Anomalous induction of ferroelectric polarization by magnetization reversal in the phase-separated multiferroic manganite ${\text{Eu}}_{0.8}{\text{Y}}_{0.2}{\text{MnO}}_3$

Regarding electronic phase separation and its magnetoelectric control in multiferroics, we have investigated magnetic and ferroelectric properties of ${\text{Eu}}_{0.8}{\text{Y}}_{0.2}{\text{MnO}}_3$ located near the boundary between a ferromagnetic phase and a ferroelectric phase. We observed special coexistence of the two phases, which fractions are tuned at an arbitrary level by changing the cooling magnetic-field strength. In addition, repeated magnetization reversals by applying an alternating magnetic field induce anomalous enhancement of ferroelectric polarization, suggesting the development of the ferroelectric phase during the magnetization reversal process.

Figure 1

(Color online) Temperature profiles of (a) magnetization along $c$, (b) electric polarization along $a$, (c) linear thermal expansion along $a$ and $b$, and lattice parameter $b$ for ${\text{Eu}}_{0.8}{\text{Y}}_{0.2}{\text{MnO}}_3$ crystals. The data in (b) and (c) were taken at 0 T, while those in (a) were obtained at 0.01 T along $c$. All the measurements were performed in the warming run. Before the measurements, the crystals were cooled from $\sim 50\text{K}$ at 0 T (ZFC; black lines) and 5 T along $c$ [FC5T; red lines (gray lines in print)]. (d) Magnetic and electric phase diagrams of ${\text{Eu}}_{1-x}{\text{Y}}_x{\text{MnO}}_3$ (reproduced from Refs. 14, 15).

Figure 2

(Color online) (a) Magnetization along $c$ and (b) electric polarization along $a$ for ${\text{Eu}}_{0.8}{\text{Y}}_{0.2}{\text{MnO}}_3$ crystals as a function of $B$ parallel to $c$ at 9 K. The measurements were done once cooling magnetic fields $B_{\text{cool}}$ were applied at $\sim 50\text{K}$ and the crystals were cooled to 9 K in the respective cooling fields.

Figure 3

(Color online) Fractions of the WFM-PE phase (solid circles) and the SAFM-FE phase (open circles) at 9 K as a function of cooling magnetic field for ${\text{Eu}}_{0.8}{\text{Y}}_{0.2}{\text{MnO}}_3$. The fractions were estimated from remanent magnetization and electric polarization in virgin curves. Grey lines are guides for the eyes. (b) Single-crystal x-ray diffraction profiles around the (060) Bragg reflection. The measurements were performed at 9 K and 0 T after the crystal was cooled from $\sim 50\text{K}$ to 9 K in the respective cooling fields.

Figure 4

(Color online) (a) Suppression of magnetization and (b) promotion of electric polarization by applying an alternating magnetic field for ${\text{Eu}}_{0.8}{\text{Y}}_{0.2}{\text{MnO}}_3$. Orange arrows denote the evolution of magnetization or electric polarization. The inset of (a) shows a magnified view of the magnetization curves. Roman numerals denote the order of measurements. Insets of (b): schematic drawings of spin configurations near the boundary between the SAFM-FE and the WFM-PE phases and a possible evolution of the SAFM-FE phase during the magnetization reversal process.