Insight into the magnetic behavior of Sr$_2$IrO$_4$:A spontaneous magnetization study

Abstract: Sr$_2$IrO$_4$ is a weak ferromagnet where the spin arrangement is canted anti-ferromagnetic (AF). Moreover, the spin-structure coupling plays and important role in magnetic behavior of Sr$_2$IrO$_4$. In this concern the magnetization under zero applied field i.e. spontaneous magnetization would be interesting to study and would give insight into the novel magnetic behavior of Sr$_2$IrO$_4$. Sophisticated techniques like neutron diffraction, $\mu$ \textit{SR} etc has been used to understand the magnetic behavior of Sr$_2$IrO$_4$ under zero applied field. To understand the magnetic behavior we have performed detail field and temperature dependent magnetization study, the measured field and temperature dependent magnetic data is analyzed rigorously. We have attempted the understand the temperature dependance of spontaneous magnetization, remanent magnetization and coercive force. We observe that the spontaneous magnetization extracted from Arrott plot shows that the Sr$_2$IrO$_4$ is not an ideal ferromagnet. The temperature dependent coercive field is found to follows Guant's model of strong domain wall pinning. Our investigation explicit the temperature dependence of various magnetic properties shows the magnetic transitions from paramagnetic to ferromagnetic phase with $T_c$ around 225 K and a low temperature evolution of magnetic magnetic moment around $T_M$ $\sim$90 K.