Abstract

Multiferroics exhibit simultaneous ferroic properties with coupled electric, magnetic, and structural orders.(1-6) Multiferroic materials have received a great deal of attention because of their potential for enabling new memory devices and information storage.(3-5) Among numerous multiferroics currently under investigation, rare-earth manganites have been most extensively studied owing to their tendency toward a strong magnetoelectric coupling, in general. They are classified into two distinct crystal classes depending on the radius of rare-earth cation. ReMnO3-type oxides with Re = La–Dy in the lanthanide series belong to orthorhombic manganites(1, 5, 6) whereas ReMnO3-type oxides with Re = Ho–Lu belong to hexagonal manganites.(7-9) Unlike perovskite-based orthorhombic manganites, hexagonal manganites possess c-axis-oriented ferroelectricity owing to the disappearance of a mirror image on the a-b plane in a polar P63cm unit cell.(7-9) Hexagonal magnetites also exhibit an antiferromagnetic (AFM) order which is governed by the intralayer Mn–O–Mn superexchange interaction. Therefore, the magnetic spins are oriented parallel to the a–b plane with a so-called 120° triangular spin configuration, which is a typical spin order of frustrated magnetic sublattices.(8-12)