Dispersive magnetic excitations in the S=1 antiferromagnet Ba$_3$Mn$_2$O$_8$

TL;DR

This study uses neutron scattering to analyze magnetic excitations in Ba$_3$Mn$_2$O$_8$, revealing a spin gap, dispersive spectrum, and confirming the S=1 dimer bond with temperature-dependent excitations.

Contribution

It provides detailed experimental characterization of magnetic excitations and exchange interactions in Ba$_3$Mn$_2$O$_8$, confirming the S=1 dimer model.

Findings

Identified a spin gap of approximately 1.0 meV.

Observed a dispersive spectrum with a bandwidth of about 1.5 meV.

Confirmed the S=1 dimer bond through wave vector dependent scattering.

Abstract

We present powder inelastic neutron scattering measurements of the S=1 dimerized antiferromagnet Ba$_3$Mn$_2$O$_8$. The $T=1.4$ K magnetic spectrum exhibits a spin-gap of $\Delta \approx 1.0$ meV and a dispersive spectrum with a bandwidth of approximately 1.5 meV. Comparison to coupled dimer models describe the dispersion and scattering intensity accurately and determine the exchange constants in Ba$_3$Mn$_2$O$_8$. The wave vector dependent scattering intensity confirms the proposed S=1 dimer bond. Temperature dependent measurements of the magnetic excitations indicate the presence of both singlet-triplet and thermally activated triplet-quintet excitations.