with sub-aJ energy consumption. Its potential application to spintronic devices is also discussed.

  12. 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.

  13. 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.

  14. 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.

  15. Spin Superfluidity in Biaxial Antiferromagnetic Insulators

    NASA Astrophysics Data System (ADS)

    Qaiumzadeh, Alireza; Skarsvâg, Hans; Holmqvist, Cecilia; Brataas, Arne

    2017-03-01

    Antiferromagnets may exhibit spin superfluidity since the dipole interaction is weak. We seek to establish that this phenomenon occurs in insulators such as NiO, which is a good spin conductor according to previous studies. We investigate nonlocal spin transport in a planar antiferromagnetic insulator with a weak uniaxial anisotropy. The anisotropy hinders spin superfluidity by creating a substantial threshold that the current must overcome. Nevertheless, we show that applying a high magnetic field removes this obstacle near the spin-flop transition of the antiferromagnet. Importantly, the spin superfluidity can then persist across many micrometers, even in dirty samples.

  16. 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.

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

    DOE PAGES

    Daniels, Matthew W.; Guo, Wei; Stocks, George Malcolm; ...

    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.

  18. Possible Correlation Between Stripe-Like Antiferromagnetic Spin Fluctuations and Superconductivity in ThFeAsN

    NASA Astrophysics Data System (ADS)

    Kumar, Jagdish

    2017-08-01

    The recently invented ThFeAsN superconductor, belonging to the family of Fe-based superconductors, has been studied using ab initio density functional theory. Our calculations demonstrate that the electronic structure of this superconductor is similar to that of other Fe-based superconductors with computed magnetic ground state showing strong dependence on atomic positions. Using relaxed atomic positions, the single- and double-stripe magnetic states are found to be energetically close to each other, which may lead to stripe-like antiferromagnetic spin fluctuations. We speculate that such energetic degeneracy among two antiferromagnetic structures may be an ideal condition for strong stripe-like antiferromagnetic spin fluctuations, which may be playing a key role in obtaining high transition temperature of 30 K. Fixed spin moment calculations demonstrate the possibility of local minima for magnetic states in ThFeAsN. The absence of long-range ordering in ThFeAsN may be due to presence of such local minima.

  19. Antiferromagnetic spin flop and exchange bias

    SciTech Connect

    Nogues, 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 (MnF{sub 2})-ferromagnetic (Fe) bilayers. Cooling and measuring in fields larger than the antiferromagnetic spin-flop field, H{sub SF}, causes an irreversible reduction of the magnitude of the exchange bias field, H{sub E}. This indicates that, contrary to what is normally assumed, the interface spin structure does not remain ''frozen in'' below T{sub N} if large enough fields are applied. (c) 2000 The American Physical Society.

  20. 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.

  1. 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.

  2. Indirect control of antiferromagnetic domain walls with spin current.

    PubMed

    Wieser, R; Vedmedenko, E Y; Wiesendanger, R

    2011-02-11

    The indirect controlled displacement of an antiferromagnetic domain wall by a spin current is studied by Landau-Lifshitz-Gilbert spin dynamics. The antiferromagnetic domain wall can be shifted both by a spin-polarized tunnel current of a scanning tunneling microscope or by a current driven ferromagnetic domain wall in an exchange coupled antiferromagnetic-ferromagnetic layer system. The indirect control of antiferromagnetic domain walls opens up a new and promising direction for future spin device applications based on antiferromagnetic materials.

  3. 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

  4. 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.

  5. 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

  6. Antiferromagnetic Spin Wave Field-Effect Transistor

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    In a collinear antiferromagnet with easy-axis anisotropy, symmetry dictates that the spin wave modes must be doubly degenerate. Theses two modes, distinguished by their opposite polarization and available only in antiferromagnets, give rise to a novel degree of freedom to encode and process information. We show that the spin wave polarization can be manipulated by an electric field induced Dzyaloshinskii-Moriya interaction and magnetic anisotropy. We propose a prototype spin wave field-effect transistor which realizes a gate-tunable magnonic analog of the Faraday effect, and demonstrate its application in THz signal modulation. Our findings open up the exciting possibility of digital data processing utilizing antiferromagnetic spin waves and enable the direct projection of optical computing concepts onto the mesoscopic scale.

  7. Antiferromagnetic Domain Wall Motion Driven by Spin-Orbit Torques.

    PubMed

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

    2016-08-19

    We theoretically investigate the 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.

  8. 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

  9. 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.

  10. 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.

  11. Spin pumping and inverse spin Hall voltages from dynamical antiferromagnets

    NASA Astrophysics Data System (ADS)

    Johansen, Øyvind; Brataas, Arne

    2017-06-01

    Dynamical antiferromagnets can pump spins into adjacent conductors. The high antiferromagnetic resonance frequencies represent a challenge for experimental detection, but magnetic fields can reduce these resonance frequencies. We compute the ac and dc inverse spin Hall voltages resulting from dynamical spin excitations as a function of a magnetic field along the easy axis and the polarization of the driving ac magnetic field perpendicular to the easy axis. We consider the insulating antiferromagnets MnF2,FeF2, and NiO. Near the spin-flop transition, there is a significant enhancement of the dc spin pumping and inverse spin Hall voltage for the uniaxial antiferromagnets MnF2 and FeF2. In the uniaxial antiferromagnets it is also found that the ac spin pumping is independent of the external magnetic field when the driving field has the optimal circular polarization. In the biaxial NiO, the voltages are much weaker, and there is no spin-flop enhancement of the dc component.

  12. 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.

  13. 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.

  14. 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.

  15. Spin-mechanical inertia in antiferromagnets

    NASA Astrophysics Data System (ADS)

    Cheng, Ran; Wu, Xiaochuan; Xiao, Di

    2017-08-01

    Angular-momentum conservation has served as a guiding principle in the interplay between spin dynamics and mechanical rotations. However, in an antiferromagnet with vanishing magnetization, new fundamental rules are required to properly describe spin-mechanical phenomena. Here we show that the Néel order dynamics affects the mechanical motion of a rigid body by modifying its inertia tensor in the presence of strong magnetocrystalline anisotropy. This effect depends on temperature when magnon excitations are considered. Such a spin-mechanical inertia can produce measurable consequences at small scales.

  16. 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.

  17. 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

  18. Antiferromagnetic anisotropy determination by spin Hall magnetoresistance

    NASA Astrophysics Data System (ADS)

    Wang, Hua; Hou, Dazhi; Qiu, Zhiyong; Kikkawa, Takashi; Saitoh, Eiji; Jin, Xiaofeng

    2017-08-01

    An electric method for measuring magnetic anisotropy in antiferromagnetic insulators (AFIs) is proposed. When a metallic film with strong spin-orbit interactions, e.g., platinum (Pt), is deposited on an AFI, its resistance should be affected by the direction of the AFI Néel vector due to the spin Hall magnetoresistance (SMR). Accordingly, the direction of the AFI Néel vector, which is affected by both the external magnetic field and the magnetic anisotropy, is reflected in resistance of Pt. The magnetic field angle dependence of the resistance of Pt on AFI is calculated by considering the SMR, which indicates that the antiferromagnetic anisotropy can be obtained experimentally by monitoring the Pt resistance in strong magnetic fields. Calculations are performed for realistic systems such as Pt/Cr2O3, Pt/NiO, and Pt/CoO.

  19. 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.

  20. 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

  1. 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.

  2. 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.

  3. Static and dynamical spin correlations of the S =1/2 random-bond antiferromagnetic Heisenberg model on the triangular and kagome lattices

    NASA Astrophysics Data System (ADS)

    Shimokawa, Tokuro; Watanabe, Ken; Kawamura, Hikaru

    2015-10-01

    Inspired by the recent theoretical suggestion that the random-bond S =1 /2 antiferromagnetic Heisenberg model on the triangular and the kagome lattices might exhibit a randomness-induced quantum spin liquid (QSL) behavior when the strength of the randomness exceeds a critical value, and that this "random-singlet state" might be relevant to the QSL behaviors experimentally observed in triangular organic salts κ -(ET) 2Cu2(CN) 3 and EtMe3Sb [Pd(dmit)2] 2 and in kagome herbertsmithite ZnCu3(OH) 6Cl2 , we further investigate the nature of the static and the dynamical spin correlations of these models. We compute the static and the dynamical spin structure factors, S (q ) and S (q ,ω ) , by means of an exact diagonalization method. In both triangular and kagome models, the computed S (q ,ω ) in the random-singlet state depends on the wave vector q only weakly, robustly exhibiting gapless behaviors accompanied by the broad distribution extending to higher energy ω . Especially in the strongly random kagome model, S (q ,ω ) hardly depends on q , and exhibits an almost flat distribution for a wide range of ω , together with a ω =0 peak. These features agree semiquantitatively with the recent neutron-scattering data on a single-crystal herbertsmithite. Furthermore, the computed magnetization curve agrees almost quantitatively with the experimental one recently measured on a single-crystal herbertsmithite. These results suggest that the QSL state observed in herbertsmithite might indeed be the randomness-induced QSL state, i.e., the random-singlet state.

  4. 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.

  5. Robust spin transfer torque in antiferromagnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Saidaoui, Hamed Ben Mohamed; Waintal, Xavier; Manchon, Aurélien

    2017-04-01

    We theoretically study the current-induced spin torque in antiferromagnetic tunnel junctions, composed of two semi-infinite antiferromagnetic layers separated by a tunnel barrier, in both clean and disordered regimes. We find that the torque enabling electrical manipulation of the Néel antiferromagnetic order parameter is out of plane, ˜n ×p , while the torque competing with the antiferromagnetic exchange is in plane, ˜n ×(p ×n ) . Here, p and n are the Néel order parameter direction of the reference and free layers, respectively. Their bias dependence shows behavior similar to that in ferromagnetic tunnel junctions, the in-plane torque being mostly linear in bias, while the out-of-plane torque is quadratic. Most importantly, we find that the spin transfer torque in antiferromagnetic tunnel junctions is much more robust against disorder than that in antiferromagnetic metallic spin valves due to the tunneling nature of spin transport.

  6. 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)

  7. 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.

  8. 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.

  9. 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.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

    Sekine, Akihiko; Nomura, Kentaro

    2016-03-01

    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.

  12. Magnonic analog of relativistic Zitterbewegung in an antiferromagnetic spin chain

    NASA Astrophysics Data System (ADS)

    Wang, Weiwei; Gu, Chenjie; Zhou, Yan; Fangohr, Hans

    2017-07-01

    We theoretically investigate the spin-wave (magnon) excitations in a classical antiferromagnetic spin chain with easy-axis anisotropy. We obtain a Dirac-like equation by linearizing the Landau-Lifshitz-Gilbert equation in this antiferromagnetic system, in contrast to the ferromagnetic system in which a Schrödinger-type equation is derived. The Hamiltonian operator in the Dirac-like equation is a pseudo-Hermitian. We compute and demonstrate relativistic Zitterbewegung (trembling motion) in the antiferromagnetic spin chain by measuring the expectation values of the wave-packet position.

  13. 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.

  14. Antiferromagnetic Correlations in Two-Dimensional Fermionic Mott-Insulating and Metallic Phases

    NASA Astrophysics Data System (ADS)

    Drewes, J. H.; Miller, L. A.; Cocchi, E.; Chan, C. F.; Wurz, N.; Gall, M.; Pertot, D.; Brennecke, F.; Köhl, M.

    2017-04-01

    We experimentally study the emergence of antiferromagnetic correlations between ultracold fermionic atoms in a two-dimensional optical lattice with decreasing temperature. We determine the uniform magnetic susceptibility of the two-dimensional Hubbard model from simultaneous measurements of the in situ density distribution of both spin components. At half filling and strong interactions our data approach the Heisenberg model of localized spins with antiferromagnetic correlations. Moreover, we observe a fast decay of magnetic correlations when doping the system away from half filling.

  15. 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).

  16. 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].

  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. Enhanced Spin Conductance of a Thin-Film Insulating Antiferromagnet

    NASA Astrophysics Data System (ADS)

    Bender, Scott A.; Skarsvâg, Hans; Brataas, Arne; Duine, Rembert A.

    2017-08-01

    We investigate spin transport by thermally excited spin waves in an antiferromagnetic insulator. Starting from a stochastic Landau-Lifshitz-Gilbert phenomenology, we obtain the out-of-equilibrium spin-wave properties. In linear response to spin biasing and a temperature gradient, we compute the spin transport through a normal-metal-antiferromagnet-normal-metal heterostructure. We show that the spin conductance diverges as one approaches the spin-flop transition; this enhancement of the conductance should be readily observable by sweeping the magnetic field across the spin-flop transition. The results from such experiments may, on the one hand, enhance our understanding of spin transport near a phase transition, and on the other be useful for applications that require a large degree of tunability of spin currents. In contrast, the spin Seebeck coefficient does not diverge at the spin-flop transition. Furthermore, the spin Seebeck coefficient is finite even at zero magnetic field, provided that the normal metal contacts break the symmetry between the antiferromagnetic sublattices.

  19. Long-range interactions in antiferromagnetic quantum spin chains

    NASA Astrophysics Data System (ADS)

    Bravo, B.; Cabra, D. C.; Gómez Albarracín, F. A.; Rossini, G. L.

    2017-08-01

    We study the role of long-range dipolar interactions on antiferromagnetic spin chains, from the classical S →∞ limit to the deep quantum case S =1 /2 , including a transverse magnetic field. To this end, we combine different techniques such as classical energy minima, classical Monte Carlo, linear spin waves, bosonization, and density matrix renormalization group (DMRG). We find a phase transition from the already reported dipolar ferromagnetic region to an antiferromagnetic region for high enough antiferromagnetic exchange. Thermal and quantum fluctuations destabilize the classical order before reaching magnetic saturation in both phases, and also close to zero field in the antiferromagnetic phase. In the extreme quantum limit S =1 /2 , extensive DMRG computations show that the main phases remain present with transition lines to saturation significatively shifted to lower fields, in agreement with the bosonization analysis. The overall picture maintains a close analogy with the phase diagram of the anisotropic XXZ spin chain in a transverse field.

  20. Exchange bias mechanism at the ferromagnetic/antiferromagnetic interface with rotatable antiferromagnetic spins: A Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Hu, Yong; Wang, Yuying; Chi, Xiaodan; Li, Xuesi; Du, An; Shi, Feng

    2017-08-01

    We perform modified Monte Carlo simulations on a ferromagnetic/antiferromagnetic bilayer structure with adjustable antiferromagnetic anisotropy and degree of exchange coupling. Generally, both the antiferromagnetic anisotropy and the degree of exchange coupling at the ferromagnetic/antiferromagnetic interface are difficult to be directly detected experimentally. However, they may play crucial roles in establishing the exchange bias properties through determining whether the antiferromagnetic spins at the interface are rotatable or pinned. Therefore, we precisely calculated the numbers of rotatable and pinned antiferromagnetic spins at the interface and analyzed their contribution to exchange bias and coercivity in the specified ranges of antiferromagnetic anisotropy and degree of exchange coupling. The simulation results may help to clarify the experimental controversies concerning the occurrence of exchange bias effect prior to the detection of pinned uncompensated antiferromagnetic spins. They can also be used to properly interpret the dependence of exchange bias on several-nanometer antiferromagnetic layer thicknesses.

  1. Quantum Spin Liquid Emerging from Antiferromagnetic Order by Introducing Disorder.

    PubMed

    Furukawa, T; Miyagawa, K; Itou, T; Ito, M; Taniguchi, H; Saito, M; Iguchi, S; Sasaki, T; Kanoda, K

    2015-08-14

    Quantum spin liquids, which are spin versions of quantum matter, have been sought after in systems with geometrical frustration. We show that disorder drives a classical magnet into a quantum spin liquid through conducting NMR experiments on an organic Mott insulator, κ-(ET)_{2}Cu[N(CN)_{2}]Cl. Antiferromagnetic ordering in the pristine crystal, when irradiated by x rays, disappears. Spin freezing, spin gap, and critical slowing down are not observed, but gapless spin excitations emerge, suggesting a novel role of disorder that brings forth a quantum spin liquid from a classical ordered state.

  2. Quantum Spin Liquid Emerging from Antiferromagnetic Order by Introducing Disorder

    NASA Astrophysics Data System (ADS)

    Furukawa, T.; Miyagawa, K.; Itou, T.; Ito, M.; Taniguchi, H.; Saito, M.; Iguchi, S.; Sasaki, T.; Kanoda, K.

    2015-08-01

    Quantum spin liquids, which are spin versions of quantum matter, have been sought after in systems with geometrical frustration. We show that disorder drives a classical magnet into a quantum spin liquid through conducting NMR experiments on an organic Mott insulator, κ -(ET) 2Cu [N (CN) 2]Cl . Antiferromagnetic ordering in the pristine crystal, when irradiated by x rays, disappears. Spin freezing, spin gap, and critical slowing down are not observed, but gapless spin excitations emerge, suggesting a novel role of disorder that brings forth a quantum spin liquid from a classical ordered state.

  3. Spin transport through the metallic antiferromagnet FeMn

    SciTech Connect

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

    2016-10-19

    Here, we investigate spin transport through metallic antiferromagnets using measurements based on spin pumping combined with inverse spin Hall effects in Ni80Fe20/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. By using this approach we can detect two distinctively different spin transport regimes, which we associate with electronic and magnonic spin currents, respectively. Furthermore, the latter can extend to relatively large distances (approximate to 9 nm) and is enhanced when the antiferromagnetic ordering temperature is close to the measurement temperature.

  4. Spin transport through the metallic antiferromagnet FeMn

    DOE PAGES

    Saglam, H.; Zhang, W.; Jungfleisch, M. B.; ...

    2016-10-19

    Here, we investigate spin transport through metallic antiferromagnets using measurements based on spin pumping combined with inverse spin Hall effects in Ni80Fe20/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. By using this approach we can detect two distinctively different spin transport regimes, which we associate with electronic and magnonic spin currents, respectively. Furthermore, the latter can extend to relatively large distances (approximate to 9 nm) and is enhanced when the antiferromagnetic ordering temperature is close tomore » the measurement temperature.« less

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. 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).

  15. 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

  16. 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.

  17. Antiferromagnetic domain wall as spin wave polarizer and retarder.

    PubMed

    Lan, Jin; Yu, Weichao; Xiao, Jiang

    2017-08-02

    As a collective quasiparticle excitation of the magnetic order in magnetic materials, spin wave, or magnon when quantized, can propagate in both conducting and insulating materials. Like the manipulation of its optical counterpart, the ability to manipulate spin wave polarization is not only important but also fundamental for magnonics. With only one type of magnetic lattice, ferromagnets can only accommodate the right-handed circularly polarized spin wave modes, which leaves no freedom for polarization manipulation. In contrast, antiferromagnets, with two opposite magnetic sublattices, have both left and right-circular polarizations, and all linear and elliptical polarizations. Here we demonstrate theoretically and confirm by micromagnetic simulations that, in the presence of Dzyaloshinskii-Moriya interaction, an antiferromagnetic domain wall acts naturally as a spin wave polarizer or a spin wave retarder (waveplate). Our findings provide extremely simple yet flexible routes toward magnonic information processing by harnessing the polarization degree of freedom of spin wave.Spin waves are promising candidates as carriers for energy-efficient information processing, but they have not yet been fully explored application wise. Here the authors theoretically demonstrate that antiferromagnetic domain walls are naturally spin wave polarizers and retarders, two key components of magnonic devices.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Spiraling spin structure in an exchange-coupled antiferromagnetic layer

    PubMed

    Yang; Chien

    2000-09-18

    Using trilayers of permalloy/FeMn/Co with various thicknesses t(AF) of the antiferromagnetic FeMn, we have observed evidence of a spiraling spin structure within FeMn. For t(AF)<90 A, the turn angle straight theta of the spiral varies as straight theta = (1.76 degrees /A)t(AF).

  3. Spin Hall effects in metallic antiferromagnets – perspectives for future spin-orbitronics

    SciTech Connect

    Sklenar, Joseph; Zhang, Wei Jungfleisch, Matthias B.; Jiang, Wanjun; Pearson, John E.; Hoffmann, Axel; Saglam, Hilal; Ketterson, John B.

    2016-05-15

    We investigate angular dependent spin-orbit torques from the spin Hall effect in a metallic antiferromagnet using the spin-torque ferromagnetic resonance technique. The large spin Hall effect exists in PtMn, a prototypical CuAu-I-type metallic antiferromagnet. By applying epitaxial growth, we previously reported an appreciable difference in spin-orbit torques for c- and a-axis orientated samples, implying anisotropic effects in magnetically ordered materials. In this work we demonstrate through bipolar-magnetic-field experiments a small but noticeable asymmetric behavior in the spin-transfer-torque that appears as a hysteresis effect. We also suggest that metallic antiferromagnets may be good candidates for the investigation of various unidirectional effects related to novel spin-orbitronics phenomena.

  4. Spin Hall effects in metallic antiferromagnets – perspectives for future spin-orbitronics

    DOE PAGES

    Sklenar, Joseph; Zhang, Wei; Jungfleisch, Matthias B.; ...

    2016-03-07

    In this paper, we investigate angular dependent spin-orbit torques from the spin Hall effect in a metallic antiferromagnet using the spin-torque ferromagnetic resonance technique. The large spin Hall effect exists in PtMn, a prototypical CuAu-I-type metallic antiferromagnet. By applying epitaxial growth, we previously reported an appreciable difference in spin-orbit torques for c- and a-axis orientated samples, implying anisotropic effects in magnetically ordered materials. In this work we demonstrate through bipolar-magnetic-field experiments a small but noticeable asymmetric behavior in the spin-transfer-torque that appears as a hysteresis effect. Finally, we also suggest that metallic antiferromagnets may be good candidates for the investigationmore » of various unidirectional effects related to novel spin-orbitronics phenomena.« less

  5. 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}.

  6. Antiferromagnetic Correlations in Two-Dimensional Fermionic Mott-Insulating and Metallic Phases.

    PubMed

    Drewes, J H; Miller, L A; Cocchi, E; Chan, C F; Wurz, N; Gall, M; Pertot, D; Brennecke, F; Köhl, M

    2017-04-28

    We experimentally study the emergence of antiferromagnetic correlations between ultracold fermionic atoms in a two-dimensional optical lattice with decreasing temperature. We determine the uniform magnetic susceptibility of the two-dimensional Hubbard model from simultaneous measurements of the in situ density distribution of both spin components. At half filling and strong interactions our data approach the Heisenberg model of localized spins with antiferromagnetic correlations. Moreover, we observe a fast decay of magnetic correlations when doping the system away from half filling.

  7. Composite spin crystal phase in antiferromagnetic chiral magnets

    NASA Astrophysics Data System (ADS)

    Osorio, S. A.; Rosales, H. D.; Sturla, M. B.; Cabra, D. C.

    2017-07-01

    We study the classical antiferromagnetic Heisenberg model on the triangular lattice with Dzyaloshinskii-Moriya interactions in a magnetic field. We focus in particular on the emergence of a composite spin crystal phase, dubbed an antiferromagnetic skyrmion lattice, that was recently observed for intermediate fields. This complex phase can be made up from three interpenetrated skyrmion lattices, one for each sublattice of the original triangular one. Following these recent numerical results, in this paper we explicitly construct the low-energy effective action that reproduces the correct phenomenology and could serve as a starting point to study the coupling to charge carriers, lattice vibrations, structural disorder, and transport phenomena.

  8. 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.

  9. 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

  10. 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.

  11. 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

  12. 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.

  13. Revealing hidden antiferromagnetic correlations in doped Hubbard chains via string correlators.

    PubMed

    Hilker, Timon A; Salomon, Guillaume; Grusdt, Fabian; Omran, Ahmed; Boll, Martin; Demler, Eugene; Bloch, Immanuel; Gross, Christian

    2017-08-04

    Topological phases, like the Haldane phase in spin-1 chains, defy characterization through local order parameters. Instead, nonlocal string order parameters can be employed to reveal their hidden order. Similar diluted magnetic correlations appear in doped one-dimensional lattice systems owing to the phenomenon of spin-charge separation. Here we report on the direct observation of such hidden magnetic correlations via quantum gas microscopy of hole-doped ultracold Fermi-Hubbard chains. The measurement of nonlocal spin-density correlation functions reveals a hidden finite-range antiferromagnetic order, a direct consequence of spin-charge separation. Our technique, which measures nonlocal order directly, can be readily extended to higher dimensions to study the complex interplay between magnetic order and density fluctuations. Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

  14. Revealing hidden antiferromagnetic correlations in doped Hubbard chains via string correlators

    NASA Astrophysics Data System (ADS)

    Hilker, Timon A.; Salomon, Guillaume; Grusdt, Fabian; Omran, Ahmed; Boll, Martin; Demler, Eugene; Bloch, Immanuel; Gross, Christian

    2017-08-01

    Topological phases, like the Haldane phase in spin-1 chains, defy characterization through local order parameters. Instead, nonlocal string order parameters can be employed to reveal their hidden order. Similar diluted magnetic correlations appear in doped one-dimensional lattice systems owing to the phenomenon of spin-charge separation. Here we report on the direct observation of such hidden magnetic correlations via quantum gas microscopy of hole-doped ultracold Fermi-Hubbard chains. The measurement of nonlocal spin-density correlation functions reveals a hidden finite-range antiferromagnetic order, a direct consequence of spin-charge separation. Our technique, which measures nonlocal order directly, can be readily extended to higher dimensions to study the complex interplay between magnetic order and density fluctuations.

  15. 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 .

  16. 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.

  17. 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.

  18. Magnon Spin-Momentum Locking: Various Spin Vortices and Dirac magnons in Noncollinear Antiferromagnets

    NASA Astrophysics Data System (ADS)

    Okuma, Nobuyuki

    2017-09-01

    We generalize the concept of the spin-momentum locking to magnonic systems and derive the formula to calculate the spin expectation value for one-magnon states of general two-body spin Hamiltonians. We give no-go conditions for magnon spin to be independent of momentum. As examples of the magnon spin-momentum locking, we analyze a one-dimensional antiferromagnet with the Néel order and two-dimensional kagome lattice antiferromagnets with the 120° structure. We find that the magnon spin depends on its momentum even when the Hamiltonian has the z -axis spin rotational symmetry, which can be explained in the context of a singular band point or a U (1 ) symmetry breaking. A spin vortex in momentum space generated in a kagome lattice antiferromagnet has the winding number Q =-2 , while the typical one observed in topological insulator surface states is characterized by Q =+1 . A magnonic analogue of the surface states, the Dirac magnon with Q =+1 , is found in another kagome lattice antiferromagnet. We also derive the sum rule for Q by using the Poincaré-Hopf index theorem.

  19. Magnon Spin-Momentum Locking: Various Spin Vortices and Dirac magnons in Noncollinear Antiferromagnets.

    PubMed

    Okuma, Nobuyuki

    2017-09-08

    We generalize the concept of the spin-momentum locking to magnonic systems and derive the formula to calculate the spin expectation value for one-magnon states of general two-body spin Hamiltonians. We give no-go conditions for magnon spin to be independent of momentum. As examples of the magnon spin-momentum locking, we analyze a one-dimensional antiferromagnet with the Néel order and two-dimensional kagome lattice antiferromagnets with the 120° structure. We find that the magnon spin depends on its momentum even when the Hamiltonian has the z-axis spin rotational symmetry, which can be explained in the context of a singular band point or a U(1) symmetry breaking. A spin vortex in momentum space generated in a kagome lattice antiferromagnet has the winding number Q=-2, while the typical one observed in topological insulator surface states is characterized by Q=+1. A magnonic analogue of the surface states, the Dirac magnon with Q=+1, is found in another kagome lattice antiferromagnet. We also derive the sum rule for Q by using the Poincaré-Hopf index theorem.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Spin ordering in a random antiferromagnetic Heisenberg spin system: Numerical simulation

    NASA Astrophysics Data System (ADS)

    Ghazali, A.; Diep, Hung T.

    1985-04-01

    We study by a Monte Carlo method, a three-dimensional classical antiferromagnetic random Heisenberg spin system with an exchange interaction which decreases exponentially with distance. We find no indication of a spin glass transition when only isotropic exchange exists. However, a gradual spin freezing is observed as T→0. In the presence of a strong enough Ising-type uniaxial magnetic anisotropy, we observe a peak in the specific heat and a stable order parameter. However, no true thermoremanent magnetization is observed.

  5. 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.

  6. 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.

  7. Nematic ordering dynamics of an antiferromagnetic spin-1 condensate

    NASA Astrophysics Data System (ADS)

    Symes, L. M.; Blakie, P. B.

    2017-07-01

    We consider the formation of order in a quasi-two-dimensional antiferromagnetic spin-1 condensate quenched from an easy-axis to an easy-plane nematic phase. We define the relevant order parameter to quantify the spin-nematic degrees of freedom and study the evolution of the spin-nematic and superfluid order during the coarsening dynamics using numerical simulations. We observe dynamical scaling in the late-time dynamics, with both types of order extending across the system with a diffusive growth law. We identify half-quantum vortices as the relevant topological defects of the ordering dynamics and demonstrate that the growth of both types of order is determined by the mutual annihilation of these vortices.

  8. 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

  9. 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.

  10. 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.

  11. Effects of the antiferromagnetic spin structure on antiferromagnetically induced perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Wang, Bo-Yao; Tsai, Ming-Shian; Huang, Chun-Wei; Shih, Chun-Wei; Chen, Chia-Ju; Lin, Kai; Li, Jin-Jhuan; Jih, Nae-Yeou; Lu, Chun-I.; Chuang, Tzu-Hung; Wei, Der-Hsin

    2017-09-01

    Antiferromagnetic (AFM) thin films are promising materials for inducing perpendicular magnetic anisotropy (PMA) in adjacent ferromagnetic (FM) films. This study demonstrates that in a selected AFM spin structure with out-of-plane uncompensated moments, the magnitude of the induced PMA in its neighboring Co/Ni film could be significantly enhanced by the establishment of a collinearlike exchange interaction between the volume moments of the AFM film and the perpendicular magnetic FM film. Detailed magnetic hysteresis loops and x-ray analysis revealed a quench of perpendicular surface anisotropy in a monolayered Fe50Mn50/Co /Ni film due to the formation of antiparallel-like coupled Fe and Mn moments. By contrast, the establishment of a three-dimensional quadratic-type AFM spin structure of an Fe50Mn50 film triggered parallel-like out-of-plane uncompensated Fe and Mn moments at the interface and reinforced the PMA induced in the Co/Ni film.

  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. 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.

  14. 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.

  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. 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)

  17. Spin pumping and inverse spin Hall effects in heavy metal/antiferromagnet/Permalloy trilayers

    NASA Astrophysics Data System (ADS)

    Saglam, Hilal; Zhang, Wei; Jungfleisch, M. Benjamin; Jiang, Wanjun; Pearson, John E.; Hoffmann, Axel

    Recent work shows efficient spin transfer via spin waves in insulating antiferromagnets (AFMs), suggesting that AFMs can play a more active role in the manipulation of ferromagnets. We use spin pumping and inverse spin Hall effect experiments on heavy metal (Pt and W)/AFMs/Py (Ni80Fe20) trilayer structures, to examine the possible spin transfer phenomenon in metallic AFMs, i . e . , FeMn and PdMn. Previous work has studied electronic effects of the spin transport in these materials, yielding short spin diffusion length on the order of 1 nm. However, the work did not examine whether besides diffusive spin transport by the conduction electrons, there are additional spin transport contributions from spin wave excitations. We clearly observe spin transport from the Py spin reservoir to the heavy metal layer through the sandwiched AFMs with thicknesses well above the previously measured spin diffusion lengths, indicating that spin transport by spin waves may lead to non-negligible contributions This work was supported by US DOE, OS, Materials Sciences and Engineering Division. Lithographic patterning was carried out at the CNM, which is supported by DOE, OS under Contract No. DE-AC02-06CH11357.

  18. 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.

  19. 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.

  20. Mechanism of spin and charge separation in one-dimensional quantum antiferromagnets

    SciTech Connect

    Mudry, C.; Fradkin, E. )

    1994-10-15

    We reconsider the problem of separation of spin and charge in one-dimensional quantum antiferromagnets. We show that spin and charge separation in one-dimensional strongly correlated systems cannot be described by the slave-boson or fermion representation within any perturbative treatment of the interactions between the slave holons and slave spinons. The constraint of single occupancy must be implemented exactly. As a result the slave fermions and bosons are not part of the physical spectrum. Instead, the excitations that carry the separate spin and charge quantum numbers are solitons. To prove this result, it is sufficient to study the pure spinon sector in the slave-boson representation. We start with a short-range resonating-valence-bond state spin liquid mean-field theory for the frustrated antiferromagnetic spin-1/2 chain. We derive an effective theory for the fluctuations of the Affleck-Marston and Anderson order parameters. We show how to recover the phase diagram as a function of the frustration by treating the fluctuations nonperturbatively.

  1. 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.

  2. Localized spin excitations in an antiferromagnetic spin system with D-M interaction

    SciTech Connect

    Evangeline Rebecca, T.; Latha, M. M.

    2016-06-15

    The existence of localized spin excitations and spin deviations along the site in a one-dimensional antiferromagnet with Dzyaloshinski-Moriya (D-M) interaction has been studied using quasiclassical approximation. By introducing the Holstein-Primakoff bosonic representation of spin operators, the coherent state ansatz, and the time dependent variational principle, a discrete set of coupled nonlinear partial differential equations governing the dynamics is derived. Employing the multiple-scale method, one, two and three solitary wave solutions are constructed and depicted graphically.

  3. 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).

  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. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Experimental realization of long-distance entanglement between spins in antiferromagnetic quantum spin chains

    NASA Astrophysics Data System (ADS)

    Sahling, S.; Remenyi, G.; Paulsen, C.; Monceau, P.; Saligrama, V.; Marin, C.; Revcolevschi, A.; Regnault, L. P.; Raymond, S.; Lorenzo, J. E.

    2015-03-01

    Entanglement is a concept that has defied common sense since the discovery of quantum mechanics. Two particles are said to be entangled when the quantum state of each particle cannot be described independently, no matter how far apart in space and time the two particles are. We demonstrate experimentally that unpaired spins separated by several hundred ångström entangle through a collection of spin singlets made up of antiferromagnetic spin-1/2 chains in a bulk material. Low-temperature magnetization and specific heat studies as a function of magnetic field reveal the occurrence of very dilute spin dimers and at least two quantum phase transitions related to the breaking of excited local triplets. The mechanism at the origin of the unpaired spins inside the quantum chains is the inter-modulation potential between two sublattices, and may be replicated using well-designed synthetic multilayers.

  11. 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.

  12. 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.

  13. 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.

  14. Negative spin Hall magnetoresistance of Pt on the bulk easy-plane antiferromagnet NiO

    NASA Astrophysics Data System (ADS)

    Hoogeboom, Geert R.; Aqeel, Aisha; Kuschel, Timo; Palstra, Thomas T. M.; van Wees, Bart J.

    2017-07-01

    We report on spin Hall magnetoresistance (SMR) measurements of Pt Hall bars on antiferromagnetic NiO(111) single crystals. An SMR with a sign opposite to conventional SMR is observed over a wide range of temperatures as well as magnetic fields stronger than 0.25 T. The negative sign of the SMR can be explained by the alignment of magnetic moments being almost perpendicular to the external magnetic field within the easy plane (111) of the antiferromagnet. This correlation of magnetic moment alignment and the external magnetic field direction is realized just by the easy-plane nature of the material without the need of any exchange coupling to an additional ferromagnet. The SMR signal strength decreases with increasing temperature, primarily due to the decrease in Néel order by including fluctuations. An increasing magnetic field increases the SMR signal strength as there are fewer domains, and the magnetic moments are more strongly manipulated at high magnetic fields. The SMR is saturated at an applied magnetic field of 6 T, resulting in a spin-mixing conductance of ˜1018 Ω-1 m-2, which is comparable to that of Pt on insulating ferrimagnets such as yttrium iron garnet. An argon plasma treatment doubles the spin-mixing conductance.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. Correlating quasiparticle excitations with quantum femtosecond magnetism in photoexcited nonequilibrium states of insulating antiferromagnetic manganites

    NASA Astrophysics Data System (ADS)

    Lingos, P. C.; Patz, A.; Li, T.; Barmparis, G. D.; Keliri, A.; Kapetanakis, M. D.; Li, L.; Yan, J.; Wang, J.; Perakis, I. E.

    2017-06-01

    We describe a mechanism for insulator-to-metal transition triggered by spin canting following femtosecond laser excitation of insulating antiferromagnetic (AFM) states of colossal magnetoresistive (CMR) manganites. We show that photoexcitation of composite fermion quasiparticles dressed by spin fluctuations results in the population of a broad metallic conduction band due to canting of the AFM background spins via strong electron-spin local correlation. By inducing spin canting, photoexcitation can increase the quasiparticle energy dispersion and quench the charge excitation energy gap. This increases the critical Jahn-Teller (JT) lattice displacement required to maintain an insulating state. We present femtosecond-resolved pump-probe measurements showing biexponential relaxation of the differential reflectivity below the AFM transition temperature. We observe a nonlinear dependence of the ratio of the femtosecond and picosecond relaxation component amplitudes at the same pump fluence threshold where we observe femtosecond magnetization photoexcitation. We attribute this correlation between nonlinear femtosecond spin and charge dynamics to spin/charge/lattice coupling and population inversion between the polaronic majority carriers and metallic quasielectron minority carriers as the lattice displacement becomes smaller than the critical value required to maintain an insulating state following laser-induced spin canting.

  4. 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.

  5. Antiferromagnetic domains and the spin{endash}flop transition in MnF{sub 2} (abstract)

    SciTech Connect

    Felcher, G.P.; Kleb, R.; Jaccarino, V.

    1997-04-01

    Polarized neutron diffraction measurements were carried out on a single crystal of anti- ferromagnetic MnF{sub 2} at different magnetic fields up to the spin{endash}flop transition. This compound orders antiferromagnetically below 67 K, and the magnetic moments of the two manganese atoms in the rutile structure are aligned antiferromagnetically along the tetragonal axis of the crystalline cell. By applying a magnetic field of H=9.27 T (at 4.2 K) along the axis the antiferromagnetic moments flop in the basal plane. From the polarization dependence of the (210) reflection it was found that just below the spin{endash}flop field the entire crystal becomes aligned in a single antiferromagnetic domain, and remains in such state even after the field is removed. The symmetry relations of the polarization for neutron diffraction peaks in different quadrants of the [001] zone were analyzed in the paramagnetic, antiferromagnetic, and spin{endash}flop regions (here polarization analysis sorted out the axial and basal plane components of the sublattice magnetization). In the spin{endash}flop region the magnetization induced along the tetragonal axis was found to be different for the two manganese atoms, an effect quantitatively explained by the misalignment of a fraction of degree of the applied field with the crystal axis. What is remarkable here is that a minute breakdown of symmetry provides a way to control antiferromagnetic domains. {copyright}{ital 1997 American Institute of Physics.}

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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

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

    SciTech Connect

    Fu, M.; Imai, T.; Han, T. -H.; Lee, Y. S.

    2015-11-05

    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 ckagome, 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 ckagome that we observed at low temperatures, these results imply that the kagome Heisenberg antiferromagnet has a spin-liquid ground state with a finite gap.

  13. 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.

  14. 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.

  15. 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    We report 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 2014 Phys. Rev. Lett.112 077206) 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 triangular-lattice antiferromagnet.

  17. 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 .

  18. Real-space imaging of non-collinear antiferromagnetic order with a single-spin magnetometer.

    PubMed

    Gross, I; Akhtar, W; Garcia, V; Martínez, L J; Chouaieb, S; Garcia, K; Carrétéro, C; Barthélémy, A; Appel, P; Maletinsky, P; Kim, J-V; Chauleau, J Y; Jaouen, N; Viret, M; Bibes, M; Fusil, S; Jacques, V

    2017-09-13

    Although ferromagnets have many applications, their large magnetization and the resulting energy cost for switching magnetic moments bring into question their suitability for reliable low-power spintronic devices. Non-collinear antiferromagnetic systems do not suffer from this problem, and often have extra functionalities: non-collinear spin order may break space-inversion symmetry and thus allow electric-field control of magnetism, or may produce emergent spin-orbit effects that enable efficient spin-charge interconversion. To harness these traits for next-generation spintronics, the nanoscale control and imaging capabilities that are now routine for ferromagnets must be developed for antiferromagnetic systems. Here, using a non-invasive, scanning single-spin magnetometer based on a nitrogen-vacancy defect in diamond, we demonstrate real-space visualization of non-collinear antiferromagnetic order in a magnetic thin film at room temperature. We image the spin cycloid of a multiferroic bismuth ferrite (BiFeO3) thin film and extract a period of about 70 nanometres, consistent with values determined by macroscopic diffraction. In addition, we take advantage of the magnetoelectric coupling present in BiFeO3 to manipulate the cycloid propagation direction by an electric field. Besides highlighting the potential of nitrogen-vacancy magnetometry for imaging complex antiferromagnetic orders at the nanoscale, these results demonstrate how BiFeO3 can be used in the design of reconfigurable nanoscale spin textures.

  19. 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.

  20. 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

  1. 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.

  2. 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

  3. 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.

  4. Antiferromagnetism in the Hubbard model using a cluster slave-spin method

    NASA Astrophysics Data System (ADS)

    Lee, Wei-Cheng; Lee, Ting-Kuo

    2017-09-01

    The cluster slave-spin method is introduced to systematically investigate the solutions of the Hubbard model including the symmetry-broken phases. In this method, the electron operator is factorized into a fermionic spinon describing the physical spin and a slave-spin describing the charge fluctuations. Following the U (1 ) formalism derived by Yu and Si [Phys. Rev. B 86, 085104 (2012), 10.1103/PhysRevB.86.085104], it is shown that the self-consistent equations to explore various symmetry-broken density wave states can be constructed in general with a cluster of multiple slave-spin sites. We employ this method to study the antiferromagnetic (AFM) state in the single band Hubbard model with the two- and four-site clusters of slave spins. While the Hubbard gap, the charge gap due to the doubly occupied states, scales with the Hubbard interaction U as expected, the AFM gap Δ , the gap in the spinon dispersion in the AFM state, exhibits a crossover from the weak- to strong-coupling behaviors as U increases. Our cluster slave-spin method reproduces not only the traditional mean-field behavior of Δ ˜U in the weak-coupling limit, but also the behavior of Δ ˜t2/U predicted by the superexchange mechanism in the strong-coupling limit. In addition, the holon-doublon correlator as functions of U and doping x is also computed, which exhibits a strong tendency toward the holon-doublon binding in the strong coupling regime. We further show that the quasiparticle weight obtained by the cluster slave-spin method is in a good agreement with the generalized Gutzwiller approximation in both AFM and paramagnetic states, and the results can be improved beyond the generalized Gutzwiller approximation as the cluster is enlarged from a single site to four sites. Our results demonstrate that the cluster slave-spin method can be a powerful tool to systematically investigate the strongly correlated system.

  5. 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.

  6. Fractionalized excitations in the spin-liquid state of a kagome-lattice antiferromagnet.

    PubMed

    Han, Tian-Heng; Helton, Joel S; Chu, Shaoyan; Nocera, Daniel G; Rodriguez-Rivera, Jose A; Broholm, Collin; Lee, Young S

    2012-12-20

    The experimental realization of quantum spin liquids is a long-sought goal in physics, as they represent new states of matter. Quantum spin liquids cannot be described by the broken symmetries associated with conventional ground states. In fact, the interacting magnetic moments in these systems do not order, but are highly entangled with one another over long ranges. Spin liquids have a prominent role in theories describing high-transition-temperature superconductors, and the topological properties of these states may have applications in quantum information. A key feature of spin liquids is that they support exotic spin excitations carrying fractional quantum numbers. However, detailed measurements of these 'fractionalized excitations' have been lacking. Here we report neutron scattering measurements on single-crystal samples of the spin-1/2 kagome-lattice antiferromagnet ZnCu(3)(OD)(6)Cl(2) (also called herbertsmithite), which provide striking evidence for this characteristic feature of spin liquids. At low temperatures, we find that the spin excitations form a continuum, in contrast to the conventional spin waves expected in ordered antiferromagnets. The observation of such a continuum is noteworthy because, so far, this signature of fractional spin excitations has been observed only in one-dimensional systems. The results also serve as a hallmark of the quantum spin-liquid state in herbertsmithite.

  7. 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.

  8. Spin-dependent quasiparticle reflection and bound States at interfaces with itinerant antiferromagnets.

    PubMed

    Bobkova, I V; Hirschfeld, P J; Barash, Yu S

    2005-01-28

    We find a novel channel of quasiparticle reflection from the simplest two-sublattice antiferromagnet (AF) on a bipartite lattice. Low-energy quasiparticles in a normal metal (N) experience spin-dependent retroreflection at AF/N interfaces. As a combined effect of antiferromagnetic and Andreev reflections, subgap Andreev states arise at an AF/superconductor (SC) interface. When the antiferromagnetic reflection dominates the specular one, Andreev bound states have almost zero energy on AF/s-wave superconductor (sSC) interfaces, whereas there are no low-energy subgap states on AF/d-wave superconductor (dSC) boundaries. For an sSC/AF/sSC junction, the bound states are found to split, due to the finite width of the AF interlayer, and carry the supercurrent. The theory developed in the present Letter is based on a novel quasiclassical approach, which applies to interfaces involving itinerant antiferromagnets.

  9. Nonlocally sensing the magnetic states of nanoscale antiferromagnets with an atomic spin sensor

    PubMed Central

    Yan, Shichao; Malavolti, Luigi; Burgess, Jacob A. J.; Droghetti, Andrea; Rubio, Angel; Loth, Sebastian

    2017-01-01

    The ability to sense the magnetic state of individual magnetic nano-objects is a key capability for powerful applications ranging from readout of ultradense magnetic memory to the measurement of spins in complex structures with nanometer precision. Magnetic nano-objects require extremely sensitive sensors and detection methods. We create an atomic spin sensor consisting of three Fe atoms and show that it can detect nanoscale antiferromagnets through minute, surface-mediated magnetic interaction. Coupling, even to an object with no net spin and having vanishing dipolar stray field, modifies the transition matrix element between two spin states of the Fe atom–based spin sensor that changes the sensor’s spin relaxation time. The sensor can detect nanoscale antiferromagnets at up to a 3-nm distance and achieves an energy resolution of 10 μeV, surpassing the thermal limit of conventional scanning probe spectroscopy. This scheme permits simultaneous sensing of multiple antiferromagnets with a single-spin sensor integrated onto the surface. PMID:28560346

  10. Nonlocally sensing the magnetic states of nanoscale antiferromagnets with an atomic spin sensor.

    PubMed

    Yan, Shichao; Malavolti, Luigi; Burgess, Jacob A J; Droghetti, Andrea; Rubio, Angel; Loth, Sebastian

    2017-05-01

    The ability to sense the magnetic state of individual magnetic nano-objects is a key capability for powerful applications ranging from readout of ultradense magnetic memory to the measurement of spins in complex structures with nanometer precision. Magnetic nano-objects require extremely sensitive sensors and detection methods. We create an atomic spin sensor consisting of three Fe atoms and show that it can detect nanoscale antiferromagnets through minute, surface-mediated magnetic interaction. Coupling, even to an object with no net spin and having vanishing dipolar stray field, modifies the transition matrix element between two spin states of the Fe atom-based spin sensor that changes the sensor's spin relaxation time. The sensor can detect nanoscale antiferromagnets at up to a 3-nm distance and achieves an energy resolution of 10 μeV, surpassing the thermal limit of conventional scanning probe spectroscopy. This scheme permits simultaneous sensing of multiple antiferromagnets with a single-spin sensor integrated onto the surface.

  11. Chiral and Critical Spin Liquids in Spin-1/2 Kagome Antiferromagnet

    NASA Astrophysics Data System (ADS)

    Sheng, Dongning; Zhu, Wei; Gong, Shoushu; Group of D. N. Sheng Team, Prof.

    2015-03-01

    The spin liquids (SL) and their phase transitions have attracted much attentions. The extended kagome antiferromagnet emerges as the primary candidate for hosting both time reversal symmetry (TRS) preserving and TRS breaking SLs based on DMRG simulations. To uncover the nature of the novel transition between them, we study a minimum XY model with the nearest-neighbor (NN) (Jxy), the second and third neighbor couplings (J2 xy =J3 xy =Jxy'). We identify the chiral SL (CSL) with the turn on of a small perturbation Jxy' ~ 0 . 06Jxy , which is characterized by topological Chern number and conformal edge spectrum as the ν = 1 / 2 fractional quantum Hall state. On the other hand, the NN XY model (Jxy' = 0) is shown to be a critical SL, characterized by the gapless spin singlet and vanishing small spin triplet excitations. The phase transition from the CSL to the critical SL is driven by the collapsing of singlet gap. By following the evolution of entanglement spectrum, we find the transition takes place through the coupling of the edge states with opposite chiralities, which merge into the bulk and become gapless neutral excitations. The effect of the NN spin- z coupling is also studied, which leads to a phase diagram with an extended regime for the gapless SL. U.S. Department of Energy, Office of Basic Energy Sciences under Grant No. DE-FG02-06ER46305 (W.Z., D.N.S.), the National Science Foundation through Grants DMR-1408560 (S.S.G).

  12. 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.

  13. Strain-modulated antiferromagnetic spin orientation and exchange coupling in Fe/CoO(001)

    SciTech Connect

    Zhu, J.; Li, Q.; Li, J. X.; Ding, Z.; Wu, Y. Z.; Hua, C. Y.; Huang, M. J.; Lin, H.-J.; Hu, Z.; Won, C.

    2014-05-21

    The effect of CoO spin orientation on exchange coupling was investigated in single-crystalline Fe/CoO/MnO/MgO(001) systems. An antiferromagnetic CoO spin reorientation transition from the in-plane direction to the out-of-plane direction was found to be associated with the in-plane strain transition in CoO film from compression to expansion. The induced uniaxial anisotropies by exchange coupling at the Fe/CoO interface are significantly stronger for the in-plane CoO spin orientation than for the out-of-plane CoO spin orientation. Our study provides a way to modify the exchange coupling in the ferromagnetic (FM)/antiferromagnetic (AFM) bilayer by modulating the strain in the AFM film.

  14. 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.

  15. Temperature dependence of ferromagnet-antiferromagnet spin alignment and coercivity in epitaxial micromagnet bilayers

    DOE PAGES

    Lee, Michael S.; Wynn, Thomas A.; Folven, Erik; ...

    2017-06-26

    In this paper, soft x-ray photoemission electron microscopy with an in situ magnetic field has been used to study the relationship between ferromagnetic and antiferromagnetic spin alignment and the switching/reversal field of epitaxial micromagnetic structures. We investigated a model system consisting of a bilayer of ferromagnetic La0.7Sr0.3MnO3 and antiferromagnetic LaFeO3 where the spin axes in each layer can be driven from mutually perpendicular (spin-flop) to parallel alignment by varying the temperature between 30 and 300 K. Results show that not only does this spin alignment noticeably influence the bilayer micromagnet coercivity compared to La0.7Sr0.3MnO3 single-layer micromagnets, but the coercivity withinmore » this materials system can be tuned over a wide range by careful balance of material properties.« less

  16. 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.

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

    SciTech Connect

    Deb, Moumita Ghosh, Asim Kumar

    2016-05-23

    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 Cu{sub 3}WO{sub 6}.

  18. 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.

  19. Real-space imaging of non-collinear antiferromagnetic order with a single-spin magnetometer

    NASA Astrophysics Data System (ADS)

    Gross, I.; Akhtar, W.; Garcia, V.; Martínez, L. J.; Chouaieb, S.; Garcia, K.; Carrétéro, C.; Barthélémy, A.; Appel, P.; Maletinsky, P.; Kim, J.-V.; Chauleau, J. Y.; Jaouen, N.; Viret, M.; Bibes, M.; Fusil, S.; Jacques, V.

    2017-09-01

    Although ferromagnets have many applications, their large magnetization and the resulting energy cost for switching magnetic moments bring into question their suitability for reliable low-power spintronic devices. Non-collinear antiferromagnetic systems do not suffer from this problem, and often have extra functionalities: non-collinear spin order may break space-inversion symmetry and thus allow electric-field control of magnetism, or may produce emergent spin–orbit effects that enable efficient spin–charge interconversion. To harness these traits for next-generation spintronics, the nanoscale control and imaging capabilities that are now routine for ferromagnets must be developed for antiferromagnetic systems. Here, using a non-invasive, scanning single-spin magnetometer based on a nitrogen–vacancy defect in diamond, we demonstrate real-space visualization of non-collinear antiferromagnetic order in a magnetic thin film at room temperature. We image the spin cycloid of a multiferroic bismuth ferrite (BiFeO3) thin film and extract a period of about 70 nanometres, consistent with values determined by macroscopic diffraction. In addition, we take advantage of the magnetoelectric coupling present in BiFeO3 to manipulate the cycloid propagation direction by an electric field. Besides highlighting the potential of nitrogen–vacancy magnetometry for imaging complex antiferromagnetic orders at the nanoscale, these results demonstrate how BiFeO3 can be used in the design of reconfigurable nanoscale spin textures.

  20. 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.

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

    PubMed

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

    2015-09-03

    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.

  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. Spin-wave spectral properties of the Mott-Hubbard antiferromagnet: The intermediate-coupling regime

    NASA Astrophysics Data System (ADS)

    Singh, Avinash

    1993-09-01

    Spectral properties of spin-wave excitations in the Mott-Hubbard antiferromagnet are studied in the intermediate-coupling regime, wherein extended-range spin couplings are present in the equivalent spin-1/2 Heisenberg model. A systematic expansion in powers of t2/U2 is developed for the spin-wave propagator in the random-phase approximation, and its quantitative usefulness is investigated. In two dimensions the spin-wave density of states exhibits a peak structure, resembling the broadening effect of spin-wave damping. Implications for recent light-pair scattering experiments in La2CuO4 wherein the complete spin-wave spectrum is accessible in principle, are discussed.

  4. Effect of antiferromagnetic interfacial coupling on spin-wave resonance frequency of multi-layer film

    NASA Astrophysics Data System (ADS)

    Qiu, Rong-ke; Cai, Wei

    2017-08-01

    We investigate the spin-wave resonance (SWR) frequency in a bicomponent bilayer and triple-layer films with antiferromagnetic or ferromagnetic interfacial couplings, as function of interfacial coupling, surface anisotropy, interface anisotropy, thickness and external magnetic field, using the linear spin-wave approximation and Green's function technique. The microwave properties for multi-layer magnetic film with antiferromagnetic interfacial coupling is different from those for multi-layer magnetic film with ferromagnetic interfacial coupling. For the bilayer film with antiferromagnetic interfacial couplings, as the lower (upper) surface anisotropy increases, only the SWR frequencies of the odd (even) number modes increase. The lower (upper) surface anisotropy does not affect the SWR frequencies of the even (odd) number modes. For the multi-layer film with antiferromagnetic interfacial coupling, the SWR frequency of modes m = 1, 3 and 4 decreases while that of mode m = 2 increases with increasing thickness of the film within a proper parameter region. The present results could be useful in enhancing our fundamental understanding and show the method to enhance and adjust the SWR frequency of bicomponent multi-layer magnetic films with antiferromagnetic or ferromagnetic interfacial coupling.

  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.

    PubMed

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

    2017-03-10

    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. Infrared probe of spin-phonon coupling in antiferromagnetic honeycomb lattice compound Li₂MnO₃.

    PubMed

    Song, Seungjae; Lee, Sanghyun; Jeon, Seyoung; Park, Je-Geun; Moon, S J

    2015-12-09

    We investigated temperature-dependent infrared-active phonon modes of honeycomb Li2MnO3 which shows an antiferromagnetic transition at T(N)  =  36 K. In the far-infrared frequency region, we observed fourteen phonon modes. We obtained the temperature dependence of each phonon mode from the analysis of optical conductivity spectra by using the Lorentz and the Fano-type oscillator models. We found that the resonance frequencies of nine phonon modes showed an anomalous behavior near T(N) that should be attributed to the spin-phonon coupling. We calculated the magnitude of the spin-phonon coupling constant from the shift in the resonance frequencies of the phonon modes below T(N). Our results suggest that Li2MnO3 is weakly frustrated and that spin-phonon coupling plays a role in antiferromagnetic ordering.

  8. 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.

  9. Simultaneous Antiferromagnetic Order and Spin-Glass-like Behavior in MnAsO(4).

    PubMed

    Aranda, Miguel A. G.; Attfield, J. Paul; Batchelor, Elaine; Shields, Greg P.; Bruque, Sebastián; Gabás, Mercedes

    1998-03-23

    A low-temperature time-of-flight neutron powder diffraction study of a simple new solid, MnAsO(4), in a sample also containing 20% Mn(2)As(2)O(7) has been performed. MnAsO(4) orders magnetically at 14.5(5) K, and the unusual antiferromagnetic structure below this temperature has been determined. Only half of the Mn(3+) spins are ordered, and the remaining "idle" spins show some spin-glass behavior evidenced by susceptibility measurements. The ordered moment is reduced to a value of 2.6 &mgr;(B) by frustration. It is not possible to determine which of the two crystallographically inequivalent Mn sublattices is magnetically ordered and which is idle. The antiferromagnetic structure of the minority phase Mn(2)As(2)O(7) which orders at 10.5(5) K has also been determined.

  10. 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.

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

    PubMed

    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.

  12. 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.

  13. Sublattice entanglement and quantum phase transitions in antiferromagnetic spin chains

    NASA Astrophysics Data System (ADS)

    Chen, Yan; Zanardi, Paolo; Wang, Z. D.; Zhang, F. C.

    2006-06-01

    Entanglement of the ground states in the S = 1/2 XXZ chain, dimerized Heisenberg spin chain, two-leg spin ladders as well as S = 1 anisotropic Haldane chain is analysed using the entanglement entropy between a selected sublattice of spins and the rest of the system. In particular, we reveal that quantum phase transition points/boundaries may be identified based on the analysis on the local extreme of this sublattice entanglement entropy, which is illustrated to be superior over the concurrence scenario and may enable us to explore quantum phase transitions in many other systems including higher dimensional ones.

  14. Spin Dimer Analysis for Antiferromagnetic Spin Exchange Interactions of Magnetic Solids with Several Unpaired Electrons per Spin Site: Trends in the Spin Exchange Parameters of the Compounds Consisting of MnF

    SciTech Connect

    Koo, H.-J.; Whangbo, M.-H.; Coste, S.; Jobic, S.

    2001-02-01

    For magnetic solids with several unpaired spins per spin site, the average spin orbital interaction energies < {Delta}e > and the average spin orbital interaction energy squares < ({Delta}e){sup 2} > were defined as a qualitative measure for the strengths of their antiferromagnetic spin exchange interactions. The trends in the antiferromagnetic spin exchange interactions of the magnetic solids containing MnF{sub 5} chains and CrX{sub 2} (X=O, S) layers were examined in terms of the < {Delta}e > and < ({Delta}e){sup 2} > values calculated for their spin dimers.

  15. Switching of spins and entanglement in surface-supported antiferromagnetic chains.

    PubMed

    Sivkov, Ilia N; Bazhanov, Dmitry I; Stepanyuk, Valeri S

    2017-06-05

    Previous experimental studies discovered universal growth of chains and nanowires of various chemical elements on a corrugated molecular network of Cu3N on the Cu(110). Herein, performing combined ab initio and quantum Hamiltonian studies we demonstrate that such chains can be used for a fast spin switching and entanglement generation by locally applied magnetic pulses. As an example, we show that in antiferromagnetic Co chains a strong entanglement between ends of chains occurs during spin switching. A novel parity effect in spin dynamics is reported. Even-numbered chains are found to exhibit significantly faster spin switching than odd-numbered counterparts. Moreover, at certain parameters of the system the dimerization effect in the spin dynamics of the chains was found. Our studies give a clear evidence that tailoring spin dynamics and entanglement can be achieved by magnetic fields and by tuning exchange interactions in supported chains.

  16. 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.

  17. 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.

  18. Entanglement in the quantum one-dimensional integer spin S Heisenberg antiferromagnet

    NASA Astrophysics Data System (ADS)

    Lima, L. S.

    2017-10-01

    We use the modified spin wave theory of Takahashi to study the entanglement entropy in the quantum one-dimensional integer spin Heisenberg antiferromagnet. We calculate the entanglement entropy of this spin system that is well known to be a quantum wire, in the classical limit (N → ∞). We obtain a decreasing the entanglement entropy with the temperature and we obtain none change in the entanglement in the point Δ = 1 at T = 0 where the system presents a quantum phase transition from a gapless phase in the spectrum Δ < 1 to a gapped phase Δ ≥ 1.

  19. 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.

  20. Order-disorder quantum phase transition in the quasi-one-dimensional spin-1/2 collinear antiferromagnetic Heisenberg model.

    PubMed

    Rufo, Sabrina; Mendonça, Griffith; Plascak, J A; de Sousa, J Ricardo

    2013-09-01

    The ground-state properties of the quasi-one-dimensional spin-1/2 antiferromagnetic Heisenberg model is investigated by using a variational method. Spins on chains along the x direction are antiferromagnetically coupled with exchange J>0, while spins between chains in the y direction are coupled either ferromagnetically (J' < 0) or antiferromagnetically (J' > 0). The staggered and the colinear antiferromagnetic magnetizations are computed and their dependence on the anisotropy parameter λ=|J'|/J is analyzed. It is found that an infinitesimal interchain coupling parameter is sufficient to stabilize a long-range order with either a staggered magnetization m_{s} (J' > 0) or a colinear antiferromagnetic magnetization m_{caf} (J' < 0), both behaving as ≃λ¹/² for λ → 0.

  1. Antiferromagnetic skyrmion crystals: Generation, topological Hall, and topological spin Hall effect

    NASA Astrophysics Data System (ADS)

    Göbel, Börge; Mook, Alexander; Henk, Jürgen; Mertig, Ingrid

    2017-08-01

    Skyrmions are topologically nontrivial, magnetic quasiparticles that are characterized by a topological charge. A regular array of skyrmions, a skyrmion crystal (SkX), features the topological Hall effect (THE) of electrons, which, in turn, gives rise to the Hall effect of the skyrmions themselves. It is commonly believed that antiferromagnetic skyrmion crystals (AFM-SkXs) lack both effects. In this Rapid Communication, we present a generally applicable method to create stable AFM-SkXs by growing a two-sublattice SkX onto a collinear antiferromagnet. As an example we show that both types of skyrmion crystals, conventional and antiferromagnetic, exist in honeycomb lattices. While AFM-SkXs with equivalent lattice sites do not show a THE, they exhibit a topological spin Hall effect. On top of this, AFM-SkXs on inequivalent sublattices exhibit a nonzero THE, which may be utilized in spintronics devices. Our theoretical findings call for experimental realization.

  2. 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.

  3. 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.

  4. 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.

  5. Chiral Spin Liquid on a Kagome Antiferromagnet Induced by the Dzyaloshinskii-Moriya Interaction

    NASA Astrophysics Data System (ADS)

    Messio, Laura; Bieri, Samuel; Lhuillier, Claire; Bernu, Bernard

    2017-06-01

    The quantum spin liquid material herbertsmithite is described by an antiferromagnetic Heisenberg model on the kagome lattice with a non-negligible Dzyaloshinskii-Moriya interaction (DMI). A well-established phase transition to the q =0 long-range order occurs in this model when the DMI strength increases, but the precise nature of a small-DMI phase remains controversial. Here, we describe a new phase obtained from Schwinger-boson mean-field theory that is stable at small DMI, and which can explain the dispersionless spectrum seen in the inelastic neutron scattering experiment by Han et al. [Nature (London) 492, 406 (2012), 10.1038/nature11659]. It is a time-reversal symmetry breaking Z2 spin liquid, with the unique property of a small and constant spin gap in an extended region of the Brillouin zone. The phase diagram as a function of DMI and spin size is given, and dynamical spin structure factors are presented.

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. Excitation spectrum of a model antiferromagnetic spin-trimer.

    SciTech Connect

    Stone, Matthew B; Fernandez-Alonso, F.; Adroja, D. T.; Dalal, N. S.; Villagran, D.; Cotton, F. A.; Nagler, Stephen E

    2007-01-01

    We present an inelastic neutron scattering (INS) study of the excitation spectrum of a quantum S=1/2 equilateral Heisenberg trimer, Cu{sub 3}(O{sub 2}C{sub 16}H{sub 23}){sub 61.2}C{sub 6}H{sub 12}. The magnetic properties of the system can be described by an ensemble of independent equilateral triangles of S=1/2 Cu{sup 2+} ions. With antiferromagnetic Heisenberg coupling, the ground state of each trimer is a degenerate pair of S=1/2 doublets, with a quartet S=3/2 excited state. Previous bulk measurements led to an estimate for the excitation energy of 28 meV. Here, we report INS measurements that can provide a direct measurement of magnetic excitation energies. These measurements are challenging since inter- and intramolecular vibrational modes associated with the organic ligands are at frequencies similar to the magnetic excitations. Measurements on a nonmagnetic compound with the same ligands as well as the temperature dependence of the neutron scattering cross section are used to identify the vibrational modes. This leads to an identification of the magnetic excitation energy as being approximately 37 meV at T=10 K, with a gradual softening with increasing temperature.

  12. 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.

  13. 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.

  14. 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.

  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. High-spin ribbons and antiferromagnetic ordering of a Mn(II)-biradical-Mn(II) complex.

    PubMed

    Fatila, Elisabeth M; Clérac, Rodolphe; Rouzières, Mathieu; Soldatov, Dmitriy V; Jennings, Michael; Preuss, Kathryn E

    2013-09-11

    A binuclear metal coordination complex of the first thiazyl-based biradical ligand 1 is reported (1 = 4,6-bis(1,2,3,5-dithiadiazolyl)pyrimidine; hfac =1,1,1,5,5,5,-hexafluoroacetylacetonato-). The Mn(hfac)2-biradical-Mn(hfac)2 complex 2 is a rare example of a discrete, molecular species employing a neutral bridging biradical ligand. It is soluble in common organic solvents and can be easily sublimed as a crystalline solid. Complex 2 has a spin ground state of S(T) = 4 resulting from antiferromagnetic coupling between the S(birad) = 1 biradical bridging ligand and two S(Mn) = 5/2 Mn(II) ions. Electrostatic contacts between atoms with large spin density promote a ferromagnetic arrangement of the moments of neighboring complexes in ribbon-like arrays. Weak antiferromagnetic coupling between these high-spin ribbons stabilizes an ordered antiferromagnetic ground state below 4.5 K. This is an unusual example of magnetic ordering in a molecular metal-radical complex, wherein the electrostatic contacts that direct the crystal packing are also responsible for providing an efficient exchange coupling pathway between molecules.

  17. 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.

  18. Neutron spin-echo study of the critical dynamics of spin-5/2 antiferromagnets in two and three dimensions

    NASA Astrophysics Data System (ADS)

    Tseng, K. F.; Keller, T.; Walters, A. C.; Birgeneau, R. J.; Keimer, B.

    2016-07-01

    We report a neutron spin-echo study of the critical dynamics in the S =5/2 antiferromagnets MnF2 and Rb2MnF4 with three-dimensional (3D) and two-dimensional (2D) spin systems, respectively, in zero external field. Both compounds are Heisenberg antiferromagnets with a small uniaxial anisotropy resulting from dipolar spin-spin interactions, which leads to a crossover in the critical dynamics close to the Néel temperature, TN. By taking advantage of the μ eV energy resolution of the spin-echo spectrometer, we have determined the dynamical critical exponents z for both longitudinal and transverse fluctuations. In MnF2, both the characteristic temperature for crossover from 3D Heisenberg to 3D Ising behavior and the exponents z in both regimes are consistent with predictions from the dynamical scaling theory. The amplitude ratio of longitudinal and transverse fluctuations also agrees with predictions. In Rb2MnF4 , the critical dynamics crosses over from the expected 2D Heisenberg behavior for T ≫TN to a scaling regime with exponent z =1.387 (4 ) , which has not been predicted by theory and may indicate the influence of long-range dipolar interactions.

  19. Magnetoresistance in antiferromagnet-based spin tunnel junctions

    NASA Astrophysics Data System (ADS)

    Jungwirth, Tomas

    2012-02-01

    To date spintronics research and applications of magnetically ordered systems have focused on ferromagnets (FMs). There are, however, fundamental physical limitations for FM materials which may make them impractical to realize the full potential of spintronics. Metal FMs offer high temperature operation but the large magnetic stray fields make them unfavorable for high-density integration and metals are unsuitable for transistor and information processing applications. FM semiconductors on the other hand do not allow for high-temperature operation. We present a concept in which these limitations are circumvented in spintronics based on antiferromagnets. The concept is based on relativistic magnetic and magneto-transport anisotropy effects in nanodevices whose common characteristics is that they are an even function of the microscopic magnetic moment vector, i.e., can be equally strong in AFMs as in FMs. As a demonstration we present our experimental observation of >100% tunneling anisotropic magnetoresistance in a device with an IrMn AFM tunnel electrode [1]. We will also discuss candidate materials for high-temperature AFM semiconductor spintronics [2].[4pt] [1] B. G. Park, J.Wunderlich, X.Marti, V.Holy, Y.Kurosaki, M.Yamada, H.Yamamoto, A.Nishide, J.Hayakawa, H.Takahashi, A.B.Shick, T.Jungwirth, Nature Mat. 10, 347 (2011). [0pt] [2] T.Jungwirth, V.Nov'ak, X.Marti, M.Cukr, F.M'aca, A.B. Shick, J.Masek, P.Horodysk'a, P.Nemec, V.Hol'y, et al., Phys. Rev. B 83, 035321 (2011).

  20. 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.

  1. 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).

  2. 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.

  3. Notes on Ground-State Properties of Mixed Spin-1 and Spin-1/2 Lieb-Lattice Heisenberg Antiferromagnets

    NASA Astrophysics Data System (ADS)

    Hirose, Yuhei; Miura, Shoma; Yasuda, Chitoshi; Fukumoto, Yoshiyuki

    2017-08-01

    Quantum Monte Carlo (QMC) simulations are performed to study ground-state properties of a mixed spin-1 and spin-1/2 Lieb-lattice Heisenberg antiferromagnet, in order to get further insight beyond the modified spin-wave (MSW) study reported in [J. Phys. Soc. Jpn. 86, 014002 (2017)]. It is confirmed that the MSW results are in good agreement with the QMC results. In particular, the scaling relation found in the MSW study, which argues that sublattice spin reductions are inversely proportional to the sublattice sizes, is observed in our QMC simulation. We present a rigorous proof for spontaneous sublattice magnetizations induced by an infinitesimal uniform magnetic field. The calculation process in the MSW theory is reexamined to clarify the mathematical structure behind the scaling relation for sublattice long-range orders.

  4. Comparison of spin dynamics and magnetic properties in antiferromagnetic closed and open molecular Cr-based rings.

    PubMed

    Adelnia, Fatemeh; Bordonali, Lorenzo; Mariani, Manuel; Bordignon, Sara; Timco, Grigore; Winpenny, Richard; Borsa, Ferdinando; Lascialfari, Alessandro

    2015-12-23

    We present magnetization and (1)H nuclear magnetic resonance (NMR) measurements performed in both closed Cr8 and open Cr8Zn antiferromagnetic molecular rings in the temperature range 1.65  <  T  <  300 K at different external magnetic fields. The magnetization measurements on Cr8Zn are consistent with a small decrease of the exchange constant J(Cr-Cr) and a much smaller gap between the singlet ground state and the first magnetic excited state when compared with the same properties of the closed ring Cr8, in agreement with previous inelastic neutron scattering results. The temperature dependence of the (1)H NMR nuclear spin lattice relaxation rate (NSLR), 1/T1(T), was found to be similar in both open and closed rings with a magnetic field dependent peak centered at a temperature of the order of the corresponding exchange constant J(Cr-Cr). Such main peak in the NSLR could be fitted with a single correlation frequency ω(c1) as in most molecular magnets. At low temperature T  <  4 K, a new feature not observed in previous NMR measurements on antiferromagnetic rings and consisting in a smaller peak of 1/T1(T) which is well resolved only in Cr8Zn, was singled out. This low-T peak indicates the presence of a second correlation frequency ω(c2) of the magnetization, found to be quite different between the two rings and thus possibly reflecting the different low temperature level structure associated with the different spin topology. The presence of ω(c2) is confirmed by the NMR spin-spin relaxation rate enhancement, which generates a two-steps wipe-out effect of the NMR signal intensity.

  5. Antiferromagnetic nuclear spin helix and topological superconductivity in 13C nanotubes

    NASA Astrophysics Data System (ADS)

    Hsu, Chen-Hsuan; Stano, Peter; Klinovaja, Jelena; Loss, Daniel

    2015-12-01

    We investigate the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction arising from the hyperfine coupling between localized nuclear spins and conduction electrons in interacting 13C carbon nanotubes. Using the Luttinger liquid formalism, we show that the RKKY interaction is sublattice dependent, consistent with the spin susceptibility calculation in noninteracting carbon nanotubes, and it leads to an antiferromagnetic nuclear spin helix in finite-size systems. The transition temperature reaches up to tens of mK, due to a strong boost by a positive feedback through the Overhauser field from ordered nuclear spins. Similar to GaAs nanowires, the formation of the helical nuclear spin order gaps out half of the conduction electrons, and is therefore observable as a reduction of conductance by a factor of 2 in a transport experiment. The nuclear spin helix leads to a density wave combining spin and charge degrees of freedom in the electron subsystem, resulting in synthetic spin-orbit interaction, which induces nontrivial topological phases. As a result, topological superconductivity with Majorana fermion bound states can be realized in the system in the presence of proximity-induced superconductivity without the need of fine tuning the chemical potential. We present the phase diagram as a function of system parameters, including the pairing gaps, the gap due to the nuclear spin helix, and the Zeeman field perpendicular to the helical plane.

  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. 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.

  8. Spin dynamics in the distorted triangular lattice antiferromagnet α -SrCr2O4

    NASA Astrophysics Data System (ADS)

    Songvilay, M.; Petit, S.; Suard, E.; Martin, C.; Damay, F.

    2017-07-01

    The spin dynamics in the distorted triangular lattice antiferromagnet α -SrCr2O4 has been investigated by inelastic neutron scattering on a single crystal. The spin wave dispersion has been mapped out in the (0 k l ) and (h k 0 ) planes, and modeled by spin wave calculations, in order to determine the intraplane and interplane exchange couplings. Comparison with α -CaCr2O4 shows that, despite the smaller lattice distortion of α -SrCr2O4 , the deviation from a perfect triangular lattice still affects the spin dynamics of the Sr compound, with a soft mode, similar to the one observed in the Ca counterpart, being observed in (020). Although α -SrCr2O4 is further away from a magnetic phase boundary than its Ca counterpart, its dynamic magnetic properties still show intriguing features, which are discussed as quantum fluctuations arising from a two-magnon continuum.

  9. 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.

  10. The spin liquid state of the Tb2Ti2O7 pyrochlore antiferromagnet: a puzzling state of affairs

    NASA Astrophysics Data System (ADS)

    Enjalran, M.; Gingras, M. J. P.; Kao, Y.-J.; DelMaestro, A.; Molavian, H. R.

    2004-03-01

    The pyrochlore antiferromagnet Tb2Ti2O7 has proven to be an enigma to experimentalists and theorists working on frustrated magnetic systems. The experimentally determined energy level structure suggests a local \\langle 111 \\rangle Ising antiferromagnet at low temperatures, T \\lesssim 10 K. An appropriate model then predicts a long-range ordered Q = 0 state below approximately 2 K. However, muon spin resonance (mgrSR) experiments reveal a paramagnetic structure down to tens of millikelvins. The importance of fluctuations out of the ground state effective Ising doublet has been recently understood, for the measured paramagnetic correlations cannot be described without including the higher crystal field states. However, these fluctuations treated within the random phase approximation (RPA) fail to account for the lack of ordering in this system below 2 K. In this work, we briefly review the experimental evidence for the collective paramagnetic state of Tb2Ti2O7. The basic theoretical picture for this system is discussed, where results from classical spin models are used to motivate the investigation of quantum effects to lowest order via the RPA. Avenues for future experimental and theoretical work on Tb2Ti2O7 are presented.

  11. 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.

  12. 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.

  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. 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.

  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. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. Measuring spin correlations in optical lattices using superlattice potentials

    SciTech Connect

    Pedersen, K. G. L.; Andersen, B. M.; Soerensen, A. S.; Bruun, G. M.; Syljuaasen, O. F.

    2011-10-15

    We suggest two experimental methods for probing both short- and long-range spin correlations of atoms in optical lattices using superlattice potentials. The first method involves an adiabatic doubling of the periodicity of the underlying lattice to probe neighboring singlet (triplet) correlations for fermions (bosons) by the occupation of the resulting vibrational ground state. The second method utilizes a time-dependent superlattice potential to generate spin-dependent transport by any number of prescribed lattice sites, and probes correlations by the resulting number of doubly occupied sites. For experimentally relevant parameters, we demonstrate how both methods yield large signatures of antiferromagnetic correlations of strongly repulsive fermionic atoms in a single shot of the experiment. Lastly, we show how this method may also be applied to probe d-wave pairing, a possible ground-state candidate for the doped repulsive Hubbard model.

  3. 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.

  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. 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.

  7. 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).

  8. 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).

  9. Electric-field-induced spin resonance in antiferromagnetic insulators: Inverse process of the dynamical chiral magnetic effect

    NASA Astrophysics Data System (ADS)

    Sekine, Akihiko; Chiba, Takahiro

    2016-06-01

    We propose a realization of the electric-field-induced antiferromagnetic resonance. We consider three-dimensional antiferromagnetic insulators with spin-orbit coupling characterized by the existence of a topological term called the θ term. By solving the Landau-Lifshitz-Gilbert equation in the presence of the θ term, we show that, in contrast to conventional methods using ac magnetic fields, the antiferromagnetic resonance state is realized by ac electric fields along with static magnetic fields. This mechanism can be understood as the inverse process of the dynamical chiral magnetic effect, an alternating current generation by magnetic fields. In other words, we propose a way to electrically induce the dynamical axion field in condensed matter. We discuss a possible experiment to observe our proposal, which utilizes the spin pumping from the antiferromagnetic insulator into a heavy metal contact.

  10. Correlation between antiferromagnetic interface coupling and positive exchange bias

    SciTech Connect

    Nogues, J.; Leighton, C.; Schuller, Ivan K.

    2000-01-01

    The induced moment in antiferromagnetic (AFM)-ferromagnetic (FM) (FeF{sub 2}-Fe and MnF{sub 2}-Fe) bilayers has been studied from the shift along the magnetization axis of the exchange-biased hysteresis loops. The magnetization shift depends strongly on the cooling field and microstructure of the AFM layer. The shift for small cooling fields can be opposite to the cooling field, indicating that, in some cases, the presence of the FM layer induces an antiferromagnetic coupling at the interface. Samples with negative magnetization shifts (antiferromagnetic coupling) exhibit large changes in exchange bias H{sub E} as a function of cooling field and positive exchange bias. Samples with positive magnetization shifts (ferromagnetic coupling) show almost no change in H{sub E} with cooling field and the exchange bias field remains always negative. These results confirm the theoretical assumption that an antiferromagnetic interface coupling is necessary to observe positive exchange bias. (c) 2000 The American Physical Society.

  11. 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.

  12. Electrical Detection of Spin Backflow from an Antiferromagnetic Insulator/Y_{3}Fe_{5}O_{12} Interface.

    PubMed

    Lin, Weiwei; Chien, C L

    2017-02-10

    Spin Hall magnetoresistance (SMR) has been observed in Pt/NiO/Y_{3}Fe_{5}O_{12} (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.

  13. 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.

  14. Creation and dynamics of two-dimensional skyrmions in antiferromagnetic spin-1 Bose-Einstein condensates

    NASA Astrophysics Data System (ADS)

    Ollikainen, T.; Ruokokoski, E.; Möttönen, M.

    2014-03-01

    We numerically simulate the creation process of two-dimensional skyrmionic excitations in antiferromagnetic spin-1 Bose-Einstein condensates by solving the full three-dimensional dynamics of the system from the Gross-Pitaevskii equation. Our simulations reproduce quantitatively the experimental results of Choi et al. [Phys. Rev. Lett. 108, 035301 (2012), 10.1103/PhysRevLett.108.035301] without any fitting parameters. Furthermore, we examine the stability of the skyrmion by computing the temporal evolution of the condensate in a harmonic potential. The presence of both the quadratic Zeeman effect and dissipation in the simulations is vital for reproducing the experimentally observed decay time.

  15. 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

  16. Existence of fermion zero modes and deconfinement of spinons in quantum antiferromagnetism resulting from algebraic spin liquid

    SciTech Connect

    Kim, Ki-Seok

    2005-12-01

    We investigate the quantum antiferromagnetism arising from algebraic spin liquid via spontaneous chiral symmetry breaking. We claim that in the antiferromagnet massive Dirac spinons can appear to make a broad continuum spectrum at high energies in inelastic neutron scattering. The mechanism of spinon deconfinement results from the existence of fermion zero modes in single monopole potentials. Neel vectors can make a hedgehog configuration around a magnetic monopole of compact U(1) gauge fields. Remarkably, in the monopole composite potential the Dirac fermion is shown to have a zero mode. The emergence of the fermion zero mode forbids the condensation of monopoles, resulting in deconfinement of Dirac spinons in the quantum antiferromagnet.

  17. 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.

  18. Quasi-two-dimensional spin correlations in the triangular lattice bilayer spin glass LuCoGaO4

    NASA Astrophysics Data System (ADS)

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

    2017-09-01

    We present a single-crystal time-of-flight neutron scattering study of the static and dynamic spin correlations in LuCoGaO4, a quasi-two-dimensional dilute triangular lattice antiferromagnetic spin-glass material. This system is based on Co2 + ions that are randomly distributed on triangular bilayers within the YbFe2O4 -type, hexagonal crystal structure. Antiferromagnetic short-range two-dimensional correlations at wave vectors Q =(" close=")1 /3 ,1 /3 ,L )">1 /3 ,1 /3 ,L develop within the bilayers at temperatures as high as | ΘCW|˜100 K and extend over roughly five unit cells at temperatures below Tg=19 K. These two-dimensional static correlations are observed as diffuse rods of neutron scattering intensity along c* and display a continuous spin freezing process in their energy dependence. Aside from exhibiting these typical spin-glass characteristics, this insulating material reveals a novel gapped magnetic resonant spin excitation at Δ E ˜12 meV localized around Q. The temperature dependence of the spin gap associated with this two-dimensional excitation correlates with the evolution of the static correlations into the spin-glass state ground state. We associate it with the effect of the staggered exchange field acting on the Seff=1 /2 Ising-like doublet of the Co2 + moments.

  19. 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.

  20. 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.

  1. 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)

  2. 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

  3. Role of RKKY torque on domain wall motion in synthetic antiferromagnetic nanowires with opposite spin Hall angles.

    PubMed

    Krishnia, S; Sethi, P; Gan, W L; Kholid, F N; Purnama, I; Ramu, M; Herng, T S; Ding, J; Lew, W S

    2017-09-15

    We experimentally show the effect of enhanced spin-orbit and RKKY induced torques on the current-induced motion of a pair of domain walls (DWs), which are coupled antiferromagnetically in synthetic antiferromagnetic (SAF) nanowires. The torque from the spin Hall effect (SHE) rotates the Néel DWs pair into the transverse direction, which is due to the fact that heavy metals of opposite spin Hall angles are deposited at the top and the bottom ferromagnetic interfaces. The rotation of both DWs in non-collinear fashion largely perturbs the antiferromagnetic coupling, which in turn stimulates an enhanced interlayer RKKY exchange torque that improved the DW velocity. The interplay between the SHE-induced torque and the RKKY exchange torque is validated via micromagnetic simulations. In addition, the DW velocity can be further improved by increasing the RKKY exchange strength.

  4. 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.

  5. 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.

  6. Barlowite: a spin-1/2 antiferromagnet with a geometrically perfect Kagome motif.

    SciTech Connect

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

    2014-11-25

    We present thermodynamic studies of a new spin-1/2 antiferromagnet containing undistorted kagome lattices-barlowite Cu-4(OH)(6)FBr. Magnetic susceptibility gives theta(CW) = -136 K, while long-range order does not happen until T-N = 15 K with a weak ferromagnetic moment mu < 0.1 mu(B)/Cu. A 60 T magnetic field induces a moment less than 0.5 mu(B)/Cu at T = 0.6 K. Specific-heat measurements have observed multiple phase transitions at T << vertical bar theta(CW)vertical bar. The magnetic entropy of these transitions is merely 18% of k(B) ln 2 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.

  7. 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.

  8. 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.

  9. Spin-Peierls instabilities of antiferromagnetic rings in a magnetic field

    NASA Astrophysics Data System (ADS)

    Lante, Valeria; Rousochatzakis, Ioannis; Penc, Karlo; Waldmann, Oliver; Mila, Frédéric

    2009-05-01

    Motivated by the intriguing properties of magnetic molecular wheels at field-induced level crossings, we investigate the spin-Peierls instability of antiferromagnetic rings in a field by exact diagonalizations of a microscopic spin model coupled to the lattice via a distortion-dependent Dzyaloshinskii-Moriya interaction. We show that, beyond the unconditional instability at level crossings for infinitesimal magnetoelastic coupling, the model is characterized by a stronger tendency to distort at higher level crossings and by a dramatic angular dependence with very sharp torque anomalies when the field is almost in the plane of the ring. These predictions are shown to compare remarkably well with available torque and nuclear magnetic resonance data on CsFe8 .

  10. 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.

  11. 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.

  12. Magnetization switching by spin-orbit torque in an antiferromagnet-ferromagnet bilayer system.

    PubMed

    Fukami, Shunsuke; Zhang, Chaoliang; DuttaGupta, Samik; Kurenkov, Aleksandr; Ohno, Hideo

    2016-05-01

    Spin-orbit torque (SOT)-induced magnetization switching shows promise for realizing ultrafast and reliable spintronics devices. Bipolar switching of the perpendicular magnetization by the SOT is achieved under an in-plane magnetic field collinear with an applied current. Typical structures studied so far comprise a nonmagnet/ferromagnet (NM/FM) bilayer, where the spin Hall effect in the NM is responsible for the switching. Here we show that an antiferromagnet/ferromagnet (AFM/FM) bilayer system also exhibits a SOT large enough to switch the magnetization of the FM. In this material system, thanks to the exchange bias of the AFM, we observe the switching in the absence of an applied field by using an antiferromagnetic PtMn and ferromagnetic Co/Ni multilayer with a perpendicular easy axis. Furthermore, tailoring the stack achieves a memristor-like behaviour where a portion of the reversed magnetization can be controlled in an analogue manner. The AFM/FM system is thus a promising building block for SOT devices as well as providing an attractive pathway towards neuromorphic computing.

  13. 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.

  14. Identification of ground-state spin ordering in antiferromagnetic transition metal oxides using the Ising model and a genetic algorithm.

    PubMed

    Lee, Kyuhyun; Youn, Yong; Han, Seungwu

    2017-01-01

    We identify ground-state collinear spin ordering in various antiferromagnetic transition metal oxides by constructing the Ising model from first-principles results and applying a genetic algorithm to find its minimum energy state. The present method can correctly reproduce the ground state of well-known antiferromagnetic oxides such as NiO, Fe2O3, Cr2O3 and MnO2. Furthermore, we identify the ground-state spin ordering in more complicated materials such as Mn3O4 and CoCr2O4.

  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. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Global phase diagram and quantum spin liquids in a spin-1/2 triangular antiferromagnet

    NASA Astrophysics Data System (ADS)

    Gong, Shou-Shu; Zhu, W.; Zhu, J.-X.; Sheng, D. N.; Yang, Kun

    2017-08-01

    We study the spin-1 /2 Heisenberg model on the triangular lattice with the nearest-neighbor J1>0 , the next-nearest-neighobr J2>0 Heisenberg interactions, and the additional scalar chiral interaction Jχ(S⃗i×S⃗j) .S⃗k for the three spins in all the triangles using large-scale density matrix renormalization group calculation on cylinder geometry. With increasing J2 (J2/J1≤0.3 ) and Jχ (Jχ/J1≤1.0 ) interactions, we establish a quantum phase diagram with the magnetically ordered 120∘, stripe, and noncoplanar tetrahedral phase. In between these magnetic order phases, we find a chiral spin liquid (CSL) phase, which is identified as a ν =1 /2 bosonic fractional quantum Hall state with possible spontaneous rotational symmetry breaking. By switching on the chiral interaction, we find that the previously identified spin liquid in the J1-J2 triangular model (0.08 ≲J2/J1≲0.15 ) shows a phase transition to the CSL phase at very small Jχ. We also compute the spin triplet gap in both spin liquid phases, and our finite-size results suggest a large gap in the odd topological sector but a small or vanishing gap in the even sector. We discuss the implications of our results on the nature of the spin liquid phases.

  1. 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.

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. Chiral and critical spin liquids in a spin-1/2 kagome antiferromagnet

    NASA Astrophysics Data System (ADS)

    Zhu, W.; Gong, S. S.; Sheng, D. N.

    2015-07-01

    The kagome spin-1/2 systems have attracted intensive attention in recent years as the primary candidate for hosting different gapped spin liquids (SLs). To uncover the nature of the novel quantum phase transition between the SL states, we study a minimum X Y model with the nearest-neighbor (NN) (Jx y), the second-NN, and the third-NN couplings (J2 x y=J3 x y=Jxy ' ). We identify the time-reversal-symmetry-broken chiral SL (CSL) with the turn on of a small perturbation Jxy '˜0.06 Jx y , which is fully characterized by the fractionally quantized topological Chern number and the conformal edge spectrum as the ν =1 /2 fractional quantum Hall state. Interestingly, the NN X Y model (Jxy '=0 ) is shown to be a critical SL state adjacent to the CSL, characterized by the gapless spin singlet and spin triplet excitations. The quantum phase transition from the CSL to the gapless critical SL is driven by the collapsing of the neutral (spin singlet) excitation gap. The effect of the NN spin-z coupling Jz is also studied, which leads to a quantum phase diagram with an extended regime for the gapless SL.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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

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

    SciTech Connect

    Wu, R.; Yun, C.; Ding, S. L.; Wen, X.; Liu, S. Q.; Wang, C. S.; Han, J. Z.; Du, H. L.; Yang, J. B.

    2016-08-07

    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{sup −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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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

  19. 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

  20. 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

  1. 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.

  2. 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.

  3. 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.

  4. Spin excitations in antiferromagnetic metallic phase of iron pnictides analyzed with a five-band itinerant model

    NASA Astrophysics Data System (ADS)

    Kaneshita, Eiji; Tohyama, Takami

    2011-03-01

    We investigate the spin wave excitation in the metallic antiferromagnetic phase of iron pnictide superconductors based on calculated neutron scattering spectra by mean-field calculations with a random phase approximation in a five-band itinerant model [E.K. & T.T., RPB 82, 094441 (2010)]. The calculated excitation spectra reproduce well spin-wave dispersions observed in inelastic neutron scattering, with a realistic magnetic moment for CaFe 2 As 2 . A particle-hole gap is found to be crucial to obtain consistent results; we predict the spin wave in LaFeAsO disappears at a lower energy than in CaFe 2 As 2 .

  5. Anisotropy of Spin Fluctuations in a Tetragonal Heavy Fermion Antiferromagnet CeRhAl 4 Si 2

    DOE PAGES

    Sakai, H.; Hattori, T.; Tokunaga, Y.; ...

    2017-06-01

    An antiferromagnetic (AFM) Kondo lattice compound CeRhAl4Si2, which exhibits successive AFM transitions at T N1=14 K and T N2=9 K in zero external field, has been microscopically investigated by means of 27Al nuclear magnetic resonance (NMR) technique. In the high temperature range, magnetic excitations of 4f electrons can be well explained by isotropic localized spin fluctuations. Below ~50 K, it begins to show a characteristic anisotropy of spin fluctuations, which suggests a competition between spin fluctuations and nesting instability in this system.

  6. Anisotropy of Spin Fluctuations in a Tetragonal Heavy Fermion Antiferromagnet CeRhAl4Si2

    NASA Astrophysics Data System (ADS)

    Sakai, H.; Hattori, T.; Tokunaga, Y.; Kambe, S.; Ghimire, N. J.; Ronning, F.; Bauer, E. D.; Thompson, J. D.

    2017-06-01

    An antiferromagnetic (AFM) Kondo lattice compound CeRhAl4Si2, which exhibits successive AFM transitions at T N1=14 K and T N2=9 K in zero external field, has been microscopically investigated by means of 27Al nuclear magnetic resonance (NMR) technique. In the high temperature range, magnetic excitations of 4f electrons can be well explained by isotropic localized spin fluctuations. Below ∼50 K, it begins to show a characteristic anisotropy of spin fluctuations, which suggests a competition between spin fluctuations and nesting instability in this system.

  7. Ultracold few fermionic atoms in needle-shaped double wells: spin chains and resonating spin clusters from microscopic Hamiltonians emulated via antiferromagnetic Heisenberg and t-J models

    NASA Astrophysics Data System (ADS)

    Yannouleas, Constantine; Brandt, Benedikt B.; Landman, Uzi

    2016-07-01

    Advances with trapped ultracold atoms intensified interest in simulating complex physical phenomena, including quantum magnetism and transitions from itinerant to non-itinerant behavior. Here we show formation of antiferromagnetic ground states of few ultracold fermionic atoms in single and double well (DW) traps, through microscopic Hamiltonian exact diagonalization for two DW arrangements: (i) two linearly oriented one-dimensional, 1D, wells, and (ii) two coupled parallel wells, forming a trap of two-dimensional, 2D, nature. The spectra and spin-resolved conditional probabilities reveal for both cases, under strong repulsion, atomic spatial localization at extemporaneously created sites, forming quantum molecular magnetic structures with non-itinerant character. These findings usher future theoretical and experimental explorations into the highly correlated behavior of ultracold strongly repelling fermionic atoms in higher dimensions, beyond the fermionization physics that is strictly applicable only in the 1D case. The results for four atoms are well described with finite Heisenberg spin-chain and cluster models. The numerical simulations of three fermionic atoms in symmetric DWs reveal the emergent appearance of coupled resonating 2D Heisenberg clusters, whose emulation requires the use of a t-J-like model, akin to that used in investigations of high T c superconductivity. The highly entangled states discovered in the microscopic and model calculations of controllably detuned, asymmetric, DWs suggest three-cold-atom DW quantum computing qubits.

  8. 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.

  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. Lattice and spin dynamics in a low-symmetry antiferromagnet NiWO4

    NASA Astrophysics Data System (ADS)

    Prosnikov, M. A.; Davydov, V. Yu.; Smirnov, A. N.; Volkov, M. P.; Pisarev, R. V.; Becker, P.; Bohatý, L.

    2017-07-01

    Lattice and magnetic dynamics of NiWO4 single crystals were studied with the use of polarized Raman spectroscopy in a wide temperature range of 10-300 K including the antiferromagnetic ordering temperature TN=62 K. Static magnetic measurements were used for characterizing the single crystals. All Raman-active phonons predicted by the group theory were observed and characterized. Magnetic symmetry analysis was used to determine possible magnetic space groups for NiWO4 which can be also applied to any other isostructural crystal with the same magnetic propagation vector k =(1 /2 ,0 ,0 ) . Although the magnetic structure of NiWO4 is relatively simple, a rich set of narrow and broad magnetic excitations with different polarization properties and temperature behavior in the very broad frequency range of 10-200 cm-1 was observed, with some modes surviving at temperatures much higher than TN up to 220 K. Part of the magnetic excitations were identified as acoustic and optical spin-wave branches which allowed us to construct exchange structure and estimate exchange and anisotropy constants with the use of linear spin-wave theory.

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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

  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. 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.

  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. High-energy spin-density-wave correlated fluctuations in paramagnetic Cr + 5 at. % V

    SciTech Connect

    Werner, S.A.; Fawcett, E.; Elmiger, M.W.; Shirane, G.

    1992-11-01

    Measurements of the magnetic fluctuations, termed spin-density-wave (SDW) paramagnons, in the nearly antiferromagnetic alloy Cr + 5 at.%V are extended up in energy to about 80 MeV. These fluctuating spin-spin correlations occur at incommensurate positions, corresponding to the SDW wavevector Q. Their characteristic energy is at least an order of magnitude larger than that of the magnetic fluctuations seen in the paramagnetic phase of pure Cr, but their intensity is more than two orders of magnitude smaller. We find that the dynamic susceptibility decreases by about 50% between temperature T = 10K and 300K.

  2. High-energy spin-density-wave correlated fluctuations in paramagnetic Cr + 5 at. % V

    SciTech Connect

    Werner, S.A. . Dept. of Physics); Fawcett, E. . Dept. of Physics); Elmiger, M.W.; Shirane, G. )

    1992-01-01

    Measurements of the magnetic fluctuations, termed spin-density-wave (SDW) paramagnons, in the nearly antiferromagnetic alloy Cr + 5 at.%V are extended up in energy to about 80 MeV. These fluctuating spin-spin correlations occur at incommensurate positions, corresponding to the SDW wavevector Q. Their characteristic energy is at least an order of magnitude larger than that of the magnetic fluctuations seen in the paramagnetic phase of pure Cr, but their intensity is more than two orders of magnitude smaller. We find that the dynamic susceptibility decreases by about 50% between temperature T = 10K and 300K.

  3. 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.

  4. 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.

  5. Devil's staircase continuum in the chiral clock spin glass with competing ferromagnetic-antiferromagnetic and left-right chiral interactions.

    PubMed

    Çağlar, Tolga; Berker, A Nihat

    2017-04-01

    The chiral clock spin-glass model with q=5 states, with both competing ferromagnetic-antiferromagnetic and left-right chiral frustrations, is studied in d=3 spatial dimensions by renormalization-group theory. The global phase diagram is calculated in temperature, antiferromagnetic bond concentration p, random chirality strength, and right-chirality concentration c. The system has a ferromagnetic phase, a multitude of different chiral phases, a chiral spin-glass phase, and a critical (algebraically) ordered phase. The ferromagnetic and chiral phases accumulate at the disordered phase boundary and form a spectrum of devil's staircases, where different ordered phases characteristically intercede at all scales of phase-diagram space. Shallow and deep reentrances of the disordered phase, bordered by fragments of regular and temperature-inverted devil's staircases, are seen. The extremely rich phase diagrams are presented as continuously and qualitatively changing videos.

  6. 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.

  7. Devil's staircase continuum in the chiral clock spin glass with competing ferromagnetic-antiferromagnetic and left-right chiral interactions

    NASA Astrophysics Data System (ADS)

    Ćaǧlar, Tolga; Berker, A. Nihat

    2017-04-01

    The chiral clock spin-glass model with q =5 states, with both competing ferromagnetic-antiferromagnetic and left-right chiral frustrations, is studied in d =3 spatial dimensions by renormalization-group theory. The global phase diagram is calculated in temperature, antiferromagnetic bond concentration p , random chirality strength, and right-chirality concentration c . The system has a ferromagnetic phase, a multitude of different chiral phases, a chiral spin-glass phase, and a critical (algebraically) ordered phase. The ferromagnetic and chiral phases accumulate at the disordered phase boundary and form a spectrum of devil's staircases, where different ordered phases characteristically intercede at all scales of phase-diagram space. Shallow and deep reentrances of the disordered phase, bordered by fragments of regular and temperature-inverted devil's staircases, are seen. The extremely rich phase diagrams are presented as continuously and qualitatively changing videos.

  8. 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.

  9. 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.

  10. Spin ordering and dynamics in the frustrated antiferromagnet YBaCo 4 O 7.1

    SciTech Connect

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

    2014-03-01

    The stoichiometric 114-layered material YBaCo407 exhibits long-range antiferromagnetic order below a Neel temperature of 106 K. Nonstoichiometric YBaCo4O7.1. which contains a relatively small amount (1.4%) of interstitial oxygen, has recently been shown to have drastically modified magnetic properties compared to the parent compound. The present experiments have used magnetization, ac susceptibility, and zero applied field NMR to study the spin configuration and spin dynamics in a single crystal of YBaCo4O7.1 as a function of temperature below 100 K. Evidence has been obtained for a magnetic transition at 80 K corresponding to some form of spin freeze-out. Based on previous results for the stoichiometric material, it is likely that the freezing process involves spins in the triangular layers in this frustrated antiferromagnet. At lower temperatures, dynamic effects persist and below 50 K a fraction of the spins, located primarily in the kagom.e layers, constitute what may be termed a viscous spin liquid component. For T < 10 K, a disordered or glasslike spin structure, with a large distribution of spin correlation times, emerges as the low-temperature state of the spin system.

  11. Magnetic order on a frustrated spin- (1)/(2) Heisenberg antiferromagnet on the Union Jack lattice

    NASA Astrophysics Data System (ADS)

    Bishop, R. F.; Li, P. H. Y.; Farnell, D. J. J.; Campbell, C. E.

    2010-07-01

    We use the coupled cluster method (CCM) to study the zero-temperature phase diagram of a two-dimensional frustrated spin-half antiferromagnet, the so-called Union Jack model. It is defined on a square lattice such that all nearest-neighbor pairs are connected by bonds with a strength J1>0 , but only half the next-nearest-neighbor pairs are connected by bonds with a strength J2≡κJ1>0 . The bonds are arranged such that on the 2×2 unit cell they form the pattern of the Union Jack flag. Alternating sites on the square lattice are thus four-connected and eight-connected. We find strong evidence for a first phase transition between a Néel antiferromagnetic phase and a canted ferrimagnetic phase at a critical coupling κc1=0.66±0.02 . The transition is an interesting one, at which the energy and its first derivative seem continuous, thus providing a typical scenario of a second-order transition (just as in the classical case for the model), although a weakly first-order transition cannot be excluded. By contrast, the average on-site magnetization approaches a nonzero value Mc1=0.195±0.005 on both sides of the transition, which is more typical of a first-order transition. The slope, dM/dκ , of the order parameter curve as a function of the coupling strength κ , also appears to be continuous, or very nearly so, at the critical point κc1 , thereby providing further evidence of the subtle nature of the transition between the Néel and canted phases. Our CCM calculations provide strong evidence that the canted ferrimagnetic phase becomes unstable at large values of κ , and hence we have also used the CCM with a model collinear semistripe-ordered ferrimagnetic state in which alternating rows (and columns) are ferromagnetically and antiferromagnetically ordered, and in which the spins connected by J2 bonds are antiparallel to one another. We find tentative evidence, based on the relative energies of the two states, for a second zero-temperature phase transition

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Antiferromagnetism in the van der Waals layered spin-lozenge semiconductor CrTe3

    DOE PAGES

    McGuire, Michael A.; Garlea, V. Ovidiu; KC, Santosh; ...

    2017-04-14

    We have investigated the crystallographic, magnetic, and transport properties of the van der Waals bonded, layered compound CrTe 3 on single-crystal and polycrystalline materials. Furthermore, the crystal structure contains layers made up of lozenge-shaped Cr 4 tetramers. Electrical resistivity measurements show the crystals to be semiconducting, with a temperature dependence consistent with a band gap of 0.3 eV. The magnetic susceptibility exhibits a broad maximum near 300 K characteristic of low dimensional magnetic systems. Weak anomalies are observed in the susceptibility and heat capacity near 55 K, and single-crystal neutron diffraction reveals the onset of long-range antiferromagnetic order at thismore » temperature. Strongly dispersive spin waves are observed in the ordered state. Significant magnetoelastic coupling is indicated by the anomalous temperature dependence of the lattice parameters and is evident in structural optimization in van der Waals density functional theory calculations for different magnetic configurations. The cleavability of the compound is apparent from its handling and is confirmed by first-principles calculations, which predict a cleavage energy 0.5 J / m 2 , similar to graphite. Based on our results, CrTe 3 is identified as a promising compound for studies of low dimensional magnetism in bulk crystals as well as magnetic order in monolayer materials and van der Waals heterostructures.« less

  17. 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.

  18. 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

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

    NASA Astrophysics Data System (ADS)

    Vlijm, Rogier; Caux, Jean-Sébastien

    2014-05-01

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

  20. 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.

  1. Block product density matrix embedding theory for strongly correlated spin systems

    NASA Astrophysics Data System (ADS)

    Gunst, Klaas; Wouters, Sebastian; De Baerdemacker, Stijn; Van Neck, Dimitri

    2017-05-01

    Density matrix embedding theory (DMET) is a relatively new technique for the calculation of strongly correlated systems. Recently, block product DMET (BPDMET) was introduced for the study of spin systems such as the antiferromagnetic J1-J2 model on the square lattice. In this paper, we extend the variational Ansatz of BPDMET using spin-state optimization, yielding improved results. We apply the same techniques to the Kitaev-Heisenberg model on the honeycomb lattice, comparing the results when using several types of clusters. Energy profiles and correlation functions are investigated. A diagonalization in the tangent space of the variational approach yields information on the excited states and the corresponding spectral functions.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Analysis of Charge-spin-orbital Fluctuations by Ab Initio Calculation and Random Phase Approximation: Application to Non-coplanar Antiferromagnet Cd2Os2O7

    NASA Astrophysics Data System (ADS)

    Uehara, Amane; Shinaoka, Hiroshi; Motome, Yukitoshi

    We present a systematic analysis on the basis of ab initio calculations and many-body perturbation theory for clarifying the dominant fluctuation in complex charge-spin-orbital coupled systems. For a tight-binding multiband model obtained from the maximally-localized Wannier function analysis of the band structure by the local density approximation, we take into account electron correlations at the level of random phase approximation. To identify the dominant fluctuation, we carry out the eigenmode analysis of the generalized susceptibility that includes all the multiple degrees of freedom: charge, spin, and orbital. We apply this method to the paramagnetic metallic phase of a pyrochlore oxide Cd2Os2O7, which shows a metalinsulator transition accompanied by a peculiar noncoplanar antiferromagnetic order of all-in all-out type. We find that the corresponding spin fluctuation is dominantly enhanced by the on-site Coulomb repulsions in the presence of strong spin-orbit coupling and trigonal crystal field splitting. Our results indicate that the combined method offers an effective tool for the systematic analysis of potential instabilities in strongly correlated electron materials.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. 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.

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

    DOE PAGES

    Han, Tian-Heng; Norman, M. R.; Wen, J. -J.; ...

    2016-08-18

    Low energy inelastic neutron scattering on single crystals of the kagome spin-liquid compound ZnCu3(OD)6Cl2 (herbertsmithite) reveals in this paper antiferromagnetic correlations between impurity spins for energy transfers h(with stroke)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.more » 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. Finally, 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.« less

  15. 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.

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

    SciTech Connect

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

    2016-08-18

    Low energy inelastic neutron scattering on single crystals of the kagome spin-liquid compound ZnCu3(OD)6Cl2 (herbertsmithite) reveals in this paper antiferromagnetic correlations between impurity spins for energy transfers h(with stroke)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. Finally, 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.

  17. Correlation functions of the integrable higher-spin XXX and XXZ spin chains through the fusion method

    NASA Astrophysics Data System (ADS)

    Deguchi, Tetsuo; Matsui, Chihiro

    2010-06-01

    For the integrable higher-spin XXX and XXZ spin chains we present multiple-integral representations for the correlation function of an arbitrary product of Hermitian elementary matrices in the massless ground state. We give a formula expressing it by a single term of multiple integrals. In particular, we explicitly derive the emptiness formation probability (EFP). We assume 2s-strings for the ground-state solution of the Bethe-ansatz equations for the spin-s XXZ chain, and solve the integral equations for the spin-s Gaudin matrix. In terms of the XXZ coupling Δ we define ζ by Δ=cos ζ, and put it in a region 0⩽ζ<π/2s of the gapless regime: -1<Δ⩽1 (0⩽ζ<π), where Δ=1 (ζ=0) corresponds to the antiferromagnetic point. We calculate the zero-temperature correlation functions by the algebraic Bethe-ansatz, introducing the Hermitian elementary matrices in the massless regime, and taking advantage of the fusion construction of the R-matrix of the higher-spin representations of the affine quantum group.

  18. 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

  19. Crystal Structure of the Spin 1/2 Honeycomb-Lattice Antiferromagnet Cu2(pymca)3(ClO4)

    NASA Astrophysics Data System (ADS)

    Honda, Zentaro; Kodama, Takafumi; Kikukawa, Reo; Hagiwara, Masayuki; Kida, Takanori; Sakai, Masamichi; Fukuda, Takeshi; Fujihara, Takashi; Kamata, Norihiko

    2015-03-01

    Using X-ray diffraction techniques, we have studied the crystal structure of a copper polynuclear coordination polymer Cu2(pymca)3(ClO4) (pymca = pyrimidine-2-carboxylate), which is found to crystallize as a trigonal crystal system, space group P31m, with the lattice constants a = 9.5904(18) Å and c = 5.9000(11) Å, at temperature T = 150 K. Each pymca ligand connects to two Cu2+ ions, forming a honeycomb network in the ab plane. The T dependence of the magnetic susceptibility of Cu2(pymca)3(ClO4) shows a broad maximum near T = 26 K, indicating low-dimensional antiferromagnetic interactions. From the crystal structure and magnetic properties, we conclude that Cu2(pymca)3(ClO4) is a good realization of a spin-1/2 honeycomb lattice antiferromagnet.

  20. 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.

  1. 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

  2. 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.

  3. Octa-Kagomé Lattice Compounds Showing Quantum Critical Behaviors: Spin Gap Ground State versus Antiferromagnetic Ordering.

    PubMed

    Tang, Yingying; Peng, Cheng; Guo, Wenbin; Wang, Jun-Feng; Su, Gang; He, Zhangzhen

    2017-09-29

    Search for a new geometrically frustrated lattice is a great challenge. Herein, we report on a successful synthesis of two new layered compounds BiOCu2(XO3)(SO4)(OH)·H2O [X = Te (1) and Se (2)] with a new type of geometrically frustrated lattice (i.e., the octa-kagomé lattice) between kagomé and star motifs. Magnetic measurements confirmed that 1 exhibits a spin gap ground state, while 2 possesses a typical antiferromagnetic ordering at low-temperature. Such different magnetic behaviors between two isostructural compounds are suggested to originate from a slightly structural modification induced by nonmagnetic XO3 anionic groups. Theoretical simulations suggest that the origin of gapped ground state in 1 may be due to the dimerization of Cu(2+) ions, while 2 may break the limiting of such dimerization, leading to an antiferromagnetic ordering.

  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. 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.

  6. Robust spin correlations at high magnetic fields in the harmonic honeycomb iridates

    DOE PAGES

    Modic, K. A.; Ramshaw, Brad J.; Betts, J. B.; ...

    2017-08-01

    Here, the complex antiferromagnetic orders observed in the honeycomb iridates are a double-edged sword in the search for a quantum spin-liquid: both attesting that the magnetic interactions provide many of the necessary ingredients, while simultaneously impeding access. Focus has naturally been drawn to the unusual magnetic orders that hint at the underlying spin correlations. However, the study of any particular broken symmetry state generally provides little clue about the possibility of other nearby ground states. Here we use magnetic fields approaching 100 Tesla to reveal the extent of the spin correlations in γ-lithium iridate. We find that a small componentmore » of field along the magnetic easy-axis melts long-range order, revealing a bistable, strongly correlated spin state. Far from the usual destruction of antiferromagnetism via spin polarization, the high-field state possesses only a small fraction of the total iridium moment, without evidence for long-range order up to the highest attainable magnetic fields.« less

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

    PubMed Central

    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

    2014-01-01

    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. PMID:24419488

  8. 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.

  9. 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.

  10. 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.

  11. Observation of spatial charge and spin correlations in the 2D Fermi-Hubbard model.

    PubMed

    Cheuk, Lawrence W; Nichols, Matthew A; Lawrence, Katherine R; Okan, Melih; Zhang, Hao; Khatami, Ehsan; Trivedi, Nandini; Paiva, Thereza; Rigol, Marcos; Zwierlein, Martin W

    2016-09-16

    Strong electron correlations lie at the origin of high-temperature superconductivity. Its essence is believed to be captured by the Fermi-Hubbard model of repulsively interacting fermions on a lattice. Here we report on the site-resolved observation of charge and spin correlations in the two-dimensional (2D) Fermi-Hubbard model realized with ultracold atoms. Antiferromagnetic spin correlations are maximal at half-filling and weaken monotonically upon doping. At large doping, nearest-neighbor correlations between singly charged sites are negative, revealing the formation of a correlation hole, the suppressed probability of finding two fermions near each other. As the doping is reduced, the correlations become positive, signaling strong bunching of doublons and holes, in agreement with numerical calculations. The dynamics of the doublon-hole correlations should play an important role for transport in the Fermi-Hubbard model. Copyright © 2016, American Association for the Advancement of Science.

  12. 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

  13. 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.

  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. Quantum correlated heat engine with spin squeezing.

    PubMed

    Altintas, Ferdi; Hardal, Ali Ü C; Müstecaplıoglu, Özgür E

    2014-09-01

    We propose a four-level quantum heat engine in an Otto cycle with a working substance of two spins subject to an external magnetic field and coupled to each other by a one-axis twisting spin squeezing nonlinear interaction. We calculate the positive work and the efficiency of the engine for different parameter regimes. In particular, we investigate the effects of quantum correlations at the end of the two isochoric processes of the Otto cycle, as measured by the entanglement of formation and quantum discord, on the work extraction and efficiency. The regimes where the quantum correlations could enhance the efficiency and work extraction are characterized.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  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. 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.

  2. 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.

  3. 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.

  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. Phase diagrams of Bose-Hubbard model and antiferromagnetic spin-1/2 models on a honeycomb lattice

    NASA Astrophysics Data System (ADS)

    Nakafuji, Takashi; Ichinose, Ikuo

    2017-07-01

    Motivated by the recent experimental realization of the Haldane model by ultracold fermions in an optical lattice, we investigate phase diagrams of the hard-core Bose-Hubbard model on a honeycomb lattice. This model is closely related with a spin-1/2 antiferromagnetic (AF) quantum spin model. Nearest-neighbor (NN) hopping amplitude is positive and it prefers an AF configuration of phases of Bose-Einstein condensates. On the other hand, an amplitude of the next-NN hopping depends on an angle variable as in the Haldane model. Phase diagrams are obtained by means of an extended path-integral Monte Carlo simulation. Besides the AF state, a 120∘-order state, there appear other phases including a Bose metal in which no long-range orders exist.

  6. Model of ultrafast demagnetization driven by spin-orbit coupling in a photoexcited antiferromagnetic insulator Cr2O3.

    PubMed

    Guo, Feng; Zhang, Na; Jin, Wei; Chang, Jun

    2017-06-28

    We theoretically study the dynamic time evolution following laser pulse pumping in an antiferromagnetic insulator Cr2O3. From the photoexcited high-spin quartet states to the long-lived low-spin doublet states, the ultrafast demagnetization processes are investigated by solving the dissipative Schrödinger equation. We find that the demagnetization times are of the order of hundreds of femtoseconds, in good agreement with recent experiments. The switching times could be strongly reduced by properly tuning the energy gaps between the multiplet energy levels of Cr(3+). Furthermore, the relaxation times also depend on the hybridization of atomic orbitals in the first photoexcited state. Our results suggest that the selective manipulation of the electronic structure by engineering stress-strain or chemical substitution allows effective control of the magnetic state switching in photoexcited insulating transition-metal oxides.

  7. 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.

  8. 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.

  9. 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.

  10. Model of ultrafast demagnetization driven by spin-orbit coupling in a photoexcited antiferromagnetic insulator Cr2O3

    NASA Astrophysics Data System (ADS)

    Guo, Feng; Zhang, Na; Jin, Wei; Chang, Jun

    2017-06-01

    We theoretically study the dynamic time evolution following laser pulse pumping in an antiferromagnetic insulator Cr2O3. From the photoexcited high-spin quartet states to the long-lived low-spin doublet states, the ultrafast demagnetization processes are investigated by solving the dissipative Schrödinger equation. We find that the demagnetization times are of the order of hundreds of femtoseconds, in good agreement with recent experiments. The switching times could be strongly reduced by properly tuning the energy gaps between the multiplet energy levels of Cr3+. Furthermore, the relaxation times also depend on the hybridization of atomic orbitals in the first photoexcited state. Our results suggest that the selective manipulation of the electronic structure by engineering stress-strain or chemical substitution allows effective control of the magnetic state switching in photoexcited insulating transition-metal oxides.

  11. Spin wave dispersion just above the magnetic order-order transition in the metallic antiferromagnet Mn3Pt

    NASA Astrophysics Data System (ADS)

    Ibuka, Soshi; Yokoo, Tetsuya; Itoh, Shinichi; Kamazawa, Kazuya; Nakamura, Mitsutaka; Imai, Motoharu

    2017-06-01

    Spin wave dispersion of the metallic antiferromagnet Mn3Pt was investigated just above the order-order transition temperature by using the inelastic neutron scattering technique. The spin wave dispersion at T = 400 K along [100], [110] and [111] directions was isotropic within the measurement accuracy. The dispersion was described by (ħω)2 = c 2 q 2 + δ2 with c = 190 meVÅ and Δ = 3.3 meV. Compared with the previous reports, the result shows that large reduction of the stiffness constant with increasing temperature. This feature is similar to that in FePt3, and will be an indication of the itinerancy of the magnetic moments.

  12. Spin dynamics in the stripe-ordered buckled honeycomb lattice antiferromagnet Ba2NiTeO6

    NASA Astrophysics Data System (ADS)

    Asai, Shinichiro; Soda, Minoru; Kasatani, Kazuhiro; Ono, Toshio; Garlea, V. Ovidiu; Winn, Barry; Masuda, Takatsugu

    2017-09-01

    We carried out inelastic neutron scattering experiments on a buckled honeycomb lattice antiferromagnet Ba2NiTeO6 exhibiting a stripe structure at a low temperature. Magnetic excitations are observed in the energy range of ℏ ω ≲10 meV having an anisotropy gap of 2 meV at 2 K. We perform spin-wave calculations to identify the spin model. The obtained microscopic parameters are consistent with the location of the stripe structure in the classical phase diagram. Furthermore, the Weiss temperature independently estimated from a bulk magnetic susceptibility is consistent with the microscopic parameters. The results reveal that a competition between the nearest-neighbor and next-nearest-neighbor interactions that together with a relatively large single-ion magnetic anisotropy stabilize the stripe magnetic structure.

  13. Collective and local excitations in Ba2CoTeO6: A composite system of a spin-1/2 triangular-lattice Heisenberg antiferromagnet and a honeycomb-lattice J1-J2 Ising antiferromagnet

    NASA Astrophysics Data System (ADS)

    Chanlert, Purintorn; Kurita, Nobuyuki; Tanaka, Hidekazu; Kimata, Motoi; Nojiri, Hiroyuki

    2017-08-01

    We report the results of multifrequency high-magnetic-field electron-spin resonance (ESR) measurements on the highly frustrated antiferromagnet Ba2CoTeO6 . This compound is magnetically composed of two subsystems A and B, which are described as a spin-1/2 triangular-lattice Heisenberg antiferromagnet and a honeycomb-lattice J1-J2 Ising antiferromagnet, respectively. Ba2CoTeO6 undergoes successive magnetic phase transitions at TN 1=12.0 K and TN 2=3.0 K. For a magnetic field H parallel to the c axis, subsystem B exhibits successive metamagnetic transitions with magnetization plateaus at one-third and one-half of the saturation magnetization. Below TN 2, we observed collective ESR modes for H ∥c , which are characteristic of a triangular-lattice Heisenberg antiferromagnet with weak easy-plane anisotropy. We also observed a local excitation mode, which can be assigned as a single flip of the Ising-like spin of subsystem B. From a detailed analysis of the collective and local ESR modes, combined with the magnetization process, we determined the magnetic parameters of subsystems A and B, and confirmed that the two subsystems are almost decoupled.

  14. 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

  15. 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.

  16. Induced spin-triplet pairing in the coexistence state of antiferromagnetism and singlet superconductivity: Collective modes and microscopic properties

    NASA Astrophysics Data System (ADS)

    Almeida, D. E.; Fernandes, R. M.; Miranda, E.

    2017-07-01

    The close interplay between superconductivity and antiferromagnetism in several quantum materials can lead to the appearance of an unusual thermodynamic state in which both orders coexist microscopically, despite their competing nature. A hallmark of this coexistence state is the emergence of a spin-triplet superconducting gap component, called a π triplet, which is spatially modulated by the antiferromagnetic wave vector, reminiscent of a pair density wave. In this paper, we investigate the impact of these π -triplet degrees of freedom on the phase diagram of a system with competing antiferromagnetic and superconducting orders. Although we focus on a microscopic two-band model that has been widely employed in studies of iron pnictides, most of our results follow from a Ginzburg-Landau analysis, and as such should be applicable to other systems of interest, such as cuprates and heavy fermion materials. The Ginzburg-Landau functional reveals not only that the π -triplet gap amplitude couples trilinearly with the singlet gap amplitude and the staggered magnetization magnitude but also that the π -triplet d -vector couples linearly with the magnetization direction. While in the mean-field level this coupling forces the d -vector to align parallel or antiparallel to the magnetization, in the fluctuation regime it promotes two additional collective modes—a Goldstone mode related to the precession of the d -vector around the magnetization and a massive mode, related to the relative angle between the two vectors, which is nearly degenerate with a Leggett-like mode associated with the phase difference between the singlet and triplet gaps. We also investigate the impact of magnetic fluctuations on the superconducting-antiferromagnetic phase diagram, showing that due to their coupling with the π -triplet order parameter the coexistence region is enhanced. This effect stems from the fact that the π -triplet degrees of freedom promote an effective attraction between

  17. 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

  18. 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.

  19. Robust antiferromagnetic spin waves across the metal-insulator transition in hole-doped BaMn2As2

    DOE PAGES

    Ramazanoglu, M.; Sapkota, A.; Pandey, Abhishek; ...

    2017-06-01

    BaMn2 As2 is an antiferromagnetic insulator where a metal-insulator transition occurs with hole doping via the substitution of Ba with K. The metal-insulator transition causes only a small suppression of the Néel temperature (TN) and the ordered moment, suggesting that doped holes interact weakly with the Mn spin system. Powder inelastic neutron scattering measurements were performed on three different samples of Ba1 - xKxMn2 As2 with x = 0 , 0.125, and 0.25 to study the effect of hole doping and metallization on the spin dynamics. We compare the neutron intensities to a linear spin-wave theory approximation to the J1more » $-$ J2 $-$ Jc Heisenberg model. Hole doping is found to introduce only minor modifications to the exchange energies and spin gap. The changes observed in the exchange constants are consistent with the small drop of TN with doping.« less

  20. 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.

  1. Damped spin-wave excitations in the itinerant antiferromagnet γ -Fe0.7Mn0.3

    NASA Astrophysics Data System (ADS)

    Ibuka, S.; Itoh, S.; Yokoo, T.; Endoh, Y.

    2017-06-01

    The collective spin-wave excitations in the antiferromagnetic state of γ -Fe0.7Mn0.3 were investigated using the inelastic neutron-scattering technique. The spin excitations remain isotropic up to high excitation energy, ℏ ω =78 meV. The excitations gradually become broad and damped above 40 meV. The damping parameter γ reaches 110(16) meV at ℏ ω =78 meV, which is much larger than that for other metallic compounds, e.g., CaFe2As2 (24 meV), La2 -2 xSr1 +2 xMn2O7 (52-72 meV), and Mn90Cu10 (88 meV). In addition, the spin-wave dispersion shows a deviation from the relation (ℏω ) 2=c2q2+Δ2 above 40 meV. The group velocity above this energy increases to 470(40) meVÅ, which is higher than that at the low energies, c =226 (5 ) meVÅ. These results could suggest that the spin-wave excitations merge with the continuum of the individual particle-hole excitations at 40 meV.

  2. 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.

  3. 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

  4. Evidence for spin correlation in tt production

    SciTech Connect

    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 with 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.

  5. 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.

  6. 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.

  7. 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.

  8. Two-magnon excitations observed by neutron scattering in the two-dimensional spin- 5 /2 Heisenberg antiferromagnet Rb2 Mn F4

    NASA Astrophysics Data System (ADS)

    Huberman, T.; Coldea, R.; Cowley, R. A.; Tennant, D. A.; Leheny, R. L.; Christianson, R. J.; Frost, C. D.

    2005-07-01

    The low-temperature magnetic excitations of the two-dimensional spin- (5)/(2) square-lattice Heisenberg antiferromagnet Rb2MnF4 have been probed using pulsed inelastic neutron scattering. In addition to dominant sharp peaks identified with one-magnon excitations, a relatively weak continuum scattering is also observed at higher energies. This is attributed to neutron scattering by pairs of magnons and the observed intensities are consistent with predictions of spin wave theory.

  9. (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.

  10. Spin frustration and magnetic ordering in triangular lattice antiferromagnet Ca3CoNb2O9

    NASA Astrophysics Data System (ADS)

    Dai, Jia; Zhou, Ping; Wang, Peng-Shuai; Pang, Fei; Munsie, Tim J.; Luke, Graeme M.; Zhang, Jin-Shan; Yu, Wei-Qiang

    2015-12-01

    We synthesized a quasi-two-dimensional distorted triangular lattice antiferromagnet Ca3CoNb2O9, in which the effective spin of Co2+ is 1/2 at low temperatures, whose magnetic properties were studied by dc susceptibility and magnetization techniques. The x-ray diffraction confirms the quality of our powder samples. The large Weiss constant θCW˜ -55 K and the low Neel temperature TN˜ 1.45 K give a frustration factor f = | θCW/TN | ≈ 38, suggesting that Ca3CoNb2O9 resides in strong frustration regime. Slightly below TN, deviation between the susceptibility data under zero-field cooling (ZFC) and field cooling (FC) is observed. A new magnetic state with 1/3 of the saturate magnetization Ms is suggested in the magnetization curve at 0.46 K. Our study indicates that Ca3CoNb2O9 is an interesting material to investigate magnetism in triangular lattice antiferromagnets with weak anisotropy. Project supported by the National Natural Science Foundation of China (Grant Nos. 11374364 and 11222433), the National Basic Research Program of China (Grant No. 2011CBA00112). Research at McMaster University supported by the Natural Sciences and Engineering Research Council. Work at North China Electric Power University supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.

  11. Common features of low-temperature spin-charge separation and superlattice formation in multiferroic manganites and antiferromagnetic cuprates.

    PubMed

    Sanina, V A; Golovenchits, E I; Zalesskii, V G; Khannanov, B Kh

    2013-08-21

    The paper reports on new results obtained for tetragonal quasi-2D antiferromagnetic Eu2CuO4 at temperatures below 30-40 K. A set of ferromagnetic resonance lines similar to ones obtained earlier for a number of multiferroic manganites (Sanina et al 2012 J. Phys.: Condens. Matter 24 346002), with similar electric polarization and local conductivity, were measured, i.e., a multiferroic behavior was revealed in Eu2CuO4 at low temperatures. We attribute these observations to the 1D superlattices that are formed due to phase separation and self-organization of charge carriers and occupy a small crystal volume, as in the multiferroic manganites studied earlier. Characteristic features of these superlattices include a spin-charge separation and conductivity in their ferromagnetic layers. It is supposed that superlattices are domain walls separating the volume antiferromagnetic domains. A similarity between the superlattices in a number of crystals having different symmetries and bulk properties suggests that a topological order similar to that of the topological insulator exists in them at low temperatures.

  12. 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.

  13. 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.

  14. 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

  15. First-Order Melting of a Weak Spin-Orbit Mott Insulator into a Correlated Metal.

    PubMed

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

    2015-06-26

    The electronic phase diagram of the weak spin-orbit Mott insulator (Sr(1-x)La(x))(3)Ir(2)O(7) is determined via an exhaustive experimental study. Upon doping electrons via La substitution, an immediate collapse in resistivity occurs along with a narrow regime of nanoscale phase separation comprised of antiferromagnetic, insulating regions and paramagnetic, metallic puddles persisting until x≈0.04. Continued electron doping results in an abrupt, first-order phase boundary where the Néel state is suppressed and a homogenous, correlated, metallic state appears with an enhanced spin susceptibility and local moments. As the metallic state is stabilized, a weak structural distortion develops and suggests a competing instability with the parent spin-orbit Mott state.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Mechanism of Basal-Plane Antiferromagnetism in the Spin-Orbit Driven Iridate Ba2IrO4

    NASA Astrophysics Data System (ADS)

    Katukuri, Vamshi M.; Yushankhai, Viktor; Siurakshina, Liudmila; van den Brink, Jeroen; Hozoi, Liviu; Rousochatzakis, Ioannis

    2014-04-01

    By ab initio many-body quantum chemistry calculations, we determine the strength of the symmetric anisotropy in the 5d5 j≈1/2 layered material Ba2IrO4. While the calculated anisotropic couplings come out in the range of a few meV, orders of magnitude stronger than in analogous 3d transition-metal compounds, the Heisenberg superexchange still defines the largest energy scale. The ab initio results reveal that individual layers of Ba2IrO4 provide a close realization of the quantum spin-1/2 Heisenberg-compass model on the square lattice. We show that the experimentally observed basal-plane antiferromagnetism can be accounted for by including additional interlayer interactions and the associated order-by-disorder quantum-mechanical effects, in analogy to undoped layered cuprates.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

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

    PubMed

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

    2016-09-16

    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. Copyright © 2016, American Association for the Advancement of Science.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Zigzag spin structure in layered honeycomb L i3N i2Sb O6 : A combined diffraction and antiferromagnetic resonance study

    NASA Astrophysics Data System (ADS)

    Kurbakov, A. I.; Korshunov, A. N.; Podchezertsev, S. Yu.; Malyshev, A. L.; Evstigneeva, M. A.; Damay, F.; Park, J.; Koo, C.; Klingeler, R.; Zvereva, E. A.; Nalbandyan, V. B.

    2017-07-01

    The magnetic structure of L i3N i2Sb O6 has been determined by low-temperature neutron diffraction, and the crystal structure has been refined by a combination of synchrotron and neutron powder diffraction. The monoclinic (C 2 /m ) symmetry, assigned previously to this pseudohexagonal layered structure, has been unambiguously proven by peak splitting in the synchrotron diffraction pattern. The structure is based on essentially hexagonal honeycomb-ordered N i2Sb O6 layers alternating with L i3 layers, all cations and anions being in an octahedral environment. The compound orders antiferromagnetically below TN=15 K , with the magnetic supercell being a 2 a ×2 b multiple of the crystal cell. The magnetic structure within the honeycomb layer consists of zigzag ferromagnetic spin chains coupled antiferromagnetically. The ordered magnetic moment amounts to 1.62 (2 ) μB/Ni , which is slightly lower than the full theoretical value. Upon cooling below TN, the spins tilt from the c axis, with a maximum tilting angle of 15 .6∘ at T =1.5 K . Our data imply non-negligible ferromagnetic interactions between the honeycomb layers. The observed antiferromagnetic resonance modes are in agreement with the two-sublattice model derived from the neutron data. Orthorhombic anisotropy shows up in zero-field splitting of Δ =198 ±4 and 218 ±4 GHz . Above TN, the electron spin resonance data imply short-range antiferromagnetic order up to about 80 K.

  13. Spin-1/2 Quantum Antiferromagnet on a Three-Dimensional Honeycomb Lattice Formed by a New Organic Biradical F4BIPBNN

    NASA Astrophysics Data System (ADS)

    Amaya, Naoki; Ono, Toshio; Oku, Yuta; Yamaguchi, Hironori; Matsuo, Akira; Kindo, Koichi; Nojiri, Hiroyuki; Palacio, Fernando; Campo, Javier; Hosokoshi, Yuko

    2017-07-01

    We have succeeded in synthesizing a new organic biradical F4BIPBNN [= 2,2'-(3,3',5,5'-tetrafluorobiphenyl-4,4'-diyl)bis(4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide)] which forms an S = 1/2 Heisenberg three-dimensional honeycomb antiferromagnet. Each site of a honeycomb layer alternately couples with upper or lower layers, which results in the unique three-dimensional honeycomb network with four nearest neighbors. At zero magnetic field, antiferromagnetic long-range order has been observed below TN = 2.7 K. Magnetic susceptibility in both paramagnetic and antiferromagnetic states and the magnetization curves are well reproduced by quantum Monte Carlo calculations with three antiferromagnetic interactions in the range of 4.3 to 6.6 K. From the concave shape of the magnetization curve, the shrinkage of spin due to spin fluctuations is evaluated to approximately 30% with respect to its classical value. The phase diagram of magnetic field versus temperature was determined by heat capacity and magnetization. In the field region below 3 T, a slight increase of TN was observed, which reflects the effect of spin fluctuations.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Multiple magnetic transitions in the spin-1/2 chain antiferromagnet SrCuTe2O6

    NASA Astrophysics Data System (ADS)

    Ahmed, N.; Tsirlin, A. A.; Nath, R.

    2015-06-01

    By using thermodynamic measurements and density-functional band-structure calculations, we explore the magnetic behavior of SrCuTe2O6 . Despite being a structural sibling of a three-dimensional frustrated system PbCuTe2O6 , this spin-1/2 quantum magnet shows remarkably different low-temperature behavior. Above 7 K, magnetic susceptibility of SrCuTe2O6 follows the spin-chain model with the antiferromagnetic intrachain coupling of J ≃49.3 K. We ascribe this quasi-one-dimensional behavior to the leading third-neighbor coupling that involves a weakly bent Cu -O ⋯O -Cu superexchange pathway with a short O ⋯O contact of 2.79 Å. Below 5 K, SrCuTe2O6 undergoes two consecutive magnetic transitions that may be triggered by the frustrated nature of interchain couplings. The field dependence of the magnetic transitions (phase diagram) is reported.

  19. 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.

  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. 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.

  5. Edge state and its stability of 2D antiferromagnetic quantum spin systems

    NASA Astrophysics Data System (ADS)

    Suzuki, Takafumi; Sato, Masahiro

    2012-02-01

    Topological insulators (TIs) [1] have been of great interest in condensed matter physics. One of the most important points is that TIs are characterized by non-local quantities such as topological quantities of the bulk or gapless surface states [2]. The TI phase and the surface states are quite stable for any time-reversal symmetric perturbations. On the other hand, the Haldane-gap state in quantum spin systems is another class of the topological state [3], because, similarly to TIs, this gapped state has no local order and is characterized by the non-local (string) order parameter or free spins at the edges. In this study, motivated by the recent development of theories for topological phases and surface states, we consider properties of edge states in 2D quantum spin systems by applying the quantum Monte Carlo method. Particularly, we focus on the three points; (1) which spin systems can have gapless edge states, (2) the stability of the gapless edge states, and (3) the difference between the edge modes of TIs and spin systems. [4pt] [1] See, for example, M. Z. Hasan and C. L. Kane, RMP82, 3045 (2010). [0pt] [2] A. P. Schnyder, et al., PRB 78, 195125 (2008), A. Kitaev, AIP Conf. Proc. 1134, 22 (2009). [0pt] [3] F.D.M. Haldane, Phys. Lett. 93A, 464 (1983); PRL50, 1153 (1983).

  6. 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

  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. 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

  9. 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.

  10. Spin-polarized Second Harmonic Generation from the Antiferromagnetic CaCoSO Single Crystal

    PubMed Central

    Reshak, A. H.

    2017-01-01

    The spin-polarized second harmonic generation (SHG) of the recently synthesized CaCoSO single crystal is performed based on the calculated electronic band structure. The calculation reveals that the spin-up (↑) channel of CaCoSO possesses a direct energy gap (Γv-Γc) of about 2.187 eV, 1.187 eV (Kv-Kc) for the spin-down (↓) channel and an indirect gap (Γv-Kc) of about 0.4 eV for the spin-polarized CaCoSO single crystal. The linear optical properties obtained reveal that the recently synthesized crystal exhibits considerable anisotropy with negative uniaxial anisotropy and birefringence favor to enhance the SHG. We have calculated the three non-zero tensor components of the SHG and found the is the dominat component, one with a large SHG of about (d33 = 6.936 pm/V at λ = 1064 nm), the half value of KTiOPO4 (KTP). As the values of (↑) < (↓) < spin-polarized are related to the values of the energy gap of (↑) 2.187 eV> (↓) 1.187 eV> spin-polarized gap 0.4 eV; therefore, a smaller energy gap gives better SHG performance. Furthermore, the microscopic first hyperpolarizability, βijk, is calculated. PMID:28406164

  11. 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.

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

    PubMed

    Hu, Lin; Wu, Xiaojun; Yang, Jinlong

    2016-07-14

    To realize antiferromagnetic spintronics in the nanoscale, it is highly desirable to identify new nanometer-scale antiferromagnetic metals with both high Néel temperature and large spin-orbit coupling. In this work, on the basis of first-principles calculation and particle swarm optimization (PSO) global structure search, we demonstrate that a two-dimensional Mn2C monolayer is an antiferromagnetic metal with a Mn magnetic moment of ∼3μB. Mn2C monolayer has an anti-site structure of MoS2 sheet with carbon atoms hexagonally coordinated by neighboring Mn atoms. Remarkably, the in-plane carrier mobility of 2D Mn2C is highly anisotropic, amounting to about 47 000 cm(2) V(-1) s(-1) in the a' direction, which is much higher than that of MoS2 monolayer. The Néel temperature of Mn2C monolayer is high up to 720 K. Due to strong spin-orbit coupling in plane, the magnetic anisotropy energy of Mn2C monolayer is larger than those of pure metals, such as Fe, Co, and Ni. These advantages render 2D Mn2C sheet with great potential applications in nanometer-scale antiferromagnetic spintronics.

  13. 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.

  14. 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.

  15. Density matrix renormalization group numerical study of the kagome antiferromagnet.

    PubMed

    Jiang, H C; Weng, Z Y; Sheng, D N

    2008-09-12

    We numerically study the spin-1/2 antiferromagnetic Heisenberg model on the kagome lattice using the density-matrix renormalization group method. We find that the ground state is a magnetically disordered spin liquid, characterized by an exponential decay of spin-spin correlation function in real space and a magnetic structure factor showing system-size independent peaks at commensurate magnetic wave vectors. We obtain a spin triplet excitation gap DeltaE(S=1)=0.055+/-0.005 by extrapolation based on the large size results, and confirm the presence of gapless singlet excitations. The physical nature of such an exotic spin liquid is also discussed.

  16. Bridging amount of spin-glasses over ferromagnetic/antiferromagnetic thin films and bit-cell dispersion of exchange bias in corresponding TA-MRAM devices

    NASA Astrophysics Data System (ADS)

    Akmaldinov, Kamil; Ducruet, Clarisse; Alvarez-Herault, Jeremy; Baltz, Vincent

    2015-03-01

    For thermally-assisted magnetic random access memories (TA-MRAM), lowering bit-cells dispersions of exchange bias is necessary. In this study, we prove that spin-glass-like phases (SG) spread over the ferromagnetic/antiferromagnetic (F/AF) storage layer are the main cause of such distributions once the film is nanofabricated into a device. In particular, we show that the less the SG, the lower the bit-cell dispersion. More precisely, the amount of SG was varied from sample to sample by sputtering various AFs: IrMn, FeMn and their alloys. Blocking temperature distributions were measured to quantify the amount of SG at the wafer level. The wafers were then patterned to obtain 1kb devices and all the cells were tested electrically. Finally, the resulting loop shift cumulative distribution functions accounting for the bit-cell dispersions were correlated to the initial amount of SG. In addition to bridging the gap between fundamental SG and a technological application, we also demonstrated that blocking temperature distributions are a versatile method to qualify TA-MRAM production batches before processing. Univ. Grenoble-Alpes/CNRS/INAC-CEA, 38000 Grenoble, France.

  17. Enhancement of the d-wave pairing correlations by charge and spin ordering in the spin-one-half Falicov-Kimball model with Hund and Hubbard coupling

    NASA Astrophysics Data System (ADS)

    Farkašovský, Pavol

    2016-08-01

    The projector quantum Monte Carlo method is used to examine the effects of the spin-independent U fd as well as spin-dependent J z Coulomb interaction between the localized f and itinerant d electrons on the stability of various types of charge/spin ordering and superconducting correlations in the spin-one-half Falicov-Kimball model with Hund and Hubbard coupling. The model is studied for a wide range of f- and d-electron concentrations and it is found that the interband interactions U fd and J z stabilize three basic types of charge/spin ordering, namely, i) the axial striped phases, ii) the regular n-molecular phases and iii) the phase-separated states. It is shown that the d-wave pairing correlations are enhanced within the axial striped and phase-separated states, but not in the regular phases. Moreover, it was found that the antiferromagnetic spin arrangement within the chains further enhances the d-wave paring correlations, while the ferromagnetic one has a fully opposite effect.

  18. 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.

  19. Pressure and magnetic field effects on a quasi-two-dimensional spin-1/2 Heisenberg antiferromagnet

    NASA Astrophysics Data System (ADS)

    Barbero, N.; Shiroka, T.; Landee, C. P.; Pikulski, M.; Ott, H.-R.; Mesot, J.

    2016-02-01

    Cu(pz)2(ClO4)2 (with pz denoting pyrazine, C4H4N2) is among the best realizations of a two-dimensional spin-1/2 square-lattice antiferromagnet. Below TN=4.21 K, its weak interlayer couplings induce a three-dimensional magnetic order, strongly influenced by external magnetic fields and/or hydrostatic pressure. Previous work, focusing on the [H ,T ] phase diagram, identified a spin-flop transition, resulting in a field-tunable bicritical point. However, the influence of external pressure has not been investigated yet. Here we explore the extended [p ,H ,T ] phase diagram of Cu(pz)2(ClO4)2 under pressures up to 12 kbar and magnetic fields up to 7.1 T via magnetometry and 35Cl nuclear magnetic resonance (NMR) measurements. The application of magnetic fields enhances TX Y, the crossover temperature from the Heisenberg to the X Y model, thus pointing to an enhancement of the effective anisotropy. The applied pressure has an opposite effect [ d TN/d p =-0.050 (8 ) K/kbar], as it modifies marginally the interlayer couplings but likely changes more significantly the orbital reorientation and the square-lattice deformation. This results in a remodeling of the effective Hamiltonian, whereby the field and pressure effects compensate each other. Finally, by comparing the experimental data with numerical simulations we estimate TBKT, the temperature of the Berezinskii-Kosterlitz-Thouless topological transition, and argue why it is inaccessible in our case.

  20. 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.

  1. 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

    Here 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 an 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 Néel phase and two different spiral phases coexist. Lastly, the magnitude of the determined exchange interactions reveals a mean field ordering temperature ≈ 4 times larger than the reported Néel temperature TN = 85 K, suggesting significant frustration arising from proximity to the tricritical point.

  2. 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.

  3. Quantum Monte Carlo study of the spin-1/2 honeycomb Heisenberg model with mixed antiferromagnetic and ferromagnetic interactions in external magnetic fields

    NASA Astrophysics Data System (ADS)

    Huang, Yi-Zhen; Su, Gang

    2017-05-01

    The continuous imaginary-time quantum Monte Carlo method with the worm update algorithm is applied to explore the ground-state properties of the spin-1/2 Heisenberg model with antiferromagnetic (AF) coupling J >0 and ferromagnetic (F) coupling J'<0 along zigzag and armchair directions, respectively, on honeycomb lattice. It is found that by enhancing the F coupling J' between zigzag AF chains, the system is smoothly crossover from one-dimensional zigzag spin chains to a two-dimensional magnetic ordered state. In absence of an external field, the system is in a stripe-ordered phase. In the presence of uniform and staggered fields, the uniform and staggered out-of-plane magnetizations appear while the stripe order remains in the x y plane, and a second-order quantum phase transition (QPT) at a critical staggered field is observed. The critical exponents of correlation length for QPTs induced by a staggered field for the cases with J >0 , J'<0 and J <0 , J'>0 are obtained to be ν =0.70046 (1 ) and 0.7086 (3 ) , respectively, indicating that both cases belong to O(3) universality. The corresponding dynamic and susceptibility exponent z and γ /ν are fitted to be 1.006572(9), 1.9412(2) and 1.004615(8), 1.96121(9) for the two cases, respectively. The scaling behavior in a staggered field is analyzed, and the ground-state phase diagrams in the plane of coupling ratio and staggered field are presented for two cases. The temperature dependence of susceptibility and specific heat of both systems in external magnetic fields is also discussed. A Kosterlitz-Thouless phase transition is found for the present system in a uniform field.

  4. 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.

  5. 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.

  6. Uncovering many-body correlations in nanoscale nuclear spin baths by central spin decoherence

    PubMed Central

    Ma, Wen-Long; Wolfowicz, Gary; Zhao, Nan; Li, Shu-Shen; Morton, John J.L.; Liu, Ren-Bao

    2014-01-01

    Central spin decoherence caused by nuclear spin baths is often a critical issue in various quantum computing schemes, and it has also been used for sensing single-nuclear spins. Recent theoretical studies suggest that central spin decoherence can act as a probe of many-body physics in spin baths; however, identification and detection of many-body correlations of nuclear spins in nanoscale systems are highly challenging. Here, taking a phosphorus donor electron spin in a 29Si nuclear spin bath as our model system, we discover both theoretically and experimentally that many-body correlations in nanoscale nuclear spin baths produce identifiable signatures in decoherence of the central spin under multiple-pulse dynamical decoupling control. We demonstrate that under control by an odd or even number of pulses, the central spin decoherence is principally caused by second- or fourth-order nuclear spin correlations, respectively. This study marks an important step toward studying many-body physics using spin qubits. PMID:25205440

  7. 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.

  8. Effect of frustrated exchange interactions and spin-half-impurity on the electronic structure of strongly correlated NiFe 2O 4

    NASA Astrophysics Data System (ADS)

    Ugendar, Kodam; Samanta, S.; Rayaprol, Sudhindra; Siruguri, V.; Markandeyulu, G.; Nanda, B. R. K.

    2017-07-01

    Spin-polarized density functional calculations, magnetization, and neutron diffraction (ND) measurements are carried out to investigate the magnetic exchange interactions and strong correlation effects in Yb substituted inverse spinel nickel ferrite. In the pristine form, the compound is found to be a mixed insulator under the Zaanen-Sawatzky-Allen classification scheme as it features both charge transfer and Mott insulator mechanisms. Estimation of magnetic exchange couplings reveals that both octahedral-octahedral and octahedral-tetrahedral spin-spin interactions are antiferromagnetic. This is typical of a spin-frustrated triangular lattice with one of the vertices occupied by tetrahedral spins and the remaining two occupied by octahedral spins. However, since the octahedral-tetrahedral interaction is dominant, it leads to a forced parallel alignment of the spins at the octahedral site which is in agreement with the results of ND measurements. The substituent Yb is found to be settled in +3 charge state, as confirmed from the x-ray photoelectron spectroscopy measurements, to behave like a spin-half-impurity carried by the localized fz (x2-y2) orbital. The impurity f spin significantly weakens the antiferromagnetic coupling with the spins at the tetrahedral site, which explains the experimental observation of a decrease in Curie temperature with Yb substitution.

  9. Finite-temperature dynamics of the spin- (1)/(2) bond alternating Heisenberg antiferromagnetic chain

    NASA Astrophysics Data System (ADS)

    Mikeska, H. J.; Luckmann, C.

    2006-05-01

    We present results for the dynamic structure factor of the S=1/2 bond alternating Heisenberg chain over a large range of frequencies and temperatures. Data are obtained from a numerical evaluation of thermal averages based on the calculation of all eigenvalues and eigenfunctions for chains of up to 20 spins. Interpretation is guided by the exact temperature dependence in the noninteracting dimer limit which remains qualitatively valid up to an interdimer exchange λ≈0.5 . The temperature induced central peak around zero frequency is clearly identified and aspects of the crossover to spin diffusion in its variation from low to high temperatures are discussed. The one-magnon peak acquires an asymmetric shape with increasing temperature. The two-magnon peak is dominated by the S=1 bound state which remains well defined up to temperatures of the order of J . The variation with temperature and wave vector of the integrated intensity for one-magnon and two-magnon scattering and of the central peak are discussed.

  10. 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.

  11. Spin order and dynamics in the diamond-lattice Heisenberg antiferromagnets CuRh2O4 and CoRh2O4

    NASA Astrophysics Data System (ADS)

    Ge, L.; Flynn, J.; Paddison, J. A. M.; Stone, M. B.; Calder, S.; Subramanian, M. A.; Ramirez, A. P.; Mourigal, M.

    2017-08-01

    Antiferromagnetic insulators on a diamond lattice are candidate materials to host exotic magnetic phenomena ranging from spin-orbital entanglement to degenerate spiral ground states and topological paramagnetism. Compared to other three-dimensional networks of magnetic ions, such as the geometrically frustrated pyrochlore lattice, the investigation of diamond-lattice magnetism in real materials is less mature. In this work, we characterize the magnetic properties of model A -site spinels CoRh2O4 (cobalt rhodite) and CuRh2O4 (copper rhodite) by means of thermomagnetic and neutron-scattering measurements, and we perform group theory analysis, Rietveld refinement, mean-field theory, and spin-wave theory calculations to analyze the experimental results. Our investigation reveals that cubic CoRh2O4 is a canonical S =3 /2 diamond-lattice Heisenberg antiferromagnet with a nearest-neighbor exchange J =0.63 meV and a Néel ordered ground state below a temperature of 25 K. In tetragonally distorted CuRh2O4 , competing exchange interactions between up to third-nearest-neighbor spins lead to the development of an incommensurate spin helix at 24 K with a magnetic propagation vector km=(0 ,0 ,0.79 ) . Strong reduction of the ordered moment is observed for the S =1 /2 spins in CuRh2O4 and captured by our 1 /S corrections to the staggered magnetization. Our work identifies CoRh2O4 and CuRh2O4 as reference materials to guide future work searching for exotic quantum behavior in diamond-lattice antiferromagnets.

  12. 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.

  13. Critical and compensation behavior of a mixed spin-5/2 and spin-3/2 Ising antiferromagnetic system in a core/shell nanowire.

    PubMed

    Alzate-Cardona, Juan David; Barrero-Moreno, María Camila; Restrepo-Parra, Elisabeth

    2017-09-04

    In this work, Monte Carlo simulations based on Metropolis algorithm were performed to study the critical and compensation temperatures of a core-shell nanowire with spins S=±5/2,±3/2,±1/2 and σ=±3/2,±1/2, respectively, considering an Ising antiferromagnetic system. The influence of nearest neighbors exchange interactions and crystal field anisotropy on the critical and compensation behaviors of the system has been analyzed. The effects of the nanowire height in the critical and compensation temperatures were evaluated. The results show that, for a system with given values of exchange interaction constants and crystal field anisotropy, a compensation point only appears if two requirements are satisfied. First, the weight of the core magnetization in the total magnetization must be greater than the weight of the shell magnetization at zero temperature. And second, the exchange constant of shell ions must be greater than a certain value. This value is, at the same time, greater than the exchange constant of core ions. The critical and compensation temperatures are very sensitive to variations in the exchange constant of the shell ions and core ions, respectively, while the crystal field anisotropy affects both temperatures. © 2017 IOP Publishing Ltd.

  14. C59o NMR shift anomalies and spin dynamics in the normal state of superconducting CeCoIn5 : Verification of two-dimensional antiferromagnetic spin fluctuations

    NASA Astrophysics Data System (ADS)

    Sakai, Hironori; Baek, Seung-Ho; Brown, Stuart E.; Ronning, Filip; Bauer, Eric D.; Thompson, Joe D.

    2010-07-01

    We have measured the Knight shifts (K) and nuclear relaxation times (T1) for C59o in CeCoIn5 under external fields along a and c axes with the goal of establishing the anisotropy of antiferromagnetic (AFM) spin fluctuations (SF). In our approach, we revisit the problem of interpreting anomalies in the relationship between Knight shift Ka,c and static susceptibility χa,c : assuming a single component susceptibility implies a temperature-dependent hyperfine coupling Aa,c(T) . Once adopted, a known discrepancy between the behaviors of T1-1 for C59o and I115n(1) sites is eliminated to within experimental uncertainties and the variation with temperature is analyzed within the framework of two-dimensional AFM SF in proximity to a quantum-critical point. Moreover, the ratio [T1a/T1c] indicates easy-plane anisotropy for T

  15. 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.

  16. A general CFT model for antiferromagnetic spin-1/2 ladders with Mobius boundary conditions

    NASA Astrophysics Data System (ADS)

    Cristofano, Gerardo; Marotta, Vincenzo; Naddeo, Adele; Niccoli, Giuliano

    2008-12-01

    We show how the low energy properties of the two-leg XXZ spin-1/2 ladders with general anisotropy parameter Δ on closed geometries can be accounted for in the framework of the m-reduction procedure developed previously (Cristofano et al 2000 Mod. Phys. Lett. A 15 547; Cristofano et al 2000 Mod. Phys. Lett. A 15 1679; Cristofano et al 2002 Nucl. Phys. B 641 547; Cristofano et al 2004 J. High Energy Phys. JHEP06(2004) 056). In the limit of quasi-decoupled chains, a conformal field theory (CFT) with central charge c = 2 is derived and its ability to describe the model with different boundary conditions is shown. Special emphasis is given to the Mobius boundary conditions which generate a topological defect corresponding to non-trivial single-spinon excitations. Then, in the case of the two-leg XXX ladders we discuss in detail the role of various perturbations in determining the renormalization group flow starting from the ultraviolet (UV) critical point with c = 2.

  17. 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.

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

    PubMed Central

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

    2015-01-01

    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. PMID:25924953

  19. Geometric correlations and breakdown of mesoscopic universality in spin transport.

    PubMed

    Adagideli, I; Jacquod, Ph; Scheid, M; Duckheim, M; Loss, D; Richter, K

    2010-12-10

    We construct a unified semiclassical theory of charge and spin transport in chaotic ballistic and disordered diffusive mesoscopic systems with spin-orbit interaction. Neglecting dynamic effects of spin-orbit interaction, we reproduce the random matrix theory results that the spin conductance fluctuates universally around zero average. Incorporating these effects into the theory, we show that geometric correlations generate finite average spin conductances, but that they do not affect the charge conductance to leading order. The theory, which is confirmed by numerical transport calculations, allows us to investigate the entire range from the weak to the previously unexplored strong spin-orbit regime, where the spin rotation time is shorter than the momentum relaxation time.

  20. 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.

  1. Quantum phase transition and magnetic plateau in three-leg antiferromagnetic Heisenberg spin ladder with unequal J1-J2-J1 legs

    NASA Astrophysics Data System (ADS)

    Wang, Shuling; Zhu, Sicong; Ni, Yun; Peng, Li; Li, Ruixue; Yao, Kailun

    2016-01-01

    Magnetic properties of spin-1/2 antiferromagnetic three-leg Heisenberg ladders, where antiferromagnetic interactions in legs are J1, J2 and J1 respectively and in the rungs are J⊥, have been investigated by bond-mean field method. As J⊥ changes, magnetization curves show different behavior. For J⊥=0.5, there are cusps in magnetization curves, while for J⊥=3.0, the 1/3 magnetization plateau appears, which can be explained by energy spectra. Furthermore, for J⊥=3.0 the 1/3 magnetization plateaus will become wider or narrow down with J2 changing. In addition, the mean-field bond parameters and the concurrences, which confirm the phase transitions, are also studied.

  2. 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

  3. Single Spin Asymmetry in Strongly Correlated Quark Model

    SciTech Connect

    Musulmanbekov, G.

    2007-06-13

    The Single Transverse - Spin Asymmetry (SSA) is analysed in the framework of the Strongly Correlated Quark Model proposed by author, where the proton spin emerges from the orbital momenta of quark and qluon condensates circulating around the valence quarks. It is shown that dominating factors of appearance of SSA are the orbiting around the valence quarks sea quark and qluon condensates and spin dependent quark-quark cross sections.

  4. 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

  5. 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.

  6. 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.

  7. The NQR observation of spin-Peierls transition in an antiferromagnetic MX-chain complex [NiBr(chxn)2]Br2.

    PubMed

    Takaishi, Shinya; Tobu, Yasuhiro; Kitagawa, Hiroshi; Goto, Atsushi; Shimizu, Tadashi; Okubo, Takashi; Mitani, Tadaoki; Ikeda, Ryuichi

    2004-02-18

    81Br Nuclear quadrupole resonance (NQR) measurement was performed in an S = 1/2 one-dimensional Heisenberg antiferromagnetic metal complex [NiBr(chxn)2]Br2 (chxn: 1R,2R-diaminocyclohexane), having a halogen-bridged MX chain structure -Br-Ni3+-Br-Ni3+-Br-. Two 81Br NQR signals were observed below 40 K, while a single signal was observed above 130 K, showing the presence of two nonequivalent bridging Br sites below 40 K. This NQR result together with previously reported magnetic susceptibility and X-ray results indicate the occurrence of a transition into a spin-Peierls state between 40 and 130 K. This communication reports the first spin-Peierls transition in metal complexes in which pure d electrons contribute to the magnetism. In addition, we demonstrated a new experimental method for studying a spin-Peierls system.

  8. 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

  9. 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.

  10. 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.

  11. Antiferromagnetic Spin Fluctuations and Unconventional Nodeless Superconductivity in an Iron-Based New Superconductor (Ca4Al2O6-y)(Fe2As2): As75 Nuclear Quadrupole Resonance Study

    NASA Astrophysics Data System (ADS)

    Kinouchi, H.; Mukuda, H.; Yashima, M.; Kitaoka, Y.; Shirage, P. M.; Eisaki, H.; Iyo, A.

    2011-07-01

    We report As75 nuclear quadrupole resonance studies on (Ca4Al2O6-y)(Fe2As2) with Tc=27K. Measurement of nuclear-spin-relaxation rate 1/T1 has revealed a significant development of two-dimensional antiferromagnetic spin fluctuations down to Tc in association with the smallest As-Fe-As bond angle. Below Tc, 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 Tc is comparable to Tc=28K in the optimally doped LaFeAsO1-y in which antiferromagnetic spin fluctuations are not dominant, we remark that antiferromagnetic spin fluctuations are not a unique factor for enhancing Tc among Fe-based superconductors, but a condition for optimizing superconductivity should be addressed from the lattice structure point of view.

  12. 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.

  13. A study of the quantum classical crossover in the spin dynamics of the 2D S = 5/2 antiferromagnet Rb2MnF4: neutron scattering, computer simulations and analytic theories

    NASA Astrophysics Data System (ADS)

    Huberman, T.; Tennant, D. A.; Cowley, R. A.; Coldea, R.; Frost, C. D.

    2008-05-01

    We report comprehensive inelastic neutron scattering measurements of the magnetic excitations in the 2D spin-5/2 Heisenberg antiferromagnet Rb2MnF4 as a function of temperature from deep in the Néel ordered phase up to paramagnetic, 0.13spin waves are found for wavevectors larger than the inverse correlation length ξ-1 for temperatures up to near the Curie-Weiss temperature, ΘCW. For wavevectors smaller than ξ-1, relaxational dynamics occurs. The observed renormalization of spin wave energies, and evolution of excitation lineshapes, with increasing temperature are quantitatively compared with finite-temperature spin wave theory and computer simulations for classical spins. Random phase approximation calculations provide a good description of the low temperature renormalization of spin waves. In contrast, lifetime broadening calculated using the first Born approximation shows, at best, modest agreement around the zone boundary at low temperatures. Classical dynamics simulations using an appropriate quantum classical correspondence were found to provide a good description of the intermediate and high temperature regimes over all wavevector and energy scales, and the crossover from quantum to classical dynamics observed around ΘCW/S, where the spin S = 5/2. A characterization of the data over the whole wavevector/energy/temperature parameter space is given. In this, T2 behaviour is found to dominate the wavevector and temperature dependence of the linewidths over a large parameter range, and no evidence of hydrodynamic behaviour or dynamical scaling behaviour found within the accuracy of the datasets. An efficient and easily implemented classical dynamics methodology is presented that provides a practical method for modelling other semiclassical quantum magnets.

  14. 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.

  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. Entanglement of strongly interacting low-dimensional fermions in metallic, superfluid, and antiferromagnetic insulating systems

    SciTech Connect

    Franca, V. V.; Capelle, K.

    2006-10-15

    We calculate the entanglement entropy of strongly correlated low-dimensional fermions in metallic, superfluid, and antiferromagnetic insulating phases. The entanglement entropy reflects the degrees of freedom available in each phase for storing and processing information, but is found not to be a state function in the thermodynamic sense. The role of critical points, smooth crossovers, and Hilbert space restrictions in shaping the dependence of the entanglement entropy on the system parameters is illustrated for metallic, insulating, and superfluid systems. The dependence of the spin susceptibility on entanglement in antiferromagnetic insulators is obtained quantitatively. The opening of spin gaps in antiferromagnetic insulators is associated with enhanced entanglement near quantum critical points.

  17. 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.

  18. 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.

  19. Spin-wave approach to the two-magnon Raman scattering in a J1 x-J1 y-J2-Jc antiferromagnetic Heisenberg model

    NASA Astrophysics Data System (ADS)

    Liu, Changle; Zhang, Anmin; Zhang, Qingming; Yu, Rong; Wang, Xiaoqun

    2017-03-01

    We study the two-magnon nonresonant Raman scattering in the (π ,π ) and (π ,0 ) in-plane ordered antiferromagnetic phases of a spin-S J1 x-J1 y-J2-Jc Heisenberg model on the tetragonal lattice within the framework of the spin-wave theory. We show that magnon-magnon interactions may significantly change the shape of spectra even in large-S cases. We discuss the effects of various tuning factors to the two-magnon Raman spectra. We find that both the magnetic frustration J2/J1 and the interlayer exchange coupling Jc may significantly affect the spectra in both the B1 g and the A1g ' channels in the (π ,π ) Néel ordered phase. Moreover, we find a splitting of the two-magnon peak in the (π ,0 ) collinear antiferromagnetic phase. We further discuss the implications of our results to the BaMnBi2 and iron pnictide systems.

  20. 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.