Optical study of the vibrational and dielectric properties of BiMnO3

Abstract

BiMnO3 (BMO), ferromagnetic (FM) below Tc = 100 K, was believed to be also ferroelectric (FE) due to a non-centro-symmetric C2 structure, until diffraction data indicated that its space group is the centro-symmetric C2/c. Here we present infrared phonon spectra of BMO, taken on a mosaic of single crystals, which are consistent with C2/c at any T > 10 K, as well as room-temperature Raman data which strongly support this conclusion. We also find that the infrared intensity of several phonons increases steadily for decreasing T, causing the relative permittivity of BMO to vary from 18.5 at 300 K to 45 at 10 K. At variance with FE materials of displacive type, no appreciable softening has been found in the infrared phonons. Both their frequencies and intensities, moreover, appear insensitive to the FM transition at Tc.

References in corpus (8)

• On the Fermi Liquid to Polaron Crossover II: Double Exchange and the Physics of "Colossal" Magnetoresistance
• First Principles Investigation of Ferromagnetism and Ferroelectricity in Bismuth Manganite
• Charge transfer in the high dielectric constant materials CaCu3Ti4O12 and CdCu3Ti4O12
• Structural anomalies at the magnetic transition in centrosymmetric BiMnO${}_3$
• Magnetic-field control of the electric polarization in BiMnO3
• Absence of ferroelectricity in BiMnO3 ceramics
• Defects of the Crystal Structure and Jahn-Teller distortion in BiMnO3
• Infrared phonon spectrum of the tetragonal helimagnet Ba${}_2$CuGe${}_2$O${}_7$