Engineering spin anisotropy of $J_{ m eff} = 1/2$ square lattices in artificial iridate superlattice

Spin anisotropy plays a decisive role in the magnetic phases of quantum materials. The same magnetic order may have the moments point along different crystallographic axes depending on the competition between anisotropy of different symmetries and may undergo a quantum phase transition to switch the spin axis. Tuning the anisotropy could thus induce new emergent states and control their properties. In this work, we engineer the artificial layered structure of the iridate superlattices to control the spin anisotropy of the Jeff = 1/2 square lattices. In particular, we integrate single-layer and bilayer Jeff = 1/2 square lattices in one superlattice structure since they present XY-anisotropy and c-axis anisotropy, respectively. By performing synchrotron x-ray diffraction, resonant x-ray magnetic scattering, magnetization, and resistivity measurements, we found that the new hybrid superlattice stabilizes a new state that is distinct from single-layer and bilayer magnetic anisotropic systems. The entire hybrid superlattice orders simultaneously through a single antiferromagnetic transition at temperatures similar to the bilayer system but with all the Jeff = 1/2 moments mainly pointing in the ab-plane similar to the single-layer system. The results show that bringing different magnetic anisotropic systems with orthogonal properties in proximity to each other is a powerful way to stabilize a unique state in the system.