Field-Driven Jahn–Teller Effect and Domain Transition in Non-Coplanar Antiferromagnet UO2

Effect of magnetic field on the non-coplanar triple-Q magnetic order in the Mott insulator UO2 was investigated. Making use of the microscopic model for the localized 5f electrons, we calculated the spin structures of U ions and the displacements of O ions simultaneously in a finite magnetic field. It was shown that the applied field induces a discontinuous isomorphic transition between the time-reversal domains in the triple-Q phase, depending on the form of the Jahn–Teller interaction. It was also shown that the transition leads to drastic change in the axial magnetostriction associated with the O-ion displacements. The relationship of these theoretical results with recent experimental observations for UO2 is discussed.