Orbital ordering promotes weakly-interacting S=1/2 dimers in the triangular lattice compound Sr3Cr2O8

TL;DR

This study investigates Sr3Cr2O8, revealing that orbital ordering induces weakly interacting S=1/2 dimers, with structural and magnetic properties characterized by neutron scattering and theoretical analysis.

Contribution

It demonstrates how orbital ordering in Sr3Cr2O8 reduces inter-dimer interactions, leading to a quasi non-dispersive magnetic excitation, combining experimental and theoretical approaches.

Findings

Structural phase transition with orbital ordering below room temperature

Reduction of inter-dimer exchange energies due to orbital configuration

Observation of a 5.4 meV magnetic excitation consistent with weakly-interacting dimers

Abstract

The weakly interacting S=1/2 dimers system Sr3Cr2O8 has been investigated by powder neutron diffraction and inelastic neutron scattering. Our data reveal a structural phase transition below room temperature corresponding to an antiferro-orbital ordering with nearly 90 degrees arrangement of the occupied 3z^2-r^2 d-orbital. This configuration leads to a drastic reduction of the inter-dimer exchange energies with respect to the high temperature orbital-disorder state, as shown by a spin-dimer analysis of the super-superexchange interactions performed using the Extended Huckel Tight Binding method. Inelastic neutron scattering reveals the presence of a quasi non-dispersive magnetic excitation at 5.4 meV, in agreement with the picture of weakly-interacting dimers.