Room-Temperature Polar Ferromagnet ScFeO_3 Transformed from a High-Pressure Orthorhombic Perovskite Phase

摘要

Multiferroic materials have been the subject of intense study, but it remains a great challenge to synthesize those presenting both magnetic and ferroelectric polarizations at room temperature. In this work, we have successfully obtained LiNbO_3-type ScFeO_3, a metastable phase converted from the orthorhombic perovskite formed under 15 Gpa at elevated temperatures. A combined structure analysis by synchrotron X-ray and neutron powder diffraction and high-angle annular dark-field scanning transmission electron microscopy imaging reveals that this compound adopts the polar R3c symmetry with a fully ordered arrangement of trivalent Sc and Fe ions, forming highly distorted ScO_6 and FeO_6 octahedra. The calculated spontaneous polarization along the hexagonal c-axis is as large as 100 μC/cm~2. The magnetic studies show that LiNbO_3-type ScFeO_3 is a weak ferromagnet with T_N = 545 K due to a canted G-type antiferromagnetic ordering of Fe~(3+) spins, representing the first example of LiNbO_3-type oxides with magnetic ordering far above room temperature. A comparison of the present compound and rare-earth orthorhombic perovskites RFeO_3 (R = La-Lu and Y), all of which possess the corner-shared FeO_6 octahedral network, allows us to find a correlation between T_N and the Fe-O-Fe bond angle, indicating that the A-site cation-size-dependent octahedral tilting dominates the magnetic transition through the Fe-O-Fe superexchange interaction. This work provides a general and versatile strategy to create materials in which ferroelectricity and ferromagnetism coexist at high temperatures.