Schwinger-Boson Mean-Field Theory of Mixed-Spin Antiferromagnet $L_2BaNiO_5$

TL;DR

This paper applies Schwinger-boson mean-field theory to a mixed-spin antiferromagnetic compound, explaining experimental phenomena like coexistence of Haldane gap and long-range order through a 3D Heisenberg model.

Contribution

It introduces a 3D mixed-spin Heisenberg model based on experimental data, providing a theoretical explanation for observed magnetic properties and excitations in $L_2BaNiO_5$.

Findings

Explains coexistence of Haldane gap and antiferromagnetic order.

Matches neutron scattering experimental results.

Analyzes low-lying excitations and Néel temperatures.

Abstract

The Schwinger-boson mean-field theory is used to study the three-dimensional antiferromagnetic ordering and excitations in compounds $L_2BaNiO_5$, a large family of quasi-one-dimensional mixed-spin antiferromagnet. To investigate magnetic properties of these compounds, we introduce a three-dimensional mixed-spin antiferromagnetic Heisenberg model based on experimental results for the crystal structure of $L_2BaNiO_5$. This model can explain the experimental discovery of coexistence of Haldane gap and antiferromagnetic long-range order below N\'{e}el temperature. Properties such as the low-lying excitations, magnetizations of $Ni$ and rare-earth ions, N\'{e}el temperatures of different compounds, and the behavior of Haldane gap below the N\'{e}el temperature are investigated within this model, and the results are in good agreement with neutron scattering experiments.