Weak ferromagnetism in a high-pressure phase of FeTiO3 with polar lattice distortion

Today's challenge in multiferroics is to identify materials in which polarization and magnetization -- normally considered contraindicated properties - are strongly coupled. Recent density functional theory calculations have predicted that the family of compounds MTiO₃ (M = Mn, Fe, Ni) are promising candidates where a polar lattice distortion can induce weak ferromagnetism. The crucial insight is that while the equilibrium one-atmosphere structure of these is ilmenite, they must be transformed to a closely related LiNbO₃-type structure. We have prepared the corresponding FeTiO₃ phase at 18 GPa and 1200 ^^oC. It shows a sharp antiferromagnetic (AF) transition at 111.5 K. FeTiO₃ also displays ferroelectric domains, and weak ferromagnetism coincident with the AF transition. Possible coupling between its polarization and weak ferromagnetism is discussed based on results of piezoelectric force microscopy (PFM), second harmonic generation (SHG), dielectric, and polarization measurements.