Journal of the Physical Society of Japan

Spin Dynamics in an Ising-Like Quantum Spin Chain with Nonmagnetic Impurities

Shinichi Itoh, Hironobu Ikeda, Daisuke Sugimoto, Kazuaki Iwasa, Roger S. Eccleston

Published Mar 15, 1995• 0 citations

Abstract

Neutron inelastic-scattering experiments on an Ising-like quantum antiferromagnetic chain with nonmagnetic impurities, CsCo c Mg 1- c Cl 3 (c=1, 0.95, 0.9, 0.85, 0.6 and 0.4), were performed. The concentration dependence of the spin dynamics showed that although the solitons and the spin-wave continuum state were stable for a small amount of nonmagnetic impurities, they vanished at c=0.8. We also observed the coexistence of Ising-cluster excitations and intra-cluster excitations at low temperatures. These results can be well interpreted by a theory incorporated with next-nearest-neighbor interactions in the chain.

DOI: 10.1143/jpsj.64.927

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Journal of the Physical Society of Japan

Spin Dynamics in an Ising-Like Quantum Spin Chain with Nonmagnetic Impurities

Shinichi Itoh, Hironobu Ikeda, Daisuke Sugimoto, Kazuaki Iwasa, Roger S. Eccleston

Published Mar 15, 1995• 0 citations

Publisher

Abstract

DOI: 10.1143/jpsj.64.927

Related papers

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S. E. Nagler, W. J. L. Buyers, Robin L. Armstrong +1 more

Journal of Applied PhysicsMar 15, 19843 citations

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Nonmagnetic impurities in an $S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1/2$ Heisenberg antiferromagnetic chain are studied using boundary conformal field theory techniques and finite-temperature quantum Monte Carlo simulations. We calculate the static structure function, ${S}_{\mathrm{imp}}(k)$ , measured in neutron scattering and the local susceptibility, ${\ensuremath{\chi}}_{i}$ measured in Knight shift experiments. ${S}_{\mathrm{imp}}(k)$ becomes quite large near the antiferromagnetic wave vector, and exhibits much stronger temperature dependence than the bulk structure function. ${\ensuremath{\chi}}_{i}$ has a large component which alternates and increases as a function of distance from the impurity.Nonmagnetic impurities in an $S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1/2$ Heisenberg antiferromagnetic chain are studied using boundary conformal field theory techniques and finite-temperature quantum Monte Carlo simulations. We calculate the static structure function, ${S}_{\mathrm{imp}}(k)$, measured in neutron scattering and the local susceptibility, ${\ensuremath{\chi}}_{i}$ measured in Knight shift experiments. ${S}_{\mathrm{imp}}(k)$ becomes quite large near the antiferromagnetic wave vector, and exhibits much stronger temperature dependence than the bulk structure function. ${\ensuremath{\chi}}_{i}$ has a large component which alternates and increases as a function of distance from the impurity.

arXiv:cond-mat/9505092Physical Review LettersJul 31, 1995153 citations

The lowest-lying excited states in the S=1/2 one-dimensional Ising-like antiferromagnet

{\mathrm{CsCoCl}}_{3}

consist of domain-wall (soliton) pair states. Although the dynamical response function S(Q,\ensuremath{\omega}) has been calculated for these states, it has not proved possible to explain the results of neutron scattering and Raman experiments without recourse to the introduction of extra terms in the spin Hamiltonian. We argue against the two modifications to the Hamiltonian of

{\mathrm{CsCoCl}}_{3}

proposed in previous papers, a staggered field term arising from a mean field approach to exchange mixing, and next-nearest-neighbor intrachain coupling, as being unphysical. Instead we derive a nearest-neighbor effective Hamiltonian, which takes account of the mixing of higher

{\mathrm{Co}}^{2+}

ion crystal-field levels in a self-consistent manner. We also present a high-resolution inelastic neutron scattering experiment on

{\mathrm{CsCoCl}}_{3}

, which has allowed the dispersion of the excited states across the Brillouin zone to be studied more carefully than before. These results give a direct measure of S(Q,\ensuremath{\omega}) in the one-dimensional phase where there is a continuum of excited states, and in the three-dimensionally ordered phases, where weak interchain interactions split the continuum into a ``Zeeman ladder'' of discrete states. The predictions of our theory are found to be in quantitative agreement with experiment.

Well-defined spin-wave excitations were observed by using pulsed neutrons from CsVC

{\mathrm{l}}_{3}

, an

S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3/2

Heisenberg antiferromagnetic chain. The observed spin-wave dispersion relation shows an enhancement of the excitation energy by a factor of 1.26, which must be compared with the quantum renormalization factor of $\ensuremath{\pi}/2$ for an

S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1/2

system. The linewidth of the spectrum at 40 K was broad and independent of

q

. The

q

-independent linewidth is the first experimental observation, which was predicted by rigorous theories for a classical chain at sufficiently low temperature.

_{1-x}

_x

)

_2

_2

_8

with

x = 2\%

and

x = 5\%

, where non-magnetic Mg

^{2+}

ions fragment the Co

^{2+}

spin chains into finite segments. Combining inelastic neutron scattering and numerical calculations, we identify distinct regimes with fundamentally different low-energy quantum excitations: spinons confined to chain boundaries, and a cluster mode in shorter chains corresponding to a collective reversal of the Néel-ordered segment without classical analogue. Our results demonstrate how chemical substitution acts as a quantum microscope providing direct access to boundary-shaped excitations in strongly correlated spin systems.

Nonmagnetic impurities in an

S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1/2

Heisenberg antiferromagnetic chain are studied using boundary conformal field theory techniques and finite-temperature quantum Monte Carlo simulations. We calculate the static structure function,

{S}_{\mathrm{imp}}(k)

, measured in neutron scattering and the local susceptibility, ${\ensuremath{\chi}}_{i}$ measured in Knight shift experiments.

{S}_{\mathrm{imp}}(k)

becomes quite large near the antiferromagnetic wave vector, and exhibits much stronger temperature dependence than the bulk structure function. ${\ensuremath{\chi}}_{i}$ has a large component which alternates and increases as a function of distance from the impurity.