# Magnetization plateau of the $S=2$ antiferromagnetic Heisenberg chain with anisotropies

## TL;DR

This study explores the conditions under which a magnetization plateau appears in the $S=2$ antiferromagnetic Heisenberg chain with anisotropies, revealing different formation mechanisms and phase diagrams through numerical analysis.

## Contribution

It introduces a detailed analysis of the 1/2 magnetization plateau in the $S=2$ chain, identifying mechanisms and the influence of biquadratic interactions.

## Key findings

- A magnetization plateau at half saturation can occur with suitable anisotropies.
- Two different mechanisms form the 1/2 plateau depending on anisotropy parameters.
- Biquadratic interactions enhance the plateau via the Haldane mechanism.

## Abstract

We investigate the $S=2$ antiferromagnetic quantum spin chain with the exchange and single-ion anisotropies in a magnetic field, using the numerical exact diagonalization of finite-size clusters and the level spectroscopy analysis. It is found that a magnetization plateau possibly appears at a half of the saturation magnetization for some suitable anisotropy parameters. The level spectroscopy analysis indicates that the 1/2 magnetization plateau is formed by two different mechanisms, depending on the anisotropy parameters. The phase diagram of the 1/2 plateau states and some typical magnetization curves are also presented. In addition the biquadratic interaction is revealed to enhance the plateau induced by the Haldane mechanism.