One- and two-magnon excitations in a one-dimensional antiferromagnet in a magnetic field

Heilmann, I. U.; Kjems, Jørgen; Endoh, Y.; Reiter, George; Shirane, G.; Birgeneau, R. J.

doi:10.1103/physrevb.24.3939

Cited by 94 publications

(42 citation statements)

References 36 publications

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“…The existence of these modes, despite the disorder, bears a striking similarity to the behavior in thermally disordered spin chains with easy plane anisotropy. As first predicted by Villain [6], well-defined long wavelength transverse modes have been observed in a number of one-dimensional anisotropic spin systems including CsNiF 3 [7] and (CD 3 ) 4 NMnCl 3 [8]. The measurement of such excitations in the domain state of a three-dimensional random field Ising magnet indicates that these long-lived transverse modes occur more generally than previously realized, irrespective of the nature of the anisotropy, the system's spatial dimension, or the type of disorder.…”

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confidence: 69%

“…In marked contrast to the phonons in the relaxors, we observe well-defined long wavelength excitations transverse to the ordering axis, despite the absence of long range order, and find no measurable effect on the spin waves from the domain structure. We identify the persistence of these modes as an apparently generic feature of disordered magnetic systems with anisotropy, as first realized in thermally disordered spin chains [6,7,8].The experiments were performed on a diluted antiferromagnet, Mn x Zn 1−x F 2 with x = 0.5, cooled in a magnetic field parallel to the Ising axis. The physics of the diluted Ising antiferromagnet in a uniform field can be mapped directly on to that of a random field Ising magnet [9], providing a method for experimental realization of the random field system.…”

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confidence: 98%

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confidence: 99%

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Spin wave propagation in the domain state of a random field magnet

Leheny

Lee

Shirane

et al. 2003

The European Physical Journal B - Condensed Matter

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Inelastic neutron scattering with high wave-vector resolution has characterized the propagation of transverse spin wave modes near the antiferromagnetic zone center in the metastable domain state of a random field Ising magnet. A well-defined, long wavelength excitation is observed despite the absence of long-range magnetic order. Direct comparisons with the spin wave dispersion in the long-range ordered antiferromagnetic state reveal no measurable effects from the domain structure. This result recalls analogous behavior in thermally disordered anisotropic spin chains but contrasts sharply with that of the phonon modes in relaxor ferroelectrics.PACS numbers: 75.30. Ds, 75.50.Lk Disorder in a condensed matter system can strongly influence mode propagation through the medium, providing a unique perspective on its microscopic behavior. To gain a more comprehensive understanding of such effects from disorder, we have performed a neutron scattering study of the long wavelength spin waves of the frozen domain state of a random field magnet. Despite the wealth of attention directed at the random field problem [1], little attention has been directed toward the spin wave dispersion in these systems. Our study has been motivated in part by experiments on the phonons in several relaxor ferroelectrics including Pb(Zn 1/3 Nb 2/3 )O 3 and Pb(Mg 1/3 Nb 2/3 )O 3 that have demonstrated interesting anomalies associated with the disorder in these systems [2,3,4,5]. Specifically, at wave vectors near 0.2 A −1 , the dispersion of the transverse optic branch appears to drop precipitously into the acoustic branch. This phenomenon has been identified with a sharply wavevector dependent overdamping associated with the presence of polar nanoregions in the relaxors [2]. To test the generality of such behavior for systems with disorder, we have performed a search for analogous effects in the spin waves of the domain state of the random field magnet. In marked contrast to the phonons in the relaxors, we observe well-defined long wavelength excitations transverse to the ordering axis, despite the absence of long range order, and find no measurable effect on the spin waves from the domain structure. We identify the persistence of these modes as an apparently generic feature of disordered magnetic systems with anisotropy, as first realized in thermally disordered spin chains [6,7,8].The experiments were performed on a diluted antiferromagnet, Mn x Zn 1−x F 2 with x = 0.5, cooled in a magnetic field parallel to the Ising axis. The physics of the diluted Ising antiferromagnet in a uniform field can be mapped directly on to that of a random field Ising magnet [9], providing a method for experimental realization of the random field system. MnF 2 has a tetragonal rutiletype structure with lattice constants a = 4.87Å and c = 3.31Å. The spin interaction is primarily Heisenberglike, and a weak dipolar interaction between the Mn moments accounts for the small Ising anisotropy that aligns the Mn spins along the c axis (i.e., the tetragonal axis). Dil...

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confidence: 69%

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confidence: 98%

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confidence: 99%

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Spin wave propagation in the domain state of a random field magnet

Leheny

Lee

Shirane

et al. 2003

The European Physical Journal B - Condensed Matter

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“…Comparing Eqs. (15), (16) we see that in order to accurately estimate spectral weights from experiment precise information is needed on the domain distribution since the transverse component appears with different weight.…”

Section: Domain Averagementioning

confidence: 96%

Sum rules and missing spectral weight in magnetic neutron scattering in the cuprates

Lorenzana

Seibold

Coldea³

2005

Phys. Rev. B

104

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We present estimates in the Hubbard and Heisenberg models for the spectral weight in magnetic neutron scattering experiments on the cuprates. With the aid of spin-wave theory and the time dependent Gutzwiller approximation we discuss how the spectral weight is distributed among the different channels and between high and low energies. In addition to the well known total moment sum rule we discuss sum rules for each component of the dynamical structure factor tensor which are peculiar for spin 1/2 systems. The various factors that reduce the spectral weight at the relevant energies are singled out and analyzed like: shielding factors, weight at electronic energies, multimagnon process etc. Although about 10% ∼ 15% of the naively expected weight is detected in experiments after consideration of these factors the missing weight is within the experimental uncertainties. A large fraction of the spectral weight is hard to detect with present experimental conditions.

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“…In the equation above, spin fluctuations are separated into transverse (xx, yy) and longitudinal (zz) components relative to the local spin direction, which correspond to scattering from states with odd and even number of magnons, respectively. 24 An important effect of the spin canting on the dynamical structure factor is the redistribution of the spectral weight over the two wellseparated transverse modes, 41 which overlap only at the magnetic zone boundary. As a result, Eq.…”

Section: B Dynamical Structure Factormentioning

confidence: 99%

Field-induced decay dynamics in square-lattice antiferromagnets

2010

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Dynamical properties of the square-lattice Heisenberg antiferromagnet in applied magnetic field are studied for arbitrary value S of the spin. Above the threshold field for two-particle decays, the standard spin-wave theory yields singular corrections to the excitation spectrum with logarithmic divergences for certain momenta. We develop a self-consistent approximation applicable for S ≥ 1, which avoids such singularities and provides regularized magnon decay rates. Results for the dynamical structure factor obtained in this approach are presented for S = 1 and S = 5/2.

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One- and two-magnon excitations in a one-dimensional antiferromagnet in a magnetic field

Cited by 94 publications

References 36 publications

Spin wave propagation in the domain state of a random field magnet

Spin wave propagation in the domain state of a random field magnet

Sum rules and missing spectral weight in magnetic neutron scattering in the cuprates

Field-induced decay dynamics in square-lattice antiferromagnets

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