A major focus of experimental interest in Sr2IrO4 has been to clarify how the magnetic excitations of this strongly spin-orbit coupled system differ from the predictions of an isotropic 2D spin-1/2 Heisenberg model and to explore the extent to which strong spin-orbit coupling affects the magnetic properties of iridates. Here, we present a high-resolution inelastic light (Raman) scattering study of the low-energy magnetic excitation spectrum of Sr2IrO4 and Eu-doped Sr2IrO4 as functions of both temperature and applied magnetic field. We show that the high-field (H > 1.5 T) in-plane spin dynamics of Sr2IrO4 are isotropic and governed by the interplay between the applied field and the small in-plane ferromagnetic spin components induced by the Dzyaloshinskii-Moriya interaction. However, the spin dynamics of Sr2IrO4 at lower fields (H < 1.5 T) exhibit important effects associated with interlayer coupling and in-plane anisotropy, including a spin-flop transition at Hc in Sr2IrO4 that occurs either discontinuously or via a continuous rotation of the spins, depending on the in-plane orientation of the applied field. These results show that in-plane anisotropy and interlayer coupling effects play important roles in the low-field magnetic and dynamical properties of Sr2IrO4.
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Research was supported by the National Science Foundation under Grant No. NSF DMR 14-64090. Work at the University of Kentucky was supported by the National Science Foundation via Grant No. NSF DMR 12-65162. Work at Argonne National Laboratory (crystal growth and magnetic characterization) was supported by the US Department of Energy Office of Science, Basic Energy Sciences, Materials Science and Engineering Division.
Gim, Y.; Sethi, A.; Zhao, Q.; Mitchell, J. F.; Cao, Gang; and Cooper, S. L., "Isotropic and Anisotropic Regimes of the Field-Dependent Spin Dynamics in Sr2IrO4: Raman Scattering Studies" (2016). Physics and Astronomy Faculty Publications. 436.