  Spin-orbit entangled pseudospins hold promise for a wide array of exotic
magnetism ranging from a Heisenberg antiferromagnet to a Kitaev spin liquid
depending on the lattice and bonding geometry, but many of the host materials
suffer from lattice distortions and deviate from idealized models in part due
to inherent strong pseudospin-lattice coupling. Here, we report on the
synthesis of a magnetic superlattice comprising the single ($n$=1) and the
double ($n$=2) layer members of the Ruddlesden-Popper series iridates
Sr$_{n+1}$Ir$_{n}$O$_{3n+1}$ alternating along the $c$-axis, and provide a
comprehensive study of its lattice and magnetic structures using scanning
transmission electron microscopy, resonant elastic and inelastic x-ray
scattering, third harmonic generation measurements and Raman spectroscopy. The
superlattice is free of the structural distortions reported for the parent
phases and has a higher point group symmetry, while preserving the magnetic
orders and pseudospin dynamics inherited from the parent phases, featuring two
magnetic transitions with two symmetry-distinct orders. We infer weaker
pseudospin-lattice coupling from the analysis of Raman spectra and attribute it
to frustrated magnetic-elastic couplings. Thus, the superlattice expresses a
near ideal network of effective spin-one-half moments on a square lattice.
