Magnetic and electric properties of stoichiometric BiMnO3 thin films.

It has been suggested that BiMnO3 is a material exhibiting both ferromagnetism and ferroelectricity. Stoichiometry is rather easily achieved in a polycrystalline sample, and ferromagnetic properties have been well documented for bulk samples. Stoichiometry in thin films has been difficult to obtain, and many physical properties have exhibit wide distributions mainly due to the stoichiometry problem. Thin film studies on BiMnO3 have not shown clear evidence of ferroelectricity, while other physical properties measured for the BiMnO3 films showed wide spectra, which has been attributed to cation and/or oxygen vacancies. We fabricated BiMnO3 thin films with good stoichiometry and with ferromagnetic properties comparable to those reported for stoichiometric BiMnO3: Tc ~ 105 K and M sat ~ 3.6 μB/Mn. The charge-electric field (Q-E) curve measured at 5 K was fairly linear and free from hysteresis and showed no ferroelectric order. This finding is consistent with the centrosymmetric crystal structure recently suggested by theoretical calculations and structural studies on ceramic samples of stoichiometric BiMnO3.