LiNbO₃-type InFeO₃: Room-temperature polar magnet without second-order Jahn-Teller active ions

Great effort has been devoted to developing single-phase magnetoelectric multiferroics, but room-temperature coexistence of large electric polarization and magnetic ordering still remains elusive. Our recent finding shows that such polar magnets can be synthesized in small-tolerance-factor perovskites AFeO₃ with unusually small cations at the A-sites, which are regarded as having a LiNbO₃-type structure (space group R3c). Herein, we experimentally reinforce this finding by preparing a novel room-temperature polar magnet, LiNbO₃-type InFeO₃. This compound is obtained as a metastable quench product from an orthorhombic perovskite phase stabilized at 15 GPa and an elevated temperature. The structure analyses reveal that the polar structure is characterized by displacements of In³⁺ (d¹⁰) and Fe³⁺ (d⁵) ions along the hexagonal c-axis (pseudocubic [111] axis) from their centrosymmetric positions, in contrast to well-known perovskite ferroelectrics (e.g., BaTiO₃, PbTiO₃, and BiFeO₃) where d⁰ transition-metal ions and/or 6s² lone-pair cations undergo polar displacements through the so-called second-order Jahn-Teller (SOJT) distortions. Using density functional theory calculations, the electric polarization of LiNbO₃-type InFeO₃ is estimated to be 96 μC/cm² along the c-axis, comparable to that of an isostructural and SOJT-active perovskite ferroelectric, BiFeO₃ (90-100 μC/cm²). Magnetic studies demonstrate weak ferromagnetic behavior at room temperature, as a result of the canted G-type antiferromagnetic ordering of Fe³⁺ moments below T_N ∼ 545 K. The present work shows the functional versatility of small-tolerance-factor perovskites and provides a useful guide for the synthesis and design of room-temperature polar magnets.