Room temperature ferroelectricity in multiferroic HoMnO3 ceramics

We have observed good ferroelectric loops at room temperature in hexagonal HoMnO3 (HMO) bulk ceramics sintered at 1250 °C. Microstructure and ferroelectric hysteresis loops are observed to be dependent on sintering temperature. It is observed that with an increase of sintering temperature, hexagonal a-axis is compressed and c-axis is marginally dilated with overall contraction of the hexagonal unit-cell volume. We explain the origin of ferroelectricity through relative movement of Ho ion and Mn ion within its unit-cell volume, resulting in the distortion of unit-cell volume. We argue that ferroelectric origin of hexagonal HMO at room temperature may be due to the marginal displacement of Ho ion along a-axis, that influences the exchange interaction among the Mn3+ and Ho3+ ions, causing magnetically induced ferroelectricity at room temperature.