Critical behavior of the in-plane weak ferromagnet Sr2IrO4

Critical behavior of the single-layered Sr2IrO4, which exhibits weak ferromagnetism in the ab plane, is investigated by the bulk magnetization study. Critical exponents β = 0.284 ± 0.008 and γ = 1.726 ± 0.004 with the critical temperature TC=230.8±0.9 are obtained by the Kouvel–Fisher method, and δ = 4.443 ± 0.008 is generated by the critical isotherm analysis at TC=231 K. The obtained critical exponents of Sr2IrO4 are close to prediction of the theoretical model with { d : n } = { 2 : 1 } (where d is the partial dimensionality and n is the spin dimensionality), which indicates one-dimensional ferromagnetic interaction in the two-dimensional layered material. On the other hand, the critical exponents lie between the prediction of long-range and short-range models, indicating that the short-range Heisenberg interaction alone cannot totally describe the critical behavior. It is suggested that the Dzialoshinsky–Moriya interaction caused by rotation of the octahedra and the symmetric anisotropy result into a lower spatial short-range interaction, which competes with the long-range interaction caused by expansion of 5d orbits.