Critical behavior of the in-plane weak ferromagnet Sr2IrO4

• Critical exponents ββ, γγ, δδ were obtained for weak ferromagnetic Sr2IrO4.
• Critical exponents are close to the theoretical model with d:n=2:1.
• The magnetic interaction lies between long- and short-range.

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±0.008β=0.284±0.008 and γ=1.726±0.004γ=1.726±0.004 with the critical temperature TC=230.8±0.9 are obtained by the Kouvel–Fisher method, and δ=4.443±0.008δ=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}{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.