Two-magnon scattering in spin–orbital Mott insulator Ba₂IrO₄

A spin–orbit induced Mott insulator Ba₂IrO₄ with the pseudo-spin J_eff = 1/2, showing an antiferromagnetic order (T_N = 240 K), has been investigated by Raman spectroscopy. A broad peak with the B_1g symmetry is found in a wide temperature region up to 400 K, which is ascribed to the two-magnon scattering. From the peak position and width, the exchange coupling and the antiferromagnetic correlation length are estimated to be 590 cm⁻¹ and 45 Å at 90 K, respectively. The results are compared with the antiferromagnet La₂CuO₄ with the spin S = 1/2. We conclude that there is no significant difference in the short wavelength spin-excitation between the S = 1/2 and J_eff = 1/2 systems. (author)