Thickness dependent itinerant ferromagnetism in ultrathin Ba-doped SrRuO3 films

The electronic and magnetic properties in AB⁢O₃ perovskite oxides are extremely sensitive to lattice structure, but also to dimensionality, such as the thickness in thin film-form. Here, we report the thickness-dependent electromagnetic properties of ultrathin epitaxially stabilized Sr_1-x⁢Ba_x⁢Ru⁢O₃ (x = 0.08, 0.2) thin films on a SrTi⁢O₃ (001) substrate. The results reveal that the barium doping (0.08 ≤ x ≤ 0.20) reduces Ru⁢O₆ orthorhombic distortions existing in SrRu⁢O₃ and induces a tetragonal distortion, as evidenced by out-of-plane lattice expansion. A metal-to-insulator transition, accompanied by a ferromagnetic to nonmagnetic transition occurs with reducing film thickness from 10 to 3 unit cells for both x = 0.08 and 0.2, regardless of the doping level. The results suggest that the effects of compositional vacancies and surface/interface contributions introduced via dimensional confinement are more dominant than A-site chemical disorder or structural distortion for the loss of metallicity and ferromagnetism in ultra-thin epitaxial films.