Magnetic excitations of the classical spin liquid MgCr2O4

TL;DR

This study uses inelastic neutron scattering and theoretical modeling to comprehensively understand magnetic excitations in the frustrated spin liquid MgCr2O4, revealing magnon behavior in a correlated paramagnetic state and proximity to a spiral spin-liquid phase.

Contribution

It provides a detailed microscopic Heisenberg model explaining magnetic excitations in MgCr2O4 and links these to its proximity to a spiral spin-liquid phase.

Findings

Magnetic excitations are well described by magnon propagation in a correlated paramagnetic background.

The Heisenberg model with up to third-nearest neighbor interactions accurately reproduces experimental data.

MgCr2O4 is close to a spiral spin-liquid phase, influencing its magneto-structural transition.

Abstract

We report a comprehensive inelastic neutron-scattering study of the frustrated pyrochlore antiferromagnet MgCr2O4 in its cooperative paramagnetic regime. Theoretical modeling yields a microscopic Heisenberg model with exchange interactions up to third-nearest neighbors, which quantitatively explains all the details of the dynamic magnetic response. Our work demonstrates that the magnetic excitations in paramagnetic MgCr2O4 are faithfully represented in the entire Brillouin zone by a theory of magnons propagating in a highly-correlated paramagnetic background. Our results also suggest that MgCr2O4 is proximate to a spiral spin-liquid phase distinct from the Coulomb phase, which has implications for the magneto-structural phase transition in MgCr2O4 .