Fundamental thickness limit of itinerant ferromagnetic SrRuO3 thin films

We report on a fundamental thickness limit of the itinerant ferromagnetic oxide SrRuO3 that might arise from the orbital-selective quantum confinement effects. Experimentally, SrRuO3 films remain metallic even for a thickness of 2 unit cells (uc), but the Curie temperature TC starts to decrease at 4 uc and becomes zero at 2 uc. Using the Stoner model, we attributed the TC decrease to a decrease in the density of states (No). Namely, in the thin film geometry, the hybridized Ru dyz,zx orbitals are terminated by top and bottom interfaces, resulting in quantum confinement and reduction of No.