Signature of a Griffiths phase in layered canted antiferromagnet Sr₂IrO₄

The complex magnetic nature of 5d layered iridate Sr₂IrO₄, owing to IrO₆ octahedral rotation has triggered great interest in recent years. In this article, we investigated the magnetic excitations in layered canted antiferromagnet Sr₂IrO₄ via dc magnetization measurements and report the Griffiths phase (GP) signatures above the magnetic ordering temperature T_N. The non-analytic nature of GP leads to unique critical exponent, β = 0.75(1) extracted from modified Arrott plot, in corroboration with magneto-caloric study. However, the analysis by Bray model in GP regime yields a reliable critical exponent value of β = 0.18(1), belonging to two-dimensional XYh₄ universality class. The study also suggests a new picture of largely debated insulating nature of Sr₂IrO₄ in context of GP above T_N.