Fundamental thickness limit of itinerant ferromagnetic SrRuO(3) thin films.

We report on a fundamental thickness limit of the itinerant ferromagnetic oxide SrRuO(3) that might arise from the orbital-selective quantum confinement effects. Experimentally, 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).