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

Abstract

Using first-principles techniques, we study the structural, magnetic and electronic properties of (111)-oriented (LaMnO${}_3$)${}_{2n}$$|$(SrMnO${}_3$)${}_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 La${}_{2/3}$Sr${}_{1/3}$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 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 La${}_{2/3}$Sr${}_{1/3}$MnO${}_3$ and bulk LaMnO${}_3$.

7 pages excluding references, 8 figures