Magnetic ordering and structural phase transitions in strained ultrathin SrRuO${}_3$/SrTiO${}_3$ superlattice

Abstract

Ruthenium-based perovskite systems are attractive because their Structural, electronic and magnetic properties can be systematically engineered. SrRuO${}_3$/SrTiO${}_3$ superlattice, with its period consisting of one unit cell each, is very sensitive to strain change. Our first-principles simulations reveal that in the high tensile strain region, it transits from a ferromagnetic (FM) metal to an antiferromagnetic (AFM) insulator with clear tilted octahedra, while in the low strain region, it is a ferromagnetic metal without octahedra tilting. Detailed analyses of three spin-down Ru-t${}_{2g}$ orbitals just below the Fermi level reveal that the splitting of these orbitals underlies these dramatic phase transitions, with the rotational force constant of RuO${}_6$ octahedron high up to 16 meV/Deg${}^2$, 4 times larger than that of TiO${}_6$. Differently from nearly all the previous studies, these transitions can be probed optically through the diagonal and off-diagonal dielectric tensor elements. For one percent change in strain, our experimental spin moment change is -0.14$\pm$0.06 $\hat{I}{¼}_B$, quantitatively consistent with our theoretical value of -0.1 $\hat{I}{¼}_B$.

3 figures, 1 supplementary material, accepted by Phys. Rev. Lett