Fundamental Thickness Limit of Itinerant FerromagneticSrRuO3Thin Films

Abstract

We report on a fundamental thickness limit of the itinerant ferromagnetic oxide ${\mathrm{SrRuO}}_3$ that might arise from the orbital-selective quantum confinement effects. Experimentally, ${\mathrm{SrRuO}}_3$ films remain metallic even for a thickness of 2 unit cells (uc), but the Curie temperature $T_C$ starts to decrease at 4 uc and becomes zero at 2 uc. Using the Stoner model, we attributed the $T_C$ decrease to a decrease in the density of states ($N_o$). Namely, in the thin film geometry, the hybridized Ru $d_{yz,zx}$ orbitals are terminated by top and bottom interfaces, resulting in quantum confinement and reduction of $N_o$.