Singlet-triplet dispersion reveals additional frustration in the triangular dimer compound Ba$_3$Mn$_2$O$_8$

TL;DR

This study uses neutron scattering to analyze the magnetic interactions in Ba$_3$Mn$_2$O$_8$, revealing complex frustration effects that influence its quasi-two-dimensional magnetic behavior and phase transitions.

Contribution

It provides detailed measurements of exchange interactions in Ba$_3$Mn$_2$O$_8$, uncovering additional frustration effects not previously identified.

Findings

Ferromagnetic interactions between bilayers compete with intra-bilayer interactions.

Frustration reduces effective coupling along the c-axis, leading to quasi-2D behavior.

Exchange values reproduce the four critical fields in the phase diagram.

Abstract

We present single crystal inelastic neutron scattering measurements of the S=1 dimerized quasi-two-dimensional antiferromagnet Ba$_3$Mn$_2$O$_8$. The singlet-triplet dispersion reveals nearest-neighbor and next-nearest-neighbor ferromagnetic interactions between adjacent bilayers that compete against each other. Although the inter-bilayer exchange is comparable to the intra-bilayer exchange, this additional frustration reduces the effective coupling along the c-axis and leads to a quasi-two dimensional behavior. In addition, the obtained exchange values are able to reproduce the four critical fields in the phase diagram.