Epitaxial growth and properties of metastable $BiMnO3$ thin films

Epitaxial thin films of $BiMnO3$ were deposited on single-crystal substrates of (100)-oriented $SrTiO3$ by pulsed-laser deposition. Structural analysis by x-ray diffraction, electron diffraction, and transmission electron microscopy (TEM) indicated that the films were monoclinic and twinned with two dominant orientation relationships. The first is $(111) BiMnO3 ∥ (100) SrTiO3$ and $∼[1̄01] BiMnO3 ∥ 〈010〉 SrTiO3;$ the second is $(101̄) BiMnO3 ∥ (100) SrTiO3$ and $∼[121] BiMnO3 ∥ 〈010〉 SrTiO3.$ High-resolution TEM images revealed that there is no reaction or appreciable interdiffusion at the substrate/film interface, despite the high temperature of the substrate during deposition (∼1000 K). Magnetic characterization was carried out (both magnetization versus temperature and hysteresis loops) and the results agree with previous reports of a ferromagnetic transition with $TC$∼105 K. The actual value of $TC$ in the films is a few degrees lower than the bulk material, the discrepancy being attributed to strain, nonstoichiometry, or size effects.