报告摘要：
BiFeO3 is attracting keen interest because of large electric polarization and possible multiferroic applications. However, the piezoelectric constant is as small as 60 pm/V and the presence of cycloidal spin modulation prohibits the appearance of spontaneous magnetization. The effect of Co substitution for Fe on crystal and magnetic structures of BiFe1-xCoxO3 will be discussed.

The crystal structure changes from rhombohedral one to giant tetragonal BiCoO3 type at x ~ 0.35. A monoclinic phase with ?2a ′ ?2a ′ a unit cell and Cm space group, essentially the same as those of MPB phase of PZT, was found at x ~ 0.3. Synchrotron X-ray powder diffraction revealed the occurrence of polarization rotation as functions of composition and temperature. Moreover, the enhancement of piezoelectric response was confirmed in the epitaxial thin films fabricated by PLD method.

At lower Co substitution, the rhombohedral crystal structure is preserved while the cycloidal spin modulation disappears at a room temperature. Spontaneous magnetization generated by Dzyaloshinsky-Moriya interaction appears. It is demonstrated that the ferroelectric domain switching is accompanied by the magnetization reversal.

报告人简介：
Masaki Azuma is a Professor in Materials and Structural Laboratory at Tokyo Institute of Technology since 2010. He received his bachelor degree from Faculty of Science, Kyoto University in 1990 and Ph.D. degree from Department of Chemistry, Kyoto University in 1995. Subsequently, he continued his research career at Kyoto University as Research Instructor from 1995 to 2004 and Associate Professor from 2004 to 2010. He has about 250 publications, with a total citation number of over 13000 (August 2018, google scholar). His h-index is ~55. His research interests include transition metal oxides, strongly correlated electrons, ferroelectrics, piezoelectrics, low dimensional magnets, frustration, metal insulator transition, high pressure science, and structural physics.