Magnetic behavior and thickness dependence in Co-doped BaTiO3 thin films

We fabricated epitaxial Co-doped BaTiO(3) thin films (4-80 nm thick) on Nb-doped SrTiO(3) substrates. Our results indicate that Co ions exist in the form of Co(3+) and that no Co metal clusters appear. All of the Co-doped BaTiO(3) thin films show ferromagnetic behavior and the saturated magnetization increases as the film thickness decreases, which may be attributed to the effective exchange coupling interaction between oxygen vacancies and Co 3d spins. However, as the film thickness further decreases (similar to 4 nm), the magnetization decreases, which may be mainly ascribed to surface effects. (c) 2008 American Institute of Physics.