Inelastic Neutron Scattering Study of the Spin Dynamics in the Breathing Pyrochlore System LiGa0.95In0.05Cr4O8

TL;DR

This study investigates the spin dynamics in a breathing pyrochlore system using inelastic neutron scattering, revealing changes in magnetic excitations associated with a nematic order transition driven by spin-lattice coupling.

Contribution

It provides the first inelastic neutron scattering analysis of the spin dynamics in LiGa0.95In0.05Cr4O8, highlighting the effects of spin-lattice coupling on magnetic excitations.

Findings

Above Tf, the scattering is ungapped and quasi-elastic.

Below Tf, spectral weight shifts to a broad inelastic feature at 5.8 meV.

The inelastic feature is linked to spin precessions in antiferromagnetic loops.

Abstract

The A-site ordered chromate spinels LiGa1-xInxCr4O8 host a network of size-alternating spin-3/2 Cr3+ tetrahedra known as a 'breathing' pyrochlore lattice. For the x=0.05 composition, the complex magneto-structural ordering observed in the parent x=0 material is replaced by a single transition at Tf=11 K, ascribed to the collinear nematic order caused by strong spin-lattice coupling. We present here an inelastic neutron scattering study of the spin dynamics in this composition. Above Tf , the dynamical scattering function S(Q,E) is ungapped and quasi-elastic, similar to undoped LiGaCr4O8. Below Tf , the spectral weight splits between a broad inelastic feature at 5.8 meV and toward the elastic line. The former feature can be ascribed to spin precessions within antiferromagnetic loops, lifted to finite energy by the effective biquadratic spin-lattice term in the spin Hamiltonian.