High field magnetization in an S=1 antiferromagnetic chain with bond alternation

Narumi, Yasuo; Hagiwara, Masayuki; Sato, Ritsuko; Kindo, Koichi; Nakano, Hiroki; Takahashi, Minoru

doi:10.1016/s0921-4526(97)00974-5

Cited by 128 publications

(92 citation statements)

References 18 publications

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“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] In a variety of models, the magnetization per site m z as a function of the applied magnetic field H exhibits plateaus at certain values of m z ; at those plateaus the magnetization in units of the saturation M = m z /S (here S is the spin of a magnetic ion) is "locked" at some rational number (at least, up to now no indications of the possibility to have plateaus at irrational M were found). Oshikawa et al 4 have shown that in purely one-dimensional systems the allowed values of M , at which the plateaus are possible, are given by the following condition…”

Section: Introductionmentioning

confidence: 99%

Magnetization plateaus in weakly coupled dimer spin system

Kolezhuk

1999

Phys. Rev. B

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I study a spin system consisting of strongly coupled dimers which are in turn weakly coupled in a plane by zigzag interactions. The model can be viewed as the strong-coupling limit of a two-dimensional zigzag chain structure typical, e.g., for the $(ac)$-planes of KCuCl_3. It is shown that the magnetization curve in this model has plateaus at 1/3 and 2/3 of the saturation magnetization, and an additional plateau at 1/2 can appear in a certain range of the model parameters; the critical fields are calculated perturbatively. It is argued that for the three-dimensional lattice structure of the KCuCl_3 family the plateaus at 1/4 and 3/4 of the saturation can be favored in a similar way, which might be relevant to the recent experiments on NH_4CuCl_3 by Shiramura et al., J. Phys. Soc. Jpn. {\bf 67}, 1548 (1998).Comment: serious changes in Sect. II,III, final version to appear in PR

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Section: Introductionmentioning

confidence: 99%

Magnetization plateaus in weakly coupled dimer spin system

Kolezhuk

1999

Phys. Rev. B

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“…Magnetization plateaus were observed in some quasi one-dimensional materials. 1 Theoretical arguments clarify that the appearance of the plateau is explained by an insulator-conductor transition of magnetic excitations. 2 In two-or higher-dimensional systems, magnetization plateaus have been also found in both theoretical [3][4][5] -and experimental studies.…”

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Magnetization plateaus as insulator-superfluid transitions in quantum spin systems

2000

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We study the magnetization process in two-dimensional S = 1/2 spin systems, to discuss the appearance of a plateau structure. The following three cases are considered: 1) the Heisenberg antiferromagnet and multiple-spin exchange model on the triangular lattice, 2) Shastry-Sutherland type lattice, (which is a possible model for SrCu2(BO3)2,) 3) 1/5-depleted lattice (for CaV4O9). We find in these systems that magnetization plateaus can appear owing to a transition from superfluid to a Mott insulator of magnetic excitations. The plateau states have CDW order of the excitations. The magnetizations of the plateaus depend on components of the magnetic excitations, range of the repulsive interaction, and the geometry of the lattice.PACS numbers: 75.60. Ej, 75.10.Jm In some one-dimensional spin systems, spin-densitywave states with finite spin gap appear under a finite magnetic field accompanying plateau structures in the magnetization process. Magnetization plateaus were observed in some quasi one-dimensional materials. 1 Theoretical arguments clarify that the appearance of the plateau is explained by an insulator-conductor transition of magnetic excitations. 2 In two-or higher-dimensional systems, magnetization plateaus have been also found in both theoretical 3-5 -and experimental studies. [6][7][8] In this paper, we propose a rather general picture that these twodimensional plateaus are formed owing to field-induced insulator-superfluid transitions of magnetic excitations. To demonstrate how it works, we discuss three examples in details.The first example is a family of antiferromagnets on a triangular lattice. For the S = 1/2 antiferromagnet on a triangular lattice (AFT), Nishimori and Miyashita 3 found a magnetization plateau at m/m sat = 1/3, which comes from the appearance of a collinear state with three sublattices, i.e., the so-called "uud" state. This plateau was actually observed in AFT materials like C 6 Eu(Ref. 6) and CsCuCl 3 (Ref. 7). Recently in a multiple-spin exchange (MSE) model, which is a possible model 9 for solid 3 He films, a magnetization plateau was predicted 5 at m/m sat = 1/2. In this case, the plateau is attributed to the formation of a similar collinear state but with four sublattices. The magnetization processes of these systems have been studied extensively and here we just attempt interpreting the known results to test the new picture.We take as the second example the S = 1/2 Heisenberg antiferromagnet (HAF) on the Shastry-Sutherland lattice (Shastry-Sutherland model, hereafter. See Fig. 1), 10 which is known to have an exact dimer ground state. Recently Kageyama et al. 8 found that SrCu 2 (BO 3 ) 2 realizes a lattice structure equivalent to that discussed in Ref. 10 and that it has a gapful ground state. The magnetization measurements show plateaus at m/m sat = 1/8 and 1/4. The last is the S = 1/2 HAF on the 1/5-depleted square lattice (Fig. 2), which includes a model Hamiltonian for CaV 4 O 9 . In this system, the plaquette singlet state is realized in the ground state. 11In our ...

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“…16 Such plateaus have been observed at a rational fraction of the saturation moment. 1,17 In SrCu 2 (BO 3 ) 2 , the frustrated form of the dimer lattice leads to a narrow bandwidth for triplet excitations and magnetization plateaus associated with a magnetic superlattice of localized triplets. 18,19 An unexpected feature of NH 4 CuCl 3 is the absence of a magnetization plateau at a value 1/2 of the saturation magnetization although this would correspond to the simplest superlattice.…”

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Microscopic model for the magnetization plateaus inNH4CuCl3

Matsumoto

2003

Phys. Rev. B

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A simple model consisting of three distinct dimer sublattices is proposed to describe the magnetism of NH4CuCl3. It explains the occurrence of magnetization plateaus only at 1/4 and 3/4 of the saturation magnetization. The field dependence of the excitation modes observed by ESR measurements is also explained by the model. The model predicts that the magnetization plateaus should disappear under high pressure.PACS numbers: 75.30. Cr, NH 4 CuCl 3 , TlCuCl 3 , and KCuCl 3 are isostructual quantum spin systems consisting of two-leg ladders separated by NH + 4 , Tl + , and K + ions. The two-leg ladders are composed of Cu 2+ ions with spin S = 1/2 which interact antiferromagnetically (AF) through the Cl − ions. These compounds can be considered as coupled two-leg S = 1/2 Heisenberg AF spin ladders, and show various types of magnetization curves. Shiramura et al. found that NH 4 CuCl 3 has magnetization plateaus at 1/4 and 3/4 of the saturation moment, 1 while TlCuCl 3 and KCuCl 3 have no plateaus in their magnetization curves. 2 For NH 4 CuCl 3 , Kurniawan et al. performed ESR experiments which revealed that NH 4 CuCl 3 has a finite excitation gap in the plateau regions. 3 By studying specific heat, they found AF order already at zero field and suggested a phase diagram in finite fields containing three magnetically ordered phases. 4 The origin of magnetization plateaus has attracted much interest recently. For weakly interacting dimer systems, the ground state is a spin singlet liquid with only short-range correlations between spins, and the triplet excitations require a finite excitation energy. An excited gas of triplet magnons has two characteristic energies. 5 Exchange interactions cause the transfer of excited triplets between neighboring dimers leading to a form of kinetic energy. They also lead to a short range repulsion between triplets in addition to the hard core repulsion forbidding double occupancy of a dimer. The triplet excitations are split in an external magnetic field, and the energy of the lowest component can be driven through zero. When the kinetic energy is dominant, which is realized in TlCuCl 3 and KCuCl 3 , we have no plateaus in the magnetization curve. 2 In these case, antiferromagnetic order perpendicular to the field appears simultaneously with magnetization parallel to the field, creating field-induced magnetic order, 6 which can be interpreted as a condensation of the lowest lying magnon mode. 7,8,9,10,11,12,13,14,15 In contrast to these case, when the interaction energy dominates, magnetization plateaus can appear accompanied by a magnetic superlattice. 16 Such plateaus have been observed at a rational fraction of the saturation moment. 1,17 In SrCu 2 (BO 3 ) 2 , the frustrated form of the dimer lattice leads to a narrow bandwidth for triplet excitations and magnetization plateaus associated with a magnetic superlattice of localized triplets. 18,19 An unexpected feature of NH 4 CuCl 3 is the absence of a magnetization plateau at a value 1/2 of the saturation magnetization although this...

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High field magnetization in an S=1 antiferromagnetic chain with bond alternation

Cited by 128 publications

References 18 publications

Magnetization plateaus in weakly coupled dimer spin system

Magnetization plateaus in weakly coupled dimer spin system

Magnetization plateaus as insulator-superfluid transitions in quantum spin systems

Microscopic model for the magnetization plateaus inNH4CuCl3

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