In-plane magnetic anisotropy in strontium iridate Sr2IrO4

Magnetic anisotropy in strontium iridate ($\mathrm{S}{\mathrm{r}}₂\mathrm{Ir}{\mathrm{O}}₄$) is found to be large because of the strong spin-orbit interactions. In our work, we studied the in-plane magnetic anisotropy of $\mathrm{S}{\mathrm{r}}₂\mathrm{Ir}{\mathrm{O}}₄$ and traced the anisotropic exchange interactions between the isospins in the crystal. The magnetic-field--dependent torque \ensuremath{\tau}($H$) showed a prominent transition from the canted antiferromagnetic state to the weak ferromagnetic (WFM) state. A comprehensive analysis was conducted to examine the isotropic and anisotropic regimes and probe the easy magnetization axis along the $ab$ plane. The angle-dependent torque \ensuremath{\tau}(\ensuremath{\theta}) revealed a deviation from the sinusoidal behavior, and small differences in hysteresis were observed around 0\ifmmode^\circ\else\textdegree\fi{} and 90\ifmmode^\circ\else\textdegree\fi{} in the low-magnetic-field regime. This indicates that the orientation of the easy axis of the FM component is along the $b$ axis, where the antiferromagnetic to WFM spin-flop transition occurs. We compared the coefficients of the magnetic susceptibility tensors and captured the anisotropy of the material. The in-plane \ensuremath{\tau}(\ensuremath{\theta}) revealed a tendency toward isotropic behavior for fields with values above the field value of the WFM transition.