Persistent short-range spin fluctuation in rare-earth substituted square lattice Sr2⁢Ir0.89⁢Tb0.11⁢O4

Abstract

Sr2⁢IrO4, a prototypical 𝐽eff=1/2 square lattice system, is widely studied for novel physics. While transition metal substitution effects are well explored, rare-earth doping at the Ir4+ site is less explored. Here we present a detailed magnetization and neutron diffraction study on Sr2⁢Ir1−𝑥⁢Tb𝑥⁢O4 (𝑥=0.11). The system tends to adopt an in-plane antiferromagnetic configuration with a “++++” stacking sequence. Strong spin fluctuations persist down to the lowest measured temperature, consistent with the concave shape order parameter. A pronounced magnetic diffuse scattering rod develops along the 𝐿 direction at low temperature, indicating the formation of short-range magnetic correlations with a characteristic length of ∼24⁢(2)⁢Å. This work provides a new pathway to exotic quantum phases in the strongly spin-orbit-coupled iridates.