Intrinsic ferroelectric polarization of orthorhombic manganites with E-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 RMnO 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 μC/cm2 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 μC/cm2 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. © 2012 American Physical Society.