X Bai, J A M Paddison, E Kapit, S M Koohpayeh, J-J Wen, S E Dutton, A T Savici, AI Kolesnikov, G E Granroth, C L Broholm, J T Chalker, and M Mourigal, Magnetic Excitations of the Classical Spin Liquid MgCr2O4, Phys Rev Lett 122, 097201 (2019)

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.