Imaging antiferromagnetic domain fluctuations and the effect of atomic-scale disorder in a doped spin-orbit Mott insulator

Correlated oxides can exhibit complex electronic and magnetic patterns. Understanding how magnetic domains form has been of great interest, but atomic-scale insight has been limited. We use spin-polarized scanning tunneling microscopy to image the evolution of spin-resolved modulations originating from antiferromagnetic (AF) ordering in a spin-orbit Mott insulator Sr₃Ir₂O₇ as a function of chemical composition and temperature. We find that replacing only several percent of La for Sr leads to nanometer-scale AF puddles clustering away from La substitutions preferentially located in the middle SrO layer. Thermal erasure and re-entry into the low-temperature ground state leads to a spatial reorganization of the AF puddles. Our experiments reveal multiple stable AF domain configurations at low temperature, and shed light onto spatial fluctuations of the AF order around atomic-scale disorder in electron doped Sr₃Ir₂O₇.