Hida, Kazuo
1995-01-01
The ground state of the square lattice bilayer quantum antiferromagnet with nearest and next-nearest neighbour intralayer interaction is studied by means of the modified spin wave method. For weak interlayer coupling, the ground state is found to be always magnetically ordered while the quantum disordered phase appear for large enough interlayer coupling. The properties of the disordered phase vary according to the strength of the frustration. In the regime of weak frustration, the disordered...
Cong, P. T.; Postulka, L.; Wolf, B.; van Well, N.; Ritter, F.; Assmus, W.; Krellner, C.; Lang, M.
2016-10-01
Magneto-acoustic investigations of the frustrated triangular-lattice antiferromagnet Cs2CuCl4 were performed for the longitudinal modes c11 and c33 in magnetic fields along the a-axis. The temperature dependence of the sound velocity at zero field shows a mild softening at low temperature and displays a small kink-like anomaly at TN. Isothermal measurements at T sound attenuation α reveal two closely spaced features of different characters on approaching the material's quantum-critical point (QCP) at Bs ≈ 8.5 T for B || a. The peak at slightly lower fields remains sharp down to the lowest temperature and can be attributed to the ordering temperature TN(B). The second anomaly, which is rounded and which becomes reduced in size upon cooling, is assigned to the material's spin-liquid properties preceding the long-range antiferromagnetic ordering with decreasing temperature. These two features merge upon cooling suggesting a coincidence at the QCP. The elastic constant at lowest temperatures of our experiment at 32 mK can be well described by a Landau free energy model with a very small magnetoelastic coupling constant G/kB ≈ 2.8 K. The applicability of this classical model indicates the existence of a small gap in the magnetic excitation spectrum which drives the system away from quantum criticality.
Frustrated diamond-chain quantum XXZ Heisenberg antiferromagnet in a magnetic field
Energy Technology Data Exchange (ETDEWEB)
Richter, Johannes, E-mail: Johannes.Richter@Physik.Uni-Magdeburg.DE [Institut für theoretische Physik, Otto-von-Guericke-Universität Magdeburg, P.O. Box 4120, D-39016 Magdeburg (Germany); Krupnitska, Olesia [Institute for Condensed Matter Physics, National Academy of Sciences of Ukraine, 1 Svientsitskii Street, L' viv-11, 79011 (Ukraine); Krokhmalskii, Taras [Institute for Condensed Matter Physics, National Academy of Sciences of Ukraine, 1 Svientsitskii Street, L' viv-11, 79011 (Ukraine); Department for Theoretical Physics, Ivan Franko National University of L' viv, 12 Drahomanov Street, L' viv-5, 79005 (Ukraine); Derzhko, Oleg [Institut für theoretische Physik, Otto-von-Guericke-Universität Magdeburg, P.O. Box 4120, D-39016 Magdeburg (Germany); Institute for Condensed Matter Physics, National Academy of Sciences of Ukraine, 1 Svientsitskii Street, L' viv-11, 79011 (Ukraine); Department for Theoretical Physics, Ivan Franko National University of L' viv, 12 Drahomanov Street, L' viv-5, 79005 (Ukraine); Abdus Salam International Centre for Theoretical Physics, Strada Costiera 11, I-34151 Trieste (Italy)
2015-04-01
We consider the antiferromagnetic spin-1/2 XXZ Heisenberg model on a frustrated diamond-chain lattice in a z- or x-aligned external magnetic field. We use the strong-coupling approach to elaborate an effective description in the low-temperature strong-field regime. The obtained effective models are spin-1/2 XY chains which are exactly solvable through the Jordan–Wigner fermionization. We perform exact-diagonalization studies of the magnetization curves to test the quality of the effective description. The results may have relevance for the description of the azurite spin-chain compound.
Quasiparticle excitations in frustrated antiferromagnets
Energy Technology Data Exchange (ETDEWEB)
Trumper, Adolfo E. [Instituto de Fisica Rosario (CONICET) Universidad Nacional de Rosario, Boulevard 27 de Febrero 210 bis, 2000 Rosario (Argentina)]. E-mail: trumper@ifir.edu.ar; Gazza, Claudio J. [Instituto de Fisica Rosario (CONICET) Universidad Nacional de Rosario, Boulevard 27 de Febrero 210 bis, 2000 Rosario (Argentina); Manuel, Luis O. [Instituto de Fisica Rosario (CONICET) Universidad Nacional de Rosario, Boulevard 27 de Febrero 210 bis, 2000 Rosario (Argentina)]. E-mail: manuel@ifir.edu.ar
2004-12-31
We have computed the quasiparticle wave function corresponding to a hole injected in a triangular antiferromagnet. We have taken into account multi-magnon contributions within the self-consistent Born approximation. We have found qualitative differences, under sign reversal of the integral transfer t, regarding the multi-magnon components and the own existence of the quasiparticle excitations. Such differences are due to the subtle interplay between magnon-assisted and free hopping mechanisms. We conclude that the conventional quasiparticle picture can be broken by geometrical frustration without invoking spin liquid phases.
Hida, Kazuo
1992-03-01
The quantum disordered state (QDOS) of the spin 1/2 double layer square lattice Heisenberg antiferromagnet is studied. Using the dimer expansion from the limit of the large interlayer coupling J', the staggered susceptibility χ, the antiferromagnetic structure factor Sπ and the antiferromagnetic correlation length ξ are calculated up to the 6-th order in the intralayer coupling J. The ratio analysis shows that the QDOS becomes unstable against the Néel ordering at J'/J≃2.56. The critical exponents are not inconsistent with the universality class of the 3-dimensional classical Heisenberg model, suggesting that our QDOS corresponds to that expected in the 2-dimensional square lattice Heisenberg antiferromagnet with unphysically small spin (<0.276). The results of the projector Monte Carlo simulation also confirms the dimer expansion results.
Er_{2}Ti_{2}O_{7}: Evidence of quantum order by disorder in a frustrated antiferromagnet
DEFF Research Database (Denmark)
Champion, J.D.M.; Harris, M.J.; Holdsworth, P.C.W.;
2003-01-01
Er(2)Ti(2)O(7) has been suggested to be a realization of the frustrated XY pyrochlore lattice antiferromagnet, for which theory predicts fluctuation-induced symmetry breaking in a highly degenerate ground state manifold. We present a theoretical analysis of the classical model compared...... to neutron scattering experiments on the real material, both below and above T(N)=1.173(2) K. The model correctly predicts the ordered magnetic structure, suggesting that the real system has order stabilized by zero-point quantum fluctuations that can be modeled by classical spin wave theory. However...
Frustrated 3×3 Heisenberg antiferromagnets
Moustanis, P. N.
2016-08-01
The full energy spectrum and the exact thermodynamic results of the antiferromagnetic Heisenberg Hamiltonian of the 3×3 triangular and the frustrated square lattice with periodic boundary conditions and s=1/2 are obtained. To this end the method of hierarchy of algebras is employed. It was found that the ground state of the 3×3 frustrated square lattice is a Resonating Valence Bond (RVB) state. Thermodynamic properties, like the specific heat, magnetic susceptibility, the thermal average of the square of the total Sz and entropy, for these two lattices are presented.
Energy Technology Data Exchange (ETDEWEB)
Cong, P. T., E-mail: t.pham@hzdr.de [Dresden High Magnetic Field Laboratory, Helmholtz-Zentrum Dresden-Rossendorf, D-01314 Dresden (Germany); Physics Institute, Goethe University Frankfurt, D-60438 Frankfurt am Main (Germany); Postulka, L.; Wolf, B.; Ritter, F.; Assmus, W.; Krellner, C.; Lang, M., E-mail: michael.lang@physik.uni-frankfurt.de [Physics Institute, Goethe University Frankfurt, D-60438 Frankfurt am Main (Germany); Well, N. van [Physics Institute, Goethe University Frankfurt, D-60438 Frankfurt am Main (Germany); Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, CH-5232 Villigen (Switzerland)
2016-10-14
Magneto-acoustic investigations of the frustrated triangular-lattice antiferromagnet Cs{sub 2}CuCl{sub 4} were performed for the longitudinal modes c{sub 11} and c{sub 33} in magnetic fields along the a-axis. The temperature dependence of the sound velocity at zero field shows a mild softening at low temperature and displays a small kink-like anomaly at T{sub N}. Isothermal measurements at T < T{sub N} of the sound attenuation α reveal two closely spaced features of different characters on approaching the material's quantum-critical point (QCP) at B{sub s} ≈ 8.5 T for B || a. The peak at slightly lower fields remains sharp down to the lowest temperature and can be attributed to the ordering temperature T{sub N}(B). The second anomaly, which is rounded and which becomes reduced in size upon cooling, is assigned to the material's spin-liquid properties preceding the long-range antiferromagnetic ordering with decreasing temperature. These two features merge upon cooling suggesting a coincidence at the QCP. The elastic constant at lowest temperatures of our experiment at 32 mK can be well described by a Landau free energy model with a very small magnetoelastic coupling constant G/k{sub B} ≈ 2.8 K. The applicability of this classical model indicates the existence of a small gap in the magnetic excitation spectrum which drives the system away from quantum criticality.
Spatially frustrated S = 1 Heisenberg antiferromagnet with single ion anisotropy
Pires, A. S. T.
2016-10-01
Using the SU(3) Schwinger boson formalism, I study the S = 1 square lattice Heisenberg antiferromagnet, at zero temperature, with spatially anisotropic nearest-neighbor couplings frustrated by a next-nearest neighbor interaction and single ion anisotropy. The phase diagram at zero temperature is presented. My calculations show two magnetically ordered phases separated by a quantum-disordered region for all values of the anisotropy.
Spin dynamics in geometrically frustrated antiferromagnetic pyrochlores
Gardner, J. S.; Ehlers, G.; Bramwell, S. T.; Gaulin, B. D.
2004-03-01
We have studied the spin dynamics of several antiferromagnetic pyrochlore oxides. These magnets are geometrically frustrated and only reach their ground states at temperatures much lower than that expected from mean field theory. Here we present data on the magnetic nature, especially the spin dynamics of Tb2Ti2O7, Gd2Ti2O7 and Y2Mo2O7. In these systems the ground states are found to be very different. Y2Mo2O7 freezes completely into a spin glass-like state, Tb2Ti2O7 is a cooperative paramagnetic and remains dynamic down to 15 mK and Gd2Ti2O7 enters a unique partially ordered state at {\\sim }1 K.
Energy Technology Data Exchange (ETDEWEB)
Cui, L.; Wang, F. [Suqian College, Fundamental Department, Suqian 223800 (China); Zhang, S.J. [Hubei University of Automotive Technology, Shiyan 442002 (China); Hu, Y.J., E-mail: eric8222@126.com [Hubei University of Automotive Technology, Shiyan 442002 (China)
2014-10-15
Using exact numerical diagonalization and density-matrix renormalization group method, we study the effect of magnetic frustrations due to next-nearest-neighbor bonds in a structure of periodically doping spins beside every spin side of the same sublattice of the 1D HAF linear chain, which is popularly known as Quasi-One-Dimensional Heisenberg Antiferromagnetic chain. As a result of the frustrations, the quantum disordered phase (gapped) also appears in the quantum case, except that the ferrimagnetic state in the non-frustrations case and the caned phase appeared in the classical case. For quantum disordered phase, tetramer–dimmer state is predominant and the spin gap is opened.
Nishimoto, Satoshi; Shibata, Naokazu; Hotta, Chisa
2013-01-01
Quantum spin-1/2 kagome Heisenberg antiferromagnet is the representative frustrated system possibly hosting a spin liquid. Clarifying the nature of this elusive topological phase is a key challenge in condensed matter; however, even identifying it still remains unsettled. Here we apply a magnetic field and discover a series of spin-gapped phases appearing at five different fractions of magnetization by means of a grand canonical density matrix renormalization group, an unbiased state-of-the-art numerical technique. The magnetic field dopes magnons and first gives rise to a possible Z₃ spin liquid plateau at 1/9 magnetization. Higher field induces a self-organized super-lattice unit, a six-membered ring of quantum spins, resembling an atomic orbital structure. Putting magnons into this unit one by one yields three quantum solid plateaus. We thus find that the magnetic field could control the transition between various emergent phases by continuously releasing the frustration.
Spin transport of the frustrated quasi-two-dimensional XY-like antiferromagnet
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.
Magnetocaloric properties of a frustrated Blume-Capel antiferromagnet
Directory of Open Access Journals (Sweden)
Žukovič Milan
2014-07-01
Full Text Available Low-temperature magnetization processes and magnetocaloric properties of a geometrically frustrated spin-1 Blume-Capel model on a triangular lattice are studied by Monte Carlo simulations. The model is found to display qualitatively different behavior depending on the sign of the single-ion anisotropy D. For positive values of D we observe two magnetization plateaus, similar to the spin-1/2 Ising antiferromagnet, and negative isothermal entropy changes for any field intensity. For a range of small negative values of D there are four magnetization plateaus and the entropy changes can be either negative or positive, depending on the field. If D is negative but large in absolute value then the entropy changes are solely positive.
DMRG studies of the frustrated kagome antiferromagnets and the application to volborthite
Gong, Shou-Shu; Sheng, D. N.; Yang, Kun
Motivated by the recent magnetization measurements on the high-quality single crystals of the kagome antiferromagnet volborthite, we study the ground state and magnetization properties of two kagome models proposed from the electronic structure simulations, which treat the volborthite as either the coupled trimers or the coupled frustrated chains on the kagome lattice. We study the models using density-matrix renormalization group on the cylinder geometry with the system width up to 4 legs. We find a quantum phase diagram of the models with changing couplings, and identify the magnetic properties of each phase. In the antiferromagnetic phases, we also study the magnetization curve and the different phases in the magnetic field. Finally, we compare the magetization properties of the models with the experimental observations of volborthite. NSF DMR-1157490, DMR-1408560, and the State of Florida.
Griffiths phase behaviour in a frustrated antiferromagnetic intermetallic compound
Ghosh, Krishanu; Mazumdar, Chandan; Ranganathan, R.; Mukherjee, S.
2015-10-01
The rare coexistence of a Griffiths phase (GP) and a geometrically frustrated antiferromagnetism in the non-stoichiometric intermetallic compound GdFe0.17Sn2 (the paramagnetic Weiss temperature θp ~ -59 K) is reported in this work. The compound forms in the Cmcm space group with large structural anisotropy (b/c ~ 4). Interestingly, all the atoms in the unit cell possess the same point group symmetry (Wycoff position 4c), which is rather rare. The frustration parameter, f = |θp|/TN has been established as 3.6, with the Néel temperature TN and Griffiths temperature TG being 16.5 and 32 K, respectively. The TG has been determined from the heat capacity measurement and also from the magnetocaloric effect (MCE). It is also shown that substantial difference in GP region may exist between zero field and field cooled measurements - a fact hitherto not emphasized so far.
Schwandt, David; Mambrini, Matthieu; Poilblanc, Didier
2010-06-01
We propose a general nonperturbative scheme that quantitatively maps the low-energy sector of spin-1/2 frustrated Heisenberg antiferromagnets to effective generalized quantum dimer models. We develop the formal lattice-independent frame and establish some important results on (i) the locality of the generated Hamiltonians, (ii) how full resummations can be performed in this renormalization scheme. The method is then applied to the much debated kagome antiferromagnet for which a fully resummed effective Hamiltonian—shown to capture the essential properties and provide deep insights on the microscopic model [D. Poilblanc, M. Mambrini, and D. Schwandt, Phys. Rev. B 81, 180402(R) (2010)]—is derived.
Topological thermal Hall effect in frustrated kagome antiferromagnets
Owerre, S. A.
2017-01-01
In frustrated magnets the Dzyaloshinsky-Moriya interaction (DMI) arising from spin-orbit coupling can induce a magnetic long-range order. Here, we report a theoretical prediction of the thermal Hall effect in frustrated kagome magnets such as KCr3(OH) 6(SO4) 2 and KFe3(OH) 6(SO4)2 . The thermal Hall effects in these materials are induced by scalar spin chirality as opposed to DMI in previous studies. The scalar spin chirality originates from the magnetic-field-induced chiral spin configuration due to noncoplanar spin textures, but in general it can be spontaneously developed as a macroscopic order parameter in chiral quantum spin liquids. Therefore, we infer that there is a possibility of the thermal Hall effect in frustrated kagome magnets such as herbertsmithite ZnCu3(OH) 6Cl2 and the chromium compound Ca10Cr7O28 , although they also show evidence of magnetic long-range order in the presence of applied magnetic field or pressure.
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.
Simulations of Quantum Spin Models on 2D Frustrated Lattices
Melko, Roger
2006-03-01
Algorithmic advances in quantum Monte Carlo techniques have opened up the possibility of studying models in the general class of the S=1/2 XXZ model (equivalent to hard-core bosons) on frustrated lattices. With an antiferromagnetic diagonal interaction (Jz), these models can be solved exactly with QMC, albeit with some effort required to retain ergodicity in the near-degenerate manifold of states that exists for large Jz. The application of the quantum (ferromagnetic off-diagonal) interaction to this classically degenerate manifold produces a variety of intriguing physics, including an order-by-disorder supersolid phase, novel insulating states, and possible exotic quantum critical phenomena. We discuss numerical results for the triangular and kagome lattices with nearest and next-nearest neighbor exchange interactions, and focus on the relevance of the simulations to related areas of physics, such as experiments of cold trapped atomic gasses and the recent theory of deconfined quantum criticality.
Kawamura, Hikaru; Arimori, Takuya
2002-02-18
Ordering of the geometrically frustrated two-dimensional Heisenberg antiferromagnet on a pyrochlore slab is studied by Monte Carlo simulations. In contrast to the kagomé Heisenberg antiferromagnet, the model exhibits locally noncoplanar spin structures at low temperatures, bearing nontrivial chiral degrees of freedom. Under certain conditions, the model exhibits a novel Kosterlitz-Thouless-type transition at a finite temperature associated with these chiral degrees of freedom.
Quantum frustrated and correlated electron systems
Directory of Open Access Journals (Sweden)
P Thalmeier
2008-06-01
Full Text Available Quantum phases and fluctuations in correlated electron systems with frustration and competing interactions are reviewed. In the localized moment case the S=1/2 J1 - J2 - model on a square lattice exhibits a rich phase diagram with magnetic as well as exotic hidden order phases due to the interplay of frustration and quantum fluctuations. Their signature in magnetocaloric quantities and the high field magnetization are surveyed. The possible quantum phase transitions are discussed and applied to layered vanadium oxides. In itinerant electron systems frustration is an emergent property caused by electron correlations. It leads to enhanced spin fluctuations in a very large region of momentum space and therefore may cause heavy fermion type low temperature anomalies as in the 3d spinel compound LiV2O4 . Competing on-site and inter-site electronic interactions in Kondo compounds are responsible for the quantum phase transition between nonmagnetic Kondo singlet phase and magnetic phase such as observed in many 4f compounds. They may be described by Kondo lattice and simplified Kondo necklace type models. Their quantum phase transitions are investigated by numerical exact diagonalization and analytical bond operator methods respectively.
Fractional excitations in the square-lattice quantum antiferromagnet
Dalla Piazza, B.; Mourigal, M.; Christensen, N. B.; Nilsen, G. J.; Tregenna-Piggott, P.; Perring, T. G.; Enderle, M.; McMorrow, D. F.; Ivanov, D. A.; Rønnow, H. M.
2015-01-01
Quantum magnets have occupied the fertile ground between many-body theory and low-temperature experiments on real materials since the early days of quantum mechanics. However, our understanding of even deceptively simple systems of interacting spin-1/2 particles is far from complete. The quantum square-lattice Heisenberg antiferromagnet, for example, exhibits a striking anomaly of hitherto unknown origin in its magnetic excitation spectrum. This quantum effect manifests itself for excitations propagating with the specific wavevector (π, 0). We use polarized neutron spectroscopy to fully characterize the magnetic fluctuations in the metal-organic compound Cu(DCOO)2.4D2O, a known realization of the quantum square-lattice Heisenberg antiferromagnet model. Our experiments reveal an isotropic excitation continuum at the anomaly, which we analyse theoretically using Gutzwiller-projected trial wavefunctions. The excitation continuum is accounted for by the existence of spatially extended pairs of fractional S = 1/2 quasiparticles, 2D analogues of 1D spinons. Away from the anomalous wavevector, these fractional excitations are bound and form conventional magnons. Our results establish the existence of fractional quasiparticles in the high-energy spectrum of a quasi-two-dimensional antiferromagnet, even in the absence of frustration.
Thermodynamics, geometrical frustration and quantum fluctuations in coupled spin chains
Directory of Open Access Journals (Sweden)
J. Sznajd
2009-01-01
Full Text Available The linear-perturbation real space renormalization transformation (LPRG is presented and applied to the study of quantum spin chains coupled by interchain interaction (k1 weaker than intrachain one (k. The method is examined in two exact solvable cases: Ising chains on the square and triangular lattices and quantum XY chain. For the Ising model, in the second order in the cumulant epansion, the deviation of the critical temperature from the exact value is less than 1% for 0.5 k>k1>0.15 k, but even in the case of the standard Ising model (k1=k we found the value of Tc which differs by 2% from the exact one. For the quantum XY chain the deviation of the free energy value found by using LPRG from the exact Katsura result is less than 1% for T/J>1, and for rather low temperature T/J=0.08 is about 6%. The LPRG is used to study the effects of interchain frustration on the phase transition in 2D Heisenberg spin chains with easy axis along the z direction. It is shown that contrary to the pure Ising model in systems with in-plane interactions (XY, the interchain frustration does not destroy the finite-temperature transition. However, such a frustration changes the character of the phase transition from Ising-like to, probably, Kosterlitz-Thouless-like. We have also applied the LPRG method to the calculation of the isothermal magnetocaloric coefficient (MT for several spin models in disordered phases. Is is demonstrated that in the presence of antiferromagnetic fluctuations, MT changes sign at some value of the magnetic field. Generally, MT is negative if magnetic field competes with a short-range order, and consequently it can be an indicator of the change in the short-range correlation.
Wawrzynska, E.; Coldea, R.; Wheeler, E M; Sorgel, T.; Jansen, M; Ibberson, R. M.; Radaelli, P. G.; Koza, M. M.
2007-01-01
We report a high-resolution neutron diffraction study of the crystal and magnetic structure of the orbitally-degenerate frustrated metallic magnet AgNiO2. At high temperatures the structure is hexagonal with a single crystallographic Ni site, low-spin Ni3+ with spin-1/2 and two-fold orbital degeneracy, arranged in an antiferromagnetic triangular lattice with frustrated spin and orbital order. A structural transition occurs upon cooling below 365 K to a tripled hexagonal unit cell containing t...
Spin freezing in the geometrically frustrated pyrochlore antiferromagnet Tb2Mo2O7
DEFF Research Database (Denmark)
Gaulin, B.D.; Reimers, J.N.; Mason, T.E.
1992-01-01
The magnetic metal ions in the cubic pyrochlore Tb2Mo2O7 form an infinite three-dimensional network of corner-sharing tetrahedra with a very high potential for frustration in the presence of antiferromagnetism. We have performed neutron scattering measurements which show short-range spatial...... correlations that develop continuously with decreasing temperature, while the characteristic time scale for the fluctuating moments decreases dramatically below T(f) is similar to 25 K. Therefore, this pure material, which possesses frustration that is purely geometrical in origin, displays a spin-glass state...
Neutron scattering studies of a frustrated spinel antiferromagnet in zero and high magnetic field
Energy Technology Data Exchange (ETDEWEB)
Matsuda, M [Quantum Beam Science Directorate, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195 (Japan)
2006-11-15
A review is given of the neutron scattering studies on a frustrated spinel antiferromagnet CdCr{sub 2}O{sub 4}. As observed in ZnCr{sub 2}O{sub 4}, which has been most extensively studied in the Cr-based spinel oxides, CdCr{sub 2}O{sub 4} also shows an antiferromagnetic phase transition and a structural phase transition simultaneously, indicating a strong spin-lattice coupling. The magnetic structure of CdCr{sub 2}O{sub 4}was determined by neutron scattering studies. The neutron scattering study in magnetic field up to 10 T indicates an orientation of magnetic domains.
Ab initio dynamical exchange interactions in frustrated antiferromagnets
Simoni, Jacopo; Stamenova, Maria; Sanvito, Stefano
2017-08-01
The ultrafast response to an optical pulse excitation of the spin-spin exchange interaction in transition metal antiferromagnets is studied within the framework of the time-dependent spin-density functional theory. We propose a formulation for the full dynamical exchange interaction, which is nonlocal in space, and it is derived starting from ab initio arguments. Then, we investigate the effect of the laser pulse on the onset of the dynamical process. It is found that we can distinguish two types of excitations, both activated immediately after the action of the laser pulse. While the first one can be associated to a Stoner-like excitation and involves the transfer of spin from one site to another, the second one is related to the ultrafast modification of a Heisenberg-like exchange interaction and can trigger the formation of spin waves in the first few hundred femtoseconds of the time evolution.
Quantum Phase Transitions in Anti-ferromagnetic Planar Cubic Lattices
Wellard, C J; Wellard, Cameron; Orus, Roman
2004-01-01
Motivated by its relation to an NP-hard problem we analyze the ground state properties of anti-ferromagnetic Ising-spin networks in planar cubic lattices under the action of homogeneous transverse and longitudinal magnetic fields. We consider different instances of the cubic geometry and find a set of quantum phase transitions for each one of the systems, which we characterize by means of entanglement behavior and majorization theory. Entanglement scaling at the critical region is in agreement with results arising from conformal symmetry, therefore even the simplest planar systems can display very large amounts of quantum correlation. No conclusion can be made as to the scaling behavior of the minimum energy gap, with the data allowing equally good fits to exponential and power law decays. Analysis of entanglement and especially of majorization instead of the energy spectrum proves to be a good way of detecting quantum phase transitions in highly frustrated configurations.
Spin superconductivity in the frustrated two-dimensional antiferromagnet in the square lattice
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.
Large magnetostriction and negative thermal expansion in the frustrated antiferromagnet ZnCr2Se4.
Hemberger, J; von Nidda, H-A Krug; Tsurkan, V; Loidl, A
2007-04-06
A detailed investigation of ZnCr2Se4 is presented which is dominated by strong ferromagnetic exchange but orders antiferromagnetically at TN=21 K. Specific heat and thermal expansion exhibit sharp first-order anomalies at the antiferromagnetic transition. TN is shifted to lower temperatures by external magnetic fields and finally is fully suppressed by a field of 65 kOe. The relative length change DeltaL/L(T) is unusually large and exhibits negative thermal expansion alpha below 75 K down to TN indicating strong frustration of the lattice. Magnetostriction DeltaL/L(H) reveals large values comparable to giant magnetostrictive materials. These results point to a spin-driven origin of the structural instability at TN explained in terms of competing ferromagnetic and antiferromagnetic exchange interactions.
Characterizing and quantifying frustration in quantum many-body systems.
Giampaolo, S M; Gualdi, G; Monras, A; Illuminati, F
2011-12-23
We present a general scheme for the study of frustration in quantum systems. We introduce a universal measure of frustration for arbitrary quantum systems and we relate it to a class of entanglement monotones via an exact inequality. If all the (pure) ground states of a given Hamiltonian saturate the inequality, then the system is said to be inequality saturating. We introduce sufficient conditions for a quantum spin system to be inequality saturating and confirm them with extensive numerical tests. These conditions provide a generalization to the quantum domain of the Toulouse criteria for classical frustration-free systems. The models satisfying these conditions can be reasonably identified as geometrically unfrustrated and subject to frustration of purely quantum origin. Our results therefore establish a unified framework for studying the intertwining of geometric and quantum contributions to frustration.
Classical and quantum anisotropic Heisenberg antiferromagnets
Directory of Open Access Journals (Sweden)
W. Selke
2009-01-01
Full Text Available We study classical and quantum Heisenberg antiferromagnets with exchange anisotropy of XXZ-type and crystal field single-ion terms of quadratic and quartic form in a field. The magnets display a variety of phases, including the spin-flop (or, in the quantum case, spin-liquid and biconical (corresponding, in the quantum lattice gas description, to supersolid phases. Applying ground-state considerations, Monte Carlo and density matrix renormalization group methods, the impact of quantum effects and lattice dimension is analysed. Interesting critical and multicritical behaviour may occur at quantum and thermal phase transitions.
Quantum Simulation of Frustrated Magnetism with Many Trapped Ions
Senko, Crystal
2013-05-01
A collection of trapped atomic ions is an excellent system for simulating quantum many-body physics, like magnetism, which may be difficult to access via classical computation or traditional condensed-matter experiments. Our large crystals of 10-20 ions comprise a platform to study a long-range quantum Ising model with tunable couplings in a 1D spin chain. State-dependent optical dipole forces exploit the Coulomb interaction to generate the spin-spin couplings, and fluorescence measurements on a camera are used to read out individual spin states. We investigated the spin order resulting from changing the range of antiferromagnetic interactions or the strength of an axial magnetic field, demonstrating our control over the amount of frustration present. We are turning to the study of dynamics in this system, with the aim of exploring topics including adiabaticity, spectroscopy of the Hamiltonian, the emergence of Kibble-Zurek-like behavior in a finite system, thermalization in an isolated quantum system, and nonequilibrium phase transitions. There is great promise in extending the system to 30+ spins, where computations become classically intractable. Co-authors are R. Islam, P. Richerme, W. C. Campbell, S. Korenblit, J. Smith, A. Lee, E. E. Edwards, C.-C. J. Wang, J. K. Freericks, and C. Monroe. This work is supported by grants from the U.S. Army Research Office with funding from the DARPA OLE program, IARPA, and the MURI program; and the NSF Physics Frontier Center at JQI.
Frustration-induced quantum phases in mixed spin chain with frustrated side chains
Hida, Kazuo; Takano, Ken'Ichi
2008-08-01
A mixed Heisenberg spin chain with frustrated side chains is investigated by numerical and perturbational calculations. A frustration-induced quantum partially polarized ferrimagnetic phase and a nonmagnetic spin quadrupolar phase are found adjacent to the conventional Lieb-Mattis-type ferrimagnetic phase or the nonmagnetic singlet cluster solid phases. The partially polarized ferrimagnetic phase has an incommensurate spin structure. Similar structures are commonly found in other frustration-induced partially polarized ferrimagnetic phases. Numerical results also suggest a series of almost critical nonmagnetic ground states in a highly frustrated regime if the side chain spins weakly couple to the main chain.
Watanabe, Tadataka; Hara, Shigeo; Ikeda, Shin-Ichi; Tomiyasu, Keisuke
2011-07-01
Ultrasound velocity measurements of the orbitally frustrated spinel GeCo2O4 reveal unique elastic anomalies within the antiferromagnetic phase. Temperature dependence of shear moduli exhibits a minimum within the antiferromagnetic phase, suggesting the coupling of shear acoustic phonons to molecular spin-orbit excitations. Magnetic-field dependence of elastic moduli exhibits diplike anomalies, being interpreted as magnetic-field-induced metamagnetic and structural transitions. These elastic anomalies suggest that the survival of geometrical frustration, and the interplay of spin, orbital, and lattice degrees of freedom evoke a set of phenomena in the antiferromagnetic phase.
Quantum Entanglement in Heisenberg Antiferromagnets
Subramanian, V
2004-01-01
Entanglement sharing among pairs of spins in Heisenberg antiferromagnets is investigated using the concurrence measure. For a nondegenerate S=0 ground state, a simple formula relates the concurrence to the diagonal correlation function. The concurrence length is seen to be extremely short. A few finite clusters are studied numerically, to see the trend in higher dimensions. It is argued that nearest-neighbour concurrence is zero for triangular and Kagome lattices. The concurrences in the maximal-spin states are explicitly calculated, where the concurrence averaged over all pairs is larger than the S=0 states.
Macroscopic Quantum Coherence in Antiferromagnetic Molecular Magnets
Institute of Scientific and Technical Information of China (English)
HU Hui; LO Rong; ZHU Jia-Lin; XIONG Jia-Jiong
2001-01-01
The macroscopic quantum coherence in a biaxial antiferromagnetic molecular magnet in the presence of magnetic field acting parallel to its hard anisotropy axis is studied within the two-sublattice model. On the basis of instanton technique in the spin-coherent-state path-integral representation, both the rigorous Wentzel-Kramers-Brillouin exponent and pre-exponential factor for the ground-state tunnel splitting are obtained. We find that the quantum fluctuations around the classical paths can not only induce a new quantum phase previously reported by Chiolero and Loss (Phys. Rev. Lett. 80 (1998) 169), but also have great influence on the intensity of the ground-state tunnel splitting. Those features clearly have no analogue in the ferromagnetic molecular magnets. We suggest that they may be the universal behaviors in all antiferromagnetic molecular magnets. The analytical results are complemented by exact diagonalization calculation.
Macroscopic Quantum Coherence in Antiferromagnetic Molecular Magnets
Institute of Scientific and Technical Information of China (English)
HUHui; LURong; 等
2001-01-01
The macroscopic quantum coherence in a biaxial antiferromagnetic molecular magnet in the presence of magnetic field acting parallel to its hard anisotropy axis is studied within the two-sublattice model.On the basis of instanton technique in the spin-coherent-state path-integral representation,both the rigorous Wentzel-Kramers-Brillouin exponent and pre-exponential factor for the ground-state tunnel splitting are obtained.We find that the quantum fluctuations around the classical paths can not only induce a new quantum phase previously reported by Chiolero and Loss (Phys.Rev.Lett.80(1998)169),but also have great influence on the intensity of the ground-state tunnel splitting.Those features clearly have no analogue in the ferromagnetic molecular magnets.We suggest that they may be the universal behaviors in all antiferromagnetic molecular magnets.The analytical results are complemented by exact diagonalization calculation.
Borovský, Michal; Weigel, Martin; Barash, Lev Yu.; Žukovič, Milan
2016-02-01
The population annealing algorithm is a novel approach to study systems with rough free-energy landscapes, such as spin glasses. It combines the power of simulated annealing, Boltzmann weighted differential reproduction and sequential Monte Carlo process to bring the population of replicas to the equilibrium even in the low-temperature region. Moreover, it provides a very good estimate of the free energy. The fact that population annealing algorithm is performed over a large number of replicas with many spin updates, makes it a good candidate for massive parallelism. We chose the GPU programming using a CUDA implementation to create a highly optimized simulation. It has been previously shown for the frustrated Ising antiferromagnet on the stacked triangular lattice with a ferromagnetic interlayer coupling, that standard Markov Chain Monte Carlo simulations fail to equilibrate at low temperatures due to the effect of kinetic freezing of the ferromagnetically ordered chains. We applied the population annealing to study the case with the isotropic intra- and interlayer antiferromagnetic coupling (J2/|J1| = -1). The reached ground states correspond to non-magnetic degenerate states, where chains are antiferromagnetically ordered, but there is no long-range ordering between them, which is analogical with Wannier phase of the 2D triangular Ising antiferromagnet.
Directory of Open Access Journals (Sweden)
Borovský Michal
2016-01-01
Full Text Available The population annealing algorithm is a novel approach to study systems with rough free-energy landscapes, such as spin glasses. It combines the power of simulated annealing, Boltzmann weighted differential reproduction and sequential Monte Carlo process to bring the population of replicas to the equilibrium even in the low-temperature region. Moreover, it provides a very good estimate of the free energy. The fact that population annealing algorithm is performed over a large number of replicas with many spin updates, makes it a good candidate for massive parallelism. We chose the GPU programming using a CUDA implementation to create a highly optimized simulation. It has been previously shown for the frustrated Ising antiferromagnet on the stacked triangular lattice with a ferromagnetic interlayer coupling, that standard Markov Chain Monte Carlo simulations fail to equilibrate at low temperatures due to the effect of kinetic freezing of the ferromagnetically ordered chains. We applied the population annealing to study the case with the isotropic intra- and interlayer antiferromagnetic coupling (J2/|J1| = −1. The reached ground states correspond to non-magnetic degenerate states, where chains are antiferromagnetically ordered, but there is no long-range ordering between them, which is analogical with Wannier phase of the 2D triangular Ising antiferromagnet.
Solution to the sign problem in a frustrated quantum impurity model
Hann, Connor T; Chandrasekharan, Shailesh
2016-01-01
In this work we solve the sign problem of a frustrated quantum impurity model consisting of three quantum spin-half chains interacting through an anti-ferromagnetic Heisenberg interaction at one end. We first map the model into a repulsive Hubbard model of spin-half fermions hopping on three independent one dimensional chains that interact through a triangular hopping at one end. We then convert the fermion model into an inhomogeneous one dimensional model and express the partition function as a weighted sum over fermion worldline configurations. By imposing a pairing of fermion worldlines in half the space we show that all negative weight configurations can be eliminated. This pairing naturally leads to the original frustrated quantum spin model at half filling and thus solves its sign problem.
Probing quantum frustrated systems via factorization of the ground state.
Giampaolo, Salvatore M; Adesso, Gerardo; Illuminati, Fabrizio
2010-05-21
The existence of definite orders in frustrated quantum systems is related rigorously to the occurrence of fully factorized ground states below a threshold value of the frustration. Ground-state separability thus provides a natural measure of frustration: strongly frustrated systems are those that cannot accommodate for classical-like solutions. The exact form of the factorized ground states and the critical frustration are determined for various classes of nonexactly solvable spin models with different spatial ranges of the interactions. For weak frustration, the existence of disentangling transitions determines the range of applicability of mean-field descriptions in biological and physical problems such as stochastic gene expression and the stability of long-period modulated structures.
Relief of frustration in the Heisenberg pyrochlore antiferromagnet Gd2Pt2O7
Hallas, A. M.; Sharma, A. Z.; Cai, Y.; Munsie, T. J.; Wilson, M. N.; Tachibana, M.; Wiebe, C. R.; Luke, G. M.
2016-10-01
The gadolinium pyrochlores Gd2B2O7 are among the best realizations of antiferromagnetically coupled Heisenberg spins on a pyrochlore lattice. We present a magnetic characterization of Gd2Pt2O7 , a unique member of this family. Magnetic susceptibility, heat capacity, and muon spin relaxation measurements show that Gd2Pt2O7 undergoes an antiferromagnetic ordering transition at TN=1.6 K. This transition is strongly first order, as indicated by the sharpness of the heat capacity anomaly, thermal hysteresis in the magnetic susceptibility, and a nondivergent relaxation rate in μ SR . The form of the heat capacity below TN suggests that the ground state is an anisotropic collinear antiferromagnet with an excitation spectrum that is gapped by 0.245(1) meV. The ordering temperature in Gd2Pt2O7,TN=1.6 K, is a substantial 160% increase from other gadolinium pyrochlores, which are all known to order at 1 K or lower. We attribute this enhancement in TN to the B -site cation, platinum. Despite being nonmagnetic, platinum has a filled 5 d t2 g orbital and an empty 5 d eg orbital that can facilitate superexchange. Thus, the magnetic frustration in Gd2Pt2O7 is partially "relieved," thereby promoting magnetic order.
Spin transport of the frustrated integer spin S antiferromagnetic Heisenberg chain
Energy Technology Data Exchange (ETDEWEB)
Lima, Leonardo S., E-mail: lslima@infis.ufu.br [Instituto de Física, Universidade Federal de Uberlândia, UFU, CEP:38700-128, Patos de Minas, MG (Brazil); Departamento de Física, ICEx, Universidade Federal de Minas Gerais, CEP:31270-901, Belo Horizonte, MG (Brazil)
2014-03-15
We study the effect of the nearest-neighbor (nn) and next-nearest-neighbor (nnn) interactions on spin transport in the quantum integer spin one-dimensional isotropic antiferromagnetic Heisenberg model. The Kubo formalism of the linear response theory is used to calculate the spin conductivity. We obtain the regular part of the spin conductivity, σ{sup reg}(ω), as function of the frequency at T=0 and obtain a strong effect of the (nnn) interaction on magnon transport.
Bond operator theory for the frustrated anisotropic Heisenberg antiferromagnet on a square lattice
Energy Technology Data Exchange (ETDEWEB)
Pires, A.S.T., E-mail: antpires@fisica.ufmg.br [Departamento de Fisica, Universidade Federal de Minas Gerais, Belo Horizonte, Cp 702, 30123-970 MG (Brazil)
2012-07-15
The quantum anisotropic antiferromagnetic Heisenberg model with single ion anisotropy, spin S=1 and up to the next-next-nearest neighbor coupling (the J{sub 1}-J{sub 2}-J{sub 3} model) on a square lattice, is studied using the bond-operator formalism in a mean field approximation. The quantum phase transitions at zero temperature are obtained. The model features a complex T=0 phase diagram, whose ordering vector is subject to quantum corrections with respect to the classical limit. The phase diagram shows a quantum paramagnetic phase situated among Neel, spiral and collinear states. - Highlights: Black-Right-Pointing-Pointer The quantum phase transition at zero temperature is studied. Black-Right-Pointing-Pointer The phase diagram up to the next-next-nearest neighbor coupling is calculated. Black-Right-Pointing-Pointer The energy gap is calculated in several regions of the phase diagram.
Spin liquid in a single crystal of the frustrated diamond lattice antiferromagnet CoAl2O4
DEFF Research Database (Denmark)
Zaharko, O.; Christensen, Niels Bech; Cervellino, A.
2011-01-01
We study the evidence for spin liquid in the frustrated diamond lattice antiferromagnet CoAl2O4 by means of single-crystal neutron scattering in zero and applied magnetic fields. The magnetically ordered phase appearing below T-N = 8 K remains nonconventional down to 1.5 K. The magnetic Bragg peaks...
DEFF Research Database (Denmark)
Zaharko, O.; Cervellino, A.; Tsurkan, V.
2010-01-01
Using neutron powder diffraction and Monte Carlo simulations we show that a spin-liquid regime emerges at all compositions in the diamond-lattice antiferromagnets Co(Al1−xCox)2O4. This spin-liquid regime induced by frustration due to the second-neighbor exchange coupling J2 is gradually superseded...
Frustrated antiferromagnet on generalized partial line graphs of a honeycomb lattice
Miyahara, Shin; Hotta, Chisa; Kubo, Kenn; Furukawa, Nobuo
2007-03-01
Recently we have proposed generalized partial line graphs on which tight binding models of electronic energy bands realize flat bands [1]. We study Heisenberg antiferromagnets on these structures, which are frustrated and may realize novel ground states. In this report, we focus on a generalized partial line graph created on a honeycomb lattice. The model is a honeycomb lattice composed of A and B-sublattice, where a triangle cluster sits on a site of A-sublattice and a single spin exists on a site of the B-sublattice. We assume the two-types of exchange coupling: J inside the triangle cluster and J' between the cluster and B-sublattice. In the limit J > J' and J J. Phys. Soc. Japan, 74 1918 (2005).
Frustrated antiferromagnet YbAgGe under magnetic fields and pressures
Energy Technology Data Exchange (ETDEWEB)
Kubo, Hirokazu; Umeo, Kazunori; Takabatake, Toshiro [ADSM, Hiroshima University, Higashi-Hiroshima 739-8530 (Japan); Katoh, Kenichi [Department of Applied Physics, National Defense Academy, Yokosuka 239-8686 (Japan); Ochiai, Akira, E-mail: khirokazu@hiroshima-u.ac.j [Department of Physics, Graduate School of Science, Tohoku University, Sendai 980-8578 (Japan)
2010-01-15
We present a detailed study of the field (B)- temperature (T) phase diagram under pressures (P) up to 2.7 GPa for the heavy-fermion antiferromagnet YbAgGe that crystallizes in the hexagonal ZrNiAl-type structure with a quasi-kagome lattice of Yb ions. This compound undergoes two magnetic transitions at T{sub M1} = 0.8 K and T{sub M2} = 0.65 K in zero field at ambient pressure. In the ground state, M(B) shows a metamagnetic transition at B{sub M} = 4.6 T for the easy magnetization direction B || a. This transition field decreases to 3.3 T as P is increased to 2.2 GPa. At 2.7 GPa, {rho}(B) exhibits successive transitions at 5.0, 6.0, 7.5, and 9.0 T. On the other hand, for the hard direction B || c, T{sub M} increases with applied field in the P range above 0.5 GPa. This increase of T{sub M}(B) is opposite to the decrease of T{sub M}(B) for a conventional antiferromagnetic phase. These findings suggest that the application of pressure releases in part the magnetic frustration in YbAgGe.
High-field magnetotransport in microstructures of the frustrated antiferromagnet Yb_{2}Pt_{2}Pb
Energy Technology Data Exchange (ETDEWEB)
Helm, T. [Max Planck Inst. for Chemical Physics, Dresden (Germany); Moll, P. J. W. [Max Planck Inst. for Chemical Physics, Dresden (Germany); Chan, Mun Keat [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Ramshaw, Brad [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Balakirev, Fedor Fedorovich [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2017-03-06
Frustrated quantum magnets exhibit a rich variety of non-trivial quantum ground states due to their remnant entropy at zero temperature. Most studied materials are insulators, with magnetic coupling of localized spins mediated by exchange interactions. Yb_{2}Pt_{2}Pb (YPP) is a rare example of a metallic frustrated quantum magnet, where Yb^{3+} J=7/2 moments are arranged in dimers forming a Shastry-Sutherland lattice. In addition, the itinerant charge carriers of the metal provide gapless excitations able to mediate magnetic interactions (RKKY) as well as hybridize with the 4f-states, which has been proposed to lead to a novel charge-orbital separation. YPP orders antiferromagnetically (AFM) below TN = 2.1 K, and strong g-factor anisotropy confines the spins into the ab planes. Accordingly, fields aligned parallel to the planes suppress the AFM order already below 4 T, while fields of up to 65 T along the c direction do not lead to saturation in the magnetization and step-like features even at B ~ 25 T were observed [4]. Here we probe the electronic structure of YPP by quantum oscillation and conductivity measurements in high fields, which tune the energy balance of the 4f states and thus the degree of charge-orbital separation.
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.
Sahoo, Shaon; Durga Prasad Goli, V M L; Sen, Diptiman; Ramasesha, S
2014-07-09
We study Heisenberg spin-1/2 and spin-1 chains with alternating ferromagnetic (J(F)(1)) and antiferromagnetic (J(A)(1)) nearest-neighbor interactions and a ferromagnetic next-nearest-neighbor interaction (J(F)(2)). In this model frustration is present due to the non-zero J(F)(2). The model with site spin s behaves like a Haldane spin chain, with site spin 2s in the limit of vanishing J(F)(2)and large J(F)(1)/J(A)(1). We show that the exact ground state of the model can be found along a line in the parameter space. For fixed J(F)(1), the phase diagram in the space of J(A)(1)-J(F)(2) is determined using numerical techniques complemented by analytical calculations. A number of quantities, including the structure factor, energy gap, entanglement entropy and zero temperature magnetization, are studied to understand the complete phase diagram. An interesting and potentially important feature of this model is that it can exhibit a macroscopic magnetization jump in the presence of a magnetic field; we study this using an effective Hamiltonian.
Zitzler, R.; Pruschke, Th.; Bulla, R.
2004-05-01
We discuss the magnetic phase diagram for the Hubbard model with magnetic frustration obtained within the dynamical mean-field theory. Most interesting is the appearance of a first-order paramagnetic metal to antiferromagnetic insulator transition for the magnetically frustrated lattice at half filling. For finite doping the antiferromagnetic phase is susceptible to phase separation and competes with an itinerant ferromagnetic phase (Nagaoka ferromagnetism), leading to an unexpectedly rich magnetic phase diagram.
Energy Technology Data Exchange (ETDEWEB)
Zitzler, R.; Pruschke, Th. E-mail: pruschke@theorie.physik.uni-goettingen.de; Bulla, R
2004-05-01
We discuss the magnetic phase diagram for the Hubbard model with magnetic frustration obtained within the dynamical mean-field theory. Most interesting is the appearance of a first-order paramagnetic metal to antiferromagnetic insulator transition for the magnetically frustrated lattice at half filling. For finite doping the antiferromagnetic phase is susceptible to phase separation and competes with an itinerant ferromagnetic phase (Nagaoka ferromagnetism), leading to an unexpectedly rich magnetic phase diagram.
Series Expansions for Frustrated Quantum Ising Magnets
Gelfand, M. P.; Priour, D. J.; Sondhi, S. L.
2000-03-01
We have computed the phase diagram of a frustrated Ising ladder in a transverse field via the Wolff Monte Carlo Cluster algorithm and by Pad'e Analysis of a series for the excitation spectrum about the large transverse field limit. A comparison of the two methods suggests that analysis of the perturbation series is a viable method for obtaining the phase diagrams of such systems even in cases, such as this one , where there is no phase transition down to arbitrarily small values of the transverse field. We will also discuss the application of the series technique to two dimensional systems of greater experimental interest, such as on the Kagome lattice which is also believed to realize a cooperative paramagnet at small transverse fields.
Effect of quantum phase transition on spin transport in the spatially frustrated Heisenberg model
Lima, L. S.
2017-03-01
We have used the Schwinger's boson theory to study the spin transport in the anisotropic two-dimensional spatially frustrated Heisenberg antiferromagnetic model in the square lattice. Our results show a sudden change in the AC spin conductivity σreg (ω) in the quantum phase transition point, where we have the gap of the system going to zero at critical point Dc=0. We have found a sudden change for a superconductor state in the DC limit ω → 0 independent of the value of the Drude's weight found in the quantum phase transition point. Away from it, we have obtained that the behavior of the spin conductivity changes for single peak at ω =ωp and in this case, σreg (ω) goes to zero in small ω and large ω limits.
Critical Space-Time Networks and Geometric Phase Transitions from Frustrated Edge Antiferromagnetism
Trugenberger, Carlo A
2015-01-01
Recently I proposed a simple dynamical network model for discrete space-time which self-organizes as a graph with Hausdorff dimension d_H=4. The model has a geometric quantum phase transition with disorder parameter (d_H-d_s) where d_s is the spectral dimension of the dynamical graph. Self-organization in this network model is based on a competition between a ferromagnetic Ising model for vertices and an antiferromagnetic Ising model for edges. In this paper I solve a toy version of this model defined on a bipartite graph in the mean field approximation. I show that the geometric phase transition corresponds exactly to the antiferromagnetic transition for edges, the dimensional disorder parameter of the former being mapped to the staggered magnetization order parameter of the latter. The model has a critical point with long-range correlations between edges, where a continuum random geometry can be defined, exactly as in Kazakov's famed 2D random lattice Ising model but now in any number of dimensions.
Quantum phase transitions in the Heisenberg J1-J2 triangular antiferromagnet in a magnetic field
Ye, Mengxing; Chubukov, Andrey V.
2017-01-01
We present the zero-temperature phase diagram of a Heisenberg antiferromagnet on a frustrated triangular lattice with nearest-neighbor (J1) and next-nearest-neighbor (J2) interactions, in a magnetic field. We show that the classical model has an accidental degeneracy for all J2/J1 and all fields, but the degeneracy is lifted by quantum fluctuations. We show that at large spin S , for J2/J11 , the transition remains first order, with a finite hysteresis width, but for S =1 /2 and, possibly, S =1 , there appears a new intermediate phase without a quasiclassical long-range order.
Long-range interactions in antiferromagnetic quantum spin chains
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.
Spin jam induced by quantum fluctuations in a frustrated magnet.
Yang, Junjie; Samarakoon, Anjana; Dissanayake, Sachith; Ueda, Hiroaki; Klich, Israel; Iida, Kazuki; Pajerowski, Daniel; Butch, Nicholas P; Huang, Q; Copley, John R D; Lee, Seung-Hun
2015-09-15
Since the discovery of spin glasses in dilute magnetic systems, their study has been largely focused on understanding randomness and defects as the driving mechanism. The same paradigm has also been applied to explain glassy states found in dense frustrated systems. Recently, however, it has been theoretically suggested that different mechanisms, such as quantum fluctuations and topological features, may induce glassy states in defect-free spin systems, far from the conventional dilute limit. Here we report experimental evidence for existence of a glassy state, which we call a spin jam, in the vicinity of the clean limit of a frustrated magnet, which is insensitive to a low concentration of defects. We have studied the effect of impurities on SrCr9pGa12-9pO19 [SCGO(p)], a highly frustrated magnet, in which the magnetic Cr(3+) (s = 3/2) ions form a quasi-2D triangular system of bipyramids. Our experimental data show that as the nonmagnetic Ga(3+) impurity concentration is changed, there are two distinct phases of glassiness: an exotic glassy state, which we call a spin jam, for the high magnetic concentration region (p > 0.8) and a cluster spin glass for lower magnetic concentration (p jam is a unique vantage point from which the class of glassy states of dense frustrated magnets can be understood.
Multicritical point in a diluted bilayer Heisenberg quantum antiferromagnet.
Sandvik, Anders W
2002-10-21
The S=1/2 Heisenberg bilayer antiferromagnet with randomly removed interlayer dimers is studied using quantum Monte Carlo simulations. A zero-temperature multicritical point (p(*),g(*)) at the classical percolation density p=p(*) and interlayer coupling g(*) approximately equal 0.16 is demonstrated. The quantum critical exponents of the percolating cluster are determined using finite-size scaling. It is argued that the associated finite-temperature quantum critical regime extends to zero interlayer coupling and could be relevant for antiferromagnetic cuprates doped with nonmagnetic impurities.
[mu]SR magnetic response in frustrated antiferromagnets of type RMn[sub 2] (R = rare earth)
Energy Technology Data Exchange (ETDEWEB)
Weber, M. (Physics Dept., TU Munich, Garching (Germany)); Asch, L. (Physics Dept., TU Munich, Garching (Germany)); Kratzer, A. (Physics Dept., TU Munich, Garching (Germany)); Kalvius, G.M. (Physics Dept., TU Munich, Garching (Germany)); Muench, K.H. (Physics Dept., TU Munich, Garching (Germany)); Ballou, R. (Lab. Louis Neel, CNRS, 38 Grenoble (France)); Deportes, J. (Lab. Louis Neel, CNRS, 38 Grenoble (France)); Waeppling, R. (Dept. of Physics, Univ. of Uppsala (Sweden)); Litterst, F.J. (Inst. for Metal Physics, TU Braunschweig (Germany)); Klauss, H.H. (Inst. for Metal Physics, TU Braunschweig (Germany)); Niedermayer, C. (Faculty for Physics, Univ. Konstanz (Germany)); Chappert, J. (CEA/DRFMC, CEN Grenoble, 38 (France))
1994-07-01
Zero, longitudinal and transverse field [mu]SR was carried out in the antiferromagnets YMn[sub 2], Y[sub 0.95] Tb[sub 0.15] Mn[sub 2], Y[sub 0.9]Tb[sub 0.1]Mn[sub 2], Y[sub 0.99] Sc[sub 0.01] Mn[sub 2], Y[sub 0.98]Sc[sub 0.02]Mn[sub 2] and TbMn[sub 2]. The dynamics of Mn magnetic moments above T[sub N] is typical for an itinerant antiferromagnet. Within a certain temperature range above T[sub N] part of the material enters a randomly ordered (spin glass like) magnetic state as an out-come of frustration. At temperatures above [approx] 150 K the muon spin relaxation rate indicates that the muon has become mobile. (orig.)
Signature of frustrated moments in quantum critical CePd1 -xNixAl
Sakai, Akito; Lucas, Stefan; Gegenwart, Philipp; Stockert, Oliver; v. Löhneysen, Hilbert; Fritsch, Veronika
2016-12-01
CePdAl with Ce 4 f moments forming a distorted kagome network is one of the scarce materials exhibiting Kondo physics and magnetic frustration simultaneously. As a result, antiferromagnetic (AF) order setting in at TN=2.7 K encompasses only two-thirds of the Ce moments. We report measurements of the specific heat, C , and the magnetic Grüneisen parameter, Γmag, on single crystals of CePd1 -xNixAl with x ≤0.16 at temperatures down to 0.05 K and magnetic fields B up to 8 T . Field-induced quantum criticality for various concentrations is observed with the critical field decreasing to zero at xc≈0.15 . Remarkably, two-dimensional AF quantum criticality of Hertz-Millis-Moriya type arises for x =0.05 and x =0.1 at the suppression of three-dimensional magnetic order. Furthermore, Γmag(B ) shows an additional contribution near 2.5 T for all concentrations, which is ascribed to correlations of the frustrated one-third of Ce moments.
Chern-Simons theory for frustrated quantum magnets
Kumar, Krishna; Fradkin, Eduardo
2013-03-01
We study the problem of frustrated quantum magnets by mapping models with Heisenberg spins, which are hard-core bosons, onto a problem of fermions coupled to a Chern-Simons gauge field. Similar methods have been used successfully in the case of unfrustrated systems like the square lattice. However, in the case of frustrated systems there always exists some arbitrariness in defining the problem. At the mean-field level these issues can be over looked but the effects of fluctuations, which are generally strong in these systems, are expected to alter the mean-field physics. We discuss the difficulties involved in setting up this problem on a triangular or kagome lattice and some approaches to tackle these issues. We study the effects of fluctuations in these systems and the possibility of spin-liquid type phases.
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.
Quantification of quantum discord in a antiferromagnetic Heisenberg compound
Energy Technology Data Exchange (ETDEWEB)
Singh, H., E-mail: chiranjib@iiserkol.ac.in; Chakraborty, T., E-mail: chiranjib@iiserkol.ac.in; Mitra, C., E-mail: chiranjib@iiserkol.ac.in [Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur Campus, Mohanpur -741252, Nadia, West Bengal (India)
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.
Spin frustration and magnetic ordering in triangular lattice antiferromagnet Ca3CoNb2O9
Dai, Jia; Zhou, Ping; Wang, Peng-Shuai; Pang, Fei; Munsie, Tim J.; Luke, Graeme M.; Zhang, Jin-Shan; Yu, Wei-Qiang
2015-12-01
We synthesized a quasi-two-dimensional distorted triangular lattice antiferromagnet Ca3CoNb2O9, in which the effective spin of Co2+ is 1/2 at low temperatures, whose magnetic properties were studied by dc susceptibility and magnetization techniques. The x-ray diffraction confirms the quality of our powder samples. The large Weiss constant θCW˜ -55 K and the low Neel temperature TN˜ 1.45 K give a frustration factor f = | θCW/TN | ≈ 38, suggesting that Ca3CoNb2O9 resides in strong frustration regime. Slightly below TN, deviation between the susceptibility data under zero-field cooling (ZFC) and field cooling (FC) is observed. A new magnetic state with 1/3 of the saturate magnetization Ms is suggested in the magnetization curve at 0.46 K. Our study indicates that Ca3CoNb2O9 is an interesting material to investigate magnetism in triangular lattice antiferromagnets with weak anisotropy. Project supported by the National Natural Science Foundation of China (Grant Nos. 11374364 and 11222433), the National Basic Research Program of China (Grant No. 2011CBA00112). Research at McMaster University supported by the Natural Sciences and Engineering Research Council. Work at North China Electric Power University supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.
Spin-Ice State of the Quantum Heisenberg Antiferromagnet on the Pyrochlore Lattice
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.
Spin-Ice State of the Quantum Heisenberg Antiferromagnet on the Pyrochlore Lattice.
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.
Quantum Nucleation of Antiferromagnetic Bubbles with Tetragonal and Hexagonal Symmetries
Institute of Scientific and Technical Information of China (English)
PAN Hui; ZHU Jia-Lin; L(U) Rong
2004-01-01
We study the quantum nucleation in a nanometer-scale antiferromagnet placed in a magnetic field at an arbitrary angle. We consider the magnetocrystalline anisotropy with tetragonal symmetry and that with hexagonal symmetry, respectively. Different structures of the tunneling barriers can be generated by the magnitude and the orientation of the magnetic field. We use the instanton method in the spin-coherent-state path-integral representation to calculate the dependence of the rate of quantum nucleation and the crossover temperature on the orientation and strength of the field for bulk solids and two-dimensional films of antiferromagnets, respectively. We find that the rate of quantum nucleation and the crossover temperature from thermal-to-quantum transitions depend on the orientation and strength of the external magnetic field distinctly, which can be tested by use of existing experimental techniques.
Frustrated quantum magnetism in the 6H-perovskites
Quilliam, Jeffrey
I will review the recent state of research on the 6H-perovskites, Ba3MA2O9, a large class of materials that can accommodate many different magnetic ions on ostensibly triangular lattices. This class of materials has given rise to several important discoveries in recent years, including quantum spin liquids, a quantum spin-orbital liquid and the first perfectly triangular spin-1/2 antiferromagnet. Many of these materials also provide an interesting interplay of magnetic, orbital and charge degrees of freedom. Others suffer from high levels of site disorder, which leads to interesting physics, at least in the case of the spin-orbital liquid candidate Ba3CuSb2O9. I will primarily discuss our recent work on the materials Ba3MSb2O9, where M = Cu, Ni and Co using the techniques of nuclear magnetic resonance (NMR), muon spin rotation (μSR) and ultrasound velocity measurements.
Enjalran, Matthew; Del Maestro, Adrian; Gingras, Michel J. P.
2008-03-01
The rare-earth pyrochlore gadolinium titanate, Gd2Ti2O7, represents an excellent experimental realization of a Heisenberg antiferromagnet (AFM) in a frustrated geometry with weak long-range dipole-dipole interactions (approximately 20% of nearest neighbor AFM exchange). Experiments on Gd2Ti2O7 in a magnetic field reveal a complex phase diagram associated with the breaking of spatial symmetries of the pyrochlore lattice as the field is applied along select symmetry directions. We study a model of classical Heisenberg spins (O(3) symmetry) on a pyrochlore lattice with exchange and dipolar interactions within mean-field theory. Using parameters relevant to the material system, we develop phase diagrams in finite magnetic fields. Our results our compared to experiments on Gd2Ti2O7 (and Gd2Sn2O7).
Kermarrec, E.; Marjerrison, C. A.; Thompson, C. M.; Maharaj, D. D.; Levin, K.; Kroeker, S.; Granroth, G. E.; Flacau, R.; Yamani, Z.; Greedan, J. E.; Gaulin, B. D.
2015-02-01
We report the crystal structure, magnetization, and neutron scattering measurements on the double perovskite Ba2YOsO6 . The F m 3 ¯m space group is found both at 290 K and 3.5 K with cell constants a0=8.3541 (4 ) Å and 8.3435 (4 ) Å, respectively. Os5 + (5 d3 ) ions occupy a nondistorted, geometrically frustrated face-centered-cubic (fcc) lattice. A Curie-Weiss temperature θ ˜-700 K suggests the presence of a large antiferromagnetic interaction and a high degree of magnetic frustration. A magnetic transition to long-range antiferromagnetic order, consistent with a type-I fcc state below TN˜69 K, is revealed by magnetization, Fisher heat capacity, and elastic neutron scattering, with an ordered moment of 1.65(6) μB on Os5 +. The ordered moment is much reduced from either the expected spin-only value of ˜3 μB or the value appropriate to 4 d3 Ru5 + in isostructural Ba2YRuO6 of 2.2(1) μB, suggesting a role for spin-orbit coupling (SOC). Triple-axis neutron scattering measurements of the order parameter suggest an additional first-order transition at T =67.45 K, and the existence of a second-ordered state. Time-of-flight inelastic neutron results reveal a large spin gap Δ ˜17 meV, unexpected for an orbitally quenched, d3 electronic configuration. We discuss this in the context of the ˜5 meV spin gap observed in the related Ru5 +,4 d3 cubic double perovskite Ba2YRuO6 , and attribute the ˜3 times larger gap to stronger SOC present in this heavier, 5 d , osmate system.
High-field spin dynamics of antiferromagnetic quantum spin chains
DEFF Research Database (Denmark)
Enderle, M.; Regnault, L.P.; Broholm, C.;
2000-01-01
The characteristic internal order of macroscopic quantum ground states in one-dimensional spin systems is usually not directly accessible, but reflected in the spin dynamics and the field dependence of the magnetic excitations. In high magnetic fields quantum phase transitions are expected. We...... present recent work on the high-field spin dynamics of the S = I antiferromagnetic Heisenberg chains NENP (Haldane ground state) and CsNiCl3 (quasi-1D HAF close to the quantum critical point), the uniform S = 1/2 chain CTS, and the spin-Peierls system CuGeO3. (C) 2000 Elsevier Science B,V. All rights...
Quantum Lifshitz Field Theory of a Frustrated Ferromagnet.
Balents, Leon; Starykh, Oleg A
2016-04-29
We propose a universal nonlinear sigma model field theory for one-dimensional frustrated ferromagnets, which applies in the vicinity of a "quantum Lifshitz point," at which the ferromagnetic state develops a spin wave instability. We investigate the phase diagram resulting from perturbations of the exchange and of magnetic field away from the Lifshitz point, and uncover a rich structure with two distinct regimes of different properties, depending upon the value of a marginal, dimensionless, parameter of the theory. In the regime relevant for one-dimensional systems with low spin, we find a metamagnetic transition line to a vector chiral phase. This line terminates in a critical end point, beyond which there is at least one multipolar or "spin nematic" phase. We show that the field theory is asymptotically exactly soluble near the Lifshitz point.
μ SR insight into the impurity problem in quantum kagome antiferromagnets
Gomilšek, M.; Klanjšek, M.; Pregelj, M.; Luetkens, H.; Li, Y.; Zhang, Q. M.; Zorko, A.
2016-07-01
Impurities, which are unavoidable in real materials, may play an important role in the magnetism of frustrated spin systems with a spin-liquid ground state. We address the impurity issue in quantum kagome antiferromagnets by investigating ZnCu3(OH) 6SO4 (Zn-brochantite) by means of muon spin spectroscopy. We show that muons dominantly couple to impurities, originating from Cu-Zn intersite disorder, and that the impurity spins are highly correlated with the kagome spins, allowing us to probe the host kagome physics via a Kondo-like effect. The low-temperature plateau in the impurity susceptibility suggests that the kagome spin-liquid ground state is gapless. The corresponding spin fluctuations exhibit an unconventional spectral density and a nontrivial field dependence.
Metallic magnets without inversion symmetry and antiferromagnetic quantum critical points
Energy Technology Data Exchange (ETDEWEB)
Fischer, I.A.
2006-07-01
This thesis focusses on two classes of systems that exhibit non-Fermi liquid behaviour in experiments: we investigated aspects of chiral ferromagnets and of antiferromagnetic metals close to a quantum critical point. In chiral ferromagnets, the absence of inversion symmetry makes spin-orbit coupling possible, which leads to a helical modulation of the ferromagnetically ordered state. We studied the motion of electrons in the magnetically ordered state of a metal without inversion symmetry by calculating their generic band-structure. We found that spin-orbit coupling, although weak, has a profound effect on the shape of the Fermi surface: On a large portion of the Fermi surface the electron motion parallel to the helix practically stops. Signatures of this effect can be expected to show up in measurements of the anomalous Hall effect. Recent neutron scattering experiments uncovered the existence of a peculiar kind of partial order in a region of the phase diagram adjacent to the ordered state of the chiral ferromagnet MnSi. Starting from the premise that this partially ordered state is a thermodynamically distinct phase, we investigated an extended Ginzburg-Landau theory for chiral ferromagnets. In a certain parameter regime of the Ginzburg-Landau theory we identified crystalline phases that are reminiscent of the so-called blue phases in liquid crystals. Many antiferromagnetic heavy-fermion systems can be tuned into a regime where they exhibit non-Fermi liquid exponents in the temperature dependence of thermodynamic quantities such as the specific heat capacity; this behaviour could be due to a quantum critical point. If the quantum critical behaviour is field-induced, the external field does not only suppress antiferromagnetism but also induces spin precession and thereby influences the dynamics of the order parameter. We investigated the quantum critical behavior of clean antiferromagnetic metals subject to a static, spatially uniform external magnetic field. We
Quantum Monte Carlo Study of Random Antiferromagnetic Heisenberg Chain
Todo, Synge; Kato, Kiyoshi; Takayama, Hajime
1998-01-01
Effects of randomness on the spin-1/2 and 1 antiferromagnetic Heisenberg chains are studied using the quantum Monte Carlo method with the continuous-time loop algorithm. We precisely calculated the uniform susceptibility, string order parameter, spatial and temporal correlation length, and the dynamical exponent, and obtained a phase diagram. The generalization of the continuous-time loop algorithm for the systems with higher-S spins is also presented.
Frustration in a transverse Ising nanoisland with an antiferromagnetic spin configuration
Energy Technology Data Exchange (ETDEWEB)
Kaneyoshi, T., E-mail: kaneyosi@is.nagoya-u.ac.Jp
2015-09-01
The phase diagrams, saturation magnetizations and temperature dependences of magnetizations in a transverse Ising nanoisland with an antiferromagnetic spin configuration are studied by the uses of the effective-field theory with correlations (EFT) and the mean-field approximation (MFA), in order to clarify whether the MFA can be successfully applied to the theoretical discussions of naonoislands. From these investigations, we have found a lot of unexpected characteristic phenomena in these properties, when the value of an interlayer coupling takes a large value. We have also found that the applications of the MFA to the magnetic properties are extremely restricted for nanoislands, when the value of an interlayer coupling takes a large value, in contrast to a number of bulk studies.
Criticality without Frustration for Quantum Spin-1 Chains
Bravyi, Sergey; Caha, Libor; Movassagh, Ramis; Nagaj, Daniel; Shor, Peter W.
2012-11-01
Frustration-free (FF) spin chains have a property that their ground state minimizes all individual terms in the chain Hamiltonian. We ask how entangled the ground state of a FF quantum spin-s chain with nearest-neighbor interactions can be for small values of s. While FF spin-1/2 chains are known to have unentangled ground states, the case s=1 remains less explored. We propose the first example of a FF translation-invariant spin-1 chain that has a unique highly entangled ground state and exhibits some signatures of a critical behavior. The ground state can be viewed as the uniform superposition of balanced strings of left and right brackets separated by empty spaces. Entanglement entropy of one half of the chain scales as (1)/(2)logn+O(1), where n is the number of spins. We prove that the energy gap above the ground state is polynomial in 1/n. The proof relies on a new result concerning statistics of Dyck paths which might be of independent interest.
Criticality without frustration for quantum spin-1 chains
Bravyi, Sergey; Movassagh, Ramis; Nagaj, Daniel; Shor, Peter
2012-01-01
Frustration-free (FF) spin chains have a property that their ground state minimizes all individual terms in the chain Hamiltonian. We ask how entangled the ground state of a FF quantum spin-s chain with nearest-neighbor interactions can be for small values of s. While FF spin-1/2 chains are known to have unentangled ground states, the case s=1 remains less explored. We propose the first example of a FF translation-invariant spin-1 chain that has a unique highly entangled ground state and exhibits some signatures of a critical behavior. The ground state can be viewed as the uniform superposition of balanced strings of left and right parentheses separated by empty spaces. Entanglement entropy of one half of the chain scales as log(n)/2 + O(1), where n is the number of spins. We prove that the energy gap above the ground state is polynomial in 1/n. The proof relies on a new result concerning statistics of Dyck paths which might be of independent interest.
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 [https://doi.org/10.7566/JPSJ.85.033705" xlink:type="simple">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.
Revealing novel quantum phases in quantum antiferromagnets on random lattices
Directory of Open Access Journals (Sweden)
R. Yu
2009-01-01
Full Text Available Quantum magnets represent an ideal playground for the controlled realization of novel quantum phases and of quantum phase transitions. The Hamiltonian of the system can be indeed manipulated by applying a magnetic field or pressure on the sample. When doping the system with non-magnetic impurities, novel inhomogeneous phases emerge from the interplay between geometric randomness and quantum fluctuations. In this paper we review our recent work on quantum phase transitions and novel quantum phases realized in disordered quantum magnets. The system inhomogeneity is found to strongly affect phase transitions by changing their universality class, giving the transition a novel, quantum percolative nature. Such transitions connect conventionally ordered phases to unconventional, quantum disordered ones - quantum Griffiths phases, magnetic Bose glass phases - exhibiting gapless spectra associated with low-energy localized excitations.
Symmetry Reduction in the Quantum Kagome Antiferromagnet Herbertsmithite
Zorko, A.; Herak, M.; Gomilšek, M.; van Tol, J.; Velázquez, M.; Khuntia, P.; Bert, F.; Mendels, P.
2017-01-01
Employing complementary torque magnetometry and electron spin resonance on single crystals of herbertsmithite, the closest realization to date of a quantum kagome antiferromagnet featuring a spin-liquid ground state, we provide novel insight into different contributions to its magnetism. At low temperatures, two distinct types of defects with different magnetic couplings to the kagome spins are found. Surprisingly, their magnetic response contradicts the threefold symmetry of the ideal kagome lattice, suggesting the presence of a global structural distortion that may be related to the establishment of the spin-liquid ground state.
Quantum phase transition between cluster and antiferromagnetic states
Son, Wonmin; Fazio, Rosario; Hamma, Alioscia; Pascazio, Saverio; Vedral, Vlatko
2011-01-01
We study a Hamiltonian system describing a three spin-1/2 cluster-like interaction competing with an Ising-like exchange. We show that the ground state in the cluster phase possesses symmetry protected topological order. A continuous quantum phase transition occurs as result of the competition between the cluster and Ising terms. At the critical point the Hamiltonian is self-dual. The geometric entanglement is also studied. Our findings in one dimension corroborate the analysis of the two dimensional generalization of the system, indicating, at a mean field level, the presence of a direct transition between an antiferromagnetic and a valence bond solid ground state.
Quantum criticality in partially frustrated CePd{sub 1-x}Ni{sub x}Al
Energy Technology Data Exchange (ETDEWEB)
Fritsch, Veronika; Kittler, Wolfram [Physikalisches Institut, Karlsruher Institut fuer Technologie (KIT), 76131 Karlsruhe (Germany); Woitschach, Sarah; Stockert, Oliver [Max-Planck-Institut fuer Chemische Physik Fester Stoffe, Dresden (Germany); Loehneysen, Hilbert von [Physikalisches Institut, Karlsruher Institut fuer Technologie (KIT), 76131 Karlsruhe (Germany); Institut fuer Festkoerperphysik, Karlsruher Institut fuer Technologie (KIT), 76021 Karlsruhe (Germany)
2013-07-01
In the antiferromagnetic (AF) heavy-fermion system CePdAl the magnetic Ce ions form a network of equilateral triangles in the (001) plane, similar to the kagome lattice, with one third of the Ce moments not participating in the long-range order due to geometrical frustration. The Neel temperature T{sub N} = 2.7 K is reduced upon replacing Pd by Ni in CePd{sub 1-x}Ni{sub x}Al, with T{sub N} → 0 for x ∼ 0.14. At this concentration the specific heat C exhibits a C/T ∝ - log T dependence. This and the linear T{sub N}(x) dependence are indicative of two-dimensional (2D) critical AF fluctuations within the conventional description of quantum criticality after Hertz, Millis and Moriya, in marked contrast to the three-dimensional (3D) magnetic order found by neutron diffraction experiments in CePdAl. We discuss the role of frustration when approaching the quantum critical point in Ni-substituted CePdAl on the basis of measurements of the magnetization, specific heat, electrical resistivity, and neutron diffraction experiments.
Impurities near an antiferromagnetic-singlet quantum critical point
Mendes-Santos, T.; Costa, N. C.; Batrouni, G.; Curro, N.; dos Santos, R. R.; Paiva, T.; Scalettar, R. T.
2017-02-01
Heavy-fermion systems and other strongly correlated electron materials often exhibit a competition between antiferromagnetic (AF) and singlet ground states. Using exact quantum Monte Carlo simulations, we examine the effect of impurities in the vicinity of such an AF-singlet quantum critical point (QCP), through an appropriately defined "impurity susceptibility" χimp. Our key finding is a connection within a single calculational framework between AF domains induced on the singlet side of the transition and the behavior of the nuclear magnetic resonance (NMR) relaxation rate 1 /T1 . We show that local NMR measurements provide a diagnostic for the location of the QCP, which agrees remarkably well with the vanishing of the AF order parameter and large values of χimp.
A model for ensemble NMR quantum computer using antiferromagnetic structure
Kokin, A A
2000-01-01
The one-dimensional homonuclear periodic array of nuclear spins I = 1/2,owing to hyperfine interaction of nuclear spins with electronic magneticmoments in antiferromagnetic structure, is considered. The neighbor nuclearspins in such array are opposite oriented and have resonant frequenciesdetermined by hyperfine interaction constant, applied magnetic field value andinteraction with the left and right nuclear neighbor spins. The resonantfrequencies difference of nuclear spins, when the neighbor spins have differentand the same states, is used to control the spin dynamics by means of selectiveresonant RF-pulses both for single nuclear spins and for ensemble of nuclearspins with the same resonant frequency. A model for the NMR quantum computer of cellular-automata type based on anone-dimensional homonuclear periodic array of spins is proposed. This model maybe generalized to a large ensemble of parallel working one-dimensional arraysand to two-dimensional and three-dimensional structures.
Quantum Phase Transitions and Dimerized Phases in Frustrated Spin Ladder
Institute of Scientific and Technical Information of China (English)
WEN Rui; LIU Guang-Hua; TIAN Guang-Shan
2011-01-01
In this paper, we study the phase diagram of a frustrated spin ladder model by applying the bosonization technique and the density-matrix renormalization-group (DMRG) algorithm. Effect of the intra-chain next-nearestneighbor (NNN) super-exchange interaction is investigated in detail and the order parameters are calculated to detect the emergence of the dimerized phases. We find that the intra-chain NNN interaction plays a key role in inducing dimerized phases.
Superfluid and antiferromagnetic phases in ultracold fermionic quantum gases
Energy Technology Data Exchange (ETDEWEB)
Gottwald, Tobias
2010-08-27
In this thesis several models are treated, which are relevant for ultracold fermionic quantum gases loaded onto optical lattices. In particular, imbalanced superfluid Fermi mixtures, which are considered as the best way to realize Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states experimentally, and antiferromagnetic states, whose experimental realization is one of the next major goals, are examined analytically and numerically with the use of appropriate versions of the Hubbard model. The usual Bardeen-Cooper-Schrieffer (BCS) superconductor is known to break down in a magnetic field with a strength exceeding the size of the superfluid gap. A spatially inhomogeneous spin-imbalanced superconductor with a complex order parameter known as FFLO-state is predicted to occur in translationally invariant systems. Since in ultracold quantum gases the experimental setups have a limited size and a trapping potential, we analyze the realistic situation of a non-translationally invariant finite sized Hubbard model for this purpose. We first argue analytically, why the order parameter should be real in a system with continuous coordinates, and map our statements onto the Hubbard model with discrete coordinates defined on a lattice. The relevant Hubbard model is then treated numerically within mean field theory. We show that the numerical results agree with our analytically derived statements and we simulate various experimentally relevant systems in this thesis. Analogous calculations are presented for the situation at repulsive interaction strength where the N'eel state is expected to be realized experimentally in the near future. We map our analytical results obtained for the attractive model onto corresponding results for the repulsive model. We obtain a spatially invariant unit vector defining the direction of the order parameter as a consequence of the trapping potential, which is affirmed by our mean field numerical results for the repulsive case. Furthermore, we observe
Local quenches in frustrated quantum spin chains: global vs. subsystem equilibration
Diez, Mathias; Haas, Stephan; Venuti, Lorenzo Campos; Zanardi, Paolo
2010-01-01
We study the equilibration behavior following local quenches, using frustrated quantum spin chains as an example of interacting closed quantum systems. Specifically, we examine the statistics of the time series of the Loschmidt echo, the trace distance of the time-evolved local density matrix to its average state, and the local magnetization. Depending on the quench parameters, the equilibration statistics of these quantities show features of good or poor equilibration, indicated by Gaussian, exponential or bistable distribution functions. These universal functions provide valuable tools to characterize the various time-evolution responses and give insight into the plethora of equilibration phenomena in complex quantum systems.
Digital quantum simulation of the statistical mechanics of a frustrated magnet.
Zhang, Jingfu; Yung, Man-Hong; Laflamme, Raymond; Aspuru-Guzik, Alán; Baugh, Jonathan
2012-06-06
Many problems of interest in physics, chemistry and computer science are equivalent to problems defined on systems of interacting spins. However, most such problems require computational resources that are out of reach with classical computers. A promising solution to overcome this challenge is quantum simulation. Several 'analogue' quantum simulations of interacting spin systems have been realized experimentally, where ground states were prepared using adiabatic techniques. Here we report a 'digital' quantum simulation of thermal states; a three-spin frustrated magnet was simulated using a nuclear magnetic resonance quantum information processor, and we were able to explore the phase diagram of the system at any simulated temperature and external field. These results help to identify the challenges for performing quantum simulations of physical systems at finite temperatures, and suggest methods that may be useful in simulating thermal open quantum systems.
Quantum phase transition induced by Dzyaloshinskii-Moriya interactions in the kagome antiferromagnet
Cepas, Olivier; Fong, C. M.; Leung, P. W.; Lhuillier, C.
2008-01-01
We argue that the S=1/2 kagome antiferromagnet undergoes a quantum phase transition when the Dzyaloshinskii-Moriya coupling is increased. For $DD_c$ the system develops antiferromagnetic long-range order. The quantum critical point is found to be $D_c \\simeq 0.1J$ using exact diagonalizations and finite-size scaling. This suggests that the kagome compound ZnCu$_3(OH)$_6$Cl$_3$ may be in a quantum critical region controlled by this fixed point.
Institute of Scientific and Technical Information of China (English)
JI An-Chun; TIAN Guang-Shan
2007-01-01
In the present paper, we investigate the quantum phase transition in a spatially anisotropic antiferromagnetic Heisenberg model of S = 1 with single-ion energy anisotropy. By using the Schwinger boson representation, we calculate the Gaussian correction to the critical value Jc⊥ caused by quantum spin fluctuations. We find that, for the positive single-ion energy, a nonzero value of Jc⊥ is always needed to stabilize the antiferromagnetic long-range order in this model. It resolves a difference among literature and shows clearly that the effect of quantum fluctuations may qualitatively change a result obtained by the mean-field theories on lower-dimensional systems.
Kumar, Manoranjan; Parvej, Aslam; Soos, Zoltán G
2015-08-12
The spin-1/2 chain with isotropic Heisenberg exchange J1, J2 > 0 between first and second neighbors is frustrated for either sign of J1. Its quantum phase diagram has critical points at fixed J1/J2 between gapless phases with nondegenerate ground state (GS) and quasi-long-range order (QLRO) and gapped phases with doubly degenerate GS and spin correlation functions of finite range. In finite chains, exact diagonalization (ED) estimates critical points as level crossing of excited states. GS spin correlations enter in the spin structure factor S(q) that diverges at wave vector qm in QLRO(q(m)) phases with periodicity 2π/q(m) but remains finite in gapped phases. S(q(m)) is evaluated using ED and density matrix renormalization group (DMRG) calculations. Level crossing and the magnitude of S(q(m)) are independent and complementary probes of quantum phases, based respectively on excited and ground states. Both indicate a gapless QLRO(π/2) phase between -1.2 < J1/|J2| < 0.45. Numerical results and field theory agree well for quantum critical points at small frustration J2 but disagree in the sector of weak exchange J1 between Heisenberg antiferromagnetic chains on sublattices of odd and even-numbered sites.
Energy Technology Data Exchange (ETDEWEB)
Zhu, Rengui, E-mail: rgzhu@mail.ahnu.edu.cn; Hu, Gangsan
2013-06-15
A frustrated Heisenberg model on a stacked square lattice in a striped antiferromagnetic spin order is studied by the Green's function approach. Besides the intra- and inter-layer exchange couplings, the single-ion anisotropy (J{sub s}) is also considered. The expressions of the spin spectrum gap (Δ), the transition temperature (T{sub N}) and the zero-temperature average spin (〈S{sup z}〉{sub 0}) are derived analytically. Their dependences on the single-ion anisotropy are investigated. We find they are all increasing functions of J{sub s}. We make a further estimation of the magnitude of J{sub s} according to the experimental temperature T{sub N}=138K of the pure compound LaFeAsO.
Liu, R. M.; Zhuo, W. Z.; Chen, J.; Qin, M. H.; Zeng, M.; Lu, X. B.; Gao, X. S.; Liu, J.-M.
2017-07-01
We study the thermal phase transition of the fourfold degenerate phases (the plaquette and single-stripe states) in the two-dimensional frustrated Ising model on the Shastry-Sutherland lattice using Monte Carlo simulations. The critical Ashkin-Teller-like behavior is identified both in the plaquette phase region and the single-stripe phase region. The four-state Potts critical end points differentiating the continuous transitions from the first-order ones are estimated based on finite-size-scaling analyses. Furthermore, a similar behavior of the transition to the fourfold single-stripe phase is also observed in the anisotropic triangular Ising model. Thus, this work clearly demonstrates that the transitions to the fourfold degenerate states of two-dimensional Ising antiferromagnets exhibit similar transition behavior.
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.
Relaxation of antiferromagnetic order in spin-1/2 chains following a quantum quench.
Barmettler, Peter; Punk, Matthias; Gritsev, Vladimir; Demler, Eugene; Altman, Ehud
2009-04-03
We study the unitary time evolution of antiferromagnetic order in anisotropic Heisenberg chains that are initially prepared in a pure quantum state far from equilibrium. Our analysis indicates that the antiferromagnetic order imprinted in the initial state vanishes exponentially. Depending on the anisotropy parameter, oscillatory or nonoscillatory relaxation dynamics is observed. Furthermore, the corresponding relaxation time exhibits a minimum at the critical point, in contrast to the usual notion of critical slowing down, from which a maximum is expected.
Digital Quantum Simulation of the Statistical Mechanics of a Frustrated Magnet
Zhang, Jingfu; Laflamme, Raymond; Aspuru-Guzik, Alán; Baugh, Jonathan
2011-01-01
Many interesting problems in physics, chemistry, and computer science are equivalent to problems of interacting spins. However, most of these problems require computational resources that are out of reach by classical computers. A promising solution to overcome this challenge is to exploit the laws of quantum mechanics to perform simulation. Several "analog" quantum simulations of interacting spin systems have been realized experimentally. However, relying on adiabatic techniques, these simulations are limited to preparing ground states only. Here we report the first experimental results on a "digital" quantum simulation on thermal states; we simulated a three-spin frustrated magnet, a building block of spin ice, with an NMR quantum information processor, and we are able to explore the phase diagram of the system at any simulated temperature and external field. These results serve as a guide for identifying the challenges for performing quantum simulation on physical systems at finite temperatures, and pave t...
Classical spin and quantum-mechanical descriptions of geometric spin frustration.
Dai, Dadi; Whangbo, Myung-Hwan
2004-07-08
Geometric spin frustration (GSF) in isolated plaquettes with local spin s, i.e., an equilateral-triangle spin trimer and a regular-tetrahedron spin tetramer, was examined on the basis of classical spin and quantum-mechanical descriptions to clarify their differences and similarities. An analytical proof was given for how the state degeneracy and the total spin S of their ground states depend on the local spin s. The quantum-mechanical conditions for the occurrence of GSF in isolated plaquettes were clarified, and their implications were explored. Corner sharing between plaquettes and how it affects GSF in the resulting spin systems was examined.
Scaling relations of three-dimensional random-exchange quantum antiferromagnets
Tan, Deng-Ruei; Jiang, Fu-Jiun
2015-11-01
The thermal and ground state properties of a class of three-dimensional (3D) random-exchange spin-1/2 antiferromagnets are studied using first principles quantum Monte Carlo method. Our motivation is to examine whether the newly discovered universal scaling properties, which connect the Néel temperature and the staggered magnetization density, for the clean 3D quantum dimerized Heisenberg models remain valid for the random-exchange models considered here. Remarkably, similar to the clean systems, our Monte Carlo results indicate that these scaling relations also emerge for the considered models with the introduced antiferromagnetic randomness. The scope of the validity of these scaling properties for the 3D quantum antiferromagnets is investigated as well.
Quantum vs Classical Magnetization Plateaus of S=1/2 Frustrated Heisenberg Chains
Hida, Kazuo; Affleck, Ian
2005-06-01
The competition between quantum and classical magnetization plateaus of S=1/2 frustrated Heisenberg chains with modified exchange couplings is investigated. The conventional S=1/2 frustrated Heisenberg chain is known to exhibit a 3-fold degenerate \\uparrow\\downarrow\\uparrow-type classical plateau at 1/3 of the saturation magnetization accompanied by the spontaneous Z3 translational symmetry breakdown. The stability of this plateau phase against period 3 exchange modulation which favors the \\bullet\\hskip -1pt-\\hskip -1pt\\bullet \\uparrow-type quantum plateau state (\\bullet\\hskip -1pt-\\hskip -1pt\\bullet = singlet dimer) is studied by bosonization, renormalization group and numerical diagonalization methods. The ground state phase diagram and the spin configuration in each phase are numerically determined. The translationally invariant Valence Bond Solid-type model with 4-spin and third neighbor interactions, which has the exact \\bullet\\hskip -1pt-\\hskip -1pt\\bullet \\uparrow-type quantum plateau state, is also presented. The phase transition to the classical \\uparrow\\downarrow\\uparrow-type ground state is also observed by varying the strength of 4-spin and third neighbor interactions. The relation between these two types of models with quantum plateau states is discussed.
Quantum disordered insulating phase in the frustrated cubic-lattice Hubbard model
Laubach, Manuel; Joshi, Darshan G.; Reuther, Johannes; Thomale, Ronny; Vojta, Matthias; Rachel, Stephan
2016-01-01
In the quest for quantum spin liquids in three spatial dimensions (3D), we study the half-filled Hubbard model on the simple cubic lattice with hopping processes up to third neighbors. Employing the variational cluster approach (VCA), we determine the zero-temperature phase diagram: In addition to a paramagnetic metal at small interaction strength U and various antiferromagnetic insulators at large U , we find an intermediate-U antiferromagnetic metal. Most interestingly, we also identify a nonmagnetic insulating region, extending from intermediate to strong U . Using VCA results in the large-U limit, we establish the phase diagram of the corresponding J1-J2-J3 Heisenberg model. This is qualitatively confirmed—including the nonmagnetic region—using spin-wave theory. Further analysis reveals a striking similarity to the behavior of the J1-J2 square-lattice Heisenberg model, suggesting that the nonmagnetic region may host a 3D spin-liquid phase.
Energy Technology Data Exchange (ETDEWEB)
Ye, Jinwu, E-mail: jy306@ccs.msstate.edu [Beijing Key Laboratory for Terahertz Spectroscopy and Imaging, Key Laboratory of Terahertz Optoelectronics, Ministry of Education, Department of Physics, Capital Normal University, Beijing 100048 (China); Department of Physics and Astronomy, Mississippi State University, P.O. Box 5167, MS 39762 (United States); Chen, Yan, E-mail: yanchen99@gmail.com [Department of Physics, Surface Physics Laboratory (National Key Laboratory) and Lab of Advanced Materials, Fudan University, Shanghai (China)
2013-04-11
By using the dual vortex method (DVM), we develop systematically a simple and effective scheme to use the vortex degree of freedoms on dual lattices to characterize the symmetry breaking patterns of the boson insulating states in the direct lattices. Then we apply our scheme to study quantum phases and phase transitions in an extended boson Hubbard model slightly away from 1/3 (2/3) filling on frustrated lattices such as triangular and Kagome lattice. In a triangular lattice at 1/3, we find a X-CDW, a stripe CDW phase which was found previously by a density operator formalism (DOF). Most importantly, we also find a new CDW-VB phase which has both local CDW and local VB orders, in sharp contrast to a bubble CDW phase found previously by the DOF. In the Kagome lattice at 1/3, we find a VBS phase and a 6-fold CDW phase. Most importantly, we also identify a CDW-VB phase which has both local CDW and local VB orders which was found in previous QMC simulations. We also study several other phases which are not found by the DVM. By analyzing carefully the saddle point structures of the dual gauge fields in the translational symmetry breaking sides and pushing the effective actions slightly away from the commensurate filling f=1/3(2/3), we classified all the possible types of supersolids and analyze their stability conditions. In a triangular lattice, there are X-CDW supersolid, stripe CDW supersolid, but absence of any valence bond supersolid (VB-SS). There are also a new kind of supersolid: CDW-VB supersolid. In a Kagome lattice, there are 6-fold CDW supersolid, stripe CDW supersolid, but absence of any valence bond supersolid (VB-SS). There are also a new kind of supersolid: CDW-VB supersolid. We show that independent of the types of the SS, the quantum phase transitions from solids to supersolids driven by a chemical potential are in the same universality class as that from a Mott insulator to a superfluid, therefore have exact exponents z=2, ν=1/2, η=0 (with
Schmidt, Sebastian
2016-07-01
Artificially engineered light-matter systems constitute a novel, versatile architecture for the quantum simulation of driven, dissipative phase transitions and non-equilibrium quantum many-body systems. Here, we discuss recent experimental as well as theoretical works on the simulation of geometrical frustration in interacting photonic systems out of equilibrium. In particular, we review two recent discoveries at the interface of quantum optics and condensed matter physics: (i) the experimental achievement of Bosonic condensation into a flat energy band and (ii) the theoretical prediction of crystalline phases of light in a frustrated qubit-cavity array. We show that this new line of research leads to novel and unique tools for the experimental investigation of frustrated systems and holds the potential to create new phases of light and matter with interesting spatial structure.
Extended quantum critical phase in a magnetized spin-1/2 antiferromagnetic chain
DEFF Research Database (Denmark)
Stone, M.B.; Reich, D.H.; Broholm, C.
2003-01-01
Measurements are reported of the magnetic field dependence of excitations in the quantum critical state of the spin S=1/2 linear chain Heisenberg antiferromagnet copper pyrazine dinitrate (CuPzN). The complete spectrum was measured at k(B)T/Jless than or equal to0.025 for H=0 and H=8.7 T, where...
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.
Fractional excitations in the square-lattice quantum antiferromagnet
DEFF Research Database (Denmark)
Piazza, B. Dalla; Mourigal, M.; Christensen, Niels Bech
2015-01-01
Quantum magnets have occupied the fertile ground between many-body theory and low-temperature experiments on real materials since the early days of quantum mechanics. However, our understanding of even deceptively simple systems of interacting spin-1/2 particles is far from complete. The quantum ...
Konstantinidis, N P
2015-02-25
The antiferromagnetic Heisenberg model on the icosahedron presents unconventional properties at the classical and quantum level, which originate in the frustrated nature of the interactions between the spins. Here we examine the importance of the connectivity of the icosahedron for the appearance of a magnetization discontinuity as a function of an external field which separates two families of lowest energy configurations. We also investigate the transition from the classical to the quantum limit. The influence of connectivity on the magnetic properties is revealed by considering the cluster as being made up of a closed strip of a triangular lattice with two additional spins attached. The classical magnetization discontinuity is shown to evolve continuously from the discontinuity effected by these two spins when they are uncoupled to the cluster. In the second part the transition from the classical to the quantum limit is examined by focusing on the low energy spectrum, taking fully into account the spatial and the spin symmetry of the model in the characterization of the states. A symmetry analysis of the highly degenerate lowest energy classical manifold identifies as its direct fingerprint the low energy quantum states for spin magnitude as low as s = 1, with the latter following a tower of states behavior which relates to the icosahedron having a structure reminiscent of a depleted triangular lattice. The classical character of the AHM for small s is also detected on the ground state energy and correlation functions. On the other hand the classical magnetization discontinuity in a field eventually disappears for small s, after a weak reentrant behavior.
Ziat, D.; Aczel, A. A.; Sinclair, R.; Chen, Q.; Zhou, H. D.; Williams, T. J.; Stone, M. B.; Verrier, A.; Quilliam, J. A.
2017-05-01
We have performed magnetic susceptibility, heat capacity, muon spin relaxation, and neutron-scattering measurements on three members of the family Ba3M Ru2O9 , where M =In , Y, and Lu. These systems consist of mixed-valence Ru dimers on a triangular lattice with antiferromagnetic interdimer exchange. Although previous work has argued that charge order within the dimers or intradimer double exchange plays an important role in determining the magnetic properties, our results suggest that the dimers are better described as molecular units due to significant orbital hybridization, resulting in one spin-1/2 moment distributed equally over the two Ru sites. These molecular building blocks form a frustrated, quasi-two-dimensional triangular lattice. Our zero- and longitudinal-field μ SR results indicate that the molecular moments develop a collective, static magnetic ground state, with oscillations of the zero-field muon spin polarization indicative of long-range magnetic order in the Lu sample. The static magnetism is much more disordered in the Y and In samples, but they do not appear to be conventional spin glasses.
Quantum oscillations in antiferromagnetic CaFe(2)As(2) on the brink of superconductivity.
Harrison, N; McDonald, R D; Mielke, C H; Bauer, E D; Ronning, F; Thompson, J D
2009-08-12
We report quantum oscillation measurements on CaFe(2)As(2) under strong magnetic fields-recently reported to become superconducting under pressures of as little as a kilobar. The largest observed carrier pocket occupies less than 0.05% of the paramagnetic Brillouin zone volume-consistent with Fermi surface reconstruction caused by antiferromagnetism. On comparing several alkaline earth AFe(2)As(2) antiferromagnets (with A = Ca, Sr and Ba), the dependences of the Fermi surface cross-sectional area F(α) and the effective mass m(α)(*) of the primary observed pocket on the antiferromagnetic/structural transition temperature T(s) are both found to be consistent with the case for quasiparticles in a conventional spin-density wave model. These findings suggest that the recently proposed strain-enhanced superconductivity in these materials occurs within a broadly conventional spin-density wave phase.
Physical realization of a quantum spin liquid based on a complex frustration mechanism
Balz, Christian; Lake, Bella; Reuther, Johannes; Luetkens, Hubertus; Schönemann, Rico; Herrmannsdörfer, Thomas; Singh, Yogesh; Nazmul Islam, A. T. M.; Wheeler, Elisa M.; Rodriguez-Rivera, Jose A.; Guidi, Tatiana; Simeoni, Giovanna G.; Baines, Chris; Ryll, Hanjo
2016-10-01
Unlike conventional magnets where the magnetic moments are partially or completely static in the ground state, in a quantum spin liquid they remain in collective motion down to the lowest temperatures. The importance of this state is that it is coherent and highly entangled without breaking local symmetries. In the case of magnets with isotropic interactions, spin-liquid behaviour is sought in simple lattices with antiferromagnetic interactions that favour antiparallel alignments of the magnetic moments and are incompatible with the lattice geometries. Despite an extensive search, experimental realizations remain very few. Here we investigate the novel, unexplored magnet Ca10Cr7O28, which has a complex Hamiltonian consisting of several different isotropic interactions and where the ferromagnetic couplings are stronger than the antiferromagnetic ones. We show both experimentally and theoretically that it displays all the features expected of a quantum spin liquid. Thus spin-liquid behaviour in isotropic magnets is not restricted to the simple idealized models currently investigated, but can be compatible with complex structures and ferromagnetic interactions.
Sknepnek, Rastko; Vojta, Thomas; Vojta, Matthias
2004-08-27
We present Monte Carlo simulations of a two-dimensional bilayer quantum Heisenberg antiferromagnet with random dimer dilution. In contrast with exotic scaling scenarios found in other random quantum systems, the quantum phase transition in this system is characterized by a finite-disorder fixed point with power-law scaling. After accounting for corrections to scaling, with a leading irrelevant exponent of omega approximately 0.48, we find universal critical exponents z=1.310(6) and nu=1.16(3). We discuss the consequences of these findings and suggest new experiments.
Entanglement in the quantum one-dimensional integer spin S Heisenberg antiferromagnet
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.
Quantum-spin-liquid states in the two-dimensional kagome antiferromagnets ZnxCu4-x(OD)6Cl2.
Lee, S-H; Kikuchi, H; Qiu, Y; Lake, B; Huang, Q; Habicht, K; Kiefer, K
2007-11-01
A three-dimensional system of interacting spins typically develops static long-range order when it is cooled. If the spins are quantum (S=1/2), however, novel quantum paramagnetic states may appear. The most highly sought state among them is the resonating-valence-bond state, in which every pair of neighbouring quantum spins forms an entangled spin singlet (valence bonds) and these singlets are quantum mechanically resonating among themselves. Here we provide an experimental indication for such quantum paramagnetic states existing in frustrated antiferromagnets, Zn(x)Cu(4-x)(OD)(6)Cl(2), where the S=1/2 magnetic Cu2+ moments form layers of a two-dimensional kagome lattice. We find that in Cu(4)(OD)(6)Cl(2), where distorted kagome planes are weakly coupled, a dispersionless excitation mode appears in the magnetic excitation spectrum below approximately 20 K, whose characteristics resemble those of quantum spin singlets in a solid state, known as a valence-bond solid, that breaks translational symmetry. Doping with non-magnetic Zn2+ ions reduces the distortion of the kagome lattice, and weakens the interplane coupling but also dilutes the magnetic occupancy of the kagome lattice. The valence-bond-solid state is suppressed, and for ZnCu(3)(OD)(6)Cl(2), where the kagome planes are undistorted and 90% occupied by the Cu2+ ions, the low-energy spin fluctuations become featureless.
Institute of Scientific and Technical Information of China (English)
LIU Zhao-Sen; Sechovsk(y) Vladimir; Divi(s) Martin
2011-01-01
@@ A Usov-type quantum model based on a mean-field approximation is utilized to simulate the magnetic structure of an assumed rare-earth nanoparticle consisting of an antiferromagnetic core and a paramagnetic outer shell.We study the magnetic properties in the presence and absence of an external magnetic field.Our simulation results show that the magnetic moments in the core region orientate antiferromagnetically in zero external magnetic field; an applied magnetic field rotates all of the magnetic moments in the paramagnetic shell completely to the field direction, and turns those in the core (which tries to maintain its original antiferromagnetic structure) towards the orientation in some degree; and the paramagnetic shell does not have a strong influence on the magnetic configuration of the core.%A Usov-type quantum model based on a mean-field approximation is utilized to simulate the magnetic structure of an assumed rare-earth nanoparticle consisting of an antiferromagnetic core and a paramagnetic outer shell. We study the magnetic properties in the presence and absence of an external magnetic field. Our simulation results show that the magnetic moments in the core region orientate antiferromagnetically in zero external magnetic field; an applied magnetic field rotates all of the magnetic moments in the paramagnetic shell completely to the Geld direction, and turns those in the core (which tries to maintain its original antiferromagnetic structure) towards the orientation in some degree; and the paramagnetic shell does not have a strong influence on the magnetic configuration of the core.
Dai, Yan-Wei; Cho, Sam Young; Batchelor, Murray T.; Zhou, Huan-Qiang
2017-01-01
The von Neumann entanglement entropy is used to estimate the critical point hc/J ≃0.143 (3 ) of the mixed ferro-antiferromagnetic three-state quantum Potts model H =∑i[J (XiXi+1 2+Xi2Xi +1) -h Ri] , where Xi and Ri are standard three-state Potts spin operators and J >0 is the antiferromagnetic coupling parameter. This critical point value gives improved estimates for two Kosterlitz-Thouless transition points in the antiferromagnetic (β model, where Δ and β are, respectively, the chirality and coupling parameters in the clock model. These are the transition points βc≃-0.143 (3 ) at Δ =1/2 between incommensurate and commensurate phases and βc≃-7.0 (1 ) at Δ =0 between disordered and incommensurate phases. The von Neumann entropy is also used to calculate the central charge c of the underlying conformal field theory in the massless phase h ≤hc . The estimate c ≃1 in this phase is consistent with the known exact value at the particular point h /J =-1 corresponding to the purely antiferromagnetic three-state quantum Potts model. The algebraic decay of the Potts spin-spin correlation in the massless phase is used to estimate the continuously varying critical exponent η .
Excitation-Gap Scaling near Quantum Critical Three-Dimensional Antiferromagnets.
Lohöfer, M; Wessel, S
2017-04-07
By means of large-scale quantum Monte Carlo simulations, we examine the quantum critical scaling of the magnetic excitation gap (the triplon gap) in a three-dimensional dimerized quantum antiferromagnet, the bicubic lattice, and identify characteristic multiplicative logarithmic scaling corrections atop the leading mean-field behavior. These findings are in accord with field-theoretical predictions that are based on an effective description of the quantum critical system in terms of an asymptotically free field theory, which exhibits a logarithmic decay of the renormalized interaction strength upon approaching the quantum critical point. Furthermore, using bond-based singlet spectroscopy, we identify the amplitude (Higgs) mode resonance within the antiferromagnetic region. We find a Higgs mass scaling in accord with field-theoretical predictions that relate it by a factor of sqrt[2] to the corresponding triplon gap in the quantum disordered regime. In contrast to the situation in lower-dimensional systems, we observe in this three-dimensional coupled-dimer system a distinct signal from the amplitude mode also in the dynamical spin structure factor. Its width is observed to vanish proportional to the Higgs mass in the accessible proximity to the quantum critical point.
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.
2013-01-01
This book covers all principal aspects of currently investigated frustrated systems, from exactly solved frustrated models to real experimental frustrated systems, going through renormalization group treatment, Monte Carlo investigation of frustrated classical Ising and vector spin models, low-dimensional systems, spin ice and quantum spin glass. The reader can - within a single book - obtain a global view of the current research development in the field of frustrated systems.This new edition is updated with recent theoretical, numerical and experimental developments in the field of frustrated
Remanent Magnetization: Signature of Many-Body Localization in Quantum Antiferromagnets
Ros, V.; Müller, M.
2017-06-01
We study the remanent magnetization in antiferromagnetic, many-body localized quantum spin chains, initialized in a fully magnetized state. Its long time limit is an order parameter for the localization transition, which is readily accessible by standard experimental probes in magnets. We analytically calculate its value in the strong-disorder regime exploiting the explicit construction of quasilocal conserved quantities of the localized phase. We discuss analogies in cold atomic systems.
Han, Tianheng
New physics, such as a quantum spin liquid, can emerge in systems where quantum fluctuations are enhanced due to reduced dimensionality and strong frustration . The realization of a quantum spin liquid in two-dimensions would represent a new state of matter. It is believed that spin liquid physics plays a role in the phenomenon of high-Tc superconductivity, and the topological properties of the spin liquid state may have applications in the field of quantum information. The Zn-paratacamite family, ZnxCu4-- x(OH)6Cl2 for x > 0.33, is an ideal system to look for such an exotic state in the form of antiferromagnetic Cu 2 + kagome planes. The x = 1 end member, named herbertsmithite, has shown promising spin liquid properties from prior studies on powder samples. Here we show a new synthesis by which high-quality centimeter-sized single crystals of Znparatacamite have been produced for the first time. Neutron and synchrotron xray diffraction experiments indicate no structural transition down to T = 2 K. The magnetic susceptibility both perpendicular and parallel to the kagome plane has been measured for the x = 1 sample. A small, temperature-dependent anisotropy has been observed, where chi z / chip > 1 at high temperatures and chiz / chip fingerprint of the quantum spin liquid state in herbertsmithite. (Copies available exclusively from MIT Libraries, libraries.mit.edu/docs - docs mit.edu)
Qin, Yanqi; Normand, Bruce; Sandvik, Anders; Meng, Zi Yang
We investigate the quantum phase transition in an S=1/2 dimerized Heisenberg antiferromagnet in three spatial dimensions. By means of quantum Monte Carlo simulations and finite-size scaling analyses, we get high-precision results for the quantum critical properties at the transition from the magnetically disordered dimer-singlet phase to the ordered Neel phase. This transition breaks O(N) symmetry with N=3 in D=3+1 dimensions. This is the upper critical dimension, where multiplicative logarithmic corrections to the leading mean-field critical properties are expected; we extract these corrections, establishing their precise forms for both the zero-temperature staggered magnetization, ms, and the Neel temperature, TN. We present a scaling ansatz for TN, including logarithmic corrections, which agrees with our data and indicates exact linearity with ms, implying a complete decoupling of quantum and thermal fluctuation effects close to the quantum critical point. These logarithmic scaling forms have not previously identified or verified by unbiased numerical methods and we discuss their relevance to experimental studies of dimerized quantum antiferromagnets such as TlCuCl3. Ref.: arXiv:1506.06073
Mott glass phase in a diluted bilayer Heisenberg quantum antiferromagnet
Ma, Nv-Sen; Sandvik, Anders W.; Yao, Dao-Xin
2015-09-01
We use quantum Monte Carlo simulations to study a dimer-diluted S = 1/2 Heisenberg model on a bilayer square lattice with intralayer interaction J1 and interlayer interaction J2. Below the classical percolation threshold pc, the system has three phases reachable by tuning the interaction ratio g = J2/J1: a Néel ordered phase, a gapless quantum glass phase, and a gapped quantum paramagnetic phase. We present the ground-state phase diagram in the plane of dilution p and interaction ratio g. The quantum glass phase is certified to be of the gapless Mott glass type, having a uniform susceptibility vanishing at zero temperature T and following a stretched exponential form at T > 0; χu exp(-b/Tα) with α < 1. At the phase transition point from Neel ordered to Mott glass, we find that the critical exponents are different from those of the clean system described by the standard O(3) universality class in 2+1 dimensions.
Quantum phase transition of the randomly diluted heisenberg antiferromagnet on a square lattice
Kato; Todo; Harada; Kawashima; Miyashita; Takayama
2000-05-01
Ground-state magnetic properties of the diluted Heisenberg antiferromagnet on a square lattice are investigated by means of the quantum Monte Carlo method with the continuous-time loop algorithm. It is found that the critical concentration of magnetic sites is independent of the spin size S, and equal to the two-dimensional percolation threshold. However, the existence of quantum fluctuations makes the critical exponents deviate from those of the classical percolation transition. Furthermore, we found that the transition is not universal, i.e., the critical exponents significantly depend on S.
Quantum selection of order in an XXZ antiferromagnet on a Kagome lattice.
Chernyshev, A L; Zhitomirsky, M E
2014-12-05
Selection of the ground state of the kagome-lattice XXZ antiferromagnet by quantum fluctuations is investigated by combining nonlinear spin-wave and real-space perturbation theories. The two methods unanimously favor q=0 over sqrt[3]×sqrt[3] magnetic order in a wide range of the anisotropy parameter 0≤Δ≲0.72. Both approaches are also in accord on the magnitude of the quantum order-by-disorder effect generated by topologically nontrivial, looplike spin-flip processes. A tentative S-Δ phase diagram of the model is proposed.
Bao, Wei; Broholm, C.; Aeppli, G.; Carter, S. A.; Dai, P.; Rosenbaum, T. F.; Honig, J. M.; Metcalf, P.; Trevino, S. F.
1998-11-01
Magnetic correlations in all four phases of pure and doped vanadium sesquioxide (V2O3) have been examined by magnetic thermal-neutron scattering. Specifically, we have studied the antiferromagnetic and paramagnetic phases of metallic V2-yO3, the antiferromagnetic insulating and paramagnetic metallic phases of stoichiometric V2O3, and the antiferromagnetic and paramagnetic phases of insulating V1.944Cr0.056O3. While the antiferromagnetic insulator can be accounted for by a localized Heisenberg spin model, the long-range order in the antiferromagnetic metal is an incommensurate spin-density wave, resulting from a Fermi surface nesting instability. Spin dynamics in the strongly correlated metal are dominated by spin fluctuations with a ``single lobe'' spectrum in the Stoner electron-hole continuum. Furthermore, our results in metallic V2O3 represent an unprecedentedly complete characterization of the spin fluctuations near a metallic quantum critical point, and provide quantitative support for the self-consistent renormalization theory for itinerant antiferromagnets in the small moment limit. Dynamic magnetic correlations for ħω
Entropy Evolution in the Magnetic Phases of Partially Frustrated CePdAl
Lucas, S.; Grube, K.; Huang, C.-L.; Sakai, A.; Wunderlich, S.; Green, E. L.; Wosnitza, J.; Fritsch, V.; Gegenwart, P.; Stockert, O.; v. Löhneysen, H.
2017-03-01
In the heavy-fermion metal CePdAl, long-range antiferromagnetic order coexists with geometric frustration of one-third of the Ce moments. At low temperatures, the Kondo effect tends to screen the frustrated moments. We use magnetic fields B to suppress the Kondo screening and study the magnetic phase diagram and the evolution of the entropy with B employing thermodynamic probes. We estimate the frustration by introducing a definition of the frustration parameter based on the enhanced entropy, a fundamental feature of frustrated systems. In the field range where the Kondo screening is suppressed, the liberated moments tend to maximize the magnetic entropy and strongly enhance the frustration. Based on our experiments, this field range may be a promising candidate to search for a quantum spin liquid.
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.
The antiferromagnetic cross-coupled spin ladder: Quantum fidelity and tensor networks approach
Chen, Xi-Hao; Cho, Sam Young; Zhou, Huan-Qiang; Batchelor, Murray T.
2016-05-01
We investigate the phase diagram of the cross-coupled Heisenberg spin ladder with antiferromagnetic couplings. For this model, the results for the existence of the columnar dimer phase, which was predicted on the basis of weak coupling field theory renormalization group arguments, have been conflicting. The numerical work on this model has been based on various approaches, including exact diagonalization, series expansions and density-matrix renormalization group calculations. Using the recently-developed tensor network states and groundstate fidelity approach for quantum spin ladders, we find no evidence for the existence of the columnar dimer phase. We also provide an argument based on the symmetry of the Hamiltonian, which suggests that the phase diagram for antiferromagnetic couplings consists of a single line separating the rung-singlet and the Haldane phases.
Mazzucchi, Gabriel; Caballero-Benitez, Santiago F.; Mekhov, Igor B.
2016-08-01
Ultracold atomic systems offer a unique tool for understanding behavior of matter in the quantum degenerate regime, promising studies of a vast range of phenomena covering many disciplines from condensed matter to quantum information and particle physics. Coupling these systems to quantized light fields opens further possibilities of observing delicate effects typical of quantum optics in the context of strongly correlated systems. Measurement backaction is one of the most funda- mental manifestations of quantum mechanics and it is at the core of many famous quantum optics experiments. Here we show that quantum backaction of weak measurement can be used for tailoring long-range correlations of ultracold fermions, realizing quantum states with spatial modulations of the density and magnetization, thus overcoming usual requirement for a strong interatomic interactions. We propose detection schemes for implementing antiferromagnetic states and density waves. We demonstrate that such long-range correlations cannot be realized with local addressing, and they are a consequence of the competition between global but spatially structured backaction of weak quantum measurement and unitary dynamics of fermions.
Mazzucchi, Gabriel; Caballero-Benitez, Santiago F; Mekhov, Igor B
2016-08-11
Ultracold atomic systems offer a unique tool for understanding behavior of matter in the quantum degenerate regime, promising studies of a vast range of phenomena covering many disciplines from condensed matter to quantum information and particle physics. Coupling these systems to quantized light fields opens further possibilities of observing delicate effects typical of quantum optics in the context of strongly correlated systems. Measurement backaction is one of the most funda- mental manifestations of quantum mechanics and it is at the core of many famous quantum optics experiments. Here we show that quantum backaction of weak measurement can be used for tailoring long-range correlations of ultracold fermions, realizing quantum states with spatial modulations of the density and magnetization, thus overcoming usual requirement for a strong interatomic interactions. We propose detection schemes for implementing antiferromagnetic states and density waves. We demonstrate that such long-range correlations cannot be realized with local addressing, and they are a consequence of the competition between global but spatially structured backaction of weak quantum measurement and unitary dynamics of fermions.
Frustrated spin model as a hard-sphere liquid.
Mostovoy, M V; Khomskii, D I; Knoester, J; Prokof'ev, N V
2003-04-11
We show that one-dimensional topological objects (kinks) are natural degrees of freedom for an antiferromagnetic Ising model on a triangular lattice. Its ground states and the coexistence of spin ordering with an extensive zero-temperature entropy can easily be understood in terms of kinks forming a hard-sphere liquid. Using this picture we explain effects of quantum spin dynamics on that frustrated model, which we also study numerically.
Magnons in the quantum dimer antiferromagnet Sr{sub 3}Cr{sub 2}O{sub 8}
Energy Technology Data Exchange (ETDEWEB)
Quintero-Castro, Diana Lucia; Lake, Bella [Helmholtz Zentrum Berlin, Berlin 14109 (Germany); Institut fuer Festkoerperphysik, Technische Universitaet Berlin, D-10623 Berlin (Germany); Wheeler, Elisa Maria; Islam, Nazmul [Helmholtz Zentrum Berlin, Berlin 14109 (Germany)
2011-07-01
Sr{sub 3}Cr{sub 2}O{sub 8} consists of a three-dimensional frustrated arrangement of antiferromagnetically coupled pairs of Cr ions or dimers. The Cr ions are in the unusual 5+ valence state resulting in one electron in the 3d shell and a spin value of 1/2 while a tetrahedral crystal field ensures that this electron occupies the doubly degenerate eg orbitals. Below room temperature Sr{sub 3}Cr{sub 2}O{sub 8} undergoes a cooperative Jahn Teller distortion that lifts the orbital degeneracy so that only the 3z{sup 2}-r{sup 2} orbital is occupied. The low temperature structure is characterized by monoclinic crystal symmetry and antiferro-orbital ordering. The transition also gives rise to spatially anisotropic exchange paths and results in three crystal twins. We have grown single crystals of Sr{sub 3}Cr{sub 2}O{sub 8} and have performed DC susceptibility measurements, high field magnetisation and powder and single crystal inelastic neutron scattering experiments. The data reveals a singlet ground state and gapped triplet excitations consisting of three modes, coming from the three crystal twins. Using a random phase approximation, we have extracted the magnetic exchange interactions within the dimer and between dimers. Sr{sub 3}Cr{sub 2}O{sub 8} is a candidate for the study of the critical properties in the quantum phase transition as the magnetic field can drive a Bose Einstein condensation of magnons.
Quantum critical response function in quasi-two-dimensional itinerant antiferromagnets
Varma, C. M.; Zhu, Lijun; Schröder, Almut
2015-10-01
We reexamine the experimental results for the magnetic response function χ''(q ,E ,T ) for q around the antiferromagnetic vectors Q , in the quantum-critical region, obtained by inelastic neutron scattering, on an Fe-based superconductor and on a heavy-fermion compound. The motivation is to compare the results with a recent theory, which shows that the fluctuations in a generic antiferromagnetic model for itinerant fermions map to those in the universality class of the dissipative quantum-XY model. The quantum-critical fluctuations in this model, in a range of parameters, are given by the correlations of spatial and temporal topological defects. The theory predicts a χ''(q ,E ,T ) (i) which is a separable function of (q -Q ) and of (E ,T ) , (ii) at criticality, the energy-dependent part is ∝tanh(E /2 T ) below a cutoff energy, (iii) the correlation time departs from its infinite value at criticality on the disordered side by an essential singularity, and (iv) the correlation length depends logarithmically on the correlation time, so that the dynamical critical exponent z is ∞ . The limited existing experimental results are found to be consistent with the first two unusual predictions from which the linear dependence of the resistivity on T and the T lnT dependence of the entropy also follow. More experiments are suggested, especially to test the theory of variations on the correlation time and length on the departure from criticality.
Quantum entanglement in trimer spin-1/2 Heisenberg chains with antiferromagnetic coupling
Del Cima, O M; da Silva, S L L
2015-01-01
The quantum entanglement measure is determined, for the first time, for antiferromagnetic trimer spin-1/2 Heisenberg chains. The physical quantity proposed to measure the entanglement is the distance between states by adopting the Hilbert-Schmidt norm. The method is applied to the new magnetic Cu(II) trimer system, 2b.3CuCl_2.2H_2O, and to the trinuclear Cu(II) halide salt, (3MAP)_2Cu_2Cl_8. The decoherence temperature, above which the entanglement is suppressed, is determined for the both systems. A correlation among their decoherence temperatures and their respective exchange coupling constants is established.
Large off-diagonal magnetoelectric coupling in the quantum paraelectric antiferromagnet EuTiO3
Shvartsman, V. V.; Borisov, P.; Kleemann, W.; Kamba, S.; Katsufuji, T.
2010-02-01
The third-order E2H2 -type magnetoelectric (ME) response of polycrystalline EuTiO3 changes sign under magnetic bias and shows a large anomaly at the antiferromagnetic (AF)-paramagnetic phase boundary below TN≈5.3K . It is attributed to critical fluctuations of the AF order parameter reinforced by quantum paraelectric polar correlations. The underlying biquadratic spin-lattice coupling involves electric field induced Dzyaloshinskii-Moriya interaction as described within mean-field approximation. Single domaining by ME annealing (or cooling) significantly enhances the response by additional EH and EH2 effects.
Institute of Scientific and Technical Information of China (English)
JI An-Chun; TIAN Guang-Shan
2006-01-01
In the present paper, we calculate the Gaussian correction to the critical value Jc⊥ caused by quantum spin fluctuation in a two-dimensional spatially anisotropic Heisenberg antiferromagnet with integer spin S. Previously, someauthors computed this quantity by the mean-field theory based on the Schwinger boson representation of spin operators.However, for S = 1, their result is much less than the one derived by numerical calculations. By taking the effect ofquantum spin fluctuation into consideration, we are able to produce a greatly improved result.
Sikkenk, Tycho S.; Coester, Kris; Buhrandt, Stefan; Fritz, Lars; Schmidt, Kai P.
2017-02-01
The classical Ising model on the frustrated three-dimensional (3D) swedenborgite lattice has disordered spin liquid ground states for all ratios of inter- and intraplanar couplings. Quantum fluctuations due to a transverse field give rise to several exotic phenomena. In the limit of weakly coupled kagome layers we find a 3D version of disorder by disorder degeneracy lifting. For large out-of-plane couplings one-dimensional macrospins are formed, which realize a disordered macrospin liquid phase on an emerging two-dimensional triangular lattice. We speculate about a possibly exotic version of quantum criticality that connects the polarized phase to the macrospin liquid.
Quantum Chromodynamics, Antiferromagnets and XY Models from a Unified Point of View
Hofmann, Christoph P
2016-01-01
Antiferromagnets and quantum XY magnets in three space dimensions are described by an effective Lagrangian that exhibits the same structure as the effective Lagrangian of quantum chromodynamics with two light flavors. These systems all share a spontaneously broken internal symmetry O($N$) $\\to$ O($N$-1). Although the respective scales differ by many orders of magnitude, the general structure of the low-temperature expansion of the partition function is the same. In the nonabelian case, logarithmic terms of the form $T^8 \\ln T$ emerge at three-loop order, while for $N$=2 the series only involves powers of $T^2$. The manifestation of the Goldstone boson interaction in the pressure, order parameter, and susceptibility is explored in presence of an external field.
Quantum chromodynamics, antiferromagnets and XY models from a unified point of view
Hofmann, Christoph P.
2017-03-01
Antiferromagnets and quantum XY magnets in three space dimensions are described by an effective Lagrangian that exhibits the same structure as the effective Lagrangian of quantum chromodynamics with two light flavors. These systems all share a spontaneously broken internal symmetry O (N) → O (N - 1). Although the respective scales differ by many orders of magnitude, the general structure of the low-temperature expansion of the partition function is the same. In the nonabelian case (N ≥ 3), logarithmic terms of the form T8 ln T emerge at three-loop order, while for N = 2 the series only involves powers of T2. The manifestation of the Goldstone boson interaction in the pressure, order parameter, and susceptibility is explored in presence of an external field.
Vinit, A.; Raman, C.
2017-01-01
We have experimentally investigated the quench dynamics of antiferromagnetic spinor Bose-Einstein condensates in the vicinity of a zero temperature quantum phase transition at zero quadratic Zeeman shift q . The rate of instability shows good agreement with predictions based upon solutions to the Bogoliubov-de Gennes equations. A key feature of this work was removal of magnetic field inhomogeneities, resulting in a steep change in behavior near the transition point. The quadratic Zeeman shift at the transition point was resolved to 250 mHz uncertainty, equivalent to an energy resolution of kB× (12 pK). A small (2-3 σ ) shift of the transition point was observed, from q =0 to q =+650 mHz, whose physical mechanism is currently unknown. In this work, we demonstrate a sub-Hz precision measurement of a phase transition in quantum gases. It paves the way toward observing shifts of the transition point due to finite particle number N that scale as 1 /N , and also to potential Heisenberg limited spectroscopy with antiferromagnetic spinor gases [L.-N. Wu and L. You, Phys. Rev. A 93, 033608 (2016), 10.1103/PhysRevA.93.033608].
Fermi surface reconstruction and multiple quantum phase transitions in the antiferromagnet CeRhIn5.
Jiao, Lin; Chen, Ye; Kohama, Yoshimitsu; Graf, David; Bauer, E D; Singleton, John; Zhu, Jian-Xin; Weng, Zongfa; Pang, Guiming; Shang, Tian; Zhang, Jinglei; Lee, Han-Oh; Park, Tuson; Jaime, Marcelo; Thompson, J D; Steglich, Frank; Si, Qimiao; Yuan, H Q
2015-01-20
Conventional, thermally driven continuous phase transitions are described by universal critical behavior that is independent of the specific microscopic details of a material. However, many current studies focus on materials that exhibit quantum-driven continuous phase transitions (quantum critical points, or QCPs) at absolute zero temperature. The classification of such QCPs and the question of whether they show universal behavior remain open issues. Here we report measurements of heat capacity and de Haas-van Alphen (dHvA) oscillations at low temperatures across a field-induced antiferromagnetic QCP (Bc0 ≈ 50 T) in the heavy-fermion metal CeRhIn5. A sharp, magnetic-field-induced change in Fermi surface is detected both in the dHvA effect and Hall resistivity at B0* ≈ 30 T, well inside the antiferromagnetic phase. Comparisons with band-structure calculations and properties of isostructural CeCoIn5 suggest that the Fermi-surface change at B0* is associated with a localized-to-itinerant transition of the Ce-4f electrons in CeRhIn5. Taken in conjunction with pressure experiments, our results demonstrate that at least two distinct classes of QCP are observable in CeRhIn5, a significant step toward the derivation of a universal phase diagram for QCPs.
Kim, Heung-Sik; Kim, Yong Baek; Kee, Hae-Young
2016-12-01
There have been tremendous experimental and theoretical efforts toward the discovery of a quantum spin-liquid phase in honeycomb-based-lattice materials with strong spin-orbit coupling. Here the bond-dependent Kitaev interaction between local moments provides strong magnetic frustration and, if it is the only interaction present in the system, it will lead to an exactly solvable quantum spin-liquid ground state. In all of these materials, however, the ground state is in a magnetically ordered phase due to additional interactions between local moments. Recently, it has been reported that the magnetic order in the hyperhoneycomb material, β -Li2IrO3 , is suppressed upon applying hydrostatic pressure and the resulting state becomes a quantum paramagnet or possibly a quantum spin liquid. Using ab initio computations and strong-coupling expansion, we investigate the lattice structure and resulting local moment model in pressurized β -Li2IrO3 . Remarkably, the dominant interaction under high pressure is not the Kitaev interaction or further neighbor interactions, but a different kind of bond-dependent interaction. This leads to strong magnetic frustration and may provide a platform for discovery of a new kind of quantum spin-liquid ground state.
Hida, Kazuo
2006-07-01
The multiple reentrant quantum phase transitions in the S=1/2 antiferromagnetic Heisenberg chains with random bond alternation in the magnetic field are investigated by the density matrix renormalization group method combined with interchain mean field approximation. It is assumed that odd numbered bonds are antiferromagnetic with strength J and even numbered bonds can take the values JS and JW (JS > J > JW > 0) randomly with the probabilities p and 1- p, respectively. The pure version ( p=0 and 1) of this model has a spin gap but exhibits a field-induced antiferromagnetism in the presence of interchain coupling if Zeeman energy due to the magnetic field exceeds the spin gap. For 0 < p < 1, antiferromagnetism is induced by randomness at the small field region where the ground state is disordered due to the spin gap in the pure version. At the same time, this model exhibits randomness-induced plateaus at several values of magnetization. The antiferromagnetism is destroyed on the plateaus. As a consequence, we find a series of reentrant quantum phase transitions between transverse antiferromagnetic phases and disordered plateau phases with the increase of magnetic field for a moderate strength of interchain coupling. Above the main plateaus, the magnetization curve consists of a series of small plateaus and jumps between them. It is also found that antiferromagnetism is induced by infinitesimal interchain coupling at the jumps between the small plateaus. We conclude that this antiferromagnetism is supported by the mixing of low-lying excited states by the staggered interchain mean field even though the spin correlation function is short ranged in the ground state of each chain.
Spin dynamics and magnetic correlation length in two-dimensional quantum heisenberg antiferromagnets
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.
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.
Zou, Haiyuan; Zhao, Erhai; Liu, W. Vincent
2017-08-01
Motivated by the experimental realization of quantum spin models of polar molecule KRb in optical lattices, we analyze the spin 1 /2 dipolar Heisenberg model with competing anisotropic, long-range exchange interactions. We show that, by tilting the orientation of dipoles using an external electric field, the dipolar spin system on square lattice comes close to a maximally frustrated region similar, but not identical, to that of the J1-J2 model. This provides a simple yet powerful route to potentially realize a quantum spin liquid without the need for a triangular or kagome lattice. The ground state phase diagrams obtained from Schwinger-boson and spin-wave theories consistently show a spin disordered region between the Néel, stripe, and spiral phase. The existence of a finite quantum paramagnetic region is further confirmed by an unbiased variational ansatz based on tensor network states and a tensor renormalization group.
Anomalous curie response of impurities in quantum-critical spin-1/2 Heisenberg antiferromagnets.
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*.
Quantum entanglement and criticality of the antiferromagnetic Heisenberg model in an external field.
Liu, Guang-Hua; Li, Ruo-Yan; Tian, Guang-Shan
2012-06-27
By Lanczos exact diagonalization and the infinite time-evolving block decimation (iTEBD) technique, the two-site entanglement as well as the bipartite entanglement, the ground state energy, the nearest-neighbor correlations, and the magnetization in the antiferromagnetic Heisenberg (AFH) model under an external field are investigated. With increasing external field, the small size system shows some distinct upward magnetization stairsteps, accompanied synchronously with some downward two-site entanglement stairsteps. In the thermodynamic limit, the two-site entanglement, as well as the bipartite entanglement, the ground state energy, the nearest-neighbor correlations, and the magnetization are calculated, and the critical magnetic field h(c) = 2.0 is determined exactly. Our numerical results show that the quantum entanglement is sensitive to the subtle changing of the ground state, and can be used to describe the magnetization and quantum phase transition. Based on the discontinuous behavior of the first-order derivative of the entanglement entropy and fidelity per site, we think that the quantum phase transition in this model should belong to the second-order category. Furthermore, in the magnon existence region (h entanglement which can be described by a free bosonic field theory is observed, and the central charge c is determined to be 1.
Hirose, Yuhei; Oguchi, Akihide; Fukumoto, Yoshiyuki
2016-09-01
We study Heisenberg antiferromagnets on a diamond-like decorated square lattice perturbed by further neighbor couplings. The second-order effective Hamiltonian is calculated and the resultant Hamiltonian is found to be a square-lattice quantum-dimer model with a finite hopping amplitude and no repulsion, which suggests the stabilization of the plaquette phase. Our recipe for constructing quantum-dimer models can be adopted for other lattices and provides a route for the experimental realization of quantum-dimer models.
Dynamic scaling of the restoration of rotational symmetry in Heisenberg quantum antiferromagnets
Weinberg, Phillip; Sandvik, Anders W.
2017-08-01
We apply imaginary-time evolution with the operator e-τ H to study relaxation dynamics of gapless quantum antiferromagnets described by the spin-rotation-invariant Heisenberg Hamiltonian H . Using quantum Monte Carlo simulations to obtain unbiased results, we propagate an initial state with maximal order parameter msz (the staggered magnetization) in the z spin direction and monitor the expectation value 〈ms〉 as a function of imaginary time τ . Results for different system sizes (lengths) L exhibit an initial essentially size independent relaxation of 〈ms〉 toward its value in the infinite-size spontaneously symmetry broken state, followed by a strongly size dependent final decay to zero when the O (3 ) rotational symmetry of the order parameter is restored. We develop a generic finite-size scaling theory that shows the relaxation time diverges asymptotically as Lz, where z is the dynamic exponent of the low-energy excitations. We use the scaling theory to develop a practical way of extracting the dynamic exponent from the numerical finite-size data, systematically eliminating scaling corrections. We apply the method to spin-1 /2 Heisenberg antiferromagnets on two different lattice geometries: the standard two-dimensional (2D) square lattice and a site-diluted 2D square lattice at the percolation threshold. In the 2D case we obtain z =2.001 (5 ) , which is consistent with the known value z =2 , while for the site-diluted lattice we find z =3.90 (1 ) or z =2.056 (8 ) Df , where Df=91 /48 is the fractal dimensionality of the percolating system. This is an improvement on previous estimates of z ≈3.7 . The scaling results also show a fundamental difference between the two cases; for the 2D square lattice, the data can be collapsed onto a common scaling function even when 〈ms〉 is relatively large, reflecting the Anderson tower of quantum rotor states with a common dynamic exponent z =2 . For the diluted 2D square lattice, the scaling works well only for
Monte carlo simulation study of the square lattice S=1/2 quantum heisenberg antiferromagnet
Kim, J K
1999-01-01
For the two dimensional S= 1/2 isotopic quantum Heisenberg antiferromagnet on a square lattice, we report our results of an extensive quantum Monte Carlo simulation for various physical observables such as the correlation length xi, the staggered magnetic susceptibility chi sub S sub T , the structure factor peak value S(Q), the internal energy epsilon, and the uniform susceptibility chi sub u. We find that chi sub S sub T approx chi sup 2 T and S(Q) approx xi sup 2 T sup 2 , in agreement with the predictions of the conventional theory but in disagreement with recent experiments. Our estimate of the spin stiffness constant rho sub s and spin wave velocity c, from the low temperature behavior of the chi sub u is shown to be consistent with the theoretical prediction of the low temperature behavior of the epsilon, and of the xi provided an additional correction up to T sup 2. However, our data are definitely inconsistent with the scenario of the crossover for the xi.
Spin-S kagome quantum antiferromagnets in a field with tensor networks
Picot, Thibaut; Ziegler, Marc; Orús, Román; Poilblanc, Didier
2016-02-01
Spin-S Heisenberg quantum antiferromagnets on the kagome lattice offer, when placed in a magnetic field, a fantastic playground to observe exotic phases of matter with (magnetic analogs of) superfluid, charge, bond, or nematic orders, or a coexistence of several of the latter. In this context, we have obtained the (zero-temperature) phase diagrams up to S =2 directly in the thermodynamic limit owing to infinite projected entangled pair states, a tensor network numerical tool. We find incompressible phases characterized by a magnetization plateau versus field and stabilized by spontaneous breaking of point group or lattice translation symmetry(ies). The nature of such phases may be semiclassical, as the plateaus at the 1/3th ,(1-2/9S)th, and (1-1/9S)th of the saturated magnetization (the latter followed by a macroscopic magnetization jump), or fully quantum as the spin-1/2 1/9 plateau exhibiting a coexistence of charge and bond orders. Upon restoration of the spin rotation U (1 ) symmetry, a finite compressibility appears, although lattice symmetry breaking persists. For integer spin values we also identify spin gapped phases at low enough fields, such as the S =2 (topologically trivial) spin liquid with no symmetry breaking, neither spin nor lattice.
Volume-wise destruction of the antiferromagnetic Mott insulating state through quantum tuning
Frandsen, Benjamin A.; Liu, Lian; Cheung, Sky C.; Guguchia, Zurab; Khasanov, Rustem; Morenzoni, Elvezio; Munsie, Timothy J. S.; Hallas, Alannah M.; Wilson, Murray N.; Cai, Yipeng; Luke, Graeme M.; Chen, Bijuan; Li, Wenmin; Jin, Changqing; Ding, Cui; Guo, Shengli; Ning, Fanlong; Ito, Takashi U.; Higemoto, Wataru; Billinge, Simon J. L.; Sakamoto, Shoya; Fujimori, Atsushi; Murakami, Taito; Kageyama, Hiroshi; Alonso, Jose Antonio; Kotliar, Gabriel; Imada, Masatoshi; Uemura, Yasutomo J.
2016-08-01
RENiO3 (RE=rare-earth element) and V2O3 are archetypal Mott insulator systems. When tuned by chemical substitution (RENiO3) or pressure (V2O3), they exhibit a quantum phase transition (QPT) between an antiferromagnetic Mott insulating state and a paramagnetic metallic state. Because novel physics often appears near a Mott QPT, the details of this transition, such as whether it is first or second order, are important. Here, we demonstrate through muon spin relaxation/rotation (μSR) experiments that the QPT in RENiO3 and V2O3 is first order: the magnetically ordered volume fraction decreases to zero at the QPT, resulting in a broad region of intrinsic phase separation, while the ordered magnetic moment retains its full value until it is suddenly destroyed at the QPT. These findings bring to light a surprising universality of the pressure-driven Mott transition, revealing the importance of phase separation and calling for further investigation into the nature of quantum fluctuations underlying the transition.
Hong, Tao; Qiu, Y; Matsumoto, M; Tennant, D A; Coester, K; Schmidt, K P; Awwadi, F F; Turnbull, M M; Agrawal, H; Chernyshev, A L
2017-05-05
The notion of a quasiparticle, such as a phonon, a roton or a magnon, is used in modern condensed matter physics to describe an elementary collective excitation. The intrinsic zero-temperature magnon damping in quantum spin systems can be driven by the interaction of the one-magnon states and multi-magnon continuum. However, detailed experimental studies on this quantum many-body effect induced by an applied magnetic field are rare. Here we present a high-resolution neutron scattering study in high fields on an S=1/2 antiferromagnet C9H18N2CuBr4. Compared with the non-interacting linear spin-wave theory, our results demonstrate a variety of phenomena including field-induced renormalization of one-magnon dispersion, spontaneous magnon decay observed via intrinsic linewidth broadening, unusual non-Lorentzian two-peak structure in the excitation spectra and a dramatic shift of spectral weight from one-magnon state to the two-magnon continuum.
Phase diagram of the Kondo-Heisenberg model on honeycomb lattice with geometrical frustration
Li, Huan; Song, Hai-Feng; Liu, Yu
2016-11-01
We calculated the phase diagram of the Kondo-Heisenberg model on a two-dimensional honeycomb lattice with both nearest-neighbor and next-nearest-neighbor antiferromagnetic spin exchanges, to investigate the interplay between RKKY and Kondo interactions in the presence of magnetic frustration. Within a mean-field decoupling technology in slave-fermion representation, we derived the zero-temperature phase diagram as a function of Kondo coupling J k and frustration strength Q. The geometrical frustration can destroy the magnetic order, driving the original antiferromagnetic (AF) phase to non-magnetic valence bond solids (VBS). In addition, we found two distinct VBS. As J k is increased, a phase transition from AF to Kondo paramagnetic (KP) phase occurs, without the intermediate phase coexisting AF order with Kondo screening found in square lattice systems. In the KP phase, the enhancement of frustration weakens the Kondo screening effect, resulting in a phase transition from KP to VBS. We also found a process to recover the AF order from VBS by increasing J k in a wide range of frustration strength. Our work may provide predictions for future experimental observation of new processes of quantum phase transitions in frustrated heavy-fermion compounds.
Wheeler, E M; Coldea, R.; Wawrzynska, E.; Sorgel, T.; Jansen, M; Koza, M. M.; Taylor, J; Adroguer, P.; Shannon, N.
2009-01-01
We report inelastic neutron scattering measurements of the spin dynamics in the layered hexagonal magnet 2H-AgNiO2 which has stacked triangular layers of antiferromagnetically-coupled Ni2+ spins (S=1) ordered in a collinear alternating stripe pattern. We observe a broad band of magnetic excitations above a small gap of 1.8 meV and extending up to 7.5 meV, indicating strongly dispersive excitations. The measured dispersions of the boundaries of the powder-averaged spectrum can be quantitativel...
Towards photonic quantum simulation of ground states of frustrated Heisenberg spin systems.
Ma, Xiao-song; Dakić, Borivoje; Kropatschek, Sebastian; Naylor, William; Chan, Yang-hao; Gong, Zhe-xuan; Duan, Lu-ming; Zeilinger, Anton; Walther, Philip
2014-01-07
Photonic quantum simulators are promising candidates for providing insight into other small- to medium-sized quantum systems. Recent experiments have shown that photonic quantum systems have the advantage to exploit quantum interference for the quantum simulation of the ground state of Heisenberg spin systems. Here we experimentally characterize this quantum interference at a tuneable beam splitter and further investigate the measurement-induced interactions of a simulated four-spin system by comparing the entanglement dynamics using pairwise concurrence. We also study theoretically a four-site square lattice with next-nearest neighbor interactions and a six-site checkerboard lattice, which might be in reach of current technology.
DEFF Research Database (Denmark)
Kenzelmann, M.; Cowley, R.A.; Buyers, W.J.L.
2002-01-01
is in agreement with quantum Monte Carlo calculations for the spin-1 chain. xi is also consistent with the single mode approximation, suggesting that the excitations are short-lived single particle excitations. Below T=12 K where three-dimensional spin correlations are important, xi is shorter than predicted......We have mapped from the quantum to the classical limit the spin excitation spectrum of the antiferromagnetic spin-1 Heisenberg chain system CsNiCl3 in its paramagnetic phase from T=5 to 200 K. Neutron scattering shows that the excitations are resonant and dispersive up to at least T=70 Ksimilar...
Essler, F H L; Its, A R; Korepin, V E; Essler, Fabian H L; Frahm, Holger; Its, Alexander R; Korepin, Vladimir E
1996-01-01
We consider quantum correlation functions of the antiferromagnetic spin-\\frac{1}{2} Heisenberg XXZ spin chain in a magnetic field. We show that for a magnetic field close to the critical field h_c (for the critical magnetic field the ground state is ferromagnetic) certain correlation functions can be expressed in terms of the solution of the Painlev\\'e V transcendent. This establishes a relation between solutions of Painlev\\'e differential equations and quantum correlation functions in models of {\\sl interacting} fermions. Painlev\\'e transcendents were known to describe correlation functions in models with free fermionic spectra.
Topological Many-Body States in Quantum Antiferromagnets via Fuzzy Super-Geometry
Hasebe, Kazuki
2013-01-01
Recent vigorous investigations of topological order have not only discovered new topological states of matter but also shed new light to "already known" topological states. One established example with topological order is the valence bond solid (VBS) states in quantum antiferromagnets. The VBS states are disordered spin liquids with no spontaneous symmetry breaking but most typically manifest topological order known as hidden string order on 1D chain. Interestingly, the VBS models are based on mathematics analogous to fuzzy geometry. We review applications of the mathematics of fuzzy super-geometry in the construction of supersymmetric versions of VBS (SVBS) states, and give a pedagogical introduction of SVBS models and their properties [arXiv:0809.4885, 1105.3529, 1210.0299]. As concrete examples, we present detail analysis of supersymmetric versions of SU(2) and SO(5) VBS states, i.e. UOSp(N|2) and UOSp(N|4) SVBS states whose mathematics are closely related to fuzzy two- and four-superspheres. The SVBS sta...
Quantum simulating the frustrated Heisenberg model in a molecular dipolar crystal
Energy Technology Data Exchange (ETDEWEB)
Zhou, Yan-Li, E-mail: ylzhou@nudt.edu.cn [College of Science, National University of Defense Technology, 410073 Changsha (China); Ou, Bao-Quan [College of Science, National University of Defense Technology, 410073 Changsha (China); Wu, Wei [College of Science, National University of Defense Technology, 410073 Changsha (China); State Key Laboratory of High Performance Computing, National University of Defense Technology, 410073 Changsha (China)
2015-10-23
We study the simulation of spin models with polar molecules in a dipolar crystal. We employ a master equation approach to describe the dynamics of the system and to research the dissipation of the model. The reduced dynamics of the polar molecules lead to frustrated Heisenberg models with tuneable long-range interactions, via spin-dependent dipole–dipole interactions forces to the lattice vibrations. The influence of the lattice vibrations is calculated and analyzed in detail. - Highlights: • We simulate spin models with polar molecules in a dipolar crystal. • We employ a master equation to describe the dynamics of the system. • The influence of the lattice vibrations is calculated.
Magnetic phase diagrams of classical triangular and kagome antiferromagnets
Energy Technology Data Exchange (ETDEWEB)
Gvozdikova, M V [Department of Physics, Kharkov National University, 61077 Kharkov (Ukraine); Melchy, P-E; Zhitomirsky, M E, E-mail: mike.zhitomirsky@cea.fr [Service de Physique Statistique, Magnetisme et Supraconductivite, UMR-E9001 CEA-INAC/UJF, 17 rue des Martyrs, 38054 Grenoble (France)
2011-04-27
We investigate the effect of geometrical frustration on the H-T phase diagrams of the classical Heisenberg antiferromagnets on triangular and kagome lattices. The phase diagrams for the two models are obtained from large-scale Monte Carlo simulations. For the kagome antiferromagnet, thermal fluctuations are unable to lift degeneracy completely and stabilize translationally disordered multipolar phases. We find a substantial difference in the temperature scales of the order by disorder effect related to different degeneracy of the low- and the high-field classical ground states in the kagome antiferromagnet. In the low-field regime, the Kosterlitz-Thouless transition into a spin-nematic phase is produced by unbinding of half-quantum vortices.
Magnetic phase diagrams of classical triangular and kagome antiferromagnets.
Gvozdikova, M V; Melchy, P-E; Zhitomirsky, M E
2011-04-27
We investigate the effect of geometrical frustration on the H-T phase diagrams of the classical Heisenberg antiferromagnets on triangular and kagome lattices. The phase diagrams for the two models are obtained from large-scale Monte Carlo simulations. For the kagome antiferromagnet, thermal fluctuations are unable to lift degeneracy completely and stabilize translationally disordered multipolar phases. We find a substantial difference in the temperature scales of the order by disorder effect related to different degeneracy of the low- and the high-field classical ground states in the kagome antiferromagnet. In the low-field regime, the Kosterlitz-Thouless transition into a spin-nematic phase is produced by unbinding of half-quantum vortices.
Approximate eigenvalue determination of geometrically frustrated magnetic molecules
Directory of Open Access Journals (Sweden)
A.M. Läuchli
2009-01-01
Full Text Available Geometrically frustrated magnetic molecules have attracted a lot of interest in the field of molecular magnetism as well as frustrated Heisenberg antiferromagnets. In this article we demonstrate how an approximate diagonalization scheme can be used in order to obtain thermodynamic and spectroscopic information about frustrated magnetic molecules. To this end we theoretically investigate an antiferromagnetically coupled spin system with cuboctahedral structure modeled by an isotropic Heisenberg Hamiltonian.
Li, Zixiang; Yao, Hong; Wang, Fa; Lee, Dung-Hai
Superconductivity is an emergent phenomena in the sense that the energy scale at which Cooper pairs form is generically much lower than the bare energy scale, namely the electron kinetic energy bandwidth. Addressing the mechanism of Cooper pairing amounts to finding out the effective interaction (or the renormalized interaction) that operates at the low energies. Finding such interaction from the bare microscopic Hamiltonian has not been possible for strong correlated superconductors such as the copper-oxide high temperature superconductor. In fact even one is given the effective interaction, determining its implied electronic instabilities without making any approximation has been a formidable task. Here, we perform sign-free quantum Monte-Carlo simulations to study the antiferromagnetic, superconducting, and the charge density wave instabilities which are ubiquitous in both electron and hole doped cuprates. Our result suggests only after including both the nematic and antiferromagnetic fluctuation, are the observed properties associated with these instabilities reproduced by the theory.
Disordered ground states in a quantum frustrated spin chain with side chains
Takano, Ken'Ichi; Hida, Kazuo
2008-04-01
We study a frustrated mixed spin chain with side chains, where the spin species and the exchange interactions are spatially varied. A nonlinear σ model method is formulated for this model, and a phase diagram with two disordered spin-gap phases is obtained for typical cases. Among them, we examine the case with a main chain, which consists of an alternating array of spin-1 and spin- (1)/(2) sites, and side chains, each of which consists of a single spin- (1)/(2) site, in great detail. Based on numerical, perturbational, and variational approaches, we propose a singlet cluster solid picture for each phase, where the ground state is expressed as a tensor product of local singlet states.
Topological Many-Body States in Quantum Antiferromagnets via Fuzzy Supergeometry
Directory of Open Access Journals (Sweden)
Keisuke Totsuka
2013-04-01
Full Text Available Recent vigorous investigations of topological order have not only discovered new topological states of matter, but also shed new light on “already known” topological states. One established example with topological order is the valence bond solid (VBS states in quantum antiferromagnets. The VBS states are disordered spin liquids with no spontaneous symmetry breaking, but most typically manifest a topological order known as a hidden string order on the 1D chain. Interestingly, the VBS models are based on mathematics analogous to fuzzy geometry. We review applications of the mathematics of fuzzy supergeometry in the construction of supersymmetric versions of VBS (SVBS states and give a pedagogical introduction of SVBS models and their properties. As concrete examples, we present detailed analysis of supersymmetric versions of SU(2 and SO(5 VBS states, i.e., UOSp(N|2 and UOSp(N|4 SVBS states, whose mathematics are closely related to fuzzy two- and four-superspheres. The SVBS states are physically interpreted as hole-doped VBS states with a superconducting property that interpolates various VBS states, depending on the value of a hole-doping parameter. The parent Hamiltonians for SVBS states are explicitly constructed, and their gapped excitations are derived within the single-mode approximation on 1D SVBS chains. Prominent features of the SVBS chains are discussed in detail, such as a generalized string order parameter and entanglement spectra. It is realized that the entanglement spectra are at least doubly degenerate, regardless of the parity of bulk (superspins. The stability of the topological phase with supersymmetry is discussed, with emphasis on its relation to particular edge (superspin states.
Sereni, J. G.; Giovannini, M.; Gómez Berisso, M.; Gastaldo, F.
2016-11-01
Low temperature thermal and magnetic measurements performed on ferro-magneticl (FM) alloys of composition Ce2.15(Pd1-x Ag x )1.95In0.9 are presented. Pd substitution by Ag depresses {{T}\\text{C}}(x) from 4.1 K down to 1.1 K for x = 0.5, which is related to the increase of band electrons, with a critical concentration extrapolated to {{x}\\text{cr}}≈ 0.6 . The {{T}\\text{C}}(x) decrease is accompanied by a weakening of the magnetization of the FM phase. At high temperature (T > 30 K) the inverse magnetic susceptibility reveals the presence of robust magnetic moments (2.56≥slant ~{μ\\text{eff}}≥slant 2.4 {μ\\text{B}} ), whereas the low value of the Curie-Weiss temperature {θP}≈ -10 K excludes any relevant effect from Kondo screening. The specific heat jump at {{T}\\text{C}}(x) decreases accordingly, while an anomaly emerges at a fixed temperature {{T}\\ast}≈ 1 K. This unexpected anomaly does not show any associated sign of magnetism checked by AC-susceptibility measurements. Since the total magnetic entropy (evaluated around T={{T}\\text{C}}(x=0) ) practically does not change with Ag concentration, the transference of degrees of freedom from the FM component to the non-magnetic T * anomaly is deduced. The origin of this anomaly is attributed to an arising magnetic frustration of the ground state and the consequent entropy bottleneck produced by the divergent increasing of density of excitations at low temperature.
Quantum Spin Liquid in Frustrated One-Dimensional LiCuSbO4
DEFF Research Database (Denmark)
Dutton, S. E.; Kumar, M.; Mourigal, M.;
2012-01-01
A quantum magnet, LiCuSbO4, with chains of edge-sharing spin-1/2CuO6 octahedra is reported. While short-range order is observed for T2 K data.......A quantum magnet, LiCuSbO4, with chains of edge-sharing spin-1/2CuO6 octahedra is reported. While short-range order is observed for T2 K data....
Sarkar, Subhajit; Chaudhury, Ranjan; Paul, Samir K.
2017-01-01
The available results from the inelastic neutron scattering experiment performed on the quasi-two dimensional spin 1/2 anti-ferromagnetic material La2CuO4 have been analysed theoretically. The formalism of ours is based on a semi-classical like treatment involving a model of an ideal gas of mobile vortices and anti-vortices built on the background of the Néel state, using the bipartite classical spin configuration corresponding to an XY-anisotropic Heisenberg anti-ferromagnet on a square lattice. The results for the integrated intensities for our spin 1/2 model corresponding to different temperatures, show occurrence of vigorous unphysical oscillations, when convoluted with a realistic spectral window function. These results indicate failure of the conventional semi-classical theoretical model of ideal vortex/anti-vortex gas arising in the Berezinskii-Kosterlitz-Thouless theory for the low spin magnetic systems. A full fledged quantum mechanical formalism and calculations seem crucial for the understanding of topological excitations in such low spin systems. Furthermore, a severe disagreement is found to occur at finite values of energy transfer between the integrated intensities obtained theoretically from the conventional formalism and those obtained experimentally. This further suggests strongly that the full quantum treatment should also incorporate the interaction between the fragile-magnons and the topological excitations. This is quite plausible in view of the recent work establishing such a process in XXZ quantum ferromagnet on 2D lattice. The high spin XXZ quasi-two dimensional antiferromagnet like MnPS3 however follows the conventional theory quite well.
Intertwined nematic orders in a frustrated ferromagnet
Iqbal, Yasir; Ghosh, Pratyay; Narayanan, Rajesh; Kumar, Brijesh; Reuther, Johannes; Thomale, Ronny
2016-12-01
We investigate the quantum phases of the frustrated spin-1/2 J1-J2-J3 Heisenberg model on the square lattice with ferromagnetic J1 and antiferromagnetic J2 and J3 interactions. Using the pseudofermion functional renormalization group technique, we find an intermediate paramagnetic phase located between classically ordered ferromagnetic, stripy antiferromagnetic, and incommensurate spiral phases. We observe that quantum fluctuations lead to significant shifts of the spiral pitch angles compared to the classical limit. By computing the response of the system with respect to various spin rotation and lattice symmetry-breaking perturbations, we identify a complex interplay between different nematic spin states in the paramagnetic phase. While retaining time-reversal invariance, these phases either break spin-rotation symmetry, lattice-rotation symmetry, or a combination of both. We therefore propose the J1-J2-J3 Heisenberg model on the square lattice as a paradigmatic example where different intimately connected types of nematic orders emerge in the same model.
Dynamics of disordered and frustrated magnets
Woo, Na Yoon
Gd3Ga5O12 (GGG) is an insulating Heisenberg antiferromagnet. It is highly frustrated owing to its garnet structure, which is composed of elementary triangles with dominant antiferromagnetic interactions. We studied the effect of disorder in this geometrically frustrated system by changing the level of disorder in GGG:Ndx with x ranging from 0 to 1%. We measured the AC magnetic susceptibility in both the linear and nonlinear regimes and characterized the low temperature phases. As a result, we observed signatures of short range order in the 0% and 0.1% crystals, but not in the 1% sample, indicating that the order is suppressed in the 1% sample because of increasing frustration. The Nd doping compensates for the Gd-Ga off stoichiometry and pushes the system to a more perfectly frustrated state. We used the non-linear response to characterize the evolution of isolated spin clusters as a function of x. The Nd doping effectively relieves the net disorder. Hence the sample with the highest doping presents the smallest net correlated moments and the smallest onset field to activate the clusters from the background spin bath. The second project we report addresses the nonequilibrium dynamics of two related spin glasses. The model systems are the Ising magnets LiHo xY1--xF4 with x = 0.167 and 0.198. Although both systems undergo spin glass transitions, the mechanism that drives the phase transition is known to be different. The diluted sample is more affected by entanglement and in the concentrated system, the random field plays a more important role. In this thesis, we performed preliminary thermal and quantum aging experiments to compare the two systems. In the classical aging measurement, with temperature as the pertinent variable, the decay is exponential and measures primarily the response of the lattice. However quantum aging measurements using transverse field probe the spin relaxation character. The x = 0.167 and 0.198 crystals decay in opposite directions
PREFACE: Geometrically frustrated magnetism Geometrically frustrated magnetism
Gardner, Jason S.
2011-04-01
Frustrated magnetism is an exciting and diverse field in condensed matter physics that has grown tremendously over the past 20 years. This special issue aims to capture some of that excitement in the field of geometrically frustrated magnets and is inspired by the 2010 Highly Frustrated Magnetism (HFM 2010) meeting in Baltimore, MD, USA. Geometric frustration is a broad phenomenon that results from an intrinsic incompatibility between some fundamental interactions and the underlying lattice geometry based on triangles and tetrahedra. Most studies have centred around the kagomé and pyrochlore based magnets but recent work has looked at other structures including the delafossite, langasites, hyper-kagomé, garnets and Laves phase materials to name a few. Personally, I hope this issue serves as a great reference to scientist both new and old to this field, and that we all continue to have fun in this very frustrated playground. Finally, I want to thank the HFM 2010 organizers and all the sponsors whose contributions were an essential part of the success of the meeting in Baltimore. Geometrically frustrated magnetism contents Spangolite: an s = 1/2 maple leaf lattice antiferromagnet? T Fennell, J O Piatek, R A Stephenson, G J Nilsen and H M Rønnow Two-dimensional magnetism and spin-size effect in the S = 1 triangular antiferromagnet NiGa2S4 Yusuke Nambu and Satoru Nakatsuji Short range ordering in the modified honeycomb lattice compound SrHo2O4 S Ghosh, H D Zhou, L Balicas, S Hill, J S Gardner, Y Qi and C R Wiebe Heavy fermion compounds on the geometrically frustrated Shastry-Sutherland lattice M S Kim and M C Aronson A neutron polarization analysis study of moment correlations in (Dy0.4Y0.6)T2 (T = Mn, Al) J R Stewart, J M Hillier, P Manuel and R Cywinski Elemental analysis and magnetism of hydronium jarosites—model kagome antiferromagnets and topological spin glasses A S Wills and W G Bisson The Herbertsmithite Hamiltonian: μSR measurements on single crystals
Energy Technology Data Exchange (ETDEWEB)
Yamasaki, Hisatsugu [Department of Applied Physics, Osaka City University, Osaka 558-8585 (Japan); Natsume, Yuhei [Graduate School of Science and Technology, Chiba University, Chiba 263-8522 (Japan); Terai, Akira [Department of Applied Physics, Osaka City University, Osaka 558-8585 (Japan); Nakamura, Katsuhiro [Department of Applied Physics, Osaka City University, Osaka 558-8585 (Japan)
2004-09-01
We investigate the frustrated quantum three-spin model (S{sub 1},S{sub 2},S{sub 3}) of spin = 1/2 on a triangle, in which spins are coupled with lattice-vibrational modes through the antiferromagnetic exchange interaction depending on distances between spin sites. The present model corresponds to the dynamic Jahn-Teller system E{sub g} - e{sub g} proposed by Longuet-Higgins et al (1958 Proc. R. Soc. A 244 1). This correspondence is revealed by using the transformation to Nakamura-Bishop's bases used in Phys. Rev. Lett. 54 861 (1985). Furthermore, we elucidate the relationship between a chiral order parameter {chi}-circumflex = S{sub 1}{center_dot}(S{sub 2}xS{sub 3}) in the spin system and the electronic orbital angular momentum l-circumflex{sub z} in E{sub g} - e{sub g} vibronic model: the regular oscillatory behaviour of the expectation value <{chi}-circumflex> with increasing energy can be found as in the case of
DEFF Research Database (Denmark)
Gammelmark, Søren; Eckardt, André
2013-01-01
We theoretically study the adiabatic preparation of an antiferromagnetic phase in a mixed Mott insulator of two bosonic atom species in a one-dimensional optical lattice. In such a system one can engineer a tunable parabolic inhomogeneity by controlling the difference of the trapping potentials...... felt by the two species. Using numerical simulations we predict that a finite parabolic potential can assist the adiabatic preparation of the antiferromagnet. The optimal strength of the parabolic inhomogeneity depends sensitively on the number imbalance between the two species. We also find...
Masuda, Hidetoshi; Sakai, Hideaki; Tokunaga, Masashi; Yamasaki, Yuichi; Miyake, Atsushi; Shiogai, Junichi; Nakamura, Shintaro; Awaji, Satoshi; Tsukazaki, Atsushi; Nakao, Hironori; Murakami, Youichi; Arima, Taka-hisa; Tokura, Yoshinori; Ishiwata, Shintaro
2016-01-01
For the innovation of spintronic technologies, Dirac materials, in which low-energy excitation is described as relativistic Dirac fermions, are one of the most promising systems because of the fascinating magnetotransport associated with extremely high mobility. To incorporate Dirac fermions into spintronic applications, their quantum transport phenomena are desired to be manipulated to a large extent by magnetic order in a solid. We report a bulk half-integer quantum Hall effect in a layered antiferromagnet EuMnBi2, in which field-controllable Eu magnetic order significantly suppresses the interlayer coupling between the Bi layers with Dirac fermions. In addition to the high mobility of more than 10,000 cm(2)/V s, Landau level splittings presumably due to the lifting of spin and valley degeneracy are noticeable even in a bulk magnet. These results will pave a route to the engineering of magnetically functionalized Dirac materials.
Thompson, J. D.; McClarty, P. A.; Prabhakaran, D.; Cabrera, I.; Guidi, T.; Coldea, R.
2017-08-01
The frustrated pyrochlore magnet Yb2 Ti2 O7 has the remarkable property that it orders magnetically but has no propagating magnons over wide regions of the Brillouin zone. Here we use inelastic neutron scattering to follow how the spectrum evolves in cubic-axis magnetic fields. At high fields we observe, in addition to dispersive magnons, a two-magnon continuum, which grows in intensity upon reducing the field and overlaps with the one-magnon states at intermediate fields leading to strong renormalization of the dispersion relations, and magnon decays. Using heat capacity measurements we find that the low- and high-field regions are smoothly connected with no sharp phase transition, with the spin gap increasing monotonically in field. Through fits to an extensive data set of dispersion relations combined with magnetization measurements, we reevaluate the spin Hamiltonian, finding dominant quantum exchange terms, which we propose are responsible for the anomalously strong fluctuations and quasiparticle breakdown effects observed at low fields.
Lorenzana, J.; Sawatzky, G.A
1995-01-01
We calculate the effective charge for multimagnon infrared absorption assisted by phonons in a perovskitelike antiferromagnet and we compute the spectra for two-magnon absorption using interacting spin-wave theory. The full set of equations for the interacting two-magnon problem is presented in the
Understanding and controlling complex states arising from magnetic frustration
Energy Technology Data Exchange (ETDEWEB)
Zapf, Vivien [Los Alamos National Laboratory
2012-06-01
Much of our national security relies on capabilities made possible by magnetism, in particular the ability to compute and store huge bodies of information as well as to move things and sense the world. Most of these technologies exploit ferromagnetism, i.e. the global parallel alignment of magnetic spins as seen in a bar magnet. Recent advances in computing technologies, such as spintronics and MRAM, take advantage of antiferromagnetism where the magnetic spins alternate from one to the next. In certain crystal structures, however, the spins take on even more complex arrangements. These are often created by frustration, where the interactions between spins cannot be satisfied locally or globally within the material resulting in complex and often non-coplanar spin textures. Frustration also leads to the close proximity of many different magnetic states, which can be selected by small perturbations in parameters like magnetic fields, temperature and pressure. It is this tunability that makes frustrated systems fundamentally interesting and highly desirable for applications. We move beyond frustration in insulators to itinerant systems where the interaction between mobile electrons and the non-coplanar magnetic states lead to quantum magneto-electric amplification. Here a small external field is amplified by many orders of magnitude by non-coplanar frustrated states. This greatly enhances their sensitivity and opens broader fields for applications. Our objective is to pioneer a new direction for condensed matter science at the Laboratory as well as for international community by discovering, understanding and controlling states that emerge from the coupling of itinerant charges to frustrated spin textures.
Frustrated Magnetism in Low-Dimensional Lattices
Tovar, Mayra
2011-12-01
In this dissertation we present the results of a theoretical investigation of spin models on two-dimensional and quasi one-dimensional lattices, all unified under the concept of quantum frustrated antiferromagnetism, and all discussing various aspects of the antiferromagnetic Heisenberg model on the kagome lattice. In the Introduction (Chapter 1), we discuss at some length such concepts as frustration and superexchange, among others, which are of common relevance in the rest of the chapters. In Chapter 2, we study the effect of Dzyaloshinskii-Moriya (DM) interactions on the zero-temperature magnetic susceptibility of systems whose low energy can be described by short-range valence bond states. Our work shows that this treatment is consistent with the experimentally observed non-vanishing susceptibility---in the specified temperature limit---of the spin-1/2 kagome antiferromagnetic compound ZnCu3(OH)6Cl2, also known as herbertsmithite. Although the objective of this work is explaining the aforementioned characteristic of the experimental system, our methods are more general and we apply them to the checkerboard and Shastry-Sutherland lattices as well. In Chapter 3, we discuss our findings in the study of ghost-mediated domain wall interactions in the diamondback ladder. These domain walls are the the spin excitations---the kinks and the antikinks---separating the ground states along one chain of the ladder. While as individual entities an antikink is energy costly and a kink energy free, our study finds that both interact via the ghosts that they produce in the opposite side of the ladder from where they are located. Through the study of these ghosts, we find that domain walls proliferate in the system above a critical value of the system's coupling constants. It is this proliferation that makes their treatment as free, non-interacting particles impossible, so we study here their interactions both quantitatively and qualitatively, in a region where the latter are
Phase Diagram of the Frustrated Hubbard Model
Zitzler, R.; Tong, N.-H.; Pruschke, Th.; Bulla, R.
2004-07-01
The Mott-Hubbard metal-insulator transition in the paramagnetic phase of the one-band Hubbard model has long been used to describe similar features in real materials like V2O3. In this Letter we investigate the antiferromagnetic phase of this model with frustration. At T=0 we find a first-order transition from a paramagnetic metal to an antiferromagnetic insulator. We show that even in the presence of strong magnetic frustration, the paramagnetic metal-insulator transition is hidden inside an extended antiferromagnetic region. This raises the question of whether the one-band Hubbard model with frustration is sufficient to describe the phase diagram of V2O3 or similar transition metal oxides even qualitatively.
Directory of Open Access Journals (Sweden)
G. Palma
2015-06-01
Full Text Available Motivated by the numerical simulation of systems which display quantum phase transitions, we present a novel application of the meron-cluster algorithm to simulate the quantum antiferromagnetic Heisenberg model coupled to an external uniform magnetic field both in one and in two dimensions. In the infinite volume limit and at zero temperature we found numerical evidence that supports a quantum phase transition very close to the critical values B_c=2 and B_c = 4 for the system in one and two dimensions, respectively. For the one dimensional system, we have compared the numerical data obtained with analytical predictions for the magnetization density as a function of the external field obtained by scaling-behaviour analysis and Bethe Ansatz techniques. Since there is no analytical solution for the two dimensional case, we have compared our results with the magnetization density obtained by scaling relations for small lattice sizes and with the approximated thermodynamical limit at zero temperature guessed by scaling relations. Moreover, we have compared the numerical data with other numerical simulations performed by using different algorithms in one and two dimensions, like the directed loop method. The numerical data obtained are in perfect agreement with all these previous results, which confirms that the meron-algorithm is reliable for quantum Monte Carlo simulations and applicable both in one and two dimensions. Finally, we have computed the integrated autocorrelation time to measure the efficiency of the meron algorithm in one dimension.
Large-N theory of the Sp(N) Heisenberg quantum antiferromagnet on an anisotropic triangular lattice
Chung, Chung-Hou; Marston, Brad
2000-03-01
The magnetic properties of the two-dimensional layered organic superconductors κ-(BEDT-TTF)_2X are modeled by a spin-1/2 Heisenberg quantum antiferromagnet on an anisotropic triangular lattice. The phase diagram is ascertained by means of a large-N expansion of the Sp(N) generalization of the physical SU(2) \\cong Sp(1) Heisenberg magnet.(S. Sachdev and N. Reed, Int. J. Mod. Phys. B5), 219 (1991). The phase diagram is presented in the two-dimensional parameter space of J_1/J_2, the ratio of the nearest to next-nearest neighbor Heisenberg exchange, and the ratio nb / N, which sets the strength of the quantum fluctuations. At large nb / N (equivalent to the large-spin limit of the physical SU(2) model) quantum effects are small, the ground states break global Sp(N) spin-rotational symmetry, and exhibit magnetic long-range-order (LRO). At small nb / N, however, quantum fluctuations overwhelm the tendency to order and there is only short-range magnetic order (SRO). The LRO and SRO phases can be further classified into two types depending on the size of the anisotropy: (i) ground states with commensurate, collinear, spin correlations; and (ii) ground states with incommensurate, coplanar, spin correlations. Finite-N corrections due to a Berry's phase term modify the character of the SRO phases, leading in the case of the commensurate state to spin-Peierls order and the confinement of spinons.
Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi2-δAs2.
Luo, Yongkang; Ronning, F; Wakeham, N; Lu, Xin; Park, Tuson; Xu, Z-A; Thompson, J D
2015-11-03
The easily tuned balance among competing interactions in Kondo-lattice metals allows access to a zero-temperature, continuous transition between magnetically ordered and disordered phases, a quantum-critical point (QCP). Indeed, these highly correlated electron materials are prototypes for discovering and exploring quantum-critical states. Theoretical models proposed to account for the strange thermodynamic and electrical transport properties that emerge around the QCP of a Kondo lattice assume the presence of an indefinitely large number of itinerant charge carriers. Here, we report a systematic transport and thermodynamic investigation of the Kondo-lattice system CeNi2-δAs2 (δ ≈ 0.28) as its antiferromagnetic order is tuned by pressure and magnetic field to zero-temperature boundaries. These experiments show that the very small but finite carrier density of ~0.032 E-/formular unit in CeNi2-δAs2 leads to unexpected transport signatures of quantum criticality and the delayed development of a fully coherent Kondo-lattice state with decreasing temperature. The small carrier density and associated semimetallicity of this Kondo-lattice material favor an unconventional, local-moment type of quantum criticality and raises the specter of the Nozières exhaustion idea that an insufficient number of conduction-electron spins to separately screen local moments requires collective Kondo screening.
Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi2−δAs2
Luo, Yongkang; Ronning, F.; Wakeham, N.; Lu, Xin; Park, Tuson; Xu, Z.-A.; Thompson, J. D.
2015-01-01
The easily tuned balance among competing interactions in Kondo-lattice metals allows access to a zero-temperature, continuous transition between magnetically ordered and disordered phases, a quantum-critical point (QCP). Indeed, these highly correlated electron materials are prototypes for discovering and exploring quantum-critical states. Theoretical models proposed to account for the strange thermodynamic and electrical transport properties that emerge around the QCP of a Kondo lattice assume the presence of an indefinitely large number of itinerant charge carriers. Here, we report a systematic transport and thermodynamic investigation of the Kondo-lattice system CeNi2−δAs2 (δ ≈ 0.28) as its antiferromagnetic order is tuned by pressure and magnetic field to zero-temperature boundaries. These experiments show that the very small but finite carrier density of ∼0.032 e−/formular unit in CeNi2−δAs2 leads to unexpected transport signatures of quantum criticality and the delayed development of a fully coherent Kondo-lattice state with decreasing temperature. The small carrier density and associated semimetallicity of this Kondo-lattice material favor an unconventional, local-moment type of quantum criticality and raises the specter of the Nozières exhaustion idea that an insufficient number of conduction-electron spins to separately screen local moments requires collective Kondo screening. PMID:26483465
DEFF Research Database (Denmark)
Enderle, M.; Kiefer, K.; Klopperpieper, A.;
2000-01-01
Uniform S = 1 and 1/2 Heisenberg antiferromagnetic chains have a quantum singlet ground state which is an eigenstate of the total spin with S(tot) = 0. However, the 'internal' order of these ground states is quite different, and is reflected in gapless excitations in the S = 1/2 state, while the S...
Antiferromagnetic spintronics.
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.
DEFF Research Database (Denmark)
Gammelmark, Søren; Eckardt, André
2013-01-01
We theoretically study the adiabatic preparation of an antiferromagnetic phase in a mixed Mott insulator of two bosonic atom species in a one-dimensional optical lattice. In such a system one can engineer a tunable parabolic inhomogeneity by controlling the difference of the trapping potentials f...... that during the preparation finite size effects will play a crucial role for a system of realistic size. The experiment that we propose can be realized, for example, using atomic mixtures of rubidium 87 with potassium 41, or ytterbium 168 with ytterbium 174....
Energy Technology Data Exchange (ETDEWEB)
Neto, Minos A., E-mail: minos@pq.cnpq.br [Departamento de Fisica, Universidade Federal do Amazonas, 3000, Japiim, Manaus, 69077-000 AM (Brazil); Roberto Viana, J., E-mail: vianafisica@bol.com.br [Departamento de Fisica, Universidade Federal do Amazonas, 3000, Japiim, Manaus, 69077-000 AM (Brazil); Ricardo de Sousa, J., E-mail: jsousa@edu.ufam.br [Departamento de Fisica, Universidade Federal do Amazonas, 3000, Japiim, Manaus, 69077-000 AM (Brazil); National Institute of Science and Technology for Complex Systems, 3000, Japiim, Manaus, 69077-000 AM (Brazil)
2012-08-15
In this work we study the critical behavior of the quantum spin-1/2 anisotropic Heisenberg antiferromagnet in the presence of a longitudinal field on a body centered cubic (bcc) lattice as a function of temperature, anisotropy parameter ({Delta}) and magnetic field (H), where {Delta}=0 and 1 correspond the isotropic Heisenberg and Ising models, respectively. We use the framework of the differential operator technique in the effective-field theory with finite cluster of N=4 spins (EFT-4). The staggered m{sub s}=(m{sub A}-m{sub B})/2 and total m=(m{sub A}+m{sub B})/2 magnetizations are numerically calculated, where in the limit of m{sub s}{yields}0 the critical line T{sub N}(H,{Delta}) is obtained. The phase diagram in the T-H plane is discussed as a function of the parameter {Delta} for all values of H Element-Of [0,H{sub c}({Delta})], where H{sub c}({Delta}) correspond the critical field (T{sub N}=0). Special focus is given in the low temperature region, where a reentrant behavior is observed around of H=H{sub c}({Delta}){>=}H{sub c}({Delta}=1)=8J in the Ising limit, results in accordance with Monte Carlo simulation, and also was observed for all values of {Delta} Element-Of [0,1]. This reentrant behavior increases with increase of the anisotropy parameter {Delta}. In the limit of low field, our results for the Heisenberg limit are compared with series expansion values. - Highlights: Black-Right-Pointing-Pointer In the lat decade there has been a great interest in the physics of the quantum phase transition in spins system. Black-Right-Pointing-Pointer Effective-field theory in cluster with N=4 spins is generalized to treat the quantum spin-1/2 Heisenberg model. Black-Right-Pointing-Pointer We have obtained phase diagram at finite temperature for the quantum spin-1/2 antiferromagnet Heisenberg model as a bcc lattice.
Strongly Coupled Systems: From Quantum Antiferromagnets To Unified Models For Superconductors
Chudnovsky, V
2002-01-01
I discuss the significance of the antiferromagnetic Heisenberg model (AFHM) in both high-energy and condensed-matter physics, and proceed to describe an efficient cluster algorithm used to simulate the AFHM. This is one of two algorithms with which my collaborators and I were able to obtain numerical results that definitively confirm that chiral perturbation theory, corrected for cutoff effects in the AFHM, leads to a correct field-theoretical description of the low- temperature behavior of the spin correlation length in various spin representations S. Using a finite-size-scaling technique, we explored correlation lengths of up to 105 lattice spacings for spins S = 1 and 5/2. We show how the recent prediction of cutoff effects by P. Hasenfratz is approached for moderate correlation lengths, and smoothly connects with other approaches to modeling the AFHM at smaller correlation lengths. I also simulate and discuss classical antiferromagnetic systems with simultaneous SO(M) and SO( N) symmetries, which have bee...
Strongly Coupled Systems From Quantum Antiferromagnets To Unified Models For Superconductors
Chudnovsky, V
2002-01-01
I discuss the significance of the antiferromagnetic Heisenberg model (AFHM) in both high-energy and condensed-matter physics, and proceed to describe an efficient cluster algorithm used to simulate the AFHM. This is one of two algorithms with which my collaborators and I were able to obtain numerical results that definitively confirm that chiral perturbation theory, corrected for cutoff effects in the AFHM, leads to a correct field-theoretical description of the low- temperature behavior of the spin correlation length in various spin representations S. Using a finite-size-scaling technique, we explored correlation lengths of up to 105 lattice spacings for spins S = 1 and 5/2. We show how the recent prediction of cutoff effects by P. Hasenfratz is approached for moderate correlation lengths, and smoothly connects with other approaches to modeling the AFHM at smaller correlation lengths. I also simulate and discuss classical antiferromagnetic systems with simultaneous SO(M) and SO( N) symmetries, which have bee...
Ghorbani, Elaheh; Shahbazi, Farhad; Mosadeq, Hamid
2016-10-12
Using the modified spin wave method, we study the [Formula: see text] Heisenberg model with first and second neighbor antiferromagnetic exchange interactions. For a symmetric S = 1/2 model, with the same couplings for all the equivalent neighbors, we find three phases in terms of the frustration parameter [Formula: see text]: (1) a commensurate collinear ordering with staggered magnetization (Néel.I state) for [Formula: see text], (2) a magnetically gapped disordered state for [Formula: see text], preserving all the symmetries of the Hamiltonian and lattice, which by definition is a quantum spin liquid (QSL) state and (3) a commensurate collinear ordering in which two out of the three nearest neighbor magnetizations are antiparallel and the remaining pair are parallel (Néel.II state), for [Formula: see text]. We also explore the phase diagram of a distorted [Formula: see text] model with S = 1/2. Distortion is introduced as an inequality of one nearest neighbor coupling with the other two. This yields a richer phase diagram by the appearance of a new gapped QSL, a gapless QSL and also a valence bond crystal phase in addition to the previous three phases found for the undistorted model.
Ghorbani, Elaheh; Shahbazi, Farhad; Mosadeq, Hamid
2016-10-01
Using the modified spin wave method, we study the {{J}1}-{{J}2} Heisenberg model with first and second neighbor antiferromagnetic exchange interactions. For a symmetric S = 1/2 model, with the same couplings for all the equivalent neighbors, we find three phases in terms of the frustration parameter \\barα={{J}2}/{{J}1} : (1) a commensurate collinear ordering with staggered magnetization (Néel.I state) for 0≤slant \\barα≲ 0.207 , (2) a magnetically gapped disordered state for 0.207≲ \\barα≲ 0.369 , preserving all the symmetries of the Hamiltonian and lattice, which by definition is a quantum spin liquid (QSL) state and (3) a commensurate collinear ordering in which two out of the three nearest neighbor magnetizations are antiparallel and the remaining pair are parallel (Néel.II state), for 0.396≲ \\barα≤slant 1 . We also explore the phase diagram of a distorted {{J}1}-{{J}2} model with S = 1/2. Distortion is introduced as an inequality of one nearest neighbor coupling with the other two. This yields a richer phase diagram by the appearance of a new gapped QSL, a gapless QSL and also a valence bond crystal phase in addition to the previous three phases found for the undistorted model.
Magnetic frustration in ferric fluorides investigated by Moessbauer spectrometry
Energy Technology Data Exchange (ETDEWEB)
Greneche, J.-M. [UPRESA CNRS 6087, Faculte des Sciences, Universite du Maine, Laboratoire de Physique de l' Etat Condense (France)
1999-11-15
The origin of magnetic frustration in antiferromagnetic ionic systems is discussed in terms first of cationic topology and then of competing superexchange and supersuperexchange interactions. Some selected examples based on ferric fluorides and oxyfluorides are presented to illustrate both the origins of magnetic frustration and the contribution of zero-field and in-field Moessbauer experiments.
Varma, Chandra M.
2016-08-01
The anomalous transport and thermodynamic properties in the quantum-critical region, in the cuprates, and in the quasi-two dimensional Fe-based superconductors and heavy-fermion compounds, have the same temperature dependences. This can occur only if, despite their vast microscopic differences, a common statistical mechanical model describes their phase transitions. The antiferromagnetic (AFM)-ic models for the latter two, just as the loop-current model for the cuprates, map to the dissipative XY model. The solution of this model in (2+1)D reveals that the critical fluctuations are determined by topological excitations, vortices and a variety of instantons, and not by renormalized spin-wave theories of the Landau-Ginzburg-Wilson type, adapted by Moriya, Hertz and others for quantum-criticality. The absorptive part of the fluctuations is a separable function of momentum \\mathbf{q} , measured from the ordering vector, and of the frequency ω and the temperature T which scale as \\tanh (ω /2T) at criticality. Direct measurements of the fluctuations by neutron scattering in the quasi-two-dimensional heavy fermion and Fe-based compounds, near their antiferromagnetic quantum critical point, are consistent with this form. Such fluctuations, together with the vertex coupling them to fermions, lead to a marginal fermi-liquid, with the imaginary part of the self-energy \\propto \\text{max}(ω,T) for all momenta, a resistivity \\propto T , a T\\ln T contribution to the specific heat, and other singular fermi-liquid properties common to these diverse compounds, as well as to d-wave superconductivity. This is explicitly verified, in the cuprates, by analysis of the pairing and the normal self-energy directly extracted from the recent high resolution angle resolved photoemission measurements. This reveals, in agreement with the theory, that the frequency dependence of the attractive irreducible particle-particle vertex in the d-wave channel is the same as the irreducible
Doyle, Peter G; Snell, J Laurie
1995-01-01
In this expository article, we discuss the rank-derangement problem, which asks for the number of permutations of a deck of cards such that each card is replaced by a card of a different rank. This combinatorial problem arises in computing the probability of winning the game of `frustration solitaire'. We discuss and exhibit the solution to a related problem, Montmort's `Probleme du Treize', which dates back to circa 1708.
Abrahams, Elihu; Wölfle, Peter
2012-02-28
We use the recently developed critical quasiparticle theory to derive the scaling behavior associated with a quantum critical point in a correlated metal. This is applied to the magnetic-field induced quantum critical point observed in YbRh(2)Si(2), for which we also derive the critical behavior of the specific heat, resistivity, thermopower, magnetization and susceptibility, the Grüneisen coefficient, and the thermal expansion coefficient. The theory accounts very well for the available experimental results.
Energy Technology Data Exchange (ETDEWEB)
Jaramillo, R.; Feng, Y.; Rosenbaum, T. F.; Harvard Univ.; Univ. of Chicago
2010-05-01
We explore the behavior of the nested bandstructure of chromium as a function of temperature and pressure to the point where magnetism disappears. X-ray diffraction measurements of the charge order parameter suggest that the nesting condition is maintained at high pressure, where the spin density wave ground state is destabilized by a continuous quantum phase transition. By comparing diffraction line-shapes measured throughout the temperature-pressure phase diagram we are able to identify and describe three regimes: thermal near-critical, weak coupling ground state, and quantum critical.
Quantum Monte Carlo simulation of antiferromagnetic spin ladder (C5H12N)2CuBr4
Freitas, Augusto S.
2016-07-01
In this paper I present a Quantum Monte Carlo (QMC) study of the magnetic properties of an antiferromagnetic spin ladder (C5H12N)2CuBr4. This compound is the prototype of the Heisenberg model for a two leg spin ladder in the presence of an external magnetic field. The susceptibility phase diagram has a rounded peak in the vicinity of T=7.4 K, obeys Troyer's law for low temperatures, and Curie's law for high temperatures. I also study the susceptibility diagram in low temperatures and I found the spin gap Δ=9.26 K, in good concordance with the experimental value, 9.5 K. In high field, I present a diagram of magnetization as a function of temperature. In the vicinity of a critical field, Hci, the magnetization scales with T1/2 and this result was found also in the QMC simulation. In all the results, there is a very good concordance with the experimental data. I also show in this paper that the spin gap is null and the susceptibility is proportional to T for low temperatures when relatively high values of the ladders' coupling is taken in account.
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.
Global phase diagram and quantum spin liquids in a spin-1/2 triangular antiferromagnet
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.
Energy Technology Data Exchange (ETDEWEB)
Parente, Walter E.F.; Pacobahyba, J.T.M.; Araújo, Ijanílio G. [Departamento de Física, Universidade Federal de Roraima, BR 174, Km 12. Bairro Monte Cristo. CEP: 69300-000 Boa Vista, Roraima (Brazil); Neto, Minos A., E-mail: minos@pq.cnpq.br [Universidade Federal do Amazonas, Departamento de Física, 3000, Japiim, 69077-000, Manaus-AM (Brazil); Ricardo de Sousa, J. [Universidade Federal do Amazonas, Departamento de Física, 3000, Japiim, 69077-000, Manaus-AM (Brazil); National Institute of Science and Technology for Complex Systems, 3000, Japiim, 69077-000, Manaus-AM (Brazil); Akinci, Ümit [Department of Physics, Dokuz Eylül University, Tr-35160 Izmir (Turkey)
2014-04-15
In this paper we study the quantum spin-1/2 anisotropic Heisenberg antiferromagnet model in the presence of a Dzyaloshinskii–Moriya interaction (D) and a uniform longitudinal (H) magnetic field. Using the effective-field theory with a finite cluster N=2 spin (EFT-2) we calculate the phase diagrams in the H−T and D−T planes on a simple cubic lattice (z=6). We have only observed second order phase transitions for values between Δ∈[0,1], where the cases were analysed: Ising (Δ=1), anisotropic Heisenberg (Δ=0.6) and isotropic Heisenberg (Δ=0). - Highlights: • Anisotropic Heisenberg antiferromagnet on a simple cubic lattice. • Effective-field theory. • Dzyaloshinskii–Moriya interaction.
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). 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.
Jakiel, Jacek; Kantor, Wiesław
2014-10-01
The frustrated total internal reflection theories (FTIR) from previous century are thoroughly recalculated from the, so called, monodromy operator's point of view - a theory lunched by Born and Wolf [Principles of Optics (Pergamon Press, 1975), Chap. 1.6] and Arnold [Geometric Methods in the Theory of Ordinary Differential Equations (Springer, 1987)]. Monodromy is a theory of simultaneous solution (for both reflection and transmission amplitudes) of one dimensional Schrödinger equation (for the wavefunction and its derivative) and the Maxwell equation (for electric and magnetic fields). Introducing new quantities: the dwell distance and the phase distance, we get general Goos-Hänchen (G-H) shift formula for optical tunneling for three layer system with refraction indexes n0, n1, n2. This formula reduces itself to expressions known from the scientific literature for infinite air gap (infinite width of second layer). Extension to many layers is possible.
Electrical switching of an antiferromagnet.
Wadley, P; Howells, B; Železný, J; Andrews, C; Hills, V; Campion, R P; Novák, V; Olejník, K; Maccherozzi, F; Dhesi, S S; Martin, S Y; Wagner, T; Wunderlich, J; Freimuth, F; Mokrousov, Y; Kuneš, J; Chauhan, J S; Grzybowski, M J; Rushforth, A W; Edmonds, K W; Gallagher, B L; Jungwirth, T
2016-02-05
Antiferromagnets are hard to control by external magnetic fields because of the alternating directions of magnetic moments on individual atoms and the resulting zero net magnetization. However, relativistic quantum mechanics allows for generating current-induced internal fields whose sign alternates with the periodicity of the antiferromagnetic lattice. Using these fields, which couple strongly to the antiferromagnetic order, we demonstrate room-temperature electrical switching between stable configurations in antiferromagnetic CuMnAs thin-film devices by applied current with magnitudes of order 10(6) ampere per square centimeter. Electrical writing is combined in our solid-state memory with electrical readout and the stored magnetic state is insensitive to and produces no external magnetic field perturbations, which illustrates the unique merits of antiferromagnets for spintronics.
Antiferromagnetic Ising model on the swedenborgite lattice
Buhrandt, Stefan; Fritz, Lars
2014-01-01
Geometrical frustration in spin systems often results in a large number of degenerate ground states. In this work, we study the antiferromagnetic Ising model on the three-dimensional swedenborgite lattice, which is a specific stacking of kagome and triangular layers. The model contains two exchange
Nunes, Wagner A; de Sousa, J Ricardo; Viana, J Roberto; Richter, J
2010-04-14
The ground state phase diagram of the quantum spin-1/2 Heisenberg antiferromagnet in the presence of nearest-neighbor (J(1)) and next-nearest-neighbor (J(2)) interactions (J(1)-J(2) model) on a stacked square lattice, where we introduce an interlayer coupling through nearest-neighbor bonds of strength J(), is studied within the framework of the differential operator technique. The Hamiltonian is solved by effective-field theory in a cluster with N=4 spins (EFT-4). We obtain the sublattice magnetization m(A) for the ordered phases: antiferromagnetic (AF) and collinear (CAF-collinear antiferromagnetic). We propose a functional for the free energy Ψ(μ)(m(μ)) (μ=A, B) to obtain the phase diagram in the λ-α plane, where λ=J()/J(1) and α=J(2)/J(1). Depending on the values of λ and α, we found different ordered states (AF and CAF) and a disordered state (quantum paramagnetic (QP)). For an intermediate region α(1c)(λ) α(2c)(λ), and below λ(1), we have the AF and CAF semi-classically ordered states, respectively. At α=α(1c)(λ) a second-order transition between the AF and QP states occurs and at α=α(2c)(λ) a first-order transition between the AF and CAF phases takes place. The boundaries between these ordered phases merge at the critical end point CEP≡(λ(1), α(c)), where α(c)≈0.56. Above this CEP there is again a direct first-order transition between the AF and CAF phases, with a behavior described by the point α(c) independent of λ ≥ λ(1).
Holes in Heisenberg antiferromagnets
Chen, Yang
1990-05-01
In this Brief Report we show that a recent model proposed by Shankar [Phys. Rev. Lett. 63, 203 (1989)], describing the motion of holes in quantum antiferromagnets is equivalent to the Schwinger model [Phys. Rev. 128, 2425 (1962)] in 1+1 dimensions. Some exact results are deduced. In addition to the superconducting long-range order found by Shankar, it is shown that there is a 2pF hole density wave existing with the superconducting pairing instability.
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^{'}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.
Li, Peng; Su, Haibin; Dong, Hui-Ning; Shen, Shun-Qing
2009-08-12
We study a triangular frustrated antiferromagnetic Heisenberg model with nearest-neighbor interactions J(1) and third-nearest-neighbor interactions J(3) by means of Schwinger-boson mean-field theory. By setting an antiferromagnetic J(3) and varying J(1) from positive to negative values, we disclose the low-temperature features of its interesting incommensurate phase. The gapless dispersion of quasiparticles leads to the intrinsic T(2) law of specific heat. The magnetic susceptibility is linear in temperature. The local magnetization is significantly reduced by quantum fluctuations. We address possible relevance of these results to the low-temperature properties of NiGa(2)S(4). From a careful analysis of the incommensurate spin wavevector, the interaction parameters are estimated as J(1)≈-3.8755 K and J(3)≈14.0628 K, in order to account for the experimental data.
The Heisenberg antiferromagnet on the square-kagomé lattice
Directory of Open Access Journals (Sweden)
J. Richter
2009-01-01
Full Text Available We discuss the ground state, the low-lying excitations as well as high-field thermodynamics of the Heisenberg antiferromagnet on the two-dimensional square-kagomé lattice. This magnetic system belongs to the class of highly frustrated spin systems with an infinite non-trivial degeneracy of the classical ground state as it is also known for the Heisenberg antiferromagnet on the kagomé and on the star lattice. The quantum ground state of the spin-half system is a quantum paramagnet with a finite spin gap and with a large number of non-magnetic excitations within this gap. We also discuss the magnetization versus field curve that shows a plateaux as well as a macroscopic magnetization jump to saturation due to independent localized magnon states. These localized states are highly degenerate and lead to interesting features in the low-temperature thermodynamics at high magnetic fields such as an additional low-temperature peak in the specific heat and an enhanced magnetocaloric effect.
Anisotropic spin model of strong spin-orbit-coupled triangular antiferromagnets
Li, Yao-Dong; Wang, Xiaoqun; Chen, Gang
2016-07-01
Motivated by the recent experimental progress on the strong spin-orbit-coupled rare-earth triangular antiferromagnet, we analyze the highly anisotropic spin model that describes the interaction between the spin-orbit-entangled Kramers' doublet local moments on the triangular lattice. We apply the Luttinger-Tisza method, the classical Monte Carlo simulation, and the self-consistent spin wave theory to analyze the anisotropic spin Hamiltonian. The classical phase diagram includes the 120∘ state and two distinct stripe-ordered phases. The frustration is very strong and significantly suppresses the ordering temperature in the regimes close to the phase boundary between two ordered phases. Going beyond the semiclassical analysis, we include the quantum fluctuations of the spin moments within a self-consistent Dyson-Maleev spin-wave treatment. We find that the strong quantum fluctuations melt the magnetic order in the frustrated regions. We explore the magnetic excitations in the three different ordered phases as well as in strong magnetic fields. Our results provide a guidance for the future theoretical study of the generic model and are broadly relevant for strong spin-orbit-coupled triangular antiferromagnets such as YbMgGaO4, RCd3P3 , RZn3P3 , RCd3As3 , RZn3As3 , and R2O2CO3 .
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'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.
Spontaneous alignment of frustrated bonds in an anisotropic, three-dimensional Ising model
Jalabert, Rodolfo A.; Sachdev, Subir
1991-07-01
The Ising model on a three-dimensional cubic lattice with all plaquettes in the x-y frustrated plane is studied by use of a Monte Carlo technique; the exchange constants are of equal magnitude, but have varying signs. At zero temperature, the model has a finite entropy and no long-range order. The low-temperature phase is characterized by an order parameter measuring the openZ4 symmetry of lattice rotations which is invariant under Mattis gauge transformation; fluctuations lead to the alignment of frustrated bonds into columns and a fourfold degeneracy. An additional factor-of-2 degeneracy is obtained from a global spin flip. The order vanishes at a critical temperature by a transition that appears to be in the universality class of the D=3, XY model. These results are consistent with the theoretical predictions of Blankschtein et al. This Ising model is related by duality to phenomenological models of two-dimensional frustrated quantum antiferromagnets.
Critical spin dynamics of the 2D quantum Heisenberg antiferromagnets Sr2CuO2Cl2 and Sr2Cu3O4Cl2.
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.
O2- -to-F- substitution on the quasi-two-dimensional quantum antiferromagnet (CuCl)LaNb2O7
Tassel, C.; Kobayashi, Y.; Mitsuoka, S.; Takeiri, F.; Ajiro, Y.; Kageyama, H.
2011-09-01
We present the preparation of the electron-doped quasi-two dimensional quantum antiferromagnet (CuCl)LaNb2O7 by two step-wise topochemical reactions. The first step involves a reductive fluorination of the insulating layered perovskite RbLaNb2O7 using polytetrafluoroethylene that allows electric conduction in the perovskite blocks. The product RbLaNb2O6F was then ion-exchanged with copper dichloride to yield (CuCl)LaNb2O6F. The synchrotron x-ray diffraction study indicates that the structure of the final compound is different from that of the pure (CuCl)LaNb2O7.
Ferreiro, Diego U; Komives, Elizabeth A; Wolynes, Peter G
2014-11-01
Biomolecules are the prime information processing elements of living matter. Most of these inanimate systems are polymers that compute their own structures and dynamics using as input seemingly random character strings of their sequence, following which they coalesce and perform integrated cellular functions. In large computational systems with finite interaction-codes, the appearance of conflicting goals is inevitable. Simple conflicting forces can lead to quite complex structures and behaviors, leading to the concept of frustration in condensed matter. We present here some basic ideas about frustration in biomolecules and how the frustration concept leads to a better appreciation of many aspects of the architecture of biomolecules, and especially how biomolecular structure connects to function by means of localized frustration. These ideas are simultaneously both seductively simple and perilously subtle to grasp completely. The energy landscape theory of protein folding provides a framework for quantifying frustration in large systems and has been implemented at many levels of description. We first review the notion of frustration from the areas of abstract logic and its uses in simple condensed matter systems. We discuss then how the frustration concept applies specifically to heteropolymers, testing folding landscape theory in computer simulations of protein models and in experimentally accessible systems. Studying the aspects of frustration averaged over many proteins provides ways to infer energy functions useful for reliable structure prediction. We discuss how frustration affects folding mechanisms. We review here how the biological functions of proteins are related to subtle local physical frustration effects and how frustration influences the appearance of metastable states, the nature of binding processes, catalysis and allosteric transitions. In this review, we also emphasize that frustration, far from being always a bad thing, is an essential feature
Spin diffusion and torques in disordered antiferromagnets
Manchon, Aurelien
2017-02-01
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.
Correlated adatom trimer on a metal surface: a continuous-time quantum Monte Carlo study.
Savkin, V V; Rubtsov, A N; Katsnelson, M I; Lichtenstein, A I
2005-01-21
The problem of three interacting Kondo impurities is solved within a numerically exact continuous-time quantum Monte Carlo scheme. A suppression of the Kondo resonance by interatomic exchange interactions for different cluster geometries is investigated. It is shown that a drastic difference between the Heisenberg and Ising cases appears for antiferromagnetically coupled adatoms. The effects of magnetic frustrations in the adatom trimer are investigated, and possible connections with available experimental data are discussed.
Entanglement frustration in multimode Gaussian states
Lupo, Cosmo; Facchi, Paolo; Florio, Giuseppe; Pascazio, Saverio
2011-01-01
Bipartite entanglement between two parties of a composite quantum system can be quantified in terms of the purity of one party and there always exists a pure state of the total system that maximizes it (and minimizes purity). When many different bipartitions are considered, the requirement that purity be minimal for all bipartitions gives rise to the phenomenon of entanglement frustration. This feature, observed in quantum systems with both discrete and continuous variables, can be studied by means of a suitable cost function whose minimizers are the maximally multipartite-entangled states (MMES). In this paper we extend the analysis of multipartite entanglement frustration of Gaussian states in multimode bosonic systems. We derive bounds on the frustration, under the constraint of finite mean energy, in the low and high energy limit.
Hubbard model with geometrical frustration
Energy Technology Data Exchange (ETDEWEB)
Lee, Hunpyo
2009-10-15
At first we present the details of the dual fermion (DF), the cluster extension of dynamical mean field theory (CDMFT) and continuous-time quantum Monte Carlo (CT QMC) methods. Using a panoply of these methods we explore the Hubbard model on the triangular and hyperkagome lattice. We find a first-order transition and continuous transition on the triangular and hyper-kagome lattice, respectively. Moreover, we find the reentrant behavior due to competition between the magnetic correlation and itinerancy of electrons by source of geometrical frustration on both lattices. (orig.)
Competing magnetic interactions in quantum thin films
Energy Technology Data Exchange (ETDEWEB)
Bueno, M.J. [Departamento de Física, CCEN, Universidade Federal da Paraíba, Cidade Universitária, 58051-970 João Pessoa, PB (Brazil); Faria, Jorge L.B. [Instituto de Física, Universidade Federal de Mato Grosso, 78060-900 Cuiabá, MT (Brazil); Arruda, Alberto S. de, E-mail: aarruda@fisica.ufmt.br [Instituto de Física, Universidade Federal de Mato Grosso, 78060-900 Cuiabá, MT (Brazil); Craco, L. [Instituto de Física, Universidade Federal de Mato Grosso, 78060-900 Cuiabá, MT (Brazil); Sousa, J. Ricardo de, E-mail: jsousa@ufam.edu.br [Departamento de Física, Universidade Federal do Amazonas, 69077-000 Manaus, AM (Brazil)
2013-07-15
In this work we study the quantum spin-1/2 Heisenberg model in two dimensions, with a nearest-neighbor short-range antiferromagnetic exchange (J) and a long-range ferromagnetic dipole–dipole (E{sub d}) coupling. Using the double-time Green's function method within the random phase approximation (RPA) we obtain the magnon dispersion relation as function of frustration parameter δ (δ being the ratio between exchange and dipolar interactions δ=J/E{sub d}). We study the competition between long-range ferromagnetic dipole–dipole interaction and short-range antiferromagnetic exchange in stabilizing the magnetic long-range order in a two-dimensional system. We find that the ferromagnetic order is stable at small k up to critical value of frustration δ{sub c}=0.04375. For frustration higher than the critical value (δ>δ{sub c}) our magnetic system is disordered. - Highlights: ► Competition between interactions short-range (exchange J) and long-range dipole–dipole (E{sub d}) is studied. ► The quantum spin-1/2 Heisenberg model in two dimensions is used as example. ► The interactions are exchange (antiferromagnetic) and ferromagnetic dipole–dipole. ► The double-time Green's function method and RPA is used to obtain the dispersion relations of the acoustic branch. ► The system has ferromagnetic order stable for values less than critical of frustration (J/E{sub d})
Order and excitations in large-S kagome-lattice antiferromagnets
Chernyshev, A. L.; Zhitomirsky, M. E.
2015-10-01
We systematically investigate the ground-state and the spectral properties of antiferromagnets on a kagomé lattice with several common types of the planar anisotropy: X X Z , single-ion, and out-of-plane Dzyaloshinskii-Moriya. Our main focus is on the role of nonlinear, anharmonic terms, which are responsible for the quantum order-by-disorder effect and for the corresponding selection of the ground-state spin structure in many of these models. The X X Z and the single-ion anisotropy models exhibit a quantum phase transition between the q =0 and the √{3 }×√{3 } states as a function of the anisotropy parameter, offering a rare example of the quantum order-by-disorder fluctuations favoring a ground state which is different from the one selected by thermal fluctuations. The nonlinear terms are also shown to be crucial for a very strong near-resonant decay phenomenon leading to the quasiparticle breakdown in the kagomé-lattice antiferromagnets whose spectra are featuring flat or weakly dispersive modes. The effect is shown to persist even in the limit of large spin values and should be common to other frustrated magnets with flat branches of excitations. Model calculations of the spectrum of the S =5 /2 Fe-jarosite with Dzyaloshinskii-Moriya anisotropy provide a convincing and detailed characterization of the proposed scenario.
A spin-1 kagome antiferromagnet
Tovar, Mayra; Shtengel, Kirill; Refael, Gil
2010-03-01
We study a spin-1 antiferromagnet on the kagom'e lattice. We start by constructing a Klein-type SU(2) symmetric Hamiltonian which contains Heisenberg interactions between nearest and next-nearest neighbors as well as three-body terms. Our model Hamiltonian has an extensive degenerate ground state whose manifold is spanned by the AKLT-like valence bond states. We also perturb the parent Hamiltonian by introducing an enhancement to the nearest neighbor antiferromagnetic Heisenberg interactions. By projecting this perturbation onto the basis spanned by the unperturbed ground states, we derive an effective Hamiltonian which is dual to that of the transverse field antiferromagnetic Ising model on the triangular lattice. Based on the parameters of our model, we find it to be in the order-by-disorder phase. The ground state is a valence bond crystal stabilized by quantum fluctuations. We also discuss excitations, both magnetic and non-magnetic, and address their possible relevance to experiment.
Hieida, Yasuhiro; Okunishi, Kouichi; Akutsu, Yasuhiro
1997-02-01
The product-wave-function renormalization group method, a new numerical renormalization group scheme proposed recently, is applied to one-dimensional quantum spin chains in a magnetic field. We find the zero-temperature magnetization curve of the spin chains, which excellently agrees with the exact solution in the whole range of the field.
Magnetic frustration effects in uranium intermetallics
Energy Technology Data Exchange (ETDEWEB)
Jiang, Yu; Booth, C. H.; Tobash, P. H.; Gofryk, K.; Torrez, M. A.; Ronning, F.; Bauer, E. D.; Thompson, J. D.
2010-06-10
The effect of geometrical frustration on the development of the heavy-fermion state and quantum criticality is studied in UAuCu{sub 4}, UAuPt{sub 4}, UAu{sub 3}Ni{sub 2} samples through measurements of their magnetic susceptibility, heat capacity, and electrical resistivity. In addition, since lattice disorder can play a large role in defining magnetic properties in frustrated systems, extended X-ray absorption fine structure (EXAFS) data have also been obtained. The local structure results show a strong correlation with the magnetic properties in these samples.
Geometric frustration in gadolinium gallium garnet: a Monte Carlo study
Petrenko, Oleg A.; Paul, Don McK.
1999-06-01
We have studied the magnetic properties of the frustrated triangular antiferromagnet Gd3Ga5O12 (GGG) by means of classical Monte Carlo simulations. Low-temperature specific heat, magnetization, susceptibility, autocorrelation function and neutron scattering function have been calculated for several models including different types of magnetic interactions and with the presence of an external magnetic field. In order to reproduce the experimentally observed properties of GGG, the simulation model must include nearest neighbor exchange interactions and also dipolar forces. In zero field there is a tendency to form incommensurate short-range magnetic order around positions in reciprocal space where antiferromagnetic Bragg peaks appear in an applied magnetic field.
Energy Technology Data Exchange (ETDEWEB)
Hong, Fang [Institute for Superconducting and Electronic Materials, Australian Institute of Innovative Materials, University of Wollongong, Innovation Campus, Squires Way, North Wollongong, New South Wales 2500 (Australia); Center for High Pressure Science and Technology Advanced Research, 1690 Cailun Rd. Pudong, Shanghai 201203 (China); The Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, MS 80R0114, Berkeley, California 94720 (United States); Yue, Binbin, E-mail: yuebb@hpstar.ac.cn, E-mail: cheng@uow.edu.au [Center for High Pressure Science and Technology Advanced Research, 1690 Cailun Rd. Pudong, Shanghai 201203 (China); The Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, MS 80R0114, Berkeley, California 94720 (United States); Wang, Jianli [Institute for Superconducting and Electronic Materials, Australian Institute of Innovative Materials, University of Wollongong, Innovation Campus, Squires Way, North Wollongong, New South Wales 2500 (Australia); The Australian Nuclear Science and Technology Organization (ANSTO), Bragg Institute, Lucas Heights, New South Wales 2234 (Australia); Studer, Andrew [The Australian Nuclear Science and Technology Organization (ANSTO), Bragg Institute, Lucas Heights, New South Wales 2234 (Australia); Fang, Chunsheng; Wang, Xiaolin; Dou, Shixue; Cheng, Zhenxiang, E-mail: yuebb@hpstar.ac.cn, E-mail: cheng@uow.edu.au [Institute for Superconducting and Electronic Materials, Australian Institute of Innovative Materials, University of Wollongong, Innovation Campus, Squires Way, North Wollongong, New South Wales 2500 (Australia)
2016-09-05
We studied the temperature dependent magnetic phase evolution in spin frustrated TbMnO{sub 3} affected by Fe doping via powder neutron diffraction. With the introduction of Fe (10% and 20%), the long range incommensurate magnetic orderings collapse. When the Fe content is increased to 30%, a long-range antiferromagnetic ordering develops, while a spin reorientation transition is found near 35 K from a canted G-type antiferromagnetic ordering to a collinear G-type antiferromagnetic ordering. This work demonstrates the complex magnetic interactions existing in transition metal oxides, which helps to understand the frustrated spin states in other similar systems and design magnetic materials as well.
Phase Transitions in Frustrated Vector Spin Systems: Numerical Studies
Loison, Damien
The following sections are included: * Introduction * Breakdown of symmetry * Symmetry in the high-temperature region * Breakdown of symmetry for ferromagnetic systems * Breakdown of symmetry for frustrated systems * Stacked triangular antiferromagnetic lattices * bct helimagnets * Stacked J1-J2 square lattices * The simple cubic J1-J2 lattice * J1-J2-J3 lattice * Villain lattice and fully frustrated simple cubic lattice * Face-centered cubic lattice (fcc) * Hexagonal-close-packed lattice (hcp) * Pyrochlores * Other lattices * STAR lattices * Dihedral lattices VN,2 * Right-handed trihedral lattices V3,3 * P-hedral lattices VN,P * Ising and Potts-VN,1 model * Ising and Potts-N,2 model * Landau-Ginzburg model * Cubic term in Hamiltonian * Summary * Phase transitions between two and four dimensions: 2 Potts model * O(N)/O(N - P) breakdown of symmetry for d = 3 * Z2 ⊗ SO(N)/SO(N - 1) breakdown of symmetry for d = 3 * Z3 ⊗ SO(N)/SO(N - 1) breakdown of symmetry for d = 3 * Zq ⊗ O(N)/O(N - 2) and other breakdown of symmetry in d = 3 * Conclusion * O(N) frustrated vector spins in d = 2 * Introduction * Non frustrated XY spin systems * Frustrated XY spin systems: Z2 ⊗ SO(2) * Frustrated XY spin systems: Z3 ⊗ SO(2) * Frustrated XY spin systems: Z2 ⊗ Z2 ⊗ SO(2) and Z3 ⊗ Z2 ⊗ SO(2) * Frustrated Heisenberg spin systems: SO(3) * Frustrated Heisenberg spin systems: Z2 ⊗ SO(3), Z3 ⊗ SO(3) … * Topological defects for N ≥ 4 * General conclusions * Acknowledgments * Appendix A: Monte Carlo simulation * Appendix B: Renormalization group: Landau-Ginzburg theory, expansions in fixed dimension d = 3 and for d = 4 - ɛ and its implications for experiments * References
Stability of Frustration-Free Hamiltonians
Michalakis, Spyridon
2011-01-01
We prove stability of the spectral gap for gapped, frustration-free Hamiltonians under general, quasi-local perturbations. We present a necessary and sufficient condition for stability, which we call "Local Topological Quantum Order" and show that this condition implies an area law for the entanglement entropy of the groundstate subspace. This result extends previous work by Bravyi et al., on the stability of topological quantum order for Hamiltonians composed of commuting projections with a common zero-energy subspace. We conclude with a list of open problems relevant to spectral gaps and topological quantum order.
Frustrated polymer crystal structures
Lotz, B.; Strasbourg, 67083
1997-03-01
Several crystal structures or polymorphs of chiral or achiral polymers and biopolymers with three fold conformation of the helix have been found to conform to a common and -with one exception(Puterman, M. et al, J. Pol. Sci., Pol. Phys. Ed., 15, 805 (1977))- hitherto unsuspected packing scheme. The trigonal unit-cell contains three isochiral helices; the azimuthal setting of one helix differs significantly from that of the other two, leading to a so-called frustrated packing scheme, in which the environment of conformationally identical helices differs. Two variants of the frustrated scheme are analyzed. Similarities with frustrated two dimensional magnetic systems are underlined. Various examples of frustration in polymer crystallography are illustrated via the elucidation or reinterpretation of crystal phases or polymorphs of polyolefins, polyesters, cellulose derivatives and polypeptides. Structural manifestations (including AFM evidence) and morphological consequences of frustration are presented, which help diagnose the existence of this original packing of polymers.(Work done with L. Cartier, D. Dorset, S. Kopp, T. Okihara, M. Schumacher, W. Stocker.)
Glassy Spin Dynamics in Geometrically Frustrated Buckled Colloidal Crystals
Zhou, Di; Wang, Feng; Li, Bo; Lou, Xiaojie; Han, Yilong
2017-04-01
Geometrical frustration arises when the lattice geometry prevents local interaction energies from minimizing simultaneously. Whether and how geometrically frustrated spins or charges in clean crystals exhibit glassy dynamics remain elusive due to the lack of measurements on microscopic dynamics. Here, we employ buckled monolayer colloidal crystals to mimic frustrated antiferromagnetic Ising spins on triangular lattices and measure single-spin dynamics using video microscopy. Both attractive and repulsive colloidal crystals buckled into zigzag stripes with glassy dynamics at low effective temperatures in experiment and simulation. The simple local spin configurations enable uncovering correlations among structure, dynamics, and soft vibrational modes. Machine learning analysis further reveals facilitated dynamics to be an important mechanism of structural relaxation. Moreover, our simulation reveals a similar structure and dynamics in lattice Coulomb liquids. Hence, spin-lattice coupling and long-range interaction can similarly lift degeneracy, induce a rugged landscape, and, thus, produce glassy dynamics.
Frustration in Vicinity of Transition Point of Ising Spin Glasses
Miyazaki, Ryoji
2013-09-01
We conjecture the existence of a relationship between frustration and the transition point at zero temperature of Ising spin glasses. The relation reveals that, in several Ising spin glass models, the concentration of ferromagnetic bonds is close to the critical concentration at zero temperature when the output of a function about frustration is equal to unity. The function is the derivative of the average number of frustrated plaquettes with respect to the average number of antiferromagnetic bonds. This relation is conjectured in Ising spin glasses with binary couplings on two-dimensional lattices, hierarchical lattices, and three-body Ising spin glasses with binary couplings on two-dimensional lattices. In addition, the same argument in the Sherrington--Kirkpatrick model yields a point that is identical to the replica-symmetric solution of the transition point at zero temperature.
Perspective: Geometrically frustrated assemblies
Grason, Gregory M.
2016-09-01
This perspective will overview an emerging paradigm for self-organized soft materials, geometrically frustrated assemblies, where interactions between self-assembling elements (e.g., particles, macromolecules, proteins) favor local packing motifs that are incompatible with uniform global order in the assembly. This classification applies to a broad range of material assemblies including self-twisting protein filament bundles, amyloid fibers, chiral smectics and membranes, particle-coated droplets, curved protein shells, and phase-separated lipid vesicles. In assemblies, geometric frustration leads to a host of anomalous structural and thermodynamic properties, including heterogeneous and internally stressed equilibrium structures, self-limiting assembly, and topological defects in the equilibrium assembly structures. The purpose of this perspective is to (1) highlight the unifying principles and consequences of geometric frustration in soft matter assemblies; (2) classify the known distinct modes of frustration and review corresponding experimental examples; and (3) describe outstanding questions not yet addressed about the unique properties and behaviors of this broad class of systems.
Acid-base chemistry of frustrated water at protein interfaces.
Fernández, Ariel
2016-01-01
Water molecules at a protein interface are often frustrated in hydrogen-bonding opportunities due to subnanoscale confinement. As shown, this condition makes them behave as a general base that may titrate side-chain ammonium and guanidinium cations. Frustration-based chemistry is captured by a quantum mechanical treatment of proton transference and shown to remove same-charge uncompensated anticontacts at the interface found in the crystallographic record and in other spectroscopic information on the aqueous interface. Such observations are untenable within classical arguments, as hydronium is a stronger acid than ammonium or guanidinium. Frustration enables a directed Grotthuss mechanism for proton transference stabilizing same-charge anticontacts.
Antiferromagnetic Ising Model in Hierarchical Networks
Cheng, Xiang; Boettcher, Stefan
2015-03-01
The Ising antiferromagnet is a convenient model of glassy dynamics. It can introduce geometric frustrations and may give rise to a spin glass phase and glassy relaxation at low temperatures [ 1 ] . We apply the antiferromagnetic Ising model to 3 hierarchical networks which share features of both small world networks and regular lattices. Their recursive and fixed structures make them suitable for exact renormalization group analysis as well as numerical simulations. We first explore the dynamical behaviors using simulated annealing and discover an extremely slow relaxation at low temperatures. Then we employ the Wang-Landau algorithm to investigate the energy landscape and the corresponding equilibrium behaviors for different system sizes. Besides the Monte Carlo methods, renormalization group [ 2 ] is used to study the equilibrium properties in the thermodynamic limit and to compare with the results from simulated annealing and Wang-Landau sampling. Supported through NSF Grant DMR-1207431.
Paramagnetic and Antiferromagnetic Spin Seebeck Effect
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.
Quasiparticle interactions in frustrated Heisenberg chains
Vanderstraeten, Laurens; Haegeman, Jutho; Verstraete, Frank; Poilblanc, Didier
2016-06-01
Interactions between elementary excitations in quasi-one-dimensional antiferromagnets are of experimental relevance and their quantitative theoretical treatment has been a theoretical challenge for many years. Using matrix product states, one can explicitly determine the wave functions of the one- and two-particle excitations, and, consequently, the contributions to dynamical correlations. We apply this framework to the (nonintegrable) frustrated dimerized spin-1/2 chain, a model for generic spin-Peierls systems, where low-energy quasiparticle excitations are bound states of topological solitons. The spin structure factor involving two quasiparticle scattering states is obtained in the thermodynamic limit with full momentum and frequency resolution. This allows very subtle features in the two-particle spectral function to be revealed which, we argue, could be seen, e.g., in inelastic neutron scattering of spin-Peierls compounds under a change of the external pressure.
Exact zero modes in frustrated Haldane chains
Chepiga, Natalia; Mila, Frédéric
2017-08-01
We show that the effective coupling between the spin-1/2 edge states of a spin-1 chain of finite length can be continuously tuned by frustration. For the J1-J2 model with nearest- and next-nearest-neighbor antiferromagnetic interactions, we show that the effective coupling in a chain of length L changes sign N ≃0.38 L times in the window 0.28 ≲J2/J1≲0.75 where the short-range correlations are incommensurate. This implies that there are N zero modes where the singlet and the triplet are strictly degenerate, i.e., N values of J2/J1 where the spin-1/2 edge states are completely decoupled. We argue that this effect must be generic for all incommensurate phases with localized edge states, and we briefly discuss a few experimental implications.
Pati, Swapan K; Rao, C N R
2005-12-15
In view of the variety of low-temperature magnetic properties reported recently for kagome lattices with transition-metal ions in different oxidation states, we have investigated the low-energy spectrum and low-temperature thermodynamic properties of antiferromagnetic kagome lattices with varying magnitudes of site spins, employing quantum many-body Heisenberg models. The ground state and the low-lying excitation spectrum are found to depend strongly on the nature of the spin magnitude of the magnetic ions. The system remains highly frustrated if spins are half-odd-integer in magnitude, while the frustration is very weak or almost absent for integer spins or mixed-spin systems. In fact, for a mixed-spin kagome system with a certain magnitude, the whole system behaves as a classical magnet with a ferrimagnetic ground state without any frustration. These theoretical findings are consistent with a few experimental observations recently reported in the literature and would be of value in designing new kagome systems with unusual and interesting low-temperature magnetic properties.
Supersymmetry protected topological phases of isostatic lattices and kagome antiferromagnets
Lawler, Michael J.
2016-10-01
I generalize the theory of phonon topological band structures of isostatic lattices to frustrated antiferromagnets. I achieve this with a discovery of a many-body supersymmetry (SUSY) in the phonon problem of balls and springs and its connection to local constraints satisfied by ground states. The Witten index of the SUSY model demands the Maxwell-Calladine index of mechanical structures. "Spontaneous supersymmetry breaking" is identified as the need to gap all modes in the bulk to create the topological isostatic lattice state. Since ground states of magnetic systems also satisfy local constraint conditions (such as the vanishing of the total spin on a triangle), I identify a similar SUSY structure for many common models of antiferromagnets including the square, triangluar, kagome, pyrochlore nearest-neighbor antiferromagnets, and the J2=J1/2 square-lattice antiferromagnet. Remarkably, the kagome family of antiferromagnets is the analog of topological isostatic lattices among this collection of models. Thus, a solid-state realization of the theory of phonon topological band structure may be found in frustrated magnetic materials.
Mussardo, G.; Giudici, G.; Viti, J.
2017-03-01
In this paper we introduce and study the coprime quantum chain, i.e. a strongly correlated quantum system defined in terms of the integer eigenvalues n i of the occupation number operators at each site of a chain of length M. The n i ’s take value in the interval [2,q] and may be regarded as S z eigenvalues in the spin representation j = (q - 2)/2. The distinctive interaction of the model is based on the coprimality matrix \\boldsymbolΦ : for the ferromagnetic case, this matrix assigns lower energy to configurations where occupation numbers n i and n i+1 of neighbouring sites share a common divisor, while for the anti-ferromagnetic case it assigns a lower energy to configurations where n i and n i+1 are coprime. The coprime chain, both in the ferro and anti-ferromagnetic cases, may present an exponential number of ground states whose values can be exactly computed by means of graph theoretical tools. In the ferromagnetic case there are generally also frustration phenomena. A fine tuning of local operators may lift the exponential ground state degeneracy and, according to which operators are switched on, the system may be driven into different classes of universality, among which the Ising or Potts universality class. The paper also contains an appendix by Don Zagier on the exact eigenvalues and eigenvectors of the coprimality matrix in the limit q\\to ∞ .
Ferrimagnetic states in S = 1/2 frustrated Heisenberg chains with period 3 exchange modulation
Hida, K.
2007-04-01
The ground state properties of the S = 1/2 frustrated Heisenberg chain with period 3 exchange modulation are investigated using the numerical diagonalization and density matrix renormalization group (DMRG) method. It is known that this model has a magnetization plateau at one third of the saturation magnetization Ms. On the other hand, the ground state is ferrimagnetic even in the absence of frustration if one of the nearest neighbour bond is ferromagnetic and the others are antiferromagnetic. In the present work, we show that this ferrimagnetic state continues to the region in which all bonds are antiferromagnetic if the frustration is strong. This state further continues to the above-mentioned 1/3 plateau state. In between, we also find the noncollinear ferrimagnetic phase in which the spontaneous magnetization is finite but less than Ms/3. The intuitive interpretation for the phase diagram is given and the physical properties of these phases are discussed.
Ferrimagnetic states in S = 1/2 frustrated Heisenberg chains with period 3 exchange modulation
Energy Technology Data Exchange (ETDEWEB)
Hida, K [Divison of Material Science, Graduate School of Science and Engineering, Saitama University, Saitama, Saitama, 338-8570 (Japan)
2007-04-11
The ground state properties of the S = 1/2 frustrated Heisenberg chain with period 3 exchange modulation are investigated using the numerical diagonalization and density matrix renormalization group (DMRG) method. It is known that this model has a magnetization plateau at one third of the saturation magnetization M{sub s}. On the other hand, the ground state is ferrimagnetic even in the absence of frustration if one of the nearest neighbour bond is ferromagnetic and the others are antiferromagnetic. In the present work, we show that this ferrimagnetic state continues to the region in which all bonds are antiferromagnetic if the frustration is strong. This state further continues to the above-mentioned 1/3 plateau state. In between, we also find the noncollinear ferrimagnetic phase in which the spontaneous magnetization is finite but less than M{sub s}/3. The intuitive interpretation for the phase diagram is given and the physical properties of these phases are discussed.
Neurobiological basis of frustration
Directory of Open Access Journals (Sweden)
Justel, Nadia
2010-12-01
Full Text Available The main feature shared by the phenomena involving unexpected changes of reinforcement is that there is a discrepancy between expected and received reward. Consequently, the behavior is modified according to this difference; the animals have an emotional response to the surprising reward change, called frustration. Some of the paradigms that are commonly used to study these problems are: consummatory Successive Negative Contrast and consummatory Extinction. This review describes the major works that investigate the neuroanatomical and neurophysiological mechanisms involved in these studies, and the main tasks related with the administration of drugs that modulate the memory of the surprising reward changes.
Large-scale numerical investigations of the antiferromagnetic Heisenberg icosidodecahedron
Energy Technology Data Exchange (ETDEWEB)
Ummethum, Joerg [Department of Physics, Bielefeld University, P.O. Box 100131, D-33501 Bielefeld (Germany); Schnack, Juergen, E-mail: jschnack@uni-bielefeld.de [Department of Physics, Bielefeld University, P.O. Box 100131, D-33501 Bielefeld (Germany); Laeuchli, Andreas M. [Inst. f. Theoretische Physik, Innsbruck University, Technikerstr. 25, 6020 Innsbruck (Austria)
2013-02-15
We present up to date investigations of the antiferromagnetic Heisenberg icosidodecahedron by means of the density matrix renormalization group method. We compare our results with modern correlator product state as well as Lanczos calculations. - Highlights: Black-Right-Pointing-Pointer Results of unprecedented accuracy for energies and correlation functions of a frustrated spin system. Black-Right-Pointing-Pointer Relevance for a large set of magnetic molecules. Black-Right-Pointing-Pointer Demonstration of accuracy of DDMRG.
Asymptotic dynamics of a frustrated model with spherical constraint
Energy Technology Data Exchange (ETDEWEB)
Mendoza-Coto, Alejandro [Departamento de Física, Universidade Federal do Rio Grande do Sul, CP 15051, 91501-970 Porto Alegre (Brazil); Díaz-Méndez, Rogelio, E-mail: rogelio@fisica.uh.cu [Nanophysics Group, Electric Engineering Faculty, CUJAE, CP 19390, La Habana (Cuba); Group of Complex Systems, Physics Faculty, University of Havana, CP 10400, La Habana (Cuba)
2013-11-15
We solve the Langevin dynamics of a continuum model with a spherical constraint, considering a ferromagnetic exchange and a long-range antiferromagnetic interaction. Analytical results within the Hartree approximation show an equivalence in the form of spatial and auto-correlation functions in the long time regime between this model and the recently studied Ginzburg–Landau frustrated model. The low-temperature behavior is discussed in the context of glassy dynamics. The emergence of interesting features regarding the establishment of the saturated phase is also analyzed in the view of recent literature. - Highlights: • We solve the long-time dynamics of a model with ferro and antiferromagnetic interactions and spherical restriction. • We find the critical behavior of spatial and self-correlations. • The new results are analyzed in the frame of existing literature on glassy states and thin films.
Classical Spin Liquid on the Maximally Frustrated Honeycomb Lattice
Rehn, J.; Sen, Arnab; Damle, Kedar; Moessner, R.
2016-10-01
We show that the honeycomb Heisenberg antiferromagnet with J1/2 =J2=J3, where J1 , J2 , and J3 are first-, second-, and third-neighbor couplings, respectively, forms a classical spin liquid with pinch-point singularities in the structure factor at the Brillouin zone corners. Upon dilution with nonmagnetic ions, fractionalized degrees of freedom carrying 1 /3 of the free moment emerge. Their effective description in the limit of low temperature is that of spins randomly located on a triangular lattice, with a frustrated sublattice-sensitive interaction of long-ranged logarithmic form. The X Y version of this magnet exhibits nematic thermal order by disorder. This comes with a clear experimental diagnostic in neutron scattering, which turns out to apply also to the case of the celebrated planar order by disorder of the kagome Heisenberg antiferromagnet.
Phase-space networks of geometrically frustrated systems
Han, Yilong
2009-11-01
We illustrate a network approach to the phase-space study by using two geometrical frustration models: antiferromagnet on triangular lattice and square ice. Their highly degenerated ground states are mapped as discrete networks such that the quantitative network analysis can be applied to phase-space studies. The resulting phase spaces share some comon features and establish a class of complex networks with unique Gaussian spectral densities. Although phase-space networks are heterogeneously connected, the systems are still ergodic due to the random Poisson processes. This network approach can be generalized to phase spaces of some other complex systems.
Tailoring magnetic frustration in strained epitaxial FeRh films
Witte, Ralf; Kruk, Robert; Gruner, Markus E.; Brand, Richard A.; Wang, Di; Schlabach, Sabine; Beck, Andre; Provenzano, Virgil; Pentcheva, Rossitza; Wende, Heiko; Hahn, Horst
2016-03-01
We report on a strain-induced martensitic transformation, accompanied by a suppression of magnetic order in epitaxial films of chemically disordered FeRh. X-ray diffraction, transmission electron microscopy, and electronic structure calculations reveal that the lowering of symmetry (from cubic to tetragonal) imposed by the epitaxial relation leads to a further, unexpected, tetragonal-to-orthorhombic transition, triggered by a band-Jahn-Teller-type lattice instability. The collapse of magnetic order is a direct consequence of this structural change, which upsets the subtle balance between ferromagnetic nearest-neighbor interactions arising from Fe-Rh hybridization and frustrated antiferromagnetic coupling among localized Fe moments at larger distances.
Magnetic and structural properties of antiferromagnetic VF{sub 3}
Energy Technology Data Exchange (ETDEWEB)
Reuvekamp, Patrick; Kremer, Reinhard; Eger, Roland [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, D-70569 Stuttgart (Germany); Nenert, Gwilherm; Hansen, Thomas [Institut Laue-Langevin, 38042 Grenoble (France)
2013-07-01
We report on a magnetic and structural investigation of layered antiferromagnetic system vanadium (III) fluoride. VF{sub 3} crystallizes in a distorted ReO{sub 3} structure (R anti 3c) with rotated undistorted VF{sub 6} octahedra. The V{sup +3} cations are arranged in a triangular lattice with the possibility of exhibiting magnetic frustration. Polycrystalline samples of VF{sub 3} were investigated using heat capacity, dielectric, magnetic susceptibility and neutron powder diffraction methods. Combining our results, we confirmed that VF{sub 3} undergoes long-range antiferromagnetic order at ∝19 K in accordance with literature. The antiferromagnetic order results in a magnetic structure with the magnetic moments alternating between a parallel and b parallel alignments in the ab plane. A second phase transition can be seen at ∝120 K in the heat capacity and dielectric measurements possibly associated to a minute structural distortion.
User Frustrations as Opportunities
Directory of Open Access Journals (Sweden)
Michael Weiss
2012-04-01
Full Text Available User frustrations are an excellent source of new product ideas. Starting with this observation, this article describes an approach that entrepreneurs can use to discover business opportunities. Opportunity discovery starts with a problem that the user has, but may not be able to articulate. User-centered design techniques can help elicit those latent needs. The entrepreneur should then try to understand how users are solving their problem today, before proposing a solution that draws on the unique skills and technical capabilities available to the entrepreneur. Finally, an in-depth understanding of the user allows the entrepreneur to hone in on the points of difference and resonance that are the foundation of a strong customer value proposition.
The Berezinskii-Kosterlitz-Thouless transition and correlations in the XY kagome antiferromagnet
Cherepanov, V B; Podivilov, E V
2001-01-01
The problem of the Berezinskii-Kosterlitz-Thouless transition in the highly frustrated XY antiferromagnetic is solved. The transition temperature is found. It is shown that the spin correlation function exponentially decays with distance even in the low-temperature phase, in contrast to the order parameter correlation function, which decays algebraically with distance
Extending the Family of V(4+) S=(1/2) Kagome Antiferromagnets.
Clark, Lucy; Aidoudi, Farida H; Black, Cameron; Arachchige, Kasun S A; Slawin, Alexandra M Z; Morris, Russell E; Lightfoot, Philip
2015-12-14
The ionothermal synthesis, structure, and magnetic susceptibility of a novel inorganic-organic hybrid material, imidazolium vanadium(III,IV) oxyfluoride [C3 H5 N2 ][V9 O6 F24 (H2 O)2 ] (ImVOF) are presented. The structure consists of inorganic vanadium oxyfluoride slabs with kagome layers of V(4+) S=${{ 1/2 }}$ ions separated by a mixed valence layer. These inorganic slabs are intercalated with imidazolium cations. Quinuclidinium (Q) and pyrazinium (Pyz) cations can also be incorporated into the hybrid structure type to give QVOF and PyzVOF analogues, respectively. The highly frustrated topology of the inorganic slabs, along with the quantum nature of the magnetism associated with V(4+) , means that these materials are excellent candidates to host exotic magnetic ground states, such as the highly sought quantum spin liquid. Magnetic susceptibility measurements of all samples suggest an absence of conventional long-range magnetic order down to 2 K despite considerable antiferromagnetic exchange.
Directory of Open Access Journals (Sweden)
Yarash K. Abuev
2017-01-01
Full Text Available Abstract. Objectives A computer simulation of the antiferromagnetic structures described by the three-vertex Potts model on a triangular lattice is performed, taking into account the antiferromagnetic exchange interactions between the nearest J1 and second J2 neighbours. The main goal of the computer simulation was to elucidate the effects of ground state and areas of frustration on the thermodynamic and magnetic properties of antiferromagnetic structures described by the lowdimensional Potts model. Method The computer simulation is based on the Monte Carlo method. This method is implemented using the Metropolis algorithm in combination with the Wolff claster algorithm. The computer simulation was carried out for low-dimensional systems with periodic boundary conditions and linear dimensions L = 24124. Results On the basis of heat capacity and entropy analysis, phase transitions were observed in the considered model to possess exchange interaction parameters J1 <0 and J2 <0 in the variation intervals 0r<0.2 and 1.0
Spin-Mechanical Inertia in Antiferromagnet
2016-01-01
The conservation of angular momentum has served as a guiding principle in the coupled dynamics of quantum spins and mechanical rotations. However, in an antiferromagnet with vanishing magnetization, new fundamental rules are required to properly describe spin-mechanical phenomena. Here we demonstrate that the Neel 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 temperat...
Seabra, Luis; Sindzingre, Philippe; Momoi, Tsutomu; Shannon, Nic
2016-02-01
A large part of the interest in magnets with frustrated antiferromagnetic interactions comes from the many new phases found in applied magnetic field. In this article, we explore some of the new phases which arise in a model with frustrated ferromagnetic interactions, the J1-J2-J3 Heisenberg model on a square lattice. Using a combination of classical Monte Carlo simulation and spin-wave theory, we uncover behavior reminiscent of some widely studied frustrated antiferromagnets, but with a number of new twists. We first demonstrate that, for a suitable choice of parameters, the phase diagram as a function of magnetic field and temperature is nearly identical to that of the Heisenberg antiferromagnet on a triangular lattice, including the celebrated 1 /3 -magnetization plateau. We then examine how this phase diagram changes when the model is tuned to a point where the classical ground state is highly degenerate. In this case, two new phases emerge: a classical, finite-temperature spin liquid, characterized by a "ring" in the spin structure factor S (q ) ; and a vortex crystal, a multiple-Q state with finite magnetization, which can be viewed as an ordered lattice of magnetic vortices. All of these new phases persist for a wide range of magnetic fields. We discuss the relationship between these results and published studies of frustrated antiferromagnets, together with some of the materials where these new phases might be observed in experiment.
Energy Technology Data Exchange (ETDEWEB)
Zhu, Jian-xin [Los Alamos National Laboratory; Dai, Jianhui [ZHEJIANG UNIV; Si, Qimiao [RICE UNIV
2009-01-01
Some of the high {Tc} iron pnictides contain rare-earth elements, raising the question of how the existence and tunability of a d-electron antiferromagnetic order influences the heavy fermion behavior of the f-moments. With CeOFeP and CeOFeAs in mind as prototypes, we derive an extended Anderson lattice model appropriate for these quaternary systems. We show that the Kondo screening of the f-moments are efficiently suppressed by the d-electron ordering. We also argue that, inside the d-electron ordered state (as in CeOFeAs), the f-moments provide a rare realization of a quantum frustrated magnet with competing J{sub 1}-J{sub 2}-J{sub 3} interactions in an effective square lattice. Implications ofr the heavy fermion physics in broader contexts are also discussed.
Energy Technology Data Exchange (ETDEWEB)
Lapa, Rodrigo S.; Mendonça, Griffith [Departamento de Fi' sica, Universidade Federal de Minas Gerais, CP 702, 30161-970 Belo Horizonte, MG (Brazil); Universidade Federal do Amazonas, Departamento de Fi' sica, 3000, Japiim, 69077-000 Manaus, AM (Brazil); Roberto Viana, J. [Universidade Federal do Amazonas, Departamento de Fi' sica, 3000, Japiim, 69077-000 Manaus, AM (Brazil); Ricardo de Sousa, J., E-mail: jsousa@ufam.edu.br [Universidade Federal do Amazonas, Departamento de Fi' sica, 3000, Japiim, 69077-000 Manaus, AM (Brazil); National Institute of Science and Technology for Complex Systems, Universidade Federal do Amazonas, Departamento de Fisica, 3000, Japiim, 69077-000 Manaus, AM (Brazil)
2014-11-15
We have studied the quantum spin-1/2 frustrated Heisenberg model with two ferromagnetic interactions: nearest-neighbor (NN) with different coupling strengths J{sub 1} and J{sub 1}{sup ′} along x and y directions, respectively, competing with a next-nearest-neighbor (NNN) with coupling J{sub 2}. Using the effective-field theory we obtain the ground-state phase diagram in the (λ,α) space, where λ=J{sub 1}{sup ′}/J{sub 1} and α=J{sub 2}/J{sub 1}. Depending on the values of λ and α we observe three different states: ferromagnetic (F), collinear ferromagnetic (CF) and quantum paramagnetic (QP). We observe a QP state between the ordered F and CF phases in the region λ{sub 1}<λ<1 (λ{sub 1}≃0.62). - Highlights: • We study the ferromagnetic J{sub 1}−J{sub 1}{sup ′}−J{sub 2} model on an anisotropic square lattice by using effective-field theory. • We obtain the ground phase diagram in the λ−α plane (λ=J{sub 1}{sup ′}/J{sub 1} and α=J{sub 2}/J{sub 1}). • A comparison with the results of the antiferromagnetic J{sub 1}−J{sub 1}{sup ′}−J{sub 2} model. • We propose a functional for the free energy.
Path integrals for dimerized quantum spin systems
Energy Technology Data Exchange (ETDEWEB)
Foussats, Adriana, E-mail: afoussats@gmail.co [Facultad de Ciencias Exactas, Ingenieria y Agrimensura and Instituto de Fisica Rosario (UNR-CONICET), Av. Pellegrini 250, 2000 Rosario (Argentina); Greco, Andres [Facultad de Ciencias Exactas, Ingenieria y Agrimensura and Instituto de Fisica Rosario (UNR-CONICET), Av. Pellegrini 250, 2000 Rosario (Argentina); Muramatsu, Alejandro [Institut fuer Theoretische Physik III, Universitaet Stuttgart, Pfaffenwaldring 57, D-70550 Stuttgart (Germany)
2011-01-11
Dimerized quantum spin systems may appear under several circumstances, e.g. by a modulation of the antiferromagnetic exchange coupling in space, or in frustrated quantum antiferromagnets. In general, such systems display a quantum phase transition to a Neel state as a function of a suitable coupling constant. We present here two path-integral formulations appropriate for spin S=1/2 dimerized systems. The first one deals with a description of the dimers degrees of freedom in an SO(4) manifold, while the second one provides a path-integral for the bond-operators introduced by Sachdev and Bhatt. The path-integral quantization is performed using the Faddeev-Jackiw symplectic formalism for constrained systems, such that the measures and constraints that result from the algebra of the operators is provided in both cases. As an example we consider a spin-Peierls chain, and show how to arrive at the corresponding field-theory, starting with both an SO(4) formulation and bond-operators.
Magnetic structure and interactions in the quasi-1D antiferromagnet CaV{sub 2}O{sub 4}
Energy Technology Data Exchange (ETDEWEB)
Pieper, Oliver; Lake, Bella [Helmholtz-Zentrum Berlin fuer Materialien und Energie, Berlin (Germany); Technische Universitaet Berlin, Institut fuer Festkoerperphysik, Berlin (Germany); Daoud-Aladine, Aziz [ISIS Facility, Rutherford Appleton Lab., Chilton (United Kingdom); Reehuis, Manfred [Helmholtz-Zentrum Berlin fuer Materialien und Energie, Berlin (Germany); Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany); Prokes, Karel; Klemke, Bastian; Kiefer, Klaus [Helmholtz-Zentrum Berlin fuer Materialien und Energie, Berlin (Germany); Yan, Jiaqiang; Niazi, Asad; Johnston, David C. [Ames Lab., Departement of Physics and Astronomy, Iowa State University, Ames (United States); Honecker, Andreas [Universitaet Goettingen, Institut fuer Theoretische Physik, Goettingen (Germany)
2009-07-01
CaV{sub 2}O{sub 4} is a spin-1 antiferromagnet where the magnetic vanadium ions are arranged on quasi-one-dimensional zig-zag chains with frustrated antiferromagnetic exchange interactions. Here we present high temperature susceptibility and single-crystal neutron diffraction measurements, which are used to deduce the magnetic structure, dominant exchange interactions and orbital configurations. The results suggest that at high temperatures of CaV{sub 2}O{sub 4}, the zig-zags behave as Haldane chains but at low temperatures, orbital ordering lifts the exchange frustration and the zig-zags become spin-1 ladders.
Spin dynamics in highly frustrated pyrochlore magnets
Petit, Sylvain; Guitteny, Solène; Robert, Julien; Bonville, Pierre; Decorse, Claudia; Ollivier, Jacques; Mutka, Hannu; Mirebeau, Isabelle
2015-01-01
This paper aims at showing the complementarity between time-of-flight and triple-axis neutron scattering experiments, on the basis of two topical examples in the field of geometrical magnetic frustration. Rare earth pyrochlore magnets R2Ti2O7 (R is a rare earth) play a prominent role in this field, as they form model systems showing a rich variety of ground states, depending on the balance between dipolar, exchange interactions and crystal field. We first review the case of the XY antiferromagnet Er2 Ti2 O7. Here a transition towards a Néel state is observed, possibly induced by an order-by-disorder mechanism. Effective exchange parameters can be extracted from S(Q,ω). We then examine the case of the spin liquid Tb2 Ti2 O7. Recent experiments reveal a complex ground state characterized by "pinch points" and supporting a low energy excitation. These studies demonstrate the existence of a coupling between crystal field transitions and a transverse acoustic phonon mode.
Spiral versus modulated collinear phases in the quantum axial next-nearest-neighbor Heisenberg model
Oitmaa, J.; Singh, R. R. P.
2016-12-01
Motivated by the discovery of spiral and modulated collinear phases in several magnetic materials, we investigate the magnetic properties of Heisenberg spin S =1 /2 antiferromagnets in two and three dimensions, with frustration arising from second-neighbor couplings in one axial direction [the axial next-nearest-neighbor Heisenberg (ANNNH) model]. Our results clearly demonstrate the presence of an incommensurate spiral phase at T =0 in two dimensions, extending to finite temperatures in three dimensions. The crossover between Néel and spiral order occurs at a value of the frustration parameter considerably above the classical value 0.25, a sign of substantial quantum fluctuations. We also investigate a possible modulated collinear phase with a wavelength of four lattice spacings and find that it has substantially higher energy and hence is not realized in the model.
Direct measurement of antiferromagnetic domain fluctuations.
Energy Technology Data Exchange (ETDEWEB)
Shpyrko, O. G.; Isaacs, E. D.; Logan, J. M.; Feng, Y.; Aeppli, G.; Jaramillo, R.; Kim, H. C.; Rosenbaum, T. F.; Zschack, P.; Sprung, M.; Narayanan, S.; Sandy, A.; Univ. of Chicago; Univ. College London
2007-05-03
Measurements of magnetic noise emanating from ferromagnets owing to domain motion were first carried out nearly 100 years ago1, and have underpinned much science and technology2, 3. 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 nanometer-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 micrometer 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.
Band structure and itinerant magnetism in quantum critical NbFe2
Energy Technology Data Exchange (ETDEWEB)
Subedi, A. P. [University of Tennessee, Knoxville (UTK); Singh, David J [ORNL
2010-01-01
We report first-principles calculations of the band structure and magnetic ordering in the C14 Laves phase compound NbFe{sub 2}. The magnetism is itinerant in the sense that the moments are highly dependent on ordering. We find an overestimation of the magnetic tendency within the local spin-density approximation, similar to other metals near magnetic quantum critical points. We also find a competition between different magnetic states due to band-structure effects. These lead to competing magnetic tendencies due to competing interlayer interactions, one favoring a ferrimagnetic solution and the other an antiferromagnetic state. While the structure contains Kagome lattice sheets, which could, in principle, lead to strong magnetic frustration, the calculations do not show dominant nearest-neighbor antiferromagnetic interactions within these sheets. These results are discussed in relation to experimental observations.
Molavian, Hamid R; Gingras, Michel J P; Canals, Benjamin
2007-04-13
The Tb2Ti2O7 pyrochlore magnetic material is attracting much attention for its spin liquid state, failing to develop long-range order down to 50 mK despite a Curie-Weiss temperature thetaCW approximately -14 K. In this Letter we reinvestigate the theoretical description of this material by considering a quantum model of independent tetrahedra to describe its low-temperature properties. The naturally tuned proximity of this system near a Néel to spin ice phase boundary allows for a resurgence of quantum fluctuation effects that lead to an important renormalization of its effective low-energy spin Hamiltonian. As a result, Tb2Ti2O7 is argued to be a quantum spin ice. We put forward an experimental test of this proposal using neutron scattering on a single crystal.
James C. McGroddy Prize for New Materials Talk: Geometrically Frustrated Materials
Ramirez, Arthur
2011-03-01
Geometrical frustration occurs when interacting degrees of freedom do not ``fit'' into the lattice that they occupy and, as a result, are under-constrained at low temperature. While the early ideas behind geometrical frustration originate in Wannier's triangular antiferromagnetic Ising model and Anderson's resonating valence bond model, they are broadened here to define an entire class of magnetic materials whose structures are based on triangular or tetrahedral units. When the degree of misfit is high, conventional long range order is suppressed and thermodynamic spectral weight is pushed to energies much lower than the mean field value. Out of this low energy spectral weight, new states of matter are found to emerge experimentally, such as spin liquid on the kagome lattice and spin ice on the pyrochlore lattice. The concept of geometrical frustration can be broadened beyond magnetism to describe a frustrated soft mode that can lead to persistent negative thermal expansion and giant dielectric constants. A brief review will be given of recent work on excitations in frustrating lattices, including the prediction of, and evidence for, magnetic monopoles in spin ice, and the relevance of frustrated hopping for topological insulators.
Antiferromagnetic spin-orbitronics
Manchon, Aurelien
2015-05-01
Antiferromagnets have long remained an intriguing and exotic state of matter, whose application has been restricted to enabling interfacial exchange bias in metallic and tunneling spin-valves [1]. Their role in the expanding field of applied spintronics has been mostly passive and the in-depth investigation of their basic properties mostly considered from a fundamental perspective.
Nanoparticles of antiferromagnetic materials
DEFF Research Database (Denmark)
Madsen, Daniel Esmarch
2008-01-01
I denne Ph.D. afhandling studeres forskellige egenskaber ved antiferromagnetiske nanopartikler. I en ideel antiferromagnet er spinnene orienteret således at der ikke er et resulterende magnetisk moment. I nanopartikler af antiferromagnetiske materialer er denne kompensation på grund af forskellig...
Li, B.; Luo, X. H.; Wang, H.; Ren, W. J.; Yano, S.; Wang, C.-W.; Gardner, J. S.; Liss, K.-D.; Miao, P.; Lee, S.-H.; Kamiyama, T.; Wu, R. Q.; Kawakita, Y.; Zhang, Z. D.
2016-06-01
Competition between ferromagnetic and antiferromagnetic phases on frustrated lattices in hexagonal Laves phase compound Hf0.86Ta0.14Fe2 is investigated by using neutron diffraction as a function of temperature and magnetic fields and density-functional-theory calculations. At 325 K, the compound orders into the 120° frustrated antiferromagnetic state with a well-reduced magnetic moment, and an in-plane lattice contraction simultaneously sets in. With further cooling down, however, the accumulated distortion in turn destabilizes this susceptible frustrated structure. The frustration is completely relieved at 255 K when the first-order transition to the ferromagnetic state takes place, where a colossal negative volumetric thermal expansion, -123 ×10-6 /K, is obtained. Meanwhile, the antiferromagnetic state can be suppressed by few-tesla magnetic fields, which results in a colossal positive magnetostriction. Such delicate competition is attributed to the giant magnetic fluctuation inherent in the frustrated antiferromagnetic state. Therefore, the magnetoelastic instability is approached even under a small perturbation.
Spin liquid nature in the Heisenberg J1-J2 triangular antiferromagnet
Iqbal, Yasir; Hu, Wen-Jun; Thomale, Ronny; Poilblanc, Didier; Becca, Federico
2016-04-01
We investigate the spin-1/2 Heisenberg model on the triangular lattice in the presence of nearest-neighbor J1 and next-nearest-neighbor J2 antiferromagnetic couplings. Motivated by recent findings from density-matrix renormalization group (DMRG) claiming the existence of a gapped spin liquid with signatures of spontaneously broken lattice point group symmetry [Zhu and White, Phys. Rev. B 92, 041105 (2015), 10.1103/PhysRevB.92.041105 and Hu, Gong, Zhu, and Sheng, Phys. Rev. B 92, 140403 (2015), 10.1103/PhysRevB.92.140403], we employ the variational Monte Carlo (VMC) approach to analyze the model from an alternative perspective that considers both magnetically ordered and paramagnetic trial states. We find a quantum paramagnet in the regime 0.08 ≲J2/J1≲0.16 , framed by 120∘ coplanar (stripe collinear) antiferromagnetic order for smaller (larger) J2/J1 . By considering the optimization of spin-liquid wave functions of a different gauge group and lattice point group content as derived from Abrikosov mean-field theory, we obtain the gapless U(1 ) Dirac spin liquid as the energetically most preferable state in comparison to all symmetric or nematic gapped Z2 spin liquids so far advocated by DMRG. Moreover, by the application of few Lanczos iterations, we find the energy to be the same as the DMRG result within error bars. To further resolve the intriguing disagreement between VMC and DMRG, we complement our methodological approach by the pseudofermion functional renormalization group (PFFRG) to compare the spin structure factors for the paramagnetic regime calculated by VMC, DMRG, and PFFRG. This model promises to be an ideal test bed for future numerical refinements in tracking the long-range correlations in frustrated magnets.
Organometallic frustrated Lewis pair chemistry.
Erker, Gerhard
2011-08-07
Frustrated Lewis pairs are playing an increasingly important role in organometallic chemistry. Examples are presented and discussed where organometallic systems themselves serve as the Lewis base or Lewis acid components in frustrated Lewis pair chemistry, mostly through their attached functional groups. Activation of dihydrogen takes place easily in many of these systems. This may lead to the generation of novel catalyst systems but also in many cases to the occurrence of specific reactions at the periphery of the organometallic frameworks. Increasingly, FLP reactions are used to carry out functional group conversions in organometallic systems under mild reaction conditions. The limits of typical FLP reactivity are explored with selected organometallic examples, a discussion that points toward new developments, such as the discovery of facile new 1,1-carboboration reactions. Learning more and more about the broad spectrum of frustrated Lewis pair chemistry helps us to find novel reactions and applications.
Carvalho, R. C. P.; Pereira, M. S. S.; de Oliveira, I. N.; Strečka, J.; Lyra, M. L.
2017-09-01
We introduce an exactly solvable hybrid spin-ladder model containing localized nodal Ising spins and interstitial mobile electrons, which are allowed to perform a quantum-mechanical hopping between the ladder’s legs. The quantum-mechanical hopping process induces an antiferromagnetic coupling between the ladder’s legs that competes with a direct exchange coupling of the nodal spins. The model is exactly mapped onto the Ising spin ladder with temperature-dependent two- and four-spin interactions, which is subsequently solved using the transfer-matrix technique. We report the ground-state phase diagram and compute the fermionic concurrence to characterize the quantum entanglement between the pair of interstitial mobile electrons. We further provide a detailed analysis of the local spin ordering including the pair and four-spin correlation functions around an elementary plaquette, as well as, the local ordering diagrams. It is shown that a complex sequence of distinct local orderings and frustrated correlations takes place when the model parameters drive the investigated system close to a zero-temperature triple coexistence point.
Lawler, Michael
I generalize the theory of phonon topological band structures of isostatic lattices to highly frustrated antiferromagnets. I achieve this with a discovery of a many-body supersymmetry (SUSY) in the phonon problem of balls and springs which also applies to geometrically frustrated magnets. The Witten index of the SUSY model, when restricted to the single body problem (meaningful for linearized phonons), is then shown to be the Calladine-Kane-Lubensky index of mechanical structures that forms the cornerstone of the phonon topological band structure theory. ``Spontaneous supersymmetry breaking'' is then identified as the need to gap all modes in the bulk to create the topological state. The many-body SUSY formulation shows that the topology is not restricted to a band structure problem but extends to systems of coupled bosons and fermions that are in principle also realizable in solid state systems. The analogus supersymmetry of the magnon problem turns out to be particularly useful for highly frustrated magnets with the kagome family of antiferromagnets an analog of topological isostatic lattices. Thus, a solid state realization of the theory of phonon topological band structure may be found in highly frustrated magnets. However, our results show that this topology is protected not
Frustration effects in spinel compound GeCo2O4 studied by ultrasound velocity measurements
Watanabe, Tadataka; Hara, Shigeo; Ikeda, Shin-Ichi
2009-03-01
Ultrasound velocity measurements of the cubic spinel GeCo2O4 in the single crystal have been performed for the investigations of shear and compression moduli. The shear moduli reveal the absence of Jahn-Teller activity despite the presence of the orbital degeneracy in the Co2+ ions. This Jahn-Teller inactivity indicates that the intersite orbital-orbital interaction is much stronger than the Jahn-Teller coupling. The compression moduli reveal that the dominant path of the exchange interactions for the antiferromagnetic transition lies in the [111] direction. This exchange-path anisotropy is consistent with the antiferromagnetic structure with the wave vector q parallel [111], suggesting the presence of bond frustration among several ferromagnetic and antiferromagientic interactions. In the JT-inactive condition, the bond frustration can be induced by geometrical orbital frustration of t2g-t2g interaction between the Co2+ ions which can be realized in the pyrochlore lattice of the high spin Co2+ with t2g -orbital degeneracy. In GeCo2O4, the tetragonal elongation below TN releases the orbital frustration by quenching the orbital degeneracy.
Thickness-dependent cooperative aging in polycrystalline films of antiferromagnet CoO
Ma, Tianyu; Cheng, Xiang; Boettcher, Stefan; Urazhdin, Sergei; Novozhilova, Lydia
2016-07-01
We demonstrate that thin polycrystalline films of antiferromagnet CoO, in bilayers with ferromagnetic Permalloy, exhibit slow power-law aging of their magnetization state. The aging characteristics are remarkably similar to those previously observed in thin epitaxial Fe50Mn50 films, indicating that these behaviors are likely generic to ferromagnet/antiferromagnet bilayers. In very thin films, aging is observed over a wide temperature range. In thicker CoO, aging effects become reduced at low temperatures. Aging entirely disappears for large CoO thicknesses. We also investigate the dependence of aging characteristics on temperature and magnetic history. Analysis shows that the observed behaviors are inconsistent with the Neel-Arrhenius model of thermal activation, and are instead indicative of cooperative aging of the antiferromagnet. Our results provide new insights into the mechanisms controlling the stationary states and dynamics of ferromagnet/antiferromagnet bilayers, and potentially other frustrated magnetic systems.
Katayama, Kazuya; Kurita, Nobuyuki; Tanaka, Hidekazu
2015-06-01
We have systematically investigated the variation of the exchange parameters and the ground state in the S =1/2 kagome-lattice antiferromagnet (Rb1 -xCsx )2Cu3SnF12 via magnetic measurements using single crystals. One of the parent compounds, Rb2Cu3SnF12 , which has a distorted kagome lattice accompanied by four sorts of nearest-neighbor exchange interaction, has a disordered ground state described by a pinwheel valence-bond-solid state. The other parent compound, Cs2Cu3SnF12 , which has a uniform kagome lattice at room temperature, has an ordered ground state with the q =0 spin structure. The analysis of magnetic susceptibilities shows that with increasing cesium concentration x , the exchange parameters increase with the tendency to be uniform. It was found that the ground state is disordered for x 0.53 . The pseudogap observed for x 0.53 approach zero at xc≃0.53 . This is indicative of the occurrence of a quantum phase transition at xc.
Bhattacharjee, Suraka; Chaudhury, Ranjan
2016-11-01
The generalized spin stiffness constant for a doped quantum antiferromagnet has been investigated both analytically and numerically as a function of doping concentration at zero temperature, based on the strongly correlated t-J model on two-dimensional square lattice. The nature of the theoretical dependence of the stiffness constant on doping shows a striking similarity with that of the effective exchange constant, obtained from the combination of other theoretical and experimental techniques in the low doping region. This correspondence once again establishes that spin stiffness can very well play the role of an effective exchange constant even in the strongly correlated semi-itinerant systems. Our theoretical plot of the stiffness constant against doping concentration in the whole doping region exhibits the various characteristic features like a possible crossover in the higher doping regions and persistence of short range ordering even for very high doping with the complete vanishing of spin stiffness occurring only close to 100% doping. Our results receive very good support from various other theoretical approaches and also brings out a few limitations of some of them. Our detailed analysis highlights the crucial importance of the study of spin stiffness for the proper understanding of magnetic correlations in a semi-itinerant magnetic system described by the strongly correlated t-J model. Moreover, our basic formalism can also be utilized for determination of the effective exchange constant and magnetic correlations for itinerant magnetic systems, in general in a novel way.
Domain-wall spin dynamics in kagome antiferromagnets.
Lhotel, E; Simonet, V; Ortloff, J; Canals, B; Paulsen, C; Suard, E; Hansen, T; Price, D J; Wood, P T; Powell, A K; Ballou, R
2011-12-16
We report magnetization and neutron scattering measurements down to 60 mK on a new family of Fe based kagome antiferromagnets, in which a strong local spin anisotropy combined with a low exchange path network connectivity lead to domain walls intersecting the kagome planes through strings of free spins. These produce unfamiliar slow spin dynamics in the ordered phase, evolving from exchange-released spin flips towards a cooperative behavior on decreasing the temperature, probably due to the onset of long-range dipolar interaction. A domain structure of independent magnetic grains is obtained that could be generic to other frustrated magnets.
Frustration: A common user experience
DEFF Research Database (Denmark)
Hertzum, Morten
2010-01-01
The use of computer applications can be a frustrating experience. This study replicates previous studies of the amount of time users – involuntarily – spend trying to diagnose and recover from problems they encounter while using computer applications such as web browsers, email, and text processi...
Watanabe, Tadataka; Hara, Shigeo; Ikeda, Shin-Ichi
2008-09-01
Ultrasound velocity measurements of cubic spinel GeCo2O4 in single crystal were performed for the investigation of shear and compression moduli. The shear moduli in the paramagnetic state reveal the absence of Jahn-Teller activity despite the presence of orbital degeneracy in the Co2+ ions. Such a Jahn-Teller inactivity indicates that the intersite orbital-orbital interaction is much stronger than the Jahn-Teller coupling. The compression moduli in the paramagnetic state near the Néel temperature TN reveal that the most relevant exchange path for the antiferromagnetic transition lies in the [111] direction. This exchange-path anisotropy is consistent with the antiferromagnetic structure with the wave vector q∥[111] , suggesting the presence of bond frustration due to competition among a direct ferromagnetic interaction and several distant-neighbor antiferromagnetic interactions. In the Jahn-Teller-inactive condition, the bond frustration can be induced by geometrical orbital frustration of t2g-t2g interaction between the Co2+ ions, which can be realized in the pyrochlore lattice of the high-spin Co2+ with t2g -orbital degeneracy. In GeCo2O4 , the tetragonal elongation below TN releases the orbital frustration by quenching the orbital degeneracy.
Probing spin frustration in high-symmetry magnetic nanomolecules by inelastic neutron scattering
DEFF Research Database (Denmark)
Garlea, V.O.; Nagler, S.E.; Zarestky, J.L.;
2006-01-01
Low temperature inelastic neutron scattering studies have been performed to characterize the low energy magnetic excitation spectrum of the magnetic nanomolecule {Mo(72)Fe(30)}. This unique highly symmetric cluster features spin frustration and is one of the largest discrete magnetic molecules st...... of the temperature dependence of the observed neutron scattering are explained by a quantum model of the frustrated spin cluster. However, no satisfactory theoretical explanation is yet available for the observed magnetic field dependence....
Meddar, Lynda; Josse, Michael; Deniard, Philippe; La, Carole; André, Gilles; Damay, Françoise; Petricek, Vaclav; Jobic, Stéphane; Whangbo, Myung-Hwan; Maglione, Mario; Payen, Christophe
2010-01-01
The effects of substituting nonmagnetic Mg2+ and Zn2+ ions for the Mn2+ (S = 5/2) ions on the structural, magnetic and dielectric properties of the multiferroic frustrated antiferromagnet MnWO4 were investigated. Polycrystalline samples of Mn1-xMgxWO4 and Mn1-xZnxWO4 (0
Antiferromagnetic order and spin glass behavior in Dy{sub 2}CuIn{sub 3}
Energy Technology Data Exchange (ETDEWEB)
Siouris, I.M., E-mail: jsiou@pme.duth.gr [Democritus University of Thrace (DUTH), Production and Management Engineering Department, Materials Laboratory, 67100 Xanthi (Greece); Kremer, R.K. [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, D-70569 Stuttgart (Germany); Hoelzel, M. [Technische Universitaet Muenchen, Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II), 85748 Garching (Germany)
2011-11-15
The magnetic properties of the intermetallic compound Dy{sub 2}CuIn{sub 3} have been investigated. Ac and dc-susceptibility measurements indicate an onset of antiferromagnetic ordering at T{sub N}=19.5 K and an additional frequency dependent transition at T{sub ds}{approx}9 K. Neutron diffraction studies confirm the ordered transition at 19.5{+-}1 K. The magnetic unit cell can be described by the propagation vector k=(0.25,0.25,0) with the magnetic moment {mu}=2.63(4){mu}{sub B}/Dy{sup 3+} parallel to the c-axis. Nevertheless, neutron diffraction reveals no additional magnetic phase transition around or below 9 K, which suggests that, at lower temperatures, a spin glass state may be formed in coexistence with the antiferromagnetic mode as a result of frustration and the antagonism between ferromagnetic and antiferromagnetic exchange interactions. - Highlights: > Dy{sub 2}CuIn{sub 3} is characterized by the dominance of antiferromagnetic (AF) interactions. > Geometric frustration and crystal field effects prevent the formation of the full magnetic moment on the Dy ions. > Two magnetic regimes are recognized: an AF state and a mixed AF-glassy state. > The antiferromagnetic structure of the compound has been determined.
Energy Technology Data Exchange (ETDEWEB)
Zapf, Vivien [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Jaime, Marcelo [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Chikara, Shalinee [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Fisher, Ian [Stanford Univ., CA (United States); Batista, C. D. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Tennessee, Knoxville, TN (United States)
2017-03-01
BaCuSi_{2}O_{6} is a well-known quantum magnet that exhibits a Bose-Einstein Condensation quantum phase transition in applied magnetic fields. It contains Cu dimers that form singlets in zero magnetic field, and in applied fields as the singlet-triplet gap is suppressed a quantum phase transition occurs to canted XY antiferromagnetism between critical fields H_{c1} = 23 T and H_{c2} = 59 T. In addition, as the temperature is lowered, a rare frustrationinduced dimensional reduction has been proposed from three to two dimensions. Recently, however, a controversy has arisen about the details of the magnetic ordering due to the discovery of a tetragonal to orthorhombic structural transition at 100 K with an incommensurate modulation along the b-axis. Multiple magnon modes were observed in neutron diffraction studies, while NMR found modulation of the spin structure along both the ab plane and the c-axis. In this scenario the material is still a Bose-Einstein condensate system but the frustration is not perfect, calling into question the dimension reduction scenario. A recent study of BaCuSi_{2}O_{6} combining inelastic neutron diffraction and density functional theory suggest that the material isn’t even frustrated at all and that the spins are ordered ferromagnetically in the a-b plane and antiferromagnetically along the c-axis. After a detailed symmetry analysis we have concluded that the magnetic scenario postulated by this most recent unfrustrated theory6 will render BaCuSi_{2}O_{6} a multiferroic between H_{c1} and H_{c2}, with electric polarization in easy axis of the a-b plane for magnetic fields along the c-axis via an inverse Dzyaloshinskii-Moriya mechanism. Electric polarization is a sensitive symmetry probe of magnetic order, since magnetic systems that break spatial inversion symmetry can induce an overall ferroelectricity in the crystalline lattice. In pulsed magnetic fields
Antiferromagnetic hedgehogs with superconducting cores
Energy Technology Data Exchange (ETDEWEB)
Goldbart, P.M.; Sheehy, D.E. [Department of Physics and Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)
1998-09-01
Excitations of the antiferromagnetic state that resemble antiferromagnetic hedgehogs at large distances but are predominantly superconducting inside a core region are discussed within the context of Zhang{close_quote}s SO(5)-symmetry-based approach to the physics of high-temperature superconducting materials. Nonsingular, in contrast with their hedgehog cousins in pure antiferromagnetism, these texture excitations are what hedgehogs become when the antiferromagnetic order parameter is permitted to {open_quotes}escape{close_quotes} into superconducting directions. The structure of such excitations is determined in a simple setting, and a number of their experimental implications are examined. {copyright} {ital 1998} {ital The American Physical Society}
Antiferromagnetic noise correlations in optical lattices
DEFF Research Database (Denmark)
Bruun, Niels Bohr International Academy, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark, Georg Morten; Syljuåsen, F. T.; Pedersen, K. G. L.;
2009-01-01
We analyze how noise correlations probed by time-of-flight experiments reveal antiferromagnetic (AF) correlations of fermionic atoms in two-dimensional and three-dimensional optical lattices. Combining analytical and quantum Monte Carlo calculations using experimentally realistic parameters, we...... show that AF correlations can be detected for temperatures above and below the critical temperature for AF ordering. It is demonstrated that spin-resolved noise correlations yield important information about the spin ordering. Finally, we show how to extract the spin correlation length and the related...
High-Tc spin superfluidity in antiferromagnets.
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.
Wang, Bo-Yao; Lin, Po-Han; Tsai, Ming-Shian; Shih, Chun-Wei; Lee, Meng-Ju; Huang, Chun-Wei; Jih, Nae-Yeou; Wei, Der-Hsin
2016-08-01
This study demonstrates the effect of antiferromagnet-induced perpendicular magnetic anisotropy (PMA) on ferromagnetic/antiferromagnetic/ferromagnetic (FM/AFM/FM) trilayers and reveals its interplay with a long-range interlayer coupling between separated FM layers. In epitaxially grown 12 monolayer (ML) Ni/Co/Mn/5 ML Co/Cu(001) films, magnetic hysteresis loops and element-resolved magnetic domain imaging showed that the magnetization direction of the top layers of 12 ML Ni/Co films could be changed from the in-plane direction to the perpendicular direction, when the thickness of the Mn films (tMn) was greater than a critical value close to the thickness threshold associated with the onset of AFM ordering (tMn=3.5 ML). The top FM layers exhibited a significantly enhanced PMA when tMn increased further, and this enhancement can be attributed to a strengthened AFM ordering of the volume moments of the Mn films, as evidenced by the presence of induced domain frustration. By contrast, the long-range interlayer coupling presented clear effects only when tMn was at a lower coverage.
Resolving the frustration of fatigue.
Harpham, W S
1999-01-01
Fatigue is a ubiquitous side effect of many cancer therapies. Nevertheless, after treatment is complete, many survivors continue to feel a profound tiredness that affects almost all aspects of life. Even after recovery, patients are often frustrated by their continuing need for extra rest. In this deeply personal, first-person account, a physician relates the various ways that cancer-related fatigue can affect family dynamics, job responsibilities, social interactions, finances, and intimacy. Clinicians can help by searching for treatable medical conditions, but also by taking cancer-related fatigue, and the frustrations it causes, seriously. Patients should be reassured that the fatigue they feel is real, and that by learning personal energy conservation, they should be able to improve their abilities to function, to socialize, to interact with others, and ultimately to adjust to a "new normal" baseline.
When a local Hamiltonian must be frustration-free.
Sattath, Or; Morampudi, Siddhardh C; Laumann, Chris R; Moessner, Roderich
2016-06-07
A broad range of quantum optimization problems can be phrased as the question of whether a specific system has a ground state at zero energy, i.e., whether its Hamiltonian is frustration-free. Frustration-free Hamiltonians, in turn, play a central role for constructing and understanding new phases of matter in quantum many-body physics. Unfortunately, determining whether this is the case is known to be a complexity-theoretically intractable problem. This makes it highly desirable to search for efficient heuristics and algorithms to, at least, partially answer this question. Here we prove a general criterion-a sufficient condition-under which a local Hamiltonian is guaranteed to be frustration-free by lifting Shearer's theorem from classical probability theory to the quantum world. Remarkably, evaluating this condition proceeds via a fully classical analysis of a hardcore lattice gas at negative fugacity on the Hamiltonian's interaction graph, which, as a statistical mechanics problem, is of interest in its own right. We concretely apply this criterion to local Hamiltonians on various regular lattices, while bringing to bear the tools of spin glass physics that permit us to obtain new bounds on the satisfiable to unsatisfiable transition in random quantum satisfiability. We are then led to natural conjectures for when such bounds will be tight, as well as to a novel notion of universality for these computer science problems. Besides providing concrete algorithms leading to detailed and quantitative insights, this work underscores the power of marrying classical statistical mechanics with quantum computation and complexity theory.
When a local Hamiltonian must be frustration-free
Sattath, Or; Morampudi, Siddhardh C.; Laumann, Chris R.; Moessner, Roderich
2016-06-01
A broad range of quantum optimization problems can be phrased as the question of whether a specific system has a ground state at zero energy, i.e., whether its Hamiltonian is frustration-free. Frustration-free Hamiltonians, in turn, play a central role for constructing and understanding new phases of matter in quantum many-body physics. Unfortunately, determining whether this is the case is known to be a complexity-theoretically intractable problem. This makes it highly desirable to search for efficient heuristics and algorithms to, at least, partially answer this question. Here we prove a general criterion—a sufficient condition—under which a local Hamiltonian is guaranteed to be frustration-free by lifting Shearer’s theorem from classical probability theory to the quantum world. Remarkably, evaluating this condition proceeds via a fully classical analysis of a hardcore lattice gas at negative fugacity on the Hamiltonian’s interaction graph, which, as a statistical mechanics problem, is of interest in its own right. We concretely apply this criterion to local Hamiltonians on various regular lattices, while bringing to bear the tools of spin glass physics that permit us to obtain new bounds on the satisfiable to unsatisfiable transition in random quantum satisfiability. We are then led to natural conjectures for when such bounds will be tight, as well as to a novel notion of universality for these computer science problems. Besides providing concrete algorithms leading to detailed and quantitative insights, this work underscores the power of marrying classical statistical mechanics with quantum computation and complexity theory.
Antiferromagnetic spin Seebeck effect.
Energy Technology Data Exchange (ETDEWEB)
Wu, Stephen M.; Zhang, Wei; KC, Amit; Borisov, Pavel; Pearson, John E.; Jiang, J. Samuel; Lederman, David; Hoffmann, Axel; Bhattacharya, Anand
2016-03-03
We report on the observation of the spin Seebeck effect in antiferromagnetic MnF2. A device scale on-chip heater is deposited on a bilayer of MnF2 (110) (30nm)/Pt (4 nm) grown by molecular beam epitaxy on a MgF2(110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF2 through the inverse spin Hall effect. The low temperature (2–80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop transition corresponding to the sudden rotation of antiferromagnetic spins out of the easy axis is observed in the spin Seebeck signal when large magnetic fields (>9T) are applied parallel to the easy axis of the MnF2 thin film. When the magnetic field is applied perpendicular to the easy axis, the spin-flop transition is absent, as expected.
Antiferromagnetic Spin Seebeck Effect
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.
Phase transition in Heisenberg stacked triangular antiferromagnets: end of a controversy.
Ngo, V Thanh; Diep, H T
2008-09-01
By using the Wang-Landau flat-histogram Monte Carlo (MC) method for very large lattice sizes never simulated before, we show that the phase transition in the frustrated Heisenberg stacked triangular antiferromagnet is of first order, contrary to results of earlier MC simulations using old-fashioned methods. Our result lends support to the conclusion of a nonperturbative renormalization group performed on an effective Hamiltonian. It puts an end to a 20-year -long controversial issue.
Classical Heisenberg antiferromagnet on a garnet lattice: a Monte Carlo simulation
2000-01-01
We have studied a classical antiferromagnet on a garnet lattice by means of Monte Carlo simulations in an attempt to examine the role of geometrical frustration in Gadolinium Gallium Garnet, Gd3Ga5O12 (GGG). Low-temperature specific heat, magnetisation, susceptibility, the autocorrelation function A(t) and the neutron scattering function S(Q) have been calculated for several models including different types of magnetic interactions and with the presence of an external magnetic field applied a...
Magnetization damping in noncollinear spin valves with antiferromagnetic interlayer couplings
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.
Spin order and dynamics in the diamond-lattice Heisenberg antiferromagnets CuRh2O4 and CoRh2O4
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.
Topological frustration of artificial spin ice
Drisko, Jasper; Marsh, Thomas; Cumings, John
2017-01-01
Frustrated systems, typically characterized by competing interactions that cannot all be simultaneously satisfied, display rich behaviours not found elsewhere in nature. Artificial spin ice takes a materials-by-design approach to studying frustration, where lithographically patterned bar magnets mimic the frustrated interactions in real materials but are also amenable to direct characterization. Here, we introduce controlled topological defects into square artificial spin ice lattices in the form of lattice edge dislocations and directly observe the resulting spin configurations. We find the presence of a topological defect produces extended frustration within the system caused by a domain wall with indeterminate configuration. Away from the dislocation, the magnets are locally unfrustrated, but frustration of the lattice persists due to its topology. Our results demonstrate the non-trivial nature of topological defects in a new context, with implications for many real systems in which a typical density of dislocations could fully frustrate a canonically unfrustrated system.
Magnetic frustration of graphite oxide
Lee, Dongwook; Seo, Jiwon
2017-01-01
Delocalized π electrons in aromatic ring structures generally induce diamagnetism. In graphite oxide, however, π electrons develop ferromagnetism due to the unique structure of the material. The π electrons are only mobile in the graphitic regions of graphite oxide, which are dispersed and surrounded by sp3-hybridized carbon atoms. The spin-glass behavior of graphite oxide is corroborated by the frequency dependence of its AC susceptibility. The magnetic susceptibility data exhibit a negative Curie temperature, field irreversibility, and slow relaxation. The overall results indicate that magnetic moments in graphite oxide slowly interact and develop magnetic frustration. PMID:28327606
Frustrated Ferromagnetic Spin Chain near the Transition Point
Institute of Scientific and Technical Information of China (English)
ZHU Ren-Gui
2011-01-01
@@ The one-dimensional quantum spin-1/2 model with nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic interaction is considered.The Hamiltonian is firstly rewritten in a form with rotated spin operators,then bosonized by using the linear spin wave approximation and then treated by using the Green function approach.An integral expression of the quantum correction to the classical ground state energy is derived.The critical behavior of the ground state energy in the vicinity of the transition point from the ferromagnetic to the singlet ground state is analyzed by numerical calculation and the result is-8γ2.%The one-dimensional quantum spin-1/2 model with nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic interaction is considered. The Hamiltonian is firstly rewritten in a form with rotated spin operators, then bosonized by using the linear spin wave approximation and then treated by using the Green function approach. An integral expression of the quantum correction to the classical ground state energy is derived. The critical behavior of the ground state energy in the vicinity of the transition point from the ferromagnetic to the singlet ground state is analyzed by numerical calculation and the result is -8r2.
Antiferromagnetic spin Seebeck Effect
Wu, SM; W. Zhang; Kc, A; Borisov, P.; Pearson, JE; Jiang, JS; Lederman, D.; Hoffmann, A.; Bhattacharya, A
2015-01-01
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 t...
Kondo Screening and Fermi Surface in the Antiferromagnetic Metal Phase
Yamamoto, Seiji; Si, Qimiao
2006-03-01
We address the Kondo effect deep inside the antiferromagnetic metal phase of a Kondo lattice Hamiltonian with SU(2) invariance. The local- moment component is described in terms of a non-linear sigma model. The Fermi surface of the conduction electron component is taken to be sufficiently small, so that it is not spanned by the antiferromagnetic wavevector. The effective low energy form of the Kondo coupling simplifies drastically, corresponding to the uniform component of the magnetization that forward-scatters the conduction electrons on their own Fermi surface. We use a combined bosonic and fermionic (Shankar) renormalization group procedure to analyze this effective theory and study the Kondo screening and Fermi surface in the antiferromagnetic phase. The implications for the global magnetic phase diagram, as well as quantum critical points, of heavy fermion metals are discussed.
Exploration of Artificial Frustrated Magnets
Energy Technology Data Exchange (ETDEWEB)
Samarth, Nitin [Pennsylvania State Univ., University Park, PA (United States); Schiffer, Peter [Univ. of Illinois, Urbana, IL (United States); Crespi, Vincent [Univ. of Illinois, Urbana, IL (United States)
2015-02-17
This program encompasses experimental and theoretical studies of arrays of nanometer-scale magnets known as “artificial frustrated magnets”. These magnets are small and closely spaced, so that their behavior as a collective group is complex and reveals insights into how such collections of interacting objects behave as a group. In particular, the placement of the magnets is such that the interactions between them are “frustrated”, in that they compete with each other. These systems are analogs to a class of magnetic materials in which the lattice geometry frustrates interactions between individual atomic moments, and in which a wide range of novel physical phenomena have been recently observed. The advantage to studying the arrays is that they are both designable and resolvable: i.e., the experiments can control all aspects of the array geometry, and can also observe how individual elements of the arrays behave. This research program demonstrated a number of phenomena including the role of multiple collective interactions, the feasibility of using systems with their magnetism aligned perpendicular to the plane of the array, the importance of disorder in the arrays, and the possibility of using high temperatures to adjust the magnet orientations. All of these phenomena, and others explored in this program, add to the body of knowledge around collective magnetic behavior and magnetism in general. Aside from building scientific knowledge in an important technological area, with relevance to computing and memory, the program also gave critical support to the education of students working on the experiments.
La{sub 2}NiTiO{sub 6}: A 3D S=1 fcc Heisenberg antiferromagnet
Energy Technology Data Exchange (ETDEWEB)
Karolak, Michael; Edelmann, Martin; Sangiovanni, Giorgio [Institut fuer Theoretische Physik und Astrophysik, Universitaet Wuerzburg (Germany)
2015-07-01
A DFT+DMFT analysis of the double perovskite La{sub 2}NiTiO{sub 6} reveals the crystal to exhibit a nearly unfrustrated three-dimensional ordering of local magnetic moments of S=1 on an fcc sublattice. In DFT, La{sub 2}NiTiO{sub 6} shows a peculiar bandstructure in which the Ni e{sub g} bands are half-filled and split from bands of other character by at least 0.5 eV. The bandwidth of Ni e{sub g} is around 0.8 eV, which is attributed to strongly reduced hopping amplitudes caused by the Ti sites. By Wannier projection on the correlated subspace of only Ni e{sub g}, an effective direct exchange model is derived to obtain quantitative values for the superexchange coupling between Ni sites. Comparing nearest-neighbour to next-nearest-neighbour coupling, the latter exceeds the former by a factor of 4 at minimum. This causes a nearly unfrustrated antiferromagnetic ordering of the local moments, whose Neel temperature is low not as a result of frustration but of strong correlation, as is revealed by an investigation of the kinetic and potential energy differences between ordered an unordered phase. The double perovskite La{sub 2}NiTiO{sub 6} is identified as an interesting S=1 quantum antiferromagnet on a three-dimensional fcc sublattice. By means of Density Functional Theory (DFT) in combination with Dynamical Mean Field Theory (DMFT) it is demonstrated that this material is a high-spin d-electron system deep in the Heisenberg limit and established that its paramagnetic Mott phase persists down to low temperatures not because of frustration effects but rather for the strong coupling physics. Our many-body calculations on an ab initio-derived multi-orbital basis predict indeed a kinetic energy gain when entering the magnetically ordered phase. The strong-coupling nature is assessed from a multi-orbital DFT+DMFT analysis of the energetic balance between the ordered and disordered phase, which reveals a kinetic-energy-driven ordering. La{sub 2}NiTiO{sub 6} emerges thus as a
Energy Technology Data Exchange (ETDEWEB)
Watanabe, Tadataka [Department of Physics, College of Science and Technology (CST), Nihon University, Chiyoda-ku, Tokyo 101-8308 (Japan); Hara, Shigeo; Ikeda, Shin-Ichi, E-mail: tadataka@phys.cst.nihon-u.ac.j [Nanoelectronics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan)
2009-03-01
Ultrasound velocity measurements of the cubic spinel GeCo{sub 2}O{sub 4} in the single crystal have been performed for the investigations of shear and compression moduli. The shear moduli reveal the absence of Jahn-Teller activity despite the presence of the orbital degeneracy in the Co{sup 2+} ions. This Jahn-Teller inactivity indicates that the intersite orbital-orbital interaction is much stronger than the Jahn-Teller coupling. The compression moduli reveal that the dominant path of the exchange interactions for the antiferromagnetic transition lies in the [111] direction. This exchange-path anisotropy is consistent with the antiferromagnetic structure with the wave vector q || [111], suggesting the presence of bond frustration among several ferromagnetic and antiferromagientic interactions. In the JT-inactive condition, the bond frustration can be induced by geometrical orbital frustration of t{sub 2g}-t{sub 2g} interaction between the Co{sup 2+} ions which can be realized in the pyrochlore lattice of the high spin Co{sup 2+} with t{sub 2g} -orbital degeneracy. In GeCo{sub 2}O{sub 4}, the tetragonal elongation below T{sub N} releases the orbital frustration by quenching the orbital degeneracy.
Institute of Scientific and Technical Information of China (English)
周琼; 李晋斌
2011-01-01
The Antiferromagnetic Heisenberg Model with spin 1/2 on a square lattice was simulated by using the Stochastic Series Expansion (SSE) Quantum Monte Carlo Method. The temperature dependence of the internal energy, specific heat and uniform susceptibility was observed. The results showed that specific heat has a maximum at kT/J = 0.6 and uniform susceptibility saturates at kT/J = 1 for the isotropy case. And the size of lattice also affects the temperature dependence of these thermodynamic quantities. For the anisotropy case, energy decreases with anisotropic parameter g increasing. Susceptibility changes slowly with temperature for g ＜ 1 and exponentially decay for g ＞ 1 in the low temperature region and its behaviors approach consistent for different g in the high temperature region.%采用Stochastic Series Expansion(SSE)量子蒙特卡洛方法对正方晶格中自旋为1/2的反铁磁海森堡模型进行计算机模拟,给出能量、比热及均匀磁化率与温度的变化关系.结果表明:在各向同性情况下,温度约在kT/J=0.6处,比热有峰值,温度约在kT/J=1处,均匀磁化率达到饱和,且晶格大小的有限性对热力学量与温度的变化行为有一定的影响;在各向异性情况下,能量随着各向异性参数g的增加而减小,且在低温区,当g1时,均匀磁化率随温度降低向零指数衰减,在高温区,对不同各向异性参数g,均匀磁化率随温度变化行为趋于一致.
Local-TQO and Stability of Frustration-Free Hamiltonians
Pytel, Justyna; Michalakis, Spyridon
2012-02-01
The attention of the condensed matter and mathematical physics communities has recently focused on Hamiltonians with low-energy sectors exhibiting some form of topological order. In our work [1], we present a generalization of the result of Bravyi et al. [2,3] on the stability of topological quantum order for Hamiltonians composed of commuting projections with a common zero-energy subspace. In particular, the commutativity condition can be removed: We prove stability of the spectral gap for gapped, frustration-free Hamiltonians under general, quasi-local perturbations. Also, we will discuss the ``Local Topological Quantum Order'' and ``Local-Gap'' conditions sufficient for proving stability. [4pt] [1] S. Michalakis and J. Pytel, Stability of Frustration-Free Hamiltonians. arXiv:1109.1588 (2011).[0pt] [2] S. Bravyi and M.B. Hastings, A short proof of stability of topological order under local perturbations. arXiv:1001.4363. [0pt] [3] S. Bravyi, M.B. Hastings, and S. Michalakis, Topological quantum order: stability under local perturbations. J. Math. Phys. 51, 093512 (2010).
A model for doping-dependent magnetic frustration and ordering in a triangular lattice
Sheshadri, K.; Chainani, A.
2013-10-01
The family of cobaltates AxCoO2 (A = Na, Li, K), with a crystal structure consisting of a layered triangular lattice of Co ions, exhibits a fascinating range of coupled spin, charge and ion ordering phenomena as a function of electron doping content x. Based on these experimental observations, we investigate an extended Ising (J\\text{-}J') model for suppression of magnetic frustration caused by electron doping in a quasi-2-dimensional nearest-neighbour antiferromagnetic triangular lattice. As determined by geometry and bond-counting, it is found that magnetic frustration can be quantified by a frustration index fub and its magnitude is a non-monotonic function of x. A mean-field calculation is carried out to determine the temperature-dependent magnetization, spin-entropy and heat capacity for the obtained structures with the lowest energy (≡ lowest fub) for each x. The calculations reveal that the magnetic-ordering temperature TC exhibits an anti-correlation with fub as a function of x. In addition, as seen in thermopower experiments, an anomalous spin-entropy is obtained for the high-doping cases when J'>0.7J . The results indicate the importance of doping-dependent magnetic frustration in the layered cobaltates.
Superconductivity, antiferromagnetism, and neutron scattering
Energy Technology Data Exchange (ETDEWEB)
Tranquada, John M., E-mail: jtran@bnl.gov; Xu, Guangyong; Zaliznyak, Igor A.
2014-01-15
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. - Highlights: • High-temperature superconductivity is closely associated with antiferromagnetism. • Antiferromagnetic spin fluctuations coexist with the superconductivity. • Neutron scattering is essential for characterising the full spectrum of spin excitations.
Coverage versus Supply Cost in Facility Location: Physics of Frustrated Spin Systems
Yeung, Chi Ho; Li, Bo
2013-01-01
A comprehensive coverage is crucial for communication, supply and transportation networks, yet it is limited by the requirement of extensive infrastructure and heavy energy consumption. Here we draw an analogy between spins in antiferromagnet and outlets in supply networks, and apply techniques from the studies of disordered systems to elucidate the effects of balancing the coverage and supply costs on the network behavior. A readily applicable, coverage optimization algorithm is derived. Simulation results show that magnetized and antiferromagnetic domains emerge and coexist to balance the need for coverage and energy saving. The scaling of parameters with system size agrees with the continuum approximation in two dimensions and the tree approximation in random graphs. Due to frustration caused by the competition between coverage and supply cost, a transition between easy and hard computation regimes is observed. We further suggest a local expansion approach to greatly simplify the message updates which shed...
Coverage versus supply cost in facility location: Physics of frustrated spin systems
Yeung, Chi Ho; Wong, K. Y. Michael; Li, Bo
2014-06-01
A comprehensive coverage is crucial for communication, supply, and transportation networks, yet it is limited by the requirement of extensive infrastructure and heavy energy consumption. Here, we draw an analogy between spins in antiferromagnet and outlets in supply networks, and apply techniques from the studies of disordered systems to elucidate the effects of balancing the coverage and supply costs on the network behavior. A readily applicable, coverage optimization algorithm is derived. Simulation results show that magnetized and antiferromagnetic domains emerge and coexist to balance the need for coverage and energy saving. The scaling of parameters with system size agrees with the continuum approximation in two dimensions and the tree approximation in random graphs. Due to frustration caused by the competition between coverage and supply cost, a transition between easy and hard computation regimes is observed. We further suggest a local expansion approach to greatly simplify the message updates which shed light on simplifications in other problems.
Onset of antiferromagnetism in heavy-fermion metals
Schroder; Aeppli; Coldea; Adams; Stockert; v. Lohneysen H; Bucher; Ramazashvili; Coleman
2000-09-21
There are two main theoretical descriptions of antiferromagnets. The first arises from atomic physics, which predicts that atoms with unpaired electrons develop magnetic moments. In a solid, the coupling between moments on nearby ions then yields antiferromagnetic order at low temperatures. The second description, based on the physics of electron fluids or 'Fermi liquids' states that Coulomb interactions can drive the fluid to adopt a more stable configuration by developing a spin density wave. It is at present unknown which view is appropriate at a 'quantum critical point' where the antiferromagnetic transition temperature vanishes. Here we report neutron scattering and bulk magnetometry measurements of the metal CeCu(6-x)Au(x), which allow us to discriminate between the two models. We find evidence for an atomically local contribution to the magnetic correlations which develops at the critical gold concentration (x(c) = 0.1), corresponding to a magnetic ordering temperature of zero. This contribution implies that a Fermi-liquid-destroying spin-localizing transition, unanticipated from the spin density wave description, coincides with the antiferromagnetic quantum critical point.
Intertwining of Frustration with Magneto-Elastic Coupling in the Multiferroic LuMnO3
Yano, Shin-ichiro; Louca, Despina; Chi, Songxue; Matsuda, Masaaki; Qiu, Yiming; Copley, John R. D.; Cheong, Sang-Wook
2014-02-01
Residual magnetic frustration in the multiferroic LuMnO3 may be key towards understanding magneto-elastic coupling in hexagonal manganites. Critical magnetic scattering present well above the magnetic ordering temperature TN persists below, as observed by inelastic neutron scattering. The magnetic fluctuations are confined in two dimensions implied by the characteristic wavevector dependence of the magnetic structure factor that changes from symmetric to asymmetric across TN. The low dimensionality of the magnetic structure is also evident in the temperature dependence of the commensurate antiferromagnetic intensity which follows a mean field exponent of β ˜ 0.2.
Intertwining of Frustration with Magneto-Elastic Coupling in the Multiferroic LuMnO3
Energy Technology Data Exchange (ETDEWEB)
Yano, Shin-ichiro [University of Virginia; Louca, Despina [University of Virginia; Chi, Songxue [ORNL; Matsuda, Masaaki [ORNL; Copley, John R. D. [National Institute of Standards and Technology (NIST), Gaithersburg, MD; Cheong, Sang-Wook [Rutgers University
2014-01-01
Residual magnetic frustration in the multiferroic LuMnO3 may be key towards understanding magneto-elastic coupling in hexagonal manganites. Critical magnetic scattering present well above the magnetic ordering temperature TN persists below, as observed by inelastic neutron scattering. The magnetic fluctuations are confined in two dimensions implied by the characteristic wavevector dependence of the magnetic structure factor that changes from symmetric to asymmetric across TN. The low dimensionality of the magnetic structure is also evident in the temperature dependence of the commensurate antiferromagnetic intensity which follows a mean field exponent of 0.2.
Energy Technology Data Exchange (ETDEWEB)
Li, W. C.; Song, X.; Feng, J. J.; Zeng, M.; Gao, X. S.; Qin, M. H., E-mail: qinmh@scnu.edu.cn [Institute for Advanced Materials and Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, South China Normal University, Guangzhou 510006 (China); Jia, X. T. [School of Physics and Chemistry, Henan Polytechnic University, Jiaozuo 454000 (China)
2015-07-07
In this work, the effects of the random exchange interaction on the phase transitions and phase diagrams of classical frustrated Heisenberg model are investigated by Monte Carlo simulation in order to simulate the chemical doping effect in real materials. It is observed that the antiferromagnetic transitions shift toward low temperature with the increasing magnitude of the random exchange interaction, which can be qualitatively understood from the competitions among local spin states. This study is related to the magnetic properties in the doped iron-based superconductors.
Lounis, S
2014-07-01
How does magnetism behave when the physical dimension is reduced to the size of nanostructures? The multiplicity of magnetic states in these systems can be very rich, in that their properties depend on the atomic species, the cluster size, shape and symmetry or choice of the substrate. Small variations of the cluster parameters may change the properties dramatically. Research in this field has gained much by the many novel experimental methods and techniques exhibiting atomic resolution. Here we review the ab-initio approach, focusing on recent calculations on magnetic frustration and occurrence of non-collinear magnetism in antiferromagnetic nanostructures deposited on surfaces.
Ultrasound velocity measurements in orbital-degenerate frustrated spinel MgV2O4
Ishikawa, T.; Watanabe, T.; Hara, S.; Islam, A. T. M. N.; Wheeler, E. M.; Lake, B.
2015-03-01
Ultrasound velocity measurements of the orbital-degenerate frustrated spinel MgV2O4 are performed in the disorder-free high-purity single crystal which exhibits successive structural and antiferromagnetic phase transitions, and in the disorder-introduced single crystal which exhibits spin-glass-like behavior. The measurements reveal coexisting two types of anomalous temperature dependence of the elastic moduli in the cubic paramagnetic phase: Curie-type softening with decreasing temperature, and softening with a characteristic minimum with decreasing temperature. These elastic anomalies should respectively originate from the coexisting orbital fluctuations and spin-cluster excitations.
Spin relaxation in geometrically frustrated pyrochlores
Dunsiger, Sarah Ruth
This thesis describes muSR experiments which focus on systems where the magnetic ions occupy the vertices of edge or corner sharing triangular units, in particular the pyrochlores A2B2O7. The scientific interest in pyrochlores is based on the fact that they display novel magnetic behaviour at low temperatures due to geometrical frustration. The ground state of these systems is sensitively dependent on such factors as the range of the spin-spin interactions, disorder, anisotropy, thermal and quantum fluctuations. For example, Y2Mo2O7 shows many features reminiscent of a conventional spin glass, even though this material has nominally zero chemical disorder. It is found that the muon spin polarisation obeys a time-field scaling relation which indicates that the spin-spin autocorrelation function has a power law form in time, in stark contrast with the exponential form often assumed for conventional magnets above their transition temperature. Gd2Ti2O7 shows long range order, but only at a temperature much lower than its Curie-Weiss temperature, a signature of a frustrated system. In the paramagnetic regime, it is well described by an isotropic Heisenberg Hamiltonian with nearest neighbour couplings in the presence of a Zeeman interaction, from which the spin-spin autocorrelation function may be calculated as a power series in time. The muon spin relaxation rate decreases with magnetic field as the Zeeman energy becomes comparable with the exchange coupling between Gd spins. Thus, an independent measure of the exchange coupling or equivalently the Gd spin fluctuation rate is extracted. By contrast, Tb2Ti2O7 has been identified as a type of cooperative paramagnet. Short range correlations develop below 50 K. However, there is no long range ordering down to very low temperatures (0.075 K). The Tb3+ ion is subject to strong crystal electric field effects: point charge calculations indicate that this system is Ising like at low temperatures. Thus this system may be
Frustration, culmination, and inertia in Kimaragang grammar
Directory of Open Access Journals (Sweden)
Paul Kroeger
2017-06-01
Full Text Available The FRUSTRATIVE particle in Kimaragang marks unrealized expectations or intentions, counterfactuals, etc. Copley & Harley (2010 propose a unified account for frustratives, non-culminating accomplishments (‘I killed the snake but it didn’t die’ and the “imperfective paradox”, based on Dowty’s (1979 concept of “inertia”. I argue that this analysis makes the wrong predictions for Kimaragang. The distribution of frustratives and non-culminating accomplishments in Kimaragang reveals a number of differences not predicted by the Copley & Harley analysis. These differences in distribution reflect in part a difference in the kind of expectation that is involved. In non-culminating accomplishments, the unachieved result is specified by the meaning of the verb, whereas frustrative clauses may involve expectations that are based on cultural factors, knowledge of the world, etc. I sketch out an alternative analysis of Kimaragang frustratives which treats expectation and intention as modal concepts.
Teacher frustration and professional development: Causes, consequences and practical implications
DEFF Research Database (Denmark)
Noesgaard, Signe Schack
2017-01-01
The influence of frustration on the effectiveness of teacher professional development has previously been overlooked. This study of in-service teachers who become frustrated during professional development interventions considers the development of two Danish science teachers. Frustration theory...
Ordering on geometrically frustrating lattices : The perspective of TOF neutron crystallography
Radaelli, Paolo G.; Chapon, Laurent; Gutmann, Matthias; Bombardi, Alessandro; Blake, Graeme; Schmidt, Marek; Cheong, Sang-Wook
2006-01-01
Geometrical frustration arises when geometrical constraints promote a locally degenerate ground state. A periodic system with this local geometry may ‘‘freeze’’ on cooling forming ‘‘ices’’ or remain liquid down to the lowest temperatures due to quantum effects. A third possibility is that of a struc
On Integrable Quantum Group Invariant Antiferromagnets
Cuerno, R; Gómez, C
1992-01-01
A new open spin chain hamiltonian is introduced. It is both integrable (Sklyanin`s type $K$ matrices are used to achieve this) and invariant under ${\\cal U}_{\\epsilon}(sl(2))$ transformations in nilpotent irreps for $\\epsilon^3=1$. Some considerations on the centralizer of nilpotent representations and its representation theory are also presented.
Energy Technology Data Exchange (ETDEWEB)
Sousa, Griffith Mendonça A., E-mail: griffith_mas@hotmail.com; Pires, A.S.T.
2014-03-15
The Neel and collinear ordered phases of the two-dimensional S=1 antiferromagnet with next and next near neighbor exchange interactions and easy axis single ion anisotropy, on the square lattice, are studied at low temperature using a Modified Spin Wave Theory. We calculate the low-temperature quantities as a function of the temperature, frustration and anisotropy. We calculate also the phase diagram at T=0. We found a disordered phase separating the Neel and collinear phases. - Highlights: • The phase diagrams in zero temperature. • The critical temperature was studied as a function of frustration and D. • The sublattice magnetizations and the gap were studied.
Impurity-induced antiferromagnetic domains in the periodic Anderson model
Benali, A.; Bai, Z. J.; Curro, N. J.; Scalettar, R. T.
2016-08-01
A central feature of the periodic Anderson model is the competition between antiferromagnetism, mediated by the Ruderman-Kittel-Kasuya-Yosida interaction at small conduction electron-local electron hybridization V , and singlet formation at large V . At zero temperature, and in dimension d >1 , these two phases are separated by a quantum critical point Vc. We use quantum Monte Carlo (QMC) simulations to explore the effect of impurities which have a local hybridization V*Vc . We measure the suppression of singlet correlations and the antiferromagnetic correlations which form around the impurity, as well as the size of the resulting domain. Exact diagonalization calculations for linear chains allow us to verify that the qualitative features obtained at intermediate coupling and finite T persist to strong coupling and T =0 , regimes which are difficult to access with QMC. Our calculations agree qualitatively with NMR measurements in CeCoIn5 -xCdx .
National Research Council Canada - National Science Library
Yarash K. Abuev; Albert B. Babaev; Pharkhat E. Esetov
2017-01-01
Objectives A computer simulation of the antiferromagnetic structures described by the three-vertex Potts model on a triangular lattice is performed, taking into account the antiferromagnetic exchange...
Fermion Bound States Around Skyrmions in Doped Antiferromagnets
Institute of Scientific and Technical Information of China (English)
寇谡鹏
2003-01-01
We show the skyrmion effects in doped antiferromagnets for the uniform flux phase. The low-energy effective theory of the t′-J model can be mapped onto the massive quantum electrodynamics. There exist Fermion bound states around skyrmions. For each sublattice, there exist induced fractional fermion numbers around the skyrmions. The total induced fermion number is zero due to the "cancelling effect" between two sublattices with opposite charges.
Frustrated topological symmetry breaking: Geometrical frustration and anyon condensation
Schulz, Marc D.; Burnell, Fiona J.
2016-10-01
We study the phase diagram of a topological string-net-type lattice model in the presence of geometrically frustrated interactions. These interactions drive several phase transitions that reduce the topological order, leading to a rich phase diagram including both Abelian (Z2) and non-Abelian (Ising×Ising¯ ) topologically ordered phases, as well as phases with broken translational symmetry. Interestingly, one of these phases simultaneously exhibits (Abelian) topological order and long-ranged order due to translational symmetry breaking, with nontrivial interactions between excitations in the topological order and defects in the long-ranged order. We introduce a variety of effective models, valid along certain lines in the phase diagram, which can be used to characterize both topological and symmetry-breaking order in these phases and in many cases allow us to characterize the phase transitions that separate them. We use exact diagonalization and high-order series expansion to study areas of the phase diagram where these models break down and to approximate the location of the phase boundaries.
Institute of Scientific and Technical Information of China (English)
Shan Chuan-Jia; Cheng Wei-Wen; Liu Tang-Kun; Huang Yan-Xia; Li nong
2008-01-01
By using the method of density-matrix renormalization-group to solve the different spin-spin correlation functions,the nearest-neighbouring entanglement (NNE) and the next-nearest-neighbouring entanglement (NNNE) of one-dimensional alternating Heisenberg XY spin chain are investigated in the presence of alternating the-nearestneighbouring interaction of exchange couplings,external magnetic fields and the next-nearest neighbouring interaction.For a dimerised ferromagnetic spin chain,the NNNE appears only above a critical dimerized interaction,meanwhile,the dimerized interaction a effects a quantum phase transition point and improves the NNNE to a large extent.We also study the effect of ferromagnetic or antiferromagnetic next-nearest neighbouring (NNN) interaction on the dynamics of NNE and NNNE.The ferromagnetic NNN interaction increases and shrinks the NNE below and above a critical frustrated interaction respectively,while the antiferromagnetic NNN interaction always reduces the NNE.The antiferromagnetic NNN interaction results in a large value of NNNE compared with the case where the NNN interaction is ferromagnetic.
Neutron scattering studies of three one-dimensional antiferromagnets
Kenzelmann, M
2001-01-01
observed in the disordered phase of spin-1/2 chains. The magnetic order of the one-dimensional spin-1/2 XY antiferromagnet Cs sub 2 CoCl sub 4 was investigated using neutron diffraction. The magnetic structure has an ordering wave-vector (0, 0.5, 0.5) for T < 217 mK and the magnetic structure is a non-linear structure with the magnetic moments at a small angle to the b axis. Above a field of H = 2.1 T the magnetic order collapses in an apparent first order phase transition, suggesting a transition to a spin-liquid phase. Low-dimensional magnets with low-spin quantum numbers are ideal model systems for investigating strongly interacting macroscopic quantum ground states and their non-linear spin excitations. This thesis describes neutron scattering experiments of three one-dimensional low-spin antiferromagnets where strong quantum fluctuations lead to highly-correlated ground states and unconventional cooperative spin excitations. The excitation spectrum of the antiferromagnetic spin-1 Heisenberg chain CsNi...
Creation of an antiferromagnetic exchange spring
Energy Technology Data Exchange (ETDEWEB)
Scholl, A.; Liberati, M.; Arenholz, E.; Ohldag, H.; Stohr, J.
2004-04-06
We present evidence for the creation of an exchange spring in an antiferromagnet due to exchange coupling to a ferromagnet. X-ray magnetic linear dichroism spectroscopy on single crystal Co/NiO(001) shows that a partial domain wall is wound up at the surface of the antiferromagnet when the adjacent ferromagnet is rotated by a magnetic field. We determine the interface exchange stiffness and the antiferromagnetic domain wall energy from the field dependence of the direction of the antiferromagnetic axis, the antiferromagnetic pendant to a ferromagnetic hysteresis loop. The existence of a planar antiferromagnetic domain wall, proven by our measurement, is a key assumption of most exchange bias models.
Emergent lattices with geometrical frustration in doped extended Hubbard models
Kaneko, Ryui; Tocchio, Luca F.; Valentí, Roser; Gros, Claudius
2016-11-01
Spontaneous charge ordering occurring in correlated systems may be considered as a possible route to generate effective lattice structures with unconventional couplings. For this purpose we investigate the phase diagram of doped extended Hubbard models on two lattices: (i) the honeycomb lattice with on-site U and nearest-neighbor V Coulomb interactions at 3 /4 filling (n =3 /2 ) and (ii) the triangular lattice with on-site U , nearest-neighbor V , and next-nearest-neighbor V' Coulomb interactions at 3 /8 filling (n =3 /4 ). We consider various approaches including mean-field approximations, perturbation theory, and variational Monte Carlo. For the honeycomb case (i), charge order induces an effective triangular lattice at large values of U /t and V /t , where t is the nearest-neighbor hopping integral. The nearest-neighbor spin exchange interactions on this effective triangular lattice are antiferromagnetic in most of the phase diagram, while they become ferromagnetic when U is much larger than V . At U /t ˜(V/t ) 3 , ferromagnetic and antiferromagnetic exchange interactions nearly cancel out, leading to a system with four-spin ring-exchange interactions. On the other hand, for the triangular case (ii) at large U and finite V', we find no charge order for small V , an effective kagome lattice for intermediate V , and one-dimensional charge order for large V . These results indicate that Coulomb interactions induce [case (i)] or enhance [case(ii)] emergent geometrical frustration of the spin degrees of freedom in the system, by forming charge order.
Characterization of the Dilute Ising Antiferromagnet
Energy Technology Data Exchange (ETDEWEB)
Wiener, T.
2000-09-12
A spin glass is a magnetic ground state in which ferromagnetic and antiferromagnetic exchange interactions compete, thereby creating frustration and a multidegenerate state with no long range order. An Ising system is a system where the spins are constrained to lie parallel or antiparallel to a primary axis. There has been much theoretical interest in the past ten years in the effects of applying a magnetic field transverse to the primary axis in an Ising spin glass at low temperatures and thus study phase transitions at the T=0 limit. The focus of this study is to search for and characterize a new Ising spin glass system. This is accomplished by site diluting yttrium for terbium in the crystalline material TbNi{sub 2}Ge{sub 2}. The first part of this work gives a brief overview of the physics of rare earth magnetism and an overview of experimental characteristics of spin glasses. This is followed by the methodology used to manufacture the large single crystals used in this study, as well as the measurement techniques used. Next, a summary of the results of magnetic measurements on across the dilution series from pure terbium to pure yttrium is presented. This is followed by detailed measurements on particular dilutions which demonstrate spin glass behavior. Pure TbNi{sub 2}Ge{sub 2} is an Ising antiferromagnet with a several distinct metamagnetic states below 17 K. As the terbium is alloyed with yttrium, these magnetic states are weakened in a consistent manner, as is seen in measurements of the transition temperatures and analysis of Curie-Weiss behavior at high temperature. At low concentrations of terbium, below 35%, long range order is no longer present and a spin-glass-like state emerges. This state is studied through various measurements, dc and ac susceptibility, resistivity, and specific heat. This magnetic behavior was then compared to that of other well characterized spin glasses. It is concluded that there is a region of concentration s for which a spin
Characterization of the Dilute Ising Antiferromagnet
Energy Technology Data Exchange (ETDEWEB)
Wiener, Timothy [Iowa State Univ., Ames, IA (United States)
2000-09-12
A spin glass is a magnetic ground state in which ferromagnetic and antiferromagnetic exchange interactions compete, thereby creating frustration and a multidegenerate state with no long range order. An Ising system is a system where the spins are constrained to lie parallel or antiparallel to a primary axis. There has been much theoretical interest in the past ten years in the effects of applying a magnetic field transverse to the primary axis in an Ising spin glass at low temperatures and thus study phase transitions at the T=0 limit. The focus of this study is to search for and characterize a new Ising spin glass system. This is accomplished by site diluting yttrium for terbium in the crystalline material TbNi_{2}Ge_{2}. The first part of this work gives a brief overview of the physics of rare earth magnetism and an overview of experimental characteristics of spin glasses. This is followed by the methodology used to manufacture the large single crystals used in this study, as well as the measurement techniques used. Next, a summary of the results of magnetic measurements on across the dilution series from pure terbium to pure yttrium is presented. This is followed by detailed measurements on particular dilutions which demonstrate spin glass behavior. Pure TbNi_{2}Ge_{2} is an Ising antiferromagnet with a several distinct metamagnetic states below 17 K. As the terbium is alloyed with yttrium, these magnetic states are weakened in a consistent manner, as is seen in measurements of the transition temperatures and analysis of Curie-Weiss behavior at high temperature. At low concentrations of terbium, below 35%, long range order is no longer present and a spin-glass-like state emerges. This state is studied through various measurements, dc and ac susceptibility, resistivity, and specific heat. This magnetic behavior was then compared to that of other well characterized spin glasses. It is concluded that there is a region of
Introduction to Frustrated Magnetism Materials, Experiments, Theory
Lacroix, Claudine; Mila, Frédéric
2011-01-01
The field of Highly Frustrated Magnetism has developed and expanded considerably over the last 15 years. Originating with canonical geometric frustration of interactions, it today extends over other phenomena with many degrees of freedom, including magneto-elastic couplings, orbital degrees of freedom, dilution effects, and electron doping. It is also demonstrated that the concept of frustration impacts many other fields in physics beyond magnetism. This book represents a state-of-the-art review aimed at a broad audience with tutorial chapters and more topical ones, which encompass solid-state chemistry as well as experimental and theoretical physics.
Magnetic Orders and Fluctuations in the Dipolar Pyrochlore Antiferromagnet
Cepas, Olivier; Shastry, B. Sriram
2005-03-01
While the classical Heisenberg antiferromagnet on the pyrochlore lattice does not order, we will discuss, from a theoretical standpoint, possible magnetic phases induced by the dipole-dipole interactions. Such interactions play a role in systems such as Gd2Ti2O7 or Gd2Sn2O7 in stabilizing exotic forms of magnetic order, a subject of current debate. We will also argue that the external magnetic field induces multiple transitions, one of which is associated with no obvious broken symmetry, but can be characterized by a disorder parameter. Finally, Monte-Carlo simulations and Landau-Ginzburg expansion show that the dipolar Heisenberg model exhibits a fluctuation-induced first-order transition, thanks to the frustration and a continuous set of soft modes.
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.
Thermophoresis of an antiferromagnetic soliton
Kim, Se Kwon; Tchernyshyov, Oleg; Tserkovnyak, Yaroslav
2015-07-01
We study the dynamics of an antiferromagnetic soliton under a temperature gradient. To this end, we start by phenomenologically constructing the stochastic Landau-Lifshitz-Gilbert equation for an antiferromagnet with the aid of the fluctuation-dissipation theorem. We then derive the Langevin equation for the soliton's center of mass by the collective coordinate approach. An antiferromagentic soliton behaves as a classical massive particle immersed in a viscous medium. By considering a thermodynamic ensemble of solitons, we obtain the Fokker-Planck equation, from which we extract the average drift velocity of a soliton. The diffusion coefficient is inversely proportional to a small damping constant α , which can yield a drift velocity of tens of m/s under a temperature gradient of 1 K/mm for a domain wall in an easy-axis antiferromagnetic wire with α ˜10-4 .
Atomic spin-chain realization of a model for quantum criticality
Toskovic, R.; van den Berg, R.; Spinelli, A.; Eliens, I. S.; van den Toorn, B.; Bryant, B.; Caux, J.-S.; Otte, A. F.
2016-07-01
The ability to manipulate single atoms has opened up the door to constructing interesting and useful quantum structures from the ground up. On the one hand, nanoscale arrangements of magnetic atoms are at the heart of future quantum computing and spintronic devices; on the other hand, they can be used as fundamental building blocks for the realization of textbook many-body quantum models, illustrating key concepts such as quantum phase transitions, topological order or frustration as a function of system size. Here, we use low-temperature scanning tunnelling microscopy to construct arrays of magnetic atoms on a surface, designed to behave like spin-1/2 XXZ Heisenberg chains in a transverse field, for which a quantum phase transition from an antiferromagnetic to a paramagnetic phase is predicted in the thermodynamic limit. Site-resolved measurements on these finite-size realizations reveal a number of sudden ground state changes when the field approaches the critical value, each corresponding to a new domain wall entering the chains. We observe that these state crossings become closer for longer chains, suggesting the onset of critical behaviour. Our results present opportunities for further studies on quantum behaviour of many-body systems, as a function of their size and structural complexity.
Quantum Coherence and Random Fields at Mesoscopic Scales
Energy Technology Data Exchange (ETDEWEB)
Rosenbaum, Thomas F. [Univ. of Chicago, IL (United States)
2016-03-01
We seek to explore and exploit model, disordered and geometrically frustrated magnets where coherent spin clusters stably detach themselves from their surroundings, leading to extreme sensitivity to finite frequency excitations and the ability to encode information. Global changes in either the spin concentration or the quantum tunneling probability via the application of an external magnetic field can tune the relative weights of quantum entanglement and random field effects on the mesoscopic scale. These same parameters can be harnessed to manipulate domain wall dynamics in the ferromagnetic state, with technological possibilities for magnetic information storage. Finally, extensions from quantum ferromagnets to antiferromagnets promise new insights into the physics of quantum fluctuations and effective dimensional reduction. A combination of ac susceptometry, dc magnetometry, noise measurements, hole burning, non-linear Fano experiments, and neutron diffraction as functions of temperature, magnetic field, frequency, excitation amplitude, dipole concentration, and disorder address issues of stability, overlap, coherence, and control. We have been especially interested in probing the evolution of the local order in the progression from spin liquid to spin glass to long-range-ordered magnet.
Bold diagrammatic Monte Carlo method applied to fermionized frustrated spins.
Kulagin, S A; Prokof'ev, N; Starykh, O A; Svistunov, B; Varney, C N
2013-02-15
We demonstrate, by considering the triangular lattice spin-1/2 Heisenberg model, that Monte Carlo sampling of skeleton Feynman diagrams within the fermionization framework offers a universal first-principles tool for strongly correlated lattice quantum systems. We observe the fermionic sign blessing--cancellation of higher order diagrams leading to a finite convergence radius of the series. We calculate the magnetic susceptibility of the triangular-lattice quantum antiferromagnet in the correlated paramagnet regime and reveal a surprisingly accurate microscopic correspondence with its classical counterpart at all accessible temperatures. The extrapolation of the observed relation to zero temperature suggests the absence of the magnetic order in the ground state. We critically examine the implications of this unusual scenario.
Parents and School Proprietors Frustrating National Education ...
African Journals Online (AJOL)
Parents and School Proprietors Frustrating National Education Policy: What ... of the National Policy on Education which envisaged that all children would remain in ... roles that stakeholders – parents, school proprietors, school administrators, ...
Yang, Ming; Zhang, Su-Yun; Guo, Wen-Bin; Tang, Ying-Ying; He, Zhang-Zhen
2015-09-21
A novel copper compound, Cu13(VO4)4(OH)10F4, featuring two types of two-dimensional extended kagome-like and triangular lattices, exhibits long-range antiferromagnetic ordering at ∼3 K, a strong spin-frustration effect with f = 21 and a spin-flop transition at 5 T.
Superconductivity, antiferromagnetism, and neutron scattering
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.
Correlated spin networks in frustrated systems
Stone, Thomas E.; McKay, Susan R.
2010-08-01
We introduce a network model for frustrated spin systems based on highly correlated spin fluctuations, to quantify and visualize their ordering. This model shows that networks of strongly correlated but non-contiguous spins exist at low temperatures on a triangular Ising lattice with competing nearest-neighbor interactions. This finding is consistent with chaotic renormalization-group trajectories previously reported for frustrated hierarchical lattices.
Competing antiferromagnetic and spin-glass phases in a hollandite structure
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.
Three-sublattice skyrmion crystal in the antiferromagnetic triangular lattice
Rosales, H. D.; Cabra, D. C.; Pujol, Pierre
2015-12-01
The frustrated classical antiferromagnetic Heisenberg model with Dzyaloshinskii-Moriya (DM) interactions on the triangular lattice is studied under a magnetic field by means of semiclassical calculations and large-scale Monte Carlo simulations. We show that even a small DM interaction induces the formation of an antiferromagnetic skyrmion crystal (AF-SkX) state. Unlike what is observed in ferromagnetic materials, we show that the AF-SkX state consists of three interpenetrating skyrmion crystals (one by sublattice), and most importantly, the AF-SkX state seems to survive in the limit of zero temperature. To characterize the phase diagram we compute the average of the topological order parameter which can be associated with the number of topological charges or skyrmions. As the magnetic field increases this parameter presents a clear jump, indicating a discontinuous transition from a spiral phase into the AF-SkX phase, where multiple Bragg peaks coexist in the spin structure factor. For higher fields, a second (probably continuous) transition occurs into a featureless paramagnetic phase.
Evidence for Intertwining of Superconductivity and Antiferromagnetism in a Cuprate
Tranquada, John; Xu, Zhijun; Stock, C.; Chi, S. X.; Kolesnikov, A. I.; Xu, G. Y.; Gu, G. D.
2014-03-01
We have used inelastic neutron scattering to measure the low-energy, incommensurate antiferromagnetic spin excitations both above and below the superconducting transition temperature (Tc = 32 K) of La1.905Ba0.095CuO4. While the magnetic excitations in optimally-doped cuprates typically show the development of a spin gap and magnetic resonance below Tc, our sample shows no such effect. Instead strong, gapless spin excitations coexist with bulk superconductivity. To understand this, we note that previous transport measurements have shown that the superconducting layers are decoupled by a magnetic field applied along the c-axis, resulting in a state with frustrated interlayer Josephson coupling, similar to LBCO with x = 1 / 8 , where it has been proposed that pair-density-wave superconductivity occurs. This suggests that, in a similar fashion, the spatially modulated antiferromagnetic correlations (which we see directly in the x = 0 . 095 sample) are intertwined with a spatially modulated superconducting pair wave function. Work at BNL supported by Office of Basic Energy Sciences, US DOE, under Contract No. DE-AC02-98CH10886.
Polarized neutron scattering on geometrically frustrated magnets with Swedenborgite structure
Energy Technology Data Exchange (ETDEWEB)
Valldor, Martin [II. Physikalisches Institut, Universitaet Koeln (Germany); Sanders, Yvonne; Schweika, Werner [Institut fuer Festkoerperforschung, Forschungszentrum Juelich (Germany)
2009-07-01
Diffuse scattering of polarized neutrons on cobaltate polycrystalline samples with Swedenborgite structure, ABaCo{sub 3}BO{sub 7} (A=Y Ca, and B=Co Fe,Al,Zn) was used to study the change in magnetic order depending on chemical composition. The atomic structure contains alternate stacking of kagome and triangular layers of metal ions, all in tetrahedral oxygen coordination. Geometrical frustration of antiferromagnetically coupled spins should suppress long-range order even at low temperatures despite strong spin-spin coupling in the Swedenborgites. The diffuse magnetic scattering in Y{sub 0.5}Ca{sub 0.5}BaCo{sub 4}O {sub 7} reveals two dimensional (2D) spin correlations on the Kagome sublattices towards the entropically favoured V3*V3 structure and suggests a decoupling of layers on triangular sites. Co-substitution by Al and Zn yields similar diffuse magnetic scattering, however, spin dilution results in even more disordered spin liquid or spin glass states. With B=Fe or Co, differences in the magnetic scattering evolve, indicating the onset of spin correlations perpendicular to the Kagome layers.
Possibility of a two-dimensional spin liquid in CePdAl induced by partial geometric frustration?
Energy Technology Data Exchange (ETDEWEB)
Fritsch, V. [Universitaet Augsburg, Institut fuer Physik, Experimentalphysik VI (Germany); Karlsruher Institut fuer Technologie (Germany); Grube, K.; Kittler, W.; Taubenheim, C.; Loehneysen, H. von [Karlsruher Institut fuer Technologie (Germany); Huesges, Z.; Lucas, S.; Stockert, O. [Max-Planck-Institut fuer chemische Physik fester Stoffe, Dresden (Germany); Green, E. [Hochfeldzentrum Dresden-Rossendorf (Germany)
2015-07-01
CePdAl crystallizes in the hexagonal ZrNiAl structure, where the magnetic ions form a distorted kagome lattice. At T{sub N} = 2.7 K the onset of antiferromagnetic (AF) order is observed. Neutron scattering experiments revealed a partial frustration in the distorted kagome planes of this structure: two-thirds of the Ce moments form ferromagnetic chains, which are antiferromagnetically coupled, the remaining third do not participate in any long-range order. Along the c-axis the magnetic moments exhibit an amplitude modulation. Accordingly, the kagome planes are stacked on top of each other, resulting in corrugated AF planes parallel to the c-axis formed by the ordered magnetic moments, which are separated by the frustrated moments. It is an intriguing and yet unresolved question if this third of frustrated moments forms a spin liquid state in CePdAl. Based on measurements of specific heat, thermal expansion, magnetization and electrical resistivity we want to discuss this possibility.
Grüneisen parameter studies on heavy fermion quantum criticality
Gegenwart, Philipp
2016-11-01
The Grüneisen parameter, experimentally determined from the ratio of thermal expansion to specific heat, quantifies the pressure dependence of characteristic energy scales of matter. It is highly enhanced for Kondo lattice systems, whose properties are strongly dependent on the pressure sensitive antiferromagnetic exchange interaction between f- and conduction electrons. In this review, we focus on the divergence of the Grüneisen parameter and its magnetic analogue, the adiabatic magnetocaloric effect, for heavy-fermion metals near quantum critical points. We compare experimental results with current theoretical models, including the effect of strong geometrical frustration. We also discuss the possibility of using materials with the divergent magnetic Grüneisen parameter for adiabatic demagnetization cooling to very low temperatures.
Spin dynamics and spin freezing in the triangular lattice antiferromagnets FeGa2S4 and NiGa2S4
Zhao, Songrui; Dalmas de Réotier, P.; Yaouanc, A.; MacLaughlin, D. E.; Mackie, J. M.; Bernal, O. O.; Nambu, Y.; Higo, T.; Nakatsuji, S.
2012-08-01
Magnetic susceptibility and muon spin relaxation (μSR) experiments have been carried out on the quasi-2D triangular-lattice spin S=2 antiferromagnet FeGa2S4. The μSR data indicate a sharp onset of a frozen or nearly frozen spin state at T*=31(2) K, twice the spin-glass-like freezing temperature Tf=16(1) K. The susceptibility becomes field dependent below T*, but no sharp anomaly is observed in any bulk property. A similar transition is observed in μSR data from the spin-1 isomorph NiGa2S4. In both compounds the dynamic muon spin relaxation rate λd(T) above T* agrees well with a calculation of spin-lattice relaxation by Chubukov, Sachdev, and Senthil in the renormalized classical regime of a 2D frustrated quantum antiferromagnet. There is no firm evidence for other mechanisms. At low temperatures, λd(T) becomes temperature independent in both compounds, indicating persistence of spin dynamics. Scaling of λd(T) between the two compounds is observed from ˜Tf to ˜1.5T*. Although the μSR data by themselves cannot exclude a truly static spin component below T*, together with the susceptibility data they are consistent with a slowly fluctuating “spin gel” regime between Tf and T*. Such a regime and the absence of a divergence in λd(T) at T* are features of two unconventional mechanisms: (1) binding/unbinding of Z2 vortex excitations, and (2) impurity spins in a nonmagnetic spin-nematic ground state. The absence of a sharp anomaly or history dependence at T* in the susceptibility of FeGa2S4, and the weakness of such phenomena in NiGa2S4, strongly suggest transitions to low-temperature phases with unconventional dynamics.
Mihalco, Michael E.; McKay, Susan R.
2006-03-01
We apply the Niemeijer-van Leeuwen cluster approximation [1] to frustrated Ising models on a triangular lattice. The homogeneous Ising antiferromagnet is fully frustrated and shows no ordered phase. Frustration can be relieved via the addition of quenched randomness through either dilution or the introduction of ferromagnetic bonds. The result is a rich phase diagram with different types of ordering depending upon the details of the quenched disorder. [2] Using a binning procedure to retain the full distribution of interactions under rescaling [3], we are able to calculate the phase diagram of this system, with each phase having its own characteristic attractor. This model system provides a two-dimensional example of the impacts of tunable frustration on short- and long-range order. 1. T. Niemeijer and J.M.J. van Leeuwen, Phys. Rev. Lett. 31, 1411 (1973); Physica (Utr.) 71, 17 (1974). 2. G. S. Grest and E.G. Gabl, Phys. Rev. Lett. 43, 1183 (1979); H. Kaya and A.N. Berker, Phys. Rev. E 62, 1469 (2000).; M. Robinson, M.S. Thesis, University of Maine (2003). 3. E. Hartford and S. McKay, J. Appl. Phys. 70, 6068 (1991); E. Hartford, Ph.D. Thesis, University of Maine (1994); A. Falicov, A.N. Berker, and S.R. McKay, Phys. Rev. B 51, 8266 (1995).
The anti-ferromagnetic Ising model on the simplest pure Husimi lattice: An exact solution
Energy Technology Data Exchange (ETDEWEB)
Jurčišinová, E., E-mail: jurcisine@saske.sk [Institute of Experimental Physics, SAS, Watsonova 47, 040 01 Košice (Slovakia); Jurčišin, M., E-mail: jurcisin@saske.sk [Institute of Experimental Physics, SAS, Watsonova 47, 040 01 Košice (Slovakia); Bobák, A., E-mail: andrej.bobak@upjs.sk [Department of Theoretical Physics and Astrophysics, Faculty of Science, P.J. Šafárik University, Park Angelinum 9, 040 01 Košice (Slovakia)
2013-11-22
The anti-ferromagnetic spin-1/2 Ising model on the pure Husimi lattice with three sites in the elementary polygon (p=3) and the coordination number z=4 is investigated. It represents the simplest approximation of the anti-ferromagnetic Ising model on the two-dimensional kagome lattice which takes into account effects of frustration. The exact analytical solution of the model is found and discussed. It is proven that the model does not exhibit the first order as well as the second order phase transitions. A detailed analysis of the magnetization properties is performed and the existence of the magnetization plateaus for low temperatures is shown. All possible ground states of the model are found and discussed.
Solution of the antiferromagnetic Ising model on a tetrahedron recursive lattice.
Jurčišinová, E; Jurčišin, M
2014-03-01
We consider the antiferromagnetic spin-1/2 Ising model on the recursive tetrahedron lattice on which two elementary tetrahedrons are connected at each site. The model represents the simplest approximation of the antiferromagnetic Ising model on the real three-dimensional tetrahedron lattice which takes into account effects of frustration. An exact analytical solution of the model is found and discussed. It is shown that the model exhibits neither the first-order nor the second-order phase transitions. A detailed analysis of the magnetization of the model in the presence of the external magnetic field is performed and the existence of the magnetization plateaus for low temperatures is shown. All possible ground states of the model are found and discussed. The existence of nontrivial singular ground states is proven and exact explicit expressions for them are found.
Macroscopic anisotropy and symmetry breaking in the pyrochlore antiferromagnet Gd2Ti2O7
Hassan, A. K.; Lévy, L. P.; Darie, C.; Strobel, P.
2003-06-01
In the Heisenberg antiferromagnet Gd2Ti2O7, the exchange interactions are geometrically frustrated by the pyrochlore lattice structure. This ESR study reveals a strong temperature dependent anisotropy with respect to a [111] body diagonal below a temperature TA=80 K, despite the spin only nature of the Gd3+ ion. Anisotropy and symmetry breaking can nevertheless appear through the superexchange interaction. In the presence of anisotropic exchanges, short range planar correlations restricted to specific Kagomé planes are sufficient to explain the two ESR modes studied in this work.
Magnetic resonance in the pyrochlore antiferromagnet Gd2Ti2O7
Sosin, S. S.; Smirnov, A. I.; Prozorova, L. A.; Balakrishnan, G.; Zhitomirsky, M. E.
2006-06-01
An electron spin resonance study of frustrated pyrochlore Gd2Ti2O7 is performed in a wide frequency band for a temperature range 0.4 30K , which covers paramagnetic and magnetically ordered phases. The paramagnetic resonance reveals a spectroscopic g factor of about 2.0 and a temperature-dependent linewidth. In ordered phases magnetic resonance spectra are distinctive for a nonplanar cubic (or tetrahedral) antiferromagnet with an isotropic susceptibility. In the high-field-saturated phase, weakly dispersive soft modes are observed and their field evolution is traced.
Sekiguchi, Kazutaka; Hida, Kazuo
2017-08-01
Ground-state and finite-temperature properties of S = 1/2 Heisenberg ladders with a ferromagnetic leg, an antiferromagnetic leg, and antiferromagnetic rungs are studied. It is shown that a partial ferrimagnetic phase extends over a wide parameter range in the ground state. The numerical results are supported by an analytical calculation based on a mapping onto the nonlinear σ model and a perturbation calculation from the strong-rung limit. It is shown that the partial ferrimagnetic state is a spontaneously magnetized Tomonaga-Luttinger liquid with incommensurate magnetic correlation, which is confirmed by a DMRG calculation. The finite-temperature magnetic susceptibility is calculated using the thermal pure quantum state method. It is suggested that the susceptibility diverges as T-2 in the ferrimagnetic phases as in the case of ferromagnetic Heisenberg chains.
On the concept of frustrated Lewis pairs.
Fontaine, Frédéric-Georges; Stephan, Douglas W
2017-08-28
In this concept article, we consider the notion of 'frustrated Lewis pairs' (FLPs). While the original use of the term referred to steric inhibition of dative bond formation in a Lewis pair, work in the intervening decade demonstrates the limitation of this simplistic view. Analogies to known transition metal chemistry and the applications in other areas of chemistry are considered. In the light of these findings, we present reflections on the criteria for a definition of the term 'frustrated Lewis pair'. Segregation of the Lewis acid and base and the kinetic nature of FLP reactivity are discussed. We are led to the conclusion that, while an all-inclusive definition of FLP is challenging, the notion of 'FLP chemistry' is more readily recognized.This article is part of the themed issue 'Frustrated Lewis pair chemistry'. © 2017 The Author(s).
Exploring frustrated magnetism with artificial spin ice
Gilbert, Ian; Ilic, B. Robert
2016-10-01
Nanomagnet arrays known as artificial spin ice provide insight into the microscopic details of frustrated magnetism because, unlike natural frustrated magnets, the individual moments can be experimentally resolved and the lattice geometry can be easily tuned. Most studies of artificial spin ice focus on two lattice geometries, the square and the kagome lattices, due to their direct correspondence to natural spin ice materials such as Dy2Ti2O7. In this work, we review experiments on these more unusual lattice geometries and introduce a new type of nanomagnet array, artificial spin glass. Artificial spin glass is a two-dimensional array of nanomagnets with random locations and orientations and is designed to elucidate the more complex frustration found in spin glass materials.
Large topological Hall effect in the non-collinear phase of an antiferromagnet.
Sürgers, Christoph; Fischer, Gerda; Winkel, Patrick; Löhneysen, Hilbert V
2014-03-05
Non-trivial spin arrangements in magnetic materials give rise to the topological Hall effect observed in compounds with a non-centrosymmetric cubic structure hosting a skyrmion lattice, in double-exchange ferromagnets and magnetically frustrated systems. The topological Hall effect has been proposed to appear also in presence of non-coplanar spin configurations and thus might occur in an antiferromagnetic material with a highly non-collinear and non-coplanar spin structure. Particularly interesting is a material where the non-collinearity develops not immediately at the onset of antiferromagnetic order but deep in the antiferromagnetic phase. This unusual situation arises in non-cubic antiferromagnetic Mn5Si3. Here we show that a large topological Hall effect develops well below the Néel temperature as soon as the spin arrangement changes from collinear to non-collinear with decreasing temperature. We further demonstrate that the effect is not observed when the material is turned ferromagnetic by carbon doping without changing its crystal structure.
Frustrated bistability as a means to engineer oscillations in biological systems
Krishna, S.; Semsey, S.; Jensen, M. H.
2009-09-01
Oscillations play an important physiological role in a variety of biological systems. For example, respiration and carbohydrate synthesis are coupled to the circadian clock in cyanobacteria (Ishiura et al 1998 Science 281 1519) and ultradian oscillations with time periods of a few hours have been observed in immune response (NF-κB, Hoffmann et al 2002 Science 298 1241, Neson et al 2004 Science 306 704), apoptosis (p53, Lahav et al 2004 Nat. Genet. 36 53), development (Hes, Hirata et al 2002 Science 298 840) and growth hormone secretion (Plotsky and Vale 1985 Science 230 461, Zeitler et al 1991 Proc. Natl. Acad. Sci. USA 88 8920). Here we discuss how any bistable system can be 'frustrated' to produce oscillations of a desired nature—we use the term frustration, in analogy to frustrated spins in antiferromagnets, to refer to the addition of a negative feedback loop that destabilizes the bistable system. We show that the molecular implementation can use a wide variety of methods ranging from translation regulation, using small non-coding RNAs, to targeted protein modification to transcriptional regulation. We also introduce a simple graphical method for determining whether a particular implementation will produce oscillations. The shape of the resulting oscillations can be readily tuned to produce spiky and asymmetric oscillations—quite different from the shapes produced by synthetic oscillators (Elowitz and Leibler 2000 Nature 403 335, Fung et al 2005 Nature 435 118). The time period and amplitude can also be manipulated and these oscillators are easy to reset or switch on and off using a tunable external input. The mechanism of frustrated bistability could thus prove to be an easily implementable way to synthesize flexible, designable oscillators.
Spin-orbital short-range order in the honeycomb-based quantum magnet Ba3CuSb2O9
Nakatsuji, Satoru
2013-03-01
The realization of quantum correlated matter beyond one dimension has been vigorously pursued in geometrically frustrated spin systems for decades. In frustrated magnetic materials, however, symmetry breaking of orbital and chemical origin is usually found to induce semi-classical spin freezing. In this talk, I present a contrast case where spins and possibly orbitals remain in a liquid state down to low temperature even in a highly disordered structure of 6H-perovskite Ba3CuSb2O9. Our comprehensive experimental analysis indicates that the geometrical frustration of Wannier's Ising antiferromagnet on a triangular lattice can be exploited to build a nano-structured bipartite honeycomb lattice from electric dipolar spin-1/2 molecules. Despite a strong local Jahn-Teller distortion about the Cu2+ ion, the resulting spin-orbital random bond lattice not only retains hexagonal symmetry averaged over time and space, but it supports a gapless excitation spectrum without spin freezing down to ultralow temperatures. This is the work based on the collaboration with K. Kuga, K. Kimura, R. Satake, N. Katayama, E. Nishibori, H. Sawa, R. Ishii, M. Hagiwara, F. Bridges, T. U. Ito, W. Higemoto, Y. Karaki, M. Halim, A. A. Nugroho, J. A. Rodriguez-Rivera, M. A. Green, C. Broholm. This work is partially supported by Grant-in-Aid for Scientific Research (No. 20340089,21684019) from JSPS, by Grant-in-Aid for Scientific Research on Priority Areas (No. 1951010,19052003) from MEXT, Japan.
Val'kov, V. V.; Zlotnikov, A. O.
2016-12-01
On the basis of the periodic Anderson model, the microscopic Ginzburg-Landau equations for heavy-fermion superconductors in the coexistence phase of superconductivity and antiferromagnetism have been derived. The obtained expressions are valid in the vicinity of quantum critical point of heavy-fermion superconductors when the onset temperatures of antiferromagnetism and superconductivity are sufficiently close to each other. It is shown that the formation of antiferromagnetic ordering causes a decrease of the critical temperature of superconducting transition and order parameter in the phase of coexisting superconductivity and antiferromagnetism.
Space Group Symmetry Fractionalization in a Chiral Kagome Heisenberg Antiferromagnet.
Zaletel, Michael P; Zhu, Zhenyue; Lu, Yuan-Ming; Vishwanath, Ashvin; White, Steven R
2016-05-13
The anyonic excitations of a spin liquid can feature fractional quantum numbers under space group symmetries. Detecting these fractional quantum numbers, which are analogs of the fractional charge of Laughlin quasiparticles, may prove easier than the direct observation of anyonic braiding and statistics. Motivated by the recent numerical discovery of spin-liquid phases in the kagome Heisenberg antiferromagnet, we theoretically predict the pattern of space group symmetry fractionalization in the kagome lattice SO(3)-symmetric chiral spin liquid. We provide a method to detect these fractional quantum numbers in finite-size numerics which is simple to implement in the density matrix renormalization group. Applying these developments to the chiral spin liquid phase of a kagome Heisenberg model, we find perfect agreement between our theoretical prediction and numerical observations.
[French validation of the Frustration Discomfort Scale].
Chamayou, J-L; Tsenova, V; Gonthier, C; Blatier, C; Yahyaoui, A
2016-08-01
Rational emotive behavior therapy originally considered the concept of frustration intolerance in relation to different beliefs or cognitive patterns. Psychological disorders or, to some extent, certain affects such as frustration could result from irrational beliefs. Initially regarded as a unidimensional construct, recent literature considers those irrational beliefs as a multidimensional construct; such is the case for the phenomenon of frustration. In order to measure frustration intolerance, Harrington (2005) developed and validated the Frustration Discomfort Scale. The scale includes four dimensions of beliefs: emotional intolerance includes beliefs according to which emotional distress is intolerable and must be controlled or avoided as soon as possible. The intolerance of discomfort or demand for comfort is the second dimension based on beliefs that life should be peaceful and comfortable and that any inconvenience, effort or hassle should be avoided. The third dimension is entitlement, which includes beliefs about personal goals, such as merit, fairness, respect and gratification, and that others must not frustrate those non-negotiable desires. The fourth dimension is achievement, which reflects demands for high expectations or standards. The aim of this study was to translate and validate in a French population the Frustration and Discomfort Scale developed by Harrington (2005), assess its psychometric properties, highlight the four factors structure of the scale, and examine the relationships between this concept and both emotion regulation and perceived stress. We translated the Frustration Discomfort Scale from English to French and back from French to English in order to ensure good quality of translation. We then submitted the scale to 289 students (239 females and 50 males) from the University of Savoy in addition to the Cognitive Emotional Regulation Questionnaire and the Perceived Stress Scale. The results showed satisfactory psychometric
Hida, Kazuo; Iino, Takashi
2012-03-01
Low temperature properties of the spin-1/2 frustrated ladder with ferromagnetic rungs and legs, and two different antiferromagnetic next nearest neighbor interactions are investigated using the modified spin wave approximation in the region with ferromagnetic ground states. The temperature dependence of the magnetic susceptibility and magnetic structure factors is calculated. The results are consistent with the numerical exact diagonalization results in the intermediate temperature range. Below this temperature range, the finite size effect is significant in the numerical diagonalization results, while the modified spin wave approximation gives more reliable results. The low temperature properties near the limit of the stability of the ferromagnetic ground state are also discussed.
Magnetic properties of doped kagomé antiferromagnet
Koretsune, Takashi; Ogata, Masao
In order to clarify the carrier doping effect in the frustrated system, we study the t-J model on the kagomé lattice using high-temperature expansion method. As in the triangular lattice [T. Koretsune, M. Ogata, Phys. Rev. Lett. 89 (2002) 116401], the sign of hopping integral t is important in the kagomé lattice. When tOgata, J. Phys. Soc. Japan 72 (2003) 2437]. On the contrary, in the case of t>0, it is found that uniform spin susceptibility is strongly suppressed with hole doping. The peak of spin susceptibility, which is expected to be around T=J/20 in the Heisenberg model, goes to high temperature region. Furthermore, short-range magnetic correlation is enhanced with hole doping. This is interesting since nearest-neighbor spin correlation without hole doping itself is strongly enhanced by quantum fluctuation. These behavior are qualitatively similar to those of the triangular lattice. However, the difference from non-frustrated lattices as square lattice is more prominent in the kagomé lattice, which is related to the fact that frustration in the kagomé lattice is strong enough to destabilize the magnetic order in the Heisenberg model even at T=0.
Al-Khalili, Jim
2003-01-01
In this lively look at quantum science, a physicist takes you on an entertaining and enlightening journey through the basics of subatomic physics. Along the way, he examines the paradox of quantum mechanics--beautifully mathematical in theory but confoundingly unpredictable in the real world. Marvel at the Dual Slit experiment as a tiny atom passes through two separate openings at the same time. Ponder the peculiar communication of quantum particles, which can remain in touch no matter how far apart. Join the genius jewel thief as he carries out a quantum measurement on a diamond without ever touching the object in question. Baffle yourself with the bizzareness of quantum tunneling, the equivalent of traveling partway up a hill, only to disappear then reappear traveling down the opposite side. With its clean, colorful layout and conversational tone, this text will hook you into the conundrum that is quantum mechanics.
Educational Technologies: Impact on Learning and Frustration
Hove, M. Christina; Corcoran, Kevin J.
2008-01-01
Educators are increasingly using educational technologies at the postsecondary level although little research has investigated the effects of such technologies on learning. Our research explored the effects of traditional lecture, slide-show-supplemented lecture, and virtual learning environment (VLE) on learning and frustration among college…
Diagnosis and Treatment of Academic Frustration Syndrome
Grover, Paul L.; Tessier, Kenneth E.
1978-01-01
A random sample of medical students was compared with others who were unable to cope with unanticipated academic frustration. Techniques of attribution therapy and desensitization in the counseling of these students proved to be effective in improving coping behavior in six of seven cases. (Author/LBH)
Numerical study of the spin-flop transition in anisotropic spin-1/2 antiferromagnets
Yunoki, S
2002-01-01
Magnetization processes of the spin-1/2 antiferromagnetic XXZ model in two and three spatial dimensions are studied using a quantum Monte Carlo method based on stochastic series expansions. A recently developed operator-loop algorithm enables us to show clear evidence of a first-order phase transiti
Thermoinduced magnetization in nanoparticles of antiferromagnetic materials
DEFF Research Database (Denmark)
Mørup, Steen; Frandsen, Cathrine
2004-01-01
We show that there is a thermoinduced contribution to the magnetic moment of nanoparticles of antiferromagnetic materials. It arises from thermal excitations of the uniform spin-precession mode, and it has the unusual property that its magnitude increases with increasing temperature. This has...... the consequence that antiferromagnetism is nonexistent in nanoparticles at finite temperatures and it explains magnetic anomalies, which recently have been reported in a number of studies of nanoparticles of antiferromagnetic materials....
Large anomalous Hall effect in a half-Heusler antiferromagnet
Suzuki, T.; Chisnell, R.; Devarakonda, A.; Liu, Y.-T.; Feng, W.; Xiao, D.; Lynn, J. W.; Checkelsky, J. G.
2016-12-01
The quantum mechanical (Berry) phase of the electronic wavefunction plays a critical role in the anomalous and spin Hall effects, including their quantized limits. While progress has been made in understanding these effects in ferromagnets, less is known in antiferromagnetic systems. Here we present a study of antiferromagnet GdPtBi, whose electronic structure is similar to that of the topologically non-trivial HgTe (refs ,,), and where the Gd ions offer the possibility to tune the Berry phase via control of the spin texture. We show that this system supports an anomalous Hall angle ΘAH > 0.1, comparable to the largest observed in bulk ferromagnets and significantly larger than in other antiferromagnets. Neutron scattering measurements and electronic structure calculations suggest that this effect originates from avoided crossing or Weyl points that develop near the Fermi level due to a breaking of combined time-reversal and lattice symmetries. Berry phase effects associated with such symmetry breaking have recently been explored in kagome networks; our results extend this to half-Heusler systems with non-trivial band topology. The magnetic textures indicated here may also provide pathways towards realizing the topological insulating and semimetallic states predicted in this material class.
Spin-orbit coupled jeff=1 /2 iridium moments on the geometrically frustrated fcc lattice
Cook, A. M.; Matern, S.; Hickey, C.; Aczel, A. A.; Paramekanti, A.
2015-07-01
Motivated by experiments on the double perovskites La2ZnIrO6 and La2MgIrO6 , we study the magnetism of spin-orbit coupled jeff=1 /2 iridium moments on the three-dimensional, geometrically frustrated, face-centered cubic lattice. The symmetry-allowed nearest-neighbor interaction includes Heisenberg, Kitaev, and symmetric off-diagonal exchange. A Luttinger-Tisza analysis shows a rich variety of orders, including collinear A -type antiferromagnetism, stripe order with moments along the {111 } direction, and incommensurate noncoplanar spirals, and we use Monte Carlo simulations to determine their magnetic ordering temperatures. We argue that existing thermodynamic data on these iridates underscores the presence of a dominant Kitaev exchange, and also suggest a resolution to the puzzle of why La2ZnIrO6 , but not La2MgIrO6 , exhibits "weak" ferromagnetism.
DEFF Research Database (Denmark)
Zhang, N.G.; Henley, C.L.; Rischel, C.;
2002-01-01
We study the low-lying eigenenergy clustering patterns of quantum antiferromagnets with p sublattices (in particular p = 4). We treat each sublattice as a large spin, and using second-order degenerate perturbation theory, we derive the effective (biquadratic) Hamiltonian coupling the p large spins....... In order to compare with exact diagonalizations, the Hamiltonian is explicitly written for a finite-size lattice, and it contains information on energies of excited states as well as the ground state. The result is applied to the face-centered-cubic Type-I antiferromagnet of spin 1/2, including second...
Bond-Dilution Effects on Two-Dimensional Spin-Gapped Heisenberg Antiferromagnets
Yasuda, Chitoshi; Todo, Synge; Matsumoto, Munehisa; Takayama, Hajime
2001-01-01
Bond-dilution effects on spin-1/2 spin-gapped Heisenberg antiferromagnets of coupled alternating chains on a square lattice are investigated by means of the quantum Monte Carlo method. It is found that, in contrast with the site-diluted system having an infinitesimal critical concentration, the bond-diluted system has a finite critical concentration of diluted bonds, $x_{c}$, above which the system is in an antiferromagnetic (AF) long-range ordered phase. In the disordered phase below $x_{c}$...
Experimental Realization of a Quantum Pentagonal Lattice
Yamaguchi, Hironori; Okubo, Tsuyoshi; Kittaka, Shunichiro; Sakakibara, Toshiro; Araki, Koji; Iwase, Kenji; Amaya, Naoki; Ono, Toshio; Hosokoshi, Yuko
2015-01-01
Geometric frustration, in which competing interactions give rise to degenerate ground states, potentially induces various exotic quantum phenomena in magnetic materials. Minimal models comprising triangular units, such as triangular and Kagome lattices, have been investigated for decades to realize novel quantum phases, such as quantum spin liquid. A pentagon is the second-minimal elementary unit for geometric frustration. The realization of such systems is expected to provide a distinct platform for studying frustrated magnetism. Here, we present a spin-1/2 quantum pentagonal lattice in the new organic radical crystal α-2,6-Cl2-V [=α-3-(2,6-dichlorophenyl)-1,5-diphenylverdazyl]. Its unique molecular arrangement allows the formation of a partially corner-shared pentagonal lattice (PCPL). We find a clear 1/3 magnetization plateau and an anomalous change in magnetization in the vicinity of the saturation field, which originate from frustrated interactions in the PCPL. PMID:26468930
Purely antiferromagnetic magnetoelectric random access memory
Kosub, Tobias; Kopte, Martin; Hühne, Ruben; Appel, Patrick; Shields, Brendan; Maletinsky, Patrick; Hübner, René; Liedke, Maciej Oskar; Fassbender, Jürgen; Schmidt, Oliver G.; Makarov, Denys
2017-01-01
Magnetic random access memory schemes employing magnetoelectric coupling to write binary information promise outstanding energy efficiency. We propose and demonstrate a purely antiferromagnetic magnetoelectric random access memory (AF-MERAM) that offers a remarkable 50-fold reduction of the writing threshold compared with ferromagnet-based counterparts, is robust against magnetic disturbances and exhibits no ferromagnetic hysteresis losses. Using the magnetoelectric antiferromagnet Cr2O3, we demonstrate reliable isothermal switching via gate voltage pulses and all-electric readout at room temperature. As no ferromagnetic component is present in the system, the writing magnetic field does not need to be pulsed for readout, allowing permanent magnets to be used. Based on our prototypes, we construct a comprehensive model of the magnetoelectric selection mechanisms in thin films of magnetoelectric antiferromagnets, revealing misfit induced ferrimagnetism as an important factor. Beyond memory applications, the AF-MERAM concept introduces a general all-electric interface for antiferromagnets and should find wide applicability in antiferromagnetic spintronics.
Partial order of frustrated Potts model
Energy Technology Data Exchange (ETDEWEB)
Igarashi, Ryo [CCSE, Japan Atomic Energy Agency, Higashi-Ueno, Taito, Tokyo 110-0015 (Japan); Ogata, Masao, E-mail: igarashi.ryo@jaea.go.j [Deaprtment of Physics, University of Tokyo, Hongo, Bunkyo, Tokyo 133-0033 (Japan)
2010-01-01
We investigate a 4-state ferromagnetic Potts model with a special type of geometrical frustration on a three dimensional diamond lattice. We find that the model undergoes unconventional phase transition; half of the spins in the system order in a two dimensional hexagonal-sheet-like structure while the remaining half of the spins stay disordered. The ordered sheets and the disordered sheets stack one after another. We obtain fairly large residual entropy using the Wang-Landau Monte Carlo simulation.
Dynamic zero modes of Dirac fermions and competing singlet phases of antiferromagnetic order
Goswami, Pallab
2016-01-01
In quantum spin systems, singlet phases often develop in the vicinity of an antiferromagnetic order. Typical settings for such problems arise when itinerant fermions are also present. In this work, we develop a theoretical framework for addressing such competing orders in an itinerant system, described by Dirac fermions strongly coupled to an O(3) nonlinear sigma model. We focus on two spatial dimensions, where upon disordering the antiferromagnetic order by quantum fluctuations the singular tunneling events also known as (anti)hedgehogs can nucleate competing singlet orders in the paramagnetic phase. In the presence of an isolated hedgehog configuration of the nonlinear sigma model field, we show that the fermion determinant vanishes as the dynamic Euclidean Dirac operator supports fermion zero modes of definite chirality. This provides a topological mechanism for suppressing the tunneling events. Using the methodology of quantum chromodynamics, we evaluate the fermion determinant in the close proximity of m...
Search for the Heisenberg spin glass on rewired square lattices with antiferromagnetic interaction
Surungan, Tasrief; Bansawang B., J.; Tahir, Dahlang
2016-03-01
Spin glass (SG) is a typical magnetic system with frozen random spin orientation at low temperatures. The system exhibits rich physical properties, such as infinite number of ground states, memory effect, and aging phenomena. There are two main ingredients considered to be pivotal for the existence of SG behavior, namely, frustration and randomness. For the canonical SG system, frustration is led by the presence of competing interaction between ferromagnetic (FM) and antiferromagnetic (AF) couplings. Previously, Bartolozzi et al. [Phys. Rev. B73, 224419 (2006)], reported the SG properties of the AF Ising spins on scale free network (SFN). It is a new type of SG, different from the canonical one which requires the presence of both FM and AF couplings. In this new system, frustration is purely caused by the topological factor and its randomness is related to the irregular connectvity. Recently, Surungan et. al. [Journal of Physics: Conference Series, 640, 012001 (2015)] reported SG bahavior of AF Heisenberg model on SFN. We further investigate this type of system by studying an AF Heisenberg model on rewired square lattices. We used Replica Exchange algorithm of Monte Carlo Method and calculated the SG order parameter to search for the existence of SG phase.
GdPtPb: A noncollinear antiferromagnet with distorted kagome lattice
Manni, S.; Bud'ko, Sergey L.; Canfield, Paul C.
2017-08-01
In the spirit of searching for Gd-based, frustrated, rare earth magnets, we have found antiferomagnetism (AF) in GdPtPb, which crystallizes in the ZrNiAl-type structure that has a distorted kagome lattice of Gd triangles. Single crystals were grown and investigated using structural, magnetic, transport, and thermodynamic measurements. GdPtPb orders antiferromagnetically at 15.5 K, arguably with a planar, noncollinear structure. The high temperature magnetic susceptibility data reveal an "anti-frustration" behavior having a frustration parameter, |f | =|Θ | /TN=0.25 , which can be explained by mean field theory within a two-sublattice model. Study of the magnetic phase diagram down to T =1.8 K reveals a change of magnetic structure through a metamagnetic transition at around 20 kOe and the disappearance of the AF ordering near 140 kOe. In total, our work indicates that GdPtPb can serve as an example of a planar, noncollinear AF with a distorted kagome magnetic sublattice.
Energy Technology Data Exchange (ETDEWEB)
Mastrogiuseppe, D; Gazza, C; Dobry, A [Facultad de Ciencias Exactas IngenierIa y Agrimensura, Universidad Nacional de Rosario and Instituto de Fisica Rosario, Boulevard 27 de Febrero 210 bis, 2000 Rosario (Argentina)], E-mail: dmastro@ifir.edu.ar
2008-04-02
We consider the ground state and the elementary excitations of an array of spin-Peierls chains coupled by elastic and magnetic interactions. It is expected that the effect of the magnetic interchain coupling will be to reduce the dimerization amplitude and that of the elastic coupling will be to confine the spin one-half solitons corresponding to each isolated chain. We show that this is the case when these interactions are not frustrated. On the other hand, in the frustrated case we show that the amplitude of dimerization in the ground state is independent of the strength of the interchain magnetic interaction in a broad range of values of this parameter. We also show that free solitons could be the elementary excitations when only nearest neighbour interactions are considered. The case of an elastic interchain coupling is analysed on a general energetic consideration. To study the effect of the magnetic interchain interaction the problem is simplified to a two-leg ladder, which is solved using density matrix renormalization group (DMRG) calculations. We show that the deconfinement mechanism is effective even with a significantly strong antiferromagnetic interchain coupling.
Self-similarity of phase-space networks of frustrated spin models and lattice gas models
Peng, Yi; Wang, Feng; Han, Yilong
2013-03-01
We studied the self-similar properties of the phase-spaces of two frustrated spin models and two lattice gas models. The frustrated spin models included (1) the anti-ferromagnetic Ising model on a two-dimensional triangular lattice (1a) at the ground states and (1b) above the ground states and (2) the six-vertex model. The two lattice gas models were (3) the one-dimensional lattice gas model and (4) the two-dimensional lattice gas model. The phase spaces were mapped to networks so that the fractal analysis of complex networks could be applied, i.e. the box-covering method and the cluster-growth method. These phase spaces, in turn, establish new classes of networks with unique self-similar properties. Models 1a, 2, and 3 with long-range power-law correlations in real space exhibit fractal phase spaces, while models 1b and 4 with short-range exponential correlations in real space exhibit nonfractal phase spaces. This behavior agrees with one of untested assumptions in Tsallis nonextensive statistics. Hong Kong GRC grants 601208 and 601911
Ultrasound Velocity Measurements in the Orbital-Degenerate Frustrated Spinel MgV2O4
Watanabe, Tadataka; Ishikawa, Takashi; Hara, Shigeo; Islam, A. T. M. Nazmul; Wheeler, Elisa M.; Lake, Bella
2014-03-01
Magnesium vanadate spinel MgV2O4 is a geometrically frustrated magnet with t2 g-orbital degeneracy of V3+ (3d2), which undergoes a cubic-to-tetragonal structural transition at Ts = 65 K and an antiferromagnetic (AF) transition at TN = 42 K. For MgV2O4, it is considered that the occurrence of t2 g-orbital order at Ts causes the release of frustration by the AF ordering at TN lower than Ts. We performed ultrasound velocity measurements in high-purity single crystal of MgV2O4. Temperature dependence of the tetragonal shear modulus (C11 -C12)/2 exhibits huge Curie-type softening in the cubic paramagnetic (PM) phase (T >Ts), which should be a precursor to the cubic-to-tetragonal lattice distortion at Ts. The trigonal shear modulus C44(T) exhibits softening with an upturn curvature in the cubic PM phase, indicating a coupling of the lattice to magnetic excitations. These softenings suggest the coexistence of the dynamical Jahn-Teller effect and the dynamical magnetic state in the cubic PM phase.
SP (N) Treatment of Frustrated Spin Dimer Systems in Magnetic Field
Maltseva, Marianna; Flint, Rebecca; Coleman, Piers
2007-03-01
We present a Schwinger boson treatment of a frustrated bilayer dimer spin system using a reformulation of the SP (N) approach to frustrated spin systems. Unlike previous SP (N) approaches[1], our starting model is composed uniquely of SP (N) spin generators, which permits a more symmetric treatment of antiferromagnetic and ferromagnetic bonds. We apply our methods to model the spin condensation process that occurs in Ba CuSi2O6. One of the issues of particular interest is the dependence of the interlayer order-from-disorder effects[4] on the applied magnetic field, and the interesting possibility that these couplings vanish at the critical field[2,3]. [1] S. Sachdev, N. Read, International Journal of Modern Physics B 5, 219 (1991). [2] S. E. Sebastian, N. Harrison, C. D. Batista, L. Balicas, M. Jaime, P. A. Sharma, N. Kawashima, I. R. Fisher, Nature 441, pp 617-620 (2006). [3] C. D. Batista, J. Schmalian, N. Kawashima, S. E. Sebastian, N. Harrison, M. Jaime, I. R. Fisher, cond-mat/0608703. [4] M. Maltseva, P. Coleman, Phys. Rev. B 72, 174415-9 (2005).
Stabilization of Néel order in frustrated magnets with increasing magnetic field
Schmidt, Burkhard; Siahatgar, Mohammad; Thalmeier, Peter
2013-01-01
For low-dimensional frustrated quantum magnets, the dependence of the staggered moment ms on a magnetic field is nonmonotonic: For small and intermediate fields, quantum fluctuations are gradually suppressed, leading to an increase of ms (H). For large applied magnetic fields however, the classically expected monotonous decrease is recovered. For the same reasons, the Néel ordering temperature TN of such compounds first increases and then exhibits a reentrant behavior as a function of the field strength. The quantitative analysis of this behavior is an excellent tool to determine the frustration parameter of a given compound. We have derived a general linear spin-wave (LSW) theory in the presence of a magnetic field. Based on our LSW theory, including a small interlayer coupling, we use a self-consistent approach determining TN by the condition of a vanishing total moment. We apply our findings to the recently measured field dependence of the magnetic ordering temperature TN of Cu(pz)2 (ClO4)2 in the framework of the S = 1/2 two-dimensional J1-J2 Heisenberg model. The observed increase with increasing field strength can be understood naturally using an intermediate frustration ratio J2/J1 ≈ 0.2, which is in accordance with the field dependence of the staggered moment.
Femtosecond optomagnetism in dielectric antiferromagnets
Bossini, D.; Rasing, Th
2017-02-01
Optical femtosecond manipulation of magnetic order is attractive for the development of new concepts for ultrafast magnetic recording. Theoretical and experimental investigations in this research area aim at establishing a physical understanding of magnetic media in light-induced non-equilibrium states. Such a quest requires one to adjust the theory of magnetism, since the thermodynamical concepts of elementary excitations and spin alignment determined by the exchange interaction are not applicable on the femtosecond time-scale after the photo-excitation. Here we report some key milestones concerning the femtosecond optical control of spins in dielectric antiferromagnets, whose spin dynamics is by nature faster than that of ferromagnets and can be triggered even without any laser heating. The recent progress of the opto-magnetic effect in the sub-wavelength regime makes this exciting research area even more promising, in terms of both fundamental breakthroughs and technological perspectives.
Antiferromagnetic topological nodal line semimetals
Wang, Jing
2017-08-01
We study three-dimensional nodal line semimetals (NLSMs) with magnetic ordering and strong spin-orbit interaction. Two distinct classes of magnetic NLSMs are proposed. The first class is band-inversion NLSM where the accidental line node is induced by band inversion and locally protected by glide mirror plane and the combined time-reversal and inversion symmetries. This can be viewed as a trivial stacking of the two-dimensional antiferromagnetic Dirac semimetals. The second class is essential NLSM where the nodal features are filling enforced by specific magnetic symmetry group. We further provide two concrete tight-binding models for magnetic NLSMs which belong to these two different classes, respectively. We conclude with a brief discussion on the possible material venues and the experimental implications for such phases.
Spatially anisotropic Heisenberg kagome antiferromagnet
Apel, W.; Yavors'kii, T.; Everts, H.-U.
2007-04-01
In the search for spin-1/2 kagome antiferromagnets, the mineral volborthite has recently been the subject of experimental studies (Hiroi et al 2001 J. Phys. Soc. Japan 70 3377; Fukaya et al 2003 Phys. Rev. Lett. 91 207603; Bert et al 2004 J. Phys.: Condens. Matter 16 S829; Bert et al 2005 Phys. Rev. Lett. 95 087203). It has been suggested that the magnetic properties of this material are described by a spin-1/2 Heisenberg model on the kagome lattice with spatially anisotropic exchange couplings. We report on investigations of the {\\mathrm {Sp}}(\\mathcal {N}) symmetric generalization of this model in the large \\mathcal {N} limit. We obtain a detailed description of the dependence of possible ground states on the anisotropy and on the spin length S. A fairly rich phase diagram with a ferrimagnetic phase, incommensurate phases with and without long-range order and a decoupled chain phase emerges.
High magnetic field magnetization of a new triangular lattice antiferromagnet
Energy Technology Data Exchange (ETDEWEB)
Zhou, H. D. [Univ. of Tennessee, Knoxville, TN (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States). National High Magnetic Field Lab. (MagLab); Stritzinger, Laurel Elaine Winter [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Harrison, Neil [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2017-03-23
In CsV(MoO_{4})_{2}, the magnetic V^{3+} ions with octahedral oxygen-coordination form a geometrically frustrated triangular lattice. So fare, there is no magnetic properties reported on it. Recently, we successfully grew single crystals of CsV(MoO_{4})_{2} by using flux method. The susceptibility shows a sharp drop around 24 K, representing a long range magnetic ordering. To understand the physical properties of this new triangular lattice antiferromagnet (TLAF), we pursued high field magnetization measurements to answer two questions: (i) what is the saturation field, which will be very useful to calculate the exchange interaction of the system? (ii) Will it exhibit spin state transition, such as the up up down phase with 1/3-saturation moment as other TLAFs? Recently, we performed VSM measurements in Cell 8, Tallahassee, NHMFL, the results show that the magnetization reaches 0.38 MuB at 34 T, which is just 19% of the full moment of 2 MuB for V^{3+} (3d^{2}) ions. Apparently we need higher field to reach 1/3 value or full moment.
Phase Diagram of the Frustrated Square-Lattice Hubbard Model: Variational Cluster Approach
Misumi, Kazuma; Kaneko, Tatsuya; Ohta, Yukinori
2016-06-01
The variational cluster approximation is used to study the frustrated Hubbard model at half filling defined on the two-dimensional square lattice with anisotropic next-nearest-neighbor hopping parameters. We calculate the ground-state phase diagrams of the model in a wide parameter space for a variety of lattice geometries, including square, crossed-square, and triangular lattices. We examine the Mott metal-insulator transition and show that, in the Mott insulating phase, magnetic phases with Néel, collinear, and spiral orders appear in relevant parameter regions, and in an intermediate region between these phases, a nonmagnetic insulating phase caused by the quantum fluctuations in the geometrically frustrated spin degrees of freedom emerges.
Quantum signatures of a molecular nanomagnet in direct magnetocaloric measurements.
Sharples, Joseph W; Collison, David; McInnes, Eric J L; Schnack, Jürgen; Palacios, Elias; Evangelisti, Marco
2014-10-22
Geometric spin frustration in low-dimensional materials, such as the two-dimensional kagome or triangular antiferromagnetic nets, can significantly enhance the change of the magnetic entropy and adiabatic temperature following a change in the applied magnetic field, that is, the magnetocaloric effect. In principle, an equivalent outcome should also be observable in certain high-symmetry zero-dimensional, that is, molecular, structures with frustrated topologies. Here we report experimental realization of this in a heptametallic gadolinium molecule. Adiabatic demagnetization experiments reach ~200 mK, the first sub-Kelvin cooling with any molecular nanomagnet, and reveal isentropes (the constant entropy paths followed in the temperature-field plane) with a rich structure. The latter is shown to be a direct manifestation of the trigonal antiferromagnetic net structure, allowing study of frustration-enhanced magnetocaloric effects in a finite system.
Spin-phonon interaction in antiferromagnetics
Energy Technology Data Exchange (ETDEWEB)
Grigorashchuk, I.M.; Nitsovich, V.M.; Tovstyuk, K.D.
1975-01-01
The vibrational spectrum and the sound velocity in antiferromagnetics are obtained in the general form in pseudoharmonic approximation with allowance for the anharmonisms of all orders. Starting from experimentally defined dependence of the Debye-Waller factor on the temperature a corollary is put forward that in some antiferromagnetics under the temperature lower than T/subN/ the appearance of the narrow band of paramagnetic states is possible. In antiferromagnetics where the transition metal-dielectric described by the Habbard model is possible this results in the appearance of the additional transition dielectric-metal-dielectric. (auth)
Directory of Open Access Journals (Sweden)
A. B. Babaev
2015-01-01
Full Text Available Using Monte-Carlo simulations, we investigated phase transitions and frustrations in the three-state Potts model on a triangular lattice with allowance for antiferromagnetic exchange interactions between nearest- neighbors J1 and next- nearest- neighbors J2. The ratio of the next-nearest- neighbor and nearest- neighbor exchange constants r=J2/J1 is chosen within the 0÷2 range. Based on the analysis of the entropy, specific heat, system state density function, and fourth order Binder cumulants, the phase transitions in the Potts model with interactions J1<0 and J2<0 are shown to be found in value ranges of 0 r<0.2 and 1.0
Murtazaev, Akai K.; Babaev, Albert B.; Magomedov, Magomed A.; Kassan-Ogly, Felix A.; Proshkin, Alexey I.
2016-11-01
Using Monte Carlo simulations, we investigated phase transitions and frustrations in the three-state Potts model on a triangular lattice with allowance for antiferromagnetic exchange interactions between nearest-neighbors J1 and next-nearest-neighbors J2. The ratio of the next-nearest-neighbor and nearest-neighbor exchange constants r=J2/J1 is chosen within the range of 0≤r≤2. Based on the analysis of the entropy, specific heat, system state density function, and fourth order Binder cumulants, the phase transitions in the Potts model with interactions J1<0 and J2<0 are shown to be found in value ranges of 0≤r<0.2 and 1.25≤r≤2.0. In an intermediate range of 0.2≤r≤1.0 the phase transition fails and the frustrations are revealed.
Dönni, A.; Ehlers, G.; Maletta, H.; Fischer, P.; Kitazawa, H.; Zolliker, M.
1996-12-01
The heavy-fermion compound CePdAl with ZrNiAl-type crystal structure (hexagonal space group 0953-8984/8/50/043/img8) was investigated by powder neutron diffraction. The triangular coordination symmetry of magnetic Ce atoms on site 3f gives rise to geometrical frustration. CePdAl orders below 0953-8984/8/50/043/img9 with an incommensurate antiferromagnetic propagation vector 0953-8984/8/50/043/img10, and a longitudinal sine-wave (LSW) modulated spin arrangement. Magnetically ordered moments at Ce(1) and Ce(3) coexist with frustrated disordered moments at Ce(2). The experimentally determined magnetic structure is in agreement with group theoretical symmetry analysis considerations, calculated by the program MODY, which confirm that for Ce(2) an ordered magnetic moment parallel to the magnetically easy c-axis is forbidden by symmetry. Further low-temperature experiments give evidence for a second magnetic phase transition in CePdAl between 0.6 and 1.3 K. Magnetic structures of CePdAl are compared with those of the isostructural compound TbNiAl, where a non-zero ordered magnetic moment for the geometrically frustrated Tb(2) atoms is allowed by symmetry.
Institute of Scientific and Technical Information of China (English)
Hu Jing-Guo; Stamps R L
2006-01-01
The rotational anisotropies in the exchange bias structures of ferromagnetism/antiferromagnetism 1/antiferromagnetism 2 are studied in this paper. Based on the model, in which the antiferromagnetism is treated with an Ising mean field theory and the rotational anisotropy is assumed to be related to the field created by the moment induced on the antiferromagnetic layer next to the ferromagnetic layer, we can explain why in experiments for ferromagnetism (FM)/antiferromagntism 1 (AFM1)/antiferromagnetism 2 (AFM2) systems the thickness-dependent rotational anisotropy value is non-monotonic, i.e. it reaches a minimum for this system at a specific thickness of the first antiferromagnetic layer and exhibits oscillatory behaviour. In addition, we find that the temperature-dependent rotational anisotropy value is in good agreement with the experimental result.
Giant Anomalous Hall Effect in the Chiral Antiferromagnet Mn3Ge
Kiyohara, Naoki; Tomita, Takahiro; Nakatsuji, Satoru
2016-06-01
The external field control of antiferromagnetism is a significant subject both for basic science and technological applications. As a useful macroscopic response to detect magnetic states, the anomalous Hall effect (AHE) is known for ferromagnets, but it has never been observed in antiferromagnets until the recent discovery in Mn3Sn . Here we report another example of the AHE in a related antiferromagnet, namely, in the hexagonal chiral antiferromagnet Mn3Ge . Our single-crystal study reveals that Mn3Ge exhibits a giant anomalous Hall conductivity |σx z|˜60 Ω-1 cm-1 at room temperature and approximately 380 Ω-1 cm-1 at 5 K in zero field, reaching nearly half of the value expected for the quantum Hall effect per atomic layer with Chern number of unity. Our detailed analyses on the anisotropic Hall conductivity indicate that in comparison with the in-plane-field components |σx z| and |σz y|, which are very large and nearly comparable in size, we find |σy x| obtained in the field along the c axis to be much smaller. The anomalous Hall effect shows a sign reversal with the rotation of a small magnetic field less than 0.1 T. The soft response of the AHE to magnetic field should be useful for applications, for example, to develop switching and memory devices based on antiferromagnets.
Phase diagram and spin correlations of the Kitaev-Heisenberg model: Importance of quantum effects
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.
Unusual Kondo-hole effect and crystal-field frustration in Nd-doped CeRhIn5
Rosa, P. F. S.; Oostra, A.; Thompson, J. D.; Pagliuso, P. G.; Fisk, Z.
2016-07-01
We investigate single crystals of Ce1 -xNdxRhIn5 by means of x-ray-diffraction, microprobe, magnetic susceptibility, heat capacity, and electrical resistivity measurements. Our data reveal that the antiferromagnetic transition of CeRhIn5, at TNCe=3.8 K, is linearly suppressed with xNd. We associate this effect with the presence of a "Kondo hole" created by Nd substitution. The extrapolation of TNCe to zero temperature, however, occurs at xc˜0.3 , which is below the two-dimensional percolation limit found in Ce1 -xLaxRhIn5 . This result strongly suggests the presence of a crystal-field induced magnetic frustration. Near xNd˜0.2 , the Ising antiferromagnetic order from Nd3 + ions is stabilized and TNNd increases up to 11 K in NdRhIn5. Our results shed light on the effects of magnetic doping in heavy-fermion antiferromagnets and stimulate the study of such systems under applied pressure.
Glazkov, V. N.; Smirnov, A. I.; Sanchez, J. P.; Forget, A.; Colson, D.; Bonville, P.
2006-02-01
Single-ion anisotropy is of importance for the magnetic ordering of the frustrated pyrochlore antiferromagnets Gd2Ti2O7 and Gd2Sn2O7. The anisotropy parameters for Gd2Sn2O7 were measured using the electron spin resonance technique. The anisotropy was found to be of the easy plane type, with the main constant D = 140 mK. This value is 35% smaller than the value of the corresponding anisotropy constant of the related compound Gd2Ti2O7.
Gifts and exchanges problems, frustrations, and triumphs
Katz, Linda S; Denning, Catherine
2013-01-01
This important book explores the many questions challenging librarians who work with gifts and exchanges (G&E) as part of their daily responsibilities. Too often, because of shrinking library budgets, library gifts are considered burdensome and unprofitable drains on both financial and personnel resources. However, Gifts and Exchanges: Problems, Frustrations, . . . and Triumphs gives you solutions that will allow you to embrace your library's gifts as rewards. In this book, you will discover the latest ways of disposing unwanted materials, planning and holding book sales and auctions, and oper
Elasticity and Fluctuations of Frustrated Nanoribbons
Grossman, Doron; Sharon, Eran; Diamant, Haim
2016-06-01
We derive a reduced quasi-one-dimensional theory of geometrically frustrated elastic ribbons. Expressed in terms of geometric properties alone, it applies to ribbons over a wide range of scales, allowing the study of their elastic equilibrium, as well as thermal fluctuations. We use the theory to account for the twisted-to-helical transition of ribbons with spontaneous negative curvature and the effect of fluctuations on the corresponding critical exponents. The persistence length of such ribbons changes nonmonotonically with the ribbon's width, dropping to zero at the transition. This and other statistical properties qualitatively differ from those of nonfrustrated fluctuating filaments.
Frustration induced oscillator death on networks
Gade, Prashant M.; Rangarajan, Govindan
2013-09-01
An array of identical maps with Ising symmetry, with both positive and negative couplings, is studied. We divide the maps into two groups, with positive intra-group couplings and negative inter-group couplings. This leads to antisynchronization between the two groups which have the same stability properties as the synchronized state. Introducing a certain degree of randomness in signs of these couplings destabilizes the anti-synchronized state. Further increasing the randomness in signs of these couplings leads to oscillator death. This is essentially a frustration induced phenomenon. We explain the observed results using the theory of random matrices with nonzero mean. We briefly discuss applications to coupled differential equations.
Dynamic zero modes of Dirac fermions and competing singlet phases of antiferromagnetic order
Goswami, Pallab; Si, Qimiao
2017-06-01
In quantum spin systems, singlet phases often develop in the vicinity of an antiferromagnetic order. Typical settings for such problems arise when itinerant fermions are also present. In this paper, we develop a theoretical framework for addressing such competing orders in an itinerant system, described by Dirac fermions strongly coupled to an O(3) nonlinear sigma model. We focus on two spatial dimensions, where upon disordering the antiferromagnetic order by quantum fluctuations the singular tunneling events also known as (anti)hedgehogs can nucleate competing singlet orders in the paramagnetic phase. In the presence of an isolated hedgehog configuration of the nonlinear sigma model field, we show that the fermion determinant vanishes as the dynamic Euclidean Dirac operator supports fermion zero modes of definite chirality. This provides a topological mechanism for suppressing the tunneling events. Using the methodology of quantum chromodynamics, we evaluate the fermion determinant in the close proximity of magnetic quantum phase transition, when the antiferromagnetic order-parameter field can be described by a dilute gas of hedgehogs and antihedgehogs. We show how the precise nature of emergent singlet order is determined by the overlap between dynamic fermion zero modes of opposite chirality, localized on the hedgehogs and antihedgehogs. For a Kondo-Heisenberg model on the honeycomb lattice, we demonstrate the competition between spin Peierls order and Kondo singlet formation, thereby elucidating its global phase diagram. We also discuss other physical problems that can be addressed within this general framework.
Dynamic rotor mode in antiferromagnetic nanoparticles
DEFF Research Database (Denmark)
Lefmann, Kim; Jacobsen, H.; Garde, J.
2015-01-01
We present experimental, numerical, and theoretical evidence for an unusual mode of antiferromagnetic dynamics in nanoparticles. Elastic neutron scattering experiments on 8-nm particles of hematite display a loss of diffraction intensity with temperature, the intensity vanishing around 150 K...
The frustrations of online students. Causes and preventative actions
Directory of Open Access Journals (Sweden)
Federico Borges Sáiz
2005-06-01
Full Text Available The frustrations of online students, which are the result of repeated, serious and problematic situations, have not been studied sufficiently to date. Indeed, the consequences of student's frustrations can lead to a load that has to be borne by all the agents involved in the e-learning: students, teachers and institutions.This study highlights the inadequate actions, or complete lack thereof, in terms of each of the agents involved in e-learning, which lead to frustration and serious problems for the student in carrying out their activities. It also provides a list of useful actions to help prevent the causes of frustration identified.
Frustration under pressure: Exotic magnetism in new pyrochlore oxides
Directory of Open Access Journals (Sweden)
C. R. Wiebe
2015-04-01
Full Text Available Pyrochlore structures, of chemical formula A2B2O7 (A and B are typically trivalent and tetravalent ions, respectively, have been the focus of much activity in the condensed matter community due to the ease of substitution of rare earth and transition metal ions upon the two interpenetrating corner-shared tetrahedral lattices. Over the last few decades, superconductivity, spin liquid states, spin ice states, glassy states in the absence of chemical disorder, and metal-insulator transitions have all been discovered in these materials. Geometric frustration plays a role in the relevant physics of all of these phenomena. In the search for new pyrochlore materials, it is the RA/RB cation radius ratio which determines the stability of the lattice over the defect fluorite structure in the lower limit. Under ambient pressure, the pyrochlores are stable for 1.36 ≤ RA/RB ≤ 1.71. However, using high pressure synthesis techniques (1-10 GPa of pressure, metastable pyrochlores exist up to RA/RB = 2.30. Many of these compounds are stable on a timescale of years after synthesis, and provide a means to greatly enhance exchange, and thus test theories of quantum magnetism and search for new phenomena. Within this article, we review new pyrochlore compounds synthesized via high pressure techniques and show how the ground states are extremely sensitive to chemical pressure.
Chiral spin liquid in a frustrated anisotropic kagome Heisenberg model.
He, Yin-Chen; Sheng, D N; Chen, Yan
2014-04-04
Kalmeyer-Laughlin (KL) chiral spin liquid (CSL) is a type of quantum spin liquid without time-reversal symmetry, and it is considered as the parent state of an exotic type of superconductor--anyon superconductor. Such an exotic state has been sought for more than twenty years; however, it remains unclear whether it can exist in a realistic system where time-reversal symmetry is breaking (T breaking) spontaneously. By using the density matrix renormalization group, we show that KL CSL exists in a frustrated anisotropic kagome Heisenberg model, which has spontaneous T breaking. We find that our model has two topological degenerate ground states, which exhibit nonvanishing scalar chirality order and are protected by finite excitation gap. Furthermore, we identify this state as KL CSL by the characteristic edge conformal field theory from the entanglement spectrum and the quasiparticles braiding statistics extracted from the modular matrix. We also study how this CSL phase evolves as the system approaches the nearest-neighbor kagome Heisenberg model.
Yamamoto, A
2003-01-01
This paper investigates the relation between the temperature dependence of magnetoresistance (MR) and spin frustration in LaMnO sub 3 sub + subdelta when Ni is doped into the Mn site. The specimens experience magnetic frustration introduced by the competition between antiferromagnetic (AFM) and ferromagnetic (FM) interactions. According to the temperature dependence of magnetization after cooling the specimen in zero field and non-zero field, Ni-doped specimens behave like cluster glasses. This magnetic frustration at the low temperature is believed to result from the disordered spin structure between AFM and FM phases in these specimens. When the structural symmetry in the specimen is higher, the FM arrangement increases by double the exchange interaction. However, MR decreases in the same temperature region for the same reason. We suggest that the temperature dependence of MR below the Curie temperature in the Ni-doped specimen is controlled by the change of magnetization that occurs with structural change.
Spin-orbit dilution effects on the magnetism of frustrated spinel Ge(Co1-xMgx)2O4
Agata, Ryotaro; Takita, Shota; Ishikawa, Takashi; Watanabe, Tadataka
2015-03-01
We investigated magnetic properties of spinel oxides Ge(Co1-xMgx)2O4 with x = 0 ~ 0.5 to study the spin-orbit dilution effects on the magnetism of spin-orbit frustrated spinel GeCo2O4. We discovered that the magnetic moment per single Co2+ ion is decreased with increasing nonmagnetic Mg2+ concentration, which indicates the spin-orbit decoupling caused by the spin-orbit dilution. Additionally, small-amount substitution of Mg2+ for Co2+ causes the rapid increase of the positive Weiss temperature indicating the enhancement of ferromagnetic interactions, while the Mg2+ substitution suppresses the antiferromagnetic ordering resulting in the appearance of spin glass behavior. The present results suggest that the spin-orbit dilution causes the spin-orbit decoupling and the reinforcement of ferromagnetic frustration in GeCo2O4.
Many-body ab initio study of antiferromagnetic {Cr7M } molecular rings
Chiesa, A.; Carretta, S.; Santini, P.; Amoretti, G.; Pavarini, E.
2016-12-01
Antiferromagnetic molecular rings are widely studied both for fundamental quantum-mechanical issues and for technological applications, particularly in the field of quantum information processing. Here we present a detailed first-principles study of two families—purple and green—of {Cr7M } antiferromagnetic rings, where M is a divalent transition metal ion (M =Ni2 + , Mn2 +, and Zn2 +). We employ a recently developed flexible and efficient scheme to build ab initio system-specific Hubbard models. From such many-body models we systematically derive the low-energy effective spin Hamiltonian for the rings. Our approach allows us to calculate isotropic as well as anisotropic terms of the spin Hamiltonian, without any a priori assumption on its form. For each compound we calculate magnetic exchange couplings, zero-field splitting tensors, and gyromagnetic tensors, finding good agreement with experimental results.
Energy Technology Data Exchange (ETDEWEB)
Shuaibu, A. [Department of Physics, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia and Physics Department, Faculty of Science, Nigerian Defence Academy, P.M.B 2109, Kaduna (Nigeria); Rahman, M. M. [Physics Department, Faculty of Science, Nigerian Defence Academy, P.M.B 2109, Kaduna (Nigeria)
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.
Energy Technology Data Exchange (ETDEWEB)
Rojas, Onofre, E-mail: ors@dex.ufla.br [Departamento de Ciencias Exatas, Universidade Federal de Lavras, 37200-000, Lavras-MG (Brazil); Strečka, Jozef [Department of Theoretical Physics and Astrophysics, Faculty of Science, P.J. Šafárik University, Park Angelinum 9, 040 01 Košice (Slovakia); Lyra, Marcelo L. [Instituto de Física, Universidade Federal de Alagoas, 57072-970, Maceio-AL (Brazil)
2013-05-03
The spin-1/2 Ising–Heisenberg tetrahedral chain is exactly solved using its local gauge symmetry (the total spin of the Heisenberg bonds is locally conserved) and the transfer-matrix approach. Exact results derived for spin–spin correlation functions are employed to obtain the frustration temperature. In addition, we have exactly calculated a concurrence quantifying thermal entanglement. It is shown that the frustration and threshold temperature coincide at sufficiently low temperatures, while they exhibit a very different behavior in the high-temperature region when tending towards completely different asymptotic limits. The threshold temperature additionally shows a notable reentrant behavior when it extends over a narrow temperature region above the classical ground state without any quantum correlations. -- Highlights: ► Using local gauge symmetry we solved the spin-1/2 Ising–Heisenberg tetrahedral chain. ► The frustration temperature was calculated using the correlation functions. ► Thermal entanglement, concurrence and threshold temperature were analyzed. ► The zero-field specific heat was exactly calculated and discussed.
Non-collinearity and spin frustration in the itinerant kagome ferromagnet Fe(3)Sn(2).
Fenner, L A; Dee, A A; Wills, A S
2009-11-11
Frustrated itinerant ferromagnets, with non-collinear static spin structures, are an exciting class of material as their spin chirality can introduce a Berry phase in the electronic scattering and lead to exotic electronic phenomena such as the anomalous Hall effect (AHE). This study presents a reexamination of the magnetic properties of Fe(3)Sn(2), a metallic ferromagnet, based on the two-dimensional kagome bilayer structure. Previously thought of as a conventional ferromagnet, we show using a combination of SQUID (superconducting quantum interference device) measurements, symmetry analysis and powder neutron diffraction that Fe(3)Sn(2) is a frustrated ferromagnet with a temperature-dependent non-collinear spin structure. The complexity of the magnetic interactions is further evidenced by a re-entrant spin glass transition ([Formula: see text] K) at temperatures far below the main ferromagnetic transition (T(C) = 640 K). Fe(3)Sn(2) therefore provides a rare example of a frustrated itinerant ferromagnet. Further, as well as being of great fundamental interest our studies highlight the potential of Fe(3)Sn(2) for practical application in spintronics technology, as the AHE arising from the ferromagnetism in this material is expected to be enhanced by the coupling between the conduction electrons and the non-trivial magnetic structure over an exceptionally wide temperature range.
The 8th International Conference on Highly Frustrated Magnetism (HFM 2016)
Gardner, J. S.; Kao, Y. J.
2017-04-01
The 8th International Conference on Highly Frustrated Magnetism 2016 (HFM 2016) took place between the 7th and 11th of September 2016 at the GIS Convention Center at National Taiwan University, Taipei, Taiwan. Over 260 participants from all over the world, attended the meeting making it the largest HFM to-date and revealing the impressive growth in the community since the original meeting in Waterloo, Canada where 80 participants attended. Preceding the meeting a school was held at the National Synchrotron Radiation Research Center to help those new to the field understand the material they were likely to see at HFM2016. Our thanks to the international speakers who attended this school John Chalker, Michel Kenzelmann, Philippe Mendels, Luigi Paolasini, Kirrily Rule, Yixi Su, Isao Watanabe and those from Taiwan W. T. Chen, Y-J, Kao, L. J. Chang and C. S. Ku, for their enlightening presentations. The HFM 2016 conference consisted of five plenary talks by H Takagi, B D Gaulin, L Balents, Y Tokura and S T Bramwell, 20 invited and 40 contributed presentations, and about 160 poster presentations from all aspects of theoretical and experimental frustrated magnetism. During the conference period, many stimulating discussions were held both inside and outside the conference room. Excursions to Taipei 101 and the National Palace Museum, as well as several organized dinners and receptions allowed the participants to initiate collaborations and discuss the hottest issues. The subjects covered in the conference included: · Quantum frustrated magnetism and spin liquids · Novel ordering of geometrically frustrated magnets · Frustration effect on the coupling to lattice, orbital and charge degrees of freedom · Exotic phenomena induced by macroscopic degeneracy · Field effect on frustrated magnetism etc. These proceeding represent a very small, but valuable contribution to the community. I hope you enjoy reading them. In view of the rapid growth of the field, it has been
Susceptibility of the 2D spin-1 / 2 Heisenberg antiferromagnet with an impurity.
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.
Frustrated Lewis pairs: Design and reactivity
Indian Academy of Sciences (India)
Sanjoy Mukherjee; Pakkirisamy Thilagar
2015-02-01
The interaction of a Lewis acid with a Lewis base results in the formation of a Lewis acid–base adduct. Understanding Lewis acids and bases is central to conceptualizing chemical interactions and constitutes a major portion of metal–ligand chemistry. Sterically encumbered/constrained Lewis pairs cannot form acid–base adducts, but such ‘Frustrated Lewis Pairs’ (FLPs), with their unquenched electronic demands can be elegantly used to simultaneously react with a third species, resulting in unusual reactivity of small molecules. Such unusual reactions, explored only in the last few years, have found several applications, e.g., heterolytic splitting of H2, activation of small molecules (CO2, N2O, etc.). FLPs have opened new opportunities in synthetic chemistry, covering organic, main group as well as transition metal chemistry. The design strategies adopted for FLP systems and their unique reactivity are discussed here.
Aluminium Diphosphamethanides: Hidden Frustrated Lewis Pairs.
Styra, Steffen; Radius, Michael; Moos, Eric; Bihlmeier, Angela; Breher, Frank
2016-07-04
The synthesis and characterisation of two aluminium diphosphamethanide complexes, [Al(tBu)2 {κ(2) P,P'-Mes*PCHPMes*}] (3) and [Al(C6 F5 )2 {κ(2) P,P'-Mes*PCHPMes*}] (4), and the silylated analogue, Mes*PCHP(SiMe3 )Mes* (5), are reported. The aluminium complexes feature four-membered PCPAl core structures consisting of diphosphaallyl ligands. The silylated phosphine 5 was found to be a valuable precursor for the synthesis of 4 as it cleanly reacts with the diaryl aluminium chloride [(C6 F5 )2 AlCl]2 . The aluminium complex 3 reacts with molecular dihydrogen at room temperature under formation of the acyclic σ(2) λ(3) ,σ(3) λ(3) -diphosphine Mes*PCHP(H)Mes* and the corresponding dialkyl aluminium hydride [tBu2 AlH]3 . Thus, 3 belongs to the family of so-called hidden frustrated Lewis pairs.
Anomalous Hall Effect in Geometrically Frustrated Magnets
Directory of Open Access Journals (Sweden)
D. Boldrin
2012-01-01
space mechanism based on spin chirality that was originally applied to the pyrochlore Nd2Mo2O7 appears unsatisfactory. Recently, an orbital description based on the Aharonov-Bohm effect has been proposed and applied to both the ferromagnetic pyrochlores Nd2Mo2O7 and Pr2Ir2O7; the first of which features long-ranged magnetic order while the latter is a chiral spin liquid. Two further examples of geometrically frustrated conducting magnets are presented in this paper—the kagome-like Fe3Sn2 and the triangular PdCrO2. These possess very different electronic structures to the 3-dimensional heavy-metal pyrochlores and provide new opportunities to explore the different origins of the AHE. This paper summarises the experimental findings in these materials in an attempt to unite the conflicting theoretical arguments.
Ferrimagnetism in delta chain with anisotropic ferromagnetic and antiferromagnetic interactions
Dmitriev, D. V.; Krivnov, V. Ya
2016-12-01
We consider analytically and numerically an anisotropic spin-\\frac{1}{2} delta-chain (sawtooth chain) in which exchange interactions between apical and basal spins are ferromagnetic and those between basal spins are antiferromagnetic. In the limit of strong anisotropy of exchange interactions this model can be considered as the Ising delta chain with macroscopic degenerate ground state perturbed by transverse quantum fluctuations. These perturbations lift the ground state degeneracy and the model reduces to the basal XXZ spin chain in the magnetic field induced by static apical spins. We show that the ground state of such a model is ferrimagnetic. The excitations of the model are formed by ferrimagnetic domains separated by domain walls with a finite energy. At low temperatures the system is effectively divided into two independent subsystems, the apical subsystem described by the Ising spin-\\frac{1}{2} chain and the basal subsystem described by the XXZ chain with infinite zz interactions.
Nematic ordering dynamics of an antiferromagnetic spin-1 condensate
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.
Antiferromagnetic domain wall motion driven by spin-orbit torques
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
Strečka, Jozef; Ekiz, Cesur
2015-05-01
The geometrically frustrated spin-1/2 Ising-Heisenberg model on triangulated Husimi lattices is exactly solved by combining the generalized star-triangle transformation with the method of exact recursion relations. The ground-state and finite-temperature phase diagrams are rigorously calculated along with both sublattice magnetizations of the Ising and Heisenberg spins. It is evidenced that the Ising-Heisenberg model on triangulated Husimi lattices with two or three interconnected triangles-in-triangles units displays in a highly frustrated region a quantum disorder irrespective of temperature, whereas the same model on triangulated Husimi lattices with a greater connectivity of triangles-in-triangles units exhibits at low enough temperatures an outstanding quantum order due to the order-by-disorder mechanism. The quantum reduction of both sublattice magnetizations in the peculiar quantum ordered state gradually diminishes upon increasing the coordination number of the underlying Husimi lattice.
Purely antiferromagnetic magnetoelectric random access memory
Kosub, Tobias; Kopte, Martin; Hühne, Ruben; Appel, Patrick; Shields, Brendan; Maletinsky, Patrick; Hübner, René; Liedke, Maciej Oskar; Fassbender, Jürgen; Schmidt, Oliver G.; Makarov, Denys
2017-01-01
Magnetic random access memory schemes employing magnetoelectric coupling to write binary information promise outstanding energy efficiency. We propose and demonstrate a purely antiferromagnetic magnetoelectric random access memory (AF-MERAM) that offers a remarkable 50-fold reduction of the writing threshold compared with ferromagnet-based counterparts, is robust against magnetic disturbances and exhibits no ferromagnetic hysteresis losses. Using the magnetoelectric antiferromagnet Cr2O3, we demonstrate reliable isothermal switching via gate voltage pulses and all-electric readout at room temperature. As no ferromagnetic component is present in the system, the writing magnetic field does not need to be pulsed for readout, allowing permanent magnets to be used. Based on our prototypes, we construct a comprehensive model of the magnetoelectric selection mechanisms in thin films of magnetoelectric antiferromagnets, revealing misfit induced ferrimagnetism as an important factor. Beyond memory applications, the AF-MERAM concept introduces a general all-electric interface for antiferromagnets and should find wide applicability in antiferromagnetic spintronics. PMID:28045029
Dipolar order by disorder in the classical Heisenberg antiferromagnet on the kagome lattice.
Chern, Gia-Wei; Moessner, R
2013-02-15
Ever since the experiments which founded the field of highly frustrated magnetism, the kagome Heisenberg antiferromagnet has been the archetypical setting for the study of fluctuation induced exotic ordering. To this day the nature of its classical low-temperature state has remained a mystery: the nonlinear nature of the fluctuations around the exponentially numerous harmonically degenerate ground states has not permitted a controlled theory, while its complex energy landscape has precluded numerical simulations at low temperature, T. Here we present an efficient Monte Carlo algorithm which removes the latter obstacle. Our simulations detect a low-temperature regime in which correlations asymptote to a remarkably small value as T→0. Feeding these results into an effective model and analyzing the results in the framework of an appropriate field theory implies the presence of long-range dipolar spin order with a tripled unit cell.
NMR study of pyrochlore lattice antiferromagnet, melanothallite Cu2OCl2
Nishiyama, Masahide; Oyamada, Akira; Itou, Tetsuaki; Maegawa, Satoru; Okabe, Hirotaka; Akimitsu, Jun
2011-09-01
The melanothallite Cu2OCl2 is a new example of pyrochlore-like antiferromagnet, which is composed of 3d transition metal electrons. We performed Cu- and Cl-NMR experiments on powder samples of Cu2OCl2 below transition temperature TN = 70 K and we observed six resonant peaks of Cu nuclei, which are composed of three symmetric peaks corresponding to 63Cu and three corresponding to 65Cu. The Cu nuclei feel the strong hyperfine fields because of ordered magnetic moments and the electric field gradients. We determined the spin structure by analyzing the Cu-NMR spectra. The melanothallite has an all-in-all-out spin structure. The spin lattice relaxation rates T1-1 of Cu- and Cl-NMR in the ordered phase are proportional to the temperature; This suggests that although long-range ordering occurs at rather high temperature, the large spin fluctuations caused by the geometrical frustration still remain.
Magnetic phase diagram of the antiferromagnetic pyrochlore Gd2 Ti2 O7
Petrenko, O. A.; Lees, M. R.; Balakrishnan, G.; Paul, D. Mck
2004-07-01
Gd2Ti2O7 is a highly frustrated antiferromagnet on a pyrochlore lattice, where apart from the Heisenberg exchange the spins also interact via dipole-dipole forces. We report on low-temperature specific heat measurements performed on single crystals of Gd2Ti2O7 for three different directions of an applied magnetic field. The measurements reveal the strongly anisotropic behavior of Gd2Ti2O7 in a magnetic field despite the apparent absence of a significant single-ion anisotropy for Gd3+ . The H-T phase diagrams are constructed for H∥[111] , H∥[110] , and H∥[112] . The results indicate that further theoretical work beyond a simple mean-field model is required.
Yasuda, Shinya; Todo, Synge
2013-12-01
We present a method that optimizes the aspect ratio of a spatially anisotropic quantum lattice model during the quantum Monte Carlo simulation, and realizes the virtually isotropic lattice automatically. The anisotropy is removed by using the Robbins-Monro algorithm based on the correlation length in each direction. The method allows for comparing directly the value of the critical amplitude among different anisotropic models, and identifying the universality more precisely. We apply our method to the staggered dimer antiferromagnetic Heisenberg model and demonstrate that the apparent nonuniversal behavior is attributed mainly to the strong size correction of the effective aspect ratio due to the existence of the cubic interaction.
Optical spectra of CdMnSe of nano-ferro- and antiferro-magnets.
Proshchenko, Vitaly; Dahnovsky, Yuri
2015-10-28
We study optical transitions in CdSe quantum dots doped by Mn atoms. At low concentrations the transitions are spin-forbidden. Nevertheless, strong light absorption was experimentally found. To explain this effect we propose a new mechanism that includes two or more Mn atoms closely placed to each other containing the electrons with opposite spin projections. In this case the spin-flip is unnecessary. In addition we study absorption from quantum dots containing two Mn atoms with different multiplicities. We find that the strongest absorption from the gap is for an antiferromagnetic arrangement. The obtained results confirm the experimental concentration dependencies.
Energy Technology Data Exchange (ETDEWEB)
Tutsch, Ulrich; Postulka, Lars; Wolf, Bernd; Lang, Michael; Well, Natalija van; Ritter, Franz; Krellner, Cornelius; Assmus, Wolf [Physikalisches Institut, Goethe-University Frankfurt (Germany)
2015-07-01
The system Cs{sub 2}CuCl{sub 4-x}Br{sub x} (0 ≤ x ≤ 4) is a quasi-two-dimensional Heisenberg antiferromagnet with a triangular in-plane arrangement of the spin-spin couplings. The ratio J{sup '}/J of the corresponding coupling constants determines the degree of frustration in the system and has been found to be 0.34 (x = 0) and 0.74 (x = 4) for the border compounds. One may ask whether for some intermediate Br concentration an even higher degree of frustration can be reached. Indeed, some indications have been reported by Ono et al. Here, we present specific heat C and susceptibility χ measurements below 1 K in magnetic fields B up to 13.5 T for the intermediate compound Cs{sub 2}CuCl{sub 2}Br{sub 2}, which, due to site-selective substitution, shows a well-ordered halide sublattice. Indications for an antiferromagnetic transition are observed around 90 mK for B = 0. A small field of B = 0.14 T is sufficient to fully suppress this anomaly. Taking into account the high saturation field of about 20 T, extrapolated from χ(T = const, B) scans at low temperatures, this small ordered region in the B-T plane clearly indicates a high degree of frustration in Cs{sub 2}CuCl{sub 2}Br{sub 2}.
Magnetic anisotropy in the frustrated spin-chain compound β -TeVO4
Weickert, F.; Harrison, N.; Scott, B. L.; Jaime, M.; Leitmäe, A.; Heinmaa, I.; Stern, R.; Janson, O.; Berger, H.; Rosner, H.; Tsirlin, A. A.
2016-08-01
Isotropic and anisotropic magnetic behavior of the frustrated spin-chain compound β -TeVO4 is reported. Three magnetic transitions observed in zero magnetic field are tracked in fields applied along different crystallographic directions using magnetization, heat capacity, and magnetostriction measurements. Qualitatively different temperature-field diagrams are obtained below 10 T for the field applied along a or b and along c , respectively. In contrast, a nearly isotropic high-field phase emerges above 18 T and persists up to the saturation that occurs around 22.5 T. Upon cooling in low fields, the transitions at TN 1 and TN 2 toward the spin-density-wave and stripe phases are of the second order, whereas the transition at TN 3 toward the helical state is of the first order and entails a lattice component. Our microscopic analysis identifies frustrated J1-J2 spin chains with a sizable antiferromagnetic interchain coupling in the b c plane and ferromagnetic couplings along the a direction. The competition between these ferromagnetic interchain couplings and the helical order within the chain underlies the incommensurate order along the a direction, as observed experimentally. While a helical state is triggered by the competition between J1 and J2 within the chain, the plane of the helix is not uniquely defined because of competing magnetic anisotropies. Using high-resolution synchrotron diffraction and 125Te nuclear magnetic resonance, we also demonstrate that the crystal structure of β -TeVO4 does not change down to 10 K, and the orbital state of V4 + is preserved.
Quantum Gravity as an Information Network: Self-Organization of a 4D Universe
Trugenberger, Carlo A
2015-01-01
I propose a quantum gravity model in which the fundamental degrees of freedom are pure information bits. The Hamiltonian is a very simple network model consisting of a ferromagnetic Ising model for space-time vertices and an antiferromagnetic Ising model for the links between them. As a result of the frustration arising between these two terms, the ground state self-organizes as a new type of low-clustering, lattice-like graph with finite Hausdorff dimension. The model has three quantum phases: a mean field phase in which the spectral and Hausdorff dimensions coincide and are larger then 4. A fluctuations-dominated phase in which the Hausdorff dimension can only be 4 and the spectral dimension is lower than the Hausdorff dimension and a disordered phase in which there is no space-time interpretation. The large-scale dimension 4 of the universe is related to the upper critical dimension 4 of the Ising model. An ultraviolet fixed point at the lower critical dimension of the Ising model is conjectured to imply t...
Yasuda, Chitoshi; Todo, Synge; Matsumoto, Munehisa; Takayama, Hajime
2002-01-01
Dilution effects on spin-1/2 quantum Heisenberg antiferromagnets with a non-magnetic spin-gapped ground state are studied by means of the qunatum Monte Carlo simulation. In the site-diluted system, an antiferromagnetic long-range order (AF-LRO) is induced at an infinitesimal concentration of dilution due to an effective coupling $\\tilde{J}_{mn}$ between induced magnetic moments. In the bond-diluted case, on the other hand, the AF-LRO is not induced up to a certain concentration of dilution du...
Universality in antiferromagnetic strange metals
Maier, Stefan A.; Strack, Philipp
2016-04-01
We propose a theory of metals at the spin-density-wave quantum-critical point in spatial dimension d =2 . We provide a first estimate of the full set of critical exponents (dynamical exponent z =2.13 , correlation length ν =1.02 , spin susceptibility γ =0.96 , electronic non-Fermi liquid ητf=0.53 , spin-wave Landau damping ητb=1.06 ), which determine the universal power laws in thermodynamics and response functions in the quantum-critical regime relevant for experiments in heavy-fermion systems and iron pnictides. We present approximate numerical and analytical solutions of Polchinski-Wetterich-type flow equations with soft frequency regulators for an effective action of electrons coupled to spin-wave bosons. Performing the renormalization group in frequency instead of momentum space allows to track changes of the Fermi-surface shape and to capture Landau damping during the flow. The technique is easily generalizable from models retaining only patches of the Fermi surface to full, compact Fermi surfaces.
Room Temperature Antiferromagnetic Ordering of Nanocrystalline Tb1.90Ni0.10O3
Mandal, J.; Dalal, M.; Sarkar, B. J.; Chakrabarti, P. K.
2017-02-01
Nanocrystalline Ni-doped terbium oxide (Tb1.90Ni0.10O3) has been synthesized by the co-precipitation method followed by annealing at 700°C for 6 h in vacuum. The crystallographic phase and the substitution of Ni2+ ions in the lattice of Tb2O3 are confirmed by Rietveld analysis of the x-ray diffraction pattern using the software MAUD. High-resolution transmission electron microscopy is also carried out to study the morphology of the sample. Magnetic measurements are carried out at different temperatures from 5 K to 300 K using a superconducting quantum interference device (SQUID) magnetometer. The dependence of the magnetization of Tb1.90Ni0.10O3 as a function of temperature ( M- T) and magnetic field ( M- H) suggests the presence of both paramagnetic and antiferromagnetic phase at room temperature, but antiferromagnetic phase dominates below ˜120 K. The lack of saturation in the M- H curve and good fitting of the M- T curve by the Johnston formula also indicate the presence of both paramagnetic and antiferromagnetic phase at room temperature. Interestingly, an antiferromagnetic to ferromagnetic phase transition is observed below ˜40 K. The result also shows a high value of magnetization at 5 K.
Superconductivity in the vicinity of antiferromagnetic order in CrAs.
Wu, Wei; Cheng, Jinguang; Matsubayashi, Kazuyuki; Kong, Panpan; Lin, Fukun; Jin, Changqing; Wang, Nanlin; Uwatoko, Yoshiya; Luo, Jianlin
2014-11-19
One of the common features of unconventional superconducting systems such as the heavy-fermion, high transition-temperature cuprate and iron-pnictide superconductors is that the superconductivity emerges in the vicinity of long-range antiferromagnetically ordered state. In addition to doping charge carriers, the application of external pressure is an effective and clean approach to induce unconventional superconductivity near a magnetic quantum critical point. Here we report on the discovery of superconductivity on the verge of antiferromagnetic order in CrAs via the application of external pressure. Bulk superconductivity with Tc≈2 K emerges at the critical pressure Pc≈8 kbar, where the first-order antiferromagnetic transition at T(N)≈265 K under ambient pressure is completely suppressed. The close proximity of superconductivity to an antiferromagnetic order suggests an unconventional pairing mechanism for CrAs. The present finding opens a new avenue for searching novel superconductors in the Cr and other transition metal-based systems.
Breaking the geometric magnetic frustration in controlled off-stoichiometric LuMn1+zO3+δ compounds.
Figueiras, F G; Karpinsky, D; Tavares, P B; Das, Soma; Leitão, J V; Brück, E H; Moreira, J Agostinho; Amaral, V S
2016-05-11
This study explores controlled off-stoichiometric LuMn1+zO3+δ (|z| LuMnO3 intrinsic hexagonal symmetry and ferroelectric properties. X-ray powder diffraction measurements evidenced a single phase P63cm structure. Thermo-gravimetric experiments show a narrow impact of oxygen vacancies while a distinguishable gas exchange at ∼700 K, a surprisingly lower temperature when compared to perovskite systems. A comparison of different nominal ceramics revealed pertinent structural and magnetic property variations owing to subtle self-doping effects. Deviations from the archetypal antiferromagnetic state were detected below ∼90 K suggesting local rearrangements of the nominal Mn(3+) ions matrix, breaking the ideal geometrical spin frustration, leading to a non-compensated magnetic structure.
Novel multiferroic state and ME enhancement by breaking the AFM frustration in LuMn1-xO3.
Figueiras, F G; Karpinsky, D; Tavares, P B; Gonçalves, J N; Yañez-Vilar, S; Moreira Dos Santos, A F; Franz, A; Tovar, M; Agostinho Moreira, J; Amaral, V S
2017-01-04
This study provides a comprehensive insight into the effects of controlled off-stoichiometry on the structural and multiferroic properties of the hexagonal manganite LuMn1-xO3+δ (x = 0.02; δ ∼ 0), supported by neutron powder diffraction measurements confirming single phase P63cm symmetry and evidencing a relevant ferromagnetic component, below TN ∼ 90 K, which breaks the archetypal geometrically frustrated antiferromagnetic state typically ascribed to LuMnO3. The perturbations in the triangular disposition of spins prompt an additional electric polarization contribution and a clear enhancement of the magnetoelectric coupling which are in good agreement with the results of first principles calculations. In addition, Raman spectroscopy, dielectric permittivity, pyroelectric current and magnetic measurements as a function of temperature point out the precursor effects of the magnetic phase transitions involving a strong coupling between spins, lattice and electric order, even above the Néel temperature.
Petrenko, O. A.; Ritter, C.; Yethiraj, M.; McK Paul, D.
1998-05-01
We report the results of powder neutron scattering measurements on the magnetic correlations in the frustrated antiferromagnet Gd3Ga5O12. A clear view of the short-range magnetic order has been obtained for a temperature range 0.14-5 K. At T~0.14 K there is a partial transition to a phase with a much longer correlation length. We argue that the low-temperature phase is not an ordinary spin glass, as was suggested by bulk properties measurements, but rather a mixture of a spin-liquid state with a set of rigid magnetic pieces nucleated around impurity centers. The experimental data are compared with the results of Monte Carlo simulations performed for several models.
Geometrically frustrated coarsening dynamics in spinor Bose-Fermi mixtures
Phuc, Nguyen Thanh; Momoi, Tsutomu; Furukawa, Shunsuke; Kawaguchi, Yuki; Fukuhara, Takeshi; Ueda, Masahito
2017-01-01
Coarsening dynamics theory describes equilibration of a broad class of systems. By studying the relaxation of a periodic array of microcondensates immersed in a Fermi gas, which mediates long-range spin interactions to simulate frustrated classical magnets, we show that coarsening dynamics can be suppressed by geometrical frustration. The system is found to eventually approach a metastable state which is robust against random field noise and characterized by finite correlation lengths together with the emergence of topologically stable Z2 vortices. We find universal scaling laws with no thermal-equilibrium analog that relate the correlation lengths and the number of vortices to the degree of frustration in the system.
Spin glass behavior of the antiferromagnetic Heisenberg model on scale free network
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.
Search for the Heisenberg spin glass on rewired cubic lattices with antiferromagnetic interaction
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.
Classical Heisenberg antiferromagnet on a garnet lattice: A Monte Carlo simulation
Petrenko, O. A.; Paul, D. McK.
2001-01-01
We have studied a classical antiferromagnet on a garnet lattice by means of Monte Carlo simulations in an attempt to examine the role of geometrical frustration in gadolinium gallium garnet Gd3Ga5O12 (GGG). Low-temperature specific heat, magnetization, susceptibility, the autocorrelation function A(t), and the neutron scattering function S(Q) have been calculated for several models including different types of magnetic interactions and with the presence of an external magnetic field applied along the principal symmetry axes. A model, which includes only nearest-neighbor exchange J1, neither orders down to the lowest temperature nor does it show any tendency towards forming a short-range coplanar spin structure. This model, however, does demonstrate a magnetic field induced ordering below T~0.01J1. In order to reproduce the experimentally observed properties of GGG, the simulated model must include nearest-neighbor exchange interactions and also dipolar forces. The presence of weak next-to-nearest exchange interactions is found to be insignificant. In zero field S(Q) exhibits diffuse magnetic scattering around positions in reciprocal space where antiferromagnetic Bragg peaks appear in an applied magnetic field.
Energy Technology Data Exchange (ETDEWEB)
Babaev, A. B., E-mail: b-albert78@mail.ru; Magomedov, M. A.; Murtazaev, A. K. [Russian Academy of Sciences, Amirkhanov Institute of Physics, Dagestan Scientific Center (Russian Federation); Kassan-Ogly, F. A.; Proshkin, A. I. [Russian Academy of Sciences, Institute of Metal Physics, Ural Branch (Russian Federation)
2016-02-15
Phase transitions (PTs) and frustrations in two-dimensional structures described by a three-vertex antiferromagnetic Potts model on a triangular lattice are investigated by the Monte Carlo method with regard to nearest and next-nearest neighbors with interaction constants J{sub 1} and J{sub 2}, respectively. PTs in these models are analyzed for the ratio r = J{sub 2}/J{sub 1} of next-nearest to nearest exchange interaction constants in the interval |r| = 0–1.0. On the basis of the analysis of the low-temperature entropy, the density of states function of the system, and the fourth-order Binder cumulants, it is shown that a Potts model with interaction constants J{sub 1} < 0 and J{sub 2} < 0 exhibits a first-order PT in the range of 0 ⩽ r < 0.2, whereas, in the interval 0.2 ⩽ r ⩽ 1.0, frustrations arise in the system. At the same time, for J{sub 1} > 0 and J{sub 2} < 0, frustrations arise in the range 0.5 < |r| < 1.0, while, in the interval 0 ⩽ |r| ⩽ 1/3, the model exhibits a second-order PT.
Mesoscopic modelling of frustration in microemulsions.
Duvail, Magali; Dufrêche, Jean-François; Arleth, Lise; Zemb, Thomas
2013-05-21
The swelling behaviour of water-oil microemulsions - considering a surfactant layer between oil and water - has been studied using a two level-cuts Gaussian random field approach based on the Helfrich formalism. Microstructures and scattering properties of microemulsions have been calculated for different amounts of oil (and water) for flexible and rigid microemulsions. When the stiffness, the spontaneous curvature of the interfacial film, and the surface to volume ratio of the immiscible fluids are varied, the microemulsion topology and morphology change in order to minimize the microemulsion free energy. Our simulations point out a change in the microemulsion morphology as a function of the surfactant film rigidity and the composition of oil, water and the surfactant. Locally lamellar structures are found for rigid microemulsions, whereas for more flexible ones, the connected-droplet and/or bicontinuous structures are preferred. Furthermore, we show that the microemulsion swelling versus the volume fraction gives a specific signature of the microemulsion microstructure. This allows for discriminating between different types of microemulsions: flexible, frustrated and unfrustrated (close to bi-liquid foams), and connected structures as molten hexagonal and cubic phases. The universal swelling behaviour is compared to different analytic expressions of Disordered Open Connected (DOC) models for the microemulsion swelling versus the volume fraction.
Magnetic remanent states in antiferromagnetically coupled multilayers
Energy Technology Data Exchange (ETDEWEB)
Kiselev, N.S., E-mail: m.kyselov@ifw-dresden.d [IFW Dresden, Postfach 270116, D-01171 Dresden (Germany); Donetsk Institute for Physics and Technology, 83114 Donetsk (Ukraine); Roessler, U.K.; Bogdanov, A.N. [IFW Dresden, Postfach 270116, D-01171 Dresden (Germany); Hellwig, O. [San Jose Research Center, Hitachi Global Storage Technologies, San Jose, CA 95135 (United States)
2010-05-15
In antiferromagnetically coupled multilayers with perpendicular anisotropy unusual multidomain textures can be stabilized due to a close competition between long-range demagnetization fields and short-range interlayer exchange coupling. In particular, the formation and evolution of specific topologically stable planar defects within the antiferromagnetic ground state, i.e. wall-like structures with a ferromagnetic configuration extended over a finite width, explain configurational hysteresis phenomena recently observed in [Co/Pt(Pd)]/Ru and [Co/Pt]/NiO multilayers. Within a phenomenological theory, we have analytically derived the equilibrium sizes of these 'ferroband' defects as functions of the antiferromagnetic exchange, a bias magnetic field, and geometrical parameters of the multilayers. In the magnetic phase diagram, the existence region of the ferrobands mediates between the regions of patterns with sharp antiferromagnetic domain walls and regular arrays of ferromagnetic stripes. The theoretical results are supported by magnetic force microscopy images of the remanent states observed in [Co/Pt]/Ru.
Antiferromagnetism in chromium alloy single crystals
DEFF Research Database (Denmark)
Bjerrum Møller, Hans; Trego, A.L.; Mackintosh, A.R.
1965-01-01
The antiferromagnetism of single crystals of dilute alloys of V, Mn and Re in Cr has been studied at 95°K and 300°K by neutron diffraction. The addition of V causes the diffraction peaks to decrease in intensity and move away from (100), while Mn and Re cause them to increase and approach (100) so...
The electronic structure of antiferromagnetic chromium
DEFF Research Database (Denmark)
Skriver, Hans Lomholt
1981-01-01
The author has used the local spin density formalism to perform self-consistent calculations of the electronic structure of chromium in the non-magnetic and commensurate antiferromagnetic phases, as a function of the lattice parameter. A change of a few per cent in the atomic radius brings...
Zhang, F. B.; Li, Q. J.; Zhao, Z. Y.; Fan, C.; Li, S. J.; Liu, X. G.; Zhao, X.; Sun, X. F.
2014-03-01
We report a systematic study on the low-temperature thermal conductivity (κ) of R2Ti2O7 (R = Gd and Er) single crystals with different directions of magnetic field and heat current. It is found that the magnetic excitations mainly act as phonon scatterers rather than heat carriers, although these two materials have long-range magnetic orders at low temperatures. The low-T κ (H) isotherms of both compounds show rather complicated behaviors and have good correspondences with the magnetic transitions, where the κ (H) curves show drastic dip- or steplike changes. In comparison, the field dependencies of κ are more complicated in Gd2Ti2O7, due to the complexity of its low-T phase diagram and field-induced magnetic transitions. These results demonstrate the significant coupling between spins and phonons in these materials and the ability of heat-transport properties probing the magnetic transitions.
Effect of rare earth dopants on the magnetic ordering of frustrated h-YMnO3
Sharma, Neetika; Das, A.; Prajapat, C. L.; Singh, M. R.
2016-12-01
In this report the combined effects of chemical pressure and R-Mn interaction on the structural and magnetic properties of frustrated h-YMnO3 have been investigated. Towards this, neutron powder diffraction and magnetization measurements were carried out on isostructural compounds Y1-xRxMnO3(R=Yb, Er, Tb, Ho; x≤0.2) with hexagonal structure (P63cm space group). The dopants are evenly distributed between the two Yttrium sites. The unit cell volume shows a linear increase with average A-site ionic radii, . The average apical a and planar p bond lengths are found to increase with . The tilting angle of the MnO5 polyhedron decreases linearly with increase in , whereas the buckling angle remains constant. No significant change in TN (within 10 K) is observed on doping. The temperature variation of the volume indicates an anomalous reduction in volume at TN which is found to be correlated with the square of the antiferromagnetic Mn moment. A spin reorientation behavior (evident from a change in the irreducible representation (IR) Γ3 to Γ4) is observed on decreasing from 1.019 Å (Y) to 1.012 Å (Yb) similar to that reported in external pressure studies on YMnO3. Additional interaction between the doped R and Mn influences the magnetic structure in the case of Ho and Tb doped samples. With Ho doping at Y site, the magnetic structure is described by IR Γ3 alone for 5 K≤T<35 K and a mixture of Γ3 and Γ4 for T≥35 K. However, in Tb doped sample, the magnetic structure is better described by Γ4Tb,Mn IR with additional moment on Tb. The frustration parameter, f reduces from 6 to 1 in the doped samples. A combination of chemical pressure effect and magnetic coupling between the magnetic R ion and Mn moments thus describes the magnetic structures and relieves the frustration effects inherent to the quasi-two dimensional Mn moment ordering.
Frustration and fulfillment of needs in dissociative and conversion disorders.
Ishikura, Reiji; Tashiro, Nobutada
2002-08-01
We reviewed all patients with dissociative disorders (nine patients with dissociative amnesia or dissociative fugue) and conversion disorders (10 patients) who were admitted and treated during the past 15 years. Needs frustrated at the appearance of the symptoms and those fulfilled at discharge were studied in both groups using Maslow's hierarchy of needs. The patients of both groups who encountered troubles in their life events were found to have frustrated needs. These symptoms tended to be accompanied more often by frustrations regarding a 'need for love' in the dissociative disorders group and by frustration in the need for 'self-esteem and self-actualization' in the conversion disorders group. In addition, needs of lower orders were already threatened at onset in many patients. The symptoms disappeared in patients in whom the situation completely improved (needs were fulfilled), but the symptoms were alleviated or unchanged in those in whom the problems remained unresolved.
Enhanced π-frustration in carbo-benzenic chromophores.
Baglai, Iaroslav; Maraval, Valérie; Bijani, Christian; Saffon-Merceron, Nathalie; Voitenko, Zoia; Volovenko, Yulian M; Chauvin, Remi
2013-09-28
The synthesis, structure, and absorption spectra of highly π-frustrated carbo-benzenes with indolic enamine substituents more or less directly conjugated to the C18 macro-aromatic core are described, and their peculiar reactivity is analyzed.
Acceptance of disability: determinants of overcoming social frustration.
Morozova, Elena Valeryevna; Shmeleva, Svetlana Vasilyevna; Sorokoumova, Elena Aleksandrovna; Nikishina, Vera Borisovna; Abdalina, Larisa Vasilyevna
2015-01-25
The article is devoted to the subjective reaction of patients at different stages of disabling disease, in the context of the formation of a specific cognitive-emotional and motivational model of "internal picture of disability", depending on the severity of social frustration as the most important deconditioning factor. We wanted to identify psychological determinant of the specificity of adaptive activity of the patient to the situation disabling disease, depending on the level of increase social frustration. Nature of adaptation to the disabling disease depending on the level of increase social frustration expressed by: 1) decrease in self-esteem of patient self-efficacy with an increase in subjective experience of disability; 2) the growing tension of personal protective mechanisms; 3) reductions coping competence, which, depending on the rise of frustration, becomes effective instead of the rational-intelligent, more maladaptive emotional.
Complexation of Nitrous Oxide by Frustrated Lewis Pairs
Otten, Edwin; Neu, Rebecca C.; Stephan, Douglas W.
2009-01-01
Frustrated Lewis pairs comprised of a basic yet sterically encumbered phosphine with boron Lewis acids bind nitrous oxide to give intact PNNOB linkages. The synthesis, structure, and bonding of these species are described.
Frustration and fulfillment of needs in dissociative and conversion disorders
National Research Council Canada - National Science Library
ISHIKURA, REIJI; TASHIRO, NOBUTADA
2002-01-01
...) and conversion disorders (10 patients) who were admitted and treated during the past 15 years. Needs frustrated at the appearance of the symptoms and those fulfilled at discharge were studied in both groups using Maslow's hierarchy of needs...
Order by virtual crystal field fluctuations in pyrochlore XY antiferromagnets
Rau, Jeffrey G.; Petit, Sylvain; Gingras, Michel J. P.
2016-05-01
Conclusive evidence of order by disorder is scarce in real materials. Perhaps one of the strongest cases presented has been for the pyrochlore XY antiferromagnet Er2Ti2O7 , with the ground state selection proceeding by order by disorder induced through the effects of quantum fluctuations. This identification assumes the smallness of the effect of virtual crystal field fluctuations that could provide an alternative route to picking the ground state. Here we show that this order by virtual crystal field fluctuations is not only significant, but competitive with the effects of quantum fluctuations. Further, we argue that higher-multipolar interactions that are generically present in rare-earth magnets can dramatically enhance this effect. From a simplified bilinear-biquadratic model of these multipolar interactions, we show how the virtual crystal field fluctuations manifest in Er2Ti2O7 using a combination of strong-coupling perturbation theory and the random-phase approximation. We find that the experimentally observed ψ2 state is indeed selected and the experimentally measured excitation gap can be reproduced when the bilinear and biquadratic couplings are comparable while maintaining agreement with the entire experimental spin-wave excitation spectrum. Finally, we comment on possible tests of this scenario and discuss implications for other order-by-disorder candidates in rare-earth magnets.
Roy, Beas
This doctoral thesis emphasizes on the study of frustrated systems which form a very interesting class of compounds in physics. The technique used for the investigation of the magnetic properties of the frustrated materials is Nuclear Magnetic Resonance (NMR). NMR is a very novel tool for the microscopic study of the spin systems. NMR enables us to investigate the local magnetic properties of any system exclusively. The NMR experiments on the different systems yield us knowledge of the static as well as the dynamic behavior of the electronic spins. Frustrated systems bear great possibilities of revelation of new physics through the new ground states they exhibit. The vandates AA'VO(PO4)2 [AA' ≡ Zn2 and BaCd] are great prototypes of the J1-J2 model which consists of magnetic ions sitting on the corners of a square lattice. Frustration is caused by the competing nearest-neighbor (NN) and next-nearest neighbor (NNN) exchange interactions. The NMR investigation concludes a columnar antiferromagnetic (AFM) state for both the compounds from the sharp peak of the nuclear spin-lattice relaxation rate (1/T1) and a sudden broadening of the 31P-NMR spectrum. The important conclusion from our study is the establishment of the first H-P-T phase diagram of BaCdVO(PO4)2. Application of high pressure reduces the saturation field (HS) in BaCdVO(PO4)2 and decreases the ratio J2/J1, pushing the system more towards a questionable boundary (a disordered ground state) between the columnar AFM and a ferromagnetic ground state. A pressure up to 2.4 GPa will completely suppress HS. The Fe ions in the `122' iron-arsenide superconductors also sit on a square lattice thus closely resembling the J1-J2 model. The 75As-NMR and Nuclear Quadrupole Resonance (NQR) experiments are conducted in the compound CaFe2As2 prepared by two different heat treatment methods (`as-grown' and `annealed'). Interestingly the two samples show two different ground states. While the ground state of the `as
Thermodynamic properties of the 2D frustrated Heisenberg model for the entire J1 -J2 circle
Mikheyenkov, A. V.; Shvartsberg, A. V.; Valiulin, V. E.; Barabanov, A. F.
2016-12-01
Using the spherically symmetric self-consistent Green's function method, we consider thermodynamic properties of the S = 1 / 2J1 -J2 Heisenberg model on the 2D square lattice. We calculate the temperature dependence of the spin-spin correlation functions cr = , the gaps in the spin excitation spectrum, the energy E and the heat capacity CV for the whole J1-J2-circle, i.e. for arbitrary φ, J1 = cos (φ), J2 = sin (φ). Due to low dimension there is no long-range order at T ≠ 0, but the short-range holds the memory of the parent zero-temperature ordered phase (antiferromagnetic, stripe or ferromagnetic). E(φ) and CV(φ) demonstrate extrema "above" the long-range ordered phases and in the regions of rapid short-range rearranging. Tracts of cr(φ) lines have several nodes leading to nonmonotonic cr(T) dependence. For any fixed φ the heat capacity CV(T) always has maximum, tending to zero at T → 0, in the narrow vicinity of φ = 155 ° it exhibits an additional frustration-induced low-temperature maximum. We have also found the nonmonotonic behaviour of the spin gaps at φ = 270 ° ± 0 and exponentially small antiferromagnetic gap up to (T ≲ 0.5) for φ ≳ 270 °.
Evidence for a gapped spin-liquid ground state in a kagome Heisenberg antiferromagnet.
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.
Spin-1/2 Heisenberg Antiferromagnet on the Spatially Anisotropic Kagome Lattice
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).
Self-assembly of magnetic Ni nanoparticles into 1D arrays with antiferromagnetic order.
Bliznyuk, V; Singamaneni, S; Sahoo, S; Polisetty, S; He, Xi; Binek, Ch
2009-03-11
In this paper, we report on the magnetic properties of isolated nanoparticles and interacting nanochains formed by the self-assembly of Ni nanoparticles. The magnetic properties were studied using superconducting quantum interference device (SQUID) magnetometry and magnetic force microscopy (MFM). We demonstrate that single-domain Ni nanoparticles spontaneously form one-dimensional (1D) chains under the influence of an external magnetic field. Furthermore, such magnetic field-driven self-assembly in conjunction with surface templating produces regular arrays of 1D nanochains with antiferromagnetic intra-chain order. The antiferromagnetic order, which is in striking contrast to what is found for non-interacting nanoparticle assemblies within the chains, can be evidenced from MFM and SQUID measurements.
Self-assembly of magnetic Ni nanoparticles into 1D arrays with antiferromagnetic order
Bliznyuk, V.; Singamaneni, S.; Sahoo, S.; Polisetty, S.; He, Xi; Binek, Ch
2009-03-01
In this paper, we report on the magnetic properties of isolated nanoparticles and interacting nanochains formed by the self-assembly of Ni nanoparticles. The magnetic properties were studied using superconducting quantum interference device (SQUID) magnetometry and magnetic force microscopy (MFM). We demonstrate that single-domain Ni nanoparticles spontaneously form one-dimensional (1D) chains under the influence of an external magnetic field. Furthermore, such magnetic field-driven self-assembly in conjunction with surface templating produces regular arrays of 1D nanochains with antiferromagnetic intra-chain order. The antiferromagnetic order, which is in striking contrast to what is found for non-interacting nanoparticle assemblies within the chains, can be evidenced from MFM and SQUID measurements.
Fragile antiferromagnetism in the heavy-fermion compound YbBiPt
Energy Technology Data Exchange (ETDEWEB)
Ueland, Benjamin G. [Ames Laboratory; Kreyssig, Andreas [Ames Laboratory; Prokes, K. [Helmholtz-Zentrum Berlin fur Materialien und Energie; Lynn, J. W. [NIST Center for Neutron Research; Harriger, L. W. [NIST Center for Neutron Research; Pratt, D. K. [NIST Center for Neutron Research; Singh, D. K. [NIST Center for Neutron Research; Heitmann, T. W. [University of Missouri; Sauerbrei, Samantha [Ames Laboratory; Saunders, Scott M. [Ames Laboratory; Mun, E. D. [Ames Laboratory; Budko, Serguei L. [Ames Laboratory; McQueeney, Robert J. [Ames Laboratory; Canfield, Paul C. [Ames Laboratory; Goldman, Alan I. [Ames Laboratory
2014-05-08
We report results from neutron scattering experiments on single crystals of YbBiPt that demonstrate antiferromagnetic order characterized by a propagation vector, τAFM = (121212), and ordered moments that align along the [1 1 1] direction of the cubic unit cell. We describe the scattering in terms of a two-Gaussian peak fit, which consists of a narrower component that appears below TN≈0.4 K and corresponds to a magnetic correlation length of ξn≈ 80 Å, and a broad component that persists up to T*≈ 0.7 K and corresponds to antiferromagnetic correlations extending over ξb≈ 20 Å. Our results illustrate the fragile magnetic order present in YbBiPt and provide a path forward for microscopic investigations of the ground states and fluctuations associated with the purported quantum critical point in this heavy-fermion compound.
Žukovič, Milan; Tomita, Yusuke; Kamiya, Y.
2017-07-01
We study critical and magnetic properties of a bilayer Ising system consisting of two triangular planes A and B, with the antiferromagnetic (AF) coupling JA and the ferromagnetic (FM) one JB for the respective layers, which are coupled by the interlayer interaction JAB by using Monte Carlo simulations. When JA and JB are of the same order, the unfrustrated FM plane orders first at a high temperature Tc 1˜JB . The spontaneous FM order then exerts influence on the other frustrated AF plane as an effective magnetic field, which subsequently induces a ferrimagnetic order in this plane at low temperatures below Tc 2. When short-range order is developed in the AF plane while the influence of the FM plane is still small, there appears a preemptive Berezinskii-Kosterlitz-Thouless-type pseudocritical crossover regime just above the ferrimagnetic phase transition point, where the short-distance behavior up to a rather large length scale exponentially diverging in ∝JA/T is controlled by a line of Gaussian fixed points at T =0 . In the crossover region, a continuous variation in the effective critical exponent 4/9 ≲ηeff≲1/2 is observed. The phase diagram by changing the ratio JA/JB is also investigated.
Magnetic field dependence of muon spin relaxation in geometrically frustrated Gd2Ti2O7
Dunsiger, S. R.; Kiefl, R. F.; Chakhalian, J. A.; Greedan, J. E.; Macfarlane, W. A.; Miller, R. I.; Morris, G. D.; Price, A. N.; Raju, N. P.; Sonier, J. E.
2006-05-01
Muon spin relaxation has been investigated in the geometrically frustrated antiferromagnet Gd2Ti2O7 as a function of magnetic field and temperature. Well above the magnetic ordering temperature of Tc=1K , the field dependence of the muon spin relaxation rate (T1-1) originates from field-induced changes in the spectral density of Gd fluctuations. This allows one to determine both the autocorrelation time and magnitude of the fluctuating local magnetic field at the muon. Well below Tc a coherent precession signal is observed, corresponding to a much smaller quasistatic local magnetic field. At low temperatures T1-1 levels off, at a constant value which is much larger than reported recently for a single crystal of Gd2Ti2O7 [Yaouanc , Phys. Rev. Lett. 95, 047203 (2005)]. A magnetic field of 2T completely quenches the low-temperature spin relaxation in the present sample. These results indicate that the ordered state is characterized by low-frequency dynamics which are most likely due to residual crystalline disorder.
Ultrasound Velocity Measurements in the Geometrically Frustrated Spinel MgCr2O4
Watanabe, Tadataka; Kousaka, Yusuke; Tomiyasu, Keisuke
2012-02-01
Magnesium chromite spinel MgCr2O4 is a geometrically frustrated magnet with the Néel temperature TN˜13 K, and the Weiss temperature θW= -390 K. Recent inelastic neutron scattering experiments provided a compelling evidence for the spin molecular ground states in not only the paramagnetic phase but also the antiferromagnetic phase. We performed ultrasound velocity measurements of MgCr2O4 in all the symmetrically independent elastic moduli of C11, (C11-C12)/2, and C44. Temperature dependence of all of these elastic moduli exhibits a remarkable softening in the paramagnetic phase. Taking into account the absence of orbital degrees of freedom in Cr^3+ (3d^3) in MgCr2O4, the spin degrees of freedom should play a significant role for the elastic softening. The most probable origin for the elastic softening in the paramagnetic phase is the strong coupling of the acoustic phonons to the molecular spin fluctuations.
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.
Khmelevskyi, Sergii; Ruban, Andrei V.; Mohn, Peter
2016-05-01
Mn-Ga alloys close to the M n3Ga stoichiometry can be synthesized in three different crystal modifications: hexagonal, tetragonal, and face-centered cubic, both in bulk and in thin-film forms. The magnetic ordering of these modifications is varying from noncollinear antiferromagnetic in the hexagonal case to ferrimagnetic order in the tetragonal one, whereas it is still unknown for the atomically disordered fcc structure. Here we study the onset of magnetic order at finite temperatures in these systems on a first-principles basis calculating the interatomic magnetic exchange interactions in the high-temperature paramagnetic regime. We employ the disordered local moment formalism and the magnetic force theorem within the framework of the local spin-density approximation and Monte Carlo simulations taking also the effects of atomic disorder in fcc alloys into account. In particular we find the origin of the stabilization of the noncollinear 3 k structure in competition between antiferromagnetic inter- and in-plane couplings of frustrated kagome planes in hexagonal M n3Ga and predict the antiferromagnetic-1 collinear order due to frustration in fcc alloys. Special attention is paid to the effects of the off-stoichiometry and the consequences of atomic disorder. We calculate the site-preference energy of Ga antisite atoms in the tetragonal structures in the range of the compositions from M n3Ga to M n2Ga and slightly beyond and confirm the earlier explanation of the effect of magnetization increase due to Ga preferentially occupying one of the Mn sites.
π-electron S = ½ quantum spin-liquid state in an ionic polyaromatic hydrocarbon
Takabayashi, Yasuhiro; Menelaou, Melita; Tamura, Hiroyuki; Takemori, Nayuta; Koretsune, Takashi; Štefančič, Aleš; Klupp, Gyöngyi; Buurma, A. Johan C.; Nomura, Yusuke; Arita, Ryotaro; Arčon, Denis; Rosseinsky, Matthew J.; Prassides, Kosmas
2017-07-01
Molecular solids with cooperative electronic properties based purely on π electrons from carbon atoms offer a fertile ground in the search for exotic states of matter, including unconventional superconductivity and quantum magnetism. The field was ignited by reports of high-temperature superconductivity in materials obtained by the reaction of alkali metals with polyaromatic hydrocarbons, such as phenanthrene and picene, but the composition and structure of any compound in this family remained unknown. Here we isolate the binary caesium salts of phenanthrene, Cs(C14H10) and Cs2(C14H10), to show that they are multiorbital strongly correlated Mott insulators. Whereas Cs2(C14H10) is diamagnetic because of orbital polarization, Cs(C14H10) is a Heisenberg antiferromagnet with a gapped spin-liquid state that emerges from the coupled highly frustrated Δ-chain magnetic topology of the alternating-exchange spiral tubes of S = ½ (C14H10)•- radical anions. The absence of long-range magnetic order down to 1.8 K (T/J ≈ 0.02 J is the dominant exchange constant) renders the compound an excellent candidate for a spin-½ quantum-spin liquid (QSL) that arises purely from carbon π electrons.
Nonequilibrium quantum mechanics: A "hot quantum soup" of paramagnons
Scammell, H. D.; Sushkov, O. P.
2017-01-01
Motivated by recent measurements of the lifetime (decay width) of paramagnons in quantum antiferromagnet TlCuCl3, we investigate paramagnon decay in a heat bath and formulate an appropriate quantum theory. Our formulation can be split into two regimes: (i) a nonperturbative, "hot quantum soup" regime where the paramagnon width is comparable to its energy; (ii) a usual perturbative regime where the paramagnon width is significantly lower than its energy. Close to the Neel temperature, the paramagnon width becomes comparable to its energy and falls into the hot quantum soup regime. To describe this regime, we develop a new finite frequency, finite temperature technique for a nonlinear quantum field theory; the "golden rule of quantum kinetics." The formulation is generic and applicable to any three-dimensional quantum antiferromagnet in the vicinity of a quantum critical point. Specifically, we apply our results to TlCuCl3 and find agreement with experimental data. Additionally, we show that logarithmic running of the coupling constant in the upper critical dimension changes the commonly accepted picture of the quantum disordered and quantum critical regimes.
Antiferromagnetic order in hybrid electromagnetic metamaterials
Miroshnichenko, Andrey E.; Filonov, Dmitry; Lukyanchuk, Boris; Kivshar, Yuri
2017-08-01
We demonstrate experimentally a new type of order in optical magnetism resembling the staggered structure of spins in antiferromagnetic ordered materials. We study hybrid electromagnetic metasurfaces created by assembling hybrid meta-atoms formed by metallic split-ring resonators and dielectric particles with a high refractive index, both supporting optically-induced magnetic dipole resonances of different origin. Each pair (or ‘metamolecule’) is characterized by two interacting magnetic dipole moments with the distance-dependent magnetization resembling the spin exchange interaction in magnetic materials. By directly mapping the structure of the electromagnetic fields, we demonstrate experimentally that strong coupling between the optically-induced magnetic moments of different origin can flip the magnetisation orientation in a metamolecule creating an antiferromagnetic lattice of staggered optically-induced magnetic moments in hybrid metasurfaces.
Antiferromagnetic exchange mechanism of superconductivity in cuprates
Plakida, N M
2001-01-01
One examines theory of superconducting coupling resulted from antiferromagnetic exchange in terms of which one explains strong dependence of T sub c superconducting transition temperature on alpha lattice constant. Calculations are based on the Hubbard p-d two-region model within strong correlation limit. DELTA pd excitation high energy at antiferromagnetic exchange of two particles from different Hubbard subregions results in suppression o delay effects and in coupling of all particles in conductivity subregion with Fermi energy E sub F >= DELTA pd : T sub c approx = E sub F exp(-1/lambda), where lambda propor to J. T sub c (alpha) and isotopic effect are explained by J exchange interaction dependence on alpha and on zero oscillations of oxygen ions
Shape-induced anisotropy in antiferromagnetic nanoparticles
H. Gomonay; Kondovych, S.; Loktev, V.
2013-01-01
High fraction of the surface atoms considerably enhances the influence of size and shape on the magnetic and electronic properties of nanoparticles. Shape effects in ferromagnetic nanoparticles are well understood and allow to set and control the parameters of a sample that affect its magnetic anisotropy during production. In the present paper we study the shape effects in the other widely used magnetic materials -- antiferromagnets, -- which possess vanishingly small or zero macroscopic magn...
Spin Transport in Ferromagnetic and Antiferromagnetic Textures
Akosa, Collins A.
2016-12-07
In this dissertation, we provide an accurate description of spin transport in magnetic textures and in particular, we investigate in detail, the nature of spin torque and magnetic damping in such systems. Indeed, as will be further discussed in this thesis, the current-driven velocity of magnetic textures is related to the ratio between the so-called non-adiabatic torque and magnetic damping. Uncovering the physics underlying these phenomena can lead to the optimal design of magnetic systems with improved efficiency. We identified three interesting classes of systems which have attracted enormous research interest (i) Magnetic textures in systems with broken inversion symmetry: We investigate the nature of magnetic damping in non-centrosymmetric ferromagnets. Based on phenomenological and microscopic derivations, we show that the magnetic damping becomes chiral, i.e. depends on the chirality of the magnetic texture. (ii) Ferromagnetic domain walls, skyrmions and vortices: We address the physics of spin transport in sharp disordered magnetic domain walls and vortex cores. We demonstrate that upon spin-independent scattering, the non-adiabatic torque can be significantly enhanced. Such an enhancement is large for vortex cores compared to transverse domain walls. We also show that the topological spin currents owing in these structures dramatically enhances the non-adiabaticity, an effect unique to non-trivial topological textures (iii) Antiferromagnetic skyrmions: We extend this study to antiferromagnetic skyrmions and show that such an enhanced topological torque also exist in these systems. Even more interestingly, while such a non-adiabatic torque inuences the undesirable transverse velocity of ferromagnetic skyrmions, in antiferromagnetic skyrmions, the topological non-adiabatic torque directly determines the longitudinal velocity. As a consequence, scaling down the antiferromagnetic skyrmion results in a much more efficient spin torque.
Spin transfer in antiferromagnets (Conference Presentation)
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.
Spin Seebeck Effect Signals from Antiferromagnets
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.
Model calculation of thermal conductivity in antiferromagnets
Energy Technology Data Exchange (ETDEWEB)
Mikhail, I.F.I., E-mail: ifi_mikhail@hotmail.com; Ismail, I.M.M.; Ameen, M.
2015-11-01
A theoretical study is given of thermal conductivity in antiferromagnetic materials. The study has the advantage that the three-phonon interactions as well as the magnon phonon interactions have been represented by model operators that preserve the important properties of the exact collision operators. A new expression for thermal conductivity has been derived that involves the same terms obtained in our previous work in addition to two new terms. These two terms represent the conservation and quasi-conservation of wavevector that occur in the three-phonon Normal and Umklapp processes respectively. They gave appreciable contributions to the thermal conductivity and have led to an excellent quantitative agreement with the experimental measurements of the antiferromagnet FeCl{sub 2}. - Highlights: • The Boltzmann equations of phonons and magnons in antiferromagnets have been studied. • Model operators have been used to represent the magnon–phonon and three-phonon interactions. • The models possess the same important properties as the exact operators. • A new expression for the thermal conductivity has been derived. • The results showed a good quantitative agreement with the experimental data of FeCl{sub 2}.
Robust spin transfer torque in antiferromagnetic tunnel junctions
Saidaoui, Hamed Ben Mohamed
2017-04-18
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.
Frustration and Self-Ordering of Topological Defects in Ferroelectrics
Nahas, Y.; Prokhorenko, S.; Bellaiche, L.
2016-03-01
A first-principles-based effective Hamiltonian technique is used to investigate the interplay between geometrical frustration and the ordering of topological defects in a ferroelectric nanocomposite consisting of a square array of BaTiO3 nanowires embedded in a Ba0.15 Sr0.85 TiO3 matrix. Different arrangements of the wires' chiralities geometrically frustrate the matrix, which in response exhibits point topological defects featuring self-assembled ordered structures spatially fluctuating down to the lowest temperatures. These fluctuations thereby endow the system with residual configurational entropy from which many properties characteristic of geometric frustration, such as the ground state degeneracy and the broadness of the dielectric response, are further found to originate.
More Opportunities than Wealth: A Network of Power and Frustration
Mahault, Benoit; Nisoli, Cristiano
2015-01-01
We introduce a minimal agent-based model to qualitatively conceptualize the allocation of limited wealth among more abundant opportunities. We study the interplay of power, satisfaction and frustration in distribution, concentration, and inequality of wealth. Our framework allows us to compare subjective measures of frustration and satisfaction to collective measures of fairness in wealth distribution, such as the Lorenz curve and the Gini index. We find that a completely libertarian, law-of-the-jungle setting, where every agent can acquire wealth from, or lose wealth to, anybody else invariably leads to a complete polarization of the distribution of wealth vs. opportunity. The picture is however dramatically modified when hard constraints are imposed over agents, and they are limited to share wealth with neighbors on a network. We then propose an out of equilibrium dynamics {\\it of} the networks, based on a competition between power and frustration in the decision-making of agents that leads to network coevo...
Frustration and Self-Ordering of Topological Defects in Ferroelectrics.
Nahas, Y; Prokhorenko, S; Bellaiche, L
2016-03-18
A first-principles-based effective Hamiltonian technique is used to investigate the interplay between geometrical frustration and the ordering of topological defects in a ferroelectric nanocomposite consisting of a square array of BaTiO_{3} nanowires embedded in a Ba_{0.15}Sr_{0.85}TiO_{3} matrix. Different arrangements of the wires' chiralities geometrically frustrate the matrix, which in response exhibits point topological defects featuring self-assembled ordered structures spatially fluctuating down to the lowest temperatures. These fluctuations thereby endow the system with residual configurational entropy from which many properties characteristic of geometric frustration, such as the ground state degeneracy and the broadness of the dielectric response, are further found to originate.
Frustrations among graduates of athletic training education programs.
Bowman, Thomas G; Dodge, Thomas M
2013-01-01
Although previous researchers have begun to identify sources of athletic training student stress, the specific reasons for student frustrations are not yet fully understood. It is important for athletic training administrators to understand sources of student frustration to provide a supportive learning environment. To determine the factors that lead to feelings of frustration while completing a professional athletic training education program (ATEP). Qualitative study. National Athletic Trainers' Association (NATA) accredited postprofessional education program. Fourteen successful graduates (12 women, 2 men) of accredited professional undergraduate ATEPs enrolled in an NATA-accredited postprofessional education program. We conducted semistructured interviews and analyzed data with a grounded theory approach using open, axial, and selective coding procedures. We negotiated over the coding scheme and performed peer debriefings and member checks to ensure trustworthiness of the results. Four themes emerged from the data: (1) Athletic training student frustrations appear to stem from the amount of stress involved in completing an ATEP, leading to anxiety and feelings of being overwhelmed. (2) The interactions students have with classmates, faculty, and preceptors can also be a source of frustration for athletic training students. (3) Monotonous clinical experiences often left students feeling disengaged. (4) Students questioned entering the athletic training profession because of the fear of work-life balance problems and low compensation. In order to reduce frustration, athletic training education programs should validate students' decisions to pursue athletic training and validate their contributions to the ATEP; provide clinical education experiences with graded autonomy; encourage positive personal interactions between students, faculty, and preceptors; and successfully model the benefits of a career in athletic training.
Theories on Frustrated Electrons in Two-Dimensional Organic Solids
Directory of Open Access Journals (Sweden)
Chisa Hotta
2012-08-01
Full Text Available Two-dimensional quarter-filled organic solids are a promising class of materials to realize the strongly correlated insulating states called dimer Mott insulator and charge order. In their conducting layer, the molecules form anisotropic triangular lattices, harboring geometrical frustration effect, which could give rise to many interesting states of matter in the two insulators and in the metals adjacent to them. This review is concerned with the theoretical studies on such issue over the past ten years, and provides the systematic understanding on exotic metals, dielectrics, and spin liquids, which are the consequences of the competing correlation and fluctuation under frustration.
Geometrical frustration in an element solid: (beta)-rhombohedral boron
Energy Technology Data Exchange (ETDEWEB)
Ogitsu, T; Gygi, F; Reed, J; Udagawa, M; Motome, Y; Schwegler, E; Galli, G
2009-05-19
Although a comprehensive understanding of the basic properties of most elemental solids has been achieved, there are still fundamental, open questions regarding simple substances, e.g. boron. Based on an Ising model that describes the intrinsic defect states in elemental boron, we show that this system is the only known element to exhibit geometrical frustration in its solid form. Interestingly, we find that the peculiar transport properties of boron that have been reported over the past forty years originate from the presence of geometrical frustration.
Polarity continuation and frustration in ZnSe nanospirals
Li, Luying; Tu, Fanfan; Jin, Lei; Choy, Wallace C. H.; Gao, Yihua; Wang, Jianbo
2014-01-01
ZnSe nanospirals including structures with polarity continuation and polarity frustration are simultaneously observed at atomic resolution. Through careful analysis of polarity within each dumbbell based on aberration-corrected high-angle annular-dark-field imaging, polarity continuation across parallel polytype interfaces as well as the surrounding Z-shape faulted dipoles is verified. Moreover, polarity frustration across regions with different stacking sequence, which would lead to accumulations of boundary interface charges in the triangular-shaped mixed regions with potential optoelectronic applications, is carefully studied. PMID:25502957
Dynamic magnetic hysteresis and nonlinear susceptibility of antiferromagnetic nanoparticles
Kalmykov, Yuri P.; Ouari, Bachir; Titov, Serguey V.
2016-08-01
The nonlinear ac stationary response of antiferromagnetic nanoparticles subjected to both external ac and dc fields of arbitrary strength and orientation is investigated using Brown's continuous diffusion model. The nonlinear complex susceptibility and dynamic magnetic hysteresis (DMH) loops of an individual antiferromagnetic nanoparticle are evaluated and compared with the linear regime for extensive ranges of the anisotropy, the ac and dc magnetic fields, damping, and the specific antiferromagnetic parameter. It is shown that the shape and area of the DMH loops of antiferromagnetic particles are substantially altered by applying a dc field that permits tuning of the specific magnetic power loss in the nanoparticles.
Dynamics of antiferromagnetic skyrmion driven by the spin Hall effect
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.
Frustrated magnetism in Yb{sub 2}Fe{sub 12}P{sub 7}
Energy Technology Data Exchange (ETDEWEB)
Grube, Kai; Zocco, Diego A.; Weber, Frank; Kuntz, Sebastian; Loehneysen, Hilbert von [Karlsruhe Institute of Technology, Institut fuer Festkoerperphysik, 76021 Karlsruhe (Germany); Baumbach, Ryan [National High Magnetic Field Laboratory, Tallahassee (United States); Hamlin, James [Departement of Physics, University of Florida, Gainesville (United States); Lum, Ivy; Maple, M. Brian [Department of Physics, University of California, San Diego (United States); Lynn, Jeff; Huang, Qingzhen [NIST Center for Neutron Research, Gaithersburg (United States); Janoschek, Marc [Los Alamos National Laboratory (United States)
2016-07-01
Yb{sub 2}Fe{sub 12}P{sub 7} is characterized by a low magnetic transition temperature of T{sub N} ∼1 K and the breakdown of Fermi-liquid behavior. These properties suggest the proximity to a quantum critical point (QCP). The non-Fermi-liquid (NFL) behavior, however, does not conform to the standard QCP scenario described by the Hertz-Millis-Moriya theory. We measured thermal expansion, magnetostriction and magnetization. The pressure dependence was studied up to 15 GPa using resistivity measurements in piston cylinder and diamond anvil cells. The measurements reveal that only a small fraction of the Yb moments participate in the long-range magnetic order. The Grueneisen ratio does not diverge for T → 0 indicating that the NFL behavior is not related to a nearby pressure-induced QCP. In view of the unusual noncentrometric crystal structure, our observations might point to geometric frustration of the magnetic moments.
Zhao, Hongbo; Engelbrecht, Jan R.
2000-03-01
At the Mean Field level (G. Murthy and R. Shankar, J. Phys. Condens. Matter, 7) (1995), the frustration due to an external field first makes the uniform BCS ground state unstable to an incommensurate (qne0) superconducting state and then to a spin-polarized Fermi Liquid state. Our interest is how fluctuations modify this picture, as well as the normal state of this system which has a quantum critical point. We use the Fluctuation-Exchange Approximation for the 2D Attractive Hubbard Model, to study this system beyond the Mean-Field level. Earlier work in zero field has shown that this numerical method successfully captures the critical scaling of the KT superconducting transition upon cooling in the normal state. Here we investigate how the pair-breaking external field modifies this picture, and the development of incommensurate pairing.
Field dependence of the magnetic correlations of the frustrated magnet SrDy2O4
Gauthier, N.; Fennell, A.; Prévost, B.; Désilets-Benoit, A.; Dabkowska, H. A.; Zaharko, O.; Frontzek, M.; Sibille, R.; Bianchi, A. D.; Kenzelmann, M.
2017-05-01
The frustrated magnet SrDy2O4 exhibits a field-induced phase with a magnetization plateau at 1 /3 of the saturation value for magnetic fields applied along the b axis. We report here a neutron scattering study of the nature and symmetry of the magnetic order in this field-induced phase. Below T ≈0.5 K, there are strong hysteretic effects, and the order is short- or long-ranged for zero-field and field cooling, respectively. We find that the long-range ordered magnetic structure within the zigzag chains is identical to that expected for the one-dimensional axial next-nearest neighbor Ising (ANNNI) model in longitudinal fields. The long-range ordered structure in field contrasts with the short-range order found at zero field, and is probably reached through enhanced quantum fluctuations with increasing fields.
Entanglement distribution in a two-dimensional 5-site frustrated J1-J2 spin system
Jafarpour, Mojtaba; Ghanavati, Soghra; Afshar, Davood
2015-11-01
We have studied several ground states and their entanglement structure for a two-dimensional 5-site frustrated J1-J2 system in the presence and absence of an external magnetic field. We have used concurrence as a measure of bipartite entanglement and the Meyer-Wallach measure and its generalizations as the measures of multipartite entanglement. They provide a total of eight measures which lead to 30 entanglement quantities for each possible ground state. Computing these 30 quantities for several ground states, we have provided a detailed exposition of the entanglement distribution in each state. We have also categorized them into separable states, not showing entanglement for any bipartition; globally-entangled states, showing entanglement for all the bipartitions, and the states in between. It turns out that by adjusting the external magnetic field, conditioned on the values of the interaction parameters, one may generate specific ground states belonging to a specific class, appropriate for specific tasks in quantum information theory.
Sandvik, A W; Singh, R R
2001-01-15
We use quantum Monte Carlo simulations and numerical analytic continuation to study high-energy spin excitations in the two-dimensional S = 1/2 Heisenberg antiferromagnet at low temperature. We present results for both the transverse (x) and longitudinal (z) dynamic spin structure factors Sx,z(q,omega) at q = (pi,0) and (pi/2, pi/2). Linear spin-wave theory predicts no dispersion on the line connecting these momenta. Our calculations show that in fact the magnon energy at (pi,0) is 10% lower than at (pi/2, pi/2). We also discuss the transverse and longitudinal multimagnon continua and their relevance to neutron scattering experiments.
Directory of Open Access Journals (Sweden)
V.V. Kulish
2015-06-01
Full Text Available The paper investigates the antiferromagnetic vector distribution in an antiferromagnetic film with a system of antidots. A static distribution of the antiferromagnetic vector is written and a method – based on the minimization of the antiferromagnet energy – that allows reducing the number of boundary conditions required for finding the constants of this distribution is proposed. Equations for the distribution constants are obtained for the both cases of minimizing the antiferromagnet energy by one and by two distribution constants that enter the expression for the antiferromagnet energy. The method is illustrated on a system of one isolated antidot. For such system, one additional condition – for the case when two boundary conditions on the surface of the antidot are given – and two additional conditions – for the case when one boundary condition on the surface of the antidot is given – on the distribution constants are written.