Magnetic excitations of the gapped quantum spin dimer antiferromagnet Sr$_{3}$Cr$_{2}$O$_{8}$

TL;DR

This study investigates the magnetic excitations in Sr$_{3}$Cr$_{2}$O$_{8}$, revealing three gapped modes and quantifying exchange interactions, thereby enhancing understanding of orbital order effects in gapped quantum magnets.

Contribution

The paper provides detailed experimental characterization of Sr$_{3}$Cr$_{2}$O$_{8}$'s magnetic excitations and quantifies exchange interactions using neutron scattering and modeling, highlighting the impact of orbital ordering.

Findings

Identification of three gapped dispersive modes.

Determination of dimer coupling J₀ = 5.55 meV.

Ratio of interdimer to intradimer exchange J'/J₀ = 0.64.

Abstract

Sr$_{3}$Cr$_{2}$O$_{8}$ consist of a lattice of spin-1/2 Cr$^{5+}$ ions, which form hexagonal bilayers and which are paired into dimers by the dominant antiferromagnetic intrabilayer coupling. The dimers are coupled three-dimensionally by frustrated interdimer interactions. A structural distortion from hexagonal to monoclinic leads to orbital order and lifts the frustration giving rise to spatially anisotropic exchange interactions. We have grown large single crystals of Sr$_{3}$Cr$_{2}$O$_{8}$ and have performed DC susceptibility, high field magnetisation and inelastic neutron scattering measurements. The neutron scattering experiments reveal three gapped and dispersive singlet to triplet modes arising from the three twinned domains that form below the transition thus confirming the picture of orbital ordering. The exchange interactions are extracted by comparing the data to a Random Phase Approximation model and the dimer coupling is found to be $J_{0}=5.55$ meV, while the ratio of interdimer to intradimer exchange constants is $J'/J_{0}=0.64$. The results are compared to those for other gapped magnets.