Emergent half-metal with mixed structural order in (111)-oriented ${\left({\mathrm{LaMnO}}_3\right)}_{2n}|{\left({\mathrm{SrMnO}}_3\right)}_n$ superlattices

Using first-principles techniques, we study the structural, magnetic, and electronic properties of (111)-oriented ${\left({\mathrm{LaMnO}}_3\right)}_{2n}|{\left({\mathrm{SrMnO}}_3\right)}_n$ superlattices of varying thickness ($n=2,4,6$). We find that the properties of the thinnest superlattice ($n=2$) are similar to the celebrated half-metallic ferromagnetic alloy ${\mathrm{La}}_{2/3}{\mathrm{Sr}}_{1/3}{\mathrm{MnO}}_3$, with quenched Jahn-Teller distortions. At intermediate thickness ($n=4$), the $a^{-}{a}^{-}{a}^{-}$ tilting pattern transitions to the $a^{-}{a}^{-}{c}^{+}$ tilting pattern, driven by the lattice degrees of freedom in the ${\mathrm{LaMnO}}_3$ region. The emergence of the Jahn-Teller modes and the spatial extent needed for their development play a key role in this structural transition. For the largest thickness considered ($n=6$), we unveil an emergent separation of Jahn-Teller and volume-breathing orders in the ground-state structure with the $a^{-}{a}^{-}{c}^{+}$ tilting pattern, whereas it vanishes in the antiferromagnetic configurations. The ground state of all superlattices is half-metallic ferromagnetic, not affected by the underlying series of structural transitions. Overall, these results outline a thickness-induced crossover between the physical properties of bulk ${\mathrm{La}}_{2/3}{\mathrm{Sr}}_{1/3}{\mathrm{MnO}}_3$ and bulk ${\mathrm{LaMnO}}_3$.