  We studied the ferroelectric and ferromagnetic properties of compressive
strained and unstrained BiMnO3 thin films grown by rf-magnetron sputtering.
BiMnO3 samples exhibit a 2D cube-on-cube growth mode and a pseudo-cubic
struc-ture up to a thickness of 15 nm and of 25 nm when deposited on (001)
SrTiO3 and (110) DyScO3, respectively. Above these thicknesses we observe a
switching to a 3D island growth and a simultaneous structural change to a
monoclinic structure characterized by a (00l) orientation of the monoclinic
unit cell. While ferromagnetism is observed below Tc = 100 K for all samples,
signatures of room temperature ferroelectricity were found only in the
pseudo-cubic ultra-thin films, indicating a correlation between electronic and
structural orders.
