Neutron-scattering study of magnetism in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Nd</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">BaNiO</mml:mi></mml:mrow><mml:mrow><mml:mn>5</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Sachan, V.; Buttrey, D. J.; Tranquada, J. M.; Shirane, G.

doi:10.1103/physrevb.49.9658

Cited by 45 publications

(56 citation statements)

References 13 publications

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“…Attention to these systems has been driven by the different crystalline and magnetic structures of the members that change according to the nature of the R and M elements, providing in some cases examples of low-dimensional magnetism [3][4][5] .…”

Section: Introductionmentioning

confidence: 99%

R - M interactions in (R = Y or Gd; M=Cu or Zn)

Goya

Mercader

Steren

et al. 1996

J. Phys.: Condens. Matter

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R 2 BaMO 5 (R = Gd, Y and M = Cu, Zn) oxides have been studied by specific heat, dc magnetic susceptibility, and electron-paramagnetic-resonance (EPR). For one member of the series without magnetic moment at M, namely Gd 2 BaZnO 5 , measurements reveal long range antiferromagnetic order at T N (Gd 2 BaZnO 5 ) = 2.3±0.1K, much lower than the Curie-Weiss temperature of Θ=15.9±0.3K. This indicates the existence of competing interactions that introduce a large degree of magnetic frustration in the system. For Y 2 BaCuO 5 the Cu-Cu interactions are responsible for the broad maximum in the magnetic contribution to the specific heat centered at 18.5±0.01K that stretches beyond the instrumental limit of 25K. The strong Cu-Cu interactions also present in Gd 2 BaCuO 5 , combined with the Gd-Cu interaction, polarize the Gd sublattice giving measurable contributions to the specific heat in the same temperature range. In addition, they broaden the Gd EPR line and saturate its integrated intensity. The ordering temperature of Gd ions is raised to T N (Gd 2 BaCuO 5 )=12.0±0.1K.

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Section: Introductionmentioning

confidence: 99%

R - M interactions in (R = Y or Gd; M=Cu or Zn)

Goya

Mercader

Steren

et al. 1996

J. Phys.: Condens. Matter

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“…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].In previous studies the attempts to determine the polarization of the Ni-chain spin excitations in R 2 BaNiO 5 were performed using unpolarized neutrons. In this type of experiment, for scattering vectors almost along the chain direction (crystallographic a-axis) one only sees only the fluctuation of spin components along the b-and 1…”

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confidence: 99%

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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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“…1 With advance in both experiments 2,3 and numerical techniques, 4 the prediction by Haldane is now generally accepted. More recently, a series of experiments on the family of quasi-one-dimensional materials with a general formula R 2 BaNiO 5 , 3,[5][6][7][8][9][10][11][12] where R is one of magnetic rare-earth elements, substituting fully or partially Y have made it possible to study the effect of a staggered magnetic field on a Sϭ1 spin chain. The compound Y 2 BaNiO 5 is believed to be a good realization of the Sϭ1 Haldane gap system.…”

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Effects of substituting the rare-earth ionRby nonmagnetic impurities inR2BaNiO5: Theory and numerical density-matrix renormalization-group results

Lou

2000

Phys. Rev. B

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In this paper we study the effect of substituting R ͑rare-earth ion͒ by nonmagnetic ions in the spin-1 chain material R 2 BaNiO 5 . Using a strong-coupling expansion and numerical density-matrix renormalization-group calculations, we show that spin-wave bound states are formed at the impurity site. Experimental consequences of the bound states are pointed out.The antiferromagnetic Heisenberg spin chain has been a subject of immense interest since Haldane pointed out that the low-energy physics of integer and half integer spin chains are fundamentally different.1 With advance in both experiments 2,3 and numerical techniques, 4 the prediction by Haldane is now generally accepted. More recently, a series of experiments on the family of quasi-one-dimensional materials with a general formula R 2 BaNiO 5 , 3,[5][6][7][8][9][10][11][12] where R is one of magnetic rare-earth elements, substituting fully or partially Y have made it possible to study the effect of a staggered magnetic field on a Sϭ1 spin chain. The compound Y 2 BaNiO 5 is believed to be a good realization of the Sϭ1 Haldane gap system. 3 The Sϭ1 spins are coming from the Ni 2ϩ ions. Other members have additional magnetic ions R 3ϩ (R Y ) positioned between two neighboring Ni chains. The coupling between these ions and Ni 2ϩ ions are weak. Nevertheless, these magnetic ions are antiferromagnetically ordered below certain Néel temperature T N , and the ordering affects the Ni chains by providing them an effective background staggered magnetic field. It is expected that the three modes of the Haldane triplet will be splitted by the staggered field at TϽT N , with the longitudinal mode energy increases roughly twice as fast as the transverse ones with decreasing temperature below T N .13-16 These effects were indeed observed in neutron-scattering experiments. [9][10][11] In this paper we shall study the effect of replacing R ions by nonmagnetic impurities. In the case of pure Sϭ1 Haldane spin chains, the effect of replacing a spin by a nonmagnetic ion has received much attention because of the theoretical prediction of Sϭ1/2 excitations localized at the ends of broken Sϭ1 spin chains. 17 The existence of end excitations with fractional spin magnitudes are believed to be a general property of Heisenberg spin chains and is a consequence of the topological properties of these systems.17 However, the effect of substituting R by nonmagnetic impurities is very different. As far as the Ni 2ϩ chain is concerned, the replacement of an R 3ϩ ion by a nonmagnetic impurity just alters the local effective ͑staggered͒ magnetic field seen by the spin chain, and the topological character of the spin chain is unaffected. Therefore topological Sϭ1/2 end excitations are not expected to be induced by the R-ion substitutions. Nevertheless, we shall show in the following that although topological end excitations are not induced by R-ion substitutions, Sϭ1 magnon bound states are formed around the impurity and give rise to observable effects on the system. Our starting point is the e...

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Neutron-scattering study of magnetism inNd2BaNiO5

Cited by 45 publications

References 13 publications

R - M interactions in (R = Y or Gd; M=Cu or Zn)

R - M interactions in (R = Y or Gd; M=Cu or Zn)

Polarized-Neutron Observation of Longitudinal Haldane-Gap Excitations inNd2BaNiO5

Effects of substituting the rare-earth ionRby nonmagnetic impurities inR2BaNiO5: Theory and numerical density-matrix renormalization-group results

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