  The electronic and magnetic properties in ABO3 perovskite oxides are
extremely sensitive to lattice structure but also the dimensionality, such as
the thickness in thin film form. Here, we report the thickness-dependent
electro-magnetic properties of ultrathin epitaxially stabilized Sr1-xBaxRuO3 (x
= 0.08, 0.2) thin films on SrTiO3 (001) substrate. The results reveal that the
Ba-doping (0.08 < x < 0.20) reduces RuO6 orthorhombic distortions existing in
SrRuO3 and induces a tetragonal distortion as evidenced by out-of-plane lattice
expansion. A metal-to-insulator transition, accompanied by a ferromagnetic to
non-magnetic transition occurs with reducing film thickness from 10 to 3
unit-cell (u.c.) 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.
