Magnetic excitations in the quantum spin system KCuCl

Cavadini, N.; Henggeler, W.; Furrer, A.; Güdel, Hans‐Ulrich; Krämer, Karl; Mutka, H.

doi:10.1007/s100510050642

Cited by 83 publications

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“…Whatever the precise structure may turn out to be, a magnetic-field induced ordering transition can occur in all anisotropic spin systems with a singlet-triplet excitation gap, including weakly coupled Ising-like chains, spin-Peierls chains, and ensembles of spin dimers. Other possible candidate materials with spin gaps include KCuCl 3 [8], CuGeO 3 [9], α ′ − NaV 2 O 5 [10], and the homologous series of cuprates Sr n Cu n+1 O 2n+1 [11].…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional ordering in weakly coupled antiferromagnetic ladders and chains

Wessel

Haas

2000

Phys. Rev. B

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A theoretical description is presented for low-temperature magnetic-field induced threedimensional (3D) ordering transitions in strongly anisotropic quantum antiferromagnets, consisting of weakly coupled antiferromagnetic spin-1/2 chains and ladders. First, effective continuum field theories are derived for the one-dimensional subsystems. Then the Luttinger parameters, which determine the low-temperature susceptibilities of the chains and ladders, are calculated from the Bethe ansatz solution for these effective models. The 3D ordering transition line is obtained using a random phase approximation for the weak inter-chain (inter-ladder) coupling. Finally, considering a Ginzburg criterion, the fluctuation corrections to this approach are shown to be small. The nature of the 3D ordered phase resembles a Bose condensate of integer-spin magnons. It is proposed that for systems with higher spin degrees of freedom, e.g. N-leg spin-1/2 ladders, multi-component condensates can occur at high magnetic fields.

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Section: Introductionmentioning

confidence: 99%

Three-dimensional ordering in weakly coupled antiferromagnetic ladders and chains

Wessel

Haas

2000

Phys. Rev. B

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“…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.…”

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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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“…The magnetic ground state is the spin singlet with the excitation gap Δ/k B ≈ 7.5 K. 8,9) The magnetic excitations in TlCuCl 3 were investigated by Oosawa et al, 10) who found that the lowest excitation occurs at Q = (0, 0, 1) and its equivalent reciprocal points, as observed in KCuCl 3 . 11,12) The origin of the gap is the strong antiferromagnetic interaction J = 5.26 meV on the planar dimer Cu 2 Cl 6 in the double chain. The * E-mail: tanaka@lee.phys.titech.ac.jp neighboring dimers couple magnetically along the chain and in the (1, 0, −2) plane.…”

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Observation of Field-Induced Transverse Néel Ordering in the Spin Gap System TlCuCl₃

et al. 2001

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Neutron elastic scattering experiments have been performed on the spin gap system TlCuCl 3 in magnetic fields parallel to the b-axis. The magnetic Bragg peaks which indicate the fieldinduced Néel ordering were observed for the magnetic field higher than the gap field H g ≈ 5.5 T at Q = (h, 0, l) with odd l in the a * − c * plane. The spin structure in the ordered phase was determined. The temperature and field dependence of the Bragg peak intensities and the phase boundary obtained were discussed in connection with a recent theory which describes the field-induced Néel ordering as a Bose-Einstein condensation of magnons.KEYWORDS: TlCuCl 3 , spin gap, field-induced magnetic ordering, spin structure, neutron elastic scattering, BoseEinstein condensation of magnonsThe singlet ground state with the excitation gap (spin gap) is a notable realization of the macroscopic quantum effect in quantum spin systems. When a magnetic field is applied in the spin gap system, the gap Δ is suppressed and closes completely at the gap field H g = Δ/gμ B . For H > H g the system can undergo magnetic ordering due to three-dimensional (3D) interactions. Such field-induced magnetic ordering was studied first for Cu(NO 3 ) 2 · 5 2 H 2 O. 1) However, the magnetic properties near H = H g have not been investigated because of the very low ordering temperature, the maximum of which is 0.18 K. Recently, the study of fieldinduced magnetic ordering has been revived, because the spin gap has been found in many quantum spin systems. Field-induced 3D ordering has been observed in several quasi-one-dimensional spin gap systems. [2][3][4][5][6] This paper is concerned with field-induced magnetic ordering in TlCuCl 3 . This compound has a monoclinic structure (space group P 2 1 /c). 7) TlCuCl 3 contains planar dimers of Cu 2 Cl 6 , in which Cu 2+ ions have spin-1 2 . These dimers are stacked on top of one another to form infinite double chains parallel to the crystallographic aaxis. These double chains are located at the corners and center of the unit cell in the b−c plane, and are separated by Tl + ions. The magnetic ground state is the spin singlet with the excitation gap Δ/k B ≈ 7.5 K. 8, 9) The magnetic excitations in TlCuCl 3 were investigated by Oosawa et al., 10) who found that the lowest excitation occurs at Q = (0, 0, 1) and its equivalent reciprocal points, as observed in KCuCl 3 . 11, 12) The origin of the gap is the strong antiferromagnetic interaction J = 5.26 meV on the planar dimer Cu 2 Cl 6 in the double chain. The * E-mail: tanaka@lee.phys.titech.ac.jp neighboring dimers couple magnetically along the chain and in the (1, 0, −2) plane.Our previous magnetic measurements revealed that TlCuCl 3 undergoes 3D magnetic ordering in magnetic fields higher than the gap field H g ≈ 5.5 T. 9) The magnetization exhibits a cusplike minimum at the ordering temperature T N . The phase boundary on the temperature vs field diagram is independent of the field direction when normalized by the g-factor, and can be represented by the power lawwith φ = 2.2...

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Magnetic excitations in the quantum spin system KCuCl

Cited by 83 publications

References 0 publications

Three-dimensional ordering in weakly coupled antiferromagnetic ladders and chains

Three-dimensional ordering in weakly coupled antiferromagnetic ladders and chains

Microscopic model for the magnetization plateaus inNH4CuCl3

Observation of Field-Induced Transverse Néel Ordering in the Spin Gap System TlCuCl₃

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Magnetic excitations in the quantum spin system KCuCl

Cited by 83 publications

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Three-dimensional ordering in weakly coupled antiferromagnetic ladders and chains

Three-dimensional ordering in weakly coupled antiferromagnetic ladders and chains

Microscopic model for the magnetization plateaus inNH4CuCl3

Observation of Field-Induced Transverse Néel Ordering in the Spin Gap System TlCuCl3

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Observation of Field-Induced Transverse Néel Ordering in the Spin Gap System TlCuCl₃