Intrinsic ferroelectric polarization of orthorhombic manganites with<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>E</mml:mi></mml:math>-type spin order

Abstract

By directly measuring electrical hysteresis loops using the Positive-Up Negative-Down (PUND) method, we determined accurately the remanent ferroelectric polarization ${P}_{r}$ of orthorhombic $R$MnO${}_{3}$ ($R$ $=$ Ho, Tm, Yb, and Lu) compounds below their $E$-type spin ordering temperatures. We found that LuMnO${}_{3}$ has the largest ${P}_{r}$ of 0.17 $\ensuremath{\mu}$C/cm${}^{2}$ at 6 K in the series, the value of which allows us to predict that its single-crystal form can produce a ${P}_{r}$ of at least 0.6 $\ensuremath{\mu}$C/cm${}^{2}$ at 0 K. Furthermore, at a fixed temperature, ${P}_{r}$ decreases systematically with increasing rare earth ion radius from $R$ $=$ Lu to Ho, exhibiting a strong correlation with the variation of the in-plane Mn--O--Mn bond angle and Mn--O distances. Our experimental results suggest that the contribution of the Mn ${t}_{2g}$ orbitals may dominate the ferroelectric polarization.