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 TN. 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 TN.