Large electric polarization in high pressure synthesized orthorhombic manganites $R$MnO$_{3}$ (R=Ho,Tm,Yb and Lu) by using the double-wave PE loop measurements

The magnitude of electric polarization via the conventional pyroelectric current and/or PE loop measurements often is ambiguous due to resistive components of the sample. To avoid this, a new technique called the double-wave method has been recently developed [1], in which only hysteretic PE components can be measured. Using this technique, we have measured the ferroelectric polarization of the orthorhombic $R$MnO$_{3}$ (R=Ho, Tm, Yb, and Lu) synthesized under high pressure. Large remnant polarization P$_{r}$ up to 920 $\mu $C/m$^{2}$ is observed at 10 K for LuMnO$_{3}$. Furthermore, the P$_{r}$ vs. temperature data from the PE loop has shown consistency with that measured through the pyroelectric current measurements, supporting a theoretical prediction of large polarization in the $E$-type spin structure in this system [2]. We also discuss the influence of thermal histories on the ferroelectric domain dynamics and possible internal bias field effects originating from oxygen vacancies in $R$MnO$_{3}$. [1] M. Fukunaga, \textit{et al.} J. Phys. Soc. Jpn. \textbf{77}, 064706 (2008). [2] I. A. Sergienko,\textit{ et al}. Phys. Rev. Lett., \textbf{97, }227204 (2006)