Magnetic and quantum entanglement properties of the distorted diamond chain model for azurite

We present the results of magnetic properties and entanglement of the distorted diamond chain model for azurite using pure quantum exchange interactions. The magnetic properties and concurrence as a measure of pairwise thermal entanglement have been studied by means of variational mean-field like treatment based on Gibbs-Bogoliubov inequality. Such a system can be considered as an approximation of the natural material azurite, Cu3(CO3)2(OH)2. For values of exchange parameters, which are taken from experimental results, we study the thermodynamic properties, such as azurite specific heat and magnetic susceptibility. We also have studied the thermal entanglement properties and magnetization plateau of the distorted diamond chain model for azurite

Magnetic properties of the quantum spin-1/2 XX diamond chain: The Jordan-Wigner approach

The Jordan-Wigner transformation is applied to study magnetic properties of the quantum spin-1/2 $XX$ model on the diamond chain. Generally, the Hamiltonian of this quantum spin system can be represented in terms of spinless fermions in the presence of a gauge field and different gauge-invariant ways of assigning the spin-fermion transformation are considered. Additionally, we analyze general properties of a free-fermion chain, where all gauge terms are neglected and discuss their relevance for the quantum spin system. A consideration of interaction terms in the fermionic Hamiltonian rests upon the Hartree-Fock procedure after fixing the appropriate gauge. Finally, we discuss the magnetic properties of this quantum spin model at zero as well as non-zero temperatures and analyze the validity of the approximation used through a comparison with the results of the exact diagonalization method for finite (up to 36 spins) chains. Besides the $m=1/3$ plateau the most prominent feature of the magnetization curve is a jump at intermediate field present for certain values of the frustrating vertical bond.Comment: 12 pages, 9 figures, accepted for publication in Eur. Phys. J.

Complex Field Induced States in Linarite PbCuSO4 OH 2 with a Variety of High Order Exotic Spin Density Wave States

Low temperature neutron diffraction and NMR studies of field induced phases in linarite are presented for magnetic fields H amp; 8741;b axis. A two step spin flop transition is observed, as well as a transition transforming a helical magnetic ground state into an unusual magnetic phase with sine wave modulated moments amp; 8741; H. An effective J 1 amp; 8722;J 2 single chain model with a magnetization dependent frustration ratio amp; 945;ef f amp; 8722;J 2 J 1 is proposed. The latter is governed by skew interchain couplings and shifted to the vicinity of the ferromagnetic critical point. It explains qualitatively the observation of a rich variety of exotic longitudinal collinear spin density wave, SDWp, states 9 amp; 8805; p amp; 8805;

Superlattice correlations in Tb2Ti2O7 under the application of [110] magnetic field

We report an analysis of neutron diffraction from single crystals of the spin liquid pyrochlore Tb2Ti2O7 under the application of magnetic fields along the crystallographic 110 direction. Such a perturbation has been shown to destroy the spin liquid ground state and induce long range order, although the nature of the ordered state was not immediately determined. Recently, it has been proposed that the ordered state is characterized by spin ice like correlations, evincing an emergent ferromagnetic tendency in this material despite the large negative Curie Weiss constant. Here, we argue instead that the ordered state is dominated by Q 0 correlations that emerge either from strong antiferromagnetism or magnetoelastic distortion of the crystal. In contrast to previous reports, we observe no evidence for re entrant behavior in the high field limit. Extreme sensitivity of the ordered state to the alignment of the applied field is suggested to account for these discrepancies

Magnon-phonon coupling and two-magnon continuum in the two-dimensional triangular antiferromagnet CuCrO2

CuCrO2 is a manifestation of a two-dimensional triangular antiferromagnet which exhibits an incommensurate noncollinear magnetic structure similar to a classical 120 ordering. Using the inelastic neutron scattering technique, direct evidence of a magnon-phonon coupling in CuCrO2 is revealed via the mixed magnon-phonon character of the excitation mode at 12.5 meV as well as a minimum at the zone boundary. A simple model Hamiltonian that incorporates an exchange-striction type magnon-phonon coupling accurately reproduces the observed features. Also, continuum excitations originating from the interaction between quasiparticles are observed with strong intensity at the zone boundary. These features of the magnetic excitations are key to an understanding of the emergent excitations in noncollinear antiferromagnetic compounds. © 2016 American Physical Society1781sciescopu

A Characterization of the Computational Power of Rule-based Visualization

Declarative visualization is a paradigm in which the process of visualization is treated as a mapping from some domain (typically a program) to an image. One means of declaring such mappings is through the use of rules which specify the relationship between the domain and the image. This paper examines the computational power of such rule-based mappings. Computational power is measured using three separate criteria. The first of these uses the Chomsky hierarchy, in which computational power is treated as string-acceptance; with this criterion we are able to show that certain rule-based models are equivalent in power to Turing machines. The second criterion is the evaluation of recursive functions, while the third is a more informal consideration of the abstractive capabilities of the mapping. Keywords: declarative visualization, computational power, rule-based mappings Correspondence: All communications regarding this paper should be addressed to Dr. Gruia-Catalin Roman office: (314) 935-6190 Department of Computer Science secretary: (314) 935-6160 Washington University fax: (314) 935-7302 Campus Box 1045 One Brookings Drive Saint Louis, MO 63130-4899 [email protected] 1 1

Magnetic excitations in the ordered phases of praseodymium hexaboride

We have made the first inelastic neutron scattering measurements on single crystal PrB6, studying the magnetic excitations in the ordered phases. The lowest energy mode has a minimum energy of ≈1.0 meV at the magnetic zone centre, with a significant dispersion along the [001] direction, but very little dispersion along [110]. Interactions out to fourth nearest neighbours are required to explain the [001] dispersion. Measurements of the temperature dependence of the excitations show a strong softening and broadening of the lowest energy mode at the magnetic zone centre between 2 K (commensurate phase) and 5 K (incommensurate phase)

Magnetic Soft Modes in the Distorted Triangular Antiferromagnet alpha CaCr2O4

In this Letter, we explore the phase diagram and excitations of a distorted triangular lattice antiferromagnet. The unique two dimensional distortion considered here is very different from the isosceles type distortion that has been extensively investigated. We show that it is able to stabilize a 120 spin structure for a large range of exchange interaction values, while new structures are found for extreme distortions. A physical realization of this model is CaCr2O4, which has a 120 structure but lies very close to the phase boundary. This is verified by inelastic neutron scattering which reveals unusual rotonlike minima at reciprocal space points different from those corresponding to the magnetic order. DOI 10.1103 PhysRevLett.109.127203 PACS numbers 75.30.Et, 61.05.F , 75.10.Hk, 75.30.Ds In frustrated antiferromagnets AF , the magnetic interactions compete and it is impossible to satisfy them all simultaneously. This competition causes degenerate ground states to occur, and the system fluctuates between them, suppressing long range magnetic order to temperatures well below the Curie Weiss temperature [1]. Most frustrated magnets do eventually order, and in the case of isotropic or Heisenberg interactions a compromise is often reached where the magnetic interactions are all partially satisfied by a noncollinear arrangement of the magnetic moments. The triangular lattice Heisenberg antiferromagnet TLHAF is one of the simplest examples of an extended frustrated magnetic system; however, open questions remain concerning its physical properties. For spin 1, different spin liquid phases have been proposed [2,3], while spin 1 2 and large spin systems order in a helical structure where the angle between nearest neighbor spins is 120 . Introduction of antiferromagnetic next nearest neighbor interactions modifies the excitations and drives the magnetic structure from helical to collinear when the ratio of next nearest to nearest neighbor interactions is greater than the critical value of 0.125 [4]. In the collinear phase, quantum fluctuations lift the classical degeneracy and select collinear stripe order via the mechanism of order by disorder [5]; they also significantly alter the spin wave excitation spectra around certain regions of the Brillouin zone [4]. Most physical realizations of triangular lattices are distorted. The distortion usually constitutes a shortening of the neares

Neutron scattering investigations of the partially ordered pyrochlore Tb2Sn2O7

Neutron scattering measurements have been performed on polycrystalline Tb2Sn2O7 at temperatures above and below that of the phase transition, TN 0.87 K, to investigate further the spin dynamics in the magnetically ordered state. In particular, new neutron spin echo results are presented showing a dependence on Q in the dynamics. We show evidence of the coexistence of static ferromagnetism and dynamically fluctuating spins down to 30 mK and we make a comparison of this partially ordered system to the spin liquid Tb2Ti2O