Low-energy magnetic excitations in the spin-orbital Mott insulatorSr2IrO4

S. Bahr, A. Alfonsov, G. Jackeli, G. Khaliullin, A. Matsumoto, T. Takayama, H. Takagi, B. Büchner, V. Kataev
2014 Physical Review B  
We report a high-field electron spin resonance study in the sub-THz frequency domain of a single crystal of Sr_2IrO_4 that has been recently proposed as a prototypical spin-orbital Mott insulator. In the antiferromagnetically (AFM) ordered state with noncollinear spin structure that occurs in this material at T_ N≈ 240 K we observe both the "low" frequency mode due to the precession of weak ferromagnetic moments arising from a spin canting, and the "high" frequency modes due to the precession
more » ... the AFM sublattices. Surprisingly, the energy gap for the AFM excitations appears to be very small, amounting to 0.83 meV only. This suggests a rather isotropic Heisenberg dynamics of interacting Ir^4+ effective spins despite the spin-orbital entanglement in the ground state.
doi:10.1103/physrevb.89.180401 fatcat:qn3m4bwsejhnzgx46yy4cst4d4