Journal of Applied Physics

Field-induced transition of the Haldane antiferromagnets

Tôru Sakai

Published Jun 1, 2001• 2 citations

Abstract

The field-induced long-range antiferromagnetic order in the quasi-one-dimensional S=1 antiferromagnet is investigated with the exact diagonalization of finite chains and the mean field approximation for the interchain interaction. In the presence of the single-ion anisotropy D, we present the phase diagrams in the plane of the magnetic field H and the temperature T for H∥D and H⊥D. It is found that the two boundary curves of the ordered phase for H∥D and H⊥D have two intersections in the case of D>0 (XY like), while no intersection in the case of D<0 (Ising like).

DOI: 10.1063/1.1357848

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Journal of Applied Physics

Field-induced transition of the Haldane antiferromagnets

Tôru Sakai

Published Jun 1, 2001• 2 citations

Publisher

Abstract

DOI: 10.1063/1.1357848

Related papers

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Tôru Sakai

The ground-state magnetization process of the $S=1$ antiferromagnetic chain with the easy-axis single-ion anisotropy described by negative $D$ is investigated. It is numerically found that a phase transition between two different gapless phases occurs at an intermediate magnetic field between the starting and saturation points of the magnetization for $\ensuremath{-}1.49<D<\ensuremath{-}0.35.$ The transition is similar to the spin flopping, but it is second order and not accompanied with any significant anomalous behaviors in the magnetization curve. We also present the phase diagrams in the $m\ensuremath{-}D$ and $H\ensuremath{-}D$ planes which reveal a possible re-entrant transition.The ground-state magnetization process of the $S=1$ antiferromagnetic chain with the easy-axis single-ion anisotropy described by negative $D$ is investigated. It is numerically found that a phase transition between two different gapless phases occurs at an intermediate magnetic field between the starting and saturation points of the magnetization for $\ensuremath{-}1.49<D<\ensuremath{-}0.35.$ The transition is similar to the spin flopping, but it is second order and not accompanied with any significant anomalous behaviors in the magnetization curve. We also present the phase diagrams in the $m\ensuremath{-}D$ and $H\ensuremath{-}D$ planes which reveal a possible re-entrant transition.

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{\mathit{H}}_{\mathit{c}1}

(=\ensuremath{\Delta}), where \ensuremath{\Delta} is the Haldane gap. It is also found that the transverse spin correlation has the asymptotic form 〈

{\mathit{S}}_{0}^{\mathit{x}}

{\mathit{S}}_{\mathit{r}}^{\mathit{x}}

〉\ensuremath{\sim}(-1

{)}^{\mathit{r}}

${\mathit{r}}^{\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\eta}}}$, and the transverse staggered susceptibility ${\mathrm{\ensuremath{\chi}}}_{\mathrm{st}}^{\mathit{x}\mathit{x}}$ diverges between

{\mathit{H}}_{\mathit{c}1}

and

{\mathit{H}}_{\mathit{c}2}

(=4). The exponent \ensuremath{\eta} has a minimum (\ensuremath{\eta}\ensuremath{\simeq}0.3) at magnetization m\ensuremath{\simeq}1/3 and \ensuremath{\eta}\ensuremath{\simeq}0.5 at

{\mathit{H}}_{\mathit{c}1}

and

{\mathit{H}}_{\mathit{c}2}

. If the system is quasi-one-dimensional, even small interchain couplings can create a canted N\'eel order, within a mean-field approximation for interchain interactions. This is consistent with a recent NMR measurement for Ni(

{\mathrm{C}}_{2}

{\mathrm{H}}_{8}

{\mathrm{N}}_{2}

{)}_{2}

{\mathrm{NO}}_{2}

(

{\mathrm{ClO}}_{4}

) (NENP) at low temperature.

The field-induced transition in one-dimensional

S=1

Heisenberg antiferromagnets with single-ion anisotropy in the presence of a transverse magnetic field is obtained on the basis of the Schwinger-boson mean-field theory. The behaviors of the specific heat and susceptibility as functions of temperature as well as the applied transverse field are explored, which are found to be different from the results obtained under a longitudinal field. The anomalies of the specific heat at low temperatures, which might be indicative of a field-induced transition from a Luttinger liquid phase to an ordered phase, are explicitly uncovered under the transverse field. A schematic phase diagram is proposed. The theoretical results are compared with experimental observations.

We investigate the magnetization process for a quasi-one-dimensional

S=1

antiferromagnet with bond alternation. By combining the density matrix renormalization group method with the interchain mean-field theory, we discuss how the interchain coupling affects the magnetization curve. It is found that the width of the magnetization plateau is considerably reduced upon introducing the interchain coupling. We obtain the phase diagram in a magnetic field. The effect of single-ion anisotropy is also addressed.

The ground-state magnetization process of the

S=1

antiferromagnetic chain with the easy-axis single-ion anisotropy described by negative

D

is investigated. It is numerically found that a phase transition between two different gapless phases occurs at an intermediate magnetic field between the starting and saturation points of the magnetization for $\ensuremath{-}1.49<D<\ensuremath{-}0.35.$ The transition is similar to the spin flopping, but it is second order and not accompanied with any significant anomalous behaviors in the magnetization curve. We also present the phase diagrams in the $m\ensuremath{-}D$ and $H\ensuremath{-}D$ planes which reveal a possible re-entrant transition.