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Natural ferroelectric order near ambient temperature in HoFeO3: A member of RFeO3 orthoferrites

Current scenario in multiferroics demands a breakthrough discovery of promising materials after BiFeO3. Recently, the controversial discovery of room temperature ferroelectricity (FE) in SmFeO3 [PRL 107, 117201 (2011); 113, 217203 (2014)] inspires the investigation of HoFeO3. Here, we report a natural ferroelectric order below 210 K (TFE) along c-axis with reasonably large polarization and low-field strong magnetoelectric coupling. Synchrotron and neutron diffraction results confirm that a shift of O atoms along c-axis of polar Pbn21 structure causes FE in HoFeO3. The exchange striction mechanism is suggested to elucidate the ferroelectric order. The results create a renewed attention for searching promising candidates with a natural ferroelectric order and higher TFE in the rest of the RFeO3 series.