Room-temperature ferroelectric polarization in multiferroic BiMnO3

Single-phase multiferroic BiMnO3 ceramic was synthesized via high-pressure and high-temperature solid-state reaction. Microstructure modification accompanied by emergence of superlattice due to electron-beam irradiation was observed wherein by means of electron diffraction (ED) combined with high-resolution transmission electron microscopy (HRTEM). It was clearly evidenced that the well-established C2 monoclinic substructure (I) of BiMnO3 is metastable and prone to transform into a new pseudo-cubic superstructure (I*) with larger unit cell and higher symmetry. Magnetic characterization manifesting a unique ferromagnetic phase transition at 103K has corroborated our speculation that as-prepared BiMnO3 ceramic is free of polymorphism at room temperature. Weak ferromagnetism characterized by a well-saturated ferromagnetic hysteresis loop was manifested in the bulk BMO with Curie temperature TC 105K. Modestly saturated ferroelectric hysteresis loops were observed at room temperature. In light of comprehensive evaluation, we can conclude the synthetic BiMnO3 ceramic displays ferromagnetic and ferroelectric ordering simultaneously, i.e. ferroelectromagnetism below its ferromagnetic Curie temperature TM 105K. r 2006 Published by Elsevier B.V. PACS: 61.10.Nz; 62.50.+p; 75.30.Cr; 77.22.Ch; 77.80.Bh