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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Published in Physical Review B, v. 93, issue 2, 024405, p. 1-7.

©2016 American Physical Society

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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.

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