Unified Picture for the Spin Resonance Mode in Cr-Based Spinel Oxides Using Inelastic Neutron Scattering

Geometrical frustration is a phenomenon present in lattices that are based on triangles or tetrahedra. It may prevent long-range magnetic order and lead to highly degenerated ground states with exotic spin-spin correlations and emergent excitations. The spinel oxide ACr 2 O 4 is a canonical geometrically frustrated magnet. Transition metal chromium (Cr) atoms, which are arranged into a crystal structure with an octagonal base, form a pyrochlore lattice with corner-sharing tet-rahedra. The pyrochlore lattice consists of alternating stacked kagome and triangle planes along the [111] di-rection and is highly frustrated. These Cr spinel oxides become ordered at a lower temperature than that the Curie-Weiss model predicts; this is to do with them be-ing highly frustrated. The Cr spinel oxide ACr 2 O 4 exhibit exotic excitation spectra dominated by a dispersionless sharp resonance mode instead of conventional dispersive spin waves in the magnetically ordered states. Currently, there is not a unified description of the resonance mode. Furthermore, there is also not clear causation for the underlying magnetic exchange interaction that induces the resonance mode among different types of Cr spinel oxides. The study the nature spin and 4 8 performed MERLIN direct geometry chopper spectrometer the a dispersionless resonance and dispersive spin-wave