Atypical multiferroicity of HoCrO3 in bulk and film geometry

Abstract

We report ferroelectricity in antiferromagnetic HoCrO₃ with a reasonably large value of spontaneous electric polarization (∼0.32 μC cm⁻² at 10 K) from the measurement of pyroelectric current. The appearance of ferroelectricity is further confirmed in the film geometry. Intriguingly, the onset of polar order is observed at a significantly higher temperature (∼240 K) than the Néel temperature (T_N = 142 K). The survival of remanent polarization is confirmed from the electric polarization hysteresis loops above and below T_N for polycrystalline and film specimens. Structural analysis suggests that polar oxygen octahedral rotations and Ho displacements in the non-centrosymmetric Pna2₁ space group engineer ferroelectricity. The results indicate that occurrence of polar order in HoCrO₃ resembles neither the typical case of proper ferroelectrics nor the improper ferroelectrics.