Ruthenium-based perovskite systems are attractive because their structural, electronic, and magnetic properties can be systematically engineered. The ${\mathrm{SrRuO}}_3/{\mathrm{SrTiO}}_3$ 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 metal to an antiferromagnetic 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 $\mathrm{Ru}-t_{2g}$ orbitals just below the Fermi level reveal that the splitting of these orbitals underlies these dramatic phase transitions, with the rotational force constant of ${\mathrm{RuO}}_6$ octahedron high up to $16\mathrm{meV}/{\mathrm{Deg}}^2$, 4 times larger than that of ${\mathrm{TiO}}_6$. Differently from nearly all the previous studies, these transitions can be probed optically through the diagonal and off-diagonal dielectric tensor elements. For a 1% change in strain, our experimental spin moment change is $-0.14\pm 0.06$ ${\mu }_B$, quantitatively consistent with our theoretical value of $-0.1$ ${\mu }_B$.

• Received 19 January 2012

DOI:https://doi.org/10.1103/PhysRevLett.109.157003