Coexistence of ferroelectricity and ferromagnetism in BiFeO3–BaTiO3 thin films at room temperature

( Bi 0.7 Ba 0.3 ) ( Fe 0.7 Ti 0.3 )O 3 films have been constructed on Nb-doped SrTiO3 (100) by the pulsed-laser deposition technique, and their physical properties have been examined. The films exhibit both ferroelectricity and ferromagnetism (weak ferromagnetism) with Pr=2.5 μC/cm2 and Mr=0.2 emu/g at room temperature. The film-thickness dependence of their magnetic and electric properties (size effect) is also discussed simultaneously. The dielectric constants of the films decrease with reducing film thickness below 1000 Å. The magnetic Curie temperature of the films, on the other hand, does not change at all down to 250 Å.