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Zheludev, A.; Hill, J. P.; Buttrey, D. J.

doi:10.1103/physrevb.54.7216

Cited by 34 publications

(42 citation statements)

References 26 publications

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“…This three dimensional antiferromagnetic matrix generates an effective staggered magnetic field on the Ni 2+ chains whose intensity can be tuned by varying the temperature below T N . In this way, experiments have been able to investigate the effects of a staggered field on the Haldane gap, the staggered magnetization and the susceptibility 31,32 . Stimulated by these experiments, few analytical and numerical studies attempted a theoretical analysis of spin chains in staggered fields by use of semiclassical mappings 12,14 and DMRG 33 .…”

Section: Heisenberg Model In An External Fieldmentioning

confidence: 99%

Nonlinear sigma models and quantum spin systems

Gliozzi

Parola

2001

Phys. Rev. B

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Microscopic models of quantum antiferromagnets are investigated on the basis of a mapping onto effective low energy hamiltonians. Lattice effects are carefully taken into account and their role is discussed. We show that the presence of an external staggered magnetic field modifies in a non trivial way the usual mapping onto the non linear sigma model, leading to the appearance of new terms, neglected in previous works. Our analysis is compared with Lanczos diagonalizations of S = 1 Heisenberg chains in a staggered field, confirming the validity of the single mode approximation for the evaluation of the dynamical structure factor. The results are relevant for the interpretation of experiments in quasi-one dimensional compounds. Microscopic realizations of SU(4) spin chains are also discussed in the framework of spin-orbital lattice systems. The low energy physics is shown to be described by sigma models with topological angle θ in one dimension. This mapping strongly suggests that the one dimensional CP 3 model (with θ = π) undergoes a second order phase transition as a function of the coupling.

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Section: Heisenberg Model In An External Fieldmentioning

confidence: 99%

Nonlinear sigma models and quantum spin systems

Gliozzi

Parola

2001

Phys. Rev. B

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“…The orthorhombic crystal structure of R 2 BaNiO 5 compounds is discussed in great detail elsewhere [16] and we only note here that the S = 1 Ni 2+ chains run along the a axis of the crystal (Ni-Ni spacing a = 3.85Å), with the R 3+ sites positioned in-between these chains. The Néel temperature for Nd 2 BaNiO 5 is T N = 48 K. Long range magnetic ordering gives rise to magnetic Bragg reflections of the type ( 2 ), with m, k and n integer [17,18]. The Ni 2+ moments are confined in the (a, c) crystallographic plane and are aligned roughly along the c axis [17,19].…”

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Polarized-Neutron Observation of Longitudinal Haldane-Gap Excitations inNd2BaNiO5

et al. 1999

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Polarized and unpolarized inelastic neutron scattering is used to study Haldane-gap excitations in the mixed-spin linear-chain antiferromagnet Nd2BaNiO5. The longitudinal mode, polarized along the direction of ordered moments, is observed for the first time. The model of isolated Haldane chains in a static staggered exchange field, that is known to work very well for static properties and transverse spin excitations in R2BaNiO5 compounds, fails to explain new results for the longitudinal spin gap. 75.30.Ds,75.50.Ee,75.40.Gb The novel quantum-disordered ground state and the famous Haldane gap in the magnetic excitation spectrum [1] have kept integer-spin one-dimensional (1-D) Heisenberg antiferromagnets (AF) at the center of attention of condensed matter physicists for almost 2 decades. Among the more recent developments are studies of such systems in external magnetic fields (comprehensive bibliography can be found in Refs. [2][3][4]). As the uniform magnetic field H is increased, the Haldane triplet splits linearly with H, one of the three excitations decreases in energy and eventually softens at some critical field H c . The result is a transition to a radically new phase with long-range magnetic order (see for example Refs. [5,6]) The effect of strong a staggered field H π , to which the Haldane chain is most susceptible, is expected to be no less dramatic. According to recent theoretical results [7,8] and numerical simulations [9], all three Haldane gap energies increase quadratically with H π . The degeneracy of the Haldane triplet is removed: for the excitation polarized along the direction of induced moments (longitudinal mode) the gap increases three times more rapidly than for the two transverse modes. The longitudinal mode is of particular interest, as it is a purely quantum feature, totally absent in the classical spin wave theory that predicts a pair of transverse order-parameter excitations (magnons).The discovery of coexistence of Haldane gap excitations and magnetic long-range order in R 2 BaNiO 5 (R=magnetic rare earth) compounds [10-14] presented a unique opportunity to investigate experimentally the effect of a strong staggered field on Haldane spin chain. In R 2 BaNiO 5 the initially quantum-disordered AF S = 1 Ni 2+ -chains become subject to an effective staggered exchange field produced by the R-sublattice, when the latter orders magnetically at low temperatures. The magnitude of this field can be tuned by varying the temperature and thereby the ordered moment on the R [8,9]. Surprisingly, the splitting of the Haldane triplet could never be found. In fact, no clear evidence for the very existence of the longitudinal mode in R 2 BaNiO 5 has been obtained: all the measured staggered field dependencies of the Haldane gap energies are in quantitative agreement with calculations for transverse excitations in isolated chains [8,13,7,9]. The present paper is aimed at resolving this mystery. We report the first direct experimental observations of the longitudinal mode in a R 2 BaNiO 5 compound u...

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“…3 The Ni +2 and Nd +3 moments are coupled antiferromagnetically along the chain ('a' axis) but coupled ferromagnetically along 'b' axis. The Ni moments start to order antiferromagnetically below 48 K, 9 and reaches its saturation value around 35 K with decreasing T. The Nd moments also orders antiferromagnetically below 48 K, but the magnitude of its moment increases relatively slowly with decreasing T. 3 The magnetic susceptibility (χ) shows a broad maximum around 26 K which was attributed to the depletion of the higher-lying level of the Kramers doublet, split by Nd-Ni magnetic interactions. 10 Inelastic neutron scattering studies revealed clear evidence for one-dimensional gap excitations.…”

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Magnetic and magnetodielectric coupling anomalies in the Haldane spin-chain system Nd2BaNiO5

et al. 2015

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We report the magnetic, heat-capacity, dielectric and magnetodielectric (MDE) behaviour of a Haldane spin-chain compound containing light rare-earth ion, Nd 2 BaNiO 5 , in detail, as a function of temperature (T) and magnetic field (H) down to 2 K. In addition to the well-known long range antiferromagnetic order setting in at (T N =) 48 K as indicated in dc magnetization (M), we have observed another magnetic transition near 10 K; this transition appears to be of a glassy-type which vanishes with a marginal application of external magnetic field (even H= 100 Oe). There are corresponding anomalies in dielectric constant (ɛ') as well with variation of T. The isothermal M(H) curves at 2 and 5 K reveal the existence of a magnetic-field induced transition around 90 kOe; the isothermal ɛ'(H) also tracks such a metamagnetic transition. These results illustrate the MDE coupling in this compound. Additionally, we observe a strong frequency dependence of a step in ɛ'(T) with this feature appearing around 25-30 K for the lowest frequency of 1 kHz, far below T N . This is attributed to interplay between crystal-field effect and exchange interaction between Nd and Ni, which establishes the sensitivity of dielectric measurements to detect such effects. Interestingly enough, the observed dispersions of the ɛ'(T) curves is essentially H-independent in the entire Trange of measurement, despite the existence of MDE coupling, which is in sharp contrast with other heavy rare-earth members in this series.

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X-ray magnetic scattering study of three-dimensional magnetic order in the quasi-one-dimensional antiferromagnetNd2BaNiO

Cited by 34 publications

References 26 publications

Nonlinear sigma models and quantum spin systems

Nonlinear sigma models and quantum spin systems

Polarized-Neutron Observation of Longitudinal Haldane-Gap Excitations inNd2BaNiO5

Magnetic and magnetodielectric coupling anomalies in the Haldane spin-chain system Nd2BaNiO5

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