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Seminar | Materials Science Seminar | Materials Science Division

Frustrated Magnetism in Mott Insulating (V1-xCrx)2O3

MSD Seminar

Abstract:  V2O3 famously features all four combinations of paramagnetic versus antiferromagnetic and metallic versus insulating states of matter in response to percent-level doping, pressure in the GPa range, and temperature below 300 K. Using time-of-flight neutron spectroscopy, we have mapped the inelastic magnetic neutron scattering cross section over a wide range of energy and momentum transfer in the chromium stabilized antiferromagnetic and paramagnetic insulating phases (AFI and PI). By fitting the measured excitation spectrum in the AFI phase, we establish a phenomenological exchange Hamiltonian and then show that density functional theory (DFT) computations can account for the exchange constants to within the experimental accuracy. We then use DFT and neutron scattering to show that the PI phase is a quasi-two-dimensional honeycomb antiferromagnet with competing near and next nearest neighbor exchange interactions that place it near a putative spin liquid phase. Treated with a Gaussian approximation, the DFT spin Hamiltonian accounts in detail for the short-range dynamic spin correlations of the PI. The magnetic frustration and degeneracy of the PI is relieved by the rhombohedral to monoclinic transition at TN = 185 K through magneto-elastic coupling. This leads to the recognition that magnetic frustration is an inherent property of the paramagnetic phase of (V1-xCrx)2O3 and plays an important role in suppressing the magnetic long-range ordering temperature and exposing the Mott metal-insulator transition. 

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