Neutron Scattering Studies of the Breathing Pyrochlore Antiferromagnet LiGaCr$_{4}$O$_{8}$

TL;DR

This study uses neutron scattering to investigate the magnetic excitations in LiGaCr$_{4}$O$_{8}$, revealing coexistence of resonance modes and spin waves, and proposing a unified understanding of spin resonances in Cr spinel oxides.

Contribution

It provides the first detailed neutron scattering analysis of LiGaCr$_{4}$O$_{8}$, demonstrating coexistence of resonance and spin wave excitations and establishing a linear relationship between resonance energy and lattice constant.

Findings

Discovery of coexistence of resonance mode and spin waves.

Quantitative description using quantum spin model and linear spin wave theory.

Linear correlation between resonance energy and lattice constant across Cr spinel oxides.

Abstract

We report neutron scattering measurements of the spinel oxide LiGaCr$_{4}$O$_{8}$, in which magnetic ions Cr$^{3+}$ form a breathing pyrochlore lattice. Our experiments reveal the coexistence of a nearly dispersionless resonance mode and dispersive spin wave excitations in the magnetically ordered state, which can be quantitatively described by a quantum spin model of hexagonal loops and linear spin wave theory with the same set of exchange parameters, respectively. Comparison to other Cr spinel oxides reveals a linear relationship between the resonance energy and lattice constant across all these materials, which is in agreement with our hexagonal loop calculations. Our results suggest a unified picture for spin resonances in Cr spinel oxides.