Magnetic ordering and structural phase transitions in strained ultrathin SrRuO$_{3}$/SrTiO$_{3}$ superlattice

TL;DR

This study uses first-principles simulations to explore how strain induces magnetic and structural phase transitions in ultrathin SrRuO$_3$/SrTiO$_3$ superlattices, revealing new insights into their electronic behavior.

Contribution

It demonstrates that strain causes a transition from ferromagnetic metal to antiferromagnetic insulator, with detailed orbital analysis and optical probing methods, which is novel in this context.

Findings

High tensile strain induces FM to AFM transition.

Orbital splitting underpins phase changes.

Transitions detectable via optical dielectric tensor.

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 $\mu_B$, quantitatively consistent with our theoretical value of -0.1 $\mu_B$.