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Structural and Magnetic Evolution of Co Substituted BiFeO3

Date: 2018-08-29
Time: 15:00
Venue: 物理所M楼238
Speaker: Hajime Hojo

Department of Advanced Materials and Engineering, Faculty of Engineering Sciences, Kyushu University

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.

Hajime Hojo is an Associate Professor in the Department of Advanced Materials and Engineering at Kyushu University. He received his B.S. in industrial chemistry in 2003 and his Ph.D. in material chemistry in 2008 from Kyoto University. From 2008 to 2011 he was a postdoctoral fellow in the lab of Prof. Yuichi Ikuhara at Tokyo University. In 2011, he was appointed as an Assistant Professor in the lab of Prof. Masaki Azuma at the Tokyo Institute of Technology. His research interests include materials chemistry and catalyst chemistry.