Breakdown of a Magnetization Plateau due to Anisotropy in Heisenberg Mixed-Spin Chains

TL;DR

This paper investigates how anisotropy affects the magnetization plateau in a spin-(1,1/2) Heisenberg ferrimagnetic chain, revealing a transition from a plateau to a gapless state of quantum and classical models.

Contribution

It demonstrates the breakdown of the magnetization plateau due to exchange anisotropy and characterizes the transition as Kosterlitz-Thouless type in quantum and classical models.

Findings

Anisotropy causes the plateau to collapse into a gapless spin-fluid state.

The transition is of Kosterlitz-Thouless type, occurring in the XY ferromagnetic region.

Classical model analysis highlights quantum effects in the transition.

Abstract

We discuss the critical behavior of the spin-(1,1/2) Heisenberg ferrimagnetic chain in a magnetic field, whose magnetization curve exhibits a plateau at a third of the full magnetization. A bond alternation stabilizes the massive state, whereas an exchange anisotropy causes the breakdown of the plateau and the onset of a gapless spin-fluid state, where the transition, lying in the XY but ferromagnetic region, is of Kosterlitz-Thouless type. In order to elucidate significant quantum effects, we investigate the model of classical version as well.